How to Correct Distortion after Welding
So you've decided to learn a new skill and have taken up welding. Regardless of whether you're trying to learn how to weld for professional or artistic reasons or simply out of curiosity, you're probably already familiar with welding distortion and the frustration it causes in your work.
Welding distortion is a problem experienced by seasoned welders and those just beginning to learn the trade. However, if you are new to the discipline, then learning how to correct these errors is a vital skill that you'll need to acquire to fix the problem when it inevitably arises - welding distortion can cause a variety of issues for a project, most notably leaving a weld structurally unsound, threatening both the aesthetic virtues and overall stability of a project.
By reading this article, you'll learn several different methods to correct this problem and gain a critical skill for anyone who works with welding metals to have. Let us show you can combat distortions that arise during welding.
Common Kinds of Welding Distortion
Before diving too deeply into repair methods, let's take a moment to look at some of the more common forms of distortion that occur when welding metals. Several factors contribute to these imperfections occurring during welding work - the type of metal used, the amount of residual stress that's applied, and the type and strength of restraints used on the metal can all affect the amount and type of distortion that occurs. Below are some of the more common distortions:
Longitudinal shrinkage: Shrinkage happening perpendicular to the weld, caused when force is applied parallel to the weld.
Transverse shrinkage: Distortions that move vertically through the weld are caused by contractions running perpendicular to the weld itself.
Bowing & dishing: Metal will curve when the weld is not balanced along the cross-section's neutral axis.
Buckling and twisting: One of the more difficult issues to resolve, often requiring substantial time investment. This issue commonly arises in especially thin metal structures.
Angular distortion: When powerful contractive force is applied to only one side of the neutral axis, the metal will bend or warp in that direction.
Welding Repair Methods
Now that we've seen some of the most common types of distortion that occur after welding and touched on the common causes of those distortions, let's go ahead and look at the primary methods used to correct these issues.
Method #1. Hammering or Pressing
The most commonly used method for correcting distortions is hammering, or the related practice of pressing. As the name implies, this method involves bending the metal back into its original shape using direct physical force, either with a hammer or mechanical press.
While this is the most common (and most straightforward) option for repairing deformation, it is not without disadvantages. Hammering metal into shape is time-consuming and requires the hammerer to expend a lot of force. On top of that, hammering can potentially damage the surface being fixed and may not be enough to fully fix every kind of distortion. When done correctly, pressing can avoid some of these issues, but not all.
Method #2. Heat Straightening
Many welders favor this process. Essentially, an oxyacetylene torch is used to carefully heat the metal in the area affected by the distortion. The metal expands under heat, and once brought to the desired temperature, the natural cooling process of metal will often bring the deformed area back to a more natural, less distorted position.
It's critical that the torch be used to carefully apply only a measured amount of heat to the metal since it may undergo molecular changes if it becomes too hot. It's also necessary to remember that the metal isn't being heated in order to be reshaped - you're merely allowing the natural properties of metal as it's heated and cooled to take its course.
Method #3. Hot Mechanical Straightening
This process is very similar to heat straightening, though not the same. Unlike the previous method, the metal must be heated all the way to the yield stress point, causing the metal to distort plastically and naturally straighten to its original position. This more intense option is better suited to severe welding distortions in metal, whereas heat straightening is better for mild imperfections.
However, this method has disadvantages since metal at this temperature is highly unpredictable - the metal and welds might fracture, and buckles and wrinkles are possible as the metal cools.
Method #4. Heat Working
Again similar to the last two methods, heat working is the most extreme option. Unlike heat or hot mechanical straightening, in this method, the metal must be heated past the yield stress point to the level where molecular changes occur. Once the metal reaches a glowing red color, it may be physically shaped into the desired position. As it's the most extreme choice, this method can lead to additional distortions, and the metal may crack after hot working.
Perhaps the single most important step when it comes to correcting welding distortions is taking steps to ensure that they never happen in the first place! While it's impossible to fully avoid or eliminate welding distortion, the steps listed below will help to reduce its frequency and severity.
#1. Don't Over-Weld
One of the simplest ways to reduce the frequency and severity of distortion is to simply use less metal on a joint. Getting exactly the right amount will ultimately save you time and materials. Using a convex bead and beveling on metal plates thicker than 0.25 inches (or double beveling very thick sheets) both help to reduce distortion.
#2. Reduce Number of Welding Passes
A good rule of thumb to keep in mind is that the more weld passes you subject metal to, the more and more noticeable shrinkages you can expect to see in the final product. It's better to have fewer weld passes with a larger electrode than many passes using a smaller one.