Lecture 5 - VAT photo polymerisation Flashcards
• Understand photopolymerisation • Understand the working curve • Be able to describe different processes in Vat Photopolymersiation • Know the advantages and disadvantages • Be able to give sample applications
Define Vat Photopolymerisation
Liquid photopolymer in a vat is selectively
cured by light-activated polymerization.
What is photopolymerisation
Photopolymerization (Light initiation) and Crosslinking of an monomer using light as the energy scource
Uses a monomer 90%
Photo initiators
other additives
Laser resin penertration depth
Penetration Depth (Dp) – the depth at which the energy intensity has been reduced to approximately 1/3 the intensity at the surface.
Please draw a laser SLA process (found in notes) lecture 4
• The laser scans the liquid surface and causes the liquid to polymerise. The platform then drops a layer which is recoated and then scanned
Projection based SLA
bottom up -pros and cons
Pros -Accurate resolution control -large part height Cons -Peeling process -Sticking to base
Projection based SLA
top down- pros and cons
+Resolution is typically higher
+ No peeling process needed
- Resin surface characteristics can affect the
quality of the part - Slower due to recoating process
- Viscosity of the resin determines the thickness of
the part.
Micro-SLA(laser based)
Name the two types….
Micro stereo-lithography
one photon absorbtion
Multiphoton stereo-lithography
-multi photon absorbtion
Describe the Post processing of VAT made products
Cleaning uncured resin
Post curing to ensure full polymerisation
Support removal
Pros of VAT
Very accurate (very low layer thickness)
Good surface finish
Large build volumes available
Low energy input
easy to remove support structure before post curing
Similar to traditional engineering polymers
Cons of VAT
Curling of large flat horizontal surfaces is a significant problem(layers shrink when curing)
The materials have to be photo-curable resins – can be toxic
Parts continue to age in sunlight which alters their appearance and mechanical
properties
A material change in the machine requires a very thorough cleaning procedure
using solvents
Materials are hygroscopic – dimensionally unstable over time
List some applications
Dentistry- Teeth aligners
Hearing aids
(EXAM)What is the advantage and disadvantages of using bottom-up imaging
over top-down for the Stereolithography process?
Example answers: Bottom-up: \+ Accurate layer thickness control \+ No sweeper \+ Part height - Sticking - Peeling process Top-Down: \+ Resolution is typically higher \+ No peeling process needed - Resin surface characteristics can affect the quality of the part - Slower due to recoating process - Viscosity of the resin determines the thickness of the part.
(EXAM)Explain the differences between micro stereolithogaphy with two-photo
polymersization processes with the use of diagrams where appropriate.
Literally the pic from lecture notes
Draw this 5-10 times till it get annoying, then stick it up in your room
(EXAM)Please describe the process using Stereolithography to print ceramics
using photosensitive resin filled up with ceramic particles.
Example answers:
Load ceramic particles into a Photopolymer
Photopolymer acts as a binder
Layers are spread like a paste to make a green part
Green parts are then fired to remove binder and sinter ceramic component
together
(1 mark is given to each point)
(EXAM)Carbon is a company invented CLIP (Continuous Liquid Interface
Production) based on bottom-up projection Stereolithography. Using
CLIP, the company can print components without the peeling process.
Please describe the reasons why the peeling process is necessary
for bottom-up Stereolithography and why it can be avoided in CLIP?
Liquid resin contains monomer photoinitiator and inhibitor. Inhibitor is a chemical
that prevents polymerization in the presence of oxygen.
Using the bottom-up projection SLA, because there is no oxygen down in the
bottom of the resin, the current layer will adhere to the surface of the vat,
damaging the part. Peeling process is therefore needed.
In CLIP, they use a special window of the bottom of the vat. This window is
oxygen permeable.
A dead zone is form on the bottom in which resin cannot be cured. In this case
the peeling process is not needed.
