Version 1.0, August 31, 2001, Copyright, Hugh Jack 1993-2001

65.4 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.

  1. - nylon
  2. - glass filled nylon
  3. - somos (elastomer)
  4. - polycarbonate
  5. - trueform (ceramic??)
  6. - sandform ??
  7. - rapid steel (metal)
  8. - 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,

  1. - inexpensive materials
  2. - safe materials
  3. - wide varieties of materials: wax for investment casting; polymers/nylon for assembly prototypes
  4. - supports not needed
  5. - reduced distortion from stresses
  6. - produce parts simultaneously

 

· Disadvantages,

  1. - rough surface finish ("stair step effect")
  2. - porosity of parts
  3. - the first layers may require a base anchor to reduce thermal effects (e.g. curl)
  4. - part density may vary
  5. - 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,

  1. - new materials
  2. - high power lasers for metal powders/etc.

 

· Selected specifications for a Sinterstation 2000 are given below,