This set of Forming Questions and Answers for Campus interviews focuses on “Friction and Lubrication in Metal Forming”.
1. The main function of the lubricant is to reduce the tensile or compressive stresses required in metal forming.
a) True
b) False
View Answer
Explanation: The main function of the lubricant is to control the frictional force that arises due to sliding contact between the sheet metal and cutting tool material during sheet metal forming operation. Lubricants are also used to prevent galling problems by protecting tool material from direct contact with the sheet material.
2. In lubrication, the boundary layer formed consists of long chain hydrocarbons with a polar head.
a) True
b) False
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Explanation: In lubrication, the performance of boundary layers and its formation basically depends on its physical and chemical adsorption. The boundary layers formed by a mechanism mainly consist of clusters and long chain hydrocarbons with a polar head. Then this polar group adheres to the surface and forms high viscosity hydrocarbon layers.
3. In the case of un-reactive contacting surfaces, the fatty acids adheres by chemical reaction during lubrication.
a) True
b) False
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Explanation: In lubrication, the hydrocarbon layers are meant to reduce the friction and wear under loading conditions. In the case of un-reactive contacting surfaces, the fatty acids only adhere by physical adsorption. For the reactive metal surfaces, the mechanism of chemical adsorption is likely to occur, which combines both the physical and chemical adsorption.
4. Boundary layers formed by chemical adsorption using additives are also called as friction modifiers.
a) True
b) False
View Answer
Explanation: In the lubrication of metal surfaces, the additives are used to form boundary layers by a mechanism of chemical adsorption. These boundary layers are also known as friction modifiers. In general, the additives used can be fatty acids, ester, or fatty amides. The boundary layer is highly resistant to contact temperature and therefore it can be used for wear and friction reduction.
5. Temperature cannot affect the friction and lubrication present during the metal forming.
a) True
b) False
View Answer
Explanation: Friction and lubrication in metal forming are greatly influenced by parameters such as temperature, mechanical properties, surface finish, sliding velocity, pressure etc. In general, the viscosity of lubricant decreases with the increase in temperature and vice-versa. And friction becomes more vigorous when the temperature is very high during the metal forming operation.
6. Strip drawing test is a method which is mainly used for evaluating the characteristics of lubricants.
a) True
b) False
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Explanation: In strip drawing test method, a strip is used which drawn between two opposite plane dies that are wider than the strip. The amount of stretching strip can change the coefficient of friction. And the test is usually performed with different speeds and different radius of the die. This test is widely used for evaluating the characteristics of lubricants which used during the process of metal forming.
7. The flow of material in die cavity solely depends on the flow-ability of material.
a) True
b) False
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Explanation: The flow of material in die cavity not only depends on the flow-ability of material, it also depends on the frictional conditions at the die and material interface. Therefore, a proper study of parameters that affect the friction is required for selecting suitable lubricants for the operation and producing better quality of metal parts.
8. The lubrication is not required when the formability of material is sufficiently large in metal forming.
a) True
b) False
View Answer
Explanation: A dry condition (no lubricant) is mainly used when the material formability is sufficiently large to form desired metal part with simple geometry. In this case, the friction is very high as no any lubricant is used during the operation, but this friction does not significantly affect the metal part quality. A dry condition is usually suitable for hot rolling forming processes.
9. Semi-synthetic fluid is a type of lubricant which is generally insoluble in water.
a) True
b) False
View Answer
Explanation: Lubricant is a material that is mainly used for reducing friction and for cooling purposes. For example, oils, soluble oils, synthetic and semi-synthetic fluids are widely used in metal forming processes. Semi-synthetic fluid is a kind of lubricant which easily mixed with water to form a fine lubricant because it includes small quantity of mineral oil, usually less than 30% of the total concentrate volume.
10. Additives can be added in a lubricant to enhance its performance during metal forming operations.
a) True
b) False
View Answer
Explanation: In metal forming process, several types of additives are mixed with lubricant to enhance the performance of the lubricant. The extreme pressure (EP) additives are generally used in heavy work metal operations. The temperature dependent EP additives, such as chlorine, phosphorus, and sulphur are mainly used to create chemical films that prevent metal to metal contact during forming operations.
Sanfoundry Global Education & Learning Series – Casting, Forming and Welding.
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