Plastic Injection Molding

[Adam Cohen]

Hello Makers,

I am very interested in making a large quantity of my prototypes.  Does anyone out there know a lot about injection molding and how much it would take to get a decent homebrew system working at the makerspace?  I am willing to spend some time working on it, especially if others out there are interested. I really don't know much about it, but the videos I have watched include large specialized machines..

Adam.

[Ron Bean]

>I am very interested in making a large quantity of my prototypes. Does
>anyone out there know a lot about injection molding and how much it would
>take to get a decent homebrew system working at the makerspace?

I have a couple of books by Vince Gingery about making a very small
one-shot injection molder. It can only hold a few ounces of plastic,
though. They built one at Sector67, it might be worth visiting them.

Try this link:
http://www.sector67.org/blog/tag/injection-molding/

I can loan you the books if you're interested.

[Kevin Crowley]

I have a similar immediate need and interest I have been in contact with some places that make and produce the part for you but so far that is a couple grand for me and more money than I have.



On making your own these are some links on books and making you own plastic injector.

http://rick.sparber.org/Articles/gpi.pdf

http://www.lindsaybks.com/dgjp/djgbk/injatt/index.html

http://www.lindsaybks.com/dgjp/djgbk/inject/index.html



These comes down to heating the plastic to melting and then using a lever powered piston to inject into the mold.



Kevin

Adam.

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[Have Blue]

Charles (who is on the list but only skims over it in digest form) has
been working on a Gingery-style injection molder:
http://heph.aest.us/blog/tag/plastic-injection-molder/

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[Kevin Crowley]

Mike,

 I like his mods on that.  The circular does make more sense than the rectangular..

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[Ron Bean]

>http://www.lindsaybks.com/dgjp/djgbk/injatt/index.html
>
>http://www.lindsaybks.com/dgjp/djgbk/inject/index.html

These are the two books I have. Note that Lindsay is retiring, and won't
accept orders after Feb 28. But the books are also available elsewhere.

[Kevin Crowley]

I would certainly like to see them.

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[Adam Cohen]

Yes please, I would like to borrow the book.

[Ron Bean]

This just showed up on the Adafruit Blog:
http://www.adafruit.com/blog/2012/11/08/protomold-design-tips-for-rapid-injection-molding-3dthursday/

Their homepage says approx $1500 for a mold, with rapid turnaround.
You can send them a CAD file for a specific quote.

[Dont let google be evil]

I've made the Gingery plastic injector, it's kinda cool, but maybe not helpful for large quantities.

I messed an orientation from the design- and last time I used it my bore/piston relation was sloppy which would usually leave a few small metal scrapings in final pieces.

It's currently had a few parts cannibalized for other projects -and hasn't been worked with in a while.

The volume of plastic can maybe be described as taking a sharpie marker with the cap on -the gray volume below the cap is about what you can shoot through it in one heat cycle. Maybe 10-15 min. a cycle?
   Gingery uses cut up scrap plastic, which needs to settle in the chamber, and I have not figured how to limit air bubbles in the center of pieces... yet.
   I say "yet" as this thing is one of those projects I haven't touched in a while.

I'd say it might not be great for large volumes -but it didn't take -that- long to build. We have better equipment at MMS than I had when I made my "FrankenGingery".

   If I was to do it again, I'd look into using re-purposed hydraulic cylinders, as a nice bore/piston turns out to be more important than Gingery suggests -and when I last looked, there were some higher volume designs that incorporated air/electric driven pistons.

ScrambledEggs

[Have Blue]

I should also note that Sector67 has a Boy 50T injection molder (an actual industrial machine), but they don't have anyone who knows how to properly set up and run it.

They'd love to get it running but need some instruction on it.

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[Brent Bublitz]

Couldn't we technically cast our own molds being that we are working up to aluminum casting, etc? How hard would it be to develop the plastic injection rig? Sounds similar to a massive extruder really.

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[Adam Cohen]

I thought about casting molds...Do people do that?

[Have Blue]

You can - I think Gingery even talks about using plaster molds for injection molding (they only hold up for maybe 10 parts or so).  Casting the molds with epoxy tooling resin would really be best, I think.

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[Shane]

CamBam does have a "mold" feature that basically inverts your design.

You could CNC the part, vacuum-form it, then cast the mold with
epoxy....

On Nov 8, 11:43 am, Have Blue <haveb...@airsoldier.com> wrote:
> You can - I think Gingery even talks about using plaster molds for
> injection molding (they only hold up for maybe 10 parts or so).  Casting
> the molds with epoxy tooling resin would really be best, I think.
>
> On 11/8/2012 11:04 AM, Adam Cohen wrote:
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> > I thought about casting molds...Do people do that?
>
> > On Thursday, November 8, 2012 10:57:16 AM UTC-6, photozz wrote:
>
> >     Couldn't we technically cast our own molds being that we are
> >     working up to aluminum casting, etc? How hard would it be to
> >     develop the plastic injection rig? Sounds similar to a massive
> >     extruder really.
>
> >     On Thu, Nov 8, 2012 at 10:18 AM, Have Blue <have...@airsoldier.com

[Kevin Crowley]

You also need to look where the mold should break apart.  I have a part that would need a two part mold that slides apart and both halves are somewhat L shaped

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[Adam Cohen]

What if I have the original part already, can I cast the mold in aluminum somehow?

[Eric Berna]

It depends upon how close your tolerances are. Metal and plastic expand when warm. This expansion and contraction will change the final size of your injected plastic parts and the intermediate molds.

Eric Berna

iOS Developed

On Nov 8, 2012, at 1:13 PM, Adam Cohen <adam.cohe...@gmail.com> wrote:

What if I have the original part already, can I cast the mold in aluminum somehow?

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[Ron Bean]

I stopped by the 'space this morning, and left the books in the Library,
on top of the bookcase.

When you're done with them, you can just shelve them back in the
bookcase.

[Kevin Crowley]

Awesome!!! Ron.

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[Dont let google be evil]

After speaking w/ you (Adam) a bit tonight, I wonder if you might be looking for a solution that is more like forming marbles, or gumballs. These are more heating and rotating than injection molding
   Maybe a jig to orient a band of plastic tubing to be shrunk over a small ball-bearing. This would protect bores, but might mess with sphere geometry a bit.
   Maybe a sort of heated pliers w/ half spheres cut on faces to "crush" a sphere from a tube w/ a steel ball or plug in it.

Cannoli

On Thursday, November 8, 2012 8:16:04 AM UTC-6, Adam Cohen wrote:

[David Buggs]

I ran across this earlier this evening

http://grabcad.com/library/inject-machine

Buggs

[Kevin Crowley]

Adam do you have a dimensioned drawing of what you want to make.  I thought I had seen a pic of what you're making but can't seem to find it.

Buggs

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[Adam Cohen]

I don't have a dimensioned drawing, but its not very complicated.

[Kevin Crowley]

I was asking because casting may be an option depending on a variety of factors incuding shape.

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[Have Blue]

Adam, if you can provide me with some simple dimensioned sketches, I can draw it up in SolidWorks for you (this is what I did for Kevin's part so that he could get it quoted through protomold.com et al)

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[Brent Bublitz]

well, hey, look what I found.
http://www.injectionmolder.net/index.htm

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[Brent Bublitz]

Also.. http://www.techkits.com/pim/index.htm

The basic concept looks verrry much like a standard screw-drive injection system.

[Adam Cohen]

So I am not sure what the mold will look like in the end. It will require some prototypes.  But basically I want to cast airsoft pellets and paintball sized balls with magnets inside.  I've got an idea of how I want to do it, but its going to take some R&D.

[Adam Cohen]

Thanks for all the replies.  Lots of options to consider. took the books home to read. Thanks Ron.

[Kevin Crowley]

Pressurized foam in a mold.  I think you are looking at a multi-step object.

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[David Buggs]

Do the magnets need to be perfectly centered in the ball?

Buggs

[Have Blue]

Being in the paintball business, I'd suggest using something pre-existing, at least for the prototyping phase.  Specifically, I'd take one of the foam rubber Reballs and use a very sharp endmill to cut a hole halfway through.  Insert magnet, and cap off the hole with a flexible casting foam (Smooth-On has some appropriate materials).  Fixturing the ball to drill it would be pretty easy - pair of aluminum plates, each with a divot from a 11/16" ball end mill almost to radius depth.

Other pre-existing alternative would be to find who owns the Perfect Circle molds and get a bunch of empty shells (Tom Kaye sold the company some years back to a place in California, I think).

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