P 332 - Analysing the formation of markings on bonded thin-walled steel components

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

P 336: Determination of application and decision criteria for an efficient application of multi-point drawing technology in the series operation of pressing plants Multi-point drawing equipment in press shops can be used to increase the drawing depths of deep-drawn components, especially those made of high-strength materials, and to improve the quality level and productivity. The aim of this research work was to demonstrate the technological advantages and to develop process-specific knowledge about initial settings and parameter influences. The research results should provide decision criteria for the introduction and industrial implementation of this technology. A computer programme for realistic finite element process simulation was developed to illustrate the technological relationships. A special feature is the elastic modelling of the hold-down device. It allows modelling of the deformation under the effect of force during the sheet metal run-in. Corresponding practical tests were carried out on a hydraulic press with 16-point drawing systems. These included conventional deep drawing without and with an elastic hold-down plate as well as multi-point drawing with the elastic hold-down plate. Sheet thickness distribution, flange tightening, contact conditions and blank holder deformations in the process were monitored and quantitatively evaluated as comparative criteria. The test materials were the soft deep-drawing steel DC 04 as a reference and ZStE 220i and H340 as isotropic or higher-strength steel grades. The investigations demonstrated in simulation and practice that the use of multi-point drawing technology can increase process reliability and at the same time extend the technological limits. Unfavourable distributions of the actually prevailing local surface pressures between the blank holder, sheet and die proved to be the cause of failures. It was shown that the use of an elastic hold-down device is a prerequisite for a functional multi-point drawing system and technologically optimised results. Advice is given on the effective initial setting of the quill forces with the aid of FEM simulation for various applications. This work contains valuable information for the technological design of multi-point drawing presses and provides new arguments for the use of this technology by steel processors. STUDIENGESELLSCHAFT STAHLANWENDUNG e.V. Publication: 2000 Authors: Dipl.-Ing. L. Klose, Dipl.-Ing. H. Bräunlich

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