Method for controlling clamping force in multiple stages in a toggle clamping device

Abstract

To provide a mold tightening force multiple control method of a toggle mold tightening device for avoiding an overloaded state of an electrically driven servomotor, in injection molding that increases a mold tightening force step by step, based on an injection fill factor of a molten resin into a metal mold cavity, using a toggle mold tightening device driven by an electrically driven servomotor.SOLUTION: A toggle mold tightening device is an electrically driven toggle mold tightening device that converts a rotational motion of an electrically driven servomotor into a linear motion by a ball screw mechanism to operate a toggle link mechanism, wherein, from a load factor of the electrically driven servomotor, a mold tightening force limit range capable of setting a mold tightening force of each step is provided, the load factor of the electrically driven servomotor uses load factor data measured within a mold tightening force automatically setting step that sets a maximum mold tightening force that is performed after a metal mold is mounted on the electrically driven toggle mold tightening device, the mold tightening force limit range is obtained from the load factor measurement data and performance data of the electrically driven servomotor.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for multi-stage control of clamping force of a toggle clamping device, which increases the clamping force in stages based on the injection filling rate of molten resin into a mold cavity. [Background technology]

[0002] Injection molding using a resin material by an injection molding machine is performed as follows. First, the resin material is supplied into the injection cylinder. The supplied resin material is plasticized and becomes molten resin by shear heat generated by the rotational movement of a screw equipped 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 screw is advanced toward the mold cavity formed by clamping a fixed mold and a movable mold attached to a mold clamping device, 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.

[0003] Here, 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, a mold clamping force (called the maximum mold clamping force) is set by adding a margin to the calculated value above, and the mold is clamped by the mold clamping device. Therefore, the mating surfaces of the fixed mold and the movable mold (called the mold PL surface) are firmly pressed.

[0004] 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 remain without being discharged from the PL surface of the mold that is firmly pressed (referred to as residual gas), causing molding defects due to residual 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. For this reason, a method of injection molding in which the injection process and the clamping process are linked has been proposed. In other words, it is a method of multi-stage control of the clamping force that gradually increases the clamping force according to the increase in the injection filling of the molten resin in the mold cavity.

[0005] On the other hand, electric toggle mold clamping devices that drive toggle link mechanisms with electric servo motors are widely used due to the effects of environmental improvement by energy saving and hydraulic oil elimination, and the effects of injection molding stability due to high repeatability. The method of controlling the mold clamping force multi-stage of this electric toggle mold clamping device is performed by arbitrarily holding the position of the toggle link mechanism within the range of maximum mold clamping force from a state where the mold PL surface is in contact but no mold clamping force is generated (called a 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, it is possible to easily perform high-precision multi-stage mold clamping force control. 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 mold clamping device.

[0006] Therefore, for example, as shown in Patent Document 1, a method of controlling a multi-stage mold clamping force has been proposed in an electric toggle mold clamping device, in which after a set mold clamping force is reached, the ball screw is rotated in the reverse direction to reduce the mold clamping force within an allowable range. The toggle link mechanism is in a bent state within the range of the maximum mold 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 saving effects and a compact mold clamping device. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 9-254211 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the method shown in Patent Document 1, the toggle link mechanism retreats toward the mold touch point by rotating the ball screw in the reverse direction, and the clamping force certainly decreases, although it is within the allowable range. Meanwhile, the injection and 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 is insufficient, causing a gap on the PL surface of the mold, and the molten resin leaks from the PL surface of the mold (called a resin burr defect). In other words, the method shown in Patent Document 1 cannot be applied to a multi-stage control method for mold clamping force in injection molding, which increases the 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 PL surface of the mold.

[0009] Therefore, 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 gradually increased based on the injection filling rate of molten resin into the mold cavity, thereby avoiding an overload condition of the electric servo motor. [Means for solving the problem]

[0010] 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 stepwise 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 a clamping force limit range is provided in which the clamping force of each stage can be set based on the load rate of the electric servo motor.

[0011] In the method for multi-stage control of clamping force of a toggle clamping device of the present invention, It is preferable that the load rate of the electric servo motor is determined using load rate data measured during an automatic mold clamping force setting process that sets the maximum mold clamping force after a mold is loaded into the electric toggle mold clamping device.

[0012] It is preferable that the mold clamping force limit range is composed of a mold clamping force danger range, in which the allowable time for continuous use of the electric servo motor is short, and a mold clamping force allowable range, which is a mold clamping force excluding the mold clamping force danger range, determined from the load factor measurement data and performance data of the electric servo motor. Effect of the Invention

[0013] According to the present invention, in injection molding using a toggle clamping device driven by an electric servo motor, in which the clamping force is gradually increased based on the injection filling rate of molten resin into a mold cavity, a method for multi-stage control of the clamping force of a toggle clamping device can be provided, which avoids an overload condition of the electric servo motor. [Brief description of the drawings]

[0014] [Figure 1] 1 is a conceptual diagram of a toggle clamping device according to the present invention. [Diagram 2] 2A to 2C are diagrams illustrating the mold opening and closing operations of the toggle clamping device of FIG. 1. [Diagram 3] FIG. 4 is a flow chart showing a method for multi-stage control of mold clamping force according to the present invention. [Figure 4] FIG. 11 is a diagram showing a procedure for setting a mold clamping force limit range based on a load factor of an electric servo motor. [Diagram 5] FIG. 4 is a diagram showing a procedure for setting the clamping force in the clamping force multi-stage control method according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Preferred embodiments for carrying out the present invention will be described below 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 means of solving the problems 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.

[0016] [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 one that bends outward, or the toggle link mechanism may be one that is 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 adjusting unit 40, a clamping drive unit 50, and a clamping control unit 60.

[0017] 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 plurality of tie bars 24. The movable platen 22 is supported by the plurality of tie bars 24 and arranged so as to be slidable 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 mated to form a mold cavity 13 surrounded by a mating surface (mold PL surface 13G). This mold PL surface 13G has the role of preventing leakage of molten resin from the mold cavity 13 and efficiently discharging volatile gases and the like released from the air in the mold cavity 13 and the molten resin.

[0018] 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 a link pin 33P so as to be rotatable and slidable, so that the bent state and the linear state of the toggle link mechanism 30 can be adjusted. The link housing 23 is incorporated in a ball screw 31 that converts a rotational motion into a 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 a linear motion by the ball screw 31, and the crosshead 32 is operated. The movable platen 22 is operated via the link 33 according to the operation of the crosshead 32. A toggle clamping device driven by an electric servo motor is called an electric toggle clamping device.

[0019] Here, with regard to 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 platen 21 and 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 the rotation angle, and the mold closing operation and the 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 or the rotation angle of the rotational motion of the electric servo motor 34, and the moving speed and the moving amount of the movable platen 22 and the movable mold 12 can be adjusted. Based on a control command from 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 with reference to FIG. 2.

[0020] Figure 2 shows the mold opening and closing operation of a toggle clamping device, with Figure 2(a) showing a state in which the toggle link mechanism 30 is bent significantly and the fixed mold 11 and the movable mold 12 are completely separated (referred to as mold opening completed), Figure 2(b) showing a state in which the toggle link mechanism 30 is bent less and the fixed mold 11 and the movable mold 12 are brought together (referred to as the mold touch point), and Figure 2(c) showing a state in which the toggle mechanism is fully extended and straight (referred to as mold clamping completed).

[0021] The mold closing operation indicates the state of movement 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 state of movement 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 stopping 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 mold opening speed) and the movement speed of the mold closing operation (referred to as mold closing speed) can also be precisely adjusted.

[0022] At the mold touch point (b), the fixed mold 11 and the movable mold 12 are mated to form the mold PL surface 13G and the mold cavity 13, but no pressing force (mold clamping force) is generated on the mold PL surface 13G. The length of the tie bars 24 connecting the fixed platen 21 to the link housing 23 at this time is defined as L1.

[0023] By moving from the mold touch point (b) to the completion of mold clamping (c) (referred to as the mold clamping operation), the tie bar 24 extends from L1 to L2 (L1 < L2). According to the amount of extension of this tie bar 24, a compressive force is generated, and the pressing force on the PL surface 13G of the mold, that is, the mold clamping force, acts. The movement from the completion of mold clamping to the mold touch point (referred to as the pressure reduction operation) relaxes the extension of the tie bar 24, and the mold clamping force also decreases. By controlling the rotation of the electric servo motor 34, an arbitrary mold clamping force can be adjusted within the range from the mold touch point to the completion of mold clamping. Injection molding using a multi-stage mold clamping force 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 this mold touch point to the completion of mold clamping.

[0024] Return to the description of FIG. 1. The die height adjustment unit 40 adjusts the mold clamping force according to the amount of extension of the tie bar 24 at the completion of mold clamping and is arranged in the link housing 23. 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-coupled to the screw portion 24G on the rear B side of the tie bar 24. By the rotation of the driven pulley 43, the movable mold 12, the movable platen 22, the toggle link portion 30, and the link housing 23 move integrally in the mold opening and closing direction (referred to as die height adjustment). By adjusting the rotation direction of the die height motor, the operation direction of the die height drive can be adjusted. Also, by adjusting the rotation amount of the die height motor 41, the movement amount of the die height adjustment can be adjusted. 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 based on the mold clamping force setting value set by the mold clamping control unit 60, the die height control unit 47 calculates the extension amount of the tie bar 24. Note that the die height adjustment is performed within the range from the mold touch point to the completion of mold opening. Also, the rotatable driven pulley 43 and the link housing 23 are connected by the support portion 45. In FIG. 1, the configuration of the drive pulley 42, the transmission belt 44, and the driven pulley 43 is shown, but it is not limited thereto. 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 the gear chain may be used.

[0025] The clamping force adjustment is performed following the die height adjustment corresponding to the extension amount of the tie bars 24 calculated based on the clamping force set 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 bars 24 is measured by the tie bar sensor TS and converted into the clamping force acting on the PL surface 13G of the mold (called the clamping force measurement value). When it is confirmed that this clamping force measurement value and the clamping force set value set by the clamping control unit 60 are within the allowable range, the clamping force adjustment is completed. If it is out of the allowable range, the pressure reduction operation and the mold opening operation are performed, and the die height adjustment is redone. In this case, the extension amount of the tie bars 24 is corrected according to the difference from the allowable range. When it is confirmed that the die height is within the allowable range after the redoing of the die height adjustment, 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. In this mold clamping force setting, the maximum mold clamping force generated when mold clamping is completed is adjusted. Injection molding is performed using the mold clamping force multi-stage control method within a range from the maximum mold clamping force when mold clamping is completed to a state in which the mold clamping force at the mold touch point is close to zero.

[0026] [Multi-stage mold clamping force control method] Next, a method for multi-stage control of clamping force using the toggle clamping device shown in Fig. 1 will be described with reference to Figs. 3 to 5. Fig. 3 shows a flow diagram of the method for multi-stage control of clamping force, and Fig. 4 shows a procedure for setting the clamping force limit range from 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. Fig. 5 shows a procedure for setting the clamping force limit range in the method for multi-stage control of clamping force. The clamping force limit range will be described later.

[0027] First, as shown in FIG. 3, a new injection mold is attached to the toggle mold clamping device 100 shown in FIG. 1. After the attachment of the injection mold is completed, the maximum mold clamping force corresponding to the mold is set in the mold clamping force control unit 60. Here, the maximum mold clamping force is a mold clamping force calculated by multiplying the projected area (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. This margin is preferably set 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, and the like. Upon receiving information on the maximum mold clamping force setting value from the mold clamping control unit 60, the die height control unit 47 calculates the extension amount of the tie bar 24 and performs automatic mold clamping force setting. It is confirmed that the mold clamping force measurement value measured by the tie bar sensor TS and the maximum mold clamping force setting value are within a preset allowable range, and the automatic mold clamping force setting is completed.

[0028] Here, in the automatic setting of the mold clamping force, the load factor of the electric servo motor 34 is measured by the mold clamping control unit 60, and correlation data between the mold clamping force and the load factor is compiled as shown in Fig. 4(a). In Fig. 4(a), the horizontal axis represents the mold clamping force, and the vertical axis represents the load factor of the electric servo motor 34. The load factor increases and decreases from the mold touch point (mold clamping force = 0) toward the completion of mold clamping (maximum mold clamping force Pmax), and the load factor reaches a maximum value at a specific mold clamping force. This is a phenomenon specific to the toggle mold clamping mechanism, and the vicinity of this maximum value of the load factor is called the dead point.

[0029] Next, as shown in FIG. 4(b), the range in which the mold clamping force can be set is classified based on the performance data of the electric servo motor 34. In FIG. 4(b), the horizontal axis indicates the load factor of the electric servo motor 34, and the vertical axis indicates the allowable time for which the electric servo motor 34 can be used continuously. In the range of a low load factor, long-term continuous use is possible, and in the range of a high load factor, the allowable time for continuous use becomes shorter in inverse proportion to the increase in the load factor. Therefore, the range is classified into a range (area D) in which the load factor is low and long-term continuous use is possible, a range (area F) in which the load factor is high and the allowable time is short, and a range (area E) in which the electric servo motor 34 stops in a short time due to an overload state. For example, a state in which safe continuous use is possible in the entire range of the injection molding operation may be defined as area D, a state in which continuous use is difficult within the range from the mold clamping operation to the mold opening operation in the injection molding operation may be defined as area F, and other states may be defined as area E.

[0030] Finally, the load factor data of the electric servo motor 34 measured by the automatic mold clamping force setting shown in Fig. 4(a) and the performance data of the electric servo motor 34 shown in Fig. 4(b) are compiled to set a mold clamping force limit range applicable to the setting values ​​of the injection mold that actually performs injection molding, as shown in Fig. 4(c). Here, area G corresponds to area E in Fig. 4(b), and area H corresponds to area F in Fig. 4(b). The mold clamping force range of areas G and H is set as the mold clamping force danger range. The mold clamping force range excluding this mold clamping force danger range is set as the mold clamping force limit range in the mold clamping control unit 60.

[0031] After the clamping force limit range is set, the process proceeds to the clamping force setting procedure of the clamping force multi-stage control method shown in Fig. 5. Here, the maximum clamping force set by the clamping force automatic setting is the clamping force obtained by multiplying the product projected area by the molding resin pressure, etc. In contrast, since there is no resin and no molding resin pressure in the mold cavity 13 before the start of injection filling of the molten resin (injection process), the maximum clamping force is obviously excessive, and the mold PL surface 13G is in a state of being strongly pressed. If the injection process is started after clamping with the 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 13G that is firmly pressed, causing molding defects due to gas residue, 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.

[0032] Therefore, as shown in Fig. 5(a), by setting an appropriate clamping force according to the resin filling rate in the mold cavity 13, the pressing force of the mold PL surface 13G 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 filling of the molten resin is completed, 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 the risk of residual gas is high. In addition, area Z, which is further below area A, is a range in which insufficient clamping force can cause gaps to form on the mold PL surface 13G, allowing the molten resin to leak out and resulting in resin burrs. This area is applied, for example, to molds having a special structure in which the mold PL surface fits together in an uneven manner, and it is not suitable for application to molds PL with a general flat structure.

[0033] Here, as shown in FIG. 5(a), it is ideal to increase the mold clamping force in synchronization with the increase in the resin filling rate, but as shown in FIG. 5(b), the mold clamping force may be set to increase in stages. In FIG. 5(b), the resin filling rate is replaced with the movement amount of the screw of the injection device (called the injection position), and the injection process from the start of filling (S0) to the end of filling (SE) is divided into six parts (S1 to S5). In addition, the divided mold clamping force corresponding to the appropriate mold clamping force is set in six stages (P1 to Pmax) according to the number of divisions of the injection position. The shaded area is the area A where the remaining gas is eliminated, and the area B above the divided mold clamping force is the range where there is a high risk of remaining gas. The number of divisions of the injection position is appropriately selected based on the product weight, the resin used, the injection filling speed, etc. The replacement of the injection filling rate with the injection position, the division of the injection position, and the setting of the divided mold clamping force are performed by the mold clamping control unit 60.

[0034] Next, the clamping force application range data shown in Fig. 4(c) and the split clamping force setting data shown in Fig. 5(b) are edited by the clamping control unit 60 to set the clamping force limit range in the clamping force multi-stage control method as shown in Fig. 5(c). In Fig. 5(c), the split clamping force P4 corresponds to region G, the split clamping forces P3 and P5 correspond to region H, and the split clamping forces P3 to P5 are set to the clamping force danger range. The other split clamping forces (P1, P2, Pmax) are set to the clamping force allowable range, and the setting of the clamping force limit range is completed. The clamping force danger range indicates that the load factor of the electric servo motor 34 is high and there is a risk of stopping due to overload, and the clamping force allowable range indicates that the load factor of the electric servo motor 34 is low and long-term continuous use is guaranteed.

[0035] Returning to the explanation of FIG. 3, the injection position is divided and the split clamping force is set. The clamping control unit 60 compares and judges the relationship between the setting value of the split clamping force set by the molding operator and the clamping force limit range set by the above-mentioned procedure. When the clamping control unit 60 judges that the setting value of the split clamping force is in the clamping force danger range, it notifies the molding operator of a change in the setting of the split clamping force. In addition, it is preferable to perform the following measures. For example, if the setting value of the split clamping force is in region G, the setting of the molding operator is not accepted. Also, if the setting value of the split clamping force is in region H, the continuous use time of the electric servo motor 34 is displayed to alert the molding operator. Alternatively, a conditional measure may be taken, such as comparing the time required to inject and fill the mold cavity 13 with the continuous use time of the electric servo motor 34, and accepting the setting of the molding operator only if the continuous use time is longer, and not accepting the setting of the molding operator if the continuous use time is shorter.

[0036] When the mold clamping control unit 60 judges that the set value of the split mold clamping force, including the setting change, is within the mold clamping force allowable range, the setting of the split mold clamping force is completed and injection molding is started. Note that after injection molding, for example, when the injection filling amount of the molten resin into the mold cavity 13 fluctuates and a resin burr defect occurs, the load factor of the electric servo motor 34 increases and the mold is overloaded, or when the heat of the molten resin causes the injection mold to expand, causing the mold clamping force acting on the mold PL to become excessive and gas leakage becomes noticeable, or when the load factor of the electric servo motor 34 increases due to the thermal expansion of the mold, and other molding abnormalities occur, and the set value of the split mold clamping force may be changed. In this case, the mold clamping control unit 60 also performs a comparison judgment of the mold clamping force limit range.

[0037] In this way, the clamping force multi-stage control method measures the load rate of the electric servo motor in the process of automatically setting the clamping force before injection molding, sets the clamping force limit range of the clamping force tolerance range and the clamping force danger range, compares and judges with the setting value of the divided clamping force of the molding operator, and issues a warning to the molding operator, thereby preventing abnormal stop due to an overloaded state of the electric servo motor during injection molding. Furthermore, the pressing force of the PL surface of the mold can be properly maintained, and air remaining in the mold cavity and volatile gases released from the molten resin can be efficiently discharged from the PL surface of the mold. This makes it possible to reliably prevent 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, void defects due to gas entrapment, and resin burr defects due to leakage of molten resin from the PL surface of the mold, thereby realizing stable production of high-quality molded products. Furthermore, it is possible to realize a compact electric toggle mold clamping device and a reduction in cost without the need to increase the capacity of the electric servo motor.

[0038] Although the preferred embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the scope described in the above-mentioned embodiments. Various modifications and improvements can be made to the above-mentioned embodiments. [Explanation of symbols]

[0039] 100 Toggle clamping device 11 Fixed mold 12 Movable mold 13 Mold Cavity 13G Mating surface (PL surface of mold) 20 Mold clamping body 21 Fixed plate 22 Movable plate 23 Link housing 24 Tie bar 24G threaded part 30 Toggle link mechanism 31 Ball screw 32 Crosshead 33 Links 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 part 46 Die height drive unit 47 Die height control section 50 Mold clamping drive unit 60 Mold clamping control section TS Tie bar sensor

Claims

1. A method for multi-stage control of clamping force of a toggle clamping device, which increases the clamping force stepwise 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, and provides a clamping force limit range in which the clamping force of each stage can be set based on a load factor of the electric servo motor; The method for multi-stage control of clamping force of a toggle clamping device, characterized in that the load rate of the electric servo motor is determined using load rate data measured within a clamping force automatic setting process that sets a maximum clamping force after a mold is loaded into the electric toggle clamping device.

2. A method for multi-stage control of clamping force of a toggle clamping device, which increases the clamping force in stages based on the injection filling rate of molten resin 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, and provides a clamping force limit range in which the clamping force of each stage can be set based on a load factor of the electric servo motor; The clamping force limit range is determined from load factor measurement data and performance data of the electric servo motor, and is composed of a clamping force danger range in which the allowable time for continuous use of the electric servo motor is short, and a clamping force allowable range, which is a clamping force excluding the clamping force danger range.

3. The mold clamping force limit range is determined based on the load factor measurement data and the performance data of the electric servo motor.

2. The method for multi-stage control of clamping force of a toggle clamping device according to claim 1, comprising: a clamping force danger range in which the allowable time for continuous use of the electric servo motor is short, and a clamping force allowable range which is a clamping force excluding the clamping force danger range.

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