Ch.7 Material Jetting Flashcards
What are the 7 technical challenges of material jetting?
- Formulation of liquid material
- droplet formation (continuous to discrete droplet)
- droplet deposition control
- droplet liquid-to-solid conversion
- Deposition on top of previous layers (interact differently with diff surface or previous printed surface)
- nozzle clogging
- droplet density
What 5 methods can be used to process material to achieve desirable characteristic for material jetting?
additives
suspending particles in carrier liquid
dissolving in solvent
melting
mixing with prepolymers with polymerization initiator
What happens during droplet formation? What is it dependent upon?
- The process of converting material from liquid to discrete droplets
- Very sensitive to small changes
- Very dependent on the relationship between the printing parameters, material properties, and hardware used
What kind of problem can occur if the impact of the droplet is not controlled correctly?
- not viscous enough –> satellite droplets (splashing during flight)
- crown effect (splash on impact)
For precise droplet deposition control, what parameters must be accounted for?
motion, velocity, size of droplet
What does droplet liquid-to-solid conversion depend on?
phase change of material occurring during flight or soon after impact
Droplet interacts differently with different surfaces (build plate, previous layer, etc.) True or False
True
what can be done to fix nozzle clogging?
periodic purge/cleaning cycle
replaceable nozzles
For best print resolution, want small droplets close together. What kind of challenges does this pose?
- Requires high nozzle density
- Crosstalk: overlapping of thermal/pressure fields
- Multiple passes over the same area (alternative to high nozzle density)
How does the continuous stream process work compared to drop-on-demand?
CS:
- Steady pressure applied to fluid reservoir in which stream breaks into droplets due to Rayleigh instability
- Droplet deposition control by charged particles passing through deflection field
DOD:
- Pressure pulse induced to produce individual droplets directly exiting nozzle
- Thermal or piezoelectric used to create pressure pulse
What is the average droplet size and frequency rate for continuous mode vs. drop-on-demand?
CS:
- Typical diameter: 150 μm
- Frequency: 80-100 kHz
DOD:
- Typical diameter: 25-120μm
- Rate: 0-2000 drops/sec
What are the advantages and disadvantages of using a continuous stream?
A:
high throughput rate
D:
Material used must be able to carry charge
Fluid in catcher wasted or reprocessed depending on material type
What are the advantages and disadvantages of using drop-on-demand
A:
-Smaller droplet size
-Higher placement accuracy
D:
-Heating can damage sensitive material if thermal DOD is used
What is the printing indicator? How is it used? What does it depend on?
The printing indicator is the ratio between the Reynolds number over the square root of the Weber number.
printing indicator between 1 and 10 –> Printing successful
Printing indicator is a function of the density, orifice radius, surface tension, and dynamic viscosity.
In which case does viscosity or surface tension dominate based on the printing indicator?
Low PI = viscosity dominates
High PI = surface tension dominates
