Oversintering occurs when radiant heat fuses unsintered powder around a feature. This can result in loss of detail in small features, like slots and holes. Oversintering depends both on the size of the feature and the wall thickness.
For example, a 0. As a rule of thumb, slots wider than 0. See this article for more design guidelines. Since SLS requires no support material, parts with hollow sections can be printed easily and accurately. Hollow sections reduce the weight and cost of a part, as less material is used. Escape holes are needed to remove the unsintered powder from the inner sections of the component. It is recommended to added to your design at least 2 escape holes with a minimum 5 mm diameter.
If high stiffness is required, parts must be printed fully solid. An alternative is to make a hollow design omitting the escape holes. This way tightly packed powder will be entrapped in the part, increasing its mass and providing some additional support against mechanical loads, without an effect on the build time. An internal honeycomb lattice structure can be added to the hollowed interior similar to the infill patterns used in FDM to further increase the stiffness of the component.
Hollowing a part this way may also reduce warping. Polyamide powder can be filled with various additives such as carbon fibers, glass fibers or aluminum to improve the mechanical and thermal behavior of the produced SLS part. Materials filled with additives are usually more brittle and can have highly anisotropic behavior. Curious about the cost and available material options for SLS? The appearance SLS printed parts can be improved to a very high standard using various post processing methods, such as media polishing, dyeing, spray painting and lacquering.
Their functionality can also be enhanced by applying a watertight coating or a metal plating. An extensive article on post processing of SLS parts can be found here. SLS parts have good, isotropic mechanical properties, making them ideal for functional parts and prototypes.
SLS requires no support, so designs with complex geometries can be easily produced. The manufacturing capabilities of SLS is excellent for small to medium batch production. SLS parts have a grainy surface finish and internal porosity that may require post processing, if a smooth surface or watertightness are required. Large flat surfaces and small holes cannot be printed accurately with SLS, as they are susceptible to warping and oversitnering.
Detailed design guidelines for each of the aspects discussed here are given in a later article of the Knowledge Base. The main characteristics of SLA are summarized in the table below:. Knowledge base. What is SLS? Get instant quote See all SLS materials.
How does SLS work? Here is how the SLS fabrication process works: I. Learn more about residual stress and how to measure the material property using a thermal analysis method. Significant efforts have been made to model and simulate the Selective Laser Sintering process as information about the temperature field in lower layers is difficult to measure. Learn how specific heat capacity can help!
Due to the still limited number of available materials for the Selective Laser Sintering process, there is a constant demand for materials with different properties. The addition of any filler to SLS powder typically has an effect on the processing behavior. Today, we investigate the crystallization behavior of PA12 powder filled with copper spheres and flakes. The modification of Selective Laser Sintering SLS powders with fillers is a good way to modify the properties of the produced parts without the necessity for new powder materials.
Learn how to assess the effect of copper fillers on the processing behavior. Therefore, thermophysical properties need to be assessed in different directions. Learn how to prepare filled samples for laser flash analysis! Conductive fillers in polymer powder, like copper spheres and flakes, influence Additive Manufacturing processes. Learn how laser flash analysis allows determination of process setting to print highest quality parts.
In general, the addition of fillers leads to an increase in mechanical performance. To understand how the stiffness or modulus change as a function of the filler geometry and filler content, Dynamic Mechanical Analysis DMA can be used. Learn more in our article. Fillers are added to a polymer matrix to improve the mechanical performance of the finished product. The orientation of such fillers depends on the processing conditions. Learn how the overall content, shape and orientation of copper fibers influence the coefficient of thermal volume expansion.
Figure 1: Schematic of an SLS machine The SLS process principle In the SLS process, a thin layer of powder is applied on the build platform and heated to just below the melting temperature of the material, which is often referred to as the build temperature heaters not shown in the schematic. It must be noted that SLS printing does not need support structures as the unsintered powder acts as the support structure for the actual object. It must be noted that the printing always starts from the bottom layer and is printed to the top.
The build chamber is allowed to cool before the part is removed. This can take a significant amount of time. Once the part is removed it is cleaned by blasting it with compressed air.
It can be further post-processed by bead blasting, dyeing, painting, powder coating, tumbling, stove enameling, metal coating, lacquering, etc. Since Selective Laser Sintering uses materials in a powdered form and the printing occurs inside a build chamber, the build chamber is always filled with the material. This proves to be a double-edged sword.
Since the chamber has to be filled with powder, the material is heated every time an object is printed. This affects the material properties and after a specific number of times, the material loses its standard properties and it cannot be reused again.
And positively, since the powder engulfs the object, it can be used to build several parts simultaneously in a single run. This helps in optimum use of the machine and material. Selective Laser Sintering is most suited for a single piece or small quantity production of high-quality parts. Therefore, Aerospace industry is the biggest beneficiary of this technology. Visit our 3D Printing Education page to read more such informative articles.
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