Manufacturing and Production Engineering

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This section introduces metrology and measurement: general metrological terms, errors in measurement, linear, angular and taper measurement, measuring instruments and limit gauges, the need for inspection, accuracy and precision, the institutions concerned with metrology, calibration, and acceptance tests on machine tools.

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Metrology — Meaning and Types • Metrology is the science of measurement — it covers the units, the standards, the instruments and the methods by which measurements are made and their accuracy established. • Scientific (fundamental) metrology — establishment and maintenance of standards; industrial (applied) metrology — measurement and inspection in manufacturing; legal metrology — measurements affecting trade, health and safety (weights and measures, fuel pumps, packaged goods). • Objects of metrology in industry: to ensure that parts are made within specified limits so that they are interchangeable, to control processes (SPC), to reduce scrap and rework, to settle disputes over quality, and to keep measuring equipment traceable.

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Standards of Measurement • Hierarchy: international standards (SI) → primary (national) standards → secondary standards → working (shop-floor) standards; each level is calibrated against the level above it, giving traceability. • The metre is defined from the speed of light in vacuum (1/299 792 458 s of travel); line standards (graduations on a scale, e.g., steel rule) vs end standards (distance between two faces, e.g., slip gauges, end bars) — end standards are more accurate but wear at the faces. • Slip (gauge) blocks: hardened, lapped steel or ceramic blocks in grades (00, 0, I/1, II/2 — calibration, inspection, workshop grades); combined by wringing (molecular adhesion of ultra-flat faces, film ≈ 0.02 μm); the minimum number of blocks is used, starting from the last decimal place. • Institutions:

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BIPM (International Bureau of Weights and Measures) and OIML internationally;

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NBSM — Nepal Bureau of Standards and Metrology keeps Nepal's national standards, operates legal metrology (weights and measures) and runs calibration laboratories;

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NIST (USA), NPL (UK/India); accreditation of laboratories under ISO/IEC 17025; quality systems under ISO 9001.

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General Metrological Terms Term Meaning Accuracy Closeness of a measured value to the true value Precision (repeatability) Closeness of repeated readings to one another — a precise instrument may still be inaccurate (bias) Least count / resolution Smallest change that can be read or detected Readability Ease with which a scale can be read (magnification, scale spacing) Sensitivity Ratio of output (scale movement) to input (change in dimension); magnification in comparators Repeatability / reproducibility Same operator, same conditions / different operators, instruments or laboratories (the R&R of Gauge R&R studies) Calibration Comparison with a standard of higher accuracy to find (and correct) the error Error / uncertainty Error = measured − true value; uncertainty = the range within which the true value is expected to lie Hysteresis, drift, backlash, dead zone Difference in reading for increasing and decreasing input; slow change with time; lost motion in mechanisms Range and span Limits within which the instrument can measure Errors in Measurement Class Examples and control Gross errors Misreading, wrong recording, wrong instrument — avoided by care and repetition Systematic (controllable) errors Calibration error (zero error, wear of anvils); environmental — temperature (all measurements referred to 20 °C), humidity, vibration, dust; support error (sag of long bars — supported at Airy points, 0.577 L apart for length); contact/stylus pressure; alignment error — violation of Abbe's principle (the line of measurement should coincide with the axis of the measuring scale); parallax Random errors Small unpredictable variations (play, friction, operator judgement) — reduced by averaging repeated readings Linear Measurement Instruments Instrument Least count / use Steel rule, calipers, dividers ≈ 0.5 mm — rough work Vernier caliper LC = 1 MSD − 1 VSD (0.02 mm typical); outside, inside, depth and step measurement Micrometer LC = pitch/number of thimble divisions = 0.5/50 = 0.01 mm (0.001 mm with vernier); outside, inside, depth, screw-thread and tube micrometers; ratchet ensures constant measuring pressure Slip gauges, end bars, height gauge Standards and setting; vernier/digital height gauge with surface plate and scriber Dial indicator / comparator 0.01 or 0.001 mm — comparative measurement, run-out, alignment; types: mechanical (Johansson Mikrokator, Sigma), optical, pneumatic (Solex — back-pressure or flow type, very high magnification, no contact wear), electrical/electronic (LVDT) Limit gauges GO and NO-GO plug (holes), ring and snap (shafts) gauges — check whether a dimension lies within limits without measuring it Coordinate measuring machine (CMM) 3-axis probe, computer evaluation of size, form and position; also optical projector, tool-maker's microscope, laser interferometer, surface-roughness tester (Ra) • Taylor's principle of limit gauge design: the GO gauge checks the maximum material condition and all dimensions/form together (full form, full length); the NO-GO gauge checks the minimum material condition and one dimension at a time.

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Gauge tolerance is usually taken as 10% of the work tolerance, with a wear allowance of about 5% on the GO gauge.

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Angular and Taper Measurement • Bevel protractor (vernier LC = 5 minutes), universal bevel protractor with acute-angle attachment; angle gauges (combined by addition and subtraction, unlike slip gauges); spirit level and clinometer. • Sine bar: standard length 100, 200 or 300 mm between roller centres; set up with slip gauges: sin θ = h/L (h = height of slip-gauge pile, L = sine-bar length).

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It is unreliable above ≈ 45° because a small error in h produces a large angular error; sine plate/centre for larger work. • Autocollimator — measures very small angular deviations (seconds of arc) for straightness and squareness of machine-tool guideways; angle dekkor. • Taper measurement: taper (per unit length) = (D − d)/L; measured with rollers/balls and slip gauges, taper gauges, sine bar, or on a CMM.

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Included angle 2α with tan α = (D − d)/2L.

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Need for Inspection and Applications of Metrology • Inspection confirms that a product conforms to the drawing and specification: incoming (raw material), first-piece, in-process (patrol) and final inspection;

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100% inspection vs sampling inspection (Chapter 7); measurement data feed SPC control charts and process capability studies. • Applications: dimensional control in machining and assembly, tool and gauge making, inspection of gears, threads and surface finish, calibration of instruments, machine-tool testing, and legal metrology in trade.

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Calibration and Machine-Tool Acceptance Tests • Calibration is done at defined intervals against masters of higher accuracy, in a controlled environment (20 °C), with results recorded in calibration certificates showing errors and uncertainty; out-of-calibration instruments are withdrawn and the work measured with them is reviewed. • Acceptance (alignment) tests on machine tools (Schlesinger tests): geometrical tests — levelling of the machine, flatness and straightness of the bed and guideways, spindle run-out (true running), parallelism of the spindle axis to the bed, squareness of the cross-slide, alignment of tailstock centre with headstock centre, axial slip of the spindle; measured with dial indicators, test mandrels, spirit levels, straight edges and autocollimators. • Performance (practical) tests: machining a test piece and measuring accuracy of size, roundness, cylindricity, flatness, parallelism and surface finish; also tests of power, speeds and feeds, noise and safety.

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The results are compared with the standards (e.g., IS/ISO test charts) before the machine is accepted.

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This section covers casting processes and moulding, sheet-metal forming and fabrication, arc, gas and resistance welding, soldering and brazing, inspection of welds, the heat-affected zone, welding defects and the metallurgical aspects of welding.

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Casting — Sand Casting Sequence • Pattern making → mould preparation (cope and drag with sand around the pattern) → core setting → gating and risering → melting and pouring → solidification and cooling → shake-out → fettling (removal of gates and risers) → cleaning → inspection and heat treatment. • Pattern materials: wood, metal, plastic, wax, polystyrene (full mould).

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Pattern types: solid (single piece), split, match-plate, cope-and-drag, loose-piece, gated, sweep, skeleton, follow board. • Pattern allowances: shrinkage (cast iron ≈ 10 mm/m, steel ≈ 20 mm/m, aluminium ≈ 13–16 mm/m), machining (2–6 mm), draft/taper (0.5–3°) for withdrawal, distortion (camber) and shake (rapping) allowance (negative).

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Moulding sand property Meaning Permeability (porosity) Ability to let gases and steam escape — otherwise blow holes Green strength / dry strength Strength of moist / baked sand to hold the mould shape Refractoriness Ability to withstand the heat of molten metal without fusing Collapsibility Sand must break down after solidification to allow free contraction (otherwise hot tears) Flowability, adhesiveness, reusability Filling around the pattern, sticking to the moulding box, reclamation • Green sand ≈ silica sand + 4–10% clay (bentonite) + 2–8% water + additives (coal dust, cereal binder). • Gating system: pouring basin → sprue (tapered to avoid air aspiration) → runner → ingate(s), with strainer/skim bob to hold slag; riser (feeder) — open or blind — feeds liquid metal during solidification to prevent shrinkage cavities and must solidify last; chills and directional solidification are used to feed heavy sections.

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Chvorinov's rule: solidification time t = k(V/A)² — the riser must have a larger volume-to-surface ratio than the casting.

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Casting process Features / use Green sand casting Cheapest and most common; large size range; poor finish and tolerance CO2 (sodium silicate) moulding Sand + sodium silicate hardened by CO2 gas — quick, strong moulds and cores Shell moulding Resin-coated sand on a heated metal pattern — good finish and tolerance, thin shells, mass production Investment (lost-wax) casting Wax pattern coated with ceramic slurry, wax melted out — excellent finish and intricate shapes, high-melting alloys, turbine blades, jewellery; costly Permanent (gravity die) casting Reusable metal mould, gravity pouring — non-ferrous, medium volumes Pressure die casting Molten metal injected at high pressure: hot-chamber for Zn, Pb, Sn; cold-chamber for Al, Mg, Cu alloys — high rate, thin walls, excellent finish; expensive dies Centrifugal casting Mould rotated — pipes, bushes and liners; impurities collect at the inner (lighter) surface; no core needed for the hole Continuous casting Billets, blooms and slabs in steel plants • Melting furnaces: cupola (grey iron), induction furnace (clean, controllable), electric arc furnace (steel), crucible and oil-fired furnaces (non-ferrous). • Casting defects: blow holes and pin holes (gas, low permeability, wet sand), shrinkage cavity (inadequate feeding/riser), misrun and cold shut (low pouring temperature or fluidity, thin sections), hot tear (restrained contraction, poor collapsibility), scab, drop, swell, inclusions and dross, mismatch/shift (dowel or box misalignment), cold shot; inspection by visual, dimensional, pressure test, dye-penetrant, magnetic-particle, ultrasonic and radiographic methods.

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Sheet-Metal Forming and Fabrication • Shearing operations (punch and die): shearing, blanking (the piece removed is the product), piercing/punching (the hole is wanted, slug is scrap), notching, trimming, lancing, parting, slitting.

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Die clearance ≈ 5–10% of sheet thickness per side; punching force F = L × t × τs (L = length of cut); shear (bevel) on the punch or die reduces the peak force. • Bending:

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V-bending, edge (wiping) bending, U-bending, roll bending, seaming, flanging, curling; bend allowance BA = θ(R + Kt) with K ≈ 0.33–0.5; minimum bend radius depends on ductility; spring-back is corrected by over-bending, bottoming or coining. • Deep drawing: blank drawn into a die by a punch with a blank holder to prevent wrinkling; limiting drawing ratio D/d ≈ 1.8–2.2 (further reduction by redrawing); defects — wrinkling, tearing, earing (anisotropy), orange peel. • Other operations: stretch forming, spinning, embossing, coining, roll forming, press brake work, shearing machines, punching and nibbling, laser/plasma cutting; dies: simple, compound, progressive and transfer dies; presses: mechanical (fast, fixed stroke) and hydraulic (full force over the stroke, adjustable). • Sheet-metal fabrication of ducts, tanks, enclosures and structures also uses joints (lock seam, riveting), welding, bolting and adhesive bonding.

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Welding Processes Process Key points SMAW (arc welding with coated electrode) Coating provides shielding gas, slag, arc stabilisers, deoxidisers and alloying;

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DCEN/DCEP polarity; cheap, portable, all positions; slag removal needed GMAW (MIG/MAG) Continuous bare wire + shielding gas (Ar, CO2, mixtures); high deposition, semi-automatic/robotic GTAW (TIG) Non-consumable tungsten electrode + argon; high-quality welds on thin sections, stainless steel and aluminium (AC for Al) SAW Arc submerged under granular flux; very high deposition for thick plates in the flat position; no visible arc FCAW, ESW, plasma arc, stud welding Flux-cored wire; electroslag for very thick sections Gas (oxy-acetylene) welding Neutral flame (O2:C2H2 ≈ 1:1, ≈ 3 200 °C) for steel; oxidising (excess O2) for brass/bronze; carburising (excess acetylene) for hard-facing and high-carbon steel; also used for cutting (oxy-fuel cutting of steel) Resistance welding H = I²Rt; spot, seam, projection, butt and flash welding — low voltage, very high current, no filler; ideal for sheet metal and robot assembly lines Solid-state welding Friction, friction-stir, ultrasonic, explosive, diffusion welding — no melting • Soldering (below 450 °C, tin-lead or lead-free alloys, flux; electrical and sheet-metal joints — low strength) vs brazing (above 450 °C, copper/silver alloy filler drawn by capillary action; stronger, joins dissimilar metals, little distortion) vs welding (fusion of the parent metal — strongest).

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Heat-Affected Zone, Weld Defects and Metallurgy • A fusion weld has the fusion (weld) zone (melted and re-solidified, cast structure), the heat-affected zone (HAZ) — not melted but changed by heat (grain growth, hardening or softening — usually the weakest and most crack-prone region) — and the unaffected base metal. • Weldability and cracking: hardenable steels may form brittle martensite in the HAZ.

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

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CE above ≈ 0.4–0.45 calls for preheating, low-hydrogen electrodes (dried), controlled interpass temperature and post-weld heat treatment (stress relieving) to avoid hydrogen (cold) cracking; hot cracking arises from sulphur/phosphorus segregation; stainless steels suffer sensitisation (weld decay) — avoided with low-carbon or stabilised grades. • Residual stress and distortion are controlled by welding sequence, back-step welding, jigs and fixtures, balanced welds and minimum weld size. • Weld defects: porosity/blow holes, slag inclusion, undercut, overlap, incomplete penetration, lack of fusion, spatter, cracks (hot and cold), distortion, excessive reinforcement, burn-through. • Inspection of welds: visual (first and cheapest, with weld gauges); liquid (dye) penetrant — surface defects in any non-porous material; magnetic particle — surface and near-surface defects in ferromagnetic materials; ultrasonic — internal defects and thickness, needs skill; radiography (X-ray/gamma) — internal defects with a permanent film record, radiation safety needed; leak/pressure tests, hardness tests, macro-etch and destructive tests (bend, tensile, nick-break) on procedure/welder qualification coupons.

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This section covers hot and cold working with their advantages and limitations, forging, rolling, drawing and extrusion, the determination of flow stress, principal stresses, the Tresca and von Mises yield criteria, and the concepts of plane stress and plane strain.

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Hot Working vs Cold Working Feature Hot working (above recrystallisation temperature, ≈ 0.5–0.75 Tm) Cold working (below recrystallisation temperature) Strain hardening None — recrystallisation occurs continuously Work (strain) hardening increases strength and hardness Force and power Low (flow stress is low) High Deformation possible Very large Limited — needs inter-stage annealing Grain structure Refines coarse cast grains, closes porosity Grains elongated and distorted; directional properties Surface finish and tolerance Poor (oxide scale, thermal contraction) Good finish and close tolerance Residual stress Practically none Residual stresses present Ductility after work Retained Reduced (may need annealing) Typical processes Rolling of ingots, forging, hot extrusion, seamless tube making Cold rolling, drawing, deep drawing, coining, shot peening, spinning • Recrystallisation temperature ≈ 0.3–0.5 Tm (absolute) — lead and tin recrystallise at room temperature, so working them is always hot working; warm working lies between the two.

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Forging • Open-die (smith) forging: upsetting, drawing down, fullering, edging, punching — simple shapes, low volume, hand or power hammer.

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Impression (closed) die forging: metal fills the die cavity with flash that builds pressure and is later trimmed — high-volume parts such as crankshafts, connecting rods, spanners, gears.

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Flashless (precision) forging, roll forging, upset forging (bolt heads), swaging, cold heading and coining. • Equipment: drop hammers (board, steam, air), counterblow hammers, mechanical and hydraulic presses (press forging works through the section, hammers on the surface). • Forged parts have grain flow following the shape → excellent strength and fatigue resistance; defects: laps, cold shuts, flakes, scale pits, incomplete filling, die wear.

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Rolling • Metal passes between rotating rolls: draft = h0 − hf; maximum draft Δhmax = μ²R (μ = friction coefficient, R = roll radius) — friction drags the metal in; beyond the neutral (no-slip) point the strip moves faster than the roll surface. • Mill types: two-high (reversing/pull-over), three-high, four-high (small work rolls with large back-up rolls — thin sheet), cluster (Sendzimir — foil), tandem and planetary mills; ring rolling, thread rolling and gear rolling. • Roll camber compensates roll bending; defects: wavy edges, zipper and edge cracks, alligatoring, folds.

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Drawing and Extrusion • Wire/rod/tube drawing (cold): the stock is pulled through a converging die (die materials: alloy steel, tungsten carbide, diamond for fine wire) — reduction per pass ≈ 20–40% (theoretical maximum ≈ 63% for ideal, frictionless conditions); needs pointing, lubrication and inter-stage annealing; tube drawing with plug or mandrel. • Extrusion: the billet is pushed through a die — direct (forward) extrusion (billet moves relative to container — high friction) and indirect (backward) extrusion (die moves; lower force, no billet-container friction); also hydrostatic, impact (collapsible tubes) and cold extrusion.

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Extrusion ratio = A0/Af; aluminium sections, tubes and cable sheathing are typical products; defects: centre-burst (chevron), piping and surface cracking.

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Flow Stress and Plasticity • Flow stress σf is the true stress needed to continue plastic deformation.

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Cold working: σ = Kεn (K = strength coefficient, n = strain-hardening exponent, ε = true strain); average flow stress σ̄ = Kεn/(1 + n) is used in forming-force calculations.

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True strain ε = ln(L/L0) = ln(A0/A) and true stress σ = F/A (instantaneous area). • Hot working: flow stress depends strongly on strain rate, σ = Cε̇m (m = strain-rate sensitivity, ≈ 0.05–0.4 at hot-working temperatures; high m gives superplasticity), and falls as temperature rises. • Principal stresses: the normal stresses on planes carrying no shear; for plane stress σ1,2 = (σx + σy)/2 ± √[((σx − σy)/2)² + τxy²]; maximum shear stress = (σ1 − σ3)/2 (Mohr's circle).

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Yield criterion Statement Shear yield strength k Tresca (maximum shear stress) Yielding when σmax − σmin = σy k = 0.5 σy — conservative, simpler von Mises (distortion energy / octahedral shear) Yielding when (σ1 − σ2)² + (σ2 − σ3)² + (σ3 − σ1)² = 2σy² k = σy/√3 = 0.577 σy — agrees better with experiment for ductile metals • Plane stress: one principal stress is zero (thin sheets, plates loaded in their plane) — typical of sheet-metal forming.

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Plane strain: strain in one direction is zero (wide rolling, forging of long billets, thick sections) — the material is constrained, and for von Mises the plane-strain flow stress = 2σf/√3 = 1.155 σf, so more force is needed. • Volume constancy in plastic deformation: ε1 + ε2 + ε3 = 0 (Poisson's ratio effectively 0.5) — the basis of forming calculations.

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This section covers electric discharge machining, ultrasonic machining, electro-chemical machining and laser beam machining, together with CNC machining and industrial robotics.

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Why Non-conventional Processes? • Conventional cutting becomes difficult with very hard and brittle materials (hardened steel, carbide, ceramics, composites), very complex or fine shapes (narrow slots, deep small holes, intricate profiles), thin fragile parts (no cutting force can be tolerated) and very close tolerance/finish requirements.

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Non-conventional processes remove material by thermal, chemical, electrochemical or mechanical (abrasive) energy instead of a sharp tool.

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Process Principle Features and applications EDM (electric discharge machining) Repeated sparks between a shaped tool electrode (cathode) and the workpiece (anode) in a dielectric (kerosene, de-ionised water) melt and vaporise metal; spark gap ≈ 10–100 μm, servo-controlled Workpiece must be electrically conductive; no cutting force; machines hardened steel, carbide; used for dies, moulds, cooling holes; tool wear (copper, graphite electrodes); recast (white) layer; wire EDM uses a 0.1–0.3 mm brass wire to cut any 2-D profile USM (ultrasonic machining) Tool vibrates at ≈ 20 kHz with 10–50 μm amplitude and drives an abrasive slurry (B4C, SiC, Al2O3) that chips the work by micro-impacts Best for hard and brittle non-conductive materials — glass, ceramics, quartz, germanium; no thermal damage; low MRR; tool (soft steel) wears ECM (electro-chemical machining) Reverse electroplating — work is the anode, shaped tool the cathode, electrolyte (NaCl/NaNO3) pumped through the gap; metal dissolves by Faraday's laws (MRR ∝ current, independent of hardness) No tool wear, no cutting force, no heat-affected zone, good finish; complex cavities, turbine blades, deburring; high capital cost, electrolyte handling and sludge disposal, conductive materials only LBM (laser beam machining) A focused coherent beam (CO2, Nd:YAG, fibre) melts and vaporises material; often assisted by a gas jet Non-contact, very small holes and narrow kerf, any material, easily automated; small HAZ; used for cutting sheet, drilling, marking, welding; low efficiency, high cost, safety precautions Others AJM/AWJM (abrasive jet and abrasive water jet), PAM (plasma arc), EBM (electron beam, in vacuum), CHM (chemical milling) Water-jet cutting gives no heat damage; plasma cuts thick conductive plate quickly CNC Machining • NC → CNC → DNC: numerical control by punched tape → a dedicated computer in each machine (program storage, editing, diagnostics, compensation) → several machines linked to a central computer (direct/distributed numerical control). • Elements: part program, machine control unit (MCU), servo drives with ball screws, feedback devices (rotary encoders, linear scales) in closed-loop control, automatic tool changer (ATC), pallet changer, coolant and chip conveyor.

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CNC lathe/turning centre, machining centre (VMC/HMC), CNC grinder, wire EDM, press brake. • Motion control: point-to-point (drilling), straight cut, and contouring (continuous path) with linear and circular interpolation; axis convention X, Y, Z with rotary A, B, C. • Programming: manual part programming with G-codes (G00 rapid, G01 linear feed, G02/G03 circular CW/CCW, G20/G21 inch/mm, G90/G91 absolute/incremental, G40–G42 cutter compensation) and M-codes (M03/M04 spindle on, M05 spindle stop, M06 tool change, M08 coolant on, M30 end of program);

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CAM systems generate the program from a CAD model and post-process it; simulation and DNC transfer. • Advantages: high accuracy and repeatability, complex shapes, lower setting and lead time, fewer fixtures, less operator skill per piece, unattended running, easy design changes, better utilisation.

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Limitations: high capital cost, skilled programmers and maintenance staff, uneconomical for very simple one-off jobs, higher downtime cost.

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Industrial Robotics • An industrial robot is a reprogrammable, multifunctional manipulator (ISO definition) consisting of links and joints, actuators (electric servo, hydraulic, pneumatic), a controller, an end effector (gripper or tool) and sensors. • Configurations:

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Cartesian (PPP), cylindrical (RPP), polar/spherical (RRP), SCARA (fast horizontal assembly), articulated (RRR — jointed arm), parallel/delta (high-speed picking). • Specifications: degrees of freedom (typically 4–6), work envelope, payload, reach, speed, repeatability (ability to return to the same point — typically ±0.02–0.1 mm) and accuracy, resolution. • Programming: teach pendant (point-to-point teaching), lead-through, textual robot languages and off-line programming/simulation from CAD. • Applications: spot and arc welding, spray painting, material handling and machine loading, palletising, assembly, inspection, packaging — chosen where work is hazardous, repetitive, heavy or requires consistent quality; collaborative robots (cobots) work beside people with force limits;

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AGVs and AS/RS handle material (Chapter 6). • Justification: labour cost saving, quality consistency, safety, and throughput — assessed with payback/NPV (Chapter 10.2); needs safety fencing, interlocks and risk assessment.

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This section covers single-point cutting tool nomenclature and geometry, the mechanics of chip formation, Merchant's circle diagram and its analysis, and tool life and tool failure.

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Chip Formation and Cutting Models • Orthogonal cutting: the cutting edge is perpendicular to the cutting velocity (two-force, plane-strain model used for analysis).

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Oblique cutting: the edge is inclined at an angle (three force components) — the practical case. • Types of chip: continuous (ductile material, high speed, large rake, good lubrication — best finish but needs chip breakers); continuous with built-up edge (BUE) (low speed, ductile material, strong adhesion — poor finish, fluctuating forces); discontinuous (brittle material such as cast iron, low rake, low speed — acceptable for brittle work). • Chip thickness ratio r = t1/t2 = sin φ/cos(φ − α) (always < 1, since the chip is thicker than the uncut layer); chip reduction coefficient = 1/r; shear angle tan φ = r cos α/(1 − r sin α); shear strain γ = cot φ + tan(φ − α). • Cutting velocity V, chip velocity Vc = rV, shear velocity from the velocity triangle.

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Single-Point Tool Nomenclature and Geometry Element Function Back rake angle (along the shank) and side rake angle Control chip flow direction and cutting force; positive rake reduces force, power and heat but weakens the edge; negative rake strengthens the edge — used with carbide/ceramic tools, hard materials and interrupted cuts End relief (front clearance) and side relief Prevent rubbing of the flank on the machined surface (typically 5–10°); too much weakens the edge End cutting edge angle (ECEA) Avoids rubbing of the trailing edge Side cutting edge angle (SCEA, approach angle) Distributes the cut over a longer edge, thins the chip, affects tool life and radial force Nose radius Strengthens the tip and improves surface finish: theoretical roughness Ra ≈ f²/(32R) • ASA (American) tool signature order: back rake, side rake, end relief, side relief, end cutting edge angle, side cutting edge angle, nose radius — e.g., 8-14-6-6-6-15-1 (mm).

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The ORS (orthogonal rake system) uses inclination angle, orthogonal rake, clearances, auxiliary cutting edge angle, principal cutting edge angle and nose radius. • Tool angles in operation vary with tool setting height and feed; chip breakers (step, groove or clamped type) control long continuous chips.

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Merchant's Circle Diagram • Merchant's circle resolves the resultant cutting force R into three pairs of components: cutting force Fc (along velocity) and thrust force Ft; friction force F and normal force N on the rake face; shear force Fs and normal force Fn on the shear plane. • Relations:

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F = Fc sin α + Ft cos α;

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N = Fc cos α − Ft sin α; coefficient of friction μ = F/N = tan β (β = friction angle);

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Fs = Fc cos φ − Ft sin φ;

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Fn = Fc sin φ + Ft cos φ. • Merchant's shear-angle relation (minimum energy):

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2φ + β − α = 90° — the shear angle increases with rake angle and decreases with friction; a larger φ means a thinner chip, less shear area and lower cutting force. • Power: cutting power P = Fc·V; specific cutting energy u = P/MRR (J/mm³) — used for machine-tool sizing and machining cost estimates. • Shear stress on the shear plane τ = Fs/As with As = (t1·w)/sin φ.

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Tool Wear, Tool Failure and Tool Life • Types of wear: flank wear (wear land VB on the clearance face — caused by abrasion; the usual tool-life criterion, VB = 0.3 mm average or 0.6 mm maximum for HSS/carbide roughing); crater wear on the rake face (diffusion and adhesion at high temperature, measured by crater depth KT); notch wear at the depth-of-cut line; nose wear. • Wear mechanisms: abrasion (hard particles), adhesion (welding and tearing of micro-junctions — BUE), diffusion (dominant at high speed/temperature), oxidation, chemical and electro-chemical wear, plastic deformation of the edge, chipping and brittle fracture (interrupted cuts), thermal cracking. • Modes of tool failure:

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(i) gradual wear (desirable — predictable), (ii) plastic deformation/temperature failure, (iii) sudden chipping or breakage (avoided by tougher grade, negative rake, rigid setup). • Taylor's tool life equation:

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VTn = C (V = cutting speed m/min, T = tool life min); n ≈ 0.1–0.15 (HSS), 0.2–0.4 (carbide), 0.4–0.6 (ceramic); extended form VTnfadb = C with a > b, so cutting speed affects tool life most, then feed, then depth of cut. • Machinability is judged by tool life, cutting force/power, surface finish and chip form; free-machining steels (with S, Pb) improve it. • Machining economics: total cost per piece = machining cost + tool cost + tool-changing cost + set-up; there is a speed for minimum cost and a (higher) speed for maximum production rate; the range between them is the 'high-efficiency machining range' — an industrial-engineering optimisation.

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This section covers the types and selection of cutting tool materials, cutting fluids and their properties, heat generation in metal cutting and the distribution of that heat between chip, tool and workpiece.

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Requirements of a Cutting Tool Material • Hot hardness (hardness retained at the high temperature of cutting), wear and abrasion resistance, toughness (to resist chipping and shock), low chemical affinity with the work (to limit diffusion and BUE), high thermal conductivity, good grindability/formability, and reasonable cost.

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Hardness and toughness pull in opposite directions — the tool material is selected for the job.

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Tool material Max. working temperature / hardness Remarks and typical use Carbon tool steel (0.8–1.3% C) ≈ 200–250 °C Cheap; loses hardness quickly — hand tools, low-speed work High-speed steel (HSS) — 18-4-1 (18% W, 4% Cr, 1% V);

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M-series with Mo; cobalt HSS ≈ 550–600 °C Tough, can be ground to sharp edges and complex shapes — drills, taps, reamers, milling cutters, form tools, low-rigidity setups Cast cobalt alloys (Stellite) ≈ 700–800 °C Cast to shape, cannot be heat treated; between HSS and carbide Cemented carbide (WC-Co) — ISO P (steel), M (stainless), K (cast iron) ≈ 900–1 000 °C 3–6 times the speed of HSS; brazed tips and throw-away indexable inserts; brittle → needs rigid machines and often negative rake Coated carbide (TiN, TiC, Al2O3, TiAlN by CVD/PVD) ≈ 1 000 °C+ Hard, low-friction surface on a tough core — the workhorse of modern turning and milling Ceramics (Al2O3, Si3N4) and cermets ≈ 1 200 °C Very high speeds, usually dry, on cast iron and hardened steel; very brittle — no interrupted cuts CBN (cubic boron nitride) ≈ 1 400 °C Hard-part turning of steels above ≈ 45 HRC; expensive Diamond (PCD, single crystal) ≈ 700 °C (graphitises above) Non-ferrous and abrasive non-metals (Al-Si alloys, composites, plastics); not used on steel because carbon diffuses into iron • Selection: match the grade to work material, operation (continuous or interrupted), machine rigidity and power, required speed and finish, and cost per edge; use indexable inserts for production and the toughest grade that will stand the speed.

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Cutting Fluids • Functions: cooling (carry away heat, keep the tool hard and the work dimensionally stable), lubrication (reduce friction at the chip-tool and tool-work interfaces, prevent BUE, improve finish — dominant at low speeds), flushing chips away, and protecting the work and machine from corrosion. • Types: straight (neat) cutting oils (mineral oils with fatty or EP additives — best lubrication, poor cooling, used at low speed/heavy cuts, broaching, gear cutting); soluble oil emulsions (oil in water, milky — good cooling with some lubrication, the common shop fluid); semi-synthetic and synthetic (chemical) fluids (water-based, clean, best cooling, long life, grinding); solid lubricants (graphite, MoS2), gases and mist (MQL — minimum quantity lubrication), compressed air and cryogenic (liquid nitrogen) cooling. • Desirable properties: high specific heat and thermal conductivity, adequate lubricity and film strength (EP additives — chlorine, sulphur, phosphorus), low viscosity for flow, high flash point (non-flammable), chemical stability and long life, non-corrosive to work and machine, non-toxic and non-irritating to skin, no bad odour (biocides against bacterial growth), transparency for visibility and low cost. • Application and health: flood, jet, high-pressure through-tool and mist application; oil mist and used coolant cause dermatitis and respiratory problems — hence skin protection, mist extraction, coolant-condition monitoring (pH, concentration by refractometer, tramp-oil removal) and proper disposal (an environmental requirement, Chapter 9).

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Dry and near-dry (MQL) machining is increasingly used with coated and ceramic tools for cost and environmental reasons.

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Heat Generation and Heat Distribution in Metal Cutting • Almost all the mechanical work of cutting converts into heat in three zones:

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(1) the primary shear zone — plastic deformation of the shear plane, ≈ 60–75% of the total heat;

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(2) the secondary zone — friction between chip and tool rake face, ≈ 20–30% (this zone gives the highest temperature, ≈ 600–1 100 °C, a little behind the cutting edge, and causes crater wear);

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(3) the tertiary zone — rubbing of the tool flank on the machined surface, ≈ 5–10%. • Distribution of heat (typical turning): the chip carries away most of the heat, ≈ 60–90%, the workpiece takes ≈ 5–20% and the tool ≈ 5–10%; as cutting speed increases, an even larger proportion leaves with the chip (less time for conduction) although the interface temperature rises. • Cutting temperature rises mainly with cutting speed (θ ∝ Va, a ≈ 0.2–0.5), and less with feed and depth of cut; it also rises with harder work material, negative rake and a dull tool. • Effects of heat: rapid tool wear (diffusion and plastic deformation), dimensional errors from thermal expansion of work and machine, poor surface integrity (burning, white layer, residual tensile stresses), and operator/chip-handling hazards. • Measurement of cutting temperature: tool-work thermocouple, embedded thermocouples, infrared/thermal imaging, temperature-sensitive paints, metallographic hardness changes in HSS tools. • Control: correct speed and feed, sharp tools with adequate rake, suitable tool material and coating, effective cutting fluid or MQL, and rigid setups.