Patent Application
20240051241
The present document relates to a laying head for a unit for winding at least one strand from a fiber bobbin. Said bobbin may include one to several fiber(s). These fibers are assembled so as to form a strand deposited around an object such as a hollow mandrel intended to form a reservoir which can, for example, receive a pressurized fluid, such as in particular hydrogen gas. It also relates to a thread winding unit.
Thread winding is a method for implementing by molding composite materials in the form of parts having an axis of revolution (cylinder, cone, etc.). This method is suitable for mass production and is mainly used to manufacture parts subjected to high mechanical stresses (tanks, pipes, etc.).
In some configurations (not represented), the laying head can also move in a direction transverse to the axis of the mandrel, turn around said transverse axis, pivot around the longitudinal axis, and possibly move on the vertical axis.
Prior to starting up the thread winding unit, the sheet is attached to the mandrel. Tensioners of the dispenser are activated to tension the fibers, limit shrinkage and compact the deposited successive layers as well as possible. A layer is defined by a winding allowing depositing the sheet over the entire surface of the mandrel that one wishes to cover. It is possible to create a helical type layer with the sheet that is deposited by forming helices in order to cover the entire surface of the cylinder and the desired areas in the hemispherical bottoms. It is possible to make a circumferential type layer where the sheet is deposited almost transversely to the axis of the mandrel over all or over a portion of the cylindrical area of the mandrel.
Structuring by thread winding allows stacking a succession of helical and/or circumferential layers in order to achieve the desired mechanical performances of the object. In general, the machine is controlled by a numerical control. This numerical control is often programmed by an operator using software dedicated to thread winding.
Contact laying machines are known which enable laying of tapes with a short length without any risk of spinning. However, these machines do not allow laying and maintaining a long continuous fiber under tension or axial mechanical stress in the direction of the fiber which is imposed and regulated.
Known processes of this type are ATL standing for Automated Tape Layer and AFP standing for Automated Fiber Placement.
The ATL process uses very wide tapes (generally from 100 to 300 mm). This technique enables deposition over surfaces with a small radius of curvature and large dimensions such as the wing of a civil aircraft. The AFP process carries out a juxtaposition of tape less than 10 mm wide and an assembly at the head outlet of up to 32 tapes.
The main applications are making of planar parts or parts with a large radius of curvature. The main idea is to replace the human hand for laying down successive plies with defined fiber orientations.
All current systems use calibrated pre-impregnated tapes (fiber/resin) with a separation film between the layers on the storage bobbin. These calibrated tapes are derived from unidirectional pre-impregnated sheets recut with the risk of partial cutting of the reinforcement on the edges. The material costs are herein high and it is necessary to have a system for winding the separation film during the draping operations.
None of these systems uses standard pre-impregnated fibers, i.e. with no separation film between the layers for implementation by thread winding. It is not possible to apply a continuous tension (or stress) in tension (in the direction of the fiber) on the strands since the strand(s) making up the sheet are cut at each end of the made part.
To date, the successive developments in the field of implementation of composite materials have for a large part been concentrated on the automation of processes. These developments are driven by the huge needs expressed in the automotive and aeronautics sectors. The development of hydrogen storage technologies (for example at 700 bar operating pressure) with the increase in gravimetric capacity (i.e. the ratio between the amount of stored hydrogen and the mass of the container), pushes composite materials to the limits of use.
Conventional thread winding processes (dedicated machines) and more robotic ones (versatile machines) have never taken into account the full impact of the process in the loss of performance. In most cases, the bobbin support is far away from the laying head and the strands pass through a large number of deflections and rollers before reaching the laying head. Each change in the direction and/or rotation causes by friction with the walls of the roller, the possibility of spinning or folding of the strand on itself. This spinning (twist) is a major source of loss of performance of the material due to the deterioration and/or premature breakage of certain threads that make up a strand. In addition, the modification of the geometry is conducive when stratifying several layers to the appearance of porosities or local excesses of matrix and/or reinforcing fiber.
There are many types of laying heads with different geometries, made of different materials. In general, an industrialist makes a trade-off that allows placing the largest amount of material per hour to the detriment of the quality of the laid material. The laying head is a major component in laying up the composite over the mandrel. The impact on the overall performance of the produced object depends on the quality of laying.
In this respect, the head as described before with reference to
In thread winding units, the laying head, such as that one described for example with reference to
Yet, it has been noticed that the presence of a one-piece roller could lead to the formation of undulations in the sheet over the mandrel, these undulations creating significant defects in the coating of carbon fibers, which could considerably reduce the expected/desired mechanical strength of the final part. It should be understood that these undulations of the sheet or of the strands on the wound part are one of the signs of a loose laying or else or with a loss of tension at the level of the sheet. After compaction, these undulations result in major defects such as folds of material or heterogeneous areas where the fiber/matrix ratio might be considerably modified.
This problem could arise both when using so-called dry strands, i.e. it is necessary to impregnate during unwinding, or strands impregnated with a partially polymerized matrix called prepregs. In the latter case, each strand has a certain level of stickiness (enabling fastening of the folds to one another over the mandrel) which considerably limits and makes it impossible for the strands to slip. It is noticed that the undulations are even greater with a one-piece roller at the outlet of the laying head.
Moreover, it should be noted that the use of guide rollers for several strands of different bobbins does not allow addressing the aforementioned problem of different distance covered by each strand, which in combination with a one-piece outlet roller further aggravates this problem.
Contact laying machines are the only ones to provide a partial response to this technical problem. They can only use a calibrated sheet (of a higher price). The tensioning level is zero or very low (in contrast with the thread winding technique) because the application by contact does not enable prestressing (tensioning) of the material.
The present document relates to a head for laying a plurality of strands each originating from a bobbin and having a longitudinal axis, the laying head comprising a plurality of pairs of line rollers for rolling the strands from the bobbins, each pair of line rollers being intended to be associated in operation with only one given strand and each pair of rollers comprising an upstream roller and a downstream roller with respect to the direction of unwinding of the strands, the line rollers being independent of each other in rotation.
According to the present document, the rotational decoupling of each roller allows guaranteeing a perfect movement of each strand without the latter being subjected to the movements of the other strands. In other words, each strand is thus moved independently of the other strands up to the downstream end of the head for laying over a mandrel.
The rollers may have axes of rotation substantially perpendicular to the direction of the strands.
Each pair of line rollers may be associated with a release roller, said release rollers being coaxial and rotatable independently of each other. Thus, two upstream and downstream rollers are associated with a given release roller which is different from the release rollers associated with the other pairs of upstream and downstream rollers.
Thus, it is possible to avoid the formation of undulations of the sheet over the mandrel, allowing guaranteeing optimum efficiency when laying the sheet over the mandrel.
The axes of rotation of the rollers may be perpendicular to the longitudinal axis.
The upstream roller and the downstream roller of a pair of line rollers may be arranged staggered with respect to the upstream and downstream rollers of another pair of rollers in a plane perpendicular to the axes of rotation of the rollers and containing the longitudinal axis. The upstream roller and the downstream roller of a pair of line rollers may be arranged staggered with respect to the upstream and downstream rollers of another pair of rollers in a plane parallel to the axes of rotation of the rollers. This parallel plane may contain the longitudinal axis.
This double staggered arrangement allows making a maximum number of strands pass in a reduced space.
The k upstream rollers of the k pairs of rollers may be arranged successively along a direction perpendicular to the longitudinal direction and so that the odd upstream rollers are carried by a first upstream pivot and the even upstream rollers are carried by a second pivot arranged downstream of the first pivot.
The k downstream rollers of the k pairs of rollers may be arranged successively along a direction perpendicular to the longitudinal direction L and so that the odd downstream rollers are carried by a third upstream pivot and the even downstream rollers are carried by a fourth pivot arranged downstream of the third pivot. Moreover, the third pivot may be arranged downstream of the second pivot.
At least two upstream rollers of two pairs of rollers may be arranged coaxially in rotation on the same upstream pivot.
At least two downstream rollers of two pairs of rollers may be arranged coaxially in rotation on the same pivot.
Each roller may comprise an annular groove for receiving a strand, this annular groove having a concave bottom surface. The bottom of the annular groove may have a variable radius of curvature, in particular with a radius of curvature which increases from the center of the annular groove towards the outside of the annular groove.
The axis of the downstream roller of each pair of rollers may be located off the plane containing the axis of rotation of the upstream roller and the axis of rotation of the release roller.
The longitudinal axis of the laying head may be positioned so that there is a plane such that all axes of rotation of the rollers are arranged on the same side of said plane.
A strand of a bobbin may be associated with each pair of rollers, the reinforcing fibers, preferably made of carbon fibers, of each strand being impregnated with a curable matrix which may in particular be made of a thermosetting material or a thermoplastic material.
The present document also relates to a device for laying a plurality of strands each originating from a bobbin, comprising a laying head as described before, said laying head being movable in rotation around the longitudinal axis.
The present document also relates to a unit for winding at least one strand consisting of the fiber(s) of at least one bobbin, the unit comprising a device as described hereinabove or a laying head described before and a robot for moving an object intended to be entirely or partially covered by said at least one strand of the bobbin.
Other features, details and advantages will appear upon reading the detailed description hereinafter, and upon analyzing the appended drawings, wherein:
Reference is now made to
Pairs of upstream 10k and downstream 12k rollers are arranged between the lateral arms B1, B2 and are independent of each other in rotation, i.e. in pairs. In the example represented in the figures, the laying head comprises four upstream rollers 101, 102, 103, 104, and four downstream rollers 121, 122, 123, 124. Each of the upstream 10k and downstream 12k rollers comprises an axis of rotation extending according to the second direction D2, the axes of the rollers are therefore perpendicular to the longitudinal direction D1 and to the longitudinal axis L of the laying head 8. The upstream 10k and downstream 12k rollers are so-called line rollers since they achieve guidance along a line of a strand Mk., this line is parallel to the longitudinal axis L. It would still be possible to qualify them as rollers guiding a strand. In the example represented in the figures, one could note the presence of four strands M1, M2, M3, M4 each associated with a pair of upstream 10k and downstream 12k rollers. It should be understood that the present disclosure covers all configurations where the number k of pairs of rollers [10k, 12k] is greater than or equal to 2. It should be obviously understood that the invention is more particularly interesting when the number of pairs of rollers is large and for example greater than or equal to four.
As shown in
It should be understood that the terms “upstream” and “downstream” refer to rollers positioned with respect to each other upstream or downstream with respect to the direction of unwinding or laying of the strands M1, M2, M3, M4, i.e. with respect to the unwinding direction of the strand. In this case, the direction of unwinding of the strand M1, M2, M3, M4 is oriented from left to right along the first direction D1.
Each pair of upstream 10k and downstream 12k line rollers is associated with a release roller 14k. The release rollers are coaxial with the axis 15. They are herein mounted on the same pivot 19. In the example of the laying head 8 represented in the figures, there are four release rollers 101, 102, 103, 104. Each pair of upstream and downstream rollers comprises a face for supporting the strand Mk which is symmetrical with respect to a plane Pk containing the first longitudinal direction D1 and the third longitudinal direction D3. The release roller associated with the pair of line rollers 10k, 12k comprises a surface for supporting the strand Mk which is also symmetrical with respect to the plane Pk. It should be understood that the aforementioned support faces are annular faces and with a circular section but that the supports are not annular.
The support faces 17 of the upstream 10k and downstream 12k line rollers are formed at the bottom of an annular groove 19. These bearing faces 17 may have a section with a concave curved shape, although represented as being substantially planar. These bottom faces 17 of the annular groove 19 may have a variable radius of curvature, in particular with a radius of curvature which increases from the center of the annular groove outwards the annular groove 19. Each upstream 10k and downstream 12k line roller may comprise two ball bearings 21 to ensure a perfectly centered rotational movement.
In the arrangement of the present description, the k rollers are arranged successively along the direction D2. The rollers 10k where k is odd are carried by the same pivot 16 and the rollers 10k where k is even are carried by the same other pivot 18. The pivot 16 is arranged upstream of the pivot 18. The rollers 12k where k is odd are carried by the same pivot 20 and the rollers 12k where k is even are carried by the same other pivot 22. The pivot 20 is arranged upstream of the pivot 22. The pivot 18 is arranged upstream of the pivot 20. The pivots 16, 18, 20, 22 are arranged upstream of the pivot 19 of the release rollers 14k. The pivots 16, 18, 20, 22 extend according to the second direction D2 and therefore extend perpendicular to the longitudinal axis L. One could observe that the pivots 16, 18, 20, 22 are arranged staggered along a plane perpendicular to the axes 161, 162, 163, 164 of the pivots 16, 18, 20, 22 and containing the longitudinal axis L (
The k upstream rollers may be arranged successively along a direction D2 perpendicular to the longitudinal direction L and so that the odd upstream rollers are carried by a first upstream pivot 16 and the even upstream rollers are carried by a second pivot 18 arranged downstream of the first pivot 16.
The k downstream rollers may be arranged successively along a direction D2 perpendicular to the longitudinal direction L and so that the odd downstream rollers are carried by a third upstream pivot 20 and the even downstream rollers are carried by a fourth pivot 22 arranged downstream of the third pivot 20. Moreover, the third pivot 20 may be arranged downstream of the second pivot 18.
In
In
The upstream line rollers comprise a first series of upstream rollers 10k where k is odd and which are carried by the same pivot 16 and a second series of upstream rollers 10k where k is even and which are carried by the same pivot 18. The downstream line rollers comprise a first series of downstream rollers 12k where k is odd and which are carried by the same pivot 20 and a second series of downstream rollers 12k where k is even and which are carried by the same pivot 22. The pivots 16, 18, 20, 22 are distinct in pairs. According to the longitudinal direction L and along the unwinding direction, one could observe that the pivots are arranged from upstream to downstream so as to have the pivot 16 of the first series of upstream rollers 10k where k is odd, the pivot 18 of the second series of upstream rollers 10k where k is even, the pivot 20 of the first series of downstream rollers 12k where k is odd, then the pivot 22 of the second series of downstream rollers 12k where k is even. A strand Mk cooperates with an upstream roller of a series of upstream rollers and a downstream roller of a series of downstream rollers. More particularly, a strand Mk with k being an odd number cooperates with an upstream roller of the first series of upstream rollers and a downstream roller of a first series of downstream rollers and a strand Mk with k being an even number cooperates with an upstream roller of the second series of upstream rollers and a downstream roller of a second series of downstream rollers. The arrangement of the rollers is such that the strands Mk with k being an even number and the strands Mk with k being an odd number are arranged alternately along the second direction D2.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014064 | Dec 2020 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2021/052457 | 12/24/2021 | WO |
