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MIG welding Aluminum

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Sir Joab

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Hey guys,
I'm in the middle of building a 1/2 VW and I need to weld new intake ports on the aluminum heads I cut in half. I have a MIG welder (unfortunately only 120V input) and 100% Argon gas, but on my test pieces I can't even get the welds to "bite". The metal from the wire just beads up on top the piece and doesn't even try to penetrate. I sanded the aluminum to try and get the cleanest surface possible, and I've tried all the power settings, and various gas pressures. The high ones just vaporize the wire all the way back into the tip. I've read all over the internet how to do it, but there's obviously something they're not telling me that I really need to hear...

I would buy a TIG welder, but my pockets aren't deep enough at this time. :depressed
 

TFF

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Usually when welding aluminum, the polarity is opposite of what you use with steel.
 

dino

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It's best to use alternating current when welding aluminum.

Dino
 

4trade

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120 amps is absolutely too low for cast aluminum welding. You can´t weld even much thinner material for that low amps.

Most MIG welders design (internal design parameters) don´t support aluminum welding very good. Aluminum need different design chart that steel, and MIG welders are design for steel welding.

I highly recommend to TIG weld that case. If you make all parts, skilled TIG welder will weld that case in couple of hours.
 

dino

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VW engine cases up to type 3 are magnesium.

Type 4 cases are aluminum alloy.

Both can be welded preferably using TIG.

Dino

Dino
 

Hot Wings

Grumpy Cynic
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Try preheating the heads. I've welded VW heads in the past with my MIG just fine, well, acceptably anyway, and the only changes are putting in the Teflon liner to replace the steel one, and swapping the CO2 for argon.


I thouhgt VW engines weren't pure aluminum and were made from an alloy.


The block/case is an alloy but the heads are pretty close to pure aluminum. Some new cases are pure aluminum, and weigh more.
 

4trade

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.....and don´t sand your weldable surfaces. Sandpaper will leave some dust and other contaminant on your surface and can make your job harder. Use file or air grinder type method for cleaning your parts. If you use small amps, surfaces must be much more cleaner that high amps (high amps can burn some level of contaminant).
 

Sir Joab

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Thanks guys, I tried out these tips and everything cleaned up to what it should look like except my puny welder isn't powerful enough to bite, even on my much thinner test piece.

So the only aluminum things I need to weld on my current airplane project are those heads. I can get a set of them done already for $600 (U.S.)... but my thought is if I can get set up to do aluminum welding for the same (or maybe a little more) cost I'd rather take that path. Is this possible? My dad has an old Oxy-Acetylene torch, but I've heard even the most optimistic welders down-play that option.

So what would you guys recommend?
 

4trade

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If you have only intake ports to weld your head´s, find somebody aluminum welder. He/ She do your welding job approx 1 hour. (depending your level of construction of parts/ fitting). Then you have good, airworthy part. Cost for job is minimal.

You find good aluminum welder usually for boat building/ repairing company, marine engine builder company (they weld those cracking fins and sometimes props) or big metal working company.
 

Head in the clouds

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So what would you guys recommend?
The right advice is here already but not necessarily all in the same post...

1. Your small welder could probably do the job but you MUST preheat the work in an oven to around 150C/300F minimum (an hour or so in your household domestic oven is fine) and, unless you can get the job done quickly you will need a friend wielding a large oxy torch with a heating tip (like a big blowtorch) to keep it very hot. Practice on the other half of the head that you're not going to use...

2. You must replace the liner in the MIG torch with a teflon one. The steel one will gall on the aly wire and make it stick to the tip and also prevent it from running out smoothly and so you will get a terrible weld full of contamination.

3. You must reverse the polarity. i.e. off the top of my head I can't remember which way but if the wire was positive for steel then you change it to negative for aly (or v.v.). You make that change near the pinch roller of the wire feeder.

4. You must use pure argon gas (as you are) and beware too high a pressure, a fast gasflow tends to pull air into the gas shielded area and make things worse. Black on the weld puddle is either not enough gas pressure or too high a gasflow. If you need more gas to properly shield the area use a larger nozzle so that the gasflow rate is reduced.

5. Aly conducts the heat away from the weld area so fast that you will need every bit of power that you can get out of your welder, and use thin wire - 0.030"/0.8mm. The thin wire will give you more trouble with sticking in the tip but them's the breaks. You will need a liner and tips to match the wire of course.

6. Clean the workpiece with alybrite before the oven.

7. Aly welds well with oxy but it is an art which requires plenty of practice. You still need the preheat and the right flux and you are keeping the air away (to prevent oxidising) with the flame rather than a shielding gas. Plenty of TIG experience helps with the dexterity required to shield and fill at the same time.

8. Consider taking the job to a welding shop...:ermm:
 

4trade

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1. Your small welder could probably do the job but you MUST preheat the work in an oven to around 150C/300F minimum
I have been welding aluminium (MIG and TIG) several miles, and i say that you cannot weld this kind of job for that low amps. If you manage to "burn" some kind of melted aluminium material that keep those parts together, it´s not airworthy or safe.
 

Sir Joab

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Some conversions use sheet plates fastened with small screws, no welding required.
BB
I thought about that, but my heads are the single-port intake. The Port was literally split in half to the point where they "Y" off to the two cylinders. In fact I split them so cleanly I can use one half on one side and the other half on the other. :gig: ...So I guess I'll have four tries to get two heads.

I have also found aluminum arc welding rods. This seems like a nice solution... Are these things any good? I've never heard of them before.
 

Dan Thomas

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I did mig welding on aluminum for some time back in the 1980s. A 120V welder is useless for that. The polarity is reversed, as others have pointed out, and I also had much better welding when I used a helium/argon mix. I ended up using two bottles (one argon, the other helium) and two flowmeters, teed to the welder's gas line, and adjusted the flows to what worked the best for the castings we were welding. Helium brings the heat up a lot and you can use less amperage.

Teflon liner, rubber roller so that the aluminum doesn't get deformed by the rollers. No preheating at all.

We also welded a lot of cast iron using nickel wire. Lots more hassle than aluminum. The best aluminum guys are those that have never welded steel. No habits to unlearn. Aluminum has a very narrow plastic state temperature band and steel welders can get frustrated by its sudden melting away into a puddle.

Oxyacetylene welding aluminum is a futile pursuit.

Dan
 

Head in the clouds

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I have been welding aluminium (MIG and TIG) several miles, and i say that you cannot weld this kind of job for that low amps. If you manage to "burn" some kind of melted aluminium material that keep those parts together, it´s not airworthy or safe.
You certainly need good welds for this but it's not impossible to do that with a small welder. My Mig is only 120A and I have easily welded billets weighing around 5kg/12lb. You definitely need to do test pieces and if you're not able to sustain a good puddle then increase the preheat temperature until you can.

The same applies with my TIG, if I am to weld aly with any sizeable mass it has to go in the oven first.
 
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