# Manufacturing Processes Questions and Answers – Roll Forming – 3

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This set of Manufacturing Processes Multiple Choice Questions & Answers (MCQs) focuses on “Roll Forming – 3”.

1. During roll forming, a flat strip is passed number of times through the rollers.
a) True
b) False

Explanation: In roll forming, a flat strip is gradually formed to the finished shape. The forming is almost exclusively accomplished by rotating contoured rolls while the material passes through the mill.

2. Which of following is necessary in order to have a good set of rolls?
a) Short horizontal distances
c) A smooth flow of material
d) Less number of forming passes

Explanation: The probability of having a good set of rolls is to follow few rules:
(1) Envision a smooth flow of material,
(2) Do not be skimpy with the number of forming passes,
(3) Avoid too short horizontal distances and too small lead-in flanges.

3. Which of the following is true in case of “too quick” forming (too few passes)?
a) It makes the tooling and the process uneconomical
b) It makes process easier
c) It distorts the product
d) Eliminate the need of a skilled operator

Explanation: “Too quick” forming (too few passes) will distort the product because of the unacceptable level of stresses generated in the metal. On the other hand, too many passes will make the tooling and the process uneconomical.

4. What is “leg length” or “leg height”?
a) The maximum vertical dimension of the profile
b) Total length of the product
c) Excess length of the product
d) Maximum width of the section

Explanation: The depth of the section, also called as “leg length” or “leg height”, is the maximum vertical dimension of the profile as it exits from the last pass. Sometimes it called as “depth of corrugation”.

5. In case of “U” channel/ section, the length of travel of the edge of the strip (effective length of the strip) ‘s’, travelling in a helical pattern having initial length ‘l’ is given by_____
a) l2 = s2 + c2
b) c2 = l2 + s2
c) s2 = l2 + c2
d) s = l2 + c2

Explanation: As we know, edge of the strip to be bend travels in a helical path, the length of the strip after bending is given by formula:
s2 = l2 + c2, where, s = final length &
l = initial length.
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6. What will be the elongation if a 1in high section is formed in four passes in a mill having a horizontal distance (between passes) of 14in?
a) 0.04%
b) 0.16%
c) 0.63%
d) 0.50%

Explanation: Here, h = 1in; number of passes = 4 and each of length = 14in
Therefore, l = 4 * 14 = 56.

Therefore,
Elongation, e = (56.022 – 56)/ 56
= 0.0004 = 0.04%.

7. During roll forming, the strain (elongation) of the outside edge fiber of the strip must remain below the uniform engineering strain (elastic limit).
a) True
b) False

Explanation: If the strain (elongation) exceeds the elastic limit, then the edge of the finished product will become permanently strained. Due to which the finished product will be wavy or the product will have a bow, camber or twist.

8. What is camber in roll forming?
a) Deviation of the strip edge from a straight line in horizontal plane
b) Deviation of the strip edge from a straight line in vertical plane
c) Difference in theoretical and actual elongation of the strip
d) Waviness of the strip

Explanation: Camber is the deviation of the strip edge from a straight line in the horizontal plane. The inside concave edge of the strip is shorter than the outside convex edge. The shorter edge will be under tension and the longer edge will be compressed.

9. When an asymmetrical section is roll formed, the finished product will have _____
a) Camber
b) Cross-bow
c) A twist
d) Waviness

Explanation: When an asymmetrical section is a roll formed, the finished product will have a twist after leaving the last pass, even if the starting material is flat.

10. When forming “Z” sections, the product is twisted in the opposite direction to compensate the machine generated twist.
a) True
b) False

Explanation: A common method used to compensate for the anticipated twist is to twist the product in the opposite direction in the mill, from pass to pass. This principle is used when forming “Z” sections. In other cases, the counter-twisting is accomplished just in the last one or two passes.

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