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Research on Tool Path Planning and Process Parameter Optimization Technology of High Speed Milling for Die

Author: ChenYing
Tutor: WangYiQiang
School: Jilin University
Course: Mechanical Manufacturing and Automation
Keywords: high speed milling tool orientation tool path planning mould free surface cuttingparameters surface quality processing efficiency
CLC: TG54
Type: PhD thesis
Year: 2012
Downloads: 354
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Abstract

High speed cutting, because of its high efficiency and high precision, can be used tocut high hardness materials. Since the1990s，it is gradually used in the complex freesurface manufacturing and is becoming an important development trend as advancedmanufacturing technology. High speed milling can improve surface quality and theprocessing efficiency in mold processing，simultaneously. It can finish all the roughand the finish machining process, even cancel the manual operation in one clamping.In general, molds and parts that processed by high speed milling are materials that aremore difficult to process and have large amount of material removal, so consumelonger time and shorten tool life. With the increase of the degree of complex shape ofwork-piece，improve machining precision and machining efficiency of the free surfaceis becoming more and more important.NC machining began to get application since the1960s，five axis NC machiningwith torus cutter show more advantages because it can improve surface quality andimprove processing efficiency. The data show that，20%-30%of the numericalcontrol machine stop production, because it can’t prepare NC program，so affects theutilization rate of the machine tool directly. Tool path is the basis and key factor inmulti-axis NC machining programming. Therefore, through the controlling ofinclinable angle, yaw angle of the tool and path planning in five axis machining toachieve accuracy in guarantee under the premise of processing to enhance theefficiency are the urgent problems.Tool path planning cooperated with craft parameter selecting generate the NCprogram. We did not consider the frequent changes of feed speed and the worseningof environment from programming in milling process itself in the past. Therefore, thispaper will research tool path planning of high speed milling and combine it withmachine tool’s dynamic characteristics from the point of system theory. Establish toolorientation and tool path optimization control theory, establish the model of parameteroptimization，and carry on effective integration and fusion. The main research contentis as follows：(1)Research on the key problems of high speed and high precision NCprogramming system. Base on the study of NC programming system and relatedproblems of high speed milling，establish the system framework of multi-axis NC machining from the optimization of tool orientation and the calculation of maximumstep-width，cooperated with the selection of optimized parameter，pointed out the keyissues of influencing accuracy and efficiency.(2)Research on tool path planning of five axis NC machining with torus cutter.Analysis the relative position relationship of the three frames in five axis NCmachining，calculated the global coordinates of the cutter location and the vector ofcutter. Based on the Dupont index line, this paper deduced the necessary andsufficient condition that can avoid gouging when milling complex surface in five axiswith torus cutter. We generated tool path by the method in this paper and compared itwith the traditional algorithm, the results indicate that the present constantscallop-height machining achieves the specified machining accuracy with fewer andshorter tool paths than the existing tool path generation approaches.(3)Optimization of the master cutter path of constant scallop-height algorithm.Analysis the relationship between the strip width and the surface characteristics, themaster cutter path have been chosen from the maximum flatness direction that canreduce the number of cutter location point, make it be related with the curvature of thesurface characteristics. The tool paths are generated by the method of self-adaptivetool orientation.(4) Research on the dynamic characteristic of velocity and acceleration. Based onconstant surface cutting rate method and MATLAB, we analysis and compare thecharacteristic of velocity and acceleration of tool path that generated by the abovethree kinds of method. Point out that strip widths are identified by both the curvaturecharacteristics of the surface and tool orientation, acceleration curve can be optimizedwhen step changes uniform, the choice of the master cutter tool path can optimize toolpath.(5) Optimization of process parameters in high speed milling. Based on the fourmain cutting parameter:a p，n，fz，ae, the experiment was carried out on plasticdie-mold steel P1.2738on a high-speed5-axis machining center by using four factorsof the four levels orthogonal test. By using maximum difference method gains thefour experimental factors on the surface roughness of the different effect, draws thetrend curve of the milling parameters on the surface roughness, and analyzes causes oftheir impact, get the best parameter combination A2B3C1D1. Based on multipleregression, we presented the prediction model for the surface roughness. In this paper, we verified the regression factor coefficients and significances of the regressionequation, the trend curve of the milling parameters on the surface roughness iscoincident with the maximum difference method. Based on artificial neural network,we presented the prediction model of surface roughness. There are one input layer offour neurons, one output layer of one neuron and one hidden layer of12neurons, themain factors are included in the input layer of the network. The average relative errorof prediction results is2.6825%while that of the multiple orthogonal regression is7.8156%, which show that the BP model can basically draw the relationship betweeninput parameters and output parameters. Based on the ANN and the genetic algorithm,we optimized the milling parameters. The objective functions are the biggestmachining material removal and the minimum surface roughness. We built Themulti-objective optimal model and gave the optimization results.(6) Based on tool path that generated by the following three method: traditionalconstant scallop algorithm, self-adaptive tool orientation method and self-adaptivetool orientation method of optimized master cutter path. Combined with the optimalparameter, we conducted the experiment on plastic die-mold steel P1.2738on ahigh-speed5-axis machining center DMU125P, the results show that the tool pathgenerated by self-adaptive tool orientation method of optimized master cutter path canimprove the processing efficiency obviously.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metal cutting and machine tools > Milling and milling machine
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