EP3562609A1

EP3562609A1 - Metal structure for performing machining operations

Info

Publication number: EP3562609A1
Application number: EP16838006.1A
Authority: EP
Inventors: Ugo Valentini
Original assignee: Valentini Utensili Speciali Srl
Current assignee: Valentini Utensili Speciali Srl
Priority date: 2016-12-30
Filing date: 2016-12-30
Publication date: 2019-11-06
Also published as: WO2018122592A1; WO2018122592A8

Abstract

A metal structure for performing machining operations, in particular a cutting tool (1) for chip removal machine tools, having a first and a second body (2, 3), which extend respectively along a first axis and a second axis (Al, A2 ), which are configured to achieve axial coupling to align the first and second axes (Al, A2) and allow the relative rotation between the first and the second body (2, 3), and a groove (12) having two opposing undercuts (16, 17); and an axial protrusion (20) of a shape substantially complementary to the groove (12); the groove (12) and the axial protrusion (20) being configured in such a way that the relative rotation of the first and of the second body (2, 3) around the first and second mutually aligned axes (Al, A2 ) determines progressive forced coupling with interference between the first and the second body (2, 3) in correspondence with the undercuts (16, 17).

Description

METAL STRUCTURE FOR PERFORMING MACHINING OPERATIONS"

TECHNICAL FIELD

The present invention relates to a metal structure for performing machining operations, in particular, the invention finds beneficial application in the manufacture of cutting tools for chip removal machines and for equipment for performing machining operations without thereby any loss of generality.

STATE OF THE ART

Cutting tools of known type generally comprise a grip portion configured to be gripped by a gripping device of a chip removal machine tool; a shank; and an end portion configured to cut and remove the material being machined. The gripping device of the machine tool can be a rotating mandrel when the chip removal machine tool is a drill or a milling machine, or a tool turret when the machine tool is a lathe. The grip portion can assume various configurations although the market is oriented towards using a few configurations that over the years have become de facto standards. The shank has the function of spacing out the end portion from the grip portion and, in many applications, to define waste channels for the chips that are produced in the cutting operations. The end portion comprises cutting edges, which can be formed directly on the end portion or extend along the inserts, which are attached to the end portion by different techniques such as for example braze welding or screwing. The cutting tool in its entirety must be made from high quality steels and subjected to heat treatment to ensure the best performance and durability. However, the grip portion, the shank and the end portion perform different functions and the required mechanical characteristics of the parts of the cutting tool are different from one another and, for this reason, it has been found that the wear of the various parts of the cutting tool is not uniform, from which it follows that the cutting tool is worn when only one of the parts of the tool is worn.

In order to overcome this drawback various technical solutions have been proposed aimed at making the cutting tool in two separate parts connected together such as for example in US 2013/034393 or WO 2007/060653, but none of these solutions is entirely satisfactory because the coupling system is complex and/or does not ensure the necessary structural continuity of the tool.

In an apparatus for performing machining operations, it is often necessary to dock together quickly and make integral two bodies in a quick and precise manner. The known apparatuses are often complicated and costly as, for example, that described in the patent application EP 1,707,307 Al .

SUBJECT-MATTER OF THE INVENTION

The purpose of the present invention is to provide a metal structure for performing machining operations, in particular a cutting tool for chip removal machines or an apparatus for performing machining operations, which is free from the drawbacks of the prior art.

In accordance with the present invention a metal structure for performing machining operations is provided, in particular a cutting tool for chip removal machine tools or an apparatus for performing machining operations, wherein the metal structure comprises at least one first and one second body, which extend respectively along a first axis and a second axis, are configured to achieve axial coupling to align the first and second axis and allow the relative rotation between the first and the second body, and at least one groove comprising two opposing undercuts; and at least one axial protrusion of a shape substantially complementary to the groove; the groove and the axial protrusion being configured in such a way that the said axial protrusion is progressively forced to interfere between the undercuts as a result of the relative rotation of the first and of the second body around the first and second mutually aligned axes.

In practice, the axial coupling ensures the alignment between the first and the second body and allows the first and the second body to rotate together for a certain angle, while the subsequent relative rotation of the first and second body achieves a forced coupling with interference between the first and the second body that ensures a good transmission of forces, structural continuity, and optimum transmission of forces between the first and the second body .

In particular, the first and the second body respectively comprise at least one first and at least one second abutting face, which are configured to define an axial stop between the first and the second body. The axial abutment between the first and second body makes it possible to guide the axial protrusion inside the undercuts and enables an extended abutment area once the forced coupling with interference is achieved.

In particular, each groove is delimited by at least one first stop face, the axial protrusion comprising at least one second stop face configured to be arranged in abutment against the first stop face so as to stop the rotation between the first and the second body. The stopping of the rotation is selected in such a way as to define a given degree of interference between the first and the second body.

In particular, each undercut is delimited by first inclined faces, and by one bottom face of the groove. The exchange of forces between the first and the second body takes place along the first inclined faces, the bottom face and the first abutting face, and thus along a relatively extended surface.

In particular, each first inclined face partly faces the bottom face. In greater detail, each first inclined face is a conical face that extends along a respective cone with axis parallel to, and offset with respect to, the first and second axes. In this way, the forces exchanged between the first and the second body have radial and axial components .

In a similar way, the axial protrusion comprises two second inclined faces, which are inclined with respect to the first and second axes, and, in particular, each second inclined face is a conical face which extends along a cone with axis offset with respect to the first and second axes. This arrangement allows achievement of a progressive insertion of the axial protrusion into the groove and to pass from an initial situation in which there is a slight clearance between the first and second inclined faces and a situation in which there is an interference.

In particular, the cones along which the first inclined faces lie have a base diameter which is smaller than the base diameter along which the second inclined faces lie. This configuration makes it possible to obtain the interference even in the situation in which the axes of the cones along which the first inclined faces lie are offset with respect to the cones along which the second inclined faces lie.

In accordance with a particular embodiment of the present invention, the first body has two grooves arranged on opposite sides with respect to the first axis, and the second body has two axial protrusions, which are arranged on opposite sides with respect to the second axis and have a shape, at least in part substantially complementary to the grooves. This embodiment is particularly effective for large metal structures.

In particular, the axial protrusions extend along respective circle arc paths to an extent less than 90°. In particular, said extent is slightly less than 90° so as to maximise the extent of axial protrusion and allow the axial insertion of the protrusion and the achievement of a groove with an engagement portion of extent equal to the extent of the axial protrusion.

With reference to a particular embodiment of the invention, each groove comprises an engagement portion and a portion configured to allow the axial insertion of an axial protrusion into the groove.

In accordance with a particular embodiment of the invention, the metal structure comprises, in addition to the interference coupling, a safety mechanism to prevent rotation between the first and the second body. The safety mechanism comprises two seats formed in the first body and two screws housed in the second body and configured to be selectively inserted into the said seats.

BRIEF DESCRIPTION OF THE FIGURES

Further characteristics and advantages of the present invention will become apparent from the following description of the non-limiting examples of embodiment, with reference to the Figures of the accompanying drawings, wherein :

- Figure 1 is a perspective view, with parts removed for clarity, of a metal structure made in accordance with a first embodiment of the present invention;

- Figure 2 is a cross-section view, with parts removed for clarity, of the metal structure of Figure 1 along the section line II-II;

- Figures 3 and 4 are partially exploded perspective views, with parts removed for clarity, of the metal structure of Figure 1;

- Figure 5 is a plan view, with parts removed for clarity and in enlarged scale, of a detail of the metal structure of Figure 1.

- Figure 6 is a cross-section view, with parts removed for clarity, of a detail of the metal structure of Figure 5 along the section line VI-VI;

- Figure 7 is a plan view, with parts removed for clarity and in enlarged scale, of a further detail of the metal structure of Figure 1.

- Figure 8 is a longitudinal cross-section view, with parts removed for clarity and in enlarged scale, of a further detail of the metal structure of Figure 7 along the section line VIII-VIII;

- Figure 9 is a cross-section view, with parts removed for clarity and in enlarged scale, of a detail of the metal structure of Figure 2;

- Figure 10 is a perspective view, with parts removed for clarity, of a metal structure made in accordance with a second embodiment of the present invention;

- Figure 11 is a cross-section view, with parts removed for clarity, of the metal structure of Figure 10 along the section line XI-XI;

- Figures 12 and 13 are partially exploded and perspective views, with parts removed for clarity, of the metal structure of Figure 10;

- Figure 14 is a plan view, with parts removed for clarity and in enlarged scale, of a detail of the metal structure of Figure 10.

- Figure 15 is a longitudinal cross-section view, with parts removed for clarity and in enlarged scale, of the detail of Figure 14 along the section line XV-XV;

- Figure 16 is a plan view, with parts removed for clarity and in enlarged scale, of a further detail of the metal structure of Figure 10;

- Figure 17 is a longitudinal cross-section view, with parts removed for clarity and in enlarged scale, of the further detail of Figure 16 along the section line XVII- XVII;

- Figure 18 is a cross-section view, with parts removed for clarity and in enlarged scale, of a detail of

Figure 11;

- Figures 19 and 20 are partially exploded perspective views, with parts removed for clarity, of the metal structure in accordance with a third embodiment of the present invention.

PREFERRED EMBODIMENTS OF THE INVENTION

With reference to Figures 1 and 2, the reference number 1 denotes in its entirety a metal structure, in this case a cutting tool for a chip removal machine and, in more detail, a drill tip. The metal structure 1 has a substantially cylindrical shape and comprises two bodies 2 and 3 coupled together, has successively a grip portion 4a and a shank 4b along the body 2, and an end portion 4c associated with the body 3 and has cutting edges 5 to engage and cut the material being machined not shown in the attached figures. The body 2 extends along an axis Al, while the body 3 extends along an axis A2 and is selectively couplable to the body 2. When the body 3 is coupled to the body 2 the axes Al and A2 are coincident.

With reference to Figure 2, the alignment of the bodies 2 and 3 is made possible by the coupling between a pin 6 which extends from the body 3 along the axis A2 and a cylindrical seat 7, which is formed in the body 2 and extends along the axis Al .

In accordance with an alternative embodiment of the present invention not shown, the pin 6 is integral with the body 2, while the cylindrical seat is formed in the body 3.

With reference to Figure 1, the body 2 has two channels 8, which are configured to remove the chips (not shown) produced in the cutting operations, extending along respective helical paths, and have concave cross-sections. Similarly, the body 2 has two channels 9, which are configured to remove the chips (not shown) produced in the cutting operations, and have identical cross-sections to the helical profiles of the channels 8 in such a way as to allow a perfect alignment of the channels 9 with the channels 8 when the body 3 is coupled to the body 2. In addition, when the body 3 is coupled to the body 2, the channels 9 define the extension of the helical paths, along which the channels 8 extend. In accordance with embodiments not shown, the bodies have channels with different paths than helical paths and are different in number to two.

The coupling includes a step of axial insertion of a portion of the bodies 2 and 3 and the subsequent relative rotation between the bodies 2 and 3 of about 90° around the coincident axes Al and A2.

With reference to Figures 3 and 4, the bodies 2 and 3 have respective abutting faces 10 and 11 that extend perpendicularly with respect to axes Al and A2 and are arranged in mutual contact as a result of the axial insertion .

With reference to Figures 3 and 6, the body 2 has a groove 12 which extends between the two abutting faces 10 from a channel 8 to the opposite channel 8 and is delimited by a bottom face 13 and two laterally inclined faces 14 and 15, which converge toward the axis Al, arranged on opposite sides of the axis Al and forming respective undercuts 16 and 17 with the bottom face 13, and by two stop faces 18 and 19, which are adjacent to the respective inclined faces 14 and 15.

With reference to Figures 4 and 8, the body 3 has an axial protrusion 20, which is centrally arranged with respect to the axis A2 and is configured to be inserted by force into the groove 12, in particular into the undercuts 16 and 17 and retained by the body 2. In the example shown the axial protrusion 20 is arranged between the abutting faces 11, is laterally delimited by two inclined faces 21 and 22, by two stop faces 23 and 24, by two channels 9, and, at the end, by an end face 25. The inclined faces 21 and 22 are divergent with respect to the axis A2 and form acute angles with the end face 25 as is better illustrated in Figure 8.

With reference to Figure 5, the inclined face 14 and the contiguous stop face 18 extend substantially along a circle arc of less than 90°. Similarly, the inclined face 15 and the contiguous stop face 19 extend along a circle arc of less than 90°. With reference to Figure 7, the opposite ends of the axial protrusion 20 extend along respective circle arcs of less than 90°.

With reference to Figure 9, when the bodies 2 and 3 are mutually coupled and forced to interference, the pin 6 is housed in the cylindrical seat 7, the abutting faces 11 are arranged in contact with the abutting faces 10, the stop faces 18 and 19 are in abutment respectively with the stop faces 23 and 24 (not shown in Figure 9) , the inclined face 14 interferes with the inclined face 22, the inclined face 15 interferes with the inclined face 21, and the bottom face 13 is pressed against the end face 25. The interference is obtained through the relative rotation between the bodies 2 and 3 after the insertion of the pin 6 into the cylindrical seat 7. This rotation determines the circumferential approach of the stop faces 18 and 23, on one side, and 19 and 24 (Figures 5 and 7) , on the other side, and the radial approach of the inclined faces 14 and 22, on one side, and 15 and 21, on the other side, until an interference between the axial protrusion 20 of the body 3 inside the groove 12 of the body 2 is achieved. In other words, the inclined faces 14, 15, 21 and 22 are dimensioned in such a way that in the initial phase of the coupling of the axial protrusion 20 in the groove 12, i.e. the relative rotation between the body 2 and the body 3, there is a small clearance between the inclined faces 14 and 22, on one side and the inclined faces 15 and 21, on the other side. The rotation progressively suppresses the clearance and achieves an interference along both the inclined faces 14 and 22 and the inclined faces 15 and 21. The inclined faces 14, 15, 21 and 22 are conical surfaces, i.e. are portions of the side surfaces of respective hypothetical cones, which are slightly offset with respect to the axes Al and A2 in such a way that the rotation about the coincident axes Al and A2 determines the radial approach of the inclined faces 14 and 22, on one side, and 15 and 21, on the other side, in a direction of rotation and the radial distancing of them for a rotation in the opposite direction. The cones along which the inclined faces 14 and 15 lie have a base diameter which is smaller than the base diameter along which the inclined faces 21 and 22 lie, so as to produce an interference. The forced coupling with interference along the inclined faces 14, 15, 21, and 22 also determines an axial compression between the bodies 2 and 3 and precisely along the bottom face 13 and the end face 25 and along the abutting faces 10 and 11.

It is evident that the same effects are achievable by inverting the position of the groove and the axial protrusion, i.e. by forming the groove on the body 3 and the axial protrusion on the body 2.

With reference to Figures 10 and 11, the reference number 101 denotes in its entirety a metal structure which, in this case, is a cutting tool for a chip removal machine and, in more detail, a drilling tool. The metal structure 101 comprises two bodies 102 and 103 coupled together, has successively a grip portion 104a and a shank 104b along the body 102, and an end portion 104c associated with the body 103 and has cutting edges 105 to engage and cut the material being machined not shown in the attached figures. The body 102 extends along an axis Al, while the body 103 extends along an axis A2 and is selectively couplable to the body 102. When the body 103 is coupled to the body 102 the axes Al and A2 are coincident.

With reference to Figure 11, the alignment of the bodies 102 and 103 is made possible by the coupling between a pin 106, which extends from the body 103 along the axis A2 and a cylindrical seat 107, which is formed in the body 102 and extends along the axis Al . In accordance with an alternative embodiment of the present invention not shown, the pin 106 is integral with the body 102, while the cylindrical seat is formed in the body 103. In a further embodiment not shown, the pin is an element which can be inserted into the cylindrical seats of both bodies.

With reference to Figure 10, the body 102 has two channels 108, which are configured to remove the chips (not shown) produced in the cutting operations, extending along respective helical paths, and have concave cross-sections. The body 103 has two channels 109, which are configured to remove the chips (not shown) produced in the cutting operations, and have identical cross-sections to the helical profiles of the channels 108 in such a way as to allow a perfect alignment of the channels 109 with the channels 108 when the body 103 is coupled to the body 102. In addition, when the body 103 is coupled to the body 102, the channels 109 define the extension of the helical paths, along which the channels 108 extend. The coupling includes a step of axial insertion of the two suitably shaped ends of the bodies 102 and 103, which includes, among other things, the insertion of the pin 106 into the cylindrical seat 107 and the subsequent relative rotation between the bodies 102 and 103 by about 90° around the coincident axes Al and A2.

With reference to Figures 12 and 13, the bodies 102 and 103 have respective abutting faces 110 and 111 that extend perpendicularly with respect to the axes Al and A2 and are arranged in mutual contact as a result of the axial insertion .

With reference to Figure 14, the body 102 has two grooves 112 which extend along respective circle arc paths to an extent less than 90°, are in communication with the two respective channels 108 and are arranged on opposite sides with respect to the axis Al . Each groove 112 is delimited by a bottom face 113, by two inclined faces 114 and 115, which converge with each other and form respective undercuts 116 and 117 (Figure 15) with the bottom face 113, and by a stop face 118, which is adjacent to the inclined faces 114 and 115 as better illustrated in Figure 14.

With reference to Figure 13, the body 103 has two axial protrusions 120, which extend along respective circle arcs, are arranged on opposite sides with respect to the axis A2 , are arranged around the axis A2 along respective circle arc paths of less than 90°, and are configured to be inserted by force into the grooves 112 and retained by the body 2. In the example shown the axial protrusion 120 is laterally delimited by the abutting face 111, by two inclined faces 121 and 122, and by a stop face 123 (Figure 16) and axially by an end face 125. The inclined faces 121 and 122 are divergent with respect to the axis A2 towards the end face 25 and thus form acute angles with the end face 125.

When the bodies 102 and 103 are mutually coupled as shown in Figure 18, the pin 106 is housed in the cylindrical seat 107, the abutting faces 111 are arranged in contact with the abutting faces 110, the stop faces 118 are in abutment respectively with the stop faces 123, the inclined faces 114 interfere with the inclined faces 122 and the inclined faces 115 interfere with the inclined faces 121. The interference is obtained through the relative rotation between the bodies 102 and 103 after insertion of the pin 106 into the cylindrical seat 107. This rotation determines the circumferential approach of the stop faces 118 and 123, on one side (Figures 14 and 16) and the radial approach of the inclined faces 114 and 122, on one side, and 115 and 121, on the other side, until an interference between the axial protrusions 120 of the body 103 inside the groove 112 of the body 102 is achieved.

In practice, the inclined faces 114, 115, 121 and 122 are dimensioned in such a way that in the initial coupling phase of the axial protrusion 120 in the groove 112, i.e. the relative rotation between the body 102 and the body 103 there is a small clearance between the inclined faces 114 and 122, on one side and the inclined faces 115 and 121, on the other side. The rotation progressively suppresses the clearance and achieves an interference along both the inclined faces 114 and 122 and the inclined faces 115 and 121.

The inclined faces 114, 115, 121 and 122 are conical surfaces, i.e. are portions of the side surfaces of respective hypothetical cones, which are slightly offset with respect to each other in such a way that the rotation about the coincident axes Al and A2 determines the radial approach of the inclined faces 114 and 122, on one side, and 115 and 121, on the other side, in a direction of rotation and the radial distancing of them for a rotation in the opposite direction. The cones along which the inclined faces 114 and 115 lie have a base diameter which is smaller than the base diameter along which the inclined faces 121 and 122 lie.

The forced coupling with interference determines an axial compression between the bodies 102 and 103 along the bottom faces 113 (Figure 15) and the end faces 125 (Figure 17) and along the abutting faces 110 and 111 (Figure 18) .

It is evident that the same geometric design is achievable by inverting the position of the groove and the axial protrusion, i.e. by forming the groove on the body 103 and the axial protrusion on the body 102.

The metal structure 101 comprises a safety mechanism to prevent accidental rotation between the body 102 and the body 103. The safety mechanism provides that the body 102 has two conical seats 126, which are arranged in correspondence with the respective bottom faces 113; and the body 103 has threaded bores 127 which extend in correspondence with the axial protrusions 120 and which are aligned with the respective conical seats 126 when the bodies 102 and 103 are completely coupled together. The metal structure 101 also comprises two screws 128, which are configured to be screwed into the threaded bores 127 and define the safety mechanism.

With reference to Figure 11, the metal structure 101 comprises a cooling channel 129 which extends along the bodies 102 and 103 and centrally through the pin 106.

With reference to Figures 19 and 20, the reference number 201 denotes in its entirety a metal structure which, in this case, is part of an apparatus for performing machining operations. The metal structure 201 comprises two bodies 202 and 203 couplable to each other and having a substantially cylindrical shape. When the body 103 is coupled to the body 102 the axes Al and A2 are coincident.

With reference to Figure 19, the alignment of the bodies 202 and 203 is made possible by the coupling between a pin 206 which extends from the body 202 along the axis Al and a cylindrical seat 207 (Figure 20), which is formed in the body 203 and extends along the axis Al . In accordance with an alternative embodiment of the present invention not shown, the pin 206 is integral with the body 203, while the cylindrical seat 207 is formed in the body 202.

The coupling portions of the bodies 202 and 203 are similar to the coupling portions of the bodies 102 and 103 and differ from the latter by the fact that the bodies 202 and 203 are devoid of chip removal channels.

With reference to Figures 19 and 20, the bodies 202 and 203 have respective abutting faces 210 and 211 that extend perpendicularly with respect to axes Al and A2 and are arranged in mutual contact as a result of the axial insertion .

With reference to Figure 19, the body 202 has two grooves 212 which extend along respective circle arc paths to an extent greater than 90°, and are arranged on opposite sides with respect to the axis Al . Each groove 212 has an engagement portion formed in a manner identical to the groove 112 and a portion 219, which is configured to allow for axial interpenetrat ion between the bodies 202 and 203. In other words, the engagement portion of each groove 112 has two undercuts 216 and 217 while the portion 219 is devoid of undercuts and is dimensioned to allow the axial insertion of one of the axial protrusions 220 of the body 203 (Figure 20) .

With the exception of the differences described, the forced coupling with interference between the bodies 202 and 203 is achieved in the same manner as described with reference to the embodiment described with reference to Figures 10 to 18. It is evident that the present invention includes variants not explicitly described without thereby departing from the protective scope of the following claims. For example, the metal structure could be a turning tool. Or the metal structure may comprise more than two bodies assembled together according to the methods described and claimed.

Claims

1. A metal structure for performing machining operations, in particular a cutting tool for chip removal machine tools, wherein the metal structure (1; 101; 201) comprises at least one first and one second body (2, 3; 102, 103; 202, 203), which extend respectively along a first axis and a second axis (Al, A2), are configured to achieve axial coupling to align the first and second axes (Al, A2 ) and allow the relative rotation between the first and the second body (2, 3; 102, 103; 202, 203), and at least one groove (12; 112; 212) comprising two opposing undercuts (16, 17; 116, 117; 216, 217) ; and at least one axial protrusion (20; 120; 220) of a shape substantially complementary to the groove (12; 112; 212); the groove (12; 112; 212) and the axial protrusion (20; 120; 220) being configured in such a way that the said axial protrusion (20; 120; 220) is progressively forced to interfere between the undercuts (16, 17; 116, 117; 216, 217) as a result of the relative rotation of the first and the second body (2, 3; 102, 103; 202, 203) around the first and second mutually aligned axes (Al, A2) .

2. The metal structure as claimed in claim 1, wherein the first and the second body (2, 3; 102, 103; 202, 203) respectively comprise at least one first and at least one second abutting face (10, 11; 110, 111; 210, 211), which are configured to define an axial stop between the first and the second body (2, 3; 102, 103; 202, 203) .

3. The metal structure as claimed in claim 1 or 2, wherein each groove (12; 112; 212) is delimited by at least one first stop face (18, 19; 118), the axial protrusion (20; 120; 220) comprising at least one second stop face (23, 24; 123) configured to be arranged in abutment against the first stop face (18, 19; 118) in order to stop the rotation between the first and the second body (2, 3; 102, 103; 202, 203) .

4. The metal structure as claimed in any one of the preceding claims, wherein each undercut (16, 17; 116, 117; 216, 217) is delimited by the first inclined faces (14, 15; 114, 115) , and a bottom face (13, 113) .

5. The metal structure as claimed in claim 4, wherein each first inclined face (14, 15; 114, 115), faces, in part, the first bottom face (13; 113),

6. The metal structure as claimed in claim 4 or 5, wherein each first inclined face (14, 15; 114, 115) is a conical face that extends along a cone whose axis is parallel to and offset with respect to the first and second axes (Al; A2 ) .

7. The metal structure as claimed in one of claims 4 to 6, wherein the axial protrusion (20; 120; 220) comprises two second inclined faces (21, 22; 121, 122), which are inclined with respect to the first and the second axis (Al, A2) .

8. The metal structure as claimed in claim 7, wherein each second inclined face (21, 22; 121, 122) is a conical face which extends along a cone with axis offset with respect to the first and second axes (Al, A2) .

9. The metal structure as claimed in claim 7 or 8 wherein the cones along which the first inclined faces (14, 15; 114, 115) lie have a base diameter which is smaller than the base diameter along which the second inclined faces (21, 22; 121, 122) lie.

10. The metal structure as claimed in any one of the preceding claims, wherein the first body (102; 202) has two grooves (112; 212) arranged on opposite sides with respect to the first axis (Al), and the second body (103; 203) has two axial protrusions (120; 220), which are arranged on opposite sides with respect to the second axis (A2) and have a shape substantially complementary to at least a portion of the grooves (112; 212) .

11. The metal structure as claimed in claim 10, wherein the axial protrusions (120; 220) extend along respective circle arc paths to an extent less than 90°.

12. The metal structure as claimed in claim 10 or 11, wherein each groove (212) comprises an engagement portion and a portion (219) configured to allow the axial insertion of an axial protrusion (220) into the groove (212) .

13. The metal structure as claimed in any one of the preceding claims and comprising a safety mechanism to prevent rotation between the first and the second body (102; 103), the safety mechanism comprising two seats (126) formed in the first body (102) and two screws (128) housed in the second body (103) and configured to be selectively inserted into said seats (126) .