Failure analysis of ball screw in the progressive induction hardening and finishing machining

Abstract

Some failure modes, such as wear, quenching and finishing cracks, are easy to produce on the surface of the ball screw during the progressive induction hardening, and can shorten the fatigue life of ball screw. The hardened layer, microstructure, tensile strength and cracks of a 55CrMo steel ball screw after induction hardening are tested or observed by experiment. Based on the results of experiment and numerical simulation, the effect of heating temperature on the austenitization, microstructure, tensile strength, grain size of austenite and stress state of the ball screw are analyzed and discussed. In the induction hardening process, high heating temperature can result in some problems such as coarse grains and melting of the eutectic Fe-FeS-MnS produced on the grain boundary, which will impact the quenching quality and service performance of ball screw. Before the phase transformation of austenite transformed to martensite, the channel top of ball screw is in the state of three-dimensional tensile stress, which leads to brittle fracture during the cooling process. In the cutting process, the mechanical and thermal stress successively generate the tensile stress in the inner and outer layers of the ball screw channel, resulting in the internal cracks formed during quenching gradually extending to the surface. The essential cause of cracks in the finishing of the ball screw is the cracks formed during the induction hardening.