A 150 ton press followed my son home... It wieghs in at around 14,000 lbs. has two platens that are 3'x3' by 4" thick and there's about 18" of total stroke. We have to come up with a hydraulic pump for it. I'm sure it will move VERY slowly with any pump that is installed.
So, is it possible to build your own press brake dies for something like this? How? What materials are needed? I'm sure you don't make it up out of cold rolled.
Cold rolled will work, but will distort/deface easier than a heat treated material. I'd suggest some 4140/42 HT. It's tough enough to stand up to the work, but easy enough to machine. By working properly, you can end up with straight, pre-hardened dies that should work well. You'll have to come up with a method of locating and holding the dies. Could be you can make some slotted adapters that mount to the platens. Mild steel would be adequate for them. Should work quite well for bending, especially with the slow moving hydraulics you spoke of.
The college I went to had a 100 ton platen press that was THE thing for making light plane ribs and formers. They had a 2x2 (3x3?) rubber pad on the upper platen, about 4 inches thick. They used male dies, wood for single use, aluminum for production, with just a couple pins for retainig indexing of the part.
Trim the flat sheet aluminum to size, place on pins, press! Complete formed rib or former. Worked really well. The students there were producing RV-4 aircraft that were destined to be registered and sold, other students were involved in CNC milling of the master forms. All pretty cool stuff.
I'm using that rubber (it's PU) for my press-brake. The company I bought the PU-sticks from is also making that special PU plates and do have a foil to protect the PU (as a wearing surface). You can even cut sheet metal on "rubber". The huge advantage is, that the dies are damned simple (cutting even works with CRS that is case hardened for short runs), the disadvantage is that you need a lot more pressure. But with 150 tons, I wouldn't worry about it that much. :-)
It seems, that they don't have a representative in the USA, but I bet you'll find something similar "over the ocean".
For those who have missed my posting for the press brake:
A big 10-4 here. Now convincing "the kid" about safety and danger is a different matter. He had a skate come out pushing the unit with my forklift. Could have tipped it over. Busted the 10 ton toe jack getting it level. Its sitting in the middle of the room waiting for a 20 ton jack from Ebay. He also dumped the new 10hp air compressor off the pallet when moving it out of the way - busted up a bunch of fittings on the compressor head.
Back in 1968, I wrecked my dad's new pickup truck. He was giving me holy hell until gramps said, "Whatever happened to my '36 Ford?" I never did find out about that old Ford, and never got any more trouble about wrecking his pickup. What goes around comes around...
They do indeed mention polyurethane, and Nick goes on to mention the trick is the hole in the bar. The piece looks to be either 1.5"x1.5" or 2"x2" square with a 3/8" or 1/2" hole all along the length. I'm sure Nick could chime in with the exact dimensions.
I could order urethane stock from McMaster Carr, but I have no idea how to drill a hole two feet long down the center of a small square. Any ideas?
Harold, thanks for the very informative post on my query.
My Dad had an old book by Alcoa that described this. No ISBN, just copyright dates of 1947 to 1962, titled "Forming Alcoa Aluminum". Maybe a library would have a copy, or maybe Alcoa still publishes it? Paraphrasing, they list two general categories of rubber-die forming: those using only pressure to form a sheet to the shape of the punch - the Guerin and Verson-Wheelon processes; and those using additional blank-holder control - the Marform and Hydroform processes. The Guerin process was the first commercial rubber-die process and was introduced by the Douglas Aircraft Company in 1935. Anyway, searches for those process names might turn up some details. They all used to use real rubber but I guess polyurethanes have taken over :-).
The Guerin process sounds like what Trevor is describing. They describe the pad as several layers of rubber cemented together, housed in a strong steel or cast iron container which is about one-third deeper than the rubber, attached to the upper ram of the press. The dies are simply laid on a platen which must fit snugly into the rubber container to prevent extruding the rubber and damaging it. A side clearance of 1/32 to 1/16" is recommended. The rubber will exert force in all directions like a hydraulic fluid. The forming pressure in psi of the rubber equals the press force in tons times 2000 divided by the platen area in square inches. The max height of the die should not be more than 2/3 of the rubber thickness. A rubber pressure of 500 psi will form 0.032" annealed aluminum, and the max pressure used in Guerin work is about
1500 psi which will form annealed 3/32" sheet.
Thought it sounded very interesting when I first read about it, but I've never found an excuse to set up and try it :-). Oh, a 150 ton press would give a pressure of 1500 psi over a platen area of 200 square inches or about 14x14". I'll leave it as an exercise for the reader to calculate the wall thickness needed for the box to contain the 1500 psi rubber :-).
-- Regards, Carl Ijames carl dott ijames aat verizon dott net (remove nospm or make the obvious changes before replying)
I have a copy of Forming Alcoa Aluminum, also Soldering Alcoa Aluminum and Machining Alcoa Aluminum. Most can be found at an on-line used book site. There's also Welding Alcoa Aluminum and Brazing Alcoa Aluminum
It would be easier to commission someone to cast it. Urethane, depending on the hardness, can be a bitch to machine---the softer it is, the less likely you'll be successful.
If you'd like to research the casting idea, please contact me on the side and I'll provide contact information for a guy in Utah that has spent the last 40 or so years working with the stuff. He was trained in the aero-space industry and is well experienced in casting the material.