CN111873481A - Compensation method for composite material forming resilience and die with adjustable forming surface - Google Patents

Compensation method for composite material forming resilience and die with adjustable forming surface Download PDF

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CN111873481A
CN111873481A CN202010626704.5A CN202010626704A CN111873481A CN 111873481 A CN111873481 A CN 111873481A CN 202010626704 A CN202010626704 A CN 202010626704A CN 111873481 A CN111873481 A CN 111873481A
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curved surface
point
compensation
regulating
points
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CN111873481B (en
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李宇航
王彦静
李祎
刘闯
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Northwestern Polytechnical University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C70/00—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts
    • B29C70/04—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts comprising reinforcements only, e.g. self-reinforcing plastics
    • B29C70/28—Shaping operations therefor
    • B29C70/40—Shaping or impregnating by compression not applied
    • B29C70/42—Shaping or impregnating by compression not applied for producing articles of definite length, i.e. discrete articles
    • B29C70/44—Shaping or impregnating by compression not applied for producing articles of definite length, i.e. discrete articles using isostatic pressure, e.g. pressure difference-moulding, vacuum bag-moulding, autoclave-moulding or expanding rubber-moulding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C33/00—Moulds or cores; Details thereof or accessories therefor
    • B29C33/30—Mounting, exchanging or centering
    • B29C33/308—Adjustable moulds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C70/00—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts
    • B29C70/04—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts comprising reinforcements only, e.g. self-reinforcing plastics
    • B29C70/28—Shaping operations therefor
    • B29C70/54—Component parts, details or accessories; Auxiliary operations, e.g. feeding or storage of prepregs or SMC after impregnation or during ageing

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Composite Materials (AREA)
  • Moulds For Moulding Plastics Or The Like (AREA)

Abstract

The invention relates to a compensation method aiming at composite material forming resilience and a mould capable of adjusting a forming surface, which comprehensively overcomes the defects of low compensation precision and large calculation amount of an SGD algorithm based on a radius variable algorithm; the adjustable profile mold for realizing the adjustment of the adjusting points from the initial point to the compensation point (point-to-point) is developed, the adjusting points selected on the designed curved surface are accurately adjusted to the corresponding positions on the compensation curved surface obtained by theoretical calculation, and the molding surface is supported by utilizing the characteristics of the composite material profile weak rigid material and the combination of the more limited profile adjusting points and the fixed points; the mechanical structure is adopted, the working environment of autoclave molding is met, and the reliability is higher; the formed curved surface does not generate large stretching and compression and is smoother; the control points are optimized to reduce stress concentration at the control points.

Description

Compensation method for composite material forming resilience and die with adjustable forming surface
Technical Field
The invention belongs to the technical field of dies, and particularly relates to a compensation method for composite material forming resilience and a die with an adjustable forming surface.
Background
The composite material skin is a main component of a modern airplane, is widely applied to wings and an airplane body, and has the characteristics of small production batch, various appearance varieties, large size difference and the like. In the traditional production, a rigid mould is generally used, and the composite material is processed by a thermal diaphragm forming method. The production was based on trial and error adjusting and trimming the mold to counteract the effects of spring back deformation of the composite after demolding. Generally, the time for manufacturing a solid mold accounts for 60 to 80 percent of the development cycle, the number of tools is large, obviously, the method wastes both time and materials, and along with the development and progress of the aircraft industry, the traditional trial-and-error method and the mold manufacturing technology cannot meet the requirements on production speed and benefit.
In view of the above-mentioned drawbacks of rigid molds, adjustable flexible molds have come into play. The research on adjustable dies by domestic and foreign experts and scholars goes through the stages of conceptual design, principle test, process verification and the like, wherein the most important is the research on a compensation method for springback deformation in the forming process of a composite material and an adjustable die developed based on the method.
1) Existing springback compensation method
And the springback compensation is to adjust the die according to the springback deformation of the composite material component in the forming process, and compensate the forming surface of the die, so that the component formed by using the compensated compensation curved surface is exactly the same as the design value. The magnitude and direction of the springback compensation needs to be determined by the springback compensation method. The existing springback compensation method is mostly based on the position difference between the selected node on the springback component and the corresponding node on the initial molding surface of the mold, and different algorithms are used for springback compensation.
The existing typical algorithms include an algorithm based on the variable of the radius and an SGD (shape globaldeformation) algorithm (Korean Shi, Yang Pan, 20319; rigid, Nayao, composite material member mold surface correction research based on a molded surface node, an aeronautical manufacturing technology, 2017(04):16-19. Niao, Chengkou, Shendanfeng, Zhongshihua, a novel algorithm SGD for molded surface modification and application thereof in springback compensation.
2) Existing adjustable profile die
In actual production, the adjustable die is a specific implementation mechanism for completing springback compensation. The existing adjustable flexible dies for composite materials are mostly multi-point adjustable flexible dies, and the dies are formed by a series of small punches with adjustable height and regular arrangement and can form discrete curved surfaces. The basic idea is to fit the three-dimensional profile of the die with discrete points, and to obtain different die profiles by adjusting the height of the small punch.
The existing typical adjustable die is a coupling type flexible multi-point die, namely a die profile is constructed and a composite material is formed by adjusting the heights of small punches at various adjusting and controlling points according to the outer envelope surface of the forming; the other is a 'sandwich' forming flexible multi-point die, which is formed by laying an elastic cushion plate on small punches so that the small punches of a lower die are spaced rather than arranged closely.
The compensation algorithm has the problem that the calculated amount and the forming precision cannot be met simultaneously. Each punch of the multi-point regulation flexible die can only be unidirectionally regulated in the vertical y direction generally, and for any one springback compensation algorithm, the compensation of the regulation point selected on the designed curved surface is in two or even three directions, otherwise, serious stress is generated in the forming surface, so that the forming surface is not smooth, and even the forming cannot be carried out when the slope of the designed curved surface is larger. Referring specifically to fig. 1, it can be seen that the control point does not reach the position of theoretical calculation after control. In addition, since the initial design profile of the multi-point adjustable flexible die is supported and fixed by the punches, a considerable number of punches need to be arranged to ensure continuity of the molding surface, which complicates the mechanical structure and the adjusting and controlling device of the die, increases the cost for producing small-lot composite material members in an aircraft, loses the advantages of the adjustable die, and also reduces the reliability thereof. In addition, when the general autoclave method is adopted for molding, the limitation of the high-temperature and high-pressure working environment on the use of the motor can greatly increase the workload of manually adjusting the punch.
Disclosure of Invention
The technical problem solved by the invention is as follows: the method is combined with the advantages and the disadvantages of the existing method and the adjustable die, the patent provides a novel springback compensation method based on discrete curvature, and the defects of low compensation precision of the variable algorithm based on the radius and large calculation amount of the SGD algorithm are comprehensively solved; the adjustable profile die for realizing adjustment of the adjusting points from the initial point to the compensation point (point-to-point) is developed, the adjusting points selected on the designed curved surface can be accurately adjusted to the corresponding positions on the compensation curved surface obtained by theoretical calculation, the multi-punch-head adjustable profile die does not support the formed curved surface by utilizing multiple densely arranged punches, but supports the formed surface by utilizing the characteristics of a composite profile weak rigid material and more limited profile adjusting blocks and fixed blocks, compared with the existing adjustable die, the number of the adjusting points is greatly reduced, and the structure is more simplified; the mechanical structure is adopted, the working environment of autoclave molding is met, and the reliability is higher; the formed curved surface does not generate large stretching and compression and is smoother; the regulation and control points are optimized to reduce the stress concentration of the regulation and control points; more importantly, a new idea different from a multipoint regulation and control mould is provided for the design of the adjustable flexible mould.
Aiming at the problems that the precision and the calculated amount of the conventional springback compensation method cannot be met simultaneously, the molding efficiency of a composite material mold is insufficient and the like, the invention provides a compensation method for springback deformation in the molding process of a composite material and a mold with an adjustable molding surface developed according to the method. According to the method, the adjustable die can be adjusted to change the die forming surface, so that the aim of quickly and accurately correcting or compensating the composite material member to be formed is fulfilled.
The technical scheme of the invention is as follows: a compensation method for composite material forming springback comprises the following steps:
the method comprises the following steps: the method for establishing the curved surface and the rebound curved surface model comprises the following substeps:
the first substep: establishing a curved surface: on any curved surface, 2N +1 discrete points are uniformly taken at equal intervals, wherein the ith discrete point is marked as Pi(xi,yi) The curve is dispersed into equal-length 2N segments and discrete pointsThe horizontal and vertical coordinates of the set can be used as data information reflecting the position and shape of the initial curved surface model, and a matrix is used
Figure BDA0002565051610000031
Recording;
and a second substep: establishing a rebound curved surface model: using 2N points P corresponding to selected discrete points on the initial surfacei′(xi,yi) Represents the position information of the rebounding curved surface by using the coordinates of the elastic curved surface
Figure BDA0002565051610000032
Recording;
step two: curvature calculation at discrete points on a curved surface
Calculating the curvatures at 2N +1 discrete points on the curved surface as the basis of subsequent compensation, wherein the method comprises the following steps:
Pi(xi,yi) Has a discrete curvature defined by two adjacent discrete points Pi-1(xi-1,yi-1) And Pi+1(xi+1,yi+1) Calculated, the formula is:
Figure BDA0002565051610000041
wherein
Figure BDA00025650516100000410
And
Figure BDA00025650516100000411
respectively represent PiTo Pi+1And Pi-1Expressed as:
Figure BDA0002565051610000042
Figure BDA0002565051610000043
step three: the establishment of the compensation surface model comprises the following substeps:
the first substep: the curvature formula of each discrete point of the compensated curved surface is as follows:
Figure BDA0002565051610000044
in the formula
Figure BDA0002565051610000045
To compensate for the discrete curvature of the back curve,
Figure BDA0002565051610000046
is a discrete curvature of the initial curved surface,
Figure BDA0002565051610000047
discrete curvature of the curved surface after springback;
and a second substep: establishing a compensation curved surface:
Figure BDA0002565051610000048
Figure BDA0002565051610000049
where ρ isdIn order to design the distance between each equal-length node of the curved surface, the upper corner marks d, s and c respectively correspond to the initial curved surface, the springback curved surface and the compensation curved surface; the coordinate value of each discrete point on the compensation curved surface can be obtained by upward recursion to obtain the compensation curved surface, and the matrix is utilized
Figure BDA0002565051610000051
And recording the data.
Step four: determining the position of the adjustable mould regulation and control point according to the obtained compensation surface model, and the method comprises the following substeps:
the first substep: according to the equidistant principle, N1 points are selected on the compensation curved surface as simulation regulation and control points, N1 is far smaller than N but more than 10, and N1 points also serve as observation points and serve as characteristic points for analyzing the deviation between the adjusted actual curved surface and the theoretical compensation curved surface;
and a second substep: based on a molar integration method, the relation between force and deflection is obtained, and the deflection at the observation point is the displacement of the point after the curved surface is regulated and controlled; (i, j) is recorded as the relative deviation of the j-th position point when the regulating and controlling point acts on the i-th position;
and a third substep: observing the relative deviation of each observation point, namely the variance of the relative distance between the actual position of each observation point and the theoretical position of each observation point obtained by the compensation curved surface after regulation and control, and selecting a group of simulated regulation and control points corresponding to the observation point with the minimum relative deviation as final regulation and control points;
step four: and (4) corresponding the final regulating point position obtained in the third step to the discrete point set in the first step, determining the regulating quantity of the point, and comparing the difference of the matrixes A and C to obtain a compensation value of the point, namely the regulating value to be regulated by the regulating point, and marking as xi.
The further technical scheme of the invention is as follows: an adjustable forming die comprises a forming component, a machine base and a molded surface regulating mechanism; the bottom of the forming component is fixedly connected with the base, the profile regulating mechanism is fixedly connected with the bottom of the base, a regulating head on the profile regulating mechanism is hinged with a regulating block on the forming component, and when the regulating mechanism moves, the forming component is driven to move for regulation.
The further technical scheme of the invention is as follows: the molding component comprises a molding surface, a regulating block and a fixing block; the molding surface is arc surface shape, a plurality of fixed blocks are arranged on the surface connected with the machine base at equal intervals, and a plurality of (selected according to the final control point position selection method) control blocks are arranged at the same time; the fixing block and the regulating block are both provided with through holes.
The further technical scheme of the invention is as follows: the machine base comprises a first bearing block, two polished rods and an aluminum profile frame; the aluminum profile frame is a square frame, the two polished rods are located in the middle of the square frame and are placed in parallel, two ends of the aluminum profile frame are fixedly connected with two symmetrical short edges of the square frame through bearing seats respectively, and all degrees of freedom of the polished rods except the polished rods rotating around the axis are limited.
The further technical scheme of the invention is as follows: the two through holes on the fixing block are sleeved in the two polished rods and are in interference fit.
The further technical scheme of the invention is as follows: the profile regulating mechanism comprises a regulating contact, a screw rod, a sliding block, a plurality of second bearing seats, a lifter, a lifting column, a screw mechanism hand wheel and a lifter hand wheel; the sliding block is provided with a plurality of through holes, the bottom of the sliding block is fixedly connected with a lifter, the plane end of the regulating contact is connected with one end of a lifting column, the U-shaped end is hinged with a regulating block of the forming member, the other end of the lifting column penetrates through the through hole in the sliding block to be spirally connected with a spiral hole in the lifter, and the penetrating direction of the lifting column is defined as the Y direction; the two screws are arranged in parallel, and after penetrating through a through hole formed in the X direction of the sliding block, the two ends of each screw are fixedly connected with the base through second bearing seats respectively; the screw mechanism hand wheel is positioned at one end of the screw rod and is fixedly connected with the screw rod, and the elevator hand wheel is fixedly connected with the internal rotating shaft of the elevator.
The further technical scheme of the invention is as follows: when a hand wheel of the screw mechanism is rotated, the slide block moves along the x direction to drive the elevator fixedly connected with the bottom of the slide block to move along the x direction, the lifting column in screw connection with the elevator is driven to move along the x direction, the regulating contact fixedly connected with the top end of the lifting column moves along the x direction to drive the regulating block to move along the x direction, and then the forming surface is regulated along the x direction; when the hand wheel of the elevator is rotated, the lifting column moves in the x direction to drive the regulating contact fixedly connected to the top end of the lifting column to move in the y direction, and the regulating block is driven to move in the y direction, so that the forming surface is regulated in the y direction.
The further technical scheme of the invention is as follows: when rotating, the hand wheel of the screw mechanism is firstly rotated
Figure BDA0002565051610000061
Angle, then rotate the hand wheel of the elevator
Figure BDA0002565051610000062
And (4) angle, repeating the two steps until the hand wheel is rotated to the position, and requiring that the hand wheel is rotated every time to ensure that the displacement of the control point is not more than 3 mm.
The further technical scheme of the invention is as follows: the molding surface is made of carbon fiber composite material or is consistent with the material of the molding member.
Effects of the invention
The invention has the technical effects that: compared with the prior art, the method has the following characteristics:
the compensation precision is high, and compared with the existing springback compensation method based on the variable of the radius and the method based on the discrete curvature springback compensation, the method for obtaining the variable of the radius springback compensation has more advantages in the aspect of the compensation precision. In order to compare the advantages and disadvantages of the two methods of springback compensation, an example is used herein to compare the two methods of springback compensation. A section line from the composite skin, measuring 1600mm, compares the discrete curvature to the radius for this variable compensation method, and the results are shown in table 1. The data in table 1 reflect that the discrete curvature compensation method better reflects the deviation of the member before and after springback, the difference between the distance between the compensation curved surface and the design curved surface and the distance between the springback curved surface and the design curved surface reaches the maximum but not more than 6mm at the end point, and the maximum deviation of the compensation result for the variable of the radius reaches 19 mm.
TABLE 1 Experimental comparison of radius change compensation and discrete curvature compensation methods
Figure BDA0002565051610000071
2, the calculated amount is much smaller than that of the SGD, the compensation curved surface can be quickly obtained, and the method is suitable for the characteristic of diversified small-batch airplane parts.
Compared with the existing multipoint mould, the flexible mould has the following characteristics:
1, a new adjustable mould structure form is provided. The multi-point die disperses the forming surface into the punch adjusting units, so that the complexity of the mechanism is greatly increased, and the mechanism adopts a point-to-point regulation mode and only selects a plurality of characteristic points on the forming surface for adjustment, so that the die is simpler in structure and more suitable for small-batch production.
2, increasing the regulation direction of the regulation point. Each regulating and controlling block of the multi-point die can be adjusted only along the height direction under the condition that the punch brings things, each regulating and controlling block of the die can be accurately adjusted along the short edge and the height of the frame, and the forming precision is improved.
3, the regulation and control contact is improved. The multi-point regulating and controlling die adopts a multi-punch form, and the contact point with a forming surface is small. The mould adopts a rotatable regulating contact, reduces the stress concentration of a forming surface, and improves the continuity and the forming precision of a curved surface.
And 4, adjusting a driving mode. The multi-point regulation and control die is driven by a motor, cannot be used in the working environment of the autoclave, and can only lock each punch with a special device before forming, so that the operation is very complicated. The driving of the die is all mechanical, the die comprises a spiral mechanism, a worm and gear mechanism, a bolt is matched and the like, the reliability of the die is improved, and the die can be directly connected with the die to be formed in a hot pressing tank.
5. The profile is made of a composite material. The thermal expansion performance of the composite material member is basically matched with that of the composite material member to be molded, and the composite material member has the characteristics of small density, small heat capacity, good repairability and the like, so that the molding precision is high.
Drawings
FIG. 1 is a schematic view of a multi-point mold
FIG. 2 cross-sectional curves of initial and rebound curves
FIG. 3 is a cross-sectional view of a compensation curve
FIG. 4 shows a mold with adjustable molding surface
FIG. 5 Molding member
FIG. 6 engine base
Figure 7 profile control mechanism
Figure 8 aluminium section
FIG. 9 bearing bracket connection detail
FIG. 10 is a schematic view of the connection between the control contacts and the control block
FIG. 11 is a graph comparing two algorithms, A-radius-based variable springback compensation curve, B-discrete curvature-based springback compensation curve, C-springback curve, D-initial curve
FIG. 12 is a schematic view of a curved surface in a two-dimensional coordinate system
Wherein 1-forming component, 2-machine base, 3-profile regulating mechanism, 11-forming surface, 12-regulating block, 13-fixing block, 21-first bearing seat, 22-polished rod, 23-aluminium profile frame, 31-regulating contact, 32-screw rod, 33-slide block, 34-second bearing seat, 35-lifter, 36-lifting column, 37-screw mechanism hand wheel and 38-lifter hand wheel
Detailed Description
Referring to fig. 1 to 12, the technical solution of the present invention is: a compensation method for springback deformation in a composite material forming process specifically comprises the following steps:
the method comprises the following steps: establishment of design curved surface and rebound curved surface model
The springback compensation is established on the basis of an initial molded surface of a mold, namely a design curved surface, and a molded surface of a member after deformation, namely a springback curved surface, so that a model of the design curved surface and the springback curved surface is required to be established firstly.
The establishment of the design surface model comprises the following steps: the two-dimensional model of the mold design curved surface can be any concave curved surface, a semicircle with a radius R is taken for explanation, the opening is vertically upward, and the origin point is at the intersection point of the symmetric axis and the two-dimensional molded surface. Now, 2N +1 discrete points are uniformly taken at equal intervals on the whole semicircular surface, wherein the ith discrete point is marked as Pi(xi,yi) The curve is dispersed into equal-length 2N sections, the horizontal and vertical coordinates of the point set can be used as data information for reflecting the initial curved surface model, and the matrix is utilized
Figure BDA0002565051610000101
And recording the data.
Wherein R represents the initial curved surface radius, 2N +1 represents the number of discrete points, pi represents the circumferential ratio,
Figure BDA0002565051610000102
representing the projection of the vector formed by the first discrete point and the origin on the x-axis,
Figure BDA0002565051610000103
representing the projection of the vector formed by the first discrete point and the origin on the y-axis,
Figure BDA0002565051610000104
representing the N +1 th discrete point and the originThe projection of the formed vector on the x-axis,
Figure BDA0002565051610000105
represents the projection of the vector formed by the N +1 th discrete point and the origin on the y axis.
The establishment of the rebound curved surface model comprises the following steps: the model after the curved surface rebound deformation is required to be established, and the model can be obtained by directly utilizing a three-dimensional scanning model of a formed component in actual production. For convenience of subsequent description, without loss of generality, the rebound characteristics of the composite material are introduced, and a typical model of the rebound curved surface is established. When the composite material member rebounds, the rebound angle of a certain point is in direct proportion to the initial curvature of the point, so that the curvature of each point on the curve can be considered to be changed from the original curvature by considering the small deformation assumption for the C-shaped member selected by the user
Figure BDA0002565051610000106
Become into
Figure BDA0002565051610000107
And considering an additional condition that the vicinity of the origin of coordinates is an initial deformation area, so that the rebound curved surface model can be obtained. Using 2N points P 'corresponding to the discrete points selected on the initial curved surface'i(xi,yi) The coordinates of the elastic surface are used for representing the position information of the elastic surface and are recorded by using a matrix B,
Figure BDA0002565051610000111
the design and rebound curved surface section curves are as shown in figure 2:
step two: curvature calculation at discrete points on a curved surface
After obtaining the model of the designed curved surface and the rebound curved surface, the curvature of 2N +1 discrete points on the curved surface needs to be calculated according to the model as the basis of the subsequent compensation. The discrete point curvature calculation method is as follows:
Pi-1(xi-1,yi-1) Has a discrete curvature defined by two adjacent discrete points Pi-1(xi-1,yi-1) And Pi+1(xi+1,yi+1) And if the calculation result is obtained, the formula is as follows:
Figure BDA0002565051610000112
wherein
Figure BDA0002565051610000113
And
Figure BDA0002565051610000114
respectively represent PiTo Pi+1And Pi-1The planar distance of (D) is calculated by the following formula
Figure BDA0002565051610000115
Figure BDA0002565051610000116
Step three: establishment of compensated surface model
The compensation curved surface is a molding surface obtained by adjusting the molding surface according to the deviation between the design curved surface and the rebound curved surface. During compensation, the difference of the curvature of the discrete point before and after rebounding is linearly added to the corresponding point of the design curved surface, so that the discrete curvature of the compensated curved surface can be obtained, and the formula is as follows:
Figure BDA0002565051610000117
in the formula
Figure BDA0002565051610000118
To compensate for the discrete curvature of the back curve,
Figure BDA0002565051610000119
is a discrete curvature of the initial curved surface,
Figure BDA00025650516100001110
discrete curvature of the surface of the curve after springback
And then the coordinate values of all corresponding points of the compensation curved surface can be obtained through deduction calculation, and the compensated curved surface is reconstructed by utilizing the interpolation curve. In the following formula ρdTo design the distance of each equidistant discrete point of the surface, the superscripts d, s, c correspond to the initial, rebound and compensation surfaces respectively,
Figure BDA0002565051610000121
can be derived from the first two of the following equations,
Figure BDA0002565051610000122
(i>2) from the latter two recursion equations. The formula is as follows:
Figure BDA0002565051610000123
Figure BDA0002565051610000124
the method can finally obtain a compensation curved surface, as shown in FIG. 3, and can also utilize a matrix
Figure BDA0002565051610000125
The coordinates of corresponding discrete points are recorded, and the characteristics of the size, direction and position of compensation quantity (namely the deviation C-A between the compensation curved surface and the corresponding discrete points on the design curved surface) are analyzed, so that the method can be used as a theoretical support for the design of the adjustable die. The method well considers the geometric characteristics of all the points of the section line, avoids losing the geometric characteristics of all the points of the curve during circular arc fitting in the rebound compensation method based on the radius change quantity, and reduces the deviation.
The further technical scheme of the invention is as follows: according to the obtained compensation surface model, determining the position of an adjustable mould regulation and control point according to the following steps:
the method comprises the following steps: according to the equidistant principle, N1 points are selected on the compensation curved surface as simulation regulation points, as an alternative scheme of a final regulation point, N1 is far smaller than N but more than 10, and the N1 points also serve as observation points and serve as characteristic points for analyzing the deviation of the adjusted actual curved surface and the theoretical compensation curved surface;
step two: the cross section line is regarded as a bending cantilever beam, the structure and material parameters are equivalent parameters of the bending cantilever beam changed from a curved surface, the fixed end is arranged in the initial deformation area at the bottom, the regulating and controlling force is sequentially applied to each simulated regulating and controlling point, and the constraint condition in the force is that the regulating and controlling point just reaches the compensation curved surface from the design curved surface. And (3) solving the relation between the force and the deflection based on a molar integral method, wherein the deflection at the observation point is the displacement of the point after the curved surface is regulated. The ith behavior in table 2 is that the ith simulated control point plays a role of control, and the jth column represents the relative deviation of the jth observation point, that is, the relative distance variance between the actual position of each observation point after control and the theoretical position of each observation point obtained by the compensation surface. The term (5,8) means the relative deviation of the position of the 8 th point when the control point acts on the 5 th position.
Step three: observing the relative deviation of each observation point, and selecting a group of simulated regulation points corresponding to the observation points with the minimum relative deviation as final regulation points. The semi-circle is used as the edge of the initial curved surface in the present example, so the position of the regulation point is selected in the present example, and the regulation point is set to the edge of the opening of the curved surface as far as possible under the condition that the actual production and processing are allowed.
It should be noted that, in the above analysis, for the case that there is a pair of control points on the cross section, when there are two or more pairs of control points, the relevant deflection calculation formula can be also applied to calculate and find the appropriate control point position.
The further technical scheme of the invention is as follows: after the position of the control point is selected according to the result of the method, the position is compared with the positions of the 2N +1 discrete points, the position can be corresponding to the discrete point set in the first technical scheme, and the compensation value of the point is obtained by comparing the difference of the matrixes A and C, namely the control value to be controlled by the control point is marked as xi.
The above method is further explained below by taking a specific example
Establishing a curved surface position model: establishing the position of the design curved surface: the initial shape of the section of the die forming surface is a semicircle with the radius of 200mm, and the opening is vertical toAnd the origin (fixed point) is at the intersection of the symmetry axis and the two-dimensional profile. Now, matlab software is used to uniformly pick 2N + 1-199 discrete points on the whole semicircular curve at equal intervals, discretize the curve, and use the coordinates of the point set as data reflecting the initial curved surface position information by using a matrix
Figure BDA0002565051610000141
And recording the data.
Establishing the position of the rebound curved surface: and (3) establishing a position model after the curved surface is subjected to rebound deformation, and directly utilizing a three-dimensional scanning model of the formed component subjected to the rebound deformation in actual production to obtain the position model. For convenience of description herein, it is assumed that when a composite member rebounds, the magnitude of the rebound angle at a point is directly proportional to the initial curvature at that point. Regarding the C-shaped member adopted in the present example, it is considered that the springback is expressed by a springback angle ds generated in any unit micro-segment of the member, and considering that the springback is a small deformation problem, it is considered that the curvature of each point on the curve is changed from 5(1/m) to 5.26(1/m), and considering that the additional condition that the vicinity of the origin of coordinates is an initial deformation region, the position of the springback curved surface can be determined by using the matrix
Figure BDA0002565051610000142
And recording the data. Interpolation using matlab gives the initial and post-rebound member cross-sectional curves shown in fig. 2.
Calculating the discrete point curvature: pi(xi,yi) Has a discrete curvature defined by two adjacent discrete points Pi-1(xi-1,yi-1) And Pi+1(xi+1,yi+1) Calculated, the formula is:
Figure BDA0002565051610000143
wherein
Figure BDA0002565051610000147
And
Figure BDA0002565051610000148
respectively represent PiTo Pi+1And Pi-1Expressed as:
Figure BDA0002565051610000144
Figure BDA0002565051610000145
and a third step of establishing the position of the compensation curved surface:
the curvature formula of each discrete point of the compensated curved surface is as follows:
Figure BDA0002565051610000146
in the formula
Figure BDA0002565051610000151
To compensate for the discrete curvature of the back curve,
Figure BDA0002565051610000152
is a discrete curvature of the initial curved surface,
Figure BDA0002565051610000153
discrete curvature of the curved surface after springback;
establishing a compensation curved surface:
Figure BDA0002565051610000154
Figure BDA0002565051610000155
where ρ isdIn order to design the distance between each equal-length node of the curved surface, the upper corner marks d, s and c respectively correspond to the initial curved surface, the springback curved surface and the compensation curved surface; the coordinate value of each discrete point on the compensation curved surface can be obtained by upward recursion to obtain the compensation curved surface, and the matrix is utilized
Figure BDA0002565051610000156
And recording the data.
Selecting simulation control points and observation points: in the embodiment, 20 regulating points with sequentially increasing distances from the end point of the curved surface are selected, the distances between the regulating points and the end point of the curved surface in the y direction are respectively 0mm,10mm,20mm.
Calculating relative deviation of observation points: the specific analysis method is that each section line is regarded as a bending cantilever beam, the structure and material parameters are equivalent parameters of the bending cantilever beam changed from a curved surface, the fixed end is in the initial deformation area, the acting point of the force is at the regulation and control point, the deflection of the observation point is the displacement of the point after the curved surface is regulated and controlled, and the displacement direction is perpendicular to the tangent line of the observation point of the initial curved surface. Based on the molar integration method, the relationship between force and deflection can be obtained. The ith row of the following table is used for regulation at the ith regulation point, and the jth column represents the relative deviation of the jth observation point. The term (5,8) means that when the regulatory site acts at the 5 th position, the position of the 8 th point is relative to the variable. It can be seen that the relative deviation of the observation point at the control point is always zero, which means that the actual profile at the control point can be adjusted to the theoretical target profile accurately without deviation.
TABLE 1 relative displacement of each observation point when selecting different analog control points
Figure BDA0002565051610000161
Evaluating the quality of different simulation regulation and control points, and determining the position and the regulation and control value of the final regulation and control point: further observing the relative deviation of other observation points, it can be found that the closer the regulation and control point is to the curve end point, the smaller the relative deviation of each observation point is, so that the position of the final regulation and control point is selected to be arranged at the edge of the opening of the curved surface as far as possible under the condition of meeting the practical production and processing allowance.
After the position of the regulation and control point is selected according to the analysis result, the regulation and control point can be corresponding to the discrete point set of the whole initial curved surface. If a control point with a y-direction distance of 20mm from the end point of the curved surface is selected, and the C-shaped shape of the initial curved surface is combined, the initial coordinate of the control point may be (199.75mm, 180.00mm), and the serial number n of the discrete point approximately corresponding to the position information matrix a of the discrete point of the initial curved surface may be obtained as 196 by comparing the position information matrix a with the discrete point of the initial curved surface. Further, the compensation value (9.62mm, -6.25mm) of the discrete point is obtained by comparing the position information of the discrete point on the initial curved surface and the rebound curved surface, namely the regulation value to be regulated and controlled by the regulation and control point, and finally the regulation and control value is converted into the angle of rotation of the corresponding slide block hand wheel and the corresponding lifter hand wheel according to the principle of a regulation and control mechanism.
The further technical scheme of the invention is as follows: an adjustable die for molding a composite material autoclave is characterized by comprising a machine base, a molded surface regulating and controlling mechanism and a molding member; the hole is arranged on the fixed block at the bottom of the forming component, and the hole and the two fixed polished rods at the upper side of the machine base realize interference fit of a hole shaft, so that the forming component is fixedly connected to the upper side of the machine base to position the forming component; a bearing seat of the profile regulating mechanism is fixedly connected with the lower side surface of the machine base by a bolt; the lift head of the profile control mechanism is articulated with a control block on the forming member, so that when the position of the lift head (fixedly connected with a control contact) is adjusted, the control block on the forming member can move together with the lift head without limiting the rotational freedom of the lift head.
The machine base is shown in figure 6 and comprises an aluminum profile frame, two polished rods and four first bearing seats. The section bar frame is formed by connecting L4040 medium-sized aluminum sections and special connecting pieces thereof, the centers of two short sides at the upper side of the section bar frame are fixedly connected with two pairs of first bearing seats by bolts, and each pair of bearing seats is coaxially matched with a polish rod to limit all degrees of freedom of the polish rod except for rotation around an axis.
The forming component is shown in figure 5 and comprises a forming surface, a fixing block and a regulating block. The part of the forming component directly contacting with the forming component is a forming surface, and a fixed block and a regulating block are designed at the lower side of the forming surface and are respectively used for supporting the weak-rigidity carbon fiber forming surface and adjusting the spatial positions of certain points on the weak-rigidity carbon fiber forming surface. The molding surface is fixedly connected with the fixed block and the regulating block by adopting an integral manufacturing or brazing method.
The profile control mechanism is shown in fig. 7 and comprises a screw mechanism, a lifter, a hand wheel, a second bearing block, an index plate and various connecting pieces. The sliding block of the screw mechanism is fixedly connected with the elevator by using a bolt, second bearing seats at two ends of the screw mechanism are fixedly connected with the machine base by using a bolt, and a U-shaped groove is designed at the end point of a lifting column of the elevator and is hinged with a regulating and controlling block on the forming component.
The further technical scheme of the invention is as follows: the input of the adjustable die is the difference xi of the coordinates of the regulating and controlling point on the initial curved surface and the compensation curved surface; the output is the required number of turns psi of two hand wheels obtained by a profile regulating mechanism according to the deviation xi and the transmission principle of the adjustable die1And Ψ2。
The further technical scheme of the invention is as follows: the method of gradually rotating the hand wheel for multiple times is adopted, namely, the hand wheel with the lead screw slide block is rotated firstly
Figure BDA0002565051610000171
Angle, then rotate the hand wheel of the elevator
Figure BDA0002565051610000172
And (4) angle, repeating the two steps until the hand wheel is rotated to the position, and requiring that the hand wheel is rotated every time to ensure that the displacement of the control point is not more than 3 mm. This is done to prevent significant straightening and shortening of the cross-sectional lines during a single step conditioning process, resulting in excessive stress strains that affect die face shaping.
The further technical scheme of the invention is as follows: when a plurality of regulating blocks are required to be arranged on the same side of the same section of the forming member, the machine base needs to be correspondingly regulated, and the number of regulating mechanisms, connecting pieces, regulating blocks and other parts is increased. The adjustment to the frame is used for fixing the helical mechanism who increases for increasing long limit section bar quantity, and the length should suitably reduce to the screw rod, does the optimization to the length of lift post. In a word, the forming and regulating principle of the die is not changed, and only some repeated expansion is carried out on a certain part of the original machine base, and a corresponding regulating mechanism and a corresponding connecting piece are added.
The further technical scheme of the invention is as follows: the molding surface is made of carbon fiber composite material or is consistent with the material of the member.
The further technical scheme of the invention is as follows: the regulation and control block is hinged with the lifter column head, only the position freedom degree of the regulation and control block is limited, the rotation freedom degree is not limited, and stress concentration is prevented.
The further technical scheme of the invention is as follows: the lifter has self-locking capability, and can not rotate when the lifting column head bears pressure.
The composite material adjustable mold of the present invention is further described in detail with reference to the accompanying drawings. An adjustable mold for an aircraft skin is shown in fig. 4 and comprises a forming member 1, a base 2 and a molded surface adjusting mechanism 3. The bearing seat of the profile control mechanism 3 is fixed on the long edge of the frame of the machine seat through a bolt.
The further scheme of the invention is that the number of turns of the hand wheel to be rotated is converted according to the obtained regulation value xi and the mechanism motion transmission ratio, and the initial position of the hand wheel is recorded by utilizing the index plate. When a hand wheel 37 of the screw mechanism is rotated, the sliding block 33 moves along the x direction to drive the elevator 35 fixedly connected with the bottom of the sliding block 33 to move along the x direction, the lifting column 36 in threaded connection with the elevator 35 is driven to move along the x direction, the regulating contact 31 fixedly connected with the top end of the lifting column 36 moves along the x direction to drive the regulating block 12 to move along the x direction, and then the molding surface 11 is regulated along the x direction; when the hand wheel 38 of the elevator is rotated, the lifting column 36 moves in the x direction, which drives the regulating contact 31 fixedly connected to the top end of the lifting column 36 to move in the y direction, and drives the regulating block 12 to move in the y direction, thereby adjusting the forming surface 11 in the y direction.
The regulation and control are carried out in multiple steps, namely, the regulating and control screw mechanism hand wheel 37 regulates and control the elevator hand wheel 38, and the steps are repeated, so that the displacement generated by the regulating and control point is not more than 3mm by rotating the single hand wheel every time until the rotation is in place. If an error occurs in the adjusting process or the adjusting value is forgotten, the record of the initial position of the hand wheel can be checked, and the zeroing processing is carried out.
And carrying out autoclave molding on the composite material by using the adjusted molding surface.
The above description is only exemplary of the present invention, and is not intended to limit the scope of the invention, so that the replacement of equivalent elements or the modification made in accordance with the scope of the present invention shall fall within the scope of the present invention. In addition, the technical features, the technical schemes and the technical schemes can be freely combined and used.

Claims (9)

1. A compensation method for composite material forming springback is characterized by comprising the following steps:
the method comprises the following steps: the method for establishing the curved surface and the rebound curved surface model comprises the following substeps:
the first substep: establishing a curved surface: on any curved surface, 2N +1 discrete points are uniformly taken at equal intervals, wherein the ith discrete point is marked as Pi(xi,yi) The curve is dispersed into 2N sections with equal length, the horizontal and vertical coordinates of the discrete point set can be used as data information for reflecting the position and the shape of the initial curved surface model, and a matrix is utilized
Figure FDA0002565051600000011
Recording;
and a second substep: establishing a rebound curved surface model: using 2N points P 'corresponding to the discrete points selected on the initial curved surface'i(xi,yi) Represents the position information of the rebounding curved surface by using the coordinates of the elastic curved surface
Figure FDA0002565051600000012
Recording;
step two: curvature calculation at discrete points on a curved surface
Calculating the curvatures at 2N +1 discrete points on the curved surface as the basis of subsequent compensation, wherein the method comprises the following steps:
Pi(xi,yi) Has a discrete curvature defined by two adjacent discrete points Pi-1(xi-1,yi-1) And Pi+1(xi+1,yi+1) Calculated, the formula is:
Figure FDA0002565051600000013
wherein
Figure FDA0002565051600000014
And
Figure FDA0002565051600000015
respectively represent PiTo Pi+1And Pi-1Expressed as:
Figure FDA0002565051600000016
Figure FDA0002565051600000017
step three: the establishment of the compensation surface model comprises the following substeps:
the first substep: the curvature formula of each discrete point of the compensated curved surface is as follows:
Figure FDA0002565051600000018
in the formula
Figure FDA0002565051600000021
To compensate for the discrete curvature of the back curve,
Figure FDA0002565051600000022
is a discrete curvature of the initial curved surface,
Figure FDA0002565051600000023
discrete curvature of the curved surface after springback;
and a second substep: establishing a compensation curved surface:
Figure FDA0002565051600000024
Figure FDA0002565051600000025
where ρ isdIn order to design the distance between each equal-length node of the curved surface, the upper corner marks d, s and c respectively correspond to the initial curved surface, the springback curved surface and the compensation curved surface; the coordinate value of each discrete point on the compensation curved surface can be obtained by upward recursion to obtain the compensation curved surface, and the matrix is utilized
Figure FDA0002565051600000026
And recording the data.
Step four: determining the position of the adjustable mould regulation and control point according to the obtained compensation surface model, and the method comprises the following substeps:
the first substep: according to the equidistant principle, N1 points are selected on the compensation curved surface as simulation regulation and control points, N1 is far smaller than N but more than 10, and N1 points also serve as observation points and serve as characteristic points for analyzing the deviation between the adjusted actual curved surface and the theoretical compensation curved surface;
and a second substep: based on a molar integration method, the relation between force and deflection is obtained, and the deflection at the observation point is the displacement of the point after the curved surface is regulated and controlled; (i, j) is recorded as the relative deviation of the j-th position point when the regulating and controlling point acts on the i-th position;
and a third substep: observing the relative deviation of each observation point, namely the variance of the relative distance between the actual position of each observation point and the theoretical position of each observation point obtained by the compensation curved surface after regulation and control, and selecting a group of simulated regulation and control points corresponding to the observation point with the minimum relative deviation as final regulation and control points;
step four: and (4) corresponding the final regulating point position obtained in the third step to the discrete point set in the first step, determining the regulating quantity of the point, and comparing the difference of the matrixes A and C to obtain a compensation value of the point, namely the regulating value to be regulated by the regulating point, and marking as xi.
2. The adjustable forming die for the compensation method of the composite material forming resilience based on the claim 1 is characterized by comprising a forming member (1), a machine base (2) and a profile regulating mechanism (3); the bottom of the forming component (1) is fixedly connected with the base (2), the molded surface regulating and controlling mechanism (3) is fixedly connected with the bottom of the base (2), a regulating and controlling head (31) on the molded surface regulating and controlling mechanism (3) is hinged with a regulating and controlling block (13) on the forming component (1), and when the regulating and controlling mechanism (3) moves, the forming component (1) is driven to move for regulation and control.
3. The adjustable forming die for the compensation method of the springback of the composite material forming as claimed in claim 2, wherein the forming member (1) comprises a forming surface (11), a regulating block (12) and a fixing block (13); the molding surface (11) is arc-surface-shaped, a plurality of fixed blocks (13) are arranged on one surface connected with the machine base (2) at equal intervals, and a plurality of regulating blocks (12) (selected according to the final regulating point position selection method) are arranged at the same time; through holes are arranged on the fixing block (13) and the regulating block (12).
4. The adjustable forming die for the compensation method of the springback of the composite material forming as claimed in claim 2, wherein said base (2) comprises a first bearing block (21), two polish rods (22) and an aluminum profile frame (23); the aluminum profile frame (23) is a square frame, the two polish rods (22) are positioned in the middle of the square frame and are placed in parallel, two ends of the two polish rods are fixedly connected with two symmetrical short sides of the square frame through bearing seats (21) respectively, and all degrees of freedom of the polish rods (22) except rotation around an axis are limited.
5. The adjustable forming die for the compensation method of the springback of the composite material forming as claimed in claim 3 or 4, wherein the two through holes on the fixed block (13) are sleeved into the two polished rods (22) and are in interference fit.
6. The adjustable forming die for the compensation method of the springback of the composite material forming as claimed in claim 2, wherein the profile control mechanism (3) comprises a control contact (31), a screw (32), a slide block (33), a plurality of second bearing seats (34), a lifter (35), a lifting column (36), a screw mechanism hand wheel (37) and a lifter hand wheel (38); the sliding block (33) is provided with a plurality of through holes, the bottom of the sliding block (33) is fixedly connected with a lifter (35), the plane end of the regulating contact (31) is connected with one end of a lifting column (36), the U-shaped end is hinged with a regulating block (12) of the forming member (1), the other end of the lifting column (36) penetrates through the through holes in the sliding block (33) to be spirally connected with a spiral hole in the lifter (35), and the direction that the lifting column (36) penetrates is defined as the Y direction; the two screws (32) are arranged in parallel, and after penetrating through holes formed in the X direction of the sliding block (33), two ends of each screw are fixedly connected with the machine base (2) through second bearing seats (34); the screw mechanism hand wheel (37) is positioned at one end of the screw rod (32) and is fixedly connected with the screw rod (32), and the lifter hand wheel (38) is fixedly connected with the rotating shaft in the lifter.
7. The adjustable forming die for the compensation method of the composite material forming springback as recited in claim 6, wherein when the hand wheel (37) of the screw mechanism is rotated, the slider (33) moves along the x direction to drive the elevator (35) fixedly connected with the bottom of the slider (33) to move along the x direction, the lifting column (36) in screw connection with the elevator (35) is driven to move along the x direction, the regulating contact (31) fixedly connected with the top end of the lifting column (36) moves along the x direction to drive the regulating block (12) to move along the x direction, and further the forming surface (11) is adjusted along the x direction; when a hand wheel (38) of the elevator is rotated, the lifting column (36) moves in the x direction, the regulating contact (31) fixedly connected to the top end of the lifting column (36) is driven to move in the y direction, the regulating block (12) is driven to move in the y direction, and then the forming surface (11) is regulated in the y direction.
8. The adjustable forming die for the compensation method of composite material forming springback as recited in claim 7, wherein the rotation is performed by first rotating a hand wheel (37) of the screw mechanism
Figure FDA0002565051600000041
Angle, then rotate the elevator hand wheel (38)
Figure FDA0002565051600000042
And (4) angle, repeating the two steps until the hand wheel is rotated to the position, and requiring that the hand wheel is rotated every time to ensure that the displacement of the control point is not more than 3 mm.
9. The adjustable forming die for the compensation method of the composite material forming springback is characterized in that the forming surface (11) is made of carbon fiber composite material or is consistent with the material of the forming component (1).
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