lo #2 manufacturing process primary secondary part 1

Manufacturing Technology 1

Manufacturing TechnologyManufacturing Technology

LO #2(Part-2) Manufacturing ProcessesReference pages in the e-text :- 11 ~ 17 : Primary & Secondary Manufacturing Processes- 230 ~ 247 & 316 ~ 326 : Casting & Molding

(See extended materials at LO 3 – Lecture Note)- 709 ~ 720 : Conditioning / Heat Treatment- 653 ~ 677 : Finishing Processes

Manufacturing Capabilities Manufacturing Capabilities (See page 7 ~ 8)(See page 7 ~ 8)

2Manufacturing Technology

Manufacturing ProcessesManufacturing Processes


Manufacturing Processes – Manufacturing Processes – Processing OperationProcessing Operation


Shaping operations alter the geometry of the starting work material by various methods. Common shaping processes include casting, forging, and machining.

Shaping Operation



Most shape processing operations apply heat, mechanical force or a combination of these to effect a change in geometry of the work material.

There are various ways to classify the shaping processes.1. Solidification processes2. Particulate processing3. Deformation process4. Material removal process

Shaping Operation



In solidification processes the starting material is heated to liquid or semifluid that cools and solidifies to form the part geometry.

Nearly all materials can be processed this way if it has relatively low melting point, such as polymers, metals, and glass ceramics.

The molted material is forced or poured into a mold to form the required shape.

Casting is the name used for metals, and molding is the common term used for plastic.

Shaping Operation – 1. Solidification

Plastic Molding processesShaping of plastic material is achieved by the

application of heat and pressure. There are many ways in which this can be done, depending on the nature of the polymer, the type and size of the product and the quantity and dimensional accuracy required.

The methods described here are Compression molding Transfer molding and Injection molding.

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Plastic molding processesForms of supply :Plastic materials used in molding are normally

in the form of powder or small chips known as granules or as

Preforms.Additives :Before molding granules are mixed with other

ingredients –Known as additives in order to modify or eliminate undesirable properties and to develop their useful characteristics.

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Additives Plasticizers- added particularly to PVC,to give greater flexibility and make

it easy to form. Stabilizers- added to avoid decomposition of PVC Lubricants- added to reduce the adhesion between polymer and hot metal

surfaces used for molding. Fillers- Used to improve physical properties (fillers could be wood flour,

cork dust, asbestos, carbon black, chalk and chopped fiber glass. Ultra-violet absorbers- added to reduce adverse effect of sunlight. Colorants- added to give the final product greater appeal, as a means of

identifying (in cable insulation) to simulate a natural or traditional product (like leather bags),

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Molding process consideration Metals have definite melting point and in general tend to be free- flowing in a

molten state but plastic have no definite melting point, they are just soft by the application of heat as thick viscous fluid hence, result high pressure is required for molding.

The viscosity is reduced by the application of heat, but there is an upper temperature limit at which the polymer begins to break down in some way. This is known as degradation.( all polymers are bad conductor of heat and are susceptible to overheating)

There is also lower limit of temperature below which the polymer will not be soft enough to flow in to the mold. Therefore the temperature of the mold must be between upper and lower limits and will directly affects the viscosity of the polymer.

All the molding process require three stages:

1) Application of heat to soften the molding material; 2) Forming to the required shape in the mold 3) Removal of heat

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Types of molding Processes1.Compression Molding:Used for thermosetting plasticsThe process is carried out in a hydraulic press with heated platens.Compression molding is used to produce a wide variety of products, including electrical and domestic fittings, toilet seats and covers, bottle tops and various closures and tableware.

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2.Transfer molding Used for thermosetting plastics This process is similar to compression molding except that the plasticizing

and molding functions are carried out separately This process is suited to the production of parts incorporating small metal

inserts, and those products having variation of section thickness can be produced.

Curing time is less and greater accuracy is achieved than with compression molding.

The main limitation of this process is the loss of material in sprue, runners and gates-as thermosetting material cure during molding, this cannot be reused.

Molding tools are usually more complex and therefore more costly than compression molding tools.

Typical products produces by this process are motor- car distributors cap and domestic electric plugs.

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Injection molding is a process in which a polymer is heated to a highly plastic state and forced to flow under high pressure into a mold cavity, where it solidifies.

The molded part, called a molding, is then removed from the cavity. The production cycle time is typically in the range of 10 to 30 sec, although cycles of 1 min or longer are not uncommon for large parts.

For small parts, the mold can be built to contain multiple cavities, also making the mold expensive. Thus, injection molding is economical only for large production quantities.


Shaping Operation – 1. Solidification – Injection MoldingInjection Molding

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Process & EquipmentProcess & Equipment


Equipment for injection molding evolved from metal die casting. A large injection molding machine is shown in Figure below. As illustrated in the schematic in Figure below, an injection molding machine consists of two principal components: (1) the plastic injection unit and (2) the mold clamping unit.


Shaping Operation – 1. Solidification – Ex) Injection MoldingInjection Molding


The injection unit is much like an extruder. It consists of a barrel that is fed from one end by a hopper containing a supply of plastic pellets.

Inside the barrel is a screw whose operation surpasses that of an extruder screw in the following respect: in addition to turning for mixing and heating the polymer, it also acts as a ram that rapidly moves forward to inject molten plastic into the mold.

A non-return valve mounted near the tip of the screw prevents the melt from flowing backward along the screw threads.

Injection Unit





The clamping unit is concerned with the operation of the mold.

Its functions are to (1) hold the two halves of the mold in proper alignment with each other; (2) keep the mold closed during injection by applying a clamping force sufficient to resist the injection force; and (3) open and close the mold at the appropriate times in the molding cycle.

The clamping unit consists of two platens, a fixed platen and a movable platen, and a mechanism for translating the latter.

Clamping Unit





ProcessProcess & EquipmentProcess & Equipment



Factors affecting selection of molding method;Type of material to be moldedThe dimensional accuracyThe required outputExample: small quantity, thermosetting plastic material and not

high degree of accuracy would favor –compression molding

Larger quantities of higher accuracy from thermosetting plastic would favor Transfer molding; while high volume production from thermo plastic material would be carried out using the injection molding process.

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In Particulate processing, the starting material are powders of metals or ceramics.

The process includes pressing of the powder into designed die, and then sintering.

Sintering is heating the material powder below its melting point make the particles adhere to each other to form one piece.

So the powder is first squeezed into a die cavity under high pressure and then heated to bond the individual particles together.

Shaping Operation – 2. Particulate Processing



Shaping Operation – 2. Particulate Processing (Ex. Sintering)



Deformation processes, in which the starting material is a ductile solid (commonly metal) that is deformed to shape the part.

In the deformation processes, the starting work part is shaped by the application of forces that exceed the yield strength of the material. For the material to be formed in this way, it must be sufficiently ductile to avoid fracture during deformation. To increase ductility (and for other reasons), the work material is often heated before forming to a temperature below the melting point. Deformation processes are associated most closely with metalworking and include operations such as forging and extrusion, shown in Figure 1.8. Figure 15.19 shows a forging operation performed by a drop hammer.

Shaping Operation – 3. Deformation Process




Forging

Extrusion



Also included within the deformation processes category is sheet metalworking, which involves bending, forming, and shearing operations performed on starting blanks and strips of sheet metal. Several sheet metal parts, called stampings because they are made on a stamping press, are illustrated in Figure 16.35.




Material removal processes are operations that remove excess material from the starting workpiece so that the resulting shape is the desired geometry. The most important processes in this category are machining operations such as turning, drilling, and milling, shown in Figure 1.9. These cutting operations are most commonly applied to solid metals, performed using cutting tools that are harder and stronger than the work metal.

Grinding is another common material removal process.

Shaping Operation – 4. Material Removal Process



Shaping Operation – 4. Material Removal Process : Finishing Processes

Grinding is a material removal process accomplished by abrasive particles that are contained in a bonded grinding wheel rotating at very high surface speeds. The grinding wheel is usually disk shaped, and is precisely balanced for high rotational speeds.



Shaping Operation – 4. Material Removal Process




Lapping is an abrasive process used to produce surface finishes of extreme accuracy and smoothness. It is used in the production of optical lenses, metallic bearing surfaces, gages, and other parts requiring very good finishes.




Honing is an abrasive process performed by a set of bonded abrasive sticks. A common application is to finish the bores of internal combustion engines. Other applications include bearings, hydraulic cylinders, and gun barrels.




Superfinishing is an abrasive process similar to honing. Both processes use a bonded abrasive stick moved with a reciprocating motion and pressed against the surface to be finished. Superfinishing differs from honing in the following respects [4]: (1) the strokes are shorter, 5 mm (3/16 in); (2) higher frequencies are used, up to 1500 strokes per minute; (3) lower pressures are applied between the tool and the surface, below 0.28 MPa (40 lb/in2); (4) workpiece speeds are lower, 15 m/min (50 ft/min) or less; and (5) grit sizes are generally smaller.




Polishing is used to remove scratches and burrs and to smooth rough surfaces by means of abrasive grains attached to a polishing wheel rotating at high speed— around 2300 m/min (7500 ft/min). Buffing is similar to polishing in appearance, but its function is different. Buffing is used to provide attractive surfaces with high luster.

Polishing

Buffing



The second major type of part processing is performed to improve mechanical or physical properties of the work material.

These processes do not alter the shape of the part, except unintentionally in some cases.

The most important property-enhancing processes involve heat treatments, which include various annealing and strengthening processes for metals and glasses.

Sintering of powdered metals is also a heat treatment that strengthens a pressed powder metal work part. Its counterpart in ceramics is called firing.

Property-enhancing Operation



Surface Processing Surface processing operations include (1) cleaning, (2) surface treatments, and (3) coating and thin film deposition processes.

Cleaning includes both chemical and mechanical processes to remove dirt, oil, and other contaminants from the surface.

Surface treatments include mechanical working such as shot peening and sand blasting, and physical processes such as diffusion and ion implantation.

Coating and thin film deposition processes apply a coating of material to the exterior surface of the work part. Common coating processes include electroplating, anodizing of aluminum, organic coating (call it painting), and porcelain enameling. Thin film deposition processes include physical vapor deposition and chemical vapor deposition to form extremely thin coatings of various substances.

Surface Processing



Surface Processing

SandblastingShot Peening



Surface Processing

Electroplating is a process that uses electric current to reduce dissolved metal cations so that they form a coherent metal coating on an electrode. The term is also used for electrical oxidation of anions onto a solid substrate, as in the formation silver chloride on silver wire to make silver/silver-chloride electrodes

Anodized Aluminum Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts.The process is called anodizing because the part to be treated forms the anode electrode of an electrical circuit. Anodizing increases resistance to corrosion and wear, and provides better adhesion for paint primers and glues when compared to anodizing done on bare metal.

Electroplating

Manufacturing Processes – Manufacturing Processes – Assembly OperationsAssembly Operations


Permanent joining processes ; include welding, brazing, soldering, and adhesive bonding. They form a joint between components that cannot be easily disconnected.

Mechanical fastening ; Certain mechanical assembly methods are available to fasten two (or more) parts together in a joint that can be conveniently disassembled. The use of screws, bolts, and other threaded fasteners are important traditional methods in this category. Other mechanical assembly techniques form a more permanent connection; these include rivets, press fitting, and expansion fits.

Permanent Joining Processes & Mechanical Fastening

(Note : Details of welding shall be studied at Fabrication and Welding course later.

lo #2 manufacturing process primary secondary part 1

Engineering