JP2001150505A - Method and apparatus for controlling mold clamping force in injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus capable of automatically controlling the necessary minimum mold clamping force of an injection molding machine without being influenced by the skillfulness of an operator. SOLUTION: In a mold clamping force control method of an injection molding machine using a toggle closing both of a movable mold and a fixed mold and injecting and charging a molten resin in the mold cavity formed by both molds to obtain a molded article, on the basis of the relation between effective mold clamping force, which is obtained by operating the detection value obtained by detecting the mold clamping force applied to the molds during a mold clamping force holding period by a mold clamping force detecting means, and the set mold clamping force, which is obtained by operating the position of a crosshead at a time of the mating state of both molds under a dry cycle state and the detection value obtained at this time, the position of the crosshead is controlled so that the mold clamping force obtained by subtracting the set mold clamping force from the effective mold clamping force enters an arbitrary allowance range to apply constant mold clamping force to both molds during a mold clamping period.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for controlling a mold clamping force in an injection molding machine, and more particularly to a method for forming a thin molded product at a low pressure without difficulty to produce a good quality molded product with little residual stress and deformation. The present invention relates to a method and an apparatus for controlling a mold clamping force of an injection molding machine that can be efficiently produced.

[0002]

2. Description of the Related Art In a conventional injection molding, a skilled operator empirically predicts a mold clamping force in consideration of molding conditions such as a molded product size and a molding material, and performs trial and error by trial-and-error. Tightening force was determined. For this reason, highly skilled operators open the mold to the extent that burrs do not occur during injection filling of the molten resin, and perform molding with a mold clamping force that is low enough to discharge gas generated in the cavity and from the molten resin. Was. In particular, when molding a thin product such as a CD disk, the molding is performed at the lowest possible pressure to prevent residual stress from remaining in the molded product, thereby preventing deformation of the molded product and optically controlling the birefringence of the molded product. The quality was prevented from deteriorating.

[0003] However, the minimum required mold clamping force (to be described later) corresponding to a mold opening force (a force for opening a mold, hereinafter also referred to as a resin reaction force) that increases as the injection filling of the molten resin proceeds. Could not be loaded). That is, there has been no control method for changing the mold clamping force set before the start of the molding cycle in accordance with the resin reaction force that changes every moment during the molding cycle. Therefore, an excessive clamping force is applied, and the CD
It has been difficult to obtain thin products such as disks at optically satisfactory quality levels.

On the other hand, since the setting of the above-mentioned mold clamping force cannot be expected by a general operator, an excessive mold clamping force is applied, so that the residual stress of the molded product becomes large, and the deformation of the molded product and The birefringence increased and it was difficult to obtain a good product. In addition, since an excessive mold clamping force is applied, the mold is worn out and maintenance is required. Japanese Patent Application Laid-Open No. 8-276479 is a prior art which has solved the above-mentioned problems.

In this prior art, a movable die and a fixed die of a disk substrate die are mounted on a movable plate and a fixed plate of a molding machine, respectively, and the movable die is moved relative to the fixed die by a mold closing operation. When moving to a predetermined distance of 0 to 0.5 mm, the injection of the molten resin from the nozzle of the injection device into the cavity of the disk substrate mold is started, and the movable mold is turned into a fixed mold. Upon detecting the contact, the hydraulic pressure supplied to the mold clamping side of the mold clamping cylinder is adjusted to maintain the mold clamping force at a predetermined value corresponding to approximately 10 to 40% of the rated mold clamping force. After the end of the injection step, the hydraulic pressure supplied to the mold clamping side of the mold clamping cylinder is increased to perform one or more stages of mold clamping pressure control. A technique for performing a cooling step is disclosed.

However, in the above prior art,
The degree of pressure reduction of the mold clamping force is not sufficient, and a mold clamping pressure exceeding the necessary minimum is applied. In addition, approximately 1 of the rated mold clamping force
The timing at which the mold clamping force corresponding to 0 to 40% is applied and the relationship between the mold clamping force and the resin reaction force are not clear, and the injection filling may be completed after the mold clamping force is applied. In this case, the outgassing may be insufficient. Also, the resin reaction force becomes larger than the mold clamping force before the end of the injection process, and once the mold is closed and a small mold clamping force of 10 to 40% of the rated load is applied, the mold is opened again to generate burrs. There is fear.

[0007] The minimum required clamping force described in paragraph [0003] refers to a state in which a slight gap is opened between the fixed mold and the movable mold so that no burr occurs even when the mold mating surface is opened. Mold clamping force required to maintain the
It varies depending on the filling behavior of the resin. That is, since only a part of the mold cavity is filled with the resin in the initial stage of the injection filling, the force for opening the mold by the filled resin is small, and the resin reaction force increases as the filling proceeds. .

In addition, air exists in the mold cavity, and in the injection molding in which the molten resin is filled at a high speed, it is necessary to quickly discharge the air out of the mold. In this case, if the fixed mold and the movable mold are tightened with a large force, there is no escape of air, and the air in the mold is adiabatically compressed and becomes high temperature, causing gas burning in the molded product and partially It enters the molten resin and causes a molded article defect called a void. Further, if a gas venting path is provided on the mold mating surface in order to improve gas venting, molten resin leaks from this part and burrs are generated, resulting in molding failure.

[0009]

SUMMARY OF THE INVENTION A method for controlling a mold clamping force of an injection molding machine in which the above-mentioned problems are solved and a minimum necessary clamping force is automatically applied without being influenced by the skill of an operator. And to provide the device.

[0010]

In order to solve the above-mentioned problems, according to the present invention, in a first aspect, both a movable mold and a fixed mold are closed to form a mold between the movable mold and the fixed mold. In a method of controlling a mold clamping force of an injection molding machine using a toggle to obtain a molded product by injection filling a molten resin into a mold cavity to be molded, a mold provided to the mold during a mold clamping force holding period is provided. The effective clamping force obtained by calculating the detected value of the clamping force detected by the clamping force detecting means, the crosshead position in the mold matching state of the two dies under a dry cycle condition, and the obtained value at that time. Based on the relationship with the set clamping force obtained by calculating the detected value, the crosshead position is adjusted so that the clamping force value obtained by subtracting the set clamping force from the effective clamping force falls within an arbitrary allowable range. To apply a constant mold clamping force between the two molds during the mold clamping period. It was and.

In the second invention, the effective mold clamping force is always larger than the set mold clamping force during the injection and filling of the molten resin according to the first invention into the mold cavity and during the pressure holding period. The crosshead position is controlled.
Further, in the third invention, the effective mold clamping force is always larger than the set mold clamping force during the pressure holding period and the cooling period after the molten resin according to the first invention is injected and filled into the mold cavity. The crosshead position is controlled as described above.

Next, in a fourth invention, a molded product is obtained by closing both the movable mold and the fixed mold and injecting and filling a molten resin into a mold cavity formed between the movable mold and the fixed mold. A mold clamping force control unit of an injection molding machine using a toggle to obtain a mold clamping force detecting unit for detecting a mold clamping force applied to the mold by a mold clamping force detection sensor during a mold clamping force holding period; A storage unit for storing the relationship between the crosshead position when the molds of both dies are aligned under a dry cycle and the mold clamping force calculated based on the detected mold clamping force at that time; and A calculation unit for calculating an effective clamping force based on a value detected by the clamping force detection unit, and a comparison control unit for comparing the effective clamping force calculated by the calculation unit with the input initial clamping force. , Crosshead position detector that detects the amount of movement of the crosshead from the mold touch point, and comparison control A mold clamping control unit that issues a command value of the mold clamping force to the mold clamping cylinder control unit in response to a signal from the mold clamping unit, and a mold clamping operation mechanism control unit that moves the crosshead back and forth based on information obtained by the mold clamping control unit. And a mold-clamping condition setting unit for setting a tolerance between the initial mold-clamping force, the effective mold-clamping force, and the set mold-clamping force, and an increase / decrease width of the mold-clamping force.

In the fifth invention, the mechanism for driving the toggle according to the fourth invention comprises a servomotor and a ball screw mechanism.

[0014]

According to the present invention, the actual clamping force applied to the mold during the clamping period (in the present invention, defined as the effective clamping force) is the clamping force transmitting member of the clamping device. Is calculated by measuring and calculating the stress of. In addition, the molds are adjusted in a state where the molten resin is not injected (also referred to as a dry cycle), and the crosshead is advanced from this state to obtain the relationship between the crosshead position and the effective mold clamping force. on the other hand,
In the actual molding cycle, a force for opening the mold due to the filling pressure of the molten resin, that is, a resin reaction force is generated. This resin reaction force increases as the injection filling progresses, and then decreases as the cooling of the filled resin progresses.

A description will be given below with reference to FIG. And the effective mold clamping force obtained from the crosshead position from the so-called touch point A where both molds contact each other during the dry cycle (the state where the mold clamping force is zero) and the stress of the mold clamping force transmitting member. , A mold clamping force (F1: line segment CB) at the time of the dry cycle corresponding to the crosshead position (point B) at a certain moment is obtained. On the other hand, the mold clamping force obtained from the stress of the mold clamping force transmitting member during the actual molding cycle at the crosshead position, that is, the effective mold clamping force (F2: line segment EG) receives a resin reaction force, so that F1
It is getting bigger. F2> F1 (Equation 1) Further, the effective mold clamping force (F
The relationship between 2) and the resin reaction force (F3: line segment EF) and the mold pressure (F4: line segment FG) acting between the fixed mold and the movable mold are as follows. F2-F3 = F4 (Equation 2) When F4 becomes minus, a gap is left in the mold. If the gap becomes large, the molten resin leaks out of the cavity and burrs are generated. Generally, it depends on the type of resin and the molding conditions, but it is generally said that no burr occurs if the gap is in the range of 0 to 0.2 mm.

One of the technical ideas of the present invention is to improve the outgassing in the mold by reducing the mold pressure (F4) as much as possible and to reduce the mold pressure applied to the molten resin in the cavity as much as possible. By reducing the size and smoothing the flow of the molten resin in the cavity, the residual stress remaining in the molded product is reduced, and the deformation of the molded product is reduced. In addition, by achieving the above technical idea by program control, even an inexperienced operator can easily and efficiently produce a molded product having little residual stress and good optical quality.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. 1 to 4 relate to an embodiment of the present invention, FIG. 1 is a configuration diagram of a mold clamping force control device of a toggle type injection molding machine according to the present invention, and FIG. 2 is a crosshead position and effective mold clamping according to the present invention. FIG. 3 is an explanatory diagram of force, resin reaction force, etc., FIG. 3 is an explanatory diagram of a control state of an effective mold clamping force and a set mold clamping force, and FIG. 4 is a flowchart of mold clamping force control.

The structure and operation of the toggle injection molding machine used in the present invention will be described with reference to FIG. The mold clamping device 1 of the injection molding machine includes a fixed platen 3 at the front end of the tie bar 2.
The link housing 4 is attached to the rear end of the tie bar, and a servo motor 8 for toggle driving (for mold clamping) is fixed to the link housing 4. By driving the cross head 12 by the servo motor 8 and the ball screw mechanism 11, the movable platen 5 sliding on the tie bar 2 via the toggle link is moved away from and close to the fixed platen 3. The movable mold 7 is mounted on the fixed platen 3, and the fixed mold 6 is mounted on the fixed platen 3.

A strain gauge is attached on the tie bar 2 as the mold clamping force detecting sensor 13, and the detection signal is transmitted to the mold clamping force detecting unit 30. A linear sensor is used as the position detection sensor 14 of the crosshead 12, and the detection signal is transmitted to the crosshead position detection unit 31. In this embodiment, since a servomotor and a ball screw mechanism are employed as the toggle drive mechanism, the crosshead position can be calculated from the rotation angle of the servomotor.

Next, the configuration and function of the mold clamping force control device will be described. The initial clamping force, the clamping speed, the tolerance between the effective clamping force and the set clamping force, and the increase / decrease width of the clamping force are input to the clamping condition setting unit 33. These input values are input to the mold clamping controller 3
4 is sent. Before starting the molding cycle, in a state where the resin is not injected (dry cycle), the relation data between the position (distance) of the crosshead from the mold matching position and the mold clamping force (F1 = F2) is obtained and stored in the storage unit 35. Let it.

Based on the initial clamping force (F0) input to the clamping condition setting unit 33, the clamping operation is performed via the clamping control unit 34 and based on a command from the clamping operation mechanism control unit 36. . Upon completion of the mold clamping operation, an injection control unit (not shown) issues a molten resin injection instruction, and the mold cavity is filled with the molten resin. As the filling of the molten resin proceeds, a resin reaction force (F3) is generated, and the tie bar stress increases against the force for opening the mold. The tie bar stress is detected by the mold clamping force detection unit 30 via the mold clamping force detection sensor 13,
The calculation unit 37 calculates and calculates the force (effective clamping force (F2)) applied to the tie bar. The calculated effective mold clamping force (F2) is compared with the input initial mold clamping force (F0) by the comparison control unit 38.

From the effective mold clamping force (F2), the initial mold clamping force (F
When the value obtained by subtracting 0) becomes larger than the allowable value previously input to the mold-clamping condition setting unit 33, the mold-clamping force increases by the increase width of the mold-clamping force previously input to the mold-clamping condition setting unit 33. Forward the crosshead position as shown. As shown in FIG. 2, the relationship between the increased value of the mold clamping force and the amount of movement of the crosshead position (setting B) is as follows: Calculation unit 3 based on the relationship between the position (distance) of
7 is calculated and calculated. The mold clamping force calculated based on FIG. 2 at the position after the crosshead movement is the set mold clamping force (F1) at the crosshead position. As the filling of the molten resin proceeds, the resin reaction force further increases, and the value obtained by subtracting the set mold clamping force (the value at the start of injection was the initial mold clamping force) from the effective mold clamping force is set in advance to the mold clamping condition setting. When the value exceeds the allowable value input to the section 33, as described above, the crosshead position is advanced so that the mold clamping force is increased by the increase width of the mold clamping force previously input to the mold clamping condition setting section 33. . Thus, the control of the mold clamping force is repeatedly performed.

When the injection filling of the molten resin is completed, a pressure-holding step is started. During the pressure-holding step, there is little change in the resin reaction force, and therefore, as shown in FIG. Then, from the end of the pressure-holding step to the cooling step (immediately before the end of the pressure-holding), the resin reaction force gradually decreases. Therefore, when the crosshead position is fixed at the final position during the period in which the resin reaction force increases, the effective mold clamping force (F2) decreases by the amount of the resin reaction force (F3) decreasing. Therefore, the value of (F2−F1) becomes small and eventually becomes zero. In this state,
This means that the maximum mold clamping force is applied when the resin reaction force is increasing. If a large clamping force is to be applied during the cooling period, the control of the clamping force may be stopped at this point. On the other hand, when it is desired to reduce the mold clamping force in accordance with the contraction and solidification of the resin, control is performed to retract the crosshead so that (F2-F1) becomes a preset allowable value. The control method in this case will be described below.

A method of controlling the mold clamping force during the period from the end of the pressure holding step to the cooling step will be described. Even during this period, the technical concept of the mold clamping force control is the same as that in the case where the resin reaction force during the injection filling step and the pressure holding period becomes large. That is, the difference between the effective mold clamping force (F2) and the mold clamping force in the dry cycle corresponding to the current crosshead position, that is, the set mold clamping force (F1) is compared. The solidification of the resin in the cavity progresses and volume shrinkage occurs, so that the resin reaction force (F3) gradually decreases. Therefore, the effective mold clamping force F2 is the resin reaction force (F3).
It gets smaller by the minute. Therefore, the value of (F2−F1) at the current crosshead position becomes smaller, and becomes zero when the solidification and shrinkage of the resin further proceeds. The fact that the effective mold clamping force (F2) and the set mold clamping force (F1) are the same means that there is no resin, that is, a dry cycle state, and no force is applied to the resin in the cavity. Will be.
In this state, only a large force acts on the mold,
Has no effect. Accordingly, mold clamping force control during the cooling period is performed for the purpose of extending the life of the mold and saving energy.

As described above, since the effective mold clamping force (F2) decreases, the set mold clamping force (F1) also needs to be decreased by the same amount. Therefore, the set mold clamping force (F1) can be reduced by retreating the crosshead position. The permissible value of (F2−F1) and the amount of movement of the crosshead position are the same as those when the resin reaction force increases. However, if the cross-head position is set so that the set mold clamping force is 0 ton or less, a gap is formed between the mold and the molded product, so that the cooling rate is reduced. Therefore, the set mold clamping force is 0
Stops the control when the load falls below ton, holds the crosshead position as it is, and opens the mold with a timeout signal

In the latter stage of the filling of the molten resin, if the injection operation is continued even after the filling of the mold cavity is completed, a pack pressure is generated. For this reason, burrs may be generated because the rising speed of the set mold clamping force cannot keep up. In order to solve this problem, it is desirable to switch the speed control to the pressure control early in the latter half of the injection to suppress the generation of the pack pressure. Also, it is desirable that the holding pressure be set to a low pressure for about one second and then shifted to the normal holding pressure condition.
However, such consideration should be made only for a resin having particularly high fluidity.

Hereinafter, comparative examples and examples will be described.

Comparative Example 1 A substantially box-shaped mold having a projected area of about 850 cm ² and a thickness of 3 mm was used, and molding was performed using a polycarbonate resin as a molding material. As the injection molding machine, a horizontal injection molding machine having a maximum clamping force of 450 tons and equipped with a servo motor / ball screw mechanism toggle drive device was used. Molding conditions were: mold temperature 85 ° C, barrel setting temperature of the injection unit 300 ° C, mold clamping force 400 tons, injection time 8 seconds,
Normal molding was performed under the conditions of a dwell time of 5 seconds and a dwell pressure of 400 kgf / cm ² . As a result, no burrs were formed on the molded product. In addition, as a result of confirming the residual stress using a polarizing plate, there were many interference fringes.

[0028]

Example 1 The initial mold clamping force was set to 200 tons at the same mold, molding material, mold temperature and barrel setting temperature as in Comparative Example 1, and the effective mold clamping force (F2) and the set mold clamping force (F1). If the difference (F2-F1) exceeds 20 tons, the set mold clamping force
The conditions for moving the crosshead forward to the crosshead position that increases by tons were set. The injection time, the dwell time and the dwell pressure were set under the same conditions as in Comparative Example 1. The control period of the mold clamping force was the injection and the initial stage of the dwelling pressure, and the control of the mold clamping force was not performed during the latter stage of the dwelling period when the resin reaction force decreases and during the cooling period. As a result, the final value of the set mold clamping force was 280 tons. This molded product was free of burrs, and the residual stress was confirmed with a polarizing plate. As a result, the number of interference fringes was half that of Comparative Example 1.

The embodiment of the mold clamping control device and the mold clamping control method of the toggle type injection molding machine having the structure according to the present invention has been described in detail above. It should not be construed that the present invention is limited to such specific examples. For example, a hydraulic cylinder can be used instead of the servomotor / ball screw mechanism as the toggle drive mechanism, and a toggle link can be used instead of the tie bar as the mounting position of the mold clamping force detection sensor.
In addition, although not enumerated one by one, the present invention can be embodied in an aspect in which various changes, modifications, improvements, and the like are added based on the knowledge of those skilled in the art. It goes without saying that, unless departing from the scope of the present invention, any of them is included in the scope of the present invention.

[0030]

As described above, according to the present invention, the minimum necessary mold clamping force is automatically applied without being influenced by the skill of the operator, so that the gas escape in the cavity is good. Even a thin object such as a CD can be easily formed. Therefore, it is possible to efficiently obtain a molded article with little residual stress and without deformation. In particular, it is suitable for molded articles used for optical applications.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a mold clamping force control device of a toggle type injection molding machine according to the present invention.

FIG. 2 shows a crosshead position and an effective clamping force according to the present invention;
It is explanatory drawing of resin reaction force etc.

FIG. 3 is an explanatory diagram of a control state of an effective mold clamping force and a set mold clamping force according to the present invention.

FIG. 4 is a flowchart of mold clamping force control according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold-clamping control device of toggle-type injection molding machine 2 Tiber 3 Fixed plate 4 Link housing 5 Movable plate 6 Fixed die 7 Movable die 8 Servo motor 10 Toggle link (toggle mechanism) 11 Ball screw (ball screw mechanism) 12 Cross head 13 Mold clamping force detection sensor 14 Cross head position detection sensor 30 Mold clamping force detection unit 31 Cross head position detection unit 33 Mold clamping condition setting unit 34 Mold clamping control unit 35 Storage unit 36 Mold clamping operation mechanism control unit 37 Operation unit 38 Comparison control Part F0 Initial mold clamping force F1 Set mold clamping force F2 Effective mold clamping force F3 Resin reaction force F4 Mold pressure A Mold touch point

Claims (5)

[Claims] 1. A toggle is used for closing a movable mold and a fixed mold and injecting and filling a molten resin into a mold cavity formed between the molds to obtain a molded product. A method of controlling a mold clamping force of an injection molding machine, the method comprising calculating a mold clamping force applied to a mold during a mold clamping force holding period by calculating a detection value detected by mold clamping force detection means. Based on the relationship between the mold clamping force and the set mold clamping force obtained by calculating the crosshead position in the mold matching state of the two dies under a dry cycle state and the detection value obtained at that time, By controlling the crosshead position so that a mold clamping force value obtained by subtracting the set mold clamping force from the mold clamping force falls within an arbitrary allowable range, a constant mold clamping force is applied between the two molds during the mold clamping period. And controlling the mold clamping force of the injection molding machine. 2. The method according to claim 1, wherein the position of the crosshead is controlled such that the effective mold clamping force is always larger than the set mold clamping force during injection filling of the molten resin into the mold cavity and also during the dwelling period. 2. The method according to claim 1, wherein the clamping force is controlled by an injection molding machine. 3. The crosshead position is controlled such that the effective mold clamping force is always larger than the set mold clamping force during the pressure holding period and the cooling period after the molten resin is injected and filled into the mold cavity. 2. The method according to claim 1, wherein:
A method for controlling a mold clamping force of an injection molding machine as described in the above. 4. A toggle is used to obtain a molded product by closing both a movable mold and a fixed mold and injecting and filling a molten resin into a mold cavity formed between the two molds. A mold clamping force control unit for an injection molding machine, wherein the mold clamping force detecting unit detects a mold clamping force applied to the mold by a mold clamping force detection sensor during a mold clamping force holding period; A storage unit for storing the relationship between the crosshead position when the two dies are aligned and the clamping force calculated based on the detected clamping force at that time; and a clamping force detection unit during the actual molding cycle. A calculation unit for calculating the effective mold clamping force based on the detected value, a comparison control unit for comparing the effective mold clamping force calculated by the calculation unit with the input initial clamping force, and a mold touch point. A crosshead position detector that detects the amount of movement of the crosshead, and a mold that receives signals from the comparison controller. A mold clamping control unit that issues a command value of the mold clamping force to the clamping cylinder control unit, a mold clamping operation mechanism control unit that moves the crosshead back and forth based on information obtained by the mold clamping control unit, and an initial mold clamping force and effective A mold clamping force control device for an injection molding machine, comprising: a mold clamping condition setting unit for setting a tolerance between a mold clamping force and a set mold clamping force and a rise / fall range of the mold clamping force. 5. The apparatus according to claim 4, wherein the mechanism for driving the toggle comprises a servomotor and a ball screw mechanism.