Fatigue Performance of Bearing Rollers Manufactured by Laser Powder Bed Fusion

Abstract

Metal additive manufacturing (AM) promises functional flexibility in the production of engineering components, and great progress has been made with respect to part geometry and overall performance criteria. The fracture and fatigue behaviors of metals depend on the sample microstructure, an aspect of metal AM for which many challenges remain. Here, we report on progress with respect to the rolling contact fatigue (RCF) performance of metal AM bearing rollers. A set of rollers was created using laser powder bed fusion from 8620HC steel powder. The print parameters were first studied with respect to laser power, laser scan speed, laser spot size, and layer thickness. A set of tapered cylindrical rollers was then manufactured using build parameters that were selected based on material density, optical microscopy, ultrasound, and residual stress measurements. The rollers were then heat-treated while still on the build plate to relieve any residual stresses. The rollers were removed from the build plate, machined to the typical product geometry, case-hardened, carburized, and ground to a final surface finish. Finally, the rollers were integrated within railroad tapered roller bearings and tested in two ways. The accelerated life test subjected the rollers to high-stress RCF that generated significant spalling on both types of rollers. The simulated service life test was designed with RCF at levels typical of in-service bearings. At the conclusion of this test, equivalent to 250,000 miles, the performance of the AM rollers was judged to be in line with rollers manufactured using traditional methods, and visual inspections showed no surface damage to any rollers. The results of this study provide a clear foundation for additional AM roller designs that can exploit the unique capabilities of the AM process.