A lot of people consider aluminum welding to be the hardest metal to weld. This in my opinion is debatable.
A characteristic of aluminum is that it has a great affinity for oxygen. The atoms of the aluminum combine with the oxygen in the air to form a high melting point oxide that covers the surface of the metal. Pure aluminum melts at 1200 degrees and the oxide that protects the metal melts around 3700 degrees. You have to clean the oxide off before welding. The thermal conductivity of aluminum is very high. In other words, when you apply heat to one area of aluminum the whole thing gets hot. For this reason, you have to apply heat much faster to the area being welded.
Aluminum has to be super clean before welding. You can clean it using a wire brush or using special aluminum cleaners that you spray on and then wipe off. It's important to remember not to use a wire brush after using it on steel or other metals. It picks up contaniments from other metals.
If you are going to be TIG welding aluminum you should use a pure tungsten, although the 2% thoriated tungsten will also work. When welding aluminum you don't sharpen your tungsten to a point. You want to have a rounded end. To get this what you can do is switch your polarity on your machine to DC+ and then hold your torch over a piece of brass and then touch the pedal. You will see the end of your tungsten begin to ball up. After a few seconds of this stop and remember to switch your polarity back to AC. The ball of the tungsten should be nice and shiny.
The amperage required to weld aluminum is a lot higher than that of steel. However, once you get it up to the right temperature you back off. A good rule of thumb to determine the right amperage that I use is this. Lets say that I'm welding 1/4'' thick aluminum. I convert that to a decimal form and this is what I set my machine too. For example in this case it will be 250 amps.
Pure argon is used when welding aluminum. It somewhat cleans the metal as its being welded. Now when welding thicker aluminum I will use a 50-50 mixture of helium and argon. By doing this you can get to your melting temperature a lot faster than with argon alone. However, the cleaning properties are not as good as with pure argon.
Before beginning the weld you switch your polarity to run on AC. Watch for the base metal to become molten before you dip your filler rod into the pool. This is where a lot of guys have trouble. They don't wait long enough to actually melt the base metal before they start applying the filler.
When welding thin aluminum, you have to have good tight fit ups or else you will find that the aluminum wants to run away from you when applying heat. A piece of brass behind the metal will help a little with this. Also, it will prevent burn through.
I think I could write a book on welding aluminum, I will try to incorporate better tips for certain applications in another blog. As I always say, try different methods and techniques because what works for me might not work for you. No two welders will weld the same.Click Here!
5 comments:
Sir, I'm a student of mechanical engineering from India and I'm currently working on a project on GTAW of stainless steel sheets. Could you please explain me about "bead on plate" method?
Hi Arun,
I am not quite sure what you mean about bead on plate method? Are you asking me about joining two pieces of Stainless steel sheets together?
hi... i am new into wlding so i need ur help... i am into a project that requires me to weld some screws head down on the back surface of a 16 swg 304 hairline finish SS sheet plates of dimensions 100 x 350 mm2.these plates have laser film pasted on one side....i tried argon welding ...but i cant do it without warping and bending the plates and also burning of the laser film and black spots on the front( which is a ctastrophy for this project.)...the hairline finish and the film on the front surface must be preserved while welding the screws on the back side and no deformation of the plates should be there.will TIG ARC welding solve this issue..is there any trick to achieve this. plz help...
I know exactly what you mean, I have also experimented with that and the fact that you are using 16 gauge and you are trying to weld screws in the middle of square piece of stainless. If you figure this one out let me know. Okay here's what I can tell you. You should use a nice thick piece of brass or aluminum on the back to act as a heat sink. You have to clamp the piece you are welding because it will warp and distort as soon as you add any heat to it. As for the laser paper, well you have to peel it back where you weld, there is no other way. I don't want to discourage you but even by doing all this it will still warp but probably not as bad. You want to keep the peice as cool as possible. Another trick is to wet some rags and place it close to the weld to absorb the heat. However, I have done all this before and I still had warpage, I have found that by making a frame out of angle iron and attaching the flat piece to that will eliminate warpage. However, this may not be practical. I would suggest using a stud gun. That is probably the best way to attach a screw with minimal heat and you wouldn't even have to peel the paper back if your heat was right. I hope this helps.
thanks tibor for ur suggestion....i found just the right equipment for my project....its a capacitor discharge stud welding machine..i found some one who uses this type of machine in my city...and got the job done...its amazing how well the studs are welded...without any burn marks or warping...and its quite fast as well ..u can weld 25-30 studs in one minute...tanks a lot tibor...i am grateful..
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