P 336 - Determination of application and decision criteria for an efficient application of multi-point drawing technology in the series operation of pressing plants

P 337: Comparison of the fatigue strength of hard-turned and ground components In competition with grinding, hard turning fulfils the demand for higher economic efficiency with better ecological compatibility. For a broad application of hard turning, it has not yet been proven that at least the performance properties, in particular the fatigue strength of components with a ground surface, can be achieved. This is where the present research project comes in and investigates whether hard turning can replace grinding, which has been the standard hard machining process to date. For the comparative investigation of grinding and turning of case-hardened components, notched round specimens made of 16MnCr5 case-hardening steel were selected as the material and subjected to 4-point alternating bending. A sufficiently small test radius ensured that the cracks only originated from the surface. To investigate the influence of tool wear during hard turning, the test specimens were turned with both new and defined worn inserts at two feed rates. Compared to ground samples, the fatigue strength was determined in the Wöhler test and the fatigue strength test. Cracking was used as the failure criterion for all test series. The fatigue tests were accompanied by metallographic analyses and residual stress measurements. The samples from hard turning with new tools always show a higher fatigue strength than the ground samples in the single-stage test with constant amplitude. The strengths decrease with tool wear; they are only lower than those of ground samples after prolonged tool use. In the fatigue strength tests with different amplitudes, no influence of tool wear was found in the load range investigated. The hard-turned samples always produced better fatigue strength values than the ground samples. With the help of a specially developed calculation concept, the Wöhler and fatigue strength results from the test series with turned specimens can be reproduced well. In contrast, the results of the test series with ground samples could not be determined satisfactorily by calculation due to the different surface topography, which was not adequately captured by the surface parameter used. As long as the tool wear during hard turning does not exceed a certain level, the fatigue strength is generally at least equal to or better than that of ground samples. The fatigue strength of hard turned samples only drops in comparison to ground samples at larger, but technically easily detectable wear mark widths. Up to this limit, hard turning is always more favourable than grinding case-hardened components, a finding that particularly benefits the small and medium-sized manufacturing industry. STUDIENGESELLSCHAFT STAHLANWENDUNG e.V. Publication: 2000 Authors: Dipl.-Ing. F. Renner, Prof. Dr.-Ing. H. Zenner, Dipl.-Ing. Ch. Borbe

P 332: Analysing the formation of markings on bonded thin-walled steel components Adhesive bonding is a suitable joining technique for the manufacture of lightweight sheet steel components due to the fact that the joining seam can be designed almost arbitrarily and is already used extensively in the series production of cars and other vehicles. However, practice shows that the curing of the preferably used single-component adhesives in paint drying ovens causes residual stresses in the bonded seam, which lead to component deformation, i.e. to visual defects (markings), but also to loss of strength. The occurrence of production-related component deformations is due to the local and temporal temperature field in the joining partners during the curing of the heat-curing adhesives. A distinction must be made between two deformation mechanisms. On the one hand, the thermal expansion or contraction and the reaction-related increase in density of the adhesive lead to deformations in the area of the bonded joint. On the other hand, relative movements of the joining partners during the oven cycle, which can be of the order of several millimetres, can be frozen as the adhesive cures. In order to understand in detail the processes that take place during the heat curing of single-component reactive adhesives and to be able to derive measures to minimise the resulting component deformations, laboratory test methods have been developed with which the various effects can be considered separately from each other as far as possible. Based on the knowledge gained from the laboratory test specimens, a component-like test specimen was initially developed, which approximates the complexity of series components and allows a wide variation in the design of the joining zone. The findings were then verified through tests on series components. The tests on realistic test specimens and series components clearly show that a holistic view of the system consisting of component, adhesive and curing process is essential to avoid markings. The type of component deformation resulting from the tempering process is determined by the combination of various geometry-, adhesive- and process-specific boundary conditions. The main result is a checklist which provides specific solution proposals for characteristic problem cases. The checklist describes the development mechanisms, the damage pattern and the proposed remedial measures. On the one hand, the formation of markings can be counteracted as early as the design phase by designing steel components to be adhesive-free and, on the other hand, markings can be minimised in existing components and processes through appropriate optimisation measures. Mark-free bonding opens up potential applications in lightweight constructions, particularly for high-strength steel sheets of low thickness, where spot joining methods only allow insufficient material utilisation or where the material is only suitable for spot welding to a limited extent. STUDIENGESELLSCHAFT STAHLANWENDUNG e.V. Publication: 2000 Authors: Prof.Dr.-lng. O. Hahn, Dipl.-Ing. G. Meschut, Dipl.-Ing. M. Eis

P 331: Development and testing of a cold-profiled structural steel body part with integrated functional elements for large-scale production The lightweight construction potential of high-strength steels is increasingly being utilised in automotive engineering. For the cold-rolled profiles used, a simple substitution of soft deep-drawing grades in roll forming - the most important cold-forming process - is often hindered by a lack of expertise in adapting the production parameters. The aim of this research project was to create a manufacturing basis for the series use of higher-strength steels and to integrate the processing of essential functional elements into the roll forming process with a view to later use as a component. The continuous roll-forming process of high-strength steel and the simultaneous introduction of integrated functional elements and add-on parts was investigated and industrially tested for an automobile cross member as a structural body part. Coming from the coil, the steel strip first passes through two production facilities in the stop and go process, which on the one hand fix reinforcing sheets to the strip with the aid of clinching elements and on the other hand insert punching nuts. This is followed by the continuous roll forming process. The brief stopping of the strip in the upstream production equipment requires appropriate strip storage or loops, which enable the pilot plant to operate continuously overall. To prevent the functional elements from colliding with the rollers, these are turned out in the corresponding contour areas around the circumference. The carrier prototype is closed by laser welding. The profiles are then cut to length. It has been demonstrated that the production of cold-profiled structural body parts made of steel with integrated functional elements is suitable for large-scale production. The manufacturing costs can be considerably reduced by processing the functional elements before the roll forming process. The results achieved in this research project will make a significant contribution to increasing the range of applications for the roll forming process and thus strengthen the competitiveness of the supplier industry, which is mostly made up of medium-sized companies. STUDIENGESELLSCHAFT STAHLANWENDUNG E.V. Publication: 1997 Authors: Dipl.-Ing. R. Schwarzwälder, Dipl.-Ing. A. Schulte, Prof.Dr.-lng. O. Hahn, ]}, Dipl.-Ing. A. Schulte