Research On The Influence Mechanism Of Cutter Orientation On Cutting Force And Planning Of Surface Machining Strategies

Compared with three-axis machining,five-axis machining has two more degrees of rotation freedom,resulting in a more complex relationship between tool and workpiece,adding new challenges to the modeling and simulation of machining process.Five axis cutting force modeling and predicting is a hot topic in recent metal cutting research.However,the past work focused on the accuracy of modeling and simulation,and the influence mechanism on cutting force are not clear for different machining strategies,especially for different cutter orientation and cutter orientation change.This dissertation focuses on the five-axis machining cutting force theory and application: Explore the influence mechanism of the cutter orientation parameters and tool path parameters on undeformed chip thickness and cutter/workpiece contact boundary curves;Research on the cutting performance index technology of relatively weak rigid process system for improving machining accuracy,machining efficiency and tool wear rate;Develop the optimization strategy of machining the freeform surface with the optimum cutting performance index.The purpose of this paper is to improve the machining accuracy and efficiency of the relatively weak rigid cutters and parts through the technologies developed from the research of cutting force.A parametric chip thickness model related to the parameters of tool orientation and orientation changes is proposed.The calculation principle of the uncut chip thikness for moving method of the cutting edge element is revealed through dot product of the edge element feed vector and the unit normal vector of the tool envelope.The parametric chip thickness model is proposed through the parameterization of the angle rotation transformation matrix and the linear transformation vector.Three decomposition models about the cutter orientation,the cutter orientation change and the cutter runout are acquired.Three related experiments are conducted to validate the decomposition models.Some analysis are conducted to study the influence mechanism of these parameters on cutting force.A symbolically solvable cutting contact boundary model related to the parameters of the cutter orientation and the path interval is proposed.The CWE boundaries are determined by three curves: the characteristic curve of the envelope,the intersection curve of the envelope and the workpiece surface,and the projective curve of the previous characteristic curve in the feed direction.Based on the proposed CWE boundary model,Margin Height method to determine the in-cutting edge is proposed,the algebraic method to predict cutting force at any cutter rotation angle is described,and it is validated much faster than the transitional discrete method with little loss of accuracy.Some machining tests with different cutter orientations and path intervals are conduct to validate the prediction accuracy.Three cutting performance indexes are proposed to study the relationships of cutting force related information and the machining accuracy,the machining efficiency and the tool wear.Force-Error index is proposed to characterize the machining error caused by the force deformation of the machining system during the process of removing unit volume material.The effects of different cutting parameters especially for cutter orientations on Force-Error index are analyzed.Specific Machining Force index is proposed to characterize the machining efficiency constrained by the peak force.The effects of different cutting parameters especially for cutter orientations on Specific Machining Force index are analyzed.Specific Cutting Energy index is proposed to characterize the energy conversion(shear or friction)during the process of removing a unit volume material,and to reflect the material removal mode(shearing,plowing and grinding)and the tool wear rate.The effects of different cutting parameters especially for feed rates on Specific Cutting Energy index are analyzed.An optimization method for freeform surface machining strategy with optimum cutting performance index is proposed.The optimization procedure has two parts: A new index,named as Optimization Degree(OD),is constructed to characterize the cutting performance index of different cutting directions and cutter orientations at a certain cutter contact point.The optimal machining strategy and tool path are acquired through evaluating the machining strategy of freeform surface through the OD at all the surface mesh points.Then,the methods to adjust feed rate using the threshold force and Specific Cutting Energy index constraint are presented.The experiments of finishing and roughing open surface are conducted to verify the effectiveness of the optimized surface machining strategy.Taking into account the influence of cutting axis interference,a small propeller surface and a large propeller surface are machined using the optimized surface machining strategy,the results are in line with the prospective.