When it comes to prototyping, injection molding still has advantages over 3D printing for the right applications.
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There are plenty of prototyping applications for 3D printing, but don’t overlook prototype injection molding just because it requires tooling. Yes, you’ll have to pay for a mold and wait for it, but you’ll also get a tool that costs less than you might expect and with the tolerances you’ll need during a production run. Plus, while traditional injection molds can take months to machine, you can get a prototype injection mold in just a few weeks – and parts in less than 14 days.
Additive manufacturing is a smart choice if your design is evolving or still in the concept stage. Unlike injection molding, you’ll never have to modify or scrap a mold as your part design changes. 3D printing also lets you choose from a wide range of plastics, including many of the same materials you can use with injection molding.
3D printing is great for early-stage projects with less than 100 parts and lead times of 1 to 15 days. But what if you need more than 100 parts? If your design is complete and you can wait a few weeks, it’s worth considering prototype injection molding. There are some sound reasons to do so, especially if your early-stage prototypes used 3D printing.
File Types and Design Flaws
Even if they’re perfect, 3D-printed prototypes won’t seamlessly become injection-molded parts. That’s because 3D printing has different design rules for specifications, such as minimum wall thickness. If the specifications aren’t adjusted and the wall for an injection molded part is too thick or too thin, the production part could be defective even if the 3D-printed prototype was not. By using the same manufacturing process for prototyping and production, you can pinpoint problems with wall thickness before high-volume production begins.
Also, 3D printing uses STL files, which define parts in terms of a triangle mesh, whereas the CAD files for injection molded parts are parameter-driven. To use your STL files with injection molding, you’ll first need to convert them from a mesh to a shape to a solid. That can introduce some problems, though it’s obviously better to address any issues during prototyping than during production.
Part Tolerances and Plastic Materials
3D printing and injection molding also have different part tolerances. With most 3D printing technologies, tolerances of at least 0.1 mm (0.004 in) are typical. Most injection molds are machined to similar tolerances, but parts with tighter tolerances are readily achievable. With injection molding, engineers can even specify two types of tolerances: commercial or fine. The surface finish of injection molded parts is typically superior to that of 3D printed parts, too.
As for materials, while it’s true that you can use many of the same plastics for both processes, the end-use properties won’t be the same. Take the strength of a PEEK prototype, for example. Injection-molded PEEK is stronger because it’s made of a single layer of material. 3D-printed PEEK is weaker because it’s produced layer-by-layer. If you need to perform testing, that just won’t do. Plus, 3D printing won’t provide you with data about your part’s moldability.
Mold Types and Costs
If you’re considering prototype injection molding, what type of tooling do you need? Aluminum molds are the least expensive and can be machined to 3D-printing equivalent tolerances. If you need tighter tolerances, choose steel. That might seem expensive, but capable manufacturers can provide you with cost-effective prototype injection molds made of soft and semi-hardened steels.
Steel costs more than aluminum, but soft and semi-hardened steels cost less than the hardened steels used in traditional higher-volume injection molds. Your mold manufacturer can also help you control tooling costs by using aluminum for the base and steel for the mold cavity. Master unit dies (MUD) with a standard frame and customizable inserts are also available and can cut tooling costs by as much as 66 percent.
Improving Late-Stage Prototyping
When it’s time for late-stage prototyping, don’t dismiss plastic injection molding for runs of more than 100 parts. If your design is complete and ready for testing, there are considerable advantages to injection molding. You’ll have to wait a few weeks to get the parts you need, but prototype injection molding takes less time than you might think and uses tooling that can be cost-effective.
Visit the Fictiv Resource Center for more about prototype injection molding, including information about commodity vs. engineering plastics and mold finishes.
