Lecture 7

Question 1

4 main print methods

Answer 1

• Photocuring
• Jetting based
• Extrusion based
• Sinter based

Question 2

4 key steps of photpolymerization

Answer 2

Exposure
initiation
Chain growth
Temination

Question 3

Exposure

Question 4

Initiation

Question 5

Chain growth

Question 6

Termination

Question 7

What is oxygen inhibitation?

Answer 7

When oxygen is present in the photopolymerisation process

Question 8

What is the core process of photpolymerisation?

Answer 8

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

Question 9

What is top-down printing? Pros & Cons?

Answer 9

• 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

Question 10

What is bottom-up prinitng? Pros & Cons?

Answer 10

• 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)

Question 11

Bottom-up printing process (general)

Answer 11

1. Positioning (to determine the layer height)
2. Exposure (UV curing of the resin to create layer)
3. Peeling (cured layer is seperated from the bottom of the Vat)
4. Lifting (and reflow of resin)
5. Pause (Time for resin to cool and stabilise)
   Repeat

Question 12

Which 3D printing methods use vat polymerisation?

Answer 12

• Stereolithography (SLA)
• Digital Light Processing (DLP)
• Liquid Crystal Display (LCD)

Question 13

How does SLA work?

Answer 13

A laser beam selectively cures teh liquid resin spot-by-spot

Question 14

How does DLP work?

Answer 14

A projector casts light over the entire layer to cure it all at once

Question 15

How does LCD work?

Answer 15

An LCD screen masks a projector’s light and cures entire layers at a time

Question 16

Pros of SLA

Answer 16

• 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

Question 17

Cons of SLA

Answer 17

• Slower print speeds
• Higher costs
• Complex electromechanical system (high maintenance and susceptibility to failure)
• Limited build volume

Question 18

Pros of DLP

Answer 18

• 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

Question 19

Cons of DLP

Answer 19

• Higher costs
• Build soze constraints
• Heat generation (wastes energy and heats up work area)
• Pixalation

Question 20

Pros of LCD printing

Answer 20

• Cheap
• No moving parts
• Very compact (LED can be placed directly below the bed)
• High resolution

Question 21

Cons of LCD printing

Answer 21

• 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

Question 22

Photopolymer jetting

Question 23

What is thermoplastic?

Answer 23

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

Question 24

Thermoplast:

Answer 24

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

Question 25

Duroplasts:

Answer 25

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

Question 26

Why are thermoplasts used in 3D printing?

Answer 26

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

Question 27

What are the common diameters of Fused Deposition Modelling (FDM) or Fused Filament Fabrication (FFF) or Material Extrusion (ME)?

Answer 27

Common diameters of 1.75 mm and 2.85 mm These materials often contain additives to conteract unwanted properties

Question 28

What are the 2 common types of ectruders?

Answer 28

Direct drive Bowden tube

Question 29

What is a "Direct Drive" extruder?

Answer 29

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

Question 30

What is a "Bowden Tube" extruder?

Answer 30

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

Question 31

In FDM, which 2 parameters does the nozzle diameter affect?

Answer 31

Quality: smaller diameters produce finer details. (It also reduces the corner radius!!) Strength: Larger diameters result in stronger prints by extruding thicker lines

Question 32

What are the 3 movement systems for FDM?

Answer 32

- 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

Question 33

Why is a print bed heated?

Answer 33

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.

Question 34

Parts are normally not printed completely solid. What is normally added?

Answer 34

Infill, with a predefined infill density and pattern (often with a characteristic staircase pattern)