Welding Aluminium

rustybarge

rustybarge

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Hi All,

I've successfully welded steel plate, no problems, And it's relatively easy with a simple arc welder.

I want to build a small 8mtr catamaran out of 6mm aluminium. I've read that it takes years of experience to weld alloy.

Is this true?

How hard is it too tack weld the plates, and how many amps would that take?

Would it be better to get in a pro. To do the welding?

Thanks,

Peter.
 
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A simple ARC welder will not do BUT a simple MIG set up will do the trick. If you can make a good arc weld with a neat and consistant weave pattern then MIG is actually easier IMHO.

Pay for an hour or so 1 to 1 tuition and practice before you start on the cat.

There are some gotchas but it is not that hard to learn. Days not years.

TIG on the other hand is HARD.
 
You could use a mig for ali, but you need the right shielding gas and wire. Argon is the norm for the gas.
TIG would be better. A lot of people say its hard, I've found its getting the "Knack" thats the key to decent welds.
I have used a mig for ali, but you need a decent pro machine with a decent sized bottle of gas. These little diy things just wont cut the mustard.
 
I'm far from being an expert welder. I have done some aluminium work but it is much harder to weld than steel as it is very easy to end up with holes in the work. I assume that it's the lower melting point that causes the problem.

Why not get a few bits of aluminium and play around with it?

FWIW I wonder if 6mm thickness is a bit OTT for a 8m boat?
 
Sometimes Wikipedia is worth a read

http://en.wikipedia.org/wiki/TIG_welding

If true then worth learning TIG for aluminium jobs. By the way, the reason it is not easy or possible to Arc Weld Aluminium is because of its high reactivity. The reason Aluminium does not corrode in normal circumstances is because as soon as you cut or break it, the surface is protected by a fine layer of corrosion which stops it proceeding further; aluminium does this spontaneously and the process is known as passivation. In the presence of oxygen all you will do at arc temperatures is produce aluminium oxide (a useful powder in its own right but not on this occasion).:)
 
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You don't TIG weld aluminium boats together! It would take for ever and the heat input would buckle everything to kingdom come. You can TIG little fittings perhaps and certainly use it for stainless, but MIG is perfect.

There are different gases and your choice is one of cost versus other benefits. The biggest help is to get a MIG gun that pulls the wire and feeds it, rather than the normal push feed used with steel welding. The aluminium wire is less stiff so can buckle and give feed problems with a normal push gun.

Finally the fit of your pieces is more critical with aluminium and make sure you use the correct disks on your grinder.

Wood workers make excellent aluminium boat builders as the tools and 'feel' of the material is similar. Steel welders often don't.
 
I think you'll need a fair bit of power to get a good weld in 6mm ally. Although it has a lower melting point, it conducts the heat away from the weld very quickly too. I think the better quality TIG sets reduce the current (or have a foot pedal for the operator to reduce the current) a few seconds into the weld, otherwise its easy to blow holes in it. As TimBennet says, TIG isn't really the way to go on a job this big, but I've never tried MIG welding aluminium and I don't know if the quality of welding set makes as much difference as it does with TIG.
 
rustybarge said:
Hi All,

I've successfully welded steel plate, no problems, And it's relatively easy with a simple arc welder.

I want to build a small 8mtr catamaran out of 6mm aluminium. I've read that it takes years of experience to weld alloy.

Is this true?

How hard is it too tack weld the plates, and how many amps would that take?

Would it be better to get in a pro. To do the welding?

Thanks,

Peter.
Click to expand...

You will end up with most of your hull on the workshop floor. :D
Get in a pro.
 
Hi Over the years ive welded most things but ali is the one I steer clear of, the set up used by a company I visit is a proper TIG unit. Mig welding ali Ive tried and would not get involved with it now as its a mare. If you only want to tack pieces together gas would do that without a problem. An old friend of mine used to fully gas weld the ali fuel tanks for the Motor cycle racing team when Sheen and co were on the scene so I can verify it works fine. If you do decide to go that route then get it properly welded by a company as with the vibration etc from the sea would split it open if not done well. Proper tig welding with the right machine in the right hands is not a long process as some believe, the company I go to in Colchester do great lumps of structural units and its quite a quick process. Hope this helps.
 
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Mixed advice here. Get onto www.mig-welding.co.uk and read the tutorials. A good mig welder with a spool gun will do the job. Gas needs to be Argon. There was a thread on the WBF about a fire boat build ( a BIG ally boat) all MIG welding. But it does need some practice. Your pic of a cat requires a huge amount of good welding, but is well worth learning the technique. Cost of good kit (weld-equipe) can be recouped after you finish, as there is always a market for good kit.
DW

My Kemppi 150amp welder is OK up to 4mm in ally. So a unit in the 200amp range sounds suitable. A spoolgun is around £50 on the 'net. Well worth the extra for such a job.
Stay away from cheepy kit built at low cost in China. Much of the good kit is also built there, but at a better controlled factory and sells at a reasonable price with a decent warranty.
 
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Mig is the only real option for hull plates, pulse transfer keeps the heat & distortion down to a minimum although a strict welding sequence still needs to be adhered to. If you buy off the shelf kits they will normally supply an assembly, tacking a welding sequence.

Normal mig torches are no good for Ali, the wire birds nests every 2 seconds, even with proper feed rollers and Teflon liners etc. push/pull torches can be used where there's a second set of drive rollers in the torch head but the torch mounted spools of wire seem to be the more popular route.

Although I haven't got much experience in hull building and not done much Ali mig welding, I have been in the welding and fabrication trade for 25 years. Building an Ali boat would be a good test of my skills to say the least, for a hobbyist - I'd say ask yourself can you afford to throw the thing in the bin when you **** it all up?!
 
You see ali fishing boats being welded up on the quay in many Brittany ports.
Maybe they all used to work for Airbus?
Maybe its something you can learn and practice. Your second fishing boat will be quite good, the third will be a stunner!
 
Aluminium isn't actually too hard to weld if you already have welding experience, the right gear and a good grasp of the principles. If you don't have these - forget it!

You need high heat inputs as Al drags the heat away quickly. The metal also doesn't glow red when hot and is "hot short". This essentially means that the base metal will just drop away suddenly with little indication it is about to do so giving you some pretty ugly holes in your work (hull!) if you let it get too hot.

The surface oxide layer that protects aluminium from further corrosion forms in as little as 20 minutes and melts at over three times the temperature of the metal itself. This makes the preparation prior to welding important.

Aluminium MIG wire has the columnar strength of, seemingly, just undercooked spaghetti. If you try and use a regular MIG torch, even one fitted with a teflon liner, you will be sent near insane by birdnests and tangles before you have even welded your first stringer. Because you are working on a hull you will need a either a "push - pull" or spool torch. This will need to be reasonably long, or you will need to hang your wire feeder off a gantry.

It also distorts like crazy, so you need to be familiar with sequence welding techniques.

Tig is too slow and amplifies distortion issues.

Whether you use MIG or TIG, top end equipment is required. Cheapies won't be up to the job just based on required duty cycles alone.

If you can do the basics, however, tacking the hull together before getting a pro to do the rest could be feasible.
 
The difference between steel and aluminium welding isn't the doing it, but the doing it well. Steel you can cobble together and although it may look like a row of seagull droppings, will probably be strong enough.

Aluminium welds can look beautiful but actually lack any strength. So it's worth learning properly and there are classes at tech colleges or pay a good, full time aluminium welder to give you a series of lessons.

Don't be intimidated by the cost of good MIG welding sets - nothing about building a boat is cheap. Again get advice and even a brand new set (with warranty and back up advice from the vendor) will not be too costly when you sell it on at the end of the job.

What will be expensive is doing a half assed job with poor tools and poor skills.
 
Although it's nice to do stuff yourself, there's not much else to be gained from DIY. A couple of good experienced guys can turn a pallet of pre cut plates into a 20'-30' hull in 2-3 days, thats not really where the money goes.
 
TimBennet said:
The difference between steel and aluminium welding isn't the doing it, but the doing it well. Steel you can cobble together and although it may look like a row of seagull droppings, will probably be strong enough.

Aluminium welds can look beautiful but actually lack any strength. So it's worth learning properly and there are classes at tech colleges or pay a good, full time aluminium welder to give you a series of lessons.

Don't be intimidated by the cost of good MIG welding sets - nothing about building a boat is cheap. Again get advice and even a brand new set (with warranty and back up advice from the vendor) will not be too costly when you sell it on at the end of the job.

What will be expensive is doing a half assed job with poor tools and poor skills.
Click to expand...

Yes, very true. Another catch with aluminium is that you need to finish off the end of the weld (crater) properly or it has a tendency to crack as it cools.
 
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