Papers by Author: Jürgen Fleischer

Abstract: The use of fiber-reinforced-plastics (FRP) contributes to an efficient implementation of lightweight design due to their outstanding specific mechanical properties. The RTM process offers great design freedom and allows the integration of functional elements during manufacturing. Embedded metal elements, so-called inserts, can be used to deal with the load transfer to structural parts. These elements have distinctive characteristics in comparison to other joining technologies. For example, detachable connections can be established with the help of inserts. Due to the fiber continuity not being interrupted and, subsequently, the FRP parts not having to be drilled, there is no local bearing stress. This paper aims at the characterization of metal inserts in FRP parts. The parts are manufactured using the RTM process with a specially adapted RTM mold with exchangeable cartridges for different insert geometries. The inserts are made of metal sheets with welded bushings and are embedded during preforming. The cured FRP specimens are tested under different load conditions to evaluate their suitability for various fields of application. Furthermore, the diameter and thickness of the metal sheet of the insert as well as the thickness of the FRP are varied to identify their influence on the failure behavior and load capacity under tensile loads.

Abstract: Within traffic engineering, the importance of lightweight space frame structures continuously grows. The space frame design offers many advantages for light weight construction but also brings challenges for the production technology. For example, the important requests concerning product flexibility and reconfiguration can only be achieved with a high technical effort, if current machine technology is used. For this reason, the collaborative research center SFB/TR10 investigates the scientific fundamentals of a process chain for the product flexible and automated production of space frame structures. An important component in space frame structures are curved extrusion profiles. Within the investigated process chain, the extrusions must be machined mechanically in order to apply holes and to prepare the extrusion ends for the following welding operation.The machining is currently done by clamping the profile into a fixture and processing it within a machining center. This procedure has two disadvantages due to the complex geometry and the partially high length of the extrusion profiles: On the one hand, a complex fixture is needed for clamping the work piece [1]. On the other hand, a machining center with a large workspace and five machine axes is required [2]. Due to this, the product flexible machining with current technology is only possible with high technical and economical effort. For this reason, a new machine concept for the product flexible machining of three dimensionally curved extrusion profiles was developed at the University of Karlsruhe. In this paper, the function of the machine is explained and a prototype is presented. In addition, investigation results of the machining accuracy are shown and possibilities for improving the precision are discussed.

Abstract: This article describes a clamping concept for the flexible machining of spatially curved profiles developed at the wbk Institute of Production Science of the Universität Karlsruhe (TH). Simple geometrical considerations form the basis of the prototypically implemented clamping system design. The approach presented in this article allows for accuracy improvements regarding the positioning of the profile in the clamping system on the basis of markings applied onto the surface of the profile. Besides, the preliminary test rig set up and first results on the detection of the markings by means of digital image processing are presented.

Abstract: The prototype for the flying cutting of spatially curved extrusion profiles developed as part of the Collaborative Research Center Transregio 10 (SFB/TR 10) was tested as an integrated part of the overall system in first test runs. The profiles resulting from this process give proof of the potential involved in both, the novel curved profile extrusion (CPE) and the automatic supporting and cutting device. For subsequent automated processing to become possible, however, the reliably achievable accuracy of extruded profiles needs to be further improved. By the example of the extruded profiles produced so far, this article discusses potential factors that may impair profile accuracy and presents approaches and methods for the improvement of accuracy.

Abstract: With a novel extrusion process which is investigated in the Collaborative Research Center Transregio 10 (SFB/TR10), it is possible to manufacture spatially curved aluminum profiles. This process is the base for an automated small and medium size batch production of light-weight frame structures. For the handling and machining of the spatially curved profiles, highly flexible machines and manufacturing equipment are needed. Today’s automated process chains do not reach a sufficient flexibility. This article introduces a new approach to handle and machine spatially curved profiles using a flexible gripping and clamping system. Firstly, the requirements concerning the process comprehensive gripping technology, which have to be fulfilled for a flexible small and medium batch production of light-weight frame structures, are specified. Subsequently, the function and design of a flexible gripping and clamping system are described. Furthermore, metrological processes to maintain a once reached condition of order during the entire process chain are depicted.

Abstract: The innovative process of curved profile extrusion facilitates the cost-effective production of lightweight structures with spatially curved profiles even for small series. Due to the extrusion process a continuous flow of material is unavoidable. The profiles have to be separated reactionlessly during the extrusion following the complex trajectory of the cut-off point in space. This paper discusses the challenges for a flying cut-off device. In addition to a concept to generate the trajectories and control the movements, the main parameters for dimensioning a cut-off device are presented. A specially designed clamping device permits to generate high accelerations. Further on, cutting results are shown especially for extruded sections with continuous reinforcing elements of steel.

Abstract: The importance of rigid and self supporting space frame structures for the automotive and aerospace industry continually increases. To meet the market requirements for a flexible and competitive small batch production, innovative machine concepts must be investigated. By integrating handling and machining capabilities into one machine structure, redundant degrees of freedom can be reduced and a former idle economic potential can be made use of. This paper introduces a systematic approach to reveal synergetic potentials that emerge by integrating two different fields of function, the handling and the machining. Therewith a matrix with technical solutions for a combination of handling and machining is generated. These solutions are the base for new machine concepts that fulfill both tasks with a minimal number of machine axes. The authors present a machine concept which is combined out of a four-axes parallel kinematics and a conventional serial kinematics. The two kinematic structures collaborate and allow the product flexible handling and machining of three dimensional rounded extrusions with a minimal technical effort. The machine concept is dimensioned and optimized for a maximal stiffness by the coupling of a multi body simulation to an external parameter optimization software. The optimization results show that the stiffness of the machine concept could be explicitly improved. This paper is based on investigations of the collaborative research centre SFB/TR10 which is kindly supported by the German Research Foundation (DFG).

Abstract: Due to economical, ecological and functional reasons, lightweight-construction is continuously gaining importance. Therefore, lightweight space frames made of pipe profiles are subsequently of higher importance in today’s technology. Today, the lower limits of the production range of lightweight space frames are set by joining processes that require jigs. For a flexible variation in a small-scale production, the use of latching elements for the pre-attachment in the jigfree assembly of frame structures serves as a good approach. In consideration of the analysis of the actual situation this article takes up this approach and points out the potential enabled by latching elements. Subsequently, the implementation of laser cutting will be motivated and the results of the first experiments on reinforced and unreinforced profiles will be discussed. To conclude this article, the challenges and approaches for the integration of this procedure to an existing handling and machining kinematics will be pointed out, and finally the implementation potentials of the procedure within an entire process-chain will also be mentioned.