What is Tack Welding?

Video Transcript

" Hello! My name is Mac and on behalf of expertvillage.com I am here to discuss arc welding and the topic today is tacking material together to be welded. Now very often different pieces of metal need to be welded together. They need to be held together while they are being welded and what we welders do in that case, is for instance, I have got a little T joint here that I tacked up. Now I want to weld this solid, if I start welding on one side or the other it is very likely that the thing will warp and be crooked when I am done. So to prevent that from happening, I take in this case my MIG welding machine. I put a couple of tacks on here, just little drops of metal on the joint to hold it together. This isn't very strong but is not meant to be. Then I square it up with a square; I take a hammer and tap it until it is in the right position. These tacks have a little bit of flexibility in them. Then on the opposite side from tacks I will run a complete beat of well. The tacks will prevent it from pulling over and warping in that direction because of metal shrinkage as the metal cools up it tends to shrink towards the side that was welded first. So the tacks will hold its square and true I put a weld on that side and then turn around and finish welding over the top of the tacks on this side. That is basically what tack welding is used for is to hold the alignment on pieces of metal, until you are done with the welding and that is basically all there is to tacking, tack one side, weld the opposite side first, then come back and weld over top of your tacks. "