ME 6302 – MANUFACTURING TECHNOLOGY - 1 Mechanical Engineering

Third Semester UNIT-4 Part A

1. How are sheet metal operations classified and what are they? [A/M 15] * Bending * Shearing * Blanking * Punching *Trimming * Parting *Slitting * Lancing * Notching *perforating * Nibbling * Embossing * Shaving * Cutoff * dinking * Coining * Deep drawing * Stretch forming *Roll forming

2. What is flanging? [A/M 15]

Flanging is a process of bending the sheet edges • The workpiece may has a plane or a curved surface. • The edge may be a straight line or a curve. 3. Estimate the force required for punching a 25 mm diameter hole through a 3.2 mm thick annealed titanium alloy Ti-6Al-4V sheet at room temperature. The UTS for this alloy can be assumed to be 1000 MPa. [M/J 16]

4. Name any two super plastic materials. [M/J 16]

Iron and steel

5. What i s shear angle? Why is it given in punches and dies? [N/D 14]

The shearing angle is provided in the die in the case of blanking operations and in the punch in the case of hole punching operations. Most often the shearing angle is provided so that the dimension H is roughly equal to or more than the plate thickness. By the way, the blanking force can be reduced by about 30% when the dimension H of the shearing angle is made equal to the plate thickness. 6. What is flanging? [N/D 14]

Flanging is a process of bending the sheet edges • The workpiece may has a plane or a curved surface. • The edge may be a straight line or a curve.

7. List out test methods for testing formability of material. [N/D 15] rolling, extrusion, forging, rollforming, stamping, and hydroforming. 8. Distinguish between piercing and blanking. [N/D 15]

Blanking Piercing

Punching or blanking is a process in which the punch removes a portion of material from the larger piece or a strip of sheet metal. If the small removed piece is the useful part and the rest is scrap, the operation is called blanking

It is a process by which a hole is cut (or torn) in metal. It is different from punching in that piercing does not generate a slug. Instead, the metal is pushed back to form a jagged flange on the back side of the hole.

The piece cut out is called as blank and may be further processed. Blanks are often cut out of a sheet or strip

A pierced hole looks somewhat like a bullet hole in a sheet of metal

Blanking wastes certain amount of material. When designing a sheet metal blanking process the geometry of blanks should be nestled as efficiently as possible to minimize the material waste.

Size of the component is generally larger in piercing than blanking.

9. What are the desirable qualities in metal for maximum stretchability? [N/D 16] (a) Maximum principal stress by FEM simulation for the Keyboard, Ecoflex layer, Merged Ecoflex layer, urethane layer and Merged urethane Layer. The inset shows the maximum stretch before failure. (b) Maximum localized principal strain by FEM simulation for the Keyboard, Ecoflex layer, Merged Ecoflex layer, urethane layer and Merged urethane Layer. (c) Maximum principal strain distribution computed by FEM simulation for the Keyboard mesh after applying the displacement. 10. What are the applications of rubber pad forming process? [N/D 16] A static friction model suitable for rubber-metal contact is presented in this dissertation. In introduction, the motivation and the aims of the research are introduced together with the background regarding the related industrial application, which is the rubber pad forming

Part B 1. (i)Explain the various properties of sheet metal. (8) [A/M 15]

• Thickness

• Area of the flattened part

• Perimeter of the flattened part

• Maximum X and Y extents of the flattened part

• Number of Holes

• Number of Bends

(ii) Describe the nibbling and notching operations. (8) [A/M 15] Nibbling

This operation is generally substituted by blanking It is designed for cutting out flat parts from sheet metal The flat parts ranges from simple and complex contours It is used only for small quantity of components Notching

Similar to blanking however the full surface of punch does not cut the metal In this operation the metal pieces are cut from the edges of a sheet

2. (i)Explain the different types of bending process. (8) [A/M 15] There are three types of bends used to form metal that any sheet metal engineer or press brake operator must be familiar with; Air Bending, Bottom Bending and Coining.

Air Bending

Air Bending is the most common type of bending process used in sheet metal shops today. In this process the work piece is only in contact with the edge of the Die and the tip of the Punch

Coining

Coining is a very basic type of bending in which the work piece is stamped between the punch and die. The material is put under enough pressure that the punch tip penetrates the material and it begins to flow into the die. This method produces excellent accuracy and repeatability, and does not require sophisticated machines to execute.

Bottom Bending

Bottom Bending has similarities to both Air Bending and Coining. In this process the die angle should match the intended angle of the work piece, adjusting a few degrees for Spring Back, hence the existence of 88 degree tooling to achieve 90 degree angles.

(ii) In detail explain the Coining and Embossing Process. (8) [A/M 15] Sheet metal embossing is a stamping process for producing raised or sunken designs or relief in sheet metal. This process can be made by means of matched male and female roller dies, or by passing sheet or a strip of metal between rolls of the desired pattern. It is often combined with Foil Stamping to create a shiny, 3D effect. The metal sheet embossing operation is commonly accomplished with a combination of heat and pressure on the sheet metal, depending on what type of embossing is required. Theoretically, with any of these procedures, the metal thickness is changed in its composition.

Metal sheet is drawn through the male and female roller dies, producing a pattern or design on the metal sheet. Depending on the roller dies used, different patterns can be produced on the metal sheet. The pressure and a combination of heat actually "irons" while raising the level of the image higher than the substrate to make it smooth. The term "impressing" refers to an image lowered into the surface of a material, in distinction to an image raised out of the surface of a material.

In most of the pressure embossing operation machines, the upper roll blocks are stationary, while the bottom roll blocks are movable. The pressure with which the bottom roll is raised is referred to as the tonnage capacity.

Embossing machines are generally sized to give 2 inches (5 cm) of strip clearance on each side of an engraved embossing roll. Many embossing machines are custom-manufactured, so there are no industry-standard widths. It is not uncommon to find embossing machines in operation

producing patterns less than 6 inches (15 cm) wide all the way up to machines producing patterns 70 inches (180 cm) wide or more.

Coining

is a form of precision stamping in which a workpiece is subjected to a sufficiently high stress to induce plastic flow on the surface of the material. A beneficial feature is that in some metals, the plastic flow reduces surface grain size, and work hardens the surface, while the material deeper in the part retains its toughness and ductility. The term comes from the initial use of the process: manufacturing of coins.

Coining is used to manufacture parts for all industries and is commonly used when high relief or very fine features are required. For example, it is used to produce coins, medals, badges, buttons, precision-energy springs and precision parts with small or polished surface features.

Coining is a cold working process similar in other respects to forging, which takes place at elevated temperature; it uses a great deal of force to plastically deform a workpiece, so it conforms to a die. Coining can be done using a gear driven press, a mechanical press, or more commonly, a hydraulically actuated press. Coining typically requires higher tonnage presses than stamping, because the workpiece is plastically deformed and not actually cut, as in some other forms of stamping. The coining process is preferred when there is a high tonnage

3. Write short notes on the following: (16) [M/J 16] (i) Shearing (ii) Blanking (iii} Clearance in shearing (iv) Spring back in bending Shearing, also known as die cutting is a process which cuts stock without the formation of chips or the use of burning or melting. Strictly speaking, if the cutting blades are straight the process is called shearing; if the cutting blades are curved then they are shearing-type operations.[2] The most commonly sheared materials are in the form of sheet metalor plates, however rods can also be sheared. Shearing-type operations include: blanking, piercing, roll slitting, and trimming. It is used in metalworking and also with paper and plastics. Blanking and piercing are shearing processes in which a punch and die are used to modify webs. The tooling and processes are the same between the two, only the terminology is different: in blanking the punched out piece is used and called a blank; in piercing the punched out piece is scrap.[1] The process for parts manufactured simultaneously with both techniques is often termed "pierce and blank." An alternative name of piercing is punching.

In particular, the clearance is the most important factor in the shearing work of sheet metals. For general shearing work of various sheet metals, the optimum clearances have been already proposed [4]. However, optimum clearances for thin sheet metals have not been proposed yet. It is not made clear that the optimum clearances for general shearing work can be applicable for also thin sheet metals or not. Recently, numerical simulation for clearances in shearing work of thin sheet metals and optimization seems to be started [5], but the research to propose the optimum clearances for thin sheet metals through experiments and measurements has not been reported

Springback is the geometric change made to a part at the end of the forming process when the part has been released from the forces of the forming tool. Upon completion of sheet metal forming, deep-drawn and stretch-drawn parts spring back and thereby affect the dimensional accuracy of a finished part. The final form of a part is changed by springback, which makes it difficult to produce the part.

4. With neat diagrams explain the process of Rubber pad forming and hydro forming (16) [M/J 16]

1.HYDRO FORMING PROCESS

In this process te pressure over the rubber membraneis controlled throughout the forming

cycle, with maximum pressure upto- 100 Mpa.This procedure allows close control of the

part during forming, to prevent 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.

2.RUBBER PAD FORMING

One of the die material is made up of a flexible material (ex. Rubber) Or (poly-urethane

material.In bending and embossing of sheet metal , the female die is replaced with a rubber

pad.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

that punch touches the top surface of the work. Then the force is appled and gradually.

increased on the 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.

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. 5. (i) What is super plastic Forming? Explain with a neat s k e t c h . (8) [N/D 14]

Manufacturing of complex lightweight automotive structures that meet cost and product goals is a

competitive challenge facing industry. Superplastic forming (SPF) is a valuable tool for the fabrication of

complex parts used in the aircraft and automobile industries. Superplastic forming (SPF) of sheet metal has

been used to produce very complex shapes and integrated structures that are often lighter and stronger than

the assemblies they replace. Superplasticity in metals is defined by very high tensile elongations, ranging

from two hundred to several thousand percent. Superplasticity is the ability of certain materials to undergo

extreme elongation at the proper temperature and strain rate.

The process typically conducted at high temperature and under controlled strain rate, can give a

ten-fold increase in elongation compared to conventional room temperature processes. Components are

formed by applying gas pressure between one or more sheets and a die surface, causing the sheets to stretch

and fill the die cavity. The evolution of pressures must be closely controlled during the process since the

alloys of interest only exhibits Superplastic behaviour for certain temperature dependent range of strain

rates. Specific alloys of titanium, stainless steel, and aluminum are commercially available with the fine-

grained microstructure and strain rate sensitivity of flow stress that are necessary for Superplastic

deformation.

The Process

SPF can produce parts that are impossible to form using conventional techniques. During the SPF process,

the material is heated to the SPF temperature within a sealed die. Inert gas pressure is then applied, at a

controlled rate forcing the material to take the shape of the die pattern. The flow stress of the material

during deformation increases rapidly with increasing strain rate. Superplastic alloys can be stretched at

higher temperatures by several times of their initial length without breaking.

Fig. 1 shows the SPF process.

Some of the materials developed for super plastic forming are:

1. Bismuth-tin (200% elongation)

2. Zinc-aluminum

3. Titanium (Ti-6Al-V)

4. Aluminum (2004, 2419, 7475)

5. Aluminum-lithium alloys (2090, 2091, 8090

Advantages of SPF Process

Superplastic forming technology offers the potential to reduce the weight and cost of automotive structural

components for advance vehicle applications.

The main advantages of this process are:

1. It is a one step process.

2. The process can be used to form complex components in shapes that are very near the final

dimension.

3. Higher material elongations.

4. Elimination of unnecessary joints and rivets.

5. Reduction of subsequent machining.

6. Minimizes the amount of scrap produced.

Applications

The process is increasingly being applied in the aerospace industry as a way of manufacturing very complex

geometries.

In automotive body panels.

In forming of aircraft frames and skins.

Diaphragm forming of plastics.

Complex shape parts – window frames,

seat structures.

(ii) Enumerate Rubber Pad forming with suitable sketch. (8) [N/D 14]

2.RUBBER PAD FORMING

One of the die material is made up of a flexible material (ex. Rubber) Or (poly-urethane

material.In bending and embossing of sheet metal , the female die is replaced with a rubber

pad.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

that punch touches the top surface of the work. Then the force is appled and gradually.

increased on the 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.

6. (i) Enumerate with a neat sketch any two type of stretch forming operations.(8)[N/D 14]

Stretch Forming Process

A-12-Hufford Extrusion Stretch Forming

Stretch forming is a metal forming process in which a piece of sheet metal is

stretched and bent simultaneously over a die in order to form large contoured parts. Stretch forming is performed on a stretch press, in which a piece of sheet metal is

securely gripped along its edges by gripping jaws. The gripping jaws are each attached to a carriage that is pulled by pneumatic or hydraulic force to stretch the

sheet. The tooling used in this process is a stretch form block, called a form die,

which is a solid contoured piece against which the sheet metal will be pressed. The most common stretch presses are oriented vertically, in which the form die rests on a

press table that can be raised into the sheet by a hydraulic ram. As the form die is driven into the sheet, which is gripped tightly at its edges, the tensile forces increase

and the sheet plastically deforms into a new shape. Horizontal stretch presses mount the form die sideways on a stationary press table, while the gripping jaws pull the

sheet horizontally around the form die.

(ii)Describe Magnetic Pulse forming with a neat sketch. (8) [N/D 14]

Electromagnetic forming (EM forming or magneforming) is a type of high velocity, cold forming process for electrically conductive metals, most commonly copper and aluminium. The workpiece is reshaped by high intensity pulsed magnetic fields that induce a current in the workpiece and a corresponding repulsive magnetic field, rapidly repelling portions of the workpiece. The workpiece can be reshaped without any contact from a tool, although in some instances the piece may be pressed against a die or former. The technique is sometimes called high velocity forming or electromagnetic pulse technology.

A special coil is placed near the metallic workpiece, replacing the pusher in traditional forming. When the system releases its intense magnetic pulse , the coil generates a magnetic field which in turn accelerates the workpiece to hyper speed[quantify] and onto the die. The magnetic pulse and the extreme deformation speed transforms the metal into a visco-plastic state – increasing formability without affecting the native strength of the material magnetic pulse forming illustration.

A rapidly changing magnetic field induces a circulating electric current within a nearby conductor through electromagnetic induction. The induced current creates a corresponding magnetic field around the conductor (see Pinch (plasma physics)). Because of Lenz's Law, the magnetic fields created within the conductor and work coil strongly repel each other.

7. (i) Explain any one stretch forming method. (8) [N/D 15]

Stretch Forming Machines

When applicable, stretch wrap forming methods provide several unique advantages over pure bending and other types of metal forming. Stretch wrap forming machines operate by stretching the metal to its elastic limit, then wrapping the part around a forming die. This process increases the metal's yield strength and actually results in a stronger part. Since stretch forming machines also keep the metal under constant tension, they minimize imperfections such as "cans" or "buckles." Stretch forming machines also perform a task in one step that would otherwise require several machines and multiple steps, improving efficiency and saving time and money. For some parts, where it would otherwise be impossible, stretch forming machines allow for production runs of that part.

In addition to the natural benefits of this forming process, ERIE Press Systems stretch forming machines offer all the advantages that you would expect from a company with over a century of experience in designing and building presses and forming machines. When you choose ERIE Press Systems for your stretch forming machines, you get more than a quality product; you gain a partner who is committed to your success, because at ERIE Press Systems, we don't just build machines; we build relationships.

The personal nature of our customer service allows us to better understand your needs through constant communication. A team leader, dedicated solely to your project, will work closely with your company from beginning to end in order to develop a solution to satisfy all of the needs of your company's specific operation.

Our team based engineering and critical path scheduling processes ensure that you will receive the level of personal attention necessary to ensure your complete satisfaction. Additionally, our continuous growth programs and our quality management systems guarantee that every stretch forming machine that leaves our facility meets the stringent standards that have made us one of the most respected names in forging and forming machine manufacturing.

Sheet Stretch Forming:

ERIE Press Systems manufactures the highest quality stretch forming machines for sheets to meet any and all tonnage, length and width specifications. We also build adaptable extrusion jaws to fit these machines.

Extrusion Stretch Forming: ERIE Press Systems designs and builds stretch forming machines for extrusions, with all associated tooling.

Contour Roll Forming:

Especially designed for stringers and frames, contour roll forming machines bend and twist on three planes and allow for theoretically unlimited lengths.

(ii) Explain the advantages and limitations of compound dies over progressive dies. (8) [N/D 15]

rogressive die: The dies which performed two or more operations at different stages every time the ram descends is known as Progressive die. The principle advantage of Progressive die is in the number of operations that can be achieved with one handling of the stock strip. The main disadvantage is that work pieces may become “dished” as they pushed through the die as they generally have very little support.

Compound die: A compound die differs from a progressive die in that it performs two or more cutting operations during one stroke of the press at one station only.

Compound dies are slower in operation than progressive dies but they have advantages for certain jobs, especially where tolerance are close (1) the cutting operation, by the action of the knockout plate ,ensures flatness of the blank.2 Large parts can be blanked in a smaller press if compound dies rather than progressive dies are used.

Combination dies: A die in which a cutting operation is combined with a noncutting operation is referred to as a combination die. The cutting operations may include blanking, piercing, trimming, and cutoff and are combined with noncutting operations which may include bending, extruding, embossing, and forming 8. (i) Briefly explain with a neat sketch hydro forming. (8) [N/D 15]

1.HYDRO FORMING PROCESS

In this process te pressure over the rubber membraneis controlled throughout the forming

cycle, with maximum pressure upto- 100 Mpa.This procedure allows close control of the

part during forming, to prevent 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. (ii) Elucidate process variables in explosive forming. (8) [N/D 15] There are various approaches; one is to place metal plate over a die, with the intervening space evacuated by a vacuum pump, place the whole assembly underwater, and detonate a charge at an appropriate distance from the plate. For complicated shapes, a segmented die can be used to produce in a single operation a shape that would require many manufacturing steps, or to be manufactured in parts and welded together with an accompanying loss of strength at the welds. There is often some degree of work hardening from the explosive-forming process, particularly in mild steel.

Explosive forming, is distinguished from conventional forming in that the punch or diaphragm is replaced by an explosive charge. The explosives used are generally high – explosive chemicals, gaseous mixtures, or propellants. There are two techniques of high – explosive forming: stand – off technique and the contact technique.

Standoff Technique . The sheet metal work piece blank is clamped over a die and the assembly is lowered into a tank filled with water. The air in the die is pumped out. The explosive charge is placed at some predetermined distance from the work piece, see Fig 9.1. On detonation of the explosive, a pressure pulse of very high intensity is produced. A gas bubble is also produced which expands spherically and then collapses. When the pressure pulse impinges against the work piece, the metal is deformed into the die with as high velocity as 120 m/s.

Fig 9.1 Sequeuce of underwater explosive forming operations.(i) explosive charge is set in position (ii) pressure pulse and gas bubble are formed as the detonation of charge occurs, (iii) workpiece is deformed, and (iv) gas bubbles vent at the surface of water.

The use of water as the energy transfer medium ensures a uniform transmission of energy and muffles the sound of the explosive blast. The process is versatile – a large variety of shapes can be formed, there is virtually no limit to the size of the work piece, and it is suitable for low – quantity production as well.

The process has been successfully used to form steel plates 25 mm thick x 4 m diameter and to bulge steel tubes as thick as 25 mm.

Contact Technique. The explosive charge in the form of cartridge is held in direct contact with the work piece while the detonation is initiated. The detonation builds up extremely high pressures (upto 30,000MPa) on the surface of the work piece resulting in metal deformation, and possible fracture. The process is used often for bulging tubes, as shown in Fig 9.2.

Fig 9.2 Schematic illustration of contact technique of explosive forming. The process is generally used for bulging of tubes.

Applications. Explosive forming is mainly used in the aerospace industries but has also found successful applications in the production of automotive related components. The process has the greatest potential in limited – production prototype forming and for forming large size components for which conventional tooling costs are prohibitively high.

9. (i) Explain the various sheet metal forming operations with neat sketches. (8) [N/D 16]

Deep drawing

Drawing is a forming process in which the metal is stretched over a form or die. In deep drawing the depth of the part being made is more than half its diameter. Deep drawing is used for making automotive fuel tanks, kitchen sinks, two-piece aluminum cans, etc. Deep drawing is generally done in multiple steps called draw reductions. The greater the depth the more reductions are required. Deep drawing may also be accomplished with fewer reductions by heating the workpiece, for example in sink manufacture.

In many cases, material is rolled at the mill in both directions to aid in deep drawing. This leads to a more uniform grain structure which limits tearing and is referred to as "draw quality" material.

Expanding

Expanding is a process of cutting or stamping slits in alternating pattern much like the stretcher bond in brickwork and then stretching the sheet open in accordion-like fashion. It is used in applications where air and water flow are desired as well as when light weight is desired at cost of a solid flat surface. A similar process is used in other materials such as paper to create a low cost packing paper with better supportive properties than flat paper alone.

Hemming and seaming

Hemming is a process of folding the edge of sheet metal onto itself to reinforce that edge.

Seaming is a process of folding two sheets of metal to together to form a joint.

Hydroforming

Hydroforming is a process that is analogous to deep drawing, in that the part is formed by

stretching the blank over a stationary die. The force required to do so is generated by the direct

application of extremely high hydrostatic pressure to the workpiece or to a bladder that is in

contact with the workpiece, rather than by the movable part of a die in a mechanical or hydraulic

press. Unlike deep drawing, hydroforming usually does not involve draw reductions—the piece is

formed in a single step.

Laser cutting

Sheet metal can be cut in various ways, from hand tools called tin snips up to very large powered shears. With the advances in technology, sheet metal cutting has turned to computers for precise cutting. Many sheet metal cutting operations are based on computer numerically controlled (CNC) laser cutting or multi-tool CNC punch press.

CNC laser involves moving a lens assembly carrying a beam of laser light over the surface of the metal. Oxygen, nitrogen or air is fed through the same nozzle from which the laser beam exits. The metal is heated and burnt by the laser beam, cutting the metal sheet. The quality of the edge can be mirror smooth and a precision of around 0.1 mm (0.0039 in) can be obtained. Cutting speeds on thin 1.2 mm (0.047 in) sheet can be as high as 25 m (82 ft) per minute. Most laser cutting systems use a CO2 based laser source with a wavelength of around 10 µm; some more recent systems use a YAG based laser with a wavelength of around 1 µm.

(ii) Discuss with neat sketch, the working of metal spinning process. (5) [N/D 16]

Metal spinning, also known as spin forming or spinning or metal turning most commonly, is a metalworking process by which a disc or tube of metal is rotated at high speed and formed into an axially symmetric part.Spinning can be performed by hand or by a CNC lathe.

Metal spinning does not involve removal of material, as in conventional wood or metal turning, but forming (moulding) of sheet material over an existing shape.

The spinning process is fairly simple. A formed block is mounted in the drive section of a lathe. A pre-sized metal disk is then clamped against the block by a pressure pad, which is attached to the tailstock. The block and workpiece are then rotated together at high speeds. A localized force is then applied to the workpiece to cause it to flow over the block. The force is usually applied via various levered tools. Simple workpieces are just removed from the block, but more complex shapes may require a multi-piece block. Extremely complex shapes can be spun over ice forms, which then melt away after spinning. Because the final diameter of the workpiece is always less than the starting diameter, the workpiece must thicken, elongate radially, or buckle circumferentially.[1]

A more involved process, known as reducing or necking, allows a spun workpiece to include reentrant geometries. If surface finish and form are not critical, then the workpiece is "spun on air"; no mandrel is used. If the finish or form are critical then an eccentrically mounted mandrel is used.

"Hot spinning" involves spinning a piece of metal on a lathe while high heat from a torch is applied to the workpiece. Once heated, the metal is then shaped as the tool on the lathe presses against the heated surface forcing it to distort as it spins. Parts can then be shaped or necked down to a smaller diameter with little force exerted, providing a seamless shoulder.

Advantages & disadvantages

Several operations can be performed in one set-up. Work pieces may have re-entrant profiles and the profile in relation to the center line virtually unrestricted.

Forming parameters and part geometry can be altered quickly, at less cost than other metal forming techniques. Tooling and production costs are also comparatively low. Spin forming, often done by hand, is easily automated and an effective production method for prototypes as well as high quantity production runs.[1]

Other methods of forming round metal parts include hydroforming, stamping, forging and casting. These other methods generally have a higher fixed cost, but a lower variable cost than metal spinning. As machinery for commercial applications has improved, parts are being spun with thicker materials in excess of 1in (25mm) thick steel. Conventional spinning also wastes a considerably smaller amount of material than other methods.

Objects can be built using one piece of material to produce parts without seams. Without seams, a part can withstand higher internal or external pressure exerted on it. For example: scuba tanks and CO2 cartridges.

One disadvantage of metal spinning is that if a crack forms or the object is dented, it must be scrapped. Repairing the object is not cost-effective.

10. With neat sketch explain the following (i) hydro forming and (ii)super plastic forming. (13) [N/D 16]

1.HYDRO FORMING PROCESS

In this process te pressure over the rubber membraneis controlled throughout the forming

cycle, with maximum pressure upto- 100 Mpa.This procedure allows close control of the

part during forming, to prevent 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. 2.SUPER PLASTIC

The Process

SPF can produce parts that are impossible to form using conventional techniques. During the SPF process,

the material is heated to the SPF temperature within a sealed die. Inert gas pressure is then applied, at a

controlled rate forcing the material to take the shape of the die pattern. The flow stress of the material

during deformation increases rapidly with increasing strain rate. Superplastic alloys can be stretched at

higher temperatures by several times of their initial length without breaking.

Advantages of SPF Process

Superplastic forming technology offers the potential to reduce the weight and cost of automotive structural

components for advance vehicle applications.

The main advantages of this process are:

7. It is a one step process.

8. The process can be used to form complex components in shapes that are very near the final

dimension.

9. Higher material elongations.

10. Elimination of unnecessary joints and rivets.

11. Reduction of subsequent machining.

12. Minimizes the amount of scrap produced.

Applications

The process is increasingly being applied in the aerospace industry as a way of manufacturing very complex

geometries.

In automotive body panels.

In forming of aircraft frames and skins.

Diaphragm forming of plastics.

ME 6302 – MANUFACTURING TECHNOLOGY - 1

Mechanical Engineering Third Semester

UNIT-5 Part A

1. Define Polyaddition. [A/M 15] Polyaddition reactions are chemical reactions in which the polymer is originated by successive

additions of functional groups (monomer A) inside of molecular structures with double bonds

(monomer B). 2. Write short notes on the application of plastics. [A/M 15]

Application Most used plastics

Abrasion resistant liners HMWPE, UHMWPE

Acid trays PVC, PP

Agitators Nylon, Acetal, PVC

Anti-corrosive liners PVC, PP

Architectural features Acrylic, Polycarbonate

Baking tray liner PTFE

Bearings Acetal, Nylon, PETP, PP

Bench tops PP, HDPE

3. Viscosity is an important property of a polymer melt in plastics shaping processes. Upon what parameters does viscosity depend? [M/J 16] 4. What is the difference between a positive mould and a negative mould in thermoforming? [M/J 16] Negative molds vs. positive molds –

both for thermoformingNegative molds: concave cavityPositive molds: convex shape 5. What i s polymerization? [N/D 14] polymerization is a process of reacting monomer moleculestogether in a chemical reaction to form polymer chains or three-dimensional networks. There are many forms of polymerization and different systems exist to categorize them. 6. List out any four types of adhesives used in adhesive bonding of plastics. [N/D 14]

7. What is the need for Rotational moulding in manufacturing p l a s t i c components? [N/D 15] 8. Make a note on Polymerization. [N/D 15]

polymerization is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks.[2][3][4] There are many forms of polymerization and different systems exist to categorize them. 9. Name the various methods of processing thermoplastics. [N/D 16]

10. Define film blowing. [N/D 16]

Part B

1. (i) Write the difference between thermoplastics and thermosetting plastics. (8) [A/M 15] (ii) Explain the injection blow moulding process. (8) [A/M 15]

2. (i) Explain the calandring process. (8) [A/M 15] (ii) Describe any two types of thermoforming process. (8) [A/M 15]

3. (i) Briefly describe the injection moulding process. (10) [M/J 16] (ii) Discuss any two of the defects that can occur in plastic injection moulding. (6) [M/J 16]

4. Explain the process of compression moulding with neat diagrams. (16) [M/J 16]

5. (i) What is transfer mru1lding? Discuss its advantages a n d limitations. (8) [N/D 14] (ii) E x p l a i n p o s i t i v e , s e m i p o s i t i v e a n d f l a s h t y p e c o m p r e s s i o n m o u l d i n g (8) [N/D 14]

6. Exp la in various types o f thermoforming method shaping thermoplastics. ( 16 ) [N/D 14]

7. (i) Explain how plastic sheets are manufactured by thermo forming. (8) [N/D 15] (ii) Explain the process of transfer moulding and its applications. (8) [N/D 15]

8. (i) Enumerate various methods of bonding thermoplastics. (8) [N/D 15] (ii) Enumerate injection moulding of plastic products. (8) [N/D 15]

9. Describe the following plastic processing methods with neat sketches (i) compression moulding and (ii) blow moulding. (13) [N/D 16]

10. (i) Why is the thermoforming a valuable method for the plastic manufacturer? Explain the process with neat sketch. (7) [N/D 16] (ii) State the purpose of the following in plastics (1) plasticizers (2) fillers and (3) stabilizer. (6) [N/D 16]