JP2008114513A - Automatic mold clamping force correction method of injection molding machine and automatic correction device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic mold clamping force correction device of an injection molding machine which can uniformly distribute a mold clamping force throughout the entire mold, and can automatically obtain a set mold clamping force. <P>SOLUTION: Four tie bars (6a, 6b, ...) have strain sensors (21a, 21b, ...) installed at specified sites, and also band heaters (24a, 24b, ...) and water jackets (27a, 27b, ...) installed at sites separated by a specified distance from the specified sites of the tie bars (6a, 6b, ...). Further, the strain level of each tie bar (6a, 6b, ...) generated during mold clamping is measured by the strain sensors (21a, 21b, ...). In order to ensure that the measured strain level coincides with a specified strain level, the effective length of each tie bar (6a, 6b, ...) is changed by controlling the temperature of the specified site of each tie bar (6a, 6b, ...) by the band heaters (24a, 24b, ...) and the water jackets (27a, 27b, ...). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an automatic mold clamping force correction method and an automatic correction apparatus for an injection molding machine provided with a toggle type mold clamping device, and more specifically, a fixed platen to which a fixed die is attached, and a movable platen to which a movable die is attached. A toggle type comprising a mold clamping housing, a plurality of, for example, four tie bars penetrating the movable platen and connecting the mold clamping housing and the fixed platen, a toggle mechanism provided between the mold clamping housing and the movable platen, etc. The present invention relates to a method for automatically correcting a mold clamping force of an injection molding machine provided with a mold clamping device, and an automatic correction device directly used for carrying out the invention of this method.

  As is well known, an electric injection molding machine equipped with a toggle type mold clamping device includes a stationary platen fixed on the mold clamping bed, a mold clamping housing provided on the mold clamping bed so as to be movable in the axial direction, and fixing. A plurality of, for example, four tie bars provided between the board and the mold clamping housing, mold thickness adjusting nuts provided at the ends of these tie bars, a movable board through which the tie bars are inserted, a mold clamping housing, A toggle mechanism provided between the movable platen, a mold opening / closing motor for driving the toggle mechanism, a mold thickness adjusting motor for rotating the mold thickness adjusting nut, and the like are included. The toggle mechanism is also well known in the art and includes a crosshead and a plurality of toggle links. The crosshead is attached to the tip of a ball screw that moves forward or backward by a mold opening / closing motor, and both ends of the toggle link are rotatably attached to the movable platen and the mold clamping housing, respectively.

  Adjustment of the mold clamping force of the toggle type mold clamping apparatus as described above is performed as follows. The mold thickness, which is the distance between the movable platen and the fixed platen, is adjusted to be smaller than the mold thickness of the fixed die and the movable die. In other words, the mold is placed between the movable platen and the fixed platen with the toggle mechanism contracted. The mold is sandwiched, and the toggle mechanism is driven by the mold opening / closing motor to hold the movable plate so that the movable plate is not opened. In this held state, the mold clamping housing is driven by the mold thickness adjusting motor in the direction in which the toggle link extends. Then, the crosshead reaches the crosshead position with respect to a predetermined mold clamping force stored in the controller. Stop the mold thickness adjustment motor and mold opening / closing motor to finish the adjustment of automatic mold clamping force. When the mold clamping operation is performed from the crosshead position when this adjustment is finished, a predetermined mold clamping force can be obtained.

  On the other hand, when the processing accuracy of the resulting molded product is low, such as when the thickness of the DVD molded by injection molding is not uniform or burrs occur in certain parts of the molded product, the clamping force distributed in the mold Is often non-uniform. Therefore, in order to uniformly distribute the mold clamping force in the mold, the mold thickness adjusting device uses an effective length of each tie bar, that is, a fixed platen and a mold clamping housing, so that the tension of each of the plurality of tie bars becomes equal during mold clamping. You must adjust the length of the tie bar between. However, the adjustment of the effective length of each of the tie bars is not possible because the effective length of each of the tie bars must be readjusted, ie, the mold thickness adjusting nut must be adjusted separately. Cannot be cleared.

JP-A-8-281747

  In Patent Document 1, a mold clamping force is calculated from strain measured by a strain sensor provided on a tie bar, and the calculated mold clamping force is compared with a set mold clamping force. A mold clamping force control method is shown in which the crosshead position of the toggle mechanism is advanced in the mold closing direction when it is small, and the crosshead position of the toggle mechanism is retracted in the mold opening direction when it is greater than the set mold clamping force.

  When the mold clamping force is to be adjusted by the conventional mold clamping force adjusting method, in the case of a toggle type mold clamping apparatus, the adjustment is performed by adjusting the effective length of the tie bar between the mold clamping housing and the fixed platen. However, if the mold temperature changes, the mold thickness changes due to thermal expansion.For example, if the mold temperature is lower than at the time of adjustment, the mold thickness is reduced, and the adjusted tie bar effective length is distorted by elastic deformation. However, there is a problem in that the required mold clamping force cannot be obtained due to insufficient strain even if the is generated. The mold clamping force control method disclosed in Patent Document 1 addresses this problem. The mold clamping force is measured by a strain sensor provided on a tie bar, and the amount of crosshead pushing, that is, the amount of toggle link elongation, is measured. Although the advantage is that the necessary clamping force can be obtained even if the mold temperature changes, it is possible to control it, but it is necessary to advance beyond the initially adjusted clamping force, that is, beyond the most advanced position of the crosshead. If the mold clamping force is insufficient, it cannot be handled.

  However, if the initially adjusted clamping force is within the adjustment range, even if the required clamping force can be obtained by the control method described in Patent Document 1, the clamping force is uniformly distributed in the mold. There is a problem about. That is, in order to evenly distribute the mold clamping force in the mold, it is necessary to adjust the effective length of each of the plurality of tie bars one by one, which takes time. Further, since the injection molding machine must be stopped, productivity is lowered. Furthermore, since the tension generated in each tie bar at the time of mold clamping is not actually known accurately, adjustment of each one by one requires skill and repeated trial and error. For this reason, adjustment takes a long time. In addition, every time injection molding is interrupted, a discarded shot is generated, which is uneconomical. In this way, even if it has been adjusted properly, if the machine part is worn out due to long-term use of the injection molding machine, the mold clamping force is not evenly distributed in the mold, resulting in defective products. In order to prevent this, it is necessary for a human to periodically adjust the effective length of the tie bar by turning the tie bar nut one by one. In particular, when molding a plurality of pick-up lenses for which a high processing accuracy is required, for example, a pickup lens for CD or DVD, is simultaneously molded by injection molding with a set of molds, the clamping force is uniformly distributed over the mold with high precision. There is a need and the frequency of adjustments is even higher. At this time, the influence of the above-described problem is further increased.

  Therefore, the present invention does not require any special adjustment work of the mold thickness adjusting device by humans, and the mold clamping force is evenly distributed in the mold with high accuracy, and therefore there is no stop of the injection molding machine for adjustment. A method for automatically correcting the mold clamping force of an injection molding machine equipped with a toggle type mold clamping device and no automatic correction directly used in the implementation of the invention of the present invention, in which no defective product is generated due to uneven mold clamping force The object is to provide a device.

  In order to achieve the above object, according to the present invention, a plurality of tie bars of a toggle type mold clamping device are provided with a strain amount measuring means at a predetermined portion of the tie bar, and are separated from the predetermined portion on the tie bar. Is provided with temperature control means for changing the temperature of the tie bar, and the effective length of the tie bar is controlled by controlling the temperature of the predetermined part of each tie bar so that the strain amount of each tie bar generated during mold clamping becomes a predetermined strain amount. Configured to change.

That is, in order to achieve the above-described object, the invention according to claim 1 includes a stationary platen, a movable platen, a mold clamping housing, and the movable platen penetrating the stationary platen and the mold clamping housing. A plurality of tie bars and a toggle mechanism provided between the mold clamping housing and the movable platen, and when the mold is clamped by driving the toggle mechanism, the reaction force of the mold clamping force on each tie bar A method for correcting a mold clamping force of an injection molding machine in which a tension due to elastic force is generated and distortion due to elastic deformation occurs in each tie bar due to the tension, and is measured at the time of mold clamping for each of the tie bars. In accordance with the amount of strain due to elastic deformation of the predetermined portion of each tie bar, the temperature of the portion of each tie bar that is spaced from the predetermined portion is changed to expand and contract, and the amount of strain due to elastic deformation of each tie bar becomes equal. Like Configured to control.
The invention according to claim 2 includes a fixed platen, a movable platen, a mold clamping housing, a plurality of tie bars that penetrate the movable platen and connect the fixed platen and the mold clamping housing, and the mold clamping. A toggle mechanism provided between the housing and the movable platen. When the toggle mechanism is driven to perform mold clamping, tension is generated in each tie bar due to reaction force of mold clamping force, and the tension causes A method of correcting the mold clamping force of an injection molding machine in which distortion due to elastic deformation occurs in each tie bar, wherein the set mold clamping force is equally divided by the number of tie bars to obtain the tension of each tie bar, The amount of strain generated at a predetermined portion of each tie bar is set as a target strain amount, and a predetermined amount is separated from the predetermined portion of each tie bar so that each strain amount of each tie bar measured during mold clamping becomes the target strain amount. Change the temperature of the part Is stretchable Te, wherein configured to control such amount of distortion due to the tension of the tie bars are equal.
According to a third aspect of the present invention, there is provided a fixed platen, a movable platen, a mold clamping housing, a plurality of tie bars penetrating the movable plate and connecting the fixed platen and the mold clamping housing, and the mold clamping. A toggle mechanism provided between the housing and the movable platen,
When the toggle mechanism is driven, each tie bar generates tension due to a reaction force of a mold clamping force, and the tension causes distortion due to elastic deformation in each tie bar. Is provided with strain measuring means for measuring the strain amount of each tie bar, and a temperature control means for changing the temperature in the vicinity of the part is provided at a part spaced by a predetermined amount from the predetermined part. The temperature control means is controlled so that the strain amount of each tie bar measured by each strain measurement means is equal, and the invention according to claim 4 is the correction apparatus according to claim 3, Each temperature control means is constituted by a heater and a water jacket, and the strain amount measuring means is constituted by a strain sensor.

As described above, according to the present invention, according to the amount of strain due to elastic deformation of a predetermined portion of each tie bar measured at the time of mold clamping for each tie bar, the portion of each tie bar separated from the predetermined portion by a predetermined amount. The temperature is changed to expand and contract, and the amount of strain due to elastic deformation of each tie bar is controlled to be equal, or the set clamping force is equally divided by the number of tie bars to obtain the tension of each tie bar. A portion spaced from the predetermined portion of each tie bar by a predetermined amount so that the strain amount generated at a predetermined portion of the tie bar is a target strain amount, and each strain amount of each tie bar measured at the time of mold clamping becomes the target strain amount. Therefore, even if the engineer does not stop the injection molding machine and adjust the clamping force, the tie bars can be expanded and contracted by changing the temperature of the tie bars. Effect unique to the present invention that Shii tension That clamping force is obtained is obtained. In addition, since the strain amount of each tie bar is controlled using the strain amount of each tie bar calculated from the set mold clamping force as a target strain amount, the mold clamping force can be uniformly distributed in the mold, and a preset die Tightening force can also be obtained. Furthermore, since the control is performed with a slight amount of thermal expansion and contraction, an effect of adjusting the strain amount, that is, the tension of the tie bar with high accuracy can be obtained. Therefore, according to the present invention, molded products such as CD and DVD can be molded with high accuracy.
In addition, according to the conventionally known mold thickness adjusting device, the mold clamping force is adjusted by the screw mechanism, so there is a risk that parts such as the screw mechanism may be worn if adjusted frequently. Since the temperature of a predetermined portion of the tie bar is changed and adjusted, there is no problem of wear of parts. This is particularly effective when molding a molded product that requires high processing accuracy.

  Embodiments according to the present invention will be described below. FIG. 1 is a front view schematically showing an injection molding machine provided with a toggle type mold clamping apparatus according to the present embodiment. As shown in the figure, the external shape or the main body of the injection molding machine according to the present embodiment is configured in substantially the same manner as a conventional injection molding machine. That is, the injection molding machine has a fixed platen 1 fixed on a bed, a mold clamping housing 5 provided on the bed so as to be movable in the axial direction at a predetermined interval from the fixed platen 1, a fixed platen 1 and a mold. A plurality of, for example, four tie bars 6a, 6b,... Provided between the fastening housing 5 and the four tie bars 6a, 6b,. The toggle mechanism 7 is driven in the closing direction and the mold opening direction.

  The injection molding machine configured in this manner is provided with a motor for adjusting the mold thickness, a motor for opening and closing the mold, a control device, and the like, which will be described in detail later. A fixed mold 4 is attached to the fixed platen 1 and a movable mold 5 is attached to the movable platen 3, respectively.

  One end of each of the tie bars 6 a, 6 b,... Is passed through the four corners of the fixed platen 1 and fixed to the fixed platen 1. The other ends of the tie bars 6a, 6b,... Pass through the four corners of the mold clamping housing 5 and extend outward. Further, on the outside of the mold clamping housing 5, screws are formed on the tie bars 6 a, 6 b,..., And tie bar nuts 8 a, 8 b,. Although not shown in FIG. 1, driven gears are respectively fixed to these tie bar nuts 8a, 8b,. On the other hand, an electric motor for adjusting the mold thickness is mounted on the mold clamping housing 5, and the drive gear provided on the output shaft of the electric motor is engaged with the driven gear in a conventionally known manner. Therefore, when the motor for adjusting the mold thickness rotates in the forward or reverse direction, the tie bar nuts 8a, 8b,... For adjusting the mold thickness are driven in the forward or reverse direction, and the mold clamping housing 5 is connected to the stationary platen 1. It moves in the direction in which the mold thickness between the movable platen 2 increases or the mold thickness decreases.

  The toggle mechanism 7 also has a conventionally known structure. That is, in the embodiment shown in FIG. 1, schematically, one cross head 14, a pair of cross links 13, 13, a pair of short links 11, 11, and a pair of long links. 12 and 12. End portions of the cross links 13 and 13 are rotatably coupled to the cross head 14 by pins. At the other end of the cross links 13, 13, the ends of the short links 11, 11 are pins, and at the ends of the short links 11, 11, the ends of the pair of long links 12, 12 are pins. It is pivotally connected. The other ends of the long links 12 and 12 are coupled to the bracket of the movable platen 2 by pins, and the other ends of the short links 11 and 11 are freely rotatable by the pins similarly to the bracket of the mold clamping housing 5. Is bound to.

  A through hole is formed in a substantially central portion of the mold clamping housing 5, and a male screw 15 whose tip is coupled to the cross head 14 is inserted into the through hole. Although not shown in FIG. 1, the female screw that is screwed with the male screw 15 to form the ball screw mechanism can be rotated with respect to the mold clamping housing 5, but the movement in the axial direction is restricted. It is provided in the mold clamping housing 5 in a state. Therefore, when the female screw is driven to rotate, the male screw 15 is driven in the axial direction, and the cross head 14 is driven in the mold closing direction or the mold opening direction. The female screw is rotationally driven in a predetermined direction by a mold opening / closing motor (not shown) provided in the mold clamping housing 5.

  .. Of the tie bars 6a, 6b,... Of the injection molding machine configured as described above, between the fixed platen 1 and the movable platen 2 in the embodiment shown in FIG. 21b,... Are provided. These strain sensors 21a, 21b,... Are connected to the strain amount measuring device 51 by signal lines a, a,. The distortion amount obtained by the distortion amount measuring device 51 is input to the computing unit 54 through the signal line b. In each of the tie bars 6a, 6b,..., A portion separated from the strain sensors 21a, 21b,... By a predetermined amount, in a portion between the movable platen 2 and the mold clamping housing 5 in the embodiment shown in FIG. Are provided with temperature sensors 23a, 23b,. The temperature sensors 23a, 23b,... And the temperature measuring device 53 are connected by signal lines c, c,..., And the temperatures of the tie bars 6a, 6b,. It is designed to be entered.

  According to the present embodiment, the tie bars 6a, 6b,... Have band heaters 24a, 24b,... As temperature control means in relation to the temperature sensors 23a, 23b,. Is provided. As described above, according to the present embodiment, the temperature sensors 23a, 23b,... And the temperature control means are provided in association with each other, so that the temperature of the tie bars 6a, 6b,. Will be measured. Electric power is supplied to the band heaters 24a, 24b,... Via the power lines 25a, 25b,..., And the water jackets 27a, 27b,. Cold water is supplied from the cold water supply devices 29a, 29b,. A control signal from the temperature regulator 55 is input to the heater power supply devices 26a, 26b,... And the chilled water supply devices 29a, 29b,.

  Next, the operation of the present embodiment will be described. A fixed mold 3 is attached to the fixed platen 1 and a movable mold 4 is attached to the movable platen 2. Then, the mold clamping force is adjusted as described above. That is, the mold thickness which is the distance between the fixed platen 1 and the movable platen 2 is adjusted to be smaller than the mold thickness of the fixed die 3 and the movable die 4, in other words, with the toggle mechanism 7 being contracted, the fixed platen The molds 3 and 4 are sandwiched between the movable platen 1 and the movable platen 2, and the toggle mechanism 7 is driven by the mold opening / closing motor to hold the movable platen 2 so that the movable platen 2 is not opened. The mold clamping housing 5 is driven in a direction in which the toggle links 11, 12,... Extend or a direction in which the cross head 14 is pushed. Then, the crosshead 14 reaches the crosshead position with respect to a predetermined mold clamping force stored in the control device. Stop the mold thickness adjustment motor and mold opening / closing motor to finish the adjustment of automatic mold clamping force. Thereby, a predetermined mold clamping force is obtained. Thereafter, it is molded as conventionally known.

  When the toggle mechanism 7 is driven to generate a clamping force for injection and filling, each tie bar 6a, 6b,... Undergoes elastic strain due to tension. The strain generated in each tie bar 6a, 6b,... Is measured by the strain sensors 21a, 21b,. In parallel with this, the temperature of each tie bar 6a, 6b,... Measured by the temperature sensors 23a, 23b,. As will be described in detail later, the strain amount of each tie bar 6a, 6b,... Input to the strain amount measuring device 51, the preset clamping force, and each tie bar 6a input to the temperature measuring device 53. .. Are calculated from the temperatures of 6b,... By the calculator 54, and the set temperatures of the tie bars 6a, 6b,. The temperature controller 55 determines whether to heat or cool each tie bar 6a, 6b,... According to the set temperature of each tie bar 6a, 6b,. That is, when heating, a command is output to the heater power supply devices 26a, 26b,... And the predetermined band heaters 24a, 24b,. In the case of cooling, a command is output to the water supply devices 29a, 29b,..., And cold water is supplied to the predetermined water jackets 27a, 27b,.

  The set temperature of each tie bar 6a, 6b,... Is the temperature for adjusting the effective length of each tie bar 6a, 6b,. When the effective length of each tie bar 6a, 6b,... Is adjusted, the amount of elastic deformation due to the tension of each tie bar 6a, 6b,. Then, the mold clamping force is evenly distributed to the tie bars 6a, 6b,... And a preset mold clamping force is obtained.

  Next, processing performed by the strain amount measuring device 51, the mold clamping force setting device 52, the temperature measuring device 53, and the temperature controller 55 shown in FIG. 1 will be described in detail with reference to the flowchart of FIG. When injection molding is performed after adjusting the mold clamping force as described above, the following processing is performed each time the mold clamping force is generated, that is, every time mold clamping is performed by injection molding. First, processing is started for the first tie bar 6a among the four tie bars 6a, 6b,.

Step S1: The strain of the tie bar 6a when the mold clamping force is generated is measured by the strain sensor 21a, and the strain amount is input to the calculator 54. This strain amount is a strain amount due to elastic deformation caused by the tension applied to the tie bar 6a as a reaction force of the mold clamping force. For example, 243 × 10 ⁻⁶ is measured as the strain amount ε.

Step S2: The amount of elastic deformation caused by the tension generated in the effective length of the tie bar 6a is calculated based on the amount of strain input in Step S1. If the effective length of the tie bar 6a is L (1.245 m), the amount of elongation λ is as follows.
λ = ε · L = 243 × 10 ⁻⁶ × 1.245 = 3.03 × 10 ⁻⁴ m = 0.303 mm.

Step S3: The mold clamping force is set in the mold clamping force setting device 52 in advance. The average tension applied to each tie bar is calculated from the set clamping force, and the theoretical value of the amount of elastic deformation caused by the tension is calculated. When the amount of elastic deformation of all the tie bars 6a, 6b,... Becomes equal to the theoretical value, each tie bar is evenly tensioned and the necessary clamping force is obtained.
For example, 40 weight ton (40 × 10 ³ × 9.81 N) is set as the set clamping force, and the sectional area of Young's modulus E (2.05 × 10 ¹¹ Pa), each tie bar 6a, 6b,. 20.0 cm ² = 2.00 × 10 ⁻³ m ² ), the theoretical value λ ₀ of the elongation amount of one tie bar is as follows.
λ ₀ = (1 / E) (W · L / S) = {1 / (2.05 × 10 ¹¹ )} {(40 × 10 ³ × 9.81 / 4) × 1.245 / 2.00 × 10 ⁻³ } = 2.98 × 10 ⁻⁴ m = 0.298 mm

Step S4: Compare and elongation amount lambda of the tie bars 6a calculated in step S2, the theoretical value lambda ₀ of the calculated amount of elongation in step S3. When lambda is equal to lambda _0, the tension applied to the tie bar 6a is appropriate, without subsequent processing with regard first tie bar 6a, starts processing in step 1 for the next tie bar 6b. When lambda is not equal to lambda _0, it performs the step S5 and subsequent steps. Here, since λ (0.303 mm) is not equal to λ ₀ (0.298 mm), the process proceeds to step S5.

  Step S5: The current temperature of the tie bar 6a measured by the temperature sensor 23a is input to the temperature setter 53. The measured temperature is not the temperature of the entire tie bar 6a but the temperature in the vicinity of the band heater 24a and the water jacket 27a (hereinafter referred to as the temperature control portion of the tie bar). In this embodiment, the temperature sensor is provided only at one location of each of the tie bars 6a,..., But in order to measure the temperature of the temperature control part of the tie bars 6a, 6b,. It may be provided.

Step S6: The temperature of the temperature control portion of the tie bar 6a is changed, and a target temperature T for causing expansion and contraction due to thermal expansion is calculated. The target temperature T is a temperature at which the elongation amount λ becomes equal to the theoretical value λ ₀ of the elongation amount after the temperature control portion of the tie bar 6a is expanded or contracted by heating or cooling.
The target temperature T is calculated as follows. First, an elongation difference Δλ, which is the difference between the elongation amount λ and the theoretical value λ ₀ of the elongation amount, is obtained. Next, the target temperature T is calculated from the table of FIG. 3 and the current temperature so that the obtained elongation difference Δλ is offset by the expansion / contraction Λ due to the change in heat of the temperature control portion of the tie bar 6a. That is, Table 1 in FIG. 3 is a correspondence table between the temperature change amount Δt of the temperature control portion of the tie bar and the thermal expansion / contraction Λ of the temperature control portion of the tie bar, and the thermal expansion / contraction Λ equal to the difference Δλ in elongation amount. From the table and read the corresponding temperature change. Then, the temperature change amount Δt is added to the current temperature t of the tie bar 6a to obtain the target temperature T. If the expansion / contraction Λ having the same thermal expansion as the elongation difference Δλ cannot be found from the table of FIG. 3, the temperature change amount Δt is obtained by calculation using a well-known linear interpolation method or the like although not described here.
Hereinafter, the target temperature T is obtained. First, the elongation difference Δλ is as follows.
Δλ = λ−λ ₀ = 0.303−0.298 = 0.005 mm
When Δλ = + 0.005 is read as expansion / contraction Λ due to thermal change from Table 1 in FIG. 3, the corresponding temperature change amount Δt is + 4.0 ° C.
If the temperature t of the temperature control portion of the current tie bar 6a is 40.0 ° C., the target temperature T is as follows.
T = t + Δt = 40.0 + 4.0 = 44.0 ° C.

In this embodiment, the temperature change Δt is obtained from the table of FIG. 3, but it may be directly calculated from the linear expansion coefficients of the tie bars 6a, 6b,. In this case, the length of the temperature control portion of the tie bar 6a is required for calculation, but the temperature control portion of the tie bar 6a is not uniform in temperature, and more than the range wound by the band heater 24a and the water jacket 27a. The temperature of the outer part also changes due to heat conduction. Therefore, it is difficult to accurately specify the temperature control portion of the tie bar 6a. However, for example, it is assumed that the temperature is uniformly changed only in the area wound by the band heater 24a and the water jacket 27a and the outer 15 mm portion. This portion can be used as a temperature control portion of the tie bar 6a.
For example, if the linear expansion coefficient α is 11 × 10 ⁻⁶ / ° C. and the length h of the temperature control portion of the tie bar 6a is 114 mm, the expansion / contraction due to thermal expansion cancels out the difference Δλ (0.005 mm) calculated above. Since Λ (= Δλ) is given by Λ = h · α · Δt, the temperature change Δt is as follows.
Δt = Λ / h / α = Δλ / h / α = 0.005 / 114 / (11 × 10 ⁻⁶ ) = 4.0 ° C.

  Step S7: The current temperature t of the tie bar 6a is compared with the target temperature T obtained in Step 6. If the target temperature T is higher, the process proceeds to Step S8. If the target temperature T is lower, the process goes to Step S9. Migrate processing. In the above example, the current temperature t of the tie bar 6a is 40.0 ° C. and the target temperature T is 44.0 ° C. Since the target temperature T is higher, the process proceeds to step S8.

  Step S8: The heater controller 26a is commanded by the temperature controller 55, and the band heater 24a is heated so that the temperature control portion of the tie bar 6a becomes the target temperature T. In the above example, heating is performed by the band heater 24a until the target temperature T reaches 24.0 ° C.

  Step S9: When the target temperature T is lower, the temperature controller 55 outputs a command to the water supply device 29a and cools with the water jacket 27a so that the temperature control portion of the tie bar 6a becomes the target temperature T.

  When the process for the tie bar 6a is completed, the process is continued from step 1 in the same manner as the tie bar 6a for the next tie bar 6b. If the processing is sequentially performed with the tie bars 6c and 6d and the processing is completed for all the tie bars, the series of processes at the time of the current mold clamping is finished. At the time of the next mold clamping, the process is started from step S1 for the tie bar 6a.

If the above processing is performed, a set clamping force can be obtained at all times, and tension is applied evenly to each tie bar, so that a predetermined clamping force can be evenly distributed in the mold.
As described above, when the temperature of the tie bar temperature control portion is changed, the elastic strain generated by the tension in the tie bar can be corrected. To correct the elastic strain is to correct the tension of the tie bar. That is, if the temperature of the tie bar temperature control part is changed, the tension generated in the tie bar can be changed. For reference, FIG. 4 is a graph showing a change in tension generated in a tie bar when the temperature of the temperature control portion of the tie bar is changed.
The graph shows that when the tie bar length L = 1.245 m, the tie bar temperature control part length h = 114 mm, and the tie bar temperature control part temperature t = 40.0 ° C., the tension W applied to the tie bar is W = It is the graph drawn as 98100N (10.0 weight Ton). The Young's modulus E = 2.05 × 10 ¹¹ Pa and the linear expansion coefficient α = 11 × 10 ⁻⁶ / ° C.
From the graph, it can be seen that when the temperature of the temperature control portion of the tie bar is increased, the tension applied to the tie bar can be decreased, and when the temperature is decreased, the tension can be increased.

By the way, the temperature control time constant for the temperature control portion of the tie bar is often longer than the mold clamping time of one injection molding process. For this reason, the temperature control does not converge at the time of one mold clamping, and the temperature control part of each tie bar reaches the target temperature at the second or subsequent mold clamping. Even during the second or subsequent mold clamping, a new target temperature different from the previous one is calculated and temperature controlled, so it is necessary to estimate the effect of time delay due to the long time constant, but the target calculated every time Since the temperature hardly fluctuates, there is no problem.
In the present embodiment, the strain amount of the tie bars 6a, 6b,... Is measured by the strain sensors 21a, 21b,. The strain sensor detects electrical resistance and measures the amount of strain from the slight difference in electrical resistance. The electrical resistance also changes due to the temperature change of the attachment portions of the strain sensors 21a, 21b,. The amount may not be measurable. For this reason, it can be considered that the influence of the heat conduction of the temperature control part of the tie bars 6a, 6b,... Is considered, but the strain sensors 21a, 21b, ... are separated from the temperature control part of the tie bars 6a, 6b,. Therefore, there is almost no influence of heat conduction and it is not a problem. However, in order to measure the strain amount more accurately, it is possible to newly provide a temperature sensor in the vicinity of the strain sensors 21a, 21b,.

  In this embodiment, band heaters 24a, 24b,... Are used for heating the temperature control portions of the tie bars 6a, 6b,..., And water jackets 27a, 27b,. Thus, heating and cooling can all be performed by a water jacket, and a cold air device can be employed for cooling. It is sufficient that the temperature control portions of the tie bars 6a, 6b,... Can be thermally expanded and contracted, and the heating method and the cooling method are not limited to the above embodiments.

  According to the present embodiment, a secondary effect can also be obtained. For example, it is possible to detect deterioration of the tie bars 6a, 6b,. The strain amount at the time of mold clamping is always measured, and when a specific tie bar deteriorates, the strain amount of the tie bar shows an abnormal value, so that it can be detected to know the abnormality. Further, according to the present embodiment, the tension is controlled so that the tie bars 6a, 6b,... Are evenly tensioned. Therefore, tie bar nuts 8a, 8b,. May be. However, it is desirable for a human to adjust the effective length of each tie bar periodically to some extent.

It is a front view showing typically an injection molding machine provided with a toggle type mold clamping device concerning an embodiment of the invention. It is a flowchart for demonstrating the effect | action of the mold-clamping-force automatic correction apparatus based on embodiment of this invention. 6 is a correspondence table between a temperature change amount Δt of the temperature control portion of the tie bar and a thermal expansion expansion Λ of the temperature control portion of the tie bar. It is a graph showing the change of the tension | tensile_strength which arises in a tie bar when the temperature of the temperature control part of a tie bar is changed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fixed platen 2 Movable platen 5 Clamping housing 6a, 6b, ... Tie bar 7 Toggle mechanism 14 Crosshead
21a, 21b, ... Strain sensors 23a, 23b, ... Band heaters 27a, 27b, ... Water jacket

Claims (4)

A fixed platen, a movable platen, a mold clamping housing, a plurality of tie bars that pass through the movable platen and connect the fixed platen and the mold clamping housing, and between the mold clamping housing and the movable platen When the mold is clamped by driving the toggle mechanism, tension is generated in each tie bar due to the reaction force of the mold clamping force, and the tension causes distortion due to elastic deformation in each tie bar. A method for correcting the mold clamping force of an injection molding machine,
For each tie bar, according to the amount of strain due to elastic deformation of the predetermined part of each tie bar measured at the time of mold clamping, the temperature of the part of each tie bar separated from the predetermined part by changing the temperature is expanded and contracted, An automatic mold clamping force correction method for an injection molding machine equipped with a toggle type mold clamping device, wherein the amount of strain due to elastic deformation of each tie bar is controlled to be equal. A fixed platen, a movable platen, a mold clamping housing, a plurality of tie bars that pass through the movable platen and connect the fixed platen and the mold clamping housing, and between the mold clamping housing and the movable platen When the mold is clamped by driving the toggle mechanism, tension is generated in each tie bar due to the reaction force of the mold clamping force, and the tension causes distortion due to elastic deformation in each tie bar. A method for correcting the mold clamping force of an injection molding machine,
The set mold clamping force is equally divided by the number of tie bars to obtain the tension of each tie bar, and the strain amount generated at a predetermined portion of each tie bar by the tension is set as the target strain amount. Is controlled so that the amount of strain due to the tension of each tie bar is equalized by changing the temperature of the portion of each tie bar that is separated from the predetermined portion by a predetermined amount so as to be equal to the target strain amount. A method for automatically correcting a mold clamping force of an injection molding machine having a toggle type mold clamping device. A fixed platen, a movable platen, a mold clamping housing, a plurality of tie bars that pass through the movable platen and connect the fixed platen and the mold clamping housing, and between the mold clamping housing and the movable platen It consists of a toggle mechanism provided,
In the injection molding machine, when the toggle mechanism is driven, each tie bar generates tension due to a reaction force of a clamping force, and the tension causes distortion due to elastic deformation in each tie bar.
For each of the tie bars, a strain measuring means for measuring the strain amount of each tie bar is provided at a predetermined portion of the tie bar, and a temperature in the vicinity of the portion is changed at a portion spaced from the predetermined portion by a predetermined amount. Temperature control means are provided,
Each temperature control means is controlled so that the strain amount of each tie bar measured by each strain measurement means is equal, The mold clamping force of an injection molding machine equipped with a toggle type mold clamping device Automatic correction device. 4. A correction apparatus according to claim 3, wherein said temperature control means is a heater and a water jacket, and said strain amount measuring means is a strain sensor, wherein the mold clamping force is automatically corrected by an injection molding machine provided with a toggle type mold clamping apparatus. apparatus.

Images