Patent Description:
In the automotive, aviation and other industries, there has been a tendency to move away from steel 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 an other object.

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.

<CIT> teaches a method of fastening a screw or similar fixation element to a thermoplastic body by applying high-frequency vibration to it to displace thermoplastic matter and cause it to flow in an interior cavity of the fixation element. <CIT>, <CIT>, <CIT>, <CIT>, and <CIT> teach securing a metallic body to a thermoplastic body by bringing the bodies into contact and subjecting the metallic body to mechanical vibration until thermoplastic material of the thermoplastic body liquefies, the metallic body is essentially fully enwrapped in the thermoplastic body, and thermoplastic material flows into recesses of the metallic body. All of these methods are suitable only for anchoring a metallic part in a deep thermoplastic object, and the required energy input and corresponding impact on the parts to be connected is substantial.

<CIT> teaches manufacturing an electronic device with a plastic housing part and a metallic housing part, wherein the plastic housing part is attached to the metallic housing part by an ultrasonic bond. The applications of the concept taught in <CIT> are limited.

A further concept of prior art approaches comprises shaping the thermoplastic body to comprise a flange-like protrusion into which a fastening element, such as a nut, is pressed. This concept, however, has the disadvantage of being more complex, as shaping plastic parts that otherwise may have a simple, for example sheet-like, form with a flange, which depending on the application needs to have a precisely defined position, may drastically increase the manufacturing cost.

It is an object of the present invention to provide a method of bonding two objects together comprising the features of claim <NUM>. The method is especially suited for bonding a second object to a first object of a polymer-based material. It is a further object to provide a connecting element according to claim <NUM>.

The method of bonding a second object to a first object, comprises the steps of:.

The liquefaction of the flow portion in this is primarily caused by friction between the vibrating second object and the surface of the first object, which friction heats the first object superficially.

A special property of the approach according to the present description is therefore also that the flow portion that has been generated in a contact zone between the first and second objects may immediately flow into existing cavities of the second object, and thereby the zone that is influenced by the heat generated during the process remains small, for example essentially restricted to the intermixing zone.

The flow behavior of the flow portion will be influenced by the fact that due to the approach according to the present invention, a material flow is generated towards the surface of the non-liquefiable material (i.e. the second object; convergent flow), to which surface, by the vibrations and friction, heat is continuously supplied. Thus, generally little heat will flow away. Therefore, a large penetration depth of thermoplastic material into the coupling structures becomes achievable even after a short process time, the flow not being stopped by heat loss of liquefied material coming into contact with cold spots. This is in contrast for example to the "Woodwelding" process as for example described in <CIT> where there is a divergent flow by liquefied material flowing away from the interface zone and thus transporting heat away into structures that have remained cold.

The first and second objects are construction components (construction elements) in a broad sense of the word, i.e. elements that are used in any field of mechanical engineering and construction, for example automotive engineering, aircraft construction, shipbuilding, building construction, machine construction, toy construction etc. Generally, the first and second objects will both be artificial, man-made objects, and at least the first object will comprise artificial material; the additional use of naturally grown (non-living matter) material, such as wood-based material, in the first and/or second object is not excluded.

The materials of the first object and of the second object may be homogeneous or inhomogeneous. For example, the first object may have the thermoplastic material and in addition comprise other, non-liquefiable material, and/or it may have a plurality of layers of thermoplastic material of different compositions. Similarly, the second object may comprise different portions of different materials, as explained in more detail hereinafter. Additionally or as an alternative, the second object may be caused to penetrate through a plurality of objects (the first object plus at least one further object) to secure the plurality of objects to each other, as also explained in more detail hereinbelow.

The coupling-in structure may be a coupling-in face, especially constituted by a proximal-most end face, with or without guiding structures (such as a guiding hole for an according protrusion of the tool), for a separate sonotrode that serves as the tool. The coupling-in structure may comprise a coupling that couples the second object directly to a vibration generating apparatus, which vibration generating apparatus then serves as the tool. Such a coupling may for example be by a thread or a bayonet coupling or similar. Thus, the second object may be at the same time a sonotrode coupled to a vibration generating apparatus.

The tool may be a sonotrode fastened to a vibration generating apparatus. Sonotrodes of this kind are for example known from ultrasonic welding.

The tool may be an intermediate piece (different from the first object), against which intermediate piece a sonotrode presses and which is of a material that does not liquefy under the conditions that apply during the process. Generally, the approach according to aspects of the invention excludes that the vibrations are coupled into second object only via first object; rather a physical contact between the second object and the vibrating tool is required.

The flow portion of the thermoplastic material is the portion of the thermoplastic material that during the process and due to the effect of the mechanical vibrations is caused to be liquefied and to flow.

The coupling structures of the second object are of a material that is not liquefiable. As explained in more detail hereinafter, this definition includes the possibility that the material is liquefiable at a substantially higher temperature than the material of the first object, such as a temperature higher by at least <NUM>°. In addition or as an alternative, the condition may hold that at a temperature at which the first object's thermoplastic material is flowable, the viscosity of the material of the second object is higher than the viscosity of the thermoplastic material of the first object by orders of magnitude, for example by at least a factor between <NUM><NUM> and <NUM><NUM>. In addition or as an alternative to comprising a different liquefiable matrix material with a different liquefaction temperature and/or different glass transition temperature, this can also be achieved by a higher filling grade of for example a fiber filler.

Coupling structures may include sequences of radial protrusions and indentations (such as ribs/grooves), openings open to the distal side, which openings define an undercut by being widened, at least into one lateral direction, towards a proximal side, etc. Any structure that defines an undercut with respect to axial directions is suitable.

In coupling structures that include sequences of radial protrusions and indentations (for example around an outer surface of a portion of the second object or along an interior surface of the second object), d depth of the intermixing zone may be defined as radial depth into which the flow portion penetrates starting at outermost protrusions,. Similarly, in coupling structures that comprise openings open to the distal side the depth of the intermixing zone may be defined as the depth into which the thermoplastic material penetrates starting at the distally facing surface.

Especially, the mechanical vibration transmitting parts of the second object may consist of metal and/or other hard materials (glasses, ceramics, etc.) and/or thermosetting plastics and/or thermoplastics that remain below their glass transition temperature during the entire process.

The second object may comprise a second thermoplastic material having a liquefaction temperature substantially higher than the liquefaction temperature of the first object thermoplastic material. Then, after the step of causing a flow portion of the thermoplastic material of the first object is liquefied, the second object may be pressed against a support or a non-liquefiable portion of the first object while coupling vibrations into the second object is continued (with a same or a higher or possibly even a lower intensity than initially) until a second flow portion of the second thermoplastic material is liquefied and leads to a deformation of the second object. Especially, this further method step may be carried out as described in <CIT>, until a foot portion and/or a head portion of the second object is created for bonding the first and second objects together by an additional rivet effect.

The methods described herein may comprise the second object, after the bonding process, reaching through the first object to the distal side, or alternatively, the distal side is left intact, i.e. an intermixing zone that comprises portions of the first and second objects does not reach to the distal side.

The second object may be anchored in a depth-effective manner by providing the second object with an anchoring portion that extends along the anchoring axis, optionally with structure elements that are arranged on a peripheral surface of the second object and/or along an inner surface of an axially extending portion of the second object.

Especially the penetration depth, by which the second objects penetrates into the first object, i.e. the axial extension of those parts of the second object that penetrate into the first object, may be larger (for example substantially larger) than a depth of the intermixing zone, i.e. the zone in which both, portions of the first and second object are present after the bonding process. In other words, in these methods comprising depth-effective anchoring, a width of the one part of the second object that penetrates into the first object in at least one lateral dimension, and often in both lateral dimensions, is smaller than the penetration depth by which the second object penetrates into the first object. The depth of the intermixing zone is then defined as the characteristic depth of the structure elements on the peripheral surface, i.e., a depth measured perpendicular to the anchoring axis.

The methods described herein may comprise, in addition or as an alternative to comprising depth-effective anchoring, a bonding surface with a plurality of structure elements that are spaced laterally from each other and/or possibly form an extended, for example circumferential, groove, the bonding surface following a surface portion of the first object. For example, if the first object is planar, the structure elements will extend along a plane.

According to the present enclosure the method may comprise a depth-effective anchoring, may comprise providing a bore in the first object prior to the step of pressing, and in the step of pressing, a part of the second object is pressed into the bore. In this, a bore diameter is preferably chosen to be less than an outer diameter of the part pressed into the bore. Such a bore may be a blind hole or a through bore. Also anchoring in other indentations such as grooves etc. is possible.

A through bore may also be advantageous if the second object is comparably thin, such as a thermoplastic sheets. The method of bonding a second object to the first object may then comprise lining the through bore with the second object, for example for the purpose of fastening a further object thereto, to serve as a feedthrough, serve as barrier that is crossable under pre-defined conditions only (as is the case for a septum or for a second object with a removable cover or similar) or have an other purpose. In embodiments of this special category, the thickness of the first object may correspond to <NUM>-<NUM> times or <NUM>-<NUM> times, especially between <NUM> times and <NUM> times the interpenetration depth (depth of the intermixing zone).

In accordance with the present invention, the bonding is carried out in a "planar bond" or "flattish bond" manner, with a comparably small penetration depth. This group of methods being according to the present disclosure may especially be suited also for bonding a second object to a first object that is comparably thin or that is sensitive to damages or has high requirements for leaving other surfaces than the one to which the second object is bonded intact.

The second object may comprise a plurality of structure elements for the liquefied material to flow into, which structure elements are spaced laterally from each other, i.e. extend along a plane which during the anchoring is parallel to a surface plane of the first object or, if the case may be, extend along an other, non-planar surface of the first object. Especially, the bond between the first and second object may be a planar bond, wherein the area of the interface between the first and second object is essentially parallel to the surface plane of the first object and has, at least in one dimension, preferably in both in-plane dimensions, substantially greater than the penetration depth, for example greater by at least a factor <NUM> or <NUM>, at least a factor <NUM>, or at least a factor <NUM>. In this, the penetration depth may be equal to the depth of the intermixing zone or may be smaller than the latter.

Methods according to the present disclosure that comprise bonding with a small penetration depth compared to the depth of the intermixing zone may also comprise bonding of the second object to a not planar surface portion of the first object. For example, the first object may have a certain proximally facing surface contour, and the second object may have an overall shape following this contour or may be deformable to do so.

Alternatively, the first object may have a countersunk or opening or opening provided with an other structure along its periphery, wherein the second object has an accordingly adapted (for example conical if the opening is countersunk) shape. If the first object is comparably thin and there are requirements for the distal surface, the structure elements of the second object may be adapted to the depth. Especially, the relative sizes of the structure elements may decrease towards distally, so that their capacity to accommodate flowable material decreases towards the distal side, and accordingly does the heat impact.

A design criterion may be that the volume of structure elements (such as indentations) into which the liquefied material can flow is larger than the displaced volume. This leads to a criterion for embodiments of the invention according to which along the surface parts that comprise the coupling structures the porosity is at least <NUM>% for a certain depth. The porosity here is defined as a fraction that empty spaces take up of the total volume, measured from an outer convex hull to a certain depth (corresponding to a depth of the intermixing zone, measured in axial direction). If this optional design criterion is fulfilled, no volume has to be displaced to the surface or sideways or similar.

More in general, the method may include causing the flow portion to flow into the indentations and preventing the flow portion from flowing to regions laterally of the second object.

To this end, optionally, in addition to providing an indentation volume satisfying the above condition, the method may also comprise pressing a (non-vibrating) retaining device against proximal surface of the first object in a vicinity of the second object, for example around the interface between the first and second objects. Such a retaining device may prevent bulges or the like around the location where the second object is anchored in the first object.

If "planar bond" or other "flattish bond" anchoring is used, the second object in addition to cavities (indentations) comprises a distal protruding structure that may for example serve as energy director. Especially, such distal protruding structure may have a shape with a portion that tapers towards the distal side, for example ending in a tip or edge or rounded distal end. In this case, a lateral distance between the distal protruding structure and the cavity accommodating the flow portion may be minimal. Especially, any spacing between such distal protruding structure and the cavity may be avoided, so that the overall shape of the second object at the distal surface is undulated between the distal protrusion and cavity.

The coupling structures that comprise an undercut with respect to axial (proximodistal) directions and thereby make a positive-fit connection possible, are pre-manufactured properties of the second object.

In addition or as an alternative, the second object may comprise a deformable portion, and the method may comprise making a structure for a positive-fit connection during the process of pressing the second object against the first object while mechanical vibrations are coupled into the second object.

For example, the second object may comprise a plurality of deformable legs or a deformable collar extending in a substantially axial direction as a deformable structure. During the process, the deformable structure is bent away from the axial direction so that after re-solidification an undercut is formed.

Methods described herein using this principle of deformation may feature the advantage that the effective anchoring area may, due to the deformation, be larger than the surface area portion of the first object penetrated by the second object, i.e. the footprint may be enlarged compared to a method without the deformation.

A further possible advantage is that for example a lightweight deformable material may be used for the deformable portion. Especially, a material may be used that is deformable at the temperature at which the process takes place but that exhibits substantial stiffness at room temperature (or, more generally, the temperature at which the assembly will be used). For example, the deformable portion may be of a thermoplastic material with a glass transition temperature that is substantially higher than the glass transition temperature of the first object thermoplastic material of which the flow portion is formed.

In a specific method of this principle, PBT (Polybutylene terephthalate) was used as the first object thermoplastic material, which material becomes flowable at temperatures of about <NUM>, and PEEK was used as a material of the second object's portion that comprises the deformable portion. PEEK is not liquid/flowable at <NUM> but is above its glass transition temperature (being about <NUM>).

More in general, if the deformable portion comprises a thermoplastic material, it may be advantageous if the glass transition temperature of the deformable portion is between the glass transition temperature of the first object thermoplastic material and the temperature at which the thermoplastic material becomes sufficiently flowable.

In this text, the liquefaction temperature or the temperature at which a thermoplastic material becomes flowable is assumed to be the melting temperature for crystalline polymers, and for amorphous thermoplastics 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 <NUM><NUM> Pa*s (especially with polymers substantially without fiber reinforcement, to below <NUM><NUM> Pa*s).

For applying a counter force to the pressing force, the first object may be placed against a support, for example a non-vibrating support. According to a first option, such a support may comprise a supporting surface vis-à-vis the spot against which the first object is pressed, i.e. distally of this spot. This first option may be advantageous because the bonding can be carried out even if the first object by itself does not have sufficient stability to withstand the pressing force without substantial deformation or even defects.

If the method described herein comprises deforming the second object during the process of pressing the second object against the first object, the support may comprise a shaping feature that assists the deformation process. For example, the support may be shaped to have a shaping protrusion or shaping indentation, to cause an outward bending or inward bending of the deformable structure, respectively.

It is further possible that the method uses a cooling effect by the support on the thermoplastic material of the first object, whereby the thermoplastic material of the first object is kept at a cooler temperature and thus remains harder at an interface to the support. Thereby, the deformable structure will be caused to deform such as not to get too close to the interface with the support.

According to a second option, the distal side of the first object may be exposed, for example by the first object being held along the lateral sides or similar. This second option features the advantage that the distal surface will not be loaded and will remain unaffected if the second object does not reach to the distal side.

The first object may be placed against a support with no elastic or yielding elements between the support and the first object, so that the support rigidly supports the first object.

The second object may comprise an inner portion and an outer portion, with a gap therebetween. Then, the coupling structures of the second object may include outer structures of the inner portion and/or inner structures of the outer portion and/or outer structures of the outer portion, and the step of causing a flow of the flow portion comprises causing a flow into the gap.

According to an option, inner and outer portions may together be of one piece.

The second object may comprise a first portion of a first material and a second portion of a second material. This group of embodiments for example may make possible to save cost if the first portion comprises critical sections, such as a thread or other structure for connecting a further element to the assembly of the first and second objects, is made of a high-quality building material, for example stainless steel, titanium, aluminum, copper, etc., whereas the second portion may comprise a lower cost material and primarily serve for stabilization of the second object with respect to the first object.

Especially, if the second object comprises an inner portion and an outer portion, the inner portion may be of the first material and the outer portion may be of the second material. Thereby, by the flow of the flow portion into the gap, the second object itself is also stabilized, in addition to being bonded to the first object.

Methods according to the present disclosure that comprise a first portion of a first material and a second portion of a second material may for example comprise embodiments of the above-discussed group that comprise a deformable portion. In these, the deformable portion may for example belong to the second portion of a second material, and mounting structure for mounting a further object to the first object or for another function may be of another, not deformable material, such as of a hard metal.

An further advantage of methods according to the present disclosure with a first and a second material (in addition to optionally comprising a deformable portion, with the above-discussed advantages) is that they provide the possibility of using a lightweight and/or low cost material for those parts of the second object that use up a lot of space (for example to yield a sufficiently large footprint in the above sense) while maintaining the possibility of having a sufficiently stable/stiff functional piece, for example with a thread or other functional structure, constituted by the first portion.

If the second material is itself capable of being deformed and possibly capable of flowing, at temperatures above the liquefaction temperature of the first object material, this approach may feature the even further advantage that the first and second portions may optionally be assembled in situ if they are initially not connected with each other or only loosely connected. For example, the second material may flow relative to the first material to embed a part of the first portion, for example in a positive-fit like manner.

The second object may constitute a mounting piece (mounting pillar, mounting plug, etc.) for mounting a further object to the first object. Especially, an inner portion of the above-described kind may comprise a mounting structure, such as a thread or bayonet fitting structure or guide bushing or snap-on structure, etc. The outer portion may serve as a fastening flange for fastening the mounting structure. Compared to prior art fastening flanges, this approach has substantial advantages:.

The second object may comprise a proximal body and, distally thereof, a plurality of distal extensions that in the step of pressing are pressed into the first object. Especially, the distal extensions may comprise at least one outer extension and at least one inner extension.

For example, the proximal body may comprise a portion in the above-mentioned sense of a second material, and, embedded therein, a portion of a first material, which portion of the first material is accessible from the proximal side also after the step of letting the thermoplastic material re-solidify, and which may have the mounting structure. The portion of the first material may extend distally to form at least one of the distal extensions (such as a central protrusion) or may be restricted to the proximal side.

The first object may be a flattish object, such as a polymer plate, for example a polymer cover.

The bond between the second object and the first object may have any purpose of a bond between two objects. For example, in the automotive or aviation industries, the bond may be a bond between a structural element of plastic (first object) and a metallic or compound material structural element.

The second object may be an anchor in the first object for fastening a further element thereto.

The second object may be a connector that bonds a further, third object to the first object by the method described herein. These methods thus concern:
A method of connecting a third object to a first object by bonding a second object to the first object and thereby securing the third object to the first object, the method comprising the steps of:.

Especially, in the step of arranging the third object relative to the first object, the third object may be placed proximally of the first object, and after the step of arranging, the second object may be caused to penetrate the third object until a distal portion thereof reaches the first object for the second object to be pressed against the first object.

For example, to this end, the third object may be of a liquefiable thermoplastic material or otherwise penetrable material for the second object to penetrate through the third object until its distal portion reaches the first object.

Then, it is further possible to arrange the coupling structure of the second object in a manner that a positive-fit connection is also caused with the third object, in addition to the connection with the first object.

In addition or as an alternative, the third object may comprise a bore through which the distal portion of the third object is guided to reach the first object.

For securing the third object to the first object, the second object may comprise a head or bridge portion that rests against a proximally facing surface portion of the third object while the distal portion of the second object is anchored in the first object.

In addition or as an alternative, if the third object comprises thermoplastic material, a positive-fit connection between the second and third objects may be caused by material of the third object penetrating into structures of the second object, in addition to material of the first object interpenetrating the coupling structures.

In addition or as yet another alternative, thermoplastic material of the third object may be caused to be welded to thermoplastic material of the first object by the effect of the second object being pressed into the assembly of the third and first objects or may be caused to interpenetrate flowable material of the first object in a non-mixing manner to yield a mechanical and/or adhesive connection after the re-solidification.

It is even an option that material of the third object that is bonded to the first object comprises an elastomeric material or other material, even if such material is not liquefiable, and even if no pre-manufactured opening is present. Especially, a cutting portion of the second object may pierce through a portion of the third object until it comes into contact with the first object placed distally thereof.

In this way (bonding of not meltable or meltable soft material to a thermoplastic first object), connections between hard and soft materials become possible, that for example cannot be processed together in hard/soft injection molding. An example would be the bonding of a damping cushion (third object) to a thermoplastic first object, such as a thermoplastic sheet.

The second object may comprise, at the surface that during the pressing and vibrating is in direct contact with the first object, structures serving as energy directors, such as edges or tips. While for ultrasonic welding and also for the "Woodwelding" process as for example described in <CIT> or <CIT>, energy directors are known, they will generally be present on the object of the material to be liquefied. Embodiments of the present invention, however, reverse this by providing energy directors on material that is not liquefied but is interpenetrated by liquefied material.

The invention also concerns a connecting element for being secured, in a method as described in this text, to a first object that comprises a thermoplastic material. More in particular, any properties of second objects that are described and/or claimed referring to the method may be properties of the connecting element and vice versa.

In this text the expression "thermoplastic material being capable of being made flowable e.g. by mechanical vibration" or in short "liquefiable thermoplastic material" or "liquefiable material" or "thermoplastic" is used for describing a material comprising 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 vibrationally moved relative to each other, wherein the frequency of the vibration has the properties discussed hereinbefore. 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 <NUM> GPa. Alternatively, the elasticity coefficient may be below this value, as the vibration conducting properties of the first object thermoplastic material do not play a role in the process since the mechanical vibrations are transferred directly to the second object by the tool.

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 comprises 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 comprise 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 comprise a filler, e.g. fibres 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 <NUM>) 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 <NUM><NUM> Pa*s (especially with polymers substantially without fiber reinforcement, to below <NUM><NUM> Pa*s)), of the thermoplastic material.

For example, the non-liquefiable material may be a metal, such as aluminum or steel, or wood, 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 <NUM> or <NUM>.

Thermoplastic materials may be: Polyetherketone (PEEK), polyesters, such as polybutylene terephthalate (PBT) or Polyethylenterephthalat (PET), Polyetherimide, a polyamide, for example Polyamide <NUM>, Polyamide <NUM>, Polyamide <NUM>, or Polyamide <NUM>, 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, polyethylene, polypropylene, and polystyrene, or copolymers or mixtures of these.

In methods according to the present disclosure in which both, the first and the second object comprise thermoplastic material, 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 <NUM>°. 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 comprise 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.

Mechanical vibration or oscillation suitable for the method according to the invention has preferably a frequency between <NUM> and <NUM> (even more preferably between <NUM> and <NUM>, or between <NUM> and <NUM>) and a vibration energy of <NUM> to <NUM> W per square millimeter of active surface. The vibrating tool (e.g. sonotrode) is e.g. designed such that its contact face oscillates predominantly in the direction of the tool axis (longitudinal vibration) and with an amplitude of between <NUM> and <NUM>, preferably around <NUM> to <NUM>. Such preferred vibrations are e.g. produced by ultrasonic devices as e.g. known from ultrasonic welding.

In this text, the terms "proximal" and "distal" are used to refer to directions and locations, namely "proximal" is the side of the bond from which an operator or machine applies the mechanical vibrations, 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". The "axis" is the proximodistal anchoring axis along which the pressure in the step of pressing is applied. The mechanical vibrations may be longitudinal vibrations with respect to the axis.

In the following, ways to carry out the invention are described referring to drawings. The drawings are schematical. In the drawings, same reference numerals refer to same or analogous elements. The drawings, unless otherwise specified, show views of cross sections along a plane parallel to the anchoring axis ("vertical" cross sections). The drawings show:.

<FIG> depicts a basic set-up. The first object <NUM> consists of a thermoplastic material, for example of polybutylene terephthalate (PBT), compact or foamed, or polycarbonate or Acrylonitrile butadiene styrene or any other thermoplastic polymer that is solid at room temperature and for example has a melting temperature of less than <NUM>.

The second object is for example metallic or of plastic (thermosetting or thermoplastic). If the second object is liquefiable, the liquefaction temperature is such that it is not flowable at temperatures at which the first thermoplastic is flowable. For example, the melting temperature of the second object material is higher than the melting temperature of the first material by at least <NUM>° o rat least <NUM>.

The second object has a structure capable of making a positive-fit connection with material of the first object after the latter has flown. More in particular, the second object has a surface portion that has an undercut with respect to axial directions (axis <NUM>). For example, the surface structure comprises at least one rib <NUM> running in a non-axial direction or at least one hump. In the depicted embodiment the second object is assumed to be rotationally symmetrical about the axis <NUM> and comprises a plurality of circumferential ribs <NUM> between which grooves <NUM> are formed.

At the distal end, the second object has a tip <NUM>, and at the proximal end, a head portion <NUM> forms a proximally facing coupling face for the mechanical vibrations.

A sonotrode <NUM> is used to press the second object against the first object while mechanical vibrations are coupled into the second object. As shown in <FIG>, liquefaction of material of the first object sets in starting at the interface to the tip <NUM>. The continued pressing of the second object into the first object will cause the second object to be moved relative to the first object in the direction of the block arrows. A flow <NUM> of liquefied thermoplastic material of the first object sets in.

<FIG> shows the configuration towards the end of the process. Because the first object will only be liquefied in a vicinity of the surface of the second object but will remain solid and thus exhibit some stiffness elsewhere, the liquefied material cannot evade arbitrarily, the pressing of the second object into the first object will generate some hydrostatic pressure on the first object, and this will cause the flow <NUM> to immediately fill the undercut structures, such as the grooves <NUM>.

After the vibrations have stopped, the liquefied thermoplastic material will again solidify, leaving the second object solidly anchored in the first object (<FIG>).

<FIG> also illustrates the penetration depth dp and the depth di of the intermixing zone (interpenetration depth) which latter is the depth into which the flow portion penetrates starting at outermost surface features of the second object, here the depth di of the intermixing zone corresponds to the depth of the grooves <NUM>. As can be seen in <FIG>, in these embodiments being not according to the claimed invention with depth-effective anchoring, the penetration depth is substantially larger than the depth of the intermixing zone.

<FIG> also shows the width w of the portion of the second object that penetrates into the first object. Clearly, the width is smaller than the penetration depth, as is a further possible characteristic of depth-effective anchoring.

The second object in this and other embodiments described in this text may have the function of serving as a connector, (nut, threaded bolt, etc.) feedthrough, bushing, other connector etc..

In <FIG>, it is assumed that the second object <NUM> is pushed through a surface of the first object <NUM> (similar considerations apply if on top of the first object, a further, third object is placed, as discussed in more detail hereinafter, for example referring to <FIG>; <FIG>). During the process, a volume corresponding to the volume of an anchoring portion of the second object (here: the shaft, i.e. the second object without the head portion <NUM>) is displaced, for example to proximal directions and/or the introduction of the second object causes a slight deformation of the whole first object.

it is and option to provide the first object with a bore <NUM> prior to the step of pressing the second object against the first object. This is, again schematically, illustrated in <FIG>.

For the diameter dh of the bore, the following considerations may apply (not only for shapes like the one shown in <FIG> but generally for a part of the second object that during the process is pressed into a bore):.

The distal tip <NUM> or edge as well as edges of the ribs or other protruding features of the coupling structure may serve as energy directors for the liquefaction of the thermoplastic material.

The embodiments according to the claimed invention described herein show a sonotrode <NUM> (or 'horn') as a separate piece that is pressed against the proximally facing coupling face of the second object.

However, especially in embodiments being not according to the claimed invention in which the second object is metallic, the second object may be a sonotrode directly coupled to a vibration generating apparatus. It may for example be provided with a proximal thread or bayonet-coupling structure or similar for being fastened to an according coupling of the vibration generating apparatus.

While the embodiments of <FIG> (being not according to the claimed invention) are assumed to have a rotational symmetry about the axis <NUM>, this is not a requirement. Rather, it may even be advantageous to provide especially the anchoring portion with a structure that deviates from a circular symmetry, as discussed hereinbelow.

<FIG> yet show an embodiment being not according to the claimed invention in which the second object <NUM> has an inner portion <NUM> and an outer portion <NUM>, with a gap <NUM> therebetween. The coupling structures are defined along an outer surface of the inner portion and/or an inner surface of the outer portion and/or an outer surface of the outer portion. In the depicted embodiment, the couplings structures (circumferentially running ribs that define grooves between them) are present only along an outer surface of the inner portion.

When the second object is pressed into the first object while thermoplastic material of the first object is liquefied, portions of the liquefied material flow into the gap (flow <NUM> in <FIG>). In addition to anchoring the second object in the first object, this material will, after completion of the process, also stabilize the inner portion and the outer portion with respect to each other.

While the first and second portions <NUM>, <NUM> in the embodiment of <FIG> are shown to be pre-assembled, generally in embodiments with two portions that are not of one piece, the portions may be assembled in-situ, for example by material of the first object connecting the portions and/or material of the second portion that has become deformable during the process or by other features.

In <FIG>, the portions are assembled prior to being anchored, and the flow portion fills the gap <NUM> between them, with the effect of yielding an additional bonding stability between the portions <NUM>, <NUM>.

For a gap between an inner portion <NUM> and an outer portion <NUM>, a minimal width of <NUM> should be present in order for the thermoplastic material to be capable to flow into.

<FIG> depicts, in a view, an embodiment being not according to the claimed invention in which the second object has a metallic inner portion <NUM>, for example of steel, and an outer portion <NUM> of a plastic, for example of PEEK. The embodiment of <FIG> has the following features that can be present together but that can also be realized individually or in combinations.

The embodiment of <FIG> is an example of an embodiment in which the second object forms a proximal body (or head portion) <NUM>, with distal protrusions extending therefrom. The distal protrusions in the depicted embodiment are formed by leg-like extensions <NUM> (outer protrusions) and the distal part of the first portion <NUM> (inner protrusion); configurations with a circumferentially running, for example skirt-like outer protrusions are possible also.

In the hereinbefore described embodiments, the second object is anchored in a depth-effective manner by providing the second object with an anchoring portion that extends along the anchoring axis, and in some embodiments with the aid of a bore in the first object. These embodiments may have a plurality of structure elements (the grooves <NUM> for example) into which liquefied material of the first object may flow, which structure elements are spaced axially from each other, such as arranged along a shaft and/or tube or similar.

In the variant of <FIG> being not according to the claimed invention, the metallic inner portion <NUM> is pre-assembled with the plastic outer portion <NUM>. To add stability to this pre-assembly, the structures <NUM> of the inner portion <NUM> extend proximally into the region of the proximal body <NUM> and are cast into material of the outer portion <NUM>.

After the process of bonding the second object <NUM> to the first object <NUM>, the effective height h of the proximal body <NUM> is higher than its initial physical axial extension, because the flow portion of the thermoplastic material has filled the gap <NUM> between the inner and outer portions (backflow) (<FIG>). A certain backflow will also take place into the central opening of the inner portion <NUM> if such central opening, as illustrated, is open to the distal side. If such backflow is to be prevented, the opening may be closed off distally, for example by a tip-shaped end element.

The situation after the process as shown in <FIG> illustrates nicely how the outer portion <NUM> serves as mounting piece for a further object, with the outer portion <NUM> replacing a prior art mounting flange, wherein the outer portion can be of a lightweight, low-cost material and still add substantial mechanical stability to the connection, especially with respect to angular momenta on an object fastened to the inner portion <NUM> (thread <NUM>).

If necessary, additional stability with respect to axial forces may be provided if the outer portion is provided with inner structures (grooves or similar) that are embedded by the flow portion of the thermoplastic material to yield an other positive-fit connection.

In the configuration depicted in <FIG>, the distal ends of the inner portion <NUM> and of the protrusions <NUM> of the outer portion <NUM> are depicted to extend to an approximately same axial depth (the bottom line is illustrated to be at equal height). This is not a requirement. Rather, the axial extensions of the inner protrusion formed by the inner portion <NUM> and of the outer protrusion/outer protrusions may generally be chosen independently of each other, depending on requirements. For example, the inner portion <NUM> may extend further than the outer portion's protrusion(s) <NUM>, or it may extend less far than the latter.

It may in special embodiments extend to not even reach the plane defined by the proximal surface in the assembled state (<FIG>, the plane reaching the bottom of arrow h) so that it is not pressed into the first object but is only embedded in flowable thermoplastic material that has flown towards proximally due to the pressing force (backflow of the flow portion).

<FIG> yet shows a variant being not according to the claimed invention in which the first (inner) portion <NUM> does not reach to the distal end of the second object. Rather, the second portion <NUM> of the plastic material comprises both, at least one distal protrusion <NUM> and at least one inner (central) distal protrusion <NUM>. As in the previous embodiments, the second object may be circularly symmetrical with respect to rotations around the axis <NUM> or may have discrete distal protrusions (such as shown in <FIG>).

The embodiment of <FIG> being according to the claimed invention, in contrast, is suitable for anchoring the second object with respect to the first object also if the first object is flat. To this end, the second object comprises a plurality of structure elements for the liquefied material to flow into, which structure elements are spaced laterally from each other, i.e. extend along a plane which during the anchoring is parallel to a surface plane of the first object. At least some of the structures elements define an undercut.

More in particular, in the embodiment of <FIG>, the second object comprises a plurality of indentations <NUM> that in cross section have the shapes of circular segments with a central angle of more than <NUM>° so that an undercut is generated. The indentations <NUM> may extend as grooves along the plane perpendicular to the drawing plane, or they may be present in other shapes and configurations.

As illustrated in <FIG>, the step of pressing and coupling vibrations into the tool will cause liquefaction to set in superficially at the interface between the first and second objects, whereafter liquefied thermoplastic material will flow into the indentations and thereby, due to the undercut, fasten the second object to the first object after re-solidification.

Yet an other optional feature of this embodiment and of other embodiments of the invention is schematically illustrated in <FIG>. When the second object is pressed against the first object, a counter force has to act on the first object. In many embodiments, this counter force will be exerted by a non-vibrating support on which the second object is placed, such as by a working table or floor or dedicated support. Such a non-vibrating support will in many cases be arranged such that the portion of the first object that is immediately underneath the second object (more in general, the portion of the first object that extends distally from the interface between the first and second objects) is supported. However, this need not be the case. In <FIG>, the support structure <NUM> is such that immediately underneath the second object there is no support for the first object, i.e. the distal side of the first object is exposed. This may be advantageous in situations where the distal surface of the first object has a well-defined shape or other properties that must not be affected by the bonding process.

The feature of having the distal surface of the first object distally of the interface to the second object exposed is independent of the other features described referring to <FIG>, i.e. it may be implemented also in other embodiments, and the embodiment of <FIG> may also be carried out in an arrangement in which the distal surface is supported.

In the embodiment of <FIG>, being an example of a planar bond, the depth di of the intermixing zone is larger than the penetration depth dp by which the second object penetrates into the first object. This nicely illustrates the fact that these embodiments are, among others, especially suited for bonding a second object to a flattish first object or other object on which depth-effective anchoring is not possible. Nevertheless, also these embodiments do not feature the hereinbefore discussed disadvantages of adhesive bonds.

The width w of the bond/of the intermixing zone in embodiments of a planar bond in at least one lateral dimension and often in both lateral dimensions is substantially larger than the penetration depth, this being a further possible characteristic of planar bonds.

With respect to <FIG> yet a combined bonding process is described being not according to the claimed invention. The second object <NUM> is assumed to have a shape similar to the one described referring to <FIG> with an anchoring portion comprising a plurality of protrusions and indentations between the protrusions. The second object comprises a thermoplastic material with a liquefaction temperature substantially higher than a liquefaction temperature of the first object. For example, the second object may be made of PEEK, while the first object is made of PBT or Polycarbonate.

The first object comprises a through bore <NUM> in which the second object is anchored.

To this end, in a first stage, illustrated in <FIG>, the second object is pressed against the first object while mechanical vibrations are coupled into it, until liquefaction of thermoplastic material of the first object sets in, so that the second object is advanced towards the distal directions, while a flow <NUM> of thermoplastic material of the first object into the indentations <NUM> of the second element takes place.

The support <NUM> against which the first object is placed in this embodiment comprises a mould portion that forms a cavity <NUM> when the first object abuts against the support. The second object is provided with an excess length so that at some stage of the process, before a distally facing stop face of the head portion <NUM> abuts against the first object, the distal end of the anchoring portion abuts against the support <NUM>. Thereafter, the pressing force and the mechanical vibrations are further applied and possibly intensified until also thermoplastic material of the second object <NUM> becomes flowable (flow <NUM> in <FIG>) and fills the cavity. This will result in the second object being bonded to the first object by an additional rivet effect (<FIG>) by way of the head portion <NUM> and a foot portion <NUM>.

The fact that thermoplastic material of the first object has flown into structures of the second object in addition to contributing to the anchoring also causes a sealing effect.

While in the embodiment of <FIG> and in other embodiments, the first and second objects are both assumed to be essentially homogeneous, this need not be the case. Rather, the first and/or second object may be a hybrid comprising portions of different materials. For illustration purposes, <FIG> depicts an embodiment being not according to the claimed invention in which a second object <NUM>, for example to be bonded to a first object in a process as illustrated referring to <FIG>, comprises a metal portion <NUM> and a distal plastic portion <NUM>, for example of PEEK.

In the variant shown in <FIG> being not according to the claimed invention, the distal plastic portion <NUM> is a sheath element connected to the metal portion <NUM> in a positive-fit like manner. <FIG> illustrates the situation after the process, with a deformed part of the plastic portion <NUM> forming the foot portion <NUM>, as illustrated hereinbefore.

Embodiments of the combined bonding process with the additional rivet effect are also especially suited for bonding a further object to the first object, with the rivet-like connector constituted by the second object securing the first and further objects to each other, as explained referring to other embodiments in more detail hereinafter.

<FIG> yet illustrates that a hybrid second object <NUM> with a metallic portion <NUM> and a plastic portion <NUM> may also be suitable as a connector in processes of the kind described hereinbefore, for example referring to <FIG>.

<FIG> shows a further embodiment of a second object <NUM> being not according to the claimed invention. Similarly to the two-piece embodiment of <FIG>, it comprises an inner part <NUM> and an outer part <NUM> between which the thermoplastic material of the first object may flow. More in particular, the inner part <NUM> is shaft-like with outer structures <NUM>, <NUM> that form an undercut with respect to axial directions. In addition or as an alternative, the outer part <NUM> has inwardly facing structures, such as the depicted groove <NUM> forming an undercut.

In the depicted embodiment, the second object is of one piece forming the inner and outer parts <NUM>, <NUM>. The gap <NUM> in embodiments like 4a, 4b, <NUM>, <NUM> and others may be viewed as opening open to the distal side encompassing the central protrusion <NUM>.

Compared to embodiments with just one pin-shaped shaft, the embodiments with an inner portion and an outer portion due to the interplay between the inner and outer portions bring about additional anchoring stability, especially if the thermoplastic material of the first object is comparably soft or thin or brittle.

In the embodiment of <FIG> being not according to the claimed invention, the second object <NUM> comprises a body <NUM> of for example solid metallic material, and an interpenetration piece <NUM> of an open porous material, such as metal foam or a metal mesh. The interpenetration piece is fastened to the solid metallic material. The body <NUM> forms at least part of the proximally facing coupling-in face, and the interpenetration piece <NUM> forms at least a part of the surface portion that is brought into contact with the first object. Due to the effect of the mechanical vibration and the pressing force, the thermoplastic material penetrates into the interpenetration piece and that due to its open porous structure forms undercuts and thus forms the coupling structures.

The embodiment of <FIG> being not according to the claimed invention is an example of an embodiment with an inwardly facing coupling structure. More in particular, the second object <NUM> has an undercut indentation <NUM> into which the thermoplastic material penetrates. An outer distal tip or edge <NUM> serves as energy director. Due to an outward bend of the distal edge <NUM>, the outer surface <NUM> of the second object also forms a coupling structure with an undercut with respect to axial directions. The embodiment of <FIG> is an example of the principle described referring to <FIG> with the depth of the intermixing zone exceeding the penetration depth being applied to an element for a point connection instead of a flattish connection.

<FIG> shows an alternative embodiment being according to the claimed invention of a flattish connection with the depth of the intermixing zone exceeding the penetration depth. The embodiment is an example of an embodiment that is optimized for a flattish connection to a first object in which the impact of the connection is to be minimized, for example because surface portions to which the second object <NUM> is not directly attached (distal surface portions and/or proximally facing surface portions around the second object) need to maintain a certain quality. The bonding principle, like in <FIG>, is based on undercut indentations <NUM>. The following measures are implemented in the embodiment of <FIG>:.

In the embodiment of <FIG>, the shown structures may extend cylindrically perpendicularly to the drawing plane. Alternatively, the indentations or the protrusions may be circular or have an other shape confined in both lateral dimensions, and be arranged in a pattern over the surface. For example, the second object may have a regular arrangement of dome shaped (especially spherical dome shaped) indentations, each surrounded by a ridge shaped protrusion. Or the mountain-like protrusions could form a pattern, with groove-like indentations between them. Also segmented and other arrangements are possible.

<FIG> also illustrates that by the depth of the intermixing zone being greater than the penetration depth, in the region of the bond to the second object, an effective thickness deff is enhanced compared to the real, physical thickness d of the object.

In the embodiment of <FIG>, due to the tip or edge shaped protrusions, a relatively large depth is required for the anchoring. In alternative configurations a compromise between the energy directing effect of edges or tips and the requirement of smaller depth can be made, for example by using rounded protrusions <NUM> as sketched in <FIG>.

Also other cross sectional shapes may be feasible, including more edgy shapes as illustrated in <FIG>Such shapes may, depending on the chosen manufacturing method, be easier to manufacture by methods such as cutting or milling. More generally, manufacturing of the first object may include material removing methods as well as casting methods,.

In contrast for example to second objects <NUM> of the kind illustrated in <FIG>, the energy impact and required pressure are higher for second objects as shown in <FIG> or also in <FIG>with a generally flat distal end face <NUM>. Objects of this kind are especially suited for anchoring in very thin first object (such as organo sheet material). The bond is optimized for maximum strength per penetration depth, whereas generally the impact of the bonding process of the first object is higher than in the embodiments of <FIG> and others.

In the hereinbefore described embodiments, the coupling structures that comprise an undercut with respect to axial (proximodistal) directions and thereby make a positive-fit connection possible are pre-manufactured properties of the second object.

Hereinafter, embodiments where this form lock structure is formed during the process by deformation are described.

<FIG> depicts a basic embodiment of this principle being not according to the claimed invention. The second object <NUM> comprises a main portion <NUM> and a plurality of deformable legs extending distally of the main portion <NUM>. The material of the second object may be such that plastic deformation of the legs and/or elastic deformation of the legs is possible. In embodiments, the second object is made of a metal, with the legs being sheet portions of a thickness sufficiently thin to make deformation under the conditions that apply during the bonding process possible. Alternatively, the second object may be of a polymer-based material with an appropriately chosen content of a reinforcement, or of any other suitable material or agglomerate.

<FIG> depicts the second object <NUM> anchored in the first object <NUM>. The legs <NUM> upon insertion under the impact of the mechanical energy and pressing force are deformed to be spread outwardly, thereby after re-solidification yielding the coupling structures.

<FIG> shows an embodiment being not according to the claimed invention that combines the principles of the embodiments of <FIG>/b and 17a/b. In addition to comprising an outer portion <NUM> with a deformable portion <NUM> (deformable leg or other deformable structure), the second object also comprises an inner portion that in the shown embodiment is not deformable.

<FIG> also illustrates two further principles that are applicable independent of the configuration of <FIG>.

Firstly, the method in embodiments further comprises pressing a retaining device <NUM> against the proximal face of the first object in a vicinity of the second object while the second object is bonded to the first object (in <FIG> the retaining device is shown on the left-hand side only, but it may also fully surround the second object). By this, bulges or the like caused by pressing the second object into the first object (c. <FIG>) are avoided.

Secondly, similarly to the embodiments of <FIG>, <FIG> and others, the process may be carried out to cause a backflow of material into the interior space of the second object, here the space between the inner and outer portions. Thereby, the proximal-most portions of the thermoplastic material that has flown during the process is proximally of the initial proximal end face. This backflow, as described hereinbefore, enhances the effective anchoring depth. In embodiments, a retaining device <NUM> of the described kind may assist the process in that a pressure is maintained around the second object, and the backflow is caused to be within the interior space/cavity instead of around it. The quantity Δh shown in the figure shows the difference by which the material has flown inside relative to the proximal end face around the second object, and this quantity Δh may also correspond to the enhanced effective anchoring depths.

<FIG> shows an example of an embodiment being not according to the claimed invention in which the support <NUM> against which the assembly of the first and second objects are pressed by the sonotrode <NUM>, has a shaping feature that assists the deformation of the deformable portion of the second object <NUM>. More in particular, in the embodiment shown in <FIG>, the support <NUM> has a shaping protrusion cooperating with a corresponding indentation of the first object <NUM>. The shaping protrusion is of a material that is not liquefiable and does not soften during the process. Also, possibly the support including the protrusion <NUM> or other shaping feature may have a cooling effect, for example by being actively cooled, so that the first object material remains hard at the interface to it. Thereby, the deformable section is guided in the deformation process, to project away from the shaping feature, as shown in <FIG>. More in particular, the deformable legs that constitute the deformable section are caused to be bent outwardly away from the shaping protrusion <NUM>.

<FIG> shows an alternative embodiment being not according to the claimed invention where the shaping feature comprises a shaping indentation <NUM>, so that the deformable legs are caused to be bent inwardly into the configuration shown in <FIG>. Various other alternatives are possible.

Generally, the second object may have the purpose of serving as an anchor for a further object to be attached to the first object, or may itself be such a second object (in the above figures, the first object are illustrated without any functional structures for such purpose, however, any such structures such as fastening structures or other functional structures are possible.

Hereinafter, embodiments in which a further object ("third object") is bonded to the first object in the bonding process by bonding the second object to it, are described.

<FIG> depicts a basic configuration being not according to the claimed invention. The second object <NUM> - serving as a connector in the embodiments in which the first object is bonded to a further, third object - is depicted to be similar to the connector of <FIG> without a head portion. Alternatively, other shapes of second objects are possible; especially all objects described in this text suitable for depth-effective anchoring, including second objects with a head portion, may be used. The third object <NUM> is shown as thermoplastic body, similar to the first object <NUM>. It lies against the proximal face of the first object <NUM>. For bonding, the second object <NUM> is driven both, through the third object <NUM> and the first object to be anchored in both, the first and third objects, as illustrated in <FIG>.

The third object may comprise a thermoplastic material capable of being welded to the thermoplastic material of the first object <NUM>. For example, it may be of a thermoplastic material with a same polymer matrix. In a region around the second object, due to the liquefaction caused in the process a weld may be caused, as indicated by the circles <NUM>. More in general, material of the third object in the process is pressed into the first object to contribute to the connection after re-solidification. This also holds if the materials of the first and third objects cannot be welded because they do not mix in the liquid state.

In addition or as an alternative to being driven through material of the third object, the second object (connector) may also be driven through a pre-made opening of the third object for its distal portion to be anchored in the first object. Such a pre-made opening may have a diameter allowing the second object to reach through it substantially without resistance (see an embodiment described hereinafter) or may encounter substantial resistance so that mechanical energy is absorbed also there.

<FIG> shows a variant of a second object <NUM> being not according to the claimed invention. This variant is distinct from the previously described embodiments in that it has a compressing structure caused by a distally facing concave portion <NUM>. This portion will cause thermoplastic material of the third object <NUM> to be pressed into the first object <NUM> yielding a more pronounced intermixing and, if applicable, weld, between the materials of the third and first objects.

<FIG> shows a further example of a second object <NUM> being not according to the claimed invention suitable as a connector in the described sense. Especially, the second object <NUM> according to <FIG> is particularly easy to manufacture and may be produced as low-cost article. More in particular, the second object comprises sheet portions for example of metal. The sheet portions form a plurality of legs <NUM> with barbs <NUM>, all legs extending from a bridge portion <NUM> and being one-piece with it. The second object may be manufactured from a punched metal sheet by merely bending the legs away from the bridge portion <NUM> and bending the legs <NUM> to have the barbs <NUM>.

Similarly, the embodiment of <FIG> being not according to the claimed invention has a head portion <NUM> (or bridge portion) with a plurality of legs extending therefrom. <FIG> shows a punched-out metal sheet as intermediate piece, and <FIG> depicts the second object <NUM> obtained by deforming this intermediate piece through bending. The legs may be provided with beads or grooves (the same holds for <FIG>) for additional stability.

In this embodiment, instead of the barbs, the legs <NUM> have distal arrow portions <NUM>. Combinations would be possible.

A further, optional feature that does not depend on the legs is constituted by a central hole <NUM> that may be used for guiding during the assembly process, for example together with a collar <NUM>. Other uses of such a hole and/or collar are possible, including the fastening of a further object to the second object.

<FIG> shows a second object being not according to the claimed invention that is formed by a perforated metal hollow cylinder <NUM>. The perforations <NUM> of the metal cylinder may be interpenetrated by thermoplastic material in the process and thereby ensure the positive-fit anchoring. To minimize proximal heating, the volume portion of the perforation might advantageously be close to or higher than <NUM>%.

The second object of <FIG> being not according to the claimed invention comprises a metal mesh <NUM> also formed into a hollow cylinder. The functioning principle is similar to the one of the hollow cylinder, with the meshes serving for interpenetration by the thermoplastic material.

Instead of being formed into a hollow cylinder, a perforated metal sheet or a mesh may be brought into other shapes for constituting a connector of the described kind. <FIG> very schematically illustrates a spiral shape as an option being not according to the claimed invention.

A further option being not according to the claimed invention in addition to cylindrical (<FIG>) and spiral shaped in which the material is stable is wave-shaped, for example extending along a length dimension. An amplitude of such a wave may be at last <NUM>-<NUM> times the thickness of the sheet or mesh.

An even further variant being not according to the claimed invention is a square (in cross section perpendicular to the axial direction) or other closed or open shape with a curve or buckling.

Second objects having structures as the ones described referring to <FIG> as well as referring to <FIG> hereinbelow may generally be very thin and therefore sensitive to buckling. To this end, depending to the application, a proximal connector structure may be advantageous to provide stability.

<FIG> shows a cap <NUM> with a groove <NUM> for serving as proximal bridge of a second object <NUM> with a spiral-shaped metal sheet or mesh to give the second object additional mechanical stability during the process.

Second objects with thin structures as the ones described referring to <FIG> as well as referring to <FIG> hereinbelow are suitable for fixation also in relatively thin first objects, with rather minimal energy input. Because of their thinness a very small volume is displaced, and the melting zones will be very local. This minimizes the overall pressure and the overall energy input.

Second objects <NUM> as connectors of the kind described referring to <FIG> may especially be suitable for fastening a first and a third object together in a staple-like or pin-like manner, by the process as described herein. In this, the way the first and third objects are arranged relative to one another with respect to the proximodistal anchoring axis may be varied, especially, it is also possible to press the connector through the first object into the third object instead of the other way round.

<FIG> show a special application of the principle of using a connector to connect a third object <NUM> to a first object <NUM>. The second object is assumed to have a hat-like shape with a circumferential protruding section <NUM> extending distally from a main body <NUM>.

In this special example being not according to the claimed invention, the third object <NUM> comprises a foam that by insertion of the second object <NUM> is compressed (compressed portion <NUM>). Optionally, the second object may comprise relaxation openings <NUM> or other shape features that allow compressed material to flow away in case the foam has thermoplastic properties (which is not necessary). <FIG> illustrates corresponding flow-out portions <NUM>.

While <FIG> illustrate fastening of a foam material third object, similarly a third object of an other material may be fastened by this approach, for example a soft and/or elastomeric material capable of being cut through by the distal structures of the second object or an object provided with a pre-manufactured bore for these structures.

In the embodiment of <FIG> being not according to the claimed invention, the third object <NUM> is provided with a bore <NUM> through which the distal portion of the second object may be advanced to be brought into contact with the first object. In this, the third object <NUM> may be thermoplastic, and the bore <NUM> may be under-dimensioned in relation to the second object so that insertion thereof encounters resistance, and material of the third object around the bore <NUM> is displaced. Alternatively, the third object may be of a not liquefiable material. Then, the bore <NUM> needs to be dimensioned so that the distal portion of the second object fits through it or the distal tip or a distal edge cuts through the third object material.

The second object in the depicted embodiment comprises a resilient barb structure <NUM> that allows pushing the distal portion of the second object through the bore <NUM> but that ensures anchoring in the first object <NUM> after liquefaction and re-solidification. The second object also has a proximal head portion <NUM> for securing the third object <NUM> against the first object <NUM>.

As an alternative to having a resilient barb structure <NUM>, the second object in a configuration like the one of <FIG> could also have a shape similar to the one of <FIG>, again with a proximal head portion <NUM>, as for example shown in <FIG>.

<FIG> depicts an embodiment being according to the claimed invention in which a second object <NUM>, for example being entirely metallic, is anchored in a through opening <NUM> of the first object. The through opening narrows towards the distal side (is countersunk), and the second object is accordingly tapered to be anchored around the opening. The first object <NUM> is assumed to be a thermoplastic sheet.

The bond of the second object to the first object is a flattish bond, similar to the one taught with respect to <FIG>; <FIG> and others, with structures for the interpenetration formed by sharp protruding structures <NUM> and indentations <NUM> - even though the bonding surface of the second object is not planar but conical.

<FIG> shows an alternative according to the claimed invention where the through opening <NUM> of the first object is not tapered but stepped, with the fastening surface that comprises the protruding structures <NUM> and the indentations <NUM> being anchored around the step.

According to yet another alternative being according to the claimed invention, illustrated in <FIG>, if the second object <NUM> is allowed to protrude above the proximal surface of the sheet-like first object <NUM>, a head-like proximal extension <NUM> of the second object may have a distal end face that comprises the structures <NUM>, <NUM> to connect the second object to the rim of the opening.

In the variant being according to the claimed invention of <FIG>, for a configuration otherwise similar to the one of <FIG>, two optional further features are realized (the features may be realized independently of each other, with advantages if they are combined):.

Both measures have the effect that more energy is absorbed and more material is liquefied at more proximal, peripheral locations than at more distal, central locations around the opening. The effect is that the distal surface of the first object is kept intact.

<FIG> shows a variant of the embodiment of <FIG> being according to the claimed invention in which however the structure elements that cause the bonding are restricted to the periphery of the second object <NUM>. In more central positions, the distal surface <NUM> serves as a stop and abutment surface and thereby precisely defines the axial relative position. In this, the considerations of <FIG> concerning the relative volumes of the protruding structures <NUM> and the indentations <NUM> may be particularly advantageous.

<FIG> is thus a very schematically illustrated example of an embodiment in which a connection zone between the first and second objects only constitutes a portion of their mutual interface. In other portions of the interface, essentially no energy is transferred, and no liquefaction will take place.

In the embodiment of <FIG> being not according to the claimed invention, protruding structures <NUM> for being anchored in the second object are attached to a main body of the second object and protrude distally in directions essentially parallel to the axial direction. The protruding structures may for example be formed similar to the structures illustrated in <FIG> and be particularly simple and cost efficient to manufacture.

In order to be stable with respect to buckling, the metal sheet or mesh may extend in a curved shape (for example by forming a cylinder) or wave shape (perpendicular to the drawing plane) or other non-straight shape, as described hereinbefore.

Claim 1:
A method of bonding a second object (<NUM>) to a first object (<NUM>), the method comprising the steps of:
- providing the first object (<NUM>), the first object comprising a thermoplastic liquefiable material in a solid state;
- providing the second object (<NUM>), the second object comprising a surface portion that has a coupling structure (<NUM>, <NUM>, <NUM>, <NUM>) with an undercut and/or is capable of being deformed to comprise such a coupling structure with an undercut, whereby the second object is capable of making a positive-fit connection with the first object;
- pressing the second object (<NUM>) against the first object (<NUM>) by a tool (<NUM>) that is in physical contact with a coupling-in structure of the second object while mechanical vibrations are coupled into the tool,
- continuing the step of pressing and coupling vibrations into the tool until a flow portion of the thermoplastic material of the first object is liquefied and flows into the coupling structure (<NUM>, <NUM>, <NUM>, <NUM>) of the second object,
- letting the thermoplastic material of the first object re-solidify to yield a positive-fit connection between the first and second objects by the liquefied and re-solidified flow portion interpenetrating the coupling structure, characterized in that the coupling structure comprises a plurality of laterally spaced openings (<NUM>) open to a distal side, which openings (<NUM>) define an undercut with respect to axial directions, wherein flowing of the flow portion comprises flowing backwards into the openings (<NUM>) defining the undercut, wherein a distal portion of the openings (<NUM>) is embedded in the first object (<NUM>) during the method.