This Small Business Innovation Research (SBIR) Phase I project aims to is develop a novel "green-state" joining process that is compatible with a unique powder injection molding feedstock used for the production of metal injection molded (MIM) parts of high complexity. This project is exploring the feasibility of forming a "perfect joint". In this context, a perfect joint is defined as one that cannot be distinguished from base material by differences in microstructure, chemistry, or other material properties. The non-homogeneity of current metal joining methods such as welding, soldering, reaction bonding, and adhesive joining limits their use in certain high performance applications in which uniform properties are highly vSalued. MIM is unique in that the shaping is done in a separate unit operation from microstructural development. In the process under development, joining will take place after shaping, but before the final thermal processing step - in such a way that the interface between two contacting molded parts is completely eliminated on a microscopic scale.
The commercial potential of this project is wide-ranging. On the commercial side, this new technology will not only find high performance applications for which uniform properties are greatly valued, but also applications that are far more common. In particular, provided it is cost effective, the new joining technology will often be used to replace joints made by current expensive joining methods. This technology is expected to greatly reduce the cost of manufacturing such items. A broad area of application is in the production of hollow products. The technology could be used to produce heat exchangers for turbine engines as well as supercomputers. Inexpensively made but high quality hollow products could conceivably replace current solid parts in applications where high weight is detrimental, e.g., aerospace. On the societal side, this project initiates the partnership between a small manufacturer and an academic institution; provides practical research experience for a graduate student; exposes minority students in local high schools to opportunities in research and local manufacturing; and strengthens the manufacturing base of the U.S., providing wealth and jobs.
The objective of this Small Business Innovation Research Phase I Project was to demonstrate the feasibility of a green-state joining process that is compatible with a unique Metal Injection Molding feedstock used for the production of parts of high complexity. Joining occurs after shaping but prior to final thermal processing. Demonstration of feasibility required a hermeticity test of the joint, a mechanical test, and microstructural evaluation. Feasibility was considered demonstrated if, at a 95% confidence level, no significant differences could be found between joint and non-joint regions of product for at least one metal. To be concise, such joints are termed "perfect." Two lines of investigation proceeded in parallel. An effort at Case Western Reserve University was based upon prior research conducted by Professor James McGuffin-Cawley that resulted in perfect joints, but which utilized a different MIM binder system. When that technology was extended to the company’s advanced MIM system, microstructural evaluation of sintered product typically showed regions of both excellent and poor joining. Voids were observed in regions where joining was poor. Extensive investigation to determine the origins of this behavior concluded that internal stresses within the green parts, generated during injection of feedstock into the mold from rapid and uneven cooling and solidification, resulted in deformation of faying surfaces. Excellent joining occurred in regions where the two surfaces came into intimate contact. Otherwise, voids appeared in the joint region. Efforts to promote consistent full intimate contact of faying surfaces proved unsuccessful. Responding to a customer’s near-term needs, the Principal Investigator led an internal effort that resulted in a MIM-joining process for a stainless steel that met or exceeded the customer’s technical requirements. Evaluation of product from the process demonstrated that two feasibility criteria, microstructural analysis and hermeticity, were achieved. Broader Impacts: Several, if not all, of the promised broader impacts were achieved: 1) A strong partnership was formed between a small manufacturer and a local academic institution; 2) A graduate student gained practical research experience and successfully defended his thesis; 3) In multiple settings, participants from the small business and the university encouraged local students, including minority students, to focus upon STEM opportunities, especially research and local manufacturing; and 4) The successful process was commercialized: the process is now used to manufacture intricate components for two models of dental handpieces for a U.S.-based medical device manufacturer. Final product is sold to both domestic and international customers. Due to this commercialization, this SBIR project has already contributed to corporate profits and U.S. employment, and has generated opportunities for the U.S. government and its subdivisions to collect taxes. Ultimately, taxes collected will more than offset the government’s investment in this Project. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
