High Speed Sintering (HSS) 3D Printing and Importance of Powder Drop Interaction in manufacturing

A.G. Avhad, H. Tan
Washington State University,
United States

Keywords: HSS, 3D printing, powder substrate, porosity, absorption criteria

Summary:

High Speed Sintering (HSS) has emerged in recent years as a new powder-based additive manufacturing process similar to Selective Laser Sintering (SLS). In this Additive Manufacturing (AM) technique, a sintering material layer is printed using an inkjet printer and then sintering process is completed using thermal radiation, mostly infrared source. A prototype model based on the working model developed at the Loughborough University, UK, is built in our college. Considering the previous research on the HSS and its potential to be a highly efficient manufacturing method, we intend to understand every individual operation in detail to improve the current knowledge in HSS. HSS is an AM method inspired from the Inkjet Printing (IJP), 3D Printing (3DP) and Layer Manufacturing Technology (LMT) and it replaces the high energy laser devices as in the SLS process. As this is a powder based AM process involving the interaction of ink and the powder substrate, it becomes necessary to understand the importance of working fluids behaviour with sintering powder substrate (nylon powder PA2200). The fluidics part in the HSS manufacturing is believed to be crucial as the fluid is expected to be absorbed into the substrate powder layer as it happens in the IJP. Furthermore, the properties of powder substrate also play an important role in the process for fluid to get absorbed. A brief study has been done to illustrate a simplistic model to determine critical properties of liquid in order to get absorbed in the powder substrates. An interesting feature of this research discusses of the change in the absorption property of same fluid in the powder with different compaction. This in turn gives a new path in selecting a powder layer substrate with appropriate compaction for efficient manufacturing. Currently, our HSS 3D printing operations use the HP’s commercially available pigmented ink and nylon powder PA2200. The pigmented inkjet ink has isopropyl alcohol as one of its important component and hence we have used aqueous solutions of isopropyl alcohol for determining the critical absorption parameters for powder substrates with different porosities. These critical parameters help choose fluid with appropriate properties to be used with respective powder substrate bed to be absorbed. We also give a simple method to calculate that there is absorption and no evaporation. We have worked with millimetre sized fluid droplets and these results will further be compared when micron sized drops will be used.