JP2662913B2 - Compression molding machine and compression molding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compression molding machine and a compression molding method for compressing and molding various metal powders, ceramic powders and the like.

[0002]

2. Description of the Related Art In a conventional powder compression molding machine, a punch is driven by a simple mechanism such as a hydraulic ram or a combination of a flywheel and a crank. Compressed at once and extracted at once. However, a large stress is acting internally on the green compact a (FIG. 5) as a molded product after compression, and when this is pulled out from the die b at a stroke, the above-mentioned stress is generated as shown in FIG. May be opened at once and cracks may occur in the compact a which is a molded product. Symbol c indicates a die plate, and symbol d indicates a punch.

It is apparent that in order to prevent this, the stress of the green compact a should be released gradually. However, conventionally, there has been no compression molding machine capable of appropriately performing such curing after compression molding. The magnitude of pressurization during curing depends on the characteristics and dimensions of the powder to be molded, and a molding machine that can cope with such changes is required.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a molding method in which cracks are less likely to occur in a compact after molding and a compression molding machine capable of executing the method.

[0005]

Means for Solving the Problems [Molding machine] A first punch and a second punch are provided which move with their punch surfaces facing each other.

[0006] Servo motors and control devices for driving the first and second punches are provided. The control device is
Means for moving the punch surfaces of the first punch and the second punch to a set position, and making the moving speed of the second punch greater than the moving speed of the first punch in the process of extruding the green compact;
A means for curing the green compact is provided for maintaining the compressive force of the first and second punches at the set pressurized value. [Molding method] After the compacting, the compact is removed from the die while pressurizing while the compact is sandwiched between the first punch and the second punch.

[0007]

The first and second punches sandwich the green compact from above and below by the curing means and pressurize the green compact when the green compact is extracted from the die.

[0008]

FIG. 1 shows a vertical compression molding machine 1 (hereinafter simply referred to as a molding machine) having a die 2, a first punch 3,
The second punch 4 is coaxially arranged with one vertical compression axis z set in the molding machine 1 as an axis. The die 2 is exchangeably attached to the center of a die plate 6 supported by a base 5 and has a vertically penetrated hole. A feeder 8 that reciprocates between a home position shown in the drawing and a position of the die 2 by an air actuator 7 is disposed on the upper surface of the die plate 6. Although not shown, powder for molding is always supplied to the feeder 8.

On the base 5, two or four vertical guide bars 9, 9 are erected in parallel, and the upper ends thereof are connected by an upper machine frame 10. And the guide bars 9, 9
Between the base 5 and the upper machine frame 10,
1, an upper movable frame 12 and a lower movable frame 13 are slidably mounted vertically in parallel with each other, and the upper machine frame 10 and the middle machine frame 11 are connected by a crank mechanism 14. Is driven by a link drive servomotor 15 attached to the motor. Drive side shaft 1 of crank mechanism 14
6. The driven side shaft 17 is disposed along the compression axis z.

[0010] The medium machine frame 11 and the upper movable frame 12 are provided with a screw / nut mechanism 20 comprising a ball screw 18 and a ball nut 19.
The mechanism 20 is driven by rotating the ball screw 18 by the upper servomotor 21 attached to the middle machine frame 11. Reference numeral 22 denotes a transmission mechanism for that purpose, which is composed of a pulley and a timing belt. Similarly, the lower movable frame 13 and the base 5 are connected by a screw / nut mechanism 25 including a ball screw 24 and a ball nut 23, and the mechanism 25 is rotated by a lower servomotor 26 attached to the base 5. It is driven by being moved. Reference numeral 27 is the transmission mechanism. The first punch 3 is provided on the lower surface of the upper movable frame 12, and the second punch 4 is provided on the upper surface of the lower movable frame 13, respectively.
29 is fixed.

The molding machine 1 is provided with a numerical controller (CNC) 30 with a built-in computer and a controller 32 having a servo amplifier 31.
5, upper servo motor 21, lower servo motor 26, air actuator 7, and upper and lower pressure sensors 2
8, 29 are connected. The CNC 30 and the servo amplifier 31 (means for moving the punch surfaces of the first punch 3 and the second punch 4 to the set positions) have the configuration shown in FIG. 2, and the servo circuit 31a of the link drive servomotor 15 and the servo circuit 31a of the first punch 3 A servo circuit 31b and a servo circuit 31c for the second punch 4 are provided. The above-mentioned servo motors each include encoders Pa, Pb, and Pc, and each include a brake.

The CNC 30 includes a central processing unit (CPU) 3
3, a memory 34, a servo interface 35, a manual input device 36, an input / output circuit (DI / DO) 37, etc., and are interconnected by a bus 38. The memory 34 includes a ROM storing a control program of the molding machine 1, a RAM used for temporarily storing data in arithmetic processing, and the like, and a memory storing a macro program and various set values. The servo interface 35 outputs a movement command (L) and a torque limit command (T) to each of the servo circuits 31 (ac), and outputs a speed addition command (F) to the second punch servo circuit 31c. I can do it. Input / output circuit (D
A display device (CRT) and a printer are connected to the I / DO) 37 so that the status of the molding operation and input data can be visually confirmed.

Each of the servo circuits 31 (a to c) includes a circuit 31
c is specifically shown, except that the speed addition command (F) is transmitted from the servo interface 35 of the CNC 30 via the digital-to-analog converter 47 in this circuit 31c. To c) are basically the same as the conventional servo circuit, and include an error register 39 (ab), a digital / analog converter (D / A converter) 40 (ab), and a speed / voltage converter (F / B). V converter)
41, a corrector 42, a torque limit circuit 43, a D / A converter 44, a corrector 45, and a power amplifier 46.

From the CNC 30 to the servo interface 3
When a movement command composed of a pulse train, which is a movement amount per unit time, is input via the control unit 5, the actual movement amount of the servo motor 26 detected by the movement command and the encoder Pc (Pa, Pb... The difference with the error register 39
(The same applies to the basic parts described above.) The D / A converter 40 converts this into an analog quantity voltage as a speed command value. Furthermore, in this circuit, speed feedback is performed to improve the response,
The signal from the encoder Pc is converted into a voltage by the F / V converter 41, and a voltage corresponding to the actual speed of the servo motor 26 is subtracted from the above speed command value, and the difference between the speed command value and the error between the command speed and the actual speed is obtained. Is amplified by the corrector 42 and output as a torque command.

This torque command is output as a voltage corresponding to the current value flowing to the armature of the servomotor 26. In response to this torque command, a torque limit circuit 43 for limiting the output torque of the servomotor 26 is used. The servo motor 26 is provided to further improve the response to the output of the torque limit circuit 43.
The voltage corresponding to the armature current from the current detector 48 for detecting the armature current is fed back, and the difference between the torque command and the feedback signal of the armature current is corrected by the corrector 4.
5, and is amplified by the power amplifier 46 to drive and control the servo motor 26. The D / A converter 44 is a CNC
This is for converting the torque limit command value from 30 into an analog signal and applying it to the torque limit circuit 43. Then, in addition to the above basic configuration, the servo circuit 31c converts the speed addition command (F) of the CNC 30 into a voltage corresponding to the speed to be added by the D / A converter 47, and performs the above D / A conversion. A circuit is added between the compensator 40 and the compensator 42, that is, a circuit for applying to the speed command position (analog voltage).

A first example of the operation of the molding machine 1 will be described first. It is assumed that necessary molding programs and data have been input. The transmission and reception and processing of data and signals inside the CNC 30 are not particularly different from those in the related art, so only the operation will be described. The operation consists of a compression step followed by a withdrawal step. At the beginning of the operation, the first punch 3 is at a position retracted above the die plate 6, and the upper movable frame 12 is at a position spaced from the middle machine frame 11 by the extension of the screw nut mechanism 20. I have. The second punch 4 has its punch surface aligned with the upper surface of the die plate 6. This position is the home position of the first punch 3 and the second punch 4.
The feeder 8 is also at the home position retracted from the punch position.

[Compression Step] The lower servo motor 26 is driven, the screw nut mechanism 25 is operated via the transmission mechanism 27, and the lower movable frame 13 is lowered by a set amount. Thereby, after the molding space 49 is formed, the servo motor 26
The brake is activated. The air actuator 7 is driven, the feeder 8 reciprocates to the die 2, and the molding space 49 is filled with molding powder. The link drive servomotor 15 is driven to operate the crank mechanism 14, and the first punch 3 descends to the set position. The upper servomotor 21 is braked. Thereby, the powder in the molding space 49 is compressed, and the green compact a is obtained. Other methods of compression include the crank mechanism 14
The powder may be compressed by pushing the lower punch 4 by driving the servo motor 26 in the direction opposite to the direction in which the upper punch 3 pushed by the button is pushed.

When compressing the powder, there are cases where the dimensions of the compact a are emphasized and cases where the powder density is emphasized.
When importance is placed on the size, the position control is performed with the movement amount of the first punch 3 as the set value as described above. When importance is placed on the powder density, the servo motor 1 is used when the first punch 3 descends.
A torque limit command corresponding to the set compression force is issued from the CNC 30 to the servo circuit 31a of No. 5, and compression is performed using the output of the servo motor 15, that is, the compression force as a set value. In this case, the end of compression is, for example, after a predetermined time has elapsed after the limit value is reached. Further, in order to make the actual compression force in the powder portion coincide with the set compression force, the detection output of the pressure sensor 28 (or 29) for detecting the compression force by the first punch 3 is used to make the CN.
The value of the torque limit command output from C30 may be feedback-controlled.

[Extraction Step] When the compression step is completed, the brake is applied to the link driving servomotor 15 to fix the middle machine frame 11 at that position. Next, the brake of the servo motor 26 with respect to the lower movable frame 13 is released, and the CNC 30 sends the second signal to the servo circuit 31c.
An upward movement command having a position (home position) where the punch surface of the punch 4 coincides with the upper surface of the die plate 6 as a target position, a speed addition command (F) and a torque limit command (T) based on set values are output. And the upper movable frame 1
The brake of the servo motor 21 for 2 is released, and the same movement command (upward) as for the servo circuit 31c is issued to the servo circuit 31b. But,
There is no speed adding circuit in the servo circuit 31b, and no torque limit command is output.

In this state, when the lower servo motor 26 and the upper servo motor 21 are driven, the rising movement speed of the second punch 4 is higher than the rising movement speed of the first punch 3 by the speed addition command (F). From the second punch 4
And rises in such a manner that the first punch 3 is pushed up. Since the torque of the upper servo motor 21 on the first punch 3 side is not limited, the torque of the lower servo motor 26 on the second punch 4 side is limited to the torque limit value (T). The punch 3 is not moved by being pushed by the second punch 4, and after all, the green compact a sandwiched between the second punch 4 and the first punch 4 is pressurized with a pressure corresponding to the torque limit value (T). While moving at the set speed (movement speed of the first punch 3). In this case, the magnitude of the torque limit value (T) (that is, pressurization) and the magnitude of the ascending speed (set speed determined by the pulse distribution speed) differ depending on the characteristics of the powder to be molded and the magnitude of the compressive force.

The upward movement of the first punch 3 and the second punch 4 stops when the punch surface of the second punch 4 coincides with the upper surface of the die plate 6. That is, the green compact a is slowly extracted from the molding space 49 while being pressurized. The speed addition commanding means, the torque limit commanding means and the related structure constitute a green compact curing means. When the extraction process is completed, the link operation between the first punch 3 and the second punch 4 is released. A brake is applied to the lower servo motor 26, a movement command for returning the first punch 3 to the home position further is output to the upper servo motor 21, and the first punch 3 retreats above the die plate 6.
As described above, the compact a after molding is extracted from the upper surface of the die plate 6, and the first punch 3 and the second punch 4 return to their home position positions, respectively, and return to the initial state. This operation example can be used even when the first punch 3 and the second punch 4 are not in a vertical positional relationship.

A second example of the operation will be described. In this example, the first punch 3 and the second punch 4 have a vertical positional relationship,
The weight of the first punch 3, that is, the portion that moves together with the first punch 3 in the extraction process (the upper movable frame 12,
The weight of the part of the screw nut mechanism) affects the pressing force on the green compact a. Therefore, the above-mentioned weight must be taken into consideration for the operation of the molding machine 1.

That is, if the pressurizing force applied by the above-mentioned weight (gravity) is G and the set pressurizing force is Ps, when Ps ≦ G, the upper servo motor 21 urges the first punch 3 upward to reduce the gravity. In the case of Ps> G, it is necessary to urge the first punch 3 downward to energize the pressurized G by gravity.

In order to facilitate the following description of the operation, an operation in the case where the influence of gravity is ignored will be described here. When a predetermined torque limit command is output to the upper servomotor 21 (no movement command is issued, that is, assuming 0), the lower servomotor 26 is driven without torque limitation to raise the second punch 4 at a predetermined speed. The upper servo motor 21 is pushed up by the lower servo motor 26 while exerting a braking force corresponding to the commanded torque limit.

This is for the following reason. When the upper servomotor 21 is pushed up by the lower servomotor 26, a position deviation occurs in an error register in the servo circuit 31b of the upper servomotor 21, and a speed command voltage corresponding to the generated position deviation is generated. The sign of this speed command voltage is the same as the sign of the speed command voltage commanded when driving the upper servomotor 21 downward.

On the other hand, since the upper servomotor 21 is rotated upward, the sign of the speed feedback voltage generated by the F / V converter 41 is a sign corresponding to the upward rotation of the upper servomotor 21, and It is the opposite of the sign of the speed command voltage. Therefore, the sign of the torque command voltage obtained from the difference between the speed command voltage and the speed feedback voltage is
Is the same as the sign of the torque command voltage generated when the motor is driven downward. The torque command voltage is limited by a torque limit command issued to the upper servomotor 21.

Normally, the gain for converting the position deviation into a speed command voltage and the gain for converting the difference between the speed command voltage and the speed feedback voltage into a torque command voltage are set to sufficiently large values, respectively. Even if a small positional deviation occurs, a large torque command voltage is generated. Therefore, when the upper servomotor 21 is pushed up by the lower servomotor 26 and a position deviation occurs, a large torque command voltage for driving the upper servomotor 21 downward is generated. However, since this torque command voltage is higher than the torque limit command issued to the upper servomotor 21, a torque command of the same magnitude as the torque limit command and driven downward is applied to the upper servomotor 21 after all. You.

With the above operation, the upper servo motor 2
1 issues a torque limit command and the lower servo motor 26
When the upper servomotor 21 is pushed up, the brake servo (motor pressure) rises while generating a braking force (pressurization) corresponding to the torque limit command.

In the operation, necessary molding programs and data are input as described above. The data includes the weight (G) relating to the first punch 3 previously obtained by the measurement. The compression step is not particularly different from the case of the first example, and will not be described.

[Extraction Step] The CPU 33 of the CNC 30 calculates the difference (G-Ps) between the own weight G of the first punch 3 and the set pressurizing force Ps, and calculates a torque limit command (T) corresponding to the absolute value of the difference. This is applied to the torque limit circuit 43 of the circuit 31b. The CPU 33 determines whether the difference (G-Ps) is positive or negative.
A sufficiently large movement command and a torque limit command (T) having a sign for driving the upper servomotor 21 of the punch 3 upward are output, and in the case of a negative value, only the torque limit command (T) is set. To the servo circuit 31c relating to the second punch 4, only a movement command targeting a position where the punch surface of the second punch 4 matches the upper surface of the die plate 6 is output, and the torque is not limited.

Therefore, when (G−Ps) ≧ 0 (FIG. 3A), the upper servo motor 21 outputs a sufficiently large movement command and a torque limit command (T) having a sign for driving upward. Therefore, a torque command voltage having a sign for driving the upper servo motor 21 upward is generated. Since this torque command voltage is usually higher than the torque limit command, the torque command actually applied to the upper servomotor 21 has the same value as the torque limit command (T). In this way, the upper servomotor 21 is driven upward while generating a torque as the torque limit command (T).

In this way, the upper servomotor 21 operates in the direction of lifting the upper movable frame 12, and the pressure on the green compact a is always (G-Ps) from the pressurized G due to the weight of the first punch 3. The reduced set preload Ps [= G- (GP
s)]. By driving the upper servo motor 21 upward while generating a predetermined torque in this way, the upward force generated by the upper servo motor 21 is subtracted from the pressurized force G due to gravity, and is smaller than the pressurized force G due to gravity. Generates pressurization and generates the first punch 3
After that, the green compact a sandwiched between the first punch 4 and the second punch 4 is moved upward while being pressurized at the set pressurizing pressure Ps.

When the second punch 4 reaches a position corresponding to the upper surface of the die plate 6 (FIG. 4), the servomotor 21 is stopped and the brake is applied. Withdrawal process is completed,
The torque limit command for the upper servomotor 21 is released. In the above, (GP
The calculation of s) and its positive / negative determination means, torque limit command means and its related structure serve as green compact curing means. A movement command for returning to the home position is further output to the first punch 3. Thus, the green compact a after the compression molding is extracted from the molding space 49 while receiving the pressurization. In the above, the first punch 3 can be raised by applying a speed command voltage (a circuit corresponding to the D / A converter 47 in the servo circuit 31c is required) to the servo circuit 31b of the upper servo motor 21. It is.

When (G-Ps) <0 (FIG. 3)
B) When the second punch 4 rises without being limited by the torque value, the first punch 3 is pushed up, and the first punch 3 is disengaged, as in the case where the influence of the pressurization G due to the gravity is ignored. A torque for moving the punch 3 downward is generated. However, the torque is given by (Ps-
G). Therefore, during the extraction process,
The green compact a is pressurized at the set pressurization Ps [= G + (Ps−G)].

When the second punch 4 reaches a position corresponding to the upper surface of the die plate 6 (FIG. 4), the servo motor 21
Stops and brakes are applied. The extraction process is completed, and the torque limit command for the first punch 3 is released. Then, similarly to the above, a movement command for returning to the home position is output to the first punch 3. Thus, the green compact a after the compression molding is extracted from the molding space 49 while receiving the pressurization.

As described above, the first and second examples of operation are both
A method in which a molding space is formed by a die, a first punch, and a second punch, and the powder filled therein is compressed to obtain a green compact, wherein the powder is compressed between the first punch and the second punch. And
After the compression is completed, a method of extracting the green compact from the die while pressurizing the green compact while holding the green compact between the first punch and the second punch is performed.

It is to be noted that the pressurization in the extraction step can be feedback-controlled using the detection output of the pressure sensor 28 (or 29). In this case, as an example, while the upper servomotor 21 is pushed up by the lower servomotor 26, the detection output of the pressure sensor 28 is set to the set preload Ps.
The magnitude and direction of the torque command applied to the upper servomotor 21 are controlled so as to coincide with the above. Operate either the move command or the speed command voltage (can also be used together) to control the magnitude of the torque command. Also, operate either the move command or the speed command voltage (can also be used together) to control the torque command. Control the sign of

The above is an embodiment, and the method of pressurizing when extracting the green compact may be by other means. In the embodiment, the case where the green compact a is withdrawn upward is described. However, in the configuration according to the first aspect, it is also easy to adopt a method of withdrawing downward. further,
In the first and second examples, the first punch 3 is withdrawn by the upper servo motor 21 by applying the pressurized force by the respective control methods, and the green compact a is extracted. However, the upper servo motor 21 is stopped. The upper punch 3 may be driven by the link driving servomotor 15, and the green compact a may be extracted while pressurizing by the respective control methods.

[0039]

According to the present invention, after the compression molding, the green compact is withdrawn under a pressurized state, and the number of accidents such as cracks in the green compact is reduced.

[Brief description of the drawings]

FIG. 1 is a front view showing a mechanism.

FIG. 2 is a block diagram of a control device.

FIG. 3 is a front view of a main part in a cross section.

FIG. 4 is a front view of a main part in a cross section.

FIG. 5 is a front view of a main part in a cross section (conventional example).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Compression molding machine 2 Die 3 1st punch 4 2nd punch 6 Die plate 12 Upper movable frame 13 Lower movable frame 15 Link drive servo motor 20 Screw nut mechanism 21 Upper servo motor 25 Screw nut mechanism 26 Lower servo motor 28, 29 Pressure sensor 32 Controller 49 Molding space

Continued on the front page (72) Inventor Takayuki Taira 3580 Kobaba, Oshino-mura, Oshino-mura, Minamitsuru-gun, Yamanashi Prefecture Inside the Product Development Laboratory, FANUC Co., Ltd. Address FANUC CORPORATION Product Development Laboratory

Claims (4)

(57) [Claims] 1. A first punch and a second punch, each of which moves with a punch surface facing each other, and a servomotor and a control device for driving the first and second punches, respectively, wherein the first punch and the second punch are punched. Means for moving the surface to the set position, and a pressure for increasing the moving speed of the second punch relative to the first punch and maintaining the compressive force of the first and second punches at the set pressurized value in the process of extracting the green compact A compression molding machine provided with powder curing means. 2. A curing means for applying a speed addition command to a speed command position in a servo circuit of a servo motor for moving a second punch, and a torque limit command corresponding to a set pressurization value to a torque command position of the servo circuit. The compression molding machine according to claim 1, wherein the compression molding is performed. 3. The curing means corresponds to a torque command position in a servo circuit of a servomotor that moves an upper first punch, and corresponds to an absolute value of a difference (G-Ps) between a weight G of the upper punch and a set applied pressure Ps. A torque limit value to be applied, and an upward movement command is output when the difference is positive, and the movement command is set to 0 when the difference is negative. 2. The compression molding machine according to 1. 4. A method of forming a molding space with a die, a first punch and a second punch, and compressing a powder filled therein to obtain a green compact, wherein a compact is formed between the first punch and the second punch. A compression molding method characterized in that, after the compression is completed, the compact is extracted from the die while pressurizing the compact while holding the compact between the first punch and the second punch.