WO2010069084A1

WO2010069084A1 - Method for producing a dimensionally stable hollow body of composite material

Info

Publication number: WO2010069084A1
Application number: PCT/CH2008/000537
Authority: WO
Inventors: Bodo Fiedler; André CARTIER; Gregor Peikert
Original assignee: Ruag Aerospace Ag
Priority date: 2008-12-16
Filing date: 2008-12-16
Publication date: 2010-06-24

Abstract

The invention relates to a method for producing dimensionally stable hollow bodies of composite material (2) by applying compactable material (17) on a dimensionally stable mould core (1). The mould core (1) with the material (17) applied thereon is surrounded by a mould (8), the material (17) being pressed against the mould (8) by heating the mould core (1) which thermally expands during the operation. While the material (17) is pressed against the mould by the thermally expanded mould core (1), it is solidified so that it forms the dimensionally stable hollow body of composite material (2) that is to be produced. After solidification of the material (17), the mould (8) is removed and the mould core (1) is removed from the cavity formed by it in the hollow body (2), whereby the dimensional stability of the mould core (1) is revoked. The method according to the invention allows for the first time to produce high-strength and very light, dimensionally stable hollow bodies of composite material with undercut cavities, which have precisely defined inner and outer contours and narrow wall thicknesses.

Description

Process for producing a dimensionally stable composite hollow body

TECHNICAL AREA

The invention relates to a method for producing a dimensionally stable composite hollow body according to the preamble of patent claim 1.

STATE OF THE ART

It is known to produce dimensionally stable composite hollow bodies in that a solidifiable material is placed on a mold core and then solidified. As a result, it is typically possible to produce hollow bodies with a precisely defined inner contour, but whose outer contour is relatively undefined.

If a hollow body having a precisely defined outer contour is to be produced with such a method, the mold core is enclosed with a mold after the application of the solidifiable material and the material is pressed against the inner wall of the mold before and during solidification. This happens in that a tube-like casing arranged between the actual mold core and the applied material is placed under an overpressure and thereby presses the material against the mold. In this case, however, the solidifiable material is lifted off the actual mold core, so that it may, before solidification of the material to a material shift, eg due to gravity come, with the result that the finished hollow body has an imprecise inner contour and Undefined wall thicknesses, which especially in heavily loaded components for aerospace is not tolerable. Furthermore, in the above methods, in particular in the production of hollow bodies with terschnittenen inner contours, the problem that the mandrel after solidification of the material in its existing form can not be removed from the hollow body formed around it.

A solution to this problem is known from EP 0 370 472 A2. To produce a composite hollow body, a mold core made of polystyrene is tightly enclosed by a first plastic film. Several layers of a fabric material impregnated with a curable binder are then placed on this plastic film and the whole is then arranged in a mold. This mold is enclosed by a second plastic film, within which a negative pressure is generated, while the interior of the first plastic film is kept at atmospheric pressure, so that the fabric layers are lifted from the first plastic film from the mold core and pressed against the walls of the mold. Subsequently, the binder of the fabric material is cured by heating, at the same time the polystyrene core shrinks or coincides, so that its remains can be easily removed from the finished hollow body. Although this method allows the production of composite hollow bodies with undercut inner contours, but otherwise also has the aforementioned disadvantages of the prior art. Another disadvantage of this method is that a multiple use of the mandrel or the mold core material system is excluded from the outset.

PRESENTATION OF THE INVENTION

It is therefore the object to provide a process for the production of dimensionally stable composite hollow bodies which does not have the disadvantages of the prior art or at least partially avoids it. This object is achieved by the method according to

Claim 1 solved.

Accordingly, the inventive method for producing a dimensionally stable composite hollow body comprises the following steps: In a first step, a dimensionally stable

Mold core provided, which has an outer contour, which corresponds substantially to the desired inner contour of the composite hollow body to be produced. Then, a solidifiable material or layers of material is placed on the dimensionally stable mold core, e.g. several layers of a soaked with epoxy resin fabric material.

In a further step, the formstable mandrel with the solidifiable material placed thereon is surrounded with a shape whose inner contour corresponds to the desired outer contour of the hollow body to be produced.

In this state, the solidifiable material arranged on the dimensionally stable mold core is attached to the

Pressed inner contour of the mold by the mold core or at least a part thereof is heated and thereby thermally expands. The pressing force required for pressing the material against the inner contour of the mold is thus provided exclusively by the fact that at least part of the material forming the dimensionally stable mandrel is heated and expands as a result of the heating.

As the solidifiable material is pressed against the inner contour of the mold by the thermally expanded mandrel, it is solidified to form a dimensionally stable composite hollow body (to be produced).

After solidification of the solidifiable material to the dimensionally stable hollow body is in further

Steps the shape, which the hollow body in Verfesti- gene has removed, and the mandrel removed from the cavity formed by this in the hollow body, for which purpose to facilitate or allow removal of the dimensional stability of the mandrel is repealed.

In other words, the invention düng thus relates to a method for producing dimensionally stable composite hollow body by applying solidifiable material to a dimensionally stable mandrel. The mold core with the material placed thereon is surrounded with a mold, wherein the material is pressed against the mold by the mold core is heated and thereby thermally expands. As the material is pressed against the mold by the thermally extended mandrel, it is solidified to form the dimensionally stable composite hollow body to be made. After the material has been solidified, the mold is removed and the mold core is removed from the hollow space formed by it in the hollow body, for which purpose the dimensional stability of the mold core is removed.

With the method according to the invention, it becomes possible for the first time to produce high-strength and very light dimensionally stable composite hollow bodies with undercut cavities which have precisely defined internal and external contours and tightly tolerated wall thicknesses. In a preferred embodiment of the method, further solidifiable material is introduced into the region between the dimensionally stable mold core and the mold prior to solidification of the applied settable material, for example by means of injection, which is subsequently solidified together with the solidifiable material already present in this region. In this way, a pore-free composite material can be formed, the surface of which meets the highest demands. In a further preferred embodiment of the method, the aforementioned method Steps repeatedly performed using the same mold core or mold core material or at least the essential components of the mold core, for producing a plurality, preferably identical dimensionally stable composite hollow body. Multiple use saves costs and material.

In yet another preferred embodiment of the method, an undercut dimensionally stable mold core is provided, and thus a dimensionally stable composite hollow body having an undercut NEN inner contour is produced. The provided mold core thus has such an outer contour that it can not be removed from the cavity formed by it after solidification of the material in its shaping form. In such embodiments, the advantages of the invention are particularly evident.

In yet another preferred embodiment of the method, an outer mold is used which, preferably circumferentially, is divided one or more times. This makes it possible to produce dimensionally stable composite hollow bodies with a rear-cut outer contour.

In a first preferred embodiment variant of the method, a dimensionally stable mold core is provided, which has been formed by evacuating a flexible sleeve of a substantially incompressible material which is filled with a free-flowing, substantially incompressible bulk material. This solidification effect of an evacuated envelope filled with loose bulk material is known, inter alia, from vacuum-packed coffee. The mold core thus formed is dimensionally stable as long as the vacuum is maintained inside the flexible casing. After the solidifiable material has solidified to form the dimensionally stable composite hollow body, the vacuum in the flexible sheath is removed for removing the mandrel from the hollow body and at least part of the bulk material is removed from the shell before the hollow body is removed flexible sheath is removed from the cavity. This makes it possible to produce with the inventive method composite hollow body with heavily undercut inner contours, the flexible shell and the bulk material can be used several times. It is further preferred that the removal of bulk material from the flexible shell takes place exclusively by gravity, so that can be dispensed with costly facilities for this purpose. Further, it is preferable that the flexible

Case after removal of at least a portion of the bulk material is evacuated from its interior, making it easier to remove from the hollow body formed around it. As a result, in particular the removal of the casing from undercut cavities is facilitated.

In a second preferred embodiment variant of the method, a dimensionally stable mold core is provided, which is formed with a flexible envelope of a substantially incompressible material within which a solid body of an incompressible material is removably arranged. To remove the dimensional stability of the mandrel and to remove the mandrel from the hollow body, the solid body is wholly or at least partially removed from the flexible shell. In order to allow removability of the solid from the flexible sheath, the solid body and the solid-receiving cavity in the flexible sheath in the removal direction without undercuts, for example cylindrical, are formed. It is also conceivable to form the solid such that its outer contour can be changed to remove or this can be removed in individual parts of the flexible sheath. Furthermore, it is also conceivable that the solid body is helically formed and the flexible shell has a corresponding blind hole-like cavity for receiving the same, wherein it can also be provided that this cavity is widened radially when screwing the solid. This variant of the inventive method is particularly suitable for the production of dimensionally stable composite hollow bodies with not or only slightly undercut cavity contours and has the advantage that the mandrel can be used multiple times and no processes are required for the formation and removal of the mandrel, which typically generate dust or dirt, so that this variant is also ideal for the production of composite hollow bodies under clean room conditions.

Advantageously, the flexible sheath is made of a material with a thermal coefficient of linear expansion at 2O ⁰ C in the range between ΞOxlO ^"5 / ^ ¹ and 35OxIO ^-6 ZK ^{" 1} , preferably between 20OxIO ^-6 ZK ^"1 and 30OxIO ^-6 ZK ^{" 1} , formed, preferably of a thermoplastic elastomer, rubber, latex or silicone. With such materials can be at reasonable wall thickness of the flexible envelope, by heating, for example, starting from room temperature to 100 ⁰ C to 200 ⁰ C relatively large thermal expansions of the flexible sheath produce, which is desirable to allow the largest possible pressing ability.

Preferably, the flexible sheath has a minimum thickness of 5 mm, preferably of 10 mm, in its shaping area.

In order to ensure a good contact pressure of the material placed on the mold core on the mold core, it is preferred that the ratio of the thickness of the flexible casing to the thickness of the solidified material layer of the finished hollow body is greater than 5.

In a third preferred embodiment variant of the method, a dimensionally stable mold core is provided, which at least partially consists of a material whose melting point is below a temperature lies, in which the material of the finished produced by the process hollow body is damaged or destroyed. To cancel the dimensional stability of the mandrel and to remove it from the hollow body of the mandrel or at least a portion of the mandrel is melted. Solid molding cores of thermoplastic elastomers are particularly suitable for this process variant. After melting of these mandrels in order to remove them from the respective cavity formed by them, the slotted material can be formed with advantage in a directly subsequent operation again by pouring into a mold to form a new mandrel.

Of course, combinations of the aforementioned embodiments and variants are provided. Thus, e.g. in the second embodiment of the arranged in the flexible shell solid may be formed of a material which, as taught in the third embodiment, can be removed by melting, without thereby the hollow body produced takes damage. In a further preferred embodiment of the method according to the invention, a fabric impregnated with a solidifiable binder is placed on the mold core, preferably an impregnated fiber fabric or scrim, preferably of carbon fibers. As a result, lightweight, high-strength composite hollow body can be produced, as required for example in aerospace.

It is advantageous that a fabric is applied, which is impregnated with a thermosetting resin, preferably with epoxy resin. In general, it is preferred if the solidifiable material is solidified by heating, even with materials which would solidify after a long time without heating. This makes it possible to heat the

Mold core for pressing the solidifiable material to the mold and heating the solidifiable material for solidifying the same in a common heating step and thereby save energy and / or time.

BRIEF DESCRIPTION OF THE DRAWINGS

Further embodiments, advantages and applications of the invention will become apparent from the dependent claims and from the following description with reference to the figures. Showing:

1 shows a vertical section through a molding tool for forming a dimensionally stable mold core for use in a first embodiment of the method according to the invention in a first state;

FIG. 2 shows a vertical section through the mold of FIG. 1 in a second state; FIG.

3 shows a vertical section through the mold of FIG. 2 after the application of solidifiable material; FIG.

4 shows a vertical section through the mold of Figure 3 with the occupied mold core arranged in a mold.

5 shows a vertical section through the mold of FIG. 4 with a dimensionally stable hollow body arranged on its mold core after removal of the mold in a first state;

6 shows a vertical section through the mold of FIG. 4 with a dimensionally stable hollow body arranged on its mold core after removal of the mold in a second state; FIG.

7 shows a vertical section through a dimensionally stable mold core and a mold when carrying out a second embodiment variant of the method according to the invention; and 8 is a vertical section through, a dimensionally stable mold core and a mold when carrying out a third embodiment of the inventive method.

WAYS FOR CARRYING OUT THE INVENTION

A first preferred embodiment of the method according to the invention is set out below with reference to FIGS. 1 to 6.

1 shows a vertical section through a molding tool for forming a dimensionally stable undercut mandrel for the production of a dimensionally stable hollow body by applying solidifiable material and then solidifying the material to form a dimensionally stable composite hollow body. In this case, the mold is shown in Fig. 1 in an upright ground state, in which it does not form a dimensionally stable mold core. As can be seen, the mold has a container 5, 7, 9, 18 with a rotationally symmetrical vacuum-tight interior 3, which is formed by a flexible sleeve 5 made of rubber and a bulk material reservoir 7, 9, 18. As can be seen, the flexible sheath 5 in the illustrated situation at room temperature and lying at ambient pressure interior 3 has an independent, defined outer shape, and has in the area which serves in their intended use of the molding of the hollow body to be formed, a wall thickness from approx. 6 mm.

The bulk material reservoir 7, 9, 18 has a bellows 18, which is arranged in a metal cup 7 and is firmly clamped on its upper side by means of the metal cup 7 and both pressure- and vacuum-tight on the edge of a metal lid 9. On its underside, the metal cup 7 has a ventilation opening 19. In the present case, the cup 7 and the lid 9 are made of stainless steel. However, it would be equally suitable For example, aluminum or fiber-reinforced plastic.

The cover 9 has a central passage opening 10, which widens in a funnel shape in the direction of the rolling bellows 18. The flexible sheath 5 forms at its end facing the rolling bellows 18 a flange portion 11, which is fastened by means of a mounting flange 12 and a plurality of fastening screws 13 pressure and vacuum tight on the top of the lid 9, such that the through hole 10 without sudden cross-sectional change in the inner contour of the flexible sheath 5 passes.

In the illustrated basic state, the part of the inner space 3 formed by the bellows 18 is approximately half filled with dry quartz sand 4. The interior 3 is connected via an opening 6 in the lid 9 with the environment in connection, ie under ambient or atmospheric pressure. The opening 6 has a filter element 14, which is designed such that, although air can be introduced into the interior 3 and removed from it, the quartz sand 4 can not pass through the opening 6.

Starting from the ground state shown in Fig. 1, the sand 4 by changing the position of the mold with respect to the direction of gravity so that the mold is oriented with the rolling bellows 18 upwards and with the flexible sheath 5 down, by gravity in free fall the rolling bellows 18 are displaced into the flexible sheath 5, wherein the funnel-shaped passage opening 10 in the lid 9 serves as a hopper. Is now in this state, the interior 3 of the

Forming tool evacuated via the opening 6 by means of a vacuum pump, the rolling bellows 18 is rolled back in the direction of the passage opening 10 until it rests on the passage opening 10 covering the sand 4. In this situation, which is shown in Fig. 2, the total volume of the inner space 3 is substantially equal the volume of sand in the interior 3 arranged amount of sand 4, and the flexible shell 5 with the sand contained therein 4 has solidified into a dimensionally stable body 1, which can serve as a mold core 1 for laying of solidifiable material. Fig. 3 shows a vertical section through the

Forming tool, after this was again oriented starting from the situation shown in Fig. 2 with the flexible sheath 5 upwards and after a pre-impregnated with epoxy resin carbon fiber fabric 17 (prepreg) was placed on the mandrel 1.

Fig. 4 shows a vertical section through the mold, after the dimensionally stable mold core 1 has been enclosed with the tissue 17 arranged thereon starting from the situation shown in Fig. 3 with a two-part mold 8, which as the inner contour of the desired outer contour of the composite hollow body to be produced having. In this case, the mold 8 surrounds a flange section 15 on the cover 9 of the container 5, 7, 9, 18 and is thereby fastened in a form-fitting manner to the molding tool. In this state, at least in places there is a small gap (not shown) between the inner contour of the mold 8 and the laid-up fabric material 17.

Starting from the state shown in Fig. 4, the entire assembly is heated in an oven of room temperature to about 180 ⁰ C and held at this temperature for a longer time. In this case, the flexible sheath 5 of the dimensionally stable mandrel 1 expands and thereby presses the fabric material 17 against the inner wall of the mold 8, while the epoxy resin impregnated with it hardens, so that the fabric 17 with the hardened epoxy resin contained therein then forms the dimensionally stable composite hollow body 2 to be produced.

Subsequently, the two-part mold 8 is removed and the interior 3 via the opening 6,. 14 connected to the environment. As a result of pressure equalization between Interior 3 and the environment, the sand 4 is mobile again and trickles back by gravity into the bulk material reservoir 7, 9, 18. The situation after performing these steps is shown in Fig. 5 in vertical section. FIG. 6 shows the molding tool with the composite hollow body 2 located thereon in vertical section in a situation after starting from the situation illustrated in FIG. 5 the interior space 3 has been placed under a slight vacuum via the opening 6. As can be seen, due to the vacuum in the inner space 3, the flexible sheath 5 has contracted in the cavity formed by it in the hollow body 2, while the rolling bellows 18 is held by the weight of the sand 4 at the bottom of the cup 7. In this state, the hollow body 2 can now easily lifted off the mold upwards or be deducted from the flexible sheath 5.

Of course, it is also possible to dispense with setting the interior space 3 under a slight vacuum to facilitate the lifting or removal of the cast hollow body 2, in particular even if no undercut cavities are formed with the mold core.

After the release of the slight vacuum in the interior 3 of the molding tool, the situation according to FIG. 1 automatically sets in again and the previously described sequence can be carried out anew in order to produce a further hollow body 2 with the same molding tool.

7 shows a vertical section through a dimensionally stable mold core and through a mold surrounding it when carrying out a second embodiment variant of the method according to the invention. As can be seen, the dimensionally stable mold core 1, on the outside of which, in turn, a fabric material 17 impregnated with a solidifiable binder, such as epoxy resin, is made of a flexible sheath 5 made of silicone, which has a cylindrical opening in its center. tion, in which as a solid body demanding a cylindrical copper tube 16 is arranged with an outer diameter corresponding to the inner diameter of the opening. The dimensionally stable mold core 1 thus formed with the fabric material 17 laid thereon is surrounded by a longitudinally split two-part mold 8, the inner contour of which corresponds to the desired outer contour of the hollow body to be produced. After enclosing the mold core 1 with the fabric material 17 arranged thereon with the mold 8 is at least in places between the outside of the fabric support 17 and the inside of the mold 8, a small gap (not shown), which then by heating the flexible sheath 5 and the resulting in thermal expansion of the sheath 5 is lifted, so that the impregnated fabric material 17 by the thermally extended flexible sheath 5 against the

Inner contour of the mold 8 is pressed. This state is maintained until the binder with which the fabric 17 is impregnated is solidified, whereby the fabric 17 then forms the dimensionally stable composite hollow body to be produced. The heating to expand the flexible sheath 5, which may also serve to solidify the applied impregnated fabric material 17 in thermosetting binders, may be e.g. by heating the entire assembly in an oven, or e.g. in that a heating element is introduced into the tube 16.

After the laid-up impregnated fabric material 17 is solidified, the mold 8 is removed and the tube 16 axially pulled out of the flexible sheath 5. Then, the flexible sheath 5 is axially removed from the hollow body formed by the solidified fabric material 17 under radial deformation, whereby the produced dimensionally stable composite hollow body is obtained as a single element. FIG. 8 shows a vertical section through a dimensionally stable mold core with a seal placed thereon. FIG. solidified material and by a surrounding this form when performing a third embodiment of the inventive method. In the present case, an identical composite hollow body as described with reference to Figures 1 to 6, but with a different embodiment of the method. As can be seen, here the dimensionally stable mandrel 1 consists of a solid mandrel made of a thermoplastic elastomer. The mold 8 is identical to the mold shown in FIG. 4. As in the previously described embodiments of the method according to the invention, after placing the solidifiable material 17 on the mold core 1, it is surrounded by the material 17 placed thereon with a mold 8 whose inner contour corresponds to the desired outer contour of the hollow body to be produced. After this enclosing there is at least in places between the outside of the material support 17 and the inside of the mold 8, a small gap (not shown), which is then canceled by heating the dimensionally stable mold core 1 and the resulting thermal expansion thereof, so that the solidifiable Material 17 is pressed by the extended mold core 1 against the inner contour of the mold 8. This state, which is shown in Fig. 8, is maintained until the material 17 is solidified, whereby this material 17 then forms the dimensionally stable composite hollow body to be produced. The heating to expand the dimensionally stable mandrel 1 takes place here by heating the entire arrangement shown in FIG. 8 in an oven to a temperature which is significantly below the melting temperature of the material of the dimensionally stable mandrel and also serves to cure the epoxy resin, with which the carbon fiber fabric 17 is soaked.

After the laid-up fabric material 17 has solidified, the temperature in the furnace is raised to a temperature which is above the melting point of the material of the mold core 1 and below the damage temperature of the mold core. fixed fabric material 17 is located, wherein the mandrel 1 is melted and the fabric material 17 is further solidified. Subsequently, the entire arrangement is removed from the oven and the now liquid material of the mold core 1 is removed by pouring out of the cavity formed by the mold core. Then, the mold 8 is removed around the formed composite hollow body, whereby it is then present as a single element.

While preferred embodiments of the invention are described in the present application, it should be clearly understood that the invention is not limited to these and may be practiced otherwise within the scope of the following claims.

Claims

1. A process for producing a dimensionally stable composite hollow body (2), comprising the steps of: a) providing a dimensionally stable mold core

(D; b) placing solidifiable material (17) on the dimensionally stable mandrel (1); c) enclosing the dimensionally stable mold core (1) with the solidified thereon

Material (17) having a shape (8) whose inner contour corresponds to the desired outer contour of the hollow body (2) to be produced; d) pressing on the dimensionally stable form core (1) arranged solidifiable material (17) to the inner contour of the mold (8) by heating and the consequent thermal expansion of at least a portion of the dimensionally stable mandrel

(D; e) solidifying the material (17) pressed onto the inner contour of the mold by the thermally extended dimensionally stable mold core (1) to form a dimensionally stable composite hollow body (2); f) removing the mold (8) from the hollow body (2); and g) removing the mold core (1) from the hollow body (2) while eliminating the dimensional stability of the mold core (1).

2. The method of claim 1, wherein prior to solidification of the applied solidifiable material (17) further solidifiable material in the region between the dimensionally stable mandrel (1) and the mold (8) is introduced, which subsequently together with the existing already in this area solidifiable material (17) is solidified.

3. The method according to any one of the preceding claims, wherein the steps a) to g) are repeatedly performed using the same mold core (1), for producing a plurality, in particular identical composite hollow body (2).

4. The method according to any one of the preceding claims, wherein an undercut dimensionally stable mold core (1) is provided and thus a dimensionally stable composite hollow body (2) is produced with a hinterschnit- tenen inner contour.

5. The method according to any one of the preceding claims, wherein a mold (8) is used, which, in particular circumferentially, is divided one or more times.

6. A method according to any one of the preceding claims, wherein a dimensionally stable mandrel (1) is provided which is filled with an evacuated flexible shell (5) of a substantially incompressible material filled with a flowable, substantially incompressible bulk material (4) is formed, and wherein for canceling the dimensional stability of the mandrel (1) and for removing the same from the hollow body (2), the vacuum in the flexible sheath (5) is released and at least a part of the bulk material (4) from the sheath (5 ) Will get removed.

7. The method of claim 6, wherein the removal of bulk material (4) from the flexible sheath (5) takes place exclusively by gravity.

8. The method according to any one of claims 6 to 7, wherein after the removal of bulk material (4) from the flexible sheath (5) the flexible sheath (5) is evacuated, to facilitate removal of the flexible sheath (5) from the hollow body (5). 2).

9. The method according to any one of claims 1 to 5, wherein a dimensionally stable mold core (1) is provided which is formed with a flexible sheath (5) made of a lent incompressible material, within which a solid body (16) of a incompressible Removable material is arranged and wherein for canceling the dimensional stability of the mandrel (1) and for removing the same from the hollow body (2) of the solid body (16) wholly or partially removed from the flexible sheath (5).

10. The method according to any one of claims 6 to

9, wherein the flexible sheath (5) made of a material having a thermal expansion coefficient at 20 ⁰ C in the range between ΞOxlO ^ / K ^"1 and 35OxIO ^-5 ZK ^{" 1} , in particular between 20OxIO ^-6 ZK ^"1 and 30OxIO ^-6 ZK ¹ , is formed, in particular from a thermoplastic elastomer, rubber, latex or silicone.

11. The method according to any one of claims 6 to

10, wherein the flexible sheath (5) has a minimum thickness of 5 mm, in particular of 10 mm.

12. The method according to any one of claims 6 to

11, wherein the ratio of thickness of the flexible sheath (5) to the thickness of the solidified material layer of the finished hollow body (2) is greater than 5.

13. The method according to any one of claims 1 to 5, wherein a dimensionally stable mold core (1) is provided, which consists at least partly of a material whose melting point is below a temperature at which the material of the finished produced by the process hollow body (2 ) is damaged or destroyed, and wherein for canceling the dimensional stability of the mandrel (1) and for removing the same from the hollow body (2) of the mandrel (1) or at least a part of the mandrel (1) is melted.

14. The method according to any one of the preceding claims, wherein a impregnated with a solidifiable binder fabric (17) is placed on the mandrel (1), in particular a fiber fabric or -gelege, in particular of carbon fibers.

15. The method according to claim 14, wherein a fabric (17) is applied, which is provided with a heat- solidifying resin, in particular with epoxy resin impregnated.

16. The method according to any one of the preceding claims, wherein the solidifiable material is solidified by heating.