Excellent points by Chuck. Shrinkage cannot be prevented, but it can be controlled. There are methods used in both the design and in the shop to overcome the effects of the heating and cooling cycles of the materials welded. Briefly, here are a few (Some previously mentioned by Chuck):
1. Do not overweld. The more metal placed in a joint, the greater the shrinkage forces.
2. Use intermittent welding rather than continuous welding when possible.
3. Use as few weld passes as possible. Fewer passes with large electrodes are preferable to a greater number of passes with small electrodes.
4. Place welds near the neutral axis. This provides smaller leverage for the shrinkage forces to pull the materials out of alignment.
5. Balance the welds around the neutral axis. This offsets one shrinkage force with another.
6. Use the backstep welding technique.
7. Anticipate shrinkage forces by placing parts out of position before welding. The required amount of preset for shrinkage to pull the parts into alignment can be determined with a few trial welds.
8. Plan the welding sequence. A well planned welding sequence involves placing weld metal at different points within the assembly so that as the assembly shrinks in one place, it counteracts the shrinkage forces of welds already made.
9. Peening is one way to remove shrinkage forces of a weld bead as it cools, but this method must be used with caution. Engineer approval should be obtained prior to peening.
10. Minimize welding time. It is desirable to finish a weld quickly, before a large volume of surrounding metal heats up and expands. Excessive heat expands the base metals more than necessary.
The welding process used, the type and size of electrode, welding current, and travel speed all affect the degree of shrinkage in welds.