Page 165 - Module DMV20173

EXERCISE 3.2

If you need only a few units of a particular casting, which process would you
use? Why?

More than one answers:
Sand casting: almost any metal cast, no limit to size, shape, weight and low tooling
cost.
Investment casting: Intricate part shape, excellent surface finish and accuracy, almost

any metal cast.

EXERCISE 4.1

Describe the cutting process that takes place when a pair of scissors cuts through
aluminium foil.

Solution:
Scissors cut by a shearing process. The material is subjected to shear stresses at

the intersection of the two blades of the scissors. Because shearing takes place in a
small localized region, low forces are required to cut with scissors. The shearing
process involves surface cracks propagating through the material until separation
occurs.

EXERCISE 4.2

Explain why cupping tests may not predict well the formability of sheet metals in
actual forming processes.

Solution:
The difficulty with cupping tests is that deformations are axisymmetric, that is, they

are the same in all directions. Sheet-metal forming operations, on the other hand,
rarely take place in an axisymmetric state of strain. However, cupping tests are easy
to perform on the shop floor and will give some approximate indication of formability.