Research On Subdivision Polishing And Trajectory Planning Of Free-Form Surfaces

With the development of the aviation, the shipbuilding, the automobile, the electrical appliances as well as the industry product more and more to the multi-varieties, small batch, high quality, the low cost direction, free curved surface of mold processing quality and the efficiency are put forward up to high request. As a result of the computer aided geometry design,mic-roelectronic technology and the numerical control technology rapid development, the free curved surface shape processing automation has already been realized basically. But its finishing processing has not been realized the automation, namely the free curved surface polishing is completed by manual mainly. The handwork polishing wastes time and its efficiency is low. At the same time the good shape precision and the surface quality is difficult to obtain. Therefore polishing technique has already become the bottleneck of restraining the high quality mold manufacture technological development. The domestic and foreign scholars positively are carrying on automatically polishing processing system development and the practical research in order to overcome question which exist low efficiency universal existence in the processing mold free curved surface. They have yielded many important results through exploring new polish method and technology. Specially in the recent 20 years, a series of autom-atically polishing method and system are successively constructed by the co-mputer technology, for example Japan developed the numerical control miller, which can realize the three dimensional curved surface polishing automatically in mold processing. It is very imperative for improving efficiency while guaranteed the mold free curved surface finishing processing precision because mold finish man-hour accounts for the high proportion in the entire mold manufacture. Polishing tool not only require proper motion according to the path ahead but also maintain the specific posture and the stable pressure necessarily as the same time. The certain working space is expensed inevitably as maintaining specific posture, the robot precision and the rigidity insufficiency is caused for increasing the robot the arm length in order to increase the working space. Therefore purely adopting the robot realization large-scale mold's free curved surface automation processing will have the working space and the precision, the rigidity contradiction. Moreover, in very many situations the mold the cavity surface is the irregular free curved surface. It brings very greatly troublesome to the automated finishing processing tool path and feed because these curved surface shapes complex. As a result of the mold free curved surface complexity, the polishing tool has the good self-regulating, namely the so-called compatibility. The polishing tool must change the tool type along with the free curved surface processing outline. Based on this, the large-scale mold free curved surface highly effective finishing processing was still a world difficult problem in particular regarding the mold free curved surface. So it is imperative for carrying on theory and technique research deeply in highly effective finishing processing. Based on "subdivision planning of the mold curved surface polishing in the virtual machine tool"to the Jilin Province science and technology hall fund project research, some questions and technique about mold free-form surface automatically highly efficiency finish are carried on developing deeply and comprehensive synthesis narration on the basis of reading and analysis the domestic and foreign literature material in the paper. Selection a topic academic and the practical application background as well as the necessity are discussed in the paper. Free-form surface characters through adopting the NURBS description mold free-form surface are researched. Subdivision planning method of artificially polishing process is analyzed and free-form surface boundary as well as adaptive subdivision planning algorithm is put forward base on curvature and fuzzy C according to the computer graph information and the NURBS curved surfaceconstruction feather. Free-form surface is divided into certain curved surface pieces through the algorithm. Those curved surface pieces are turned over classification and the race. Namely clustering curved surface piece race. The concrete example (free-form surface practicality photo see Figure 1) is carried on programming through applying for subdivision algorithm. It is simulated through Matlab. The simulation result indicated that subdivision algorithm could realize the free-form surface subdivision. The simulation result sees Figure 2: The effect factors to surface roughness are analyzed through constant scallop height of the NURBS curved surface studying in the processing polishing path topology. The formula of constant scallop height is given based on parallel polishing. The formula can forecast surface roughness. The finish idea of whole curved surface equal error and uniformity roughness is put forward through researching on free-form surface polishing path and motion and improving space parallel constant polishing. Adaptive trajectory planning is advanced base on free-form surface equal precision polishing. Row spacing and stepping of free-form surface polishing finish is inferred. So it not only can realize free-form surface equal precision processing but also can guarantee finish quality of free-form surface. Algorithm based on space parallel constant scallop height adaptive polishing finish path is inferred. The algorithm is simulated by concrete example. The simulation results (see Figure 3) indicatethat the method of trajectory planning can realize its constant scallop height adaptive polishing finish. Fig.3 Trajectory of space parallel constant scallop height Because the free-form surface subdivision algorithm produces boundary between the curved surface piece territories is the straight edge convex polygon, it is hard to produce the fair polishing trajectory within pieces. Not smooth boundary problem exists which after the mold free-form surface piece processing,it has carried on processing based on the discrete energy method of point to process the fair of the pieces. It has established fair polishing model, produced its solution way, and aimed at the concrete example to carry on simulation processing . The simulation result indicated that the fair polishing model based on the separate energy method is correct, it can realize the fair polishing between the curved surface pieces. At present ,it can realize the mold shape processing automation, but as for its final automatic finishing processing, the experience and the expert skill are also needed, its automated standard is difficult to formulate, Through analyzing the polishing skill of the skilled grinding worker,polishing processing and polishing theories, can we know, the key to establish the expert system of polishing die free-form surface, and realize automatic polishing is to determine the combination polishing order and the condition, and enables it to achieve the optimization. Through the concrete example, it has constructed the base frame of expert system of the integrated force sensor mold free-form surface subdivision polishing. According to the free form surfacepiece information, the starting value and the target value of surface roughness, it has established the expert system knowledge libraries, and according to the knowledge libraries established the smooth inference step of polishing processing and the inference process to reconcile the subsystem. At the same time this article used the breadth-first search method to determine the best order of polishing. The simulation and the experiments to the mold free-form surface work pieces have been made,the simulation result indicated that the subdivision processing efficiency had been enhanced truly. Meanwhile, the mountain animal-drawn cart cushion has rough grinds and polishing processing, and throws has performed the contrast experiment to rough grinds and polishing,the subdivision and no subdivision grinds, the subdivision and no subdivision polishing.The result indicated that the roughness value range along the curved surface work piece polishing planning is0.23μm～0.42μmand0.26μm～0.46μm.In the situation of surface roughness basic maintenance stable, the time used subdivision rough grinds is less than that of subdivision polishing.The specifically scope is: η抛=18.63%,η磨=15.19%,η抛?η磨.This indicated that the subdivision processing algorithm is feasible and the efficiency will be more obvious in use of polishing processing.