I have a customer wanting to make a large ridged part and I'm thinking a foam part would work good. I've searched groups google here and found nothing. I'm thinking the kind of process they use in the auto industry to make the foam dash with the skin formed on it by baking the part. Does anyone know the name of the process used to make these types of foam/skinned parts. I'm wondering what kind of molds are used and what foams can be used.
Ed Huesers
I saw on Mythbusters the other day, they were making foam molds. Was a two-part mixture which they dumped into the form and it expanded. Think "Great Stuff" only in bulk. I've seen it used in the construction industry for spray-on insulation for housebuilding (wouldn't use it myself, makes the walls impossible to work inside afterwards). Maybe something like that would be an option? Forget the name of the foam but someone here can probably come up with that.
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This is reaction injection molding "RIM" molding. It is a thermoset polyurethane rigid foam plastic. The two part process uses polyol and isocyante are mixed and shot into a mold. I'm pretty sure the single part stuff used to fill gaps in your foundation reacts with moisture in the air to set.
It is a high part cost, low tool cost way of making foamed plastic parts.
What is the application and how many parts does he want to make?
I've developed dozens of parts using the self skinning foam process. A master is made from balsa wood, plaster, NC machined wax, whatever. Then a two part mold is made from RTV Silicone (room temp. cured silicone) which allows for really easy extraction of the finished part even when parallel surfaces may be called for. There are many foam harnesses available and most foam manufacturers are able to come up with the exact sponginess you need. From really hard rubber like, to very light and soft. Once the tool is made, you mix 1/3 hardener with 2/3 resin, stir like crazy for 15 seconds, pour in the mold, quickly cover like in a clamshell, then put under a press as the foam will immediately boil and exert huge pressures inside the tool. In about five minutes you can demold, clean out excess flash, clean out the bleed hole, and pour the next part. This, of course, is for low production casting. As you can see, one part every 10 minutes or so.
My son is using Hydroseal Polymers Inc. 1215 Madera Way, Riverside Ca 92503 for the front foam bumper on his RCWindjammer
These foams can be made with numerous different qualities. I made some foam "projectiles" for my anti-tank gun that I made for paintball use. I got my chemicals from Miltec inc. I can give you a phone number if you email me.
They mix the chemicals, and recommend operating parameters to give you the results that you want. In my case, I was looking for a very dense, but soft foam with a thin skin and a bright orange color so I could find them later that could be poured at room temperature.
I made my mold from aluminum. I used dowel pins to line them up, and C clamps to hold them closed. I made some test molds from wood, that worked fine if coated with wax for release.
It's a UK company but look at this site.
John
It's polyurethane foam.
Hey Ed,
I've read through the replies thus far, and no-one actually mentioned your comment about the "skin" formation. My only contact with dash-board manufacture was quite some years ago at Uniroyal, where I was an outside contractor doing service and maintenance, so hardly a "technical" answer from me, but just my observation.
Unreal was doing this, as they produced a product called "Royalene", which is what you called "the surface". The molds to form these crash pads as they were called then, were wood/fibreglass and steel framed, so they were, as mentioned in another's post about RIM, cheap tooling. The Royalene was made in another part of the factory in long sheet, and in different "flavours" it was applied to a cloth to make Naugahyde, sort of an imitation leather. For the crashpads though, a bright sheet-metal stamping was placed in and fixtured with-in the mold, then the Royalene, already cut to the proper size and shape, was heated to quite flexible, placed in the mold and "vacuum formed" to the mold surface, then the foam stuff was dumped into the mold in a long "squirt" pass, and the mold closed up. I don't recall the timing, but it wasn't hours, and the mold was opened and the finished part taken out.
The point I'm making is that in that process, the "skin" was not formed by the foam against the mold, but the visible finished surface was in fact this Royalene stuff available in many colours applied to the mold form and the sheet-metal was the backer and the foam was the "soft body". In all cases the "foam" stuff was super dark gray. The surface analogy might be as to fibreglassing something, where the finished visible surface is not the fibreglass, but a "gel coat".
Maybe doesn't apply, but it was interesting to watch.
Take care.
Brian Lawson, Bothwell, Ontario
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