Method for stiffening a curved sheet-metal panel by means of a cardboard panel

A method for stiffening a curved sheet-metal panel, in which a flat cardboard panel is applied to the concave face of the curved sheet-metal panel, includes a step in which a number of parallel cuts that pass partially through the thickness of the cardboard panel are made in that face of the cardboard panel that is intended to be applied to the concave face of the sheet-metal panel. A number of adhesive strips that each cover said parallel cuts are applied to said face of the cardboard panel and said face, provided with said adhesive strips, of the cardboard panel is applied to said concave face of the sheet-metal panel.

The present invention relates to a method for stiffening a curved sheet-metal panel, in which a flat cardboard panel is applied on the concave inner face of the curved sheet-metal panel.

The invention in particular relates to the application of the method according to the invention to the stiffening of a sheet-metal part, such as the roof of a motor vehicle.

Motor vehicle roofs are generally made from sheet-metal.

Due to the small thickness of the sheet-metal, these roofs have an insufficient thickness.

It is consequently necessary to increase the thickness of these roofs.

One known method consists of fixing a flat cardboard panel on the concave inner face of the sheet-metal roof.

FIG. 1is a perspective view partially showing the body of a motor vehicle.

Below the roof1of this body, two cardboard panels2,3are shown in dotted lines.

The larger of these cardboard panels2,3is fixed between the rear crosspiece4and the middle crosspiece5.

The other cardboard panel3is fixed between the crosspiece5and the front crosspiece6.

Prior to the placement of the cardboard panel(s), double-sided adhesive strips are glued thereon so that the strips can adhere to the cardboard and to the sheet-metal of the roof.

However, in light of the thickness of the cardboard panel, the latter tends to return to its initial horizontal position.

Consequently, the adhesion of the strips tends to let go.

Likewise, most of the time, deformations of the sheet-metal of the roof can be seen that are caused during placement of the cardboard panel.

These deformations are harmful to the appearance quality of the roof and are consequently unacceptable.

The aim of the present invention is to resolve the drawbacks of the above known method.

This aim is achieved, according to the invention, using a method for stiffening a curved sheet-metal panel in which a flat cardboard panel is applied on the concave face of the curved sheet-metal panel, characterized by the following steps:a) a series of parallel cuts that pass partially through the thickness of the cardboard panel are made in that face of the cardboard panel that is intended to be applied to the concave face of the sheet-metal panel,b) a series of adhesive strips respectively covering said parallel cuts is applied to said face of the cardboard panel,c) said face of the cardboard panel provided with adhesive strips is applied on said concave face of the sheet-metal panel.

These cuts give the cardboard panel flexibility such that the latter can, during its application against the sheet-metal panel, adapt to the curved surface thereof without creating deformations.

Furthermore, in light of the cuts, the cardboard panel no longer tends to return to its flat shape and the strips no longer risk detaching from the sheet-metal panel.

Preferably, the adhesive strips are centered on the respective cuts, which makes it possible to distribute the adhesion of the strips on either side of the cuts in a balanced manner.

Also preferably, the cardboard panel comprises three parallel sheets separated from one another by a corrugated sheet, the cuts passing through two of said parallel sheets as well as the corrugated sheet comprised between them.

As a result, the parts of the cardboard panel remain connected on either side of the cuts, at least owing to the third sheet.

In the case of a roof, the sheet-metal panel is substantially rectangular and is concave in the direction of its length and in the direction of its width.

In this case, on the concave face of the cardboard panel, two series of cuts are made, one of the series being oriented in the direction of the length of the panel and the other being oriented in the direction of the width of this panel.

In this case, the cardboard panel is flexible in both directions and consequently, during its placement, it perfectly marries the concave side of the sheet-metal panel in the direction of its length and its width, without creating deformation of the sheet-metal, or a risk of detachment of the cardboard.

In the case above, preferably, only the series of cuts made in one of the two directions is covered by adhesive strips.

Also preferably, the series of cuts covered by adhesive strips is the series of cuts oriented in the direction of the length of the cardboard panel.

In one particularly advantageous version, step c) of the method is carried out by placing the cardboard panel provided with adhesive strips flat in a basin whereof the peripheral edge is applied tightly against the concave face of the sheet-metal panel, and creating a vacuum in the basin sufficient for the cardboard panel to press against the sheet-metal panel and to adhere thereto using the adhesive strips.

According to another aspect, the invention also relates to the application of the method according to the invention to the stiffening of a sheet-metal part of a motor vehicle.

This sheet-metal part can be the roof.

In this application, the cardboard, aside from its function of stiffening the roof, also has an acoustic function with respect to road noise, rain noise, etc.

The present invention also relates to a stiffening panel for a curved sheet-metal panel, said stiffening panel being obtained from cardboard and intended to be applied on the concave face of the curved sheet-metal panel, characterized in that it comprises a series of parallel cuts passing partially through the thickness of the cardboard panel from the upper face of the cardboard panel and a series of adhesive strips respectively covering said parallel cuts.

Preferably, the adhesive strips are centered on the respective cuts.

Advantageously, the cardboard panel comprises three parallel sheets separated from one another by a corrugated sheet, the cuts passing through two parallel sheets as well as the corrugated sheet being comprised between them.

In one alternative, the upper face of the cardboard panel includes two series of cuts, one of these series being oriented in the direction of the length of the panel and the other being oriented in the direction of the width of this panel. Advantageously, only the series of cuts made in one of the two directions is covered by adhesive strips. Furthermore, the series of cuts covered by adhesive strips is preferably the series of cuts oriented in the direction of the length of the cardboard panel.

Other particularities and advantages of the invention will also appear throughout the description below.

FIGS. 2 and 3show a sectional view of the cardboard panel7before it is applied on the concave inner face of the sheet-metal roof1of a motor vehicle.

As shown inFIG. 2, in a first step of the method according to the invention, a series of parallel cuts8passing partially through the thickness of the cardboard panel7is produced on the face7aof the cardboard panel7that is intended to be applied on the concave inner face of the sheet-metal roof1.

In a following step, shown inFIGS. 3 and 4, a series of adhesive strips9respectively covering the parallel cuts8is applied on the face7aof the cardboard panel7.

These adhesive strips9are preferably centered on the cuts8(seeFIG. 4).

The face7aof the cardboard panel provided with the adhesive strips9is then applied (seeFIG. 5) on the concave inner face1aof the sheet-metal roof1.

In the example illustrated byFIGS. 2, 3 and 5, the cardboard panel7comprises three parallel sheets10,11,12separated from one another by a corrugated sheet13,14.

Furthermore, the cuts8pass through two parallel sheets, i.e., the sheets10,11, as well as the corrugated sheet13comprised between them.

The sheet-metal panel1of a motor vehicle is substantially rectangular and is concave in the direction of its length and in the direction of its width.

In this case, two series of cuts8and8aare made on the face7aof the cardboard panel7.

The series of cuts8is oriented in the direction of the length of the panel7, and the other series of cuts8ais oriented in the direction of the width of this panel7, as shown inFIG. 4.

In this example, only the series of cuts8made in one of the two directions is covered by adhesive strips9.

Furthermore, the series of cuts8covered by the adhesive strips9is the series of cuts oriented in the direction of the length of the cardboard panel7.

The step of the method, as illustrated inFIG. 5, is preferably carried out by placing the cardboard panel7provided with adhesive strips9flat in a basin (not shown) whereof the peripheral edge is applied tightly against the concave face1aof the sheet-metal roof1and creating, in the basin, a sufficient vacuum for the cardboard panel7to be applied against the sheet-metal roof1and to adhere thereto owing to the adhesive strips9.

FIG. 5shows that during this step, the cardboard panel7marries the concave surface of the roof1owing to the cuts8and8a.

ThisFIG. 5in fact shows that the cuts8can open due to the concavity of the roof due to the elasticity of the adhesive strips9, which flatten between the roof1and the cardboard panel due to the forces involved.

Thus, the application of the cardboard panel7does not exert any excessive force on the roof1, and the latter does not undergo any damage during implementation of the method according to the invention.

Of course, the invention is not limited to stiffening sheet-metal roofs of motor vehicles, but may apply to the stiffening of any curved sheet-metal panel.