Manufacturing Technology Questions and Answers Part-7

1 Pick the odd one out.
a) Sulphur compounds
b) Nitrates
c) Phosphorous compounds
d) Chlorine compounds

Answer: b
Explanation: Nitrates are usually used as rust or corrosion inhibitors; whereas compounds of sulphur, chlorine and phosphor are extreme pressure additives.

2. The minimum bend radius for bending material in roll forming is one stock thickness.
a) True
b) False

Answer: a
Explanation: The minimum radius used is one stock thickness; however 2 times stock thickness is preferable. Bending radius smaller than one stock thickness is possible to use but the life of rolls reduces significantly.

3. The parts shorter than_____ the centreline spacing of rolls of the machine employed will not feed or form satisfactorily.
a) 2 times
b) 3 times
c) 4 times
d) 5 times

Answer: b
Explanation: It is preferred to produce the stock in longer lengths and cut the desired length after forming. This operation needs to carry out in a continuous automatic manner. A thumb rule on this is that, the parts shorter than 3 times the centreline spacing of rolls of the machine employed will not feed or form satisfactorily.

4. Depth of roll formed section should be kept as small as possible.
a) True
b) False

Answer: b
Explanation: Smaller depth helps to simplify tooling, reduce tooling wear and preserve the stock finish. The maximum form depth that has been established for average-size forming machines is 100 mm.

5. The waviness can be seen in the formed product if unformed areas are less than _____ wide.
a) 100 mm
b) 120 mm
c) 125 mm
d) 150 mm

Answer: c
Explanation: Wide parts show some kind of waviness unless unformed areas are less than 125 mm wide. Waviness or other type of irregularity in wide areas can be avoided with the help of longitudinal stiffening ribs.

6. Waviness at the edges can be avoided by_____
a) longitudinal stiffening ribs
b) incorporating a flange
c) using roller support at the edges
d) waviness can never be avoided

Answer: b
Explanation: Waviness or unevenness at the edges can be avoided by incorporating a flange, hem, or rib near or at the edge. Longitudinal stiffening ribs are used to minimize irregularity in the areas of the product.

7. In roll forming, exact vertical side walls are avoided.
a) True
b) False

Answer: a
Explanation: In roll forming, exact vertical side walls are avoided to reduce excessive roll wear and scoring. A draft angle equal to 0.5° or more is preferred.

8. Why blind corners and radii should be avoided while roll forming?
a) It needs an additional setup
b) It is time consuming
c) Skilled labour is a need for that
d) Less accuracy

Answer: d
Explanation: Blind corners and radii are feasible but should be avoided. Because they are less accurate than the corners formed with rollers in contact with both sides of the stock.

9. Forming of any metal, however, must be achieved with stresses above the yield stress.
a) True
b) False

Answer: a
Explanation: If the material is stressed below yield point, it would spring back to its original shape. Therefore, material should be stressed beyond the yield point. But bear in mind that stress should not exceed the maximum tensile stress; otherwise the product will crack or tear during forming

10. It is difficult to form materials with high yield and ultimate tensile strength. Why?
a) High ductility
b) High fatigue strength
c) Lower creep resistance
d) Lower elongation

Answer: d
Explanation: The larger the difference between yield and ultimate tensile strength, larger is the elongation, thus, better the chance to form the metal. It is very difficult to form metals with extremely high yield and ultimate strength and having a near zero elongation. These materials will crack at the sharp bends because the elongation in the outside fibres would be larger than maximum elongation.