JP2010188706A - Injection molding machine, molding and injection molding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an injection molding machine having such a configuration as to improve the quality of molding by controlling a variation of the inside pressure of the cavity at each shot even if properties of a molten resin fluctuate by the fluctuation of a retention time. <P>SOLUTION: The injection molding machine 1 includes a cylinder 21 having, at the tip, a nozzle 22 communicating with a cavity 13 of a mold 10, a screw 30 contained in a heating cylinder 21 and an injection drive mechanism 50 driving the screw 30 to move forward/backward in the heating cylinder 21, wherein a molten resin supplied into the cylinder and heat-molten and staying in the cylinder 21 into the cavity 13 is injected from the nozzle 22 by moving the screw 30 forward and/or backward, and a retention force is applied to the molten resin injected into the cavity 13 to form a desired molding. The machine also has a controller 60 counting the retention time of the molten resin in the cylinder 21 and controlling the forward/backward movement of the screw 30 to apply the retention force calculated according to the retention time to the molten resin in the cavity 13. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an injection molding device that fills a cavity in a mold with a molten resin and injection-molds a molded product, and a molded product molded using the injection molding device. Furthermore, the present invention relates to an injection molding method.

  For example, the injection molding apparatus is configured to melt a thermoplastic resin supplied from a hopper into a cylinder based on shearing heat generated by screw rotation and heating from a band heater wound around the cylinder, while the tip of the screw is in the cylinder. The amount is measured and the screw is moved forward at a set speed to inject the molten resin from the nozzle at the tip of the cylinder into the cavity in the mold. At this time, when the molten resin is filled in the cavity and the pressure (back pressure) received from the molten resin of the screw becomes higher than the set value as the screw moves forward, the screw is switched from speed control to pressure control. Then, by solidifying the resin while applying a predetermined pressure to the molten resin in the cavity, it is possible to improve the transferability of the mold and obtain a highly accurate molded product (for example, Patent Document 1). reference).

JP 2004-154994 A

  In the above-described conventional injection molding apparatus, a predetermined setting operation (metering, mold opening / closing, injection, pressure holding, cooling,...) Is continuously and repeatedly executed regardless of the state of the plasticized resin. However, in the case of actual continuous molding, the molten resin stays in the cylinder because the measurement time required to plasticize the resin varies due to changes in the temperature of the surrounding environment and the resin weight on the hopper. Time varies from shot to shot. If this residence time becomes longer, degradation such as decomposition, oxidation, and gelation of the resin progresses, and the viscosity of the molten resin changes greatly, and the fluidity of the molten resin and the filling property of the molten resin into the cavity also vary. Will be. For this reason, even if the holding pressure by the screw is applied to each shot, the internal pressure of the cavity fluctuates from shot to shot due to this change in viscosity. As a result, it is difficult to obtain a molded product having a desired quality.

  The present invention has been made in view of such problems, and even when the physical properties of the molten resin change due to fluctuations in residence time, the variation in the internal pressure of the cavity from shot to shot is suppressed, and the quality of the molded product is improved. It is an object of the present invention to provide an injection molding apparatus and an injection molding method that can be configured. Moreover, it aims at providing the molded article injection-molded by this injection molding apparatus.

  In order to solve the above-described problems, an injection molding apparatus according to the present invention includes a heating cylinder provided with a nozzle communicating with a cavity in a mold at a tip portion, a screw accommodated in the heating cylinder, and heating the screw. It has an injection drive part that moves forward and backward in the cylinder, and by moving the screw forward and backward, the molten resin that is supplied into the heating cylinder and heated and melted and stays is injected from the nozzle into the cavity and then injected into the cavity. An injection molding apparatus that molds a required molded product by applying a holding pressure to the molten resin, and a measurement unit that measures the residence time of the molten resin in the heating cylinder, and according to the residence time And a controller that controls the forward and backward movement of the screw so as to apply the calculated holding pressure to the molten resin in the cavity.

  In the above-mentioned invention, the metering drive unit for rotating the screw in the heating cylinder is further provided, and the molten resin in the heating cylinder is measured by retreating the screw while being rotated in the heating cylinder. Preferably, the measuring unit measures the time from the completion of the measurement of the molten resin in the heating cylinder until the start of injection of the molten resin into the cavity from the heating cylinder as the residence time.

  Further, in the above-described invention, when the holding pressure is Pc, the residence time is t, the predetermined reference holding pressure is Ps, and the predetermined resin reference residence time is tave, It is preferable to control the forward / backward movement of the screw so that the holding pressure calculated by the formula Pc = Ps · (tave / t) is applied to the molten resin in the cavity.

  Furthermore, in the above-mentioned invention, it is preferable that the reference residence time is an average value of each residence time in which the molten resin stays in the heating cylinder when it is molded a plurality of times in advance.

  Moreover, the molded product according to the present invention is molded using the injection molding apparatus having the above-described configuration.

  Furthermore, the injection molding method according to the present invention includes a metering step of introducing a resin into a heating cylinder having a screw therein, melting the resin while rotating the screw, and measuring the molten resin, and a heating cylinder. By moving the screw forward and backward, the molten resin staying in the cylinder is injected, the injection process of filling the cavity in the mold with the molten resin, and the screw is filled in the cavity by controlling the advance and retreat position of the screw An injection molding method including a pressure holding step for applying a holding pressure to the molten resin, and the holding pressure is set according to a residence time of the molten resin in the heating cylinder.

  According to the present invention, it is possible to obtain a molded product having a constant quality in which variations in dimensional accuracy and the like are suppressed.

It is a schematic block diagram of the injection molding apparatus of this embodiment. It is a figure which shows the flow of an injection molding process. It is a graph which shows a reaction rate type | formula. It is a graph which shows Arrhenius's formula. It is a graph which shows the internal pressure change of the cavity by the injection molding apparatus of this embodiment. It is a graph which shows the internal pressure change of the cavity by the injection molding apparatus of the conventional structure.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration diagram of an injection molding apparatus 1 according to the present embodiment. First, the overall configuration of the injection molding apparatus 1 will be described with reference to FIG.

  The injection molding apparatus 1 includes a mold 10 having a cavity 13 therein, an injection mechanism 20 that injects molten resin into the mold 10, and a control apparatus 60 that comprehensively controls the operation of the injection molding apparatus 1 and the like. Consists of the subject.

  The mold 10 includes a fixed mold 11 and a movable mold 12, and the mold 10 can be closed and opened by moving the movable mold 12 relative to the fixed mold 11 in the approaching or separating direction. A cavity 13 is formed in the mold 10 in a state where the fixed mold 11 and the movable mold 12 are closed. The fixed mold 11 is formed with a resin passage 14 that communicates the cavity 13 with the outside of the mold 10.

  The injection mechanism 20 includes a cylinder 21 having a nozzle portion 22 formed at the tip thereof, a screw 30 disposed in the cylinder 21, a metering drive mechanism 40 that rotatably holds the screw 30, and a forward and backward movement of the screw 30. And an injection drive mechanism 50 for holding the nozzle portion 22 so that the injection port of the nozzle portion 22 communicates with the resin passage 14 of the mold 10.

  A material receiving hopper 23 is connected to the base end side of the cylinder 21, and a resin of molding material (a pellet of thermoplastic resin) is supplied into the cylinder 21 through the hopper 23. Yes. A band heater 24 for heating the resin supplied into the cylinder 21 is wound around the outer periphery of the cylinder 21.

  The screw 30 is provided in the cylinder 21 so as to freely rotate and advance / retreat. When the screw 30 is rotationally driven around the axis by the metering drive mechanism 40 and the inside of the cylinder 21 is heated by the band heater 24, the resin supplied into the cylinder 21 from the hopper 23 is not accompanied by the rotation of the screw 30. While being melted and kneaded by heat insulation and heating from the band heater 24, it is sent to the tip side in the cylinder 21. On the other hand, when the screw 30 is moved forward and backward in the axial direction by the injection drive mechanism 50, the molten resin stored on the tip side of the cylinder 21 is injected from the nozzle portion 22 into the cavity 13 of the mold 10.

  The metering drive mechanism 40 is stretched over a drive pulley 41, a driven pulley 42 connected to the rear end of the screw 30, a servo motor 43 that rotationally drives the drive pulley 41, and the drive pulley 41 and the driven pulley 42. And a timing belt 44. The servo motor 43 is provided with a pulse coder 45 for detecting the rotational position and rotational speed of the screw 30. The rotation of the servo motor 43 is controlled by the control device 60, and the screw 30 is rotationally driven by a rotation amount corresponding to the drive control value output from the control device 60.

  The injection drive mechanism 50 includes a drive pulley 51, a servo motor 53 that rotationally drives the drive pulley 51, a driven pulley 52 that is connected to a ball screw mechanism 56 that converts a rotational motion by the servo motor 53 into a linear motion of the screw 30, And a timing belt 54 that is stretched over a driving pulley 51 and a driven pulley 52. The servo motor 53 is provided with a pulse coder 55 for detecting the advance / retreat position and the moving speed of the screw 30. The rotation of the servo motor 53 is controlled by the control device 60, and the screw 30 is moved forward and backward by a feed amount corresponding to the drive control value output from the control device 60. The injection drive mechanism 50 has a load cell 57 that detects a pressure applied to the screw 30 (back pressure acting on the screw 30 from the molten resin) as an injection pressure / holding pressure.

  Next, a process until the molded product is injection-molded by the injection molding apparatus 1 configured as described above will be described with reference to FIG. This injection molding process includes an injection process for injecting and filling molten resin into the cavity 13 from the nozzle portion 22 by the forward and backward movement of the screw 30 by closing the mold 10, and a pressure holding process for holding the screw 30 under pressure control, For cooling the molten resin in the cavity 13, for measuring the resin supplied from the hopper 23 into the cylinder 21 and used for injection molding in the next shot, and for adjusting the cycle time according to the variation of the measuring time And a taking-out step of opening the mold 10 and taking out a molded product that has been injection-molded.

  For convenience of explanation, the flow of the above process will be described in more detail based on the resin path. First, in the measurement process, after the resin is supplied into the cylinder 21, the resin is rotated by the rotation of the screw 30 and the heat from the band heater 24. Is fed forward while being melted and kneaded and stored at the tip of the cylinder 21, and the molten resin is weighed according to the retracted position of the screw 30 that moves backward by the pressure of the molten resin. When the screw 30 reaches a predetermined measurement completion position, the measurement of the molten resin is completed.

  When the measurement of the molten resin is completed, after the pause process, the mold 10 is opened, and the molded product injection-molded in the previous shot (injection molding) is taken out from the cavity 13 (extraction process). During this time, the measured molten resin is temporarily retained in the cylinder 21 while being heated by the band heater 24.

  Then, while maintaining the molten state of the resin, the screw 30 is moved forward under speed control, and the molten resin is fed from the nozzle portion 22 into the cavity 13 formed in a state where the fixed mold 11 and the movable mold 12 are combined. Is injected and filled (injection process). When the back pressure received by the screw 30 detected by the load cell 57 reaches a predetermined pressure (the screw reaches the pressure holding start position), the forward / backward movement of the screw 30 is switched from speed control to pressure control, and the melt in the cavity 13 is melted. The forward / backward movement of the screw 30 is controlled so as to apply a predetermined holding pressure to the resin (pressure holding process).

  When the holding pressure is completed, a cooling process for solidifying the molten resin (molded body, gate, runner, etc.) is performed in the mold 10, and the molded product in this shot is again passed through the above-described measurement process and pause process. Obtainable.

  By the way, in the measurement process, as various factors, for example, the supply amount into the cylinder 21 varies according to the weight of the resin put into the hopper 23, and the ambient temperature around the injection molding apparatus 1 Due to a change or the like, the measurement time of the molten resin may vary in each shot. For this reason, in the injection molding process, in order to absorb the variation in the measurement time, the above-described pause process is provided, and the total time of the measurement time and the pause time is always maintained at a constant time. In other words, when the weighing time becomes longer, the rest time is adjusted to be shorter, and when the weighing time is shorter, the rest time is adjusted to be longer. By absorbing the variation, the cycle time of the entire injection molding process is kept constant.

  However, even if a pause time corresponding to the metering time is set, this metering time fluctuates means that the time from when the measurement of the molten resin is completed until the injection of the molten resin is started (the pause time and This means that the time during which the molten resin stays in the cylinder 21 fluctuates. At this time, the molten resin staying in the cylinder 21 has a problem of causing degradation such as decomposition, oxidation, and gelation according to the length of the staying time. Here, the relationship between the residence time, the viscosity of the molten resin, and the internal pressure of the cavity 13 will be described.

Degradation due to thermal decomposition of the resin is known to be a primary reaction, and the reaction rate equation is
ln [A] = − k · t + ln [A] ₀ (1)
(See FIG. 3). Here, t is the residence time of the resin, [A] ₀ is the initial concentration of the resin before thermal decomposition, [A] is the concentration of the resin before thermal decomposition after the residence time t, and k is a reaction rate constant.

At this time, the reaction rate constant k is a constant that varies depending on the temperature of the resin to be measured, and by measuring the reaction rates k1 and k2 of the concentrations at any two temperatures T1 and T2 in advance in separate experiments, , By plotting the logarithms of the reaction rate constants k1, k2 against the reciprocal of T2, to obtain a linear relationship, the Arrhenius equation represented by the following equation (2):
lnk = −E / RT + lnB (2)
From this, the slope (= −E / RT) and the vertical axis intercept (= lnB) are obtained (see FIG. 4), and as a result, the reaction rate constant k for each temperature (total temperature to be measured) is obtained. E is the activation energy for deterioration, R is a gas constant, T is temperature (absolute temperature), and B is a frequency factor (constant).

  From the above Arrhenius equation (2), reaction rate constants k for all temperatures T when the concentration of the resin before thermal decomposition decreases with time due to deterioration of the resin (reduction in molecular weight) are obtained. From the rate equation (1), the resin concentration [A] after being deteriorated as the residence time t elapses is calculated. As is apparent from this reaction rate equation (1), when the residence time t is short, the resin concentration [A] is high, whereas when the residence time t is long, the resin concentration [A] is low. Thus, the concentration [A] of the molten resin at the time of injection also varies with the variation of the residence time t.

  On the other hand, it is known that the viscosity of the resin is proportional to the concentration [A]. According to the rate reaction equation (1), the viscosity decreases with the concentration [A] as the residence time t elapses. It turns out that it has the characteristic to do.

  At this time, if the viscosity of the resin changes with the fluctuation of the residence time t for each shot, the fluidity of the molten resin at the time of injection also changes and the filling property to the cavity 13 varies, so how much of the molten resin Even if a constant pressure (set holding pressure) preset in the holding pressure process is applied to the resin in the cavity 13 after filling, the internal pressure of the cavity 13 greatly varies from shot to shot. Specifically, when the residence time t is short, the deterioration of the resin is small, the resin concentration [A] and the viscosity of the resin are high (the resin fluidity / fillability is poor), and the cavity 13 at the time of molding is reduced. The internal pressure is lowered. On the other hand, when the residence time t is long, the deterioration of the resin is large, the viscosity of the resin is lowered together with the resin concentration [A] (the resin fluidity and filling properties are improved), and the internal pressure of the cavity 13 at the time of molding is high. Become. Thus, if the internal pressure of the cavity 13 varies, there arises a problem that it is difficult to keep the quality of the molded product by the injection molding apparatus 1 constant.

  Therefore, in the injection molding apparatus 1 of the present embodiment, the pressure control of the screw 30 in the pressure holding process is performed with a holding pressure corresponding to the residence time t of the resin in order to suppress fluctuations in the internal pressure of the cavity 13 that occurs for each shot. It is configured to control and apply this appropriately adjusted holding pressure to the resin in the cavity 13. Then, the configuration will be continuously described.

  The control device 60 of the injection molding apparatus 1 is used for temporary storage of a CPU that executes a control program for controlling the sequence operation and the like of the mold 10 and the injection mechanism 20, a ROM that stores the control program and the like, and arithmetic data. The position and speed of the screw 30 are detected on the basis of output values from the operation controller 61 that controls the opening / closing control of the mold 10 and the operation of the injection mechanism 20 and the pulse coders 45 and 55. A position detection unit 62 that performs measurement, a timer 63 that measures the residence time of the molten resin, and an arithmetic processing unit 64 that calculates the holding pressure of the screw 30 for maintaining the internal pressure of the cavity 13 constant based on the residence time of the molten resin. And have.

  The position detector 62 detects the rotational position and forward / backward position of the screw 30 based on the output values from the pulse coders 45 and 55. Further, the position detection unit 62 detects whether or not the screw 30 has reached the measurement completion position of the molten resin based on the output value from the pulse coder 55, and outputs the output value from the load cell 57 (the back pressure applied to the screw 30). Whether or not the screw 30 has reached a predetermined pressure), it is detected whether or not the screw 30 has reached a position (pressure holding start position) where switching from the injection process to the pressure holding process is performed.

  The timer 63 measures the residence time t of the molten resin in the cylinder 21 based on the advance / retreat position of the screw 30 detected by the position detection unit 62. More specifically, the timer 63 determines the time from when the screw 30 reaches the measurement completion position of the molten resin until the start of forward movement from this measurement completion position for injection of the molten resin (the screw 30 is at the measurement completion position). The waiting time) is measured as the residence time t.

The arithmetic processing unit 64 calculates a control holding pressure value that the screw 30 applies to the molten resin in the cavity 13 in the pressure holding process based on the residence time t measured by the timer 63. As described above, the control holding pressure at which the internal pressure of the cavity 13 can be kept constant from the correlation among the residence time t, the resin viscosity, and the cavity internal pressure is controlled to be in inverse proportion to the residence time t of the molten resin, for example. Any holding pressure may be used. Therefore, the average value of the residence time t measured by performing injection molding a plurality of times in advance with the injection molding apparatus 1 is defined as the average residence time tave, and is determined empirically and experimentally based on the shape of the cavity 13 and the like. If the conventional holding pressure is set holding pressure Pa, the control holding pressure Pc is
Pc = Pa · tave / t (3)
It is calculated | required by Formula (3) represented by these.

  Thereby, when the residence time t measured by the timer 63 is longer than the average residence time tave, the control holding pressure Pc in the next shot is set higher than the set holding pressure Pa, while the residence time t is the average. When the dwell time is shorter, the control holding pressure Pc in the next shot is set to be lower than the set holding pressure Pa, and the adjusted control holding pressure Pc should be applied to the resin in the cavity 13. The operation controller 61 controls the forward / backward movement of the screw 30. As a result, even if the viscosity of the molten resin varies due to fluctuations in the residence time t in each shot, the screw 30 can be controlled with the control holding pressure Pc corresponding to the fluctuation residence time t (viscosity). It becomes possible to keep the pressure in the cavity 13 filled with injection of molten resin constant regardless of the viscosity of the resin, and it is possible to improve the quality of the molded product by the injection molding apparatus 1.

  The control holding pressure Pc may be always controlled at a constant value in the pressure holding process, or may be set at several stages along with the pressure holding time so that the pressure is controlled to rise and fall. When the holding pressure is controlled to be raised and lowered step by step, naturally, a plurality of control holding pressures Pc are set.

  Next, the operation of the injection molding apparatus 1 configured as described above will be described. First, in the weighing step, the resin supplied from the hopper 23 is fed forward while being gradually melted by receiving heat from the rotation of the screw 30 and heating by the band heater 24 in the cylinder 21 as the screw 30 rotates. It is done. Then, the screw 30 gradually moves backward by the pressure of the molten resin, and when the screw 30 reaches the measurement completion position (a predetermined amount of the molten resin is stored in the cylinder 21), the measurement process is completed.

  At this time, at the same time as the screw 30 reaches the measurement completion position, the timer 63 of the control device 60 starts measuring the residence time t of the molten resin. Then, after the time adjustment is performed to absorb the variation in the measurement time in the pause process, the mold 10 is opened, and the molded product already injection molded in the mold 10 is taken out from the cavity 13.

  After the completion of taking out the molded product, the mold 10 is closed again and the screw 30 is moved forward in the axial direction to start the injection process. At this time, as the screw 30 moves forward (fluctuation in screw position), the timer 63 completes the measurement of the residence time t that has been performed so far, and the residence time t of the molten resin in this shot is determined. .

  The arithmetic processing unit 64 of the control device 60 uses the above equation (3) to calculate the next shot based on the residence time t obtained from the timer 63, the average residence time tave previously stored in the RAM, and the set holding pressure Pa. A control holding pressure Pc set in the holding pressure process is calculated.

  Subsequently, when the process proceeds to the injection step, the molten resin in the cylinder 21 is injected and filled into the cavity 13 from the nozzle portion 22 through the resin passage 14 in the mold 10 as the screw 30 moves forward. During this time, the forward movement of the screw 30 is controlled under speed control, and the back pressure of the screw 30 has reached a predetermined pressure and has reached the pressure holding start position (the molten resin is almost in the cavity 13 of the mold 10). When it is detected by the position detection unit 62, the injection process is switched to the pressure holding process. Thereby, the screw 30 is controlled so as to apply the control holding pressure Pc derived by the arithmetic processing unit 64 to the molten resin in the cavity 13.

  Accordingly, in this pressure holding step, the operation control unit 61 is configured so that the back pressure of the screw 30 from the molten resin detected from the load cell 57 is maintained at the control pressure Pc appropriately adjusted according to the residence time t. Thus, the forward / backward movement of the screw 30 is controlled. For this reason, even when the viscosity of the molten resin to be injected varies due to the residence time t varying from shot to shot, the control holding pressure Pc is applied to the cavity 13 filled with the molten resin. The internal pressure of the cavity 13 can be maintained almost constant for each shot.

  For example, in the injection molding process, as shown in FIG. 2, when the dwell time t is equal to the average dwell time tave in the first shot (t = tave), the control hold pressure Pc in the next second pressure holding process. Is set to the same pressure (Pc = Pa) as the set holding pressure Pa.

  When the residence time t is longer than the average residence time tave in the second shot (t> tave), the control holding pressure Pc is smaller than the set holding pressure Pa (Pc < Pa).

  On the other hand, when the residence time t is shorter than the average residence time tave in the third shot (t <tave), the control holding pressure Pc is higher than the set holding pressure Pa (Pc>) in the next fourth pressure holding step. Pa). Thus, in continuous molding, the residence time t in each shot can be quickly reflected in the control holding pressure Pc in the next shot.

  When the pressure holding step is completed, the measurement step and the pause step are performed again through the cooling step, and the molded product in this shot can be obtained. Actually, the results of measuring the internal pressure of the cavity in the mold in continuous molding of several tens of shots are shown in FIGS. Here, FIG. 5 is a graph showing a change in the internal pressure of the cavity 13 by the injection molding apparatus 1 of this embodiment, and FIG. 6 is a graph showing a change in the internal pressure of the cavity by the injection molding apparatus of the conventional configuration. The axis represents the time axis, and the vertical axis represents the amplitude of the internal pressure change. In the conventional apparatus, it can be seen from the fluctuation width that the internal pressure varies greatly from shot to shot. On the other hand, according to this injection molding apparatus 1, it can be seen that the variation in internal pressure is reduced to less than half that of the conventional apparatus. Therefore, since the molded product obtained by each shot in the continuous molding is molded under such a condition that the fluctuation of the internal pressure of the cavity 13 is suppressed in the pressure-holding step, variation in dimensional accuracy can be suppressed well. Yes.

  As described above, according to the injection molding apparatus 1 according to the present embodiment, even when the physical properties (concentration, viscosity, etc.) of the molten resin change due to fluctuations in the residence time of the molten resin, the variation in the quality of the molded product is suppressed. The yield in the injection molding process can be greatly improved.

  In addition, the injection molding apparatus 1 does not require complicated control for controlling the internal pressure of the cavity by providing a pressure sensor or the like for measuring the internal pressure of the cavity in the mold and controlling the molding conditions by feedback control. The manufacturing cost of the entire injection molding apparatus 1 can be reduced.

  Although the preferred embodiments of the present invention have been described above, the scope of the present invention is naturally not limited to the above-described embodiments. For example, in the above-described embodiment, the molten resin residence time is set such that when the measurement of the molten resin is completed in the cylinder (when the screw 30 reaches the measurement completion position), the screw 30 starts moving forward and injection starts. However, the present invention is not limited to this. The injection is performed when a predetermined back pressure is applied to the screw 30 from the molten resin stored at the tip of the cylinder 21 and the screw 30 starts to move backward. It is good also as time until is started. Thereby, the fluctuation | variation of the residence time of molten resin can be caught more correctly.

  In the above-described embodiment, the formula (3) has been described as an example of the calculation formula for the control holding pressure. However, the present invention is not limited to this, and in the calculation formula, the order of the residence time t is expressed as follows. It may be secondary, tertiary, etc., or may be assembled using other coefficients. Further, the value of the control holding pressure Pc corresponding to each residence time t may be stored as a data table and stored in the control device 60 without using the calculation formula.

  Furthermore, in the above-described embodiment, an example of the injection molding process is shown, but the present invention is not limited to this, and the process may be appropriately increased or decreased.

  Note that the injection molding apparatus 1 of the present embodiment is particularly effectively used when molding precision products that require high-precision injection molding.

1 Injection molding device 10 Mold (molding die)
13 Cavity 20 Injection mechanism 21 Cylinder (heating cylinder)
22 Nozzle (nozzle)
24 Band heater (heating cylinder)
30 Screw 40 Metering drive mechanism (measuring drive unit)
50 Injection drive mechanism (injection drive unit)
60 control device 61 operation control part (control part)
62 Position detection unit 63 Timer (measurement unit)
64 Arithmetic processing part (control part)

Claims (6)

A heating cylinder provided with a nozzle communicating with the cavity in the mold at the tip;
A screw housed in the heating cylinder;
An injection drive unit for driving the screw forward and backward in the heating cylinder;
By moving the screw forward and backward, molten resin that is supplied into the heating cylinder and is heated and melted and stays is injected from the nozzle into the cavity, and a holding pressure is applied to the molten resin injected into the cavity. Is an injection molding apparatus for molding a required molded product,
A measuring unit for measuring the residence time of the molten resin in the heating cylinder;
An injection molding apparatus comprising: a control unit configured to control the forward / backward movement of the screw so as to apply the holding pressure calculated according to the residence time to the molten resin in the cavity. . A metering drive for rotating the screw in the heating cylinder;
It is configured to measure the molten resin in the heating cylinder by retreating the screw in the heating cylinder while being rotated,
2. The measurement unit according to claim 1, wherein after the measurement of the molten resin in the heating cylinder is completed, the time until the molten resin starts to be injected from the heating cylinder into the cavity is measured as the residence time. Injection molding equipment.   When the holding pressure is Pc, the dwell time is t, a predetermined reference hold pressure is Ps, and a predetermined resin reference dwell time is tave, the equation Pc = Ps 3. The injection molding apparatus according to claim 1, wherein the forward / backward movement of the screw is controlled so that the holding pressure calculated by (tave / t) is applied to the molten resin in the cavity. .   The injection molding apparatus according to claim 3, wherein the reference residence time is an average value of residence times in which the molten resin stays in the heating cylinder when molding is performed a plurality of times in advance.   A molded article formed by using the injection molding apparatus according to claim 1. A metering step of introducing a resin into a heating cylinder equipped with a screw inside and measuring the molten resin by melting the resin while rotating the screw;
An injection step of injecting the molten resin staying in the cylinder by moving the screw forward and backward in the heating cylinder, and filling the cavity in the mold with the molten resin;
A pressure holding step of applying a holding pressure to the molten resin filled in the cavity by controlling the advancing / retreating position of the screw, and an injection molding method comprising:
The injection molding method, wherein the holding pressure is set according to a residence time of the molten resin in the heating cylinder.