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1/25/2018 7:38:29 AM
Posted: 7/23/2002 7:03:09 PM EST
I have a project I'm working on and I need as much info on injection molding and mold making as I can get my hands on. The medium I'll be working with is poly-carbonate. Is there any books out there that might be able to help me out? I'm looking to do this in a garage setting on a small scale. Any info on this subject would be appreciated. Thanks.
Link Posted: 7/23/2002 7:38:47 PM EST
The first thing you need to know about injection molding is that it's expensive. You'll most likely be better off contacting a firm that does outsourcing work and asking them. Do a search on google and you'll find a bunch of companies will handle the work, including mold making, etc. Doing it in your garage is unrealistic unless you have serious funds at your disposal. Remember the Alamo, and God Bless Texas...
Link Posted: 7/23/2002 7:46:51 PM EST
Ask on AR15.com and ye shall find... [url]www.lindsaybks.com/dgjp/djgbk/inject/index.html[/url] I built one of these recently and it works great. All I've used it for so far is to make the world's only (as far as I know) US made HK SL8 mag followers and floor plates to help meet US parts rule, so I can legally put a pistol grip stock on it. I don't really know anything about plastics, I've just used plastic water jugs and microwave food containers, anything that melts around 400F or less will work, could run it hotter too with an appropriate heater and thermostat. I used a heater from an old coffee maker, and a thermostat from and old electric fry pan. It was a fun DIY project if you're so inclined.
Link Posted: 7/23/2002 7:46:55 PM EST
Yes, What GBT says... Sounds like you have to do some outsourcing for that type of work... What are you making? I understand if it's a secret...Just curious =)
Link Posted: 7/23/2002 8:43:14 PM EST
This place has some small machines, but they probably still cost alot. They also sell plastics too. [url] www.mcp-group.com/rpt/rptt100ksa.html [/url]
Link Posted: 7/23/2002 9:18:44 PM EST
I used to work next to a small manufacturing concern which incidentaly made a firearm accessory some of you own. My knowledge is very general but my understanding of the process amounts to: Spend somewhere around 50 large (could be less in china to 100's depending on complexity) to have a mold designed and fabricated. Then invest in molding machines big enough to stick out both ends of your garage or contract with manufacturer, and squirt product at .xx pennies each and hope you sell enough hundreds of thousands of units to reach your break-even point and recoup your investment. Go get a few pieces of injection molded plastic and study them. Look at the difference between a quality name brand component and a cheap battery cover on your remote. Look at the difference between the finished outer surface and the inside. Do you see where there is a difference in thickness or a protrusion from the plastic, on the opposite side you will see a dimple or cupping? On the finished side of the quality piece, this won't be nearly as apparent. When the part is injected, as the pressure and heat dissipate the resin contracts, thicker areas contract more, and this dimpling occurs. The reason you don't see it on the quality piece is that the mold is "compensated", or has been engineered to account for this. In other words, to get a flat surface on a part with varying thicknesses, you have to make the mold with depressions that will produce just the right amount of of extra material so that the end result is correct after the shrinkage. This engineering costs money-duh. Look at textures. Next, every mold must enclose the part, then open to release it after injection. Look for the mold lines. On the quality parts, there are tight fits and resin doesn't escape between the mold halves. The lines of the mold openning blend into the contour of the product. Now look at a slighty more complicated mold, for example the back shell of a cordless phone. The front and back aspects of the clamshell mold are obvious, but say there is an opening at the top end for the antenna to protrude. This means that part of the mold has to retract out of that openning in a different movement than when the rest of the mold opens to release the part. If you look closely you will see the mold lines where the mold parts meet. Now if that openning is threaded, as the mold opens and releases the part, the surface of the mold which forms the thread has to be made to unscrew from the part.. More cost-you get the idea. For a production scenario, most of your costs are up front. Then as you need parts made, you pull the mold off the shelf and set it up, run your parts and stick it back on the shelf. For the small scale process described in the link, I guess it's whatever you can make of it. I'd love to see what you do.
Link Posted: 7/23/2002 9:35:59 PM EST
[Last Edit: 7/23/2002 9:40:56 PM EST by Winston_Wolf]
... Do you know Shawn at CavArms? His parents own a nicely equiped shop in Mesa here. ... edited to add: Buy [b]ASM Handbook Volume 21 Composites[/b] and read. It's equivalent to [b]Machinery's Handbook[/b] only more complete. Not cheap.
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