Used Tools:

Introduction

Magnetic pulse welding (MPW) process is an innovative, high speed forming technology, widely used in aerospace and automobile industries. This technique can be compared to explosion welding, however, instead of explosives, it uses a magnetic force to accelerate the objects.

Unlike conventional welding processes, MPW involves no melting, thus eliminating any major changes in the material properties. The usage of magnetic force to accelerate one object against the other results in a solid state weld, with no external heat source and no thermal distortions. Besides its advantages, MPW causes various interfacial phenomena, like the joule heating due to eddy currents. The Figure 1 shows a sample of two tubes that have been magnetically welded.

Figure 1 - Magnetic pulse welding sample [1]

Problem description

Electromagnetic simulation coupled to thermal analysis is performed to study the heating effect during the MPW welding process. A case study consists of a one turn coil combined with a field shaper. This article will show the multi physics capabilities of EMS to solve an electromagnetic and thermal problem in time domain using the EMS transient module. The Figure 2 shows the simulated model.

Simulation Setup

The Transient Magnetic module of EMS is used to compute and visualize magnetic fields that vary over time. It also addresses a variety of associated phenomena, such as eddy currents, power losses and magnetic forces. 

To perform an analysis using EMS, the following steps need to be performed:

1. Apply the proper material for all solid bodies.
2. Apply the necessary electromagnetic inputs.
3. Apply the necessary thermal inputs.
4. Mesh the entire model and run the solver.

Materials

Aluminum alloy AA2024-T351 is prescribed to both tube and rod. Electromagnetic, mechanical and thermal properties of the materials used for each part are summarized in Table1.

Material	Part	Density (Kg/)	Electrical conductivity (S/m)	Specific heat capacity (J/Kg.K)	Thermal conductivity (W/m.K)
Aluminum alloy 2024-T351	Tube and Rod	2700	1.74	795	143
Copper alloy	Field shaper	7900	2.66	486	36
Steel	Coil	7800	4.06	486	36

Thermal Input

 The thermal convection inputs for the ambient air body:
-The initial temperature of the simulations is set to 298 K
-Convection coefficient is set to 10 W/

Electromagnetic Inputs

In this study, a one turn solid coil is defined as a current source.

Figure 3 - Input current waveform [2]

Meshing

For the meshing, EMS estimates a global element size for the whole model by taking into consideration its volume, surface area, and other geometric details. The final generated mesh (number of nodes and elements) depends on many criteria such as the geometry and dimensions of the model, element size, and mesh tolerance. Mesh quality can be also adjusted by using the Mesh Control feature, which enables a particularly fine meshing to be applied on the rod and tube in this model (Figure 4).

Results

The numerical simulation revealed the results below, obtained after a half period of the first impulse of input current. Once the solution is completed, the following results are created: magnetic flux density, magnetic field intensity, eddy current, inductance, impedance, flux linkage, current, induced voltage, force, torque and losses etc. 

The distribution of magnetic flux density clearly indicates the shielding effect of the tube during the diffusion time that blocks the most of the magnetic field reaching inside the tube.

Figure 5 - Magnetic flux density distribution for the whole model a) Along the axial plane of the field shaper at the end of first half cycle (11µs) b).

Figure 6  shows the result comparison between EMS  and the reference [3] concerning the magnetic flux density on the external surface of the tube during the first half period of the impulse current.

The temperature distribution for the tube during first half period of the impulse current is also shown in Fig. 8. It shows the region highlighted for the sudden increase in temperature during the collision.

The Table below shows the result comparison between EMS and the reference [2] for the maximum values of temperature distribution in the tube part.

Conclusion

EMS allows to compute the magnetic field and temperature distribution in the workpiece due to induction heating, which enables better understanding of the interfacial behavior of the Electromagnetic pulse welding process. Electromagnetic and thermal results obtained correlate very well with reference results.

References

1]. Seungmin Tak , Hanbin Kang , Inseok Pack , Jinkyu Choi and Seoksoon Lee  "Numerical Simulation of Magnetic Pulse Welding Process for Aluminum Tubes to Steel Bars" Proceedings of ICTACEM 2017 International Conference on Theoretical, Applied, Computational and Experimental Mechanics December 28-30, 2017, IIT Kharagpur, India
2]. T. Sapanathan, K. Yang, D. Chernikov, R.N. Raoelison, V. Gluschenkov, N. Buiron, M. Rachik, "Thermal Effect during Electromagnetic Pulse Welding Process", in:  Materials Science Forum, Trans Tech Publ, (2017) 1662-1667.
3].  T. Sapanathan, K. Yang, R. Raoelison, N. Buiron, D. Jouaffre, and M. Rachik, “Effect of conductivity of the inner rod on the collision conditions during a magnetic pulse welding process,” in 7th International Conference on High Speed Forming, Dortmund, DOI 10.17877/DE290R-16981, 2016.