EDM

Question 1

What does EDM stand for?

Answer 1

Electrical Discharge Machining.

Question 2

What type of energy is primarily used in EDM?

Answer 2

Electrical energy.

Question 3

What are the two main types of EDM processes?

Answer 3

Plunge (die sinking) EDM and Wire EDM (WEDM).

Question 4

What is the purpose of the dielectric fluid in EDM?

Answer 4

To promote spark formation, cool electrodes, and flush away debris.

Question 5

What is the role of the tool electrode in plunge EDM?

Answer 5

To copy its negative shape onto the workpiece through sparks.

Question 6

What happens during the ignition phase in EDM?

Answer 6

An electric field forms, and dielectric fluid partially ionizes.

Question 7

What is the typical temperature range in the plasma channel during EDM?

Answer 7

4000–10000 °C.

Question 8

What is the purpose of the cavitation effect in EDM?

Answer 8

To remove molten metal from the crater.

Question 9

What are the three zones of thermal damage on an EDM-machined surface?

Answer 9

Zone A (melting/resolidification), Zone B (HAZ), Zone C (thermal effect).

Question 10

What is the “white layer” in EDM-machined surfaces?

Answer 10

A hard, brittle layer formed by chemical reactions with the dielectric fluid.

Question 11

What are the main components of debris produced during EDM?

Answer 11

Metal particles, carbon from dielectric splitting, and gas.

Question 12

What is the difference between craters at the anode and cathode in EDM?

Answer 12

Cathode craters are deeper; anode craters are wider and shallower.

Question 13

What are the four types of discharge profiles in EDM?

Answer 13

Erosion (spark), void, short circuit, and arc.

Question 14

What is the purpose of the closed-loop control system in plunge EDM?

Answer 14

To maintain a constant tool-workpiece distance via pulse shape analysis.

Question 15

What are the typical values for surface roughness (Ra) in EDM?

Answer 15

0.2–12 µm (plunge EDM); 0.2–5 µm (WEDM).

Question 16

What is the typical gap distance between the tool and workpiece in EDM?

Answer 16

0.012–0.050 mm.

Question 17

What is the Weller’s empirical formula for MRR in plunge EDM?

Answer 17

MRR = 664 × (I / Tm^1.23), where Tm is melting point.

Question 18

Why is inverse polarity used in Wire EDM (WEDM)?

Answer 18

To improve surface finish by using electrons for material removal.

Question 19

What are the main properties of a good EDM tool material?

Answer 19

Low wear, high thermal/electrical conductivity, high melting point, good machinability.

Question 20

What are the common materials used for EDM tools?

Answer 20

Graphite, copper, copper-tungsten alloys.

Question 21

What are the three types of electrode wear in EDM?

Answer 21

Corner wear, end (frontal) wear, side (lateral) wear.

Question 22

What is the purpose of corner wear compensation in EDM?

Answer 22

To maintain accuracy by compensating for concentrated spark erosion at sharp corners.

Question 23

What are the main characteristics of a dielectric fluid in EDM?

Answer 23

High ionization capacity, rapid de-ionization, low viscosity, low flammability.

Question 24

What liquids are commonly used as dielectric fluids in EDM?

Answer 24

Oils (kerosene), silicon oils, de-ionized water.

Question 25

What is the purpose of flushing in EDM?

Answer 25

To remove debris and introduce fresh dielectric for stable spark formation.

Question 26

What are the advantages of using graphite as a tool material in EDM?

Answer 26

Easy machining, lightweight, high melting point (3500 °C).

Question 27

What are the disadvantages of using copper as a tool material in EDM?

Answer 27

Higher wear at high currents, especially on thin features.

Question 28

What is the typical range for discharge current in a power transistor circuit?

Answer 28

1–200 A.

Question 29

What is the duty cycle in EDM?

Answer 29

τ = ton / (ton + toff).

Question 30

How does increasing discharge time (ton) affect MRR and surface roughness?

Answer 30

Increases MRR but worsens surface roughness.

Question 31

What is the effect of increasing current (I) on crater morphology?

Answer 31

Larger crater diameter due to wider spark channel.

Question 32

What is the typical range for pulse frequency in EDM?

Answer 32

1–200 kHz (power transistor); ~5 kHz (Lazarenko).

Question 33

What is the main advantage of the power transistor circuit over Lazarenko’s circuit?

Answer 33

Higher efficiency, controllable pulse shape, higher frequency.

Question 34

What is the typical voltage range in Lazarenko’s circuit?

Answer 34

100–500 V.

Question 35

What is the main application of Lazarenko’s circuit in EDM?

Answer 35

Finishing operations (small ton for better surface finish).

Question 36

What are the main applications of EDM in industry?

Answer 36

Molds, dies, aerospace components, biomedical implants.

Question 37

What are the pros of EDM compared to traditional machining?

Answer 37

No burrs, high precision, independence from material hardness.

Question 38

What are the cons of EDM compared to traditional machining?

Answer 38

Low MRR, conductive materials only, tool wear.

Question 39

What is the main difference between EDM and Wire EDM (WEDM)?

Answer 39

WEDM uses a wire electrode; plunge EDM uses a shaped tool.

Question 40

How is tool wear compensated in WEDM?

Answer 40

The wire is continuously renewed from a spool.

Question 41

What is the typical wire material used in WEDM?

Answer 41

Copper (0.15–0.3 mm) or molybdenum (coated, 0.03–0.15 mm).

Question 42

What is the purpose of wire tension in WEDM?

Answer 42

To prevent wire flexure during machining.

Question 43

What is the kerf in WEDM?

Answer 43

The width of the cut made by the wire.

Question 44

What is the typical dimensional tolerance achievable in WEDM?

Answer 44

±0.005 mm.

Question 45

What is the main advantage of WEDM over plunge EDM?

Answer 45

No tool wear issues (wire is continuously fed).

Question 46

What is the main disadvantage of WEDM?

Answer 46

Low MRR.

Question 47

What is micro-EDM (µEDM)?

Answer 47

EDM for micro-features (e.g., holes < 50 µm).

Question 48

What are the typical applications of µEDM?

Answer 48

Inkjet nozzles, micro-molds, medical devices.

Question 49

What is the typical diameter of electrodes used in µEDM?

Answer 49

< 1 mm (often < 100 µm after dressing).

Question 50

How is tool wear managed in µEDM?

Answer 50

Onboard dressing using a WEDM unit.

Question 51

What is the typical pulse duration (ton) in µEDM?

Answer 51

0.1–1000 ns.

Question 52

What is the main difference in dielectric fluids between macro-EDM and µEDM?

Answer 52

µEDM uses mineral oil; macro-EDM uses oil/water.

Question 53

What is the typical surface roughness (Ra) achievable in µEDM?

Answer 53

0.07–1 µm.

Question 54

What is the purpose of the Fourier model in EDM?

Answer 54

To predict heat distribution and crater formation.

Question 55

What is the heat equation used in EDM modeling?

Answer 55

∂²T/∂r² + (1/r)∂T/∂r = (1/α)∂T/∂t (cylindrical coordinates).

Question 56

What is the role of thermal diffusivity in EDM modeling?

Answer 56

Determines how quickly heat spreads in the material (α = k/ρcp).

Question 57

What is the empirical relationship between spark radius and crater radius?

Answer 57

r = 0.3Rf^0.82.

Question 58

What is the significance of the duty cycle (τ) in EDM modeling?

Answer 58

It represents the fraction of active spark time per cycle.

Question 59

What is the non-dimensional erosion energy (Ws) in EDM modeling?

Answer 59

A parameter linking pulse energy to material removal.

Question 60

What is the main difference in material removal mechanisms between anode and cathode in EDM?

Answer 60

Cathode: point-source model (ions); anode: wider craters (electrons).

Question 61

What is the purpose of the "erosion enthalpy" in EDM modeling?

Answer 61

The heat required to melt a unit mass of material.

Question 62

What is the typical range for discharge current in µEDM?

Answer 62

0.1–10 mA.

Question 63

What is the typical voltage range in µEDM?

Answer 63

60–120 V.

Question 64

What is the main advantage of µEDM over conventional EDM?

Answer 64

Higher precision for micro-features.

Question 65

What is the main disadvantage of µEDM?

Answer 65

Very low MRR.

Question 66

What is the typical electrode wear ratio in µEDM?

Answer 66

1.5–100%.

Question 67

What is the main application of µEDM in the biomedical industry?

Answer 67

Micro-scale surgical tools and implants.

Question 68

What is the main difference in flushing between macro-EDM and µEDM?

Answer 68

µEDM often uses no flushing to avoid tool instability.

Question 69

What is the typical material for electrodes in µEDM?

Answer 69

Tungsten.

Question 70

What is the main challenge in deep hole drilling with EDM?

Answer 70

Poor flushing in deep, narrow holes.

Question 71

What is the typical aspect ratio (L/D) achievable in EDM deep hole drilling?

Answer 71

Up to 1:100.

Question 72

What is the purpose of tool rotation in plunge EDM?

Answer 72

To reduce tool wear and improve flushing.

Question 73

What is the main difference between EDM and laser machining in terms of surface state?

Answer 73

EDM leaves a re-solidified layer; laser may leave minimal HAZ.

Question 74

What is the main advantage of EDM over grinding?

Answer 74

No mechanical forces (suitable for brittle materials).

Question 75

What is the main disadvantage of EDM compared to electrochemical machining?

Answer 75

EDM is slower and limited to conductive materials.

Question 76

What is the main application of EDM in the aerospace industry?

Answer 76

Machining titanium/aluminum alloys for complex components.

Question 77

What is the main advantage of EDM in machining hard materials?

Answer 77

Can machine any conductive material regardless of hardness.

Question 78

What is the main limitation of EDM in terms of workpiece materials?

Answer 78

Only conductive materials can be machined.

Question 79

What is the main advantage of EDM in producing sharp edges?

Answer 79

No burrs, sharp edges are naturally produced.

Question 80

What is the main challenge in EDM for high-precision applications?

Answer 80

Managing tool wear and debris in small gaps.