Distortions

Question 1

What is distortions?

Answer 1

A reversible or irreversible geometrical modification in shape or size.

Question 2

What is a reversible distortion?

Answer 2

A distortion (geometrical modification in shape or size) where the heating/cooling cycles are homogenous in the volume. If no phase modifications is involved when the metal cools back to room temp., then the part will return to its original size.

Question 3

What is a irreversible distortion?

Answer 3

A distortion (geometrical modification in shape or size) where the heating/cooling cycles are NOT homogenous in the volume and /or phase modifications is present when the metal have cooled back to room temp. Both size and shape distortion can happen.

Question 4

Name som possible causes of irreversible distortion.

Answer 4

Possible causes:
- Relief of residual stresses from previous manufacturing processes.
- High temp. plastic deformation (static or creep), due to weight or storing/stacking.
- Constrained theremal expansion
- Large differences in thickness -> Differential heating rates throughout the part (ex. quenching (bråkjøling))

Question 5

How can we ideally avoid distortion?

Answer 5

Each stage of heat exchange should in principle occur in the same period of time throughout the volume.

Question 6

How can we practically avoid distortion?

Answer 6

Use tables of specific maximum size relationships that should be avoided:
Ex.
for cooling in water: L>5d
for cooling in oli: L>8d