Ch.8 Binder Jetting Flashcards
Why are support structures not needed in the BJ process?
Parts are self-supporting in the powder bed
List several characteristics of a good binder material.
- easily printable
- good adhesion to previous printed layer
- contain color for attractive prints
- high chemical/thermal/corrosion resistance
- water-based binder+plaster powder: low-cost parts
- liquid-based binder+PMMA powder: react at room temperature
- wax-based binder+PMMA powder: good pattern burnout for investment casting
- polymer binder+metal
What are the functions and characteristics of an infiltrant?
Infiltrants are used as a post-processing step to achieve better mechanical properties, patterns for investment casting, or desired stiffness properties.
How do the characteristics and functions differ for metal and polymer binder jetting processes?
Polymer binder:
for investment casting
3D systems: part stiffer, not as strong, and lower elongation.
Metal binder:
bronze- make part fully dense
metal in ceramic to form ceramic-metal composites
Describe the purpose of each of the three furnace cycles in metal binder jetting processes.
1st cycle: low temp burn off polymer binder
2nd cycle: high temp lightly sinter metal particles (60% dense)
3rd cycle: infiltrate part with a low melting temp alloy (ex. Bronze) to close pores (>90% dense parts)
Advantages of binder jetting
- small part volume dispensed through print head (BJ faster than MJ)
- Customization of different material combination of powder and binder
- Metal/ceramic slurries provide higher solid loading → better quality parts
- Bonding completes at room temperature → reduces shrinkage/cracks
- Large build volume
Disadvantages of binder jetting
- need to distribute powder after each layer of binder printing adds an extra step
- Accuracy and surface finish lower compared to MJT
- More post-processing needed (additional infiltration, sintering, etc. steps)
Design specifications for BJ:
support
wall thickness
feature size
edges
details
no support
2mm, unsupported wall 3mm
2mm
2mm, length:20mm
0.5mm
Design specifications for BJ:
fillets
hole size
escape holes
1mm radius
diameter 1.5mm
diameter 5mm (at least 2 needed)
Design specifications for BJ:
shrinkage
porosity
accuracy
shrinkage
large parts: 3%
length >25: 0.8%-2%
porosity
after binder removal: 60% porous
internal porosity of end part achievable: 90-97%
accuracy
metal:0.2mm
full-color/sand:0.3mm
Design specs for Multi-jet fusion compared to SLS:
supports
accuracy
wall thickness
details
supports: no (SLS less prone to warping)
accuracy: 0.3%
wall thick: recommend 1mm
details: 0.25mm (SLS 0.3mm)
Design specs for MJF compared to SLS:
mechanical properties
cost
mech properties: MJF more homogenous
cost: MJF more cost efficient by 15%-30%
better for low density parts
SLS more cost efficient for nest and/or solid parts
