Investigations of gradient-dependent nitrided forging tools in hot bulk metal forming under cyclic thermomechanical loading
Final Report Abstract
The aim was to develop a new wear modelling method taking into account the development of hardness in nitrided tools. The focus was on the development of hardness as a function of the cyclical thermal and mechanical loads of a forging process. Since nitriding is a graded coating system, two different nitriding profiles were analysed in conjunction with the non-nitrided base material 1.2343. Since high peak temperatures in combination with high cooling rates from spray cooling can lead to partial martensite formation in forging dies, so-called re-hardening, the austenitisation behaviour was analysed under superimposed mechanical stress. It was found that the superimposed mechanical load leads to a significant reduction in the Ac1,b temperature. Subsequently, an existing test methodology for applying thermal shock cycles was fundamentally extended to take account of superimposed mechanical stress. The hardness evolution was characterised by means of stress-superimposed thermal load tests in practical cycle and time ranges. Based on the results, a calculation framework was implemented in the Simufact Forming application. This allows the hardness and wear to be predicted in a spatially resolved manner based on the material characterisation data. Finally, the developed hardness and wear model was validated using two laboratory forging processes. With regard to the unnitrided base material, the hardness-depth curves after 100, 500 and 2000 cycles could be predicted with a high degree of agreement. The wear calculation also showed good agreement under the appropriate assumption of several process variables. A hardness and wear prediction was also carried out to validate the nitrided layer material data. With regard to hardness, good agreement was achieved from cycle numbers of 1000. Finally, the wear could only be validated to a limited extent, as the unforeseen occurrence of adhesion effects restricts the applicability of the wear approach according to Archard. Finally, the usability of the developed implementation with regard to hardness and wear prediction was demonstrated using an industrial forging process.
Publications
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Experimental Characterisation of Tool Hardness Evolution Under Consideration of Process Relevant Cyclic Thermal and Mechanical Loading During Industrial Forging. Lecture Notes in Production Engineering, 3-12. Springer Berlin Heidelberg.
Müller, F.; Malik, I.; Wester, H. & Behrens, B.-A.
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Multi-Layer Wear and Tool Life Calculation for Forging Applications Considering Dynamical Hardness Modeling and Nitrided Layer Degradation. Materials, 14(1), 104.
Behrens, Bernd-Arno; Brunotte, Kai; Wester, Hendrik; Rothgänger, Marcel & Müller, Felix
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Hardness Assessment Considering Nitrided Layers Based on Tempering Tests for Numerical Wear Prediction for Forging Processes. Materials, 15(20), 7105.
Behrens, Bernd-Arno; Brunotte, Kai; Wester, Hendrik; Lorenz, Uwe & Müller, Felix
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Perspectives on data-driven models and its potentials in metal forming and blanking technologies. Production Engineering, 16(5), 607-625.
Liewald, Mathias; Bergs, Thomas; Groche, Peter; Behrens, Bernd-Arno; Briesenick, David; Müller, Martina; Niemietz, Philipp; Kubik, Christian & Müller, Felix
