SSRAO

Explanation:
Shrinkage allowance (contraction allowance) is added to the pattern dimensions to compensate for the contraction of metal during solidification and subsequent cooling to room temperature. Different metals have different shrinkage rates: Cast iron: 10 mm/m, Steel: 20 mm/m, Aluminium: 13 mm/m, Brass: 15 mm/m. The pattern is made larger than the final casting by the shrinkage amount. Machining allowance is separate and accounts for surface finishing.

Explanation:
A riser (feeder head) is a reservoir of molten metal placed above or beside the casting to feed liquid metal into the casting as it solidifies and contracts. Without a riser, shrinkage cavities (voids) form inside the casting. Riser design criteria: (1) Riser must solidify after the casting (Chvorinov's rule: t ∝ (V/A)²), (2) Riser must contain sufficient metal to feed the casting, (3) Riser must be connected to the last-to-solidify region. Types: open riser (top), blind riser (enclosed), side riser.

Explanation:
Chip thickness ratio (cutting ratio) r = t1/t2, where t1 is the uncut chip thickness (feed in orthogonal cutting) and t2 is the chip thickness after cutting. Since t2 > t1 (chip is thicker than the uncut chip), r < 1. r = sin φ / cos(φ - α), where φ is shear plane angle and α is rake angle. Higher r means thinner chip (more efficient cutting). r is related to shear plane angle: tan φ = r·cos α / (1 - r·sin α).

Explanation:
Taylor's tool life equation: VT^n = C, where V is cutting speed (m/min), T is tool life (min), n is Taylor's exponent (depends on tool-workpiece combination: HSS n=0.1-0.2, carbide n=0.2-0.4, ceramic n=0.4-0.6), and C is a constant (cutting speed for T=1 min). Extended Taylor's equation: VT^n × f^a × d^b = C (includes feed f and depth of cut d). Tool life criterion: flank wear VB = 0.3 mm (ISO standard). Higher n means tool life is less sensitive to cutting speed changes.

Explanation:
Draft (taper) is provided on the sides of a forging die to allow easy removal (ejection) of the forging from the die cavity. Without draft, the forging would lock in the die due to friction and thermal contraction. Typical draft angles: 3-7° for hammer dies, 1-3° for press dies. Inner surfaces require more draft than outer surfaces. Draft increases the material volume slightly. Modern dies with ejector pins may use smaller draft angles.

Explanation:
Merchant's circle diagram (force circle) graphically represents the force relationships in orthogonal cutting: (1) Cutting force (Fc) and thrust force (Ft) — measured forces, (2) Resultant force (R) — vector sum of Fc and Ft, (3) Friction force (F) and normal force (N) on rake face — R = √(F²+N²), (4) Shear force (Fs) and normal force on shear plane (Fn). Friction angle β = arctan(F/N) = arctan(μ). Merchant's minimum energy principle: 2φ + β - α = 90°, giving φ = 45° + α/2 - β/2.

Explanation:
Green sand mould composition: (1) Silica sand (85-95%) — base material, (2) Clay/bentonite (5-10%) — binder that gives strength when moistened, (3) Water (2-8%) — activates clay binder, (4) Additives (coal dust, wood flour) — improve surface finish and collapsibility. 'Green' refers to the moist condition, not colour. Green sand moulds are the most widely used (70% of all castings). Advantages: low cost, reusable sand, good collapsibility. Disadvantages: limited dimensional accuracy, not suitable for very large castings.

Explanation:
Specific cutting energy u = Fc × V / (MRR) = Fc / (f × d) = Fc / (b × t1), where Fc is cutting force, V is cutting speed, MRR is material removal rate, f is feed, d is depth of cut, b is width of cut, t1 is uncut chip thickness. Units: J/mm³ or N/mm². Specific energy is a material property used to estimate cutting forces and power. Typical values: aluminium 0.4-1.0 J/mm³, steel 2-4 J/mm³, titanium 3-6 J/mm³. Specific energy increases at low chip thickness (size effect).

Explanation:
Flux in welding serves multiple functions: (1) Protects the molten weld pool from atmospheric oxygen and nitrogen (prevents oxidation and porosity), (2) Removes oxides from the base metal and weld pool (slag formation), (3) Stabilises the arc (in SMAW), (4) Adds alloying elements to the weld (in some processes), (5) Controls the cooling rate (slag blanket), (6) Improves bead shape. Types: solid flux (SAW), flux-coated electrodes (SMAW), flux-cored wire (FCAW), flux paste (brazing).

Explanation:
MRR in turning = V × f × d = (π × D × N / 1000) × f × d mm³/min, where V = π×D×N/1000 is cutting speed (m/min), f is feed (mm/rev), d is depth of cut (mm), D is workpiece diameter (mm), N is spindle speed (rpm). Alternatively: MRR = π × D × N × f × d (in consistent units). The MRR determines the productivity and power consumption. Power = Fc × V = u × MRR, where u is specific cutting energy.

Explanation:
Cold working (plastic deformation below recrystallisation temperature) causes strain hardening (work hardening): (1) Increased yield strength and tensile strength, (2) Increased hardness, (3) Decreased ductility and toughness, (4) Increased dislocation density, (5) Residual stresses, (6) Grain elongation in the direction of working. The degree of cold work = (A0 - Af)/A0 × 100%. Cold working improves surface finish and dimensional accuracy. Annealing (heat treatment) can restore ductility by recrystallisation.

Explanation:
Chvorinov's rule: t = B × (V/A)^n, where t is solidification time, B is mould constant (depends on mould material, metal, and pouring temperature), V is casting volume, A is casting surface area, and n ≈ 2 (typically). The ratio V/A is the 'modulus' of the casting. Chvorinov's rule is used to: (1) Design risers (riser must have larger V/A than casting), (2) Predict solidification sequence, (3) Identify hot spots. A sphere has the maximum V/A ratio and solidifies last.

Explanation:
The parting line (parting surface) is the interface between the cope (upper half) and drag (lower half) of the sand mould. Its purpose: (1) Allows the pattern to be removed from the mould (pattern withdrawal), (2) Allows cores to be set in the mould, (3) Defines the mould assembly. The parting line location affects: draft requirements, core prints, flash formation, and dimensional accuracy. Flat parting lines are simplest; irregular parting lines are used for complex shapes.

Explanation:
Built-up edge (BUE) forms when work material welds to the tool rake face under high temperature and pressure (typically at low-to-medium cutting speeds). BUE effects: (1) Acts as a false cutting edge (changes effective rake angle), (2) Protects the tool from wear (beneficial), (3) Causes poor surface finish when BUE breaks off and adheres to machined surface (detrimental), (4) Causes dimensional inaccuracy. BUE is minimised by: high cutting speed (above BUE range), sharp tools, cutting fluids, coated tools. BUE is common when machining ductile materials (steel, aluminium).

Explanation:
Hot working (above recrystallisation temperature, typically 0.6 Tm) advantages: (1) No strain hardening — recrystallisation occurs simultaneously with deformation, (2) Large deformations possible with lower forces, (3) Porosity and segregation are reduced (welded shut), (4) Grain refinement (if controlled), (5) Improved mechanical properties (fibrous structure). Disadvantages: (1) Poor surface finish (oxidation, scale), (2) Poor dimensional accuracy, (3) Requires heating equipment. Recrystallisation temperature: steel ≈ 700°C, aluminium ≈ 150°C, copper ≈ 200°C.

Explanation:
Heat generated in resistance welding: Q = I²Rt, where I is welding current (A), R is resistance at the interface (Ω), and t is welding time (s). The interface resistance R = R_contact + R_workpiece. The heat is concentrated at the interface due to high contact resistance, forming the weld nugget. Welding parameters: current (5000-50,000 A), time (0.1-0.5 s), electrode force (1-5 kN). The nugget diameter ≈ electrode tip diameter. Q = I²Rt is Joule's (Ohm's) heating law.

Explanation:
Rake angle (α) is the angle between the tool face (rake face) and the normal to the machined surface (or the reference plane perpendicular to the cutting velocity). Positive rake angle: tool face tilts away from the workpiece (sharp, lower cutting forces, but weaker tool). Negative rake angle: tool face tilts toward the workpiece (stronger tool, higher cutting forces). Zero rake angle: tool face is perpendicular to the machined surface. Rake angle affects chip formation, cutting forces, and tool life.

Explanation:
Extrusion ratio R = A0/Af, where A0 is the initial billet cross-sectional area and Af is the final extrudate cross-sectional area. R is always > 1. True strain ε = ln(R) = ln(A0/Af). Extrusion pressure p = σ0 × ln(R) × (1 + μ cot α) (simplified), where σ0 is flow stress, μ is friction coefficient, α is die half-angle. Higher R means more deformation and higher extrusion pressure. Typical R: 10-100 for aluminium, 4-8 for steel. R determines the degree of work hardening in cold extrusion.

Explanation:
The gating system components: (1) Pouring cup/basin — receives molten metal from ladle, (2) Sprue — vertical channel that carries metal from pouring cup down to the runner level, (3) Runner — horizontal channel that distributes metal to multiple gates, (4) Gate (ingate) — final channel that controls metal entry into the mould cavity. The sprue is tapered (top larger than bottom) to maintain constant velocity and prevent aspiration of air. Sprue design uses Bernoulli's equation to determine dimensions.

Explanation:
Drawing ratio DR = D0/Dp, where D0 is blank diameter and Dp is punch diameter. The limiting drawing ratio (LDR) is the maximum DR at which drawing can be performed without failure. LDR depends on: material (normal anisotropy r-value), friction, blank holder force, die radius. Typical LDR: 1.8-2.3 for steel, 2.0-2.5 for aluminium. Higher r-value (normal anisotropy) gives higher LDR. The drawing force F = π × Dp × t × σ_UTS × (D0/Dp - 0.7) (approximate).

Explanation:
Weld bead aspect ratio = weld width / weld depth (penetration). A high aspect ratio (wide, shallow bead) is preferred for: (1) Better resistance to solidification cracking (hot cracking), (2) Better fusion at the sides, (3) Easier slag removal. A low aspect ratio (narrow, deep bead) may cause: (1) Solidification cracking (centreline cracking), (2) Incomplete fusion. Aspect ratio is controlled by: welding current, voltage, speed, electrode angle, and shielding gas. Typical aspect ratio: 1.5-3.0 for good weld quality.

Explanation:
Springback is the elastic recovery (partial unbending) that occurs when the bending load is removed. After bending, the elastic strains recover, causing the bend angle to decrease (the part springs back toward its original shape). Springback increases with: (1) Higher yield strength, (2) Lower elastic modulus, (3) Larger bend radius, (4) Thinner material. Springback compensation methods: overbending (bend beyond required angle), bottoming/coining (apply high pressure to eliminate elastic zone), stretch bending (apply tension during bending). Springback angle Δθ = θ_die - θ_part.

Explanation:
Investment casting (lost wax process) produces: (1) Complex shapes with intricate internal features, (2) Excellent surface finish (Ra 1.5-3 μm), (3) High dimensional accuracy (±0.1-0.3 mm), (4) Near-net-shape parts requiring minimal machining. Process: wax pattern → ceramic shell → dewaxing → casting → shell removal. Used for: turbine blades, dental implants, jewellery, aerospace components. Limitations: high cost, small to medium size (typically < 5 kg), slow process. The wax pattern is melted out (lost) before casting.

Explanation:
ASA (American Standards Association) tool signature: Back rake angle (αb) - Side rake angle (αs) - End relief angle (γe) - Side relief angle (γs) - End cutting edge angle (Ce) - Side cutting edge angle (Cs) - Nose radius (r). Example: 8-14-6-6-6-15-0.8 means αb=8°, αs=14°, γe=6°, γs=6°, Ce=6°, Cs=15°, r=0.8mm. The ORS (Orthogonal Rake System) uses: inclination angle, orthogonal rake, orthogonal clearance, auxiliary clearance, approach angle, auxiliary approach angle, nose radius.

Explanation:
The Forming Limit Diagram (FLD) plots the major strain (ε1) vs. minor strain (ε2) at the onset of necking/fracture for different strain paths. The Forming Limit Curve (FLC) separates safe (below) from failed (above) regions. FLD is used to: (1) Predict failure in sheet metal forming, (2) Optimise process parameters, (3) Compare formability of different materials. The FLC is determined experimentally (Nakazima test, Marciniak test). Higher FLC means better formability. FLD depends on: material, thickness, strain rate, temperature.

Explanation:
Die swell (Barus effect) occurs when the polymer extrudate expands after exiting the die. Cause: viscoelastic behaviour of polymer melts — the polymer chains are stretched and oriented during flow through the die. After exiting the die (stress relaxation), the chains recover their random coil configuration, causing the extrudate to swell. Die swell ratio B = D_extrudate/D_die > 1. B increases with: higher molecular weight, higher extrusion speed, shorter die land length, lower temperature. Die swell must be accounted for in die design.

Explanation:
The blank holder (hold-down ring) applies pressure on the flange of the blank during deep drawing to prevent wrinkling. Wrinkling occurs due to compressive circumferential stresses in the flange. Blank holder force (BHF) must be: (1) High enough to prevent wrinkling, (2) Low enough to prevent tearing (excessive BHF increases drawing force and may cause fracture at the punch nose). Optimal BHF = 0.7-1.0% of yield strength × flange area. Variable BHF (increasing with punch stroke) improves drawability.

Explanation:
The Heat Affected Zone (HAZ) is the region of base metal adjacent to the weld that: (1) Did not melt, (2) Was heated to temperatures high enough to alter its microstructure and mechanical properties. In the HAZ: grain growth occurs (near fusion line), phase transformations occur (in steels: martensite formation), residual stresses develop, hardness changes (may increase or decrease). HAZ width depends on: heat input, thermal conductivity, preheat temperature. Narrow HAZ is generally preferred. HAZ is a potential site for cracking and corrosion.

Explanation:
Forward slip S = (Vf - Vr)/Vr, where Vf is the exit (forward) velocity of the strip and Vr is the roll surface velocity. Forward slip is positive (Vf > Vr) because the strip exits faster than the roll surface speed (due to volume conservation: entry thickness × entry velocity = exit thickness × exit velocity). At the neutral point, strip velocity = roll surface velocity. Before neutral point: backward slip (strip slower than roll). After neutral point: forward slip (strip faster than roll). Typical forward slip: 2-5%.

Explanation:
ECM (Electrochemical Machining) removes material by anodic dissolution: the workpiece is the anode (+), the tool is the cathode (-), and an electrolyte (NaCl or NaNO3 solution) flows between them. Metal ions dissolve from the workpiece surface (Faraday's law: m = ZIt/F, where Z is electrochemical equivalent, I is current, t is time, F is Faraday's constant). ECM advantages: (1) No tool wear, (2) No thermal damage, (3) Complex shapes possible, (4) High MRR for hard materials. Used for: turbine blades, gun barrels, dies.

Explanation:
Machining allowance (finish allowance) is extra material added to the pattern dimensions on surfaces that will be machined after casting. It compensates for: (1) Surface roughness of the as-cast surface, (2) Dimensional inaccuracies of casting, (3) Decarburisation layer (in steel castings). Typical values: 1.5-6 mm depending on casting size and process. Surfaces that will not be machined do not need machining allowance. Machining allowance is separate from shrinkage allowance.

Explanation:
Merchant's minimum energy principle gives: φ = 45° + α/2 - β/2, where φ is shear plane angle, α is rake angle, and β is friction angle (β = arctan μ). Higher rake angle (α) → larger φ → thinner chip → lower cutting forces. Higher friction (β) → smaller φ → thicker chip → higher cutting forces. Lee-Shaffer equation: φ = 45° + α - β. Experimental results lie between Merchant's and Lee-Shaffer predictions. The shear plane angle determines chip thickness: t2 = t1 × cos(φ-α)/sin φ.

Explanation:
Electroplating deposits metal on the workpiece (cathode, -) from an electrolyte solution containing metal ions. The anode (+) is usually the plating metal (dissolves to replenish ions). At cathode: M^n+ + ne⁻ → M (metal deposition). Faraday's law: m = ZIt/F. Applications: chrome plating (hardness, corrosion resistance), nickel plating, zinc plating (galvanising), gold/silver plating (electronics, jewellery). Plating thickness: 0.001-0.1 mm. Electroless plating uses chemical reduction (no external current) for uniform coating on non-conductors.

Explanation:
Minimum bend radius R_min is limited by the tensile ductility of the material. During bending, the outer surface is in tension. If the bend radius is too small, the outer surface strain exceeds the fracture strain, causing cracking. R_min/t = (50/r) - 1, where r is the tensile reduction in area (%) and t is sheet thickness. Materials with higher ductility (higher r) can be bent to smaller radii. Minimum bend radius is typically expressed as a multiple of sheet thickness (e.g., R_min = 2t for steel, R_min = 0.5t for soft aluminium).

Explanation:
EDM (Electric Discharge Machining) removes material by thermal erosion: repeated electric sparks (discharges) between the tool (electrode) and workpiece in a dielectric fluid (kerosene or deionised water). Each spark creates a plasma channel (temperature 8000-12000°C) that melts and vaporises a small amount of material from both tool and workpiece. MRR depends on: discharge energy, frequency, polarity. EDM can machine any electrically conductive material regardless of hardness. Used for: dies, moulds, complex shapes, hardened materials.

Explanation:
Theoretical surface roughness in turning: Ra = f²/(8r) (arithmetic mean roughness) or Rmax = f²/(8r) (maximum peak-to-valley height, also written as Rt = f²/(8r)). More precisely: Rmax = f²/(8r) and Ra ≈ Rmax/4 = f²/(32r). Where f is feed (mm/rev) and r is nose radius (mm). To reduce surface roughness: decrease feed, increase nose radius. Actual Ra is higher than theoretical due to: BUE, vibration, tool wear. Typical Ra: rough turning 6-25 μm, finish turning 0.8-3.2 μm.

Explanation:
Annealing is a heat treatment process involving: (1) Heating to appropriate temperature (above recrystallisation temperature for full anneal), (2) Holding (soaking), (3) Slow cooling (furnace cooling). Effects: (1) Relieves residual stresses (stress relief anneal), (2) Softens the material (reduces hardness), (3) Improves ductility and toughness, (4) Refines grain structure, (5) Removes cold work effects (recrystallisation). Types: full anneal, process anneal, stress relief anneal, spheroidise anneal. Used before cold working operations to restore ductility.

Explanation:
Die clearance c = (D_die - D_punch)/2 (per side), where D_die is die diameter and D_punch is punch diameter. Clearance is typically 5-10% of sheet thickness (c = 0.05t to 0.10t). Effect of clearance: (1) Too small: excessive punch force, tool wear, rough cut edge, (2) Correct: clean fracture, good edge quality, (3) Too large: burr formation, poor edge quality, rollover. For blanking: punch size = blank size, die size = blank size + 2c. For punching (hole making): die size = hole size, punch size = hole size - 2c.

Explanation:
Laser Beam Machining (LBM) uses a focused laser beam to melt, vaporise, or chemically degrade material. Advantages: (1) Can machine any material (metals, ceramics, composites, polymers), (2) No tool contact (no tool wear), (3) Very small kerf width (0.1-1 mm), (4) High precision, (5) No mechanical forces, (6) Can machine very thin materials. Applications: cutting, drilling, scribing, marking, welding, surface treatment. Types: CO2 laser (10.6 μm), Nd:YAG laser (1.06 μm), fibre laser. Limitations: HAZ, recast layer, limited depth.

Explanation:
Cold shut (cold lap) is a forging defect where two streams of metal meet but do not fuse properly, leaving a seam or fold on the surface. Causes: (1) Low forging temperature (metal too viscous to flow and fuse), (2) Improper die design (metal flows around and meets itself), (3) Excessive flash (metal folds back), (4) Insufficient forging pressure. Cold shuts appear as cracks or seams on the surface. Prevention: proper die design, adequate temperature, sufficient forging pressure, proper lubrication.

Explanation:
Ultrasonic Machining (USM) uses a vibrating tool (20-40 kHz, amplitude 0.025-0.075 mm) with abrasive slurry (SiC, B4C, Al2O3 in water) to machine hard, brittle materials. Material removal by: (1) Hammering of abrasive particles by tool, (2) Cavitation erosion, (3) Chemical action of fluid. USM is most effective for brittle materials (glass, ceramics, carbides, silicon) because they fracture easily under impact. Not suitable for ductile metals (abrasive particles embed rather than cut). MRR is low (0.1-1 cm³/min). No thermal damage.

Explanation:
Porosity is the entrapment of gas bubbles in the solidifying weld metal, forming voids. Causes: (1) Moisture in electrode coating, flux, or base metal (produces H2 and CO), (2) Contamination (oil, rust, paint on base metal), (3) Insufficient shielding gas coverage, (4) High welding speed (gas cannot escape before solidification), (5) Excessive arc length. Types: distributed porosity, cluster porosity, piping porosity. Prevention: dry electrodes, clean base metal, proper shielding, correct welding parameters. Porosity reduces weld strength and fatigue life.

Explanation:
Normalising: (1) Heat steel above Ac3 (upper critical temperature) by 30-50°C, (2) Hold for sufficient time (austenitise), (3) Air cool. Results: uniform, fine-grained pearlitic structure (finer than full anneal due to faster cooling). Normalising improves: (1) Mechanical properties (strength, toughness), (2) Machinability, (3) Removes segregation and banding. Normalised steel is harder and stronger than annealed steel. Used as a conditioning treatment before hardening or as a final treatment for medium-carbon steels.

Explanation:
Abrasive Jet Machining (AJM) uses a high-velocity jet (150-300 m/s) of fine abrasive particles (Al2O3, SiC, glass beads, 10-50 μm) in a gas stream (air or N2 at 2-8 bar) directed at the workpiece. Material removal by micro-cutting and brittle fracture. Applications: deburring, cleaning, frosting glass, cutting thin sections of brittle materials. Advantages: no heat generation, no mechanical contact, can machine brittle materials. Limitations: low MRR, abrasive embedding in soft materials, nozzle wear. Not to be confused with water jet machining (WJM) which uses water.

Explanation:
True (logarithmic) strain ε = ln(L/L0) = ln(A0/Af) = -ln(Af/A0), where L0 is initial length, L is final length, A0 is initial area, Af is final area. True strain is additive (unlike engineering strain). For incompressible material: ε_1 + ε_2 + ε_3 = 0. True stress σ = F/A (instantaneous area). Engineering stress s = F/A0. Relationship: σ = s(1+e), ε = ln(1+e), where e is engineering strain. True strain is used in metal forming analysis because it correctly represents large deformations.

Explanation:
Die casting (pressure die casting) is suitable for: (1) High-volume production (thousands to millions of parts), (2) Small to medium-sized parts (typically < 25 kg), (3) Non-ferrous metals (aluminium, zinc, magnesium, copper alloys), (4) Complex shapes with thin walls, (5) Excellent dimensional accuracy (±0.05-0.1 mm) and surface finish (Ra 0.8-3.2 μm). Not suitable for ferrous metals (die life too short at high temperatures). Types: hot chamber (zinc, magnesium) and cold chamber (aluminium, copper) die casting.

Explanation:
Cutting fluid functions: (1) Cooling — reduces cutting temperature (extends tool life, prevents thermal damage to workpiece), (2) Lubrication — reduces friction at tool-chip and tool-workpiece interfaces (reduces cutting forces, improves surface finish), (3) Chip flushing — removes chips from cutting zone (prevents re-cutting), (4) Corrosion protection. Types: straight oils (best lubrication), soluble oils (emulsions, best cooling), synthetic fluids, semi-synthetic fluids. Dry machining is used for: cast iron, some aluminium alloys, and with coated tools.

Explanation:
Powder metallurgy process sequence: (1) Powder production — atomisation, reduction, electrolysis, mechanical comminution, (2) Blending/mixing — mix powders with lubricants and alloying elements, (3) Compaction (pressing) — compact powder in die under high pressure (100-900 MPa) to form 'green compact', (4) Sintering — heat below melting point (0.7-0.9 Tm) to bond particles by diffusion, (5) Finishing — sizing, coining, machining, heat treatment. PM advantages: near-net-shape, controlled porosity, unique materials (WC-Co, self-lubricating bearings).

Explanation:
According to Taylor's extended equation VT^n × f^a × d^b = C, the exponents are typically: n = 0.1-0.4 (for speed), a = 0.3-0.6 (for feed), b = 0.1-0.3 (for depth of cut). Since n < a < b in terms of sensitivity, cutting speed has the greatest influence on tool life (a 10% increase in V reduces T by much more than a 10% increase in f or d). This is why cutting speed is the primary variable in tool life studies. Depth of cut has the least influence. Cutting speed also affects temperature most significantly.

Explanation:
Sand casting is the most widely used casting process (70% of all castings) because: (1) Versatility — can cast almost any metal (ferrous and non-ferrous), (2) Size range — from grams to hundreds of tonnes, (3) Shape complexity — complex internal and external shapes possible (with cores), (4) Low tooling cost (sand moulds are inexpensive), (5) Suitable for small and large production runs. Limitations: poor surface finish (Ra 6-25 μm), poor dimensional accuracy (±1-3 mm), slow process. Used for: engine blocks, machine tool bases, pump housings.

Explanation:
GTAW (Gas Tungsten Arc Welding, TIG — Tungsten Inert Gas) uses: (1) Non-consumable tungsten electrode (W or W-Th alloy) — does not melt, (2) Inert shielding gas (Argon or Helium) — protects weld pool from atmosphere, (3) Separate filler rod (optional) — added manually. Advantages: (1) Excellent weld quality, (2) No flux/slag, (3) Suitable for thin materials, (4) Can weld most metals. Disadvantages: slow, requires skilled operator, expensive. Used for: stainless steel, aluminium, titanium, aerospace components. GMAW (MIG) uses consumable wire electrode.

Explanation:
Broaching uses a multi-tooth cutting tool (broach) where each successive tooth is slightly larger than the previous one. In a single linear pass, the broach removes material progressively until the final shape is achieved. Characteristics: (1) High production rate (one pass completes the operation), (2) Excellent surface finish and dimensional accuracy, (3) Can produce complex internal and external shapes (keyways, splines, round holes, irregular shapes), (4) High tooling cost. Types: internal broaching (pull/push), external broaching (surface broaching). Used for: keyways, splines, gear teeth, rifle barrels.

Explanation:
Electrochemical Grinding (ECG) combines: (1) Electrochemical machining (ECM) — anodic dissolution removes 90-95% of material, (2) Conventional abrasive grinding — abrasive wheel removes the oxide film and provides dimensional accuracy. The grinding wheel is the cathode; workpiece is the anode; electrolyte flows between them. Advantages over conventional grinding: (1) No thermal damage, (2) No residual stresses, (3) No burrs, (4) Longer wheel life, (5) Can machine hard materials. Used for: carbide tools, aerospace components, surgical instruments.

Explanation:
Superplastic forming (SPF) conditions: (1) Very low strain rates (10⁻⁴ to 10⁻² s⁻¹), (2) Elevated temperatures (0.5-0.6 Tm), (3) Fine grain size (< 10 μm), (4) Specific materials (Ti-6Al-4V, Al-7475, Zn-Al alloys). Elongations of 200-2000% without necking. Mechanism: grain boundary sliding. SPF is used with gas pressure forming to produce complex aerospace components (aircraft panels, engine nacelles). Advantages: complex shapes in one operation, no springback, low forming forces. Disadvantages: slow, expensive materials.

Explanation:
Shot peening bombards the surface with small spherical shots (steel, glass, ceramic) at high velocity. Effects: (1) Introduces compressive residual stresses on the surface (depth 0.1-0.5 mm), (2) Work hardens the surface, (3) Improves fatigue life (compressive stresses close surface cracks), (4) Improves stress corrosion cracking resistance. Used for: springs, gears, turbine blades, connecting rods. Peening intensity measured by Almen strip deflection. Not to be confused with shot blasting (cleaning) or grit blasting (surface preparation).

Explanation:
Continuous casting (strand casting) process: molten steel is poured into a water-cooled copper mould (oscillating), partially solidifies, and is continuously withdrawn as a strand. The strand is further cooled by water sprays and cut to length. Products: billets (< 150×150 mm), blooms (150-400 mm), slabs (width > 600 mm). Advantages: (1) High productivity (replaces ingot casting + rolling), (2) Better yield (less crop end waste), (3) Better quality (less segregation), (4) Energy savings. Over 90% of steel is now produced by continuous casting.

Explanation:
Chemical Vapour Deposition (CVD) deposits thin films by chemical reactions of gaseous precursors on a heated substrate. For cutting tool coatings: TiCl4 + N2 + H2 → TiN + HCl (at 900-1100°C). CVD coatings on cutting tools: TiN (gold colour, wear resistance), TiC (hardness), Al2O3 (thermal barrier), TiCN (multi-layer). Coating thickness: 5-20 μm. CVD advantages: uniform coating, complex shapes, strong adhesion. Disadvantages: high temperature (may affect substrate), slow deposition. PVD (Physical Vapour Deposition) is an alternative at lower temperatures.

Explanation:
Friction Stir Welding (FSW) is a solid-state joining process: a rotating tool (pin + shoulder) is plunged into the joint and traversed along it. Frictional heat (400-500°C for aluminium) plasticises the material, which is stirred and forged by the tool. No melting occurs. Advantages: (1) No melting — no solidification defects (porosity, hot cracking), (2) Low distortion, (3) No filler metal or shielding gas needed, (4) Can join dissimilar metals, (5) Excellent mechanical properties. Used for: aluminium alloys (aerospace, shipbuilding), copper, magnesium. Invented by TWI (1991).

Explanation:
Honing uses abrasive stones (honing sticks) mounted in a honing head that rotates and reciprocates simultaneously inside a bore. The crosshatch pattern produced improves oil retention. Honing removes: (1) Geometric errors (out-of-roundness, taper), (2) Surface roughness. Stock removal: 0.05-0.5 mm. Surface finish: Ra 0.1-0.8 μm. Used for: engine cylinder bores, hydraulic cylinders, gun barrels. Honing is a finishing operation after boring/reaming. Not to be confused with lapping (flat surfaces, loose abrasive) or superfinishing (very light pressure, oscillating stone).

Explanation:
Wire EDM (WEDM) uses a continuously moving thin wire (0.05-0.3 mm diameter, brass or copper) as the electrode to cut complex 2D profiles in electrically conductive materials. The wire is continuously fed from a spool to prevent wear. Deionised water is used as dielectric. Advantages: (1) Complex profiles possible (any 2D shape), (2) No cutting forces, (3) High accuracy (±0.002-0.005 mm), (4) Can cut hardened materials, (5) Taper cutting possible. Used for: dies, punches, extrusion dies, aerospace components. Kerf width = wire diameter + 2 × spark gap.