METHOD AND INSTALLATION FOR JOINING A COVER LAYER TO AN OBJECT

Abstract

A cover layer is joined to an object by a pressing force and mechanical vibration. The cover layer has a cover layer contact surface, and the object has an object contact surface, and the cover layer contact surface and the object contact surface face each other. At least one of the cover layer and the object include a joining material. The cover layer contact surface is brought into contact with the object contact surface, and a sonotrode presses the cover layer against the object and applies mechanical vibration to an outer surface of the cover layer for a time sufficient for activating the joining material. Cover layer and object are conveyed relative to the sonotrode in a continuous manner in a conveying direction throughout the steps of arranging, of bringing into contact, of pressing and of applying vibration.

Claims

1. A method for joining a cover layer to an object, the method comprising the steps of: providing the cover layer and the object, the cover layer comprising a cover layer contact surface, and the object comprising an object contact surface, wherein a least one of the cover layer and of the object comprises a joining material, arranging the cover layer and the object with the cover layer contact surface and the object contact surface facing each other, bringing the cover layer contact surface in contact with the object contact surface, using a sonotrode to press the cover layer against the object and to apply mechanical vibration to an outer surface of the cover layer for a time sufficient for activating the joining material, conveying the cover layer and object relative to the sonotrode in a continuous manner in a conveying direction throughout the steps of arranging, of bringing into contact, of pressing and of applying the vibration, wherein the step of conveying causes a sliding movement, along the conveying direction, of the cover layer relative to a coupling-out face of the sonotrode, and wherein the coupling-out face has a coupling-out face portion that is not parallel to the object contact surface so that a distance between the sonotrode and the object contact surface continuously decreases along the coupling-out face portion as function of a position along the conveying direction.

2. The method according to claim 1, and further comprising the step of applying a consolidation pressing force to the cover layer against the object by a post-pressing device arranged behind the sonotrode with reference to the conveying direction.

3. The method according to claim 2, wherein the post-pressing device comprises at least one pressing roller.

4. The method according to claim 2, wherein the post-pressing device comprises at least one pressing shoe.

5. The method according to claim 2, wherein the post-pressing device applies the consolidating pressure for a time amounting to between 50% and 300% of a time of applying the vibration.

6. The method according to claim 2, wherein the post-pressing device also applies a mechanical vibration of a frequency and amplitude not sufficient for the joining material to remain flowable.

7. The method according to claim 1, further comprising the step of using a pre-pressing device to press the cover layer against the object, the pre-pressing device pressing device arranged in front of the sonotrode with reference to the conveying direction.

8. The method according to claim 1, comprising using a plurality of sonotrodes to press the cover layer against the object and to apply the mechanical vibration, the sonotrodes being arranged one behind the other with reference to the conveying direction.

9. The method according to claim 8, wherein at least two of the plurality of sonotrodes have coupling-out faces the shapes and/or angles with respect to the object contact face of which are not identical.

10. The method according to claim 1, comprising the step of varying an orientation of the sonotrode with respect to the object contact surface during the sliding movement.

11. The method according to claim 1, and further comprising laterally guiding the cover layer relative to the object.

12. The method according to claim 11, comprising using a structural feature of the cover layer and/or of the object to laterally guide the cover layer relative to the object.

13. The method according to claim 11, wherein the sonotrode has a guiding feature defining a lateral position of the cover layer relative to the sonotrode.

14. The method according to claim 1, and further comprising the step of removing portions of the cover layer that laterally protrude from a lateral outer edge of the object after a re-solidification of the joining material.

15. The method according to claim 1, wherein the sonotrode has a coating of a not metallic material.

16. The method according to claim 1, and comprising placing a separate protection layer between the sonotrode and the cover layer during the step of applying the mechanical vibration.

17. The method according to claim 1, wherein the joining material is a thermoplastic material, and wherein activating the joining material comprises making the joining material flowable.

18. The method according to claim 17, wherein the cover layer contact surface comprises the joining material and wherein the joining material forms an energy director.

19. The method according claim 17, wherein the object contact surface does not comprise the joining material, and wherein the object contact surface forms an energy director.

20. The method according to claim 17, wherein at least a part of the object contact surface or the cover layer contact surface, which part faces the joining material, is capable of being penetrated by the joining material.

21. The method according to claim 17, wherein at least a part of the object contact surface of the cover layer contact surface, which part faces the joining material, comprises a further thermoplastic polymer being weldable to the joining material, or a thermoplastic or thermoset polymer capable of forming an adhesive connection with the joining material.

22. The method according to claim 1, wherein the joining material is a curable adhesive, and wherein activating comprises initiating and/or accelerating the curing process.

23. The method according to claim 22, comprising the further step of applying the joining material to at least one of the object and of the cover layer.

24. The method according to claim 23, wherein for applying the joining material, an applying device arranged in front of the sonotrode with reference to the conveying direction is used.

25. The method according to claim 1, wherein the joining material constitutes the whole cover layer contact surface or the whole object contact surface.

26. The method according to claim 1, wherein the cover layer is provided from a feed roller.

27. The method according to claim 1, wherein the object is one of a plurality of objects which are conveyed in succession.

28. The method according to claim 1, wherein the step of conveying is carried out with a conveying speed of at least 10 m/min and at most 200 m/min.

29. The method according to claim 1, wherein the object is solid and rigid.

30. The method according to claim 29, wherein using the sonotrode to press the cover layer against the object and to apply mechanical vibration causes at least portions of the joining material in a flowable state to interpenetrate structures of the solid object, so that after solidification of the joining material a positive fit connection between the cover layer and the object results.

31. The method according to claim 29, wherein the cover layer is an edge strip and the object is a board and wherein the edge strip is joined to one edge of the board.

32. The method according to claim 31, wherein the board comprises a board of a wood composite or is a hollow core board.

33. The method according to claim 1, wherein at least one of the cover layer and of the object comprises a sealing pad being a structure that has a slightly greater dimension than an average dimension towards the contact surface it faces, the sealing pad being arranged to lie at a lateral outer edge of the object after joining.

34. The method according to claim 1, wherein an active width being an extension, along the conveying direction, of a region in which the coupling-out face is pressed against the object surface, corresponds to at least 5 times the length of a path by which the sonotrode moves the cover layer relative to the object in a direction perpendicular to the object surface.

35. The method according to claim 34, wherein the active width is at least 1 cm

36. An installation for carrying out the method as defined in claim 1, the installation comprising: a feeding zone equipped for arranging the cover layer and the object with the contact surface of the cover layer and the contact surface of the object facing each other, and for bringing the contact surface of the cover layer in contact with the contact surface or the object, a liquefaction zone arranged downstream of the preheating zone and being equipped with a vibration device comprising at least one sonotrode arranged for applying mechanical vibration and a pressing force to an outer surface of the cover layer, an object conveyor for conveying the object in a continuous manner in a conveying direction through the feeding zone and the liquefaction zone, and a cover layer conveyor for feeding the cover layer into and through the feeding zone. wherein the sonotrode has a coupling-out face a portion of said coupling-out face is not parallel to the object contact surface of the object so that a distance between the sonotrode and the object contact surface continuously decreases along the coupling-out face portion as a function of a position along the conveying direction.

37. The installation according to claim 36, and further comprising a consolidation zone equipped with a post-pressing device arranged for further application of a pressing force to the outer surface of the cover layer.

38. The installation according to claim 36, wherein the sonotrode is stationary.

39. The installation according to claim 36, wherein the vibration device has a plurality of sonotrodes, and wherein the property of having the coupling-out face with the portion of which is not parallel to the object contact surface of the object is present in at least one of the sonotrodes.

40. The installation according to claim 36, wherein the conveyor is equipped for conveying in succession a large number of the objects which are boards.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0075] The invention and exemplified embodiments of method and installation according to the invention are described in further detail in connection with the appended figures, in which same reference signs designate same or element or elements having a same function, and wherein the figures show:

[0076] FIG. 1 an object and a cover layer joined in a stationary process according to the prior art;

[0077] FIG. 2 a schematic representation of a method for joining a cover layer to an object;

[0078] FIG. 3 a variant with multiple sonotrodes;

[0079] FIG. 4 a variant with a sonotrode with variable angle;

[0080] FIG. 5 a post-pressing device in the form of a pressing shoe;

[0081] FIGS. 6-9 pairings of objects being hollow core boards and of cover layers;

[0082] FIG. 10 an installation for carrying out the method;

[0083] FIG. 11 a variant with the joining material being an adhesive; and

[0084] FIGS. 12-15 further pairings of objects being hollow core boards and of cover layers together with sonotrodes, the respective arrangement being equipped for laterally guiding the cover layer relative to the respective object.

[0085] In this, FIGS. 1, 6-9, and 12-15 show schematic partial cross sections through a plane perpendicular to the x direction (the conveying direction if applicable), whereas FIGS. 2-5, 10 and 11 depict schematic side views.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0086] FIG. 1 shows an object 1 to which a cover layer 2 is joined in a stationary process according to the prior art, which process includes coupling mechanical vibration energy into the cover layer and/or the object to make thermoplastic material flowable and to cause it to interpenetrate structures of at least one of the elements to be joined, whereby after re-solidification a connection between the object and the cover layer results.

[0087] The cover layer 2 of FIG. 1 is assumed to include thermoplastic material. For joining, a sonotrode 6 presses the cover layer 2 against the object 1, and as a consequence of the thermoplastic material becoming flowable and of the pressing force, the cover layer and the object are subject to a relative movement by a path p. The dashed line shows the cover layer 2′ at the end of the process, with cover layer material interpenetrating the object 1.

[0088] If this process is modified to become a continuous process, according to the prior art the stationary sonotrode that is subject to the movement by the path p is replaced by a rolling sonotrode or a sequence of rolling sonotrodes. If a single rolling sonotrode is used, this implies that the process has to be carried out relatively slowly (the smaller the diameter of the sonotrode roll the slower), because the movement by the path p into the direction perpendicular to the object surface has to be made given a very short active width defined by the surface part along which the sonotrode roll makes contact with the cover layer. If a plurality of rolling sonotrodes is used, there is the challenge that the contact surfaces between subsequent rolls and the cover layer can not be arbitrarily close to each other, for geometrical reasons because of the extension of the rolls.

[0089] It is an insight of the present invention that the principles of the stationary process may be implemented in a continuous process without the mentioned disadvantages of a rolling sonotrode by means of a sonotrode that has a coupling-out face portion at an angle to the surface of the cover layer, along which the cover layer slides relative to the sonotrode.

[0090] This is illustrated in FIG. 2. The object 1 and the cover layer 2 are together conveyed in a conveying direction CD, whereas the sonotrode 6 vibrates at a stationary position.

[0091] The object 1 may for example be generally flat, board-like object having two large surfaces and edges extending along a periphery of the object. It may for example be a solid board of essentially homogeneous material distribution or a so-called hollow core boards (HCB), including two comparably hard and dense cover layers, with a less dense interlining material between the cover layers. In the case of a HCB, the process of causing flowable thermoplastic material to flow into structures of the object may include causing thermoplastic material to flow into structure of the cover layers, whereas the interlining layer may in embodiments be too soft for causing sufficient friction to make the thermoplastic material flowable.

[0092] An edge of the board-like object 1, being the upper edge in the depicted configuration, forms the object contact surface 28.

[0093] The cover layer may be a strip-like material to be joined to at least one edge of the board if the board is generally flat. The cover layer may consist of the thermoplastic material (joining material), or it may include a layer of thermoplastic material and a not thermoplastic outer layer, for example a layer including a decoration. On the side of the cover layer contact surface 28, the cover layer may include one or more energy directors, especially in the form of ribs or humps. In embodiments, the energy director(s) comprise(s) at least one longitudinally extending rib, i.e., a rib extending in the conveying direction.

[0094] Possible methods of manufacturing a cover layer or a thermoplastic portion thereof include extrusion or a calendar process, or, for special applications, by 3D printing.

[0095] If the cover layer is to be joined to an edge (such cover layers are sometimes called “edge bands”), then the band width, i.e. the extension in a dimension perpendicular to the large surfaces of the object, may be somewhat larger than the thickness of the object, and the process may include positioning the cover layer so that it projects on both sides at least by a bit, and may include removing the projecting portions of the cover layer after the step of joining.

[0096] The sonotrode has a coupling-out face 61 that is essentially plane with a foremost cover layer receiving portion 62 that is convexly curved. Alternatively, it could have other shapes with be convexly curved, plane and/or concavely curved portions.

[0097] Due to its shape and due to its position relative to the conveyed object 1 (and given the thickness of the cover layer), the coupling-out face 61 defines an active surface that is considerably larger than the active surface of a rolling sonotrode for a same object-cover-layer-combination. The angle α between the coupling-out face 61 (or at least a portion thereof) and the surface of the first object causes the cover layer to be moved along a path p in a direction perpendicular to the object surface when object surface and cover layer are conveyed by an active width a of the active surface.

[0098] By this pressing against the first object while vibration impinges, thermoplastic material of the cover layer is caused to penetrate into structures of the object 1. This is illustrated in FIG. 2 by the cover layer being moved partially into the first object on the left-hand side of the figure. This yields, after re-solidification, a connection between the cover layer and the object.

[0099] In variants, the thermoplastic material may also be present in the object (with the cover layer having structures capable of being interpenetrated by the thermoplastic material) or possibly on both, the object and the cover layer (with a weld being generated by the process. The present invention is especially advantageous, however, if the object or the cover layer has structures capable of being interpenetrated and the other one has the thermoplastic material, because in a process that involves interpenetration, the process times tend to be longer and the path by which the cover layer is moved vertically (perpendicularly to the conveying direction) is longer.

[0100] FIG. 2 also shows an optional first pre-pressing device 31, for example a pressing roller, which presses the cover layer 2 against the object 1 before the vibration is coupled into it. This optional pre-pressing device 31 may contribute to the stability of the process and may also be used for keeping the cover layer 2 in a defined position relative to the object 1 during the step of using the sonotrode to press the cover against the object and to apply mechanical vibration, thereby coupling energy into the assembly.

[0101] FIG. 2 further shows a post-pressing device 32 (or consolidating device), here being in the form of at least one pressing roller. The post-pressing device may be beneficial, for example, in view of a tendency of the material of the cover layer to relax prior to the flowable thermoplastic material being re-solidified. The function of the post-pressing device is to apply a holding pressure after the process until the thermoplastic material has become sufficiently solid.

[0102] FIG. 2 also depicts a coordinate system. In accordance with the convention used in this text, generally the +x-direction corresponds to the conveying direction, which is essentially parallel to the object surface. Directions along the y axis being also essentially parallel to the object surface, and being perpendicular to the x axis, are sometimes referred to as “lateral directions” in this text. The pressure applied by the sonotrode onto the cover layer is mostly at least approximately into the +z direction.

[0103] FIG. 3 depicts parts of an installation having a plurality of sonotrodes 6 arranged in a sequence so that the sonotrodes impinge on the cover layer one after the other. In many embodiments, the sonotrodes 6 will be arranged close to each other (the distance between the sonotrodes being exaggerated in FIG. 3) so that there is only minimal cooling and relaxation of the thermoplastic material between subsequent stages. If a plurality of sonotrodes is used, as in FIG. 3, then the sonotrodes may optionally be different in at least one of:

Dimensions

[0104] Pressure setting

Amplitude

[0105] Angle α of the coupling-out face 61 to the object contact surface 28

[0106] These parameters, which may but do not need to be different, may be adapted to optimize the joining process, depending on the materials and dimensions of the object and of the cover layer.

[0107] As illustrated in FIG. 4, the angle α between the coupling-out face 61 and the object contact surface 18 may not only be set in accordance with the particular needs, it may also be used as a variable parameter that may be adapted during the process, as illustrated by the arrow 63 in FIG. 4. A variation of the angle α does not only vary the active width a but also, given a conveying velocity, an effective forward pressing force. A variation of the angle α may be much quicker than an adaptation of the pressing force by pneumatic means. A variation—for example temporary reduction—of the pressing force may in embodiments for example be advantageous at a corner of the board-like object, i.e. the pressing force may for example be reduced by making the angle α flatter every time an object corner reaches the sonotrode 6.

[0108] The post-pressing device 32 in FIG. 2 is illustrated to include at least one pressing roller. Pressing rollers have the advantage of providing little resistance against a relative movement of the object with the cover layer. In many embodiments, however, an alternative post-pressing device having a larger active width is preferred. FIG. 5 very schematically illustrates a post-pressing device 32 in the form of a pressing shoe. The post-pressing device of the installation may include a plurality of post-pressing elements in the form of pressing shoes and/or pressing rollers arranged in a sequence. The dimensions and arrangement of the post-pressing device and the conveying velocity are adapted to each other so that the pressing force is maintained—with or without interruptions between subsequent elements—for a time sufficient to consolidate the portions of the thermoplastic material that was flowable.

[0109] FIG. 6 showing a detail of a section along a plane perpendicular to the conveying direction illustrates a few features that may be applied independently of each other:

The object 1 is a hollow core board having two building layers 11, 12 and an interlining layer 13 between the building layers 11, 12. The building layers 11, 12 may, for example, be of wood, plywood, chipboard or of a material including a thermoplastic or thermoset polymer. The interlining layer may be a lightweight core, e.g., of a foam material or of a cardboard honey comb structure or of a honeycomb (or similar) structure including thermoplastic material. When the cover layer is joined to the object, it is secured to the building layers 11, 12, whereas in embodiments the interlining layer 13 may be not stable enough for providing sufficient mechanical resistance to make the thermoplastic material flowable when the pressing force and the mechanical vibrations apply.
The cover layer 2 includes at least one energy director 21. In the depicted embodiment, the cover layer includes two energy directing ribs 21 on each side (i.e., for each building layer). The energy directing ribs extend parallel to the conveying direction.
The cover layer 2 forms outer sealing pads 23, i.e. portions that have a slightly greater dimension towards the object, whereby it is secured that after the process the connection between the cover layer and the object extends to the lateral outer edges, thereby yielding a smooth and sealing joint.

[0110] FIG. 7 shows a detail illustrating how the sealing pad 23 ensures that after the process the lateral outer edge is sealed.

[0111] FIG. 8 illustrates an even further optional feature that may but does not need to be combined with other optional features. Namely, the cover layer 2 includes at least one guiding protrusion 24, for example a guiding ridge that defines the lateral position of the cover layer 2 relative to the object, hereby extending along an inner surface of the respective building layers 11, 12. In embodiments, the cover layer may be dimensioned to extend laterally on both sides further than the thickness of the board-like object, and the process may include the post-joining step of removing laterally protruding portions of the cover layer after the joining. Nevertheless, the definition of the position of the cover layer may be beneficial in embodiments, especially if the cover layer includes structures such as the energy director(s) 21 and/or a sealing pad.

[0112] FIG. 9 shows an alternative in which the object includes the energy directors 71 and/or a sealing pad 72. The cover layer may then be absent any particular structure, and a lateral positioning of the cover layer relative to the object does not need to be precise, only depending on the lateral width of the cover layer in relation to the thickness of the object.

[0113] Structures like the energy directors 71 and/or the sealing pad may be made to the building layers 11, 12—if the object is a hollow core board—or other elements that define the object contact surface may be made by milling or an other material-removing process, and/or they may be made by a material deforming process, such as by imprinting.

[0114] FIG. 10 schematically depicts an installation for carrying out the method on a plurality of objects 1 conveyed in succession in a continuous process. The installation includes a per se known conveyor (not shown) for conveying the objects in the conveying direction CD. The cover layer 2 is for example fed-in from a feed roller 25. A deflection roller 31 also serves as pre-pressing device. FIG. 10 illustrates one single sonotrode, with the coupling-out face 61 being slightly rounded, i.e. with the angle between the coupling-out face and the object contact surface being not constant along the extension of the sonotrode (such convexly or possibly concavely rounded shape being an option for any embodiment). After the sonotrode, a post-pressing device 32 in the form of a pressing shoe is arranged.

[0115] The dashed lines in FIG. 10 illustrate two further options that are independent of each other:

A separate protection layer 4 may be conveyed—in a conveying velocity that is not necessarily identical with the conveying velocity applying to the objects—to a region between the sonotrode 6 and the cover layer 2. The mechanical vibration is then applied to the cover layer by the sonotrode through the protection layer 4. The protection layer may, for example, be provided as a strip of paper or as a strip of PTFE (Polytetrafluoroethylene). Such separate protection layer may—for example in addition or as an alternative to a protection coating of the sonotrode—serve for saving the material of the sonotrode, for reducing noise, and/or for preventing undesired marks on the surface of the cover layer after the process, etc.
At least one additional layer 5 to be fastened to the cover layer is conveyed in a conveying velocity corresponding to the conveying velocity of the objects. Such separate layer may, for example, be a decoration layer. It may be secured to the cover layer 2 by the process that includes making material of the cover layer flowable, securing lamination of the additional layer to the cover layer, or possibly by an adhesive coating of the additional layer etc. An additional layer may also be secured to the cover layer in a separate step, as a further option (not shown).

[0116] The previously described embodiments rely on the joining material being a thermoplastic material in a solid state, wherein activation includes making the material flowable. FIG. 11 shows a configuration in which the joining material is a curable adhesive in an initially flowable state. The joining material 81 is dispensed—from a dispensing device 82, to the object 1—immediately upstream of the sonotrode 6. Due to the direct or indirect (by heating caused by the vibration) effect of the vibration, the curing of the adhesive is substantially accelerated compared to a configuration without the activation, whereby behind the sonotrode and a post-pressing device 32 the joining material is sufficiently cured to secure the cover layer 2 to the object 1 at least provisionally so that the connection is stable enough for transport and further processing steps. Further curing may nevertheless take place after the process shown in FIG. 11.

[0117] In embodiments in which the joining material is a curable adhesive, the material of the object and/or of the cover layer may but do not need to be penetrable by the joining material to some extent. For example, the object may include a fiber composite with some matrix material removed at the object contact surface or an other configuration as disclosed in WO 2017/178 468. In these embodiments, the effect of the pressing force and the vibration may cause the joining material to (further) penetrate into the object and/or the cover layer, respectively, as illustrated in FIG. 11. The extent to which joining material may penetrate into the object and/or the cover layer has an influence on the path (movement in z direction) by which the cover layer is moved towards the object during the process. In many embodiments, this path p may be substantially shorter than in comparable set-ups with a thermoplastic joining material the joining mechanism of which relies on the interpenetration of object/cover layer material by the thermoplastic joining material. This in turn has an influence on the angle α or, more generally, on the deviation of the coupling-out face from a plane parallel to the object contact surface. Often, for embodiments with a curable joining layer, the angle may be flatter.

[0118] FIG. 11 shows yet another feature that is an option not only for embodiments with a curable joining material, but for any embodiment of the invention. More in particular, the coupling-out face 61 of the sonotrode has three distinct portions. An entry portion 91 is rounded convexly. A pressing portion 92 is essentially plane, at an angle to the object contact surface, or possibly slightly convex, and an exit portion 93 that is again rounded. More in general, various shapes may be suitable, with at least a portion of the coupling-out face 61 being such that a distance between the sonotrode and the object contact surface continuously decreases (which may be due to the sonotrode length continuously increasing).

[0119] FIG. 12 shows an embodiment in which, in contrast to the embodiment of FIG. 8, it is not the cover layer 2 that has a structure for defining its lateral position but the sonotrode 6 has. In FIG. 12, the sonotrode 6 has a receiving indentation 101 for receiving the cover layer 2 in a manner that its lateral (y−) position is defined. If by other means, the position of the object 1—here being illustrated as a hollow core board—is precisely defined, this also defines the position of the cover layer with respect to the object 1. In FIG. 12, a depth of the receiving indentation 101 corresponds to a thickness of the cover layer or may be smaller than this thickness.

[0120] FIG. 13 shows an embodiment in which, in contrast to the embodiments of FIGS. 6-8, it is not or not only the cover layer that include a structure, for example for forming an energy director, but in which (also) the first object 1 has such structure. In the embodiment of FIG. 13, the first object is a hollow core board in which each of the two building layers has two energy directing ribs running parallel to the x direction.

[0121] In a variant of the embodiment of FIG. 12, a receiving indentation 101 of the sonotrode 6 may be deeper than a thickness of the cover layer, whereby also the first object 1 is guided by the receiving indentation, as shown in FIG. 14. Hence, in this embodiment the relative position of the first object 1 and the cover layer 2 is fully defined by the sonotrode 6 if the lateral (y−) extension of both these objects is the same, i.e. if the width of the strip that forms the cover layer corresponds to the thickness of the board that is the first object. This kind of guidance also works if the width of the strip is somewhat smaller than the thickness of the board or vice versa. If the board is a hollow core board of the kind explained hereinbefore, it just has to be assured that both building layers 11, 12 are in contact with the cover layer during the process.

[0122] FIG. 15 shows a variant in which lateral guiding is achieved by a separate guiding element 111. The guiding element is a guiding strip, for example of Polytetrafluoroethylene (PTFE) or an other not liquefiable material with comparably low friction. The guiding strip may extend along at least the active width of the sonotrode 6 and remain stationary relative to the sonotrode. It is also possible that the guiding strip extends along a full length of the cover layer and is for example delivered together with it, such as from a roll. It has lateral guiding ridges 112 by a having a U-shaped cross section. The distance of the guiding ridges 112 corresponds to a thickness of the first object being a board. The lateral guiding ridges engage with the board along the edge to which the cover layer is to be attached, so that the lateral position of the guiding element—and thereby also of the cover layer—is defined relative to the object.