5.VAT Polymerisation Flashcards
What is VAT polymerisation?
Liquid photopolymer in a vat is selectively cured by light-activated polymerisation.
Top down or bottom up projection stereolithography is used.
A laser scans the liquid, causing the resin to polymerise. The platform moves a layer at a time. Each layer is scanned.
What is photopolymerisation?
polymerisation is the process of linking monomers to monomers, to create polymers.
Photopolymerisation is light initiated polymerisation and involves crosslinking of polymer chains.
What is the liquid polymer used in VAT?
Resin made up of several materials:
Monomer (>90 wt%): small molecules with one or several repeated units.
Photo-initiators (~ wt%): Produces radicals, light stimulus
Inhibitors (~ 0.1 wt%): prevent polymerisation in the presence of oxygen
Other additives (~ wt%)
What are the symbols in this equation?
πΆπ=π·π * ln(πΈ /πΈπ )
What is the purpose of the cure depth?
Cure depth (Cd) - to work out how long to turn on the lamp to cure 1 layer.
Penetration Depth (Dp)
Scan Velocity (Vs) = the speed (mm/s) at which the laser beam is scanned over the liquid resin.
Critical Exposure (Ec)
Energy (E)
What are the two types of projection?
Top down and bottom up
What are the pros and cons of bottom up projection?
Advantages:
- Accurate layer thickness control
- No sweeper
- part height not limited
- smaller vats used
Disadvantages:
- sticking
- Peeling process
What are the pros and cons of top down projection?
Advantages:
- Higher resolution
- No peeling process required
Disadvantages:
- Resin surface charecteristics can affect the quality of the part.
- Slower due to recoating process
- part thickness determined by the viscocity of the resin.
What is micro SLA?
- UV laser
- normal SLA limited to a resolution of 100Β΅m.
- Layer thickness decreased
- Laser beam spot size reduced to a microns.
- Increases part resolution.
What are the materials printable by VAT polymerisation?
All materials are an epoxy/acrylic formulation of non-polymerised liquid.
- Contain additives to reproduce properties of common materials (ABS, PP, PC).
- Additives to change colour and improve stability.
- Formulas kept secret by companies.
What are the post processes for VAT polymerised parts?
- Removal of supports
- Uncured resin must be removed with TPM or alcohol
- Post curing of parts to ensure they are fully polymerised and complete cross linking of bonds.
What are the proβs of VAT polymerisation?
- Accurate for an AM process:
β 50-100Β΅m
β Layer thickness
down to 25 Β΅m - Good surface finish (similar to injection moulded components)
- Parts can be mechanically and chemically smoothed, as well as painted or coated.
- Large build volumes available.
- Easy removal of support structures, if done before final curing.
- Available materials mimic traditional engineering polymers.
- Low energy input compared to thermal AM systems.
What are the cons of VAT polymerisation?
- Curling of large flat surfaces
β Occurs from each
layer shrinking when
it solidifies.
β To prevent: re-
orient part, use
supports to anchor
in place. - Materials used are often toxic
-
Materials are hygroscopic - dimensionaly unstable over time - Parts will age insunlight due to UV, alters apperance and properties.
- To change materials, thorough cleaning of VAT required.
- Orientation of part affects surface finish
- Parts need to be post cured.
What are the main applications of VAT polymerisation?
Dental applications, medical applications.
Give a 1 line summary of the parts VAT polymerisation can produce.
can build highly accurate components with smooth surface roughness
What are the two main types of VAT polymerisation machine?
laser based and image projection based
