Sand Casting Using Vacuum Formed Molds

[Geof]

On a different forum I came across this link to a design study about the Track Shoes on the Shuttle Transporter:

http://www.sfsa.org/tutorials/nasact.../TrackShoe.pdf

This was interesting enough but the most intriguing part, to me anyway, is described on pages 14, 15 and 16.

The molds for casting the new shoes were made using a technique I had never heard about before, here is an excerpt describing it:

V-Process Molding

The V-Process uses a strong vacuum applied to freeflowing, dry, unbonded sand around patterns in airtight flasks.

The process uses a specially designed, strong, highly flexible polymer film to seal the open ends of the sand mold and form the mold cavity.

The vacuum inside the mold results in a net pressure pushing in, holding the sand rigidly in the shape of the pattern, even after the pattern is removed.

I Googled and found this link:

http://www.robertssinto.com/vprocess.htm


I think this process could have tremendous potential for hobby casting and small scale production. Although you might run into patent problems using it for production if it has been patented.

[tobyaxis]

This is a great find Geof!!

Thanks for sharing it.

[mactec54]

Great find Geof

Very cool, the mind bolggles with the possibilities of this process, I wonder what the plastic film is that they are using.

[advt001]

IIRC the "V Process" has been around since the late 70's or early 80's.I think it was originally developed in Canada (Windsor Foundry?) Ford was trying to use it to make cylinder heads.We were going to play around with it a couple of years ago and do have a roll of the film.We started welding up a couple of the flasks and thats about as far as we ever got.

[Geof]

I did more Googling and found these:

http://www.thefreelibrary.com/Revisi...ng)-a017085154

http://www.castingarea.com/fa/v-process.htm

http://www.foundryworld.com/uploadfi...1451097909.pdf


V process casting originated in Japan in 1969 but even by 1995 there were fewer than 200 foundries worldwide using it. I wonder if the reason it was not more widely applied is that it was patented and now the patents are all expiring.

I also found mention of the film which is Ethylene Vinyl Acetate, also used for laminating glass so it should be fairly easily available.

[mactec54]

Hi Geof happy new year

The EVA film is used for lots of things, shrink wrap, Laminating books,pages,posters etc

I think you would have to be carefull that the EVA did not have the chlorinated part in it
but i'm sure you can find one without the chlorine

[Geof]

Happy New Year also.

Part of the reason I am intrigued with this process is that I am familiar with an analogous procedure used to make customized support cushions for severely disabled people, particularly children with cerebral palsy. In some cases a person with cerebral palsy has a very difficult time separating out muscle groups to contract them individually and this is made far worse if they are in a wheelchair with inadequate support in all directions. If they have to try and tension muscles to hold themselves upright they sometimes cannot activate just those muscles and they get caught up in spasmodic muscle contractions throughout the whole; the net result is that they often just let themselves flop because that is more comfortable.

So supportive cushions have to be made and they have to fit as close to perfect as possible so that localized contact does not cause pressure sores. The way this is done is to have a bean bag cushion that the person can be nicely positioned in with the help of therapist; then a vacuum is pulled on the cushion locking the shape. This is then used to cast a mold and then the mold is used to make a foam cushion the exact shape of the vacuum solidified bean bag and presto the kid has a custom cushion that supports them so they can relax without flopping and it is much easier to do things.

I am almost embarassed to admit that it never dawned on me to try a similar procedure using a flexible bag filled with much smaller particles than are in the bean bag, or even smaller than foundry sand for that matter. I have made molds using RTV silicone which is a messy process and of course the mold material cannot be reformed if you make a mistake or need to modify the pattern. I suspect that doing this vacuum process with very fine polyethylene beads could give a replication of detail very close to that possible with silicone.

[Kipper]

Hey Geof, See if you can lay hands on some "Vinamold" in your locale...It has fairly gross shrinkage (compared to the best Silicone') but when used thoughtfully can reproduce a mirror finish. Oh did I mention it's reusable and a fraction of the cost of Silicone

[Geof]

Thanks for the suggestion but I haven't had a need for molding anything for a couple of decades and do not anticipate it for the future. I am drifting more and more towards talking or writing about doing things but not actually doing them; retirement has that effect I find.

[tobyaxis]

Thanks for the suggestion but I haven't had a need for molding anything for a couple of decades and do not anticipate it for the future. I am drifting more and more towards talking or writing about doing things but not actually doing them; retirement has that effect I find.

You will never fully retire. Once a Machinist, Always a Machinist. Besides, who would we ask the tough questions??

Your a credit to the "Trade".