Selective Laser Sintering (SLS) & 3D Printing

Selective Laser Sintering is an additive manufacturing technology that works on the powder-bed fusion principle. Starting from a plastic powder selectively fused with the help of a laser, three-dimensional objects are produced. It is one of the oldest 3D printing technologies on the market, invented and patented in the late 1980s by Dr. Carl Deckard and Joe Beaman. At the same time, SLA and FDM 3D printing technologies were also patented for the first time.

Today, the SLS process is one of the most widely used and best developed processes. Other technologies, such as binder jetting, were developed only a few years later, but have a higher potential than the SLS process, especially in terms of productivity.

An SLS 3D printer builds objects in a powder bed by selectively sintering plastic powder layer by layer. To do this, a recoater or squeegee applies the powder to a lowerable build platform. The desired object is available to the 3D printer as a CAD file and is sliced by the software – that is, the component is cut into individual layers. Each layer forms a cross-section through the component and represents a layer during the printing process.

The laser thus sinters the powder in the first layer according to the first cross-section. Since the build area is already heated, the laser only applies the energy to the powder bed that is needed to melt the powder and generate a layer bond. Then another layer of powder is applied to the build area, and again the laser sintered a selective layer. This process sequence is repeated until the desired object is produced and can be unpacked from the powder bed.

Basically, SLS and SLM are two sides of the same coin. Both are additive manufacturing technologies that use a laser to shape powder materials into 3D objects. The main difference between the two technologies lies in the materials being processed. SLS 3D printing mainly processes plastic materials, while SLM is particularly suitable for metals. Smaller differences can also be found in the process details. In SLS, the build space and the powder are heated to just below the melting point so that the laser only has to input the remaining amount of energy to melt the powder.

In SLM, on the other hand, the build space does not heat up. Instead, it is filled with an inert gas such as nitrogen to prevent oxidation of the metal powder. Another difference lies in sintering and melting. In melting, there is a phase transition from the solid to the liquid aggregate state of the material. In sintering, on the other hand, the temperature is not high enough to melt the material completely. Instead, the material particles are agglomerated as the grain does not completely melt but heats up enough to bond with neighboring grains.

Among the biggest advantages of laser sintering are the high level of detail and the strength of the parts. In addition, no support structures are needed during the 3D printing process because the powder bed supports the parts, just as in binder jetting. Unprinted material can be recycled and reused up to 100%. Similar to all other 3D printing technologies, SLS has mainly been used to produce prototypes. However, many users are now also imaging small batches via Selective Laser Sintering (SLS) printing.

Laser sintering is one of the most advanced 3D printing processes on the market. The material portfolio available today is correspondingly broad. In addition to classic polyamides such as PA12 or thermoplastics such as TPU, special high-performance plastics such as PEK, PEEK or PEI can also be processed using SLS.

SLS is particularly popular for prototyping purposes. Whether for functional or purely visual prototypes, the attention to detail and mechanical load capacity of 3D-sintered components, as well as the availability of many different SLS materials, have contributed to the widespread use of 3D printing technology. The process is now firmly established, particularly in the aerospace, medical and automotive industries. Even applications that go beyond classic prototyping, such as small series, can now be economically mapped using selective laser sintering.

voxeljet’s Binder Jetting technology differs from SLS in many ways. SLS utilizes a laser that sinters away powdered material, typically various thermoplastic polymers. Comparatively, voxeljet’s Binder Jetting process can be adapted to fit a wide range of materials such as sand, ceramic, and plastic. Since Binder Jetting has a higher material diversity, it is suitable for a wider range of industries. SLS is typically used in rapid prototyping, and has more recently been applied to low-volume production. Industries such as automotive, aerospace and dental industry utilize SLS printing processes. voxeljet’s Binder Jetting system has a larger range of applications, as it can also be used in architecture and metal and art casting, in addition to the above industries. Binder Jetting can be used in product development and prototypes and other end use parts. The build volume of one of the largest SLS printers is up to 1,000 x 500 x 500 mm whereas voxeljet’s VX4000 printer for sand is 4 x 2 x 1 meters with a print volume of up to 111 liters per hour. Because Binder Jetting has a greater versatility of materials and applications, it has higher productivity levels than SLS making it better suited for large-scale and serial production applications.