CN117751019A - Method for producing hollow cylindrical workpieces - Google Patents

Abstract

The invention relates to a method for producing a hollow cylindrical workpiece from a solid initial workpiece, in which method a pot-shaped intermediate shape is produced without cutting into the solid initial workpiece by means of a hole-forming press, in which a pressing mandrel is pressed axially into the initial workpiece and at the same time at least one forming roller is fed on the outside of the outer workpiece, the pot-shaped intermediate shape having a solid base section and a sleeve section with a first length and a first wall thickness following the solid base section. Furthermore, the can-like intermediate shape is followed by a stretch-rolling, in which the sleeve section is stretched to a second length, which is greater than the first length, and to a second wall thickness, which is smaller than the first wall thickness.

Description

Method for producing hollow cylindrical workpieces

Technical Field

The invention relates to a method for producing hollow cylindrical workpieces, in particular hollow shafts, from solid starting workpieces.

Background

For various applications in mechanical and equipment engineering, hollow cylindrical components are required which on the one hand should be lightweight and at the same time have high strength. For example, in the production of gearboxes, a gearbox shaft is required which has high strength for torque transmission and should have as low a weight as possible to reduce the moment of inertia.

A method for producing hollow shafts is known from DE 10200503681 A1, in which a swaging method (Rundknetverfahren) is used.

From DE 1020112005106 B4 a method for producing a hollow shaft from a solid semifinished product is known, in which first two parts of the shaft are produced by means of hole-forming extrusion (bohrungsdrucken). The two parts can then be connected to each other by friction welding.

Hole forming extrusion belongs to a non-cutting forming method. In this case, a solid initial workpiece is placed in rotation in an extruder, the extrusion mandrel being pressed axially into the solid workpiece, while at least one forming roller is placed against the workpiece on the outside. By the abutment of the at least one forming roller, complex stress states are created in the workpiece, in which state the non-cutting forming is effected with the pressing mandrel pressed in axially.

A method for producing a transmission component by means of hole extrusion is known, for example, from DE 10304960 A1.

The workpieces produced by the hole-forming extrusion are generally finally subjected to cutting machining, in particular on a lathe, in order to obtain the desired final profile.

Disclosure of Invention

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

According to the invention, this object is achieved by a method with the features of claim 1. Preferred embodiments of the invention are set forth 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 method a pot-shaped intermediate shape is produced into the solid starting workpiece without cutting by means of a hole-forming press, in which hole-forming press the pressing mandrel is pressed axially into the starting workpiece and at the same time at least one forming roller is fed at the outside of the outer workpiece, the pot-shaped intermediate shape having a solid bottom section and a sleeve section with a first length and a first wall thickness following the solid bottom section, and the pot-shaped intermediate shape is then subjected to a drawing-in press, in which the sleeve section is drawn to a second length greater than the first length and a second wall thickness smaller than the first wall thickness.

The first basic idea of the invention is to create a pot-like intermediate shape from a solid initial workpiece by hole-forming extrusion. The intermediate shape is produced without cutting by means of hole-forming extrusion, wherein a material structure with uninterrupted or uncut fiber runs is produced by pressing the extrusion mandrel while simultaneously radially feeding at least one forming roller at the forming machine. The fiber orientation in the workpiece structure produced by non-cutting forming results in increased strength of the material structure.

The second basic idea of the invention is to further refine this advantageous material structure produced in the pore-forming extrusion by the fact that the pot-shaped intermediate shape is then subjected to a stretching-rolling, wherein the sleeve section of the intermediate shape is further thinned in terms of its wall thickness and the sleeve section is elongated in the axial direction. In the draw-rolling, the advantageous uninterrupted fiber course of the pore-forming extrusion is essentially preserved. At the same time, further hardening of the material structure can be promoted by the applied stress by means of stretch-rolling. The method may be performed here as a thermoforming method and/or as a cold forming method. In the stretch rolling, the pressing in of the one forming mandrel is not performed any more.

By means of a specific temperature control in the individual method steps, a specific cold hardening can be achieved and regulated, in particular, in the drawing and rolling process.

Hollow cylindrical workpieces with relatively small wall thicknesses can thus be produced overall in the case of simultaneously high strength.

In principle, in the case of hole-forming extrusion, the extrusion mandrel can be extruded only slightly into the starting workpiece or generally through the starting workpiece. A particularly advantageous embodiment of the invention consists in that in the hole-forming extrusion, the extrusion mandrel is introduced into the starting workpiece up to the central region. It may extend between about 20% to 80% of the axial length of the initial workpiece. In this way, an intermediate shape can be achieved which has, on the one hand, a sleeve section with a hardened workpiece region and, on the other hand, a workpiece region with as unchanged a material structure as possible.

According to a further development of the invention, it is particularly advantageous if, for the drawing and pressing, at least one drawing roller is fed at a transition region between the solid bottom section and the sleeve section and is moved axially toward the transition region to the free end of the sleeve section. The sleeve section can thus be thinned and additionally hardened by drawing and rolling.

According to a preferred method variant, it is provided that an annular recess is formed in the transition region prior to the drawing-pressing, into which the at least one drawing-pressing roller is placed. The annular groove can be introduced into the outer side of the workpiece in a cutting manner either without cutting or by previous cutting method steps. The introduction of the annular groove may be effected before, during or after the hole-forming extrusion. This allows for targeted stretch rolling.

According to a further development of the invention, particularly effective forming is achieved in that, during the hole-forming extrusion by the forming roller, the area of the workpiece behind the forming roller that is directed toward the extrusion mandrel is enlarged, wherein a free space is formed around the extrusion mandrel. Preferably, the at least one forming roller has a conical tilting zone at its rear side, so that a certain material flow occurs radially outwards behind the forming roller when the forming roller is fed radially to the workpiece. The feeding of the forming rollers takes place here, for example, at the same axial height at which the front region of the pressing mandrel is located, or at a distance in the axial direction of the at least one forming roller in front of the pressing mandrel. A certain radially outward material flow is supported by the combination of the forming roller and the feed, so that a certain gap or annular free space is created around the hole forming spindle when the hole forming spindle is simultaneously axially fed. In this way, a can-like intermediate shape can be produced particularly effectively.

Furthermore, according to a method variant of the invention, it is advantageous if a guide sleeve is provided at the inner diameter of the workpiece for guiding the material. The guide sleeve can be supported on the pressing mandrel, in particular in the front region. By means of such a guiding sleeve, a good guiding of the material in the hole-forming extrusion can be obtained while simultaneously reducing the frictional resistance.

A variant of the method according to the invention makes it possible to obtain a particularly advantageous shaping by radially retracting the free end of the sleeve section (eingezogen) for forming the at least one shoulder. In this case, a larger cavity can be formed in the hollow workpiece in the central region than at the retracted free end. In extreme cases, the retraction can be carried out to such an extent that the free end is as closed as possible or completely.

In this case, it is particularly advantageous if the radial retraction is carried out by radially feeding at least one retraction roller. Preferably, two, three or more retraction rollers are provided, distributed uniformly over the circumference, so that an equalization of the transverse forces acting on the entire workpiece is obtained at the time of retraction. By retracting, a single or multiple step shoulder can be formed at the free end of the workpiece.

In principle, the opposite ends 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 if the solid base section is machined, wherein at least one shoulder is formed. In the solid bottom section, there is a largely unstressed material structure, since this section is not subjected to the shaping method or is not subjected to a significant shaping method. The solid bottom section can thereby be efficiently machined, for example by turning, milling or drilling.

According to a preferred embodiment of the invention, it is provided that openings are introduced in the solid bottom section. In particular, the aperture may be coaxial with the workpiece longitudinal axis. The orifice may be embodied as a blind orifice with an intermediate wall section leading to the remaining cavity of the workpiece, or as a through hole, wherein a continuous longitudinal cavity is formed in the workpiece.

According to a further method variant, particularly good adjustment of the strength of the workpiece can be achieved in that the initial workpiece and/or the intermediate shape is provided over its axial length with a defined temperature profile in which regions with different temperatures are produced in the workpiece in order to obtain different strengths. Thus, the temperature can be adjusted for different method steps and/or in different regions, which can be either cold-forming or heat-forming. In the case of thermal deformation, the workpiece temperature is higher than the so-called recrystallization temperature of the workpiece material, so that the material structure is always newly formed and no cold hardening is established. Conversely, if the shaping occurs below the recrystallization temperature, the material grains and material structure are stretched and cold hardening may occur. In this case, in the initial phase of the method, the thermal deformation can be performed first, while in the final phase of the shaping, the cold deformation can be performed with targeted intensity adjustment. In particular, the pore-forming extrusion can be performed as thermoforming, while in particular the subsequent drawing-rolling is performed as a cold variant.

According to a further development of the invention, it is particularly expedient if the workpiece is clamped at the bottom section and actively cooled in the region of the bottom section. In particular, overheating in the bottom section with undesired annealing effects in the material can thus be avoided when pore-forming extrusion is performed at elevated temperatures. The cooling of the bottom section may be performed by a chuck of the machine.

The temperature control may be selected depending on the type of method and the desired strength characteristics of the workpiece. According to one embodiment of the invention, it is particularly advantageous if at least the pore-forming extrusion is carried out at a thermoforming temperature. Preferably, the stretch rolling may be performed as cold forming.

In principle, the starting workpiece can be manufactured in any manner, for example as a forged part, as a cast workpiece or as a workpiece which is cut to be machined. According to one embodiment of the invention, it is particularly economical to form the initial workpiece by cutting from a bar stock to length. Bar stock can be obtained reliably and cost-effectively with the most varied quality, wherein the individual workpiece length can be adjusted by means of a fixed-length cut.

Drawings

The invention is further described below with reference to a preferred embodiment schematically shown in the drawings. In the drawing:

figures 1-6 show cross-sectional views of a workpiece according to different stages in a method according to the invention;

FIG. 7 shows a cross-sectional view through a workpiece at the time of hole forming extrusion according to the present invention;

FIG. 8 shows a section through a workpiece during hole-forming extrusion with the additional use of a guide sleeve;

FIG. 9 shows a cross-sectional view through the workpiece after hole forming extrusion;

FIG. 10 shows a cross-sectional view through the work piece of FIG. 9 after forming the annular groove; and is also provided with

Fig. 11-13 show cross-sectional views through alternative initial workpieces for use in the method according to the invention.

Detailed Description

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

In a first method step according to fig. 2, the intermediate shape 20 is formed by means of hole-forming extrusion from the initial workpiece 10 according to fig. 1 using an extrusion mandrel and at least one forming roller, which are not shown in fig. 2. In the hole-forming press, the press mandrel is pressed axially into the central region of the initial workpiece 10 while simultaneously placing one or more forming rollers against the outside. The intermediate shape 20 is thus formed pot-shaped with a sleeve section 24, which sleeve section 24 has an internal cavity 25. The sleeve section 24 transitions into the substantially undeformed solid bottom section 22 via a transition region 26, the at least one forming roller travelling along until the transition region 26. The outer diameter of the solid bottom section 22 corresponds substantially to the diameter of the initial workpiece 10, whereas the outer diameter of the sleeve section 24 has a first reduction in the outer diameter by means of hole-forming extrusion with the simultaneous use of a plurality of forming rollers.

According to fig. 3, the annular groove 28 or recess is formed into the intermediate shape 20, for example by a not shown forming roller into the transition region 26. The annular groove 28 serves as a starting point for one or more stretching press rolls.

According to fig. 4, the one or more drawing rollers roll over the intermediate shape 20 starting from the annular groove 28 toward the free end of the sleeve section 24. In this stretch-rolling process, there is an extrusion mandrel in the interior space 25, wherein an extrusion mandrel of a previously hole-forming extrusion or another extrusion mandrel may be used. In the draw-rolling, the wall thickness of the sleeve section 24 is reduced from the first wall thickness according to fig. 3 to the second smaller wall thickness according to fig. 4. The workpiece material compressed in this case leads to an elongation of the sleeve section 24, as is shown schematically in fig. 4. In the case where the inner diameter remains the same, a further reduction of the outer diameter at the sleeve section 24 is obtained.

The free end region of the tubular sleeve section 24 may then be pulled radially inward by radial feed of one or more retracting rollers, with a stepped shoulder 56 formed therein, as shown intuitively in fig. 5. Here, an undercut cavity for the hollow cylindrical workpiece 50 may be formed in the central hollow cylindrical section 52.

After the non-cutting shaping, cutting operations can be carried out at the workpiece, in particular by drilling, milling and turning operations, in particular on a lathe. The first shoulder 56 can be finished in a turning manner. Additionally, the central aperture 60 may be introduced in the solid bottom section 22 by drilling and/or turning. In addition, turning removal of the outer periphery may be performed at the solid bottom section 22, thereby configuring the second shoulder 58 at the other end of the hollow cylindrical work piece 50.

The orifice 60 may extend substantially through into the cavity of the hollow cylindrical section 52 or, as shown visually in fig. 6, may be configured as a blind orifice with a continuous wall relative to the hollow cylindrical section 52.

In connection with fig. 7, hole-forming extrusion is explained in more detail in the method according to the invention, wherein a shank-shaped cylindrical extrusion mandrel 30 is pressed axially into the initial workpiece 10 in order to form the intermediate shape 20. Here, the initial workpiece 10 is placed in rotation about its central axis, wherein the initial workpiece 10 is clamped at the solid bottom section 22 at a chuck, not shown, which can be cooled. In the end-side region of the extrusion mandrel 30, one or more forming rollers 35 are radially fed to the outer periphery of the intermediate shape 20 for the purpose of hole-forming extrusion, wherein a three-dimensional stress state is built into the material, by means of which the solid starting piece 10 is constructed with the hollow sleeve section 24 by means of the extrusion mandrel 30 being pushed more and more axially into the intermediate shape 20. The workpiece material which is pressed here is pressed axially back along the pressing mandrel 30 by the at least one forming roller 35 to form the sleeve section 24.

The forming roller 35 is configured as a double cone, wherein a front cone-shaped inlet section (Einlaufabschnitt) 36 and a rear cone-shaped outlet section (auslafabschnitt) 37 are configured. By means of the rearwardly tapering rear conical outlet section 37, the workpiece material is compressed partly radially outwards, in particular in the actual forming zone, so that a certain free space is available in the front region around the extrusion mandrel 30, which results in an improved axial penetration of the extrusion mandrel 30.

According to fig. 8, an alternative embodiment for hole-forming extrusion is shown, wherein, in addition to the arrangement according to fig. 7, an axially displaceable guide sleeve 32 is also supported on the extrusion mandrel 30. In this case, the workpiece material pressed during the hole-forming press can rest partially on the guide sleeve 32 and be additionally guided by the guide sleeve 32 during the rearward displacement. This also results in easier and improved pore-forming extrusion according to the method according to the invention.

Fig. 9 shows a state corresponding to the intermediate shape 20 of fig. 2 in an enlarged view, in which a sleeve section 24 with an internal cavity 25 is formed, while leaving a solid bottom section 22 substantially undeformed. The sleeve section 24 utilizes a transition region 26 to conically transition into the larger diameter solid bottom section 22.

Corresponding to fig. 10, an annular groove 28 or depression is concavely machined (einarbeiten) in the transition region 26. Preferably, this can be done without cutting by radially feeding the respective forming roller or, if possible, in a cutting manner, for example on a lathe. One or more drawing rolls can be inserted into the annular groove 28 according to fig. 10 with positional accuracy for the subsequent drawing-rolling process.

Fig. 11 to 13 show alternative embodiments for the initial workpiece 10. The initial workpiece 10 according to fig. 11 can be a workpiece which is machined or produced by forging or casting and has a preformed shoulder 12, the shoulder 12 being formed solid and slightly conical in the exemplary embodiment shown.

According to the embodiment according to fig. 12, the initial workpiece 10 can additionally have an annular shoulder 14 in addition to the slightly conical shoulder 12.

Furthermore, according to the alternative embodiment according to fig. 13, the initial workpiece 10 can be configured with a conical shoulder 12, in which conical shoulder 12 the central bore 16 is arranged. It may be shaped or machined concavely in a cutting manner, if possible, in a previous forging process.

Claims (13)

1. Method for producing a hollow cylindrical workpiece (50) from a solid initial workpiece (10), in which method

-generating, without cutting, a pot-like intermediate shape (20) into the solid starting workpiece (10) by means of hole-forming extrusion, in which an extrusion mandrel (30) is pressed axially into the starting workpiece (10) and at the same time at least one forming roller (35) is fed at the outer side of the starting workpiece (10), the pot-like intermediate shape having a solid bottom section (22) and a sleeve section (24) with a first length and a first wall thickness next to the solid bottom section, and

-subsequently subjecting the tank-like intermediate shape (20) to a stretch-rolling in which the sleeve section (24) is stretched to a second length greater than the first length and a second wall thickness smaller than the first wall thickness,

it is characterized in that the method comprises the steps of,

the initial workpiece (10) and/or the intermediate shape (20) is provided with a defined temperature profile over its axial length, in which temperature profile regions with different temperatures are produced in the workpiece (50) in order to obtain different strengths.

2. The method according to claim 1,

it is characterized in that the method comprises the steps of,

in hole-forming extrusion, the extrusion mandrel (30) is introduced into the initial workpiece (10) up to a central region.

3. The method according to claim 1 or 2,

it is characterized in that the method comprises the steps of,

for stretch-rolling, at least one stretch-press roll is fed at a transition region (26) between the solid bottom section (22) and the sleeve section (24) and moves axially from the transition region (26) to a free end of the sleeve section (24).

4. A method according to claim 3,

it is characterized in that the method comprises the steps of,

an annular recess (28) is formed in the transition region (26) prior to the drawing and pressing, into which the at least one drawing and pressing roller is placed.

5. The method according to claim 1 to 4,

it is characterized in that the method comprises the steps of,

during hole-forming extrusion by means of the forming roller (35), the area of the workpiece behind the forming roller (35) that is directed towards the extrusion mandrel (30) is enlarged, wherein when the forming roller (35) is fed radially onto the workpiece, a certain material flow occurs radially outwards behind the forming roller (35) and a free space is formed around the extrusion mandrel (30).

6. The method according to claim 1 to 5,

it is characterized in that the method comprises the steps of,

a guiding sleeve (32) is provided at the inner diameter of the intermediate shape (20) for guiding material.

7. The method according to claim 1 to 6,

it is characterized in that the method comprises the steps of,

the free end of the sleeve section (24) is radially recessed for forming at least one first shoulder (56).

8. The method according to claim 7,

it is characterized in that the method comprises the steps of,

the radial retraction is performed by radial feeding of at least one retraction roller.

9. The method according to any one of claim 1 to 8,

it is characterized in that the method comprises the steps of,

the solid bottom section (22) is machined, wherein at least one second shoulder (58) is formed.

10. The method according to any one of claim 1 to 9,

it is characterized in that the method comprises the steps of,

an orifice (60) is introduced into the solid bottom section (22).

11. The method according to any one of claim 1 to 10,

it is characterized in that the method comprises the steps of,

the workpiece (50) is clamped at the bottom section (22) and actively cooled in the region of the bottom section (22).

12. The method according to any one of claim 1 to 11,

it is characterized in that the method comprises the steps of,

at least the pore forming extrusion is performed at a thermoforming temperature.

13. The method according to any one of claim 1 to 12,

it is characterized in that the method comprises the steps of,

the initial workpiece (10) is formed by cutting a fixed length from a bar stock.