Spot welding titanium sheet

[Colin Krusor]

I have a BPL Firelite titanium pot and I'd like to add handles to it. I have some nitrile phenolic adhesive (the kind used for automotive brake pads) that is strong and withstands high temperatures, but I'm also considering spot welding. I have a small amount of spot-welding experience, but it was a long time ago, and I've never spot-welded titanium.

Do I need to remove the oxide layer between the parts and weld them under argon? Any tips from anyone who has done this are appreciated.

[Roger Caffin]

Hi Colin

Of course removing the oxide layer and welding under argon would be excellent. However, I have spot welded 6Al4V sheet (0.5 mm, 0.8 mm) successfully with just a 'clean' surface and some pressure.

What you will find is that Ti does handle spot welding nicely, and its resistivity is much higher than either copper or brass. Yes, I have used brass electrodes successfully: they were harder than copper.

You will need to play with the settings a bit, but a good bright red is what I aim for. Sparking is definitely no-good. If you have too much of high pressure and bright red you may actually poke holes through the Ti sheet.

Cheers

[Dan Yeruski]

Roger, will carbide electrodes work well for .oo5 titanium sheet?

[Roger Caffin]

Hi Dan

> will carbide electrodes work well for .oo5 titanium sheet?
Um. Dunno, never tried that!
OK, the resistivity of copper is 10.2 (ohms/mil-ft, a stupid unit but ignore), the resistivity of Titanium is 259 (LOTs more), while the resistivity of chromium is 78.
I mention chromium because many forms of 'carbide' as used for machining use a matrix of chromium (I think). In that case, carbide rod might work.
If you are talking about carbide as used for a furnace element, I woukld have to say dunno.

In any event, it could be worth trying, but it seems likely that the carbide rods will get hot! OK, low duty cycle, optional water cooling, whatever.

Or use copper electrodes with carbide tips? But watch for sparking. I tried this with steel core tips to the electrodes and it was not very successful, so who knows?

It would be very interesting to hear from anyone who has actual experience of this!

Cheers

[Dan Yeruski]

Roger, I'm thinking of using spot welding electrodes with a tig welding electrode imbedded. That would give me pinpoint accuracy and have longevity of the carbide electrode tip. I have the carbide electrodes but have not had the time to try them. Drill a hole into the copper electrode and then press fit the carbide into it. Sounds like it should work. Will just have to play with the amperage to get it right. The tips are going to get hot but not have an effect on them. .005 should weld pretty quick.

[Roger Caffin]

Hi Dan

OK, I want to know how this one goes! Very interested.
As I said, I tried it with high tensile steel (OK, HT fencing wire) embedded, and found it sparked too much, and sometimes stuck as well.
Yeah, tips will get hot, but the plain copper ones domed over pretty quick.

Cheers

[Dan Yeruski]

I think it's going to work as long as I keeps the amps down and round off the carbide tip. I'll keep you informed.

I think the bushbuddy stove might be welded with the carbide rods. They look small and clean.

[Colin Krusor]

Dan, any updates on your attempts to spot weld thin Ti sheet?

Roger, I'm still considering investing in a spot welder for this purpose, but I don't know how to evaluate small spot welders. There are small spot welders on ebay for about $150, but they don't appear to have any controls. Is it possible there is no current control on these?

Even on the more expensive Miller models is isn't clear to me how the current would be controlled. Any advice about what to look for in a serviceable spot welder is appreciated.

[Roger Caffin]

Hi Colin

Sorry, but I don't know enough to comment either.

I built mine from an old 'several kW' transformer by stripping out all the secondary windings (being 1 mm copper), making up several bundles of about 12 wires in parallel, and rewinding with 4 windings each of 2 turns and 2 windings of 1 turn. I don't get many volts out of course, but it can put out a lot of amps!

I 'designed' this off the top of my head. I still don't know whether I did it the right way, but it seems to work – mostly. I used an old discarded pistol drill press to hold the electrodes.

I do know they control the current output on some arc welders by varying a gap in the iron core of the transformer, so that the smaller amount of metal in the gap goes into saturation first. That limits the coupling and the output.

Yes, it does seem to be all a little crude – except that controlling 200+ Amps in a device selling for $150 is not bad.

Cheers

[Dan Yeruski]

I've had success with my efforts. I'm using copper tips on my welder and controling the voltage with a voltage ratio transformer with a 20 amp capacity.

I'm welding brittle Ti and having problems forming add-on pieces. I can't make sharp bends without it breaking. I've tried welding half hard stainless steel to Ti but it burns through. I've had to revert to mechanical fasteners as addons to the Ti.

At this time I don't have the variety of Ti alloys on hand to make life easy.

[Roger Caffin]

Hi Dan

Yes, I can make reliable sharp 90 degree bends in 6Al4V alloy sheet (and wire). I use a custom hot bender for this – it's an add-on to my drill-press spot welder. I'll describe how I do it: you may be able to copy. If you succeed, let me know.

Take a short length of 1" brass rod and make a 90 degree notch across one end face, about 3/8" wide at the top. This becomes the lower electrode.

Take a short length of 1/2" brass rod and make a 90 degree wedge at the end. This becomes the upper electrode.

These two electrodes should mate reasonably well, just like an ordinary press bender.

Mount these two electrodes in your spot welder, with the 1" rod at the bottom. How you do this depends on your welder – some engineering may be needed here. Obviously, the two should align/mate properly. You will also need to be able to push the two together with a small amount of force.

Place a strip of Ti across the lower electrode and bring the upper wedge one down on the bend line. Align to suit. Press lightly so the Ti is held in position. Adjust the spot welder so that when you pulse it for maybe 1 second the Ti glows red, and press down at the same time. The Ti will bend beautifully.

While 6Al4V allow will crack if bent too hard when cold, at red heat Ti goes into a super-plastic flow regime, without losing strength. It does not need to be really bright red for this to happen. I think it works OK below spot-welding temperature.

This shows a 6Al4V Ti stove leg with two sharp bends done this way. Quite reproducible.

You may need to fine tune the electrode shapes to get the exact angle you need.

Any questions – fire away.

Cheers

[Dan Yeruski]

Hi Roger, thank you for the instructions. I'll be able to duplicate the brass electrodes.

I want to be able to take a piece of .005 and fold it over onto itself to form a "u" clip. The clip will have one end that is 1/2 inch longer than the other. That longer part will be welded to the body of my windscreen.

I foresee using the brass electrodes to bend it to a 90 and then quickly removing it and continuing to hand press it to a "u" shape while it's still hot. Do you think this will work?

This photo shows the size of the piece I want to bend:

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Thank you for your help with this project.

[Timothy Clarke]

Hi Colin and others,
I have replied to your persoal enquiry message about sharing ideas on unusual high temperature materials. I was just having a look at all the topics that you have started and you make me feel like a baby. Anyway, your welding issues might be solved by now, but I still thought that I would contribute to this discussion about welding thin titanium foil (0.005 inch or 0.125 mm) as it may help others. I have been doing it with my DIY spot welder and the welds are good (will rip out a disk of metal from one side if prized arart with a knife blade) This invention was a rare one for me as it basically worked first off. Brief description; power supply is a simple domestic arc welder with a solid state (zero switching) 40 amp relay inside controling mains power to the primary winding and a 555 timer with adjustment from about 0.02-2.5 seconds using a rotary resistor. The output of the timer is connected to the low voltage control terminals of the relay. I use the smallest welding tips (TIG I think, the ones with 0.6 mm hole through the axis). They have an M6 male thread at at one end for mounting and I shape the working end to an offset point with a rounded tip to allow me access into tight welds in corners. The welder has long arms that let me get into small containers. I use fixed weight on a rope and pully system to give a standardized mechanical closing force on the welds. I think the electrodes are copper berilium alloy. I get neglegible welding sprew (ejected molten metal) and other than making the two surfaces clean I do not do any oxide removal before welding. This welder works well with titanium foils (hard) from 0.1 -0.2 mm and also SS foils from 0.03-0.2 mm. With both metals, I can weld 0.1 mm or less to up to 0.2 mm foil, but welding 0.2 mm to 0.2 is marginal. Consequenty, I have a commercial spot welder much like the one shown above that I use for 0.2+0.2 mm and greater welds. I should say that the commercial welder has a very adjustable setting for current, but is just too strong for 0.1 mm+0.1 mm, so between the two welders I think I can weld just about every thickness that a BPL tinkerer could wish for. I can even weld 0.15 mm SS foil to a 1/4″ SS nut for my GoPro tripod mounting fitting. I make temporary welds of my Ti to SS but they will come apart when put to the test, but they can be handy for things that need to eventually come apart and for holding things togeter while another job is done. ‘Failure sometimes comes in handy’!

Hope this helps,
Tim

[Jon Fong / Flat Cat Gear]

I spot weld thin titanium foil (0.005″)  using a dental spot welder.  Extremely adjustable control and produces a nice small spot.  I have also been welding thicker sheets with a traditional spot welder: I do use a router speed controller to lower the power output (~$20).  So far, it works pretty well.

[Colin Krusor]

Thanks, Tim and Jon, for contributing to this old thread. I won’t have much time in the short term to revisit the spot welding experiments, but I’d like to get back to it as soon as I can. Your ideas here will be helpful, I’m sure.

Tim, thanks very much for your response to my note. I have a lot of ideas I’d like to explore, and I’m sure I’ll appreciate your thoughts on them. Time constraints will keep the pace of progress modest, but I’ll keep you updated.

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