SECURING A SECOND OBJECT TO A FIRST OBJECT

Abstract

A method of manufacturing a lightweight building element assembly is disclosed. The assembly firstly comprises a first object (1) being a lightweight building element that has a first outer building layer (11) and an interlining layer (13). The assembly further comprises a second object (2) secured to the first object. The method comprises firstly providing the first object, wherein the first object has an indentation (19) formed by the first outer building layer. The indentation may form a blind opening or a through opening in the first object. The method further comprises providing the second object (2), wherein the second object comprises an outer surface portion of a thermoplastic material, wherein the outer surface portion is a lateral outer surface portion with respect to an axis. The second object is brought in contact with the first object so that the lateral outer surface is in physical contact with the sidewall (14), and mechanical energy is coupled into the second object so as to cause energy absorption due to friction between the lateral outer surface and the lateral wall, until a flow portion of the thermoplastic material becomes liquefiable and flows relative to the lateral wall. After re-solidification of the thermoplastic material, the flow portion secures the second object to the first object.

Claims

1.-45. (canceled)

46. A method of manufacturing an assembly, comprising the steps of: providing a first object, wherein the first object has a proximally facing surface portion, wherein the first object has an indentation having a mouth in the proximally facing surface portion, the indentation being manufactured by pre-shaping, the indentation having a sidewall; providing a second object that has a lateral outer surface portion, wherein at least one of the lateral outer surface portion and the sidewall comprises a thermoplastic material; bringing the second object in contact with the first object so that the lateral outer surface portion is in physical contact with the sidewall; coupling mechanical energy into at least one of the first and second objects so as to cause energy absorption due to friction between the lateral outer surface portion and the sidewall, until a flow portion of the thermoplastic material becomes liquefied; and letting the flow portion re-solidify, whereby the flow portion secures the second object to the first object.

47. The method according to claim 46, wherein the sidewall has a same texture as the proximally facing surface portion in a region around the mouth.

48. The method according to claim 46, wherein the indentation extends from the proximally facing surface portion in a smooth fashion without forming a sharp edge.

49. The method according to claim 46, wherein the step of providing the first object comprises manufacturing the first object by a primary shaping process, wherein the indentation is shaped by the primary shaping process, and wherein the indentation is formed during manufacturing of the first object.

50. The method according to claim 49, wherein the primary shaping process is a molding process, and wherein the indentation and the complete first object are shaped in a same mold.

51. The method according to claim 49, wherein the primary shaping process is a one-step process, and/or wherein the first object comprises a polymer material, and the polymer material is caused to harden during the primary shaping process.

52. The method according to claim 46, wherein the second object has an anchoring portion having an outer contour adapted to the indentation , wherein an outer diameter of the anchoring portion is adapted to the indentation to yield an interference fit, and wherein a dimension of the anchoring portion is larger than a corresponding dimension of the indentation by between 2% and 20%.

53. The method according to claim 46, wherein the indentation forms a blind opening in the first object, the blind opening having a bottom with the same texture as the proximally facing surface portion in a region around the mouth.

54. The method according to claim 46, wherein the indentation forms a through opening and wherein the sidewall extends contiguously from the proximally facing surface portion of the first object with unchanged texture.

55. The method according to claim 46, wherein during the step of coupling mechanical energy into the second object, structures interpenetrated by the thermoplastic material of the second object are generated in the first object, and/or wherein the first object comprises a foam, and/or wherein the first object is a lightweight building element having a first outer building layer and an interlining layer, the first outer building layer is thinner and denser than the interlining layer, and the first outer building layer is shaped to constitute the sidewall of the indentation, and/or wherein the first object is a rear panel shelf or a panel for a car motor.

56. A method of manufacturing a lightweight building element assembly, comprising the steps of: providing a first object, the first object being a lightweight building element that has a first outer building layer and an interlining layer, wherein the first outer building layer comprises a building layer material and is thinner and more dense than the interlining layer, and wherein the first object has an indentation formed by the first outer building layer, the indentation having a sidewall of the building layer material; providing a second object that has a lateral outer surface portion of a thermoplastic material; bringing the second object in contact with the first object so that the lateral outer surface portion is in physical contact with the sidewall; coupling mechanical energy into the second object so as to cause energy absorption due to friction between the lateral outer surface portion and the sidewall, until a flow portion of the thermoplastic material becomes liquefied and flows relative to the sidewall; and letting the flow portion re-solidify, whereby the flow portion secures the second object to the first object.

57. The method according to claim 56, wherein the indentation has a mouth in a first outer building layer plane, the first outer building layer has a plane portion around the indentation, and the sidewall portion meets the plane portion at the mouth of the indentation and is contiguous with the plane portion.

58. The method according to claim 56, wherein the indentation forms a blind opening in the first object and has a bottom of the building layer material, or wherein the indentation forms a through opening in the first object.

59. The method according to claim 56, wherein the first object has, in addition to the first outer building layer, a second outer building layer, the first and second building layers sandwiching the interlining layer, wherein the indentation forms a through opening and wherein the sidewall extends contiguously from the first outer building layer along the opening to the second outer building layer.

60. The method according to claim 56, wherein the building layer material completely lines the indentation, whereby a surface, especially an entire surface, of the first object in and around the indentation is formed by the building layer material, wherein during the step of coupling mechanical energy into the second object the building layer material remains contiguous whereby the interlining layer remains shielded from the second object until the step of letting the flow portion re-solidify, or further causing the building layer material lining the indentation to be disrupted by a piercing or punching action of the second object, and wherein the flow portion comprises a portion caused to flow into structures of the interlining layer.

61. The method according to claim 56, wherein the step of providing the first object comprises manufacturing the first object by a primary shaping process, the indentation is shaped by the primary shaping process, and the building layer material comprises a polymer material that is caused to harden during the primary shaping process.

62. The method according to claim 56, wherein the building layer material comprises a fiber reinforcement.

63. The method according claim 56, wherein the interlining layer comprises a cell structure, such as a honeycomb structure, and/or a foam structure.

64. The method according to claim 56, wherein the mechanical energy comprises mechanical vibration energy, and wherein coupling the mechanical energy into the second object comprises pressing the second object against the first object by a vibrating sonotrode, and/or wherein the mechanical energy comprises mechanical rotation energy, and wherein coupling the mechanical energy into the second object comprises pressing the second object against the first object by a tool subject to rotation, and/or wherein the lateral outer surface portion has a structure of indentations and ridges, wherein the ridges form axially running lamellae, and/or wherein the second object has an anchoring portion and a functional portion one-piece with the anchoring portion, wherein the functional portion is not rotationally symmetrical with respect to rotation by any angle about an axis of the indentation.

65. The method according to claim 46, wherein the mechanical energy comprises mechanical vibration energy, and wherein coupling the mechanical energy into the second object comprises pressing the second object against the first object by a vibrating sonotrode, and/or wherein the mechanical energy comprises mechanical rotation energy, and wherein coupling the mechanical energy into the second object comprises pressing the second object against the first object by a tool subject to rotation, and/or wherein the lateral outer surface portion has a structure of indentations and ridges, wherein the ridges form axially running lamellae, and/or wherein the second object has an anchoring portion and a functional portion one-piece with the anchoring portion, wherein the functional portion is not rotationally symmetrical with respect to rotation by any angle about an axis of the indentation.

66. The method of claim 56, wherein the second object comprises an anchoring portion that forms the lateral outer surface portion, wherein during the step of bringing the second object in contact with the first object the anchoring portion is caused to be inserted in the indentation, and wherein the lateral outer surface portion is at least partly cylindrical and/or tapered, wherein the anchoring portion forms a hollow space, whereby at least a distal part of the second object is essentially tube-shaped, and wherein the anchoring portion is stepped.

67. The method of claim 46, wherein the second object comprises an anchoring portion that forms the lateral outer surface portion, wherein during the step of bringing the second object in contact with the first object the anchoring portion is caused to be inserted in the indentation, and wherein the lateral outer surface portion is at least partly cylindrical and/or tapered, wherein the anchoring portion forms a hollow space, whereby at least a distal part of the second object is essentially tube-shaped, and wherein the anchoring portion preferably is stepped.

68. The method according to claim 46, further comprising the step of providing a functional element, wherein the functional element has a functional element through opening, and wherein during the step of bringing the second object in contact with the first object, a portion of the second object is caused to extend through the functional element through opening, wherein the functional element through opening comprises a step and/or a taper, whereby a width of the functional element through opening narrows towards distally, and wherein during the step of coupling the mechanical energy into the second object the second object is caused to be pressed against the step and/or taper, and/or wherein the second object has a head portion and wherein during the step of coupling the mechanical energy into the second object, the head portion is pressed against a proximally facing surface portion of the functional element, and/or wherein the functional element is at least partially thermoplastic and is caused to be welded to the second object during the step of coupling the mechanical energy into the second object.

69. The method according to claim 56, further comprising the step of providing a functional element, wherein the functional element has a functional element through opening, and wherein during the step of bringing the second object in contact with the first object, a portion of the second object is caused to extend through the functional element through opening, wherein the functional element through opening comprises a step and/or a taper, whereby a width of the functional element through opening narrows towards distally, and wherein during the step of coupling the mechanical energy into the second object the second object is caused to be pressed against the step and/or taper, and/or wherein the second object has a head portion and wherein during the step of coupling the mechanical energy into the second object, the head portion is pressed against a proximally facing surface portion of the functional element, and/or wherein the functional element is at least partially thermoplastic and is caused to be welded to the second object during the step of coupling the mechanical energy into the second object.

70. An assembly manufactured by the method according to claim 56, the assembly comprising the first object and further comprises the second object secured to the first object, preferably comprising a lightweight building element as the first object, the lightweight building element comprising a first outer building layer forming an indentation and an interlining layer, wherein the lightweight building element preferably further has a second outer building layer, the first and second outer building layers sandwiching the interlining layer, wherein the material of the first outer building layer preferably extends continuously along the indentation to the second building layer, whereby the indentation forms a through opening, and whereby the interlining layer is at least partially shielded from an outside in a region of the indentation.

71. An assembly manufactured by the method according to claim 46, the assembly comprising the first object and further comprises the second object secured to the first object, preferably comprising a lightweight building element as the first object, the lightweight building element comprising a first outer building layer forming an indentation and an interlining layer, wherein the lightweight building element preferably further has a second outer building layer, the first and second outer building layers sandwiching the interlining layer, wherein the material of the first outer building layer preferably extends continuously along the indentation to the second building layer, whereby the indentation forms a through opening, and whereby the interlining layer is at least partially shielded from an outside in a region of the indentation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0091] In the following, ways to carry out the invention and embodiments are described referring to drawings. The drawings are schematical. In the drawings, same reference numerals refer to same or analogous elements. The drawings show:

[0092] FIG. 1 a configuration with a first object, a second object, and a sonotrode;

[0093] FIG. 2 an assembly manufactured from the configuration of FIG. 2;

[0094] FIG. 3 an alternative first object;

[0095] FIG. 4 an alternative second object;

[0096] FIG. 5 an alternative configuration with a separate functional element;

[0097] FIGS. 6 and 7 manufacturing a first object;

[0098] FIG. 8 a detail of mold parts for a manufacturing process;

[0099] FIG. 9 an even further configuration of a first object, a second object and a functional element;

[0100] FIG. 10 an assembly manufactured from the configuration of FIG. 9;

[0101] FIG. 11 a configuration with a first object, a second object, and a rotation tool;

[0102] FIGS. 12-14 different cross sections of indentations (and of according portions):

[0103] FIGS. 15 and 16 a method of manufacturing an alternative first object, and a configuration for anchoring a second object therein, respectively; and

[0104] FIGS. 17-19 different second objects.

[0105] FIGS. 1-3 and 5-11, 15 and 16 all depict the shown elements in section through a plane through the axis of the indentation (in FIG. 16, for illustration purposes the lamella structure of the second object's anchoring portion is shown in side view). FIG. 4 shows a side view of the depicted second object. FIGS. 12-14 show schematical top views, and FIGS. 17-19 depict views from an oblique angle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0106] FIG. 1 depicts a configuration with a first object 1 being a lightweight building element, a second object 2 and a sonotrode 6. The first object is placed on a non-vibrating support 7.

[0107] The first object has a first (proximal) outer building layer 11, a second outer building layer 12 and an interlining layer 13 sandwiched between the first and second outer building layers. The first outer building layer moreover forms an indentation 19 with a sidewall 14. The first outer building layer is essentially plane around the indentation 19. The sidewall is contiguous with the plane portion around the indentation.

[0108] The outer building layer(s) may have material characteristics as know in the relevant industry. Cars for example often have parts with a soft or carpet wooly/furry surface that is often non-woven.

[0109] In the depicted embodiment, the indentation forms a through opening through the first object 1. Also, in the depicted embodiment the sidewall 14 is contiguous with the second outer building layer 12, too.

[0110] The indentation in the depicted embodiment has a stepped shape with a shoulder 15 formed between a proximal sidewall 14 segment (upper sidewall segment in FIG. 1) and a distal (lower) sidewall segment 14.

[0111] The indentation may be rotationally symmetrical about an axis 20.

[0112] The second object 2 of FIG. 1 is an example of a second object that has a thermoplastic anchoring portion as well as a functional portion. The second object in this embodiment thus serves both, as connector and as functional part in that the anchoring portion is not formed by a separate element but is a portion of the part itself that is to be fastened to the first object. Embodiments that have an anchoring portion and a functional portion feature the substantial advantage that no separate connector has to be manufactured so that less parts are required in assembly processes.

[0113] The functional portion 23 is, in the embodiment of FIG. 1, one-piece with the anchoring portion 21 and is only partially illustrated. The functional part may for example comprise a connecting structure (not shown in FIG. 1) such as a peg or stud, a fastening hole, a sliding block, a button, etc. At may in addition or as an alternative carry other functional element such as a sensor, a transducer, etc.

[0114] The anchoring portion 21 forms a distal anchoring protrusion that forms a lateral (with reference to the axis 20) outer surface 24. The anchoring portion may optionally be symmetrical about the axis, for example rotationally symmetrical or symmetrical with respect to rotations around the axis by a defined discrete angle. The entire second object 2 in FIG. 1 does not have any symmetry with respect to the axis due to the functional portion.

[0115] The lateral outer surface 24 in FIG. 1 is slightly tapering. Alternatively, it may be essentially cylindrical.

[0116] For anchoring the second object 2 relative to the first object 1 the sonotrode 6 is used to press the anchoring portion into the indentation while mechanical vibrations are coupled into the anchoring portion. In the embodiment of FIG. 1, the anchoring portion has an opening 25 open towards proximally so that a guiding protrusion 61 of the sonotrode 6 may engage. In FIG. 1, the opening 25 is an axially running through opening. The anchoring portion 21 thereby is tube-like.

[0117] Due to the effect of the mechanical vibration, friction energy is absorbed at the interface between the anchoring portion and the first outer building layer material, until material of the connector becomes flowable and flows relative to the first object. FIG. 2 illustrates the assembly after the process. A flow portion 8 has interpenetrated structures of the first outer building layer material to anchor the second object 2 relative to the first object 1 by a positive fit connection and/or by a weld to matrix material of the first outer building layer/lateral wall.

[0118] In the embodiment of FIGS. 1 and 2, the anchoring portion 21 is stepped so as to cooperate with the stepped indentation. A distally facing shoulder 26 of the anchoring portion towards the end of the anchoring process is pressed against the shoulder 15 formed by the indentation, whereby an axial position of the second object relative to the first object is defined, and also additional interface area is created between the first and second objects in the region where a flow portion is generated.

[0119] FIG. 3 shows, as a variant, a first object 1 with an indentation 19 that does not form a through hole but a blind hole. The indentation therefore has in addition to a sidewall 14 also an indentation bottom 16. Sidewall and indentation bottom together line the indentation without any interruption, i.e. the building layer material completely shields the interlayer in and around the indentation.

[0120] Underneath (distally of) the indentation bottom, the interlining layer material forms, due to the above-described manufacturing process, a dense zone 17.

[0121] Anchoring takes place in the same way as illustrated referring to FIGS. 1 and 2.

[0122] As a further difference to the embodiment of FIGS. 1 and 2, the indentation is illustrated to have a sidewall 14 that is not cylindrical but that tapers. The taper angle a (in the definition used in this text and illustrated in FIG. 3, the taper angle a is the angle of the tapering surface with respect to the axis 20, thus half of the cone opening angle) in the design of the assembly is a degree of freedom that may be adapted to the angle of a possible taper of the anchoring portion. For example, the tapering angle a of the lateral sidewall may be equal to or smaller than the anchoring portion tapering angle. In special situations, for example if enhanced anchoring at the distalmost part of the anchoring portion is desired, the tapering angle of the lateral sidewall may also be greater than the tapering angle of the anchoring portion.

[0123] The features of the sidewall being tapering and of the indentation forming a blind opening are independent of each other. Thus, also a through opening of the kind shown in FIG. 1 may have a tapering sidewall, and also a blind opening may have a cylindrical lateral sidewall.

[0124] FIG. 4 shows an embodiment of a second object 2 that in contrast to the embodiment of FIG. 1 is not a connector that comprises a functional portion but a separate connector for cooperating with a separate functional element. The connector has the anchoring portion 21 as well as a proximal portion 22 that for example extends through a through opening in the functional element. The second object 2 in FIG. 4 further has a head portion 27; the structure of the proximal portion of a standalone connector as shown in FIG. 4 may be chosen to match with the functional element.

[0125] The anchoring portion 21 in FIG. 4 is tapering. It may comprise a structure of axially running lamellae 41 with indentations 42 between them or other structure deviating from a smooth conical or cylindrical outer surface. Such structure may bring about energy directing properties, i.e. due to them the energy input required for an onset of liquefaction is reduced.

[0126] FIG. 5 shows an arrangement of a first object 1 and a functional element 3 to be secured to the first object together with a second object 2 being a connector for fastening the functional element to the first object. In FIG. 5, the indentation 19 is illustrated to be a through opening. The functional element 3 has a functional element through opening 31 through which the second object 2 extends. After the second object 2 is anchored, with the anchoring portion 21 secured to the lateral wall 14 as in the above-described embodiments, the functional element is clamped between the second object's head portion 27 and the first object 1.

[0127] In the embodiment of FIG. 5, further (optional) features of an arrangement with a functional element 3 initially separate from the second object are illustrated: [0128] The functional element through opening 31 is not cylindrical but is stepped or narrows otherwise towards distally. In FIG. 5, an inward flange 33 forms an according inward shoulder. Consequently, a second object distally facing shoulder 29 may be pressed against this inward shoulder during the process to additionally secure the functional element 3 against the first object 1. [0129] Further, the functional element 3 at least in a region of the functional element through opening 31 is of thermoplastic material liquefiable by the mechanical vibration energy. This may be used in one or both of the following ways: [0130] Firstly, the mechanical vibration may be coupled through the second object into the functional element also (for example via the shoulders 29, 33 of the second object and the functional element) and may cause a liquefaction of thermoplastic material also of the functional element in contact with the first object. In the configuration of FIG. 5, thermoplastic material of the distal-most part of the functional element, at the distal surface of the inward flange 33 is pressed against the shoulder 15 of the indentation 19. A flow portion of material of the functional element may interpenetrate material of the first outer building layer 11 and/or be welded thereto. Secondly, a weld between the second object and the functional element may be caused. In FIG. 5, this may for example be the case where the shoulders 29, 33 meet. [0131] The second object has a hollow space 28 open towards distally. Due to the hollow space 28, the anchoring portion 21 is essentially tube-like, similarly to the embodiment of FIG. 1. Such a hollow space 28 or through opening 25 is an option for any embodiment of the invention. It reduces the overall amount of material needed and makes the second object lighter. It may be open towards distally, proximally or both. It is often preferable that it is open at least towards distally.

[0132] FIG. 6 illustrates a manufacturing process of a first object with indentations 19. Two layers of glass or carbon fibers soaked by liquid, PU forming material compositions 51, 52 sandwiching a dimensionally stable interlayer structure 13 (for example a honeycomb structure of a Polypropylene or cardboard or a foam, such as a PU foam) are placed in a first (lower) mold part 54. A second mold part 55 that comprises shaping protrusions 56 for the indentations is pressed against this pre-product. Due this the effect of the shaping protrusions 56, the interlayer is locally deformed and displaced. For example accelerated by the effect of a heat input, the PU forming material compositions are polymerized, whereby the first and second building layers 11, 12 comprising fiber reinforced PU are generated. If the compositions 51, 52 are of the foaming type or if in addition the compositions a foaming composition is provided, a foam filling 58 will be generated in the interlining layer structure, for example predominantly at the interfaces to the first and second building layers.

[0133] FIG. 7 shows the resulting first object, illustrated to have two indentations 19 being blind holes. The deformation process will lead to a re-orientation of the fibers, a local compaction of the interlining layer (dense zone 17), and possibly also to a matrix material (foam) enrichment and/or compaction yielding porosity for the anchoring process, in addition or as an alternative to a residual porosity between the fibers of the first building layer material.

[0134] If the indentation 19 is to be a through opening then the shaping protrusion(s) 56 can be longer so that they extend to the first mold part 54, or the first mold part may have first mold part shaping protrusions 59 at corresponding positions, as shown in FIG. 8. In either case, after forming of the first and second building layers, a thin residual layer of building layer material may remain and may have to be removed in a separate step.

[0135] The process as illustrated in FIGS. 6-8 when used for producing the first object with the indentation being a through hole brings about a special advantageous feature. At the distal end of the shaping protrusion(s) 56 or 56/59, respectively, there will be an increased density of reinforcing fibers, compared to the lateral wall due to smaller pressure. As a consequence, the porosity is locally enhanced in the wall, which may be beneficial for the anchoring process. This increased fiber density is due to the fact that the reinforcing fibers have a certain length and hence have, compared to the matrix material, less tendency to flow sideways. In the configuration of FIG. 8 with shaping protrusions coming from both sides, this increased density of fibers can be observed around the location where the two shaping protrusions meet. An additional effect can be the already mentioned re-orientation of the fibers due to the draping effect caused by the deformation process.

[0136] In the above-described embodiments, the building layer material lining the indentation is assumed to be left intact during the process, and the interlining material remains shielded by the building layer material so that the anchoring portion of the second object does not get into contact with it. FIG. 9 illustrates an example of an alternative embodiment. The second object is provided with a distal piercing or punching structure. In FIG. 9, the anchoring portion 21 has a circular distal punching edge 71. During the anchoring process, the sonotrode presses the second object towards distally. This causes the first building layer at the bottom 16 of the indentation to be pierced or punched through. After the process, the second object will be anchored with respect to both, the sidewall 14 and the interlining.

[0137] FIG. 10 illustrates the situation after anchoring, i.e. after the thermoplastic material has re-solidified. The flow portion 8 of the thermoplastic material, comprises both, portions that have flown into structures of the sidewall, for example structures formed by exposed fibers, and portions that have interpenetrated the interlining. A punched-out piece 73 of the first building layer is displaced towards distally. The hollow space 28 may comprise debris of interlining material and/or first building layer material.

[0138] As an alternative to being punched out, a bottom 16 of the indentation may be removed prior to the anchoring process, for example by drilling.

[0139] FIG. 11 illustrates the possibility that the mechanical energy input in addition or as an alternative to comprising mechanical vibration may comprise (oscillatory or continuous) rotation of the second object 2 relative to the first object. To this end, the first object may be mounted in a fixed orientation, and the second object may be pressed against the first object by a rotation tool 81 rotating around the axis 20. For rotational coupling, the second object 2 may have a not rotationally symmetrical (“rotationally symmetrical” here implying rotational symmetry with respect to rotation about any angle, i.e. the coupling structure may optionally have a discrete symmetry, such as by being hexagonal or quadratic or star-shaped in cross section or slit-shaped) coupling structure, such as a coupling indentation, cooperating with a mating rotation tool coupling structure, such as a coupling protrusion 82.

[0140] Energy input by rotational energy in addition or as an alternative to (for example longitudinal) vibration is an option for all illustrated and herein discussed embodiments, provided however, that the second object will, in many embodiments and differently from what is for example illustrated in FIG. 4, have no outer structure macroscopically deviating from a rotational symmetry around the axis 20 (but may have the mentioned coupling structure).

[0141] In the previously described embodiments, the indentation was assumed to be approximately round in cross section, i.e. rotationally symmetrical (with respect to rotation about any angle) about the axis 20. With the partial exception of the configuration of FIG. 11 that concerns the input of rotational energy, this need not be the case. Rather, as an alternative to being round (FIG. 12) in cross section, the indentation 19 may have any other shape, such as oblong (FIG. 13), oblong-curved (FIG. 14), etc. FIGS. 12-14 all schematically show cross sections through a plane perpendicular to the axis.

[0142] The anchoring portion of the second object may have an approximately adapted cross section, which however may deviate from the cross section of the indentation, for example by comprising a structure of the above-described kind with lamellae or similar.

[0143] It is, however, also possible that the outer cross section of the anchoring portion has an overall shape that differs from the cross section of the indentation, for example in that the anchoring portion is generally round (with the exception of the energy directing structures) whereas the indentation is for example oblong. Then, the resulting anchoring of the anchoring portion will be anisotropic, with a dominant anchoring at the side face portions where the indentation is narrower. This may be used for intentional anisotropies in the bending strength/flexibility, or also for some tolerance compensation.

[0144] FIG. 15 illustrates the principle that it is possible to make another object than a sandwich board by the primary shaping process. The first object 1 may for example comprise a structure of soaked fibers placed in a mould 55 having a salient feature that forms the indentation.

[0145] FIG. 16 shows the set-up for anchoring, including a second object 2 and a sonotrode. Another feature illustrated in FIG. 16, which is independent on the nature of the first object 1, is that the anchoring portion shaped to be inserted into the indentation and the indentation are adapted to each other for a press-fit, in that the anchoring portion is slightly oversized compared to the dimensions of the indentation (see the dashed lines). The anchoring method may especially comprise inserting the second object into the indentation so that a press-fit results (i.e. the second object is provisionally fixed to the first object) prior to the mechanical vibration energy input.

[0146] In the previously described embodiments, it is the first outer building layer of the lightweight building element that forms the surface both, of the sidewall and of the proximally facing surface portion around the mouth of the indentation. Like in these embodiments, in the embodiment of FIGS. 15 and 16 there is a smooth, continuous transition between the proximally facing surface portion 18 around the mouth and the sidewall 14. Also, both have a same texture.

[0147] Object 1 as shown in all figures, but especially as shown in FIG. 16, may be a homogeneous body, such as a block of foam with an indentation. As can be seen in FIG. 16, the surface portion 18 and sidewall 14 have the same texture.

[0148] FIGS. 17-19 yet show different second objects 2. The embodiment of FIG. 17 has axially running ridges between which grooves of approximately triangular cross sections are established, wherein the grooves are, given the conical shape of the second object 2, deepen towards proximally. In the embodiment of FIG. 18, the grooves are not triangular but rectangular in cross section. In further variants, the overall second object is not conical but cylindrical, and the axial length of the grooves/ridges may be chosen differently, with an example being shown in FIG. 4. FIG. 19, finally, shows an example with ridges that do not run into axial directions but circumferentially.

[0149] Generally, the second object's anchoring portion in embodiments may have a conical shape up to approx. 30 degrees cone angle or be cylindrical. The external wall of the anchoring portion may contain features that act as energy directors, particularly vertical ridges or groove (with respect to the proximodistal direction) that are parallel to each other. The maximum number of grooves on the perimeter is a function of the insert portion's diameter, cone angle and the groove geometry. The grooves can have a triangular cross-section with an angle at the bottom of the groove ranging from 10 to 90 degrees or more, or a rectangular cross-section with or without rounded edges at the bottom of the grooves. Some other groove shapes could be imagined. The number of grooves can be chosen so that they don't overlap, as to retain the conical or cylindrical body (outer profile) between the grooves. The cross-section of the grooves changes along the height of the pin (insertion direction) when the anchoring portion is conical, being deeper at the top (bigger diameter of the cone) and shallower at the bottom of the cone.