Mold clamping device, injection molding machine, and mold clamping force adjustment method

Abstract

To provide a mold clamping force adjustment method where mold clamping force adjustment is suitably executed.SOLUTION: A mold clamping device (2) of a vertical injection molder (1) includes a fixed plate (9), an upper movable plate (10), and a lower movable plate (11), where the upper movable plate (10) and the lower movable plate (11) are coupled by a tie bar (12), and a toggle mechanism (13) is provided between the fixed plate (9) and the lower movable plate (11). A mold clamping force adjustment method includes: making mold thickness larger than thickness of dies (29, 30) by turning a tie bar nut (33) by a mold thickness adjustment motor (41); then driving a crosshead (15) to a die touch position; and performing a mold thickness reducing process of reducing the mold thickness by driving the mold thickness adjustment motor (41). A stop timing of the mold thickness adjustment motor (41) is determined by monitoring an electric current of the mold thickness adjustment motor (41).SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a mold clamping unit equipped with a toggle mechanism, an injection molding machine, and a method for adjusting the clamping force of a mold clamping unit equipped with a toggle mechanism. [Background technology]

[0002] In a vertical injection molding machine, the mold clamping device is configured as described in, for example, Patent Document 1. That is, the mold clamping device includes a fixed platen fixed to a frame, an upper movable platen provided above the fixed platen, and a lower movable platen provided below the fixed platen. The upper and lower movable platen are connected by a plurality of tie bars, and a mold clamping mechanism consisting of a toggle mechanism is provided between the lower movable platen and the fixed platen. In many vertical injection molding machines, a turntable is provided above the fixed platen, and the turntable can be freely inverted. Molds are provided on the upper movable platen and the turntable, respectively. When the mold clamping mechanism is driven, these molds are opened and closed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-205877 A

[0004] In a vertical injection molding machine, a number of tie bars and a lower movable platen are connected via tie bar nuts. That is, a tie bar nut is screwed onto each of the tie bars, and the tie bar nuts are stored in a recess formed in the lower movable platen. The tie bar nuts are provided with sprockets, and a chain is wound around these sprockets and rotated by a mold thickness adjustment motor. That is, when the mold thickness adjustment motor is driven, the tie bar nuts rotate, and the effective length of the tie bars changes. That is, the mold thickness, which is the distance between the upper movable platen and the fixed platen, changes.

[0005] The mold clamping force adjustment method performed in such a vertical injection molding machine is the same as the mold clamping force adjustment method in a horizontal injection molding machine. That is, first, the mold thickness adjustment motor is driven to make the mold thickness larger than the thickness of the mold provided in the mold clamping device, that is, the mold thickness. Next, the crosshead provided in the toggle mechanism is driven to make it a mold touch position. The mold touch position is a crosshead position where the molds provided on the upper movable platen and the fixed platen touch each other when the mold clamping force is appropriately adjusted, and is a crosshead position where the required mold clamping force is obtained when the crosshead is then driven to a mold clamping completion position. Finally, the mold thickness adjustment motor is driven in a direction to reduce the mold thickness. Then, when the molds come into contact with each other with a predetermined pressing force, the mold thickness adjustment motor is stopped. The mold clamping force adjustment is completed. Summary of the Invention [Problem to be solved by the invention]

[0006] In the mold clamping force adjustment method, when the mold thickness adjustment motor is driven in the direction of reducing the mold thickness to bring the molds into contact with each other, the mold thickness adjustment motor may be stopped before the required pressing force is generated, and the appropriate mold clamping force may not be obtained.

[0007] The present disclosure provides a mold clamping device, an injection molding machine, and a mold clamping force adjustment method that allow appropriate mold clamping force adjustment.

[0008] Other objects and novel features will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0009] The present disclosure relates to a clamping device including a first, second and third platen, a toggle mechanism and a control unit. The first and second platen are connected by a plurality of tie bars, the third platen is disposed between the first and second platen, and a toggle mechanism is provided between the second and third platen. Molds are provided on the first and third platen, and the molds are opened and closed by driving a crosshead of the toggle mechanism.

[0010] The mold clamping force adjustment performed by the control unit is as follows: First, the tie bar nuts screwed onto the multiple tie bars are rotated by the mold thickness adjustment motor to perform a mold thickness increase process in which the mold thickness, which is the distance between the first and third platens, is made larger than the mold thickness of the mold. With the first and second dies separated, A crosshead drive process is performed to drive the crosshead to the die touch position, which is the crosshead position where the die should touch. Finally, a die thickness reduction process is performed to drive the die thickness adjustment motor to reduce the die thickness so that the dies come into contact with each other. The control unit stops the die thickness adjustment motor during the die thickness reduction process, but in this disclosure, the timing is determined by the current value of the thickness adjustment motor. When it is detected that the current exceeds a preset value for a preset time . Effect of the Invention

[0011] The present disclosure can reliably obtain an appropriate clamping force. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a front view showing a vertical injection molding machine according to an embodiment of the present invention. [Figure 2A] FIG. 2 is a front cross-sectional view showing a part of a lower movable platen, a tie bar, and a tie bar nut that constitute the vertical injection molding machine according to the present embodiment. [Figure 2B] FIG. 2 is a front cross-sectional view showing a part of a lower movable platen, a tie bar, and a tie bar nut that constitute the vertical injection molding machine according to the present embodiment. [Diagram 3] 4 is a flowchart of a mold clamping force adjusting method according to the present embodiment. [Figure 4A] 11 is a graph showing a change in mold thickness and a change in current of a mold thickness adjustment motor when the mold clamping force adjusting method according to the present embodiment is carried out. [Figure 4B] 11 is a graph showing a change in mold thickness and a change in current of a mold thickness adjustment motor when a conventional mold clamping force adjustment method is performed. [Figure 5A] 1 is a graph showing a change in mold thickness when a conventional mold clamping force adjustment method is performed. [Figure 5B]1 is a graph showing a change in mold thickness when a conventional mold clamping force adjustment method is performed. [Figure 5C] 1 is a graph showing a change in mold thickness when a conventional mold clamping force adjustment method is performed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Specific embodiments will be described in detail below with reference to the drawings. However, the present invention is not limited to the following embodiments. In order to clarify the description, the following description and drawings are appropriately simplified. In each drawing, the same elements are given the same reference numerals, and duplicated descriptions are omitted as necessary. In addition, hatching is omitted in some parts to avoid cluttering the drawings.

[0014] The present embodiment will be described below. <Vertical injection molding machine> As shown in FIG. 1, the vertical injection molding machine 1 of this embodiment includes a clamping device 2, an injection device 3 provided on the upper part of the clamping device 2, and a controller, i.e., a control unit 4, which controls these devices.

[0015] <Mold clamping device> The mold clamping device 2 includes a first, second, and third mold platen. First, a third mold platen, i.e., a fixed platen 9, is fixed to the housing 7. A first mold platen, i.e., an upper movable platen 10, is provided above the fixed platen 9, and a second mold platen, i.e., a lower movable platen 11, is provided below the fixed platen 9. The upper movable platen 10 and the lower movable platen 11, which are the first and second mold platens, are connected by a plurality of tie bars 12, 12, .... In this embodiment, there are three tie bars 12, 12, .... The connection length, i.e., the effective length, of these tie bars 12, 12, ... can be adjusted by a mold clamping force adjustment mechanism 32, which will be described later.

[0016] Between the lower movable platen 11 and the fixed platen 9, a toggle mechanism 13 is provided as a mold clamping mechanism. The toggle mechanism 13 is provided with a crosshead 15 for driving the toggle mechanism 13, and the crosshead 15 is driven by a ball screw mechanism 16. A mold clamping motor 18 is provided on the side of the lower movable platen 11. A drive pulley 20 is provided on the mold clamping motor 18, and a driven pulley 21 is provided on the ball screw mechanism 16, which are wound around by a timing belt 22. Therefore, when the mold clamping motor 18 rotates, the crosshead is driven and the toggle mechanism 13 is bent and extended. That is, the upper movable platen 10 and the lower movable platen 11 are driven up and down integrally, and the mold clamping device 2 opens and closes the mold. In addition, a platen drop prevention mechanism 23 is provided between the upper movable platen 10 and the fixed platen 9 to protect the upper movable platen 10 from falling during a power outage or the like.

[0017] <Turntable> Although not an essential member in the mold clamping device 2 of the vertical injection molding machine 1, in this embodiment, a turntable 24 is provided on the fixed platen 9. The turntable 24 rotates in a reversible manner around a single tie bar 12 in the center. A turntable rotation motor 26 and a rotation transmission mechanism 27 that transmits the rotation of the turntable rotation motor 26 to the turntable 24 are provided on the underside of the fixed platen 9 inside the housing 7. Therefore, when the turntable rotation motor 26 is rotated, the turntable 24 rotates.

[0018] In this embodiment, one first mold 29 is provided on the upper movable platen 10, and two second molds 30, 30 are provided on the turntable 24. When the turntable 24 rotates in the opposite direction, these two second molds 30, 30 exchange positions with each other. If the mold clamping device 2 does not include the turntable 24, only one second mold 30 is provided on the fixed platen 9.

[0019] <Mold clamping force adjustment mechanism> The mold clamping force adjustment mechanism 32 will be described. The mold clamping force adjustment mechanism 32 is a mechanism that adjusts the mold thickness to obtain an appropriate mold clamping force. The mold thickness is the distance between the mold platens on which the first and second molds 29, 30 are provided when the toggle mechanism 13 is in the mold closing state. If the turntable 24 is provided, it is the distance between the upper movable platen 10 and the turntable 24, and if the turntable 24 is not present, it is the distance between the upper movable platen 10 and the fixed platen 9.

[0020] The mold clamping force adjustment mechanism 32 is composed of tie bar nuts 33, 33, ... provided on each of the tie bars 12, 12, ... and a rotation mechanism 34 that rotates these tie bar nuts 33, 33, .... FIG. 2A shows an enlarged view of a part of the mold clamping device 2 including one tie bar 12. As shown in this figure, a male thread 35 is formed in a predetermined range on the tie bar 12, and the tie bar nut 33 is screwed into the male thread 35. Such a tie bar nut 33 is inserted into a recess 37 formed in the lower movable platen 11 and is held down by an adjustment band 38. A gap 39 is formed between the upper surface of the flange 33a of the tie bar nut 33 and the lower movable platen 11, so that the tie bar nut 33 can rotate smoothly. The size of the gap 39 can be adjusted by appropriately inserting shims of different thicknesses between the adjustment band 38 and the lower movable platen 11.

[0021] 1, the rotation mechanism 34 of the mold clamping force adjustment mechanism 32 includes a mold thickness adjustment motor 41 provided on the lower movable platen 11. A drive pulley 42 is provided on the mold thickness adjustment motor 41, and driven pulleys 44, 44, ... are provided on the tie bar nuts 33, 33, ..., and a chain 45 is wound around these. Therefore, when the mold thickness adjustment motor 41 is rotated, the tie bar nuts 33, 33, ... rotate synchronously, and the effective length of the tie bars 12, 12, ... changes. In other words, the mold thickness can be adjusted.

[0022] <Mold thickness detection mechanism> 2A, a magnetostrictive linear displacement sensor 48 is provided on the lower movable platen 11. The lower end of one tie bar 12 and the magnetostrictive linear displacement sensor 48 are connected by a connecting metal fitting 49. The mold thickness is detected by this magnetostrictive linear displacement sensor 48. However, to be precise, what is detected by the magnetostrictive linear displacement sensor 48 is the position of the lower end of the tie bar 12 that moves relatively to the lower movable platen 11.

[0023] <Injection device> The injection unit 3 is provided on the upper movable platen 10 of the mold clamping unit 2. The injection unit 3 includes a heating cylinder 51, a screw (not shown) provided in the heating cylinder 51, and a drive mechanism (not shown) for driving the screw. An injection nozzle 52 is provided at the tip of the heating cylinder 51, and the injection nozzle 52 is in contact with the first mold 29.

[0024] <Control Unit> The control unit 4 controls each device of the vertical injection molding machine 1. That is, it controls the mold clamping unit 2 and the injection unit 3. Naturally, the control unit 4 also controls the mold clamping motor 18 and the mold thickness adjustment motor 41, and the mold clamping force adjustment method according to the present embodiment described below is automatically performed by the control unit 4. The control unit 4 is provided with various setting values ​​necessary for controlling each device, and two setting values ​​are stored in order to perform the mold clamping force adjustment method. That is, as shown in FIG. 1, a default current value and a default time are preset in the control unit 4.

[0025] <Mold clamping force adjustment method> A mold clamping force adjustment method according to this embodiment will be described. The mold clamping force adjustment method is performed every time the molds 29, 30, 30 attached to the mold clamping device 2 are replaced. The description will start from a state in which the first mold 29 is attached to the upper movable platen 10 and the second molds 30, 30 are attached to the turntable 24 as shown in FIG.

[0026] As shown in FIG. 3, the control unit 4 first executes the mold thickness increasing process S1. The mold thickness increasing process S1 is a process for increasing the mold thickness or enlarging the mold thickness by driving the mold thickness adjustment motor 41 (see FIG. 1). The mold thickness is made larger than the total mold thickness of the first mold 29 and the second mold 30. At this time, the first mold 29 and the second mold 30 are not in contact with each other, so that the weight of the upper movable platen 10 (see FIG. 1) and the like acts on the tie bars 12, 12, ... and presses them downward, as shown by reference numeral 61 in FIG. 2A. On the other hand, the lower movable platen 11 is connected to the fixed platen 9 so as to hang down via the toggle mechanism 13 (see FIG. 1), so that it is lifted upward, as shown by reference numeral 62 in FIG. 2A. Therefore, the tie bar nuts 33, 33, ... are pressed against the adjustment belt 38, as shown in FIG. 2A, and a gap 39 is formed between the upper surface of the flange 33a and the lower movable platen 11.

[0027] When the mold thickness increasing process S1 is performed, the mold thickness adjusting motor 41 (see FIG. 1) is driven with a predetermined torque, so that a predetermined current value flows almost constantly to the mold thickness adjusting motor 41 as shown by reference numeral 71 in FIG. 4A. Then, the mold thickness detected by the magnetostrictive linear displacement sensor 48 (see FIG. 2A) increases gradually as shown by reference numeral 72 in FIG. 4A. When the mold thickness reaches a predetermined size, the mold thickness increasing process S1 is completed.

[0028] Next, the control unit 4 (see FIG. 1) executes the crosshead drive process S2 (see FIG. 3). That is, the mold clamping motor 18 is rotated to drive the crosshead 15 so that the crosshead position becomes the mold touch position. The mold touch position is a crosshead position where the first mold 29 and the second mold 30 touch with a predetermined pressing force when the mold clamping force adjustment is appropriately performed, and when the crosshead 15 is then driven to the mold clamping completion position, the required mold clamping force is obtained. However, in this crosshead drive process S2, the mold clamping force adjustment is not completed, so the first mold 29 and the second mold 30 are in a separated state.

[0029] Even if the crosshead 15 is driven to the die touch position, the first die 29 and the second die 30 are separated, so that the lower surfaces of the flanges 33a of the tie bar nuts 33, 33, ... are pressed against the adjustment band 38, as shown in Fig. 2A. In the crosshead drive process S2, the die thickness adjustment motor 41 (see Fig. 1) is not driven, so that the current flowing through the die thickness adjustment motor 41 is zero, as shown by reference numeral 73 in Fig. 4A, and the die thickness remains constant and does not change, as shown by reference numeral 74.

[0030] The control unit 4 starts the mold thickness reduction process (S3) as shown in Fig. 3. That is, the mold thickness adjustment motor 41 (see Fig. 1) is driven in the direction in which the mold thickness is reduced. When the mold thickness is reduced, since there is no need to lift the upper movable platen 10, etc., the torque required for the mold thickness adjustment motor 41 is relatively small. That is, the current supplied to the mold thickness adjustment motor 41 is smaller than that when the mold thickness is increased. As shown by reference numeral 75 in Fig. 4A, the current flowing through the mold thickness adjustment motor 41 becomes smaller than the current value shown by reference numeral 71. The mold thickness detected by the magnetostrictive linear displacement sensor 48 (see Fig. 2A) gradually decreases as shown by reference numeral 76.

[0031] After starting the mold thickness reduction process (S3), the control unit 4 monitors the current of the mold thickness adjustment motor 41 by process S4 shown in Fig. 3, but this process S4 and subsequent processes S5 and S6 will be explained later. Here, we will explain in detail the behavior that occurs in the mold clamping device 2 when the mold thickness reduction process is being performed, and temporarily suspend the explanation of the mold clamping force adjusting method according to this embodiment.

[0032] The behavior of the mold clamping device 2 in the mold thickness reduction process progresses as follows. When the mold thickness is reduced, the first mold 29 and the second mold 30 are separated at first, so the tie bars 12, 12, ... slowly descend together with the upper movable platen 10 (see FIG. 1). At this time, the flanges 33a of the tie bar nuts 33, 33, ... are maintained in a state in which their lower surfaces are pressed against the adjustment belt 38 as shown in FIG. 2A. However, the first mold 29 (see FIG. 1) and the second mold 30 eventually come into contact with each other. The timing of the contact is indicated by reference numeral 77 in FIG. 4A. When the contact occurs, the upper movable platen 10 (see FIG. 1) is supported by the fixed platen 9 via the first mold 29, the second mold 30, and the turntable 24. In other words, the descent is restricted. Since the tie bars 12 are connected to the upper movable platen 10, the descent of the tie bars 12 is also restricted.

[0033] In this state, when the mold thickness adjustment motor 41 continues to be driven to rotate the tie bar nuts 33, 33, ... (see FIG. 2A), the tie bar nuts 33 rise along the male threads 35 of the tie bar 12. That is, the tie bar nuts 33 move relatively upward within the recessed portion 37. At this time, the mold thickness detected by the magnetostrictive linear displacement sensor 48 (see FIG. 2A) remains constant as shown by the reference numeral 78 in FIG. 4A. This is because the lower end of the tie bar 12 does not move relatively to the lower movable platen 11.

[0034] Eventually, the tie bar nuts 33 come into contact with the upper surface of the recesses 37, as shown in Figure 2B. That is, a gap 39' is formed between the tie bar nuts 33 and the adjustment band 38. This timing is shown by reference numeral 79 in Figure 4A.

[0035] When the die thickness adjustment motor 41 (see FIG. 1) is subsequently driven to rotate the tie bar nuts 33, 33, ..., the pressing force of the contact between the first die 29 and the second die 30 increases, and the tie bar 12 is suspended by the upper movable platen 10 and an upward force acts on the tie bar 12. That is, an upward force indicated by reference numeral 63 in FIG. 2B acts on the tie bar 12. On the other hand, the lower movable platen 11 receives a force from the fixed platen 9 via the toggle mechanism 13 (see FIG. 1), and therefore a force indicated by reference numeral 64 in FIG. 2B acts on the tie bar 12. As these forces act, the torque required to rotate the tie bar nut 33 increases. Therefore, as indicated by reference numeral 80 in FIG. 4A, the current of the die thickness adjustment motor 41 (see FIG. 1) increases. The die thickness detected by the magnetostrictive linear displacement sensor 48 (see FIG. 2A) decreases slightly as indicated by reference numeral 81 in FIG. 4A. This is because the lower end of the tie bar 12 moves slightly downward relative to the lower movable platen 11.

[0036] Since the current of the mold thickness adjustment motor 41 is controlled so as to obtain a predetermined torque, the rotation of the tie bar nuts 33, 33, ... stops when the pressing force of the contact between the first mold 29 and the second mold 30 becomes a predetermined magnitude. This timing is shown by reference numeral 82 in FIG. 4A. The current of the mold thickness adjustment motor 41 remains constant thereafter as shown by reference numeral 83. Since the first mold 29 and the second mold 30 are in contact with each other with a desired pressing force, the mold thickness adjustment motor 41 may be stopped at an appropriate timing. The behavior of the mold clamping device 2 during the mold thickness reduction process is as described above. Returning to FIG. 3, the description of the process S4 and subsequent steps in the mold clamping force adjustment method according to this embodiment will be resumed.

[0037] In the mold clamping force adjusting method according to this embodiment, once the mold thickness reduction process is started (S3), the control unit 4 periodically monitors the current of the mold thickness adjustment motor 41. Monitoring the current value is essentially equivalent to monitoring the torque of the mold thickness adjustment motor 41. In step S4 in Fig. 3, it is checked whether this current value exceeds a preset current value set in the control unit 4 (see Fig. 1). If it does not exceed the preset current value, the mold thickness reduction process is continued. Then, step S4 is executed again in the next cycle.

[0038] If it is determined in step S4 that the current value of the mold thickness adjustment motor 41 exceeds the preset current value, the control unit 4 executes step S5. That is, it checks whether the time elapsed since the preset current value was exceeded exceeds the preset time set in the control unit 4 (see FIG. 1). If it does not exceed the preset current value, the mold thickness reduction process is continued and the process returns to step S4. On the other hand, if it exceeds the preset time, the process proceeds to step S6. In the graph of FIG. 4A, as shown by reference numeral 83, it is shown that the current value exceeds the preset current value for a preset time 85. In step S6, the mold thickness adjustment motor 41 (see FIG. 1) is stopped. That is, the mold thickness reduction process is completed. The mold clamping force adjustment is completed. The timing at which the mold thickness adjustment motor 41 is stopped is shown by reference numeral 84 in FIG. 4A.

[0039] In the mold clamping force adjusting method according to the present embodiment, as described above, the current value of the mold thickness adjusting motor 41 is monitored during the mold thickness reduction process, and the mold thickness reduction process is completed when the current value exceeds a predetermined current value for a predetermined time. In this way, the mold clamping force can be reliably and appropriately obtained.

[0040] <Conventional method for adjusting mold clamping force> Here, a conventional mold clamping force adjustment method will be described. In the conventional mold clamping force adjustment method, as in the mold clamping force adjustment method according to the present embodiment, the mold thickness increasing process S1, the crosshead driving process S2, and the start of the mold thickness reducing process S3 shown in FIG. 3 are performed in the same manner. However, the determination of the completion of the mold thickness reducing process, that is, the determination of stopping the mold thickness adjustment motor 41, is different from that in the mold thickness adjustment method according to the present embodiment. Specifically, in the conventional mold clamping force adjustment method, the completion of the mold thickness reducing process is determined by checking whether or not there is a change in the mold thickness. The following will be described with reference to FIGS. 5A to 5C.

[0041] 5A to 5C show changes in mold thickness detected by magnetostrictive linear displacement sensor 48 when the mold thickness reduction process is being performed. Reference numeral 77 denotes the timing when first mold 29 (see FIG. 1) and second mold 30 come into contact with each other, reference numeral 79 denotes the timing when the upper surface of flange 33a of tie bar nut 33 (see FIG. 2B) comes into contact with lower movable platen 11, and reference numeral 82 denotes the timing when the contact between first mold 29 and second mold 30 reaches an appropriate pressing force.

[0042] In the conventional mold clamping force adjustment method, when the mold thickness detected by the magnetostrictive linear displacement sensor 48 (see FIG. 2A) is monitored, as shown in FIG. 5A, the monitoring is performed at a predetermined sampling period 88. The timings of monitoring at the sampling period 88 are indicated as t1, t2, .... When detected at each of the timings t1 to t4, the mold thickness has changed. However, when detected at the timings t4 and t5, the mold thickness has not changed. In the conventional mold clamping force adjustment method, when the change in the mold thickness is, for example, 0.05 mm or less, it is determined that the mold thickness has not changed, and the mold thickness adjustment motor 41 (see FIG. 1) is stopped. In other words, the mold clamping force adjustment is completed. The timing of stopping is indicated by reference numeral 89 in FIG. 5A.

[0043] In the example described in FIG. 5A, the conventional mold clamping force adjustment method can adjust the mold clamping force appropriately. However, if the timing of the sampling period 88 is shifted, the mold thickness adjustment motor 41 may be stopped before an appropriate pressing force is generated between the first mold 29 (see FIG. 1) and the second mold 30. FIG. 5B shows such an example. The mold thicknesses detected at the timings t1, t2, and t3 change. However, the mold thicknesses detected at the timings t3 and t4 do not change. In the conventional mold clamping force adjustment method, the mold thickness adjustment motor 41 (see FIG. 1) is stopped at the timing t4. In other words, an appropriate mold clamping force cannot be obtained.

[0044] In the conventional mold clamping force adjustment method, this problem occurs not only when there is a timing shift in the sampling period 88, but also when the gap 39 between the recess 37 of the lower movable platen 11 (see FIG. 2A) and the tie bar nut 33 is large. This is because when the gap 39 is large, the straight line section from reference numeral 77 to reference numeral 79 in the graph of FIG. 5B becomes long.

[0045] In the conventional mold clamping force adjustment method, if the sampling period 88' is lengthened as shown in Fig. 5C, the above problem does not occur. That is, if the sampling period 88' is long, the mold thickness detected at each timing t1, t2, ... t4 will definitely change. If it is detected that the mold thickness has not changed at timing t4 and timing t5 and the mold thickness adjustment motor 41 (see Fig. 1) is stopped, it is guaranteed that an appropriate pressing force is generated between the first mold 29 and the second mold 30.

[0046] However, lengthening the sampling period 88' gives rise to another problem. FIG. 4B shows the change in mold thickness and the change in current of the mold thickness adjusting motor 41 (see FIG. 1) when the sampling period 88' is lengthened and a conventional mold clamping force adjustment method is performed. When the sampling period is long, a high current value continues for a long time, as shown by reference symbol 83'. In other words, the time 90 during which a high current flows through the mold thickness adjusting motor 41 becomes long. In other words, there is a problem in that a load is placed on the mold thickness adjusting motor 41.

[0047] <Modification of this embodiment> This embodiment can be modified in various ways. In the mold clamping force adjusting method according to this embodiment, when determining the timing to stop the mold thickness adjusting motor 41 (see FIG. 1) in the mold thickness reducing process, the current is monitored and the condition is that the current exceeds a preset current value for a preset time. However, the mold thickness adjusting motor 41 may be stopped if the preset current value is exceeded even temporarily. Alternatively, the motor may be stopped if the average current value within the preset time exceeds the preset current value. In any case, the timing to stop the mold thickness adjusting motor 41 is determined based on the current value of the mold thickness adjusting motor 41.

[0048] The mold clamping force adjustment method according to the present embodiment has been described as being performed in a vertical injection molding machine. However, it can also be performed in a horizontal injection molding machine. In a horizontal injection molding machine, the tie bar nuts are also rotated to adjust the mold thickness. This is because the mold clamping force adjustment is performed by a mold thickness increasing process for increasing the mold thickness, a crosshead driving process for driving the crosshead to a mold touch position, and then a mold thickness decreasing process for decreasing the mold thickness. In addition, although four tie bars are generally provided in a horizontal injection molding machine, there is no restriction on the number of tie bars.

[0049] Although the invention made by the present inventor has been specifically described above based on the embodiment, it goes without saying that the present invention is not limited to the embodiment already described, and various modifications are possible without departing from the gist of the invention. The above-described examples may be implemented in appropriate combination. [Explanation of symbols]

[0050] 1 Vertical injection molding machine 2 Mold clamping device 3 Injection unit 4 Control unit 7 Chassis 9 Fixed board 10 Upper movable plate 11 Lower movable plate 12 Tie bar 13 Toggle mechanism 15 Crosshead 16 Ball screw mechanism 18 mold clamping motor 20 drive pulley 21 driven pulley 22 timing belt 23 Platen drop prevention mechanism 24 Turntable 26 Turntable rotation motor 27 Rotation transmission mechanism 29 First die 30 second mold 32 mold clamping force adjustment mechanism 33 Tie bar nut 34 Rotation mechanism 35 Male thread 37 Recess 38 Adjustment band 39 Gap 41 Die thickness adjustment motor 42 Drive pulley 44 Driven pulley 45 Chain 48 Magnetostrictive linear displacement sensor 49 Connecting metal fitting 51 heating cylinder 52 injection nozzle

Claims

1. a first platen on which a first mold is provided; A second die plate; a third platen disposed between the first and second platens and having a second die; a plurality of tie bars connecting the first platen and the second platen; a toggle mechanism provided between the second platen and the third platen, having a crosshead, and configured to open and close the mold by driving the crosshead; A control unit, When performing mold clamping force adjustment, the control unit performs a mold thickness increasing process in which a tie bar nut screwed to the plurality of tie bars is rotated by a mold thickness adjustment motor to make the mold thickness larger than the mold thicknesses of the first mold and the second mold; a crosshead driving process for driving the crosshead to a die touch position, which is a crosshead position where the die should touch, while the first and second dies are separated from each other; a die thickness reducing process for reducing the die thickness by driving the die thickness adjusting motor so that the first die and the second die come into contact with each other; A mold clamping device, wherein the timing at which the control unit stops the mold thickness adjustment motor during the mold thickness reduction process is when it detects that the current value of the mold thickness adjustment motor has exceeded a predetermined current value for a predetermined time.

2. 2. The clamping device according to claim 1, wherein the first platen comprises an upper movable platen, the second platen comprises a lower movable platen, and the third platen comprises a fixed platen, and the clamping device is a clamping device for a vertical injection molding machine.

3. A toggle type clamping device; an injection device for injecting an injection material; A control unit and an injection molding machine comprising: The toggle-type mold clamping device includes a first mold platen on which a first mold is provided, A second die plate; a third platen disposed between the first and second platens and having a second die; a plurality of tie bars connecting the first platen and the second platen; a toggle mechanism provided between the second platen and the third platen, having a crosshead, and configured to open and close the mold by driving the crosshead; When performing mold clamping force adjustment, the control unit performs a mold thickness increasing process in which a tie bar nut screwed to the plurality of tie bars is rotated by a mold thickness adjustment motor to make the mold thickness larger than the mold thicknesses of the first mold and the second mold; a crosshead driving process for driving the crosshead to a die touch position, which is a crosshead position where the die should touch, while the first and second dies are separated from each other; a die thickness reducing process for reducing the die thickness by driving the die thickness adjusting motor so that the first die and the second die come into contact with each other; An injection molding machine, wherein the timing at which the control unit stops the mold thickness adjustment motor during the mold thickness reduction process is when it detects that the current value of the mold thickness adjustment motor has exceeded a predetermined current value for a predetermined time.

4. 4. The injection molding machine according to claim 3, wherein said first platen is an upper movable platen, said second platen is a lower movable platen, and said third platen is a fixed platen, and said injection molding machine is a vertical injection molding machine.

5. a first platen on which a first mold is provided; A second die plate; a third platen disposed between the first and second platens and having a second die; a plurality of tie bars connecting the first platen and the second platen; a toggle mechanism provided between the second platen and the third platen, having a crosshead, and configured to open and close the mold by driving the crosshead; A control unit, The mold is opened and closed by driving the crosshead of the toggle mechanism. A mold clamping force adjusting method implemented in a toggle type mold clamping device, in which a mold thickness is adjusted by rotating tie bar nuts screwed onto the plurality of tie bars by a mold thickness adjustment motor, The mold clamping force adjusting method includes a mold thickness increasing process for increasing a mold thickness to be greater than the mold thicknesses of the first mold and the second mold by driving the mold thickness adjusting motor; a crosshead driving process for driving the crosshead to a die touch position, which is a crosshead position where the die should touch, while the first and second dies are separated from each other; a die thickness reducing process for reducing the die thickness by driving the die thickness adjusting motor so that the first die and the second die come into contact with each other, A mold clamping force adjusting method in which the timing at which the control unit stops the mold thickness adjustment motor during the mold thickness reduction process is when it detects that the current value of the mold thickness adjustment motor has exceeded a predetermined current value for a predetermined time.

6. 6. The mold clamping force adjusting method according to claim 5, wherein the first platen is an upper movable platen, the second platen is a lower movable platen, and the third platen is a fixed platen, and the method is performed in a vertical injection molding machine.

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