High Density on PM Parts for Automotive Starter

High density is well known to improve both mechanical and magnetic properties. The limited number of applications of PM in automotive starters was mainly due to low cost target not compatible with the obtention of the needed density. This paper will present two successful developments in that field: a starter gear and a magnetic pole. In both cases, the use of SPSS process in cold conditions has allowed the establishment of the cost target. The magnetic pole is produced in pure iron, pressed at a density of 7.50 g/cm3 and sintered at 1120 °C. The starter gear needed high density and high hardness, associated to high toughness (resistance to pitting but also shock resistance). The paper will describe how a density of 7.65 g/cm3 was achieved in cold condition after pressing / sintering / sizing leading to hardness of 62 HRC after case hardening. Dimensional properties at that density level will be also presented and discussed. Finally, the validation tests will be described and a discussion about the obtention of high density in cold compaction will close the presentation.