Method for producing an interior trim part for a motor vehicle with an airbag weakening feature

Abstract

Method for producing an interior fitting (1) with at least one airbag weakening for a motor vehicle, comprising the following steps: - forming a main cavity (2) which corresponds to a negative mold of the interior fitting part (1) to be produced, wherein at least one movable web element (3) is arranged within the main cavity (2), which at least locally interrupts the main cavity (2); - filling the main cavity (2) with at least a first plastic melt (4), wherein the web element (3) within the main cavity (2) is enclosed by at least the first plastic melt (4); - cooling the first plastic melt (4), wherein the first plastic melt (4) is kept at or above its melting temperature; - removing the web element (3), wherein at least the first plastic melt (4) flows into a cavity (6) which is created by the removal of the web element (3); wherein within the cavity (6) at least the first plastic melt (4) forms a weld line (7) and the weld seam (7) at least partially spatially defines the airbag weakening of the interior fitting part (1); characterized in that the web element (3) consists of several adjacent partial segments (3.1 - 3.4) which are removed at different times during the removal step, so that the weld line (7) is formed with regions of different strength.

Description

Technical area

[0001] The present invention relates to a method for producing an interior trim part for a motor vehicle, in particular a passenger car, wherein the support weakening is produced by a weld seam. State of the art

[0002] Interior trim components are often weakened at specific points to allow an airbag mounted on the interior trim component to pass through the interior trim component into the vehicle interior. The weakened areas are often H- or U-shaped. These weakened areas cause the interior trim component to tear open, forming a type of flap, often referred to as an airbag flap. In modern vehicles, it is generally not desirable for the weakened areas in the interior trim component to be visible to vehicle occupants. In the prior art, the airbag flap is normally formed by weakening the interior trim component, for example, by milling or lasering. This means that material is generally removed, which makes the interior trim component significantly less mechanically resilient in the removed area.The problem with this type of weakening of the interior trim part, however, is that the worn areas usually show up on the decorative layer of the interior trim part.

[0003] US 2006 / 0034974 A1 shows a device for producing an airbag cover. US 2004 / 0140652 A1 describes an interior trim part for a vehicle with an opening for an airbag and a corresponding manufacturing method. Description of the invention

[0004] It is therefore an object of the present invention to provide a method which makes it possible to provide an interior trim part with a support weakening which has an improved surface quality and in which the weakening of the interior trim part remains largely invisible.

[0005] The object of the invention is achieved by a method having the features of the independent claim. Further advantageous embodiments of the invention can be found in the dependent claims, the description, and the accompanying drawings.

[0006] A method according to the invention for producing an interior trim part with at least one airbag weakening for a motor vehicle comprises at least the step of forming a main cavity, in particular in a mold. The main cavity essentially represents the negative mold of the interior trim part to be produced. Within the main cavity, at least one movable web element is arranged, in particular as part of the mold, which at least locally interrupts the main cavity. Furthermore, the method according to the invention comprises the step of filling the main cavity with at least a first plastic melt, wherein the web element, which has a higher melting temperature than the plastic melt, is enclosed within the cavity by at least the first plastic melt.Because the web element locally interrupts the main cavity, the first plastic melt cannot penetrate the web element, but can flow around it and enclose it within the main cavity. To ensure that the first plastic melt encloses the web element as evenly as possible within the main cavity, the first plastic melt can be introduced into the main cavity at several points.

[0007] Furthermore, the method according to the invention comprises the step of cooling the first plastic melt, wherein the first plastic melt is kept at or above its melting temperature. Depending on the temperature of the plastic melt, the cooling time can be limited to fractions of a second. The reason for this cooling is that as the temperature drops, although the plastic remains largely flowable above or at its melting temperature, its viscosity increases.

[0008] A further step of the method according to the invention consists in removing the web element, wherein at least the first plastic melt flows into a cavity created by the removal of the web element. Within the cavity, the plastic melt forms a weld line due to the prior cooling.

[0009] When opening the airbag flap, it is often very important that the airbag flap or the interior trim part first tears open at a defined point of weakness and that the resulting tear spreads from this point in a defined manner in order to ensure optimal opening of the airbag flap. This is ensured according to the invention in that the web element consists of adjacent sub-segments that are removed at different times during the removal step. For example, one sub-segment can be removed at an early point in time in order to form a mechanically resilient weld line, and further sub-segments can be removed at a later point in time in order to form weld lines that are less mechanically resilient and therefore tear open sooner, since the first and / or second plastic melt has already cooled down more in this case.

[0010] Due to the increased viscosity of the first plastic melt, it is no longer possible for the first plastic melt to fill the resulting cavity homogeneously. Instead, flow fronts form that meet and fuse together in the cavity, creating the weld line. Although the interior trim part has a closed surface in the area of the weld line, the weld line represents a local weakening of the interior trim part, which is significantly more susceptible to mechanical stress than the surrounding areas of the interior trim part, creating a predetermined breaking point. The web element integrates the weld line into the structure of the interior trim part in a defined manner.In this way, the weld line is used to weaken the interior trim part locally in a targeted manner, whereby the thickness of the interior trim part remains largely unchanged even in the area of the weld line, so that the weakening of the interior trim part is not transferred to decorative layers that can, for example, be subsequently applied to the interior trim part.

[0011] The weld seam at least partially defines the airbag weakening of the interior trim part.

[0012] It is advantageous at this point if the web element is H- or U-shaped, so that an H- or U-shaped weld seam can be introduced into the interior trim part and a typical weakening geometry can be introduced into the interior trim part, which corresponds to a typical airbag flap shape.

[0013] If, instead of a U-shaped or H-shaped airbag flap, a circumferential airbag flap is desired, which, for example, should have a square shape, it is also possible to use a web element within the method according to the invention. This creates a partial cavity within the main cavity that is spatially separated from the main cavity. In this case, during the introduction step, a first plastic melt is introduced into the main cavity and a second plastic melt is introduced into the partial cavity. Depending on the mechanical requirements, the plastic melts can be the same or different. During the cooling step, both the first and the second plastic melt are kept above or at their melting temperature.During the step of removing the web element, the first and the second plastic melts come into contact, wherein the weld line is formed at the boundary between the first and second plastic melts, which weld line at least partially spatially defines the airbag weakening of the interior trim part.

[0014] Depending on the size of the interior trim part, the size of the partial cavity may differ from the size of the main cavity. To ensure that the weld line between the first and second plastic melts can form in a defined manner, it can be advantageous if the time at which the partial cavity is filled with the second plastic melt differs from the time at which the main cavity is filled with the first plastic melt. This prevents one of the two plastic melts from cooling too much to form a weld line. For example, the plastic melt that is at risk of cooling too quickly can be poured into the corresponding cavity at a later time.

[0015] Since the mechanical properties of the weld line depend essentially on the temperature at which the corresponding melt fronts impinge on the weld line, it is advantageous to control the mechanical properties of the weld line via the cooling time of the first and / or second plastic melt. In principle, the more the melt has cooled during the formation of the weld line, the mechanically weaker the weld line will be. Therefore, if a particularly tearable weld line is desired, which should allow the airbag flap to open even under low mechanical loads, a longer cooling time is required than for a weld line that is intended to withstand higher mechanical stresses.

[0016] To ensure that no sink marks form at the weld line in the interior trim part, the removal of the web element can be followed by a re-pressing step, in which mechanical pressure is exerted on at least the first plastic melt. If, for example, the cavity is no longer completely filled with plastic melt due to increasing viscosity, re-pressing can promote the distribution of the plastic melt within this cavity.

[0017] As a rule, there is a requirement that the opened airbag flap must not detach from the interior trim part when it opens during airbag deployment. It can therefore be advantageous if a hinge element for forming an airbag flap hinge is arranged in the main cavity during or before the step of forming the main cavity. The hinge element can be a hinge textile, for example. The hinge element is preferably arranged in the main cavity such that it is partly arranged inside the future airbag flap and partly outside the future airbag flap. Even more preferably, the hinge element is cast into at least the first plastic melt. This has the advantage that the necessary hinge element is integrated directly into the interior trim part and no additional process step is necessary in which an airbag hinge has to be attached to the interior trim part.

[0018] A device for producing an interior trim part with an airbag weakening feature for a motor vehicle comprises at least a first and a second mold half, which are movable relative to one another between an open position and a closed position and, at least in the closed position, form a main cavity between them that corresponds to the negative shape of the interior trim part to be produced. Furthermore, the device comprises at least one web element and at least one first injection nozzle. A first plastic melt can be introduced into the main cavity using the first injection nozzle. However, a plurality of first injection nozzles can also be provided to introduce the first plastic melt into the main cavity.

[0019] The web element is arranged at least on the first tool half in an area of the main cavity in which the airbag weakening of the interior trim part to be produced is to be formed. The web element is movable between a locking position in which the web element projects into the main cavity and touches the second tool half, and a release position in which the web element is at least partially retracted into the first half. The web element specifically interrupts the flow of the plastic melt at the points where the weld line is to be formed. The web element advantageously has a very small width so that after the web element has been moved into the release position, only a very small cavity is formed and the plastic melt only has to travel a short distance to form the weld line.

[0020] The web element consists of independently movable, adjacent sub-segments that can be moved independently between the locking and release positions. This allows weld line sections to be formed in the interior trim part that differ from one another in their mechanical properties. However, the weld line sections form a continuous weld line, even if the weld line sections differ from one another in their mechanical properties.

[0021] If it is desired to create, for example, a square airbag flap that is to be detached in its entirety from the interior trim part, it is advantageous if the web element forms a frame that, at least in the locked position, forms a partial cavity within the main cavity that is spatially separated from the main cavity. The frame thus forms a kind of circumferential ring that prevents a plastic melt introduced into the main cavity from penetrating the partial cavity.

[0022] To ensure that the partial cavity is also filled with a plastic melt, it is advantageous if one of the mold halves has at least a second injection nozzle through which a second plastic melt can be introduced into the partial cavity. It is preferred at this point that the second injection nozzle can be controlled independently of the first injection nozzle.

[0023] Furthermore, the web element or at least partial segments of the web element can be heated in order to be able to control the temperature of the plastic melt in the area of the weld line to be produced more precisely.

[0024] Furthermore, further advantages and features of the present invention will become apparent from the following description of preferred embodiments. The features described there and above can be implemented individually or in combination, provided the features do not contradict each other. The following description of the preferred embodiments is made with reference to the accompanying drawings. In the drawings: Fig. 1 - 5 a method according to the invention in various process steps, Fig. 6 a three-dimensional representation of a main cavity according to the invention.

[0025] In Fig. 1 shows a schematic representation of a device for producing an interior trim part 1 with an airbag weakening. The device according to the invention consists of a first and a second mold half 9, 10, which, as shown, are arranged in a closed position and form a main cavity 2. Furthermore, two first injection nozzles 11 for introducing a first plastic melt 4 into the main cavity 2 are arranged in the first mold half 9. Furthermore, two web elements 3 are arranged in the first mold half 9. The web elements 3 are movable between a release position, in which the web elements 3 are arranged within the first mold half 9, and a blocking position, in which the web elements 3 protrude into the main cavity 2.

[0026] In Fig. 1, however, the web elements 3 are in a release position. A second injection nozzle 13 for applying a second plastic melt 5 is arranged in the second mold half 10.

[0027] In Fig. 2, the web elements 3 are moved into the blocking position, so that a partial cavity 8 is formed between them within the main cavity 2, which partial cavity 8 is spatially separated from the main cavity 2 by the web elements 3. At the same time, a first plastic melt 4 is introduced into the main cavity 2 via the first injection nozzles 11, and a second plastic melt 5 is introduced into the partial cavity 8 via the second injection nozzle 13. However, the web elements 3 prevent the two plastic melts 4, 5 from coming into contact. In the present exemplary embodiment, both the first and the second plastic melts 4, 5 are polypropylene.

[0028] In Fig. 3, after a brief cooling period of the plastic melts 4, 5, one of the web elements 3 is moved back into the release position. By moving the first web element 3 back into the release position, a cavity 6 is created between the first and second plastic melts 4, 5, which is immediately filled by the still liquid plastic melts 4, 5. Since the movement of the web element 3 into the release position was preceded by cooling, a weld line 7 forms at the point where the two plastic melts 4, 5 meet.

[0029] In Fig. 4, the second web element 3 is also moved back into the release position. Due to the subsequent return of the second web element 3, a weld line 7 forms between the plastic melts 4, 5 at this point, which is mechanically significantly less resilient than the weld line 7 created first. The weld lines 7 deliberately introduce a material weakening into the interior trim part 1, which serves as an airbag weakener.

[0030] In Fig. 5, the first tool half 9 is moved relative to the second tool half 10 into the opening position, so that the produced interior trim part 1 with integrated support weakening by the weld lines 7 can be removed from the tool. Subsequently, the interior trim part 1 is coated with a haptic layer and a decorative layer in a process step not shown.

[0031] Fig.Figure 6 shows a three-dimensional representation of the device, wherein, in addition to the main cavity 2, the partial cavity 8, and the web element 3, the flow fronts 14, 15 of the first and second plastic melts 4, 5 are also represented by directional arrows. The first injection nozzles 11 are distributed around the partial cavity 8 in the main cavity 2, so that the first flow fronts 14 of the first plastic melt 4 move directly toward the web element 3. At the same time, second flow fronts 15 are formed via the second injection nozzle 13, which is arranged within the partial cavity 8, and which also extend in all directions toward the web element 3. The web element 3 is divided into sub-segments 3.1 - 3.4, which can be moved independently of one another between the locking and release positions. In this way, an airbag weakening can be created that is weakened to different degrees in different areas.In the present embodiment, the lower sub-segment 3.3 is first moved into the release position. Then, simultaneously, the lateral sub-segments 3.1; 3.2 and, finally, the upper sub-segment are moved from the locking position to the release position. This not only allows weld lines with different mechanical properties to be created, but also allows a defined crack formation along the weld lines during airbag deployment.

[0032] The statements made with reference to the drawings are purely illustrative and are not to be understood as limiting in any way. List of reference symbols 1 interior part 2 Main cavity 3 web element 3.1-3.4 Subsegments 4 First plastic melt 5 Second plastic melt 6 cavity 7 Weld line 8 partial cavity 9 First tool half 10 Second tool half 11 First injection nozzle 12 frames 13 Second injector 14 Flow front first plastic 15 Flow front second plastic

Claims

[1] Method for producing an interior fitting (1) with at least one airbag weakening for a motor vehicle, comprising the following steps: - forming a main cavity (2) which corresponds to a negative mold of the interior fitting part (1) to be produced, wherein at least one movable web element (3) is arranged within the main cavity (2), which at least locally interrupts the main cavity (2); - filling the main cavity (2) with at least a first plastic melt (4), wherein the web element (3) within the main cavity (2) is enclosed by at least the first plastic melt (4); - cooling the first plastic melt (4), wherein the first plastic melt (4) is kept at or above its melting temperature; - removing the web element (3), wherein at least the first plastic melt (4) flows into a cavity (6) which is created by the removal of the web element (3); wherein within the cavity (6) at least the first plastic melt (4) forms a weld line (7) and the weld seam (7) at least partially spatially defines the airbag weakening of the interior fitting part (1); characterized by , that the web element (3) consists of several adjacent partial segments (3.1 - 3.4) which are removed at different times during the removal step, so that the weld line (7) is formed with regions of different strength. [2] Method according to claim 1, wherein the strength of the weld line (7) is controlled over a length of a cooling time of at least the first plastic melt (4) during the cooling step. [3] Method according to one of the preceding claims, wherein during the removal step, at least two sub-segments (3.1, 3.2) are first removed, in particular simultaneously, which adjoin at least in sections to at least one sub-segment (3.3, 3.4) arranged between the two sub-segments (3.1, 3.2). [4] Method according to the preceding claim, wherein the at least one sub-segment (3.3, 3.4) adjacent to the two sub-segments (3.1, 3.2) is removed after the two adjacent sub-segments (3.1, 3.2) have been removed. [5] Method according to one of the preceding claims, wherein the step of removing the web element (3) is followed by a step of repressing, in which a mechanical pressure is exerted on at least the first plastic melt (4). [6] Method according to one of the preceding claims, wherein before or during the step of forming the main cavity (2) a hinge element for forming an airbag flap hinge is arranged in the main cavity (2).

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