Lecture 7 Flashcards
4 main print methods
- Photocuring
- Jetting based
- Extrusion based
- Sinter based
4 key steps of photpolymerization
Exposure
initiation
Chain growth
Temination
Exposure
Initiation
Chain growth
Termination
What is oxygen inhibitation?
When oxygen is present in the photopolymerisation process
What is the core process of photpolymerisation?
layer-by-layer hardening through light source (typically UV)
Once a layer is hardened, teh build platform (or the light source moves to expose a new layer of liquid resin
What is top-down printing? Pros & Cons?
- Light source shines form above onto resin
- Build platform lowers as each layer is built
- Pros: Larger print area, ideal for thicker layers, less stress on part
- Cons: Hihg resin volume requiredd, gravity can affect layer consistency
What is bottom-up prinitng? Pros & Cons?
- Light source shines from below, through transparent surface
- Build platform lifts with each layer
- Pros: Lower resin usage; better for thinner layers, higher resolution layers
- Cons: May require strong adhesion to counteract peeling forces during lifting (weight of the part hanging upside down)
Bottom-up printing process (general)
- Positioning (to determine the layer height)
- Exposure (UV curing of the resin to create layer)
- Peeling (cured layer is seperated from the bottom of the Vat)
- Lifting (and reflow of resin)
- Pause (Time for resin to cool and stabilise)
Repeat
Which 3D printing methods use vat polymerisation?
- Stereolithography (SLA)
- Digital Light Processing (DLP)
- Liquid Crystal Display (LCD)
How does SLA work?
A laser beam selectively cures teh liquid resin spot-by-spot
How does DLP work?
A projector casts light over the entire layer to cure it all at once
How does LCD work?
An LCD screen masks a projector’s light and cures entire layers at a time
Pros of SLA
- Smoth surface finish
- High resolution
- Controlled heat dissipation (time for heat to dissipate as teh laser moves, reducing heat buildup)
- Consistent quality across the paint bed
- Wide range of material compatibility
Cons of SLA
- Slower print speeds
- Higher costs
- Complex electromechanical system (high maintenance and susceptibility to failure)
- Limited build volume
Pros of DLP
- Speed (cures whole layer at a time)
- No light bleed (unused light directed away)
- Quick layer times
- Low complexity
- Wide range of material compatibility
- Continous layer manufacturing possible
Cons of DLP
- Higher costs
- Build soze constraints
- Heat generation (wastes energy and heats up work area)
- Pixalation
Pros of LCD printing
- Cheap
- No moving parts
- Very compact (LED can be placed directly below the bed)
- High resolution
Cons of LCD printing
- Lightbleed (LCD pixels are never truly opaque)
- Low light energy (longer layer times)
- Exposure uniformity
- Pixalation (due to resolution of the display)
- Specialised resins needed
Photopolymer jetting
What is thermoplastic?
Type of polymer that becomes moldable upon heating and solidifies upon cooling.
Process can be repeated multiple times, allowing thermoplastics to be reshaped and reprocessed without significantly altering their chemical structure
Thermoplast:
Material that conists of linear pr branched polymer chains that are not chemically bonded to each other
This allows them to be remelted and reshaped
Duroplasts:
Material that is composed of a network of polymer chains that are chemically bonded together during teh curing process.
Once set, the bonds create a rigid structure that cannot be remelted ot reshaped
Why are thermoplasts used in 3D printing?
It allows for the layer-by-layer constuction of a part. The layer below th elayer that is currently being printed needs to be partly melted to bond the new layer to it
This would be impossible with duroplats
What are the common diameters of Fused Deposition Modelling (FDM) or Fused Filament Fabrication (FFF) or Material Extrusion (ME)?
Common diameters of 1.75 mm and 2.85 mm
These materials often contain additives to conteract unwanted properties
What are the 2 common types of ectruders?
Direct drive
Bowden tube
What is a “Direct Drive” extruder?
The motor and gears are placed in the moving printhead
Pros: Short distance to printhead, flexible materials can be printed, increased extrusion precision
Cons: Increased weight on head, more vibrations, lower printing speeds
What is a “Bowden Tube” extruder?
Extruder assembly is fixed to the machine and connected to the printhead with a tube
Pros: Lighter printhead, faster printing speeds, less vibrations
Cons: Flexible materials compress or get stuck, extrusion is inprecise due to “wiggleroom” in the tube
In FDM, which 2 parameters does the nozzle diameter affect?
Quality: smaller diameters produce finer details. (It also reduces the corner radius!!)
Strength: Larger diameters result in stronger prints by extruding thicker lines
What are the 3 movement systems for FDM?
- Cartesian system: Most common (moves in straight lines along each axis independently)
- CoreXY: Faster using one belt for X and Y movement for reduced weight on the print head
- Delta printers: 3 arms control movement, ideal for fast and smooth motion in circular or cylindrical prints
Why is a print bed heated?
When a material cools, it naturally shrinks, creating tension at the edges which can generate an upward force that makes layer peel and curl.
A heated bed keeps the part expanded and reduces this tension.
Parts are normally not printed completely solid. What is normally added?
Infill, with a predefined infill density and pattern (often with a characteristic staircase pattern)
