JPH021604B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a processing method for processing a twisted blade of a turbine or the like using a general-purpose machine tool. When manufacturing twisted blades for turbines and the like, they were obtained by precision casting or forging or by machining the material. Conventionally, machining was performed using a multi-axis copying machine using the following method. First, an unfinished twisted wing 3 having a boss 1 with a center hole, a mounting part 2, and a platform 5 is made by processing a forged material. Next, as shown in FIG. 1, the twist wing 3 is fixed by sandwiching the mounting portion 2 to the installation stand 4 of a multi-axis copying machine. twisted wings 3
As shown in Figure 2, its inner and outer surfaces are curved surfaces,
Since the shape and size of the cross section are different in the vertical direction, the shape of the twisted wing that you are trying to make is the same.
A copying model wing (not shown) with a finishing allowance Δt of 0.2 to 0.4 is made of a soft material. Then, the ventral surface 6 and back surface 7 of the twisted wing 3 fixed on the installation stand 4 are machined by imitating the model wing for copying. Thereafter, the vent surface 6 and the back surface 7 are finished by grinding, with a finishing allowance Δt remaining, while matching with a separately manufactured cross-sectional gauge. Finally, the ventral surface 6 and the back surface 7 are polished to remove the boss 1 and determine the blade length h. In this way, the twisted wing is completed. By the way, the diameter d of the copying axis of the multi-axis copying machine
is small, and since a milling cutter is used, it is necessary to increase the axial length H (H≧h), making heavy cutting difficult and prone to vibration, and therefore the machined surface is rough and cuts are likely to occur. Even if the same model blade is used, there are variations in cutter diameter D and copying axis between multi-axis copying machines, so it is necessary to provide a sufficient margin for grinding. A cross-section gauge is required, and processing requires skill. In particular, it is difficult to make the exit angle γ of the blade uniform in each cross section from the top to the corner. In this way, the machining is divided into two stages, rough machining and finishing machining, and the grinding time is long because there is a large amount of grinding allowance. Furthermore, the cost of the twisted blade is high because a copying model blade that requires skill to manufacture is required, and a multi-axis dedicated copying machine is expensive to manufacture. The purpose of the present invention is to eliminate such drawbacks and reduce the cost of processing twisted blades.By tilting the blade surface, the plane shape in the longitudinal direction becomes a single curve, and the longitudinal direction becomes a straight line. In a method for processing a twisted wing having a combination of wing surfaces,
A cylindrical cutter whose length in the longitudinal direction is longer than the length in the longitudinal direction of the wing surface is used, and the cutter is inclined relative to the wing surface to cut the wing surface. . Hereinafter, the present invention will be explained in detail based on an embodiment shown in the drawings. The present invention has been made by focusing on the fact that a twisted wing has a point in which, when tilted, the planar shape in the longitudinal direction of the wing becomes a single curved shape, which can be regarded as a combination of straight lines in the longitudinal direction of the wing. Based on this observation, this method is used to process the ventral and dorsal surfaces of the twisted wing. In this embodiment, a case will be described in which, in a general-purpose machine such as a milling machine, the axes of the installation base and the cutter are perpendicular to each other and the angle cannot be changed. Note that only the method for processing the ventral and back surfaces, which are not easy to process, will be explained, excluding the method for processing the attachment portions and the like. FIG. 3 is an explanatory diagram showing the principle of processing a twisted wing using the processing method according to the present invention, and FIGS. 4 and 5 are explanatory diagrams showing processing states of the ventral surface and back surface, respectively, by the processing method of the twisted wing according to the present invention. Figure 6 is a side view of the twist wing attached to the base of the rotor disk, Figure 7a is a sectional view taken along line A-A in Figure 6, and Figure 7b is E in Figure 6. - E line sectional view, Figures 8 and 9 are plan views converted from Figures 7a and b in order to process the ventral and back surfaces of the twist wing, respectively, and Figure 10 is a plan view of Figure 7 with the center of the curved arc. An explanatory diagram of the stacked state,
FIG. 11 shows an explanatory diagram for calculating the diameter of the cutter. The cross-sectional shape of the twisted wing 3 (see Fig. 2) corresponds to the shaded area in Fig. 3, and the ventral surface 6 and back surface 7 are both composed of a circular surface centered on the ventral surface 6 side and a straight line in contact with the circular surface. There is. These dimensions are generally displayed on a plane parallel to the X axis (turbine blade platform). For example, when processing the ventral surface 6, see Figure 3.
The inner diameter dimension display on the ventral surface 6 side of the BE surface is displayed on a plane parallel to the X axis (parallel to the base), and the center of radius ₂ is
The diameter at this time is expressed as O ₂ and becomes 2r. To process such a circular inner surface, as an approximate processing method, a cutter with a diameter D may be moved with O ₁ and O ₂ as axes. FIG. 4 is a graphical representation of this machining state. In the figure, the movement of the cutter is shown by a three-dot chain line, and the ventral surface 6 can be finished by moving the cylindrical body representing the movement of the cutter in the circumferential direction. The value of the diameter D at this time is D=2r cos θ ₁ , where θ ₁ is the inclination of the axes O ₁ and O ₂ with respect to the Z axis. In other words, when actually processing,
In this embodiment, in order to align the axes of the cutters perpendicular to the installation surface with the axes O ₁ and O ₂ , the twist blade 3 itself is tilted so that its ventral surface 6 is parallel to the Z axis. Just fix it to the installation surface. A cylindrical cutter for cutting the twisted blade 3 is used, which is equal to the diameter D of the cylindrical body and whose length in the longitudinal direction is longer than the height H of the blade. FIG. 6 shows a state in which the twisting wing is attached to the base of the rotor disk, and the center of gravity of the twisting wing 3 is placed on the central axis S of the base R.
FIGS. 7a and 7b are cross-sectional views of the blade top and the blade root of the twisted blade 3. FIG. Figure 10 shows the blade center of gravity P ₂ on the blade root cross section (Figure 7b) and the blade top cross section (Figure 7a).
The shapes of Figure 7 a and b are expressed on the same plane by superimposing the center of gravity P ₂ of the blades, and the center points of the ventral arc r ₅ are indicated by O ₁ and O ₂ , respectively, and the relative positional relationship with respect to the XY axes is shown. It is something that Figure 8 shows the movement of the blade center of gravity P _{2 of the blade top section when the blade tip center point O 2 is} superimposed on O 1 with _the blade root center point O ₁ as a reference.
The relative positional relationship dimensions of the center points O ₁ and O ₂ of the ventral arc r ₅ in Figure 0 are shown (Table 3). In addition, Fig. 8 shows the inclination of the top of the wing based on the root of the twisted wing, and the amount of movement W ₁ of the center of gravity point _{1 2} is _{1 2} , and the inclination of P ₂ with respect to the center of gravity P ₁ is shown as θ ₁ . It can be seen that θ ₁ = pln ^-1 W ₁ /H, and therefore θ ₁ = pln ^-1 displacement of the center of gravity/height of the blade root. Further, FIG. 8 shows an angle β parallel to the exit angle of the trailing edge of the ventral surface (β may be the entry angle of the cutter). Therefore, FIG. 8 shows the dimensions of the blade root of the twist wing, the center of gravity of the blade top, and the direction of approach of the cutter into the wing with respect to the cylindrical cutter with the ventral surface machined. The relative movement of the blade in the lateral direction with respect to the twist wing 3 (see Figure 8) is the center of gravity when the tip of the twist wing is tilted by θ ₁ degree with reference to the center of gravity P _{1 of} the blade root section. With respect to point P ₁ P ₂ , the cutter is advanced at an approach angle of β with respect to the X-axis until the center of the cutter is in the X-axis direction. As a result, the shape of the ventral arc _r5 is simultaneously created from the wing root to the wing tip (the ventral surface 6 is created by a straight line and a part of the ellipse). However, (1) the vertical length of the cutter should be longer than the height H of the wing, (2) the approach angle β of the cutter should be equal to the exit angle of the ventral side edge when the wing is tilted by P ₁ P ₂ . (3) When installing a blade on a general-purpose rigid end milling machine, make sure that the approach angle β is parallel to the X axis of the machine table, that is, the exit angle of the blade is
It is best to align it parallel to the axis. In addition, when machining with a standard cutter having a smaller diameter than the cutter with diameter D, you can make a template with a ventral surface shape under the conditions shown in Figure 8 and process it by following this (the template should be placed between the straight part of the trailing edge outlet of the blade and It is a simple shape consisting of the radius of a cutter). The shape of the template is the ventral radius r ₅ shown in the drawing dimensions.
The airfoil shape of each cross section may be displayed as shown in FIG. 8 with reference to the origin of the airfoil, and the airfoil shape may be formed by a radius _r5 and a straight line at the trailing edge side outlet. The template installation satisfies the conditions shown in Figure 8, and the straight part of the trailing edge exit is aligned with the
It is efficient if installed parallel to the axis. If we assume that the curved surface radius of each cross section in the drawing dimensions is approximately a radius r of a portion of an ellipse, then the above processing method is a reasonable processing method, and the inclination of each twist wing is set to θ ₁ Then, if θ ₁ ≧8°, D=
If 2rcos θ ₁ , θ ₁ ≦8°, then when the cutter diameter is assumed under the condition of D=2r, the error between the drawing dimensions and shape and the shape created by the processing method according to this example is small. The above conditions also change depending on whether this error is created on the head side of the ventral surface 6 or in the center of the ventral surface 6. Next, when processing the back surface 7 of the twist wing, the third
In the figure, since the back surface 7 is inclined by θ ₂ with respect to the Z axis, the axis of the cutter may also be inclined by θ ₂ in the same direction as the back surface 7. In addition, at this time, as mentioned above, the ventral surface 6
You can use the same cutter that was used for processing. FIG. 5 is a graphical representation of this machining state. In the figure, the movement of the cutter is shown by a cylindrical body indicated by a two-dot chain line, and by rotating the cutter into a cylindrical shape, the thick line part where the cutter and the back surface 7 of the twisting wing 3 are in contact is cut, and the cylindrical cutter is By moving the body in its circumferential direction, the entire back surface 7 is processed. That is, when actually machining, in this embodiment, the axis of the cutter, which is perpendicular to the installation surface, is tilted until it coincides with the back surface 7, so the twisting blade 3 itself is tilted so that the back surface 7 coincides with the Z axis. Just fix it to the installation surface so that it is parallel. Note that the relative movement of the cutter in the lateral direction with respect to the twisting blade 3 at this time is calculated by assuming a cylindrical body with an arbitrary diameter, and the amount of displacement of the center of the cylindrical body at the position where the cylindrical body linearly contacts the back surface 7. It is sufficient to carry out copy processing using a template that is continuously obtained. The shape of the template at this time is to display the cross-sectional airfoil shape as shown in Fig. 9 based on the origin of the back radius r ₁ , r ₂ , r ₃ , r ₄ of the drawing dimensions, and to display each radius r ₁ ,
The shape may be formed by r ₂ , r ₃ , and the straight line of the trailing edge side exit portion of r ₄ . As described above, in this embodiment, when processing the ventral surface and back surface of the twist wing, the twist wing is tilted at a certain angle depending on each case and fixed at a predetermined position, and the outer diameter dimension is determined. The twist wing is fabricated by moving the center of the cutter along a determined trajectory. Next, drawings and tables that are converted from design drawings to drawings used when using the twist wing processing method according to the present invention during processing are shown. Figures 7a and 7b are given as design drawings. In Figure 6, the twist wing is divided into equal parts in order from the top on a plane perpendicular to the page,
When the cross sections are taken from A to E, FIG. 7a is a cross-sectional view taken along the line A-A, and FIG. 7b is a cross-sectional view taken along the line E-E. Table 2 shows the dimensions of each symbol in FIG. 7a, which is a cross section taken along line A-A, and FIG. 7b, which is a cross section taken along line E-E. Table 1 shows the size of the radius _f5 in each of the cross sections A to E, and in this example, the cross section A
~E, r ₅ is constant at 13.68. From Fig _. 7, where each dimension is given as above, we first find each angle θ ₁ of the tilt in order to process the ventral surface of the twist wing. The dimensions of each part in the plan view are shown in FIG. 8 and Table 3.
The thick arrow in the figure indicates the amount of displacement at the center of the cutter. In this embodiment, D=26.92, but as described above, D<26.92 may also be used, and in that case, the amount of displacement of the center of the cutter will be different. Next, in order to process the back surface of the twist wing, the inclination angle θ ₂ is determined from Figure 7 a and b, and the obtained value θ ₂
Figure 9 and Table 4 show the converted dimensions of each part of the plan view when the twist wing is tilted by =4°48'.

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[Table] Figure 9 shows the drawing situation in Figures 7a and b, and the coordinates of the center points of the back arcs r ₁ , r ₂ , r ₃ , r ₄ are changed to the vane center of gravity point P ₁ by following the ventral surface machining procedure in Figure 10. The center of gravity of the blade when the blade arc R ₃ is superimposed on the center point of the blade root arc R ₃ , which are displayed on the same plane with P ₂ as the reference.
Movement amount of P ₁ P ₂ and tilt angle θ ₂ with respect to twist blade height H
(Fig. 4). Here, a method for determining the tilt angle will be explained with reference to FIGS. 7 to 11. FIG. 11 is a diagram showing the principle of determining the shape and dimensions of the cutter on the ventral surface, and also shows the error in the shape of the ventral surface due to the drawing dimensions and the processing method of the present invention. The solid line centered on the XY axis shows the shape of the ellipse displayed on the plane parallel to the twist platform when the cutter is tilted by β ₁ ° in the direction of α ₁ °. Therefore, the error in the ventral shape is the difference between the arc _r5 and the elliptical shape created when the cutter is tilted by θ1 _° . The method for determining the diameter D of the cutter on the ventral surface is obtained from this figure using the formula D=(r ₅ ×cosθ ₁ °)×2. However, the diameter of the cutlet was determined based on the assumption that the ventral arc r ₅ shown in the drawing is a part of an ellipse (major axis 2×r ₅ ). As shown in Figures 7a and 7b, the center of gravity of a twisted airfoil is normally planned so that it is all on the center line of the rotor disk twisting platform due to the strength of the wing, and this is the same in this example. It is. Incidentally, if the center of gravity P of each cross-sectional view of the blade shifts, the bending moment will act in addition to the centrifugal force at this point, which will be the main cause of increasing the stress value of the blade, and the safety factor will increase due to the relationship with the material allowable stress. It decreases due to the influence of moment. The reason why the inclination angle is determined based on the center of gravity P is as follows. That is, the common point or reference point for each cross-sectional shape of the turbine airfoil is only one point, the center of gravity P, and the center of the platform 5 and the center of gravity _P1 are common, and the center of gravity P is optimal as a reference point. be. Therefore, the sixth
From the dimensions shown in the drawing in Figure 7, the center of gravity P ₁ is determined based on the foot of radius r of the belly and back shape of the airfoil, as shown in Figures 8 and 9.
The relationship is determined by the inclination angle by calculating the deviation of ~ _P2 . Therefore, from the cross-sectional dimensions in Fig. 7a and b, the coordinates of the arc center point of each cross section are displayed on the same XY coordinate plane with the center of gravity _P1 of the blade root blade plate of the twisted blade as the origin, and the blade root circular arc The degree of twist of the ventral and dorsal surfaces can be determined by the coordinates of the center point O ₁ of the wing and the center point O ₂ of the wing top arc. Therefore, in the case of the ventral surface, it is as shown in Fig. 10. Next, the center point of the blade root arc in Figure 10
With O ₁ as the origin, the center point O ₂ of the wing tip arc is superimposed on O ₁ . Figure 8 shows the inclination angle of the blade in this state expressed as θ ₁ . In this state, the amount of displacement of the center of gravity points P ₁ and P ₂ is expressed by the angle of inclination when viewed from the blade root. ∴ _{1 2} = _{1 2} , and the tilt angle θ ₁ ° = pln ^-1 P ₁ P ₂ / -- / H (see Figure 8). The tilt direction α ₁ ° = tan ^-1 v ₁ / u ₁ . θ ₂ on the rear surface 7 side can also be determined in the same manner. Next, a method of calculating the machining dimensions after tilting will be explained. The cutter diameter D is D=2 as shown in Fig. 11.
It can be expressed as (r ₅ cosθ ₁ ). Therefore, D=2( _r5cosθ1 ) ₌ 2(13·68×cos10.24°)=26.92(mm). A method for calculating processing dimensions will be explained using the ventral surface 6 as an example. As shown in Fig. 8, the arc center point O ₁ ,
As shown in Figure 10, the XY coordinate values of the overlapping state of O ₂ are transposed to the state of overlapping the airfoil center of gravity points P ₁ and P ₂ , and the amount of movement of the arc center points O ₁ and O ₂ is calculated. By changing the reading, the processing dimensions can be calculated (see Tables 1 and 2). E-E cross section example K ₁ =a _3-E +a _GE =6.19 +9.46=15.65 A-A cross section l ₁ =a _GA -a _GA =15.54 -5.0=10.54 E-E cross section m ₁ =b _3-E −b _GE =12.50 −9.76=2.74 A-A cross section n ₁ =b _3-A −b _GA =17.47 −7.20=10.54 v ₁ =n ₁ −m ₁ =10.27−2.74=7.53 u ₁ =K ₁ −l ₁ =15.65−10.54=5.11 w ₁ =√ ₁ ² + ₁ ² =√5.11 ² +7.53 ² =9.10 θ ₁゜=pln ^-1 w ₁ /H=10.24゜β=ψ ₂ cosθ ₁ =24゜× 0.9841=23.62゜ψ ₂ : Wing ventral exit angle (cutting approach angle) Tables 3 and 4 are values calculated proportionally from a certain shape, so they are slightly different from the above calculation. The dorsal surface 7 can also be calculated using the same method as the ventral surface 6. According to the method for processing twisted blades according to the present invention, a dedicated copying machine is not required, the cost of the processing machine is low, and a model wing for copying is not required, resulting in significant cost savings. In addition, since cutting is performed using a cylindrical cutter whose longitudinal length is greater than the longitudinal length of the blade surface, the length of the shank portion relative to the cutter portion can be shortened. The mounting axis of the cutter can be made larger, and accuracy is improved without vibration, making heavy cutting possible. Furthermore, by inclining the plane shape in the longitudinal direction of the blade surface into a single curved shape and cutting it with a cylindrical cutter, it can be finished at one time, so no cutting allowance is required, and the exit angle, The wall thickness and shape become more accurate, and there is no need for an expert to adjust the gauge during cutting, resulting in a significant reduction in overall machining time. In addition, the blade surface portion in contact with the platform can be finished at the same time as the blade surface processing.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the conventional twisted wing processing method, Figure 2 is a perspective view of the wing surface of the twisted wing, and Figure 3 is a perspective view of the wing surface of the twisted wing.
The figure is an explanatory diagram showing the principle of processing a twisted blade by the processing method according to the present invention, Figures 4 and 5 are explanatory diagrams showing the twisted blade according to the present invention, respectively, and Figure 6 shows that the twisted blade is formed on a rotor disk. A side view of the state installed on the stand, Figures 7a and 7b are the cross section taken along the line A-A in Figure 6 and the line E-E in Figure 6, respectively, which were given as design drawings for manufacturing the twisted wing. A cross-sectional view showing the cross-sectional shape,
Figures 8 and 9 are plan views converted from Figures 7a and b in order to process the ventral and rear surfaces of the twisted wing, respectively, and Figure 10 is an explanatory diagram of Figure 7 superimposed at the center of the curved arc. , FIG. 11 is an explanatory diagram for calculating the diameter of the cutter. In the drawings, 1 is a boss, 2 is a mounting portion, 3 is a twist wing, 4 is a mounting base, 5 is a platform, 6 is a ventral surface, and 7 is a back surface.

Claims (1)

[Claims] 1. In a method for processing a twisted wing having a wing surface whose longitudinal planar shape becomes one curved state by inclination and whose longitudinal direction is a combination of straight lines, the longitudinal length of the wing surface is The blade surface is cut by using a cylindrical cutter with a length greater than or equal to the length in the longitudinal direction, and by tilting the cutter relatively to the wing surface while the cutter is in straight line contact with the wing surface. A unique twist wing processing method.