This set of Mechanical Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Cold Extrusion and Cold-Forming”.
1. If the effective flow stress for extrusion is 100 MPa and the extrusion ratio is 4, then find the ideal extrusion pressure for the process?
a) 150.5 MPa
b) 170.5 MPa
c) 138.6 MPa
d) 257.2 MPa
View Answer
Explanation: The ideal extrusion pressure is defined as:
-> P=kA*ln(Ai/Af)
-> Ai/Af = extrusion ratio = 4
-> kA = effective flow stress = 100 MPa
-> P=100 ln(4)
-> P=100*1.386=138.6 MPa
So, the ideal extrusion pressure is equal to 138.6 MPa.
2. If the drawing ratio of the cup is 1.5 and the final diameter of the workpiece is 120 mm, find the diameter of the blank?
a) 150 mm
b) 180 mm
c) 100 mm
d) 240 mm
View Answer
Explanation: The drawing ratio is given as:
-> The diameter of the blank/diameter of die
-> 1.5=d/120
-> D=180mm
So, the blank diameter will be 180 mm.
3. The pressure required to maintain the flow during indirect extrusion __________ with decreasing length of the billet.
a) increases
b) decreases
c) remains the same
d) independent of length
View Answer
Explanation: The required pressure for extrusion will decrease with decreasing length of the billet. This is because material itself acts as the resistance to the flow of the material; so, if the material is less, the resistance is also less.
4. The fir-tree cracking is associate which of the following metal working process?
a) Forging
b) Rolling
c) Extrusion
d) Casting
View Answer
Explanation: The fir-tree cracking is associated with extrusion process. It is generally observed in conical converging die for hard and brittle materials. This is also called “fish skin” defect.
5. The equivalent strain ε for plastic deformation is defined as ____________ (where E=equivalent strain, r=reduction ratio).
a) E=ln(r)
b) E=ln(1-r)
c) E=ln(1/(1-r))
d) E=ln(1/r)
View Answer
Explanation: The equivalent strain for plastic deformation is defined as:
-> E= ln(1/(1-r))
-> r=reduction ratio
-> E=equivalent strain.
6. If the bar of diameter 60 mm is drawn to a diameter of 30 mm in the metalworking process, find the equivalent strain in the material?
a) ln2
b) ln3
c) ln4
d) 2
View Answer
Explanation: Reduction ratio = final diameter/initial diameter
-> r=1/2=0.5
-> E = ln(1/(1-r))
-> ln(1/(1-0.5))
-> ln 2
-> 0.693
So, the reduction ratio is equal to 0.693.
7. The maximum stress/force that can be applied on the billet is more in indirect extrusion compared to direct extrusion.
a) True
b) False
View Answer
Explanation: The maximum force that can be applied is lower in the case of indirect extrusion because there is a limitation in load-carrying capacity of the die. Because the die(ram) for indirect extrusion is hollow, it can be made up to certain strength after which it cannot sustain load.
8. For the tube drawing by the extrusion process, the necessary component required is _____
a) die
b) ram
c) mandrel
d) billet
View Answer
Explanation: The die, ram, and billet are standard in all the extrusion process, but mandrel is the critical part in extruding tube from bars and rods.
9. The lead sheath electrical cable is made by which of the following process?
a) Wire drawing
b) Forging
c) Rolling
d) Extrusion
View Answer
Explanation: The lead sheath wire is made by the extrusion process. First, the tube of lead is manufactured and then it is coated on the electrical wiring in the same process.
10. For manufacturing short length hollow tube, the best suited method is _____________
a) direct extrusion
b) indirect extrusion
c) impact extrusion
d) die forging
View Answer
Explanation: The impact extrusion is the quick process in which a sudden high load is applied to the base material. It is used to make collapsible toothpaste tubes.
11. The capacity of the vertical extrusion press is more than the horizontal extrusion press.
a) True
b) False
View Answer
Explanation: The ability of vertical extrusion press lies in the range of 5 to 20 MN, while for the horizontal press the capacity can be as high as 150 MN.
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