Werner Homberg

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.

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.

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.

Electromagnetic Compression as Preforming Operation for Tubular Hydroforming Parts

With the aim to extent the forming limits of tube hydroforming a concept of using a previous electromagnetic compression operation will be introduced. One important limit for the possibilities of tube hydroforming is set by the initial circumference and the maximum tangential strain of the used material, whereby the initial circumference is typically determined by the smallest local circumference of the workpiece. The application of an appropriate contoured preform makes it possible to use tubes with a larger initial circumference. In the paper the investigation of the suitability of electromagnetic tube compression for the production of such a preform will be presented. The valuation is based on geometric criteria and material properties of the resulting preform which are strongly influenced by the process parameters. The discussed aspects are the roundness of the preform and the strain hardening of the material.

In-Process Punching with Pressure Fluids in Sheet Metal Forming

Abstract The economical efficiency of metal forming procedures based on pressure fluids can be increased e. g. by integrating the additional (auxiliary) operation of punching into the metal forming process. The potentialities resulting from this proceeding are discussed exemplarily for a high pressure sheet metal hydroforming process. The present investigation is using the FE method for analyzing and optimizing various approaches to in-process punching on high pressure sheet metal hydroforming. Experimental tests are carried out in order to verify the different approaches.

60 Excellent Inventions in Metal Forming

Preface -- Introduction -- Material characterization and simulation -- Sheet Metal Forming -- Hydroforming -- Bulk forming -- Impulse forming -- Bending -- Multi-material forming -- Future studies.