Welding 3/16" Plate to 1/16" Sheet Metal

[TomS]

I have a project where I need to weld 3/16" mild steel to 1/16" thick rectangular tubing. I'm using a Hobart Handler 190 Mig welder with the option of using either .023", .030" or .035" solid wire. What is the proper technique for getting good penetration yet not burning through the thin wall tubing. Here is a picture of the 3/16" piece (aka side plate stiffener) that get welded to the rectangular tubing (aka frame rail).



Tom S

 

[xalky]

Hey Tom. I saw that in your other post that you were gonna plug weld the mounts to the frame rails. I didn't comment at the time, thinking that the fisher frame rails are pretty thin walled, but I was questioning my memory. Is that how they are typically doing them? What are those brackets supporting, the front of the four link bars? Do you have a picture of what your building or something similar?

 

[Cheeseking]

Im used to fusion welding no filler with a TIG which is not apples to apples but in general the principles are likely similar. I would tend to favor the heavy material and put the heat into it so melts into the thin.

 

[Rbeckett]

Re: Welding 3/16" Plate to 1/16" Sheet Metal

The most important part of the weld you are attempting is the possibility of overheating the thin stock and creating a tear out stress point. When you lay down the bead use a semicircular motion on the mig gun and waft the heat from thick to thin. Cleanliness is also going to be very important getting a good deep penetration and weld deposit. I would get a couple of scraps and practice the torch manipulation to insure that you get it hot enough abd don't overbake the thin material if you can avoid it at all. Good luck hope this helps!!!! If your welder will pull it I would reun the .035 70-s6 wire and 75/25 gas mix for a cleaner less slag nugget. .023 is not going to get the 3/16ths very hot before it melts into the puddle and leaves you with a crappy surface weld only..

Bob

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The most important part of the weld you are attempting is the possibility of overheating the thin stock and creating a tear out stress point. When you lay down the bead use a semicircular motion on the mig gun and waft the heat from thick to thin. Cleanliness is also going to be very important getting a good deep penetration and weld deposit. I would get a couple of scraps and practice the torch manipulation to insure that you get it hot enough abd don't overbake the thin material if you can avoid it at all. Good luck hope this helps!!!! If your welder will pull it I would run the .035 70-s6 wire and 75/25 gas mix for a cleaner less slag nugget. .023 is not going to get the 3/16ths very hot before it melts into the puddle and leaves you with a crappy surface weld only..

Bob

 

[DMS]

RBeckett has some great advice.

I do a lot of stuff with 0.063" wall square tubing (actually, I think almost all of my welding projects have used it). I have a Millermatic 211, which should be pretty similar in capability to your machine. The first thing to remember is that that tubing is _VERY_ easy to burn through. The second is, sheet metal likes to buckle. Use LOTS of tack welds. Tack it every 2 inches at least. The other thing is, if you don't need to weld out fully, don't (IE, if you don't need a liquid tight seal, don't weld the whole seam). Another technique to consider is something called "backstep" welding (well, at least that is what Jodi on WeldingTipsAndTricks.com calls it). Check out some of his videos to see the technique. You also don't want to weld large stratches at a time, the heat is going to cause issues. So do short sections (say, 1") at a time. Oh, I tend to use 0.030 wire IIRC.

The main thing about welding thick to thin is where you direct your heat (as others have said). This more or less amounts to pointing the gun more at the heavy side, and less at the thin side. I like to at the weld joint, almost directly at the thick part, and let the weld puddle grow and envelop the thinner side. I have tried the "swirl" method RBeckett describes, but think I need more practice. In any case, practice on some scrap and get your voltage and wire feed rate tuned in before you start on the real parts. In general, I run at about the same feed rate for the thicker material, but at slightly lower voltage, but it's a balancing act.

 

[TomS]

Re: Welding 3/16" Plate to 1/16" Sheet Metal

Hey Tom. I saw that in your other post that you were gonna plug weld the mounts to the frame rails. I didn't comment at the time, thinking that the fisher frame rails are pretty thin walled, but I was questioning my memory. Is that how they are typically doing them? What are those brackets supporting, the front of the four link bars? Do you have a picture of what your building or something similar?

I've seen installations where the side plates are welded (Chris Alston's Chassis Works is one) and others where the side plates are bolted to the frame rails using 3/8" sheet metal screws. Seems to me welding would be stronger but I am by no means an expert welder. Maybe bolting is the way to go.

Here's a picture of a similar setup as mine. Hope it clarifies what I'm trying to do.




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Hey guys. Thanks for your input. I'll take your advice and go through the practice routine before welding on the car. With my limited welding skills I certainly don't want to screw this up.

Xalky asked a question that made me think about other installations that are bolted in. It's got me thinkin!

 

[xalky]

Is there room on the other side of the frame rail to make a U with your brackets. Those frame rails are awfully thin to be taking the brunt of the impact. I fear that if you plug weld them the way you planned that one good bump or a good hard acceleration, or a missed speed bump might rip those plugs right off the frame rail. My thinking is that if you could wrap the frame rail on 3 sides and thru bolt it right through the frame rails with a couple of plug welds added in to keep the rattles away, that's how i think I'd do it. Make it bullet proof, if you know what I mean. What the hell, why chance it. Nobody wants to find out what it feels like when thier rearend comes off the car.

If I remember correctly you can get at that area of the frame rail right from the wheel well. I think the reason why they sell the kits that way is to avoid returns. Because the frame rail widths would vary from car to car and year to year.
What do you think?

 

[TomS]

Is there room on the other side of the frame rail to make a U with your brackets. Those frame rails are awfully thin to be taking the brunt of the impact. I fear that if you plug weld them the way you planned that one good bump or a good hard acceleration, or a missed speed bump might rip those plugs right off the frame rail. My thinking is that if you could wrap the frame rail on 3 sides and thru bolt it right through the frame rails with a couple of plug welds added in to keep the rattles away, that's how i think I'd do it. Make it bullet proof, if you know what I mean. What the hell, why chance it. Nobody wants to find out what it feels like when thier rearend comes off the car.

If I remember correctly you can get at that area of the frame rail right from the wheel well. I think the reason why they sell the kits that way is to avoid returns. Because the frame rail widths would vary from car to car and year to year.
What do you think?

I love this forum!!! Ask a question and you get tons of positive feedback.

Wrapping the frame rail is an idea I hadn't thought of. But I have to agree it would be much stronger. BTW - besides plug welds the side plates and lower stiffeners get peripheral welds and the lower stiffener plates also get bolted. If the rail is a standard width I may be able to find rectangular tubing that may fit if I cut off one of the short legs. Back to the drawing board.

 

[xalky]

I love this forum!!! Ask a question and you get tons of positive feedback.

Wrapping the frame rail is an idea I hadn't thought of. But I have to agree it would be much stronger. BTW - besides plug welds the side plates and lower stiffeners get peripheral welds and the lower stiffener plates also get bolted. If the rail is a standard width I may be able to find rectangular tubing that may fit if I cut off one of the short legs. Back to the drawing board.

I didn't realize it was getting peripheral welds too. Side plates...where? On the other side of the frame rail? Why not just rework the brackets you got? Weld some vertical plates to it so as to wrap the frame rail. Well in any case, I think i got your thought juices flowing, I think you'll figure it out. The whole point is to make it rock solid so that there,s no doubt in your mind that it can take some abuse. Like I said earlier, you don't want to find out what it's like to rip the rearend out of your car, or worse, at freeway speeds!


Marcel

 

[TomS]

I didn't realize it was getting peripheral welds too. Side plates...where? On the other side of the frame rail? Why not just rework the brackets you got? Weld some vertical plates to it so as to wrap the frame rail. Well in any case, I think i got your thought juices flowing, I think you'll figure it out. The whole point is to make it rock solid so that there,s no doubt in your mind that it can take some abuse. Like I said earlier, you don't want to find out what it's like to rip the rearend out of your car, or worse, at freeway speeds!


Marcel

Marcel,

For clarification the side plates are the curved pieces in the picture at the top of this thread. The lower stiffeners are the two short pieces in the picture. The original plan was to weld the side plates to the inside of the two frame rails. The lower stiffeners bolt to the bottom of each frame rail with a square U-bolt and get welded to the side plates.

After reading your's and other's comments I've decided to revise the plan. As I said in my last reply I may look at using rectangular tubing, cutting off one of the short sides and slipping that over the existing frame rails then bolt in place. Checked with my local steel supplier and they don't have the tubing I need in stock. The back-up plan is to fabricate the U-channel out of 3/16" flat bar. So it's back to the steel supplier this afternoon to pick up what I need. Sandwiching the frame rail between two pieces of 3/16" flat bar and using through bolts should be overkill. But as you said overkill is better than leaving the rearend laying in the road.

As I move forward I'll post more pictures.

Tom S