In pocketing with contour parallel (CP) paths, the cutter encounters a varying engagement with the workpiece, which causes variation in chip load and cutting forces. This varying cutting force naturally leads to the variation of tool deflection, hence impairing machined surface accuracy. This paper presents a new tool path modification scheme, which regulates a constant cutting engagement with workpiece in 2.5D end milling. The semi-finishing path, the path prior to the finishing path, is modified by the proposed scheme such that the engagement angle along the finishing path is regulated at a desired level. By maintaining cutting engagement constant, the cutting force can be regulated approximately constant, thus minimizing the variation of tool deflection, and improving machining accuracy. The improvement of machining accuracy by applying the new tool path modification scheme is experimentally validated for the case where the proposed scheme is applied to pocketing. The machining results are analyzed and compared with the cases with conventional contour parallel path and the feed rate control scheme applied in pocketing.
In two-dimensional (2D) free-form contour machining by using a straight (flat) end mill, conventional contour parallel paths offer varying cutting engagement with workpiece, which inevitably causes the variation in cutting loads on the tool, resulting in geometric inaccuracy of the machined workpiece surface. This paper presents an algorithm to generate a new offset tool path, such that the cutting engagement is regulated at a desired level over the finishing path. The key idea of the proposed algorithm is that the semi-finish path, the path prior to the finishing path, is modified such that the workpiece surface generated by the semi-finish path gives the desired engagement angle over the finishing path. The expectation with the proposed algorithm is that by regulating the cutting engagement angle along the tool path trajectory, the cutting force can be controlled at any desirable value, which will potentially reduce variation of tool deflection, thus improving geometric accuracy of machined workpiece. In this study, two case studies for 2D contiguous end milling operations with a straight end mill are shown to demonstrate the capability of the proposed algorithm for tool path modification to regulate the cutting engagement. Machining results obtained in both case studies reveal far reduced variation of cutting force, and thus, the improved geometric accuracy of the machined workpiece contour.
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