Method for draping composite materials on a form and material suitable for said method

Abstract

The subject matter of the invention is a method for draping on a form, which includes a step of deposition on the form of a first fold support in the form of one or more polymer nonwoven fabrics. The invention further relates to a thermoplastic nonwoven material manufactured with a nonwoven fabric of polymer fibers.

Claims

1. A process of drape forming parts made of thermoplastic composite materials on a former, the process comprising: laying up on the former a support ply in the form of one or more polymer nonwoven fabrics; melting said support ply at a lower or equal temperature than the thermoplastic composite material of said part to provide a coupling surface for a first ply of a thermoplastic composite material part to be drape formed on the former; draping said first ply on said support ply; draping further plies of said part; and heating of the thermoplastic composite material part on said former and melting further at least part of said support ply of said polymer nonwoven fabric for promoting adhesion of the first ply of said part to the former.

2. The drape-forming process as claimed in claim 1, further comprising a step of needlepunching the one or more polymer nonwoven fabrics prior to the lay-up.

3. The drape-forming process as claimed in claim 2, wherein the needlepunching step is a needlepunching of 50 to 130 strokes/minute.

4. The drape-forming process as claimed in claim 1 further comprising a step of hydroentangling the one or more polymer nonwoven fabrics prior to the lay-up.

5. The drape-forming process as claimed in claim 4, wherein the prior hydroentangling step is carried out at a pressure of the order of 40 to 80 bar.

6. The drape-forming process as claimed in claim 1, further comprising a step of calendering the one or more polymer nonwoven fabrics prior to the lay-up.

7. The drape-forming process as claimed in claim 1, further comprising needlepunching, hydroentangling and calendering steps prior to the lay-up, the order of the steps being needlepunching then hydroentangling then calendering.

8. The drape-forming process as claimed in claim 1, wherein the one or more polymer nonwoven fabrics comprise polymer fibers of a first nature.

9. The drape-forming process as claimed in claim 1, wherein the one or more polymer nonwoven fabrics comprise polymer fibers of two different natures.

10. The drape-forming process as claimed in claim 1, further comprising a step of clamping the one or more polymer nonwoven fabrics to the former.

11. The drape-forming process as claimed in claim 10, wherein the step of clamping comprises a clamping selected from a mechanical clamping using screwed or clamped blocks, an electromagnetic clamping with the aid of a magnet, clamping by means of adhesive tapes or clamping by coupling strips.

12. The drape-forming process as claimed in claim 1, further comprising a step of melting the material of the one or more polymer nonwoven fabrics.

13. The drape-forming process as claimed in claim 1, further comprising a step of introducing resin by partial melting of the polymer fibers of the one or more polymer nonwoven fabrics.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages of the disclosed embodiment will become apparent on reading the description which follows of exemplary aspects of the disclosed embodiment with reference to the drawings which represent:

(2) FIG. 1: shows an example of a tool or former for producing a non-developable composite part;

(3) FIG. 2: shows a view of a lay-up of three strips forming a first ply according to the invention on the former from FIG. 1;

(4) FIG. 3: shows a view of an example of clamping of a first ply according to the invention to the former from FIG. 1;

(5) FIG. 4: shows a view of a drape forming produced on the first ply from FIG. 3.

DETAILED DESCRIPTION

(6) The presently disclosed embodiment proposes the use of a nonwoven based on polymer fibers as a base layer for the drape forming of a part on a former 1, an example of which is given in FIG. 1.

(7) The solution mainly envisaged in the presently disclosed embodiment is the use of a first ply in the form of nonwoven polymer fabric(s). The latter meet(s) the two-fold constraint of deformability and compatibility with the matrix of the composite.

(8) Unlike a woven fabric where the arrangement of fibers is defined by a weave, a nonwoven has a random arrangement of fibers. This enables it to have a more homogeneous behavior in the plane compared to a woven fabric which has two favored directions (warp and weft yarns). Depending on its construction, a nonwoven is more deformable than a woven fabric, it thus conforms to complex shapes without generating creases, unlike woven fabrics. This property makes it possible to eliminate the risks of inaccuracies of lay-up or of deviation of the sheets in different zones.

(9) The steps of manufacturing a nonwoven comprises the following steps: opening of the fibers or blending of the fibers; carding; lapping; needlepunching, hydroentangling and/or calendering, the calendering being carried out hot at a temperature that makes it possible to melt the nonwoven; conditioning.

(10) The drape forming tests were carried out on a sphere tool or former 1 as represented in FIG. 1. Two references of materials were tested during this session:

(11) TABLE-US-00001 Needle- Hydro- Calen- Cou- defor- ID PEEK punching entangling dering pling mation 1 100% 55 strokes/min no no very good poor 2 100% 55 strokes/min 40 bar no very good good

(12) The nonwoven No. 1 measures 1.10 m wide; it is therefore possible to cover the whole of the quarter sphere tool with this material. Clamping is provided at the periphery of the tool using polyimide adhesive tape.

(13) If the coupling is good, the intrinsic deformation of the nonwoven ID1 associated with the peripheral clamping appears large, and it is not optimal when there are great requirements of accuracy of lay-up of the rovings. This reference of nonwoven must then be improved.

(14) The nonwoven was modified by hydroentangling, a method of mechanically binding individual fibers which uses high-pressure water jets; this led to the nonwoven ID2 by increasing its mechanical strength and decreasing its deformability.

(15) The hydroentangling machine used for the tests measures 500 mm wide which limits the width of nonwoven strip to 400 mm.

(16) For the tests, as represented in FIG. 2, three strips 2a, 2b, 2c of this new nonwoven are positioned side-by-side on the tool to enable the drape forming.

(17) Various clamping configurations were then tested and the one offering the best guarantees is based on a double-sided adhesive tape positioned at the periphery of the part but under the drape forming zone in the overlength zone of the part. For this clamping, several squares of double-sided adhesive tape are positioned between the strips to prevent them sliding relative to one another.

(18) FIG. 3 gives an example of gripping of the nonwoven 2 by peripheral anchoring 3 with an adhesive tape, for example a thermalimide adhesive tape.

(19) The positioning is carried out by stretching the fabric over the former. The deformability of the nonwoven on a non-developable former is sufficient and it is positioned without creating creases. In the case of a surface that is more complex, bigger or associated with a more pronounced curvature, provision is made for cuts and assembling by welding.

(20) At the end of the drape forming on the configuration from FIG. 2, as represented in FIG. 4, no gap greater than 1 mm is visible between sheets 4 and no defect is visible during the drape forming of six supplementary plies 5. This reference of nonwoven associated with this clamping method therefore constitutes a satisfactory solution for coupling a first ply.

(21) A second series of tests was carried out, to better specify the conditions for manufacturing a satisfactory nonwoven, by evaluating in particular the deformability of the products and the coupling function.

(22) In order to achieve this objective, three aspects were more particularly studied, the first consisting in increasing the mechanical anchorage by doubling the needlepunching frequency, the second relating to the hydroentangling conditions and the third consisting in calendering the nonwoven in order to melt the fibers at the surface.

(23) In order to reduce the calendering temperature below the melting point of PEEK (T m=340 C.), fibers of PEI and of PEEK were mixed. This new nonwoven was then calendered at 300 C. in order to melt the PEI fibers.

(24) A nonwoven was also manufactured with black PEEK fibers in order to demonstrate a possible improvement in behavior during laser lay-up.

(25) The various references produced are presented in the table below:

(26) TABLE-US-00002 ID PEEK PEI Needlepunching Hydroentangling Calendering 2 100% 0 55 strokes/min 40 bar no 3 66% 34% 110 strokes/min 60 bar yes 4 66% 34% 55 strokes/min 60 bar no 5 0 100% 55 strokes/min 40 bar yes 6 85% 15% no black

(27) The drape-forming tests were carried out on a flat tool. Three sheets each composed of eight rovings of structural composites containing carbon fibers and having a polymer matrix, known for example under the reference AS4/PEKK FC, of inch, were draped side-by-side over the various nonwovens.

(28) The dimensions of the draped plies are therefore 305 mm wide by 1100 mm long. The dimensions of the nonwovens were 500 mm1200 mm.

(29) The clamping of the nonwovens was provided by adhesive tape at the periphery. The various configurations tested and the results obtained are presented in the table below:

(30) TABLE-US-00003 ID Coupling Deformation 2 very good good 3 very good very good 4 very good good 5 very good poor 6 very poor /

(31) These results show: that a PEEK nonwoven or a PEEK/PEI nonwoven comprising from 60% to 70% of PEEK constitutes a material that is adequate for the application; that needlepunching and in particular needlepunching of 50 to 130 strokes/minute and preferably of 110 strokes/minute with a tolerance of 5% to 10% gives a greater strength to the nonwoven; that hydroentangling of the order of 40 to 80 bar and more specifically of 60 bar with a tolerance of 5% to 10% is advantageous.

(32) The drape-forming tests have brought to light the importance of clamping the nonwovens. Specifically, depending on the positioning of the clamping, the accuracy of the drape forming varies.

(33) It was therefore necessary to develop effective clamping solutions. Several types of clamping can be used:

(34) mechanical clamping using screwed or clamped blocks;

(35) electromagnetic clamping using a magnet;

(36) clamping with coupling strips, for example known under the trademark Velcro.

(37) During the drape forming, it is advisable to take into account the movements of the lay-up head over and around the drape forming zone. This is why block clamping systems, which create overthicknesses, are positioned at the periphery of the tool.

(38) This arrangement limits their effectiveness.

(39) One alternative solution is based on the use of polymer (in this case PEEK) coupling strips positioned as close as possible to the part without disturbing the drape forming thereof.

(40) The use of such coupling strips makes it possible to distribute the coupling zones of the nonwoven over the former, certain coupling strips being positioned under portions intended to receive the drape forming which makes it possible in particular to produce parts with concave or convex shapes.

(41) The tests carried out show that the nonwovens therefore represent a suitable solution for the coupling of the first ply of drape-formed thermoplastic composites.

(42) Various nonwovens were manufactured and tested and several proved to be applicable for this application. The main advantages of polymer nonwovens are: adaptation to all tool geometries, limited additional mass on the final part; total compatibility with the manufacturing matrix; constitute a solution for enriching the surface with polymer for subsequent welding operations; simplicity of use (no vacuum cover to manufacture, etc.).

(43) The effectiveness of the solution of the presently disclosed embodiment nevertheless remains linked to the effectiveness of its clamping to the tool.

(44) For the present application, the fibers of the nonwoven are advantageously of the same material as the thermoplastic material to be used, in particular PEEK, or use a material having a lower melting point in order to facilitate the coupling of the first ply to the nonwoven.

(45) The use of PEEK fibers or of a mixture of PEEK/PEI fibers makes the solution compatible with drape forming and consolidation of the part. Furthermore, PEEK will melt at the surface during drape forming in the same way as the matrix of the laid-up prepreg and promote the adhesion of the sheet to the tool. It will finally blend perfectly with the resin of the composite during the consolidation of the part to give a composite and thus provide a surface rich in resin that will be able to be of use for possible subsequent welding operations.

(46) The prepreg material must be by nature compatible with the matrix of the composite material.

(47) As seen previously, compatible means in particular, but not only, miscible, that is to say that the mixture of the prepreg material with the matrix of the composite material is single phase between ambient temperature and the melting points thereof.

(48) According to a first solution, the material of the nonwoven is advantageously the same as that of the matrix.

(49) In the description, PEEK is used for a PEEK matrix.

(50) It is also possible to use PEEK/PEI blends, the PEI making it possible to decrease the melting point and to facilitate calendering.

(51) These materials are also suitable for a PEKK matrix.

(52) For a polyamide matrix of PA-12 type, a nonwoven made of polyamide will be used.

(53) The nonwovens used enable the coupling of the first ply without giving rise to creasing including during positioning on a complex, in particular unregulated, shape, their positioning time is brief, they do not deform the preform and ensure its geometrical integrity and they form a thermal barrier between the metal tool of the mold and the part being melted which optimizes the coupling phenomenon even more.

(54) The material of the thermoplastic nonwoven type manufactured by successive implementation of needlepunching, hydroentangling and calendering is part of the presently disclosed embodiment.