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Improvement of the Reliability of Geometrically Defined Cutting Processes by the Extension of a Novel Approach for Wear Characterisation

Machining processes assume a high significance in the industrial production of workpieces. Wear-resistant tools are required to achieve process reliability and avoid rejects. To improve the wear resistance of cemented carbide cutting tools, the preparation of cutting edges is an established process step in the manu­facturing chain. With cutting edge preparation it is possible to reduce the microdefects resulting from the tool grinding process and increase the stability of the cutting edge by forming a rounded edge. This results in a significant improvement of tool performance compared to a cutting edge that is not customised to the process.

However, the usage of prepared cutting edges also leads to new challenges. As a result of the rounded and in some cases asymmetrical shape of cutting edges, classic wear parameters like the width of flank wear land or the crater wear are more and more incompatible for an accurate assessment of the existing wear. The consequence of this is that a definition of a reliable tool life criterion is becoming more difficult.

The figure shows the challenging wear characterisation of a cemented carbide tool with prepared cutting edges. After drilling a path of Lf > 28 m in a quenched and tempered steel, no measurable wear can be determined using light microscopy. Only the high-resolution SEM image reveals the existing flank wear, which is shaped as a groove below the cutting edge. This wear is not described by any of the classic wear parameters and requires suitable microscope technology to detect it. As a result, with only a low width of flank wear land that is measurable with a light microscope, the tool life end can appear unexpectedly due to tool breakage. This results in significantly reduced process reliability because the production of reject parts is increased.

In this research project, the first new types of wear parameters that have already been developed for practical use will be extended and transferred to changed conditions. With the help of wear characterisation, it should be possible to describe the change in the microscopic shape of the cutting edge over the machining time. The aim of the study is to characterise the wear of tool with prepared cutting edges at varying forms of wear and to determine the end of tool life based on the further developed wear parameters in a user-oriented method. This is supposed to significantly increase the process reliability for machining processes.

Flank wear at a cemented carbide twist drill after a drilling length of Lf > 28 m


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