GB2074913A

GB2074913A - High-speed forging machine

Info

Publication number: GB2074913A
Application number: GB8111387A
Authority: GB
Original assignee: GFM Gesellschaft fuer Fertigungstechnik und Maschinenbau AG
Current assignee: GFM Gesellschaft fuer Fertigungstechnik und Maschinenbau AG
Priority date: 1980-05-05
Filing date: 1981-04-10
Publication date: 1981-11-11
Also published as: FR2481622A1; ATA236580A; AT365494B; DE3113965A1; DD158750A5; JPS574343A

Abstract

The machine comprises two rams 2, which strike against each other and are guided in a machine frame 1, and a mechanical drive 4-8 for reciprocating the rams. At least one of said rams has a hydraulic cushion 21 interposed between the ram and the frame. An overload-preventing device comprises a safety switch 21 which is responsive to the hydraulic pressure in the hydraulic cushion to disable the ram drive and/or to initiate the operation of a ram-adjusting device 10-12 in a ram-opening sense. In order to ensure that the rams will be relieved from load before an overload can result in damage to the machine, the hydraulic cushion communicates with a hydraulic accumulator 16. <IMAGE>

Description

SPECIFICATION High-speed forging machine This invention relates to a high-speed forging machine comprising a plurality of rams, preferably two rams, which strike against each other and are guided in a machine frame, and mechanical ramdriving means for reciprocating said rams, at least one of said rams being backed by the machine frame with a hydraulic cushion interposed between the ram and the frame, and an overload protection system being provided, which consists of a safety switch, which is responsive to the hydraulic pressure in the hydraulic cushion to disable the ram-driving means and/or to initiate the operation of a ram-adjusting device in a ramopening sense.

In high-speed forging machines which are mechanically driven it is particularly difficult to prevent an overload because the mechanical drive means impose a constraint on the motion of the rams so that the forging force cannot be limited by the drive means as is possible where a hydraulic drive is used, in which a limitation can be effected by a simple pressure relief valve. In a mechanically driven machine, such limitation would require the provision of means for limiting the torque in the drive system. For this reason, it has been attempted to protect mechanically driven highspeed forging machines against an overload by the provision of a safety switch which is responsive to the forging force exerted and operable to disable the ram-driving means or to initiate the operation of ram-adjusting means in a ram-opening sense.To ensure the response of the safety switch to the forging force, the safety switch is responsive to the deformation of a portion of the machine frame or of the ram itself during the forging operation. That deformation is detected by a strain gage. But the measurement of a deformation by a strain gage is not very reliable, at least after a certain period of time, and such an arrangement must be handled carefully and readjusted in short intervals. Besides, that known system for protection against overload has a very slow response, which in most cases takes place too late as the overload must have occurred before the corresponding deformation has been effected to which the safety switch responds.Besides, the times from the first occurrence of the force until the detection of the deformation and from the response of the safety switch to the performance of the resulting operation are relatively long in view of the fast operation of the machine. For these reasons the known overload-preventing device is highly inadequate because the machine must take up any overload at least at the beginning of its occurrence before the system for protection against overload can respond to disable the machine or to open the rams. This may take place after the occurrence of the peak load.

It has been proposed in German Patent Specification 1,950,424 to protect mechanical presses against overloads by the provision of a hydraulic system comprising a hydraulic cushion for backing the ram and a control valve system to which the hydraulic pressure in that cushion is applied. That control valve system is expensive and susceptible to trouble because the outlet valve for relieving the cushion is controlled by a pneumatic piston. In spite of that high expenditure, that system for protection against overload also responds only with a certain delay and cannot limit suddenly occurring peak loads.

For these reasons it is too slow for use with highspeed machines, The lack of an adequate protection against overload has restricted the use of high-speed forging machine to operations in which unpredictable load fluctuations will not occur, i.e., to hot-forging operations performed when the machine has already warmed up in operation. As the machine is warming up in operation, parts of the machine will expand so that the dimensions which control the forging operation will be changed; this may result in the exertion of a forging force in excess of the permissible value. On the other hand, during the cold-forging of tubes on a mandrel an occurrence of peak loads and excessively high forging forces must be expected owing to the wall thickness tolerance so that it has not been possible before to use mechanically driven high-speed forging machines for coldforging operations of that kind.

It is an object of the invention to eliminate these disadvantages and to provide a forging machine which is of the kind described first hereinbefore and which distinguishes by comprising a particularly effective system for preventing an overload, which system is functionally reliable, requires only very little maintenance, involves only a low structural expenditure and permits, e.g., a perfectly safe use of the forging machine for the cold-forging of tubes on a mandrel.

This object is accomplished according to the invention in that the hydraulic cushion communicates with a hydraulic accumulator. The hydraulic system consisting of the hydraulic cushion and the accumulator ensures the desired backing of the ram exactly until the highest permissible forging force is exerted and prevents a rising of the forging force above that limit because a non-permissible rise of the forging force above that limit will cause the hydraulic fluid to be forced from the hydraulic cushion to the accumulator so that the ram can yield to the overload. In this way the forging force can be exactly limited. The displacement of the hydraulic fluid from the hydraulic cushion into the accumulator will increase the pressure in that hydraulic system and that pressure rise can be detected by a safety switch consisting of a simple pressure-responsive switch.Depending on the setting of that pressure responsive switch, the same will respond instantaneously to the slightest pressure rise or only after a predetermined pressure rise so that either the machine may be shut down or opened immediately in response to the slightest overload or an overload in a certain range can be taken up by the accumulator while the operation of the machine is continued and the forging operation will be interrupted only when a predetermined overload has been detected. In no case does the machine frame or do mechanically moved parts of the machine have to take up an overload because the ram can yield owing to its backing by the cushion and the accumulator so that the latter will take up any overload.As the accumulator can store hydraulic energy, it will automatically restore the hydraulic cushion to an operative condition when the overload has been eliminated. The accumulator will also compensate any leakage or pressure losses so that an efficient forging will be ensured without a risk of trouble due to load fluctuations. The type of the accumulator is not critical, provided that an accumulator is used which in its capacity and performance is suitable for the conditions to be expected in the forging machine.

The accompanying drawing is a side elevation, partly in section, and shows strictly diagrammatically and by way of example a forging machine embodying the invention.

Two rams 2 are guided along straight lines in a machine frame 1 and at their ends carry tools 3.

The rams 2 are reciprocated to strike against each other by mechanical drive means, which comprises camming members 4a, 4b, which are similar in action to a claw coupling having relatively rotatable parts. Each of these camming member 4a, 4b is connected to a transverse lever 5a, 5b. Oscillating angular movements are imparted to the transverse levers by means of respective sliders 6a, 6b, which are mounted on a crankshaft 7, which is adapted to be driven. The resulting relative movement of the claws 8a, 8b of the camming members 4a, 4b reciprocation to the rams 2. Spring means Sc not shown in detail are provided to urge the ram 2 or one camming member 4a against the other camming member 4b so that the camming members 4a, 4b cannot disengage from each other.A backing member 9 is disposed on that side of the camming member 4b which is opposite to the camming member 4a.

That backing member 9 has screw threads 10 in threaded engagement with an adjusting nut 11.

The latter is adapted to be driven by a worm gear train 12 and serves to adjust the ram 2 and the tool 3 along the axis of the ram. The adjusting nut 11 is mounted in the machine frame 1 to be rotatable and axially displaceable and at its end remote from the tool 3 bears on an annular piston 13 of a piston-cylinder unit 14, the cylinder of which is rigid with the machine frame 1. The annular cylinder chamber 1 5 of that piston cylinder unit 14 surrounds the axis of the ram and communicates with a hydraulic accumulator 1 6 and with a changing system 17, which consists of a check valve 18, a pressure relief valve 19 and a hydraulic pump 20.The hydraulic system comprising the piston-cylinder unit 14 and the accumulator 16 also comprises a pressure responsive switch 21, which in response to a predetermined hydraulic pressure shuts down the drive of the crankshaft 7 and the reciprocation of the ram or operates the adjusting nut 11 in a ramopening sense.

The cooperation of the piston-cylinder unit 14, the accumulator 1 6 and the pressure-responsive switch 21 ensures that overloads will be prevented so that virtually all forging operations may be performed if the charging system 17 is used to build up in the cylinder chamber 15 of the piston cylinder unit 14 a hydraulic cushion which is under a hydraulic pressure that is selected with a view to the highest permissible forging force, i.e., a hydraulic pressure which when multiplied with the piston area equals the highest possible forging force. The pump 20 feeds hydraulic fluid from the reservoir 22 into the cylinder chamber 1 5 until the desired pressure has been reached.The check valve 18 prevents a reverse flow of the hydraulic fluid in response to a pressure rise and the pressure relief valve 1 9 permits a limitation of the pressure. When the cylinder chamber 1 5 has been filled, the hydraulic cushion in the cylinder chamber 1 5 is adapted to transmit axial force from the ram 2 to the machine frame 1. During the forging operation, force is transmitted from the tool 3 through the ram 2 and the camming members 4a, 4b to the backing member 9 and from the latter through the adjusting nut 11 and the piston-cylinder unit 14 to the machine frame 1.Because the hydraulic pressure in the cylinder chamber 1 5 is maintained by the accumulator 16, the piston-cylinder unit 14 and particularly the body of liquid under pressure in the cylinder chamber 1 5 ensures a rigid backing for the ram 2 unless the forging force exceeds its upper limit. As soon as that limit is exceeded, the overload forces the annular piston 13 into the cylinder chamber 1 5 and displaces the hydraulic liquid from the cylinder chamber 1 5 into the accumulator. As a result, the ram 2 can yield to the overload as soon as it occurs so that there is no risk of damage. The displacement of the hydraulic liquid from the cylinder chamber 1 5 into the accumulator 1 6 results in a pressure rise in the hydraulic system.

That pressure rise is detected by the pressureresponsive switch 21, which in dependence on its setting responds immediately or after a predetermined pressure rise to open the tools or to disable the ram-driving means. As soon as the forging force has decreased below the upper limit, the accumulator forces back the hydraulic fluid into the cylinder chamber 1 5 so that the hydraulic cushion required to back the ram is properly built up in the piston-cylinder unit.

Claims

CLAIM

A high-speed forging machine comprising a plurality of rams, preferably two rams, which strike against each other and are guided in a machine frame, and mechanical ram-driving means for reciprocating said rams, at least one of said rams being backed by the machine frame with a hydraulic cushion interposed between the ram and the frame, and an overload protection system being provided, which consists of a safety switch, which is responsive to the hydraulic pressure in the hydraulic cushion to disable the ram-driving means and/or to initiate the operation of a ramadjusting device in a ram-opening sense, characterized in that the hydraulic cushion communicates with a hydraulic accumulator.