Analytic model of process forces for orthogonal turn-milling
The manufacturing process of turn-milling offers high productivity, high geometrical flexibility, safe chip breaking and machining of twist-free surfaces. However, the achievable accuracies and surface qualities do not allow the substitution of finish grinding processes. Thereby the dynamic profile of process forces is one of the main disturbance values. This paper presents a new process model of orthogonal eccentric turn-milling without axial feed. Thus the focus lies on the analysis of the process forces and their dynamic behavior caused by the changing chip cross section area on the face cutting edge. The developed model considers single and multiple cutting edge tools and has a geometrical-empirical character. This model describes the process kinematics and the error inducing process forces in orthogonal turn-milling. Their dynamic profile can be analyzed and minimized using multiple cutting edge tools and customized pre-machining of the workpiece surface topography with the goal of creating a robust process to substitute the finish grinding process in high precision applications. Such applications include, for example, the main and pin bearing seats of crank shafts used in the automotive and truck industry or even for large ship engines. The key feature is to minimize the form deviation of the cylindricity, which results from straightness and roundness of the workpiece surface to below 10 µm for crank shafts used in the truck industry. The model is adjusted and verified by experimental tests.