Ch.6 Material Extrusion

Question 1

What are the 7 key features of extrusion-based AM systems?

Answer 1

material loading: pellets/powder/filament

liquidfication: heat/constant temp to keep material in a molten state

extrusion: flow function of nozzle geometry, material viscosity, pressure drop

solidification: gravity, surface tension, cooling, and drying affect part

positional control: planar plotting system

bonding: sufficient residual heat energy required

support generation: two forms- similar material or different material

Question 2

How does chamber and nozzle design affect the pressure and flow rate?

Answer 2

mass flow function of pressure drop, nozzle geometry, material viscosity

larger diameter –> more flow –> poor precision

pressure drop determined between chamber and surrounding

Question 3

Explain the challenges in determining the fill pattern based on these considerations:
- Start/stop
- offset
- gaps
- bonding

Answer 3

Start/stop:
- slight overfill and swelling in start/stop regions
- randomized

Offset:
- nozzle placed within outline by some offset to allow minimal overlap

Gaps:
- part weakened
- fill pattern not continuous, many changes in direction

Bonding:
must be laid close enough to adjacent for effective bonding

Question 4

What are the primary parameters that affect plotting and path control?

Answer 4

input pressure
temperature
nozzle diameter
material characteristics
gravity +others
temperature buildup within part

Question 5

Describe the trade-off between part precision and part strength with extrusion-based AM

Answer 5

part precision: smaller nozzle diameter, layer height, or decreased print speed (longer process time and build time)

part strength: increase infill/stronger fill pattern (increases cost, material used)

Question 6

Design considerations for material extrusion printing:
- supports & overhangs
- wall thickness

Answer 6

supports/overhangs: wall angles > 45
wall thickness: 0.8mm

Question 7

Design considerations for material extrusion printing:
- feature size
- corners
- holes

Answer 7

feature size: 2-3 times larger than nozzle diameter
corners: 45 degrees
holes: post-process to achieve desired hole diameter

Question 8

Design considerations for material extrusion printing:
- print orientation
- infill

Answer 8

print orientation: tension parallel to layer, bending normal to layers

infill: 18-20% adequate

Question 9

what are the different types of infill patterns?

Answer 9

rectangular, honeycomb: quick, strong in all directions
triangular: long print, desired for strength in walls
wiggle: desired for twist or compressive features