Investigation on the effects of process parameters for fatigue life improvement using turn assisted deep cold rolling process

Abstract

Mechanical surface enhancement (MSE) techniques have been used successfully newlineover the years to increase the fatigue life of metallic components. These techniques newlineimpart compressive residual stresses on component surfaces to counter, damage-inducing tensile stresses experienced under service loading. Deep cold rolling (DCR) is one of the mechanical surface enhancement techniques used predominantly in the automobile industry to achieve better component lives. Despite its wide application, the process is done with special purpose high cost machines. Also DCR process is not explored because the process has many parameters governing the fatigue life of components. Development of a simplified DCR process with parameters optimized to achieve fair levels of multiple responses is a need of the hour for industry and is attempted in the present work. This present research aims to study the effects of a simple turn-assisted deep cold rolling process on parts of AISI 4140 steel, which is commonly used in automobile industry with design of experiments and response surface methodology. In the preliminary study, two tools are developed which could be mounted on a lathe to implement DCR for turned parts. The tool and the set-up combination are expected to newlineimpart compressive residual stresses on the part surface and improve fatigue life and is newlinetermed turn-assisted deep cold rolling (TADCR). At the end of preliminary study, the newlineset-up is improvised by providing a back rest to reduce bending of the part. Initially, newlinescreening experiments conducted at 2 levels of seven different process parameters for newlinesurface compressive stress, surface hardness and surface finish indicate that four factors newlinerolling force, ball diameter, initial roughness of the workpiece and number of tool passes have significant effect on the TADCR process.