Geometrical And Cutting Force Induced Error Modeling And Compensation For Pocket Milling

The development of high-precision manufacturing fields such as aerospace,automobile manufacturing,and transportation construction have get more and more attention since the concept of “Industry 4.0” was presented.Thin-walled workpieces are widely used in these fields.However,the thin-walled workpieces always generate deformation as a result of its low stiffness during processing.The problem could influence the profit of the factory and limit the development of the field to some extent.Thus analyzing the deformation during thin-walled workpiece processing and developing an effective strategy to improve the machining accuracy has profound implications for our country.An infinitesimal cutting force model of flat-end milling cutter based on both shearing and ploughing mechanism is proposed by discretizing the cutting edge along the axial direction.Considering the entrance angle,exit angle and cutting thickness,milling force model is established through integrating the infinitesimal cutting force.Considering that the rotation of milling cutter presents periodic characteristics,the milling force is transformed into Fourier series forms.A fast way of calculating the displacement of nodes in the object is proposed through the analysis of stiffness matrix extracted from FEM software.Considering the negative feedback mechanism of the cutting force and the displacement,a fast iterative algorithm of calculating the cutting force induced error in one cutting step is presented by applying the force on the workpiece and the cutter.When milling thin-walled workpiece using three-axis CNC machine tool,the main error sources are geometrical error of CNC machine tool and cutting force induced error caused by milling process.The transfer matrixes of geometrical error and cutting force induced error are obtained based on the homogeneous coordinate transformation theory.On the basis of transfer chain of the CNC machine tool,the comprehensive error model is established.And the error compensation strategy based on the External machine zero-point shift function of the CNC system is proposed afterwards.The compensation strategy is applied in pocket milling.First,the geometrical error of the CNC machine tool is obtained by measuring the error term.And then the cutting force coefficients are calibrated through slot milling experiment,and the cutting force induced error is calculated using iterative algorithm.Finally,side milling of the pocket workpiece is conducted,and the comparison of cutting accuracy between cutting without error compensation and with comprehensive error compensation verifies that the compensation strategy is effective and practical.