BACKGROUND OF THE INVENTION

Field of the Invention

The invention is in the fields of mechanical engineering and construction, especially mechanical construction, for example automotive engineering, aircraft construction, railway industry, shipbuilding, machine construction, toy construction, building industries, etc. In particular, it relates to a method of—mechanically—securing a second object to a first object.

Description of Related Art

In the automotive, aviation and other industries, there has been a tendency to move away from steel-only constructions and to use lightweight material such as aluminum or magnesium metal sheets or polymers, such as carbon fiber reinforced polymers or glass fiber reinforced polymers or polymers without reinforcement, for example polyesters, polycarbonates, etc., instead.

The new materials cause new challenges in bonding elements of these materials—especially in bonding flattish object to another object. An example for this is the bonding of parts of polymer-based material to metal parts, such as metal sheets.

To meet these challenges, the automotive, aviation and other industries have started heavily using adhesive bonds. Adhesive bonds can be light and strong but suffer from the disadvantage that there is no possibility to long-term control the reliability, since a degrading adhesive bond, for example due to an embrittling adhesive, is almost impossible to detect without entirely releasing the bond. Also, adhesive bonds may lead to a rise in manufacturing cost, both, because of material cost and because of delays caused in manufacturing processes due to slow hardening processes, especially if the surfaces to be connected to each other have certain roughness and as a consequence the quickly hardening thin-layer adhesives cannot be used. Further, a flattish adhesive bond between two objects not having the same coefficient of thermal expansion may lead to additional reliability problems as the adhesive bond may be subject to substantial shearing forces in everyday use due to temperature fluctuations.

A particular challenge when bonding elements to each other is the compensation of tolerances, for example if the elements are bonded to each other with other bonds than adhesive bonds, such as by screws and nuts or by rivets. In such bonds, a precise definition of the relative locations of a fastener and the respective fastening location is required. Such a precise definition may especially be hard to reach if a manufacturing process has to be particularly economical and/or if the parts to be connected are comparably large in at least one dimension and/or react to the conditions they are subject to during manufacturing and use in a different manner (for example if they have different coefficients of thermal expansion).

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a method of mechanically securing a second object to a first object, the method overcoming disadvantages of prior art methods. It is especially an object of the invention to provide a cost-efficient method that yields a reliable connection between a thermoplastic part and a part that is not liquefiable under the conditions, under which the thermoplastic part liquefies, or that yields a reliable connection between different parts by means of a thermoplastic connection element. It is another object of the invention to provide a method that yields a reliable connection between parts and is efficient and quick.

A method according to the invention is suitable for mechanically securing a first object to a second object and includes the steps of:Providing the first object, wherein the first object includes thermoplastic material in a solid state.For example, the first object can be or include a dowel, a connector, a plug, a sealing element, an anchor piece or fixation element for a further object, a plate or board having different physical, for example different mechanical, acoustical or optical properties, or chemical, for example resistance to liquids, properties etc.Providing the second object with a generally flat sheet portion having an edge. The second object may be any object that has a flattish sheet portion. “Sheet portion” in this does not imply a necessarily homogeneous thickness. The second object may especially be a metal sheet. Alternatively, the second object may be another object having a sheet portion, for example a more complex object having a part of a metal sheet, which part constitutes the sheet portion, or an object in which a sheet portion is constituted not by a metal sheet in the narrow sense of the word (manufactured by rolling) but by a, for example, metallic part manufactured in a cast process, such as a die cast object. In an embodiment, the second object provided includes a perforation of the sheet portion, with the edge running along the perforation.Positioning the first object relative to the second object to provide an assembly including the first and second object, in which assembly the edge is in contact with the thermoplastic material.While the edge is in contact with the thermoplastic material, bringing the first object and the second object to a relative movement to each other such that a melting zone including flowable thermoplastic material is formed and such that thermoplastic material of the melting zone flows around the edge to at least partially embed the edge in the thermoplastic material.In other words, the edge and—as the case may be—adjacent portions of the sheet portion form a securing location of the second object.The melting zone is formed due to friction heat generated between the edge and the thermoplastic material that move relative to each other.The relative movement is generated by an excitation applied to at least one of the first and second object.In the method according to the invention, the relative movement includes a rotational movement.In particular, the relative movement does not consist of a movement along a straight line, for example a proximal-to-distal axis of the first or second object or a longitudinal axis of the perforation, exclusively.The relative movement can be free of any oscillatory movement along such a straight line.The relative movement can be free of any oscillatory movement.In an embodiment, the contact between the edge and the thermoplastic material established in the step of positioning the first object relative to the second object defines a plane. In such an embodiment, a rotation axis of the rotational movement can be parallel to a normal of the plane.However, the rotation axis can be defined differently, for example by a longitudinal axis of a bore or protrusion of at least one of the first and second object.Further, one can also envisage an embodiment in which the rotation axis is not parallel to the normal of the plane. In such an embodiment, the melting zone is formed at a contact point between the first and second object and expands continuously in the following during the embedding of the edge in the thermoplastic material. However, an angle between the rotation axis and the normal can be limited due to the shape of the edge. For example, the edge can be formed by a protrusion of the second object. In such an embodiment, the angle can be such that the protrusion can penetrate into the thermoplastic material in a manner that allows the generation of the meting zone along a closed line and a full embedment of the edge in the thermoplastic material. The embodiment with the rotation axis not parallel to the normal of the plane leads to a good bonding of the first object to the second object when used in combination with an oscillating rotational movement, in particular.In embodiments, the method further includes a step of applying a mechanical pressure force along an axial axis, in particular along the proximal-to-distal axis. In particular, the mechanical pressure force is such that it promotes the embedment of the edge in the thermoplastic material. The mechanical pressure force can be applied locally to the first or second object, wherein the object to which the pressure force is not applied locally is placed against a support, for example.In any embodiment, the assembly can be held by the support during the step of applying the mechanical pressure force and/or the excitation.The step of applying the mechanical pressure force can set in prior to or at the same time as the step of bringing the first and second object to a relative movement to each other.A mechanical pressure force that sets in prior to the relative movement can be favourable in terms of bonding quality, in particular in terms of bonding depth and strength of the bonding generated.In particular, the excitation can be applied from one, e.g., proximal, side of the assembly and the mechanical pressure force from an opposite, e.g., distal, side of the assembly.In an embodiment, the excitation generating the rotational movement is applied from the proximal side of the assembly to the first object and the mechanical pressure force is applied from the distal side of the assembly to the second object.Stopping the relative movement and letting the thermoplastic material resolidify to yield a positive-fit connection between the first and the second object.The mechanical pressure force can last for a time sufficient for resolidification of the thermoplastic material after stopping the relative movement.

It is an advantage of the method including the use of the rotational movement for forming the melting zone compared to methods that include only axial, for example vibrational axial, movements, that axial joining forces can be reduced. This is because the friction heat is at least partly generated by the rotational movement. Hence, the method according to the invention is advantageous for a second object with low or reduced stiffness, such as a thin (e.g., steel or aluminium) sheet and/or for a second object including a sensitive surface, for example.

The second object provided can include a space on another side of the second object than the side from which the first object is brought into contact with it.

For example, in embodiments in which the first object is positioned from a proximal side to the second object and in which the first object is brought in the relative movement to the second object, a distal side may be free along the edge (thus, if applicable, around the perforation) so that the thermoplastic material can flow immediately along the surfaces of the second object's sheet portion.

The first and/or second object can include at least one energy director, i.e., the first and/or second object can have a surface profile that defines spots or areas at which the conditions for the melting of the thermoplastic material are favourable. The edge but also the tapered protrusions forming an expansion element discussed below are examples of energy directors.

In an embodiment, the rotational movement includes a rotational movement around a rotation axis, wherein the rotational movement includes a constant direction of rotation.

In particular, the rotational movement includes the constant direction of rotation for a relevant portion of a full turn around the rotation axis, for example a quarter of a full turn or a half turn, at least.

The constant direction of rotation is either clockwise or counterclockwise. One can also envisage that the relative movement is either clockwise or counterclockwise, but it is not clockwise for a short period of time and counterclockwise for another short period of time. In particular, it is not an oscillation rotational movement.

In this embodiment, the rotational movement can be given by its rotation speed, given in turns per second, for example.

The rotation speed can be adjusted during the method.

The rotation speed or the range of rotation speed used in the method can depend on the first and second object, in particular on their composition and dimensions.

In particular, the rotational movement can be, i.e., can consist of, the rotational movement with constant direction of rotation around the rotation axis.

Alternatively, the rotational movement includes the oscillating rotational movement. In other words; the relative movement includes a back and forth oscillating rotation around the rotation axis, i.e., it switches between a clockwise or counterclockwise rotation.

In particular, the oscillating rotational movement can be characterized by a frequency and an amplitude, wherein the amplitude can be given in radians.

The frequency and/or amplitude can be adjusted during the method.

The frequency and/or amplitude or the frequency range and/or amplitude range used in the method can depend on the first and second object, in particular on their composition and dimensions.

In particular, the rotational movement can be, i.e., can consist of, the oscillating rotational movement around the rotation axis.

In an embodiment, the rotational movement includes an orbital movement.

The rotational movement can be, i.e., can consist of, the orbital movement. However, an orbital movement in combination with a rotational movement including a constant direction of rotation or in combination with an oscillating rotational movement can be envisaged.

In particular, the orbital movement is an orbital movement around a central axis.

The central axis can be normal to the plane defined by the contact between the edge and the thermoplastic material established in the step of positioning the first object relative to the second object.

The central axis can be a longitudinal axis of the perforation, for example.

It is an advantage of the embodiment including an orbital movement that the contact between the first and second object generated does not need to be rotationally symmetric with respect to the rotation axis of the first and/or second object.

In a sub-group of the embodiment including the orbital movement and further including the perforation forming the edge, the orbital movement is such that a radial extension of the melting zone is smaller than 0.5 times a diameter of the perforation, in particular smaller than 0.2 times the diameter, for example between 0.1 and 0.2 times the diameter. A melting zone with such a radial extension is advantageous in terms of a well-controllable bonding process.

In particular, a cross-section of the perforation normal the longitudinal axis of the perforation and/or normal to a rotation axis of the first or second object does not need to be circular, anymore. For example, the cross-section can be elliptic or have a 4-fold or higher, for example 6- or 8-fold, rotation symmetry with respect to the longitudinal axis or rotation axis. In particular a 12-fold or higher rotation symmetry can be advantageous in terms of creating a melting zone in a method according to the invention.

The cross-section with n-fold rotation symmetry can include straight segments, bent segments or a combination of straight and bent segments.

In an embodiment, the first object is brought into contact with the second object from a generally proximal side in the step of positioning. In addition, along the edge a space distally of the second object can be free before the flow portion becomes flowable.

In an embodiment, the first object is brought into contact with the second object from a generally proximal side in the step of positioning, and the step of bringing the first and second object to a relative movement to each other includes coupling a tool to a proximally facing coupling face of the first object, whereby a pressing force in a distal direction, i.e., towards the second object, and the rotational movement are coupled into the first object by the tool, simultaneously.

In an embodiment, at least one of the first object provided and the second object provided includes a coupling-in face. Further, a method according to this embodiment includes the step of providing a tool including a coupling-out face, wherein the coupling-out face is arranged to engage with the coupling-in face. Further, the tool is equipped to generate an excitation capable to set an object engaged to the tool by use of the coupling-out face in the rotational movement.

In particular, it is the object that is set in movement relative to the other object that includes the coupling-in face.

The method can include the step of bringing the coupling-out face in contact with the coupling-in face. This can be done prior to the step of bringing the first and second object to a relative movement to each other or it can be done prior to the step of positioning the first object relative to the second object, for example. In particular, the first or second object can be provided in a manner engaged to the tool.

In particular, the coupling-out face and the coupling-in face as well as the resulting engagement is such that the excitation and—as the case may be—the mechanical pressure force can be transferred to the object engaged.

In any embodiment including a tool, a distal end of the tool can be adapted to the shape of the edge such that the tool does not slide laterally relative to the assembly. This means that the coupling face between the sonotrode and the first object can be restricted to a region tailored to the shape of the second object and to the location of the edge. For example, the coupling-out face may be restricted to a lane following the course of the edge of the second object. In embodiments with a perforation along which the edge is formed, the coupling face can be ring shaped with a central opening, for example.

In embodiments having a perforation, the sheet portion around the perforation has a projecting (“deformed”) section projecting away from a sheet plane. The projection can be towards the first object, i.e., towards proximally if the rotational movement is coupled into the first object, or away from the first object, i.e., towards distally.

For example, the projecting (deformed) section includes a plurality of tongues, wherein the edge is constituted by end edges of the tongues.

Such tongues, or rather the gaps between the tongues, increase the torsional strength of the element including the first object secured to the second object by the method.

An increase of torsional strength by the use of tongues, in particular by the use of tongues formed by the sheet portion, is made possible by the method including the rotational movement. This is because the method including the rotational movement guarantees the generation of sufficient friction heat for forming the melting zone even when a significantly lower mechanical pressure force is applied to the assembly including the first and second object compared to a method that bases predominantly on vibrational axial, movements. Methods that base predominantly on axial movements are difficult to use for the increase of torsional strength by the use of tongues due to a limited axial stiffness of the tongues.

In particular, the use of the oscillating rotational movement is advantageous for the embodiment including a projecting (deformed) sheet portion including the plurality of tongues. For example, the method of mechanically securing the first object to the second object becomes a better controllable process due to the oscillating rotational movement. Moreover, it has been found that an amplitude of the oscillating rotational movement that is smaller than the gap between the tongues, this means the number of radians over which the gap extends, is advantageous in terms of press control and load on the tongues. Especially, if the amplitude of the oscillating rotational movement is smaller than the gap between the tongues, in the first object a polymer bridge between the tongues may remain solid, and liquefaction of such bridge may be prevented.

More generally, the use of the method including the rotational movement for generating the melting zone allows for usage of the method for second objects that are of limited stability, in particular limited axial stability, at a securing location.

The projecting (deformed) section can run continuously around a periphery of the perforation.

In embodiments, the sheet portion along the edge (thus if applicable around the perforation) is deformed so that the sheet portion projects away from a sheet plane defined. In other words: The sheet portion along the edge has a section projecting away from the sheet plane. Especially, the sheet portion may project towards the side of the first object (towards the proximal side in embodiments in which the rotational movement is coupled into the first object from a generally proximal side). Especially, the projecting section (if any) being a deformed section may be of a same metal sheet material as the sheet portion.

In this text, the term “sheet plane” denotes the plane/surface defined by the shape of the generally planar sheet portion in a region around the edge, especially around the perforation (if any). The sheet plane may be planar in the sense of extending straight into two dimensions. Alternatively, the sheet plane may be curved and thereby follow a more complex 3D shape, for example if it constitutes the surface of a complex object, such as a body of a vehicle or aircraft. In case the second object is, near the edge, deformed to project away from the sheet plane, the curvature of second object at the location from where the deformed section extends will often be much larger than the curvature of the sheet plane.

Such a deformed section may be formed by deforming a corresponding part of the sheet portion, for example by making a cut (for example by punching) and bending or otherwise deforming hence leaving a second element opening where the corresponding part of the sheet portion had initially been. In this, the deformed section may still be one-piece with the sheet section.

As an alternative to a deformed section, would also be possible to provide a section of the sheet portion that projects away from the sheet plane as a separate element secured to the sheet material, for example by welding.

As an even further alternative to a deformed section, it would be possible to manufacture a section projecting towards the side from which the first object is brought into contact, which section ends in the edge, by an ab-initio shaping process, such as by die casting or pressing or injection molding (followed by well-known subsequent processing steps) if the named section is of ceramic. In such embodiments, the sheet portion may even consist of the portion that projects towards the first object and/or the section that after the process is embedded in the flow portion i.e., there is no need to have a sheet plane that is further defined by the sheet portion.

In embodiments with a perforation and with a projecting (for example deformed) section around the perforation, the deformed section may be symmetrical, i.e., may be deformed uniformly around the perforation (this includes the possibility that the deformed section has a rough edge, for example with a sawtooth-like shape). Especially, it may be symmetrical with respect to rotation around an axis perpendicular to a sheet plane through a center of the perforation.

Alternatively, it may be asymmetrical with respect to rotation around the axis in that the height (average height in case of a rough/toothed edge) of the projecting section differs as a function of the position along the edge. In such embodiments, the asymmetry may even be such that the projecting section does not extend all around the perforation but along some segment of the edge there is no such projecting section. In this case, however, the projecting section may extend around at least 180° of the periphery so as to lock the first and second objects to each other with respect to all in-plane relative forces.

The method may include the further step of manufacturing a perforation in the second object prior to the step of positioning, for example by punching, drilling, etc. Alternatively, the perforation along which the edge is formed in embodiments may be an opening that exists in the second object anyway or has been provided in a manufacturing process.

The perforation can be generated by laser cutting.

In particular when the perforation is generated by laser cutting, the sheet portion can be cut in a manner that an undercut is formed. Such an undercut can lead to a positive-fit connection between the first object and the second object which is in addition or alternatively to the positive-fit connection based on the overall shape of the second object, in particular of the sheet portion. In any case, the positive-fit connection resulting from such an undercut can increase the pull-out resistance of the first object secured to the second object by the method.

In embodiments in which the perforation includes the projecting (protruding/deformed) section that forms the edge by its distal or proximal end, the protruding section can form the portion of the overall shape of the second object that contributes to the corresponding positive-fit connection. The protruding section can then be laser cut in a manner that the undercut is formed, wherein the undercut leads to a positive-fit connection that is in addition to the positive-fit connection resulting from the overall shape of the second object.

The envisaged pull-out resistance can be realized by designing the undercut and the undercut formed by the overall shape of the sheet portion, for example of the tongues.

The use of laser cutting for manufacturing the perforation allows for the design of undercuts of various shapes. In particular, the use of laser cutting for manufacturing tongues allows for various designs that are not producible by conventional manufacturing techniques such as punching, drilling etc.

Thereby, there is no need that the designs of the tongues generate a high stability under pressure, in particular a high axial stability, due to the use of the rotational movement for generating the melting zone requiring axial pressure only to advance the tongues into the melt.

For example, one can envisage tongues that have a lateral extension that varies in dependence of the distance from the sheet plane, this means in dependence of the axial position. Thereby, a sequence including a region with a first lateral extension and a region with a second lateral extension that differs from the first lateral extension can form the undercut.

For example, the tongues can include a bridge-like connection to the portion of the second object that form the sheet plane. In this case, the undercut is formed at the bending edge where the tongues bent away from the portion of the second object that form the sheet plane.

In an embodiment, the second object provided includes a main perforation, with the edge running along the main perforation, and a plurality of peripheral perforations being distributed along a periphery of the main perforation.

Such peripheral perforations have the effects of enhancing the footprint of the connection, of providing an additional securing against rotation, and of reducing the resistance during the process by providing further flow channels.

In particular, the peripheral perforations are smaller than the main perforation.

The main perforation can be approximately round.

The sheet portion of the second object provided can have, around the main perforation, a protruding section projecting away from a sheet plane towards a contact side, wherein the peripheral perforations can be at least partially arranged in the protruding section.

In an embodiment, the first object provided, extends along a first object axis between a proximal surface of the first object and a distal surface of the first object and includes a protrusion protruding distally from the distal surface. In such an embodiment, the method includes the further step of pushing at least a portion of the protrusion into the perforation such that the edge is in contact with at least one of a portion of a surface of the protrusion that is arranged parallel to the first object axis and a portion of the distal surface of the first object.

The first object provided can have a head portion arranged proximally of the protrusion. Hence, the head portion forms the distal and proximal surface of the first object at least partly.

If the first object provided includes the protrusion and the head portion, the step of pushing at least a portion of the protrusion into the perforation can include pushing the protrusion into the perforation such that the distal surface formed by the head portion is in contact with the edge. Hence, the melting zone formed during the step of bringing the first and second object to a relative movement to each other is formed at a distal side of the head portion.

Embodiments including the step of pushing at least a portion of the protrusion into the perforation can further include the step of expanding radially the portion of the protrusion that is pushed or has been pushed into the perforation such that the radially expanded protrusion expands beyond the edge of the perforation. In other words: the protrusion is expanded such that it cannot be pulled out of the perforation after the step of expanding radially, anymore.

In particular, the radial expansion is a radial expansion with respect to the first object axis.

This means that the expanded protrusion forms a positive-fit connection in a direction parallel to the first object axis. The positive-fit connection can be a positive-fit connection in addition to the positive-fit connection formed by thermoplastic material of the melting zone that flows around the edge to at least partially embed the edge in the thermoplastic material and the edge.

The step of expanding radially the portion of the protrusion can be applied during or after the step of pushing at least a portion of the protrusion into the perforation.

The radial expansion of the protrusion can include a collapse of the protrusion.

Embodiments including the step of expanding radially the portion of the protrusion that is pushed or has been pushed into the perforation can further include at least one of:A step of spinning the first object such that flowable thermoplastic material expands radially due to centrifugal force.In the step of providing the second object, the second object includes a distal surface and the method includes the step of bringing a distal portion of the first object, in particular a distal end of the protrusion, in contact with a rear side of the distal surface and the step of deforming the distal portion of the first object.In particular, the distal surface has a mechanically stability such that the distal portion of the first object can be deformed by pressing it against the distal surface. The deformation can include making the distal portion of the first object flowable, for example by bringing the first and second object to a relative movement to each other. For example, the second object provided is a layered board, such as a sandwich panel (sandwich board), in particular a composite sandwich panel including two face sheets and a honeycomb core (sometimes called “hollow core board” or HCB).The distal surface of the second object provided and/or the distal portion of the first object provided can include an expansion element. In the case of the distal surface, the expansion element can have the shape of a tapered protrusion, for example. In the case of the distal portion, the expansion element can have the shape of a slot, for example. Hence, the protrusion can be slotted.The distal surface of the second object provided and/or the distal portion of the first object can include an energy director.One can also envisage that the protrusion penetrates the distal surface of the second object (that does not need to have the mechanically stability in this case) and the method includes the step of providing an anvil. Then, the distal portion of the first object is expanded radially by being pressed against the anvil. Anvil and/or distal portion can have an expansion element and/or an energy director as described. The anvil can further have a head forming recess in a proximal surface. The expansion element can be arranged in the head forming recess.A step of providing a tool comprising:a counterelement arranged or arrangable distally of the first object, in particular distally of the distal end of the protrusion, wherein the counterelement can be moved along the first object axis in a proximal direction by applying a pushing force to the counterelement, and comprisinga coupling-out face arrange or arrangable at the proximal surface of the first object, for example to a coupling-in face of the first object (if present), wherein a pressing force can be applied to the first object via the coupling-out face.The counterelement and the coupling-out face are arranged such that a compression force can be applied to the first object. This means that the tool is equipped to compress at least a portion of the first object during the step of bringing the first and second object to a relative movement to each other.The portion compressed is the protrusion, in particular.Expansion of the portion of the protrusion that is pushed or has been pushed into the perforation can include making the protrusion at least partly flowable, for example by bringing the first and second object to a relative movement to each other.In particular, the protrusion is made flowable at an interface between a distal end of the protrusion and the counterelement.The counterelement and/or protrusion can include an expansion element and/or an energy director as described above.Each feature of the tool provided in an embodiment of the method including the step of expanding radially the portion of the protrusion that is pushed or has been pushed into the perforation can be in addition to any other feature of a tool provided in any other embodiment of the method.

In an embodiment, the second object, in particular a region around the edge, is pretensioned in a manner that the edge penetrates into the flowable thermoplastic material that is formed during the step of bringing the first object to a relative movement to the second object.

The edge can penetrate into the flowable thermoplastic material during the step of pushing the first object into the perforation or the first object can be pushed into the perforation without generation of a melting zone in a first step followed by step of bringing the first object and the second object to a relative movement to each other such that the melting zone is formed. In other words: the first object can be pushed into the perforation during the relative movement or prior to the relative movement.

In particular, the second object includes the protruding section including the edge, wherein the protruding section protrudes in a distal direction and the first object is pushed into the perforation from a proximal direction.

The pretension can be a static pretension.

The pretension can be generated by an elastic deformation of the second object, in particular of the region around the edge.

For example, in embodiments including providing a second object with a perforation, providing a first object including a protrusion, and the step of pushing at least a portion of the protrusion into the perforation, a diameter of the protrusion can be larger than a diameter of the perforation. In such an embodiment, the step of pushing at least a portion of the protrusion into the perforation can be carried out prior to the step of bringing the first and second object to a relative movement to each other, i.e., prior to forming the melting zone. Hence, a static pretension is generated in the second object by deforming it, in particular deforming it elastically, during the step of pushing. The pretension causes the edge to penetrate into the flowable thermoplastic material formed during the step of bringing the first object to a relative movement to the second object.

In this embodiment, the method includes the steps of: (1) pushing at least a portion of the protrusion into the perforation and (2) bringing the first and second object to a relative movement to each other such that a melting zone including flowable thermoplastic material is formed, wherein the step of pushing is applied prior to the step of bringing the first and second object to a relative movement to each other.

In particular, the edge is in contact with at least a portion of the surface of the protrusion that is arranged parallel to the first object axis. Hence, the pretension is essentially along an axis perpendicular to the first object axis and/or the edge penetrates a side but not the distal end of the protrusion.

In particular, the edge is formed by the deformed section, wherein the deformed section projects distally away from a sheet plane.

The deformed section is elastically deformable or includes spring-back properties.

The first object, in particular its protrusion, can be tapered and/or include lateral grooves.

The penetration of the edge into the first object can be promoted further by at least one of:Proving a second object that includes spring-back properties around the protrusion, for example by including leaflets, flaps, wings or tongues.Providing a second object including slots, wherein the slots are arranged radially with respect to the perforation.Radial slots (slits) are preferable in combination with orbital movements, in particular.Providing a second object including a material around the protrusion at least that this elastically deformable.

Especially in embodiments including a pretension of the region around the edge—but not only in such embodiments—, the protruding section can include at least one hole in addition to the perforation. Such a hole increases the stability of the connection generated between the first and second object, in particular the stability against rotational movements along an axis parallel to the longitudinal axis of the perforation.

The first object and the connection to the second object may in embodiments be such as to seal the perforation off, i.e., to seal a region proximally of the second object from a region distally thereof. In other words: The first object can be configured to seal a proximal side of the second object from a distal side of the first or second object by sealingly closing off the perforation. To this end, the first object may for example have a continuous body extending to the periphery, which periphery embeds the edge.

In particular, the first object provided can be watertight.

In the method according to any embodiment, the first object provided can include at least one of:A body of a not liquefiable material in addition to the thermoplastic material. Such a body of not liquefiable material may constitute a reinforcer portion of the first object. In particular, the step of bringing the first and second object to a relative movement to each other is carried out such that during the step of causing the flow portion to re-solidify, the body extends through a plane defined by the edge.However, the first object can consist of thermoplastic material, in embodiments. In embodiments with a not liquefiable body, the body of the not liquefiable material is different from a mere filler of a large number of particles but is a macroscopic body with a defined position and orientation and of a substantial size. In a sheet plane defined by the second object, the size may be for example at least 10% of first object average diameter (of a cross section perpendicular to the insertion axis) or, if applicable, of a perforation average diameter, and/or a characteristic dimension may be at least 0.1 mm in any dimension. Especially, the body may be metallic or of ceramics. Especially, the body may be such as to have a defined shape and to thereby add stiffness to the first object. By the body, the first object is defined into at least two spatially separated regions, namely the body region and the thermoplastic region. In embodiments in which the first object in addition to the thermoplastic material includes not liquefiable material, the thermoplastic material may be arranged at least on surface portions that come into contact with the edge.A fixation element for fastening a further object to the first and/or second object.In particular, the fixation element can include a fastening structure. A thread, a threaded bar, a nut, an element of a plug connection, snap lock, or bayonet lock are examples of fastening structures.The first object can be the fixation element by including the fastening structure.The first object can carry the fixation element including the fastening structure. In such embodiments, the first object may be viewed as a fastener—or anchor—for the further object. In alternative embodiments, the first object may itself constitute an object having a function different from being a mere fastener, e.g., based on different physical and/or chemical properties as mentioned.

The invention moreover concerns a connector that is a first object according to any embodiment described in this text. Hence, such a connector is suitable for being used in the method according to any embodiment.

The connector:Includes thermoplastic material in a solid state at least at an attachment location.The connector is capable of being secured to a second object that has a generally flat sheet portion having an edge, by a method that includes bringing the connector to a relative movement to the second object while the attachment location and the second object are pressed against each other, until a flow portion of the thermoplastic material due to friction heat generated between the edge and the thermoplastic material becomes flowable and flows around the edge to at least partially embed the edge in the thermoplastic material, wherein the relative movement includes a rotational movement;In particular, the rotational movement is at least one of a rotational movement with a constant direction of rotation around a rotation axis, an oscillating rotational movement around a rotation axis, and an orbital movement.The connector further includes a fastening structure equipped for cooperating with a fastening structure of a further object to secure the further object to the connector and to thereby connect the further object to the second object.A thread, a threaded bar, a nut, an element of a plug connection, snap lock, or bayonet lock are examples of fastening structures.

In an embodiment, the connector includes a portion different from the attachment location, the portion being equipped to expand radially with respect to a connector axis.

In particular, the connector can include a head portion and a protrusion that is pushed through a perforation of the second object. The portion can be part of the protrusion.

Generally, the connector axis corresponds to the first object axis.

For example, the portion can include an expansion element, in particular an expansion element of the first object as described above, or it can consist of it.

Alternatively, the portion is arranged to become flowable when spun around a rotation axis, such that the portion expands due to the centrifugal force. For getting flowable, the portion can be in contact with and/or pressed against a surface of the second object at least partly.

In this text the expression “thermoplastic material being capable of being made flowable”, in particular by the relative movement or in short “liquefiable thermoplastic material” or “liquefiable material” or “thermoplastic” is used for describing a material including at least one thermoplastic component, which material becomes liquid (flowable) when heated, in particular when heated through friction i.e., when arranged at one of a pair of surfaces (contact faces) being in contact with each other and moved relative to each other.

In some situations, for example if the first object itself has to carry substantial loads, it may be advantageous if the material has an elasticity coefficient of more than 0.5 GPa. In other embodiments, the elasticity coefficient may be below this value.

Thermoplastic materials are well-known in the automotive and aviation industry. For the purpose of the method according to the present invention, especially thermoplastic materials known for applications in these industries may be used.

A thermoplastic material suitable for the method according to the invention is solid at room temperature (or at a temperature at which the method is carried out). It preferably includes a polymeric phase (especially C, P, S or Si chain based) that transforms from solid into liquid or flowable above a critical temperature range, for example by melting, and re-transforms into a solid material when again cooled below the critical temperature range, for example by crystallization, whereby the viscosity of the solid phase is several orders of magnitude (at least three orders of magnitude) higher than of the liquid phase. The thermoplastic material will generally include a polymeric component that is not cross-linked covalently or cross-linked in a manner that the cross-linking bonds open reversibly upon heating to or above a melting temperature range. The polymer material may further include a filler, e.g., fibers or particles of material which has no thermoplastic properties or has thermoplastic properties including a melting temperature range which is considerably higher than the melting temperature range of the basic polymer.

In this text, generally a “non-liquefiable” material is a material that does not liquefy at temperatures reached during the process, thus especially at temperatures at which the thermoplastic material of the first object is liquefied. This does not exclude the possibility that the non-liquefiable material would be capable of liquefying at temperatures that are not reached during the process, generally far (for example by at least 80° C.) above a liquefaction temperature of the thermoplastic material or thermoplastic materials liquefied during the process. The liquefaction temperature is the melting temperature for crystalline polymers. For amorphous thermoplastics the liquefaction temperature (also called “melting temperature” in this text) is a temperature above the glass transition temperature at which the becomes sufficiently flowable, sometimes referred to as the ‘flow temperature’ (sometimes defined as the lowest temperature at which extrusion is possible), for example the temperature at which the viscosity drops to below 104Pa*s (in embodiments, especially with polymers substantially without fiber reinforcement, to below 103Pa*s)), of the thermoplastic material.

For example, non-liquefiable material may be a metal, such as aluminium or steel, or a hard plastic, for example a reinforced or not reinforced thermosetting polymer or a reinforced or not reinforced thermoplastic with a melting temperature (and/or glass transition temperature) considerably higher than the melting temperature/glass transition temperature of the liquefiable part, for example with a melting temperature and/or glass transition temperature higher by at least 50° C. or 80° C.

Specific embodiments of thermoplastic materials are: Polyetherketone (PEEK), polyesters, such as polybutylene terephthalate (PBT) or Polyethylenterephthalat (PET), Polyetherimide, a polyamide, for example Polyamide 12, Polyamide 11, Polyamide 6, or Polyamide 66, Polymethylmethacrylate (PMMA), Polyoxymethylene, or polycarbonateurethane, a polycarbonate or a polyester carbonate, or also an acrylonitrile butadiene styrene (ABS), an Acrylester-Styrol-Acrylnitril (ASA), Styrene-acrylonitrile, polyvinyl chloride (PVC), polyethylene, polypropylene, and polystyrene, or copolymers or mixtures of these.

In embodiments in which both, the first and the second object include thermoplastic material and no welding is desired, the material pairing is chosen such that the melting temperature of the second object material is substantially higher than the melting temperature of the first object material, for example higher by at least 50°. Suitable material pairings are, for example, polycarbonate or PBT for the first object and PEEK for the second object.

In addition to the thermoplastic polymer, the thermoplastic material may also include a suitable filler, for example reinforcing fibers, such as glass and/or carbon fibers. The fibers may be short fibers. Long fibers or continuous fibers may be used especially for portions of the first and/or of the second object that are not liquefied during the process.

The fiber material (if any) may be any material known for fiber reinforcement, especially carbon, glass, Kevlar, ceramic, e.g., mullite, silicon carbide or silicon nitride, high-strength polyethylene (Dyneema), etc.

Other fillers, not having the shapes of fibers, are also possible, for example powder particles.

In this text, the terms “proximal” and “distal” are used to refer to directions and locations, namely “proximal” is the side of the bond or assembly from which an operator or machine applies the excitation capable to generate the rotational movement of the first or second object, whereas distal is the opposite side. A broadening of the connector on the proximal side in this text is called “head portion”, whereas a broadening at the distal side is the “foot portion”.

Hereinafter, embodiments of the invention are described referring to drawings. The drawings are all schematical and not to scale. In the drawings, same reference numbers refer to same or analogous elements. The drawings are used to explain the invention and embodiments thereof and are not meant to restrict the scope of the invention. Terms designating the orientation like “proximal”, “distal”, etc. are used in the same way for all embodiments and drawings.

