Injection molding machine and method for detecting mold inner pressure

Abstract

To calculate mold inner pressure with high accuracy.SOLUTION: An injection molding machine includes: an injection device 10 that injects a resin material molten in a heating barrel 11 with a screw 20 disposed inside from a nozzle 12; a mold 75 that is made up of a fixed mold 76 and a movable mold 77 and has a cavity 75a into which the resin material is filled; a load cell 60 that detects a pressure acting on the screw 20; and a control device 100 that controls a mold inner pressure. The control device 100 includes: a pressure loss acquisition unit 111 that acquires, as a 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 in a state in which the fixed mold 76 and the movable mold 77 are open; an injection pressure acquisition unit 112 that acquires, as an injection pressure, 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 mold 75 is closed; and a virtual mold inner pressure calculation unit 114 that calculates a virtual mold inner pressure V by subtracting the pressure loss from the injection pressure.SELECTED DRAWING: Figure 5

Description

Technical Field

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

Background Art

[0002] In an injection molding machine that performs molding by injecting molten resin into a mold, in order to perform appropriate molding, it is important to perform molding while setting the pressure of the resin to an appropriate value. For this reason, in conventional injection molding machines, molding is performed while obtaining the value of the pressure of the molten resin by various methods. For example, in the injection pressure inspection device of the injection molding machine described in Patent Document 1, the pressure of the resin in the injection nozzle is calculated based on the pressure of the resin detected when purging and the pressure of the resin detected when performing normal molding, so that the pressure of the resin in the cavity can be accurately detected without being affected by the pressure loss in the heating cylinder.

[0003] Further, in the molding condition creation method described in Patent Document 2, by obtaining the resin pressure curve at the resin inlet or the end of the molding machine nozzle and the injection pressure curve with the nozzle detached from the mold, the time delay and pressure loss caused by the mechanical elements of the injection molding machine are compensated, and the molding conditions for mass production molding are obtained. Also, in the resin evaluation method using the injection molding machine described in Patent Document 3, it is described that the injection pressure at the set screw position is detected by performing injection while changing the resin temperature and the injection speed, and the mutual dependence function of pressure, speed, and temperature is obtained by the least squares method using N sets of data of combinations of injection pressure, injection speed, and resin temperature.

[0004] In addition, in the pressure control device of the injection molding machine described in Patent Document 4, in the holding pressure process, an injection pressure control process for controlling the injection pressure and an in-mold pressure control process for controlling so that the estimated in-mold pressure becomes the set in-mold pressure after executing the injection pressure control process are executed. By doing so, variations in the pressure inside the mold during the molding cycle are suppressed, enabling the molding of molded products with stable quality. Also, in the holding pressure process, by controlling so that the estimated in-mold pressure becomes the set in-mold pressure, the pressure inside the mold can be controlled with high responsiveness, thus preventing stress deformation of the molded product. Further, in the method for measuring the injection pressure in the injection molding machine described in Patent Document 5, when injecting molten resin from the heating barrel into the mold, the reaction force acting on the screw is detected using a load cell, the speed of the screw is measured to calculate the acceleration of the screw, and the inertial force of the movable member is calculated, thereby calculating the pressure of the molten resin in the heating barrel.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0006] Here, in injection molding by an injection molding machine, it may be necessary to change the type of resin material or the mold according to the target molded product. However, even when the type of resin material or the mold is changed, it is important to appropriately control the pressure of the resin material in the mold. In order to appropriately control the in-mold pressure, which is the pressure of the resin material in the mold, it is necessary to obtain the pressure of the resin material. In conventional injection molding machines, the in-mold pressure is calculated based on a detection value that can be detected by the injection device when injecting the resin material with the injection device. For example, in Patent Document 1, based on the pressure of the resin when purging and the pressure of the resin when performing normal molding, the pressure of the resin in the injection nozzle is calculated, and thus the pressure of the resin in the cavity is detected without being affected by the pressure loss in the heating cylinder.

[0007] However, when detecting the in-mold pressure based on the value detected during molding, a detection value detected before molding, such as the pressure of the resin when purging in Patent Document 1, becomes important. However, purging is different from the actual molding state. For this reason, when calculating the in-mold pressure using the pressure of the resin when purging, it is considered that the difference from the actual pressure becomes large and is calculated. From the viewpoint of accuracy when calculating the in-mold pressure, there is room for improvement.

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

Means for Solving the Problems

[0009] In order to solve the above-described problems and achieve the object, an injection molding machine according to the present invention includes an injection device that melts a resin material in a heating barrel in which a screw is disposed inside and moves the screw toward a side where a nozzle for injecting the melted resin material is located, thereby injecting the resin material from the nozzle; a mold including a fixed mold and a movable mold that open and close and having a cavity filled with the resin material injected from the nozzle in a closed state, and molding the resin material in the cavity; a pressure detection unit that detects a pressure acting on the screw when injecting the resin material; and a control device that controls the internal pressure of the mold, which is the pressure of the resin material in the mold, by controlling the movement of the screw. The control device includes: a pressure loss acquisition unit that acquires, as a pressure loss, the pressure detected by the pressure detection unit when injecting the resin material from the nozzle that contacts the fixed mold in a state where the fixed mold and the movable mold are open; an injection pressure acquisition unit that acquires, as an injection pressure, the pressure detected by the pressure detection unit when injecting the resin material from the nozzle into the cavity in a state where the fixed mold and the movable mold are closed; and a virtual internal pressure calculation unit that calculates a virtual internal pressure, which is the virtual internal pressure of the mold, by subtracting 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 from the injection pressure acquired by the injection pressure acquisition unit.

[0010] Also, in order to solve the above-described problems and achieve the object, a method for detecting the in-mold pressure according to the present invention melts a resin material in a heating barrel in which a screw is disposed inside, and moves the screw toward the side where a nozzle for injecting the melted resin material is located, thereby injecting the resin material from the nozzle. An injection device, a mold composed of a fixed mold and a movable mold that open and close, and having a cavity filled with the resin material injected from the nozzle in a closed state, and molding the resin material in the cavity. A mold, and a pressure detection unit that detects the pressure acting on the screw when injecting the resin material, and a method for detecting the in-mold pressure, which is the pressure of the resin material in the mold of an injection molding machine, includes: 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; 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; and calculating a virtual in-mold pressure, which is the virtual in-mold pressure, by subtracting the pressure loss obtained by the procedure of obtaining the pressure loss from the injection pressure or the pressure loss based on the pressure loss obtained by the procedure of obtaining the pressure loss.

Effect of the Invention

[0011] The injection molding machine and the method for detecting the in-mold pressure according to the present invention have an effect that the in-mold pressure can be calculated with high accuracy.

Brief Description of the Drawings

[0012]

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DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of an injection molding machine and a method for detecting in-mold pressure according to the present disclosure will be described in detail with reference to the drawings. Note that the present invention is not limited by this embodiment. Further, the constituent elements in the following embodiments include those that can be replaced by those skilled in the art and can be easily conceived, or those that are substantially the same.

[0014] [Embodiment] FIG. 1 is a schematic diagram showing a configuration example of an injection molding machine 1 according to an embodiment. In the following description, the vertical direction in the normal use state of the injection molding machine 1 will be described as the vertical direction Z in the injection molding machine 1, the upper side in the normal use state of the injection molding machine 1 will be described as the upper side in the injection molding machine 1, and the lower side in the normal use state of the injection molding machine 1 will be described as the lower side in the injection molding machine 1. Further, in the following description, the longitudinal direction Y of the injection molding machine 1 will be described as the longitudinal direction Y also in each part having the injection molding machine 1, and the direction orthogonal to both the vertical direction Z and the longitudinal direction Y of the injection molding machine 1 will be described as the width direction X in the injection molding machine 1.

[0015] <Injection molding machine 1> The injection molding machine 1 according to the present embodiment includes an injection device 10 and a mold clamping device 70, and the injection device 10 and the mold clamping device 70 are placed on a frame 5 disposed at the lower end of the injection molding machine 1. The injection molding machine 1 can melt a resin material with the injection device 10 to make a plasticized material, and cool and solidify the plasticized material injected from the injection device 10 with the mold clamping device 70, thereby manufacturing various desired molded products.

[0016] The injection device 10 includes a heating barrel 11, a screw 20, a rotation mechanism 40, a forward and backward movement mechanism 50, and a propulsion mechanism 30. The heating barrel 11 can heat and melt a resin material inside to make a plasticized material. Further, the heating barrel 11 is provided with a nozzle 12 for injecting the plasticized material at one end side, and the other end side is connected to a hopper 15 for raw material input. The screw 20 is disposed inside the heating barrel 11 and is movable in the axial direction inside the heating barrel 11.

[0017] The rotation mechanism 40 can introduce the resin material from the hopper 15 into the heating barrel 11 by rotating the screw 20 within the heating barrel 11.

[0018] The forward and backward movement mechanism 50 can move the screw 20 in the longitudinal direction Y within the heating barrel 11. Further, the forward and backward movement mechanism 50 can move the screw 20 toward the side where the nozzle 12 is located within the heating barrel 11 with the molten resin material stored in the portion on the end side where the nozzle 12 is located, thereby extruding the resin material from the nozzle 12. As a result, the resin material melted within the heating barrel 11 can be injected from the nozzle 12.

[0019] The mold clamping device 70 includes a fixed platen 71, a moving platen 72, a mold 75, a mold clamping drive mechanism 80, and an extrusion mechanism 85. The fixed platen 71 is disposed on the frame 5 and fixed to the frame 5. The moving platen 72 is disposed on the opposite side of the fixed platen 71 on the frame 5 from the side where the injection device 10 is located and is movably disposed relative to the fixed platen 71.

[0020] The mold 75 has a cavity 75a filled with the resin material injected from the nozzle 12 of the heating barrel 11 of the injection device 10, and it is possible to perform molding of the resin material in the cavity 75a. The mold 75 for performing molding of the resin material in this way has a fixed mold 76 and a moving mold 77 that open and close with respect to each other. The cavity 75a of the mold 75 is formed by the moving mold 77 and the fixed mold 76 when the moving mold 77 and the fixed mold 76 are closed. The fixed mold 76 is attached to the surface of the fixed platen 71 on the side where the moving platen 72 is located, and the moving mold 77 is attached to the surface of the moving platen 72 on the side where the fixed platen 71 is located. The moving mold 77 attached to the moving platen 72 faces the fixed mold 76 attached to the fixed platen 71, and when the moving platen 72 approaches the fixed platen 71, it approaches the fixed mold 76 and is combined with the fixed mold 76.

[0021] The clamping drive mechanism 80 is capable of relatively moving the moving platen 72 with respect to the fixed platen 71. By relatively moving the moving platen 72 with respect to the fixed platen 71, the mold can be closed between the moving mold 77 and the fixed mold 76, or the mold can be opened between the moving mold 77 and the fixed mold 76. In the present embodiment, the clamping drive mechanism 80 includes a so-called toggle mechanism 81, and the toggle mechanism 81 can relatively move the moving platen 72 with respect to the fixed platen 71.

[0022] The extrusion mechanism 85 includes an extrusion member 86 that extrudes the molded product after molding adhered to the inner surface of the moving mold 77, and it is possible to remove the molded product after molding from the moving mold 77.

[0023] <Injection device 10> In the following description, the side where the clamping device 70 is located with respect to the injection device 10 in the longitudinal direction Y is defined as the front, or the front side, and the opposite side of the side where the clamping device 70 is located with respect to the injection device 10 in the longitudinal direction Y is defined as the rear, or the rear side for explanation.

[0024] FIG. 2 is a detailed view of the injection device 10 shown in FIG. 1. The injection device 10 is arranged on the frame 5 via a propulsion mechanism 30. The propulsion mechanism 30 has a driving electric motor 31, and the driving force generated by the driving electric motor 31 enables the injection device 10 to move in the longitudinal direction Y with respect 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 that is in close contact with the mold 75 is arranged at its tip, that is, the front end of the heating barrel 11. Specifically, the heating barrel 11 is formed in a substantially cylindrical shape and is arranged with its axial direction along the longitudinal direction Y, and a heater 13 such as a band heater is provided. Thereby, the heating barrel 11 can melt the resin material inside. That is, the temperature of the heating barrel 11 can be increased by the heater 13, and the resin material can be heated and melted inside to form a molten resin, which is a plasticized material.

[0026] The screw 20 is disposed inside the heating barrel 11 and has a spiral shape with its axial direction along the axial direction of the heating barrel 11, that is, the screw 20 has spiral grooves on its outer peripheral surface. Thus, the screw 20 formed with a spiral shape is rotatable about its axis inside the heating barrel 11. Further, the screw 20 is movable in the axial direction of rotation inside 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, which is the shape of the heating barrel 11, and the rotation axis of the screw 20 substantially coincide, and is disposed movably in the axial direction of the heating barrel 11. The screw 20 rotatably disposed inside the heating barrel 11 can knead the molten resin by rotating inside the heating barrel 11. Therefore, the heating barrel 11 is a barrel capable of kneading the molten resin inside.

[0027] A hopper 15 is disposed at a position near the rear end of the heating barrel 11. The hopper 15 communicates with the inside of the heating barrel 11 and can supply pellets (not shown), which are granular resin materials, to the heating barrel 11.

[0028] The rotation mechanism 40 is disposed on the rear side of the heating barrel 11 in the longitudinal direction Y and can rotate the screw 20 disposed inside the heating barrel 11 around its central axis. The rotation mechanism 40 for rotating the screw 20 includes a rotation mechanism main body 41, a drive motor 43, a transmission belt 44, and a pulley 45.

[0029] The drive motor 43 is disposed, for example, above the rotating mechanism main body 41. The pulley 45 is disposed in front of the rotating mechanism main body 41 and is rotatably disposed with respect to the rotating mechanism main body 41 via a bearing 46. Further, the pulley 45 is connected to the drive shaft of the drive motor 43 via a transmission belt 44. Thereby, the pulley 45 can be rotated by the driving force of the drive motor 43 transmitted via the transmission belt 44. In this way, the pulley 45 that can be rotated by the driving force transmitted from the drive motor 43 is integrally fixed coaxially with respect to the screw 20. In other words, the rear end side of the screw 20 in the longitudinal direction Y is connected to the pulley 45. Thereby, the screw 20 disposed in the heating barrel 11 can be rotated integrally with the pulley 45 by the driving force transmitted from the drive motor 43 to the pulley 45.

[0030] A forward and backward movement mechanism 50 is disposed behind the rotating mechanism main body 41 in the longitudinal direction Y. The forward and backward movement mechanism 50 enables the screw 20 disposed in the heating barrel 11 to move in the axial direction of the screw 20. That is, the screw 20 can be advanced or retracted in the longitudinal direction Y. Specifically, the forward and backward movement mechanism 50 includes 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. 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 in the moving direction of the screw 20 when injecting the resin material from the nozzle 12 of the heating barrel 11 via the rotational position of the drive motor 51. Further, the encoder 52 of the drive motor 51 can detect the injection speed S, which is the moving speed of the screw 20 when injecting the resin material 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 also used as an injection speed detection unit that detects the injection speed S of the screw 20 in this way.

[0032] The pulley 54 is integrally connected to the screw portion 57 of the ball screw mechanism 56. The screw portion 57 of the ball screw mechanism 56 is arranged coaxially with the screw 20 and is also arranged 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 and backward movement mechanism 50 is formed in a substantially cylindrical shape, and the screw portion 57 of the ball screw mechanism 56 is screwed into the nut portion 58.

[0033] A load cell 60 is arranged between the nut portion 58 of the ball screw mechanism 56 of the forward and backward movement mechanism 50 and the rotation mechanism main body 41 of the rotation mechanism 40 in the longitudinal direction Y. The load cell 60 is arranged on the rear side of the rotation mechanism main body 41 of the rotation mechanism 40 and on the front side of the nut portion 58 of the ball screw mechanism 56 of the forward and backward movement mechanism 50.

[0034] The load cell 60 is a load measuring device that measures the load applied in the axial direction, and is composed of a strain generating body and a strain sensor (both not shown) attached to the strain generating body. In the present embodiment, the load cell 60 is arranged in a direction in which the axial direction is the longitudinal direction Y, and is formed in a substantially cylindrical shape that is flat in the longitudinal direction Y. The inner diameter of the cylinder is larger than the outer diameter of the screw portion 57 of the ball screw mechanism 56 included in the forward and backward movement mechanism 50. The load cell 60 formed in this way has the front surface in the longitudinal direction Y integrally fixed to the rotation mechanism main body portion 41 of the rotation mechanism 40, and the rear surface in the longitudinal direction Y integrally fixed to the nut portion 58 of the ball screw mechanism 56 included in the forward and backward movement mechanism 50.

[0035] The load cell 60 disposed between the rotation mechanism main body portion 41 of the rotation mechanism 40 and the nut portion 58 of the ball screw mechanism 56 included in the forward and backward movement mechanism 50 is capable of detecting the load acting in the longitudinal direction Y between the rotation mechanism main body portion 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 injecting the resin material from the nozzle 12 of the heating barrel 11 by detecting the load acting between the rotation mechanism main body portion 41 and the nut portion 58.

[0036] FIG. 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 peripheral surface. The nozzle 12 disposed at the front end in the longitudinal direction Y of the heating barrel 11 is formed in a substantially cylindrical shape with an inner diameter smaller than the inner diameter of the heating barrel 11, and is disposed to open on the front side in the longitudinal direction Y. The screw 20 disposed in the heating barrel 11 has flights 21 that project 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 a spiral groove-shaped portion between adjacent circumferential portions of the flights 21 formed in a spiral shape.

[0037] In the screw 20 formed in this way, a check ring 25 is arranged near the front end in the longitudinal direction Y. The check ring 25 is arranged in a groove portion 22 formed near the front end in the longitudinal direction Y of the screw 20. The groove portion 22 is a groove formed over one circumference in the circumferential direction of the screw 20 with the groove width direction being the axial direction of the screw 20.

[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 arranged in the groove portion 22 of the screw 20 in a form where its axis substantially coincides with the axis of the screw 20. The check ring 25 formed in a substantially cylindrical shape has an outer diameter approximately the same as the inner diameter of the heating barrel 11 and slightly smaller than the inner diameter of the heating barrel 11. Also, the inner diameter of the check ring 25 is larger than the diameter of the groove bottom of the groove portion 22 of the screw 20, and a gap is formed between the inner peripheral surface of the check ring 25 and the groove bottom of the groove portion 22 of the screw 20. Further, the width of the check ring 25 in the axial direction is smaller than the groove width of the groove portion 22 of the screw 20. For this reason, the check ring 25 can move in the groove width direction within the groove portion 22.

[0039] Also, in the screw 20, a communication portion 24 that communicates the portion in front of the groove portion 22 in the longitudinal direction Y and the inside of the groove portion 22 is formed. The communication portion 24 opens to the front groove wall 23 in the groove width direction of the groove portion 22.

[0040] <Control device 100> The injection molding machine 1 includes a control device 100 that performs various controls on the injection molding machine 1, an input unit 160 through which an operator performs input operations on 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. The input unit 160 transmits the information subjected to the input operation to the control device 100. Further, 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 separately, or may be integrally formed by being configured by a so-called touch panel type display.

[0041] Various actuators such as a motor that serves as a power source for the operation of the injection molding machine 1 and various sensors that acquire information during the operation of the injection molding machine 1 are connected to the control device 100. Thereby, the control device 100 can control the injection molding machine 1 by acquiring information during the operation of the injection molding machine 1 by the sensors and transmitting a control signal to the actuators of the injection molding machine 1. For example, the control device 100 can control the pressure of the resin material in the mold 75 by controlling the movement of the screw 20 when injecting the molten resin material from the nozzle 12 of the heating barrel 11.

[0042] FIG. 5 is an explanatory diagram of the control device 100 shown in FIG. 1. The control device 100 includes a processing unit 110, a storage unit 140, and an input / output unit 150. The processing unit 110 includes 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 each function of the processing unit 110 is realized by loading an application program held in the ROM into the RAM and executing it by the CPU to read and write data in the RAM and the ROM.

[0043] The storage unit 140 is a storage device that is electrically connected to the processing unit 110 and stores information. When controlling the injection molding machine 1 by the control device 100, the storage unit 140 stores the information acquired from the injection molding machine 1 by the processing unit 110 or the information calculated by the processing unit 110, or the processing unit 110 calls the information stored in the storage unit 140 and uses it for controlling the injection molding machine 1.

[0044] In addition, each function realized by the processing unit 110 may be stored in the storage unit 140 in advance as a program. In this case, the processing unit 110 calls the program stored in the storage unit 140 by the processing unit 110 and executes the operations according to the program by the processing unit 110, thereby executing each function. Further, the storage unit 140 may be integrally provided in the control device 100 or may be configured to be detachable from the control device 100.

[0045] The input / output unit 150 serves as a so-called interface that performs signal input / output with devices external to the control device 100. That is, various actuators and various sensors of the injection molding machine 1 connected to the control device 100, the input unit 160, and the display unit 170 are connected to the input / output unit 150. Examples of the actuators and various 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 the encoder 52 of the forward / backward movement mechanism 50, the load cell 60, and the like. The processing unit 110 of the control device 100 performs signal transmission and reception with 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] Among these, the pressure loss acquisition unit 111 is capable of obtaining the pressure loss in the injection device 10 when injecting the resin material from the nozzle 12 of the heating barrel 11. Specifically, when injecting the resin material from the nozzle 12 that contacts the fixed mold 76 in the state where the fixed mold 76 and the movable mold 77 are open, the pressure loss acquisition unit 111 acquires the pressure detected by the load cell 60 as the pressure loss. In addition, the pressure loss acquisition unit 111 acquires the pressure loss in association with the injection speed S of the screw 20 detected by the encoder 52 of the drive motor 51 of the forward and backward movement mechanism 50. The pressure loss acquisition unit 111 sets the acquired pressure loss as a pressure loss model M in association with the injection speed S and stores it in the storage unit 140.

[0048] The injection pressure acquisition unit 112 is capable of acquiring the injection pressure P when injecting the molten resin material from the heating barrel 11 into the cavity 75a of the mold 75. Specifically, when injecting the resin material from the nozzle 12 into the cavity 75a in the state where the fixed mold 76 and the movable mold 77 are closed, the injection pressure acquisition unit 112 acquires the pressure detected by the load cell 60 as the injection pressure P. In addition, 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 and backward movement mechanism 50.

[0049] Based on the pressure loss model M preset and stored in the storage unit 140 and the injection speed S of the screw 20 detected by the encoder 52 of the drive motor 51 of the forward and backward movement mechanism 50, the pressure loss calculation unit 113 is capable of obtaining the pressure loss in the injection device 10 when injecting the resin material from the nozzle 12 of the heating barrel 11.

[0050] The virtual in-mold pressure calculation unit 114 can calculate a virtual in-mold pressure V, which is the in-mold pressure of the resin material in the mold 75 when the melted resin material is injected from the heating barrel 11 into the cavity 75a of the mold 75, by means of calculation. The virtual in-mold pressure calculation unit 114 calculates the virtual in-mold pressure V by subtracting the pressure loss obtained by the pressure loss acquisition unit 111 or the pressure loss based on the pressure loss obtained by the pressure loss acquisition unit 111 from the injection pressure P obtained by the injection pressure acquisition unit 112. That is, the virtual in-mold pressure calculation unit 114 calculates the virtual in-mold pressure V by subtracting the pressure loss obtained by the pressure loss acquisition unit 111 or the pressure loss obtained by the pressure loss calculation unit 113 from the injection pressure P obtained by the injection pressure acquisition unit 112. That is, the virtual in-mold pressure calculation unit 114 calculates the virtual in-mold pressure V by performing the calculation of [virtual in-mold pressure V = injection pressure P - pressure loss]. Specifically, the virtual in-mold pressure calculation unit 114 calculates the virtual in-mold pressure V by subtracting the pressure loss from the injection pressure P with the same injection speed S.

[0051] The injection pressure determination unit 115 can determine whether the injection pressure P obtained by the injection pressure acquisition unit 112 reaches the upper limit value set for the injection pressure P based on the pressure detected by the load cell 60 when injecting the resin material from the heating barrel 11. The upper limit value set for the injection pressure P in this case is set, for example, by being selected from those preset according to the type of molded product molded by the injection molding machine 1, the type of resin material used for molding the molded product, etc., based on the type of molded product and resin material actually molded, or by directly inputting the upper limit value by the operator. The set upper limit value of the injection pressure P is stored in the storage unit 140.

[0052] The virtual internal pressure determination unit 116 can determine whether or not the virtual internal pressure V calculated by the virtual internal pressure calculation unit 114 has reached the upper limit value set for the virtual internal pressure V. The upper limit value set for the virtual internal pressure V in this case is, for example, selected from among those preset according to the type of molded product molded by the injection molding machine 1, the type of resin material used for molding the molded product, etc., based on the type of molded product and resin material actually to be molded, etc., and set thereby, or set by directly inputting the upper limit value by the operator. Further, the upper limit value of the virtual internal pressure V is set to a value lower than the virtual internal pressure V when the injection pressure P reaches the upper limit value PL. Specifically, the upper limit value of the virtual internal pressure V is set to approximately the same magnitude as the maximum value of the pressure of the resin material in the mold 75 when a good molded product is molded with the mold 75 filled with the resin material in the cavity 75a. The set upper limit value of the virtual internal pressure V is stored in the storage unit 140.

[0053] The movement control unit 120 can perform movement control of the screw 20 when injecting the resin material from the heating barrel 11 of the injection device 10. The movement control unit 120 performs movement control of the screw 20 by operating the forward / backward mechanism 50 by controlling the drive electric motor 51 included in the forward / backward mechanism 50.

[0054] Further, when performing movement control of the screw 20, the movement control unit 120 performs movement control including the virtual internal pressure V calculated by the virtual internal pressure calculation unit 114 as a determination factor during control. That is, when performing movement control of the screw 20, the movement control unit 120 performs movement control based on the virtual internal pressure V calculated by the virtual internal pressure calculation unit 114.

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

[0056] Further, the movement control unit 120 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] FIG. 6 is an explanatory diagram showing the relationship between each controller included in the movement control unit 120 and the injection device 10. The position controller 121 controls the position in the movement direction of the screw 20 when injecting the resin material from the nozzle 12 of the heating barrel 11, based on the position in the movement direction of the screw 20 detected by the encoder 52 of the drive motor 51 of the forward and backward movement mechanism 50. That is, the position controller 121 performs position control of the screw 20 while receiving feedback on the position in the movement direction of the screw 20 from the encoder 52 of the drive motor 51. The position controller 121 transmits a speed command corresponding to the position in the movement direction of the screw 20 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 performed based on the speed command stored in the storage unit 140. In the storage unit 140, for example, the speed command input by the operator through 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 moving direction of the screw 20 to the speed controller 122 so that the final injection speed S of the screw 20 becomes the speed of 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 transmitted 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 and backward 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 transmits a current value for driving the drive motor 51 of the forward and backward mechanism 50 to the current controller 123 so that the screw 20 can be moved at the injection speed S corresponding to the position in the moving direction of the screw 20.

[0060] The current controller 123 performs drive control of the drive motor 51 of the forward and backward mechanism 50 based on the current value transmitted from the speed controller 122. The current controller 123 feeds back the current value output from the current controller 123 and performs drive control of the drive motor 51 of the forward and backward mechanism 50 while 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 the upper limit value, the pressure control controller 124 performs movement control of the screw 20 based on the injection speed S set as the injection speed S when the injection pressure P reaches the upper limit value. The upper limit value set for the injection pressure P and the injection speed S set as the injection speed S when the injection pressure P reaches the upper limit value are preset as pressure commands and stored in the storage unit 140. The pressure command is stored in the storage unit 140, for example, as a value input from the input unit 160 by the operator.

[0062] The injection speed S set as the injection speed S when the injection pressure P reaches the upper limit value is set at a slower speed than the injection speed S set as the injection speed S when the injection pressure P has not reached the upper limit value. The pressure control controller 124 compares the injection pressure P with the upper limit value in the injection pressure determination unit 115 while receiving feedback on the injection pressure P from the load cell 60, and when it is determined that the injection pressure P has reached the upper limit value, the pressure control controller 124 performs movement control of the screw 20.

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

[0064] The injection speed S set as the injection speed S when the virtual internal pressure V reaches the upper limit value is set at a speed slower than the injection speed S set as the injection speed S when the virtual internal pressure V has not reached the upper limit value. The virtual internal pressure controller 125 compares the virtual internal pressure V with the upper limit value in the virtual internal pressure determination unit 116 based on the 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. When it is determined that the virtual internal pressure V has reached the upper limit value, the virtual 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 the pressure loss model M. The pressure loss acquired by the pressure loss acquisition unit 111 stores the pressure loss model M that associates the injection speed S of the screw 20 when injecting the resin material melted by moving the screw 20 in the heating barrel 11 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 injecting the melted resin material. Specifically, the pressure loss in this case is the pressure lost due to the resistance when the resin material passes through the nozzle 12 and the sliding resistance of the screw 20 against the heating barrel 11 when moving the screw 20 in the heating barrel 11 and injecting 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 the 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 measuring in advance the pressure loss when injecting the resin material from the heating barrel 11 for each injection speed S of the screw 20 by actual measurement.

[0067] <Measurement method of pressure loss> Next, a method for measuring the pressure loss by actual measurement will be described. FIG. 8 is a schematic diagram showing a measurement method when measuring the pressure loss in the method for detecting the in-mold pressure according to the embodiment. When actually measuring the pressure loss when injecting the resin material from the heating barrel 11, 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 acquired as the pressure loss. That is, when the resin material is injected with the fixed mold 76 and the movable mold 77 open, the resin material is not filled into the mold 75, so the pressure of the resin material such as when filling the resin material into the mold 75 does not act on the screw 20 that extrudes 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 heating barrel 11 acts on the screw 20 that extrudes 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 and the resin material is injected from the nozzle 12 with the fixed mold 76 and the movable mold 77 open can be used as the pressure lost in the heating barrel 11 when injecting the resin material. In the present embodiment, when acquiring the pressure loss when injecting the resin material from the heating barrel 11, purging is performed in a state where the fixed mold 76 and the movable mold 77 are opened and the nozzle 12 is brought into contact with the fixed mold 76 as described above, and the pressure detected during in-mold purging is acquired as the pressure loss. Thereby, the pressure loss at the time of injecting the resin material can be acquired with high accuracy.

[0069] That is, generally, since the temperature of the mold 75 is lower than the temperature of the nozzle 12, when the nozzle 12 contacts the mold 75, the temperature of the nozzle 12 decreases. Along with this, the temperature of the resin material located in the portion of the nozzle 12 also decreases, and the viscosity of the resin material located in the portion of the nozzle 12 increases. Therefore, the pressure loss when the resin material injected from the nozzle 12 passes through the portion of the nozzle 12 increases.

[0070] FIG. 9 is a schematic diagram showing a measurement method when measuring the pressure loss with the nozzle 12 separated from the mold 75. FIG. 10 is an explanatory diagram comparing the measurement result of the pressure loss measured with the nozzle 12 in contact with the mold 75 and the measurement result of the pressure loss measured with the nozzle 12 separated from the mold 75. The in-mold purge pressure loss Lm, which is the pressure loss obtained during in-mold purge, is larger than the resin purge pressure loss Lr, which is the pressure loss obtained during resin purge, which is a purge performed with the nozzle 12 separated from the mold 75 as shown in FIG. 9. That is, the resin purge pressure loss Lr referred to here is the pressure detected by the load cell 60 when the nozzle 12 of the heating barrel 11 is separated from the mold 75 and the molten resin material is injected outside the mold 75, and is obtained as the resin purge pressure loss Lr, which is the pressure loss during resin purge.

[0071] The in-mold purge pressure loss Lm obtained during in-mold purge is higher than the resin purge pressure loss Lr obtained during resin purge, as shown in FIG. 10. That is, when the resin material is injected with the nozzle 12 separated from the mold 75, although the pressure from the resin material in the mold 75 does not act on the screw 20 when filling the resin material into the mold 75, since the nozzle 12 is separated from the mold 75, the temperature of the nozzle 12 does not decrease. Therefore, since the temperature of the resin material located at the nozzle 12 portion does not decrease, the viscosity of the resin material located at the nozzle 12 portion is maintained in a low state. Therefore, the resin material injected from the nozzle 12 passes through the portion of the nozzle 12 without an increase in pressure loss.

[0072] When comparing the in-mold purge pressure loss Lm and the resin purge pressure loss Lr, as shown in FIG. 10, the in-mold purge pressure loss Lm is larger in pressure loss than the resin purge pressure loss Lr. However, during actual molding, the resin material is injected with the nozzle 12 in contact with the mold 75. Therefore, the in-mold purge pressure loss Lm, which is the pressure loss obtained during in-mold purge, can be obtained as a pressure loss having a magnitude closer to the pressure loss during actual molding than the resin purge pressure loss Lr, which is the pressure loss obtained during resin purge.

[0073] <Comparison of virtual mold internal pressure> Next, a comparison between the virtual mold internal pressure Vm calculated using the pressure loss Lm during mold purging and the virtual mold internal pressure Vr calculated using the pressure loss Lr during resin purging will be described. FIG. 11 is an explanatory diagram showing a comparison between the virtual mold internal pressure Vm calculated using the pressure loss Lm during mold purging, the virtual mold internal pressure Vr calculated using the pressure loss Lr during resin purging, and the actually measured mold internal pressure Va. FIG. 12 is a schematic diagram of the method for measuring the actually measured mold internal pressure Va. When the virtual mold internal pressure calculation unit 114 calculates the virtual mold internal pressure V, it 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. Here, a comparison will be described between the virtual mold internal pressure Vm calculated using the pressure loss Lm during mold purging, the virtual mold internal pressure Vr calculated using the pressure loss Lr during resin purging, and the actually measured mold internal pressure Va which is the mold internal pressure actually measured when injecting a resin material into the mold 75.

[0074] As shown in FIG. 12, the inventors of the present application measured the actually measured mold internal pressure Va using the mold 75 in which the load cell 200 is disposed, and compared the measured actually measured mold internal pressure Va with the virtual mold internal pressure Vm during mold purging calculated using the pressure loss Lm during mold purging and the virtual mold internal pressure Vr during resin purging calculated using the pressure loss Lr during resin purging. In the mold 75 shown in FIG. 12, the load cell 200 is attached to the extrusion pin 87 of the extrusion mechanism 85.

[0075] The extrusion pin 87 is disposed in the moving mold 77 and one end faces the cavity 75a. On the other end side of the extrusion pin 87 in the moving mold 77, an extrusion plate 88 of the extrusion mechanism 85 is disposed. The extrusion mechanism 85 can extrude the molded product after molding with the extrusion pin 87 and remove it from the moving mold 77 by applying a load to the extrusion plate 88 with the extrusion member 86 (see FIG. 1) to push the extrusion pin 87 toward the cavity 75a side with the extrusion plate 88.

[0076] When injecting the resin material from the nozzle 12 of the heating barrel 11 into the cavity 75a of the mold 75 shown in Fig. 12, the extrusion pin 87 is pushed by the resin material in the cavity 75a, and the load when the extrusion pin 87 is pushed is detected by the load cell 200. The actually measured in-mold pressure Va is calculated by computing Va = F / A based on the load F detected by the load cell 200 and the cross-sectional area A of the extrusion pin 87 in the direction in which the pressure acts from the resin material on the extrusion pin 87.

[0077] Since the virtual in-mold pressure V is calculated by subtracting the pressure loss obtained by the pressure loss acquisition unit 111 from the injection pressure P obtained by the injection pressure acquisition unit 112, the virtual in-mold pressure V is lower than the injection pressure P. At that time, the pressure loss Lm during mold purging is larger than the pressure loss Lr during resin purging. For this reason, the virtual in-mold pressure Vm during mold purging calculated by subtracting the pressure loss Lm during mold purging from the injection pressure P is smaller than the virtual in-mold pressure Vr during resin purging calculated by subtracting the pressure loss Lr during resin purging from the injection pressure P.

[0078] As shown in Fig. 11, the virtual in-mold pressure Vm during mold purging, which is smaller than the virtual in-mold pressure Vr during resin purging, has a pressure magnitude closer to the actually measured in-mold pressure Va. That is, when comparing the virtual in-mold pressure Vm during mold purging and the virtual in-mold pressure Vr during resin purging, the virtual in-mold pressure Vm during mold purging is closer to the actually measured in-mold pressure Va than the virtual in-mold pressure Vr during resin purging. Therefore, the pressure loss Lm during mold purging that can calculate the virtual in-mold pressure Vm during mold purging close to the actually measured in-mold pressure Va can be used as the pressure lost in the heating barrel 11 during injection of the resin material during actual molding.

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

[0080] In deriving an approximation model for the in-mold purge pressure loss Lm obtained by the pressure loss acquisition unit 111, the inventors of the present application focused on the quadratic function approximation model and the power approximation model, and compared these approximation models. The quadratic function approximation model referred to 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 (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] In order to quantitatively determine the comparison between the quadratic function approximation model and the power approximation model, the inventors of the present application examined the mean absolute error rate (hereinafter referred to as the error rate) for each resin material. First, the procedure for obtaining the error rate will be described. When obtaining the error rate, when the total number of data is n, the difference x n between the measured value and the predicted value is obtained from the following formula (3). x n = measured value - predicted value ···(3)

[0082] Next, x n obtained by formula (1) is divided by the measured value as shown in the following (4), and the absolute value y n is obtained. y n = |x n / measured value| ···(4)

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

[0084] Taking these into consideration, regarding the error rates of the quadratic function approximation model and the power approximation model, the measured data of the in-mold purge pressure loss Lm obtained by the pressure loss acquisition unit 111 is defined as α n and the data of the approximation model is defined as β n With the number of data being n, it is calculated and derived from the following formula (6). Error rate = |(α n - β n ) / α n |n ···(6)

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

[0086] When comparing the quadratic function approximation model and the power approximation model, as shown in Figure 13, the quadratic function approximation model has a lower error rate than the power approximation model, and it is possible to obtain a result that can judge that the quadratic function approximation model is more suitable for modeling the in-mold purge pressure loss Lm.

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

[0088]

Equation

[0089] Each of 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).

[0090]

Number

[0091]

Number

[0092]

Number

[0093]

Number

[0094]

Number

[0095]

Number

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

[0097]

Number

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

[0099]

Number

[0100] Based on 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 purge can be modeled using the approximation formula of the quadratic function approximation model expressed as described above in (1).

[0101] The pressure loss acquisition unit 111 models the pressure loss Lm during in-mold purge using the approximation formula of the quadratic function approximation model from the pressure loss Lm during in-mold purge acquired in advance. The pressure loss acquisition unit 111 sets the approximation model of the modeled pressure loss Lm during in-mold purge as the pressure loss model M and stores it in the storage unit 140.

[0102] <Operation of the injection molding machine 1> The injection molding machine 1 according to the present embodiment includes the above configuration, and its operation will be described below. The injection molding machine 1 takes one injection and molding operation as one cycle and repeatedly executes this cycle of injection and molding operations. Each cycle includes a plurality of steps for injecting the molding material and molding the product. Each cycle includes, for example, a mold closing step, a filling step, a holding pressure step, a mold opening step, and a takeout step.

[0103] The mold closing step is a step of moving the moving platen 72 of the mold clamping device 70 in a direction approaching the fixed platen 71 to combine the moving mold 77 and the fixed mold 76 and form a cavity 75a corresponding to the product shape between the moving mold 77 and the fixed mold 76.

[0104] The filling step is a step of injecting the molten resin, which is the resin material melted by the heating barrel 11 of the injection device 10, into the cavity 75a formed by the moving mold 77 and the fixed mold 76 attached to the mold clamping device 70.

[0105] The holding pressure process is a process of waiting in a state of maintaining the pressure of the molding resin, which is a resin material injected into the cavity 75a formed by the moving mold 77 and the fixed mold 76 attached to the mold clamping device 70, and waiting for a certain period of time until the molding resin becomes a molded product as the temperature of the molding resin decreases and solidifies. Also, in the holding pressure process, the resin material to be injected in the next cycle is sent to the end side where the nozzle 12 is located in the heating barrel 11 of the injection device 10, and the metering of the resin material, which prepares the resin material to be used in the next cycle, is also carried out during the holding pressure process.

[0106] The mold opening process is a process of moving the moving platen 72 in a direction away from the fixed platen 71 to separate the moving mold 77 from the fixed mold 76 in order to take out the molded product formed by the fixed mold 76 and the moving mold 77 attached to the mold clamping device 70.

[0107] The taking-out process is a process of taking out the molded product from the mold 75 by pushing out the molded product in a state of being attached to the moving mold 77 with the pushing member 86 of the pushing mechanism 85 after separating the moving mold 77 from the fixed mold 76.

[0108] When molding a molded product with the injection molding machine 1, the molding of the molded product is continuously performed by repeatedly executing the cycles of these injection and molding operations. Here, when injecting the molten resin material into the mold 75 in the filling process, it is necessary to appropriately control the pressure of the resin material in the mold 75. For that purpose, it is necessary to detect the in-mold pressure with high accuracy. Next, a procedure for detecting the in-mold pressure with high accuracy will be described.

[0109] <Calculation of virtual in-mold pressure> FIG. 14 is a flowchart showing the procedure until the virtual internal pressure is calculated. In order to detect the internal pressure of the mold with high accuracy, in this embodiment, before molding an actual molded product, first, a purge is performed in the injection molding machine 1 to acquire each data (step ST11). That is, the nozzle 12 is brought into contact with the stationary mold 76 in a state where the stationary mold 76 and the movable mold 77 are open, and a purge is performed in the mold by injecting a resin material from the nozzle 12 (see FIG. 8). At this time, the pressure detected by the load cell 60 while performing the purge in the mold is acquired by the pressure loss acquisition unit 111 of the processing unit 110 of the control device 100 as the pressure loss.

[0110] Further, 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 included in the forward and backward movement mechanism 50. In this way, when acquiring data while performing the purge in the mold, it is preferable to change the injection speed S and acquire data for 3 shots or more.

[0111] Next, each acquired data is input into the arithmetic expression of the approximation coefficient (step ST12). That is, by calculating the above-described expressions (7), (14), and (15) using each acquired data, the approximation coefficients a, b, and c of the quadratic function are acquired.

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

[0113] Once the approximate quadratic function is created, the injection molding machine 1 starts molding the molded product that will be the actual product (step ST14). While starting the molding with the injection molding machine 1, each data of the calculated pressure loss and the measured injection pressure is acquired (step ST15). That is, while performing the molding with the injection molding machine 1, based on the injection speed S detected by the encoder 52 of the drive motor 51 included in the forward and backward movement mechanism 50 and the approximate quadratic function created in step ST13 by the pressure loss calculation unit 113 included in the processing unit 110 of the control device 100, the pressure loss when injecting the resin material is calculated. In other words, the pressure loss is obtained based on the injection speed S detected while performing the molding with 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] Also, while performing the molding with 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 mold internal pressure V (step ST16). The calculation of the virtual mold internal pressure V is performed by the virtual mold internal pressure calculation unit 114 included in the processing unit 110 of the control device 100. The virtual mold internal pressure calculation unit 114 calculates the virtual mold internal 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] At that time, the pressure loss calculated by the pressure loss calculation unit 113 is obtained from the approximate quadratic function created from the pressure loss during in-mold purge Lm (see FIG. 10), which is the pressure loss obtained by performing in-mold purge. Therefore, the virtual mold internal pressure V calculated by the virtual mold internal pressure calculation unit 114 is the virtual mold internal pressure Vm during in-mold purge, which is the virtual mold internal pressure V calculated using the pressure loss during in-mold purge Lm calculated by the pressure loss calculation unit 113.

[0117] During the virtual in-mold purge, the virtual in-mold pressure Vm is close in magnitude to the measured in-mold pressure Va when compared with the virtual in-mold pressure Vr during resin purge, which is the virtual in-mold pressure V calculated using the pressure loss Lr during resin purge as shown in Fig. 11. Therefore, in this embodiment, a virtual in-mold pressure V close in magnitude to the measured in-mold pressure Va can be calculated, and the in-mold pressure can be controlled using the virtual in-mold pressure V close in magnitude to the measured in-mold pressure Va.

[0118] <Pressure Control during Injection Molding> Next, the pressure control when injecting the resin material in the mold 75 during the filling process will be described. Fig. 15 is an explanatory diagram showing the changes in the injection speed S, injection pressure P, and virtual in-mold pressure V during the molding of a good product. When injecting the resin material from the heating barrel 11 of the injection device 10 into the mold 75 during the filling process, the movement control unit 120 of the control device 100 detects the detection result of the encoder 52 of the drive motor 51 of the forward and backward movement mechanism 50 for the position of the screw 20 that moves during injection by the position control controller 121, and performs speed control on the screw 20 according to the position by the speed control controller 122.

[0119] When the speed control controller 122 performs speed control on the screw 20, the injection speed S of the screw 20 is controlled along the set value of the injection speed S when performing speed control based on the moving position of the screw 20. The set value of the injection speed S is set, for example, by directly inputting the set value of the injection speed S by the operator. The set value of the injection speed S may be set by being selected from those preset according to the type of the molded product molded by the injection molding machine 1, the type of the resin material used for molding the molded product, etc. based on the type of the molded product and the resin material to be actually molded.

[0120] The set value of the set injection speed S is stored in the storage unit 140 of the control device 100. When performing speed control of the screw 20, using the set value of the injection speed S stored in the storage unit 140 as the target value, a speed command corresponding to the position of the screw 20 is transmitted by the position controller 121 to the speed controller 122, and speed control is performed by the speed controller 122. The speed controller 122 performs speed control of the screw 20 based on the speed command transmitted 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 and backward mechanism 50.

[0121] Therefore, the position controller 121 and the speed controller 122 perform speed control so that the injection speed S of the screw 20 becomes the set value which is the target value of the injection speed S in the filling process, and when the injection speed S of the screw 20 reaches the set value, the injection speed S is maintained. In this case, since the resin material is filled into the mold 75 over time, the pressure of the resin material increases in the mold 75 over time. For this reason, the pressure of the resin material in the heating 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 in the mold 75 increases.

[0122] Note that for the cavity 75a of the mold 75, after the runner connected to the cavity 75a is filled with the resin material, the cavity 75a is filled with the resin material. For this reason, even after the movement of the screw 20 starts on the side where the nozzle 12 is located, the injection pressure P does not immediately increase, and the injection pressure P increases after the runner is filled with the resin material. In the filling process, the injection pressure determination unit 115 continuously determines whether or not the increasing injection pressure P has reached the upper limit value PL set for the injection pressure P.

[0123] Here, when controlling the movement of the screw 20 in the filling process, the pressure loss calculation unit 113 of the control device 100 determines 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 and backward movement 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 in-mold purge pressure loss Lm, and the pressure loss calculation unit 113 determines the pressure loss when injecting the resin material based on the pressure loss model M of the in-mold purge pressure loss Lm and the injection speed S. Further, when a plurality of pressure loss models M are stored in the storage unit 140 according to the type of the resin material, etc., the pressure loss model M that matches the conditions such as the type of the resin material in the current injection molding is used.

[0124] After the pressure loss calculation unit 113 determines the pressure loss in the injection device 10, the virtual in-mold pressure calculation unit 114 of the control device 100 subtracts the pressure loss determined 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, and determines the result as the virtual in-mold pressure V, which is the pressure of the resin material in the mold 75. Specifically, since the pressure loss determined by the pressure loss calculation unit 113 is calculated based on the pressure loss model M of the in-mold purge pressure loss Lm, the virtual in-mold pressure V determined by the virtual in-mold pressure calculation unit 114 becomes the virtual in-mold pressure Vm at the time of in-mold purge calculated using the in-mold purge pressure loss Lm. When controlling the movement of the screw 20 in the filling process, the virtual in-mold pressure V is continuously determined by the pressure loss calculation unit 113 and the virtual in-mold pressure calculation unit 114 in this way. In the filling process, the virtual in-mold pressure V determined in this way also increases as the resin material fills the mold 75 and the pressure of the resin material in the mold 75 increases, similar to the injection pressure P.

[0125] Note that for the cavity 75a of the mold 75, after the runner connected to the cavity 75a is filled with the resin material, the cavity 75a is filled with the resin material. Therefore, similar to the injection pressure P, the virtual mold internal pressure V also rises after the movement of the screw 20 starts on the side where the nozzle 12 is located and the runner is filled with the resin material. In the filling process, the virtual mold internal pressure determination unit 116 continuously determines whether the rising virtual mold internal pressure V has reached the upper limit value set for the virtual mold internal pressure V.

[0126] While maintaining the injection speed S of the screw 20 at the set value in this way, the screw 20 is moved in the heating barrel 11. 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 holding pressure process, the injection speed S is decreased. By decreasing the injection speed S in the holding pressure process, the injection pressure P acting on the screw 20 and the virtual mold internal pressure V in the mold 75 also decrease as the injection speed S decreases.

[0127] Note that even after switching to the holding pressure process, the screw 20 moves the resin material slightly into the cavity 75a of the mold 75 at a low injection speed S toward the side where the nozzle 12 is located. As a result, the resin material can be fed into the cavity 75a that is cooled in the holding pressure process and in which the resin material slightly shrinks, so that sink marks on the molded product can be suppressed.

[0128] FIG. 16 is an explanatory diagram showing a state in which the upper limit value PL of the injection pressure P is reached 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 the upper limit value. In the filling process, the cavity 75a of the mold 75 is filled with the resin material by moving the screw 20 in the heating barrel 11 in this way. However, when filling the resin material, partial clogging may occur. When partial clogging occurs during the filling of the resin material in this way, the injection pressure P tends to increase.

[0129] For example, when a plurality of cavities 75a capable of molding a molded product are formed in a mold 75, if a blockage occurs in the gate connected to some of the cavities 75a, the resin material cannot be filled into the cavities 75a where the blockage has occurred. In this case, since the space in the mold 75 where the resin material can be filled becomes smaller, when feeding the resin material from the heating barrel 11 to the mold 75 by moving the screw 20, the injection pressure P acting on the screw 20 is likely to increase.

[0130] In the filling process, since the injection pressure determination unit 115 continuously determines whether the injection pressure P has reached the upper limit value PL set for the injection pressure P, when the injection pressure P reaches the upper limit value PL due to the increase in the injection pressure P, the injection pressure determination unit 115 determines that the injection pressure P has reached the upper limit value PL. When the movement control unit 120 of the control device 100 determines that the injection pressure P detected by the load cell 60 has reached the upper limit value PL as determined by the injection pressure determination unit 115, the movement control of the screw 20 is performed based on the injection speed S set as the injection speed S when the injection pressure P reaches the upper limit value PL. That is, when the injection pressure determination unit 115 determines that the injection pressure P has reached the upper limit value PL preset and stored in the storage unit 140, the movement control unit 120 performs the movement control of the screw 20 by the pressure control controller 124.

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

[0132] However, in the filling process, after clogging occurs in the gate connected to some 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 value PL. Therefore, for the cavities 75a different from the cavities 75a connected to the clogged gate, the filling of the resin material continues. In this state, when the injection pressure P reaches the upper limit value PL, it means that the pressure of the resin material in the cavity 75a filled with the resin material is also rising.

[0133] Therefore, in the cavity 75a filled with the resin material, burrs may occur on the molded product molded in the cavity 75a along with the pressure of the resin material. Also, burrs may occur on the runner connected to the cavity 75a. Since the molded product with burrs becomes a defective product, when clogging occurs in the gate connected to some of the cavities 75a, not only the molded product molded in the cavity 75a where the clogging occurs but also the molded products molded in the other cavities 75a will be disposed of as defective products.

[0134] FIG. 17 is an explanatory diagram showing a state where the control device 100 has the virtual mold internal pressure determination unit 116 and the virtual mold internal pressure V has reached the upper limit value VL. In the present embodiment, the control device 100 has a virtual mold internal pressure determination unit 116 that determines whether or not the virtual mold internal pressure V has reached the upper limit value VL. Therefore, even when clogging occurs in the gate connected to some of the cavities 75a in the filling process, it is possible to suppress the occurrence of defects in the molded products molded in the other cavities 75a.

[0135] That is, when clogging occurs in the gate connected to some of the cavities 75a during the filling process, it becomes impossible to fill the cavity 75a in which the clogging has occurred. Therefore, the resin material fed from the heating barrel 11 into the mold 75 is filled into the other cavities 75a. At this time, in a state where a cavity 75a that cannot be filled with the resin material has occurred, the space in the mold 75 where the resin material can be filled becomes smaller, while the amount of the resin material fed from the heating barrel 11 remains the same as in the normal state. Therefore, the pressure of the resin material tends to increase in the cavities 75a where no clogging has occurred.

[0136] In this embodiment, the pressure loss calculation unit 113 obtains 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 mold internal pressure calculation unit 114 subtracts the pressure loss obtained by the pressure loss calculation unit 113 from the injection pressure P detected by the load cell 60 to obtain the virtual mold internal pressure V. In this case, since the pressure loss obtained by the pressure loss calculation unit 113 is obtained based on the pressure loss model M of the in-mold purge pressure loss Lm, the virtual mold internal pressure calculation unit 114 obtains the in-mold purge virtual mold internal pressure Vm as the virtual mold internal pressure V.

[0137] Furthermore, the virtual mold internal pressure determination unit 116 determines whether or not the virtual mold internal pressure V obtained by the virtual mold internal pressure calculation unit 114 has reached the upper limit value VL set for the virtual mold internal pressure V. When the virtual mold internal pressure determination unit 116 determines that the virtual mold internal pressure V has reached the upper limit value VL, the movement control unit 120 performs movement control of the screw 20 based on the virtual mold internal pressure V. That is, when the virtual mold internal pressure determination unit 116 determines that the virtual mold internal pressure V obtained by the virtual mold internal pressure calculation unit 114 has reached the upper limit value VL, the movement control unit 120 of the control device 100 performs movement control of the screw 20 based on the injection speed S set as the injection speed S when the virtual mold internal pressure V reaches the upper limit value VL.

[0138] The upper limit value VL of the virtual internal pressure V used for the determination in the virtual internal pressure determination unit 116 is set to a value lower than the virtual internal pressure V when the injection pressure P reaches the upper limit value PL, and is set to be approximately the same magnitude as the maximum value of the pressure of the resin material in the mold 75 when a good product is molded in the mold 75. When the virtual internal pressure determination unit 116 determines that the virtual internal pressure V obtained by the virtual internal pressure calculation unit 114 has reached the upper limit value VL preset and stored in the storage unit 140, the movement control unit 120 performs movement control of the screw 20 by the virtual internal pressure controller 125.

[0139] When the virtual internal pressure determination unit 116 determines that the virtual internal pressure V has reached the upper limit value VL, the virtual internal pressure controller 125 performs movement control of the screw 20 so that the injection speed S becomes 0. That is, when the virtual internal pressure V reaches the upper limit value VL, the virtual internal pressure controller 125 gradually decreases the injection speed S and stops the movement of the screw 20 toward the side where the nozzle 12 is located. Thereby, the filling of the resin material from the heating barrel 11 into the mold 75 is stopped. In this case, since the virtual internal pressure V obtained by the virtual internal pressure calculation unit 114 is calculated based on the injection pressure P obtained by the injection pressure acquisition unit 112, when the injection pressure P increases, the virtual internal pressure V also increases as the injection pressure P increases.

[0140] On the other hand, the upper limit value VL of the virtual internal pressure V is set to a value lower than the virtual internal pressure V when the injection pressure P reaches the upper limit value PL, and is set to be approximately the same magnitude as the maximum value of the pressure of the resin material in the mold 75 when a good product is molded in the mold 75. Therefore, when the filling of the resin material into the mold 75 is stopped due to the virtual internal pressure V reaching the upper limit value VL in a situation where the injection pressure P increases due to clogging occurring in the gate connected to some of the cavities 75a, the pressure of the resin material in the mold 75 other than the cavity 75a where the clogging has occurred becomes approximately the same as the pressure of the resin material during the molding of a good product.

[0141] Thus, even if clogging occurs in the gates connected to some of the cavities 75a, the pressure of the resin material in the other cavities 75a and runners will be approximately the same as during the molding of good products, so that good products can be molded without the occurrence of burrs. Therefore, even if clogging occurs in the gates connected to some of the cavities 75a, good products can be molded in the cavities 75a other than the cavities 75a where clogging has occurred, so that the occurrence of defective products can be suppressed.

[0142] <Effects of the Embodiment> In the injection molding machine 1 according to the above embodiment, the pressure loss acquisition unit 111 acquires, as pressure loss, the pressure detected by the load cell 60 when injecting the resin material from the nozzle 12 that contacts the stationary mold 76 in the state where the stationary mold 76 and the movable mold 77 are open. The injection pressure acquisition unit 112 acquires, as the injection pressure P, the pressure detected by the load cell 60 when injecting the resin material from the nozzle 12 into the cavity 75a in the state where the stationary mold 76 and the movable mold 77 are closed. The virtual mold internal pressure calculation unit 114 calculates the virtual mold internal 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, based on the pressure loss in the state where the viscosity of the resin material has increased due to the nozzle 12 contacting the mold 75 and the temperature of the nozzle 12 decreasing, the virtual mold internal pressure V can be calculated.

[0143] Thereby, the conditions for calculating the virtual mold internal pressure V can be made closer to the conditions when actually filling the resin material into the mold 75 with the nozzle 12 contacting the mold 75 during molding, and the calculated virtual mold internal pressure V can be made as close as possible to the magnitude of the internal pressure in the actual molding. That is, as shown in FIG. 11, since the virtual mold internal pressure Vm during mold purge is closer to the actually measured mold internal pressure Va than the virtual mold internal pressure Vr during resin purge, the virtual mold internal pressure V calculated by the virtual mold internal pressure calculation unit 114 can be made close to the magnitude of the internal pressure in the actual molding. As a result, the internal pressure of the mold can be calculated with high accuracy.

[0144] Further, 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 where the injection speeds S are the same as each other. Thereby, the virtual mold internal pressure V calculated by the virtual mold internal pressure calculation unit 114 can be calculated to be close to the magnitude of the internal pressure of the mold during actual molding regardless of the injection speed S. As a result, the internal pressure of the mold can be calculated with higher accuracy more reliably.

Explanation of Signs

[0145] 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... communication portion, 25... check ring, 30... propulsion mechanism, 31... drive motor, 40... rotation mechanism, 41... rotation mechanism main body portion, 43... drive motor, 44... transmission belt, 45... pulley, 46... bearing, 50... forward and backward movement mechanism, 51... drive 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... movable platen, 75... mold, 75a... cavity, 76... fixed mold, 77... movable mold, 80... mold clamping drive mechanism, 81... toggle mechanism, 85... extrusion mechanism, 86... extrusion member, 87... extrusion pin, 88... extrusion plate, 100... control device, 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... speed 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... load sensor

Claims

1. An injection device that melts a resin material in a heating barrel with a screw disposed inside and moves the screw toward the side where a nozzle for injecting the melted resin material is located, thereby injecting the resin material from the nozzle; A mold comprising a fixed mold and a movable mold that open and close, and having a cavity filled with the resin material injected from the nozzle in a closed state, and molding the resin material in the cavity; A pressure detection unit that detects the pressure acting on the screw when injecting the resin material; A control device that controls the internal pressure of the mold, which is the pressure of the resin material in the mold, by controlling the movement of the screw; Comprising: The control device: A pressure loss acquisition unit that acquires, as a pressure loss, the pressure detected by the pressure detection unit when injecting the resin material from the nozzle in contact with the fixed mold in a state where the fixed mold and the movable mold are open; An injection pressure acquisition unit that acquires, as an injection pressure, the pressure detected by the pressure detection unit when injecting the resin material from the nozzle into the cavity in a state where the fixed mold and the movable mold are closed; A virtual internal pressure calculation unit that calculates a virtual internal pressure, which is the virtual internal pressure of the mold, by subtracting 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 from the injection pressure acquired by the injection pressure acquisition unit; An injection molding machine, characterized by having the above.

2. An injection speed detection unit that detects an injection speed, which is the moving speed of the screw when injecting the resin material, is provided; The pressure loss acquisition unit acquires the pressure loss in association with the injection speed; The injection pressure acquisition unit acquires the injection pressure in association with the injection speed; The injection molding machine according to claim 1, wherein the virtual internal pressure calculation unit calculates the virtual internal pressure by subtracting the pressure loss from the injection pressures having the same injection speed.

3. An injection device that melts a resin material in a heating barrel with a screw disposed inside and moves the screw toward the side where a nozzle for injecting the melted resin material is located, thereby injecting the resin material from the nozzle; A mold comprising a fixed mold and a movable mold that open and close, and having a cavity filled with the resin material injected from the nozzle in a closed state, and molding the resin material in the cavity; A pressure detection unit that detects the pressure acting on the screw when injecting the resin material; A method for detecting the in-mold pressure, which is the pressure of the resin material in the mold of an injection molding machine comprising: A procedure 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; A procedure of 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 procedure of calculating a virtual in-mold pressure, which is the virtual in-mold pressure, by subtracting the pressure loss obtained by the procedure of obtaining the pressure loss from the injection pressure or the pressure loss based on the pressure loss obtained by the procedure of obtaining the pressure loss; A method for detecting in-mold pressure, characterized by including the above.

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