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

This is going to be great!

I don't claim to be an expert, but I've done some welding.

I was waist deep in a Locost project when someone offered to buy it for more than I had into it. It would have had a Volvo 4cyl eventually.



Also welded sheetmetal on a few occasions. I welded a new rocker into this VW, hard to tell but the seam was midway down the side of the car, going vertical.


Trick for minimizing shrink is completing the weld using small spot welds so as not to introduce too much heat.

Shrinkage isnt typically something that is factored into welding as its pretty small. If that is an issue then most of the time manufacturers use jigs to ensure that the panels remain the size then need to be by affixing the ends of the project.


Warping is however an issue and is rectified by making small tac welds vs long welds.

Correct and I am a welding instructor and confirm the above statements

One of the many reasons I love Kent...


https://www.youtube.com/watch?v=dcovHHOCtpQ


Sorry gents, continue discussing metal contraction....

Sort of ageee......


During heating and cooling cycles metal goes through a tranny phase.......yes thats right....and we.re not talking bathrooms here.

Fixtures don.t address residual stress induced by rapid cooling as you coin ad shrinkage. On my cellphone and train so I could further the explanation if anyone's interested.

Love the George post

Yes But warpage is handled
in industry by chill plates and lots of clamps and fixturing

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!

With automatic TIG welding on heavy wall tube/pipe at work we estimate shrinkage at about 30% of wall thickness for full penetration welds.
Hope that helpsq

What these guys said. Specially Jeff when it comes to sheet metal and Barefoot gave you the average depending on wall thickness and application. Lots of tricks you learn by trial and error over the years.

Try this, biggest challenge of my shop life to date.

Assemble by welding a complete shroud. 4 weld seams pulling in different directions trying force things out of square. Metal finish the welds and still be able to fit the hood without shrinkage. Tig welded, annealed, metal finished, Installed as one piece.

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From your aircraft days, 4130 is best gas welded to be sure the material naturalizes unless you have a big oven you can use.

The fab shops and ship yard I worked in used jig tables for hand rail. Most of the time you can't be off or they don't install.

Wait, .....

THIS ^^^ is why you love Kent?

Jeff, Rick & Barefoot; thank you very much. And, I do agree with the practice statement. I wanted to be sure I was using the correct methods when practicing and you have given me some excellent tips. I would rather have someone think my welds lack experience than lacking in knowledge! Thx again guys. Kent

https://www.youtube.com/watch?v=RPgb77Ruz7g

https://www.youtube.com/results?search_query=welder+tig
Of note is the discussion of 'brown sugar',the heat induced precipitation out of the chromolly.
Due diligence,not the hearsay of 'self-proclaimed normalizers'.
The John Force crash is illuminating,the failure mode,discovered by micrography.
https://www.youtube.com/watch?v=wVrdST1pXRk

/
https://www.google.ca/webhp?sourceid=chrome...eel&tbm=vid
With the heavy Pressure Vessel welds of 4-6" wide,the effect you describe is significant.
Training and experience circumvents the natural phenomena,the cooling and becoming smaller,delta T.
In fact,it is standard welding training to understand the 'shrinkage' of materials.
https://www.google.ca/search?q=pressure+ves...aPZDOEQ_AUIBigB
The welds I've seen in machines trade were/are awesome works of fusion art,and like any endeavor requires talent and practice.
/

Yeah you COULD read that the wrong way Rich v . Every once in a while he inadvertently (...or is it? ) tees me up a good one liner that my juvenile humor can't leave alone. I TRIED, but just kept hearing George Costanza yelling "I HAD SHRINKAGE!!!!! I HAD SHRINKAGE!!!!!"

BTW this has turned into a very informative thread aside from my contribution.

Unfortunately I was born with shrinkage ,Chris I should start proof reading. Speaking of; I forgot to ask, what are chill plates?

I think you heard from the experts. The basic problem is that as the metal is joined part of it is at a high temp and thus expanded. Particularly the puddle. So thinking about it, the smaller the puddle, I.e. Smaller the weld, the less the problem. So you can anticipate it it by starting a bit long. My favorite is little tacks followed by checking measurements. That way the puddles are smaller and as you add more tacks the cooling metal cannot shrink and is forced to stretch. Eventually the majority of the weld is in the correct length and you can fill it all. I did a stair rail for my dad, but I drilled the mounting holes after the fact.

That makes perfect sense. The more I learn about welding the more I realize how much I don't know about welding!