This set of Manufacturing Processes Multiple Choice Questions & Answers (MCQs) focuses on “Electromagnetic Forming”.
1. Which of the following is not used in electromagnetic forming process?
a) A capacitor bank
b) A forming coil
c) A foeld shaper
d) Stiffening ribs
Explanation: The EMF process uses a capacitor bank, a forming coil, a field shaper, and an electrically conductive workpiece to create intense magnetic fields that are used to do the useful work.
2. Which of the following is true about EMF process?
a) Intense electric field is produced using capacitors and coils
b) Heavy current is made to flow through the workpiece
c) Intense magnetic field is produced for few microseconds
d) Principle of electromagnetic induction is used to pre-heat the workpiece
Explanation: In EMF process, very intense magnetic field is produced by the discharge of capacitor bank into a forming coil, which lasts for only a few microseconds.
3. In EMF process, eddy currents are induced in a conductive workpiece.
Explanation: In EMF process, eddy currents are induced in the workpiece which is placed close to the coil. When these eddy currents interact with the magnetic field, cause mutual repulsion between the workpiece and the forming coil due to which workpiece is stressed beyond its yield strength, resulting in permanent deformation.
4. In EMF process, forming pulse rate is kept as high as possible
Explanation: As the workpiece surface moves inward under the influence of the pressure generated by the repulsive force, it absorbs energy from the magnetic field. To apply most of this available energy to forming, and to reduce energy loss due to permeation of the workpiece material, the forming pulse is kept short. In most forming aplications, pulses have a duration between 10 to 100 seconds.
5. For EMF process, resistivity of the workpiece material should be _____________
a) greater than 10 micro-ohm-cm
b) less than 8 micro-ohm-cm
c) less than 15 micro-ohm-cm
d) in the range 10-20 micro-ohm-cm
Explanation: The efficiency of the magnetic pulse forming depends upon the resistivity of the metal being formed. For good results, the resistivity of the material should be less than 15 micro-ohm-cm.
6. Which of the following is not true about EMF?
a) Leaves tool marks
b) Does not require lubrication
c) Does not require any cleanup
d) It is primarily applied in the forming of good conducting materials
Explanation: In EMF pressure is applied by a magnetic field, unlike other mechanical processes in which a tool contacts a workpiece. Therefore, it requires no lubrication, leaves no tool marks and requires no cleanup after forming.
7. Springback effect of the workpiece material is eliminated in EMF process.
Explanation: In EMF, the material is loaded into its plastic region, resulting in permanent deformation, so that the springback associated with mechanical processes is vertually eliminated because there is no mechanical contact.
8. The maximum pressure applied by the compression coil is approximately _______________
a) 300 MPa
b) 340 MPa
c) 375 MPa
d) 400 MPa
Explanation: The maximum pressure that can be applied by standard compression coils is approximately 340 MPa, thus process is restricted to a relatively thin-wall tube or sheet products.
9. Electromagnetic forming is rarely used to form tubular shapes.
Explanation: Electromagnetic forming is chiefly used to expand, compress, or form tubular shapes. It is occasionally used to form flat sheet, and it is often used to combine several forming and assembly operations into a single step.
10. The die used in electromagnetic process should be made of material with _________________
a) high electrical conductivity
b) low electical conductivity
c) low ductility
d) high creep resistance
Explanation: The die used in the electromagnetic process should be made of low electrical conductivity to minimize the magnetic cushion effect. Dies are generally made of steel or epoxy resin.
11. The EMF process allows increased ductility for______________ alloys.
a) Chromium – molybdenum
d) chromium – mangnese
Explanation: The EMF process allows increased ductility for certain aluminium alloys because of the lack of mechanical stress and friction normally encountered with mechanical processes.
12. Tooling for EMF process is relatively inexpensive.
Explanation: The machine and the work coils required in EMF process can be viewed as general-purpose tooling. Therefore it can be said that the tooling for this process is inexpensive.
13. EMF is primarily used for which of the following material?
b) High carbon steel
c) Chromium alloys
d) Martensitic steel
Explanation: This process is primarily applied in the forming of good conducting materials such as copper, aluminium, silver and low carbon steel. It can also be used to form a poor conductor like stainless steel.
Sanfoundry Global Education & Learning Series – Manufacturing Processes.
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