Influence of cooling of forging dies on the process-related microstructural changes in the surface zone and their effect on wear behaviour

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The surface zones of hot forging tools undergo local microstructural changes due to high loads. This affects the wear behavior significantly. Therefore, the analysis of these manipulated surface zones in die forging and their effect on wear behavior is of great importance. The microstructural changes mainly depend on the location and time dependent temperature behavior in a die which is highly influenced by the tool cooling system. The research project aims at fundamentally examining the influence of the die cooling system on the process-related microstructural changes in the surface zones. The main objective is to investigate the microstructural changes under varying cooling conditions and determine the correlation between the microstructural changes and the wear behavior. Another minor objective is to determine the influence of the combined tribological and mechanical loads on the microstructure in the surface zones of hot forging dies. The research objectives will be achieved by varying the cooling and lubrication concepts by adapting the cooling gradient through different spraying parameters and different stationary die temperatures. Functionally isolating cooling and lubrication allows a specific configuration of the cooling process through a timed regulation of the amount of coolant per area. The die will be cooled by an appropriate surface water spray cooling system. Different cooling strategies will be developed in order to configure the cooling process. The separation of the lubrication and cooling functions eliminates the conventional lubrication with water-graphite suspension, thus the die will be lubricated through electrostatic powder coating. Depending on the powder used, different friction conditions between the die and the workpiece can be generated and the tribological stresses can be varied. The mechanical stress of the die can be altered by forging steels of different strengths. The gained results of the research project should help to optimize the die cooling regarding the microstructural changes to improve wear behavior and service life efficiently.