HOT FORMING A CAST FORGING INGOT

Abstract

A method for hot forming of a cast forging ingot uses a forging device with radially guided forging dies of which each have two die parts, which can be radially moved relative to each other and of which the inner die part bearing a forging tool is drive-connected, using a hydraulic cylinder, to the other, outer die part, which can be driven using an eccentric drive. In order to provide advantageous forging conditions, the forging ingot is formed under heat, first using the forging dies driven by the eccentric drive, in near-surface forge processing with a degree of deformation which is above the critical degree of deformation and which excludes the formation of cracks, and then, with the outer die parts stopped, with the aid of the inner die parts driven by the hydraulic cylinders, in forge pressing with a bite ratio of >0.5.

Claims

1. A method for hot forming of a cast forging ingot using a forging device having radially guided forging dies, each having two die parts which can be radially moved relative to one another and of which an inner die part of the two die parts bearing a forging tool is drive-connected by a hydraulic cylinder to an other outer die part of the two die parts which can be driven by an eccentric drive, the method comprising: initially forming the forging ingot under a heat with the aid of the forging dies driven by the eccentric drive, in near-surface forge processing with a degree of deformation which is above a critical degree of deformation and which excludes the formation of cracks; following initially forming the forging ingot, stopping the outer die parts; and using the inner die parts driven by the hydraulic cylinders to forge press the ingot with a bite ratio >0.5 while the outer die parts are stopped.

2. The method according to claim 1, further comprising: subjecting the forging ingot to a finishing operation after forge pressing using the forging dies driven by the eccentric drive.

3. A forging device for hot forming of a cast forging ingot, comprising: radially guided forging dies, each having two die parts which can be radially displaced relative to one another, an inner die part of the two die parts carrying a forging tool and being drive-connected to an other outer die part of the two die parts by a hydraulic cylinder; an eccentric drive which can drive the outer die part; an eccentric shaft coupled to the eccentric drive via a coupling to an electric motor; and a pump driven by the electric motor, for acting on the hydraulic cylinder between the inner and outer die parts wherein the electric motor is a torque motor which is coaxial with the eccentric shaft a rotor of the torque motor being rotatably mounted on the eccentric shaft or an eccentric shaft extension in connection with a driver flange of the eccentric shaft, and wherein the coupling is arranged between the rotor and the driver flange.

4. The forging device according to claim 3, the coupling has a driver which is parallel to the eccentric shaft, is mounted in the rotor such that the coupling can be acted upon axially and, in a coupling position, engages positively in a driver receptacle in the driver flange.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0014] The system described herein is explained in more detail on the basis of the drawings, wherein:

[0015] FIG. 1 shows a schematic representation of the engagement of the forging tools driven by an eccentric drive for near-surface forge processing,

[0016] FIG. 2 shows a representation corresponding to FIG. 1 of the engagement of the forging tools during press forging with the aid of the hydraulically actuated forging dies, and

[0017] FIG. 3 shows a forging device according to the system described herein for carrying out the forging method in the region of a forging die in a schematic section along the eccentric shaft of the eccentric drive.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

[0018] In order to permit forging of a cast forging ingot 1 in the sense of the most uniform possible recrystallization of the cast structure in an area close to the surface, the pressed saddle length S, i.e. the length of the surface region pressed by the forging dies 2 per forging stroke, which is susceptible to cracking due to the lack of forming, is kept small in comparison with the effective engagement length L of the forging dies 2 lying opposite each other in relation to the forging ingot 1. To avoid large differences between local degrees of deformation, the forging dies 2 can advantageously be provided with an entry slope 3 of between 6 and 15?. Since the dead material subject to only slight deformation per forging stroke is located in the region of the flow sheath 4, which for simplicity is indicated in the schematic representation according to FIGS. 1 and 2 in the center of the effective engagement length L of the forging dies 2, the region of slight deformation is located in the case of the forging ratios depicted in FIG. 1 outside the pressed saddle length S, so that a largely uniform forming of the forging ingot 1 in a region close to the surface can be ensured if, in order to maintain the forging ratios, the forging tools 2 are driven with a comparatively high stroke frequency. However, the forming operation must not give rise to cracking in the surface region. 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 ingot and the number of passes dependent thereon, has proved advantageous at a deformation rate of between 0.15 and 2 per second. The accumulated degree of deformation ?=[?((?.sub.h.sup.2+?.sub.l.sup.2+?.sub.b.sup.2)].sup.1/2 is obtained from the logarithmic degrees of deformation given by the logarithmic ratios of the dimensions after and before deformation in height h, the length l and the width b of the forging ingot 1 [?.sub.h=ln(h.sub.1/h.sub.0), ?.sub.l=ln(l.sub.1/l.sub.0), ?.sub.b=ln(b.sub.1/b.sub.0)].

[0019] After preforming in the surface region, the forging ingot 1 can be subjected under the same heat to the actual forming for compaction and microstructure improvement down to the core area by a forging press, using the same forging tools 2, but under conditions of a forging press with a bite ratio B=S/h.sub.0>0.5, as illustrated in FIG. 2. Due to the large bite ratio, the deformations act right into the core of the forging ingot 1 when the cross-section is reduced accordingly, wherein it must be accepted that the flow sheath 4 will come to lie within the pressed saddle length S. However, the resulting non-uniform forming in the surface region does not play any role with regard to crack formation because recrystallization has already taken place in the regions close to the surface, which prevents cracking occurring with larger grain structures. The forging tools 2 are hydraulically driven for forging according to FIG. 2 at a forming speed <0.6 s.sup.?1, where the cross-section reduction per pass is to be greater than 15%.

[0020] Following forge pressing, the forging ingot 1 can be subjected to near-surface forge processing similar to FIG. 1 to improve dimensional accuracy and surface finish.

[0021] A forging device advantageous for carrying out the forging method according to FIGS. 1 and 2 is shown in FIG. 3, namely in the region of one of the forging dies 5 opposite each other in pairs with respect to a forging axis, each of which accommodates a forging tool. The forging die 5, which is guided for displacement radially to the forging axis in a frame 6, consists of two die parts, namely an inner die part 7 receiving the forging tool and an outer die part 8, between which and the inner die part 7 a hydraulic cylinder 9 is effective. The arrangement is such that the outer die part 8 forms a cylinder recess 10 in which the inner die part 7 engages with a piston section 11. The space 12 between the piston section 11 and the die guide 13 is also used as a cylinder space for acting on the inner die part 7.

[0022] The outer die part 8 is driven by an eccentric drive 14, which includes an eccentric shaft 15 mounted in the frame 6 and a sliding block 16 mounted on the eccentric shaft 15, which sliding block is supported with a sliding surface 17 of the sliding block 16 on the end face of the outer die part 8. The contact of the outer die part 8 with the sliding surface 17 of the slide block 16 is advantageously ensured by a resilient loading of the outer and inner die parts 7, 8, respectively, preferably with the aid of hydraulic springs, which, however, is not shown in more detail for reasons of clarity.

[0023] The eccentric drive 14 is driven by a torque motor 19 in the form of an internal rotor flanged to a housing 18 connected to the frame 6 coaxially with the eccentric shaft 15, the rotor 20 of which is rotatably mounted on an eccentric shaft extension 21. The eccentric shaft extension 21 is arranged on a driver flange 22 forming a flywheel, between which driver flange 22 and the rotor 20 a coupling 23 is provided. A driver 24 serves as the coupling 23, which can be displaced with the aid of an actuating cylinder 25 and, in the coupling position, engages in a driver receptacle 26 in the driver flange 22.

[0024] 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 die 5 is driven with a comparatively high frequency, because the two die parts 7, 8 are rigidly drive-connected to each other by the locked hydraulic cylinder 9. If, on the other hand, 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 die part 8 with the result that the inner die part 7 can be subjected to press strokes as shown in FIG. 2 by the hydraulic cylinder 9 between the two die parts 7, 8 independently of the eccentric drive 14. In order to be able to better transmit the forging forces occurring to the frame 6, an additional abutment 27 for the slide block 16 can be provided in the outer dead center position of the eccentric drive 14.

[0025] As shown in FIG. 3, the torque motor 19 can advantageously drive a hydraulic pump 28 so that hydraulic fluid is available to act on the hydraulic cylinder 9 when the coupling 23 is disengaged and the torque motor 19 is running.

[0026] Since a forging device according to FIG. 3 can be switched over in a simple manner from a drive of the forging dies 5 by eccentric drives 14 for a usual radial forging to a hydraulic drive designed for a forging press using hydraulic cylinders 9, the forging device can be used in an advantageous manner for successive processing of a cast forging ingot 1 on the one hand by radial forging and on the other hand by forging under one heat, in order to avoid crack formation in the surface region during subsequent forge pressing with the preceding near-surface radial forging of the forging ingot 1.