Selective Laser Sintering (SLS) is a 3D printing process ideal for manufacturing end-use parts and happens to be one of the easiest additive manufacturing processes to design for.
This is because SLS parts do not need support structures. So, here’s a guide on how to design parts for SLS printing, as well as some tips for the industries we work with to ensure your parts are perfect for the job.
How to Design SLS Parts
The SLS printing process creates high-precision parts with functional living hinges, complex interior features and intricate engraved details all possible. While it has some limitations (more on these below), SLS printing is a viable option for parts in various industries.
So, here are some design guidelines to follow when using SLS materials to get the most out of your parts.
1. Material Selection
The first step in the design process is choosing the right material. SLS is compatible with a wide range of thermoplastics, including Nylon (PA12, PA11), Glass-filled Nylon, and TPU (Thermoplastic Polyurethane). The material chosen will impact the mechanical properties, flexibility, and durability of the final product. For example:
Nylon PA12 – Ideal for functional prototypes and end-use parts thanks to its strength and durability.
Glass-filled Nylon – Offers enhanced stiffness and thermal resistance, perfect for automotive and aerospace applications. As well as applications in other sectors where strength and thermal/chemical resistance are key.
Carbon PA603-CF – This carbon-filled polyamide offers superior strength, precision and a smooth surface finish – so it’s great for precise parts that need to fit others, need to be robust or require good surface quality.
2. Wall Thickness
Minimum wall thickness is a critical factor in SLS design. Too thin, and the part will be fragile; too thick, and you risk warping due to uneven cooling. The recommended wall thickness for SLS parts is typically between 1.0 mm to 3.0 mm, depending on the material and the use case of the part.
Thin Walls (1.0-1.5 mm) – Ideal for small, detailed features but requires careful handling.
Thick Walls (2.5-3.0 mm) – Better for structural components but may need additional post-processing to avoid warping.
3. Minimum Clearance
The clearance tolerance for 3D printed parts depends on the desired fit with the mating parts, so this is a crucial step in the design process. Minimum clearance can vary depending on the material and geometry of the parts, but in general:
Loose fit – A clearance of about 0.3 mm is recommended
Tight fit – A clearance of about 0.15 mm is recommended
Standard fit – A clearance of about or 0.254 mm is typical
Press fit – Parts that require a press fit are often produced line-to-line, where the shaft and hole diameters are almost the same.
Minimum clearance is a tricky one to solve without seeing your part and understanding its applications. So, if you’d like help contact our team who recommend the best tolerances for your parts.
4. Designing for Complexity
One of the significant advantages of SLS is the ability to produce highly complex geometries that would be impossible or eye-wateringly expensive to create with traditional manufacturing methods. The powder material used in SLS printing really opens the door for doing a lot. Designers can use this capability to:
Incorporate Internal Channels – Create internal cooling channels or complex fluid pathways that would be unachievable with CNC machining.
Reduce Assembly – Combine multiple components into a single printed part, reducing assembly time and potential points of failure.
Add Texture – Surface textures can be directly printed onto the part to enhance grip, reduce weight, or add aesthetic value.
5. Optimising Support-Free Printing
Unlike other 3D printing technologies, SLS does not require support structures, as the unsintered excess powder acts as a natural support. This means designs can be more complex, but it doesn’t eliminate all the challenges of 3D printing. Designers should consider:
Overhangs and Angles – While SLS can handle overhangs better than FDM, steep angles (above 45 degrees) might still present issues. Gradually sloping surfaces or filleted edges can help mitigate this.
Flats – Long, flat sections should be minimised to avoid warping. SLS is much better at complex shapes than large flat surfaces, so if your parts have large surfaces, SLS might not be the best printing option for you.
Part Orientation – The orientation of the part during printing can affect surface finish, strength, and dimensional accuracy. Critical surfaces should be oriented to face upwards to reduce the staircase effect.
6. Post-Processing and Finishing
After printing, SLS parts require post-processing to achieve the desired surface finish and mechanical properties. Some common post-processing techniques include:
Vapour Smoothing – Using chemical vapour to smooth the surface, giving a uniform finish that rivals injection moulded parts. This process also increases the chemical/water resistance of the part.
Dyeing or Painting – Enhances the visual appeal of the parts, often used in consumer products or prototypes.
Machining – For critical tolerance features, post-process machining can be used to achieve precise dimensions.
7. Tolerances and Fits
Tolerances in SLS printing are generally between ±0.3% of the nominal dimension, with a minimum of ±0.3 mm. Designers should account for this in critical fit areas:
Clearance Fits – Allows for slight gaps between mating parts to ensure ease of assembly, typically requiring a tolerance of ±0.2-0.5 mm.
Interference Fits – Designed for press-fit assemblies with tolerances of ±0.1-0.3 mm.
Industry-Specific Design Tips
So there are the design guidelines for overall success when it comes to SLS printed parts. When it comes to the sectors we work with, there are some other key design aspects that should be taken into account during the design phase to ensure the parts are printed precisely as you need them.
Here’s a quick run-through of design aspects to consider for the 3D printing process for different sectors:
1. Automotive and Motorsport
Focus on reducing weight without compromising strength. Use lattice structures or hollowed-out designs to achieve lightweight, high-performance parts and materials like Carbon PA603-CF for additional support for important SLS components.
2. Aerospace
Prioritise materials with high strength-to-weight ratios and thermal resistance. Design parts with integrated features to minimise assembly and enhance reliability.
3. Medical
Biocompatibility and precision are crucial. Consider using medical-grade Nylon and designing for sterilisation processes like autoclaving.
4. Energy
Parts used in energy applications often face extreme conditions. So, choose materials that offer resistance to heat, chemicals, and wear. Also, design for modularity. This allows for easy maintenance and replacement.
If you’re designing parts for SLS and have questions, we have a team of experts who can help. Get in touch and we’ll happily help.
Conclusion
Designing for 3D printing requires a nuanced understanding of both the technology and the specific needs of your industry and the part itself. So, use design guidelines to shape your next designs.
SLS 3D printing allows you to produce innovative, high-performance parts that meet some of the most demanding standards in the world. With real-world applications in the automotive, motorsport, aerospace, medical, and energy sectors, SLS can be an excellent choice for lots of prototypes, projects and production parts.
Whether you’re optimising for weight, strength, or need complex geometries, SLS offers the flexibility to bring your designs to life with precision and efficiency. Need help with your design? Get in touch with our engineers and they’ll be happy to help you.
If your parts are ready to print, we’re here to help. We have a 3D printing facility with the latest industrial 3D printers capable of printing any projects, products or prototypes you need. Get in touch to find out more about the 3D printing process at Prototal UK.