The Research Of The Some Basic Technology For The Sculptured Surface On NC Machining

During the manufacturing of the automobile large-scale cover mould, one big issue is hard to control a uniform machining allowance of the mould if the conventional method was used to orientate the automobile cover mould, because of the large area for waiting machining of the automobile large-scale cover mould as well as the non-uniform deformation of the cast for sculptured surface. Meanwhile, the long void tool-path route elongates the maching period of mould during its rough machining, resulting in poor market responsive of automobile large-scale cover mould manufactory, high cost of mould manufactory and weak competition of industries in markets. Moreover, the maching quality of mould is hard to be guaranteed with the influence of cutter, machine tool and etc. Therefore, the rough machining and accuracy of machining are chock points to the manufacturing of the automobile large-scale cover mould, and they are also our focus in this work. The first question to be resolved is the uniformity of machining allowance. As the mould whose machining allowance goes to the processing side, this issue can be solved by the orientation of workpieces. As to the complicated deformation of machining surface, in which the void tool-path route is long, it is sloved by the method of the region of the barren machining on the processing surfaces. Three-axis maching is a common way in the maching automobile large-scale cover mould. In order to improve the maching efficiency, the related factors, e.g., the force of ball-end milling and the parameter setting in machining are studied. Considering the large area for waiting machining of the automobile cover mould and the heavy work in the rough machining, the rough machining actually takes most time of the mould on NC machining. Toward reducing this period, the supernormal parameters are set to study the relatiship between maching auracy and loaded force of cutter.This work is to improve the machining efficiency and precision based on the real requirements in the machining of the automobile large-scale cover mould. Here some basic questions on the sculptured surface being machined are studied. Main contents are summarized as the following:1) Surface matching is the basis of the NC machining and inspecting,It has important application on the machining and inspecting of the free surface (such as orientation, installation and so on). The work studies the exact matching method for the surface of the triangular mesh surface.During the process of counting,it carries through the exact matching by combining"point-point"alignment method with"point-surface"alignment method.To the same point for waiting matching,The matching point is the one, the one with the smaller distance is solved by comparing the counted distances by the"point-point"alignment method and the"point-surface"alignment method.This work also presents a dynamic ball searching method for direct searching the nearest point of the metrical point for waiting matching,the ball center is the measuring point for waiting matching, This method can quickly find out the nearest point to the measuring point from the discrete data points of the design surface, it improves the efficiency of the arithmetics.This work studies the exact surface matching method between the scatter data of the tessellated triangular mesh of the design surface and the 3D measured data, It mainly studies the influence of the surface matching effect when altering the noise of the measured data point, the number of the measured data point and the position of the measured data point.By reducing the metrical data point, the registration efficiency is further improved when dealing with massive point cloud. Several measures are used to evaluate registration accuracy, and some examples with simulated data (including noisy cases) have been done. The actual calculating examples show that the surface matching results reflects the actual instance of the surface matching,while the density of the metrical data point is the same as the discrete point of the design surface.It is the special case for the most error and the least error of the surface matching. The average error can reflect the relations of the surface matching effect with the metrical noise, the position of the data point and number of the data point.When the metrical noise increses, the most error and the average error of the surface matching increase.2)When the machining allowance for the sculptured surface of the automobile large-scale cover mould lean to the one side,the portion machining allowance of the sculptured surface transfers to the underside of the mould by the orientation and installation.It helps to decrease the machining allowance of the sculptured surface by the way.It can improve the machining effeciency for the sculptured surface of the mould.3)While barren machining along the sculptured surface of the mould,Barren machining badly affects the efficiency of the NC machining because of the different distortion of the rough surface and the asymmetry of the machining allowance, resulting in the longer empty tool-path route.In this work, a method is brought forward to solve the question with constructing barren machining region. The study closes to the design surface with the tessellated triangular mesh of surface. The study attains the efficient barren machining region by projectting the metrical data point to the tessellated triangular mesh of the design surface. The study transfers the complicated calculation for solving intersection of sculptured space surface to the calculation for solving intersection between the vertical line parallelling to the z axes and the tessellated triangular mesh surface.The study replaces the smallest protruding figure containing barren islands with oblong. The method deletes the void tool-path route and simplifies the tool-path route array.The calculating result shows that the method is succinct and effective.4) This work brings forward presents the three-milling force model for ball-end milling based on the correlation of the milling forces and the cutting area,considering the actual main affecting factors of the milling forces.A calculating method about the milling force coefficient using polynomial regression analysis method is brought forward based on the experiment resluts.The model is proved by the actual examples. The results of the calculation and the experiments indicates that the model matches the actual conditions to a certain extent.The model supplies the theory basis for the ball-end milling choosing accurately the cutting parameter on small cutting depth. It is helpful for machining in high effecincy and high precision.5) It is one of the key technological indexs for affecting the machining of the high efficiency to choose reasonable cutting parameters on NC machining. This work emploies the way to choose cutting parameter with the GA based on the actual NC machining conditions of being restricted. The work is proved by the actual workpiece machining.6) Machining the sculptured surface of the automobile large-scale cover mould, while the technical parameter value of the machine tool exceed the routine value,it must consider the machining error arisen from tool distortion because the rigidity of the workpiece and machine tool is very big. The experiment confirms that the error model considering tool deformation sensitivity is close to the actual metrical error.