Injection molding machine and flash prevention method

Abstract

When the injection molding machine is molding, the clamping force on the mold is adjusted based on the mold displacement, injection peak pressure and injection front position of the mold, so that molding is performed with an appropriate clamping force that does not generate flash and can reduce energy. The mold displacement amount is monitored during automatic operation, and the injection peak pressure and injection front position are also monitored. Automatic operation continues when there is no mold displacement change exceeding the threshold, or when there is no injection peak pressure abnormality or injection front position abnormality exceeding the threshold. When there is a mold displacement change, or an injection peak pressure abnormality or an injection front position abnormality, the operation of the injection molding machine is stopped.

Description

Technical Field

[0001] The present invention relates to an injection molding machine and a flash prevention method. Background Art

[0002] In the past, there was an injection molding machine including a clamping unit and an injection unit. The clamping unit includes a tie rod that crosses between a fixed plate fixed to a machine table and a pressure plate that can move on the machine table. The tie rods are fixed and supported on the fixed plate at one end. At the other end of the tie rod, the pressure plate is connected in a manner that the position relative to the tie rod can be adjusted. A movable plate is installed between the fixed plate and the pressure plate so that it can move along the tie rod. A toggle mechanism is installed between the pressure plate and the movable plate. The mold arranged between the movable plate and the fixed plate is closed by extending the toggle mechanism, and then a clamping force is applied to perform mold clamping.

[0003] The injection unit performs injection filling of molten resin when the mold is clamped. In addition, the injection molding machine equipped with the clamping unit and the injection unit has a molding cycle including mold closing, mold clamping, injection filling, metering, mold opening, and molded product removal. The injection molding machine repeats this molding cycle to continuously mold molded products.

[0004] When the above-mentioned injection molding machine is molding, if the mold is clamped by the maximum clamping force of the clamping unit, the molded product can be molded without generating flash. However, repeatedly applying an excessive clamping force to the mold will accelerate mold degradation. Applying an excessive clamping force will also lead to unnecessary increase in energy consumption. Therefore, if the mold can be clamped with the minimum appropriate clamping force, early degradation of the mold can be suppressed and the energy used to obtain the clamping force can be reduced.

[0005] In the past, a method for setting an appropriate mold clamping force when molding is performed by the above-mentioned injection molding machine has been proposed. For example, the method shown in Patent Document 1 uses a mold clamping force sensor composed of a tie bar sensor installed on a tie bar. Starting from the maximum value that can be applied by the mold clamping unit, molding is performed by gradually reducing the set mold clamping force at the end of each molding cycle. During injection filling, the change in the mold clamping force applied to the mold is detected based on the strain of the tie bar, and the value of the set mold clamping force is adjusted to an appropriate value based on the detected change.

[0006] In addition, in the method shown in Patent Document 2, injection molding is performed under set clamping forces of arbitrary different sizes. By detecting the maximum value of the clamping force when the mold is closed and the clamping force generated during the injection when the molten resin is injected into the mold, the clamping force at each moment is obtained in advance. Next, the maximum increase in the clamping force is calculated, which is the difference between the maximum value of the clamping force when the mold is closed and the clamping force during the injection. Two or more set clamping forces are extracted from the parts where the corresponding maximum increases in the clamping forces are different and the mold remains closed. From the combination of the two or more extracted set clamping forces and the maximum increase in the clamping force, a formula representing the maximum increase in the clamping force relative to the set clamping force is further determined. Injection is performed with a set clamping force that is less than the two or more extracted set clamping forces, and the maximum increase in the clamping force in the interval where the set clamping force is less than the two or more extracted set clamping forces is calculated.

[0007] Then, the set clamping force is determined by calculation, at which the maximum increase in the clamping force calculated based on the above formula exceeds the comparison value. The method sets the clamping force to the minimum required clamping force to maintain the mold closed immediately before the determined set clamping force.

[0008] In the method shown in Patent Document 3, molding is attempted by using a set clamping force that is sequentially decreased from the maximum clamping force to a predetermined magnitude. The mold position of the movable platen relative to the fixed platen in the injection process is detected by a mold position sensor. The set clamping force that causes the mold position change is increased by a predetermined amount, and the obtained clamping force is set to an appropriate clamping force. In addition, a lower limit value of the set clamping force is set to be sequentially decreased from the maximum clamping force. If the set clamping force reaches the limit value without changing the mold position, this method sets the limit value to an appropriate clamping force.

[0009] Patent document 1: Japanese Patent No. 5000213.

[0010] Patent document 2: Japanese Patent No. 5180357.

[0011] Patent document 3: Japanese Patent No. 4805994.

[0012] As described above, according to the above-mentioned Patent Document 1, the mold clamping force is set to be gradually reduced for molding. The mold clamping force is detected from the tie bar sensor each time molding is performed. The method shown in Patent Document 2 includes, for example, detecting the mold clamping force from the tie bar sensor when measuring the maximum increase in the mold clamping force in the interval generated by the release of the mold strain. Furthermore, the method shown in Patent Document 3 includes detecting the relative position of the fixed platen and the movable platen by means of a mold position sensor installed on the fixed platen and the movable platen.

[0013] However, as the clamping force is gradually reduced and each injection is performed, the injection pressure of the molten resin eventually exceeds the clamping force. The fixed mold and the movable mold are pushed apart and a gap is created at the clamping line (between the contact surfaces of the fixed mold and the movable mold), and the cavity size (filling space size) increases. If the injection unit injects the molten resin into the mold with the increased cavity size, the injection peak pressure drops.

[0014] Furthermore, since the enlarged cavity is filled with more molten resin than the set filling amount, a phenomenon occurs in which the injection front position of the screw of the injection unit moves forward (toward the mold clamping unit) from a predetermined position.

[0015] As described above, if the set clamping force is reduced in stages and injection filling is performed on the mold, abnormalities may occur in the injection peak pressure and the injection front position of the screw may change from a predetermined position to the front. Under such conditions, flash is likely to be generated on the molded product. Considering that the aforementioned set clamping force is adjusted to an appropriate clamping force to prevent flash, it is also effective to detect whether the injection peak pressure and the injection front position are normal during the process of gradually reducing the set clamping force. These considerations are not disclosed or taught in any way in Patent Documents 1 to 3. Summary of the invention

[0016] The object of the present invention is to adjust the clamping force on the mold based on the mold displacement of the mold detected by a mold gap detection sensor or the injection peak pressure and injection front position of an injection unit when the mold is clamped and molding is performed in an injection molding machine, so that molding can be performed without generating flash and with an appropriate clamping force that can reduce the energy required for clamping.

[0017] (Invention according to claim 1)

[0018] The present invention provides an injection molding machine to achieve the above-mentioned purpose. The injection molding machine comprises a clamping unit and an injection unit. The clamping unit is movably mounted on a movable plate along a tie rod spanning a fixed plate and a pressure plate. The mold consisting of a movable mold mounted on the movable plate and a fixed mold mounted on the fixed plate is closed by extending a toggle mechanism located between the pressure plate and the movable plate. A clamping force is applied to clamp the mold, and the injection unit injects molten resin into the clamped mold. The injection molding machine can automatically operate in a repeated molding cycle. The machine is characterized in that the machine comprises a control unit, the control unit comprises a mold gap detection sensor, an injection pressure sensor and a screw position sensor. The mold gap detection sensor detects the mold displacement of the mold whose gap between the abutting surfaces of the movable mold and the fixed mold changes as the length of the tie rod changes during injection filling. The injection pressure sensor detects the injection peak pressure, the screw position sensor detects the injection front position of the screw of the injection unit, and the mold gap detection sensor, injection pressure sensor, and screw position sensor are connected respectively, and the allowable amount without flash is set as the threshold of the mold displacement amount of the mold, and the allowable amount without flash is set as the threshold of the injection peak pressure and the injection front position. The control unit continues the automatic operation of the repeated molding cycle in the case of a mold displacement change in which the mold displacement amount exceeds the threshold when injection filling does not occur, or in the case of an injection peak pressure abnormality and an injection front position abnormality in which the injection peak pressure and the injection front position exceed the threshold when injection filling does not occur, and stops the operation of the injection molding machine in the case of the aforementioned mold displacement change, or the aforementioned injection peak pressure abnormality and the injection front position abnormality.

[0019] (Invention of Technical Solution 2)

[0020] In the above invention, it is preferred that the mold gap detection sensor is installed on either one of the end of the tie rod protruding toward the back of the pressure plate and the stationary portion on the machine side, and a sensing plate is installed on the other side opposite to the mold gap detection sensor via a gap, the mold gap detection sensor and the sensing plate are arranged in a relative positional relationship in a separation direction when the tie rod is extended, and the mold gap detection sensor detects a change in the distance between the sensing plates.

[0021] (Invention of Technical Solution 3)

[0022] In the above invention, it is preferred that the control unit performs automatic adjustment control of the mold clamping force, and the automatic adjustment control of the mold clamping force reduces the mold clamping force by a preset reduction amount before entering the next molding cycle when the molding cycle without the above-mentioned mold displacement change, or the above-mentioned injection peak pressure abnormality and the injection front position abnormality occurs for a preset number of times continuously, and increases the mold clamping force by a preset increase amount before entering the next molding cycle when the mold displacement change, or the injection peak pressure abnormality and the injection front position abnormality occur.

[0023] (Invention according to claim 4)

[0024] Furthermore, in the above invention, it is preferred that the above control unit stops the operation of the injection molding machine in the next molding cycle after the clamping force is increased by the above increase amount if the above mold displacement changes, or the above injection peak pressure anomaly and injection front position anomaly occur.

[0025] (Invention according to claim 5)

[0026] Furthermore, in the above invention, it is preferable to provide a display for displaying the detection value of the above die gap detection sensor in the form of a waveform.

[0027] (Invention according to claim 6)

[0028] Furthermore, in the above invention, it is preferable that the control unit stops the operation of the injection molding machine when the mold displacement amount reaches a preset maximum mold displacement amount.

[0029] (Invention of Technical Solution 7)

[0030] In addition, another invention provides a flash prevention method to achieve the above-mentioned purpose. The aforementioned flash prevention method is a flash prevention method for an injection molding machine that closes the mold with the help of a mold clamping unit, applies a mold clamping force to close the mold, and injects molten resin into the aforementioned mold with the help of an injection unit. The method is characterized in that an allowable amount without flash is set in advance as a threshold value of the mold displacement amount of the mold, and an allowable amount without flash is set in advance as a threshold value of the injection peak pressure and the injection front position. During the automatic operation of repeated molding cycles, the aforementioned mold displacement amount is monitored, and the aforementioned injection peak pressure and the injection front position are monitored. When the aforementioned mold displacement changes, or the aforementioned injection peak pressure abnormalities and injection front position abnormalities occur, the operation of the injection molding machine is stopped.

[0031] (Invention of Technical Solution 8)

[0032] In the above invention, it is preferred that the above injection molding machine has an automatic mold clamping force adjustment process, and the automatic mold clamping force adjustment process is that, when the molding cycles in which the above mold displacement change does not occur, or the above injection peak pressure abnormality and injection front position abnormality do not occur are continuous for a predetermined number of times, the mold clamping force is reduced by a predetermined reduction amount before entering the next molding cycle, and when the mold displacement change occurs, or the injection peak pressure abnormality and injection front position abnormality occur, the mold clamping force is increased by a predetermined increase amount before entering the next molding cycle.

[0033] (Invention of Technical Solution 9)

[0034] Furthermore, in the above invention, it is preferred that, in the next molding cycle after the mold clamping force is increased by the above-mentioned increasing amount in the above-mentioned mold clamping force automatic adjustment process, if the above-mentioned mold displacement change occurs, or the above-mentioned injection peak pressure anomaly and injection front position anomaly occur, the operation of the injection molding machine is stopped.

[0035] Effects of the Invention

[0036] According to the present invention, it is possible to manufacture good molded products without flash generation without applying a clamping force or injection pressure greater than necessary to the mold, and less load is applied to the injection molding machine and the mold, which can extend the life of the injection molding machine and the mold and also help save energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is an explanatory diagram showing an example of the injection molding machine of the present invention.

[0038] Figure 2 This is an explanatory diagram showing an example of an injection molding machine in a state where a mold clamping unit cover is removed.

[0039] Figure 3 This is an explanatory diagram showing an example of a mounting state of a die gap detection sensor.

[0040] FIG. 4( a ) is a flowchart showing a control flow of automatic operation of the injection molding machine.

[0041] FIG. 4( b ) is a flow chart showing the flow of automatic adjustment of the mold clamping force of the injection molding machine. DETAILED DESCRIPTION

[0042] based on Figure 1 The present invention will be described in detail with reference to the embodiment shown in FIG. 4 . Figure 1 and Figure 2 The present invention shows an injection molding machine 1 as an embodiment of the present invention, which includes a toggle-type mold clamping unit 2 and an injection unit 3. The molding cycle includes mold closing, mold clamping, injection filling of molten resin, metering, mold opening, and molded product removal. The injection molding machine 1 can perform automatic operation to repeat the molding cycle to manufacture molded products.

[0043] (Clamping unit)

[0044] The toggle-type clamping unit 2 has a fixed plate 5, a pressure plate 6, a tie rod 7, and a movable plate 8. The fixed plate 5 is fixed on the machine table 4. The pressure plate 6 is movably arranged on the machine table 4. The tie rod 7 spans the fixed plate 5 and the pressure plate 6. The tie rods 7 are fixed to the fixed plate 5 at one end. The other end of the tie rod 7 passes through and is connected to the pressure plate 6 in a position-adjustable manner. The movable plate 8 is installed movably along the tie rod 7. A toggle mechanism 9 is installed between the pressure plate 6 and the movable plate 8. The movable plate 8 moves along the length direction of the tie rod 7 by the extension and retraction of the toggle mechanism 9.

[0045] (Injection unit)

[0046] The injection unit 3 is a device for injecting and filling the molten resin into the mold 12. The mold 12 is composed of a fixed mold 10 provided on the fixed platen 5 and a movable mold 11 provided on the movable platen 8. The injection nozzle 14 at the end of the heating cylinder 13 surrounded by the heater and heated abuts against the mold 12.

[0047] (Toggle mechanism)

[0048] The toggle mechanism 9 has a drive shaft 16, a crosshead 17, an toggle rod 18, an toggle rod 19, and an toggle arm 20. The drive shaft 16 is driven by the mold clamping motor 15 to rotate axially. The crosshead 17 is threadedly engaged with the drive shaft 16. The toggle rod 18 is pivotally supported by the crosshead 17. The toggle rod 19 is pivotally supported by the pressure plate 6. The toggle arm 20 is pivotally supported by the movable plate 8. The toggle rods 18 and 19, and the toggle rod 19 and the toggle arm 20 are connected to each other by a connecting rod. The axial rotation of the drive shaft 16 moves the crosshead 17 forward and backward to move the movable plate 8, thereby closing and opening the mold 12. This action also applies a clamping force to the mold 12.

[0049] (Pressure plate)

[0050] The tie rod 7 passes through the pressure plate 6, so the end of the tie rod 7 is located on the back side of the pressure plate 6 (the side opposite to the movable plate) in a protruding manner. A threaded portion 7a is formed at the protruding end of each tie rod 7. A nut member 21 threadedly engaged with the threaded portion 7a is rotatably mounted on the pressure plate 6. In this way, the pressure plate 6 is connected to the tie rod 7 via the nut member 21 threadedly engaged with the threaded portion of the end of the tie rod 7. As described later, by rotating the nut member 21, the position of the pressure plate 6 can be adjusted relative to the tie rod 7.

[0051] The nut member 21 rotates synchronously via a drive transmission mechanism 22 located on the back of the pressure plate 6. The mold clamping unit 2 also includes a mold thickness motor 23 as a drive source for adjusting the mold clamping position. The driving force from the mold thickness motor 23 is transmitted to the nut member 21 as a rotational force via the aforementioned drive transmission mechanism 22. The nut member 21 rotates, thereby the pressure plate 6 moves along the length direction of the tie rod 7, and then the toggle mechanism 9 and the movable plate 8 also move integrally. In order to generate the desired clamping force, the mold thickness motor 23 is operated to position the pressure plate 6, and the toggle mechanism 9 is extended in the state where the pressure plate 6 is positioned to generate the set clamping force (desired clamping force).

[0052] (Mold position sensor, mold thickness sensor)

[0053] The mold position sensor 24 is installed from the fixed platen 5 to the movable platen 8. Figure 2 As shown, the mold position sensor 24 includes a sensor body 24a, a rod 24b, and a detection member 24c. The sensor body 24a is fixed to the upper part of the fixed disk 5. The rod 24b extends from the sensor body 24a to the upper part of the movable disk 8. The rod 24 can movably pass through the detection member 24c fixed to the upper part of the movable disk 8, thereby measuring the position of the rod 24b passing through the detection member 24c. The mold position sensor 24 is installed throughout the fixed disk 5 and the movable disk 8 to measure the distance between the fixed disk 5 and the movable disk 8 linearly (linear displacement measurement). The control unit described later controls the operation of the mold clamping motor 15 based on the detection value detected by the aforementioned mold position sensor 24, thereby setting the position of the movable mold 11 when the mold is opened and closed.

[0054] A mold thickness sensor 25 is attached to the rotating shaft of the mold thickness motor 23. A control unit described later controls the operation of the mold thickness motor 23 based on a detection value detected by the mold thickness sensor 25 to set the mold clamping force.

[0055] (Mold gap detection sensor)

[0056] Furthermore, the injection molding machine 1 according to the present embodiment includes a mold gap detection sensor 26 on the back side of the pressure plate 6. Figure 3 As shown, the end of the lower tie rod 7 of the tie rod 7 protrudes to the back side of the pressure plate 6. The sensor support 28 is mounted on the end surface 27 of the end of the tie rod 7 and hangs down, and the mold gap detection sensor 26 is mounted on the lower part of the sensor support 28.

[0057] The mold gap detection sensor 26 is located at a position corresponding to the sensing plate 29 that is fixed to the stationary part of the machine table 4. The mold gap detection sensor 26 is opposite to the sensing plate 29 in the length direction of the tie bar 7, and directly detects the distance displacement between the mold gap detection sensor 26 and the sensing plate 29. The mold gap detection sensor 26 is arranged on the side opposite to the fixed plate 5 side of the sensing plate 29 in the following positional relationship: when the tie bar 7 is extended, the gap 30 between the mold gap detection sensor 26 and the sensing plate 29 becomes larger. As described later, when the mold 12 generates mold displacement (change in the gap between the contact surfaces of the fixed mold 10 and the movable mold 11 that contact each other) during injection filling, the tie bar 7 is extended. The extension and contraction of the tie bar 7 including the extension of the tie bar 7 corresponds to the distance displacement. Therefore, the mold gap detection sensor 26 is a sensor that detects mold displacement. In addition, even if the tie bar 7 is maximally contracted, the gap 30 is ensured between the mold gap detection sensor 26 and the sensing plate 29 so that the mold gap detection sensor 26 does not contact the sensing plate 29.

[0058] The mold gap detection sensor 26 directly detects the distance displacement between the sensing plate 29 fixed to the stationary part of the machine table 4. Now, it is assumed that the clamping force set for mold clamping in the injection molding machine 1 is applied to the mold 12, and then the injection filling pressure of the molten resin exceeds the clamping force. In this case, the movable mold 11 and the movable plate 8 are pushed in the direction of opening the mold 12. This force acts as a force in the direction of pushing the pressure plate 6 including the toggle mechanism 9 backward, and finally becomes a force in the direction of extending the tie rod 7 connected to the pressure plate 6 via the nut member 21.

[0059] If the length of the tie bar 7 changes due to the above-mentioned force in the direction of extending the tie bar 7, it is detected as a change in the distance from the mold gap detection sensor 26 to the sensing plate 29. If the above-mentioned mold displacement occurs due to the injection filling pressure after the mold 12 is molded, the mold displacement amount corresponds to the distance to the sensing plate 29 detected by the mold gap detection sensor 26. The mold gap detection sensor 26 is positioned to detect this change in the mold displacement amount.

[0060] In the illustrated embodiment, the sensing plate 29 is mounted on the machine table 4 and the die gap detection sensor 26 is mounted on the end of the tie rod 7. However, the positional relationship between the die gap detection sensor 26 and the sensing plate 29 in the present invention is not limited to this configuration. The configuration may also be reversed. Specifically, the die gap detection sensor 26 may be mounted on the stationary portion of the machine table 4, and the sensing plate 29 may be mounted on the end of the tie rod 7 below, so that the end-mounted sensing plate 29 is opposite to the die gap detection sensor 26.

[0061] The mold gap detection sensor 26 is not limited to being used opposite to the sensing plate 29. As described above, it is assumed that the injection filling pressure of the molten resin exceeds the mold clamping force, and the length of the tie bar 7 changes due to the force in the direction of stretching the tie bar 7. In this case, strain is generated in the tie bar 7 itself. The change in strain corresponds to the expansion and contraction of the tie bar 7. By detecting the strain of the tie bar 7, the mold displacement of the mold 12 corresponding to the expansion and contraction of the tie bar 7 can be detected.

[0062] Therefore, as another example of the above-mentioned embodiment, the mold gap detection sensor 26 configured to detect the mold displacement of the mold 12 based on the strain of the tie bar 7 is located at a portion of at least one of the tie bars 7 that generates strain during injection filling. For example, a sensor that detects the strain of the tie bar 7 can be mounted using a mounting member at a position where the portion of the tie bar 7 located between the fixed platen 5 and the movable platen 8 does not collide with other components such as the movable platen 8, or a position where the portion of the tie bar 7 located between the pressure platen 6 and the movable platen 8 does not collide with other components such as the movable platen 8 and the pressure platen 6, and the sensor can be used as the mold gap detection sensor 26. A sensor that directly detects the size of the gap between the abutting surfaces of the fixed mold 10 and the movable mold 11 that abut against each other during injection filling can also be used as the mold gap detection sensor 26.

[0063] (Injection pressure sensor)

[0064] The injection unit 3 includes an injection pressure sensor 31 and a screw position sensor 32. The injection pressure sensor 31 detects the injection peak pressure during injection filling when the molten resin is injected into the mold 12. During the injection filling, the screw located at the heating cylinder 13 moves forward. The screw position sensor 32 detects the injection front position of the screw during the injection filling.

[0065] (Control Unit)

[0066] The injection molding machine 1 includes a control unit 33. The control unit 33 has a function of controlling the operation of the injection molding machine 1. The control unit 33 is connected to the mold clamping motor 15, the mold thickness motor 23, the mold position sensor 24, the mold thickness sensor 25, the mold gap detection sensor 26, the injection pressure sensor 31, and the screw position sensor 32.

[0067] During injection molding, the control unit 33 operates the mold clamping motor 15 based on the signal from the mold position sensor 24 to close and open the mold 12. In addition, the control unit 33 is configured to operate the mold thickness motor 23 based on the signal from the mold thickness sensor 25 to apply the set mold clamping force to the mold 12 to close the mold.

[0068] When the molten resin is injected into the mold 12 for molding, the injection molding machine 1 can implement the following flash prevention method based on the signals (detection values) obtained from the mold gap detection sensor 26, the injection pressure sensor 31 and the screw position sensor 32. The purpose is to avoid excessive mold clamping force and prevent the mold line of the mold 12 from opening too much to generate flash on the molded product.

[0069] (Flash prevention method)

[0070] As described above, when the injection filling pressure exceeds the clamping force applied to the mold during molding by a conventional injection molding machine, mold displacement occurs and a gap is generated in the mold surface line. This makes it easy to generate flash on the molded product. Therefore, the present injection molding machine 1 implements a method for preventing the molding cycle that generates flash from being repeated during automatic operation, and also implements a method for preventing excessive clamping force and adjusting the clamping force so that the mold's mold surface line does not open too much.

[0071] (Modular displacement)

[0072] First, during injection filling, the control unit 33 of the injection molding machine 1 has a preset threshold value for the mold displacement amount of the mold 12. The threshold value of the mold displacement amount is the maximum allowable value (allowable threshold value) of the mold displacement amount within the range where flash is not generated during molding. The threshold value of the mold displacement amount can be determined by the user of the injection molding machine 1 based on experience.

[0073] The mold displacement amount during injection filling into the fully clamped mold 12 is detected by the mold gap detection sensor 26. The control unit 33 receives a signal (detection value) from the mold gap detection sensor 26, thereby the control unit 33 always monitors the mold displacement amount of the mold 12 during injection filling, and compares the detected mold displacement amount with a threshold value.

[0074] (Peak injection pressure)

[0075] The injection molding machine 1 has a preset injection filling pressure and a preset filling amount relative to the mold 12. When the molten resin is injected into the mold 12, the injection peak pressure is detected by the injection pressure sensor 31. If the injection filling pressure is greater than the set clamping force applied to the mold 12 and the mold displacement changes until the parting line opens, the cavity of the mold 12 (the space filled with the molten resin) becomes larger. This reduces the injection peak pressure.

[0076] The control unit 33 has a preset threshold value for the injection peak pressure during injection filling. The threshold value of the injection peak pressure is the maximum value (allowable amount) of the injection peak pressure that is allowed in the range where flash is not generated (flash non-generating range). The peak pressure value set as the threshold value of the injection peak pressure is determined by the user of the injection molding machine 1 based on experience.

[0077] As described above, the injection peak pressure is received by the control unit 33 as a detection value from the injection pressure sensor 31. The control unit 33 always monitors the injection peak pressure during injection filling and compares the detected injection peak pressure value with the aforementioned threshold value of the injection peak pressure.

[0078] (Injection front position)

[0079] Furthermore, when the injection molding machine 1 injects and fills the molten resin into the mold 12 at the predetermined injection filling pressure and the predetermined filling amount as described above, the injection frontmost position is detected by the screw position sensor 32 .

[0080] Assume that the injection filling pressure is greater than the set clamping force applied to the mold 12 and the mold displacement changes until the mold 12 opens at the parting line, thereby increasing the cavity size of the mold 12. In this case, since an excessive amount of molten resin is filled into the cavity, the injection front position of the screw moving in the heating cylinder 13 is located forward (on the mold side) compared to when the cavity has a normal field size.

[0081] Therefore, the control unit 33 has a threshold value preset relative to the injection front position during injection filling. The threshold value of the injection front position is the maximum value (allowable amount) that can be allowed for the injection front position in the range where flash is not generated (flash non-generating range). And, the value of the threshold value of the injection front position is determined by the user of the injection molding machine 1 based on experience.

[0082] (Automatic operation)

[0083] The molding cycle of the injection molding machine 1 sequentially performs mold closing, mold clamping, injection filling of molten resin, mold opening, and molded product removal as described above. When the control unit 33 is in automatic operation, the control unit 33 operates to repeat the aforementioned molding cycle so that the molded product is continuously molded. The control unit 33 further operates so that the molding cycle including automatic adjustment of the clamping force can be repeated during the automatic operation.

[0084] The flowchart of Fig. 4(a) includes a flow A of the operation of the control unit 33 for repeating the molding cycle during automatic operation. In the flowchart, "automatic operation start" serves as the starting point of the flow A of the operation.

[0085] (Step A1: Processing)

[0086] Assume that the automatic operation of the injection molding machine 1 is selected to start, and then the molding cycle starts. As the process of step A1, the control unit 33 performs mold closing and mold clamping based on the set mold clamping force, and after the mold clamping is completed, the injection filling by the injection unit 3 is started. In the flowchart, it is expressed as "mold clamping completed / injection started", but here the control unit 33 controls the process until the pressure maintenance is completed and the mold is ready to be opened.

[0087] (Step A2: Confirmation)

[0088] When the clamping unit 2 and the injection unit 3 in the above step A1 are operated, the detection values ​​detected by the mold gap detection sensor 26, the injection pressure sensor 31, and the screw position sensor 32 are received by the control unit 33. It should be understood that the control unit 33 also receives the detection values ​​and signals from other sensors, and processes these detection values ​​and signals as information when performing control, and the description thereof is omitted. In step A2 after step A1, the control unit 33 makes a determination. The determination in step A2 involves the mold displacement detected by (multiple) sensors, or the injection peak pressure and the injection front position.

[0089] In step A2, the control unit 33 compares the mold displacement detected by the mold gap detection sensor 26 with the threshold of the mold displacement, and determines whether the detected mold displacement exceeds the aforementioned threshold. Optionally, the control unit 33 compares the injection peak pressure detected by the injection pressure sensor 31 with the threshold of the injection peak pressure, and compares the injection front position detected by the screw position sensor 32 with the threshold of the injection front position. The control unit 33 determines whether the detected injection peak pressure exceeds the threshold relative to the injection peak pressure, and determines whether the injection front position exceeds the threshold relative to the injection front position.

[0090] (Step A2Y: Determine content)

[0091] Step A2 is shown as branching according to whether it is determined to be yes or no. Step A2Y indicates the content determined to be yes. Specifically, the content determined is the content of "the detected mold displacement exceeds the mold displacement threshold and there is a mold displacement change that produces flash". Optionally, the content determined is "the detected injection peak pressure exceeds the injection peak pressure threshold and the detected injection front position also exceeds the injection front position threshold, and injection peak pressure anomalies and injection front position anomalies that produce flash occur".

[0092] (Step A2N: Determine content)

[0093] Step A2N indicates the content of the determination of No. The content of the determination of No is, "the detected mold displacement does not exceed the mold displacement threshold and there is no mold displacement change that generates flash". Optionally, the content of the determination is, "the detected injection peak pressure does not exceed the injection peak pressure threshold and the injection front position does not exceed the injection front position threshold, and there is no injection peak pressure abnormality or injection front position abnormality that generates flash".

[0094] (Step A3: Processing)

[0095] If the control flow passes through the above-mentioned determination step A2 and the determination step A2N, the control unit 33 proceeds to the stage of step A3 for performing the process of "mold opening". In step A3, the control unit 33 causes the mold clamping unit 2 to open the mold. Before the determination step A4 shown after the mold opening step A3, the control unit 33 performs processes such as taking out the molded product. In order to make the operation of the control unit 33 easy to understand, the description of this process is omitted.

[0096] (Step A4: Confirmation)

[0097] Step A4 is a step for determining the start of automatic adjustment of the mold clamping force. In step A4, the control unit 33 determines whether the automatic adjustment start switch of the mold clamping force is on (SW-ON). Whether the automatic adjustment start switch of the mold clamping force is on or off is always transmitted to the control unit 33.

[0098] If the clamping force automatic adjustment start switch is determined to be off (determination result is no), the control flow returns to the processing of the above-mentioned step A1 (mold clamping completion / injection start). That is, the control unit 33 enters the control of the next molding cycle. The control flow in the case where the clamping force automatic adjustment start switch is determined to be on (determination result is yes) will be described later.

[0099] (Step A5: Processing)

[0100] The control unit 33 performs processing for determining that a mold displacement change occurs during injection filling at step A5 after the above determination at step A2Y.

[0101] (Step A6: Processing)

[0102] The control unit 33 performs a process of determining that there is an influence on the molded product and that the good product determination is abnormal in step A6 after the above step A5.

[0103] (Forming machine stops)

[0104] After the control unit 33 has determined that there is an impact on the molded product and that the good product determination is abnormal in the above step A6, the operation of the injection molding machine is stopped. The moment when the operation of the injection molding machine is stopped is the end point of the process A of the "automatic operation start" action of the control unit 33. The control of the automatic operation ends here. If the control of "automatic adjustment of mold clamping force" is performed as described later and the control process passes through steps A1, A2 (A2Y), A5, and A6 as part of the control of "automatic adjustment of mold clamping force", the control of "automatic adjustment of mold clamping force" also ends here.

[0105] (Automatic clamping force adjustment)

[0106] If the answer in step A4 of the automatic operation control flow A is yes, the control unit 33 performs the control flow B for automatic adjustment of the mold clamping force shown in FIG. 4 (b). In the automatic adjustment of the mold clamping force, the mold clamping force is set to be gradually reduced, and the presence or absence of a change in the mold displacement of the mold 12, or an abnormal injection peak pressure and an abnormal injection front position are determined. If there is a change in the mold displacement, or an abnormal injection peak pressure and an abnormal injection front position are present, the mold clamping force is increased.

[0107] Fig. 4(b) shows the control flow B of the automatic clamping force adjustment. In the flow chart, "start automatic clamping force adjustment" is the starting point (start) of flow B. The control of the automatic clamping force adjustment has steps similar to a part of the control of the automatic operation described above.

[0108] (Step B1: Processing)

[0109] When the control of the automatic adjustment of the mold clamping force is started, the control flow proceeds to step B1. The processing of step B1 is the same as step A1 in the automatic operation.

[0110] (Step B2: Determination)

[0111] After the processing of step B1 is completed, the control unit 33 enters the determination step B2. The determination of step B2 is the same as the above step A2. The contents of steps B2Y and B2N correspond to the cases where the determination of step B2 is yes or no, and are also the same as steps A2Y and A2N, respectively.

[0112] (Step B3: Processing)

[0113] The process of step B3 after step B2N is the same as the process of step A3 described above. In addition, the control unit 33 performs processes such as taking out the molded product before the next step, and the description of this process is omitted to facilitate understanding of the operation of the control unit 33.

[0114] (Step B4: Determination)

[0115] Step B4 after the above step B3 is a step for determining whether the number of repetitions associated with the molding performed via the above step B3 should be used to count the number of moldings as the number of repetitions. The number of repetitions performed by repeated molding with the same set mold clamping force (same mold clamping pressure) can be set in advance as the set number in the control unit 33. If it is found that the number of repetitions associated with the molding of the stage via the above step B3 is inconsistent with the set number, it is determined that the number of moldings that should be further counted (addition is performed in addition control, and subtraction is performed in subtraction control) with the associated number of repetitions (determination result: Y). Then, as shown in the flowchart, the process returns to step B1. In this case, in the next molding cycle, the mold is clamped again under the same set mold clamping force.

[0116] On the other hand, if the number of repetitions associated with the molding at the stage through the above step B3 is consistent with the set number of times, it is determined that the associated number of repetitions should not be further used to count the number of moldings (determination result N). That is, the above determination N means that molding based on the same set mold clamping force is continuously performed for the set number of times, so that molding is performed in a state where the set mold clamping force is reduced in the next molding cycle.

[0117] (Step B5: Processing)

[0118] In step B5, the control unit 33 clears the number of repetitions of the forming.

[0119] (Step B6: Processing)

[0120] In the stage of step B6 after step B5, the control unit 33 performs processing to reduce the clamping force by a constant pressure amount and set the reduced clamping force as the set clamping force. After that, the control flow returns to the processing of step B1. In this case, in the next molding cycle, the mold 12 is clamped under the reduced set clamping force and injection filling is performed.

[0121] (Step B7: Processing)

[0122] Based on the determination result of step B2Y, the control unit 33 performs the process of "mold opening" as step B7. The process of this step B7 is the same as the above-mentioned step B3.

[0123] (Step B8: Processing)

[0124] After the processing of the above step B7 is completed, the control unit 33 performs the processing of "increasing the clamping force" in step B8. In this step B8, the control unit 33 increases the clamping force by a constant pressure amount and sets the increased clamping force as the set clamping force. After that, the control flow returns to the processing of the above step A1. In this case, in the next molding cycle, the mold 12 is clamped under the increased set clamping force and injection filling is performed.

[0125] In the above automatic adjustment of the mold clamping force, if there is no mold displacement change that causes flash, or no abnormality in the injection peak pressure and the injection front position, the next molding cycle is molded again with the set mold clamping force set in the current molding cycle. If there is no mold displacement change, or no abnormality in the injection peak pressure or the injection front position in the molding cycle of the set number of repetitions, the mold clamping force is reduced, and molding is performed at the set mold clamping force with the reduced mold clamping force.

[0126] In the automatic adjustment of the mold clamping force, if a mold displacement change occurs or an abnormality occurs in the injection peak pressure and the injection forward position during molding at the set mold clamping force with the mold clamping force reduced, the mold clamping force is increased and molding is performed at the increased set mold clamping force. If a mold displacement change occurs or an abnormality occurs in the injection peak pressure and the injection forward position during molding at the increased set mold clamping force, the control unit 33 stops the operation of the injection molding machine as described above.

[0127] As described above, in the automatic adjustment of the clamping force, the control unit 33 monitors the mold displacement that generates flash, or the injection peak pressure and the injection front position, and adjusts the clamping force. Thus, an appropriate clamping force is set with extremely high accuracy so that the mold 12 does not open too much during injection filling. This provides an injection molding machine 1 with a function of adjusting the clamping force relative to the injection filling pressure. Thus, good molded products can be continuously molded with energy saving at the set clamping force so that the mold 12 does not open too much, while suppressing the generation of flash.

[0128] The mold clamping force is set to decrease in the process of step B6 and increase in the process of step B8. The reduction amount and increase amount in step B6 and step B8 are set in advance by the user of the injection molding machine 1 in the control unit 33. The reduction amount and increase amount do not need to be the same.

[0129] (Display Controller)

[0130] like Figure 1 As shown in the figure, the injection molding machine 1 includes a touch panel type operation panel 34 capable of inputting various setting information, etc. As shown in the figure, in the operation panel 34, a display controller 35 for displaying the detection values ​​detected by the mold position sensor 24, the mold thickness sensor 25, and the mold gap detection sensor 26 in the form of waveform display or the like is installed in the control unit 33. The display controller 35 operates under the control of the control unit 33, and the detection values ​​detected by the above sensors are displayed in a set manner on the display 34a of the operation panel 34.

[0131] In this embodiment, under the control of the display controller 35, the mold displacement detected by the mold gap detection sensor 26 is always displayed in the form of a waveform, which has the advantage that the injection molding machine user can easily visually confirm the frequency of mold displacement changes exceeding the above threshold.

[0132] (Monitor and module displacement maximum values)

[0133] As described above, the user of the injection molding machine 1 sets the threshold value of the mold displacement in the control unit 33. However, due to a defect in the mold 12, a mold displacement change exceeding the threshold value of the mold displacement may occur during injection filling. In this case, the mold displacement change is confirmed and the mold clamping force is set to increase. Unless the defect in the mold 12 is resolved, the problem of increasing the set mold clamping force every time a molding cycle passes occurs.

[0134] In order to deal with the above problem, the maximum mold displacement amount is set as one of the monitoring items in the control unit 33 that obtains the detection value detected by the mold gap detection sensor 26. The control unit 33 includes a monitor 36 that receives the detection value detected by the mold gap detection sensor 26. The monitor 36 compares the mold displacement amount detected by the mold gap detection sensor 26 with the maximum mold displacement amount. If the mold displacement amount is the maximum mold displacement amount, the monitor 36 outputs to the control unit 33 to indicate this situation.

[0135] When the control unit 33 receives the output indicating that the mold displacement amount is the maximum value of the mold displacement amount, as shown in the stage of the above-mentioned step A5, a process is performed to determine that the condition of the mold displacement change during injection filling occurs. After the process of determining that the condition of the mold displacement change during injection filling occurs in step A5, the control unit 33 performs a process of determining that there is an impact on the molded product and that the good product determination is abnormal in step A6. Then, as described above, the control unit 33 stops the operation of the injection molding machine 1.

[0136] In this manner, through the operation of the monitor 36 receiving the detection value detected by the mold gap detection sensor 26 , the control unit 33 can stop the operation of the injection molding machine 1 before the mold 12 fails.

[0137] (Monitor and good product confirmation)

[0138] The monitor 36 incorporated in the control unit 33 is described as receiving the detection value detected by the mold gap detection sensor 26. However, the monitor 36 can receive detection values ​​and signals from various sensors provided in the injection molding machine 1, not just the mold gap detection sensor 26.

[0139] For example, the monitor 36 is configured to perform a good product determination with respect to the molded product based on a signal received from a predetermined sensor, and to send the determination of whether it is a good product as a signal to the control unit 33. If the monitor 36 determines that the molded product is determined to be defective, the control unit 33 receives the determination and performs processing to determine that the molded product is affected and there is an abnormality in the good product determination in step A6. Then, the control unit 33 stops the operation of the injection molding machine 1.

[0140] In this manner, through the operation of the above-mentioned monitor 36, the control unit 33 can stop the operation of the injection molding machine 1 before defective molded products are continuously produced.

[0141] Description of Reference Numerals

[0142] 1…Injection molding machine

[0143] 2…Clamping unit

[0144] 3…Injection unit

[0145] 4…Machine

[0146] 5…Fixed plate

[0147] 6…pressure plate

[0148] 7…Tie rod

[0149] 8…Movable plate

[0150] 10…Fixed mold

[0151] 11…Movable mold

[0152] 12…Mold

[0153] 15…Mold clamping motor

[0154] 23…Mold thickness motor

[0155] 24…Mold position sensor

[0156] 25…Mold thickness sensor

[0157] 26…Mold gap detection sensor

[0158] 28...Sensor support

[0159] 29…Sensor board

[0160] 30…Gap

[0161] 31…Injection pressure sensor

[0162] 32…Screw position sensor

[0163] 33…Control unit

[0164] 34…Operation panel

[0165] 35…Display controller

[0166] 36…Monitor

[0167] A…Control flow of automatic operation by the control unit

[0168] B…Control flow of automatic clamping force adjustment by the control unit.

Claims

1. An injection molding machine, comprising a clamping unit and an injection unit, wherein the clamping unit includes a movable platen, the movable platen being movably mounted along a tie rod, the tie rod spanning a fixed platen and a pressure platen, the injection unit being capable of closing a mold consisting of a movable mold mounted on the movable platen and a fixed mold mounted on the fixed platen through the clamping unit, and clamping the mold by applying a clamping force through the extension of a toggle mechanism between the pressure platen and the movable platen, and the injection unit injects and fills the clamped mold with molten resin, thereby being capable of performing automatic operation of repeating a molding cycle, The injection molding machine also has a mold gap detection sensor, an injection pressure sensor, a screw position sensor and a control unit. The mold gap detection sensor is configured to detect the mold displacement of the mold. The mold displacement refers to the change in the gap between the abutting surfaces of the movable mold and the fixed mold as the length of the tie rod changes during injection filling. The injection pressure sensor is configured to detect the injection peak pressure. The screw position sensor is configured to detect the injection front position of the screw of the injection unit. The control unit is configured to be connected to the mold gap detection sensor, the injection pressure sensor and the screw position sensor, and is characterized in that: The allowable amount without flash is set as the threshold of the mold displacement of the mold, and the allowable amount without flash is set as the threshold of the injection peak pressure and the injection front position. The control unit continues the automatic operation of the repeated molding cycle when the mold displacement amount exceeds the threshold value during injection filling, or when the injection peak pressure and the injection front position exceed the threshold value during injection filling, and the injection peak pressure and the injection front position are abnormal. In the event of the aforementioned mold displacement change, or the aforementioned injection peak pressure abnormality and injection front position abnormality, the operation of the injection molding machine is stopped. The mold gap detection sensor is installed on one of the end of the tie rod protruding to the back of the pressure plate and the stationary part on the machine side, and a sensing plate is installed on the other side to face the mold gap detection sensor via a gap. The mold gap detection sensor and the sensing plate are arranged in a relative positional relationship in a direction away from each other when the tie bar is extended, and the mold gap detection sensor detects a change in the distance between the mold gap detection sensor and the sensing plate.

2. The injection molding machine according to claim 1, characterized in that The aforementioned control unit performs control of automatic adjustment of the mold clamping force, and the control of automatic adjustment of the mold clamping force includes: When the molding cycle without the aforementioned mold displacement change, or the aforementioned injection peak pressure abnormality and injection front position abnormality occurs continuously for a preset number of times, the mold clamping force is reduced by a preset reduction amount and the next molding cycle is entered. When mold displacement changes, or injection peak pressure abnormalities and injection front position abnormalities occur, the mold clamping force is increased by a preset increase amount before entering the next molding cycle.

3. The injection molding machine according to claim 2, characterized in that The control unit stops the operation of the injection molding machine in the next molding cycle after the mold clamping force is increased by the previously set increase amount if the mold displacement change occurs or the injection peak pressure abnormality and the injection front position abnormality occur.

4. The injection molding machine according to any one of claims 1 to 3, characterized in that A display is provided which is configured to display the detection value of the die gap detection sensor in the form of a waveform.

5. The injection molding machine according to any one of claims 1 to 3, characterized in that The aforementioned control unit stops the operation of the injection molding machine when the mold displacement amount reaches a preset maximum mold displacement amount.

6. A flash prevention method, wherein the flash prevention method is a flash prevention method for an injection molding machine, wherein the mold is closed by a mold clamping unit, a mold clamping force is applied thereto to close the mold, and a molten resin is injected into the mold by an injection unit, wherein the method is characterized in that: include: A mold gap detection sensor is installed on one of the end of the tie rod protruding to the back of the pressure plate of the mold clamping unit and the fixed part on the machine side, and a sensing plate is installed on the other side to face the mold gap detection sensor via a gap. The mold gap detection sensor and the sensing plate are arranged in a relative positional relationship in a direction away from each other when the tie rod is extended, and the mold gap detection sensor detects mold displacement of the mold. The allowable amount without flash is set in advance as the threshold of the mold displacement, and the allowable amount without flash is set in advance as the threshold of the injection peak pressure and the injection front position. In the automatic operation of the repeated molding cycle, the mold displacement is monitored, and the injection peak pressure and the injection front position are monitored. When the aforementioned mold displacement change occurs, or the aforementioned injection peak pressure abnormality and injection front position abnormality occur, the operation of the injection molding machine is stopped.

7. The flash prevention method according to claim 6, characterized in that: With automatic adjustment steps for clamping force, The aforementioned automatic clamping force adjustment steps include: When the molding cycle without the aforementioned mold displacement change, or the aforementioned injection peak pressure abnormality and injection front position abnormality occurs continuously for a preset number of times, the mold clamping force is reduced by a preset reduction amount and the next molding cycle is entered. When mold displacement changes, or injection peak pressure abnormalities and injection front position abnormalities occur, the mold clamping force is increased by a preset increase amount and the next molding cycle is entered.

8. The flash prevention method according to claim 7, characterized in that: In the next molding cycle after the clamping force is increased by the previously set increase amount in the aforementioned automatic clamping force adjustment step, if the aforementioned mold displacement change occurs, or the aforementioned injection peak pressure abnormality and injection front position abnormality occur, the operation of the injection molding machine is stopped.

Images