The turbine runner blade is a complex curved sculpture body part. It is very difficult to manufacture. In the past, the traditional manufacturing process of “sand casting→manual shovel→three-dimensional model inspection” was adopted in the past, which has low processing efficiency and high labor intensity. Blade profile accuracy is difficult to guarantee. At present, computer simulation processing technology has been applied abroad to realize the five-axis linkage numerical control machining of turbine runner blades, which greatly improves the machining efficiency and blade profile machining accuracy.

The three Gaobazhou hydro-generator units manufactured by Dongfang Electric Machinery Co., Ltd. are high-head axial-flow units. The diameter of the turbine runner is 5.8m. The rotor blades are twisted from the inlet edge to the outlet, and the blades are turned back. The edge has an outer skirt, and the side of the blade has a large inner skirt on the side of the hub. The curved surface R from the spherical surface of the flange to the edge of the inlet and the outlet gradually changes to zero along the surface of the space. At the request of the user, the complete set of blades (3 sets × 5 pieces) of the unit is processed by 5FZG gantry mobile five-axis linkage CNC machine tool. The development and application of CNC tools has become one of the key factors for the success of machining.

First, the selection of tools

The following factors should be considered when selecting a CNC tool for machining blades:

1. The tool geometry should be able to adapt to the processing of convex and concave surfaces, and should have good cutting performance and chip breaking and chip removal performance.
   
2. When selecting a tool, the parameters of the tool and the blade should be calculated according to the machine power, the milling head speed, the blade material, etc., and the blade, the tool bar, the milling head, etc. need to be verified by the simulation processing and the interference check.
   
3. Different diameter tools can be used for simulation processing check. Under the condition of sufficient machine power, rigidity and milling head speed, large diameter tools should be selected as much as possible to improve machining efficiency.
   

After design calculation and simulation processing verification, the following four kinds of tools were selected to process the high damzhou unit blades: 160°D200 face milling cutter head for rough milling the blade surface; 2D100 corn milling cutter for processing the blade inlet and outlet edges and Outer edge; 3D100 ball end mill for machining the transition surface between the blade surface and the flange sphere; 4D125R face milling cutter for finishing the blade surface.

Second, the localization of the tool

In order to ensure the processing quality, the imported CNC blades (Kennametal, Sandvik products) were all used in the processing of the first unit blades. Since the blade material is Ni and Cr-containing stainless steel, the material has good toughness, high processing temperature and large tool consumption. Although imported tools are light in processing and high in cutting efficiency, they are expensive (5,000 to 32,000 yuan each) and have a long lead time, which is detrimental to reducing processing costs and ensuring production progress. To this end, we have made some localization research on some tools.

1. Cooperated with Mianjiang Tools Factory to develop a 60° face milling cutter. Kennametal's imported cutter head is the right cutter (positive cutter), and the left cutter (anti-die) is not produced. Only the blade can be used 4 times. The localized positive and negative milling cutters increase the number of blades used to eight. In addition, the original imported tool adopts the lever type pressing structure, which is more complicated in design and manufacture. We changed the screw pressing structure and proved successful through trial processing.
   
2. Developed D100 spiral corn milling cutter in cooperation with Mianjiang Tools Factory. Due to the large and uneven processing of the spiral corn milling cutter, we have selected the vertical structure and the blade with the chip flute to improve the tool strength and chip fluency.
   
3. Large-size non-standard tools, due to the long cutting edge structure, are difficult to develop locally, so imported tools are still used.
   
4. The R125 face milling cutter is a precision milling cutter with a small amount of processing and is not easily damaged, so there is no need to localize it.

Third, the localization of the blade

Although the imported blades used for processing blades have excellent performance, they are expensive and expensive, and it is necessary to carry out localization development. The imported blades are all coated blades of stainless steel and the blade geometry is complex. For example, the 60° face milling insert adopts a curved front angle of 15° (see Figure 1); the corn milling insert has 3 chip flutes on one side and 2 flutes on the other side (see Figure 2); R face milling cutter The front face of the piece has a complex texture (see Figure 3). Therefore, the development of blade molds is very difficult. Localized blades must meet the following requirements: 1 good material, suitable for blade processing; 2 shape accuracy and dimensional accuracy, to meet processing requirements.

After careful investigation of processing capabilities, we selected Zhuzhou Cemented Carbide Factory for localized development of blades. The specific blade grades developed are: CN351 60° face milling cutter; CN351 corn milling cutter; CN351 ball end milling cutter; YB235R face milling cutter. The domestically produced knives and blades have been produced and used with good results, which proves that the localization development is successful.

Fourth, the repair of the tool

In the production process, the ball end mill is seriously damaged and consumes a lot. The price of this tool imported is nearly 20,000 yuan. In order to reduce the processing cost, it is necessary to repair the damaged ball end mill.

First, the repaired part of the tool is repaired, and then the contour of the tool is ground with a grinder, and the seat of the tool is repaired with a cyclone. In order to correct the welding deformation, it is necessary to re-tapping the blade by pressing the screw hole with M3.5 tap. Although the repaired tool is not as accurate as the original tool, it can fully meet the processing requirements. We have repaired 14 tools and saved a total of 277,000 yuan.

V. Benefit Analysis

The localization of CNC machining tools for turbine blades has greatly reduced the cost of machining tools. The domestic price of the 60° face milling cutter is 1580 yuan (the imported milling cutter is 12500 yuan); the domestic D100 spiral corn milling cutter is priced at 3,000 yuan (the imported milling cutter is 31980 yuan); the 60° face milling cutter is priced at 75 yuan. (Imported blade is 174.75 yuan); domestic corn milling cutter unit price is 45 yuan (imported blade is 83.97 yuan); domestic ball-end milling blade unit price is 25 yuan (imported blade is 62.24 yuan); domestic R face milling cutter unit price It is 32 yuan (80 yuan for imported blades). The processing efficiency of domestic blades can reach 70% to 80% of imported blades, and the price is less than 1/2 of imported blades. In the processing of the blades of the three Gaobazhou turbines, the blades of the first unit were all processed with imported blades, and the cost of the blades was 89,000 yuan. The blades of the second unit were mostly processed with domestic blades, and the cost of the blades was reduced to 37,000 yuan. The blades of the third unit are all processed by domestic blades, and the cost of the blades is only 32,000 yuan.