Chapter 9: Controlling Distortion
Wise men learn from other men's mistakes, fools by their own.
Since welding processes expose the workpiece to high temperatures, weldinduced distortion is always present. We will investigate how distortion affects workpieces and present several methods to reduce its effects. These methods are often simple, but without them many workpieces would be ruined.
How Expansion & Contraction Cause Distortion
What happens to the dimensions of a metal cube evenly heated to a temperature below its melting point and then allowed to cool gradually back to room temperature?
Because no metal in the cube is restrained, as the temperature rises it expands at the same amount in all three dimensions. Increases in length are proportional to temperature. The metal cube returns to its preheat dimensions when it cools to room temperature. Regardless of its shape, a metal object will return to its original dimensions on returning to room temperature if it is not restrained and gradually heated and cooled. See Figure 9-1.
Figure 9-1: Exaggerated three-dimensional changes in unrestrained metal cube on flat surface.
What happens to the dimensions of a solid metal cube restrained in one dimension (as between the jaws of a very rigid vice) when evenly heated from room temperature to a temperature below its melting point and then allowed to cool back to room temperature?
As the temperature rises, the metal expands and the volume of the cube increases. See Figure 9-2. Since the cube cannot move horizontally (the X direction) due to the...