| CNC milling is widely used in aviation,aerospace,national defense,ships and other advanced manufacturing fields because of its high efficiency and high precision.At present,it is still a major problem to be solved urgently that the unreasonable selection of cutting parameters and the deterioration of machining quality and the aggravation of tool wear caused by the chatter caused by the improper tool path.However,the selection of machining parameters in practical production is still relying on human experience,while conservative machining parameters to guarantee stability to a certain extent,but also leads to great waste of the performance of manufacturing equipment,and based on discrete tool path directly generated CAM machining will also lead to inefficient and machine tool vibration.Therefore,in-depth research including milling stability analysis,cutting parameter optimization,smooth path generation and other aspects of the research,for improving the quality and efficiency of milling has important significance.In order to solve the problem of efficiency and quality in milling,a machining parameter optimization method for high efficiency and low carbon milling is proposed,which takes into account the constraint of 3-D stability,so as to reduce the processing time and carbon emission under the premise of guaranteeing the processing quality.A method of tool path generation based on unsteady heat conduction theory is proposed to improve the dynamic performance of milling by improving path smoothness.A tool path smoothing method based on Catmull-ROM spline is developed to improve the continuity of tool path in multi-axis milling.A numerical control milling process optimization system is developed to realize the engineering application of the theoretical algorithm.Specific research contents include the following aspects:(1)A 3-D cutting stability prediction model based on the improved full discretization method is proposed.On this basis,a cutting parameter optimization model is constructed with the machine tool performance,tool life,surface roughness and cutting stability as constraints and the machining time and carbon emission as objective functions.In order to solve the cutting parameter optimization model and assist decision-making,a multi-objective optimization method based on markov clustering and bidirectional action mechanism of firefly algorithm and a multi-objective decision method based on pseudo weight parameter vector are proposed.(2)A method of generating smooth tool path in NC milling based on unsteady thermal conductivity theory is proposed.Respectively for the different characteristics of cavity with island,closed cavity and opened cavity,different thermal boundary conditions and the difference equation for the generation of tool path,and based on the calculation method of Hausdorff distance to ensure machining without residual.A migration method of temperature field propagation rule based on cubic Hermite polynomial interpolation was proposed to ensure the relative uniformity of the line spacing between tool paths.(3)An analytical C~3 continuous tool path smoothing method for NC milling based on Catmull-rom spline is proposed.By inserting the adjustable Catmull-rom spline on the corner of the adjacent discrete segment,and the control points and adjustment parameter are optimized to suppress smoothing tool path and the deviation between the original tool path,then replace the remaining line with Catmull-rom,to achieve the position of the tip point and the displacement of the tool axis relative to the tip point to maintain C~3 continuity.(4)a complete prototype system of NC milling optimization is developed based on Visual Studio.The system can realize the functions of workpiece management,3-D machining stability region prediction,machining parameter optimization and decision-making,tool path generation and so on.Its interface is simple and friendly,which provides a practical assistant tool for the first-line technologist. |
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