24 FCAW Distortion Control
Distortion is the same thing as warping. In the past, the terms “warpage” or ‘warping” were typically used. Nowadays, people tend to say “distortion.” When metal gets hot it expands, when it cools down it shrinks. If metal heats and cools unevenly, it will expand and contract unevenly (distortion). Metal will always distort towards the heat.
Not all metals distort the same way. How much metal distorts depends on how well it conducts heat and how fast it expands. Under the same circumstances, stainless steel will distort more than carbon steel because stainless has lower thermal conductivity (it conducts less heat) and it expands faster.
You cannot totally prevent distortion, but it can be controlled to an “acceptable level”. An acceptable level of distortion will not compromise the integrity of the weld.
Distortion control is an important consideration in welding to ensure that the final welded structure or component maintains its desired shape and dimensions. Flux cored arc welding (FCAW) is a welding process that can be prone to distortion due to its high heat input and deposition rates. Here are some techniques to help control distortion when using FCAW:
- Weld Sequence Planning: Plan your weld sequence carefully to distribute the heat and distortion evenly. Start welding at the center and move outward, alternating sides to minimize the accumulation of heat in one area.
- Tack Welding: Use tack welds to hold parts in place before making full welds. This helps to secure the components and minimizes distortion during the welding process.
- Use Jigs and Fixtures: Employ jigs, fixtures, and clamps to hold parts in their intended positions. These tools can prevent movement during welding, reducing the likelihood of distortion.
- Preheat and Interpass Temperature Control: Preheating the base metal and controlling the interpass temperature can help reduce the overall temperature gradient, preventing excessive distortion. Follow recommended preheat and interpass temperature guidelines for the material being welded.
- Faster Welding Travel Speed: Faster travel speeds can reduce the heat input and allow the heat to dissipate more evenly. This can help control distortion, especially in thicker materials.
- Backstep Welding Technique: Utilize the backstep or skip welding technique, where you weld small sections and move backward. This approach minimizes the overall heat input and reduces distortion.
- Peening: Use peening (light hammering) immediately after welding to distribute residual stresses and reduce distortion. Be cautious not to cause surface damage.
- Stringer Bead Welding: Stringer bead welding (single pass) rather than wide-weave bead welding can help reduce the amount of heat introduced and control distortion.
- Control Welding Direction: Consider welding uphill to help minimize distortion. Welding uphill provides better control over the heat distribution and cooling rate.
- Fixturing and Restraint: Strategically use fixturing and restraint to minimize warping. Adequate support and controlled restraint can help prevent undesired movement during welding.
- Post-Weld Heat Treatment: Depending on the material and the application, post-weld heat treatment (stress relieving) can be applied to release residual stresses and reduce distortion.
- Welding Techniques and Parameters: Adjust your welding parameters, such as voltage, current, and wire feed speed, to control heat input. Experiment with different techniques to find the optimal settings for distortion control.
- Monitor and Inspect: Regularly monitor the parts during welding to detect any signs of distortion. Inspect for alignment and dimensional changes, making adjustments as needed.
Remember that controlling distortion in welding involves a combination of proper planning, technique, and material-specific considerations. Experimentation and practice will help you identify the best distortion control strategies for your specific FCAW applications.
