Milling Accuracy Assessment Based On The Z-Map Simulation Model

NC simulation can simulate the manufacturing process before machining parts, topredict in advance processing quality in the condition that the NC program and theprocessing parameters are in a given, to find in advance potential problems on the partprocessing and propose appropriate solutions, to optimize NC program and machiningparameters. The current NC simulation is to simulate dynamically machining processfor collision test, and don’t give a reasonable evaluation of machining simulationresults, then a NC simulation system that can predict and analyses the quality of thesimulation results has important practical significance.This dissertation researched the method of evaluating milling precision, capableof verifying three-axis CNC milling simulation results, and extracted the geometricinformation of simulation virtual part. These work can be used to analyze and predictproduct quality. After the NC simulation processing was completed, this papercompleted to take along arbitrary cross-section of the virtual work piece, in thecross-section measured coordinate and related geometric quantities; it also detectedthree-dimensional dynamic virtual work piece-related dimensions, at last assessedprocessing accuracy depending on the designing size and simulation accuracy.Firstly, the data structure and modeling features of Z-Map model was analyzed, themain methods of verifying the processing accuracy was researched, and summarizedthe main contour extraction algorithm. According to the principle of contour trackingin the image processing and the applications of Freeman chain, this paper came upwith the special contour extraction algorithm based on Z-Map model, the algorithmcan extract the full contours of arbitrary graphics in binary image, it made up the defectthat the traditional algorithm could only extract a single contour, but also had a highefficiency.Secondly, this dissertation detected the feature point of the boundary points whichconstitute the extracted outlines. The method of using Freeman chain code, the methodof using scale-space to characterize the curvature and the tangential direction of thecurve was studied, then according to the curvature variation of contour boundarypoints to detect feature points, on the feature points on the boundary point sequence graph partitioning. This dissertation studied the method of using Hough transform andthe least square method to extract lines and arcs, analyzed their strengths andweaknesses and the main scope in which they were used frequently, this paper used theleast squares method to fit each section boundary point which is divided by featurepoint and got the curve which had a high fitting precision. Finally, these curves isoutput to the processing inspection window of the simulation system, to detect thecoordinates and geometric quantities, overall considerate the designing size and thesimulation accuracy to test the results of NC simulation, evaluated the merits of itsprecision.This dissertation was based on the NC Partner system researched by our group,established a NC simulation system which could conduct an inspection of machiningresults.