Abstract
A method of anchoring a connector in a first object is provided, wherein the connector includes thermoplastic material in a solid state. The method includes bringing the connector into physical contact with the first object, rotating the connector relative to the first object around a proximodistal rotation axis and exerting a relative force by the connector onto the first object, until a flow portion of the thermoplastic material of the connector becomes flowable and flows relative to the first object, and stopping rotation of the connector, whereby the flow portion anchors the connector relative to the first object, wherein a distal end of the connector is equipped for cutting/punching into the first object and/or for removing material therefrom.
Claims
1. A method of anchoring a connector in a first object, wherein the connector comprises thermoplastic material in a solid state, the method comprising the steps of: bringing the connector into physical contact with the first object, rotating the connector relative to the first object around a proximodistal rotation axis and exerting a relative force by the connector onto the first object, until a flow portion of the thermoplastic material of the connector becomes flowable and flows relative to the first object, and stopping rotation of the connector, whereby the flow portion anchors the connector relative to the first object, wherein at least one of the following conditions is fulfilled: A. the connector is shaped so that a distal-most end thereof is different from a contact point on the proximodistal rotation axis; B. a portion of the connector has a macroscopic surface roughness; C. the connector comprises a portion of a second material different from the thermoplastic material, wherein said second material is solid and does not become flowable, and wherein said portion either extends to the distal end or extends through a middle plane perpendicular to the axis, or both; D. during the step of rotating, the connector is subject to an orbital movement; E. the connector has an inner portion and a proximal connecting portion with a distally facing connecting protrusion, wherein during the step of rotating, the connecting protrusion is pressed against a proximally facing end face of the first object and a surface part of the inner portion is pressed against a first object structure distally of the proximally facing end face; F. the first object comprises a structure of fibers or a foam material, and the flow portion is caused to flow into the structure of fibers or into pores of the foam material, respectively.
2. The method according to claim 1, wherein the relative force is a pressing force.
3. The method according to claim 1, wherein at least a region of the first object, in which region the flow portion flows, comprises non-liquefiable material.
4. The method according to claim 1, wherein at least condition A. is fulfilled, and wherein the distal-most end forms one of: a circular contact line; a saw-tooth structure; an edge running different from circumferentially, an abrasive area; a hollow, sleeve-like distal end; a cutting and/or punching structure of the second material.
5. The method according to claim 1, wherein at least condition A. is met, comprising the step of punching out a portion of an outermost layer of the first object prior to rotating the connector and/or at an initial rotation stage while the connector is rotated.
6. The method according to claim 1, wherein at least condition B. is met, wherein the arithmetic average surface roughness of the distal end face portion is at least 20 □m.
7. The method according to claim 1, wherein at least condition B is met, wherein at least a distal end face portion of the connector has a macroscopic surface roughness.
8. The method according to claim 1, wherein at least condition C is met, wherein the non-liquefiable material forms a distal cutting/punching and/or material removal feature.
9. The method according to claim 8, and further comprising a step of causing the body of the non-liquefiable material to retract relative to the thermoplastic material during the step of exerting the relative force.
10. The method according to claim 1, wherein the first object is a lightweight building element having a first building layer and an interlining layer, wherein the first building layer is thinner and more dense than the interlining layer.
11. The method according to claim 10, wherein the first object further comprises a second building layer wherein the second building layer is thinner and more dense than the interlining layer.
12. The method according to claim 10, further comprising a step of: by the action of the rotation and/or the relative force, displacing a portion of the first building layer with respect to the interlining layer.
13. The method according to claim 12, wherein the step of applying the relative force to displace the portion of the first building layer comprises displacing the portion towards a distal direction, thereby causing material of the interlining distally of the portion to be compressed.
14. The method according to claim 12, further comprising causing the portion to be punched out by the effect of the first pressing force.
15. The method according to claim 10, and further comprising causing the first outer building layer to be pierced as a result of the application of the relative force at the location where the connector is in physical contact with the first object or in a vicinity thereof.
16. The method according to claim 1, wherein at least condition E. is met, and wherein the connecting portion extends radially outwardly from the inner portion.
17. The method according to claim 16, wherein the connecting portion is a flange extending radially outwardly from the inner portion, and wherein the anchoring portion is a circumferential ridge extending distally from the flange.
18. The method according to claim 1, wherein at least condition F. is met, wherein the material of the first object is a non-woven fiber material.
19. The method according to claim 1, wherein at least condition F. is met, wherein the connector is pressed into the first object prior to an onset of the rotation.
20. The method according to claim 1, wherein the connector as a region with a cross section that continually increases towards proximally, and wherein during the step of rotating, this region is pressed into the first object.
21. The method according to claim 20, wherein said region has a structure of ribs and grooves.
22. The method according to claim 1, wherein the connector has a weakening feature, and wherein the step of rotating is carried out until the connector collapses at the location of the weakening feature for enhancing a flow of the flow portion towards radially outwardly.
23. A connector, usable in a method according to claim 1, the connector having an axis and comprising thermoplastic material in a solid state, the connector comprising a proximal engagement structure that is not rotationally symmetrical and is equipped for cooperating with a rotating tool for setting the connector into rotation around the axis, wherein at least one of the following conditions is fulfilled: A. the connector is shaped so that a distal-most end thereof is different from a contact point on the proximodistal rotation axis; B. the connector has a macroscopic surface roughness; C. the connector comprises a portion of a second material different from the thermoplastic material, wherein said second material is solid and does not become flowable (during the process), and wherein said portion either extends to the distal end or extends through a middle plane perpendicular to the axis, or both; E. the connector has an inner portion and a proximal connecting portion with a distally facing connecting protrusion.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0114] In the following, ways to carry out the invention and embodiments are described referring to drawings. The drawings are schematic in nature. In the drawings, same reference numerals refer to same or analogous elements. The drawings show:
[0115] FIGS. 1-3 sections through a first configuration during different method steps;
[0116] FIGS. 4-12 alternative connectors or details thereof;
[0117] FIG. 13 an other configuration;
[0118] FIG. 14 an even further connector;
[0119] FIGS. 15-17 further configurations;
[0120] FIG. 18 a process diagram;
[0121] FIG. 19 an even further configuration;
[0122] FIG. 20 a configuration with a first object being a structure of fibers;
[0123] FIGS. 21 and 22, during two different stages, a configuration with a first object being a foam material;
[0124] FIGS. 23 and 24 two embodiments of connectors; and
[0125] FIG. 25 a partial cross section through an even further connector.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0126] The configuration of FIG. 1 includes a first object 1 being a sandwich board with a first building layer 11, a second building layer 12, and an interlining 13 between the building layers. The first and second building layers may include a fiber composite, such as a continuous glass or continuous carbon fiber reinforced resin. The interlining may be any suitable lightweight material, for example a honeycomb structure of cardboard, of a plastic material or of a composite.
[0127] An often seen interlining structure is a honeycomb structure with walls forming the honeycomb structure extending approximately perpendicular to the building layer plane between the building layers. For example lightweight building elements of which the interlining layer includes honeycombs of paper, which is covered by a polymer based material such as by a mixture of polyurethane (PU) and reinforcing fibers.
[0128] The interlining may include barrier foils and/or web and/or adhesive layers at the interfaces to the building layers. Especially, an additional adhesive may bond the building layers 11, 12 to the interlining 13. In an example, a slightly foaming adhesive on polyurethane basis is used. Possible pores in the adhesive may contribute to the anchoring in the various embodiments of the invention. The face that in the depicted orientation is the upper face in this text is denoted as the proximally facing face. The connector 3 is bonded to the first object 1 from the proximal side.
[0129] The connector 3 includes thermoplastic material at least on a distal end thereof. It may, for example, consist of the thermoplastic material. The connector in the embodiment of FIG. 1 and other embodiments described hereinafter has a head portion and a distally protruding shaft portion 32. The shaft portion ends in a distal edge 33, for example formed by a circumferential ridge.
[0130] The connector 3 includes a proximally facing engagement opening 36 for a rotation tool 6 to engage. The engagement opening is a blind opening having a non-circular cross section—for example a rectangular or hexagonal cross section—so that the rotation tool 6 may transfer an angular moment to the connector to rotate the connector 3 about a rotation axis 20 that may extend parallel to the proximodistal direction. In general, any non-circular cross section of the engagement opening and corresponding outer cross section of the rotation tool or more in general any not rotationally symmetrical engagement structure is possible; also a force fit connection between the rotation tool and the connector may be used to rotate the connector.
[0131] For anchoring the connector in the first object, the connector is pressed against the first object and rotated. Prior to bringing the connector 3 in contact with the first object 1, optionally a pilot hole may be made in the first object (not shown in FIG. 1).
[0132] By the joint application of the pressing force and the rotation, the connector is driven into the first object 1. Due to the effect of the distal edge 33 formed by the connector, in an initial phase a circular portion of the first building layer 11 is detached from the main portion and/or is disintegrated by the impact of the rotation and the pressing force, whereby the connector may start penetrating into the first object 1.
[0133] Subsequently (and possibly to some extent also during penetration through the first building layer 11), the energy absorbed especially due to friction between the rotating connector and the first object causes a flow portion 8 of material of the connector to be made flowable (FIG. 2). The pressing force and possibly also to some extend the centrifugal forces cause the flow portion to be displaced. Depending on the material of the first object, also material of the first object may optionally be made flowable, and in some embodiments a common melt of material of the first object and the connector may be generated, which common melt after re-solidification results in a weld. In FIG. 2, fragments 16 of the detached portion of the first building layer are illustrated as merely displaced but not molten; in other embodiments this portion may be at last partially molten and intermixed with the flow portion.
[0134] FIG. 3 shows the connector anchored in the first object with the flow portion 8 re-solidified and interpenetrating structures of the first object, whereby an anchoring results, which anchoring is at least partly due to a positive-fit connection between the re-solidified flow portion and the structures of the first object.
[0135] In the embodiment of FIGS. 1-3, the connector is used to secure a second object 2 for example being a metal plate to the first object by the head portion 31 that in the final state (FIG. 3) clamps the second object 2 against the proximal surface of the first object. However, —this pertains to this embodiment and any other embodiment of the present invention—other approaches of securing a second object to the first object 1 may be used, including providing the connector with an engagement structure for a fastener (screw, pin, etc.) that fastens the second object, providing the connector with an engagement structure directly for the second object (such as a structure for a clip connection, a thread, etc.), integrating the second object into the connector, etc.
[0136] In accordance with an aspect of the invention, the connector has a (especially distally facing) contact surface that during the anchoring process comes into contact with the first object, which contact surface defines more than one contact point when the connector is brought into contact with an essentially flat surface of the first object. More in concrete, the contact surface in FIG. 1 includes the circumferential distally facing ridge ending in an edge 33. The edge in the embodiment of FIG. 1 is peripheral with respect to the shaft portion 32, whereby it contributes to detaching the mentioned circular portion, effectively punching out an opening in the first building layer 11 into which opening subsequently the shaft is advanced (FIG. 2).
[0137] FIG. 4 shows an alternative connector, where the distal end forms a tube portion 37 ending in a distal edge with a saw tooth structure 34. By this, the detaching of a circular portion of the first building layer is done in a sawing manner. The distal saw tooth structure—as well as other distal structures having a punching effect—may not only contribute to the breaking through the first building layer 11 but may also have an effect in further advancing the connector 3 into the less dense layer (interlining 13 in the illustrated examples) underneath.
[0138] The connector 3 shown in FIG. 4 has a further feature that is optional for any embodiments and that does not necessarily have to be combined with the sawtooth structure. Namely, the connector has a collar 35 of axially running ribs that protrude radially from the diameter of the tube portion and/or shaft portion (i.e., from an essentially cylindrical or possibly (in other embodiments) slightly conical outer surface). The collar 35 is immediately distally of the head portion 31, it comes into contact with a rim of the first building layer 11 around the opening caused by the introduction of the connector towards the end of the anchoring process. Thereby, additional friction is caused between the comparably harder first building layer and the connector, and thermoplastic material of the connector will be caused to flow also at this proximal position, whereby it will cause an additional connection with the first building layer and/or a sealing.
[0139] Instead of axially running ribs, other such proximal radially protruding features may be present distally of the head portion, for example at least one circumferential rib, a step feature, an array of protrusions, for example forming a chess-board-like pattern, etc.
[0140] FIG. 5 illustrates another embodiment of a connector with a distal tube portion 37 and proximally thereof a shaft portion. As further difference to the embodiment of FIG. 1 (that is independent of the more pronounced tube portion) is the shape of the head portion. Namely, the head portion 31 is conical, whereby it may, for example, be pressed into the opening of a second object 2 of the kind illustrated in FIGS. 1-3, so that it may sealingly engage the second object.
[0141] FIG. 6 illustrates a variant of a connector 3 that has a distal end that is generally flat with a cutting feature 34 formed at a position approximately centrally with respect to the axis 20. When the connector is brought into contact with the first building layer and set into rotational movement, the cutting feature will work into the material of the first building layer, which first building layer during the subsequent process will be slowly consumed away in a milling manner when the connector further penetrates into it. This may be assisted by a roughness (see hereinafter) or other structure along the periphery of the shaft portion 21.
[0142] In embodiments, such cutting feature may slightly protrude radially and/or distally for enhanced effectiveness. Also, a cutting feature may, in an alternative, formed by an element of a non-liquefiable material in accordance with condition example, for example, as cutting platelet of ceramics or of a metal, which may during the process retract in the manner described hereinafter referring to FIG. 8.
[0143] The embodiment of FIG. 7 is an example of a ‘hybrid’ connector, i.e., a connector that does not consist of the thermoplastic liquefiable material only but that includes a portion of a different material. It is in particular an example of a connector that includes a portion of not liquefiable material (i.e., metallic material in the shown embodiment) that forms a distal separating and/or material removing structure.
[0144] More in concrete, the connector 3 of FIG. 7 includes a thermoplastic part being an essentially cylindrical body 30 of the thermoplastic material and includes a metallic part being a metal sleeve 40 having a distal cutting edge 41 protruding distally from the body 30 and a proximal bulge 42. When the connector is pressed against the first object 1 while being rotated, the bulge 42 assists in mechanically stabilizing the metal sleeve 40 with respect to the body 30 so that it can exert a pressing force on the first object until a circular portion of the first building layer is cut out, and pressed into the first object 1. During this, some heat will be absorbed by the metal sleeve 40. As soon as the distal end of the body 30 comes into contact with the first object, additional heat will be absorbed at the interface between the body 30 and the first object, whereby the anchoring process described referring to FIGS. 1-3 may take place. Due to the heat generated, thermoplastic material proximally of the sleeve (reference number 39 in FIG. 7) may become softened, whereby the sleeve may be pressed into the body 30, so that after some time, especially when the distal end of the connector 3 reaches the second building layer 12 (if any), then the sleeve is fully retracted into the body 30 and the edge 41 does not have any cutting effect any more.
[0145] The principle shown referring to FIG. 7 does not depend on the shape of the connector body 30 and pertains equally to other shapes, including shapes with a conical body and/or with a head portion.
[0146] FIG. 8 shows an other embodiment that implements the principle of FIG. 7. In this embodiment, the thermoplastic part (body) 30 forms an outer sleeve, and the metallic part 40 forms an inner sleeve ending in a distal edge 41. A plurality of outward protrusions 43 of the inner sleeve 40 or a single, for example circumferential outward protrusion engage(s) into corresponding indentations of the thermoplastic body 30. The outward protrusion(s) 43 may have, as illustrated in FIG. 8, a sloped, ramp-like shape towards proximally to reduce resistance against the retracting movement that withdraws the cutting edge after the metallic part has become sufficiently hot, as described referring to FIG. 7.
[0147] The arrangement of outer and inner sleeves could be reversed in FIG. 8; then optionally the thermoplastic body instead of an inner sleeve could be an inner bolt. Embodiments with the not liquefiable part being an outer sleeve may especially be advantageous for making thermoplastic material of the body flowable a contact between the first building layer and the thermoplastic material is not necessary and for example not desired—heat absorption and making flowable then primarily takes place at the interface between the interlining layer and/or the second building layer (if any) on the one hand and the body of the connector on the other hand.
[0148] FIG. 9 shows yet another embodiment of a hybrid connector. The metallic part 40 forms the proximal head as well as the engagement opening 36 and has a metallic part shaft portion 42 that however does not reach to the distal end. For a strong stability, especially against shear forces, however, the metallic part reaches rather far towards distally, for example, the metallic part may extend at least through a middle plane 200 (perpendicular to the axis 20) of the connector.
[0149] The connector of FIG. 9 is shown to have a rounded distal end, however, as illustrated by the dotted line, it could also have other shapes, including shapes with a distal radially outer ridge, similar to FIG. 1.
[0150] In a variant of the embodiment of FIG. 9, the metallic part could extend through the entire length of the connector and distally end in a tip or blade thereby making the breaking through/pierce/cut through a high-strength first building layer possible. In this variant, the bore generated in the first building layer by the metallic part is smaller than a diameter of the connector and primarily serves for weakening the first building layer without entirely removing it—thereby the flowing of flowable thermoplastic material underneath the first building layer and integrating in an anchoring structure may be further improved.
[0151] FIGS. 10 and 11 show distal ends of connectors of two different shapes. The distal end surfaces have a roughened portion 38, whereby the connectors impinge on the first building layer in an abrasive manner.
[0152] More in particular, the roughness (Ra, arithmetic average roughness) of such roughened portion is at least 10 μm or at least 20 μm or even at least 50 μm.
[0153] FIG. 12 illustrates another aspect of the invention. Namely, the connector during the process may, according to this aspect, be not only subject to rotational movement but during the rotation the rotation axis itself moves, especially rotates around a parallel orbit axis while maintaining its orientation (orbital movement). Thereby, the anchoring effect may be enhanced.
[0154] FIG. 13 shows an even further aspect. The connector is anchored in the first object 1 being a lightweight building element from a face side instead of through a first building layer. The diameter of the shaft portion 32 (or a tube portion or similar) may be chosen such that it is slightly larger than a thickness of the interlining 13 but smaller than a thickness of the entire lightweight building element, whereby a good anchoring with respect to all, the first and second building layers 11, 12 as well as the interlining may result.
[0155] FIG. 14 illustrates an even further aspect. According to this aspect, the connector 3 has a variable radial width. In the shown embodiment, the connector is formed by a body of axial bars connected by circumferentially running bridges, alternatingly arranged proximally and distally, respectively. Thereby, the radius of the whole connector can be varied by elastic (and/or plastic) deformation of the bars/bridges and their connections.
[0156] FIG. 14 illustrates the connector 3 in a compressed configuration in which it may be inserted in a pre-made bore in the first object 1, which pre-made bore at least goes through the first building layer 11. Then, as illustrated in FIG. 15, as soon as the force that elastically compresses the connector is released and/or (also if no such radial compressing force was present initially) due to the centrifugal forces, the radial extension of the connector becomes bigger, whereby an additional anchoring effect is achieved, especially if the connector extends to distally of the first building layer 11, as shown in 15, and is stabilized by a blind rivet effect in addition to the anchoring by the thermoplastic material interpenetrating structures of the first object and/or a weld.
[0157] FIG. 16 shows an embodiment with a connector 3 that has a distal body portion 131 and a plurality of elastically deformable tongues 132 that deformed radially inwardly for introduction through the pre-made bore and resiz radially outwardly after they are distally of the first building layer, as illustrated in FIG. 16. For anchoring, the rotation and a pulling force are coupled into the connector, whereby the thermoplastic material of the connector is liquefied in contact with the first building layer 11, along its distally facing surface. For coupling the pulling force into the connector, the body portion 131 may, in addition to the engagement opening 136 also include a structure that allows coupling a pulling force into it, for example a snap-in structure 136.
[0158] FIG. 17 illustrates an example of process control, for embodiments that include exerting a pressing force (thus embodiments other than the embodiment of FIG. 16). An apparatus 60 is configured to rotate the rotation tool 6 and to exert the pressing force. The apparatus includes an electronic control including a pressing force measuring device 61.
[0159] FIG. 18 shows the pressing force 71 and the rotation 72 as a function of time for a pressing force controlled process. The pressing force 71 may be configured to rise during an initial phase until the first building layer is broken through and/or removed by the rotating connector 3. Then, the pressing force goes back due to the lower resistance in the interlining layer. As soon as the distal end of the connector reaches the second building layer or denser structures nearby it, with the abrasive and/or cutting structures at the distal end consumed away or retracted in the meantime (as described for the embodiments hereinbefore), the pressing force required for moving the connector forward goes up again. As soon as a threshold value p.sub.t is reached, the rotation is switched off, whereas the pressing force is maintained for some time thereafter until the thermoplastic material has re-solidfied;
[0160] FIG. 19 illustrates, in combination, two further principles that apply both to first objects being lightweight building elements, for example sandwich boards. These two principles may be applied independently, though, i.e., it is possible to carry out the method with the first principle but without the second principle, or also to carry out the method with the second principle but without the first principle, in addition the combination being an option.
[0161] The first principle is that the connector 3 is used to punch out a portion (fragment 16) of the first building layer 11. To this end, the connector has a circumferential distal edge 33, in the depicted embodiment formed by a tube portion 37. Such circumferential distal edge 33 capable of punching out a portion of the first building layer 11 is also a property of the above-described embodiments of FIGS. 1 and 5.
[0162] The punching step, by the distal edge 33 may be carried out prior to the onset of the rotational movement, during the onset, or thereafter.
[0163] The second principle is that the connector 3 has a proximal connecting portion 81 with a distally facing connecting protrusion 82 that is arranged to penetrate into material of the first object from a proximal end face thereof. Especially, the connecting portion may form a flange, for example a proximal flange, around an inner portion (which inner portion in FIG. 19 is the tube portion but which inner portion could have an other shape also), with a distally facing, for example circumferential connecting protrusion of the thermoplastic material. The connecting protrusion may form a circumferential ridge distally ending in an edge. The connecting protrusion may extend around the axis 20 uninterruptedly or for example also interruptedly.
[0164] The anchoring process may then include the step of causing a material portion of the inner portion to become flowable and to flow relative to the second building layer 12 and, for example, penetrate into structures of the second building layer and/or structures immediately adjacent the second building layer—and, for example, at the same time causing an other material portion, of the connecting portion 81 to become flowable and to be pressed into structures of the first building layer 11 from proximally. More in general, the method may include anchoring an inner portion of the connector distally of a first building layer 11 and anchoring a radially-outer connecting portion by pressing it against a proximally-facing surface of the first building layer while being rotated.
[0165] FIG. 20 illustrates the principle of anchoring a connector 3 in a first object 1 being a structure of fibers 101, for example a nonwoven fabric. Especially, the fibers may have the property of not becoming flowable at the temperatures at which the thermoplastic material flows, i.e., a non-liquefiable material according to the definition used in the present text.
[0166] The connector 3 used to be anchored relative to the structure of fibers differs from the previous embodiments in that it is adapted to the material. More in concrete, if anchored from a proximally facing surface of the structure of fibers, the connector will be capable of penetrating less deeply compared to sandwich board for example. This is because if an object (connector) is pressed against the fibers, this will result in an enhanced mechanical resistance due to the density that locally increases by compression of the structure. Therefore, a width w of the structures that penetrate into the structure of fibers will often be substantially larger than a depth d thereof.
[0167] In embodiments, the connector includes at least one circumferential ridge 91, 92 extending around the rotation axis 20, which ridge 91, 92 forms an anchoring portion of the connector.
[0168] The following options exist: [0169] Prior to the onset of the rotations, the connector may be pressed by an axial movement into the material of the first object 1. Thereby, locally, at the location of the anchoring portion(s), the fiber structure is compressed to yield a compressed portion 102 that is illustrated schematically in FIG. 20. It has been found that this may assist the anchoring process in that the friction between the material of the first object 1 and the thermoplastic material of the anchoring portion(s) is enhanced yielding an enhanced energy absorption, while also the resistance against the fibers merely being pulled along in the rotational movement is also enhanced. [0170] In addition or as an alternative, the depth d and the process parameters are chosen in a manner that after the process, the anchored connector 3 still has the distinct anchoring portion(s) 91, 92. I.e., the material of the anchoring portion(s) is not completely smeared out by the process but an in-depth anchoring of the connector by the anchoring portion results. [0171] In addition or as yet another alternative, the process is carried out until a distally facing surface portion 94 of a main body 90 abuts against a proximally facing surface of the first object 1.
[0172] FIG. 21 illustrates an even further embodiment in which the connector is anchored, by the rotation, in a first object being an object of a compressible foam, for example as Expanded Polysterene (EPS) or Expanded Polypropylene (EPP). In the illustrated embodiment, the first object 1 is a foam with closed pores 105; the method would also be applicable for open porous compressible foams.
[0173] Especially, the foam may be of a material that is not liquefiable according to the definition of the present, i.e., if the foam is of a thermoplastic material, its liquefaction temperature is substantially higher than a liquefaction temperature of the connector thermoplastic material.
[0174] Alternatively, the foam material may be liquefiable and for example—but not necessarily—capable of being welded to the thermoplastic material of the connector. Thereby, the effect of the positive fit that results in anchoring may be supplemented by a material bond (i.e., weld).
[0175] The connector 3 may optionally have a distal structure according to condition A above. FIG. 21 shows the distal end of the connector forming a shallow circumferential protrusion 111.
[0176] Also for anchoring in a foam material, the connector may optionally be pressed into material of the first object (foam material) by an axial movement prior to the onset of the rotations. The effect of such compression is, similar to the above-described example, increased friction, together with an enhanced mechanical stability.
[0177] FIG. 22 shows the configuration after the anchoring process. The flow portion 8 interpenetrates structures of the first object, for example by penetrating into pores that were opened in the process and/or already open pores and/or other structures. An intertwined configuration of the flow portion and these structures results.
[0178] FIG. 22 also illustrates a compressed zone 106 distally of the connector 3. This compressed zone may result prior to the onset of the rotational movement by the connector being pressed into the material of the first object, and/or may result by the joint action of the pressing force and the rotational movement. The compressed zone 106 is mechanically stabilized by the re-solidified flow portion and/or by the connector being anchored as a whole.
[0179] FIG. 23 shows a further embodiment of a connector 3. The connector is based on the principle described referring to FIGS. 1, 5 and 19 by including a distal edge 33 capable of punching a hard first building layer or other rigid structure of the first object.
[0180] Such structures with a distal edge and a tube portion 37 proximally thereof are also suitable for being anchored relatively deeply in comparably dense material without being subject to too high a compression.
[0181] A further feature of the embodiment of FIG. 23 is that it comprises, similarly for example to the embodiment of FIG. 6, a region with a cross section (perpendicular to the axis 20) that continually increases towards proximally, whereby when the connector is pressed into the first object while rotated there is a continuous pressing force and friction along the periphery, which feature enhances the overall liquefaction efficiency.
[0182] In contrast to the embodiment of FIG. 6, however, the region of continually increasing cross section has a structure of ribs 121 intermittent with grooves 122 running axially along each other. The ribs define a homogeneous tapering enveloping rotation surface (surface of revolution) rotationally symmetrical around the axis 20. However, since the grooves are between them, the energy input required for making them flowable is reduced compared to a massive cross section with homogeneous surface as in FIG. 6. Therefore, the process is quicker compared to a connectors with a massive cross section.
[0183] The embodiment of FIG. 24 is based on the same principle. However, the tube portion 37 has an extended length, (axial dimension), whereby the embodiment of FIG. 24 is especially suited for being anchored in comparably thick objects of limited density, such as sandwich boards with a relatively thick interlining layer.
[0184] FIG. 25 illustrates a further optional principle that may be present in addition or as an alternative to the tapering region with or without ribs. Namely, the connector 3 may include an inner or outer weakening feature, such as an inner groove 142 assisting a collapse and an effect of lateral expansion of liquefied thermoplastic material, for example immediately distally of the first building layer. Especially, the centrifugal force will contribute to such lateral expansion, and a locally weakened zone next to the inner groove 142 or other local weakening feature may serve as a plastic hinge in this.
