This set of Manufacturing Processes Multiple Choice Questions & Answers (MCQs) focuses on “Electrochemical Grinding”.
1. In electro-chemical grinding, grinding wheel is used as a cathode.
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.
2. ECG is suitable for which of the following materials?
a) Tungsten carbide
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.
3. 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.
4. As compared to electrochemical machining (ECM), ECG consumes less power.
Explanation: Power required for ECG is less than for ECM since the machining area is smaller and the abrasive grinding wheel removes the oxide film, thus preventing the excess use of chemical/electrolyte.
5. 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.
6. In ECG, rate of formation of oxide film is faster than that in ECM.
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.
7. 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.
8. Which of the following is true for ECG?
a) Higher the grinding wheel rpm, higher is the MRR
b) Higher the current density, faster the removal rate
c) Stronger the electrolyte, poor surface finish
d) Higher the hardness of the workpiece, lower the current density required
Explanation: The removal rate for ECG is governed by the current density, just as in ECM: as with ECM, the higher the current density, the faster the removal rate and better the resulting surface finish.
9. Feed rates in ECG vary with a grinding method.
Explanation: In ECG. Feed rates vary with different parameters, depending on the grinding method: if the feed rate is running too slowly for the application, a large overcut will be produced that will result in poor surface finishes and tolerances and if the feed rate is too fast, the abrasive particles will be prematurely forced in too the workpiece, resulting in excessive wheel wear.
10. Which of the following is true about ECG?
a) Lower MRRs when grinding hard, heat sensitive materials
b) Machining of soft metals like aluminium can be easily done
c) Difficult to machine materials with high hardness like tungsten carbide
d) Burr-free sharpening of needles
Explanation: Applications of ECG are as follows;
(1) Single largest use for ECG is in the manufacturing and remanufacturing of turbine blades and vanes for aircraft turbine engines
(2) Grinding of tungsten carbide tool inserts
(3) Re-profiling worn locomotive traction motor gears
(4) Burr-free sharpening of hypodermic needles
(5) Grinding of surgical needles, other thin wall tubes, and fragile parts
(6) Machining of fragile or very hard and tough material – honey comb, thin walled tubes and skins
(7) High MRR’s when grinding hard, tough, stringy, work-hardenable or heat sensitive materials.
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