Welding Tips and Tricks

I'm designing a box that will be in a juice processing facility. It will require wash down, but it is not be in contact with any food product. My plan is to get the thing laser cut (there are some features that will be cut that are not shown) and then they will bend up the sides and I will weld up the corners. The dimensions are not shown, but are roughly 18" tall, 10" wide, and 6" deep. The material will either be 10 or 11 ga 304 SS. The box will be exposed to vacuum and the front flange will have a seal... so it needs to be very flat when done.

Any thoughts on welding sequence? Setting up the purge right?

1. I'm concerned about distortion - especially anything that might cause that front flange not to be flat
2. Should I design in a gap in the corners or should they be touching?
3. Should I try and purge the entire box or handle each corner at a time?

I'm an engineer not a welder, but I really like building stuff and I like to learn. I will be using an Everlast machine that is capable of pulse.Thanks!

If the front (open) side needs to seal to something I'd suggest having the front face 'letterbox' surface laser-cut from perhaps a slightly thicker grade stainless and weld the sides/walls to the front flange on the edge instead of folding/bending them over and (butt)welding the 45 degree joints.

Quenching/cooling the material with a wet rag and first doing lots and lots of tacks to stabilise it and then short 'back step' welds (letting it cool each time) shoud keep the distortion to a minimum. If your fitup is good and tight you may be able to autogenous weld it. Purging is a given..

I suspect you'd have a very hard time in your original design to get/keep the mating surface flat enough with the bends and the addition of the welding distortion on the corners that's going to want to buckle it.

Of course we don't know the type or thickness of the gasket material you intend to use, so how much distortion it can handle would be something you know

Bye, Arno.

If you are having the material laser cut and sheet broken, make the box from 2 panels:
Top, right side and bottom panel all with the front lip already bent in. Then the back panel and left side as second part. Tack the back and left side to the first section in the corners, and along the length. Setup a purge chamber, and weld it autogenously.

Arno, I'm planning on using a 1/4" thick silicone gasket. Should be pretty forgiving.

CJ, I was trying to avoid the long welds on the back. Do you feel like that won't add more distortion because the welds will be longer.

There are holes that will be laser cut on the left and right panels that need to be aligned to eachother. I would think that the two pieces should be top/back and left/bottom/right so that the holes align better, but that would make the welds on the back panel even longer.

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It really doesn't matter whether the welds are long or short, stainless, carbon or aluminum. Thin metal WILL DISTORT.

By using pieces that have brakes in them, it does help add some rigidity, but not nearly enough to eliminate YOU needing to go SLOWLY, and make short welds to limit distortion.

With a stainless box I welded (11ga, 22"x10") I used pulse, autogenous, and ran about 2" then skipped to another side. Keep moving after making short welds, even let the part cool or air cool it periodically. A wet rag is fine, but dousing with water would not be my recommendation.

Stainless is terrible at managing and releasing its own heat. Thick chill blocks of aluminum clamped around help, some .25"x2"x2" ally angle clamped on the inside while you weld the outside corners would be a great way to stabilize and suck heat out. Also will help with a back purge.

You can use .25" or > flat stock ally clamped on the outside, just away from the joints to help while you weld the outside corners. It's all about patience and heat management. (Comes with experience from having screwed the pooch enough times to learn to WAIT, and WAIT a little longer, no, not yet...) Know what I mean?