Robotic welding aluminium

[Fingerz]

Hello and thank You in advance! I have been charged with setting up and programming an old GE P-50 welding robot to Mig weld .060" and .080" aluminium. I am using .035 aluminium wire and a Miller deltaweld 450 welder. I have done a fair amount of laser welding in the past but am not very experienced with mig welding. I was hoping that someone could give me some advice on where to start as far as speed, amperage, voltage, wire feed rate, etc. Weld quality is more important than speed for this application. Any tips tricks or info would be greatly appreciated!
Thanks, Fingerz

 

[attilon]

Hi!
Al has great heat conductibility.
The equipment manufacturers such as Miller, Esab and Fronius have synergic database for welding. They have for aluminium too. If quality is most important, it depends on the legths of the weld. The longer you weld, the more heat you introduce the space between the Al plates will get wider and wider. Thus you should be very carefull with the heat you introduce. To controll this, the welding current comes lower and lower according to a certain current slope, that manufacturers programmed in the memory unit of the source. If your source is not synergic, that's also not that big problem (I hope), ask your Miller dealer to give you this database and you programme it into your robot.

The synergic sources have inside database, you only introduce parameters as type and thikness of parent material, gas type, type and diameter of wire, and it gives you the wirefeed, volts and you can only fine-tune them, depending on your specific task, several percent + or -. This way you can not miss too big with the parameters.

Other problem would be Al2O3 from the surface of the plates, it is 4 times heavier then Al, so when welding, it goes to the root of the weld, or remains inside the weld, anyway, you have a fair chance for craks. Clean material is essential. The ionised Ar gas brakes that oxid while welding, if there is not too much.

If you weld tubes, you might want to protect the root from inside with forming gas (I would use Ar, but you have to check the pressure inside the tubes, it can blow upwards the weld), and outside you weld it.

 

[28021973]

If you are not an experienced Aluminium mig welder, you have got a big hill to climb..!

Even if you get all the parameters, I guarentee you will still have problems.

Wire feed consistency is the key. You need a push/pull wire feed unit. Keep the length of your welding torch short if possible without too big an angle in it. Use a shorter hose package.

Your contact tips must be the aluminium rated type i.e they are slightly bigger inner diameter due to the aluminium wire expanding with heat. Get a rep to supply you with alu rated..!

Try and use only 15kg welding spools of wire if possible.

Gas flow is critical, pre gas flow is critical as well. Make sure you program a pre gas flow before you ignite the arc.

You may find you welds are very cold and porous at the start, try starting your weld lenghts 5mm or so down the seam, then quickly drive the robot back to the start with the arc on, then weld over the top.

Failing this for total removal of porous weld, you can try a lighter gas i.e Helium, it's expensive but its fantastic for alu welding.

If you want anymore help let us know....

 

[attilon]

What 28021973 says about beginning the welding works if you weld manually, with the robot it is slightly other style. You attach a pair of weld-beginning plates in front and behind the seam (they are at least 50mm long) and you begin the welding on the plates, so the porous part will be on these plates, when you arrive to weld the actual seam the porous part was long left behind, you make the weld, and you finish on the other pair of plates, attached at the end of the seam. After that you cut the plates down.

I wouldn't use He. That is used for stainless steel. At the aluminium welding process you use Ar, because they are heavy molecules, with a much higher ionizing potential, so at welding you phisically bombard and destroy the Al2O3 from the surface of the Alu plates. You have to do this because the melting point of the Al is at about 723 Celsius while Al2O3 from the surface has roughly 2500 Celsius melting point. Helium is not heavy enough for this purpose.

You could use some Ar75%He25% gas. That would help. Also you could use pulsed welding current, it has the same effect as a.c. current at WIG welding.
Also 28021973 is right about the contact tips and push/pull unit.

 

[28021973]

You cannot use welding plates on an inside corner, this only works in basic welding theory i.e. on long straight weld seams.

You would end up with tooling costing you 10x the price by adding this to all weld seams, if it was at all possible.
Then there would be additional costs for clamping and unclamping sequences in the process, plc programming, cross communications between plc and robot. Access for the torch, what about a tandem wire feed torch, its a lot larger than a standard mig torch.

We had porosity in a job using aluminium and the Welding Institute recommended using Helium, the lighter molecules in Helium allow the gas to escape in the early part of the weld before the weld pool cools. Because the weld pool is cold at the beginning due to good conductivity of ALU, this traps the ARGON underneath the surface of the weld causing porosity. Hence, no need for welding plates..!

http://www.twi.co.uk

ionization properties = 24.587 Helium
ionization properties = 39.948 Argon
Correct on this assumption.


Attilion - Your theory is 100% correct I cannot disagree with you, but in Practise, and I have over 10yrs ALU robot mig welding experience, it doesnt work.
Until im prooved otherwise, I will live and die by my own methods.

 

[attilon]

Yes, you are right about the use of welding plates, you use them where you can, not everywhere. It really depends on the aplication you have.

Also that's why I like welding. It can work in many ways, and then people wouldn't try something else if they already found a way. And they are right about it.

I also have some experience with many kinds of aplications, beeing welding engineer for eight years. I'm also sure that with the "begin somewhere and come back" starting method you can never garantee that underneath the start you wouldn't left some pores, but if you dont't have other choise, that would be the best shot you've got.

Regarding shield gases, ionization properties and arc stability (Ar, He and Ar-He) for Aluminium MIG you can check this link:

http://www.praxair.com/praxair.nsf/0/b09d9336e459a16285256561007b0c29?OpenDocument

Now the materials welded by Fingerz are thin, so keeping this in mind I'd do as follows: first I'd try pure argon, if it wouldn't be ok, then I'd try Ar+He, and only if that wouldn't give the required quality only then I'd shift to pure He.

 

[Fingerz]

Thank you both for the input ,it is greatly appreciated! After a few hours of actual testing i've had the best luck with 1-2 cm/sec welding speed and 80amp/120 volts. However these settings burn through right at the end of the weld/edge of the part, so I'm going to try to speed it up the last 3/4 of an inch or cool it down. I have already realized the EXTREME importance of part consistency, it doesn't take much of a gap to ruin the weld. Ar seems to be working quite well, little to no trouble with porousity. Thanks again and I'm sure I'll be back with some more questions