Metal sleeve and method for producing it

Abstract

A method for producing a metal sleeve includes providing a first metal sleeve semi-finished product having a metal body. The metal body surrounds an inner channel. At least one groove is located in the metal body on the side of the inner channel. The first metal sleeve semi-finished product is pressed into a first die by means of a punch and in the process is formed by impact extrusion into the metal sleeve to be produced. The first die is designed such that a proximal front edge, which is spaced apart from the distal front edge and delimits the groove in the proximal direction, is formed in the metal body on the side of the inner channel. A metal sleeve includes a metal body which surrounds an inner channel running between a proximal and a distal opening. The inner channel has at least one groove set back into the metal body, running in the longitudinal direction of the inner channel and stepped on both sides by a distal and a proximal front edge. The proximal front edge of the groove is produced by impact extrusion. A method for producing a gearbox is provided.

Claims

1. A method for producing a pressed metal sleeve comprising: providing a semi-finished product comprising a metal body, wherein the metal body of the semi-finished product surrounds an inner channel of the semi-finished product running between a proximal opening of the metal body of the semi-finished product and a distal opening of the metal body of the semi-finished product, and wherein at least one groove, which is stepped on one side, is located in the metal body of the semi-finished product on a side of the inner channel of the semi-finished product, this groove of the semi-finished product running continuously from a distal front edge of the metal body of the semi-finished product to the proximal opening of the metal body of the semi-finished product, and pressing the semi-finished product into a first die by means of a first punch thereby forming the semi-finished product by impact extrusion into a pressed metal sleeve, wherein the semi-finished product is inserted into the first die with the proximal opening of the metal body of the semi-finished product at a front of a die opening of the first die, wherein the first die is designed such that a proximal front edge of the pressed metal sleeve, which is spaced apart from the distal front edge of the metal body of the semi-finished product and delimits a pressed metal sleeve groove being formed in the proximal direction, is formed in the metal body of the semi-finished product on the side of the inner channel of the semi-finished product, and wherein the first die has an inner contour, which extends in the axial direction from the die opening for inserting the semi-finished product and has a cross-sectional tapering which is spaced apart from the die opening, and the semi-finished product is pressed into the first die by means of the first punch to the extent that the proximal opening of the metal body of the semi-finished product lies behind and the distal front edge of the metal body of the semi-finished product lies in front of the cross-sectional tapering, wherein the pressed metal sleeve comprises a pressed metal sleeve body which surrounds a pressed metal sleeve inner channel running between a proximal opening of the pressed metal sleeve and a distal opening of the pressed metal sleeve, wherein the pressed metal sleeve inner channel comprises the pressed metal sleeve groove set back into the pressed metal sleeve body, running in a longitudinal direction of the pressed metal sleeve inner channel and stepped on both sides by a distal front edge of the pressed metal sleeve and the proximal front edge of the pressed metal sleeve, a proximal front edge of the pressed metal sleeve groove is produced by the impact extrusion during pressing, and a width of a groove area of the pressed metal sleeve groove decreases steadily in a proximal direction in an area of the proximal front edge of the pressed metal sleeve to a width of less than 25% of a maximum width of the groove area.

2. The method according to claim 1, wherein the inner contour of the first die in an area of cross-sectional tapering has a first area with a first cross section which is constant in an axial direction, a transition area adjoining the first area on a side facing away from the die opening and with a cross section decreasing in the axial direction from the first cross section to a second smaller cross section and a second area adjoining the transition area on the side facing away from the die opening and with a second cross section which is constant in the axial direction, wherein an inner contour in the transition area has a maximum angle of 25 to 55 to an axial axis of the inner channel of the semi-finished product.

3. The method according to claim 1, wherein a degree of deformation on the cross-sectional tapering is in a range between 30 and 45%.

4. The method according to claim 1, wherein the semi-finished product is provided by providing a preliminary semi-finished product with a preliminary semi-finished metal body, wherein the preliminary semi-finished metal body surrounds a preliminary semi-finished inner channel running between a proximal opening of the preliminary semi-finished product and a distal opening of the preliminary semi-finished product, and by pressing the preliminary semi-finished product into a second die by means of a second punch thereby forming the preliminary semi-finished product by impact extrusion into the semi-finished product, wherein a mandrel is arranged and designed in the second die in such a way that a preliminary semi-finished groove, which is stepped on one side, is formed in the preliminary semi-finished metal body on a side of the preliminary semi-finished inner channel and runs continuously from a distal front edge of the preliminary semi-finished product to the proximal opening of the preliminary semi-finished product.

5. The method according to claim 4, wherein the mandrel in the second die has at least one lateral bulge running in a longitudinal direction of the mandrel for forming the at least one preliminary semi-finished groove which is stepped on one side.

6. The method according to claim 1, further comprising pressing the pressed metal sleeve into a further die by means of a further punch thereby further forming the pressed metal sleeve by impact extrusion, wherein the further die has an inner contour, which extends from a die opening of the further die for inserting the pressed metal sleeve and has a cross-sectional tapering which is spaced apart from the die opening of the further die, and the pressed metal sleeve is pressed into the further die by means of the further punch to the extent that the proximal opening of the pressed metal sleeve lies behind and the proximal front edge of the pressed metal sleeve lies in front of the cross-sectional tapering.

7. The method according to claim 3, wherein the degree of deformation on the cross-sectional tapering is in the range between 35 and 40%.

8. The method according to claim 4, further comprising pressing the pressed metal sleeve into a third die by means of a third punch thereby further forming the pressed metal sleeve by impact extrusion, wherein the third die has an inner contour, which extends from a die opening of the third die for inserting the pressed metal sleeve and has a cross-sectional tapering which is spaced apart from the die opening of the third die, and the pressed metal sleeve is pressed into the third die by means of the third punch to the extent that the proximal opening of the pressed metal sleeve lies behind and the proximal front edge of the pressed metal sleeve lies in front of the cross-sectional tapering.

9. The method according to claim 2, wherein the degree of deformation on the cross-sectional tapering is in the range between 30 and 45%.

10. A method for producing a pressed metal sleeve comprising: providing a semi-finished product comprising a metal body, wherein the metal body of the semi-finished product surrounds an inner channel of the semi-finished product running between a proximal opening of the metal body of the semi-finished product and a distal opening of the metal body of the semi-finished product, and wherein at least one groove, which is stepped on one side, is located in the metal body of the semi-finished product on a side of the inner channel of the semi-finished product, this groove of the semi-finished product running continuously from a distal front edge of the metal body of the semi-finished product to the proximal opening of the metal body of the semi-finished product, and pressing the semi-finished product into a first die by means of a first punch thereby forming the semi-finished product by impact extrusion into a pressed metal sleeve, wherein the semi-finished product is inserted into the first die with the proximal opening of the metal body of the semi-finished product at a front of a die opening of the first die, wherein the first die is designed such that a proximal front edge of the pressed metal sleeve, which is spaced apart from the distal front edge of the metal body of the semi-finished product and delimits a pressed metal sleeve groove being formed in a proximal direction, is formed in the metal body of the semi-finished product on the side of the inner channel of the semi-finished product, and wherein the first die has an inner contour, which extends in an axial direction from the die opening for inserting the semi-finished product and has a cross-sectional tapering which is spaced apart from the die opening, and the semi-finished product is pressed into the first die by means of the first punch to the extent that the proximal opening of the metal body of the semi-finished product lies behind and the distal front edge of the metal body of the semi-finished product lies in front of the cross-sectional tapering, wherein the pressed metal sleeve comprises a pressed metal sleeve body which surrounds a pressed metal sleeve inner channel running between a proximal opening of the pressed metal sleeve and a distal opening of the pressed metal sleeve, wherein the pressed metal sleeve inner channel comprises the pressed metal sleeve groove set back into the pressed metal sleeve body, running in a longitudinal direction of the pressed metal sleeve inner channel and stepped on both sides by a distal front edge of the pressed metal sleeve and the proximal front edge of the pressed metal sleeve, a proximal front edge of the pressed metal sleeve groove is produced by the impact extrusion during pressing.

11. The method according to claim 10, wherein the inner contour of the first die in an area of the cross-sectional tapering has a first area with a first cross section which is constant in an axial direction, a transition area adjoining the first area on a side facing away from the die opening and with a cross section decreasing in the axial direction from the first cross section to a second smaller cross section and a second area adjoining the transition area on the side facing away from the die opening and with a second cross section which is constant in the axial direction, wherein an inner contour in the transition area has a maximum angle of 25 to 55 to an axial axis of the inner channel of the semi-finished product.

12. The method according to claim 10, wherein a degree of deformation on the cross-sectional tapering is in a range between 30 and 45%.

13. The method according to claim 10, wherein the semi-finished product is provided by providing a preliminary semi-finished product with a preliminary semi-finished metal body, wherein the preliminary semi-finished metal body product surrounds a preliminary semi-finished inner channel running between a proximal opening of the preliminary semi-finished product and a distal opening of the preliminary semi-finished product, and by pressing the preliminary semi-finished product into a second die by means of a second punch thereby forming the preliminary semi-finished product by impact extrusion into the semi-finished product, wherein a mandrel is arranged and designed in the second die in such a way that a preliminary semi-finished groove, which is stepped on one side, is formed in the preliminary semi-finished metal body on a side of the preliminary semi-finished inner channel and runs continuously from a distal front edge of the preliminary semi-finished product to the proximal opening of the preliminary semi-finished product.

14. The method according to claim 13, wherein the mandrel in the second die has at least one lateral bulge running in a longitudinal direction of the mandrel for forming the preliminary semi-finished groove which is stepped on one side.

15. The method according to claim 10, further comprising pressing the pressed metal sleeve into a further die by means of a further punch thereby further forming the pressed metal sleeve by impact extrusion, wherein the further die has an inner contour, which extends from a die opening of the further die for inserting the pressed metal sleeve and has a cross-sectional tapering which is spaced apart from the die opening of the further die, and the pressed metal sleeve is pressed into the further die by means of the further punch to the extent that the proximal opening of the pressed metal sleeve lies behind and the proximal front edge of the pressed metal sleeve lies in front of the cross-sectional tapering.

16. The method according to claim 12, wherein the degree of deformation on the cross-sectional tapering is in the range between 35 and 40%.

17. The method according to claim 13, further comprising pressing the pressed metal sleeve into a third die by means of a third punch thereby further forming the pressed metal sleeve by impact extrusion, wherein the third die has an inner contour, which extends from a die opening of the third die for inserting the pressed metal sleeve and has a cross-sectional tapering which is spaced apart from the die opening of the third die, and the pressed metal sleeve is pressed into the third die by means of the third punch to the extent that the proximal opening of the pressed metal sleeve lies behind and the proximal front edge of the pressed metal sleeve lies in front of the cross-sectional tapering.

18. The method according to claim 11, wherein the degree of deformation on the cross-sectional tapering is in the range between 30 and 45%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the present invention are described below by means of exemplary embodiments of the metal sleeve and of the method for producing it, wherein reference is made to the accompanying figures.

(2) FIGS. 1-2 show a schematic illustration of a method for producing a metal sleeve from the prior art,

(3) FIG. 3 shows a metal sleeve from the prior art which was produced by the method described in FIGS. 1-2,

(4) FIGS. 4-5 show a first method step for producing a second metal sleeve semi-finished product from a solid metal body according to an exemplary embodiment of the method for producing a metal sleeve,

(5) FIG. 6 shows a second method step for producing a first metal sleeve semi-finished product from the second metal sleeve semi-finished product according to the exemplary embodiment of the method according to the invention for producing a metal sleeve,

(6) FIG. 7 shows a third method step for producing a metal sleeve from the first metal sleeve semi-finished product according to the exemplary embodiment of the method for producing a metal sleeve,

(7) FIG. 8 shows a fourth method step for the further processing of the produced metal sleeve according to the exemplary embodiment of the method for producing a metal sleeve,

(8) FIG. 9 shows a second metal sleeve semi-finished product as can be produced using the method step from FIGS. 4-5 and as can be used for the method step from FIG. 6,

(9) FIG. 10 shows a first metal sleeve semi-finished product as can be produced using the method step from FIG. 6 and as can be used for the method step in FIG. 7,

(10) FIG. 11 shows a metal sleeve as can be produced using the method step from FIG. 7 and as can be used for the method step in FIG. 8,

(11) FIG. 12 shows a further processed metal sleeve as can be produced using the method step in FIG. 8,

(12) FIG. 13 shows an illustration of the groove contour in the area of the proximal front edge,

(13) FIG. 14 shows an image of the fibre structure of a metal sleeve in the area of the proximal front edge, in which the proximal front edge of the metal sleeve was produced by radial forging, and

(14) FIG. 15 shows an image of the fibre structure of a metal sleeve in the area of the proximal front edge, in which the proximal front edge of the metal sleeve was produced by impact extrusion.

DETAILED DESCRIPTION OF THE INVENTION

(15) FIGS. 1-2 schematically show a method for producing a metal sleeve from the prior art. A metal sleeve produced using this method from the prior art is illustrated in cross section in FIG. 3.

(16) In the first step of the method from the prior art (FIG. 1), firstly a sleeve-shaped semi-finished product 2 is pulled over a mandrel 4 which has radial bulges 6 on its peripheral side. Using four radially arranged forging hammers 8 (only two of which forging hammers are visible in the cross-sectional view in FIG. 1) the semi-finished product 2 is then in an area spaced apart from its distal opening 10 and from its proximal opening 12 pressed from the outside against the bulges 6 of the mandrel 4 by radial forging, so that in this area grooves corresponding to the bulges 6 are inserted into the inner channel 14 of the semi-finished product 2.

(17) In the second step of the method from the prior art (FIG. 2), the mandrel 4 is withdrawn from the semi-finished product 2 and a further mandrel 18 without any bulges is moved into the semi-finished product 2. Using the four radially arranged forging hammers 8, the semi-finished product 2 is then in an area facing the proximal opening 12 pressed from the outside against the mandrel 18 by radial forging, so that the grooves 20 inserted into the inner channel 14 in the first step are delimited in the proximal direction.

(18) A metal sleeve 22 produced in this way is illustrated in FIG. 3. The groove 20 has a distal front edge 24 facing the distal opening 10 and a proximal front edge 26 facing the proximal opening 12. A metal sleeve produced by radial forging like the metal sleeve 22, particularly in the area of the proximal front edge 26, has a fibre orientation which is characteristic for radial forging.

(19) The disadvantage of the method from the prior art outlined with the aid of FIGS. 1-2 lies in the long production time of 40 to 45 seconds per metal sleeve 22, which is required for radially forging the grooves in the first step and for delimiting the grooves in the proximal direction in the second step.

(20) An exemplary embodiment for the method according to the invention for producing a metal sleeve is now described below with the aid of FIGS. 4-8, wherein in each of these figures a method step of the method is illustrated. FIGS. 4 to 8 are in each case split into two, wherein the right side illustrates the situation at the beginning and the left side illustrates the situation at the end of the respective method step.

(21) The method steps illustrated in FIGS. 4 to 6 and 8 are optional method steps according to preferred embodiments of the method according to the invention.

(22) In addition, the results of the forming operations on the metal body obtained using the individual method steps are illustrated in FIGS. 9 to 12. In particular, FIG. 9 shows a second metal sleeve semi-finished product 120 in cross section, FIG. 10 shows a first metal sleeve semi-finished product 140 in cross section, FIG. 11 shows a metal sleeve 160 in cross section and FIG. 12 shows a further processed metal sleeve 180 in cross section.

(23) FIG. 4 shows a tool 200 for cup backward impact extrusion. The tool 200 has a die 210 for cup backward impact extrusion and an associated punch tool 250. The die 210 has an inner contour 214 extending from the die opening 212 in the axial direction 202, wherein the inner contour is cylindrically formed and is delimited at the bottom by a bottom punch 216. The punch tool 250 has a central punch 252 which can be moved in the axial direction with great force into the opening 212 of the die 210. In addition, the punch tool 250 has a sleeve 254 which is arranged around the punch 252 and is movable in the axial direction with respect to it.

(24) At the beginning of the first method step, firstly a cylindrical solid metal body 100 is inserted into the die 210 (right side of FIG. 4). The solid metal body on both abutting faces has a central indentation 102 and 104 respectively, so that the punches 252 and 216 can be centred better on the metal body 100. When the first method step is carried out, the punch 252 is then pressed with great force into the solid metal body 100, so that the material of the solid metal body begins to flow and flows into the area surrounding the punch 252. In this way, a cup-shaped metal body 110 is produced (left side of FIG. 4).

(25) Subsequently, the cup-shaped metal body 110 is inserted into a punching tool 300 (FIG. 5, right side) by means of which the bottom 112 of the cup-shaped metal body 110 is punched out of the cup-shaped metal body 110 through the downward movement of a punch 310, so that a second metal sleeve semi-finished product 120 results. (FIG. 5, left side). The second metal sleeve semi-finished product 120 produced in this way is illustrated in FIG. 9. The second metal sleeve tool 120 has a metal body 122 which surrounds an inner channel 128 running between a distal opening 124 and a proximal opening 126.

(26) In the second method step illustrated in FIG. 6, the second metal sleeve semi-finished product 120 is processed into a first metal sleeve semi-finished product 140. A second impact extrusion tool 400 having a second die 410 and a second punch 450 is used for this purpose. The second die 410 has an inner contour 414 extending in the axial direction 402 from the die opening 412 for inserting the second metal sleeve semi-finished product 120 and having a cross-sectional tapering 416 spaced apart from the die opening 412. In addition, a mandrel 430, which on its outside has four bulges 432 distributed over the periphery, is arranged in the die.

(27) At the beginning of the method step, the second metal sleeve semi-finished product 120 is inserted with the proximal opening 126 at the front into the die opening 412 (FIG. 6, right side) and then is pressed under high pressure into the second die 410 by means of a punch 452 of the punch tool 450. By means of the cross-sectional tapering 416 of the inner contour of the second die 410 and the bulges 432 of the mandrel 430 arranged in this area, four grooves 150, which are stepped on one side and distributed over the periphery, are inserted into the metal body 122 of the second metal sleeve semi-finished product 120, these grooves 150 running continuously from a distal front end 152 to the proximal opening 126, 146 (FIG. 6, left side).

(28) The first metal sleeve semi-finished product 140 produced in this way is illustrated in FIG. 10. The metal body 142 of the first metal sleeve semi-finished product 140 has a distal opening 144 and a proximal opening 146, between which an inner channel 148 runs. The inner channel has four grooves 150 distributed in the peripheral direction which are each stepped on one side by a distal front edge 152 and run continuously to the proximal opening 146.

(29) This first metal sleeve semi-finished product 140 is processed further into a metal sleeve 160 in the third method step illustrated in FIG. 7. A first impact extrusion tool 500 having a first die 510 and a first punch tool 550 which has a punch 552 is used for this purpose. The first die 510 has an inner contour 514 extending in the axial direction 502 from the die opening 512 for inserting the first metal sleeve semi-finished product 140 and having a first cross-sectional tapering 516 and a second cross-sectional tapering 518.

(30) The inner contour 414 of the first die 510 above the second cross-sectional tapering 518 has a first area 520 with a first cross section which is constant in the axial direction and below the second cross sectional tapering 518 has a second area 522 with a second smaller cross section which is constant in the axial direction. The cross sectional tapering 518 itself forms a transition area between the first area 520 and the second area 522, in which the cross section decreases from the first larger to the second smaller cross section. The angle of the inner contour 414 to the axial axis or to the axial direction 402, respectively, is essentially constant in this transition area and preferably lies in the range between 25 and 55, preferably between 30 and 50, in particular between 35 and 45. At the beginning of the method step, the first metal sleeve semi-finished product 140 is inserted with the proximal opening 146 at the front into the die opening 512 and a mandrel 530 is introduced on the part of the punch tool 550 into the inner channel 148 of the second metal sleeve semi-finished product (FIG. 7, right side). The mandrel 530 in sections has a cylindrical shape adapted to the inner channel 148 of the first metal sleeve semi-finished product 140.

(31) The first metal sleeve semi-finished product 140 is then pressed with great force into the first die 510 by means of the punch 552, in fact, to the extent that the proximal opening 146 of the first metal sleeve semi-finished product 140 lies behind and the distal front edge 152 lies in front of the second cross-sectional tapering 518. The material of the metal body 142 is formed through the second cross-sectional tapering 518 by impact extrusion, wherein a proximal front edge 174 delimiting the groove 150 in the proximal direction is formed (FIG. 7, left side).

(32) The degree of deformation by which the metal body 142 is formed at the second cross-sectional tapering 518, is preferably in the range between 30 and 45%, preferably between 35 and 40%. The degree of deformation results from the ratio of the cross-sectional areas which are available for the metal body 142 in the first die 510 directly in front of and behind the cross-sectional tapering 158. For example, if the cross section of the first die 510, which owing to the mandrel 530 is essentially annular, in front of the cross-sectional tapering 518, i.e. in the first area 520, has an area Q.sub.1 and behind the cross-sectional tapering 518, i.e. in the second area 522, has an area Q.sub.2=0.65.Math.Q.sub.1, then the degree of deformation U=1Q.sub.2/Q.sub.1=35%.

(33) The force with which the first metal sleeve semi-finished product 140 is pressed into the first die 510 in particular is dependent on the material of the metal sleeve, on its cross section and on the cross-sectional tapering (in particular on the degree of deformation). For certain metal sleeves these forces can, for example, lie in a range of 200 to 250 t.

(34) The metal sleeve 160 produced in this method step is precisely illustrated in FIG. 11. The metal sleeve 160 has a metal body 162 which surrounds an inner channel 168 running between a distal opening 164 and a proximal opening 166. Four grooves 170 are inserted into the inner channel 168 uniformly distributed over the periphery of the same, each of these grooves 170 being delimited and stepped on both sides by a distal front edge 172 facing the distal opening 164 and a proximal front edge 174 facing the proximal opening 166.

(35) The outer contour of the metal sleeve 160 in the area of the proximal front edge 174 has a contour corresponding to the cross-sectional tapering 518 for producing the proximal front edge 174, this contour having a maximum angle to the axial axis 176 of the inner channel 168. The maximum angle of the proximal front edge 172 to the axial axis 176 of the inner channel 168 is indicated by in FIG. 11. The maximum angle of the cross-sectional tapering 518 to the axial axis 502 of the die 510 and to the axial axis 178 of the inner channel 168, respectively, and hence the angle is preferably chosen such that the ratio / is greater than 1, preferably greater than 1.1.

(36) FIG. 8 shows a fourth method step for processing the metal sleeve 160 further into the further processed metal sleeve 180 illustrated in FIG. 12. An impact extrusion tool 600 having a third die 610 and a third punch tool 650 which has a punch 652 is used for this purpose. The third die has an inner channel 614 extending from the die opening 612 in the axial direction 602 and having a first cross-sectional tapering 616, a second cross-sectional tapering 618 and a third cross-sectional tapering 620.

(37) At the beginning of the process, the metal sleeve 160 is inserted with the proximal opening 166 at the front into the die opening 612 (FIG. 8, right side) and then pressed with great force into the third die 610 by means of the punch 652. The metal sleeve 160 is pressed into the third die 610 to the extent that the proximal opening 166 of the metal sleeve 160 lies behind and the proximal front edge 174 lies in front of the third cross-sectional tapering 620. In this way, with the third cross-sectional tapering 620 an additional step can be formed into the area of the metal body 162 arranged between the proximal front edge 174 and the proximal opening 166 and hence the cross section of the inner channel 168 can be set to a certain size in this area without adversely affecting the previously completed groove 170 (FIG. 8, left side).

(38) The further processed metal sleeve 180 produced using the method step described in FIG. 8, is illustrated in FIG. 12. The further processed metal sleeve 180 essentially differs from the metal sleeve 160 by the fact that the inner channel 188 running between the distal opening 184 and the proximal opening 186 has a further cross-sectional tapering 196 arranged between the proximal front edge 194 of the groove 190 and the proximal opening 186, so that the inner and outer cross section of the metal body 182 in the area of the proximal opening 186 is adapted independently of the cross section in the area of the groove 190.

(39) FIG. 13 shows the groove contour of the groove, in fact, on the one hand, with a proximal front edge (groove contour 702) produced according to the prior art by radial forging and with a proximal front edge (groove contour 704) produced by impact extrusion corresponding to the method described with the aid of FIGS. 5 to 8. The groove contours are in each case illustrated as an equal-area projection into a plane.

(40) Both groove contours 702 and 704 have two axial areas 712, 714 respectively, in which the groove contour runs essentially parallel to the axial axis of the respective metal sleeve, and a proximal front edge area 716 and a distal front edge area 718, by means of which the groove areas 720 enclosed by the groove contours in each case are delimited in the proximal and distal direction respectively.

(41) As can be seen from FIG. 13, in the proximal front edge area 716 the groove contour 704 produced by impact extrusion has a substantially rounder almost semi-circular shape, whilst the groove contour 702 produced by radial forging rather has the shape of a rectangle rounded at the corners. In particular, a straight groove contour section running essentially transverse to the axial direction is produced in the proximal area of the proximal front edge during the radial forging process.

(42) The smallest rectangle 708 embedding the groove area in the proximal front edge area is also illustrated in FIG. 13. As can be seen from FIG. 13, the groove area of the impact-extruded metal sleeve delimited by the groove contour 704 is much smaller than the groove area of the groove area of the radially forged metal sleeve delimited by the groove contour 702. In particular, the groove area of the impact-extruded metal sleeve in the proximal front edge area is less than 85%, in particular less than 80%, of the area of the rectangle 708.

(43) The impact-extruded metal sleeve can be distinguished from a radially forged metal sleeve in this way.

(44) In addition, a metal sleeve in which the proximal front edge has been produced by impact extrusion can also be distinguished from a metal sleeve in which the proximal front edge has been produced by radial forging by the fibre orientation which is characteristic for impact extrusion. Typical examples of the fibre orientations in the area of the proximal front edge which are characteristic for radial forging and for impact extrusion respectively are illustrated below by means of FIGS. 14 and 15.

(45) FIG. 14 shows an image of the fibre structure of a first metal sleeve 800 in the area of the proximal front edge, wherein the proximal front edge 802 of the first metal sleeve 800 has been produced by radial forging, and FIG. 15 shows an image of the fibre structure of a second metal sleeve 900 in the area of the proximal front edge 902, wherein the proximal front edge 902 of the second metal sleeve 900 has been produced by impact extrusion. For these images, the first and second metal sleeves 800, 900 were respectively cut open in the longitudinal direction and the respective cut face polished and then etched, so that the fibre structures of the metal sleeves 800, 900 became visible.

(46) As can be seen from FIG. 14, the first metal sleeve 800 has a fibre orientation in the area of the proximal front edge 802 which on the whole is heavily deformed by compression and distorted, with a large number of interruptions and displacements of the individual fibres. In particular, the fibre orientation in the area of the proximal front edge 802 differs greatly from the clearly smoother fibre orientation in the areas 804, 806 abutting on this area of the proximal front edge 802. This fibre orientation, which is deformed by compression and distorted and is typical for radial forging, in the area of the proximal front edge 802 is brought about by the forming forces transferred to the metal sleeve 800 in the radial direction by the forging hammers.

(47) The fibre orientation of the metal sleeve 900 illustrated in FIG. 15 is, in contrast, very smooth and does not have any appreciable deformations by compression, distortions or interruptions in the area of the proximal front edge 902, but essentially follows the contour of the metal body. The fibre orientation of the metal sleeve 900 in the area of the proximal front edge 902 is comparable with the fibre orientation in the areas 904, 908 abutting on this area of the proximal front edge 902. Such a fibre orientation typical for impact extrusion is achieved by causing the metal material of the metal sleeve 900 to flow during the impact extrusion process.

(48) In addition to examples of characteristic fibre orientations, FIGS. 14 and 15 also show examples of characteristic outer contours 820, 920 of the metal sleeves 800, 900, which have been produced by radial forging and impact extrusion respectively. In the case of the radially forged metal sleeve 800, the forging hammers acting on the metal sleeve from the outside produce a relatively sharp bend 822, on which the outer contour has a very large angle to the axial axis of the inner channel. In FIG. 14, this angle is almost at 90. In the case of the metal sleeve 902, the outer contour in the area of the proximal front edge 902 is directly determined by the contour at the cross-sectional tapering of the first die (518 in FIG. 7), so that a smoother course of the outer contour 920 is made possible with a maximum angle to the axial axis of the inner channel of at most 75, at most 60 or even at most 45 respectively.