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Analysis of discharge-dependent surface integrity of cemented carbide forming dies machined by sinking EDM and its influence on the tribological characteristics and the resulting fatigue behavior

Subject Area Metal-Cutting and Abrasive Manufacturing Engineering
Term from 2016 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 290130034
 
Final Report Year 2025

Final Report Abstract

Cemented carbides consist of hard materials that are bound in a metal matrix. Within the scope of this research project, only tungsten carbide-cobalt composites were analysed, whereby different hard material grain sizes and different cobalt and binder contents were considered. Due to the possibility of varying these components independently of each other, carbides can cover a very diverse range of properties and thus also applications. Carbides are also characterised by the fact that they are significantly harder and more resistant to wear than steels, but at the same time tougher and less susceptible to fracture than pure hard materials. They are therefore ideally suited for use as tool materials, in the case of this research project as forming tools. At the same time, however, these properties also make them difficult to process conventionally, which is why electrical discharge machining (EDM) with its thermophysical and therefore force-free working principle represents a promising alternative. However, the workpieces are subjected to stress during EDM due to the thermal material removal, which can lead to damage. One of the aims of this research project is therefore to identify these stresses and damage in the workpiece and subsequently reduce them. To this end, the differences between EDM of steel, which has been studied much more extensively to date, and cemented carbide were first identified. Beside the material, the electrical parameters within the machining technologies developed by the machine manufacturers specifically for cemented carbide machining were analysed and their influence on the machining result investigated. In addition, different tool electrode materials were compared with each other in terms of removal rate and wear. In the next step, the surface integrity of the cemented carbides machined using different machining technologies was analysed. This included surface roughness, hardness, crack toughness, thickness of the resolidified layer, thickness of the heat-affected area and residual stresses, whereby the latter could only be measured on the surface. To determine the component functionality, the next step was to investigate flexural fatigue strength, flexural fracture strength and tribological properties. In addition to the various machining technologies, machining was also carried out on a different machine tool and two different post-treatments were compared. As the final element of this research project, a complex geometry with two different machining technologies was machined from two hard metal stamps and impressed into a thick sheet about 7300 times each in an endurance test. This showed that the machining process can be accelerated without compromising the quality of the component.

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