METHOD OF MANUFACTURING A SHEET-LIKE COMPOSITE PART WITH IMPROVED COMPRESSION STRENGTH

Abstract

Sheet-like composite parts are manufactured by: a) providing a substantially planar arrangement (A, B, A′) comprising a core layer (B) of a fleece material made of fleece thermoplastic fibers and reinforcement fibers, sandwiched between a pair of skin layers (A, A′), of a skin thermoplastic and optionally reinforcing fibers, the faces of the core layers adjacent and substantially parallel the skin layers, b) heating and pressing the sandwich arrangement (A,B,A′) followed by cooling, thereby obtaining the composite part, wherein the compression strength of the composite part is improved by selecting a core layer (B) which is a core layer having reinforcement fibers predominantly oriented in a direction (Z) perpendicular to the first and second faces.

Claims

1. A method of manufacturing a sheet-like composite part, comprising the following process steps: a) providing a substantially planar arrangement (A, B, A′) comprising a core layer (B) sandwiched between a pair of skin layers (A, A′), a first face of the core layer being adjacent and substantially parallel to a first one (A) of said skin layers and a second face of the core layer being adjacent and substantially parallel to the other one (A′) of said skin layers, the skin layers (A, A′) each comprising a skin thermoplastic and optionally reinforcement fibers, the core layer (B) comprising a fleece material made of fleece thermoplastic fibers and reinforcement fibers, b) heating and pressing the sandwich arrangement (A,B,A′) followed by cooling, thereby obtaining the composite part, wherein the core layer (B) is a Z-oriented core layer having reinforcement fibers that are predominantly oriented in an orientation direction (Z) perpendicular to the first and second faces.

2. The method according to claim 1, wherein said Z-oriented core layer (B) is formed by: i) providing at least one sheet of a pre-consolidated low weight reinforced thermoplastic with an upper face, a lower face and a sheet thickness (T); ii) cutting the sheet into a plurality of substantially congruent core stripes each having a stripe length (L) and a stripe width (W), each core stripe comprising an upper face portion and a lower face portion spaced apart by a stripe thickness corresponding to said sheet thickness (T); iii) arranging the core stripes in a face-on-face manner, optionally with a separation layer therebetween, thereby forming a core stack with a stack length (L.sub.stack) corresponding to said stripe length (L), with a stack height (H.sub.stack) corresponding to said stripe width (W) and with a stack width (W.sub.stack) corresponding to a multiple of said stripe thickness (T); optionally repeating steps i) to iii) to form further core stacks; whereby said at least one core stack forms said Z-oriented core layer with exposed first and second faces for applying thereto surface layers (A) and (A′) to form said sandwich arrangement (A, B, A′) for subsequent process step b).

3. The method according to claim 2, wherein a separation layer is present, and the separation layer is a reinforcement fabric.

4. The method according to claim 2, wherein the Z-oriented core layer comprises a single core stack.

5. The method according to claim 2, wherein the Z-oriented core layer comprises at least two core stacks, the core stacks optionally having different stack heights (H.sub.stack1, H.sub.stack2).

6. The method according to claim 2, wherein at least one core stack comprises core stripes with different compositions.

7. The method according to claim 2, wherein said pre-consolidated low weight reinforced thermoplastic has a reinforcement fiber content of 35 to 80 wt-% and an air voids content of 20 to 80 vol-%.

8. The method according to claim 2, wherein the core stripes are heated before being arranged into a core stack for subsequently applying skin layers (A, A′) and carrying out process step b).

9. The method according to claim 2, wherein unheated core stripes are arranged into a core stack, followed by applying skin layers (A, A′) and carrying out process step b).

10. The method according to claim 2, wherein said reinforcement fibers are selected from the group consisting of glass fibers, carbon fibers, aramid fibers, basalt fibers, natural fibers, high-melting thermoplastic fibers, and mixtures thereof.

11. The method according to claim 2, wherein said fleece thermoplastic and said skin thermoplastic are independently selected from the group consisting of PP, PEI, PES, PSU, PPSU, PPA, PPO, PEEK, PPS, PA, PEAK, PEKK, PC and mixtures thereof.

12. The method according to claim 2, wherein at least one skin layer (A, A′) comprises a reinforcement sheet consisting of a woven fabric, non-crimp fabric or a unidirectional fiber arrangement.

13. The method according to claim 2, wherein the core layer (B) provided before processing step b) has an areal weight of 250 to 10,000 g/m.sup.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The above mentioned and other features and objects of this invention and the manner of achieving them will become more apparent and this invention itself will be better understood by reference to the following description of various embodiments of this invention taken in conjunction with the accompanying drawings, wherein:

[0032] FIG. 1 shows an arrangement to be processed according to prior art, as a perspective view;

[0033] FIG. 2 shows a core layer of the arrangement of FIG. 1, also as a perspective view;

[0034] FIG. 3 shows an arrangement to be processed according to a first embodiment, as a perspective lateral view;

[0035] FIG. 4 shows an arrangement similar to that of FIG. 3, but with just three core stripes, as a perspective longitudinal view;

[0036] FIG. 5 shows an arrangement to be processed according to a second embodiment with non-identical core stripes, as a perspective longitudinal view;

[0037] FIG. 6 shows an arrangement to be processed according to a third embodiment with separation layers between core stripes, as a perspective longitudinal view; and

[0038] FIG. 7 shows an arrangement to be processed according to a fourth embodiment with non-identical core stripe heights, as a perspective longitudinal view.

DETAILED DESCRIPTION OF THE INVENTION

[0039] It will be understood that the figures are not necessarily drawn to scale. In some instances, relative dimensions are substantially distorted for ease of visualization. Identical or corresponding features in the various figures will generally be denoted with the same reference numerals.

[0040] A method of manufacturing a sheet-like composite part according to prior art is shown in FIGS. 1 and 2. As generally shown in FIG. 1, the method starts by providing a substantially planar arrangement (A, B, A′) comprising a core layer B sandwiched between a pair of skin layers, namely an upper skin layer A and a lower skin layer A′. In the example shown, the core layer B is made up of two individual layers B1 and B2 stacked on top of each other.

[0041] A first face of the core layer B is adjacent and substantially parallel to the upper skin layer A whereas the second face of the core layer is adjacent and substantially parallel to the lower skin layer A′.

[0042] The two skin layers A, A′ each comprise a skin thermoplastic and optionally reinforcement fibers. The core layer B, i.e. each one of the individual layers B1 and B2, comprises a fleece material F made of fleece thermoplastic fibers and further comprising reinforcement fibers R1, R2, etc.

[0043] As illustrated in FIG. 2, the orientation of reinforcement fibers R1, R2, etc. in each core layer is predominantly in the layer plane, i.e. in the plane spanned by directional vectors X and Y. More precisely, the reinforcement fibers are oriented in such manner that their longitudinal fiber direction does not have a substantial component in the out-of-plane direction Z. It should be noted that this also applies to curved fibers, in which case one has to consider the local fiber direction at any point along the fiber.

[0044] The basic concept of the present invention is now illustrated in FIGS. 3 and 4. In contrast to the situation shown in FIGS. 1 and 2, there is now a substantial amount of reinforcement fibers R1, R2, etc. having a directional component perpendicular to the faces of the core layer, i.e. along the out-of-plane direction Z. In the example shown in FIGS. 3 and 4, this is achieved by having the core layer B made up by a plurality of substantially congruent core stripes B1, B2, B3, etc. all consisting of a material which is the same as or is similar to the one used for the core layer exemplified in FIG. 2. But in contrast to the arrangement shown in FIG. 1, the core stripes are oriented with their planes being perpendicular to the skin layers A and A′. This is achieved by flipping each core stripe by 90°.

[0045] More specifically, the Z-oriented core layer B of the arrangement shown in FIGS. 3 and 4 can be formed by the following method. First, one provides a pre-consolidated low-weight reinforced thermoplastic (also called “LWRT”) with an upper face, a lower face and a sheet thickness T. Subsequently, this sheet is cut into a plurality of substantially congruent core stripes each having a stripe length L and a stripe width W and further comprising an upper face portion and a lower face portion spaced apart by a stripe thickness corresponding to the sheet thickness T. The core stripes are then arranged in a face-on-face manner, thereby forming a core stack with a stack length L.sub.stack corresponding to the stripe length L, and with a stack height H.sub.stack corresponding to the stripe width W. Evidently, the stack has a stack width W.sub.stack corresponding to a multiple of the individual stripe thickness T. The core stack thus obtained forms a Z-oriented core layer with exposed first and second faces for applying thereto surface layers A and A′.

[0046] The sandwich arrangement A, B, A′ thus obtained can then be subjected to a heating and pressing step followed by cooling, thereby obtaining a sheet-like composite part with excellent compression strength properties.

[0047] A second embodiment is exemplified in FIG. 5. In this case, an arrangement with non-identical LWRT core stripes B1, B2, B3 is used. These core stripes have substantially identical geometry, but they do not all have the same composition. For example, the various core stripes could have somewhat different fiber content and/or somewhat different porosity. It is also possible to use core stripes with different types of reinforcement fibers, e.g. some stripes with carbon fibers and other stripes with glass fibers.

[0048] A third embodiment is exemplified in FIG. 6. In this case, an arrangement with substantially identical LWRT core stripes B1, B2, B3 is used. However, the arrangement further comprises separation layers S, particularly fabric layers, arranged between the core stripes.

[0049] A fourth embodiment is shone in FIG. 7. In this case, an arrangement having three LWRT core stripes B1, B2, B3 having different stripe heights is used. The core stripes are substantially, but not strictly congruent. In the particular example shown, the stripe height progressively increases, thereby forming a stair-like configuration, resulting in a progressively increasing thickness of the sandwich arrangement. Other geometric configurations are of course possible and useful.