BONDING OBJECTS TOGETHER

Abstract

A method of bonding a first object to a second object includes the steps of: providing the first object including thermoplastic material in a solid state, providing the second object including a proximal surface, applying a mechanical pressing force and a mechanical excitation capable to liquefy the thermoplastic material until a flow portion of the thermoplastic material is flowable and penetrates into structures of the second object, and stopping the mechanical excitation and letting the thermoplastic material resolidify to yield a positive-fit connection between the first and the second object. The second object has a region of low density, wherein the protrusion penetrates the region of low density at least partly before the thermoplastic material is made flowable, and wherein the first object includes a protruding portion after the step of letting the thermoplastic material resolidify, the protruding portion at least partly penetrates the region of low density.

Claims

1. A connector for being bonded to an item, wherein: the connector extends between a proximal end and a distal end and comprises a connector body forming a proximal surface and a distal surface, the connector comprises thermoplastic material in a solid state, the connector comprises a plurality of protrusions that protrude from the distal surface, and the protrusions comprise the thermoplastic material at outer surfaces.

2. The connector according to claim 1, wherein the distal surface forms a stopping surface.

3. The connector according to claim 1, wherein the protrusions consist of the thermoplastic material.

4. The connector according to claim 1, wherein the plurality of protrusions comprise a protrusion of a first kind and a protrusion of a second kind, and wherein the protrusion of the first kind is designed for being anchored in the item and the protrusion of the second kind is designed for being anchored in an object different from the item.

5. The connector according to claim 1, wherein the item is a car body.

6. The connector according to claim 4, wherein the object comprises a metal sheet, a foil, a cover layer or cladding.

7. The connector according to claim 1, wherein the connector comprises a structure designed and arranged to promote local compression of the item when forced into the item.

8. The connector according to claim 1, wherein the connector comprises a structure in a form of one or more barbs.

9. The connector according to claim 1, wherein the connector comprises a protrusion region distally of the connector body and wherein the protrusion region comprises the plurality of protrusions.

10. The connector according to claim 1, wherein the protrusions are arranged in a protrusion region distally of the distal surface of the connector body, and wherein between the distal surface and the protrusion a pedestal-like transition portion is arranged.

11. The connector according to claim 1, wherein tips of the protrusions comprise a structure in a form of one or more indentations, and wherein the indentations preferably comprise an acute opening angle.

12. The connector according to claim 1, wherein tips of the protrusions comprise a pyramid-like shape.

13. A method of bonding the connector according to claim 1 to an item comprising a rigid cover layer and a region of low density that is separate from the rigid cover layer, the method comprising: piercing the connector through the rigid cover layer of the item, and penetrating the connector into the region of low density in order to bond the connector to the item, wherein the region of low density is arranged on a side of the rigid cover layer facing away from the distal surface of the connector.

14. The method according to claim 13, wherein a compressed region is established in the region of low density.

15. A method of connecting an item having a region of low density to an object, the method comprising: penetrating the connector according to claim 1 through a pre-formed opening in the object, and pressing the distal surface of the connector onto the proximal surface of the item and thereby clamping the object between the item and the connector.

16. The method according to claim 15, wherein a compressed region is established in the region of low density.

17. A functional part having integrated therein at least one connector in accordance with claim 1.

18. The functional part according to claim 17, wherein the connector forms part of a car body.

19. A connector for being bonded to an item, wherein: the connector extends between a proximal end and a distal end and comprises a connector body forming a proximal surface and a distal surface and the connector comprises thermoplastic material in a solid state the connector comprises a plurality of protrusions that protrude from the distal surface the protrusions comprise the thermoplastic material at outer surfaces, and the connector is equipped to attach a further object to the proximal end of the connector.

20. The connector according to claim 19, wherein the protrusions consist of the thermoplastic material.

21. The connector according to claim 19, wherein the item is a car body.

22. The connector according to claim 19, wherein the connector comprises a protrusion region distally of the connector body and wherein the protrusion region comprises the plurality of protrusions.

23. The connector according to claim 19, wherein the distal surface of the connector body comprises a functional region, and wherein the functional region does not comprise any protrusions.

24. The connector according to claim 19, wherein the protrusions are arranged in a protrusion region distally of the distal surface of the connector body, and wherein between the distal surface and the protrusion a pedestal-like transition portion is arranged.

25. The connector according to claim 19, wherein the protrusions are arranged in at least two concentric circles at an outer circumference of the distal surface of the connector.

26. The connector according to claim 19, wherein the connector includes a fixation element at the distal surface of the connector, and the protrusions are arranged in at least two concentric circles at an outer circumference of a distal surface of the fixation element.

27. A functional part having integrated therein at least one connector in accordance with claim 19.

28. The functional part according to claim 27, wherein the at least one connector forms part of a car body.

29. A fixation element designed to be bonded to an item, wherein: the fixation element comprises a fixation element body defining a ring-shaped through hole and having a proximal surface and a distal surface, the fixation element comprises thermoplastic material, and a plurality of protrusions protrude from the distal surface.

30. The fixation element according to claim 29, wherein the protrusions comprise the thermoplastic material at outer surfaces.

31. The fixation element according to claim 29, wherein the protrusions are arranged in a protrusion region distally of the distal surface of the fixation element body, and wherein between the distal surface and the protrusions a pedestal-like transition portion is arranged.

32. The fixation element according to claim 29, wherein the tips of the protrusions comprise a structure in a form of one or more indentations, and wherein the indentations preferably comprise an acute opening angle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0357] Hereinafter, embodiments of the invention are described referring to drawings. The drawings are all schematic and not to scale. In the drawings, the same reference numbers refer to same or analogous elements. The drawings are used to explain the invention and embodiments thereof and are not meant to restrict the scope of the invention. Terms designating the orientation like “proximal”, “distal”, etc. are used in the same way for all embodiments and drawings.

[0358] The drawings show:

[0359] FIG. 1 An assembly of a first and second object before bonding the first object to the second object;

[0360] FIG. 2 The first object and the second object during the bonding process;

[0361] FIG. 3a A sectional view of an exemplary bonding location;

[0362] FIGS. 3b-3d A sectional view of another exemplary bonding location at three stages of the bonding process;

[0363] FIGS. 4 and 5 Exemplary embodiments of the first object;

[0364] FIGS. 6 and 7 An exemplary embodiment of a first object including an element of a connection device;

[0365] FIGS. 8 and 9 An exemplary embodiment of a first object forming the element of the connection device;

[0366] FIGS. 10-13 An exemplary embodiment of the method of bonding the first object to a second object including an increasing density along an axis of forcing the first object into the second object;

[0367] FIGS. 14 and 15 A sectional view of a third object attached to the second object by use of the first object and an embodiment of the method;

[0368] FIG. 16A further embodiment of the first object;

[0369] FIGS. 17a-17e Further embodiments of the first object including a structure for promoting local compression of the second object;

[0370] FIG. 18A sectional view of an object attached to the second object by use of the first object, a further object and an embodiment of the method;

[0371] FIGS. 19a and 19b A sectional view of a third object before and after its attachment to the second object by use of the first object;

[0372] FIGS. 20a and 20b A sectional view of a first object before and after its attachment to a second object including a rigid proximal top layer;

[0373] FIGS. 21a and 21b A sectional view of an exemplary embodiment of a first object including protrusions of different length before and after its attachment to a second object;

[0374] FIGS. 22 and 23 Sectional views of further exemplary embodiments of a first object including protrusions of different length after its attachment to a second object;

[0375] FIG. 24 An exemplary embodiment of the method including a support for the second object;

[0376] FIGS. 25a and 25b An exemplary embodiment of a second object designed for protecting edges of the first object;

[0377] FIGS. 26a-26e Sectional views of the attachment of a third object to the second object by use of the first object at different stages of the bonding procedure;

[0378] FIGS. 27a-27d Sectional views of the attachment of another third object to the second object by use of the first object at different stages of the bonding procedure;

[0379] FIG. 28 An exemplary embodiment of a first object including a plurality of protrusions, wherein a volume of the plurality of protrusions is limited;

[0380] FIGS. 29a and 29b A sectional view of a first object being bonded to a further type of the second object before and after bonding;

[0381] FIGS. 30a and 30b A sectional view of yet another type of a second object and a first object being bonded to this type of second object before and after bonding;

[0382] FIG. 31A sectional view of a further third object being bonded to the second object by the use of a first object;

[0383] FIGS. 32a and 32b Sectional views of a first object being bonded to a second object by a method including the step of providing an adhesive;

[0384] FIGS. 33a and 33b An exemplary embodiment of a first object being a connector;

[0385] FIGS. 34-39 Various exemplary embodiments of the protrusion region of the first object and the device, respectively;

[0386] FIGS. 40-43 Various exemplary embodiment of the first object and the device, respectively;

[0387] FIGS. 44-46 Three exemplary embodiments of the first object equipped for preventing the generation of destructive natural oscillations;

[0388] FIGS. 47-49 Exemplary embodiments of first objects including a fixation element and a connecting element;

[0389] FIGS. 50 and 51 An alternative fixation of the third object to the second object by the first object;

[0390] FIGS. 52 and 53 Sectional views of the attachment of a third object to the second object by the use of a first object;

[0391] FIGS. 54a and 54b Sectional views of the attachment of a metal sheet without pre-drilled openings to the second object by use of the first object;

[0392] FIG. 55 An exemplary embodiment of a first object that can be used in a method according to FIGS. 54a and 54b;

[0393] FIG. 56A basic arrangement of the first and second object before bonding the first object to the second object by applying a sonotrode to the second object;

[0394] FIGS. 57a and 57b Exemplary application of the method according to FIG. 56 before and after bonding;

[0395] FIG. 58 An embodiment of the method in which the sonotrode is applied to the second object and a force for advancing the protrusion into the region of low density is applied to the first object; and

[0396] FIG. 59 Two representative stress-strain-curves for a panel formed by an incoherent material.

DETAILED DESCRIPTION OF THE INVENTION

[0397] A method according to the invention includes providing a first object 1, providing a second object 2 and arranging the first object relative to the second object such that the first object 1 is in physical contact with a proximal surface 4 of the second object 2 and such that an assembly of the first and second object is formed. An exemplary embodiment of such an assembly is shown in FIG. 1.

[0398] In the embodiment shown, both the first object 1 and the second object 2 expand over an extended area. The first object 1 can be of the same size as the second object. However, it is also possible that the first object 1 covers the proximal surface 4 of the second object 2 partly and/or locally, only.

[0399] The second object 2 and/or the first object 1 can be non-plane. In particular in configurations in which the second object 2 expands over a larger area than the first object 1, the second object 2 can be non-plane, for example by having a shape adapted to a shape of a surface that has to be covered by the second object 2, whereas the first object 1 is plane. The plane first object 1 can then be bonded to a plane proximal surface region of the second object 2 or the first object 1 can be deformed during the bonding process such that its shape becomes adapted to the shape of the second object 2.

[0400] In the embodiment shown, the first object 1 expands between a proximal end 5 and a distal end 6 and consists of thermoplastic material.

[0401] The first object 1 includes tapered protrusions 9 in the shape of ridges at its distal end 6, in the embodiment shown in FIG. 1.

[0402] The ridges protrude from a body 7 of the first object 1 (also called first object body or device body), the body 7 forming the proximal end 5 of the first object 1.

[0403] The body 7 and/or elements 15 of a connecting device attached or attachable to the body 7 can be equipped for connecting a further object to the first object 1.

[0404] The second object 2 includes an increasing density in a direction normal to the proximal surface 4 and it includes structures 10, for example pores, into which liquefied material can penetrate.

[0405] The increasing density can be due to a change in the composition of the second object 2 along the direction and/or due to a decrease in the structures, for example.

[0406] Due to such changes, the second object 2 includes a region 22 of a density that is lower than the density of a region 23 that is arranged distally of the region 22 of low density.

[0407] The region 22 of a density that is lower than the density of a region 23 arranged distally of it is also called the proximal region 22, whereas the region 23 arranged distally of the proximal region 22 is also called the further region 23.

[0408] In the embodiment shown in FIG. 1, the second object 2 includes a plurality of fibers that are at least partly embedded in a plastic (enlarged part of FIG. 1). The portions of the fibers that are not embedded in the plastic form a soft surface layer. The soft surface layer has a density that is lower than the density of the second object 2 in regions where the fibers are embedded in the plastic.

[0409] Hence, both the composition and the density of structures 10 change in the direction normal to the proximal surface 4. The soft surface layer corresponds to the region 22 of low density and the regions with the fibers embedded in the plastic corresponds to region 23 of high density.

[0410] The density profile of second object 2 of FIG. 1 is shown next to the enlarged part of the second object 2. The second object 2 can include further density regions, for example a second region of low density forming a proximal surface of the second object 2 or a transition region that extends between a region of low and high density.

[0411] As pointed out above, the region of high density can include a plurality of structures, voids, openings, etc. Further, it can be compressible, for example compressible to a critical density and/or in a manner that the region of high density provides a critical compressive strength. The term “critical” relates to a density and/or compressive strength needed for the liquefaction of the thermoplastic material in the method.

[0412] FIG. 2 shows the assembly of the first and second object during the step of applying a mechanical pressing force (indicated by an arrow in FIG. 2) and mechanical oscillations (indicated by a doubled-headed arrow) along an axis 8 that is essentially perpendicular to the proximal surface 4 of the second object 2.

[0413] The mechanical pressing force as well as the mechanical oscillations are applied by a sonotrode 20 including a coupling-out face 21 that is in physical contact with a proximal surface 4 of the first object 1.

[0414] In the embodiment shown, the coupling-out face 21 is designed to expose a portion of the first object 1 to mechanical oscillations and/or the mechanical pressing force, only. Hence, well-defined, local bonding locations 13 are generated during the bonding process. Four bonding locations 13 are shown in FIG. 2. However, the number of bonding locations 13 depends on the shape and size of the first object 1, the shape and material of the second object 2, and the demands on the bond (e.g., its strength), for example.

[0415] An advantage of the bonding method shown is that the number and arrangement of bonding locations 13 can be adapted easily and even during the bonding by applying the sonotrode 20 to positions on the proximal surface of the first object 1.

[0416] In the embodiment shown, the mechanical pressing force is directed along the axis 8 of the mechanical oscillations, too. However, the mechanical pressing force sets in prior to the mechanical oscillations. This has the effect of the protrusions 9 penetrate through the region 22 of low density before being liquefied, at least. By doing so, the bonding of the first and second object is not restricted to the proximal surface 4 only, but relies on structures 10 within the second object 2. In other words: Deep anchoring in contrast to surface anchoring as established by adhesives for example is generated.

[0417] The density profile of the second object 2 can be such that there is no need to start applying the mechanical pressing force prior to the mechanical oscillations. In this case, liquefaction of the thermoplastic material 3 sets in as soon as the density of the second object has reached a value that allows compression of the thermoplastic material 3 to such an extent that liquefaction sets in.

[0418] The second object is shown in a schematic way in FIG. 2, only. The second object shown in FIG. 2 can correspond to the second object shown in FIG. 2, 3 or 10-13, in particular.

[0419] FIG. 3a shows a sectional view along the AA-axis shown in FIG. 2 and for a second object 2 as shown in FIG. 1.

[0420] The combined effect of mechanical pressure and mechanical oscillation has caused the portions of the thermoplastic material 3 of the protrusion 9 in contact with the region 23 of high density to liquefy and to penetrate into the structures 10 of the second object 2. This results in a positive-fit connection, in particular in a positive-fit connection with respect to the axis 8 of the oscillation (i.e. a positive-fit preventing a relative movement of the first and second objects normal to the proximal surface 4) between first and second object after resolidification of the liquefied thermoplastic material 3.

[0421] FIGS. 3b-3d show sectional views of the establishment of a bonding between the first object 1 and a second object 2 with a constant density profile in the direction perpendicular to the proximal surface 4 of the second object 2.

[0422] FIG. 3b shows the situation before pushing the protrusions 9 of the first object 1 into the second object 2.

[0423] FIG. 3c shows the situation during the step of pushing the protrusions 9 and the body 7, if the density of the second object is such that the body can be pushed into the second object without destroying the first or second object and/or their properties, in the second object 2.

[0424] The penetration of the protrusions 9 and, as the case may be, the body 7 compresses the second object 2 locally around the distal end of the protrusions 9, at least. This leads to the density profile needed to liquefy the thermoplastic material 3 of the protrusions 9 by applying the mechanical pressing force and the mechanical excitation.

[0425] FIG. 3d shows the situation after the step of stopping the mechanical excitation. Liquefied thermoplastic material 3 has penetrated into the structures 10 of the second object 2.

[0426] The liquefied thermoplastic material 3 can penetrate regions of the second object 2 that are not compressed or slightly compressed only. In this case, the bonding of the first to the second object goes even deeper into the second object 2 than given by a protruding portion 91 that guarantees a deep-effective anchoring.

[0427] FIG. 4 shows an embodiment of the first object 1 similar to the one shown in FIGS. 1 and 2 as it is provided in the method for bonding the first object 1 to the second object 2.

[0428] One can envisage protrusions 9 other than the ones shown in FIG. 4. FIG. 5 shows an exemplary embodiment of a first object 1, wherein the protrusions 9 are given by a plurality of tips.

[0429] The protrusions 9 protrude from a distal surface 28 of the body 7 of the first object 1. They are arranged in a protrusion region 90 that is located distally of the distal surface 28 of the body 7 of the first object 1.

[0430] The first object 1 further includes a proximal surface 29 of the body 7 of the first object 1 (hidden in FIGS. 4 and 5, see FIGS. 6, 8 and 9), the proximal surface forms the proximal end 5 of the first object 1 during and after the method.

[0431] The method shown in FIGS. 1-3 can be used for bonding an element 15 of a connecting device to the second object 2. This can be done by a first object 1 including such an element 15.

[0432] The first object 1 can include one or more elements 15 of a connecting device. For example, a plurality of elements 15 can be arranged on the proximal surface of the first object 1 according to FIG. 4 or 5.

[0433] FIG. 6 shows an exemplary embodiment of the first object 1 including an element 15 of a connection device. FIG. 7 shows a sectional view of the first object 1 with applied sonotrode 20.

[0434] In the embodiment shown, the element 15 of the connection device is a rod including an inner thread.

[0435] The first object 1 includes a coupling-in face 11 that is arranged on the proximal surface of the first object 1 around the protruding element 15, in the embodiment shown.

[0436] The distal end of the sonotrode 20, i.e., the end of the sonotrode 20 including the coupling-out face 21, is adapted to the first object 1 by including an opening into which the rod can be inserted such that it is not loaded during the bonding process.

[0437] In the embodiment of FIG. 6, the protrusions 9 are ridge-like, again. However, the first object 1 can include protrusions that are differently shaped, such as tips.

[0438] The first object 1 can include one, two, three or four tips, for example. A small number of protrusions 9 can be sufficient in embodiments in which the first object 1 is small and/or defines one bonding location 13 by itself, as shown in FIG. 7.

[0439] Again, the protrusions 9 are arranged in a protrusion region 90 distally of the distal surface 28 of the body 7 of the first object 1.

[0440] The area of the coupling-out face 21 can be equal to or larger than the area of the proximal surface, in particular if the first object 1 defines one bonding location 13 by itself.

[0441] FIGS. 8 and 9 shows a schematic view and a sectional view of a first object 1 that is in fact a connector 16. In other words, the first object 1 includes an element of a latching mechanism mounted on a thermoplastic device that is capable of being bonded to the second object 2 by any embodiment of the bonding method.

[0442] FIG. 9 shows a sectional view of the first object 1. In the exemplary embodiment shown, the protrusions 9 are separated from each other by gaps 27 that extend down to the proximal surface 29 of the body 7 of the first object 1.

[0443] In the embodiment shown, the protrusions 9 are arranged and designed such that flat regions of the proximal surface 29 extend between them. The flat surfaces can act as stopping surfaces.

[0444] FIGS. 10-12 shows an embodiment of the method in which the first object 1, e.g., a first object 1 according to FIGS. 4-9, penetrates into the region of high density before the liquefaction of the thermoplastic material 3 sets in.

[0445] In FIGS. 10-13, the second object includes a proximal surface layer 17, a distal surface layer 18 and a core layer 19, wherein the density of the distal and proximal surface layer is lower than a density of the core layer 17. However, the method described in the following is also suitable for a second object 2 with a density profile that is generated differently, for example for the second object 2 according to FIG. 1.

[0446] For example, the proximal and distal surface layers include or essentially consist of a damping material, whereas the core layer 17 consists of the damping material embedded in another material or it is composed by materials other than the damping material. The other materials are denser than the damping material and they can show a higher mechanical stability than the damping material.

[0447] FIG. 10 shows the situation after the step of applying to the first object 1 a first mechanical pressure force (indicted by the small arrow on top of FIG. 10) that is smaller than a second mechanical pressure force applied to the first object 1 in a subsequent step of the method. No mechanical oscillations have been applied, so far.

[0448] The protrusions 9 of the first object 1 have penetrated through the proximal surface layer 17 but not into the core layer 19.

[0449] FIG. 11 shows the situation during the step of applying the second mechanical pressure force (indicted by the large arrow on top of FIG. 11). No mechanical oscillations have been applied, so far.

[0450] The protrusions 9 have penetrated into the core layer 19 and are capable to penetrate into the core layer 19, further. This means, the movement of the first object 1 relative to the second object 2 along the penetration axis is not prevented by any element of the first or second object.

[0451] In particular, an optionally present stopping surface does not yet generate a counter force to the pressure force applied such that a further penetration of the first object 1 into the second object 2 is prevented.

[0452] If the stage shown in FIG. 11 is established, the mechanical oscillations (indicated by the doubled-headed arrow) are applied.

[0453] FIG. 12 shows the situation after the bonding process. Thermoplastic material 3 has penetrated into structures 10 of the core layer 19 and forms a positive-fit connection between the first and second object, in particular a positive-fit connection normal to the penetration direction of the first object 1.

[0454] However, the protrusion 9 has not disappeared completely, for example by being “smeared out” during the method. Rather the protruding portion 91 resists at the position at which the protrusion 9 was before applying the mechanical oscillations. This leads to a deep effective anchoring, for example.

[0455] The stopping surface 12 generated a counterforce to the second mechanical pressure force in a final phase of the bonding process, wherein the counterforce was such that the movement of the first object 1 towards the distal surface layer 18 was limited. Hence, a maximum penetration depth of the first object 1 into the second object 2 is defined by the stopping surface 12 and the length of the protrusions 9 normal to the stopping surface.

[0456] In the embodiment shown, the stopping surface 12 is a surface of the first object 1 that expands normal to the penetration direction of the first object 1, i.e. normal to the axis 8 of the mechanical oscillations.

[0457] In the embodiment shown, the length of the protrusions 9 is such that a distal surface 14 of the second object 2 is neither in contact nor affected by the thermoplastic material 3. Further, the density of the core layer 19 (the region 23 of high density) at any bonding location 13 at least is such that liquefaction of the thermoplastic material is possible without need for a further material or surface being involved.

[0458] The core layer shown 19 includes a material or consists of a composite that generates the mechanical stability of the second object 2. The second object 2 can be bendable, in particular elastically bendable. Nevertheless, the material or composite of the core layer 19 is such that the thermoplastic material 3 can liquefy at an interface between the thermoplastic material 3 and the material or composite of the core layer 19 under the effect of mechanical oscillations and the mechanical pressure force. In particular, the material or composite includes the rigidity needed for the liquefaction.

[0459] In particular, the physical properties of the distal layer 18 are neither needed nor involved in the liquefaction of the thermoplastic material 3.

[0460] FIG. 13 shows the bonding establish by a method according to FIGS. 10-12 but without applying the second mechanical pressure or with simultaneous application of the second mechanical pressure force and the mechanical oscillations.

[0461] The penetration depths of the thermoplastic material 3 is limited to the proximal surface region 17 and adjacent regions of the core layer 19.

[0462] FIGS. 14 and 15 show sectional views through an assembly of a first object, second and third object, wherein the third object 30 is attached to the second object 2 by the first object 1 and wherein the first object 1 is bonded to the second object 2 by an embodiment of the method.

[0463] The third object 30 includes a third object proximal surface 31 and a third object distal surface 32. The third object 30 is arranged relative to the second object 2 such that its distal surface 32 is in physical contact to the proximal surface 4 of the second object 2.

[0464] In the embodiment shown in FIG. 14, the third object 30 can have any density profile from the third object proximal surface 31 to the third object distal surface 32 that can be penetrated by the protrusion(s) 9 of the first object 1.

[0465] In particular, the third object 30 can have any density profile described in respect of the second object 2.

[0466] Hence, it is possible that the first object 1 is bonded to the third object 30 by the use of the corresponding steps of the method and corresponding structures 35 of the third object 30.

[0467] In the embodiment shown in FIG. 15, the third object 30 includes a region 36 of low density at its proximal surface 31, too. Further, the first object 1 includes a protrusion 33 of a first kind and a protrusion 34 of a second kind.

[0468] The protrusion 33 of the first kind has a length and a diameter such that the distal end of the protrusion 33 of the first kind penetrates the region 22 of low density of the second object 2 at least partly and such that the distal end of the protrusion 33 of the first kind penetrates into structures 10 of the second object 2 during the bonding process.

[0469] The protrusion 34 of the second kind has a length and a diameter such that the distal end of the protrusion 34 of the second kind penetrates the region 36 of low density of the third object 30 at least partly and such that the distal end of the protrusion 34 of the first kind penetrates into structures 35 of the third object 30 during the bonding process.

[0470] In particular, the diameter of the protrusion 33 of the first kind is larger than the diameter of the protrusion 34 of the second kind.

[0471] FIGS. 16 and 17a-17e show exemplary embodiments of the first object 1.

[0472] The embodiment shown in FIG. 16 corresponds to the embodiment provided in a method leading to the assembly of the first, second and third object as shown in FIG. 15.

[0473] FIGS. 21-23 show other configurations in which embodiments of the first object 1 according to FIG. 16 can be used.

[0474] There is no need for cross-sectional areas of the protrusion 33 of the first kind and the protrusion 34 of the second kind that are identical and/or that are circular.

[0475] However, in many embodiments of the first object 1 shown in FIG. 16, the cross-sectional area of the protrusion 33 of the first kind is larger than the cross-sectional area of the protrusion 34 of the second kind.

[0476] FIG. 16 indicates a thickness 26 of the protrusions 9 and their extension 25 in distal direction. The extension is equal to the distance of the most distal point of the protrusion to the distal surface 28 of the body 7 of the first object 1. The embodiments of the first object 1 shown in FIGS. 17a-e do not only increase locally the density of the second object 2 by the protrusion displacing material of the second object 2 (for example as shown in FIGS. 3b-3d) but also by including structures 24 that are designed and arranged specifically to promote local compression of the second object 2, in particular of the region 22 of low density.

[0477] Further, the structures 24 shown are designed and arranged to pull down fibrous material of the second object 2 and/or to felt such material further and/or to embed the protrusions 9 including such structures 24 better in the material of the second object 2, for example for distributing any load over a larger area.

[0478] The embodiments of the first object 1 shown in FIGS. 17a, 17b and 17 e include so-called barbs 24, i.e., structures that have a shape and are arranged at the protrusion 9 such that they are capable to increase the density of the second object 2 faced by the protrusion 9 in function of the penetration depth of the protrusion 9.

[0479] The barbs can be arranged at a distal end of the protrusion 9, as shown in FIG. 17a. This leads to a local compression of the second object 2 that favors the liquefaction of the thermoplastic material 3 arranged around the distal end of the protrusion.

[0480] Alternatively or in addition, the barbs 24 can be arranged at the lateral side of the protrusion 9. As examples, FIG. 17 b show drag down barbs that are small compared to the size of the protrusion 9 and FIG. 27e show catching barbs that have a size such that they contribute to the overall shape of the protrusion.

[0481] There is no need for a homogenous distribution of the barbs 24 at the lateral side. Rather, the barbs 24 can be arranged such that the liquefaction of the thermoplastic material 3 sets in at certain positions on the protrusion 9 and/or that the penetration of the second object 2 by liquefied thermoplastic material is restricted along a specific direction.

[0482] In FIGS. 17c and 17d, the structure 24 designed and arranged to promote local compression of the second object 2 is given by the shape of the distal end of the protrusion, in particular by having multiple tips that cause catching of fibers, for example.

[0483] In particular, barbs are suitable for use in fibrous second objects 2 where they can collect fibers during penetration and hence increase the density of fibers around the protrusion 9.

[0484] The barbs can be made of the thermoplastic material 3 or a harder material.

[0485] Barbs made of the thermoplastic material 3 can increase the embedding of the protrusion 9 and the protruding portion 91 respectively, further.

[0486] Barbs can also be arranged at the protrusion 33 of the first kind and/or at the protrusion 34 of the second kind.

[0487] The first object 1 shown in FIGS. 14-17 can further include at least one element 15 of a connecting device.

[0488] The first object 1 shown in FIGS. 14-17 can be a connector as described above.

[0489] FIG. 18 shows a sectional view of the result of an embodiment of the method in which an object 100 different to the first and second object is attached to the second object by connecting a further object 40 to the first object 1.

[0490] In the embodiment shown, the first object 1 is a reinforcement element.

[0491] The further object 40 is a fixing element, such as a nail, that has a distal end 41 in the shape of a tip. The further object 40 including further an attachment location 42 that is arranged to penetrate the object 100 to be attached to the second object 2 and to penetrate into the body 7 of the first object 7.

[0492] The first object 1 is bonded to the second object 2 by the method in any one of the embodiments described previously. In particular, the first object 1 is bonded to the second object 2 by a method that results in the protruding portion 91 being present in the second object after the step of stopping the mechanical excitation and letting the thermoplastic material solidify.

[0493] FIG. 19a shows a sectional view of a third object 30 before its attachment to the second object 2 by bonding the first object 1 to the second object 2. In the embodiment depicted, the third object includes thermoplastic material in the regions at which the third object 30 is pierced by the protrusions 9, at least. For example, the third object 30 shown in FIG. 19 can be a thermoplastic foil.

[0494] FIG. 19b shows a sectional view of the third object 30 attached to the second object 2. A weld 203 is formed between the first object 1 and the third object 30 during the method of bonding the first object 1 to the second object 2. This is a result of the third object 3 including thermoplastic material in the regions at which it is pierced by the protrusion.

[0495] The thermoplastic material of the third object 30 as well as the thermoplastic material 3 of the first object 1 arranged at the proximal end of the protrusions 9 and/or the neighboring thermoplastic material of the distal surface 28 of the body 7 are such that they liquefy under the mechanical pressing force and mechanical excitation applied. However, one can envisage that the condition for liquefaction of the thermoplastic material(s) is only met after compression of the second object 2 by pushing the body 7 into the second object 2.

[0496] FIG. 19b shows a mechanism that is able to increase the quality of the bond between the first and second object further. Although shown in combination with establishing a weld 203 between the first and the third object, the mechanism can be used in any embodiment of the method—independent of the presence of a third object 30.

[0497] An embodiment including the mechanism has a second object 2 that includes thermoplastic material in the region(s) at which a bond between the first and the second object is established. The thermoplastic material is capable to liquefy or at least soften under the impact of the mechanical pressure and mechanical excitation applied during the method of bonding the first object 1 to the second object 2. In a variant of the embodiment, the thermoplastic material can only be liquefied/soften after its compression by pushing the protrusions 9 and/or the body 7 into the second object 2.

[0498] Due to the liquefaction or soften, the second object 2 includes a region 202 with changed structural properties after the step of letting the (in this case “all”) thermoplastic material resolidify. A higher density and/or material of the second object 2 that is better interlinked are examples of the changed structural properties.

[0499] FIGS. 20a and 20b show the bonding of a first object 1 to a second object 2 including a proximal top layer 200 that is not part of the region 22 of low density.

[0500] For example, the proximal top layer 200 is the rigid cover layer of a hollow core board (HCB).

[0501] FIG. 20a shows the situation after positioning the first object 1 relative to the second object 2. The protrusions 9 of the first object 2 are designed to penetrate the proximal top layer 200 without deforming significantly. Further, they can include a distal tip or edge.

[0502] FIG. 20b depicts the situation after bonding the first object 1 to the second object 2. Shown is the case in which the unaffected layer arranged distally of the proximal top layer 200 is not dense enough to lead to a liquefaction of the thermoplastic material 3 within a time frame that is practical in professional use. Again, it is the establishment of a compressed region 201 that makes the bonding of the first object 1 to the second object 2 possible.

[0503] FIGS. 21-23 show embodiments of the method including protrusions that are adapted in length, for example adapted to a thickness of the second object 2, to a layered structure of the second object 2, to the mechanical properties of the body 7, to the shape of the body, and/or fabrication steps following the bonding of the first object 1 to the second object 2.

[0504] FIGS. 21a and 21b show an embodiment in which the first object 1 includes a protrusion 33 of a first kind and a protrusion 34 of a second kind, wherein the protrusion 33 of the first kind is longer than the protrusion 34 of the second kind.

[0505] The protrusion(s) 33 of the first kind has a length that is longer than the thickness of the second object 2 in direction of penetration of the protrusion 33 of the first kind into and through the second object 2.

[0506] In this case, the method includes the further step of providing an anvil 60 including a deformation recess 61. The deformation recess 61 is positioned such that the distal end of the protrusion 9 engages with the deformation recess 61 after penetrating the second object 2. The distal end of the protrusion 9 can then be deformed in a distal head 62 by applying mechanical pressure and mechanical excitation to the first object 1 or to the anvil 60.

[0507] The protrusion(s) 34 of the second kind has a length that allows for bonding the first object 1 to the second object 2 within the second object 2 and according to any embodiment of the method, e.g., by the method including establishing a compressed region 201.

[0508] An arrangement of the protrusions in which the protrusions 33 of the first kind are arranged close to ending, this means lateral, edge 210 of the body 7 and the protrusions 34 of the second kind are arranged radially inside the protrusions 33 of the first kind can be advantageous in configurations in which for example: [0509] The body 7 of the first object 1 is not stiff enough to remain in position over a larger area and/or over time; [0510] The second object 2 is deformed after bonding the second object 2 to it in preliminary but enduring manner.

[0511] FIG. 22 shows a further arrangement of protrusions 9 of different length after bonding the first object 1 to the second object 2. In the embodiment shown, the length of the remaining protruding portions 91 correlate with the length of protrusions.

[0512] The embodiment shown in FIG. 22 is an example of a first object 1 including protrusions that are optimized in terms of material costs and forces acting on the bond between the first and second object in a specific application. The embodiment shown is particularly suitable for applications in which the bonded first and second item are bent, this means applications that cause bending forces.

[0513] FIG. 23 shows an embodiment in which the second object 2 includes a layered structure. Again, the first object 1 includes a protrusion 33 of a first kind and a protrusion 34 of a second kind. The length of the protrusions is adapted such that the bond is formed either in a first region 204 of low density or in a second region 205 of low density that is arranged more distally than the first 204 region of low density.

[0514] FIG. 23 shows a simple arrangement of the layers forming the second object 2. However, the length and arrangement of protrusions 33 of the first kind, protrusions 34 of the second kind and—as the case may be—of protrusions of further kinds can be adapted to more complex arrangement of layers. In particular, the layers do not need to run parallel to each other, to be constant in thickness and/or to expand over the whole expansion of the second object 2. For example, layers, such as layers of low density, can be arranged locally, this means only at positions at which the bonding of the first object 1 to the second object 2 has to occur.

[0515] Further, there is no need that the second object 2 includes a rigid proximal top layer 200 or rigid layers 206 between regions of low density.

[0516] In principle, there is no need for any rigid layer 206 or any region of a density that gives the second object 2 load bearing capacity. In this case, the method can include the step of providing a support 63 during the method of bonding the first object 1 to the second object 2, at least. This configuration is shown in FIG. 24.

[0517] FIG. 24 shows the situation immediately after the liquefaction of the thermoplastic material 3 has set in. If the second object 2 includes no region of high density at all, a compressed region 201 needs to be established before liquefaction of the thermoplastic material 3 sets in.

[0518] The anvil 60 is an example of such a support 63. However, the support 63 can also be given by an item to which the second object 2 is attached.

[0519] FIG. 25a shows an application of a method in which the mechanical pressing force and the mechanical excitation are applied locally to the first object 1 and in which the step of applying the mechanical pressing force and the mechanical excitation is repeated several times at different positions on the first and second object 1. Hence, there are several bonding locations 13 that are not arranged on a single plane and that cannot be addressed in a single step of applying the mechanical pressing force and the mechanical excitation.

[0520] In the application shown, the first object 1 is a protection for an edge or corner of the second object 2.

[0521] FIG. 25b shows a sectional view of the first object 1 according to FIG. 25a attached to the second object 2. A first bonding location 13 is arranged at a first side of the second object 2 and a second bonding location 13 is arranged at a second side of the second object 2, which is non parallel to the first side.

[0522] In the embodiment shown, the first object 1 is pushed into the second object 2 in a manner that the distal surfaces 28 of the body 7 are at the same level as the corresponding surfaces of the second object 2. This arrangement of first and second object is not specific for the application shown in FIGS. 25a and 25b but can be realized in any embodiment of the method including a second object 2 with a proximal surface 4 that allows for pushing in the first object body 7.

[0523] In many embodiments, the corresponding surfaces of the second object 2 are the proximal surfaces 4.

[0524] An effect of pushing the body 7 into the second object 2 such that the distal surface(s) 28 of the body 7 is/are at the same level as the corresponding surface(s) of the second object 2 is a global compression of the second object 2 in the region in which the body 7 is pushed into the second object 2, at least. The resulting compressed region 201, in particular in combination with the local compression caused by the protrusions 9, can be a requirement for efficient liquefaction of the thermoplastic material 3, as described above in detail.

[0525] FIGS. 26 and 27 show embodiments of a method including the further steps of providing a third object 30 and attaching the third object 30 to the second object 2 by bonding the first object 1 to the second object 2 according to any embodiment of the method of bonding the first object 1 to the second object 2.

[0526] In the embodiment shown in FIGS. 26 and 27, the third object 30 includes a through bore 230 defining an opening 231 in a distal side of the third object 30.

[0527] The embodiments of the third object 30 shown in FIGS. 26 and 27 include the optional feature of a region 232 around the through bore 230 that is bent in distal direction. Consequently, the distal opening 231 in total or at least a part of it is displaced in distal direction with respect to portions of the third object 30 that are not arranged in close proximity of the through bore 230.

[0528] The method shown in FIGS. 26 and 27 includes the step of bringing the distal surface 32 of the third object 30 in contact with the proximal surface 4 of the second object 2 and pushing the bent region 232 into the second object 2. By doing so, the bent region 232 establishes the compressed region 201 in a region of the second object 2 that is located in proximity of the bent region. Optionally, the third object 30 can be pressed further towards the second object 2 such that a global compressed region 201 as indicated in FIG. 26b results.

[0529] In particular, the bent region has a mechanical stability such that it can take the load generated during the step of pushing the bent region 232 into the second object 2.

[0530] In embodiments of the method, in which a bent region 232 is pushed into the second object 2, the method can include the further step of providing a pushing- and holding down device. In other words: the third object 30 and/or the bent region 232 is not pushed into the second object 2 by a pressing force applied to the first object, but by a pressing force applied to the third object 30 by the use of the pushing- and holding down device.

[0531] The compressed region 201 located in proximity of the bent region 232 is further compressed in the subsequent step of pushing the protrusion 9 through the distal opening 231 into the second object 2. This kind of establishing a compressed region 201 or increase the density of a compressed region 201 has been described in detail, already. However, it is important to note, that the establishment or increase is not or not only the result of liquefied material penetrating into the second object 2 but of a solid portion of the protrusion 9 penetrating into the second object 2 before its liquefaction. The portion of the protrusion 9 is transformed into the protruding portion 91 during the step of liquefying the thermoplastic material 3.

[0532] Hence, it is the compression resulting from pushing the protrusion 9 into the second object in combination with the compression resulting from pushing the bent region 232 into the second object 2 that establishes the density profile needed to liquefy the thermoplastic material 3 of the protrusion 9 during the step of applying the mechanical pressing force and the mechanical excitation and to bond first object 1 to the second object 2.

[0533] However, one can envisage to provide a third object 30 without bent region 232 and to design the protrusion in a manner that the compressed region 201 established by pushing the protrusion 9 into the second object 2 is sufficient to establish the density profile needed to cause liquefaction of the thermoplastic material 3 during the step of applying the mechanical pressing force and the mechanical excitation.

[0534] In FIGS. 26a to 26d, the third object 30 is a metal sheet, for example an aluminum sheet, including the optional feature of the region 232 around the through bore 230 that is bent in distal direction. Further, the bent region 232 is designed such that it can be deformed elastically. In particular, the rim 233 forming the distal opening 231 includes notches 234 extending in proximal direction, this means towards the portions of the third object 30 that are not part of the bent region 232. An embodiment of such a resulting bent region 232 in shown in FIG. 26e.

[0535] In embodiments including an elastically deformable bent region 232, a diameter of the protrusion 9 can be larger than a diameter of the bent region 232. Hence, an elastic deformation in the sense of a widening of the bent region 232 and the rim 233 is established. This is indicated by two black arrows in FIG. 26b.

[0536] The following two effects are caused after pushing at least a portion of the protrusion 9 through the through bore 230 (FIG. 26c): First, the protrusion 9 penetrating the second object 2 effects a further local compression of the compressed region 201 resulting from pushing the bent region 232 into the second object 2. The protrusion 9 penetrating the second object 2 can cause an extension of the compressed region 201, in particular an extension in distal direction. Second, the elastically deformed bent region 232 causes a compressing force 239 on a portion of the protrusion 9. This compressing force is indicated in FIG. 26b by two black arrows.

[0537] The compressing force 239 leads to a melting zone 236 on the protrusion 9 during the step of applying the mechanical pressing force and the mechanical excitation at the area where the compressing force 239 applies. In other words: thermoplastic material 3 of the protrusion 9 liquefies due to the compressing force 239 and the mechanical pressing force and the mechanical excitation applied during the corresponding step. This causes an embedding of the bent region 232 in the protrusion 9 (more exactly in the protruding portion 91) in addition to the positive-fit connection established by the thermoplastic material that has penetrated the material of the second object 2.

[0538] This means, that the method according to FIGS. 26a-26e includes the further step of embedding the bent region 232 at least partly in the protruding portion 91.

[0539] FIG. 26d shows a sectional view of an exemplary embodiment of an attachment based on an embodiment of the method including the further step of embedding the bent region 232 at least partly in the protruding portion 91.

[0540] FIGS. 27a to 27c shows another embodiment of the method including the step of providing a third object with a bent region 232.

[0541] In the embodiment shown, the bent region 232 is designed in a manner that the distal opening 231 is a radial opening with respect to an insertion axis 235 along which the first object 1 is moved relative to the second object 2 during the method of bonding the first object 1 to the second object 2.

[0542] Again, the compressed region 201 is established by pushing the bent region 232 into the second object 2.

[0543] In contrast to the embodiment of FIG. 26, the bent region 232 is not designed to generate a compressing force 239 to the protrusion 9. However, the bent region 232 and the protrusion 9 are designed such that the protrusion 9 deforms towards the distal opening 231 in a step of pressing the protrusion 9 onto a portion of the bent region 232.

[0544] In the embodiment shown in FIG. 27, the bent region 232 includes a portion arranged perpendicular to the insertion axis 235. This portion, in particular in combination with a protrusion that deforms when pressed against the portion, can direct the protrusion 9 towards the distal opening 231 in the step of pressing the protrusion 9 onto the portion of the bent region 232.

[0545] For example, the protrusion can include a deformation cavity 93 or regions of limited mechanical stability that favor a deformation of the protrusion 9 in a predefined direction.

[0546] Alternatively or in addition, the protrusion 9 can include a deformation surface 94 that is designed in a manner that a contact surface between the protrusion 9 and the portion of the bent region 232 is established that favors the deformation of the protrusion 9 in a predefined direction.

[0547] FIG. 27d shows an exemplary embodiment of such a protrusion 9. However, there is no need that the protrusion 9 includes a portion that is bent towards the distal opening 231 and/or a deformation cavity as long as the portion of the bent region 232 against which the protrusion is pressed has a mechanical stability such that it is able to absorb the mechanical load applied during the method.

[0548] For example, the protrusion 9 can straight or tapered and/or rotationally symmetric with respect to the protrusion axis 92.

[0549] One can envisage that the portion of the bent region 235 that directs the protrusion 9 towards the opening 231 is not perpendicular (i.e. at 90 degrees) to the insertion axis 235, but at an angle smaller than 90 degrees, for example between 30 and 80 degrees or between 50 and 80 degrees.

[0550] A deformation of the protrusion 9 towards the distal opening 231 can include a softening or partial softening of the protrusion 9.

[0551] In a variant of the embodiments shown in FIGS. 26 and 27, the third object 30 provided does not include the through bore 230 and the bent region 232 if present. Rather, the through bore 230 and the bent region 232, if present, are produced in a further step of the method. This further step is performed after the step of bringing the distal surface 32 of the third object 30 in contact with the proximal surface 4 of the second object 2, in particular.

[0552] FIG. 28 shows an exemplary embodiment of a first object 1 including a plurality of protrusions 9, wherein the summarized volume of all protrusions 9 fulfills a condition for the volume.

[0553] In many embodiments including a plurality of protrusions 9, the protrusions are arranged in a subarea of the area formed by the distal surface 14 of the second object. The subarea defines a base 211 of the protrusion region 90. In FIG. 28, the base 211 is the area within the dashed line that on the distal surface 14.

[0554] The total volume of the protrusion region 90 can be calculated from the base 211 and a value or function corresponding to or approximating the extension 25 of the protrusions 9 in distal direction.

[0555] In many embodiments (but not all, FIGS. 15, 16, 21-23 for example), the protrusions 9 have an equal extension 25 in distal direction. In other words: they have an equal length. In this case, the value corresponding to the extension 25 of the protrusions 9 is their length.

[0556] The protrusions 9 within the protrusion region 90 are separated by gaps 27, this means void space. This space fills the volume of the protrusion region 90 not covered by the protrusions 9.

[0557] The volume condition fulfilled by the exemplary embodiment shown in FIG. 28, but also by many other embodiments of the first object 1, is the following: The volume of the protrusions 9 is half of the volume of the void space or less. In other words: The volume of the protrusions 9 corresponds to ⅓ or less of the total volume of the protrusion region 90, for example ¼, ⅕ or less than ⅕, such as 1/10.

[0558] FIG. 29 shows an embodiment of the method in which the (or a) region 23 of high density forms the proximal region of the second object 2 and the region 22 of low density is arranged distally of the region 23 of high density.

[0559] Further, the optional feature of a support 63 that can be present during bonding the first object 1 to the second object 2 only, or an item to which the second object 2 is or will be attached, or an integral part of the second object 2.

[0560] FIG. 29a shows the situation before bonding the first object 1 to the second object 2. FIG. 29b shows the situation after bonding the first object 1 to the second object 2.

[0561] FIGS. 29a and 29b depict an embodiment of the second object 2 in which the region 23 of high density is compressible, too. This is indicated by the doubled headed arrow that visualized the local compression of the region 23 of high density caused by the impact of the first object 1 that has been pushed through the region 23 of high density and that has been anchored in the region 22 of low density.

[0562] The region 23 of high density is such that it is deformable, in particular compressible. This allows for pushing in the first object 1 in a manner that it does not protrude from the proximal surface 4 of the second object after bonding. Further, it results in a compression of the region 22 of low density that is in addition to the compression effected by the protrusion 9 penetrating the region 22 of low density. Again, it is this compressed region 201 that leads to an efficient liquefaction of the thermoplastic material 3.

[0563] In the embodiment shown, there is no need that the protrusion 9 gets in contact with the support 63 thanks to the compression of the region 22 of low density.

[0564] In the embodiment of FIG. 29, the body 7 of the first object 1 is reduced to a head.

[0565] FIG. 30 shows a sectional view of a first object 1 bonded to yet another type of the second object 2. According to this embodiment, the second object 2 provided is characterized by a proximal top layer 200 arranged on a region 22 of low density, wherein the region 22 of low density is arranged on a region 23 of high density that is capable to give mechanical stability to the second object 2.

[0566] Such configurations including a proximal top layer arranged on a region 22 of low density arranged on a region 23 of high density can be found in items that must be rigid and comfortable to touch. Sometimes, such items are also called “softtouch” or items having a “softtouch surface”.

[0567] In embodiments, the proximal top layer is leather, artificial leather or a foil, and the region 22 of low density includes or consists of foam or another porous and resiliently deformable material. The region 23 of high density can then be any kind of a support.

[0568] An example of a “softtouch item” having the structure described is a dashboard, for example a car dashboard.

[0569] As an example, FIG. 30 shows a first object 1 being a display element that is bonded to a second object 2 being a dashboard having the structure described previously.

[0570] FIG. 30a shows the second object 2 (the dashboard) as provided, this means including the proximal top layer 200 and the region 22 of low density which is arranged on the region 23 of high density. The second object 2 provided includes further a feedthrough 207 designed to accommodate the first object 1 (the display element) and wires 209 that may be present.

[0571] FIG. 30b shows the situation after insertion of the first object (the display element) into the second object 2 (the dashboard). The bonding method and the mechanism including a compressed region 201, a protruding portion 91 and liquefied thermoplastic material 3 that has penetrated into structures 10 of the region 22 of low density (e.g., the foam) is the same as described previously.

[0572] Instead of mounting the first object 1 (the display element, for example) as a whole, one can also envisage to bond a connector 16 to the second object 2 first and the actual element to be attached to the second object 2 in a subsequent step. This embodiment is indicated in FIG. 30b by dashed lines.

[0573] In this embodiment and using the example of the display element to be mounted to the dashboard again, the first object 1 is the connector 16 and the display element is a third object 30 to be mounted to second object 2, this means to the dashboard, by the use of the first object 1.

[0574] For example, the connector 16 includes an element 15 for attaching the display element (the third object 30) to the connector 16, for example by a clamping mechanism.

[0575] The protrusions 9 can be designed to penetrate the proximal top layer 200 without need for a preceding perforation of the proximal top layer 200. In particular, the protrusions 9 can be designed to penetrate the proximal top layer 200 without becoming flowable.

[0576] It goes without saying that the first object 1 attached to the second object 2 characterized by the proximal top layer 200 arranged on the region 22 of low density can be any embodiment of the first object 1 disclosed, for example a connector. In this case, the second object 2 does not include any features that are specific for mounting the display element. For example, it does not include the feedthrough 207.

[0577] FIG. 31 shows a sectional view of a third object 30 being attached to the second object 2 including a region 22 of low density by a first object 1, wherein the first object 1 includes a head 212 and a protrusion 9 that is arranged distally of the head 212.

[0578] The third object 30 can include a pre-drilled opening or the third object 30 and the protrusion 9 can be designed such that the protrusion can penetrated the third object 30 in a step of pressing the first object 1 towards the third object 30.

[0579] The head 212 is designed in a manner that a portion of the third object 30 is clamped between the head 212 and the second object, in particular the proximal surface 4 of the second object 2.

[0580] Again, bonding of the first object 1 to the second object 2 is established by the generation of a compressed region 201 during the step of pushing the protrusion 9 into the second object 2.

[0581] FIGS. 32a and 32b shows an embodiment of the method including the further step of providing an adhesive 240 prior to the step of pushing the protrusion(s) 9 into the second object 2.

[0582] FIG. 32a shows the situation after providing the adhesive 240 on the proximal surface 4 of the second object 2.

[0583] In this embodiment, the first object 1 can include, as an optional feature, a retention protrusion 213 arranged in the region of the lateral end of the body 7. The retention protrusion 213 protrudes from the distal surface 28 of the body 7 into the distal direction.

[0584] The retention protrusion 213 is designed to prevent the adhesive 240 to be pressed laterally beyond the lateral extension of the first object 1, in particular the first object body 7. In other words: the retention protrusion 213 is designed to prevent a reduction of the amount of adhesive contributing to the bonding of the first object 1 to the second object 2 during the bonding process.

[0585] In particular, the retention protrusion 213 prevents a contamination with adhesive 240 of areas of the proximal surface 4 of the second object 2 that are external areas after the bonding process.

[0586] The retention protrusion 213 as well as the protrusions 9 can define retention openings 214 in which adhesive can accumulate.

[0587] FIG. 32b shows the situation after bonding the first object 1 to the second object 2 by the method including the further step of providing an adhesive 240.

[0588] The adhesive 240 is pressed into the second object 2 during the step of pressing the first object 1 into the second object 2. Hence, a zone 241 penetrated by adhesive 240 is generated around the protrusions 9, at least. In this zone 241, the material forming the region of low density 22 is augmented by the adhesive. For example, the region of low density 22 includes fibers that are stuck together due to the presence of the adhesive.

[0589] Hence, the further step of providing the adhesive 240 is a further approach to improve the quality, in particular the mechanical stability and reliability, of the first object 1 being bonded to the second object 2 by the method.

[0590] FIGS. 33a and 33b show another exemplary embodiment of a first object 1 being a connector 16.

[0591] The connector 16 shown includes the protrusion region 90 with a plurality of protrusions 9 and a connecting structure defining a connecting location defined with respect to all dimensions (x, y, z). The connecting structure in the depicted embodiment is constituted by a connector peg 250 that is one-piece with the protrusions 9 and the body 7.

[0592] The connecting structure—the connector peg 250 in the shown embodiment—is especially such that it is arranged laterally. This means that the arrangement of the connecting structure 250 is not symmetrical with respect to the insertion axis 235 but is off-center with respect to the axis 235. The insertion axis 235 is the axis along which generally the pressing force is applied during insertion and along which the movement during insertion will take place at least predominantly. The insertion axis 235 is generally a characteristic axis of the first object, such as a rotation axis, a central axis and/or it coincides with the protrusion axis. The latter can be the case when the first object 1 includes a single protrusion 9 or a central protrusion 9. Thus, the axis is especially defined by the protrusion and/or the overall shape of the first object 1.

[0593] Thereby, the position of the connecting location depends on the angle of rotation around the axis 235. Hence, when the connector is positioned relative to the second object 2 and anchored therein, not only the position but also its orientation may have to be defined.

[0594] An example of an according connecting structure may, for example, be a structure (like the peg) that protrudes away from the protrusion(s) into a defined direction, such as a pivot of a hinge or similar, a structure for clipping another item onto, an anchor for a thread connection, etc.

[0595] The connector 16 of FIGS. 33a and 33b includes a plate-like body 7 defining the distally facing stopping surface 12. From the body 7 towards proximally, the connector includes a base wall 253 from which the connector peg 250 protrudes laterally. The base wall is arranged off-center with respect to the axis 235. Further, the connector includes a plurality of reinforcing walls 254 extending perpendicularly to the base wall 253 and enhancing the mechanical stability with respect to forces acting on the connector peg.

[0596] The distally facing stopping surface defines the z position of the connecting structure after the process in that the pressing force is applied until the stopping surface 12 abuts against the proximal surface 4 of the second object 2.

[0597] The connector 16 in the embodiment of FIGS. 33a and 33b may, for example, be a mount of a rear parcel shelf of an automobile.

[0598] The sonotrode 20 used for anchoring the connector may be shaped to be adapted to the shape of the connector. Especially, as shown in FIG. 33a, the connector may be shaped to impinge, from proximally, on the body 7 by engaging between the reinforcing walls 254 and the base wall 253. In addition or as an alternative, it would also be possible to provide a protruding collar 255 of the connector 16, as shown in dotted lines in FIG. 33a. The arrangement with the sonotrode engaging between the walls directly on the body 7, with the sonotrode having indentations for reinforcing wall(s) if necessary, though, features the advantage that the pressing force and vibration (more generally the mechanical excitation) are coupled straight into the protrusions.

[0599] In embodiments that include a connecting location the position and/or orientation of which depends on the orientation of the connector around its axis 235, it may be necessary to guide the orientation of the connector during the anchoring process, because due to the vibration input (more generally the mechanical excitation) the connector may be subject to some uncontrolled twisting movements during insertion. In the embodiment of FIGS. 33a and 33b, the base wall 253 and/or the reinforcing walls 254 may be used for this, together with a corresponding shape of the sonotrode, whereby the orientation of the sonotrode defines the orientation of the connector.

[0600] The exemplary embodiment of FIGS. 33a and 33b includes further the optional feature of a cutting structure 252 that is designed to penetrate a proximal top layer, for example.

[0601] The embodiment of FIG. 33, but also of FIG. 7, for example, includes using a sonotrode adapted to the geometry of the first object 1 being the connector. This is not always necessary. One can envisage embodiments of a first object 1 being a connector in which the body 7 forms a generally flat coupling surface for a generic sonotrode.

[0602] The connector can include at least one process controlling abutment protrusion if the number and/or arrangement and/or dimensions of the protrusions 9 are such that the connector cannot be held in a desired position relative to the second object at the beginning of applying a mechanical pressing force and—as the case may be—the mechanical excitation. This abutment protrusion(s) together with the protrusions can give a stable standing to the connector when the connector is brought into contact with the proximal surface of the second object. In other words: the connector position is well-defined and stable.

[0603] An abutment protrusion of this kind may, during the subsequent process, collapse or melt away. It does not necessarily have to penetrate into the volume of the second object.

[0604] In addition to stabilizing the connector during an initial stage of the process, it can also dampen undesired bending vibrations when the body 7 has a substantial lateral extension.

[0605] FIGS. 34-39 show various exemplary embodiments of the protrusion region 90 of the first object 1 and the device, respectively.

[0606] In the exemplary embodiment shown in FIG. 34, the protrusions 9 include a protrusion axis 92 that does not run parallel to the normal of the distal surface 28 of the body 7 of the first object 1.

[0607] The protrusion axis 92 running not parallel to the normal defines a direction into which the protrusion 9 deforms during the method in any one of the embodiments disclosed.

[0608] A further consequence of the protrusion axis 92 that does not run parallel to the normal of the distal surface 28 of the body 7 of the first object 1 is that the length of the protrusion is larger than the extension 25 of the protrusion in distal direction.

[0609] At least the following features are shown in the exemplary embodiments of the first object 1 depicted in FIGS. 34-39: [0610] The functional region 50. In the embodiments of FIGS. 38 and 39, the functional region is given by the distal mouth of a through bore that extends from the proximal surface 29 to the distal surface 28 of the body 7 of the first object 1. [0611] A first object 1 including a through bore can be applied for stabilizing or fixing the edge of the feedthrough established, e.g., punched into the second object 2. [0612] The gaps 27 between the protrusions 9, wherein the volume of the gaps and the volume of the protrusions have the ratio described above. [0613] An extension 25 of the protrusion 9 in distal direction and a thickness 26 of the protrusion 9 that are such that the ratio between the extension 25 and the thickness 26 is as described above, this means at least 1, in particular between 1 and 5, for example between 1.5 and 4 or between 2 and 3.

[0614] FIGS. 40-43 show perspective views of various exemplary embodiments of the first object 1 and the device, respectively.

[0615] Various connection elements 15 of a connecting device are shown in addition to the features related to the protrusion region 90. The elements are arranged on the proximal surface 29 of the body 7 of the first object 1.

[0616] The embodiments shown include a connection location 51 at which the elements 15 of the connecting device are connected to the first object 1. In the embodiments shown, the connection location 51 includes and is restricted to a portion of the proximal surface 29 of the body 7 of the first object 1 that is opposite to the functional region 50 arranged on the distal surface 28 of the body 7 of the first object 1.

[0617] The connection element 15 of the first object 1 shown in FIG. 40 is suited for attaching cables and/or wires to the first, and hence to the second, object.

[0618] The connection element 15 of the first object 1 shown in FIG. 42 is an example of a connection element suited for screwing an item to the first, and hence to the second, object. The connection element shown can include a longitudinal opening that goes through to the distal surface 28 of the body 7 the first object 1.

[0619] The connection element 15 of the first object 1 shown in FIG. 42 is suited for attaching plate- and/or sheet-like items to the first, and hence to the second, object.

[0620] The connection element 15 of the first object 1 shown in FIG. 43 is an example of a connection element for clip solutions.

[0621] First objects 1 as shown in FIGS. 34-43, for example, are bonded to the second object 2 by the use of a sonotrode 20 that is applied at the portion of the proximal surface 29 of the first object 1 not covered by the connection element 15 or any element of a connecting device, usually. Further, the mechanical excitation, this means the mechanical oscillations, are preferably applied along the axis 8 that runs at an angle, in particular normal, to the proximal surface 29.

[0622] In this case, the coupling-out face 21 of the sonotrode 20 extends preferably over an area of the proximal surface 29 of the first object 1 during the step of applying the mechanical pressing force and the mechanical excitation that is comparable with the opposite area covered by protrusions 9 on the distal surface 28 of the first object 1. For example, the area in contact with the coupling-out face 21 covers at least 80% of the area covered by protrusions on the distal surface 28 of the first object 1. For example, it extends over an area that is 0.8 to 2 times the area covered by protrusions 9, in particular 0.8 to 1.5, 0.8 to 1.2 or 0.8 to 1 times. In other words: the radial extension of the area of the proximal surface 29 is at least 80% of, in particular larger than, the radial extension of the area covered by protrusions on the distal surface 28 in any radial direction.

[0623] The coupling-out face 21 can protrude over the body 7 of the first object 1.

[0624] FIGS. 44-49 show exemplary embodiments of first objects 1 that include features capable to prevent the generation of natural oscillation in the first object body 7 of a strength that can be destructive for the first object body 7.

[0625] The embodiment according to FIG. 44 includes a damping element 52 arranged at the distal surface of the first object body.

[0626] The damping element 52 gets in contact with the proximal surface 4 of the second object 2 or—as the case may be—with the proximal surface 31 of the third object 3 during the method of bonding the first object 1 to the second object 2. Thereby, natural oscillation generated in the first object body 7 during the step of applying the mechanical excitation to liquefy the thermoplastic material 3 can be damped due to the physical contact generated between the damping element 52 and the second 2 or—as the case may be—the third object 3.

[0627] In the embodiment shown, the damping element 52 includes thermoplastic material, too. In other words, the damping element 52 is not only capable to damp the natural oscillation but also to enhance the bonding between the first and second (or third) object.

[0628] The embodiments according to FIGS. 45 and 46 include a plurality of distinct protrusion regions 90 that are designed to minimize the energy of the mechanical excitation needed to liquefy the thermoplastic material.

[0629] Further, FIGS. 45 and 46 each show a set of protrusion regions capable to tune away the frequency of the natural oscillations of the first object body 7 from the frequency applied to cause liquefaction of the thermoplastic material.

[0630] At least one of the protrusion regions 90 can be arranged to act as a damping element 52 too, as shown in FIGS. 45 and 46. However, it is not mandatory that one protrusion region of the plurality of protrusion regions is designed and arranged as a damping element 52.

[0631] FIGS. 47 and 48 show a first object 1 including a fixation element 1.1 designed to be bonded to the second object 2 by a method according to the invention and a connecting element 1.2 designed to be bonded to the fixation element 1.1.

[0632] The fixation element 1.1 includes a fixation element connection means 110 and the connecting element 1.2 includes a connecting element connection means 120 that are adapted to one another in a manner that the bond between the fixation element 1.1 and the connecting element 1.2 can be established.

[0633] In the embodiment shown, the fixation element connection means 110 is a through hole in the body 7.1 of the fixation element 1.1 and the connecting element connection means 120 is a protrusion with a diameter adapted to a diameter of the through hole.

[0634] The protrusion 120 includes thermoplastic material and is designed in a manner that it can be bonded to the second object 2 after being pushed through the through hole 110 in the body 7.1 of the fixation element 1.1.

[0635] In addition or alternatively, the protrusion 120 includes thermoplastic material and is designed in a manner that it can weld to thermoplastic material of the fixation element 1.1, in particular of thermoplastic material 3 of the protrusions 9 designed to bond the fixation element 1.1 to the second object 2 by the method.

[0636] One can also envisage other means for bonding the connecting element 1.2 to the fixation element 1.1, for example clamping means, clipping means and/or the elements of a bayonet lock.

[0637] FIG. 49 shows the fixation element 1.1 of a first object 1 including a fixation element 1.1 and a connecting element 1.2 in detail.

[0638] The body 7.1 of the fixation element 1.1 and of the corresponding connecting element 1.2 includes thermoplastic material. The fixation element 1.1 includes a fixation element energy director 111 and the connecting element 1.2 includes possibly a connecting element energy director 120. Such energy director (111 and 120) define a region where thermoplastic material of the fixation element 1.1 and of the connecting element 1.2 liquefies in a further step of applying a mechanical pressing force and mechanical excitation.

[0639] The further step causes a connection (in particular, a weld) between the fixation element 1.1 and the connecting element.

[0640] In particular, the further step is applied after the step of applying the mechanical pressing force and the mechanical excitation causing liquefaction of thermoplastic material of the protrusion(s). This means, the further step is applied after bonding the fixation element 1.1 to the second object 2.

[0641] An advantage of a method including two steps of applying mechanical pressing force and mechanical excitation, a first one for bonding the fixation element 1.1 to the second object 2 and a second one for bonding the connection element 1.2 to the fixation element 1.1, is at least one of the following: [0642] The energy acting on portions of the first object 1 that bear the element of a connecting device 15 can be reduced; [0643] The coupling-out face 21 of the sonotrode 20 can be adapted to the shape of the fixation element 1.1 and/or the shape of the connection element 1.2; [0644] Any issue based on a frequency of a natural oscillation of the first object body 7 close to the frequency of the mechanical excitation needed during bonding the first object 1 (this means the fixation element 1.1) to the second object 2 can be avoided.

[0645] FIGS. 50 and 51 show a further method for fixing a third object 30 to the second object 2 by the first object 1.

[0646] According to this method (FIG. 50) the third object 30 is glued on the proximal surface 29 of the first object body 7.

[0647] A first object 1 designed for use in the method according to FIGS. 50 and 51 includes a proximal surface 29 that extends over a wide area. FIG. 51 shows such a first object 1. In particular, the first object body 7 forms an area on which the third object 30 can be fixed.

[0648] In addition, the first object 1 designed for use in the method according to FIGS. 50 and 51 can include any one of the features for preventing destructive natural oscillations presented with respect to FIGS. 44-48.

[0649] First objects 1 in any of the embodiments discussed above, for example as shown in FIGS. 1-5, 14, 16, 17, 20, 26a, 28, 29a, 31 and 34-43, can be used to attach a third object 30 to the second object 2.

[0650] In particular, the third object 30 can be a sheet material, for example a metal sheet.

[0651] The attachment of the third object 30 can include the at least local compression of the second object 2, wherein the compression is in a manner that the critical density and/or the critical compressive strength is generated.

[0652] FIG. 52 shows a sectional view of the arrangement and design of a first object 1, a second object 2 and a sheet material 30, wherein the sheet material 30 is to be fixed to the second object 2 by the first object 1.

[0653] The sheet material 30 shown includes through bores 230 that are adapted in shape and number to the protrusion(s) 9 of the first object 1.

[0654] For example, the protrusions 9 can be ridges as shown in FIGS. 1 and 5, for example. In this case, the sheet material 30 can include through bores 230 in the shape of longitudinal slits.

[0655] For example, the first object 1 can include a protrusion region 90 as shown in FIGS. 5, 28, 34, 36 and 37 for example. In this case, the sheet material 30 can include through bores 230 with a round or rectangular footprint.

[0656] For example, the first object 1 can include a protrusion region 90 as shown in FIGS. 35, for example. In this case, the sheet material 30 can include through bores 230 in the shape of circular slits.

[0657] The through bores 230 can be such that a position of the sheet material 30 relative to the first object 1 can be adjusted. In the case of a first object 1 including a protrusion region 90 with a plurality of protrusions 9 that are arranged along a line, the sheet material 30 can include per line of protrusions 9 a through bore 230 in the shape of a longitudinal slit.

[0658] FIG. 53 shows a sectional view of a further arrangement and design of a first object 1, a second object 2 and a sheet material 30, wherein the sheet material 30 is to be fixed to the second object 2 by the first object 1.

[0659] According to this exemplary arrangement, the first object 1 can include at least two protrusions 9 and the corresponding method includes the step of arranging the first object 1, the second object 2 and the third object 30 such that at least one protrusion 9 is arranged beyond a radial end of the material sheet and at least one protrusion 9 is in contact with the proximal end of the third object 30.

[0660] Third object 30 can include a through bore 230 of the kind described with respect to FIG. 52 and the first object 1 can be arranged relative to the second object such that at least one protrusion engages with the through bore 230.

[0661] In the embodiment shown, the third object 30 includes a flange 237 designed for being positioned on the second object and for being attached to the second object by the first object. The flange 237 includes the through bore 230.

[0662] In particular, the first object 1 can be as shown in FIGS. 1-5, 20, 28 and 34-43, for example.

[0663] In the embodiment of FIG. 53, the third object is a metal sheet. If the third object 30 is a metal sheet, the metal sheet 30 is or can be heated during the method. This can cause local melting of the second object 2, which leads to a further increase in density of the region of low density 22 and a further reinforcement thereof. In other words, the second object 2 can be transformed locally to a coherent material.

[0664] FIGS. 54a and 54b visualize a method for fixing a third object 30 that is a metal sheet to the second object 2, wherein the metal sheet 30 has no through bores 230 for the protrusion(s) 9.

[0665] The method includes the further steps of: [0666] Arranging the first object 1, the second object 2 and the metal sheet 30 relative to each other such that the proximal surface 31 of the metal sheet 30 is in contact with the protrusions 9 and such that the distal surface 32 of the metal sheet 30 is in contact with the second object 2. [0667] Pressing the first object 1 to the metal sheet 30 such that the first object 1 and the metal sheet 30 are vibrationally coupled to each other. [0668] Applying the mechanical vibrations to the first object 1 and increasing the pressing force such that the metal sheet 30 deforms into the second object 2. [0669] Increasing the pressing force further until the protrusion(s) 9 penetrate the metal sheet 30. In other words, a penetration region 260 is generated in the metal sheet 30. [0670] Liquefaction of the thermoplastic material that has penetrated the metal sheet in the compressed region 201 of the second object and/or pressing the liquefied thermoplastic material in the compressed region 201.

[0671] This embodiment of the method is appropriate for material sheets in general. However, application of this method to metal sheets 30 has the advantage that the metal sheet heats the second object 2 during the method. This can cause local melting (melting zone 261) of the second object 2, which leads to a further increase in density of the compressed region 201 and to further reinforcement of the region of low density 22. In other words, the second object 2 can be transformed locally to a coherent material.

[0672] FIG. 55 shows an exemplary embodiment of a first object that can be used in the method according to FIGS. 54a and 54b. The embodiment shown includes: [0673] A first row of protrusions and a second row of protrusions. In the embodiment shown, the protrusions of the first row have the same length than the protrusions of the second row. Further the protrusions are tapered. [0674] A first region 263 on the distal surface of the first object 1 that is offset in distal direction from a second region 264 on the distal surface. In the embodiment shown, the second region 264 (central region) is more distal than the first region 263 (region between the two rows of protrusions). [0675] In particular, the more distal region is arranged to damp natural oscillations during the method, in particular during a final phase of the method when the energy coupled into the objects is highest. [0676] A channel 262 for material flow.

[0677] A first object as shown in FIG. 55 can help to avoid destructive natural oscillations and destructive deformations of the third object 30, in particular if the third object is a metal sheet 30.

[0678] FIG. 56 shows a sectional view of a basic arrangement of the first and second object for an embodiment of the method in which the sonotrode 20 is applied to the second object 2.

[0679] In the exemplary arrangement shown, the first object 1 is an item to which the protrusions 9 are connected. One can envisage configurations in which the proximal surface 29 of the first object 1 is not or not easily accessible. For example, the item can be a part of a car body.

[0680] In particular in such configurations, the second object 2 can be placed relative to the protrusions 9 such that the protrusions 9 are in contact to the portions of the second object 2 that should be penetrated by the protrusions 9 at least partly during the method.

[0681] In the embodiment shown in FIG. 56, the second object 2 is a cover including a first region 204 of low density that forms an open laying surface and a second region 205 of low density in which the positive-fit connection between the first and the second object is to be formed. However, this structure is not mandatory for the method/application shown in FIG. 56 (and FIGS. 57a and 57b). The second object 2 can have a more sophisticated structure or it can be homogeneous.

[0682] FIGS. 57a and 57b show an exemplary application of the embodiment of the method in which the sonotrode 20 is applied to the second object 2.

[0683] FIG. 57a shows the arrangement of first object 1, second object 2 and sonotrode before the step of applying the mechanical pressing force and the mechanical excitation capable to liquefy the thermoplastic material.

[0684] FIG. 57b shows the situation after bonding the first object 1 to the second object 2.

[0685] FIGS. 57a and 57b show: [0686] A second object 2 that is a cover for the first object 1, for example a part of a car body, wherein the cover is adapted or adaptable in shape to the first object 1. [0687] A plurality of protrusions 9 that are arranged on the first object 1 in a manner that the cover 2 can be reliably fixed to the first object 1. [0688] The item 2 that is arranged on the first object 1 such that bonding locations on the proximal surface 4 of the item 2 are in contact with the protrusions. [0689] The sonotrode 20 that is applied locally and sequentially to regions of the distal surface 14 of the item 2 that correspond to positions of the protrusions 9. [0690] The sonotrode is applied to the item 2 until the item has reached a desired end position relative to the first object 1.

[0691] FIG. 58 shows a variation of the method in which the second object 2 is placed between the first object 1 and the sonotrode 20.

[0692] According to this variation, any force for advancing the protrusion(s) 9 into the second object 2 is applied to the first object 1 (indicated by the arrow below the first object 1).

[0693] The sonotrode 20 is in contact to the distal surface 14 of the second object 2 and couples mechanical oscillations into second object 2. Further, it acts as a support for the second object 2, but it does not push actively the second object 2 towards the first object 1.

[0694] This arrangement of applying the sonotrode to the second object 2 and any pushing force to the first object 1 has the effect that a compressed region 201 is generated around the protrusion(s), wherein the compression of the distal surface 14 of the second object 2 is kept minimal.

[0695] FIG. 59 shows two stress-strain-curves (A and B) that are representative for the experimental results that led to the surprising finding that various incoherent materials are suitable for use in bonding methods relying on the liquefaction of thermoplastic material by the use of a mechanical pressing force and a mechanical excitation, in particular vibrations.

[0696] The relative behavior of stress-stain curves A and B shows the influence of a changing surface via which load is applied to the material. The indenter of curve B has a larger surface area in contact with the material that the indenter of curve A.

[0697] FIG. 59 shows the observed first region in which the stress depends approximately linear on strain, the observed transition region and the observed second region in which the stress depends approximately linear on strain.

[0698] The straight lines that approximate the approximately linear dependence in the different regions of linear dependencies are represented as dashed lines.

[0699] The strain c at which the slope of the first region of approximately linear dependency and the slope of the second region of approximately linear dependency cross is a characteristic value of the stress-strain behavior of the material. The characteristic value can be used to define a minimal compression needed in embodiments of the method in which the positive-fit connection is to be established in the region of low density.