Instructables

Home Plastic Injection Molding with an Epoxy Mold.

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Picture of Home Plastic Injection Molding with an Epoxy Mold.
I made an epoxy mold of an existing plastic item. Then I was able to make copies of that item using a home plastic injection molding machine.

This process should work for many different types of items or models. Note that the original item must have a parting line without undercuts. That means the model must be able to be separated into two halves from which the new molded part can be easily removed.

Here are the steps:

 
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Step 1: Frame for holding the epoxy.

Picture of Frame for holding the epoxy.
Epoxy is a two-part liquid that eventually hardens into a solid material. To create a mold from epoxy, you need need a frame to hold the liquid epoxy until it hardens. The mold will consists of two halves, so the frame must also be constructed as two halves that fit together.

This is a pre-made aluminum mold frame that I purchased from LNS Technologies at www.easyplasticmolding.com.

I could have tried to make my own frame, but this one was affordable and already had steel alignment pins to align the two halves.

Step 2: Mount the original model into the first half of the mold frame.

Picture of Mount the original model into the first half of the mold frame.
I super-glued a round piece of plastic to the model (a topical fish). This was used to suspend the fish in the cavity of the mold frame. It also forms a channel (called a sprue) that allows the melted plastic to enter into the mold during the final injection step.

Note: this mold frame had cutouts for sprues on all 4 sides, so I had to block the other three cutouts. But, I noticed that the epoxy mold frames on the www.easyplasticmolding.com website now only have a single sprue cutout, so this may no longer be necessary.

Step 3: Mix & pour the epoxy for the first half of the mold.

Picture of Mix & pour the epoxy for the first half of the mold.
I purchased a quart of two-part marine epoxy from Tap Plastics (www.tapplastics.com). It comes in two 8 oz bottles marked Part A & Part B. I mixed equal parts of A & B, being careful not to introduce air bubbles into the mix.

Then I carefully poured the epoxy mix into the mold frame to surround 1/2 of the tropical fish. Again, pour slowly to avoid creating air bubbles in the epoxy.
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rippa70010 months ago
This is great and I have something I want to make. How strong in the plastic that gets injected? Could you make neat door knobs from it? Also, do you need the injector? Could you keep one of the other holes open and pour i molten plastic? I've not seen these DIY injectors but they look fun. Thanks
techkits (author)  rippa7003 months ago
Thanks for your interest. Thermoplastics like ABS or Polystyrene can make very strong parts. Some automobiles are composed of up to 20% injection molded plastic parts. Molten thermoplastics are very thick and will not pour into a mold. The molten plastic must be forced into the mold under high pressure (often several tons).

The Model 150A injector shown can create over 1,000 lbs per sq. inch (PSI) of injection pressure.

There are some 2-part liquid polyester casting resins from (tapplastics) that can be poured into a mold.
rippa700 techkits3 months ago
Thanks Techkits - that's very inteersting. I might give that a play one of these days. I solved my casting issue with a high grade casting plaster mixed with a polymer. Very hard and strong. Thanks for the tech info. Much appreciated.
techkits (author)  rippa70010 months ago
From what I've read, different types of thermoplastics can have varying properties. I believe polystyrene or ABS can be very strong. I think they make Legos and automotive dashboards from certain grades of ABS plastic.

If you want to use thermoplastics, then some sort of injection machine would be required. But I suspect that if you were using a 2-part liquid polyester casting resin, you could mix it up & just pour it into the epoxy mold. I'm not sure how to avoid bubbles when pouring a liquid resin.
rippa700 techkits10 months ago
Thanks techkits - I have spoken to someone who recommends a special casting plaster so will try that first. Love your work - keep inspiring us!
alangol rippa70010 months ago

Hi rippa700

I would love more info on the special casting plaster??

gulnar10 months ago
Great instructible! Have you tried this for something not made of plastic? I'm afraid it might get stuck in the epoxy, but maybe you have other experiences :) I might try that for jewelry making, though silicone compounds may be better for metals and waxes.
techkits (author)  gulnar10 months ago
I've tried two different thermoplastic materials with the epoxy mold (polypropylene & polyethylene), but have not yet tried non-plastic materials. If sticking to the epoxy was a concern, I would at least try spraying the mold with a non-stick coating beforehand.

One nice thing I discovered about the aluminum mold frame is that I can remove the epoxy mold & inject plastic directly into it without the frame. Then the frame can be re-used to make other epoxy molds.
rayleb10 months ago
Did you have to grease or wax the original before pouring the epoxy?
finnr rayleb10 months ago
techkits (author) in reply to makenai3 days ago
Yes, I coated the fish model with automotive wax to keep the epoxy from adhering to it. I've heard that non-stick cooking spray may also work.
Dominic Bender10 months ago
I did not know there was such a thing as a desk-based plastic injection system. Thanks for sharing!
makenai10 months ago
Did you have to coat the fish with anything to prevent sticking?
techkits (author)  makenai10 months ago
Yes, I coated the fish model with automotive wax to keep the epoxy from adhering to it. I've heard that non-stick cooking spray may also work.
Thanks for a nice clear Instructable ... it's got me thinking.
ngadhno9 months ago

This is nice instructable, however I don't see this as HOME project with that pricey mold injection machine. So maybe you should change the title of this project.
Anyway thank you for sharing this. :)

Lazy Glen10 months ago
I'm on both sides of this. It does look a lot like an ad for the company. But I do like the idea that they have an "add to your drill press" kit to do home injection molding.

Unless that epoxy can be removed from the aluminum mold, I would not call $95 affordable to do a few copies of a fish.
drnation Lazy Glen10 months ago

Hey Lazy, They mention trying to make their own frames. But look at them. So if they make them on their mill are you guys going to dis 'em for not making them with a file? And they have to be precise with alignment pins. You could do it with your trusty Dremel. But you will burn up time, bits, and maybe your Dremel. I liked his fish. And the whole idea is to make a few, not a bunch. Decide for yourself about what you can or cannot afford but don't dis the poster because he thought that was cheaper than his time and effort, especially before knowing the system really worked.

CEVMarauder10 months ago
This is neat, but as someone else pointed out, shilling for that company pretty hard. I notice that the company just happens to have a photo from this Instructable on their page ("Works even with epoxy molds".)

Oh, and that "home" model of injection molder just happens to cost $1500.

We need an instructable on building an injection molder.
I think that recently a toy company has put out an injection molding toy car making machine. I am sure you can make your own molds to fit the machine. I think it costs somewhere around $50.00.

My grandson got one for christmas. Uses wax like large crayons. Not useful for much.

Ouch! What proof do you have they were "shilling?" Just because someone uses a tool does not mean they are shilling. Had they not provided the source lots of folks would have asked for it. Should I use a hand drill in an instructable just because it is cheaper? How much about home injection molding did you know before you saw this post?

Without people like this poster listing the source of machines he used and places he obtained materials from, I for one would never enjoy the experience of being able to repeat similar projects. One mans expensive is another mans pocket money. I paid $3000 for a camera to photographs steps of making things. Surely $1500 for someone interested in making plastic items in low numbers is no worse? We are after all talking about occupying ourselves during idle hours, are we not? Do you have nothing nice to say about this wonderful and clear method of making low run plastic items? I think its a fantastic idea and will be ordering a small injection moulder for myself once I settle on the machine that suits me. Will you also say I'm shilling if I provide the source of my components? To the author: Thank you for information I have never been able to find before. I've got some carvings I made that I will be injecting thanks to your post.

Must be nice to be able to afford expensive toys.

Indeed we do, and for my taste, something larger in scale. I've spent a little time at it, but haven't come up with much yet. The problem gets to be keeping constant heat the greater the mass, and the force needed to push the plastic into the mold cavity.
cliffyd10 months ago
ya this is instructables, basically everything was made for you. I'd rather see homemade injector, homemade box, own epoxy stuff like that.
drnation cliffyd10 months ago

So make 'em.

drnation10 months ago

Boy you guys are tough. Every thing taught here is different. Some are cheap. Some are dumb. Some are easy and some are hard. Most people think injection molding costs thousands of dollars and even those of you who are griping the most probably didn't know this option was available. Also without knowing about this machine you would be hard put to just think up and engineer and build a home made machine. Now you know that is an option. So lighten up! Congrats on your instructable and thanks for it. Nice fish.

grunthos10 months ago

For anyone who wants to make their own injection molding machine, an excellent book is "The secrets of building a plastic injection molding machine" by Vincent Gingery. Find it in a library:

http://www.worldcat.org/title/secrets-of-building-...

A nice build log of the book's machine is at

http://rick.sparber.org/pi.htm

Snidely7044810 months ago

I researched the 150A , and the price, at $1,500, seemed a bit high for a unit for a hobbyist.

agguilar10 months ago

Thanks for sharing!

rippa70010 months ago
The shop recommended Crystacast with some SP201 polymer in the water. The polymer makes it hard and seals the surface. The shop were very helpful so I will let you know how it goes - maybe post a new instructable. Here's the link specialplasters.co.uk might be posting this twice as not sure if it went.....
walklands10 months ago
Great instructable, thanks for sharing. I for one will be trying this out. We use a high capacity hot glue gun at school if the kids want to make prototypes for their projects before we use the injection moulding machine. We had a pupil make his own anti vibration mounts this year.
lgilber10 months ago
Very informative. However, while I'm sure the Model 150A injection molding machine is easy to use, I would hardly call $1500 affordable.
matthieutje6510 months ago
cool project, to bad you need a injection molding machine...thought this instructable would be more about a "home made injection molding machine" :) as an extra for those reading this: if some people would like to do the same, without a plastic injection machine, you can use a fastcast polyurethane resin into those mould, fastcast PU hardens in around 10min this makes it possible to make multiple replicas of a part
octopop10 months ago
Home injection molding instructions: buy this injection molding machine? How is this not just an ad for an injection molding machine?
Seems like it is more of a how to on making an epoxy mold... of course you will need a machine to use it. Just like you would have to buy a printer if this was a "make your own paper" or "make your own toner" instructions.

There are other ways to injection mold out there. our local Techshop has a 20t injection mold press.
alcurb10 months ago
Nice instructable. Expensive hobby ! 3D printers are getting cheaper.
qqqqqa10 months ago
Hey, we can all read. No need to hammer the point. It's not the first time nor will it be the last time this type of thing happens, I suspect.
Take away what you can from this instruction and enjoy. Forget or ignore the other stuff. BTW, I don't know this guy or the company. I'm just interested in acquiring knowledge. Peace!
spark master10 months ago
neato, I know know what the aluminum bits I got for free were. Injection mold equipment minus the injection unit......ah well another hobby averted and I got 30 cents a pound for the mold copes......gggrrrr

nice instructable though
Kinnishian10 months ago
Nothing against companies making instructables, there are actually a few like that. It's perfectly ok! Any quality instructable contribution, and this one honestly is one, is appreciated [unless its deceptive somewhere pretending there wasn't any option besides their company's product.]

People take pretty quick offense though when it seems like undeclared vested interests :p.
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