This set of Manufacturing Processes Multiple Choice Questions & Answers (MCQs) focuses on “Electro-Chemical Machining – 2”.
1. Which of the following holds true about electro-chemical machining?
a) Material is removed from the cathode and deposited on the anode
b) Material is removed from the anode and carried away by the electrolyte
c) Major drawback is that the finished product has residual stresses
d) It can also be used for all non-metals
Explanation: In ECM, material is depleted from anode workpiece (positive pole) and transported to a cathode tool (negative pole) in an electrolyte bath, but instead of depositing it on cathode, it is carried away by the electrolyte which flows rapidly between two poles.
2. ECM process is based on which of the following laws?
a) Coulomb’s law
b) Faraday’s law
c) Law of definite proportions
d) Law of chemical combination
Explanation: that if two electrodes are placed in a bath containing a conducting liquid and a DC potential is applied across them, then metal can be depleted from the anode and plated on the cathode – process universally used in electroplating by making the workpiece the cathode. In ECM, the material is removed and hence the workpiece is made the anode.
3. Which of the following conditions are desirable for ECM?
a) High value DC and low value electric potential
b) Low value DC and high value electric potential
c) High value DC and high value electric potential
d) Low value DC and low value electric potential
Explanation: In ECM, high value DC (may be as high as 40,000A) and a low value of electric potential (in the range of 5-25V) across the IEG is desirable.
4. In ECM, material removal rate does not depend on chemical properties of the anode material.
Explanation: Only electrically conductive workpieces can be machined by ECM process. In this process workpiece material work as an anode, therefore the chemical properties of the anode material largely govern the MRR.
5. Which of the following materials can be used for making work holding devices?
c) Graphite fibres
Explanation: Work holding devices are made of electrically non-conductive materials having good thermal stability, and low moisture absorption properties. For example, graphite fibres-reinforced plastics, plastics, perspex, etc.
6. In ECM, shape of the cathode does not affect the shape of the machined product.
Explanation: In ECM, workpiece is used as an anode and cathode is made up of some conducting materials like aluminium, copper, brass, titanium, etc. In this process, product gets the shape which is inverse as that of the tool (cathode).
7. Which of the following is true about ECM process?
a) Unable to machine high strength materials
b) Excessive tool wear
c) It gives burr free surface
d) Surface hardness of the workpiece gets reduced
Explanation: Following are the advantages of ECM process;
• Can be used to machine complex cavities in high strength material
• Applications in aerospace industry, jet engines parts and nozzles
• ECM process gives a burr free surface
• No thermal damage
• Lack of tool forces prevents distortion of the part
• No tool wear.
8. Tool used in ECM should have higher rigidity.
Explanation: In ECM, rigidity of the tool construction and material is important because the high pressure can cause deflection of the tool. Therefore, materials like copper-tungsten, titanium, cupro-nickel, stainless steel, etc. are used for making tools.
9. The tool in ECM should have which of the following properties?
a) High machinability
b) Lower corrosion rate
c) High softness
d) High conductive resistance
Explanation: Tool material should have following properties:
• High electrical and thermal conductivity
• Good stiffness
• High machinability- particularly important if complex shaped tools are required
• High corrosion resistance- to protect itself from corrosive electrolytes
• High rigidity.
10. For ECM, tool dimensions are different from the actual mirror dimensions of the part to be machined.
Explanation: In ECN, tool dimensions must be slightly different from the nominal mirror dimensions of the completed part to allow for ECM overcut. Designer must also determine the nature and the extent of the required deviation or gap allowances from the mirror image configuration, while providing a uniform and sufficiently high flow rate of electrolyte in the gap to allow a practical MRR.
Sanfoundry Global Education & Learning Series – Manufacturing Processes.
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