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TIG, MIG, and Aluminum Welding

SOLs,

I have been reading the comments on welding aluminum and thought I would add my 2 cents. I am by no means a welding expert but I have taken TIG and MIG welding classes at a local community college.

While overall welding is a simple concept, the devil is really in the details. Fortunately, we don't usually have to worry about them, the metallurgists and welder manufacturers do. Also in our favor, steel is pretty amenable to welding. Other metals, including aluminum are much harder to weld properly and they require welding equipment of increasing degrees of complexity. The TIG welder is about the most complex welding machine car restoration people will ever need to use.

First off, lots of people are probably wondering what a TIG or a MIG really is. They are both types of metal welding equipment. The fundamental purpose of both is to heat metal to its liquid state and allow discrete parts to be joined. Often, additional metal (filler) is added in this process. The 'IG' part in both TIG and MIG stands for Inert Gas. This is one aspect both type of welders have in common. During the welding process, the heated metal is bathed in an inert gas. This is done to prevent oxidation which would otherwise quickly burn the heated metal. A great example of this oxidation is the operation of a cutting torch which heats metal and then blows compressed air on the surface.

Otherwise the two types of welders are quite different. A MIG welder applies electrical power to a metal wire which is then fed through the center of the inert gas cone. A ground clamp is attached to the parts which need to be welded. When the wire gets close enough to the grounded parts, the current arcs across the gap and generates enough heat to melt the wire and the parts in the weld zone. Notice that the heat source and the filler material are the same. BTW, you can run your MIG using a flux core wire without the additional inert gas. In this case, flux vaporizes in the weld zone and displaces the air. However, this process is kind of a cross between traditional arc welding and MIG welding. The low price "MIG" welders you see advertised use a flux core wire and say 'wire feed welder' in the fine print.

A TIG welder separates the heat source from the filler material. The TIG welder has an electrode made of an inert high melting point metal (usually tungsten and some trace alloying metal) The current runs through this electrode, which you hold in your hand, and arcs to the parts you want to weld. With the electrode, you heat a specific area which then turns into a nice pool of molten metal (provided you've done everything else right!) By developing a molten pool on two discrete parts, you can cause them to flow together. If you choose to add filler material, you add it much the same way as when brazing or soldering, i.e. by manually inserting it into the weld zone.

TIG welder power supplies are typically very sophisticated and give you lots of flexibility. However, two aspects of the power supply are critical for aluminum welding. First, you can weld using an alternating current (AC). The reason this is so significant is that combined with argon as the inert gas, the TIG welder will clean the surface of the aluminum. Its pretty neat to see this happen too. As the metal heats up, all sorts of oxidation will fly out of the weld zone. No matter how hard you try manually to clean the aluminum before welding, it will still have some oxidation on it. The second aspect is a continuously variable power supply, usually by means of a foot pedal. This allows you to very precisely control the amount of heat added to the work. Aluminum doesn't give many visual cues before it melts and the foot pedal helps prevent burning huge holes in the work.

Some people have discussed aluminum welding attachments for MIG welders, but I haven't had much luck with them except with brand new new, thick metal. Without the ability to clean the surface, they don't seem to be able to handle the old, contaminated aluminum we have to deal with in restorations very well. You can get a weld, but it really won't be the quality you want. Also, I'd really be surprised if the MIG attachment could add new material in corroded areas. I think your best bet to get a Healey shroud welded is to get access to a TIG machine or find a professional that has one. I found a good aluminum welder at the local airport aircraft repair facility.

Feedback

SOLs,

Thanks for all the compliments on my TIG and MIG welding post. I had no idea there was so much interest in the topic. My apologies for the delay in responding ... all I can say is that I have officially finished all my Christmas shopping.

You mention having Al welding done at the local airport; is that SFO or SJC or Oakland? Probably SFO as it has the largest repair facilities?

My BJ8 has a few stress cracks on the front and rear shrouds that will need welding. Would you mind sharing information on the welder you used? I'm in Fremont so all three airports are well within reach.

Unfortunately, The last bit of TIG welding I did was back in Illinois (at the Airport near St. Charles). I would try any of the airports you mention and also try San Jose State college (university?). San Jose advertises its welding program (the HEAVY METAL - Hot Careers ads) and you could probably get access to a machine or get a good recommendation there.

I used a machine made by Hobart; any high end TIG machine will work. Be careful of the newer low cost TIG machines on the market (a Miller machine comes to mind); they cut cost in a number of areas such as eliminating the high frequency component of the alternating current supply and they won't work as well.

Thanks for the very informative post. I am in the market for a wire welder that I can be used with 120vac household current. I have looked at the TIP welder (an outfit out of Ohio that has good service) that can only be used with the inert gas, and the Lincoln Weld Pack 100 that can be used with or without the inert gas. The TIP welder is around $400 complete, and the Lincoln is around $400 without the gas conversion kit. The gas conversion kitfor the Lincoln is another $100+.

I've been told that since the quality of the weld without the gas is so poor that it would be wise to not bother with a flux type welder, so maybe I should go with the TIP? Any suggestions?

First, I think you can get good welds with the flux core wire. However, it is definitely easier to weld with the gas. If your welding skills are anything like mine, I would get the gas setup. We just don't weld often enough to stay in practice and don't need added challenge from the machine.

Second, I have no real basis to rate the TiP welder. I have used the Lincoln machine you mention and liked it. These welders are mass produced and I find it difficult to believe that TiP can really produce the same welder for 20% less than Lincoln. Check the fine print. Does the TiP machine have a continuously variable wire feed rate and current supply? How do the duty cycles compare?

I've seen some pretty good welding using the gas torch, proper goggles, and pieces of cut up old shrouds for the proper filler metal.

Absolutely, Ken!

In the late 40's and early 50's when the Healey works was building cars, they gas welded aluminum all the time...and got awful good at it! Inert gas welders and wire-feeds hadn't been invented yet--and out in the English countryside I guess nobody thought to tell them you can't gas-weld aluminum, so they just did it. And much of it was mighty pretty work.

Agreed. I am always amazed at the work of truly skilled tradesman. I really didn't mean to imply TIG and MIG welding are the only ways to join aluminum. However, I do think they (esp. TIG) represent the best alternatives currently available.

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