JP2811536B2 - Estimation method of resin pressure in mold 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 for producing an injection-molded article, which is required for quickly predicting a dimensional change of the molded article caused by a change in environmental temperature and the occurrence of molding defects. The resin pressure estimation method.

[0002]

2. Description of the Related Art Fluctuations in the quality of molded products that occur during injection molding of molded products are mainly governed by temperature changes such as changes in the atmospheric temperature, mold temperature and molten resin temperature of the place where an injection molding machine is installed. Is done. These temperature changes affect the flowability, shrinkage, crystallinity, etc. of the molten resin during the process of filling the molten resin into the mold. As a result, the temperature and pressure of the molten resin in the mold cavity fluctuate, and as a result, the dimensions of the molded product fluctuate and molding failure occurs.

Therefore, as one method for monitoring a change in the quality of a molded product caused by the above-mentioned temperature change, a resin pressure sensor is provided in a mold cavity, and the resin pressure sensor in the mold is measured by the resin pressure sensor. A method of detecting a change in the quality of a molded article according to the fluctuation state or performing feedback control based on a detection value of the resin pressure sensor so that the resin pressure in the mold becomes a predetermined value is adopted.

[0004]

However, in the above-mentioned prior art, the resin pressure sensor is expensive, and its installation and adjustment are troublesome. In addition, the molded product is not required unless the resin pressure in the mold fluctuates. Since a change in quality cannot be detected, there is a problem that an appropriate measure for preventing a change in the quality of a molded product cannot be taken before injection molding and filling a molten resin into a mold cavity.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and quickly predicts the fluctuation of the resin pressure in a mold before injecting and filling a molten resin into a cavity of the mold. Accordingly, it is an object of the present invention to realize a method for estimating a resin pressure in a mold in injection molding in which an appropriate measure for preventing a change in quality of a molded product and occurrence of molding failure can be performed.

[0006]

In order to achieve the above object, a method for estimating a resin pressure in a mold in injection molding according to the present invention is directed to a method for estimating a molten resin by using a mold having a runner portion, a gate portion and a cavity portion. And a pressure-holding / cooling step of additionally replenishing the cavity with the molten resin by pressurizing the screw to compensate for the volume shrinkage accompanying cooling of the molten resin injected and filled. In the injection molding, measured values of the mold temperature and the molten resin temperature immediately before the start of the injection filling are set in advance.
By using a relational expression that is established between the holding pressure set value to be applied and the resin pressure in the mold in the pressure holding / cooling stage, the mold in the pressure holding / cooling stage is obtained immediately before the start of the injection filling. It is characterized by quickly estimating a change in resin pressure in the inside.

[0007]

[0008]

The temperature of the mold and the temperature of the molten resin immediately before the injection and filling of the molten resin into the cavity of the mold are measured, and the resin in the mold in the pressure-holding / cooling stage is determined based on the measured value and the set value of the pressure-holding pressure. Pressure changes can be quickly estimated.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is an explanatory diagram of an analysis model assumed to derive a formula for predicting a change in resin pressure in a mold according to the present invention.

First, in the present analysis model, the molten resin flow path composed of the runner part 2, the gate part 3, and the cavity part 4 of the mold 1 is approximated by the following simple shape.

The runner 2 is a circular pipe having a radius R (m), the gate 3 is a rectangle having a width W (m), a height 2 · B (m), and a length L (m), and the cavity 4 is a thickness. It is assumed that the flow path is a rectangular flow path of S (m) and volume Vs (m ³ ).

The pressure of the resin in the runner section 2 is maintained at a pressure P _L (MPa).
It is assumed that the holding pressure P _L is constant independently of the time t (s).

The resin pressure P _C (t) (MPa) in the mold is assumed to indicate the average resin pressure in the cavity portion 4 and the flow direction z (m) and the direction y (m) perpendicular thereto. Is not considered.

Sectional position x (m) of resin in cavity 4
Temperature T _C (t, x) Distant, the average temperature of the cross-sectional direction T of the
_C (t) (℃) Distant, T _C is also an average temperature of the cavity plane each section, does not consider the temperature distribution.

The temperature of the resin that passes through the gate 3 and fills the cavity 4 is defined as T _L (t, x, y) (° C.).
_L (t, x, y) is analyzed as an unsteady heat conduction in the gate unit 3 in which the temperature at the time of filling is an initial value in the pressure-holding cooling process.

The change in the resin temperature in the gate portion 3 and the cavity portion 4 is treated as unsteady heat conduction of a rectangular plate and an infinite flat plate, respectively. However, assuming that heat transfer in the holding pressure cooling process is only heat conduction, the temperature at the start of holding pressure is uniformly set to T.
Assume _INI . Viscous heating is only taken into account during the filling process. The flow of the molten resin passing through the gate 3 is assumed to be a one-dimensional flow of the incompressible fluid, and the volume flow rate during the pressure-holding cooling process is defined as Q _H (t) (m ³ / s). The compression ratio β _C and the thermal expansion coefficient κ _C of the molten resin in the cavity 4 depend on the pressure and the temperature. For simplification, the average compression ratio and the thermal expansion coefficient are obtained from the pvT data of the molten resin. , These are assumed to be constant values.

The molten resin is assumed to be an Arrhenius-type temperature-dependent power fluid. At time t = to, the molten resin is supplied to the cavity 4, the runner 2 and the gate 3.
Suppose that That is, it is assumed that time t = to is the end point of the filling process.

The resin density in the cavity 4 is expressed as ρ _C
(t) (kg / m ³ ).

FIG. 2 is a graph showing a change in resin pressure in the mold and a change in resin temperature in the mold during injection molding.

As shown in FIG. 2, the filling process shows a relatively low resin pressure, and when the cavity is filled with the resin, the resin is rapidly compressed and reaches a maximum value in a short time.
After reaching the maximum value, the resin pressure decreases due to the volume shrinkage of the resin caused by cooling, but the molten resin is supplied to the cavity portion 4, so that the resin pressure decreases upward. Thereafter, when the fluidity of the resin supplied from the runner portion 2 to the cavity portion 4 gradually decreases due to cooling and disappears, the supply of the resin to the cavity portion 4 is stopped. From this point,
The resin in the cavity 4 exhibits a pressure drop corresponding to volume contraction when the mass is constant. The compression stage from the completion of filling until the resin pressure in the mold reaches the maximum value, and the process in which the volume shrinkage caused by cooling after reaching the maximum value and the resin flow compensating for this progress at the same time as the pressure-holding / cooling stage Call. Formulated under the above assumptions is as follows.

Equation of continuity: dρ _C / dt = ρ _C · Q _H / V _S (1) Steady flow of exponential fluid at the gate:

[0023]

(Equation 8)

[0024]

(Equation 9)

[0025]

(Equation 10) [Analysis of resin pressure in mold] Equations (1), (4), (7)
The following equation is derived from the equation.

[0026] _{dD C / dt = -Kn · F} C 1 / n · D C 1 / n · (κ C / β C) · d T C / dt ····· (20) However, D _C = P _L- P _C (t), Kn = K _O / (β _C · V
_S ) In the compression stage, the flow rate of the molten resin from the runner section 2 to the cavity section 4 changes rapidly. On this occasion,
Since the shear rate greatly changes, it is necessary to treat the resin as a non-Newtonian fluid in consideration of the shear rate dependence of the viscosity. In addition, since the compression stage is very short, the volume shrinkage due to the cooling of the resin during this stage is considered to be negligible. On the other hand, in the dwelling / cooling stage,
The flow rate of the molten resin supplied to the cavity 4 is relatively small. For this reason, the shear rate dependence of the viscosity becomes relatively small, so that a Newtonian fluid (n = 1) is used. In this case, the resin pressure in the mold in the compression stage and the pressure-holding / cooling stage is expressed by the following equation.

Compression stage (to <t ≦ t _I ) dD _C / dt = −K ⁿ · F _C ^{1 / n} · D _C ^{1 / n} (21) Holding pressure / cooling stage (t _I < _{t ≦ t f) dD C /} dt = -K 1 · F C · D C - (κ C / β C) · d T C / dt ····· (22) where, t _f (s) is Indicates the end time of the calculation.

The solution of the equation (21) is given by the following equation.

D _C ^{1-1 / n} −D _O ^{1-1 / n} = K ⁿ · (1 / n -1) · I _Fn (to, t) (23) The solution is given by

[0030]

[Equation 11] By substituting equation (25) into equation (24), the resin pressure in the mold at the holding pressure / cooling stage is expressed by the following equation.

[0031]

(Equation 12) (26) The first term of the pressure gradient D _I, the time integral I _F (t _I, t) of the temperature dependent term F _C liquidity pressure increase due to the resin flow to the cavity as determined by Show.
A similar interpretation holds for equation (23). The second term indicates a pressure drop due to volume shrinkage caused by cooling the resin in the cavity 4 under a constant mass. The third term indicates the pressure rise due to resin flow additionally caused by volume contraction due to cooling. That is, I _FT (t _I , t) is
It is the most basic quantity that characterizes the cooling stage, and means a pressure increase due to the supply of molten resin that compensates for volume shrinkage caused by cooling. According to the above analysis, the change in the resin pressure in the mold during the pressure-holding / cooling stage is caused by the resin flow caused by the pressure gradient from the heating cylinder to the cavity 4, the volume contraction of the resin caused by cooling, and the volume contraction. It was analytically expressed that it was determined as the sum of the three effects of the additional molten resin flow due to the resulting pressure gradient. These effects are basically based on the temperature dependence coefficient T of the resin fluidity.
a, thermal expansion coefficient κ _C and compression rate β _C.

[Relationship between Temperature Change and Resin Pressure Change in Mold] (1) Linear Approximation of Temperature Dependent Term of Fluidity Mold temperature T _W and injected molten resin temperature T _R are T _W ′ and T _W , respectively. _R ′, and as a result, the resin temperature _TL of the gate portion 3 changes to _TL ′. These relationships are represented by the following equations.

[0033]

(Equation 13) Here, δTgen (° C.) indicates a temperature rise due to viscous heat generation during filling under the conditions of T _W and T _R.

F _C ′ = exp (−Ta / T _L ′), F _C = ex
Substituting equation (27) into p (−Ta / _TL ), the following equation is obtained.

[0035]

[Equation 14] In the equation (28), 1 / 1n (F _C ') and 1 / 1n
(F _C) by a Taylor expansion, and ignoring higher-order terms, the following equation is obtained.

F _C ′ = δ _X （(F _CO ′ / F _CO ) ・ ( T _O / T _O ′) ² ＦF _C + {1-δ _X （( T _O / T _O ′) ² ｝ F _CO ′ (29) where F _CO and F _CO ′ are appropriate temperatures for tailor expansion, and are set so as to satisfy the following equation.

F _CO = exp (−Ta / T _O ), F _CO ′ = exp
_{(-Ta / T O '),} T O' ≒ δ X · T O + γ X · ΔT W
+ Φ _X · ΔT _{R In} addition, from equation (27), the following equation is established.

[0038] _{d T L '/ dt ≒ δ} X · d T L / dt ····· (30) (2) Resin temperature is injected with the resin pressure variation metal temperature T _W of the mold in the compression stage T _R But T
_W ', T _R' changes, the holding pressure P _L is changed to P _L ', as a result, P molten resin pressure from P _C in the mold of the compression phase
Assume that it has changed to _C ′. In this case, equation (29) is changed to (2
3) By substituting into the equation, the following equation is obtained.

[0039]

(Equation 15) (3) Change in resin pressure in the mold in the pressure-holding / cooling stage By substituting the expressions (29) and (30) into the expression (26) as in the compression stage, the following relationship is established.

[0040]

(Equation 16) (31) and (32) is a formula that relates the mold temperature T _W, a change of the molten resin temperature T _R and the holding pressure P _L resin pressure P _C in the respective change and types are emitted .

Time integral term I_Fn(T_O , T), I_F(t_I ,
t), I_FT(T_I , T) and I_T(t_I , T);T
_C (t_I )-T _C (t) is when the mold temperature is T_W , Molten wood injected
Fat temperature is T_R Value at the reference molding shot
And T_W And T_R Is T_W 'And T_R ’
If so, there is no need to calculate them again. Sand
C, δ_X , A₁ , B₁ , An, and Bn are calculated,
Pressure change in the mold during the pressure stage and the packing / cooling stage
P_C 'Can be obtained. This means that the actual molding
This is important when determining the change in resin pressure inside the mold. One
In other words, when the calculation requires time before the molding operation
If the interval integral term is determined, the temperature immediately before the start of injection
T which is the measured value_W 'And T_R 'And ask before driving
Using the time integral term and equations (31) and (32)
By calculating the resin pressure change in the mold quickly
Can be.

[Procedure for Parameter Estimation and Application to Control] (1) Compression Stage In order to be a model applicable to process control, the first condition is that an actual measurement value can be expressed with high accuracy. next,
It needs to be able to calculate at high speed. Furthermore, in order to be applicable to different molding environments, materials, molds and injection molding machines, it is required that the data can be easily calculated by providing data on necessary resin properties and mold shapes.
However, in many cases, there is an error between the measured value and the calculated value. In the present invention, a procedure for minimizing the estimation error is determined by adjusting parameters in the model.

First, preliminary molding is performed before production, and optimal parameters in the equations (31) and (32) are determined so as to minimize the difference from the actually measured value. In the production stage, the resin pressure change in the mold is calculated using the determined parameters. Assuming that an actual measured value of the resin pressure in the mold in the molding shot as a reference is given, the prediction is limited to the amount of change in the resin pressure in the mold between molding shots. Even when the measured value of the resin pressure in the mold cannot be obtained, the resin pressure in the mold is calculated back using the measured value of the molded article weight, the prediction equation of the resin temperature change in the mold, and the equation of state of Spencer & Gilmore. As such, this procedure is applicable.

The holding pressure is given as an oil pressure for pressurizing the screw, and its maximum pressure depends on the capacity of the machine. Here, the maximum hydraulic pressure is set to 100%, and the holding pressure P _HS is handled in units of%. The holding pressure is usually proportional to the molten resin pressure in the heating cylinder, but there is a pressure gradient from the heating cylinder to the gate, and the relationship between the holding pressure and the resin pressure before the gate depends on the flow path shape and resin flow. Depends on gender. However, the largest pressure gradient is that between the gate and the cavity. For simplicity, a proportional relationship between the dwell pressure and the molten resin pressure before the gate is assumed, and the molten resin pressure P _L before the gate is considered to be a dwell pressure in resin pressure units.

P _L = K _PL · P _HS (33) K _PL (MPa /%) is basically determined by the injection molding machine, but depends on the material and the mold. Under the above assumption, a parameter for representing a change in the resin pressure in the mold in the compression stage is estimated by the following procedure. The calculation of the heat conduction of the gate portion shown by the equation (8) is unnecessary in the following.

Under the molding conditions where the mold temperature is T _W , the temperature of the molten resin to be injected is T _R, and the holding pressure is P _HS , the resin pressure P _C (t) in the mold is actually measured. Next, determine the phi (t) by the following equation obtained by modifying with P _C (31) equation. φ (t) = Kn · (1 / n−1) · I _Fn (t _O , t) = D _C ^{1-1 / n} −D _O ^{1-1 / n} (34) D _C = K _PL · P _HS −P _C (t), D _O = K _PL · P _HS
−P _CO , to <t ≦ t _I. t _I is the time when the in-mold pressure reaches the maximum value under these molding conditions.

The mold temperature was changed to T _W ′, the temperature of the molten resin to be injected was changed to T _R ′, and the holding pressure was changed to P _HS ′, and the measured in-mold pressure value P _C (t )'When,
Using the φ (t) obtained in the above, parameters are determined such that the difference between the left side and the right side of the following equation is minimized.

D _C ′ ^{1-1 / n} −D _O ′ ^{1-1 / n} = An · φ (t) + Bn · (tt ₀ ) · Kn · (1 / n−1) (35) Where D _C ′ = K _PL · P _HS ′ −P _C (t) ′, D _O ′ =
K _PL · P _HS ′ −P _CO ′. The parameters to be optimized are K _PL , Kn, T _O , T _INI , δT gen, n and Ta
It is. As initial values of n and Ta, measurement data of resin properties are used. The initial value of K _PL, using the specific values of the injection molding machine. As the initial value of Kn, the gate dimension of the mold and the value calculated by equation (6) are used.

As the initial value of T _O , an average value of the resin temperature T _R to be injected under the standard molding conditions and the resin flow stop temperature T _nf is used. The initial value of T _INI is set to T _R, δTgen is a 0 ° C..

During the actual molding, the mold temperature T _W ′ and the injected molten resin temperature T
Measure _R 'and calculate An and Bn. Next, using the equation (35), the resin pressure P _C ′ in the mold at the molding shot is obtained.
Is calculated.

(2) Holding Pressure / Cooling Stage The flow of the molten resin caused by the pressure gradient from the heating cylinder to the cavity becomes remarkable in the compression stage where the pressure gradient is large. Is relatively small, it is considered that the flow of the molten resin due to the pressure gradient is also small. Then, (26)
In the first term of the equation, it is assumed that K ₁ · I _F (t _I , t) is small, and is approximated by the following equation.

[0052] _{D C = D I + (κ} C / β C) · [T C (t I) - T C (t)] -K 1 · I FT (t I, t) ····· (36 However, t _I <t ≦ tf. Using equation (36),
The optimal parameters are determined by the following procedure.

The resin pressure P _C (t) in the mold is actually measured under the molding conditions where the mold temperature is T _W , the temperature of the molten resin to be injected is T _R, and the holding pressure is _PHS . Next, Expression (14) is calculated by the forward difference method in the range of time t _I <t ≦ t _f , and T _C (t) is obtained from Expression (18). From this result, (κ _C / β _C ) · [ T _C (t _I ) −T _{C in} equation (32)
(t)] and I _T (t _I , t). Next, the measured pressure P
_{Using C} (t) and equation (36), the third on the right side of equation (36)
The term can be calculated by the following equation.

K ₁ · I _FT (t _I , t) = − [D _C −D _I ] + (κ _C / β _C ) · [ T _C (t _I ) −T _C (t)]・ (37) The mold temperature is T _W ′, and the temperature of the molten resin to be injected is T
_R 'and holding pressure P _HS' while varying the, the resulting resin pressure measurement Pc in the mold (t) 'under the condition of changing, in the obtained _{[T C (t I) -} T C (t)], I _T (t _I , t) and K ₁ ·
Using I _FT (t _I , t), parameters are determined such that the difference between the left side and the right side of the following equation obtained by modifying equation (32) is minimized.

[0055] _{D C '-D I' = δ} X · (κ C / β C) · [T C (t I) - T C (t)] -δ X · [A 1 · K 1 · I FT ( _{t I, t) + B 1} · K 1 · I T (t I, t)] ····· (38) _{However, D C '= K PL ·} P HS' -P C (t) ', D I '= K _PL · P _HS ' -P _CI , and t _I <t ≦ t _f .
The parameters to be optimized are K ₁ , T _O , T _INI , δTgen
, Ta and κ _C / β _C. The initial value of K _1, using the calculated values of the gate dimension of the mold and (6). κ _C
The initial value of / β _C is calculated by the following equation using the equation of Spencer & Gilmore.

Κ _C / β _C = (P _CI + π _i ) / ( T _O +273) (39) The resin pressure P _C ′ in the mold during actual molding is estimated by the following procedure.

As shown in FIG. 3, the mold temperature T _W ′ and the molten resin temperature T _R ′ to be injected are measured at the same time as the start of the injection (Step S1), and δ _X , (32) are obtained by the equation (27).
A ₁ and B _{1 according to} the formula, An,
Bn is calculated (step S2).

After that, the resin pressure P _CI ′ = P _C (t = t _I ) ′ in the mold at the end of the compression stage is calculated using the equation (35) (step S3), and then the equation (38) is used. , The resin pressure P _C ′ in the mold at time t in the holding pressure / cooling stage
= Calculates the P _C (t) '(Step S4).

FIG. 4 shows the result of comparison between the calculated value and the actually measured value according to the present invention.

As apparent from FIG. 4, the difference between the actually measured value and the calculated value according to the present invention is a maximum of 1.0 MPa, and the resin pressure in the mold can be estimated with high accuracy.

In the present invention, the injection molding machine used has an injection device for injecting and filling the molten resin into the cavity of the mold clamped by the mold clamping device. And pressurized by the above, the molten resin is additionally supplied to the cavity portion.

An example of an in- mold resin pressure estimating apparatus used for carrying out the in- mold resin pressure estimating method in injection molding according to the present invention will be described with reference to FIG.

[0063] die T _W, and the molten resin temperature T _R of the mold temperature sensor 5 and the molten resin temperature sensor 6 is a temperature sensor for measuring provided, the detected temperature measurement signal by these temperature sensors 5 and 6 Are provided to amplify the voltage to 5 V or 10 V in the full range, and the amplified temperature measurement signal is formed so as to be input to the arithmetic processing unit 9.

In order to optimize the unknown parameters of the equations (31) and (32), as described in [Procedure for Estimating Parameters and Application to Control], it is necessary to measure the resin pressure in the mold. Become. Therefore, an in-mold pressure sensor 10 and an amplifier 11 for amplifying the in-mold pressure measurement signal to 5 V or 10 V in a full range are provided, and the amplified in-mold pressure measurement signal is input to an arithmetic processing unit 9 which is an arithmetic unit. It is formed as follows.

The setting unit 12 sets the holding pressure set value P _HS and the unknown parameter group (K _PL , Kn, n, Ta, T _O , T).
_INI , δTgen, K ₁ , κ _C / β _C ) are provided for the operator to input initial values.
Are set to be sent to the arithmetic processing unit 9.

The arithmetic processing section 9 calculates the temperature measured value T _W ,
Calculating a set value sent from the setter 12 and T _R, receives an injection start command signal 14 sent from the sequence controller 13, in accordance with the procedure shown in FIG. 3, the estimated value of the resin pressure in the mold It is formed so that. Further, the set value is displayed on the display unit 15, output as an analog voltage signal via the amplifier 16, and output as a digital signal. Arithmetic processing unit 9
Furthermore, [Procedures for parameter estimation and control]
According to the procedure described in the section, the formula (31) and (3)
2) the unknown parameter group in the formula _{(K PL, Kn, n,} Ta,
It is formed to calculate the optimum values of T _O , T _INI , δT gen, K ₁ , κ _C / β _C, etc.

During the actual molding, the injection operation of the injection molding machine is started by an injection start command signal 14 given by the sequence controller 13. When the arithmetic processing unit 9 inputs the injection start command signal 14, the arithmetic processing unit 9 immediately enter a mold temperature T _W and injected the molten resin temperature T _R.

Next, in accordance with the procedure shown in FIG. 3, the estimated resin pressure value in the mold is calculated and displayed on the display unit 15, and at the same time, is output as an analog signal and a digital signal.

When calculating the optimum values of the unknown parameters in the equations (31) and (32), the arithmetic processing unit 9
Is measured type internal pressure P _C (t), and enter the mold temperature T _W and injected the molten resin temperature T _R, according to the procedure described in the section [Application procedure of the estimation and control parameters, the optimum The value is calculated, displayed on the display unit 15, and stored at the same time.

[0070]

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

Before the molten resin is injected and filled into the mold cavity, the change in the resin pressure in the mold can be quickly estimated. For this reason, it is possible to estimate in advance the fluctuation of the molded product dimensions and the occurrence of molding defects, so that it can be effectively applied to monitoring of quality and process control for maintaining stability.

Further, since there is no need to provide a resin pressure sensor in the mold, the equipment cost can be reduced accordingly.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an analysis model assumed to derive a prediction formula of a resin pressure change in a mold according to the present invention,
(A) is a schematic sectional view of a flow path, and (b) is a schematic perspective view showing a shape of a gate portion.

FIG. 2 is a graph showing a change in resin pressure and a change in molten resin temperature in a mold in injection molding.

FIG. 3 is a flowchart showing a procedure for calculating a change in resin pressure in a mold according to the present invention.

FIG. 4 is a graph comparing an estimated value and a measured value of a change in resin pressure in a mold according to the present invention.

[5] One of the resin pressure estimating apparatus in the mold used in the practice of the resin pressure estimation method in the mold in the injection molding according to the present invention
It is a block diagram showing an example .

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 mold 2 runner section 3 gate section 4 cavity section 5 mold temperature sensor 6 molten resin temperature sensor 7, 8, 11, 16 amplifier 9 arithmetic processing section 10 in-mold pressure sensor 12 setting device 13 sequence control device 14 injection start command Signal 15 display

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B29C 45 / 57,45 / 46-45/60 B29C 45/76-45/78

Claims (1)

(57) [Claims] 1. A filling step of injecting and filling a molten resin into a cavity portion of a mold having a runner portion, a gate portion, and a cavity portion, and in order to compensate for volume shrinkage accompanying cooling of the injected and filled molten resin, In injection molding having a pressure-holding / cooling step of additionally replenishing the molten resin into the cavity by pressing the screw, the measured values of the mold temperature and the molten resin temperature immediately before the start of the injection filling are set in advance. By using a relational expression that holds between the holding pressure set value and the resin pressure in the mold in the pressure holding / cooling stage, at the time immediately before the start of the injection filling, the pressure in the mold in the pressure holding / cooling stage is reduced. A method for estimating resin pressure in a mold in injection molding, wherein a change in resin pressure is quickly estimated.