Contribution to the evaluation of fracture behavior of carbide extrusion dies
- Prof. Dr.-Ing. M. Geiger
- Prof. Dr.-Ing. H.W. Bergmann
The aim of this project was an analysis of the fracture behavior of conventional tungsten carbide based hard material. By doing this, the progression of the breakdown and the failure mechanism of cold forging dies were investigated. The toll load caused by the forming process was calculated using the finite element method. The simulation runs are showing a stress peak at the inlet of the tool shoulder with a combined compression and shear load. Furthermore, the crack growth was calculated for a given incipient crack.
A comparison between static and periodic bending strength showed, that an appraisal of the fatigue strength is not possible only knowing the static bending strength. Fracture tests with superposing tensile and compression stress have shown, that the normal stress hypothesis is applicable for the analyzed material and commonly occurring compression stresses up to 2.000 N/mm2
Defects of the microstructure beneath the surface of the specimen are causing the failure, cracks on the surface could not be observed. Due to this fact, a reduction of the number of microstructure defects should be aim of the optimization of the tool material.
The result of the project showed, that working with a pre-cracked tool is possible, if the crack leads within a short distance in a zone with compression stress. The tool loads occurring in practice are in the range of the fatigue strength of these materials. Due to this, the results of static fracture tests should be used in combination with finite element calculations to lay out the tool.