Beginning welders and even those that are more experienced commonly struggle with the problem of weld distortion, (warping of the base plate caused by heat from the welding arc). Distortion is troublesome for a number of reasons, but one of the most critical is the potential creation of a weld that is not structurally sound.
Distortion in a weld results from the expansion and contraction of the weld metal and adjacent base metal during the heating and cooling cycle of the welding process. Doing all welding on one side of a part will cause much more distortion than if the welds are alternated from one side to the other. During this heating and cooling cycle, many factors affect shrinkage of the metal and lead to distortion, such as physical and mechanical properties that change as heat is applied.
Follow this checklist in order to minimize distortion in the design and fabrication of weldments:
- Do not overweld
- Control fitup
- Use intermittent welds where possible and consistent with design requirements
- Use the smallest leg size permissible when fillet welding
- For groove welds, use joints that will minimize the volume of weld metal. Consider double-sided joints instead of single-sided joints
- Weld alternately on either side of the joint when possible with multiple-pass welds
- Use minimal number of weld passes
- Use low heat input procedures. This generally means high deposition rates and higher travel speeds
- Use welding positioners to achieve the maximum amount of flat-position welding. The flat position permits the use of large-diameter electrodes and high-deposition-rate welding procedures
- Balance welds about the neutral axis of the member
- Distribute the welding heat as evenly as possible through a planned welding sequence and weldment positioning
- Weld toward the unrestrained part of the member
- Use clamps, fixtures, and strongbacks to maintain fitup and alignment
- Prebend the members or preset the joints to let shrinkage pull them back into alignment
- Sequence subassemblies and final assemblies so that the welds being made continually balance each other around the neutral axis of the section