Has anyone ever seen a mold built for a part like this?

[Jim Estes]

I have to figure out how to built a mold for this part. The only mold I have seen that can make a part like this was the molds that were used to make the agitator for GE washing machines sever years ago. They were built in several segments that pulled away from the part to allow release of the flutes.

Does anyone know of a simple way to build this. If you split the part down the middle in two segments, there is a lot of undercut to the flutes.

I split it into 8 segments and there is still a little bit of undercut on the flutes.

Any suggestions?

Jim

[krazatchu]

I'd like to know how thats done too...

Sorry I dont have the answer, I have been looking....

[lerman]

I don't see the undercut on the flutes. What am I missing?

Ken

[Jim Estes]

That's what I said at first, then I made a program to cut the electrode to burn the part. When I simulated the cut, I noticed that there was a big flat spot on the side of the flute. That is what I am calling an undercut, meaning that the part does not pull straight out of the cavity. Because the pitch of the flute is so large, it cuts into the cavity underneath itself. If you look at the cutaway view, you will notice that you can see part of the flute above the cutaway section, but you cannot see the flute below the cutaway view. The part you can see does not have part in front of it, therefore, to be pulled from the mold, it would have to move down to where the cutaway section is.

The best thing I can come up with is that this needs to be an unscrewing mold, and even then it needs to have the upper portion created by a contoured parting line that matches the pitch of the flute.

Jim

[Ronaldf]

This is more complex than a normal unscrewing mold.
Most unscrewing mold are for internal threads. You can
normally rotate the cores after the mold has been opened.
In this case the rotation must be started at the exact
time the press starts to open. Also rotation speed must
match the opening speed of the press.

Good Luck With This One

Ron Stevens
ron@softmold.com
http://www.softmold.com

[krazatchu]

Lerman... exactly what you said.... You can't see the undercut...

When ur looking normal to the cutaway view... the undercut can't be seen...

Here are some pics of a part I'm working on... I have arrived at the conclusion that I will have to machine them instead of molding.... Allthough, it would be nice to have the option...

On another note... I had also thought about unscrewing the piece from the mold... but that only works if the helical pitch is constant...

Perhaps this is done with some kind of soft/silicone mold... I know nothing of mold techniques so it's just a guess....

Michael

[Kevin Taylor]

Can you split the mould and unscrew the part? to remove the finished part generating the cavaty could be another thing good luck kevin

[Jim Estes]

Just to update you guys about this mold. I am planning to build a mold with four slides (cams) that pull away from the flute and eject the part by sleeve. I did some measuring and the undercut in 4 segments is just about 0.035" and that isn't enough to deform the part out of tolerance. The material is a fiberglass filled material and it will be very hard after cooling, however if the cycle is fast enough the part will have enough flex to overcome the undercut.

I will still be using the contoured parting line to create the upper portion, and I will have to use a CNC Sink EDM to burn the flute into the 4 slides.

This will be a fun project.
I might post pics when I get it done.

Jim

[Jim Estes]

With an unscrewing mold, we would have to modify the center hole to have much larger flats so that the part would not rotate, the spin the cavity, this would push the part forward out of the mold.

There are several ways to unscrew a part, some parts must be unscrewed as the mold opens, this type usually has a high pitch screw connecting the two halves of the mold via gears, as the mold opens the core spins.

Another type is the classic bottle cap mold, where the mold opens and then a rack and pinion mechanism spins the cores out and then the caps are ejected.

Some molds a hydraulic motor to spin the cores.

I thought I was going to have to build an unscrewing mold with this one, and that was going to be very, very complicated, since the cavity was what was going to have to be spun. I had never seen that done before.

With the slides, it is much less complicated. The upper portion and the contoured parting line is the tough part.

Jim

[miljnor]

can you show finished mold when done?

I don't know much about molds but would sure like to see the finished product (mold).

[leland]

Mold making is an art....lots of nuances to learn.....but modern flexible mold material...such as Silicon..(the most expensive$) can easily handle undercuts that are on your original.

I have used a company in PA...for years...it is called Polytek

hhtp://polytek.com

they have a great catalog....that gives a bit of instruction also.

You will need: plasticene clay......Art store
shims....I use aluminum roofing flashing
vasoline ...drug store
mold material...I use polyurithene room temp vulcanizing
mother mold material...I have used plaster....but a buttery tecture.....room temp vulcanizing, hard plastic is much better.

You should go to the library and get some books...or surf the web and educate yourself about how to make a mold....

But your's could be made in 2 parts.....

[Wiseco]

Hey Jim,

Maybe this could help you out if you have not finished with that project.

August design tip from Protomold