Five axis machining technology for runner blades o

2022-08-08
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Five axis machining technology of large hydraulic turbine runner blades

the five axis linkage machining technology of large hydraulic turbine runner blades is one of the important symbols to characterize the manufacturing level of hydraulic turbines. Runner blade is a key component of hydraulic turbine, and its manufacturing accuracy has a direct impact on the efficiency and other hydraulic performance of the unit, so the profile processing requires high accuracy. Domestic hydraulic turbine blades have been manufactured by sand casting for a long time, which is formed by manual shovel grinding and tested by three-dimensional template. However, the manual shovel grinding method not only has poor labor environment, high labor intensity and low efficiency, but also has poor blade surface quality, which reduces the efficiency of hydraulic turbines. At present, the five axis NC machining technology of large turbine blades has become one of the key technologies in the world power generation equipment manufacturing industry, 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 processing and five axis linkage CNC technology

I. blade modeling

(1) blade modeling is composed of blade profile and hub. The blade surface is a free-form surface with high requirements for smoothness and continuity, and its section line is a complex free-form curve. NX software 3 is used Limit protection: electronic limit CAD module, according to the two-dimensional design drawing, input the coordinates of section data points in the z-x plane, and simulate the closed spline curve. According to its section radius, stretch it into a surface along the Z direction, and project the spline line onto the surface along the Y direction as a group of three-dimensional section lines of the blade surface, as shown in Figure 1

(2) generate ten closed three-dimensional section lines, as shown in Figure 2

(3) sweep through ten section lines and generate a smooth blade surface entity, as shown in Figure 3

(4) generation of blade hub. The creation of the hub is relatively simple. First create its section line string, and then use the rotate command to rotate the section line string to create the hub rotating body, as shown in Figure 4

finally, the blade surface and hub are adjusted in time according to the processing technology, and the fuselage is trimmed and chamfered to create the blade entity, as shown in Figure 5

II. Blade processing

1 Blade processing and clamping process

the blade is of cast structure and made of martensitic stainless steel. On the basis of sand casting, the surface allowance is generally 5 ~ 20mm. The clamping process is very important. Generally, the following methods are used: Based on the rotating axis line of the blade hub, weld the process shaft on the hub, rough turn the flange end face, and then drill two center holes on the process shaft and flange end face. The corresponding fixture adopts two center seats, one is the fixed center seat, which is placed at the flange end; The other is an axially adjustable center seat, which is placed on the process shaft end on the rim. The flange end face is marked with the blade processing position. Using fixtures and marks, according to the three-dimensional surface data after blade modeling, with the help of the function of the machine tool, find the machining position, generally set it at the center of the wheel hub to determine the zero point of the workpiece, and weld the lug on the reverse side of the machining surface, and use the universal Jack and adjustable pull rod to clamp and weld, as shown in Figure 6

2. Rough machining of blades

(1) using NX software cam module, rough machining can adopt layered cutting of cavity milling (cavity_mill) in three-axis contour milling (mill_contour)

the main processing parameters are set as follows: the tool adopts Ф 63r6 rough milling cutter. The zero point of the workpiece is set at the center of the wheel hub, and the safe clearance distance is 20mm higher than the highest point of the wheel hub. Each layer (global depth per cut) is 2mm, the step distance (Stepover) is 3mm, and the part side stock is 0.5mm. The spindle speed is 1500rpm and the feed rate is 2000mmpm. The rough machining tool path is shown in Figure 7

(2) in NX software, cutting simulation (VERICUT) and integrated simulation and verification (is&v) can verify the tool path of multi axis linkage machining, replace the trial machining process, visually and truly see whether the tool design is reasonable, check the over cutting and under cutting of blades in the machining process, and seek the optimal machining method and process scheme, which can ensure the accuracy of machining surface and the quality of blades, Effectively avoid the phenomenon of damaging the workpiece and fixture in the actual processing, and improve the processing efficiency. Rough machining dynamic simulation (verify) is shown in Figure 8

(3) post builder. Post processing is a very important part of forming NC program. The format of tool position source file must be converted through post processing, and the file that generates NC code format can be accepted by NC machine tools. Different NC systems have different code formats. Combined with the post-processing constructor of NX, compile a reasonable post-processing file, and set the machine parameters (such as the maximum stroke of the linear axis, the rotation angle range of the AC rotating axis, the G command, the setting of the M function, the RTCP function, the setting of the program head and tail and a series of information) one by one, so as to generate a correct NC code program that can be accepted by the NC machine tool, so that it can be applied to production. The operator calls in the above NC program according to the program list (program name, program path, tool number, etc.), and the step mark can be clearly seen when the blade surface is roughened on site and the cutting fluid is sprayed, as shown in Figure 9

3. Blade finishing

(1) using NX software cam module, the finishing can adopt variable_contour machining in mill_multi_axis

the main processing parameters are set as follows: the tool adopts Ф The 4-edge cutting finishing of 63R 8 provides them with carbon fiber semi cured material face milling cutters. For the drive method, select the surface area, the projection vector is in the positive direction of the Z axis, the tool axis is in the normal to drive direction, and the part stock is set to 0mm. The internal and external tolerances of parts are 0.001. The spindle speed is 3000rpm and the feed rate is 2000mmpm

through the optimization of milling methods and milling parameters, the blade can be milled with high precision, high efficiency and low tool consumption

(2) the dynamic verify of finish machining is shown in Figure 11

(3) integrated simulation and verification (is&v), in versions above NX4 software, various types of machine tools and post-processing in NX software library can be customized or called. It can simulate the whole machining process of machine tools and parts (see Figure 12), comprehensively consider the characteristics of the controller and tool configuration, simulate the real machine tool movement with animation, and detect the collision between machine tool parts, fixtures, tool parts and IPW. By comparing the processed parts with the desired parts to improve the quality of the processing process, expensive and time-consuming dryruns can be avoided, so as to reduce costs and reduce operator intervention. By reducing collision and reducing the risk of damage to machine tools, fixtures and workpieces, it is an ISV advanced simulation superior to cutting simulation (VERICUT)

(4) gmb2560x five axis five linkage CNC machine tool produced by ZOJE Machine Tool Co., Ltd. is used for processing, equipped with advanced German Siemens 840D CNC system and servo controller. The author finished the blade surface at a customer's site in Hangzhou (see Figure 13). Most of the blades were cut and machined in one clamping. The surface milling cutter was always perpendicular to the workpiece surface (normaltodrive). The blade surface was as smooth as a mirror, and there was no need to manually shovel grind and polish. Effectively ensure the machining accuracy of blades and greatly improve the machining efficiency

III. conclusion

with the gradual maturity of China's five axis CNC machining technology, China's large-scale turbine manufacturing has reached the international advanced level. The innovation of blade technology has a significant effect on improving quality, improving machining efficiency, reducing tool costs and improving economic benefits

the NC machining of blades will bring huge economic benefits to the long-term operation of the unit for every 1% increase in the output efficiency of the runner. (end)

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