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Is welding copper to aluminum acceptable for thermal dissipation applications.

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LAN_403

Arcstarter

Mon Jul 26 2010, 09:59PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

I am wondering if it is a good idea to make a spot welder with some large wire and an old 720 watt NST core, which i could probably run like 2kw through continuous for spot welding copper tubing to aluminum.

Also, i have so aluminum sheeting and some misc pieces of alum, would spot welding aluminum sheets upright onto a block of aluminum make a usable heatsink? Some PC heatsinks are not extruded but made in a way something similar to this, but i don't know about the spot welding.

Mike

Mon Jul 26 2010, 11:46PM

Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317

I suppose it would work but you would need to weld quite a few sheets and if you only weld 'spots' and not a continuous weld the heat won't transfer very well to the fins. Most heatsinks I see are machined with a CNC anyways.

klugesmith

Tue Jul 27 2010, 12:01AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

The mechanical and thermal joint between fin and base plate is critical.
Most heatsinks I see are extruded, skived

, or otherwise formed by plastic deformation of a workpiece.
IMHO, CNC machining is too slow, expensive, and wasteful of material to be the primary fab method in most production heatsinks. Even machining with special setups (e.g. using a stack of slitting saws and spacers) is the exception rather than the rule.

Welding Cu to Al is impossible by definition, at least in the USA, where I was taught that "weld" implies fusion of the base metal, and mingling of the melted portions of parts to be joined.

Mike

Tue Jul 27 2010, 03:06AM

Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317

Ah you are probably right there klugesmith, I was just implying they are machined from a solid piece of metal typically. Though I do wonder about those very large thick fins, they wouldn't also be skived would they?

Nik

Tue Jul 27 2010, 03:45AM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

You can technically weld copper to aluminum but it isn't really an option in your case. Interesting process none the less.

Mike

Tue Jul 27 2010, 04:28AM

Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317

hmm, while watching that video I came across a video from muggyweld.com that claims a rod that can weld any metal to any other metal (exception of magnesium and cast iron) they show in the video a piece of aluminum welding to brass very easily and nicely,

Is this for real? here is the rod

Maybe this is very old news and im under a rock in the welding world :)

Electroholic

Tue Jul 27 2010, 09:49AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

I know the type of heatsink you are talking about, they are not spot welded, but rather "glued" with low thermal resistance silicone.

UltraMagnus

Tue Jul 27 2010, 04:20PM

Registered Member #2875 Joined: Mon May 24 2010, 08:28AM
Location: England
Posts: 42

Railway tracks are sometimes welded using thermite, it might be possible to user copper (II) oxide - aluminium thermite to weld them together

Mike

Tue Jul 27 2010, 06:08PM

Registered Member #58 Joined: Thu Feb 09 2006, 05:40AM
Location: Tri-Cities, Washington, US
Posts: 317

Somehow I can't imagine thermite being used very easily to weld aluminum and copper on a heatsink considering how small that is and how hot thermite gets. Seems like a lot of work, might as well by some used huge hsinks.

dmg

Tue Jul 27 2010, 06:28PM

Registered Member #2628 Joined: Fri Jan 15 2010, 12:23AM
Location:
Posts: 627

Electroholic wrote ...

I know the type of heatsink you are talking about, they are not spot welded, but rather "glued" with low thermal resistance silicone.

I use a method as Electroholic said, particularly right now with my bridge, in my case, its mostly to compact then dissapate, but I figure why not, so I usually just put a layer of thermal grease (or a sil pad) across where the 2 pieces are joining, and use several bolts to tighten everything up very well, usually works okay,

in the picture its two AL heatsinks, but I dont see why this method cant be used for copper and AL, you are not welding anything, and all it takes is some thermal compound and a few bolts.

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