WO2022268405A1

WO2022268405A1 - Method for producing a hollow cylindrical workpiece

Info

Publication number: WO2022268405A1
Application number: PCT/EP2022/063016
Authority: WO
Inventors: Benedikt Nillies; Bernd RUDERT; Ralf Grünewald
Original assignee: Leifeld Metal Spinning Gmbh; Winkelmann Powertrain Components Gmbh & Co. Kg
Priority date: 2021-06-23
Filing date: 2022-05-13
Publication date: 2022-12-29
Also published as: EP4108355A1; CN117751019A

Abstract

The invention relates to a method for producing a hollow cylindrical workpiece from a solid initial workpiece, in which a cup-shaped intermediate form is produced in the solid initial workpiece without cutting by drilling pressure, in which a rolling mandrel is pressed axially into the initial workpiece and at the same time at least one forming roller is provided on an outer face of the outer workpiece. The intermediate form has a solid bottom portion and a sleeve portion attached to the bottom portion with a first length and a first wall thickness. The cup-shaped intermediate form is further subjected to stretch-flow forming in the course of which the sleeve portion is stretched to a second length, which is longer than the first length, and to a second wall thickness which is smaller than the first wall thickness.

Description

PROCESS FOR MANUFACTURING A HOLLOW CYLINDRICAL WORKPIECE

The invention relates to a method for producing a hollow-cylindrical workpiece, in particular a hollow shaft, from a solid starting workpiece.

Hollow cylinder components are required for various applications in mechanical and plant engineering. In the production of gears, for example, gear shafts are required that have a high level of strength for torque transmission and should have the lowest possible weight to reduce the mass moment of inertia.

A method for producing a hollow shaft is known from DE 10 2005 036 681 A1, a rotary swaging method being used.

DE 102012 005 106 B4 discloses a method for producing a hollow shaft from a solid semi-finished product, with two parts of the shaft first being produced by spinning a bore. The two parts can then be connected to one another by friction welding.

Bore spinning is one of the non-cutting forming processes. A solid starting workpiece is set in rotation in a spinning machine, with a spinning mandrel being pressed axially into the solid workpiece, while at the same time at least one forming roller is applied to the workpiece on the outside. By applying the at least one forming roller, a complex clamping state is generated in the workpiece, in which chipless forming with egg nem axial impressions of the spinning mandrel is made possible. A method for producing a transmission part by means of bore spinning is known, for example, from DE 10304960 A1.

The workpieces produced by the bore spinning are usually subjected to a machining process, in particular on a lathe machine, from closing, in order to obtain a desired final contour.

The invention is based on the object of specifying a method with which hollow-cylindrical workpieces can be efficiently produced with the lowest possible weight and particularly high strength.

According to the invention, the object is achieved by a method having the features of claim 1. Preferred embodiments of the invention are set out in the dependent claims.

According to the invention, a method is provided for producing a hollow-cylindrical workpiece from a solid starting workpiece, in which the solid starting workpiece is machined without cutting by bore spinning, in which a spinning mandrel is pressed axially into the starting workpiece and at the same time at least one forming roller is infed on an outside of the outer workpiece , a cup-shaped intermediate form is produced, which has a solid bottom section and an adjoining sleeve section with a first length and a first wall thickness, and the cup-shaped intermediate form is then subjected to flow-ironing, in which the sleeve section is reduced to a second length, which is greater than a first length, and ironed to a second wall thickness less than the first wall thickness.

A first basic idea of the invention is to produce a cup-shaped intermediate form from a solid starting work piece by bore spinning. The intermediate form is produced without cutting by bore spinning, a material structure with an unbroken or uncut fiber flow being produced by pressing in the spinning mandrel with simultaneous radial delivery of at least one forming roller on a forming machine. The fiber flow in the workpiece structure created by non-cutting forming leads to increased strength in the material structure. A second basic idea of the invention is to further improve this advantageous material structure, which is produced during bore spinning, by subsequently subjecting the cup-shaped intermediate form to spin-ironing, with a sleeve section of the intermediate form being further thinned in its wall thickness and the Sleeve section is lengthened in the axial direction. With flow ironing, the advantageous uninterrupted fiber flow of bore spinning is basically retained. At the same time, pressure rolling can further strengthen the material structure through the applied stresses. This process can be carried out as a hot forming process and/or as a cold forming process. With this stretch-forming rollers, there is no longer any impression of one forming mandrel.

Targeted temperature control in the individual process steps can in particular be used to achieve and set a targeted strain hardening, in particular in the case of flow-forming.

Overall, a hollow-cylindrical workpiece with a relatively small wall thickness can be produced with high strength at the same time.

Basically, when spinning a hole, the spinning mandrel can penetrate only slightly into the starting workpiece or penetrate it completely. A particularly advantageous embodiment of the invention consists in the spinning mandrel being introduced into the starting workpiece up to a central area during drilling. This can extend between about 20% and 80% of the axial length of the starting workpiece. As a result, an intermediate form can be achieved which, on the one hand, has a sleeve section with a solidified workpiece area and, on the other hand, has a workpiece area with a largely unchanged material structure.

According to a further development of the invention, it is particularly advantageous that, for stretching, at least one flow-forming roll is fed to a transition area located between the solid base section and the sleeve section and is moved axially to the transition area to the free end of the sleeve section. As a result, the sleeve section can be thinned and additionally strengthened in a targeted manner by the spin-forming process. According to a preferred variant of the method, it is provided that an annular recess is formed in the transition region before the flow-ironing rollers, into which the at least one flow-ironing roller is attached. The annular recess can be introduced into the outside of the workpiece either without cutting or by cutting by means of a previous cutting process step. The annular recess can be introduced before, during or after the bore spinning. This allows targeted stretch-forming.

According to a further development of the invention, particularly efficient forming is achieved in that a workpiece area behind the forming roller, which is directed towards the spinning mandrel, is widened during bore spinning by the forming roller, with a free space being formed around the spinning mandrel. The at least one forming roller preferably has a conically beveled area on its rear side, so that when the forming roller is moved radially towards the workpiece, a certain material flow is set radially outwards behind the forming roller. Since the infeed of the forming roller takes place at approximately the same axial height as a front region of the spinning mandrel or the at least one forming roller rushes the spinning mandrel axially a certain distance ahead. The combination of the forming roller and the feed supports a certain material flow radially outwards, so that a certain amount of play or an annular free space is generated around the bore mandrel when the bore mandrel is fed in axially at the same time. In this way, the pot-shaped intermediate form can be produced particularly efficiently.

Furthermore, according to a method variant of the invention, it can be advantageous that a guide sleeve for guiding the material is provided on an inner diameter of the workpiece. The guide sleeve can be mounted on the spinning mandrel, in particular in a front area. With such a guide sleeve, good guidance of the material during bore spinning can be achieved with a simultaneous reduction in frictional resistance.

According to a variant of the method according to the invention, a particularly advantageous shape can be achieved in that the free end of the sleeve section is drawn in radially to form at least one corrugated shoulder. In this case, a larger cavity can be formed in the hollow workpiece in a central area be formed than at the retracted free end. In extreme cases, the retraction can be carried out so far that the free end is largely or completely closed.

It is particularly advantageous that the radial drawing-in is carried out by radially adjusting at least one drawing-in roller. Two, three or more feed rollers distributed evenly over the circumference are preferably provided, so that the lateral forces on the entire workpiece are compensated during the feed. By drawing in, a single or multi-stage corrugated shoulder can be formed at the free end of the workpiece.

In principle, the opposite end with the solid bottom section of the workpiece can also be formed without cutting. According to a further development of the invention, it is particularly advantageous that the solid base section is machined by machining, with at least one corrugated shoulder being formed. There is a largely unstressed material structure in the solid bottom section, since this section was not subjected to any or any significant forming process. This means that the solid floor section can be efficiently processed by turning, milling or drilling.

According to a preferred embodiment of the invention, it is provided that a hole is made in the solid base section. In particular, the bore can be coaxial with the longitudinal axis of the workpiece. The bore can be designed as a blind hole with an intermediate wall section to the rest of the cavity of the workpiece or as a through hole, with a continuous longitudinal cavity being formed in the workpiece.

A particularly good setting of the strength of the workpiece can be achieved according to a further variant of the method in that the initial workpiece and/or the intermediate form is provided with a defined temperature profile over its axial length, in which areas with different temperatures are generated in order to achieve different strengths in the workpiece will. For example, temperatures can be set for different process steps and/or in different areas, which allow either cold forming or hot forming. In the case of hot forming, the workpiece temperature temperature above the so-called recrystallization temperature of the workpiece material, so that the material structure is constantly reformed and no strain hardening develops. On the other hand, if forming takes place below the recrystallization temperature, the material grains and the material structure are stretched and strain hardening can occur. In this case, in an initial phase of the process, hot forming can first be carried out, while in a final phase of the forming, cold forming is carried out with a targeted setting of strength. In particular, the bore spinning can be carried out as hot forming, while in particular the subsequent flow-ironing is carried out as cold forming.

According to a development of the invention, it can be particularly expedient for the workpiece to be clamped at the bottom section and actively cooled in the area of the bottom section. In particular, when the bore spinning is carried out at an elevated temperature, overheating in the bottom section with undesirable annealing effects in the material can be avoided. The bottom section can be cooled via the machine’s chuck.

A temperature control can be selected depending on the type of process and the desired strength properties of the workpiece. According to one embodiment of the invention, it is particularly advantageous that at least the bore spinning is carried out at a hot forming temperature. Preferably, the flow-ironing can be done as a cold working.

In principle, the starting workpiece can be produced in any way, for example as a forged part, a cast workpiece or a pre-machined workpiece. According to one embodiment of the invention, it is particularly economical if the starting workpiece is formed by cutting bar material to length. Rod material can be obtained reliably and inexpensively in a wide variety of qualities, whereby an individual workpiece length can be set by cutting to length.

The invention is described in more detail below with reference to preferred exemplary embodiments, which are illustrated schematically in the drawings. In the drawings show: 1-6 cross-sectional views of a workpiece according to different stages in a method according to the invention;

7 is a cross-sectional view through a workpiece being drilled according to the invention;

8 shows a cross-sectional view through a workpiece during drilling with the additional use of a guide sleeve;

9 shows a cross-sectional view through a workpiece after drilling;

FIG. 10 is a cross-sectional view through the workpiece of FIG. 9 after an annular recess has been formed; and

11-13 cross-sectional views through alternative starting workpieces for the method according to the invention.

According to FIG. 1, a solid metal cylinder can be used as the starting workpiece 10, which cylinder is formed, for example, by cutting a rod to length.

In a first process step according to FIG. 2, an intermediate form 20 is formed from the starting workpiece 10 according to FIG. 1 by bore spinning using a spinning mandrel (not shown in FIG. 2) and at least one forming roller. In the case of this bore spinning, a spinning mandrel is pressed axially into a central region of the starting workpiece 10 while one or more forming rolls are simultaneously applied to the outside. Through this, the intermediate mold 20 is formed in the shape of a pot with a sleeve section 24 having an inner cavity 25 . The sleeve section 24 transitions via a transition region 26, up to which at least one forming roller has run along, into a substantially undeformed, solid base section 22. The outside diameter of the solid bottom section 22 essentially corresponds to the diameter of the starting workpiece 10, while in contrast the outside diameter of the sleeve section 24 exhibits a first reduction in the outside diameter as a result of the borehole spinning with the simultaneous use of one or more forming rollers. According to FIG. 3, an annular recess 28 or depression in the intermediate form 20 is formed in the transition region 26 by a forming roller, not shown. The annular recess 28 serves as a starting point for one or more flow ironing rolls.

According to FIG. 4, starting from the annular recess 28, the one or more flow-ironing rolls run over the intermediate mold 20 towards the free end of the fluff section 24. In this flow-ironing process, there is a spinning mandrel in the interior space 25, with the spinning mandrel of the previous drilling being approximately press or another spinning mandrel can be used. During pressure ironing, the wall thickness of sleeve section 24 is reduced from a first wall thickness as shown in FIG. 3 to a second, smaller wall thickness as shown in FIG . With the same inner diameter, there is a further reduction in the outer diameter of the sleeve section 24.

A free end area of the tubular sleeve section 24 can then be drawn in radially inwards by ra diales delivery of one or more drawing-in rollers, with a stepped corrugated shoulder 56 being formed, as illustrated clearly in FIG. An undercut cavity for the hollow-cylindrical workpiece 50 can be formed in the central hollow-cylindrical section 52 .

After the non-cutting forming, the workpiece can be machined, in particular by drilling, milling and in particular by turning on a lathe. Here, the first set of shafts 56 can be finished rotating. In addition, a central bore 60 can be introduced into the massive Bodenab section 22 by drilling and/or turning. In addition, the outer circumference of the solid base section 22 can be turned, so that a second shaft shoulder 58 is formed at the other end of the hollow-cylindrical workpiece 50 .

The bore 60 can basically go through and extend into the cavity of the hollow cylinder section 52 or, as is clearly shown in FIG. be formed as a blind hole with a continuous wall opposite the cylinder section 52 Hohlzy.

In connection with FIG. 7, the bore spinning in the method according to the invention Shen is explained in more detail, with a shank-shaped cylindrical spinning mandrel 30 being pressed axially into the starting workpiece 10 to form an intermediate form 20 . The starting workpiece 10 is rotated about its central axis, the starting workpiece 10 being clamped on the solid bottom section 22 on a chuck (not shown) which can be cooled. In the area of the end face of the spinning mandrel 30, one or more forming rollers 35 are placed radially on the outer circumference of the intermediate mold 20 for bore spinning, whereby a three-dimensional state of stress is formed in the material, through which the solid starting workpiece 10 with a hollow sleeve section 24 is formed, by the spinning mandrel 30 further and further into the intermediate form 20 penetrates axially. The workpiece material thereby displaced is displaced axially backwards along the spinning mandrel 30 to form the sleeve section 24 under the action of the at least one forming roller 35 .

The forming roller 35 is double-cone-shaped, with a front conical inlet section 36 and a rear conical outlet section 37 being formed. Due to the rear conical outlet section 37, which tapers towards the rear, workpiece material is partially displaced radially outwards, in particular in the actual forming zone, so that a certain free space in the front area around the spinning mandrel 30 can result, which improves axial penetration the spinning mandrel 30 allows.

According to FIG. 8, an alternative embodiment for the bore spinning is shown, in addition to the arrangement according to FIG. The workpiece material displaced during bore spinning can partially rest on the guide sleeve 32 and be additionally guided by it when shifted backwards. This also leads to easier and improved bore spinning according to the method of the invention. FIG. 9 shows, in an enlarged view, the state of the intermediate mold 20 corresponding to FIG. 2, wherein a fluff section 24 is formed with an internal cavity 25, while a substantially undeformed solid bottom section 22 remains. The sleeve portion 24 is tapered in the larger-diameter solid bottom section 22 with a transition area 26 on.

In this transitional region 26, as shown in FIG. 10, an annular recess 28 or depression is incorporated. This can preferably be done without cutting by radial infeed of a corresponding forming roller or, if necessary, also by cutting, for example on a lathe. In this ring-shaped recess 28 according to FIG. 10, one or more flow-ironing rolls can then be inserted in a precisely positioned manner for the subsequent flow-ironing process.

In the figures 11 to 13 alternative configurations for the starting workpiece 10 are shown. The starting workpiece 10 according to FIG. 11 can be a pre-machined workpiece or a workpiece manufactured by forging or casting with a preformed shoulder 12, which in the illustrated embodiment is solid and slightly conical.

According to the embodiment according to FIG. 12, the starting workpiece 10 can also have an annular shoulder 14 in addition to a slightly conical shoulder 12 .

Furthermore, according to the alternative embodiment according to FIG. 13, the starting workpiece 10 can be designed with a conical shoulder 12 in which a central hole 16 is arranged. This can optionally be formed in a previous forging process or machined into it.

Claims

PATENT CLAIMS

1. A method for producing a hollow-cylindrical workpiece (50) from a solid starting workpiece (10), in which the solid starting workpiece (10) is machined without cutting by bore spinning, in which a spinning mandrel (30) is pressed axially into the starting workpiece (10) and at the same time at least one forming roller (35) is infed on an outside of the starting workpiece (10), a pot-shaped intermediate mold (20) is produced, which has a solid base section (22) and an adjoining sleeve section (24) with a first length and having a first wall thickness, and the cup-shaped intermediate form (20) is then subjected to flow ironing in which the sleeve portion (24) is ironed to a second length which is greater than the first length and to a second wall thickness which is smaller as the first wall thickness, characterized in that the starting workpiece (10) and/or the intermediate form (20) over its axial length ge is provided with a defined temperature profile in which areas with different temperatures to achieve under different strengths in the workpiece (50) are generated.

2. The method according to claim 1, characterized in that during bore spinning the spinning mandrel (30) is introduced into the starting workpiece (10) up to a central region.

3. The method according to claim 1 or 2, characterized in that that for ironing, at least one ironing roller is fed to a transition area (26) which lies between the solid base section (22) and the sleeve section (24) and is moved axially from the transition area (26) to the free end of the sleeve section (24).

4. The method according to claim 3, characterized in that in the transition area (26) in front of the flow-ironing, an annular recess (28) is formed, in which the at least one Ab flow-forming roller is attached.

5. The method according to any one of claims 1 to 4, characterized in that during bore spinning by the forming roller (35), a workpiece area behind the forming roller (35), which is directed towards the spinning mandrel (30), is widened, with the radial infeed of the Forming roller (35) to the workpiece, a certain material flow radially outwards behind the forming roller (35) is turned on and around the spinning mandrel (30) a free space is formed.

6. The method according to any one of claims 1 to 5, characterized in that a guide sleeve (32) for guiding the material is provided on an inner diameter of the intermediate mold (20).

7. The method according to any one of claims 1 to 6, characterized in that the free end of the sleeve section (24) is drawn in radially to form at least one first shaft shoulder (56).

8. The method as claimed in claim 7, characterized in that the radial drawing-in is carried out by radially advancing at least one drawing-in roller.

9. The method according to any one of claims 1 to 8, characterized in that that the solid bottom section (22) is machined, with at least one second shaft shoulder (58) being formed.

10. The method according to any one of claims 1 to 9, characterized in that a bore (60) is introduced into the solid base section (22).

11. The method according to any one of claims 1 to 10, characterized in that the workpiece (50) is clamped on the bottom section (22) and is actively cooled in the region of the bottom section (22).

12. The method according to any one of claims 1 to 11, characterized in that at least the bore spinning is carried out at a hot forming temperature.

13. The method according to any one of claims 1 to 12, characterized in that the starting workpiece (10) is formed by cutting to length from a rod material.