A Measuring Point Planning Method for Bent-Twisted Thin-Walled Blades Considering Machining Deformation

Abstract

The present invention relates to a measuring point planning method for a bent and twisted thin-walled blade considering machining deformation. The present invention budgets the machining deformation error generated during the machining of the thin-walled blade, and divides the second blade cross-section curve according to the average value area of the machining deformation error. The present invention adopts the chord tolerance method to enable the measuring points to be adaptively distributed on the second blade cross-section curve, so that the distribution of measuring points increases in the area with large machining deformation error on the second blade cross-section curve, and the distribution of measuring points decreases in the area with small machining deformation error, making a more reasonable division of the measuring point distribution on the blade surface. The distribution of measuring points not only conforms to the distribution of the blade curvature characteristics, but also adapts to the machining deformation error distribution, reflecting the true machining state of more blades with fewer measuring points, and improving the accuracy and efficiency of in-machine inspection of the blade.

Description

Technical Field

[0001] The present invention relates to the field of machining accuracy of numerical control machine tools, and more particularly, to a method for measuring point planning of curved and twisted thin-walled blades considering machining deformation. Background Art

[0002] As an important component of an aero-engine, the machining accuracy of blades plays a crucial role in the overall performance of the engine. In the five-axis machining of blades, the true machining state of the blades is reflected by extracting the data information of the measuring points on the blade surface. The number and distribution of the measuring points play a decisive role in improving the measurement accuracy and efficiency. Therefore, it is necessary to analyze the method for measuring point planning of blades.

[0003] The design of curved and twisted thin-walled blades is completed by lofting and fitting a group of two-dimensional sectional curves. To ensure the aerodynamic requirements and energy conversion efficiency, as Figure 1 shown, the middle arc of the two-dimensional sectional curve of the curved and twisted thin-walled blade is not parallel to the blade chord line, resulting in wing bending, and there is a twist angle between the chord lines at the blade tip and the blade root, resulting in twist. The thin-walled characteristics of the blade are mainly reflected in the deformation and vibration generated during the machining process. Domestic and foreign scholars mainly conduct measuring point planning for blades from two aspects: the geometric characteristics of the blades and model reconstruction, but do not consider the machining deformation error generated during the machining process of the blades. This leads to the distribution of the measuring points not matching the distribution of the machining deformation error, and it is impossible to accurately reflect the true machining state of the blades. Therefore, a method for measuring point planning of blades considering machining deformation is necessary. Summary of the Invention

[0004] The problem solved by the present invention is how to plan the distribution of measuring points for blades with machining deformation errors and accurately reflect the true machining state of the blades.

[0005] To solve the above problems, the present invention provides a method for measuring point planning of curved and twisted thin-walled blades considering machining deformation, which specifically includes:

[0006] Step 1: Establish a three-dimensional blade model of the curved and twisted thin-walled blade;

[0007] Step 2: Intercept a plurality of first blade sectional curves on the three-dimensional blade model along the blade height direction; obtain the leading edge points and trailing edge points of each first blade section according to the middle arc of each first blade sectional curve, and respectively fit all the leading edge points and trailing edge points to obtain a leading edge contour line and a trailing edge contour line;

[0008] Step 3: Obtain the number of second blade sectional curves actually required to be measured for the blade according to the blade height and a preset proportional coefficient; adaptively obtain the distribution points of the second blade sectional curves from the leading edge contour line and the trailing edge contour line, and then obtain the second blade sectional curves;

[0009] Step 4: Use the chord tolerance method to adaptively distribute measurement points on the second blade cross-section curve;

[0010] Step 5: Calculate the average milling force exerted on the blade during the machining process;

[0011] Step 6: Mesh the blade surfaces on the front and back of the three-dimensional blade model, forming M×N force application points on each blade surface; predict the machining deformation error of the force application points on each blade surface by applying the average milling force to each force application point;

[0012] Step 7: Obtain the machining deformation error distribution on the second blade cross-section curve based on the position of the second blade cross-section curve on the blade surface;

[0013] Step 8: Calculate the average value of the machining deformation error based on the machining deformation error obtained in Step 6; divide the machining deformation error distribution on the second blade cross-section curve according to the average value; then, in combination with the curvature of the second blade cross-section curve in each region, adaptively distribute the measurement points in each measurement point, extract the measurement points in each region and combine them to obtain the distribution of the measurement points on the corresponding second blade cross-section curve.

[0014] The beneficial effects of the present invention are as follows: By predicting the machining deformation error generated during the machining of thin-walled blades, the second blade cross-section curve is divided according to the average value region of the machining deformation error. The present invention uses the chord tolerance method to enable the measurement points to be adaptively distributed on the second blade cross-section curve, so that the measurement points are increased in the region with large machining deformation error on the second blade cross-section curve, and the measurement points are reduced in the region with small machining deformation error, making a more reasonable division of the measurement point distribution on the blade surface. The distribution of the measurement points not only conforms to the distribution of the blade curvature characteristics but also adapts to the machining deformation error distribution, reflecting the true machining state of more blades with fewer measurement points, and improving the accuracy and efficiency of in-machine inspection of the blade.

[0015] Preferably, in Step 2, the first blade cross-section curve is intercepted on the three-dimensional blade model along the blade height direction by using the equal-height method.

[0016] Preferably, the number of the second blade cross-section curves in Step 3 is:

[0017] m = c·L

[0018] In the formula, m is the number of the second blade cross-section curves, c is the proportionality coefficient; L is the height of the blade;

[0019] The specific obtaining of the second blade cross-section curve includes:

[0020] Using the chord tolerance method, m distribution points are obtained from the leading edge contour line and the trailing edge contour line respectively, and m second blade section curves are obtained on the three-dimensional blade model by connecting the distribution points on the leading edge contour line and the trailing edge contour line.

[0021] Preferably, the calculation formula for the average milling force in step 5 is:

[0022]

[0023]

[0024]

[0025] In the formula, F t is the tangential component force; F r is the radial component force; F a is the axial component force; a p is the cutting depth; v t is the cutting speed, v t = nπD / 1000, where n is the tool diameter and D is the spindle speed; f e is the feed rate; a e is the cutting width; ψ is the tool rake angle.

[0026] Preferably, the specific process of obtaining the machining deformation error distribution on the second blade section curve in step 7 includes: obtaining the machining deformation errors on the two blade surfaces according to the prediction, and using drawing software to draw the deformation error nephogram; according to the positions of the second blade section curve on the two blade surfaces respectively, intercepting a preset number of points, and drawing the machining deformation error distribution on the second blade section curve.

[0027] Preferably, the specific process of obtaining measurement points in each area of the second blade section curve by using the chord tolerance method in step 8 is as follows: calculating the chord deviation by using the curvature of each area of the second blade section curve respectively, making the measurement points adaptively distributed in each area of the second blade section curve by using the chord tolerance method, integrating the machining deformation error into the blade surface, then obtaining the second blade section curve with the machining deformation error distribution through the position where the second blade section is located, and then partitioning the second blade section curve according to the average value of the machining deformation error. By combining the curvature of the blade section curve in different areas, the chord tolerance method is used to adaptively distribute the measurement points of the section curves in different areas, so as to obtain a more reasonable distribution of measurement points on the second blade section curve. Description of the Drawings

[0028] Figure 1 It is a two-dimensional section curve diagram of a curved and twisted thin-walled blade in the prior art;

[0029] Figure 2Schematic diagram of the first blade cross-section curve intercepted in Step 2;

[0030] Figure 3 Schematic diagram of the leading edge point and trailing edge point of the first blade cross-section curve;

[0031] Figure 4 Schematic diagram of the leading edge contour line and trailing edge contour line;

[0032] Figure 5 Schematic diagram of the distribution of distribution points on the leading edge contour line and trailing edge contour line;

[0033] Figure 6 Schematic diagram of the 6 second blade cross-section curves obtained in Step 3;

[0034] Figure 7 Distribution diagram of measurement points based on the curvature of the second blade cross-section curve in Step 4;

[0035] Figure 8 Schematic diagram of the force points on the front blade surface and back blade surface of the three-dimensional blade model;

[0036] Figure 9 Schematic diagram of the machining deformation error of the force points on the front blade surface and back blade surface of the three-dimensional blade model;

[0037] Figure 10 Cross-section diagram of the machining deformation error of the 6 second blade cross-section curves on the front blade surface;

[0038] Figure 11 Cross-section diagram of the machining deformation error of the 6 second blade cross-section curves on the back blade surface;

[0039] Figure 12 Schematic diagram of the region division of the second blade cross-section curve considering the machining deformation error;

[0040] Figure 13 Overall measurement point distribution diagram of the curved and twisted thin-walled blade. Detailed implementation manner

[0041] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention will be given with reference to the accompanying drawings.

[0042] A measurement point planning method for a curved and twisted thin-walled blade considering machining deformation specifically includes:

[0043] Step 1: Use 3D software to establish a three-dimensional blade model of the curved and twisted thin-walled blade;

[0044] Step 2: Preset the interval distance equal-height method to intercept a number of first blade cross-section curves on the three-dimensional blade model along the blade height direction, as Figure 2As shown; obtaining the leading edge point and trailing edge point of each first blade cross-section curve according to the mid-arc line of each first blade cross-section curve, as Figure 3 shown, fitting the point sets composed of the leading edge points and trailing edge points respectively with NURBS curves to obtain the leading edge contour line and trailing edge contour line, as Figure 4 shown;

[0045] Step 3: Obtaining the number of second blade cross-section curves that need to be actually measured for the blade according to the height of the blade and a preset proportionality coefficient; the number of second blade cross-section curves is:

[0046] m = c·L

[0047] In the formula, m is the number of second blade cross-section curves, c is the proportionality coefficient; L is the height of the blade; the proportionality coefficient in this specific embodiment is preset to 0.2, and the height of the blade is 30. Therefore, the number of second blade cross-section curves in this specific embodiment is 6;

[0048] Using the chord tolerance method, 6 distribution points are adaptively obtained from the leading edge contour line and trailing edge contour line respectively, as Figure 5 shown, connecting the distribution points on the leading edge contour line and trailing edge contour line to obtain 6 second blade cross-section curves on the three-dimensional blade model, as Figure 6 shown;

[0049] Step 4: Adopting the chord tolerance method to perform adaptive distribution of measurement points on the second blade cross-section curve. Since the machining deformation error generated during the blade machining process is not considered, the distribution of measurement points is as Figure 7 shown; Therefore, this specific embodiment is further modified on this basis and proceeds to Step 5;

[0050] Step 5: The blade in this specific embodiment adopts the point milling machining method. Therefore, calculate the average milling force received by the blade during the machining process;

[0051]

[0052]

[0053]

[0054] In the formula, F t is the tangential component force; F r is the radial component force; F a is the axial component force; a p is the cutting depth; v t is the cutting speed, v t = nπD / 1000, n is the tool diameter, D is the spindle speed; f e is the feed rate; a eis the cutting width; ψ is the tool rake angle, specifically the angle between the tool, the normal vector of the blade, and the tool axis vector;

[0055] Step 6: Mesh the blade surfaces on the front and back of the three-dimensional blade model. M×N force application points are formed on each blade surface. In this specific embodiment, 15×11 force application points are evenly distributed in the u and v directions of the blade surface, as Figure 8 shown; Use finite element simulation software to predict the machining deformation error of the force application points on each blade surface by applying the average milling force to each force application point, as Figure 9 shown; The finite element simulation software in this specific embodiment is, for example, the abaqus software of the prior art, and will not be elaborated here;

[0056] Step 7: According to the machining deformation errors predicted on the two blade surfaces, use drawing software of the prior art to draw the deformation error nephogram; and according to the positions of the second blade section curve on the two blade surfaces respectively, intercept 10 points and draw the machining deformation error distribution on the second blade section curve, as Figure 10 - 11 shown;

[0057] Step 8: Calculate the average value of the machining deformation error according to the machining deformation error obtained in Step 5; Divide the machining deformation error distribution on the second blade section curve according to the average value. In this specific embodiment, the second blade section curve is divided into 6 regions according to the average value, as Figure 13 shown; Then, in combination with the curvature of the second blade section curve in each region, use the chord tolerance method to adaptively distribute the measuring points at each measuring point, extract the measuring points in each region and combine them to obtain the overall measuring point distribution of the curved and twisted thin-walled blade, as Figure 13 shown.

[0058] The blade section curve in this specific embodiment is the NURBS curve P(u). The NURBS curve is called the non-uniform rational B-spline curve, and its mathematical definition is as follows:

[0059]

[0060] In the formula, N i,k (u) is the k-th B-spline basis function; d i is the control vertex of the curve; ω i is the weight factor of the control vertex;

[0061] The blade surface in this specific embodiment is a free surface obtained by lofting the blade section curve and is represented by the NURBS surface S(u,v); The NURBS surface of degree k in the u direction and degree l in the v direction is expressed in the form of a bivariate piecewise rational vector-valued function, and its mathematical definition is as follows:

[0062]

[0063] where N i,k (u) and N j,l (v) are the non-uniform rational B-spline basis functions of degree k along the u-direction and degree l along the v-direction of the surface, respectively. d i,j (i = 0, 1, …, m; j = 0, 1, …, n) are the surface control vertices; ω i,j is the weight factor of the control vertex;

[0064] The chord tolerance method in this specific embodiment is specifically a method for interpolating points on a NURBS curve. During the interpolation process, the distribution of the measurement points on the second blade cross-section curve is completed by controlling the chord deviation; the chord deviation is calculated using the curvature of the second blade cross-section curve, and the calculation formula is as follows:

[0065]

[0066] where δ is the chord deviation; ρ i is the radius of curvature at the parameter value u i on the NURBS curve P(u); L i is the length of the vector between two adjacent points on the curve; The calculation formula of L i is:

[0067]

[0068] where:

[0069] k i is the curvature at any point on the NURBS curve P(u),

[0070] u i+1 is on the NURBS curve P(u), given the parameter value u i of the previous point, the parameter value of the next point is calculated, and its expression is as follows:

[0071]

[0072] P(u i+1 ) The Taylor expansion of the NURBS curve P(u) at the parameter value u i+1 at the parameter value u i is:

[0073] P(u i+1 ) = P(u i ) + P'(u i ) × (u i+1 - u i ) +

[0074] The distribution density of measurement points on the curve can be controlled by the magnitude of the chord deviation; the present invention can make the measurement points adaptively distributed on the curve of the second blade cross-section by using the chord tolerance method.

[0075] Although the present disclosure is disclosed as above, the scope of protection of the present disclosure is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications will all fall within the scope of protection of the present invention.

Claims

1. A measuring point planning method for curved and twisted thin-walled blades considering machining deformation, characterized in that, specifically including: Step 1: Establish a three-dimensional blade model of the curved and twisted thin-walled blade; Step 2: Intercept a number of first blade cross-section curves on the three-dimensional blade model along the blade height direction; obtain the leading edge point and trailing edge point of each first blade cross-section according to the mid-arc line of each first blade cross-section curve, and fit all the leading edge points and trailing edge points respectively to obtain the leading edge contour line and trailing edge contour line; Step 3: Obtain the number of second blade cross-section curves actually required to be measured on the blade according to the blade height and a preset proportional coefficient; adaptively obtain the distribution points of the second blade cross-section curves from the leading edge contour line and the trailing edge contour line, and then obtain the second blade cross-section curves; Step 4: Use the chord tolerance method to perform adaptive distribution of measuring points on the second blade cross-section curves; Step 5: Calculate the average milling force received by the blade during the machining process; Step 6: Perform mesh division on the blade surfaces on the front and back of the three-dimensional blade model, and form M×N stress points on each blade surface; predict the machining deformation error of the stress points on each blade surface by applying the average milling force to each stress point; Step 7: Obtain the machining deformation error distribution on the second blade cross-section curves according to the positions of the second blade cross-section curves on the blade surfaces; Step 8: Calculate the average value of the machining deformation error according to the machining deformation error obtained in Step 6; perform regional division on the machining deformation error distribution on the second blade cross-section curves according to the average value; use the chord tolerance method to obtain measuring points in each region of the second blade cross-section curves, and then combine the curvature of the second blade cross-section curves in each region to make the adaptive distribution of the measuring points in each region, extract the measuring points in each region and combine them to obtain the distribution of the measuring points on the corresponding second blade cross-section curves.

2. A measuring point planning method for curved and twisted thin-walled blades considering machining deformation according to Claim 1, characterized in that, in Step 2, the first blade cross-section curves are intercepted on the three-dimensional blade model along the blade height direction by the equal-height method.

3. A measuring point planning method for curved and twisted thin-walled blades considering machining deformation according to Claim 1, characterized in that, the number of the second blade cross-section curves in Step 3 is: ； In the formula, is the number of the second blade cross-sectional curves, is the proportionality coefficient; is the height of the blade; the obtaining of the second blade cross-section curves specifically includes: Using the chord tolerance method, obtain distribution points from the leading edge contour line and the trailing edge contour line respectively, and connect the distribution points on the leading edge contour line and the trailing edge contour line to obtain second blade section curves on the three-dimensional blade model.

4. A measuring point planning method for curved and twisted thin-walled blades considering machining deformation according to Claim 1, characterized in that, the calculation formula for the average milling force in Step 5 is: ； ； ； In the formula, is the tangential component force; is the radial component force; is the axial component force; is the cutting depth; is the cutting speed, , is the tool diameter, is the spindle speed; is the feed rate; is the cutting width; is the tool inclination angle.

5. A measuring point planning method for curved and twisted thin-walled blades considering machining deformation according to Claim 1, characterized in that, the obtaining of the machining deformation error distribution on the second blade cross-section curves in Step 7 specifically includes: according to the predicted machining deformation errors on the two blade surfaces, use drawing software to draw the deformation error nephogram; according to the positions of the second blade cross-section curves on the two blade surfaces respectively, intercept a preset number of points and draw the machining deformation error distribution on the second blade cross-section curves.

6. A measuring point planning method for curved and twisted thin-walled blades considering machining deformation according to Claim 1, characterized in that, In step 8, the chord tolerance method is used to obtain measurement points in each region of the second blade cross-section curve. Specifically, the chord deviation is calculated using the curvature of each region on the second blade cross-section curve, and the chord tolerance method is used to adaptively distribute the measurement points in each region of the second blade cross-section curve.

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