Home Plastic Injection Molding With an Epoxy Mold.

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Introduction: 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:

Step 1: 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 - https://www.techkits.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.

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.techkits.comwebsite 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.

I purchased a quart of two-part 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. Tap also sells colorants that can be added to the epoxy. I added black colorant to better see the mold surface after curing.

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.

Step 4: Let the First Half of the Epoxy Mold Harden.

I left the mold frame with the model & epoxy sit undisturbed overnight. By the next day, the epoxy was completely hardened & was able to remove the model to check this first half of the mold.

Before starting on the second half of the epoxy mold, I had to coat the first half with automotive car wax. This prevents the second pouring of liquid epoxy from bonding to the first half. Without this step, I would have ended up with a solid block of epoxy instead of two halves that can be separated!

Then I put the fish model back into the frame & set the second half of the mold frame onto the the first half. The second half of the mold frame has a top removable plate that allowed me to mix another batch of epoxy & then pour it over the first half. (Sorry, I didn't take a photo of this second pouring step)

Step 5: Now I Have the Second Half of the Epoxy Mold.

Again. I allowed the epoxy to harden overnight. Then I was able to pry the two frame halves apart (thanks to the automotive wax) and now I had the second half of the mold.

I hope you can see in the photo that the epoxy was able to pick up even the tiny printing details that were on the side of the original item.

Step 6: My Bench Model Plastic Injection Molding Machine.

I had previously purchased a Model 150A injection molding machine from LNS Technologies. It was affordable & it is easy to use.

I placed the two halves of the epoxy frame mold together. The frame has steel alignment pins, which automatically aligns the two halves. I clamped the mold into the Model 150A & injected some yellow melted plastic into the epoxy mold.

Step 7: A Nice Copy of the Original Item.

Well, this worked even better than I had expected!

Opening the epoxy mold revealed that the newly molded part was basically identical to the original item (minus the painted stripes, of course).

I have injected several more copies of the fish using this epoxy mold & have not yet noticed any degradation in the details. I don't expect that epoxy molds would be a durable as solid aluminum or steel molds, but it certainly seems like a simple low-cost alternative for making limited number of molded items.

2 People Made This Project!

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85 Discussions

The process scales down nicely - depends on what you want to do. There are folks who actually do injection molding with hot glue guns.

Did you have to grease or wax the original before pouring the epoxy?

1 reply

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.

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.

Dear TechKits, what was the type/name of the two-part epoxy you used from Tap Plastics? They have dozens of different formulations. I realize this project was done in 2014, but I am hoping you still receive the comments from this thread and can help. With thanks, JB

How many cycles of injections does to epoxy mold last?

Do you have to cool it between injections?

I was thinking of doing the same but with clay to create the mold.

Tried using lubricant wax and non stick cooking oil. it is very difficult to remove the model from epoxy mold. How can i make it easier?

1 reply

Carnauba car wax worked for me, but make sure it is Carnauba.

Hi! Does the object used need to be coated in anything before pouring onto it? Won’t the epoxy stuck to it?

1 more answer

Carnauba car wax worked for me, but make sure it is Carnauba.

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8 months ago

do you have or know of anywhere that has a bigger mold frame that can make something 5 inches x 2.5 inches?

How does the air escape from the mold while injecting the molten plastic?

What is the name of the marine epoxy you used? There are 4 different ones at tapplastics. The side A does not come in 8 Oz per website.

1 reply

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.

1 reply

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.