The present application is a National Phase entry of PCT Application No. PCT/FR2014/000108, filed May 20, 2014, which claims priority from FR Patent Application No. 1301172, filed May 22, 2013, which applications are hereby incorporated by reference in their entireties.
The present invention relates to the manufacture of parts made of composite material by automatic fiber layup machines, and more particularly to a method of defining fiber trajectories on a layup surface for automatic layup machines.
There are known composite material parts produced by methods called fiber placement, by superposing several plies of fiber in different directions. In this document, the term “fiber placement” refers to the placement of tows, in which each ply is made by laying up in contact on a mold of bands side by side, each band being formed of several independent tows arranged side by side, and the placement of bands in which each ply is formed by laying up in contact on a mold of bands side by side, each band being formed of a single tow, of a greater width than in the case of the placement of tows. The tows typically used are unidirectional and include a multitude of filaments. The laid fibers can be pre-impregnated with resin or not. The technology for the placement of tows, using tows of a smaller width, enables laying up on layup surfaces of complex shapes. Parts are manufactured by automatic placement machines, to which are given the trajectories of fibers to produce the plies. In the case of the placement of tows, these machines are typically called fiber placement machines or AFP machines (Automated Fiber Placement) and tape placement machines or ATP machines (Automated Tape Placement) in the case of the placement of bands.
The fiber trajectories are typically defined by software by means of a rosette, consisting of a system of axes associated to a transfer method which enables the definition of a fiber direction on all points of a surface. Today there are different rosettes, based on different transfer methods, which are recognized and used in the aerospace sector according to the layup surface, such as for example Cartesian rosette or the translation rosette.
Each trajectory is generated by defining the direction of the trajectory at different analysis points of the layup surface, also called propagation points, by transfer of the axes system to said analysis point according to the associated transfer method. These transfers of the axis system for the propagation points require calculation time which can prove to be relatively long, particularly in the case of complex surfaces.
The trajectories obtained are then typically subjected to a curvature analysis, commonly called “steering” analysis, and/or an angular deviation analysis. The steering analysis at an analysis point of a trajectory consists of calculating the value of the mean radius of curvature in the plane tangent to the surface at the analysis point.
Following these analysis results, the trajectories must be redefined manually to adjust the trajectories to the acceptable or achievable minimum radii of curvature with a given fiber, and to the maximum angular deviation desired by the designer of the part. Therefore, the definition of the trajectories can prove to be long and tedious.
In the case of non-continuous layup surfaces comprising recesses and/or embossments, in particular for producing reinforcements, the positioning of prefabricated reinforcements, the positioning of honeycombs or others, the definition of satisfactory trajectories at the level of these discontinuities proves to be complicated, and requires lengthy manual operations.
The purpose of embodiments of the present invention is to propose a solution aiming to overcome at least one of the aforementioned disadvantages.
To this end, embodiments of the present invention provides a method for defining the fiber trajectories on a layup surface for producing at least one ply having a given theoretical orientation, for the production of parts made of composite material by the laying up of fibers, including the steps of:
The use of such a simplified transfer surface for the transfer of direction data proves itself to be particularly effective for the definition of acceptable trajectories in terms of the radius of curvature and of angular deviation in the case of non-continuous layup surfaces, having recesses and/or embossments generating ramps.
The method according to embodiments of the invention can be implemented automatically under the form of software. The method according to embodiments of the invention can be used for producing parts made of composite material by laying up fibers, whether by layup by contact, such as by placement of tows or by placement of bands, or by layup without contact such as by filament winding. The method according to embodiments of the invention is of particular interest in the case of the placement of tows on non-planar layup surfaces.
The direction data associated to a transfer method are constituted of a classic rosette or a combination of classic rosettes, or of a constraint grid and/or constraint curves, associated to a transfer method comprising a method for weighting the constraint vectors of the curves and/or the grid, such as described in the patent application filed by the applicant, and entitled “Method for defining fiber trajectories from curves or constraint grid”.
Embodiments of the present invention also concerns a process for manufacturing parts made of composite materials by an automatic fiber layup machine, characterized in that the trajectories of the fibers for the layup of plies by the layup machine are defined by the method for defining the trajectory as described previously.
Embodiments of the present invention also concern a computer program comprising a set of instructions capable of implementing the method for defining the trajectory such as described previously, when the program is executed on a computer.
The invention will be better understood, and the other objectives, details, characteristics and advantages will appear more clearly during the detailed explanatory description which follows several specific embodiments currently preferred from the invention, with reference to the appended schematic drawings, in which:
According to the embodiments of invention, as shown in the figure, the trajectories of the fibers are defined from a transfer surface by using possibly classic rosettes, constraint curves and/or a constraint grid, and/or constraint curves obtained from an angular deviation grid. The trajectories can be generated by using a vector field composed of a mesh of the layup surface in which a direction vector is associated to each element.
The vector field is obtained using the Cartesian transfer of the vector X of the global rosette on each element 92 of the mesh, the Cartesian transfer of the vector X on the element consisting of a normal projection of the vector X on the plane of the relevant element, the projected vector of the so-called projected rosette constituting the direction vector 11 of the element.
Trajectories 81 of the fiber for a ply orientation at 0° can then be generated from this vector field 1, as shown in
An analysis of the radius of curvature can then be performed on these thus obtained trajectories.
An analysis of the radius of curvature and/or angular deviation can be performed directly from the vector field, without generating trajectories, this analysis may for example be displayed on the vector field by assigning different colors to the vectors according to the values of the radius of curvature or the angular deviation.
Fiber trajectories for other ply orientations, such as 90°, +45° or −45°, can be generated from the same vector field 1, by performing a corresponding rotation of the direction vectors.
With reference to
A mesh 21 is defined from these geometric constraints, each element of the mesh being formed of at least four nodes, then a constraint vector T is assigned to each node N of the mesh to form the constraint grid 2.
To form the vector field, the direction of each mesh element is defined in the following manner.
As shown in
With reference to
D1=∥T1×w1+T2×w2+T3×w3+T4×w4∥
The direction vector of the element is then obtained by a transfer by normal projection of this vector D1 to the central point P1 of the element.
With reference to
To form the vector field, the direction vector of each element of the mesh is defined in the following manner.
Considering the central point P2 of an element on
One calculates the normalized weights w5, w6, at central point P2, of the two projected points, these normalized weights being a function of the distances d5 and d6 between the central point and the projected points:
w5=1−(d5/(d5+d6))
w6=1−(d6/(d5+d6))
One then defines the vector D2, which corresponds to the direction vector of the element, by weighting the two tangent vectors T5, T6 by their respective normalized weights w5, w6:
D2=∥T5×w5+T6×w6∥
The vector D2 of the element corresponds to the direction vector D2 thus obtained. The vector field obtained from these constraint curves 3 is similar to that 101 previously obtained by means of the constraint grid.
With reference to
Constraint curves are generated on the layup surface by defining for each constraint curve the propagation directions at different points of analysis also called propagation points. The propagation direction at a propagation point P3 is defined in the following manner.
With reference to
Next one performs a normal projection of said point P3 on the angular deviation grid, the projected point P′3 belonging for example to the element of the grid defined by the four nodes N′1, N′2, N′3, N′4 One performs a calculation of the normalized weights w7, w8, w9, w10 at the projected point P′3 of the four nodes. These normalized weights, also called barycentric coordinates of the projected point, are calculated according to a method known per se, depending on the distance between said projected point and said nodes. One performs a weighting of the four maximum angular deviation values Va, Vb, Vc, Vd by the normalized weights to obtain an authorized maximum angular deviation value α associated to said projected point:
α=w7×Va+w8×Vb+w9×Vc+w10×Vd
Next one determines a tolerance sector around the reference direction TR by defining direction limits L1 and L2 at an angle of +α and −α around the reference direction. Furthermore one determines a geodesic direction G corresponding to the propagation direction at the propagation point P3 of a geodesic curve.
This is followed by a reorientation of the reference direction within the limits of the authorized angular deviation value. If the geodesic direction G is included in the tolerance sector, then the propagation direction at the propagation point is defined as being the geodesic direction. If the geodesic direction is not included in the tolerance sector, then the propagation direction at the propagation point is defined as being the direction limit L1 or L2 the closest to the geodesic direction.
Obtaining a vector field is carried out according to the method described previously with constraint curves 3 of
D3=∥w11×T11+w12×T12∥
The direction vector of the element corresponds to the vector D3, preferably after a 90° rotation of the vector D3 to have a vector field concerning the plies at 0° by default.
The vector field 301 obtained from these constraint curves is shown in
A vector field can also be obtained from a constraint vector grid and an angular deviation grid. In this case, for the generation of the constraint curves according to the method explained above with reference to
One defines a so-called continuous transfer surface which corresponds to a simplified surface of the lay-up surface. In this case, the transfer surface corresponds to the layup surface without its central recess. This transfer surface is defined by a so-called transfer mesh.
To form the vector field, the direction vector of each element of the mesh 191 of the layup surface is defined in the following manner, with reference to
According to an alternative embodiment of the invention, such as is illustrated by the arrow in a discontinuous line in
According to another embodiment, the vector field is obtained from a constraint vector grid and a transfer surface. In this case, for the definition of the cutting plane A2 according to the method explained above with reference to
According to another embodiment illustrated in
The direction of the propagation at the point P6 is then obtained as described previously with reference to
According to another embodiment, the vector field is obtained from a constraint vector grid, an angular deviation grid and a transfer surface. In this case, for the definition of the cutting plane A4 above, the definition of the reference direction T″R is made, not from the Cartesian rosette, but from the constraint vector grid, by normal projection of the point P′6 on the constraint grid and definition of a vector D1 according to the weighting method explained previously with reference to
According to other embodiments, such as illustrated in
Furthermore, a vector field obtained according to the invention can be reintroduced as an input of the method according to the invention to obtain a new vector field.
Depending on the type of layup surface, different vector fields can be used for the definition of trajectories of the plies of different orientations. By way of example, with reference to
The use of a vector field enables shear analyses to be performed quickly, in order to verify that the angle between the trajectories of different orientations are well within an acceptable range of values. Advantageously, as previously, the direction vectors of the vector fields are all defined for an orientation at 0°. In the case of the vector field for the plies at 90°, a 90° rotation of the direction vectors is performed to generate trajectories at 90°. Similarly, in the case of the field vectors for the plies at +/−45°, a rotation of more or less 45° of the direction vectors is performed to generate the trajectories at +45° or −45°. These different vector fields with the direction vectors defined for an orientation at 0°, allows a quick and easy comparison of the direction vectors for the shear analysis.
Although the invention has been described in conjunction with several specific embodiments, it is obvious that it is in no way limited thereto and includes all technical equivalents of the described means as well as their combinations if they are within the scope of the invention.
Number | Date | Country | Kind |
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13 01172 | May 2013 | FR | national |
Filing Document | Filing Date | Country | Kind |
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PCT/FR2014/000108 | 5/20/2014 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2014/188084 | 11/27/2014 | WO | A |
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4696707 | Lewis | Sep 1987 | A |
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Entry |
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PCT International Search Report for PCT/FR2014/000108, mailed Oct. 21, 2014, 4 pgs. |
Number | Date | Country | |
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20160082672 A1 | Mar 2016 | US |