ME3162 Cheatsheet PDF

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Summary

Metal FormingCold WorkingPlastic deformation below recrystallization temperature. The material is work hardened, i. strain hardened.Advantages Increased strength in the direction of cold working Increased surface hardness and wear resistance Good dimension tolerances and surface finish (finishing op...

Description

b.

Metal Forming Cold Working

Breaks up and distributes more evenly brittle films/particles of hard constituents c. Breaks up and refines cast structure of any ingot or casting Can be faster than cold working

Plastic deformation below recrystallization temperature. The material is work hardened, i.e. strain hardened.

7.

Advantages

Disadvantages

1. 2. 3. 4.

Increased strength in the direction of cold working Increased surface hardness and wear resistance Good dimension tolerances and surface finish (finishing operations not needed) Small parts can be shaped quickly

1. 2. 3.

4.

Disadvantages 1. 2. 3. 4. 5.

Some metals are too brittle to be cold worked conventionally Work hardening makes subsequent operations difficult or impossible Large parts and high strength metal alloys need much energy to work Reduces corrosion resistance, increases electrical resistance, changes magnetic properties Needs annealing to relieve stress caused by work hardening

Hot Working Plastic deformation above recrystallization temperature. The material is stress relieved since the material is totally annealed. Theoretically, the upper limit is the melting point, but we try to keep the material low to minimize oxidation. Advantages 1.

2.

3. 4. 5. 6.

5. 6. 7. 8. 9.

Some metals cannot be hot worked Oxide layer on surface Dimensional control difficult because of a. Metal contraction on cooling b. Oxide scales on surface Expensive and difficult to maintain high temperatures, dangerous and expensive to handle hot metal Accurate temperature control difficult because of uneven heating Difficulty of lubrication at very high temperatures Decarburization of steel, i.e. loss of carbon from the workpiece Carbon pick-up, i.e. absorption of carbon from the environment into the workpiece Expensive dies required

Rolling    

Only ductile metals can be cold rolled Zinc and Magnesium cannot be cold rolled Wire cannot be rolled economically if diameter is smaller than 5 mm Usually, metal starts off thick and must be hot rolled to below a certain thickness before it can be cold rolled. Before cold rolling, the metal oxide layer is usually removed by pickling in acid and washed in acetone

Less danger of metal cracking. Therefore, can work larger sections and make extreme shapes without Extrusion ruptures and tears  Convenient for low melting point and softer metals, Grain refinement possible (giving tougher material) provided they are ductile enough, e.g. Al a. Grain growth takes place as temperature rises  Must be done HOT for steel b. At recrystallization temperature,  Can result in workpiece surface defects when the recrystallization produces small grains metal leaves the extrusion chamber c. Normal grain growth takes place again. Grain Wire cannot be extruded properly if the diameter is  size can be controlled by controlling the less than 10mm temperature  Minimum thickness of hollow tube 1 mm No strain hardening, hence, no annealing needed Hot Extrusion (cheaper)  For long pieces of uniform cross section Less power needed than cold working, can use smaller  Maximum cross section diameter: Al (60 cm), Steel machines (15 cm) Repairs casting defects, e.g. blow holes, porosity  Economical way to make small parts in large Improves ductility as material becomes more quantities homogeneous a. Better diffusion of alloy constituents

Cold Extrusion 

Work hardening causes the metal to be hard to extrude after a while, hence the process must be completed fast

Hydrostatic Extrusion  

For extruding brittle metals For achieving high reduction of cross-sectional area

Tensile Drawing  

  

To reduce the cross section of bars and tubes To produce high performance bars and seamless tubes of very high strength (through work hardening) and straightness Must be done cold Gives rise to directional properties (Higher tensile strength in the direction of drawing) Reduction in cross-sectional area per pass is usually below 40%. After a number of draws, material becomes too hard and brittle and must be annealed to be drawn further

Forging Metal is deformed by sudden blows, or by using high pressure to squeeze it between dies. Of all processes, forging gives the best mechanical properties    

Durable, reliable High strength, toughness, fatigue strength, surface hardness, wear resistance Dense Flow lines cannot be removed by annealing

Drop Forging   

Superior mechanical properties due to fibrous structure Comparatively high rate of production High density of product

Press Forging         

For larger sections which cannot be easily handled by forging hammers For finishing operations (Usually preformed on other machines) For secondary operations (correct dimensional size and improve surface quality) Smooth surface Good tolerances and accurate dimensions Good penetration of pressure Quieter than drop forging Structural quality more uniform than drop forging More expensive

Upset Forging 

Used to shape bolts, nails, rivets, gear blanks with stems, etc

Arc Welding  

Roll Forging 

Reduces cross-section of short lengths of bar stock to make leers, axles, drills, leaf springs. Cross-section is changed or thickness reduced while stock length increased

Sheet Metal Working 

Minimum thickness 0.1 mm, maximum thickness 2 or 3 mm

Sheet Metal Drawing     

Usually done cold unless metal sheet is too thick Common materials: mild steel, stainless steel, Al alloys, Cu, any material that is ductile enough Thin-walled seamless metal cups Where uniformity and close tolerances are important (Better than impact extrusion) Directional properties

Rubbed Pad Forming  

Money is saved because rubber pad plays the role of the die Reduces metal spring back after forming

Shearing  

Fast Amenable to large scale production and automation

Hole Punching Punch Diameter =Hole Diameter + Allowance Die Diameter=Punch Diameter+2 (Clearance ) Blanking Die Diameter=Blank Diameter− Allowance Punch Diameter =Diediameter −2 ( Clearance )

Welding Gas Welding      

When electricity is not available For welding thin sheets below 2 mm Equipment is cheap, portable, versatile No electrical supply needed Can weld thin sheets Not for Al (Good conductor of heat, heat will not be concentrated)

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For joining sections of 2 mm thickness or more For faster welding with more localized heating, greater depth of penetration than gas welding since it delivers more heat to the weld joint than gas welding For welding materials with high heat conductivity, e.g. aluminium and copper alloys

Submerged Arc Welding      

 

For welding thick sections and sheets. Generally, not for sheets below 8 mm Commonly used for bridges and rails Automatic feed of electrode and flux Molten flux forms protective coating over weld, hence eye shield is not needed High currents yield higher welding speeds than other welding methods Can join thick sections with a single pass (for low C steels, nickel, non-ferrous metals and their alloys, e.g. bronze and brass) Needs lots of space and investment Automation is necessary since joint cannot be seen

Metal Inert Gas Welding & Tungsten Inert Gas Welding      

MIG same as arc welding but with an inert gas shield TIG can weld thin to moderate sections (1 – 5 mm) TIG needs more space than MIG because the former uses a filler rod Both used for welding stainless steels, Mg, Al, Cu and Ti alloys. MIG is commonly automated and much faster than TIG Without the inert gas shield, Cu, Mg and Al oxidise rapidly in air to form brittle oxides.

Friction Welding    

Can join dissimilar metals Fast Only for welding round sections than can be clamped in a rotating chuck Stainless steel sheets can be friction welded

Resistance Welding (Spot Welding & Seam Welding) 

 

Convenient way of welding sheet metal of roughly the same thickness. Needs to be in sheet form. Metals need to be the same type Electrodes should be of low resistance and workpieces should be of higher resistance (e.g. various steels) Can be used for stainless steel sheets

      

Difficult for aluminium, copper, brass and silver Heat is localized Fast No filler metal needed Easily automated for large scale production Initial equipment cost can be quite high May be difficult to join sheets of different thicknesses

Laser Beam Welding 

 

For welding fine wires, thin foils which are inaccessible by other methods and welding jobs requiring high precision Energy easily controlled Tiny (0.1 mm) Heat Affected Zone

Electron Beam Welding     

For welding turbine blades Since it is done in vacuum, danger of oxidation is negligible Energy easily controlled Tiny HAZ (0.1 mm) Vacuum is needed, much time is spent evacuating the chamber

Riveting  

Aluminium, Copper, Brass Nor for cast iron and high carbon steel which are too brittle

Casting Sand Casting Advantages     

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No limit to size of mould. Can be used to produce huge parts. Cheap No directional properties Complicated shapes can be produced conveniently and cheaply Can produce almost finished shape, requiring only a little machining for dimensional accuracy and smooth surface Sand casting can also do thin walls of 1 mm, but you have to expect sand casting defects

Disadvantages   

Rough surface due to sand mould Each mould can be used to produce only one casting Very slow process. Not for large scale production.

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Poor dimensional tolerances because metals shrink on solidification and shrinks further on cooling from melting point to room temperature

Die Casting

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For copper and its alloys (e.g. brass and bronze), all types of steels, zinc, aluminium and its alloys, cast iron

Advantages

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    

Composite structure Controlled density Good dispersion in alloys High purity of metal Low machining costs (subsequent machining is usually not necessary) Close tolerance ( ±10 μm )

Ideal for low melting point metals (Al, Zn, Pb, Cu,  Fully automated Mg and Sn alloys)  Moulds/dies are relatively cheap   More expensive than sand casting but castings have  Porous, unsound and impure castings can be recycled  No waste material (scrap) better dimensional tolerances into furnace (no wastage) High speed production for small parts   Best surface finish and tolerances of all casting  Physical properties and surface finish are usually  Uniform composition processes, except investment casting adequate for immediate application  Much thinner sections can be cast than in sand casting Disadvantages  Quick and convenient process to prepare metals for (thin walls of 1 mm) secondary hot working operations like rolling,  High cost for raw materials. Scale of production must  Can be used for mass production to produce 1000 to extrusion, forging be large to justify cost (Normally for ¿ 100,000 100000 castings  Secondary operations make use of the existing heat in parts)  Production rate is high the solidified metal  Dies must be very simple since the powders cannot  Steel is difficult to die cast because dies need to be flow around corners. Complex shapes need several made of even high melting point materials Investment Casting punches, otherwise density will not be uniform  Turbine fan can be die casted Advantages  Size of product is limited by size of dies. Products are   Extremely good surface finish usually less than 15 kg Can cast very complicated shapes, e.g. jewellery,  Hot Chamber Die Casting  Storage of powders difficult (Need to be stored in  Only suitable for low melting point metals (Pb, Sn, Zn statues, turbine blades, gears vacuum or non-oxidizing atmosphere) alloys)  No need to machine subsequently. Saves money and  Powder size is not consistent time, especially for steels and hard alloys that are  Products could be brittle, since porosity lowers tensile Cold Chamber Die Casting difficult to machine strength, ductility, fatigue endurance limit Advantages over Hot Chamber  Wide range of alloys are suitable for investment  Difficult to handle low melting point metals as they casting (steels, bronze, nickel-based alloys, titanium,  Can be used for non-ferrous metals of higher melting tend to melt when sintered point (Al, Mg, Cu alloys) magnetic materials) Slight shrinkage on sintering and cooling to room   Close tolerances achievable even for high melting  Liquid metal in contact with injection cylinder walls for temperature only a short time (less alloying takes place with the point metals that need to cool down from the melt  Cannot be bent or cold worked subsequently due to through a large temperature range steel equipment) brittleness  Cannot make threads in-situ (must machine later) Disadvantages Centrifugal Casting  Minimum thickness about 1 mm and maximum  For casting large pipes. Also, for grey cast iron  Expensive thickness about 2.5 × D cylinder liners for internal combustion engines  Castings cannot be too large Advantages  

  

Centrifugal castings of finer grain size because of fast cooling (tougher) Cleaner castings can be produced because lighter non-metallic impurities segregate towards the inner radius where they can be subsequently machined or chopped off Highly dense structure, free of defects Automation is possible with high production rates Can cast large pipes accurately

Powder Metallurgy 

Advantages 



Continuous Casting 

To make blooms, billets and slabs without having to cast ingots first

Metal powders are compressed and sintered to form a metal product

 

High melting point metals can be fabricated below their melting points. Only commercially viable method to fabricate tungsten, tantalum and molybdenum in large quantities Non-metallic constituents can be introduced, and their contents can be controlled Controlled porosity Lamellar structure

Pipe & Tube Production Induction Welding of Cold Rolled Strip   

To make low cost and low strength tubes of various steels. Weld joint limits strength of tube Not for tubes below 10 – 15 mm Not for good conductors of electricity like aluminium, copper, brass (extruded instead)

Seam Welding of Metal Strip 

Seam welded by hot pressure welding, electrical resistance welding or SAW, depending on tube size

Hollow Extrusion 



For making high-performance seamless tubes and pipes For large hole with thin walls

Mannesmann Process  

For making reliable tubes and pipes of any size that must not have any weld joint. Generally, for a small hole in a very thick wall

Casting with Central Core 

For making large pipes of cast iron, steel and other metals

Roll Bending and Welding  

Roll bend thick metal strip into a pipe and weld the seam using SAW For making very thick and large pipes

Spiral Welding of Metal Strip 

For making extremely large pipes

Welding from Separate Metal Sheets 

For making extremely large pipes

Drawing and Pressing of Sheet 

For making very small tubes of thin wall thickness

Electrical Discharge Machining Die-Sinking EDM   



To machine moulds and dies To drill small holes that are too small for conventional tool bits To machine materials that are too hard for conventional machining, e.g. sintered tungsten carbide, hardened tool steels To machine tin-walled parts that are too weak to withstand the cutting forces of conventional tools, e.g. aluminium sheets in aluminium honeycomb

Advantages 

 

Can machine any hard material so long as it is conducting, e.g. hardened tool steels, hard special alloys, carbides Products are completely burr free Close tolerances (average a few microns). Dimensional accuracy improves as current is decreased

  

Can machine intricate configurations, narrow slots, blind cavities, small and deep holes No mechanical strains induced in the workpiece Can produce sharper corners than conventional machining

   

Low coefficient of friction Cheap Used for load bearing if dimensions not critical Poor dimensional stability

Aramids

 Very  strength and stiffness  Bulletproof Both the electrode and workpiece must be electrically conductive Polyesters  There is electrode wear which might result in products Polycarbonate with poor dimensional tolerances  High impact stress  Slow metal removal rate (Not for large scale  Can stand boiling water production)  Transparent  Recast surface layer has high residual stresses and high roughness (matte surface finish). To achieve a PET better surface finish, the rate of metal removal must  High boiling point but changes shape be reduced Polyolefins Microstructurally altered surface layer   Corrosion resistant Wire-Cut EDM  Non-toxic  For machining hard conducting materials  Waxy surface  For high precision machining, e.g. teeth on gears Polyethylene below 1 mm in diameter  Very light  For machining complicated profiles, including bevels  Can stand very corrosive materials (wire can be at an angle to the vertical)  Cannot stand boiling water

Disadvantages 

Thermoplastics Acetal (Polyacetal)  

Very  strength but not boiling water Used for load-bearing components

Acrylic  

Most transparent Became opaque from UV

Cellulosics   

Extremely cheap Comes in many forms Transparent unless altered

Fluorocarbons (Teflon)     

Can stand  temperature and corrosive environments Low coefficient of friction Low surface energy (non-stick) Expensive Heaviest of all common plastics

Polyamides Nylon 

Excellent toughness & wear resistance

Polypropylene     

Stronger Can stand boiling water Soft Floats in water More expensive

Refer book for LDPE (extremely cheap), HDPE, UHMWPE and PP

Polyurethane  

Replacement for rubber Used in non-foam (solid) form

Styrenes      

Cheap Transparent Good for low and sub-zero temperature Non-toxic Will get dented Brittle

ABS   

Opaque Impact resistant Cannot stand boiling water

SAN

  

Transparent Can stand boiling water More brittle

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Silicone  

Vinyls (PVC)     

Cheapest Transparent Rigid and hard Cannot stand boiling water Toxic

THERMOSETTING RESINS Generally, can be used at higher temperatures but brittle

Amino Plastics (Urea/Melamine Formaldehyde)    

Hard surface Wear resistant Strong Stain resistant

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High flexural strength Tough Obsolete and seldom used

Epoxy       

High strength Very chemically inert Very corrosion resistant Dimensionally very stable Excellent adhesive Tends to be brittle Expensive

Phenolic (Bakelite)  

Excellent chemical, electrical and heat resistance Extremely hard and bri...