Electric Discharge Machining (EDM) MCQ Quiz in मराठी - Objective Question with Answer for Electric Discharge Machining (EDM) - मोफत PDF डाउनलोड करा

Concept:

The electrode feed rate is the velocity with which the tool moves toward the workpiece 

The electrode feed rate,

f = ξ J

Where J  = Current density​​

J = I/A

\(f =\frac{Δ V}{ρ_s L}×\frac{E}{Fρ} \)

Where L = Gap between tool and workpiece, ρ_s  = Resistivity

Calculation:

Given:

F = 96500 coulomb per mole

\(E = \frac{Atomic \ Weight }{valency}=\frac{56}{2}=28 \ g/mole\)

The specific MRR,

 \(ξ =\frac{E}{Fρ}=\frac{28\ (g/mole)}{96500\ ( C/mole)×7.8 (g/cm^3)}= 3.72×10^{-5} \ cm^3/A.s\)

J = I/A = ΔV/RA = ΔV/ρ_sL   

⇒ ξ  = 3.72 × 10^-5 × 7.2

⇒ ξ  = 2.678 × 10^-4 cm/s

⇒ ξ  = 0.00268 mm/sec

Concept:

\({\rm{Power}} = \frac{{0.5 \times C \times V_d^2}}{t}\)

Calculation:

Given:

Cycle time (t) = 0.7 × 10^-3 sec, Capacitance (C) = 10 μF, Voltage = 150 Volts

Now,

\({\rm{Power}} = \frac{{0.5 \times C \times V_d^2}}{t}\)

\({\rm{Power}} = \frac{{0.5 \times 10 \times {{10}^{ - 6}} \times {{\left( {150} \right)}^2}}}{{0.7 \times {{10}^{ - 3}}}}\)

∴ Power = 0.16 kW

Concept:

The MRR in wire-cut EDM process is given as, MRR = Cross-section of cut(CSA) x Wire feed

MRR = (D + 2x) × t × f

Calculation:

Given:

t = 5 mm, D = 1 mm, x = 0.5 mm, f = 20 mm/min

Concept:

For maximum power dissipation in RC type EDM generator,

V_d^* = 0.72 V₀      ---(1)

So, for maximum power dissipation in RC type EDM generator, total energy discharged through the spark gap,

\(E = \dfrac{1}{2} CV_d^{\star 2}\)     ---(2)

Calculation:

Given:

C = 21 μF, V₀ = 220 V

By using equation (1),

V_d^* = 0.72 × 220 = 158.4 V

By using equation (2),

\(E\; = \dfrac{1}{2} \times 21 \times {10^{ - 6}} \times {158.4^2}\)

⇒ E = 0.263 J

Machining quality of EDM depends upon several pre-built parameters. These parameters control the machining process and can prominently change the output such as production time, surface roughness over cut and dimensional accuracy in addition to the desired removal rate and electrode wear rate. Some of the common input parameters are

Gap Voltage: Potential difference between anode and cathode for a cycle

Peak Current: Maximum current that is used in machining per cycle

Pulse on time: Time duration between two consecutive pulses

Duty cycle: Percentage of pulse on time over sum of pulse on time and pulse off time

Spark gap: Distance between electrode and the workpiece

Flushing pressure: Pressure at which the dielectric is dissipated.

Concept:

The metal removal rate can be related to the melting point approximately by the following empirical formula,

\(MRR=\frac{KI}{T^{1.23}_m}\)

MRR = Material Removal Rate, K = Constant of proportionality whose value is 664 in SI unit, I = Discharge current, T_m = Melting temperature of work metal in °C.

Calculation:

Given:

I = 25 amp, T = 1083°C

\(MRR=\frac{KI}{T^{1.23}_m}=\frac{664 \times 25}{1083^{1.23}}=3.07~\frac{mm^3}{sec}\)

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 which controls spark discharges and is subject 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 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.

Power input \(= \frac{E}{{{t_c}}}\) 

\(E = \left( {energy} \right) = \frac{1}{2}C\cdot V_d^2\)

\({t_c}\left( {cycle\;time} \right) = RC\cdot In\left( {\frac{{{V_o}}}{{{V_o} - {V_d}}}} \right)\)

Given, V_o = 220 V

V_d = 110 V

R = 40 Ω

C = 20 μF

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 subjected to an electric voltage.
• The current used during EDM is Pulsed DC
• 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 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.

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, work piece is connected to positive terminal and tool is connected to 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 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 coolent.