Dec 2, 2012 at 11:39 pm #1296680
Colin KrusorBPL Member
@ckrusorLocale: Northwest US
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.Dec 3, 2012 at 1:41 am #1932709
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.
CheersDec 4, 2012 at 7:47 am #1932980
Roger, will carbide electrodes work well for .oo5 titanium sheet?Dec 4, 2012 at 1:08 pm #1933054
> 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!
CheersDec 9, 2012 at 8:53 am #1934270
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.Dec 9, 2012 at 3:15 pm #1934339
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.
CheersDec 9, 2012 at 5:11 pm #1934364
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.Jan 2, 2013 at 9:52 pm #1940434
Colin KrusorBPL Member
@ckrusorLocale: Northwest US
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.Jan 3, 2013 at 1:12 am #1940454
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.
CheersJan 3, 2013 at 8:26 am #1940507
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.Jan 3, 2013 at 12:13 pm #1940553
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.
CheersJan 3, 2013 at 6:52 pm #1940670
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:
Thank you for your help with this project.
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