Selective Laser Sintering (SLS) Flashcards
1
Q
Whtas the definition of selective laser sintering (SLS)?
A
Sintering of nonmetallic powders in layer-wise process to generate components.
2
Q
What are the 10 SLS process stages?
A
- Whole chamber is filled with inert gas
- Powder cylinders heated to 50°C below Tmelt
- While powder is being heated to correct temperature:
a) roller begins to roll out 50-100 µm layers onto the build platform (intital layer=20mm)
b) Prior to each spread of powder, the platfrom drops by one layer thickness
c)The termperature of the powder is gradually increased to 80% Tmelt or T melt-20°C
d)Process continues until approximaelty 20mm of virgin powder bed has been deposited and the bed is at the requisite temperature (intital layer ready) - Laser scans first part to be built
- Build platform drops a layer
- Further deposit of powder is applied
- stages 4-6 repeated until the end
- 3-9 cm of powder is deposited in the top of the top of the part to ensure cooling is even
- part cooled in machine for a couple of hours
- part broken out manually after cooled
3
Q
Why is powder recycling important, why cant all powders be recycled and how is the powder recycled?
A
- Makes process more environmentally friendly
- powders are expensive
- They have been subject to thermal processing by the various heaters in the machines. This results in further cross linking in the polymer particles and leads to it becoming impossible to process by SLS
- Remove powder from the part cake manually
- Discard and very hard powder surrounding the parts
- Filter the powder and removing any large particles
- Mix the old powder with the new powder in a certain ratio depending on each manufacturer
4
Q
Why is it important to raise the powder temperature?
A
- heating powder from rooom temp to melt temp creates high thermal gradients
- These generate thermal stresses
- There are already problems with shrinkage inducing stress
- Stress generation causes deformation of the solidified material.
