JP2631069B2 - Method and apparatus for controlling holding pressure in injection molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for controlling a holding pressure in injection molding.

[0002]

2. Description of the Related Art Injection molding is performed in the presence of various temperature changes such as seasonal changes, temperature changes in the morning and evening, rising and stopping of molding. In addition, various properties of the plastic material such as the melt viscosity and the shrinkage ratio are characterized by a large dependence on temperature. For this reason, the temperature change is a main cause of changing the quality of the molded product including the shape and size and the weight accuracy.

[0003] Generally, the temperature change is determined by the mold temperature,
Appears as fluctuations such as cooling water temperature and heating cylinder temperature. As a result, the temperature of the resin before it is filled into the mold, cooled and solidified, is changed, and the reproducibility of the resin pressure and flow speed is impaired, and the shape and dimensions of each molding cycle vary. become. In order to solve such a problem, the state of the resin such as pressure and temperature is kept constant every shot, or even if a temperature change is an inevitable factor, a predetermined molded product quality is obtained. It is necessary to take a method of controlling pressure and the like.

Conventionally, in order to solve such a problem caused by temperature change, a resin pressure sensor or a resin temperature sensor is mounted in a mold, and the pressure (P), temperature (T), and temperature of a molding material (resin) are increased. A method for controlling the resin pressure in the mold based on PVT characteristic data, which is basic physical property data indicating the relationship of specific volume (V), so that the specific volume of a molded article matches a target value regardless of a temperature change. (JP-A-63
-3926, JP-A-63-3927).

In the above-mentioned conventional method, the resin pressure in the mold and the resin temperature in the mold after the resin is filled in the mold are measured every moment, and the measured values and the PVT characteristic data are used. In addition, a control method is employed in which the resin pressure in the mold is feedback-controlled so as to obtain a target molded product specific volume. Some of them detect the resin pressure in the mold, but do not perform feedback control on this.
A method of using a shut-off nozzle or a gate valve to control the time at which the supply of resin to a mold is mechanically shut off has also been reported (DE4026731). Furthermore, regarding the method of obtaining the resin temperature in the mold, a method of directly obtaining the temperature by measurement or a method of indirectly estimating the resin temperature in the mold from the measured values of the mold temperature and the heating cylinder temperature have been reported. (US Pat. No. 4,983,336).

[0006]

However, the above-mentioned prior art has the following problems.

In any case, it is necessary to mount the resin pressure sensor in the mold, which is not economical, and it takes time to adjust and mount the pressure sensor.

Next, since the molten resin filled in the mold is rapidly cooled, the viscosity increases in a short time and is solidified. The increase and solidification of the viscosity makes it impossible to control the pressure of the resin anymore by pressing the screw. For this reason, after filling the mold with the resin, it is difficult to control by measuring and controlling the pressure and temperature of the resin in the mold that shows a rapid rise in viscosity and solidification. In particular, since the shape and dimensions of the molded product are determined when the resin in the mold loses fluidity and the supply of resin to the cavity is interrupted, the resin pressure and resin temperature in the mold at the time when the fluidity disappears are determined. It is necessary to maintain the state. However, for the reasons described above, there is no freedom to control the resin behavior at this point, and the method of measuring the resin pressure and the resin temperature in the mold and then feedback-controlling them to obtain a predetermined quality. This problem is remarkable, particularly in a mold having a small thickness or a small gate, because cooling and solidification proceeds more rapidly. That is, the method of detecting and controlling the pressure and temperature after filling the resin into the mold naturally has a limit in its controllability. The use of shut-off nozzles and valve gates requires additional equipment and is limited to special cases in terms of economy, setup, and even maintainability.

When the temperature of the resin in the mold is indirectly estimated from the temperature of the mold and the temperature of the heating cylinder, conventionally, a heat conduction analysis solution in which the heat transfer coefficient between the mold and the resin is regarded as infinite is considered. Since the approximation formula takes into account only the first term of the series, the calculation accuracy is poor. As a result, there has been a problem in estimating and controlling the quality of the molded article with high accuracy. Furthermore, since calculating the resin temperature in the mold requires additional data such as the thickness of the molded product and the effective thermal diffusivity, there is a problem that it takes time to collect these data.

The above problems mainly relate to the control method. In addition to this, there are the following problems in terms of the contribution of practical control quality improvement.

First, when a high-temperature nozzle comes into contact with a low-temperature die, heat transfer from the nozzle toward the die occurs, and the resin temperature at the tip of the nozzle rapidly drops. Then, the amount of resin flowing into the mold from the nozzle becomes unstable. For this reason, it is important to consider the heat transfer from the nozzle to the mold as one of the temperature changes in controlling the molded product weight and shape dimensions with high accuracy. However, a measurement method capable of capturing heat transfer from a nozzle to a mold with sufficient accuracy and control based on the measurement method have not been reported.

Next, even if the mold temperature changes, the change in temperature is temporarily caused from the surface of the mold cavity, such as a change in the atmospheric temperature or a change in the temperature of the resin filled in the mold. The effect of the mold temperature change on the quality of the molded product differs depending on whether the mold temperature changes from the inside of the mold, such as a change in cooling water temperature. It will be. Therefore, distinguishing between temporary mold temperature changes caused by the cavity surface and changes in mold cooling capacity caused by changes in cooling water temperature is highly accurate in predicting and controlling molded product quality. is important. However, in the related art, there has been no report on a method of measurement and control that treats them separately. For this reason, in maintaining the stability of quality, the accuracy of the conventional control was not satisfactory.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and does not require mounting a resin pressure sensor and a resin temperature sensor in a mold. To provide a pressure-holding control method and apparatus for injection molding that can control the quality of a molded article with high accuracy, while achieving sufficient controllability that is not affected by temperature and without requiring special equipment such as a shut-off nozzle and a gate valve. With the goal.

[0014]

In order to achieve the above-mentioned object, the present invention provides a method for controlling a dwelling pressure in injection molding, wherein a molten resin in a heating cylinder of an injection molding machine is fed to a resin in a nozzle and a mold by advancing a screw. A filling step of filling the cavity through the flow path, and after filling the molten resin into the cavity, press the screw to compensate for the molten resin contracting as it is cooled and solidified in the cavity. In the injection molding having a pressure-holding step of replenishing the molten resin, at a point immediately before the screw starts to advance at the beginning of the filling step, the nozzle tip temperature (TR
), The temperature of the spool part (TS), the temperature of the mold cavity wall surface (TW), and the temperature of the cooling water for the mold (TE). Based on these measured values (TR, TS, TW, TE), The estimated value (TC (tnf)) of the resin temperature in the mold at the time (tnf) at which the weight of the molded article can be considered to be substantially determined in the holding pressure stage, is then estimated. ^* ) Time required to achieve (tnf)
The resin pressure (PC ^* (tnf)) in the mold is obtained from the estimated value (TC (tnf)) of the resin temperature in the mold, and further, the resin pressure (PC ^* (tnf)) in the mold is achieved. calculated from the resin pressure in the mold coercive pressure setpoint (PL ^*) required (PC ^* (tnf)) and the respective measurement values (TR, TS, TW, TE ) to, then, the pressure-holding In the stage, the holding pressure is controlled based on the holding pressure set value (PL ^* ) obtained in advance in the filling stage.

Further, the resin temperature (TC (t)) in the mold in the pressure holding stage is calculated by the following equation: TC (t) = TCS (t) + (TRS-TCS (t)) / (TRS-TWS) .DELTA.TW + (TCS (t) -TWS) / (TRS-TWS) .DELTA.TR + e.DELTA.TE where TCS (t) is the resin temperature in the mold at time t in the shot when a good product is molded. TC (t): any Resin temperature in mold at time t of shot TRS: Nozzle tip temperature of shot in which good product was molded TR: Nozzle tip temperature of arbitrary shot TWS: Mold cavity wall surface temperature of shot in which good product was molded Tw: Any TES: Cooling water temperature of a shot in which a non-defective product is molded TE: Cooling water temperature of an arbitrary shot e: Cooling water temperature coefficient to be set ΔTW = TW−TWS ΔTR = TR−TRS ΔTE = Estimated by TE-TES, the resin pressure in the mold at the packing stage (t))
Is calculated by the following equation: PC (t) = a ₁ · T W + a ₂ · TS + b · TR + c · PL
+ D However, PC (t): the resin pressure PL in the mold at time t at any shots: coercive pressure value a ₁ in any of the _{shots, a 2, b, c,} d: estimating a constant to be set.

Further, the molded article weight (WC) is calculated by the following equation: VC / WC = ω + {R '. (TC (t) +273)} / (P
C (t) + πi) where, VC: cavity volume of the mold ω, R′πi: set material constant WC: resin pressure in the mold (PC (t)), resin temperature in the mold (T
C (t)) Molded product weight in shot. Estimate by

In addition, the time (tnf) in the dwell stage for evaluating the resin pressure in the mold (PC (t)) and the resin temperature in the mold (TC (t)) is determined as follows.

TCS (tnf) = Tnf, where Tnf is the flow stop temperature determined by the material. That is, tnf is the resin temperature TCS (t) in the mold at the molding shot which is a reference for molding a good product, and is the flow stop temperature. It is time to reach Tnf.

According to the present invention, there is provided an injection molding apparatus comprising a heating cylinder, a screw disposed therein, and a screw driving means for reciprocating and rotating the screw in an axial direction. A temperature sensor for measuring the temperature (TR) at the tip of the nozzle and a temperature sensor for measuring the temperature (TS) of the spool portion in an injection molding machine having a mold clamping device for clamping a mold. , A temperature sensor for measuring the mold cavity wall surface temperature (TW), a temperature sensor for measuring the mold cooling water temperature (TE), and a target molding based on these measured values. A control operation unit for calculating a holding pressure set value (PL ^* ) required to obtain a product weight target value (WC ^* );
L ^* ) to a pressure control valve amplifier, and a setting monitor for monitoring set values and measured values required for calculating the holding pressure set value (PL ^* ). It is a feature.

[0020]

The heat transfer from the nozzle to the mold can be known by the temperature sensors attached to the nozzle tip and the spool. As a result, the temperature of the resin filled in the mold can be detected.

A mold temperature sensor mounted near the wall surface of the mold cavity and a cooling water temperature sensor mounted on the piping section of the cooling water of the mold make the temperature in two senses indicated by the mold temperature, namely, the resin temperature. The flow resistance and the cooling capacity for the air can be grasped.

Next, in the injection pressure-holding stage, at the beginning of filling, just before the screw starts to advance, the above-mentioned nozzle tip temperature (TR), spool temperature (TS), mold cavity The wall surface temperature (TW) and the mold cooling water temperature (TE) were measured, and the measured values (T
R, TS, TW, TE), the resin temperature (TC (t)) in the mold in the subsequent pressure-holding stage is estimated by a quick and highly accurate prediction formula, and the estimated resin temperature in the mold is estimated. Calculate the resin pressure (PC ^* (t)) in the mold at the dwell stage required to achieve the target molded product weight target value (WC ^* ), and calculate the resin pressure (PC ^* ( t) Calculate the holding pressure set value (PL ^* ) necessary to obtain). The above calculation is completed in several tens of msec before the screw starts moving forward. As described above, the calculated holding pressure set value (PL ^* ) is output to the pressure control valve amplifier when the holding pressure stage comes.

Therefore, simple control that does not require an in-mold pressure sensor, an in-mold resin temperature sensor, a shut-off nozzle, a gate valve, and the like is possible. Also, since the holding pressure set value (PL ^* ) set in the holding pressure stage is determined quickly before filling, it is not necessary to measure every moment in the holding pressure stage, and the feedback control is not required. No matter how quickly the resin solidifies in the mold, it can be controlled, and can be applied to thin products and gate shapes. further,
Control is possible in consideration of heat transfer from the nozzle to the mold and the cooling capacity of the mold.

[0024]

An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is an explanatory view showing an embodiment of a pressure-holding control device in injection molding according to the present invention. Heating cylinder 1
The screw 1 disposed inside the heating cylinder 10 is configured to reciprocate in the axial direction in the heating cylinder 10 by the driving force of the hydraulic cylinder 11 and the motor M, that is, to advance and retreat in the left and right directions in the drawing, and to be rotated. I have. A nozzle resin channel 2a communicating with the heating cylinder 10 and the mold 3 is formed in the nozzle 2 provided at the tip of the heating cylinder 10, and the mold 3 includes a fixed mold 3a and a movable mold 3a. 3b, a spool portion 3c and a cavity 3e are provided therein in order from the side close to the nozzle 2.

As shown in FIGS. 2 and 3, a heat-sensitive portion of a temperature sensor 4a is attached to a concave portion formed on the outer peripheral surface of a tip portion 2b of the nozzle 2, and a nozzle is provided at a rear portion thereof. Heater 12 and nozzle temperature control thermocouple 13
Is installed.

FIGS. 4 and 5 show the spool portion 3c.
As shown in the figure, the heat-sensitive portion of the temperature sensor 4b is attached by the annular temperature sensor attachment 14.

Further, as shown in FIG. 6, a heat-sensitive portion of a temperature sensor 4c is mounted at a depth of 3 mm to 10 mm from the surface of the cavity 3e of the movable mold 3b. The heat sensing part of the temperature sensor 4d is attached to the cooling water pipe 3f of the mold 3b. The temperature sensors 4c and 4d may be provided on the fixed mold 3a, or may be provided on both the movable side and the fixed side to calculate the average value.

Each of these temperature sensors 4a, 4b, 4c, 4
d are connected to the respective amplifiers 5a, 5a in the controller 5.
A / D converters 5e and 5d through b, 5c and 5d, respectively.
f, 5g, 5h, and each A / D converter 5
Output terminals of e, 5f, 5g, and 5h are connected to input terminals of the control operation unit 5i, respectively.

The control operation section 5i is provided with the A / D converter 5
Outputs of e, 5f, 5g, and 5h, each of the equations (1) to (5) and constants TRS, TWS, Tnf, e, R ', ω, πi, which are set by the setting monitor 5j. , VC, WC,
Various set values including a ₁ , a ₂ , b, c, and d, and an injection start signal (S 1) and a pressure holding start signal (S 2) for measuring various timings output from the sequence controller 6. The microcomputer is constituted by a microcomputer which inputs and calculates a holding pressure set value (PL ^* ) and outputs it to the switch 5k as an analog signal. At the same time, the control operation unit 5i
The control start signal (S3) indicating that the calculated holding pressure set value (PL ^* ) can be output to the pressure control valve amplifier 8 is output to the switch 5k.
Output as a digital signal. Also, the control operation unit 5i
Is the nozzle tip temperature (TR) and the spool temperature (TS)
), The mold cavity wall surface temperature (TW), and the mold cooling water temperature (TE) are output to the setting monitor 5j as measured values,
Further, the set pressure holding value (PL ^* ), the estimated value of the resin temperature in the mold (TC (tnf)), and the weight of the molded product (WC) are output as calculated values. In the setting monitor section 5j, a time (tPL) for controlling to the pressure holding set value (PL ^* ) in the pressure holding stage can be set.
PL) is used as a time during which the control operation unit 5i outputs the pressure holding set value (PL ^* ) to the switch 5k.

The switching unit 5k outputs an injection start signal (S1), which is a digital signal input from the sequence control unit 6,
When the pressure-holding start signal (S2) and the control start signal (S3) are all in the ON state, the pressure-holding set value (PL ^* ) input from the control calculation unit 5i is output to the pressure control valve amplifier 8; If at least one of S1, S2, S3) is in the OFF state, the analog output (A
I) is output to the pressure control valve amplifier 8. That is, the control time (tpL) from the start of the pressure holding stage
Only during this period, the pressure holding set value (PL ^* ) is output to the pressure control valve amplifier 8.

The pressure control valve amplifier 8 amplifies the input holding pressure set value (PL ^* ) and outputs the amplified value to the pressure control valve 9. Then, the hydraulic pressure in the hydraulic cylinder 11 becomes equal to the holding pressure set value (P
L ^* ).

Here, a method for controlling the dwell pressure in the injection molding of the present invention will be described.

In the injection holding pressure stage of an arbitrary molding shot, in the initial stage of filling immediately before the screw 1 starts to advance, the nozzle tip temperature (TR), spool temperature (TS), mold cavity wall surface temperature. (TW) and the mold cooling water temperature (TE) are detected.

Next, a preset nozzle tip temperature (TRS), a mold cavity wall surface temperature (TWS), a mold cooling water temperature (TES), and a cooling water temperature coefficient (e) of a shot of a good molding are set. The estimated value (TC (tnf)) of the resin temperature in the mold of the current molding shot is estimated using the following equation.

TC (tnf) = TCS (tnf) + (TRS-TCS (tnf)) / (TRS-TWS) .DELTA.TW + (TCS (tnf) -TWS) / (TRS-TWS) .DELTA.TR + e.DELTA.TE. ... (1) where ΔTW = TW−TWSΔTR = TR−TRSΔTE = TE−TEStnf is the resin temperature (TCS (t)) in the mold in a non-defective molding shot as a reference for each material. Is the time in the pressure-holding stage at which the flow stop temperature (Tnf) is reached, and is defined by the following equation.

TCS (tnf) = Tnf (2) Here, (tnf) is a quantity whose existence can be assumed as a constant, and need not be obtained as a numerical value.
Is simply substituted into (TCS (tnf)) in equation (1), and (TC
(tnf)).

Next, a predetermined molded product weight target value (WC ^* ), (TC (tnf)) obtained by equation (1), and SP
ENCER &GILMORE's equation of state [Spence
er, R .; S. Gilmore, G .; D ,: Jour
nal of AppliedPhysics, Vo
l. 20, p. 502 (1949)], the resin pressure (PC ^* (tnf)) in the mold to achieve the molded product weight target value (WC ^* ) is obtained by the following equation.

PC ^* (tnf) = R '. (TC (tnf) +273) / (VC / WC ^* -. Omega.)-. Pi.i (3) where VC is a set mold cavity volume. ω, R ', πi: Material constants to be set Resin pressure in the mold (PC (t)), holding pressure set value (PL), mold cavity wall surface temperature (TW), spool temperature (TS)
), The relationship with the nozzle tip temperature (TR) is approximated by the following equation.

PC (t) = a ₁ · T W + a ₂ · TS + b · TR + c · PL + d (4) Pressure holding for achieving PC ^* (tnf) represented by the equation (3) The set value (PL ^* ) is obtained by the following equation from the equation (4).

The ^{PL * = {PC * (tnf} ) -a 1 · TW -a 2 · TS -b · TR -d} / c ····· (5) _{However, a 1, a 2, b} , c , d: the above constants set, moldings weight target value (WC ^*) required to achieve the current molding shots coercive pressure setpoint (PL ^*) is obtained. Since the calculations of the equations (1) to (4) are completed in several tens of msec, in the filling stage, the holding pressure set value (PL ^* ) can be quickly obtained before the screw 1 starts moving forward.

Next, the meaning of the above control will be described with reference to FIGS.

FIG. 8 shows a change in resin temperature in the mold between molding shots.

As shown in FIG. 8, a fixed time (tnf)
The resin temperature in the mold is TCS (tnf) = Tnf in a shot in which a good product is molded. However, the mold cavity wall surface temperature (TW), the cooling water temperature (TE), and the nozzle tip temperature (TR) Changes, (TC '(tnf)), (TC
″ (Tnf)). (TC ′ (tnf)),
(TC "(tnf)) can be calculated by equation (1) as described above.

FIG. 9 shows a change in the resin pressure in the mold between molding shots.

As shown in FIG. 9, a fixed time (tnf
The resin pressure in the mold in () is, in a shot in which a good product is molded, PCS (tnf) = Pnf, but the mold cavity temperature (TW), spool temperature (TS), nozzle tip temperature (TR), And when the holding pressure (PL) changes, (PC
'(Tnf)) and (PC "(tnf)).
(PC '(tnf)) and (PC "(tnf)) can be calculated by equation (5) as described above.
) Is obtained, the resin temperature (TC) in these molds
And the resin pressure in the mold (PC) satisfy (3)
It is expressed by an equation. Then, (PC) is obtained by using the equation (3), and if the holding pressure set value (PL ^* ) is calculated based on the equation (5), the holding pressure control for obtaining a predetermined molded article weight (WC) is obtained. Becomes possible.

After the above, when the pressure-holding stage comes, the pressure is controlled to the determined pressure-holding set value (PL ^* ). The above calculation indicates that the molded article weight (WC) can be predicted with high accuracy by the resin temperature and the resin pressure in the mold at a fixed time when the resin in the mold almost loses its fluidity. Based on

Next, all steps of this embodiment will be described with reference to FIG.

The injection start signal (S1) is input from the sequence controller 6 to the controller 5 (step 101).
The control calculation unit 5i determines the nozzle tip temperature (TR) (step 102) and the spool temperature (TS) (step 1).
03), mold cavity wall surface temperature (TW) (Step 1)
04) and cooling water temperature for mold (TE) (step 1)
05) is measured. Next, using these measured values, the resin temperature in the mold (TC (tn
f)) (Step 106) is calculated. Then, the resin pressure (PC ^* (tn) in the mold to achieve the molded product weight target value (WC ^* )
f)) is calculated from the equation (3) (step 107), and the holding pressure set value (PL ^* ) required to achieve the resin pressure (PC ^* (tnf)) in the mold is calculated from the equation (5). Calculation (Step 108)
I do.

When the above calculation is completed, the control operation unit 5i
Outputs the control start signal (S3) and the pressure holding set value (PL ^* ) to the switch 5k (step 109), and outputs the pressure holding start signal (S3).
It waits for 2) to be input from the sequence controller 6 (step 110).

Thereafter, when the sequence control device 6 outputs a pressure-holding start signal (S2) to the control operation unit 5i and the switch 5k, the switch 5k outputs the pressure-holding set value (PL ^* ) output from the control operation unit 5i. Is output to the pressure control amplifier 8 (step 11).
1) Yes. At the same time, the control calculation unit 5i starts calculating the control time (step 112), and when the control time becomes equal to or longer than the preset tPLS (step 113), sets the control start signal (S3) to the OFF state, and maintains the pressure. Set value (PL ^* )
Output (Step 114), (Step 115)
I do. Then, the switch 5k switches to output the analog output (AI) of the machine control device to the pressure control valve amplifier 8, and sets the pressure holding set value (P
The control according to L ^* ) ends.

[0052]

Since the present invention is configured as described above, the following effects can be obtained.

It is possible to eliminate the fluctuation of the quality of the molded article caused by the temperature change and to stably produce the molded article with high dimensional accuracy.

Further, it has a simple structure which does not require mounting a resin pressure sensor and a resin temperature sensor in a mold, and has high controllability and applicability which are not affected by the thickness of the molded product and the gate shape.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention.

FIG. 2 shows a cross-sectional view of the attachment of a temperature sensor to a nozzle portion.

FIG. 3 shows a front view of mounting a temperature sensor on a nozzle portion.

FIG. 4 is a cross-sectional view of a temperature sensor attached to a spool portion.

FIG. 5 shows a front view of attachment of a temperature sensor to a spool portion.

FIG. 6 is a sectional view of a mold in which a temperature sensor on a wall surface of a mold cavity and a temperature sensor for mold cooling water are mounted.

FIG. 7 is a flowchart showing the steps of this embodiment.

FIG. 8 is a graph showing a change in resin temperature in a mold between molding shots.

FIG. 9 is a graph showing a change in resin pressure in a mold between molding shots.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Screw 2 Nozzle 2a Nozzle resin flow path 2b Nozzle tip 3 Mold 3a Fixed mold 3b Movable mold 3c Spool section 3d Spool flow path 3e Cavity 3f Cooling water pipe (movable side) 3g Cooling water pipe (fixed side) 4a to 4d Temperature sensors 5a to 5d Amplifiers 5e to 5h A / D converters 5i Control calculation unit 5j Setting monitor unit 5k Switch 6 Sequence control device 7 Machine control device 8 Pressure control valve amplifier 9 Pressure control valve 10 Heating cylinder 11 Hydraulic cylinder 12 Nozzle heater 13 Nozzle temperature control thermocouple 14 Temperature sensor mounting bracket 15 Locate ring

Claims (6)

(57) [Claims] 1. A filling step of filling molten resin in a heating cylinder of an injection molding machine into a cavity through a nozzle and a resin flow path in a mold by advancing a screw, and after filling the molten resin into the cavity. In order to compensate for the shrinkage of the molten resin as it is cooled and solidified in the cavity, a pressure-holding step of pressing the screw and replenishing the molten resin is included in the injection molding. Immediately before starting the forward movement, the nozzle tip temperature (TR), the spool temperature (TS), the mold cavity wall temperature (TW), and the mold cooling water temperature (TE) are measured. Value (T
R, TS, TW, TE), the time (tn) at which the molded article weight can be considered to be substantially determined in the subsequent dwelling stage.
f) Estimate the estimated value of the resin temperature in the mold (TC (tnf)),
Next, the resin pressure (PC ^* ) in the mold at the time (tnf) required to achieve the predetermined molded product weight target value (WC ^* ) ^.
(tnf)) is determined from the estimated value of the resin temperature in the mold (TC (tnf)), and further, the holding pressure set value (PC ^* (tnf)) required to achieve the resin pressure (PC ^* (tnf)) in the mold. PL ^* ) and the resin pressure (PC ^* (tnf)) in the mold and the measured values (TR, TS)
, TW, TE), and then, when the dwelling stage is started, the dwelling set value (P) previously determined in the filling stage is obtained.
A holding pressure control method in injection molding, wherein the holding pressure is controlled based on L ^* ). 2. The resin temperature (TC) in the mold during the pressure-holding stage.
2. A pressure-holding control method in injection molding according to claim 1, wherein (t)) is estimated by the following equation. TC (t) = TCS (t) + (TRS-TCS (t)) / (TRS-TWS) .DELTA.TW + (TCS (t) -TWS) / (TRS-TWS) .DELTA.TR + e.DELTA.TE where TCS ( t): Resin temperature in the mold at time t in a shot when a good product is molded TC (t): Resin temperature in the mold at time t of an arbitrary shot TRS: Nozzle tip temperature of a shot in which a good product is molded TR: Nozzle tip temperature of any shot TWS: Mold cavity wall surface temperature of non-defective shot TW: Mold cavity wall surface temperature of any shot TES: Cooling water temperature of non-defective shot TE: Any E: Cooling water temperature coefficient to be set ΔTW = TW−TWS ΔTR = TR−TRSΔTE = TE−TES 3. The resin pressure (PC) in the mold during the dwelling stage.
2. The pressure-holding control method in injection molding according to claim 1, wherein (t)) is estimated by the following equation. PC (t) = a ₁ · T W + a ₂ · TS + b · TR + c · PL
+ D However, PC (t): the resin pressure PL in the mold at time t at any shots: coercive pressure value a ₁ in any of the _{shots, a 2, b, c,} d: constants set 4. The method according to claim 1, wherein the weight of the molded product (WC) is estimated by the following equation. VC / WC = ω + {R ′ · (TC (t) +273)} / (P
C (t) + πi) where, VC: cavity volume of the mold ω, R′πi: set material constant WC: resin pressure in the mold (PC (t)), resin temperature in the mold (T
C (t)) Molded product weight in shot. 5. The time (t) in the pressure-holding stage for evaluating the resin pressure in the mold (PC (t)) and the resin temperature in the mold (TC (t)).
2. The method according to claim 1, wherein nf) is determined as follows. TCS (tnf) = Tnf where Tnf: flow stop temperature determined by the material. That is, tnf means that the resin temperature TCS (t) in the mold in the molding shot serving as a reference for forming a non-defective product reaches the flow stop temperature Tnf. It is time. 6. An injection device comprising a heating cylinder, a screw disposed therein, a screw driving means for reciprocating and rotating the screw in an axial direction, and a mold clamping device for clamping a mold. A temperature sensor for measuring the nozzle tip temperature (TR), a temperature sensor for measuring the spool temperature (TS), and a mold cavity wall temperature (TW). A temperature sensor for measuring the temperature of the cooling water for the mold (TE) and a temperature sensor for measuring the cooling water temperature for the mold (TE), and a target molded product weight target value (WC ^* ) is obtained based on these measured values. a control arithmetic unit for calculating a holding pressure setpoint (PL ^*) necessary for the switcher to output-holding pressure setpoint to (PL ^*) to the pressure control valve amplifiers,-holding pressure setpoint (PL ^* Monitors set values and measured values required for calculation of) And a pressure monitor for injection molding, comprising: