JP7613262B2 - Judgment device and mold clamping device - Google Patents

Description

The present invention relates to a mold clamping device that is applied to molding devices such as injection molding machines and die casting machines, and in particular to a mold platen that constitutes the mold clamping device.

The mold clamping device is equipped with a fixed platen, whose position is fixed during molding, and a movable platen, which moves back and forth relative to the fixed platen. A fixed mold and a movable mold are attached to the fixed platen and the movable platen, respectively, and the material to be molded, molten resin (injection molding machine) or molten metal (die casting machine), is supplied to the cavity formed between the fixed mold and the movable mold.

2. Description of the Related Art With respect to a mold clamping device, distortion is measured in order to ensure that the device operates normally.
For example, in Patent Document 1, strain gauges are attached to multiple locations on the back side of a fixed platen, and the distortion at multiple locations is measured in advance when the mold is normally clamped, and the distortion is set as a reference value.Then, the distortion is measured during the actual mold clamping operation, and the measured distortion is compared with the reference distortion. When the difference between the two exceeds a preset upper limit, the mold clamping is judged to be defective.
Furthermore, Patent Document 2 discloses a method for detecting abnormalities in mold clamping of an injection molding machine, which detects the axial load of multiple tie bars that make up a mold clamping device and generates an alarm when the variation in the load between axes exceeds a preset tolerance for variation.
Furthermore, Patent Document 3 proposes stopping the operation of the mold clamping device when the amount of strain detected by a strain gauge provided on the fixed mold exceeds a set value that is equal to or less than the elastic limit.

Japanese Patent Application Publication No. 10-291061 Special Publication No. 1-45409 JP 2006-102783 A

According to Patent Documents 1 to 3, damage to the platen including the fixed platen and the movable platen can be prevented by detecting the stress generated in the clamping device. However, although Patent Documents 1 to 3 can detect excessive stress, it is only temporary at the time of detection and does not correspond to continuous use of the clamping device. According to this, if the reference strain is set to a value at the one-shot destruction level of the material, there is a possibility that significant damage has already occurred to the platen when the actual measured strain reaches the reference strain. In this case, it is necessary to immediately stop the molding machine. However, if the reference strain is set to a value sufficiently lower than the one-shot destruction level, there is almost no damage to the platen when the actual measured strain reaches the reference strain. However, according to Patent Documents 1 to 3, even if no damage has occurred to the platen, a warning based on the detection of an abnormality will be issued if the actual measured value reaches the reference value even once. However, even if a state in which no damage occurs to the platen or no inconvenience occurs, such as a normal operating variation of the molding machine, a warning will be issued each time. In this case, even though the clamping device can be left alone, the operator must stop work or the molding machine each time to deal with the problem, which reduces workability and productivity. Furthermore, fatigue failure caused by repeated stress is one of the common damage modes of mold plates produced in castings, but the strain caused by fatigue stress, which is the cause of fatigue failure, is significantly lower than a single fracture. In other words, Patent Documents 1 to 3 provide some insight into fatigue failure, but as mentioned above, there is a risk of this reducing workability and productivity.

The present invention aims to provide a device that can determine the risk of abnormalities in the mold plate caused by repeated stress, i.e., fatigue failure, and issue a warning before it occurs.

The determining device of the present invention determines the fatigue state of a mold platen that constitutes a mold clamping device.
This judgment device includes a memory unit that stores historical data of actual stress values measured on a mold plate, a display unit that displays the historical data of the actual stress values, and a judgment unit that makes a judgment on the measured actual stress values.
The determination unit performs a first determination as to whether or not a measured actual stress value exceeds a predetermined allowable stress value.
The display unit is capable of displaying history data relating to actual stress values determined in the first determination to exceed the allowable stress value.

The storage unit according to the present invention preferably stores the actual number of times that the actual stress value has exceeded the allowable stress value since the history data was accumulated.
Moreover, the determination unit preferably performs a second determination as to whether or not the actual number of times exceeds a predetermined allowable number of times.
Further, the display unit preferably displays a warning based on a result of the second determination by the determination unit.

The history data displayed on the display unit according to the present invention preferably includes one or both of the actual number of times and the ratio of the actual number of times to the allowable number of times.

In the determination device of the present invention, preferably, the display of the history data on the display unit is performed based on an external request, and the display of the warning on the display unit is performed within a predetermined period of time after it is determined in the second determination that the actual number of times exceeds a predetermined allowable number of times.

The mold clamping device of the present invention comprises a fixed platen that supports a fixed mold, a movable platen that supports a movable mold, and any of the determination devices described above that determine the fatigue status of the fixed platen and the movable platen.

According to the judgment device of the present invention, past history data in which the actual stress value exceeds the allowable stress value can be displayed on the display unit. The operator and other relevant parties who refer to this display can recognize the fatigue status of the fixed platen and movable platen based on the history data. This allows the relevant parties to carefully prepare for maintenance of the clamping device, such as taking measures to reduce the clamping force in order to reduce distortion of the fixed platen and movable platen and reduce fatigue, inspecting for any abnormalities, or making prior arrangements for replacing the fixed platen and movable platen.

1 is a diagram showing a schematic configuration of a mold clamping device according to an embodiment of the present invention; 2 is a diagram showing the configuration of a control unit having an abnormality determination function of the mold clamping unit according to the present embodiment. FIG. 11 is a diagram illustrating an example of history data stored in a storage unit of a control unit. FIG. 11 is a diagram showing an example of extracting and displaying an actual distortion amount that exceeds an allowable distortion amount from history data stored in a storage unit; FIG. FIG. 13 is a diagram showing an example of a visual warning display by a storage unit. 11 is a diagram illustrating an example of a procedure for determining an abnormality by a determination unit of a control unit. FIG. 13 is a table showing another example of history data.

The following describes a mold clamping device 10 according to one embodiment of the present invention with reference to the attached drawings. As an example, the following describes a mold clamping device 10 that is applied to an injection molding machine.

[Mechanical configuration of the mold clamping device 10: FIG. 1]
As shown in FIG. 1, the mold clamping device 10 has a base frame 11 on one end of which a fixed platen 12 is fixedly mounted on the upper surface thereof, the fixed mold 14 being supported thereon.
A movable platen 13, which holds a movable mold 15 and faces the fixed platen 12, is disposed on the upper surface of the other end of the base frame 11 so as to be movable forward and backward. A guide rail 26 is laid on the base frame 11, and a linear bearing 27, which is guided by the guide rail 26, supports the movable platen 13 via a pedestal 28.

The fixed platen 12 and the movable platen 13 are provided with a first sensor 31 and a second sensor 33, each of which is a strain gauge. In FIG. 1, the sensors are provided at positions where their presence is clear, but preferably, they are provided at the portions of the fixed platen 12 and the movable platen 13 that are subject to large deformation during operation of the clamping device 10. The portions that are subject to large deformation are, for example, diagonal lines connecting the hydraulic clamping cylinders 18 arranged at the four corners of the fixed platen 12 and the movable platen 13. In this case, it is preferable to provide ribs along or parallel to the diagonal line and provide strain gauges on the diagonal ribs. Here, the four hydraulic clamping cylinders 18 arranged at diagonal positions apply clamping forces that compress the dies (fixed die 14 and movable die 15) arranged in the center of the area surrounded by these hydraulic clamping cylinders 18 from the outside of the dies in the axial direction, so that the deflection strain on the diagonal line is the largest. Therefore, the bending stress acting on the platen (fixed platen 12 and movable platen 13) is transmitted to the diagonal ribs provided along or parallel to the diagonal line, so by providing strain gauges on these diagonal ribs, the bending stress acting on the platen can be detected with high accuracy. Also, although an example is shown here in which only one first sensor 31 is provided on the fixed platen 12 and only one second sensor 33 is provided on the movable platen 13, multiple first sensors 31 and second sensors 33 can also be provided on the fixed platen 12 and movable platen 13, respectively. Measurement of the strain of the fixed platen 12 and movable platen 13 by the first sensor 31 and second sensor 33 can be performed continuously or intermittently.

Four hydraulic clamping cylinders 18, each with a small stroke and a large cross-sectional area, are provided at the four corners of the fixed platen 12. A ram 16 sliding inside the hydraulic clamping cylinders 18 has a tie bar 17 connected to one side of each ram 16. When the opposing movable platen 13 approaches for clamping, the tie bar 17 passes through four insertion holes formed in the movable platen 13.
A hydraulic mechanism 35 is connected to the hydraulic clamping cylinder 18. The hydraulic mechanism 35 supplies hydraulic oil to the clamping side chamber 18a and the mold opening side chamber 18b of the hydraulic clamping cylinder 18 based on instructions from the control device 40.

The means for moving the movable platen 13 is composed of a ball screw shaft 25 driven by a servo motor 22 via power transmission gears 23 and 24. The ball screw shaft 25 is installed parallel to the moving direction of the movable platen 13, and is rotatably supported by a bearing housing 20 held by the fixed platen 12 with its axial direction restrained, and is rotatably supported by a ball screw nut 21 held by the movable platen 13. The number of rotations and rotation speed of the ball screw shaft 25 are controlled via the servo motor 22 by a control device (not shown).
A plurality of ring grooves (or male threads) of equal pitch are formed at the tip of each tie bar 17. A split nut 29 having a ring-shaped inner groove (female thread) that meshes with the ring groove of each tie bar 17 is provided on the side surface of the movable platen 13 opposite the die.

[Control device 40: Figs. 1, 2, 3, 4, and 5]
The mold clamping device 10 is equipped with a control device 40 that controls the operation and functions of the mold clamping device 10 .
The operation of the mold clamping device 10 corresponds to the operation from the mold open state in which the fixed mold 14 and the movable mold 15 are separated, to moving the movable platen 13 toward the fixed platen 12 to bring the fixed mold 14 and the movable mold 15 into close contact, and then completing mold clamping by applying a predetermined mold clamping force. Also, the function of the control device 40 is to store the measured distortion amount En of the platen during the mold clamping state after mold clamping is completed, and to determine whether or not there is a possibility of mechanical abnormality occurring in the fixed platen 12 and the movable platen 13 based on the stored measured distortion amount En and the allowable distortion amount Et.

[Configuration of the control device 40: FIG. 2]
2, the control device 40 includes a display unit 41 for displaying necessary information, and an input unit 43 that is operated by an operator and receives input of, for example, mold thickness information, mold clamping force information, etc. The control device 40 includes a storage unit 45 for storing various information required for molding, an instruction unit 47 for instructing each operation of the mold clamping device 10, and a judgment unit 49 for judging whether or not there is a possibility of a mechanical abnormality occurring. Note that, in this example, the judgment unit 49 is independent of the instruction unit 47 in order to clarify the existence of the judgment unit 49, but the instruction unit 47 may also have the function of the judgment unit 49. The control device 40 is configured as a computer device, the input unit 43 is configured of soft keys or hard keys, and the display unit 41 is configured of, for example, an LCD (Liquid Crystal Display).

[Memory unit 45: FIG. 3]
The memory unit 45 stores the measured distortion amount En during clamping in each molding cycle sent from the first sensor 31 and the second sensor 33 in the clamping state. The measured distortion amount En may be measured continuously over time, or may be measured only once at any timing from the completion of clamping pressure increase to clamping pressure decrease, or may be measured multiple times and the maximum value or average value may be selected. The measured distortion amount En sent from the first sensor 31 is related to the fixed platen 12, and the measured distortion amount En sent from the second sensor 33 is related to the movable platen 13. Note that n is a positive integer including 0 as an example. FIG. 3 shows the measured distortion amount En (history data) stored and accumulated in the memory unit 45 in a table format. In order to distinguish between the measured distortion amount En related to the fixed platen 12 and the measured distortion amount En related to the movable platen 13, the former is represented as the measured distortion amount EAn, and the latter is represented as the measured distortion amount EBn.

The measured distortion amounts EAn and EBn are stored in association with the date and time of measurement and the number of clamping operations, as shown in Fig. 3. The measured distortion amounts EAn shown here are symbolized as EA00, EA01, EA02, EA03... in chronological order, and the measured distortion amounts EBn are symbolized as EB00, EB01, EB02, EB03... in chronological order, but the distortion amounts actually stored may be dimensionless values or values having a length dimension.
The number of mold clamping times is preferably the number of times that the clamping pressure is increased after the mold is closed, regardless of whether the mold clamping device 10 is operated manually or automatically. For example, in Fig. 3, the number of mold clamping times at the time of mold clamping at which the actual distortion amount EA00 of the fixed platen 12 was measured is "N". This indicates that the number of mold clamping times since the first mold clamping pressure increase was performed at the time of mold clamping at which the actual distortion amount EA00 was measured is the "N"th time.

As is well known, distortion occurs due to applied stress. Therefore, although the measured distortion amount En is the subject here, the measured stress (σn) can also be the subject. Therefore, in this embodiment, both the measured distortion amount En and the measured stress (σn) are defined as the actual stress value. Similarly, the allowable distortion amount Et and the allowable stress σt to be compared with the measured distortion amount En and the measured stress (σn) are defined as the allowable stress value.

The historical data in FIG. 3 also includes the results of comparing the measured strain amount EAn of the fixed platen 12 and the measured strain amount EBn of the movable platen 13 with the allowable strain amount Et (EAt, EBt). This comparison result indicates whether the measured strain amount En (EAn, EBn) exceeds the allowable strain amount Et (EAt, EBt) (En>Et). Here, the allowable strain amount Et is a reference value for determining whether a large strain that leads to fatigue failure has occurred in the fixed platen 12 and the movable platen 13. In the historical data, if the measured strain amount En exceeds the allowable strain amount Et, the comparison index is stored in the storage device 45 as "1", and if the measured strain amount En is equal to or less than the allowable strain amount Et, the comparison index is stored as "0". The determination (first determination) of whether the measured strain amount (actual stress value) En exceeds the allowable strain amount (allowable stress value) Et is performed in the determination unit 49.

The allowable strain amount Et is stored in the memory unit 45. This allowable strain amount Et may be commonly applied to both the measured strain amount EAn and the measured strain amount EBn, or may be applied individually, such as the actual number of times TAn applied to the measured strain amount EAn and the actual number of times TBn applied to the measured strain amount EBn. As an example, if the difference in bending stiffness between the fixed platen 12 and the movable platen 13 is small, a common actual number of times Tn is applied, whereas if the difference in bending stiffness between the fixed platen 12 and the movable platen 13 is large, individual actual numbers TAn and TBn are applied.

3 includes the actual number Tn, which is the total number of times that the measured distortion amount EAn of the fixed platen 12 and the measured distortion amount EBn of the movable platen 13 exceeded the allowable distortion amount Et. This actual number Tn includes the actual number TAn and the actual number TBn corresponding to the fixed platen 12 and the movable platen 13, respectively. For example, in FIG. 3, the actual number TAn of the fixed platen 12 is "n" from the measured distortion amount EA00 to the measured distortion amount EA02. This indicates that the number of times that the measured distortion amount EAn exceeded the allowable distortion amount Et before the measured distortion amount EA00 was measured was n times. Since the judgment unit 49 judges that the measured distortion amount EA03 exceeded the allowable distortion amount Et, the judgment unit 49 counts up and adds "1" to the actual number Tn stored in the storage device 45 to make it "n+1", indicating that the actual number Tn has been updated. Similarly, the measured strain amount EA10 exceeds the allowable strain amount Et, so "1" is added to make it "n+2". The same is true for EBn and TBn.

The actual number of times Tn (TAn) is compared with the allowable number of times Tt, as described below. This allowable number of times Tt is a reference value for determining (second determination) whether or not a large distortion that leads to fatigue failure has occurred in the fixed platen 12 and the movable platen 13, or whether or not the number of times has reached a limit. The allowable number of times Tt is stored in the memory unit 45. The allowable number of times Tt may be applied commonly to the actual number of times TAn and the actual number of times TBn, or may be applied individually, such as the allowable number of times TAt applied to the actual number of times TAn and the allowable number of times TBt applied to the actual number of times TBn.

In addition to the above history data, the memory unit 45 also stores information necessary to instruct the operation of the drive elements of the mold clamping device 10, such as the servo motor 22 and the hydraulic mechanism 35, as well as other information.

[Indication section 47: Figs. 4 and 5]
The instruction unit 47 reads out various information stored in the memory unit 45 in accordance with instructions and selections from the operator, and generates operation command information.
In addition, in accordance with an instruction from the operator, the instruction unit 47 extracts from the history data of Fig. 3 past history data in which the measured strain En exceeds the allowable strain Et, i.e., the comparison index with the allowable strain Et is "1", and displays it on the display unit 41. This history data is displayed on the display unit 41 as shown in Fig. 4, for example. The operator can recognize the fatigue state of the fixed platen 12 and the movable platen 13 by referring to this history data.
Furthermore, the measurement date and time and number of clamping operations stored in memory unit 45 along with the historical data are not used to evaluate the fatigue state, but by checking the fatigue state in comparison with the measurement date and time during maintenance inspection or after the occurrence of fatigue failure, it is possible to determine the period of time required to reach that fatigue state.
Alternatively, by recognizing the fatigue state by comparing with the number of clamping operations, it is possible to grasp the number of clamping operations required to reach that fatigue state. When there is a large difference in production volume over a certain period due to differences in machine operation rate and production cycle, it is preferable to compare with the number of clamping operations rather than the measurement date and time. In this way, a more accurate understanding of the fatigue state can be obtained by comparing with the number of clamping operations, for example, even when comparing a case where the machine is stopped for a long period with a case where the operation rate is high and the production volume is large.

In FIG. 4, the actual strain amount En, the comparison result with the allowable strain amount Et, and the actual number of times Tn are displayed, but it is also possible to display only one of the actual strain amount En, the comparison result, and the actual number of times Tn, for example. An operator can recognize the fatigue state of the fixed platen 12 and the movable platen 13 with just one of these.

Furthermore, the instructing unit 47 causes the display unit 41 to display a warning based on the determination result in the determining unit 49, which will be described next. This warning display is displayed on the display unit 41, for example, as shown in Fig. 5. By referring to this warning display, the operator can recognize the degree of progress of the fatigue state of the fixed platen 12 and the movable platen 13 and the degree of risk of fatigue failure, and also serves as a starting point for performing maintenance on the fixed platen 12 and the movable platen 13.
Note that the example in Figure 5 shows an example in which the actual number Tn or the allowable number Tt has been reached for the fixed platen 12, and the actual number Tn or the allowable number Tt has not been reached for the movable platen 13, but it is also possible that both the actual number Tn or the allowable number Tt has been reached for both the fixed platen 12 and the movable platen 13.

Note that while FIG. 5 shows an example of a visual warning being issued by displaying a specific display on the display unit 41, it is also possible to have an auditory warning be issued via a speaker provided in the control device 40, or to issue only an auditory warning. Also, while an example of issuing a warning via the control device 40 that controls the mold clamping device 10 is shown here, if there is a device that centrally monitors multiple injection molding machines, for example, the control device 40 that controls the mold clamping device 10 can display a warning via communication to this centralized monitoring device.

[Determination unit 49: FIG. 6]
6, the judgment unit 49 compares the actual number of times Tn with the allowable number of times Tt to judge whether or not the number of times that excessive distortion has occurred in the fixed platen 12 and the movable platen 13 has reached a limit (second judgment) and judges whether or not to issue a warning. A specific example of this procedure will be described in the section on molding operations after completion of mold clamping.

[Operation until mold clamping is complete: Figure 1]
The operation performed by the control device 40 until the completion of mold clamping will be described with reference to FIG.
1, that is, from a state in which the movable platen 13 is sufficiently separated from the fixed platen 12 as shown by the solid line, until the fixed platen 14 and the movable platen 15 are closed as shown by the two-dot chain line, the movable platen 13 moves by the rotation of the ball screw shaft 25 driven by the servo motor 22. During this process, the movable platen 13 slowly accelerates, moves at a constant speed, and then decelerates so that the fixed platen 14 comes into contact with the movable platen 15.

When the movable platen 13 stops at this position, the split nut 29 operates and the inner ring groove of the split nut 29 engages with the ring groove at the tip of the tie bar 17, connecting the tie bar 17 and the split nut 29.

After the tie bars 17 and the split nuts 29 are joined, the hydraulic mechanism 35 is operated to increase the pressure in the clamping side chamber 18a of the hydraulic clamping cylinder 18, thereby performing compression clamping. For example, if the center of gravity of the molten resin pressure generated in the cavity is located lower than the center of the clamping device 10, the clamping force by the lower tie bars 17 may be made larger than the clamping force by the upper tie bars 17, as described above.
After the mold clamping is completed in this manner, molten resin is injected from the injection barrel 30 into the cavity formed by the fixed mold 14 and the movable mold 15 to form a molded product.

[Molding operation after mold clamping is completed: Figures 1, 3, and 6]
When the mold clamping is completed, the determination unit 49 acquires the measured distortion amounts EAn, EBn of the fixed platen 12 and the movable platen 13 measured by the first sensor 31 and the second sensor 33 (FIG. 6, S101). Note that in FIG. 6, the measured distortion amounts EAn, EBn are collectively represented as the measured distortion amount En. The same applies to the other allowable distortion amounts EAt, EBt, etc.

When the judgment unit 49 acquires the measured distortion amounts EAn, EBn, it compares the magnitude relationship with the respective allowable distortion amounts EAt, EBt (FIG. 6 S103, first judgment). If the measured distortion amounts EAn, EBn are greater than the allowable distortion amounts EAt, EBt (FIG. 6 S103 Y), the measured distortion amounts EAn, EBn are associated with being greater than the allowable distortion amounts EAt, EBt and stored in the memory unit 45 (FIG. 6 S105). The accumulation of stored data is as shown in FIG. 3, and the comparison index "1" in FIG. 3 represents the association. If the measured distortion amounts EAn, EBn are less than the allowable distortion amounts EAt, EBt (FIG. 6 S103 N), the measured distortion amounts EAn, EBn are stored in the memory unit 45 without the association. The determination unit 49 continues to compare the newly acquired actual strain amounts EAn, EBn with the allowable strain amounts EAt, EBt, and stores the comparison results in the storage unit 45 in the same manner as above (FIG. 6 S101, S103, S105). Note that if the capacity of the storage unit 45 is sufficiently large, the actual strain amounts EAn, EBn may be stored in the storage unit 45 even if they are equal to or smaller than the allowable strain amounts EAt, EBt.

The determination unit 49 counts the actual number TAn, TBn of measured strain amounts EAn, EBn larger than the allowable strain amounts EAt, EBt (FIG. 6, S107). The counting result is as shown in the actual number Tn column in FIG.
When the determination unit 49 counts the actual counts TAn, TBn, it compares the actual counts TAn, TBn with the allowable counts TAt, TBt stored in the storage unit 45 to determine whether they are greater than or smaller than each other (Tn>Tt) (FIG. 6, S109, second determination). If the actual counts TAn, TBn exceed the allowable counts TAt, TBt (FIG. 6, S109, Y), it notifies the instruction unit 47 to display a warning on the display unit 41 (FIG. 6, S111). Based on this notification, the instruction unit 47 displays, for example, the warning shown in FIG. 5 on the display unit 41.
The above steps (S101 to S111) are continued until a predetermined molding cycle is completed (S113 Y).

[effect]
The above-described mold clamping device 10 provides the following advantages.
The clamping apparatus 10 can display past history data in which the measured distortion amount En exceeds the allowable distortion amount Et on the display unit 41. An operator and other relevant parties who refer to this display can recognize the fatigue state of the fixed platen 12 and the movable platen 13 based on the history data. This allows the relevant parties to carefully prepare for maintenance of the clamping apparatus 10, such as taking measures to reduce the clamping force in order to reduce distortion of the fixed platen 12 and the movable platen 13 and reduce fatigue, inspecting for any abnormalities, or making prior arrangements for replacing the fixed platen 12 and the movable platen 13.

The clamping device 10 also issues a warning that fatigue failure may occur in the fixed platen 12 and the movable platen 13 based on a judgment of whether the actual number Tn or the allowable number Tt has been reached. Based on this warning, relevant parties can take measures to reduce the clamping force in order to reduce distortion of the fixed platen 12 and the movable platen 13 and reduce fatigue, inspect for abnormalities, or replace the fixed platen 12 and the movable platen 13, thereby preventing fatigue failure from actually occurring in the fixed platen 12 and the movable platen 13.

In addition to the above, the configurations given in the above embodiments can be selected or appropriately changed to other configurations without departing from the spirit of the present invention.
The configuration of the mold clamping device 10 is merely an example, and for example, in the mold clamping device 10, the rotational driving force is converted into the reciprocating movement of the movable platen 13 by the ball screw shaft 25 to perform mold clamping and mold opening, but the drive mechanism for mold closing and mold opening of the present invention is not limited to this. For example, mold closing and mold opening may be performed using a toggle link mechanism.

The distortion data (FIG. 3) stored in the memory unit 45 may include other data. For example, as shown in FIG. 7, in addition to the actual number of times Tn, it may include the ratio of the actual number of times Tn to the allowable number of times Tt. This ratio may then be displayed on the display unit 47 as past history data. The operator and other relevant parties who refer to the display relating to this ratio can easily intuitively recognize the period until the allowable number of times is reached.

The history data based on the distortion data stored in the memory unit 45 can be displayed on the display unit 41 regardless of the operator's instructions. For example, it can be displayed before the mold closing operation begins, at a specific time, or at any other time.

The strain data stored in the memory unit 45 includes the measured strain amount En, and stress can be calculated directly from the strain according to Hooke's law. Therefore, the measured strain amount En of the strain data may be replaced with the measured stress (σn), or the strain data may include both the measured strain amount En and the measured stress (σn). When the measured stress (σn) is included, an allowable stress (σt) is prepared, and the measured stress (σn) is compared with the allowable stress (σt).

The risk of fatigue failure can be evaluated using known fatigue evaluation methods, but it is particularly preferable to use the linear cumulative damage rule (Minor's rule). Normally, the clamping force varies depending on the molded product, so the clamping force (amount of distortion of the mold platen) generated during mold clamping changes when the molded product changes. In this case, some molded products have a large amount of distortion of the mold platen, while others have a small amount of distortion. Fatigue failure does not only occur when the maximum stress value generated in the load history during operation exceeds the fatigue limit, but also progresses when the product is repeatedly operated in a state where the peak value of the repeated stress fluctuates. In this case, if the degree of fatigue is evaluated only based on the number of times the maximum stress value in the stress history reaches the fatigue limit value, the degree of progression of fatigue failure may be misjudged. Therefore, instead of setting the allowable stress value and allowable number of times corresponding to the maximum stress value generated in the load history to a constant value, the linear cumulative damage rule is used to accumulate the irregularly fluctuating actual stress value and express it as the fatigue damage degree, and the life until fatigue failure can be accurately predicted.

10 Mold clamping device 11 Base frame 12 Fixed platen 13 Movable platen 14 Fixed mold 15 Movable mold 16 Ram 17 Tie bar 18 Hydraulic mold clamping cylinder 18a Mold clamping side chamber 18b Mold opening side chamber 20 Bearing housing 21 Ball screw nut 22 Servo motor 23 Power transmission gear 25 Ball screw shaft 26 Guide rail 27 Linear bearing 28 Base 29 Split nut 30 Injection barrel 31 First sensor 33 Second sensor 35 Hydraulic mechanism 40 Control device 41 Display unit 43 Input unit 45 Memory unit 47 Instruction unit 49 Determination unit En, EAn, EBn Actual distortion amount Et, EAt, EBt Allowable distortion amount Tn, TAn, TBn Actual number of times Tt, TAt, TBt Allowable number of times

Claims (5)

An apparatus for determining a fatigue state of a mold platen constituting a mold clamping device, comprising:
A memory unit that stores historical data of actual stress values measured on the mold platen;
A display unit that displays historical data of the actual stress value;
A determination unit that determines the actual stress value measured,
The determination unit is
performing a first determination as to whether the measured actual stress value exceeds a predetermined allowable stress value;
The display unit is
In the first determination, the history data regarding the actual stress value determined to exceed the allowable stress value can be displayed.
The apparatus for determining the mold plate is characterized in that
The storage unit is
storing the actual number of times that the actual stress value has exceeded the allowable stress value since the historical data was accumulated;
The determination unit is
making a second determination as to whether the actual number of times exceeds a predetermined allowable number of times;
The display unit is
displaying a warning based on a result of the second determination by the determination unit.
The determination device according to claim 1 .
The history data displayed on the display unit is
The determination device according to claim 2 , further comprising one or both of the actual number of times and a ratio of the actual number of times to the allowable number of times.
The display of the history data on the display unit is performed based on an external request,
The display of the warning on the display unit is performed within a predetermined period of time after it is determined in the second determination that the actual number of times exceeds the predetermined allowable number of times.
The determination device according to claim 2 or 3.
A fixed platen supporting a fixed mold;
A movable platen supporting a movable die;
and a determination device according to any one of claims 1 to 4, which determines fatigue states of the fixed platen and the movable platen.
A mold clamping device characterized by:

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