66.4 SELECTIVE LASER SINTERING (SLS)

---

Powdered material is fused together in layers using a laser

The powders need fine grains and thermo-plastic properties so that it becomes viscous, flows, then solidifies quickly.

- nylon

- glass filled nylon

- somos (elastomer)

- polycarbonate

- trueform (ceramic??)

- sandform ??

- rapid steel (metal)

- copper polyamide (metal)

invented in 1986 by Carl Deckard

marketed by DTM corp. (Sinterstation 2000)

The process uses a heated chamber (near the powder melting temperature)

The product is split into slices from the .STL file and created one layer at a time by spreading layers of powder, sintering the powder with a CO2 laser, then adding new layers of powder and sintering until done.

When done the part is inside a cake of powder, and putty knives and spatulas are used to remove the loose powder

Supports not needed as the unsintered powder supports overhangs/etc.

powder can be reused

slow cooling of the parts can prevent distortion due to internal stresses.

The laser is about 50W infrared (about 10000nm) This power level is much higher than stereolithography

Optics and x-y scanner are similar to SL

the process chamber runs hot to decrease the power required from the laser, and reduce thermal shrinkage that would be caused by a difference in operation and cooling temperatures.

The hot chamber is filled with nitrogen (98% approx.) to reduce oxidation of the powder.

rate of production is about 0.5-1" per hour

Advantages,

- inexpensive materials

- safe materials

- wide varieties of materials: wax for investment casting; polymers/nylon for assembly prototypes

- supports not needed

- reduced distortion from stresses

- produce parts simultaneously

Disadvantages,

- rough surface finish ("stair step effect")

- porosity of parts

- the first layers may require a base anchor to reduce thermal effects (e.g. curl)

- part density may vary

- material changes require cleaning of machine

DTM markets the Sinterstation 2000 for $250,000(US) to $497,000(US) depending upon the selection of 1, 2, or 3 materials (investment casting wax, nylon, or polycarbonate). The Sinterstation 2500 starts at $400,000

Development is being done on,

- new materials

- high power lasers for metal powders/etc.

Selected specifications for a Sinterstation 2000 are given below,