FIELD OF THE DISCLOSURE

The present disclosure relates to a method and a device for the production of a hol low or partially hollow fiber composite part. BACKGROUND OF THE DISCLOSURE

Methods and devices for the production of hollow fiber composite products are known. In the known processes often an auxiliary body is used, which is inflated inside a mold to press the fibers arranged thereon against a wall of the cavity of the mold, before the part is cured to obtain its final shape. EP2227377B1 , published in the name of the applicant on 1 5.09.2010 shows a process and an apparatus for manufacturing components made of fiber compo sites, in particular hollow parts or parts with undercuts, by using three-dimension- ally preformed hollow blow molding cores, as a supporting and positioning aid for the fibers and/or prepregs to be processed. DE102007027755A1 , published in the name of BMW AG on 18.1 2.2008 shows a process for producing a fiber-reinforced plastic component, wherein a thermo plastic hollow core is at least partially coated with a layer of reinforcing fibers and a plastic matrix, which is subsequently cured. WO08034687A1 , published in the name of BSH Bosch and Siemens Home Appli ance GmbH on 27.03.2008 shows a method for producing a hot water reservoir wherein an optionally preformed plastic body is surrounded with a fibrous rein forcement material, feeding the surrounded plastic body into a supporting mold, 5 closing the supporting mold, tempering the supporting mold such that the plastic melts, applying a force inside the plastic body such thatthe molten plastic is pressed to the outside and together with the surrounding fiber material forms a hot water reservoir.

EP1009622B1 , published in the name of Volvo Personvagnar AB on 02.01 .2003 o shows a method for the molding of hollow bodies which comprise at least one layer of reinforced plastic. According to the disclosure, the method can be applied within different areas where there is a need for hollow bodies which comprise reinforced plastic, for example within the area of the manufacture of vehicle components made of reinforced plastic. 5 SUMMARY OF THE DISCLOSURE

A critical aspect of the production process of a hollow fiber composite part or an at least partially hollow non-closed fiber composite part based on the aid of an inflat able auxiliary body is to accurately position the arrangement of the fibers on the auxiliary body during production. The term partially hollow fiber composite part is directed to a non-closed concave body which is only partially surrounding the aux iliary body during production.

Especially when producing products with non-closed bodies or components with undercuts, unwanted slipping or wrinkling of the fibers during expansion of the auxiliary body by inflating and the thereby pressing of the fibers against an inner surface of the cavity of a mold, has to be avoided to obtain a high degree of shape retention and optical appearance from the outside.

To be able to interconnect the fibers to the auxiliary body and keep the fibers in position, usually auxiliary layers or adhesives are used in the processes known from the prior art. These auxiliary layers and adhesives often remain on the component or have to be removed in an additional process step. Depending on the desired properties of the final product, these additional layers or adhesives can be prob lematic as they usually mix with the resin of the matrix. These inclusions can dete riorate the mechanical properties of the composite part or negatively influence the aesthetic properties, e.g. when the fibers of the composite product shall be visible from the outside across at least partially transparent matrix material.

In the method according to the present disclosure, for producing of a hollow or an at least partially hollow fiber composite part at least one layer of reinforcing fibers is embedded in a matrix material. At least one balloon-shaped inflatable auxiliary body is provided which encompasses a closed volume and is at least partially made from e.g. an expandable film. One advantage of the method is that fiber composite parts with highly variable surface geometries can be produced. Also fiber compo site parts can be produced wherein the balloon-shaped inflatable auxiliary body is only partially covered. In a variation of the method preformed auxiliary layers can be arranged between an outer surface of the auxiliary body and the at least one layer of reinforcing fibers. In the following throughout the present disclosure the term auxiliary body is used as a substitute for the term balloon-shaped inflatable auxiliary body. The terms are to be regarded as mutually interchangeable and equivalent. The auxiliary body is preferably produced from a thermally deformable material. Depending on the application typically the following materials can be used: e.g. polypropylene (PP), polyethylene terephthalate (PET), polycarbonate (PC), polyamides (PA), polymethyl methacrylate (PMMA), polybutylene tereph thalate (PBT, PBTP), polyurethane (PUR), acrylic films. The material is chosen de pending on the manufacturing process of the auxiliary body. In a preferred varia tion the auxiliary body can comprise at least one opening for the introduction of a fluid to increase the internal volume. Alternatively, or in addition the auxiliary body can also be inflated by using a propellant to increase the internal volume.

The auxiliary body usually comprises an outer surface with at least one zone which is suitable to receive a retaining clip therein. The use of a retaining clip e.g. allows to produce fiber composite parts with undercuts, such that all outer sides of the hollow or at least partially hollow fiber composite part have a flawless surface. As the retaining clip locally fixates the at least one layer of reinforcing fibers to the at least one zone, unwanted slipping and wrinkling can be avoided or at least be sub stantially reduced.

As the auxiliary body is made as a balloon-shaped inflatable auxiliary body, the outer surface of the expandable film should usually not be penetrated in an un- wanted manner, e.g. by penetrating the outer surface by the retaining clip. Holes caused for example by the retaining clip could cause a leakage of the balloon shaped body, preventing that the auxiliary body can be inflated in the desired man ner. Alternatively, an auxiliary body can be used wherein the outer surface has a construction with self-sealing properties. In an alternative variation or in addition, the retaining clip can be designed such that the holes caused by the penetration of the auxiliary body by the retaining clip, are sealed by the retaining clip itself such that no leakage occurs. It should be prevented that inflated fluid, e.g. air or a pro pellant, can leak from the internal volume of the balloon-shaped auxiliary body through such holes and negatively impact the quality of the fiber composite part. For example, inclusions, e.g. air bubbles in the matrix material, may deteriorate the mechanical and aesthetic properties of the fiber composite part. To avoid that the outer surface of the balloon-shaped auxiliary body is penetrated by the retaining clip, the at least one zone is preferably designed as a pad and/or a rib forming an integral part of the auxiliary body. Alternatively or in addition, the pad and/or rib can also be interconnected to the outer surface, e.g. by gluing or welding. In this variation the pad and/or rib may be arranged in form of a thickening which is de- signed such that an inserted retaining clip does not penetrate through the expand able film of the auxiliary body but only penetrates into the thickening. Good results can be achieved with the method when the at least one zone is designed as an insert which is embedded into the outer surface of the auxiliary body. Preferably a mount- ing surface of the insert is essentially flush with the surrounding outer surface of the auxiliary body. In a preferred variation of the method the at least one insert comprises an undercut designed to be at least partially encompassed by the ex pandable film of the auxiliary body. Good results can be achieved when the insert is made by a polymer in form of a chip or a rectangular plate. To make it easier for an operator to fix the at least one layer of reinforcing fibers onto the at least one zone of the auxiliary body with a retaining clip, the at least one zone can comprise an insert which is made of a softer material compared to the material of the auxiliary body.

During production at least one layer of reinforcing fibers is arranged on the outer surface of the auxiliary body and at least one layer of reinforcing fibers is fixed to the zone by at least one retaining clip from the outside. In a preferred variation the at least one layer of reinforcing fibers is applied in form of a dry woven fabric and/or in the form of continuous fibers. The dry woven fabric and/or the continuous fibers may be prepared by wrapping and/or in the form of prepregs. The fibers of the at least one layer of reinforcing fibers are typically bonded to one another by means of RTM by the matrix material. Therefore, a mold is provided which comprises a cavity and the auxiliary body and the thereon arranged at least one layer of rein forcing fibers is arranged at least partially in the cavity. The at least one layer of reinforcing fibers is arranged in a gap between the outer surface of the auxiliary body and an inner surface of the cavity. The auxiliary body is inflated to a defined extend and the gap and the therein arranged at least one layer of reinforcing fibers is flooded with a matrix material. Preferably a modified resin transfer molding pro cess (RTM) is used wherein the at least one layer of reinforcing fibers is typically a layer of dry fibers. Afterthe mold is closed preferably a resin-hardener mixture from a mixing and metering unit is injected between the outer wall of the cavity and the auxiliary body such that the at least one layer of reinforced fibers is impregnated. To increase the adhesion of the at least one layer of reinforcing fibers to the outer surface of the auxiliary body, the inner wall of the cavity of the mold can have a rough or textured surface. During the production of the fiber composite part, es pecially while flooding the gap with a matrix material, high forces are applied onto the retaining clip and the thereto interconnected zone. When the zone comprises an insert, the at least one insert can comprise an undercut to prevent that the at least one insert is detached form the auxiliary body by the high forces. Good results can be achieved when the undercut of the insert is designed as a chamfer. Alterna tively, also other geometries are possible. In another variation the at least one insert has a shape essentially formed like a mushroom on the side facing the closed vol ume of the auxiliary body. In a next step, the auxiliary body is inflated such that the gap is reduced and the at least one layer of reinforcing fibers is pressed against the inner surface of the cavity of the mold by the outer surface of the auxiliary body. Typically, by creating a pres sure difference, the at least one layer of reinforcing fibers is pressed against the outer wall of the cavity such that the fiber composite part acquires its final geome try. The pressure difference is preferably generated by filling the auxiliary body from the outside, e.g. by means of compressed air. Alternatively, or as a supplement, the auxiliary body is filled with a defined volume of gas and then sealed. In a preferred variation the cavity is vacuumed by at least one suction means to remove remaining air from the cavity. In a next step the matrix material is cured. The matrix material is typically cured by heating the mold to accelerates the curing of the injected resin (e.g. epoxy). One advantage of the resin transfer molding process according to the disclosure is that hollow blow molded fiber composite components and/or blow molded fiber composite components with undercuts can be produced. A further advantage is the possibility of producing complex geometries and/or to integrate functional components into the component (e.g. metal inserts as connecting ele ments). After curing the matrix material, the hollow or at least partially hollow fiber composite part comprising the at least one layer of reinforcing fibers embedded in the matrix material is removed from the cavity. Depending on the geometry and the desired mechanical and aesthetic properties, the auxiliary body can remain with the fiber composite part or alternatively be removed. In a preferred variation of the method the auxiliary body is removed from the fiber composite part outside of the cavity. Preferably, the auxiliary body is removed through an opening in the fiber composite part after the fibers have been bonded together by the matrix material.

Depending on the geometry of the desired fiber composite part, the auxiliary body can comprise undercuts or complex geometries. To make it easier for the operator to position the retaining clip at the at least one zone which is suitable to receive a retaining clip therein and to avoid that the auxiliary body is penetrated by the re taining clip in an unwanted manner, the method can comprise a positioning aid. Preferably , the positioning aid for the retaining clip is an auxiliary frame designed as a template for positioning the at least one retaining clip. After arranging the at least one layer of reinforcing fibers onto the outer surface of the auxiliary body, it is difficult to localize the exact position of the at least one insert. To prevent that the auxiliary body is damaged and leaks, the positioning aid can be used to localize the zone. Especially with geometries comprising an undercut, a positioning aid de signed as a template can be used which has an outer contour essentially corre- sponding to the contour of the undercut. Preferably such a template can be placed onto the at least one layer of fibers arranged onto the auxiliary body and comprises at least one cut-out that is arranged essentially congruent to the at least one zone, such that the retaining clip can be position stable interconnected to the at least one zone. Alternatively, the zone of the outer surface comprises a positioning aid for the retaining clip such that the retaining clip is arranged essentially centered at the at least one zone. Good results can be achieved particularly for an automated pro cess, wherein the retaining clip is fixed to the at least one zone of the auxiliary body. It can be beneficial if a positioning aid is arranged at or within the at least one zone. The positioning aid can be a RFID tag or any other radio element configured to guide a device for placing the retaining clip or indicate the position of the at least one zone to the device. The inflatable auxiliary body for producing a fiber composite part according the method of the present disclosure comprises an auxiliary body which is made from an expandable film and designed to encompass a closed volume and wherein the inflatable auxiliary body comprises an outer surface with at least one zone suitable to receive a retaining clip. In a preferred variation of the method the auxiliary body is formed by blow-molding an expandable film. Therefore, liquid plastic is typically pressed out of a nozzle in the form of a ring such that a tube is formed. After reach ing a certain length the tube is squeezed at the bottom end and then inflated after being placed in a closed blow mold provided for this purpose. Preferably the auxil iary body has a geometry which is designed being constantly or variably 1 % to 20% smaller than the geometry of the cavity of the mold.

In a variation where the zone of the auxiliary body comprises at least one insert, the at least one insert can preferably be placed within a tool. Good results can be achieved when the at least one insert is temporarily held inside a cavity of a tool to form the auxiliary body by at least one suction means such that the insert is drawn against the inner surface of the cavity. The at least one suction means may be de signed as a bore within the wall of the cavity of the tool. The suction means is con figured to pull the at least one insert against the wall of the cavity and to fix the at least one insert securely in position. After arranging the at least one insert in the tool, the preferably preformed balloon-shaped auxiliary body is placed in the tool. In a preferred variation the auxiliary body comprises at least one connector config ured to interconnect the auxiliary body to a counter connector arranged at the mold. After closing the production mold the at least one auxiliary body is inflated within the cavity of the production mold. The auxiliary body is pressed against the wall of the cavity of the tool and the tool is heated up such that the film of the aux iliary body at least partially plasticizes. Alternatively, also the auxiliary body can be inflated with a medium which is hot enough such that the auxiliary body at least partially plasticizes. The at least partially plasticized expandable film of the auxiliary body is configured to at least partially enclose the at least one insert. In a preferred variation the at least one insert is designed with an undercut. The undercut of the insert can be at least partially embedded by the at least partially practiced expand able film of the auxiliary body. When the auxiliary body is made by blow molding, the at least one insert may also be arranged within the blow-mold before the auxiliary body is blow molded. The insert can be arranged in the mold by a form lock or by a force lock. Preferably the at least one insert is arranged at the inner surface of the cavity of the blow-mold, such that the insert embedded into the expandable film and flush with the sur- rounding expandable film of the auxiliary body. Alternatively, the auxiliary body can be also made in a first step and the at least one insert is later on embedded into the auxiliary body. Therefore, the auxiliary body is heated up and at least partially plasticized such that the at least one insert can be encompassed by the at least par tially plasticized expandable film of the auxiliary body. The at least one insert can also be at least partially plasticized such that the material of the at least one insert and the material of the expandable film of the auxiliary body at least partially mix. At least one layer of reinforcing fibers is arranged on the outer surface of the aux iliary body and at least one layer of reinforcing fibers is fixed to the zone by at least one retaining clip from the outside. The auxiliary body is designed such that it is self-stable in an inflated state. A self-table auxiliary body has the advantage that the at least one layer of reinforcing fibers can be arranged on the outer surface and the at least one layer of reinforcing fibers can be fixed to the at least one zone by at least one retaining clip from the outside without the need to constantly keep the auxiliary body under pressure. Therefore, the auxiliary body can be blow molded, after the curing be removed from the mold and the at least one layer of reinforcing fibers can be arranged outside the mold. Depending on the production volume it can be more cost efficient to produce the auxiliary body by injection molding. Good results can be achieved when the auxil iary body is made from at least two parts which are interconnected to each other along at least one joint by welding or gluing. To be able to arrange a rib or a patch at the inner surface of the auxiliary body, the auxiliary body is preferably made from at least two parts. The two parts can be injection molded and joined together. Pref erably, the at least two parts are welded together in form of a butt-joint. Depending on the geometry of the desired fiber composite part, it is preferable to produce the auxiliary body with more than one chamber. In a preferred variation the auxiliary body comprises at least two chambers which chambers are fluidly interconnected to each other. As the auxiliary body is preferably made by injection and/or blow molding, in a variation wherein the auxiliary body comprises at least two chambers, the at least two chambers of the auxiliary body can be made in an integral manner. Alternatively, the at least two chambers can be made separately and joint together.

It is to be understood that both the foregoing general description and the following detailed description present embodiments, and are intended to provide an over view or framework for understanding the nature and character of the disclosure. The accompanying drawings are included to provide a further understanding, and are incorporated into and constitute a part of this specification. The drawings illus trate various embodiments, and together with the description serve to explain the principles and operation of the concepts disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS The herein described disclosure will be more fully understood from the detailed de scription given herein below and the accompanying drawings which should not be considered limiting to the disclosure described in the appended claims. The draw ings are showing:

Fig. 1 shows a schematic cross-sectional view of a first embodiment of the auxiliary body with thereon arranged layer of reinforcing fibers; Fig. 2 shows a schematic perspective view of a mold and an exemplary em bodiment of an auxiliary body with thereon arranged layer of reinforcing fibers for producing a fiber composite part;

Fig. 3 shows a schematic cross-sectional view of a mold and a therein placed auxiliary body for producing a fiber composite part;

Fig. 4 shows a schematic cross-sectional view of a cut-out of an auxiliary body and thereon fixed layer of reinforcing fibers;

Fig. 5 shows a schematic cross-sectional view of an embodiment of an auxil iary body with two chambers and a positioning aid; Fig. 6 shows a schematic perspective view of an exemplary embodiment of an auxiliary body with two chambers;

Fig. 7 shows a schematic cross-sectional view of a tool and a therein placed auxiliary body.

DESCRIPTION OF THE EMBODIMENTS Reference will now be made in detail to certain embodiments, examples of which are illustrated in the accompanying drawings, in which some, but not all features are shown. Indeed, embodiments disclosed herein may be embodied in many dif ferent forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Whenever possible, like reference numbers will be used to refer to like components or parts.

Figure 1 shows a schematic cross-sectional view of a first embodiment of the aux iliary body 4 with thereon arranged layer of reinforcing fibers 2. The shown auxil iary body 4 is designed as a balloon-shaped inflatable auxiliary body 4 for produc ing a fiber composite part 1 which is made from an expandable film 5 designed to encompass a closed volume. The shown auxiliary body 4 comprises an outer sur face 6 with several zones 7, wherein each zone 7 is designed to receive at least one retaining clip 8. As best visible in Figure 1 , the method for producing a fiber com posite part 1 comprises at least one layer of reinforcing fibers 2 which is then em bedded in a matrix material 3. The at least one layer of reinforcing fibers 2 is ar- ranged on the outer surface 6 of the auxiliary body 4 and fixed to the zone 7 by at least one retaining clip 8 from the outside. The zone 7 can be designed as a thick ening 13 or it can be designed as a pad 14 and/or a rib 1 5 and/or comprise an insert 16. In the shown embodiment the insert 16 is designed as a pad 14. The at least one zone 7 is made in an integral manner with the outer surface 6 of the aux- iliary body 4.

Figure 2 shows a schematic perspective view of a mold 9 and an exemplary em bodiment of an auxiliary body 4 with thereon arranged layer of reinforcing fibers 2 for producing a fiber composite part 1 . As best visible in Figure 2 a mold 9 is pro vided which comprises a cavity 10 in which cavity 10 the auxiliary body 4 and the thereon arranged at least one layer of reinforcing fibers 2 is arranged. Figure 3 shows a schematic cross-sectional view of a mold 9 and a therein placed auxiliary body 4 for producing a fiber composite part 1 . When producing the hollow or at least partially hollow fiber composite part 1 the shown auxiliary body 4 is inflated to a defined extend and the remaining gap 1 1 between the auxiliary body 4 and the inner surface 1 2 of the cavity 10 is flooded with a matrix material 3. The auxil iary body 4 is inflated such that the gap 1 1 is reduced and the at least one layer of reinforcing fibers 2 is pressed against the inner surface 1 2 of the cavity 10 of the mold 9 by the outer surface 6 of the auxiliary body 4. The shown mold 9 comprises a relief opening 29, which is designed such that excessive matrix material 3 is pressed out of the cavity 10 through the relief opening 29. After curing the matrix material 3 within the cavity 10 of the mold 9, the at least one layer of reinforcing fibers 2 embedded in the matrix material 3 is removed from the cavity 10. Depend ing on the geometry and purpose of the fiber composite part 1 , the auxiliary body 4 is removed from the fiber composite part 2 outside of the cavity 10.

Figure 4 shows a schematic cross-sectional view of a cut-out of an auxiliary body 4 and thereon fixed layer of reinforcing fibers 2. As best visible in Figure 4, the shown insert 16 comprises an undercut 18 which is designed to be encompassed by the expandable film 5 of the auxiliary body 4. In the shown embodiment the insert 16 is embedded into the outer surface 6 of the auxiliary body 4 such that a mounting surface 17 of the insert 16 is essentially flush with the surrounding outer surface 6. To increase the mechanical stability of the embedded insert 16, the undercut 18 of the insert 16 is designed as a chamfer 19 which is arranged substantially along the entire circumference of the insert 16. To make it easier for the user to insert the retaining clip 8, the insert 16 can be made from a softer material than the auxiliary body 4. Figure 5 shows a schematic cross-sectional view of an embodiment of an auxiliary body 4 with two chambers 26 and a positioning aid 27. As best visible in Figure 5, in another embodiment the auxiliary body 4 is made from at least two parts 24 which are interconnected to each other along at least one joint 25, pref- erably by welding or gluing. Figure 6 shows a schematic perspective view of an ex emplary embodiment of an auxiliary body 4 with two chambers 26. The at least two chambers 26 are preferably fluidly interconnected to each other. For a more precise fixing of the retaining clips 8, a positioning aid 27 for the retaining clip 8 can be used. The shown positioning aid 27 is designed as an auxiliary frame de signed as a template 28 for positioning the at least one retaining clip 8. Alterna tively, the zone 7 of the outer surface 6 can comprises a positioning aid 27 for the retaining clip 8 such that the retaining clip 8 is arranged essentially centered at the at least one zone 6.

Figure 7 shows a schematic cross-sectional view of a tool 20 and a therein placed auxiliary body 4. The shown auxiliary body 4 can be made by blow-molding an ex pandable film 5 and is designed such that it is self-stable in an inflated state. Pref erably the auxiliary body 4 can have a geometry which is designed being constantly or variably 1 % to 20% smaller than the geometry of the cavity 10 of the mold 9. The preformed auxiliary body 4 may be placed inside a cavity 21 of a tool 20 to form the auxiliary body 4. At least one suction means 23 is preferably arranged at and/or in the wall of the cavity 21 . The suction means 23 is configured to draw the insert 16 against the inner surface 22 of the cavity 21 of the tool 20. In the shown embodiment the at least one suction means 23 is designed as a bore within the wall of the cavity 21 of the tool 10 and fixes the at least one insert 16 securely in posi tion. The auxiliary body 4 is then pressed against the wall of the cavity 21 of the tool 20. In a first variation the tool 20 is heated up such that the expandable film 5 of the auxiliary body 4 at least partially plasticizes. Alternatively, the auxiliary body 4 can be inflated with a medium which is hot enough such that the auxiliary body 4 at least partially plasticizes. The at least partially plasticized expandable film 5 of the auxiliary body 4 is configured to at least partially enclose the at least one insert 16. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without depart ing from the Spirit and scope of the disclosure. LIST OF DESIGNATIONS

1 Fiber composite part 16 Insert

2 Layer of reinforcing fi- 20 17 Mounting surface bers 18 Undercut (insert)

5 3 Matrix material 19 Chamfer (undercut)

4 Auxiliary body 20 Tool

5 Expandable Film 21 Cavity (tool)

6 Outer surface (auxiliary 25 22 Inner surface (tool) body) 23 Suction means 0 7 Zone (outer surface) 24 Two parts (auxiliary

8 Retaining clip body)

9 Mold 25 Joint (auxiliary body)

10 Cavity (mold) 30 26 Two chambers (auxiliary

1 1 Gap body) 5 12 Inner surface (cavity) 27 Positioning aid

13 Thickening (zone) 28 Template (positioning

14 Pad aid)

1 5 Rib 35 29 Relief opening