Effect of Hardenability and Press Quenching on Distortion of Crown Wheels

Press quenching is used to control distortion of large transmission components, e.g. case hardened crown wheels. The unsystematic distortion arises from non-uniformity in the steel properties and processing conditions and is a major concern for gear manufactures. In the present work a methodology is developed to analyze how various properties and parameters influence the distortion during press quenching of crown wheels. To obtain realistic quenching characteristics, to be used for simulation, a number of experiments are carried out on an industrial press quenching machine. In addition, the distortion potential from hardenability is surveyed on a set of non-press quenched crown wheels and quantified by 3D-scanning. Based on the experimentally obtained quenching characteristics the press quenching process is simulated by FEM. Impact of steel properties, quenching characteristics and processing conditions on the distortion is discussed and analyzed in relation to the experiments. From the results it may be concluded that press quenching is a powerful tool that can limit the impact of distortion carriers. However, to exploit the full capability of press quenching and thereby increase process optimization it is necessary to better quantify the distortion carriers in the parts to be hardened.