Above: Complex structure printed in SLS 3D Printer/ Image Credit Sinterit
Selective Laser Sintering or SLS is one of the widely used 3D printing technologies across the globe. In this article we will learn everything about the SLS 3D printing technology, benefits of the technology and the material used in SLS 3D Printing. 3D printing refers to the process of turning three-dimensional CAD designs into solid objects.
Let us learn about the SLS 3D printing in depth.
The Inventors
Patented in 1980’s by Carl Deckard, an undergraduate student at the University of Texas and his academic advisor Dr. Joe Beaman, the idea of SLS was born while working on a summer job. Dr. Joeman got interested in the project and managed to get funds for the project. Carl Deckard further completed his Masters and Ph.D. degree and got involved with Beaman to create a manufacturing technology that further became additive manufacturing technology.
What is SLS 3D Printing?
Selective Laser Sintering also known as Laser Sintering uses laser technology to fuse small grains of elastomer material and nylon into layers in a 3D structure. The technology is convenient and affordable at the same making it one of the most preferred way to build prototypes and parts used in various industries like aerospace, wearables, machine parts, and production tools.
How SLS 3D Printing Works?
Above: A Diagrammatic representation of the working of Selective Laser Sintering Technology
Laser sintering uses a process known as Powder Bed Fusion which uses a laser to melt and fuse powdered material together to build 3D objects. A computer controlled powerful laser passes through the scanning system and falls on the bed filled with the powdered material. It draws the pattern of each cross-section of the 3D image onto the bed of powder. The laser selectively binds the particles by raising their temperature just below boiling point or just above its melting point which fuses the particles to create a solid form. Since the part being made is engulfed by the powdered material, the solid part is self-supporting, there is no need for supports structures to build a 3D object using SLS technology.
The building of the 3D object starts from the bottom layer. Once the first layer is formed the bed drops down by approximately 50 to 100 microns (depending on the layer thickness, laser strength, material properties, etc.). A roller then rolls one layer quantity of powder from the second bed to this first bed thus exposing a new layer of powder. This new layer of powder is again exposed to the laser beam and the laser traces the desired cross-section to solidify the powder and fusing the new layer to the previous layer of the part.
The process continues until the complete 3D model is built. When the object is completely formed, it is allowed to cool in the 3D printer before it is removed. The part is removed by brushing off all the excess powder surrounding the part. The part is then basted with compressed air so the powder sticking to the part is completely removed. Parts made in SLS machines are pretty fine and generally, do not require any sort of post-processing, but, if required, can be done by sandpaper, bead blasting, lacquering, etc.
Why choose SLS 3D Printing?
With so many 3D printing technologies available, the big question is why to choose Selective Laser Sintering over the others. One of the primary reasons that favor use of SLS 3D Printing is no need of support structures while building the 3D model.
Above: An Example of SLS 3D Printer – The Formlabs Fuse 1 SLS 3D Printer /Image Credit: Formlabs
Support structures are not new in the field of engineering and we often see it being used when constructing bridges. As we know the 3D printing works by building a layer over the other but what if the upper layers are wider than the layer beneath it. In such cases, using a support structure becomes evident that increasing material costs and wastage of material as well. In SLS, there is no need for support structures as the layer of the powder itself acts as a support when the layers are being built. This gives a lot of design freedom and also cuts the costs that are otherwise spent on support structures.
The SLS 3D printing technology is suitable to make living hinges, moving parts, highly complex designs, and interlocking parts as well. Whether you need a series of complex end-use parts or functional prototypes, you can use SLS for both. With SLS it is possible for companies to build 3D models fast while keeping the costs under control. Here are some of the manufacturing scenarios where using SLS is more beneficial
- Build large and complex parts of dimensions up to 700 x 380 x 580 meters in one piece
- Economical prices and fast lead times
- Durable and functional parts or prototypes
- Direct production of low-volume projects
- Lightweight designs having complex lattice structures
- Personalized products where you require unique complex design built as one-off products
- Freedom of design which is not hampered due to support structure
What all can be 3D Printed using SLS Technology?
SLS 3D Printing can be used to build a variety of objects using materials like metal, ceramics, glass, plastics, and many more. SLS technology is useful in industries where a few number of items are needed such as aerospace industry. SLS is also used in applications like fuel tanks, ductwork, brackets, and functional prototyping.
SLS 3D Printing is successfully being used to build prototypes of aircraft parts. Since airplanes are not made in large numbers and they have limited life, making physical molds to build aircraft parts is not cost-effective. Also, there is always a problem of storing physical molds in right conditions and ensure they do not get damaged or suffer from corrosion.
Above: Examples of 3D printed objects printed using SLS Technology/Image Credit: Formlabs
With SLS, things are different. All you have to do is store the STL files digitally and use them to reprint. Also, you can make changes to the design if you want to redesign a specific part. SLS is highly effective in creating tough and complex geometrical designs which require no additional tooling. Products made from Laser Sintering are water-tight, heat-resistant, strong and repeatable.
Materials used in SLS 3D Printing
We now will look at some of the popular materials used in SLS 3D Printing technology.
Above: Removing material from the final 3D printed part in an SLS printer/Image Credit: i.materialise
PA12
PA12, also known as polyamide powder, is the most popular material used in SLS 3D Printing technology. It is highly thermal resistant and useful to build end-use parts or functional prototypes. It is resistant to most chemicals and offers excellent long-term stability. It is possible to make the products water-tight by using the impregnation method. The PA material is bio-compatible and food safe.
Alumide
Another popular material used in SLS 3D Printing technology is Alumide. It is a combination of polyamide powder and aluminum powder. It is highly resistant to heat and used to build non-porous with a metallic look. The components made by Alumide can be machined easily and they are primarily used wind tunnel testing in the automotive industry, illustrative models with a metallic appearance, jig manufacturing, and small production runs.
PA-GF
Also known as Polyamide-glass filled, the material shows characteristics such as high density, good stiffness, and tensile strength. The products made with PA-GF are lighter and used in functional tests with high thermal loads.
TPU 92A-1
It is a thermoplastic polyurethane which is known for tensile strength and fully functional flexibility. The products developed using TPU 92A-1(rubber-like polyurethane) have qualities of the high tear, durable elasticity, abrasion resistance, good thermal resistance, high resistance to dynamic loading, and snappy response. The material is also food same in specific conditions.
SLS 3D printing is no doubt the most popular 3D printing technology due to its ability to create complex and large 3D structure without any support structures. The availability of a large variety of materials used in 3D printing gives it an edge over other 3D printing technologies.
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