Ever since I bought my Millermatic 130XP MIG welder, I’ve been having problems welding holes in sheetmetal.
I’m using the lowest voltage setting, and a wire speed of 45, as the chart on the machine suggests. I’m using a mixture of carbon dioxide and argon gas, with the flow set to 20 cubic feet per hour The wire is 0.023-inch ER70S6, and I’m using a contact tip with a 0.023 hole. The polarity is set correctly. The thickness of the sheetmetal on my car is between 30 thousands to around 45 thousands.
I removed the paint from the front fender and attempted to fill three small holes by putting a spot of weld over them. The holes did not fill easily, and the area of “welding tries” is now 1x2 inches, and expanding, with troubling panel distortion.
I have tried using a magnetic hole plug welding fixture with only a little improvement. I recently purchased some 4- and 8-inch magnetic copper backers, which I have not yet used.
I believe that nozzle of the gun should be flush with the contact tip, but on my gun, the contact tip is recessed almost 1/4 inch. The nozzle I’m currently using is a Radnor 21-50 Tweco-style copper, with a 1/2-inch bore, and I have seven other size nozzles. Yesterday I went to the welding store and bought a nozzle that is about 0.20 inches shorter. The inside diameter of the tip measures about 3/8 inch.
I have three questions:
One, what should I be trying to achieve as far as a nozzle/tip relationship? Two, which nozzle should I be using? Three, what are some other factors that I need to consider to get a decent weld?
Via the Internet
I wish more people who write me would be as detailed with their description—thanks!
I normally keep the contact tip flush with the nozzle or slightly recessed. I usually use a 1/2- or 5/8-inch nozzle, but again, I don’t think you’ll see very much difference for filling holes with any of the nozzle sizes you mentioned. I don’t think there is any problem with your machine, the settings, or the gun and nozzle. I suspect the problem is with your welding procedure, as I’m sure you know different metalworkers use different techniques. As long as you are getting the results you want, the specific approach you take isn’t so important. Since you are not getting the results you want, we’ll dig a little deeper.
The largest hole I would consider filling by MIG welding alone is about 1/4-inch diameter. If the hole is larger than 1/4 inch, it’s best to fit a sheetmetal plug into the hole, tack-weld it, hammer the plug to ensure it’s flush, then finish weld it. This way, you can fill a hole of any size in an efficient manner.
Now that you have a “mess” that’s 1x2 inches, your best bet is to cut it out completely, cut a sheetmetal path to fit, and weld it into place.
If you are just learning to weld, it’s best to practice on scrap metal until you build some control with your machine, and to find what procedure works best for you. The first step would be just laying down beads on a scrap piece. Then you can try filling small holes, and then try filling larger holes with plugs fitted into them.
There is some benefit on backing a hole or patch with a copper pad when welding, and this is easy on flat panels. Unfortunately, on a contoured panel, there will very likely be an air gap between the copper and the metal you’re welding, which defeats the effectiveness of using the copper backer as a heat sink, although it still offers the advantage of providing a surface you can load the filler wire against, and the molten weld metal won’t stick to the copper.
Contact me again if you’re still having problems.
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