A new and promising approach to the reduction of greenhouse gas emissions is the use of improved lightweight constructions based on multi-material systems comprising sheet metal with local carbon fibre reinforced plastic (CFRP) reinforcements. The CFRP is used to reinforce highly stressed areas and can be aligned to specific load cases. The locally restricted application of CFRP means that the material costs can be effectively reduced by comparison to parts made entirely of CFRP on account of the expensive production process requiring the use of an autoclave. These parts are thus only used in high-priced products. The production of hybrid CFRP steel structures in a mass production process calls for an efficient production technology. Current research work within the scope of a collaborative research project running at the University of Paderborn is concentrating on the development of manufacturing processes for the efficient production of automotive structural components made up of sheet metal blanks with local CFRP patches. The project is focusing especially on basic research into the production of industrial components. The aim of the investigation is to create an efficient and controlled process for producing CFRP reinforced steel structures from semi-finished hybrid steel-CFRP material. This includes tool concepts and an appropriate process design to permit short process times. The basis of an efficient process design is an in-depth knowledge of the material behaviour, and hence a thorough characterisation was performed. Material parameters were determined for both simulation and forming. For this, monotonic tensile, shear and bending tests were conducted using both uncured prepregs and cured CFRP specimens. To achieve an accurate simulation of the forming process, a special material model for carbon fibre prepregs has been developed which also includes the anisotropic material behaviour resulting from fibre orientation, the viscoelastic behaviour caused by the matrix and the hardening effects that prevail during curing. Recent results show good qualitative agreement and will be presented in this paper. In order to control the properties of the hybrid components, four different tool concepts for the prepreg press technology have been developed and tested. The concepts are presented and the results of experimental investigations are discussed in this paper.
During the manufacture of metal parts, geometrical deviations can appear. The reasons for this can be a variation in the properties of the semi-finished product, or wear phenomena on the punch-bending machine itself or on the punch-bending tool. When geometrical deviations appear, the process parameters normally have to be adjusted manually. The choice of the most appropriate process parameters is currently based on the operator's experience. Unfortunately, this is a time-consuming and expensive procedure right at the early stages of a production scenario. In addition, the trend towards reduced part sizes with tight tolerances, made of high strength materials, is drastically increasing the requirements regarding the production process. In order to reduce the scrap rate and the setup time for production scenarios, it is necessary to implement corrective action during the process by means of a special control strategy. A self-correcting control strategy based on a closed-loop control approach is thus under development at the University of Paderborn. The first step in this strategy involved conducting simulations is to identify those process variables, e.g. the strength or the geometrical properties of the material, which have a significant influence on the process. Once correlations between input and output variables had been established, different self-correcting control strategies were set up. To validate the simulation and to test the quality of the self-correcting control strategies, a special experimental tool, mapping the most important bending operations, was constructed at the University of Paderborn. The experimental tool is equipped with an additional measurement device and can be operated on a universal testing machine. Finally, the self-correcting control strategies were tested under production conditions on the original tool in order to take any additional influences of the punch-bending machine into consideration. In this paper, recent investigations are presented that were conducted in a collaborative project at the University of Paderborn together with two industrial partners. The results of the correlation between the variables governing the process, the development of a suitable measurement method, and a first approach to a self-correcting control strategy are set out.
Ein Schlüssel, die Wirtschaftlichkeit von Biegeverfahren zu steigern, liegt in der Nutzung von Self-X-Technologien. Dabei werden in die heute rein mechanisch gesteuerten Werkzeuge und Maschinen entsprechende Komponenten integriert, welche die kontinuierliche Einhaltung der Soll-Größen sicherstellen. Das Projekt „Self-X-Pro“ des Spitzenclusters „it’s OWL“ zielt auf die Weiterentwicklung von Biegeverfahren zu intelligenten technischen Systemen, die eine Selbstkorrektur realisieren. The key to increasing the efficiency of bending processes lies in the use of Self-X-technologies. This is achieved by integration of Self-X-components in purely mechanically driven tools and machinery to ensure continuous compliance of the required nominal values. The project “Self-X-Pro“ within the leading-edge cluster “it’s OWL“ aims at the advancement of bending processes into intelligent engineering systems where self-correction is realized.
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