JP5956869B2 - Molding machine - Google Patents

Description

  The present invention relates to a molding machine such as a die casting machine.

  After injecting molten metal (molten metal material) into the cavity constituted by the mold, the pressure pin is protruded into the cavity to locally pressurize the molten metal in the cavity, thereby suppressing nest formation. Die casting machines are known. Here, if the timing for starting the movement of the pressurizing pin into the cavity (starting timing of local pressurization) is not appropriate, an appropriate squeeze effect cannot be obtained and the occurrence of nests cannot be suppressed. Therefore, various methods for determining the timing for moving the pressure pin into the cavity have been proposed.

  For example, Patent Document 1 discloses a method for determining the start timing of local pressurization based on the temperature of a molten metal. Further, for example, Patent Document 2 discloses a method for determining the start timing of local pressurization based on the solidified state of the molten metal at the gate. Further, for example, Patent Document 3 discloses a method for determining the start timing of local pressurization based on injection pressure and mold temperature.

Japanese Patent Laid-Open No. 04-94854 JP 07-47458 A Japanese Patent Laid-Open No. 2001-246452

  Each of the various methods described above has advantages and disadvantages. For example, when based on the temperature of the molten metal, a temperature sensor that can withstand the high temperature of the molten metal is required. Further, for example, in the case of being based on the solidified state of the molten metal, an exploration pin that is taken in and out of the gate is necessary. Further, for example, when based on the injection pressure, the injection pressure varies depending on the state of the gate and the like, and there is a possibility that the start timing of local pressurization cannot be set appropriately. Therefore, it is desirable to provide a die casting machine capable of appropriately determining the start timing of local pressurization by a new method and to diversify the technology.

A molding machine according to an aspect of the present invention includes an injection device that injects a molding material into a cavity, a pressing member that moves into the cavity and pressurizes the molding material in the cavity locally, and the pressurization A pressure driving device for driving the member; a gas pressure sensor for detecting a gas pressure in the cavity provided in a pipe outside the mold constituting the cavity; and a gas pressure sensor detected during injection. And a control device that controls the pressurization driving device by determining the timing of starting the movement of the pressurizing member into the cavity with respect to a point in time when the gas pressure satisfies a predetermined condition.

  Preferably, the injection device injects a molding material into the cavity filled with air or an inert gas, and the predetermined condition is a condition satisfied by a gas pressure higher than atmospheric pressure.

  Preferably, the predetermined condition is that the gas pressure reaches a predetermined set pressure higher than the atmospheric pressure.

  Preferably, the predetermined condition is that the gas pressure reaches a maximum value.

  Preferably, the apparatus further includes an active gas supply device that supplies an active gas into the cavity, and the injection device supplies molten metal as a molding material to the cavity filled with the active gas supplied from the active gas supply device. Injecting and the said predetermined conditions are the conditions satisfy | filled by the gas pressure lower than atmospheric pressure.

  Preferably, the predetermined condition is that the gas pressure reaches a predetermined set pressure lower than the atmospheric pressure.

  Preferably, the predetermined condition is that the gas pressure reaches a minimum value.

  Preferably, the control device determines that the molded product is defective when the gas pressure does not reach the set pressure before the injection process reaches a predetermined stage.

  According to the present invention, the timing of local pressurization can be determined appropriately.

The schematic diagram which shows the structure of the principal part of the die-casting machine which concerns on the 1st Embodiment of this invention. 2A is a cross-sectional view showing details of the periphery of the gas pressure sensor, and FIG. 2B is a view of a part of the fixed mold as viewed from the moving mold side. The figure for demonstrating the outline | summary of the injection | pouring operation | movement in the die-casting machine of FIG. FIG. 4 is a partially enlarged view of FIG. 3. The flowchart which shows an example of the procedure of the process which concerns on the control of the local pressurization in the die-casting machine of FIG. The flowchart which shows the other example of the procedure of the process which concerns on the control of the local pressurization in the die-casting machine of FIG. The schematic diagram which shows the structure of the principal part of the die-casting machine concerning the 2nd Embodiment of this invention. The figure for demonstrating the outline | summary of the injection operation in the die-casting machine of FIG. FIG. 9 is a partially enlarged view of FIG. 8.

  FIG. 1 is a schematic diagram illustrating a configuration of a main part of a die casting machine 1 according to an embodiment of the present invention.

  The die casting machine 1 includes, for example, a mold clamping device (not shown) that clamps the fixed mold 101 and the movable mold 103, and a cavity 105 formed by the fixed mold 101 and the movable mold 103 that are clamped. An injection device 3 for injecting molten metal, a local pressurizing device 5 for locally pressurizing the molten metal in the cavity 105, and a die-cast product formed by solidification of the molten metal in the cavity 105 are transferred from the moving mold 103 or the fixed mold 101. And an extrusion device (not shown) for extruding.

  The die casting machine 1 has a gas pressure sensor 7 for detecting the gas pressure in the cavity 105 and a control device 9 for controlling each of the above devices.

  The injection device 3 includes, for example, a sleeve 11 communicating with a cavity, a plunger 13 inserted into the sleeve 11, a hydraulic injection cylinder 15 that can drive the plunger 13, and a hydraulic pressure that supplies hydraulic fluid to the injection cylinder 15. Circuit 17.

  After the molten metal is poured into the sleeve 11 from the hot water supply port 11 a formed in the sleeve 11, the plunger 13 advances toward the cavity 105 in the sleeve 11, whereby the molten metal in the sleeve 11 is injected into the cavity 105. The

  The injection device 3 includes, for example, a position sensor 19 that detects the position of the plunger 13 (piston of the injection cylinder 15) and a hydraulic pressure sensor 21 that detects the pressure on the head side of the injection cylinder 15. The detection values of these sensors are output to the control device 9 and used for control of the injection device 3.

  The local pressurizing device 5 includes, for example, a pressurizing pin 23 that can move into the cavity 105 and a hydraulic pressurizing cylinder 25 that can drive the pressurizing pin.

  For example, hydraulic fluid is supplied from the hydraulic circuit 17 to the pressure cylinder 25. After the cavity 105 is filled with the molten metal by the injection device 3, the pressure pin 23 advances (protrudes) into the cavity 105 by the driving force generated by the pressure cylinder 25, so that the molten metal in the cavity 105 is localized. Pressurized.

  The gas pressure sensor 7 is, for example, a capacitance type, piezoresistive type, or vibration type pressure sensor, and outputs an electric signal having a signal level corresponding to the pressure in the cavity 105 to the control device 9.

  FIG. 2A is a cross-sectional view showing details of the periphery of the gas pressure sensor 7 and corresponds to a partially enlarged view of FIG. FIG. 2B is a view of the fixed mold 101 as viewed from the movable mold 103 side in the range shown in FIG.

  The fixed mold 101 and the movable mold 103 are configured with an air vent 107 for exhausting the cavity 105. The air vent 107 is formed in, for example, a jagged gap (a chill vent 107 c) formed between the fixed mold 101 and the movable mold 103, and communicates between the chill vent 107 c and the outside of the mold. And an exhaust passage 107a.

  A pipe 109 is connected to the end of the exhaust passage 107a on the outside of the mold, and the pipe 109 is branched into a branch path 109a and a branch path 109b. The end of the branch path 109a is closed, and the end of the branch path 109b is open to the atmosphere.

  The gas pressure sensor 7 is connected to the branch path 109a. Accordingly, the gas pressure sensor 7 directly detects the gas pressure in the branch passage 109a, and thereby indirectly detects the gas pressure in the cavity 105.

  A check valve 29 is provided in the branch path 109b. The check valve 29 allows the flow from the cavity 105 side to the atmosphere and prohibits the flow in the opposite direction.

  The control device 9 is constituted by a computer including a CPU, a ROM, a RAM, and an external storage device, for example. The control device 9 is based on a preset program, various set values, and various sensors (7, 19, 21, etc.), and various devices (a mold clamping device not shown, the hydraulic circuit 17 of the injection device 3). Etc.) is output to the control signal.

  FIG. 3 is a diagram showing an outline of the injection operation in the die casting machine 1, and FIG. 4 is a partially enlarged view of FIG. In these drawings, the horizontal axis indicates time t. The vertical axis indicates the injection speed V, the injection position D (position of the plunger 13), the molten metal pressure Pm, and the gas pressure Pg in the cavity 105. Note that details are omitted as appropriate in these drawings. The molten metal pressure Pm is the pressure of the molten metal in the cavity 105, and is slightly different from the injection pressure (pressure that the plunger 13 applies to the molten metal).

  The time point t0 corresponds to the start of injection. That is, at a time point t0, a predetermined injection start condition is satisfied, for example, molten metal is supplied to the sleeve 11, and the control device 9 drives the injection cylinder 15 to start the plunger 13 moving forward.

  At time points t0 to t1, low speed injection is performed as indicated by the injection speed V. That is, the control device 9 controls the injection cylinder 15 to advance the plunger 13 at a relatively low speed. By performing injection at a low speed, air entrainment due to the molten metal is suppressed.

  During the low speed injection (t0 to t1), the injection position D gradually increases. The injection pressure (not shown) is relatively low. The molten metal pressure Pm and the gas pressure Pg are substantially equal to the atmospheric pressure.

  From time t1 to t2, high speed injection is performed. That is, the control device 9 switches the speed of the plunger 13 at a high speed when a predetermined high speed switching condition is satisfied (time point t1), for example, the position of the plunger 13 detected by the position sensor 19 reaches a predetermined high speed switching position. Thus, the injection cylinder 15 is controlled. As a result, the molten metal is quickly filled into the cavity 105 without delaying the solidification of the molten metal.

  During the high speed injection (t1 to t2), the injection position D increases more rapidly than during the low speed injection. The injection pressure (not shown) is larger than that during low speed injection. On the other hand, the molten metal pressure Pm does not change much. The gas pressure Pg rises as the cavity 105 is filled with the molten metal because the molten metal is filled into the cavity 105 faster than the exhaust from the air vent 107.

  At time t2, the cavity 105 is almost filled with molten metal. Accordingly, the plunger 13 receives a reaction force from the molten metal, and the injection speed V decreases rapidly. Note that the control device 9 may perform appropriate deceleration control. At time t4, the injection speed V becomes zero.

  During this time, the increase amount of the injection position D also decreases, and the increase amount becomes 0 at time t4. The molten metal pressure Pm increases rapidly when the cavity 105 is filled with the molten metal. That is, pressure increase is performed. At time 4, the molten metal pressure Pm reaches the final pressure (casting pressure).

  The gas pressure Pg reaches a peak (maximum) at a time point t3 from the start of deceleration to the end of pressure increase (between t2 and t4). More specifically, the time point t3 is a time point when the molten metal is almost filled in the cavity 105 (a time point when the deceleration of the plunger 13 is almost finished).

  After time t4, the control device 9 controls the injection cylinder 15 so as to maintain the injection pressure at the completion of the pressure increase (hold pressure). However, the molten metal pressure Pm decreases with the solidification shrinkage of the molten metal (t4 to t5). During this time, the injection speed and the injection position do not change. The gas pressure Pg gradually decreases as the exhaust from the cavity 105 proceeds and becomes equal to the atmospheric pressure.

  The control device 9 determines the timing for starting the local pressurization based on the time point when the gas pressure Pg satisfies a predetermined condition. For example, in the example of FIG. 3, the time point t5 when a predetermined set time td has elapsed is set as the local pressurization start timing with the time point t3 when the gas pressure Pg reaches a peak.

  The set time td is set for the control device 9 by a worker through a predetermined input device, for example. However, the set time td may be set by the manufacturer of the die casting machine 1, or may be automatically set by the control device 9 based on various measurement values obtained in a trial run or the like, It may be corrected for each molding cycle by the control device 9 based on a measured value of a parameter that affects the solidification state of the molten metal such as temperature.

  And the control apparatus 9 will drive the pressurization cylinder 25, and will start advance of the pressurization pin 23, when the determined start timing comes. Thereby, the molten metal pressure Pm starts to rise.

  FIG. 5 is a flowchart illustrating an example of a processing procedure related to control of local pressurization. This process is executed by the control device 9 for each molding cycle. In addition, the start time of the said process may be made into the appropriate time (for example, injection start time) in a shaping | molding cycle.

  In step S <b> 1, the control device 9 acquires a detection value of the gas pressure Pg from the gas pressure sensor 7.

  In step S2, the control device 9 determines whether or not the acquired gas pressure Pg has reached a predetermined set pressure. The set pressure is a peak value of the gas pressure Pg obtained in the trial run or the previous molding cycle, or a value slightly lower than this. Thereby, the time (t3) when the gas pressure Pg substantially reaches the peak can be specified. The set pressure may be set manually by an operator or automatically set by the control device 9.

  If the control device 9 determines that the gas pressure Pg has reached the set pressure, the control device 9 proceeds to step S3. If it is determined that the gas pressure Pg has not reached the set pressure, the control device 9 proceeds to step S5.

  In step S3, the control device 9 determines whether or not a predetermined set time td has elapsed from the time point (t3) when it is determined that the set pressure has been reached in step S2, and waits until it is determined that it has elapsed. When it is determined that the set time td has elapsed, the process proceeds to step S4.

  In step S <b> 4, the control device 9 drives the pressure cylinder 25 and starts to advance the pressure pin 23. Thereby, local pressurization is performed.

  In step S5, the control device 9 determines whether or not the period in which the gas pressure Pg that has reached the set pressure is to be detected has passed, based on appropriate parameters related to the progress of the injection process.

  For example, the control device 9 determines whether or not the speed of the plunger 13 detected by the position sensor 19 is zero. In addition, for example, the control device 9 determines whether or not a predetermined time has elapsed since the start of injection. For example, the control device 9 determines whether or not the pressure detected by the hydraulic pressure sensor 21 has reached the final pressure.

  When the control device 9 determines that the period to be detected has not passed, the control device 9 returns to step S1. Thereby, it is repeatedly determined whether or not the set pressure in step S2 has been reached.

  On the other hand, when it is determined that the period to be detected has passed, the control device 9 proceeds to step S6. In step S6, the control device 9 determines that the molded die-cast product is a defective product, and executes an appropriate process according to the determination.

  For example, the control device 9 performs notification processing for transmitting to the worker that a defective product has occurred via a display device or an audio device. Further, for example, a process for transporting the taken die-cast product to a transport destination different from the non-defective product is performed.

  FIG. 6 is a flowchart illustrating another example of a processing procedure related to control of local pressurization. This process is executed for each molding cycle by the control device 9 as in the process of FIG. It is the same as in FIG. 5 that the start time of the process may be an appropriate time.

  In step S <b> 11, the control device 9 acquires the detected value of the gas pressure Pg from the gas pressure sensor 7 as in step S <b> 1 of FIG. 5.

  In step S12, the control device 9 determines whether or not the acquired gas pressure Pg has reached the peak, and waits until it is determined that it has reached. This determination is made based on, for example, whether or not the gas pressure Pg has risen to some extent and then has fallen to some extent based on time-series data up to the present time. If the control device 9 determines that the gas pressure Pg has reached the peak, the control device 9 specifies the time point (t3) and proceeds to step S13.

  In step S13, the control device 9 determines whether or not a predetermined set time td has elapsed from the time point (t3) of the peak specified in step S12, and waits until it is determined that it has elapsed. When it is determined that the set time td has elapsed, the process proceeds to step S14.

  In step S14, the control device 9 determines whether parameters other than the gas pressure Pg related to the progress of the injection process satisfy a predetermined condition. For example, the control device 9 determines whether or not the injection position D, the injection pressure, or the molten metal pressure has reached a predetermined value (or range).

  The condition of step S14 preferably requires that the time period set with reference to the time point when the condition of step S12 is satisfied is satisfied. For example, it is determined whether the parameters other than the gas pressure Pg have reached a predetermined value before the gas pressure Pg reaches the peak or within a predetermined period before and after the peak.

  And the control apparatus 9 progresses to step S15, when it determines with the conditions regarding parameters other than gas pressure Pg being satisfy | filled, and when it determines with not being satisfy | filled, it progresses to step S16. Steps S15 and S16 are the same as steps S4 and S6 in FIG.

  In step S14, conditions relating to parameters other than the gas pressure Pg are also determined, so that an erroneous start timing is suppressed when an abnormal change occurs in the gas pressure Pg.

  As described above, in this embodiment, the die casting machine 1 includes the injection device 3 that injects the molten metal into the cavity 105, and the pressure pin 23 that moves into the cavity 105 and locally pressurizes the molding material in the cavity 105. And the pressure cylinder 25 for driving the pressure pin 23, the gas pressure sensor 7 for detecting the gas pressure Pg in the cavity 105, and the gas pressure detected by the gas pressure sensor 7 during injection satisfy a predetermined condition. And a control device 9 that controls the pressurization cylinder 25 by determining the start timing (t5) of the pressurization pin 23 into the cavity 105 with reference to the time point (t3).

  Therefore, it is possible to appropriately determine the timing for starting local pressurization by a method different from the conventional method. This method has the following advantageous effects, for example. Since the gas pressure Pg peaks when the filling of the molten metal into the cavity 105 is almost completed, it is easy to grasp when the molten metal is filled. As a result, the movement start timing of the pressure pin 23 can be set to an appropriate time. In addition, the gas pressure sensor 7 is inexpensive and has a long life because it does not contact the hot molten metal. In addition, since the gas pressure sensor 7 can be externally attached to the mold, the mold only needs to be provided with a female thread portion for mounting, and no major design change occurs.

  In the present embodiment, the control device 9 determines that the formed die-cast product is defective when the gas pressure Pg does not reach the set pressure before the injection process reaches a predetermined stage (Steps S2, S5, and S5). S6).

  Therefore, the process for determining the start timing of local pressurization and the process for determining defective products are partially shared. As a result, the operation of the die casting machine 1 is simplified and the operation can be easily grasped. In addition, the operator has fewer parameters to set and the burden is reduced.

<Second Embodiment>
FIG. 7 is a schematic diagram illustrating a configuration of a main part of a die casting machine 201 according to the second embodiment.

  The die casting machine 201 is different from the first embodiment in that the die casting machine 201 is configured as a die casting machine that performs a PF (nonporous) die casting method. Specifically, the die casting machine 201 includes an active gas supply device 231 that supplies an active gas (for example, oxygen) to the cavity 105.

  The active gas supply device 231 includes, for example, a cylinder 233 that holds compressed active gas, a communication channel 235 that communicates the cylinder 233 and the sleeve 11, and a valve 237 that opens and closes the communication channel 235. Yes. The control device 9 controls the supply of the active gas to the cavity 105 by controlling the valve 237.

  FIG. 8 is a diagram illustrating an outline of the injection operation in the die casting machine 201, and corresponds to FIG. 3 of the first embodiment. FIG. 9 is a partially enlarged view of FIG. 8 and corresponds to FIG. 4 of the first embodiment.

  Also in the die casting machine 201, the control device 9 drives the injection cylinder 15 as in the first embodiment. Accordingly, as in the first embodiment, low-speed injection (t10 to t11), high-speed injection (t11 to t13), decelerated injection, and pressure increase (t13 to t14) are performed.

  However, before the start of injection (before time t10), the air in the cavity 105 is replaced with the active gas. Specifically, the control device 9 moves the plunger 13 to a position where the hot water supply port 11 a is blocked by the plunger tip 13 a of the plunger 13, opens the valve 237, and supplies the active gas to the sleeve 11. Thereafter, when a predetermined time elapses, the control device 9 closes the valve 237. Note that the gas pressure in the cavity 105 is maintained at substantially atmospheric pressure by the action of the check valve 29, for example.

  Then, the control device 9 retracts the plunger tip 13a, supplies the molten metal from the hot water supply port 11a to the sleeve 11, and starts injection. When the molten metal is injected into the cavity 105, the active gas in the cavity 105 reacts with the molten metal. Thereby, a die-cast product with few pores (nests) is formed.

  Changes in the injection speed V, the injection position D, and the molten metal pressure Pm are substantially the same as those in the first embodiment. On the other hand, the gas pressure Pg becomes a reduced pressure state when the active gas in the cavity 105 reacts with the molten metal, and falls below the atmospheric pressure. Specifically, the gas pressure Pg becomes lower than the atmospheric pressure during the high-speed injection (t11 to t13). In the meantime, the gas pressure Pg becomes a peak (minimum) (t12).

  Also in the second embodiment, similarly to the first embodiment, the control device 9 determines the timing for starting the local pressurization based on the time point when the gas pressure Pg satisfies a predetermined condition. For example, in the example of FIG. 8, the time point t15 when a predetermined set time td has elapsed from the time point t12 when the peak is reached is the local pressurization start timing.

  The processing executed by the control device 9 may be the same as the processing shown in FIG. 4 or FIG. However, the set pressure in step S2 is a negative pressure, and the peak in step S12 is a point at which it is minimized.

  The present invention is not limited to the above embodiment, and may be implemented in various aspects.

  The molding machine is not limited to a die casting machine. For example, as in the first embodiment, a molding machine that performs injection while the cavity is filled with air or an inert gas may be an injection molding machine that uses a resin as a molding material.

  The molding machine is not limited to horizontal mold clamping horizontal injection, and may be horizontal mold clamping vertical injection, for example. Further, the molding machine is not limited to the cold chamber type, and may be a hot chamber type. The mold clamping device may be a toggle type or a direct pressure type. The drive device of the injection device is not limited to a hydraulic cylinder, and may be, for example, an electric motor or a combined device of an electric motor and a hydraulic cylinder.

  The pressurizing member may be of an appropriate shape and size as long as the molten metal can be locally pressurized by moving toward the cavity, and is not limited to a pin-shaped member protruding into the cavity. Further, the driving device for the pressurizing member is not limited to the hydraulic cylinder, and may be an electric type, for example.

  When the gas pressure reaches the set pressure as a reference for determining the local pressurization start timing, the set pressure is not limited to a value equivalent to the peak value of the gas pressure, but 80% of the peak value, It may be an appropriate value. In other words, the reference time point is not limited to the gas pressure peak time point. In this case, the reference time point may be before the peak or after the peak.

  In the present application, the determination as to whether or not the set pressure has been reached includes not only the determination as to whether or not the gas pressure is equal to the set pressure, but also the gas pressure with respect to the set pressure. Judgment whether or not it is within the predetermined range considering errors, etc., judgment whether the gas pressure rising from the pressure lower than the set pressure has exceeded the set pressure, and lowering from the pressure higher than the set pressure It is assumed that the determination includes whether or not the gas pressure being operated has fallen below the set pressure.

  The local pressurization start timing may not be when the set time (td) has elapsed from the reference time, but may be the reference time itself. In other words, the set time may be zero. In this case, the reference time point may be a time point when the gas pressure reaches a peak as described above, or may be a time point other than that.

  The procedures shown in FIGS. 5 and 6 may be modified by appropriately combining them. For example, in FIG. 6, it may be determined whether or not the detected peak value (step S12) exceeds a predetermined set pressure (step S2). Further, for example, in FIG. 5, determination regarding parameters other than the gas pressure (step S <b> 14) may be performed. In this case, it is preferable that step S14 requires that the time period set based on the time point when the condition of step S2 is satisfied be satisfied.

  DESCRIPTION OF SYMBOLS 1 ... Die casting machine (molding machine), 3 ... Injection device, 7 ... Gas pressure sensor, 9 ... Control device, 23 ... Pressurization pin (pressurization member), 25 ... Pressurization cylinder (pressurization drive device), 105 ... cavity.

Claims (8)

An injection device for injecting a molding material into the cavity;
A pressure member that moves into the cavity and locally pressurizes the molding material in the cavity;
A pressure driving device for driving the pressure member;
A gas pressure sensor provided in a pipe outside the mold constituting the cavity and detecting a gas pressure in the cavity;
Control for controlling the pressurization driving device by determining the start timing of the pressurization member to move into the cavity with reference to the time when the gas pressure detected by the gas pressure sensor satisfies a predetermined condition during injection Equipment,
Having a molding machine. The injection device injects a molding material into the cavity filled with air or an inert gas,
The molding machine according to claim 1, wherein the predetermined condition is a condition that is satisfied by a gas pressure higher than atmospheric pressure. The molding machine according to claim 2, wherein the predetermined condition is that the gas pressure reaches a predetermined set pressure higher than atmospheric pressure. The molding machine according to claim 2, wherein the predetermined condition is that the gas pressure reaches a maximum value. An active gas supply device for supplying an active gas into the cavity;
The injection device injects molten metal as a molding material into the cavity filled with the active gas supplied from the active gas supply device,
The molding machine according to claim 1, wherein the predetermined condition is a condition that is satisfied by a gas pressure lower than atmospheric pressure. The molding machine according to claim 5, wherein the predetermined condition is that the gas pressure reaches a predetermined set pressure lower than atmospheric pressure. The molding machine according to claim 5, wherein the predetermined condition is that the gas pressure reaches a minimum value. The molding machine according to claim 3 or 6, wherein the control device determines that the molded product is defective when the gas pressure does not reach the set pressure before the injection process reaches a predetermined stage.

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