Modern Machining Processes
Modern machining processes, also called non‑traditional or advanced machining processes, are used when conventional methods are impractical due to material hardness, toughness, brittleness, complex geometry, or required precision. They often use forms of energy other than direct mechanical cutting — such as abrasives, electrical discharges, electrochemical reactions, high‑energy beams, or plasma — to remove material.
Abrasive‑Jet Machining (AJM)
Principle: AJM uses a high‑velocity stream of carrier gas (air, nitrogen, CO₂) containing fine abrasive particles (aluminium oxide, silicon carbide) directed at the work surface to erode material by micro‑chipping.
Equipment & Setup
- Gas supply and pressure regulator.
- Abrasive feeder and mixing chamber.
- Nozzle (tungsten carbide or sapphire) to accelerate the abrasive jet.
- Workholding fixture and enclosure to contain abrasives.
Process Parameters
- Gas pressure: 2–10 bar.
- Abrasive size: 10–50 μm.
- Stand‑off distance: 0.5–15 mm.
- Material removal rate (MRR) increases with pressure and decreases with particle size.
Applications
Deburring, cleaning, etching glass, cutting thin non‑metallic sheets, micro‑machining brittle materials.
Advantages
- No thermal damage to workpiece.
- Can machine hard and brittle materials.
- Minimal cutting forces.
Limitations
- Low MRR compared to conventional machining.
- Nozzle wear affects accuracy.
- Abrasive contamination and disposal issues.
Ultrasonic Machining (USM)
Principle: USM removes material by micro‑chipping and erosion using abrasive slurry between a vibrating tool and the workpiece. The tool oscillates at ultrasonic frequency (20–40 kHz) with small amplitude (15–50 μm).
Equipment & Setup
- Ultrasonic transducer (magnetostrictive or piezoelectric).
- Tool horn and tool (soft ductile material like brass, mild steel).
- Abrasive slurry (SiC, Al₂O₃ in water).
- Workpiece fixture and slurry circulation system.
Process Parameters
- Frequency: 20–40 kHz.
- Amplitude: 15–50 μm.
- Abrasive size: 10–100 μm.
- Static load on tool: 0.2–2 N.
Applications
Machining hard and brittle materials like glass, ceramics, carbides, precious stones; drilling small holes; intricate shapes.
Advantages
- No heat‑affected zone.
- Can produce complex cavities in hard materials.
- Good surface finish.
Limitations
- Low MRR.
- Tool wear.
- Not suitable for ductile metals.
Electrochemical Machining (ECM)
Principle: ECM removes material by anodic dissolution in an electrolytic cell. The workpiece is the anode, the tool is the cathode, and a conductive electrolyte flows between them under high current density.
Equipment & Setup
- Power supply (low voltage 5–30 V, high current up to thousands of amps).
- Tool (cathode) shaped to desired cavity.
- Electrolyte system (pump, filter, heat exchanger).
- Workholding and sealing arrangements.
Process Parameters
- Voltage: 5–30 V.
- Current density: 10–100 A/cm².
- Electrolyte: NaCl or NaNO₃ aqueous solution.
- Gap: 0.1–0.6 mm.
Applications
Complex cavities in hard alloys, turbine blades, dies, deburring, shaping difficult‑to‑machine materials.
Advantages
- No tool wear.
- Stress‑free, burr‑free surfaces.
- Can machine very hard materials.
Limitations
- High initial cost.
- Electrolyte disposal and corrosion issues.
- Only conductive materials can be machined.
Electric‑Discharge Machining (EDM)
Principle: EDM removes material by a series of rapidly recurring electrical discharges between a tool electrode and the workpiece, both submerged in a dielectric fluid. Each spark melts and vaporizes a small volume of material.
Equipment & Setup
- Pulse power supply.
- Tool electrode (graphite, copper, copper‑tungsten).
- Dielectric fluid system (kerosene, deionized water).
- Servo control to maintain spark gap.
Process Parameters
- Gap: 0.01–0.5 mm.
- Open‑circuit voltage: 50–300 V.
- Peak current: 0.1–500 A.
- Pulse on/off times control MRR and finish.
Applications
Die sinking, mold making, machining hard alloys, micro‑holes, intricate cavities.
Advantages
- Can machine any conductive material regardless of hardness.
- Complex shapes possible.
- No cutting forces.
Limitations
- Slow MRR.
- Tool wear.
- Heat‑affected zone and recast layer.
Electron‑Beam Machining (EBM)
Principle: EBM uses a focused beam of high‑velocity electrons to melt and vaporize material in a vacuum. The kinetic energy of electrons converts to heat upon impact, enabling precise, high‑energy density machining.
Equipment & Setup
- Electron gun (cathode, anode, focusing and deflection coils).
- High‑voltage power supply (30–200 kV).
- Vacuum chamber to prevent electron scattering.
- Workholding fixtures inside the chamber.
Process Parameters
- Beam current: 0.1–2 A.
- Spot size: as small as 0.1 mm.
- Power density: up to \(10^7\) W/mm².
- Pulse or continuous beam operation.
Applications
Drilling fine holes in turbine blades, fuel injectors, printing nozzles; cutting thin sheets; micro‑machining.
Advantages
- Extremely high precision and aspect ratio.
- Can machine very hard or brittle materials.
- Minimal mechanical stresses.
Limitations
- Requires vacuum environment.
- High equipment cost.
- Limited to small workpieces that fit in chamber.
Laser‑Beam Machining (LBM)
Principle: LBM uses a concentrated beam of coherent light (laser) focused on the workpiece to melt, vaporize, or thermally stress material for removal. Energy density is extremely high at the focal point.
Equipment & Setup
- Laser source (CO₂, Nd:YAG, fiber laser).
- Optical system (mirrors, lenses) to focus and direct beam.
- Beam delivery enclosure and safety interlocks.
- Assist gas system (oxygen, nitrogen, argon) for cutting and debris removal.
Process Parameters
- Power: tens of watts (micro‑machining) to several kilowatts (cutting).
- Spot size: 0.01–1 mm.
- Pulse duration: nanoseconds to continuous wave.
- Cutting speed depends on material, thickness, and power.
Applications
Cutting, drilling, marking, surface treatment of metals, ceramics, polymers; micro‑electronics fabrication.
Advantages
- No tool wear.
- Can process hard, brittle, or soft materials.
- Non‑contact process with minimal mechanical distortion.
Limitations
- Thermal effects (HAZ, recast layer).
- Reflective materials can be difficult to process.
- High capital cost and safety requirements.
Plasma‑Arc Machining (PAM)
Principle: PAM uses a high‑temperature, high‑velocity jet of ionized gas (plasma) to melt and blow away material. An electric arc between an electrode and the workpiece ionizes the gas.
Equipment & Setup
- Power supply (DC, 20–200 V, hundreds of amps).
- Plasma torch with electrode (tungsten) and nozzle.
- Plasma‑forming gas supply (argon, nitrogen, hydrogen, air).
- Cooling system for torch.
Process Parameters
- Plasma temperature: 11,000–28,000 °C.
- Gas flow rate: 0.5–5 m³/h.
- Cutting speed depends on material thickness and current.
Applications
Cutting stainless steel, aluminium, copper alloys; gouging; profile cutting thick plates.
Advantages
- High cutting speeds for thick sections.
- Can cut any electrically conductive material.
- Good edge quality with minimal finishing.
Limitations
- Wider kerf than laser or waterjet.
- Heat‑affected zone and possible distortion.
- Noisy and produces intense light — requires shielding.