The paper focuses on the issue of controlling the cutting conditions in finishing machining of compliant workpieces, such as typically thin blades, in order to eliminate undesirable vibration and achieve high quality machined surfaces while also increasing productivity in machining processes. Workpiece vibration along the toolpath results from excitation of the workpiece by cutting forces. A strategy of calculating the overall level of workpiece vibration excited by cutting forces at different spindle speed levels as a multifrequency problem was proposed for specific use with long thin blades. The proposed strategy allows for very efficient identification of blade sections with critical increase of vibration level at different spindle speed values. This enables determination of the optimized spindle speed levels and feed rate along the blade to avoid increased workpiece vibration. A method for continuous control of the spindle speed and feed rate during finishing machining was proposed and successfully tested and verified through real machining tests. The machined surface quality improvement was proven.
Efficient and productive manufacturing of freeform shapes requires a suitable three-dimensional CAD model at the entrance to the CAM system. The paper deals with the impact of NURBS or B-spline CAD model geometric continuity on the accuracy and productivity of 5-axis ballend milling of freeform surfaces. The relationships between a different order of CAD model geometric continuity and the quality of the toolpath generated in CAM system is analysed and demonstrated on example of Blisk blade profile. In order to reveal the pure effect of CAD geometry on the quality of the machined surface, linear interpolation of individual positions of CL points is considered and no further smoothing of the toolpath is applied. In addition to the commonly used indicator of toolpath quality represented by the distance of CL points, the discrete curvature of a toolpath in a form of a piecewise linear discrete curve is introduced and its dependence on the curvature and continuity of the underlying CAD model is demonstrated. It is shown that the higher order of CAD model geometric continuity significantly eliminates sharp changes in the distance of CL points and smoothes the discrete curvature of the toolpath. Finally, it is experimentally verified that increasing the continuity of the CAD model from G 0 to G 3 , while maintaining the same cutting conditions, leads to CAD model continuity in CNC machining an increase in workpiece accuracy and a reduction in machining time, without the need to smooth the toolpath generated in the CAM system.
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