Polymers 1 - Powder Based Processes Flashcards
List all basic powder based polymer AM processes
- Z-printing (not actually polymers, but you should see why I’ve included it here!)
- Laser Sintering
- High Speed Sintering (in process of commercialisation)
- Others (a brief mention)
What is the history of Z printing?
- 1993 - core technology developed at MIT
- Licensed the technology to a number of companies for different applications/material
- In this lecture, focus is on plaster/starch-based materials
- (Similar process also used for metals & ceramics)
- Technology licensed to Z-Corporation for production of commercial systems; 3D Systems now owns Z-Corporation…
What happens during z-printing?
‘Layer-by-layer approach to selectively bind and adhere layers of powder to form a solid object’
In simpler terms
Use an ink-jet printhead to deposit a binder (glue) onto the required cross-section.
What are the process steps of z-printing?
- Deposit a layer of powder
- Print cross-section
- Drop platform by one layer & deposit next layer of powder
or more analytically
- Fill powder supply area with loose powder
- Check and/or replace binder cartridge
- Import .stl file & add colour if relevant
- Deposit layer of powder from powder supply area
- Print binder onto cross-section
- Lower powder bed piston by one layer
- Raise powder delivery piston & deposit next layer of powder
- Remove part from powder ‘cake’
- Post-process
What is the post-processing required for z-printing?
- Vacuum/wash away loose powder (gently!)
- This leaves you with a ‘green’ part;
a) Relatively weak
b) Porous - Often infiltrate (e.g. with wax/epoxy) for:
a) Strength
b) Colour vividness
What are the advantages of z-printing?
- Office-friendly (Low heat, noise etc.)
- Ease of use:
a) Does not require large amounts of training
b) E.g. easier to use for whole design team - Speed – use of ink-jet technology allows relatively fast printing of build volume
- System & material costs relatively low
- Can print full-scale colour!
What are the limitations of z-printing?
- Weakness of ‘green’ part
a) Can lead to damage during clean-up
b) Limitations on thin features - Generally low mechanical properties when compared with other AM processes
- Only surface colour
What are the applications of z-printing?
Most often used for visualisation models, rather than structural parts
Many of its main uses are a direct result of ability to produce coloured parts
Some examples: • Architectural models • Consumer/ergonomic trials • Finite Element models • Medical applications (developing)
What is z-printing most used for?
Most often used for visualisation models, rather than structural parts; Many of its main uses are a direct result of ability to produce coloured parts
Examples of use of z-printing in industry?
- Architectural models
- Consumer/ergonomic trials
- Finite Element models
- Medical applications (developing)
Why is z-printing used for architectural models?
- Often one-off models so it’s good for time and cost savings especially over the labour intensive hand-crafting!
- Much easier visualisation than 2D plans or even 3D CAD model for e.g. to inform general public/tendering processes
- Detail (people, trees)
- colour capacity!
Which process would you use for a consumer trial?
z-printing as colour is a real benefit; enhanced realism, can test colour preferences with focus group
How can z-printing be used in FE analysis?
E.g. apply FEA stress plot to surface of part
• Useful for visualisation & to aid in re-design process
• Can extend this to testing – does your part fail in the same place as your model predicts?
• Consumer use – looks ‘a bit sciencey’…
How can we use z-printing in medical applications?
E.g. surgical practice:
• Reproduce similar visual appearance
• Similar ‘feel’ – different materials/binders?
• Appearance during 3D imaging
What is the history of Laser Sintering
- Process patented by Ross Householder in 1979
- Carl Deckard (University of Texas) continued this work
- First commercial machine produced by DTM Corporation in 1992 (later ‘merged with’ 3D Systems)
Can laser sintering be used similarly in metals or other materials that are not polymers?
Yes!
Who are the current main suppliers of Laser Sintering systems?
3D Systems (Selective Laser Sintering ®) and EOS GmbH but WATCH OUT FOR PATENTS EXPIRING!
Large overlap between capabilities and materials of each supplier!
How do the EOS and 3D Systems Laser Sintering systems differ from each other?
- Large overlap between capabilities and materials of each supplier
- Differences:
a) pre-heating of powder (3D Systems)
b) Blade for powder deposition (EOS) vs roller system (3D Systems)
What happens during the laser sintering process?
Parts built by selectively scanning and sintering cross- sections of powdered material
Normally conducted in a nitrogen atmosphere
Why does Laser Sintering take place in a nitrogen atmosphere?
- Safety
2. Oxidation
What is the step by step process of Laser Sintering?
- Fill powder supply area with loose powder
- Pre-heat powder (and sometimes feed area)
- Import .stl file & nest/orientate parts
- Deposit layer of powder from powder supply area
- Scan cross-section with CO2 laser
- Lower powder bed piston by one layer
- Raise powder delivery piston & deposit next powder layer
- Cool-down
- Remove part from powder ‘cake’
- Post-process
What is the typical post processing requirement for Laser Sintering?
- Brush away loose powder
- Common to bead-blast parts to remove remaining powder/improve surface finish
- Depending on material – un-used powder can be recycled to an extent
What are the advantages of Laser Sintering for polymers?
- No need for supports (self supporting process for polymers!)
- Allows more complex designs;
a) Assemblies produced as one
b) Less post-processing required
c) Time-saving
d) Better surface finish on down-facing surfaces - Relatively high mechanical properties & stability of properties
- Build through build volume (not area)
What are the limitations of Laser Sintering for polymers?
- Surface finish of parts
- Speed of process (setup and pre-heat; laser scan time for cross sections)
- Material changeover on older systems
- Warpage of parts
- Mechanical properties affected by thermal variations
- Powder can have health & safety issues
