How to make a mold out of polyethylene Plastic?

[BigChad]

I been molding resin with an aluminum master using a silicone mold and it's working ok, but when pouring excess material into a polyethylene measuring cup the resin doesn't stick at all. My question is, how to make a mold out of the polyethylene plastic. I've seen small trays with shapes and designs being offered at various websites. My countless hours of searching the web has me thinking the only way to do it would be through and injection process?? Any help would be much appreciated!!

Chad

[happyiceage]

how to make a mold out of the polyethylene plastic?
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If just a few quantity, why not buy a plasitc block and machining it directly by CNC? Just like the way to make a prototype. Also, there is 3D laser rapid prototype machine could do it, but it will use a special plastic material to instead of polyethylene.

[BigChad]

I guess I could try that, but the cylinder shaped object can't have a parting line after curing.

[RomanLini]

Then you will need quite a lot of draft angle, especially if it is deep. And if you have a hard mold that is one piece (non separating) you will find it very difficult to remove the part even with a mold made from a slippery plastic.

[BigChad]

Originally Posted by RomanLini Then you will need quite a lot of draft angle, especially if it is deep. And if you have a hard mold that is one piece (non separating) you will find it very difficult to remove the part even with a mold made from a slippery plastic.

That's what I was thinking also. Was thinking just use a 2 piece mold and put the resin parts in a vibratory bowl to knock off the slight parting line. Iv'e had success using silicone molds for low production runs, but need to step up the quality and manufacturer ability of the process. I can't seem to find ANYTHING on how to make a plastic 2 piece mold, have kicked the idea around of maybe somehow using glass or ceramic also for 2 piece. I can't seem to find any info on how to melt plastic around a master other then injection process. I did find some Sculpey oven bake clay I'm going to try, it's like a puddy you can press around a master then bake it, worth a shot at this point. I appreciate all the comments and help!!

[judleroy]

I have made hundreds of injection type molds out of plastic. I tried polyethylene, teflon, acetal, and others before deciding on polypropylene as having the best natural mold release for the polyurethane I was casting. They were all 2 or 3 piece molds machine on a CNC mill. It even works for gang molds. You need to machine flowthrough passages in the mold for air release. Use a squeeze bottle like they use in restaurants for ketchup to inject the mold. Make sure to squeeze out whatever is left after each pour and when it hardens you can peel out what's left in the bottle and reuse it indefinitely. It is great for close to injection quality prototypes and small production runs. Hope this helps. Good luck.
Judleroy