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Welding Myths Part 3: A weld is never as strong as the parent material

Topics: Laser welding

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To go along with the last post on welding myths and non-weldable materials, I also often get grudging calls from a designer who has been “forced” to add a weld to a design.

Customer: “How much do I have to overdesign this part for this weld?”

Me: “Why do you want to overdesign?”

Customer: “Well, the weld is going to weaken the part!  I need to beef it up to compensate.”

Au contraire.  Weld strength, which by the way is an ambiguous term, is related to the parent material characteristics, part configuration and weld parameters.  So, to refer back to welding myth #2 (If it’s metal, I can weld it), if Mr. Customer designed his part out of 303 stainless steel, the weld is indeed going to be weaker than the parent material and will be a failure point.  However, that same part made from annealed 304L may actually be stronger at the weld.  SURPRISE!

Solutions for weld strength

It's true that in many cases the weld will lead to softening or hardening of the material in the region in and adjacent to the weld, but very often this can be addressed by choosing a different material or by simply adding a post weld heat-treatment to restore characteristics to those of the parent material.

Quick example: A hot topic in the news right now is guns.  Believe it or not, modern guns are employing laser welding more and more frequently.

Well, guns are made from carbon and alloy steel (most of the time) and these materials don’t always play well after welding.  However, a few hours in an oven at a few hundred degrees will make the difference between a part that will survive a few tens of shots, or tens of thousands of shots.

The takeaway – Don’t fall into the trap of believing that a weld will be the weakest point of your part.  Talk to someone in the know, and use welding to make you look like a hero on your next “impossible” design.

 

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