METHOD FOR PRODUCING A DECORATIVE PART WITH A THREE-DIMENSIONALLY SHAPED SURFACE

Description

[0001] The invention relates to a method for producing a decorative part with a three-dimensionally shaped surface, a decorative part with a three-dimensionally shaped surface, and a system of forming tool and auxiliary film for forming an arc-shaped material that is not fluid-tight, in particular not gas-tight.

[0002] In vehicles, but also in other applications, decorative parts are used which originally utilize arc-shaped materials such as foils or veneers for a decorative layer that determines the visual appearance.

[0003] Since such decorative elements, or their visible surface and thus also their decorative layers, are often designed in three dimensions and therefore do not extend in just one plane, the foils or veneers must be transformed from their initially arc-shaped, i.e., essentially flat and planar, extension into a three-dimensionally deformed or stretched geometric shape suitable for the decorative element.

[0004] For such forming processes, high-pressure forming is often used in the prior art, as is known, for example, from EP 0 371 425 A2. According to this known method, an arc-shaped material is clamped into a forming cavity of a forming tool, as is known, for example, from DE 41 13 568 C1, and subjected to high pressure from one side by means of gas or air, so that the material is pressed against a forming part of the forming cavity, causing it to deform.

[0005] However, with veneers, i.e., with very thin, arched wood and generally with rigid, porous and / or crack-prone materials, the problem with the method proposed by EP 0 371 425 A2 is that the material itself is not, or at least not permanently, gas-tight. Consequently, when subjected to high pressure, the material is not reliably, or at least not sufficiently, pressed against the shaping part of the mold cavity, so that the material cannot be geometrically deformed in the required manner and reliably, and is unintentionally damaged.

[0006] Therefore, the document EP 2 322 339 A2 proposes the use of an auxiliary film which rests loosely on the arc-shaped material and seals it, so that the high pressure acts on the arc-shaped material via the auxiliary film. To position the arc-shaped material in the mold cavity, it is clamped between the tool halves of the forming tool, whereby predetermined breaking points and / or shrinkage zones are provided by cuts in the arc-shaped material, through which the arc-shaped material can deform as intended in the mold cavity despite being fixed by the tool halves.

[0007] However, this method has the disadvantage that the blanks, which must be provided from the arc-shaped material for forming, are comparatively large, as they must extend outwards from the mold cavity to be fixed in place. Furthermore, it is also disadvantageous that the blank, made of arc-shaped material that is potentially prone to cracking, must be positioned along the sealing surfaces of the forming tool, thus complicating the sealing of the mold cavity.

[0008] These disadvantages lead on the one hand to a waste of material and on the other hand to the need for a comparatively elaborate sealing of the mold cavity, resulting in overall higher manufacturing costs and increased maintenance requirements.

[0009] Methods for manufacturing a decorative part and decorative parts manufactured by such methods are also known from document US 4,447,282 A. Furthermore, methods for manufacturing a decorative part and aspects of such methods are also known from documents WO 2003 / 082546 A2, DE 3727926 A1, JP S55-121034 A and JP S60-157838 A.

[0010] The invention is therefore based on the objective of overcoming the aforementioned disadvantages and providing a method for the cost-effective and simple production of a decorative part with a three-dimensionally shaped surface starting from an arc-shaped and non-fluid-dense material, which is particularly prone to cracking.

[0011] This problem is solved by the combination of features according to claim 1.

[0012] According to the invention, a method for producing a decorative element is proposed, wherein the decorative element has a three-dimensionally shaped surface and the method starts with an arc-shaped material that is at least not permanently fluid- or gas-tight. The material is preferably a porous, rigid, and / or crack-prone material, in particular a natural material, and more specifically wood. The material can also be a veneer. The term "arc-shaped" or "arc-formed" is understood to mean that the material initially exists, for example, as a thin layer, like a sheet of paper, and extends essentially in a flat plane, such that the extent of the material in the plane is a multiple of the extent of the material perpendicular to the plane.The method according to the invention comprises at least the following steps, which are preferably carried out in the given order: . a. Cutting the material into a near-net-shape blank or cutting out a near-net-shape blank from the material, wherein the blank extends in one plane; it should be noted that cutting or cutting can also be referred to as contouring the material, since the material is given the contour of the blank. Near-net-shape also means, in particular, that after the subsequent application of pressure to the blank and the associated forming of the blank into the layered body, no or substantially no further cutting or removal of large quantities of material is necessary. For example, near-net-shape can be understood to mean that the area of ​​the blank is equal to the area of ​​the layered body in the decorative part or only slightly larger, e.g., 1% to 10% or 1% to 5% larger than the area of ​​the layered body in the decorative part. b.Arranging the raw part on a fluid-tight, in particular gas-tight, auxiliary film and aligning the raw part with or to the auxiliary film so that the auxiliary film projects beyond the raw part on each side in the plane and surrounds the raw part in a frame-like manner with a section free of the raw part; for aligning the raw part with or to the auxiliary film, position marks can be provided on the auxiliary film and, for example, printed on it, or a positioning aid, such as a positioning gauge, can be used. The auxiliary film itself is a film made of, for example, plastic, which can be elastically or plastically deformable, but retains its fluid- or gas-tightness when deformed as intended.Joining the auxiliary film to the blank aligned with it to form a unit; By joining the auxiliary film to the blank, for example by means of an adhesive mentioned later, the blank is fixed to the auxiliary film in such a way that pressure acting against the gas- or fluid-tight auxiliary film can be exerted on the blank. The blank itself remains correspondingly not gas- or fluid-tight. d. Arranging the blank connected to the auxiliary film in a mold cavity of a forming tool, wherein the mold cavity is separated by the auxiliary film in a gas- or fluid-tight manner into a forming first part and a second part to be pressurized.The blank is then brought into a predetermined position and orientation within the first part of the mold cavity by means of the auxiliary film. In this position and orientation, the blank is completely enclosed within the mold cavity and fixed by the auxiliary film. Crucially, the blank is entirely within the mold cavity and, in particular, does not extend between the sealing surfaces of the forming tool (mentioned later). Alternatively, the auxiliary film can extend between the sealing surfaces and thus serve as an integral sealing lip. Preferably, the blank is free on all sides with respect to its planar extent within the mold cavity and, at least initially, does not directly contact the forming tool.Introducing a fluid, in particular a gas, and especially air, into the second part of the mold cavity, so that the auxiliary film is pressurized on its side facing the second part. The pressurized or high-pressure auxiliary film presses the blank on its side facing the first part against a wall of the first part of the mold cavity, which corresponds to the three-dimensionally shaped surface of the decorative part, thereby transforming the previously flat blank into a layered body with a shape corresponding to the three-dimensionally shaped surface.

[0013] In summary, the invention relates to a method for producing a decorative part with a three-dimensionally shaped surface from an arc-shaped, non-fluid-tight material. A near-net-shape blank is formed from the arc-shaped material and bonded in one piece with a fluid-tight auxiliary film. The resulting unit is positioned in a forming tool or its mold cavity such that the blank is completely and freely arranged within the mold cavity. Subsequently, the auxiliary film is pressurized by a fluid on a side facing away from the blank, causing the blank to be pressed against a forming wall of the forming tool and formed into a layered body.

[0014] Because a near-net-shape blank is contoured from the arc-shaped material before forming, there is no or significantly less waste after forming, so that, compared to the state of the art, more layered bodies or more decorative parts can be produced from a given amount of material.

[0015] In addition, because the raw part, which like the original material is not fluid- or gas-tight, is arranged completely within the mold cavity, the sealing of the tool halves can be done more easily and, as explained below, with the help of the auxiliary film.

[0016] This results in resource-efficient and cost-effective production.

[0017] Furthermore, an advantageous further development of the procedure includes the following steps, preferably in the given order: f. Removing the layer body with the auxiliary film from the forming tool; g. Removing the auxiliary film, and in particular the entire auxiliary film, from the layer body; h. Arranging the layer body in an injection mold; i. Back-injecting or overmolding the layer body with a carrier layer to stabilize and reinforce the layer body.

[0018] Back injection molding means that the carrier layer is injected onto the back of the layer body and does not extend to a visible side of the later decorative part or to a visible side of the layer body.

[0019] In contrast, overmolding is understood to mean that the carrier layer is arranged both on the back and at least partially on the visible side of the layer body and may also extend into the layer body to fill cracks.

[0020] Depending on the desired optical appearance, the layered body can, for example, be back-injected or overmolded with a colorless and preferably transparent and / or translucent plastic.

[0021] Alternatively, the procedure may comprise the following steps, preferably in the given order: f. Removing the layer body with the auxiliary film from the forming tool; g. Removing the free section of the auxiliary film, and in particular only the free section, from the layer body; h. Arranging the layer body with the auxiliary film in an injection mold; i. Back-injecting or overmolding the layer body with a carrier layer to stabilize and reinforce the layer body.

[0022] As before, back injection or overmolding can be carried out, for example, with a colorless and preferably transparent and / or translucent plastic.

[0023] According to this variant of the process, the auxiliary film, which is not reusable anyway, remains sandwiched between the layer body and the carrier layer, thus effectively preventing the plastic from penetrating the layer body, for example during back injection molding.

[0024] Furthermore, the auxiliary film can also serve as an integral part of sealing the injection mold and / or separating a visible surface of the layered body from the back, so that no material can unintentionally reach the visible side during overmolding or back injection.

[0025] In overmolding, for example, it may also be provided that the carrier layer only covers the edge areas of the layer body, so that these are enclosed by the carrier layer and no trimming of the layer body is necessary, since protrusions on the raw part intended to increase process reliability, which are also found on the layer body, lie within the carrier layer.

[0026] A further advantageous embodiment of the method provides that the forming tool comprises a first tool half, which defines the first part of the mold cavity, and a second tool half, which defines the second part of the mold cavity. The auxiliary film is positioned between sealing surfaces provided on the first and second tool halves before step e. and, in particular, during or in step d., and is pressed between them by closing the tool halves. The sealing surfaces are preferably located on the walls of the tool halves that surround the mold cavity. The auxiliary film positioned between the sealing surfaces seals the first and second tool halves against each other and, in particular, also against the mold cavity. Accordingly, the auxiliary film acts simultaneously as a sealant and, in particular, as a sealing lip for sealing the mold cavity.Therefore, it is not absolutely necessary, and preferably not intended, that additional sealing materials are provided between the tool halves to seal the mold cavity.

[0027] To facilitate the arrangement of the auxiliary film with the blank attached to it and fixed within the mold cavity, it may also be provided that corresponding alignment aids or elements are provided on the forming tool and on the auxiliary film. For example, it may be provided that projections, such as pins, are provided on the forming tool, and in particular on the first half of the tool, and that corresponding recesses, such as elongated holes, are provided on the auxiliary film as alignment aids, by which the auxiliary film, and with it the blank, is brought into a predetermined position and orientation in the first part of the mold cavity in step d.

[0028] Furthermore, the alignment aids or the projections and the associated recesses can also be coded, so that the auxiliary foil can only be arranged on the tool half in a single predetermined way.

[0029] Although the alignment elements can be provided within the sealing surfaces, it is advantageous for improving the sealing if the alignment elements are arranged outside the sealing surfaces and outside the mold cavity on the forming tool.

[0030] The auxiliary film is preferably a single-use and therefore non-reusable sacrificial film, although it can still be recyclable.

[0031] In step b., the raw part is preferably glued to the auxiliary film using an adhesive and / or an adhesive tape, wherein the adhesive or the adhesive tape is further preferably temperature-resistant so that it withstands the temperatures generated during pressure application as intended and the raw part does not detach from the auxiliary film.

[0032] The adhesive does not necessarily have to be applied as adhesive tape or double-sided adhesive tape, but can also be applied, for example, as a spray film to the raw part or the auxiliary film and thus sandwiched between them.

[0033] A further aspect of the invention relates to a decorative element as defined by the features of claim 8. Such a decorative element has a three-dimensionally shaped surface with a visible side and a reverse side, wherein the decorative element or parts thereof are preferably manufactured using the method proposed according to the invention. The decorative element has a layered body on the visible side, which is three-dimensionally shaped corresponding to the surface of the decorative element, and a support layer on the reverse side for stabilizing and reinforcing the layered body. The layered body is formed from a material that is initially arc-shaped and not fluid-tight, and in particular not gas-tight, such as wood, and specifically a veneer.The layer body is preferably porous and / or has cracks, whereby openings formed in the layer body can be closed, for example, by a visible protective layer or the carrier layer.

[0034] Furthermore, one aspect of the invention relates to a system according to the features of claim 10, comprising a forming tool and an auxiliary film for forming or three-dimensionally stretching an arc-shaped material that is not fluid-tight and, in particular, not gas-tight, and which, as explained, is particularly porous and / or prone to cracking. In order to nevertheless be able to form such a non-fluid-tight or non-gas-tight material, or a blank produced therefrom, by applying high pressure with a fluid, the forming tool is provided to have a two-part mold cavity: a first tool half, which defines the first part of the mold cavity, and a second tool half, which defines the second part of the mold cavity.The first and second mold halves each have sealing surfaces for direct contact with the auxiliary film. These sealing surfaces are designed to be pressed against the auxiliary film, creating a fluid-tight seal between the mold halves and the mold cavity, effectively dividing them into two parts. This allows the blank to be fully positioned within the mold cavity and pressed against the second, forming part of the mold cavity via the auxiliary film. Preferably, no further sealing element, and in particular no sealing lip or similar component, is required on or between the mold halves.

[0035] Preferably, the proposed forming tool is used to carry out the method according to the invention and / or to produce the decorative part proposed according to the invention. Regardless, the physical features of the forming tool described in relation to the method also apply to the forming tool included in the system.

[0036] The features disclosed above can be combined in any way, provided that this is technically possible and they do not contradict each other.

[0037] Other advantageous embodiments of the invention are characterized in the dependent claims or are described in more detail below together with the description of the preferred embodiment of the invention with reference to the figures. The figures show: Fig. 1-9 Steps of a process for manufacturing a decorative part; Fig. 10 a unit consisting of auxiliary film and raw part; Fig. 11 an auxiliary film with layer body; Fig. 12 a decorative part.

[0038] The figures are schematic examples. Identical reference symbols in the figures indicate identical functional and / or structural features.

[0039] The following show Figures 1 to 9 the steps of a method proposed according to the invention, in particular for the production of a decorative part 10 as shown by way of example in Figure 12, wherein the Figures 1 to 9 present the steps in a preferred order and the Figures 10 and 11 intermediate products resulting in particular from the process in the manufacture of the decorative part 10 according to Figure 12 depict.

[0040] The decorative part 10, as it is used, for example, in Figure 12The decorative element 10, as depicted, has a multi-layered structure and a three-dimensionally shaped surface 11, i.e., extending out of a plane. In addition to a rear carrier layer 70 and a visible decorative layer formed by a layer body 50, the decorative element 10 can also have further layers and, in particular, a transparent protective layer covering the layer body 50, also visible on the side.

[0041] If a naturally occurring, arc-shaped material, such as wood, particularly in the form of veneer, is to be used as the starting material for the layered body 50, the problem often arises that such materials are not, or at least not permanently or reliably, fluid-tight, and especially not gas-tight. Accordingly, these materials cannot be reliably formed into the required shape using a deep-drawing process known and widely used in the prior art as high-pressure forming, since gas tightness is an essential prerequisite for this process.

[0042] The proposed method initially provides that, according to step a., a near-net-shape blank 20 is contoured from the starting material. This can be done by cutting the starting material to form the blank 20 or by cutting the blank 20 out of the starting material. Since the blank 20 is already near-net-shape and, for example, has the same or only a slightly larger area than the layered body 50 in the finished decorative part 10, more blanks 20 can be produced from a given quantity of the natural material than with many of the methods known from the prior art.

[0043] This raw part 20 is arranged on an auxiliary film 30 according to steps b. and c., aligned with or to it, and connected to it, so that the raw part 20 and the auxiliary film 30 form a unit, as schematically shown in Figure 1 visible and for example in Figure 10The auxiliary foil 30 is larger than the raw part 20 with respect to its extent in the plane of the raw part 20, so that the auxiliary foil 30 surrounds the raw part 20 with a free section 33 in a frame-like manner.

[0044] According to step d. and as in Figures 1 and 2 As shown, the unit consisting of auxiliary film 30 and blank 20 is arranged in a forming tool 40 or in a mold cavity of a forming tool 40, such that the mold cavity is divided by the auxiliary film 40 into a first part 41 and a second part 42. It is of great importance that the blank 20 is positioned in the first part 41 of the mold cavity by means of the auxiliary film 30 in such a way that the blank 41 is free on all (four) sides in the plane of its extent. The edge faces 21 of the blank 20 thus have a predetermined distance to the walls of the forming tool 40 that form the mold cavity.

[0045] To clarify this feature, namely that the raw part 20 is completely arranged in the mold cavity and is free on all sides in the plane, the following is shown in Figure 10 An imaginary inner wall edge 48 of the walls of the forming tool 40 that define the mold cavity is shown, which makes it clear that the blank 20 does not extend, in particular, between the sealing surfaces 46 of the forming tool 40 which will be explained below.

[0046] To enable simple and quick positioning of the blank in its predetermined position within the first part 41 of the mold cavity in step d., alignment aids 37, 47 are provided in the form of pins 47 on the forming tool 40 and corresponding oval recesses 37 in the auxiliary film 30. Thus, by guiding the auxiliary film 30 with the recesses 37 over the pins 47, the blank is automatically brought into the predetermined position and orientation.

[0047] The alignment aids 37, 47 are in the Figure 1 and 10 The illustrations are exemplary and can also be implemented differently. For example, pins 47 can be shown as on the right side of the Figure 1 indicated within the sealing surfaces 46 of the forming tool 40 or as shown on the left side of the Figure 1 indicated and, due to the improved seal, advantageously provided outside the sealing surfaces 46 of the forming tool 40.

[0048] These different variants are also found in Figure 10 The recesses 37 are indicated by the imaginary lines of the inner wall edge 48 and the outer wall edge 49. On the right side of the illustration, the recesses 37 are located within the sealing surfaces 46 bounded by the inner wall edges 48 and the outer wall edges 49, and on the left side of the illustration, the recesses 37 are located outside the sealing surfaces 46 bounded by the inner wall edges 48 and the outer wall edges 49.

[0049] Once the blank 20 has been placed in the first part 41 of the mold cavity in this predetermined position, the two tool halves 44, 45 of the forming tool 40 are closed, so that the auxiliary film 30 extends between the sealing surfaces 46 of the forming tool 40 and seals the mold cavity to the outside. Accordingly, the auxiliary film 30 acts as a sealing lip to seal the mold cavity, so that additional sealing materials are not necessarily required on the forming tool 40 for this purpose.

[0050] As in Figure 2As shown, a fluid, in particular a gas, and further in particular air, is then introduced into the second part 42 of the mold cavity, so that the fluid-tight auxiliary film 30 is pressurized on its second side 32. The pressure acting on the second side 32 of the auxiliary film is transferred to the raw part 20 on the first side 31 of the auxiliary film 30, so that the raw part 20, together with the auxiliary film 30, is pressed into the first part 41 of the mold cavity and, as shown in Figure 3 The raw part 20, which conforms to a shaping wall 43, is shown to be formed by the surface 11 of the decorative part 10. Depending on the properties of the starting material, the pressure can then be maintained or further steps can be carried out until the raw part 20, conforming to the shaping wall 43, is permanently transformed into a layered body 50, which accordingly has a shape corresponding to the surface 11 of the decorative part 10.

[0051] The deformation and shaping process takes place regardless of whether the starting material is already leaky before the process or becomes leaky during the process, for example due to cracking.

[0052] The remaining unit consisting of the auxiliary film 30 and the blank 20 formed into the layered body 50 is removed from the forming tool 40 and is shown by way of example in the Figures 4 and 11 depicted.

[0053] According to the present procedure, this unit will now, as in Figure 5 visible, dissolved and the layer body 50 separated from the auxiliary film 30.

[0054] The auxiliary film 30 is preferably a sacrificial film that can only be used once, but is recyclable, so that it can be disposed of or recycled after separation from the layer body 50.

[0055] The now separated layer body 50 can then be processed as described in Figure 6shown, inserted between the tool halves 61, 62 of an injection mold 60, the tool halves 61, 62 forming a cavity 63 closed and, as shown in Figure 7 As shown, the material is back-injected. For this purpose, an injection molding material, in particular plastic, is introduced into the cavity 63 via a supply line 67, so that a carrier layer 70 is formed in the cavity 63 or in the injection mold 60, which is integrally connected to the layer body 50 and reinforces the layer body.

[0056] The unit consisting of layer body 50 and carrier layer 70 can, as in Figure 8 shown, taken from the injection mold 60.

[0057] In Figure 9The unit consisting of layer body 50 and carrier layer 70 is shown again separately, which already essentially corresponds to the decorative part 10, wherein the surface 11 of the decorative part 10 is determined on the visible side by the layer body 50 and may optionally be supplemented by a protective layer not shown.

[0058] The invention is not limited in its implementation to the preferred embodiments specified above. Rather, a number of variants are conceivable which make use of the solution presented even in fundamentally different designs.

Claims

1. A method for manufacturing a decorative part (10) with a three-dimensionally moulded surface (11) based on an arc-shaped and non-fluid-tight material, comprising at least the steps: a. cutting the material into a near-net-shape blank (20) or cutting out a near-net-shape blank (20) from the material, wherein the blank (20) extends in a plane; b. arranging the blank (20) on a fluid-tight auxiliary film (30) and aligning the blank (20) with the auxiliary film (30), so that the auxiliary film (30) protrudes beyond each side of the blank (20) in the plane and surrounds the blank (20) with a free section (33) in form of a frame; c. connecting the auxiliary film (30) with the blank (20) aligned with it into one unit; d. arranging the blank (20) connected to the auxiliary film (30) in a mould cavity of a forming tool (40), wherein the auxiliary film (30) separates the mould cavity, in a fluid-tight manner, into a forming first part (41) and a second part (42) that is to be impinged with pressure, and wherein the blank (20) is, by means of the auxiliary film (30), placed in a predefined position and pose in the first part (41) of the mould cavity in which the blank (20) is completely arranged and is fixed by the auxiliary film (30); e. introducing a fluid into the second part of the mould cavity, so that the auxiliary film (30) is pressurised on its side (32) facing the second part (42), the pressurised auxiliary film (30) presses the blank (20), on its side (31) facing the first part (41), in a forming manner against a wall (43) of the first part (41) which corresponds with the three-dimensionally moulded surface (11) of the decorative part (10), and the previously plane blank (20) is formed into a layered body (50) with a form corresponding to the three-dimensionally moulded surface (11).

2. The method according to claim 1, further having the steps: f. removing the layered body (50) with the auxiliary film (30) from the forming tool (40); g. removing the auxiliary film (30) from the layered body (50); h. arranging the layered body (50) in an injection tool (60); i. back-injecting or overmoulding the layered body (50) with a carrier layer (70) for stabilisation and strengthening the layered body (50).

3. The method according to claim 1, further having the steps: f. removing the layered body (50) with the auxiliary film (30) from the forming tool (40); g. removing the free section (33) of the auxiliary film (30) from the layered body (50); h. arranging the layered body (50) with the auxiliary film (30) in an injection tool (60); i. back-injecting or overmoulding the layered body (50) with a carrier layer (70) for stabilisation and strengthening the layered body (50).

4. The method according to any one of the preceding claims, wherein the forming tool (40) has a first tool half (44) determining the first part (41) of the mould cavity and a second tool half (45) determining the second part (42) of the mould cavity, and wherein, before step e., the auxiliary film (30) is pressed between sealing areas (46) provided on the first tool half (44) and the second tool half (45) and seals first tool half (44) and the second tool half (45) against each other.

5. The method according to any one of the preceding claims, wherein alignment aides (37, 47) that correspond to each other are provided on the forming tool (40) and on the auxiliary film (30), which, in step d., bring the auxiliary film (30) and with it the blank (20) into a predefined position and pose in the first part (41) of the mould cavity.

6. The method according to any one of the preceding claims, wherein the auxiliary film (30) is a single-use sacrificial film.

7. The method according to any one of the preceding claims, wherein the blank (20), in step b., is adhered to the auxiliary film (30) with an adhesive and / or adhesive tape.

8. A decorative part (10) with a three-dimensionally moulded surface (11) with a visible side (S) and a reverse side (R) facing away from it, wherein the decorative part (10) has, towards the visible side (S), a layered body (50) that is three-dimensionally formed in correspondence with the surface (11) of the decorative part (10) and, towards the reverse side (R), a carrier layer (70) for stabilising and strengthening the layered body (50), wherein the layered body (50) is moulded from an arc-shaped and non-fluid-tight material, wherein the layered body (50) is porous and / or has cracks, and wherein the layered body (50) is back-injected with the carrier layer (70).

9. The decorative part according to the previous claim, manufactured according to the method according to any one of claims 1 to 7.

10. A system of forming tool (40) and auxiliary film (30) for forming an arc-shaped and non-fluid-tight material, wherein the forming tool (40) has a two-part mould cavity, a first tool half (44) determining a first part (41) of the mould cavity and a second tool half (45) determining a second part (42) of the mould cavity, wherein the first tool half (44) and the second tool half (45) each have sealing areas (46) for immediate contact with the auxiliary film (30), which are configured to be pressed against the auxiliary film (30) and to seal the tool halves (44, 45) against each other and the mould cavity, separating the mould cavity into the two parts (41, 42) in a fluid-tight manner, and wherein the first tool half (44) has a forming wall (43) corresponding to the three-dimensionally moulded surface (11) of a decorative part (10).