This set of Powder Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Tool Materials – Applications of Cemented Carbides”.
1. ______ is the most important application of cemented carbides.
b) Cutting Tools
c) Drilling Tools
d) Deep drawing Tools
Explanation: The most important application of cemented carbides is in the form of tools for metal cutting and machining of abrasive materials because 70% of cemented carbides produced today are used for cutting tools.
2. Which of the following is not a characteristic of cemented carbide cutting tools?
a) Extremely hard
b) Very brittle
c) High red hardness
d) Low red hardness
Explanation: Cemented carbide cutting tools are Extremely hard, possess High red hardness and are very brittle. The cutting speed with the use of carbide-tipped tools is increased six to eight times over that with the customary high-speed steel tools.
3. Cemented carbide cutting tool is advantageous in mass production.
Explanation: Cemented carbide cutting tool is advantageous in mass production owing to their very slow change in shape from wear thereby maintaining close dimensional tolerances with less frequent tool grinding and more rapid removal of workpiece.
4. ________ occurs due to material built-up at the cutting edge.
a) Brazing cracks
b) Comb-type cracks
d) Grinding cracks
Explanation: During the cutting of soft and tough materials, the formation of built-up edge takes place, part or entire of which breaks away periodically and some portion of the cutting edge may also be taken away along with the built-up edge, this leads to deterioration of cutting edge by crumbling.
5. Which of the following is not a cause for failure of the cutting tools?
b) Hair-type cracks
c) Grinding cracks
d) Thermal shocks
Explanation: The causes for the failure of cutting tools are: edge crumbling, comb-type cracks, grinding cracks, thermal shocks, brazing cracks, incorrect tool geometry, inadequate rigidity of the machine tools, oxidation of the cutting edge and bad handling.
6. The phenomenon of ______ occurs by the combination of considerable pressure, high temperature and longer time of contact only within a certain speed range.
a) Brazing cracks
b) Grinding cracks
d) Built-up edge
Explanation: The phenomenon of built-up edge occurs by the combination of considerable pressure, high temperature and longer time of contact only within a certain speed range (mostly at low cutting speed) exceeding which built-up edge tends to become smaller and eventually disappears.
7. The wear due to the indenting action of hot, rough, hard and coiled chips behind the cutting-edge leads to ________
b) Grinding cracks
d) Built-up edge
Explanation: The wear due to the indenting action of hot, rough, hard and coiled chips behind the cutting-edge leads to the formation of grooves or craters. The craters become deeper and deeper as the time of operation is increased and thus the edge of the crater begins to approach the cutting edge more and more. Cratering, due to adhesion or welding, finally leads to edge crumbling thereby interrupting the cutting operation.
8. _______ composition of the carbide cutting tool is suitable for roughing operations.
Explanation: High-Co composition of the carbide cutting tool is suitable for roughing operations, whereas, low-Co compositions are used for light, high-speed machining cuts because of extremely high hardness.
9. High TiC content (25-60%) is used particularly for _________
a) High finish turning and drilling of steel
b) Roughing operation
c) Medium cuts and speeds on steel
d) Rough cuts on Cast iron
Explanation: High TiC content (25-60%) is used particularly for high finish turning and drilling of steel. Cemented TiC grades have also been used for high-speed machining cuts on difficult-to-machine materials.
10. Composite tips, consisting of a thin layer of TiC-Co bonded on a WC-Co grade use is rapidly increasing.
Explanation: Composite tips, consisting of a thin layer of TiC-Co bonded on a WC-Co grade use is rapidly increasing, because the surface layer accords good resistance to wear and cratering and considerable improvement in elevated temperature strength while the base renders good strength, toughness, and higher thermal conductivity.
11. Cemented carbide dies replace diamond dies for hole diameters between _______
a) 0.004-0.04 inch
b) 0.04-0.4 inch
c) 0.4-0.9 inch
d) 0.004-0.1 inch
Explanation: For fine drawing (i.e. for sections below 0.004 inch) diamond dies are superior, but for drawing of larger sections, i.e. for hole diameters between 0.04-0.4-inch, cemented carbide dies replace diamond dies because diamond dies fail due to inadequate compressive strength.
12. High-pressure nozzle made of cemented carbides are used in ________ industry.
b) Sheet processing
Explanation: High-pressure nozzle made of cemented carbides are used in the chemical industry. Extruding, compacting, and sizing tools made of cemented carbide are used in the sheet processing industry. In the textile industry, thread guides and mattress needled are made of cemented carbide. Drilling tools made of cemented carbide are used in the mining industry.
13. __________ are widely used as projectile cores for armor piercing weapons.
a) Sintered friction material
c) Cemented carbide
d) Dispersion strengthened material
Explanation: Cemented carbide are widely used as projectile cores forarmor piercing weapons and also find use in high precision measuring instruments such as micrometer calipers, in hardness testers such as cemented carbide balls and pyramid indentors.
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