Levich Institute Seminar Announcement, 04/24/2007
Steinman Hall, Room #312
(Chemical Engineering Conference Room)
Dr. James Stevenson
"Thermal Flow Instability in Metal Injection Molding: Experiment and Simulation"
Metal injection molding (MIM) is similar to plastic molding in many respects, but MIM compounds (metal powders with polymer binders) are more susceptible to thermally induced flow instability because of their higher thermal diffusivity. The flow patterns for a 17-4PH MIM compound were observed and simulated for mold filling through a diaphragm gate over a range of filling times and melt-mold interface temperatures. Simulation predicted the observed free annular jet and internal voids in the molded part and also predicted that initial contact with the outside wall of the gate would eliminate the jet, thereby reducing voids and surface defects. Parts made using a mold with a thicker gate verified these predictions. For combinations of operating conditions and mold geometry that gave large thermally induced viscosity gradients, both observation and simulation showed unstable, asymmetric flow. In these cases, flow slowed and stopped in one region of the gate and accelerated in other regions. When the flow was inherently unstable, simulations predicted an exponential growth in maximum temperature differences at symmetric locations in the mold gate. Based on 34 experimental observations and 102 simulations, a boundary was established between regions of stable and unstable flow in terms of the dimensionless Graetz number Gz (ratio of characteristic heat conduction time to fill time) and B, a dimensionless ratio indicating the sensitivity of viscosity to temperature differences in the mold. To establish a common basis for comparison of simulation and experiment, the melt-mold interface temperature was estimated using a heat transfer coefficient, which was a fixed value for experiment and a parameter for simulation.
BRIEF ACADEMIC/EMPLOYMENT BACKGROUND:
Jim Stevenson is a Corporate Fellow in the Advanced Technology organization of Honeywell Aerospace. His current work involves the application of polymeric materials in the aerospace environment. Projects include noise attenuation using novel materials for engine inlet and exhaust housings, high temperature composites for propulsion structures, nano and microscale materials for electronic housings, and novel configurations and elastomers for flow control. Jim heads the Composite Materials Council, a group which advocates and enables the use of composites in aerospace applications. Prior work included material and process optimization for metal injection molding, funded by a $5.7 million NIST ATP program. Jim helped develop novel rapid prototyping technology for a DARPA advanced turbine blade project. While in the plastics business at Honeywell, he worked on thin-wall injection molding, and multifunctional laminate structures and processes. Jim has as a certification Six Sigma (Black Belt) and Design for Six Sigma.
Prior to joining Honeywell, Stevenson was Director of Research at Trexel, a start-up company commercializing microcellular foam technology. At Trexel, he initiated work on microcellular injection molding, which is now the dominant application for Trexel’s business. Previously Jim served in technical and management positions with GenCorp in Akron, OH. He supervised GenCorp’s Extrusion Research Facility and developed several novel extrusion and molding applications, including curved extrusion technology, process instrumentation and control systems, die designs and procedures, mold runner optimization strategies, and reactive materials modeling.
Early in his career, Stevenson was an Associate Professor with tenure in the Chemical Engineering Department at Cornell University. He
was a founding member of the Cornell Injection Molding Project, which was the forerunner of the C-Mold software company. He also conducted research on polymer rheology and transport in biomedical
systems. Stevenson has edited a book Innovation in Polymer Processing: Molding, published more than 60 papers, and holds 14 patents. He earned a Ph.D. in Chemical Engineering at the University of
Wisconsin and a B.S.Ch.E from Rensselaer Polytechnic Institute.