P 1373 - Optimizing of cutting tools for high strength materials by means of deep cryogenic treatments and coatings

P 1374 - Ultrasonic-assisted machining of hybrid materials As part of the European joint research project, the project consortium consisting of the Fraunhofer Institute for Machine Tools and Forming Technology IWU together with the Fraunhofer Institute for Process Engineering and Packaging IVV as well as Politechnika Wrocławska (PWr) and the Belgian Welding Institute (BWI) researched innovative methods for ultrasonically assisted joining of metal-plastic composites (MCP). The MCPs investigated as part of the research project consist of two metallic cover layers and a polymer core layer. This class of materials plays an important role in lightweight construction products. Due to their excellent specific stiffness, good thermal insulation properties and high acoustic damping capacity, they offer a high substitution potential for monolithic metallic materials. The joining of MFAs to metallic structures represents a major challenge. Due to the specific properties of the MFAs, the use of conventional joining techniques (e.g. spot welding, clinching or semi-tubular riveting) is limited or only possible with increased technical effort. The main objective of HybriSonic was to apply adapted and improved conventional joining technologies to MKV without a significant increase in process time or deterioration in joint quality. The basic approach is the localised melting of the polymer layer by ultrasonic waves and the displacement of the molten material by pressure on the cover sheets. Two different strategies were investigated for this purpose. In the first approach (one-step approach), the joining tool is directly superimposed by ultrasonic waves and the polymer layer is melted during the joining process and displaced from the joining zone. This approach was used for clinching and resistance spot welding. In processes such as semi-tubular self-pierce riveting or friction stir spot welding, the joining tool cannot be used to couple the ultrasonic waves into the MKV. A second, two-stage approach was investigated for these joining processes. Here, the polymer layer in the joining area is displaced in an upstream process step of sheet metal forming. The MKVs can then be joined as monolithic materials. The investigated approaches were validated for a large number of representative industrial material combinations and products and the advantages and limitations of the technology were recorded. Systematic and objective findings were obtained on the applicability of these novel joining concepts for industrial applications. Publication: 2022 Authors: Prof. Dr.-Ing. W.-G. Drossel, Prof. Dr.-Ing. J.-P. Majschak

P 1379 - Determination of forming limit curves at elevated temperatures The main objective of the project was to develop a new method for the frictionless determination of forming limit curves for hot forming processes. Test concepts and possible sample geometries were determined on the basis of extensive patent and literature research. Using an existing biaxial tensile testing machine, new specimen shapes were to be developed with the aid of numerical simulations, which reflect the three essential points of FLC with the uniaxial tensile load, the plane strain load and the equibiaxial tensile load. Two manganese drill steels were selected for the investigations, the standard material 22MnB5 and the new material 34MnB5. First, the material behaviour was determined as a function of temperature and strain rate in the high-speed tensile test and transferred to material cards for LS-DYNA. Based on this, the numerical design of the test process and the specimen moulds for the uniaxial tensile load, the plane strain load and the equibiaxial tensile load were carried out in parallel. New clamping jaws and inductive heating of the specimens were integrated into the biaxial tensile testing machine. The measurement concept consisting of optical local strain measurement and temperature measurement was tested and validated. Experimental investigations were then carried out to determine friction-free temperature-dependent forming limit curves in the temperature range of 550°C - 800°C and their validation in the punch-bound Nakazima test at 500 °C mould temperature. The results of the tests show that a friction-free determination of the forming limit curve is possible at different temperatures. Finally, the results were verified experimentally and numerically on the demonstrator component "B-pillar base". The benefits of the research results for steel applications are particularly relevant to companies in the toolmaking and automotive industries and their suppliers. They will be directly supported by more precise characteristic values for press-hardenable steels for the numerical design of hot sheet metal forming processes. Car manufacturers and their suppliers will be able to use the exact characteristic values to design components and then design the process in a shorter period of time and with a more robust process window, which will lead to lower manufacturing costs and thus secure the market position of these companies. Toolmaking companies also benefit from knowing the exact failure behaviour of press-hardenable steels. This makes it possible to realise more robust and cost-effective tool technologies for processing these materials, which reduces the effort involved in setting up and adapting the hot forming tools. Greater process reliability also means fewer cost, scheduling and quality problems. Publication: June 2022 Authors: Prof. Dr.-Ing. M. Dix, Dr.-Ing. R. Müller

P 1315 - Control of heat input during GMAW thick-wire welding using the example of fine-grain structural steels GMAW thick-wire welding with wire diameters up to d = 4.0 mm is a promising high-performance welding process which, however, has not yet enabled reproducible and economical joint welding of long weld seams. The applicability of the high-performance welding process in the area of temperature-sensitive, high-strength fine-grain structural steels was also previously unknown. In the research project, the new welding process was analysed and validated with regard to its suitability for the material-specific processing of fine-grain structural steels in the thick plate range (t ? 10 mm). The base material S690Q (1.8931) was used as the reference material for the group of high-strength fine-grain structural steels within the process qualification. In preliminary tests, a thermophysical material characterisation was carried out on a dilatometer, whereby the critical limit ranges of the cooling times t8/5 were defined and confirmed (5 s ? t8/5 ? 15 s). Within the project, systematic welding tests were carried out to analyse the influence of different wire diameters on the welding behaviour and the welding result at the upper technical test limit for MSG thick-wire welding. Solid wires of type G69 with diameters of d = 2.4; 3.0; 3.2 and 4.0 mm were used for this purpose. The solutions for controlling the energy input into the base material were aimed at extending the determined technical test limit in the upper performance range. For example, upstream wire heating, which was achieved by increasing the contact tube spacing (?s = 30 mm), resulted in a reduction in the absolute welding power requirement of up to 20 %. With the solid wire, deposition rates of approximately MR = 20 kg/h could be achieved. This corresponded to an increase in deposition rate of approx. 30 %. Furthermore, the use of a basic cored wire with a diameter of d = 3.0 mm had a positive effect on the welding behaviour and allowed deposition rates of up to approx. MR = 30 kg/h to be achieved. A separate cold wire feed into the melt during the welding process made it possible to increase the deposition rate of the thick wire process by up to 60 %. Alternatively, significantly reduced cooling times t8/5 could be realised with the help of targeted process adaptation: - Use of cored wire - 35 % - Increased contact tube spacing - 25 - Cold wire feed - 10 % In addition to the direct control of the energy and heat input into the base material, this made it possible to increase economic efficiency by increasing the deposition rate during GMAW thick-wire welding. With the process combination of cored wire, increased contact tube spacing and cold wire feed, maximum deposition rates of approx. MR = 45 kg/h were achieved in the project, which represents the current maximum value for GMAW thick wire welding. The pulsed and alternating current technologies were not considered to be effective in terms of reducing the energy input for the GMAW thick-wire welding process. In comparison with submerged arc welding, the potential of GMAW thick-wire welding was determined with regard to welding parameters and economic parameters, as well as mechanical-technological quality values for joint welds of fine-grain structural steels. Here, t = 20 mm thick sheets of grade S690Q were welded together in only 70 % of the time and with 60 % of the total costs of the submerged arc welding process using GMAW thick wire welding, while saving on powder costs and powder handling. In addition, MSG thick-wire welding enables joint welds up to t = 25 mm with just two welding beads. The process qualification (tensile tests, hardness measurements, notch impact tests and bending tests) did not result in any negative impairment of the mechanical-technological quality values of the high-strength fine-grain structural steel (S690Q) used in the case under consideration with regard to the cooling times t8/5 and processing using GMAW thick-wire welding. It was reproducibly and economically possible to place the failure location of the welded high-strength component outside the weld seam and the heat-affected zone. Publication: 2021 Authors: Prof. Dr.-Ing. Hensel, Dr.-Ing. M. Kusch, Dr.-Ing. A. Hälsig, ]}, M. Sc. J. Kimme

P 1314 - Space-forming load-bearing structures made of sandwich elements In addition to their outstanding space-enclosing function and thermal insulation properties, (steel) sandwich elements have load-bearing properties that allow loads to be transferred in and out of their plane. Single-storey buildings, such as small warehouses, petrol station shops and car washes, can therefore only be built with sandwich elements without additional load-bearing frame substructures. There is a lack of verification methods, in particular for load transfer, which would enable this economical construction method. The aim of the research project was to validate existing calculation approaches for load-bearing and serviceability and the detailed solutions for load transfer and distribution by means of experimental investigations and, if necessary, to develop them further. The knowledge gained from the holistic consideration of the construction method should then serve as a basis for the acquisition of a building authority approval. To achieve these goals, a self-supporting construction made of sandwich elements was first designed as an example object. For this purpose, all necessary construction drawings and detailed solutions for the formation of the load application points and joints were worked out and defined for this application. Experimental investigations into the load-bearing behaviour of a self-supporting construction made of sandwich elements were carried out using a test matrix defined in the research proposal. The extensive local and global axial compression tests were carried out on test specimens, taking into account a practical and application-related design of the load application points. The deformations and maximum loads were measured. The measured loads were then statistically evaluated and the actual local and global load-bearing capacity as well as the failure behaviour of the self-supporting construction made of sandwich elements were analysed. The analytically determined ultimate loads in the ultimate and serviceability limit states were used as a reference. It was found that the experimentally determined loads were far higher than the analytically calculated values. This showed that the design of the structure with the existing design approaches provides conservative results and is therefore on the safe side. The design of the load introduction structure for uplifting forces could also be ensured using a presented design approach. In order to ensure a holistic view of the construction, an economic and ecological analysis of the construction method was carried out. In the economic analysis, it was shown that self-supporting constructions made of sandwich elements without a steel substructure save approx. 9% of the investment costs and approx. 10% of the heating costs. The life cycle assessment also showed that the construction method results in emission and energy savings and is more environmentally friendly. Overall, the research report provides a sound scientific and technical basis for the design, construction and dimensioning of self-supporting structures made of sandwich elements, as well as the necessary test results and analyses for obtaining building authority approval. Publication: September 2022 Authors: Univ.-Prof. Dr.-Ing. D. Ungermann, M.Sc. G. A. Eseme