6. Material Jetting

Question 1

What is material jetting?

Answer 1

Droplets of material selectively deposited

Question 2

What are the stages of material jetting?

Answer 2

1. Droplet ejection
2. Droplet flight
3. Drop impact
4. Drop spreading
5. Drop solidification

Question 3

What are the 2 types of material jetting? include subcategories

Answer 3

• Continuous
• Drop on demand:
  1.Piezoelectric
  2.Thermal

Question 4

Explain a continuous flow system.

Answer 4

• Constantly flowing
• Jet breaks into droplets
• If nothing is being printed, fluid returns to reservoir

Question 5

Explain drop on demand.

Answer 5

• Droplets produced directly from nozzle when required.

Question 6

Compare continuous and DoD material jetting.

Answer 6

Continuous:
- High speed graphical
applications

DoD:
- Main method for
material jetting
- Higher accuracy
- Smaller droplets
- Lower waste
- Wider range of
materials

Question 7

Explain the 2 types of drop on demand actuators.

Answer 7

Thermal actuators:
- Resistor used to heat liquid in reservoir

• Heating element creates bubble in reservoir causing a droplet to be forced out of the nozzle

Piezoelectric actuators:

• Material charged up due to mechanical stress
• The material changes shape causing size of reservoir to decrease forcing droplet out of nozzle

Question 8

Compare thermal actuation to piezoelectric actuation for drop on demand.

Answer 8

Thermal:

Pros: Cheaper print heads

Cons: burnt material on heating element reduces lifetime and performance, Thermal cycling causes degradation of material

Piezoelectric:

Pros: Wider range of materials, More viscous material

Question 9

What is jettability? how is it determined?

Answer 9

The parameter to asses a materials printability using material jetting.

Determined by:

Viscosity - low enough to fill reservoir quickly

Surface tension - high enough to prevent unwanted dripping from nozzle, low enough to allow droplet to break from nozzle

Assessed using Reynolds, Weber and Ohnesorge numbers.

Question 10

What are the issues with material jetting?

Answer 10

Ejection - inconsistent or no ejection

Flight - satellite formation or material drying out before impact

Impact - splashing, bouncing

Spreading - wettability (surface tension)

Solidification - coffee staining (particles formed in a hollow ring)

Question 11

What materials can be printed using material jetting?

Answer 11

• Polymers & waxes
• Metals and Ceramics
• Most common are UV cured materials (after printing)

Question 12

Describe Objet.

Answer 12

Polyjet technology that uses jetting to dispense photosensitive material.

Each layer is cured using UV light.

Question 13

What are the pros and cons of objet technology?

Answer 13

Advantages

• Dissolvable support structures
• Multi-materials
• Translucent and colored parts
• Different material properties
• Smooth surfaces
• Fast process

Disadvantages

• High material and equipment cost
• Wastage of material through roller leveling process.

Question 14

What are the pros of material jetting?

Answer 14

• Good part edge quality
• High resolution
• Possible with multi materials
• Multiple heads printing multiple materials
• Different mech properties

Question 15

What are the cons of material jetting?

Answer 15

Material properties are limiting, sometimes too weak

Question 16

What are some applications of material jetting?

Answer 16

• Concept models e.g shoe soles
• Jewellery
• Multi materials e.g medical models
• Shock absorption
• Gaskets, plugs and seals
• Over moulding
• Biomedical and optics
  Electronic packaging

Question 17

What are the material curing methods for material jetting?

Answer 17

• UV (Most common)
• Thermoset (Thermally cured)
• Thermoplastic (cure on cooling)