JP3279446B2 - Injection molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention enables gas injection molding, which is a kind of hollow injection molding, in which molten resin is injected into a cavity of a mold and high-pressure gas is injected into the resin in the cavity. It relates to an injection molding machine.

[0002]

2. Description of the Related Art Gas injection molding in which a molten resin is injected into a cavity of a mold and an inert gas such as a high-pressure nitrogen gas is injected into the molten resin before the molten resin in the cavity is solidified, A holding pressure is applied to the resin from inside the resin,
Since the front side of the resin is pressed against the inner wall of the cavity,
Good products without sink marks and the like can be molded, and the weight of molded products (products) can be reduced. In rare cases, the amount of gas injected into the resin may be several tens of percent or more of the volume of the molded product, but is usually 10% or less of the volume of the molded product. The gas injected therein is discharged from the molded article.

[0003] The gas pressure injected into the molten resin is 200
Sometimes reaching ~300kg / cm ^2, Therefore conventionally, once stored high pressure gas to a high pressure gas tank, to take a method to release the high pressure gas from the high-pressure gas tank, was common. For example, in Japanese Patent Application Laid-Open No. 6-321431, a hydraulically driven booster compressor is driven by a hydraulic drive source of an injection molding machine, and the gas increased in pressure by the compressor is stored in a high-pressure tank.

Further, Japanese Patent Application Laid-Open No. 63-139716,
In Japanese Patent Application Laid-Open No. 1-128814, gas from a tank is compressed and increased in pressure by a compressor, and this is injected into resin through a metering cylinder.

[0005]

When the high-pressure gas tank discharges high-pressure gas, the high-pressure gas tank is bulky, and the relatively large high-pressure gas tank is subject to various legal regulations. There was a problem that was troublesome. In addition, if relatively large high-pressure gas tanks are installed near individual injection molding machines, the equipment becomes larger,
There was also a problem that the space factor was bad. For this reason, it is conceivable to use a very small-capacity high-pressure gas tank. However, in this case, when releasing gas for each shot,
From the beginning of gas release to the end of gas release, the gas pressure gradually decreases, and non-defective molding cannot be performed. (What is necessary is that the resin is very soft at the beginning of gas release and the resistance from the resin is small, but the resin solidifies. As the resistance increases, the resistance from the resin increases and a large gas pressure is required.)

Further, in the case of employing a method of compressing and increasing the pressure of gas from a tank by a compressor, it is necessary to use a large and expensive centrifugal type or axial type compressor as an attempt to increase the pressure of the gas at once. For this reason, the equipment becomes large, and when the compressor is installed near each injection molding machine, there arises a problem that the space factor is deteriorated. For this reason, it is conceivable to install a large compressor that also serves as a plurality of injection molding machines in a place away from the group of injection molding machines.However, this increases the length of the air piping and causes problems such as safety. In addition, pressure loss due to the length of the pipe also poses a problem.

In the above-mentioned JP-A-63-139716 and JP-A-1-128814, a metering cylinder (metering piston device) is used to keep the amount of gas injected into the resin constant. The dispensing cylinder is provided with a pressure increasing function to assist the compressor. However, such a configuration requires a drive source for each of the compressor and the dispensing cylinder, and thus has a problem in that the number of parts increases and the cost increases.

Further, in order to keep the amount of gas injected into the resin constant, Japanese Patent Application Laid-Open No. 63-139716, Japanese Patent Application Laid-Open No. 1-128814, and Japanese Patent Publication No.
In the publication No. 171, a metering cylinder (metering piston device) or a hydraulic ram having a variable capacity chamber is used. In these conventional techniques, gas is injected into the resin by the metering cylinder or the hydraulic ram. No consideration was given to the pressure control at the time.

The present invention has been made in view of the above points,
An object of the present invention is to provide a high-pressure gas supply device that can be relatively compactly installed near an injection molding machine and that can be reduced in cost.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention enables gas injection molding by injecting a molten resin into a cavity of a mold and pressing a high-pressure gas into the resin in the cavity. An injection molding machine is provided with a gas pressure raising mechanism by a gas compression cylinder, which pressurizes a gas from a source of an inert gas by a driving force of an electric servomotor. And the gas pressure raising mechanism is
Baud for converting the rotation of the electric servomotor into linear motion
Screw mechanism and the gas from the source of the inert gas.
Piston driven by the ball screw mechanism
Two primary gases side-by-side, which pressurize the gas by the body
The compression cylinder and the two first gas compression cylinders
When placed in parallel with the first gas compression cylinder,
The two first gas compression cylinders respectively
Pressurized gas is introduced, and the ball screw mechanism
The piston body is driven to move gas into the cavity.
One second gas which is pressurized to a pressure for injecting into the resin in the inside
Compression cylinder and the piston of this second gas compression cylinder.
Ball screw of the ball screw mechanism connected to the tongue body
And the piston bodies of the two first gas compression cylinders
The two shaft-shaped connecting members connected to each other are
A connection member connected to a body, the first gas pressure
During the compression operation by the compression cylinder and the second gas compression system.
The time of the compression operation by the Linda means that the electric servo motor
It is configured such that the rotation direction can be switched.

[0011]

The gas pressure raising mechanism includes a rotation → linear motion conversion mechanism for converting the rotation of the electric servomotor into a linear motion, a first gas compression cylinder, and a second gas compression cylinder. The compression cylinder introduces gas from a source of inert gas, and pressurizes the gas with a piston driven by a rotation-to-linear motion conversion mechanism. At this time, the electric servomotor rotates in the first direction. Further, the second gas compression cylinder introduces the gas pressurized by the first gas compression cylinder and pressurizes the gas into the resin in the cavity by the piston body driven by the rotation → linear motion conversion mechanism. Boost up to At this time, the electric servomotor rotates in the second direction opposite to the previous direction.

Accordingly, since the gas is pressurized in two stages by a single electric servomotor, the required high pressure can be easily obtained, and the gas pressurizing mechanism can be made compact and inexpensive. Therefore, even if a gas pressure increasing mechanism is attached to each injection molding machine, the space factor is improved, and the layout in the factory becomes easy. In addition, a variable-capacity gas compression cylinder makes it possible to obtain a necessary and sufficient amount of high-pressure gas for each shot, so that high-pressure gas can be small in volume and legal regulations are reduced, making management and operation simple. Becomes

Further, since the electric servomotor is used as the drive source for boosting the pressure, pressure feedback control can be easily performed, and the gas pressure during the gas pressure injection process into the resin can be feedback-controlled to a value in accordance with the set conditions. Therefore, the pressure control by gas pressure can be performed precisely, which greatly contributes to the molding of good products.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments. FIG. 1 is an explanatory view showing an outline of a high-pressure gas supply device of an injection molding machine according to one embodiment of the present invention. In the figure, 1 is an air intake, 2 is a filter, 3 is a mist separator, 4 and 5 are pressure reducing valves, 6 is a nitrogen gas generator (nitrogen gas generator), 7 is a flow meter, 8 is a throttle valve, 9,
10 is a check valve, 11 is a gas pressure raising mechanism, 12 is an electric servomotor, 13, 14, 15 are pressure gauges, 16 and 17 are switching control valves controlled by air, 18 and 19 are electromagnetic control valves, and 20 is A molding die composed of a fixed die and a movable die, and 21 is a cavity forming a molding space.

The air taken in from the inlet 1 is
After the dust is removed by the filter 2 and the moisture and oil are removed by the mist separator 3, the dust is supplied to the nitrogen gas generator 6 via the pressure reducing valve 4. Further, air is also supplied from the mist separator 3 to the electromagnetic control valves 18 and 19 via the pressure reducing valve 5. In the nitrogen gas generator 6, oxygen is removed from the atmosphere by a known filter method or an adsorption method,
Generates and outputs nitrogen gas. In addition, the pressure of the atmosphere taken in from the inlet 1 is about 5 kg / cm ² , and in this embodiment, the pressure of the nitrogen gas discharged from the nitrogen gas generator 6 is set to about 3 kg / cm ² . .

The nitrogen gas output from the nitrogen gas generator 6 is supplied through a flow meter 7, a throttle valve 8, and a check valve 9 to a gas booster mechanism 11 whose details will be described later. The pressure is increased (compressed) to a set pressure for press-fitting into the resin in the cavity 21 by the gas pressure increasing mechanism 11 that is driven and controlled in 12. The high-pressure nitrogen gas output from the gas pressure raising mechanism 11 is injected (injected) into a resin (not shown) in the cavity 21 via a switching control valve 16 controlled by air from an electromagnetic control valve 18. Further, when the timing of the exhaust gas after the solidified product is reached, the switching control valve 16 is closed, and nitrogen gas is released to the atmosphere or the like through the switching control valve 17 controlled by air from the electromagnetic control valve 19. . In this embodiment, the high-pressure nitrogen gas is injected into the resin from the molding die 20, but the injection point of the high-pressure nitrogen gas may be a nozzle of an injection mechanism.

Next, details of the gas pressure raising mechanism 11 will be described. In the present embodiment, the gas pressure increasing mechanism 11 includes two first gas compression cylinders 22 and one second gas compression cylinder 23, and the nitrogen gas from the nitrogen gas generator 6 Through the check valve 9, the first paired
Is introduced into the compression chamber 22a of the gas compression cylinder 22. Also, the first gas compression cylinder 22
The pressurized (compressed) nitrogen gas is introduced into the compression chamber 23 a of the second gas compression cylinder 23 via the check valve 10, and further pressurized (compressed) by the second gas compression cylinder 23. It has become.

As shown in FIG. 1, the electric servo motor 12
A pulley 24 is fixed to the output shaft of the motor. A timing belt 26 is stretched between the pulley 24 and a nut body 25 with a pulley.
The nut body 25 with the pulley is rotationally driven by the rotation of the nut. The nut body 25 with a pulley is held so as to be rotatable but not displaceable in the axial direction. A ball screw 27 is screwed to the nut body 25 with a pulley. The ball screw 27 moves in the axial direction. That is, a known ball screw mechanism constitutes a rotation → linear motion conversion mechanism for converting the rotation of the electric servomotor 12 into a linear motion.

[0019] the ball screw 27, together are connected via a suitable coupling mechanism piston body 23b of the second gas compression cylinder 23 is necessary, the connecting member 28 Oyo
And connecting member 29 (as shown in the drawing, two
The piston body 22b of the first gas compression cylinder 22 is connected via the shaft- like connecting members 29, 29) . Therefore, when the electric servomotor 12 rotates in the first direction and the ball screw 27 is driven in the direction A in the drawing, the nitrogen gas in the compression chamber 22a of the first gas compression cylinder 22 is released by the piston body 22b. The compressed gas is pressurized and introduced into the compression chamber 23 a of the second gas compression cylinder 23 via the check valve 10. In this embodiment, the first gas compression cylinder 22 is configured to increase the pressure of the nitrogen gas from about 3 kg / cm ^{2 to} about 30 kg / cm ² .

When the electric servomotor 12 rotates in the second direction and the ball screw 27 is driven in the direction B, the compression chambers of the first gas compression cylinder 22 to the second gas compression cylinder 23 are moved. The nitrogen gas introduced into 23a is compressed by piston body 23b, and the pressure is further increased.

FIG. 2 shows the second gas compression cylinder 23 when 588 cc (maximum) of nitrogen gas having a gas pressure of 30 kg / cm ² is introduced into the compression chamber 23a of the second gas compression cylinder 23. Compression stroke of the piston body 23b, the generated gas pressure in the compression chamber 23a and the compression chamber 23a.
FIG. 4 is a graph showing a relationship between the volume of nitrogen gas and the volume of nitrogen gas. As shown in the figure, before the compression operation by the second gas compression cylinder 23, the gas pressure of 30 kg / cm ² increases as the compression stroke increases, and as the compression stroke increases, the gas pressure increases. The gas volume (gas amount) in the chamber 23a becomes smaller. In this embodiment, the cavity 2
100 kg / cm ² -270 k
expects to press-fitting the high-pressure nitrogen gas in the range of g / cm ^2, thus the 270 kg / cm ^2, up to 58
cc of gas can be supplied. Here, for example, in the case of a 180-ton class machine (injection molding machine), even for a molded product having a capacity of about 300 cc, which is close to the upper limit capacity value, a gas amount of about 30 cc at most is almost sufficient. In a class machine, there is quite room for performance.

The graph characteristic of FIG. 2 illustrates a case where the capacity (gas amount) of the compression chamber 23a before the compression operation is 588 cc, but it depends on the value of the capacity of the compression chamber 23a before the compression operation. Thus, a similar graph is obtained. In the present embodiment, a system controller (not shown) of the machine stores a table storing graph diagram characteristics according to the value of the capacity (gas amount) of the compression chamber 23a before such a compression operation, or
The program has a program for calculating the graph diagram characteristics based on the value of the capacity (gas amount) of the compression chamber 23a before the compression operation. The volume of the compression chamber 23a (the position of the piston body 23b) before the compression operation is determined based on the cavity volume value given at the initial setting of the molding conditions and the gas pressure set value at the start of press-fitting into the resin. The system controller decides in advance with a margin.

Here, the accurate value of the gas pressure in the compression chamber 23a can be detected by the pressure gauge 15, and the compression stroke is constantly detected by an encoder (not shown) attached to the electric servomotor 12. Since it is possible, the system controller of the machine which takes in these detection information sets the gas pressure condition value during the gas press-in stroke set by the operator (in this embodiment, the gas pressure settable in multiple stages along the time axis). Based on the pressure value, the pressure feedback control of the electric servomotor 12 is performed via the servo amplifier during the pressure increasing operation by the second gas compression cylinder 23. That is, in the present embodiment, before the compression operation of the second gas compression cylinder 23, the compression based on the gas pressure in the compression chamber 23a and the position information of the piston body 23b (encoder information of the electric servomotor 12). Based on the capacity of the chamber 23a, the system controller of the machine calculates the compression stroke necessary to obtain the set gas pressure, and controls the drive of the electric servomotor 12 via the servo amplifier based on the calculated value. At this time, the electric servomotor 12 is configured to perform feedback control (current value feedback control) on the drive current value corresponding to the output torque calculated from the set gas pressure value, thereby achieving pressure feedback control. You.

In this embodiment, the gas amount of the high-pressure nitrogen gas to be injected into the resin is not accurately measured. As described above, the cavity volume value given at the initial setting of the molding conditions and the amount of the high-pressure nitrogen gas injected into the resin are not measured. Based on the gas pressure set value at the start of press-fitting, the volume of the compression chamber 23a before compression (the piston body 23
b) is determined in advance by the system controller with a margin. Then, when the gas is injected into the resin, the servo control is performed by the current value feedback control so that the set gas pressure value and the actually measured gas pressure value (here, the actually measured driving current value corresponding to the actually measured gas pressure value) match. The motor 12 is driven (pressure feedback control by using the measured pressure value of the pressure gauge 15 is of course also possible). The reason for this is that gas injection into the resin in the first place is an alternative to applying a holding pressure via the cushion resin with a screw or the like,
This is from the viewpoint that pressure control is the control item that should be given the highest priority. Experiments have confirmed that the amount of high-pressure nitrogen gas injected into the resin is substantially stable even when such control is performed.

Next, the operation of this embodiment will be described. Before the compression operation of the nitrogen gas in the one-shot molding cycle, the switching control valves 16 and 17 are in the closed position. In this state, the nitrogen gas is supplied from the nitrogen gas generator 6 through the check valve 9 and the like. It is introduced into the compression chamber 22a of the first gas compression cylinder 22. When a predetermined amount of nitrogen gas is stored in the compression chamber 22a, the servomotor 12 is driven to move the ball screw 27 in the direction of arrow A in FIG. 22b also moves in the direction of arrow A, and the nitrogen gas in the compression chamber 22a is compressed and pressurized, and the pressurized nitrogen gas is transmitted through the check valve 10 to the compression chamber of the second gas compression cylinder 23. 23a.

Next, the servo motor 12 is driven in the opposite direction by pressure feedback control as described above, and the ball screw 27 moves in the direction of arrow B in FIG. Thereby, the piston body 2 of the second gas compression cylinder 23
3b moves in the direction of arrow B by a predetermined compression stroke,
The nitrogen gas in the compression chamber 23a of the second gas compression cylinder 23 is raised to a set pressure value. Then, at a timing when a predetermined amount of the molten resin is injected into the cavity 21, the switching control valve 16 is opened by the electromagnetic control valve 18, and a high-pressure nitrogen gas having a predetermined set pressure is injected into the molten resin in the cavity 21. .

[0027] Even after the switching control valve 16 is opened, the servo motor 12 continues to be driven by the pressure feedback control. For example, if the gas pressure set value during the gas injection process is a constant value, the pressure becomes a constant value. Is maintained (that is, the drive current value (torque value) corresponding thereto is kept constant) by gradually moving the piston body 23b in the direction of arrow B, and monitoring the measured pressure value while maintaining the pressure feedback. Perform control.

If the gas pressure conditions for the gas injection step into the resin are set in multiple stages (or stepless curves), the gas pressure is similarly variably controlled according to the set conditions during the gas injection step. For example, in the case of the gas pressure setting condition as shown in FIG. 3, after a predetermined time t1 from the start of gas injection, the gas pressure is further increased from P1 to P2.
While moving the piston body 23b in the direction of arrow B, the pressure P
Pressure feedback control is performed while monitoring the measured pressure value by the pressure gauge 15 so that the measured value corresponds to the measured value corresponding to 2. Further, after a predetermined time t2 from the start of gas injection, while moving the piston body 23b in the direction of arrow A so as to reduce the gas pressure from P2 to P3, the pressure is adjusted so as to become an actually measured value corresponding to the pressure P3. Pressure feedback control is performed while monitoring the actually measured pressure value by the total 15.

Thereafter, when the resin in the cavity 21 has solidified, the piston body 23b is rapidly driven in the direction of arrow A to decompress the inside of the compression chamber 23a, and the high-pressure nitrogen gas in the resin and the pipeline is removed. Collected in the compression chamber 23a. Thereafter, the switching control valve 16 is closed by the electromagnetic control valve 18, and then the switching control valve 17 is opened for a short time by the electromagnetic control valve 19, so that the nitrogen in the resin which is still considerably higher than the atmospheric pressure can be obtained. Releases gas and nitrogen in short pipes.

With the above operation, the operation of the high-pressure gas supply device in the one-shot molding cycle is completed.

As described above, according to this embodiment, the pressure of the nitrogen gas is increased in two stages, so that the required high pressure can be easily obtained, and the gas pressure increasing mechanism can be made compact and inexpensive. obtain. Therefore, even if a gas pressure increasing mechanism is attached to each injection molding machine, the space factor is improved, and the layout in the factory becomes easy. In addition, a variable-capacity gas compression cylinder makes it possible to obtain a necessary and sufficient amount of high-pressure gas for each shot, so that high-pressure gas can be small in volume and legal regulations are reduced, making management and operation simple. Becomes

Further, since the electric servomotor is used as the drive source for boosting the pressure, pressure feedback control can be easily performed, and the gas pressure in the gas press-in process can be feedback-controlled according to the set conditions. Hold pressure control can be performed precisely, greatly contributing to good molding.

[0033]

As described above, according to the present invention, it is possible to provide a high-pressure gas supply device which can be relatively compactly installed near an injection molding machine and can be reduced in cost. In addition, since an electric servomotor is used as the drive source for boosting,
The pressure feedback control can be easily performed, and thus, a better non-defective product can be achieved.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an outline of a high-pressure gas supply device of an injection molding machine according to one embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a compression stroke of a piston body of a second gas compression cylinder and a generated gas pressure and a gas volume in a compression chamber in a high-pressure gas supply device of an injection molding machine according to one embodiment of the present invention. It is a graph figure showing an example.

FIG. 3 shows an injection molding machine according to one embodiment of the present invention.
It is explanatory drawing which shows an example of the gas pressure setting condition at the time of a gas press-in stroke.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 air intake 2 filter 3 mist separator 4,5 pressure reducing valve 6 nitrogen gas generator (nitrogen gas generator) 7 flow meter 8 throttle valve 9,10 check valve 11 gas pressure increasing mechanism 12 electric servomotor 13,14, 15 Pressure gauge 16, 17 Switching control valve 18, 19 Electromagnetic control valve 20 Mold for molding 21 Cavity 22 First gas compression cylinder 22a Compression chamber 22b Piston body 23 Second gas compression cylinder 23a Compression chamber 23b Piston body 24 Pulley 25 Nut body with pulley 26 Timing belt 27 Ball screw

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-141216 (JP, A) JP-A-5-177656 (JP, A)

Claims (1)

(57) [Claims] An injection molding machine capable of injecting a molten resin into a cavity of a mold and injecting a high-pressure gas into the resin in the cavity. A gas boosting mechanism using a gas compression cylinder, which boosts the pressure by the driving force of an electric servomotor, wherein the gas boosting mechanism converts a rotation of the electric servomotor into a linear motion, and generates the inert gas. Two first gas compression cylinders arranged side by side, which introduce gas from a source and pressurize the gas by a piston body driven by the ball screw mechanism; and a second gas compression cylinder between the two first gas compression cylinders. The two gas compression cylinders are arranged in parallel with one another, and the gases pressurized by the two first gas compression cylinders are introduced into the gas compression cylinders. A second gas compression cylinder that pressurizes gas to a pressure for injecting the gas into the resin in the cavity by a piston body driven by the piston mechanism; and the second gas compression cylinder connected to the piston body of the second gas compression cylinder. Two ball screws respectively connected to a ball screw of a ball screw mechanism and piston bodies of the two first gas compression cylinders;
And a connecting member for integrally connecting the two shaft-shaped connecting members. The electric servo is used for a compression operation by the first gas compression cylinder and a compression operation by the second gas compression cylinder. An injection molding machine characterized in that the rotation direction of a motor can be switched.