Master Decomposition Curve for Binders Used in Powder Injection Molding
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INTRODUCTION
POWDER injection molding (PIM) is a technology in which thermoplastic polymeric material with a high content of solid particles (e.g., metal and ceramic particles) is molded into a desired shape in a closed die. The powder-binder mixture is formed into a green component using conventional plastic injection molding technology. This green compact is subsequently processed to near full density by removing the binder and then sintering the remaining powder. The PIM is a net-shape processing method that involves building in quality rather than attempting to obtain it by postprocessing.[1] This results in greater product shape complexity than available in die compaction. Because PIM is a binder-assisted forming technique, binder removal without loss of product integrity is a crucial point. The process of binder removal is termed ‘‘debinding.’’ A multicomponent binder can overcome distortion problems by leaving one component in the compact to hold the particles in place while a lower stability component is removed. Often, the lower molecular weight binder component is dissolved into a fluid in a process termed ‘‘solvent debinding.’’ Thermal debinding, a conventional heat treatment in
GAURAV AGGARWAL, Graduate Student, and IVI SMID, Associate Professor of Engineering Science and Mechanics, are with the Center for Innovative Sintered Products, The Pennsylvania State University, University Park, PA 16802-6809, USA. Contact e-mail: [email protected] SEONG-JIN PARK, Associate Research Professor of CAVS and Adjunct Professor of Mechanical Engineering and RANDALL M. GERMAN, Chair Professor of Mechanical Engineering and Director of CAVS, are with the Center for Advanced Vehicular Systems, Mississippi State University, Mississippi State, MS 39722, USA. Manuscript submitted March 1, 2006. Article published online April 13, 2007. 606—VOLUME 38A, MARCH 2007
a gas atmosphere, is used to remove higher molecular weight components of the binder systems. It is still not clear how the different binder components in their respective weight percentages are affected by the heat treatment in detail. As a consequence, binder removal from the molded parts is a time-consuming step, which is a limitation to PIM processing. Therefore debinding has been studied to explore its kinetics of extracting the binder as fast as possible.[2–5] Previously, debinding cycles were based on ‘‘trial and error’’ until an adequate time-temperature cycle was achieved. With the use of a multicomponent binder system, achieving an economical and effective debinding cycle while maintaining the compact’s shape can be quite difficult. To counter this, thermogravimetric analysis (TGA) and differential thermal analysis (DTA) are used to determine the weight percent of the binder component left as a function of time and temperature. This protocol is to show heating at points of rapid weight loss to avoid compact damage to expedite the debinding process and lower the overall cost. Still, a large number of TGA and DTA experiments are needed to opti
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