Overmolding Electronics With a Plastic Injection Molding Machine

Introduction: Overmolding Electronics With a Plastic Injection Molding Machine

In this Instructable I am going to show how to overmold electrical components, in particular a prototype microwave antenna with a capacitor that took approximately 1.5oz of plastic to overmold!

Overmolding certainly isn’t restricted to just electronics. It has a wide variety of applications, and can be found almost anywhere. For example, knife or screw driver handles are overmolded. Many times overmolding is also used to integrate metal bolts or nuts inside a plastic part, such as in cases of plastic housings.

A lot of time overmolding is used not only for protection and sealing of the components, but also to hold them together. One of the biggest advantages of overmolding is that it creates one whole assembly as plastic flows around individual parts, as opposed to bolting or gluing the separate parts together.

First you have to have a mold for holding the components together. The mold can be made out of metal (in this case aluminum) or epoxy (if only a few prototype parts have to be made). There are also often mounting provisions inside the mold, to hold the parts in a particular position while the plastic flows around them.

The mounting provisions can be tabs or holes, where components are anchored for their exact location. You can see in this mold there are mounting holes where bolts and electrical circuit are plugged in. Through holes are also common, for example to let a cable come out of the mold while the end of it is being overmolded.

Second you have to assemble all of the components inside the mold prior to putting it in a machine and injecting with plastic. Often times there are also internal spacers for adding even more precision to exact location of the parts. You can see in this example there are two little spacers that go on the ends of the antenna. This way the deflector plate will be separated from the wire and won’t short circuit.

Levon Fiore @ Medium Machinery, LLC see our
Small Manual Benchtop Plastic Injection Molding Machine

Step 1: Injection Molding Plastic Around Components

Once you have all of the components arranged in the mold, it’s time to inject it with plastic! Here are some common overmolding pitfalls to avoid:

1. Once you assemble all of your components in a mold and closed it, make sure to only keep it in upright position. The components can easily fall out of their mounting holes and overmolding won’t work. This one is pretty obvious, but sometimes it’s easy to slip up and tilt the mold when you are busy producing part with all the equipment running.

2. Use lower pressure. If the pressure of the machine is set too high it will crush all of the electronics. In this case the plastic pressure is set at 6000psi out of maximum 13500psi.

3. Use higher temperature. Of course overheating plastic should always be avoided, but avoid setting the temperature where plastic won’t flow easily. The problem with hard flowing plastic is that it can ‘catch’ some of your components and displace or damage them. If you are working with very intricate assembly, you can also pre-heat the mold to make it even easier for plastic to flow around. In this example HDPE plastic was used, and the machine was set at 385F.

4. Let the plastic cool inside the mold under pressure. Once you are done injecting, let the mold cool under pressure for a while. If you relieve the pressure too early (before plastic gets a chance to solidify inside the mold), the plastic will backflow out of the mold and you will end up with a distortion of some sort. In this case a large amount of plastic was injected so the cooling time was set at 2 minutes.

Levon Fiore @ Medium Machinery, LLC see our
Small Manual Benchtop Plastic Injection Molding Machine

Step 2: Finishing Overmolded Plastic Part

Once you finish injecting, you are almost done! Here the only things you would do is take the part out of the mold and cut off any excess plastic.

You can see how I am cutting excess plastic with a chisel and then pushing the part out of the mold with a screw driver.

Levon Fiore @ Medium Machinery, LLC see our
Small Manual Benchtop Plastic Injection Molding Machine

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