Method for forming a groove and flow-forming machine

Abstract

The invention relates to a method and a flow-forming machine for inserting a groove in a cylindrical, thin workpiece. The workpiece is rotated relative to at least one spinning roller. The spinning roller is provided with a profile corresponding to the groove to be shaped. The spinning roller is radially infed to the workpiece and the groove is shaped. A particularly precise forming of the groove is brought about in that simultaneously with the radial infeeding of the spinning roller and the shaping of the groove, the workpiece is axially upset by means of at least one punch.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to a method for forming a groove into a thin wall of a workpiece.

[0003] The invention also relates to a flow-forming machine, particularly for performing the method.

[0004] Prior Art

[0005] A method and machine of the related art can e.g. be gathered from JP-A-11 277 153. Further methods for shaping grooves by spinning are known from DE-C-275 000 or GB-A-2 213 749. Although these methods permit the non-cutting shaping of grooves, the geometrical accuracy is limited.

[0006] For making packing rings on pistons grooves with precise flanks and edges are required at-the transition to the piston area and for this purpose cutting has hitherto been necessary. The latter is complicated and costly, is associated with material losses and destroys material fibres in the structure.

[0007] Further methods and means for the production of inside or outside grooves on cylindrical hollow bodies can e.g. be gathered from DE 36 05 440 C2. The latter discloses a swaging device with which it is possible to shape or insert a groove. The shaping of grooves by means of such swaging devices is very complicated if a high precision of the resulting groove is required.

[0008] In the spinning method known from German patent 1 221 599 a cylindrical sheet metal body is held between two spinning rollers, one of which presses a groove into the sheet metal wall by means of a convex contour. Corresponding to said convex contour and as a function of the depth of the groove to be inserted, wall thickness changes arise, which particularly in the radial, lateral areas of the groove can lead to undefined wall changes. Grooves produced in this way are problematical if e.g. packing rings are to be inserted in them requiring precise lateral flanks with respect to the groove.

SUMMARY OF THE INVENTION

[0009] The object of the invention is to provide a method and a machine with which it is possible to insert in an efficient manner and with a particularly high geometrical accuracy grooves in sheet metal bodies.

[0010] According to the invention this object is achieved by a method having the features of claim 1 and a flow-forming machine with the features of claim 11. Preferred embodiments of the invention are given in the dependent claims.

[0011] The method according to the invention is characterized in that a spinning roller with a convex profile and adjacent support areas is infed and that the groove, including its corner areas is formed in geometrically accurate manner in accordance with the convex profile and the support areas of the spinning roller laterally adjacent thereto. It is a fundamental idea of the invention that simultaneously with the radial shaping of the groove a clearly defined, axial upsetting movement is performed, through which in defined manner material is fed into the vicinity of the groove. The specific shape of the spinning roller ensures a clearly defined material flow and a precise forming or shaping, including of the corner areas or edges of the groove. This counteracts an undesired wall thickness change in the vicinity of the groove. According to the invention it is possible to obtain a precisely defined shape and wall thickness in the vicinity of the groove. Material can in particular flow form both sides of the spinning roller into the forming or working zone. Thus, with such a flow-forming method it is not only possible to produce simple parts, but even high precision components, e.g. brake pistons for motor vehicle brake systems. The spinning roller according to the invention, despite the axial upsetting movement, permits the insertion of grooves, even on conical workpieces.

[0012] According to a first embodiment of the invention the spinning roller is positioned outside the workpiece and for inserting an outer groove is infed radially inwards to the workpiece. It is alternatively possible for the spinning roller to be positioned within the workpiece and for inserting an inner groove is infed radially outwards to the workpiece. As a result of both method variants, which can also be combined, a large number of different groove shapes can be obtained.

[0013] A rapid and efficient performance of the method is achieved according to the invention in that the workpiece is axially fixed between two displaceable spindle elements in punch form and which are both axially moved during upsetting. The spindle elements constructed as punches have in each case a first, radially directed stop face, against which engages an axial end of the workpiece. The movement of the two spindle elements is preferably by the same amount, but is oppositely directed.

[0014] Alternatively the workpiece is axially fixed between a movable spindle element and a stationary spindle element and during axial fixing the movable spindle element and the spinning roller are moved axially to the stationary spindle element, the movable spindle element being moved with a higher axial velocity than the spinning roller. In particular, the axial velocity of the spindle element is roughly twice as high as that of the spinning roller.

[0015] The facing spindle element, which is axially stationary with respect to the casing, has a correspondingly constructed abutment surface, so that bilaterally a clearly defined upsetting force can be exerted and transmitted.

[0016] A further method efficiency rise is brought about according to the invention in that the workpiece is centred during axial fixing. For this purpose at least one of the spindle elements has a centring receptacle. This centring receptacle can either be a centring hole corresponding to the external diameter of the workpiece or a centring mandrel corresponding to the internal diameter of the workpiece.

[0017] For a particularly precise forming of the groove it is preferable that during the axial upsetting of the workpiece the punch is moved in a clearly defined manner and in the vicinity of the groove a workpiece wall thickness remains virtually unchanged or is increased in planned manner.

[0018] The latter is preferably further developed in that the movement of the punch is performed as a function of the radial infeeding of the spinning roller in accordance with a predetermined control program. Said control program is filed in a known CNC control with which a servomechanism for the one or more spinning rollers and simultaneously during working also the axial drive for at least one punch are controlled. Whereas the infeeding of the spinning roller conventionally takes place linearly, according to the invention it is preferable for the axial upsetting movement to be performed in accordance with a clearly defined program sequence and not continuously. For a particularly precise formation of the groove an increased axial material feed into the vicinity of the groove being formed can take place at the beginning and/or end of the forming movement.

[0019] A particularly precise formation of the groove is achievable according to the invention in that said groove is formed between the spinning roller on one side and an opposite roller on the other side. During the shaping of an outer groove by the radial infeeding of a spinning roller from the outside an eccentric opposite roller is provided on a spindle element and is eccentrically mounted to the spindle axis. This eccentric mounting of a relatively small eccentric roller makes it possible, following the shaping of the groove, to remove the same without difficulty from the spindle element.

[0020] A particularly good formation of the groove is also ensured according to the invention in that during the shaping of the groove the workpiece is supported along its axial length on the outer circumference and/or inner circumference. This supporting action ensures that during axial upsetting there is no undesired bending out in any area other than the groove to be shaped.

[0021] A particularly good shaping of the corner areas of the groove is brought about according to the invention in that with the end of the radial infeeding of the spinning roller a certain axial upsetting is carried out. In the end position the spinning roller contour is fully applied to the workpiece circumference and a calibration takes place in this holding position. As a result of a final upsetting further material is forced into the working or forming area, so that there is an uninterrupted formation of the groove in accordance with the roller contour.

[0022] With respect to the machine or apparatus, the invention is characterized in that the spinning roller has a convex profile and support areas laterally adjacent thereto, which are formed in accordance with the groove and the corner area thereof to be worked. With such a flow-forming machine it is possible to perform or bring about the previously described method and the resulting advantages in a preferred manner.

[0023] According to a preferred further development of the flow-forming machine according to the invention, both spindle elements in the form of punches have a radial, circumferentially directed stop face. This not only permits a reliable upsetting of the workpiece, but also a centred reception and a good supporting of the workpiece during the upsetting process.

[0024] The workpiece can e.g. be constituted by a pipe, a taper or a cup-shaped workpiece with a closed bottom surface. With such a workpiece with a closed bottom, such as a brake piston, it can be appropriate to provide on at least one of the spindle elements a compressed air or venting device for rapid workpiece ejection.

[0025] According to another preferred embodiment of the invention, both spindle elements are displaceably mounted and in each case have a separate drive. Thus, in the case of an axially stationary spinning roller, in defined manner material can be introduced bilaterally into the working zone of the groove. With asymmetrically constructed grooves the displacement movement of the two spindle elements can take place in non-uniform manner for a corresponding asymmetrical material feed.

[0026] In an alternative variant of the invention, one spindle element is displaceably mounted and driven, whereas the other spindle element is stationary and the spinning roller is axially movable. In order to also bring about a relative movement of the stationary spindle element with respect to the spinning roller, the movable spinning element is moved axially more rapidly in defined manner than the spinning roller.

[0027] A particularly high geometrical accuracy in the vicinity of the groove and very small wall thickness tolerances are brought about according to the invention in that the radial and/or axial infeeding of the spinning roller is controlled simultaneously and as a function of the punch movement.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The invention is described in greater detail hereinafter relative to preferred embodiments and the attached drawings, wherein show:

[0029] FIG. 1 A part cross-sectional view through a machine during the shaping of a groove in a cup-shaped workpiece.

[0030] FIG. 2 A part cross-sectional view corresponding to FIG. 1 through a machine during the shaping of a groove in a drum-shaped workpiece.

[0031] FIG. 3 A part cross-sectional view through a machine during shaping of a groove using an opposite roller.

[0032] FIG. 4 A part cross-sectional view through a machine during the shaping of a groove in a complex rotationally symmetrical workpiece.

[0033] FIG. 5 A part cross-sectional view through a machine when shaping a groove in a workpiece with a conical area.

[0034] A flow-forming machine 10 according to the invention is shown in FIG. 1, the upper drawing half showing the state prior to the shaping of the groove and the lower drawing half the state on concluding groove shaping or insertion.

[0035] For performing the method according to the invention initially a cup-shaped, cylindrical workpiece 40 with a base 44 is inserted by means of a not shown supply device in the flow-forming machine 10. Two spindle elements 20, 22 drivable in rotary manner are axially infed with respect to a spindle axis 17 on either side of the workpiece 40. The first spindle element 20 and second spindle element 22 are substantially identically constructed, so that the structure of the spindle elements 20, 22 will be described solely in conjunction with the first spindle element 20.

[0036] So that during axial fixing the cylindrical workpiece 40 is simultaneously centred, the first spindle element 20 has a reception hole 30, whose diameter forms a fit with the external diameter of the workpiece 40. A bevel 31 at the entrance to the reception hole 30 makes it easier to insert the workpiece 40 in said hole 30. Up to a given depth the reception hole 30 is formed in the sleeve-like spindle element 20, so that a shoulder 32 is formed. The shoulder 32 serves as a stop face for a cover plate 35 of an ejector ram 34. The cover plate 35 which has a larger diameter than the cylindrical ejector ram 34 has at its top end a face serving as a stop for the workpiece 40.

[0037] The workpiece 40 is axially clamped between the two stop faces of the cover plates 35 of the two spindle elements 20, 22, which leads to a non-rotary connection to both spindle elements 20, 22. The latter are rotated by means of a not shown rotary drive and then a part sectionally shown spinning roller 12 with a convex profile 14 and support areas 16 laterally adjacent thereto is radially infed. The convex profile 14 is formed for the shaping of a groove 42 or outer groove 46 in the workpiece 40. The contour of the support areas 16 corresponds to the workpiece areas adjacent to the groove 42. Between the convex profile 14 and support areas 16 is formed a clearly defined transition 15, which can be a radius or an edge.

[0038] Simultaneously with a first contact of the convex profile 14 of the spinning roller 12 with an outside of the workpiece 40 by means of a not shown axial drive, such as a hydraulic cylinder or recirculating ball screw, an additional axial pressure is exerted on the workpiece 14, so that with the shaping of the groove 42 material is fed axially into the working area, so that there can be a clearly defined, geometrically accurate formation of the groove 42.

[0039] To avoid an undesired or uncontrolled wall thickness reduction in the working area, as a result of the controlled axial displacement between one of the two spindle elements 20, 22 or both spindle elements 20, 22 material is precisely fed in in accordance with a predetermined control program. Through this combination of radial shaping of the groove by means of the spinning roller 12 and the axial material feeding through the spindle elements 20, 22 acting as punches, a combination of a flow-forming and a folding process is obtained, which leads to high geometrical accuracy with respect to the groove 42 or outer groove 46 to be made. In particular, in accordance with the transitions 15 of the spinning roller 12, the corner areas 43 are shaped in a clearly defined manner and extend between the groove 42 and the adjacent areas of the rotationally symmetrical workpiece 40.

[0040] Following the shaping of the groove 42 the spinning roller 12 is radially reset and the two spindle elements 20, 22 are axially spaced from the workpiece and the ejection of the workpiece 40 can take place simultaneously through a displacement of the ejector ram 34 relative to the surrounding sleeve-like spindle element 20, 22.

[0041] FIG. 2 shows the flow-forming machine 10 of FIG. 1 during the working of a cylindrical, base-free workpiece 40′. The method sequence for shaping the groove takes place in the manner described relative to FIG. 1.

[0042] Another variant of a flow-forming machine 10′ according to the invention can be gathered from FIG. 3. Whilst a first spindle element 20 is constructed as in the previously described flow-forming machines, the second spindle element 22′ is provided with an opposite roller 28 for a high precision shaping of a groove 42′ on a workpiece 40′. In accordance with the contour of the groove 42′ to be shaped by a convex profile 14′ of a spinning roller 12′, the outside of the opposite roller 28 has a corresponding concave profile 29 with adjacent support areas 25. Thus, the corner areas 43′ can also be very precisely shaped on the inside.

[0043] The external diameter of the opposite roller 28 is smaller than the internal diameter of the hollow cylindrical workpiece 40′, the opposite roller 28 being mounted so as to rotate eccentrically about an eccentric axis 27 relative to the spindle axis 17.

[0044] In addition to the opposite roller 28 the second spindle element 22′ has a radially directed abutment face 21′ and the workpiece 40′ engages firstly against the latter and secondly against a cover plate 35 of the first spindle element 20.

[0045] Following the shaping of the groove 42′, the first spindle element 20, in which the workpiece 40′ is retained centrally with respect to the spindle axis 17, is moved axially away from the workpiece 40′. Thus, the workpiece 40′ can be freed from the opposite roller 28 following a corresponding resetting of the spinning roller 12′.

[0046] The universality of the method according to the invention can be gathered from the further embodiments of FIGS. 4 and 5. According to FIG. 4 a complex, stepped workpiece 40″ is worked. The cylindrical support areas 16 of the spinning roller 12 ensure a reliable material flow into the working area and an exact forming of the groove 42″ with its corner areas 43″.

[0047] By infeeding a correspondingly constructed spinning roller 12 or an inclining of said spinning roller 12 according to FIG. 5, it is also possible to work non-cylindrical workpieces, particularly conical workpieces 40′″. The support areas 16 of the spinning roller 12 prevent an undesired bending in of the workpiece 40′″.

Claims

1. Method for forming a groove into a thin wall of a workpiece, in which the workpiece is axially fixed, the workpiece is rotated relative to at least one spinning roller, for shaping a groove, the spinning roller is radially infed to a working area of the workpiece and with the radial infeeding of the spinning roller and the shaping of the groove, the workpiece is axially upset,  wherein a spinning roller with a convex profile and support areas laterally adjacent thereto is infed and the groove with its corner areas is formed in geometrically accurate manner corresponding to the convex profile and the laterally adjacent support areas of the spinning roller.

2. Method according to claim 1, wherein the spinning roller is located outside the workpiece and is radially inwardly infed to the workpiece for shaping an outer groove.

3. Method according to claim 1, wherein the spinning roller is located within the workpiece and is radially outwardly infed to the workpiece for shaping an inner groove.

4. Method according to claim 1, wherein the workpiece is axially fixed between two movable spindle elements as punches, both of which are axially moved during upsetting.

5. Method according to claim 1, wherein the workpiece is axially fixed between a movable spindle element and a stationary spindle element and that during axial upsetting the movable spindle element and the spinning roller are moved axially to the stationary spindle element, the movable spindle element being moved at a higher axial velocity than the spinning roller.

6. Method according to claim 1, wherein during the axial upsetting of the workpiece the punch is moved in a clearly defined manner and in the vicinity of the groove a wall thickness of the workpiece remains virtually unchanged or is increased in planned manner.

7. Method according to claim 1, wherein the movement of the punch is carried out as a function of the radial infeeding of the spinning roller in accordance with a predetermined control program.

8. Method according to claim 1, wherein the groove is formed between the spinning roller on one side and an opposite roller on the other side.

9. Method according to claim 1, wherein during the shaping of the groove, the workpiece is supported along its axial length on the outer circumference and/or inner circumference.

10. Method according to claim 1, wherein on ending the radial infeed of the spinning roller for shaping the corner areas a certain axial upsetting is performed.

11. Flow-forming machine, particularly for performing a method according to one of the claims 1 to 10, having two spindle elements between which can be fixed a workpiece, at least one radially adjustable spinning roller, a rotary drive for rotating the workpiece relative to the spinning roller at least one axial drive for the axial movement of at least one spindle element for upsetting and control means with which, for a clearly defined shaping of a groove, at least one spindle element is moved axially and relatively towards the spinning roller,  wherein the spinning roller has a convex profile and support areas laterally adjacent thereto and which are constructed in accordance with the groove to be formed and the corner areas thereof.

12. Flow-forming machine according to claim 11, wherein both spindle elements, as punches, have a radial stop face and a circumferentially directed stop face.

13. Flow-forming machine according to claim 11, wherein a holding device and/or an ejector is provided on at least one of the spindle elements.

14. Flow-forming machine according to claim 11, wherein both spindle elements are displaceably mounted and in each case have a separate drive.

15. Flow-forming machine according to claim 11, wherein one spindle element is displaceably mounted and driven, whereas the other spindle element is stationary and that the spinning roller is axially movable.

16. Flow-forming machine according to claim 11, wherein the radial and/or axial infeeding of the spinning roller is controlled as a function of the punch movement.