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Navigate the selection process by matching key part attributes with printing processes and materials.

Greg Thompson

September 28, 2017

6 Min Read
Which 3D printing technique is right for you?

3D printing may only account for a tiny fraction of finished goods—0.01 percent to be precise—but its impact is proving to be anything but small.

3D printing is allowing automakers to design new and lighter parts, faster than ever. It’s allowing aviation companies to reduce aircraft engines from several hundreds of separate parts to a dozen parts. And it’s allowing medical and healthcare companies to customize everything from prosthetics and spinal implants to hearing aids.

But determining how and when to use 3D printing is no simple task. You need to establish if 3D printing is a good fit for your application as well as identify which 3D printing process and material best meet your specific needs.

The right fit?

Part geometry is where 3D printing gains an edge, literally and figuratively. Subtractive manufacturing processes like machining are inherently limited in the features they can mill, while additive manufacturing technology is much more conducive to producing more-complex parts with intricate features. Think of it this way: 3D printing is a good option for parts that are difficult to manufacture, and a great option for parts that are impossible to manufacture traditionally.

But before implementing 3D printing, determine first if it’s truly the best choice for your prototyping or end-use part needs.

For example, while material availability in 3D printing continues to improve, CNC machining offers more grades of materials. Additionally, machined parts generally have better mechanical properties, surface finishes and functionality than their 3D-printed counterparts.

If you’re not sure which option is the right choice, don’t hesitate to reach out to a contract manufacturer that offers both. They can help guide you to the process that’s best suited for your part.

Greg Thompson, the author of this article, will participate in a panel discussion on 3D printing versus injection molding at PLASTEC Minneapolis, one of six co-located shows at the Midwest’s largest advanced manufacturing event, in November. He will be joined by peers from Carbon and PTI Engineered Plastics in a lively discussion on the prospect of 3D printing competing with injection molding in certain production volumes and applications. The event will welcome more than 600 suppliers and thousands of attendees to the Minneapolis Convention Center on Nov. 8 and 9, 2017. Go to the event website for more information and to register to attend.

Finding your process

If 3D printing is suitable for your part, there are a growing number of technologies and materials from which to choose. When reviewing each, make sure your preferred process can accommodate part requirements in cosmetics, materials and functionality.

Stereolithography (SL) is best suited for early prototype parts where cosmetic attributes, such as fine features or smooth finishes, are important. It is a good fit for applications like visual aids, form and fit testing, concept models or patterns, and microfluidics.

SL can be used with the greatest variety of plastic materials that offer varying levels of resolution, color and clarity, stiffness and feel, impact resistance, temperature tolerance and water resistance. It also can easily support secondary processes, such as plating for increased durability, paint finishes, clear part finishing, decals and graphics.

Keep in mind that SL is a logical choice for prototyping parts that prioritize cosmetic attributes above functionality. SL parts only mimic their molded counterpart; they do not provide the same strength and durability.

Selective laser sintering (SLS) uses thermoplastic nylon powder, rather than liquid resin, as the foundation to build parts. This creates parts with high strength and temperature resistance.

SLS doesn’t achieve as precise a resolution as SL, but it compensates with durability. This is what makes SLS ideal for functional prototypes and end-use production parts. Example applications include jigs and fixtures, concept models and sample pieces, and living-hinge and snap-fit features for parts used in industries like aerospace, automotive and medical.

Multi Jet Fusion (MJF) is similar to SLS technology and creates durable prototypes and functional end-use parts, but there are a few differences between the two processes.

MJF offers a finer minimum-feature resolution, improved surface finish and more consistent mechanical properties. It also offers faster overall build speeds, allowing for larger part quantities in shorter time frames. Conversely, SLS provides a larger available build envelope, better small-feature accuracy, broader material selection and multiple colors, since parts can be dyed.

MJF is regularly used for components like brackets, clips, and housings, and parts requiring high strength or temperature resistance.

PolyJet is a good fit for parts that require different levels of hardness (durometer) and multiple colors in a single part build. Other 3D-printing processes require multiple builds and secondary finishing to achieve the same result as PolyJet parts. It’s also a good option for quickly and inexpensively simulating over-molded or elastomeric parts before moving to two-material injection molded parts for concept or trade show models.

Potential applications include prototyping rubber seals and semi-rigid gaskets that need a “just right” durometer for the auto industry, or orthopedic implants and dental prostheses for fit-testing in the medical industry. Consumer or industrial uses include complex appliance components, flexible snap-fit cases or electronics housings with plastic covers.

Direct metal laser sintering (DMLS) can produce strong, nearly fully dense metal parts that, like SLS and MJF, can serve as functional prototypes or end-use production parts. The process is used for many of the applications on the market today such as medical instruments, heat sinks and aerospace componentry.

Metal 3D printing uses a range of alloys and it can be used to create organic geometries, internal features and challenging passages that could not be cast or otherwise machined. However, larger parts or increased part quantities will make DMLS cost prohibitive compared to machining.

Finding a partner

As with any manufacturing process, the success of implementing 3D printing is partially dependent on the company you turn to for help. When evaluating a manufacturer, consider whether it can not only meet your 3D printing needs but also support you as you move through your development cycle.

For example, does it have capabilities in 3D printing as well as CNC machining or injection molding to help you transition from prototyping to low-volume production? Does it have enough in-house capacity to prevent supply disruptions? If it outsources work, you may end up working with several contacts, have inconsistent parts, or spend more time trying to get a design right, which can lengthen production time.

Finally, choose a partner that brings the benefits of digital manufacturing to your project. This could include allowing you to upload your part’s 3D CAD model online for instant feedback on manufacturing costs. Or it could involve design reviews with one of the vendor’s engineers, which can occur as quickly as one hour after a design is uploaded.

Tailor your approach

When it comes to 3D printing, it’s important to remember that there’s no one-size-fits-all solution. Each part and application will determine the technique and material that is the right fit. Identify what your needs are up front, and use them to guide you through the selection process. As 3D-printing technologies advance, the question isn’t whether you should consider the technology, but rather at which stage it will be the best fit.

Greg Thompson, Global Product Manager, 3D Printing, at Proto Labs has held product leadership roles at General Mills, Polaris and Andersen Windows, along with running his own successful product consulting business. Thompson holds a BS, MS and MBA in engineering and finance. He will participate in a panel discussion on 3D printing versus injection molding at PLASTEC Minneapolis in November. For more information on the event, click here.

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