Wednesday, 04 March 2009 17:51

Hey Toby 11---TIG Welding and Voltage Ratings

Written by Toby Chess

Hey Toby—Can you explain what TIG welding is? I recently took an ICAR class about aluminum welding and TIG welding was mentioned as a method of welding aluminum.

—Ole from WLA.

Hey Ole—TIG stands for Tungsten Inert Gas. It is an arc welding process that uses a tungsten electrode (non-consumable) to heat up the metal and filler rod is added to produce a weld. MIG (metal inert gas) is the choice welding method for aluminum in a body shop. MIG is relatively easy to learn and it does not need high frequency current to produce an arc for welding. On the other hand, TIG welding uses high frequency electricity to produce the arc. This whole high frequency theory is as clear as mud to me, so I wrote to Miller Electric and this is what they wrote back.

“That is, the current must heat the tungsten so it becomes a better emitter of electrons; at that point, the arc can jump from the tungsten to the work piece. One traditional option for solving DC arc starting problems, and the standard method for improving AC arc starts, involves superimposing a high frequency (HF) current over the welding current. Basically, the HF current forms a path for the welding current to follow and so the arc can be established. Unfortunately, HF interferes with CNC machines, computers and other electronic equipment because its frequency is similar to a radio’s and can be “broadcasted” (one user of continuous HF reported that it affected the accounting computer... and was changing invoice figures!).

Note that inverter-based TIG machines offer an “HF start only” feature that provides a brief burst of HF at the start of the weld. Inverter-based machines do not experience as much difficulty with arc starts or arc stumbling because the machine operates so quickly. In fact, all good inverters eliminate the need for continuous HF when AC welding on aluminum and other non-ferrous metals.” What is interesting to note is that high frequency will destroy nearly all electronic equipment near the machine (I found in the literature that a safe zone is about 20 foot diameter around the machine.)

This fact along with the more difficult master and more complex, TIG has not been the welding of choice is in the body shop until now. Miller Electric has introduced a TIG welder that uses inverter technology to maintain the arc and eliminates the harmful effects of high frequency. More on this machine later, but I would like to explain some of the basics of TIG welding as it pertains to aluminum welding. Aluminum, when exposed to the atmosphere (oxygen) and moisture produces a compound called aluminum oxide. This material coats the outer skin of the aluminum to protect it (very similar to a scab forming on a cut).

Aluminum melts at 1184 degrees Fahrenheit, but the outer layer of aluminum oxide melts at over 3200 degrees Fahrenheit. Also the oxide is heavier than the aluminum and molten oxide sinks into the molten aluminum, which produces a poor weld. Knowing this fact is the reason why it so important to remove the aluminum oxide prior to welding. With TIG welding, you can use DC current positive (electrode is positively charged), DC current negative and AC. AC current is the recommended setting for most aluminum welding applications.

During the welding process the electrode and base material alternated between negative and positive 120 times a second. The switching between positive and negative creates a cleaning action which removes the oxide from the weld (TIG welding produces a very clean weld). TIG welding as I previously mentioned is a slower process than MIG welding. The slow speed of TIG welding allows impurities and gases to escape to the surface of the puddle. When gas is trapped in the puddle a pocket or void is created (AKA porosity) and again TIG eliminates porosity. Another advantage is that TIG produces a very narrow heat affect zone when compared with MIG welding. Let’s take a quick look at TIG equipment. The torch consists of a handle, tungsten electrode and a ceramic cup. The torch can be air or water cooled. The torch is connected to the power supply with cables, hoses for the shielding gas and a hose for the water if applicable. Shielding gas for aluminum is 100 percent argon for collision repair welding (100%Helium is also used for aluminum, but is not recommended for collision repair). The heat (voltage) is regulated by a foot control.

If you want more information on TIG welding, I would suggest you take I-CARs WCA 04 class. Let’s look at this new TIG welder from Miller Electric. It is called the Diversion 165. It uses Inverted Technology (no high frequency is generated) and is safe to use around vehicles. It will weld aluminum from .75mm to 4.8 mm. It is priced right—under $2000 and takes very little time to set up. I purchased this unit and when I conduct I-CAR’s WCA 04 in the shop, I bring along the unit and teach your techs how to TIG weld. This is great hands-on training for only 2 I-CAR coupons. What a deal. I want to thank all of you who took me up on teaching I-CARs Aluminum repair class with its hands-on training (180 students since I wrote the article last December).   

Hey Toby—I want to purchase a new MIG welder and I looked at a 120 volt machine as well as 220 volt unit, but I can’t decide on which one. Got any suggestions?

---Jeffrey in LA

Hey Jeff—Great question. I have been using the Miller 140 auto-set machines for I-CAR qualification tests. It is a 120 volt machine and a real work horse. Each machine has over 500 hours use time and not one single problem. The only drawback is that will not handle .035 wire. Before proceding, I think it’s a good idea to think about what voltage really is, and how it will influence your decision. In electricity we have current, volts, and resistance. Current units are amps, basically the volume of electricity.

Volts are like the pressure, and resistance is the heat generated from the restriction in the current flow. If you look at water as an analogy (because you can see water), let’s say that you are going to have a party this weekend and you need to fill the wading pool for the kids and the big pool for the adults. You can fill the kiddy pool with a garden hose, but it will take forever to fill the big pool that way. What to do? Get a fire hose and it will do the trick. In welding, 0.023 wire is the garden hose and 0.035 wire is the fire hose. 0.023 wire (0.030 also) is the recommended wire for most collision applications. 0.035 is needed for repairs on frames (thickermetal). Let’s go back to the fire hose. If you were able to hook up the fire hose to a house hose bib, you would not get enough water. With 0.023 wire, you are restricted with the amount of current that it can handle (volume). You can handle more current or volume with 0.035 wire. The problem is that 120 volts has a limited amount of pressure and therefore it will not handle 0.035 wire. To increase the pressure, you will need a 220 volt machine, but they (machines) don’t handle 0.023 wire as well as 0.030 and 0.035 wire. Another consideration is price. 220 volt machines are usually one one-half to two-times the price of a 120 volt machine. It’s now in your ball park. Hold on for one second. There is a new machine on the market that will do it all. Miller Electric just introduced a new MIG welder designed for the body shop. It is the Miller 211. This machine works on both 120 volts and 220 volts. It also welds aluminum (you will need to add a spool gun). It will weld steel from .8 MM (24 gauge) to 9.5 MM or 3/8 of an inch. It has the auto-set feature and costs less then $1200. I have one of these units and it is a fantastic piece of equipment.

I sure hope this information helps and keep in touch and let me know what you have decided. The type of power supply used, either DC, a direct current or AC, an alternating current depends on the materials being fused. A DC current is usually used to weld steel, nickel, and titanium. This is the more usual procedure and also the one described earlier in TIG Welding. The AC, on the other hand, is used for welding magnesium and aluminum.

The AC method causes the electrode to alternate between positive and negative throughout the welding process. Since the electrons are now traveling in alternating directions, the tungsten electrode will not overheat. In addition, the positive ion bombardment would clean the work piece of impurities half the time (when electrode is positive and base metal negative).

 

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