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Additive Manufacturing > Polymers 2 - Photopolymerisation Processes > Flashcards

Polymers 2 - Photopolymerisation Processes Flashcards

1
Q

Which are the most important photo-polymerisation processes?

A
  1. Stereolithography

2. Jetting (Objet)

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2
Q

What does stereolithography mean?

A

Greek origin it means ‘3-dimensional printing’

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3
Q

What is the history of stereolithography?

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

2. Term covers a range of similar processes

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4
Q

Does the term stereolithography refer to one process?

A

Term covers a range of similar processes

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5
Q

What is the generic principle of stereolithography?

A

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

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6
Q

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

A

3D Systems

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7
Q

What is the working principle of stereolithography?

A

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

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8
Q

Describe the process of stereolithography step-by-step

A
  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
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9
Q

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

A
  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.)
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10
Q

What are the advantages of stereolithography?

A
  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!)
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11
Q

What are the limitations of stereolithography?

A
  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
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12
Q

What are the characteristics of the Mammoth SL machine?

A
  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
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13
Q

What are the applications of the Mammoth SL machine?

A

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

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14
Q

Are there any desktop stereolithography printers?

A
  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!

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15
Q

What is the Envisiontec Perfunctory process

A
  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
  1. Builds ‘upside down’ so no need for levelling/recoating
    and minimal support requirement
  2. Small, accurate systems, particularly useful for dental, jewellery, hearing aids, etc.
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16
Q

What are the digital wax systems?

A
  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’
17
Q

Describe the Solid Ground Curing process

A
  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!!
18
Q

Describe the Araldite Digitalis technology

A
  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…)
19
Q

Who developed the Araldite Digitalis technology?

A

Developed by Huntsman (material specialists)

3D Systems acquired Huntsman Materials Division, including this

Not heard much since…!

20
Q

What is the background to jetting?

A
  1. Major process owned and commercialised by Objet Geometries (Israel)
  2. Objet merger with Stsratasys
  3. Polyjet & Polyjet Matrix technologies
21
Q

Mention all stereolithography system technologies available on the market!

A
  1. Araldite Digitalis
  2. Solid Ground Curing
  3. Digital Wax
  4. Envisiontec Perfunctory
  5. Mammoth SL
22
Q

Describe the working principle of the jetting technology!

A
  1. Printhead jets droplets of build (and support) material in required cross-section
  2. Layer is immediately UV-Cured
23
Q

Mention all jetting system technologies available on the market!

A

Polyjet & Polyjet Matrix technologies (Objet + Stratasys)

24
Q

How do Polyjet matrix (Connex) systems function?

A
  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
25
Q

What are the benefits of jetting?

A
  1. Fast build rates (small parts)
  2. Use in office environment
  3. Can produce good accuracy / small features
  4. Functional grading (some processes)
26
Q

What are the limitations of jetting?

A
  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
27
Q

What are the applications of photo polymerisation?

A
  1. Jewellery
  2. Dental
  3. Consumer trials
  4. Large-scale tooling
  5. Exhibition pieces
28
Q

How can we use photo polymerisation in jewellery?

A
  1. Often used as patterns for casting
  2. Some use as direct production
  3. Reduced manufacturing constraints and small, intricate features
29
Q

How can we use photo polymerisation in dental applications?

A

E.g. 3Dent TM dental printer from Envisiontec

Small build volumes, but accurate parts…!

30
Q

How can we use photo polymerisation in consumer trials?

A

E.g. Objet Connex product prototypes

More realistic testing is possible when materials are similar to real life…

31
Q

How can we use photo polymerisation in large scale tooling?

A

E.g. Tushino Power Machine Tools, casting of custom turbines from an SL master

‘Burnout’ mass reduced by use of honeycomb structure

32
Q

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

A

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)

Additive Manufacturing (9 decks)

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