Weld Distortion

Predicting Weld Distortion Means Planning For Success

It is critical to work with a manufacturer who can predict and plan for weld distortion. This distortion is a dimensional change in metal caused by stresses that develop during welding. The level of weld distortion can vary depending on how parts are clamped or restrained, how parts are stress relieved, or the choice of welding process.

Unanticipated distortion can slow down schedules, increase costs, or even render a finished product useless. Experienced manufacturers can predict and manage this phenomenon — or at least create a plan to deal with distortion when the welding is finished.

Different Types of Weld Distortion

Weld distortion falls into three main categories:

  • Transverse shrinkage, which occurs across the width of the weld seam,
  • Longitudinal shrinkage, which occurs along the length of the weld seam, and
  • Angular distortion, which results in a bend at a joint.

In most applications, all three occur at the same time in varying degrees. Welding teams must predict which type of distortion is most likely to impact the process, the likely severity of the distortion, the possible ramifications and the best courses of action to mitigate and minimize the effects of distortion.

Predicting Weld Distortion

Manufacturers have two options. They can either take a rudimentary, pen-and-paper approach to predicting weld distortion, or they can invest in sophisticated software to make predictions for them.

Advanced software has drawbacks. First of all, it is expensive, and that cost is inevitably passed on to the customer. Second, predictive software is not as reliable when building one-of-a-kind custom parts that don't have any precedent and may not be made again. Finally, it is easy for builders to develop an over-reliance on software formulas and ignore their hard-earned instincts.

The most reliable method is found in the gray area between the computer and the pen-and-paper. When teams understand the scientific method that software uses to develop simulations, they can integrate those formulas when drawing their own conclusions through the traditional pen-and-paper process.

No matter which methodology is used to predict and mitigate weld distortion, teams must recognize their own limitations or the limitations of their chosen software. If teams treat their conclusion as gospel and design the entire manufacturing process around it, they are setting themselves up for disaster.

Here, experience is irreplaceable and invaluable.

Over time, experienced manufacturers develop gut instincts that tell them to heed or ignore the formula. The formula is a guide, but the best designers will adlib if their instincts tell them to veer off track.

It is important for manufacturers to recognize where reality deviates from the underlying assumptions behind formulas and software. The truly experienced will use the science of welding to find a balance between these rigid formulas and their own intuition.

Addressing Weld Distortion

Once the team predicts the type and severity of weld distortion they are most likely to encounter, it is time to develop a minimization and mitigation strategy.

For some jobs, the solution is stress relief. In other cases, straightening or forming could get the best results. Maybe welders start with a formed shell diameter that is bigger than they need so it can shrink safely into tolerance as it is being welded together. In many applications, it is best to simply start with extra material and then machine it away after welding is complete. In some instances, however, post-weld machining is not an option. Distortion prediction is most critical in these cases.

Any action should be taken with return on investment (ROI) in mind:

  • What is the ROI as it applies to the cost of mitigating weld distortion?
  • What techniques can be reasonably applied to get the most ROI for the amount of work put in?
  • What gives the customer the best value?

In other words, it is not worth adding $1,000 worth of fixturing to avoid spending $500 on post-weld machining.

When metal is welded, it can shrink, bend and distort. This distortion can ruin a project if a plan isn't in place to predict, prevent or mitigate it. The ability to predict and plan for weld distortion is so important that the best manufacturers teach it and conduct periodic training to keep everyone fresh and up to date. In the end, the most powerful tool in the war against weld distortion is experience.

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