K. S. Weil, E. A. Nyberg, K. L. Simmons, Pacific Northwest National Laboratory, Richland, WA
Powder injection molding (PIM) is an economical, net-shape process for manufacturing large volumes of complex-shaped parts. Traditional methods of PIM employ a high volume fraction of polymer in the metal powder/binder mixture, which in addition to being difficult to remove entirely during burn-out, has a tendency to de-gas in the removal process, causes undesired dimensional and shape changes in the component, and is a source of impurities in the material as well as undesired gaseous byproducts that are vented into the atmosphere. We have recently developed a binder system that is unique because only a small volume fraction of binder (< 5 – 10 vol%) is required for injection molding; the remainder of the mixture consists of the alloy powder and binder solvent. Because of the nature of decomposition in the binder system and the small amount used, the binder can be eliminated almost completely from the pre-sintered component during the initial stage of a two-step heat treatment process and collected for re-use in fabricating additional parts. Results from impurity testing with titanium have shown that the final densified product contains the same level of carbon as the original starting powder.
Summary: We have developed a powder injection molding technique that is requires only a small amount of binder for processing. Additionally, because of its volatility, the binder can be collected after removal for re-use in fabricating additional parts.