EP2727714B1

EP2727714B1 - Method for hot-forming a piece with a mechanical press

Info

Publication number: EP2727714B1
Application number: EP13382392.2A
Authority: EP
Inventors: Andoitz Aranburu Irastorza; Unai Argarate Belategi
Original assignee: Fagor Arrasate S Coop
Current assignee: Fagor Arrasate S Coop
Priority date: 2012-10-30
Filing date: 2013-10-04
Publication date: 2019-05-15
Anticipated expiration: 2033-10-04
Also published as: ES2458269A1; EP2727714A3; CN103786359B; ES2728145T3; CN103786359A; ES2458269B1; EP2727714A2

Description

TECHNICAL FIELD

The present invention is related to methods for hot-forming pieces with mechanical presses, in which the dies of said mechanical presses must remain closed for a certain time, particularly hot stamping processes in which the formed piece cools down inside the closed dies.

PRIOR ART

Mechanical presses comprising a bottom die arranged in a mount, a top portion including a top die movable with respect to the mount along guides, a motor driving said press, and a crankshaft, the motor being arranged coupled to the crankshaft by transmission means, are known. The mechanical press further comprises a mechanism coupling the crankshaft to a carriage where the top die is secured, transmitting the movement of the crankshaft to the top die, said carriage being moved along the guides.
JPH03238200A discloses a mechanical press where improvement in operability is made, by controlling the oil pressure of a hydraulic cylinder interposed to the pressurizing point of the mechanical press, by a hydraulic control mechanism to apply relative motions to the pressurizing point, thereby controlling a pressurizing speed.
JPS63299900A discloses a mechanical press where, to improve dynamic accuracy of the press, the bottom dead center position of a slide is detected through a sensor, it is compared with a setting reference value, and the die height is adjusted based on the difference between the detected value and the setting value.
JPS59137133A discloses a mechanical press where, to enable forming with high accuracy with a relatively simple construction, the change in a die height is electrically detected and the pressure of a protector hydraulic chamber is controlled with the resulting signal.
Mechanical presses adapted for forming processes such as the stamping or forging generally operate continuously without stopping at bottom dead center. However, when hot stamping is performed sometimes the actual dies are responsible for cooling the formed piece, and to that end the press has to remain at bottom dead center for a specific time. This situation can be problematic when starting up the press again because the mechanism has to withstand enormous stress and can end up breaking or excessively deteriorating.
Document US 20120192615 A1 belonging to the present applicant discloses a method according to the preamble of claim 1 and a mechanical press adapted for hot stamping in which it remains at bottom dead center for a specific time. To that end, the press comprises a lubricating bearing coupled to the mechanism, inside which the crankshaft is housed. When the press starts up, the lubricating bearing withstands stress as it is excessively lubricated, such that the mechanism does not end up breaking or excessively deteriorating due to these start ups.

DISCLOSURE OF THE INVENTION

An object of the invention is to provide a method for hot-forming a piece with a mechanical press.
The method according to the invention is defined by claim 1 and is configured for hot-forming a piece with a mechanical press comprising a top die and a bottom die adapted for forming a piece between both when they close on one another, and a mechanism that is adapted for displacing at least one die with its movement.
The method comprises a forming step in which the dies close on one another for forming a piece, a cooling step in which the dies remain closed at bottom dead center in which the piece is formed between the dies and a backward step in which the dies open up.
The method further comprises a discharging step, which occurs during the cooling step, in which at least part of a fluid present in a hydraulic chamber associated with the mechanism is discharged from the hydraulic chamber and a filling step, which occurs during the backward step, in which at least part of said discharged fluid fills the hydraulic chamber again. Therefore, by discharging the fluid from the hydraulic chamber the force that has to be exerted by the mechanism to start the machine up again decreased, preventing or greatly reducing the risk that the mechanism ends up breaking or excessively deteriorating when performing said operation.
These and other advantages and features of the invention will become evident in view of the drawings and the detailed description of the invention.

DESCRIPTION OF THE DRAWINGS

Figure 1 shows a sectional view of an example of a mechanical press, without its circuitry.
Figure 2 shows a sectional view of a detail of the mechanical press of Figure 1, where a hydraulic chamber is shown.
Figure 3 schematically shows the sectioned view of Figure 2, with a hydraulic circuit.

DETAILED DISCLOSURE OF THE INVENTION

With reference to Figures 1 and 2, where a mechanical press 100 that is adapted for forming processes, particularly hot-forming processes, is shown by way of example, the mechanical press 100 comprises a table 2 on which there is arranged a bottom die 2b and a carriage 3 to which there is fixed a top die 3b, said dies being adapted for forming a piece between both when they close, a motor not depicted in the drawings for causing the movement of at least one of the dies 2b or 3b with respect to the other die 2b or 3b so that they close on one another or open up, a crankshaft 6 coupled to the motor and a mechanism 8 with which at least one of the dies 2b and 3b is coupled to the crankshaft 6 and the rotary movement of the crankshaft 6 is transformed into linear movement of at least one die 2b or 3b. The mechanism 8 can be of the crank-connecting rod type or of the link drive type, for example. For the sake of clarity, it shall be stated hereinafter that the top die 3b is the die that moves towards the bottom die 2b for forming the piece, but other options (either the bottom die 2b being the die that moves, or both dies 2b and 3b moving) are also possible.
During its operation, the mechanical press 100 transforms rotary movement of the crankshaft 6 into linear movement of the top die 3b by means of the mechanism 8, varying the force generated by said mechanical press 100 along its travel according to the angle of force application, the greatest force being generated at bottom dead center of said mechanical press 100, where both dies 2b and 3b are in contact (or separated only by the piece being formed).
The mechanical press 100 is adapted for working in forming processes, such as hot-stamping or forging, where the piece to be formed cools down between the top die 3b and the bottom die 2b, i.e., the mechanical press 100 remains at bottom dead center for a specific time in order to cool the piece. Accordingly, the crankshaft 6 has to withstand high stress when it is operated for separating the top die 3b from the bottom die 2b.
The mechanical press 100 comprises a hydraulic chamber 4 arranged at the feet of the mechanism 8 for damping or absorbing possible overloads while forming the piece, and an actuator device adapted for causing at least part of the fluid present in the hydraulic chamber 4 to be discharged from the hydraulic chamber 4 when the mechanical press 100 is at bottom dead center in which the piece is formed between the dies 2b and 3b, and causing at least part of said fluid to return to the hydraulic chamber 4 once the mechanical press 100 leaves bottom dead center. Therefore, when the dies 2b and 3b move closer to one another the hydraulic chamber 4 contains the fluid necessary for withstanding the forces that are generated and for withstanding a possible overload, and when the dies 2b and 3b open up as a result of there being less fluid present in the hydraulic chamber 4 since at least part of the fluid present has been discharged while closing the dies 2b and 3b, the force to be withstood is also less, and the mechanism 8 of the mechanical press 100 has to withstand less mechanical stress, which involves a decrease in the risk of breaking for this reason and/or an increase in the service life of the mechanism 8. The fluid is preferably oil, although it could be any other fluid having analogous or similar features.
The mechanical press 100 remains at bottom dead center for a specific cooling time, and the actuator device is preferably adapted for causing at least part of the fluid present in the hydraulic chamber 4 to be discharged from the hydraulic chamber 4 when, with the mechanical press 100 at bottom dead center, there is still a specific discharging time left to conclude the cooling time. The discharging time is less than the cooling time. The discharging time is preferably less than about 1 second.
The mechanical press 100 comprises a tank 10 that is communicated with the hydraulic chamber 4, and an accumulator 5 that is communicated with the tank 10 and with the hydraulic chamber 4. The tank 10 receives the fluid discharged from the hydraulic chamber 4, and the accumulator 5 receives at least part of the fluid present in the tank 10, which later returns to the hydraulic chamber 4 from the accumulator 5, once the mechanical press 100 leaves bottom dead center. The mechanical press 100 comprises a pump 11 arranged between the tank 10 and the accumulator 5 to pump the fluid present in the tank 10 towards the accumulator 5.
The actuator device of the mechanical press 100 comprises a discharge valve 40 arranged between the hydraulic chamber 4 and the tank 10 and communicated with the hydraulic chamber 4 and the tank 10, to allow or prevent fluid discharge from the hydraulic chamber 4 towards the tank 10, and a filling valve 90 arranged between the accumulator 5 and the hydraulic chamber 4 and communicated with the accumulator 5 and the hydraulic chamber 4, to allow or prevent fluid fill from the accumulator 5 towards the hydraulic chamber 4. The discharge valve 40 is preferably a servo-valve, such that the amount of fluid that is discharged from the hydraulic chamber 4 can be precisely controlled.
The mechanical press 100 further comprises a first common conduit 12 that is attached at one end to the hydraulic chamber 4 and at the other end to a branch 13 that is communicated with the inlet of the discharge valve 40 and with the outlet of the filling valve 90, and a second common conduit 15 that is attached at one end to the inlet of the filling valve 90 and at the other end to a branch 16 that is communicated with the accumulator 5 and with the tank 10.
Preferably, the mechanical press 100 further comprises an overload valve associated with the hydraulic chamber 4, not depicted in the drawings. If an overload is detected in the hydraulic chamber 4, the overload valve is opened to release the die from the thrust of the mechanism 8 so that the different components present in the mechanical press 100 do not break due to the overload.
In one example not shown in the drawings, the mechanical press 100 can comprise a plurality of hydraulic chambers 4, and an actuator device associated with each hydraulic chamber 4. Each hydraulic chamber 4 likewise comprises the conduits and the pump 11 discussed above and necessary for carrying out the filling and discharging thereof. The mechanical press 100 can comprise a single tank 10, a single accumulator 5 and a single pump 11 associated with all the hydraulic chambers 4. In this example, the mechanical press 100 further comprises a movement sensor adapted for causing the movement in all the hydraulic chambers 4 to be the same, getting the corresponding die to maintain its orientation. The movement sensor is associated with each of the hydraulic chambers 4 and can detect the movement of the mechanism 8 on each hydraulic chamber 4 at least when fluid is discharged from the hydraulic chambers 4, and it is also associated with each of the discharge valves 40, such that it can act on the discharge valve 40 according to the movement detected in the different hydraulic chambers 4 to maintain the orientation of the corresponding die. Alternatively, in another configuration the mechanical press 100 can comprise a movement sensor associated with each hydraulic chamber 4 and its corresponding discharge valve 40, and in any of the discussed configurations, the mechanical press 100 can even comprise control means (microcontroller, microprocessor or a similar device) communicated with the movement sensor (or movement sensors), the control means being the one which acts on the discharge valves 40. The control means can in turn be control means specific for this function or they can be the main control means of the mechanical press 100 responsible for performing the functions characteristic of the mechanical press 100.
The mechanical press 100 can further comprise an overload valve such as that discussed above associated with each hydraulic chamber 4, or a single overload valve for all the hydraulic chambers 4.
The invention is related to a method for hot-forming a piece with a mechanical press. The mechanical press is a mechanical press 100 like the one discussed before, in any of its examples and configurations.
The method comprises a forming step in which the dies 2b and 3b of the mechanical press 100 close on one another for forming a piece, a cooling step in which the dies 2b and 3b remain closed at bottom dead center in which the piece is formed between the dies 2b and 3b, and a backward step in which the dies 2b and 3b open up.
The method further comprises a discharging step, which occurs during the cooling step, in which at least part of a fluid present in a hydraulic chamber 4 of the mechanical press 100 is discharged from the hydraulic chamber 4, and a filling step, which occurs during the backward step, in which at least part of said discharged fluid fills the hydraulic chamber 4 again. Therefore, when the dies 2b and 3b move closer to one another the hydraulic chamber maintains the fluid necessary for withstanding the forces that are generated, and when the dies 2b and 3b open up as a result of there being less fluid present in the hydraulic chamber, the force to be withstood is also less, and the mechanism 8 of the mechanical press 100 has to withstand less mechanical stress, which involves a decrease in the risk of breaking for this reason and an increase in the service life of the mechanism 8.
The dies 2b and 3b remain closed for a specific cooling time, at least part of the fluid present in the hydraulic chamber 4 being discharged from said hydraulic chamber 4 when there is still a specific discharging time left to conclude the cooling time, the discharging time being less than the cooling time. The discharging time is preferably less than about 1 second. The advantages discussed in the preceding paragraph are thus achieved while at the same time assuring that with the mechanical press 100 at bottom dead center, the necessary distance is maintained between the table 2 and the carriage 3 of the press, and with it sufficient force is exerted between both dies 2b and 3b for forming and cooling the formed piece.
The method to be implemented in the example of the mechanical press 100 comprising a plurality of hydraulic chambers 4 further comprises a verification step in which the movement of each of the mechanisms 8, in their respective hydraulic chambers 4, is verified. The verification step occurs while the mechanical press 100 is at bottom dead center, and more specifically while the fluid present in the hydraulic chambers 4 is being discharged. The method also comprises an alignment step that is performed when it is detected in the verification step that not all the mechanisms 8 move the same way. In the alignment step, action is taken on the movement of at least one of the mechanisms 8 so that the movement of all the mechanisms 8 is the same and to thus maintain the orientation of the corresponding die.

Claims

Method for hot-forming a piece with a mechanical press comprising a top die (3b) and a bottom die (2b) adapted for forming a piece between both when they close on one another, and a mechanism (8) that is adapted for displacing at least one die (2b, 3b) with its movement, the method comprising a forming step in which the dies (2b, 3b) close on one another for forming a piece, a cooling step in which the dies (2b, 3b) remain closed at bottom dead center in which the piece is formed between the dies (2b, 3b), and a backward step in which the dies (2b, 3b) open up, characterized in that it further comprises a discharging step, which occurs during the cooling step, in which at least part of a fluid present in a hydraulic chamber (4) associated with the mechanism (8) is discharged from the hydraulic chamber (4), and a filling step, which occurs during the backward step, in which at least part of said discharged fluid fills the hydraulic chamber (4) again.
Method according to claim 1, wherein the dies remain closed for a specific cooling time, at least part of the fluid present in the hydraulic chamber (4) being discharged from said hydraulic chamber (4) when there is still a specific discharging time left to conclude the cooling time, the discharging time being less than the cooling time.
Method according to claim 2, wherein the discharging time is less than about 1 second.
Method according to any of claims 1 to 3, which is adapted for being implemented in a mechanical press (100) with a plurality of hydraulic chambers (4) and a mechanism (8) associated with each hydraulic chamber (4), and comprising a verification step in which the movement of the mechanisms (8) is verified while the mechanical press (100) is at bottom dead center, and an alignment step in which action is taken on the movement of a corresponding mechanism (8) if it is detected during the verification step that said mechanism (8) moves differently from the remaining mechanisms (8).