Study On High Efficiency NC Machining Strategies And Parameter Optimization Oriented To Mould Cavity Machining

In order to meet the demands of higher accuracy, shorter lead-time and lower cost to every industry or trade, the industry of mould is using the Digital manufacture technology to accelerate the technological progress extensively. As the most important stage of mould digital manufacture process, NC machining is one of the main influential factors to the production cycle and quality. Mould cavity, which is the crucial component of the mould, is the most difficult and time-consuming part in the NC machining. Hence, improving the efficiency of mould cavity machining for shortening the production cycle and lowering the cost has become the urgent problem to be solved.Based on the above-mentioned understanding, this paper has launched the high efficiency strategies of NC machining and machining parameters optimization oriented mould cavity, the main research contents are as follows:Considering the characteristics and the concept of two dimensional equivalent cutting-load in mould cavity roughing, the cutting force curved surface model is created by the method of least square fitting for scatter cutting force points. At the same time, the function of feedrate and effective cutting depth is obtained using polynomial fitting method. According to the cutting conditions of different cutter location, feedrates are calculated and written in G-code file. By the use of different cutting-depth coefficients for end milling cutter and ball milling cutter respectively, the model of cutting force curved surface model will be more generalized. The cutting force curved surface model is tested by a typical mould cavity roughing, thinning down machining time and balanced cutting-load can be attained. The presented feedrate scheduling characterized by balancing the cutting-loads in mould cavity roughing will be more significative in high speed machining.The strategy of mould cavity roughing oriented machining features and cutting tool life is also presented in this paper. On the base of constant distance offset tool paths, the cutting critical regions on cutting layers are extracted. Then the mould cavity roughing can be divided into combinations of the five machining features, that is, drilling, expanding hole, pocketing, side cutting and clean corners. On principle of tool life being most long, the machining features of pocketing can be confirmed and the strategy is carried out under the environment of the CAM system, PowerMILL, developed by Delcam Company.To realize the high efficiency finishing for mould cavity, a superior strategy based on machining geometric model (Tool-ZMap) is accordingly proposed, in which an ordered series of toroidal cutters and ball milling cutters sorted by diameter size are optimally selected. Based on the established Tool-ZMap model, individual cutting areas pertinent to each cutter are consequently calculated. Each cutter only deals with its corresponding area in practice. Scan cutting strategy and contour cutting strategy are adopted for shallow areas and steep areas respectively. Using this presented strategy, the machining feature recognitionduring machining process can be avoided. In addition, the poor rigidity of cutter used in high speed machining can also be improved. Combining with an illustrative example, the advanced machining strategy further proves to be general and effective.Based on the ZMap model of workpiece and the discrete cutting tool model, a geometric simulation for surface topography oriented sculptured surface machining using ball milling cutter is realized. Using the analytical expression of chip thickness, the chip profile is obtained. As a result, the geometric parameters used in the instantaneous cutting force prediction and feedrate optimization are provided.Using the differential geometry as an analysis tool, a dual-mechanism cutting force model with the corrected Z axis-direction cutting force is created. Using the numerical method, the instantaneous cutting forces are obtained. In production, the shearing constant and ploughing constant can be supposed as a constant respectively, which can reduce the difficulties in cutting-coefficients regression significantly. Using the cutting force model, the feedrate is optimized. As a result, the machining time thins down without sacrificing surface quality.Using the factorial design of experiments combined with technique of regression, the surface roughness mathematical model in mould cavity finishing is created. The influences of machining parameters such as axial depth of cut, radial depth of cut, feed per-tooth and cutting speed are analyzed. An optimal method (Genetic Algorithm) is used to obtain the optimized combination of cutting parameters. The surface roughness mathematical model combing with the Genetic Algorithm will allow us to predict the surface quality of mould cavity finishing and control it in advance.