EP4414099A2 - Method for hot forming a cast forging block using a forging apparatus - Google Patents

Abstract

A forging device for hot forming a cast forging block (1) with radially guided forging dies (5) is described, each of which has two die parts (7, 8) which can be displaced radially relative to one another, of which the inner die part (7) carrying a forging tool (2) is drive-connected to the other outer die part (8) by a hydraulic cylinder (9), with an eccentric drive (14) which can drive the outer die part (8), the eccentric shaft (15) of which is connected to an electric motor via a coupling (23), and with a pump (28) which can be driven by the electric motor for pressurizing the hydraulic cylinder (9) between the inner and outer die parts (7, 8). In order to create advantageous design conditions, it is proposed that a torque motor (19) designed as an internal rotor, coaxial with the eccentric shaft (15), is provided as the electric motor, the rotor (20) of which is rotatably mounted on the eccentric shaft (15) or an eccentric shaft extension (21) following a driver flange (22) of the eccentric shaft (15), and that the coupling (23) is arranged between the rotor (20) and the driver flange (22).

Description

The invention relates to a forging device for hot forming a cast forging block with radially guided forging dies, each of which has two die parts that can be displaced radially relative to one another, of which the inner die part carrying a forging tool is drive-connected to the other outer die part by a hydraulic cylinder, with an eccentric drive that can drive the outer die part, the eccentric shaft of which is connected to an electric motor via a coupling, and with a pump that can be driven by the electric motor to pressurize the hydraulic cylinder between the inner and outer die parts.

In order to convert the cast structure of a cast forging block into a largely pore-free, recrystallized structure, the forging block is subjected to hot forming by press forging. A large bite ratio, i.e. the ratio of the pressed length of the forging saddle to the diameter of the forging block before the press stroke, is intended to achieve core forming sufficient to reduce the pores despite a small reduction. However, due to the large bite ratio, there are significant differences in the degree of deformation caused by the press stroke of the forging tool over the pressed length of the forging saddle, which leads to cracks in the surface area.

In order to be able to hot-form workpieces with a forging device either by forging with slow forming speed and high forces at a high bite ratio or by radial forging with higher forming speeds and small bite ratios, it is known ( WO 2015/118502 A1 , EP 1 093 871 A2 ), the forging dies, which hold a forging tool and are guided radially to the forging axis, are composed of two die parts, between which a hydraulic cylinder is provided. The outer of the two stamp parts is driven by an eccentric drive which, when the hydraulic cylinder between the two stamp parts is locked, drives the inner stamp part, which holds a forging tool, in the sense of radial forging with a comparatively high number of blows. However, if the outer stamp part is uncoupled from its eccentric drive and held in place, the inner stamp part can be driven in the sense of press forging by applying pressure to the hydraulic cylinder between the two stamp parts while the outer stamp part is held in place. The uncoupling of the upper stamp part from the eccentric drive can be achieved by a clamping wedge that can be moved in a clamping gap between the stamp guide and the outer stamp part ( WO 2015/118502 A1 ), which supports the outer punch part against a forging stroke. However, it is also possible ( EP 1 093 871 A2 ), a clutch must be provided in the drive train between the eccentric and the electric motor provided for the eccentric drive, so that in the event of decoupling, forces from the outer stamp part can be transferred via the eccentric to the eccentric shaft bearing without torque loading of the eccentric, if the eccentric is preferably in the outer dead center position.

Regardless of the type of decoupling of the outer punch part from the eccentric drive, the difficulty in forging presses remains that with a bite ratio >0.5, as is required to influence the structure in the core area of the forging block ( EP 1 747 076 B1 ), an uneven loading of surface areas over the compressed length of the forging saddle is unavoidable, which entails the risk of cracking in the surface area.

To avoid cracking despite good forging of the core area of a forging block, a forging process was proposed ( EP 0 255 635 A2 ), in which the workpiece is only displaced or moved between an upper and a lower saddle of the forging press in the workpiece stretching direction as far as possible before the respective forging stroke. is shifted so that the bite edge of the previous bite on the workpiece comes to lie within the saddle edges. This means that the pressed saddle length and thus also the bite ratio decreases with each forging pass carried out with a bite offset, so that a forging process is present that starts from a largest bite ratio with gradually decreasing bite ratios, which leads to uneven loading of surface areas over the pressed length of the forging saddle, particularly in the area of the largest bite ratio, and thus to the risk of cracks forming in the surface area.

For a press with an eccentric drive it is known ( EN 10 2015 222 995 A1 ), to provide the eccentric shaft at one end with a flywheel that can be driven by a flywheel motor and can be detachably coupled to the eccentric shaft using a coupling. At the opposite end, the eccentric shaft is permanently connected to a torque motor that accelerates the eccentric shaft to the speed of the flywheel for the press stroke before the flywheel is coupled to the eccentric shaft for the press stroke. The interaction of the flywheel motor and the torque motor means that the installation space for the press stroke drive can be kept comparatively small. However, such an eccentric shaft drive is not very suitable for the outer punch part of the punch parts of a forging device that can be radially displaced against one another, the inner punch part of which carries a forging tool and is drive-connected to the outer punch part by a hydraulic cylinder.

The invention is therefore based on the object of designing a forging device for hot forming a cast forging block by forging presses in such a way that, despite an advantageous influence on the microstructure in the core area of the forging block, crack formation in the surface area can be largely excluded.

Starting from a forging device of the type described above, the invention solves the problem by providing a torque motor coaxial to the eccentric shaft and designed as an internal rotor as the electric motor. whose rotor is rotatably mounted on the eccentric shaft or an eccentric shaft extension following a driving flange of the eccentric shaft, and that the coupling is arranged between the rotor and the driving flange.

The coupling between the motor and the eccentric shaft can preferably have a driver which is parallel to the eccentric shaft and mounted in the rotor so that it can be axially loaded and which, in the coupling position, positively engages in a driver receptacle in the driver flange.

As a result of these measures, the eccentric shaft is driven directly by the associated torque motor in the coupling position. Since in this case the hydraulic cylinder between the inner and outer punch parts is locked, the forging punches are only driven in the sense of radial forging by the associated eccentric drives with a comparatively small stroke and high stroke frequency. In contrast, with decoupled eccentric drives, the inner punch parts can be actuated by the hydraulic cylinders between the inner and outer punch parts in the sense of forging presses with a comparatively large stroke and low stroke frequency. The forging forces are transmitted via the outer punch parts to the eccentric shaft and via this to the frame that holds the forging punches. To avoid torques on the eccentric shaft caused by this, it is advantageous to hold it in the outer dead center position in the decoupled position. The hydraulic cylinders for driving the inner punch parts are actuated by pumps that are driven by the torque motors.

In order to refine the cast structure in a near-surface area through recrystallization so that during the subsequent forging process the locally varying loads on the forging block over the pressed length of the forging saddle can no longer cause cracking, it is necessary to ensure that the deformation is as uniform as possible over the pressed saddle length in order to avoid dead material in this area, i.e. material with a low degree of deformation. This is achieved by radial forging with a degree of deformation that is low enough to avoid cracking but is large enough for recrystallization, i.e. above the critical degree of deformation, which specifies the minimum deformation to provide sufficient recrystallization nuclei for recrystallization. For this purpose, the forging dies are driven by the eccentric drives, with the help of which, at a comparatively high stroke frequency, a short pressed saddle length is achieved in comparison to the effective engagement length of the forging tools, so that the flow cut and thus the dead material in the area of the flow cut is outside the length of the crack-prone surface pressed by the forging tool.

In the subsequent processing of the forging block with the same forging tools, which are now hydraulically operated in the sense of forging presses with a large bite ratio >0.5, an effective structural improvement can be achieved right down to the core of the forging block, but only if this forging press is carried out at the same heat in order to avoid grain growth due to reheating and thus an increase in the risk of cracking.

Fig. 1

eine schematische Darstellung des Eingriffs der durch einen Exzentertrieb angetriebenen Schmiedewerkzeuge zur oberflächennahen Schmiedebearbeitung,

Fig. 2

eine der Fig. 1 entsprechende Darstellung des Eingriffs der Schmiedewerkzeuge während des Pressschmiedens mithilfe der hydraulisch betätigten Schmiedestempel und

Fig. 3

eine erfindungsgemäße Schmiedevorrichtung ausschnittsweise im Bereich eines Schmiedestempels in einem schematischen Schnitt entlang der Exzenterwelle des Exzentertriebs.

The subject matter of the invention is shown by way of example in the drawing.

Fig.1

a schematic representation of the engagement of the forging tools driven by an eccentric drive for near-surface forging,

Fig.2

one of the Fig.1 corresponding representation of the engagement of the forging tools during press forging using the hydraulically operated forging punches and

Fig.3

a forging device according to the invention in detail in the area of a forging die in a schematic section along the eccentric shaft of the eccentric drive.

In order to carry out a forging process of a cast forging block 1 in the sense of a recrystallization of the cast structure as uniformly as possible in a In order to enable the forging tools 2 to be used for forming the surface area close to the surface, the pressed saddle length S, i.e. the length of the surface area pressed by the forging tools 2 per forging stroke and susceptible to cracking due to the lack of deformation, is kept small in comparison to the effective engagement length L of the forging tools 2 opposite one another in relation to the forging block 1. To avoid large differences between local degrees of deformation, the forging tools 2 can advantageously be provided with an inlet slope 3 between 6 and 15°. Since the dead material, which is subject to only a small amount of deformation per forging stroke, is located in the area of the flow sheath 4, which in the schematic representation according to the Fig. 1 and 2 For the sake of simplicity, the area of low deformation is indicated in the middle of the effective engagement length L of the forging tools 2, this area of low deformation is in the Fig.1 shown forging conditions outside the pressed saddle length S, so that a largely uniform deformation of the forging block 1 in an area close to the surface can be ensured if the forging tools 2 are driven at a comparatively high stroke frequency to maintain these forging conditions. However, the deformation must not lead to cracking in the surface area. For this reason, the degree of deformation must be limited. For steel materials, an accumulated degree of deformation of 0.2 to 1, preferably 0.2 to 0.6, depending on the initial cross-section of the forging block and the number of passes dependent on this, has proven advantageous, namely at a deformation speed of between 0.15 and 2 per second. The accumulated degree of deformation ϕ = [2/3(ϕ _h ² + ϕ _l ² + ϕ _b ² )] ^1/2 results from the logarithmic degrees of deformation, which are determined by the logarithmic ratios of the dimensions after and before the deformation in the height h, the length I and the width b of the forging block 1 [ϕ _h = ln(h ₁ /h ₀ ), ϕ _l = ln(l ₁ /l ₀ ), ϕ _b = ln(b ₁ /b ₀ )].

After this pre-forming in the surface area, the forging block 1 can be subjected to the actual forming in the same heat for compaction and structural improvement down to the core area by forging presses, using the same forging tools 2, but under forging press conditions with a bite ratio B = S/h ₀ >0.5, as in the Fig.2 is illustrated. Due to the large bite ratio, the deformations affect the core of the forging block 1 with a corresponding reduction in cross-section, whereby it must be accepted that the flow sheath 4 comes to lie within the pressed saddle length S. However, the resulting non-uniform deformation in the surface area plays no role in terms of crack formation, because recrystallization has already taken place in these areas close to the surface, which prevents crack formation that occurs with larger grain structures. The forging tools 2 are used for forging pressing according to the Fig.2 Hydraulically driven with a forming speed of < 0.6 s ^-1 , whereby the cross-sectional reduction per pass should be greater than 15%.

Following forging, the forging block 1 can be one of the Fig.1 similar near-surface forging to improve dimensional accuracy and surface quality.

To carry out such a forging process, according to the Fig.3 a forging device is used with forging punches 5 arranged in pairs opposite one another with respect to a forging axis, each of which holds a forging tool. The forging punches 5, which are guided radially to the forging axis in a frame 6, are made up of two punch parts, namely an inner punch part 7 which holds the forging tool, and an outer punch part 8, between which and the inner punch part 7 a hydraulic cylinder 9 is effective. The arrangement is such that the outer punch part 8 forms a cylinder recess 10, into which the inner punch part 7 engages with a piston section 11. The space 12 between the piston section 11 and the punch guide 13 is also used as a cylinder space for loading the inner punch part 7.

An eccentric drive 14 is used to drive the outer stamp part 8, which comprises an eccentric shaft 15 mounted in the frame 6 and a sliding block 16 mounted on the eccentric shaft 15, which with its sliding surface 17 on the front side of the outer stamp part 8. The contact of the outer stamp part 8 with the sliding surface 17 of the sliding block 16 is advantageously ensured by a resilient loading of the outer or inner stamp part 7, 8, preferably with the aid of hydraulic springs, which, however, is not shown in more detail for reasons of clarity.

The eccentric drive 14 is driven by a torque motor 19 designed as an internal rotor, flanged to a housing 18 connected to the frame 6 coaxially to the eccentric shaft 15, the rotor 20 of which is rotatably mounted on an eccentric shaft extension 21. This eccentric shaft extension 21 is arranged on a driver flange 22 forming a flywheel, between which and the rotor 20 a coupling 23 is provided. A driver 24 serves as the coupling 23, which can be displaced using an actuating cylinder 25 and in the coupling position engages in a driver receptacle 26 in the driver flange 22.

In the coupled engagement position, the driver flange 22 and the eccentric shaft 15 are thus driven by the torque motor 19, so that the forging punch 5 is driven at a comparatively high frequency, because the two punch parts 7, 8 are rigidly connected to one another by the locked hydraulic cylinder 9. If, however, the coupling 23 is released and the eccentric drive 14 is held in the outer dead center position shown, the sliding block 16 forms a fixed abutment for the outer punch part 8, with the result that the inner punch part 7 is moved by the hydraulic cylinder 9 between the two punch parts 7, 8 independently of the eccentric drive 14 to perform pressing strokes in accordance with the Fig.2 In order to be able to better transfer the forging forces that occur to the frame 6, an additional abutment 27 for the sliding block 16 can be provided in the outer dead center position of the eccentric drive 14.

As the Fig.3 shows, the torque motor 19 can advantageously drive a hydraulic pump 28 so that when the clutch 23 is released and the torque motor 19 is running, hydraulic fluid is available to actuate the hydraulic cylinder 9.

Since a forging device according to the Fig.3 can be easily switched from a drive of the forging dies 5 by eccentric drives 14 for a conventional radial forging to a hydraulic drive designed for forging pressing by means of hydraulic cylinders 9, this forging device can advantageously be used for the successive processing of a cast forging block 1 on the one hand by radial forging and on the other hand by forging pressing in one heat in order to avoid cracking in the surface area during the subsequent forging pressing with the preceding near-surface radial forging of the forging block 1.

Claims (2)

Forging device for hot forming a cast forging block (1) with radially guided forging dies (5), each of which has two die parts (7, 8) which can be radially displaced relative to one another, of which the inner die part (7) carrying a forging tool (2) is connected to the other outer die part (8) by a hydraulic cylinder (9), with an eccentric drive (14) which can drive the outer die part (8), the eccentric shaft (15) of which is connected to an electric motor via a coupling (23), and with a pump (28) which can be driven by the electric motor for actuating the hydraulic cylinder (9) between the inner and outer die parts (7, 8), characterized in that a torque motor (19) which is coaxial with the eccentric shaft (15) and designed as an internal rotor is provided as the electric motor, the rotor (20) of which is mounted on the eccentric shaft (15) or a Eccentric shaft extension (21) is rotatably mounted, and that the coupling (23) is arranged between the rotor (20) and the driving flange (22). Forging device according to claim 1, characterized in that the coupling (23) has a driver (24) which is parallel to the eccentric shaft (15) and mounted in the rotor (20) so as to be axially acted upon and which, in the coupling position, positively engages in a driver receptacle (26) in the driver flange (22).

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