12/7/2015 Nicholas Meisel
School of Engineering Design, Technology, and Professional Programs (SEDTAPP)
The Pennsylvania State University
213J Hammond Building, University Park, PA, 16802, U.S.A.
nam20@psu.edu
ASME Member

Christopher Williams
Design, Research, and Education for Additive Manufacturing Systems Laboratory,
Virginia Tech
413D Goodwin Hall, 635 Prices Fork Road, Blacksburg, VA, 24061, U.S.A.
cbwill@vt.edu
ASME Member
The PolyJet material jetting additive manufacturing (AM) process is uniquely qualified to create complex, multi-material structures.  However, key manufacturing constraints need to be explored and understood in order to guide designers in their use of the PolyJet process including 1) minimum manufacturable feature size, 2) removal of support material, 3) survivability of small features during cleaning, and 4) the self-supporting angle in the absence of support material.  In this study, the authors used a series of experiments to identify statistically significant geometric and process parameters and how they impact part manufacturability.  Support material removal was found to be limited by the cross-sectional area of small channels in the part; a minimum cross-sectional area approximately equal to the diameter of the cleaning water jet spray results in the highest percentage of support material removed from small channels (Figure 1).  The process’s minimum resolvable feature size was shown to rely on surface finish and feature shape, as well as the interactions between surface finish and orientation, surface finish and feature direction, and orientation and feature direction.  If a designer can account for the ideal configuration of these variables, then it is possible to manufacture features that are half the size of a more general “worst-case” scenario.  Feature survivability during the cleaning process was tied to cross-sectional area (for rigid features) and feature connectivity (for flexible features), with flexible features requiring significantly larger feature diameters to survive when fixed at both ends.  Finally, the self-supporting angle in the absence of support material was driven by the orientation of the surface with respect to the roller in the print head assembly, with y-dominated specimens offering better self-supporting angles.  Experimental design studies such as these are crucial to provide designers with the knowledge to ensure that their proposed designs are manufacturable with the PolyJet process, whether designed manually or by an automated method, such as topology optimization.

Figure 1. Mean support material removed from channels of various areas
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