JPH0788907A - Speed control of injection molding machine - Google Patents

Abstract

PURPOSE:To suppress the adverse effect caused by the closing characteristics of a check valve to the min. and to stabilize the quality of a molded product by changing over the injection speed of an injection screw when either one of the pressure of an injection cylinder, the pressure of a resin and the internal pressure of a mold measured by a pressure detector reaches a preset pressure. CONSTITUTION:A position detector 30 for detecting the position of an injection screw 3, a pressure detector 40 and the speed operator 50a calculating the time differential value of the position of the injection screw detected through the position detector 30 or the injection speed detector for detecting the injection speed of the injection screw 3 are provided. The injection speed of the injection screw 3 is controlled so as to set a filling process to a plurality of injection speeds. The speed changeover at a plurality of the alteration and changeover points of an injection speed is performed by changing over the injection speed of the injection screw 3 when either one of the pressure of an injection cylinder 5, the pressure of a resin and the internal pressure of a mold 9 measured by the pressure detector 40 reaches a preset pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed control method in a filling process of an injection molding machine, and in particular, injection molding in consideration of suppressing adverse effects of variations in closing characteristics of check valves during injection. The present invention relates to a speed control method for a machine.

[0002]

2. Description of the Related Art Conventionally, in injection molding of molten resin,
As shown in FIG. 4, the horizontal axis represents the position S or time t of the injection screw, the vertical axis represents the injection speed V or pressure P of the injection screw, and the filling step S for filling the molten resin into the mold cavity at high speed. ₁ and injection control is performed by a pressure-holding step S _{2 in} which pressure is applied to the resin in the mold cavity after molding with molten resin to mold the resin. In many cases, the filling step S ₁ sets the pressure control valve of the hydraulic circuit to high pressure. Set so that the opening of the flow control valve is changed over time so as to change the speed in multiple stages based on the elapsed time from the start of injection or the forward position of the injection screw, or according to the stroke position of the injection screw. Then, the injection speed of the piston of the injection cylinder, that is, the injection screw is controlled by adjusting the flow control valve, and the molten resin is melted at such a high speed that the resin in the cavity does not entrap air. Shall fill into the cavity, after the molten resin has been filled in the cavity is secured to a relatively small opening the flow control valve, a pressure-holding step S ₂ of adjusting the hydraulic pressure by the pressure regulating valve, the pressure-holding step S ₂ changes the opening of the pressure adjusting valve so that a predetermined pressure can be applied to the molten resin filled in the cavity with the passage of time, and the molten resin is cooled in the cavity so that the resin shrinks. The product shape and size are prevented from causing an error with respect to the cavity shape size, and a large residual stress is not generated inside the product.

Generally, in the injection process control in the filling process, the control target values of the injection speeds of a plurality of stages are switched when the detected value of the injection screw coincides with the preset injection speed position as described above. FIG. 5 shows an embodiment in this case, in which three speed setting values V are set in the filling step S ₁ .
The situation of changes in the speed V and the pressure P when switching control to ₁ , V ₂ and V ₃ is shown. By the way, the operation of the check valve for preventing the molten resin in front of the injection screw from flowing backward to the injection screw side during injection is not always the same at every shot, and is slightly different.

[0004]

As described above, although there are some rare cases where the changeover of the injection speeds in the filling process is performed in the past, in most cases, the injection screw is changed at a preset position. Position changeover was performed at all the changeover change points when the point reached. In this case, when the closing of the check valve is delayed, the amount of resin filled in the mold cavity at the same screw position becomes smaller as much backflow occurs than when the closing of the check valve is early. Therefore, V- that shifts from the filling process to the pressure holding process
Since the preset pressure switching is generally performed at the P switching point, the injection screw position (hereinafter, referred to as the injection screw position) where the VP switching is performed in the shot when the check valve is closed late.
The V-P switching position) is closer to the screw forward limit side. In this way, the region controlled by the set speed at the final stage of the filling process becomes longer. From Figure 5, compared to the last stage injection distance S _A of閉Ri fast shot A check valve, it can be seen that a large final stage injection distance S _B slow shot B is閉Ri of the check valve. In particular, when a resin material such as nylon having a low melt viscosity and a strong temperature dependence of the melt viscosity is molded, the check valve closing characteristic varies more greatly from shot to shot than the other resin materials. The -P switching position also varies, the variation width of the region controlled by the final stage set speed increases, and the variation width of the final-stage injection time also increases. FIG. 6 shows a situation in which the final stage injection speed time in conventional position switching varies from shot to shot due to variations in closing of check valves. In this way, in shots where the check valve closes slowly, the injection time becomes longer and the resin in the mold cavity is cooled more by the longer injection time, and the flow resistance in the mold cavity is reduced. As the size of the mold becomes larger, the amount of filling in the cavity is insufficient, and a light defective molded product is produced.
As described above, conventionally, the variation in the closing characteristics of the check valve, which is different for each shot, causes the resin filling amount in the cavity to be inconsistent, which causes the variation in the weight of the molded product and the variation in the molding quality.

[0005]

In order to solve the above problems, in the present invention, a position detector for detecting the position of an injection screw, a pressure detector, and an injection screw detected through the position detector. In an injection molding machine equipped with a speed calculator for calculating a time differential value of a position or an injection speed detector of an injection screw, and controlling the injection speed of the injection screw at multiple injection speeds during the filling process, When all of the speed switching at the change switching point of the injection speed of the stage reaches the preset set pressure which is one of the injection cylinder pressure or the resin pressure or the mold internal pressure measured by the pressure detector, The injection speed of the injection screw is switched.

[0006]

In the present invention, all the injection speed change switching points in the filling process are changed from the conventional injection screw position switching to pressure switching, and, for example, the operating hydraulic pressure of the injection cylinder during injection is preset. Since the injection speed is switched to the set value when the value is reached, the position of the injection screw at each switching point is almost the same as that of the shot with a quick check valve closing, even in the shot with a slow check valve closing. Since the injection screw shifts toward the front side to the same extent, the total injection time for shots with a slow check valve closing increases by the delay immediately after the start of the filling process, but the length and time of the final stage injection speed setting area are It becomes almost the same as the earlier shot, and the change from shot to shot is avoided. Therefore, the final stage injection time is stable without being affected by the variation in the closing characteristics of the check valve.
The filling amount in the cavity is constant and the quality of the molded product is stable.

[0007]

Embodiments of the present invention will be described below in detail with reference to the drawings. 1 to 3 relate to an embodiment of the present invention,
FIG. 1 is a configuration diagram of an injection control device in an injection molding machine, and FIG.
FIG. 3 is a characteristic curve diagram showing injection process control, and FIG. 3 is an explanatory diagram showing data of the final injection speed time of the filling process for each shot. In FIG. 1, an injection molding machine 100 includes a hopper 1
Injection screw (screw) in the heating cylinder 2 equipped with
3 is arranged so as to be rotatable and movable forward and backward, and a connecting rod 4 connected to the screw 3 is provided at the rear end of the screw 3.
Penetrates through the frame 7, and the connecting rod 4 and the screw 3 are rotated by the hydraulic motor 6 fixed to the rear end of the frame 7. The frame 7 is connected to the piston rods 5b of the pair of left and right injection cylinders 5, and the piston 5a is configured so that the piston rod 5b, the frame 7, the connecting rod 4 and the injection screw 3 can reciprocate integrally. The position of the injection screw 3 is determined by the movement of the lever 7a connected to the frame 7 by the screw position detector 30.
Measured by On the other hand, the injection cylinder 5 has a hydraulic pressure source 1
0 and the hydraulic unit 20 connected thereto are connected by piping, and the working oil pressure is measured by the pressure detector 40. The nozzle 2a at the tip of the heating cylinder 2 is pressed against the nozzle opening of the mold 9 to supply the molten resin inside the heating cylinder 2 to the cavity 9a. The injection control device 50 has a speed calculator 50a, a differentiator 50b, and a pressure calculator 50c built therein. The position information of the screw 3 and the pressure information of the injection cylinder pressure are input, and the speed command and the pressure command are output. Explaining the operation of the injection molding machine 100, the resin material is supplied from the hopper 1 into the heating cylinder 2 by rotating the injection screw 3 by the hydraulic motor 6, and the resin material passes through the groove space formed by the heating cylinder 2 and the screw 3. During this, the resin material is heated and melted, and is stored in front of the screw 3. With that,
The screw 3 is gradually retracted, and when the screw 3 reaches a predetermined position, the hydraulic motor 6 is stopped and the measuring process is completed. Next, a servo valve (not shown) installed in the vicinity of the injection cylinder 5 is controlled to send hydraulic oil to the injection cylinder 5, and the screw 3 is advanced to inject the molten resin into the cavity 9 a of the mold 9. In the initial stage of the injection process, the forward movement of the screw 3 causes a part of the molten resin in front of the screw 3 to flow back through the screw groove, but thereafter, the check valve 8 is seated on the check seat 8a to prevent the backflow.
The operation in which the check valve 8 is seated on the check seat 8a is
It is related to the pressure difference before and after the check valve due to the forward movement of the screw 3 and the accompanying backflow of the molten resin in front of the screw, and its timing varies from shot to shot. In the injection process (filling process), the injection speed of the screw 3 is controlled, and in the pressure-holding process (pressure-holding process), any one of the oil pressure, the resin pressure, and the mold internal pressure of the injection cylinder (in the embodiment of FIG. 1, the injection cylinder is used). Adopt pressure) to control the pressure.

In the present invention, as shown in FIG.
Multiple injection speeds in the filling process (high speed in the embodiment of FIG. 2)
Degree set value V₁, V₂, V₃) All the changeover points of
Use pressure switching instead of position switching and set with pressure detector 40.
The set pressure P corresponds to the set pressure corresponding to each changeover switching point.
When they arrive, the injection speed is switched (V₁→
V ₂, V₂→ V₃). Do this
Then, as shown in FIG. 2, the check valve 8 is closed slowly.
The pressure curve at Yot B shows that the check valve 8 is closed.
Compared to the pressure curve of shot A earlier,
Each change switching point and V-P switching without changing the upstream delay
Bring to the point and set the speed switching pressure at the final stage injection speed switching point.
Fixed value Pv₂Of A shot at position S reaching
At the VP switching point, the VP switching pressure set value Pc is reached and final
A shot at position S where the step injection speed setting area ends
Since the deviation from the height is almost the same, the final stage injection distance
S_BIs the final shot distance S of A shot_AAlmost the same as
It This was confirmed by molding experiments and actual machine tests.
It was That is, when the check valve 8 is closed slowly,
As you can see, the V-P switching position approaches the screw forward side, but
The pressure during filling at the screw position before
It's relatively low compared to the earlier shots of V-
Before the P switch position is reached, the check valve 8 for that shot
By using the pressure during filling as a means to determine the state of closure
It turns out that it is possible. Therefore, close the check valve
As a control method that minimizes the effects of
When the pressure during filling reaches a preset value, the next stage
Perform injection process control that switches to the injection speed setting value.
Conventionally, all injection speed switching is position switching by
Of shot-to-shot variation in injection process control
The length and time of the final stage injection speed range are minimized to minimize
Variations in the weight of shaped products and the resulting variations in quality of molded products
It has become possible to prevent sticking. As explained above,
According to the present invention, the low-viscosity that the check valve closes easily varies.
The injection time in the final stage is stable even when molding resin
Therefore, the quality of molded products that could not be achieved by the conventional control method
Stabilization can be achieved. FIG. 3 shows the final stage according to the present invention
It is a graph in which the injection time tn is connected for each shot.
However, compared to the measurement result of the conventional method shown in FIG.
It can be seen that the step ejection time tn is stable. Especially,
With a resin material such as Ron, which has a strong temperature dependence of melt viscosity
Is due to variations in check valve closing with the conventional control method.
Therefore, the final stage injection time tn varies, and as a result,
With the same V-P switching pressure, pressure control is entered and the pressure holding process begins.
However, it is necessary to keep the total mold filling amount constant when switching V-P.
I can't. If the check valve closes slowly, the final stage
Melt inside the mold because the time to control at the injection set speed becomes longer
The cause is that the temperature of the resin decreases and the viscosity increases.
It In the present invention, the start point and end point of the final stage injection set speed are
Last stage injection time to switch depending on the set pressure
tn does not depend on the closed state of the check valve and is almost always
As stated above, it will be a fixed time.
Is stable.

[0009]

As described above, according to the method of the present invention, the injection time in the final stage of the filling process is stabilized, so that the quality of the molded product is stable and the operation with high reliability is continued. You can

[Brief description of drawings]

FIG. 1 is a configuration diagram of an injection control device of an injection molding machine according to an embodiment of the present invention.

FIG. 2 is a characteristic curve diagram showing injection process control according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram showing data of final-stage injection time according to the embodiment of the present invention.

FIG. 4 is a graph showing an example of conventional injection control.

FIG. 5 is an explanatory diagram illustrating an example of conventional injection control.

FIG. 6 is an explanatory diagram showing data of final stage injection time in conventional injection control.

[Explanation of symbols]

1 hopper 2 heating cylinder 3 injection screw (screw) 4 connecting rod 5 injection cylinder 5a piston 5b piston rod 6 hydraulic motor 7 frame 7a lever 8 check valve 8a check sheet 9 mold 9a cavity 10 hydraulic power source 20 hydraulic unit 30 screw position detection 40 Pressure detector 50 Injection controller 50a Speed calculation unit 50b Differentiator 50c Pressure calculation unit 100 Injection molding machine A Shot with quick closing check valve B Shot with slow closing check valve P Pressure Pv ₁ Speed switching pressure setting Value Pv ₂ Speed switching pressure setting value Pc V-P switching pressure setting value Pk Holding pressure setting value S Position S ₁ Filling process S ₂ Holding pressure process S _A check Final stage injection distance S _B check in the early closing of the valve S _B check Final stage injection distance for shots with slow valve closure V speed (Injection speed) V ₁ speed setting value V ₂ the speed setting value V ₃ speed setpoint (last stage speed setting value) t time tn last stage injection time N number of shots

Claims (1)

[Claims] 1. A position detector for detecting an injection screw position, a pressure detector, and a speed calculator for calculating a time differential value of the injection screw position detected through the position detector or an injection speed detector of the injection screw. In an injection molding machine that is equipped with and that controls the injection speed of the injection screw at multiple injection speeds during the filling process, all the speed changes at the changeover switching points of the injection speeds of the multiple steps are measured by the pressure detector. Of the injection cylinder pressure, the resin pressure, or the pressure inside the mold reaches a preset pressure, and the injection speed of the injection screw is switched. Method.