Performance analyses of eroded and nitrided forging dies

• Applicant: Professor Dr.-Ing. Bernd-Arno Behrens
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: from 2006 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 13470728

For the production of forging tools different manufacturing processes are used. According to the manufacturing process, different microstructural changes occur in the edge layers of the tools. These changes can directly influence the tool performance and affect the wear resistance and hence the die life. The research work during the first period was focused on the investigation of the microstructural changes as a result of different manufacturing processes (turning, milling, eroding) in the fabrication of forging tools using a commercially available hot working steel. Afterwards forging dies were manufactured with defined process parameters and adopted in serial forging tests. In the course of the first period assured knowledge was gained regarding the influence of the microstructural edge layer changes on the life time of forging dies as a result of different manufacturing processes.Within the previous research work it could be proved that the solidified martensitic edge layer as a result of the eroding process could lead to a significant wear reduction. Nevertheless, an early spalling of the solidified layer due to a high hardness gradient of the basic material is possible. Furthermore, research revealed that, among other edge layer conditions, the development of residual stresses in the edge layers during the forging application depends on the manufacturing process used for the tools. Tensile stresses caused by eroding processes are reduced during the application and turned into compression stresses. Compression stresses are measurable even after a high number of forging cycles in the case of forging dies produced by eroding. Regarding alternative production technologies (turning and milling) stress free conditions in the edge layers were measured after identical life times.The aim of this research project is to achieve a higher wear resistance of forging dies by using the manufacturing technology electro discharge machining (EDM) in combination with an adjusted hardness gradient in the edge layers to avoid early spalling of the martensitic layers. This will be achieved by the use of the nitriding process. Furthermore, the development of residual stresses depending on the manufacturing process must be clarified. Here, a complex correlation between the formation and the development of residual stresses can be supposed. The development of residual stresses will be measured using a high-resolution measurement interval. Since compression stresses could have a positive influence on the die life this knowledge is of high interest. The transferability of the results will be investigated on the example of an industry related impact extrusion forging process.

• DFG Programme: Research Grants