Method and related device for cutting plastic film

Abstract

The present invention relates to a method for cutting a plastic film and a related device, in particular, to a device for cutting a plastic film arranged on a body part for masking or decoration, the device comprising a sonotrode mounted on a controlled mechanism, the sonotrode of the device having a cutting end, the cutting end having a flat surface and provided with a partial element forming a protrusion, the height of the protrusion protruding from the flat surface being substantially equal to the thickness of the film, the partial element forming the protrusion being able to move freely. The present invention also relates to a method using the above device.

Description

Technical Field

[0001] The invention relates to the field of decoration or treatment of motor vehicle body parts. More specifically, the invention relates to a method for cutting a plastic film previously arranged on a body part. Such a plastic film can be used in particular for partial masking before a subsequent finishing or assembly operation or for decorating a body part. For example, such masking can be intended to save an area from being sprayed with paint or to preserve future adhesive tracks. Background Art

[0002] For example, it is known to use masking techniques (also known as masking) to delineate areas of an automotive component that are to be painted and areas that are not to be painted.

[0003] The masking operation aims at placing small-sized sheets of film at some locations on the part to be painted. This placement process is complex and is usually done manually. In order to obtain a certain precision, at least one edge of the masking film or strip must be positioned very accurately at the border of the area along a relief or embossing of the part, such as a groove, a molding edge, or a natural edge of the part. However, it is difficult or even impossible to place large sheets of masking film on the body part with high positioning accuracy because the masking film is flexible and can wrinkle. Robots can be used to position the masking film strip or sheet in order to have a precise reference system relative to the part to be masked. The use of robots to position the sheets of film is also complicated, considering the flexibility of the film and the formation of wrinkles.

[0004] However, the requirements regarding the quality of the painted surface require very sharp and flawless transitions. Therefore, the position tolerance of the border between painted and unpainted areas is very small, around + / - 0.1 mm.

[0005] This requirement is incompatible with known positioning devices. Therefore, there is no method for very accurate large-area masking of body parts by obtaining a precise (clear) masking boundary without obvious reliefs to delimit two areas: one to be decorated by the film and one to be undecorated, or, when the finishing operation is a painting operation, one to be painted and one to be unpainted.

[0006] So the situation can be improved. Summary of the invention

[0007] The invention has for example an object to improve the cutting accuracy of plastic films, in particular in the case of masking operations prior to painting of automotive parts.

[0008] The invention relates to an ultrasonic device for cutting a plastic film "in situ" after it has been arranged on a body part, the device comprising a sonotrode which can be mounted on a controlled mechanism, the cutting end of the sonotrode having a substantially flat surface which forms the bottom provided with a partial element forming a projection (or bulge), the height of which protrudes from the flat surface being substantially equal to the thickness of the film, the partial element forming the projection being ideally able to move freely.

[0009] The ultrasonic device for cutting a membrane may also include one or more of the following features considered alone or in combination:

[0010] The local element forming the projection is a wire which is freely movable (rotatable) beneath the sonotrode, which advantageously enables automatic tangential positioning to a predetermined cutting path and results in a high cutting accuracy.

[0011] The diameter of the metal wire is between 50 and 400 microns. Thus, the wire with reduced diameter is flexible and becomes movable and freely orientable under the sonotrode, which also gives it flexible characteristics and resistive characteristics suitable for ultrasonic cutting.

[0012] The device is configured to achieve renewal of the wire by automatically unwinding the reel, the unwinding being continuous or discontinuous. Advantageously, this makes it possible to renew the portion of the wire that cuts the plastic film by ultrasound after a predetermined number of component cuts, and avoids cutting operations with excessively worn portions of the wire.

[0013] The invention also relates to a method for cutting a plastic film arranged on a component by means of a device as described above. Thus, the plastic film is cut directly on the component, rather than pre-cut on a cutting frame or anvil, which has the advantage of avoiding transfer. Thus, it is possible to cut plastic films with the same thickness as the wire, which is particularly interesting for masking in applications related to the painting of automotive parts.

[0014] The method for cutting the plastic film according to the present invention may further include one or more of the following features considered individually or in combination:

[0015] The method includes arranging a plastic film for shielding on the component before the sonotrode and the component are relatively moved along a predetermined cutting path.

[0016] This method uses a wire having a diameter substantially equal to the thickness of the plastic film. Thus, in addition to allowing a high cutting precision to be obtained, the correspondence between the diameter of the wire and the thickness of the sheet of material to be cut makes it possible to easily and quickly remove debris inside or outside the contour of the part formed after the cutting, or more generally, those portions of the film that are not useful for masking.

[0017] This method uses a wire whose diameter is greater than the thickness of the plastic film. Thus, in the case of applications related to the painting of a support part, a groove having a depth less than the diameter of the wire can be formed in the support part, which groove corresponds to the contour of the mask formed after cutting, and which can better delimit the painted area from the unpainted area.

[0018] The method uses a wire with a length between 8 and 15 mm, preferably 10 mm. Such a length advantageously gives the wire great flexibility and great mobility with respect to its diameter, so as to optimize the free positioning of the tangent along the predetermined cutting trajectory.

[0019] The method comprises the steps of removing the cut film in the case of a masking operation or overmolding, painting or bonding the part, removing the remaining film, or applying a varnish to the cut film in the case where the cut film remains on the part for decorative purposes.

[0020] Finally, the invention relates to a body part obtained by a cutting method as described above, comprising a cut plastic film and / or a groove dug along a predetermined trajectory. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The invention will be better understood on reading the following description, given by way of example only and without limiting character, and made with reference to the accompanying drawings, in which:

[0022] Figure 1 A device for cutting a sheet of plastic film according to a specific and non-limiting embodiment of the invention is shown.

[0023] Figure 2 Shown included in Figure 1 The sonotrode in the cutting device shown is located in the vicinity of the body component on which the plastic film to be cut is arranged.

[0024] Figure 3a The ultrasonic welding electrode is shown in the cutting operation of a membrane arranged on a body part. Figure 2 Shown in.

[0025] Figure 3b The ultrasonic welding electrode, the component, and the plastic film are shown at the end of the cutting operation of the plastic film. Figure 2 and Figure 3a Shown in.

[0026] Figure 4 An example of a vehicle body component and the cutting path of a plastic film for masking purposes are shown.

[0027] Figure 5 Shown in Figure 4The step of arranging the masking film on the body part has been shown in FIG.

[0028] Figure 6 The cut portion of the plastic masking film is removed after the cut portion of the plastic masking film is removed. Figure 4 and 5 The steps in which areas of a body component are painted are shown.

[0029] Figure 7 Shown in Figures 4 to 6 , which has been partially painted after the cut-out parts of the masking film have been removed.

[0030] Figure 8 A comparison of the position of a cutting element along a predetermined trajectory according to the prior art (8a) and the invention (8b) is shown, depending on whether the cutting element is rectangular or has free rotational movement. DETAILED DESCRIPTION

[0031] Figure 1 A device 1 for cutting a plastic film 3 arranged on a body part 5 is shown. The device 1 for cutting comprises a sonotrode 7 which is moved by a robot 9. The sonotrode 7 is usually made of metal, such as titanium, aluminum or steel, or any other material suitable for its function. The sonotrode 7 may or may not have been heat treated. It is configured to release vibration energy at its end.

[0032] The sonotrode 7 has a longitudinal axis 71 which is substantially perpendicular to the component during cutting. Figure 2 , 3a 3a and 3b) has a plane or substantially flat surface which is cleverly provided with a partial element 11 forming a protrusion which protrudes below the flat surface by a height substantially equal to the thickness of the plastic film 3. According to a preferred embodiment of the invention, the element 11 is a metal cutting strip or wire segment which is freely movable in angular orientation in the space around the longitudinal axis 71 of the sonotrode 7. The term "cutting strip" is here understood to mean the active / protruding part below the base of the sonotrode. The metal wire can be made of copper, for example, and can be wound on a reel. According to a variant of this embodiment, the cutting strip (element 11) has axial symmetry with respect to the axis 71 and has, for example, the shape of a pin, a tenon or a hemisphere and a height equal to the thickness of the plastic film 3 with respect to the flat or substantially flat cutting surface. Thus, in both embodiments, the element 11 is angularly positioned in a manner which is indifferent to the shape of the cutting trajectory, without having to fix the angular position by a specific control of the controlled mechanism (robot).

[0033] During the cutting operation, vibrations in the form of ultrasound are transmitted to the sonotrode 7 until they reach the element 11, which forms a protrusion on the flat or substantially flat surface of the cutting end 73. When the cutting end 73 is positioned in contact with the membrane 3, the vibrations transmitted to the element 11 forming the protrusion generate a thermal effect, thereby cutting the membrane 3 arranged on the body part 5.

[0034] Thus, the robot 9 moves the element 11 along a predetermined trajectory, for example the trajectory 13, and cuts the plastic film 3 arranged on the body part 5 according to this trajectory. The various actuators of the robot 9 for initiating the movement are not shown, since they are not useful for understanding the invention. For example, it can be a common industrial robot carrying a sonotrode 7.

[0035] Advantageously, the use of an element 11 forming a protrusion on the flat surface of the cutting end 73 of the sonotrode 7 makes it possible to avoid the need to control the orientation of a cutting tool (e.g. a rectangular knife or a blade) in order to follow a predetermined cutting trajectory. Thus, the cutting accuracy is improved and the robot 9 is simplified, since it is not necessary to control the movement of the element 11 forming the cutting tool around the longitudinal axis 71 of the sonotrode 7. Figure 8 A detailed description is given to illustrate the advantages of each.

[0036] The cutting accuracy is obtained by the positioning accuracy caused only by the robot and by the sharpness of the cut made locally by the element 11 (for example, by the thinness of the wire and its free positioning when the element 11 is a part of a wire).

[0037] According to a preferred embodiment of the present invention, the ultrasonic generator 7' is configured to operate at a frequency between 20 and 120 KHz, preferably between 50 and 90 KHz, and more preferably at 70 KHz or very close to 70 KHz, and the element 11 is a copper wire segment having a diameter between 50 and 400 microns and a length between 5 and 20 mm, preferably between 8 and 15 mm, and more preferably equal to 10 mm.

[0038] The term "length of the wire segment" is understood here to mean the length of that portion of the wire which is located between the flat or substantially flat surface of the cutting end 73 of the sonotrode 7 and the end of the wire segment. This portion of the wire can move freely. Thus, the wire has mobility, flexibility, length and diameter around the longitudinal axis 71 of the sonotrode 7, so that the resulting finesse of the cut is increased.

[0039] The movability of the partial element 11 in the form of a small diameter wire is particularly advantageous because it allows the cutting element 11 to have a predetermined cutting trajectory (i.e. Figure 1 The track 13 in the example shown has the capability of being freely positioned tangentially.

[0040] The cutting accuracy achieved in this way is particularly suitable for finishing or assembly operations on automotive parts, for example Figure 1 The masking operation before painting of the component 5 shown. It often happens that the appearance component has one or more areas that must be protected, which must remain unpainted. This is the case, for example, with areas that are desired to be transparent to allow backlighting, or areas for carrying decorative elements, or areas for fixing one appearance part to another by gluing. Therefore, it must be possible to delimit the painted and unpainted areas very precisely, for example.

[0041] like Figure 1 As shown, the device 1 according to the invention is particularly suitable for masking operations aimed at delimiting such areas.

[0042] The masking method according to the invention consists in using a device 1 to cut a plastic masking film 3 so as to define the area outside a predetermined track 13 as the area to be painted, and the area inside the track 13 as the area not to be painted, or vice versa. Depending on whether the area to be painted is inside or outside the closed track 13, the part of the cut masking film 3 to be removed before spraying the paint is inside or outside the track 13.

[0043] The use of the device 1 for cutting a plastic film 3 arranged on an automotive component 5 comprises the following preliminary steps: arranging a (or more) large-sized plastic film 3, which is able to cover one (or more) areas on the surface of the component 5 in a large, coherent and integrated manner, and then relatively displacing the sonotrode 7 relative to the component 5 on the visible surface of the component 5 so that the element 11 forming the protrusion travels along a predetermined trajectory 13 (which is the cutting trajectory) on the plastic film 3. The plastic film 3 can be arranged by gluing or by using an electrostatic effect, which keeps the plastic film 3 immobile on the component 5. The plastic film is usually a piece of film that is almost rectangular and is released directly from a dispensing roll and arranged, and then cut into a certain length when the area to be protected is completely covered. Therefore, the film can be cut into slices along the width of the roll without taking other precautions. The precise cutting of the slice along the predetermined trajectory 13 is then completed by the movement of the sonotrode 7 along the predetermined cutting trajectory 13. During the step of relative movement of the sonotrode 7 and the component 5, the flat or substantially flat cutting end 73 remains in contact with the plastic film 3, so that the local element 11 forming the projection cuts the film 3 along the trajectory 13. The cutting is achieved by the local heating of the plastic film 3 caused by the vibration of the element 11 forming the projection. The clever use of a wire with a diameter equal to the thickness of the plastic film 3, or the clever use of a hemispherical shape protruding from the flat cutting surface of the cutting end 73, makes it possible to achieve cutting over the entire thickness of the plastic film. Such cutting offers the advantage of making it possible to easily and without difficulty remove the portion of the film that is not intended to be masked during the step of spraying the paint.

[0044] According to a variant of the above-described cutting method, a wire having a diameter greater than the thickness of the plastic film 3 is used, which, in addition to precisely cutting the plastic film 3, has the effect of forming a groove 15 (at the bottom) in the body part 5 by heating the thermoplastic material of the body part 5 under the effect of vibration. Figure 3b The groove 15 can be seen in FIG. 1 . Advantageously, the groove 15 formed along the predetermined track 13 can further better define the painted area and the unpainted area, because the groove can slightly absorb the paint and thus limit the diffusion of the paint outside the groove 15 by capillary action.

[0045] According to a variant of the embodiment of the invention, a step of smoothing the plastic film 3 is performed before the step of relative movement of the sonotrode and the body part 5. This smoothing step is performed, for example, by means of a robot equipped with a smoothing device, which is placed on the part and moves along a predetermined trajectory 13 to remove or fade out defects that may arise during the laying of the plastic film 3 on the body part 5. These defects may be, for example, wrinkles, bubbles. The robot or any other equivalent actuator provided for this purpose, for example a smoothing device of the pad, brush or shim type, is flexible enough to crush bubbles, flatten wrinkles or compact the plastic film without the risk of damaging the film.

[0046] According to a variant of an embodiment of the invention, the device 1 for cutting the plastic film 3 used in the cutting process includes a device for replacing the useful part of the wire constituting the element 11 of the protrusion. The device for replacing the useful part of the wire can be activated manually or automatically. In the case of automatically activating the device for replacing the useful part of the wire (i.e. the cutting strip), the device can be suitable for releasing the wire continuously or discontinuously. The wire can be released toward the flat or substantially flat surface of the cutting end 73 of the ultrasonic welding electrode 7 by a groove (or distribution channel) dug longitudinally or obliquely in the end of the ultrasonic welding electrode 7 and leading to the outside of the ultrasonic welding electrode 7 (for example, leading to the reel of an automatically controlled unwinding machine). The wire release device can be combined with a cutting device for cutting the wire to cut off the used part. Therefore, the wire part forming the protrusion can be renewed after one or more cutting operations, and the cutting accuracy can be maintained by using the wire part that is not worn by the cutting operation.

[0047] Figure 2 A sonotrode 7 used by a cutting device 1 according to the invention is shown, which is in the immediate vicinity of a body part 5 on which a plastic film 3 having dimensions greater than those of the part 5 is arranged. The cutting end 73 of the sonotrode 7 has a local element 11 which is located on a flat surface of the cutting end 73 and forms a protrusion on the surface. The element 11 is a wire (at the bottom) located in a supply channel inside the sonotrode. Figure 3a 7 (visible in the figure), so that the wire is positioned perpendicular to the cutting surface of the cutting end 73 or inclined relative to the cutting surface where the wire emerges from the groove in the sonotrode. The wire is then automatically placed parallel to the surface of the component and naturally oriented in the direction that forms the tangent of the cutting trajectory during the movement of the sonotrode 7. In fact, the length characteristics, diameter characteristics and flexibility characteristics are cleverly defined so that during the relative movement of the sonotrode 7 and the component 5, the surface of the sonotrode 7 is in contact with the plastic film 3, the wire can move freely about the longitudinal axis 71 and is freely positioned in a manner tangential to the trajectory followed by the cutting end 73 of the sonotrode 7, wherein the cutting end 73 cuts the plastic film 3 due to the vibrations caused by the converter 7' (ultrasonic generator coupled to the sonotrode 7).

[0048] Figure 3a It shows that during the cutting operation of the plastic film 3, Figure 2 The flat or substantially flat surface of the cutting end 73 is kept in contact with the plastic film 3, and the local element 11 forming the projection and moving in vibration cuts the film 3 by locally heating the film 3. Figure 3a A partial cross-sectional view of the end of the sonotrode 7 is shown, showing an internal groove (or wire feed channel) opening on the periphery of the sonotrode. According to an alternative embodiment of the invention, the element 11 can remain locked in a groove allowing it to be positioned, or can be secured by means of a Figure 3a The wire release device (not shown) releases continuously or discontinuously, wherein the wire release device is suitable for sliding the wire in the wire feed channel of the ultrasonic welding electrode 7. In this figure, it can be seen that the local element 11 forming the protrusion realizes the cutting in the thickness of the plastic film 3.

[0049] According to a variant of the embodiment of the invention, the wire feed channel is not perpendicular to the flat or substantially flat surface 73 of the sonotrode (base), but rather at an angle of about 10 to 40 degrees to the surface 73 of the sonotrode 7. Advantageously, this enables the wire portion forming the protrusion, useful for cutting the plastic film, to be free from mechanical stresses (bending, twisting, etc.) when the predetermined trajectory 13 follows the main direction, without too sharp turns or bends.

[0050] Such an inclined wire feed channel without elbows inside the sonotrode prevents the wire from bending too much and makes the “natural” positioning of the wire along the predetermined trajectory 13 easier.

[0051] Figure 3b The sonotrode 7 is shown slightly withdrawn from the component 5 on which the plastic film 3 is arranged, at the end of the cutting operation by relative movement of the sonotrode 7 and the component 5, wherein the sonotrode is kept in contact with the plastic film 3 along a predetermined cutting trajectory during the cutting operation. We can see the groove 15 formed in the thickness of the plastic film 3 by the partial element 11 forming a protrusion. This groove thus delimits two parts of the plastic film 3 after cutting, one or the other of which can be quickly and easily removed from the component by a simple manual removal operation. The mask can thus be removed in one piece without breaking.

[0052] Figure 4An example of a body part 5 of a motor vehicle is shown, together with an example of a predetermined cutting trajectory 13 which is defined for performing masking, thereby defining areas to be painted outside the trajectory 13 and areas to be exempted from painting inside the trajectory 13. The cutting trajectory of the plastic film arranged for masking purposes thus corresponds to the delimitation of the painted area relative to the unpainted area.

[0053] Figure 5 , 6 7 show the successive steps of painting a body part 5 (the skin of the bumper) by carrying out masking using the cutting method according to the invention. Figure 1 The device 1 shown. The body part 5 is already Figure 4 Components shown in . Figure 5 The body component 5 is shown after a plastic film 3 has been arranged over the entire component (the plastic film 3 is shown transparent here). Figure 6 The part is shown being painted on the area to be painted after the plastic film 3 has been cut along a predetermined cutting path 13 and the portion of the plastic film outside the cutting path 13 has been removed. The portion of the plastic film 3 remaining after the portion outside the path 13 is removed realizes a masking which enables the areas of the body part 5 other than the area to be painted (i.e., the areas each still covered by a portion of the plastic film, which appear "zigzag" in the figure) to be protected from being painted. Figure 7 The body part 5 is shown after the remaining parts have been removed from its plastic film 3 (in a “zigzag” manner), showing a clear demarcation between painted and unpainted areas along a predetermined trajectory.

[0054] Figure 8 The successive positions of the cutting element along the predetermined cutting trajectory 13 are shown, which differ depending on whether the cutting element has an elongated or rectangular cutting shape (element 110) or is freely movable (element 11). The sonotrode 7 is carried by the arm 91 of the robot 9. The connection between the arm 91 of the robot 9 and the sonotrode 7 is not articulated. Figure 8 The left-hand portion of the cutting tool 10 marked 8a shows the successive positions of the rectangular cutting element 110 which must be rotated in order to adopt a position tangential to the trajectory 13. The successive orientations of the arm 91 of the robot show the need to position the arm 91 and therefore the sonotrode 7 so that the cutting element 110 has a position oriented along a tangent to the trajectory 13. This configuration of the cutting tool, which corresponds to the prior art, does not allow to follow curves (turns) accurately. Figure 8The right-hand portion of the part marked 8b shows the successive positions of a cutting line whose characteristics allow it to be freely moved and thus freely positioned when the sonotrode carrying it traverses the predetermined cutting trajectory 13. The cutting element is of a type that is “indifferent” to the shape of the predetermined trajectory 13. This is the case with elements of the cutting wire type, but it is also the case when the element forms a protrusion symmetrical about any axis perpendicular to the longitudinal axis of the sonotrode 7 (i.e., for example, a hemisphere, a pin or a tenon). In this case, the arm 91 of the robot 9 can maintain the same orientation along the predetermined cutting trajectory 13. Thus, in addition to the high cutting accuracy obtained thanks to the cutting device 1 according to the invention and the cutting method using the same, it is advantageously possible to avoid having to control an additional movement, namely a rotational movement of the cutting tool 110, in order to bring the tangential position of the cutting tool into line with the predetermined cutting trajectory 13.

[0055] The invention is not limited to cutting methods for masking operations, but also includes other operations, such as decorating or preparing parts for assembly. Thus, the plastic film 3 can be cut, for example, from a decorative film and / or a luminous film remaining on a body part.

[0056] The plastic film can be produced in a usable roll of constant width (and with predetermined dimensions). It is envisaged that the arrangement of the plastic film can be achieved in particular by gluing, or that the plastic film is maintained on the body part by means of an electrostatic effect. Its use and cutting can be designed for the purpose of overmolding with another plastic, in particular a translucent material, to produce a decorative element for a body part.

[0057] In other words, the device 1 according to the invention is suitable for the precise cutting of a plastic film 3 arranged on a body part 5. The device 1 comprises a sonotrode 7 which is moved in vibration by means of an ultrasonic generator 7'. The sonotrode 7 is mounted on a controlled mechanism 9 (robot). The cutting end of the sonotrode 7 of the device 1 for cutting a plastic film 3 has a flat surface 73 (also called "bottom"), which is provided with a partial element 11 forming a protrusion, the height of which exceeds the flat surface being substantially equal to the thickness of the plastic film 3. The partial element 11 forming a protrusion is ideally free to move, in particular around the longitudinal axis 71 of the sonotrode 7. According to a preferred embodiment of the invention, the partial element 11 forming a protrusion is a metal wire, for example made of copper, with a diameter between 50 and 400 micrometers. The device 1 may comprise means configured to achieve the renewal of the wire portion forming the protrusion by automatically unwinding the coil continuously or discontinuously.

[0058] The method according to the invention for cutting a plastic film 3 arranged on a component 5 by means of a device 1 comprises:

[0059] A plastic film 3 serving as a masking film is arranged on the component 5; and

[0060] The sonotrode 7 and the component 5 are moved relative to each other along a predetermined cutting trajectory 13 , and during the movement along the trajectory 13 , the cutting end 73 of the sonotrode remains in contact with the plastic film 3 .

[0061] The method according to the invention can use a wire having a diameter substantially equal to the thickness of the plastic film 3 or a wire having a diameter greater than the thickness of the plastic film 3. In the case of using a wire having a diameter greater than the thickness of the plastic film 3, implementation of the method advantageously allows the formation of a groove 15 in the component 5 in which the plastic film 3 is arranged.

[0062] Advantageously, the method for cutting the plastic film 3 uses a wire having a length between 8 and 15 mm, preferably 10 mm.

[0063] According to a variant of the method, a previous step of unit geometry calibration is carried out before the step of relative movement of sonotrode 7 and component 5 .

[0064] The invention also relates to a body part 5 obtained by the above method, comprising a groove corresponding to the predetermined cutting path and / or a portion of a plastic film, which portion is overmolded or not overmolded and is used, for example, for decorative purposes. Advantageously, the body part obtained by implementing the method according to the invention can be free of any relief of the type of embossing, groove, ridge, style ridge on the predetermined cutting path 13, since it is not necessary to position such a shape arranged on the visible surface of the part in order to precisely define the cutting path, including when the cutting path is positioned "fully skinned" on the body part.

[0065] The present invention is not limited to the above-mentioned embodiments, but more generally relates to any device for cutting a plastic film or a plastic film sheet arranged on a component, the device comprising an ultrasonic welding electrode mounted on a controlled mechanism (such as a robot), the ultrasonic welding electrode having a cutting end, the cutting end having a flat surface (bottom), the flat surface being provided with a local element, the local element forming a protrusion protruding from the flat surface and having a height substantially equal to the thickness of the plastic film or film sheet, the local element forming the protrusion and being in the shape of a pin, a tenon, a hemisphere or ideally being able to move freely, such as a wire.

[0066] List of reference numerals:

[0067] 1: Cutting device

[0068] 3: Plastic film

[0069] 5: Body parts

[0070] 7: Ultrasonic welding electrode

[0071] 7': Ultrasonic generator

[0072] 9: Robots

[0073] 11: Cutting element forming a protrusion

[0074] 13: Predetermined cutting trajectory

[0075] 15: Grooves formed in body parts.

Claims

1. A device (1) for cutting a plastic film (3) arranged on a vehicle body part (5), the device comprising a sonotrode (7), the device (1) being characterized in that the sonotrode (7) has a cutting end (73), the cutting end having a flat surface, the flat surface being provided with a partial element (11) forming a protrusion, the height of the protrusion protruding from the flat surface being equal to the thickness of the plastic film (3), the partial element (11) forming the protrusion being freely movable, wherein: The protrusion-forming partial element (11) is a metal wire.

2. The device (1) according to claim 1, wherein: The diameter of the metal wire is between 50 and 400 microns.

3. The device (1) according to claim 2, is configured to realize the renewal of the metal wire by automatically unwinding the reel.

4. A method for cutting a plastic film (3) arranged on a vehicle body component (5), the method being implemented using a device (1) as claimed in any one of claims 1 to 3.

5. The method according to claim 4, wherein: A plastic film (3) is arranged on the body part (5), The ultrasonic welding electrode (7) and the body component (5) are moved relative to each other along a predetermined cutting trajectory (13).

6. The method according to any one of claims 4 and 5, wherein: The diameter of the metal wire is equal to the thickness of the plastic film (3).

7. The method according to any one of claims 4 and 5, wherein: The diameter of the metal wire is greater than the thickness of the plastic film (3).

8. The method according to any one of claims 4 to 5, wherein the length of the metal wire is between 8 and 15 mm.

9. The method according to any one of claims 4 to 5, wherein the length of the metal wire is 10 mm.

10. The method according to any one of claims 4 to 5, comprising a preliminary step of unit geometry calibration prior to the relative movement step of the sonotrode (7) and the body part (5).

11. A car body component (5) comprising a cut plastic film and / or a groove (15) dug along a predetermined trajectory (13), the car body component (5) being obtained by a method according to any one of claims 4 to 10.

12. The body component (5) according to claim 11, which has no reliefs of the type of embossing, grooves or ridges along the predetermined trajectory (13).

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