KurzfassungIn diesem Artikel werden zwei Neuerungen bei der numerischen Simulation von induktiven Randschichthärteprozessen vorgestellt, welche bei schwierigen Fragestellungen als unterstützendes Werkzeug zur Prozessauslegung verwendet werden können. Zum einen wird ein 3-D-Modell für die Simulation beim Vorschubhärten komplexer Bauteile gezeigt. In diesem Fall steht das Konzept der Modellierung im Fokus. Für einen Härteinduktor mit einer sehr aufwendigen Bestückung an Feldkonzentratoren, welcher beim Härten von Großlager-innenringen zum Einsatz kommt, wird die Anwendung beispielhaft demonstriert. Es wird gezeigt, dass das Modell durch den Vergleich von Simulationsergebnissen und Experimenten verifiziert werden konnte. Zum anderen wird ein inverses, numerisches Berechnungsverfahren vorgestellt, welches sich auf die Verwendung von Optimierungsalgorithmen stützt. Ausgehend von einem Härteprofil wird dabei auf die Abmessungen und die Position des Induktors relativ zum Werkstück sowie die elektrischen Parameter zurückgeschlossen. Anhand des Beispiels einer Hohlwelle wird gezeigt, dass mithilfe dieses Ansatzes eine effektive Prozessauslegung erfolgen kann.

In the present paper, a new numerical model for calculating martensite microstructure in induction surface hardening processes is introduced. The model was developed with the help of the Department of Electrotechnology and Converter Engineering (LETI). It takes into account the heating as well as the quenching process and uses the temperature history of a work piece to calculate martensite formation. The calculation is based on an empirical equation found by Koistinen and Marburger [1]. A comparison between the heat distribution within a work piece at the end of the heating process and the distribution of martensite after quenching is performed for different process parameters. Thus, it is determined, in which case the temperature distribution is sufficient to predict the hardened layer and in which case the microstructure has to be calculated to receive accurate results. The model is verified by comparing simulation results with different experiments.

In the present paper, a new numerical model for calculating martensite microstructure in induction surface hardening processes is introduced. It takes into account the heating as well as the quenching process and uses the temperature history of a work piece to calculate martensite formation. The calculation is based on an empirical equation found by Koistinen and Marburger [1].A comparison between the heat distribution within a work piece at the end of the heating process and the distribution of martensite after quenching is performed for different process parameters. Thus, it is determined, in which case the temperature distribution is sufficient to predict the hardened layer and in which case the microstructure has to be calculated to receive accurate results. The model is verified by comparing simulation results with different experiments.

Perfecting the induction process relies on fine-tuning every small detail. For the tool, this means the complex development process for the inductors using design software, high-precision production, and the correct positioning of the tool in the machine’s connection system. Applying different new and highly advanced 3D technologies such as FEM & CFD analysis and 3D printing of inductors will lead to a drastic increase of efficiency and the highest reproducibility for the entire process. When this happens, computer-aided accuracies of the inductors are compared with real manufactured inductors using 3D optical measurement methods and will reveal the advantages of this new process technology. The precision and process repeatability of this technology is showcased by various experimental test series’ that take the daily operational challenges for induction hardening as a benchmark.

Inductive surface hardening falls under the standard heat treatment of automobile drive train components. Wheel hubs, kingpins and various axle shafts will, for instance, be hardened. Two different inductor concepts are generally used for such processes: ring or line inductors. Many geometric boundary conditions must be taken into account when line inductors are used. The adjustment of the hardness transitions of a component includes the length of the inductor and also, for instance, the arrangement of the supply leads. The use of field concentrators will also have a significant effect on the result. This article deals with tests and numerical calculations for a sample component on which these effects were examined.