SSRAO

Explanation:
Non-traditional machining (NTM) processes are preferred when: (1) Workpiece material is very hard (HRC > 60), brittle, or heat-sensitive, (2) Complex internal geometries (deep holes, intricate profiles) are required, (3) Very thin or fragile workpieces that cannot withstand cutting forces, (4) High surface integrity is required (no residual stresses, no HAZ), (5) Conventional tools cannot machine the material (e.g., carbides, ceramics, composites). NTM processes use electrical, chemical, thermal, or mechanical energy instead of cutting tools.

Explanation:
EDM material removal mechanism: (1) A spark (electric discharge) occurs between the tool (electrode) and workpiece across a small gap (0.01-0.5 mm) in a dielectric fluid, (2) The spark creates a plasma channel at 8,000-12,000°C, (3) Material melts and vaporises from both tool and workpiece surfaces, (4) The dielectric fluid flushes away the molten debris (resolidified as spherical particles). Each spark removes a tiny crater. MRR depends on discharge energy (E = ½CV²), frequency, and polarity. EDM can machine any electrically conductive material.

Explanation:
Dielectric fluid functions in EDM: (1) Insulation — maintains electrical insulation between tool and workpiece between discharges (prevents continuous arc), (2) Ionisation — breaks down at the right voltage to initiate the spark at the narrowest gap point, (3) Cooling — quenches the plasma channel after each discharge, (4) Flushing — carries away the eroded debris (resolidified particles) from the gap. Common dielectrics: kerosene (hydrocarbon oil) for die-sinking EDM, deionised water for wire EDM. Dielectric must have: high dielectric strength, low viscosity, good flushing ability.

Explanation:
ECM MRR from Faraday's law: Mass removed per unit time = ZI/F, where Z = M/(nF) is electrochemical equivalent (M = atomic mass, n = valency, F = 96,485 C/mol). Volume MRR = ZI/(ρF) = MI/(nFρ). For iron (M=56, n=2, ρ=7.8 g/cm³): MRR = 56×I/(2×96485×7.8) = 3.72×10⁻⁵ × I cm³/s. ECM current: 1,000-40,000 A. Voltage: 5-30 V. Gap: 0.1-0.5 mm. MRR is proportional to current I (not I²). ECM has no tool wear (tool is cathode, only workpiece dissolves anodically).

Explanation:
USM is most effective for hard, brittle materials because: (1) Material removal is by brittle fracture — abrasive particles impact the surface and cause micro-chipping, (2) Brittle materials fracture easily under impact loading, (3) Ductile materials deform plastically rather than fracture (abrasive particles embed rather than cut). USM cannot machine soft, ductile metals effectively. Applications: glass, ceramics (Al2O3, SiC, Si3N4), carbides (WC-Co), silicon, quartz, gemstones. USM is used for: drilling, slotting, and contouring of brittle materials.

Explanation:
USM abrasive slurry: (1) Abrasive particles: B4C (boron carbide — hardest, best MRR), SiC, Al2O3, diamond powder, (2) Particle size: 100-800 mesh (10-150 μm), (3) Vehicle: water (most common) or oil, (4) Concentration: 30-60% by weight. The slurry is pumped between the vibrating tool and workpiece. Harder abrasives give higher MRR. Finer particles give better surface finish. B4C is preferred for maximum MRR. Diamond is used for very hard materials. The slurry must be continuously circulated to remove debris and maintain fresh abrasive.

Explanation:
LBM material removal mechanisms: (1) Melting — laser energy melts the material, (2) Vaporisation — at higher intensities, material vaporises directly, (3) Ablation — rapid removal of material by vaporisation and plasma formation. The laser beam is focused to a small spot (0.01-0.5 mm diameter) achieving very high power density (10⁶-10¹² W/cm²). Assist gas (O2 for steel, N2 for stainless steel, Ar for aluminium) blows away molten material and prevents oxidation. LBM can machine any material (metals, ceramics, composites, polymers).

Explanation:
EBM requires a vacuum (10⁻⁴ to 10⁻⁶ torr) because: (1) Electrons scatter when they collide with air molecules, losing energy and focus, (2) The electron gun (cathode) would oxidise in air, (3) The focused beam would be defocused by air molecules. The electron beam is generated by a heated cathode (tungsten filament), accelerated by high voltage (50-200 kV), and focused by electromagnetic lenses to a spot of 0.01-0.2 mm. Power density: 10⁶-10⁹ W/cm². EBM can machine any material. Limitation: vacuum requirement makes it slow and expensive for large workpieces.

Explanation:
AJM process: (1) Abrasive particles (Al2O3, SiC, glass beads, 10-50 μm) are mixed with gas (air or N2) in a mixing chamber, (2) The mixture is accelerated through a nozzle (0.3-0.5 mm diameter) to 150-300 m/s, (3) The high-velocity abrasive jet erodes the workpiece by micro-cutting and brittle fracture. Gas pressure: 2-8 bar. Standoff distance: 0.5-5 mm. Applications: deburring, cleaning, frosting glass, cutting thin brittle materials, drilling small holes. Not to be confused with AWJM (water jet with abrasive) which uses water as the carrier.

Explanation:
Tool Wear Ratio (TWR) = Volume of tool worn / Volume of workpiece removed. Lower TWR is better (less tool wear per unit of material removed). TWR depends on: (1) Polarity — straight polarity (workpiece +, tool -) gives higher MRR but more tool wear; reverse polarity (workpiece -, tool +) gives less tool wear, (2) Pulse duration — longer pulses reduce TWR, (3) Tool material — graphite has lower TWR than copper for steel workpieces. Typical TWR: 0.01-0.5 (1-50%). Graphite electrodes: TWR ≈ 0.01-0.1. Copper electrodes: TWR ≈ 0.1-0.5.

Explanation:
CHM maskant functions: (1) Protects areas not to be machined from the etchant, (2) Must adhere well to the workpiece surface, (3) Must be resistant to the etchant, (4) Must be easily removable after machining. Maskant types: rubber (neoprene, butyl rubber), polyvinyl chloride (PVC), polyethylene. Process: clean → apply maskant → scribe and peel → etch → remove maskant → clean. Etchants: FeCl3 (for aluminium, copper), HNO3+HF (for titanium), NaOH (for aluminium), HCl+HNO3 (for steel). Etch factor = depth of etch / undercut.

Explanation:
EDM surface characteristics: (1) Matte, non-directional surface with micro-craters from each spark, (2) Ra typically 0.4-12.5 μm (rough EDM) to 0.1-0.4 μm (finish EDM with low energy), (3) Recast layer (white layer) — resolidified material, 1-25 μm thick, very hard and brittle, (4) Heat affected zone (HAZ) below the recast layer, (5) Residual tensile stresses in the recast layer. The recast layer may need to be removed for fatigue-critical applications. Surface finish improves with lower discharge energy (lower current, shorter pulse duration).

Explanation:
PAM plasma temperature: 8,000-28,000°C (much higher than any conventional flame). The plasma is created by: (1) Passing gas (Ar, N2, H2, or mixtures) through a constricted electric arc, (2) The gas is ionised to form plasma (fourth state of matter), (3) The plasma jet exits the nozzle at high velocity (300-600 m/s). PAM can cut any electrically conductive material. Advantages: high MRR, can cut thick plates (up to 150 mm), faster than laser for thick sections. Disadvantages: large HAZ, poor surface finish (Ra 6-25 μm), produces fumes and UV radiation.

Explanation:
IBM (Ion Beam Machining) / FIB (Focused Ion Beam) removes material by sputtering: (1) Ions (Ga+, Ar+) are accelerated to high energy (5-30 keV), (2) Ions bombard the workpiece surface, (3) Momentum transfer knocks out surface atoms (sputtering), (4) Material is removed atom by atom. MRR is extremely low (nm³/s to μm³/s). Achieves atomic-level precision. Applications: semiconductor device modification, TEM sample preparation, nano-scale machining, surface analysis. FIB can also deposit material (ion beam deposition using organometallic precursors). Requires vacuum environment.

Explanation:
PCM (Photochemical Machining) / Photo-etching process: (1) Apply photoresist to workpiece, (2) Expose to UV light through a photomask (artwork), (3) Develop — exposed areas become soluble (positive resist) or insoluble (negative resist), (4) Etch — chemical etchant removes unprotected metal, (5) Strip — remove remaining photoresist. Applications: printed circuit boards (PCBs), lead frames, precision metal parts, decorative items. Advantages: high precision (±0.025 mm), no mechanical stresses, complex shapes, simultaneous production of many parts. Used for: electronics, aerospace, medical devices.

Explanation:
In EDM, the gap (0.01-0.5 mm) is maintained by a servo control system: (1) The gap voltage is monitored continuously, (2) If gap voltage drops (gap too small — short circuit risk), the servo retracts the tool, (3) If gap voltage rises (gap too large — no discharge), the servo advances the tool, (4) The servo maintains the gap at the set voltage (typically 20-80% of open circuit voltage). The servo system is critical for stable EDM operation. Modern EDM machines use adaptive control to optimise pulse parameters in real time.

Explanation:
In WEDM, the wire (0.05-0.3 mm diameter, brass or copper) is continuously fed from a supply spool through the workpiece to a take-up spool at 0.1-15 m/min. Reasons: (1) The wire electrode wears due to spark erosion — continuous feeding ensures fresh wire is always in the cutting zone, (2) Prevents wire breakage from excessive wear, (3) Maintains consistent gap geometry and surface finish. The wire is used only once (not reused). Deionised water is used as dielectric (better flushing, lower cost than oil). Kerf width = wire diameter + 2 × spark gap.

Explanation:
In ECG: (1) ECM (anodic dissolution) removes approximately 90-95% of the material — the electrolyte dissolves the workpiece anodically, forming an oxide film, (2) The abrasive wheel (metal-bonded with Al2O3 or diamond) removes the oxide film (5-10% of material) and provides dimensional accuracy and surface finish. The abrasive action prevents passivation (oxide film buildup) that would stop ECM. Advantages over conventional grinding: (1) No thermal damage, (2) No residual stresses, (3) No burrs, (4) Longer wheel life (wheel only removes soft oxide, not hard metal), (5) Can grind very hard materials.

Explanation:
WJM uses pure water jet (200-400 MPa, 600-900 m/s) — suitable for soft materials (rubber, foam, food, textiles). AWJM adds abrasive particles (garnet 80-200 mesh, Al2O3, SiC) to the water jet in a mixing chamber, enabling cutting of hard materials: metals, ceramics, composites, glass, stone. AWJM parameters: water pressure 200-400 MPa, abrasive flow rate 0.1-1 kg/min, standoff distance 1-5 mm. Advantages: no HAZ, no mechanical stresses, can cut any material, complex shapes. Limitations: slow for thick sections, abrasive cost, noise, wet process.

Explanation:
Industrial lasers for machining: (1) CO2 laser (10.6 μm, infrared) — most common for cutting metals, plastics, wood; high power (up to 20 kW CW); absorbed well by most materials, (2) Nd:YAG laser (1.06 μm, near-infrared) — pulsed or CW; better for metals (higher absorption), drilling, welding; can be fibre-delivered, (3) Fibre laser (1.07 μm) — high efficiency, excellent beam quality, increasingly replacing CO2 and Nd:YAG, (4) Excimer laser (UV, 193-351 nm) — for polymers, semiconductors, medical devices (LASIK eye surgery). CO2 and Nd:YAG/fibre lasers dominate industrial machining.

Explanation:
ECM surface characteristics: (1) Burr-free — no mechanical forces, no burr formation, (2) Stress-free — no mechanical or thermal stresses (cold process), (3) No HAZ — no heat generation in workpiece, (4) Good surface finish: Ra 0.1-1.6 μm (comparable to grinding), (5) No tool marks — electrochemical dissolution is isotropic. ECM is ideal for: aerospace components (turbine blades), medical implants, and parts requiring high surface integrity. The surface finish depends on: current density, electrolyte, gap, and workpiece material. ECM cannot machine non-conductive materials.

Explanation:
USM tool vibration: frequency 20-40 kHz (ultrasonic range, above human hearing), amplitude 0.025-0.075 mm (25-75 μm). The tool is driven by a magnetostrictive or piezoelectric transducer that converts electrical energy to mechanical vibration. A booster and horn (sonotrode) amplify the amplitude. The vibrating tool hammers abrasive particles against the workpiece. The tool material must be tough (not brittle) — typically soft steel or stainless steel. The tool shape is the negative of the desired cavity shape.

Explanation:
MAF process: (1) Magnetic abrasive particles (iron particles bonded with Al2O3 or SiC) are placed between the workpiece and magnetic poles, (2) The magnetic field aligns the particles into flexible 'brushes' that conform to the workpiece surface, (3) The workpiece rotates and the magnetic brush finishes the surface by micro-cutting. Achieves: Ra 0.01-0.1 μm, removes burrs, finishes complex surfaces. Advantages: flexible tool (conforms to surface), no tool wear, can finish complex geometries (internal surfaces, curved surfaces). Used for: finishing of cylindrical surfaces, internal surfaces, flat surfaces.

Explanation:
ECD (Electrochemical Deburring) removes burrs by anodic dissolution: (1) The workpiece (anode) and a shaped tool (cathode) are placed in an electrolyte, (2) The tool is shaped to concentrate the electric field at the burr location, (3) The burr (which protrudes and has higher current density) dissolves preferentially, (4) The rest of the part is protected by the tool geometry and low current density. Advantages: (1) Removes burrs from inaccessible areas, (2) No mechanical forces, (3) Fast (seconds to minutes), (4) Can deburr multiple parts simultaneously. Used for: hydraulic components, fuel injectors, gears.

Explanation:
Additive Manufacturing (AM) / Rapid Prototyping builds parts by adding material layer by layer (bottom-up), unlike conventional machining (subtractive — removes material) or forming (deformative). AM advantages: (1) Complex geometries (internal channels, lattice structures, undercuts) impossible with conventional machining, (2) No tooling required, (3) Customisation at no extra cost, (4) Reduced material waste. AM processes: SLA (stereolithography), SLS (selective laser sintering), FDM (fused deposition modelling), SLM (selective laser melting), EBM (electron beam melting). Used for: prototypes, medical implants, aerospace components.

Explanation:
SLS process: (1) A thin layer of powder (polymer, metal, ceramic, or composite) is spread on the build platform, (2) A CO2 laser selectively sinters (fuses) the powder according to the cross-section of the part, (3) The platform lowers by one layer thickness (0.05-0.15 mm), (4) A new powder layer is spread, (5) Process repeats until the part is complete. Advantages: no support structures needed (unsintered powder supports the part), wide range of materials. Disadvantages: rough surface finish (Ra 5-15 μm), porous parts (for polymers). SLM (Selective Laser Melting) fully melts metal powder for denser parts.

Explanation:
FDM process: (1) Thermoplastic filament (ABS, PLA, PEEK, nylon) is fed into a heated nozzle (200-400°C), (2) The nozzle extrudes molten plastic in a controlled pattern on the build platform, (3) The material solidifies immediately, (4) The platform lowers and the next layer is deposited. Layer thickness: 0.05-0.4 mm. Advantages: low cost, wide range of materials, easy to use. Disadvantages: anisotropic properties (weak in Z-direction), visible layer lines, support structures needed for overhangs. FDM is the most widely used AM process for prototyping and end-use parts.

Explanation:
SLA process: (1) A UV laser traces the cross-section of the part on the surface of a liquid photopolymer resin, (2) The UV light cures (polymerises) the resin where it strikes, (3) The build platform lowers by one layer thickness (0.025-0.15 mm), (4) A new layer of resin covers the surface, (5) Process repeats. SLA produces: (1) Excellent surface finish (Ra 0.5-2 μm), (2) High dimensional accuracy (±0.025-0.1 mm), (3) Complex geometries. Disadvantages: limited materials (photopolymers), support structures needed, post-curing required, parts may be brittle. SLA was the first commercial AM process (3D Systems, 1986).

Explanation:
Electroforming: (1) A mandrel (pattern) of the desired shape is used as the cathode, (2) Metal is electrodeposited to a significant thickness (0.5-50 mm) on the mandrel, (3) The mandrel is removed (dissolved, melted, or mechanically separated) to leave a free-standing metal part. Electroplating deposits a thin coating (0.001-0.1 mm) on a permanent substrate. Electroforming advantages: (1) Exact replication of mandrel surface (Ra < 0.1 μm), (2) Complex internal shapes, (3) No machining required. Used for: waveguides, moulds, nozzles, phonograph masters, jewellery. Materials: nickel, copper, iron.

Explanation:
NTM processes are classified by energy source: (1) Mechanical energy: USM (ultrasonic vibration + abrasive), AJM (kinetic energy of abrasive jet), WJM/AWJM (kinetic energy of water/abrasive jet), (2) Thermal energy: EDM (electric spark), LBM (laser), EBM (electron beam), PAM (plasma arc), IBM (ion beam), (3) Chemical energy: CHM (chemical etching), PCM (photochemical etching), (4) Electrochemical energy: ECM (anodic dissolution), ECG (ECM + grinding), ECD (electrochemical deburring). Each energy source has different capabilities, limitations, and applications.

Explanation:
EDM requires electrical conductivity because: (1) The spark (electric discharge) must flow between the tool and workpiece, (2) The workpiece must be able to conduct electricity to complete the circuit. EDM can machine: all metals (steel, aluminium, titanium, Inconel, tungsten carbide), graphite, and conductive ceramics (TiN, TiC). EDM cannot machine: non-conductive materials (glass, ceramics like Al2O3, polymers, wood). For non-conductive materials: USM, LBM, CHM, or AWJM are used. The minimum electrical conductivity required: approximately 0.01 S/cm.

Explanation:
ECM electrolytes: (1) NaCl (sodium chloride, common salt) — most common, low cost, high conductivity, but causes stray corrosion (attacks unintended areas), (2) NaNO3 (sodium nitrate) — more expensive, better dimensional accuracy (less stray corrosion), preferred for precision work, (3) NaClO3 (sodium chlorate) — for specific applications. Electrolyte concentration: 10-25% by weight. Flow rate: 10-50 L/min at 0.5-2 MPa pressure. The electrolyte must: (1) Have high electrical conductivity, (2) Not passivate the workpiece, (3) Be safe and non-toxic, (4) Be stable at operating conditions.

Explanation:
LBW advantages over arc welding: (1) Narrow, deep weld bead (high aspect ratio) due to focused laser beam, (2) Small HAZ (rapid heating and cooling), (3) Low distortion (less heat input), (4) High welding speed (up to 10 m/min for thin sheets), (5) Can weld dissimilar metals, (6) No filler metal required, (7) Can weld in difficult-to-access locations. Disadvantages: (1) High equipment cost, (2) Precise joint fit-up required (gap < 0.1 mm), (3) Reflective materials (aluminium, copper) are difficult to weld. Used for: automotive (tailored blanks), electronics, medical devices, aerospace.

Explanation:
EBW characteristics: (1) Very narrow, deep welds — aspect ratio (depth/width) up to 25:1 (vs. 1:1 for arc welding), (2) Minimal HAZ — concentrated energy, rapid heating/cooling, (3) Very low distortion — small heat input, (4) No contamination — vacuum environment prevents oxidation, (5) Can weld reactive metals (titanium, zirconium) without shielding gas. Disadvantages: (1) Vacuum requirement (expensive, slow), (2) High equipment cost, (3) X-ray radiation hazard, (4) Limited workpiece size (vacuum chamber). Used for: aerospace (titanium structures), nuclear industry, precision instruments.

Explanation:
ECM is most suitable for: (1) Hard, difficult-to-machine materials — Inconel, titanium alloys, hardened steel, cobalt alloys (ECM removes material regardless of hardness), (2) Complex shapes — turbine blades (aerofoil profiles), gun barrels (rifling), (3) Thin-walled parts (no cutting forces), (4) Parts requiring no HAZ or residual stresses. ECM advantages for hard materials: (1) MRR is independent of material hardness, (2) No tool wear, (3) No thermal damage. ECM is used extensively in aerospace (turbine blades, discs) and defence (gun barrels, missile components).

Explanation:
LBD advantages for small hole drilling: (1) Hole diameter: 0.025-1.5 mm (very small holes possible), (2) High production rate (up to 1000 holes/min for percussion drilling), (3) Can drill at any angle (including very acute angles), (4) Can drill hard materials (ceramics, carbides, composites), (5) No tool wear, (6) No mechanical forces. Applications: turbine blade cooling holes (angled, in Inconel), fuel injector nozzles, printed circuit boards, watch jewels, aircraft skin. Limitations: taper in hole, recast layer, limited depth-to-diameter ratio (typically < 10:1).

Explanation:
Ultrasonic Welding (USW): (1) High-frequency vibration (20-40 kHz) is applied perpendicular to the joint interface, (2) Friction at the interface generates heat (100-200°C for polymers, 300-500°C for metals), (3) The material softens and plastic deformation occurs, (4) A solid-state bond forms. USW is used for: (1) Thermoplastics (ABS, polycarbonate, nylon) — most common application, (2) Thin metal sheets (aluminium, copper) — electronics, (3) Dissimilar materials. Advantages: fast (< 1 second), no filler material, no flux, clean process. Used for: automotive interior parts, medical devices, electronics packaging.

Explanation:
FSW is a solid-state joining process: (1) A rotating tool (pin + shoulder) is plunged into the joint, (2) Frictional heat (400-500°C for aluminium, below melting point) plasticises the material, (3) The tool traverses along the joint, stirring and forging the plasticised material, (4) No melting occurs — solid-state bond. Advantages: (1) No solidification defects (porosity, hot cracking), (2) Low distortion, (3) No filler metal or shielding gas, (4) Can join dissimilar metals (Al-Cu, Al-steel), (5) Excellent mechanical properties (equal to or better than base metal). Invented by TWI (1991). Used for: aerospace, shipbuilding, automotive.

Explanation:
Diffusion Bonding: (1) Clean surfaces are brought into intimate contact, (2) Heat (0.5-0.8 Tm) and pressure (1-300 MPa) are applied for extended time (minutes to hours), (3) Atoms diffuse across the interface, forming a metallurgical bond, (4) No melting occurs. Advantages: (1) Can join dissimilar materials (metal-ceramic, metal-metal), (2) No HAZ, (3) Excellent joint properties, (4) Complex shapes possible (combined with superplastic forming — SPF/DB). Disadvantages: (1) Slow process, (2) Requires clean surfaces (vacuum or inert atmosphere), (3) High equipment cost. Used for: aerospace (titanium structures), nuclear, electronics.

Explanation:
Explosive Welding (EXW): (1) Explosive is placed on the flyer plate (cladder), (2) Detonation creates a high-velocity collision (200-500 m/s) between flyer and base plate, (3) The collision creates a jet of surface material that cleans the surfaces, (4) The high pressure (10-100 GPa) causes plastic deformation and atomic bonding at the interface, (5) A characteristic wavy interface forms. Advantages: (1) Can join dissimilar metals (Al-steel, Cu-steel, Ti-steel), (2) Large areas possible, (3) No HAZ, (4) Strong bond. Used for: cladding (corrosion-resistant lining), transition joints (ship hulls, pressure vessels).

Explanation:
ECM vs. EDM comparison: ECM advantages: (1) No recast layer (no thermal effects — cold process), (2) No HAZ, (3) No residual stresses, (4) No tool wear, (5) Better surface finish (Ra 0.1-1.6 μm vs. 0.4-12.5 μm for EDM), (6) Higher MRR for large areas. EDM advantages: (1) Better dimensional accuracy (±0.005-0.025 mm vs. ±0.025-0.1 mm for ECM), (2) Can machine complex 3D shapes (die-sinking), (3) Simpler setup, (4) No electrolyte handling. ECM is preferred for: turbine blades, gun barrels, parts requiring high surface integrity. EDM is preferred for: dies, moulds, complex cavities.

Explanation:
Laser Surface Treatment processes: (1) Laser hardening — rapid heating and self-quenching of steel surface (martensite formation), (2) Laser alloying — melting surface with alloying elements to improve properties, (3) Laser cladding — depositing a layer of different material on the surface (wear/corrosion resistance), (4) Laser shock peening — high-power pulsed laser creates shock waves that introduce compressive residual stresses (improves fatigue life), (5) Laser annealing — selective heat treatment. Advantages: precise control, localised treatment, no distortion of bulk material. Used for: automotive (camshafts, cylinder bores), aerospace (turbine blades).

Explanation:
ECM gap: 0.1-0.5 mm (100-500 μm). The gap is maintained by: (1) Electrolyte flow (high pressure, 0.5-2 MPa) that flushes away dissolved material and maintains the gap, (2) Servo control that moves the tool at the same rate as material is removed. The gap determines: (1) Current density (J = V/ρ_e × gap), (2) MRR, (3) Surface finish, (4) Dimensional accuracy. Smaller gap → higher current density → higher MRR → better accuracy. The gap must be maintained precisely to avoid short circuits (gap too small) or reduced MRR (gap too large). Electrolyte velocity: 5-50 m/s.

Explanation:
HAZ in LBM: The laser beam heats the material to very high temperatures at the cutting zone. Heat conducts into the surrounding material (thermal conduction), raising its temperature above critical transformation temperatures. This causes: (1) Microstructural changes (grain growth, phase transformations), (2) Hardness changes, (3) Residual stresses. HAZ width depends on: laser power, cutting speed, material thermal conductivity. High cutting speed → narrow HAZ. Pulsed lasers → smaller HAZ than CW lasers. HAZ is minimised by: high cutting speed, short pulse duration, high peak power. HAZ is a concern for fatigue-critical applications.

Explanation:
EDM was invented by Soviet scientists Boris Romanovich Lazarenko and Natalya Ivanovna Lazarenko in 1943. They discovered that controlled electric sparks could be used to erode metal while studying the erosion of electrical contacts. The first EDM machine was built in the USSR in 1943. Commercial EDM machines became available in the 1950s. The process was independently developed in the USA by Harold Stark, Victor Harding, and Jack Beaver around the same time. EDM revolutionised the manufacture of dies and moulds for hard materials.

Explanation:
USM was developed specifically for hard, brittle, non-conductive materials: glass, ceramics (Al2O3, SiC, Si3N4, ZrO2), carbides (WC-Co), silicon, quartz, germanium, gemstones. These materials: (1) Cannot be machined by EDM/ECM (non-conductive), (2) Are too hard for conventional machining, (3) Are too brittle for conventional machining (fracture under cutting forces). USM removes material by brittle fracture — ideal for brittle materials. USM can also machine conductive materials but is less efficient than EDM for those. USM is the preferred process for: glass drilling, ceramic machining, silicon wafer processing.

Explanation:
WJM (pure water jet, no abrasive) is most suitable for soft, non-metallic materials: rubber, foam, leather, textiles, food products (meat, bread, vegetables), paper, cardboard, plastics. The water jet (200-400 MPa, 600-900 m/s) cuts by hydraulic fracture and erosion. WJM cannot cut hard materials (metals, ceramics) — for these, AWJM (with abrasive) is needed. WJM advantages for food cutting: (1) No contamination (water is food-safe), (2) No heat (no cooking), (3) Clean cut, (4) No blade to sharpen. WJM is also used for: paint stripping, surface cleaning, concrete cutting.

Explanation:
ECM vs. Electroplating: ECM — workpiece is anode (+), tool is cathode (-), workpiece material dissolves (anodic dissolution), material is removed. Electroplating — workpiece is cathode (-), anode (+) is the plating metal, metal ions deposit on the workpiece (cathodic deposition), material is added. Both use DC current and electrolyte solutions. ECM uses high current (1000-40,000 A) and small gap (0.1-0.5 mm). Electroplating uses low current and larger gap. ECM is a machining process (removes material); electroplating is a coating process (adds material).

Explanation:
LBM uses electromagnetic radiation (photons) — the laser beam is absorbed by the workpiece material, converting light energy to heat. This absorption occurs regardless of electrical conductivity. LBM can machine: metals, ceramics, glass, polymers, composites, wood, paper — any material that absorbs the laser wavelength. The absorption depends on: material optical properties (reflectivity, absorptivity), laser wavelength, and surface condition. Highly reflective materials (polished aluminium, copper) are difficult to machine with CO2 lasers but can be machined with shorter wavelength lasers (Nd:YAG, fibre). This is the key advantage of LBM over EDM and ECM.

Explanation:
AJM is NOT suitable for soft, ductile metals because: (1) Abrasive particles embed into the soft surface rather than cutting it, (2) The surface becomes contaminated with embedded abrasive, (3) Material removal is inefficient. AJM is suitable for: (1) Hard, brittle materials (glass, ceramics), (2) Deburring of machined parts, (3) Frosting/etching of glass, (4) Cleaning of metal surfaces (removing rust, paint, scale), (5) Cutting thin sections of brittle materials, (6) Drilling small holes in brittle materials. The process is similar to sandblasting but uses finer abrasive and more controlled conditions.

Explanation:
White layer (recast layer) in EDM: (1) Formed when melted workpiece material resolidifies on the surface instead of being flushed away by the dielectric, (2) Thickness: 1-25 μm (depends on discharge energy), (3) Properties: very hard (higher hardness than base material), brittle, contains micro-cracks, (4) Composition: for steel — untempered martensite, retained austenite, carbides, (5) Residual stresses: tensile (promotes fatigue crack initiation). The white layer must be removed for fatigue-critical applications (by light grinding, polishing, or chemical etching). Below the white layer is the HAZ (heat affected zone).

Explanation:
ECM limitations: (1) Workpiece must be electrically conductive (cannot machine ceramics, glass, polymers), (2) Electrolyte handling — corrosive, requires disposal, (3) Dimensional accuracy limited by stray corrosion (±0.025-0.1 mm), (4) High capital cost (power supply, electrolyte system), (5) Tooling cost (shaped cathode for each part), (6) Hydrogen gas evolution (explosion risk), (7) Slow for small features. ECM advantages: no tool wear, no HAZ, no residual stresses, high MRR for large areas, can machine any conductive material regardless of hardness. ECM is most economical for high-volume production of complex shapes in hard materials.

Explanation:
LBM limitations: (1) Reflective materials — polished copper (reflectivity > 95% at 10.6 μm), aluminium (reflectivity > 90%) reflect most of the CO2 laser energy, making machining difficult and potentially damaging the laser optics. Solution: use shorter wavelength lasers (Nd:YAG, fibre) or roughen the surface, (2) HAZ and recast layer, (3) Taper in drilled holes, (4) Limited depth-to-diameter ratio for drilling, (5) High equipment cost, (6) Safety hazards (eye protection, fumes). LBM is most effective for: steel, stainless steel, titanium, ceramics, composites, polymers.

Explanation:
PAM limitations: (1) Electrically conductive materials only — the plasma arc is maintained between the electrode and workpiece, requiring electrical conductivity, (2) Large HAZ (10-20 mm) — high heat input, (3) Poor surface finish (Ra 6-25 μm), (4) Produces fumes, UV radiation, and noise, (5) Limited to 2D cutting (cannot produce complex 3D shapes), (6) Taper in cut. PAM advantages: (1) High MRR (can cut 150 mm thick steel), (2) High cutting speed (up to 10 m/min for thin sheets), (3) Can cut any conductive metal. Used for: structural steel, stainless steel, aluminium, titanium cutting in shipbuilding, construction, heavy fabrication.

Explanation:
SLM vs. SLS: SLM (Selective Laser Melting) — fully melts metal powder (complete fusion), producing parts with density > 99.5%, mechanical properties comparable to wrought material. SLS (Selective Laser Sintering) — partially fuses powder (sintering), producing porous parts (for polymers) or requiring infiltration (for metals). SLM uses higher laser power and energy density than SLS. SLM materials: stainless steel, titanium, aluminium, Inconel, cobalt-chrome. SLM applications: aerospace (Ti-6Al-4V brackets), medical implants (porous titanium), tooling (conformal cooling channels). SLM is also called DMLS (Direct Metal Laser Sintering) or LPBF (Laser Powder Bed Fusion).

Explanation:
EBAM (Electron Beam Additive Manufacturing) / EBM (Electron Beam Melting): (1) An electron beam (50-60 kV) melts metal powder (or wire) in a vacuum chamber, (2) Parts are built layer by layer on a powder bed, (3) The vacuum environment prevents oxidation (ideal for reactive metals like titanium), (4) The entire powder bed is preheated (600-700°C for titanium), reducing residual stresses. Advantages over SLM: (1) Higher build rate, (2) Less residual stress (hot process), (3) Better for reactive metals. Disadvantages: (1) Rougher surface finish, (2) Vacuum requirement, (3) Limited materials. Used for: titanium aerospace components, medical implants.

Explanation:
ECH (Electrochemical Honing) combines: (1) ECM (anodic dissolution) — removes 90-95% of material rapidly, (2) Conventional honing (abrasive stones) — removes the oxide film and provides dimensional accuracy and surface finish. The honing tool is the cathode; workpiece bore is the anode; electrolyte flows through the tool. ECH advantages over conventional honing: (1) Higher MRR (3-5× faster), (2) No glazing of abrasive stones (ECM keeps stones sharp), (3) No thermal damage, (4) Better surface finish (Ra 0.1-0.4 μm). Used for: engine cylinder bores, hydraulic cylinders, gun barrels, compressor cylinders. ECH is particularly effective for hard materials (hardened steel, Inconel).

Explanation:
Laser Shock Peening (LSP): (1) A high-power pulsed laser (1-10 GW/cm²) irradiates the surface through a transparent overlay (water or glass), (2) The laser ablates a thin surface layer, creating a plasma, (3) The plasma is confined by the overlay, generating a shock wave (1-10 GPa), (4) The shock wave propagates into the material, causing plastic deformation and compressive residual stresses. LSP advantages over shot peening: (1) Deeper compressive stresses (up to 1 mm vs. 0.3 mm for shot peening), (2) Better surface finish (no surface roughening), (3) Precise control. Used for: turbine blades, aircraft structural components, medical implants.

Explanation:
ECDM (Electrochemical Discharge Machining) / ECAM (Electrochemical Arc Machining): combines ECM and EDM to machine non-conductive materials. Process: (1) Tool (cathode) and auxiliary electrode (anode) are immersed in electrolyte (NaOH or KOH), (2) Electrolysis generates hydrogen bubbles around the tool, (3) At critical voltage (20-30 V), the bubble film breaks down and electric discharges occur between tool and workpiece, (4) The discharges thermally erode the non-conductive workpiece. Can machine: glass, ceramics, quartz, silicon. Advantages over USM: higher MRR, can produce complex shapes. Limitations: poor surface finish, limited depth. Used for: microfluidic devices, MEMS, glass drilling.