Patent Description:
The present invention is further directed to a fastener for implementing the above-mentioned method.

It is known, for example, in the technical field of joining fasteners to workpieces to weld metallic bolts to metallic workpieces. This method, known as "stud welding", is used, in particular, in the automotive industry in order to weld bolts to car body panels, wherein fixing clips made of plastic are fixed to connect to the bolts, to which fixing clips cables, wires etc. are fixed.

Due to the fact that composite materials that are able to be welded less well or are non-metallic are being increasingly used, for example, in car body construction, such as plastics, fibre composite components, etc., the adhesive bonding technique (or gluing technique or adhering technique) has been established as a joining method in car body panel construction in particular. Instead of welding the bolts to workpieces, they are adhesively bonded (or glued) to the workpiece.

<CIT> discloses a fastener (also called glue stud) with an application area comprising a joining material adapted to be activated by means of heat treatment for forming a joining assembly. <CIT> discloses a fastener comprising an application section with a first adhesive material and a second adhesive material, the first adhesive material covering completely the second adhesive material. A heating body is used to melt the adhesive layers such that both adhesives can be mixed. <CIT> discloses a joining device for joining a fastener to a workpiece.

<CIT> is directed to a method for joining at least two components using a dual hardening adhesive composition. The glue stud is provided with an adhesive composition comprises two different adhesives, one being for UV curing at the edge and the other adhesive being adapted to cure slower underneath the flange of the stud by a second mechanism. The use of two different adhesive is particularly burdensome and necessitates mixing the two different adhesive.

<CIT> discloses a method for joining a fastener with a shaft-shaped anchor section, a flange and a joining material which is pre-applied to an application section of the flange. Anchor section and flange are made of an inductively heatable material. The heating of the joining material before the placing on the carrier surface of the workpiece is carried out inductively, by induction energy being introduced into the flange of the fastening element via an inductive field shaper, so that anchor section and flange and also, as a result of this, indirectly, the joining material which has been applied to them, are heated.

After the application of the fastening element to the workpiece, the inductive energy supply is terminated and the adhesive solidifies to produce the adhesive bond.

For mass production, the length of time required to perform the joining method is of particular significance. Besides, the use of a reactive hotmelt concept with induction limits the application to particular surfaces which don't have a high thermal conductivity, in order to avoid a quick heat dissipation, and/or which will not be damaged during a hot curing process.

A method for joining a fastening element to a surface section of a component is known from document <CIT>, wherein the fastening element has an adhesive surface, to which a thermally meltable and curable adhesive is applied, comprising the steps of first preheating the adhesive to a first temperature in order to melt it, heating the surface section to a second temperature and applying the adhesive surface to the surface section, wherein the adhesive, after the adhesive surface is applied to the surface section, is heated to a third temperature in order to cure the adhesive and thereby fasten the fastening element permanently to the component. The various steps of this method can be cumbersome and there is a need to simplify such methods and to further reduce the length of time, at the same time having good joining results. Furthermore, there is a need for a method for joining the fastening element, wherein the fastening element has good storage stability and avoids an undesired chemical cross-linking reaction of the joining material before the actual adhesive method.

It is an object of the present invention to provide a method for joining a fastener, notably a glue stud, to a workpiece which overcomes these drawbacks, and in particular a joining method enabling a wide range of material to be used for a joining process with a glue stud without altering the joining performance or the length of time required to perform the joining.

Accordingly, the present invention provides a method according to claim <NUM>. More particularly the present invention is directed to a method for joining a fastener to a workpiece, the method comprising the steps of:.

Characterized in that the adhesive is an UV-curing adhesive and the method further comprises the steps of.

The UV-radiation allows to provide a method which is not dependent on heat. Therefore, it broadens the range of applicable material. Besides, UV curing adhesives can be quickly cured, notably with a cycle time of less than <NUM> seconds. Thus, the fastener can be pre-assembled to the workpiece such as not to move anymore. The fastener is pre-secured to the workpiece due to the adhesive cured on the edge of its flange and the adhesive underneath the flange can slowly cure. Besides, the application of the adhesive can be made directly at the joining spot, so that no transport of fastener with a pre-applied adhesive is needed. The adhesive on the fastener is cured through two different mechanisms. The first mechanism is UV curing which gives green strength within a few seconds, thus allowing further manipulation of the fastener and the workpiece until the second curing mechanism consisting of the curing in the area underneath the flange ends. The second curing mechanism gives assembly strength.

In an embodiment, the anchor section is a shaft-shaped anchor section. The fastener is for instance a stud with a threaded shaft. However, in other embodiment, the fastener may be a nut plate or any of the type of fastener.

In an embodiment, the application section is arranged at the centre of the flange. For instance, the flange can be circular and the application section is located at the centre of the flange. In other embodiments, the flange may be rectangular or may have any other shape. The flange may also have more than one application section, the applications section being at distance of the outer edge of the flange.

In an embodiment, the outer edge of the flange is provided with notches which are regularly arranged around the outer edges, and wherein the adhesive is squeezed up to the notches such that the adhesive extends at least partially in the notches. The notches form openings in which the adhesive can squeeze. Besides, the notches allow to increase the fillet length.

In an embodiment, the fastener provided with adhesive rotates when facing the workpiece such that the edges of the notches distribute the adhesive. Thus, a better distribution of the adhesive is realized. Such rotation also allows a better mixing of the activator and the adhesive in some cases. However, such rotation is not mandatory. The fastener can be glued to the workpiece without rotation, as long as the adhesive is squeezed up to the edge of the flange.

In an embodiment, the method further comprises the step of applying an activator on the application section before applying the adhesive. Depending on the material used for the fastener, the activator may not be necessary to cure the adhesive. More particularly, for non-metal material, the presence of an activator is necessary, whereas for metal materials, the application of an activator may be avoided.

In an embodiment, the adhesive entirely covers the activator provided on the application section. The adhesive may also just partially cover the activator, and both are mixed during the joining when the fastener is pushed against the workpiece, for example.

In an embodiment, the method further comprises the step of applying an activator on a carrier surface of the workpiece. Depending on the material used for the workpiece, the activator may not be necessary to cure the adhesive.

In an embodiment, the flange comprises a groove and the groove delimits the application section, and wherein the adhesive flows beyond and above the groove to reach the outer edge when the flange is pushed against the workpiece. The groove allows to materially delimit the application section. The groove can be circular. For instance, the flange and the groove are circular. In other embodiment, the flange may have a rectangular shape, and the groove may be circular or rectangular. For manual joining process, the use of a groove is not mandatory.

In an embodiment, the adhesive is applied through a bonding device and a continuous rotation is applied to the fastener or the bonding device during the step of applying the adhesive. The rotation allows a better distribution of the adhesive on the application surface without dropping.

In an embodiment, the fastener provided with the adhesive is moved in rotation until said fastener is pushed against the workpiece. In other words, when handling the fastener before the joining process, the fastener with the adhesive rotates, in order to avoid dropping or losing adhesive but also in order to avoid adhesive being unevenly distributed on the application surface. Indeed, uneven distribution of the adhesive could lead to a not completely closed fillet which could lead to a decreased ageing resistance, UV-fixture strength and bond strength. As previously mentioned, once pushed against the workpiece, the rotation can stop.

In an embodiment, 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.

In an embodiment, the bonding device further comprises a nozzle for applying the adhesive, and wherein the flange is eccentrically aligned with the nozzle during the step of applying the adhesive.

The present invention also provides a joining device according to claim <NUM>. Accordingly, the present invention is also directed to a joining device for joining a fastener to a workpiece according to the method described above and comprising a collet adapted to be coupled to the anchor section of the fastener, a linear drive and a rotation module adapted to drive the collet <NUM> in order to linearly move and rotate the collet, and a UV light unit arranged at the vicinity of the collet.

In an embodiment, the UV light unit is arranged around the collet.

In an embodiment, the rotation module is a first rotation module adapted to rotate the collet around a first axis, and the joining device further comprises a second rotation module adapted to rotate the collet around a second axis, the second axis being orthogonal to the first axis. The first axis may correspond to the anchor axis when the fastener is within the collet.

Finally, the present invention is directed to a joining apparatus comprising a joining device as mentioned above, a fastener feeder and a bonding device.

The present disclosure is also directed to a fastener adapted to be used according to the method described above, wherein the fastener comprises a shaft-shaped 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 arranged at the center of the stud, and being at a non-zero distance from the outer edge, wherein the fastener is a one-piece metal fastener, and the outer edge of the flange is provided with notches which are regularly arranged around the outer edges.

For example, the flange is a circular flange with a flange diameter, and the notches are partly circular and have a notch diameter, and wherein the notch diameter is between <NUM>/<NUM> and <NUM>/<NUM> of the flange diameter.

Eventually, the fastener comprises at least three notches.

For instance, the flange comprises a groove, the groove is arranged between the notches and the application section.

Additionally, he groove may be circular groove, wherein the groove is at least <NUM>,<NUM> deep and extends at least at <NUM> from the notches. More particularly, a groove of less than <NUM> is difficult to realize for such studs. Besides, the groove should be at a minimum distance from the edge of the flange, notably for an automated process in order to avoid the adhesive to leak up to the edge of the flange before the joining process.

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:.

<FIG> shows a perspective view of a fastener <NUM>. The fastener <NUM> comprises a shaft-shaped anchor section <NUM> which extends between a first end section <NUM> and a second end section <NUM> along an anchor axis X. However, the fastener may also comprise an anchor section which is not shaft-shaped. The fastener <NUM> further comprises a flange <NUM> formed on and extending radially to the first end section <NUM> of the anchor section <NUM>. The flange <NUM> can be a circular flange with a flange diameter D. The flange <NUM> is radially delimited by an outer edge <NUM> and comprises an application section <NUM>. This application section <NUM> forms a joining surface for joining the fastener <NUM> to a workpiece <NUM>.

The anchor section <NUM> can be a threaded section adapted to be connected to a component (not shown) to reliably join the workpiece <NUM> to the component. The fastener is thus a threaded stud for instance.

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

The application section <NUM> is formed on the flange <NUM> on its face opposite the anchor section <NUM>. The application section <NUM> is for instance arranged at the centre of the flange and extend at a predetermined distance from the edge <NUM>. The application section <NUM> is for example delimited by a groove <NUM> arranged on the flange <NUM>. The groove <NUM> can be a circular groove.

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.

The application section <NUM> is adapted to receive an adhesive <NUM>. 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 <NUM> and/or an anaerobical reaction.

Before applying the adhesive <NUM>, the application section <NUM> can be prepared, and an activator <NUM> can be applied first on the application section <NUM>. The use of an activator <NUM> 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.

The activator <NUM> can be applied manually or automatically. The section for applying the activator <NUM> can correspond to the application section <NUM> or can be a smaller area. For instance, a drop or spray applicator can be used to apply the activator on the application section.

The groove <NUM> is notably adapted to prevent the activator <NUM> to spread beyond the application section <NUM>. The activator <NUM> usually comprises a solvent-based part and a curing accelerating part. Once the activator <NUM> has been applied on the application section <NUM> (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 <NUM> to <NUM> seconds. The flash off time can be reduced with air flow. The activator remains active for several hours.

The adhesive <NUM> is applied on the application section <NUM>, 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 <NUM> as described above.

The adhesive <NUM> is an UV-curing adhesive. The adhesive <NUM> may be applied manually or automatically. The adhesive <NUM> is applied on top of the activator and cover the activator. The adhesive <NUM> is applied on the application section <NUM> and does not spread beyond the groove <NUM>, when applied. The adhesive <NUM> is thus applied at a distance from the edge <NUM> of the flange <NUM>.

Before joining the fastener <NUM> to the workpiece <NUM>, the workpiece <NUM> can eventually be prepared and an activator can be applied on the workpiece <NUM>. The activator is for instance the same as the one used on the fastener <NUM>. 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).

For joining the fastener <NUM> to the workpiece <NUM>, the flange <NUM> of the fastener <NUM> with the adhesive <NUM> pre-applied, is pushed against the workpiece <NUM> (and more particularly a section of the workpiece destined to receive it). The pre-applied adhesive <NUM> is then squeezed out up to the outer edge of the flange and slightly spread over the flange <NUM>.

The adhesive <NUM> squeezed out at the outer edge <NUM> of the flange <NUM> is then cured via UV radiation at the fillet of the flange <NUM>. Thus, a pre-assembly of the fastener <NUM> on the workpiece is made, the cured adhesive at the fillet of the flange <NUM> allows the fastener <NUM> to be maintained in place and thus the adhesive <NUM> under the flange <NUM> (non-visible and thus not cured by UV radiation) can slowly cure through the reaction notably between the activator <NUM> and the adhesive <NUM>.

Once the UV radiation has been made and the adhesive <NUM> squeezed at the fillet of the flange is cured, the workpiece <NUM> 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 <NUM> 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.

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

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

Following the UV-curing the adhesive <NUM> 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.

For an automatic assembly of the fastener <NUM> to the workpiece <NUM>, a joining device <NUM> can be used, as schematically depicted in <FIG>. The joining device <NUM> comprises for instance a collet <NUM> adapted to receive the anchor section <NUM> of the fastener <NUM>, a linear drive <NUM> and a rotation module <NUM> adapted to drive the collet <NUM> in order to linearly move and rotate the collet <NUM>, and thus actuate the fastener <NUM> when the anchor section <NUM> is received in the collet <NUM>.

<FIG> shows the joining device <NUM> with the collet <NUM> in a rest position. In order to load the fastener <NUM>, the collet <NUM> 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 <NUM> of the fastener <NUM> can then be inserted inside the collet <NUM> and maintained in the collet <NUM>.

A fastener feeder <NUM> can be provided to feed the fasteners <NUM>. The fastener feeder <NUM> can have a load pin <NUM> adapted to contact the flange <NUM> of the fastener <NUM>. The load pin <NUM> pushes the flange of the fastener such that the anchor section penetrates the collet <NUM> until it reaches an end position.

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

<FIG> shows a second interlock feature I2 arranged on the flange of the fastener <NUM>. 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 <NUM> with regard to the load pin <NUM> as long as the fastener is not in its end position within the collet <NUM>. 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 <NUM>. Thus, a correct positioning of the fastener within the collet <NUM> is ensured. As depicted n <FIG>, 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 <NUM>.

Eventually a rotation of the collet <NUM> can be made in order to secure the anchor section <NUM>, notably when the anchor section <NUM> is threaded. The collet <NUM> with the fastener <NUM> can then be moved back into the casing or housing of the joining device <NUM>, for example, in order to minimize interference with the environment.

The casing <NUM> can be moved in order to reach a position where the adhesive <NUM> can be applied to the application area of the fastener <NUM>. For example, the casing <NUM> can be rotated and the collet <NUM> translates up to a position where the application section <NUM> 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 <NUM> may be provided the collet <NUM> may.

The adhesive <NUM> can be applied to the application section <NUM> as depicted in <FIG>. The adhesive can be applied by a bonding device <NUM> 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 <NUM> deg with regard to the axis of the nozzle Xn. Eventually the bonding device <NUM> and the fastener feeder <NUM> can be parts of the same unit.

A rotation of the fastener <NUM> around its shaft during the application allows a better repartition of the adhesive <NUM>. The rotation prevents the adhesive <NUM> 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.

Once the adhesive <NUM> has been applied to the application section <NUM>, the fastener <NUM> can be joined to the workpiece <NUM>. 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> 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 <NUM>.

The rotation of the fastener <NUM> can eventually continue during the rotation of the casing in order to maintain a good repartition of the adhesive on the application area.

The collet <NUM> translates up to the workpiece <NUM> such that the flange <NUM> (and more particularly the application area) faces the workpiece and then enters into contact with the workpiece <NUM>. By entering into contact with the workpiece <NUM> and due to the pushing forces, the adhesive <NUM> squeezes up to the edge of the flange.

A UV-light <NUM> 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 <NUM> can be circularly arranged such that UV radiation is provided simultaneously around the flange <NUM>. 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 <NUM> is a UV-light system <NUM> comprising a plurality of UV-LEDs regularly arranged around the collet <NUM>, in order to flash the entire edge of the flange <NUM>. More particularly, the UV-rays are arranged inclined with regard to the first axis or the anchor axis X.

The UV-curing allows the adhesive <NUM> to solidify at the edge of the flange <NUM>. 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.

Eventually, the joining device <NUM> may rotate the fastener <NUM> when said fastener <NUM> contacts the workpiece <NUM> in order to better spread the adhesive <NUM>. For instance, the joining device may rotate the collet (and thus the fastener <NUM>) around a first rotation axis X with the first rotation module <NUM>. More particularly, when the flange <NUM> 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 <NUM> 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.

The present fastener <NUM> 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 <NUM> 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 <NUM>, thermoplastic materials, low energy plastics like polypropylene and polyethylene (notably with UV-dual-curing acrylics specially designed for those low-energy surfaces).

Claim 1:
Method for joining a fastener (<NUM>) to a workpiece, the method comprising the steps of:
- providing a workpiece (<NUM>);
- providing a fastener (<NUM>) including an anchor section which extends between a first end section and a second end section along an anchor axis (X); a flange (<NUM>) formed on and extending radially to the first end section of the anchor section (<NUM>), the flange being radially delimited by an outer edge (<NUM>), and the flange at least partially forms an application section (<NUM>), the application section being at a non-zero distance from the outer edge, wherein the fastener (<NUM>) is a one-piece metal fastener (<NUM>);
- applying an adhesive (<NUM>) on the application section,
wherein the adhesive (<NUM>) is an UV-curing adhesive and the method further comprises the steps of
- arranging the flange of the fastener (<NUM>) on the carrier surface of the workpiece (<NUM>) and pushing said flange (<NUM>) against the workpiece such that the adhesive is squeezed toward the outer edges until it reaches the outer edges of the flange (<NUM>);
- curing the adhesive (<NUM>) at the outer edge (<NUM>) of the flange by applying an UV radiation, such that the fastener is pre-assembled to the workpiece;
- finishing the curing of the adhesive (<NUM>) underneath the flange by anaerobical curing.