The Development of Processes Which Result in the Maximum Service Life of Light Weight Alloy Wheels

Author:  Sachs, George
Source:  Kelsey-Hayes Wheel Company
Doc ID:  1955007
Year of Publication:  1955
Abstract:  
The principal objective of this investigation was the determination of the effect of various surface rolling conditions on the fatigue-strength properties of case forged magnesium alloys. This study was part of the development of magnesium-alloy truck wheels by the Kelsey-Hayes Wheel Company on contract with Detroit Arsenal. The first problem concerned the strengthening, by surface rolling, of the wheel section, most liable to fail, in light-weight construction, namely the fillet rim. It was desired, from experimentation under varying conditions, to develop surface-rolling conditions, which would result in a considerable increase in fatigue strength and endurance limit of the fixed-rim section, without impairing the metal surface. The surface of this section was machined, prior to surface rolling, to a fine-machined finish, between 30 and 50 microinch. The tests were performed on a suitably-selected test specimen. The shape of this "model-test" specimen incorporated the important features of the fixed-rim fillet which determined its fatigue characteristics. The investigation covered a sufficient range of surface rolling conditions to allow prediction of suitable operating conditions for the production of actual wheels, improved by means of this process. When rolling processes are applied to the metallic bodies whose surfaces have varying curvatures, the determination of the roll geometry, i.e., scaling of diameters and radii of the roll, is of a decisive inportance. It has been suggested that for surface rolling a given material, a definite maximum value of Hertz pressure can be used as a guide for this scaling. If this were true, tests with tools and metal surfaces having different curvatures would give identical effects for forces, yielding equal values of such pressures. Furthermore, it would be possible to predict the forces required to produce a definite maximum pressure, and thus a definite rolling effect for surfaces with different curvatures. This report is composed of three parts: (1) Summary of results of analysis of Hertz' pressure, when applied to the metallic surfaces having geometry of the test specimen and wheel rim; (II) Mathematical relationships of Hertz' analysis; (III) Additional problems relating to the force on the roll and geometry of the rolled surfaces, in connection with rolling of the test specimen and wheel rim; (IV) Universal curves.