ANCHORING A JOINING ELEMENT IN AN OBJECT

Abstract

A joining element has an anchoring portion for in-depth anchoring in the object and a head portion arranged proximally of the anchoring portion with respect to an insertion axis. The head portion has a lateral outer surface that has a structure that is well-defined, especially within tight tolerances. The joining element is positioned relative to an object of a non-liquefiable material such that the anchoring portion reaches into an opening of the object or is placed adjacent a mouth thereof. Then, the joining element is pressed towards a distal direction, to press the anchoring portion into the opening, while mechanical vibration energy is coupled into the joining element by a tool, in an amount and for a time sufficient for liquefaction of a portion of the thermoplastic material to cause interpenetration of the thermoplastic material into structures of the object.

Claims

1. A method of anchoring a joining element in an object, the method comprising the steps of: providing a joining element, the joining element comprising an anchoring portion for in-depth anchoring in the object, and a head portion proximally of the anchoring portion, the head portion having a lateral outer surface with a well-defined structure, the joining element comprising a thermoplastic material at least on a surface of the anchoring portion; positioning the joining element relative to the object in a manner that the anchoring portion reaches into an opening of the object or is placed adjacent a mouth thereof; and pressing the joining element towards a distal direction and at the same time coupling mechanical vibration energy into the joining element by a tool in an amount and for a time sufficient for liquefaction of a portion of the thermoplastic material to cause interpenetration of the thermoplastic material into structures of the object, wherein the method comprises leaving the lateral outer surface of the head portion intact.

2. The method according to claim 1, wherein an insertion axis is defined to be a proximodistal axis along which the pressing force is applied, wherein a surface of the object, in which the opening has a mouth, is plane, wherein a head portion axis is defined to be perpendicular to the plane surface of the object after anchoring, and wherein the head portion axis coincides with the insertion axis.

3. The method according to claim 1, wherein an insertion axis is defined to be a proximodistal axis along which the pressing force is applied, wherein a surface of the object, in which the opening has a mouth, is plane, wherein a head portion axis is defined to be perpendicular to the plane surface of the object after anchoring, and wherein the head portion axis is at a nonzero angle to the insertion axis.

4. The method according to claim 1, wherein the head portion is symmetrical about rotations around a head portion axis.

5. The method according to claim 1, wherein the pressure and the mechanical vibration are applied by pressing the tool against a proximal end face of the head portion.

6. The method according to claim 5, wherein in the step of pressing, a coupling-out face of the tool is pressed against the proximal end face of the joining element, a tool-joining-element-interface being formed between the coupling-out face and the proximal end face, wherein the interface has a smaller radial extension than a radial extension of the head portion.

7. The method according to claim 6, wherein the head portion comprises a proximal protrusion a radial extension of which is smaller than the radial extension of the head portion.

8. The method according to claim 7, wherein the proximal protrusion is ring-shaped or disc-shaped.

9. The method according to claim 6, wherein the coupling-out face of the tool has a radial extension which is smaller than the radial extension of the head portion.

10. The method according to claim 1, wherein the head portion comprises a recess open to the proximal side, and wherein the pressure and the mechanical vibration are applied by the tool to a coupling face within the recess.

11. The method according to claim 1, wherein the anchoring portion comprises a proximally-facing coupling face in a vicinity of the head portion, and wherein the step of pressing and coupling vibration energy into the joining element comprises pressing the tool against the coupling face of the anchoring portion.

12. The method according to claim 11, wherein the anchoring portion comprises an anchoring portion body and at least one protrusion facing distally away from the anchoring portion body.

13. The method according to claim 12, wherein the opening comprises an opening lateral wall and an opening ground terminating the opening distally, and wherein during the step of pressing and coupling the vibration energy into the joining element the at least one protrusion is pressed through a surface of the opening ground.

14. The method according to claim 12, wherein the at least one protrusion is arranged essentially at lateral positions of the coupling face.

15. The method according to claim 11, wherein the step of pressing and coupling vibration energy into the joining element is carried out until the coupling face is flush with a surface of the object or is below this surface.

16. The method according to claim 1, wherein the joining element is one-piece and consists of the thermoplastic material.

17. The method according to claim 1, further comprising providing, in the step of providing the joining element, the joining element comprising a liquefiable part that comprises the thermoplastic material, and a non-liquefiable part.

18. The method according to claim 17, wherein at least a part of the head portion that comprises at least a portion of the structured lateral outer surface is formed by the non-liquefiable part.

19. The method according to claim 17, wherein the structured lateral outer surface of the head portion is made of the thermoplastic material, and wherein the non-liquefiable part is an insert element integrated in the liquefiable part.

20. The method according to claim 17, wherein the non-liquefiable part comprises a proximally facing coupling surface, wherein in the step of pressing the joining element towards a distal direction and coupling mechanical vibration energy into the joining element the tool is pressed against the coupling surface while it is subject to vibrations.

21. The method according to claim 20, wherein the coupling face is offset with respect to a proximal end face of the joining element.

22. The method according to claim 21, wherein the head portion comprises a recess in the proximal end face, and the coupling face is arranged at the bottom of the recess.

23. The method according to claim 22, wherein the recess has an aspect ratio of at least 0.5.

24. The method according to claim 20, wherein the non-liquefiable part comprises a coupling plate and a spike portion extending distally therefrom.

25. The method according to claim 17, wherein the liquefiable part and the non-liquefiable part are coupled or couplable together by at least one of: a press fit; an adhesive bond; interpenetration of structures the non-liquefiable part by material of the liquefiable part so that a positive-fit connection results.

26. The method according to claim 17, further comprising providing the joining element as an integral, pre-manufactured element that comprises the liquefiable part and the non-liquefiable part.

27. The method according to claim 17, further comprising providing the liquefiable part and the non-liquefiable part of the joining element as separate parts and further comprising assembling the liquefiable part and the non-liquefiable part during the step of pressing and coupling vibration energy into the joining element and/or after this step.

28. The method according to claim 27, comprising causing a further portion of the material of the liquefiable part, by the effect of the vibration energy and the pressing that cause the interpenetration of the thermoplastic material into structures of the object, to be liquefied and to penetrate into structures of then non-liquefiable part to yield, after re-solidification, a positive-fit connection between the liquefiable part and the non-liquefiable part.

29. The method according to claim 1, wherein a proximal end face of the joining element comprises a guiding hole, and wherein in the step of positioning, a guiding protrusion of the tool is inserted to cooperate with the guiding hole.

30. The method according to claim 1, wherein in the step of coupling mechanical vibration energy into the joining element, the tool is caused to vibrate with a frequency between 10 kHz and 50 kHz.

31. The method according to claim 1, wherein in the step of pressing, a mechanical pressure of at least 10.sup.5N/m.sup.2 is applied by the tool to the joining element.

32. The method according to claim 1, comprising the further step of placing a mould tool relative to the head portion so that the lateral outer surface is at least partially in contact with a mould surface portion being a negative of the lateral outer surface and maintaining the physical contact between the mould tool and the head portion during at least a portion of the pressing.

33. A joining element for being anchored, with the aid of a thermoplastic material and mechanical vibration, in an object of material penetrable by the liquefied thermoplastic material, the joining element comprising an anchoring portion for in-depth anchoring in the object, and a head portion proximally of the anchoring portion, the joining element comprising a thermoplastic material at least on a surface of the anchoring portion, wherein at least one of the following conditions is met: the head portion comprises a proximal protrusion a radial extension of which is smaller than the radial extension of the head portion; the head portion comprises a recess open to the proximal side, the recess having a width sufficient for a tool to engage the joining element within the recess to couple mechanical vibration into the joining element, so that that portions of the thermoplastic material near the surface of the anchoring portions liquefy while a lateral outermost surface portion of the head portion remains intact; the joining element comprises a liquefiable part and a non-liquefiable part and the non-liquefiable part forms a proximally facing coupling-in face for coupling the mechanical vibration into the joining element by a tool; the anchoring portion comprises an anchoring portion body and at least one protrusion facing distally away from the anchoring portion body, wherein the anchoring portion body forms a proximally-facing coupling face in a vicinity of the head portion.

34. An assembly, comprising the joining element of claim 33 and further comprising a tool adapted to a proximally facing coupling face of the joining element and capable of coupling the mechanical vibration into the joining element.

35. A joining element for being anchored, with the aid of a thermoplastic material and mechanical vibration, in an object of material penetrable by the liquefied thermoplastic material, the joining element comprising a shaft for serving as an anchoring portion for in-depth anchoring in the object, and an a head portion with a distally facing shoulder or a border line between the head portion and the anchoring portion, the joining element comprising a thermoplastic material at least on a surface of the anchoring portion, wherein at least one of the following conditions is fulfilled: the head portion comprises a recess open to a proximal end, the recess extending axially substantially through the entire head portion; the anchoring portion comprises at least one groove running in axial direction, the groove having a depth of at least 15% of an average shaft diameter.

36. The joining element according to claim 35 with the head portion comprising a recess open to a proximal end, wherein a lateral extension of the recess amounts to at least 40% of a head diameter of the head portion and an axial extension of the recess amounts to at least 80% of an axial extension of the head portion.

37. The joining element according to claim 35, the anchoring portion comprising a plurality of grooves on lateral sides of the shaft.

38. The joining element according to claim 37, wherein the grooves are arranged on opposite lateral sides of the shaft in a staggered arrangement.

39. The joining element according to claim 38, wherein the shaft, in a section perpendicular to a proximodistal shaft axis, has an essentially S-shaped cross section.

40. An apparatus for carrying out the method according to claim 1, the apparatus comprising a joining element positioner, a holding device for holding the object and a sonotrode for pressing the joining element towards a distal direction and at the same time coupling mechanical vibration energy into the joining element in an amount and for a time sufficient for liquefaction of a portion of the thermoplastic material to cause interpenetration of the thermoplastic material into structures of the object, the apparatus being configured to leave the lateral outer surface of the head portion intact.

41. The apparatus according to claim 40, being configured to stop a forward movement of the sonotrode relative to the object as soon as a predetermined condition is met.

42. The apparatus according to claim 41, wherein the predetermined condition is that an outcoupling face of the sonotrode has reached a position at a predetermined distance from the object.

43. The apparatus according to claim 42, the apparatus further comprising a distance sensor adapted for sensing the distance between the sonotrode and the object.

44. The apparatus according to claim 40, further comprising a mould tool configured to be placed relative to the head portion when the anchoring portion reaches into the opening, so that the lateral outer surface is at least partially in contact with a mould surface portion being a negative of the lateral outer surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0137] Hereinafter, principles and embodiments of the invention are described in further detail in connection with appended Figures, which are all schematic. In the drawings, same reference numbers refer to same or analogous elements. The figures show:

[0138] FIGS. 1a and 1b longitudinal sections (sections along a plane parallel to the axis) illustrating anchoring of a joining element according to the prior art;

[0139] FIGS. 2a-2e longitudinal sections illustrating anchoring a joining element by a method according to the invention;

[0140] FIG. 3 a variant of the joining element of FIG. 2a;

[0141] FIGS. 4a-4b details of longitudinal sections illustrating anchoring another joining element by a method according to the invention;

[0142] FIG. 5 a longitudinal section illustrating anchoring yet another joining element by a method according to the invention;

[0143] FIGS. 6-7 longitudinal sections illustrating further joining elements;

[0144] FIG. 8 longitudinal sections illustrating anchoring an even further joining element by a method according to the invention;

[0145] FIGS. 9-10 variants of the joining element of FIG. 8;

[0146] FIGS. 11 a longitudinal section illustrating anchoring a joining element in a board with an end face having a non-perpendicular angle to the board plane;

[0147] FIG. 12 a longitudinal section illustrating anchoring a further joining element by a method according to the invention;

[0148] FIG. 13 a variant of the joining element of FIG. 13;

[0149] FIG. 14 longitudinal sections of a joining element comprising two separate parts;

[0150] FIGS. 15a-15b longitudinal sections illustrating anchoring a further joining element comprising two separate parts;

[0151] FIG. 16 longitudinal sections illustrating anchoring yet another joining element comprising two separate parts;

[0152] FIGS. 17a-17c details of connections between joining element parts and the anchoring in longitudinal section;

[0153] FIGS. 18-19 a connection between parts of a further joining element, and such a further joining element after anchoring;

[0154] FIGS. 20-21 longitudinal sections of yet further joining elements composed of two parts;

[0155] FIG. 22 a joining element as shown in FIG. 20 anchored in a board with an end face having a non-perpendicular angle to the board plane;

[0156] FIGS. 23a-25 yet another joining element in top view and a longitudinal section and a top view of a sonotrode usable for anchoring it;

[0157] FIGS. 26-29 transversal sections (sections perpendicular to the insertion axis) of anchoring portions of further embodiments of joining elements;

[0158] FIGS. 30-32 details illustrating further embodiments of the first group of embodiments;

[0159] FIGS. 33a and 33b an embodiment of a joining element of the third group;

[0160] FIG. 34 the principle underlying the fifth group;

[0161] FIGS. 35a and 35b a further embodiment of a joining element; and

[0162] FIGS. 36 and 37 principles of an apparatus for carrying out the method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0163] A joining element 1 as illustrated in FIG. 2a comprises a head portion 11 and an anchoring portion 12. Between the head portion and the anchoring portion, a distally facing shoulder 18 is formed, which shoulder serves as stop face in the anchoring process described hereinafter.

[0164] The joining element 1 may be essentially symmetric with respect to a rotation around its axis 10, with the possible exception of energy concentrating elements (not shown in FIG. 2a), such ribs or humps, of an outer surface of the anchoring portion 12.

[0165] The head portion 11 has a lateral outer surface that is shaped to engage into a corresponding structure of a female part of a further object so that the object into which the joining element is anchored and the further object may be assembled to one another. Especially, the lateral outer surface has a structure 13 that makes a positive-fit connection with the female part possible, in a manner that forces in axial directions (with respect to the axis 10) can be transferred between the head portion 11 and the female part in a positive-fit manner (in positive-fit connections, the connecting force in contrast to frictional fits has a component perpendicular to the surface—the joined objects are in each other's way).

[0166] More in particular, in the depicted embodiment, the head portion has at least one groove 14.

[0167] In this embodiment and in any other embodiment discussed in this text, the head portion may be shaped according to the teaching of WO 2013/104422, incorporated herein by reference in its entirety, and has the function to serve as male part of a joint described therein.

[0168] The head portion 11 further has a proximal protrusion 15 that is ring-shaped and has a thickness (axial extension) t of typically 2 mm or less. A radial extension of the proximal protrusion 15 is less than an extension of the lateral outermost surface 14 of the head portion 11 by a significant difference d of for example at least 0.5 mm, or at least 1 mm. A proximally facing coupling surface constituted by the proximal protrusion is perpendicular to the axis 10 and is flat, with the optional exception of a guiding hole 16 (that may optionally axially extend further into the head portion than illustrated and possibly even into the anchoring portion) that may serve to align the joining element with a sonotrode, for example by cooperating with an according guiding protrusion 61 of the sonotrode.

[0169] In the embodiment of FIG. 2a, the joining element is one-piece and consists of a thermoplastic material.

[0170] A sonotrode 6 is used to carry out the anchoring process as illustrated in FIG. 2b. The shape of a distal coupling face of the sonotrode is adapted to the shape of the proximal end face of the joining element.

[0171] In order to carry out the process, the joining element is placed relative to the object 2 in a manner that the anchoring portion 12 protrudes into an opening 3 in the object.

[0172] The opening may be dimensioned, as schematically illustrated in FIG. 2b and for example taught in WO 98/042988, to have a radial extension slightly larger than the radial extension of the anchoring portion, so that the anchoring portion may be inserted essentially force-free. Alternatively, it is also possible to dimension the opening such that upon introduction of the joining element, an interference fit results between the joining element and the object, as for example taught in Swiss patent application 00 824/14 incorporated herein by reference in its entirety.

[0173] In FIG. 2b also the surface 20 of the object is shown, in which surface 20 the opening 3 has a mouth, i.e. from which surface 20 the opening extends into the interior of the object 2.

[0174] During the process, the sonotrode 6 presses the joining element into a distal direction against the object while vibrations are coupled from the sonotrode 6 into the joining element via the coupling faces until the thermoplastic material under the effect of the vibrations and pressure starts liquefying and is pressed into structures of the object, as illustrated in FIG. 2c. This will result in a zone 8 in which the object is interpenetrated by the thermoplastic material, which, after re-solidification, leads to a positive-fit connection between the joining element 1 and the object 2.

[0175] The anchoring portion 12 may comprise energy directing features such as a distal tip 19 and/or radial ribs or humps or other features. Such energy directing features proximally of the distal end (the region of the joining element proximally of the distal end and distally of the head portion may be referred to as “shaft portion”) may cause liquefaction and thus ultimately an interpenetration zone 8 also laterally around the shaft portion, as illustrated in FIG. 2c.

[0176] Due to a non-perfect coupling between the sonotrode 6 and the proximal surface of the joining element, in an interface zone immediately adjacent the coupling face, and due to the contact pressure, some deformation of the thermoplastic material may arise during the process. Because of the pressing force, this will lead to thermoplastic material being pressed out into lateral directions. Due to the deformation zone, such material portions 9 that have flown out will not interfere with the structured lateral outermost surface.

[0177] Also, due to the construction with the interface not reaching radially as far as the lateral outermost surface, the mechanical load on that zone 19 of the lateral outermost surface that is the closest to the sonotrode 6 is subject to a comparably minimal mechanical load (the arrows in FIG. 2d schematically illustrate the mechanical load) and thus will not be subject to any tendency to become deformed.

[0178] In practice, the relative dimensions of a (optional) guiding protrusion 61 and of a (also optional) guiding hole 16 of the head portion 11 may be adapted to each other so that the guiding protrusion does not reach to the ground of the guiding hole 16, as illustrated in FIG. 2e. Thereby, it is clearly defined that the pressing force and the vibrations are coupled into the joining element only via the protrusion 15, with no portion being coupled into the bottom of the guiding hole, making the system particularly well-defined.

[0179] The proximal-most part of a variant of the joining element of FIG. 2a is depicted in FIG. 3. In this variant, firstly the guiding hole 16 is more pronounced. Secondly, the guiding hole is conical. Thirdly, there is a smooth transition between the side walls of the guiding hole and the proximal coupling face. The smooth transition is provided in the form of a curved section 31 of the surface. Due to this curved section, the stress upon the interface zone is further reduced.

[0180] FIG. 4a yet shows a variant with a non-plane coupling face. The coupling face of the joining element 1 is continuously curved to cooperate with a correspondingly curved outcoupling face of the sonotrode 6. Also this design leads to a stress distribution without local stress concentrations at the interface.

[0181] Additionally, the width W.sub.S of the sonotrode, as in the previous embodiment, is smaller than the width W.sub.H of the head portion. Therefore material portions 9 that have flown out because of a local softening of the thermoplastic material in the deformation zone will again not interfere with the structure of the outermost surface part of the head portion 11, as illustrated in FIG. 4b.

[0182] FIG. 30 shows an other variant with a non-plane coupling face. In contrast to the embodiment of FIGS. 4a and 4b, the coupling face of the joining element 1 is convexly curved instead of concavely, and the coupling face of the sonotrode 6 is concavely curved instead of convexly.

[0183] An even further embodiment that is similar to the embodiment of FIG. 2a is depicted in FIG. 31. In the embodiment of FIG. 31, the joining element has a guiding protrusion 17 cooperating with a guiding indentation 63 of the sonotrode 6, instead of the opposite.

[0184] In the embodiment of FIG. 32, the joining element does not have a proximal protrusion. Rather, the lateral extension of the sonotrode 6 that is placed in a well-defined position relative to the joining element 1, for example by a guiding protrusion 61 cooperating with a corresponding guiding indentation 16 of the joining element, ensures that the outer lateral surface of the head portion remains intact. To this end, the difference d correspond to about the depth f of the indentations of the lateral outer surface or is larger than the same so that the sonotrode cannot put any force on an undercut of the head. Thus in some embodiments, the condition d>=f holds.

[0185] In accordance with an even further variant (see for example FIG. 36 further below), the sonotrode may have no guiding feature at all. Especially, in embodiments in which the joining element has a proximal protrusion 15, the lateral extension of the distal sonotrode outcoupling face may be somewhat larger than the surface of the proximal protrusion 15. Then, an exact positioning of the sonotrode relative to the joining element is not necessary for preventing a deformation of the lateral outer surface of the head portion.

[0186] The embodiments described referring to FIGS. 2a-4b are embodiments of the first group of embodiments implementing the first concept.

[0187] An example of an embodiment of the second group of embodiments implementing the first concept is depicted in FIG. 5. The joining element in contrast to the previously described embodiments is not one-piece but comprises two parts, a liquefiable part 22 and a non-liquefiable part 21. The non-liquefiable part 21 is approximately nail shaped with the proximal-most section forming the coupling face. The lateral outermost portion of the head portion 11 as well as the anchoring portion are constituted by the liquefiable part 21.

[0188] In an example, the non-liquefiable part is made of a metal or of wood or of a thermosetting plastic or of a thermoplastic with a glass transition temperature substantially above the glass transition temperature of the liquefiable part.

[0189] The embodiment of FIG. 6 is a further example of the second group of embodiments. In this example, the head portion (head) entirely belongs to the non-liquefiable part 21 and is for example made of wood or a non-liquefiable plastic.

[0190] The non-liquefiable part in the depicted embodiment also comprises a shaft portion extending into the anchoring portion, with the liquefiable part being essentially provided as coating of the shaft portion.

[0191] FIG. 7 shows yet another example of a joining element with a coupling face of a non-liquefiable material. The coupling face is constituted by a plate portion 25 of a non-liquefiable part 21, the non-liquefiable part further comprising a spike portion 26 extending distally from the plate portion and enhancing the mechanical coupling between the non-liquefiable part and the liquefiable part.

[0192] FIG. 8 depicts an embodiment of the third group of embodiments, implementing the second concept. The joining element 1 is one-piece and consists of thermoplastic material. It has a recess 33 open to the proximal side, with a bottom of the recess defining a coupling face 30 for a sonotrode 6 dimensioned so that its distal end can be introduced into the recess 33 with its distal coupling-out face pressing against the coupling face 30.

[0193] The aspect ratio of the recess is for example at least 0.5 or at least 1; in the depicted embodiment it is about 1.5.

[0194] The embodiment of FIG. 9 is distinct from the embodiment of FIG. 8 in that the recess 33 is not cylindrical but has a surface shaped that is curved in axial section. The coupling face 30 is constituted by the inner surface of the joining element in the recess (or the portions thereof that are not parallel to the axis), with the less steep portions and the portions at the ground of the recess being subject to higher pressing forces than the steeper portions. Due to the concave shape, this automatically brings about a force distribution that preserves the more proximal and more lateral sections of the head portions.

[0195] Yet another variant is shown in FIG. 10. The recess 33 has a stepped surface, with the coupling face 33 being distributed over the steps and the ground of the recess.

[0196] The embodiments of FIGS. 9 and 10 are examples of embodiments in which recess extends into a substantial part of the head portion so that the head portion is constituted by an approximately tuboid body the material strength s of which varies within a certain range. Due to this design, the shape of the joining element 1 is optimized for injection molding. In injection molding often solid volumes have the potential problem of being difficult to entirely fill without any bubble formation. Designs like the ones of FIGS. 9 and 10 (as well as a variant of the design of FIG. 8 with the recess axially extending essentially through the entire head) solve this problem in the head region.

[0197] Designs like the ones of FIGS. 9 and 10 may therefore be especially advantageous in embodiments where the joining element is a one-piece injection molded object.

[0198] Designs like the ones of FIGS. 8-10 may also be used for embodiments in which the recess 33 mainly serves as guiding hole with the sonotrode also acting on the proximal end face, especially embodiments of the first group of embodiments. Of course, also combinations are possible, in which the coupling face is partly constituted by the proximal end face around the rim of the recess and partly by the bottom and/or side face and/or shoulders of the recess.

[0199] Also in the variant of FIG. 11, the joining element 1 consists of the thermoplastic material. In this variant, compared to the embodiment of FIG. 8, the anchoring portion 12 has a comparably reduced axial extension and/or a larger radial width. Also, the recess 33 extends further into the joining element. These differences (reduced axial extension of the anchoring portion, enhanced radial with, enhanced axial extension of the recess) may all be implemented independently or in any combination.

[0200] A larger radial width may at least partly compensate the reduction of anchoring strength due to the anchoring portion being shorter. An enhanced depth of the recess 33 may in certain configurations make a liquefaction of the thermoplastic material over an entire width of the anchoring portion easier because the sonotrode is close to the liquefaction site, and may therefore be operated with higher power and/or higher frequencies without risking any deformation of the head portion.

[0201] Embodiments like the ones of FIG. 11 with a shorter anchoring portion may especially be suited for configurations in which the joining element is anchored in a comparably thin object 2 and/or in situations in which the joining element has to be anchored in a board-like object along an edge, where the narrow side surface along the edge is at a non-rectangular angle to the board plane, for example at 45° or, more generally, at an angle between 30° and 60°, especially between 35° and 55°—as schematically illustrated in FIG. 11.

[0202] FIGS. 33a and 33b show, in a view and in a cross section, respectively, a further example of an embodiment according to the third group. In addition to the features described referring to FIG. 8, in the figures also the energy directors 29 are illustrated. The energy directors may be provided in the form of ribs or humps or steps and have the function of causing a particularly pronounced absorption of mechanical vibration energy so as to cause an onset of liquefaction there—similar to energy directors known from ultrasonic welding.

[0203] FIG. 12 illustrates a further variant of an embodiment of the third group of embodiments. It also belongs to the second group of embodiments. In contrast to the embodiment of FIG. 8, the coupling face is a surface of a non-liquefiable part 21, namely of a coupling plate arranged at the bottom of the recess 33.

[0204] FIG. 13 shows an embodiment where the non-liquefiable part 21 coupling plate has a plate portion 25 and a spike portion 26 extending distally from the plate portion.

[0205] Generally, embodiments that have a liquefiable part and a non-liquefiable part may be manufactured by injection-molding the liquefiable part in presence of the non-liquefiable part (insert molding/overmolding). However, it is also possible to manufacture the liquefiable part and the non-liquefiable part as separate items and to assemble them thereafter.

[0206] This is illustrated for the variant of FIG. 14. The liquefiable part comprises, in addition to the recess 33 and extending distally therefrom a stepped opening for the non-liquefiable part 21 comprising a broader section 34 for the plate portion 25 and a narrower section 35 for the spike portion 26.

[0207] The plate portion 25 further forms a guiding hole 16 for the sonotrode (which guiding hole is an optional feature for the other embodiments, too).

[0208] While the option to assemble the liquefiable and non-liquefiable parts after manufacturing in this description is illustrated referring to FIG. 14 and some of the following figures, it is an option also for other embodiments. On the other hand, it would be possible to manufacture a joining element 1 having features like the ones illustrated in FIG. 14 or having the shape and/or a coupling structure of joining elements described hereinafter also by insert molding/overmolding or the like.

[0209] Referring to the embodiment of FIG. 14, yet an other optional feature is illustrated: The opening 33, 34, 35 axially extends through the entire liquefiable part to the distal end. This cannulation may have advantages in the manufacturing process, namely it may prevent void formation in the injection molding process. This advantage is independent on whether the joining element 1 is manufactured by insert molding/overmolding or whether it is assembled in a subsequent step.

[0210] The cannulation feature of the embodiment of FIG. 14 may be implemented also in the other embodiments, both for one-piece joining elements consisting of thermoplastic material or for elements comprising a plurality of parts.

[0211] Again referring to the joining elements comprising a plurality of initially separate parts, in accordance with an option, the assembly of the parts may be done after the step of causing interpenetration of structures of the object by portions of the thermoplastic material. In this, the steps of pressing the joining element towards a distal direction and coupling mechanical vibration into the joining element concerns the part that has the thermoplastic material only.

[0212] An according embodiment is illustrated in FIGS. 15a and 15b. The liquefiable part 22 is one-piece and consists of the thermoplastic material. It has a shaft portion 36 for being introduced into the opening in the object 2 and for being anchored therein, and a coupling portion 37 for cooperating with an according coupling feature 39 of the non-liquefiable part 21. In the depicted embodiment, it further comprises a broadening portion 38 that may cause an additional anchoring near the object surface and/or serve as stop defining the anchoring depth.

[0213] In the depicted embodiment, the coupling between the liquefiable part 22 and the non-liquefiable part 21 (that again may be made of wood or a non-liquefiable plastic) is a mechanical snap fit coupling. Small deformations of the proximal-most portion of the liquefiable part during anchoring do not disable the coupling in any way.

[0214] If other couplings with a more critical mechanism were chosen, measures described in this text (such as a controlled deformation zone, an offset coupling face, etc.) may be used for the liquefiable part 22 to keep the portion that couples to the non-liquefiable part functional.

[0215] As an alternative to assembling the parts prior to the insertion and to assembling the parts after the anchoring, assembly may also be made during the process. This principle is illustrated in FIG. 16. The liquefiable part 22 is positioned relative to the object 2, and the non-liquefiable part 21 is positioned relative to the liquefiable part when the sonotrode both, presses the parts together and presses the parts against the object when the vibrations are coupled into it.

[0216] For example, the liquefiable part 22 comprises a proximal recess, such as a conical or cylindrical recess 41, into which a corresponding distal protrusion 42 of the non-liquefiable part is placed in the step of positioning.

[0217] By the effect of the pressure and vibrations, not only thermoplastic material of the liquefiable part is liquefied to penetrate into structures of the object but also a fit between the liquefiable and non-liquefiable parts results.

[0218] FIGS. 17a and 17b show, schematically, a detail of the connection between the liquefiable part and the non-liquefiable part after the process in two variants. The non-liquefiable part comprises structures that form, an undercut, such as pores 44, grooves, etc. into which the liquefiable material is pressed after it has become flowable. After re-solidification, this results in a positive-fit connection between the liquefiable and non-liquefiable parts.

[0219] FIG. 17c shows that the thermoplastic material of the liquefiable part 22 by the impinging mechanical vibration energy has liquefied both, to interpenetrate structures of the object 2 as well as of the non-liquefiable part 21.

[0220] In addition or as an alternative, the connection may comprise a press fit connection, as schematically illustrated in FIG. 18. To this end, the non-liquefiable part comprises a slightly conical protrusion 42 (in the Figure, the opening angle of the cone is drawn somewhat exaggerated) and is pressed into a slightly undersized corresponding opening of the liquefiable part. FIG. 18 illustrates the situation before a force is applied, with a distance d remaining. As a result of the pressing the non-liquefiable part 21 is advanced relative to the liquefiable part by at most the distance d and thereby a press fit results. A possible slight elastic deformation may assist the fitting effect. Additionally effects like a surface roughness, or adhesion may contribute.

[0221] Combinations with the positive-fit approach described referring to FIGS. 17a and 17b are possible.

[0222] FIG. 19 illustrates an example of a joining element of the kind described referring to FIGS. 16-18 anchored in an object.

[0223] The embodiment of FIG. 20 may be of a pre-manufactured (molded; assembled prior to the anchoring) kind, or may be assembled in-situ during the anchoring process as described referring to FIGS. 17-19. Instead of the rather small pores or grooves, the non-liquefiable part has a shaft portion with at least one proximally facing shoulder that in the shown embodiment shows distally of a groove 44. Such a shoulder may, in analogy to the embodiments of FIGS. 17-19, cause a positive-fit connection between the liquefiable and non-liquefiable parts.

[0224] The embodiment of FIG. 20 has a relatively short, relatively wide anchoring portion with at least one ring-shaped distal protrusion serving as energy director. Instead of such a ring-shaped protrusion or a tip as described hereinbefore, a distal energy director may have another shape and for example comprise a plurality of ribs, humps, etc.; like in all other embodiments there may be in addition or as an alternative an energy director on the lateral surface of the anchoring portion shaft.

[0225] The embodiment of FIG. 21 is distinct from the embodiment of FIG. 20 in that the anchoring portion is more elongate and has a distal tip.

[0226] Generally, wider and shorter anchoring portions are suited for anchoring on a large surface of a board or other object with limited depth, or for anchoring on a narrow side at a non-perpendicular angle to the large surface (flat side; the board plane), as illustrated, for joining element of the kind shown in FIG. 21, in FIG. 22. Longer anchoring portions are suitable for anchoring in bulky objects or on the small side of boards if the narrow side is at a perpendicular angle to the flat side.

[0227] An embodiment of the fourth group of embodiments is depicted in FIGS. 23a and 23b. The anchoring portion comprises an anchoring portion body 51 with an angular ridge-shaped distal protrusion 52. The anchoring portion body 51 generally has a disc-shape, with the head portion being concentric with the anchoring portion body 51, and with the width of the head portion 11 being smaller than the width of the anchoring portion body. The coupling face 57 is formed around the head portion 11.

[0228] Like in other embodiments of the fourth group of embodiments, the distal protrusion is placed axially underneath the coupling face 57 and not for example underneath the center of the head portion 11.

[0229] As to a single ridge-shaped protrusion forming a ring around the lateral position of the head portion a plurality of concentric such protrusion rings could be present.

[0230] The opening 3 in the object has in-plane (lateral) dimensions that match the corresponding dimensions of the anchoring portion body 51. The depth of the opening approximately corresponds to the thickness (axial extension) of the anchoring portion body without the protrusions.

[0231] The anchoring body portion 51 may have—this being an optional feature for all embodiments—further energy directors on lateral sides.

[0232] An example of a sonotrode 6 suitable for the joining element 1 of FIGS. 23a and 23b and also for the joining element of FIG. 25 described hereinafter is shown in FIGS. 24a and 24b. The sonotrode is generally dome-shaped with an open space 62 being dimensioned to accommodate the head portion 11.

[0233] The distal end face forms the outcoupling face 7 of the sonotrode. For the anchoring process, the joining element is placed with the anchoring portion body above the mouth of the opening 3 or in the opening 3, and the sonotrode is positioned relative to the joining element with the outcoupling face 7 against the coupling face 57 and the head portion protruding into the open space 62. The sonotrode may yet comprise an optional guiding protrusion (not shown) proximally of the open space cooperating with a proximal guiding hole of the head portion 11 to define the exact position.

[0234] Under the common effect of the pressing force and the mechanical vibrations, the thermoplastic material of the protrusion 52 as well as, if present, thermoplastic material at the lateral energy directors is caused to liquefy and to thereby anchor the joining element in the object 2.

[0235] FIG. 25 yet illustrates another embodiment. The anchoring portion may for example comprise a plurality of spike-like protrusions 52 arranged regularly around the head portion, distally of the anchoring portion body 51.

[0236] FIG. 34 illustrates an embodiment of the fifth group of embodiments. A mould 90 comprising two shells 91 each having a surface portion 92 that corresponds to a negative of the lateral outer surface structure 13 of the head portion 11 is placed relative to the joining element 1 for the anchoring process. During the step of pressing, the surface portion of the mould 90 remains in contact with the surface structure 13. During possible forward movements of the joining element, the mould makes the same movement. For example, to this end the mould shells 91 may be coupled to a frame that also carries a transducer to which the sonotrode is coupled. If any softening or melting of the head portion 11 would occur during the step of pressing, the outer surface structure 13 of the head portion 11 would still be kept intact by the mould, and the mould is preferably released only after the head portion 11 has re-solidified, thereby maintaining its intended outer surface structure 13.

[0237] As alternative to what is depicted in FIG. 34, the joining element may optionally also comprise features described hereinbefore referring to the first, second, third or fourth group of embodiments.

[0238] Hereinafter, referring to FIGS. 26-29, all showing cross sections through the anchoring portion perpendicular to the insertion axis, concepts of optimizing the design of the joining element in terms of injection molding according to the second aspect are discussed, in addition to the discussion referring to FIGS. 9, 10, 11 and 14.

[0239] Especially in embodiments where the anchoring portion has a comparably long and/or comparably thick shaft, the prevention of voids within the injection molded parts is an issue also in the region of the anchoring portion. This teaching thus applies to all embodiments with an anchoring portion consisting of the thermoplastic material, being substantially elongate and extending in an axial region away from the head portion, as for example the embodiments of FIGS. 2a-5, 7-22.

[0240] FIG. 26 shows a cross section through a shaft of an anchoring portion. The cross section deviates from a generally round shape (dotted line) in that it comprises a plurality of lobes 71 with axially running grooves 72 therebetween. The grooves 72 are distinct from mere spaces between energy directing ribs in that they are deeper (for example they have a depth of at least 10%, at least 15%, at least 20% or at least 25% of the diameter of the shaft), and that the lobe 71 between them does not peak in a sharp edge (this, of course, does not exclude the existence of one or more energy directing ribs or similar on such a lobe). Also, when inserted in the opening 3, the grooves will be within the space defined by a radial extension of the opening. After the anchoring process, the grooves optionally may remain empty and define a hollow space.

[0241] Different shapes of lobes 71 are possible, depending on a desired balance between mechanical strength and flow optimization during injection molding. FIG. 27 illustrates an according alternative cross section.

[0242] By the design that comprises lobes with grooves therebetween, the distance between material portions in a center of the shaft and the mold walls is substantially reduced, this optimizing injection molding process.

[0243] In the embodiment of FIG. 28, the cross section through the shaft portion is generally S-shaped, thus with two staggered grooves of substantial depth extending from opposite sides into the volume of the shaft.

[0244] Especially, the grooves in the depicted configuration are as deep as to extend across a middle plane (perpendicular to the groove direction), i.e. the depth d.sub.g of the groove is greater than 50% of the local extension e at that place. Generally, the depth will be substantial, for example at least 30% or at least 40% or at least 50% of the extension.

[0245] This design features substantial advantages. Firstly, the homogeneity of the material strength in the above-discussed sense (differences between distances of innermost portions from a mold wall are comparably homogeneous) can be designed, by choosing appropriate shapes and depths of the groove, to be almost perfect. Secondly, by this design a main beam 81 and two side beams 82, 83 are formed that provide substantial mechanical strengths with respect to loads acting in directions along a major axis 85, whereas the mechanical strength along a minor axis 86 is reduced compared to a full cylinder (the major and minor axes are in-plane axes and not to be confused with the insertion axis that is perpendicular to the drawing plane in FIG. 28). In this, the mechanical stability becomes comparable to a T-bar (or multiple T-bar) design.

[0246] This teaching can be readily generalized to only one groove or to more than two staggered grooves (for example as sketched in FIG. 29), for higher numbers of grooves at the price of increasingly lower stability in directions along the minor axis.

[0247] FIG. 28 also illustrates optional energy directing ribs 54. Optionally, the shaft can be designed to be slightly oversized in the direction of the minor axis, if the thermoplastic at insertion temperature is slightly elastic so that the construction provides a spring effect pressing the side beams 82, 83 against the wall of the opening.

[0248] For use, the joining element having an anisotropic shaft cross section as taught in FIG. 29 in the step of arranging/positioning the major axis is oriented along an axis along which the primary in-plane mechanical load is expected. Often in furniture industry or construction industry, this direction is well-defined by the application.

[0249] A further example of an embodiment combining the first and second aspects of the invention is illustrated in FIGS. 35a and 35b. FIG. 35b shows the joining element in longitudinal section, wherein the section plane is chosen to go through the axially running grooves 28 visible in FIG. 35a. The joining element 1 consists of thermoplastic material. It is configured according to the first group of embodiments of the first aspect of the invention and comprises a proximal protrusion 15 of the kind described hereinbefore. The recess 33 in this embodiment does not serve for positioning the sonotrode (it may optionally but not necessarily serve as guiding indentation) but by extending through the entire head portion 11 it realizes the teaching of the second aspect of the invention.

[0250] The embodiment of FIGS. 35a and 35b also has energy directing structures 29. An apparatus 100 for carrying out the method is very schematically shown in FIG. 36. The apparatus has a positioning device 101 positioning the joining element 1 relative to the object 2 and the opening 3 therein, and a sonotrode 6. Further, the apparatus has a control 103 controlling the sonotrode 6 and the positioning device 101. The apparatus also has a holding device 104 for holding the object 2 during the anchoring process. The apparatus may have further means, such as a transporting device for conveying the object 2, a drilling device for making the opening 3, a storage for storing a stock of the joining elements, a feeder for feeding the joining elements 1, etc.

[0251] Furthermore, the apparatus 100 comprises a distance sensor 102 adapted for sensing the distance DS between the sonotrode 6 and the object 2—more in particular in the depicted embodiment the distance between the coupling-out face of the sonotrode 6 and the surface 20 of the object—and connected to the control 103. The distance sensor 102 may be based on any suitable principle, such as laser distance measurement, radar distance measurement, ultrasonic distance measurement, and mechanical distance measurement. When a pre-set distance DS* between sonotrode 6 and object 2 has been reached, meaning that joining element 1 is in its correct final mounted position, as measured by means of distance sensor 102, the control 103 stops the further movement and vibrating action of sonotrode 6.

[0252] More particularly, the control 103 is configured to control a forward (distal) movement the sonotrode 6 undergoes when the vibrations and the pressing force are coupled into the joining element 1. Especially, the control 103 may be configured to stop a forward movement of the sonotrode 6 when the outcoupling face is at the predetermined distance DS=DS* from the surface 20 in which the opening 3 has a mouth. More in concrete, in embodiments the forward movement of the sonotrode stops as soon as the shoulder 18 (if any) reaches the surface 20. The pre-determined distance DS* thus may for example correspond to the axial extension e, possibly minus a small extra distance that accounts for a slight deformation of the object surface 20 and for a possible deformation of the proximal protrusion 15.

[0253] An alternative pre-determined condition that may be set to stop the forward movement of the sonotrode 6 is a sudden rise in mechanical resistance (due to the shoulder 18 abutting against the surface 20) or a sudden change in the vibration absorption characteristic, also caused by the shoulder 18 abutting against the surface 20.

[0254] This means for automatically stopping a forward movement is a further measure that protects the head portion from being deformed at the lateral outer surface.

[0255] FIG. 37 yet very schematically illustrates that the apparatus may have different spatially separated stations for carrying out the different steps. For example, the apparatus may have a positioning station 111 in which the joining element(s) 1 is/are inserted in the object 2, for example with an interference fit, and an anchoring station 112 in which the sonotrode(s) 6 act(s) on the joining element(s) 1.