JPH0890619A - Injection molding device - Google Patents

Abstract

PURPOSE: To obtain an injection molding device that never causes a difference in a final in-mold pressure even with the change of the viscosity, elasticity, or the like of a molding material, contributes to a product quality enhancement, can stabilize a cycle time, and can raise a productivity. CONSTITUTION: A hydraulic cylinder 12 is so controlled as to make the speed of an injection screw 10 constant. The hydraulic cylinder 12 is so controlled as to lower the speed of the injection screw 10 at a constant acceleration if an internal nozzle pressure increases to a predetermined threshold or more in a last stage of injection molding. At the same time, a pressure of a molding material in a mold 4 is predicted by calculating a pressure increase in the mold 4. When the predicted in-mold pressure reaches a predetermined pressure, an acceleration constant control is changed over to a dwell control.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding device.

[0002]

2. Description of the Related Art Injection molding is carried out by injection-filling a molding material such as heat-melted plastics or rubber into a cavity of a mold, and after cooling, it is taken out as a molded product. The injection molding machine includes a plasticizing device that heats and melts a molding material, an injection device that injects a molding material, a mold clamping device that holds a mold to open and close and clamp it, and an automatic control of the operation of each of these devices. It is composed of a control device and the like.

By the way, in order to improve the productivity of injection molding, a mold temperature is kept low with a thermoplastic resin and a mold temperature is kept high with a thermosetting resin, while high-speed filling with a high injection pressure into the cavity. It is effective to do. However,
When the filling is completed with the high injection pressure, high pressure stress is accumulated in the cavity, which may cause burr leakage. Therefore, it is necessary to set the mold clamping force of the mold large. Therefore, when high injection pressure and high-speed filling are performed, there is a problem that an injection molding machine becomes large and expensive.

Therefore, conventionally, a method has been adopted in which the injection pressure is switched to a low pressure (holding pressure) immediately before the filling is completed and the injection is completed at the low pressure to reduce the mold clamping force. For example, burr leakage can be prevented by detecting the stroke position of the injection screw of the injection device and switching the injection pressure from high pressure to low pressure at the stroke position of the injection screw corresponding to before the completion of filling.

However, the stroke position of the injection screw corresponding to before the completion of filling changes depending on the viscosity of the molding material and the like, and it is difficult to detect the time immediately before the completion of actual filling from the stroke position of the injection screw. Therefore, in the method of switching the injection pressure from the high pressure to the low pressure based on the stroke position, at the exact time before the completion of injection,
There is a possibility that the injection pressure cannot be switched from high pressure to low pressure, which causes flash leakage.

Therefore, as shown in FIG. 3, the injection speed (the speed of the injection screw) is controlled to be constant, the molding material (for example, rubber) is filled in the mold immediately before the completion of the injection, and the injection speed is a fixed amount ΔV. A method is adopted in which the injection pressure is switched to the holding pressure when the pressure drops. This method will be described in more detail.

As shown in FIG. 3, when the injection pressure is equal to or lower than the upper limit value of the device, the injection speed can be controlled to be constant. Immediately before the completion of the filling into the mold, the molding material is almost filled into the mold and further filled (compressed), so that the injection pressure increases. When the injection pressure reaches the upper limit value, it becomes more difficult to keep the injection speed constant, and the injection speed decreases (decelerates). The pressure of the molding material in the mold starts to increase at the same time when the injection speed decreases. The time when the injection speed drops by a certain amount ΔV is determined to be the time when the filling is completed, and at this time, the injection pressure is switched to the holding pressure (about 1/3 of the injection pressure when the injection speed is constant). By switching to the holding pressure, the internal pressure of the mold can be suppressed to the required internal pressure or less, and it is possible to prevent the occurrence of burrs and the like.

[0008]

However, the control of the injection molding apparatus shown in FIG. 3 has the following problems. That is, when the injection pressure reaches the upper limit value, speed control becomes difficult, and the drop state of the injection speed depends on the viscosity and elasticity of the molding material as shown by dotted line A or dotted line B in FIG. Change. The pressure rises in the mold corresponding to the injection velocity drop curves A and B are respectively curves a and
b.

For this reason, when the injection pressure is uniformly switched to the holding pressure with the preset amount of decrease ΔV in the injection speed, in the case of the curve A and the curve B, the in-mold pressure at the time of switching to the holding pressure is , And α and β respectively, which are different. For this reason, a difference occurs in the final pressure in the mold, resulting in variation in product quality (quality deterioration).

Further, the time required for the pressure in the mold to reach the required pressure in the mold is T _{A in} the case of curve a and T _{B in} the case of curve b, causing variations in cycle time. I will end up. As a result, productivity decreases. The present invention has been made in view of such an actual situation, and even if the viscosity or elasticity of the molding material changes, the difference in the final pressure in the mold does not occur, which contributes to the improvement of product quality and the cycle An object of the present invention is to provide an injection molding device capable of stabilizing time and improving productivity.

[0011]

In order to achieve the above object, an injection molding apparatus according to the present invention comprises a mold in which a cavity is formed, and an extruder in which a nozzle is pressed against an injection port of the mold. , Inside the extruder, by moving at a predetermined pressure in the nozzle direction, the injection screw for injecting the molten molding material into the cavity in the mold at a predetermined injection pressure from the nozzle, and the screw Driving means for moving at a predetermined pressure in the nozzle direction, a position sensor for detecting the position of the injection screw, speed detection means for detecting the moving speed of the injection screw, and a nozzle for detecting the pressure of the molding material in the nozzle. Internal pressure detection means,
The speed control means for controlling the drive means so that the speed of the injection screw detected by the speed detection means becomes constant, and the nozzle internal pressure detected by the nozzle internal pressure detection means is equal to or higher than a predetermined threshold value. In this case, based on the position of the injection screw detected by the position sensor and the acceleration control unit that controls the driving unit so that the speed of the injection screw drops at a constant acceleration, the volume of the molding material filled in the mold. The change is calculated, the pressure increase in the mold is calculated based on the change in volume, and the pressure predicting means for predicting the pressure of the molding material in the mold, and the in-mold pressure predicted by the pressure predicting means are , A holding pressure switching means for controlling the driving means so as to switch to the holding pressure control when a predetermined pressure is reached.

[0012]

When the injection molding is started, the speed control means controls the driving means so that the speed of the injection screw (injection speed) becomes constant, and the injection molding is performed. In the control in which the injection speed is constant, as shown in FIG. 2, the nozzle internal pressure detected by the nozzle internal pressure detecting means increases to some extent as the injection molding time (t) elapses, but is almost constant. In the final stage of injection molding, the molding material (for example, rubber) is almost filled in the mold, and if injection molding is still performed at a constant speed, the molding material in the mold is compressed. The pressure and injection pressure (such as the hydraulic pressure acting on the drive means) increase.

The nozzle internal pressure detecting means successively detects the nozzle internal pressure. When the pressure in the nozzle reaches a preset pressure (threshold value Pth, lower than the upper limit value), the acceleration control means controls the driving means to decrease the injection speed at a preset constant acceleration. The threshold Pth
Must be lower than the upper limit of the pressure that the device can handle. Otherwise, the injection speed cannot be controlled with the acceleration kept constant.

At the same time, when the pressure in the nozzle reaches the threshold value Pth, the pressure predicting means is activated to sum the volume V ₁ of the cavity in the mold and the volume V ₂ of the molding material in the nozzle. Calculate V. The position of the injection screw, which changes from time to time, is detected by the position sensor, and the volume change dV of the molding material filled in the cavity of the mold is calculated from the data. This volume change (amount of deposition elimination) is calculated moment by moment by multiplying the movement amount of the injection screw by the cross-sectional area of the nozzle. For the volume V ₂ of the molding material in the nozzle, the volume of the tip (mold side) from the current position of the injection screw is calculated from the geometric shapes of the nozzle and the injection screw. Next, the pressure increase dP of the molding material in the cavity of the mold is calculated by the following formula.

[0015]

## EQU1 ## dP = G.times.dV / V (where G is the compression elastic modulus of the molding material) The current in-mold pressure P is predicted from the pressure increase dP. As shown in FIG. 2, when the predicted in-mold pressure P reaches a preset required in-mold pressure Pd, the holding pressure switching means controls the driving means to switch to the holding pressure control. In the holding pressure control, the injection pressure is controlled to be a fraction, preferably about 1/3, of that in the injection control in which the injection speed is constant.

When injection molding is performed by the injection molding apparatus according to the present invention, even if the viscosity or elasticity of the molding material changes, the holding pressure control is switched according to the predicted pressure of the molding material in the mold. There is no difference in the pressure inside the mold. Therefore, the quality of the obtained injection molded product is improved.

Further, when the pressure in the nozzle reaches a predetermined threshold value, the injection speed is lowered with a constant acceleration, so that the time until the pressure in the mold reaches the required pressure in the mold becomes substantially constant. , The cycle time is stabilized and the productivity is improved. Further, since the filling amount required for the die pressure to reach the required die pressure is calculated, it is not necessary to actually measure the injection speed drop amount ΔV (see FIGS. 3 and 4) for each die. Productivity can be improved.

Furthermore, since the pressure inside the mold is calculated,
It is economical because it is not necessary to attach a pressure sensor to each mold. It should be noted that mounting the pressure sensor at a predetermined position in the mold without affecting the shape of the cavity also increases the manufacturing cost of the mold, and it is preferable not to mount the pressure sensor if possible.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The injection molding apparatus according to the present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 1 is a schematic configuration diagram of an injection molding apparatus according to an embodiment of the present invention, and FIG. 2 is a graph showing a control method of the injection molding apparatus of the embodiment.

As shown in FIG. 1, the injection molding apparatus according to this embodiment has a mold 4 having a cavity 2 formed therein.
The mold 4 is separable, and a product molded by injection molding can be taken out. The nozzle 6 of the extruder 8 is provided at the injection port of the mold 4 into the cavity 2.
Of the molding material (for example, rubber or synthetic resin) in the nozzle 6 by moving the injection screw 10 axially movable in the extruder 8 toward the nozzle 6. It can be injected into the cavity 2 of the mold 4.

The injection screw 10 moves in the extruder 8 by the forward / backward movement of the injection hydraulic cylinder 12 as a driving means while rotating by a screw driving hydraulic motor (not shown). The injection hydraulic cylinder 12 is controlled by a servo valve 18. A variable displacement pump (hydraulic pump) is connected to the servo valve 18, and the servo driver 20 controls the pressure feeding direction and the fluid pressure of the pressure fluid that is pressure-fed from the variable displacement pump to thereby cause an injection hydraulic cylinder. 12 is drive-controlled, and as a result, the injection speed and injection pressure of the injection screw 10 are controlled.

The servo valve 20 is connected to a computer 22 through an interface (not shown) and is controlled by the computer 22. The computer 22 is programmed to have the following means. That is, the computer 22 has a nozzle internal pressure detection means 26, a speed control means 32, an acceleration control means 34, a holding pressure switching means 36, a pressure prediction means 38, a hydraulic pressure detection means 28, and a speed detection means 30. The nozzle internal pressure detecting means 26 is means for detecting the nozzle internal pressure based on a signal from the pressure sensor 24 mounted so as to detect the pressure inside the nozzle 6.

The hydraulic pressure detecting means 28 is means for detecting the hydraulic pressure based on a signal from the pressure sensor 16 mounted so as to detect the hydraulic pressure (injection pressure) in the hydraulic cylinder 12. The speed detecting means 30 is a means for obtaining an injection speed by time-differentiating it based on a signal from the position sensor 14 that detects the axial movement position of the injection screw 10.

The speed control means 32 sends a drive signal to the servo driver 20 using the injection speed signal detected by the speed detection means 30 and the hydraulic pressure data from the hydraulic pressure detection means 28 as a feedback signal to send the drive signal to the servo driver 20. The injection speed is controlled to be constant. Acceleration control means 34
Drives the servo driver 20 by differentiating the injection speed detected by the speed detection means 30 with time to obtain the acceleration of the injection screw 10 and using the data and the hydraulic pressure data from the hydraulic pressure detection means 28 as feedback signals. A signal is sent and the injection screw 10 is controlled so as to decelerate at a constant acceleration. The control is performed after the control by the speed control means, and the switching timing is determined based on the data from the nozzle internal pressure detection means 26.

The holding pressure switching means 36 is the oil pressure detecting means 2
Using the hydraulic pressure data at 8 as a feedback signal,
A drive signal is sent to the servo driver 20 to drive and control the hydraulic cylinder 12 so as to perform pressure holding control. In the holding pressure control, the injection pressure is controlled to be a fraction, preferably about 1/3, of that in the injection control in which the injection speed is constant. The pressure holding control is performed after the control by the acceleration control means 34, and the switching timing thereof is determined based on the data from the pressure prediction means 38.

Next, a control method of the injection molding apparatus according to this embodiment will be described with reference to FIGS. 1 and 2. At the start of injection molding, a signal is sent from the speed control means 32 to the servo driver 20 so that the speed of the injection screw 10 (injection speed) is constant, the hydraulic cylinder 12 is drive-controlled, and injection molding is performed. In the control in which the injection speed is constant, as shown in FIG. 2, the nozzle internal pressure detected by the nozzle internal pressure detection means 24 increases to some extent as the injection molding time (t) elapses, but is almost constant. In the final stage of injection molding, the cavity 2 of the mold 4 is almost filled with the molding material, and when the injection molding is still performed at a constant speed, the molding material in the cavity 2 is compressed. And the injection pressure (the hydraulic pressure of the hydraulic cylinder 12) increase.

The nozzle internal pressure detecting means 26 sequentially detects the nozzle internal pressure. When the pressure in the nozzle reaches a preset pressure (threshold value Pth, lower than the upper limit value), the speed control means 32 switches to the acceleration control means 34, and the acceleration control means 34 sends a drive signal to the servo driver 20. To reduce the injection speed of the injection screw 10 at a preset constant acceleration. The threshold Pth
Must be lower than the upper limit of the pressure that the device can handle. Otherwise, the injection speed cannot be controlled with the acceleration kept constant.

At the same time, when the pressure in the nozzle reaches the threshold value Pth, the pressure predicting means 38 is activated to sum the volume V ₁ of the cavity in the cavity ₂ and the volume V ₂ of the molding material in the nozzle 6. The calculated volume V is calculated. The position sensor 14 detects the position of the injection screw 10 that changes from time to time, and calculates the volume change dV of the molding material filled in the cavity of the mold from the data. This change in volume (amount of deposition exclusion) is calculated by multiplying the amount of movement of the injection screw 10 by the cross-sectional area of the nozzle 6.
Calculate from moment to moment. Volume V ₂ of molding material in the nozzle 6
Is the tip (mold side) from the current position of the injection screw 10.
Volume is calculated from the geometry of the nozzle and the injection screw. Next, the pressure increase dP of the molding material in the cavity 2 of the mold 4 is calculated by the following formula.

[0029]

## EQU00002 ## dP = G.times.dV / V (where G is the compression elastic modulus of the molding material) The current in-mold pressure P is predicted from the pressure increase dP. As shown in FIG. 2, when the predicted in-mold pressure P reaches a preset required in-mold pressure Pd, a drive signal is sent from the holding pressure switching means 36 shown in FIG. 1 to the servo driver 20, Switch to holding pressure control. In holding pressure control,
The injection pressure is controlled to be a fraction, preferably about ⅓, of the injection control with a constant injection speed.

The present invention is not limited to the above-described embodiments, but can be variously modified within the scope of the present invention. For example, the driving means is not limited to the hydraulic cylinder 12, but may be another fluid pressure cylinder or an electric motor.

Further, in the above embodiment, the nozzle internal pressure detecting means 26 detects the nozzle internal pressure based on the signal from the pressure sensor 24 provided in the nozzle 6, but the present invention is not limited to this, and the hydraulic cylinder is not limited thereto. Pressure sensor 1 provided in 12
It is also possible to indirectly measure the nozzle internal pressure based on the output signal from 6. This is because the hydraulic pressure of the hydraulic cylinder 12 and the pressure inside the nozzle 6 have a correlation. In the case of that embodiment, it is not necessary to provide a pressure sensor in the nozzle 6.

[0032]

As described above, according to the present invention, even if the viscosity or elasticity of the molding material changes,
Since the holding pressure control is switched according to the predicted pressure of the molding material in the mold, there is no difference in the final pressure in the mold.
Therefore, the quality of the obtained injection molded product is improved.

Further, when the pressure in the nozzle reaches a predetermined threshold value, the injection speed is decreased with a constant acceleration, so that the time until the pressure in the mold reaches the required pressure in the mold becomes substantially constant. , The cycle time is stabilized and the productivity is improved. Further, since the filling amount required for the die pressure to reach the required die pressure is calculated, it is not necessary to actually measure the injection speed drop amount ΔV (see FIGS. 3 and 4) for each die. Productivity can be improved.

Furthermore, since the pressure inside the mold is calculated,
It is economical because it is not necessary to attach a pressure sensor to each mold. It should be noted that mounting the pressure sensor at a predetermined position in the mold without affecting the shape of the cavity also increases the manufacturing cost of the mold, and it is preferable not to mount the pressure sensor if possible.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an injection molding apparatus according to an embodiment of the present invention.

FIG. 2 is a graph showing a control method of the injection molding apparatus of the embodiment.

FIG. 3 is a graph showing a control method of an injection molding device according to a conventional example.

FIG. 4 is a graph showing a problem of a control method of an injection molding device according to a conventional example.

[Explanation of symbols]

 2 ... Cavity 4 ... Mold 6 ... Nozzle 8 ... Extruder 10 ... Injection screw 12 ... Hydraulic cylinder 14 ... Position sensor 16, 24 ... Pressure sensor 18 ... Servo valve 20 ... Servo driver 22 ... Computer 26 ... Nozzle internal pressure detection means 28 ... hydraulic pressure detecting means 30 ... speed detecting means 32 ... speed controlling means 34 ... acceleration controlling means 36 ... holding pressure switching means 38 ... pressure predicting means

Claims (1)

[Claims] 1. A mold (4) having a cavity (2) formed therein, an extruder (8) in which a nozzle (6) is pressed against an injection port of the mold (4), and the extruder (8). ), The molten molding material is injected from the nozzle (6) into the cavity (2) in the mold (4) at a predetermined injection pressure by moving in the nozzle (6) direction with a predetermined pressure. An injection screw (10), a driving means (12) for moving the screw (10) in the nozzle (6) direction at a predetermined pressure, and a position sensor (14) for detecting the position of the injection screw (10). A speed detecting means (30) for detecting the moving speed of the injection screw (10), a nozzle internal pressure detecting means (26) for detecting the pressure of the molding material in the nozzle (6), and the speed detecting means (30 ) Injection screen detected by As the speed of over (10) is constant, the driving means (1
When the nozzle internal pressure detected by the nozzle internal pressure detection means (26) and the speed control means (32) for controlling 2) becomes equal to or higher than a predetermined threshold value, the speed of the injection screw (10) is constant acceleration. Acceleration control means (34) for controlling the drive means (12) so as to descend at
Based on the position of the injection screw detected by the position sensor (14), the volume change of the molding material filled in the mold is calculated, and the pressure increase in the cavity (2) is calculated based on the volume change. Pressure predicting means (38) for predicting the pressure of the molding material in the cavity (2), and when the in-mold pressure predicted by the pressure predicting means (38) reaches a predetermined pressure, a holding pressure is maintained. An injection molding apparatus having a holding pressure switching means (36) for controlling the driving means (12) so as to switch to control.