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

Simulation of Wrinkle Formation in Free Electromagnetic Tube Compression

A 3-dimensional (3D) finite element (FE) simulation of free electromagnetic (EM) tube compression was performed with the aim of predicting wrinkle formation. Staggered coupling was applied between the EM and mechanical parts of the problem. The full 360° portion of the problem was modelled since the wrinkle formation does not represent any symmetry in circumferential direction. The initial geometric imperfections of the tube were measured and included in the model to trigger buckling. The deformed geometry with the wrinkles could be predicted accurately

Influence of Different Strain Rates on the Flow Curve and the Formability of Thin Aluminium and Tinplate Sheets

Due to this high number of produced units and the very thin sheet metals used for beverage cans, precise production processes with high production volumes are necessary. To save expenses, while optimising these processes, numerical simulation methods are exploited. Considering this, it is indispensable to identify the material behaviour as exactly as possible. In practise, often results of quasi static tensile tests are used, although these are insufficient for the precise modelling of the material behaviour during can production, since strain rates of up to 10³ s-1 can occur, here. Therefore, quasi static and high speed tensile test have been done on specimens featuring the typical materials and thicknesses of semi-finished parts used for beverage can production. The results were compared with similar materials at higher sheet metal thicknesses and authenticated by numerical simulation. It was shown that there is an influence of the strain rate on the material behaviour and it is necessary to determine material characteristics at strain rates, which are close to the process speed. Furthermore, the results were classified in their signification for beverage can production and forming technologies in general

Investigation of the Process Chain Bending-Electromagnetic compression-Hydroforming on the Basis of an Industrial Demonstrator Part

The increasing significance of lightweight construction concepts requires innovative and adapted production technologies and process chains for the manufacturing of complex parts made of typical lightweight materials. The feasibility and potential of such a process chain consisting of the steps Bending - Electromagnetic compression (EMC) Hydroforming is shown in the present paper on the basis of a demonstrator part similar to a structural component from the automotive industry. Here, special focus is put on the requirements on the production steps and the workpiece properties. Furthermore, the development and testing of EMC-equipment that is optimally adapted to the special forming task is described

Agile Production of Sheet Metal Aviation Components Using Disposable Electromagnetic Actuators

Electromagnetic forming is a process used to produce high strain rates that improve the formability of sheet metal. The objective of this paper is to discuss the feasibility of the use of disposable actuators during electromagnetic forming of two aluminum components: an industry part whose main feature is a convex flange with two joggles, and a simple part with a one-dimensional curve throughout. The main forming complications after the parts were formed using conventional methods were the presence of wrinkles and excessive springback. The goal of this work is to use large, controlled electromagnetic impulses to minimize the springback of these components from a roughformed shape, with the end result being a dimensionally correct part. The optimum test protocols for electromagnetic calibration of the components were determined by optimizing parameters such as design of the actuator, tool material, and capacitor discharge energy. The use of disposable actuators for electromagnetic calibration of the parts showed significant reductions in springback compared to the parts which were only preformed using conventional techniques (hydroforming and rubber-pad forming). Springback was decreased in the curved component by up to 87%. For the flanged component, the wrinkles were eliminated, the joggles were formed properly, and the average bending angle of the part was improved from 95.3° to 90.3°, very near the target bending angle of 90°. This study demonstrates that these forming techniques can be used to improve current sheet metal production processes

Process Analysis and Physical Simulation of Electromagnetic Joining of Thin-Walled parts

To avoid typical problems when connecting different metallic materials as aluminum and titanium as e.g. the formation of intermetallic phases, electromagnetic welding represents an alternative technology to conventional (i.e. usually thermal) joining processes. Although feasibility and potential of this technique are already proved, the fundamental correlations of part- and process-parameters have not yet been investigated systematically. As an approach to examine these, the performance of model experiments and supplementary technological tests is suggested. The resulting connection quality is evaluated using metallographic methods

Development of design principles for form-fit joints in lightweight frame structures

Based on fundamental technological investigations, alternative joining strategies using electromagnetic forming (EMF) for the flexible production of lightweight frame structures are developed in the collaborative research project SFB/TR10. The results of these investigations will also be used to create general design principles for the joining process itself as well as for the joining zone. The focus of this article will be on dominating form-fit joints of aluminum frame structures and the parameters which have a significant influence on the strength of those joints. For the development of design principles regarding the joining zone, the groove geometry of the connection elements was varied in terms of size and shape, and the influence of those variations was analyzed. In terms of the joining process itself the effect on the joint strength of different forming pressures for a given groove geometry was also investigated. In the first step these experiments were performed on solid mandrels. In order to reduce the weight of the structure, experiments were then performed with hollow connection elements and similar groove geometries to analyze how the reduced stiffness of those elements affected the strength of the joints

Process Model and Design for Magnetic Pulse Welding by Tube Expansion

In this paper a design methodology for magnetic pulse welding processes is presented. To examine fundamental correlations of part- and process-parameters, a model experiment is used. Different impacting conditions are tested and the effect on the joint quality is evaluated by metallographic analysis. Conclusions regarding suitable impacting parameters are drawn. Electromagnetic expansion tests are carried out in parallel with the aim of adjusting the impacting parameters via typical process parameters. Therefore, the forming velocity is measured online and the impacting angle is varied via the geometry of the joining zone. To verify that the tendencies observed in the model experiment occur also in magnetic pulse welding, the influence of the impacting parameters on the joint quality is investigated for magnetic pulse welded tubes, too. Finally, the results of both investigation paths are combined and serve as a basis for target-oriented design of magnetic pulse forming processes