New measurement method for process control of inductive heating operations of metals into the semi-solid state

• Applicant: Professor Dr.-Ing. Alexander Verl
• Subject Area: Production Systems, Operations Management, Quality Management and Factory Planning ; Production Automation and Assembly Technology
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 271002868

In thixoforming, heated workpieces in a semi-solid phase are formed. Semi-solid materials have special properties which are positive for forming. Workpieces for thixoforming are often heated inductively, as this type of heating enables high outputs and efficiencies as well as precise control of the inducted power. Challenges in inductive heating arise due to the uneven heat input due to the skin effect. This makes it difficult to obtain a homogeneous liquid phase fraction in the workpiece, especially at high heating rates.For the measurement of the liquid phase fraction, a current measurement based on the recorded currents at the inductor was developed, which is based on the already known time constant measurement. Due to the skin effect, the currents responsible for heating are concentrated in the edge area of the workpiece. This carries the risk of melting off the edge areas, while the center of the workpiece has not yet reached the liquid phase fraction required for the forming process. Although the melting of the edge areas can be prevented by measured value acquisition and monitoring, but it is not known when the inside of the workpiece has adjusted due to heat conduction effects.On the basis of the values for the liquid phase fraction that can be measured in the edge area of the workpiece, the liquid phase fraction inside the workpiece is to be determined on the basis of a heating model. The model is supported by the measured values of the developed measuring in order to make as accurate a statement as possible about the propagation of the heat energy in the workpiece and the associated melting processes. This heating model will be investigated and implemented in this research project.The heating model will first be tested together with the developed current-based measurement by offline evaluation. Subsequently, the measured quantity acquisition and the heating model will be implemented on the control hardware.

• DFG Programme: Research Grants
• Co-Investigator: Dr.-Ing. Armin Lechler