Powder Metallurgy Multiple Choice Questions & Answers on “Postsintering Secondary Operations – Steam Treatment, Machining, Joining & Plating – 2”.
1. Which of the following additive is added to improve the tool life of steel parts?
a) Copper
b) Bismuth
c) Lead
d) Sulphur
Answer: d
Clarification: The machinability can be improved by incorporating certain additions in powder mix like lead, copper, graphite, sulphur or a metal sulphide. Sulphur is added to improve the tool life and surface finish of P/M steel parts by mixing it in powder compact.
2. What is added to brass to improve the machining of parts made by brass?
a) Copper
b) Lead
c) Bismuth
d) Tin
Answer: b
Clarification: The addition of lead to brass improves the machining of the parts made by brass. These additions are incorporated to improve machinability, as these additives tend to coat the cutting tool and provide lubrication.
3. Which kind of porosity leads to longer tool life?
a) Very high
b) Very low
c) Either very high or very low
d) Moderate
Answer: c
Clarification: Longer tool life is achieved when the porosity is either very high or very low because the material hardness and residual porosity also affect the tool life. For very low-density parts, tool life may be improved by infiltrating the pores with a low-melting metal before machining.
4. Which of the following tool control systems is now widely used?
a) Multi-axis computer-controlled tool control system
b) Multi-lines computer-controlled tool control system
c) Multi-plane computer-controlled tool control system
d) Multi-surface computer-controlled tool control system
Answer: a
Clarification: The Multi-axis computer-controlled tool control system is now recently used tool control system which enables high-precision fabrication of P/M parts free from cracks and machining of components with the most intricate geometry.
5. Which of the following process is used for removing any ‘rag’ on edges?
a) Derigging
b) Defragging
c) Deluding
d) Deburring
Answer: d
Clarification: Deburring is a process done with sintered parts for removing any ‘rag’ on edges, resulting from the compacting operation or a machining step.
6. Which of the following metal joining process is not applicable for P/M parts?
a) GTAW
b) Extrusion welding
c) Friction welding
d) Laser beam welding
Answer: b
Clarification: The major metal joining processes applicable for P/M parts include resistance projection welding, gas tungsten arc welding (GTAW), gas metal arc welding, electron beam welding, laser beam welding and friction welding.
7. Electrical resistance welding is preferred over oxyacetylene and arc welding for joining P/M parts.
a) True
b) False
Answer: a
Clarification: Electrical resistance welding is preferred over oxyacetylene and arc welding for joining P/M parts. This is done to avoid the possibility of oxidation of the interiors of the porous P/M parts by oxyacetylene and arc welding processes.
8. Porous parts must be resin impregnated before plating.
a) True
b) False
Answer: a
Clarification: The porous parts must be resin impregnated prior to plating to seal the micro pores to protect from invasion and entrapment. Resin impregnation discards porosity and bleedout.