METHOD OF ANCHORING A FIRST OBJECT IN A SECOND OBJECT

Abstract

A method for joining two objects by anchoring an insert portion provided on a first object in an opening provided on a second object. 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. During the step of inserting the insert portion in the opening and/or during anchorage a clamping force is applied to opposing surfaces of the second object to prevent the second object from cracking or bulging.

Claims

1. A method of anchoring a first object in a second object, the method comprising the steps of: providing the first object comprising a first material and providing 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 having an end face; wherein the second object further comprises an opening having a mouth in the end face, the opening having an opening axis and 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, and wherein said first and second materials constitute at least part of opposite surface areas of insert portion and opening capable of being pressed against each other, applying a clamping force to the second object while the insert portion is at least partially inserted in the opening, the clamping force acting between clamping elements acting on opposing surfaces arranged so that the opening is between opposing surfaces when the clamping force is applied, the clamping force acting in a direction non-parallel to the opening axis, anchoring the insert portion of the first object in the opening by transferring energy suitable for at least partial liquefaction of the first material to the vicinity of said opposite surface areas in an amount and for a time sufficient, for liquefaction of the first material and interpenetration of the first and second materials in the 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.

2. The method according to claim 1, wherein the step of applying a clamping force is carried out at least during an initial stage of the step of anchoring.

3. The method according to claim 1, wherein the opening and the insert portion are adapted to each other for the insert portion (6) to be positioned in the opening with an interference fit, and wherein the opposite surface areas of insert portion and opening are pressed against each other in the interference fit.

4. The method according to claim 3, comprising the further step of establishing the interference fit by placing the insert portion in the opening and applying an interference force prior to the step of anchoring.

5. The method according to claim 4, wherein the step of applying a clamping force is carried out at least during an initial stage of the step of establishing the interference fit.

6. The method according to claim 5, wherein the step of applying a clamping force is carried out continuously during the step of establishing the interference fit and continuing also during at least an initial stage of the step of anchoring.

7. The method according to claim 1, wherein the second object has a board shaped section defining two broad surfaces and a narrow side face between the broad surfaces, wherein said end face is the narrow side face of the board shaped section.

8. The method according to claim 1, wherein the direction of the clamping force is perpendicular to the opening axis.

9. The method according to claim 1, wherein the clamping force is controlled by controlling a pressure of a gas or fluid exerting its pressure on the clamping element.

10. The method according to claim 1, wherein a clamping pressure exceeds 0.4 N/mm2.

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

12. The method according to claim 1, wherein the clamping force is constant or follows a controlled time dependent profile, wherein preferably the clamping force is controlled so as to be released after an interference force has been reduced.

13. The method according to claim 1, wherein the clamping force is applied by holding the clamping elements at a fixed position relative to one another.

14. The method according to claim 13, comprising holding the clamping elements at the fixed position relative to one another by controlling a knee lever comprising a first lever arm and a second lever arm connected to at least one of the clamping elements.

15. The method according to claim 1, wherein for at least one of the clamping elements a clamping surface area, which is an area of an interface between said clamping element and a surface portion of the second object against which it is pressed during clamping, is smaller than the surface against which it is pressed by at least a factor 5, preferably by at least a factor 10.

16. The method according to claim 1, wherein for at least one of the clamping elements a clamping surface area corresponds to at most 20 times, preferably at most 15 times an area of the insert portion as seen in a projection on a plane perpendicular to a direction of the clamping force, and preferably at least 1.5 times, or at least 2.5 times said area of the insert portion as seen in a projection on a plane perpendicular to the direction of the clamping force.

17. The method according to claim 1, wherein the second object has a plurality of openings, the step of providing the first object comprising providing a corresponding number of first objects, wherein the step of applying the clamping force comprises applying the clamping force for each of the openings individually, simultaneously or in sequence.

18. The method according to claim 1, comprising the step of at least partially inserting the insert portion in the opening prior to the step of anchoring, wherein during the step of anchoring the second object is at a substantially same location as during the step of inserting.

19. The method according to claim 1, comprising the step of at least partially inserting the insert portion in the opening, and further comprising moving the second object from an insertion station to an anchoring station after the step of inserting and prior to the step of anchoring.

20. The method according to claim 19, comprising applying the clamping force during the step of at least partially inserting the insert portion and maintaining the clamping force applied at least until the step of anchoring sets in, preferably keeping the clamping force applied during at least a portion of the anchoring step.

21. The method according to claim 1, wherein in the step of applying the clamping force, the clamping force two clamping elements are opposing and arranged so that the opening is between the clamping elements.

22. The method according to claim 1, wherein the second material is one of fibrous, porous, comprising penetrable surface structures, and not able to resist penetration on application of pressure.

23. The method according to claim 1, wherein the second material is one of chipboard, wood, fibre board, plywood and cardboard.

24. The method according to claim 1, wherein the first material comprises a thermoplastic polymer with an elasticity coefficient of at least 0.5 GPa.

25. A machine for carrying out the method according to claim 1, comprising an insertion mechanism capable of inserting the insert portion (6) at least partially in the opening, an anchoring tool capable of transferring the energy suitable for liquefaction of the first material to the first object or the second object, or both, for the anchoring step, and further comprising a clamping mechanism capable of applying the clamping force to the second object during insertion or anchoring or both.

26. The machine according to claim 25, comprising an insertion station and an anchoring station separate therefrom, wherein the clamping mechanism is capable of applying the clamping force at least in the anchoring station.

27. The machine according to claim 26, being equipped for carrying out the steps of inserting and of anchoring at a same station.

28. The machine according to claim 27, further comprising a gripping arrangement adapted for holding the first object in place for insertion, wherein the anchoring tool is adapted for contacting the first object adjacent to the gripping arrangement and for inserting the insertion portion into the opening.

29. The machine according to claim 25, comprising a plurality of clamping elements defining an according number of clamping sites, wherein a distance between the clamping sites is adjustable.

30. The machine according to claim 25, wherein at least one of the clamping elements is provided with a non-sticking arrangement adapted for facilitating release of the clamping element from the second object after release of the clamping force, preferably said non-sticking arrangement comprising a non-sticking pad, for example made from low friction material, and/or a gas supply for supplying release gas to a position between the clamping element and the second object.

31. The machine according to claim 25, wherein the machine further comprises a pressurized fluid cylinder, such as a pressurized gas cylinder or a hydraulic cylinder, for attenuating the clamping element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The invention and embodiments thereof are described in further detail in connection with the appended drawings that are all schematical. Same reference numbers refer to same or analogous elements. In the drawings:

[0062] FIG. 1 illustrates an embodiment of the method according to the invention;

[0063] FIG. 2 shows an example with the clamping force being applied simultaneously to two anchoring sites;

[0064] FIGS. 3a and 3b show a further example with the clamping force being applied simultaneously to two anchoring sites;

[0065] FIG. 4 illustrates a clamping element with a non-sticking pad

[0066] FIG. 5 illustrates using pressurized air for preventing any sticking;

[0067] FIGS. 6 and 7 illustrate clamping surface areas;

[0068] FIGS. 8 and 9 show examples for the application of pressure, vibration and clamping force as a function of the time;

[0069] FIG. 10 illustrates a principle of applying the clamping force by a knee lever mechanism;

[0070] FIG. 11 illustrates the principle of applying the clamping force simultaneously to two anchoring sites by a machine with clamping elements having a variable distance;

[0071] FIG. 12 shows the principle of inserting and subsequently anchoring the first object at a same station;

[0072] FIG. 13 shows the principle of inserting and subsequently anchoring the first object at subsequent stations; and

[0073] FIG. 14 illustrates a second object with a stepped cross section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0074] FIG. 1 depicts a board 1 of for example chipboard being the second object in a method according to the invention. The board has two opposed broad surfaces 3 and a narrow side face 4 with a blind opening 2. A fitting element 5 having a head portion 8 and an insert portion 6 serves as the first object in the method. The fitting element 5 in the depicted embodiment includes a thermoplastic material, for example a polyamide and is, according to an embodiment, made entirely or almost entirely from this thermoplastic material, whereas in alternative embodiments it may include a core of a not thermoplastic material with a coating of a thermoplastic material.

[0075] The insert portion 6 has a slightly oversized cross section compared to the opening 2 so that the insert portion is held in an interference fit in the opening 2 after the insert portion 6 has been introduced, for example by a pressing force acting in a direction of an axis 20 of the opening. Due to the interference fit, opposite surface areas 18, 19 of the insert portion 6 and the opening 2 are pressed against each other. In the subsequent anchoring step, a vibrating tool, namely a sonotrode 11 is used to couple mechanical vibration energy into the fitting element 5 to liquefy portions of the thermoplastic material of the fitting element 5, and preferably of the insert portion 6, that then penetrate into structures of the board 1 and yield, after the energy input stops, the above-described anchoring.

[0076] During the step of inserting and/or during the step of anchoring a clamping force is applied to the site where the anchoring takes place. In the depicted configuration, the clamping force is applied between a movable clamping element 21 and a support 22 serving as a second clamping element.

[0077] In embodiments that include establishing an interference fit, and in which the clamping force is applied during both steps, the clamping force serves for strengthening the second object 1 including the opening 2 (or a plurality of openings) and the penetrable material for better withstanding the establishment of the interference fit and the anchoring step. Also in embodiments that do not include the step of establishing the interference fit prior to the step of anchoring but in which the oversized section of the insert portion is only introduced during the application of the mechanical vibration, a similar strengthening results.

[0078] The clamping force to be applied may, for example, be achieved by connecting the movable clamping element 21 to, for example, a pressurized gas or air cylinder 16, as schematically sketched, a hydraulic cylinder, or a mechanic screw. In particular air cylinders and hydraulic cylinders are convenient in that the clamping pressure may be controlled by controlling the air- or hydraulic pressure.

[0079] FIG. 2 illustrates such an example of strengthening the first object 1 including the opening 2 (or a plurality of openings) and the penetrable material for better withstanding the establishment of the interference fit and the anchoring step. The object 1 again is, e.g., a chipboard and the openings extend from a narrow side thereof. FIG. 2 shows the board 1 viewed in the direction of its narrow side 4, and illustrates: on the left hand side: before the step of establishing the interference fit, in the middle: between the step of establishing the interference fit and the anchoring step, and on the right hand side: after the anchoring step. Prior to the step of establishing the interference fit, the board is strengthened by being clamped together with a pair of clamping jaws 21, 22. The clamping prevents bulging outwards of the board broad surfaces 3 on establishing the interference fit and such weakening the latter. This means that the clamping allows establishing a stronger interference fit than would be possible without it and therefore a stronger anchorage. As the stress of the interference fit is substantially relaxed during the anchoring step, since in the anchoring step the thermoplastic material of the fitting element 5 is at least partly liquefied, the clamping can be released after the anchoring step.

[0080] The depicted configuration of FIG. 2 is an example of the clamping elements covering a plurality of anchoring sites, i.e. a plurality of openings is between two clamping elements 21, 22. However, it is also possible, and often advantageous, to apply the clamping force simultaneously or one after the other to a plurality of clamping sites with separate clamping elements. FIG. 3a shows an example of a board 1, viewed in the direction of its broad side 3, that includes four anchoring sites 26, 27, 28, 29. For the step of establishing the interference fit (if any) and/or for the step of anchoring, a plurality of first, movable clamping elements 21 is used. In the depicted configuration, the anchoring sites 26, 27, 28, 29 are arranged at two opposed narrow side faces. Therein, at least the clamping and interference fit establishing/anchoring steps for the (two) anchoring sites 26, 27; 28, 29 of the same narrow side face 4 may be done simultaneously, with the possibility of carrying out the according step simultaneously for all four sites 26, 27, 28, 29.

[0081] As shown in FIG. 3b, in which the board 1 is viewed from one of its narrow side faces 4, the respective opposed clamping elements may be second clamping elements 25 on a support 24. It is also possible to directly place the board 1 on such a support 24 (which then serves as clamping element), or to use second clamping elements that are also movable and for example belong to a clamping jaw.

[0082] As the clamping elements are to exert a considerable pressure on the board 1 (in an example with chipboard as the penetrable material and with fittings 5 having an insert portion 6 of a diameter of about 7 mm, the necessary clamping pressure has been found to exceed 0.4 N/mm.sup.2), depending on the surface properties of the board 1 there may be a certain risk of the clamping elements 21, 25 sticking to the broad surfaces when the clamping pressure is to be released. To this end, the clamping elements 21, 25 may be provided with a non-sticking pad 32 or surface coating, as schematically illustrated in FIG. 4. Such a non-sticking pad 32 or surface coating may, for example, include PTFE, for example sold under the trademark Teflon. The non-sticking pad 32 or surface coating may be held by a clamping element body 31 of conventional machinery material, such as stainless steel.

[0083] A further possibility of dealing with the risk of sticking is shown in FIG. 5, where a clamping element 21 is provided with an air channel 35 opening towards the broad surface 3 of the board 1 and through which pressurized air is blown after the clamping process to release the clamp 21 from the broad surface 3 of the board 1.

[0084] FIG. 6 illustrates the principle of a clamping surface area optimized for the process. The interpenetration zone 41, in which a sort of composite material is formed as the thermoplastic material is liquefied, has, in a projection perpendicular to the broad side plane, an area slightly exceeding the dimension of the insert portion 6. Depending on the requirements, it may be advantageous that the clamping surface 42 covers the interpenetration zone 41 and extends somewhat beyond it. In situations, it may be advantageous if the clamping surface 42 (in contrast to what is shown in the schematic illustration of FIG. 1) extends to the edge between the broad surface 3 and the narrow side face 4 because in some materials this edge is particularly prone to damages. The area of the clamping surface 42 is preferably smaller than the total area of the broad surface 3, which faces the clamping element 21 and against which the clamping element 21 is pressed, by at least a factor 5.

[0085] Whereas in FIG. 6 the clamping surface 42 is illustrated to be rectangular, other shapes of clamping surfaces 42 are possible, including trapezoid as shown in FIG. 7. In FIG. 7, the edge of the board is assumed to be on the right hand side (same orientation as FIG. 6).

[0086] FIGS. 8 and 9 illustrate the possibility of coordinating the clamping pressure with the insertion and/or the mechanical energy input (in FIG. 8, U denotes the input power of ultrasonic vibration, P the pressure; in FIG. 9 F.sub.i is an interference force and F.sub.c a clamping force, the x-axis corresponds to the time in both figures).

[0087] As sketched in FIG. 8, the clamping pressure 51 may set in prior to the mechanical energy input 52. This may, for example, be advantageous in case, as further described hereinafter, the insertion and, if applicable, establishing an interference fit is carried out at a same station. In this case, the clamping force may set in at, or just before, the time the insert portion starts being pressed into the opening. If no interference fit is established prior to anchoring, the clamping force may be lower initially or set in only when the anchoring step starts. The energy input may stop prior to the clamping force being released (52a), at the same time or thereafter (52b). In the latter case, with energy input stopping after the clamping force being released (52b), it is beneficial that clamping force is not released before liquefaction and infiltration has caused a substantial reduction in the interference force.

[0088] FIG. 9 shows that the interference force 54 may relax as a consequence of the liquefaction process, and the clamping force 55 may stop after such relaxation. The onset of the respective forces is illustrated to be synchronized. Synchronization may be optimized to minimize the lag time.

[0089] As shown, the interference force can initially be higher than the clamping force as long as the crossover of both curves is below the damage threshold of the board material.

[0090] Furthermore, since the board material has an certain initial resistance against splittingthe clamping force does not need to be higher than the interference force, actually, only the sum of clamping force, damage threshold and some safety margin has to be higher than the interference force.

[0091] Instead of applying a constant pressure or a pressing force/pressure profile, the clamping force may be applied by holding the clamping elements at a fixed position relative to one another during the clamping step. Then, the clamping force may be zero or very small until the insertion of the insert portion starts exerting an expanding force on the board.

[0092] FIG. 10 very schematically shows an according mechanism employing the above mentioned fixed position. The clamping element 21 is held by a knee lever including a first lever arm 61.1 and a second lever arm 61.2, the second lever arm connected to a counter element 64 that, for example, together with a support 22 may form a load frame and may be held at a fixed distance to the support 22. At the onset of the process, the knee joint is brought into its correct position, for example by being moved (by any suitable means) into the direction of the arrow. A stop 65 is illustrated at a position in which the knee lever is moved slightly over the neutral point, so that the knee lever becomes self-locking and no external force needs to be applied for clamping.

[0093] Other locking mechanisms locking a distance between two clamping elements are possible.

[0094] FIG. 11 illustrates schematically the possibility of providing a manufacturing machine with clamping elements 21 having a variable, adjustable distance D. Thereby, the machine becomes very flexible for inserting parallel fitting elements 5 at different mutual distances D, and still see to it that clamping is achieved, by means of the clamping elements 21, at the relevant locations, i.e. in the current position of the fitting elements 5.

[0095] As previously mentioned, a machine for carrying out the method may include means for inserting the insert portion in the opening and means for carrying out the anchoring step at a same station or at different stations. FIG. 12 shows a station for performing both, the inserting step and the anchoring step.

[0096] A gripper 71 is used for holding the first object (fitting element 5) in place for insertion, substantially without exerting pressure. The sonotrode 11 exerts the pushing force for the insertion step until the insert portion 6 is inserted in the opening 2 to a sufficient depth for the fitting element 5 being held therein. If applicable, the pressing force is exerted until the interference fit is established.

[0097] The gripper 71 is then removed, and, for the anchoring step, the sonotrode 11 starts coupling mechanical energy into the fitting element 5 while still or again exerting a pressing force. The clamping force is exerted by means of the clamping element 21 and the support 22 during the anchoring step and/or during the insertion step, preferably during both the insertion step and the anchoring step.

[0098] FIG. 13 illustrates a machine with two stations, namely an insertion station 81 in which first objects (here: fitting elements 5) are inserted into openings 2 of a second object (here: board 1), and an anchoring station 82 in which sonotrodes 11 apply mechanical vibration energy to the fitting elements 5. After insertion of the fitting elements 5 into the board 1 at the insertion station 81, the board 1 is moved to the anchoring station 82 where the anchoring process is carried out. Generally, for embodiments with different stations for insertion and anchoring (not only in the depicted configuration), the following possibilities apply: [0099] In accordance with a first possibility (illustrated in FIG. 13), there is no clamping element at the insertion station 81. The clamping force, applied by means of, e.g., clamping elements 21, is only applied for the anchoring process in the anchoring station 82. [0100] In accordance with a second possibility, a clamping force is applied during the insertion step performed at the insertion station 81, the clamping force is, then released and is again applied for the anchoring step performed at the anchoring station 82. [0101] In accordance with a third possibility there is no clamping element at the anchoring station 82. The clamping force is only applied for the insertion process in the insertion station 81. [0102] In accordance with a fourth possibility, a clamping force is applied at the insertion station 81, and it is upheld during movement and, at least initially, during the anchoring step performed at the anchoring station 82. This may for example be done by a mechanical clamp mounted to the board at the insertion station 81 and then moving along with the board 1, wherein the mechanical clamping is released at the anchoring station 82, after at least a part of the liquefaction of the insert portion 6. Alternatively, a clamping mechanism that moves along with the board 1 may be provided. In this case, the clamping mechanism may optionally at the same time hold the board 1 and carry out, or contribute to, the relative movement from the insertion station 81 to the anchoring station 82.

[0103] FIG. 14 illustrates a second object with a stepped cross section of the insertion portion 6 of the fitting element 5. The first cross section (diameter d.sub.1) approximately corresponds to the cross section of the opening 2 in the board 1 or is slightly smaller than it so that the according first insertion portion section 6.1 may be introduced into the opening 2 without substantial interference force being exerted on the board 1. The second cross section (diameter d.sub.2) is oversized, meaning that the second cross section, being the cross section of the second insertion portion section 6.2, is larger than the cross section of the opening 2 in the board 1 so that inserting this second insertion portion section 6.2 provides for an interference fit. In a machine according to the above-mentioned first possibility, the insertion station may introduce the insert portion only to the extent illustrated in FIG. 14, i.e. so that there is no substantial interference force. This makes the stepped cross section (or other cross sections that at least locally are larger at more proximal positions than at more distal positions) attractive in combination with methods/machines in which there is no clamping at an insertion station, as there will be a need for clamping first at the subsequent anchoring station when the second insertion portion section 6.2 is forced into the opening 2 by means of the sonotrode.