Investigation on comprehensive performance of the EFI by MIM technology

Abstract

Metal Injection Molding (MIM) technology is introduced into EFI production processing. Magnetic circuit of EFI is designed, and three different kinds of EFI samples are manufactured. Through comparisons of simulation and ex- periments, comprehensive performance of one EFI sample, which is made of Fe-based nanocrystalline soft magnetic alloy by MIM is found to be obviously better than that of others, which are made of traditional material and processing. The dynamic response times of opening and closing are respectively shorter by 32.5% and 62.2%, and dynamic flow range is wider by 8.3%. The electronic fuel injector (EFI) is a key actuator of gasoline engine, which decides precision of fuel injection, so characteristics of EFI, such as accuracy, consistency and stability, are mostly important for engine fuel injecting system. The key parts of injector are traditionally made of soft magnetic alloy bar through metal machining process, technology of which is characterized by low efficiency, material utilization and poor consistency. Moreover, cutting stress, caused while cut- ting, would lead to permeability of soft magnetic materials decreasing, coercivity and magnetic wastage increasing (1). Metal Injection Molding (MIM) known as the most popular parts forming technology, is a new near-net shaping technique (2). MIM technology is a product of multi- disciplinary cross-penetration, such as plastic injection molding polymer chemistry, powder metallurgy technology and metal material science (3). High density, high precision and high strength parts can be manufactured rapidly by MIM technology. MIM can be traced back to 1920's, when ceramic spark plug was prepared with process of powder injection molding. Several decades from then, powder injection molding was mainly applied to ceramic injection molding. Until 1979, Par- match Co., establishedby Wiech, turned its application from powderinjection molding into metal injection molding for first time (4). Through almost twenty years of development, MIM technol- ogy is widely used in aerospace, weapon, car, tools, teeth materials, medical materials, national defense and people's livelihood industry (5-12), for its advantages of high productivity, high precision and high performance.