Method of joining two objects

Abstract

A method for joining two objects by anchoring an insert portion provided on one of the objects in an opening provided on the other one of the objects. The anchorage is achieved by liquefaction of a thermoplastic material and interpenetration of the liquefied material and a penetrable material, the two materials being arranged on opposite surfaces of the insert portion and the wall of the opening. Before such liquefaction and interpenetration, an interference fit is established in which such opposite surfaces are pressed against each other, and, for the anchoring, mechanical vibration energy and possibly a shearing force are applied, wherein the shearing force puts a shear stress on the interference fit.

Claims

1. A method of joining a first and a second object, the method comprising the steps of: providing the first object comprising a first material and the second object comprising a second material, wherein the first material is solid and comprises thermoplastic properties and wherein the second material is solid and is penetrable by the first material when in a liquefied state, the second object further comprising an opening having a depth and the first object further comprising an insert portion having a length, wherein the opening and the insert portion are adapted to each other for the insert portion to be positioned in the opening with an interference fit, and wherein said first and second materials constitute at least part of opposite surface areas of insert portion and opening pressed against each other in the interference fit, establishing the interference fit by forcing the insert portion into the opening, the opening being undersized with respect to the insert portion, wherein during the step of forcing the insert portion into the opening no vibration energy is transferred to either the first or second object, after establishing the interference fit, anchoring the insert portion in the opening by transferring energy suitable for liquefaction of the first material to the vicinity of said opposite surface areas in an amount and for a time sufficient, for liquefaction of a flow portion of the first material, the flow portion of the first material being material of the insert portion, and interpenetration of the second material by the flow portion in a vicinity of said opposite surface areas; stopping the transfer of energy for a time sufficient for the first material liquefied during the step of anchoring to re-solidify and thereby establish anchoring of the insert portion in the opening.

2. The method according to claim 1, wherein, in the step of anchoring, the transferred energy is mechanical vibration energy.

3. The method according to claim 2, wherein, in addition to the mechanical vibration energy, a shearing force is applied to the interference fit, the shearing force acting between the two objects.

4. The method according to claim 1, wherein, the insert portion is oriented within the opening with the length substantially parallel to the depth, and wherein the interference fit is established between lateral sides of the insert portion and a lateral wall of the opening.

5. The method according to claim 4, wherein the interference fit is established by forcing the insert portion into the opening with the aid of the interference force being directed substantially parallel to the length and to the depth and being applied to a proximal face of one of the two objects.

6. The method according to claim 3, wherein the shearing force is directed substantially parallel to the length and to the depth and is applied to a proximal face of one of the two objects.

7. The method according to claim 6, wherein, during the step of anchoring, movement of the two objects relative to each other caused by the shearing force is prevented or limited.

8. The method according to claim 7, wherein said movement is prevented or limited by a distal end of the insert portion being positioned to abut a bottom of the opening, by a restriction in an opening cross section or by an auxiliary anvil positioned in the opening.

9. The method according to claim 2, wherein the interference force, the mechanical vibration energy and, if applicable, the shearing force are applied to the first object.

10. The method according to claim 1, wherein first object is completely formed from the first material.

11. The method according to claim 1, wherein lateral sides of the insert portion comprise energy directing structures in the form of ridges extending substantially parallel to the length.

12. The method according to claim 1, wherein the second material is solid during the steps of establishing the interference fit and of anchoring.

13. The method according to claim 12, wherein the second material is one of fibrous, porous, comprising penetrable surface structures.

14. The method according to claim 13, wherein the second material is one of chipboard, fibre board, wood, plywood and cardboard.

15. The method according to claim 1, wherein cross sections of the insert portion and of the opening are adapted to each other by not having a same shape so that the interference fit is limited to only parts of the circumference of the cross sections.

16. The method according to claim 1, wherein cross section pairing of the insert portion and the opening differs along the depth of the opening such that the interference fit is restricted to predetermined areas along the depth.

17. The method according to claim 16, wherein the interference fit is restricted to areas that do not extend to a mouth of the opening.

18. The method according to claim 1, wherein the insert portion comprises an interior opening accessible from a proximal side of the first object, wherein the step of establishing the interference fit comprises the sub-steps of placing the insert portion relative to the opening and of thereafter inserting an expansion element in the interior opening to cause an expansion of the insert portion within the opening for establishing the interference fit.

19. The method according to claim 1, wherein the insert portion is a distal portion of the first object, wherein the method comprises the further step of providing a third object, the third object having a third object opening, wherein a proximal portion of the first object is adapted to be inserted in the third object opening, and wherein the interference force and the vibration are applied to the third object while the proximal portion of the first object is in the third object opening.

20. The method according to claim 19, wherein the third object opening and the proximal portion of the first object are adapted to each other for the proximal portion to be positioned in the third object opening with an interference fit.

21. The method according to claim 19, wherein at an onset of the step of transferring energy the second object and the third object are positioned relative to each other so that a mouth of the opening of the second object and a mouth of the third object opening being at a distance from each other, and wherein during the step of transferring energy, the second object and the third object are pressed against each other to reduce the distance between the mouth of the opening of the second object and the mouth of the third object opening.

22. The method of claim 21, wherein the steps of transferring energy and of pressing the second object and the third object against each other are carried out until the second object abuts against the third object, whereby the first object constitutes a blind rivet securing the second and third objects to each other.

23. A method of joining a first and a second object, the method comprising the steps of: providing the first object comprising a first material and the second object comprising a second material, wherein the first material is solid and comprises thermoplastic properties and wherein the second material is solid and is penetrable by the first material when in a liquefied state, the second object further comprising an opening having a depth and the first object further comprising an insert portion having a length, wherein said first and second materials constitute at least part of opposite surface areas of insert portion and opening pressed against each other in an interference fit, establishing the interference fit by positioning the insert portion between wall parts of the opening and clamping the wall parts against the insert portion, after establishing the interference fit, anchoring the insert portion in the opening by transferring energy suitable for liquefaction of the first material to the vicinity of said opposite surface areas in an amount and for a time sufficient, for liquefaction of a flow portion of the first material, the flow portion of the first material being material of the insert portion, and interpenetration of the second material by the flow portion in a vicinity of said opposite surface areas; stopping the transfer of energy for a time sufficient for the first material liquefied during the step of anchoring to re-solidify and thereby establish anchoring of the insert portion in the opening.

24. A method of joining a second and a third object using a first object, the method comprising the steps of: providing the first object comprising a first material, the second object comprising a second material and the third object comprising a third material, wherein the first material is solid and comprises thermoplastic properties and wherein the second and third materials are solid and is penetrable by the first material when in a liquefied state, the second object further comprising a second object opening, the third object further comprising a third object opening, and the first object further comprising an distal portion and a proximal portion, establishing a first interference fit by forcing the distal portion into the second object opening, the second object opening being undersized with respect to the distal portion, and establishing a second interference fit by forcing the proximal portion into the third object opening, the third object opening being undersized with respect to the proximal portion, after establishing the first interference fit and the second interference fit, anchoring the first object in the second object opening and in the third object opening by transferring energy suitable for liquefaction of the first material in an amount and for a time sufficient, for liquefaction of a flow portion of the first material, and interpenetration of the second material and of the third material by the flow portion; stopping the transfer of energy for a time sufficient for the first material liquefied during the step of anchoring to re-solidify and thereby establish anchoring of the first object in the second object opening and in the third object opening to join the second object to the third object.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is described in further detail in connection with the appended FIGS., wherein:

(2) FIG. 1 illustrates the already above briefly discussed example of a preferred embodiment of the method according to the invention;

(3) FIGS. 2A and 2b show two examples of vibration transfer from the vibrating tool to the free object;

(4) FIGS. 3A and 3B show two examples for the pairing of distal end of the insert portion and bottom of the opening anchorage at the bottom of the opening in addition to the lateral anchorage;

(5) FIG. 4 is a flow diagram of the method as illustrated in FIG. 1;

(6) FIGS. 5 to 8 show examples of matched pairs of cross sections of insert portions and openings applicable e.g. in the method as illustrated in FIG. 1;

(7) FIGS. 9 and 10 show examples of free objects with a not liquefiable core;

(8) FIGS. 11 to 16 show examples of longitudinal sections of matched insert portions and openings applicable, e.g., in the method as illustrated in FIG. 1;

(9) FIGS. 17 and 18 illustrate examples of proximal portions connected to insert portions anchored in an opening, e.g., in the method as illustrated in FIG. 1;

(10) FIG. 19 illustrates an embodiment of an insert portion with a hollow distal end;

(11) FIG. 20 illustrates an embodiment of the method according to the invention in which the interference fit is established by clamping wall parts of the opening around the insert portion;

(12) FIG. 21 shows an example of an embodiment with an insert portion with a plurality of wings;

(13) FIGS. 22 and 23 illustrate further examples of embodiments with a cross section pairing of insert portion and opening differing along the depth of the opening such that the interference fit is restricted to predetermined areas arranged along this depth;

(14) FIG. 24 shows an example of an embodiment in which the interference force is caused from an inside of the insert portion; and

(15) FIG. 25 schematically depicts a machine for carrying out a process as described herein.

(16) In the figures, same reference numbers refer to same or analogous elements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(17) FIG. 1 illustrates the above already briefly described preferred embodiment of the method according to the invention, wherein the two objects, or the insert portion and the opening respectively, are shown in section parallel to a depth of the opening (longitudinal section). On the left hand side of FIG. 1 the two objects to be joined are illustrated.

(18) The anvil object 1 includes the blind opening 2 having a depth D, a lateral wall 3, being substantially parallel to or forming an only small angle with the depth D, and a bottom 4, being e.g. substantially perpendicular to the depth D. The anvil object 1 further includes the penetrable material, which is arranged to constitute at least part of the lateral wall 3, e.g. the total of the lateral wall and in addition the bottom wall. Therein the anvil object 1 may be made fully of the penetrable material or may further include portions of other materials. The free object 5 includes a distally arranged insert portion 6 and it further includes the thermoplastic material, which constitutes at least part of the lateral surface 7 of the insert portion 6. Therein the free object 5 may be fully made of the thermoplastic material, as illustrated or only partly.

(19) Insert portion 6 and opening 2 are adapted to each other in the above described manner (interfering cross sections, axial length of insert portion sufficient for enabling abutment of its distal end 10 on bottom 4). The free object 5 may further include a proximal portion 8 (e.g. shaped like a head), wherein a proximal face 9 thereof is equipped for applying tools used during the step of establishing the interference fit and during the anchoring step.

(20) In the middle of FIG. 1 the two objects 1 and 5 are shown after establishment of the interference fit. The distal end 10 of the insertion portion 6, which is, e.g., blunt, abuts the bottom 4 of the opening 2 and the insert portion 6 is retained in the opening 2 by an interference fit, which acts mainly laterally (lateral surfaces of insert portion and lateral wall of opening are pressed against each other). For positioning the insert portion 6 in the opening 2 the interference force 20 is applied to the proximal face 9 of the free object 5 using any suitable tool (not illustrated). Alternatively, the interference fit can be established by providing the anvil object 1, e.g., in a plurality of sections which all include parts of the opening and by closing the sections around the insert portion 6, wherein the force by which the sections are moved against each other constitutes the interference force (see FIG. 20).

(21) On the right hand side of FIG. 1 the two objects 1 and 5 are shown when joined, i.e. after the anchoring step. The free element 5 is anchored in the opening 2 in the area of its lateral surfaces 7 (or in the region of the lateral wall 3 of the opening 2 respectively) and in the region of the distal end 10 of the insert portion (or the bottom 4 of the opening 2 respectively). The anchoring step is carried out with the help of a vibrating tool 21, which is pressed against the proximal face 9 of the free object 5.

(22) The length L of the insert portion 6 being originally greater than the depth D of the opening 2 allows movement of the free object 5 or its proximal portion 8 respectively against the anvil object 1 for compensating for the liquefied material, which is displaced during the anchoring step. At the latest when the proximal portion 8 abuts the surface of the anvil object 1 the anchoring step is to be terminated, unless further anchoring is desired between the distal face of the proximal portion 8 and the surface of the anvil object 1. Termination of the anchoring step can alternatively or in addition be determined by a predetermined time interval for the anchoring step or by a predetermined maximum value of the shearing force 22.

(23) FIGS. 2A and 2B illustrate two alternatives for carrying out the anchoring step, which alternatives regard the interface between the vibrating tool and the proximal face of the free object as briefly mentioned already further above.

(24) For the alternative as illustrated in FIG. 2A the vibrating tool 21 is only pressed against (not connected to) the proximal face of the free object 5 with the aid of the shearing force 22, wherein it is preferable to design the vibrating tool for maximal longitudinal vibration at its distal face. This means that only the one part of the vibration directed against the anvil object are transferred to the free object 5 (hammering effect, illustrated by a plurality of small arrows 23). If, with such an arrangement only lateral anchorage is to be achieved, care has to be taken, that there still is room at the bottom of the opening for a small displacement of the distal end of the insert portion and the shearing force 22 may be small. If anchorage also at the bottom of the opening is desired as illustrated in FIG. 1, the shearing force does not only help to overcome the interference fit for enabling the friction but it also serves the bottom anchorage as known from e.g. WO 98/042988.

(25) For the alternative as illustrated in FIG. 2B, the vibrating tool 21 is rigidly connected to the free object 5, the connection being able to transmit the total vibration (double arrow 24) to the free object 5. If no anchorage at the bottom is desired, if the vibratory energy is large enough for overcoming the interference fit, and if the anvil object is sufficiently stably fixed or has a sufficient inertia, no additional shearing force is necessary for achieving lateral anchorage. Such method is in particular applicable when the opening is not a blind opening but a through tunnel. If the opening still includes a bottom and anchorage in this bottom in addition to the lateral anchorage is desired, a sufficient shearing force for such bottom anchorage is needed, which in addition may supplement the vibration for overcoming the interference fit.

(26) FIGS. 3A and 3B illustrate two alternatives for achieving stronger bottom anchorage, wherein only the distal end of the insert portion 6 of the free object 5 and the opening 2 of the anvil object 1 are shown. According to FIG. 3A a tapering distal end 10 of the insert portion 6 is paired with a substantially flat bottom surface 4 of the opening 2. According to FIG. 3B a substantially blunt distal end 10 of the insert portion 6 is paired with an opening bottom 4 including a cone or similar shape having at least one elevation. While the alternative according to FIG. 3A favors interpenetration parallel to the depth of the opening, the alternative according to FIG. 3B favors lateral diversion of the liquefied material.

(27) FIG. 4 is a flow diagram of the method according to the invention. This diagram shows that the method includes the following steps: step 25 of providing the two objects, step 26 of establishing the interference fit between the insert portion and the opening with the aid of the interference force, step 27 of anchoring the insert portion in the opening with the aid of mechanical vibratory energy and possibly the additional shearing force, and finally step 28 of stopping the vibration and of re-solidification of the material liquefied in the anchoring step. The time sequence of steps 25 to 28 is the illustrated one and cannot be altered. However, there may be pauses between step 25 and 26 and/or between steps 26 and 27, wherein, as mentioned further above, a pause between step 25 and 26 has to be carefully planned if either one of the thermoplastic and the penetrable material have creeping tendencies.

(28) FIGS. 5 to 8 illustrate exemplary pairs of cross sections of insert portion and opening adapted to each other to be suitable at least for the preferred embodiment of the method according to the invention as illustrated in FIG. 1. Therein the cross section 30 of the insert portion is shown with a continuous line and is projected over the cross section 31 of the opening, which is shown with a broken line. The drawn cross sections 30 and 31 are the cross sections of the provided elements (before the steps of establishing the interference fit and before the anchoring step). The oversize of the insert portion is not drawn in scale (too large). For strictly cylindrical (circular or other cylinder) insert portions and openings the shown cross sections 30 and 31 will extend over most of the axial insert length and opening depth. For other forms of insert portions and/or openings the cross sections may change in form and/or size along the axial insert length and/or opening depth.

(29) FIG. 5 shows two circular cross sections 30 and 31 with the required oversize of the cross section 30 of the insert portion. Such a cross section pairing will result in a uniform anchorage on the whole circumference of insert portion and opening provided that the penetrable material of the lateral opening wall is uniform in the areas of the interference fit.

(30) FIG. 6 shows a circular cross section 31 for the opening and a cross section 30 for the insert portion with a plurality of ribs 32. The ribs 32 serve as energy directing structures. If sufficiently sharp, the ribs 32 may penetrate the lateral wall of the opening on establishing the interference fit, which has to be taken into consideration when determining the interference of the cross sections. If only the ribs are oversized but not the valleys therebetween, anchorage will only occur in the vicinity of these ribs. Similar effects can be achieved by equipping the cross section 31 of the opening with points protruding from the opening wall while still keeping the cross section 30 of the insert portion substantially circular.

(31) FIG. 7 shows a pairing of a circular cross section 31 for the opening and a cross section 30 for the insert portion, which has indentations 33 of a sufficient depth, such that in their area no interference fit will be established and therewith no anchorage will occur. Also in this case the indentations may be provided in the wall of the opening instead of in the insert portion.

(32) In the embodiment if FIG. 8, the insert portion in at least one depth has a star shaped cross section. The star-shaped cross section includes sharp edges 32 that like in the embodiments of FIGS. 6 and 7 may serve as energy directors. The depth of the indentations 33 between the edges is such that even if the edges cut into the penetrable material, there remains some space into which in the anchoring step some thermoplastic material may flow. This may especially be advantageous in case the penetrable material has a comparably low porosity.

(33) In contrast to the embodiments of FIGS. 6 and 7, in the embodiment of FIG. 8 anchorage may occur along the full periphery of the insert portion.

(34) FIG. 9 depicts a free object 5 with a core 82 of a for example metallic material embedded in a thermoplastic coating 71.

(35) In embodiments with the object that includes the thermoplastic material further includes material that does not soften or liquefy under the conditions of the anchoring step, the thermoplastic material does not need to constitute the entire surface. Rather, it is sufficient if at least part of the surface area, loaded by the interference fit is constituted by the thermoplastic material. FIG. 10 shows an example where the thermoplastic material 81 is only present at the distal end. Alternatives with for example axially extending strips of the thermoplastic material are possible, too.

(36) FIGS. 11 to 16 show pairings of insert portions and openings suitable for the method according to the invention, wherein the insert portions and openings are sectioned along the insert portion length or the opening depth respectively, and wherein again the section 35 of the insert portion is shown with a continuous line and is projected over the section 36 of the opening, which is drawn as broken line. Again the sections 35 and 36 are the sections of the elements as provided (i.e. before the step of achieving the interference fit and before the anchoring step).

(37) FIG. 11 shows a pairing of a tapering insert portion with a tapering opening, wherein the tapering is consists of a plurality of steps 37, wherein the steps on insert portion and opening have substantially the same axial lengths, and wherein the cross sections of insert portion and opening between steps are adapted to each other in substantially the same manner (similar oversize).

(38) FIG. 12 shows a pairing of a tapering insert portion with a tapering opening, wherein the tapering in both cases is continuous and has an angle A relative to the insert portion length and the opening depth of not more than 10 to 15?. The cross sections of insert portion and opening over insert portion length and opening depth have preferably all similar forms but decreasing sizes.

(39) FIG. 13 illustrates the already further above discussed embodiment using an auxiliary anvil 40 positioned in a through opening and serving for counteracting the shearing force and possibly also the interference force. If the auxiliary anvil 40 is to be removed from the opening, care is to be taken when designing the anvil surface and the distal end of the insert portion that no connection between the two is effected in the anchoring step. Like the bore bottom of FIG. 3B, the auxiliary anvil may have a face directed towards the insert portion including an elevation, which may function as energy directing element for liquefaction at the distal end of the insert portion.

(40) FIG. 14 illustrates the already further above discussed embodiment in which movement of the insert portion in the opening is limited by a step 41 in the opening where the cross section of the opening is reduced in such a manner that the distal end of the insert portion cannot be moved past the step neither under the influence of the interference force nor under the influence of the shearing force.

(41) FIG. 15 illustrates a further exemplified embodiment of the method according to the invention wherein the object 5 including the insert portion and the thermoplastic material constitutes a sort of blind rivet. A distal portion 5.1. of the object 5 is to be anchored in an opening of a first object 1.1 including the penetrable material and a proximal portion 5.2 of the object 5 is to be anchored in an opening of a second object 1.2 including the penetrable material. Therein the interference force, the vibration and, if applicable, the shearing force are preferably applied to object 1.2 (free object) and object 1.1 is kept stable (anvil object) wherein object 5 functions as both free and anvil object.

(42) FIG. 16 illustrates a pairing of longitudinal sections 35 and 36 of insert portion and opening in which interference fit and anchorage are limited to predefined areas alternating with areas of no interference fit and anchorage along the longitudinal axis of the insertion portion or the opening depth respectively. This is achieved by cross sections of alternating sizes. The same effect can be achieved by pairing a cylindrical insert portion with an opening including portions of differing cross section sizes or vice versa. If the vibrating tool 21 is designed and energized for longitudinal vibration it is advantageous to arrange the above named areas of interference fit and anchorage at locations with large amplitude and the above named areas with no interference fit and no anchorage at locations with small amplitude. This means with maximum longitudinal amplitude at the distal face of the vibrating tool and the proximal face of the free object, that areas with interference fit and anchorage are preferably arranged at distances from the proximal face of n times ?/2 (n=integer) and areas of no interference fit and no anchorage therebetween (at distances of ?/4, 3?/4, 5?/4 etc.). This is shown in the diagram on the right hand side of FIG. 16.

(43) FIGS. 17 and 18 show further exemplary embodiments of proximal ends of insert portions anchored in openings, which are achievable with the method according to the invention and in particular with the preferred embodiment thereof as illustrated in FIG. 1. Both FIGS. 17 and 18 are partial sections parallel to the axial length of the insert portion or the opening respectively, wherein only a mouth region of the opening and a proximal portion of object 5 are shown.

(44) FIG. 17 shows an object 5 with an insert portion only (no proximal portion), which is anchored in the opening with its proximal face 9 flush with the surface of the object 1 or in the mouth of the opening, respectively. This is achieved by dimensioning the object 5 with a length greater than the opening depth wherein the difference substantially corresponds with the expected shortening of object 5 during the anchoring step due to thermoplastic material penetrating the lateral and bottom wall of the opening. In the same manner, i.e. by corresponding difference between insert portion length and opening depth it is possible to achieve any desired position of the proximal face 9 relative to the mouth of the opening.

(45) FIG. 18 shows a headed object 5, e.g. similar to the one shown in FIG. 1, wherein the head-shaped proximal portion 8 is countersunk in a corresponding enlargement of the opening cross section adjacent to the mouth of the opening.

(46) FIG. 19 illustrates an embodiment of an insert portion 6 with a hollow distal end. The distal end of the insert portion 6 is provided with a hollow space 61 so that the distal end 10 is somewhat flexible and provides less resistance to deformations when the insert portion is subject to a radial compression force, compared to an embodiment with a blunt distal end. Due to this, during introduction into the opening the interference force rises gradually instead of being particularly strong initially.

(47) FIG. 20 illustrates an embodiment of the method according to the invention in which, as mentioned already further above, the interference fit is established not by forcing the insert portion into the opening but by positioning the insert portion between wall parts of an opening and clamping the wall parts against the insert portion. In the illustrated exemplary embodiment the wall parts are constituted by narrow surfaces of boards (anvil objects 1.3 and 1.4), e.g. chipboards, which extend substantially parallel and which constitute between them the opening 2. The insert portion 6 has the form of a lath. In the step of establishing the interference fit, the insert portion is positioned and clamped between the wall parts wherein the anvil objects 1.3 and 1.4 are pressed against the free object 5 (interference force 20). FIG. 20 shows above the objects before the step of establishing the interference fit and below after the anchoring step.

(48) In the embodiment of FIG. 21, the free object 5 has a plurality of wings 62 attached to the insert portion 6. The wings 62 may be comparably soft and thereby assist the location of the insert portion 6 in the correct position in the opening 2 without causing cracking in the anvil object 1. Especially, in embodiments, the cross section of the insert portion body (i.e. that part of the insert portion that is not constituted by the wings 62) may approximately correspond to the cross section of the opening 2 or be even slightly lower than the latter so that the interference force is only present at the location of the wings 62. This embodiment may be suited for especially weak or brittle penetrable material.

(49) In a variant, the wings 62 may be dimensionally stable and serve as cutting blades. Also in this variant, the wings 62 may stabilize the insert portion during insertion.

(50) Embodiments with the wings 62 are examples of embodiments that are particularly suited for processes in which the insert portion 6 is shot into the opening, for example comparable to an air gun like process.

(51) FIG. 22 shows, further to FIG. 16, an example of an embodiment with a cross section pairing of insert portion and opening differing along the depth of the opening such that the interference fit is restricted to predetermined areas arranged along this depth. Especially, in the embodiment of FIG. 22 the interference fit is restricted to deeper sections thus minimizing the risk of cracks or other damages at the rim of the opening where the second object 1 is weakest, especially if it is board shaped and the opening extends from the narrow face.

(52) To this end, the opening is stepped, whereas the insert portion is essentially cylindrical (with the possible exception of energy directors and/or a slight taper).

(53) An opening having an inner (distal), smaller diameter section 2.1 and an outer (proximal) larger diameter section 2.2 may for example be manufactured by a dual drilling process, with two different drills. Also drills with a step feature are possible.

(54) The cross section (diameter d.sub.1 in the depicted embodiment assuming an approximately circular cross section) of the inner section 2.1 will be smaller than the cross section (diameter d.sub.i) of the insert portion to generate the interference fit, whereas the cross section (diameter d.sub.2) of the outer section 2.2 may approximately correspond to the diameter of the insert portion or may even be slightly larger.

(55) FIG. 23 illustrates a variant of the embodiment of FIG. 22 with multiple steps. The diameters of the respective sections are such that no interference fit is present in the depicted configuration where the insert portion is only partially inserted, and an interference fit will arise if the distal-most section 6.2 of the insert portion is pressed into the innermost portion 2.1 of the opening and the more proximal section 6.1 enters the middle section 2.2 of the opening but not within the proximal-most section 2.3 of the opening.

(56) FIG. 24 shows a further embodiment. In this, the anvil object 1 is assumed to be a board having two broad surfaces 81, 82 a narrow side face 83, with the opening 2 in the narrow side face. In embodiments with a board shaped section of the anvil object, there is a particular risk of cracks generated upon introduction of the insert portion in the opening, or of portions flaking off).

(57) The embodiment of FIG. 24 is an example of an embodiment in which the interference force is caused from an inside of the free object 5, starting, for example, only immediately prior to the anchoring step. To this end, the free object 5 is provided with an interior opening 70 into which an expansion element 71 is pushed, the expansion element having at least in some axial depths a cross section larger than a cross section of the interior opening. The insert portion 6 and the opening 2 may be adapted to each other so that no interference fit or an interference fit with only a small interference force is established when the insert portion 6 is in the opening 5 before the expansion element 71 is placed. The expansion element 71 may for example be introduced by a force exerted by the vibrating tool 21 (sonotrode) immediately prior to the step of causing the mechanical vibration to impinge on the free object by the vibrating tool 21.

(58) A configuration with the anvil object having a board shaped section and with the opening extending from the narrow side face is applicable to all embodiments described in this text. Applications include the furniture industry, where a head portion 8 of the free object 5 may serve male part of a joint co-operating a female parts of a second furniture part, for example as described in as WO 2013/104422 by Inter Ikea Systems B.V.

(59) FIG. 25 yet schematically illustrates elements of a machine for carrying out the method described herein in an automated manner. The machine includes, in addition to the vibrating tool 21, a gripping arrangement 91 for positioning the free object 5 relative to the anvil object 1 prior to the step of establishing the interference fit and also, at least in part, during this step. For establishing the interference fit, the vibrating tool 21, prior to being subject to the vibrations, may be used, for example by pressing the insert portion into the opening. Alternatively, the machine may include a separate insertion station, where the interference fit is established by a corresponding insertion tool, for example a pusher tool.

(60) The vibrating tool is connected to a vibration source 92, such as a piezoelectric transducer, that causes the vibrating tool to vibrate.

(61) The machine may optionally further include an opening producing device, such as a drilling device 93, including a drill 94 the diameter of which is adapted to an outer diameter of the insert portion 6 in a manner that when the insert portion is inserted in the opening the interference fit is established, i.e. the drill 94 is configured to form an opening with a diameter somewhat less than an outer diameter of the insert portion.

(62) The machine may be an automated machine for mass production, including several stations and transport means for conveying the anvil object from station to station. For example, the machine may include an opening forming (drillings) station, an insertion station, and an anchoring station, as well as means for conveying anvil objects from station to station in a cycled manner. A machine may include further stations, such as a cutting-to-size station, arranged before the opening forming station. In addition or as an alternative, it may include storages for unprocessed anvil objects, processed anvil objects (to which the objects are conveyed after the method has been carried out) and/or for free objects.

Example

(63) An anchoring device of polyamide (PA 6.6 filled with 15% of glass fibers) was joined to a porous structural foam of a density in the range of 0.5 to 0.8 g/cm.sup.3, using the method as illustrated in FIG. 1. The opening provided in the foam was a blind bore. The inserted portion of the device was cylindrical, had a circular cross section (no energy directing structures) with a diameter being 3% oversized to create the interference fit, an overlength of 25% with respect to the bore depth, and a blunt distal end. The device was forced into the opening which necessitated an interference force of about 10 MPa related to the device cross section. In the inserted position the distal end of the device abutted the bottom of the blind bore. For the anchoring step, the foam was locally fixed (anvil object) and ultrasonic vibration was coupled into the proximal face of the device (free object) and simultaneously the pin was pressed against the bottom of the opening with a shearing force of about twice the interference force, using a stationary ultrasonic device by Branson (Series 2000). Therein the device was not attached to the sonotrode of the ultrasonic device. The anchoring step was carried out with a vibration frequency of about 20 kHz and a longitudinal amplitude at the distal end of the sonotrode in the range of 50 to 90 ?m. After about 0.3 sec of anchoring time the device was fully seated in the foam and the vibration was stopped.

(64) The overlength of the device was consumed by displacement of the thermoplastic material into the bottom of the opening, and possibly also by an increase of the depth of the opening due to either the interference force or the shearing force, and further by radial displacement of the thermoplastic material. The anchorage on the lateral sides of the device was very uniform all around the device and in particular along its length. For removing the device from the foam a force had to be applied which was about twice the force needed for removal of an identical device anchored with a similar method in a non-undersized bore (no lateral interference fit and therefore hardly any lateral anchorage). This allows the conclusion that the lateral anchorage induced by the lateral interference fit contributes about the same amount of retention strength as the anchorage at the bottom of the bore.

(65) If a similar device is anchored in a similar opening using the same equipment but applying the vibration already during the forcing of the pin into the opening, the bulk of the device needs to be moved during the anchoring step for the full opening depth, which at least doubles the time needed for the anchoring step.