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What materials can be used in SLS?
Polymers, ceramics and metals
Describe the SLS process (8 steps)
1. Build chamber or platform is heated
2. Slice files fed to CO2 laser
3. Fine layer of powder applied to the platform/last layer
4. Laser scans slice file onto the top layer of powder
5. Powder partially fuses to adjacent particles and layer below
6. Repeat 3-5 for each layer
7. Unused powder removed and recycled
8. Post Processing
How is the SLS system designed to improve the part quality?
Powder is supplied from either side of the platform, preventing powder from building up due to part structure.
Counter-rotating roller levels and compacts the powder
Construction takes place in a controlled atmosphere.
What are the advantages of SLS?
Powders are easy to produce
Close to virgin material properties
No supports
Safer than SLA
Suitable for functional testing
Efficient recycling
Can produce multiple parts in z direction
Little post processing
What are the limitations of SLS?
Part can be distorted by heat
More energy than SLA (10000x)
Cooling can induce stresses
Dust and particles must be contained and controlled.
Can create trapped pockets of powder.
How are SLS parts post processed?
Must be carefully and evenly cooled to prevent warping. Part is removed from powder cake by brushing or air blowing. Some excess powder is recycled.
Describe temperature control in SLS
Important, especially for crystalline polymers. Chamber is heated to 10/20 degrees below melting point of the powder, so relatively little energy comes from the laser. When cooling the part, temperature must decrease at a controlled rate, as rapid cooling can cause warping, reduced crystallisation, and unpredicted physical properties. Cooling too quickly reduces the recycleable powder. The edge of the powder cake can cool faster than the middle, causing distortion to the part.
What is the main difference between SLS systems offered by 3D Systems and EOS?
3D Systems machines can use all their materials, EOS had different ranges for Polymer and Sand
Describe the Duraform polymer used in 3D Systems' SLS products
The most common type of polymer used, Duraform is made of polyamide 12, a heat and chemical resistant material. The material is made of fine particles, allowing for higher resolution. When the part is finished, it is cooled from 173 to room temperature over a number of hours.
Describe the Sandform Zr2 sand used in 3D Systems' SLS products
Consists of a polymer, coated with Zirconium. Grain size varies from 35-210 microns. Used to produce sand castings.
What are the advantages of SLS compared with SLA?
Supports aren't required, reducing material costs. Properties are more stable over time. Acheives a more consistent finish.
What are the advantages of SLA compared with SLS?
Commecialised much earlier, so more experience. Higher accuracy and resolution. Smoother finish. Lower energy consumption.