Chill block, warpage... TIG welding thin aluminum questions

The copper block does not have to be very big, but it adsorbs heat. So the bigger it is, the longer before you have to let it cool down. I would use something at least an eighth inch thick, but would prefer something 1/2 inch thick. For long seams, you might consider kludging up something with circulating water.

Dan

I would not re-design something unless it is third-world design.

Aluminum is just fine if greased correctly and the Al is larger by a percentage than the copper.

The metal tab and mounting header is a copper heat spreader made for impulse heating. If you spread the heat across a surface then it remains active.

Simple air between - a.k.a. mechanical attachment without grease is not a good idea at all. If not greased, buy some at Radio Shack or DigiKey. Use it between the SCR/Triac and the insulator? and there to the large heat sink.

Mart> >

Um... no, it was designed right here in Cincinnati...Pretty simple though, a few pieces of curved aluminum plate, makes a 3D shape when welded together...I guess you could design it in a third world country... Besides, I'm paid to weld, and the design I got is the design they want. Do you routinely redesign the things you weld?

You routinely weld greased aluminum? How does that work out for you? Do you use a silcone type grease to avoid trapping hydrogen in the molten aluminum?

What's that Lassie? You say that Martin H. Eastburn fell down the old sci.engr.joining.welding mine and will die if we don't mount a rescue by Mon, 11 Jan 2010 20:51:36 -0600:

I think you got the wrong post. This thread is about welding aluminum sheet, and controlling the distortion with chill blocks, not how to properly attach semiconductors to heat sinks.

NO NO.

Si Grease is used to pass the heat from a semic> Mart>> I would not re-design something unless it is third-world design. >>

Aluminum is not a semi-conductor...

Did you actually read the thread?

What I think Martin was referring to is using the silicone heat sink grease AWAY from the weld area to make the chill block couple to the aluminum being welded better. He was probably referring to mounting semiconductors because that is the use that most people are familiar with.

I would be nervous about doing this for three reasons: First, it would be a requirement to keep it out of the weld area. Second, it's a major PITA to clean up. Third, its fairly expensive stuff.

I think that Martin's idea would be worth experimenting with, because a chill block is not going to carry off much heat if it is not in solid contact with the aluminum. Clamping chill blocks to large pieces is a problem.

Regards, BobH

Martin, I think you are confusing this thread with the one that Dan posted about servicing the electronics on a welder. This one is about TIG welding long outside corners of 0.060 aluminum.

Warm> The SCR /Triac is semiconductor that needs a heat sink.

Given that the OP is worried about blowing through, one could be forgiven for thinking that the OP does not have the requisite skills for the job.

As the OP, I'd say that if I felt fully confident in my abilities, I wouldn't have asked. If you think the only people who should post are people who don't have questions, it is going to get very dull around here.

My usual stuff is frames MIG welded from 1/8" Al or 16 ga steel and aluminum 1x box tube. I have occasional call for TIG, but I have not tried to weld 10 foot seams in 1/16" sheet before. For me, trying to limit overpenetration in an outside corner is a challenge.

The parts were delayed, I started the job today. So far, not too bad, Some sections look downright pretty, most are acceptable, a few will have to get ground down and done again. By stitching, I have been able to keep the heat down and getting a little oil-canning on the top surface, but not seeing warpage.

Since you claim to be an expert at 1/16" Al sheet, what are your suggestions? That is why I asked in the first place.

The SCR /Triac is semiconductor that needs a heat sink. It was wired to the pcb and mounted on Al to keep it cool.

Mart> Mart>> NO NO.

Skill is a matter of self-development. It cannot be gained by a text message.

Ok if you want to compare experiences - Ticket for Unlimited Thickness Structural Steel, 30 years experience with Mig, Tig, OA, Submerged Arc, Steel, SS. Al, Pressure Vessels, Road making machinery, Yacht building...

From what you have said it seems that you are not doing to bad. The fact that you can weld it at all means you have reasonable skill to start with so I will give you the same advice that my welding instructor gave me 30+ years ago - PRACTICE. One of the tasks he set for us was to tig coke cans together bottom to bottom. Yes it is possible, mind you it is best if they are empty first.

Take your time, relax and keep your eye on the puddle. Don't be afraid to play with your settings.

Be very careful in ever using copper chill blocks on aluminum sheet. It is the same problem with TIG welding copper on an aluminum welding table. The copper and aluminum can fuse very easily creating a spot of aluminum bronze on both parts.

You will want to use a steel backing block with a very small hammer to tap the edges together after tacking.

You will want tack welds every 2 inches before welding. It's a shame you couldn't have a flanged edge on both pieces. Makes it so much easier.

You will find a pulser makes this process so much easier.

Tungsten size doesn't really matter that much. Your amperage will be very low.

Oooh! Thank you, I'm glad I didn't try to build a chiller Actually, the aluminum is cooling faster than I expected. This is just so different from the stuff I've been doing for the last 20 years. The chance to do this came up, and we were slow, so I'm glad I bought the Syncrowave and taught myself TIG!

Yep, and I finally designed and fabricated a decent clamp that actually holds the parts in the proper place for tacking, and accommodates all the differences between the sections.

I've been doing about 4" spacing, I'll try tightening it up. I need to work on making the tacks disappear under the welds.

Yeah, remember when you used to work for other people? Asking the guy who will actually weld it about his opinion on the design might cause trouble, better to get it cut quickly, before anybody thinks too hard! :-)

I have suggested that if we ever do this again, we should ask for flanges.

Got a spare PC 300 under your desk? Send paypal invoice!

Yep, I was using the Ernie Rule. I found that shading the arc balance toward penetration made a positive difference. The later ones are looking very good. I expect to have a lot of re-work on the first one once it gets cleaned up, but the others are pleasing me. Maybe the first one is only surface ugly.

I'm getting real good at picking up my pedal between my feet as I scoot my chair between welds.

Thank you for your help. Ernie posts are always worth reading! Did you ever get that text done?

Stuart

You mean the long rumored, yet never completed, TIG welding bible?

Not with my current work schedule.