Using SLS 3D Printing Technology for Your Product Design Prototypes

Rapid prototyping using Selective Laser Sintering (SLS) is very popular among design engineers working in many sectors including medical, architectural, consumer products, automotive, aerospace – and many others.

Typically, SLS technology is sometimes perceived as involving longer lead times than other 3D printing technologies, such as SLA, DLP or FDM. But this is not the case, as much depends on the designer’s goals and property requirements for the part, and some prototyping bureaus (including Prototype Projects) offer next day dispatch on SLS parts.

What is SLS?

SLS is an additive manufacturing process whereby a high-powered laser fuses cross-section layers of plastic particles into a 3D Model using instructions contained within a CAD file.

Importantly, SLS is excellent for producing parts with mechanical properties and isotropic behaviour. SLS can also be used for small run additive manufacturing (and batch manufacturing) of functional parts.

Most parts are currently made in engineering plastic, most commonly in Nylon (PA12), though other materials are available.

Printed parts are cleaned or blasted to remove excess powder, but can also be processed further to achieve the desired surface finish and colour, thereby improving mechanical properties or appearance.

For a prototyping bureau such as Prototype Projects, a distinct advantage of SLS is that it needs no support structures, and parts can be added during the build, unlike other processes. The benefit of this for the designer is that freeform geometries can be achieved with SLS that would not be possible with other 3D printing methods. There is therefore greater scope to create functional parts with complex geometries including hollow sections (the latter of which means less material use and therefore lower cost).

SLS snapshot

Before we go further, let’s take a quick snapshot look of some of the basic facts about SLS. If you’re a design engineer, by using SLS you will get parts that:

• Allow great scope for creative design freedom and freeform geometries
• Can include hollow spaces as well as functioning and moving elements
• Are ideal for functional testing
• Can be produced quickly, for faster time to market
• Are durable enough to withstand loads and friction
• Withstand bending and flexing
• Can be used as end components
• Can be machined, drilled and tapped
• Can be smoothed, painted, dyed and treated to resist chemicals, light and moisture

Key Advantages of SLS

Isotropic mechanical properties

SLS is a process consisting of a build-up of multiple bonded layers of material (hence the term additive manufacturing) resulting in a part of extraordinary strength and isotropic mechanical properties, making it ideal for the production of functional parts and prototypes.

Stiffness

If a high level of part stiffness is required, the part must be designed and printed fully solid.

Typical mechanical properties of SLS printed using PA12 are:

Other considerations

Warping

SLS parts with large flat surfaces may warp, though this can be avoided to a degree by the prototyping engineer. Design engineers can mitigate the effects of warping by reducing part volume.

 Escape holes 

Escape holes must be designed into SLS parts to allow for the removal of excess (unsintered) powder from inside the part. Ideally each part should have 2 escape holes.

Finishing

Various post-processing (or finishing) options can be applied to SLS parts to improve aesthetics, surface smoothness and part functionality. Finishing processes include polishing, dyeing, spray painting and lacquering, as well as improving functionality of the part using a range of coatings.

The addition of coatings is particularly important for functional parts and can be used to provide resistance to:

• Moist or humid conditions
• Ultraviolet rays
• Chemicals
• Colour fading or degrading
• Wear and tear
• Other substances and elements such as salt-water or oil

Characteristics of SLS parts

For a full table of SLS part characteristics including build sizes, please see this article.

Design applications

SLS can be used to produce many functional features including axles, threads, tanks and hinges. Achievable complex geometries include undercuts, negative draft and interior features.

Materials

Prototype Projects offers PA12 polyamide (nylon), a synthetic thermoplastic polymer which offers excellent dimensional stability as well as high levels of wear and chemical resistance.

Feature guidelines for product designers

Interested in finding out more about 3D Printing or need to order a quote?

Request a quote on our website or call us on 01763 249760. Or if you would like to arrange a visit to our 3D Printing facilities in Royston, contact Prototype Projects.

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