Gallery, Projects and General > The Design Shop
Microwave owen transformer spot welder?
SwarfnStuff:
Hey Bill, Thanks for posting Dan Gelbart's spot welding tutorial. I went to check it out and recalled that he has many very good tutorials on prototyping which in a way is what we get up to in our play-pens.
Or, at least I seem to, even if I have plans I seem to adjust / modify them for the materials at hand or more often because I messed up on some part.
I have added his page to my bookmarks figuring from there I can wander off to his many other topics.
John B
PekkaNF:
Been busy with the work and flu&other seasonal hinderaces....
I have a concept for mechanics, I was going to rocker type. Mainly because of the simplicity and I don't need high cycle time. However the pneumatic cylinder I have is too smal for normal rocker, I need to make swing arm to have eneough force and to keep the whole contraption compact.
I have two problems:
1) How to hook up the current from tranny to electrode holder
2) How to make the electode holder adjustable and I would like very much to able to adjust the holder position and to swap the holder and to turn it over (other end having 90 degree mount for electrode and other 45 degree or special).
Both would be simple if I had two big chuncks of copper. Big square piece, 20 mm bore for electrode holder and four bolt mount. Really elegant solution. Copper has excelent electrical and mechanical properties for this part. But I don't have it, nor I can easily get one!
I was considering similar construction of aluminium, I have it, easy to machine and I have a special clamps to connect copper cable to aluminium. Main problem I have is that I don't believe there is a good enough electrical contact between this aluminium bar and 20 mm copper bar (electrode holder).
I was thinking of "tinning" the 20 mm hole (for electrode holder) in this aluminium block, but I never have soldered aluminium and googling it produced mainly special fluxes and solders that seems proprietary, expensive, dubious mixtures of mainly tin and rest of it mainly zink....resulting in about 25% conductivity of the aluminium. Could aswell use steel or brass....equally bad results and wole lot cheaper.
Only way I can think of using the aluminium mount, is to make a sleeve of copper tube. Standard sixe OD22, ID 20 would be close enough and probably could get two metre piece without breaking the bank. This thin sleeve should work well when clampd between rod and split block, and still have enough of cross section area to conduct the current.
There might even be insulator material that would survive between the copper sleeve and aluminium block?
Is there a problem I don't see or would this work?
Pekka
awemawson:
Pekka,
Seasons greetings to you.
It's notoriously hard to get good very low resistance contacts reliably on aluminium due to the inevitable oxide film that grows. It can be done, and contact surfaces need covering with petroleum jelly or similar to exclude air as far as possible. At the currents you are probably using I would anticipate problems.
Bite the bullet and buy some copper block or find something that can be 're-purposed'
PekkaNF:
Thanks. Ham and turkey to you too!
I have scoured local scrappies, small shops and put some adds on local bulletinboards. I haven't got a piece of reasonably copperish copper yet.
I put two more adds on local hobby boards, but if I don't get answer on few days I'll try something else. Like copper sleeve as a conductor and aluminium or steel block as a support.
I have some AL/CU connectors and I have seen propper electricias using them/grease/torguewrench and works. Not really something I'd like to rely on low voltage/high current application.
Pekka
Pekka
JHovel:
Merry Christmas!
It is possible to tin aluminium properly - against mine and others' 'common sense' - and I have been shown, taught and done it, all the while shaking my head in disbelief.
The process is to heat the aluminium to soldering temperature (using an oxy torch in mine case, because the aluminium moves the heat away so fast, you have to keep pushing more in fast). While it is hot, vigorously brush the surface with a stainless steel brush to remove the oxide layer. Apply ordinary tinning flux to this shiney hot layer and add solder/tinning rod. This sort of floats on the hot surface without seemingly joining the aluminium. Vigourously wirebrush the solder/tin into the aluminium surface until you see it actually 'mixing in' and suddenly it 'alloys' with the hot aluminium surface. You can then add solder/tin to that surface and it flows like ordinary soldering does. However, the last step only works for a very short time! It seems that the aluminium insists on putting an oxide layer between the pure aluminium and the alloyed layer if you keep it hot enough.....
Once you see it all happeneing in front of your eyes, you will shake your head in disbelief like I did and then use the process whenever necessary.
Cheers,
Joe
PS: I learnt about this while doing a course on leading car panels, including aluminium car panels.
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