Towards determining the influence parameters on the distortion of gear wheels made from the steel grade 20MnCr5 (SAE 5120), in this work the analysis of the distortion of disks is presented. The parameter identification was performed by means of the design of experiments (DoE). According to a comprehensive approach to distortion engineering, the entire manufacturing chain was considered from casting to the final heat treatment. Due to the complexity of this manufacturing chain the investigation was divided into two parts, the processes before the final heat treatment and the final heat treatment process itself. Here, in part I, the results of the investigation of the processes before the final heat treatment are discussed while in part II the results of the final heat treatment are presented. Releasing the accumulated distortion potential of the influence parameters of the processes from casting to cutting by a standard case hardening led to characteristic size changes of the disks. For the shape changes the cutting strategy showed a high influence on the change of dishing. Assuming that the cutting strategy can continuously be varied there should be a strategy for which no change of the dishing occurs, which would provide the means for compensation of distortion.

Realising the system-oriented approach of "Distortion Engineering", the influence of multiple parameters on the distortion of cylindrical gears was investigated by design of experiments. Aim of this research work was to investigate the effect of production parameters before the final heat treatment. The established experimental design focuses on the analysis of two main parts of gear distortion. One part is the distortion of the teeth themselves; the other part is a displacement of the teeth due to the distortion of the disk-shaped base body. The selection of the varied parameters is partly based on results of a system-oriented experiment with disks. Therefore several influences on the base body distortion are known. In comparison to the analysis of disk distortion the interpretation of gear distortion measurements requires significantly extended effort. Besides a determination of the distortion of the complex involute tooth profile, it has to be distinguished between a change of the tooth profile and a change of the base body.

In this work the applied approach to ‘Distortion Engineering’ is based on the consideration of the entire manufacturing chain of disks, from casting to the final heat treatment, made from the steel grade 20MnCr5 (SAE 5120). Part II presents the results of the investigations concerning the final heat treatment parameters on the distortion of the disks, whereas part I describes the effect of the influence parameters from casting to cutting. The disk geometry was selected, in order to reduce the expected complexity of influence parameters in gear wheel distortion. The parameter identification took place by means of the design of experiments (DoE). Volume flow rate of quenching gas, hardening temperature and carburizing depth have the expected effect on the volume change of the disks. In addition, occurring differences in the size changes of the inner and the outer surfaces were detected. For the shape changes it was found, that the choice of the loading tool shows the main influence. Furthermore a change in the loading tool does clearly affect the dishing behavior of the disks. Whereas, a relevant influence of the carburizing depth on the shape changes of disks could not be identified in this investigation. As a conclusion from the results presented in part I and II it is assumed that the identified parameters of disk distortion also effect the distortion of gear wheels.

Untersuchung der Krä fte in verschiedenen Eingriffsbereichen beim Wä lzfrä sen und deren Einfluss auf den Werkstü ckverzug T. KohlhoffBy hobbing, distortion potential is induced into the workpiece, which leads to distortion of the gear teeth in the subsequent heat treatment process. To investigate the generation of distortion by hobbing precisely, the analysing methods have to be adapted to the process. To be able to choose adequate methods, preliminary investigations are accomplished to analyse the dimension and shape of the machining induced distortion. Since the hobbing process is divided into three regions with different process conditions, the influence of these differences on the distortion has to be considered. Therefore a variation of the facewidth is performed and the occurring forces are measured to analyse the process conditions. The results are used to derive suitable research and analysing methods.

This study presents investigations on the fundamental mechanisms of part distortion during the machining of disks (cylindrical gear base bodies). The work focuses on the effects of machining induced residual stresses and inhomogeneous material removal. In this context the workpiece clamping was investigated as a major impact factor on the distortion. In order to analyze and describe the complex shape deviations, an appropriate distortion characterization method was developed. Since the distortion of disks directly affects the gear wheel quality, the results will help to understand the formation of gear distortion as well as to reduce and compensate it.