DE102011002906A1 - Shaping core used for draping unidirectional unbent fiber layers for producing continuous fiber reinforced component, has flexible soft strips whose bending curvatures are extended along concentric direction - Google Patents

Abstract

The shaping core (1) drapes the unidirectional unbent fiber layers (3) as a package of superimposed fiber layers. Flexible soft strips are provided in a bending direction perpendicular to the package of superimposed fiber layers, while contacting over the entire surface of the fiber layer package. The strips are decoupled such that a mutual displacement is possible. The bending curvatures of strips are extended along concentric direction. The strips are made of resilient metal such as steel or aluminum, and plastic. An independent claim is included for method for draping unidirectional unbent fiber layers.

Description

The invention relates to a forming mandrel for draping unidirectional 0 ° fiber layers. Furthermore, the invention relates to a corresponding method for draping unidirectional 0 ° fiber layers, in which the forming core according to the invention is used. The advantage of the forming core and of the method consists in a wrinkle-free draping of these unidirectional 0 ° fiber layers, in particular of pre-impregnated continuous fibers, the so-called prepregs.

The field of application of the invention is the preforming of 0 ° fiber layers for the production of components from continuous fiber-reinforced fiber composites with non-axial fiber progression, for example, following the component contour and / or stress. Hitherto, methods for shaping fiber layers whose fiber angles are non-tangential to the bending line (→ 0 ° ≦ φ ≦ 180 °) have been known by spreading on elastic cores. That's how it describes WO 2009/115734 A2 a method and apparatus for producing a bent portion of composite material. The resulting section is made from at least one composite band extending along a longitudinal axis. The composite tape is formed by laminating at least two layers of unidirectional reinforcing fibers that are aligned in a defined manner. The tape is draped over a jig having a substantially oblong planar or mainly planar landing surface with a particular shape corresponding to the desired area and extending over a reference line. The tape is applied stepwise and simultaneously deformed along the reference line so that in the parts having a radius of curvature other than ∞, the fibers in the application plane fan out following the curve.

The US 7,513,769 B2 describes a method and apparatus for forming elongated composite members having a desired cross-sectional geometry formed across the length of the component. The device may comprise a base on which a substantially elongated mandrel is mounted. One or more rollers configured to engage at least partially complementary to the mandrel are configured to at least partially position one or more layers of the composite onto the mandrel. To press the thorn. The mandrel may be disposed on a turntable and formed with a curved elongate geometry to form at least partially curved or arcuately elongated composite components. Said device is intended to enable the formation of elongate components from resin impregnated materials while maintaining the materials in a substantially uncured state. The formed components can then be cured with a skin or other composite material.

The disadvantage of the two above-mentioned methods and devices is that 0 ° fiber layers can not be spread apart in a fiber-parallel manner or wrinkle-free can be compressed. Another possibility for the preforming of 0 ° fiber layers consists in the defined, parallel to the "bending line" extending filing of fiber layers by means of fiber laying devices, the so-called automatic fiber placement in a CNC system (CNC = Computerized Numerical Control). The disadvantage of Automatic Fiber Placement is that it is a very time-consuming, expensive and time-consuming process, due to the need for a parallel deposit of so-called tows, which are fiber ropes with a typical width of b = 6.35 mm.

Finally, another variant for the preforming of fiber layers in laying down and sewing dry fibers on a thin carrier material, which may be a woven fabric, a knitted fabric or fleece, into a preform for injection technologies, as with reinforcing structures of the Case is that produced by the company Hightex GmbH. The disadvantage is that with such a method, the processing of prepregs is not possible. Prepregs are semi-finished products made of preimpregnated fiber layers, which are already impregnated in an uncured plastic matrix.

The DE 40 02 087 A1 describes a method and apparatus for depositing unidirectional preimpregnated fiber ribbons on double curved bodies or surfaces. In the apparatus, there are substantially provided a donor roll for the sliver, two pass rolls, a shear roll and a forming roll cooperating therewith, a guide roll and a pinch roller for pressing the sliver onto the surface. By dividing the shear roll into a number of rotatable roll segments, and by allowing the forming roll to be contoured to any desired shape, a variable run length of the fibers across the width of the sliver and a smooth overlay of the sliver on each doubly curved surface without wrinkles and waves be achieved. This device is intended as a module on an automatic banding machine for the production of large series. As a solution for smaller series, this solution is not suitable because of the resulting machine costs.

The invention has for its object to provide an apparatus and a method for draping unidirectional 0 ° fiber layers, in which. the fibers of a fiber layer to be processed are supported so that they do not can be upset. In particular, both the device and the method should be favorable in terms of cost. The apparatus and method are further intended to enable processing of prepregs.

The solution to this problem consists in a Umformkern for draping unidirectional 0 ° fiber layers, which is designed as a package of several superimposed, full-surface contacting, flexible strips that are perpendicular to the intended bending direction. According to the bending soft strips are mutually shear decoupled, so that mutual displacement is possible on each other, wherein at a bend of the Umformkerns the curvatures of all strips are concentric.

According to the concept of the invention, the forming core is thus equipped with a fiber kinematically equivalent distortion kinematics. This is realized in particular by the package shear decoupled, bending soft, perpendicular to the bending direction stripes, wherein the bending process, a shear distortion of the strip package occurs, which is comparable to the shear distortion when bending a paperback book. It is important that the adjacent strips touch the entire surface, but at the same time allow each other to move towards each other.

In one embodiment of the invention, an elastic metal material, such as steel or aluminum, is provided as strip material. Alternatively, an elastic plastic can be used, in which case the plastics Teflon (PTFE), polyethylene (PE) or polypropylene (PP) are preferred.

• a) Auflegen einer gestreckten Faserlage von unidirektionalen Faserschichten auf auf einem erfindungsgemäßen Umformkern, der in allen oben genannten Ausführungen vorliegen kann, und Andrücken der Faserlage an den Umformkern, wobei der Faserverlauf parallel zu den Streifen ausgerichtet wird;
• b) Umformen des Umformkerns mit der Faserlage, wobei aus der gestreckten Faserlage eine Preform entsteht; und
• c) Abnehmen der aus der Faserlage erzeugten Preform und Laminieren im Härtewerkzeug.

Another aspect of the invention relates to a method for draping unidirectional 0 ° fiber layers, in which the following, consecutively proceeding process steps a) to c) are carried out:

• a) applying a stretched fiber layer of unidirectional fiber layers on a Umformkern invention, which may be present in all the above embodiments, and pressing the fiber layer to the core, wherein the fiber profile is aligned parallel to the strip;
• b) forming the Umformkerns with the fiber layer, wherein the preform is formed from the stretched fiber layer; and
• c) removing the preform produced from the fiber layer and laminating in the hardening tool.

Preferably, in method step b), the forming core is reshaped with the fiber layer along a bending template. Alternatively, the forming process in method step b) can also be realized without a bending template in that the converter core is actuated and thus deformed at discrete interpolation points with the aid of a plurality of controlled drives, thereby generating a freely programmable curve or shape. In particular, CNC-controlled linear axle drives can be used for this purpose.

The radius of curvature of the adjacent strips of the Umformkerns increased or reduced by the inventive arrangement in each case by the strip thickness. Thus, the curvatures of all strips are concentric. The inventive method reshapes unidirectional 0 ° fiber layers by distortion of the textile fabric in the area. In the process, the fiber layer is taken up during the forming process and thereby supported so that the fibers are not compressed. It is achieved in this way by targeted shear distortion between the fibers a kinematically "clean" deformation. In this way, a wrinkle-free draping of the unidirectional 0 ° fiber layers takes place. As a further advantage, there is a potential for material savings through a Kraftfluss- and thus material-appropriate fiber architecture, which causes a higher fiber efficiency. Not least, an energy and cost-efficient forming process is possible by the inventive method. Therefore, the use of expensive fiber placement equipment can be dispensed with.

In a preferred embodiment of the method according to the invention, prior to carrying out method step a), placing the stretched fiber layer on the forming core, the forming core is preheated in a method step a ₀ ). If necessary, the forming core or alternatively only the prepreg layer can be heated to soften the matrix material for the forming of prepregs.

In a further development of the method, after laying the stretched fiber layer on the forming core in a further method step a ₁ ), a fiber-parallel unwinding of the fiber layer is additionally effected in order to produce single-curved profile cross sections.

Preferably, after step b) as an intermediate step b ₁ ) cooling of the preform.

As a simple curved profile cross-sections in particular L, Z or U-sections may be provided.

Further details, features and advantages of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings. Show it:

1 : a schematic representation of the behavior of the strips in the core during the bending process;

2 : a schematic representation of the Umformkerns with the fiber layer before and after the distortion and

3 : A schematic representation of the production of an L-shaped preform.

The strip package according to the invention for simulating the distortion kinematics consists of flexurally soft, mutually decoupled strips. The material used is various elastic metals or plastics - for example steel, aluminum, Teflon (PTFE), polyethylene (PE), polypropylene (PP) and the like. For the forming. If necessary, the forming core or alternatively only the prepreg layer can be heated by prepregs in order to soften the matrix material.

The 1 shows a schematic representation of a section of a Umformkern 1 with flexible, mutually sheared decoupled strips 2 and their behavior during the bending process. The transformer core 1 has a distortion kinematics equivalent to a fiber layer to be processed. This is decoupled by the package (decoupling), soft bending, perpendicular to the bending direction stripes 2 realized. In this way, a shear distortion occurs as in bending a paperback book. The neighboring strips touch each other 2 over the entire surface, but allow each other to move towards each other. The radius of curvature R of adjacent strips 2 increases or reduces by the arrangement according to the invention in each case by the strip thickness t. In this way, the curvatures of all strips run 2 (Number i) of the Umformkerns 1 concentric.

The following figures 2 and 3 each show embodiments for producing a curved, planar or L-shaped preform 5 with contour following fiber course.

It shows the 2 a schematic representation of the Umformkerns 1 with a fiber layer 3 before and after a distortion caused by a forming process on a bending template 4 he follows. The 2 , Figure A, shows the core 1 with the fiber layer 3 in stretched form. The figure B in 2 represents the transformer core 1 with an applied 0 ° -fiber layer 3 represents.

Finally, the 2 in Figure C the core 1 with shear-distorted 0 ° fiber layer 3 represents.

a₀

gegebenenfalls Vorwärmen des Umformkerns 1;

a

Auflegen der gestreckten Faserlage 3 auf den gestreckten Umformkern 1 und Andrücken, beispielsweise von Hand, durch Vakuum oder Ähnliches;

a₁

faserparalleles Abwickeln der Faserlage 3 zur Erzeugung eines L-Profilquerschnitts;

b

Umformen entlang einer Biegeschablone 4 und

c

Abnehmen der so erzeugten Preform 5 und Laminieren im Härtewerkzeug.

The 3 shows a schematic representation of the production of an L-shaped preform 5 , The forming process takes place along a bending template 4 , The following production process is planned:

a ₀

optionally preheating the Umformkerns 1 ;

a

Placing the stretched fiber layer 3 on the stretched core 1 and pressing, for example, by hand, by vacuum or the like;

a ₁

fiber-parallel unwinding of the fiber layer 3 for generating an L-profile cross-section;

b

Forming along a bending template 4 and

c

Removal of the preform thus produced 5 and laminating in the hardening tool.

The 3 shows in Figure A first the Umformkern 1 with unwound L-profile. In Figure B the 3 becomes the stretched L-profile of the fiber layer 3 shown schematically before forming. The 3 Figure C shows the deformed L-profile of the fiber layer 3 and in Figure D, finally, the L-profile preform 5 ,

LIST OF REFERENCE NUMBERS

1

Umformkern

2

strip

3

fiber layer

4

bending template

5

Preforming, preform

R

Radius, radius of curvature

t

Strip thickness Number of strips

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2009/115734 A2 [0002]
• US 7513769 B2 [0003]
• DE 4002087 A1 [0006]

Claims (10)

Transformer core ( 1 ) for the draping of unidirectional 0 ° -fiber layers, which as a package of several superimposed, completely contacting, flexible strips ( 2 ) is formed, which are perpendicular to the intended bending direction, characterized in that the flexible strips ( 2 ) are thrust-decoupled with each other, so that a mutual displacement is possible on each other, wherein at a bend of the Umformkerns ( 1 ) the curvatures of all strips ( 2 ) run concentrically. Transformer core ( 1 ) according to claim 1, characterized in that the strip material is an elastic metal material or plastic. Transformer core ( 1 ) according to claim 2, characterized in that it is provided as an elastic metal material steel or aluminum. Transformer core ( 1 ) according to claim 2, characterized in that as elastic plastic Teflon (PTFE), polyethylene (PE) or polypropylene (PP) is provided. Process for the draping of unidirectional 0 ° fiber layers, in which the following successive process steps a) to c) are carried out: a) application of a stretched fiber layer ( 3 ) of unidirectional 0 ° fiber layers on the core ( 1 ) according to one of claims 1 to 4 and pressing the fiber layer ( 3 ) to the core ( 1 ), whereby the fiber course parallel to the strips. ( 2 ) is aligned; b) forming the Umformkerns ( 1 ) with the fiber layer ( 3 ), wherein from the stretched fiber layer ( 3 ) a preform ( 5 ) arises; and c) removing the fiber layer ( 3 ) produced preform ( 5 ) and laminating in the hardening tool. A method according to claim 5, characterized in that the forming of the Umformkerns ( 1 ) with the fiber layer ( 3 ) along a bending template ( 4 ) he follows. A method according to claim 5, characterized in that the forming of the Umformkerns ( 1 ) with the fiber layer ( 3 ) takes place by the Umformkern ( 1 ) is controlled at discrete points using a plurality of controlled drives and thus deformed, and in this way a freely programmable form is generated. Method according to one of claims 5 to 7, characterized in that before laying the stretched fiber layer ( 3 ) on the core ( 1 ) in a method step a ₀ ) the conversion core ( 1 ) is preheated. Method according to one of claims 5 to 8, characterized in that for the forming of prepregs, if necessary, the forming core ( 1 ) or only the prepreg layer is heated to soften the matrix material. Method according to one of claims 5 to 9, characterized in that after placing the stretched fiber layer ( 3 ) on the core ( 1 ) in a further method step a ₁ ) a fiber-parallel unwinding of the fiber layer ( 3 ) to produce single curved profile cross sections.

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