JPH10193199A - Device for protecting die of direct acting type press and method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To judge the position of load value of being rapidly stood up in the real working time, to surely detect double blanks and to prevent a die from being broken by setting one piece of work on a die before real press working, lowering a slide, pressing, setting the thickness allowable range making the slide position when the load value is stood up rapidly as the standard thickness position and storing them. SOLUTION: A load applied on a slide is detected with a machining side pressure sensor 32 in the pressurizing machining time, the slide position that this load is stood up rapidly is detected with a slide position sensor 33. These detecting signals are inputted in a controller 40 of a general computer controlling unit. The controller 40 judges the slide position as the double blanks when it exists except the thickness allowable range set in a test, and it outputs the control command to a servo valve 13 and a transfer signal outputting circuit 38. Based on this control command, the servo valve 13 switches the flow rate of the hydraulic oil and the direction, supplies it to a hydraulic cylinder 4 and drives the slide to the raising direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a die protection device and a method for a linear motion press in which a slide such as a hydraulic press is driven linearly.

[0002]

2. Description of the Related Art Conventionally, when performing press forming or cutting of a work such as a plate material in a press machine, two or more works such as a plate material are carried into one mold by a carry-in device (hereinafter, referred to as double work). Pressing or cutting two or more workpieces in this way may overload the mold and damage the mold. Therefore, in order to prevent mold breakage,
A thickness measuring device for measuring the thickness of a work such as a plate material carried into a mold has been provided. When the measured thickness of the work does not fall within the predetermined allowable width, it is determined that the work is a double blank, and the press machine is emergency stopped.

[0003]

However, in a conventional thickness measuring apparatus, it is necessary to set predetermined thickness allowable width data for measuring a double blank for each type of work. It is very troublesome and troublesome for workers. In addition, a setting error or the like is likely to occur, and the actual press work is often performed without noticing the setting error. For this reason, even if there is a double blank, it cannot be detected and the mold may be damaged.

In a conventional mechanical press or the like,
Even when a double blank is detected and the press machine is stopped in an emergency, the workpiece may be hit in the double blank state due to the influence of the slide coasting distance or the delay of the brake start time. There is also a problem of damage.

The present invention has been made in view of the above-mentioned problems, and it is easy to set data for double blank detection, and it is possible to reliably detect double blanks and prevent mold damage. It is an object of the present invention to provide a die protection device for a direct-acting press and a method thereof.

[0006]

Means for Solving the Problems, Functions and Effects In order to achieve the above-mentioned object, the invention according to claim 1 is characterized in that a slide vertically movable on an upper part of a press machine and a slide of the press machine are provided. A bolster disposed at a lower portion and opposed to the slide, a mold attached to the lower surface of the slide and an upper surface of the bolster, a hydraulic cylinder 4 for vertically moving the slide, and discharge from a hydraulic pump. And a servo valve 13 for controlling the hydraulic cylinder 4 to raise or lower the pressure by controlling the pressurized oil, detects that a plurality of workpieces have been carried into the mold, stops machining, In a die protection device for a linear motion press for protecting a die, a slide position sensor 33 for detecting a position in a height direction of the slide, and a pressurization of the hydraulic cylinder 4 when the slide is pressurized and lowered. A working side pressure sensor 32 for detecting a pressure for increasing the pressure, a rising side pressure sensor 31 for detecting a pressure for raising the hydraulic cylinder 4 when the slide is raised, and the detected pressure side pressure value and A load calculating means for calculating a load applied to the slide based on the pressure value on the rising side; The slide position when the load value input from the means 42 suddenly rises is determined by the slide position sensor 3.
The reference sheet thickness teaching means 43 stores the input slide position as the reference plate thickness position H1.
Based on the stored reference plate thickness position H1, a plate thickness allowable range for determining the double blank of the work is set and stored. The slide position when the actual load value suddenly rises from the load calculating means 42 is input from the slide position sensor 33. When the input slide position is outside the allowable thickness range, a double blank generation signal is output. Blank determination means 45 for outputting
And a servo valve output calculating means 46 for outputting a control command for the servo valve 13 for driving the hydraulic cylinder 4 in the opposite direction to the pressure processing when the double blank generation signal is inputted. And a servo valve command output means 47 for receiving and controlling the servo valve 13.

According to the first aspect of the present invention, the load applied to the slide during the press working is detected, and the slide position where this load rises sharply is detected. This slide position indicates the slide position when the slide comes into contact with the upper surface of the work carried into the mold, and indicates the thickness of the work. It is possible to determine whether or not. That is, before pressing work on an actual work,
The slide position at which the load value suddenly rises when a test run is performed on a number of actual workpieces is defined as a reference plate thickness position H1, and based on the reference plate thickness position H1, the thickness of the work is allowed in consideration of variations in the thickness of the work. Set the range and store. At the time of actual press work, it is determined whether or not the detected slide position is within the allowable thickness range. Move to As a result, the double blank can be reliably detected, and it is possible to prevent the die from being damaged by applying an overload to the die when the double blank occurs.

According to a second aspect of the present invention, in the die protecting apparatus for a direct-acting press according to the first aspect, the double blank determining means 45 receives the double blank generation signal, and the work A carry-in command output means 48 for outputting a carry-in stop command to a carry-in device for carrying in a mold is provided.

According to the second aspect of the invention, when the occurrence of double blank is detected, the carrying-in operation of the carrying-in device is stopped, so that the start-up or stop control for the carrying-in device during the interlocking operation with the carrying-in device is ensured. Therefore, the interlocking operation can be easily performed.

According to a third aspect of the present invention, there is provided the die protection device for a linear motion press according to the first aspect, wherein the hydraulic cylinder 4 and the servo valve 13 for driving the same are arranged in the same manifold block. 10.

According to the third aspect of the present invention, the hydraulic cylinder for moving the slide up and down, the servo valve for controlling the hydraulic cylinder, the pilot solenoid valve and the like are mounted on the same manifold block. Since the piping between the hydraulic devices is built in the manifold block, the control response of the hydraulic cylinder is extremely improved. As a result, the responsiveness when the slide is moved in the opposite direction at the time of double blank detection is improved, and die damage can be prevented.

According to a fourth aspect of the present invention, a lower surface of a slide disposed vertically above and below the press machine, and a lower portion of the press machine and a position facing the slide are provided. Attach a mold to the top of each bolster,
The hydraulic cylinder 4 is controlled to raise or lower the slide, detect that a plurality of workpieces have been carried into the mold, stop machining, and protect the mold with a direct-acting press mold. In the die protection method, before the actual press work, one work set in the die is processed while the slide is being pressed and lowered, and the slide position where the load applied to the slide rapidly rises is defined as a reference plate thickness position H1. After detecting and storing a thickness allowable range based on the detected reference thickness position H1, the slide position at which the load applied to the slide rapidly rises when the pressure is lowered in the actual press work is stored. A method of moving the slide in a direction opposite to that in the pressing process when it is determined that a double blank occurs when the slide position is out of the allowable thickness range. And

According to the fourth aspect of the present invention, the load applied to the slide at the time of press working is detected, and the slide position at which this load rapidly rises is detected. This slide position indicates the slide position when the slide comes into contact with the upper surface of the work carried into the mold, and indicates the thickness of the work. It is possible to determine whether or not. That is, before pressing work on an actual work,
The slide position at which the load value suddenly rises when a test run is performed on a number of actual workpieces is defined as a reference plate thickness position H1, and based on the reference plate thickness position H1, the thickness of the work is allowed in consideration of variations in the thickness of the work. Set the range and store. At the time of actual press work, it is determined whether or not the detected slide position is within the allowable thickness range. Move to As a result, the double blank can be reliably detected, and it is possible to prevent the die from being damaged by applying an overload to the die when the double blank occurs.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a die protection device for a direct-acting press according to the present invention will be described below. In the following description, a hydraulic press is taken as an example, but the present invention is not limited to this, and the present invention can be applied to other direct-acting presses such as a linear drive press combining an electric motor and a ball screw. It is.

First, a first embodiment will be described with reference to FIGS. FIG. 1 is a side sectional view of a hydraulic press according to the present invention. In the figure, C frames 7 are arranged on the left and right of the rear part of the main body of the hydraulic press 1, a bed 9 is provided below the C frame 7, and the bolster 3 is installed above the bed 9. Also, C frame 7
A hydraulic cylinder 4 is disposed as a slide driving means on the upper part of the cylinder. The hydraulic cylinder 4 includes a servo valve 13 for driving the cylinder, solenoid valves 24 and 25 for pilot hydraulic pressure of the servo valve 13, and the same metal block 10 (hereinafter referred to as a manifold block 10) forming a manifold. ), And has an integrated structure in which piping and the like connected by the manifold block 10 are eliminated. Further, a slide 2 is disposed above the C frame 7 and below the hydraulic cylinder 4 at a position facing the bolster 3 so as to be vertically movable.
The slide 2 is driven up and down by a hydraulic cylinder 4.
Lower mold (not shown) provided on the upper surface of the bolster 3
And an upper die (not shown) provided on the lower surface of the slide 2.

In the vicinity of the opening of the C frame 7,
An auxiliary frame 8 having substantially the same shape as the opening is provided. The lower end of the auxiliary frame 8 is rotatably attached to the side surface of the C frame 7 by a pin 8a. Further, a slide position sensor 33 composed of, for example, a linear sensor is disposed between the upper end side of the auxiliary frame 8 and the rear side of the slide 2.

The slide position sensor 33 has a sensor rod 33a whose axis is parallel to the moving direction of the slide 2 and is supported by the rear part of the slide 2, and is inserted into the sensor rod 33a. A sensor head 33b attached to the upper end of the auxiliary frame 8. Then, as the slide 2 moves up and down, the sensor rod 33a moves up and down with respect to the sensor head 33b, whereby the position of the slide 2 is raised from the upper surface of the bolster 3 by the position detection unit inside the sensor head 33b. It is to be detected as. The position signal of the slide 2 detected by the slide position sensor 33 is input to a controller 40 described later, and the controller 40 drives the hydraulic cylinder 4 based on the position signal to move the position of the slide 2 to a predetermined motion. Control to follow the curve.

FIG. 2 shows an example of the above-mentioned motion curve. Data defining the motion curve is previously set and stored by a motion setting switch 35 and a controller 40 described later. In the motion curve shown in the figure, first, the slide 2 is at the upper limit position U (point A in the drawing).
To the processing start position B at a predetermined high descent speed,
Next, the workpieces placed on the dies (upper die and lower die) are lowered to a lower limit position L (point C in the drawing) at a predetermined low speed while pressing. Then, after maintaining the position and the pressing force at the lower limit position L for a predetermined time (to the point D in the drawing), the ascending from the lower limit position L to the predetermined position (the point E in the drawing) at a predetermined low speed, and further to the upper limit position Ascend to U (point F in the figure) at a predetermined high ascending speed and stop, stop for a predetermined time (including time 0), and end one stroke. At the time of actual press work, this process is repeatedly performed.

FIG. 3 is a block diagram showing the hardware configuration of the mold protection device according to the present invention. Ascending side pressure sensor 3
Reference numeral 1 denotes a pressure sensor disposed in a cylinder chamber (not shown) below the hydraulic cylinder 4 (that is, on the slide side of the piston inside the hydraulic cylinder 4), and detects a pressure for raising the slide 2. I do. The processing-side pressure sensor 32 is a pressure sensor disposed in a cylinder chamber (not shown) above the hydraulic cylinder 4 (that is, on the side opposite to the slide 2 with the piston interposed therebetween). The pressure of the hydraulic cylinder 4 for processing the material is detected. The slide position sensor 33 detects the position of the slide 2 in the height direction as described above. The detection signals of these sensors are input to the controller 40.

Further, the controller 40 is provided with a motion setting switch 35 and an operation mode selection switch 36. The motion setting switch 35 is set to slide 2
The predetermined motion curve can be set, for example, to set the pressing force, the high-speed rising speed for raising or lowering the mold, the high-speed falling speed, the low-speed rising speed, or the moving speed such as the low-speed falling speed. Each of the setting switches can be set or set to a target position (for example, a pressurization start position, a lower limit position, an upper limit position, etc.) on the motion curve. These set values are stored in the controller 40 as motion data corresponding to each motion curve.
Is stored in a predetermined memory area. The operation mode selection switch 36 can select a press operation mode, and can at least select a teaching mode in which a slide position for detecting a double blank can be taught and stored. The selected mode signal is input to the controller 40.

The controller 40 is composed of a general computer control device mainly composed of a microcomputer, for example. The controller 40 receives the detection signal of each sensor and the signal from each switch, performs predetermined calculation and determination processing described later, and controls the servo valve 13 and the carry-in signal output circuit 38 based on the processing result. Output command. The servo valve 13 switches the flow rate and direction of the hydraulic oil discharged from a hydraulic pump (not shown) based on the control command and supplies the hydraulic oil to the hydraulic cylinder 4.
Control the speed and direction of expansion and contraction. Thereby, the slide 2 is controlled along a predetermined motion curve, and when it is determined that the slide is a double blank, the slide 2 is driven in a direction for protecting the mold (upward direction). Further, the carry-in signal output circuit 38 outputs a command signal to a carry-in device (not shown) for carrying the material into the mold based on the control command from the controller 40.

Next, the functional configuration of the die protection device of the hydraulic press according to the present invention will be described based on the functional configuration block diagram shown in FIG. The load detecting means 41 detects the load applied to the slide 2, and in the present embodiment, detects the load based on the pressure applied to the cylinder chamber of the hydraulic cylinder 4 that drives the slide 2. That is, the calculation is performed based on the difference between the load due to the pressure obtained from the pressure value Pp detected by the processing side pressure sensor 32 of the hydraulic cylinder 4 and the pressure value Ps detected by the rising side pressure sensor 31. The load calculating means 42 calculates a load applied to the slide 2 by receiving a reaction force from the workpiece at the time of press working, based on the detected load signal (here, the pressure signal). The load is determined by, for example, calculating the load that the pressure oil in the upper cylinder chamber pushes down from the product of the processing side pressure value Pp of the hydraulic cylinder 4 and the sectional area of the upper cylinder chamber. The load received by the lower cylinder chamber is obtained from the product of the cross-sectional area of the chamber, and the load can be calculated from the difference between the two loads. The detection of the load applied to the slide 2 is not limited to the method based on the load difference. For example, the strain of the C frame 7 of the press body is detected by a strain gauge sensor, and the load is determined based on the magnitude of the strain. It is also possible to calculate a value.

Further, the reference thickness teaching means 43 includes:
When the operation mode is the teaching mode, the position data from the slide position sensor 33 and the load value calculated by the load calculation unit 42 are input while the workpiece is actually being pressure-processed, and a load is applied to the slide. The slide position at the time of the depression is stored as a reference plate thickness position H1. Then, the allowable value setting means 44 sets and stores an allowable thickness range having a predetermined allowable width with respect to the reference thickness position H1 in consideration of the thickness variation of the work.

Here, the reference plate thickness position H1 will be described in detail with reference to FIGS. FIG. 5 shows a temporal change of the slide position near the lower limit position L of the set motion curve. At this time, it is assumed that the upper surface of the mold 51 corresponds to the slide position H0. Now, assuming that only one work 52 is inserted into the upper surface of the mold 51 when the slide 2 descends at a low speed (normal state), the upper surface of the first work 52a and the slide position H1 are set.
Assuming that two workpieces 52 are inserted into the upper surface of the mold 51 (at the time of abnormality) at time t1,
Time t between the upper surface of the second work 52b and the slide position H2.
Contact at 2 FIG. 6 shows a change in load at the time of contact between the slide 2 and the work. In the case of a normal number of works, the load suddenly rises at time t1, that is, at the slide position H1, and the number of abnormal works increases. In this case, the load suddenly rises at time t2, that is, at the slide position H2. This makes it possible to detect a double blank based on the slide position when the load suddenly rises. Therefore, the reference plate thickness teaching means 43 stores the slide position H1 when the slide 2 comes into contact with the upper surface of the work having a normal plate thickness which is not a double blank as the reference plate thickness position H1. H1 is the criterion for double blank determination.

Incidentally, the reference plate thickness position H1 is n times (n times).
Is a natural number of 2 or more).
The setting may be made based on an average value of n pieces of contact position data. Further, the allowable width of the above-described thickness allowable range may be set from the maximum value and the minimum value of the contact position at this time or from the deviation value.

When the operation mode is the production mode in which the forming and cutting press work is performed under the actual load, for example, the continuous stroke mode, the double blank determination means 45 calculates the load calculated by the load calculation means 42 during the processing. Monitor the value,
The slide position at the time when this load value suddenly increases is captured. Then, the slide position and the allowable value setting means 4 are set.
Then, when the slide position is higher than the allowable thickness range, it is determined that a double blank is abnormal, and a double blank occurrence signal is output.

The servo valve output calculating means 46
When a double blank generation signal is input from the double blank determination means 45, a speed command value and a direction control command for raising the slide 2 at a predetermined ascending speed by a predetermined distance, no matter where the slide 2 is located. Is output to the servo valve command output means 47. Further, the servo valve command output means 47 outputs an operation signal to the servo valve 13 in response to the above control command,
At a predetermined speed. Also, the carry-in command output means 48
When a double blank generation signal is input from the double blank determination means 45, the controller outputs a carry-in stop command to a carry-in device (not shown) via the carry-in signal output circuit.

Next, an example of a method for controlling the die protection device of the direct-acting press according to the present invention will be described with reference to an example of a control flowchart shown in FIG. Note that the step numbers of the respective processes are indicated by adding S. In S1, the operator switches the operation mode selection switch 36 to select the teaching mode. At this time, the controller 40 inputs the teaching mode signal (reference sheet thickness teaching means 43). Next, in S2, the worker installs the work on the mold and starts press working with an actual load. At this time, the controller 40 (reference sheet thickness teaching means 43) inputs a position signal from the slide position sensor 33, determines whether the processing has been started by a change in the slide position from the upper limit position U in the downward direction, and starts processing. Wait in S2 until you do. When processing is started, in S3 (reference plate thickness teaching means 43), a slide position at which the load value rapidly increases is detected. The load value under the actual load is calculated based on the load value (load detecting means 41), the respective pressure signals input from the ascending side pressure sensor 31 and the processing side pressure sensor 32, and (load calculating means 42). . After this,
In S4 (permissible value setting means 44), a permissible thickness range is set for the detected slide position and stored. As described above, the teaching of the allowable thickness range by the press working on the actual work is completed, and the process proceeds to S5.

Next, in S5, the operator switches the operation mode selection switch 36 to select a production mode (for example, a production mode such as a continuous mode or a safety single-stroke mode). At this time, the controller 40 inputs the corresponding mode signal (double blank determination means 45). Next, S
At 6, the operator starts press working with an actual load, and the controller 40 (double blank determining means 45) inputs a slide position signal to determine whether or not processing has started, and waits at S6 until processing starts. . When processing is started, a slide position at which the load value sharply increases is detected in S7 (double blank determination means 45). Here, the load value under the actual load is calculated based on the pressure values detected by the ascending-side pressure sensor 31 and the processing-side pressure sensor 32 as in S3.
Thereafter, in S8 (double blank determining means 45), it is determined whether or not the detected slide position is within the stored allowable thickness range.
Move to

Then, in S9 (double blank determining means 45), it is determined whether or not to continue the processing.
Returning to step 6, the above-described double blank prevention processing is performed on the next work, and if the processing is not to be continued, the flow chart processing ends. Here, the determination of processing continuation is performed, for example,
This can be performed depending on whether the operation mode selection switch 36 has been switched, or whether the slide 4 has stopped moving for a predetermined time set in the motion curve, for example, the stop time at the upper limit position.

If the detected slide position is not within the allowable thickness range in S8, a double blank generation signal is output in S10. As a result, (servo valve output calculation means 46) calculates and outputs a control command value of the servo valve 13 in the slide ascending direction, and the slide 2 ascends to protect the mold. At the same time, the (loading command output means 48) outputs a loading stop command to the loading device.
Thereafter, this control flow ends.

As described above, the actual work is pressed and the slide position where the slide contacts the upper surface of only one work is taught as the reference plate thickness position H1, and the reference plate thickness position H1 and the work position of the work are taught. The allowable thickness range is set based on the variation in the thickness. This eliminates the operator's setting mistakes and can reliably detect double blanks,
Also, the setting work becomes easy. Furthermore, when a double blank occurs, the slide is moved at a predetermined speed by a predetermined distance in a direction opposite to the direction at the time of press working, so that the mold can be prevented from being damaged by the double blank. In addition, since the carrying-in operation of the carrying-in device is stopped, the start and stop during the interlocking operation with the carrying-in device can be reliably controlled.

When driving the hydraulic cylinder,
Servo valves and their solenoid valves for pilot pressure oil are attached to the same manifold block, and piping between these hydraulic devices is provided in the manifold block.
The controllability of the hydraulic cylinder 4 is greatly improved, and therefore, it is possible to raise the slide with good responsiveness when a double blank occurs. Thus, the coasting distance of the slide is reduced, and the mold can be prevented from being damaged.

[Brief description of the drawings]

FIG. 1 is a side view of a main part of a hydraulic press according to the present invention.

FIG. 2 is an explanatory diagram of a motion curve according to the present invention.

FIG. 3 shows a hardware block diagram of a mold protection device according to the present invention.

FIG. 4 is a block diagram showing a functional configuration of a mold protection device according to the present invention.

FIG. 5 shows a temporal change diagram of a slide position for explaining a double blank detection method according to the present invention.

FIG. 6 is a time change diagram of a load value for explaining a double blank detection method according to the present invention.

FIG. 7 shows an example of a flowchart of the mold protection device according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Hydraulic press, 2 ... Slide, 3 ... Bolster, 4 ... Hydraulic cylinder, 7 ... C frame, 8 ... Auxiliary frame, 9 ...
Bed: 10: Manifold block, 13: Servo valve, 24, 25: Pilot solenoid valve, 31: Upside pressure sensor, 32: Processing side pressure sensor, 33: Slide position sensor, 33a: Sensor rod, 33b: Sensor head , 35: motion setting switch, 36: operation mode selection switch, 38: carry-in signal output circuit, 40: controller, 41: load detecting means, 42: load calculating means, 43 ...
Reference thickness teaching means, 44... Tolerance setting means, 4
5: double blank determination means, 46: servo valve output calculation means, 47: servo valve command output means, 48: carry-in command output means.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI B30B 15/26 B30B 15/26 F16P 7/00 F16P 7/00

Claims (4)

[Claims] 1. A slide disposed vertically above and below a press machine, a bolster disposed below the press machine and at a position facing the slide, and a lower surface of the slide and a bolster of the bolster. A mold attached to the upper surface, a hydraulic cylinder (4) that moves the slide up and down, and a servo that controls the hydraulic oil discharged from the hydraulic pump to switch the hydraulic cylinder (4) up or down. A valve (13), in a die protection device of a direct acting press for detecting that a plurality of works are carried into the die, stopping the processing and protecting the die, A slide position sensor (33) for detecting a position in the direction, and the hydraulic cylinder when the slide is pressurized and lowered.
(4) Processing side pressure sensor that detects the pressure for pressurizing
(32) a rising pressure sensor (31) for detecting a pressure for raising the hydraulic cylinder (4) when the slide is raised.
Load calculating means for calculating a load applied to the slide on the basis of the detected pressure side pressure value and rising side pressure value.
(42) and before the actual press work, slide one of the workpieces set in the mold by lowering the slide to pressurize, and the slide when the load value input from the load calculating means (42) suddenly rises. The reference position is input from a slide position sensor (33), and the input slide position is stored as a reference plate thickness position H1. A reference plate thickness teaching means (43). Based on the stored reference plate thickness position H1, An allowable value setting means (44) for setting and storing a thickness allowable range for judging a double blank of the work, and a load of an actual load inputted from the load calculating means (42) at the time of pressurizing and lowering of the actual press work. A double blank determination in which a slide position when the value rises sharply is input from a slide position sensor (33) and a double blank generation signal is output when the input slide position is outside the allowable thickness range. Step (45) and a servo valve output calculation for outputting a control command for a servo valve (13) for driving the hydraulic cylinder (4) in the opposite direction to the pressure processing when the double blank generation signal is input. A die protection device for a direct-acting press, comprising: a means (46); and a servo valve command output means (47) for receiving the control command and controlling the servo valve (13). 2. The die protection device for a linear motion press according to claim 1, wherein the work is carried into the die upon receiving the double blank generation signal output by the double blank determination means (45). A die protection device for a direct-acting press, further comprising a carry-in command output means (48) for outputting a carry-in stop command to the carry-in device. 3. The die protection device for a linear motion press according to claim 1, wherein the hydraulic cylinder (4), the servo valve (13) for driving the hydraulic cylinder, and the like are arranged in the same manifold block (10). A die protection device for a linear motion press, wherein the die protection device is attached to a die. 4. A mold is provided on a lower surface of a slide disposed vertically above and below a press machine, and on an upper surface of a bolster disposed below the press machine and at a position facing the slide. Attach and control the hydraulic cylinder (4) to raise or lower the slide, detect that a plurality of workpieces have been loaded into the mold, stop processing, and protect the mold. In the method of protecting a die of a direct-acting press, a single work set on the die is processed while the slide is being pressed down before the actual press work, and a slide position at which a load applied to the slide rapidly rises. Is detected as the reference plate thickness position H1, and the detected reference plate thickness position H1 is detected.
After setting and storing the thickness allowable range based on the above, at the time of pressurizing and lowering in the actual press work, the slide position at which the load applied to the slide rapidly rises is compared with the stored thickness allowable range. When the slide position is out of the allowable thickness range, it is determined that a double blank has occurred, and the slide is moved in a direction opposite to that in the press working.