Research On Dynamic Simulation And Optimization Technology Of Milling Process For Frame Parts Of Marine Diesel Engine

With CNC milling process under the frame parts of marine diesel engine as the research object of this paper, several problems corresponding to mechanics, dynamic modeling and simulation of milling process were researched. With the modal experiment of "machine-tool-workpiece" machining system, stability and dynamic milling force and chatter stability model for both peripheral milling with end milling cutter and multi-tooth intermittent facing milling with inserted cutter have been built. Dynamic simulation results were used as the constraints to achieve multi-objective optimization of cutting parameters in milling process. Based on the theoretical research achievements, several related functional modules were designed, and comparative analysis experiments with original parameters and optimized parameters have got satisfactory results.In the mechanics modeling of end milling frame parts, instantaneous stiffness mechanics model was taken to obtain the static cutting force, power and spindle torque.While in the dynamics modeling, two degrees of freedom processing model was built. The transfer function of machining system was obtained by hammer impact tests, and then the peak method was used to identify modal parameters in modal analysis. Analytic algorithm was used to obtain frequency solution of chatter stability lobes. A numerical method was introduced to solve the milling dynamic differential equations, and then time domain solutions, such as dynamic cutting force, vibration displacement and so on were obtained. As for the further research of dynamic modeling and simulation of end milling, the reason for variable pitch cutter strong effect in improving stability against chatter have been analysed. Combined with the enterprise actual cutting situation, a new variable pitch milling cutter was designed. The simulation results shows variable pitch distribution can significantly improve the chatter stability in milling process; thereby the material removal rate (MRR) has been improved by 25%.As for the mechanics and dynamics modeling of face milling frame parts, the geometry model of inserted cutter was defined firstly.Considering the thin wall workpiece in machining process, the cutting system was divided into two subsystems, which were "machine - spindle - tool" and "workpiece - Fixture". Subsystem transfer function and modal parameters were obtained by two hammer tests respectively. Then the important physical quantities that have strong impact on processing quality, such as static and dynamic cutting force, vibration, displacement and so on were simulated by applying the numerical integration algorithm to slove the dynamic differential equations. Then theory of process damping caused by the limit of clearance angle, friction and wear was studied, finding that process damping can be very effective in improving stability against chatter with low speed milling. Orthogonal test using inserted cutter in intermittent milling process was designed, then using MALDAQ module of commercial software CutPro to do vibration tests in intermittent process, and researching on the relationship between cutting frequency, cutting parameters and the forced vibration through FFT analysis.Taking above dynamic modeling and simulation results as constraints of multi-objective parameter optimization for milling process, genetic multi-objective optimization algorithm was used to optimize process parameters. In order to implement human-machine interactive operation, the computer aided optimal system"EasyCut"for choosing process parameter has been developed according to software engineering thoughts and mixed programming technology based on MATLAB-GUIDE software.