1 The die used in electromagnetic process should be made of material with _________________
a) high electrical conductivity
b) low electical conductivity
c) low ductility
d) high creep resistance
Explanation: The die used in the electromagnetic process should be made of low electrical conductivity to minimize the magnetic cushion effect. Dies are generally made of steel or epoxy resin.
2. The EMF process allows increased ductility for______________ alloys.
a) Chromium – molybdenum
b) aluminium
c) nickel
d) chromium – mangnese
Explanation: The EMF process allows increased ductility for certain aluminium alloys because of the lack of mechanical stress and friction normally encountered with mechanical processes.
3. Tooling for EMF process is relatively inexpensive.
a) True
b) False
Explanation: The machine and the work coils required in EMF process can be viewed as general-purpose tooling. Therefore it can be said that the tooling for this process is inexpensive.
4. EMF is primarily used for which of the following material?
a) Silver
b) High carbon steel
c) Chromium alloys
d) Martensitic steel
Explanation: This process is primarily applied in the forming of good conducting materials such as copper, aluminium, silver and low carbon steel. It can also be used to form a poor conductor like stainless steel.
5. In electro-chemical grinding, grinding wheel is used as a cathode.
a) True
b) False
Explanation: ECG is similar to electro-chemical machining, only difference is the abrasive grinding wheel is used as a cathode instead of a tool shaped like the contour to be machined.
6. ECG is suitable for which of the following materials?
a) Tungsten carbide
b) Polymers
c) Iron
d) Nickel
Explanation: ECG is used primarily to machine difficult to cut alloys such as stainless steel, hastelloy, inconel, monel, waspally and tungsten carbide, heat treated workpieces, fragile or therm-sensitive parts, or parts for which stress-free and burr free results are required.
7. In ECG, grinding action removes ____________
a) workpiece material from the surface
b) corroded surface layer making workpiece ready for electro-chemical process
c) oxide film formed on the surface
d) particles removed from surface after chemical action
Explanation: ECG removes metal by combination of electro-chemical and grinding actions. The grinding action removes the buildup of oxide film on the surface of the workpiece
8. Nozzles are used to _____________
a) spray coolant on the wheel
b) ensure proper wetting of the wheel
c) spray chemical directly on the work piece
d) nozzles are not used in ECG
Explanation: Nozzles are used to ensure proper wetting action of the wheel. Nozzle creates a partial vacuum and causes the electrolyte to be sucked up, filling the cavities around the grit. The rotation of the wheel carries the electrolyte into the area of contact.
9. In ECG, rate of formation of oxide film is faster than that in ECM.
a) True
b) False
Explanation: The electrolyte used in ECG is designed to enable faster formation of oxide films on the workpiece, whereas in ECM, the oxide film must dissolve at once in the electrolyte.
10. Electrolyte in ECG should provide _____________
a) lower chemical activity
b) allowance to stray currents
c) high stock removal efficiency
d) higher corrosion tendency
Explanation: Desirable electrolyte should provide: high conductivity, high stock removal efficiency, passivation to limit stray currents, good surface finishes and corrosion inhibition.