Measurement of High magnetic field pulses inside Magnetic welding coil is challenge. Recently promising measurements were recorded in situ with BeScal magnetic field measurement system employing CMR sensor.
Magnetic forming and welding with high pulsed magnetic field are used for decades, but in recent years are getting more and more interest form manufacturing and research. Still, there are numerous challenges limiting wider adoption of the technology, particularly in process parametrization. Here, CMR sensors can help.
During design of Magnetic Pulse Welding (MPW) or Electromagnetic Forming (EMF) technological processes determination of acting loads and the resulting deformation of the workpiece is one of the key challenges. Engineers have to evaluate:
Machine parameters (capacity, the inner inductance, the inner resistance, the ringing frequency and the charging energy),
Tool parameters (the geometry, the inductance, and the material of the coil, the fieldshaper properties, and the die/mandrel) and
Workpiece parameters (the geometry, the material, the electrical conductivity, and the mechanical properties like flow stress and strain at failure).
Evaluation is far from straightforward, because for the same charging energy of the capacitor completely different loads can occur depending on the machine, the coil, and the workpiece properties. Different loads will lead to significantly different forming (welding) results. Thus, the charging energy, frequently stated as process parameter, is not sufficient to describe the loads and expected process result. Since Magnetic Pressure is the acting force in magnetic forming and welding, measuring this pressure during transient processes would help to design and calibrate MPW and EMF processes. During the operation of MPW and EMF devices, extremely high pulsed magnetic fields (typical magnetic pulse values of 20 Tesla, but may reach even 50 Tesla) are generated. As the amplitude and direction of the magnetic field changes simultaneously during magnetic pulse, measurement of such high magnetic fields becomes complicated. Existing high magnetic field measurement methods using B-dot, Hall or magnetooptical sensors are applicable in case of known magnetic field direction, but accuracy of these methods is low when the direction of magnetic field is not determined in advance or direction is changing during transient process. Also, aforementioned sensors are too big to fit into the gap between the coil (or fieldshaper) and workpiece, which is typically less than half a millimeter. Colossal Magneto-Resistance sensors due to tiny size and low sensitivity dependence on orientation offer new opportunities for MPW and EMF monitoring . Recently, high magnetic field pulses were recorded and measured in situ during magnetic welding with BeScal magnetic field measurement system employing CMR sensor at Institute of Forming Technology and Lightweight Components of TU Dortmund university. Tiny CMR sensor was placed between the fieldshaper and workpiece and magnetic field pulse was measured during magnetic pulse welding machine capacitor discharge. The measurements registered magnetic pulse development inside the coil assuming transient electromagnetic processes and mechanical movement and compression of the workpiece. The results were compared against theoretical modeling and allowed to improve the MPW process model. References: V. Psyk, D. Risch, B.L. Kinsey, A.E. Tekkaya, M. Kleiner. Electromagnetic forming—A review, Journal of Materials Processing Technology 211 (2011) 787–829. O. Liebfried, S. Balevicius, S. Bartkevicius, M.J. Loffler, J. Novickij, M. Schneider, V. Stankevic, N.Zurauskiene, Manganite Sensors array for measurements of Magnetic field distribution, 1st Euro-Asian Pulsed Power Conference (EAPPS 06).
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