This set of Basic Forming Questions and Answers focuses on “Advantage and Disadvantage of Hot and Cold Forming”.
1. Materials like lead (Pb) and tin (Sn) can be hot worked at room temperature.
a) True
b) False
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Explanation: Hot working or hot forming of materials is normally performed at the temperature above than its re-crystallization temperature, but for materials like lead (Pb) and tin (Sn), the hot working can be done at room temperature because these materials possess very low crystallization temperature.
2. Hot working of brittle materials is not possible as they do not show yielding behaviour.
a) True
b) False
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Explanation: At high temperature, the materials generally have great amount of ductility and so there is no limit or restriction on the amount of hot working that can be performed on a metal. Hence, even the brittle materials can be used for the hot working. In hot working, the grain structure of material is refined which enhances the mechanical properties of material.
3. In the hot working of materials, porosity may increase in the material rather than decrease.
a) True
b) False
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Explanation: In the hot working of materials, the porosity always decreases and reaches to negligible amount in the material. The high temperature of the material makes dynamic changes in the material and the gases entrapped in the material loses out and vapourized due to the high temperature of material. This minimizes the amount of porosity in the material.
4. Hot working does not affect the properties like tensile strength, hardness etc. when the process is performed properly.
a) True
b) False
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Explanation: When the hot working process is properly carried out, then hot work does not affect the mechanical properties like tensile strength, hardness, corrosion resistance, etc. The shear stress is reduced at the higher temperature, so this process does not require much force to obtain the desired deformation, due to this properties remains same.
5. In hot working of material, the continuous reformation of grains can be possible in material.
a) True
b) False
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Explanation: In hot working of materials, it is possible to continuously reform the grains in material. It requires proper controlling of temperature and rate of hot working. In hot working, very favourable grain size can be obtained which further enhances the mechanical properties of material. And no any residual stresses are present in the material during hot working which also gives rise to better mechanical properties.
6. In cold working, larger deformation can be obtained more rapidly than that obtained by the hot working.
a) True
b) False
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Explanation: The mechanical properties, elongation and izod values are enhanced in the hot working of materials. In hot working, the other properties like directional properties and fibre are also produced in the material which helps in achieving the larger deformation more rapidly than that obtained by the cold working, as the material is present in the plastic state.
7. The surface finish obtained by cold working is better than that achieved by the hot working of material.
a) True
b) False
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Explanation: In the hot working of metals, rapid oxidation or scale formation and surface de-carburization processes occur on the surface of metal due to the presence of high temperature. This results in a poor surface finish of the metal and the metal loss too. But in cold working, the temperature is kept moderate which maintains the better surface finish of the metal.
8. In the hot working of steel material, steel metal may lose its strength due to carbon loss.
a) True
b) False
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Explanation: In the hot working of steel material, the carbon content can be disturbed; means the carbon loss can occur from the surface of steel metal which leads to losing of its strength. This is a major drawback which can also weaken the surface layer that gives rise to fatigue crack which may further result in complete failure of the metal component.
9. The hot working process is mainly used for achieving the high dimensional accuracy of the metal.
a) True
b) False
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Explanation: In the hot working of metal components, the temperature is very high, which is more than the re-crystallization temperature of the metal. This high temperature leads to high thermal expansion of the metal component. This expansion varies the shape and size of the metal, so the dimensional accuracy of the metal component cannot be achieved by hot working.
10. The cold working of material facilitates its cutting operation due to a decrease in its ductility.
a) True
b) False
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Explanation: In the cold working of material, the material is deformed plastically which increases the strain hardening. This further increases its strength by losing its ductility; the loss of ductility is useful in machining operation. The breaking of chips becomes much easier due to less ductility, which further facilitates the cutting operation of material.
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