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Summary

COLD WORKING (page 5) Plastic deformation happens below recrystallization temp.(0 Tm) strength (directional) surface hardness + wear resistance  surface finish & tolerance No oxide layer Some too brittle to be cold-worked Subsequent operations difficult Large parts need ↑energy ↓corrosion...

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COLD WORKING (page 5) Plastic deformation happens below recrystallization temp.(0.25 Tm) strength (directional) surface hardness + wear resistance surface finish & tolerance No oxide layer Some too brittle to be cold-worked Subsequent operations difficult Large parts need ↑energy ↓corrosion resistance ↑electrical resistance Needs annealing to relieve stress

TENSILE DRAWING (page 19) For very small diameter To reduce cross section of bars and tubes Seamless tubes of very high strength Stronger than cold rolling Best straightness Must be done COLD - Directional properties use mandrel to create the central hole to get hollow cross-section area

HOT WORKING (page 5)

FORGING (page 22)

Plastic deformation happens above recrystallization temp.(0.75 Tm) metal cracking (esp. for brittle materials at low temp e.g. Zn Mo, Mg, W. Grain refinement possible No annealing needed power Repairs casting defects ductility Faster Oxide layer Some metals cannot Difficult dimensional control Expensive

Strongest of all manufacturing processes Durable, reliable Very  strength  toughness  fatigue strength  surface hardness  wear resistance Suitable for mass production Any metal can use Creates fibrous structure which cannot be removed Expensive Hammer Forging  Drop Forging – split dies  Superior mechanical properties Comparatively high production rate High density  Press Forging (fast) Better homogeneity & quieter than drop forging Smooth surface Good tolerance and accurate dimension Better than hammer forging For finishing, secondary and larger sections More expensive  Upset Forging Done along its length  Roll Forging

ROLLING ( page 8) To  thickness Only ductile metals can be cold rolled Zn & Mg cannot Cold rolling – Shining surface + small thickness Better homogeneity – tough Cheaper than extrusion For thin materials  Cold  Hot

EXTRUSION (page 14) For soft material and uniform cross section Create tube with no seam No point of weakness Steel hard to extrude unless want seamless - Prefer rolling Can produce hollow sections Good dimensional accuracy (straight) Surface defects when metal leaves chamber expensive  Direct (forward)  Indirect – no frictions between billet and cylinder walls  Impact  Hot Long pieces of uniform cross section

SHEET METAL WORKING (page 29) (room temp) Usually mild steel Start with blank or sheet metal to form thin metal products Usually done cold unless sheet too thick SHEET METAL DRAWING (making seamless cups) Shallow drawing (< 0.5 diameter) Deep drawing (> 0.5 diameter)

WELDING (page 48) Low carbon steels excellent for welding Higher carbon steel and iron need special techniques Non-ferrous need special techniques Quick, convenient Cheap Only affect the weld area microstructural properties Dependent on human factors Defects are common (porosity, inclusions)(structural) Dimensional defects- warpage GAS WELDING (page 54) For thin sheets (2mm) Will burn thin sections Faster and greater depth of penetration Must have  heat conductivity Slow Flux corrode aluminium RESISTANCE WELDING (spot & seam welding) (p61) Ideal for steels – high resistance Impossible for low resistance metals (good conductors) Both metal must about same thickness Localized heat Fast No filler metal Easily automated High cost Difficult to join different thickness

SUBMERGED ARC WELDING (page 57) Automatic feed Molten flux forms protective coating  welding speed For sheets > 8mm Lots of space and $ Automation necessary FRICTION WELDING (inertia welding) (page 60) Can join dissimilar metals Fast Only for ROUND sections

LASER BEAM WELDING ( page 63) For inaccessible parts cause tiny (0.1mm) Energy easily controlled (Advantages same as Electron Beam except EBW need  vacuum) SAND CASTING (uses expendable sand mold) (p66) No size limit Cheap No directional properties Can make complicated shapes Good for m.p. metals Require only a little machining Rough surface Slow Poor dimensional tolerances Defects ( page 70)

DIE CASTING ( permanent metal mold) (page 73) Ideal for  m.p. materials  production rate Better surface finish and tolerances only 2nd to investment casting Can be used for non-ferrous metals  alloying One directional

Parting line (MOST CASTING) CENTRIFUGAL CASTING(page 75) Finer grain size – tougher Cleaner Dense structure, free of defects  production rates Best mechanical properties for casting Accurate CONTINUOUS CASTING (page 76) For recycling Don’t need to cast ingots Fully automated Cheap Quick INVESTMENT CASTING (precision casting) (p77) Very good surface finish Complicated shapes good tolerances no need to machine subsequently Can use high m.p. metals Good for Tungsten and Cobalt (hard to machine) Expensive Limited size

 

Cold (very little use) Hydrostatic Less likely to crack Very thin tube + brittle materials High reduction in cross-sectional area

POWDER METALLURGY (page 80) Strength determined by density  m.p. materials can fabricate below m.p. Close to final shape Non-metallic constituents can be added  tolerances No waste  speed  cost Die must be simple & one direction Size limited by dies Difficult to store – oxidize easily Brittle – can’t bend or cold work subsequently  tensile strength  ductility, fatigue Difficult for low m.p. – melt Minimum thickness about 1mm and max thickness about 2.5D INDUCTION WELDING OF COLD ROLLED STRIP(P87) Low cost Will have seam Low strength Welded by Electrical Resistance welding Not good for good conductors (REFER BOOK. SHORT CHAPTER)

ELECTRICAL DISCHARGE MACHINING (page 93) Used to make molds Harden before machine DIE SINKING EDM All automated Can machine hard material as long as conducting  tolerance No mechanical strains

RUBBER PAD FORMING No need die SHEARING (large scale)

Trim out smaller sheet Fast Blanking (save round part) Piercing (throw round part) PLASTICS (page 109) Colour choices Good Thermal insulation Good Electrical insulation Good Corrosion resistance Light Easy to process Cheap Rigid plastics can be made flexible by adding plasticisers transparent or translucent plastics can be made opaque by adding dyes Cannot repair Absorbs odours Not for  temperature Creep under load Weak mechanical properties Deteriorate under Sun ROUGH COSTING OF PLASTIC (PAGE 117)! INJECTION MOLDING (page 121) Thermoplastics only Similar to die casting Large scale production Will have parting line

COMPRESSION MOLDING (page 122) Thermoset only Similar to press forging Large scale but slower than Injection TRANSFER MOLDING( page 123) Same as Compression No flash Can mold small intricate parts

METAL INERT GAS WELDING (page 58) No need to remove flux Ideal for sheet metal & positional work Don’t need to replace electrode (TIG)need more space More flexibility (TIG) More expensive CALENDARING( page 131) Thermoplastics only Similar to rolling Thinner than Extrusion THERMOFORMING ( page 132) Thermoplastics only Similar to sheet metal forming Match mold forming Vacuum forming Pressure forming/blow forming CASTING (page 134) For prototyping ( small scale) Thermoplastics and thermosets Cheap PLASTISOL MOLDING (page 134) Coating

LAMINATING (both thermoplastic & thermosets) Coating Plane flat sheets only REINFORCED MOLDING (page 136) Making composites Not limited to plane flat sheets FOAM MOLDING (page 137) Create sponge-like material

BRASS Corrosion resistant Strong Durable Gold Expensive STAINLESS STEEL Silver Durable

Slow ALL CASTING SHRINKS – POOR TOLERANCE Casting defects – porosity, cracking (fast cooling) All casting not very strong

TIPS Pipe and tube Material  Aluminium, copper, brass: EXTRUSION |Softer, lower m.p.  Cheaper  Steel, stainless steel: COLD ROLLING |When welding might have air trapped  For low strength application only |Steel is expensive for extrusion For high strength use, EXTRUSION or MANNESSMANN  create seamless tubes

For raw material must always HOT ROLL Normally the raw material comes in big blocks  Hot roll faster in reducing size Cold rolling always the BEST and CHEAPEST for bar with uniform cross section  quick mass production Die casting more expensive than sand casting Aluminum is dull Forging even more expensive If diameter >10mm, cannot extrude directly

Workpiece and electrode must be electrically conductive Very slow Recast surface layer has high residual stress and high roughness (matte surface finish) Electrode wear – poor tolerance WIRE CUT EDM High precision machining Complicated profiles

REACTION INJECTION MOLDING Hybrid of Compression and Injection EXTRUSION ( page 124) Thermoplastics only Very large scale No need high temperature BLOW MOLDING ( page 125) Thermoplastic only Large scale ROTATIONAL MOLDING ( page 130) Thermoplastics only Cheap Slow Small scale

THERMOPLASTICS (page 110) Acetal (Polyacetyl) 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 Can stand  temperature and corrosive environments  coefficient of friction  surface energy (non-stick) Expensive Heaviest of all common plastics Polyamides Nylon Excellent toughness & wear resistance  coefficient of friction Cheap Used for load bearing if dimensions not critical Poor dimensional stability Aramids

Corrosion free Expensive MILD STEEL Cheap Strong Corrodes MEDIUM CARBON STEEL Strong Expensive ALUMINIUM Corrosion resistant Strong Not as shiny

Low density polyethylene Non-toxic and chemically inert. Squeezable

THERMOSETTING RESINS Generally can be used at higher temperatures but brittle

High density polyethylene

Amino Plastics (Formaldehyde) Hard surface Wear resistant Strong Stain resistant

Ultra-high molecular weight polyethylene Wear resistant surface. Eg. Surgical implants The higher the density, the more opaque 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  for low and sub-zero temperature Non-toxic Will get dented Brittle

Caseins 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 Excellent chemical, electrical and heat resistance Extremely hard and brittle Polyesters  weathering characteristics Corrosion resistance

Very  strength and stiffness Bulletproof Polyesters Polycarbonate  impact stress Can stand boiling water Transparent PET High boiling point but changes shape Polyolefins Corrosion resistant Non-toxic Waxy surface

ABS Opaque Impact resistant Cannot stand boiling water SAN Transparent Can stand boiling water More brittle

Polyurethane Flexible Last much longer than Styrofoam More expensive Silicone Soft and rubbery Often used to replaced rubber when  temperature is encountered Convenient for making large objects and for joining/sealing purposes

Vinyls (PVC) Cheapest Transparent Rigid and hard Cannot stand boiling water

Polyethylene Very light Can stand very corrosive materials Cannot stand boiling water

MACHINING AND MACHINE TOOLS

For small ae / dt

Shear plane model

Cutting Rotational motion of the workpiece at V relative to the tool

Material removal rate

ae −depth of cut∨a p−width of workpiece Machining time

Chip cross-section area Ac

A c =f a p where f is the feed per revolution

f=

Vf

t m=

lw +d t if face milling Vf

Drilling Undeformed chip thickness

nw

Material removal rate

Z w =A c V av=f a p V av

kr is the major cutting edge angle Machining time

The apparent shear strength of the material s on the shear plane

TOOL WEAR AND TOOL LIFE

¿ πf a p n w (d m +a p) Power required

lw is the length of the drilled hole nt is the rotational frequency of the tool

energy

Material removal rate

Pm= p s Z w ps – specific cutting

Electrical power consumed

Pe =

Pm ❑m

Vertical milling

MECHANICS OF METAL CUTTING Specific cutting energy

Specific cutting energy ps :

Maximum undeformed chip thickness

Vf f if face milling ¿ af = = N N nt Economics of metal cutting operation Average cost per workpiece

Average cost per workpiece

Depreciation time

Where

Tool cost a) Regrindable tools

(b) Disposable inserts

Tool changing time

Minimum Cost Cutting speed Number of tools required Machine Tool Maximum Power Restriction

c,  and  are constants

t = tool life Machining time

Maximum Force Restriction

Tool life Surface Finish

Minimum Production Time Cutting speed

R is tool nose radius

where

Tool life Tooling cost and tool changing cost per workpiece Estimation of cost Factors Total Machine and Operator Rates Number of tools per workpiece

Total production time = no. of pieces x (loading time + tool return time + rough cut time + finish cut time)

t mr=

Volume of removed material Zw...