Injection Molding Help

[cjs83]

I am trying to get into doing some plastic mold injection. I want to make knife handles, using Zytel or anything else that will work and give me the colors that I like. I can learn to make the molds without too many problems, but I can't really find anything on injecting. If anyone knows of any websites or books that I could look at to get me started in the right path I would greatly appreciate it.

I would like to buy a used machine, but if the cost is going to be too great then I might just make one.

Can anyone help?

[TAB]

Check out the the SPE libarary. They offer a lot of books on molding but they are not cheap.

good luck. I don't think making your own molding machine is an option.

[ToyMaker]

for a quick introduction see here

it's not the be-all end-all resource, but it will at least introduce some basic terminology and some beginners gotchas.

robotic regards,

Tom
= = = = =
"I'm happy to report he's bright-eyed and tushy-bailed."
- - attorney having bailed a client out of jail

[vacpress]

lindsay publications or the gingery press or whatever they are claled have a simplistic book desribing a machine made of angle iron and alumnium, a heater cartridge, and a manual lever ram design.. probably can be built for a few hundred $$. i dunno if it would be worth it though.. it could maybe make knife handles, but with 1 mold, the rate would be slow!

[trubleshtr]

Injection machines are nothing more than glorified glue guns.....would be fun to build one, I think it would be difficult to keep the temperatures consistant without a PID. Tonage produced would have to be considered if you used hydraulics......I'm intriguied with the hand lever idea......KISS.
I think "Engle" has a web site, don't know how much detail you'd get off them, I have a few of their manuals kicking around if you have specific design questions.???

[ynneb]

You could always consider using resin. That way no heat is involved and the stuff flows like water.
You can add colours to it as you desire. The moulds can be made out of latex rubber or even better silicon rubber. I have friends who make toilet seats out of resin and it comes out a treat.
www.trend.com.au then go and see the chow bowls and toilet seats

[cjs83]

Thanks for all of the info.

I'm not wanting to mass produce the handles in any sense of the meaning. I make custom knives, and I just want to be able to try different handle designs. Right now I CNC everything from titanium and carbon fiber.

I have searched the net over and I can't find the information that I need. I need to know the terminology that is used in the molding industry so that I can understand what I'm reading.

Also, does anyone know of anyone who deals in used mold injection machines? Someone told me about a company, Barrett of Garrett, but I haven't found them yet.

[vacpress]

AH - just a few? Use resin!

heres what you need: http://www.smoothon.com/

Or some other material supplier. You need to make a pattern - either CNC or hand carve it.

make a mold of the pattern- this can be easy or hard depending on lots of variables

pour a resin into the mold and let it harden - take out part - hand finishing

i can recoend this approach: get RTV Rubber from a supply Shop. Get the resin you want - lets jsut say your gonna make em clear plastic. get some clear plastic resin of a acceptable durability.

Now CNC your pattern from CAD drawings. take this patern, mount it on a board on a dowel rod about .5" round and .1-2" long. This will become your pour spout. its upside down. Coat the whole thing in petrolium jelly.. light coat - with a brush. this will pick up brush strokes! so be carefull to make it smooth.

Mix Up and paint on a coat of rubber. Repeat when cured. Next, add something like fine sand, cabosil glass powder, or some extender to make your liquid rubber thicker. gump a bunch onto your mold and smooth down. Get an even coating all around the handle - maybe 1/2-3/4in. Remember, you will be cutting this guy along 1 seam to make an opening to get your handle out, make one side thicker. Next step is to make a plaster mother mold. I like to use tuperware containers with some release agent to make perfect plaster molds-

take the coated handle and dowel rod off the board. put this whole thing in a tupperware dish about 1inch deeper than the rubber mold is tall. mix plaster and pour upto 1/2 of the handle. Let harden. mold release palster surface and mold-mix and pour plaster over the whole thing-let harden

the halves will release easily! its amazing the first time you do it.

if you want more info - i will tell you what products to get, then walk you through it. I have done this a bunch. i will take pictures and post them ina minute. ive got some good examples of this.

[vacpress]

this process i mentioned can be improved by using a machined wax pattern, and silicone mold material to make the mold. no release is needed, and the part will come out with amazing surface detail. better make that wax pattern right!

what i outlined is a fairly basic starting point to how prototype parts are fabricated many times. even whena big cnc or SLA machine is used to make the patterns, some engineers end up mixing resin, degassing bubbles, pouring, oven curing, etc.. whats nice is: a DIY type can get the same results at home with minimal fuss.

the drawback:thes echemicals are expensive!

[vacpress]

Heres some pictures. This is the closed mold. notice the shape of the tuperware?

[vacpress]

This Is the inside of the mold. The yellow thing is the rubber mold. It was a small piece. A housing for a child protection prototype. It was poured in hard resin that took 2 hours to demold.

[BT1]

Try,

www.plastics.com

and click through to the forums.

BT1