Tuesday, July 13, 2010

The Secret of Steel: Arc Welding Thin (0.02") Sheet Metal

"Was mich nicht umbringt, macht mich stärker."
(i.e. "That which does not kill us makes us stronger.")
Friedrich Nietzsche

This article assumes that you are familiar with arc welding; you perform all tasks described here at your own risk.

I wrote this article, because most of what you find regarding this topic on the net will be negative. Most people will want to encourage you to invest the extra buck to buy a MIG welder or ask you to buy weird stuff like Eastwoods' Stitchwelder. As it turns out, most of those people giving such recommendations actually never did arc weld thin sheet metal or never bothered trying, which brings up the following question.

Why Would You Want to Arc-Weld Thin Sheet Metal
The truth is you actually do not want to if you have other options. Unfortunately, not everyone is willing to afford a nice MIG welder and all the pricy accessories like shielding gas cylinders, regulators and spare parts for the wire feed mechanism that all too often breaks. Moreover a MIG welder is quite sizable. If you like me do not have your own shop and prefer to work in the field, you need something small and versatile to carry around. In my case a cheap inverter worked best. In addition to being small it actually runs of regular 115V-15A sockets.

Another good way to weld thin sheet metal is brazing. However, as with MIG welding you have to worry about gas cylinders and if your equipment fails or is improperly maintained you not only risk redecorating your place, but probably your neighbours' place as well.

I am not trying to build a case for arc welding thin sheet metal here, but it is possible if mobility, size, and cost are pressing factors.

What Are the Drawbacks
First of all it is very difficult and will take considerable practice. In addition to that, arc welding creates lots of heat and will in almost all cases create heat distortion. For example, welding (visible) car panels will be quite difficult. For thin sheet metal, TIG, MIG and gas welding will be easier than arc welding. If you still decide to use an arc welder go on...

What Do You Need
  • A DC ARC welder that can go as low as 20-25 amps (if yours doesn't you may consider getting a current limiting diode, or get the Stitchwelder that has one)
  • E6018 (aka. farmer rods) or better E7018 1/16" welding rods (which need to be baked before use)
  • Thin sheet metal, 0.021" was what I used
  • Lots and lots of practice (described below)
Practice, Practice, Practice
The first thing you should get used to is to strike the arc at very low amps and avoiding burning holes into the sheet. That can best be practiced by padding. Padding refers to adding more material on a sheet of base metal. You are basically burning the rods down on top of the metal in straight lines.
  • Set up your arc welder to straight polarity (DCEN) that will keep the heat on the rod and not on the base metal,
  • Dial down to 20-30 amps,
  • Set up the sheet, preferably over two bricks so that the bottom of the sheet is hanging in the air.
The rationale of the last point is to make it harder (or more realistic for auto body welding). If you use a backing plate or even a heat sink (a block of brass or copper) it will make it very easy.

Padding
The first thing to do is to strike an arc. At those low amps the touch-start is not an option, as soon as the rod will touch the sheet it will stick. The only way it worked for me was the match striking technique. You strike the sheet and as soon as the arc starts you pull it off to maintain a continuous arc. Move to the working area and do some straight lines. And trust me this is way easier said than done. For the start your either have issues with sticking rods or happily turning your sheet into Swiss cheese. After each weld clean of the slag, brush the area clean and inspect the weld. After you clean off the slag you will probably see a big mess. See my first trials with reverse polarity; I just turned the sheet into Swiss cheese.

wrong polarity (DCEN) -> Swiss cheese

straight polarity (DCEP) looks a bit better

Butt Joints
This is probably something that you anticipate doing on your truck or car in the far future to put in patch panels for rust repair. A butt joint is to place two pieces of sheet metal together side by side and then welding them together. Especially when welding thin metal it takes considerable skill because you easily burn off the edges of the joints and actually tear your joint apart than making one. As you see in the picture only one joint actually looks reasonably sound (closing both eyes on heat distortion). The trick here is to work towards the joint. You do not in any case want to start filling the joint directly. As soon as the rod touches one of the corners, you will burn a bigger hole. Instead start from the sides of the base metal and do a couple stitches (about 1/2 in) around the joint. Let it cool off, clean it and do more stitches until you have a continuous ring around the joint. This will reinforce the thin sheet metal and prevent it from burning away as you near the joint.

Drawing to come.

Now fill in the gap in several stitches. Filling here is tricky because you will still burn holes. In order to reduce the heat, use a whipping motion by pushing and pulling the rod into the puddle in the joint, move quickly and after each 1/2 inch wait, let it cool off and clean it. Because you might burn holes, you need to repeat the process until the sheets stick together. Heat distortion and deformation will be an issue. Trust me; this would have been much easier with a MIG welder. Below failed and succeeded attempts.
The good: left side ones; bad and ugly: right side ones

Tee Joints
To come.

Before Work on Your Car or Something Important
Because under your car or whatever precious item you want to fix is probably pricy, you may want to practice a bit more. Try padding, butt joints and tee joints in vertical position upwards, downwards and overhead. After you master that, you may consider yourself capable of arc welding thin sheet metal. When you work on your car be sure to take safety precautions, starting from disconnecting the battery taking everything out that can catch fire up to having a fire extinguisher ready. Especially the oil sprayed behind the panels and inside the frame to keep the rust off is very likely to catch fire. When welding frames, you should grind the weld down to check the quality. Poor welds will actually weaken your frame.

Conclusion
Yes arc welding sheet metal is difficult, tedious and probably a bit insane but it is feasible. I would compare it to performing plastic surgery with butcher knives. Every surgeon can operate a scalpel, but only a few could work with any tool. Now you know the secret of arc welding thin metal sheets.

References
Manowar: The Secret of Steel

3 comments:

  1. I like this blog its very informative and attractive also. Thanks to author for this post it’s very easy to understand. sheet metal fabrication companies

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  2. Great informative post. I get more information from this. That information is so helpful to us.Will be visit again on your website.

    Metal welding

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  3. Arc metal and steel arc welding are now most common in construction process.

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    ReplyDelete