JP2720120B2 - Method for molding long objects obtained by compressing powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder compression molding method for obtaining a long object, such as a guide rod or a plunger, whose axial length in a longitudinal direction is relatively long with respect to a cross-sectional diameter by compressing powder.

[0002]

2. Description of the Related Art When a long object is formed by compression molding of a powder with its axial direction (longitudinal direction) coincident with the compression direction, the compression density is reduced at an intermediate portion in the axial direction as shown in FIG.
The strength of the compact a, which is a molded product, tends to decrease. Note that reference numeral b denotes an upper punch, c denotes a lower punch, and d denotes a die. This is presumably because the compressive force is reduced in the intermediate portion by the frictional resistance between the powder particles at both ends. However, in the conventional powder molding machine, since one cycle is composed of one powder filling step and a compression step for the molding space, when the long object is compressed in the axial direction and molded, the molding space is reduced. It is inevitably deeper, and as a result, only a molded product having a low powder density in the middle part can be obtained.

Further, in a conventional molding machine, for example, as shown in FIG. 6, conductive portions (m) made of metal powder and insulating portions (s) made of ceramic powder are alternately formed in the axial direction by changing the powder. As a result, it is impossible to obtain a molded product (compact a) having partially different characteristics.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a powder compression molding method capable of obtaining a long product having no portion having a low powder density in the axial direction by compression molding.

[0005]

A powder filling step and a compression step are alternately repeated in a molding process of one cycle while extending the molding space in the axial direction after the compression step. Thus, the molded portion formed by the current compression step is sequentially connected to the molded portion formed by the previous compression step in the compression direction to form a long object.

[0006]

The compression molding operation is partially performed sequentially, so that the entire powder has a uniform powder density. By means of connecting the next molded part to the previous molded part by compression, an integral long molded product is constituted as a whole.

[0007]

FIG. 1 shows a vertical powder compression molding machine 1 (hereinafter simply referred to as a molding machine 1) used for carrying out the method of the present invention.
It is. The molding machine 1 has 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 constantly 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.

The middle machine frame 11 and the upper movable frame 12 have 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 servo motor 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 composed of 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. Is driven. 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 includes 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 have the configuration of FIG. 2, and the servo circuit 31 a of the link driving servomotor 15 and the servo circuit 3 of the first punch 3
1b and a servo circuit 31c for the second punch 4.
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 can output a movement command (L) and a torque limit command (T) to each of the servo circuits 31 (ac).

Each of the servo circuits 31 (a to c) includes a circuit 31
Although only c is specifically shown, it is basically the same as a conventional servo circuit, and includes an error register 39 (ab), a digital / analog converter (D / A converter) 40 (a to
b), speed-voltage converter (F / V converter) 41, compensator 4
2. It includes a torque limit circuit 43, a D / A converter 44, a compensator 45, and a power amplifier 46.

When a movement command composed of a pulse train, which is a movement amount per unit time, is input from the CNC 30 via the servo interface 35, the movement command is detected by the encoder Pc (Pa, Pb...). The difference between the actual movement amount of the servo motor 26 and the actual movement amount of the servo motor 26 is calculated by an error register 39 (a to c... Convert to voltage. Further, in this circuit, speed feedback is performed in order to improve responsiveness, and a signal from the encoder Pc is converted to an F / V converter 4.
Then, the voltage corresponding to the actual speed of the servo motor 26 is subtracted from the speed command value, and the difference between the speed command value and the error between the command speed and the actual speed is amplified by the corrector 42 to obtain a torque command. Output.

This torque command is output as a voltage corresponding to the current value flowing to the armature of the servomotor 26. In response to the 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 47 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.

The method of the present invention is executed by the following operation of the molding machine 1. 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. 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 lower servo motor 26 is driven, the screw nut mechanism 25 is operated via the transmission mechanism 27, the lower movable frame 13 is lowered by the set amount h1 (FIG. 3A), and the molding space 48 (FIG. 1) is It is formed. And servo motor 2
At 6 the brake is activated. The molding space 48 is a part of the green compact a to be actually obtained as a molded product in the axial direction, and is referred to as a molding space 48a. The air actuator 7 is driven, the feeder 8 reciprocates to the die 2, and the molding space 48a is filled with molding powder (FIG. 3).
I). The link drive servomotor 15 is driven to operate the crank mechanism 14, and the first punch 3 descends to the set position (FIG. 3B). The upper servomotor 21 is braked. As a result, the powder in the molding space 48a is compressed, and a partial green compact a1 (molded portion) is obtained.

When compressing the powder, there are cases where the size of the green compact a to be obtained as a molded product is emphasized and the case where the powder density is emphasized. The position control is performed by setting the movement amount of the first punch 3 as a set value. When importance is placed on the powder density, the servo circuit 31a of the servo motor 15
A torque limit command corresponding to the set compression force is issued from the NC 30, and compression is performed using the output of the servo motor 15, that is, the compression force as a set value. In this case, compression ends 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 output is output from the CNC 30 using the detection output of the pressure sensor 28 (or 29) for detecting the compression force by the first punch 3. In some cases, the value of the torque limit command itself is feedback-controlled. In FIGS. 3 and 4, the pressure sensors 28 and 29 are shown in FIG.
, But should be shown in every figure.

In the above, the first powder filling step and the compression step are completed. Next, the CNC 30 issues the same movement command to the upper servo motor 21 and the lower servo motor 26, and synchronously moves the first punch 3 and the second punch 4 downward by h2. That is, the green compact a1, which was previously compression-molded, is moved downward by h2 (see FIG. 3).
C). Then, the CNC 30 releases the link operation between the upper servomotor 21 and the lower servomotor 26, activates the brake on the lower servomotor 26 to fix its position, and then drives the upper servomotor 26 to drive the first punch 3 out. Retreat to the upper home position. This allows
At the location of the die 2, a new molding space 48b having the bottom surface of the previous compact a1 is formed (FIG. 3D). That is,
The previous molding space 48a is extended in the direction of the compression axis z. The compression axis z is the axial direction (longitudinal direction) of the final molded product
Is the same as

Next, as in the previous case, the new molding space 48b is filled with the powder by the feeder 8, and is similarly compression molded. The new green compact a2 is the previous green compact a
Since the powder filled in the upper part of 1 is directly compressed and formed, it is integrated with the green compact a1. The depth h of the extended molding space 48 varies depending on the characteristics of the powder to be supplied and the magnitude of the compression force set at each stage. When the depth h2 of the extended molding space 48b is different from the depth h1 of the previous molding space 48a, the difference is absorbed by driving the upper servo motor 21. By doing so, the operating angle (degree of expansion) of the link mechanism 14 caused by the difference in the depth does not need to be changed, and the optimal operating angle can be maintained for compression as in the previous case. When the change in the operating angle can be tolerated, the degree of elongation of the link mechanism 14 by the link driving servomotor 15 changes without driving the upper servomotor 21, and the above difference is absorbed.

Next, as in the case of FIG. 3C, the green compacts a1 and a2 are moved downward by h3 as they are sandwiched between the first and second punches 3 and 4, and then the first green compacts a1 and a2 are pressed. Punch 3 retreats to the home position. Thereby, the green compact a2
A molding space 48c is further formed above the molding space 48 (a,
It is formed by extending b) (FIG. 4E). In the same manner, the extended molding space 48c is filled with powder in the subsequent powder filling step, and then the compact a3 is formed integrally by the compression step.
a3 is moved downward to extend the molding space 48 (ac) (FIG. 4f). However, the extendable range is mainly limited by the depth of the die 2.

In this way, the powder filling step and the compression step are repeated while extending the molding space after the compression step, and the moldings (the compacts a1 to an
After one cycle of molding is completed, the upper punch 3 is retracted to the home position at the timing when the molding space 48 is extended, and then the punch surface of the lower punch 4 is moved to the upper surface of the die 2. The molded product is extruded onto the upper surface of the die plate 6. At this time, the upper punch 3 may be moved synchronously with the lower punch 4. The long green compact a, which is a molded product, is sufficiently compressed at each stage, so that there is little difference in the powder density as a whole and the strength is high.

According to this molding method, different kinds of powders are successively compression-molded and integrated to easily obtain a molded article comprising portions having different characteristics in the axial direction. That is, the powder to be filled into the molding space 48 may be changed to a necessary powder at each stage. However, for efficient molding, it is preferable to prepare the feeder 8 for each type of powder.

The above is the embodiment. As an apparatus for carrying out the method of the present invention, one having a crank mechanism and a screw nut mechanism driven by a servomotor has been described. However, the method of the present invention is not limited by the structure of such a drive source and apparatus. However, in the case of using a servomotor as in the embodiment, it is easy to perform fine control on the position of the punch and the compression force, and the method of the present invention can be carried out better. Also,
The extension of the molding space can also be performed by moving the die plate 6 with respect to the punch.

[0024]

As a molded product, a long green compact having a uniform powder density and high strength even in the axial middle portion can be obtained. Further, it is possible to obtain a green compact having partially different characteristics in the axial direction.

[Brief description of the drawings]

FIG. 1 is a schematic front view.

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

FIG. 3 is a diagram showing the order of operation.

FIG. 4 is a diagram showing the order of operation.

FIG. 5 is a front view for explaining a conventional example.

FIG. 6 is a front view for explaining a conventional example.

[Explanation of symbols]

2 Die 3 First punch 4 Second punch a Green compact 48 Molding space 48 (a, b ...) Extended molding space

Continued on front page (72) Inventor Takayuki Taira 3580 Kobaba, Oshino-mura, Oshino-mura, Minamitsuru-gun, Yamanashi Pref. Address FANUC CORPORATION Product Development Laboratory (56) References JP-A-49-37807 (JP, A) JP-A-58-215299 (JP, A)

Claims (1)

(57) [Claims] 1. A method of compressing and molding a powder filled in a molding space with a punch, comprising a powder filling step and a compression step in one cycle of a molding step, and extending the molding space in the axial direction after the compression step. , By alternately connecting the molded part formed by the current compression step to the molded part formed by the previous compression step sequentially in the compression direction. Molding method.