What type of Welder? stick? mig?

[clive milne]

Originally Posted by marki

Welding aluminium without a spool gun or at the very least a Teflon liner could result in expensive damage to the torch and the machine itself.

I'm curious, specifically what damage do you fear doing to the hand piece or machine?

[DIYman (Doug)]

Many years ago I bought some flux covered aluminium rods for use on a DC arc welder. They were bloody expensive and although I am an experienced arc welder they were not easy to use. I had to run a grinder over all my welds to make them look anywhere half decent.

I still have the old dob mount around at home on which the welding was done. Its kept hidden at the back of the shed. I shudder every time I stumble across the mount during my annual shed clean outs. When the mount was in use, old experienced club members would look at it (and my welding no doubt ), mutter something under their breath and walk away.

One day the mount will disappear at the bottom of a junk verge collection and that source of embarrassment will be out of my life once and for all.

[marki]

Originally Posted by clive milne

I'm curious, specifically what damage do you fear doing to the hand piece or machine?

My machine is only 180A max which means I can only use very thin wire for Al, (0.35-0.45"). It is very fragile. My machine has V groove rollers on the main feed which causes the wire to chip and this clogs the liner and small flakes of Al are nearly impossible to move once deposited. The thin wire also buckles and burns back easily adding an even bigger headache and the liner must be replaced far too regularly to make it worth while. Spool gun = short wire feed = no bending or flaking = happy welder.

[wasyoungonce (Brendan)]

I've been trying to teach myself stick..very average so far but getting better. Found I needed smaller electrods. I was trying 2.5mm on a 100 amp cheapie arc. Went to 1.5 & 2mm and much better.

I booked myself into tafe mig/tig course, 28 hrs. Sure...I won't be proficient on that time on training but hey it's a start.

I'll never be a pro but just wanted to learn enough to get by.

[StutzJr]

Great thread, very informative stuff. I'm also interested in doing a tafe welding course eventually.

I have a specific question relating to the welding of fine gauge wire thermocouple junctions. I'd like to know the best option(s) for welding precision grade thermocouple wires ~24 AWG (0.5 mm diameter or less). The idea is to twist a short length at the end of two wires of dissimilar metals and then fuse them together into a small bead. Soldering is not an option due to the introduction of contaminants and the intended temperature range of the t/c. Similarly with silver soldering.
I have found that a butane torch is not hot enough and/or is not able to fuse the wires without oxidation. I have tried capacitor discharge (resistance welding) with carbon terminals but do not have a large enough capacitor to get an effective weld. A workmate has a MAPP gas burner but I expect it will only be a marginal improvement over the butane torch.
I've been advised by a local supplier to try a neutral flame on an oxy welder. I don't have access to any oxy-acetylene gear but I am considering investing in an oxy/MAPP welding kit. I've also been eyeing the aformentioned bunnings special arc welders.. Lastly I have been hearing a lot recently about jewellers using HHO welders (hydrogen-oxy derived from water) but I believe that these units are pretty rare and expensive around here.
Can anyone here suggest what technique/equipment would be the best option for my application?

[wasyoungonce (Brendan)]

Originally Posted by StutzJr

Great thread, very informative stuff. I'm also interested in doing a tafe welding course eventually...............

I have a specific question relating to the welding of fine gauge wire thermocouple junctions. I'd like to know the best option(s) for welding precision grade thermocouple wires ~24 AWG (0.5 mm diameter or less). .............

IMHO...maybe 3 methods (depends on junction type or wires used):
1. Use an oxy torch to melt the wires together.
2. Spot weld them, maybe pass an inert gas over them when doing so. This way the junction fusing is just a product of the metals used in the wire. I did see someone using a capacitor discharge bank to spot weld small stuff. This may be ideal for this if you use the actual thermocouple wires as the electrodes (aka do not introduce other metals)
3. TIG weld fuse them using no filler, if it doesn't completely ionise the wires! For the same reasons and also noting TIG gasses from the hand-piece will keep the joint from oxidising and introducing contaminants.

IMHO the only real method that will work is spot welding or oxy torch.

The reason no filler is that the thermocouple junction it self is produces a voltage proportional to the metals used...like Chromel/Alumel. Introducing another 3rd element metal will throw the junction way out.

Week 2 of my Tafe welding course...they won't cover stuff like this...just from memory from Jet engine thermocouples.

[StutzJr]

I wouldn't expect to answer this specific application with the tafe course but it's still something I'd be interested in.
From your methods I'd be more likely to choose options 1 or 2. I don't know anyone with TIG gear and I get the impression it would not be a beginner's option.
When I was trying the capacitor discharge method I used a 25V 220000 uF cap. I had the negative lead wrapped around a carbon rod from a C cell battery with the tip ground out into a well and a drop of glycerine inside to minimise oxidation. I held with tc juction just short of the tip with a crocodile clip attached to a decent copper cable. When I contacted the tip with the carbon rod inside the glycerol drop I got a flash spot weld with minimal oxidation but it barely held the wires together. If I had a larger capacitor bank it might work but I've also read it would work better if the junction was held in contact with the carbon rod and the current was switched with a mosfet. That's starting to sound more complicated and I can see the oxy torch having more uses if I can only justify the cost.

[wasyoungonce (Brendan)]

Yep sounds like more current needed to fuse..or putting all that current into a very short pulse hence mosfet switching.

Has me wondering if an old car coil can mosfet switched be made to supply a arc to join them. probably the coil inductance will delay the current too much hence most people go for capacitive discharge spot welding?

[StutzJr]

I think the cap discharge is just the easier option. I haven't looked into the switching/coil option as I haven't had time yet. A quick youtube search for "photonicinduction melt" shows an extreme example... I figure if the switching circuit gets too elaborate then I might as well fork out for an off the shelf arc welder.

Oh and I never know that mexico city was so close to geetroit! lol