Manufacturing Technology

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Casting (founding) produces a part by pouring molten metal into a mould cavity and letting it solidify.

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It is the most economical way to make complex, large or hollow shapes.

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This section covers patterns and moulds, cores, gating and risering, melting, the main casting processes, cleaning of castings, defects and applications.

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Cast (Mould) Making:

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Patterns • Sequence: pattern making → moulding & core making → melting → pouring → solidification & cooling → shake-out → fettling (cleaning) → inspection. • Pattern: replica of the casting used to form the mould cavity.

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Materials: wood (most common, cheap, easy to shape; absorbs moisture), metal (Al, cast iron, brass — long life, mass production), plastics, wax (investment casting), plaster, polystyrene (full-mould/lost-foam). • Types: single-piece (solid), split (two-piece, most common for complex shapes), loose-piece, match-plate (both halves on one plate — machine moulding, mass production), gated, cope-and-drag, sweep (symmetrical large shapes like bells), skeleton (large castings, few numbers), follow-board, segmental.

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Pattern allowance Purpose / typical value Shrinkage (contraction) Pattern made LARGER to compensate for solid contraction.

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CI ≈ 10 mm/m (1%), steel ≈ 20 mm/m (2%), Al ≈ 13 mm/m, brass ≈ 15 mm/m.

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Pattern maker's rule (contraction scale) used Machining (finish) Extra metal on surfaces to be machined Draft (taper) Taper 1–3° on vertical faces for easy withdrawal of pattern from sand (more on internal surfaces) Distortion (camber) Pattern deliberately distorted to offset warping of long/U-shaped castings Shake (rapping) Pattern made SMALLER because rapping enlarges cavity — the only NEGATIVE allowance • Pattern colour code (common convention): black — surfaces left unmachined; red — surfaces to be machined; yellow — core prints; red stripes on yellow — seats of loose pieces.

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Moulding Sand and Moulds • Moulding sand = silica sand (SiO2, refractory base) + clay binder (bentonite, fire-clay, kaolinite;

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5–20%) + water (2–8%) + additives (sea coal/coal dust — better finish, prevents metal penetration; cereal binders, wood flour, silica flour). • Types: green sand (moist, not baked — most common), dry sand (baked mould — larger castings), loam sand (≈ 50% clay — large castings with sweep patterns), facing sand (next to pattern), backing (floor) sand, parting sand (prevents cope and drag sticking), core (oil) sand, CO2 sand (sodium silicate binder hardened by CO2 gas). • Properties: permeability (allows gases/steam to escape — low permeability causes blowholes), refractoriness (withstand high temperature), green strength, dry strength, hot strength, cohesiveness (sand grains stick together), adhesiveness (sticks to flask), collapsibility (breaks down as casting contracts — prevents hot tears), flowability. • Sand testing: permeability number PN = VH/(pAT) on a standard 50.8 mm × 50.8 mm specimen; grain fineness (AFS number), clay content, moisture content, strength, mould hardness. • Flask parts: cope (top), drag (bottom), cheek (middle).

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Moulding methods: bench, floor, pit and machine moulding (jolt, squeeze, jolt-squeeze, sand slinger).

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Cores • Core: sand body placed in the mould to form internal cavities/holes.

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Made in core boxes from core sand (sand + oil/resin binders) and usually baked for strength. • Core requirements: high collapsibility, permeability, refractoriness, strength, smooth surface. • Core prints (projections on pattern) form seats to locate and support the core.

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Chaplets are metal supports for cores that FUSE into the casting (same metal as casting). • Core types: horizontal, vertical, balanced, hanging, drop core, ram-up core.

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Gating System, Risers and Chills • Gating system: pouring basin (cup) → sprue (down-gate) → sprue well → runner → ingates → mould cavity.

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Slag traps: skim bob, strainer core, ceramic filters. • Sprue is tapered (smaller at bottom) to prevent aspiration (air being sucked in as the stream accelerates). • Gates: top gate (fast, favourable thermal gradient but turbulence/erosion), bottom gate (smooth, less erosion, unfavourable thermal gradient), parting-line gate (most common), step gate (tall castings). • Gating ratio (sprue : runner : gate areas): non-pressurised e.g.

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4 (less turbulence — Al, Mg); pressurised e.g.

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1 with gate smallest (fuller runners, ferrous castings). • Riser (feeder): reservoir of molten metal that feeds the casting to compensate for liquid and solidification shrinkage; must solidify LAST.

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Types: open (top) and blind; top and side risers.

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Exothermic or insulating sleeves keep risers hot. • Chvorinov's rule: solidification time t = B (V/A)² — modulus V/A.

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Riser modulus should be ≥ 1.2 × casting modulus.

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Best practical riser shape: cylinder with H = D (sphere ideal but hard to mould). • Chills (metal inserts, external or internal) speed up cooling locally to achieve directional solidification towards the riser. • Fluidity (ability to fill thin sections) increases with superheat (pouring temperature above liquidus); eutectic alloys have good fluidity.

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Metal Melting Furnace Used for Key points Cupola Cast iron Vertical shaft; charge = coke (fuel) + pig iron + scrap + limestone (flux); metal:coke ≈ 8–10 :

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1; zones: well, combustion (tuyere/oxidising), reducing, melting, preheating, stack Electric arc furnace (EAF) Steel, alloy steel Direct arc between graphite electrodes and charge; steel scrap recycling Induction furnace (coreless) Steel, alloys, non-ferrous Clean, precise temperature control, electromagnetic stirring, no contamination Crucible furnace (pit/tilting) Non-ferrous (Al, brass, bronze) Small quantities; oil, gas or coke fired Reverberatory furnace Non-ferrous in large quantities (Cu, Al) Flame and heat reflected from roof onto charge Casting Processes Process Principle Typical products / remarks Sand casting Expendable sand mould Any size/metal; engine blocks, machine beds, pump casings; rough finish Shell moulding (Croning) Resin-bonded sand on heated metal pattern (~200–250 °C) forms thin shell Good accuracy & finish; crankshafts, small gears, valve bodies Investment (lost-wax) casting Wax pattern coated with ceramic slurry; wax melted out; metal poured Precision casting — best accuracy & finish, complex shapes: turbine blades, jewellery, dental, surgical parts, art castings (Patan metal craft) Full-mould / lost-foam Polystyrene pattern left in sand, vaporises on pouring No parting line, no cores; automotive parts Plaster / ceramic mould Plaster or ceramic slurry mould Non-ferrous (plaster), fine detail Gravity (permanent mould) die casting Metal mould, metal poured under gravity Pistons, Al parts; better properties than sand casting Hot-chamber die casting Injection chamber (gooseneck) immersed in molten metal Low-melting alloys:

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Zn, Sn, Pb, Mg; fastest cycle Cold-chamber die casting Metal ladled into separate chamber, then injected at high pressure Higher-melting alloys:

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Al, Cu (brass), Mg Low-pressure die casting Metal pushed up into mould by gas pressure Al wheels, cylinder heads True centrifugal casting Mould rotated about its own axis; no core needed Pipes, tubes, bushes, liners; dense outer skin, impurities move to inner surface Semi-centrifugal Rotation about axis of symmetry, central core possible Wheels, pulleys, gear blanks Centrifuging Several cavities arranged around a central sprue Small intricate parts Squeeze casting Metal solidifies under high pressure Near-net shape, high integrity parts Slush casting Metal poured and drained once a thin skin freezes Hollow ornaments, toys, lamp bases (low-melting alloys) Continuous casting Molten metal solidified continuously in water-cooled mould Slabs, billets, blooms in steel plants Cleaning the Castings (Fettling) and Defects • Steps: shake-out/knock-out (remove casting from sand) → core removal → removal of gates and risers (sawing, hammering for CI, gas/abrasive cutting) → removal of fins and adhering sand by tumbling (rattling), shot/sand blasting, wire brushing, chipping and snag grinding → heat treatment → inspection.

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Defect Cause Blowholes / gas porosity Low permeability, excess moisture, hard ramming, gas in metal Shrinkage cavity Insufficient feeding — poor riser design/location Misrun Metal solidifies before filling cavity — low fluidity, low pouring temperature, thin sections Cold shut Two streams of metal meet but do not fuse — low pouring temperature Hot tear (hot crack) Restrained contraction during solidification — poor collapsibility of sand/cores Scab / buckle / rat tail Expansion of sand at mould surface (silica expansion), poor sand Swell Soft ramming — mould wall moves under metal pressure Defect Cause Shift (mismatch) Misalignment of cope and drag or core Fin / flash Metal flows into gap at parting line Drop Portion of cope sand falls into the cavity — weak sand, poor ramming Metal penetration / fusion Coarse sand, high pouring temperature, low refractoriness Inclusions Slag, sand or oxide trapped in metal • Applications of foundry: engine blocks, cylinder heads, pistons, crankshafts, pump and valve bodies, machine-tool beds, turbine casings and blades, pipes, manhole covers, bells, statues.

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Advantages: complex internal shapes, very large parts, almost any metal, economical in quantity.

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Limitations: porosity, lower dimensional accuracy (sand), environmental and safety issues.

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Heat treatment is controlled heating and cooling of metals in the solid state to change their microstructure and properties.

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This section covers the TTT diagram, annealing, normalising, hardening, tempering, isothermal treatments, surface and case hardening (carburising, cyaniding, nitriding), material modification, solidification control and powder metallurgy.

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Purpose and the TTT Diagram • Purposes: relieve internal stresses, improve machinability, refine grain size, increase hardness and wear resistance, improve toughness and ductility, homogenise composition, modify electrical/magnetic properties. • TTT (time-temperature-transformation) / isothermal transformation diagram: 'C'-shaped curves showing start and finish of austenite transformation at constant temperature.

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Nose ≈ 550 °C for plain carbon eutectoid steel.

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Above nose → pearlite (coarse → fine); below nose → bainite; below Ms (martensite start) → martensite. • Critical cooling rate: minimum cooling rate that just misses the nose, producing 100% martensite.

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Alloying elements (except Co) shift the C-curve to the RIGHT → lower critical cooling rate → better hardenability (oil or air hardening). • CCT diagram (continuous cooling transformation) is used for practical continuous cooling.

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Process Heating Cooling Result / use Full annealing 30–50 °C above A3 (hypo-eutectoid) or above A1 (hyper-eutectoid); soak Furnace (very slow) Coarse pearlite; softest, max ductility & machinability; relieves stresses Process (sub-critical) annealing 550–650 °C (below A1) Air or furnace Recrystallises cold-worked steel (between wire-drawing passes) Spheroidising Just below A1 for long time (or cycling) Slow Spherical cementite in ferrite; best machinability of high-carbon/tool steels Stress-relief annealing 500–650 °C Slow Removes residual stresses from welding, casting, machining Diffusion (homogenising) annealing 1000–1200 °C, long time Slow Removes chemical segregation in castings/ingots Normalising 40–50 °C above A3/Acm Still air Fine pearlite, refined grain; stronger & harder than annealed; castings, forgings Hardening Above A3 (hypo) / above A1 (hyper) Quench in water, brine or oil Martensite — maximum hardness, brittle, high internal stress Tempering Re-heat hardened steel below A1 (150–650 °C) Air Reduces brittleness & stress, increases toughness; some hardness lost Quenching, Hardenability and Tempering • Quenching severity (fastest → slowest): brine > water > oil > molten salt > air.

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Faster quench → higher hardness but more distortion and risk of quench cracks. • Hardness of martensite depends mainly on carbon content.

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Hardenability = depth to which steel can be hardened — increased by alloying (Mn, Cr, Mo, Ni) and larger grain size.

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Measured by the Jominy end-quench test. • Retained austenite (high-carbon/alloy steels) is converted by sub-zero (cryogenic) treatment. • Tempering ranges: low 150–250 °C (cutting tools, gauges — keeps hardness, relieves stress); medium 350–450 °C (springs — troostite); high 500–650 °C (shafts, gears, axles — sorbite; 'hardening + high tempering' = toughening/quenching & tempering).

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Temper colours: straw ≈ 220 °C, brown, purple, blue ≈ 300 °C. • Temper embrittlement in some alloy steels around 350–575 °C — reduced by adding Mo.

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Isothermal Treatments • Austempering: quench into a salt bath held ABOVE Ms (≈ 250–400 °C), hold until transformation is complete → bainite.

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Good toughness and ductility, minimal distortion and cracking; no tempering needed. • Martempering (marquenching): quench to just above Ms, hold to equalise temperature, then air-cool through the martensite range → martensite with less distortion and cracking; tempering follows. • Patenting: isothermal treatment of high-carbon wire to fine pearlite before drawing.

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Surface Hardening and Case Hardening • Goal: hard, wear-resistant case + tough, ductile core (gears, cams, camshafts, crankshafts, pins).

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Process Medium / temperature Key features Carburising Carbon added to low-C steel (< 0.2% C) at 900–950 °C: pack (charcoal + BaCO3 energiser), gas (CH4, propane) or liquid (salt bath) Deep case (0.5–2 mm); must be QUENCHED and tempered afterwards; most widely used Cyaniding Liquid bath of sodium cyanide (NaCN) at 800–870 °C — adds C and N Thin case (0.1–0.3 mm), quick (30–60 min), then quench; bath is highly TOXIC; small parts, screws, nuts Carbonitriding Gas atmosphere of hydrocarbon + ammonia, 700–900 °C — C and N Gas equivalent of cyaniding; thin, hard case Nitriding Ammonia (NH3) gas at 500–550 °C (below A1) — N forms hard nitrides Hardest case (≈ 1000–1100 HV), no quenching needed, least distortion, good fatigue & corrosion resistance; needs alloy steels with Al, Cr, Mo (Nitralloy); long cycle (20–100 h); thin case Flame hardening Oxy-acetylene flame heats surface, then water spray Medium-carbon steels (0.35–0.6% C); large parts; no composition change Induction hardening High-frequency induced current heats surface layer (skin effect), then quench Fast, selective, clean; higher frequency → shallower case; gears, shafts, crankshaft journals Laser / electron-beam hardening Focused beam heats very thin surface Precise local hardening with minimal distortion Material Modification and Solidification Control • Precipitation (age) hardening of non-ferrous alloys (duralumin, some stainless steels): solution treatment → quench → ageing (natural at room temperature or artificial at 100–200 °C).

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Over-ageing lowers strength. • Surface modification: shot peening and surface rolling (compressive residual stress, better fatigue life), cladding and hard-facing, electroplating, anodising, ion implantation, PVD/CVD coatings (TiN on cutting tools). • Solidification process control: faster cooling and inoculation (grain refiners, e.g., Ti-B in Al, Mg in SG iron) give finer grains; directional solidification and single-crystal casting (turbine blades) eliminate grain boundaries for creep resistance; rapid solidification produces amorphous metals (metallic glasses).

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Powder Metallurgy (P/M) • Steps: powder production → blending/mixing → compaction → sintering → secondary (finishing) operations. • Powder production: atomisation (liquid stream broken by gas/water jets — most common), chemical reduction of oxides (Fe, W, Mo), electrolysis (high-purity Cu, Fe), mechanical comminution (ball milling of brittle materials), carbonyl process. • Blending with lubricants (zinc stearate) and binders.

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Compaction in dies (100–800 MPa) gives a fragile green compact.

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Isostatic pressing (CIP/HIP) gives uniform density. • Sintering: heating in a protective (reducing) atmosphere to ≈ 70–90% of the melting point of the main constituent — particles bond by solid-state diffusion; strength rises, some shrinkage. • Secondary operations: sizing/coining, infiltration (filling pores with lower-melting metal e.g.

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Cu into Fe), impregnation (filling pores with oil — self-lubricating bearings), machining, heat treatment, plating. • Applications: cemented carbide cutting tools (WC + Co binder), self-lubricating porous bronze bearings, tungsten lamp filaments, refractory metal parts (W, Mo), cermets, friction materials (brake pads, clutch plates), permanent magnets, small gears, cams, filters. • Advantages: near-net shape, very little material waste (~97% utilisation), controlled porosity, can combine materials that cannot be melted/alloyed (metal-ceramic), high-melting metals, good dimensional accuracy, mass production. • Limitations: expensive powders and dies, size and shape limited (no undercuts/threads easily), lower strength and ductility due to porosity, non-uniform density, powders may be hazardous (explosive/toxic).

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Metal working (mechanical working/forming) changes the shape of metal by plastic deformation without removing material.

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This section covers the advantages of metal working, hot working (rolling, forging, extrusion), cold working (rolling, drawing, squeezing, bending, shearing), shot peening and hobbing.

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Advantages of Metal Working • No material wasted as chips (high material utilisation); high production rates. • Improves mechanical properties: grain refinement and favourable grain flow (fibre) following the contour of the part → higher strength, fatigue and impact resistance (forged crankshafts vs cast). • Closes internal voids and porosity; breaks up coarse cast structure.

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Hot Working vs Cold Working • Distinction is the recrystallisation temperature (≈ 0.4 Tm in kelvin), NOT room temperature.

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Hot working is ABOVE it, cold working BELOW it.

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(For lead and tin, room-temperature working is hot working.) Feature Hot working Cold working Temperature Above recrystallisation temperature Below recrystallisation temperature Force / power Low High Deformation per pass Large Limited; intermediate annealing needed Strain hardening None (recrystallisation occurs) Yes — strength & hardness ↑, ductility ↓ Grain structure Refined, porosity closed Elongated, distorted grains; anisotropy Surface finish & accuracy Poor (oxidation, scaling, thermal contraction) Excellent, close tolerances, bright surface Residual stresses Few Present Examples Hot rolling, forging, extrusion, piercing, hot spinning Cold rolling, wire/tube drawing, coining, bending, shearing, deep drawing Rolling • Metal is passed between rotating rolls and its thickness reduced by compressive forces.

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Hot rolling breaks down ingots into blooms (square, > 150 mm), billets (smaller square, 40–150 mm) and slabs (rectangular, for plates and sheets). • Rolling mills: two-high (reversing or non-reversing), three-high (no reversing needed), four-high (small work rolls backed up by large back-up rolls — less roll deflection; sheets and plates), cluster (Sendzimir) (very thin foils, hard materials), tandem/continuous mills. • Neutral (no-slip) point: roll surface speed = strip speed.

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Before it the strip moves slower than the rolls; after it faster (forward slip).

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Maximum draft Δhmax = μ²R. • Special rolling: shape rolling (I-beams, rails, channels), thread rolling (cold; stronger threads, no chips), ring rolling (bearing races), roll piercing (seamless tubes — Mannesmann process).

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Forging • Shaping by compressive force of hammer blows or presses, usually hot.

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Grain flow gives superior strength. • Types: open-die (smith/hand) forging — simple shapes, large parts; closed/impression-die (drop) forging — metal fills die cavity, excess forms flash in the gutter; press forging (slow squeeze, deeper penetration, uniform deformation); upset forging (increase diameter by reducing length — bolt heads, valves); roll forging; swaging; precision (flashless) forging. • Operations: upsetting (increase cross-section), drawing down (reduce cross-section, increase length), fullering (reduce section with fuller tool), edging (distribute metal), punching, bending, cutting. • Products: crankshafts, connecting rods, gears, axles, hand tools (spanners, hammers), turbine discs, bolts. • Forging defects: laps and folds, cold shuts, unfilled sections, scale pits, die shift (mismatch), cracks, flakes (internal hydrogen cracks).

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Extrusion Type Description Remarks Direct (forward) Ram pushes billet through a fixed die; product moves in SAME direction as ram Most common; high friction between billet and container Indirect (backward/reverse) Die mounted on hollow ram; product moves OPPOSITE to ram No relative motion of billet and container → less friction and force Hydrostatic Billet pushed by pressurised fluid Very low friction; brittle materials Impact extrusion Punch strikes a slug at high speed (usually cold) Collapsible tubes (toothpaste), cans, battery cases Tube extrusion Mandrel inside die forms hollow section Seamless tubes • Extrusion ratio = billet area / product area.

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Products: aluminium window/door sections, rods, tubes, heat sinks, copper tubes. • Defects: centre burst (chevron cracking), piping (tail-pipe), surface cracking (fir-tree/bamboo cracks at high temperature/speed).

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Cold Rolling, Drawing and Squeezing • Cold rolling: sheets, strips and foils with bright finish, accurate thickness and higher strength (e.g., CRCA sheets). • Wire drawing: wire is PULLED through a converging die (tensile process) to reduce diameter; lubricated; multiple dies in tandem with intermediate annealing.

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Theoretical maximum reduction per pass ≈ 63% (practically 30–45%). • Tube drawing: with fixed plug, floating plug, moving mandrel or no mandrel (tube sinking). • Deep drawing: flat blank pushed by a punch into a die to form a cup; blank holder prevents wrinkling.

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Limiting drawing ratio ≈ 2.

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Defects: wrinkling (low blank-holder force), tearing (excessive force), earing (anisotropy).

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Ironing thins walls (beverage cans). • Squeezing operations (cold, closed die): coining (fine surface detail, different relief on each face, no flash — coins, medals), sizing, cold heading (bolt and rivet heads, nails), riveting, staking, swaging, embossing (raised/sunk design on sheet, thickness nearly uniform), hubbing/hobbing. • Other forming: spinning (axisymmetric hollow parts on a lathe), stretch forming (aircraft skins), high-energy-rate forming (explosive, electrohydraulic, electromagnetic).

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Bending and Shearing • Bending:

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V-bending, edge (wiping) bending, roll bending (plates into cylinders), tube bending.

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Outer fibres in tension, inner in compression; neutral axis shifts towards inside. • Springback: partial elastic recovery after bending — compensated by overbending, bottoming or coining.

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Springback increases with yield strength and bend radius, decreases with E. • Shearing: cutting sheet between a punch and die.

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Blanking — the punched-out piece is the PRODUCT; punching/piercing — the hole is wanted, punched piece (slug) is scrap.

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Others: notching, lancing, slitting, perforating, nibbling, trimming, shaving. • Clearance between punch and die ≈ 5–10% of sheet thickness per side.

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In blanking, die = blank size and clearance on PUNCH; in punching, punch = hole size and clearance on DIE. • Shearing force F = L·t·τu (L = perimeter).

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Providing shear (angle) on punch or die reduces maximum force.

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Shot Peening and Hobbing • Shot peening: bombarding the surface with small hard steel/glass/ceramic shots at high velocity → thin plastically deformed surface layer with compressive residual stress → greatly improved fatigue life and resistance to stress-corrosion cracking.

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Used on springs, gears, shafts, connecting rods, turbine blades, aircraft parts. • Hobbing (cold hubbing): pressing a hardened master punch (hob) into a softer die blank to form a mould or die cavity — used for plastic moulds and dies with multiple identical cavities. • Gear hobbing (machining): generating spur and helical gears and worm wheels with a rotating worm-shaped hob cutter — the most productive gear-cutting method.

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Machine tools remove material in the form of chips to produce accurate shapes.

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This section summarises metal-cutting theory and tool materials, then the types and operations of lathes, milling, drilling, grinding and boring machines, shapers, sawing, broaching and presses.

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(Basic workshop use of these machines is in Chapter 1.5.) Metal Cutting Fundamentals • Orthogonal cutting: cutting edge ⊥ to cutting velocity (2-D, one chip-flow direction).

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Oblique cutting: edge inclined (3-D; most practical operations). • Chip types: continuous (ductile materials, high speed, positive rake, good lubrication — best finish); continuous with built-up edge (BUE) (ductile materials at low speed — poor finish); discontinuous (brittle materials — cast iron, brass; or very low speed); serrated/segmented (low-conductivity materials like Ti). • Merchant's theory: shear angle φ = 45° + α/2 − β/2 (α = rake angle, β = friction angle).

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Chip thickness ratio r = t/tc = sin φ / cos(φ − α) (< 1). • Single-point tool signature (ASA): back rake, side rake, end relief, side relief, end cutting-edge angle, side cutting-edge angle, nose radius. • Taylor's tool-life equation:

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VTn = C. n ≈ 0.1–0.15 for HSS, 0.2–0.4 for carbides, 0.5–0.7 for ceramics.

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Cutting speed has the greatest effect on tool life, then feed, then depth of cut. • Tool wear: flank wear (on clearance face; usual tool-life criterion VB ≈ 0.3 mm), crater wear (on rake face; diffusion at high speed/temperature), notch wear, chipping. • Cutting fluids: cool the tool, lubricate, flush chips, prevent BUE and corrosion (soluble oils, straight oils, synthetics).

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MRR in turning = f × d × V.

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Tool material Hot hardness (approx.) Notes High-carbon steel ≈ 250 °C Cheap; hand tools, low speed High-speed steel (HSS) 18-4-1 ≈ 600 °C Tough; drills, taps, milling cutters, broaches Cast cobalt alloys (Stellite) ≈ 800 °C Co-Cr-W; between HSS and carbide Cemented carbides (WC-Co) ≈ 1000 °C P grade (blue) — steels;

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K grade (red) — cast iron, non-ferrous;

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M (yellow) — both; made by P/M; brazed or insert Coated carbides (TiN, TiC, Al2O3) Higher Longer life, most common today Ceramics (Al2O3, Si3N4) / cermets ≈ 1200 °C High-speed finishing; brittle CBN (cubic boron nitride) Very high Hardened steels, superalloys Diamond (PCD) Hardest Non-ferrous, plastics, composites;

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NOT for ferrous metals (carbon diffuses into iron) Lathe:

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Types and Operations • Types: engine (centre) lathe (general purpose), bench lathe, speed lathe (wood, polishing, spinning — no feed mechanism), tool-room lathe (high precision), capstan and turret lathes (semi-automatic mass production; capstan = ram type, light work; turret = saddle type, heavy work — hexagonal turret holds multiple tools), automatic lathes (single- and multi-spindle, Swiss-type), CNC lathe/turning centre, vertical turret lathe/boring mill (large diameter heavy work). • Operations: facing, plain/step turning, taper turning, eccentric turning, threading (lead screw + change gears), knurling, grooving, parting-off, chamfering, drilling, reaming, boring, tapping, spinning. • Machining time T = L/(f·N) per pass.

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Thread cutting: change-gear ratio = pitch of work / pitch of lead screw.

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Types and Operations • Types: column-and-knee — horizontal (plain), vertical, universal (table can swivel for helical milling); bed type (production); planer type (plano-miller, very large work);

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CNC machining centres; special (thread, profile, duplicating). • Operations: plain (slab) milling, face milling, side milling, straddle milling (two side cutters on one arbor — two parallel faces), gang milling (several cutters simultaneously), form milling, profile milling, end milling, slot and keyway milling, T-slot, gear cutting, helical milling, saw (slitting) milling. • Indexing (dividing head 40:1): simple indexing = 40/N turns; angular indexing = θ°/9° turns; compound indexing (two index plates); differential indexing for numbers not possible by simple indexing (e.g., primes like 97, 127). • Up (conventional) vs down (climb) milling — see 1.5.

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MRR = width × depth × table feed.

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Drilling, Boring and Grinding Machines • Drilling machines: portable, sensitive (bench), upright/pillar, radial (large, heavy work — arm swings), gang (several spindles in a row, different operations), multiple-spindle (many holes simultaneously), deep-hole drilling (gun drilling).

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Operations: drilling, reaming, boring, counterboring, countersinking, spot facing, tapping, trepanning. • Boring machines (enlarge and true existing holes): horizontal boring machine (large prismatic workpieces — also drills, mills; boring bar), vertical boring mill (work rotates on a horizontal table — very large diameter heavy work like turbine casings), jig boring machine (very precise hole location, tool rooms — jigs, fixtures, dies), precision (fine) boring machines. • Grinding machines: surface grinder (horizontal or vertical spindle, reciprocating or rotary table, magnetic chuck), cylindrical (external/internal), centreless (work supported on a work-rest between grinding wheel and rubber-bonded regulating wheel inclined 3–8° to give axial feed; through-feed or in-feed; no centres needed — pins, rollers, long bars), tool-and-cutter, creep-feed. • Fine finishing: honing (bonded abrasive sticks, cross-hatch pattern — engine cylinder bores), lapping (loose abrasive — very flat, very fine finish; gauge blocks), superfinishing, polishing, buffing.

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Shaper, Planer and Slotter Feature Shaper Planer Slotter Cutting motion TOOL reciprocates horizontally WORK (table) reciprocates Tool reciprocates VERTICALLY Feed Work (table) fed Tool fed Work fed Work size Small–medium Large, heavy Internal surfaces, keyways Tools Single tool Several tools simultaneously Single tool • Shaper types: crank (most common), geared, hydraulic; horizontal, vertical, travelling-head; plain and universal (table swivels). • Clapper box lets the tool lift on the return stroke to avoid rubbing.

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Quick-return ratio typically 3:2.

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Cutting speed V = NL(1 + m)/1000 m/min (m = return/cutting time ratio).

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Sawing and Broaching • Power hacksaw: reciprocating blade, cuts on forward stroke; simple, slow.

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Band saw: continuous blade — straight and contour cutting, horizontal (cut-off) and vertical (contour).

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Circular saw: cold saw (toothed disc) and abrasive cut-off wheel.

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Friction sawing for hard materials. • Saw tooth sets (to cut a wider kerf than blade): raker, wavy, straight/alternate. • Broaching: a long multi-tooth tool (broach) with teeth of successively increasing height (rise per tooth) — roughing, semi-finishing and finishing teeth — completes the surface in a single stroke.

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No separate feed motion (feed is built into the tool). • Internal broaching: keyways in hubs, splines, square/hexagonal and irregular holes; external (surface) broaching.

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Push or pull broaches. • Advantages: very high productivity, accuracy and finish; roughing and finishing in one pass.

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Limitations: broach is expensive and special for each shape → suited only to mass production; blind holes cannot be broached easily.

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Presses and Press Tools • Presses: mechanical (crank, eccentric, knuckle-joint — very high force near bottom, used for coining; toggle; screw/friction) — fast; hydraulic — full force throughout stroke, adjustable, slower; deep drawing, forging.

31

C-frame/gap (OBI — open back inclinable) and straight-side (H-frame). • Press specification: capacity (tonnage), stroke, shut height, strokes per minute, bed area.

32

Parts: ram (slide), bolster plate, die set, stripper, pilots, stock guides.

33

Die type Operation Simple die One operation per stroke at one station Compound die Two or more CUTTING operations (e.g., blanking + piercing) at ONE station in one stroke — accurate washers Progressive die Several operations at SUCCESSIVE stations; strip advances each stroke, a finished part per stroke Combination die Cutting + non-cutting operations (e.g., blanking + drawing) at one station Transfer die Separate stations; part transferred mechanically between them — large parts

1

Welding joins materials by fusion or pressure to form a permanent joint.

2

This section covers welding fundamentals, weld joints, applications of arc, gas and spot (resistance) welding, other processes, brazing and soldering, and welding defects.

3

(Basic arc and gas welding practice is in Chapter 1.5.) Fundamentals of Welding • Classification: fusion welding (arc, gas, thermit, electron-beam, laser — base metal melts); resistance welding (spot, seam, projection, flash butt — heat from I²R plus pressure); solid-state welding (forge, friction, friction-stir, ultrasonic, explosive, diffusion, cold pressure — no melting). • Weld zones: fusion zone (melted and solidified), heat-affected zone (HAZ) (not melted but microstructure altered — often the weakest/most brittle region), unaffected base metal. • Weldability of steel falls with carbon and alloy content.

4

Carbon equivalent CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15.

5

CE < 0.4 → good weldability; higher CE needs preheating and low-hydrogen electrodes.

6

Cast iron has poor weldability. • Welding positions (easiest → hardest): flat (1G/1F) → horizontal (2G) → vertical (3G) → overhead (4G).

7

Types of Welded Joints • Joints: butt, lap, tee (T), corner, edge. • Butt-joint edge preparations: square (thin plates, < 5 mm), single-V, double-V (thick plates — less filler and distortion), single/double-U, J, bevel. • Weld types: fillet (lap, T, corner joints), groove (butt), plug and slot welds, spot and seam welds, surfacing (hard-facing). • Weld terms: root, face, toe, reinforcement, throat, leg, penetration, bead.

8

Arc Welding Processes and Applications Process Key features Applications SMAW (manual metal arc / stick) Flux-coated consumable electrode;

9

AC or DC; portable, versatile Structural steel, repairs, pipelines, general fabrication GMAW (MIG/MAG) Continuous consumable wire + inert (Ar, He — MIG) or active (CO2 — MAG) shielding gas; high deposition Automobile bodies, Al and stainless fabrication, mass production GTAW (TIG) Non-consumable tungsten electrode, argon shielding, separate filler rod;

10

AC for Al/Mg (cathodic cleaning of oxide) High-quality welds on thin sheet, Al, Mg, Ti, stainless; aerospace; root passes in pipes SAW (submerged arc) Arc buried under granular flux; automatic; very high current and deposition; no visible arc or spatter Thick plates, ship building, pressure vessels, pipes — FLAT position only FCAW Tubular wire filled with flux Outdoor construction, heavy fabrication Plasma arc Constricted arc, very high temperature Precision welding and cutting Electroslag Resistance heating of molten slag; vertical Very thick sections (> 50 mm) Stud welding Stud acts as electrode Attaching studs to plates (shear connectors) • Electrode coding (AWS) E 7018:

11

70 = 70 ksi (≈ 480 MPa) minimum tensile strength;

12

8 = coating type/current (low-hydrogen, iron-powder).

13

Low-hydrogen electrodes must be kept dry (baked). • Power sources:

14

AC (transformer — cheap, no arc blow) and DC (rectifier, generator, inverter — stable arc; required for some electrodes).

15

Arc blow (magnetic deflection of arc) occurs with DC — remedy: use AC, change earth position. • Arc welding safety: filter glass shade 10–14 against UV/IR radiation; fume extraction; insulated holders; dry gloves.

16

Gas Welding Applications • Oxy-acetylene (≈ 3200 °C), oxy-hydrogen (lower temperature — lead, thin Al), air-acetylene (brazing/soldering).

17

See 1.5 for flame types. • Applications: thin sheet metal (< 3–6 mm), repair and maintenance work, welding of non-ferrous metals, brazing and braze-welding, heating and bending, oxy-fuel gas cutting of steel. • Equipment: oxygen and acetylene cylinders, pressure regulators, hoses (oxygen black/green, acetylene red/maroon), blowpipe (torch), flashback arrestors and non-return valves. • Advantages: portable, cheap, no electricity needed, good control on thin sheets.

18

Limitations: slow, large HAZ, more distortion, not suited to thick sections.

19

Spot (Resistance) Welding and Other Processes • Resistance welding heat H = I²Rt (Joule heating) — highest at the interface between sheets (contact resistance); joint made under pressure.

20

Very high current (thousands of amperes), low voltage (≈ 1–10 V), short time. • Spot welding: overlapping sheets clamped between water-cooled copper-alloy electrodes; weld 'nugget' forms at interface.

21

Cycle: squeeze → weld → hold → off.

22

Applications: automobile bodies, appliances, sheet-metal furniture, electronic parts; fast and easily automated (robots).

23

Limited to thin sheets in lap joints. • Seam welding: roller (wheel) electrodes give continuous overlapping spots — leak-tight joints (fuel tanks, drums, radiators).

24

Projection welding: embossed projections concentrate current — nuts and bolts to sheets.

25

Flash butt welding: rails, chains, rings, tool shanks.

26

Upset butt welding: wires, rods. • Thermit welding: exothermic reaction of Al powder with iron oxide (Fe2O3) (≈ 2500–3000 °C) — joining railway rails and repairing heavy sections. • Friction welding: rotation + axial pressure (solid state) — shafts, dissimilar metals (Al-steel).

27

Friction-stir welding: non-consumable rotating pin traverses joint — Al alloys, aerospace. • Electron-beam welding (vacuum, deep narrow welds, minimal HAZ), laser beam welding (precision, automation), ultrasonic welding (plastics, foils, wires), explosive welding (cladding dissimilar metals), diffusion bonding.

28

Brazing and Soldering Feature Welding Brazing Soldering Base metal Melts Does NOT melt Does NOT melt Filler melting point ≈ base metal > 450 °C (below base metal) < 450 °C Joint mechanism Fusion Capillary action + diffusion Capillary action + adhesion Strength Highest Medium–high Lowest Dissimilar metals Difficult Easy Easy Heat distortion High Low Very low • Brazing fillers: brass/spelter (Cu-Zn), silver alloys (Ag-Cu-Zn — 'silver soldering / hard soldering'), copper, Al-Si, Ni alloys.

29

Flux: borax, fluorides.

30

Joint clearance ≈ 0.025–0.25 mm for capillary flow. • Types of brazing: torch (manual), furnace (mass production, controlled atmosphere), induction, dip (salt bath or molten metal), resistance, infrared, vacuum brazing.

31

Braze welding: filler deposited in a groove without capillary action — repair of cast iron. • Brazing applications: carbide tips on tool shanks, copper pipes in refrigeration/AC, heat exchangers, radiators, bicycle frames, joining dissimilar metals. • Soldering: soft solders Sn-Pb (63/37 eutectic melts at 183 °C;

32

60/40), lead-free Sn-Ag-Cu (SAC) for electronics (RoHS).

33

Fluxes: rosin (electronics — non-corrosive), zinc chloride/acid flux (sheet metal — corrosive, must be cleaned), ammonium chloride. • Soldering methods: soldering iron, torch, dip, wave soldering (through-hole PCBs), reflow soldering (surface-mount electronics).

34

Applications: electrical and electronic connections, PCBs, plumbing, tin cans, sheet-metal work.

35

Defects of Welding Defect Cause Remedy Porosity / blowholes Moisture, rust, oil, damp electrodes, poor gas shielding Clean joint, dry electrodes, proper shielding Slag inclusion Improper cleaning between passes, low current Remove slag between runs, correct technique Incomplete fusion Low current, high speed, wrong angle Increase heat input, proper manipulation Incomplete penetration Low current, improper root gap/edge preparation Correct joint design, higher current Undercut Groove melted into base metal at weld toe — excessive current, long arc, wrong angle Reduce current and arc length Overlap Weld metal flows over base without fusing — low current, slow travel Increase current and speed Cracks (hot/cold) High restraint, high carbon, hydrogen (cold cracking), impurities (S, P — hot cracking) Preheat, low-hydrogen electrodes, control cooling Spatter High current, long arc, arc blow Correct parameters Distortion Non-uniform heating and cooling Clamping, tack welds, back-step and balanced sequence, preheating Burn-through Excessive heat on thin sheets Lower current, backing strip • Weld inspection: visual, dye penetrant (surface cracks), magnetic particle (surface/near-surface in ferromagnetic), radiography (internal porosity, inclusions), ultrasonic (internal defects, thickness) — see Chapter 7.6 on NDT.

1

Computers now drive both design (CAD) and manufacturing (CAM).

2

This section covers the principles and benefits of CAD/CAM, CNC machines and part programming, additive manufacturing and rapid prototyping, and flexible manufacturing systems.

3

Computer-Aided Design (CAD) • CAD: use of computers to create, modify, analyse and optimise designs.

4

Design process: recognition of need → definition → synthesis → analysis & optimisation → evaluation → presentation (drafting). • Geometric modelling:

5

2-D drafting; wireframe (edges only — ambiguous, no surfaces/volume); surface modelling (Bezier, B-spline, NURBS — car bodies, aircraft skins); solid modelling — CSG (constructive solid geometry:

6

Boolean union, difference, intersection of primitives) and B-rep (boundary representation: faces, edges, vertices); feature-based parametric modelling (history tree, dimensions drive geometry). • Geometric transformations (translation, rotation, scaling, reflection) use homogeneous coordinates — 3 × 3 matrix in 2-D, 4 × 4 in 3-D. • Software:

7

AutoCAD, SolidWorks, CATIA, Creo, Siemens NX, Inventor, Fusion 360.

8

FEA (stress, thermal, vibration), CFD, kinematic/dynamic simulation, optimisation. • Data exchange formats:

9

IGES, STEP (ISO 10303 — product data exchange), DXF (2-D AutoCAD), STL (triangulated surface for 3-D printing), Parasolid (.xₜ), ACIS (.sat).

10

Computer-Aided Manufacturing (CAM) and Benefits • CAM: use of computers to plan, manage and control manufacturing — NC part programming and tool-path generation, CAPP (computer-aided process planning: variant/retrieval using group technology, and generative), robotics, automated inspection (CMM), production planning (MRP/ERP). • CAD/CAM workflow:

11

CAD model → CAM tool-path (cutter location data) → post-processor converts to machine-specific G-code → CNC machine. • CIM (computer-integrated manufacturing) links CAD, CAM, planning, control and business functions through a common database. • Benefits of CAD/CAM: higher design productivity and accuracy, easy modification and reuse, better visualisation, analysis before prototyping (fewer physical prototypes), shorter lead time, consistent quality, less scrap and rework, better documentation, direct link from design to manufacturing, supports automation and customisation.

12

CNC in Manufacturing • NC (numerical control — punched tape) → CNC (dedicated microcomputer on each machine; programs stored and edited) → DNC (direct/distributed NC — central computer feeds several CNC machines). • Elements: part program, machine control unit (MCU), servo drives and motors, ball screws, feedback devices (encoders, linear scales).

13

Closed-loop (with feedback, servo motors — accurate) vs open-loop (stepper motors, no feedback). • Motion control: point-to-point (drilling), straight-line, contouring/continuous path (milling complex profiles — interpolation). • Axes (ISO 841 / right-hand rule):

14

X = horizontal, ⊥ Z (longest travel);

15

Y by right-hand rule; rotary A, B, C about X, Y, Z.

16

Machine zero vs work (program) zero. • Programming: manual (G & M codes, word-address format N G X Y Z F S T M), APT (Automatically Programmed Tools language), CAM-generated; canned cycles (G81 drilling); subprograms. • Machining centre (milling-based, with automatic tool changer (ATC) and pallet changer) and turning centre (CNC lathe with turret). • Advantages: accuracy and repeatability, complex contours, short set-up, flexibility for small batches, less skilled operator, reduced inspection.

17

Limitations: high initial cost, skilled programming and maintenance.

18

G code Function M code Function G00 Rapid positioning M00 Program stop G01 Linear interpolation (feed) M01 Optional stop G02 / G03 Circular interpolation CW / CCW M02 End of program G04 Dwell M03 / M04 Spindle ON clockwise / counter-clockwise G17 / G18 / G19 XY / ZX / YZ plane M05 Spindle stop G20 / G21 Inch / metric input (Fanuc) M06 Tool change G28 Return to reference (home) M08 / M09 Coolant ON / OFF G40 / G41 / G42 Cutter radius compensation off / left / right M30 End of program and rewind (reset) G90 / G91 Absolute / incremental dimensions M98 / M99 Call subprogram / return Additive Manufacturing (AM) and Rapid Prototyping • Additive manufacturing (3-D printing): builds parts layer by layer directly from a 3-D CAD model — opposite of subtractive machining.

19

CAD model → STL file → slicing into layers → build → post-processing (support removal, curing, finishing). • Rapid prototyping (RP): quick fabrication of physical models from CAD for design verification, form-fit-function testing and communication.

20

Rapid tooling: moulds/dies made using AM.

21

Reverse engineering:

22

3-D scanning of existing part → CAD model.

23

First commercial process: stereolithography (Chuck Hull, 1986).

24

AM category (ISO/ASTM 52900) Process examples Material / feature Vat photopolymerisation SLA (stereolithography), DLP Liquid photopolymer resin cured by UV laser/projector; excellent finish Material extrusion FDM / FFF Thermoplastic filament (PLA, ABS, PETG) extruded through heated nozzle; cheapest, most common Powder bed fusion SLS (polymers — nylon), SLM / DMLS (metals), EBM (electron beam in vacuum — Ti) No support needed for SLS; functional metal parts Material jetting PolyJet, MultiJet Droplets of photopolymer; multi-material, colour Binder jetting 3-D printing (3DP) Liquid binder on powder bed (sand moulds, metals, ceramics) Sheet lamination LOM (laminated object manufacturing) Sheets of paper/plastic/metal cut and bonded Directed energy deposition DED, LENS Powder/wire melted by laser as deposited — repair of blades, large metal parts • Benefits of AM: complex geometries (lattices, internal cooling channels), no tooling, mass customisation (dental aligners, implants, prosthetics), part consolidation, less material waste, rapid design iteration, on-demand spare parts. • Limitations: slow and costly for large volumes, limited build size, rough surface/stair-step effect, anisotropic properties, limited material range, need for post-processing.

25

Flexible Manufacturing System (FMS) • FMS: a group of CNC machine tools (workstations) linked by an automated material-handling and storage system (AGVs, conveyors, robots, AS/RS) and controlled by a central computer, able to process a variety of parts with minimal changeover. • Position: mid-volume, mid-variety production — between transfer lines (high volume, low variety) and stand-alone CNC/job shops (low volume, high variety). • Types of flexibility: machine, routing, process, product (mix), volume, expansion.

26

Flexible manufacturing cell (FMC) = smaller unit (2–3 machines). • Group technology (GT): parts with similar design/manufacturing features grouped into part families (Opitz, MICLASS coding) → cellular manufacturing. • Benefits of FMS: higher machine utilisation, reduced work-in-process and lead time, lower labour cost, quick response to design changes, consistent quality.

27

Limitations: very high investment, complex planning, limited to certain part families. • Industrial robots: configurations — Cartesian (gantry), cylindrical, polar (spherical), articulated (jointed arm — most versatile), SCARA (assembly); end effectors (grippers, welding torches, spray guns); degrees of freedom usually 5–6; applications — welding, painting, material handling, assembly.