When developing your skills in using an SLS process, one of your key factors to consider is your build packet. The qualities of your parts are completely dependient on your ability to produce and improve the placement of parts within the build packet. Here are some helpful tips and tricks to better improve the quality of your SLS parts using your build packet software.
1. Know your software-
There is a variety of different software available for people to use in order to produce their build packets. Some are proprietary, that are included in software with the machines, and can differ between machine manufacturers. Others are more general use, such as Materialize Magics™ which can be used with many different types of printer to set up the build packet. Regardless of your software of choice, spend the time to get to know it. Learn the limitations of the software, and any helpful tools or commands it may be able to do. Many of the software's are able to do such things as collision detection, or be able to edit and fix STL files internally, which is very useful for poorly generated STLs. By utilizing the software to its full potential, you can really take your production to the next level.
2. Spacing -
One of the key needs for making parts that are accurate to design is making sure that your spacing is correct. By spacing your parts with around 4-5mm of spacing between them, you allow enough spacing for the heat produced by the laser to diffuse through the powder, and not cause any adverse affects on your other parts. This can be especially important in the case of small holes, as any warpage to smaller holes can cause them to become more elliptical, or at worst fully close. Keeping the 4-5mm spacing also helps to maintain powder between them, as all that heat will also start to ruin the powder within it. Some software actually provides the ability to check for this spacing within the collision detection.
3. Knowing Desired Surface Finish-
Like all methods of 3D printing, SLS is a layered process. This means that for any part oriented in the z axis, it is possible to see the different layers that make up the part. This is further worsened in the case that your part has a slanted edge along the Z direction, by which stepping will now occur. Stepping is not an attractive feature on a part, both aesthetically and mechanically, and keeping the amount of stepping down is important to the quality of the part produced. Thus it is imperative when placing your part to keep your parts oriented so the majority of the part is in along the X-Y plane. Placing the essential areas of a part in the X-Y plane also increases clarity of that section. If, for example, you had a part with writing on one side. By placing the writing in the x-y plane, such that it would be readable while being sintered, you'll get the best resolution on the writing.
4. Desired Mechanical Properties-
Similar to surface finish, mechanical properties also vary in the Z direction. 3D printed parts are not isotropic (meaning that they can withstand the same amount of force in the x-y-z directions), though they have grown closer with the advances in additive manufacturing. Parts are weaker in the Z direction because this is where the different layers that fuse together. They are not as well fused as those in the x-y plane, causing for weaker mechanical properties. Therefore if you plan to exhibit a stress on the part, it would be in your best interest to make the areas where the stress concentration will be greatest in the x-y plane.
There are many more layers to the best placement of parts, and every part is different. There may need to be some trial and error for finding what works best for you, and for your parts. But hopefully with these few tips and tricks you can get started on your way.