P 680 - Determination of damage mechanisms in stainless steel bonds as a contribution to production safety and reliability

P 689 - Investigations on turning and deep drilling of low-sulphur steels The necessary properties of steel materials can be derived from the requirements in automotive, mechanical engineering and plant construction. If the highest mechanical requirements have to be met, it is advantageous to reduce the sulphur content of engineering steels, as the influence of the sulphur content on the reduction of fatigue strength and fracture toughness is known from numerous studies. In contrast, the machinability is positively influenced by high sulphur contents. Tool wear is reduced and chip breaking is more favourable. As part of this research project, the machining of lightly sulphur-alloyed and low-sulphur engineering steels was analysed in order to work out the influence of the sulphur content in detail. The manufacturing processes of turning and deep drilling with twist drills and single-lip drills were analysed. The influence of sulphur was determined with regard to the most important criteria of process behaviour. Both tool-related and workpiece-related parameters were analysed. The possibility of compensating for the influence of sulphur was investigated by varying the tool design, the cutting values and the cooling lubricant concept. The experimental investigations were substantiated by further tests, which were largely adapted to the boundary conditions of industrial production. The optimisation potential of machining low-sulphur steels was confirmed by using tools and cutting values from industrial processes. The results of the turning process show that the sulphur content has only a minor effect on tool wear. For numerous test points, comparable wear behaviour was observed when machining the normal sulphur-containing grade compared to the low-sulphur grade. This could be determined by recording the wear, but also the cutting force. The influence of sulphur on chip breaking is clear. When machining the low-sulphur steels, a process-favourable chip breakage could not be observed for all cutting value combinations. However, it is possible to compensate for the influence of the sulphur content by adapting the shape of the indexable insert and the feed rate. The results of the deep hole drilling tests show comparable effects of the sulphur content on turning with regard to tool wear and chip breaking. In deep hole drilling, the chip shape can be improved by adjusting the grinding and chip topography. In addition to the sulphur content, there are significant differences in process behaviour and hole quality due to the deep hole drilling concept. Twist drills are suitable for high feed rates that enable high productivity. Polished flutes and adapted cutting edge contours produce favourably shaped chips even when machining low-sulphur steels. The main advantage of the single-lip deep hole drilling tools lies in the good hole quality, which is characterised in particular by a low centre run-out and a low-defect surface. Overall, the results show that turning and deep hole drilling can also be designed efficiently for machining low-sulphur steels. As part of this study, the necessary process knowledge was determined to enable productive machining of low-sulphur steels. The research project was carried out at the Institute of Machining Technology, Technical University of Dortmund, Robert Bosch GmbH, Stuttgart, Deutsche Edelstahlwerke GmbH, Siegen and Witten sites, Swiss Steel AG, Emmenbrücke, and Saarstahl AG, Völklingen, with technical support and financial assistance from the Forschungsvereinigung Stahlanwendung e. V., Düsseldorf, with funds from the Stiftung Stahlanwendungsforschung, Essen. Authors: D. Biermann, K. Weinert, F. Felderhoff, K. Klenke, J. Krause, W. Hockauf, E. Wüstner, H. Roelofs Publication: 2009