aluminium spot welder arms

[chrisg3103]

had a search and couldnt find anything. is there any reason aluminium cant be used to make spot welder arms?

actually did some maths
as an example a 16mm dia 500mm arm
copper arm
resistivity of 1.68x10-8
density of 8.96 g/cm3

would weigh 2.25kg and be rather expensive

aluminium arm
resitivity of 2.82x10-8
density of 2.7 g/cm3

to make the same resistance of the copper one aluminium would need to be 26mm dia. but would only weigh 1.1 kg and be a damn site cheaper! only disadvantage i can think of is it would heat up rather fast so would have a low duty cycle? would rather take lots of breaks than spend a few £100 i dont need to. possibly the mechanical propertys of aluminium, but at that thickness wouldnt the arm be stiffer than the copper one? any input from more experianced types appreciated

 

[Harry Worth]

Ally arms

Sorry not an experienced type - but might be that Aluminium is prone to surface oxidisation whereas copper isn't quite so prone.

 

[chrisg3103]

forgot to add would be using copper rods/tips for the actual welding part, just the arm material

 

[rtbcomp]

Physical strength at a guess. The tips have to be under some pressure and ally is softer and weaker than copper.

 

[Paul.]

Although aluminium has a conductivity of about 60% of that of copper, the residual surface oxide is an insulator, in a spot welding circuit the machine has to have minimal resistance with the mating surfaces of the joint giving the greatest resistance, there will also be issues with the different materials in the circuit causing reactions, such as the brass clamps that the arms fit to, and the joint between the arms and the tips, there is a special conductive grease for sealing water cooled tips into spot welder arms which may help, you would need to mechanically clean the joint then coat it immediately to exclude the atmosphere, it soon melts when it gets warm though.
For a very low duty cycle and for the relatively low cost involved, its probably worth a try, keep the arms short to minimize flexing, but before using it on anything critical do some practice welds and peel test them.

 

[chrisg3103]

sounds interesting, found silver grease at rs and silver paint at maplins

not much for your money though not just use copper grease picking up some plasma cut parts tomorrow at my local welding place so will ask about the spot welding grease. will indeed do experiments first, need to replace about 90% of the panels on a mini pickup

 

[brightspark]

sounds interesting, found silver grease at rs and silver paint at maplins

not much for your money though not just use copper grease picking up some plasma cut parts tomorrow at my local welding place so will ask about the spot welding grease. will indeed do experiments first, need to replace about 90% of the panels on a mini pickup

coppaslip grease is an insulator electrical not a conductor i did a flash test on it at 500 volts

 

[Robotstar5]

There are aluminium spot welding arms used, we had them at Longbridge on robot welders, some over 1 metre long. We had to use a special plate at the transition from Al to copper. The idea was to cut down on weight which allowed higher speed movements between welds.
I think they were supplied by Nimak

 

[Paul.]

Different application, but same problem, I have worked on desalination plants where copper busbars are bolted to aluminum blocks, we used to tin the copper side of the joint with solder to make a transition between the dissimilar metals, there was also a jointing paste used on some joints, they also make a special lightweight busbar which is a lamination of an aluminium core with a copper outer, Not applicable to spot welding I know but just thought I'd mention it.

 

[brightspark]

Different application, but same problem, I have worked on desalination plants where copper busbars are bolted to aluminum blocks, we used to tin the copper side of the joint with solder to make a transition between the dissimilar metals, there was also a jointing paste used on some joints, they also make a special lightweight busbar which is a lamination of an aluminium core with a copper outer, Not applicable to spot welding I know but just thought I'd mention it.

corect they brought a special solder out to tin the copper stopping the corosion

 

[chrisg3103]

failing the aluminium arms how about nice strong thin steel arms for the clamping force with copper ends linked with nice cheap welding cable! might be a bit heavy but about £10 for a 1 metre spot welder arm

got some experimenting to do.....

 

[Paul.]

Typical current on a small diy spotwelder is up to 7000 amps, on industrial pedestal models 35 - 40,000 amps, but only 3 or 4 volts, perhaps one of the sparky's could calculate a cable csa for it.
There are air operated head units that are fed from remote transformers, so the cables are available.

 

[Robotstar5]

Not sure about CSA but a single jumper cable is about 40mm dia & a kickless cable about 60mm dia. Has to be very fine stranded cable due to the movement or "kick" caused by the current pulse.