SLS 3D printing

Selective laser sintering (SLS) is an industrial 3D printing process that produces accurate prototypes and functional production parts in as fast as 1 day. Multiple nylon-based materials and a thermoplastic polyurethane (TPU) are available, which create highly durable final parts that require heat resistance, chemical resistance, flexibility, or dimensional stability. With SLS 3D printing, no support structures are required making it easy to nest multiple parts into a single build and an economical solution for when higher volumes of 3D-printed parts are required.

Characteristics of SLS

Printer Parameters

In SLS almost all process parameters are preset by the machine manufacturer. The default layer height used is 100-120 microns.

A key advantage of SLS is that it needs no support structures. The unsintered powder provides the part with all the necessary support. For this reason, SLS can be used to create freeform geometries that are impossible to manufacture with any other method.

Taking advantage of the whole build volume is very important when printing with SLS, especially for small batch productions. A bin of a given height will take about the same time to print, independent of the number of parts it contains. This is because the re-coating step determines the total processing time (laser scanning occurs very rapidly) and the machine will have to cycle through the same number of layers. Bin packing may affect lead times of small orders, as operators usually wait until a bin is filled before starting a print.

Layer Adhesion

In SLS, the bond strength between the layers is excellent. This means that SLS printed parts have almost isotropic mechanical properties.

SLS parts have excellent tensile strength and modulus, comparable to the bulk material, but are more brittle (their elongation at break is much lower). This is due to the internal porosity of the final part.

A typical SLS printed part is about 30% porous.

Porosity gives SLS parts their characteristic grainy surface finish. It also means that SLS parts can absorb water, so they can be easily dyed in a hot bath to a large range of colors but also that they require special post-processing if they are to be used in a humid environment.

Shrinkage & Warping

SLS parts are susceptible to shrinkage and warping: as the newly sintered layer cools, its dimensions decrease and internal stresses buildup, pulling the underlying layer upwards

3 to 3.5% shrinkage is typical in SLS, but machine operators take this into account during the build preparation phase and adjust the size of the design accordingly.

Oversintering

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.

Powder Removal

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.

Common SLS Materials

The most widely used SLS material is Polyamide 12 (PA 12), also known as Nylon 12. The price per kilogram of PA 12 powder is approximately $50 - $60. Other engineering thermoplastics, such as PA 11 and PEEK, are also available but are not as widely used.

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.

Post Processing( Standard &Custom)

SLS parts produces parts with a powdery, grainy surface finish that can be easily stained. 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.

Ｇalaxy3DM SLS 3D Printing Common SLS Materials

The most widely used SLS material is Polyamide 12 (PA 12), also known as Nylon 12. 

Other engineering thermoplastics, such as PA 11 and PEEK, are also available but are not as widely used.

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.

Galaxy3DM SLS 3D printing Post Processing

Additional post process can be applied to improve the appearance or mechanical properties of parts produced with SLS. 

Surface Finish and Post-Processing Options:

Standard:Bead blast to remove all powder, which leaves a consistent overall texture.
Secondary options: a primer or dye color that can be applied as well as taps and inserts.

Additional post processes can be applied to improve the appearance or mechanical properties of parts produced with SLS. 

Available surface finishes for SLS 3D printing

SLS parts can be dyed by immersing in a warm color bath to a variety of colors. The color penetration reaches an approximate depth of 0.5 mm and covers all surfaces.

3.Tumble smoothing:

Electroplating (nickel, copper or gold) is an ideal solution for parts that require a metallic appearance, without the high costs associated with metal 3D printing.