|Tig Welding How To - Tig Welding Aluminum Castings with A Miller Dynasty 200 Amp Inverter
By Jody Collier
One of the things you learn if you have a small Miller Dynasty 200 a/c d/c inverter Tig welder is how to do welding on thick aluminum castings with less amperage. I have had the opportunity to weld with two really popular Tig welding inverters that are capable of Tig welding aluminum using 115v or 230v power; the Miller Dynasty 200dx and the Lincoln Invertec v205t. Both machines are high quality power sources but both of these welding machines are limited to around 200 amps output. Being limited to 200 amps makes you weld smarter not hotter. Instead of just setting the amperage to 275 and plowing ahead like you would on a heavy duty Tig Welding Machine, you have to use your head. Preheating thick aluminum parts is a proven way to reduce the amperage required to weld. But when you are in your garage and do not have access to a heat treat furnace or oxy-fuel torch, how do you preheat? Well, here are a few tricks I have learned:
Use a gas grill. But make sure the aluminum part to be welded does not contain anything harmful that is going to taint the burgers you might want to cook next week. (It would actually be a good idea to have a cheap grill dedicated for preheating aluminum parts)
Wrap the part in aluminum foil and place it on the stove on medium heat until the heat conducts through the part. (About one or two beers later the part will be warm enough to weld)
Use a small propane torch and keep it moving until the part is hot enough. (Just hot enough to sizzle spit should be ok.)
Another tip for reducing the amperage needed to Tig weld aluminum is to use a 50/50 or 80/20 argon/helium gas mix. The added helium really makes a difference. Not only will you need less amperage, but the aluminum will puddle quicker and cleaner than with pure argon. Trust me on this one!
Lastly, I recommend using as small a Tig cup as possible. Some people refer to them as Tig welding nozzles but in any case it is the ceramic tip that goes on the end of the Tig torch that directs the shielding gas to the weld and protects the tungsten electrode from being oxidized. Using a small Tig cup requires less shielding gas. For example a #7 cup might require 15-20 cfh whereas a #4 cup will only require 8-10 cfh. That much less gas blowing on the part makes a big difference in the amperage required. In addition to this, the arc energy that is dissipated in the form of cathodic etching (also called cleaning action) will only go where there is gas shielding so there is extra arc energy available to be focused at the weld puddle.
I reminded myself of all these tips just last night when I welded a 4 inch machined ingot of 6061 aluminum using a Miller Dynasty 200 amp Tig welding inverter. I needed to replace some material that had been miscut by a machine shop on a prototype part that already had a lot of machining time invested. I used the exact welding tips I mentioned earlier in this article: I placed the part on the stove and preheated it to around 200 F (exactly one beer). I used a 50-50 argon/helium mix, and I used a 3/32 dia thoriated electrode with a #4 ceramic Tig nozzle. I was really surprised when I only needed about 170 amps to get the job done, even though the part was pretty massive.