Electric Discharge Machining (EDM) MCQ Quiz - Objective Question with Answer for Electric Discharge Machining (EDM) - Download Free PDF

Explanation:

Maximum Material Removal Rate (MRR) in EDM Process

• In Electrical Discharge Machining (EDM), the Material Removal Rate (MRR) is defined as the volume of material removed from the workpiece per unit time during the machining process. It is an essential parameter for evaluating the efficiency of the EDM process. The MRR depends on several factors, including the discharge energy, pulse current, pulse duration, and properties of the workpiece material.
• EDM is a non-conventional machining process where material removal occurs due to the erosive effect of electrical discharges (sparks) between the tool electrode and the workpiece. These discharges generate intense localized heat, which melts and vaporizes the material. The molten material is then flushed away by a dielectric fluid.
• The maximum MRR in the EDM process is influenced by the energy per spark, which is determined by the pulse current, pulse duration, and voltage. The higher the energy per spark, the greater the material removal. However, excessive energy can lead to poor surface finish and damage to the tool electrode. Under optimal conditions, the maximum MRR in EDM is approximately 5000 mm³/min.

Factors Affecting MRR in EDM:

• Discharge Energy: Higher discharge energy increases the MRR but may compromise surface quality.
• Pulse Current: Increasing the pulse current enhances the spark energy, leading to higher MRR.
• Pulse Duration: Longer pulse durations result in more material removal per discharge but can affect precision.
• Material Properties: The MRR varies depending on the thermal conductivity, melting point, and electrical resistivity of the workpiece material.
• Dielectric Fluid: The type and flow of the dielectric fluid affect the flushing of debris and influence the MRR.

Explanation:

Material Removal Rate (MRR) in EDM Process:

• In Electrical Discharge Machining (EDM), the Material Removal Rate (MRR) refers to the volume of material removed from the workpiece per unit time. It is a critical performance parameter as it directly affects the productivity and efficiency of the machining process. The RC relaxation circuit is one of the types of circuits used in EDM to control the discharge energy by regulating the resistance and capacitance in the circuit.

Working Principle of RC Relaxation Circuit in EDM:

• In the RC relaxation circuit, a capacitor is charged to a certain voltage through a resistor. Once the voltage across the capacitor reaches a predetermined threshold value, it discharges through the gap between the tool and the workpiece, creating a spark. This spark generates intense heat, which melts and vaporizes a small portion of the workpiece material, resulting in material removal. The process then repeats as the capacitor recharges.

In the RC relaxation circuit, the resistance (R) plays a crucial role in determining the time constant of the charging cycle. The time constant (τ) of the circuit is given by:

τ = R × C

Where:

• R is the resistance in the circuit.
• C is the capacitance in the circuit.

When the resistance (R) is increased, the time constant (τ) becomes larger. This means that the capacitor takes more time to charge to the required voltage level. Consequently, the frequency of discharges decreases, resulting in fewer sparks per unit time. Since MRR is directly proportional to the number of sparks generated per unit time, an increase in resistance reduces the MRR.

Explanation:

Electro-Discharge Machining (EDM):

• Electrical Discharge Machining (EDM) is a manufacturing process whereby a desired shape is obtained by using electrical discharges (sparks). 
• Material is removed from the work-piece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid which controls spark discharges and subject to an electric voltage.
• In EDM, the workpiece is connected to positive terminal and tool is connected to the negative terminal.
• EDM has the lowest specific power requirement and can achieve sufficient accuracy.

Dielectric fluid 

The dielectric fluids used in EDM process is required to perform the following functions:

1. To act as a coolant between the tool and the work-piece.
2. To act as a conducting medium when ionised and allow the spark to pass from tool to work-piece.
3. To act as a quenching medium for the spark.
4. To act as a flushing medium to carry away the vaporised machined par- ticles.

The dielectric fluid should possess the following properties for efficient electro- discharge machining process:

1. It is essential for the fluid to have high dielectric strength to remain electrically non-conducting untill the break-down voltage is reached.
2. The characteristics of the dielectric fluid should be such as to be able to de- ionize rapidly after discharging and make it an effective insulating medium for next discharging cycle.
3. The dielectric fluid must be inexpensive and chemically non-reactive to the tool, work-piece and the plant equipment.
4. It must not evolve toxic vapours or gases during operation.
5. The dielectric fluid should possess low viscosity to be able to carry away the machined particles from the spark-gap.

The dielectric fluids normally used in EDM process are liquid hydrocarbon prod- ucts such as paraffin, light transformer oil, white spirit, kerosene and de-ionized water.

Explanation:

Electro-Discharge Machining (EDM):

• Electrical Discharge Machining (EDM) is a manufacturing process whereby a desired shape is obtained by using electrical discharges (sparks). 
• Material is removed from the workpiece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid that controls spark discharges and is subjected to an electric voltage.
• In EDM, the workpiece is connected to the positive terminal, and the tool is connected to the negative terminal.
• EDM machines are equipped with a servo control mechanism that automatically maintains a constant gap of approximately 0.02 to 0.05 mm between the tool and workpiece.
• EDM has the lowest specific power requirement and can achieve sufficient accuracy.

• The accuracy and surface finish which are dependent on the overcut produced can be easily controlled by varying the frequency and current. The over cut is increased by increasing current and by decreasing frequency.
• For optimum metal removal and better surface finish, high frequency and maximum possible current are used.
• For roughing operation, low frequency and high current are used and for finishing application, high frequency and low current settings are used.
• In EDM a fluid is used to act as a dielectric and to help carry away debris.
• Quite often kerosene-based oil is used as dielectric in EDM.
• The dielectric fluid is circulated through the tool at a pressure of 0.35 N/m2 or less to free it from eroded metal particles, it is circulated through a filter and acts as a coolant.

Explanation:

Electrical discharge machining (EDM) is a manufacturing process whereby a desired shape is obtained by using electrical discharges (sparks). Material is removed from the workpiece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid and subject to an electric voltage.

EDM has the lowest specific power requirement and can achieve sufficient accuracy.

Prime requirements EDM tool Material

1. It should be electrically conductive.

2. It should have good machinability, thus allowing easy manufacture of complex shapes.

3. It should have a low erosion rate or good work-to-tool wear ratio.

4. It should have low electrical resistance.

5. It should have a high melting point.

6. It should have high electron emission

The usual choices for tool (electrode) materials are

Copper, brass, alloys of zinc and tin, hardened plain carbon steel, copper graphite, and graphite, etc.

Explanation:

Electro-Discharge Machining (EDM):

• Electrical Discharge Machining (EDM) is a manufacturing process whereby a desired shape is obtained by using electrical discharges (sparks). 
• Material is removed from the work-piece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid which controls spark discharges and subject to an electric voltage.
• In EDM, the workpiece is connected to positive terminal and tool is connected to the negative terminal.
• EDM has the lowest specific power requirement and can achieve sufficient accuracy.

• The accuracy and surface finish which are dependent on the overcut produced can be easily controlled by varying the frequency and current. The over cut is increased by increasing current and by decreasing frequency.
• For optimum metal removal and better surface finish, high frequency and maximum possible current is used.
• For roughing operation, low frequency and high current are used and for finishing application, high frequency and low current settings are used.
• In EDM a fluid is used to act as a dielectric and to help carry away debris.
• Quite often kerosene-based oil is used as dielectric in EDM.
• The dielectric fluid is circulated through the tool at a pressure of 0.35 N/m2 or less to free it from eroded metal particles, it is circulated through a filter and acts as a coolant.

• Only electrically conducting material can be machined by EDM like steel, cast iron, Titanium and some other metals.

Explanation:

Electro-Discharge Machining (EDM):

• Electrical Discharge Machining (EDM) is a manufacturing process whereby a desired shape is obtained by using electrical discharges (sparks). 
• Material is removed from the workpiece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid that controls spark discharges and is subjected to an electric voltage.
• In EDM, the workpiece is connected to the positive terminal, and the tool is connected to the negative terminal.
• EDM machines are equipped with a servo control mechanism that automatically maintains a constant gap of approximately 0.02 to 0.05 mm between the tool and workpiece.
• EDM has the lowest specific power requirement and can achieve sufficient accuracy.

• The accuracy and surface finish which are dependent on the overcut produced can be easily controlled by varying the frequency and current. The over cut is increased by increasing current and by decreasing frequency.
• For optimum metal removal and better surface finish, high frequency and maximum possible current are used.
• For roughing operation, low frequency and high current are used and for finishing application, high frequency and low current settings are used.
• In EDM a fluid is used to act as a dielectric and to help carry away debris.
• Quite often kerosene-based oil is used as dielectric in EDM.
• The dielectric fluid is circulated through the tool at a pressure of 0.35 N/m2 or less to free it from eroded metal particles, it is circulated through a filter and acts as a coolant.

Explanation:

Some of the non-conventional machining processes and their shape applications are explained below:

Concept:

\(Duty\ factor = \frac{Pulse \ on \ time}{Total\ time}\)

Calculation:

Given:

Frequency (f) = 10 kHz, Pulse off-time = 40 μs

\(Total \ time =\frac{1}{10\ \times10^3 }\) s

Total time = 100 μs

Pulse on time = Total Time - Pulse off-time

Pulse on time = 100 - 40 = 60 μs

\(Duty\ factor = \frac{Pulse \ on \ time}{Total\ time}\)

\(Duty\ factor = \frac{60}{100}\)

Duty factor = 0.6

Explanation:

EDM process is summarized as :

• With the application of voltage, an electric field build-up between the two electrodes at the position of least resistance. The ionization leads to the breakdown of the dielectric which results in the drop of voltage and the beginning of the flow of current.
• Electrons and ions migrate to anode and cathode respectively at very high current density. A column of vapour begins to form and the localized melting of work commences. The discharge channel continues to expand along with the substantial increase of temperature and pressure.
• When the power is switched off, the current drops; no further heat is generated, and the discharge column collapses. A portion of molten metal evaporates explosively and/or is ejected away from the electrode surface. With the sudden drop in temperature, the remaining molten and vaporized metal solidifies. A tiny crater is thus generated at the surface.
• The residual debris is flushed away along with products of decomposition of dielectric fluid. The application of voltage initiates the next pulse and the cycle of events.

Hence for the above procedure, it is necessary that wire and sample are electrically conducting.

Explanation:

Electro-Discharge Machining (EDM):

• Electrical Discharge Machining (EDM) is a manufacturing process whereby a desired shape is obtained by using electrical discharges (sparks). 
• Material is removed from the work-piece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid which controls spark discharges and subject to an electric voltage.
• In EDM, the workpiece is connected to positive terminal and tool is connected to the negative terminal.
• EDM has the lowest specific power requirement and can achieve sufficient accuracy.

• The accuracy and surface finish which are dependent on the overcut produced can be easily controlled by varying the frequency and current. The over cut is increased by increasing current and by decreasing frequency.
• For optimum metal removal and better surface finish, high frequency and maximum possible current is used.
• For roughing operation, low frequency and high current are used and for finishing application, high frequency and low current settings are used.
• In EDM a fluid is used to act as a dielectric and to help carry away debris.
• Quite often kerosene-based oil is used as dielectric in EDM.
• The dielectric fluid is circulated through the tool at a pressure of 0.35 N/m2 or less to free it from eroded metal particles, it is circulated through a filter and acts as a coolant.

• Only electrically conducting material can be machined by EDM like steel, cast iron, Titanium and some other metals.

Computer chip → Photochemical Machining

Metal forming dies and modes → Electrodischarge Machining

Turbine blade → Electrochemical Machining

Glass → Ultrasonic Machining

Explanation:

The unconventional machining process and its characteristics and the application areas are discussed in the table below:

Explanation:

Electro-Discharge Machining (EDM):

• Electrical Discharge Machining (EDM) is a manufacturing process whereby a desired shape is obtained by using electrical discharges (sparks). 
• Material is removed from the workpiece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid that controls spark discharges and is subjected to an electric voltage.
• In EDM, the workpiece is connected to the positive terminal, and the tool is connected to the negative terminal.
• EDM has the lowest specific power requirement and can achieve sufficient accuracy.

• The accuracy and surface finish which are dependent on the overcut produced can be easily controlled by varying the frequency and current. The overcut is increased by increasing current and by decreasing frequency.
• For optimum metal removal and better surface finish, high frequency and maximum possible current are used.
• For roughing operation, low frequency and high current are used and for finishing application, high frequency and low current settings are used.
• In EDM a fluid is used to act as a dielectric and to help carry away debris.
• Quite often kerosene-based oil is used as dielectric in EDM.
• The dielectric fluid is circulated through the tool at a pressure of 0.35 N/m2 or less to free it from eroded metal particles, it is circulated through a filter and acts as a coolant.

Explanation:

Electro-Discharge Machining (EDM):

• Electrical Discharge Machining (EDM) is a manufacturing process whereby a desired shape is obtained by using electrical discharges (sparks). 
• Material is removed from the workpiece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid that controls spark discharges and subjected to an electric voltage and that's why it has high MRR.
• MRR is affected by
  • Current
  • Voltage
  • Pulse on time / Frequency
  • The melting point of work material
  • Thermal conductivity of work material
• ​MRR increases with an increase in all the above-mentioned parameters except for the melting point of the workpiece.
• In EDM, the workpiece is connected to the positive terminal, and the tool is connected to the negative terminal.
• EDM has the lowest specific power requirement and can achieve sufficient accuracy.

• The accuracy and surface finish which are dependent on the over-cut produced can be easily controlled by varying the frequency and current. The over-cut is increased by increasing current and by decreasing frequency.
• For optimum metal removal and better surface finish, high frequency and maximum possible current are used.
• For roughing operation, low frequency and high current are used and for finishing application, high frequency and low current settings are used.
• In EDM a fluid is used to act as a dielectric and to help carry away debris.
• Quite often kerosene-based oil is used as dielectric in EDM.
• The dielectric fluid is circulated through the tool at a pressure of 0.35 N/m2 or less to free it from eroded metal particles, it is circulated through a filter and acts as a coolant.​