SLS 3D printing is a power bed 3D printing technology known for its accuracy and no support structure. However, quality SLS 3D printed parts are achievable only by following the right skill and a set of SLS designs. This article shows how SLS 3D printing works, tips on SLS design, and common design applications for a successful printing process.
How does SLS 3D Printing work
SLS is a 3D printing technology employed by many prototyping services that use a laser to sinter polymer powder and build a part layer by layer according to a CAD model. Below is an explanation of how the technology works:
First, the powder material is heated to a high temperature and deposited in thin layers (about 0.1mm) by the recoating blade on the build platform. Afterward, the laser scans the surface of the build platform.
After scanning, the laser selectively sinters the powder material to solidify it. Scanning continues until the selective sintering is complete. Afterward, the build platform will move down a layer height. During this process, the unsintered powder is still in the build platform. As a result, SLS parts do not need support structures.
The recoating blade then deposits a new powder layer, and the process repeats until all printing is complete. On printing, the container will contain unsintered powder and the sintered part.
Tips For Designing Custom Parts with SLS 3D Printing
Like part manufacturing processes such as injection molding, die casting, and all CNC machining operations, SLS 3D printing comes with its challenges. Here are several tips that can help optimize your SLS design process.
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General Tolerances
Dimensional tolerance depends on the printed parts’ dimension and the sophistication of the 3D printer. Although necessary, you should limit tolerance to areas where it is very important. For example, parts that require assembling. Most SLS printers have ± 0.3mm and ± 0.05mm printing accuracy.
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Wall Thickness
The wall thickness of SLS 3D printed parts determines their stability during and after printing. Generally, having a thick wall prevents printed parts from collapsing during printing or breaking after printing.
According to SLS 3D printing enthusiasts, the minimum wall thickness should be between 0.7mm (PA 12) and 2.0mm (carbon-polyamide). However, it is also possible to have a wall thickness of about 0.6mm, although you would need a support structure.
Printing with a wall thickness of less than 0.5mm will lead to the printed parts over thickening due to the laser heat.
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Hole Size
SLS printing supports printing holes directly, unlike other 3D printing and non-3D printing processes. However, the hole must not be smaller than 1.5mm in diameter. Printing less than 1.5mm can lead to unsintered powder filling the hole. As a result, print at a hole size larger than 1.5mm in diameter.
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Escape Holes
The power bed technology also allows you to make hollow parts to reduce weight and material use. However, the unsintered powder can enter the hollow part during printing. As a result, escape holes are necessary to remove the unsintered material. The escape should have a minimum of 3.5mm in diameter.
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Warping of large flat surfaces
Warping is a 3D print defect that occurs due to uneven cooling after printing, especially with large flat surfaces. Therefore, such surfaces should be avoided. However, if they are a crucial part of the design, you should use support structures (this may not always solve the problem).
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Engraving and Embossing
For parts that need engraving or embossing, you can improve visibility by designing the parts with a minimum depth of 1mm. This is important to account for post-processing, such as media tumbling that can lead to it wearing off. For texts, you should use a minimum depth of 2mm for clarity.
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Interlocking parts
SLS 3D printing is suitable for printing mating and moving parts without needing the parts to be separate. It would be best if you designed parts that need to interlock with a minimum clearance of 0.5mm. This clearance will aid in removing unsintered powder to prevent the parts from fusing.
Common design applications
SLS 3D printed parts are applicable in part manufacturing or prototyping services in several industries. Below are some common design applications of the process:
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Axles
Nylon is applicable in prototyping axles due to its smoothness, chemical resistance, low friction mechanism, and low velocity. When using nylon in making running axles, the recommended bearing surface clearance is 0.3mm. Furthermore, proper removal of the unsintered powder is necessary to maintain a smooth-running shaft.
The CAD model design should incorporate escape holes with a minimum of 3.5mm in diameter wherever possible and a clearance of 2mm between the clearance shaft hole and the running shaft axle to remove the unsintered powder.
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Integrated hinges
SLS printing is applicable in designing integrated hinges. A trapezoid-shaped pocket accommodating a semi-spherical ball will produce a hinge with low friction and sufficient stability. Furthermore, there should be a 0.2mm clearance between the sphere and the pocket and a 0.3mm clearance for other gaps.
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Tanks
SLS nylon is applicable in custom tank design. When custom designing tanks, the recommended wall thickness should be greater than 1mm, and there should be escape holes to remove excess and unsintered powder. Furthermore, the tank can be coated to function in aggressive fluids such as fuels or improve its water tightness.
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Threads
SLS 3D printed parts have a high frictional surface. As a result, there can be issues when assembling threaded SLS 3D printed parts. A better option would be to use SLS nylon for just one connection (either hole or bolt).
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Living Hinges
SLS 3D printing is the most suitable technique for making functional living hinges. To make the hinges, anneal it by heating it and flexing it back and forth. The living hinge should be 0.3-0.8mm thick with a minimum length of 5mm.
Conclusion
SLS 3D printing is popular due to its accuracy and no support structure. However, quality SLS 3D printed parts are only achievable by following a set of SLS design guides and experience. This article talks about SLS 3D printing, tips for custom design parts, and some applications of the process. Following these tips, be rest assured of flawless SLS parts
