Polymers 2 - Photopolymerisation Processes Flashcards
Which are the most important photo-polymerisation processes?
- Stereolithography
2. Jetting (Objet)
What does stereolithography mean?
Greek origin it means ‘3-dimensional printing’
What is the history of stereolithography?
- First commercial AM process - available since late 80s
2. Term covers a range of similar processes
Does the term stereolithography refer to one process?
Term covers a range of similar processes
What is the generic principle of stereolithography?
Photo-curable resin exposed to UV/visible light source.
This exposure leads to phase change in the resin to solidify in the layer.
Main western supplier of stereolithography systems is 3D Systems
Who is the main supplier of stereolithography systems in the west?
3D Systems
What is the working principle of stereolithography?
UV laser scans surface of photo-curable resin to produce cross-section
Describe the process of stereolithography step-by-step
- 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 are the typical post-processing requirements for stereolithography processes?
- 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 stereolithography?
- Support removal restricts geometry & affects down- facing surfaces
- Hazardous materials
- Post-processing time & equipment which add time and cost and risk for damage
- 2D nesting only
What are the characteristics of the Mammoth SL machine?
- Designed by 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
What are the applications of the Mammoth SL machine?
Patterns for vacuum forming, low volume production of large, complex parts
Are there any desktop stereolithography printers?
- Small number of desktop SL systems starting to appear
- Better surface finish/resolution than extrusion-based systems
- But… somewhat higher machine costs & materials
Time will tell whether these really take off!
What is the Envisiontec Perfunctory process
- SL process with digital light 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’ so no need for levelling/recoating
and minimal support requirement - Small, accurate systems, particularly useful for dental, jewellery, hearing aids, etc.
What are the digital wax systems?
- 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’
Describe the Solid Ground Curing process
- 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!!
Describe the Araldite Digitalis technology
- MicroLight Switch technology; UV light fed through fiber optics to 40,000 micro shutters; Light directed onto surface of photopolymer, all at 90°
- It is High resolution (micron-sized spots)
- Full bed exposed simultaneously (think back to rationale behind HSS…)
Who developed the Araldite Digitalis technology?
Developed by Huntsman (material specialists)
3D Systems acquired Huntsman Materials Division, including this
Not heard much since…!
What is the background to jetting?
- Major process owned and commercialised by Objet Geometries (Israel)
- Objet merger with Stsratasys
- Polyjet & Polyjet Matrix technologies
Mention all stereolithography system technologies available on the market!
- Araldite Digitalis
- Solid Ground Curing
- Digital Wax
- Envisiontec Perfunctory
- Mammoth SL
Describe the working principle of the jetting technology!
- Printhead jets droplets of build (and support) material in required cross-section
- Layer is immediately UV-Cured
Mention all jetting system technologies available on the market!
Polyjet & Polyjet Matrix technologies (Objet + Stratasys)
How do Polyjet matrix (Connex) systems function?
- 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 yet perfect)
- Full colour systems now available
What are the benefits of jetting?
- Fast build rates (small parts)
- Use in office environment
- Can produce good accuracy / small features
- Functional grading (some processes)
What are the limitations of jetting?
- 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 the applications of photo polymerisation?
- Jewellery
- Dental
- Consumer trials
- Large-scale tooling
- Exhibition pieces
How can we use photo polymerisation in jewellery?
- Often used as patterns for casting
- Some use as direct production
- Reduced manufacturing constraints and small, intricate features
How can we use photo polymerisation in dental applications?
E.g. 3Dent TM dental printer from Envisiontec
Small build volumes, but accurate parts…!
How can we use photo polymerisation in consumer trials?
E.g. Objet Connex product prototypes
More realistic testing is possible when materials are similar to real life…
How can we use photo polymerisation in large scale tooling?
E.g. Tushino Power Machine Tools, casting of custom turbines from an SL master
‘Burnout’ mass reduced by use of honeycomb structure
How can we use photo polymerisation in large scale 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)
