Matthias Kleiner

Analysis of Process Parameters and Forming Mechanisms within the Electromagnetic Forming Process

Electromagnetic forming (EMF) is a typical high speed forming process using the energy density of a pulsed magnetic field to form workpieces made of metals with high electrical conductivity like e.g. aluminium. In view of new lightweight constructions, special forming processes like EMF gain importance for the associated materials. For a better understanding of the working mechanisms and the process prediction a coupling of electromagnetical and structure-mechanical models, advanced simulation tools as well as detailed experimental investigations with on-line measurements of the ultra-fast deformation of significant workpiece areas is required. New results of research concerning correlations among workpiece properties, strain rate, and acting magnetic pressure are presented.

Combined Methods for the Prediction of Dynamic Instabilities in Sheet Metal Spinning

Abstract A technological and mathematical understanding of the sheet metal spinning process allows to predict dynamic instabilities which lead to wrinkling and other defects in the workpiece depending on the axial feed of the roller tool, the design and the number of the forming passes as well as the angular velocity of the workpiece. The development and combined application of methods of statistical design of experiments, nonlinear time series analysis and finite element analysis yields insight into the dominant effects. The results will allow to predict wrinkling and to design and control the process as to avoid it. Preventing workpiece damage by wrinkling, this methods will help to significantly improve process efficiency.

Analysis of Residual Stresses in High-Pressure Sheet Metal Forming

Abstract The further development of innovative forming processes like sheet metal hydroforming is only possible with the help of detailed knowledge about the workpiece properties and their formation depending on the particular process strategy. Up to now, the detailed understanding regarding the formation of residual stresses in hydroforming processes like the high-pressure sheet metal forming (HBU) is insufficient. Therefore, numerical (FEM) and experimental investigations on the residual stresses induced in HBU-formed workpieces have been carried out. The results show that a higher fluid pressure leads to significantly lower residual stresses in addition to an improved accuracy of form and dimensions.

Thermodynamic Modeling of Complex Systems

The thermodynamic behavior of complex pure fluids and mixtures is strongly affected by specific interactions like association (hydrogen bonding) and electrostatic interactions of permanent or induced dipoles. The modeling of those systems requires a physical model that is able to explicitly account for these specific interactions. This contribution describes the state of the art in modeling of complex fluids using analytical equations of state. Many applications demonstrate that those models can successfully be applied to describe and even to predict the phase behav ior of a whole variety of substances ranging from small gas molecules up to organic solvents and polymeric systems.

Integration of Electromagnetic Calibration into the Deep Drawing Process of an Industrial Demonstrator Part

In recent years a steadily growing interest in applying lightweight construction concepts could be observed. This development is accompanied by an increasing demand for innovative forming strategies suitable for extending the forming limits of the typical lightweight materials. Deep drawing combined with an integrated electromagnetic calibration step is an example of such a technology. The feasibility and potential of this process combination is analyzed on the basis of a demonstrator part from the automotive industry. Thereby, aspects related to the practicability of the electromagnetic forming process itself are regarded as well as points related to the deep drawn preform. The concept of a 3D-coil insert, integrated into a deep drawing punch in order to realize the calibration in the deep drawing process, is introduced and based on the experimental results, conclusions regarding the applicability of the process combination are drawn.

Process Characterization of Sheet Metal Spinning by Means of Finite Elements

Sheet Metal Spinning is a flexible manufacturing process for axially-symmetric hollow components. While the process itself is already known for centuries, process planning is still based on undocumented expertise, thus requiring specialized craftsmen for new process layouts. Current process descriptions indicate a vast scope of different dynamic influences while the underlying mechanical model uses a simple static approach. Thus, a 3D Finite Element Model of the process has been set up at IUL in order to analyze the process in detail, providing online as well as cross sectional data of the specimen formed. Within the scope of this article, the results of the above mentioned Finite Element Analysis (FEA) are presented and discussed with respect to the qualitative stress distributions introduced in the existing theoretical models. Main emphasis of this paper is set on a discussion of the qualitative stress distribution, which is, to the current state, only known in theory.

Surface reconstruction for incremental forming

In spite of extensive efforts being made with regard to virtual process optimization technology, the production of prototype parts is still a necessity. With respect to the production of sheet metal parts in low quantities, incremental sheet metal forming (ISMF) is a highly interesting process. ISMF allows the production of complex parts with drastically reduced costs in tooling and machinery compared to conventional processes like deep drawing. However, ISMF, with it’s incremental nature, introduces the need for generating a tool path considering both final geometry and process-induced deviations or constraints. Consequently, for the generation of the tool path a (tool path) surface, with an adequate offset, is necessary. That is why, within the scope of extensive research work at the Institute of Forming Technology and Lightweight Construction (IUL), a special correction module has been developed, determining this offset e.g. depending on the workpiece geometry. This paper presents the algorithm, the application, and the effect on the produced parts. Furthermore, a concept for an extension regarding further constraints like elastic workpiece behavior is presented.

Experimental and Finite Element Analysis of Capabilities and Limits of a Combined Pneumatic and Mechanical Deep-Drawing Process

Abstract In the last ten years various forming processes with working medium - like hydraulic counter-pressure deep drawing (also known as hydromechanical deep drawing) or hydroforming - are more and more used for different applications especially in the automotive industry. Recently another process was proposed: the so-called pneumomechanical deep drawing combines a preforming, which uses a gaseous working medium like air, carbon dioxide or nitrogen, with a deep drawing in the same, specially designed tool system. The paper presents research work on process and tools as well as on their application to sheet metal forming. Process capabilities and limits are analysed through forming experiments, strain measurements based on an optical system and through corresponding finite element calculations.

Joining by Forming of Lightweight Frame Structures

Joining of lightweight frame structures in small quantities is subject to specific conditions, which are exemplarily determined for joining by forming processes. Experimental investigations have been carried out to evaluate both feasibility and capability of joining by forming processes. Joining has been accomplished by compressing or expanding cylindrical profiles using rigid tools for rolling-in processes, fluid active medium for hydro-forming as well as active energy for electromagnetic forming.

Springback Analysis of Sheet Metals Regarding Material Hardening

The phenomenon of springback of thin-walled sheet metal parts after forming is a well known problem of forming technology in general, but particularly since the finite element simulation offers the opportunity to predict geometrical and material properties after forming. Irrespective of the intensive efforts in the previous years, a reliable and accurate prediction of springback deviations by use of the finite element simulation is still not possible. This paper deals with the numerical and experimental analysis of the springback effect itself, which dependents on the final stress states of a part after the forming process. Experimental investigations have been carried out to analyze geometrical accuracy in loaded and unloaded conditions to isolate the springback effect. Additional finite element simulations have been conducted in order to compare the experimental and numerical results and to determine the geometrical differences and their reasons. Two experimental set-ups are being discussed: Air bending on the one hand, which offers good access to the specimen in the testing equipment, and draw bending on the other hand, which is characterized by a simple strain state, but also by strain reversal within the tests. Both experiments were carried out using DP600 and X5CrNi18.10 with three different sheet thicknesses and bend radii and were compared with according FE-models. An additional shear test experiment has been developed to characterize the material behavior of the tested sheet metals for strain reversal. Furthermore, the importance of the Bauschinger effect and usable hardening models were analyzed. This study intended to investigate reasons for insufficient form and dimensional accuracy between simulations and experiments after springback and to propose modeling methods to improve the accuracy.