Ch.4 VAT Photopolymerization Flashcards
What are the two primary polymer materials used in VAT photopolymer?
Acrylate, Epoxy
What are the advantages and disadvantages of Acrylates?
Advantage: high reactivity –> faster rate of production
Disadvantage:
- oxygen inhibition
- weak parts: prone to curling and shrinkage
What are the advantages and disadvantages of Epoxy?
Advantage:
- stronger parts
- less curling/shrinkage
- excellent adhesion
- no oxygen inhibition
Disadvantage:
- brittle parts
- sensitive to humidity
- slower photo speed
What is the difference between irradiance and exposure?
Irradiance: laser power per unit area
Exposure: energy per unit area (extent of resin cure)
How does irradiance and exposure affect solidification, scan pattern, and quality of a build?
- high irradiance –> faster solidification
- high exposure –> deeper penetration –> smoother surface/higher resolution
- high irradiance, low exposure –> less intricate scan pattern
- low irradiance, high exposure –> intricate scan pattern –> increases resolution
Solidification: H(x,y,z)=f(penetration depth)
Quality: maximum irradiance H0 at center of beam
Scan pattern and speed: exposure equation E(x,y,z) = f(Vs, Dp)
How does increasing penetration depth affect the cure depth in the working curve equation?
steeper slope –> rate to achieve desired cure depth faster with shorter exposure time
How does increasing critical exposure or maximum exposure in the working curve equation affect the cure depth?
increase Ec –> higher minimum exposure needed to initiate cure –> decrease in cure depth
increase Emax –> longer exposure/more power –> increases cure depth
What are the primary system components in a VP process?
Recoating: re-coater blade spreads and deposits a new layer of resin
Platform: holds part, controls build height for a new layer
Vat: holds resin
Laser & optics: solid-state laser, mirrors, galvanometer
Control system: prevent blade accidents, laser beam controller, environment controller
What are the advantages and disadvantages of the Weave scan pattern?
Advantage:
- reduce post-cure curl distortion
- 99% cure at surface, 96% through
Disadvantage:
- distortion in corners
- micro-fissures
- internal stress during part build and post-cure
What are the primary scan patterns in the VP process?
Weave
Star-Weave
ACES
What are the advantages and disadvantages of the Star-Weave scan pattern?
Advantage:
- solves micro-fissure issues by staggered hatch pattern
- alternating scan sequence –> minimize shrinkage during build
- eliminates stress concentrations between vectors
Disadvantages:
- 96% cure
- post-cure shrinkages and internal stress
What are the advantages and disadvantages of the ACES scan pattern?
Advantage:
- 98% cure
- reduce post-cure shrinkage and internal stress
Disadvantage:
- more scan vectors involved
- increased user complexity
What is the consequence of SLA printing a hollow part without drainage holes?
the trapped uncured resin within a part can cause pressure imbalance (cupping)
walls should be 2mm thick, drainage holes 3.5 mm for every internal cavity
For SLA printing, what is the design consideration for print orientation?
- minimize cross-sectional area along z-axis
Do SLA prints have isotropic properties? Why or why not?
Yes, because layers are chemically interconnected
