JP7673582B2 - Method for controlling clamping force in multiple stages in a toggle clamping device - Google Patents

Description

The present invention relates to a method for controlling the clamping force of a toggle clamping device in multiple stages, which gradually increases the clamping force based on the injection filling rate of molten resin into the mold cavity.

Injection molding using a resin material with an injection molding machine is carried out as follows. First, the resin material is fed into the injection cylinder. The fed resin material is plasticized and becomes molten resin by shear heat generated by the rotational movement of the screw with a spiral flight and heat from a heater or the like installed in the injection cylinder, and is stored in the injection cylinder at the tip of the screw. Next, the fixed mold and the movable mold attached to the mold clamping device are clamped (called the mold clamping process), and the screw is advanced toward the mold cavity to be formed, and the molten resin stored in the injection cylinder is injected and filled (called the injection process). After pressure holding filling to compensate for solidification shrinkage caused by cooling and solidifying of the molten resin, and cooling and holding in the mold cavity, the mold is opened and the molded product is removed from the mold cavity. This series of molding operations is repeated until the required number of molded products is obtained.

The pressing force (called mold clamping force) between the fixed mold and the movable mold in the mold clamping process is set according to the size of the mold cavity. Specifically, it is a calculated value obtained by multiplying the projected area of the mold cavity in the mold clamping direction (called the product projected area) by the molding resin pressure. Note that this molding resin pressure varies depending on the type of resin material used, the gate position and number of gates in the mold cavity, the temperature of the molten resin and the mold, the product weight, the product thickness, the time required for injection filling, etc. For this reason, the mold clamping force obtained by adding a margin to the calculated value above is set as the maximum mold clamping force, and the mold is clamped by the mold clamping device. Therefore, the mating surface of the fixed mold and the movable mold (called the mold PL surface) is firmly pressed.

If the injection process is performed after the clamping process with this maximum clamping force, the air remaining in the mold cavity and the volatile gases released from the molten resin will not be expelled from the mold PL surface that is firmly pressed, but will remain (called residual gas), causing molding defects due to residual gas such as poor transfer of the product design pattern, incomplete filling due to gas accumulation, poor appearance such as weld patterns and gas flow patterns, and void defects due to gas entrapment. For this reason, a method of injection molding in which the injection process and clamping process are linked has been proposed. In other words, it is a multi-stage control method of clamping force that gradually increases the clamping force in response to an increase in the injection filling of the molten resin in the mold cavity.

On the other hand, electric toggle clamping devices that drive toggle link mechanisms with electric servo motors are widely used due to the effects of environmental improvement through energy saving and hydraulic oil elimination, and the effects of injection molding stability due to high repeatability. The clamping force multi-stage control method of this electric toggle clamping device is performed by arbitrarily holding the position of the toggle link mechanism within the range of maximum clamping force from a state where the mold PL surfaces are aligned but no clamping force is generated (called the mold touch point). The toggle link mechanism at this time is within the range from a bent state to a straight state. By utilizing the high-precision control of the electric servo motor and the boosting characteristics of the toggle link mechanism, highly accurate multi-stage control of the clamping force can be easily performed. On the other hand, due to the characteristics of the toggle link mechanism, it has been confirmed that when the toggle link mechanism is held at a certain position, the load on the electric servo motor becomes excessive and it cannot be held (called an overload state). This requires an increase in the capacity of the electric servo motor, which leads to issues of increased size and cost of the clamping device.

For example, as shown in Patent Document 1, a method of controlling the clamping force in multiple stages has been proposed for an electric toggle clamping device, in which after a set clamping force is reached, the ball screw is rotated in the reverse direction within the allowable range of the clamping force to reduce the clamping force within the allowable range. The toggle link mechanism is in a bent state within the range of the maximum clamping force from the mold touch point. This is said to reduce the torque (or load factor) of the electric servo motor, resulting in energy savings and a more compact clamping device.

Japanese Patent Application Publication No. 9-254211

However, in the method shown in Patent Document 1, by rotating the ball screw in the reverse direction, the toggle link mechanism retreats toward the mold touch point, and the clamping force definitely decreases, although it is within the allowable range. Meanwhile, the injection filling of the molten resin into the mold cavity continues, and the filling rate increases. As the filling rate of the molten resin increases, the required clamping force must increase. The method shown in Patent Document 1 goes against this logic, and the clamping force becomes insufficient, causing gaps on the mold PL surface, and the molten resin leaks from the mold PL surface (called a resin burr defect). In other words, the method shown in Patent Document 1 cannot be applied to the multi-stage mold clamping force control method for injection molding, which increases the mold clamping force in response to an increase in the filling rate of the molten resin in the mold cavity and actively removes gas from the mold PL surface.

The present invention aims to provide a method for multi-stage control of the clamping force of a toggle clamping device, which is driven by an electric servo motor, in injection molding in which the clamping force is increased stepwise based on the injection filling rate of molten resin into the mold cavity. The object of the present invention is to provide a method for multi-stage control of the clamping force of a toggle clamping device, which is driven by an electric servo motor, in order to avoid an overload condition of the electric servo motor.

The method for multi-stage control of clamping force of a toggle clamping device of the present invention comprises the steps of:
A method for multi-stage control of clamping force of a toggle clamping device, which increases the clamping force in stages based on a filling rate of a molten resin injected into a mold cavity, comprising:
The toggle clamping device is an electric toggle clamping device that converts the rotational motion of an electric servo motor into linear motion using a ball screw mechanism to operate a toggle link mechanism, and is characterized in that when the load rate of the electric servo motor exceeds a predetermined threshold, it takes evasive action to reduce the load rate.

In the method for multi-stage control of clamping force of a toggle clamping device of the present invention,
The avoidance action is preferably performed by rotating the electric servo motor in a direction that increases the mold clamping force.

The present invention provides a method for multi-stage control of the clamping force of a toggle clamping device that is driven by an electric servo motor and that gradually increases the clamping force based on the injection filling rate of molten resin into the mold cavity.

1 is a conceptual diagram of a toggle clamping device according to the present invention. 2A to 2C are diagrams illustrating the mold opening and closing operations of the toggle clamping device of FIG. 1 . FIG. 4 is a flow chart showing a method for multi-stage control of clamping force of a toggle clamping device according to the present invention. FIG. 4 is a diagram showing the load factor characteristics of an electric servo motor. FIG. 13 is a diagram showing an avoidance action for reducing the load factor of an electric servo motor.

Below, preferred embodiments for carrying out the present invention will be described with reference to the drawings. Note that the following embodiments do not limit the inventions according to the claims. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solutions of the inventions according to the claims. Furthermore, in the present embodiments, the scales and dimensions of each component may be exaggerated, and some components may be omitted.

[Toggle clamping device]
First, the toggle clamping device according to the present invention will be described with reference to Fig. 1. Fig. 1 shows a conceptual diagram of a toggle clamping device. In the following description, the toggle clamping device according to the present invention is based on a horizontally arranged toggle clamping device in which the toggle link mechanism is bent inward, but is not limited to this. For example, the toggle link mechanism may be bent outward, or the toggle link mechanism may be vertically arranged.
The toggle clamping device 100 shown in FIG. 1 includes a clamping main body 20, a toggle link mechanism 30, a die height adjustment unit 40, a clamping drive unit 50, and a clamping control unit 60.

The mold clamping body 20 has a fixed platen 21, a movable platen 22, and a link housing 23 arranged in a line, and the fixed platen 21 and the link housing 23 are connected by a number of tie bars 24. The movable platen 22 is supported by the tie bars 24 and is arranged so as to be able to slide between the fixed platen 21 and the link housing 23. The fixed mold 11 is attached to the fixed platen 21, and the movable mold 12 is attached to the movable platen 22. The fixed mold 11 and the movable mold 12 are joined together to form a mold cavity 13 surrounded by the mold PL surface 14. This mold PL surface 14 has the role of preventing leakage of molten resin from the mold cavity 13 and discharging volatile gases released from the air and molten resin within the mold cavity 13.

The toggle link section 30 is disposed between the movable platen 22 and the link housing 23, and the movable platen 22 and the link housing 23 are connected by a plurality of links 33. The other end of the link 33 is connected to the crosshead 32. The link 33, the crosshead 32, the movable platen 22, and the link housing 23 are connected to each other by link pins 33P so as to be rotatable and slidable, and the bent state and linear state of the toggle link mechanism 30 can be adjusted according to the position of the crosshead 32. The link housing 32 incorporates a ball screw 31 that converts rotational motion into linear motion, and the tip of the ball screw 31 is connected to an electric servo motor 34. With this configuration, the rotational motion of the electric servo motor 34 is converted into linear motion by the ball screw 31, and the crosshead 32 is caused to move linearly. The movable platen 22 is operated via the link 33 according to the linear motion of the crosshead 32. A toggle clamping device driven by an electric servo motor is called an electric toggle clamping device.

Here, regarding the operation of the movable platen 22 or the movable mold 12, the direction approaching the fixed platen 21 and the fixed mold 11 is defined as the forward direction F, the direction away from the fixed mold 11 is defined as the backward direction B, the operation toward the forward direction F is defined as the mold closing operation, and the operation toward the backward direction B is defined as the mold opening operation. The electric servo motor 34 has a built-in measuring device (called an encoder) that measures the rotation direction and the rotation amount or rotation angle, and the mold closing operation and mold opening operation are adjusted by adjusting the rotation direction of the rotational motion of the electric servo motor 34. In addition, the position of the crosshead 32 can be adjusted by adjusting the rotation amount and rotation angle of the rotational motion of the electric servo motor 34, and the moving speed and moving amount of the movable platen 22 and the movable mold 12 can be adjusted. Based on the control command of the mold clamping control unit 60, the mold clamping drive unit 50 adjusts the rotational motion of the electric servo motor 34. Details will be described using FIG. 2.

Figure 2 shows the mold opening and closing operation of a toggle clamping device. Figure 2(a) shows the state where the toggle link mechanism is bent significantly and the fixed mold 11 and the movable mold 12 are completely separated (called mold opening completion), Figure 2(b) shows the state where the toggle link mechanism is bent less and the fixed mold 11 and the movable mold 12 are joined (called the mold touch point), and Figure 2(c) shows the state where the toggle mechanism is fully extended and in a straight line (called mold clamping completion). At the mold touch point, the mold clamping force is close to zero, and at mold clamping completion, the mold clamping force is at its maximum value.

The mold closing operation indicates the movement state from mold opening completion (a) to the mold touch point (b), and the rotation direction of the electric servo motor 34 at this time is defined as the mold closing rotation. The mold opening operation indicates the movement state from the mold touch point to mold opening completion, and the rotation direction of the electric servo motor 34 at this time is defined as the mold opening rotation. By adjusting the rotation amount or rotation angle of the electric servo motor 34, the stop position of the movable platen 22 or movable mold 12 is adjusted within the range from mold opening completion to the mold touch point. Furthermore, by adjusting the rotation speed of the electric servo motor 34, the movement speed of the mold opening operation (referred to as the mold opening speed) and the movement speed of the mold closing operation (referred to as the mold closing speed) can also be precisely adjusted.

At the mold touch point (b), the fixed mold 11 and the movable mold 12 come together to form the mold PL surface and the mold cavity 13, but no pressing force (called mold clamping force) is generated on the mold PL surface. At this time, the length of the tie bar 24 connecting the fixed platen 21 to the link housing 23 is defined as L1.

The movement from the mold touch point (b) to the completion of mold clamping (c) (called the mold clamping operation) causes the tie bar 24 to expand from L1 to L2 (L1<L2). A compressive force is generated according to the amount of expansion of the tie bar 24, and a pressing force against the mold PL surface, that is, the mold clamping force, acts. The movement from the completion of mold clamping to the mold touch point (called the pressure reduction operation) relieves the expansion of the tie bar 24, and the mold clamping force also decreases. By controlling the rotation of the electric servo motor, the mold clamping force can be adjusted to any value within the range from the mold touch point to the completion of mold clamping. Injection molding using a mold clamping force multi-stage control method that gradually increases the mold clamping force according to the injection filling of molten resin into the mold cavity 13 utilizes the adjustment range of the mold clamping force from the mold touch point to the completion of mold clamping.

Returning to the explanation of FIG. 1, the die-height adjustment unit 40 adjusts the clamping force according to the extension amount of the tie bar 24 when the clamping is completed, and is disposed in the link housing 24. The die-height motor 41 rotates the driven pulley 43 via the drive pulley 42 and the transmission belt 44. The driven pulley 43 is screw-connected to the threaded portion 24G on the rear B side of the tie bar 24, and the rotation of the driven pulley 43 moves the movable mold 12, the movable platen 22, the toggle link portion 30, and the link housing 23 together in the mold opening/closing direction (called die-height adjustment). The operating direction of the die-height drive can be adjusted by adjusting the rotation direction of the die-height motor. Also, the movement amount of the die-height adjustment can be adjusted by adjusting the rotation amount of the die-height motor 41. The rotation adjustment of the die-height motor 41 is performed by the die-height drive unit 46 based on the control command value of the die-height control unit 47. The die height control unit 47 is connected to the mold clamping control unit 60, and the extension amount of the tie bars 24 is calculated in the die height control unit 47 based on the mold clamping force setting value set in the mold clamping control unit 60. The die height adjustment is performed within the range from the mold touch point to the completion of mold opening. The rotatable driven pulley 43 and the link housing 23 are connected by the support unit 45. In FIG. 1, the configuration is a drive pulley 42, a transmission belt 44, and a driven pulley 43, but is not limited to this. For example, a configuration of a drive gear, a gear chain, and a driven chain may be used, or a configuration using a transmission gear instead of a gear chain may be used.

The clamping force adjustment is performed following the die height adjustment corresponding to the extension amount of the tie bar 24 calculated based on the clamping force setting value. The clamping force adjustment is completed by driving the electric servo motor 34 to perform the clamping operation. At this time, the actual extension amount of the tie bar 24 is measured by the tie bar sensor TS and converted into the clamping force acting on the mold PL surface (called the clamping force measurement value). When it is confirmed that this clamping force measurement value and the clamping force setting value set by the clamping control unit 60 are within the allowable range, the clamping force adjustment is completed. If it is outside the allowable range, a pressure reduction operation and a mold opening operation are performed, and the die height adjustment is redone. In this case, the extension amount of the tie bar 24 is corrected according to the difference from the allowable range. After the die height adjustment is redone, when it is confirmed that it is within the allowable range, the clamping force adjustment is completed. The die height adjustment and the clamping force adjustment are collectively called the clamping force setting, and the automatic operation of the clamping force setting is called the automatic clamping force setting. This mold clamping force setting adjusts the maximum mold clamping force that occurs when mold clamping is complete. Injection molding is performed using the mold clamping force multi-stage control method within a range from the maximum mold clamping force at the time of mold clamping completion to a state where the mold clamping force at the mold touch point is close to zero.

[Method for multi-stage control of mold clamping force]
Next, a method for multi-stage control of mold clamping force using the electric toggle mold clamping device shown in Fig. 1 will be described with reference to Fig. 3 to Fig. 5. Fig. 3 shows a flow of the method for multi-stage control of mold clamping force, Fig. 4 shows the load factor characteristics of the electric servo motor 34, and Fig. 5 shows avoidance actions for reducing the load factor of the electric servo motor 34. The load factor indicates the relative ratio of the effective torque to the rated torque of the electric servo motor 34, and a load factor of 100% or more is defined as an overload state.

First, as shown in FIG. 3, step 1 is started, and the maximum clamping force according to the mold cavity 13 is set in the clamping force control unit 60. Here, the maximum clamping force is the clamping force calculated by multiplying the projected area (called the product projected area) of the mold cavity 13 in the mold opening and closing direction by the molding resin pressure, and adding a margin to this calculation result. It is preferable to set this margin because the molding resin pressure varies depending on the type of resin material used, the gate position and number of gates in the mold cavity, the temperature of the molten resin and the mold, the product weight, the product thickness, the time required for injection filling, etc. Upon receiving information on the maximum clamping force setting value from the clamping control unit 60, the die height control unit 47 calculates the extension amount of the tie bar 24 and performs automatic clamping force setting. It is confirmed that the clamping force measurement value measured by the tie bar sensor TS and the maximum clamping force setting value are within a preset allowable range, and the automatic clamping force setting is terminated.

The maximum clamping force set by the automatic clamping force setting is the clamping force obtained by multiplying the product projected area by the molding resin pressure, etc. In contrast, there is absolutely no resin in the mold cavity 13 before the start of the injection filling of the molten resin (injection process), and there is no molding resin pressure either, so the maximum clamping force is clearly excessive, and the mold PL surface is firmly pressed. If the injection process is started after clamping with this maximum clamping force, the air remaining in the mold cavity 13 and the volatile gases released from the molten resin remain (gas residue) without being discharged from the mold PL surface that is firmly pressed, causing molding defects due to gas residue, such as poor transfer of the product design pattern, poor filling due to gas accumulation, poor appearance such as weld patterns and gas flow patterns, and void defects due to gas entrapment.

Therefore, as shown in Figure 4 (a), by setting an appropriate clamping force according to the resin filling rate in the mold cavity 13, the pressure on the mold PL surface can be optimized and residual gas can be eliminated. The resin filling rate is the flow projected area of the molten resin injected and filled into the mold cavity 13, projected in the mold opening and closing direction. As the injection process progresses, the flow projected area increases, and when the molten resin is completely filled, the flow projected area and the product projected area become the same. The appropriate clamping force is the clamping force obtained by multiplying this flow projected area by the molding resin pressure, etc. Therefore, the area A (shaded area) below the appropriate clamping force is the range where residual gas can be eliminated, and the area B above the appropriate clamping force is the range where there is a high risk of residual gas. In addition, area Z, which is further below area A, is a range where the clamping force is insufficient, causing gaps on the surface of the mold PL, which allows the molten resin to leak out and result in resin burrs. For example, this is used for molds PL that have a special structure where the surface of the mold PL fits together unevenly, and it is not recommended to use this on molds PL with a general flat structure.

During the process of automatically setting the clamping force, the clamping control unit 60 simultaneously measures the change in the load rate of the electric servo motor 34, as shown in FIG. 4(b). In FIG. 4(b), the horizontal axis represents the clamping force, and the vertical axis represents the load rate of the electric servo motor 34. From the mold touch point (clamping force = 0) toward the completion of clamping (maximum clamping force Pmax), the load rate increases as the clamping force increases. The load rate reaches a maximum value at a specific clamping force, and then decreases toward the maximum clamping force Pmax. This is a phenomenon unique to toggle clamping devices, and the range (area C) that indicates this maximum value of the load rate is called the dead point of the toggle link mechanism.

Next, the measurement data of the load rate of the electric servo motor 34 shown in FIG. 4(b) and the design data showing the performance of the electric servo motor 34 are edited by the mold clamping control unit 60 to set the mold clamping force limit range as shown in FIG. 4(c). In FIG. 4(c), the horizontal axis represents the load rate of the electric servo motor 34, and the vertical axis represents the allowable time for which the electric servo motor 34 can be used continuously. Here, since this is a mold clamping force multi-stage control method that gradually increases the mold clamping force based on the injection filling rate of the molten resin into the mold cavity, at least during the injection process, the electric servo motor 34 must be able to be used continuously without worrying about overloading. Therefore, it is preferable that the threshold value Y is set longer than the injection time. The region H, where the allowable time is shorter than the threshold value Y, is set as the mold clamping force danger range where there is a high risk that the electric servo motor 34 will be overloaded during molding operation, and the region D, where the allowable time is longer than the threshold value Y, is set as the mold clamping force allowable range where the electric servo motor 34 can be used continuously without worrying about overloading. In addition, in the mold clamping force danger range, the limit allowable time YT until an overload state occurs is calculated from the relationship between the load rate of the electric servo motor 34 and the allowable time, and is used to take action to avoid the overload state, which will be described later.

Here, as shown in FIG. 4(a), it is ideal to continuously increase the clamping force in sync with the increase in the resin filling rate, but as shown in FIG. 5(a), the clamping force may be set to increase in stages. In FIG. 5(a), the horizontal axis represents the resin filling rate and the amount of movement of the screw of the injection device (called the injection position), and the vertical axis represents the clamping force. The injection position is divided into nine parts (S1 to S8) from the start of filling (S0) to the end of filling (SE). In addition, nine stages of split clamping force equivalent to the appropriate clamping force (P0 to Pmax, black circles in the figure) are set according to the number of injection position divisions. The number of injection position divisions is appropriately selected based on the product weight, resin used, injection filling speed, etc. The replacement of the injection filling rate with the injection position, and the division of the injection position and the setting of the split clamping force are performed by the clamping control unit 60.

Return to the explanation of FIG. 3. After completing the division of the injection position and the division clamping force setting, proceed to step 2. First, based on the control command of the clamping control unit 60, the electric servo motor 34 is rotated by the clamping drive unit 50 to close the mold, and the initial mold clamping (state of division clamping force P0 in FIG. 5(a)) is performed, and then the injection process is started. After the injection process is started, the clamping force is multi-stage controlled to gradually increase the clamping force based on the resin filling rate in the mold cavity 13. As described above, the resin filling rate is replaced by the divided injection position, and the clamping force multi-stage control is performed based on the injection position. In addition, since the flow projection area at the time of completion of filling is the same as the product projection area, the clamping force at the time of completion of filling is set to the maximum clamping force. After that, pressure holding filling is performed to compensate for the solidification shrinkage caused by the cooling and solidification of the molten resin (called the pressure holding process), the surplus resin is cooled and held in the mold cavity 13 (called the cooling process), and the mold is opened to remove the molded product from the mold cavity 13.

In the multi-stage control of the clamping force from the initial clamping force to the maximum clamping force, the load rate of the electric servo motor 34 is monitored. Details will be described with reference to FIG. 3 and FIG. 5. In the multi-stage control of the clamping force, as shown in FIG. 5(a), the injection process is started in the state of initial clamping (injection position S0, clamping force P0), and the injection filling of the molten resin into the mold cavity 13 is started. Based on the movement of the injection position (from S0 to SE) corresponding to the filling rate of the resin, the clamping force is increased stepwise (from P0 to Pmax). FIG. 5(b) shows the load rate of the electric servo motor 34 superimposed on this multi-stage control of the clamping force. The load rate also increases in accordance with the stepwise increase in the clamping force, and the load rate peaks at a maximum value at a specific injection position, after which the load rate decreases in accordance with the stepwise increase in the clamping force, and the load rate is lowest at the maximum clamping force. The range showing the maximum value of this load rate corresponds to the dead point of the toggle link mechanism. The white circles in the figure indicate the monitored load factor (F0 to F8) of the electric servo motor 34 that corresponds to the mold clamping force (P0 to Pmax).

Here, if the monitored load rate falls outside the clamping force danger range (area H) obtained in FIG. 4(c), the clamping force multi-stage control is continued. If the monitored load rate falls within the clamping force danger range (load rates F4 and F5 in the figure), the monitoring timer is started, and when the elapsed time of the monitoring timer reaches the limit allowable time YT obtained in FIG. 4(c), an avoidance action is taken to reduce the load rate of the electric servo motor 34. As an avoidance action, the electric servo motor 34 is rotated to close the mold in a direction that increases the clamping force. Specifically, the clamping force is increased from P4 to P6. As a result, the load rate F4 in the clamping force danger range of area H is reduced to the load rate F6 in the clamping force allowable range, and an overload state of the electric servo motor 34 can be avoided. Naturally, since the clamping force is increasing, the occurrence of resin burr defects in which molten resin leaks from the mold PL surface can be reliably prevented. In addition, the mold clamping force is not increased excessively, so the pressing force on the mold PL surface can be maintained at an appropriate level and does not inhibit gas release from the mold PL surface.

If the elapsed time of the monitoring timer is within the limit allowable time YT at the clamping force P4 and the clamping force multi-stage control continues and transitions to the clamping force P5, it is preferable to perform the following avoidance action. That is, since the load factor of the electric servo motor 34 is increasing at the clamping force P4 stage, the elapsed time of the clamping force P4 is added and the elapsed time is monitored at the clamping force P5. When the added elapsed time reaches the limit allowable time YT, the electric servo motor 34 is rotated to close the mold, and the avoidance action is performed to increase the clamping force from P5 to P6. Note that the avoidance action is aimed at increasing the clamping force and reducing the load factor of the electric servo motor 34 to transition from the clamping force danger range to the clamping force allowable range, so the clamping force after transition may be selected within the range of the clamping force Pmax from the clamping force P6. Note that even if the clamping force is in the danger range, if the elapsed time is within the limit allowable time YT, the clamping force multi-stage control continues as it is.

In this way, in the method for controlling the clamping force of an electric toggle clamping device, which gradually increases the clamping force based on the injection filling rate of molten resin into the mold cavity, the load rate of the electric servo motor is monitored, and if the load rate exceeds a threshold value, avoidance action is taken to reduce the load rate. This makes it possible to avoid situations such as interruption of molding due to overload on the electric servo motor. In addition, it is possible to reduce the size and cost of the toggle clamping device without the need to increase the capacity of the electric servo motor. Naturally, energy saving effects can also be achieved with the electric servo motor.

In addition, by setting an appropriate clamping force based on the flow projection area of the molten resin in the mold cavity, the pressing force of the mold PL surface can be maintained at an appropriate state, and air remaining in the mold cavity and volatile gases released from the molten resin can be efficiently discharged from the mold PL surface, and the high gas venting effect can reliably avoid molding defects caused by remaining gas, such as poor transfer of the product design pattern, non-filling defects due to gas accumulation, appearance defects such as weld patterns and gas flow patterns, and void defects due to gas entrapment.In addition, setting an appropriate clamping force can avoid excessive clamping force, which is expected to have the effect of extending the life of the mold and toggle clamping device.

Furthermore, the avoidance action of reducing the load rate of the electric servo motor rotates the electric servo motor to close the mold in a direction that increases the mold clamping force. This prevents the occurrence of resin burr defects caused by insufficient mold clamping force that creates gaps on the mold PL surface and causes molten resin to leak out. In other words, dangerous actions such as rotating the electric servo motor to open the mold in a direction that reduces the mold clamping force, contrary to an increase in the injection filling rate of the molten resin, and inducing resin burr defects, are never performed.

The above describes a preferred embodiment of the present invention, but the technical scope of the present invention is not limited to the scope described in the above embodiment. Various modifications and improvements can be made to the above embodiment.

For example, the resin filling rate is replaced with the injection position in the method for controlling the clamping force in multiple stages, but the injection position may be the time elapsed from the start of filling (called the injection time). The load rate of the electric servo motor is used, but the torque value or current value of the electric servo motor, which shows a behavior similar to the load rate, may be used. For example, the clamping force measured by a measuring means such as a tie bar sensor is used to perform the clamping force multi-stage control or avoidance action, but a calculated clamping force value calculated from the multiplying characteristic of the toggle link mechanism may be used, or the crosshead position that controls the bending state of the toggle link mechanism may be used instead. When the crosshead position is used instead, the amount of rotation of the electric servo motor may be used as the crosshead position.

Reference Signs List 100 Toggle clamping device 11 Fixed mold 12 Movable mold 13 Mold cavity 14 Mold PL surface 20 Mold clamping main body 21 Fixed platen 22 Movable platen 23 Link housing 24 Tie bar 24G Screw section 30 Toggle link mechanism 31 Ball screw 32 Crosshead 33 Link 33P Link pin 34 Electric servo motor 40 Die height adjustment section 41 Die height motor 42 Drive pulley 43 Driven pulley 44 Transmission belt 45 Support section 46 Die height drive section 47 Die height control section 50 Mold clamping drive section 60 Mold clamping control section TS Tie bar sensor

Claims (3)

A method for multi-stage control of clamping force of a toggle clamping device, which increases the clamping force in stages based on a filling rate of a molten resin injected into a mold cavity, comprising:
The toggle clamping device is an electric toggle clamping device that converts a rotational motion of an electric servo motor into a linear motion by a ball screw mechanism to operate a toggle link mechanism,
A method for multi-stage control of clamping force of a toggle clamping device, characterized in that avoidance action is taken to reduce the load factor based on a limit allowable time that is determined in advance from the relationship between the load factor of the electric servo motor and the allowable time for which the electric servo motor can be continuously used.
The method for multi-stage control of mold clamping force of a toggle mold clamping device according to claim 1 , wherein the avoidance action is to rotate the electric servo motor in a direction in which the mold clamping force increases.
When the elapsed time since the monitored load rate of the electric servo motor is included in the mold clamping force danger range reaches the limit allowable time, the avoidance action is performed,
3. A method for multi-stage control of clamping force of a toggle clamping device as described in claim 1 or claim 2, wherein the clamping force danger range is a range in which an overload state of the electric servo motor is determined to occur in the relationship between the load rate of the electric servo motor and the allowable time for continuous use of the electric servo motor.

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