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Selective Laser Sintering (SLS®)

Diagram of SLS MachineSelective Laser Sintering (SLS) is a powder based Rapid Prototyping method. The process uses a layer system of building up a part with each layer of powder being sintered separately by a laser. As each layer is sintered it slowly constructs the part step by step. There are various grades of materials used each with there own characteristics but each are used the same way within the SLS machine. The SLS machine basically consists of 3 Powder beds and a Laser. Two of the powder beds hold the feed powder and the third bed holds the part. The part bed is middle of the beds with the laser acting directly perpendicular to this bed. A roller is used to push the layers of powder over the part bed and all three beds have their own heater source. The process itself is a very simple repeatable one. The building of the parts is a repeatable two step process.

Step 1

A roller is positioned beside one of the feed beds. This feed bed then raises a set amount (Usually < 0.1mm) and the roller pushes the raised powder across, covering the part bed with a Powder Layer.

Step 2

With the layer of powder present the laser starts to etch out the desired shape of the part in the powder in effect melting the powder. Once this is done the part bed drops down the set amount and the process continues from the opposite side with the other feed bed raising and the roller distributing another layer of powder over the part bed and the laser etches out the shape. The part is built up in slices with each layer of powder representing a single slice of the part. As the laser melts/sinters the powder each layer fuses together to give a full solid part. Because of the fact that the part is made up in slices very complex shapes and designed can be manufactured that would otherwise be impossible by conventional means.

 

Selective Laser Sintering (SLS) is a process by which Laser Sintering.com manufactures 3D prototypes. SLS machines fuse or sinter thin layers of powdered thermoplastic materials or metals using a laser beam to create three dimensional functional prototypes. The SLS process has the widest selection of material properties of any Rapid Prototyping process. Sintered parts will be exceptionally durable, and they'll also maintain their material properties long after they're built. Producing a pre-production durable SLS of a part can significantly enhance the geometric visualization of a product, as well as communication among project team members. This physical model can be use for photo-optic stress analysis as well as dynamic vibrational analysis, which further extends engineering design capabilities.

Finishing Options

Highlights of Laser Sintering

SLS (Selective Laser Sintering)
DMLS (Direct Metal Laser Sintering)
» Perfect for functional and robust parts, including living hinges and snap fits » Replaces the need for 4th and/or 5th Axis Machining
» Ideal for 1 – 2 prototypes and up to 100+ parts » Excellent tolerances
» Tool-less manufacturing » Pure Alloys
» Heat deflection up to 285°F » Reduces part delivery from weeks to days
» Excellent for chemical resistance » Parts can be post machined, welded and more
» Quick-turn deliveries » Heat deflection up to 2000°C
» Less post-finishing requirements than SLA » Equal to wrought in strength
» Paintable and platable » 99.99% dense
» Incredible Surface Quality » Reduce part delivery from weeks to days

SLS© vs. SLA Comparison

Material Properties: The SLA (stereolithography) process is limited to photosensitive resins which are typically brittle. The SLS process can utilize polymer powders that, when sintered, approximate thermoplastics quite well.

Surface Finish: The surface of an SLS part is smooth yet has a powdery feel. The smoother surface of an SLA part typically wins over SLS when an appearance model is desired. In addition, if the temperature of uncured SLS powder gets too high, excess fused material can collect on the part surface. This can be difficult to control since there are so many variables in the SLS process. In general, SLA is a better process where fine, accurate detail is required. However, a varnish-like coating can be applied to SLS parts to seal and strengthen them.

Dimensional Accuracy: SLA is more accurate immediately after completion of the model, but SLS is less prone to residual stresses that are caused by long-term curing and environmental stresses. Both SLS and SLA suffer from inaccuracy in the z-direction (neither has a milling step), but SLS is less predictable because of the variety of materials and process parameters. The temperature dependence of the SLS process can sometimes result in excess material fusing to the surface of the model, and the thicker layers and variation of the process can result in more z inaccuracy. SLA parts suffer from the "trapped volume" problem in which cups in the structure that hold fluid cause inaccuracies. SLS parts do not have this problem.

Support Structures: SLA parts typically need support structures during the build. SLS parts, because of the supporting powder, sometimes do not need any support, but this depends upon part configuration. Marks left after removal of support structures for parts cause dimensional inaccuracies and cosmetic blemishes.

Machining Properties: In general, SLA materials are brittle and difficult to machine. SLS thermoplastic-like materials are easily machined.

Size: SLS and SLA parts can be made the same size, but if sectioning of a part is required, SLS parts are easier to bond.

Investment Casting: The investment casting industry has been conservative about moving to RP male models, so SLS models made from traditional waxes, etc. are preferred. Sterolithography.com, however, utilizes a special process which allows SLA models to be more suitable for investment casting. Since SLA resins do not melt but burn to form ash, this special method modifies the build process so that the interior of the model is hollow with a supporting latticework. When the ceramic is fired, the modified SLA model collapses and any ash is minimal because of the small total quantity of material.

Selective Laser Sintering Investment Casting

Selective Laser Sintering Investment Castings is a dual process by which Laser Sintering.com generates finely detailed and accurate 3D prototypes. The SLS Investment casting machines fuse or sinter thin layers of traditional waxes or other material using a laser beam to create three dimensional prototypes. The wax assembly is now dipped multiple times in a ceramic slurry, and the desired metal is poured into the hot ceramic shell. The parts are individually removed after the shell is removed and the mold cools. The SLS/IC process has a wide selection of materials including Aluminum 319, 356 & 380; Bronze 421; Magnesium and ZA-12 (Zinc).

Investment Castings are common in the fields of electronics, avionics, aerospace, automotive, pump and valve applications and military command equipment. Sintercasted parts are a wise investment because they are exceptionally durable, and they'll also maintain their material properties long after they're built. Producing a pre-production durable casting of a part can significantly enhance the geometric visualization of a product, as well as communication among project team members. This physical model can be use for photo-optic stress analysis as well as dynamic vibrational analysis, which further extends engineering design capabilities.

 
 
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