Spin forming process and apparatus for manufacturing articles by spin forming

Abstract

A spin forming process and apparatus is disclosed. A workpiece (e.g. sheet metal) is rotated with respect to a forming roller which bears against one of the outer and inner surfaces of the workpiece to deform the workpiece towards a required shape. First and second support rollers bears against the opposite surface of the workpiece. Computer control of the positions of the forming roller and the first and second support rollers allow non-axisymmetric shapes to be manufactured by spin-forming.

Claims

1. A spin forming process for manufacturing an article of a required shape from a workpiece, the workpiece having, with reference to the required shape of the article, an outer surface and an inner surface, wherein the process comprises: mounting the workpiece at a mounting region, there being defined a proximal end of the workpiece and a distal end of the workpiece, the proximal end of the workpiece being closer than the distal end of the workpiece to the mounting region of the workpiece; rotating the workpiece with respect to a forming tool, the forming tool bearing against one of the outer and inner surfaces of the workpiece to deform the workpiece towards the required shape, the forming tool comprising a forming roller having a width in a direction parallel to a rotation axis of the forming roller; providing a first support which bears against the opposite surface of the workpiece compared with the forming tool, the first support comprising a first support roller having a width in a direction parallel to a rotation axis of the first support roller, the workpiece rotating with respect to the first support; and providing a second support which bears against the opposite surface of the workpiece compared with the forming tool, the second support comprising a second support roller having a width in a direction parallel to a rotation axis of the second support roller, the workpiece rotating with respect to the second support, the rotation of the workpiece being about a workpiece rotation axis defining an axial direction of the workpiece, and wherein the rotation of the workpiece further defines a radial direction of the workpiece perpendicular to the axial direction of the workpiece, and wherein the first support is disposed proximally of the second support and the forming tool is disposed distally of the second support so that no overlap occurs between the width of the forming roller and the width of the second support roller in at least one of the axial direction of the workpiece and the radial direction of the workpiece.

2. The spin forming process according to claim 1 wherein the thickness of the workpiece is substantially unchanged when the required shape of the article is formed.

3. The spin forming process according to claim 1 wherein an initial thickness of the workpiece is t.sub.0 and a final thickness of the workpiece is t.sub.1, and inequality (1) is satisfied, for values of less than 90:
t.sub.1>t.sub.0 sin inequality (1) wherein angle as the angle between the rotational axis A of the workpiece and the tangent to the internal surface of the workpiece, the tangent being drawn in a plane containing the rotational axis A of the workpiece.

4. The spin forming process according to claim 1 wherein the required shape of the article is an axisymmetric shape.

5. The spin forming process according to claim 1 wherein the required shape of the article is a non-axisymmetric shape.

6. The spin forming process according to claim 1 wherein there is provided a third support for bearing against the same surface of the workpiece as the second support and the workpiece rotates with respect to the third support.

7. The spin forming process according to claim 6 wherein the third support is located distally of the first support and laterally of the second support.

8. The spin forming process according to claim 6 wherein the second and third supports are laterally offset from the first support.

9. The spin forming process according to claim 6 wherein the first, second and third supports are provided at least at the points of closest contact between the workpiece and a notional mandrel which would be required to form the article to the required shape from the workpiece using the forming tool.

10. The spin forming process according to claim 6 wherein there is provided a fourth support, the workpiece rotating with respect to the fourth support, the fourth support being located substantially in register with the forming tool.

11. The spin forming process according to claim 10 wherein the fourth support is controlled to vary the thickness of the workpiece during the forming process.

12. The spin forming process according to claim 10, wherein the process is a shear spinning process or a tube spinning process.

13. The spin forming process according to claim 6 wherein the forming tool is disposed distally of the third support.

14. The spin forming process according to claim 7 wherein one or more of the first, second and third supports are independently positionable under machine control with respect to the rotating workpiece.

15. The spin forming process according to claim 8 wherein one or more of the first, second and third supports are independently positionable under machine control with respect to the rotating workpiece.

16. The spin forming process according to claim 1 wherein the forming tool is positionable under machine control with respect to the rotating workpiece.

17. The spin forming process according to claim 1 wherein one or more of the first and second supports are independently positionable under machine control with respect to the rotating workpiece.

18. The spin forming process according to claim 1 wherein the forming tool bears against the outer surface of the workpiece and the first and second supports bear against the inner surface of the workpiece.

19. The spin forming process according to claim 1 wherein the forming tool bears against the inner surface of the workpiece and the first and second supports bear against the outer surface of the workpiece.

20. An apparatus for manufacturing an article of a required shape from a workpiece by spin forming, the workpiece having, with reference to the required shape of the article, an outer surface and an inner surface, the apparatus comprising: a base; a rotatable workpiece mount operatively associated with the base, the rotatable workpiece mount providing for rotatable mounting of the workpiece in the apparatus at a mounting region of the workpiece, there being defined a proximal end of the workpiece and a distal end of the workpiece, the proximal end of the workpiece being closer than the distal end of the workpiece to the mounting region of the workpiece; a forming tool operatively associated with the base for bearing against one of the outer and inner surfaces of the workpiece to deform the workpiece towards the required shape, the forming tool comprising a forming roller having a width in a direction parallel to a rotation axis of the forming roller; a first support operatively associated with the base for bearing against the opposite surface of the workpiece compared with the forming tool, the first support comprising a first support roller having a width in a direction parallel to a rotation axis of the first support roller; and a second support operatively associated with the base for bearing against the opposite surface of the workpiece compared to the forming tool, the second support comprising a second support roller having a width in a direction parallel to a rotation axis of the second support roller, wherein the apparatus is operable to cause the workpiece to rotate with respect to the first and second supports, and wherein the rotation of the workpiece is about a workpiece rotation axis defining an axial direction of the workpiece, and wherein the rotation of the workpiece defines a radial direction of the workpiece perpendicular to the axial direction of the workpiece, the first support being disposed proximally of the second support and the forming tool being disposed distally of the second support so that no overlap occurs between the width of the forming roller and the width of the second support roller in at least one of the axial direction of the workpiece and the radial direction of the workpiece.

21. The apparatus according to claim 20 wherein there is provided a third support operatively associated with the base for bearing against one of the inner and outer surfaces of the workpiece, the apparatus being operable to allow the workpiece to rotate with respect to the third support.

22. The apparatus according to claim 21 wherein there is provided a fourth support operatively associated with the base, the workpiece rotating with respect to the fourth support, the fourth support being located substantially in register with the forming tool.

23. The apparatus according to claim 21 wherein the forming tool is disposed distally of the third support.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments of the invention are described below, with reference to the following drawings:

(2) FIG. 1 illustrates a known conventional spin forming process.

(3) FIG. 2 shows the typical axisymmetric shapes that can be formed using the process of FIG. 1.

(4) FIG. 3 illustrates a known shear spinning process.

(5) FIG. 4 shows the typical axisymmetric shapes that can be formed using the process of FIG. 3.

(6) FIG. 5 shows a schematic sectional view (parallel to the axis of rotation) of a spin forming process and apparatus according to an embodiment of the invention.

(7) FIG. 6 shows a schematic end view (perpendicular to the axis of rotation) of the spin forming process and apparatus of FIG. 5.

(8) FIG. 7 illustrates the results of finite element modelling of a spin forming process.

(9) FIG. 8 shows some three dimensional shapes and wall profiles that can be formed using embodiments of the invention.

(10) FIGS. 9 and 10 show views corresponding to FIGS. 5 and 6, incorporating the blending roller (first internal support roller) arm and the support roller (second and third internal support roller) arms.

(11) FIG. 11 shows a schematic isometric view of an assembled apparatus according to an embodiment of the invention.

(12) FIG. 12 shows a plan view of the apparatus of FIG. 11.

(13) FIG. 13 shows a view of a forming roller module for use in the apparatus of FIG. 11.

(14) FIG. 14 shows a view of a blending roller (first internal support roller) module for use in the apparatus of FIG. 11.

(15) FIG. 15 shows a view of a support roller (second and third internal support roller) module for use in the apparatus of FIG. 11.

(16) FIG. 16 shows a schematic sectional view (parallel to the axis of rotation) of a spin forming process and apparatus according to another embodiment of the invention.

(17) FIG. 17 shows a schematic end view (perpendicular to the axis of rotation) of the spin forming process and apparatus of FIG. 16.

(18) FIGS. 18 and 19 show a modified embodiment based on FIGS. 16 and 17 respectively.

(19) FIGS. 20 and 21 show a modified embodiment based on FIGS. 5 and 6 respectively.

(20) FIGS. 22 and 23 show a modified embodiment based on FIGS. 18 and 19 respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS, FURTHER OPTIONAL FEATURES OF THE INVENTION

(21) The preferred embodiments of the invention provide a modified spin forming process. In this disclosure, the term spin forming is used interchangeably with metal spinning although it is acknowledged that the preferred embodiments may work with starting materials other than metal, e.g. ductile plastics materials. However, in the most preferred embodiments of the invention, the starting material is a metallic material, typically sheet metal.

(22) In the preferred embodiments of the present invention, there is provided a flexible spin forming process, in which the role of the mandrel is provided by a suitable arrangement of internal support rollers. This also allows, where desired, for the manufacture of non-axisymmetric components.

(23) With reference to FIG. 7, finite element modelling of a spin forming process of a work piece 50 using forming roller 52 reveals that the work piece 50 contacts the mandrel at only 3 locations, for each position of roller 52 with respect to work piece 15. These are: first location 54 located proximal to the rotatable mounting position of the work piece and axially aligned with roller 52; and second 56 and third 58 locations, each spaced distally from the first location and offset laterally from the first location and the position of roller 52.

(24) According to a preferred embodiment of the invention, the mandrel can therefore be replaced using a corresponding arrangement of internal supports, the work piece being allowed to rotate with respect to the internal supports.

(25) FIG. 5 shows a schematic sectional view (parallel to the axis of rotation) of a spin forming process and apparatus according to a preferred embodiment of the invention. FIG. 6 shows a schematic end view of this embodiment. In these drawings, initial work piece 30 is formed of sheet metal. During the process, this initial work piece is gradually deformed towards the desired final shape of article 33. Work piece 30 is rotatably held by tailpiece 32 for rotation about rotational axis A. Forming roller 36 is rotatably held by forming roller arm 38 and bears against outer surface 40 of the work piece.

(26) An arrangement of internal support rollers bears against the internal surface 42 of the work piece. First internal support roller 44 (also referred to herein as a blending roller) is provided proximal to the tail stock end of the article 33. Second 46 (and third 48see FIG. 6) internal support rollers are provided distally from the first internal support roller 44 and laterally offset from the first internal support roller 44. The forming roller 36 is distally spaced from the first, second and third internal support rollers but is not laterally offset from the first internal support roller 44.

(27) The configuration illustrated in FIGS. 5 and 6 has two main advantages compared to a conventional spinning process. Firstly, the configuration is flexible as there is no need for a specific mandrel for each desired shape of the finished article. Secondly, where it is possible to control the movement of the rollers radially (and, optionally, laterally), in addition to allowing movement parallel to the axis of rotation, means that production of non-axisymmetric articles is possible.

(28) FIG. 8 shows some examples of three dimensional shapes of different complexity that are possible using the preferred embodiment of the invention. A circular cup can be formed using the present invention but also using conventional spin forming. However, an elliptical cup and a rectangular cup cannot be formed by conventional spin forming. Furthermore, a kidney bean shaped cup is a highly complex shape, having a cross section including a re-entrant. This shape is also possible using preferred embodiments of the invention.

(29) FIG. 8 also shows wall profiles that can be formed using embodiments of the invention. The linear profile can be formed using conventional spin forming. The linear stepped profile can also be formed by conventional spin forming, as can the second order profile. However, of course, specific mandrel shapes must be generated for such processes. It is more difficult to form the re-entrant profile shown in FIG. 8 using conventional spin forming, since a suitably-shaped mandrel would be difficult to remove from the finished product. Such shapes can be formed in a straightforward manner using the preferred embodiments of the present invention, since the internal supports provide the required mandrel-like support, but control of their position allows these complex shapes to be formed.

(30) FIGS. 9 and 10 show views corresponding to FIGS. 5 and 6, but show blending roller arm 60 and support roller arms 62, 64. The linear arrows in FIG. 10 indicate that blending roller arm 60 and support roller arms 62, 64 can be controlled to move parallel to the rotational axis A. In addition to this, in preferred embodiments, blending roller arm 60 and support roller arms 62, 64 can be moved radially, in order to provide corresponding control of the position of the internal support rollers. Furthermore, in still further preferred embodiments, blending roller arm 60 and support roller arms 62, 64 can additionally be moved laterally (i.e. in a direction perpendicular to rotational axis A and perpendicular to the radial direction, in order to provide precise positioning of the internal support rollers at the required locations for suitable support of the internal surface of the work piece. Reference here to the lateral direction encompasses control of the support roller arms 62, 64 in order to adjust the rotational angle between support roller arms 62, 64, thus lateral offset has the same meaning here as circumferential offset.

(31) Control of the rotational speed of the work piece, the position of forming roller 36 and the positions of the internal support rollers 44, 46 and 48 is typically provided by computer numerical control (CNC), in a manner which will be understood by the skilled person.

(32) FIGS. 11-15 show views of a complete apparatus according to an embodiment of the invention.

(33) FIG. 11 shows a schematic isometric view of an assembled apparatus 80 according to an embodiment of the invention. The apparatus is supported on base plate 82 which is in turn supported on a supporting frame 84. FIG. 12 shows a plan view of the apparatus 80. Work piece 94 is rotatably supported by spindle 92. Three identifiable modules interact with work piece 94. These are blending roller module 86, support roller module 88 and forming roller module 90. These are described in more detail with reference to FIGS. 13-15.

(34) FIG. 13 shows forming roller module 90. Forming roller 92 is rotatably supported by forming roller arm 94. Forming roller arm 94 is rigidly attached to forming roller arm plate 96. Forming roller arm plate 96 is shown removed from radial positioning means 98 however, in use, forming roller arm plate 96 is attached to radial positioning means 98. The radial position of forming roller 92 can be adjusted by suitable control of radial motor 100 in combination with radial ballscrew and radial linear guide 104 radial positioning means 98 is in turn supported on axial positioning means 106 the axial position of forming roller 92 is therefore controlled by suitable control of axial motor 108, axial ballscrew 110 and axial linear guide 112. FIG. 14 shows the blending roller module 86. In this embodiment, radial motion of the blending roller 114 is motorised but axial motion of blending roller 114 is manually controlled. In further preferred embodiments, the axial motion of the blending roller may be under motorised control, implemented in a manner which will be understood by the skilled person.

(35) In FIG. 14, blending roller 114 is held on blending roller arm 116 radial movement of blending roller 114 is controlled by suitable control of radial motor 118 in combination with radial linear guide 120 and radial ballscrew 122. Axial linear guide 124 provides control of the axial position of blending roller 114. FIG. 15 shows support roller module 88 second and third internal support rollers 126, 128 are rotatably mounted with respect to respective internal support roller arms 130, 132. Radial position of the second and third internal support rollers 126, 128 is provided independently by radial motors 134, 136 radial ballscrew 138 and radial linear guide 140 are shown only with respect to radial motor 136. Axial position of second and third internal support rollers 126, 128 is provided in this embodiment by single axial motor 142 and corresponding axial ballscrew 144 and linear guide 146. In alternative embodiments, the linear position of second and third internal support rollers 126, 128 can be provided independently, by providing independent corresponding axial motors, ballscrews and linear guides as will be apparent to the skilled person.

(36) Using appropriate control of the positions of the various rollers in the apparatus of FIGS. 11-15, work piece 94 can be subjected to spin forming, forming roller 92 bearing against the outer surface of the work piece and blending roller 114 and second and third internal support rollers 126, 128 bearing against the inner surface of the work piece, in place of a mandrel. Accordingly, the shape of the article formed can be varied from run to run of the apparatus, without the need for different mandrels, only requiring suitable numerical control of the position of the rollers. Furthermore, non-axisymmetric articles can be manufactured as discussed above.

(37) The present inventors have also realised that embodiments of the present invention can be used to carry out shear spinning and/or tube forming processes. FIG. 3 illustrates a conventional shear spinning process. There are three main differences from a conventional spinning process: there is a change in thickness dictated by the wall angle (); shear spinning is carried out in a single pass, the roller following the mandrel profile; and the shear spinning roller (forming tool) has a sharp radius at its tip.

(38) Thus, in further embodiments of the invention, a shear spinning process is provided, in which a mandrel is replaced by rollers. There are different options for this. In one embodiment, illustrated in FIGS. 16 and 17, workpiece 230 is supported at the internal surface by first internal support roller 244 located close to mandrel 232, and second 246 and third 248 internal support rollers located distally of the first internal support roller 244. Second 246 and third 248 internal support rollers are offset laterally from each other. Main forming roller 236 is held by forming arm 238. The main forming roller is a shear spinning rollerwith a sharp nose radius at the end. During the process, the second and third support rollers move together with the main forming roller, both radially and axially, with a radial offset from the main forming roller equal to the final thickness of the workpiece. It is possible for the toolpath to be a single pass, but this is not necessarily essential. In other embodiments, the thickness of the workpiece can be reduced in stages, to reduce the roller arm forces.

(39) The inventors consider that in the shear spinning embodiments of the present invention, careful control of toolpath is important. The shear spinning toolpath is more aggressive than conventional spinning embodiments and consist of mainly straight lines.

(40) FIGS. 18 and 19 illustrate another embodiment of the invention, which is a modification of the embodiment illustrated in FIGS. 16 and 17. Therefore similar features are not described again here, and similar reference numbers are used for similar features. In this embodiment, a fourth internal support roller 250 is added. This is positioned directly under the main forming roller, to provide better control over final thickness of the workpiece. Fourth internal support roller 250 is therefore located distally from the first internal support roller 244, but is axially aligned with it, and has the second and third internal support rollers 246, 248 laterally offset on either side of it. It is noted that this configuration exerts high forces on the roller arms, so a relatively stiff machine is typically required.

(41) It is noted here that an apparatus having four internal support rollers, in the manner indicated in FIGS. 18 and 19 can be operated in conventional spinning or shear spinning mode, typically by controlling the operation of the fourth internal support roller in order to control the thickness of the workpiece. In some embodiments, the fourth internal support roller could be switched in and out of use during a single process for manufacturing a component. This allows control in order to achieve a variation in the thickness of the final workpiece.

(42) In a further embodiment, it is possible to use the apparatus with four internal support rollers in order to carry out tube spinning, with wall angle set to =0. It is again noted that this configuration exerts high forces on the roller arms, so a relatively stiff machine is typically required.

(43) The present inventors have also realised that the present invention can be used with the forming tool bearing against the inner surface of the workpiece. In an embodiment based on conventional spinning, this is illustrated in FIGS. 20 and 21, showing the spin forming of a cup-shaped workpiece into a flat plate using an internal forming tool, an internal support and an external support.

(44) A similar approach can be set out with respect to shear spinning. This is illustrated in FIGS. 22 and 23, in which an internal shear spinning forming tool is used, with an internal first support roller and external second, third and fourth support rollers.

(45) The approach shown in FIGS. 22 and 23 shows how the process based on conventional spin forming can be combined with the process based on shear spinning. In FIG. 22, the workpiece is first formed into a cup shape using the process based on conventional spin forming. Then the workpiece is subjected to shear spin forming using an internal forming tool. This allows the thickness of the workpiece to be reduced.

(46) Thus, forming in both directions can be used to manufacture lightweight components. Carrying out combined spin forming (i.e. based on both conventional and shear spin forming), it is possible to produce components with varying wall thickness in a single component. The thickness can be structurally optimised, allowing the production of structurally optimised, lightweight components.

(47) As an example, it is possible to manufacture a 45 degree cone with varying thickness (along the axis). This is done by first shear-spinning a component with varying wall angle to obtain varying thickness along the wall. Then, reverse conventional spinning is carried out (using an internal forming tool and external second and third support rollers) to straighten the workpiece back to 45 degrees. Since conventional spinning preserves existing thickness, the combined result of this process would give 45 degree cone with varying thickness.

(48) In order to provide precise control of the shape of the workpiece during the process, preferred embodiments of the invention utilise at least one sensor (not shown) adapted to sense the shape of the workpiece during the process. A control system may be provided in order to provide feedback control in order to compare the measured workpiece geometry with the required (or calculated) workpiece geometry. Thus, there is provided a means for comparing a difference between the target workpiece shape and the actual workpiece shape. Where a significant difference is detected, the apparatus is controlled in order to reduce this difference. Suitable control may be control of the position of the forming tool and/or supports, speed of rotation of the workpiece, etc.

(49) The preferred embodiments of the invention have been described by way of example. On reading this disclosure, modifications to these embodiments, further embodiments and modifications thereof will be apparent to the skilled person and accordingly fall within the scope of the present invention.