GB2611891A

GB2611891A - A precursor for making off-axis composite material

Info

Publication number: GB2611891A
Application number: GB2216338.0A
Authority: GB
Inventors: Martin Curtis Richard; Anthony Ford Roger
Original assignee: Individual
Current assignee: Individual
Priority date: 2022-11-03
Filing date: 2022-11-03
Publication date: 2023-04-19
Also published as: GB202216338D0

Abstract

A uniaxial, precursor material 1 for making 2-ply off-axis composite material, wherein a linear, angular, transverse line of weakness 2 is periodically introduced into a continuous uniaxial prepreg tape. The precursor may be subsequently converted into 2-ply off-axis strip material 8 by folding at the weakened lines 9, followed by heating and consolidation. The lines of weakness are preferably introduced by laser perforation or a cutting wheel, if the precursor is to be stored on reel. Alternately, the lines of weakness may be introduced by the edge of a heated blade, followed by immediate folding. The folds maybe locked in position consolidation in a hot press. The prepreg tape may include a matrix and reinforcements. A method is also provided. The uniaxial prepreg tape may be used in composite structural parts such as spars and stringers.

Description

A Precursor for making Off-axis Composite Material This invention relates to materials and methods for making 2 ply off-axis fibre composite materials.

Background to the Invention

The design and manufacture of structural parts from uniaxial fibre composite materials requires the assembly of a semi-finished laminate, composed of prepreg plies with the requisite fibre orientations. The off-axis component of this work involves manual procedures that generate considerable prepreg waste and can lack accuracy, due to human error. There are automated methods for aligning off-axis fibres, such as automated tape laying [ATL] and automated fibre placement [AFP] of slit prepreg, but the high cost of the equipment and of prepreg slitting have limited the scope of such processes. This invention provides a precursor material that can be consistently and accurately converted into 2-ply off-axis material.

Summary of the Invention

The production of some composite structural parts, in particular long, linear parts, such as spars and stringers, is a slow manual procedure. A uniaxial prepreg tape has to be oriented, cut to length and then fixed in position within the part's laminate layup. A cumbersome operation, that is subject to human error. Some automated processes for producing off-axis prepreg have been developed, including the use of robotic cutting, pick up and placing [WO 2008057146 A2] and tape winding processes [US 10076883 B2], but their complexity has also limited their scope of application. This invention aims to meet the outstanding need for a consistent and accurate method for producing 2-ply off-axis composite material, without significant waste generation and using relatively simple and inexpensive equipment.

Brief Description of the Drawings

The invention is illustrated but not limited by the following description, with reference to the accompanying drawings, that are schematic and not to scale.

Figure 1 shows a length of uniaxial, precursor material with linear, transverse, angular lines of weakness, and illustrates folding to produce 2-ply off-axis material.

Figure 2 shows a preferred embodiment of the equipment required to introduce linear, transverse, angular lines of weakness into a uniaxial prepreg.

Figure 3 illustrates the unidirectional or alternate folding operations required to convert the uniaxial, off-axis precursor material into 2-ply off-axis material.

Referring to the Figures: Figure 1 illustrates a length of uniaxial precursor tape [1] showing a linear, transverse, angular line of weakness [2], that is sequentially applied at a constant axial spacing [3]. In Figure 2, a supply of uniaxial prepreg tape [4] is sequentially drawn across a cutting device [5], by a set of nip rollers [6]. The cutting device [5] introduces periodic, linear, transverse, angular lines of weakness by interrupted cutting [2], before the resulting uniaxial precursor tape [1] is collected on reel by a tension controlled wind up unit [7].

Figure 3 illustrates the folding operations required to convert a uniaxial, precursor tape [1], into 2-ply off-axis material. A supply of precursor tape on-reel is manually drawn off and folded unidirectionally [9] or alternately [10], before the required folded length [8] is consolidated in an autoclave or a hot press.

Detailed Description of the Invention

The purpose of this invention is to provide 2-ply off-axis composite material, with consistently accurate fibre orientation, with little or no waste generation. Much off-axis material is currently produced from uniaxial prepreg by a manual procedure that requires the uniaxial prepreg tape to be oriented, cut to length and then fixed in position within a laminate layout; a manual procedure that may not ensure a consistent accuracy of the off-axis fibre orientation throughout a structural part.

Consistent accuracy is achieved with this invention by automating the periodic introduction of linear, transverse, angular lines of weakness into a uniaxial prepreg tape. The cuts or perforations are periodic narrow linear slits, the length and spacing of which will depend on the prepreg composition and thickness and therefore must be established experimentally. These lines may be introduced by any of those means known to those skilled in the art, but preferably by laser perforation, using a fibre laser mounted on an XY table. Synchronisation of the cutting device [5] with the nip rollers [6] is under computer control. This configuration provides rapid and accurate setting up of the following line of weakness variables: 1] angle, 2] axial spacing and 3] perforation dimensions and spacing, and offers flexibility with regard to the width of the uniaxial prepreg tape. It also has the advantage of low maintenance, because of the long operating life and non-contact nature of the fibre laser. The resulting precursor is immediately available for conversion to 2-ply off-axis material by unidirectional or alternating folding, either manually or automatically, along the lines of weakness as illustrated in Figure 3. The required length of the folded tape may then be consolidated in a hot press, or collected and stored on reel for future conversion.

Alternative methods of generating lines of weakness include: Pierced perforations, using a mechanically guided cutting wheel with peripheral teeth sized and spaced to suit the specific uniaxial prepreg: Heating using a hot blade, or focussed infrared radiation, to soften the matrix. In this case, the lines of weakness are transitory and must be folded without delay. The invention is restricted to thermoplastic uniaxial prepreg tapes, because their rigidity ensures an accurate folding angle.

Figure 1, shows a length of uniaxial off-axis precursor tape [1] with linear, transverse, angular lines of weakness [2], that are sequentially applied at a constant axial spacing [3]. Figure 2 shows a supply of lightly tensioned uniaxial prepreg tape [4], that is sequentially metered by a set of driven nip rollers [6], across a cutting device [5], consisting of a computer controlled XY table and a fibre laser, that periodically introduces linear, transverse, angular lines of weakness [2], with an axial spacing [3], into the uniaxial prepreg tape [4]. The resulting uniaxial precursor tape [1] is then collected on reel by a tension controlled wind up unit [7] Figure 3 shows the unidirectional [9] or alternate [10] folding of the precursor tape [1] to produce 2-ply off-axis material [8].

Example

Linear, angular, transverse lines of weakness with perforations 2.5mm long at 3.5mm pitch were periodically introduced into a 50mm wide, uniaxial prepreg of Celstran® CFR-TP GF70-01 polypropylene/E glass fibre, fibre volume fraction 46.5 and thickness 0.25mm, by a computer controlled system consisting of a 1000mm wide XY table, equipped with a SPI CW fibre laser, wavelength 1070nm, average power 200 watts and a synchronised set of nip rollers. The transverse angle of the line of weakness was set at 30 degrees and the axial spacing of the lines of weakness at 86.6mm. The resulting precursor tape was then folded unidirecfionally to produce 2-ply off-axis material of width 28.87mm and fibre orientation of +/-30 degrees.

Claims

Claims: 1 A uniaxial, precursor material for making 2-ply off-axis composite material, wherein a linear, angular, transverse line of weakness is periodically introduced into a continuous uniaxial prepreg tape.
2. A uniaxial precursor material as claimed in Claim 1, wherein the precursor tape is folded along the lines of weakness, unidirecfionally or alternately, to produce 2 ply off-axis material.
3. A uniaxial precursor material as claimed in Claims 1 and 2 wherein the lines of weakness are introduced by any method known to those skilled in the art, but preferably by laser perforation or a cutting wheel, if the precursor is to be stored on reel. Alternately, the lines of weakness may be introduced by the edge of a heated blade, followed by immediate folding.
4. A uniaxial precursor material as claimed in Claims 1,2, and 3 wherein the folds are locked in position by any method known to those skilled in the art, but preferably by consolidation in a hot press.
A uniaxial precursor material as claimed in Claims 1, 2, 3 and 4 wherein the matrix of the uniaxial prepreg tape is any of those thermoplastic matrices known to those skilled in the art.
6. A uniaxial, precursor material as claimed in Claims 1, 2, 3, 4 and 5 wherein the reinforcement of the uniaxial prepreg tape is any of those reinforcements known to those skilled in the art.
7. 2-ply off-axis material made from uniaxial, precursor material as claimed in Claims 1, 2, 3, 4, 5 and 6.
8. A method wherein a linear, angular, transverse line of weakness is periodically introduced into a continuous uniaxial prepreg tape.
9. A method as claimed in Claim 8 wherein the precursor tape is folded along the lines of weakness, unidirectionally or alternately, to produce 2-ply off-axis material.
10. A method as claimed in Claims 8 and 9, wherein the folds are locked in position by consolidation in a hot press.
11 A method as claimed in Claims 8, 9 and 10 wherein the matrix of the uniaxial prepreg tape is any of those thermoplastic matrices known to those skilled in the art.
12 A method as claimed in Claims 8, 9, 10 and 11 wherein the reinforcement of the uniaxial prepreg tape is any of those reinforcements known to those skilled in the art.