CN114692339B - Surface reconstruction method of blisk blade based on edge compensation - Google Patents
Surface reconstruction method of blisk blade based on edge compensation Download PDFInfo
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Abstract
本发明公开了一种基于缘头补偿的整体叶盘叶片曲面重构方法，包括根据叶身截面数据点进行NURBS曲线拟合叶身截面线，并拟合得到中弧线；根据中弧线端点切矢计算缘头点，并按照缘头点和缘头区域半径分割得到缘头曲线，并根据所述闭合叶身截面曲线的缘头加工公差，将缘头曲线进行平移、偏置得到缘头补偿曲线，得到新的曲线组拟合NURBS曲面，并以轮毂曲面和围带曲面作为边界进行裁剪、重参得到了考虑缘头补偿的用于实际加工的后缘曲面、叶盆曲面和叶背曲面，为后续加工过程中提升了整体叶盘的叶片划分质量，使半精加工时分区域铣削更高效，同时可以在加工是有效补偿缘头处机床减速带来的加工误差，提高加工效率的同时确保了加工的精度。
The present invention discloses a method for reconstructing the curved surface of an integral blade disk based on edge compensation, comprising fitting a blade section line with a NURBS curve according to blade section data points, and fitting to obtain a mid-arc line; calculating an edge point according to a tangent vector at an end point of the mid-arc line, and obtaining an edge curve by segmenting the edge point and an edge area radius; translating and offsetting the edge curve according to an edge machining tolerance of the closed blade section curve to obtain an edge compensation curve, obtaining a new curve group fitting NURBS surface, and cutting and re-parameterizing the rear edge surface, blade basin surface and blade back surface for actual machining taking edge compensation into consideration with a hub surface and a shroud surface as boundaries, thereby improving the blade division quality of the integral blade disk in subsequent machining processes, making regional milling more efficient during semi-finishing machining, and effectively compensating for machining errors caused by machine tool deceleration at the edge during machining, thereby improving machining efficiency and ensuring machining accuracy.
Description
Technical Field
The invention relates to the technical field of geometric modeling of engine blisks, in particular to a method for reconstructing curved surfaces of blades of a blisk.
Background
The blisk is a core component of an aeroengine, and the modeling quality and the shaping precision of the blisk directly influence the service performance of the engine. Because the blisk has a complex structure, and the profile of the blade is a space free-form surface, the blade is processed by adopting a five-axis numerical control milling mode, and a series of working procedures such as channel slotting, semi-finishing, finishing and the like are required to be carried out from a part blank to the final forming of the blisk.
The complex twisted blade is a key component affecting the aerodynamic performance of the blisk, and the curved surface reconstruction of the blade is a precondition of CAM (Computer Aided Manufacturing ), and the curved surface reconstruction efficiency and precision directly affect the machining efficiency and precision of the final part.
The existing method for constructing the curved surface of the blade generally constructs a complete curved surface according to the blade profile data of the blade, and the front edge area and the rear edge area of the blade are difficult to automatically divide, so that the follow-up semi-finishing of the divided areas is not facilitated, and the processing efficiency is affected.
In addition, the finish machining of the blisk blade adopts a surrounding milling mode to ensure the profile quality, and because the curvature change near the blade edge head is extremely large and is influenced by the tracking performance of a numerical control machine tool, the machine tool can perform proper deceleration at the blade edge head machining position to reduce linkage errors, so that numerical control machining is performed according to a theoretical blade profile, and certain over-cutting can be generated at the edge head.
Disclosure of Invention
The invention aims to avoid the defects of the prior art and provide the integral blade disc blade curved surface reconstruction method based on the edge head compensation, which is used for carrying out the area division according to the blade body data of the blade disc of the engine or the gas turbine, considering the influence of the edge head compensation on the efficiency of the curved surface reconstruction of the blade disc blade and the area processing during the semi-finishing of the integral blade disc blade, and the influence of the torsion degree of the blade profile on the multi-axis numerical control processing precision of the blade disc during the finishing, ensuring the efficiency of the blade profile reconstruction and simultaneously being beneficial to shortening the processing period and improving the final forming precision of the part.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows: a blisk blade curved surface reconstruction method based on edge head compensation comprises the following steps:
Step 1: according to the section data points of the blisk blade, NURBS curve fitting is carried out to obtain n closed blade section curves of the blade;
Step 2: according to the closed blade section curve, iterating to calculate a mean camber line characteristic point so as to obtain a fitting mean camber line of the closed blade section curve;
step 3: making a straight line along the tangential direction of the end point of the fitting camber line, wherein the straight line intersects with the closed blade section curve to obtain a front edge sharp point and a rear edge sharp point of the closed blade section curve;
Step 4: setting the radiuses of a front edge area and a rear edge area of the closed blade section curve, and respectively taking the front edge sharp point and the rear edge sharp point as circle centers, making a circle in a plane where the closed blade section curve is located, wherein the intersection point of the circle and the front edge area and the rear edge area of the closed blade section curve divides the closed blade section curve into four curves which are respectively a front edge curve, a rear edge curve, a blade basin curve and a blade back curve;
Step 5: according to the edge head machining tolerance of the closed blade section curve, translating and biasing the front edge curve and the rear edge curve to obtain a front edge head compensation curve and a rear edge head compensation curve, bridging the blade basin curve and the blade back curve with the edge head compensation curve respectively, and then connecting the bridged blade basin curve and the blade back curve to obtain a blade basin compensation curve and a blade back compensation curve;
Step 6: fitting NURBS curved surfaces of the leading edge head compensation curve, the trailing edge head compensation curve, the blade basin compensation curve and the blade back compensation curve which are obtained in the step 5 through curve groups to obtain four area curved surfaces of the blade, wherein the four area curved surfaces are respectively a leading edge curved surface, a trailing edge curved surface, a blade basin curved surface and a blade back curved surface;
Step 7: designating a hub curved surface and a shroud curved surface, taking the hub curved surface and the shroud curved surface as an upper cutting boundary and a lower cutting boundary, cutting a front edge curved surface, a rear edge curved surface, a leaf basin curved surface and a leaf back curved surface of the blade according to the boundaries, and respectively carrying out curved surface re-parameterization on the cut regional curved surfaces to obtain the front edge curved surface, the rear edge curved surface, the leaf basin curved surface and the leaf back curved surface of the blade which are required by actual processing.
Further, the calculation method of the mean camber line feature point and the mean camber line in the step 2 is as follows:
Step 21: according to a closed blade section curve C=C (t), dispersing the closed blade section curve C=C (t) in an equal chord height difference mode to obtain a discrete point C (t i) (i=1, L, k), and according to the curvature radius of any point on the curve, calculating the curvature radius rho of all points on the closed blade section curve by using a formula (1):
and obtaining a point C (t m) with the largest radius of curvature among the discrete points C (t i) (i=1, l, k);
step 22: calculating a mean camber line characteristic point P i corresponding to the discrete point C (t i), and according to a geometric relation (2) of points on a mean camber line:
wherein n is the unit principal French of the discrete point C (t i) on the closed-blade-body section curve, the unit principal French is directed to the inner side of the closed-blade-body section curve, and d is the closed-blade-body section curve section thickness value, thereby establishing the equation:
f(ξ,d)＝|C(ξ)-C(ti)+d·(n(ξ)-n(ti))|2 (3)
Carrying out minimum value search by adopting a damping Newton method, wherein the value range of parameters is xi epsilon (t i+1,1)∪(0,ti-1), d epsilon (0, infinity) until the parameters (xi i,di) meeting the condition f (xi, d) =0 are searched for to stop, and then calculating a mean camber line characteristic point P i according to the geometric relational expression (2) of the point on the mean camber line;
Step 23: and (3) taking the point C (t m) as a first point, iteratively calculating a mean camber line characteristic point P m corresponding to the first point C (t m) according to the step (22), then increasing the number m, calculating a mean camber line characteristic point P m+1, repeating the increasing operation, when no solution exists according to the formula (3), enabling the discrete point C (t i) to be close to the edge head, stopping the increasing operation, decreasing the number m for the same operation, and performing NURBS curve fitting on all the mean camber line characteristic points P i(i＝m-n1,L m,L,m+n2 according to the point position sequence to obtain a fitted mean camber line C Γ.
Further, the step3 specifically includes:
Accessing a unit tangent vector τ 0 at an endpoint C Γ0 of the fitted mean camber line C Γ to create a straight line l with two points of the mean camber line feature point P 0 corresponding to C Γ0 and C Γ0, wherein:
P0＝CΓ0+2d·τ0
wherein d is a section thickness value at the endpoint of C Γ0, and the intersection point of the straight line l and the blade section curve C is obtained to obtain two edge tip points, wherein the curvature radius rho in the two edge tip points is larger and is the trailing edge tip point C t, and the smaller is the leading edge tip point C l.
Further, the step of cutting the closed blade section curve in the step 4 is as follows:
Setting a front edge area radius R l and a rear edge area radius R t of the closed blade section curve, respectively taking a front edge sharp point C l and a rear edge sharp point C t as circle centers and taking the front edge area radius R l and the rear edge area radius R t as radii to create a circle O l and a circle O t in a plane where the section curve C is located, solving intersection points of the circle O l and the circle O t and the section curve C to obtain four points of C l1、Cl2、Ct1、Ct2, and dividing the closed curve C according to the four points to obtain four dividing curves: a leading edge curve, a trailing edge curve, a leaf basin curve and a leaf back curve.
Further, the specific calculation step of the edge head compensation curve in the step 5 is as follows:
Recording the edge head machining tolerance of the closed blade section curve as +/-delta, translating the front edge curve and the rear edge curve outwards by delta/3-delta/2 along the endpoint tangential vector tau of the fitting camber line C Γ, and then outwards carrying out curve offset on the translated front edge curve and rear edge curve in the plane of the closed blade section curve by delta/6-delta/5 to obtain the front edge head compensation curve and the rear edge head compensation curve; and finally shortening the head end and the tail end of the leaf basin curve and the tail end of the leaf back curve by 2 delta-3 delta respectively, bridging the head end and the tail end of the leaf basin curve and the tail end of the leaf back curve respectively with the front edge curve and the tail edge curve, and connecting the bridging section curve with the leaf basin curve and the leaf back curve respectively to obtain a leaf basin compensation curve and a leaf back compensation curve.
Further, the specific method in the step 7 comprises the following steps:
Step 71: designating a hub curved surface S hub and a shroud curved surface S shr as cutting boundaries, and cutting four area curved surfaces of the blade according to the boundaries;
Step 72: uniformly extracting N equal u parameter lines from the front edge curved surface S le in S le, wherein N is the maximum value of the number of discrete points on the front edge curved surface in all sections:
Wherein the method comprises the steps of Fitting the parameter lines into NURBS curved surfaces again for the number of discrete points on the front edge curved surfaces in the kth cross-sectional layer to obtain the front edge curved surfaces which are finally and practically processed; and repeating the curved surface re-parameterization step to obtain the actually processed trailing edge curved surface, the leaf basin curved surface and the leaf back curved surface.
The beneficial effects of the invention are as follows: according to the method, the efficient damping Newton iterative algorithm is adopted, the mean camber line of the blade profile section is accurately calculated, the blade profile curved surface is divided according to the mean camber line, edge head compensation and curved surface reconstruction are carried out, on one hand, the blade dividing efficiency of the blisk is improved, efficient zoning milling is conveniently carried out during semi-finishing, on the other hand, the edge head can be reconstructed according to the trend of the blade edge head profile, and machining errors caused by machine tool speed reduction at the edge head are further compensated.
Drawings
FIG. 1 is a general flow chart of the present invention;
FIG. 2 is a schematic view of an engine blade disc structure;
FIG. 3 is a schematic view of a blade airfoil section curve and discrete points;
FIG. 4 is a schematic diagram of a step 2 fitting mean camber line according to the present invention;
FIG. 5 is a schematic diagram of steps 3 and 4 of the present invention;
FIG. 6 is a schematic view of the structure of the front and back curved surfaces of the edge head compensation.
Detailed Description
The principles and features of the present invention are described below with reference to the drawings, the examples are illustrated for the purpose of illustrating the invention and are not to be construed as limiting the scope of the invention.
In order to achieve the above object, the present invention provides the following embodiments:
example 1: as shown in fig. 1-6, a blisk blade curved surface reconstruction method based on edge head compensation comprises the following steps:
Step 1: according to the section data points of the blisk blade, NURBS curve fitting is carried out to obtain n closed blade section curves of the blade;
step 2: according to the closed blade section curve, iteration calculating a mean camber line characteristic point to obtain a fitting mean camber line of the closed blade section curve by fitting, wherein the calculation method of the mean camber line characteristic point and the mean camber line comprises the following steps:
Step 21: according to a closed blade section curve C=C (t), dispersing the closed blade section curve C=C (t) in an equal chord height difference mode to obtain a discrete point C (t i) (i=1, L, k), and according to the curvature radius of any point on the curve, calculating the curvature radius rho of all points on the closed blade section curve by using a formula (1):
and obtaining a point C (t m) with the largest radius of curvature among the discrete points C (t i) (i=1, l, k);
step 22: calculating a mean camber line characteristic point P i corresponding to the discrete point C (t i), and according to a geometric relation (2) of points on a mean camber line:
wherein n is the unit principal French of the discrete point C (t i) on the closed-blade-body section curve, the unit principal French is directed to the inner side of the closed-blade-body section curve, and d is the closed-blade-body section curve section thickness value, thereby establishing the equation:
f(ξ,d)＝|C(ξ)-C(ti)+d·(n(ξ)-n(ti))|2 (3)
Carrying out minimum value search by adopting a damping Newton method, wherein the value range of parameters is xi epsilon (t i+1,1)∪(0,ti-1), d epsilon (0, infinity) until the parameters (xi i,di) meeting the condition f (xi, d) =0 are searched for to stop, and then calculating a mean camber line characteristic point P i according to the geometric relational expression (2) of the point on the mean camber line;
Step 23: and (3) taking the point C (t m) as a first point, iteratively calculating a mean camber line characteristic point P m corresponding to the first point C (t m) according to the step (22), then increasing the number m, calculating a mean camber line characteristic point P m+1, repeating the increasing operation, when no solution exists according to the formula (3), enabling the discrete point C (t i) to be close to the edge head, stopping the increasing operation, decreasing the number m for the same operation, and performing NURBS curve fitting on all the mean camber line characteristic points P i(i＝m-n1,L m,L,m+n2 according to the point position sequence to obtain a fitted mean camber line C Γ.
Step 3: and making a straight line along the tangential direction of the end point of the fitting camber line, wherein the straight line intersects with the closed blade section curve to obtain a front edge sharp point and a rear edge sharp point of the closed blade section curve, and the specific steps are as follows:
Accessing a unit tangent vector τ 0 at an endpoint C Γ0 of the fitted mean camber line C Γ to create a straight line l with two points of the mean camber line feature point P 0 corresponding to C Γ0 and C Γ0, wherein:
P0＝CΓ0+2d·τ0
wherein d is a section thickness value at the endpoint of C Γ0, and the intersection point of the straight line l and the blade section curve C is obtained to obtain two edge tip points, wherein the curvature radius rho in the two edge tip points is larger and is the trailing edge tip point C t, and the smaller is the leading edge tip point C l.
Step 4: setting the radiuses of a front edge area and a rear edge area of the closed blade section curve, and respectively taking the front edge sharp point and the rear edge sharp point as circle centers, making a circle in a plane where the closed blade section curve is located, wherein the intersection point of the circle and the front edge area and the rear edge area of the closed blade section curve divides the closed blade section curve into four curves which are respectively a front edge curve, a rear edge curve, a blade basin curve and a blade back curve; the step of cutting the closed blade section curve is as follows:
Setting a front edge area radius R l and a rear edge area radius R t of the closed blade section curve, respectively taking a front edge sharp point C l and a rear edge sharp point C t as circle centers and taking the front edge area radius R l and the rear edge area radius R t as radii to create a circle O l and a circle O t in a plane where the section curve C is located, solving intersection points of the circle O l and the circle O t and the section curve C to obtain four points of C l1、Cl2、Ct1、Ct2, and dividing the closed curve C according to the four points to obtain four dividing curves: a leading edge curve, a trailing edge curve, a leaf basin curve and a leaf back curve.
Step 5: according to the edge head machining tolerance of the closed blade section curve, translating and biasing the front edge curve and the rear edge curve to obtain a front edge head compensation curve and a rear edge head compensation curve, bridging the blade basin curve and the blade back curve with the edge head compensation curve respectively, and then connecting the bridged blade basin curve and the blade back curve to obtain a blade basin compensation curve and a blade back compensation curve; the specific calculation steps of the edge head compensation curve are as follows:
Recording the edge head machining tolerance of the closed blade section curve as +/-delta, translating the front edge curve and the rear edge curve outwards by delta/3-delta/2 along the endpoint tangential vector tau of the fitting camber line C Γ, and then outwards carrying out curve offset on the translated front edge curve and rear edge curve in the plane of the closed blade section curve by delta/6-delta/5 to obtain the front edge head compensation curve and the rear edge head compensation curve; and finally shortening the head end and the tail end of the leaf basin curve and the tail end of the leaf back curve by 2 delta-3 delta respectively, bridging the head end and the tail end of the leaf basin curve and the tail end of the leaf back curve respectively with the front edge curve and the tail edge curve, and connecting the bridging section curve with the leaf basin curve and the leaf back curve respectively to obtain a leaf basin compensation curve and a leaf back compensation curve.
Step 6: fitting NURBS curved surfaces of the leading edge head compensation curve, the trailing edge head compensation curve, the blade basin compensation curve and the blade back compensation curve which are obtained in the step 5 through curve groups to obtain four area curved surfaces of the blade, wherein the four area curved surfaces are respectively a leading edge curved surface, a trailing edge curved surface, a blade basin curved surface and a blade back curved surface;
Step 7: designating a hub curved surface and a shroud curved surface, taking the hub curved surface and the shroud curved surface as an upper cutting boundary and a lower cutting boundary, cutting a front edge curved surface, a rear edge curved surface, a leaf basin curved surface and a leaf back curved surface of the blade according to the boundaries, and respectively carrying out curved surface re-parameterization on the cut regional curved surfaces to obtain the front edge curved surface, the rear edge curved surface, the leaf basin curved surface and the leaf back curved surface of the blade which are required by actual processing; the specific method comprises the following steps:
Step 71: designating a hub curved surface S hub and a shroud curved surface S shr as cutting boundaries, and cutting four area curved surfaces of the blade according to the boundaries;
Step 72: uniformly extracting N equal u parameter lines from the front edge curved surface S le in S le, wherein N is the maximum value of the number of discrete points on the front edge curved surface in all sections:
Wherein the method comprises the steps of Fitting the parameter lines into NURBS curved surfaces again for the number of discrete points on the front edge curved surfaces in the kth cross-sectional layer to obtain the front edge curved surfaces which are finally and practically processed; and repeating the curved surface re-parameterization step to obtain the actually processed trailing edge curved surface, the leaf basin curved surface and the leaf back curved surface.
According to the blisk blade curved surface reconstruction method based on edge head compensation, the trailing edge curved surface, the leaf basin curved surface and the leaf back curved surface which are used for actual machining and consider the edge head compensation are obtained, so that the blade dividing efficiency of the blisk is improved in the subsequent machining process, the area milling is more efficient in semi-finishing, machining errors caused by machine tool speed reduction at the edge head can be effectively compensated during machining, and machining precision is ensured while machining efficiency is improved.
The method can be generally used for reconstructing the curved surface of the blisk blade based on edge head compensation of a conventional aeroengine and a gas turbine, the whole steps can be carried out in various drawing software, and the flow of the method is shown in the figure 1 and comprises the following steps:
S1) importing blade body section data of the blisk blade, and carrying out NURBS curve fitting according to the section data points to obtain n closed blade body section curves.
S2) based on the blade section curve, iteratively calculating the mean camber line characteristic points of the section curve, and fitting the mean camber line characteristic points into a mean camber line, wherein the specific steps are as follows:
s21) for the blade section curve c=c (t), it is discretized in a mode of equal chord height difference, and a set of discrete points C (t i) (i=1, l, k) is obtained, as shown in fig. 3. Radius of curvature according to a point on the curve:
The radius of curvature ρ of all the discrete points is calculated, and the point C (t m) having the largest radius of curvature in the point group C (t i) is acquired.
The mean camber line feature point P i corresponding to the discrete point C (t i) is calculated. As shown in the lower left of fig. 4, according to the geometrical relationship of the mean camber line feature points:
Where n is the unit principal French (inwardly directed) of point C (t i) on the cross-sectional curve and d is the cross-sectional thickness value, thereby establishing the equation:
f(ξ,d)＝|C(ξ)-C(ti)+d·(n(ξ)-n(ti))|2 (1-3)
and (3) carrying out minimum value search by adopting a damping Newton method, wherein the value range of the parameter is xi epsilon (t i+1,1)∪(0,ti-1), d epsilon (0 and infinity). Setting the iteration precision delta and the maximum iteration number k max, if the iteration number k is smaller than k max and f (ζ, d) < delta, considering that the parameter (ζ i,di) meeting the condition f (ζ, d) =0 is searched, stopping the iteration, and then calculating the mean camber line feature point P i according to the formula (1-2).
S23) calculating a mean camber line characteristic point P m by taking a point C (t m) as a first point according to the method in the step S22), increasing the number m after winding to obtain a mean camber line characteristic point P m+1, repeating the increasing operation, and when the iteration number k is more than k max, the formula (1-3) has no solution, wherein C (t i) approaches the edge head, and stopping the increasing operation. And then the number m is decremented, and the same operation is performed. All the mean camber line feature points P i(i＝m-n1,L m,L,m+n2) are subjected to NURBS curve fitting according to the point position sequence, and a mean camber line C Γ is obtained.
S3) calculating the leading edge cusp and the trailing edge cusp, as shown in the upper right of fig. 4, accessing the unit tangent τ 0 at the end point C Γ0 of the camber line C Γ, creating a straight line l through both points C Γ0 and P 0, wherein:
P0＝CΓ0+2d·τ0 (1-4)
Where d is the cross-sectional thickness value at that end point. And obtaining a sharp point of the edge by solving the intersection point of the straight line l and the section curve C, and the other sharp point of the edge is the same, wherein the curvature radius rho in the two sharp points of the edge is larger as a sharp point C t of the trailing edge, and the smaller as a sharp point C l of the leading edge.
S4) performing curve segmentation on the closed section: setting a front edge region radius R l and a rear edge region radius R t, respectively taking a front edge sharp point C l and a rear edge sharp point C t as circle centers and taking a front edge region radius R l and a rear edge region radius R t as radii to create a circle O l and a circle O t in a plane where a section curve C is located, solving intersection points of the circle O l and the circle O t and the section curve C to obtain four points of C l1、Cl2、Ct1、Ct2, and dividing a closed curve C according to the four points to obtain four curves: a leading edge curve, a trailing edge curve, a leaf basin curve and a leaf back curve.
S5) constructing a head compensation curve, if the machining tolerance of the head is recorded as +/-delta, translating the head curve outwards by delta/3 along the tangential vector tau of the end point of the mean camber line, and then carrying out plane curve offset on the translated head curve outwards by delta/6 to obtain a new front edge and a new rear edge head compensation curve. And finally shortening the head end and the tail end of the leaf basin and the leaf back curve by 2 delta respectively, bridging the head end and the tail end of the leaf basin and the leaf back curve respectively, and connecting the bridged section curve with the leaf basin and the leaf back curve to obtain a new leaf basin curve and a new leaf back curve.
S6) fitting the four new curves to the NURBS curved surface through the curve groups to preliminarily obtain the regional curved surface of the blade: leading edge curve S le, trailing edge curve S te, basin curve S suc, and back surface S pre, as shown in FIG. 2.
S7) constructing four regional curved surfaces with complete parameters, wherein the method comprises the following specific steps:
s71) designates a hub curved surface S hub and a shroud curved surface S shr, and cuts the regional curved surface according to the boundary as a cutting boundary.
S72) re-parameterizing the clipped split area curved surface. As shown in fig. 6, for the leading edge curved surface S le, N equal u parameter lines are uniformly extracted at S le, where N is the maximum value of the number of discrete points located on the leading edge curved surface in all the sections:
Wherein the method comprises the steps of Is the number of discrete points in the kth cross-sectional layer that lie on the leading edge curve.
And re-fitting the parameter lines into NURBS curved surfaces to obtain final front edge curved surfaces, and repeating the operations to obtain rear edge curved surfaces, leaf basin curved surfaces and leaf back curved surfaces, namely the rear edge curved surfaces, leaf basin curved surfaces and leaf back curved surfaces which are actually processed.
The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the precise form disclosed, and any such modifications, equivalents, and alternatives falling within the spirit and scope of the invention are intended to be included within the scope of the invention.
Claims (4)
1. The blisk blade curved surface reconstruction method based on edge head compensation is characterized by comprising the following steps of:
Step 1: according to the section data points of the blisk blade, NURBS curve fitting is carried out to obtain n closed blade section curves of the blade;
Step 2: according to the closed blade section curve, iterating to calculate a mean camber line characteristic point so as to obtain a fitting mean camber line of the closed blade section curve;
step 3: making a straight line along the tangential direction of the end point of the fitting camber line, wherein the straight line intersects with the closed blade section curve to obtain a front edge sharp point and a rear edge sharp point of the closed blade section curve;
Step 4: setting the radiuses of a front edge area and a rear edge area of the closed blade section curve, and respectively taking the front edge sharp point and the rear edge sharp point as circle centers, making a circle in a plane where the closed blade section curve is located, wherein the intersection point of the circle and the front edge area and the rear edge area of the closed blade section curve divides the closed blade section curve into four curves which are respectively a front edge curve, a rear edge curve, a blade basin curve and a blade back curve;
Step 5: according to the edge head machining tolerance of the closed blade section curve, translating and biasing the front edge curve and the rear edge curve to obtain a front edge head compensation curve and a rear edge head compensation curve, bridging the blade basin curve and the blade back curve with the edge head compensation curve respectively, and then connecting the bridged blade basin curve and the blade back curve to obtain a blade basin compensation curve and a blade back compensation curve;
The specific calculation steps of the edge head compensation curve are as follows:
Recording the edge head machining tolerance of the closed blade section curve as +/-delta, translating the front edge curve and the rear edge curve outwards by delta/3-delta/2 along the endpoint tangential vector tau of the fitting camber line C Γ, and then outwards carrying out curve offset on the translated front edge curve and rear edge curve in the plane of the closed blade section curve by delta/6-delta/5 to obtain the front edge head compensation curve and the rear edge head compensation curve; finally, shortening the head end and the tail end of the leaf basin curve and the leaf back curve by 2 delta-3 delta respectively, bridging the head end and the tail end of the leaf basin curve and the tail end of the leaf back curve respectively with the front edge curve and the tail edge curve, and connecting the bridged section curve with the leaf basin curve and the leaf back curve respectively to obtain a leaf basin compensation curve and a leaf back compensation curve;
Step 6: fitting NURBS curved surfaces of the leading edge head compensation curve, the trailing edge head compensation curve, the blade basin compensation curve and the blade back compensation curve which are obtained in the step 5 through curve groups to obtain four area curved surfaces of the blade, wherein the four area curved surfaces are respectively a leading edge curved surface, a trailing edge curved surface, a blade basin curved surface and a blade back curved surface;
Step 7: designating a hub curved surface and a shroud curved surface, taking the hub curved surface and the shroud curved surface as an upper cutting boundary and a lower cutting boundary, cutting a front edge curved surface, a rear edge curved surface, a leaf basin curved surface and a leaf back curved surface of the blade according to the boundaries, and respectively carrying out curved surface re-parameterization on the cut regional curved surfaces to obtain the front edge curved surface, the rear edge curved surface, the leaf basin curved surface and the leaf back curved surface of the blade which are required by actual processing, wherein the specific method comprises the following steps:
Step 71: designating a hub curved surface S hub and a shroud curved surface S shr as cutting boundaries, and cutting four area curved surfaces of the blade according to the boundaries;
Step 72: uniformly extracting N equal u parameter lines from the front edge curved surface S le in S le, wherein N is the maximum value of the number of discrete points on the front edge curved surface in all sections:
Wherein the method comprises the steps of Fitting the parameter lines into NURBS curved surfaces again for the number of discrete points on the front edge curved surfaces in the kth cross-sectional layer to obtain the front edge curved surfaces which are finally and practically processed; and repeating the curved surface re-parameterization step to obtain the actually processed trailing edge curved surface, the leaf basin curved surface and the leaf back curved surface.
2. The method for reconstructing a curved surface of a blisk blade based on edge head compensation as set forth in claim 1, wherein the method for calculating the mean camber line feature points and the mean camber lines in the step 2 is as follows:
Step 21: according to a closed blade section curve C=C (t), dispersing the closed blade section curve in an equal chord height difference mode to obtain discrete points C (t i) i=1, … and k, and according to the curvature radius of any point on the curve, calculating the curvature radius rho of all points on the closed blade section curve by using a formula (1):
And obtaining a point C (t m) with the largest radius of curvature among the discrete points C (t i) i=1, …, k;
Step 22: calculating a mean camber line characteristic point P i corresponding to the discrete point C (t i), and according to the geometric relation of points on the mean camber line:
wherein n is the unit principal French of the discrete point C (t i) on the closed-blade-body section curve, the unit principal French is directed to the inner side of the closed-blade-body section curve, and d is the closed-blade-body section curve section thickness value, thereby establishing the equation:
f(ξ，d)＝|C(ξ)-C(ti)+d·(n(ξ)-n(ti))|2 (3)
Carrying out minimum value search by adopting a damping Newton method, wherein the value range of parameters is xi epsilon (t i+1,1)∪(0,ti-1), d epsilon (0, infinity) until the parameters xi i,di meeting the condition f (xi, d) =0 are searched for to stop, and then calculating a mean camber line characteristic point P i according to the geometric relational expression (2) of the point on the mean camber line;
Step 23: and (3) taking the point C (t m) as a first point, iteratively calculating a mean camber line characteristic point P m corresponding to the first point C (t m) according to the step (22), then increasing the number m, calculating a mean camber line characteristic point P m+1, repeating the increasing operation, when no solution exists according to the formula (3), enabling the discrete point C (t i) to be close to the edge head, stopping the increasing operation, decreasing the number m for the same operation, and carrying out NURBS curve fitting on all the mean camber line characteristic points P i,i＝m-n1,…m,…,m+n2 according to the point position sequence to obtain a fitted mean camber line C Γ.
3. The method for reconstructing the curved surface of the blisk blade based on edge head compensation according to claim 1, wherein the step 3 is specifically:
Accessing a unit tangent vector τ 0 at an endpoint C Γ0 of the fitted mean camber line C Γ to create a straight line l with two points of the mean camber line feature point P 0 corresponding to C Γ0 and C Γ0, wherein:
P0＝CΓ0+2d·τ0
wherein d is a section thickness value at the endpoint of C Γ0, and the intersection point of the straight line l and the blade section curve C is obtained to obtain two edge tip points, wherein the curvature radius rho in the two edge tip points is larger and is the trailing edge tip point C t, and the smaller is the leading edge tip point C l.
4. The method for reconstructing the curved surface of the blisk blade based on edge head compensation according to claim 1, wherein the step of segmenting the closed blade section curve in the step 4 is as follows:
Setting a front edge area radius R l and a rear edge area radius R t of the closed blade section curve, respectively taking a front edge sharp point C l and a rear edge sharp point C t as circle centers and taking the front edge area radius R l and the rear edge area radius R t as radii to create a circle O l and a circle O t in a plane where the section curve C is located, solving intersection points of the circle O l and the circle O t and the section curve C to obtain four points of C l1、Cl2、Ct1、Ct2, and dividing the closed curve C according to the four points to obtain four dividing curves: a leading edge curve, a trailing edge curve, a leaf basin curve and a leaf back curve.
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