Papers by Author: Horst Meier

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Authors: Horst Meier, H. Ermert, P. Knoll, Oliver Keitmann-Curdes
Abstract: With fluid forming processes getting more and more common in industrial application a lot of research is carried out to analyze the forming behavior of sheet metal within these processes. In order to gather experimental information about the forming behavior of the workpiece, an imaging system is presented, that will allow determining the actual shape within the forming process. The system has to be functional in liquid media as well as in a high pressure environment. Therefore an ultrasonic based system has been chosen, consisting of a small number of transducers which are alternately used as transmitter and receiver. It is possible to cover 100 by 100 mm² with only 10 by 10 transducers by the use of special algorithms. The reconstruction of the echographic images from the recorded data is done by a SAFTalgorithm (synthetic aperture focusing technique) followed by an analysis with special contourdetection algorithms, which are able to scan the image for contour data. It can be shown that the accuracy of the reconstruction is quite good in the 2.5-dimensional domain, if appropriate contour models for the description are used. Because of the small number of transducers and the specular reflection of the signals, the quality of the image can be improved significantly by the extension of the SAFT algorithm with an angle-weighted factor. The three dimensional reconstruction is also possible and will be demonstrated for simple geometries. The ability for sampling more complex geometries and enhancing the accuracy will be achieved by the integration of three dimensional contour models and three dimensional angle-weighting.
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Authors: Horst Meier, O. Dewald, Jian Zhang
Abstract: This paper describes a new sheet metal forming process for the production of sheet metal components for limited-lot productions and prototypes. The kinematic based generation of the shape is implemented by means of a new forming machine comprising of two industrial robots. Compared to conventional sheet metal forming machines this newly developed sheet metal forming process offers a high geometrical form flexibility and also shows comparatively small deformation forces for high deformation degrees. The principle of the procedure is based on flexible shaping by means of a freely programmable path-synchronous movement of the two robots. The sheet metal components manufactured in first attempts are simple geometries like truncated pyramids and cones as well as spherical cups. Among other things the forming results could be improved by an adjustment of the movement strategy, a variation of individual process parameters and geometric modifications of the tools. Apart from a measurement of the form deviations of the sheet metal with a Coordinate Measurement Machine rasterised and deformed sheet metals were used for deformation analyses. In order to be able to use the potential of this process, a goal-oriented process design is as necessary as specific process knowledge. In order to achieve process stability and safety the essential process parameters and the process boundaries have to be determined.
465
Authors: Horst Meier, Roman Laurischkat, C. Bertsch, Stefanie Reese
Abstract: The main influence on the dimensional accuracy in incremental sheet metal forming results from the compliance of the involved machine structures and the springback effects of the workpiece. This holds especially for robot based sheet metal forming, as the stiffness of the robot’s kinematics compared to a conventional machine tool is low, resulting in a significant deviation of the planned tool path and therefore in a shape of insufficient quality. To predict these deviations, a coupled process structure model has been implemented. It consists of a finite element (FE) approach to simulate the sheet forming and a multi body system (MBS) modeling the compliant robot structure. The forces in the tool tip are computed by the FEA, while the path deviations due to these forces can be obtained using the MBS model. Coupling both models gives the true path driven by the robots. Built on this path prediction, mechanisms to compensate the robot’s kinematics can be implemented. The current paper describes an exemplary model based path prediction and its validation.
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Authors: Horst Meier, B. Buff, V. Smukala
Abstract: This paper describes new developments in incremental, robot-based sheet metal forming (Roboforming). Roboforming is a dieless sheet metal forming process which ensures cost-effective manufacturing of prototype parts and small batches. An approach for increasing the part accuracy in Roboforming is presented. It is developed in a cooperative project funded by the German Federal Ministry of Education and Research called Roboforming. The project concentrates on the development of an industrial applicable system design. The use of standard components allows a modular and scalable set-up. A servo loop, consisting of sensors and a programming system, represents the basis of this design and shall guarantee higher part accuracies by measuring the deviations between a formed part and its target geometry. The deviations are used to derive corrected tool paths. The correction is performed by an adjustment vector for every point on the tool path. The theory for this strategy and first results are presented in this paper.
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Authors: Yalin Kiliclar, Roman Laurischkat, Stefanie Reese, Horst Meier
Abstract: The principle of robot based incremental sheet metal forming is based on flexible shaping by means of a freely programmable path-synchronous movement of two tools, which are operated by two industrial robots. The final shape is produced by the incremental infeed of the forming tool in depth direction and its movement along the geometry’s contour in lateral direction. The main problem during the forming process is the influence on the dimensional accuracy resulting from the compliance of the involved machine structures and the springback effects of the workpiece. The project aims to predict these deviations caused by resiliences and to carry out a compensative path planning based on this prediction. Therefore a planning tool is implemented which compensates the robot’s compliance and the springback effects of the sheet metal. Finite element analysis using a material model developed at the Institute of Applied Mechanics (IFAM) [1] has been used for the simulation of the forming process. The finite strain constitutive model combines nonlinear kinematic and isotropic hardening and is derived in a thermodynamical setting. It is based on the multiplicative split of the deformation gradient in the context of hyperelasticity. The kinematic hardening component represents a continuum extension of the classical rheological model of Armstrong–Frederick kinematic hardening which is widely adopted as capable of representing the above metal hardening effects. The major problem of low-order finite elements used to simulate thin sheet structures, such as used for the experiments, is locking, a non-physical stiffening effect. Recent research focuses on the large deformation version of a new eight-node solid-shell finite element based on reduced integration with hourglass stabilization. In the solid-shell formulation developed at IFAM ([2], [3]) the enhanced assumed strain (EAS) concept as well as the assumed natural strain (ANS) concept are implemented to circumvent locking. These tools are very important to obtain a good correlation between experiment and simulation.
875
Authors: Horst Meier, Jan Brüninghaus, B. Buff, Alfred Hypki, Adrian Schyja, V. Smukala
Abstract: This paper describes a new development in incremental, robot-based sheet metal forming (Roboforming). Roboforming is a dieless sheet metal forming process which ensures cost-effective manufacturing of prototype parts and small batches. Its principle is based on flexible shaping by means of a freely programmable path synchronous movement of two industrial robots driving work-piece independent forming tools. The final shape is produced by the incremental inward motion of the forming tool in depth direction and its movement along the contour in lateral direction on a heli-cal path. The supporting tool, with its simple geometry, holds the sheet on the backside by moving syn¬chronously along the outer contour, at constant depth. In this way no special dies are needed. For mil¬ling machines, which are used in numerous incremental forming approaches, CAD/CAM inter¬faces exist for generating necessary tool paths. For industrial robots only a few simple solutions emerge, which do not have the potential of classical CAD/CAM interfaces and are unusable for co-operating robot systems. While the two coupled robot programs can be programmed manually for simple geometries, this approach does not work for complex geometries. In this paper a further de-velopment in robot programming systems is presented that is now able to derive helical tool paths from any CAD file and generate two cooperating programs for the forming and the sup¬porting tools. The helixes pitch is variable and dependent on the geometry’s wall angle. To increase the part accu¬racy a process database is used, that stores relevant information about the process pa¬rameters, sensor data and used equipment. Based on this information strategies for increasing the part accuracy can be applied.
143
Authors: Horst Meier, V. Smukala, O. Dewald, Jian Zhang
Abstract: This paper describes a new development of an incremental, robot based sheet metal forming process for the production of sheet metal components for limited-lot productions and prototypes. The kinematic based generation of the shape is implemented by means of two industrial robots, which are interconnected to a cooperating robot system. Compared to other incremental sheet metal forming machines this system offers a high geometrical form flexibility without the need of any workpiece dependent tools. The principle of the procedure is based on flexible shaping by means of a freely programmable path-synchronous movement of two robots. So far, the final shape is produced by the incremental infeed of the forming tool in depth direction and its movement along the contour in lateral direction on each level. The counter tool, with its simple geometry, was used to support the sheet metal on the backside by moving synchronously along the outer contour, constantly on the same level. This corresponds to a fixed backplate used in other incremental sheet metal forming processes. Due to the use of a new robot system with extended control algorithms for cooperating robots, it will be possible to release the counter tool from its constant path on the outer contour and support the forming tool right on the opposite side of the sheet to generate a predefined gap between the two hemispherical tools. This way at each moment a small part of a full die, as it is used in other processes, is simulated without the need of producing a workpiece dependent die. The extended payload of the new robot system gives the opportunity to form steel blanks, for the first time.
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