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BlogMolding and Casting Design Tips
SLS 3D printed plastic parts

Using SLS 3D Printing to Create a Prototype for Injection Molding

3D printing design “snapshots” lead to better outcomes when preparing to invest in injection mold tooling.

By Greg Paulsen
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Is Your Part Ready for Injection Molding?

Injection molding is an at-scale manufacturing technology that can produce consistent plastic parts at a significantly cheaper unit price than most other processes. It offers a high variety of plastic options, colors, cosmetics, and configurations. Injection molding requires a machined set of tools, such as a mold core and cavity, that when closed is injected with molten plastic. The plastic cools inside the cavity, the mold opens, and a part is ejected. This process is repeated thousands of times to make parts in full production.

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A diagram showing how injection molding works.

However, injection mold tooling can be pricey and often takes weeks to produce. Once created, a tool is very difficult to modify for a revision change. To prevent potentially thousands of dollars of headaches we recommend prototyping early and often to test and validate your design before molding. Xometry’s 3D printing services offer many options for prototyping, including Selective Laser Sintering.

Selective Laser Sintering: Low-Cost Rapid Prototyping

Selective Laser Sintering, a 3D printing process better known as SLS, is an economical way of prototyping designs. SLS is a 3D printing technology that can produce hundreds of parts per build. It works by fusing plastic powder, typically nylon, together with a laser on a layer-by-layer basis to build a 3-dimensional object from CAD data. SLS parts can produce complex organic shapes, such as those designed for injection molding at a low cost and with short lead times.

Because the costs are low for SLS 3D prototyping, it is the go-to process for making physical models of design iterations. A good analogy is making “snapshots” of a design that can be tested and validated, just like taking a digital picture. Designers can make many of these snapshots to help direct the design to an optimized state. Rapid prototyping mitigates design errors that could be present in hard tooling. SLS parts are durable enough to even be used for initial user testing and low volume production. Designers should be sure their design is appropriate for injection molding, and that they are taking a look at uniformity, undercuts, and draft. Check out our video below for 3 essential injection molding principles.

Moving from SLS Validation to Injection Molding

Once the design is near-final, we recommend choosing a photopolymer process such as stereolithography (SLA) 3D printing for a final review before moving on to mold tooling. SLA is slightly more expensive than SLS but has a better surface finish and detail resolution to mimic molded part results. If everything looks good as an SLA print, the part should be ready for Xometry’s injection molding services.

Using the same instant quoting interface for Xometry 3D printing, you can select injection molding to start specifying the needs of your part. Apply initial quantities and any notes on the project you may have to submit your quote. Xometry’s expert engineering team will work with you to finalize pricing, lead times, and any other details required. If you want to prepare for your discussion, check out this video on the 3 things you need to discuss with your molder.

Greg Paulsen
They call me the Director of Application Engineering at Xometry. This means I not only get to produce great design-for-manufacturing content, but also consult on a variety of custom manufacturing projects using CNC machining, additive manufacturing, sheet metal, urethane casting, and injection molding. If you have a question, I'm your guy.

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