multi-layered sheet metal

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Robert Bondi
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Joined: Sun Jan 11, 2009 12:33 am
Location: Austin, TX

Re: multi-layered sheet metal

Post by Robert Bondi »

Awesome. Thanks for all the tips. I only have to make 1 panel for the passenger side; driver side looks fine in same area of floor pan.

I was thinking about 1/4" plywood consistent with your 5mm estimate. I understand your plan of attack and will attempt that. Can save my shot bag, but that nylon tear drop hammer will likely still be useful to shape the cup. I will be starting from a 12"x12" 20-gauge sheet metal piece...did acquire 18-gauge and 20-gauge based on your 19-gauge info. Plan to make my template in posterboard.

Yeah, tempted to see if I can find the inert CO2/Ar welding gas somewhere nearby. Every good HW store has a welding section, but never the gas nor even empty cylinders. I also don't have a feel for how often I'm doing this...storing a pressurized gas cylinder can be a hazard from my research lab days. Maybe there is an easy way to do this like exchanging propane tanks for the backyard griller? Or maybe inert gas is common at the typical tool rental place?

Shears or nibblers are also tempting as Mike pointed out. Good brands seem to start around $160.

Other questions:
1. Good way to ground the work piece on the car? I've been thinking about putting some M8 bolts in those holes for the subframe tie rod and confirming electrical continuity to the repair area. I've removed the subframe bolt for better access (you refer to this as the threaded rod)
2. I got a bunch of welding magnets to fixture the repair piece for initial tack welds. You have a better approach? Worth drilling a few little holes for lap welds or just stick to the repair panel perimeter?

Robert
Robert
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Re: multi-layered sheet metal

Post by dutch »

How often will you use it... That`s always the question and goes for any tool. Personally, I hate crap tools and since most el cheapo or knock off`s are crap, I tend to stay away from those. But that`s just me. There`s good el cheapo`s and crap among proffesional tools as well!

Ground; When you make the panel in the order I had in mind, you already have a hole where the subframe bolt goes. I would put it back in and use that for ground. It`s the closed position and it will protect the threads in the hole from damage by welding splatter. They will find their way in there, along with your ears... :D

The bent 90 degree part of the new panel that is spotwelded to the edge of the inner fender, together with the hole for the frame bolt kind of determine the position of the rest of the panel. I`d use a couple vise grips on that lip to fix and weld it ( drill a couple holes and weld them up ) and work my way around by pushing or hammer.
The magnets will be useful when making the template though.
dutch
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Re: multi-layered sheet metal

Post by dutch »

I`m not in the States and I don`t know what would be a good option for the welding gas...
I rent a Co2 mix , Ar for tig and acethylene and oxi. I don`t use them all the time but and it is I think about $75 per year for each on rental , but I never have to worry about cylinders getting filled or not passing safety checks or what ever.
It hurts a little when I get the bill but after payment it`s all forgotten and I can weld whatever I need to for another year.
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Robert Bondi
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Location: Austin, TX

Re: multi-layered sheet metal

Post by Robert Bondi »

Thanks for the continued tips! Forming the actual repair panel is now in progress.

Great advice on the shielding gas and where the name MIG itself originates. Path of least resistance, although likely not the cheapest, was to buy a cylinder on the exchange basis premise. I really wanted to rent to start, but couldn't find anything locally. This set me back almost $400. I now own the cylinder (about 18" high or 1/2 meter) and about $50 each time to exchange it for a full cylinder of C25 shielding gas (75%Ar/25%CO2). A few picture highlights:

Shielding gas cylinder
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Much cleaner welds with the shielding gas....so much less spatter as everyone indicated
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Warping issue with too much heat. I've been trying to take the advice of weld segments and move around to give the latest weld area a chance to cool. That's 18 gauge sheet with some 20 gauge strips. Also, some places are just straight weld bead practice that penetrate deeper, so that's worse on the warping issue.
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Robert
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Re: multi-layered sheet metal

Post by dutch »

nice. The gas really helps.

Looking at the welds I would say you need less wire and / or more amps.

The most important to understand when welding ( sheet ) metal , is the why it warpes.

When you heat the metal it expands and when it cools down again, the hot molecules on the edge of hot and cold are compressed because of the expanding. This makes the surface area smaller than it was before heating up. That`s what causes distortion. That said, mig welding small parts and having it cool down inbetween creates and uneven heating of the panel and therefor an uneven shrink and uneven distortion. This creates a wavy panel which is really hard to correct. When I need to get panel really straight, I gas weld. ( tig works fine too, but I suck at tig welding...) With oxi acethylene I introduce a lot of heat but I weld in the longest pass possible so the heat and shrink are even which leaves me with hardly any distortion, just a little shrinkage.
Since you need heat to actually make two parts melt together, there will always be some kind of distortion. Now, this is all info which is not really intersting for your panel repair. Just get it in there ,solid and water tight. The best way to keep mig welds straight in my experience is to tag the panel about every 3/4", grind the tags down a bit ( not too much) then weld between and grind the weld immediately. one time heat, one time shrink and less mass to hold heat. Go crossway around the panel and let it cool down non forced in between welds. Hope this helps.
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Robert Bondi
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Re: multi-layered sheet metal

Post by Robert Bondi »

Thanks for all the tips! I finished the actual weld repair panel on the car. I think I managed to execute most of the advice given. It's not terribly pretty, but I think it is functional and no damage on the interior side, so those main goals were satisfied. Not surprisingly, my practice weld beads are much nicer than what I was able to accomplish under the car for a variety of reasons. Anyway, here are the highlight pictures and some comments:

Damage region prepared @ right rear subframe mount
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Initial poster board template
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Panel forming
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Panel forming
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Panel forming. This turned out really well.
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Turns out a jigsaw worked fairly nicely with an appropriate blade for metal and using 1/4" plywood backing.
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I used 4 layers to protect the interior in this sequence. Nothing got through the foil and just a little bit of wet towel steam seen a few times with the assistance of my helper.
1. Welder's putty and aluminum foil to fill all those spaces that might pass sparks
2. A sheet of aluminum foil over the whole area on the inside
3. Wet towel
4. Welder's blanket
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Image of the bottom layer of protection (post-weld)
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Initial fitting of 20 gauge steel panel
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Initial fitting of 20 gauge steel panel
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Incremental tack welding and forming. This wasn't easy. A few tacks broke in the forming/shaping process. Things got easier further in with less degrees of freedom to fight in the repair piece. The bottle jack was really helpful at some points to help bend the repair panel into place.
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Complete perimeter tack welding.
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Finished welding with a perimeter bead. This isn't very pretty and a couple holes were opened too.
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Application of POR-15. I also used POR-15 patch which is a higher viscosity product that comes in a tube like toothpaste. I used the thicker patch over all my weld seams to both fill those couple holes and mask the roughness of my amateur weld beads.
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Complete POR-15. Silicone was used around the subframe bolt guide boss to fill/seal the gap just as BMW had filled the space with a soft foam gasket.
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Finished and top-coated
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Finished and top-coated
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Robert
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Joined: Sat Apr 15, 2023 8:22 am

Re: multi-layered sheet metal

Post by dutch »

Well, for a first time repairjob, I`d say you did great 👍
I can`t see how much of the factory metal was cut out underneath the patch panel, but make sure you do some additional rust prevention in there after welding. Same goes for the inside of the rocker panel.
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