ROTATIONAL WELDED ANCHOR AND ASSOCIATED ASSEMBLY METHOD

Abstract

The invention relates to a fixing pin (16) intended to be fixed by rotational welding in an opening (18) of a plastic support (10). The fixing pin (16) comprises a weldable fixing body (22) having an external frustoconical face (24) of revolution about a principal axis (A) extending from a large base (26) intended to be flush with a surface of the support (10) to a small base (28) intended to be axially driven into the opening (18) of the support (10). The pin is characterized in that the external frustoconical face (24) of the body has an apex angle (α) of between 24° and 25°. Figure for the abstract: 3

Description

Title of the invention: ROTATION WELDING FIXING DOWEL AND ASSOCIATED ASSEMBLY METHOD Technical field of the invention

[0001] The invention relates to a fixing pin which is intended to be fixed by rotational welding in an orifice of a support made of plastic material, the fixing pin comprising a welding fixing body which has an external face of truncated cone shape of revolution around a main axis which extends from a large base intended to be flush with a surface of the support, to a small base intended to be pushed axially into the orifice of the support. Technical background

[0002] It is known to produce sandwich structure panels for many applications, in particular for making vehicle walls or partitions. Such panels generally have a core made of plastic material, for example expanded PET, sandwiched between two plies of composite materials which make it possible to give the panel its strength. Such panels are advantageously light and strong.

[0003] It is often necessary to fix various objects to the panel. However, the plastic core has a consistency that is not compatible with the direct use of fixing screws. When screwed directly into the core of the panel, the screws have very low tear resistance.

[0004] It has already been proposed to first fix dowels with particularly prominent threads in the panel, and then to screw the fixing screws into the dowels. However, although the pull-out resistance is slightly improved, it remains insufficient for most applications.

[0005] The invention proposes to solve these problems by proposing a dowel and a method of fixing the dowel in the panel which make it possible to obtain excellent resistance to tearing. Summary of the invention

[0006] The invention provides a fixing pin which is intended to be fixed by rotational welding in an orifice of a support made of plastic material, the fixing pin comprising a welding fixing body which has an external face of frustoconical shape of revolution around a main axis which extends from a large base intended to be flush with a surface of the support, to a small base intended to be driven axially into the orifice of the support.

[0007] The dowel is characterized in that the fixing body has a central bore smooth blind which opens only through a free axial end face of the dowel, the fixing body being solid between the central bore and its external truncated cone face.

[0008] This makes it possible to obtain a simple dowel to produce and a very rigid fixing body so as to promote rotation welding.

[0009] According to another characteristic of the dowel produced according to the teachings of the invention, the frustoconical external face of the body has an angle at the apex which is between 24° and 25°. This angle in fact makes it possible to obtain particularly effective friction between the dowel and the support. Thus, a dowel is obtained which is quick to fix with a particularly solid fixing of the dowel.

[0010] According to another characteristic of the dowel produced according to the teachings of the invention, the angle at the apex of the frustoconical external face of the fixing body is substantially equal to 24.5°.

[0011] According to another characteristic of the dowel produced according to the teachings of the invention, the dowel comprises a centering point of conical shape of revolution around the main axis which extends axially in the continuity of the frustoconical external face of the body from the small base, a summit of the centering point forming a first axial end of the dowel.

[0012] According to another characteristic of the dowel produced according to the teachings of the invention, the centering point has an angle at the apex greater than the angle at the apex of the frustoconical external face of the fixing body.

[0013] According to another characteristic of the dowel produced according to the teachings of the invention, the centering point has an angle at the top of approximately 90°.

[0014] According to another characteristic of the dowel produced according to the teachings of the invention, the dowel is produced in a single piece from a plastic material, for example by molding.

[0015] According to another characteristic of the dowel produced according to the teachings of the invention, the large base of the fixing body forms the free end face of the dowel.

[0016] According to another characteristic of the dowel produced according to the teachings of the invention, the large base has an imprint intended to allow coupling with a tool for rotating around its main axis.

[0017] The invention also relates to a method of assembling the fixing dowel, produced according to the teachings of the invention, with a support of plastic material, the plastic material of the support having a melting temperature substantially equal to that of the material constituting the fixing body of the dowel, the method comprising chronologically:

[0018] - a step of drilling an orifice in a face of the support;

[0019] - a step of positioning the small base of the fixing body of the dowel of fixing in the opening of the orifice;

[0020] - a step of axially driving and rotating the fixing pin to a sufficient speed and with sufficient axial thrust so that the friction between the frustoconical external face of the fixing body and the material constituting the support causes the simultaneous melting of a surface layer of the external face of the fixing body and the material in contact with the support, the molten materials of the fixing pin and the support mixing;

[0021] - a cooling step which occurs when the large base of the body of fixing is substantially flush with the face of the support, during which rotation is interrupted so that the molten plastic material mixture solidifies to achieve the fixing by welding the fixing pin into the support.

[0022] According to another characteristic of the assembly method carried out according to the teachings of the invention, the diameter of the drilling is substantially equal to the diameter of the large base of the fixing body. Brief description of the figures

[0023] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which reference will be made to the appended drawings which are described succinctly below.

[0024] [Fig. 1] is a perspective view showing a sandwich structure panel comprising a plastic core sandwiched between two plies.

[0025] [Fig. 2] is a perspective view which represents an anchor produced according to the teachings of the invention.

[0026] [Fig.3] is an axial sectional view of the dowel shown in [Fig.2].

[0027] [Fig.4] is a sectional view of the panel of [Fig.l] after a step of punching a fold.

[0028] [Fig.5] is a view similar to [Fig.4], in which a hole has been drilled in the panel, with the dowel of [Fig.2] positioned in the hole.

[0029] [Fig.6] is a view similar to that of [Fig.5], in which the dowel has been driven and welded to the panel by rotation in the hole. Detailed description of the invention

[0030] In the remainder of the description, an axial orientation directed along the main axis of the fixing pin will be adopted, without limitation. Radial directions directed orthogonally to the main axis of the pin will also be adopted.

[0031] In the remainder of the description, longitudinal, vertical and transverse orientations indicated by the trihedron "L,V,T" of the figures will also be adopted.

[0032] [Fig.l] shows a composite panel 10 comprising a core 12 taken sandwiched between two plies 14 of composite material. Each ply 14 is made of the same composite material. The panel 10 here has a rectangular shape.

[0033] This is for example a panel 10 which can be used for the interior design of boats, airplanes, trucks, trains, etc.

[0034] The core 12 is for example a solid structural plate made of thermoplastic foam, such as recycled polyethylene terephthalate (recycled PET). It is for example a core of expanded PET.

[0035] Each ply 14 comprises a reinforcement impregnated with a matrix. The reinforcement is formed from a piece of fabric. The fabric is for example made of basalt fibers. The fabric can be woven or non-woven.

[0036] The matrix comprises, for example, a resin that can be polymerized by heating, also called "thermosetting", such as epoxy. Alternatively, the matrix is ​​a resin that can be polymerized at room temperature, for example around 20°C.

[0037] Alternatively, the matrix comprises a thermoplastic resin.

[0038] These materials have the advantage of being easily recyclable. They are advantageously bio-sourced and recycled materials.

[0039] [Fig. 2] shows a fixing pin 16 which is intended to be fixed by rotation welding in an orifice 18 of a support made of plastic material, here in an orifice 18 of the composite panel. The fixing pin 16, after having been fixed to the panel 10, is intended to receive a fixing screw 20 to allow an element to be fixed to the panel, as will be described in detail later with reference to Figures 4 to 6.

[0040] Referring to Figures 2 and 3, the fixing dowel 16 comprises a welding fixing body 22 which is radially delimited by an external face 24 which has a frustoconical shape of revolution around a main axis "A". As its name indicates, the fixing body 22 has the function of fixing the dowel 16 to its support, here to the panel 10. The fixing body 22 thus extends from a large base 26 intended to be substantially flush with the surface of the support 10, to a small base 28 intended to be pushed deep into the orifice 18 of the support 10. The large base 26 and the small base 28 each have a circular contour. The diameter "D1" of the large base is greater than the diameter "D2" of the small base 28.

[0041] The external face 24 is here devoid of protuberances. More particularly, the external face 24 is here devoid of threads. The external face 24 may nevertheless have roughness at the microscopic level in order to improve its coefficient of friction.

[0042] The frustoconical external face 24 of the body 22 has an angle "a" at the apex which is between 24° and 25°. The angle "a" at the apex of the frustoconical external face 24 of the body 22 is preferably substantially equal to 24.5°.

[0043] The dowel 16 here comprises a centering point 30 of conical shape of re- evolution around the main axis "A" which extends axially in the continuity of the frustoconical external face 24 of the body 22 from the small base 28 to a summit 32 which forms a first free axial end of the dowel 16. The centering point 30 has the function of guiding and maintaining the dowel 16 coaxially with the orifice 18 during its insertion.

[0044] The centering point 30 has an angle "|3" at the apex greater than the angle "a" at the apex of the truncated external face 24 of the body 22. The point has, for example, an angle "|3" at the apex of approximately 90°.

[0045] The dowel 16 has a second free end axially opposite the centering tip 30. The second free end is formed by a free end face 36. The free end face 36 extends in a plane orthogonal to the main axis "A" of the dowel 16. The free end face 36 has a circular contour.

[0046] The dowel 16 here comprises a head 34 which is arranged at the axial end opposite that of the centering point 30. The head 34 is here in the form of a cylindrical section of revolution of the same diameter as the large base 26. The head 34 is thus arranged in the extension of the body 22. The head 34 has a free face which forms the free end face 36 of the dowel 16.

[0047] In a variant of the invention not shown, the head has a diameter greater than that of the large base 26, and it is intended to protrude relative to the surface of the panel 10 when the dowel 16 is fixed to the panel 10.

[0048] According to yet another variant, the dowel does not have a head, the free end face of the dowel then being formed directly by the large base 26 of the fixing body 22.

[0049] The fixing pin 16 is made in a single piece from a plastic material, for example by molding. Said plastic material has a melting temperature which is substantially equal to the melting temperature of the material constituting the core 12 of the panel 10. It is for example a pin 16 made from PET, PETG, recycled PET, or any other suitable plastic material.

[0050] The screw 20 which is intended to be fixed to the dowel 16 is here a self-tapping screw 20. To receive this screw 20 and allow it to be guided, the body 22 has a smooth blind central bore 38 which opens only through the free end face 36. Such a bore 38 is generally known under the name "pilot hole".

[0051] Such a smooth bore 38 allows the dowel to be used in association with several types of fixing such as a screw for metal, a screw for wood or even a chemical fixing.

[0052] The central bore 38 is coaxial with the main axis "A". The bore 38 has a diameter which is less than the nominal diameter of the screw 20. Preferably, the diameter of the bore 38 is substantially equal to the diameter at the bottom of the thread of the screw 20.

[0053] The dowel 16 also has sufficient rigidity to allow its rotational friction and its insertion into the core 12 of the panel 14 without substantially undergoing deformations. For this purpose, the body 22 is solid between the central bore 38 and its external frustoconical face 24. The fixing body 22 is here in the form of a solid block in which the central bore 38 is made.

[0054] Furthermore, the free end face 36 of the pin 16 has an imprint 40 intended to allow coupling with a tool for rotating around its main axis. The imprint 40 may be in the form of one or more notches made in the free end face 36, and / or in the form of one or more protuberances made on the free end face 36.

[0055] By way of non-limiting example, this is a rectangular profile notch which diametrically crosses the opening of the central bore 38. The small side of the rectangular profile here has a dimension smaller than that of the diameter of the central bore 38.

[0056] In a variant not shown, these are several notches distributed regularly around the main axis "A".

[0057] A method of assembling the fixing dowel 16 with a plastic material support, here with the panel 10, is now described with reference to FIGS. 4 to 6. The dowel 16 preferably has an axial length less than the thickness of the core 12 so that the dowel 16 does not pass right through the core once assembled.

[0058] When, as is the case here, the face of the panel 10 has a fold 14 which covers the core 12, a preliminary punching step is carried out. During this step, the fold 14 is punched using a suitable tool, for example a punch or a point, to create a perforation 42 in the fold 14 at the location where it is desired to fix the dowel 16, as shown in [Fig. 4].

[0059] At the end of this preliminary step, a step of drilling an orifice in a face of the support is carried out. During this step, a drill (not shown) equipped with a drill bit or a conical cutter is used to drill the orifice 18. When the preliminary punching step has been carried out, the perforation 42 makes it possible to correctly position the tip of the drill bit or cutter. The orifice 18 obtained is shown in [Fig.5].

[0060] The maximum diameter of the orifice 18, at the interface with the fold 14, is substantially equal to the diameter "Dl" of the large base 26 of the fixing body 16.

[0061] Furthermore, the orifice 18 has a depth which is here less than the length of the fixing body 22. Preferably, the depth of the orifice 18 is here chosen so that the centering tip 30 of the dowel 16 can be introduced into the orifice 18.

[0062] The orifice 18 has a substantially conical shape.

[0063] After the drilling step, during a positioning step, the small base 28 of the body 22 of the fixing pin 16 in the opening of the orifice 18, as shown in [Fig. 5]. More particularly, the centering tip 30 is inserted axially into the orifice 18 until it is in contact with the core 12. In this position, at least a portion of the body 22 remains outside the orifice 18.

[0064] Next, a step of axially driving and rotating the fixing dowel 16 is implemented. During this step, a tool 44 is coupled to the dowel 16 by interlocking with the imprint 42. The tool 44 is rotated at high speed, for example by a drill, around the main axis "A" of the dowel 16. At the same time, the tool 44 applies an axial thrust of the dowel 16 towards the panel 10. The rotation speed of the dowel 16 is sufficient so that, combined with the axial thrust, the frustoconical external face 24 of the body 22 rubs against the material constituting the core 12. This causes heating of the material constituting the dowel 16, on the one hand, and heating of the material constituting the core 12, on the other hand.

[0065] As explained previously, the plastic material of the support, here of the core 12, has a melting temperature substantially equal to that of the material constituting the body 22 of the dowel 16.

[0066] The rotation speed and the axial thrust are sufficient to cause the simultaneous melting of a surface layer of the external face 24 of the body 22 and a surface layer of the orifice 18. The molten materials of the dowel and the support then mix. The melting of the material constituting the support, here the core 12, also allows the dowel 16 to penetrate axially deeper into the core 12.

[0067] When the dowel 16 has been driven in sufficiently, for example when the large base 26 is flush with the face of the support, here of the core 12, a cooling step is implemented. During this step, the rotation and the thrust are interrupted so that the mixture of molten plastic materials interposed between the dowel 16 and the core 12 solidifies to achieve the fixing by welding of the dowel 16 in the support. Thus, in section, horn shown in [Fig.6], a welding zone 46 at the interface between the dowel 16 and the core 12 is formed from the solidified mixture which ensures the fixing of the dowel 16 in the core 12.

[0068] At the end of the process of assembling the dowel 16 with the panel 10, it is possible to fix an object to the panel 10 by means of a screw 20 which is screwed into the central bore 38 of the dowel 16. It has been observed that with such an assembly, the dowel 16 was capable of withstanding a tightening torque of up to 17 Nm without being torn from the panel 10. This makes it possible to tighten the screw 20 without risking breaking the welded connection between the dowel 16 and the core 12.

Claims

Claims

1. Fixing dowel (16) which is intended to be fixed by rotational welding in an orifice (18) of a support (10) made of plastic material, the fixing dowel (16) comprising a body (22) for fixing by welding which has an external face (24) of frustoconical shape of revolution around a main axis (A) which extends from a large base (26) intended to be flush with a surface of the support (10), to a small base (28) intended to be pushed axially into the orifice (18) of the support (10), the fixing body (22) comprising a smooth blind central bore (38) which opens only through a free axial end face (36) of the dowel (16), the fixing body (22) being solid between the central bore (38) and its external frustoconical face (24),characterized in that said dowel also comprises a centering point (30) of conical shape of revolution around the main axis (A) which extends axially in the continuity of the external truncated cone-shaped face (24) of the body from the small base (28), a top (32) of the centering point (30) forming a first axial end of the dowel (16).,

2. Fixing anchor (16) according to the preceding claim, characterized in that the frustoconical external face (24) of the body has an angle (a) at the apex which is between 24° and 25°.

3. Fixing anchor (16) according to the preceding claim, characterized in that the angle (a) at the top of the frustoconical external face (24) of the fixing body (22) is substantially equal to 24.5°.

4. Fixing dowel (16) according to one of the preceding claims, characterized in that the centering point (30) has an angle (|3) at the apex greater than the angle (a) at the apex of the frustoconical external face (24) of the fixing body (22).

5. Fixing anchor (16) according to the preceding claim, characterized in that the centering point (30) has an angle (|3) at the top of approximately 90°.

6. Fixing anchor (16) according to any one of the preceding claims, characterized in that it is made in a single piece from a plastic material, for example by molding.

7. Fixing dowel (16) according to any one of the preceding claims, characterized in that the large base (26) of the fixing body (22) forms the free end face (36) of the dowel (16).

8. Fixing anchor (16) according to any one of the preceding claims, characterized in that the large base (26) has an imprint (42) intended to allow coupling with a tool (44) for rotation around its main axis (A).

9. Method for assembling the fixing dowel (16) according to any one of the preceding claims with a support (12) of plastic material, the plastic material of the support (12) having a melting temperature substantially equal to that of the material constituting the body (22) for fixing the dowel (16), the method chronologically comprising: - a step of drilling an orifice (18) in a face of the support (10); - a step of positioning the small base (28) of the body (22) for fixing the fixing dowel (16) in the opening of the orifice (18);- a step of axially driving and rotating the fixing pin (16) at a sufficient speed and with sufficient axial thrust so that the friction between the frustoconical external face (24) of the fixing body (22) and the material constituting the support (12) causes the simultaneous melting of a surface layer of the external face (24) of the fixing body (22) and of the material in contact with the support, the molten materials of the fixing pin (16) and of the support (12) mixing; - a cooling step which occurs when the large base (26) of the fixing body (22) is substantially flush with the face of the support (12), during which the rotation is interrupted so that the mixture of molten plastic material solidifies to achieve the fixing by welding of the fixing pin (16) in the support (12).;

10. Method according to the preceding claim, characterized in that the diameter of the drilling is substantially equal to the diameter of the large base (26) of the fixing body (22).

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