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Question for material scientists
I remember this site had quite a few material scientists / engineers. I have a friend who wants to find out more about molding plastics. Could somebody direct me to a reputable forum where he would find the answers to his questions? Thanks a bunch!
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Question for material scientists
What kind of molding and what kind of plastics? I have experience in production vacuum forming ABS and styrene.
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Question for material scientists
earthwkrs,
Not sure what kind of plastic he had in mind. He wanted to pour liquified plastic into a mold to make a part for some toy he was working on. Not vacuum molding as he has no equipment for that. His idea was that it would be cheaper to make a mold and pour a part than to machine it out of steel/aluminum.
Since I know less than nothing about plastics and don't know the right question to ask (since I'm not the one making the part) I thought I'd ask folks here who know to point me in the direction of a quality web forum on that type of stuff. I remember Eric Peters was also expert on plastics, but apparently he's no longer around.
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Eric seems to go away for extended periods then show up again later. He always provided good info and I wish he'd come around again. You haven't been around much yourself, Denis. Good to have you back  sorry I can't contribute anything useful to this thread 
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The name of the process excapes me, but there a process that uses some sort of lasers or light sources that shine into a liguid resin in a clear tank. Where the light intersects it solidifies the resin. The part looks as if it were molded of clear plastic. The part would have be drawn on a CAD system I have to think in orderot input in the system. He might be able to find a college that trains in this, or find a prototype making shop who has one.
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The process you are referring to is stereolithogrophy also known as rapid prototyping. This is a very slow process and is used to verify a part prior to going to production. Too expensive for more than a couple of parts. Depending on the quantity of parts and the shape of part your friend wants to make dictates the process used to make it. If it is just a couple pieces and he doesn't care how much plastic he uses then the poured mold is fine and you can file the burrs away after. If it is a hollow part like a ball, doll, bottle, fuel tank etc.. it can be blow molded. If it has intricate shape with webs and gussets or is a deep drawn part then the process is injection molded. There is the RIM process too but that is used for layered and larger parts usually used in automotive and other larger panels. Compression molding and thermo forming are a heat and compress process also used in layers of different or similar materials. However this isn't used for toys normally.
A plastic organization to see is SPE.
Some of the plastic machinery companies to visit are Bekum, Uniloy,
Boy, Arburg, Milicron, Graham, and Sidel to name a few.
Hope this helps.
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And don't forget SMC (sheet molded compound) which is used for making complete inner/outer door panels, deck lids, rear hatches, hoods, and rear spoilers, and pickup rear fenders and whole beds.
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Thank you ALL for all the responses.
It seems like if you want to make a quality plastic part, you'll have to invest a godly amount into equipment, one way or another.
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Dennis, you don't have to invest in large amounts of capital. Plastics like Acrylic and Polyurethane can be poured in some configurations and they will set in molds that can be made from soft materials. I have replicated parts by taking an impression and making a silicone rubber mold (cavity) and filling that cavity with acrylic casting compound. Such a process can make dozens of parts economically. This is fine for a few prototypes but you can't make more than a few per day.
In the past, I have even made molds using the SLA process and that mold cavity was prepared to accept casting resin. You pour in the mixed resin, let it cure and open the mold to get your parts. With this process, you don't even have to have an original part to make a silicone mold.
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