Electrical, Electrochemical and Thermal Machining

Introduction and Context

Conventional machining removes material by mechanical contact between a cutting tool and a workpiece. Electrical, electrochemical and thermal machining processes remove material through electrical discharges, electrochemical dissolution, melting, vaporization or combinations of these mechanisms. They are therefore especially valuable when the workpiece is very hard, brittle, electrically conductive, heat-resistant, miniature, or geometrically complex.

These processes are commonly called non-traditional or advanced machining processes. The term does not imply that mechanical effects are absent; rather, the dominant energy-transfer mechanism is not the direct shearing action of a conventional cutting edge. Their engineering importance lies in the ability to machine hardened dies, turbine components, microfeatures, deep cavities and difficult-to-cut superalloys.

The choice of process must consider five linked outcomes:

1. Material-removal physics—how material is detached or dissolved.
2. Accuracy and geometry—dimensional tolerance, overcut, taper and feature resolution.
3. Surface integrity—roughness, recast layers, heat-affected zones, residual stress and metallurgical alteration.
4. Productivity—material-removal rate, tool wear, setup time and energy consumption.
5. Application suitability—material conductivity, thickness, geometry, accessibility and production volume.

Learning Objectives

After studying this chapter, the reader should be able to:

• explain the operating principles of EDM, wire EDM, ECM, laser beam machining, electron beam machining and plasma arc machining;
• distinguish electrical discharge, electrochemical, photothermal, electron-beam and plasma-removal mechanisms;
• interpret the principal process variables and their influence on accuracy, surface integrity and productivity;
• select an appropriate process for representative manufacturing problems;
• evaluate limitations, environmental concerns and safety requirements; and
• analyze an integrated advanced-machining case.

1. Classification and Selection Logic

Advanced machining processes may be classified according to the dominant energy source.

A useful first decision is whether the workpiece must conduct electricity. EDM, wire EDM and ECM require an electrically conductive workpiece. Laser machining can process both conductive and nonconductive materials, although optical absorption, reflectivity and thermal properties determine its effectiveness. Electron-beam machining generally requires a vacuum chamber, while plasma arc cutting is particularly productive for conductive sheet and plate.

2. Electrical Discharge Machining

2.1 Principle of operation

Electrical discharge machining removes material from an electrically conductive workpiece by a sequence of controlled sparks between an electrode tool and the workpiece. The tool and workpiece are separated by a small dielectric-filled gap. A pulsed direct-current supply raises the voltage until dielectric breakdown occurs. A plasma channel then forms, current flows briefly, and the localized temperature becomes high enough to melt and partly vaporize small volumes of both workpiece and, to a lesser extent, electrode.

When the pulse ends, the plasma collapses. The dielectric flushes molten debris away, and the molten material rapidly solidifies or is removed from the gap. Repetition of millions of such discharges creates the desired cavity.

The tool does not normally contact the workpiece. A servo system continuously adjusts the electrode position to maintain a suitable spark gap. If the gap is too large, discharges cease; if it is too small, arcing or short-circuiting occurs.

2.2 Energy and removal rate

For a rectangular voltage-current pulse, the ideal electrical energy delivered during one pulse is approximated by:

where E_p is pulse energy in joules, V is discharge voltage in volts, I is discharge current in amperes, and t_on is pulse-on time in seconds. This is an idealized expression; actual energy transferred to the workpiece is lower because of losses in the generator, plasma channel, dielectric and electrode.

If f is the pulse frequency in hertz, the ideal average power is:

The equation assumes approximately constant voltage and current during each pulse. For a pulse period T, the duty factor is:

For a rectangular pulse train, f = 1/T, so P_avg = V I D. In practice, measured power should be used when pulse waveforms are nonrectangular.

A simplified material-removal relationship is:

where MRR is volumetric removal rate in m³/s, η_w is the fraction of average power effectively producing workpiece removal, ρ is workpiece density in kg/m³, and L_m is the effective specific energy of melting and vaporization in J/kg. This model is useful for trends, not exact production prediction, because energy partition, crater geometry, flushing and debris removal vary with conditions.

2.3 Process variables

• Discharge current: Increasing current generally increases crater size and MRR but worsens roughness and may increase the recast layer.
• Pulse-on time: Longer pulses normally increase individual crater size and removal per discharge. Excessive duration can produce deeper thermal damage.
• Pulse-off time: Adequate off-time allows dielectric recovery and debris removal. Too little off-time promotes arcing and unstable machining.
• Gap voltage: It influences breakdown and gap size. Excessive gap may reduce dimensional control; insufficient gap encourages short circuits.
• Dielectric flushing: Pressurized fluid, side flushing or electrode rotation removes debris and stabilizes the process.
• Electrode polarity: Polarity affects electrode wear and workpiece energy distribution. The optimum choice depends on pulse conditions and electrode material.

2.4 Accuracy and surface integrity

EDM accuracy is affected by spark-gap size, tool wear, servo control, flushing, thermal distortion and electrode geometry. The cavity is normally larger than the electrode because of the lateral spark gap. This enlargement is called overcut or overburn. Fine finishing passes use lower-energy pulses to reduce crater size.

The EDM surface usually contains overlapping craters, a rapidly resolidified recast layer, and a heat-affected zone beneath it. The recast layer may contain microcracks, retained phases, electrode material and altered hardness. In dies and fatigue-sensitive components, these effects may require polishing, low-energy finishing, heat treatment or removal of the damaged layer.

2.5 Tool electrodes and applications

Common electrode materials include copper, graphite, copper-tungsten and brass. Selection depends on conductivity, wear resistance, machinability, cost and required geometry. EDM is used for die and mould cavities, injection-mould tools, extrusion dies, turbine cooling holes, hardened steel components and removal of broken taps or drills.

Its major advantages are the ability to machine hardened materials without conventional cutting forces and the production of intricate cavities. Its limitations include the need for conductivity, relatively low removal rates for large volumes, electrode fabrication, dielectric management and thermal surface damage.

3. Wire Electrical Discharge Machining

Wire EDM replaces the shaped electrode with a continuously moving, electrically conductive wire, commonly brass or coated brass. The wire follows a programmed path while sparks remove material from a conductive workpiece immersed in dielectric fluid, usually deionized water.

Because the wire is continuously renewed, tool wear does not accumulate in the same way as in die-sinking EDM. The process can cut intricate profiles, narrow slots, punches, dies and hardened plates. The wire never mechanically contacts the workpiece; the controlled gap produces a kerf wider than the wire diameter.

3.1 Geometry and accuracy

The final profile is influenced by wire diameter, spark gap, wire deflection, flushing pressure, workpiece thickness and thermal conditions. A typical strategy is a high-energy rough cut followed by one or more low-energy skim cuts. Skim cuts reduce roughness, taper and dimensional error.

Wire EDM can generate taper by independently controlling upper and lower wire guides. This capability is useful for punches, extrusion dies and components with sloped walls. However, very thick workpieces may suffer from nonuniform flushing and changing discharge conditions along the cut.

3.2 Wire EDM performance

Higher pulse energy generally increases cutting speed but creates a rougher surface and a thicker recast layer. Excessive speed relative to discharge capacity can cause wire breakage. The wire must be tensioned and transported continuously; worn or contaminated dielectric reduces process stability.

Wire EDM is preferred over die-sinking EDM when the desired geometry is a through-profile and a separate shaped electrode would be expensive. It cannot, however, produce a closed internal cavity without a starting hole or access passage.

4. Electrochemical Machining

4.1 Electrochemical principle

Electrochemical machining removes material by controlled anodic dissolution. The workpiece is connected as the anode and the shaped tool is the cathode. An electrolyte flows through the small interelectrode gap. When direct current is applied, metal atoms at the workpiece surface lose electrons and enter the electrolyte as ions or reaction products.

Unlike EDM, ECM does not depend on spark formation. The tool is not consumed by thermal cratering, and there is no recast layer or heat-affected zone when the process is properly controlled. The final shape is determined by the tool, gap distribution, current density and electrolyte flow.

A simplified relation between dissolved mass and electric charge is given by Faraday’s law:

where m is dissolved mass in kg, M is molar mass in kg/mol, I is current in amperes, t is machining time in seconds, z is the number of electrons exchanged per atom, and F is Faraday’s constant, approximately 96,485 C/mol. The equation assumes constant current efficiency and a single dominant electrochemical reaction.

For volumetric removal, if ρ is density, then:

where V is removed volume in m³ when consistent SI units are used. Real removal differs because current efficiency, secondary reactions, alloy composition and sludge formation influence dissolution.

4.2 ECM process variables

• Current density: Higher current density generally increases removal rate but may promote stray corrosion, gas generation and instability.
• Interelectrode gap: A smaller, uniform gap improves localization but demands accurate servo control and clean electrolyte flow.
• Electrolyte: Sodium chloride provides high conductivity and productivity but may increase corrosion; sodium nitrate can provide better dimensional control in some applications.
• Flow rate and pressure: These remove reaction products, maintain conductivity and reduce temperature gradients.
• Tool shape: Since dissolution occurs normal to the local electric field, tool design must compensate for overcut and stray removal.

4.3 Strengths and limitations

ECM produces burr-free surfaces and introduces little mechanical stress. It is suitable for difficult-to-machine conductive alloys, turbine blades, deburring, profiling, die sinking and simultaneous machining of multiple parts. Since there is no tool-workpiece contact, delicate components are not mechanically deformed.

Its disadvantages include high capital cost, electrolyte handling, corrosion of equipment, hydrogen evolution, sludge disposal and difficulty machining electrically insulating materials. Dimensional accuracy can be poorer than that of fine EDM when the electric field spreads beyond the intended region. Environmental control is therefore central to ECM design.

5. Laser Beam Machining

Laser beam machining uses a focused coherent light beam to heat, melt and vaporize material. A lens concentrates optical energy into a small spot. Material may be expelled by vapor pressure, assist-gas momentum or both. Pulsed lasers are used for drilling, marking and micromachining; continuous-wave or high-repetition systems are common for cutting and welding-related operations.

Laser-material interaction depends on wavelength, absorptivity, reflectivity, thermal conductivity, heat capacity, melting temperature and vaporization temperature. A simplified fluence relationship is:

where H is pulse fluence in J/m², E_p is pulse energy in joules and A is illuminated area in m². The equation assumes uniform energy distribution over the stated area; real Gaussian beams produce a spatially varying fluence.

A Gaussian beam is often described by its beam radius, but practical machining is governed by focus quality, spot size, pulse duration, repetition rate and absorptivity. Short pulses reduce heat diffusion and can produce smaller heat-affected zones. Longer pulses often provide greater throughput but increase thermal damage.

5.1 Process characteristics

Assist gases have different functions. Oxygen can increase cutting speed in steels through exothermic oxidation, while nitrogen or argon can reduce oxidation and improve edge appearance. Gas pressure must be sufficient to expel molten material without destabilizing the cut.

Laser machining offers no tool wear in the conventional sense, rapid CNC reprogramming, narrow kerfs and noncontact processing. It can machine metals, ceramics, polymers, composites and some transparent materials using suitable wavelengths and pulse regimes. Limitations include reflectivity of metals, recast and heat-affected zones, taper, dross, high equipment cost and hazards from direct or reflected radiation.

6. Electron Beam Machining

Electron beam machining accelerates electrons through a high voltage and focuses them electromagnetically onto the workpiece. When electrons strike the surface, their kinetic energy is converted primarily into heat. Material melts and vaporizes in a small region, while vapor pressure ejects material.

The process is normally performed in a vacuum. Vacuum reduces electron scattering and prevents oxidation, permitting very high power density and precise energy delivery. Electron beam machining can produce small holes, slots and cuts in difficult materials. It is also used in electron-beam welding and additive manufacturing, although those are distinct process applications.

Important variables include accelerating voltage, beam current, focus, pulse duration, beam diameter, working distance and traverse speed. Increasing beam current or reducing spot size raises power density, but excessive energy produces a large heat-affected zone and unstable vaporization.

The main limitations are vacuum-chamber size, pump-down time, equipment cost, X-ray generation and restricted workpiece dimensions. Electron beam machining is therefore selected when exceptional precision or very high energy density justifies low flexibility and high capital cost.

7. Plasma Arc Machining and Cutting

A plasma is an ionized gas containing electrons, ions and neutral particles. In plasma arc machining, a gas is forced through an electric arc between an electrode and the workpiece or through a transferred arc system. The constricted arc produces a high-temperature, high-velocity plasma jet that melts the workpiece; the gas stream expels the molten metal.

Plasma cutting is productive for conductive sheets and plates, including carbon steel, stainless steel, aluminium and copper alloys. Compared with oxyfuel cutting, plasma can cut materials that do not support the required oxidation reaction and often provides higher speed on suitable thicknesses.

Cut quality depends on arc current, voltage, gas type, gas flow, torch height, travel speed, nozzle condition and material thickness. Excessive speed may leave an incomplete cut; insufficient speed increases dross and bevel. Plasma produces a heat-affected zone, thermal distortion, fumes, ultraviolet radiation and electrical hazards. Ventilation, appropriate shielding and consumable inspection are essential.

8. Comparative Evaluation

No process is universally superior. EDM is often selected for a hard conductive die cavity; wire EDM for a precise hardened profile; ECM for burr-free production of conductive components; laser for flexible thin-sheet cutting or microfeatures; electron beam for specialized high-precision vacuum work; and plasma for productive cutting of conductive plate.

9. Worked Examples

Example 1: Ideal EDM pulse energy and average power

An EDM generator produces rectangular pulses of 120 V and 15 A. The pulse-on time is 100 μs and the pulse period is 400 μs. Determine ideal pulse energy, duty factor and average electrical power.

Convert pulse duration:

t_on = 100 × 10^-6 s.

The duty factor is:

Therefore:

These are ideal electrical values. The actual workpiece-removal power is lower because only a fraction of the energy reaches the workpiece and produces effective removal.

Example 2: Faradaic mass removal in ECM

Suppose a metal with molar mass 55.85 g/mol dissolves through a two-electron reaction at 1000 A for 60 s. Assume 90% current efficiency. Find the dissolved mass.

Using m = η MIt/(zF) with η = 0.90, M = 0.05585 kg/mol, z = 2, and F = 96,485 C/mol:

The result assumes one dominant reaction and constant efficiency. Alloy passivation, gas evolution and changing electrolyte conditions can cause actual removal to differ.

10. Applied Case: Precision Die Insert Manufacture

Background

An illustrative tooling company must manufacture a hardened steel die insert containing a deep, complex cavity with sharp internal features. The finished insert requires high dimensional accuracy, and conventional milling after hardening would cause excessive tool wear and vibration.

Problem analysis

The material is electrically conductive and already hardened. A shaped cavity is required rather than a simple through-profile. Surface integrity is important because cracks in the cavity could reduce die fatigue life. A process must also accommodate inspection and finishing.

Approach and solution

The company selects a hybrid route. First, high-speed milling produces the preform before hardening, leaving a controlled machining allowance. After hardening, die-sinking EDM generates the intricate cavity using a copper-tungsten electrode. Rough EDM uses higher pulse energy for productivity, followed by finishing passes with lower current and shorter pulse-on time. Dielectric filtration and optimized flushing are used to prevent debris accumulation.

Critical surfaces are inspected using coordinate measurement and surface roughness measurement. Where fatigue-critical regions show an excessive recast layer, light polishing or controlled material removal is performed. A separate wire EDM operation produces a nearby precision insert profile and reference features.

Outcome

The route avoids excessive mechanical cutting forces and allows the hardened cavity to be produced accurately. The main trade-off is the time and cost of electrode manufacture, EDM cycle time and post-EDM surface conditioning. The process is successful because roughing, finishing, inspection and surface-integrity control are treated as one manufacturing system rather than as isolated operations.

Learning points

• Material hardness alone does not determine process choice; conductivity and geometry are equally important.
• Roughing and finishing conditions should not be identical.
• Surface integrity must be specified alongside dimensional accuracy.
• Electrode design and dielectric flushing can determine practical productivity.
• Hybrid manufacturing often provides a better solution than reliance on a single process.

11. Surface Integrity, Quality and Measurement

Quality evaluation should include dimensional error, geometric error, roughness, metallurgical alteration and functional performance. Common measurements include coordinate-measuring-machine inspection, optical microscopy, profilometry, hardness testing, microscopy of cross-sections and residual-stress assessment where necessary.

A low roughness value does not automatically indicate a defect-free surface. An EDM surface may have acceptable average roughness but contain microcracks. A laser-cut edge may be dimensionally correct but contain dross or a hardened heat-affected zone. ECM may produce a smooth, burr-free surface but suffer from stray corrosion if the electrolyte is poorly controlled.

Process qualification should therefore connect process parameters to the requirements of the component: fatigue strength, wear, sealing, corrosion resistance, electrical contact, dimensional fit and service temperature.

12. Productivity, Economics and Sustainability

Productivity is not simply material-removal rate. A broader evaluation includes setup, tooling, electrode manufacture, consumables, inspection, rework, energy, maintenance and waste treatment. For a low-volume complex die, EDM may be economical despite a low volumetric removal rate because it avoids expensive cutting tools and reduces risk. For high-volume burr removal, ECM may justify specialized tooling. For sheet production, plasma or laser cutting may dominate because rapid tool changes are unnecessary.

Environmental and safety issues include:

• dielectric fire risk and aerosol exposure in EDM;
• electrolyte corrosion, metal-containing sludge and hydrogen evolution in ECM;
• laser radiation, fumes and reflected-beam hazards;
• X-rays, high voltage and vacuum hazards in electron-beam equipment; and
• ultraviolet radiation, noise, fumes and electrical hazards in plasma systems.

Engineering controls should include interlocks, guarding, extraction, coolant or electrolyte containment, filtration, grounding, personal protective equipment and documented maintenance. Waste streams must be characterized before disposal or recycling. Compliance with applicable occupational-safety, electrical, radiation and environmental regulations is part of professional process selection.

13. Contemporary Developments

Modern systems increasingly combine sensors, adaptive control and digital manufacturing. EDM controllers can monitor voltage and current waveforms to classify normal sparks, arcs and short circuits. Wire EDM machines compensate for wire deflection and thermal effects. ECM research uses pulsed current, shaped tools and localized electrolyte jets to improve resolution. Laser systems use galvanometer scanners, beam shaping, ultrashort pulses and machine-vision alignment. Plasma systems employ automatic torch-height control and nesting software to reduce scrap.

Artificial intelligence is most useful when it supports, rather than replaces, physical understanding. Machine-learning models can predict roughness, detect unstable discharges, estimate tool wear or identify defective cuts from sensor signals. Their reliability depends on representative training data, calibration, traceability and detection of conditions outside the training range. Safety-critical decisions should retain physical limits, alarms and human oversight.

Best-Practice Guidelines

1. Define material, geometry, tolerance and surface-integrity requirements before choosing a process.
2. Separate roughing and finishing conditions.
3. Maintain stable dielectric, electrolyte, gas or vacuum conditions.
4. Use flushing and filtration systems appropriate to the removal rate.
5. Validate the process using both dimensional and metallurgical inspection.
6. Monitor consumables such as electrodes, wire, nozzles and filters.
7. Control thermal damage in fatigue- or corrosion-sensitive parts.
8. Include energy, waste and safety requirements in the process plan.
9. Use simulation and adaptive control, but verify models experimentally.
10. Document parameter windows and inspection results for repeatability.

Chapter Summary

Electrical, electrochemical and thermal machining processes remove material without relying primarily on a conventional cutting edge. EDM and wire EDM use repeated electrical sparks to melt and vaporize conductive materials; die-sinking EDM creates cavities while wire EDM creates accurate through-profiles. ECM removes conductive material by anodic dissolution and can produce burr-free surfaces without thermal damage. Laser beam machining uses focused optical energy, electron beam machining uses high-speed electrons in vacuum, and plasma arc machining uses a high-temperature ionized gas jet.

Process selection requires simultaneous consideration of removal physics, workpiece requirements, accuracy, overcut, taper, surface integrity, productivity, consumables, environmental impact and safety. Higher energy commonly increases removal rate but can worsen roughness, recast, heat-affected zones or dimensional control. Successful manufacturing therefore uses controlled roughing and finishing, suitable flushing or shielding, inspection and—where necessary—a hybrid process route.

Key Terms

Electrical discharge machining (EDM): Removal of conductive material by controlled electrical sparks.

Die-sinking EDM: EDM using a shaped electrode to form a cavity.

Wire EDM: EDM using a continuously moving wire to cut a profile.

Dielectric: Insulating fluid that permits controlled breakdown and carries away EDM debris.

Spark gap: Small separation between tool and workpiece across which discharge occurs.

Overcut: Enlargement of a machined feature beyond the nominal tool or programmed geometry.

Recast layer: Rapidly resolidified material remaining on a thermally machined surface.

Heat-affected zone: Material altered by heat without necessarily being melted.

Electrochemical machining (ECM): Material removal by anodic dissolution in an electrolyte.

Anode: Electrode at which oxidation and metal dissolution occur in ECM.

Cathode: Electrode at which reduction occurs; the ECM tool is normally the cathode.

Current efficiency: Fraction of supplied electrochemical charge producing the intended reaction.

Faraday’s law: Relationship between electric charge and amount of electrochemical reaction.

Laser beam machining: Noncontact machining using focused optical energy.

Fluence: Energy delivered per unit area, commonly expressed in J/m².

Electron beam machining: Thermal machining by a focused high-speed electron beam.

Plasma arc machining: Thermal machining using an ionized, high-temperature gas jet.

Material-removal rate: Volume or mass of material removed per unit time.

Surface integrity: Combined description of surface topography, metallurgy, stress and defects.

Duty factor: Ratio of pulse-on time to total pulse period.

Review Questions

Short Answer Questions

1. Why must the workpiece be electrically conductive in EDM and ECM?
2. What is the function of dielectric fluid in EDM?
3. Distinguish a recast layer from a heat-affected zone.
4. Why is deionized water commonly used in wire EDM?
5. State two advantages and two limitations of plasma arc cutting.

Long Answer Questions

1. Explain the operating cycle of die-sinking EDM and discuss the effects of current, pulse duration and flushing.
2. Compare EDM and ECM with respect to removal mechanism, tool wear, accuracy and surface integrity.
3. Describe laser beam machining and explain how beam energy, pulse duration and assist gas affect cutting quality.
4. Explain the construction and operation of a plasma arc cutting system and identify its principal safety hazards.
5. Develop a process-selection argument for manufacturing a hardened steel die containing both a deep cavity and a precision through-profile.

Analytical / Application Questions

1. An EDM system operates at 150 V and 12 A with a pulse-on time of 80 μs and a pulse period of 320 μs. Calculate ideal pulse energy, duty factor and average electrical power. State why actual removal power is lower.
2. A component requires a burr-free, stress-sensitive surface on a conductive nickel alloy. Compare ECM and EDM and recommend one process, including the conditions under which your recommendation could change.
3. A laser-cut stainless-steel sheet shows excessive dross and a wide heat-affected zone. Analyze at least four possible causes and propose parameter or equipment changes to improve the cut.

Multiple Choice Questions with Answers

Question 1

Which mechanism is dominant in die-sinking EDM?

A. Mechanical shearing by a rotating tool

B. Anodic dissolution in an electrolyte

C. Localized melting and vaporization caused by electrical sparks

D. Chemical oxidation without electrical energy

Correct Answer: C. Localized melting and vaporization caused by electrical sparks

Question 2

What is the principal function of dielectric fluid in EDM?

A. To act as a permanent cutting tool

B. To control spark breakdown and remove debris

C. To increase mechanical contact between electrodes

D. To dissolve the workpiece continuously by chemical reaction

Correct Answer: B. To control spark breakdown and remove debris

Question 3

Which process normally produces no recast layer when properly controlled?

A. ECM

B. EDM

C. Laser beam machining

D. Plasma arc cutting

Correct Answer: A. ECM

Question 4

A wire EDM machine is especially suitable for producing which feature?

A. A deep blind cavity using a shaped electrode

B. A precise through-profile in hardened conductive plate

C. A nonconductive ceramic cavity without special treatment

D. A large forged surface by bulk material removal

Correct Answer: B. A precise through-profile in hardened conductive plate

Question 5

In ECM, the workpiece is normally connected as the:

A. Cathode

B. Insulator

C. Anode

D. Dielectric

Correct Answer: C. Anode

Question 6

For a rectangular EDM pulse, which expression gives ideal pulse energy?

A. E_p = V/I/t_on

B. E_p = V I t_on

C. E_p = I/(V t_on)

D. E_p = V + I + t_on

Correct Answer: B. E_p = V I t_on

Question 7

An EDM pulse has 100 μs on-time and a 400 μs period. What is its duty factor?

A. 0.025

B. 0.25

C. 2.5

D. 4.0

Correct Answer: B. 0.25

Question 8

Why is electron beam machining generally performed in a vacuum?

A. To increase mechanical friction

B. To prevent all material heating

C. To reduce electron scattering and oxidation

D. To supply electrolyte to the workpiece

Correct Answer: C. To reduce electron scattering and oxidation

Question 9

Which factor most directly increases the heat-affected zone in thermal machining?

A. Lower energy input and shorter interaction time

B. Higher thermal energy delivered to the workpiece

C. Elimination of the assist gas in every process

D. Use of a nonconductive dielectric in ECM

Correct Answer: B. Higher thermal energy delivered to the workpiece

Question 10

Which process is generally most appropriate for high-productivity cutting of conductive metal plate?

A. Plasma arc cutting

B. Die-sinking EDM

C. ECM with a blind shaped tool

D. Electron beam machining in a small vacuum chamber

Correct Answer: A. Plasma arc cutting