me 6302 manufacturing technology 1notes with question paper

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ME6302-MANUFACTURING TECHNOLOGY I II /III MECHANICAL ENGINEERING 1 ME – 6302 MANUFACTURING TECHNOLOGY - I ASSISTANT PROFESSOR DEPARTMENT OF MECHANICAL ENGINEERING G.GOPINATH GOPINATH.G

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Page 1: ME 6302 manufacturing technology 1notes with question paper

ME6302-MANUFACTURING TECHNOLOGY –I II /III MECHANICAL ENGINEERING

1 S.SENTHIL KUMARAN 2015-2016

ME – 6302 MANUFACTURING TECHNOLOGY - I

By

Mr. S.SENTHIL KUMARAN.M.E.

ASSISTANT PROFESSOR

DEPARTMENT OF MECHANICAL ENGINEERING

SASURIE COLLEGE OF ENGINEERING

VIJAYAMANGALAM – 638 056

G.GOPINATH

G.GOPINATH

COURSE FILE : MT 1 AUTHOR : GOPINATH.G ASST.PROF MECHANICAL DEPARTMENT

GOPINATH.G

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ME6302-MANUFACTURING TECHNOLOGY –I II /III MECHANICAL ENGINEERING

2 S.SENTHIL KUMARAN 2015-2016

QUALITY CERTIFICATE

This is to certify that the e-course material

Subject Code : ME-6302

Subject : Manufacturing technology -I

Class : II Year MECHANICAL

Being prepared by me and it meets the knowledge requirement of the university curriculum.

Signature of the Author

Name: S.SENTHIL KUMARANDesignation: ASSISTANT PROFESSOR.

This is to certify that the course material being prepared by Mr.S.Senthil Kumaran is of adequate quality. He hasreferred more than five books among them minimum one is from aboard author.

Signature of HD

Name: E.R.Sivakumar

SEAL

G.GOPINATH

G.GOPINATH

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ME6302 MANUFACTURING TECHNOLOGY – I L T P C3 0 0 3

OBJECTIVES:· To

–Types and applications – Moulding machines– Types and applications; Melting furnaces : Blastand Cupola Furnaces; Principle of special castingprocesses : Shell - investment – Ceramic mould – Pressure die casting - Centrifugal Casting - CO2process – Stir casting; Defects in Sand casting

introduce the concepts of basic manufacturing processes and fabrication techniques, such asmetal casting, metal joining, metal forming and manufacture of plastic components.

UNIT I METAL CASTING PROCESSES 9Sand Casting : Sand Mould – Type of patterns - Pattern Materials – Pattern allowances –Mouldingsand Properties and testing – CoresUNIT II METAL JOINING PROCESSES 9Operating principle, basic equipment, merits and applications of : Fusion welding processes :Gas welding - Types – Flame characteristics; Manual metal arc welding – Gas Tungsten arc welding- Gas metal arc welding – Submerged arc welding – Electro slag welding; Operating principle andapplications of : Resistance welding - Plasma arc welding – Thermit welding – Electron beamwelding – Friction welding and Friction Stir Welding; Brazing and soldering; Weld defects: types,causes and cure.

UNIT III METAL FORMING PROCESSES 9Hot working and cold working of metals – Forging processes – Open, impression and closed dieforging – forging operations. Rolling of metals– Types of Rolling – Flat strip rolling – shape rollingoperations – Defects in rolled parts. Principle of rod and wire drawing – Tube drawing – Principles ofExtrusion – Types – Hot and Cold extrusion.

UNIT IV SHEET METAL PROCESSES 9Sheet metal characteristics – shearing, bending and drawing operations – Stretch forming operations– Formability of sheet metal – Test methods –special forming processes-Working principle andapplications – Hydro forming – Rubber pad forming – Metal spinning– Introduction of Explosiveforming, magnetic pulse forming, peen forming, Super plastic forming – Micro forming

UNIT V MANUFACTURE OF PLASTIC COMPONENTS 9Types and characteristics of plastics – Moulding of thermoplastics – working principles and typicalapplications – injection moulding – Plunger and screw machines – Compression moulding, TransferMoulding – Typical industrial applications – introduction to blow moulding –Rotational moulding – Filmblowing – Extrusion – Thermoforming – Bonding of Thermoplastics.

TOTAL: 45 PERIODS

GOPINATH.GAP/MECH

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UNIT Sr.No TITLE PAGENO.

REMARKS

1 I METAL CASTING PROCESS

1.1 MANUFACTUTING 7

1.1.1 Moulding 7

1.1.2 Casting 7

1.1.3 Foundry 7

1.2 Sand Casting/Sand Moulding 7

1.3 Types of Sand 7

1.4 Patterns & Materials used forpatterns

8

1.4.1 Types of patterns8

1.4.2 Pattern Allowance 8

1.5 Steps in Sand Casting 9

1.6 Melting Furnaces 9

1.7 Special Casting Process 10

1.7.1 Centrifugal Casting 10

1.7.2 CO2 Process 11

1.7.3 Investment Casting 13

1.7.4 Shell Moulding 131.8 Casting Defects 15

1.9 NDT for Finding casting Defects 15

2 II METAL JOINING PROCESS2.1 Welding 162.2 Types Of Welding 16

2.3 GAS Welding 16

GOPINATH.GAP/MECH

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UNIT Sr.No TITLE PAGENO.

REMARKS

2.4 ARC Welding 20

2.5 Special Welding Process 21

2.5.1 Submerged Arc Welding 21

2.5.2 Laser Beam Welding 22

2.5.3 Electron Beam Welding 23

2.5.4 Plasma Arc Welding 24

2.5.5 Thermit welding 25

2.5.6 TIG – MIG Welding 26

2.5.7 Resistance Welding 27

3. III METAL FORMING PROCESS

3.1 COLD working & HOT Working 28

3.2 Rolling 29

3.2.1 Defects in Rolled Parts 30

3.3 Forging 31

3.3.1 Defects in Forged Parts 32

3.4 Extrusion and Drawing 33

4. IV SHEET METAL PROCESS

4.1 Shearing operations 34

4.2 Bending Operations 37

4.3 Stretch forming Operations 37

4.4 Special forming Operations 38

4.4.1 Hydro forming 38

4.4.2 Rubber Pad forming 39

GOPINATH.GAP/MECH

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4.4.3 Peen forming 40

5 V MANUFACTURE OF PLASTICCOMPONENTS

5.1 Types of Plastics 41

5.2 Injection Moulding 41

5.3 Blow Moulding 42

5.4 Rotational Moulding 45

5.5 Transfer Moulding 46

5.6 Compression Moulding 47

QUESTION BANK WITH ANSWER

1. I UNIT –I (2 MARKS & 16 MARKS) 49

2. II UNIT –II (2 MARKS & 16 MARKS) 57

3. III UNIT –III (2 MARKS & 16 MARKS) 70

4.IV UNIT –IV (2 MARKS & 16 MARKS) 79

5.V UNIT –V (2 MARKS & 16 MARKS) 87

GOPINATH.GAP/MECH

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MANUFACTURING TECHNOLOGY-1UNIT –I

METAL CASTING PROCESSPREREQUISTE DISCUSSION1.Manufacturing

Manufacturing in its broadest sense is the process of converting raw materials intouseful products.• IT Includes

i) Design of the productii) Selection of raw materials andiii) The sequence of processes through which the product will

be manufactured. Casting.Any Product in the engineering industry will be manufactured in the below methods

1. By totally deforming the metal to the required shape. (Casting /Forming)1. By joining two metals. (Welding)2. By removing the excess material from the raw stock.(Machining)

1.1.1Moulding .It is the process of preparing the cavity required for casting using the pattern (Physical

Model), Moulding sand, Moulding boxes,(Cope, Drag, cheek) and other tools.1.1.2Casting.

Casting is the process of producing metal parts by pouring molten metal into themould cavity of the required shape and allowing the metal to solidify. The solidifiedmetal piece is called as "casting".

1.1.3FoundryIt is the place where both moulding and casting is done.

1.2. Sand Casting /Sand Moulding.

Sand Casting is simply melting the metal and pouring it into a preformed cavity, calledmold, allowing (the metal to solidify and then breaking up the mold to remove casting. Insand casting expandable molds are used. So for each casting operation you have to form anew mold.

1.3 Types of sanda) Green-sand - mixture of sand, clay, and water,Binders (Molases, Linseed oil); "Green"means mold contains moisture at time of pouring.b) Dry-sand - organic binders rather than clay and mold is baked to improve strengthc) Skin-dried - drying mold cavity surface of a green-sand

- mold to a depth of u p t o 25 mm, using torches or heatingd)Core Sande)Baking sandf)Loam Sandg)Parting sand, Etc.,

1.4Patterns

GOPINATH.GAP/MECH

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Patterns are the replica or physical models of the final required shape of the casting, madeby wood (teak,magony,pine), plastics, Metals, Plaster of paris etc.,

1.4.1Types of patterns.1.Solid pattern2.Split piece pattern3.Three piece pattern4.Loose piece pattern5.Match plate pattern6.Segmental pattern7.Sweep patten8.skeleton Pattern9.shell Pattern.

1.4.2Pattern Allowance.Allowance are the extra dimensional compensation give to the pattern in order to attain

the correct shape and size of the final solidified metal casting.Five types of allowances weretaken into consideration for various reasons. They are1.4.2.1.Shrinkage allowance

Any metal when heated to liquid stage and solidified will undergo change in dimension.Mostly the dimension of the product will be reduced, then the actual size of the pattern.Hence the patterns are made slightly in larger dimensions.(3%-5%)

1.4.2.2.Draft allowanceIt will be difficult to remove the pattern from the mould cavity (without disturbing themould) after ramming of sand. Hence the pattern (wooden or metal pattern) is slightlygiven 2 o– 3 o TAPER in the z - axis or vertical direction.

1.4.2.3. Finish allowanceIt is otherwise called as machining allowance .The pattern is made slightly 5mm -10mmlarge in dimension than the required final part dimension. After casting the extramaterial is removed from the solidified material by machining.

1.4.2.4.Shake or Rapping allowance.Before withdrawing the pattern it is rapped and thereby the size of the mould cavityincreases. Actually by rapping , the external sections move outwards increasing the sizeand internal sections move inwards decreasing the size. This allowance is kept negativeand hence the pattern is made slightly smaller in dimensions 05.1.0 mm.

1.4.2.5.Distortion allowance.Some material might tend to bend or distort from the actual size or dimensions. Hence

the pattern is give counter balance degree or angle of recess so that the material will be inthe required dimension when solidified in the mould cavity.

GOPINATH.GAP/MECH

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1.5 Steps in Sand CastingThe cavity in the sand mold is formed by packing sand around a pattern,separating themold into two halves

• The mold must also contain gating and riser system• For internal cavity, a core must be included in mold• A new sand mold must be made for each part

1. Pour molten metal into sand mold2. Allow metal to solidify3. Break up the mold to remove casting4. Clean and inspect casting5. Heat treatment of casting is sometimes required toimprove metallurgical properties.

1.6. FURNACES USED FOR MELTING METALS FOR CASTING.

1.6.1 Types of furnace used in a casting industry.–Crucible Furnace– Electric-arc Furnace– Induction Furnace

--ReverbratoryfurnaceBlast Furnace

- Cupola Furnace.1.6.1.1.Cupola Furnace

• A continuous flow of iron emerges from the bottom of the furnace.• Depending on the size of the furnace, the flow rate can be as high as 100 tonesper hour..At the metal melts it is refined to some extent, which removes contaminants.This makes this process more suitable than electric furnaces for dirty charges.

GOPINATH.GAP/MECHGOPINATH.G

AP/MECH

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1.7. SPECIAL CASTING PROCESS.

1.7.1.Centrifugal castingCentrifugal casting uses a permanent mold that is rotated about its axis at aspeed between300 to 3000 rpm as the molten metal is poured.Centrifugal forcescause the metal to be pushed out towards the mold walls, where itsolidifies after cooling.Centrifugal casting has greater reliability than staticcastings. They are relatively free from gas and shrinkage porosity. Surfacetreatments such as case carburizing, flame hardening and have to be usedwhen a wear resistant surface must be combined with a hard tough exteriorsurface.One such application is bimetallic pipe consisting of two separateconcentric layers ofdifferent alloys/metals bonded together.

1.7.2. CARBON DI OXIDE PROCESS MOULDING.

Working PrincipleThe highly flowable mixture of pure dry silica sand and sodium silicate binder is

rammed or blown into the mould or core box. Carbon –dioxide gas at a pressure ofabout 1.5 bar is diffused through the mixture (of sand and sodium silicate) to initiate thehardening reaction which takes from a few seconds to a few minutes depending uponthe size of core or mould.Passage of carbon-dioxide through the sand containingsodium silicate produces carbonic acid in the aqueous solution, this causes a rise in theSiO2- Na2O ratio and the formation of a colloidal silica gel which hardens and forms abond between the sand grains. The reaction is represented by the following equation.

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NaSiO3 + CO2 --------- NaCO3 + SiO2

(Sodium Silicate) (Silica Gel)

Carbon Dioxide Moulding Operation

This sand is mixed with 3 to 5 % sodium silicateliquid base binder in Muller for 3 to 4 minutes.Additives such as coal powder, wood flour sea coal,and dextrin may be added to b improve its

properties. Aluminium oxide Kaolin clay may alsoadded to the sand. Patterns used in this method may becoated with Zinc of 0.05 mm to 0.13 mm and thenspraying a layer of aluminium or brass of about 0.25mm thickness for good surface finish and good results.Advantages

• Operation is speedy since we can use the mould and cores immediately afterprocessing.• Heavy and rush orders• Floor space requirement is less• Semi skilled labor may be used.

DisadvantagesDifficult in reusing the moulding sand.

1.7.3.Investment CastingInvestment casting produces very high surface quality and dimensionalaccuracy. Investment casting is commonly used for precision equipmentsuch as surgical equipment, for complex geometries and for preciousmetals.This process is commonly used by artisans to produce highly detailed artwork.The first step is to produce a pattern or replica of the finishedmould. Wax is most commonly used to form the pattern, althoughplastic is also used.

Patterns are typically mass-produced by injecting liquid or semi-liquidwax into a permanent die.Prototypes, small production runs and specialty projects can also be

undertaken by carving wax models.Cores are typically unnecessary but can be used for complex internal

structures. Rapid prototyping techniques have been developed to produceexpendable patterns.Several replicas are often attached to a gating system constructed of

the same material to form a tree assembly. In this way multiple castingscan be produced in a single pouring.

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NaSiO3 + CO2 --------- NaCO3 + SiO2

(Sodium Silicate) (Silica Gel)

Carbon Dioxide Moulding Operation

This sand is mixed with 3 to 5 % sodium silicateliquid base binder in Muller for 3 to 4 minutes.Additives such as coal powder, wood flour sea coal,and dextrin may be added to b improve its

properties. Aluminium oxide Kaolin clay may alsoadded to the sand. Patterns used in this method may becoated with Zinc of 0.05 mm to 0.13 mm and thenspraying a layer of aluminium or brass of about 0.25mm thickness for good surface finish and good results.Advantages

• Operation is speedy since we can use the mould and cores immediately afterprocessing.• Heavy and rush orders• Floor space requirement is less• Semi skilled labor may be used.

DisadvantagesDifficult in reusing the moulding sand.

1.7.3.Investment CastingInvestment casting produces very high surface quality and dimensionalaccuracy. Investment casting is commonly used for precision equipmentsuch as surgical equipment, for complex geometries and for preciousmetals.This process is commonly used by artisans to produce highly detailed artwork.The first step is to produce a pattern or replica of the finishedmould. Wax is most commonly used to form the pattern, althoughplastic is also used.

Patterns are typically mass-produced by injecting liquid or semi-liquidwax into a permanent die.Prototypes, small production runs and specialty projects can also be

undertaken by carving wax models.Cores are typically unnecessary but can be used for complex internal

structures. Rapid prototyping techniques have been developed to produceexpendable patterns.Several replicas are often attached to a gating system constructed of

the same material to form a tree assembly. In this way multiple castingscan be produced in a single pouring.

ME6302-MANUFACTURING TECHNOLOGY –I II /III MECHANICAL ENGINEERING

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NaSiO3 + CO2 --------- NaCO3 + SiO2

(Sodium Silicate) (Silica Gel)

Carbon Dioxide Moulding Operation

This sand is mixed with 3 to 5 % sodium silicateliquid base binder in Muller for 3 to 4 minutes.Additives such as coal powder, wood flour sea coal,and dextrin may be added to b improve its

properties. Aluminium oxide Kaolin clay may alsoadded to the sand. Patterns used in this method may becoated with Zinc of 0.05 mm to 0.13 mm and thenspraying a layer of aluminium or brass of about 0.25mm thickness for good surface finish and good results.Advantages

• Operation is speedy since we can use the mould and cores immediately afterprocessing.• Heavy and rush orders• Floor space requirement is less• Semi skilled labor may be used.

DisadvantagesDifficult in reusing the moulding sand.

1.7.3.Investment CastingInvestment casting produces very high surface quality and dimensionalaccuracy. Investment casting is commonly used for precision equipmentsuch as surgical equipment, for complex geometries and for preciousmetals.This process is commonly used by artisans to produce highly detailed artwork.The first step is to produce a pattern or replica of the finishedmould. Wax is most commonly used to form the pattern, althoughplastic is also used.

Patterns are typically mass-produced by injecting liquid or semi-liquidwax into a permanent die.Prototypes, small production runs and specialty projects can also be

undertaken by carving wax models.Cores are typically unnecessary but can be used for complex internal

structures. Rapid prototyping techniques have been developed to produceexpendable patterns.Several replicas are often attached to a gating system constructed of

the same material to form a tree assembly. In this way multiple castingscan be produced in a single pouring.

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Advantages– Parts of great complexity and intricacy can be cast– Close dimensional control and good surface finish– Wax can usually be recovered for reuse– Additional machining is not normally required - this is a net shape process

Disadvantages– Many processing steps are required– Relatively expensive process

1.7.4.Shell-moldingShell-mold casting yields better surface quality and tolerances.The 2-piece pattern is made of metal (e.g. aluminum or steel), it is heated tobetween 175°C- 370°C, and coated with a lubricant, e.g. silicone spray. Eachheated half-pattern is covered with a mixture of sand and a thermoset resin/epoxybinder. The binder glues a layer of sand to the pattern, forming a shell. Theprocess may be repeated to get a thicker shell.The assembly is baked to cure it.Thepatterns are removed, and the two half-shells joined together to form the mold;metal is poured into the mold. When the metal solidifies, the shell is broken to getthe part.

Advantages of shell mouldingSmoother cavity surface permits easier flow of molten metal and better

surface finish on castingGood dimensional accuracyMachining often not requiredMold collapsibility usually avoids cracks in castingCan be mechanized for mass production

Disadvantages of shell moulding.More expensive metal patternDifficult to justify for small quantities

1.8..Casting Defects.

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Advantages– Parts of great complexity and intricacy can be cast– Close dimensional control and good surface finish– Wax can usually be recovered for reuse– Additional machining is not normally required - this is a net shape process

Disadvantages– Many processing steps are required– Relatively expensive process

1.7.4.Shell-moldingShell-mold casting yields better surface quality and tolerances.The 2-piece pattern is made of metal (e.g. aluminum or steel), it is heated tobetween 175°C- 370°C, and coated with a lubricant, e.g. silicone spray. Eachheated half-pattern is covered with a mixture of sand and a thermoset resin/epoxybinder. The binder glues a layer of sand to the pattern, forming a shell. Theprocess may be repeated to get a thicker shell.The assembly is baked to cure it.Thepatterns are removed, and the two half-shells joined together to form the mold;metal is poured into the mold. When the metal solidifies, the shell is broken to getthe part.

Advantages of shell mouldingSmoother cavity surface permits easier flow of molten metal and better

surface finish on castingGood dimensional accuracyMachining often not requiredMold collapsibility usually avoids cracks in castingCan be mechanized for mass production

Disadvantages of shell moulding.More expensive metal patternDifficult to justify for small quantities

1.8..Casting Defects.

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Advantages– Parts of great complexity and intricacy can be cast– Close dimensional control and good surface finish– Wax can usually be recovered for reuse– Additional machining is not normally required - this is a net shape process

Disadvantages– Many processing steps are required– Relatively expensive process

1.7.4.Shell-moldingShell-mold casting yields better surface quality and tolerances.The 2-piece pattern is made of metal (e.g. aluminum or steel), it is heated tobetween 175°C- 370°C, and coated with a lubricant, e.g. silicone spray. Eachheated half-pattern is covered with a mixture of sand and a thermoset resin/epoxybinder. The binder glues a layer of sand to the pattern, forming a shell. Theprocess may be repeated to get a thicker shell.The assembly is baked to cure it.Thepatterns are removed, and the two half-shells joined together to form the mold;metal is poured into the mold. When the metal solidifies, the shell is broken to getthe part.

Advantages of shell mouldingSmoother cavity surface permits easier flow of molten metal and better

surface finish on castingGood dimensional accuracyMachining often not requiredMold collapsibility usually avoids cracks in castingCan be mechanized for mass production

Disadvantages of shell moulding.More expensive metal patternDifficult to justify for small quantities

1.8..Casting Defects.

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Casting defectsDefects may occur due to one or more of the following reasons:

– Fault in design of casting pattern– Fault in design on mold and core– Fault in design of gating system and riser– Improper choice of moulding sand– Improper metal composition– Inadequate melting temperature and rate of pouring

Some common defects in castings:a) Misruns b) Cold Shut c) Cold Shot d) Shrinkage Cavity e) Microporosity f) HotTearing

a)MisrunsIt is a casting that has solidified before completely filling the mold cavity.

Typical causes include1) Fluidity of the molten metal is insufficient,2) Pouring Temperature is too low,3) Pouring is done too slowly and/or4) Cross section of the mold cavity is too thin.b) Cold Shut

A cold shut occurs when two portion of the metal flow together, but thereis lack of

fusion between them due to premature freezing, Its causes are similar to those of aMisruns.c) Cold Shots

When splattering occurs during pouring, solid globules of the metal areformed that

become entrapped in the casting. Poring procedures and gating systemdesigns that avoid splattering can prevent these defects.d) Shrinkage Cavity

This defects is a depression in the surface or an internal void in the castingcaused by

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solidification shrinkage that restricts the amount of the molten metal availablein the last region to freeze.e) Microporosity

This refers to a network of a small voids distributed throughout the castingcaused by

localized solidification shrinkage of the final molten metal in the dendritic structure.f) Hot Tearing

This defect, also called hot cracking, occurs when the casting is restrained orearly stages

of cooling after solidification.

1.9 Non-destructive methods used for finding casting Defects.

The various casting defects may be on the surface, under the surface of the solidified casting.These defects are found out by the below mentioned non-Destructive Inspection methods.

1. Ultra Sonic Inspection2. Liquid Penetrant Inspection3. Magnetic Particle Inspection

1.9.1.Ultra sonic Inspection.Ultrasonic sound waves are in the frequency decibel which cannot be heared by a human

ear. The bats use this kind of sound waves in-order to find the obstacles while flying. Thesewaves will be reflected back to the source when obstructed. Similarly, in ultrasonic testing thereis a probe which sends the ultrasonic sound waves into the metal part that is to be inspected. Thesound waves will be reflected back after hitting the other end of the metal.

If there is a crack in the middle of the metal part, then the sound waves will be reflectedbefore in advance.

This process is shown in the monitor as a graph. Thus the crack is identified and decidedwheather to rectify the crack or reject the metal part.

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1.9.2. LPT (Liquid Penetrant Testing)

Chemicals Used.

1. Cleaner2. Potassium Permanganate solution3. Developer.

Initially the Casted Metal Part to be inspected is cleaned using Cleaner. Dust, oil, Grease etc areremoved. Then potassium permanganate solution is sprayed over the surface of the metal partand allowed to remain for 5 – 7 mins. Then the potassium permanganate solution is cleaned.

Now developer is applied over the surface. Due to capillary action the rose/pink colourpotassium permanganate liquid will reach the surface of the crack. And now the crack will bevisible in pink/rose color.Thus the surface cracks are inspected on the casting.

ADVANTAGES & LIMITATIONS OF LPT

Cost of the chemicals is low when compared to UT & MPT.

Huge / Large size components can be inspected, only on the particular area, where it is required.

Time taken is less.

1.9.3.MPT Magnetic Particle testing.

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This method of inspection is used on magnetic ferrous castings for detecting invisiblesurface or slightly subsurface defects. Deeper subsurface defects are not satisfactorily detectedbecause the influence of the distorted lines of magnetic flux (owing to a Discontinuity) on themagnetic particles spread over the casting.

The defects commonly revealed by magnetic particle inspection are quenching cracks,overlaps, thermal cracks, seams , laps, grinding cracks, fatigue cracks, hot tears Etc,

Working Principle.

When a piece of metal is place in a magnetic field and the lines of magnetic flux getintersected by a discontinuity such as a crack or slag inclusion in a casting, magnetic poles areinduced on either side of the discontinuity. The discontinuity causes an abrupt change in the pathof magnetic flux flowing through the casting normal to the discontinuity, resulting in a localflux leakage field and interference with the magnetic lines of force. This local flux disturbancecan be detected by its effect upon magnetic particles which are attracted to the region ofdiscontinuity and pile up and bridge over the discontinuity.

A surface crack is indicated (under favorable conditions) by a line of fine particlesfollowing the crack outline and a subsurface defect by a fuzzy collection of the magneticparticles on the surface near the discontinuity. Maximum sensitivity of indication is obtainedwhen the discontinuity lies in a direction normal to the applied magnetic field and when the

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UNIT - II

METAL JOINING PROCESS

PREREQUISTE DISCUSSION

2.1.WeldingWelding is a materials joining process which produces coalescenceof materials by heating them to suitable temperatures with orwithout the pplication of pressure or by the application of pressurealone, and with or without the use of filler material. Welding is used formaking permanent joints. It is used in the manufacture ofautomobile bodies, aircraft frames, railway wagons, machine frames,structural works, tanks, furniture, boilers, general repair work and shipbuilding.

2.2. Types of weldingGAS WeldingARC Welding

2.3 GAS WELDING Sound weld is obtained by selecting proper size of flame, filler material andmethod of

moving torch The temperature generated during the process is 33000c. When the metal is fused, oxygen from the atmosphere and the

torch combines with molten metal and forms oxides, results defectiveweld

Fluxes are added to the welded metal to remove oxides Common fluxes used are made of sodium, potassium. Lithium and borax. Flux can be applied as paste, powder, liquid. solid coating or gas.

2.3.1GAS WELDING EQUIPMENT

1. Gas CylindersPressureOxygen – 125 kg/cm2Acetylene – 16 kg/cm22. RegulatorsWorking pressure of oxygen 1 kg/cm2Working pressure of acetylene 0.15kg/cm2Working pressure varies dependsupon the thickness of the work pieceswelded.3. Pressure Gauges4. Hoses5. Welding torch6. Check valve7. Non return valve

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2.3.2FLAMES PRODUCED DURING GAS WELDING

Three basic types of oxyacetylene flames used in oxyfuel-gas welding and cuttingoperations:

(a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing flame.

Addition of more oxygen give a brightwhitish cone surrounded by the transparent

blue envelope is called Neutral flame (It has a balance of fuel gas and oxygen)(32000c)

• Used for welding steels, aluminium, copper and cast iron

oxygen give a bright whitish cone surrounded by the transparentblue envelope is called Neutral flame (It has a balance of fuel gas and oxygen)(32000c)

• Used for welding steels, Aluminium, copper and cast iron.

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Oxygen is turned on, flame immediately changes into a long white inner area (Feather)

surrounded by a transparent blue envelope is called Carburizing flame (30000c)

Advantages of Gas welding.

1.Simple Equipment2.Portable3.Inexpensive4.Easy for maintenance and repair

Disadvantages Of Gas welding

1.Limited power Density2.Very low welding speed.3.High total heat input per unit length4.Large Heat affected Zone5.Severe Distortion6.Not recommended for welding reactive metals such as titanium and Zirconium.

2.3.3. Difference between Gas Welding and Arc Welding.

Sr NoGAS WELDING ARC WELDING

1.Heat is produced by the GasFlame

Heat is produced by Electric Arc

2. The flame temperature isabout 3200oC The temperature of Arc is about 4000oC

3. Separate Filler rodintroduced

Arc Producing as well as filler rod material is theelectrode.

4. Suggested for thin materials Suggested for medium and thick materials

5. Gas welded parts do nothave much strength

Arc welded parts have very high strength

6. Filler metal may not be thesame parent metal

Filler metal must be same or an alloy of the parentmetal

7. Brazing and soldering aredone using gas

Brazing and soldering can’t be carried out by electricarc.

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2.4. ARC WELDING

Uses an electric arc to coalesce metalsArc welding is the most common method of welding metalsElectricity travels from electrode to base metal to ground

2.4.1.Arc welding Equipments• A welding generator (D.C.)

or Transformer (A.C.)• Two cables- one for work

and one for electrode• Electrode holder• Electrode• Protective shield• Gloves• Wire brush• Chipping hammer• Goggles

2.4.2.Electrode

Electrode is a thin rod made up of same as that of parent material. Flux is coated over theelectrode to avoid oxidation. It is mostly connected to the negative polarity.

Two Basic Types of AW Electrodes Consumable – consumed during welding process

Source of filler metal in arc welding Nonconsumable – not consumed during welding process

Filler metal mustbe added separately

Consumable ElectrodesForms of consumable electrodes

• Welding rods (a.k.a. sticks) are 9 to 18 inches and 3/8 inch orless in diameter and must be changed frequently

• Weld wire can be continuously fed from spools with longlengths of wire, avoiding frequent interruptions

In both rod and wire forms, electrode is consumed by arc and added to weld joint asfiller metal.

Nonconsumable Electrodes Made of tungsten which resists melting Gradually depleted during welding (vaporization is principal mechanism) Any filler metal must be supplied by a separate wire fed into weld pool

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2.4.3.FluxA substance that prevents formation of oxides and other contaminants inwelding, or dissolves them and facilitates removal Provides protective atmosphere for welding Stabilizes arc Reduces spattering

2.4.4.STEPS FOLOWED IN ARC WELDING :• Prepare the edges to be joined and maintain the proper position

• Open the acetylene valve and ignite the gas at tip of the torch

• Hold the torch at about 45deg to the work piece plane

• Inner flame near the work piece and filler rod at about 30 – 40 deg

• Touch filler rod at the joint and control the movement according tothe flow of the material

Advantages

Most efficient way to join metalsLowest-cost joining methodAffords lighter weight through better utilization of materialsJoins all commercial metalsProvides design flexibility

Disadvantages• Manually applied, therefore high labor cost.• Need high energy causing danger• Not convenient for disassembly.• Defects are hard to detect at joints.

2.5. SPECIAL WELDING PROCESS2.5.1.Submerged arc welding

• Weld arc is shielded by a granular flux , consisting of silica, lime,manganese oxide,

calcium fluoride and other compounds.• Flux is fed into the weld zone by gravity flow through nozzle

Thick layer of flux covers molten metal

• Flux acts as a thermal insulator ,promoting deep penetration of heat into the work

piece• Consumable electrode is a coil of bare round wire fed automatically through atube• Power is supplied by 3-phase or 2-phase power lines

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2.5.2.Laser Beam Welding (LBW)

Fusion welding process in which coalescence is achieved byenergy of a highly concentrated, coherent light beam focused on joint Laser = "light amplification by stimulated emission of radiation" LBW normally performed with shielding gases to prevent oxidation

Filler metal not usually added High power density in small area, so LBW often used for small parts

Working

The laser WELDING system consists of a power source, a flash lamp filled with Xenon,lasing material, focusing lens mechanism and worktable. The flash tube flashes at a rate ofthousands per second. As a result of multiple reflections, Beam power is built up to enormouslevel.

The output laser beam is highly directional and strong, coherent and unicromatic with awavelength of 6934oA. It goes through a focusing device where it is pinpointed on the workpiece, fusion takes place and the weld is accomplished due to concentrated heat produced.Laser beam welding process is shown in the figure.

Advantages.

1.Wide variety of metals can be welded.2.Thermal damage is minimum.3.Weld metal is purified.4.Good ductility and mechanical properties.5.Welds are vaccum tight.6.filler metal is not used.

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7.No effect on heat treated components.

Limitations.

1.Low welding Speed.2.Limited to thickness of 1.5mm.3.Materials like Mg cannot be welded.

APPLICATIONS

Radio Engineering andMicroelectronics.

2.5.3.Electron Beam Welding (EBW)Fusion welding process in which heat for welding is provided by a highly-

focused, high-intensity stream of electrons striking work surface Electron beam gun operates at:

High voltage (e.g., 10 to 150 kV typical) to accelerate electrons Beam currents are low (measured in milliamps)

Power in EBW not exceptional, but power density is

Working

The Kinetic energy of the electrons is converted into intense heat energy when the electrons areabsorbed by the metal piece over a small area of the weld, producing deep penetration weld with adepth/width ratio as high as 15. This results in a narrow, almost parallel weld with very little distortion and asmall width of the heat affected zone. There is no possibility of contamination by atmospheric gases becauseprocess is carried out in vaccum.

Advantages High-quality welds, deep and narrow profiles Limited heat affected zone, low thermal distortion High welding speeds No flux or shielding gases needed

Disadvantages High equipment cost Precise joint preparation & alignment required Vacuum chamber required Safety concern: EBW generates x-rays

Comparison: LBW vs. EBW

No vacuum chamber required for LBW No x-rays emitted in LBW Laser beams can be focused and directed by optical lenses and mirrors LBW not capable of the deep welds and high depth-to-width ratios of EBW

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Maximum LBW depth = ~ 19 mm (3/4 in), whereas EBW depths = 50 mm (2 in)

2.5.4.PLASMA ARC WELDING

Principle:Plasma Arc welding is a constricted arc process. The arc is constrained with the help of a water

cooled small diameter nozzle which squeezes the arc, increases its pressure, temperature and heatintensely and thus improves stability, arc shape and heat transfer, characteristics

There are two methods of Plasma Arc Welding

(A) Transferred Arc(B)Non- Transferred Arc.

(a)Transfered ArcHere the electrical circuit is between the tungsten electode and the work piece. Work piece acts as

anode and the tungsten electrode as cathode. The arc is transferred from the electrode to the work pieceand hence the term transferred. Here the arc force is directed away from the plasma torch and into thework piece, hence capable of heating the work piece to a higher temperature.

(b)NON-Transferred Arc.

In Non-transferreed type, power is directly connected with the electrode and the torch of nozzle.The electrode carries the same current. Thus ,ionizing a high velocity gas that is strewing towards the

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workpiece. The main advantage of this type is that the spot moves inside the wall and heat the incominggas and outer layer remains cool. This type of plasma has low thermal efficiency.Advantages

1.Ensures arc stability.2.Produces less thermal distortion3.The process is readily automated.

Disadvantages.

1.Excessive noise is produced.2.Equipment is complicated and expensive.3.Large amount of ultraviolet and infrared rays are emitted.

2.5.5.THERMIT WELDING.

FW process in which heat for coalescence is produced by superheated molten metal from thechemical reaction of thermite Thermite = mixture of Al and Fe3O4 fine powders that produce an exothermic

reaction when ignited Also used for incendiary bombs Filler metal obtained from liquid metal Process used for joining, but has more in common with casting than welding

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Fig: Thermit welding: (1) Thermit ignited; (2) crucible tapped, superheated metalflows into mold; (3) metal solidifies to produce weld joint.Applications joining of railroad rails Repair of cracks in large steel castings and forgings Weld surface is often smooth enough that no finishing is required

2.5.6.TIG& MIG WELDING

Inert Gas WeldingFor materials such as Al or Ti which quickly form oxide layers, a method to place an inertatmosphere around the weld puddle had to be developed

Metal Inert Gas (MIG)• Uses a consumable electrode (filler wire made of the base metal)• Inert gas is typically Argon

Gas Tungsten Arc Welding (GTAW)Uses a non-consumable tungsten electrode and an inert gas for arc shielding Melting point of tungsten = 3410 C (6170 F) A.k.a. Tungsten Inert Gas (TIG) welding

In Europe, called "WIG welding" Used with or without a filler metal

When filler metal used, it is added to weld pool from separate rod or wire

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Applications: aluminum and stainless steel most common

Advantages High quality welds for suitable applications No spatter because no filler metal through arc Little or no post-weld cleaning because no flux

Disadvantages Generally slower and more costly than consumable electrode AW processes

2.5.7. RESISTANCE WELDING.

Resistance Welding (RW)A group of fusion welding processes that use a combination of heat and pressure toaccomplish coalescenceHeat generated by electrical resistance to current flow at junction to be weldedPrincipal RW process is resistance spot welding (RSW

Components in Resistance Spot Welding Parts to be welded (usually sheet metal) Two opposing electrodes Means of applying pressure to squeeze parts between electrodes Power supply from which a controlled current can be applied for a specified

time durationAdvantages No filler metal required High production rates possible Lends itself to mechanization and automation Lower operator skill level than for arc welding

Good repeatability and reliability.

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Applications: aluminum and stainless steel most common

Advantages High quality welds for suitable applications No spatter because no filler metal through arc Little or no post-weld cleaning because no flux

Disadvantages Generally slower and more costly than consumable electrode AW processes

2.5.7. RESISTANCE WELDING.

Resistance Welding (RW)A group of fusion welding processes that use a combination of heat and pressure toaccomplish coalescenceHeat generated by electrical resistance to current flow at junction to be weldedPrincipal RW process is resistance spot welding (RSW

Components in Resistance Spot Welding Parts to be welded (usually sheet metal) Two opposing electrodes Means of applying pressure to squeeze parts between electrodes Power supply from which a controlled current can be applied for a specified

time durationAdvantages No filler metal required High production rates possible Lends itself to mechanization and automation Lower operator skill level than for arc welding

Good repeatability and reliability.

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Applications: aluminum and stainless steel most common

Advantages High quality welds for suitable applications No spatter because no filler metal through arc Little or no post-weld cleaning because no flux

Disadvantages Generally slower and more costly than consumable electrode AW processes

2.5.7. RESISTANCE WELDING.

Resistance Welding (RW)A group of fusion welding processes that use a combination of heat and pressure toaccomplish coalescenceHeat generated by electrical resistance to current flow at junction to be weldedPrincipal RW process is resistance spot welding (RSW

Components in Resistance Spot Welding Parts to be welded (usually sheet metal) Two opposing electrodes Means of applying pressure to squeeze parts between electrodes Power supply from which a controlled current can be applied for a specified

time durationAdvantages No filler metal required High production rates possible Lends itself to mechanization and automation Lower operator skill level than for arc welding

Good repeatability and reliability.

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UNIT III

METAL FORMING PROCESS

3.PREREQUISTE DISCUSSION

The Materails to be used in places where the component is subjected to very high Impact load,Shock Load, intermittant load and in Power transmission lines, Need to be produced with dense grainstructure. This requirement can be acheived by manufacturing process such as Forging, Rolling,Extrusionand Drawing.

3.1.COMPARISION BETWEEN HOT WORKING AND COLD WORKING

SR NO HOT WORKING COLD WORKING1.

Hot working is done aboverecrystallisation temperature

Cold working isdone belowrecrystallisation temperature.

2.

Refinement of grains takes place Grain structure is distorted.

3.

Impurities and porosity are removed frommetals after hot working.

Impurities and porosities exist in metalafter cold working.

4.

Residual stresses are eliminated. Residual stresses are not eliminated.

5.

Rapid oxidation or scaling of surfacesoccurs which results in poor surface finish.

No oxidation and hence good surfacefinish is obtained.

6.

Close dimensional tolerances cannot bemaintained.

Close dimensional tolerances can beobtained.

7 Toolling and handling costs are more. Tooling and handling costs are less

8.

Mecanical properties such asToughness,ductility,elongation areimproved.

Cold w2orking decreaseselongation,reduction in area , hardness,tensile strength. Fatigue strength areimproved.

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3.2.ROLLING

Rolling is the most rapid method of forming metals into desired shapes by plastic deformation inbetween rolls.

The forming of bars, plates , sheets, rails and other steel sections are produced by rolling.

3.2.1.Classification of Rolling mill based on number of rolls.

1.Two High Rolling Mill.

2.Three high Rolling Mill

3.Four high Rolling Mill

4. Multi Rolling Mill.

5.Universal Rolling Mill

6.Planetary Rolling Mill.

1.Two High Rolling Mill.

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3.2.2. DEFECTS IN ROLLED PARTS

There are two types of major defects on the rolled products.

(a) SURFACE DEFECTS(b) INTERNAL SURFACE DETECTS.

(a) SURFACE DEFECTS Major surface defects on rolled products are scales, rust,scratches,cracks, and pits. These defects occurs on the rolled products due to the impurities andinclusions present in the original cast materials.,

(b).INTERNAL SURFACE DEFECTS

i. WAVINESS OR WAVY EDGES.

It occurs due to the bending of rolls. The rolls acts as a straight beam. If the material flow iscontinuous and to maintain this continuity, strains with in the material should adjust with itself. There arecompressive strain on the edges and tensile strain at the centre. The edges are restrained from expandingfreely in the longitudinal direction because of which wavy edges on the sheet will be produced.

ii. Zipper Cracks

It occurs due to poor material ductility, at the rolling temperatureCamber is provided to avoid thisdefect., Camber is providing slightly large diameter at the center of rolls than that at the edges.

iii. FOLDS

Folds occur if the reduction per pass is very less.

iv. Alligatoring.

It is the splitting of work piece along the horizontal plane on exit, with top and bottom part followingthe rotation of their respective rolls.

v. Lamination.

These are small cracks which may develop when reduction in thickness is excessive.

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3.3.FORGING

3.3.1. COMPARISON BETWEEN PRESS FORGING AND DROP FORGING.

SR NO Press forging Drop Forging1. It is a Faster process Slow Process2. Die alignment is easier Die alignment is difficult3. Operation is quite Noisy operation4. Quality of product is good Quality of product is fair.5. Stroke and ram speed is high It is low.6. It is one stroke operation Multiple stroke operation.7. Range is 20 tons to 1500 tons. Range upto 10 tons

8. Shapes formed are dense and homogeneous instructure.

Coarse and not homogenous instructure.

3.3.2. Forging operationsForging is a process in which the work piece is shaped by compressive forces applied through various diesand tools. It is one of the oldest metalworking operations. Most forgings require a set of dies and a pressor a forging hammer. A Forged metal can result in the following: -

Decrease in height, increase in section - open die forging Increase length, decrease cross-section, called drawing out. Decrease length, increase in cross-section on a portion of the

length - upsetting Change length, change cross-section, by squeezing in closed

impression dies - closed die forging. This results in favorable grainflow for strong parts

3.3.3. Types of forging Closed/impression die forging Electro-upsetting Forward extrusion Backward extrusion Radial forging Hobbing

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Isothermal forging Open-die forgig Upsetting Nosing Coining

Commonly used materials include• Ferrous materials: low carbon steels• Nonferrous materials: copper, aluminum and their alloys

3.3.3.1Open-Die Forging

Open-die forging is a hot forging process in which metal is shaped byhammering or pressing between flat or simple contoured dies.

Equipment. Hydraulic presses, hammers.

Materials. Carbon and alloy steels, aluminum alloys, copper alloys, titaniumalloys, all forgeable materials.

Process Variations. Slab forging, shaft forging, mandrel forging, ring forging,upsetting between flat or curved dies, drawing out.

Application. Forging ingots, large and bulky forgings, preforms for finished forgings.

Closed Die ForgingIn this process, a billet is formed (hot) in dies (usually with two halves) such that the flow

of metal from the die cavity is restricted. The excess material is extruded through arestrictive narrow gap and appears as flash around the forging at the die parting line.

Equipment. Anvil and counterblow hammers, hydraulic, mechanical, and screw presses.

Materials. Carbon and alloy steels, aluminum alloys, copper alloys, magnesiumalloys, beryllium, stainless steels, nickel alloys, titanium and titanium alloys, iron andnickel and cobalt super alloys.

Process Variations. Closed-die forging with lateral flash, closed-die forging withlongitudinal flash, closed-die forging without flash.

Application. Production of forgings for automobiles, trucks, tractors, off-highwayequipment, aircraft, railroad and mining equipment, general mechanical industry, andenergy-related engineering production.

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3.3.4.DEFECTS IN FORGED PARTS

1.Unfilled Sections.

In this some of the die cavity are not completely filled by the flowing metal.

2.Cold Shuts.

This appears as small cracks at the corners of the forging. Caused due to improper design of die.

3.Scale Pits.This is seen as irregular depositions on the surface of forging. This is primarily caused because of

improper cleaning of the stock used for forging.The oxides and scales gets embedded into the finish forging surface.When the forging is cleaned by pickling, these are seen as deputations on the forging surfaces.

4.Die Shifts.

This is caused by the mis-alignment of the half dies, making the two halves of te forging to be ofimproper shape. It is also called as mismatch.

5..Flakes.These are basically ruptures caused by the improper cooling of the large forging. Rapid cooling

causes the exterior to cool quickly causing internal fractures.

6.Improper Grain Flow.Due to improper design of the die, which makes the flow of the metal to be not in the final intended

direction?

7.Laps.Laps are formed by webbuckling during forging. To avoid laps web thickness should be increased

and properly edesigned.

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UNIT IV

SHEET METAL PROCESS

PREREQUISITE DISCUSSION

Now a day the automobile component, aircraft and ship building involves the usage of thin sheets ofvarious metals. If the thickness of the metal is less than six ‘mm’ then it is called as sheet. Hence theknowledge about the sheet metal processing is necessary. This unit deals how the sheet metals are processedfor meeting the requirement & Involves methods in which sheet metal is cut into required dimensionsand shape; and/or forming by stamping, drawing, or pressing to the final shape. The surface finish of thesheet metals processed by this methods are good when compared to other process like welding, machiningetc., A special class of metal forming where the thickness of the piece of material is small comparedto the other dimensions. Cutting into shape involve shear forces Forming Processes involve tensile stresses.

4. The Major operations of sheet Metal are;(A) Shearing,(B) Bending,(C) Drawing and(D) Squeezing

4.1. ShearingThe mechanical cutting of materials without the information of chips or the use of Burning ormelting for straight cutting blades: shearing for curved blades: blanking, piercing, notching, trimmingClassifications of Shearing Processes

BlankingPunchingPiercingTrimmingSlittingNotchingNibblingShavingDinkingPerforatingLancingCutoffSpring Back

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Blanking.Cutting a piece from the sheet metal by leaving enough scrap around the opening to assure that the

punch has enough metal to cut along its entire edge, during which a metal work piece is removed from theprimary metal strip or sheet when it is punched.Punching.

It is the operation to produce circular holes on a sheet metal by a punch and a die. Here the piercedmetal is the final product then the operation is called as punching.

Piercing.It is an operation to produce holes of any desired shape. Piercing produces a raised hole rather than acut hole. Piercing refers to punching a hole.

Trimming.It is the operation of cutting and removing unwanted excess metal from the periphery of a previously

formed /forged/cast component.SlittingShearing process used to cut rolls of sheet metal into several rolls of narrower width used to cut a wide coil

of metal into a number of narrower coils as the main coil is moved through the slitter. Shearingoperations can be carried by means of a pair of circular blades.

NotchingSame as piercing- edge of the strip or black forms part of the punch-out perimeter. In this process the

metal is removed from the side (OR) EDGE of a sheet to get the desired shape.Nibbling

Produces a series of overlapping slits/notches. A machine called nibbler moves a small straight punchup and down rapidly into a die.Shaving

Finishing operation in which a small amount of metal is sheared away from the edge of analready blanked part .can be used to produce a smoother edge. The rough edges of a blanked part areremoved by cutting thin strip of metal along the edge on the periphery.Dinking

Used to blank shapes from low-strength materials such as rubber, fiber and clothPerforating.

Process of making multiple holes which are small in diameter and closed together.Lancing.

Lancing refers to leaving a tab without removing any material. It is an operationof cutting on one sideand bending on the other side to form a sort of tab (or) Louver. No metal is removed in this operation.Lancing refers to leaving a tab without removing any material. It is an operationof cutting on one sideand bending on the other side to form a sort of tab (or) Louver. No metal is removed in this operation.

Cutting Off.In this operation a piece is removed from a strip by cutting along a single line.Parting The sheet issheared into two (Or) more pieces.

Spring backThe elastic recovery of the material after unloading of the tools.

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4.2. Bending

The plastic deformation of metals about a linear axis with little or no change in the surface area. Thepurpose of bending is to form sheet metal along a straight line

4.3. STRETCH FORMING OPERATIONS

In this process, the sheet metal is clamped along the edges and then stretched over a die (OR) FORMBLOCK, which moves upward, downward (or) side ways, depending on the particular machine.

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It is used to make aircraft wing-skin panels, automobile door panels and window frames.The desirable qualities in the metal for maximum strechability are as follows.

1.Fine grain structure.2.toughness.3.LARGE SPREAD between the tensile yield and ultimate strength.

Working.

It consists of placing the sheet –metal under a tensile load over a forming block and stretching it beyondits elastic limit and to te plastic range, thus cause a permanent set to take place.

Two Basic Forms of Stretch forming are,

1.Stretch forming,2.Stretch – Wrap forming.

Advantages1. In a single operation, blanks can be stretched.2. Heat treatment before and after stretching process is not required.3. Spring back effect is minimized.4. Tooling cost is low.5. Direct bending is not introduced, and plastic deformation is due to pure tension.6. It is suitable for low volume production.

Disadvantages.

1.uneven thickness of blank cannot be stretched.2.The maintanence cost of the hydraulic cylinders is high.

4.4. SPECIAL FORMING PROCESS.

4.4.1.HYDRO FORMING PROCESS

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In this process te pressure over the rubber membraneis controlled throughout the forming cycle, withmaximum pressure upto- 100 Mpa.This procedure allows close control of the part during forming, toprevent wrinkling (or) tearing. This process is called hydroform or fluif – Forming Process.Hydro forming isa Drawing process.

Advantages of Hydro-formimg Process.

1.It is used for Mass production.2.Tools can be quickly changed.3.Complicted shapes , sharp corners can be made by this method.4.Spring back, Thining off metals are removed.

4.4.2.RUBBER PAD FORMING

One of the die material is made up of a flexible material (ex. Rubber) Or (poly-urethanematerial.In bending and embossing of sheet metal , the female die is replaced with a rubberpad.Pressure in the rubber pad forming is usually in the order of10Mpa.

The blank is placed under the punch called male die.Then the ram (femal part) is moved so thatpunch touches the top surface of the work. Then the force is appled and gradually. increased onthe blank through the rubber pad.

The blank holder ring is used to distribute uniform pressure throughout the blank.

Thus the required shape is formed on the sheet metal between male and female parts.

Advantages of rubber pad forming.

1.Number of shapes can be formed on one rubber pad.2.Thining in metal balank does not take place.\3.setting time of the tool is less.4.Wrinkle – free , shrink flanges can be produced.

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Disadvantages

1.Rapid wearing of rubber Pads is a problem in this process.2.Accurate sharp corners cannot be made by this process.3.Loss of pressure between hydraulic fluid and rubber pad which is a major problem

Aplications.

Flanged Cylinders.Rectangular cups,Spherical Domes.Unsymmetrical shaped components can be made.

4.4.3.PEEN FORMING PROCESS.

This process is used to produce curvature on thin sheet metals by shot peening on surface of the sheet.A stream of metal shots is blasted against the surface of the blank.This process is also called as peen forming technique.

Peening is done with cast- iron (or) Steel shot discharged eitherfrom a rotating wheel by an air blast made from a nozzle.

Advantages of Peen forming

Complex shapes can be easily produced .Die and Punch is not used.Peening is used as a salvage operations for distorted parts (OR) correcting part.

Disadvantages of peen forming.

This process requires longer time for forming the required shape.

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Requires additional devices for forcing out metal shots.

Applications of peen forming.Specific portions on crankshafts , connecting rods, gearsHoney comb panels like aircraft wings and large tubular shapes can be produced.

UNIT -V

MANUFACTURING OF PLASTIC COMPONENTS

PREREQUISITE DISCUSSION

Plastics are the best alternatives used in the areas where the component size is very small and weightreduction is required in order to minimize the cost of material. Hence knowledge about various types ofplastics, its properties, production method etc is very important.

5.1.TYPES OF PLASTICS

Plastics are of two types1.Thermo plastics2.Thermosetting Plastics

Common plastics USED in molding are• HDPE (stiff bottle, toys, cases, drum)• LDPE (flexible bottle)• PP (higher temperature bottle)• PVC (clear bottle, oil resistant containers)• PET (soda pop bottle)• Nylon (automotive coolant bottle, power steering reservoir)

5.2.INJECTION MOULDING.

Injection MoldingMost widely used process. Suitable for high production of thermoplastics. Charge fedfrom a hopper is heated in a barrel and forced under high pressure into a mold cavity.Several types. Variety of parts can be made.

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Basic components:mold pieces (define the geometry of the part), and sprue, gates, runners, vents, ejection pins,cooling system

There are two types of injection moulding.1. Plunger type injection moulding.2. Screw type injection moulding.

In screw type injection moulding machine the plunger is replaced by a screw.A receiprocating screw nowforces the material into the mould.since the screw action generally helps to pack the materials better , a givenplunger travel will push more material into the cavity. Finally the action of the screw , as it rotates andmixes, adds energy to the melt.

Band heaters are still needed to fully heat the melt. All of this results in a much better and more consistentpart.

Virtually all industrial presses are screw type presses.

5.3. BLOW MOULDING

Blow Moldingused to make thermoplastic bottles and hollow sections. Starting material is a

round heated solid-bottom hollow tube – perform.Perform inserted into two die halves and air is blown inside to complete the

process

General steps• Melting the resin- done in extruder• Form the molten resin into a cylinder or tube (this tube is called parison)• The parison is placed inside a mold, and inflated so that the plastic is pushed outwardagainst the cavity wall• The part is allowed to cool in the mold and is then ejected• The part is trimmedThe parison can be formed by

A)Extrusion processB)Injection molding process

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(A)Extrusion blow molding– Parison is formed from by forcing the plastic through an extrusion

die.

Material enters the die, flow around the mandrel so that extrudate wouldbe cylindrical

– The die would have a hole at the center so that air could be blowninto the cylinder

– In some blow molding operations, the air is introduced from the bottomthrough an inlet

This process can be;– continuous extrusion blow molding

• During the process, the extrusion runs continuously, thus making acontinuous parison.• using multiple mold to match the mold cycle to the extrusion speed

– Intermittent extrusion blow molding• During the process, the extruder is stopped during the time that themolding occur• use either reciprocating screw or an accumulator system

• In this system, the output of the extruder is matched by having multiple molds which sealand blow the parison and then move away from extruder to cool and eject

• In practical case, the mold cycle is longer than time required to extrude a new parison• If the mold cycle is twice than time needed for creating a parison, a two mold system can

be used• The method is sometimes called rising mold system - system of which two or more molds

are used to mold parts from one extruder during continuous process

b) Injection Blow Molding• The parison is formed by the injection of molten resin into a mold cavity and around a

core pin• The parison is not a finished product, but it is subjected to subsequent step to form the

final shape• Second step, blowing of the intermediate part in a second mold• Because of distinct separation of the two steps, the parison made by injection molding is

called a perform

Process• The mold is closed• Resin is then injected to form a cylindrical part• The mold is opened and perform is ejectedThe perform can be stored until the finished blow molded is needed.The flexibility of separating the two cycles has proven useful in manufacture ofsoda pop bottle.

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Comparison of extrusion and injection blow molding

Sr no(a)Extrusion blowmolding

(b)Injection blow molding

1.– It is best suited for bottleover 200g in weight, shorterruns and quick tool changeover

• Best suited for long runs and smallerbottles

• No trim scrap

– Machine costs are comparable toinjection blow molding • Higher accuracy in final part

Tooling costs are 50% to 75% lessthan injection machine

It requires sprue and head trimming

Better transparencies with injectionblow molding, because

crystallizationcan be bettercontrolled

Total cycle is shorter thaninjection (since the parisonand blowing can be done using the same machine)

• Can lead to improve mechanicalproperties from improved parison design.

Wider choiceof resin

• Uniform wallthickness

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5.4.ROTATIONAL MOULDING.

It is also known as Rotomoulding, rotocasting or spin casting.

The thin walled metal mould is a split female mould made of two pieces and is designed to be rotated abouttwo perpendicular axes. The steps followed in rotational moulding are.

STEP-1

A predetermined amount of plastic , powder or liquid form , is deposited in one half of a mould.

STEP – 2

The mould is closed.

STEP -3

The mould is rotated biaxially inside an oven. The hollow part should be rotated through two or more axes,rotating at different speeds, in order to avoid the accumulatiuon of polymer powder.

STEP – 4

The plastic melts and forms a coating over the inside surface of the mould.

STEP -5

The mould is removed from the oven and cooled usually by fan. The polymer must be cooled so thatit solidifies and can be handled safely by the operator.The part will shrink on cooling, coming away from themould and facilitating easy removal of the part.

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STEP-6

The part is removed from the mould.

Advantages of rotational moulding

1. Moulds are relatively inexpensive.

2. Different parts can be moulded at same time.

3.Very large hollow parts can be made.

4.Parts are stress free.

5.Very little scrap is produced.

Limitations of rotational moulding.

1.Moulding Cycles are long 10-20 mins

2.It is not possible to make some sharp threads.

3.Cannot make parts with tight tolerance.

5.5.TRANSFER MOULDING.

Transfer Molding A process of forming articles by fusing a plastic material in a chamber then forcing the

whole mass into a hot mold to solidify. Used to make products such as electrical wall receptacles and circuit breakers Similar to compression molding except thermosetting charge is forced into a heated

mold cavity using a ram or plunger.Examples: electrical switchgear, structural parts

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Process Variables• Amount of charge• Molding pressure• Closing speed• Mold temperature• Charge temperature• Cycle timeAdvantages

• Little waste (no gates, sprues, or runners in many molds)• Lower tooling cost than injection molding• Good surface finish• Less damage to fibers• Process may be automated or hand-operated

• Material flow is short, less

Disadvantages• High initial capital investment• Labor intensive• Secondary operations maybe required• Long molding cycles may be needed.

5. 6.COMPRESSION MOULDING.

Compression Molding• The process of molding a material in a confined shape by applying pressure and usuallyheat.• Almost exclusively for thermoset materials• Used to produce mainly electrical products

Thermoset granules are “compressed” in a heated mold to shape required.Examples: plugs, pot handles, dishware

Applications of compression moulding.

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1.Dishes , Handles , container caps, fittings, electrical and electronic components.

2.Scoops, spoilers, hoods, fenders.

3.Polyester fiber glass resin systems (SMC/BMC)

MANUFACTURING TECHNOLOGY-1UNIVERSIT QUESTION BANK WITH ANSWERS

UNIT –IMETAL CASTING PROCESS

PART –A (2 Marks)1 State any four types of patterns. (May 2006)

Ans: The various types of patterns which are commonly used areas follows:1) Single piece or solid pattern2) Two piece or split pattern3) Loose piece pattern4) Cope and drag pattern5) Gated pattern

2 Mention any two advantages and disadvantages of die casting. (May=2006)Ans: Advantages:• It is a very fast process.• Moulds have longer life.• Better surface can be obtained.

Limitations:• Moulds are much costlier.• This method is not suitable for small quantity production.• Shape and weight of the casting is limited.

3 Write the requirements of good pattern. (May 2007)Ans: Simple in design• Cheap and readily available• Light in mass• Surface id smooth

• Have high strength4.What is core venting? (May 2007)Ans: While pouring the mould with molten metal mould walls and cores heat up rapidly and releases largeamount of gases. In order to prevent casting defects these gases must be vented out. For this purpose coreventing are used. Core venting are incorporated in the core box itself.5.What function of core ? (May 2008)

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Ans: Functions of core are:• Core provides a means of forming the main internal cavity for hollow casting.• Core provides external undercut feature.• Cores can be inserted to obtain deep recesses in the casting.

• Cores can be used to increase the strength of the mould.

6. Which process is called lost waxing method? Why? (May 2008)Ans: Investment casting process is also known as Lost-wax process. The term investmentrefers to a clock or special covering apparel. In investment casting, the clock is a refractory mould whichsurrounds the precoated wax pattern.

7. What is the function of core prints? (Dec. 2008)Ans:

1. Core prints are basically extra projections provided on the pattern.2. They form core seats in the mould when pattern is embedded in the sand for mould

making.3. Core seats are provided to support all the types of cores.4. Though the core prints are the part of pattern, they do not appear on the cast part.

8. What are the advantages and applications of ceramic moulds? (Dec. 2008)Ans: Advantages:

• It is less expensive• Intricate objects can be casted.• Castings of thin sections and which do not require machining can be produced.Applications:

• It is mainly used for all material using better ingredient in slurry.

9. What are the pattern materials? (Dec. 2008)Ans:1) Wood 2) Metal 3) Plastic4) Plaster 5) Wax

10. Explain the term fettling. (Dec. 2009)Ans: Fettling is the name given to cover all those operations which help the casting to givea good appearance. It includes the removal of cores, sand, gates, risers, runners and otherUnwanted projections from the casting.

11. What are the applications of casting?Ans: Transportation vehicles (in automobile engine and tractors)

• Machine tool structures• Turbine vanes and power generators• Mill housing• pump filter and valve

12. Mention the specific advantages of Co2 moulding Process.1.Gives strength and hardness to core.2.Process cost is less.3.It saves time on heating.

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4.It can be stored for long use.

13. Define AFS grain- fineness number.It is defined as the ratio between the total products and total percentage of sand retained on pan and

each sieve.AFS grain fineness number =sum of products /total sum of the % of sand retained on pan andeach sieve.14. Classify moulding Machines.

1.Squeezer Machine.2.Jolt machine.3.Jolt – squeezer Machine.4.Slinging Machines.5.Patten draw Machines.

15.what are the different types of furnaces used for casting.1.Cupola Furnace.2.Open Hearth furnace3.Crucible Furnace.4.Pot Furnace.5.Electric Furnace.

16.State the main functions of tuyeres in cupola furnace.The tuyers are used to supply air to the coke bed for complete burning.

Part-B (16 Marks)

1. What are the pattern allowances? Explain briefly each. (Nov/Dec- 2013) (16)Five types of allowances were taken into consideration for various reasons. They are1.Shrinkage allowance

Any metal when heated to liquid stage and solidified will undergo change in dimension. Mostly thedimension of the product will be reduced, then the actual size of the pattern. Hence the patterns aremade slightly in larger dimensions.(3%-5%)

2.Draft allowanceIt will be difficult to remove the pattern from the mould cavity (without disturbing the mould) afterramming of sand. Hence the pattern (wooden or metal pattern) is slightly given 2 o– 3 o TAPER in thez - axis or vertical direction.

3. Finish allowanceIt is otherwise called as machining allowance .The pattern is made slightly 5mm -10mm large indimension than the required final part dimension. After casting the extra material is removed fromthe solidified material by machining.

4.Shake or Rapping allowance.Before withdrawing the pattern it is rapped and thereby the size of the mould cavity increases.Actually by rapping , the external sections move outwards increasing the size and internal sectionsmove inwards decreasing the size. This allowance is kept negative and hence the pattern is madeslightly smaller in dimensions 05.1.0 mm.

5.Distortion allowance.Some material might tend to bend or distort from the actual size or dimensions. Hence the pattern is

give counter balance degree or angle of recess so that the material will be in the required dimensionwhen solidified in the mould cavity.

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2. Explain the CO2 process of core making state its advantages and applications. (16)

Working PrincipleThe highly flowable mixture of pure dry silica sand and sodium silicate binder is rammed or

blown into the mould or core box. Carbon –dioxide gas at a pressure of about 1.5 bar is diffusedthrough the mixture (of sand and sodium silicate) to initiate the hardening reaction which takes froma few seconds to a few minutes depending upon the size of core or mould.Passage of carbon-dioxide through the sand containing sodium silicate produces carbonic acid in the aqueous solution,this causes a rise in the SiO2- Na2O ratio and the formation of a colloidal silica gel which hardensand forms a bond between the sand grains. The reaction is represented by the following equation.

NaSiO3 + CO2 --------- NaCO3 + SiO2

(Sodium Silicate) (Silica Gel)

Carbon Dioxide Moulding OperationThis sand is mixed with 3 to 5 % sodium silicateliquid base binder in Muller for 3 to 4 minutes.Additives such as coal powder, wood flour sea coal,and dextrin may be added to b improve its

properties. Aluminium oxide Kaolin clay may alsoadded to the sand. Patterns used in this method maybe coated with Zinc of 0.05 mm to 0.13 mm andthen spraying a layer of aluminium or brass ofabout 0.25 mm thickness for good surface finishand good results.Advantages

• Operation is speedy since we can use the mould and cores immediately after processing.• Heavy and rush orders• Floor space requirement is less• Semi skilled labor may be used.

DisadvantagesDifficult in reusing the moulding sand.

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3. Write a short note on ‘Green sand mould’ and shell Moulding.

Sand Casting (Green sand mould) is simply melting the metal and pouring it into apreformed cavity, called mold, allowing (the metal to solidify and then breaking up themold to remove casting. In sand casting expandable molds are used. So for each castingoperation you have to form a new mold.

– Sand with a mixture of water and bonding clay– Typical mix: 90% sand, 3% water, and 7% clay– to enhance strength and/or permeability

Sand – Refractory for high temperature.TYPES OF SAND

a) Green-sand molds - mixture of sand, clay, and water; “Green" means mold contains moisture

at time of pouring.b) Dry-sand mold - organic binders rather than clay and mold is baked to improvestrengthc) Skin-dried mold - drying mold cavity surface of a green-sand

– mold to a depth of 10 to 25 mm, using torches orheating

Steps in Sand CastingThe cavity in the sand mold is formed by packing sand around a pattern, separating the mould into twohalves.The mold must also contain gating and riser system For internal cavity, a core must be included inmold A new sand mold must be made for each part

1. Pour molten metal into sand mold2. Allow metal to solidify3. Break up the mold to remove casting4. Clean and inspect casting5. Heat treatment of casting is sometimes required to improve metallurgical properties

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Steps in shell-moldingShell-mold casting yields better surface quality and tolerances.The process is described as follows:The 2-piece pattern is made of metal (e.g. aluminum or steel), it is heated to between 175°C-370°C, and coated with a lubricant, e.g. silicone spray. Each heated half-pattern is coveredwith a mixture of sand and a thermoset resin/epoxy binder. The binder glues a layer of sand tothe pattern, forming a shell. The process may be repeated to get a thicker shell.The assembly isbaked to cure it.The patterns are removed, and the two half-shells joined together to form themold; metal is poured into the mold. When the metal solidifies, the shell is broken to get thepart.

Advantages of shell mouldingSmoother cavity surface permits easier flow of molten metal and better surface

finish on castingGood dimensional accuracyMachining often not requiredMold collapsibility usually avoids cracks in castingCan be mechanized for mass production

Disadvantages of shell moulding.More expensive metal patternDifficult to justify for small quantities

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Steps in shell-moldingShell-mold casting yields better surface quality and tolerances.The process is described as follows:The 2-piece pattern is made of metal (e.g. aluminum or steel), it is heated to between 175°C-370°C, and coated with a lubricant, e.g. silicone spray. Each heated half-pattern is coveredwith a mixture of sand and a thermoset resin/epoxy binder. The binder glues a layer of sand tothe pattern, forming a shell. The process may be repeated to get a thicker shell.The assembly isbaked to cure it.The patterns are removed, and the two half-shells joined together to form themold; metal is poured into the mold. When the metal solidifies, the shell is broken to get thepart.

Advantages of shell mouldingSmoother cavity surface permits easier flow of molten metal and better surface

finish on castingGood dimensional accuracyMachining often not requiredMold collapsibility usually avoids cracks in castingCan be mechanized for mass production

Disadvantages of shell moulding.More expensive metal patternDifficult to justify for small quantities

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Steps in shell-moldingShell-mold casting yields better surface quality and tolerances.The process is described as follows:The 2-piece pattern is made of metal (e.g. aluminum or steel), it is heated to between 175°C-370°C, and coated with a lubricant, e.g. silicone spray. Each heated half-pattern is coveredwith a mixture of sand and a thermoset resin/epoxy binder. The binder glues a layer of sand tothe pattern, forming a shell. The process may be repeated to get a thicker shell.The assembly isbaked to cure it.The patterns are removed, and the two half-shells joined together to form themold; metal is poured into the mold. When the metal solidifies, the shell is broken to get thepart.

Advantages of shell mouldingSmoother cavity surface permits easier flow of molten metal and better surface

finish on castingGood dimensional accuracyMachining often not requiredMold collapsibility usually avoids cracks in castingCan be mechanized for mass production

Disadvantages of shell moulding.More expensive metal patternDifficult to justify for small quantities

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4. Briefly explain about Investment casting.Investment Casting

Investment casting produces very high surface quality and dimensional accuracy.Investment casting is commonly used for precision equipment such as surgicalequipment, for complex geometries and for precious metals.This process is commonly used by artisans to produce highly detailed artwork.The first step is to produce a pattern or replica of the finished mould. Wax ismost commonly used to form the pattern, although plastic is also used.Patterns are typically mass-produced by injecting liquid or semi-liquid wax

into a permanent die.Prototypes, small production runs and specialty projects can also be undertaken by

carving wax models.Cores are typically unnecessary but can be used for complex internal structures.

Rapid prototyping techniques have been developed to produce expendable patterns.Several replicas are often attached to a gating system constructed of the same

material to form a tree assembly. In this way multiple castings can be produced in asingle pouring.

Casting with expendable mould: Investment Casting

advantages– Parts of great complexity and intricacy can be cast

– Close dimensional control and good surface finish– Wax can usually be recovered for reuse– Additional machining is not normally required - this is a net shape process

Disadvantages– Many processing steps are required– Relatively expensive process

5.Explain about MPT Magnetic Particle testing in detail.

This method of inspection is used on magnetic ferrous castings for detecting invisible surface orslightly subsurface defects. Deeper subsurface defects are not satisfactorily detected because the influence ofthe distorted lines of magnetic flux (owing to a Discontinuity) on the magnetic particles spread over thecasting.

The defects commonly revealed by magnetic particle inspection are quenching cracks, overlaps,thermal cracks, seams , laps, grinding cracks, fatigue cracks, hot tears Etc,

Working Principle.

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4. Briefly explain about Investment casting.Investment Casting

Investment casting produces very high surface quality and dimensional accuracy.Investment casting is commonly used for precision equipment such as surgicalequipment, for complex geometries and for precious metals.This process is commonly used by artisans to produce highly detailed artwork.The first step is to produce a pattern or replica of the finished mould. Wax ismost commonly used to form the pattern, although plastic is also used.Patterns are typically mass-produced by injecting liquid or semi-liquid wax

into a permanent die.Prototypes, small production runs and specialty projects can also be undertaken by

carving wax models.Cores are typically unnecessary but can be used for complex internal structures.

Rapid prototyping techniques have been developed to produce expendable patterns.Several replicas are often attached to a gating system constructed of the same

material to form a tree assembly. In this way multiple castings can be produced in asingle pouring.

Casting with expendable mould: Investment Casting

advantages– Parts of great complexity and intricacy can be cast

– Close dimensional control and good surface finish– Wax can usually be recovered for reuse– Additional machining is not normally required - this is a net shape process

Disadvantages– Many processing steps are required– Relatively expensive process

5.Explain about MPT Magnetic Particle testing in detail.

This method of inspection is used on magnetic ferrous castings for detecting invisible surface orslightly subsurface defects. Deeper subsurface defects are not satisfactorily detected because the influence ofthe distorted lines of magnetic flux (owing to a Discontinuity) on the magnetic particles spread over thecasting.

The defects commonly revealed by magnetic particle inspection are quenching cracks, overlaps,thermal cracks, seams , laps, grinding cracks, fatigue cracks, hot tears Etc,

Working Principle.

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4. Briefly explain about Investment casting.Investment Casting

Investment casting produces very high surface quality and dimensional accuracy.Investment casting is commonly used for precision equipment such as surgicalequipment, for complex geometries and for precious metals.This process is commonly used by artisans to produce highly detailed artwork.The first step is to produce a pattern or replica of the finished mould. Wax ismost commonly used to form the pattern, although plastic is also used.Patterns are typically mass-produced by injecting liquid or semi-liquid wax

into a permanent die.Prototypes, small production runs and specialty projects can also be undertaken by

carving wax models.Cores are typically unnecessary but can be used for complex internal structures.

Rapid prototyping techniques have been developed to produce expendable patterns.Several replicas are often attached to a gating system constructed of the same

material to form a tree assembly. In this way multiple castings can be produced in asingle pouring.

Casting with expendable mould: Investment Casting

advantages– Parts of great complexity and intricacy can be cast

– Close dimensional control and good surface finish– Wax can usually be recovered for reuse– Additional machining is not normally required - this is a net shape process

Disadvantages– Many processing steps are required– Relatively expensive process

5.Explain about MPT Magnetic Particle testing in detail.

This method of inspection is used on magnetic ferrous castings for detecting invisible surface orslightly subsurface defects. Deeper subsurface defects are not satisfactorily detected because the influence ofthe distorted lines of magnetic flux (owing to a Discontinuity) on the magnetic particles spread over thecasting.

The defects commonly revealed by magnetic particle inspection are quenching cracks, overlaps,thermal cracks, seams , laps, grinding cracks, fatigue cracks, hot tears Etc,

Working Principle.

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When a piece of metal is place in a magnetic field and the lines of magnetic flux get intersected by adiscontinuity such as a crack or slag inclusion in a casting, magnetic poles are induced on either side of thediscontinuity. The discontinuity causes an abrupt change in the path of magnetic flux flowing through thecasting normal to the discontinuity, resulting in a local flux leakage field and interference with the magneticlines of force. This local flux disturbance can be detected by its effect upon magnetic particles which areattracted to the region of discontinuity and pile up and bridge over the discontinuity.

A surface crack is indicated (under favorable conditions) by a line of fine particles followingthe crack outline and a subsurface defect by a fuzzy collection of the magnetic particles on thesurface near the discontinuity. Maximum sensitivity of indication is obtained when the discontinuitylies in a direction normal to the applied magnetic field and when the strength of magnetic field is just

enoughto

saturate thesection

beinginspected.

11. What are the defects occur in products made by casting process. Explain with neat sketch.(NOV/DEC 2013) (16)

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Casting defectsDefects may occur due to one or more of the following reasons:

– Fault in design of casting pattern– Fault in design on mold and core– Fault in design of gating system and riser– Improper choice of moulding sand– Improper metal composition– Inadequate melting temperature and rate of pouring

Some common defects in castings:a) Misruns b) Cold Shut c) Cold Shot d) Shrinkage Cavity e) Microporosity f) Hot TearingMisruns:a)Misruns

It is a casting that has solidified before completely filling the mold cavity.Typical causes include1) Fluidity of the molten metal is insufficient,2) Pouring Temperature is too low,3) Pouring is done too slowly and/or4) Cross section of the mold cavity is too thin.b) Cold Shut

A cold shut occurs when two portion of the metal flow together, but there is lack offusion between them due to premature freezing, Its causes are similar to those of a Misruns.c) Cold Shots

When splattering occurs during pouring, solid globules of the metal are formed thatbecome entrapped in the casting. Poring procedures and gating system designs thatavoid splattering can prevent these defects.d) Shrinkage Cavity

This defects is a depression in the surface or an internal void in the casting caused bysolidification shrinkage that restricts the amount of the molten metal available in the lastregion to freeze.e) Microporosity

This refers to a network of a small voids distributed throughout the casting caused bylocalized solidification shrinkage of the final molten metal in the dendritic structure.f) Hot Tearing

This defect, also called hot cracking, occurs when the casting is restrained or early stagesof cooling after solidification.

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UNIT – II

METAL JOINING PROCESS

1 List out any four arc welding equipment. (May 2006)Ans: The most commonly used equipments for arc welding are as follows:(a) A.C or D.C. machine(b) Wire brush(c) Cables and connectors(d) Ear thing clamps(e) Chipping hammer

2 What are the special features of friction welding? (May 2007)Ans:

• Friction welding is a solid state welding process where coalescence is produced by the heat obtainedfrom mechanically induced sliding motion between rubbing surfaces.

• The work parts are held together under pressure.• Its operating is simple.• Power required for the operation is low.• It is used for joining steels, super alloys, non-ferrous metals and combinations of

metals.3.Define resistance welding process. (May 2006, May 2007)Ans: Resistance welding is a process where coalescence is produced by the heat obtained from resistanceoffered by the workpiece to the flow of electric current in a circuit of which the workpiece is a part and bythe application of pressure.4.What is the purpose of flux? (May 2008)Ans: 1) It acts as shield to weld.

2) To prevent atmospheric reaction of molten metal with atmosphere.

5. How can slag inclusions in welding be avoided? (May 2008)Ans: Avoid multi layer welding

• Reduce arc length• Increase electrode angle• Avoid using large electrode

6 How does brazing differ from braze welding? (Dec. 2008)Ans:Brazing Braze WeldingThe filler alloy is fed to one or morepoints in the assembly and it isdrawn into the rest of the joint bycapillary action.

The filler alloy is depositeddirectly at the point where it isdesired.

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7 Why flux is coated on filler rods? (Dec. 2008)Ans: The coating improves penetration and surface finish.

• Suitable coating will improve metal deposition rates.

8 What is the application of carburizing flame? (Dec. 2009) Ans:• Carburizing flame is generally used for: o Welding oflow alloy steel rodso Non-ferrous metalso High carbon steel

9 What are the diameter and length of the electrodes available in the market? (Dec. 2009)Ans: Standard length of electrodes are 250 mm, 300 mm and 450 mm.

• Standard diameters of electrodes are 1.6,2 ,2.5, 3.2, 4,5,6,7,8, and 9 mm.

10. Classify various ARC welding processes

(i) Arc welding• Carbon arc

• Metal arc

• Metal inert gas

• Tungsten inert gas

• Plasma arc

• Submerged arc

• Electro-slag

11. Classify various GAS welding processes

(ii) Gas Welding• Oxy-acetylene

• Air-acetylene

• Oxy-hydrogen

12. Name the various methods of Resistance Welding

B UTTSpotSeam

Projection & Percussion.13. What is ‘Brazing’

It is defined as the t3echnique of joining two dissimilar or similar materials by addition ofspecial filler material. Brazing gives a much stronger joint than soldering but requires greater heatwhich cannot be obtained from copper in soft soldering.

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14.Mention the applications of friction welding.

Used in refrigeration.Used in super alloys.Making simple forging.Production of taper and reamer drillsProduction of axle shafts , valves and gears.

15.Name the chemicals used in flux Manufacure.

1.Chlorides2.Borax and boric acid.3.Borates4.Fluorides.

Part-B (16Marks)

1. Define welding, mention its types, Explain Arc welding with a neat sketch andMention its advantages and limitations. (16) (NOV/DEC 2010)

WeldingWelding is a materials joining process which produces coalescence ofmaterials by heating them to suitable temperatures with or without thepplication of pressure or by the application of pressure alone, and with or withoutthe use of filler material. Welding is used for making permanent joints. It is used inthe manufacture of automobile bodies, aircraft frames, railway wagons, machineframes, structural works, tanks, furniture, boilers, general repair work and shipbuilding.

Types of weldingARC WeldingGas Welding

Arc weldingUses an electric arc to coalesce metalsArc welding is the most common method ofwelding metalsElectricity travels from electrode to base metalto ground

Arc welding Equipments• A welding generator (D.C.)

or Transformer (A.C.)• Two cables- one for work

and one for electrode• Electrode holder

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• Electrode• Protective shield• Gloves• Wire brush• Chipping hammer• Goggles

Electrode

Electrode is a thin rod made up of same as that of parent material. Flux is coated over the electrode toavoid oxidation. It is mostly connected to the negative polarity.

Two Basic Types of AW Electrodes Consumable – consumed during welding process

Source of filler metal in arc welding Nonconsumable – not consumed during welding process

Filler metal must be addedseparately

Consumable ElectrodesForms of consumable electrodes

• Welding rods (a.k.a. sticks) are 9 to 18 inches and 3/8 inch or less indiameter and must be changed frequently

• Weld wire can be continuously fed from spools with long lengths ofwire, avoiding frequent interruptions

In both rod and wire forms, electrode is consumed by arc and added to weld joint as filler metal.

Nonconsumable Electrodes Made of tungsten which resists melting Gradually depleted during welding (vaporization is principal mechanism) Any filler metal must be supplied by a separate wire fed into weld pool

FluxA substance that prevents formation of oxides and other contaminants in welding, ordissolves them and facilitates removal Provides protective atmosphere for welding Stabilizes arc Reduces spattering

Welding practice & equipmentSTEPS :• Prepare the edges to be joined and maintain the proper position

• Open the acetylene valve and ignite the gas at tip of the torch

• Hold the torch at about 45deg to the work piece plane

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• Inner flame near the work piece and filler rod at about 30 – 40 deg

• Touch filler rod at the joint and control the movement according to the flowof the material

AdvantagesMost efficient way to join metalsLowest-cost joining methodAffords lighter weight through better utilization of materialsJoins all commercial metalsProvides design flexibility

Disadvantages• Manually applied, therefore high labor cost.• Need high energy causing danger• Not convenient for disassembly.• Defects are hard to detect at joints.

2. Define welding, mention its types, Explain Gas welding with a neat sketch andMention the equipments used , types of flames produced and give its advantagesand limitations. (16) APR /MAY -2010

WeldingWelding is a materials joining process which produces coalescence ofmaterials by heating them to suitable temperatures with or without theapplication of pressure or by the application of pressure alone, and with orwithout the use of filler material. Welding is used for making permanent joints. It isused in the manufacture of automobile bodies, aircraft frames, railway wagons,machine frames, structural works, tanks, furniture, boilers, general repair work andship building.

Types of weldingARC WeldingGas Welding

GAS WELDING Sound weld is obtained by selecting propersize of flame, filler material and method of

moving torch The temperature generated during theprocess is 33000c. When the metal is fused, oxygen from the

atmosphere and the torch combines withmolten metal and forms oxides, resultsdefective weld

Fluxes are added to the welded metal toremove oxides Common fluxes used are made of sodium, potassium. Lithium and borax. Flux can be applied as paste, powder, liquid. solid coating or gas.

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GAS WELDING EQUIPMENT

1.Gas CylindersPressureOxygen – 125 kg/cm2Acetylene – 16 kg/cm22. RegulatorsWorking pressure of oxygen 1 kg/cm2Working pressure of acetylene 0.15 kg/cm2Working pressure varies depends upon the thickness of the work pieces welded.3. Pressure Gauges4. Hoses5. Welding torch6. Check valve7. Non return valve

Three basic types of oxyacetylene flames used in oxyfuel-gas welding andcutting operations:

(a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing flame.

Addition of more oxygen give a brightwhitish cone surrounded by the transparent

blue envelope is called Neutral flame (It has a balance offuel gas and oxygen) (32000c)

• Used for welding steels, aluminium, copper and cast iron

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oxygen give a bright whitish cone surrounded by the transparentblue envelope is called Neutral flame (It has a balance of fuel gas and oxygen) (32000c)

• Used for welding steels, aluminium, copper and cast iron

Oxygen is turned on, flame immediately changes into a long white inner area (Feather)surrounded by a transparent blue envelope is called Carburizing flame (30000c)

Advantages of Gas welding.

1.Simple Equipment2.Portable3.Inexpensive4.Easy for maintenance and repair

Disadvantages Of Gas welding

1.Limited power Density2.Very low welding speed.3.High total heat input per unit length4.Large Heat affected Zone5.Severe Distortion6.Not recommended for welding reactive metals such as titanium and Zirconium.

3. Give the Difference between Gas Welding and Arc Welding.

Sr NoGAS WELDING ARC WELDING

1.Heat is produced by the GasFlame

Heat is produced by Electric Arc

2. The flame temperature isabout 3200oC The temperature of Arc is about 4000oC

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3. Separate Filler rod introduced Arc Producing as well as filler rod material is theelectrode.

4. Suggested for thin materials Suggested for medium and thick materials

5. Gas welded parts do not havemuch strength

Arc welded parts have very high strength

6. Filler metal may not be thesame parent metal

Filler metal must be same or an alloy of the parent metal

7. Brazing and soldering aredone using gas

Brazing and soldering can’t be carried out by electric arc.

4. Explain Submerged arc welding with a neat sketch. State its advantages and disadvantages.(NOV/DEC-2011).

Submerged arc welding• Weld arc is shielded by a granular flux , consisting of silica, lime, manganese oxide,

calcium fluoride and other compounds.• Flux is fed into the weld zone by gravity flow through nozzleThick layer of flux covers molten metal

• Flux acts as a thermal insulator ,promoting

deep penetration of heat into the work piece• Consumable electrode is a coil of bare roundwire fed automatically through a tube• Power is supplied by 3-phase or 2-phasepower lines

5. Explain the method of laser beam welding and give their applications (APR/MAY 2014)(16)

Laser Beam Welding (LBW)

Fusion welding process in whichcoalescence is achieved by energy of ahighly concentrated, coherent light beamfocused on joint

Laser = "light amplification by stimulated emission of radiation" LBW normally performed with shielding gases to prevent oxidation

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Filler metal not usually added High power density in small area, so LBW often used for small parts

Working

The laser WELDING system consists of a power source, a flash lamp filled with Xenon, lasing material,focusing lens mechanism and worktable. The flash tube flashes at a rate of thousands per second. As aresult of multiple reflections, Beam power is built up to enormous level.

The output laser beam is highly directional and strong, coherent and unicromatic with a wavelength of6934oA. It goes through a focusing device where it is pinpointed on the work piece, fusion takes place andthe weld is accomplished due to concentrated heat produced. Laser beam welding process is shown in thefigure.

Advantages.

1.Wide variety of metals can be welded.2.Thermal damage is minimum.3.Weld metal is purified.4.Good ductility and mechanical properties.5.Welds are vaccum tight.6.filler metal is not used.7.No effect on heat treated components.

Limitations.1.Low welding Speed.2.Limited to thickness of 1.5mm.3.Materials like Mg cannot be welded.

APPLICATIONS

Radio Engineering and Microelectronics.6. Explain the method of electron beam welding and given their applications (16)

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Electron Beam Welding (EBW)Fusion welding process in which heat for welding is provided by a highly-

focused, high-intensity stream of electrons striking work surface Electron beam gun operates at:

High voltage (e.g., 10 to 150 kV typical) to accelerate electrons Beam currents are low (measured in milliamps)

Power in EBW not exceptional, but power density is

Working

The Kinetic energy of the electrons is converted into intense heat energy when the electrons areabsorbed by the metal piece over a small area of the weld, producing deep penetration weld with adepth/width ratio as high as 15. This results in a narrow, almost parallel weld with very little distortion and asmall width of the heat affected zone. There is no possibility of contamination by atmospheric gases becauseprocess is carried out in vaccum.

Advantages High-quality welds, deep and narrow profiles Limited heat affected zone, low thermal distortion High welding speeds No flux or shielding gases needed

Disadvantages High equipment cost Precise joint preparation & alignment required Vacuum chamber required Safety concern: EBW generates x-rays

Comparison: LBW vs. EBW

No vacuum chamber required for LBW No x-rays emitted in LBW Laser beams can be focused and directed by optical lenses and mirrors LBW not capable of the deep welds and high depth-to-width ratios of EBW

Maximum LBW depth = ~ 19 mm (3/4 in), whereas EBW depths = 50 mm (2 in)

7. Describe plasma Arc welding and give their applications (NOV/DEC 2011) (16)

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Principle:Plasma Arc welding is a constricted arc process. The arc is constrained with the help of a water

cooled small diameter nozzle which squeezes the arc, increases its pressure, temperature and heatintensely and thus improves stability, arc shape and heat transfer, characteristics

There are two methods of Plasma Arc Welding

1.Transferred Arc2.Non- Transferred Arc.

1.Transfered ArcHere the electrical circuit is between the tungsten electode and the work piece. Work piece acts as

anode and the tungsten electrode as cathode. The arc is transferred from the electrode to the work pieceand hence the term transferred. Here the arc force is directed away from the plasma torch and into thework piece, hence capable of heating the work piece to a higher temperature.

2.NON-Transferred Arc.

In Non-transferreed type, power is directly connected with the electrode and the torch of nozzle.The electrode carries the same current. Thus ,ionizing a high velocity gas that is strewing towards theworkpiece. The main advantage of this type is that the spot moves inside the wall and heat the incominggas and outer layer remains cool. This type of plasma has low thermal efficiency.Advantages

1.Ensures arc stability.2.Produces less thermal distortion3.The process is readily automated.

Disadvantages.

1.Excessive noise is produced.2.Equipment is complicated and expensive.3.Large amount of ultraviolet and infrared rays are emitted.

8. Explain Thermit welding and given their applications (16)

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FW process in which heat for coalescence is produced by superheated molten metal from thechemical reaction of thermite Thermite = mixture of Al and Fe3O4 fine powders that produce an exothermic

reaction when ignited Also used for incendiary bombs Filler metal obtained from liquid metal Process used for joining, but has more in common with casting than welding

Fig: Thermit welding: (1) Thermit ignited; (2) crucible tapped, superheated metalflows into mold; (3) metal solidifies to produce weld joint.Applications joining of railroad rails Repair of cracks in large steel castings and forgings Weld surface is often smooth enough that no finishing is required

9. Explain TIG and MIG welding in detail.

Inert Gas WeldingFor materials such as Al or Ti which quickly form oxide layers, a method to place an inertatmosphere around the weld puddle had to be developed

Metal Inert Gas (MIG)• Uses a consumable electrode (filler wire made of the base metal)• Inert gas is typically Argon

Gas Tungsten Arc Welding (GTAW)

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Uses a non-consumable tungsten electrode and an inert gas for arc shielding Melting point of tungsten = 3410 C (6170 F) A.k.a. Tungsten Inert Gas (TIG) welding

In Europe, called "WIG welding" Used with or without a filler metal

When filler metal used, it is added to weld pool from separate rod or wire Applications: aluminum and stainless steel most common

Advantages High quality welds for suitable applications No spatter because no filler metal through arc Little or no post-weld cleaning because no flux

Disadvantages Generally slower and more costly than consumable electrode AW processes

10. What is resistance welding; Mention the various types of Resistance welding. Explain in detailsabout spot welding.

Resistance Welding (RW)A group of fusion welding processes that use a combination of heat and pressure toaccomplish coalescence Heat generated by electrical resistance to current flow at junction to be welded

Principal RW process is resistance spot welding (RSW

Components in Resistance Spot Welding Parts to be welded (usually sheet metal) Two opposing electrodes Means of applying pressure to squeeze partsbetween electrodes Power supply from which a controlled current can be applied for a specified

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Uses a non-consumable tungsten electrode and an inert gas for arc shielding Melting point of tungsten = 3410 C (6170 F) A.k.a. Tungsten Inert Gas (TIG) welding

In Europe, called "WIG welding" Used with or without a filler metal

When filler metal used, it is added to weld pool from separate rod or wire Applications: aluminum and stainless steel most common

Advantages High quality welds for suitable applications No spatter because no filler metal through arc Little or no post-weld cleaning because no flux

Disadvantages Generally slower and more costly than consumable electrode AW processes

10. What is resistance welding; Mention the various types of Resistance welding. Explain in detailsabout spot welding.

Resistance Welding (RW)A group of fusion welding processes that use a combination of heat and pressure toaccomplish coalescence Heat generated by electrical resistance to current flow at junction to be welded

Principal RW process is resistance spot welding (RSW

Components in Resistance Spot Welding Parts to be welded (usually sheet metal) Two opposing electrodes Means of applying pressure to squeeze partsbetween electrodes Power supply from which a controlled current can be applied for a specified

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Uses a non-consumable tungsten electrode and an inert gas for arc shielding Melting point of tungsten = 3410 C (6170 F) A.k.a. Tungsten Inert Gas (TIG) welding

In Europe, called "WIG welding" Used with or without a filler metal

When filler metal used, it is added to weld pool from separate rod or wire Applications: aluminum and stainless steel most common

Advantages High quality welds for suitable applications No spatter because no filler metal through arc Little or no post-weld cleaning because no flux

Disadvantages Generally slower and more costly than consumable electrode AW processes

10. What is resistance welding; Mention the various types of Resistance welding. Explain in detailsabout spot welding.

Resistance Welding (RW)A group of fusion welding processes that use a combination of heat and pressure toaccomplish coalescence Heat generated by electrical resistance to current flow at junction to be welded

Principal RW process is resistance spot welding (RSW

Components in Resistance Spot Welding Parts to be welded (usually sheet metal) Two opposing electrodes Means of applying pressure to squeeze partsbetween electrodes Power supply from which a controlled current can be applied for a specified

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time durationAdvantages No filler metal required High production rates possible Lends itself to mechanization and automation Lower operator skill level than for arc welding Good repeatability and reliability

UNIT III

METAL FORMING PROCESS

1 What are the four major drawbacks of hot working? (May 2006)Ans:

• As hot working is carried out at high temperatures, a rapid oxidation orscaleformation takes place on the metal surface which leads to poor surface finish and lossof metal.

• Due to the loss of carbon from the surface of the steel piece being worked, the surface layer loses itsstrength.

• This weakening of the surface layer may give rise to fatigue crack which results in failure of the part.• Close tolerance cannot be obtained.• Hot working involves excessive expenditure on account of high tooling cost.

2. Explain why parts produced by Forging is preffered when compared to other machining andwelding process.

2 Classify the types of extrusion. (May 2006)Ans: Extrusion

1. Hot Extrusion2. Cold Extrusion3. Hot extrusion

(A)Direct extrusion,(B) Indirect extrusion,(C)Tube extrusion

3 What is the difference between a bloom and a billet? (May 2007)Ans: A bloom has a square cross section with minimum size of 150x150 mm and a billetissmaller than bloom and it may have any square section from 38 mm upto the size of a bloom.

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4 What is impact extrusion ? (May 2007)Ans: The raw material is in slug form which have been turned from a bar or punched froma strip. By using punch and dies, the operation is performed. The slug is placed in the die and struck fromtop by the punch opareting at high pressure and speed.

5 Why are a number of passes required to roll a steel bar? (May 2008)Ans: To reduce the thickness and to increase the width of the bar number of passesarerequired.

6 How are seamless tubes produced? (May 2008)Ans: Seamless tubing is a popular and economical raw stock for machining because itsaves drilling and boring of parts. The piercing machine consists of two rapered rolls, called as piercingrolls.

7 What is Sejournet process? (Dec. 2008)Ans: That extrusion process which is based both on the use of a lubricantin a viscouscondition at extrusion temperature and on a separation between the lubrication of the chamber wall and dieis called Sejournet process.

8 What is skew rolling ?(Dec. 2008)Ans: The rolls are powered and the workpiece is in due to frictional force between metaland surface. The torque on the rolls is being zero.

9 Explain the term Extrusion process. (Dec.2009)Ans: The extrusion process consists of compressing a metal inside achamber to force itoutthrough a small opening which is called as die. Any plastic material can be successfully extruded. A largenumber of extruded shapes which are commonly used are tubes, rods, structural shapes and lead coveredcables. During the process, a heated cylindrical billet is placed in the container and forced out through a steeldie with the help of aramor plunger.

10 What are the disadvantages of forging processes? (Dec. 2009)Ans:

• Complicated shapes cannot be produced.• Generally used for large parts.• Because of cost of dies, process is costly.

11.Define Impact extrusion.

Ans.It is a cold working process of making required shape by striking slugs of metal by high impact. It isused for making tooth paste ,shaving cream and collapsible medicine tubes.

12.What is meant by cold spinning.It is the operation of shaping very thin metals by pressing against aform while it is rotating , It is carried out at room temperature.

13.Define Hot Spinning.It is the process of making circular cross section or a dish or head from circular , heavy plates by spinningsheet metal.

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14.What is wire drawing.Drawing of metal through a small aperture die and wounding in the form of coil is called wire drawing. Theaperture is generally below 16mm diameter.

15.What is meant by deep Drawing.It is the process of making cup shaped parts from sheet metal

blanks, where the depth of the cup is greater than that of the diameter of the cup.

Part-B (16 Marks)

1. Compare HOT working and Cold Working.

SR NO HOT WORKING COLD WORKING1.

Hot working is done aboverecrystallisation temperature

Cold working isdone belowrecrystallisation temperature.

2.

Refinement of grains takes place Grain structure is distorted.

3.

Impurities and porosity are removed frommetals after hot working.

Impurities and porosities exist in metalafter cold working.

4.

Residual stresses are eliminated. Residual stresses are not eliminated.

5.

Rapid oxidation or scaling of surfacesoccurs which results in poor surface finish.

No oxidation and hence good surfacefinish is obtained.

6.

Close dimensional tolerances cannot bemaintained.

Close dimensional tolerances can beobtained.

7 Toolling and handling costs are more. Tooling and handling costs are less

8.

Mecanical properties such asToughness,ductility,elongation areimproved.

Cold w2orking decreaseselongation,reduction in area , hardness,tensile strength. Fatigue strength areimproved.

2. Define rolling and discuss according to the classification. (APR/MAY-2010) (16)

Rolling is the most rapid method of forming metals into desired shapes by plastic deformation inbetween rolls.

The forming of bars, plates , sheets, rails and other steel sections are produced by rolling.

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Classification of Rolling mill based on number of rolling mills.

1.Two High Rolling Mill.

2.Three high Rolling Mill

3.Four high Rolling Mill

4. Multi Rolling Mill.

5.Universal Rolling Mill

6.Planetary Rolling Mill.

1.Two High Rolling Mill.

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This Mill has two rolls. Both the rolls rotate in a constant direction about the horizontal axis. Theprinciple operation of this process is reduction of cross sectional area of stock and increasing the length. Thismethod is used for both cold and hot rolling operation.

3. What are the defects in rolled parts?

There are two types of major defects on the rolled products.

1. SURFACE DEFECTS2. INTERNAL SURFACE DETECTS.

1.SURFACE DEFECTS

Major surface defects on rolled products are scales, rust, scratches,cracks, and pits.

These defects occurs on the rolled products due to the impurities and inclusions present in the original castmaterials.,

II.Internal surface defects

1.waviness or wavy edges.

It occurs due to the bending of rolls. The rolls acts as a straight beam. If the material flow iscontinuous and to maintain this continuity, strains with in the material should adjust with itself. There arecompressive strain on the edges and tensile strain at the centre. The edges are restrained from expandingfreely in the longitudinal direction because of which wavy edges on the sheet will be produced.

2.Zipper Cracks

It occurs due to poor material ductility, at the rolling temperatureCamber is provided to avoid thisdefect., Camber is providing slightly large diameter at the center of rolls than that at the edges.

3. FOLDS

Folds occur if the reduction per pass is very less.

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4. Alligatoring.

It is the splitting of work piece along the horizontal plane on exit, with top and bottom part followingthe rotation of their respective rolls.

5.lamination.

These are small cracks which may develop when reduction in thickness is excessive.

4..Give the advantage of press forging over drop forging

SR NO Press forging Drop Forging1. It is a Faster process Slow Process2. Die alignment is easier Die alignment is difficult3. Operation is quite Noisy operation4. Quality of product is good Quality of product is fair.5. Stroke and ram speed is high It is low.6. It is one stroke operation Multiple stroke operation.7. Range is 20 tons to 1500 tons. Range upto 10 tons

8. Shapes formed are dense and homogeneous instructure.

Coarse and not homogenous instructure.

5. Define Forging, Mention its types , differentiate between open die forging and closed die forging.

Forging operationsForging is a process in which the workpiece is shaped by compressive forces applied through

various dies and tools. It is one of the oldest metalworking operations. Most forgingsrequire a set of dies and a press or a forging hammer.A Forged metal can result in the following: -

Decrease in height, increase in section - open die forging Increase length, decrease cross-section, called drawing out. Decrease length, increase in cross-section on a portion of the

length - upsetting Change length, change cross-section, by squeezing in closed

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impression dies - closed die forging. This results in favorable grainflow for strong parts

Types of forging Closed/impression die forging Electro-upsetting Forward extrusion Backward extrusion Radial forging Hobbing Isothermal forging Open-die forgig Upsetting Nosing Coining

Commonly used materials include• Ferrous materials: low carbon steels• Nonferrous materials: copper, aluminum and their alloys

Open-Die Forging

Open-die forging is a hot forging process in which metal is shaped byhammering or pressing between flat or simple contoured dies.

Equipment. Hydraulic presses, hammers.

Materials. Carbon and alloy steels, aluminum alloys, copper alloys, titaniumalloys, all forgeable materials.

Process Variations. Slab forging, shaft forging, mandrel forging, ring forging,upsetting between flat or curved dies, drawing out.

Application. Forging ingots, large and bulky forgings, preforms for finished forgings.

Closed Die ForgingIn this process, a billet is formed (hot) in dies (usually with two halves) such that the flow

of metal from the die cavity is restricted. The excess material is extruded through arestrictive narrow gap and appears as flash around the forging at the die parting line.Equipment. Anvil and counterblow hammers, hydraulic, mechanical, and screw presses.Materials. Carbon and alloy steels, aluminum alloys, copper alloys, magnesiumalloys, beryllium, stainless steels, nickel alloys, titanium and titanium alloys, iron andnickel and cobalt super alloys.

Process Variations. Closed-die forging with lateral flash, closed-die forging withlongitudinal flash, closed-die forging without flash.

Application. Production of forgings for automobiles, trucks, tractors, off-highway

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equipment, aircraft, railroad and mining equipment, general mechanical industry, andenergy-related engineering production.

6.What are the defects in forgings? Explain it with neat sketches, (Apr/May-2011) (16)

1.Unfilled Sections.

In this some of the die cavity are not completely filled by the flowing metal.

2.Cold Shuts.

This appears as small cracks at the corners of the forging. Caused due to improper design of die.

3.Scale Pits.This is seen as irregular depositions on the surface of forging. This is primarily caused because of

improper cleaning of the stock used for forging.The oxides and scales gets embedded into the finish forging surface.When the forging is cleaned by pickling, these are seen as deputations on the forging surfaces.

4.Die Shifts.

This is caused by the mis-alignment of the half dies, making the two halves of te forging to be ofimproper shape. It is also called as mismatch.

5..Flakes.These are basically ruptures caused by the improper cooling of the large forging. Rapid cooling

causes the exterior to cool quickly causing internal fractures.

6.Improper Grain Flow.Due to improper design of the die, which makes the flow of the metal to be not in the final intended

direction.

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7.Laps.Laps are formed by webbuckling during forging. To avoid laps web thickness should be increased

and properly edesigned.

UNIT - IV

SHEET METAL PROCESS

1 What is punching operation ?Ans : It is the cutting operation with the help of which various shaped holes are produced in the sheet metal.It is similar to blanking; only the main difference is that, the hole is the desired product and the materialpunched out to form a hole is considered as a waste.

2 What is super plastic forming operation ?Ans: Superplastic forming is a metalworking process for forming sheet metal. It works upon the theory ofsuperplasticity, which means that a material can elongate beyond 100% of its original size.

3 What is press brake?Ans: Press brake (bending brake) is an open frame press used for bending, cutting and forming. Generally, ithandless long workpieces in the form of strips. Usually press brake have long dies and suitable and suitablefor making long straight line bends.

4 Define hydro forming process.Ans : Hydro forming is a process which can be carried out in two ways:

1) Hydro - mechanical forming2) Electro - hydraulic forming Hydro - mechanical forming: In this method , the blank is placed over

the punch whose shape is similar to inner of the find workpiece.Electro - hydraulic forming : This method involves the conversion of electrical energy into mechanicalenergy in a liquid medium. Electric spark in a liquid produces shock waves and pressures which can be usedfor metal forming.

5 Give the difference between punching and blanking.Ans:

Blanking : It is the cutting operation of a flat metal sheet. The article punched out is known as blank.Blank is the required product of the operation and the metal left behind is considered as a waste.

Punching: It is similliar to blanking; only the main difference is that, the hole is the desired productand the material punched out to form a hole is considered as a waste.

6 How is hydro forming is similar to rubber forming ?Ans : In both the sheet metal working processes sheet metal is pressed between a die and rubber block.

Under pressure, the rubber and sheet metal are driven into the die and confirm to its shape byforming the part.

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7 What do you mean by minimum bend radius?Ans: It is the radius of curvature on inside surface of the bend. If the bend radius is too small, then crackingof a material on the outer tensile surface takes place. To prevent any damage to punch and die, the bendradius should not be less than 0.8mm.

8 Define limiting drawing ratio.Ans : It is the ratio of finished shell diameter (d) to the radius of bottom corner(r).

9 Define Embossing.Ans : With the help of this operation, specific shapes or figures are produced on the sheet metal.

It is used for decorative purpose or giving details like names, trade marks, specifications, etc. On thesheet metal.

10. What are the factors affecting shearing operation?

Shape and material of punchDie,speedof punching,lubricationClearance between punch & die.

11. Define Blanking.A finite shape of sheet metal is removed and blocked by shearing the entire contour using a die and a

punch. The portion removed, which is the required part is called as blank and the operation is called asblanking.

12.What is meant by Dimpling.

irst hole is punched and then it is expanded into a flange. flange may be produced by piercing with asharp punch when ther bend angle is less than900, as n fittings with conical ends.this process is also called asFLAIRING.

13.Define Notching.It refers to the removing pieces from the edge. In this process, the metal is removed from the side

(or) edge of a sheet to get the desired shape.

14.define Stretch forming.

The sheet metal is placed under a tensile load over a forming block and stretching it beyond its elasticlimit and to the plastic range, thus cause permanent set to take place.this process is useful in makingprototype models of aircraft and automotive parts.

15.Define WrinklingIt is caused by compressive stresses in the plane of the sheet . It can be objectionable or can be useful

in imparting stiffness to parts. It can be controlled by proper tool and die design.

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PART-B (16-marks)

1. Describe shearing operations in a sheet metal work with a neat sketch (16)

Sheet Metal FormingInvolves methods in which sheet metal is cut into required dimensions and shape; and/orforming by stamping, drawing, or pressing to the final shapeA special class of metal forming where the thickness of the piece of material issmall compared to the other dimensionsCutting into shape involve shear forcesForming Processes involve tensile stresses

The Major operations of sheet Metal are;1) Shearing,2) Bending,3) Drawing and4) Squeezing

ShearingThe mechanical cutting of materials without the information of chips or the use of

burning or melting for straight cutting blades: shearing for curved blades: blanking,piercing, notching, trimming,Lancing.

Slittingshearing process used to cut rolls of sheet metal into several rolls of narrower widthused to cut a wide coil of metal into a number of narrower coils as the main coil ismoved through the slitter.Blankingduring which a metal workpiece is removed from the primary metal strip or sheet when it ispunched.

Notchingsame as piercing- edge of the strip or black forms part of the punch-out perimeter

NibblingProduces a series of overlapping slits/notches

Shavingfinishing operation in which a small amount of metal is sheared away from the edge of

an already blanked part- can be used to produce a smoother edge

DinkingUsed to blank shapes from low-strength materials such as rubber, fiber and cloth

SpringbackThe elastic recovery of the material after unloading of the tools

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2.Describe the various sheet metal making operations with neat sketch.

1.Bending is the process by which a straightline is transformed into a curved length.

2.Shearing. (refer previous question)

3.Drawing

It is the process of producing hollow objects (ex.utencils) by using an semicircular punch and Die.

4.Deep Drawing.If the depth of the hole is greater than that of the diameter then the drawing operation is called deep

drawing.

5.Forming.Changing the shape of the sheet metals without cutting, shearing or drawing.

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3. Explain any one method of stretch forming operation with a neat sketch (16)

In this process, the sheet metal is clamped along the edges and then stretched over a die (OR) FORMBLOCK, which moves upward, downward (or) side ways, depending on the particular machine.

It is used to make aircraft wing-skin panels, automobile door panels and window frames.The desirable qualities in the metal for maximum strechability are as follows.

1.Fine grain structure.2.toughness.3.LARGE SPREAD between the tensile yield and ultimate strength.

Working.

It consists of placing the sheet –metal under a tensile load over a forming block and stretching it beyondits elastic limit and to te plastic range, thus cause a permanent set to take place.

Two Basic Forms of Stretch forming are,

1.Stretch forming,2.Stretch – Wrap forming.

ADVANTAGES.7. In a single operation, blanks can be stretched.8. Heat treatment before and after stretching process is not required.9. Spring back effect is minimized.10. Tooling cost is low.

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11. Direct bending is not introduced, and plastic deformation is due to pure tension.12. It is suitable for low volume production.

DISADVANTAGES

1.uneven thickness of blank cannot be stretched.2.The maintanence cost of the hydraulic cylinders is high.

4. Explain hydro forming process with its neat sketches. State their advantageand applications

\

In this process te pressure over the rubber membraneis controlled throughout the forming cycle, withmaximum pressure upto- 100 Mpa.This procedure allows close control of the part during forming, toprevent wrinkling (or) tearing. This process is called hydroform or fluif – Forming Process.

Hydro forming is a Drawing process.

Advantages of Hydro-formimg Process.

1.It is used for Mass production.

2.Tools can be quickly changed.

3.Complicted shapes , sharp corners can be made by this method.

4.Spring back, Thining off metals are removed.

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5.Explain about Rubber Pad Forming.

One of the die material is made up of a flexible material (ex. Rubber) Or (poly-urethanematerial. In bending and embossing of sheet metal , the female die is replaced with a rubberpad.Pressure in the rubber pad forming is usually in the order of10Mpa.

The blank is placed under the punch called male die.Then the ram (femal part) is moved so thatpunch touches the top surface of the work. Then the force is appled and gradually increased onthe blank through the rubber pad.

The blank holder ring is used to distribute uniform pressure throughout the blank.

Thus the required shape is formed on the sheet metal between male and female parts.

ADVANATAGES OF RUBBER PAD FORMIMNG.

1.Number of shapes can be formed on one rubber pad.2.Thining in metal balank does not take place.\3.setting time of the tool is less.4.Wrinkle – free , shrink flanges can be produced.

DISADVANTAGES

1.Rapid wearing of rubber Pads is a problem in this process.

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2.Accurate sharp corners cannot be made by this process.3.Loss of pressure between hydraulic fluid and rubber pad which is a major problem

APPLICATIONS.

Flanged Cylinders.Rectangular cups,Spherical Domes.Unsymmetrical shaped components can be made.

6. Explain peen forming process with a neat sketch (Nov/Dec -2010) (16)

This process is used to produce curvature on thin sheet metals byshot peening on surface of the sheet.

A stream of metal shots is blasted against the surface of theblank.

This process is also called as peen forming technique.Peening is done with cast- iron (or) Steel shot discharged eitherfrom a rotating wheel by an air blast made from a nozzle.

ADVANTAGES OF PEEN FORMING

Complex shapes can be easily produced .Die and Punch is not used.Peening is used as a salvage operations for distorted parts (OR) correcting part.DISADVANTAGES OF PEEN FORMING

This process requires longer time for forming the required shape.Requires additional devices for forcing out metal shots.APPLICATIONS.

Specific portions on crankshafts , connecting rods, gearsHoney comb panels like aircraft wings and large tubular shapes can be produced.

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UNIT -V

MANUFACTURING OF PLASTIC COMPONENTS

PART-A (2 Marks)1 What are the characteristic of thermoplastics ? (May 2006)ANS: Themoplastics polymers soften when heated and harden, when cooled.These types of polymers are

soft and ductile. They have low melting temperature and can be repeatedly moulded and remoulded to therequired shapes.

2 List out the material for processing of plastics?ANS: The following metioned are the various polymer additives used in practice:

(1) Filler material (2) Plasticizers (3)Stabilizers(4) colorants (5)Flame retardants (6) Reinforcements

(7)Lubricants.3 List the advantage of cold forming of plastics? (MAY 2007)ANS:

ADVANTAGES:• Cold forming can be carried out at room temperature• It is used to produce filament and fibres• It is a simple process.

4 What is film blowing? (May 2007)Ans: In this process a heated doughy paste of plastic compound is passed through a series of hot rollers,where it is squeezed into the from of thin sheet of uniform thickness. It is used for making plastic sheets andfilms.

5 What are the types of plastics ? (May 2008)Ans: Polymers are classified in two major categoies:

o Thermoplastic polymers (Soften when heated and harden when cooled) o Thermosetting polymers(Soften when heated and permanently hardened when cooled).

6 What is compression moulding? (May 2008)Ans: The main objective is to melt the material due to compression.

7 Name the parts made by rotational moulding. (Dec. 2008)Ans: Rotational moulding process is mostly used for the production of toys in P.V.C like horse, boats, etc.Larger containers upto 20 m3 capacity, fuel tanks of automobile are made from polythene and nylon. Thisprocess is also used for production of large drums, boat hulls, buckets, housings and carrying cases.

8 What is parison ? (Dec.2008)Ans: Blow moulding consists of extrusion of the heated tubular plastic piece called as parison which istransferred to the two piece mold.

9 Define degree of polyenerization. (Dec. 2009)Ans: It is the number of repetitive units present inone molecule of a polymer.

Degree of polymerisation =Molecular weight of a polymerMolecular weight of a single monomer

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10 What is rotational mouldig of plastics? (Dec. 2009)Ans:

• Rotataional moulding also called as roto-moulding.• A measured amount of polyemer power is placed in a thin walled metal mould and the mould is

closed.• Then the mould is rotated about two mutually perpendicular axes as it is heated.

11.What are the two types of polymerization.

1.addition polymerization

2.Condensation polymerization

12. Rubber is a ___________________ Polymer

Rubber is a Organic Polymer.

13.Write the two types of Injection Moulding.

1.Ram Or plunger type injection moulding2.Screw type Injection Moulding

14.Define PolymerPolymers are long chain molecules and are formed by polymerization process,linking and cross

linking a particular building block called monomer, a unit cell.\15.Define Plastics.

Plastic is defined as the organic polymer which can be moulded into any required shape with the helpof heat and pressure.

Part-B (16 Marks)

1. Explain the working principles and application of Injection Moulding. (NOV/DEC-2012)(16)

Injection MoldingMost widely used process. Suitable for high production of thermoplastics. Charge fedfrom a hopper is heated in a barrel and forced under high pressure into a mold cavity.Several types. Variety of parts can be made.

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Basic components:mold pieces (define the geometry of the part), and sprue, gates, runners, vents, ejection pins,cooling system

There are two types of injection moulding.3. Plunger type injection moulding.4. Screw type injection moulding.

In screw type injection moulding machine the plunger is replaced by a screw.A receiprocating screw nowforces the material into the mould.since the screw action generally helps to pack the materials better , a givenplunger travel will push more material into the cavity. Finally the action of the screw , as it rotates andmixes, adds energy to the melt.

Band heaters are still needed to fully heat the melt. All of this results in a much better and more consistentpart.

Virtually all industrial presses are screw type presses.

2.Explain the working principles and application of Blow Moulding. Mention Its types .

Blow Moldingused to make thermoplastic bottles and hollow sections. Starting material is a

round heated solid-bottom hollow tube – perform.Perform inserted into two die halves and air is blown inside to complete the

process

General steps• Melting the resin- done in extruder• Form the molten resin into a cylinder or tube (this tube is called parison)• The parison is placed inside a mold, and inflated so that the plastic is pushed outwardagainst the cavity wall• The part is allowed to cool in the mold and is then ejected• The part is trimmed

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The parison can be formed by

A)Extrusion processB)Injection molding process

Extrusion blow molding– Parison is formed from by forcing the plastic through an extrusion

die.

Material enters the die, flow around the mandrel so that extrudate wouldbe cylindrical

– The die would have a hole at the center so that air could be blowninto the cylinder

– In some blow molding operations, the air is introduced from the bottomthrough an inlet

This process can be;continuous extrusion blow molding

• During the process, the extrusion runs continuously, thus making acontinuous parison. using multiple mold to match the mold cycle to theextrusion speed

Intermittent extrusion blow molding• During the process, the extruder is stopped during the time that themolding occur• use either reciprocating screw or an accumulator system

• In this system, the output of the extruder is matched by having multiple molds which sealand blow the parison and then move away from extruder to cool and eject

• In practical case, the mold cycle is longer than time required to extrude a new parison• If the mold cycle is twice than time needed for creating a parison, a two mold system can

be used• The method is sometimes called rising mold system - system of which two or more molds

are used to mold parts from one extruder during continuous process

b) Injection Blow Molding• The parison is formed by the injection of molten resin into a mold cavity and around a

core pin• The parison is not a finished product, but it is subjected to subsequent step to form the

final shape• Second step, blowing of the intermediate part in a second mold• Because of distinct separation of the two steps, the parison made by injection molding is

called a perform

Process• The mold is closed• Resin is then injected to form a cylindrical part• The mold is opened and perform is ejectedThe perform can be stored until the finished blow molded is needed.The flexibility of separating the two cycles has proven useful in manufacture ofsoda pop bottle.

GOPINATH.GAP/MECH

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Common plastics for blow molding• HDPE (stiff bottle, toys, cases, drum)• LDPE (flexible bottle)• PP (higher temperature bottle)• PVC (clear bottle, oil resistant containers)• PET (soda pop bottle)• Nylon (automotive coolant bottle, power steering reservoir)

3. Explain the working principles and application of Rotational Moulding.5.

It is also known as Rotomoulding, rotocasting or spin casting.

The thin walled metal mould is a split female mould made of two pieces and is designed to be rotated abouttwo perpendicular axes.

STEP-1

A predetermined amount of plastic , powder or liquid form , is deposited in one half of a mould.

STEP – 2

The mould is closed.

STEP -3

The mould is rotated biaxially inside an oven. The hollow part should be rotated through two or more axes,rotating at different speeds, in order to avoid the accumulatiuon of polymer powder.

STEP – 4

The plastic melts and forms a coating over the inside surface of the mould.

STEP -5

GOPINATH.GAP/MECH

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The mould is removed from the oven and cooled usually by fan. The polymer must be cooled so thatit solidifies and can be handled safely by the operator.The part will shrink on cooling, coming away from themould and facilitating easy removal of the part.

STEP-6

The part is removed from the mould.

Advantages of rotational moulding

1. Moulds are relatively inexpensive.

2. Different parts can be moulded at same time.

3.Very large hollow parts can be made.

4.Parts are stress free.

5.Very little scrap is produced.

Limitations of rotational moulding.

1.Moulding Cycles are long 10-20 mins

2.It is not possible to make some sharp threads.

3.Cannot make parts with tight tolerance.

6. Explain the working principles and application of Transfer Moulding.

GOPINATH.GAP/MECH

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Transfer Molding A process of forming articles by fusing a plastic material in a chamber then forcing the

whole mass into a hot mold to solidify. Used to make products such as electrical wall receptacles and circuit breakers Similar to compression molding except thermosetting charge is forced into a heated

mold cavity using a ram or plunger.Examples: electrical switchgear, structural parts

Process Variables• Amount of charge• Molding pressure• Closing speed• Mold temperature• Charge temperature• Cycle timeAdvantages

• Little waste (no gates, sprues, or runners in many molds)• Lower tooling cost than injection molding• Good surface finish• Less damage to fibers• Process may be automated or hand-operated• Material flow is short, less chance of disturbing inserts, causing product stress,

and/or erodingmolds.

Disadvantages• High initial capital investment• Labor intensive• Secondary operations maybe required• Long molding cycles may be needed.

6.Explain the working principles and application of compression Moulding.

GOPINATH.GAP/MECH

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Compression Molding• The process of molding a material in a confined shape by applying pressure and usuallyheat.• Almost exclusively for thermoset materials• Used to produce mainly electrical products

Thermoset granules are “compressed” in a heated mold to shape required.Examples: plugs, pot handles,

dishware

Applications of compression moulding.

1.Dishes , Handles , container caps, fittings, electrical and electronic components.

2.Scoops, spoilers, hoods, fenders.

3.Polyester fiber glass resin systems (SMC/BMC)

GOPINATH.GAP/MECH