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Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
There are jumper straps made of copper plated onto aluminum: there is one here from a Miller welding machine, copper on one side, aluminum on the other. Copper plated on aluminum?
Registered Member #2390
Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381
You cant "technically" weld copper to aluminum. However, you can join the two by using a method called plug welding. Plug welding is basically drilling a large enough hole through one piece, countersinking it, then finally welding that space (filling the countersink and hole with weld) to the piece behind it. You would use the same filler rod as the piece behind the hole. Sort of forming your own rivet. The problem you will have is the lack of heat transfer. The natural oxide that forms on aluminum will create an insulated surface between itself and the copper, blocking most of your heat transfer. The other thing that needs to be considered is the different thermal expansion rates of the two different materials. They would need to be arranged so that the material that expands faster is the one with the hole, the slower is the piece that forms the welded "rivet". Anything can be done, you just need to study the application. If arranged opposite of the above, the piece with the hole would crack, or snap off your rivet, depending on tensile strength. On Point, to your question about the aluminum sheet to the aluminum block. Yes it would work, efficiently no. Same reason as above (the oxide). In a situation like that, you would be better off machining dovetails into the block and onto the edges of your plates. Then you would press the plate into the block. Would this work? Yes, more efficient than a single machined part, no. The answer lies in how much heat you need to dissipate without destroying the part you are cooling. Whew! Thats all, my finger tips hurt!
Registered Member #2390
Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381
Yes sir! Tig or GTAW (gas tungsten arc welding) (same thing) would actually be the preferred and most reliable method. Just make sure your machine is capable of being set to ac. If not, it will be impossible to weld al. Copper can be welded using dc. If you have the setting for ac, set your machine to 150 amp output (providing you have a foot pedal or fingertip output control) use 100% argon gas set to a 5-8 cu, ft/min output. Use a pure tungsten (green banded). Depending on material thickness your tungsten diameter may vary, give me some more detail on your material thicknesses and such and i can tell you exactly what to use. On a side note, when you weld al, you use whats called a balled tungsten as opposed to sharpened. The best way to "ball" the tungsten is to leave the machine set to ac for welding al and strike an arc over a ferrous metal (steel or stainless steel work the best) for a few seconds and the ball will form. Then youre ready to go! A more direct answer. Without looking deeper into the expansion of copper and al under extreme heat, off the top of my head al expands faster due to its high conductivity of heat. This would mean your "plug" should be copper. I dont thinnk that is what you are shooting for. Unless you weld a copper "plug" through the al plate, in which case you would use a cu filler and a direct current setting on your machine. Same 100% argon gas. Knowing the way it needs to be done can you give some more detail on exactly (dimensions and all) of what you want to do? If you can, i can probably provide better help which i am more than happy to do!
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Is welding copper to aluminum acceptable for thermal dissipation applications.
