Injection molding machine and method for detecting mold internal pressure

Abstract

An injection molding machine (1) comprises: an injection device (10) that injects, from a nozzle (12), a resin material that has been melted in a heating barrel (11) inside of which a screw (20) is disposed; a mold (75) that comprises a fixed mold (76) and a mobile mold (77) and has a cavity (75a) that is filled with the resin material; a load cell (60) that detects pressure acting on the screw (20); and a control device (100) that controls mold internal pressure. The control device (100) comprises: a pressure loss acquisition unit (111) that acquires, as a pressure loss, pressure detected by the load cell (60) when the resin material has been injected from the nozzle (12) contacting the fixed mold (76) in a state in which the fixed mold (76) and the mobile mold (77) are open; an injection pressure acquisition unit (112) that acquires, as an injection pressure, a pressure detected by the load cell (60) when the resin material has been injected from the nozzle (12) into the cavity (75a) in a state in which the mold (75) is closed; and a virtual mold internal pressure calculation unit (114) that calculates a virtual mold internal pressure V by subtracting the pressure loss from the injection pressure.

Description

Injection molding machine and method for detecting mold internal pressure

[0001] The present invention relates to an injection molding machine and a method for detecting mold internal pressure.

[0002] In an injection molding machine that performs molding by injecting molten resin into a mold, it is important to perform molding while maintaining the resin pressure at an appropriate value in order to perform proper molding. For this reason, conventional injection molding machines perform molding while obtaining the pressure value of the molten resin using various methods. For example, an injection pressure testing device for an injection molding machine described in Patent Document 1 calculates the resin pressure in the injection nozzle based on the resin pressure detected during purging and the resin pressure detected during normal molding, thereby accurately detecting the resin pressure in the cavity without being affected by pressure loss in the heating cylinder.

[0003] In addition, the molding condition creation method described in Patent Document 2 obtains molding conditions for mass production molding by obtaining a resin pressure curve at the resin inlet or the end of the molding machine nozzle and an injection pressure curve when the nozzle is removed from the mold, thereby compensating for time delays and pressure losses due to the mechanical elements of the injection molding machine.In addition, Patent Document 3 describes a resin evaluation method using an injection molding machine, which detects the injection pressure at a set screw position by injecting while changing the resin temperature and injection speed, and then determines an interdependence function of pressure, speed, and temperature by the least squares method using data on N combinations of injection pressure, injection speed, and resin temperature.

[0004] In addition, a pressure control device for an injection molding machine described in Patent Document 4 includes an injection pressure control process for controlling the injection pressure during a pressure holding process, and a mold cavity pressure control process for controlling the estimated mold cavity pressure to a set mold cavity pressure after the injection pressure control process. This suppresses variations in the pressure inside the mold between molding cycles, enabling the molding of molded products of stable quality. Furthermore, by controlling the estimated mold cavity pressure to a set mold cavity pressure during the pressure holding process, the pressure inside the mold can be controlled with high responsiveness, preventing stress deformation of the molded product. In addition, Patent Document 5 describes a method for measuring the injection pressure in an injection molding machine. When molten resin is injected from a heated barrel into a mold, a load cell is used to detect the reaction force acting on the screw, and the screw speed is measured to calculate the screw acceleration, and the inertia force of the movable member is calculated to calculate the pressure of the molten resin in the heated barrel.

[0005] Japanese Patent Laid-Open No. 11-115023 Japanese Patent Laid-Open No. 2000-355033 Japanese Patent Laid-Open No. 2002-331558 Japanese Patent Laid-Open No. 2016-159589 Japanese Patent Laid-Open No. 2003-191285

[0006] In injection molding using an injection molding machine, the type of resin material or mold may be changed depending on the desired molded product. However, even when the type of resin material or mold is changed, it is important to properly control the pressure of the resin material inside the mold. To properly control the mold cavity pressure, which is the pressure of the resin material inside the mold, it is necessary to obtain the pressure of the resin material. In conventional injection molding machines, the mold cavity pressure is calculated based on a value detected by the injection device when the resin material is injected by the injection device. For example, in Patent Document 1, the pressure of the resin inside the injection nozzle is calculated based on the pressure of the resin during purging and the pressure of the resin during normal molding, thereby detecting the pressure of the resin inside the cavity without being affected by pressure loss inside the heating cylinder.

[0007] However, when detecting the mold cavity pressure based on a value detected during molding, a value detected before molding, such as the resin pressure when purging is performed in Patent Document 1, becomes important, but purging differs from the actual molding state. Therefore, when calculating the mold cavity pressure using the resin pressure when purging is performed, it is conceivable that the calculated pressure will differ greatly from the actual pressure, and there is room for improvement in terms of accuracy when calculating the mold cavity pressure.

[0008] The present invention has been made in view of the above, and has an object to provide an injection molding machine and a method for detecting mold pressure that can calculate mold pressure with high accuracy.

[0009] In order to solve the above-mentioned problems and achieve the object, the injection molding machine of the present invention comprises: an injection device that melts a resin material in a heated barrel having a screw disposed inside, and moves the screw toward a nozzle that injects the molten resin material, thereby injecting the resin material from the nozzle; a mold that consists of a fixed mold and a movable mold that open and close, and has a cavity that is filled with the resin material injected from the nozzle when the mold is closed, and molds the resin material in the cavity; a pressure detection unit that detects the pressure acting on the screw when the resin material is injected; and a control device that controls the movement of the screw to control the mold internal pressure, which is the pressure of the resin material in the mold. the control device comprises: a pressure loss acquisition unit that acquires, as a pressure loss, the pressure detected by the pressure detection unit when the resin material is injected from the nozzle that is in contact with the fixed mold when the fixed mold and the movable mold are in an open state; an injection pressure acquisition unit that acquires, as an injection pressure, the pressure detected by the pressure detection unit when the resin material is injected from the nozzle into the cavity when the fixed mold and the movable mold are in a closed state; and a virtual internal mold pressure calculation unit that calculates a virtual internal mold pressure, which is the virtual internal mold pressure, by subtracting, from the injection pressure acquired by the injection pressure acquisition unit, the pressure loss acquired by the pressure loss acquisition unit or a pressure loss based on the pressure loss acquired by the pressure loss acquisition unit.

[0010] In order to solve the above-mentioned problems and achieve the object, a method for detecting mold internal pressure according to the present invention includes an injection device that melts a resin material in a heated barrel having a screw disposed inside, and injects the resin material from a nozzle by moving the screw toward a side where a nozzle is located for injecting the molten resin material; a mold that consists of a fixed mold and a movable mold that open and close and has a cavity that is filled with the resin material injected from the nozzle when closed, and molds the resin material in the cavity; and a pressure detection unit that detects the pressure acting on the screw when the resin material is injected. The method for detecting mold internal pressure includes the steps of bringing the nozzle into contact with the fixed mold while the fixed mold and the movable mold are open, injecting the resin material from the nozzle, and acquiring the pressure detected by the pressure detection unit as a pressure loss; injecting the resin material from the nozzle into the cavity while the fixed mold and the movable mold are closed, and acquiring the pressure detected by the pressure detection unit as an injection pressure; and calculating a virtual mold internal pressure, which is the virtual mold internal pressure, by subtracting from the injection pressure the pressure loss acquired in the step of acquiring the pressure loss or a pressure loss based on the pressure loss acquired in the step of acquiring the pressure loss.

[0011] The injection molding machine and the method for detecting mold internal pressure according to the present invention have the advantage of being able to calculate the mold internal pressure with high accuracy.

[0012] FIG. 1 is a schematic diagram showing an example of the configuration of an injection molding machine according to an embodiment. FIG. 2 is a detailed diagram of the injection unit shown in FIG. 1. FIG. 3 is a detailed diagram of the heating barrel shown in FIG. 2. FIG. 4 is a detailed diagram of the check ring shown in FIG. 3. FIG. 5 is an explanatory diagram of the control device shown in FIG. 1. FIG. 6 is an explanatory diagram showing the relationship between each controller of the movement control unit and the injection unit. FIG. 7 is an explanatory diagram showing an example of a pressure loss model. FIG. 8 is a schematic diagram showing a measurement method for measuring pressure loss in a mold cavity pressure detection method according to an embodiment. FIG. 9 is a schematic diagram showing a measurement method for measuring pressure loss with the nozzle separated from the mold. FIG. 10 is an explanatory diagram comparing the measurement results of pressure loss measured with the nozzle in contact with the mold and the measurement results of pressure loss measured with the nozzle separated from the mold. FIG. 11 is an explanatory diagram showing a comparison of the virtual mold cavity pressure calculated using the pressure loss during mold cavity purging and the virtual mold cavity pressure calculated using the pressure loss during resin purging with the actual mold cavity pressure. FIG. 12 is a schematic diagram showing the measurement method for the actual mold cavity pressure. Fig. 13 is a chart comparing the error rates of a quadratic function approximation model and a power approximation model. Fig. 14 is a flow chart showing the procedure for calculating the virtual mold internal pressure. Fig. 15 is an explanatory diagram showing changes in injection speed, injection pressure, and virtual mold internal pressure when molding a non-defective product. Fig. 16 is an explanatory diagram showing a state in which the injection pressure has reached its upper limit in a case in which the control device does not have a virtual mold internal pressure determination unit and does not determine whether the virtual mold internal pressure has reached its upper limit. Fig. 17 is an explanatory diagram showing a state in which the control device has a virtual mold internal pressure determination unit and the virtual mold internal pressure has reached its upper limit.

[0013] Hereinafter, an embodiment of an injection molding machine and a method for detecting mold internal pressure according to the present disclosure will be described in detail with reference to the drawings. Note that the present invention is not limited to this embodiment. Furthermore, the components in the following embodiments include those that are replaceable and easily conceivable by a person skilled in the art, or those that are substantially the same.

[0014] 1 is a schematic diagram showing an example of the configuration of an injection molding machine 1 according to an embodiment. In the following description, the up-down direction of the injection molding machine 1 in normal use will be referred to as the up-down direction Z of the injection molding machine 1, the upper side of the injection molding machine 1 in normal use will be referred to as the upper side of the injection molding machine 1, and the lower side of the injection molding machine 1 in normal use will be referred to as the lower side of the injection molding machine 1. In the following description, the longitudinal direction Y of the injection molding machine 1 will also be referred to as the longitudinal direction Y of each component that includes the injection molding machine 1, and the direction perpendicular to both the up-down direction Z and the longitudinal direction Y of the injection molding machine 1 will be referred to as the width direction X of the injection molding machine 1.

[0015] <Injection Molding Machine 1> The injection molding machine 1 according to this embodiment has an injection unit 10 and a mold clamping unit 70, and the injection unit 10 and the mold clamping unit 70 are mounted on a frame 5 that is located at the lower end of the injection molding machine 1. The injection molding machine 1 melts a resin material into a plasticized material in the injection unit 10, and then cools and solidifies the plasticized material injected from the injection unit 10 using the mold clamping unit 70, thereby making it possible to manufacture various desired molded products.

[0016] The injection device 10 includes a heating barrel 11, a screw 20, a rotation mechanism 40, a forward / backward movement mechanism 50, and a propulsion mechanism 30. The heating barrel 11 is capable of heating and melting a resin material therein to form a plasticized material. The heating barrel 11 also includes a nozzle 12 at one end for injecting the plasticized material, and the other end is connected to a hopper 15 for introducing raw material. The screw 20 is disposed inside the heating barrel 11 and is movable axially within the heating barrel 11.

[0017] The rotation mechanism 40 rotates the screw 20 inside the heating barrel 11 , thereby making it possible to introduce the resin material from the hopper 15 into the heating barrel 11 .

[0018] The forward / backward movement mechanism 50 is capable of moving the screw 20 in the longitudinal direction Y within the heating barrel 11. Furthermore, the forward / backward movement mechanism 50 can extrude the resin material from the nozzle 12 by moving the screw 20 toward the nozzle 12 while the molten resin material is stored in the end portion of the heating barrel 11 where the nozzle 12 is located. This allows the resin material molten within the heating barrel 11 to be injected from the nozzle 12.

[0019] The mold clamping unit 70 has a fixed platen 71, a movable platen 72, a mold 75, a mold clamping drive mechanism 80, and an ejection mechanism 85. The fixed platen 71 is disposed on a frame 5 and fixed to the frame 5, and the movable platen 72 is disposed on the frame 5 on the opposite side of the fixed platen 71 from the side on which the injection unit 10 is located, and is disposed so as to be movable relative to the fixed platen 71.

[0020] The mold 75 has a cavity 75a that is filled with a resin material injected from the nozzle 12 of the heated barrel 11 of the injection device 10, and the resin material can be molded in the cavity 75a. The mold 75 that molds the resin material in this manner has a fixed mold 76 and a movable mold 77 that open and close relative to each other. The cavity 75a of the mold 75 is formed by the movable mold 77 and the fixed mold 76 when the movable mold 77 and the fixed mold 76 are in a closed state. The fixed mold 76 is attached to the surface of the fixed platen 71 on the side where the movable platen 72 is located, and the movable mold 77 is attached to the surface of the movable platen 72 on the side where the fixed platen 71 is located. The movable mold 77 attached to the movable platen 72 faces the fixed mold 76 attached to the fixed platen 71, and when the movable platen 72 approaches the fixed platen 71, it approaches the fixed mold 76 and is combined with the fixed mold 76.

[0021] The mold clamping drive mechanism 80 is capable of moving the movable platen 72 relative to the fixed platen 71, and by moving the movable platen 72 relative to the fixed platen 71, it is possible to close the movable mold 77 and the fixed mold 76, or to open the movable mold 77 and the fixed mold 76. In this embodiment, the mold clamping drive mechanism 80 is provided with a so-called toggle mechanism 81, which is capable of moving the movable platen 72 relative to the fixed platen 71.

[0022] The ejection mechanism 85 includes an ejection member 86 that pushes out the molded product that has adhered to the inner surface of the movable die 77 after molding, and enables the molded product to be removed from the movable die 77 after molding.

[0023] <Injection device 10> In the following description, the side where the mold clamping device 70 is located relative to the injection device 10 in the longitudinal direction Y will be referred to as the front or front side, and the side opposite the side where the mold clamping device 70 is located relative to the injection device 10 in the longitudinal direction Y will be referred to as the rear or rear side.

[0024] Fig. 2 is a detailed view of the injection device 10 shown in Fig. 1. The injection device 10 is disposed on the frame 5 via a propulsion mechanism 30. The propulsion mechanism 30 has a drive motor 31, and the drive force generated by the drive motor 31 enables the injection device 10 to move in the longitudinal direction Y relative to the frame 5.

[0025] The heating barrel 11 of the injection device 10 extends forward in the longitudinal direction Y, and a nozzle 12 is disposed at its tip, i.e., the front end of the heating barrel 11, so as to be in close contact with the mold 75. Specifically, the heating barrel 11 is formed in a substantially cylindrical shape, is disposed with its axis oriented along the longitudinal direction Y, and is provided with a heater 13 such as a band heater. This allows the heating barrel 11 to melt the resin material therein. In other words, the heater 13 can increase the temperature of the heating barrel 11, and the resin material therein can be heated and melted to become a molten resin, which is a plasticized material.

[0026] The screw 20 is disposed inside the heating barrel 11 and has a helical shape whose axial direction is aligned with the axial direction of the heating barrel 11; that is, the screw 20 has a helical groove on its outer circumferential surface. The screw 20, which is formed in this manner to have a helical shape, is rotatable about its axial center within the heating barrel 11. The screw 20 is also movable in the direction of its rotation axis within the heating barrel 11. In other words, the screw 20 is disposed inside the heating barrel 11 such that the central axis of the cylinder that forms the heating barrel 11 and the rotation axis of the screw 20 substantially coincide with each other, and is disposed so as to be movable in the axial direction of the heating barrel 11. The screw 20, which is rotatably disposed inside the heating barrel 11, is capable of kneading the molten resin by rotating inside the heating barrel 11, and therefore the heating barrel 11 is a barrel capable of kneading the molten resin therein.

[0027] A hopper 15 is disposed near the rear end of the heating barrel 11. The hopper 15 is connected to the interior of the heating barrel 11 and is capable of supplying pellets (not shown) that are granular resin material to the heating barrel 11.

[0028] The rotation mechanism 40 is disposed behind the heating barrel 11 in the longitudinal direction Y, and is capable of rotating the screw 20 disposed inside the heating barrel 11 about its central axis. The rotation mechanism 40 that rotates the screw 20 includes a rotation mechanism main body 41, a driving motor 43, a transmission belt 44, and a pulley 45.

[0029] The drive motor 43 is disposed, for example, above the rotation mechanism main body 41. The pulley 45 is disposed in front of the rotation mechanism main body 41 and is rotatable relative to the rotation mechanism main body 41 via a bearing 46. The pulley 45 is connected to the drive shaft of the drive motor 43 via a transmission belt 44, allowing the pulley 45 to rotate by the driving force of the drive motor 43 transmitted via the transmission belt 44. In this way, the pulley 45, which can rotate by the driving force transmitted from the drive motor 43, is fixed coaxially and integrally to the screw 20. In other words, the rear end of the screw 20 in the longitudinal direction Y is connected to the pulley 45. As a result, the screw 20 disposed in the heating barrel 11 can rotate integrally with the pulley 45 by the driving force transmitted from the drive motor 43 to the pulley 45.

[0030] A forward / backward movement mechanism 50 is disposed behind the rotation mechanism main body 41 in the longitudinal direction Y. The forward / backward movement mechanism 50 is capable of moving the screw 20 disposed inside the heating barrel 11 in the axial direction of the screw 20. In other words, the forward / backward movement mechanism 50 is capable of moving the screw 20 forward and backward in the longitudinal direction Y. More specifically, the forward / backward movement mechanism 50 has a drive motor 51, a transmission belt 53, a pulley 54, and a ball screw mechanism 56.

[0031] The drive motor 51 has an encoder 52 that detects the rotational position and rotational speed of the drive motor 51, and the drive shaft of the drive motor 51 is connected to a pulley 54 via a transmission belt 53. The encoder 52 of the drive motor 51 can detect the position of the screw 20 in the movement direction when the resin material is injected from the nozzle 12 of the heating barrel 11, via the rotational position of the drive motor 51. The encoder 52 of the drive motor 51 can also detect the injection speed S, which is the movement speed of the screw 20 when the resin material is injected from the nozzle 12 of the heating barrel 11, by detecting the rotational speed of the drive motor 51. The encoder 52 of the drive motor 51 is thus also used as an injection speed detection unit that detects the injection speed S of the screw 20.

[0032] The pulley 54 is integrally connected to a threaded portion 57 of the ball screw mechanism 56. The threaded portion 57 of the ball screw mechanism 56 is disposed coaxially with the screw 20, and is also disposed coaxially with the pulley 45 of the rotation mechanism main body 41. The nut portion 58 of the ball screw mechanism 56 of the forward / reverse mechanism 50 is formed in a substantially cylindrical shape, and the threaded portion 57 of the ball screw mechanism 56 is threadedly engaged with the nut portion 58.

[0033] A load cell 60 is disposed in the longitudinal direction Y between the nut portion 58 of the ball screw mechanism 56 of the forward / reverse movement mechanism 50 and the rotation mechanism main body 41 of the rotation mechanism 40. The load cell 60 is disposed behind the rotation mechanism main body 41 of the rotation mechanism 40 and in front of the nut portion 58 of the ball screw mechanism 56 of the forward / reverse movement mechanism 50.

[0034] The load cell 60 is a load measuring device that measures a load applied in the axial direction, and is composed of a strain element and a strain sensor (both not shown) attached to the strain element. In this embodiment, the load cell 60 is disposed with its axial direction oriented in the longitudinal direction Y, and is formed in a generally cylindrical shape that is flattened in the longitudinal direction Y, with the inner diameter of the cylinder being larger than the outer diameter of the threaded portion 57 of the ball screw mechanism 56 of the forward / reverse movement mechanism 50. The load cell 60 thus formed has its front surface in the longitudinal direction Y integrally fixed to the rotation mechanism main body 41 of the rotation mechanism 40, and its rear surface in the longitudinal direction Y integrally fixed to the nut portion 58 of the ball screw mechanism 56 of the forward / reverse movement mechanism 50.

[0035] The load cell 60, which is disposed between the rotation mechanism main body 41 of the rotation mechanism 40 and the nut portion 58 of the ball screw mechanism 56 of the forward / reverse mechanism 50, is capable of detecting the load acting in the longitudinal direction Y between the rotation mechanism main body 41 and the nut portion 58. The load cell 60 is used as a pressure detection unit that detects the pressure acting on the screw 20 when the resin material is injected from the nozzle 12 of the heating barrel 11 by detecting the load acting between the rotation mechanism main body 41 and the nut portion 58.

[0036] 3 is a detailed view of the heating barrel 11 shown in FIG. 2. As shown in FIG. 3, the heating barrel 11 is formed in a substantially cylindrical shape, and a heater 13, such as a band heater, is disposed on the outer circumferential surface. The nozzle 12, which is disposed at the front end of the heating barrel 11 in the longitudinal direction Y, is formed in a substantially cylindrical shape with an inner diameter smaller than the inner diameter of the heating barrel 11, and is disposed so as to open to the front side in the longitudinal direction Y. The screw 20 disposed within the heating barrel 11 has flights 21 that protrude outward in the radial direction of the screw 20 and are formed in a spiral shape centered on the axis of the screw 20. As a result, the screw 20 has spiral groove-shaped portions between adjacent orbital portions of the spirally formed flights 21.

[0037] A check ring 25 is disposed in the screw 20 formed in this manner near the front end in the longitudinal direction Y. The check ring 25 is disposed in a groove 22 formed in the screw 20 near the front end in the longitudinal direction Y. The groove 22 has a groove width direction that is aligned with the axial direction of the screw 20, and is a groove formed around one circumference of the screw 20 in the circumferential direction.

[0038] FIG. 4 is a detailed view of the check ring 25 shown in FIG. 3 . The check ring 25 is formed in a substantially cylindrical shape and is disposed in the groove 22 of the screw 20 with its axis substantially aligned with the axis of the screw 20. The substantially cylindrical check ring 25 has an outer diameter that is approximately the same as but slightly smaller than the inner diameter of the heating barrel 11. The inner diameter of the check ring 25 is larger than the diameter of the groove bottom of the groove 22 of the screw 20, forming a gap between the inner circumferential surface of the check ring 25 and the groove bottom of the groove 22 of the screw 20. The width of the check ring 25 in the axial direction is smaller than the groove width of the groove 22 of the screw 20. This allows the check ring 25 to move in the groove width direction within the groove 22.

[0039] The screw 20 is also formed with a communication portion 24 that connects the portion of the screw 20 that is forward of the groove portion 22 in the longitudinal direction Y with the inside of the groove portion 22. The communication portion 24 opens to the groove wall 23 on the front side of the groove portion 22 in the groove width direction.

[0040] <Control device 100> The injection molding machine 1 has a control device 100 that performs various controls of the injection molding machine 1, an input unit 160 through which an operator performs input operations to the injection molding machine 1, and a display unit 170 that displays various information. Both the input unit 160 and the display unit 170 are connected to the control device 100, and the input unit 160 transmits the input information to the control device 100. The display unit 170 displays the information transmitted from the control device 100. The input unit 160 and the display unit 170 may be configured as separate units, or may be formed integrally by being configured as a so-called touch panel display.

[0041] The control device 100 is connected to various actuators such as motors that serve as power sources for the operation of the injection molding machine 1, and various sensors that acquire information during operation of the injection molding machine 1. This allows the control device 100 to control the injection molding machine 1 by transmitting control signals to the actuators of the injection molding machine 1 while acquiring information during operation of the injection molding machine 1 using the sensors. The control device 100 can control the pressure of the resin material in the mold 75, for example, by controlling the movement of the screw 20 when the molten resin material is injected from the nozzle 12 of the heating barrel 11.

[0042] 5 is an explanatory diagram of the control device 100 shown in FIG. 1 . The control device 100 has a processing unit 110, a storage unit 140, and an input / output unit 150. The processing unit 110 has a CPU (Central Processing Unit) that performs arithmetic processing, and a RAM (Random Access Memory) and a ROM (Read Only Memory) that function as memories for storing various information. All or part of the functions of the processing unit 110 are realized by loading an application program stored in the ROM into the RAM and executing it on the CPU, thereby reading and writing data from and to the RAM and ROM.

[0043] The memory unit 140 is a storage device that is electrically connected to the processing unit 110 and stores information. When the control device 100 controls the injection molding machine 1, information acquired from the injection molding machine 1 by the processing unit 110 and information calculated by the processing unit 110 are stored in the memory unit 140, and the information stored in the memory unit 140 is called up by the processing unit 110 and used to control the injection molding machine 1.

[0044] Each function realized by the processing unit 110 may be stored in advance as a program in the storage unit 140. In this case, the processing unit 110 executes each function by calling up the program stored in the storage unit 140 and executing operations in accordance with the program in the processing unit 110. The storage unit 140 may be provided integrally with the control device 100, or may be configured to be detachable from the control device 100.

[0045] The input / output unit 150 is a so-called interface that inputs and outputs signals to and from devices external to the control device 100. That is, the various actuators and sensors of the injection molding machine 1, the input unit 160, and the display unit 170, which are connected to the control device 100, are connected to the input / output unit 150. Examples of the actuators and sensors connected to the input / output unit 150 include the heater 13 of the heating barrel 11 of the injection device 10, the drive motor 31 of the propulsion mechanism 30, the drive motor 43 of the rotation mechanism 40, the drive motor 51 and encoder 52 of the forward / reverse mechanism 50, and the load cell 60. The processing unit 110 of the control device 100 transmits and receives signals to and from these external devices via the input / output unit 150.

[0046] The processing unit 110 functionally includes a pressure loss acquisition unit 111, an injection pressure acquisition unit 112, a pressure loss calculation unit 113, a virtual mold internal pressure calculation unit 114, an injection pressure determination unit 115, a virtual mold internal pressure determination unit 116, and a movement control unit 120.

[0047] Of these, the pressure loss acquisition unit 111 is capable of calculating the pressure loss in the injection device 10 when the resin material is injected from the nozzle 12 of the heated barrel 11. Specifically, the pressure loss acquisition unit 111 acquires, as the pressure loss, the pressure detected by the load cell 60 when the resin material is injected from the nozzle 12 that is in contact with the fixed mold 76 when the fixed mold 76 and the movable mold 77 are in an open state. The pressure loss acquisition unit 111 also acquires the pressure loss by correlating it with the injection speed S of the screw 20 that is detected by the encoder 52 of the drive motor 51 of the forward / reverse mechanism 50. The pressure loss acquisition unit 111 associates the acquired pressure loss with the injection speed S, sets it as a pressure loss model M, and stores it in the storage unit 140.

[0048] The injection pressure acquisition unit 112 is capable of acquiring the injection pressure P when the molten resin material is injected from the heating barrel 11 into the cavity 75a of the mold 75. In detail, the injection pressure acquisition unit 112 acquires, as the injection pressure P, the pressure detected by the load cell 60 when the resin material is injected from the nozzle 12 into the cavity 75a in a state in which the fixed mold 76 and the movable mold 77 are closed. Furthermore, the injection pressure acquisition unit 112 acquires the injection pressure P in association with the injection speed S of the screw 20 detected by the encoder 52 of the drive motor 51 of the forward / reverse mechanism 50.

[0049] The pressure loss calculation unit 113 is capable of calculating the pressure loss in the injection device 10 when the resin material is injected from the nozzle 12 of the heating barrel 11, based on the pressure loss model M that has been set in advance and stored in the memory unit 140 and the injection speed S of the screw 20 detected by the encoder 52 of the drive motor 51 of the forward / reverse mechanism 50.

[0050] The virtual internal mold pressure calculation unit 114 is capable of calculating a virtual internal mold pressure V, which is the internal mold pressure that is the pressure of the resin material inside the mold 75 when the molten resin material is injected from the heating barrel 11 into the cavity 75a of the mold 75. The virtual internal mold pressure calculation unit 114 calculates the virtual internal mold pressure V, which is the virtual internal mold pressure, by subtracting the pressure loss acquired by the pressure loss acquisition unit 111 or the pressure loss based on the pressure loss acquired by the pressure loss acquisition unit 111 from the injection pressure P acquired by the injection pressure acquisition unit 112. In other words, the virtual internal mold pressure calculation unit 114 calculates the virtual internal mold pressure V by subtracting the pressure loss acquired by the pressure loss acquisition unit 111 or the pressure loss calculated by the pressure loss calculation unit 113 from the injection pressure P acquired by the injection pressure acquisition unit 112. In other words, the virtual internal mold pressure calculation unit 114 calculates the virtual internal mold pressure V by calculating [virtual internal mold pressure V = injection pressure P - pressure loss]. More specifically, the virtual mold internal pressure calculation unit 114 calculates the virtual mold internal pressure V by subtracting the pressure loss from the injection pressure P when the injection speed S is the same.

[0051] The injection pressure determination unit 115 is capable of determining whether the injection pressure P acquired by the injection pressure acquisition unit 112 has reached an upper limit set for the injection pressure P, based on the pressure detected by the load cell 60 when the resin material is injected from the heated barrel 11. The upper limit set for the injection pressure P in this case is set, for example, by selecting from pre-set values ​​according to the type of molded product to be molded by the injection molding machine 1 and the type of resin material used to mold the molded product, based on the type of molded product and resin material to be actually molded, or by the operator directly inputting the upper limit value. The set upper limit for the injection pressure P is stored in the storage unit 140.

[0052] The virtual mold pressure determination unit 116 is capable of determining whether the virtual mold pressure V calculated by the virtual mold pressure calculation unit 114 has reached an upper limit set for the virtual mold pressure V. In this case, the upper limit set for the virtual mold pressure V is set, for example, by selecting from preset values ​​corresponding to the type of molded product to be molded by the injection molding machine 1 and the type of resin material used to mold the molded product based on the type of molded product and resin material to be actually molded, or by directly inputting the upper limit value by the operator. The upper limit of the virtual mold pressure V is set to a value lower than the virtual mold pressure V when the injection pressure P reaches the upper limit PL. Specifically, the upper limit of the virtual mold pressure V is set to a value approximately equal to the maximum pressure of the resin material in the mold 75 when a good molded product is molded using the mold 75 whose cavity 75a is filled with resin material. The set upper limit of the virtual mold pressure V is stored in the memory unit 140.

[0053] The movement control unit 120 is capable of controlling the movement of the screw 20 when the resin material is injected from the heating barrel 11 of the injection device 10. The movement control unit 120 controls the drive motor 51 of the forward / backward movement mechanism 50, thereby operating the forward / backward movement mechanism 50 and controlling the movement of the screw 20.

[0054] Furthermore, when controlling the movement of the screw 20, the movement control unit 120 controls the movement by including the virtual mold internal pressure V calculated by the virtual mold internal pressure calculation unit 114 as a determination factor during control. In other words, when controlling the movement of the screw 20, the movement control unit 120 controls the movement based on the virtual mold internal pressure V calculated by the virtual mold internal pressure calculation unit 114.

[0055] Specifically, when controlling the movement of the screw 20 when injecting a resin material from the heated barrel 11 of the injection device 10, the movement control unit 120 basically controls the movement based on the injection speed S that is set for the position in the movement direction of the screw 20. Furthermore, when the injection pressure determination unit 115 determines that the injection pressure P has reached the upper limit set for the injection pressure P, or when the virtual internal mold pressure determination unit 116 determines that the virtual internal mold pressure V has reached the upper limit set for the virtual internal mold pressure V, the movement control unit 120 controls the movement of the screw 20 based on the injection pressure P acquired by the injection pressure acquisition unit 112 or the virtual internal mold pressure V calculated by the virtual internal mold pressure calculation unit 114. In other words, by controlling the movement of the screw 20 in this manner, the control device 100 controls the internal mold pressure, which is the pressure of the resin material in the mold 75.

[0056] The movement control unit 120 also includes a position controller 121 , a speed controller 122 , a current controller 123 , a pressure controller 124 , and a virtual mold internal pressure controller 125 .

[0057] 6 is an explanatory diagram showing the relationship between each controller of the movement control unit 120 and the injection device 10. The position controller 121 controls the position of the screw 20 in the movement direction when the resin material is injected from the nozzle 12 of the heating barrel 11, based on the position of the screw 20 in the movement direction detected by the encoder 52 of the drive motor 51 of the forward / backward movement mechanism 50. That is, the position controller 121 controls the position of the screw 20 while receiving feedback about the position of the screw 20 in the movement direction from the encoder 52 of the drive motor 51. The position controller 121 transmits a speed command corresponding to the position of the screw 20 in the movement direction detected by the encoder 52 to the speed controller 122.

[0058] The speed command transmitted from the position controller 121 to the speed controller 122 is based on the speed command stored in the storage unit 140. For example, the speed command input by an operator via the input unit 160 is stored in the storage unit 140. The speed command stored in the storage unit 140 is the upper limit value of the injection speed S of the screw 20, and the position controller 121 transmits a speed command corresponding to the position in the movement direction of the screw 20 to the speed controller 122 so that the final injection speed S of the screw 20 becomes the upper limit value.

[0059] The speed controller 122 controls the injection speed S of the screw 20 when injecting the resin material from the nozzle 12 of the heating barrel 11, based on the speed command sent from the position controller 121 and the injection speed S of the screw 20 detected by the encoder 52 of the drive motor 51 of the forward / backward movement mechanism 50. That is, the speed controller 122 controls the injection speed S of the screw 20 while receiving feedback on the injection speed S of the screw 20 from the encoder 52 of the drive motor 51. The speed controller 122 sends to the current controller 123 a current value for driving the drive motor 51 of the forward / backward movement mechanism 50, which can move the screw 20 at the injection speed S corresponding to the position in the movement direction of the screw 20.

[0060] The current controller 123 controls the drive of the drive motor 51 of the forward / reverse mechanism 50 based on the current value transmitted from the speed controller 122. The current controller 123 controls the drive of the drive motor 51 of the forward / reverse mechanism 50 by feeding back the current value output from the current controller 123 and comparing it with the current value transmitted from the speed controller 122. The drive control of the drive motor 51 by the current controller 123 is performed via an amplifier 180 that amplifies the power supplied to the drive motor 51.

[0061] When the injection pressure determination unit 115 determines that the injection pressure P has reached its upper limit, the pressure controller 124 controls the movement of the screw 20 based on the injection speed S that is set as the injection speed S when the injection pressure P has reached its upper limit. The upper limit that is set for the injection pressure P and the injection speed S that is set as the injection speed S when the injection pressure P has reached its upper limit are set in advance as pressure commands and stored in the storage unit 140. As the pressure command, for example, a value input by the operator from the input unit 160 is stored in the storage unit 140.

[0062] The injection speed S, which is set as the injection speed S when the injection pressure P reaches the upper limit, is set to a speed slower than the injection speed S, which is set as the injection speed S when the injection pressure P does not reach the upper limit. The pressure controller 124 receives feedback on the injection pressure P from the load cell 60 and compares the injection pressure P with the upper limit in the injection pressure determination unit 115, and when it is determined that the injection pressure P has reached the upper limit, the pressure controller 124 controls the movement of the screw 20.

[0063] When the virtual mold internal pressure determination unit 116 determines that the virtual mold internal pressure V has reached its upper limit, the virtual mold internal pressure controller 125 controls the movement of the screw 20 based on the injection speed S, which is set as the injection speed S when the virtual mold internal pressure V has reached its upper limit. The upper limit set for the virtual mold internal pressure V and the injection speed S, which is set as the injection speed S when the virtual mold internal pressure V has reached its upper limit, are set in advance as a virtual mold internal pressure command and stored in the storage unit 140. As the virtual mold internal pressure command, for example, a value input by the operator from the input unit 160 is stored in the storage unit 140.

[0064] The injection speed S, which is set as the injection speed S when the virtual mold internal pressure V has reached its upper limit, is set to a speed slower than the injection speed S, which is set as the injection speed S when the virtual mold internal pressure V has not reached its upper limit. The virtual mold internal pressure controller 125 compares the virtual mold internal pressure V with the upper limit in the virtual mold internal pressure determination unit 116 based on feedback of the injection speed S of the screw 20 from the encoder 52 of the drive motor 51 and the pressure loss model M, and when it is determined that the virtual mold internal pressure V has reached its upper limit, the virtual mold internal pressure controller 125 controls the movement of the screw 20.

[0065] Next, the pressure loss acquired by the pressure loss acquisition unit 111 will be described. FIG. 7 is an explanatory diagram showing an example of a pressure loss model M. The pressure loss acquired by the pressure loss acquisition unit 111 is stored as a pressure loss model M that associates the injection speed S of the screw 20 when the screw 20 is moved within the heating barrel 11 to inject the molten resin material from the nozzle 12 with the pressure loss for each injection speed S. The pressure loss in this case is the pressure lost in the heating barrel 11 when the molten resin material is injected from the heating barrel 11. Specifically, the pressure loss in this case is the pressure lost due to the resistance of the resin material when passing through the nozzle 12 and the sliding resistance of the screw 20 relative to the heating barrel 11 when the screw 20 is moved within the heating barrel 11 to inject the resin material from the heating barrel 11.

[0066] The pressure loss model M is set for each type of resin material, for example, as shown in Fig. 7. The pressure loss model M shown in Fig. 7 shows pressure loss models M for three types of resin materials: resin A, resin B, and resin C. The pressure loss model M is set by actually measuring in advance the pressure loss when the resin material is injected from the heating barrel 11 for each injection speed S of the screw 20.

[0067] <Method for Measuring Pressure Loss> Next, a method for measuring pressure loss by actual measurement will be described. FIG. 8 is a schematic diagram showing a method for measuring pressure loss in the mold cavity pressure detection method according to the embodiment. When measuring pressure loss when injecting a resin material from the heated barrel 11 by actual measurement, the nozzle 12 is brought into contact with the fixed mold 76 with the fixed mold 76 and the movable mold 77 open, and the resin material is injected from the nozzle 12, and the pressure detected by the load cell 60 is obtained as the pressure loss. In other words, when the resin material is injected with the fixed mold 76 and the movable mold 77 open, the resin material does not fill the mold 75, and therefore the pressure of the resin material, which is the same as when filling the mold 75, does not act on the screw 20 extruding the resin material. Therefore, when the resin material is injected with the fixed mold 76 and the movable mold 77 open, only the pressure based on the resistance when injecting the resin material from the heated barrel 11 acts on the screw 20 extruding the resin material.

[0068] Therefore, the value detected by the load cell 60 when the nozzle 12 is brought into contact with the fixed mold 76 with the fixed mold 76 and the movable mold 77 open and the resin material is injected from the nozzle 12 can be used as the pressure lost in the heated barrel 11 during injection of the resin material. In this embodiment, when obtaining the pressure loss during injection of the resin material from the heated barrel 11, the pressure detected during in-mold purging, which is purging performed with the fixed mold 76 and the movable mold 77 open and the nozzle 12 in contact with the fixed mold 76, is obtained as the pressure loss. This makes it possible to obtain the pressure loss during injection of the resin material with high accuracy.

[0069] That is, since the temperature of the mold 75 is generally lower than the temperature of the nozzle 12, the temperature of the nozzle 12 drops when the nozzle 12 comes into contact with the mold 75. Accordingly, the temperature of the resin material located in the nozzle 12 area also drops, and the viscosity of the resin material located in the nozzle 12 area increases. Therefore, the pressure loss of the resin material injected from the nozzle 12 increases when it passes through the nozzle 12 area.

[0070] FIG. 9 is a schematic diagram showing a measurement method for measuring pressure loss with the nozzle 12 separated from the mold 75. FIG. 10 is an explanatory diagram comparing the results of pressure loss measurements with the nozzle 12 in contact with the mold 75 and with the nozzle 12 separated from the mold 75. The pressure loss during mold purging, Lm, which is the pressure loss obtained during mold purging, is larger than the pressure loss during resin purging, Lr, which is the pressure loss obtained during resin purging, which is purging performed with the nozzle 12 separated from the mold 75, as shown in FIG. 9 . In other words, the pressure loss during resin purging, Lr, is the pressure detected by the load cell 60 when the nozzle 12 of the heated barrel 11 is separated from the mold 75 and the molten resin material is injected outside the mold 75.

[0071] As shown in FIG. 10 , the pressure loss Lm during mold purging acquired during mold purging is higher than the pressure loss Lr during resin purging acquired during resin purging. That is, when the resin material is injected with the nozzle 12 separated from the mold 75, the screw 20 is not subjected to pressure from the resin material in the mold 75 when the resin material is filled into the mold 75. However, because the nozzle 12 is separated from the mold 75, the temperature of the nozzle 12 does not decrease. Therefore, the temperature of the resin material located in the nozzle 12 area does not decrease, and the viscosity of the resin material located in the nozzle 12 area is maintained low. Therefore, the resin material injected from the nozzle 12 passes through the nozzle 12 area without increasing pressure loss.

[0072] 10, when the pressure loss Lm during mold purging is compared with the pressure loss Lr during resin purging, the pressure loss Lm during mold purging is greater than the pressure loss Lr during resin purging, but during actual molding, the resin material is injected with the nozzle 12 in contact with the mold 75. Therefore, the pressure loss Lm during mold purging, which is the pressure loss obtained during mold purging, can be obtained as a pressure loss closer in magnitude to the pressure loss during actual molding than the pressure loss Lr during resin purging, which is the pressure loss obtained during resin purging.

[0073] <Comparison of Virtual Mold Pressures> Next, a comparison will be described between the virtual mold pressure Vm calculated using the pressure loss Lm during mold purging and the virtual mold pressure Vr calculated using the pressure loss Lr during resin purging. Fig. 11 is an explanatory diagram showing a comparison between the virtual mold pressure Vm calculated using the pressure loss Lm during mold purging and the virtual mold pressure Vr calculated using the pressure loss Lr during resin purging, and the measured mold pressure Va. Fig. 12 is a schematic diagram showing a method for measuring the measured mold pressure Va. When the virtual mold pressure calculation unit 114 calculates the virtual mold pressure V, it calculates it by subtracting the pressure loss acquired by the pressure loss acquisition unit 111 from the injection pressure P acquired by the injection pressure acquisition unit 112. Here, we will explain the comparison between the virtual mold pressure Vm calculated using the pressure loss Lm during mold purging, the virtual mold pressure Vr calculated using the pressure loss Lr during resin purging, and the actual mold pressure Va, which is the mold pressure actually measured when resin material is injected into the mold 75.

[0074] The inventors of the present application measured the actual mold pressure Va using a mold 75 equipped with a load sensor 200 as shown in Fig. 12, and compared the measured actual mold pressure Va with a virtual mold pressure Vm during mold purging calculated using a pressure loss Lm during mold purging and a virtual mold pressure Vr during resin purging calculated using a pressure loss Lr during resin purging. In the mold 75 shown in Fig. 12, the load sensor 200 is attached to an ejector pin 87 of an ejector mechanism 85.

[0075] The ejector pins 87 are disposed in the movable mold 77, with one end facing the cavity 75a. A ejector plate 88 of the ejector mechanism 85 is disposed on the other end of the ejector pins 87 in the movable mold 77. The ejector mechanism 85 applies a load to the ejector plate 88 with an ejector member 86 (see FIG. 1 ) to push the ejector pins 87 toward the cavity 75a with the ejector plate 88, thereby enabling the molded product to be pushed out by the ejector pins 87 and removed from the movable mold 77.

[0076] 12, when a resin material is injected from the nozzle 12 of the heated barrel 11 into the cavity 75a of the mold 75, the ejector pin 87 is pressed by the resin material in the cavity 75a, and the load applied to the ejector pin 87 is detected by the load sensor 200. The measured internal mold pressure Va is calculated by calculating Va=F / A based on the load F detected by the load sensor 200 and the cross-sectional area A of the ejector pin 87 in the direction in which the pressure from the resin material acts on the ejector pin 87.

[0077] Since the virtual internal mold pressure V is calculated by subtracting the pressure loss acquired by the pressure loss acquisition unit 111 from the injection pressure P acquired by the injection pressure acquisition unit 112, the virtual internal mold pressure V is lower than the injection pressure P. At that time, the pressure loss Lm during mold purging is greater in value than the pressure loss Lr during resin purging. Therefore, the virtual internal mold pressure Vm during mold purging calculated by subtracting the pressure loss Lm during mold purging from the injection pressure P is smaller in value than the virtual internal mold pressure Vr during resin purging calculated by subtracting the pressure loss Lr during resin purging from the injection pressure P.

[0078] The hypothetical mold pressure Vm during mold purging, which is smaller than the hypothetical mold pressure Vr during resin purging, is closer in magnitude to the measured mold pressure Va, as shown in Fig. 11. That is, when the hypothetical mold pressure Vm during mold purging and the hypothetical mold pressure Vr during resin purging are compared, the hypothetical mold pressure Vm during mold purging is closer to the measured mold pressure Va than the hypothetical mold pressure Vr during resin purging. Therefore, the pressure loss Lm during mold purging, which can be used to calculate the hypothetical mold pressure Vm during mold purging that is closer to the measured mold pressure Va, can be used as the pressure loss in the heated barrel 11 when the resin material is injected during actual molding.

[0079] <Modeling of pressure loss Lm during in-mold purging> When setting the pressure loss model M, the pressure loss Lm during in-mold purging for each injection speed S is acquired by the pressure loss acquisition unit 111, and an approximation model of the acquired pressure loss Lm during in-mold purging is derived and modeled to set the pressure loss model M. Next, modeling of the pressure loss Lm during in-mold purging will be described.

[0080] In deriving an approximation model of the pressure loss Lm during in-mold purging acquired by the pressure loss acquisition unit 111, the inventors of the present application focused on a quadratic function approximation model and a power approximation model, and compared these approximation models. The quadratic function approximation model here is an approximation model that can be expressed by the following formula (1). The power approximation model is an approximation model that can be expressed by the following formula (2). In the following formulas (1) and (2), a, b, and c are approximation coefficients. x is the injection speed. y is the pressure loss. y=ax ２ +bx+c...(1) y=ax ｂ ... (2)

[0081] The inventors of the present application have studied the mean absolute error rate (hereinafter referred to as the error rate) for each resin material in order to quantitatively judge the comparison between the quadratic function approximation model and the power approximation model. First, the procedure for calculating the error rate will be explained. When calculating the error rate, the difference x between the actual measured value and the predicted value when the total number of data is n is ｎ is calculated using the following formula (3): ｎ = measured value - predicted value ... (3)

[0082] Next, x calculated by equation (1) ｎ is divided by the measured value as shown in (4) below, and the absolute value y ｎ Find y ｎ = | x ｎ / measured value | ... (4)

[0083] The error rate is calculated using the formula (4) ｎ The error rate can be calculated by dividing the sum of the data by the number of data n as shown in the following formula (5). １ +y ２ +...+y ｎ ) / n ... (5)

[0084] Considering these, the error rate of the quadratic function approximation model and the power approximation model is calculated by using the actual measurement data of the pressure loss Lm during purging inside the mold, which is acquired by the pressure loss acquisition unit 111, as a ｎ Then, the approximate model data β ｎ The error rate was calculated and derived using the following formula (6) with the number of data being n. ｎ -βｎ ) / α ｎ |n ... (6)

[0085] Fig. 13 is a chart comparing the error rates of the quadratic function approximation model and the power approximation model. The inventors of the present application measured the pressure loss when melting and injecting a resin material in the heated barrel 11, and calculated the error rates of the quadratic function approximation model and the power approximation model using the above formula (6). As a result, the results shown in Fig. 13 were obtained. Fig. 13 shows an example of the calculation results of the error rates when ABS material, PP (polypropylene) material, and PC (polycarbonate) material are used as the resin materials injected from the nozzle 12.

[0086] When the quadratic function approximation model and the power approximation model are compared, as shown in FIG. 13, the quadratic function approximation model has a lower error rate than the power approximation model, and the results indicate that the quadratic function approximation model is more suitable for modeling the pressure loss Lm during in-mold purging.

[0087] In order to model the pressure loss Lm during in-mold purging using a quadratic function approximation model, an approximation formula is derived. In deriving the approximation formula for the quadratic function approximation model, the coefficients a, b, and c of the approximation formula are derived after measuring the pressure loss, using x as the injection speed, y as the pressure loss, and n as the number of data. Of the coefficients a, b, and c of the approximation formula, the coefficient a can be derived from the following formula (7).

[0088]

[0089] The elements A, B, C, D, E, and F in formula (7) can be derived from the following formulas (8), (9), (10), (11), (12), and (13), respectively.

[0090]

[0091]

[0092]

[0093]

[0094]

[0095]

[0096] The coefficient b can be derived from the following equation (14).

[0097]

[0098] The coefficient c can be derived from the following equation (15).

[0099]

[0100] From these, the coefficients a, b, and c of the approximation formula of the quadratic function approximation model can be derived, and the pressure loss Lm during in-mold purging can be modeled using the approximation formula of the quadratic function approximation model expressed as in (1) above.

[0101] The pressure loss acquisition unit 111 models the pressure loss Lm during in-mold purging using an approximation formula of a quadratic function approximation model based on the previously acquired pressure loss Lm during in-mold purging. The pressure loss acquisition unit 111 sets the approximation model of the modeled pressure loss Lm during in-mold purging as a pressure loss model M and stores it in the storage unit 140.

[0102] <Operation of Injection Molding Machine 1> The injection molding machine 1 according to this embodiment includes the configuration described above, and its operation will be described below. The injection molding machine 1 repeatedly executes a cycle of injection and molding operations, with one injection and molding operation being one cycle. Each cycle includes multiple steps for injecting molding material and molding a product. Each cycle includes, for example, a mold closing step, a filling step, a pressure holding step, a mold opening step, and an ejection step.

[0103] The mold closing process is a process in which the movable platen 72 of the mold clamping device 70 is moved in a direction approaching the fixed platen 71, thereby combining the movable mold 77 and the fixed mold 76 and forming a cavity 75a corresponding to the product shape between the movable mold 77 and the fixed mold 76.

[0104] The filling process is a process in which molten resin, which is a resin material melted by the heated barrel 11 of the injection device 10, is injected into a cavity 75a formed by a movable mold 77 and a fixed mold 76 attached to the mold clamping device 70.

[0105] The pressure dwelling process is a process in which the pressure of the molding resin, which is the resin material injected into the cavity 75a formed by the movable mold 77 and fixed mold 76 attached to the mold clamping device 70, is maintained, and the process waits for a certain period of time until the temperature of the molding resin drops and solidifies, turning the molding resin into a molded product. Also, in the pressure dwelling process, the resin material to be injected in the next cycle is sent to the end side of the heating barrel 11 of the injection device 10 where the nozzle 12 is located, and the resin material to be used in the next cycle is prepared; the resin material is also measured during the pressure dwelling process.

[0106] The mold opening process is a process in which the movable platen 72 is moved away from the fixed platen 71 and the movable mold 77 is moved away from the fixed mold 76 in order to remove the molded product formed by the fixed mold 76 and the movable mold 77 attached to the mold clamping device 70.

[0107] The removal process is a process in which, after the movable mold 77 is separated from the fixed mold 76, the molded product attached to the movable mold 77 is pushed out by the extrusion member 86 of the extrusion mechanism 85, thereby removing the molded product from the mold 75.

[0108] When molding a molded product using the injection molding machine 1, these injection and molding operation cycles are repeatedly executed to continuously mold the molded product. When injecting molten resin material into the mold 75 in the filling process, it is necessary to appropriately control the pressure of the resin material inside the mold 75. To do this, it is necessary to detect the mold pressure with high accuracy. Next, a procedure for detecting the mold pressure with high accuracy will be described.

[0109] Calculation of Virtual Mold Pressure: Figure 14 is a flow diagram showing the procedure for calculating the virtual mold pressure. To accurately detect the mold pressure, in this embodiment, before molding an actual molded product, the injection molding machine 1 first performs mold purging to acquire various data (step ST11). Specifically, the nozzle 12 is brought into contact with the fixed mold 76, with the fixed mold 76 and the movable mold 77 in an open position, and resin material is injected from the nozzle 12 to perform mold purging (see Figure 8). During this process, the pressure detected by the load cell 60 during mold purging is acquired as a pressure loss by the pressure loss acquisition unit 111 of the processing unit 110 of the control device 100.

[0110] Furthermore, the pressure loss acquisition unit 111 acquires the pressure loss in association with the injection speed S based on the detection result from the encoder 52 of the drive motor 51 of the forward / reverse mechanism 50. In this way, when acquiring data while performing in-mold purging, it is preferable to change the injection speed S and acquire data for three or more shots.

[0111] Next, the acquired data are input into the equation for calculating the approximation coefficients (step ST12). That is, the acquired data are used to calculate the above-mentioned equations (7), (14), and (15), thereby obtaining the approximation coefficients a, b, and c of the quadratic function.

[0112] Next, an approximate equation of a quadratic function is created (step ST13). That is, the pressure loss acquisition unit 111 creates an approximate equation of a quadratic function from the above-mentioned equation (1) using the approximate coefficients a, b, and c acquired in step ST12. In this way, the pressure loss acquisition unit 111 can set the pressure loss model M by creating an approximate equation of a quadratic function.

[0113] Once the quadratic function approximation equation has been created, the injection molding machine 1 begins molding the molded product that will become the actual product (step ST14). Once molding has begun in the injection molding machine 1, data on the calculated pressure loss and the measured injection pressure are acquired while molding is being performed (step ST15). That is, while molding is being performed in the injection molding machine 1, the pressure loss calculation unit 113 of the processing unit 110 of the control device 100 calculates the pressure loss when injecting the resin material based on the injection speed S detected by the encoder 52 of the drive motor 51 of the forward / reverse mechanism 50 and the quadratic function approximation equation created in step ST13. In other words, the pressure loss is calculated based on the injection speed S detected while molding is being performed in the injection molding machine 1 and the set pressure loss model M. The pressure loss calculation unit 113 calculates the pressure loss in association with the injection speed S.

[0114] Furthermore, while molding is being performed by the injection molding machine 1, the injection pressure acquisition unit 112 included in the processing unit 110 of the control device 100 acquires the pressure detected by the load cell 60 as the injection pressure P. The injection pressure acquisition unit 112 acquires the injection pressure P in association with the injection speed S.

[0115] Next, the pressure loss is subtracted from the injection pressure P to calculate the virtual internal mold pressure V (step ST16). The calculation of the virtual internal mold pressure V is performed by a virtual internal mold pressure calculation unit 114 included in the processing unit 110 of the control device 100. The virtual internal mold pressure calculation unit 114 calculates the virtual internal mold pressure V by subtracting the pressure loss calculated by the pressure loss calculation unit 113 from the injection pressure P acquired by the injection pressure acquisition unit 112.

[0116] In this case, the pressure loss calculated by the pressure loss calculation unit 113 is found from an approximation equation of a quadratic function created from the pressure loss Lm during mold purging, which is the pressure loss obtained by purging the mold interior (see FIG. 10 ). Therefore, the virtual mold pressure V calculated by the virtual mold pressure calculation unit 114 is the virtual mold pressure Vm during mold purging, which is the virtual mold pressure V calculated using the pressure loss Lm during mold purging calculated by the pressure loss calculation unit 113.

[0117] 11, the virtual mold pressure Vm during mold purging is closer in magnitude to the measured mold pressure Va than the virtual mold pressure Vr during resin purging, which is the virtual mold pressure V calculated using the pressure loss Lr during resin purging. Therefore, in this embodiment, a virtual mold pressure V close in magnitude to the measured mold pressure Va can be calculated, and the mold pressure can be controlled using the virtual mold pressure V close in magnitude to the measured mold pressure Va.

[0118] <Pressure Control During Injection Molding> Next, pressure control when injecting resin material into mold 75 in the filling step will be described. Fig. 15 is an explanatory diagram showing changes in injection speed S, injection pressure P, and virtual mold internal pressure V when molding a non-defective product. When injecting resin material from the heated barrel 11 of the injection device 10 into mold 75 in the filling step, the movement control section 120 of the control device 100 uses a position controller 121 to detect the position of the screw 20 that moves during injection, as detected by the encoder 52 of the drive motor 51 of the forward / backward movement mechanism 50, and uses a speed controller 122 to control the speed of the screw 20 in accordance with the position of the screw 20.

[0119] When the speed of the screw 20 is controlled by the speed controller 122, the injection speed S of the screw 20 is controlled in accordance with the set value of the injection speed S when the speed control is performed based on the movement position of the screw 20. The set value of the injection speed S is set, for example, by an operator directly inputting the set value of the injection speed S. The set value of the injection speed S may be set by selecting from preset values ​​according to the type of molded product to be molded by the injection molding machine 1, the type of resin material used to mold the molded product, etc., based on the type of molded product and resin material to be actually molded, etc.

[0120] The set value of the injection speed S is stored in the storage unit 140 of the control device 100. When controlling the speed of the screw 20, the set value of the injection speed S stored in the storage unit 140 is used as a target value, and a speed command according to the position of the screw 20 is sent by the position controller 121 to the speed controller 122, and speed control is performed by the speed controller 122. The speed controller 122 controls the speed of the screw 20 based on the speed command sent from the position controller 121, while receiving feedback of the injection speed S from the encoder 52 of the drive motor 51 of the forward / reverse mechanism 50.

[0121] For these reasons, the position controller 121 and the speed controller 122 control the injection speed S of the screw 20 during the filling process so that the injection speed S of the screw 20 becomes a set value, which is a target value of the injection speed S, and once the injection speed S of the screw 20 reaches the set value, the injection speed S is maintained. In this case, the resin material is filled into the mold 75 over time, and the pressure of the resin material increases over time within the mold 75. Therefore, the pressure of the resin material within the heated barrel 11 also increases, and the injection pressure P acting on the screw 20 when injecting the resin material also increases as the resin material is filled into the mold 75 and the pressure of the resin material within the mold 75 increases.

[0122] Note that the resin material is filled into the cavity 75a of the mold 75 after the runner connected to the cavity 75a is filled with the resin material. Therefore, even after the screw 20 starts to move toward the side where the nozzle 12 is located, the injection pressure P does not increase immediately, but increases after the runner is filled with the resin material. During the filling process, the injection pressure determination unit 115 continuously determines whether the increasing injection pressure P has reached an upper limit value PL set for the injection pressure P.

[0123] When controlling the movement of the screw 20 in the filling process, the pressure loss calculation unit 113 of the control device 100 calculates the pressure loss in the injection device 10 when injecting the resin material based on the injection speed S detected by the encoder 52 of the drive motor 51 of the forward / reverse mechanism 50 and the pressure loss model M stored in the storage unit 140. In this case, the pressure loss model M is the pressure loss model M of the pressure loss Lm during in-mold purging, and the pressure loss calculation unit 113 calculates the pressure loss when injecting the resin material based on the pressure loss model M of the pressure loss Lm during in-mold purging and the injection speed S. In addition, when a plurality of pressure loss models M are stored in the storage unit 140 according to the type of resin material, etc., the pressure loss model M that matches the conditions of the current injection molding, such as the type of resin material, is used.

[0124] After the pressure loss in the injection device 10 is calculated by the pressure loss calculation unit 113, the virtual mold pressure calculation unit 114 of the control device 100 calculates the virtual mold pressure V, which is the pressure of the resin material in the mold 75, by subtracting the pressure loss calculated by the pressure loss calculation unit 113 from the injection pressure P acquired by the injection pressure acquisition unit 112 based on the pressure detected by the load cell 60. More specifically, the pressure loss calculated by the pressure loss calculation unit 113 is calculated based on the pressure loss model M of the pressure loss Lm during mold purging, and therefore the virtual mold pressure V calculated by the virtual mold pressure calculation unit 114 is the virtual mold pressure Vm during mold purging calculated using the pressure loss Lm during mold purging. When the movement of the screw 20 is controlled in the filling process, the virtual mold pressure V is continuously calculated by the pressure loss calculation unit 113 and the virtual mold pressure calculation unit 114 in this manner. In the filling step, the virtual mold internal pressure V thus obtained also increases, similar to the injection pressure P, as the resin material is filled into the mold 75 and the pressure of the resin material inside the mold 75 increases.

[0125] Note that, since the resin material is filled into the cavity 75a of the mold 75 after the resin material has been filled into the runner connected to the cavity 75a, the virtual internal mold pressure V also rises after the screw 20 starts to move toward the side where the nozzle 12 is located and the resin material has been filled into the runner, similar to the injection pressure P. During the filling process, the virtual internal mold pressure V, which rises in this way, is continuously judged by the virtual internal mold pressure judging unit 116 as to whether it has reached an upper limit value set for the virtual internal mold pressure V.

[0126] In this way, the screw 20 is moved within the heating barrel 11 while maintaining the injection speed S of the screw 20 at a set value, and when the position of the screw 20 reaches the switching position H, which is the reference position for switching between the filling process and the pressure holding process, the injection speed S is reduced. By reducing the injection speed S in the pressure holding process, the injection pressure P acting on the screw 20 and the virtual mold pressure V in the mold 75 also decrease as the injection speed S decreases.

[0127] Even after switching to the pressure holding process, the screw 20 slows down the injection speed S and moves to the side where the nozzle 12 is located to slightly feed the resin material into the cavity 75a of the mold 75. This allows the resin material to be fed into the cavity 75a, where the resin material is cooled and shrinks slightly during the pressure holding process, even during the pressure holding process, thereby suppressing sink marks on the molded product.

[0128] 16 is an explanatory diagram showing a state in which the injection pressure P reaches its upper limit PL when the control device 100 does not have the virtual mold internal pressure determination unit 116 and does not determine whether the virtual mold internal pressure V has reached its upper limit. In the filling step, the resin material is filled into the cavity 75a of the mold 75 by moving the screw 20 within the heated barrel 11 as described above, but partial clogging may occur during filling of the resin material. If partial clogging occurs during filling of the resin material in this way, the injection pressure P is likely to rise.

[0129] For example, if the mold 75 has multiple cavities 75a capable of molding a molded product, and a clog occurs in a gate connected to one of the cavities 75a, the resin material will no longer be able to fill the clogged cavity 75a. In this case, the space in the mold 75 that can be filled with the resin material will become smaller, and therefore, when the screw 20 is moved to feed the resin material from the heated barrel 11 into the mold 75, the injection pressure P acting on the screw 20 will likely increase.

[0130] In the filling process, the injection pressure determination unit 115 continuously determines whether the injection pressure P has reached an upper limit PL set for the injection pressure P, and when the injection pressure P increases to reach the upper limit PL, the injection pressure determination unit 115 determines that the injection pressure P has reached the upper limit PL. When the injection pressure determination unit 115 determines that the injection pressure P detected by the load cell 60 has reached the upper limit PL, the movement control unit 120 of the control device 100 controls the movement of the screw 20 based on the injection speed S set as the injection speed S when the injection pressure P has reached the upper limit PL. In other words, when the injection pressure determination unit 115 determines that the injection pressure P has reached the upper limit PL set in advance and stored in the memory unit 140, the movement control unit 120 controls the movement of the screw 20 using the pressure control controller 124.

[0131] When the injection pressure determination unit 115 determines that the injection pressure P has reached the upper limit PL, the pressure controller 124 controls the movement of the screw 20 so that the injection speed S becomes 0. That is, when the injection pressure P has reached the upper limit PL, the pressure controller 124 gradually reduces the injection speed S and stops the movement of the screw 20 toward the side where the nozzle 12 is located. This stops the filling of the resin material from the heated barrel 11 into the mold 75.

[0132] However, in the filling process, after a clog occurs in a gate connected to one of the cavities 75a, the filling of the resin material from the heating barrel 11 into the mold 75 continues until it is determined that the injection pressure P has reached the upper limit PL. Therefore, the filling of the resin material continues into the cavities 75a other than the cavities 75a connected to the clogged gate. In this state, the fact that the injection pressure P has reached the upper limit PL means that the pressure of the resin material in the cavities 75a being filled with the resin material is also increasing.

[0133] Therefore, in the cavity 75a filled with the resin material, burrs may occur in the molded product molded in that cavity 75a due to the pressure of the resin material. Burrs may also occur in the runners connected to the cavity 75a. Molded products with burrs are deemed defective, so if a blockage occurs in the gate connected to one of the cavities 75a, not only the molded product molded in the clogged cavity 75a but also the molded products molded in the other cavities 75a will be disposed of as defective products.

[0134] 17 is an explanatory diagram showing a state in which the control device 100 has a virtual mold internal pressure determination unit 116 and the virtual mold internal pressure V has reached the upper limit value VL. In this embodiment, the control device 100 has the virtual mold internal pressure determination unit 116 that determines whether the virtual mold internal pressure V has reached the upper limit value VL. Therefore, even if a blockage occurs in a gate connected to some of the cavities 75a during the filling process, it is possible to prevent defects from occurring in molded products molded in the other cavities 75a.

[0135] In other words, if a clog occurs in a gate connected to some of the cavities 75a during the filling process, the clogged cavities 75a cannot be filled, and the resin material sent from the heated barrel 11 to the mold 75 will instead fill the other cavities 75a. In this case, when there are cavities 75a that cannot be filled with resin material, the space in the mold 75 that can be filled with resin material becomes smaller, but the amount of resin material sent from the heated barrel 11 remains the same as usual, so the pressure of the resin material is likely to increase in cavities 75a that are not clogged.

[0136] In this embodiment, the pressure loss calculation unit 113 calculates the pressure loss in the injection device 10 based on the injection speed S detected by the encoder 52 and the pressure loss model M, and the virtual internal mold pressure calculation unit 114 calculates the virtual internal mold pressure V by subtracting the pressure loss calculated by the pressure loss calculation unit 113 from the injection pressure P detected by the load cell 60. In this case, the pressure loss calculated by the pressure loss calculation unit 113 is calculated based on the pressure loss model M of the pressure loss Lm during mold purging, so the virtual internal mold pressure calculation unit 114 calculates the virtual internal mold pressure Vm during mold purging as the virtual internal mold pressure V.

[0137] Furthermore, a virtual mold pressure determination unit 116 determines whether the virtual mold pressure V calculated by the virtual mold pressure calculation unit 114 has reached an upper limit value VL set for the virtual mold pressure V, and if the virtual mold pressure determination unit 116 determines that the virtual mold pressure V has reached the upper limit value VL, a movement control unit 120 controls the movement of the screw 20 based on the virtual mold pressure V. That is, if the virtual mold pressure determination unit 116 determines that the virtual mold pressure V calculated by the virtual mold pressure calculation unit 114 has reached the upper limit value VL, the movement control unit 120 of the control device 100 controls the movement of the screw 20 based on the injection speed S, which is set as the injection speed S when the virtual mold pressure V has reached the upper limit value VL.

[0138] The upper limit value VL of the virtual mold internal pressure V used for judgment in the virtual mold internal pressure judgment unit 116 is set to a value lower than the virtual mold internal pressure V when the injection pressure P reaches the upper limit value PL, and is set to a magnitude approximately equal to the maximum value of the pressure of the resin material inside the mold 75 when a non-defective product is molded with the mold 75. When the virtual mold internal pressure judgment unit 116 judges that the virtual mold internal pressure V calculated by the virtual mold internal pressure calculation unit 114 has reached the upper limit value VL set in advance and stored in the memory unit 140, the movement control unit 120 controls the movement of the screw 20 using the virtual mold internal pressure controller 125.

[0139] When the virtual mold pressure determination unit 116 determines that the virtual mold pressure V has reached the upper limit VL, the virtual mold pressure controller 125 controls the movement of the screw 20 so that the injection speed S becomes 0. That is, when the virtual mold pressure V has reached the upper limit VL, the virtual mold pressure controller 125 gradually reduces the injection speed S and stops the movement of the screw 20 toward the side where the nozzle 12 is located. This stops the filling of the resin material from the heating barrel 11 into the mold 75. In this case, the virtual mold pressure V calculated by the virtual mold pressure calculation unit 114 is calculated based on the injection pressure P acquired by the injection pressure acquisition unit 112, and therefore, when the injection pressure P increases, the virtual mold pressure V also increases in accordance with the increase in injection pressure P.

[0140] On the other hand, the upper limit VL of the virtual mold pressure V is set to a value lower than the virtual mold pressure V when the injection pressure P reaches the upper limit PL, and is set to a value approximately equal to the maximum pressure of the resin material inside the mold 75 when a non-defective product is molded using the mold 75. For this reason, in a situation where the injection pressure P increases due to clogging of the gates connected to some of the cavities 75a, when the filling of the resin material into the mold 75 is stopped because the virtual mold pressure V reaches the upper limit VL, the pressure of the resin material inside the mold 75 other than the cavities 75a where the clogging has occurred will be approximately equal to the pressure of the resin material when a non-defective product is molded.

[0141] As a result, even if a gate connected to some of the cavities 75a is clogged, the pressure of the resin material in the other cavities 75a and runners will be about the same as when a good product is molded, so good products can be molded without generating burrs. Therefore, even if a gate connected to some of the cavities 75a is clogged, good products can be molded in the cavities 75a other than the clogged cavity 75a, so the occurrence of defective products can be reduced.

[0142] <Effects of the embodiment> In the injection molding machine 1 according to the above embodiment, the pressure detected by the load cell 60 when the resin material is injected from the nozzle 12 in contact with the fixed mold 76 in a state where the fixed mold 76 and the movable mold 77 are open is acquired as a pressure loss by the pressure loss acquisition unit 111, and the pressure detected by the load cell 60 when the resin material is injected from the nozzle 12 into the cavity 75 a in a state where the fixed mold 76 and the movable mold 77 are closed is acquired as an injection pressure P by the injection pressure acquisition unit 112. The virtual internal mold pressure calculation unit 114 calculates the virtual internal mold pressure V by subtracting the pressure loss acquired by the pressure loss acquisition unit 111 from the injection pressure P acquired by the injection pressure acquisition unit 112 as described above. Therefore, it is possible to calculate the virtual internal mold pressure V based on the pressure loss in a state where the viscosity of the resin material increases as a result of the nozzle 12 coming into contact with the mold 75 and the temperature of the nozzle 12 decreasing.

[0143] This allows the conditions for calculating the virtual mold pressure V to be closer to the conditions when the nozzle 12 is brought into contact with the mold 75 during actual molding to fill the mold 75 with resin material, and the calculated virtual mold pressure V can be made as close as possible to the magnitude of the mold pressure during actual molding. In other words, as shown in Figure 11, the virtual mold pressure Vm during mold purging is closer to the actually measured mold pressure Va than the virtual mold pressure Vr during resin purging, so the virtual mold pressure V calculated by the virtual mold pressure calculation unit 114 can be made closer to the magnitude of the mold pressure during actual molding. As a result, the mold pressure can be calculated with high accuracy.

[0144] Furthermore, the pressure loss acquisition unit 111 acquires the pressure loss in association with the injection speed S, the injection pressure acquisition unit 112 acquires the injection pressure P in association with the injection speed S, and the virtual mold internal pressure calculation unit 114 calculates the virtual mold internal pressure V by subtracting the pressure loss from the injection pressure P having the same injection speed S. This allows the virtual mold internal pressure V calculated by the virtual mold internal pressure calculation unit 114 to be calculated so as to be closer to the magnitude of the mold internal pressure during actual molding, regardless of the injection speed S. As a result, the mold internal pressure can be calculated more reliably and with higher accuracy.

[0145] DESCRIPTION OF SYMBOLS 1...injection molding machine, 5...frame, 10...injection device, 11...heating barrel, 12...nozzle, 13...heater, 15...hopper, 20...screw, 21...flight, 22...groove portion, 23...groove wall, 24...communicating portion, 25...check ring, 30...propulsion mechanism, 31...driving motor, 40...rotation mechanism, 41...rotation mechanism main body, 43...driving motor, 44...transmission belt, 45...pulley, 46...bearing, 50...forward / reverse mechanism, 51...driving motor, 52...encoder, 53...transmission belt, 54...pulley, 56...ball screw mechanism, 57...screw portion, 58...nut portion, 60...load cell, 70...mold clamping device, 71...fixed platen, 72...moving platen, 75...mold, 75a...cavity, 76...fixed Mold, 77...movable mold, 80...mold clamping drive mechanism, 81...toggle mechanism, 85...ejection mechanism, 86...ejection member, 87...ejector pin, 88...ejector plate, 100...controller, 110...processing unit, 111...pressure loss acquisition unit, 112...injection pressure acquisition unit, 113...pressure loss calculation unit, 114...virtual mold internal pressure calculation unit, 115...injection pressure determination unit, 116...virtual mold internal pressure determination unit, 120...movement control unit, 121...position control controller, 122...velocity control controller, 123...current control controller, 124...pressure control controller, 125...virtual mold internal pressure controller, 140...storage unit, 150...input / output unit, 160...input unit, 170...display unit, 180...amplifier, 200...weight sensor

Claims

1. An injection device which melts a resin material in a heated barrel with a screw disposed inside, and injects the resin material from a nozzle by moving the screw towards a side where a nozzle is located that injects the molten resin material; a mold which consists of a fixed mold and a movable mold which open and close, and has a cavity into which the resin material injected from the nozzle is filled when the mold is closed, and which molds the resin material in the cavity; a pressure detection unit which detects the pressure acting on the screw when the resin material is injected; and a control device which controls the movement of the screw to control the internal mold pressure, which is the pressure of the resin material inside the mold; wherein the control device comprises: a pressure loss acquisition unit which acquires, as a pressure loss, the pressure detected by the pressure detection unit when the resin material is injected from the nozzle that is in contact with the fixed mold when the fixed mold and the movable mold are in an open state; an injection pressure acquisition unit that acquires, as an injection pressure, the pressure detected by the pressure detection unit when the resin material is injected from the nozzle into the cavity with the fixed mold and the movable mold closed; and a virtual internal mold pressure calculation unit that calculates a virtual internal mold pressure, which is the virtual internal mold pressure, by subtracting, from the injection pressure acquired by the injection pressure acquisition unit, the pressure loss acquired by the pressure loss acquisition unit or a pressure loss based on the pressure loss acquired by the pressure loss acquisition unit.

2. An injection molding machine as described in claim 1, further comprising an injection speed detection unit which detects an injection speed, which is the moving speed of the screw when injecting the resin material, wherein the pressure loss acquisition unit acquires the pressure loss in correspondence with the injection speed, the injection pressure acquisition unit acquires the injection pressure in correspondence with the injection speed, and the virtual mold internal pressure calculation unit calculates the virtual mold internal pressure by subtracting the pressure loss from the injection pressure when the injection speeds are the same.

3. A method for detecting mold internal pressure, which is the pressure of the resin material in the mold of an injection molding machine comprising: an injection device which melts a resin material in a heated barrel having a screw disposed inside, and which injects the resin material from the nozzle by moving the screw towards a side where a nozzle is located that injects the molten resin material; a mold which consists of a fixed mold and a movable mold which open and close, and has a cavity which is filled with the resin material injected from the nozzle when the mold is closed, and which molds the resin material in the cavity; and a pressure detection unit which detects the pressure acting on the screw when the resin material is injected, the method comprising the steps of: bringing the nozzle into contact with the fixed mold with the fixed mold and the movable mold open, injecting the resin material from the nozzle, and obtaining the pressure detected by the pressure detection unit as a pressure loss; and injecting the resin material from the nozzle into the cavity with the fixed mold and the movable mold closed, and obtaining the pressure detected by the pressure detection unit as an injection pressure. a step of calculating a virtual internal mold pressure, which is a virtual internal mold pressure, by subtracting from the injection pressure the pressure loss acquired in the step of acquiring the pressure loss or a pressure loss based on the pressure loss acquired in the step of acquiring the pressure loss.

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