Rapid Freeze Prototyping is a process that builds 3D ice parts by depositing water droplets layer-by-layer in a sub-zero temperature environment. The objectives of this research were to understand the physics of the process, develop strategies to reduce build time and improve accuracy, and identify suitable support materials. Sugar solution was found to be a better support material than salt solution. Methods to increase heat transfer, such as chilling plates and liquid nitrogen cooling, significantly reduced build time by allowing faster layer deposition. The process shows potential for applications like investment casting of metal parts.

1. Rapid Freeze Prototyping

2. Objectives
• Generating a scientific understanding of the
physics of the RFP process.
• Developing a part building strategy to reduce
build time and increase dimensional accuracy.
• Identifying the support material for fabrication
of complex 3D ice parts.
• Developing techniques for investment casting
with ice patterns.

3. Process parameters:
Freezer temperature: .20 °C.
Nozzle frequency: 200 to 900 Hz
The technology, called Freeze Cast
Process (FCP), was developed by
DURAMAX Co.

5. Slant Wall Building and Vertical Wall
Building

6. Properties of support material
Qualities of support material:
• Should not be soluble in water
• A similar contact angle to water
• Non-toxic and environmentally benign
• Easily obtainable and Easily removable

7. Phase diagram of salt
solution
Phase diagram for sugar
solution

8. Comparison between Sugar and Salt support material
• The salt solution became the first choice due to the larger range
in which can remove the support material and leave the ice as
was originally deposited.
• A known amount of water was frozen completely, then a known
amount of the support material was placed on top of the ice in
the container and allowed to freeze. This was done in a –60° C
freezer to ensure that both materials were completely frozen. The
results of these experiments showed that the salt solution would
not be an acceptable choice because it degraded the ice part too
much.
• The difference in the mass of the ice from the end of the
experiment to the initial amount of water was less than 2.4% each
time for the sugar solution, but the difference was up to 40% for
the salt solution. Thus the sugar solution was deemed a suitable
choice for the support material

10. Effect of heat transfer on process
As heat transfer increases
• Much shorter wait times between build layers
• ensures that thin-walled ice structures could be built.
Methods to increase heat transfer
• Very significant reduction in part build time was achieved
using a chilling plate to increase the rate of cooling of
deposited water by conduction.
• coolant passages filled with liquid nitrogen to decrease
the substrate temperature.
• Forced convection implemented with the use of a fan to
circulate cold air produced desirable reduction of build
time but with undesirable formation of frost .

11. Advantages
• cheaper equipment and material
• cleaner material and process
• less energy consumption
• faster building speed
• better surface finish.

12. Different ice parts built by RFP

15. APPLICATIONS
• Investment Casting:

16. Conclusions
• A suitable support material has been identified and tested for use in the
Rapid Freeze Prototyping process. The support material identified is a
eutectic sugar solution.
• The rate of diffusion decrease as the ambient temperature decreases and
the change in the ice wall height due to the diffusion becomes negligible
when the temperature around the ice part being built is lower than -20 °
C.
• The variable parameters in RFP, i.e. the water feed rate and the scan
speed, can be altered to achieve the desired layer thickness, line width,
surface roughness and minimum
• The research result presented has shown that by increase of heat transfer,
much shorter wait times between build layers are possible than what
could be achieved previously in the Rapid Freeze Prototyping process.

17. References
• Wei Zhang, Ming C. Leu, “Investment Casting with Ice Patterns Made by Rapid
Freeze Prototyping” 66-72.
• Frances D. Bryant and Ming C. Leu, “Study on incorporating support material
in rapid freeze prototyping”, 416-427.
• Frances D. Bryant*, Guanghua Sui., and Ming C. Leu, “A study on effects of
process parameters in rapid freeze prototyping”, Rapid Prototyping Journal,
Vol. 9(2003) 19–23.
• Ming Leu, Sriram P. Isanaka, Von L. Richards, “Increase of Heat Transfer to
Reduce Build Time in Rapid Freeze Prototyping”, Dept. of Mechanical and
Aerospace Engineering, Missouri University of Science and Technology, USA,
219-230
• Zhang, W., Leu, M. C., Ji, Z., and Yan Y., “Rapid Freezing Prototyping with
Water,” Journal of Materials and Design, Vol. 20, June 1999.
• Fukai, J., Zhao, Z., Poulikakos, D., Megaridis, C., and Miyatake, O., "Modeling of
the Deformation of a Liquid Droplet Impinging Upon a Flat Surface," Physics of
Fluids A, Vol.5, 1993.
• Dorsey, N. E., “Properties of Ordinary Water-Substance in All Its Phases:
Water-Vapor, Water, and All the Ices,” 1940.
• Qingbin Liu, Ming C. Leu, “Finite Element Analysis of Solidification in Rapid
Freeze Prototyping” Journal of Manufacturing Science and Engineering, Vol.
129, AUGUST 2007, 810-820.