Control method for injection molding machine and injection molding machine

Abstract

In order to more reliably improve the quality of a molded product, in a control method for an injection molding machine (1) including a metering process in which a resin material is melted by rotating a screw (60) while retreating the screw (60) in a heating cylinder (50) in which the resin material is melted, in order to stop the retreat of the screw (60) at the completion of the metering process, the rotational speed of the screw (60) is reduced from a point in time at which the retreat speed of the screw (60) is reduced before the completion of the metering process in the metering process; the rotational speed and rotational direction of the screw (60) are controlled so that the back pressure of the pressure of the melted resin metered in the metering process becomes a target pressure that is lower than the back pressure at the completion of the metering process at the arrival of a target time.

Description

Technical Field

[0001] This invention relates to a control method for an injection molding machine that injects molten resin material to form a mold, and to an injection molding machine itself. Background Technology

[0002] In the metering process of injecting resin into a metal mold in an injection molding machine, the screw is rotated inside the heating tank to melt and mix the resin material, while the screw is retracted to a predetermined position. This conveys the amount of molten resin to be injected into the metal mold in the next injection cycle to the front end of the heating tank, thus metering the molten resin. Furthermore, in conventional injection molding machines, there are machines that perform a predetermined screw action after metering to ensure the pressure reduction of the metered molten resin and the quality of the molded product. However, because the pressure of the molten resin at the front end of the heating tank increases after metering, it is possible for the metered molten resin to leak from the nozzle at the front end of the heating tank, resulting in defects such as variations in the amount of resin used in molding or appearance defects in the molded product. Therefore, conventional injection molding machines include those that perform a predetermined screw action after metering the molten resin to suppress these defects.

[0003] For example, in the injection molding machine described in Patent Document 1, after the molten resin is metered, the screw is retracted to a retraction stop point, and during a predetermined period of retraction, the retraction speed is reduced and the screw is rotated in the opposite direction to prevent excessive reverse rotation and to adjust the depressurization with high precision. This allows for a more accurate determination of the metering conditions to obtain a uniform amount of metered resin in a shorter time. Furthermore, in the injection apparatus described in Patent Document 2, the molten material is depressurized by rotating the screw by a predetermined rotation angle in the opposite direction of the plasticizing rotation immediately after the plasticizing of the molding material has ended, achieving degassing of the molten material with a simple structure.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2007-253606

[0007] Patent Document 2: Japanese Patent Application Publication No. 2008-143022 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] As a method to reduce the pressure of the metered molten resin, examples include backdrafting (so-called reverse suction) by retracting the screw to a specified position or a specified amount, or rotating the screw in the opposite direction by a specified rotation angle, as described above. However, when backdrafting is performed, the pressure of the molten resin at the front end of the heating tank after metering drops sharply and locally. Therefore, molten resin at the rear end of the heating tank, i.e., the hopper side into which the resin material is fed, may flow through the retaining ring on the screw into the front end of the heating tank. In this case, the weight stability of the molded product may decrease due to the change in the amount of resin metered. Furthermore, when the pressure of the molten resin drops sharply and locally due to backdrafting, pore-like negative pressure voids are easily generated in the molten resin, and gas generated from the molten resin tends to accumulate in these voids. In this case, so-called silver streaks, which appear as silvery marks, may occur on the surface of the molded product, or the surface of the metal mold may be contaminated by the gas. The gas generated from the molten resin can be associated with a decrease in the quality of the molded product.

[0010] Furthermore, when the screw is briefly reversed at a predetermined angle after the molten resin is metered, the overall pressure inside the heating tank is drastically reduced to near atmospheric pressure. This results in gas being generated from the molten resin as a whole, rather than locally, and gas that cannot be discharged to the hopper tends to accumulate inside the heating tank. Additionally, during the cooling period between the completion of the metering process in the heating tank and the completion of the curing time required for the resin filled into the metal mold, gas is continuously generated from the molten resin, and the amount of gas that cannot be discharged to the hopper tends to increase over time. Moreover, adjusting the amount and duration of reverse rotation is difficult when the screw is briefly reversed at a predetermined angle after the molten resin is metered. Excessive settings can lead to excessive pressure drop in the molten resin, causing air entrapment and molding defects such as silver streaks, thus reducing the quality of the molded product.

[0011] As such, various adverse conditions may occur when back suction is performed to reduce the pressure of the metered molten resin, or when the screw is rotated in the opposite direction at a specified rotation angle for a short time. It is very difficult to properly reduce the pressure of the metered molten resin without degrading the quality of the molded product.

[0012] The present invention was made in view of the above, and the object is to provide a control method for an injection molding machine and an injection molding machine that can more reliably improve the quality of molded articles.

[0013] Methods used to solve problems

[0014] To address the aforementioned issues and achieve the objectives, the control method for the injection molding machine of the present invention includes a metering step of metering molten resin by rotating and retracting a screw within a heated tank in which resin material is molten; in order to stop the retraction of the screw upon completion of the metering step, the rotational speed of the screw is reduced from a point in the metering step where the retraction speed of the screw is reduced before the completion of the metering step; the rotational speed and direction of the screw are controlled so that the back pressure, which is the pressure of the molten resin measured in the metering step, becomes a target pressure at the target time that is lower than the back pressure at the completion of the metering step.

[0015] Furthermore, in order to solve the aforementioned problems and achieve the objectives, the injection molding machine of the present invention includes:

[0016] A heating tank is used to melt the resin material inside, turning it into molten resin.

[0017] The screw is rotatably disposed within the heating barrel and is movable within the heating barrel in the direction of the rotation axis.

[0018] The back pressure detection unit detects the back pressure, which is the pressure of the molten resin pressed out by the screw within the heating tank; and

[0019] The control unit controls the rotation and movement of the screw, and extrudes molten resin into the heating tank by rotating and retracting the screw simultaneously. The molten resin extruded by the screw is metered based on the back pressure detected by the back pressure detection unit. To stop the screw's retraction upon completion of the metering process (which is the metering step for the molten resin), the control unit decelerates the screw's rotation speed during the metering process from the point where the screw's retraction speed is decelerated before the completion of the metering process. The control unit controls the screw's rotation speed and direction so that the back pressure detected by the back pressure detection unit at the target time is a target pressure lower than the back pressure at the completion of the metering process.

[0020] Invention Effects

[0021] The control method for the injection molding machine of the present invention and the injection molding machine have the effect of improving the quality of the molded products more reliably. Attached Figure Description

[0022] Figure 1 This is a perspective view of an injection molding machine according to an embodiment.

[0023] Figure 2This is a sectional view showing the main part of the apparatus structure of the injection molding machine according to the relevant embodiments.

[0024] Figure 3 This is a top view showing the main parts of the apparatus structure of the injection molding machine according to the relevant embodiments.

[0025] Figure 4 yes Figure 2 A detailed diagram of the heating tank is shown.

[0026] Figure 5 yes Figure 4 Detailed diagram of the retaining ring shown.

[0027] Figure 6 This is an explanatory diagram regarding the period of pressure reduction control for molten resin.

[0028] Figure 7 This is an explanatory diagram regarding the decompression control of molten resin in an injection molding machine according to a relevant embodiment.

[0029] Figure 8 This is an explanatory diagram showing the change in overall pressure of the molten resin inside the heating tank when pressure reduction control is applied.

[0030] Figure 9 This is an explanatory diagram showing the change in overall pressure of the molten resin inside the heating tank during backflow.

[0031] Figure 10 This is an explanatory diagram showing the change in overall pressure of the molten resin inside the heating tank when the screw is rotated in the opposite direction at a specified rotation angle for a short period of time.

[0032] Figure 11 This is a variation of the control method for the injection molding machine according to the embodiment, and is an explanatory diagram for the case where the target pressure is an arbitrary set pressure.

[0033] Figure 12 This is a variation of the control method for the injection molding machine according to the implementation method, and is an explanatory diagram for the case where the target time is an arbitrary offset time. Detailed Implementation

[0034] The following describes in detail, based on the accompanying drawings, the control method for the injection molding machine of this disclosure and embodiments thereof. However, this invention is not limited to these embodiments. Furthermore, the elements constituting the following embodiments include those that can be substituted and readily conceived by those skilled in the art, or those that are substantially the same.

[0035] [Implementation Method]

[0036] Figure 1 This is a perspective view of injection molding machine 1 according to the embodiment. Figure 2This is a sectional view showing the main part of the apparatus structure of the injection molding machine 1 according to the relevant embodiment. Figure 3 This is a top view showing the main components of the injection molding machine 1 according to the embodiment. In the following description, the vertical direction of the injection molding machine 1 in its normal operating state is defined as the vertical direction Z, the upper side of the injection molding machine 1 in its normal operating state is defined as the upper side, and the lower side of the injection molding machine 1 in its normal operating state is defined as the lower side. Furthermore, in the following description, the length direction Y of the injection molding machine 1 is also defined as the length direction Y in each part containing the injection molding machine 1, and the direction orthogonal to both the vertical direction Z and the length direction Y of the injection molding machine 1 is defined as the width direction X of the injection molding machine 1.

[0037] <Injection Molding Machine 1>

[0038] The injection molding machine 1 of this embodiment is configured with a base 5 and an injection device 10 and a mold clamping device 15 disposed on the base 5. In addition, the injection molding machine 1 has a display unit 101 for displaying various information of the injection molding machine 1 and an input unit 102 for use when the operator inputs operations on the injection molding machine 1, which are disposed near the center in the length direction Y.

[0039] The base 5 is formed in a generally rectangular shape with its length direction being the length direction Y of the injection molding machine 1. A first track 6 is disposed on the upper surface of the base 5. Two first tracks 6 are disposed on the base 5 in the width direction X, and both first tracks 6 extend along the length direction of the base 5. The injection device 10 is movably mounted on the first track 6 along the extension direction of the first track 6, thereby allowing the injection device 10 to be movably disposed in the length direction Y.

[0040] The mold clamping device 15 is disposed on one side of the injection unit 10 in the longitudinal direction Y on the base 5. The mold clamping device 15 has a mold clamping mechanism that opens and closes the metal mold (not shown) assembled on the mold clamping mechanism. The mold clamping device 15 is preferably driven by a servo motor, but it can also be driven by hydraulic pressure. The injection molding machine 1 of this embodiment has a cover on the outside of the injection unit 10 and the mold clamping device 15. Figure 1 The illustration shows the injection device 10 and the mold closing device 15 being covered by covers.

[0041] <Injection Device 10>

[0042] In the following description, the side of the injection device 10 and the mold clamping device 15 located relative to the injection device 10 in the length direction Y is defined as the front or front side, and the opposite side of the side of the injection device 10 and the mold clamping device 15 located relative to the injection device 10 in the length direction Y is defined as the rear or rear side.

[0043] The injection device 10 includes a frame 20, a heating tank 50, a screw 60, a rotation mechanism 70 for rotating the screw 60, a forward / backward mechanism 80 for moving the screw 60 forward and backward, and a propulsion mechanism 40 for the injection device 10. The frame 20 is formed by a base 21 and an upper frame 30 mounted on the base 21. The base 21 is a flat frame in the vertical direction Z, and legs 24 are arranged at four points on both sides in the length direction Y and on both sides in the width direction X. The four legs 24 are movably mounted on two first tracks 6 arranged on the base 5 along the extension direction of the first tracks 6. Thus, the base 21 is slidably supported relative to the base 5 in the length direction Y.

[0044] The propulsion mechanism 40 includes a drive motor 41 and a ball screw mechanism 43. The drive motor 41 is mounted on the rear wall 23 located on the rear side of the base 21 in the longitudinal direction Y. The drive motor 41 is arranged with its drive shaft extending in the longitudinal direction Y, and the drive shaft of the drive motor 41 passes through the rear wall 23 of the base 21 and is connected to the threaded portion 44 of the ball screw mechanism 43 via a connecting mechanism 42. Thus, when the drive motor 41 is driven, the driving force of the drive motor 41 is transmitted from the drive shaft via the connecting mechanism 42, and the ball screw mechanism 43 can rotate by the transmitted driving force.

[0045] The threaded portion 44 of the ball screw mechanism 43 extends in the longitudinal direction Y and passes approximately through the center of the base 21 in the width direction X. Its front end in the longitudinal direction Y is rotatably supported by the front wall 22 of the base 21 located on the front side in the longitudinal direction Y. Furthermore, the nut portion 45 of the ball screw mechanism 43 is fixed to the upper surface of the base 5 inside the base 21. Thus, when the propulsion mechanism 40 is driven by the drive motor 41, the threaded portion 44 of the ball screw mechanism 43 rotates by the driving force transmitted from the drive motor 41, and the threaded portion 44 can move relative to the nut portion 45 fixed to the base 5 in the extending direction of the threaded portion 44. Therefore, the propulsion mechanism 40 can move the base 21 supporting the threaded portion 44 relative to the base 5 on which the nut portion 45 is fixed in the longitudinal direction Y, and can move the frame 20 having the base 21 in the longitudinal direction Y on the first track 6 disposed on the base 5. Thus, the propulsion mechanism 40 enables the injection device 10 to move in the length direction Y.

[0046] The upper frame 30 is formed into a square frame shape and is rotatably mounted on the front end of the base 21 in the longitudinal direction Y by a support pin 33. Furthermore, the upper frame 30 is fixed to the base 21 in a non-rotatable state by a fixing thread 34 that secures the upper frame 30 to the base 21 at a location other than where the support pin 33 is located. Therefore, the upper frame 30 is configured such that if the fixing thread 34 is removed and the fixation by the fixing thread 34 is released, it can rotate relative to the base 21 about the support pin 33.

[0047] The upper frame 30 has a front wall 31 that extends upwards in the vertical direction Z from the mounting portion that is mounted to the base 21. The heating barrel 50 is mounted on the front wall 31 of the upper frame 30. The heating barrel 50 extends forward from the front wall 31 in the longitudinal direction Y, and a nozzle portion 52 that is in close contact with the metal mold is disposed at its front end, i.e., the front end of the heating barrel 50. Therefore, the heating barrel 50 is disposed on the upper side of the frame 20 in the vertical direction Z and on the front side of the frame 20 in the longitudinal direction Y.

[0048] In detail, the heating tank 50 is formed in a generally cylindrical shape and is arranged along the length Y direction in the axial direction, and is equipped with a heater 51 such as a belt heater (see reference). Figure 4 Thus, the heating chamber 50 can melt the resin material inside. That is, the heating chamber 50 can be heated and melted inside by the heater 51, becoming molten resin as a plasticizer.

[0049] The screw 60 is disposed inside the heating tank 50 and has a helical shape with its axial direction aligned with the axial direction of the heating tank 50; that is, the screw 60 has helical grooves on its outer circumferential surface. Thus, the helical screw 60 can rotate about its axial center within the heating tank 50. Furthermore, the screw 60 can move within the heating tank 50 in the direction of its rotational axis. In other words, the screw 60 is configured such that the central axis of the cylinder shaped like the heating tank 50 is substantially aligned with the axis of rotation of the screw 60, and it is also configured to move in the axial direction of the heating tank 50. The screw 60, rotatably disposed within the heating tank 50, can mix the molten resin by rotating inside the heating tank 50; therefore, the heating tank 50 is a tank capable of mixing molten resin internally.

[0050] A hopper 55 is disposed near the side of the heating tank 50 on which the upward frame 30 is mounted. The hopper 55 communicates with the interior of the heating tank 50 and is capable of supplying resin-based pellets (not shown) as raw material resin into the heating tank 50.

[0051] Furthermore, on the upper frame 30, second tracks 35 are respectively arranged on the side walls 32 on both sides in the width direction X of the upper frame 30. The second tracks 35 extend in the length direction Y, that is, they extend approximately parallel to the heating barrel 50.

[0052] The rotating mechanism 70 is positioned rearward of the heating tank 50 in the longitudinal direction Y, enabling the screw 60, disposed inside the heating tank 50, to rotate about a central axis. The rotating mechanism 70, which rotates the screw 60, includes a main body 71, a drive motor 73, a transmission belt 74, and pulleys 75. The main body 71 has a support rod 72 extending in the width direction X, which is slidably mounted on two second tracks 35 in the width direction X. Thus, the main body 71 is movably mounted on the second tracks 35 via the support rod 72.

[0053] A drive motor 73 is disposed on the upper side of the main body 71 of the rotating mechanism. A pulley 75 is disposed in front of the main body 71 of the rotating mechanism and is rotatably disposed relative to the main body 71 of the rotating mechanism via a bearing 76. Furthermore, the pulley 75 is connected to the drive shaft of the drive motor 73 via a transmission belt 74, thereby enabling the pulley 75 to rotate by the driving force of the drive motor 73 transmitted via the transmission belt 74. In this way, the pulley 75, which can rotate by the driving force transmitted from the drive motor 73, is coaxially and integrally fixed relative to the screw 60. In other words, the rear end of the screw 60 in the length direction Y is connected to the pulley 75. Thus, the screw 60 disposed in the heating tank 50 can rotate integrally with the pulley 75 by the driving force transmitted from the drive motor 73.

[0054] A forward / reverse mechanism 80 is disposed behind the main body 71 of the rotating mechanism in the longitudinal direction Y. The forward / reverse mechanism 80 enables the screw 60 disposed within the heating barrel 50 to move in the axial direction of the screw 60. That is, the screw 60 can move forward or backward in the longitudinal direction Y. In detail, the forward / reverse mechanism 80 includes a drive motor 81, a transmission belt 83, a pulley 84, and a ball screw mechanism 86. The drive motor 81 is disposed to the side in the width direction X of the upper frame 30. Furthermore, the drive motor 81 has an encoder 82 for detecting the rotational position of the drive motor 81, and the drive shaft of the drive motor 81 is connected to the pulley 84 via the transmission belt 83.

[0055] The pulley 84 is rotatably supported on the upper frame 30 by the bearing 85. The threaded portion 87 of the ball screw mechanism 86 is integrally connected to the pulley 84. The threaded portion 87 of the ball screw mechanism 86 is coaxially arranged with the screw 60, and is also coaxially arranged with respect to the pulley 75 on the main body 71 of the rotating mechanism. The nut portion 88 of the ball screw mechanism 86 in the forward / reverse mechanism 80 is formed in a generally cylindrical shape, and the threaded portion 87 of the ball screw mechanism 86 is screwed into this nut portion 88.

[0056] A force gauge 90 is disposed between the nut portion 88 of the ball screw mechanism 86 of the forward / reverse mechanism 80 and the main body portion 71 of the rotary mechanism 70, along the length Y direction. The force gauge 90 is disposed on the rear side of the main body portion 71 of the rotary mechanism 70 and the front side of the nut portion 88 of the ball screw mechanism 86 of the forward / reverse mechanism 80.

[0057] The force gauge 90 is a load cell that measures the load applied in the axial direction. It consists of a strain generator and a strain sensor (both omitted from the illustration) mounted on the strain generator. In this embodiment, the force gauge 90 is arranged with the axial direction as its length direction Y, and is formed in a generally cylindrical shape that is flat in the length direction Y. The inner diameter of the cylinder is larger than the outer diameter of the threaded portion 87 of the ball screw mechanism 86 in the forward / reverse mechanism 80. The front side of the force gauge 90 in the length direction Y is integrally fixed to the rotating mechanism body 71 of the rotating mechanism 70, and the rear side in the length direction Y is integrally fixed to the nut portion 88 of the ball screw mechanism 86 in the forward / reverse mechanism 80. The force gauge 90, which is disposed between the rotating mechanism body 71 of the rotating mechanism 70 and the nut portion 88 of the ball screw mechanism 86 in the forward / reverse mechanism 80, can detect the load acting in the length direction Y between the rotating mechanism body 71 and the nut portion 88.

[0058] Figure 4 yes Figure 2 A detailed drawing of the heating tank 50 is shown. The heating tank 50 is as follows... Figure 4 As shown, a heater 51, which is formed in a generally cylindrical shape, has a belt heater or the like disposed on its outer peripheral surface. The nozzle portion 52 of the heating barrel 50, located at its front end in the longitudinal direction Y, is formed in a generally cylindrical shape with an inner diameter smaller than the inner diameter of the heating barrel 50, and is disposed with an opening at the front side in the longitudinal direction Y. A screw 60 disposed within the heating barrel 50 has a helical blade 61 that protrudes radially outward from the screw 60 and is formed in a helical shape centered on the axis of the screw 60. Thus, adjacent surrounding portions of the screw 60 with the helical blade 61 have helical groove-like portions relative to each other.

[0059] On the screw 60 thus formed, a retaining ring 65 is disposed near the front end in the longitudinal direction Y. The retaining ring 65 is disposed in a groove 62 formed near the front end in the longitudinal direction Y of the screw 60. The groove 62 is a groove formed around the circumference of the screw 60 with the groove width direction in the axial direction of the screw 60.

[0060] Figure 5 yes Figure 4 A detailed view of the retaining ring 65 is shown. The retaining ring 65 is formed in a generally cylindrical shape and is disposed in the groove 62 of the screw 60 with its axis roughly aligned with the axis of the screw 60. The outer diameter of the generally cylindrical retaining ring 65 is the same as, but slightly smaller than, the inner diameter of the heating barrel 50. Furthermore, the inner diameter of the retaining ring 65 is larger than the diameter of the bottom of the groove 62 of the screw 60, and a gap is formed between the inner circumferential surface of the retaining ring 65 and the bottom of the groove 62 of the screw 60. In addition, the width of the retaining ring 65 in the axial direction is smaller than the groove width of the groove 62 of the screw 60. Therefore, the retaining ring 65 can move in the groove width direction within the groove 62.

[0061] Furthermore, a connecting portion 64 is formed on the screw 60, which connects the front portion of the groove 62 in the longitudinal Y direction to the inside of the groove 62. The connecting portion 64 opens on the groove wall 63 on the front side in the groove width direction of the groove 62.

[0062] Furthermore, the injection molding machine 1 includes a control unit 100 that performs various controls on the injection molding machine 1. The control unit 100 includes a CPU (Central Processing Unit) for performing arithmetic processing, and RAM (Random Access Memory) and ROM (Read Only Memory) that function as storage for various information. All or part of the functions of the control unit 100 are implemented by loading an application program stored in ROM into RAM and executing it through the CPU, and by reading and writing data from RAM or ROM.

[0063] Both the display unit 101 and the input unit 102 are connected to the control unit 100. The display unit 101 displays information transmitted from the control unit 100. Furthermore, the input unit 102 transmits input operation information to the control unit 100. Additionally, the encoder 82 mounted on the drive motor 81 of the forward / reverse mechanism 80 or the force gauge 90 mounted between the forward / reverse mechanism 80 and the rotation mechanism 70 are connected to the control unit 100, enabling the transmission of detection results to the control unit 100. Moreover, the heater 51 of the injection device 10, the drive motor 73 of the rotation mechanism 70, the drive motor 81 of the forward / reverse mechanism 80, and the drive motor 41 of the propulsion mechanism 40 are connected to the control unit 100 and operate via control signals from the control unit 100.

[0064] <Function of Injection Molding Machine 1>

[0065] The injection molding machine 1 according to this embodiment includes the structure described above, and its operation will be explained below. The injection molding machine 1 repeatedly performs the injection-molding cycle, with one injection-molding action constituting one cycle. Figure 6 This is an illustrative diagram regarding the period of pressure reduction control for molten resin. Figure 6 The upper section illustrates the processing steps in the mold closing device 15, and the lower section illustrates the processing steps in the injection device 10. Each cycle includes the injection of resin material used in molding and multiple steps for molding the article. Each cycle includes, for example, an injection step, a cooling step, a mold opening step, a removal step, an intermediate step, a mold closing step, and a metering step.

[0066] The injection process is a process in which the nozzle 52 of the heating barrel 50 of the injection device 10 is pressed against the through-hole of the fixed metal mold (not shown) of the mold clamping device 15, and molten resin, which is the resin material melted by the heating barrel 50, is injected into the space between the movable metal mold (not shown) and the fixed metal mold.

[0067] The cooling process involves the resin material, i.e. the molding resin, injected into the space between the fixed metal mold and the movable metal mold of the mold clamping device 15, cooling down and solidifying, and then waiting for a certain period of time until the molding resin becomes a molded product.

[0068] The mold opening process is a process in which the movable metal mold separates from the fixed metal mold in order to remove the molded product formed by the fixed metal mold and the movable metal mold of the mold closing device 15.

[0069] The removal process is a process in which the molded article is ejected from the moving metal mold by the ejection component (not shown) provided by the mold closing device 15.

[0070] Intermediate processes are those processes in which the molded part ejected from the moving metal mold is moved to a designated position and obtained.

[0071] The mold closing process is a process of combining the movable metal mold and the fixed metal mold of the mold closing device 15 to form a space between the movable metal mold and the fixed metal mold that corresponds to the shape of the product.

[0072] The metering process is a process of conveying molten resin to be injected in the next cycle to the end side of the nozzle portion 52 of the heating tank 50 of the injection device 10, preparing the resin material for use in the next cycle. The metering process is as follows: Figure 6 As shown, the cooling process is carried out during the cooling process in the mold closing device 15.

[0073] When molding an article using injection molding machine 1, these injection-molding cycles are repeatedly executed. During these repeated cycles, the control unit 100 continuously heats the heating tank 50 with heater 51 so that the resin material in the heating tank 50 can be smoothly injected. As a result, the heating tank 50 holds the resin material in a molten state.

[0074] The control unit 100 performs control while determining the start or end date of each step within the injection molding cycle. To determine the start or end date of each step, for example, a flag is pre-defined in the initial or final step of each step in the program used by the control unit 100 to operate the injection molding machine 1. Thus, the control unit 100 can determine the start or end date of each step during the execution of the program used to operate the injection molding machine 1. That is, by defining the flag, the control unit 100 can determine that the process has moved to the next step when the flag is executed before or after the processing of a step in each step.

[0075] Furthermore, when a process change occurs, the control unit 100 causes the display unit 101 to display the process change. That is, the display unit 101 displays the current process of the injection molding machine 1. Thus, the operator can identify the current operating status of the injection molding machine 1 by visually viewing the display unit 101.

[0076] <Metrification Process>

[0077] In the injection molding machine 1 of this embodiment, pressure reduction control is performed on the resin material that has been metered in the metering step during each step of the injection-molding cycle. Next, the metering step performed before the pressure reduction control of the resin material will be described in detail. The resin material metered in the metering step is fed into the hopper 55 in the form of pellets and supplied from the hopper 55 to the heating tank 50. The heating tank 50 is heated by the heater 51, thereby creating a high temperature inside the heating tank 50. The resin material supplied to the heating tank 50 in the form of pellets melts inside the heating tank 50, becoming molten resin.

[0078] In the metering process, the screw 60 is rotated and moved rearward in the length direction Y within the heating tank 50 where the resin material is molten. The rotation of the screw 60 is performed by a rotating mechanism 70. That is, the rotating mechanism 70 is driven by a drive motor 73, and the driving force generated by the drive motor 73 is transmitted to the pulley 75 by the transmission belt 74, and then from the pulley 75 to the screw 60, thereby causing the screw 60 to rotate.

[0079] The rotation direction of the screw 60 here is the direction in which molten resin between adjacent surrounding portions of the spiral blades 61 of the screw 60 is conveyed towards the front end in the length direction Y, i.e., the side where the nozzle portion 52 is located. In the following description, the direction of rotation of the screw 60 that conveys molten resin towards the front side in the length direction Y is described as forward rotation, and the opposite direction is described as reverse rotation.

[0080] Furthermore, the movement of the screw 60 to the rearward side in the longitudinal direction Y, i.e., the retraction of the screw 60, is performed by the forward-retracting mechanism 80. When the screw 60 is retracted by the forward-retracting mechanism 80, the drive motor 81 of the forward-retracting mechanism 80 is driven. The driving force generated by the drive motor 81 is transmitted to the pulley 84 by the transmission belt 83, and then transmitted from the pulley 84 to the threaded portion 87 of the ball screw mechanism 86, causing the threaded portion 87 to rotate. As a result, the nut portion 88 of the ball screw mechanism 86 moves in the longitudinal direction Y. Together with the nut portion 88, the force gauge 90 and the rotating mechanism 70 as a whole move in the longitudinal direction Y while being supported by the second track 35. Consequently, the screw 60, which is connected to the pulley 75 of the rotating mechanism 70, also moves in the longitudinal direction Y together with the pulley 75 of the rotating mechanism 70, and the screw 60 retracts.

[0081] In the metering process, the screw 60 is rotated forward and then retracted simultaneously, thereby conveying the molten resin in the heating tank 50 towards the front end of the heating tank 50. That is, in the metering process, the control unit 100 controls the rotation and movement of the screw 60 to expel the molten resin from the heating tank 50 towards the front end of the heating tank 50. At this time, the control unit 100 uses the amount of movement of the screw 60 when partially expelling the molten resin towards the front end of the heating tank 50 while retracting, and the pressure of the molten resin delivered to the front end of the heating tank 50, to meter the molten resin.

[0082] In this case, the measurement of molten resin refers to the amount of molten resin accumulated in the portion of the heating tank 50 located in the length direction Y, in front of the bit ring 65, that is injected into the metal mold (not shown) of the mold clamping device 15 in one injection process, ensuring the amount of molten resin used in one injection process.

[0083] Here, when the molten resin is conveyed to the front end during the metering process, the retaining ring 65 disposed on the screw 60 is pushed forward by the molten resin conveyed to the front end and is pressed against the groove wall 63 on the front side of the groove portion 62 formed on the screw 60 (see reference). Figure 5 Therefore, a gap is formed between the groove wall 63 on the rear side of the groove 62 formed on the screw 60 and the retaining ring 65. Molten resin located further rear than the retaining ring 65 passes through this gap, and then between the inner circumferential surface of the retaining ring 65 and the bottom of the groove 62, and is pressed out towards the connecting portion 64. Thus, during the metering process, when the screw 60 presses the molten resin towards the front of the retaining ring 65, the molten resin located further rear than the retaining ring 65 is pressed towards the front of the retaining ring 65.

[0084] The amount of movement of the screw 60 in the metering process control is obtained based on the detection result of the encoder 82 on the drive motor 81 of the forward / reverse mechanism 80. That is, the forward / reverse mechanism 80 moves the screw 60 in the length direction Y by transmitting the driving force generated by the drive motor 81 to the screw 60, and the encoder 82 can detect the rotational position of the rotating body (not shown) on the drive motor 81. Therefore, the control unit 100 obtains the position of the screw 60 in the length direction Y by obtaining the rotational position of the rotating body of the drive motor 81 detected by the encoder 82.

[0085] The encoder 82 of the drive motor 81 of the forward / reverse mechanism 80 is a screw position detection unit that detects the position of the screw 60 in the length direction Y within the heating barrel 50. During the metering process, the control unit 100 obtains the position of the screw 60 in the length direction Y based on the detection result detected by the encoder 82 of the drive motor 81 of the forward / reverse mechanism 80, thereby obtaining the amount of retraction of the screw 60.

[0086] Furthermore, the pressure of the molten resin delivered to the front end of the heating tank 50 is detected using the results of a force gauge 90. The force gauge 90 is used as a back pressure detection unit to detect the back pressure of the molten resin being pressed out by the screw 60 towards the front end within the heating tank 50.

[0087] If we were to explain the detection of the back pressure of the molten resin in the force gauge 90, when the screw 60 pushes the molten resin in the heating tank 50 toward the front end of the heating tank 50, the screw 60, through the reaction force of the molten resin being pushed forward, acts on the rear side in the length direction Y. The force acting on the screw 60 in the length direction Y is transmitted from the screw 60 to the pulley 75 of the rotating mechanism 70, and from the pulley 75 to the main body 71 of the rotating mechanism, and thus to the force gauge 90 fixed to the main body 71 of the rotating mechanism.

[0088] Since the side opposite to the side of the force gauge 90 that is fixed to the main body 71 of the rotating mechanism is fixed to the nut 88 of the ball screw mechanism 86 in the forward / reverse mechanism 80, the force acting on the force gauge 90 in the longitudinal direction Y from the main body 71 of the rotating mechanism 70 is a force that compresses the force gauge 90 in the longitudinal direction Y. The force gauge 90 detects the magnitude of the force acting on it and transmits it to the control unit 100. The control unit 100 obtains the magnitude of the force sent from the force gauge 90 as the force acting on the screw 60 in the longitudinal direction Y.

[0089] In the metering process, the control unit 100 obtains the magnitude of the force acting on the screw 60 in the length direction Y based on the detection results detected by the force gauge 90, and obtains the back pressure of the molten resin pressed forward by the screw 60. That is, in the metering process, the control unit 100 obtains the position of the screw 60 in the length direction Y based on the detection results detected by the encoder 82, obtains the back pressure of the molten resin based on the detection results detected by the force gauge 90, obtains the amount of molten resin pressed into the heating tank 50 at the front end side where the nozzle part 52 is located, and performs metering of the molten resin.

[0090] As described above, in the metering process, the control unit 100, while rotating and retracting the screw 60 within the heating tank 50, forces molten resin out towards the front end within the heating tank 50. Based on the position of the screw 60 detected by the encoder 82 and the back pressure detected by the force gauge 90, the metering of the molten resin pressed out by the screw 60 is performed. Thus, in the metering process, the metering of the molten resin injected from the heating tank 50 into the metal mold of the mold clamping device 15 is performed in a single injection process.

[0091] Here, in the metering process, the pressure of the molten resin injected in the injection process increases. However, if the pressure of the molten resin remains high, undesirable conditions such as leakage of molten resin from the nozzle section 52 may occur when the molded part is removed from the metal mold. Therefore, in this embodiment, the pressure of the molten resin after metering is reduced. Next, the pressure reduction control of the molten resin after metering in the metering process will be explained.

[0092] <Resin decompression control after metering>

[0093] Figure 7 This is an explanatory diagram regarding the decompression control of molten resin in the injection molding machine 1 according to the relevant embodiment. The decompression control of the metered molten resin is performed during the metering process, and also during the cooling process in the mold clamping device 15. That is, the metering process is also performed during the cooling process, so both the metering process and the decompression control of the molten resin are performed during the cooling process. Therefore, the metering process and decompression control are continuously performed in the injection unit 10 during the cooling process in the mold clamping device 15.

[0094] During the metering process, while the screw 60 is retracted, molten resin is pressed out towards the front end of the heating tank 50 through the screw 60. However, the control unit 100 controls the moving speed of the screw 60 so that the position of the screw 60 in the length direction Y stops at the position where the metering of the molten resin is completed.

[0095] That is, the control unit 100 begins to decelerate the retraction speed of the screw 60 during the metering process at a point earlier than the point when the metering of the molten resin is completed. Alternatively, the deceleration of the retraction speed of the screw 60 during the metering process begins at a position forward in the length direction Y of the screw 60 compared to the position of the screw 60 in the length direction Y when the metering of the molten resin is completed. In this case, the point at which the deceleration of the screw 60 begins or the position at which the deceleration begins is the decompression start point. The decompression start point in this case has both the temporal point at which the deceleration of the screw 60 begins and the spatial position in the length direction Y at which the deceleration of the screw 60 begins.

[0096] Furthermore, during the metering process, the rotational speed of the forward-rotating screw 60 also begins to decelerate from the decompression initiation point. That is, in order to stop the retraction of the screw 60 upon completion of the metering process, the control unit 100 decelerates the rotational speed of the screw 60 from the point in time when the retraction speed of the screw 60 is decelerated before the completion of the metering process. Thus, the decompression initiation point for the deceleration of the screw 60's retraction speed is the control point or position at which decompression begins for the molten resin whose pressure has been increased during the metering process.

[0097] In the metering process, the screw 60 retracts along the length Y direction. At the start of decompression, the retraction speed begins to decrease, and at the point when the metering of the molten resin is completed, the retraction speed reaches 0, and the movement of the screw 60 along the length Y direction stops. Furthermore, the rotational speed of the screw 60 in the metering process also begins to decrease at the start of decompression. At the point when the metering of the molten resin is completed and the retraction speed of the screw 60 reaches 0, the rotational speed reaches 0 and stops, or reaches a rotational speed close to 0.

[0098] In addition, the back pressure of the molten resin between the start of decompression and the completion of metering is easily reduced due to the deceleration of the screw 60's rotational speed. However, due to the deceleration of the screw 60's retraction speed, the back pressure is easily maintained. Therefore, the effects of the two on the back pressure are offset, and the back pressure does not change much or is limited to a slight decompression.

[0099] Once the metering process is completed, the retraction speed of the screw 60 becomes 0 and the movement of the screw 60 in the length direction Y stops. Then, the rotation speed and rotation direction of the screw 60 are controlled so that the back pressure of the molten resin metered in the metering process becomes a target pressure at the target time that is lower than the back pressure at the completion of the metering process. That is, the control unit 100 controls the rotation speed and rotation direction of the screw 60 so that the back pressure detected by the force gauge 90 becomes the target pressure at the target time.

[0100] In this embodiment, the target time is the moment when the cooling of the molding resin, which is the molten resin injected into the metal mold (not shown), which is formed from the molten resin molten in the heating tank 50, is completed. That is, the target time is the cooling completion time, which is the moment when the cooling process in the mold closing device 15 is completed. Furthermore, in this embodiment, the target pressure is 0 MPa. Therefore, the control unit 100 controls the rotation speed and rotation direction of the screw 60 so that the back pressure of the molten resin detected by the force gauge 90 is 0 MPa at the cooling completion time.

[0101] Furthermore, when controlling the rotation speed and direction of the screw 60 to ensure that the back pressure of the molten resin reaches the target pressure at the target time, the control unit 100 controls the rotation speed and direction of the screw 60 so that the back pressure of the molten resin gradually decreases from the pressure at the completion of metering to the target time. The control setting of the back pressure of the molten resin by the control unit 100 represents a pressure reduction control target for the change in back pressure relative to time from the completion of metering of the molten resin to the target time. For example, the pressure reduction control target is set such that the change in the back pressure of the molten resin from the pressure at the completion of metering to the target time is a linear function of the target pressure.

[0102] The control unit 100 continuously compares the back pressure of the molten resin obtained from the measurement result of the force gauge 90 from the completion of the molten resin metering to the target time with the pressure reduction control target. If the obtained back pressure is lower than the pressure reduction control target, the back pressure is increased; if the obtained back pressure is higher than the pressure reduction control target, the back pressure is decreased.

[0103] The back pressure of the molten resin is controlled by adjusting the rotation of the screw 60. Specifically, since the screw 60 stops moving in the Y-direction, the back pressure of the molten resin increases when the screw 60 rotates in the forward direction and decreases when it rotates in the reverse direction. Therefore, when the back pressure of the molten resin obtained from the force gauge 90 is lower than the pressure reduction control target at the same moment, the screw 60 is rotated in the forward direction. Conversely, when the back pressure of the molten resin obtained from the force gauge 90 is higher than the pressure reduction control target at the same moment, the screw 60 is rotated in the reverse direction. Furthermore, in both cases, the rotation speed of the screw 60 is increased when the deviation between the back pressure of the molten resin obtained from the force gauge 90 and the pressure reduction control target is large, and the rotation speed of the screw 60 is decreased when the deviation is small.

[0104] The back pressure of the molten resin located at the front end of the heating tank 50 is controlled by depressurization after metering is completed in the metering process, as described above, and becomes the target pressure when the target time is reached. That is, in this embodiment, the back pressure of the molten resin is gradually depressurized after the metering process is completed, and becomes 0 MPa, which is the target pressure, when the cooling completion time, which is the target time, is reached. In the control of depressurizing the back pressure of the molten resin after the metering process, the back pressure is gradually reduced towards the target time, and is depressurized to the target pressure when the target time is reached, as described above.

[0105] Here, since the back pressure of the molten resin is reduced and controlled by rotating the screw 60 within the heating tank 50, during the pressure reduction control, not only the back pressure of the molten resin at the front end within the heating tank 50 changes, but also the overall pressure of the molten resin within the heating tank 50. Next, the change in the overall pressure of the molten resin within the heating tank 50 during the pressure reduction control of the molten resin's back pressure will be explained.

[0106] <Pressure changes of the molten resin inside the heating tank 50>

[0107] Figure 8 This is an explanatory diagram regarding the pressure change of the molten resin throughout the heating tank 50 when pressure reduction control is applied. Additionally, Figure 8 A graph representing the pressure of the molten resin R at each position along the length Y of the heating tank 50, by means of... Figure 8 The curve shown on the upper side represents the pressure of the molten resin R, while the curve shown on the lower side represents the pressure change caused by pressure reduction control at each position along the length Y of the heating tank 50.

[0108] In controlling the reduction of back pressure of molten resin R, since the back pressure is reduced by rotating the screw 60, the pressure of the molten resin R inside the heating tank 50, excluding the front end side of the heating tank 50 (i.e., excluding the side forward of the Bica ring 65), also changes with the rotation of the screw 60. Specifically, in controlling the reduction of back pressure of molten resin R, after the metering process is completed, in order to smoothly reduce the back pressure, the rotation of the screw 60 is continuously controlled from the time of metering completion to the target time. Therefore, the molten resin R inside the heating tank 50 located behind the Bica ring 65 also moves in the length direction Y with the rotation of the screw 60.

[0109] At this time, the pressure exerted on the molten resin R located on the rear side of the bicarbone ring 65 during the metering process by the spiral blade 61 of the screw 60 in the forward direction is reduced, or the pressure direction becomes the rearward direction. Therefore, when the back pressure of the molten resin R is reduced, as the back pressure is gradually reduced, the pressure of the molten resin R located on the rear side of the bicarbone ring 65 also decreases. Figure 8 It gradually decreases as shown.

[0110] <Effects of the Implementation Method>

[0111] The control method and injection molding machine 1 described above, in order to stop the retraction of the screw 60 upon completion of the metering process, decelerate the rotational speed of the screw 60 from the point where its retraction speed is reduced before the completion of the metering process. Therefore, at the point where the screw 60 stops retraction, its rotation can be stopped or its rotational speed can be brought close to zero. This prevents a sharp drop in the back pressure of the molten resin R due to the screw 60 stopping its rotation before retraction stops, or a sharp increase in the back pressure of the molten resin R due to the screw 60 continuing to rotate after retraction stops.

[0112] Furthermore, after the metering process is completed, the rotation speed and direction of the screw 60 are controlled so that the back pressure of the molten resin R becomes the target pressure when the target time is reached, thus suppressing the rapid change of the pressure of the molten resin R in the heating tank 50.

[0113] That is, as a method to reduce the back pressure of the molten resin R after the metering process is completed, as envisioned in conventional injection molding machines 1, methods such as reverse suction and rotating the screw 60 in the opposite direction at a predetermined rotation angle for a short time can be cited. However, in these methods, adverse conditions may occur due to the rapid change in the pressure of the molten resin R.

[0114] Figure 9 This is an explanatory diagram regarding the change in pressure of the molten resin R throughout the heating tank 50 during backflow. Figure 9 This diagram illustrates the pressure change of the molten resin R during a so-called back suction operation, where the screw 60 is retracted while its rotation has stopped. After the metering process is completed, in the case where back suction is performed to reduce the back pressure of the molten resin R on the front side within the heating tank 50, as... Figure 9 As shown, the back pressure of the molten resin R on the front side inside the heating tank 50 abruptly becomes 0 MPa.

[0115] Therefore, within the heating tank 50, the pressure of the molten resin R located further rear of the retaining ring 65 tends to become higher than the pressure of the molten resin R located in front of the retaining ring 65. Consequently, the molten resin R located further rear of the retaining ring 65 within the heating tank 50 tends to flow through the retaining ring 65 and to the front of the retaining ring 65. Consequently, during the metering process, the amount of molten resin R metered in front of the retaining ring 65 changes, and the weight of the molded article formed using this molten resin R tends to change relative to the desired weight.

[0116] Furthermore, when the back pressure of the molten resin R drops sharply due to back suction after the metering process, gas G is easily generated from the molten resin R. In this case, the gas G generated from the molten resin R may easily cause so-called silver streaks, which appear as silvery marks, on the surface of the molded article formed using the molten resin R.

[0117] Figure 10 This is an explanatory diagram showing the change in pressure of the molten resin R throughout the heating tank 50 when the screw 60 rotates in the opposite direction at a specified rotation angle for a short time. Figure 10 This diagram illustrates the change in pressure of the molten resin R when the screw 60 is suddenly rotated in the opposite direction by a predetermined rotation angle, with the movement of the screw 60 in the longitudinal direction Y completely stopped. After the metering process is completed, when the screw 60 is suddenly rotated in the opposite direction by a predetermined rotation angle, as shown... Figure 10 As shown, within the heating tank 50, the pressure of the molten resin R drops sharply to around 0 MPa. Therefore, gas G is easily generated from the molten resin R and tends to accumulate within the heating tank 50.

[0118] Furthermore, if the screw 60 is suddenly reversed at a predetermined rotation angle, the waiting time from the completion of the metering process to the cooling and solidification of the molten resin R injected into the metal mold becomes longer, and gas G may be continuously generated during this waiting time. In this case, silver streaks may easily occur on the surface of the molded article due to the generated gas G.

[0119] In contrast, in this embodiment, after the metering process is completed, control is performed to ensure that the back pressure of the molten resin R reaches the target pressure at the target time. Therefore, after the metering process is completed, it is possible to suppress the movement of the molten resin R through the retaining ring 65 in the length direction Y. Consequently, it is possible to suppress the weight change of the molten resin R metered at the front end within the heating tank 50, and to suppress the weight change of the molded article from the desired weight.

[0120] Furthermore, by controlling the back pressure of the molten resin R to reach the target pressure at the target time, abrupt changes in the pressure of the molten resin R within the heating tank 50 can be suppressed. This suppresses the generation of gas G in the molten resin R due to a sharp drop in pressure. Consequently, silver streaks on the surface of the molded article caused by gas G generated in the molten resin R can be suppressed.

[0121] Furthermore, by controlling the back pressure of the molten resin R to reach the target pressure at the target time, leakage of the molten resin R from the nozzle section 52 due to high back pressure can be suppressed when the molded article is removed from the metal mold of the clamping device 15. This suppresses variations in the amount of molten resin R used in the molded article caused by leakage of molten resin R after metering. As a result, the quality of the molded article can be improved more reliably.

[0122] Furthermore, since the target pressure is 0 MPa, the back pressure of the molten resin R at the front end of the heating tank 50 can be made 0 MPa at the point when the cooling of the molding resin in the metal mold of the mold clamping device 15 is completed. This allows for more reliable pressure reduction of the molten resin R's back pressure when cooling in the metal mold of the mold clamping device 15 is completed, while simultaneously suppressing a sharp drop in the back pressure of the molten resin R after the metering process. Consequently, while suppressing the generation of gas G caused by a sharp drop in the back pressure of the molten resin R, the back pressure of the molten resin R can be reduced more reliably, and leakage of the molten resin R from the nozzle section 52 can be suppressed. As a result, the quality of the molded product can be improved more reliably.

[0123] Furthermore, since the target time is the moment when the molding resin in the metal mold formed from the molten resin R molten in the heating tank 50 has cooled completely, the back pressure of the molten resin R, which has been metered, can be reduced at the point when the molding resin has cooled completely. Therefore, while suppressing the generation of gas G caused by a sharp drop in the back pressure of the molten resin R, the back pressure of the molten resin R can be reduced more reliably at the point when the molding resin has cooled completely, thus preventing leakage of the molten resin R from the nozzle section 52. As a result, the quality of the molded product can be improved more reliably.

[0124] [Variation Example]

[0125] In addition, in the above implementation, the target pressure is 0 MPa, but the target pressure may be anything other than 0 MPa. Figure 11 This is a variation of the control method for the injection molding machine 1 according to the embodiment, and is an explanatory diagram showing the case where the target pressure is an arbitrary set pressure. The target pressure at the target time after the metering process is completed can also be, for example, as shown below. Figure 11As shown, the target pressure can be set to a pressure higher than 0 MPa, or it can be a set pressure based on the molten resin. For example, if the molten resin is a foaming resin used for foam molding, and the back pressure of the molten resin is excessively reduced before injection into the metal mold, the gas contained in the molten resin may over-foam before molding. Therefore, in such cases, the back pressure that can suppress the foaming of the gas contained in the molten resin can be set as the target pressure. Thus, when using a foaming resin in the molten resin, the desired foam molding can also be performed. As such, the target pressure can also be a set pressure based on the molten resin. As a result, regardless of the type of molten resin, the quality of the molded product can be improved more reliably.

[0126] Furthermore, in the above-described embodiments, the target time is the time when the molding resin has completed cooling, but the target time may also be any other time when the molding resin has completed cooling. Figure 12 This is a variation of the control method for the injection molding machine 1 according to the embodiment, illustrating the case where the target time is an arbitrary offset time. After the metering process is completed, the target time for reducing the pressure of the molten resin to the target pressure can be, for example, as shown below. Figure 12 The time shown is earlier than the time when the molding resin has finished cooling. That is, the target time can also be set as an offset time earlier than the time when the molding resin has finished cooling in the metal mold formed from the molten resin molten in the heating tank 50. Therefore, even if the actual reduction of the back pressure of the molten resin progresses slowly relative to the reduction control of the back pressure of the molten resin achieved by controlling the rotation speed and direction of the screw 60, the delay in back pressure change can be absorbed, and the actual back pressure of the molten resin can be more reliably reduced to the target pressure when the molding resin has finished cooling. As a result, the quality of the molded product can be improved more reliably.

[0127] Label Explanation

[0128] 1…Injection molding machine; 5…Base; 6…First track; 10…Injection unit; 15…Mold clamping unit; 20…Frame; 21…Base; 22…Front wall; 23…Rear wall; 24…Leg; 30…Upper frame; 31…Front wall; 32…Side wall; 33…Support pin; 34…Fixing threaded part; 35…Second track; 40…Propulsion mechanism; 41…Drive motor; 42…Connecting mechanism; 43…Ball screw mechanism; 44…Threaded part; 45…Nut part; 50…Heating tank; 51…Heater; 52…Nozzle part; 55…Hopper; 60…Screw; 61… 62…Spiral blade; 63…Slot wall; 64…Connecting part; 65…Snap ring; 70…Rotating mechanism; 71…Main body of rotating mechanism; 72…Support rod; 73…Drive motor; 74…Drive belt; 75…Pulley; 76…Bearing; 80…Forward and backward mechanism; 81…Drive motor; 82…Encoder; 83…Drive belt; 84…Pulley; 85…Bearing; 86…Ball screw mechanism; 87…Threaded part; 88…Nut part; 90…Force gauge; 100…Control part; 101…Display part; 102…Input part; R…Molten resin; G…Gas.

Claims

1. A control method for an injection molding machine, comprising a metering step of metering molten resin by rotating and retracting a screw simultaneously within a heated tank in which resin material is molten, characterized in that... In order to stop the screw's retraction upon completion of the aforementioned metering process, the screw's rotational speed is reduced from the point in the metering process where the screw's retraction speed is reduced before the completion of the metering process. The rotational speed and direction of the screw are controlled so that the back pressure, which is the pressure of the molten resin measured in the metering process, becomes a target pressure at the target time that is lower than the back pressure at the completion of the metering process. The rotational speed and direction of the screw are controlled by continuously comparing the back pressure detected by the back pressure detection unit with the pressure reduction control target, so that the back pressure decreases smoothly from the back pressure at the completion of the metering process toward the target pressure.

2. The control method for an injection molding machine as described in claim 1, characterized in that, The target pressure mentioned above is 0 MPa.

3. The control method for an injection molding machine as described in claim 1, characterized in that, The target pressure mentioned above is based on the set pressure of the molten resin.

4. The control method for the injection molding machine as described in any one of claims 1 to 3, characterized in that, The aforementioned target time is the moment when the resin formed in the metal mold from the molten resin molten in the aforementioned heating tank has cooled completely.

5. The control method for the injection molding machine as described in any one of claims 1 to 3, characterized in that, The aforementioned target time is set as an offset time earlier than the time when the resin being molded in the metal mold formed from the molten resin melted in the aforementioned heating barrel has cooled completely.

6. An injection molding machine, comprising: A heating tank is used to melt the resin material inside, turning it into molten resin. The screw is rotatably disposed within the heating barrel and is movable within the heating barrel in the direction of the rotation axis. The back pressure detection unit detects the back pressure, which is the pressure of the molten resin pressed out by the screw within the heating tank; and The control unit controls the rotation and movement of the screw, and extrudes molten resin into the heating tank by rotating and retracting the screw simultaneously. The amount of molten resin extruded by the screw is measured based on the back pressure detected by the back pressure detection unit. Its features are, In order to stop the screw's retraction when the metering process, which is the process of metering the molten resin, is completed, the control unit reduces the screw's rotational speed from the point when the screw's retraction speed is reduced before the metering process is completed. The control unit controls the rotation speed and direction of the screw so that the back pressure detected by the back pressure detection unit becomes a target pressure lower than the back pressure at the completion of the metering process when the target time is reached. The control unit continuously compares the back pressure detected by the back pressure detection unit with the pressure reduction control target based on the detected back pressure, so that the detected back pressure gradually decreases from the back pressure at the completion of the metering process toward the target pressure.

Images