Donkervoort D8 GTO(welding question)

"Josh Welton" (watchtheprettylight)
11/18/2013 at 14:51 • Filed to: weldopnik, donkervoort, copper, brown dog welding, race car, welding

I know it's not new. But it's cool. And something !!!error: Indecipherable SUB-paragraph formatting!!! I just found on it made me scratch my head...

376hp. 1533lbs. 0-60 in negative seconds.

No, not that. This:

Donkervoort calls the GTO’s core a hybrid chassis. Designed by Mr Donkervoort and former Maserati chief chassis engineer Paul Fickers, it is an intricate scaffold of laser-cut and copper-welded steel tubing , abetted by stressed carbon fibre composite panels and aluminium double-wishbones at all four wheels.

Wait...what? "copper-welded steel tubing"

I'm interested in this. You can weld or braze copper to steel a few different ways. But I wonder why they'd weld steel to steel with copper? I do it in my sculptures for contrast(not copper, but silicon bronze). I'm even doing it on a bike I'm building just for the heck of it. I've got a couple thoughts in my head, but none really make a ton of sense. And the pics they showed here rule a few processes out: !!!error: Indecipherable SUB-paragraph formatting!!!

Hard to see from the pics in that link, but it looks like they are mig welding the chassis with silicon bronze(tig pics look like they are welding an aluminum tank). They might be tigging the chassis too, might be doing something else with that wire machine. Either way the welds look "gold;" I wonder why they're going away from traditional tig for this chassis, a chassis that is gonna see a lot of track days? I know a bit about metallurgy, but I'm not an engineer. Any ideas???

DISCUSSION (14)

Party-vi > Josh Welton
11/18/2013 at 15:04

Dumb question, but do they mean the tubing is actually copper-welded instead of say cold-rolled or hot-rolled? Also, why not chromoly tubing?

DrJohannVegas > Josh Welton
11/18/2013 at 15:11

My one and only one idea is that, for some reason, they are welding an alloy with a propensity to crack in the weld area, so going to copper gets them some benefits in terms of the integrity of the bead. But, I am scratching my head here.

wacopalypsenow > Josh Welton
11/18/2013 at 15:13

Would it have something to do with copper's low melting point being better capable of penetrating and bonding deeper into the outer layer of steel without compromising the structural integrity of steel with higher temperatures.

/fuckifiknow

RamblinRover Luxury-Yacht > Josh Welton
11/18/2013 at 15:15

My only guess is that they're doing something funny to get away from weld-related stress patterning in the tubing. I.e. not welding at full iron welding temps, but using copper. An additional advantage to this would be ductility at the welds - combine the "no heat alteration of substrate" and "weld ductility", and I can only think they're shooting for controlled flex between rigid elements that would stress fracture if traditionally welded. Possibly high carbon with some level of treatment.

Copper as an alloy with steel isn't typical, but the two have excellent surface adhesion, so...

m2m, apex detective > Josh Welton
11/18/2013 at 15:16

Maybe you can get something out of this?

Watch from ~ 3:30 mins if the embedding gets borked.

//edit: Just saw that you had already taken a look at pictures. Eh, just watch it for kicks; it has Donkervoort Jr in it.

Josh Welton > wacopalypsenow
11/18/2013 at 15:32

Until I know what they actually mean by "copper," it's hard to say. So often industry guys either dumb terms down, hype known terms as something they're not, or are presented to the public through hype people that don't have a clue or lost something in translation from the originator. It doesn't look like copper, it looks like a silicon bronze weld(braze).

Josh Welton > RamblinRover Luxury-Yacht
11/18/2013 at 15:37

Yeah, I've used SiB for the same reasons on cast iron. I didn't want to go through the preheat/postheat process, so I cheated it and "welded" it cold. Like I mentioned in another comment, I'd be interested in what they're calling "copper." Could be something lost in translation. The pics make it look like they are using SiB, but they're pretty low resolution.

Josh Welton > Party-vi
11/18/2013 at 15:39

I'm not sure they aren't? Another thing that may have gotten lost in translation. That's a super light frame for being steel.

RamblinRover Luxury-Yacht > Josh Welton
11/18/2013 at 15:45

I can only say this: and that is that people who use brazing on very thin rusty metal I have to weld, in places I can't grind it out nor effectively burn it out with a torch, have earned my hatred. Had to rebuild a firewall for a Land-Rover which had had some half-assed patches put in place, so A: the sandblasting hadn't really done its work there, and B: I had to imperil the metal trying to un-braze it to go back together.

I know I could have rebrazed it, but the existing brazing had (surprise!) experienced some corrosion and was on top of rust, so that wasn't a good option either. Also, that would have cocked up the plating on the piece I was welding to it more than MIG-welding, so...

Josh Welton > RamblinRover Luxury-Yacht
11/18/2013 at 15:50

I almost think they're using CM and not steel. The frame is so small they'd be able to do everything raw and weld it with actual CM rod(which you don't typically want to do) then literally post heat the entire frame at once. You'd have a super lightweight frame that's got strength and ductility. Maybe they're using something like chromoly and tig brazing it with SiB to keep the heat input down and skipping any kind post heat. But really, with that thin of cm they'd pry be able to weld it with er80s-d2 with no post heat anyways. If they're having issues with cracking, it's a design issue and not a weld issue.

Josh Welton > DrJohannVegas
11/18/2013 at 15:50

If they're having issues with cracking welds, I'd say they need to go back to the drawing board with design.

Josh Welton > RamblinRover Luxury-Yacht
11/18/2013 at 15:52

I'm dealing with that on an old Triumph frame I'm trying to pretty up. Nasty, hard, ugly, shitty brazes that are borderline impossible to clean up.

RamblinRover Luxury-Yacht > Josh Welton
11/18/2013 at 15:58

I'd say CM + SiB is sounding pretty likely, and if their design is fiddly enough it might distort with a whole-assembly treatment, it'd make some sense. They were bragging a hell of a lot about weight, after all.

"Design issue" here probably means, though, the frame designer doesn't want to model any kind of non-uniform characteristics in his tubing, and doesn't know or want to know what would happen under flex doing anything *but* brazing.

I've done FEA before, and being able to say "Oh, and it's basically glued here" is very liberating to the lazy - anything beyond a basic rigid connection gets hard to characterize.

RamblinRover Luxury-Yacht > Josh Welton
11/18/2013 at 16:11

I eventually settled for just burning most of it - did some violence to the parent metal, but better soft parent metal that's a little burned than metal that's badly overworked from trying to grind, or metal with assorted dribbly swelled places, failure to penetrate, or oxidation from the braze staying. There was a little bit of zinc present when it all went back together from the galvanized replacement, so I just made sure I was welding hot enough that it fluxed the worst of the remaining surface gunge. Flash rusting/torch touched surface porosity from getting the braze melty.

/Isnotacompetentwelder