EP2832508A1

EP2832508A1 - Method for forming a trim element having a layer of ligneous material with a three-dimensional shape

Info

Publication number: EP2832508A1
Application number: EP13306089.7A
Authority: EP
Inventors: Hugo Piccin
Original assignee: Faurecia Innenraum Systeme GmbH
Current assignee: Faurecia Innenraum Systeme GmbH
Priority date: 2013-07-29
Filing date: 2013-07-29
Publication date: 2015-02-04
Anticipated expiration: 2033-07-29
Also published as: EP2832508B1

Abstract

The method comprises the following steps:
- providing a substantially planar layer of ligneous material (2),
- shaping the layer of ligneous material (2) in order to obtain the three-dimensional shape of the trim element to be produced.

The shaping step comprises at least the following successive steps:
- deforming the layer of ligneous material (2) to an intermediate shape between the initial planar shape and the final three-dimensional shape of the layer of ligneous material (2),
- stabilizing the layer of ligneous material (2) having the intermediate shape in order to reach the moisture equilibrium of the ligneous material,
- deforming the layer of ligneous material to the final three-dimensional step.

Description

The present invention relates to a method for producing a trim element having a three-dimensional shape and comprising at least a layer of ligneous material, the method comprising the following steps:

providing a substantially planar layer of ligneous material
shaping the layer of ligneous material in order to obtain the three-dimensional shape of the trim element to be produced.

The invention also relates to a trim element produced by such a method.
Trim elements are for example used to line a part of the compartment of a vehicle, for example to cover a dashboard and/or a door panel or other parts of the compartment. In order to improve the aesthetics of the compartment, trim elements having the aspect of wood are particularly appreciated. The trim elements comprise a layer of ligneous material, which can be made of natural wood or of a resin matrix comprising wood fibers for example, arranged to be visible from the exterior of the trim elements in order to confer a wood aspect to the trim element.
However, such layers of ligneous material are not easy to shape, in particular if the trim element has to have a complex three-dimensional shape, for example a shape having an undercut, i.e. a part of the trim element that forms a concave cavity with the rest of the trim element. It is indeed very difficult to bend the layer of ligneous material without generating cracks in the layer or without breaking the layer
A known method for bending a layer of ligneous material is the method for producing wood barrels, for example for storing wine. However, such a method, which is mainly manual, is not adapted for the automotive industry and is time consuming. Furthermore, such a method is not adapted for layer of ligneous material having a thickness less than 20 mm, which is the case for a layer of ligneous material used in a trim element for an automotive vehicle. Indeed, in such a trim element, the layer of ligneous material has to be an thin as possible, for weight reduction reasons and for providing a flexible ligneous material able to adapt to the variations in shape of the part to be covered by the trim element
One of the aims of the invention is to propose a method for producing a trim element, compatible with the automotive industry and wherein a thin layer of ligneous material can be shaped into a complex three-dimensional shape, without degrading the layer of ligneous material.
To this end, the invention relates to a method of the afore-mentioned type, wherein the shaping step comprises at least the following successive steps:

deforming the layer of ligneous material to an intermediate shape between the initial planar shape and the final three-dimensional shape of the layer of ligneous material,
stabilizing the layer of ligneous material having the intermediate shape in order to reach the moisture equilibrium of the ligneous material,
deforming the layer of ligneous material to the final three-dimensional step.

The shaping step is carried out progressively with a stabilization step of the layer of ligneous material, which guaranties a satisfactory shaping of the layer of ligneous material without forming cracks or breaking the layer, even when said layer is thin and when the final three-dimensional shape is complex. The method can be entirely industrialized and has a throughput compatible with the automotive industry.
According to other features of the method according to the invention:

the stabilizing step is a humidifying step, wherein the layer of ligneous material is humidified to reach the moisture equilibrium of the ligneous material,
the layer of ligneous material is humidified to reach a moisture of the layer of ligneous material substantially comprised between 7% and 9%,
the method further comprises a stabilization step carried out prior to deforming the layer of ligneous material from the initial planar shape to the intermediate shape,
the step of deforming of the layer of ligneous material to the final three-dimensional shape involves creating an undercut in the three-dimensional shape of the layer of ligneous material,
the step of deforming the layer of ligneous material from the initial planar shape to the intermediate shape comprises the step of placing the layer of ligneous material having the initial shape in a first forming tool comprising a first part and a second part, said parts defining together a space having the intermediate shape of the layer of ligneous material and applying a pressure on the layer of ligneous material between the first and second parts of the first forming tool such that said layer acquires the intermediate shape,
the step of deforming the layer of ligneous material from the intermediate shape to the final shape comprises the step of placing the layer of ligneous material having the intermediate shape in a second forming tool comprising a first part and a second part, said parts defining together a space having the final shape of the layer of ligneous material and applying a pressure on the layer of ligneous material between the first and second parts of the second forming tool such that said layer acquires the final shape,
the first part of the first forming tool is also the first part of the second forming tool, such that the layer of ligneous material remains in said first part between the first deformation step and the second deformation step,
the second part of the second forming tool comprises at least one drawer movable between a retracted position, wherein the second part can be moved relative to the first part of the second forming tool, and an active position without interfering with said first part, wherein the second part defines with the first part a final three-dimensional shape comprising at least one undercut,
the layer of ligneous material is heated at least during the deformation steps up to a temperature corresponding to the melting point of the lignin present in said layer of ligneous material, and
a flexible backing layer is arranged on the back side of the layer of ligneous material prior to its deformation in order to form a planar flexible complex, the whole complex being deformed during the shaping step of the method.

The invention also relates to a trim element comprising a three dimensionally shaped ligneous material produced by the method as described above.
Other aspects and advantages of the invention will appear upon reading the following description, given by way of example and made in reference to the appended drawings, wherein:

Fig. 1 is a cross-section view of a complex comprising a layer of ligneous material used for producing a trim element, the complex being placed in a first forming tool,
Fig. 2 is a cross-section view of the complex of Fig. 1 after a first deformation step placed in a second forming tool,
Fig. 3 is a cross-section view of the complex during a second deformation step, and
Fig. 4 is a cross-section view of the complex obtained at the end of the method according to the invention.

In the following description, the term "front" is used to designate what is turned towards the exterior of the trim element, i.e. toward the inside of a vehicle compartment for example, and the term "back" is used to designate what is turned towards the interior of the trim element, i.e. toward the body of a vehicle for example.
In reference to Fig. 1, there is described a complex 1 forming the front of a trim element to be produced with the complex 1.
The complex 1 comprises a layer of ligneous material 2. The layer of ligneous material 2 is for example formed of one layer of natural wood or of a superposition of wood layers. Alternatively, the layer of ligneous material can be formed of wood fibers embedded in a resin matrix or a layer of veneer. The layer of ligneous material 2 is sufficiently thin to have a certain flexibility and thus be adapted to be deformed up to a certain extent. The layer of ligneous material for example presents a thickness substantially comprised between 0.1 and 2 mm. According to a particular embodiment, the thickness of the layer of ligneous material 2 is inferior to 0.5 mm.
According to the embodiment shown in the figures, the complex 1 further comprises a backing layer 4. The backing layer 4 extends directly on the back face of the layer of ligneous material 2 and is attached to said back face, for example by gluing. The backing layer 4 is made of a flexible material. By flexible, it is meant that the backing layer 4 is not rigid and can be shaped. The material of the backing layer is for example a textile, such as a woven or a non-woven fabric, or paper or cardboard or a film of plastic material.
The complex 1 formed by the assembly of the layer of ligneous material 2 and of the backing layer 4 is therefore flexible and is adapted to be deformed up to a certain extent, such that it can acquire a three-dimensional shape corresponding to the shape of the part to be lined by the trim element of the invention. The total thickness of the complex 1 is for example comprised between 0,5 mm and 4 mm.
According to the embodiment shown in the figures, the complex 1 can further comprise a coating layer 6 applied on the front face of the layer of ligneous material 2 and intended to form the visible face of the trim element, whereas the visible face is formed by the front face of the layer of ligneous material when the complex does not comprise the coating layer. The coating layer 6 is for example a primer layer or a layer of polyurethane or a layer of varnish. The coating layer protects de layer of ligneous material from ultraviolet radiations which can cause an accelerated aging of the layer of ligneous material. The coating layer 6 is further arranged such that the layer of ligneous material remains visible from outside the trim element by being translucent or transparent. The coating layer can also be arranged to modify the aspect of the layer of ligneous material, for example by being colored. The coating layer 6 is arranged such that the complex 1 remains flexible and able to be shaped when the coating layer 6 is applied on the front face of the layer of ligneous material 2.
The complex 1 described above is substantially planar when assembled, as shown in Fig. 1, and has to be shaped in order to be adapted to trim a part of the compartment of a vehicle for example. By planar, it is meant that the complex 1 is substantially flat when laid on a planar surface. However, since the complex 1 is flexible, it can adopt other shapes in its initial state, but these shapes are not stable. In particular, the complex 1 is able to conform to the shape of a surface on which it is laid but will not keep this shape when removed from the surface.
According to the invention, the method is in particular adapted to form a complex 1 having a final three-dimensional shape comprising at least one undercut 8, as shown in Fig. 4. By undercut 8, it is meant that a part of the complex 1 is bent such as to form a concave cavity 10 with the rest of the complex. According to the embodiment shown in Fig. 4, the back face of the complex forms the interior of the concave cavity 10. However, it is to be understood that the final three-dimensional shape is not limited to the formation of an undercut but can be another complex three-dimensional shape. By final three-dimensional shape, it is meant that, in its final state, the shape of the complex 1 is stable, i.e. the complex 1 is no longer flexible and retains its three-dimensional shape.
The method for shaping the complex 1 from the substantially planar initial shape shown in Fig. 1 to the final three-dimensional shape shown in Fig. 4, without damaging the complex 1, and more particularly the layer of ligneous material 2, will now be described.
In a first step, the complex 1 is subjected to a stabilizing step wherein the layer of ligneous material is subjected to a treatment arranged to reach the moisture equilibrium of the ligneous material contained in the layer of ligneous material.
By moisture equilibrium of the ligneous material, it is meant that the ligneous material can neither be subjected to a desorption nor to an adsorption of moisture. Such a moisture equilibrium is reached when the moisture of the layer of ligneous material substantially comprised between 7% and 9%. In order to reach the moisture equilibrium, the complex 1 is for example placed in a humidified atmosphere such that the layer of ligneous material 2 is humidified until its moisture is substantially comprised between 7% and 9%. In particular cases, the moisture in the ligneous material can be greater than 12%, but then the visible veneer surface has to be reworked while wood fibers are rising in the veneer. Alternatively, the first stabilizing step can be performed on the layer of ligneous material prior to its assembly with the other layers of the complex 1.
The complex 1, in its initial planar shape, is then placed in a first forming tool 12, as shown in Fig. 1. The first forming tool is for example a compression tool and comprises a first part 14 and a second part 16 movable relative to each other between an open position, wherein the complex 1 can be placed in the tool 12, and a closed position wherein a particular three-dimensional intermediate shape is defined between a wall 18 of the first part 14 and a wall 20 of the second part 16. The intermediate three-dimensional shape is a simple shape, for example a curved shape.
When the complex 1 is placed in the first forming tool 12, the front face of the complex 1 is applied against the wall 18 of the first part 14 such that the complex adopts the shape of said wall 18, since the complex is flexible. The wall 18 of the first part 14 is for example heated up to a temperature corresponding to the melting point of the lignin present in the layer of ligneous material 2, for example a temperature substantially comprised between 90°C and 130°C depending on the ligneous material, the second part of the tool remaining at a temperature around 30°C. Preferably, the wall 20 of the second part is cooled down to present a temperature around 25°C The layer of ligneous material is therefore heated.
The first forming tool 12 is then closed such that the wall 20 of the second part 16 of the first forming tool 12 is applied against the back face of the complex 1 and applies a pressure on the complex 1. The combined effect of the temperature and of the pressure causes the complex 1 to plastically deform, i.e. the ligneous material is subjected to a necking in the area where it is deformed., to adopt the shape of the intermediate three-dimensional shape defined by the first and second parts 14 and 16 of the first forming tool 12 in its closed position and to retain this intermediate shape, since the deformation is a plastic deformation. Consequently, at the end of this first deformation step, the complex 1 has acquired a simple intermediate three-dimensional shape. Since the shape is simple, the deformation of the complex 1 does not impart an important stress on the layer of ligneous material 2, which can deform without cracking or breaking between its initial shape and its intermediate shape.
Alternatively, the layers of the complex 1 can be placed one by one in the first forming tool, i.e. without being attached to each other, and the first deformation step can also cause the layers of the complex 1 to be assembled together. Alternatively, some of the layers of the complex 1 can be assembled prior to the first deformation step and be assembled with the other layers of the complex 1 during the first deformation step. In another variant, the layer of ligneous material 2 can be subjected to the first deformation step alone and be assembled with the other layers of the complex 1 after the first deformation step.
After the first deformation step, the second part 16 of the first forming tool 12 is moved to the open position and the complex 1 is left in the first part 14.
After the first deformation step, a stabilization step is carried out. The stabilization step is substantially as described previously and is carried out such that the moisture equilibrium of the ligneous material contained in the layer of ligneous material is reached. The stabilization step can be carried out, for example, while the complex 1 remains in the first part 14 of the first forming tool 12, by placing the first forming tool in a humidified atmosphere. Similarly, the first stabilization step described previously can be carried out after the complex 1 has been placed in the first part 14 of the first forming tool 12 by placing said first part 14 in a humidified atmosphere prior to closing the first forming tool 12 to carry out the first deformation step. Alternatively, the stabilization step can be carried out while the first forming tool 12 is still in its closed position. The stabilization step is also a cooling step of the layer of ligneous material, said cooling taking place in an atmosphere having a humidity around 50%. In particular, to reach a moisture equilibrium around 7%, the layer of ligneous material is placed in an atmosphere at 23°C and having a relative humidity of 55%.
The stabilization step enables to stabilize the layer of ligneous material in its intermediate shape such that the layer of ligneous material does not tend to further deform or to return to its initial shape after the first deformation step. The stabilization step can also be used to release internal tensions in the layer of ligneous material, which can cause a further warpage of said layer, i.e. a further deformation of the layer added to the deformation caused by the first forming tool 12.
Once the complex 1 and its layer of ligneous material 2 are stabilized, a second deformation step, using a second forming tool 22 is carried out, as shown in Figs. 2 and 3.
The second forming tool 22 comprises a first part 14 and a second part 24 movable relative to each other between an open position (Fig. 2) and a closed position (Fig. 3) wherein a particular three-dimensional final shape is defined between a wall 18 of the first part 14 and a wall 26 of the second part 24. According to an embodiment, the first part 14 of the second forming tool 22 is the same part as the first part of the first forming tool 12, the complex 1 remaining in the first part 14 during the first and second deformation steps. Alternatively, the second forming tool 22 can be entirely distinct from the first forming tool 12. The second part 24 of the forming tool 22 is arranged to form with the first part 14 the final shape of the complex 1 to be obtained or another intermediate shape if at least one other deforming step is needed to obtain the complex final three-dimensional shape of the complex 1 without damaging the layer of ligneous material. In the following description, only two deforming steps will be described, such that the second part 24 of the second forming tool 22 forms with the first part 14 a final three-dimensional shape with an undercut in order to obtain a complex 1 as shown in Fig. 4.
To this end, the second part 24 for example comprises at least one drawer 28 movable between a retracted position, wherein the second part 24 can be moved between the open and closed position without interfering with the first part 14, and an active position, wherein, when the second part 24 is in the closed position, the drawer 28 and the wall 26 of the second part 24 define with the wall of the first part 14 the space having the final three-dimensional shape, as shown in Fig. 3. Consequently, when the second part 24 moves from the open to the closed position, the drawer 28 is placed in its retracted position, and when the second part 24 is in closed position, the drawer 28 is deployed in its active position to form with the first and second parts 14 and 24 the shape of the complex 1 to be obtained. Depending on the shape to be obtained, the second part 24 and/or the first part 14 can comprise one or more drawers allowing to form a complex shape in active position and to move the parts of the forming tool relative to each other in the retracted position.
When the second part 24 is in the closed position and the drawer(s) 28 in the active position, a pressure is applied on the complex 1 having the intermediate shape until it acquires the final shape defined by the second forming tool 24. During this second deformation step, the wall 18 of the first part 14 can be heated as during the first deformation step up to a temperature corresponding to the melting point of the lignin present in the layer of ligneous material 2 for allowing a plastic deformation of the complex 1 from the intermediate shape to the final shape.
When the second deformation step is completed, the drawer(s) are moved in the retracted position and the second part 24 in the open position so that the complex 1 having the stable final shape can be retrieved from the second forming tool 22.
If needed, another stabilization step can occur prior to retrieving the complex 1 from the first part 14 of the second forming tool 24 to obtain a stabilized and stable three-dimensional complex 1.
As disclosed previously, if the complex 1 needs to be further deformed, another stabilization step followed by another deformation step are carried out. The determination of the number of deformation steps depends on the complexity of the shape of the complex 1 to be obtained. The deformation steps are carried out such that said steps do not cause cracking or breaking of the layer of ligneous material. Since the deformation steps can be carried out progressively, with stabilization steps in-between, the stress applied to the layer of ligneous material during each deformation step can be reduced.
As described above, the method can be carried out in several steps in tools corresponding to various deformation states of the layer of ligneous material. The deformation of the layer of ligneous material then occurs progressively step by step until a final shape is attained. This step by step process avoids that fissures or breaks are formed in the layer of ligneous material.
The first and second forming tools 12 and 22 have been described as compression tools. However, one of said tool could be an injection tool arranged to form an injection cavity, wherein an injection material is injected to form a support layer on the back face of the complex 1. Alternatively, such a support layer (not shown) could be formed after the complex 1 has acquired its final shape by placing the finished complex in an injection tool.
The complex has been described as comprising two or three layers. However, it is to be understood that the complex could comprise more layers, on its front face and/or on its back face.
The method disclosed above can be entirely industrialized and do not require manual steps to be carried out.

Claims

Method for producing a trim element having a three-dimensional shape and comprising at least a layer of ligneous material (2), the method comprising the following steps:
- providing a substantially planar layer of ligneous material (2),

- shaping the layer of ligneous material (2) in order to obtain the three-dimensional shape of the trim element to be produced,
characterized in that the shaping step comprises at least the following successive steps:
- deforming the layer of ligneous material (2) to an intermediate shape between the initial planar shape and the final three-dimensional shape of the layer of ligneous material (2),

- stabilizing the layer of ligneous material (2) having the intermediate shape in order to reach the moisture equilibrium of the ligneous material,

- deforming the layer of ligneous material to the final three-dimensional step.
Method according to claim 1, wherein the stabilizing step is a humidifying step, wherein the layer of ligneous material (2) is humidified to reach the moisture equilibrium of the ligneous material
Method according to claim 2, wherein the layer of ligneous material (2) is humidified to reach a moisture of the layer of ligneous material substantially comprised between 7% and 9%.
Method according to any one of claims 1 to 3, wherein the method further comprises a stabilization step carried out prior to deforming the layer of ligneous material (2) from the initial planar shape to the intermediate shape.
Method according to any one of claims 1 to 4, wherein the step of deforming of the layer of ligneous material (2) to the final three-dimensional shape involves creating an undercut (8) in the three-dimensional shape of the layer of ligneous material (2).
Method according to any one of claims 1 to 5, wherein the step of deforming the layer of ligneous material (2) from the initial planar shape to the intermediate shape comprises the step of placing the layer of ligneous material (2) having the initial shape in a first forming tool (12) comprising a first part (14) and a second part (16), said parts defining together a space having the intermediate shape of the layer of ligneous material (2) and applying a pressure on the layer of ligneous material (2) between the first and second parts (14, 16) of the first forming tool (12) such that said layer acquires the intermediate shape.
Method according to claim 6, wherein the step of deforming the layer of ligneous material (2) from the intermediate shape to the final shape comprises the step of placing the layer of ligneous material (2) having the intermediate shape in a second forming tool (22) comprising a first part (14) and a second part (24), said parts defining together a space having the final shape of the layer of ligneous material (2) and applying a pressure on the layer of ligneous material (2) between the first and second parts (14, 24) of the second forming tool (22) such that said layer acquires the final shape.
Method according to claim 6 and 7, wherein the first part (14) of the first forming tool (12) is also the first part (14) of the second forming tool (22), such that the layer of ligneous material (2) remains in said first part (14) between the first deformation step and the second deformation step.
Method according to claim 7 or 8, wherein the second part (24) of the second forming tool (22) comprises at least one drawer (28) movable between a retracted position, wherein the second part (24) can be moved relative to the first part (14) of the second forming tool (22), and an active position without interfering with said first part (14), wherein the second part (24) defines with the first part (14) a final three-dimensional shape comprising at least one undercut (8).
Method according to any one of claims 1 to 9, wherein the layer of ligneous material (2) is heated at least during the deformation steps up to a temperature corresponding to the melting point of the lignin present in said layer of ligneous material (2).
Method according to any one of claims 1 to 10, wherein a flexible backing layer (4) is arranged on the back side of the layer of ligneous material (2) prior to its deformation in order to form a planar flexible complex (1), the whole complex (1) being deformed during the shaping step of the method.
Trim element comprising a three dimensionally shaped ligneous material produced by the method according to any one of claims 1 to 11.