DIY Injection Molding – How to Get Started

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Injection Molding is one of the most commonly used manufacturing techniques in the world. It basically involves injecting a melted plastic mixture into the cavity of a tightly held mold. The injected plastic takes the shape of the mold as it flows freely into the mold when it is hot. Then, the plastic mixture inside the mold is allowed to cool down. The plastic mixture takes the shape of the mold and ultimately solidifies.

One can make a mold as per the shape and size of any kind of end product that needs to be manufactured. Making these molds is expensive because the designing and creation of the mold require highly-skilled professionals that can handle a complex process.

Injection molding molds are often made using steel or aluminum. Depending on the design of your end product, you can either make one mold for the entire product or you can make multiple molds for multiple sections of one part. You would then have to fit those multiple sections together to form the final product.

As you can imagine, injection molding is a process of manufacturing that is geared towards high-volume repetition. One can repeatedly make identical copies of the same design over and over. This process is very useful in applications where a large number of identical units are to be manufactured.

The large volume part is important because the initial high cost of making the mold gets spread over a large number of units. That brings down the cost per unit. Injection molding will be an expensive and time-consuming process if one is trying to make a single.

It may sound like injection molding is something that only large corporations can carry out on an industrial scale. However, you can put together your very own injection molding setup as well. You can use some simple resources and put in a little bit of effort to make your own injection molded model.

In this article, we will focus on DIY Injection Molding. We will explore how you can use an epoxy mold and make multiple copies of any plastic item which you may have at your home. Epoxy molds will be significantly cheaper than steel or aluminum molds. However, they might not be as durable as steel and aluminum molds.

If you intend to do a DIY injection molding operation for only a few copies or smaller volumes of replicas, then epoxy will be strong enough without any major degradation. However, if you want to make hundreds or thousands of copies of your plastic item, then you might need a better mold than an epoxy one.

The model that our DIY Injection Molding setup will create will have no undercuts. Your plastic item which you want to replicate should also not have any undercuts. The reason for this limitation is the fact that undercuts are not easy to make using injection molding and one needs to adopt advanced techniques to achieve an undercut.

Our DIY Injection Molding process will deliver a part which will have a part line as every model we make will be able to separate into two halves. One good practice is to orient the model in such a way that the parting line does not spoil the aesthetics of the product. For now, this consideration may not necessarily be a high priority. However, if the part lines do bother you, then think about a better orientation so that the part lines end up on a section of the product which is not immediately visible from the front.

Step 1 – Get frames to make the mold

The first step in our injection molding setup is to create a mold. We will use epoxy to create our mold. Epoxy is actually a two-part liquid. It is initially in liquid form, but it can then be poured into a mold or frame. It then solidifies and hardens.

You need to get a frame in which you can pour the epoxy to make your molds. You will need two frames for two molds. Moth these molds will clamp against each other. Each mold will make one section of your injection molded part. You can buy a frame for making your epoxy mold here.

You can always make your own frame, but that will add a significant amount of time to the whole process. If you really want to make your own frame, then make sure that the frames have a cavity for the epoxy to pour itself in and that they also have alignment pins so that the two frames line up correctly. The link we posted above is for a set of frames which have the alignment pins and the cavity.

Step 2 – Setup the model/item in the mold

Once you have your frames in place, proceed with setting up the frames for the mold creation. In order to create a mold, you will need epoxy and the actual item that you are trying to replicate using injection molding. The mold has to take the shape of your item.

You will have to suspend your item in one of the mold frames such that there is enough room for the epoxy to flow above and below the surface of the item. The item should not touch the frame. You can use a plastic pipe to hold the item. The plastic pipe can be hollow so that it also allows you to pour the epoxy into the frame.

You can use the cavity or sprue in the frame to let the plastic pipe pass through. Your item which is to be replicated can be super glued to the plastic pipe. If your frames have any other cavities or sprues besides the one that you are using to hold your item in the frame, then seal those. Otherwise, the epoxy will leak out of those cavities.

Step 3 – Pour in the epoxy

Now that your mold frame is ready with the item in place, pour in the epoxy. One quart of a two-part epoxy should be enough for a regular sized frame. The two-part epoxy will have two bottles labeled as Part A and Part B. You have to mix both these parts in equal quantities. When you are mixing the two parts, ensure that there are no air bubbles in your mixture.

You can also add colorants to your epoxy mixture if you want your mold to have a specific color. A suitable color that allows you to see the mold surface after the epoxy has hardened is recommended. Generally, dark colors allow you to see the mold surface details quite well.

Once your epoxy mixture is ready, pour it steadily into the frame which has the item suspended in it. You will want to pour enough epoxy so that one half of your item gets submerged into the epoxy liquid. While pouring, make sure that no air bubbles get formed.

Step 4 – Leave overnight for epoxy to harden

Now let the epoxy in the first frame harden. That way, you will create one half of your mold. Creating the mold is a two-step process. You want to create the first half and then think about the other half. After the epoxy in the first frame hardens, remove the item which you are replicating. You can check the hardened epoxy and make sure whether all the important details of your item have formed correctly or not.

Before you begin setting up the second frame which will create a mold for the other half of your item, coat the epoxy mold which is already formed with automotive car wax. This step is important because you do not want the epoxy poured in the second frame to stick and bond with the epoxy surface produced in the first frame. If the two epoxy mold halves stick together, then you will end up with a solid block of epoxy and then separating the two without damaging your item’s mold design will be a huge challenge.

Step 5 – Make the second half of the mold

Place the item back into the first frame. The first frame will already have the hardened epoxy in it. Now place the second frame onto the first one and align it correctly. The second frame will have a removable plate that will allow you to pour epoxy in the second frame. That way, the second half of your mold can begin to take shape.

You will then leave the second plate’s epoxy to harden overnight. The next day, you will have to pry open the two plates which are pushed up against each other. This separation of the frames should not be difficult because of the automotive car wax which you had applied on the first half of the mold.

What you should see is an almost mirror image of your item formed into the epoxy mold which would now be formed on the second frame.

Step 6 – Set up your epoxy molds on an injection molding machine

Now that you have your epoxy molds ready, you can finally set them up on an injection molding machine before pouring in molten plastic. There are quite a few injection molding machines available online which are fit for a DIY or domestic work environment. We suggest the Model 150A from LNS Technologies.

The Model 150A is a relatively cheaper alternative to expensive injection mold tooling machines and injection molding machines. The Model 150A has clamps which will hold your epoxy molds together and pressed up against one another with some degree of pressure. The clamp frames have alignment pins which will ensure that the two halves of your epoxy mold are correctly oriented.

The Model 150A also has a small chamber in which you can put your plastic pellets or tiny cut-up pieces of plastic soda bottles. A temperature controller allows you to set the temperature that you want your molten plastic mixture to be. The molten plastic then gets injected into your mold cavity through the machine’s injector.

Step 7 – Inject the plastic and let it harden

Once you have set up your injection molding machine, pour in your plastic pellets. You can choose whatever color you want. Plastic pellets of multiple colors are available in the market off-the-shelf. After you melt the plastic by setting an appropriate temperature, push down the lever of the 150A machine and inject the plastic via the cavity in your epoxy mold.

Then, let the plastic cool down before prying apart the two halves of the mold. You might need a screwdriver or a knife to pull apart the two epoxy mold surfaces. What you will see inside is an exact replica of your original item. Any paint job or painted lines will not be visible. However, you can paint your replica in post-processing.

Thus, you can create replicas of whatever items you want to using a simple injection molding process that you can perform in your garage. You only need a few tools and materials to start making interesting new things. The whole setup will not cost you a lot of money either.