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20 Cards in this Set

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Describe the material used for SLA
SLA uses epoxy or acrylic resins which are photopolymers in the UV range. They are comprised of monomers and photo initiators. The photoinitiators use the energy from the UV laser to create free radicals, which are able to bind the monomers together. The polymers used for SLA come in a wide range with different properties.
What are the advantages of the Vantico 7560 resin?
High tensile and flexural strength
Hardest polymer
Low viscosity, making it easier to spread evenly for each layer
Highest density available
What are the limitations of the Vantico 7560 resin?
Not flexible - short elongation @ break
What are the advantages of the DSM 11120 resin?
Lower viscosity than 9920
Higher tensile and flexural strength than 9920
What are the limitations of the DSM 9920 resin?
Comparitively very high viscosity
Lowest strength and hardness
Describe the process used by SLA
Each point of material in the part or support is cured by a UV laser, the intesity and speed of which is controlled to ensure full curing. The platform/previous layer is posistioned under the surface of the resin at a depth of one layer, and a blade runs across the resin to ensure it is evenly spread over the top. The laser then scans the cross section defined by the slice file, the part is lowered, and the process repeats. The part is removed and rinsed in a solvent to remove the supports.
Why is it important to expose the resin to the laser for the correct amount of time?
Too little and the part will delaminate. Too much will cause curling affecting later layers. The laser must cure enough material to join the layers together
Why can the gaussian profile of the laser intensity affect the part?
Produces a series of gaussian shapes, which have to be overlapped in order to account for the curvature of the profile and not leave gaps. Also means the cure depth of the laser has to be slightly deeped than the layer depth. Edges can be made jagged by the profile of the laser curing.
Describe the problem of trapped volumes.
When the cross section of a part creates a closed ring, and this material is not cured, when the blade sweeps across, a wave forms in the ring which cannot escape it, this creates a large short wave which is forced over the ring, potentially damaging the part.
What are build styles, and why are they important
Build style determines the pattern the laser uses to scan the resin, and it can help prevent shrinkage and directional weakness
Describe the Trihatch build style
Each layer is scanned in a different direction by the laser, at 60 degree increments. Each layer thus shrinks in a different direction, and the overall shrink of the part is decreased.
Describe the Weave build style
Layer alternates between scanning back and forth along the x or y axis, so the shrink of the part is divided between them. 250 micron gaps are left between the scan lines which make inter-layer bonds stronger
Describe the Starweave build style
The scan points of each layer are staggered, so that the guassian shape of the beam bonds each point to two above and below. This decreases crack propagation
Describe the ACES build style
Stands for Accurate Clear Epoxy Solid. Developed for epoxy resins, and involves partially curing each layer to shrink it before the next layer is applied, this reduces overall shrinkage.
Describe the Quickcast build style
Developed for use in sacrificial casting. Solid sections of parts are shells filled with a honeycomb structure, reducing material cost.
Describe the cleaning of SLA parts
Removed from chamber and rinsed with solvent. Apart from quickcast parts, most parts can be automatically cleaned
Describe the post-curing of SLA parts
Post-curing is usually required to give complete curing of the model and increase strength through cross-linking of polymers. Larger parts take longer to cure, and light must be applied to all surfaces to ensure the part is evenly cured.
What are the health and safety issus of SLA?
Toxic resins
Material must be stored in a controlled atmosphere.
Resins are generally hygroscopic and must be protected from moisture
What are the advantages of SLA?
Robust parts
Good surface finish
Large volume
Indirect tooling
Evolving well as a technology
What are the disadvantages of SLA?
The process and materials are expensive
Lasers have a limited life
Trapped volumes
Stair stepping from orientation and laser shape
Limited materials
Hazardous resins
Postprocessing often required