A Question for our Welder's/Fabricator's Options

[76-914]

I've been trying to figure out how you guy's deal with shrinkage. Not for body panels but just general welding. (And no, I did not shrink my car when I installed the Engman Kit) As an example, let's say I'm welding on a 10' piece of pipe that will become a stair rail. Of course it turns 90' on each end and will have flanged ends that screw to the wall. If the 90' elbows are welded on then the length of the rail will shorten "x" inches. Can this be prevented with pre heating. If so, do you apply heat to the entire piece or just where the weld will be? Do you accept that shrinkage will occur and just do not drill any matching holes until after the weld? Is there a formula that adjusts for this shrinkage? Do you bolt it in place then weld to prevent shrinkage? Also, I don't remember this being a problem with gas welding but that was years ago. My imagination or not? TIA, Kent (IMG:style_emoticons/default/beerchug.gif)

[Jeff Hail]

Shrinkage happens and yes you have to anticipate it. There are methods in controlling shrinkage the biggest is slowing down and not heating up large areas.

Fixtures and braces that resist movement is one. On panels that have access to both sides hammer forging a weld will aid in ironing out the area that pulled together a bit. Heat paste is a good thermal barrier to keep heat from walking the panel, reduces shrink and warping (oil canning).

Backer plates and sleeves will cut shrink down while keeping the joint from creeping together on a seam or butt. If its an enclosed box like a rocker or a sail panel this works well. They also act as a sink. Not the kitchen or bathroom.

Tack welding a panel on its perimeter in multiple spots will help cut down on the tug O war.

Panel fitment on a butt is critical. I've seen too many guys fit both panels to touch and not leave a small gap for wire fill. This error usually results in poor weld integrity since its really surface only. The backside always looks cruddy with poor fill and bridging. Then they try to fix it by making another pass and adding more heat back into it. Lots of grinding later and its still warped.

An old trick body men still use today when replacing a quarter panel. It looks crazy but it works is adding stretch while they are welding. When they go to weld up the qtr panel to the rocker and pillar they will put a floor jack under the rocker to get the weight of the rear of the vehicle to actually pull down resisting the shrink. If you have seen it in action and I have thousands of time it works. With the suspension unloaded on that corner it gives a bit of control to the tech on how the metal is behaving. After everything cools it ends up where it should.

The tech who didn't usually has tight gaps at the upper door frame to pillar. Most people would not notice it or it may be covered up by a garnish or trim. Anyone on this forum (Rick) knows what I'm talking about.

The biggest error will always be too much heat to fast. I always remind guys that's why a MIG has a trigger on the gun and its ok to take your finger off. Its not a machine gun. Last.. watch the puddle..don't make one.

Practice, practice!

[cary]

I always remind guys that's why a MIG has a trigger on the gun and its ok to take your finger off.

Practice, practice!