Magnetic Pulse Welding of Sheets – Process Modelling

Magnetic pulse welding involves the application of a controlled electromagnetic impulse and consequent high velocity impact between two overlapped parts, which leads to plastic deformation and consolidation between the parts along the interface without melting. The key variables in magnetic pulse welding include a high magnitude discharge energy of damped sinusoidal nature, the coil type and geometry and the materials, thicknesses and geometry of the overlapped metallic sheets. A computer-based coupled electromagnetic and dynamic mechanical analysis of magnetic pulse welding of sheets is presented in this work to provide an insightful understanding of the evolution of joints, which is otherwise intractable for monitoring due to the high speed of the process and the presence of a high electromagnetic field. The computed results show that such a computational process model can serve as a robust design tool for a fundamental understanding as well as for the identification of suitable conditions for achieving a defect-free, reliable joint

Development of a maximum entropy approach for the thermomecanical modelling of the rotary friction welding process

A multi-physics modelling of rotary friction welding process based on a Maximum Entropy approach is proposed. This approach will be able to solve coupled thermomechanical problems. Because strains are very high locally around the welded area, the remeshing time in a classical finite element method is very important. The use of this meshless method should reduce simulations time and the numerical diffusion phenomena

Magnetic Pulse Spot Welding: Application to Al/Fe Joining

Magnetic pulse welding is a rapid process (takes place within few micro seconds) that joins both homogeneous and heterogeneous materials in the solid state. The process involves applying variable high current on an inductor to generate Lorentz forces on to the conductive primary part (flyer). To realize the weld it is necessary to accelerate the flyer to impact on to the secondary stationary part (base material) at a very high velocity attained over the distance, called air gap, between the parts. It is typically possible to perform welding of tubes and sheets provided there is an optimized air gap between the parts to be welded. As part of our work we have developed an innovative approach (Magnetic Pulse Spot Welding-MPSW) that eliminates the delicate task of maintaining the aforementioned air gap between the plates. The proposed method opens better viable perspectives for heterogeneous assembly of automotive structures or connecting batteries in a quasi-cold state. The developed approach has been validated on the heterogeneous assembly Al/Fe by tensile tests (quasi-static and dynamic) that attested the quality of welds

Material Constitutive Behavior Identification at High Strain Rates Using a Direct-Impact Hopkinson Device

Modern numerical simulation techniques allow nowadays obtaining accurate solutions of magnetic pulse and electrohydraulic forming/welding processes. However, one major difficulty persists: the identification of material constitutive equations behavior at levels of high strain rates reached by these processes, and which varies between 103 and 105 s-1. To address this challenge, a direct-impact Hopkinson system was developed at ECN. It permits to perform dynamic tests at very high strain rates exceeding the range of the traditional Split Hopkinson Pressure Bars and hence enable us to identify constitutive models for a wide range of strain rates. The alloy used to test this device was Ti-6Al-4V. Strain rates up to 2.5×103 s-1 were attained

Electrohydraulic Crimping of 316L Tube in a 316L Thick Ring

During the electrohydraulic forming process a high current, up to one hundred of kilo amperes, is discharged between two electrodes immersed in a water tank. This creates plasma that generates a primary shock wave and secondary pressure waves. If these pressures are applied in a tube, it is then possible to deform dynamically this tube against a ring, leading to crimping. This process presents several advantages: it is possible to deform internally tubes of diameters ranging from a few millimetres to several centimetres, no lubrication is needed and because the process is dynamic, the spring back is limited and some materials can present an improved behaviour compared to quasi-static forming. In this paper, we present an original electrohydraulic crimping device. We successively present the operating principle of our system, the time evolution of the crimping pressure and the strain rate in the tube for two kinds of pulse shaper. Finally crimping tests are done to evaluate the efficiency of the process

Simulation de l'écoulement des pâtes cimentaires par un modèle diphasique

La modélisation de l'écoulement des pâtes cimentaires est un problème difficile car le matériau a non seulement un comportement rhéologique complexe mais il peut également présenter des hétérogénéités induites par l'écoulement. L'apparition de ces hétérogénéités résulte de la filtration de phases fluides au travers de phases solides et peut conduire au blocage de l'écoulement. Pour modéliser l'écoulement d'un tel matériau il est nécessaire de prendre en compte la présence d'au moins deux phases. Dans notre modélisation nous considérons que les deux phases sont continues et admettent un comportement rhéologique en loi de puissance. Le couplage entre les deux phases est pris en compte au moyen d'une loi de Darcy généralisée à un fluide en loi de puissance. Le modèle est résolu par la méthode des éléments finis et validé dans le cas d'un test d'écrasement. Nous montrons que ces simulations permettent d'établir des diagrammes d'ouvrabilité des pâtes cimentaires

Un Modéle Thermodynamique de Fluide Electro-Rhéologique

none3G. NAPOLI; DROUOT R; RACINEUX GNapoli, Gaetano; Drouot, R; Racineux, G

Development of a maximum entropy approach for the thermomecanical modelling of the rotary friction welding process

A multi-physics modelling of rotary friction welding process based on a Maximum Entropy approach is proposed. This approach will be able to solve coupled thermomechanical problems. Because strains are very high locally around the welded area, the remeshing time in a classical finite element method is very important. The use of this meshless method should reduce simulations time and the numerical diffusion phenomena