Property-control in forging on screw presses by energy dosage and local actuators

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Closed-die forging usually has the goal of shaping a workpiece at reduced forming forces and utilizing the microstructural changes occurring at high homologous temperatures to set the properties for the application. The evolution of the microstructure can be considered as a dynamic system during hot forming. It is controlled by the temporal evolution of the temperature and velocity fields at the material points in the workpiece. Variations in the initial microstructure and the friction and heat transfer conditions lead to variations in properties. When forging on screw presses, the workpiece is brought into shape with several blows. Here it generally seems possible to control the dynamic system of microstructure evolution over the course of the blows. Adaption of impact energy and interpass times between impacts could be used to compensate for deviations, e.g., with respect to temperature, due to a delayed transport of the workpiece. Usually, it is not possible to specifically influence critical workpiece areas during drop forging. There is a lack of degrees of freedom in the tools, so that forming energy cannot be locally introduced in a targeted manner. So far, no work is known which uses the impact energy specifically as a control variable to directly control the microstructure and property formation during forging. Also, no local impact on critical locations is possible because actuators in forging tools that go beyond the knock-off function are currently not state-of-the-art. The subject of this project proposal is the research, implementation and validation of observer and closed-loop control strategies for the global and local property control of energy-bonded forging on screw presses. If the target microstructure is specified in a specific area in the workpiece, an optimal impact sequence can be calculated as a reference using static optimization methods. The development of the microstructure is then estimated from measured sensor values during the course of the process. A first sub-goal is the development of an energy-based material model, i.e. the formulation and validation of material equations for the property-determining microstructural variables on the basis of the energy introduced into the microstructure by forming. The material model shall be combined with an online process model based on interpolated FEM solutions. Here, an equation of motion for the boundary of the domain with fulfilled microstructural requirement is to be derived. This model forms the basis for the control, which is to be implemented as a follow-up control between the actual state and the target state of the domain boundary. The developed solution is first tested virtually using an FEM model and then transferred to the screw press of the chair of mechanical design and manufacturing.