Engineering Questions with Answers - Multiple Choice Questions
Manufacturing Processes – Electro-Chemical Machining – 1
1 - Question
Electro-chemical machining is opposite of electrochemical coating.
Explanation: In electrochemical or galvanic coating, some another material is coated on the workpiece metal; whereas in Electro-chemical machining, material is removed from the workpiece
2 - Question
ECM can also be called as un-controlled anodic dissolution.
Explanation: ECM can be thought of a controlled anodic dissolution at atomic level of the workpiece that is electrically conductive by a shaped tool due to flow of high current at relatively low potential difference through an electrolyte which is quite often water based neutral salt solution.
3 - Question
For ECM of steel which is used as the electrolyte?
c) Deionised water
Explanation: During ECM, there will be reactions occurring at the electrodes i.e. at the anode or workpiece and at the cathode or the tool along with within the electrolyte. For electrochemical machining of steel, generally a neutral salt solution of sodium chloride (NaCl) is taken as the electrolyte.
4 - Question
MRR is ECM depends on _____________
a) hardness of work material
b) atomic weight of work material
c) thermal conductivity of work material
d) ductility of work material
Explanation: In ECM, material removal takes place due to an atomic dissolution of work material. Electrochemical dissolution is governed by Faraday’s laws. Also, for ECM, MRR= IA/(Fρv), where I= current, ρ= density of the material, A= atomic weight, v= valency, F= faraday’s constant.
5 - Question
For which of the following ECM cannot be undertaken?
b) Nickel based superalloy
c) Aluminium oxide
d) Titanium alloy
Explanation: ECM can machine any electrically conductive work material irrespective of their hardness, strength or even thermal properties. In ECM, material is removed from the workpiece by oxidizing it. Aluminium oxide cannot be oxidized further; therefore it cannot be machined by ECM.
6 - Question
Commercial ECM is carried out at a combination of ___________
a) low voltage high current
b) low current low voltage
c) high current high voltage
d) high voltage only
Explanation: As we know, in ECM, MRR= IA/(Fρv), where I= current. Therefore, the amount of electrochemical dissolution or deposition is proportional to the amount of charge passed through the electrochemical cell, i.e. m∝Q, where m = mass of material dissolved or deposited Q = amount of charge passed
7 - Question
In ECM of pure iron a material removal rate of 600 mm3/min is required. What will be the current requirement?
Explanation: MRR= IA/(Fρv) MRR = 600 mm3/min = 600/60 mm3/s = 10 mm3/s = 10×10-3cc/s A= 56, v= 2, F= 96500 coulomb, and ρ = 7.8 gm/cc Therefore, I= (96500*10*10-3*7.8*2)/56 I= 268.8A.
8 - Question
In ECM operation of pure iron an equilibrium gap (h) of 2 mm is to be kept. What will be the supply voltage (v), if the total overvoltage is 2.5 Volts. The resistivity(r) of the electrolyte is 50 Ω-mm and the set feed rate (f) is 0.25 mm/min.
Explanation: h= c/f Where, c= (v- overvoltage)*A/(F*ρ*r*v) Therefore, c= (v-2.5)*56/(96500*7.8*10-3*50*2) c= (v-2.5)/1344.1 Now, h= c/f 2= [(v-2.5)/1344.1]/[0.25/60] Therefore, v= 13.2 volts.
9 - Question
In ECM, workpiece acts as a cathode.
Explanation: In ECM, material is depleted from anode workpiece and transported to a cathode tool in an electrolyte bath. Electrolyte flows rapidly between two poles to carry off depleted material, so it does not plate onto tool.
10 - Question
Electrolyte used in ECM should have _____________
a) high specific heat
b) lower resistance to film formation on the workpiece
c) higher viscosity
d) corrosive nature
Explanation: Desirable properties of the electrolytes are as follows: • High electrical conductivity – for easy ionization • Low viscosity – for easy flow • High specific heat – to carry more heat • Chemical stability – to be chemically neutral or does not disintegrate during the reaction • Resistance to formation of passivating film on the workpiece surface • Non corrosiveness and non-toxicity • Inexpensiveness and easy availability.