Aluminium Welding With Backing Bar

Thanks for the info.

We are using MIG, TIG puts to much heat into PM.

The preperation is before welding and then we do the acetone cleaning prior to welding.

The area is pretty much draft free and the gas flow 19lpm.

We have just bought a Bernard Centre fire torch for the next unit I hope that gives us better results.

Have you used aluminium extrusions with the backing strip before? This is the first time for me and I believe this must be part of the reason, I just cant seem to nail it down.

Thanks again

David

Since you are using MIG, beware to use a push pull system to be assured that the wire comes evenly and steady. I think you use a little too much current to run faster, not allowing the material to melt down enough.

(normally MIG should build up a bit more) Once you trigger for wire, get used to the sound of the gas, close to your ear. Gas needs to flow, but higher volume AND low pressure. You gave a pretty good picture, but make me one closer without flash but good light. I hope to be able to tell more.

We have welded almost everything that can be welded, had stuff from micro plasma welding, up to 400 Amps - Also the attack angle is important.

Use a big diameter gas nozzle. The gas must protect until the material sets.

If this is new to you, make sure you SEE and understand your melting pot. Use a lighter shade screen till you become familiar with it.

Try on samples and cut your welds to see mistakes. Make also sure that your backing is dry and close, to avoid air pockets.

As far as the welding wire: make sure it is free of oxidation on the reel too. Welding material: if this is in doubt try on a sample with TIG and use a few small strips, cut from your base stock channel. You can also try a smaller diameter size wire if your Push Pull can handle it. Wire diameter and material should go together.

This is the guy I want to trouble shoot any problems I might be having with Alum/ welding. Great Job!

Great answer again,

We are doing a few test piece this week and lowering the amps and travel speed will be one.

Pure Argon will also be used on several test pieces.

We will also be using the new centre fire torch that looks like it will solve any shielding issues.

We are using a push torch withy teflon liner and havent had any visible issues with the wire feed I shall take a closser look.

I plan on doing some macro on sample welds as the x ray is difficult to interpret and I suspect the porosity is in the penetration caught in the backing bar grove.

I will be fishing next week so I will send you better pictures of the joint etc when I return I will also have the results of the next 40 x rays.

Thanks again

David and Welders

I think your problem may be in the mixture of helium/Argon. I have not had a problem with polarity, but that may be a possibility. Lastly, your wire. Your welding supply rep should be willing to to bring you a couple of different types of wire.

good comment Bert, I had the rep in yesterday for the different Wire types he will only give a good price these days, no more free samples due to economy!

Thanks Dave and Team

Clean with 80 grit disks or paper and use 100% Argon. Any oxidation on alum. will cause problems.

dvmdsc said it well! clean-pure argon - absolutely! perfectly dry electrode perfectly clean surfaces - no iron possibly there is drift of grit from adjacent grinding operations or other work gas shield must be perfect Might try a competing welding supplier for wire. Good luck!

Good advice here. My only contribution is to inquire as to whether you're using DC or AC current / strongly advise you to use AC current in your MIG when welding AL. Good luck. Rayzer

Agree with all on the pure argon. I use steel wire brushes by hand, but never touch anything but clean aluminum with them. Not even any dust. Stainless brushes are probably better, but my clean steel bristles have not ever caused me grief. I would avoid any solvent, unless you know there is greasy contamination, in which case get it cleaned off long before welding. The brushing can be minutes before welding. You will have air behind the welding. Getting air 'washed off' the back will be difficult. Easier if you are welding pipe, by just filling it with Ar. Try TIG once, with a clean electrode. More flexible. If it works perfectly, you will know that air-behind or stuff on the backing strip are NOT the problem.

Fix one thing at a time, so you will know the exact problem when it goes away. Best of luck.

Aluminum welding is bit tricky compared to CS, SS & AS.

MIG is the best bet comped to TIG and you are in the right track.

But the parameters set by you is on the lower side. Al welding requires more heat input comparatively and Please increase the Amps to 160-170 and voltage to 24 -25 or so to get better results. A medium stick out of 15 mm is OK. Forward technique is also good.

Using of 1.2 mm filler wire is good (it is the minimum size available in the market) for Al welding and Magnesium ( good strength and crack resistance) & silicon based wires are OK.

Argon will be OK compared to mixed gases. Pl. make sure the purity level is 99.99 % and not 99.97 % as second type of gas may have more mount of moisture content. Less than 50 ppm in the gas ( moisture content) is good for aluminum.

You have mentioned of elongated pores and it could be mainly due to moisture pick up from the atmosphere and need not be due to shielding gas alone.

The atmosphere contains (at places like Indonesia, Ceylon, Indian-coastal areas) lot of moisture / humidity - which is more than 80 % and will definitely produce pores especially during Aluminum welding. Hydrogen from the moisture gets induced during welding very fast and to be eliminated.

Hydrogen is the main cause of porosity in Al- alloy welds. It has very high solubility in solid Al. If moisture, oil, grease (hydro carbons) are present of the solid filler wire or on the joint surface, the hydrogen generated by the welding arc is dissolved in the molten weld pool and released during solidification. The high freezing rate (of Al), especially in the case of MIG welding of Al prevents hydrogen from escaping out of weld metal and the result is porosity. Unlike in steels, even an extremely small amount of hydrogenous material can cause considerable porosity in Al & Al -alloy welds.

This could be avoided by a fast & short preheating to max.of 120 deg C for materials up to (3 to 5.% Mg – to avoid a decrease in mechanical properties) on the joint surface and between main plate and back up plate recess (gap) before welding .

Maintaining a inter pass temp. of 150 deg.C max. during welding. Seal weld the gap (at joint recess) on either side of the joint initially and then proceed on the mid area.

We have done bus bar welding of Al for projects in Ceylon and qualified welders taking above care. The rejection / rework rate was brought down to 1-2% compared to earlier 25%.

Best of luck.

Sridhar.

Hi All, Thanks for all the great comments and advice.

I believe we have cracked it. We changed our torch to a Bernard centre fire that claims better shielding gas coverage and does look the part.

We also made a heat sink which also acts as a guide for the welding torch and stops the shielding gas from blowing away so fast.

I think that the heat sink allowed the weld to cool at a slower rate allowing the entrapped gas to escape. I was fishing so I didn't see the welding only the results. Next car I will post some pics.

Thanks again David and Team