Polymers 2 - Photopolymerisation Processes

Question 1

Which are the most important photo-polymerisation processes?

Answer 1

1. Stereolithography

2. Jetting (Objet)

Question 2

What does stereolithography mean?

Answer 2

Greek origin it means ‘3-dimensional printing’

Question 3

What is the history of stereolithography?

Answer 3

1. First commercial AM process - available since late 80s

2. Term covers a range of similar processes

Question 4

Does the term stereolithography refer to one process?

Answer 4

Term covers a range of similar processes

Question 5

What is the generic principle of stereolithography?

Answer 5

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

Question 6

Who is the main supplier of stereolithography systems in the west?

Answer 6

3D Systems

Question 7

What is the working principle of stereolithography?

Answer 7

UV laser scans surface of photo-curable resin to produce cross-section

Question 8

Describe the process of stereolithography step-by-step

Answer 8

1. Position perforated build platform
2. Fill resin vat & ensure no bubbles
3. Import .stl file, orientate & add supports
4. Laser-scan required cross-section of resin (first few layers will be lattice-type supports)
5. Lower build platform by one layer
6. Wiper blade spreads new layer of resin
7. Remove platform & parts from machine
8. Post-process

Question 9

What are the typical post-processing requirements for stereolithography processes?

Answer 9

1. Parts (still attached to platform) immersed in chemical solution to remove excess resin
2. Remove parts (and supports) from build platform & post-cure parts in UV oven
3. Remove supports (manual process e.g. snap off by hand, scalpel etc.)
4. Finishing (e.g. sanding, painting etc.)

Question 10

What are the advantages of stereolithography?

Answer 10

1. Structural integrity of parts:
   • Parts have undergone a chemical change
   • Can be used for functional testing/use
   • Usable for tooling (e.g. injection moulding)
2. Relatively good surface finish (especially top surface)
3. Well-established process (Often people simply stick to what they know!)

Question 11

What are the limitations of stereolithography?

Answer 11

1. Support removal restricts geometry & affects down- facing surfaces
2. Hazardous materials
3. Post-processing time & equipment which add time and cost and risk for damage
4. 2D nesting only

Question 12

What are the characteristics of the Mammoth SL machine?

Answer 12

1. Designed by Materialise to meet demand for large scale parts
2. Previously individual sections would be produced and glued together
3. Maximum part size 2100 x 680 x 800 mm
4. ‘Curtain re-coating’
5. Reservoir of resin moves across surface of bed to deposit new layer – less problems than with wiper system

Question 13

What are the applications of the Mammoth SL machine?

Answer 13

Patterns for vacuum forming, low volume production of large, complex parts

Question 14

Are there any desktop stereolithography printers?

Answer 14

1. Small number of desktop SL systems starting to appear
2. Better surface finish/resolution than extrusion-based systems
3. But… somewhat higher machine costs & materials

Time will tell whether these really take off!

Question 15

What is the Envisiontec Perfunctory process

Answer 15

1. 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

2. Builds ‘upside down’ so no need for levelling/recoating
   and minimal support requirement
3. Small, accurate systems, particularly useful for dental, jewellery, hearing aids, etc.

Question 16

What are the digital wax systems?

Answer 16

1. Small SL systems, specifically designed for dental & jewellery applications
2. Range of resins for lost-wax casting, ceramic resin for dental applications
3. Also builds ‘upside down’

Question 17

Describe the Solid Ground Curing process

Answer 17

1. Resin covered with mask, and subjected to UV light
2. Excess liquid removed from layer
3. Gaps filled with wax
4. Layer machined prior to next layer
5. Complexity & material wastage led to their demise!!

Question 18

Describe the Araldite Digitalis technology

Answer 18

1. MicroLight Switch technology; UV light fed through fiber optics to 40,000 micro shutters; Light directed onto surface of photopolymer, all at 90°
2. It is High resolution (micron-sized spots)
3. Full bed exposed simultaneously (think back to rationale behind HSS…)

Question 19

Who developed the Araldite Digitalis technology?

Answer 19

Developed by Huntsman (material specialists)

3D Systems acquired Huntsman Materials Division, including this

Not heard much since…!

Question 20

What is the background to jetting?

Answer 20

1. Major process owned and commercialised by Objet Geometries (Israel)
2. Objet merger with Stsratasys
3. Polyjet & Polyjet Matrix technologies

Question 21

Mention all stereolithography system technologies available on the market!

Answer 21

1. Araldite Digitalis
2. Solid Ground Curing
3. Digital Wax
4. Envisiontec Perfunctory
5. Mammoth SL

Question 22

Describe the working principle of the jetting technology!

Answer 22

1. Printhead jets droplets of build (and support) material in required cross-section
2. Layer is immediately UV-Cured

Question 23

Mention all jetting system technologies available on the market!

Answer 23

Polyjet & Polyjet Matrix technologies (Objet + Stratasys)

Question 24

How do Polyjet matrix (Connex) systems function?

Answer 24

1. Two materials (e.g. rigid, flexible, transparent or a combination) combined in varying ratios within the same build
2. Allows production of variable properties throughout a single part
3. Functional grading? (Not yet perfect)
4. Full colour systems now available

Question 25

What are the benefits of jetting?

Answer 25

1. Fast build rates (small parts) 2. Use in office environment 3. Can produce good accuracy / small features 4. Functional grading (some processes)

Question 26

What are the limitations of jetting?

Answer 26

1. Can be slow for large build areas 2. Support removal can be an issue 3. Cost of systems & materials can be high 4. Recycled material cannot generally be used – materials are highly filtered

Question 27

What are the applications of photo polymerisation?

Answer 27

1. Jewellery 2. Dental 3. Consumer trials 4. Large-scale tooling 5. Exhibition pieces

Question 28

How can we use photo polymerisation in jewellery?

Answer 28

1. Often used as patterns for casting 2. Some use as direct production 3. Reduced manufacturing constraints and small, intricate features

Question 29

How can we use photo polymerisation in dental applications?

Answer 29

E.g. 3Dent TM dental printer from Envisiontec Small build volumes, but accurate parts...!

Question 30

How can we use photo polymerisation in consumer trials?

Answer 30

E.g. Objet Connex product prototypes More realistic testing is possible when materials are similar to real life...

Question 31

How can we use photo polymerisation in large scale tooling?

Answer 31

E.g. Tushino Power Machine Tools, casting of custom turbines from an SL master ‘Burnout’ mass reduced by use of honeycomb structure

Question 32

How can we use photo polymerisation in large scale exhibition pieces?

Answer 32

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)