Surface Residual Stresses in Dry Turning of 0.45% C Steel

Residual stresses in a surface layer determine many exploitation characteristics of machined surface. Depending on their kind and the type of applied loading, the influence of residual stresses can be negative or positive. Tensile residual stresses usually exert highly detrimental impact on several functional aspects such as strength, fatigue life, corrosion, wear resistance, etc., whereas compressive residual stresses are considered to have a beneficial effect on these features. The residual stresses found in mechanical parts are mainly generated in the final steps of machining process and are highly dependent on the machining conditions used. The increasing trend in industrial practice to eliminate cutting fluids from machining processes substantially changes machining conditions and influences the relationship between factors causing residual stresses. The main purpose of the presented investigations was to identify the relationship between residual stresses in a surface layer and the method of cooling employed. Using the X-ray diffraction method, residual stresses generated in both the cutting (circumferential) and feed (axial) directions were analysed. On the basis of empirical results the influence of turning with and without the application of emulsion on residual stresses was identified for a broad range of cutting parameters. The results showed that the method of cooling and cutting parameters exert a substantial influence on residual stresses. In the used range of cutting conditions, tensile residual stresses were detected. The elimination of cutting fluid from a turning process of C45 steel increased the magnitude of residual stresses in the surface layer. Residual stresses in the cutting direction turned out to be higher than in the feed direction in most cases of cutting conditions. INTRODUCTION Residual stresses in a surface layer determine many exploitation characteristics of machined parts. Depending on their kind and the type of applied loading, the influence of residual stresses can be negative or positive. Tensile residual stresses usually exert highly detrimental impact on several functional aspects such as strength, fatigue life, corrosion, wear resistance, etc., whereas compressive residual stresses are considered to have a beneficial effect on these features. Furthermore, the residual stresses in surface layer after machining may also cause dimensional instability of components (distortion) [1,2,4]. Therefore, the knowledge of residual stresses in the surface layer is important when critical structural components are machined, especially if the objective is to reach high quality and reliability levels. The direct impacts of residual stresses on the functional behaviour of a part are relatively well known [5,8,10]. Nevertheless, a number of questions regarding the generation of residual stresses in machining, their type, values and distribution persists [4,10,11]. 304 Copyright ©JCPDS-International Centre for Diffraction Data 2009 ISSN 1097-0002