WO2007035168A1

WO2007035168A1 - Tool

Info

Publication number: WO2007035168A1
Application number: PCT/SE2006/050337
Authority: WO
Inventors: Håkan JOHANSSON; Petter SJÖDIN
Original assignee: Johansson Hakan; Sjoedin Petter
Priority date: 2005-09-23
Filing date: 2006-09-15
Publication date: 2007-03-29
Also published as: SE0502111L; SE529106C2

Abstract

A tool for creating a profiled recess in a sandwich structure which comprises two thin rigid face sheets separated by a relatively thick, light and soft core, which tool comprises an elongate body (2) intended to rotate about its axial direction, and a cutting portion with at least one movable arm configuration (4) comprising a first arm portion (6) with a first and a second end, which first end is fastened articulatedly to the body and is pivotable in a substantially radial plane, a second arm portion (8), in the form of a cutting sheath (8), with a first end (D), a second end which is arranged for articulation relative to the body (2), is pivotable in a substantially radial plane and is arranged for movement in the axial direction, and a central portion to which the second end of the first arm portion (6) is articulatedly fastened, the distance between the articulation (A) of the first end of the first arm portion (6) and the articulation (C) of the central portion of the second arm portion (8) being in principle equal to the distance between the articulation (C) of the central portion of the second arm portion (8) and the articulation (B) at the latter' s second end. The invention also relates to a method for creating a profiled recess, intended for fastening purposes, in a sandwich structure, or for creating a hole through a sandwich structure.

Description

TOOL

TECHNICAL FIELD

The present invention relates to a tool according to the preamble of claim 1 for creating a profiled recess in a sandwich structure. The present invention also relates to a method according to the preamble of claim 15 for using a tool to create a profiled recess, intended for fastening purposes, in a sandwich structure.

BACKGROUND

A structural sandwich is a special form of laminated composite comprising two or more different materials bonded to one another in such a way that the best characteristics of the respective materials are utilised in order to afford combined structural advantages.

A sandwich comprises two thin rigid face sheets separated by a relatively thicker, lighter and softer core. Using a low-density core to separate the face sheets makes it possible to increase the flexural rigidity considerably without appreciable weight increase. The face sheets are bonded to the core in order to be able to conduct force between the components. Subjecting a sandwich to bending results in compressive and tensile forces in the respective face sheets and shearing forces in the core, i.e. a sandwich acts much like an I- beam.

A problem with sandwich structures of this kind is that it is difficult to create a good fastening by making a hole in them. This is because the load from a fastening needs to be spread over a large surface, since the thin face sheets and weak core of the sandwich structure cannot cope with particularly large local loads. Such a fastening also needs decreasing rigidity out towards the edges of the sandwich structure in order to avoid causing stress concentrations. According to the state of the art, such a fastening is created by making it beforehand, i.e. before the face sheet is applied. A disadvantage of that method is that present-day techniques make it necessary to predetermine the locations of all fastenings before the sandwich panel is put together and assembled, which is very time-consuming and very impractical. Nor are the intended locations of fastenings always known before the sandwich structures are used.

One way of creating fastenings in existing/completed sandwich structures is to use ordinary drills, which results in straight holes. The problem with that solution is that a fastening in a straight hole in a sandwich is usually very weak, so such a fastening is not usable in practice to cope with normal and heavy loading.

Another way of creating fastenings in existing/completed sandwich structures is to use an ordinary milling tool. However, a milling tool cannot make an optimum load-absorbing cavity in a sandwich structure with an entry hole in the face sheet which is substantially smaller than the cavity created by the tool. A normal milling tool therefore needs to be used before the sandwich structure is assembled. Using such a tool on a completed sandwich panel entails replacing or repairing the cut face sheet. The result is a weaker sandwich structure with an uneven surface.

OBJECT OF THE INVENTION

The object of the present invention is to provide fastenings in an assembled sandwich structure which make optimum load absorption possible.

SUMMARY OF THE INVENTION

This and other objects indicated by the description set out below are achieved by a tool and a method as above which further exhibit the features indicated in the characterising part of the attached independent claims 1 and 15. Preferred embodiments of the tool according to the invention are defined in the respective attached dependent claims 2-14 and 16-17.

The fact that the tool according to the invention as formulated in claim 1 is characterised by at least one movable arm configuration which comprises a first arm portion with a first and a second end, which first end is fastened articulatedly to the body and is pivotable in a substantially radial plane, a second arm portion in the form of a cutting sheath with a first end D, a second end which is arranged for articulation relative to the body, is pivotable in a substantially radial plane and is arranged for movement in the axial direction, and a central portion to which the second end of the first arm portion is fastened articulatedly, the distance between the articulation A at the first end of the first arm portion and the articulation C at the central portion of the second arm portion being in principle equal to the distance between the articulation C at the central portion of the second arm portion and the articulation B at the second end of the latter, makes it possible to use this tool for creating fastenings in an assembled sandwich structure which make optimum load absorption possible, i.e. the tool can be used to cut out in an assembled sandwich structure a cavity whose geometry makes fastenings in said sandwich structure with optimum load absorption possible without destroying the face sheet. The tool needs only a relatively small hole to enter by, expands thereafter during use, i.e. when the tool rotates, as a result of centrifugal force, and creates a cavity substantially larger than the entry hole. A major advantage of this tool is that an optimum load-absorbing cavity for fastenings in sandwich structures can be created after the sandwich has been assembled. There is therefore no need for each fastening to be planned and set up beforehand. An optimum load-absorbing cavity with an entry hole substantially smaller than the cavity can thus be created afterwards without resulting in the face sheet having to be repaired/replaced by a weaker or heavier structure. The tool preferably comprises also the features of claim 2. The advantage is that the first end of the cutting sheath moves parallel with the face sheet and cuts out the core up against the inside of the face sheet when the cutting sheath during rotation opens out by centrifugal force, thereby helping to achieve the optimum geometry.

The tool preferably comprises also the features of claim 3. The advantage is that the spigot which constitutes the articulation at the second end of the cutting sheath can safely run along the body.

The tool preferably comprises also the features of claim 4. The advantage is that a hole can be drilled by the tool and there is consequently no need for any hole predrilling.

The tool preferably comprises also the features of claim 5. An advantage is that the cutting sheath can during use be opened out by said means, which may be necessary if centrifugal force is not sufficient. A further advantage is that the cutting sheath can be closed up after use, make it easier to withdraw the tool through the entry hole.

The tool preferably comprises also the features of claim 6. An advantage of using a spring is that it is easy to add to the tool and provides a way of opening out and closing up the cutting sheath which results in safe operation.

The tool preferably comprises also the features of claim 7. An advantage is that the cutting sheath can be opened out and closed up by operating the rod.

The tool preferably comprises also the features of claim 8. The advantage of a dolly is that the tool can during use be held firmly at a certain depth, in an axial direction and a radial direction. The tool preferably comprises also the features of claim 9. The advantage is that the dolly can be adjusted for face sheets of different thicknesses.

The tool preferably comprises also the features of claim 10. The advantage is that cuttings or the like arising during use can be removed simultaneously and need not be sucked away after use.

The tool preferably comprises also the features of claim 11. The advantage is that cuttings or the like arising during use can be sucked away simultaneously through the hole by a suction machine or the like applied at the hole.

The tool preferably comprises also the features of claim 12. The advantage of arranging the duct in this way is that the radial difference between the inlet and outlet of the duct during rotation generates a negative pressure so that superfluous cuttings are automatically removed.

The tool preferably comprises also the features of claim 13. The advantage of arranging the duct in this way is that it makes it possible to suck superfluous cuttings up directly through the cutting sheath.

The tool preferably comprises also the features of claim 14. The advantage is that during rotation the threads lead away the material being cut away.

The fact that the tool according to the invention as formulated in claim 15 is characterised by creating in an assembled sandwich structure a recess with a cross-sectional profile which is substantially funnel-shaped in the thickness direction of the sandwich structure and which has its widest section nearest to the face sheet makes it possible to achieve fastenings in an assembled sandwich structure which provide optimum load absorption, i.e. it is possible in an assembled sandwich structure to cut out a cavity whose geometry makes fastenings with optimum load absorption possible in said sandwich structure, with an entry hole in the face sheet which is substantially smaller than said cavity. A major advantage is that an optimum load- absorbing cavity for fastening purposes in sandwich structures can be created after the sandwich has been assembled. There is therefore no need for each fastening to be planned and set up beforehand. The cavity can thus be created afterwards, with an entry hole substantially smaller than the cavity created by the tool, without resulting in the face sheet having to be repaired/replaced by a weaker or heavier structure.

DESCRIPTION OF THE DRAWINGS

The present invention will be better understood by reading the following detailed description in conjunction with the attached drawings, in which the same reference notations refer to the same items throughout the various depictions, in which:

Fig. 1 depicts a perspective view of a first embodiment of a tool according to the present invention;

Fig. 2 depicts a cross-section of the tool along the line A-A in Fig. 1;

Fig. 3 depicts an enlargement of the section circled in Fig. 2;

Fig. 4 depicts a side view of a second embodiment of a tool according to the present invention;

Fig. 5 depicts schematically an optimum geometry for a load-absorbing fastening created by the tool according to the present invention, in which the movement is depicted geometrically;

Fig. 6 depicts a side view of the tool according to Fig 1;

Fig. 7 depicts a side view of a third embodiment of a tool according to the present invention; Fig. 8 depicts a cross-section of a fourth embodiment of the tool according to the present invention; and

Figs. 9a, 9b and 9c depict a method for making a cavity and fastening with a tool according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Figs. 1 and 2 depict the tool according to a first embodiment of the present invention, for creating a profiled recess in a sandwich structure which comprises two thin rigid face sheets separated by a relatively thick, light and soft core, which tool comprises an elongate body 2 intended to rotate about its axial direction, which body comprises an insertion end 2a and a control end 2b, the insertion end being the portion of the body which is intended to be inserted in an existing hole through the face sheet to a certain depth in the core of the sandwich structure or is intended to drill to a corresponding depth. The tool further comprises a movable arm configuration 4 which itself comprises a first arm portion 6, in the form of a link arm 6, with a first and a second end, which first end is articulatedly fastened to the body 2 and is pivotable in a substantially radial plane, a second arm portion 8 in the form of a cutting sheath 8, with a first end D, a second end which is arranged for articulation relative to the body, is pivotable in a substantially radial plane and is arranged for movement in the axial direction in a groove 10 running axially in the body, in which groove 10 the articulation B, where the articulation B comprises a guide spigot B, is adapted to running, and a central portion to which the second end of the first arm portion 6 is articulatedly fastened, the distance between the articulation A at the first end of the first arm portion 6 and the articulation C at the central portion of the second arm portion being in principle equal to the distance between the articulation C at the central portion of the second arm portion 8 and the articulation B at the latter' s second end. Fig. 3 depicts the portion of the body 2 to which the arm configuration 4 is connected. As mentioned above, there are three articulations, A, B and C, at which the arm configuration 4 is fastened and which represent positions between the links of the arm configuration 4. A constitutes a moment- free fastening between the body 2 and the link arm 6, B a moment-free fastening between the body 2 and the cutting sheath 8, and C a moment-free fastening between the cutting sheath 8 and the link arm 6. The cutting sheath 8 is thus fastened articulatedly to the body 2 at the two points B and C. The lower end B of the cutting sheath 8 is adapted to sliding in the groove 10 within the body 2 via a guide spigot B. The midpoint C of the cutting sheath 8 is fastened articulatedly to the body 2 at the point A in the continuation of the groove 10 via a link arm 6. The link arm 6 is adapted to rotating freely about the z axis. The effective length of the link arm 6 is preferably half of the length of the cutting sheath 8. This length relationship results in the first end D of the cutting sheath 8 being able to travel only in the x direction according to Fig. 3.

The body 2 may be cylindrical or of any other geometrical shape. The cutting sheath 8 and the body 2 have to be so designed that the cutting sheath 8 can move unhindered. The cutting sheath 8 may be articulated to the link arm 6 in various ways, but the total effective length between the articulations A and C has to be substantially the same as the total effective length between B and C and between C and D on the cutting sheath 8.

As may be seen, for example, in Fig. 1 , the tool preferably comprises also a dolly 12 which, during use, is adapted to holding the tool at a certain depth in the face sheet of the sandwich structure and to holding the body 2 axially perpendicular to the sandwich structure. The dolly 12 has preferably a platelike configuration and is disposed about the control end 2b of the body nearest to the insertion end 2a. The dolly 12 is preferably settable so that the tool can be adjusted for face sheets of different thickness by means of two nuts 13a, 13b, which are also adapted to locking against one another. The dolly, during use, is thus adapted to holding the tool at a certain depth in the face sheet of the sandwich structure and to holding the body axially perpendicular to the sandwich structure. The dolly 12 is preferably equipped with ball bearings 12a to allow the body 2 to rotate freely relative to the face sheet. This dolly 12 may also be provided with a handle which makes more powerful fixing to the sandwich panel possible, e.g. when a pull-and-push rod is used for respectively opening out and closing up the cutting sheath 8. The dolly further comprises a thin flange 14 situated where the insertion end 2a of the body 2 meets the dolly 12 and adapted to precisely fitting in the hole through the face sheet, thus simplifying the handling of the tool by locating the tool during use.

Removal of cuttings from the cavity is usually unnecessary because the material cut away is of very low density and therefore decreases in volume when machined. The control end 2b of the body comprises, as may be seen in Fig. 1, a tool neck 16 for clamping in a rotating machine (not depicted).

Fig. 4 depicts a second embodiment of the tool according to the present invention, whereby the arm configuration 4 comprises two link arms 6 and two cutting sheaths 8 disposed in a manner corresponding to that described above with reference to Figs. 1-3.

When the tool rotates (Figs. 1 and 3), the cutting sheath 8 expands out from the body 2. The second portion of the cutting sheath 8 moves along the body's slide groove 10 in the y direction, while its upper portion D moves only in the x direction out from the body 2, as may be seen in Fig. 3. It thus follows an imaginary laminate/face sheet. The cutting sheath 8 has an outer cutting surface 8a intended to machine the material while at the same time the tool rotates and opens out. This total movement generates an optimum load- absorbing geometry of parabolic shape according to Fig. 5. The driving force in this movement is centrifugal force generated by a rotating machine in which the tool is fastened. As mentioned above, removal of cuttings is normally unnecessary. If removal of cuttings is necessary, however, this can be done by means, for example, of a longitudinal hole or a longitudinal duct arranged in the body 2 and a suction machine connected to the hole and adapted to sucking out the cuttings. Alternatively, a longitudinal hole/longitudinal duct may be arranged in the body 2, with a duct with an inlet and an outlet, which inlet is arranged at the insertion end 2a of the body 2 within the cutting sheath 8, while the outlet is arranged in the radial continuation of the control portion 2b of the body 2. The radial difference between the exit and entry holes generates during rotation a negative pressure so that superfluous cuttings are removed. Another alternative is a duct with an inlet and an outlet, which inlet is disposed at the first end D of the cutting sheath 8, the duct being further arranged to run through the cutting sheath 8 and up through the body 2, and the outlet of the duct being situated in the body 2 on the side of the dolly 12 which is opposite to the body's insertion end 2a. With such a solution the cuttings can be sucked up directly through the cutting sheath. A further alternative is to provide the body 2 with threads which carry cuttings as in a conventional drill.

The cutting sheath 8 is normally operated by using the centrifugal force resulting from its rotation. Fig. 7 depicts an alternative/complement to centrifugal force whereby a tension or compression spring 22 disposed within the body 2 is intended to be used for operating the cutting sheath 8. An alternative depicted in Fig. 8 is a rod 24 which is built into the body 2, fastened in the rotation tool and adapted to pulling the cutting sheath 8 out when a rotation machine (not depicted) connected to a control portion of the rod is drawn in. This requires a counterforce via, for example, a handle fastened in the dolly 12.

The built-in rod 24 mentioned above and depicted in Fig. 8 may be used for closing up the tool after use. Alternatively, as depicted in Fig. 7, it is possible to use a tension or compression spring disposed within the body 2, said spring being weaker than the corresponding centrifugal force. A further variant is to use a magnet on the body 2 or the cutting sheath 8, said magnet being weaker than the corresponding centrifugal force which opens out the cutting sheath 8.

Providing the body 2 with different cross-sections makes it possible to increase the strength of the tool, particularly with regard to fastenings. The link arm 6 may be articulated relative to the body 2 concentrically or non- concentrically. Arranging it non-concentrically may increase the strength of the tool. The tool may be provided with one or more articulated cutting sheaths 8, e.g. two of them as in the embodiment depicted in Fig. 4. The tool may be provided with a self-tapping tip at the insertion end of the body 2, thereby obviating any need for predrilling according to Fig. 9a Cl to make it possible to place the tool in its initial position, as may be seen in Fig. 9a C2. The surface of the cutting sheath 8 may be provided with, for example, cutting edges, rasps or knife edges. The cutting sheath 8 may be equipped with extra weight in the form of high-density material, e.g. lead, to increase the centrifugal force during rotation. The geometry of the cutting sheath 8 may vary along its length to adjust the centre of mass inertia or to adjust the geometry of the cavity. The tip D of the cutting sheath 8 has to be so designed that the cavity links at a small angle (regular transition) to the face sheet. The tool may with advantage also be used for making holes through the sandwich structure according to Figs. 9b and 9c. The cutting sheath 8 may be equipped with a resilient tip D which makes it possible for it to follow the often uneven surface of the face sheet and its adhesive.

This tool is a milling tool intended to be fastened in a rotating machine.

The tool is further intended to cut out an optimum load-absorbing cavity, see Fig. 6, in sandwich structures, without destroying the face sheet. The tool needs only a small hole to enter by and is adapted to expanding thereafter during rotation. The cavity may subsequently be filled with a suitable adhesive and, where applicable, a fastening made of, for example, plastic or metal. The fastening may have internal threads which together with a screw can fasten securely to the sandwich panel, as may be seen in Fig. 9a, C6-C7. It is also possible to screw directly into the hardened or solidified adhesive.

As previously mentioned, the tool is intended to be used as an aid to achieving optimum fastenings, and Fig. 9a depicts a method for doing so. The method comprises the following steps:

1. If the tool is not self-tapping, the first step is to drill a hole which corresponds to the size of the tool before use, Cl.

2. The tool is placed in position by locking the dolly with the nuts 13a,

13b according to the thickness of the face sheet and of any adhesive present.

3. The tool is connected to a rotating machine via the neck 16 of the tool.

4. The tool is placed in the sandwich structure or, if no predrilling is required, the tool drills down to an initial position, C2.

5. The rotating machine is started and the tool begins to rotate. The centrifugal force generated urges the cutting sheath out from the body, while the tool cuts out a rotationally symmetrical cavity with optimum load- absorbing geometry.

6. The closing-up mechanism, if any, is used and the tool is pulled out of the structure.

7. Any remaining cuttings in the cavity are removed, e.g. by a vacuum cleaner.

8. The cavity is filled with a suitable adhesive, C5.

9. The relevant fastening is fitted, C6. 10. When the adhesive has hardened or solidified, the fastening can be applied, Cl.

11. The tool may also be used for making optimum load-absorbing holes through sandwich structures. Making such a hole involves following the above procedure also from the opposite side of the sandwich panel. Figs. 9b and 9c show what such a hole looks like, and Fig. 9c depicts such a hole reinforced with adhesive or the like.

Claims

1. A tool for creating a profiled recess in a sandwich structure which comprises two thin rigid face sheets separated by a relatively thick, light and soft core, which tool comprises an elongate body (2) intended to rotate about its axial direction, and a cutting portion, characterised by at least one movable arm configuration (4) which comprises a first arm portion (6) with a first and a second end, which first end is fastened articulatedly to the body and is pivotable in a substantially radial plane, a second arm portion (8), in the form of a cutting sheath (8), with a first end (D), a second end which is arranged for articulation relative to the body (2), is pivotable in a substantially radial plane and is arranged for movement in the axial direction, and a central portion to which the second end of the first arm portion (6) is articulatedly fastened, the distance between the articulation (A) and the first end of the first arm portion (6) and the articulation (C) at the central portion of the second arm portion (8) being in principle equal to the distance between the articulation (C) at the central portion of the second arm portion (8) and the articulation (B) at the latter' s second end.

2. A tool according to claim 1, characterised in that the distance between the articulation (A) at the first end of the first arm portion (6) and the articulation (C) at the central portion of the second arm portion (8) is in principle equal to the distance between the articulation (C) at the central portion of the second arm portion (8) and the first end (D) of the second arm portion (8).

3. A tool according to claim 1 or 2, characterised by a groove (10) running axially in the body, in which groove the articulation (B), where the articulation comprises a guide spigot (B) of the second end of the second arm portion (8), is adapted to running.

4. A tool according to any one of claims 1-3, characterised in that a drill bit is disposed at the insertion end (2a) of the body.

5. A tool according to any one of claims 1-4, characterised by an arm movement means (22; 24) arranged relative to said body (2) and intended, when the body (2) rotates, to open out the cutting sheath (8) and, when the body (2) is at rest, to close the cutting sheath (8) back close to the body.

6. A tool according to claim 5, characterised in that the arm movement means comprises a spring (22).

7. A tool according to claim 5, characterised in that the arm movement means comprises a rod (24) disposed axially through the body (2) and movable axially relative to the body (2), which rod (24) has one end connected to the articulation (B) at the second end of the cutting sheath (8), and the other end connected to a means arranged for rotation.

8. A tool according to any one of claims 1-7, characterised by a dolly (12) which is connected to the body (2) and which, during use, is adapted to holding the tool at a certain depth in the face sheet of the sandwich structure and to holding the body axially perpendicular relative to the sandwich structure.

9. A tool according to any one of claims 1-8, characterised in that the dolly (12) is adjustable along the centreline of the body.

10. A tool according to any one of claims 1-9, characterised by a removal means disposed in the body (2) and intended to remove material which has been cut away.

11. A tool according to claim 10, characterised in that the removal means comprises a duct which runs axially through the body and through which material cut away is intended to be removed by a suction means connected to the body (2).

12. A tool according to claim 10, characterised in that the removal means comprises a duct with an inlet and an outlet, which inlet is disposed at the insertion end (2a) of the body (2) within the cutting sheath (8), while the outlet is disposed in the radial continuation of the control portion (2b) of the body (2).

13. A tool according to claim 10, characterised in that the removal means comprises a duct with an inlet and an outlet, which inlet is disposed at the first end (D) of the cutting sheath (8), which duct is further arranged to run through the cutting sheath (8) and up through the body (2), the outlet of the duct being situated on the body (2) on the side of the dolly (12) which is opposite to the body's insertion end (2a).

14. A tool according to claim 10, characterised in that the removal means comprises threads disposed in the axial direction of the body.

15. A method for using a tool to create a profiled recess, intended for fastening purposes, in a sandwich structure comprising first and second thin rigid face sheets (26, 28) which are separated by a relatively thick, light and soft core (30), characterised in that in an assembled sandwich structure it creates a first recess with a cross-sectional profile which is substantially funnel-shaped in the thickness direction of the sandwich structure and which has its widest section nearest to the first face sheet, and with a first entry hole (32) through the first face sheet which is substantially smaller than the widest section of the profile.

16. A method according to claim 15, characterised by creating, opposite to said first entry hole (32), a second recess with a cross-sectional profile which is substantially funnel-shaped in the thickness direction of the sandwich structure and which has its widest section nearest to the second face sheet (28), and with a second entry hole (34) through the second face sheet (28) which is substantially smaller than the widest section of the profile, the first recess and the second recess thus forming an hourglass-shaped cross-sectional profile.

17. A method according to claim 15, characterised the steps of:

- drilling a hole in the sandwich structure down to a desired depth in the core;

- causing the tool to rotate in said hole so that a cutting portion of the tool swings out and creates a recess with said profile.