Process-independent force and surface model for oblique cutting of fiber reinforced polymers

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Fiber reinforced polymers are often used in lightweight design. Due to the orthotropic material properties, the cutting mechanisms during chip removal differ significantly from those of isotropic materials. So far, the fundamental mechanisms have been investigated primarily for orthogonal cutting. However, oblique cutting is generally present in industrial practice, in which a three-dimensional cutting process occurs due to the spatial engagement conditions of the tool’s cutting edges. The spatial engagement conditions result from a combination of the 3D spatial orientation of the cutting edge and the cutting direction with respect to the fiber.Preliminary studies reveal a significant influence of the 3D spatial cutter-fiber-orientation on the cutting forces and the resulting cutting surface. The surface integrity can affect the mechanical behavior of lightweight structures under static and dynamic loads. In particular, occurring fiber pull-out is critical for the surface integrity. The objective of the project is a cutting force and surface model for the machining of fiber reinforced polymers with particular consideration of oblique cutting. The prediction of cutting forces is based on a semi-empirical model, which has a process-independent validity. The model will be transferred to milling. Furthermore a transfer to drilling out and countersinking is envisaged in a second project phase. Innovative experimental setups enable efficient and comprehensive identification of cutting force coefficients for the first time, also under high cutting speed as well as arbitrary orientation of the cutter and cutting direction relative to the fiber. The surface model is developed from the correlation between the spatial load situation and the measured surface condition. It allows the prediction of critical cutting conditions with respect to surface quality, in particular fiber pull-out. The rotation-angle-dependent simulation of the process forces and the cutting surfaces allows conclusions to be drawn about the process-specific mechanisms in terms of 3D spatial engagement conditions, which has not been possible up to now because of the focus on orthogonal cutting. Compared to the mere mechanistic force modelling by calibration in a drilling or milling process, the semi-empirical model shows the load distribution along the cutting edge. This enables the analysis of phenomena which are only affecting a small region of the cutter and shows optimization potential in terms of surface quality.