In the context of all the buzz around 3D printing, the term “injection molding” may sound like a ho-hum and low-tech term. However, depending upon your design requirements, there is an important place for both processes and 3D printing (additive manufacturing) is not poised to take over injection molding any time soon.
Although 3D printing is showing significant improvements in technology and materials, injection molding still utilizes true material properties. And, once the initial high manufacturing costs are paid, the per unit price with injection molding drops to pennies.
3D printing produces parts more slowly and at a higher cost in comparison but without the initial cost for tooling. That said, over the last decade or two, high-speed, automated injection molding machines cutting mold detail from aluminum provide a better cost and speed advantage over traditional tooling. And, it is nearly impossible for a single 3D printer to keep up with the speed of injection molding. However, in terms of accessibility, 3D printing may replace many injection-molded pieces thereby reducing the demand for that process.
3DP? Injection molding? When to choose which process
Deciding to choose injection molding should not be an afterthought — it needs to come into the initial stages of your part design. And a key consideration is volume. CNC machining or 3D printing make the most sense if you need a handful of parts, but the injection molding option should be an early consideration especially if you are thinking high volume and even if you don’t immediately go with these higher volumes.
“When quantity begins to creep up, it can be much more beneficial to jump into injection molding sooner rather than later,” says Tony Holtz, applications engineer at custom prototype and on-demand part production manufacturer Protolabs. “We have discussions with thousands of engineers who are doing early prototyping through 3D printing but don’t take into consideration injection molding. It’s possible to paint yourself into a corner with something that isn’t manufacturable through injection molding as not all geometries can be produced, whereas nearly any part geometry can be done through 3D printing. This situation may force you to stick with 3D printing at higher production costs or send you back to the designing board and prototyping a second time.”
Holtz also notes that other than volumes of parts or complexity, material properties also play a significant deciding factor. Not all 3D-printed materials can be used over a long life of a product or hold the same properties for heat or strength to those comparable to injection molding.
Another fundamental consideration is the operations and equipment costs for the processes. With 3D printing, you have the physical printer followed by any secondary equipment needed to finish the parts, so there are very few moving parts to the completed job. With injection molding, there are many more moving pieces to complete the parts, such as the melting of the material resins, injecting the melted plastic into the mold, ejecting the finished part, and removal of sprues and gates from the parts before packaging.
Deciding whether 3D printing or injection molding for prototyping or manufacturing makes sense for your project depends greatly upon your project needs. Lead time for tooling, tooling costs, speed, and part costs are all considerations that vary between the processes. One isn’t necessarily better than the other — it’s just determining which process is a better fit for the production of your part.