JPH07102593B2 - Injection control method of injection molding machine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling an injection molding machine, and more particularly to a method for controlling an injection plunger or a screw during a transition from a filling step to a pressure holding step in an injection step.

[0002]

2. Description of the Related Art The injection process controls the injection speed based on the stroke position of a plunger (including a screw in the case of a screw in-line type. The same applies hereinafter) and the injection pressure based on the elapsed time. It consists of a pressure-holding process. A deceleration section is provided to reduce the speed of the plunger immediately before the completion of filling, and the pressure-holding process is switched to when the injection pressure starts to sharply increase due to completion of filling or when the plunger reaches a preset completion position. . In the case of the latter switching based on the position, it is common to use the monitoring of the injection pressure or the switching based on the injection pressure. The reason for providing such a deceleration section is that when the stroke is continued to the end at a high speed, a high peak pressure is generated at the time of completion of filling, the molten resin overflows on the parting surface of the cavity, and burrs are generated.

However, if the above method is adopted and the overpack is excessively handled, another defective molded product is likely to occur in a mold having a complicated cavity shape and a long resin flow path. This is because the speed of the deceleration section is set too low or the deceleration section is set longer than necessary, and the speed of the tip of the resin flowing into the cavity slows down, lowering the temperature and This is because it is difficult to reach the tip of the mold and a short shot occurs, or the weld lines are generated because the tips of the resin that has wrapped around the mold are not sufficiently joined.

In order to prevent the occurrence of such defective molded products, an optimum deceleration section is set to keep the moving speed of the plunger in the filling process as high as possible while preventing the peak pressure from being generated when the filling is completed. It is important to switch from the filling process to the pressure holding process. For this reason, for example, in the case where the injection operation is performed by hydraulic pressure, as a switching valve for the hydraulic circuit of the injection cylinder, a servo valve that is fast in response and suitable for closed loop control, and a highly responsive proportional electromagnetic directional flow path control valve are three-way closed control valves. Some valves are used as valves, and both speed control and pressure control are performed by a single valve.

[0005]

As described above, the deceleration section between the filling step and the pressure holding step is indispensable, but a peak pressure is generated due to a slight setting error or a change in resin viscosity during molding. It is difficult to make adjustments such as burrs and short shots and weld lines due to insufficient filling.Therefore, setting an appropriate deceleration section during actual work should be based on years of experience. It was decided after several trial moldings.

Therefore, an object of the present invention is to prevent the occurrence of burrs and weld lines by automatically setting the deceleration section to an optimum state.

[0007]

According to the present invention, the injection pressure at the time of completion of filling is detected, and this is determined by a preset allowable range Δ.
If the deceleration section setting condition, that is, the deceleration section length L and / or the deceleration section plunger speed V or the set value of the deceleration rate β of the plunger is changed, the filling step to the pressure holding step is performed. The speed control is smoothly shifted to the pressure control without causing a peak pressure or a pressure drop that exceeds a preset range at the time of switching.

The length L of the deceleration section, the plunger speed V and the deceleration rate β of the deceleration section decelerate by a preset adjustment amount α when the injection pressure at the time of completion of filling falls below a preset allowable range Δ. When the length L of the section is shortened, the plunger speed V in the deceleration section is increased or the deceleration rate β thereof is decreased, and when the injection pressure at the time of completion of filling exceeds the set allowable range Δ, The length L of the deceleration section is increased, the plunger speed V in the deceleration section is decreased, or the deceleration rate β is increased. The above setting conditions L, V, and β may be changed by changing the conditions individually or by combining them.

[0009]

When the setting conditions such as the length L of the deceleration section, the plunger speed V, and the deceleration rate β thereof are set incorrectly, or the setting conditions of the deceleration section do not match the actual molding conditions due to changes in the resin viscosity. In this case, as described above, molding defects such as burrs due to overpack and weld lines due to short shots are likely to occur. Naturally, overpacks are common
Occurs when the resin viscosity is low and the injection pressure after filling is abnormally high . The short shot is likely to occur when the injection pressure at the time of completion of filling is lowered. Therefore, if the injection pressure at the time of injection completion is out of the allowable range Δ, changing the setting condition of the deceleration section to cancel it will avoid overpacking and short shots due to setting mistakes and changes in molding conditions. Therefore, it becomes possible to always perform molding under the optimum conditions.

[0010]

EXAMPLE An example shown in the drawings will be described below. FIG. 1 is a block diagram of a control device for carrying out the method of the present invention, schematically showing a screw-in-line injection unit. In the figure, 1 is a screw barrel, 2 is a screw (plunger), 3 is a hopper, 4 is an injection cylinder, 5
Is a position detector that detects the stroke position of the screw 2,
6 is a hydraulic pump, 7 is an oil tank, 8 is a proportional electromagnetic directional flow control valve that controls the flow rate and pressure of the hydraulic pressure supplied to the injection cylinder 4, and 9 is a pressure sensor. The position detector 5 detects the stroke position of the screw 2 by rotating the rotary encoder by a rack and pinion mechanism and counting the pulse thereof.

The detection signal of the position detector 5 is the counter 11
Is fed back to the driver 12 and the arithmetic and control unit 13, and the detection value of the pressure sensor 9 is fed back to the driver 12 and the arithmetic and control unit 13 via the AD converter 14. A microcomputer is actually used as the arithmetic and control unit 13, various set values are input from the input unit 15, and the molding condition and the control condition are displayed on the display unit 16 by characters and graphs. The control signal output from the arithmetic and control unit 13 is given to the control valve 8 via the driver 12. In the block diagram of FIG. 1, the detected stroke position and injection pressure of the screw are also input to the driver 12 to perform feedback control with respect to the set value given to the driver 12, but feedback of this part is omitted. It is also possible to do so.

FIG. 3 is a graph showing the velocity and injection pressure of the plunger at the time of injection. From the point d in the center of the horizontal axis, the filling process is on the right and the pressure holding process is on the left. In the filling process, the stroke position is plotted on the horizontal axis. Therefore, the pressure-holding step is a diagram in which the horizontal axis represents time and the injection speed and the injection pressure are illustrated. The one-dot chain line S is the set value of the injection speed, and the dotted line T is the actual plunger speed. The injection speed is switched to, for example, three stages, a deceleration section having a length L is taken between the points c and d, and the injection speed in this section is set to V. The chain double-dashed line P is the set value of the injection pressure in the pressure-holding process, and is reduced to three levels as time passes. The solid line Q shows the change in the actual injection pressure from the start of filling to the completion of holding pressure. Of course, these injection speed control and holding pressure control patterns may differ depending on the material and shape of the molded product.

In the deceleration section L shown in FIG. 3, the injection pressure Q decreases as the plunger speed T decreases, and the injection pressure Pd at the completion of filling is the injection pressure (holding pressure The pressure is slightly lower than the initial value Pe and converges to the holding pressure Pe after a slight peak pressure is generated. Δ is a range set as an allowable range of the injection pressure Pd when the filling is completed. The value of the pressure Pd at the time of completion of filling decreases when the deceleration section L is lengthened or the set speed V in the deceleration section is decreased, and it increases when it is reversed.

In FIG. 4, the length L of the deceleration section is longer than necessary, and in FIG. 5, the set value V of the injection speed in the deceleration section is too low, so that the pressure Pd at the completion of filling is low. In such a case, short shots and weld lines are likely to occur. See also FIG.
Is because the length L of the deceleration section is too short, and in FIG. 7, the set value V of the injection speed in the deceleration section is too high.
This shows a state in which the pressure Pd at the time of completion of filling is high. In such a case, burr due to overpack is likely to occur.

The above example is an example in which the set value V of the injection speed in the deceleration section is set to a constant value. The injection speed in this deceleration section is Va- with the deceleration rate β as shown in FIG. β
It can also be set as a function of time such as t (Va is the injection speed immediately before the start of deceleration and t is the elapsed time after the start of deceleration). In this case, for example, if the deceleration rate β is too large, the injection pressure Pd at the time of completion of filling decreases as shown in FIG.
If is too small, the injection pressure at the completion of filling becomes high as shown in FIG .

FIG. 2 is a flow chart showing a procedure of control executed by the arithmetic and control unit 13 of FIG. 1, and the number of times the injection pressure Pd at the time of completion of filling exceeds or falls below a preset allowable range Δ n _a. Or n _b is a preset number of times n
_When it becomes ₀ , control is performed so as to correct the set value of the length L of the deceleration section and the injection speed V. Length of deceleration section L
The injection speed V and the injection speed V can be controlled by correcting only one of them or by correcting both. Further, when the injection speed in the deceleration section is set at the deceleration rate β as shown in FIG. 8, the injection speed is corrected by the correction of the deceleration rate β. In FIG. 2, it is shown in parentheses that β is controlled instead of V in the case of FIG. Further, in the control of FIG. 2, a control method in which a correction coefficient α set to a value such as 0.1 or 0.05 is preset and the set value is changed by a ratio indicated by the correction coefficient is adopted. are doing.

In FIG. 2, when the molding operation is started,
Initial values L ₀ and V ₀ (β
₀ ) is substituted (step 21). Then, when the molding cycle is executed and the filling process is completed, the injection pressure Pd at the completion of filling detected during molding is called (step 22). Then, in steps 23 and 24, it is judged whether or not the injection pressure Pd is within the allowable range. If it is within the allowable range, the next molding cycle is directly started. When the injection pressure Pd at the time of completion of filling is out of the allowable range, the process branches at step 23 or 24 depending on whether the injection pressure Pd is out of the higher range or lower range, and steps 25 and 2 are executed.
The number n _a of exceeding the allowable range and the number n _b of falling below the allowable range in 6 are counted. And n _a and n
_{If b} has not reached the set number of times, the next molding cycle is started without changing the set value.

When the number of times n _a that the pressure Pd at the time of completion of filling exceeds the allowable range reaches the set number of times n ₀ , step 2
In step 7, the length L of the deceleration section is increased by a preset adjustment amount α, the injection speed V in the deceleration section is decreased, or the deceleration rate β of the injection speed in the deceleration section is increased. Then reset the count value n _a, enters the next molding cycle. On the contrary, when the number n _{b of} times the pressure Pd at the time of completion of filling is below the allowable range reaches the set number n ₀ , the length L of the deceleration section is shortened by the adjustment amount α in step 28, or the injection speed in the deceleration section is reduced. Speed up V,
Alternatively, the deceleration rate β of the injection speed in the deceleration section is reduced, the count value n _b is reset, and the next molding cycle is started.

In the above case, the setting condition L, V or β of the deceleration section is corrected every time the control passes through step 27 or 28. As an example of how the set value changes when the correction is repeatedly performed in the case of the deceleration section length L, when the injection pressure Pd deviates to the higher side, the first set value is L = L. ₀ , the set value after the first correction is L = (1 + α) L ₀ , and the set value after the second correction is L = (1 + α) ² L ₀ . After the second correction, when the injection pressure comes off to the lower side, the correction in the opposite direction is entered, and the set value after the third correction is L = (1 + α) ² (1-α)
It becomes L ₀ . In this way, the set value of the length L of the deceleration section is converged to the optimum condition while being corrected in geometric progression. This means that the injection speed V or its deceleration rate β
The same applies to the correction of.

As described above, according to the method of the present invention, the length L of the deceleration section, the injection speed V, or the deceleration rate β thereof converges to the optimum values, so that the molding conditions are automatically set at the start of molding. It is possible. In such cases,
It is preferable to slightly change the setting of the adjustment amount α and the like between the condition setting at the start of molding and the actual molding operation after entering the steady state. That is, at the start of molding, the number of times n ₀ is set to the minimum value 1 so that the optimum deceleration condition is reached early, and α is also set large as necessary. On the other hand, at the time of actual forming work, n _{0 is set} to a large _value so as not to be affected by a sudden abnormality, and α
Should be set small.

Allowable range Δ of injection pressure Pd at the time of completion of filling
In general, the upper limit thereof is set to a pressure substantially equal to the holding pressure Pe of the first stage so that the peak pressure does not rise when the filling is completed and the pressure holding step is performed. However, when the molded product has a simple shape and a large wall thickness, it is preferable to set the allowable range lower than this. Moreover, the shape of the molded product is complicated,
Especially when the tip of the mold cavity is narrow and resin does not reach easily or there is a weld part, the allowable pressure is set higher overall and a slight peak pressure is set when the filling is completed. The resin is steadily filled up to the tip of the mold by pressure.

In the above embodiment, the hydraulic injection device has been described. However, it is an electric injection device for converting the rotation of an electric servomotor into a linear motion through a ball screw to perform an injection operation. Can perform similar control, and the injection control method of the present invention can be adopted regardless of the type of drive source.

[0023]

According to the control method of the present invention described above, it is possible to smoothly shift from the filling step to the pressure holding step without causing a sudden change in injection pressure.
Avoids the risk of bulging due to overpacking in the molded product due to excessive peak pressure when the filling process is completed, and the risk of short shots and weld lines due to too low pressure when the filling is completed. can do. Since the setting conditions are corrected by following changes in the resin viscosity during molding, the occurrence of defective products due to changes in molding conditions during molding work can be avoided, and during trial operation at the start of molding. There is an effect that the deceleration condition can be automatically set.

[Brief description of drawings]

FIG. 1 is a block diagram schematically showing a control system of an injection device.

FIG. 2 is a flowchart showing a control procedure.

FIG. 3 is a graph showing changes in injection speed and injection pressure in an injection process.

FIG. 4 is a graph showing a pressure change when a deceleration section becomes long.

FIG. 5 is a graph showing a pressure change when the injection speed in the deceleration section is slow.

FIG. 6 is a graph showing changes in injection pressure when the deceleration section is short.

FIG. 7 is a graph showing a pressure change when the injection speed in the deceleration section is high.

FIG. 8 is a graph showing another example of speed setting in the deceleration section.

FIG. 9 is a graph showing a pressure change when the deceleration rate in the deceleration section is large.

FIG. 10 is a graph showing a pressure change when the deceleration rate in the deceleration section is small.

[Explanation of symbols]

 2 Injection plunger or screw Pd Injection pressure at completion of filling Δ Allowable range of injection pressure at completion of filling L Length of deceleration section c Start point of deceleration section d Filling completion point V Injection speed of deceleration section β Injection speed of filling section Deceleration rate

Claims (2)

[Claims] 1. A filling process comprises program controlling the advancing speed of an injection plunger or screw (2) as a function of its position, and a pressure-holding process programs the holding pressure given to the injection plunger or screw (2) as a function of elapsed time. In the injection control method of the injection molding machine which controls and provides a deceleration section at the end of the filling process and shifts to the pressure holding process, the injection pressure (Pd) at the completion of filling in one or a plurality of injection cycles is detected, and The detected value (Pd) is compared with a preset allowable range (Δ), and when the detected value (Pd) falls below the allowable range (Δ), the deceleration section length (L) is shortened and / or When the set value is changed to increase the forward speed (V) of the injection plunger or screw (2) in the deceleration section, and the detected value (Pd) exceeds the allowable range (Δ), First, the set value is changed so as to increase the length (L) of the deceleration section and / or decrease the forward speed (V) of the injection plunger or screw (2) in the deceleration section, and then the subsequent injection is performed. An injection control method for an injection molding machine, characterized by executing a cycle. 2. In the filling step, the forward speed of the injection plunger or screw (2) is program-controlled as a function of its position, and in the pressure holding step the holding pressure given to the injection plunger or screw (2) is programmed as a function of elapsed time. In the injection control method of the injection molding machine which controls and provides a deceleration section at the end of the filling process and shifts to the pressure holding process, the injection pressure (Pd) at the completion of filling in one or a plurality of injection cycles is detected, and The detected value (Pd) is compared with a preset allowable range (Δ), and when the detected value (Pd) falls below the allowable range (Δ), the deceleration rate (β) of the injection plunger or the screw (2) in the deceleration section. ) Is decreased or the length of the deceleration section (L) is shortened along with this, the detected value (Pd) exceeds the allowable range (Δ). In this case, the deceleration rate (β) of the injection plunger or screw (2) in the deceleration section is increased or the set value is changed in the same direction as the length (L) of the deceleration section is increased, and then the subsequent injection is performed. An injection control method for an injection molding machine, characterized by executing a cycle.