JPWO2016059767A1 - Life prediction method for ball screw mechanism for mold clamping of toggle type mold clamping device and toggle type mold clamping device - Google Patents

Abstract

The present invention provides a ball screw mechanism life prediction method that can be predicted easily by a controller of an injection molding machine while requiring a relatively small amount of calculation for the prediction while the prediction is relatively accurate. In a mold clamping ball screw mechanism (24) for driving a toggle mechanism (14) of a toggle type mold clamping device (2), an operable time which is a time during which the mold clamping ball screw mechanism (24) can be operated. Predict (Lt). The theoretical formula is simplified based on the theoretical formula representing the life of the ball screw mechanism, and the operable time (Lt) is given as a one-variable function with the mold clamping force (KS) as one variable. Based on this one-variable function, the lifetime of the mold clamping ball screw mechanism (24) is predicted. In the preferred embodiment, the one-variable function is composed of the following exponential functions. Lt = α · KSβ where α and β are constants. [Selection] Figure 1

Description

  The present invention relates to a life prediction method for predicting the life of a ball screw mechanism for clamping a mold that drives the mold clamping device of an injection molding machine equipped with a toggle type mold clamping device, and a toggle in which such a life prediction method is implemented. The present invention relates to a mold clamping device.

  The injection molding machine is composed of an injection device for injecting resin and a mold clamping device for clamping a mold as is well known in the art. There are various types of mold clamping apparatuses, but a toggle type mold clamping apparatus having a mold clamping mechanism including a toggle mechanism is well known. The toggle type mold clamping device is provided with a fixed plate to which a fixed mold is attached, a mold clamping housing, and a slidably provided between the fixed plate and the mold clamping housing so that a movable mold can be attached. A movable platen, a plurality of tie bars connecting the fixed platen and the mold clamping housing, and a toggle mechanism. The toggle mechanism connects the mold clamping housing and the movable platen, and when the toggle mechanism is driven, the movable platen is driven to open and close the mold. There are various types of toggle mechanisms, but a relatively frequently used type includes a pair of short links, a pair of long links, a pair of cross links, and a cross head. One end of each of the pair of short links is pivotally attached to the mold clamping housing, one end of each of the pair of long links is pivotally attached to the movable platen, and the other end of each of the short link and the long link is They are connected to each other so as to be rotatable. The cross head and the pair of short links are connected by a pair of cross links. When the crosshead is driven in the axial direction by a predetermined drive mechanism, the pair of short links and long links bend and extend, and the toggle mechanism is driven to open and close the mold.

  In an electric injection molding machine in which each device is driven by a motor, the cross head is driven by a motor and a ball screw mechanism. The ball screw mechanism includes a ball screw, a ball nut that is screwed to the ball screw, and a plurality of balls that roll between the ball screw and the ball nut. The ball screw mechanism is excellent because it reduces the friction between the ball screw and ball nut by using multiple balls and can efficiently convert rotational force into axial force. However, the ball surface peels off when used in an environment where a load is applied. Deterioration progresses by doing. Since the ball screw mechanism that drives the crosshead is subjected to a large load during mold clamping, it may deteriorate quickly and need to be replaced in several years. Replacement of the ball screw mechanism must be performed after the operation of the injection molding machine is stopped for a predetermined time. If a failure of the ball screw mechanism occurs at an unexpected timing, it will be forced to stop production for a long period of time, which will hinder production planning. If the life of the ball screw mechanism can be appropriately predicted, replacement of the ball screw mechanism can be planned, and the production plan can be avoided. Manufacturers that manufacture ball screw mechanisms provide the following formulas that predict the life of the ball screw mechanism.

The basic dynamic load rating C _a is applied to the ball screw mechanism such that when a plurality of ball screw mechanisms are rotated under the same conditions, 90% of the ball screw mechanisms can rotate 1 million without causing metal peeling due to deterioration. It is the load in the axial direction. The load coefficient _fw is a coefficient that is taken into account depending on the presence or absence of an impact received during rotation. If there is no impact, 1.0 is adopted. In the ball screw mechanism for mold clamping, since the impact is small, it can be considered as 1.2. Rated fatigue life L is the life of the ball screw mechanism when the axial load F _a is a load of the predetermined axis direction is driven ball screw mechanism while acting, are those indicated by the number of rotation, 1-1 Formula Given by. From the rated fatigue life L and the rotation speed n, a life time L _t that represents the life of the ball screw mechanism in terms of time is given by Formula 1-2. By the way, in Formula 1-1, although the axial load _Fa is a constant value, the load generally changes, and the load also changes in the ball screw mechanism for mold clamping. The manufacturer of the ball screw mechanism also provides an equation for calculating the life of the ball screw mechanism when the axial load changes as follows.

2-1 formula is In calculating the service life of the ball screw mechanism an axial load is changed, an equation for calculating the average axial load F _m is an axial load average. When driving the ball screw mechanism over n times, the first, second, ... axial load F _1, F 2 acting on the n-th ball screw mechanism in each, _... F _n, the rotational speed n ₁ at that time, n ₂ ,... n _n and the driving times t ₁ , t ₂ ,... t _n at that time, and the average axial load F _m is calculated therefrom. In fact, equations 1-1 can be inevitably derived from equations 1-1. Considering the reciprocal of 1-1, the left side is 1 / L, which can be said to be the damage that the ball screw mechanism will receive per rotation, and the ball screw mechanism has reached the end of its life once the damage for L rotations has accumulated. It can be judged. Meanwhile 1-1 inverse of formula on the right side is proportional to the cube of the axial load F _a. In other words, damage the ball screw mechanism receives is proportional to the cube of the axial load F _a per rotation. Then, when the axial loads F ₁ , F ₂ ,... F _n change, the cumulative value of damage that the ball screw mechanism will receive is F ₁ ³ · n ₁ · t ₁ + F ₂ ³ · n ₂ · t ₂ + ... proportional to F _n ³ · n _n · t _n . That is, it is proportional to the axial load F ₁ , F ₂ ,... F _n raised to the third power, multiplied by the number of rotations at that time, and added. Then, this equation is related to the average damage of the ball screw mechanism per rotation that is divided by n ₁ · t ₁ + n ₂ · t ₂ + ... n _n · t _n which is the total number of rotations. , Which is the 1/3 power of this, becomes the equation 2-1. As a result, an average axial load _Fm is obtained. Substituting the axial load F _a In this manner the average axial load F _m which is calculated based on the 2-1 formula in 1-1 type, so that the nominal fatigue life L is obtained as 2-3 formula . Formula for the average rotational speed n _m is the rotational speed of the average of the ball screw mechanism is obtained as 2-2 equation. The rated fatigue life L obtained, lifetime L _t as 2-4 Expression from this average engine speed n _m is obtained. Therefore, in the ball screw mechanism for mold clamping, if the axial load at each timing can be detected and the rotation speed and driving time at that time can be obtained, the average axial load F _m can be calculated. Lifespan can be calculated.

JP 2000-238106 A

  Another method for estimating the life of the ball screw mechanism is proposed in Patent Document 1. In the method described in Patent Document 1, the energy at the timing of detecting the moving speed of the ball screw when driving the ball screw mechanism and the current supplied to the motor and multiplying these by a predetermined torque coefficient and acting on the ball screw mechanism. Calculate When the energy acting on the ball screw mechanism is accumulated, the total energy acting on the ball screw mechanism is obtained. If the total energy exceeds the preset life energy, it is determined that the life has been reached.

In a toggle type mold clamping device, it is important to predict the life of a ball screw mechanism for mold clamping as described above. The life of the ball screw mechanism can be predicted by using equations 2-1 to 2-4. The life can also be predicted by the method described in Patent Document 1. However, there are problems with these methods. First, although it is a case where it estimates based on 2-1 Formula-2-4 Formula, there exists a problem that calculation is difficult. The axial load acting on the ball screw mechanism for mold clamping changes in a complicated manner, and it is virtually impossible to accurately detect the axial load, the number of rotations of the ball screw, and the driving time at each timing. . Even if these can be detected with high accuracy, the calculation amount becomes enormous if it is successively calculated by the equation 2-1, etc., and cannot be calculated by the controller of the injection molding machine. That is, the lifetime cannot be calculated substantially based on the formulas 2-1 to 2-4. In the method described in Patent Document 1, only the moving speed of the ball screw when driving the ball screw mechanism and the current supplied to the motor are detected, and the lifetime is predicted from the total energy calculated and accumulated from these, The calculation can be sufficiently performed in the controller of the injection molding machine. However, it is not always clear whether the lifetime can be accurately predicted. According to 1-1 expression that manufacturers are manufacturing a ball screw mechanism is provided, contribution to the rated疲寿life L axial load F _a as described above is given by the inverse of the cube. That is, when the axial load _Fa is small, the life is hardly affected, but when it is large, the life is drastically affected. However, in the method disclosed in Patent Document 1, since the current is detected should be proportional to the torque of the motor, it is considered that current is generally a physical quantity that is proportional to the axial load F _a In the energy calculation, the current is not raised to the third power. That will be estimates reduce the degree of contribution of the axial load F _a for life in the method described in Patent Document 1 differs from the 1-1 type. Then, there is no guarantee that the life of the ball screw mechanism for mold clamping can be accurately predicted.

  Therefore, the present invention predicts the life of a ball screw mechanism for clamping a toggle type mold clamping device, while requiring a relatively accurate calculation and a small amount of calculation required for the prediction. It is an object of the present invention to provide a method for predicting the life of a ball screw mechanism that can be easily predicted.

According to a first aspect of the present invention, in order to achieve the above object, in the mold clamping ball screw mechanism that drives the toggle mechanism of the toggle type mold clamping device, the time during which the mold clamping ball screw mechanism can be operated without deterioration. Is given by a one-variable function whose variable is one of the mold clamping forces, and the life is predicted based on the one-variable function. It is configured as a life prediction method.
The invention according to claim 2 is the method according to claim 1, wherein the one-variable function is an exponential function, and is configured as a method for predicting the life of the ball screw mechanism for clamping a toggle type clamping device. The
According to a third aspect of the present invention, in the method according to the first aspect, the one-variable function comprises a polynomial, and is configured as a method for predicting a life of a ball screw mechanism for a clamping mold of a toggle type clamping apparatus. .
According to a fourth aspect of the present invention, in the method according to the third aspect, the polynomial comprises a quadratic equation, and is configured as a method for predicting the life of a ball screw mechanism for clamping a toggle type clamping device.
The invention according to claim 5 is configured as a toggle type mold clamping device in which the life of the ball screw mechanism for mold clamping is predicted by the life prediction method according to claims 1 to 4.

  As described above, according to the present invention, in the mold clamping ball screw mechanism that drives the toggle mechanism of the toggle type mold clamping device, the operable time that is the time during which the mold clamping ball screw mechanism can be operated without deterioration is reduced. The variable is given by a one-variable function including one mold clamping force, and the life is predicted based on the one-variable function. That is, since the variable gives the operable time by only one function, the amount of calculation required for the life prediction is small. Therefore, it can be easily predicted by the controller of the injection molding machine. As will be described later, the operation time is given as a one-variable function with the mold clamping force as one variable, which can be realized by analyzing the characteristics of the toggle type mold clamping device and setting predetermined conditions. This is substantially the same as predicting the life of the ball screw mechanism based on the theoretical formulas 2-1 to 2-4. In other words, it can be said that the prediction of the life of the ball screw mechanism for mold clamping is sufficiently accurate. According to yet another invention, the one-variable function is an exponential function. According to another invention, the one-variable function is a polynomial. According to yet another invention, the polynomial consists of a quadratic expression. Thus, since it is given by a relatively simple one-variable function, there is an effect that only a small amount of calculation is necessary for predicting the lifetime.

It is a front view which shows the injection molding machine provided with the toggle type | mold clamping apparatus which concerns on embodiment of this invention. FIG. 3 is a graph showing an axial load acting on a mold clamping ball screw mechanism of a toggle type mold clamping apparatus according to an embodiment of the present invention, and FIG. 3A shows the effect on the mold clamping ball screw mechanism when a mold clamping force is generated. (B) is a graph showing changes in the axial load acting on the ball screw mechanism for mold clamping in each step of the molding cycle. It is a graph which shows prediction of the lifetime of the ball screw mechanism for mold clamping of the toggle type mold clamping apparatus which concerns on embodiment of this invention.

  The method of predicting the life of the ball screw mechanism for mold clamping according to the present embodiment can be applied to a general electric injection molding machine equipped with a toggle type mold clamping device. Initially, the injection molding machine 1 which concerns on this Embodiment is demonstrated. The injection molding machine 1 includes a toggle type mold clamping device 2 provided on a bed 4 and an injection device 3 provided similarly to be slidable on the bed 4. The injection device 3 includes a heating cylinder 6, a screw (not shown) that can be driven in the rotation direction and the axial direction in the heating cylinder 6, and an injection nozzle provided at the tip of the heating cylinder 6 as is well known in the art. 7 etc.

  The toggle type mold clamping device 2 is also well known in the art, and includes a stationary platen 9 to which a stationary die K1 is attached, a movable platen 10 to which a movable die K2 is attached, a mold clamping housing 12, and a stationary platen. Are connected to the mold clamping housing 12 and a toggle mechanism 14 provided between the mold clamping housing 12 and the movable platen 10. A toggle mechanism 14 is also well known, and a pair of short links 16 and 16 having one end pivotally attached to the mold clamping housing 12, and one end being pivotally attached to the short links 16 and 16. A pair of long links 17, 17 whose other ends are pivotally attached to the movable platen 10, a cross head 18 that drives the toggle mechanism 14, and a cross link that connects the cross head 18 and the short links 16, 16. 20 and 20.

  In the present embodiment, the driving mechanism for driving the cross head 18 includes a mold clamping motor 22, a mold clamping ball screw mechanism 24, and a pair of mold clamping ball screw mechanisms 24 that transmit the rotational force of the mold clamping motor 22. The pulleys 25 and 26 and a belt 27 are included. The mold clamping ball screw mechanism 24 includes a ball screw 29, a ball nut 30 screwed into the ball screw 29, and a plurality of balls (not shown) that roll in the ball nut 30. In this embodiment, A ball nut 30 is provided on the cross head 18.

  With this configuration, when the mold clamping motor 22 is driven and the crosshead 18 is driven via the mold clamping ball screw mechanism 24, the toggle mechanism 14 is bent and stretched, and the movable platen 10 is slid to toggle type. The mold clamping device 2 is opened and closed.

  In predicting the lifetime of the mold clamping ball screw mechanism 24 according to the present embodiment using the above-described theoretical formulas 2-1 to 2-4, the present inventor considered the characteristics of the toggle mold clamping device 2. We have succeeded in simplifying the theoretical formula by examining the above and by setting predetermined conditions. First, the characteristics of the toggle type mold clamping device 2 examined by the present inventor will be described, and then a method for deriving a simplified theoretical formula will be described.

When the cross mold 18 is driven with a predetermined axial force, the toggle type mold clamping apparatus 2 can obtain a mold clamping force KS for clamping the molds K1, K2 at a predetermined magnification. This magnification is theoretically obtained from the structure of the toggle mechanism 14, but varies depending on the bending / extension state of the toggle mechanism 14 rather than a constant value. The axial force to be driven varies depending on the mold clamping force KS to be obtained. These relationships are shown in FIG. Since the axial force for driving the cross head 18 is equal to the axial load F acting on the clamping ball screw mechanism, the axial direction acting on the clamping ball screw mechanism when various clamping forces KS are obtained. The load F is also the same as the graph of FIG. Although the axial load changes in the mold clamping process, the maximum axial load F _max in the mold clamping process is shown in the graph. The toggle type mold clamping device 2 has a range of mold clamping force KS that can be generated depending on the model, and in a given model, as shown in the graph of FIG. KS can be generated in the range of KS ₁ kN to KS ₂ kN, and the maximum axial load F _max acting on the mold clamping ball screw mechanism at that time is F _max1 kN to F _max2 kN.

The present inventors have, in each of steps constituting the molding cycle was investigated how general the change in axial load F _x acting on the ball screw mechanism for mold clamping. The axial load F _x is calculated from the torque that drives the mold clamping motor 22, that is, from the current supplied to the mold clamping motor 22. State of a change in the axial load F _x in each step was obtained as shown in FIG. 2 of the graph of the code 35 (B). In the graph, mold closing (A) indicates the mold closing process from the mold open state until the molds K1 and K2 contact each other, and mold clamping (B) indicates the mold clamping force from the state where the molds K1 and K2 contact each other. The mold clamping process until the generation is performed, the holding (Z) is the injection process for injecting the molds K1 and K2, and the pressure holding process for holding the pressure, and the mold loosening (C) is the mold clamped. A mold loosening process in which K1 and K2 are shifted to a contact state where no mold clamping force is generated and a mold opening process (D) indicates a mold opening process in which the mold is opened. It can be seen that the maximum axial load F _max is generated in the mold clamping process among all the processes. Considering the average axial load averaged at each step change in the axial load F _x, so the stepped graph shown by reference numeral 36 in the FIG. 2 (B). A specific method for obtaining the average axial load obtained by averaging in each step will be described later. When the average axial load for each step is given as described above, the mold clamping ball screw mechanism 24 is provided. It is possible to calculate the average axial load F _m necessary for calculating the lifetime of By the way, since the pressure-holding process held in a state where the mold clamping ball screw mechanism 24 is stopped should not affect the life, only the mold closing process, the mold clamping process, the mold loosening process, and the mold opening process are calculated. For example, an average axial load F _m that is an average axial load in the molding cycle is obtained. When the average axial load F _m is calculated based on the above-described equation 2-2, the equation 3-1 is obtained.

_{Here, F A, F B, F} C, F D each mold closing step, the mold clamping process, the mold slow process, the axial load of the average in the mold opening _{process, n A, n B, n} C, n D Are the number of rotations of the ball screw mechanism 24 for mold clamping in the mold closing process, mold clamping process, mold loosening process, and mold opening process, respectively, t _A , t _B , t _C , and t _D are the mold closing process, mold clamping process, The drive time of the ball screw mechanism 24 for mold clamping in the mold loosening process and the mold opening process is shown. Similarly, based on the formula 2-2, the average rotation speed of the clamping ball screw mechanism 24 in the molding cycle, that is, the average rotation speed _nm is obtained.

Now, the axial load _F A of the average in each _step, F _B, F C, a method of obtaining the _{F D} will be described. These respective axial load measured in Step F _x, i.e. the axial load F _x indicated by reference numeral 35 in FIG. 2 (B) is obtained by averaging in each step as follows Get. First, each process is equally divided into a plurality of time widths. For example, in the case of a mold closing process, the mold closing process is equally divided into 10 time zones. Next, the axial load F _x in each of the divided time zones is read from the graph of reference numeral 35, and the average axial loads F _A , F _B , F _C , and F _D in each step using the equation 2-1. Ask for. At this time, since each time zone is equally spaced, the drive times t ₁ , t ₂ ,... T _n all have the same value. Then, the rotational speed of the mold clamping ball screw mechanism 24 at each step rpm n _1, n 2 assuming a constant, _... n _n can be calculated as the same value for any. Axial load _F A of the average in the respective steps _Thus, F _B, F _C, can be obtained _{F D.} The inventor performs a molding cycle in a toggle type mold clamping device of a predetermined model to measure a change in the axial load, and based on that, average axial loads F _A , F _B , F _C , was calculated the F _D, as shown in the graph of the code 36 in FIG. 2 (B), the mold closing step, the mold clamping process, the mold slow process, the average axial load F in the respective mold opening process _{a, F B, F C,} F D is 0.3-fold, respectively for the maximum axial load _{F max,} 0.75 times, 0.45 times, it became 0.3 times. Substituting this result into equation 3-1, equation 4-1 is obtained.

By the way, in the toggle type mold clamping device 2, there is a possibility that the mold opening / closing stroke in the mold opening process or the mold opening process may be different if the types of the molds K 1, K 2 are changed. However, in a general molding cycle, the mold opening process and the mold opening / closing stroke in the mold opening process are approximately ½ of the maximum mold opening / closing stroke possible in the model. That is, the mold opening process and the mold opening / closing stroke in the mold opening process are operated so as to be constant regardless of the types of the molds K1, K2. Therefore, in the case of predicting the lifetime according to the present invention, the mold opening process and the mold opening / closing stroke in the mold opening process are required to be ½ of the maximum mold opening / closing stroke. If the mold opening / closing stroke is determined, the rotational speeds n _A and n _D of the mold clamping ball screw mechanism 24 in the mold closing process and the mold opening process are operated at a constant value, so that the mold clamping ball screw mechanism 24 is driven in each process. Times t _A and t _D can be necessarily calculated. The rotational speeds n _B and n _{C of the} ball screw mechanism 24 for mold clamping and the driving times t _B and t _{C in the} mold clamping process and the mold loosening process can be given at substantially constant values depending on the model. The numerical values of n _{A to} n _D and t _{A to} t _D are substituted into Equation 4-1. Then, the average axial load F _m in the molding cycle is obtained as a function having the maximum axial load F _max as the only variable.

Thus the obtained function, calculated by substituting various values for the maximum axial load F _max, to obtain an average axial load F _m in each as specific numerical values. Note that a value that can be taken by the maximum axial load F _max to be substituted is determined according to the model of the toggle type mold clamping apparatus 2. That is, in the toggle type mold clamping device 2 according to the present embodiment, the range shown in the graph of FIG. 2A, that is, F _max1 kN to F _max2 kN can be taken. An appropriate number, for example, 7 points is selected from these ranges, and the maximum axial load F _max is substituted into the function obtained above to calculate the average axial load F _m . 4-2 Expression from such a manner calculated average axial load F _m, to calculate the lifetime L _t in each based on the 4-3 formula. Note that the load coefficient _fw is calculated as 1.2. Then, the combination consisting of the maximum axial load F _max and lifetime L _t is a plurality of sets, obtained for example seven sets. The mold clamping force KS corresponding to the maximum axial load F _max in each group is read from the graph of FIG. 2A and combined with the life time L _t . Then a combination consisting of a mold clamping force KS and lifetime L _t is a plurality of sets, obtained for example seven sets. These pairs, plotted abscissa clamping force KS, the vertical axis in the graph and lifetime L _t. For example, a combination comprising a mold clamping force KS and lifetime L _t is if seven pairs, point 7 as shown in FIG. 3 is plotted on a graph. Here, the life time L _t is expressed by a one-variable function f () having the mold clamping force KS as one variable as in the following equation.
L _t = f (KS) 5-1 Equation One-variable function f () can use various functions, and any function can be used as long as all of the plotted points can be approximately satisfied. May be. As a preferable example of such a one-variable function f (), the following exponential function can be given.
L _t = α · KS ^β 5-2 where α and β are constants α and β may be determined by the least square method or the like so as to approximate a plurality of points plotted on the constant graph.
Another preferable example of the one-variable function f () is the following polynomial.
L _t = a _n · KS ⁿ + a _n-1 · KS ^n-1 + ... a ₁ · KS ¹ + a ₀ · KS ⁰ 5-3 where a _n , a _n-1 , ... are constants The constants a _n , a _n−1 ,... May be determined by the least square method or the like so as to approximate a plurality of points plotted on the graph.

As described above, the present inventor simplified the theoretical formulas of the formulas 2-1 to 2-4 by examining the characteristics of the toggle type mold clamping device 2 and setting predetermined conditions. The formula 5-2 or the formula 5-3 could be obtained. Equation 5-2 represents the life time L _t, that is, the operable time of the mold clamping ball screw mechanism 24 as an exponential function with the mold clamping force KS as one variable, and Equation 5-3 represents a polynomial. Is. Formula 5-2 or formula 5-3 is stored in the controller of the injection molding machine 1. Based on this one-variable function, the controller can calculate the operable time of the mold clamping ball screw mechanism 24 from the mold clamping force KS. That is, the lifetime of the mold clamping ball screw mechanism 24 can be predicted.

In addition, even if the polynomial shown by 5-3 type | formula is a quadratic type like the following 5-4 type | formula fully endures practical use.
L _t = a ₂ · KS ² + a ₁ · KS + a ₀ Formula 5-4 The curve shown in FIG. 3 is approximated by a quadratic formula of Formula 5-4.

As described above, the toggle mold clamping device 2 has a different range of mold clamping force KS that can be generated depending on the model. That is, the graph in FIG. 2A differs depending on the model. Also, different by _n A _~n D in 4-1 _formula, also t A ~t _D model. However, in any model, if the calculation is performed by the method described above, the operable time of the mold clamping ball screw mechanism can be expressed by a one-variable function f () with the mold clamping force KS as one variable.

According to the present invention, it has been described that the life time L _t can be predicted by a one-variable function f () with the mold clamping force KS as one variable, thereby predicting the life of the ball screw mechanism 24 for mold clamping. However, the predictable lifetime may be the number of times the molding cycle can be performed. Since the time required for one molding cycle is substantially constant, the ability to predict the life time L _t is the same as the ability to predict the number of possible molding cycles.

In the present invention, it has been described that the life time L _t is predicted by a one-variable function f () with the mold clamping force KS as one variable. That is, it was explained that there is one variable. However, the life time L _t may be predicted by giving a function with higher prediction accuracy by adding a correction term due to other factors such as temperature. A function including such a correction term should include not only one mold clamping force KS but also temperature as a variable. However, the magnitude of the correction by the correction term is expected to be considerably small, and the life time L _t is substantially larger than that predicted by the one-variable function f () having the mold clamping force KS as one variable. There should be no difference.

DESCRIPTION OF SYMBOLS 1 Injection molding machine 2 Toggle type clamping device 9 Fixed board 10 Movable board 12 Mold clamping housing 13 Tie bar 14 Toggle mechanism 18 Cross head 22 Mold clamping motor 24 Mold clamping ball screw mechanism

Claims (5)

In the mold clamping ball screw mechanism that drives the toggle mechanism of the toggle type mold clamping apparatus, the variable operation time is a time during which the mold clamping ball screw mechanism can be operated without deterioration from one of the mold clamping forces. A life prediction method for a ball screw mechanism for a clamping mold of a toggle type mold clamping device, characterized in that the life is predicted based on the one-variable function. The method according to claim 1, wherein the one-variable function is an exponential function. 2. The method according to claim 1, wherein the one-variable function comprises a polynomial. 4. The method according to claim 3, wherein the polynomial comprises a quadratic equation. A toggle-type mold clamping device in which the life of the ball screw mechanism for mold clamping is predicted by the life prediction method according to claim 1.

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