3D printing for sheet metal, sort of

Incremental_sheet_forming

Incremental sheet forming makes a single sheet metal part by pushing a polished ball against the metal while under CNC control.

My mechanical engineer buddy Dave Ruigh came across a Ford Motor video of how they can prototype a single sheet metal part using CNC (computer numerical control). It’s technically called “Two Point Incremental Sheet Forming.”

Dave noted: “I see a Faro logo on the stylus head (they make 3D digitizers). Looks like they are generating the toolpath in Catia V5. These are Fanuc hexapod robots. Pretty damned slick.”

Then audio guru Steve Williams chimed in: “Is this truly 3D printing? Is there a class of this that involves plastic sheet deformation as an alternative to sheet metal stamping, which was sort of what they were comparing. What is the plastic and how common is the sheet deformation (presumably through heat) method, compared to depositing layers of material as in normal 3D stuff?” To this Dave replied:

“They are forming metal sheets with this process, not plastic. 3D printing is just a made up buzzword that broadly covers any rapid prototyping technique. I guess we could call it “unconventional fabrication technology,” or UFT, if you would prefer. That said, you might do a similar process with plastic sheet using heat. Plastics tend to deform nonlinearly though (they stretch a lot, then spring back), which makes predicting their formed shape difficult.”

“Guess we’re gonna have to call it “Incremental Sheet Forming.” Specifically, “Two Point Incremental Sheet Forming.” Ford claims this tech is patented, but I’ve yet to find it. This work at the Computer and Automation Research Institute of the Hungarian Academy of Sciences does seem to predate the Ford work.”

This is a slap-my-forehead, “why didn’t I think of that” technology. When I was in the auto biz we did short-run prototyping with Kirksite dies. Instead of H3 tool steel, the die was machined out of a high-strength zinc + 4% aluminum alloy that had a brand name of Kirksite. It was invented in 1929 and called Zamak by the Germans. Thing is, how often do you want just one prototype part? I always said you need three. One to hold, one to install and compare against the old part, and one that gets shipped to the show in Duluth so the sales guys can peddle it before its ready to sell.

So Dave Ruigh was the guy that told me how modern tool and die folks just carve the male form in carbon with a 5-axis machine and then EDM (electrical discharge machine) the tool steel to near-net shape. Polish it up and stamp away. So now I assume you could just high-speed machine (another thing Dave taught me) the Kirksite, mount it into a press and bang out 10 to 500 parts depending on how rude the die had to get with the sheet metal.

The major problem with this incremental forming is that it will not show if the die is manufacturable or if the shape of the sheet-metal can be made in high volume with a die. When you prototype something you should also be prototyping whether you can make more than one. So if Ferrari wants to make some goofy fighter-plane-looking chin spoiler, this “incremental sheet forming” is ideal. They are only going to make 5 parts total. Better yet, when some rich yuppie prangs the car as he drives home from the dealership, the fine folks at Ferrari can slooooooowly make another one for him and charge him the requisite $10 or $20 grand of machine time it takes.

What do you figure Dave? A big expensive machine like in the video needs to make $150 per hours of spindle time? A stylus, a spindle, either way you have to pay for the machine. So I wonder if a part that you can incrementally form cost $10k, could you make 100 parts for $20k using Kirksite?

Oh, I suspect that Ford claim of “first” is because they have a lower cup that follows the stylus whereas the Hungarians just pushed the sheet metal into a female die.

And here is 26 glorious minutes melting steel and stamping it out the old-fashioned way in the 1936 Flint Michigan GM plant.

Aaaarrrrrgggg matey, that thar is real sheet metal work,….

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