DE102018203722A1 - Process for producing a fiber composite component - Google Patents

Abstract

The invention relates to a method for producing a fiber composite component (50) which has a planar plastic body (52) made of matrix material (30) with embedded fiber reinforcement (54) in skeleton form, including a skeleton preform (1) in a mold cavity (11). a mold (10) is compacted and infiltrated with matrix material (30) and the fiber composite component is produced with curing of the matrix material, comprising the steps of: producing a skeletal preform (1) with a plurality of interconnected webs (100, 101, ...) , Infiltrating the skeletal preform (1) with matrix material (30), for which purpose it is introduced into a sprue area (40) in the skeletal preform (1), which runs along the central longitudinal areas of the webs (100, 101, ...) from where the matrix material (30) propagates in the skeletal preform (1), wherein by providing an excess of material on the skeletal preform (1) and compacting it, a throttle region (42) is created, de r is laterally around the sprue area (40) of the skeletal preform (1) around and in which the fiber volume fraction compared to the fiber volume fraction in the sprue area (40) is increased.

Description

The invention relates to a method for producing a fiber composite component.

Fiber composite components are lightweight and yet have a high stability. They have a fiber reinforcement incorporated in a plastic matrix. Flat fiber composite components can be produced, for example, in the RTM process (Resin Transfer Molding Process). Here, a semi-finished fiber product is impregnated by injecting a matrix material. The semi-finished fiber product is inserted as a near-net shape preform in the cavity of a mold, which forms a negative mold of the component to be produced. The cavity is filled with a matrix material, e.g. a resin, injected. The matrix material flows into and through the fiber layers of the preform and can emerge after its impregnation or impregnation on risers. The matrix material is cured in the mold, e.g. under increased pressure or at elevated temperature. After curing, the fiber composite component can be removed. In the known RTM process, the fiber reinforcement is used over the entire component over the entire surface, which leads to high waste and, accordingly, high costs of the components.

In order to reduce the cost of expensive fiber reinforcements and to optimize the cost of such components, it is known to fabricate fiber composite structural members. In the skeleton construction, the rigidity of the components is achieved via a fiber-reinforced framework-like structure. This skeleton structure is closed by additional material. The fiber reinforcement can be used according to the load path and only in those areas where fiber reinforcement is necessary to achieve the desired component properties. As a result, the amount of fiber material to be used or the waste can be significantly reduced.

For example, it is known to produce fiber-reinforced rods in the pultrusion process, to transform them into a skeleton and to overmold by injection molding with a thermoplastic matrix, which then produces the Au-βengeometrie of the component. Such a method requires many steps and is therefore complicated and expensive.

Against this background, it is an object of the invention to provide a method which does not have the disadvantages described above or to a lesser extent. In particular, a simple method is to be specified, with which flat fiber composite components with reduced use of expensive fiber reinforcements can be produced reliably.

The object is achieved by a method according to claim 1. Further advantageous embodiments emerge from the subclaims and the following description.

The invention relates to a method for producing a fiber composite component which has a sheet-like plastic body of matrix material with fiber reinforcement embedded in skeletal form embedded therein. To produce the fiber composite component, a skeleton preform is first formed. The skeleton preform is formed from semi-finished fiber, wherein the fiber material is arranged in webs and a plurality of webs are formed into an arbitrary skeletal shape. For example, the webs can be arranged at right angles to each other or at an angle to a framework or form a bionic structure. The webs are connected to each other or merge into each other, between the webs remain gaps.

To produce the fiber composite component, the skeletal preform is taken up in a mold cavity which images the shape of the flat fiber composite component to be produced, the mold cavity is filled with matrix material and the matrix material is cured.

The molding tool, which is e.g. An RTM (Resin Transfer Molding) tool usually has two mold halves which form the mold or a cavity. The mold cavity is virtually a negative mold of the fiber composite component to be produced. The skeleton preform is received between the mold halves in the mold cavity. However, because the mold cavity replicates the shape of the sheet-like fiber composite component, the skeletal preform does not fill the entire mold cavity, but covers only part of the bottom surface of the mold cavity. In the closed mold remain next to the skeletal preform, in particular between the webs, cavities without semi-finished fiber.

According to the invention, the method now comprises the steps:
Surface introduction of the matrix material first in a gate region of the skeletal preform, which extends along the central longitudinal regions of the webs, from where the matrix material propagates in the skeletal preform. According to the invention, by providing an excess of material on the skeleton preform and compacting it in the mold cavity, a throttle region is created which extends laterally around the skeleton preform and in which the fiber volume fraction is increased in relation to the fiber volume fraction of the remaining preform region.

The matrix material is therefore not added selectively at one or a few gate points, but flat over the sprue area brought in. The sprue area extends over the middle longitudinal area of the webs. As a result, the flow paths can be shortened and optimized. In this case, the term center longitudinal region is understood to mean a region which extends along the longitudinal axis of each web (and to a certain extent laterally beside it). For example, the center-long range can be the middle 30 percent or 20 percent or less of the web width. If the preform is inserted into the mold, then the web width extends in the closing plane of the mold and the height of the webs along the closing axis of the mold.

If the skeleton preform is inserted into the mold, then the webs with an upper and lower side in the direction of the mold halves and are compacted by the wall of the mold. Since the mold cavity replicates the shape of the fiber composite component, the skeletal preform does not completely fill the mold cavity, but rather cavities remain, which exist in particular between the webs of the skeletal preform. At the sides, therefore, the webs of the skeletal preform are at least partially exposed, i. without contact to the wall of the mold. Therefore, the risk of race tracking is particularly high. Race tracking refers to the advancement of the resin or the matrix material due to permeability differences in or on the semifinished fiber products. Matrix material injected into the semifinished fiber tends to choose the lightest flow path. Instead of a complete impregnation of the semifinished fiber there is therefore the risk that the matrix material penetrates into the areas without semi-finished fiber, whereby the semifinished fiber is only insufficiently integrated in the matrix material or air pockets can remain.

Due to the proposed procedure race tracking can now be reliably prevented. If the matrix material is e.g. injected from the upper mold half of the mold into the mold cavity, the matrix material first comes into contact with the skeleton preform at the top of the runner. The sprue area is laterally surrounded by the throttle area, in which due to the increased fiber volume fraction, the permeability for the matrix material is reduced. In the throttle area, an overcompaction of fiber material is deliberately generated. This is e.g. achieved in that the skeleton preform in the area which is to represent the throttle area later, targeted too high, i. is formed with a too large ridge height. Thus, more fiber material is provided than is necessary for the desired ridge height. In the mold cavity, this material surplus is pressed, whereby the semifinished fiber product is pressed into the skeleton preform in the closing direction of the mold and the proportion of fiber material in this web section is increased in a precisely defined manner.

The overcompaction forms a kind of barrier for the matrix material. The barrier acts like a choke which increases the flow resistance and slows the matrix flow to the sides out of the preform. The matrix material is initially distributed in the sprue area, preferably over the entire height of the webs. There, however, it has only very small flow paths, since it is already introduced over the gate area. Only then does the matrix material pass through the throttle area outwards into the lateral areas and end faces of the skeleton structure.

In addition, the throttle area prevents backflow of matrix material, which once flowed through this area. In addition to a complete impregnation of the skeletal preform so can continue to reliably prevent unwanted inclusion of air.

The supply of the matrix material preferably takes place via a distribution system with a plurality of matrix distribution channels. The matrix distribution channels are fluidically connected to a surface of the mold cavity in the mold. The matrix material flows through the distribution system through the matrix distribution channels and from there into the mold cavity, where it enters the gate area of the skeletal preform. The matrix material may be spread over a plurality of gate locations, e.g. are formed as openings of the distribution channels in the mold cavity, get into the preform.

However, it is particularly preferred if the matrix distribution channels are formed as grooves, which are open to the skeleton preform. This achieves a particularly large-area entry of matrix material into the sprue area. The grooves preferably open directly to the sprue area of the skeletal preform.

The matrix material injected into the skeletal preform infiltrates the entire fibrous material. Due to the shape of the component - the fiber composite component is a flat plastic body in which the skeleton structure is integrated - the mold cavity also has cavities in which there is no fiber material of the preform. These cavities, which u.a. Forming gaps between the webs of the skeleton preform are filled in the process with matrix material and harden as pure matrix areas, when using e.g. a resin form pure resin areas. In one embodiment, it is provided that the matrix material first emerges from the webs of the skeletal preform, fills the cavities in the mold cavity and forms the sheet-like plastic body.

In an alternative process, it is conceivable that after infiltration of the skeleton Preform with matrix material further matrix material adjacent to the skeleton preform is introduced into the mold cavity to form the flat plastic body. In other words, initially only the skeletal preform is impregnated with matrix material in the manner described above. In order to fill the cavities in the mold cavity, a further matrix material is additionally supplied, for example via a second mixing head and a second distribution system.

The feeding of the matrix material into the mold cavity can take place from one or both sides. Consequently, the matrix distribution grooves can be arranged only in one or both mold halves of the mold.

When the matrix material fills the cavity, one or more functional elements, e.g. Bolts or threaded bushes to be integrated into the component. The functional elements may e.g. be arranged in the mold, so that they are partially enclosed by the matrix material and after the hardening of the same form-fitting integrated into the component.

Furthermore, it is conceivable that additional functional elements are generated by the matrix material itself, e.g. in the form of connection points or additional ribbing of the fiber composite component.

The matrix material used is preferably a thermosetting matrix material, e.g. used a resin. In principle, however, the use of thermoplastic matrix materials is also conceivable.

The skeleton preform makes it possible to use fiber materials only where a fiber reinforcement in the component is necessary. Preferably, the webs of the skeleton preform along the load paths of the component are arranged. It is particularly preferred if the skeleton preform is produced by juxtaposing and stacking strips of semifinished fiber product, wherein each web includes a plurality of strips stacked on top of each other. The semi-finished fiber products are preferably semifinished products with oriented long fibers or continuous fibers. The semi-finished fiber products may e.g. present as a scrim, tissue or braid. The reinforcing fibers are all known reinforcing fibers, e.g. Carbon fibers, glass fibers or aramid fibers or metallic reinforcing fibers in question. To achieve high component stiffnesses, carbon fibers are preferably used - alone or in combination with other fibers.

By first cutting strips from the semifinished fiber product, the waste can be reduced to a minimum. By choosing the strip width and length can be very easily webs of different shapes are formed, even the placement of the strip in curved gradients is possible. The storage of the strips to the skeleton preform may e.g. through direct fiber placement (DFP).

Preferably, each textile layer of a web is formed by a strip. However, two or more strips next to each other can form a textile layer of a web.

Each web is formed by a plurality of stacked strips of semi-finished fiber. The strips may be loose on each other or fixed together, e.g. by sewing or a binder. The strips are preferably deposited along the central longitudinal axis of the web and stacked one above the other. To achieve high strengths, it is particularly preferred if strips are used which extend over the entire length of a web. However, individual layers may also be formed by two or more juxtaposed strips, as well as e.g. Also strips are stored transversely to the central longitudinal axis or at an angle inclined to the central longitudinal axis.

The cross section of the webs (viewed transversely to the central longitudinal axis) is e.g. determined by the choice of the width and number of stiffeners and by the arrangement of the strips to each other.

In a preferred embodiment, it is provided that reduces the height of the webs in the throttle area from the sprue to the outside. In other words, the webs may have a cross section which has the greatest height in the sprue area and whose height decreases towards the sides. If the web is then compacted, the fiber material excess in the region of lesser height causes a greater increase in the fiber volume fraction than in the case of greater web height. It can e.g. In a particularly simple manner, a quasi-continuous increase in the throttle effect can be realized within the throttle area. Together with the reduced flow cross-section (due to the reduced height), the impregnation of the fiber material can be ensured even with webs with high height to width ratio.

It may be particularly advantageous if the webs in the throttle area before compaction have a step-shaped height change and this is compacted in the closed mold to a continuous change in height. In other words, the webs of the skeleton structure prior to compaction may have a step-shaped outer contour, which is then pressed to produce the throttle region in the mold cavity such that the compacted webs in the throttle region have no stepped, but a continuous surface profile. By selecting the height of the steps, the degree of compaction can be regulated in a particularly simple manner. At the end of each stage, there is a particularly large amount of material surplus, so that a particularly high proportion of fiber volume occurs below this area when the skeletal preform is compacted. It has been found that the provision of several stages is a particularly simple means of regulating the throttling effect. By choosing the height of the steps and varying the overhang of the steps, the flow behavior of the matrix in each web of the skeletal preform can be easily regulated.

For achieving the above-described overcompaction, it has been found to be particularly advantageous if the webs are compacted in the mold so that the width of their cross-sections in the compacted outer region is continuously reduced. In other words, the mold cavity has a continuous contour in the region of the step-shaped contour of the preform, so that closing the mold causes the steps to disappear and instead a continuous transition takes place. In the area of the steps, there is overcompaction, but this varies over the depth of the steps. It has been found that the above-described effect in the manner of a semi-permeable membrane is achieved particularly effectively by this form of overcompaction.

The step-shaped height change of the webs can optionally be formed on only one side (top or bottom). In one embodiment, an even greater throttle effect is generated by the step-shaped height change of the webs in the throttle area is formed by the provision of stages both on an upper side of the webs, as well as on the opposite bottom.

The step-shaped height change of the webs is particularly easy to produce by layers of semi-finished fiber with different widths are stacked on each other. Thus, e.g. To achieve a particularly fine gradation in each layer of semi-finished fiber, the width of the web can be reduced. However, two or more layers of identical width may be stacked on top of each other.

Further advantages, features and details of the invention will become apparent from the following description in which, with reference to the drawings, embodiments of the invention are described in detail. The features mentioned in the claims and in the description may each be essential to the invention individually or in any desired combination. If the term "can" is used in this application, it is both the technical possibility and the actual technical implementation.

• 1 schematische Skelett-Preform
• 2 Draufsicht auf die Skelett-Preform im Formnest
• 3 Schnitt A-A durch die Skelett-Preform von 1
• 4 Schnitt B-B der Skelett-Preform im geschlossenen Formwerkzeug und
• 5 Schnittansicht eines mit dem Verfahren hergestellten Faserverbundbauteils.

Embodiments will be explained below with reference to the accompanying drawings. Show:

• 1 schematic skeleton preform
• 2 Top view on the skeleton preform in the form nest
• 3 Cut AA through the skeletal preform of 1
• 4 Section BB of the skeletal preform in the closed mold and
• 5 Sectional view of a fiber composite component produced by the method.

1 shows an exemplary skeletal preform 1 as a truss-like structure with several webs 2 . 3 . 4 . 5 . 6 which are arranged at right angles to each other. This form of skeletal preform is exemplary, other forms and arrangements of webs, such as oblique arrangements or curved courses are also conceivable, as bionic structures. Preferably, the webs run along the main load paths in the fiber composite component to be produced.

The skeletal preform 1 gets into a mold 10 where they are in the mold nest 11 between the two mold halves 12 . 13 of the mold 10 (S. 4 ) is recorded. 2 shows a schematic plan view of the mold half 13 as well as the skeleton preform placed on it 1 , The skeletal preform covers only part of the mold cavity 11 - There remain cavities 14 . 15 . 16 . 17 . 18 . 19 , which are formed in the later part as pure matrix areas without fiber reinforcement.

Is the mold 10 closed, so the matrix material via a distribution system 20 with several matrix distribution channels 21 to 25 added. The matrix distribution channels are, for example, in one or both mold halves 12 . 13 of the mold 10 intended. To explain the location of the distribution system 20 in relation to the skeletal preform 1 are the matrix distribution channels 21 to 25 in 2 additionally marked. The distribution channels 21 to 25 each run in a central longitudinal region of the webs 2 to 6 , As a result, a shortening of the flow paths is achieved, which must cover the matrix material in the webs.

3 shows a sectional view AA through the skeletal preform 1 , Every jetty 2 . 3 . 4 . 5 . 6 is made up of several superimposed strips (named by way of example) 100 . 101 . 102 . 103 , ...) formed by semifinished fiber. Preference is given to using semi-finished fiber products with oriented long or continuous fibers. The strips can lie loosely on one another or be fixed by a binder or seams, for example. In an upper region (with respect to the subsequent injection of matrix material) and in a lower region, strips of decreasing width are stacked on each other, so that a cross section with a step-shaped height change 7 results.

4 shows the cross section AA the skeletal preform 1 with closed mold 10 , The feeding of the matrix material 30 takes place via the distribution channels 21 to 25 , The distribution channels can, as in 4 shown, in particular be formed as grooves, the skeleton preform 1 are open. The matrix material 30 passes through the distribution channels 21 to 25 in contact with the skeletal preform 1 and spreads there in a sprue area 40 out, along the middle longitudinal areas of the webs 2 to 6 extends and extends over the entire bridge height.

The bridges 2 . 3 . 4 . 5 . 6 be through the mold 10 compacted. In the area of the stepped height change 7 an excess of fiber material is provided, which is pressed in the mold, partially overcompacted. This creates a throttle area 42 in which the fiber volume content is increased. The formerly stepped outer contour of the webs is through the mold halves 12 . 13 compressed so that the height of the webs no longer stepped, but continuously changes. The wall of the mold halves is provided in this area, for example, with a slope.

The throttle area 42 is laterally surrounding the sprue area 40 formed, which - in the plan view of the preform located in the mold - a contiguous gate area 40 which results laterally completely from the throttle area 42 is surrounded.

In the throttle area there is an increased flow resistance for the matrix material 30 , Therefore, this is distributed via the feed channels 21 to 25 infiltrated matrix material 30 first in the sprue area 40 and slowly spreads through the throttle area 42 in the direction of the sides, so that no air is trapped in the semi-finished fiber. The cavities 14 to 19 next to the skeletal preform are filled with matrix material, with a backflow into the skeletal preform 1 due to the throttle area 42 is prevented (indicated by the crossed out arrows in 4 ).

In the illustrated embodiment, the matrix material flows 30 on the sides of the webs of the rib preform 1 and fill the cavities 14 to 19 , The cavities 14 to 19 can also be filled by further matrix material, that via a separate second distribution system directly into the cavities into the mold cavity 11 is introduced.

A plan view of the resulting fiber composite component 50 is in 5 shown. It contains a flat plastic body 52 from matrix material into which the skeleton preform 1 provided fiber reinforcement 54 is integrated. Optionally, the fiber composite component 50 eg with functional elements in the form of webs 56 or attachment elements 58 be provided, for example, by the matrix material 30 to be trained with.

LIST OF REFERENCE NUMBERS

1

Skeletal preform

2 to 6

Stege

7

stepped height change

10

mold

11

cavity

12, 13

mold halves

14 to 19

cavities

20

distribution system

21 to 25

Matrix distribution channels

30

matrix material

40

Angus area

42

throttle region

50

Fiber composite component

52

flat plastic body

54

fiber reinforcement

56

rib

58

connecting element

100, 101, ...

Strip of semi-finished fiber

Claims (10)

A method for producing a fiber composite component (50), which has a planar plastic body (52) of matrix material (30) with embedded fiber reinforcement (54) in skeleton form, including a skeleton preform (1) in a mold cavity (11) of a molding tool (10 ) is compacted and infiltrated with matrix material (30) and the fiber composite component is produced with curing of the matrix material, comprising the steps: producing a skeletal preform (1) with a plurality of interconnected webs (100, 101, ...), infiltrating the skeleton -Preform (1) with matrix material (30), what this in a runner (40) in the Skeleton preform (1) is introduced, which extends along the central longitudinal regions of the webs (100, 101, ...), from where the matrix material (30) in the skeletal preform (1) propagates. wherein by providing an excess of material on the skeletal preform (1) and compacting the same, a throttle region (42) is created which extends laterally around the sprue area (40) of the skeletal preform (1) and in which the fiber volume fraction relative to the fiber volume fraction in the Gating area (40) is increased. Method according to Claim 1 in which the matrix material (30) is supplied via a distribution system (20) having a plurality of distribution channels (21, 22, 23, 24, 25). Method according to Claim 2 in which the distribution channels (21, 22, 23, 24, 25) are formed as grooves, which are open to the skeleton preform (1). Method according to one of the preceding claims, wherein the matrix material (30) from the skeleton preform (1) emerges and filling of cavities (14, 15, 16, 17, 18, 19) in the mold cavity (11) the plastic sheet body ( 52). Method according to one of the preceding Claims 1 to 4 in which, after the infiltration of the skeletal preform (1) with matrix material (30), further matrix material adjacent to the skeletal preform (1) is introduced into the mold cavity (11) to form the two-dimensional plastic body (52). Method according to one of the preceding claims, wherein the skeletal preform (1) is produced by juxtaposing and stacking strips (100, 101, ...) of semifinished fiber products, each web having a plurality of strips (100, 101, ... ) includes. Method according to one of the preceding claims, wherein the height of the webs (2, 3, 4, 5, 6) reduces in the throttle region (42) from the sprue area (40) to the outside. Method according to Claim 7 , wherein the webs (2, 3, 4, 5, 6) in the throttle region (42) prior to compaction, a step-shaped height change (7) and this compacted in the closed mold (10) to a continuous change in height. Method according to Claim 8 in that the stepped height change (7) of the webs (2, 3, 4, 5, 6) in the throttle region (42) is formed by the provision of stages both on an upper side of the webs, as well as on the opposite bottom. Method according to Claim 8 or 9 , to produce the step-shaped height change (7) strips of semi-finished fiber with different widths are stacked on each other.

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