JPH06320588A - Holding pressure control method and apparatus in injection molding - Google Patents

Abstract

(57) [Summary] [Purpose] It is not necessary to mount a resin pressure sensor and a resin temperature sensor in a mold, and it is possible to control the quality of molded products with high accuracy regardless of temperature changes. [Composition] At the beginning of the filling stage, immediately before the screw starts to move forward, the nozzle tip temperature (TR), the spool temperature (TS), the mold cavity wall surface temperature (TW)
And mold cooling water temperature (TE) are respectively measured (steps 101 to 105), and based on these measured values,
Estimate the estimated value of the resin temperature (TC (tnf)) in the mold at the time (tnf), at which it can be considered that the weight of the molded product is almost fixed in the pressure holding stage (step 106), and achieve the target value of the molded product weight (WC ^* ). Resin pressure (PC ^* ) in the mold at the time (tnf)
(tnf)) is obtained from the above (TC (tnf)) (step 10
8) Further, the holding pressure set value (PL ^* ) required to achieve the resin pressure (PC ^* (tnf)) in the mold is obtained, and the holding pressure is controlled based on this (step 111).

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Injection molding is carried out under various temperature changes such as seasonal changes, morning and evening temperature changes, and molding start-up and interruption. In addition, various physical properties of plastic materials such as melt viscosity and shrinkage ratio are characterized by large dependence on temperature. For this reason, the temperature change is the main cause of fluctuations in the quality of the molded product such as the shape size and the weight accuracy.

Generally, the above-mentioned temperature change is the mold temperature,
It appears as fluctuations in cooling water temperature, heating cylinder temperature, and so on. As a result, the temperature of the resin until it is filled in the mold, cooled, solidified, and taken out changes, and the reproducibility of the resin pressure and flow rate is impaired, causing variations in the shape and dimensions for each molding cycle. become. To solve these problems, the state of the resin such as pressure and temperature is kept constant every shot, or even if the temperature change is an unavoidable factor, a predetermined molded product quality can be obtained. It is necessary to take measures to control the pressure.

In order to solve such a problem caused by a temperature change, conventionally, a resin pressure sensor or a resin temperature sensor is mounted in a mold, and a pressure (P), a temperature (T) of a molding material (resin), and A method of controlling the resin pressure in the mold so that the specific volume of the molded product matches the target value regardless of the temperature change, based on the PVT characteristic data which is the basic physical property data showing the relationship of the specific volume (V). Has been taken (JP-A-63
-3926 and 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 mold is filled with the resin are measured every moment, and these measured values and the PVT characteristic data are used. A control method is used in which the resin pressure in the mold is feedback-controlled so that the target specific volume of the molded product is obtained. Also, among these, although the resin pressure in the mold is detected, this is not feedback controlled,
A method has also been reported in which a shut-off nozzle or a gate valve is used to control the time at which the resin supply to the mold is mechanically shut off (DE4026731). Furthermore, as for the method of obtaining the resin temperature in the mold, it is also reported to obtain it directly by measuring it, or to indirectly estimate the resin temperature in the mold from the measured values of mold temperature and heating cylinder temperature. (US4983336).

[0006]

However, the above-mentioned conventional techniques have the following problems.

First, in any case, it is necessary to mount the resin pressure sensor in the mold, which is uneconomical, and moreover, it takes time to adjust and mount this pressure sensor.

Next, since the molten resin filled in the mold is rapidly cooled, its viscosity increases and is solidified in a short time. The increase in viscosity and solidification make it impossible to control the pressure of the resin sufficiently by pressing the screw. Therefore, even if it is attempted to measure and control the pressure and temperature of the resin in the mold which shows a rapid increase in viscosity and solidification after the mold is filled with the resin, the control becomes difficult. In particular, the shape and size of the molded product are determined when the resin in the mold loses its fluidity and the resin supply to the cavity is interrupted. It is necessary to maintain the state of. However, for the reasons described above, the degree of freedom to control the resin behavior is lost at this point, and the method of feedback-controlling these after measuring the resin pressure and the resin temperature in the mold is to obtain a predetermined quality. This problem is remarkable because the cooling and solidification progresses more rapidly, especially in a die having a thin wall or a small gate. In other words, the controllability of the method of detecting and controlling the pressure and temperature of the mold after filling it with resin is naturally limited. When using a shut-off nozzle or a valve gate, additional equipment is required, and it is limited to a special case in terms of economical efficiency, setup property, and maintainability.

Further, in the case of indirectly estimating the resin temperature in the mold from the mold temperature and the heating cylinder temperature, conventionally, a heat conduction analysis solution in which the heat transfer coefficient between the mold and the resin is regarded as infinity is used. Since it is an approximate expression that considers only the first term in the series, the calculation accuracy is poor, and as a result, there is a problem in estimating and controlling the quality of the molded product with high accuracy. Furthermore, in calculating the resin temperature in the mold, additional data such as the wall thickness of the molded product and the effective thermal diffusivity are required, so that there is a problem that it takes time and effort to collect these data.

The above problems are mainly related to the control system. In addition to this, there are the following problems in terms of contributing to the practical improvement of control quality.

First, when the high temperature nozzle and the low temperature mold contact each other, heat is transferred from the nozzle toward the mold, and the resin temperature at the tip of the nozzle sharply drops. Then, the amount of resin flowing from the nozzle into the mold becomes unstable. Therefore, it is important to consider the heat transfer from the nozzle to the mold as one of the temperature changes in order to control the weight and shape of the molded product with high accuracy. However, heretofore, there has been no report on a measurement method capable of capturing heat transfer from a nozzle to a mold with sufficient accuracy and control based on the measurement method.

[0012] Next, even if the mold temperature changes, it also causes a temperature change temporarily brought from the mold cavity surface, such as a change in the atmospheric temperature and a change in the temperature of the resin filled in the mold. However, the influence of the mold temperature change on the quality of the molded product differs depending on whether it is a change in the cooling water temperature or a change in the mold cooling capacity that occurs inside the mold. Will be things. Therefore, distinguishing between the temporary mold temperature change caused by the cavity surface and the mold cooling capacity change caused by the change of the cooling water temperature is effective in predicting and controlling the molded product quality with high accuracy. is important. However, the related art has not reported a measurement and control method that handles them separately. Therefore, in maintaining the stability of quality, the accuracy of the conventional control is not satisfactory.

The present invention has been made in view of the problems of the above-mentioned conventional techniques, and it is not necessary to mount a resin pressure sensor and a resin temperature sensor in a mold, and the thickness of a molded product and the shape of a gate. To provide a pressure holding control method and device in injection molding capable of controlling the quality of a molded product with high accuracy, which can obtain a sufficient controllability regardless of the temperature and does not require special equipment such as a shut-off nozzle or a gate valve. With the goal.

[0014]

In order to achieve the above object, the method of controlling the holding pressure in injection molding according to the present invention is such that the molten resin in the heating cylinder of the injection molding machine is moved forward by the screw so that the resin in the nozzle and the resin in the die are moved. After the filling step of filling the cavity through the flow path and filling the cavity with the molten resin, the screw is pressed to compensate for shrinkage of the molten resin as it cools and solidifies in the cavity. In the injection molding having a pressure-holding step for replenishing the molten resin, the nozzle tip temperature (TR
), Spool temperature (TS), mold cavity wall surface temperature (TW), and mold cooling water temperature (TE), and based on these measured values (TR, TS, TW, TE), The estimated value of the resin temperature in the mold (TC (tnf)) at the time (tnf) at which the weight of the molded product can be considered to be almost fixed in the holding pressure stage is estimated, and then the preset target value of the molded product weight (WC ^* ) The time (tnf) required to achieve
The resin pressure (PC ^* (tnf)) in the mold is obtained from the estimated value (TC (tnf)) of the resin temperature in the mold, and the resin pressure (PC ^* (tnf)) in the mold is further achieved. The holding pressure setting value (PL ^* ) required for the above is obtained from the resin pressure (PC ^* (tnf)) in the mold and the respective measured values (TR, TS, TW, TE), and then the holding pressure is set. When the step is entered, the holding pressure is controlled based on the holding pressure set value (PL ^* ) previously obtained in the filling step.

Further, the resin temperature (TC (t)) in the mold at the pressure holding stage is expressed 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 However, TCS (t): Resin temperature in the mold at time t in the shot when a good product is molded TC (t): Any Resin temperature in the mold at the time t of 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 temperature of a shot in which a good product is molded TW: Any Mold die wall surface temperature of the above shot TES: Cooling water temperature of the shot in which a good product is molded TE: Cooling water temperature of any shot e: Set cooling water temperature coefficient ΔTW = TW-TWS ΔTR = TR -TRS ΔTE = Estimated by TE-TES, the resin pressure in the mold (PC (t))
The following equation PC (t) = a ₁ · TW + a ₂ · TS + b · TR + c · PL
+ D However, PC (t): Resin pressure in the mold at time t in an arbitrary shot PL: Holding pressure set value in an arbitrary shot a ₁ , a ₂ , b, c, d: Estimated by a set constant.

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

In addition, the time (tnf) at the pressure holding stage for evaluating the resin pressure (PC (t)) in the mold and the resin temperature (TC (t)) in the mold 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 reference molding shot when a good product is molded. It is the time to reach Tnf.

A pressure holding control device in injection molding according to the present invention is an injection device including a heating cylinder, a screw disposed inside the heating cylinder, and screw driving means for reciprocating and rotating the screw in the axial direction. In an injection molding machine equipped with a mold clamping device for clamping a mold, a temperature sensor for measuring the temperature (TR) of the nozzle tip and a temperature sensor for measuring the spool temperature (TS). , Temperature sensor for measuring mold cavity wall surface temperature (TW), temperature sensor for measuring mold cooling water temperature (TE), and target molding based on these measured values A control calculation unit for calculating a holding pressure set value (PL ^* ) required to obtain a product weight target value (WC ^* ), and the holding pressure set value (P ^* )
A switch for outputting L ^* ) to the pressure control valve amplifier, and a setting monitor unit for monitoring the set value and the measured value necessary for calculating the holding pressure set value (PL ^* ). It is a feature.

[0020]

The heat transfer from the nozzle to the die 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 pipe part of the mold cooling water provide a temperature in two meanings of the mold temperature, that is, a resin. It is possible to grasp the flow resistance and the cooling capacity with respect to.

Next, in the injection pressure-holding stage, at the beginning of filling, just before the screw starts to move forward, the nozzle tip temperature (TR), the spool temperature (TS), the mold cavity, The wall surface temperature (TW) and the mold cooling water temperature (TE) were measured, and each measured value (T
Based on 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 Then, the resin pressure (PC ^* (t)) in the mold at the pressure-holding stage required to achieve the target molded product weight target value (WC ^* ) is calculated, and the resin pressure (PC ^* (PC ^* ( Calculate the holding pressure setting value (PL ^* ) required to obtain t)). The above calculation is completed in several tens of msec before the screw starts to move forward. As described above, the calculated holding pressure set value (PL ^* ) is output to the pressure control valve amplifier at the holding pressure stage.

Therefore, it is possible to perform a simple control that does not require an in-mold pressure sensor, an in-mold resin temperature sensor, a shut-off nozzle, a gate valve, or the like. Further, since the holding pressure set value (PL ^* ) set in the holding pressure stage is quickly determined before filling, it is not necessary to measure every moment in the holding pressure stage, and feedback control is not necessary. However, no matter how rapidly the resin solidifies in the mold, it can be controlled and can be applied regardless of the thin-walled product or the gate shape. further,
It is possible to control the heat transfer from the nozzle to the mold and the cooling capacity of the mold.

[0024]

Embodiments 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 of the present invention. Heating cylinder 1
The screw 1 disposed inside the cylinder 0 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 move forward and backward in the left and right directions in the drawing, and rotate. There is. A nozzle resin passage 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 the fixed mold 3a and the movable mold. 3b, and inside thereof, a spool portion 3c and a cavity 3e are provided in order from the side closer to the nozzle 2.

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

The spool portion 3c is shown in FIGS.
As shown in, the heat-sensitive portion of the temperature sensor 4b is attached by an annular temperature sensor attachment fitting 14.

Further, as shown in FIG. 6, a heat sensitive portion of a temperature sensor 4c is attached to a position of a depth of 3 mm to 10 mm from the surface of the cavity 3e of the movable side mold 3b, and the movable side mold is attached. A heat sensitive portion of a 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 side mold 3a, or may be provided on both the movable side and the fixed side to obtain the average value thereof.

Each of these temperature sensors 4a, 4b, 4c, 4
Each signal output terminal of d is connected to each amplifier 5a, 5a in the control device 5.
b, 5c, 5d via A / D converters 5e, 5 respectively
f, 5g, 5h, each A / D converter 5
The output terminals of e, 5f, 5g, and 5h are connected to the input terminals of the control calculation unit 5i, respectively.

The control calculation section 5i includes the A / D converter 5
e, 5f, 5g, 5h output, each equation shown in equations (1) to (5) and each constant TRS, TWS, Tnf, e, R ', ω, πi set by the setting monitor unit 5j. , VC, WC,
Various set values including a ₁ , a ₂ , b, c, d, and an injection start signal (S1) and a pressure holding start signal (S2) for timing various timings output from the sequence controller 6 are set. It is composed of a microcomputer which inputs and calculates a holding pressure set value (PL ^* ) and outputs it as an analog signal to the switch 5k. At the same time, the control calculation unit 5i
A control start signal (S3) indicating that the calculated holding pressure set value (PL ^* ) can be output to the pressure control valve amplifier 8 is sent to the switch 5k.
Output as a digital signal to. In addition, the control calculation unit 5i
Is the nozzle tip temperature (TR) and spool temperature (TS
), Mold cavity wall surface temperature (TW) and mold cooling water temperature (TE) are output to the setting monitor section 5j as measured values,
Furthermore, the holding pressure set 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 unit 5j, the time (tPL) for controlling the holding pressure setting value (PL ^* ) in the holding pressure stage can be set,
PL) is used as the time when the control calculation unit 5i outputs the holding pressure set value (PL ^* ) to the switch 5k.

The switch 5k has an injection start signal (S1), which is a digital signal input from the sequence controller 6,
When the holding pressure start signal (S2) and the control start signal (S3) are all in the ON state, the holding pressure set value (PL ^* ) input from the control calculation unit 5i is output to the pressure control valve amplifier 8. If even one of S1, S2, S3) is OFF, the analog output (A
It has a circuit configuration for outputting I) to the pressure control valve amplifier 8. That is, the control time (tpL) from the start of the pressure holding stage
Only during the period, the holding pressure set value (PL ^* ) is formed to be output to the pressure control valve amplifier 8.

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

Here, the holding pressure control method in the injection molding of the present invention will be described.

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

Next, the nozzle tip temperature (TRS), the mold cavity wall surface temperature (TWS), the mold cooling water temperature (TES), and the cooling water temperature coefficient (e) of the preset shot for good molding are set. Then, the estimated value (TC (tnf)) of the resin temperature in the mold of the current molding shot is estimated by 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) However, ΔTW = TW-TWS ΔTR = TR-TRS ΔTE = TE-TES tnf is the resin temperature (TCS (t)) in the mold in the shot of good product molding, which is a reference, for each material. It is the time in the holding pressure stage at which the flow stop temperature (Tnf) determined by 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 it is not necessary to obtain this as a numerical value, (Tnf)
By substituting for (TCS (tnf)) in equation (1)
(tnf)) can be obtained.

Next, the preset target weight value (WC ^* ) of the molded product, (TC (tnf)) obtained from the equation (1), and SP
ENCER & GILMORE equation of state [Specc
er, R.R. S. Gilmore, G .; D ,: Jour
nal of Applied Physics, Vo
l. 20, p. 502 (1949)], the resin pressure (PC ^* (tnf)) in the mold for achieving the target weight value (WC ^* ) of the molded product is calculated by the following equation.

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

PC (t) = a ₁ · TW + a ₂ · TS + b · TR + c · PL + d (4) Holding pressure for achieving PC ^* (tnf) represented by the equation (3) The set value (PL ^* ) is calculated 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: a constant set or more, the current holding pressure setting value (PL ^* ) of the molding shot required to achieve the target weight value (WC ^* ) of the molded product is obtained. Since the calculation of equations (1) to (4) is completed in several tens of msec, the holding pressure set value (PL ^* ) can be quickly obtained before the screw 1 starts to advance in the filling stage.

Next, the meaning of the above control will be described with reference to FIGS. 8 and 9.

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

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

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

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

After the above, when the holding pressure stage comes, the holding pressure setting value (PL ^* ) thus obtained is controlled. The above calculation shows that the weight of molded product (WC) can be predicted with high accuracy by the resin temperature in the mold and the resin pressure in the mold at a fixed time when the resin in the mold almost loses its fluidity. Is based on.

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

An injection start signal (S1) is input from the sequence controller 6 to the controller 5 (step 101).
Then, 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 mold cooling water temperature (TE) (step 1
05) is measured. Next, using these measured values, from the equations (1) and (2), the resin temperature (TC (tn
f)) (step 106) is calculated. Then, the resin pressure in the mold to achieve a molded article weight target value ^{(WC *) (PC * (} tn
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 obtained from the equation (5). Calculation (step 108)
To do.

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

After that, when the sequence control device 6 outputs the pressure holding start signal (S2) to the control calculation unit 5i and the switching unit 5k, the switching unit 5k outputs the pressure holding set value (PL ^* ) output by the control calculation unit 5i. Is output to the pressure control amplifier 8 (step 11
1) Do. At the same time, the control calculation unit 5i starts the calculation of the control time (step 112), and when the control time becomes equal to or more than the preset tPLS (step 113), the control start signal (S3) is turned off to hold the pressure. Set value (PL ^* )
Output of (step 114), (step 115)
To 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 holding pressure set value (P
The control by L ^* ) ends.

[0052]

Since the present invention is configured as described above, it has the following effects.

Variations in the quality of molded products due to temperature changes can be eliminated, and molded products with high dimensional accuracy can be stably produced.

Further, the resin pressure sensor and the resin temperature sensor need not be installed in the mold, and the controllability and applicability are not affected by the thickness of the molded product or the gate shape.

[Brief description of drawings]

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

FIG. 2 shows a cross-sectional view of mounting a temperature sensor on a nozzle portion.

FIG. 3 shows a front view of a temperature sensor attached to a nozzle portion.

FIG. 4 is a cross-sectional view of mounting a temperature sensor on a spool portion.

FIG. 5 shows a front view of mounting a temperature sensor on a spool portion.

FIG. 6 is a cross-sectional view of a mold for mounting a temperature sensor on a wall surface of a mold cavity and a temperature sensor for mold cooling water.

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

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

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

[Explanation of symbols]

 1 Screw 2 Nozzle 2a Nozzle Resin Flow Path 2b Nozzle Tip 3 Mold 3a Fixed Side Mold 3b Movable Side Mold 3c Spool Part 3d Spool Flow Path 3e Cavity 3f Cooling Water Piping (Movable Side) 3g Cooling Water Piping (Fixed Side) ) 4a-4d Temperature sensor 5a-5d Amplifier 5e-5h A / D converter 5i Control calculation part 5j Setting monitor part 5k Switching device 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)

[Claims] 1. A filling step of filling a molten resin in a heating cylinder of an injection molding machine into a cavity by advancing a screw through a resin flow path in a nozzle and a mold, and after filling the molten resin into the cavity. In injection molding having a pressure-holding step of pressing the screw to replenish the molten resin in order to compensate for shrinkage of the molten resin as it cools and solidifies in the cavity, Immediately before starting the forward movement, the nozzle tip temperature (TR), spool temperature (TS), mold cavity wall surface temperature (TW), and mold cooling water temperature (TE) were measured, and these measurements were made. Value (T
Based on R, TS, TW, TE), the time (tn) at which the weight of the molded product can be considered to be almost fixed in the subsequent holding stage.
f) Estimate the resin temperature in the mold (TC (tnf)),
Next, the resin pressure (PC ^* ) in the mold at the time (tnf) required to achieve the preset target weight value (WC ^* ) of the molded product ^.
(tnf)) from the estimated value of the resin temperature in the mold (TC (tnf)), and the holding pressure setting value (PC ^* (tnf)) required to achieve the resin pressure (PC ^* (tnf)) in the mold. PL ^* ) is the resin pressure in the mold (PC ^* (tnf)) and the measured values (TR, TS)
, TW, TE), and when the holding pressure stage is entered, the holding pressure set value (P
A holding pressure control method in injection molding, characterized in that the holding pressure is controlled based on L ^* ). 2. The temperature of the resin in the mold (TC
The 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 However, TCS ( t): Resin temperature in mold at time t in shot when good product is molded TC (t): Resin temperature in mold at time t of arbitrary shot TRS: Nozzle tip temperature of shot in which good product is molded TR: Nozzle tip temperature of any shot TWS: Mold cavity wall surface temperature of shot with good product TW: Mold cavity wall temperature of arbitrary shot TES: Cooling water temperature of shot with good product TE: Any Cooling water temperature of shot e: Set cooling water temperature coefficient ΔTW = TW-TWS ΔTR = TR-TRS ΔTE = TE-TES 3. The resin pressure (PC
The pressure holding control method in injection molding according to claim 1, wherein (t)) is estimated by the following equation. PC (t) = a ₁ · TW + a ₂ · TS + b · TR + c · PL
+ D However, PC (t): Resin pressure in the mold at time t at any shot PL: Holding pressure set value at any shot a ₁ , a ₂ , b, c, d: Set constant 4. The holding pressure control method in injection molding according to claim 1, wherein the weight (WC) of the molded product is estimated by the following state equation. VC / WC = ω + {R '. (TC (t) +273)} / (P
C (t) + πi) where VC is the cavity volume of the mold ω, R′πi: Material constant to be set WC: Resin pressure in the mold (PC (t)), resin temperature in the mold (T
The weight of the molded product in the shot of C (t)). 5. A time (t) in a pressure holding stage for evaluating the resin pressure (PC (t)) in the mold and the resin temperature (TC (t)) in the mold.
The pressure holding control method in injection molding according to claim 1, wherein nf) 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 standard molding shot when a good product is molded, reaches the flow stop temperature Tnf. It's time. 6. An injection device including a heating cylinder, a screw disposed inside the heating cylinder, screw driving means for reciprocating and rotating the screw in the axial direction, and a mold clamping device for clamping the mold. In an injection molding machine equipped with, a temperature sensor for measuring the nozzle tip temperature (TR), a temperature sensor for measuring the spool temperature (TS), and a mold cavity wall surface temperature (TW) Temperature sensor for measuring the temperature of the cooling water for the mold (TE), and based on each of these measured values, the target value of the weight of the molded product (WC ^* ) is obtained. Control calculation unit for calculating the holding pressure set value (PL ^* ) necessary for the pressure control valve amplifier, the switch for outputting the holding pressure set value (PL ^* ) to the pressure control valve amplifier, and the holding pressure set value (PL ^*). ) Monitor the set values and measured values required for calculation A holding pressure control device in injection molding, comprising: