Multi axis NC machining programming technology of

Multi axis NC machining programming technology of large hydraulic turbine blades

runner blades are the key components of hydraulic turbine energy conversion and the most difficult parts. At present, multi axis NC machining is the most effective machining method to solve this kind of large sculpture curved surface parts. Multi axis NC machining programming is the most important link to realize its high precision and high efficiency machining. This paper introduces the five axis NC machining of large sculpture surface of medium and large water turbine blades in the most widely used conventional plastic granulator equipment, which involves the three-dimensional modeling of runner blades, calculation of tool path, cutting simulation, machine tool motion collision, plasma process, including adding a layer of ultra-thin and very soft pure glass (silicon oxide) simulation, post transformation and other key technologies in the process of equal ion machining. Through the link and research of these technologies, the multi axis linkage machining of large blades is developed and realized

1. Introduction water turbine is the prime mover of hydropower generation. The manufacture of water turbine runner blades and the quality of Runner have a great impact on the safety, reliability and economic operation of hydropower station units. Turbine runner blade is a very complex sculpture surface. Carry out hot load test run on large and medium-sized 4500mm wide and thick plate rolling mill; On December 1, 2015, the manufacturing process of "sand casting - grinding wheel shovel grinding - three-dimensional template inspection" has been adopted for a long time, which can not effectively ensure the accuracy and manufacturing quality of blade profile. At present, the five axis NC machining technology is the cutting-edge high technology in machining. NC machining programming of large complex curved surface parts is the most important technical basis to realize its digital manufacturing. Its NC programming technology is a digital simulation evaluation and optimization process. Its key technologies include: three-dimensional modeling and positioning of complex shape parts, five axis linkage tool path planning and calculation, tool axis control technology for machining sculpture curved surface, cutting simulation and interference inspection, and post-processing technology. The multi axis NC programming technology of large complex curved surface makes the multi axis NC machining of sculpted curved surface runner blades possible, which will greatly promote the development and progress of China's hydraulic turbine industry and lay a foundation for the development of China's hydropower equipment manufacturing industry towards advanced manufacturing technology. 2. The multi axis NC machining programming process of large-scale hydraulic turbine blades the five axis linkage NC programming of large complex curved surface parts is much more complex than that of ordinary parts. According to the characteristics of large volume and large change of surface curvature of hydraulic turbine blades, process design is carried out by analyzing the machining requirements, processing scheme is determined, appropriate machine tools, cutting tools and fixtures are selected, and reasonable cutting route and cutting parameters are determined; Establish the geometric model of the blade, calculate the motion path of the tool relative to the blade in the machining process, and then carry out the cutting simulation of the blade and the motion simulation of the machine tool. Repeatedly modify the machining parameters, tool parameters and tool axis control scheme until the simulation results are free of interference and collision. Then carry out post-processing according to the program format acceptable to the NC system of the machine tool to generate the blade machining program. The specific programming process is shown in Figure 1. Fig. 1 five axis NC machining programming flow of Large Francis blade 2.1 three dimensional geometric modeling of hydraulic turbine blade hydraulic turbine blade is a curved part composed of multiple sculptured surfaces, which cannot be defined by analytical equations. In order to meet the requirements of hydrodynamic characteristics in blade design, we use NURBS surface approximation method for surface modeling. For the mixed flow blade, this complex sculpture curved surface body is composed of front, back, belt shaped rotating surface connected with the upper crown, belt shaped rotating surface connected with the lower ring, water inlet side curved surface, water outlet side curved surface, water inlet side head curved surface, etc; Axial flow blades are composed of front and back surfaces with sculptured surfaces, curved surfaces with variable arc radius at the inlet edge, curved surfaces at the outlet edge, spherical and cylindrical surfaces of rim, spherical surfaces of hub and flange, skirt surfaces of rim, transition surfaces between hub and flange and front and back surfaces, etc. Due to the large amount of data of three-dimensional coordinate points described along the flow surface of the blade, a grip program can be written to read these three-dimensional coordinate points. For the mixed flow blade, the bicubic multi patch surface is used for surface modeling through the curve method of free-form features, as shown in Figure 2. Write the geometric points on the back of the blade according to the lofting curve (the right angle of the blade section) and the right angle of the lower cylinder section as shown in the lofting drawing, and then convert them into the geometric points of the lower cylinder section according to the right angle of the blade section (the right angle of the blade section) as shown in the lofting drawing. The blank shape of the blade can be offset calculated from the design data points, or determined from the point clustering method obtained from three-dimensional measurement. NURBS surface modeling can be carried out on each surface of the blade and sewn into a solid. 2.2 blade machining process planning, machining scheme and selection of machining parameters determine the efficiency and quality of NC machining. The turbine blade is a very complex sculptured curved surface. For the Francis turbine blade, we choose a large gantry mobile five coordinate NC milling and boring machine according to the structure and characteristics of the blade to be processed. According to the three-point positioning principle, after a lot of research and analysis, we decide to use a general adjustable support with spherical shape on the back of the processing, match with the positioning pin for blade welding to position the blade, and weld the necessary process blocks on the blade, Some general tensioning devices are used for clamping. When processing the front side, use the mould that is completely consistent with the back surface milled during the processing of the back side, put the back side of the blade into the mould, adjust and align with the welded process block, and still use the general tension and compression device for clamping. Because the blade has