Dip brazing

[Chad D]

At a former employer, we used to use dip brazing on complex aluminum chassis for mil-spec electronica that had to survive pretty harsh (helicopter gunfire) vibration environments.  I know fixturing is a real pain, but it would seem to be very well suited to fabricated aluminum intakes of any flavor.  I've always wanted to try to make an ultralight intake using the process, has anyone else already broken this ground?

http://www.mech-tronics.com/f_brz.htm

[jayb]

I have never seen that technique before.  I wonder how expensive it would be to get it done?

[WConley]

At Ford we did furnace brazing of a thinwall built-up aluminum intake for the 1990's 1.9L Escort.

The process worked very well and there were very few rejects, as long as you kept the parts clean.

Not sure if dip brazing is close to the same process though...

[Chad D]

The stuff we did used a paste filler, then was preheated and dipped into a molten sodium bath.  The fillet at the joints was smaller radius than you'd see with water meniscus in a clean glass, made no-filler TIG welds look coarse.  We fixtured everything, our biggest piece was a chassis that went from three four inch thick slabs of complex machined billet merged to one after brazing, final outer dimensions 19"x24"x12".  Once we got the fixtures right, we had only one reject due to improper assembly of the fixture, no further machining required.

The brazing process itself wasn't terribly expensive, but getting the fixtures right to prevent dimensional changes during brazing was pretty complex and thus expensive from an engineering standpoint.  If you could design the fixtures yourself or figure how to make the parts self-fixturing, it should be pretty reasonable, certainly less than paying a good welder to weld a whole sheet metal intake.

[Cyclone Joe]

Hello Chad,

I have experience with both the salt bath dip braze and vacuum brazing.  You might consider as an alternative for the dip brazing tooling, is to leave enough stock to clean it up with a final machine operation.  On dip braze parts I've designed previously, we would leave stock on the ends of the parts and at critical interfaces for clean up.  Also, we would attempt to straighten the parts mechanically after quench but before tempering.  I think an intake manifold would be well suited for this manufacturing approach if you had enough volume.

Given this is an intake, you could get away with a T4 temper (naturally age).

I'll try to find out what it costs for dip brazing on Monday.

thanks
Joe

[Chad D]

The amplifier chassis that we were brazing wasn't a candidate for post braze machining, it had to be right, or be mechanically straightened, due to the design of the subassembly mounting locations.  I do agree that an intake manifold would likely be a good candidate for your suggestions.  Jay would probably have a good answer (or SWAG) for this, considering his intake fab work.

[Cyclone Joe]

Hi Chad,

I was able to get some figures on salt bath dip brazing, finally.  To tack weld and then braze, it costs ~ 4,500 per part.  This is brazing ~100 linear inches.  We're using three different vendors across the US and they're about the same.

Joe

[Chad D]

Hi Chad,

I was able to get some figures on salt bath dip brazing, finally.  To tack weld and then braze, it costs ~ 4,500 per part.  This is brazing ~100 linear inches.  We're using three different vendors across the US and they're about the same.

Joe

Yowza.  Not cost effective at this scale, certainly.  Apparently Uncle Sam paid well for their fancy chassis.  Thanks for the update.  Any idea how furnace brazing compares?

[Cyclone Joe]

Yeah, I wish it was Uncle Sam, but in reality it's you and I who paid for it.  Then again, the cost associated to running that process is the main driver, with it being an art-form a close second.

As for the vacuum braze process, you'd need to be able to pull vacuum on the ID of the part, or at least clamp it tightly.  Unless you had high volume it wouldn't be cost effective. I recall the cost of just the Argon used to generate an inert atmosphere in the oven was ~ $4,500 per run.

At that point, it would be cheaper just to have it all laser welded, which if they can get a line of sight, would be the preferred method.  Faster, cleaner, cheaper and plenty of vendors.

Joe