Teaching Injection Moulding Through 3D Printed Tools

Injection moulding can be difficult to understand when students only see it as a diagram, video or finished plastic part. I ran a short studio exercise with first-year design students exploring the process through a simple set-up: 3D printed moulds, wax sticks and a hot glue gun.

The aim was not to recreate industrial injection moulding in a fully technical way. It was to give students a hands-on experience of the basic principles behind the process: how material enters a mould, how it flows, how it cools, how the tool closes, and how small design decisions can affect the final part.

The object was deliberately simple: a spinning top. That simplicity helped. Students could inject the wax, open the mould, remove the part and test it almost immediately. If the top spun well, they could see why. If it failed, the problem was usually visible in the part.

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A Small Object With Big Lessons

The moulds were designed to show features commonly used in injection moulding tool design, including mould halves, parting lines, gates, alignment, cavities and release. By keeping the outcome small and playful, students could focus less on complexity and more on the relationship between tool, material and process.

Using wax also made the learning immediate. It heated quickly, flowed quickly and cooled quickly. That created a useful level of unpredictability. Students were not just being told about manufacturing defects; they were seeing them appear in their own parts.

When Things Go Wrong

This was where the exercise became most valuable. Some parts had flash where the mould had not sealed fully. Some had cavities or incomplete sections where the wax did not flow consistently. Some cooled too quickly before the mould filled. Others showed variation depending on pressure, timing, temperature or how the students held the tool.

These defects were not treated as failures of the exercise. They were the point of the exercise. The wax made the process visible. It showed that manufacturing is not only about the design of the part, but also about the design of the tool, the behaviour of the material and the control of the process.

Learning by Feeling the Process

For first-year students, this kind of activity is important because it turns an abstract manufacturing process into something physical.

By injecting wax into 3D printed moulds, students could feel the resistance of the material, see the importance of clamping, notice how quickly cooling affects flow, and understand why tool design matters.

It also created useful conversations around design for manufacture. Where should the gate go? How does the part release? Why does flash happen? What causes an incomplete fill? How might the mould be improved? What would change if this were scaled into a real manufacturing process?

At this stage, the aim is not technical perfection. It is to help students build early manufacturing intuition.

Why This Matters

This was a small studio exercise, but it opened up a bigger conversation about making, testing and manufacturing thinking. The value was not in producing perfect spinning tops. The value was in helping students see the connection between design decisions and manufacturing outcomes.

A part is not just shaped by the designer. It is shaped by the mould, the material, the process and the conditions of making. For me, that is the kind of learning that is worth building into first year. It gives students an early experience of manufacturing as something active, physical and sometimes messy. It shows them that defects are not just marks on a failed part; they are clues.

And sometimes, a small wax spinning top can teach that better than a lecture slide.

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Next Step: A More Controlled Wax Injection Set-Up

One of the useful outcomes of this exercise was seeing both the value and the limits of the hot glue gun approach. It worked well as a low-cost way to introduce the basic principles of injection moulding, but it also created a lot of process variation. Temperature, pressure, flow rate and cooling were all difficult to control, which is partly why the defects became so visible.

For the next version of the exercise, I am looking at introducing a dedicated wax injector. The model I am considering is a small wax injector with digital temperature control, pressurised by a hand pump.

The aim is not to remove the messiness from the learning. It is to give students a more consistent process, so we can better separate issues caused by the tool from issues caused by mould design, gate position, flow, clamping, cooling and release.

That should allow the project to move from a simple simulation of injection moulding towards a more controlled studio-based manufacturing exercise.

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