Study on Method to Predict Life Span of Die Used for Soft Magnetic Core Motor

Abstract

This paper describes a method to predict the life span of a die used for motors manufactured using a soft magnetic composite; in the study, a claw-teeth motor was used. The method involves performing stress analysis for a die and carrying out fatigue tests using test pieces. In the analysis, the soft magnetic composite was considered to be in powder form on the basis of its yield function, which was derived using a simple method. In addition to the analysis, we describe a simpler and more effective method in which the soft magnetic composite is considered to be a boundary condition. In the fatigue tests, we used test pieces that simulated the shape and construction material of the die. To predict the life span of the die, we evaluate the SN diagram, which represents the relationship between the maximum stress and fatigue life, with respect to the stress generated in the die. The life expectancy of a new die, which is about 100 rounds of use, is found to coincide substantially with its actual life. Furthermore, we explain how it is possible to extend the life span of a die to the targeted life span, i.e., more than 200,000 rounds of use, by changing its shape to reduce the stress.