Highly detailed vacuforming

More than likely you need a better vacuum source. I've given some thought to building a vacuum machine and have talked to people who know something about it. A high volume vacuum pump(not a shop vac) and a 10gal tank to contain a vacuum until you open the valve to evacuate the air under the plastic, would work better. You also need to minimize the dead air space below the mold plenum.

Thanx for your reply!

Dead airspace..you mean the air thats underneath the mold right? I used clay to make it minimal and taped the sides so almost all of the air is sucked down thru the holes in the mold. I will post pics of my machine and results soon.
The thing is for "regular" vacuforming the shopvac works excellent and details are excellent on the insides but it seems that with female molds you would need way more pressure. Especially with small emblems the plastic is not sucked into those spots.

I'm going to try one more thing with a lit on top of the frame where the styrene is clamped. I leave some holes on the vac table open and on the frame drill some holes on the inside edges. Hopefully the air coming thur these holes will create a vacuum on top of the mold so you get 2 actions: One of the tiny holes in the mold and one from the surrounding holes forcing the air down on the hot styrene and mold.
I hope it will do the job.

This is how I do it.

Use a female pull for the vacuum surface. drill a bunch(the more, the better) holes in the pull area.



attach the female pull to the top of the box with a good seal. Make the holes as small as possible with a micro drill. The plastic will pull into the holes of they are too big and you will have to sand them off the surface.

I think Hatewall got you covered pretty well.

Female molds are tougher than male molds, also vac-forming will only give you good detail on one side(ie. the side closest to the mold).

QUOTE: Originally posted by Hatewall This is how I do it. Use a female pull for the vacuum surface. drill a bunch(the more, the better) holes in the pull area.

How do you fabricate your female mold?

vacuu-form it over the pattern. the next pull will be down into it.

Hatewall, thanks very much for the clear pics.
I did it in the exact same fashion although I Iplaced the female mold on the vacuumtable and taped it.


Here's the (test) female mold I formed in 2.5mm styrene. As you can see the details inside are really good...good enough to use for a resin cast.
I will make a pic of this test mold with the holes drilled in the details will not transfer good enough on the formed parts.

And this is my machine:

QUOTE: Originally posted by Hatewall vacuu-form it over the pattern. the next pull will be down into it.

Don't you have a problem with soft detail using a male vacuum pull for a female mold? Don't you have mold deflection problems or do you reinforce the mold? Do you have any pics of your set up?

Sorry guys..server is down. Hopefully the pics will be there later on.

If you prep the original part good enough by reinforcing the back using PU foam or other product you get really good results.
I read that the best stuff to use for a female mold is 0.60 low density polyethylene.

Here are some of

Here you can see the detail on the inside of formed parts. This is a door panel you can see the leather structure.

A pic of the formed female test mold

The female mold with holes drilled and taped on the vac table.
At first I only drilled small holes later on I tried the bigger holes to see what happened.

A closeup of one of the problem areas, emblems. It's hard to see in this pic but the detail is really good. I pressed clay in this emblem to check the detail and it's really good.

A pic of the formed result details are not good enough, you can see that the Impala emblem faded because probably the air had no way of getting into these lower parts.
I heated the 0.5mm styrene really well it drooped about 2 inches before forming just to make susre it was soft enough to reproduce the fine details.
Enjoy the pics! I'm going to try the direct method of Hatewell by applieng the vacuum cleaner directly to the mold.

unless you can get a small enough bit to drill into those letters, it's going to be hard to pull into them. A large quantity of tiny holes is preferable to bigger holes, even when there is room for them. You want a nice uniform layout of holes to even out the vacuum pull.

The pattern needs to be approached as the piece of art, not the finished pull. The skill is in the pattern. I almost always make the box out of plex with the top of the box having a general shape of the shape going down into the box cut out of it. Then you can just use liquid cement to glue the flange down to the top of the box. It's not something you can reuse (except for duplicate parts) since your mold becomes one solid piece of plastic with a hole in it for the vacuum hose.

As an example to go with the simple image I posted, the top piece of plex on the box would have a hole cut in it slightly larger than the hemisphere fitting down in it. Almost all of the flange is supported by plex and is the surface to glue the flange to.

The top plex will support the flange so it doesn't deflect. The curved parts will support them selves.

Hope that makes sense.

Adding to what hatewall said, checking the pattern/mold with clay will give you misleading results as the clay get into the smaller areas easier than the plastic sheeting.

Good idea but better suited for resin or similar molds.

I understand completely! Thank you very much for your explanation!
I'm going to make a new female mold and build a box for it with the hose directly attached. So basicly you get a vac-box for every part of your kit.
I'm also going to try the lit trick when it doesn't give the right result because for the emblem areas I need a good downward pressure too.

Thanx!

QUOTE: Originally posted by Model Museum Adding to what hatewall said, checking the pattern/mold with clay will give you misleading results as the clay get into the smaller areas easier than the plastic sheeting. Good idea but better suited for resin or similar molds.

Perhaps your right but looking at all these vacu formed plane kits I see very good results. I think the same results can be achieved with car models too since it is a lowcost way of producing a nice kit. I also have seen to many resin car kits that were a disaster you had to do so much sanding and smoothing that it was really no fun anymore. I understand this has to do with who produces these kits.

About the clay your completely right although the 1mm polyethylene gets as soft as clay.
Yesterday I tried pressing the hot plastic in the emblem area and the result was pretty good. The problem really lays in the air pressure. I hope to show you all good results soon when it all works out.

1mm?? I use 0.5mm & 0.3mm sheets.

For the pulled example in the pics I used 0.5mm and for the female mold I used 2.5mm.
I used up to 3mm in that same female mold with almost the same result as with the 0.5mm. Because it takes longer for the 3mm styrene to get hot it also means that it stays soft for a longer period of time.
I let the thicker styrene droop down to about 5 to 8cm before I place it on my mold. At that point the styrene is really soft like clay...placing your finger on the material will leave a nice fingerprint behind...and a blister..hehehe.
try it you will find out that under the right circumstances it work pefect leaving you with thicker parts to work with although 3mm is way to thick.

Can you use pressure instead of vacuum on your female molds?