Research on the technology of blade root cleaning

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Research on the technology of blade grubbing with four coordinate numerical control machine tool

1. Preface

the blade is processed with four coordinate numerical control machine tool, and the blade profile can meet the processing requirements, but the grubbing of UG software can not meet the processing requirements, so it must be manually modified to meet the requirements

2. Clamping method of four coordinate machine tool and blade

2.1 machine tool condition

four coordinate numerical control machine tool is an economical machine tool for machining blade profile surface, but it can't process the spatial surface of the connecting surface of blade root. The four coordinate machine tool has only x, y, Z and a axes. Without C axis, the spindle cannot rotate

2.2 clamping method of blade

as shown in Figure 1, the blade is positioned on the bottom surface of the tenon, positioned on the back surface, pressed on the basin surface, and clamped with the top of the blade tip. If the blade profile is perpendicular to the direction of the main shaft, i.e. Z axis, the connecting surface of the blade root must be machined with the side edge of the tool. In this clamping mode, the four coordinate machine tool whose spindle cannot rotate cannot process the shape of spatial surface

Fig. 1 blade clamping

3. Blade root condition

there are roughly two kinds of blades requiring root cleaning, one is turbine blade, the other is compressor blade

3.1 steam turbine blade

the blade profile twist angle of steam turbine blade is large, and the blade basin and back curvature are large. The connection of blade root is generally a plane with angle, such as Dongfang third stage and Nanjing eleventh stage, and there are also parts connected by conical surface, such as SAIC third and fourth stages

3.2 compressor blade

compressor blade is a stator blade with small root torsion angle, little change in root and tip torsion angle, and gentle blade shape. The curvature of blade basin and back is small. The connection of blade root is a conical surface, and the rotation axis is above the blade shape, so the middle of the connection surface is low and both sides are high; The other is the rotor blade with larger twist angle of blade root, larger twist angle between blade root and blade tip, and twisted blade shape. The curvature of blade basin and blade back is small, and the connection of blade root is also conical, but the rotation axis is below the blade tenon, so the middle of the connection surface is high and both sides are low

4. The function and limitations of clearing root of Guanzi blade in UG software

ug software is a powerful software integrating cad/cam/cae, but it is a general software after all, with its limitations and shortcomings. To make it meet the requirements of blade processing, it can be achieved by modifying its program

the method of variable contour machining or fixed contour machining in the processing module of the software is used for root cleaning

4.1 multi axis milling

multi axis milling can be applied to the two kinds of compressor blades introduced above, but in order to program, it is necessary to remake the part root surface, that is, offset the blade root curve to the blade direction equidistantly to form three to four surfaces, and the intersection with the blade surface is connected into a surface through the throughcurves function of the surface. This surface comes from the blade surface, and must be consistent with the blade surface, Therefore, it can be used as the geometry of back chipping

operation process: enter the multi axis milling of the processing module, select the driving surface (surfacearea) mode to drive, click the new processing surface, and select the processing direction, rake direction and size, processing accuracy and number of processing cycles

4.2 fixed axis milling

fixed axis milling can be applied to the steam turbine blades introduced above. It adopts boundary drive, and the blade basin and blade back are processed on one side respectively. Therefore, the boundary line should be made, and the shape and size should meet the requirements of parallel to the wireframe trend of the blade shape, and the cutter can throw out the part surface during processing

operation process: enter the fixed axis milling of the processing module, select the boundary drive mode to drive, click the boundary curve as the closed boundary wireframe in sequence, select the parallel line mode, step distance, angle and projection direction, and then select the blade shape as the processing geometry to generate the tool path program. If the connecting surface is relatively large, you can string the tool path program generated by changing the machining allowance in turn to form the processing program, so as to realize the processing of layer by layer stripping

4.3 machining effect and defects

since the root should be used as the machining benchmark, the allowance is generally large, so it is impossible to select only one knife for root cleaning. It is necessary to consider adding coarse root cleaning and semi fine root cleaning, that is, the allowance of several procedures should be kept consistent, and the tool path should be connected continuously. The radius of the last root cleaning knife should be consistent with the root radius and size on the drawing

the height of the blade connecting surface processed by the processing program compiled by the fixed axis milling can roughly meet the requirements of the process specification, but the difference between the surfaces at the junction of the basin and the back tool path is large, and the subsequent polishing process is not easy to deal with

the tool path program generated by variable axis milling is displayed in two dimensions with the tool, and you can see whether it is overcut. Generally speaking, the tool path is in the shape of "8". When overcutting occurs, some positions are far from the surface, and the highest point of the milled part root is 2mm ~ 3mm from the final size, which is far from meeting the processing requirements. And the larger the tool is, the larger the error value is

5. solutions

after many studies, there are relatively feasible improvement methods for root cleaning of various blades, so that the four coordinate root cleaning allowance can meet the requirements of the process specification as much as possible. The following are several classifications of the improved program. All methods are processed with UG software and VERICUT software

(1) for the compressor stator blade, because the blade shape is relatively flat, the value of X in the *.cls tool path source file can be directly modified, so that the tool path line will no longer be overcut to meet the processing requirements

Figure 2 blade overcut simulation

(2) for compressor rotor blades, because the blade shape is relatively twisted, if only the x value in the tool path source file is changed, the root will be lower, but the blade shape will be overcut. Therefore, we cannot only change the x value, but also the Y, Z, I, J and K values, that is, replace the over cut program with the over cut program. Compared with the two, the x value (absolute value) is larger, and the Y, Z, I, J and K values are similar, which is consistent with the upper and lower change law. However, the program of cutting can come from the same position of the previous circle or the same position of another program, provided that the difference between the front and back cannot be too large, the tool changes greatly, and the sudden increase of the cutting edge in the actual processing will lead to tool breakage. The following is 117e3547 φ 10. Program modification method of ball cutter back chipping

if there is no modification, overcut will be found during simulation, as shown in Figure 2

the corresponding program can be found in the *.cls file. The following is the overcut program segment:

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through the combination of simulation and UG software, the whole program is replaced by the program with the increase of x value

but the approximate y value. Finally, it is modified as:

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6. effect and conclusion

although the effect of the modified procedure through the above methods is not as realistic as five coordinates from the perspective of fixed investment expenditure and the acceleration of plastic product production, it has reduced the cutting allowance as much as possible, reduced the cutting frequency and the workload of polishing workers, and gave full play to the function of four coordinate milling plane. And after the above modifications, once compiled, the program can be used repeatedly without further modification, and the goal of once and for all is achieved. (end)

Copyright © 2011 JIN SHI