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

Influence of Axial Workpiece Positioning during Magnetic Pulse Welding of Aluminum-Steel Joints

Magnetic Pulse Welding (MPW) offers a method to economically join similar and dissimilar metals without the need for external physical or chemical binders, while avoiding the adverse heating effects seen in many welding techniques. MPW allows for the fabrication of joints via the harnessing of Lorentz forces, which result from discharging a current pulse through a coil. In the process an outer piece (flyer) is accelerated onto an inner piece (parent), and welding is achieved using propagating impact fronts. There are several geometrical factors to be considered including the flyer-coil distance, the parentflyer distance, as well as the axial relationship between flyer and coil (working length). Various shapes of the front are possible and each configuration has its own advantages and drawbacks. The goal of this work is to show not only how the aforementioned parameters are related, but also ways to optimize front propagations, which are vital to the welding result. This is done primarily by determining the influence of the working length of tubular MPW specimens. It is shown that for steel-aluminum joints in the given arrangements, three different front regimes exist, which are related to geometrical factors. These results are especially useful to avoid seemingly favorable but nevertheless suboptimal conditions for flyer movement that would reduce weld quality and energy efficiency of the process

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

Inter- and intramolecular aryl-aryl-interactions in partially fluorinated ethylenedioxy-bridged bisarenes

Weddeling J-H, Vishnevskiy Y, Neumann B, Stammler H-G, Mitzel NW. Inter- and intramolecular aryl-aryl-interactions in partially fluorinated ethylenedioxy-bridged bisarenes. Chemistry - A European Journal. 2020;26(68):16111-16121.Several ethylenedioxy-bridged bisarenes with a variety of type and number of aryl groups were synthesized to study non-co-va-lent dispersion-driven inter- and intramolecular aryl - aryl-interactions in the solid state and gas phase. Intramolecular interactions are pre-fe-rably found in the gas phase. DFT calculations of dispersion-cor-rec-ted energy scans for rotations around the ethy-lene-dioxy-bridge and optimized structures show larger inter-acting aromatic groups to in-crea-se the dispersion energy. Single molecule structures generally a-dopt folded conformations with short intramolecular aryl-aryl-con-tacts. Gas electron diffraction experiments were per-formed exem-pla-rily for 1-(pentafluorophenoxy)-2-(phenoxy)-ethane. A new pro-cedure for struc-ture refinement was developed to deal with the confor-ma-tional com-plexity of such molecules. The results are an experimental con-fir-ma-tion of the existence of folded conformations of this molecule with short -intramolecular aryl-aryl distances in the gas phase. Solid-state struc-tures are dominated by stret-ched structures with-out intra-mo-le-cular aryl - aryl-interactions but in-ter-actions with neigh--boring molecules. © 2020 Wiley-VCH GmbH