SBIR Phase I: Development of a Metal Aggregate Rapid Tooling Process for Casting Aluminum Alloys

This Small Business Innovation Phase I Research project aims to develop a novel rapid tooling material for inexpensive production of low volume and prototype castings. This rapid tooling material offers the ease of molding typical to sand molding yet is comparable in properties and performance to metallic permanent molds. The mold comprises a metallic aggregate with a silicate binder, thermally processed to achieve appropriate hardness and dimensional stability. The project will address the following: (1) manufacturing of a complex mold; (2) characterization of the mold material; (3) analysis of the dimensional accuracy and surface roughness of castings produced with this mold; (4) determination of the cooling rates during solidification of aluminum cast in the mold; (5) evaluation of the thermal fatigue resistance and durability of the mold; (6) determination of the lead time to fabricate rapid tooling by this method; Castings made in these molds are expected to cool faster resulting in higher ultimate strength, ductility and elongation. In addition, because of the finer dendrite arm spacing, a shorter homogenization time during heat-treating is anticipated. These attributes make this material attractive not only for rapid tooling but also for contoured chills in sand casting. These would be used to increase local extraction of heat from solidifying aluminum, thereby improving mechanical properties in critical sections of the casting. The broader (commercial) impact from this project would be a metallic aggregate mold technique that lends itself to rapid and inexpensive forming of molds for prototype development castings. The mold so produced has potential applications in metal mold casting processes such as gravity permanent mold, low pressure and die-casting and injection molded plastic parts. The most apparent commercial application for the metal aggregate is in molds for low volume, high strength aluminum castings. Used as a permanent mold the metal aggregate mold provides integral venting, eliminating the need for mechanically created vents thus saving time and cost. Another potential application of the metal aggregate material is in manufacturing of shaped chills for sand casting. As a moldable material the metal aggregate fits the pattern to form a thermally conductive mold otherwise not readily achievable. The company's principal product is aluminum impellers made by a process, which utilizes a combination of permanent and sand molds. Core gases trapped by the permanent mold during the casting process are a major cause of defects, resulting in scrap rates in excess of five percent. A durable, permeable tool could substantially reduce that tooling cost, leading to more rapid implementation of impeller innovations, hence more energy efficient refrigeration designs.