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Five-axis NC Machining Technology of Large X-Type Francis Turbine Blade

Posted by: Fymicohuang 2021-07-29 Comments Off on Five-axis NC Machining Technology of Large X-Type Francis Turbine Blade

Turbine runner blades are complex sculptural curved parts. In the manufacturing process of large and medium-sized units, the long-term use of “sand casting-grinding wheel grinding-three-dimensional template detection” manufacturing technology can no longer meet the requirements of technological progress and cannot be effectively used. To ensure the accuracy of blade profile and manufacturing quality, it cannot meet the requirements of today’s power generation equipment market competition. “The 5-axis linkage Cnc Machining technology of large hydraulic turbine blades” is one of the key technologies in the manufacturing of power generation equipment in the world today, and it is also the cutting-edge high-tech in today’s machining technology. It involves three-dimensional modeling of computer-aided products, computer simulation simulation processing, five-axis CNC technology, complex metal cutting technology, three-dimensional surface measurement and positioning technology, and blank manufacturing.

The runner blade of the Three Gorges Turbine is a new and efficient x-shaped Francis blade. Its runner diameter is nearly 10 meters, and the weight of a single blade is nearly 20 tons after processing. It is currently the world’s largest Francis blade see. X-shaped blade shape Francis runner shape X-shaped Francis blade is a new type of Francis blade designed by foreign countries using the full ternary flow theory design method in the late 1990s. It has many advantages such as high hydraulic efficiency. There is a big difference in shape from traditional mixed-flow blades. The curvature of the blades varies considerably and the degree of spatial distortion is large. If the blades are placed as flat as possible, the height difference between the highest point and the lowest point is very large, with two diagonals. The height is the same, and its horizontal projection is X-shaped, so it is called X-shaped blade. The thickness of this blade varies greatly, and the maximum thickness is about 20 times the minimum thickness. In view of these characteristics, special consideration must be given to the machining plan, such as the positioning of blade machining, anti-deformation, tool adaptability in five-axis machining, and tool axis control methods and tools in five-axis machining tool position calculation. Interference calculations and other issues. For large blades, the processing area is reasonably divided through simulation processing, and each area adopts different tools and different tool axis control methods to improve processing efficiency.

X-type mixed-flow blade CNC machining process plan X-type mixed-flow blade manufacturing main process is as described. Three-dimensional profile measurement of blade blanks CNC machining blade blanks, and the margins of the profile (front and back) are required to be distributed as evenly as possible Generally, the single-sided margin* is preferably 7mm15mm. For sole to guide the torsion distribution is different, in order to use computer analysis in the next step to find the best clamping position of “the blank margin distribution * is uniform”, you must correct The three-dimensional profile of each blank is measured, looking for a measurement method that is economical, efficient, accurate, convenient for computer data acquisition and processing, and easy to change measurement standards. For this reason, a mechanical contact three-coordinate scriber and a non-contact high-precision photoelectric three-dimensional theodolite measuring system are developed to measure the blade blanks. The second method is more adaptable. The three-dimensional shape value point data of the blade blank is collected through three-dimensional measurement for calculation and analysis.

2.2 Computer automatic margin distribution calculation Since the actual distribution of the margin of each blade blank is different, in order to ensure that all processed surfaces have a certain margin during processing, the most effective way is to measure the three-dimensionality of each blank The surface data is used to simulate the entity of the blank with a computer, and at the same time, the design data is modeled as a three-dimensional entity. The designed three-dimensional blade entity is automatically searched by the software for the degrees of freedom in each direction and nested in the blank entity, and multi-objective and multi-variable optimization calculations are performed to find the “best” position and distribute the “best” conditions according to the margin. Install it. According to these requirements, numerical algorithms have been studied and corresponding software has been developed. And the tool position track is changed by the programming software according to the “best” position through the positioning support relationship. This can greatly save the installation and alignment time on the machine tool, and fundamentally solve the problem of positioning and alignment difficulties for large-scale mixed-flow blades.

2.3 Positioning datums and fixtures in blade processing Large blades are sculptured curved surfaces with complex shapes. Compared with general regular geometry parts, their positioning datums are complex. Not only the “benchmark” must be considered, but also the “margin distribution on each processed surface” is evenly considered. How to cleverly use simple and feasible fixtures, in conjunction with the blade blank measurement auxiliary automatic margin calculation technology, to conveniently and quickly adjust the positioning and clamping of each blade blank, which is not only to improve the efficiency of clamping and alignment, but also to ensure that each blade The blank (with different margin distribution) can correctly process the blade profile. Through research and analysis, simulation on the computer, a more general-purpose mixed-flow blade processing fixture was designed and developed, as shown in Figure 4.

Machining Francis Blade Fixture 2.4 Division of Processing Area and Machining Tool There are 11 curved surfaces in the processing part of the large X-shaped Francis blade. Considering the limitation of the swing angle of the machine tool (which can be determined by the simulation processing described later), the blade head surface should also be divided Processed into 3 curved surfaces. In this way, the blade is divided into 13 curved areas, and different areas use different tools and different tool axis control methods for simulation processing. Determine the parameters of the tool and its connecting system according to the tool interference calculation, cutting simulation, machine tool simulation, etc. described later. The principle is to use large-diameter curved surface milling cutters as much as possible under the condition of no collision and interference between the machine tool and the workpiece and fixtures to improve processing efficiency. The front and back large surfaces of the blade are rough milled by medium 200 curved face milling cutters with five-axis linkage, and 160 curved face milling cutters are used for finish milling; the groove surface of the blade adopts 1204>160 large cutting depth face milling cutters with five-axis linkage or three-axis linkage Side milling processing; the blade head surface is rough milled with 100 spiral corn, and then processed with a curved face milling cutter of 80 square stones; the water outlet is processed with a 100 spiral corn end mill with five-axis linkage side milling.

2.5 Surface inspection after blade finishing. The blade is manufactured by traditional manual spade grinding method, and the three-dimensional template is used for inspection. For CNC machining, the accuracy cannot meet the requirements, and the cost of the three-dimensional template is high, which is very uneconomical. After processing the coriander profile, drill positioning holes on the profile as a precision datum. The processed profile detection method can use 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 of the processed blade, and the accuracy analysis of the comparison between the measured three-dimensional blade and the designed three-dimensional blade entity is developed at the same time Detection software.

Computer simulation processing of X-shaped blades 3.1 Blade simulation processing The computer simulation processing of blades is the most critical and technical work in the multi-axis CNC machining process of blades, and it is the basis for assisting the formulation of process plans and processing procedures. Through the auxiliary processing, it is repeatedly modified to find a reasonable processing plan and specific processing method, and then the tool position (CCL) is used in the special post-processing program related to the machine tool to generate a code program that can control the processing of the machine tool. The main task is to carry out secondary development on the CAMAND software of SDRC Company to realize simulation processing. The simulation processing and programming of the blade is shown in Figure 5.

3.2 Five-axis tool position calculation and tool interference check calculation. According to the aforementioned initial processing plan and dividing the processing area, define the geometric parameters of the tool used, including the geometry of the blade, the geometry of the cutter head, the length of the cutting edge, the tool holder and the connection system Geometry, etc., and then define the parameters related to the machine tool, including some machine tool features and restrictions, the range of space that can be processed, the milling head angle and swing angle restrictions and directions, etc., to construct the machine tool configuration file. Then calculate the five-axis linkage tool position of each area according to the initial processing method and the tool axis control method, and combine with the collision interference check described later to check whether the area division is reasonable. Under the condition of no collision, try to use a large-diameter face milling cutter to improve processing efficiency. After finding a more reasonable area division, further adjust the tool axis control mode, in-out tool control and other factors that may cause collisions in the machining method, and then perform tool position calculation and simulation check described later to modify various parameters. It is worth noting that, in order to improve the cutting conditions of the tool, when calculating the five-axis tool position, the leadangle and tiltangle should be given. Under the condition of no collision, the interference check calculation of the tool C (cutter disc and cutting edge) and the tool holder should be performed. Tool interference can be further used Vericut for cutting simulation to check the shape. If there is interference, repeat the aforementioned steps to modify multiple factors that may affect, until a tool position without interference or collision is generated in the simulation, and it is regarded as a usable tool position . Depending on the specific situation of the blade blank, add the cutting parameters of the tool on the basis of this tool position and related processing parameters, and then calculate multiple roughing tool positions and finishing tool positions respectively. This tool position is the final machining tool Bit for post-processing to generate processing code.

3.3 Cutting contour simulation and interference effect inspection Because the blade profile is complex, it is divided into multiple areas, and different areas are processed with different tools and different tool axis control methods. In order to further check the interference of the tool and the tool receiving in each area, Vericut software was used to simulate the cutting circle. Since the status of the blank is different for each piece, offsets are made on each surface of the design blade model and stitched into a solid to define the blank. Figure 6 is a simulation of the cutting circle of a mixed-flow blade. If a problem is found, the tool position is recalculated.

3.4 Machine tool simulation and collision check large blade processing, for the safety of the machine tool and the workpiece, it is necessary to carry out machine tool simulation to prevent the collision of the milling head and the interference of the cutter. If collision and interference are found in the simulation, the processing plan and processing method must be modified. Use CAMAND to construct an NC milling head (such as ) for blade processing. According to the structure and motion relationship of the milling head, define the primary geometry and secondary geometry of the primary axis according to the simulation function requirements of the CAMAND software, and Define the relationship between the 4th axis and the 5th axis. In Simulation, continuous or single-step control can be used to simulate the spatial movement of the milling head and the tool holder during the machining process to check whether the milling head and tool holder collide and interfere with the workpiece and fixture. The B axis of the NC milling head of the 5FZG machine tool is mechanically limited (360), so it is safer to set (358) in the machine configuration file. During continuous processing, when the B angle accumulates to 358, use the Windup function of CAMAND to raise the tool to A safety plane, reverse and move back one step before cutting in, so as not to damage the tool and scratch the machined surface. During the simulation process, the movement of the milling head can be observed consistent with the real machining. For the parts that may collide, Single-step forward and backward control can be used for careful observation, and the value of each coordinate axis can be queried for easy analysis to modify the process plan and processing method. The machine tool simulation and the previously described tool position calculation and tool interference check must be coordinated with each other , After repeated modification, a reasonable and “assured” tool position can be calculated.

3.5 Post-processing and processing programs are issued for the 5FZG machine tool post-processor, and then cooperate with the machine tool configuration file (MachineToolConfigurationFile) written for the 5FZG machine tool to convert the aforementioned reasonable intermediate tool position (ITP) to generate a controllable machine tool. Processing code.

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

The CNC machining of X-shaped blades utilizes the five-axis CNC machining technology for large-scale X-shaped Francis turbine blades developed above. On the five-axis CNC flyover milling C5FZG of German SCHIESS Company, Dongfang Electric Co., Ltd. successfully processed F3 .3m runner with X-shaped Francis blades. Figure 8 is a photo during processing. The general processing process is to install the fixture according to the programmed machining direction of the machine tool blank, hoist the blade and align it, measure the tool setting point on the fixture, convert the workpiece zero point according to the blank measurement processing data and place it in the NC zero offset register, first use The inspection program checks the school child allowance. In processing, the inlet, outlet, upper crown and lower ring are first processed according to the program, and then according to the margin distribution, each processing area is rough milled or finish milled according to the program. After the coriander is processed on the back, the front is processed on the front mold. After various inspections, the processed blades fully meet the design requirements, and the blade profile accuracy is much higher than the IEC standard.

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

In response to the needs of this project, corresponding research and development were made, and it was used for the first time and successfully used in the CNC machining of the F3.3m runner blades of the Three Gorges Power Station, which has achieved obvious benefits and manufactured the intermediate test unit and the Three Gorges turbine for the Three Gorges unit. The NC machining of blades laid the technical foundation. In order to keep up with the world’s advanced level and manufacture the Three Gorges unit as soon as possible, it is necessary to carry out good and optimization as soon as possible.

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