METHOD FOR JOINING A FASTENER TO A WORKPIECE

Abstract

A method for joining a fastener to a workpiece that comprises the steps of: (a) providing a workpiece, (b) providing a one-piece metal fastener including an anchor section which extends along an anchor axis, a flange formed on and extending radially to the anchor section, the flange being radially delimited by an outer edge, and the flange at least partially forms an application section located at a non-zero distance from the outer edge; (c) applying a UV-curing adhesive on the application section; (d) arranging the fastener on the workpiece by pushing the flange against the workpiece and squeezing the adhesive toward the outer edges; (e) curing the adhesive exposed at the outer edge of the flange by applying an UV radiation; and (f) curing the adhesive between the flange and workpiece by anaerobic curing.

Claims

1. A method for joining a fastener to a workpiece, the method comprising the steps of: providing a workpiece; providing a fastener including an anchor section which extends between a first end section and a second end section along an anchor axis; a flange formed on and extending radially to the first end section of the anchor section, the flange being radially delimited by an outer edge, and the flange at least partially forms an application section, the application section being at a non-zero distance from the outer edge, wherein the fastener is a one-piece metal fastener; applying an adhesive that is a UV-curing adhesive on the application section, arranging the flange of the fastener on a carrier surface of the workpiece including pushing the flange against the workpiece and thereby squeezing the adhesive toward the outer edges until the adhesive reaches the outer edge of the flange; curing the adhesive at the outer edge of the flange by applying an UV radiation; finishing the curing of the adhesive underneath the flange by anaerobical curing.

2. The method according to claim 1, wherein during the step of providing the fastener the outer edge of the flange includes notches regularly arranged around the outer edge, and wherein during the step of arranging the flange of the fastener on the carrier surface of the workpiece the adhesive is squeezed up to the notches such that the adhesive extends at least partially into the notches.

3. The method according to claim 2, wherein the step of arranging the flange of the fastener on the carrier surface of the workpiece further includes rotating the fastener provided with adhesive when facing the workpiece such that the notches distribute the adhesive.

4. The method according to claim 1, further comprising the step of applying an activator on the application section before the step of applying the adhesive.

5. The method according to claim 4 wherein during the step of applying the adhesive the adhesive entirely covers the activator provided on the application section.

6. The method according to claim 1, further comprising the step of applying an activator on the carrier surface of the workpiece before the step of arranging the flange of the fastener on the carrier surface of the workpiece.

7. The method according to claim 1, wherein during the step of providing a fastener the flange includes a groove and the groove delimits the application section, and wherein during the step of arranging the flange of the fastener on the carrier surface the adhesive flows beyond and above the groove to reach the outer edge when the flange is pushed against the workpiece.

8. The method according to claim 1, wherein during the step of applying the adhesive the adhesive is applied through a bonding device and a rotation is applied to the fastener or the bonding device.

9. The method according to claim 8, wherein the shaft-shaped anchor section is held by a collet during the step of applying the adhesive, and wherein the collet is connected to a rotation module and rotates the fastener.

10. The method according to claim 8, wherein the bonding device further includes a nozzle for applying the adhesive, and wherein during the step of applying the adhesive the flange is eccentrically aligned with the nozzle.

11. A joining device for joining a fastener to a workpiece, the fastener including an anchor section extending along an anchor axis; a flange formed on and extending radially to the anchor section, the flange being radially delimited by an outer edge, and the flange at least partially forms an application section, the application section being at a non-zero distance from the outer edge, and the fastener is a one-piece metal fastener; and wherein the joining device comprises: a collet operable for holding the anchor section of the fastener; a linear drive and a rotation module operable to drive the collet to linearly move and rotate the collet, a UV light unit arranged at the vicinity of the collet.

12. The joining device according to claim 11, wherein the UV light unit is arranged around the collet.

13. The joining device according to claim 11, wherein the rotation module is a first rotation module operable to rotate the collet around a first axis, and the joining device further comprises a second rotation module operable to rotate the collet around a second axis, the second axis being orthogonal to the first axis.

14. The joining device according to claim 11 and further comprising a fastener feeder and a bonding device.

15. A method for joining a fastener to a workpiece, the method comprising the steps of: providing a workpiece; providing a fastener including an anchor section which extends between a first end section and a second end section along an anchor axis, a flange formed on and extending radially to the first end section of the anchor section, the flange being radially delimited by an outer edge, and the flange at least partially forms an application section, the application section being at a non-zero distance from the outer edge, wherein the fastener is a one-piece metal fastener; applying an adhesive that is a UV-curing adhesive on the application section; arranging the fastener on a carrier surface of the workpiece including pushing the flange against the workpiece and squeezing the adhesive toward the outer edges until the adhesive reaches the outer edge of the flange; applying an UV radiation and curing the adhesive exposed at the outer edge of the flange; curing of the adhesive between the flange and the workpiece by anaerobic curing.

16. The method according to claim 15, wherein during the step of providing the fastener the outer edge of the flange includes notches regularly arranged around the outer edge, and wherein during the step of arranging the fastener on the carrier surface of the workpiece the adhesive is squeezed into the notches.

17. The method according to claim 16, wherein during the step of arranging the fastener on a carrier surface of the workpiece includes rotating the fastener provided with adhesive when facing the workpiece such that the edges of the notches distribute the adhesive.

18. The method according to claim 15, further comprising the step of applying an activator on the application section before the step of applying the adhesive.

19. The method according to claim 18 wherein during the step of applying the adhesive the adhesive entirely covers the activator provided on the application section.

20. The method according to claim 15, further comprising the step of applying an activator on a carrier surface of the workpiece before the step of arranging the fastener on the carrier surface of the workpiece.

21. The method according to claim 15, wherein the step of applying the adhesive the adhesive is applied through a bonding device and the step further includes rotating at least one of the fastener or the bonding device.

22. The method according to claim 21, wherein during the step of applying the adhesive the shaft-shaped anchor section is held by a collet and the collet is connected to a rotation module operable for rotating the fastener.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] A specific embodiment of the present invention will now be described, by way of example only and with reference to the accompanying drawings, of which:

[0038] FIG. 1 shows a fastener for performing a joining according to the invention, the fastener comprising a shaft-shaped anchor section, a flange and an adhesive applied on an application section of the flange.

[0039] FIG. 2 shows a top view of the fastener of FIG. 1.

[0040] FIG. 3A to FIG. 3C schematically show a device for applying adhesive to the flange of the fastener and for joining said fastener to a workpiece.

[0041] FIG. 4 shows a fastener according to a second embodiment for performing a joining according to the invention, the fastener comprising a shaft-shaped anchor section, a flange and interlock means arranged on the flange.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] FIG. 1 shows a perspective view of a fastener 10. The fastener 10 comprises a shaft-shaped anchor section 12 which extends between a first end section 14 and a second end section 16 along an anchor axis X. However, the fastener may also comprise an anchor section which is not shaft-shaped. The fastener 10 further comprises a flange 18 formed on and extending radially to the first end section 14 of the anchor section 12. The flange 18 can be a circular flange with a flange diameter D. The flange 18 is radially delimited by an outer edge 20 and comprises an application section 22. This application section 22 forms a joining surface for joining the fastener 10 to a workpiece 24.

[0043] The anchor section 12 can be a threaded section adapted to be connected to a component (not shown) to reliably join the workpiece 24 to the component. The fastener is thus a threaded stud for instance.

[0044] The anchor section may also be a threaded hole. The fastener can thus be a nut plate.

[0045] The application section 22 is formed on the flange 18 on its face opposite the anchor section 12. The application section 22 is for instance arranged at the centre of the flange and extend at a predetermined distance from the edge 20. The application section 22 is for example delimited by a groove 26 arranged on the flange 18. The groove 26 can be a circular groove.

[0046] In another embodiment (not shown), the flange may comprise two or more application sections. The application sections are at a non-zero distance from the outer edge of the flange.

[0047] The application section 22 is adapted to receive an adhesive 28. In the present case the adhesive is an UV-curing adhesive, and more particularly an UV-dual curing adhesive, adapted to be cured by a UV radiation and/or by an activator 30 and/or an anaerobical reaction.

[0048] Before applying the adhesive 28, the application section 22 can be prepared, and an activator 30 can be applied first on the application section 22. The use of an activator 30 is not mandatory. Notably if the stud is composed of a material which is reactive with regards to anaerobic curing reactions, like copper for instance.

[0049] The activator 30 can be applied manually or automatically. The section for applying the activator 30 can correspond to the application section 22 or can be a smaller area. For instance, a drop or spray applicator can be used to apply the activator on the application section.

[0050] The groove 28 is notably adapted to prevent the activator 30 to spread beyond the application section 22. The activator 30 usually comprises a solvent-based part and a curing accelerating part. Once the activator 30 has been applied on the application section 22 (or any other section where the activator can be later mixed with the adhesive), the solvent-based part flashes off and the curing accelerating part remains at the surface of the application area. Generally, the solvent-based part flashes off in 20 to 60 seconds. The flash off time can be reduced with air flow. The activator remains active for several hours.

[0051] The adhesive 28 is applied on the application section 22, either directly (if for instance the fastener is composed of a material which is reactive with regards to anaerobic curing reactions, like copper), or after the application of the activator 30 as described above.

[0052] The adhesive 28 is an UV-curing adhesive. The adhesive 28 may be applied manually or automatically. The adhesive 28 is applied on top of the activator and cover the activator. The adhesive 28 is applied on the application section 22 and does not spread beyond the groove 26, when applied. The adhesive 28 is thus applied at a distance from the edge 20 of the flange 18.

[0053] Before joining the fastener 10 to the workpiece 24, the workpiece 24 can eventually be prepared and an activator can be applied on the workpiece 24. The activator is for instance the same as the one used on the fastener 10. The activator is applied manually or automatically. The activator usually comprises a solvent-based part and a curing accelerating part. Once the activator has been applied on the workpiece, and more particularly on the section of the workpiece destined to receive the fastener, the solvent-based part flashes off and the curing accelerating part remains at the surface of the workpiece. The activator remains functional for several hours. The use of an activator on the workpiece is not mandatory, notably if a material is used is considered as being reactive with respect to anaerobic curing reactions (for instance copper).

[0054] For joining the fastener 10 to the workpiece 24, the flange 18 of the fastener 10 with the adhesive 28 pre-applied, is pushed against the workpiece 24 (and more particularly a section of the workpiece destined to receive it). The pre-applied adhesive 28 is then squeezed out up to the outer edge of the flange and slightly spread over the flange 18. The adhesive 28 squeezed out at the outer edge 20 of the flange 18 is then cured via UV radiation at the fillet of the flange 18. Thus, a pre-assembly of the fastener 10 on the workpiece is made, the cured adhesive at the fillet of the flange 22 allows the fastener 10 to be maintained in place and thus the adhesive 28 under the flange 18 (non-visible and thus not cured by UV radiation) can slowly cure through the reaction notably between the activator 30 and the adhesive 28.

[0055] Once the UV radiation has been made and the adhesive 28 squeezed at the fillet of the flange is cured, the workpiece 24 can be further used for other applications. Notably on automotive assembly lines, the fastener is first joined to the workpiece and then used hours later to assemble a component through the fastener. With the present fastener 10 being pre-assembled on the workpiece just by UV radiation, the workpiece can move forward in the vehicle manufacturing line assembly, thus saving manufacturing time.

[0056] The outer edge 20 of the flange 18 may be provided with notches 32, as seen in FIG. 1 and FIG. 2. The notches 32 may be regularly arranged around the outer edge. The notches 32 are for instance C-shaped or circular or semi-circular as depicted in FIG. 1 and FIG. 2, but they also can be V-shaped or U-shaped. The notches 32 form openings 34. The notches 32 increase the total length of the section where the adhesive 28 can be cured through UV radiation. So, the notches 32 allow to increase the joining forces at the edge of the flange 18. The notch diameter Dn is for example between 1/20 and ⅕ of the flange diameter D.

[0057] In an embodiment, the fastener 10 can rotate when it comes into contact with the workpiece 24. The rotation can accelerate the mixing of the activator and the adhesive. Besides, the rotation squeezes the adhesive 28 toward the edges 20 and the openings 34 provided by the notches. The adhesive 28 is pushed toward the edges of the notches 32. When the rotation stops, enough adhesive 28 remains in the opening 34 formed by the notches 32. More particularly, the adhesive 28 is concentrated on the edge of the flange. The adhesive 28 can thus be cured via UV-radiation at the edge 20. Only the adhesive visible is cured by the UV radiation. This allows to perform a first bonding between the workpiece 24 and the fastener at the edge 20 of the flange 18. This allows a certain amount of bonding strength, especially with respect to assembly torque loads.

[0058] Following the UV-curing the adhesive 28 chemically cures underneath the remaining fastener’s flange due to the activator and the adhesive being mixed, giving the joint ultimate strength. Anaerobically curing is used.

[0059] For an automatic assembly of the fastener 10 to the workpiece 24, a joining device 36 can be used, as schematically depicted in FIG. 3A to FIG. 3C. The joining device 36 comprises for instance a collet 38 adapted to receive the anchor section 12 of the fastener 10, a linear drive 40 and a rotation module 42 adapted to drive the collet 38 in order to linearly move and rotate the collet 38, and thus actuate the fastener 10 when the anchor section 12 is received in the collet 38.

[0060] FIG. 3A shows the joining device 36 with the collet 38 in a rest position. In order to load the fastener 10, the collet 38 can for example move forward in the direction of arrow A until the collet extends outside the casing of the joining device. The anchor section 12 of the fastener 10 can then be inserted inside the collet 38 and maintained in the collet 38.

[0061] A fastener feeder 50 can be provided to feed the fasteners 10. The fastener feeder 50 can have a load pin 54 adapted to contact the flange 18 of the fastener 10. The load pin 54 pushes the flange of the fastener such that the anchor section penetrates the collet 38 until it reaches an end position.

[0062] The fastener 10 may be provided with a first interlock feature I1. The first interlock feature I1 is arranged at the second end section 16 and is provided to securely couple the fastener within the collet once the fastener has been pushed into its end position in the collet 38. As depicted for instance in FIG. 4, the first interlock feature may be in the form of four chamfers provided on the second end 16 of the shaft to cooperate with a square recess arranged at the end of the collet.

[0063] FIG. 4 shows a second interlock feature I2 arranged on the flange of the fastener 10. The second interlock feature is arranged to be coupled to a complementary element arranged on the load pin to form second interlock means and such that second interlock means prevent a rotation of the fastener 10 with regard to the load pin 54 as long as the fastener is not in its end position within the collet 36. The second interlock feature prevent the fastener to rotate with regard to the load pin as long as it has not reached its end position within the collet 38. Thus, a correct positioning of the fastener within the collet 38 is ensured. As depicted n FIG. 4, the second interlock feature is in the form of four grooves regularly arranged on the flange. However, the second interlock feature may have shapes, as long as such shapes are adapted to prevent an unwanted rotation of the fastener, as long as it is coupled to the load pin 54.

[0064] Eventually a rotation of the collet 38 can be made in order to secure the anchor section 12, notably when the anchor section 12 is threaded. The collet 38 with the fastener 10 can then be moved back into the casing or housing of the joining device 36, for example, in order to minimize interference with the environment.

[0065] The casing 44 can be moved in order to reach a position where the adhesive 28 can be applied to the application area of the fastener 10. For example, the casing 44 can be rotated and the collet 38 translates up to a position where the application section 22 faces an adhesive dosing outlet. For example, a second rotation module may be provided for the rotation of the casing (and the collet) around a second axis X2. In an alternative or additional embodiment, a second rotation module 52 may be provided the collet 36 may

[0066] The adhesive 28 can be applied to the application section 22 as depicted in FIG. 3B. The adhesive can be applied by a bonding device 46 comprising a nozzle (or dosing outlet) for applying the adhesive. The flange can be eccentrically aligned with the nozzle during the step of applying the adhesive. Besides, the anchor axis may form an angle between 10deg and 80 deg with regard to the axis of the nozzle Xn. Eventually the bonding device 46 and the fastener feeder 50 can be parts of the same unit.

[0067] A rotation of the fastener 10 around its shaft during the application allows a better repartition of the adhesive 28. The rotation prevents the adhesive 28 of moving to a single direction or even dripping of the fastener due to gravitation. The rotation also prevent a possible contamination of the joining device with adhesive.

[0068] Once the adhesive 28 has been applied to the application section 22, the fastener 10 can be joined to the workpiece 24. For instance, the joining device moves up to the workpiece and to the area where the fastener has to be fixed. The joining device and more particularly the casing with the collet may for instance rotate, as visible in FIG. 3C to align the fastener and the workpiece. The fastener is aligned such that the anchor axis X is sensibly orthogonal to the plane formed by the workpiece 24.

[0069] The rotation of the fastener 10 can eventually continue during the rotation of the casing in order to maintain a good repartition of the adhesive on the application area.

[0070] The collet 38 translates up to the workpiece 24 such that the flange 18 (and more particularly the application area) faces the workpiece and then enters into contact with the workpiece 24. By entering into contact with the workpiece 24 and due to the pushing forces, the adhesive 28 squeezes up to the edge of the flange.

[0071] A UV-light 48 being either incorporated within the joining device or being a separated piece is switched on in order to cure the adhesive visible on the edge of the flange and directly at the fillet. The UV-light 48 can be circularly arranged such that UV radiation is provided simultaneously around the flange 18. UV radiation are thus directed all around the flange and can cure the adhesive at the fillet or at the edge. The flange is thus concentrically arranged with regard to the UV light. In another embodiment, the UV light can be moved around the edge of the flange to cure the adhesive. The UV light can be arranged according to any form. More particularly, the repartition of the UV light depends on the shape of the flange. The UV radiations encompass the entire edges of the flange. For instance, the UV-light 48 is a UV-light system 48 comprising a plurality of UV-LEDs regularly arranged around the collet 36, in order to flash the entire edge of the flange 18. More particularly, the UV-rays are arranged inclined with regard to the first axis or the anchor axis X.

[0072] The UV-curing allows the adhesive 28 to solidify at the edge of the flange 18. The UV curing generates a sufficient fixation of the fastener until the adhesive underneath the flange and not cured by the UV radiation, because not visible from the outside, is cured to at least green strength.

[0073] Eventually, the joining device 36 may rotate the fastener 10 when said fastener 10 contacts the workpiece 24 in order to better spread the adhesive 28. For instance, the joining device may rotate the collet (and thus the fastener 10) around a first rotation axis X with the first rotation module 42. More particularly, when the flange 18 comprises notches, it allows enough adhesive to flow within the opening formed by the notches. By rotating, the edges of the notches push the adhesive 28 which remain in a particular amount at such edges when the rotation stops. Thus, the rotation enable enough adhesive to remain within the openings. Said adhesive is then cured via the UV radiation.

[0074] The present fastener 10 can be used with a wide range of UV-dual-curing adhesives with particularly good bonding performance, notably with regard to the epoxy system often used. This allows for using a broad range of UV-dual-curing adhesives with superior bonding performance compared to known epoxy system. The present fastener 10 can be used with workpieces made of a wide range of materials such as steel, high strength steel, thermoset polymers, Aluminium, notably aluminium having any kind of thickness, and particularly with a thickness of less than 1 mm, thermoplastic materials, low energy plastics like polypropylene and polyethylene (notably with UV-dual-curing acrylics specially designed for those low-energy surfaces).

[0075] The fasteners may be packed and shipped as bulk good without any climate control or shelf-life while adhesives may be transported with state-of-the-art processes. The bonding cycle time is particularly reduced with less than 10 seconds for immediate loadability.