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PRODUCTION PROCESS

Experimental investigation of specific cutting forces and estimation of the heat partitioning under increasing tool wear in machining nickel‑based super alloy IN 718 Thorsten Augspurger1   · Daniel Schraknepper1 · Thomas Bergs1,2 Received: 28 January 2020 / Accepted: 22 June 2020 © The Author(s) 2020

Abstract Presented are an experimental setup and affiliated methodology to measure the specific cutting forces in the milling process with proceeding tool wear at simplified orthogonal milling kinematics. The cutting forces, cutter rotation angle and chip temperature are acquired by a time sensitive measuring system consisting of a synchronized dynamometer, ratio pyrometer and spindle encoder. The approach allows the accurate acquisition of cutting forces under defined engagement conditions and thus constitutes a valuable basis for cutting force modelling and tool wear monitoring approaches. The results show uniformly and linearly increasing forces over the entire range of undeformed chip thickness due to wear. Besides a mechanical view on the cutting process, also the thermal domain was included into the analysis. Therefore, a ratio pyrometer was used as part of the synchronized measurement system tracking the chips backside temperature in order to estimate a virtually continuous heat flow into the chip. This heat flow increased with wear and process power, which indicates that the chip’s temperature can be used as process monitoring variable for tool wear. Keywords  Metal cutting · Specific cutting forces · Tool wear · Temperatures · Heat partitions · Monitoring

1 Introduction and state of the art In cutting technology the force is a key indicator of the process capability in order to reach quality related as well as economic manufacturing targets. It determines the mechanical power dissipated into sensible heat causing in their interaction alternations in the workpiece microstructure as well as tool wear [1]. Finally, the force acting on the tool determines its deflection, thus machining accuracy. The energy required and transformed in the cutting process is in particular relevant for the manufacturing of safety critical workpieces made of super alloys such as Inconel 718 or other difficult-to-cut materials. They are used in aero turbines due to their high temperature resistance, * Thorsten Augspurger [email protected]‑aachen.de 1



Laboratory for Machine Tools and Production Engineering (WZL) of RWTH Aachen University, Campus Boulevard 30, 52074 Aachen, Germany



Fraunhofer Institute for Production Technology, Steinbachstraße 17, 52074 Aachen, Germany

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enabling an increased entrance temperature and thus efficiency of the turbine. The benefits in the application of the materials are accompanied by disadvantages in the machining process in form of high work hardening rates, abrasiveness and at the same time high toughness and low temperature diffusivity [2]. The low temperature diffusivity causes heat concentration zone in the machined surface layer which may alter the surface integr