Forging apparatus

Abstract

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

Description

[0001] The invention relates to a forging device for hot forming a cast forging block with radially guided forging dies, each having two die parts which 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 which can drive the outer die part and whose eccentric shaft is connected to an electric motor via a coupling, and with a pump which can be driven by the electric motor for pressurising the hydraulic cylinder between the inner and outer die parts.

[0002] To transform the cast structure of a cast forging ingot into a largely pore-free, recrystallized structure, the forging ingot 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 ingot before the press stroke, is intended to achieve core forming sufficient for pore reduction despite a small reduction. However, due to the large bite ratio, significant differences arise 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 cracking in the surface area.

[0003] In order to be able to hot-form workpieces with a forging device, either by forging with a 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 = preamble of claim 1) to assemble forging punches that hold a forging tool and are guided radially to the forging axis from two punch parts, between which a hydraulic cylinder is provided. The outer of the two punch parts is driven by an eccentric drive, which, when the hydraulic cylinder between the two punch parts is locked, drives the inner punch part, which holds a forging tool, in the sense of radial forging with a comparatively high impact rate.However, if the outer punch part is decoupled from its eccentric drive and held fixed in place, the inner punch part can be driven in the sense of press forging by applying pressure to the hydraulic cylinder between the two punch parts while the outer punch part is held fast. The decoupling of the upper punch part from the eccentric drive can be achieved by a clamping wedge that can be moved in a clamping gap between the punch guide and the outer punch 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) to provide a clutch in the drive train between the eccentric and the electric motor provided for the eccentric drive, so that when decoupled, forces from the outer punch part can be transferred via the eccentric to the eccentric shaft bearing without torque loading on the eccentric, provided the eccentric is preferably in the outer dead center position.

[0004] Regardless of the type of decoupling of the outer punch part from the eccentric drive, the difficulty in forging 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 pressed length of the forging saddle is unavoidable, which entails the risk of crack formation in the surface area.

[0005] To avoid crack formation 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 offset or pushed between an upper and a lower saddle of the forging press in the workpiece stretching direction before each forging stroke only far enough that the bite edge of the previous bite on the workpiece lies 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, resulting in a forging process starting from a largest bite ratio with gradually decreasing bite ratios. This 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 crack formation in the surface area.

[0006] In a press with an eccentric drive, it is known (DE 10 2015 222 995 A1) to provide the eccentric shaft at one end with a flywheel driven by a flywheel motor, which can be releasably coupled to the eccentric shaft using a coupling. At the opposite end, the eccentric shaft is permanently connected to a torque motor, which 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 allows the installation space for the press stroke drive to be kept comparatively small. However, such an eccentric shaft drive is not very suitable for the outer punch section of the punch parts of a forging device that can be radially displaced against one another and whose inner punch section, which carries a forging tool, is drive-connected to the outer punch section by a hydraulic cylinder.

[0007] 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.

[0008] Starting from a forging device of the type described at the outset, the invention achieves the stated object in that a torque motor designed as an internal rotor, coaxial with the eccentric shaft, is provided as the electric motor, the rotor of which is rotatably mounted on the eccentric shaft or an eccentric shaft extension following a driving flange of the eccentric shaft, and in that the coupling is arranged between the rotor and the driving flange.

[0009] 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 as to be axially loaded and which, in the coupling position, positively engages in a driver receptacle in the driver flange.

[0010] As a result of these measures, the eccentric shaft is driven directly by the associated torque motor in the coupling position. Since the hydraulic cylinder between the inner and outer punch sections is locked in this case, the forging punches are driven solely by the associated eccentric drives, with a comparatively small stroke and high stroke frequency, in the sense of radial forging. In contrast, with decoupled eccentric drives, the inner punch sections can be actuated by the hydraulic cylinders between the inner and outer punch sections, in the sense of forging, with a comparatively large stroke and low stroke frequency. The forging forces are transmitted via the outer punch sections to the eccentric shaft, and via this to the frame supporting the forging punches.To avoid the resulting torque on the eccentric shaft, it is advantageously held in the outer dead center position when decoupled. The hydraulic cylinders that drive the inner ram parts are pressurized by pumps driven by the torque motors.

[0011] To refine the cast structure in a near-surface area through recrystallization to such an extent that the locally varying loads on the forging block over the pressed length of the forging saddle can no longer cause crack formation during subsequent forging, it is necessary to ensure the most uniform deformation possible across the pressed length of the saddle to avoid dead material in this area, i.e., material with only a low degree of deformation. This is achieved by radial forging with a degree of deformation that is low enough to prevent crack formation but sufficient for recrystallization, i.e., above the critical degree of deformation, which specifies the minimum deformation required 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 compared to the effective engagement length of the forging tools, so that the flow sheath and thus the dead material in the area of ​​the flow sheath is located outside the length of the crack-prone surface pressed by the forging tool.

[0012] In the subsequent processing of the forging block with the same forging tools, which are now hydraulically operated in the sense of a forging press 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.

[0013] The drawing shows the subject matter of the invention as an example. Fig. 1a schematic representation of the engagement of the forging tools driven by an eccentric drive for near-surface forging, Fig. 2one of the Fig. 1 corresponding representation of the engagement of the forging tools during press forging with the aid of the hydraulically operated forging punches and Fig. 3 a forging device according to the invention in detail in the area of ​​a forging punch in a schematic section along the eccentric shaft of the eccentric drive.

[0014] In order to enable forging of a cast forging block 1 in the sense of the most uniform recrystallization of the cast structure in a region 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, which is susceptible to cracking due to the still missing deformation, is kept small in comparison to the effective engagement length L of the forging tools 2 opposite each other with respect to the forging block 1. To avoid large differences between local degrees of deformation, the forging tools 2 can advantageously be provided with an entry slope 3 between 6 and 15°. Since the dead material, which is subject to only slight deformation per forging stroke, is located in the area of ​​the flow sheath 4, which in the schematic representation according to the Fig. 1 und 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. Fig. 1 shown forging conditions outside the pressed saddle length S, so that a largely uniform deformation of the forging block 1 in a region 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 give rise to crack formation 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 associated number of passes, 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 i 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 l and the width b of the forging block 1 [φ h = In(h 1 / h 0 ), φ i = In(I 1 / I 0 ), φ b = In(b 1 / b 0 )].

[0015] After this pre-forming in the surface area, the forging block 1 can be subjected to the actual forming process for compaction and structural improvement down to the core area by forging at the same heat, using the same forging tools 2, but used under forging conditions with a bite ratio B = S / h 0 >0.5, as described in the Fig. 2 is illustrated. Due to the large bite ratio, with a corresponding cross-sectional reduction, the deformations affect the core of the forging block 1, whereby it must be accepted that the flow shear 4 comes to lie within the pressed saddle length S. However, the resulting non-uniform deformation in the surface area plays no role with regard to crack formation, because recrystallization has already taken place in these near-surface areas, which prevents crack formation that occurs with larger grain structures. The forging tools 2 are used for forging according to Fig. 2 hydraulically driven with a forming speed < 0.6 s -1<, whereby the cross-sectional reduction per pass should be greater than 15%.

[0016] Following forging, the forging block 1 can be one of the Fig. 1 similar near-surface forging to improve dimensional accuracy and surface quality.

[0017] 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 holding a forging tool. The forging punches 5, which are guided radially to the forging axis in a frame 6, are composed of two punch parts, namely an inner punch part 7 holding the forging tool, and an outer punch part 8, between which and the inner punch part 7 a hydraulic cylinder 9 acts. 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 pressurizing the inner punch part 7.

[0018] The outer punch part 8 is driven by an eccentric drive 14, which comprises an eccentric shaft 15 mounted in the frame 6 and a sliding block 16 mounted on the eccentric shaft 15, which is supported with its sliding surface 17 on the end face of the outer punch part 8. The contact of the outer punch part 8 with the sliding surface 17 of the sliding block 16 is advantageously ensured by a spring-loaded action on the outer or inner punch part 7, 8, preferably by means of hydraulic springs, although this is not shown in detail for reasons of clarity.

[0019] The eccentric drive 14 is driven by a torque motor 19, designed as an internal rotor and flanged to a housing 18 connected to the frame 6 coaxially with the eccentric shaft 15. The motor's rotor 20 is rotatably mounted on an eccentric shaft extension 21. This eccentric shaft extension 21 is arranged on a drive flange 22 forming a flywheel, between which and the rotor 20 a clutch 23 is provided. A drive member 24 serves as the clutch 23. This drive member is displaceable by means of an actuating cylinder 25 and, in the clutched position, engages in a drive recess 26 in the drive flange 22.

[0020] In the coupled engagement position, the driving 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 each other 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 according to the Fig. 2 In order to better transmit the forging forces occurring 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.

[0021] 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 act on the hydraulic cylinder 9.

[0022] Since a forging device according to the Fig. 3 can be switched in a simple manner from a drive of the forging punches 5 by eccentric drives 14 for a conventional radial forging to a hydraulic drive designed for a forging press by means of hydraulic cylinders 9, this forging device can be used advantageously for the successive processing of a cast forging block 1 on the one hand by radial forging and on the other hand by forging presses in one heat in order to avoid crack formation in the surface area during the subsequent forging presses with the preceding near-surface radial forging of the forging block 1.

Claims

1. Forging device for hot forming a cast forging ingot (1) with radially guided forging dies (5), each of which has two die parts (7, 8) that can be radially displaced relative to each other, 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) that can drive the outer die part (8), whose eccentric shaft (15) is connected to an electric motor via a coupling (23), and with a pump (28) driven by the electric motor for actuating the hydraulic cylinder (9) between the inner and outer die parts (7, 8), characterized in that the electric motor is a torque motor (19) designed as an internal rotor and coaxial with the eccentric shaft (15), the rotor (20) of which is mounted rotatably on an eccentric shaft extension (21) in connection with a driver flange (22) of the eccentric shaft (15) or on the eccentric shaft (15) and in that the coupling (23) is arranged between the rotor (20) and the driver flange (22).

2. 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 is mounted in the rotor (20) so as to be axially actuatable, and which, in the coupling position, engages positively in a driver receptacle (26) in the driver flange (22).

Images