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6004 |
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Tuesday, May 21, 2019, Saal Brüssel 12:40 PM Brazing for tool applications |
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Improved process control during induction brazing |
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Julian Hebing* / RWTH Aachen University, Germany Kirsten Bobzin / Surface Engineering Institute, Germany Mehmet Öte/ Surface Engineering Institute, Germany Stefanie Wiesner/ Surface Engineering Institute, Germany |
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Brazing by means of inductive heating is a very widespread process variant in industry. The process is characterized by very fast local heating and excellent automation. Due to the so-called "skin effect", the transmittable power and thus the temperature decreases sharply from the component surface to the core. Furthermore, by using superficial temperature measurement methods, for example a pyrometer, no obvious information can be gathered about the temperature inside the brazing gap. Consequently, low temperatures inside the brazing gap can result in insufficient wetting of the substrate by the filler metal. On the other hand, exaggerated temperature regimes, which are usually adjusted to reach a sufficient temperature in the core, often lead to high residual stresses or to the formation of undesirable hard phases in the brazing seam. In this work, new approaches are presented that indirectly allow gathering of information about the condition of the filler metal and thus the temperature in the brazing gap. For the investigations, thermal effects such as the sinking of the substrate due to the melting of the filler metal were analysed by means of dilatometer measurements on the example of a hard metal-steel brazing joint. Furthermore, disturbances such as the austenitisation of the steel substrate and the evaporation of flux were investigated. Subsequently, the results were validated by displacement and force measurements during induction brazing process. The results show that by using force and displacement sensors, the point of complete melting of the filler metal can be detected. Thus, the attainment of the melting temperature inside the brazing seam can be monitored dearly. Based on this information, the brazing process and the process reliability can be optimized. |