Abstract

Inductive welding is a popular method for making metallic tubes used in a variety of industries. A majority of these induction tube welding systems use internal magnetic flux controllers (impeders) to limit the current flowing on the ID of the tube under the induction coil. As higher power, solid state IGBT power supplies become more widely available for tube welding, and demand for lower cost tubes with higher strength to weight ratios increases, magnetic loading of these impeders is also increasing. Traditionally, impeders are made of ferrites which have a low saturation flux density and can become saturated in these demanding conditions. Saturation of the impeder results in greater currents on the tube ID and lower process efficiency and weld quality. In order to expand the upper operating range of these more demanding systems while maintaining the weld quality, a change in impeder material from ferrites to soft magnetic composites (SMC) with greater saturation flux densities is suggested, as well as the addition of external magnetic controllers (bridges). In this paper, a comparison is made between induction systems with impeders constructed from traditional ferrites and those utilizing bridges and impeders made from SMCs. To do this, a simulation study will be used to estimate impeder flux density, required coil current, and temperature distribution at the end of heating when using impeders made of the two materials, with and without bridges. By soft coupling 3-D electromagnetic models with 2-D electromagnetic and thermal models, a fast and accurate depiction of the welding process can be achieved. A case study is presented comparing simulation results to experimental results.

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