Welding & metal working equipment choices
This is the section where I get to discuss working with aluminum and in particular welding. I will concentrate on two areas-
One of the reasons I thought this site would be a great idea is to get feed back from those people who, unlike me, really have experience building aluminum boats. I have included another opinion on welding equipment below and I urge you to read this E-mail, as it was written by a very experienced professional, Bruce Cope. I on the other hand, have no aluminum boat-building experience.
Also I have included list of my personal tips at the end of this section.
There are several sites and many books which tell you how to weld and what the different welding processes are. I think it is enough to say that you will find most of what you need in my list of essential books to buy.
This is a list of useful internet sites to visit when you have time.
Equipment for welding MIG
The first site I have listed above describes the MIG welding process in detail while the second gives a brief overview of the the Miller XMT 304 CC/CV power supply which was my second choice (should it have been my first choice?). When combined with a 1 pound, 200A Spoolmatic gun and possibly a TIG torch for welding thinner stuff and stainless steel, this would represent a more common choice for welding up aluminum boats. Note that this power supply is DC only and thus is not ideal for TIG welding aluminum. Very rough pricing would be about $2800 P.S. + $1000 S.G. and then the consumables on top of that. Not very different costs from my TIG setup (see next section below). Before we get to that here is a very impotant view point on the subject of welding equipment choice.
E-mail by Bruce Cope
Adriaan,
I couldn't stop myself from writing this E-mail. I saw your home page address on the metal boat bulletin board. After reading the bulletin board, I see that very few of the people on it have any actual experience building boats. If you are really going to build a 34 ft boat in aluminum I would advise you to MIG weld it, not TIG weld it. If you TIG weld it two things will happen---it will take forever to weld---and the boat will be so warped and distorted when you have finally finished, it will very disappointing. I speak from experience, otherwise I wouldn't be writing this letter.
I have been building aluminum boats of all types professionally since
1973. I personally have welded together at least 250 aluminum boats ranging in size from 8ft to 55ft,and have been part of the building and welding crew on at least another 100 boats that were up to 150 ft long, including Canada 11-our America's cup boat in 1987. I own an aluminum boatbuilding company out here in British Columbia. We build sportfishing boats from 14 to 25 ft and sailboats up to 50 ft. My company is not large (we have 3 MIG welders and 2 Tig welders) but we have a lot of experience. I would hate to see you making such a basic mistake and ruining your project just for the lack of a bit of information. We use Tig welding for small jobs where the welds will be visible in the finished product-such as hand rails, radar arches, - or the fittings on fuel and water tanks (not the seams)-- for repairing the occasional flaw in a Mig weld on a seam. We also Tig weld short (say 2 in.) butt welds in thin material (.065in. to .125in.) on the windscreen area of a small power boat for instance.
All other welding is done with Mig. We do use a lot of pulse Mig, but it is not required at all for the job you are doing-pulse Mig is most useful for material .125 in. and under.
Boat yards don't use Mig just because it is faster than Tig - we use it because it does a better job in most cases (it generates much less heat). Mig welding aluminum is harder to learn than Tig, it is smokey, makes sparkes that burn your clothes, does not make as pretty a weld, and the welding guns are sometimes difficult to keeep running smoothly, but you can easily build a 34 ft sailboat without a Tig welder, but not without a Mig welder. For the first 14 years of my boatbuilding career I rarely saw and almost never used a Tig welder. It was only when I started building small boats out of light material (.065"to .125") that I purchased a couple Tig welders.
It is ideal to have both types, but if you can only have one, make sure it is a good Mig welder.
Another piece of advice---a lot of welder salesmen don't know much about fabricating and welding-they like to make you think they do though. The best thing you could do if you doubt my advice is to go to a boatyard that builds aluminum boats-pleasure or commercial-of the size you are contemplating-and look at what they are using- I guarantee that they will be Mig welding the hull and using Tig only for small fittings and handrails etc.
Regards
Bruce
The first site I have listed above describes the TIG welding process in detail while the second gives a brief overview of the Thermal Arc 300 GTSW welder that I eventually purchased.
The important practical difference between MIG and TIG is that TIG requires two hands to weld, one hand for the torch and one for the filler rod. Both processes weld aluminum to Lloyd's standards. If you enjoy gas welding then TIG will probably appeal most. I find that I have a great deal of control over the weld puddle, especially with a torch mounted amp control. For TIG welding aluminum you will need to use a pure tungsten electrode in the torch (1/8" electrode for 1/4" aluminum), a high frequency start, so that you don't need to touch the work piece with the electrode, together with an AC (square wave is good) power cycle setting.
Front panel of my welder. Two settings not found on conventional welders are - wave balance and AC frequency. I found both extremely useful.
The aluminum you would purchase to build a sailboat is probably as close to perfectly manufactured as anything you will ever come across. A quantitative element analysis, to check the grade probably would not hurt though. Lloyd's requires it for some categories of construction. I haven't looked into this any further yet. What determines how sound the hull turns out in the end is the design details and the quality of the welds joining the plates. In my opinion, the only way to know for sure how good the welds are is to weld them yourself but then I am biased. Note that you probably can't see a poorly penetrated weld after the fact, unless you have done a lot of aluminum welding yourself. The weld-bead looks just fine (except to a really cynical trained eye) but based on my destructive testing there is a lot less strength available, especially if the bead is ground flush.
This cold weld (above) will have no strength! There is no fusion between the root weld on the inside and this weld on the outside. This example is fairly obvious. Other examples are often less so, unless you have had a little welding experience and have got your eye in.
This weld is contaminated with tungsten splatter. I touched the TIG-torch electrode with the filler rod by accident (makes a minor pop as it explodes). You do this a lot when you begin. Stop - switch off the welding power - remove the tungsten electrode - remove contamination by cutting the end of the tungsten off - regrind & refit the tungsten - back chip the weld and start over. This is why you keep several spare tungsten electrodes handy in the pocket of your leather welding jacket. Then you do the regrinding only when you run out. It is a pain when you first begin but you soon learn not to touch the filler wire to the electrode.
A reasonably good-looking weld. Note the HAZ (heat affected zone) either side of the weld bead. I did this in two 2" welds. Welding from right to left, the right section first, followed by the left section (i.e. not a back-step weld). There is enough heat so that the penetration is good and the overlapping weld beads are nicely fused. This is critical to water/air tightness. Now, just looking at this weld you could not tell that I didn't back chip the root pass! It will have really poor strength if I now grind the weld bead flush, because even though you can not see it, I know that the fusion between the root (inside) weld and this final pass is not great
In the multi-chine construction I am undertaking, I weld the root seam on the outside of the hull followed by the final weld on the inside in 1/4" plate (In other designs it may be the other way around). Proper fusion between the two welds is critical strength wise. Back chipping carefully and completely is the key. I can't over emphasize the back chipping as it really does make a huge difference to fusion and hence strengh.
A test weld I broke completely. Look carefully and you will see the see soot in center of the weld where there is no fusion. This is the result of not backchipping the root pass deeply enough. The weld was still hard to break though, until I tried the same thing with with the weld bead ground flush. That broke very easily, because there is so little fused weld metal left.
This test piece shows how in 1/4" alloy, even with back chipping, not applying enough current results in poor fusion at the edges, though the section in the middle did fuse properley. Poor fusion is the most common defect at the beginning of each weld where there is insufficient heat to start with. Carefully watching the weld pool form, is the surest way to avoid this. Thankfully it is quite easy to observe proper fusion as the weld pool forms. The secret is to watch the weld pool not the arc.
Testing the weld by bending it in a vice using a 4 lb. sledge hammer. Welding from right to left you can see that failure begins at the start of the weld bead , where the weld is coolest and the fusion is less perfectly complete. Also a factor of course, is the notch effect caused by not welding right to the edge. Aluminum is very sensitive to notch effect!
This next section of from the above sample weld, is very tough you can see that failure is beginning to show at the edges of the weld- small surface cracks are just visible.
In order to get the weld to break one has to do some serious crunching in a vise well beyond 90 degrees. This is what I want to achieve in all the welds.
Weld porosity is another factor that you can't easily determine. X-rays might reveal a serious problem - there may be other Lab methods I don't know about. I think the best way to avoid it, is to understand where the hydrogen in the weld comes from (read about it in the books I have recommended), and to eliminate possible sources. This includes buying good quality Argon (or Argon-Helium mixed) shielding gas. Another source, are hydro-carbon deposits like oils and of course water. Figure out how to degrease, clean and dry the whole plate or extrusion, keeping in mind that often the order you do things is important to a successful result (don't use your clean st/st wire brush on a oily plate - degrease the plate first). Then you need to pedantically stick to a good regimen and don't be tempted to cut any corners!
Just a word regarding my personal welding experience so you know where I am coming from.
I have quite a lot of experience stick welding steel with an oil cooled conventional transformer type machine. This machine would draw about 45A at 220V 50Hz. I mostly weld thinner steel tubing etc. using standard electrodes (6013) but I also use low hydrogen electrodes (7018) in thicker load bearing stuff. I am completely new to welding aluminum. Read " I am a novice". It is also my first long term taste of owning an inverter type welder (trying out at the dealer doesn't count). I bought a 230V, 50-60Hz, single phase, inverter type, Thermal Arc 300 GTSW with a 200A, CK, air-cooled torch, a slide control for current control and an auto darkening weld helmet - no free hand to flip a lens when TIG welding (how did I ever get by without one?)
All the welding gear except the bottle of argon gas and its regulator. The TIG torch with sliding current control attached. Below the torch from (left to right) are - conventional type ceramic gas hood, collet body, collet, torch seal - below that is, a tungsten electrode - then comes - a gas lens type ceramic hood, gas lens type collet body, collet - and finally another tungsten electrode below that.
I am very pleased with my practice results welding aluminum so far. The sliding amp control on the torch (does the same as a foot pedal) is great for controlling the weld puddle. I just back off the current as things heat up (generally ~ 180 A for 1/4" 6063 test pieces, once I have the weld puddle started - I expect that bigger sheets will need more juice). I also use my new welder to stick-weld steel, with a pipe-welder's twist type electrode holder. The specifications show that this welder will draw up to 96A at 220V single phase and on top of that the high frequency inverter is a lot more efficient than a 50-60 Hz transformer type I owned before. That is a lot more power than I had - more than I need for stick welding. Comparing it with my old machine is unfair, but I will say this. That extra power is most welcome and the DC option for steel welding, is a significant improvement w.r.t. splatter. In aluminum that extra power is great for getting the weld pool going quickly. I am glad I didn't buy a 200A machine (though it might just do most welding jobs).
If I compare welding steel to welding aluminum I can summarize my experiences thus far with the following-
Straight horizontal welding is not noticeably more difficult than welding steel though there is more preparation involved. Out of position welding is easier! Overhead welding has much less tendency for the weld pool to 'drop out'. Up-welds looked pretty on my second go. I think this is because there is a good surface tension in molten aluminum, coupled with its low density. Steel by comparison can be a right devil when it comes to out of position welding, especially upside down. Steel has a high density coupled with low surface tension.
I have acquired a couple of gas lens collet bodies for the TIG torch - as apposed to standard collet bodies - as they supposedly improve the inert gas coverage of the weld zone. They do not seem to make a whole lot of difference but do allow slightly lower gas flow rates for similar coverage.
A word about TIG welding versus MIG welding. I felt less in control of the fusion process with MIG, but then my try-out was limited to about 12 passes in aluminum. MIG is a more difficult process to master properly. I don't think welding speed is an issue if you're only welding a couple of inches at a time and then moving to the other side of the hull to weld symmetrically. This is important to limit distortion each time the weld cools. Moving and getting comfortably positioned takes longer than the welding with the TIG process. With MIG you can sometimes weld longer sections with less distortion faster because less heat goes into the weld zone.
Certainly the downside of TIG welding is more heat into the weld with more distortion possible. I will have a lot more to say about this later, as the building progresses, and I get to the big weld-up.
What did it all cost me. (October 1997)
Prices excluding taxes in US$ from Rochester Welding Supply Corp.
A note about the grades of alloy suitable for marine use, that is in salt water, and the filler wire used to join them.(more to be found here).
The alloy grade that was specified in my plans is 5083 H321. The filler wire for TIG welding this is 5356 (or 5086).