Five-axis linkage CNC machining technology for large X-type Francis turbine blades

The turbine runner blade is a complex sculpture curved body part. In the manufacturing process of large and medium-sized units, the manufacturing process of “sand casting, grinding wheel, and a three-dimensional model inspection” has long been unable to meet the requirements of technological progress, and it has not been effective. The blade profile accuracy and manufacturing quality are guaranteed, and it is not able to meet the competition requirements of today's power generation equipment market. "The 5-axis linkage CNC machining technology for large-scale turbine blades" is one of the key technologies in the manufacture of power generation equipment in the world today, and it is also the cutting-edge high technology in today's machining technology. It involves three-dimensional modeling of computer-aided products, computer simulation and simulation processing, five-axis CNC technology, complex metal cutting technology, three-dimensional surface measurement and positioning technology, and blank manufacturing.

The Three Gorges turbine runner blade is a new type of high-efficiency x-type mixed flow blade. Its runner diameter is nearly 10 meters, and the weight of a single blade is nearly 20 tons. It is the largest mixed-flow blade in the world. See 圄1, 圄2. X The type of blade-shaped mixed-flow runner model X-type mixed-flow blade is a new type of mixed-flow blade designed by the foreign ternary flow theory design method in the late 1990s, which has many advantages such as high hydraulic efficiency. Compared with the traditional mixed flow vane, the shape of the vane has a large difference, and the curvature of the vane changes considerably. The degree of space distortion is large. If the vane is placed as flat as possible, the height difference between the highest point and the lowest point is large, and the height of the two diagonals is large. Quite, its horizontal projection is X-shaped, so it is called X-shaped blade. The thickness of the blade varies greatly, with a maximum thickness of about 20 times the minimum thickness of the left stone. In view of these characteristics, special consideration must be given to the machining plan, such as the positioning of the blade machining, anti-deformation, tool adaptability in the five-axis linkage machining, and the tool axis control method and tool in the calculation of the five-axis linkage tool position. Interference calculation and other issues. For large blades, the machining area is divided by simulation, and different tools and different tool axis control methods are used in each area to improve the processing efficiency.

X-type mixed-flow blade CNC machining process scheme X-type mixed-flow blade manufacturing main process such as 圄3 2.1 The three-dimensional surface measurement of the blade blank CNC machining of the blade blank, requiring the balance of the profile (front and back) to be as evenly distributed as possible Generally, the single-sided margin is preferably 7mm15mm. The deflection distribution of the 鳎 噬 厦 厦 是 是 是 是 是 是 是 , , , , , , 为了 为了 为了 为了 为了 为了 为了 为了 为了 为了 为了 为了 为了 为了 为了 为了 为了 为了 为了 为了 为了 为了 为了 为了A three-dimensional profile of a blank is measured to find a measurement method that is economical, efficient, accurate, easy to computer data acquisition and processing, and easy to change the measurement reference. For this purpose, a mechanical contact type three-coordinate scriber and a non-contact high-precision photoelectric three-dimensional theodolite measuring system have been developed to measure the blade blank, and the second method is better adapted. The three-dimensional value point data of the blade blank is collected by three-dimensional measurement for calculation and analysis.

2.2 Computer automatic margin distribution calculation Because the actual distribution of the margin of each blade blank is different, in order to ensure that all processing surfaces have a certain margin during processing, the most effective way is to measure the three dimensions through each blank. Profile data, computer simulation of the blank entity, and three-dimensional solid modeling of the design data. The designed 3D blade entity is automatically searched by software for each direction of freedom, nested in the blank entity, multi-objective multivariate optimization calculation, seeking the "best" position, and distributing the "best" condition according to the margin Install it. Based on these requirements, numerical algorithms were studied and the corresponding software was developed. And the programming software changes the tool path by positioning the support relationship according to the "best" position. This can greatly save the installation and alignment time on the machine tool, and fundamentally solve the problem of positioning and alignment difficulties for the large mixed flow blade.

2.3 Positioning Datum and Fixture in Blade Machining Large blades are sculpted curved bodies with complex shapes. Compared with general regular geometric parts, the positioning reference is complicated. It is necessary to consider not only the "benchmark" but also the "distribution of the margin on each machined surface". How to skillfully use simple and feasible fixtures, combined with blade blank measurement assisted automatic margin calculation technology, to easily and quickly adjust the positioning and clamping of each blade blank, not only to improve the clamping efficiency, but also to ensure each blade The blank (different balance distribution) can correctly process the blade profile. Through research and analysis, a more common mixed-flow blade machining fixture was designed and developed on the computer, as shown in 圄4.

Machining mixed flow vane fixture 2.4 Machining area division and machining tool Large X-shaped mixed flow vane machining part has 11 curved surfaces, taking into account the limitation of the machine tool swing angle (determined by the simulation processing described later), the blade head surface is also divided Processed into 3 curved surfaces. In this way, the blade is divided into 13 curved surface regions, and different regions are simulated by different tools and different tool axis control modes. The parameters of the tool and its coupling system are finally determined according to the tool interference calculation, the cutting simulation, the machine tool simulation, etc. of the simulation processing described later. The principle is to use large diameter surface milling cutters as much as possible to improve the machining efficiency when the machine tool does not collide and interfere with the workpiece and the fixture. The front and back sides of the blade are made of medium-200 surface-face milling cutter with five-axis joint roughing and 160 curved surface milling cutters. The groove surface of the blade adopts 1204>160 large cutting depth face milling cutter for five-axis linkage or three-axis. Side milling; blade head surface is 100-screw corn rough milling, and then 80 left stone curved face milling cutter; 100-axis spiral corn end mill 5-axis linkage side milling is used at the water outlet.

2.5 Profile inspection after blade finishing The traditional manual shovel method is used to manufacture the blade, which is checked by stereoscopic model. For CNC machining, the accuracy can not meet the requirements, and the three-dimensional model is expensive, which is uneconomical. After machining the profile surface, the positioning hole is drilled on the profile as a fine reference. The processed profile inspection method can adopt a measurement method similar to that of the blade blank, that is, the high-precision photoelectric theodolite measurement system is used to perform three-dimensional comparative measurement on the processed blade, and at the same time, the accuracy analysis of comparing the three-dimensional blade with the design three-dimensional blade entity is developed. Detection software.

Computer simulation processing of X-shaped blades 3.1 Blade simulation processing The computer simulation processing of the blade is the most critical and technically strong work in the blade multi-axis linkage CNC machining process, and is the basis for assisting in formulating the process plan and programming. Through the auxiliary processing, it is necessary to modify the Shanshan to seek a reasonable processing plan and a specific processing method, and then use the tool position CCL) for the machine-related special post-processing program to generate a code program that can control the machining of the machine tool. The main work is secondary development on SDRC's CAMAND software to achieve simulation processing. The simulation processing and programming of the blade is shown in 圄5.

3.2 Five-axis tool position calculation and tool interference check calculation According to the above initial machining plan and dividing the machining area, define the geometric parameters of the tool used, including the geometry of the blade, the geometry of the cutter head, the cutting edge length, the tool holder and the connection system. Geometric shapes, etc., then define machine-related parameters, including some machine features and limitations, machineable space range, milling head angle and swing angle limit and direction, etc. According to the initial machining pass mode and the tool axis control method, the five-axis linkage tool position in each area is calculated, and the collision area inspection described later is combined to check whether the area division is reasonable. In the case of no collision, try to use a large diameter face milling cutter to improve the processing efficiency. After finding a more reasonable area division, further adjust the tool axis control mode, the entry and exit knife control, etc., which are mainly likely to cause collision, and then carry out the tool position calculation and the simulation test described later, and adjust the parameters. It is worth noting that in order to improve the cutting conditions of the tool, when calculating the five-axis tool position, the lead angle and tiltangle should be given. Under the condition of no collision, the tool C cutter head and the cutting edge) and the tool bar are subjected to interference check calculation. Tool interference can be further verified by Vericut's cutting simulation. If there is interference, repeat the above steps to modify the factors that may be affected until the tool position without interference and collision is generated and used as the available tool position. . Depending on the specific conditions of the blade blank, the cutting parameters of the tool are added to the tool position and the relevant machining parameters, and then a plurality of roughing tool positions and finishing tool positions are respectively calculated, and the tool position is the final machining tool position. For post processing to generate processing code.

3.3 Cutting shape simulation and interference check Because the blade profile is complex, it is divided into multiple areas, and different areas are processed by different tools and different tool axis control methods. In order to further check the tool interference and the connection of each area, the Vericut software was used to perform the cutting shape simulation. Since each piece of the blank condition is different, the sides of the design blade model are offset and stitched into a solid to define the blank.圄6 is a mixed flow blade cutting 圄 simulation. If a problem is found, recalculate the location.

3.4 Machine Tool Simulation and Collision Inspection Large blade machining is necessary for machine tool and workpiece safety to prevent milling head collision and tool interference. If collisions and interferences are found in the simulation, the machining plan and machining method must be modified. Using CAMAND to construct the NC milling head for machining the blade (such as 圄7), according to the structure and motion relationship of the milling head, define the primary geometry and the secondary geometry (SecondaryGeometry) according to the CAMAND software simulation function requirements. The relationship between the fourth axis and the fifth axis is defined. In Simulation, continuous or single-step control can be used to simulate the spatial movement of the milling head and the toolholder during the machining process, and to check whether the milling head and the toolholder collide and interfere with the workpiece and the fixture. The B axis of the 5FZG machine NC milling head is mechanically limited (360), so it is set in the machine configuration file (358 is safer. When the B angle is accumulated to 358 during continuous machining, use the CAMAND Windup function to raise the knife to A safety plane, reversing and stepping back and feeding again, so as not to damage the tool and scratch the machined surface. During the Simulation simulation, the movement of the milling head consistent with the actual machining can be observed. For possible collisions, Single step forward and backward control for easy observation, and the values ​​of each coordinate axis can be queried for analysis to modify the process plan and machining method. The machine tool simulation and the previously described tool position calculation and tool interference check must be coordinated. After repeated revisions, a reasonable and "reliable" position can be calculated.

3.5 Post-processing and machining program The post-processor dedicated to the 5FZG machine is issued, and the machine tool configuration file (MachineToolConfigurationFile) written for the 5FZG machine is used to convert the aforementioned intermediate tool position (ITP) into a controllable machine tool. Processing code.

Due to the CNC memory limitation of the 5FZG machine tool, taking into account the various processing steps, the 3300 blade is divided into more than 20 machining programs, about 3MB, and the program is transmitted by the PCIN communication software of the Sinumerik880M RS232 serial port of the PC and the processing machine.

The NC machining of X-shaped blades utilizes the five-axis linkage CNC machining technology developed by the above-mentioned large-scale X-type Francis turbine blades. On the five-axis CNC bridge milling C5FZG of SCHIESS in Germany, Dongfang Electric Co., Ltd. successfully processed F3. X-type mixed flow vanes for .3m runners.圄8 is a photo at the time of processing. The general process is to install the fixture according to the programmed machine blank machining direction, hoist the blade and align it, measure the tool setting point on the fixture, convert the blank measurement data to the workpiece zero point and place it in the NC zero offset register. The inspection program checks the amount of school children. In the processing, the inlet and outlet sides and the upper crown and the lower ring are processed according to the program, and then according to the distribution of the allowance, the machining areas are rough-milled or finished. After the back side is machined, the front side is machined on the front tire. After processing the blades, all the inspections meet the design requirements, and the blade profile accuracy is much higher than the IEC standard requirements.

5 Conclusion X-type mixed flow blade is a new type of high-efficiency mixed flow blade. How to use 5 axis linkage CNC machining technology to process it accurately and efficiently, involves a lot of research and development work.

In response to the demand of this project, the corresponding research and development was carried out, and it was successfully used for the first time and successfully used in the numerical control processing of the F3.3m runner blade of the Three Gorges Power Station. The obvious benefits were obtained, and the intermediate test unit and the Three Gorges turbine were manufactured for the Three Gorges unit. The CNC machining of the blade lays the technical foundation. In order to keep up with the world's advanced level and manufacture the Three Gorges units as soon as possible, we must carry out the improvement and optimization as soon as possible.

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