Lecture 7 Flashcards
What are the two photo-polermerisation processes?
Stereolithography
Jetting (Objet)
What does stereolithography mean?
3 - dimensional printing
the term covers a range of similar processes
When did the first commercial Stereolithography AM process come available?
in the late 80’s
What are the generic pricipals for Sterolithography?
Photo-curable resin
Exposed to UV/visible light source
Leads to phase change in the resin to solidify the layer
(UV laser scans surface of photo-curable resin to produce cross-section)
Who is the main supplier to the west for Sterolithograpy?
Main Western supplier is 3D Systems
(major focus here)
What are the general parts of the process for steriolithography
Position perforated build platform
Fill resin vat & ensure no bubbles
Import .stl file, orientate & add supports
Laser-scan required cross-section of resin (first few layers will be lattice-type supports)
Lower build platform by one layer
Wiper blade spreads new layer of resin
Remove platform & parts from machine
Post-process
What is the general for post processing in sterolithography?
Parts (still attached to platform) immersed in
chemical solution to remove excess resin
Remove parts (and supports) from build platform & post-cure parts in UV oven
Remove supports (manual process e.g. snap off by hand, scalpel etc.)
Finishing (e.g. sanding, painting etc.)
What are the advantages of stereolithography?
Structural integrity of parts
Parts have undergone a chemical change
Can be used for functional testing/use
Usable for tooling (e.g. injection moulding)
Relatively good surface finish (especially top surface)
Well-established process
(Often people simply stick to what they know!)
What are the limitations of Sterolithography?
Support removal restricts geometry & affects down-facing surfaces
Hazardous materials
Post-processing time & equipment
- Adds time & cost
- More chance of damage
2D nesting only
What is different about mammoth SL to normal stereolithography?
Designed (Materialise) to meet demand for large scale parts
Previously individual sections would be produced and glued together
Maximum part size 2100 x 680 x 800 mm
‘Curtain re-coating’ - Reservoir of resin moves across surface of bed to deposit new layer – less problems than with wiper system
Patterns for vacuum forming, low volume
production of large, complex parts
What are some general pros and cons to desktop stereolithography systems?
Small number of desktop SL systems starting to
appear
Better surface finish/resolution than extrusion-based systems
higher machine costs & materials than other systems
What does the Envisiontec Perfactory system do differently to standard stereolitoghraphy systems?
Digital Light Processing technology
Often found in theatre projection systems
Array of micro-mirrors directs UV light onto surface of resin
Modify grey-scale to control cure
Builds ‘upside down’ - No need for levelling/recoating - Minimise supports
Small, accurate systems, particularly useful for
dental, jewellery, hearing aids, etc
.
(stereolithography question)
What are Digital Wax and what systems used for?
Small SL systems, specifically designed for dental & jewellery applications
Range of resins for lost-wax casting, ceramic resin for dental applications
Also builds ‘upside down’
(Stereolithography technique)
What are the general techniques for using solid ground curing?
Resin covered with mask, and subjected to UV light
Excess liquid removed from layer
Gaps filled with wax
Layer machined prior to next layer
Complexity & material wastage led to their demise!!
(Stereolithography technique)
What is the Araldite Digitalils system, how does it work?
Uses MicroLight Switch technology
UV light fed through fiber optics to 40,000 microshutters
Light directed onto surface of photopolymer, all at 90°
High resolution (micron-sized spots)
Full bed exposed simultaneously (think back to rationale behind HSS…)
Process designed around the material by material specialists (Huntsman)
3D systems aquired Huntsman Materials division including this - not heard much since
What is a major area of research in stereolithography at the moment?
Interest in multi-photon polymerisation
Small (micron-scale) parts
E.g. nerve guidance channels for nerve repair
Cellular scaffolds
What are the major companies involved in Jetting?
Major process owned and commercialised by Objet Geometries (Israel)
Objet merger with Stratasys
Polyjet & Polyjet Matrix technologies
What is involved in the jetting process?
Printhead jets droplets of build (and support) material in required cross-section
Layer is immediately UV-cured
What is involved with Polyjet matrix (Connex) systesms?
Two materials (e.g. rigid, flexible, transparent or a combination) combined in varying ratios within the same build
Allows production of variable properties throughout a single part
Functional grading? (Not quite yet)
Full colour? (Apparently ‘on its way’)
What are the advantages of the Jetting process?
Fast build rates (small parts)
Use in office environment
Can produce good accuracy / small features
Functional grading (some processes)
What are the limitations of the jetting process
Can be slow for large build areas
Support removal can be an issue
Cost of systems & materials can be high
Recycled material cannot generally be used–materials are highly filtered
What are some Photo-polymerisation applications?
Jewellery - Often used as patterns for casting - Some use as direct production - Reduced manufacturing constraints and small, intricate features
Dental - E.g. 3Dent ™ dental printer from Envisiontec - Small build volumes, but accurate parts…
Consumer trials - E.g. Objet Connex product prototypes - More realistic testing is possible when materials are similar to real life…
Exhibition pieces - E.g. replica of King Tutankhamun (Mammoth SL) - Allows much wider audience for rare/delicate items - Much of this type of activity is based upon other areas (e.g. medical imaging)
There has been a move away from the one machine does everything approach to AM - what has there been a move towards?
- design a small, high accuracy machine for
production of small, intricate parts - Large machine for bigger, less complex parts
