When designing a product, it’s important to have a prototype on hand so that components can be tested for fit and function. Once you have a prototype, adjustments to the design including material, shape, aesthetics, and manufacturability can be made. This step is crucial for any successful product launch, because without proper prototype testing, a design team is pretty well flying blind. I’m Trevor, a 4th year engineering co-op student from the University of Waterloo, and today I’ll be comparing two popular ways to create prototypes in today’s world: 3D printing and injection molding. 

3D Printer at Thalmic Creating Myo Prototype Parts
3D Printer at Thalmic Labs Creating Myo Prototype Parts

Both methods have their strengths and weaknesses, and offer different benefits at different stages in the design process. 3D printing is a new and emerging technology which has become a bit of a buzzword in recent years. Although there are many ways to 3D print, essentially all methods work by adding layers of a material in select locations. The materials are then heated and rapidly cooled so that they harden in place. 3D printing allows complex geometry to be simply created as little thought is needed for tooling paths in comparison to more traditional methods.

Injection molding began six thousand years ago in the form of casting. Evolving from this, injection molding today refers to heating a resin, pressing the molten form into a metallic mold, allowing it to cool, and then ejecting this cooled piece in one smooth transition. This is a very popular method of mass producing parts as each piece can be outputted extremely quickly. It’s also used to create prototypes late in the development cycle of a product design in order to get an early preview of a nearly finished product.

One of the biggest differences between the two methods above is their ability to produce on different scales. The fact that 3D printing is cost-effective on a smaller scale means that it can be used for quick one offs of a product. However, as quantities increase, injection molding becomes more and more economic, which is largely the reason why it’s used for mass production of nearly any plastic part in today’s world.

3D Printed Myo Parts ready to be assembled.
3D Printed Myo Parts ready to be assembled.

There are many other factors that come into play when choosing what method is best for prototype development. For example, 3D printing doesn’t provide proper insight into the manufacturability of a product, as injection molding will eventually be used if the product is made on a mass scale. The many constraints that come with injection molding aren’t clear when constructing a piece using a 3D printer. Design guidelines such as proper geometry (incorrect wall thickness can lead to unwanted warping), ejection pin locations (marks where the piece is pushed out of a mold), gate locations (where the molten resin is injected into the mold), knitting lines (where “waves” of molten resin reconnect after maneuvering around an obstacle), and others must all be taken into consideration.

Another thing to take into consideration is that while an extremely wide variety of materials (thousands) are capable of being injection molded, only a handful of materials can currently be 3D printed. This means a product that’s 3D printed will likely have a very different look, feel, and mechanical properties than the finished product.

3D Printed Myo in Makerbot Printed Assembly Jigs
3D Printed Myo Armband held in place for assembly with Makerbot Printed Jigs

One advantage that 3D printing has over injection molding is that a 3D printer can be purchased and placed in-house at a relatively low cost, allowing for a design team to conveniently create their own product. This is a stark contrast to injection molding where the machine required makes it virtually impossible to have in office.

Although many other factors could be compared between these two prototype procedures, the outcome is already clear. While 3D printing is extremely useful in the early stages of a product, injection molding is absolutely the best path to take when creating a more formalized and finalized prototype.

Have you ever used a 3D printer before? Tell us what you’ve used and what you’ve made in the comments below!


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