Name: Pushkar Kamble
Department: Mechanical Engineering
Program: Ph.D (4th year)
Name of supervisor: Prof. K P Karunakaran
About Project: Additive Manufacturing (AM) has grown out of its primary use as rapid prototyping technique. Several functional parts are being additively manufactured and used directly as a finished or semi-finished product in various ways. Apart from metals and polymers, several non-traditional materials are being explored for AM. Our research is mainly focused on additive manufacturing of ice using water or aqueous solutions of various materials. There are several applications of the ice AM products. Ice parts can be used as patterns for investment casting in place of wax. Ice is better in many aspects than wax. Ice contracts upon liquification, which helps in easy mould making where wax tends to expand and exerts force on the mould walls and increase cracking tendency in moulds. Wax releases harmful hydrocarbons during melting and burnout, whereas ice is environment friendly and evaporates without any trace. AM ice templates can be used to create microfluidic channels. Micro-scale ice templates can be poured with photopolymers that can be cured with light and ice is melted away to realize micro-channels in the polymeric parts. Support material removal for resin-based AM processes is a tedious task. Ice can be used as a support material for the polymer-based AM where photopolymer is model material. Water and photopolymer can be printed simultaneously. Once the AM of the part is completed, it can be simply maintained at room temperature to melt away the support structure.
Multi-jet deposition of ice is the novelty of the process. In several AM processes, the CAD model is sliced and the slice geometry is converted to g-code file that is sent to he controller. The material deposition head follows the paths as per the g-code and deposits the material as required. However, in multi-jet deposition approach we developed, the CAD model is sliced into a list of bitmap images. The images are rasterized and converted to the multi-jet printhead readable files. The bitmap data is stored as a sequence of the bits in the postscript file to operate the nozzles in the multi-jet printhead as per required. Multi-jet printhead moves over the substrate in the pre-programmed raster pattern with selective opening and closing the relevant nozzles as per the postscript file and deposits the material as per the raster image data. This approach is known as drop-on-demand (DoD) approach. Multi-jet printing of low-viscosity liquids like water has a lot of scope for exploration.
As a part of the research, we have made a prototype of the ice 3D AM machine. A commercial printhead is retrofitted as a material deposition head on the X-Y axes. X and Y axes are belt driven axes with NEMA 23 stepper motors as prime movers. Printhead system is mounted on the X axis. Z motion is given to the work platform with the help of ball screws driven by NEMA 23 stepper motors. The work envelope is properly insulated to maintain the temperature of the process at -20°C. Refrigeration system is used along with liquid N2 to cool the work space.
As a part of the case study, prismatic geometries are selected for AM. The results show that the multi-jet printing of the low viscosity liquids like water is possible. The parts with height 5mm are printed as a proof-of-concept experiments. The layer thickness is found to be 0.06 mm. The layer thickness can be controlled with DPI (dots-per-inch). Higher the DPI, higher is the layer thickness. The layer thickness of 0.06 mm can be achieved with 360 dpi. However, water tends to expand during phase change, hence the measured average part height is 5.18 mm. Hence, an approximate increase of 4% in the dimensions is observed.
Ice serves as a great non-proprietary, easily available, cheap and clean material for AM for the applications stated above. Investment casting of jewelry and dental implants is the main focus of the study on the application side. The specialized slurries and molding techniques are being explored that can suit the ice material. There are certain challenges in the ice AM. Cooling system is a challenge since the AM machines needs variable cooling rates. Humidity plays a key role in the surface texture of the ice; hence process humidity control is also challenge. Overcoming these challenges with focused research will bring breakthrough in the investment casting industry.