Postdoc in Mechanical Engineering - Pr. Franck Andrés GIROT MATA - LTC AENIGME (# of pos: 1)

A postdoctoral position in Magnetic Pulse Finite Element Modelling for Dissimilar Material Components Assembly is available in the research group of Advanced Manufacturing at the Laboratories for Trans-border Cooperation - LTC AENIGME. This is an initiative between the Department of Mechanical Engineering of the Faculty of Engineering of Bilbao and the Institute of Mechanics and Engineering of Bordeaux. It brings together researchers from UPV / EHU, UBx, ENSAM and INP Bordeaux.

The aim of the research line where the postdoctoral researcher is hiring is to model the magnetic pulse processes for joining dissimilar materials, as are Magnetic Pulse Welding (MPW) and Magnetic Pulse Riveting (MPR). Both technologies are at high speed and due to their electromagnetic pulse source; a multiphysical coupled modelling is required (electromagnetic, thermal and mechanical).

Conventional welding processes present difficulties in joining new combinations of metals. Today's innovations introduce more and more dissimilar assemblies that meet new challenges, such as the requirement for lightweight, structural reinforcement, and other functional specifications. High-speed impact welding methods allow different metal combinations to be joined. The high pressure, short duration and low temperature bonding present the main particular characteristic of these methods. Welding involves a strong interfacial collision using the magnetic impulse (MPW). The use of electromagnetic pulse to provide a significant Lorentz force makes MPW an attractive method relative to other welding processes. The MPW is particularly promising in terms of cost, reliability, ease of use, flexibility, pace of work, absence of consumption requirements and eco-efficiency.

Conventional riveting techniques, such as press riveting and pneumatic riveting, can damage composite material structures, and have difficulties in deformation of high-strength materials and large aluminum rivets. In addition, pneumatic riveting is noisy and harmful to the operator due to the vibrations generated. These aspects limit the advancement of the development of lightweight structures in the transport sector. The magnetic pulse riveting technology has been developed to improve the quality of the rivets and to respond to the limitations of traditional methods, its most important advantages being deformation at high speeds, high impact force and uniformity of deformation. Electromagnetic rivets can obtain uniform interference, which facilitates its application in riveting of composite structures. In addition, electromagnetic pulses can generate high pressures exceeding the yield strength of large-size aluminum and high-strength alloy rivets.

Magnetic pulse processes contribute positively to achieve energy efficient industrial technologies. The input energy used to discharge through the electromagnetic coil suffers very low losses what makes highly efficient energetically, compared to other conventional processes that need to use large amounts of energy in order to melt the material to weld and moving mechanical elements to apply the force to induce the rivet plasticity. One of the keys, in terms of low energy use, is the direct use of the inertial forces generated during the pulse directly to form the material.

The modeling of all magnetic pulse shaping operations requires a transient electromagnetic calculation to obtain the currents and forces generated. The prediction of the deformation result is simulated in the last stage by means of an explicit structural simulation, since the forming process is carried out on time scales of about 100 μs. For a correct calculation of the forces generated during the process, it is necessary to couple the electromagnetic and mechanical simulation.

The type of modeling to be carried out for the simulation of the different operations of the electromagnetic process combines the electromagnetic and structural-mechanical models, so multiphysics simulation software is required. In this case, the Ansys LS-Dyna software will be used.

The scientific technological objectives pursued by this research line are:

• Develop a Finite Element model for the simulation of the welding and riveting processes by means of magnetic impulse.
• Validate the developed models with experimental results.
• Quantify the existing deviations between the FEM models and the results of the experimental validation.
• Develop a model to predict and correlate energy efficiency of the input energy and the model results.