JPH04341818A - Dwell control method of multi-cavity mold and device in injection molding - Google Patents

Abstract

PURPOSE:To prevent inequalty in density of molded products to be generated by a change in a temperature condition among mold cavities each, by a method wherein a dwell set up for minimizing the sum of squared deviation from a target product density established for each mold cavity is obtained by operation, which is controlled to a dwell set up value. CONSTITUTION:Molten resin accumulated on the front part 1a of a screw is cast into mold cavities 5b, 5c each of a multi-cavity mold 5 by forward movement of the screw 1 through resin flow paths 4a, 5a. To replenish the cast molten resin contracting as the molten resin is cooled solidified within the cavities 5b, 5c each, the molten resin is replenished by pressing a screw 1A. On this occasion, the dwell set up value for minimizing the sum of squared deviations from density, weight and specific capacity of a target product is obtained by an operation processing part in a control device 7 and a dwell value is controlled to the dwell set up value.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a method and device for controlling pressure holding in a multi-cavity mold in injection molding, and in particular, in a multi-cavity mold, pressure control caused by changes in temperature conditions such as mold temperature, injection resin temperature, etc. This invention relates to new improvements to eliminate variations in molded product quality between mold cavities.

0002

[Prior Art] In general, many injection molded products are manufactured using multi-cavity molds that can produce multiple molded products in one molding cycle, as is unnecessary to refer to literature. Therefore, it is necessary that the amount of resin filled in each mold cavity be uniform, and in achieving this, the mold design, including the runner and gate, plays an important role.

0003

[Problem to be solved by the invention] However, even after the runner and gate are designed to uniformly fill each mold cavity, in actual injection molding production, the amount of filling varies between each mold cavity. An imbalance may occur. This is mainly due to variations in temperature conditions such as mold temperature and injection resin temperature. Therefore, variations in temperature conditions could result in short shots in one mold cavity and overpack in another mold cavity. Further, there have been problems in that the dimensions of the molded product in one mold cavity are larger than the standard, while in another mold cavity the dimensions are smaller than the standard. However, no method has been developed to solve the imbalance in molded product weight, dimensions, etc. between mold cavities caused by such changes in temperature conditions.

The present invention has been made to solve the above-mentioned problems, and in particular, it is possible to set a holding pressure that minimizes the difference in resin density between mold cavities regardless of changes in temperature conditions. The purpose of the present invention is to provide a holding pressure control method and device for a multi-cavity mold in injection molding, which makes the resin density uniform for each mold cavity by determining the holding pressure set value and controlling the holding pressure to the set value. shall be.

[0005]

[Means for Solving the Problems] The holding pressure control method for a multi-cavity mold in injection molding according to the present invention is such that the molten resin accumulated in the front part of the screw is moved through the nozzle part resin flow path and the resin in the mold by advancing the screw. A filling step of injecting into each mold cavity of a multi-cavity mold through a flow path and compressing the screw to compensate for the molten resin shrinking as it cools and solidifies within each mold cavity. In the injection pressure holding stage consisting of the pressure holding stage for replenishing the molten resin, the sum of squares of deviations from the target product density, weight, specific volume, etc. set for each mold cavity of the multi-cavity mold is calculated. This is a method of calculating a holding pressure setting value to minimize the holding pressure setting value and controlling the holding pressure setting value.

More specifically, the density of the material in each mold cavity is ρK (K is the number of the mold cavity, K=1
...N, N is the number of cavities), pressure PK, temperature TK
The pressure PK in the mold cavity is expressed by a relational expression between the pressure PK, the holding pressure PL, and the mold temperature TW.
K and the injection resin temperature TRK, the resin temperature TK in the multi-cavity mold at the pressure holding stage in the filling stage is estimated in advance, and the resin temperature TK and the resin temperature TK are set for each mold cavity. the target value ρK* of the density of the molded product and the pressure of the material in the mold cavity,
From the above relational expression of temperature and density, a pressure target value PK1* in the mold that achieves the target value ρK* of density for each mold cavity is calculated, and the pressure target value PK1* is calculated.
The holding pressure PLK* that achieves this is calculated from the relational expression among the mold temperature TWK, the injection resin temperature TRK, the pressure PK in the mold, and the holding pressure PLK, and from the holding pressure PLK*, the target of each mold cavity is further calculated. Calculate the holding pressure PL1* that minimizes the sum of squares of deviations from the value ρK*, and calculate the holding pressure PL1*.
*This is a method that controls the

More specifically, the relationship among the resin temperature TK in the multi-cavity mold, the resin pressure PK in the multi-cavity mold, and the resin density ρK in the multi-cavity mold is expressed by the following Spencer-Gilmore state. This is a method expressed by an equation (shown in equation 1).

More specifically, the method is to express the relationship among the resin pressure PK in the mold cavity, the mold temperature TWK, the injection resin temperature TRK, and the holding pressure PL using a polynomial (shown by two equations).

More specifically, when estimating the resin temperature TK in the multi-cavity mold in the pressure holding stage in advance in the filling stage, the temperature at a certain fixed time in the pressure holding stage is used, and At the time tg when the resin temperature TK in the multi-cavity mold in the pressure holding stage reaches the flow stop temperature Tg determined by the molding material, at the mold temperature TWSK and the injection resin temperature TRSK, which are based on the fixed time, Time tg for estimating the resin temperature TK in the multi-cavity mold
Then, by measuring the mold temperature, the mold temperature TWK used in the calculation is determined, and by measuring the resin temperature of any of the resin flow paths, the injection resin temperature TRK used in the calculation is determined.
The resin temperature TK(tg) in the multi-cavity mold at the time tg is calculated using the preset mold temperature TWSK, the injection resin temperature TRSK, and the temperature Tg.
This is a method to find using equations 3, 4, and 5.

More specifically, when determining the mold temperature TWK used in the calculation by measuring the mold temperature TWK, the temperature measurement value TWFK on the fixed mold side and the temperature measurement value TWMK on the movable mold side are used. This is a method of calculating using any one of formulas 6, 7, and 8.

More specifically, when determining the injection resin temperature TRK used in the calculation by measuring the resin temperature in any of the resin flow paths, the measured values at the start of filling and the end of filling, or the measured values from the start of filling are used. This method uses the average value or maximum value of the measured values until the end.

More specifically, the holding pressure set value is a set value for a setting device, hydraulic ram pressure, nozzle resin pressure, or pressure within a multi-cavity mold.

More specifically, the sum of squares of deviations from the target density ρK* set for each mold cavity is calculated as 9
The density ρK of the material in the mold cavity is expressed by one equation, and the resin pressure PK in the mold cavity is expressed by two equations.
The resin temperature TK (tg) in the mold cavity is 3, 4, 5.
Each expression is expressed as the holding pressure setting value PL that minimizes G in formula 9.
* is calculated and controlled using equations 10, 11, 12, and 13.

More specifically, a mold temperature sensor provided in the multi-cavity mold, a resin temperature sensor provided in either the multi-cavity mold or the resin flow path in the nozzle, and a temperature sensor provided from the resin temperature sensor. mold temperature,
an amplifier for inputting and amplifying the measured value of the injection resin temperature; an A/D converter for A/D converting the measured value; and an A/D converter for A/D converting the measured value; It includes at least an arithmetic processing unit that calculates a holding pressure set value using a molded product weight target value, and a holding pressure control unit that outputs the holding pressure set value as a voltage signal to a servo valve amplifier that controls a servo valve. , the amplifier, the A/D converter, the arithmetic processing section, and the pressure holding control section form a control device.

[0015]

[Operation] In the pressure holding control method and apparatus for a multi-cavity mold in injection molding according to the present invention, the molded product density target value ρk* for each mold cavity, the reference mold temperature TWSK, and the injection resin temperature TRSK are prepared in advance. , flow stop temperature Tg, material constant R1, ρo, πi, coefficient a1K
, a2K, b1K, b2K, c1K, and d1K are set in advance. Next, in the actual filling and pressure holding stage, first, the mold temperature TWK and the injection resin temperature TRK are determined by measurement in the filling stage. Next, just before completing the filling stage and entering the pressure holding stage, the resin temperature TK in the mold is determined using equations 3, 4, and 5.
(tg), and this resin temperature TK (tg) and

From Equation 14 of [Equation 7], the resin pressure target value P of the mold cavity K is calculated.
Calculate K*. Also, this resin temperature TK (tg) and resin pressure target value PK*

The weighting coefficient LK of the mold cavity K (K is the number of cavities) is calculated using Equation 15 of [Equation 8], and the above-mentioned TWK, TR
K, PK* and

The molded product density ρ of each mold cavity K can be calculated using Equation 16 of [Equation 9]
Calculate the holding pressure PLK* to achieve K*. Finally, LK and PLK* obtained as described above,

[
From Equation 17 of Equation 10, the sum of squares of the deviation from the target density ρK* is

Calculate the holding pressure PL* that minimizes Equation 18 of [Formula 11]. Therefore, the holding pressure PL* determined as above is set as the holding pressure set value, converted into a voltage signal, and outputted to the servo valve amplifier to control the holding pressure set value.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the method for controlling pressure holding in a multi-cavity mold for injection molding according to the present invention will be described in detail below with reference to the drawings.

[0017] In the figure, the symbol 1 is a cylinder having a screw 1A, and this screw 1A is
By the motor 2 and cylinder chamber 3 at the rear of the cylinder 1,
It is provided so that it can rotate and move forward and backward. Said cylinder 1
A nozzle 4 having a nozzle resin flow path 4a is provided at the front part of the cylinder 1, and a screw front part 1a is formed at the front part 1B of the cylinder 1.

The nozzle 4 is provided with a mold 5 consisting of a fixed mold 5A and a movable mold 5B.
A is provided with an in-mold resin flow path 5a, and between each of the molds 5A and 5B (assuming that there are K mold cavities, K is the number of mold cavities). 1st
In communication with the resin flow path 5a, a first mold cavity 5b, a second mold cavity 5c, a first cavity runner part 5d,
A second cavity runner section 5e, a first cavity gate section 5f, and a second cavity gate section 5g are each formed.

The fixed mold 5A is provided with a first mold temperature sensor 6a and a second mold temperature sensor 6b, and the movable mold 5B is provided with a third mold temperature sensor 6c and a fourth mold temperature sensor 6c. A temperature sensor 6d, a first runner resin temperature sensor 6e, and a second runner resin temperature sensor 6f are connected.

The measured values of each of the sensors 6a to 6f are measured by each amplifier 8a to 8f and each A/D converter 9a of the control device 7.
~9f is input to the arithmetic processing unit 10, and the holding pressure PL* from this arithmetic processing unit 10 is input to the holding pressure control unit 11.
has been entered.

[0021] The arithmetic processing section 10 and the pressure holding control section 11
The injection start signal 12a from the sequence control unit 12 is
and pressure holding start signal 12b are respectively input, and the coefficients R1, ρo, πi, a1K, a2K
, b1K, b2K, c1K, d1K, TWSK, TRS
A setting device 13 for inputting a set value 13a consisting of K, Tg, and ρk* is connected, and the aforementioned control device 7
It is comprised of amplifiers 8a to 8f, A/D converters 9a to 9f, an arithmetic processing section 10, a pressure holding control section 11, and a setting device 13.

Voltage signal 11a from the pressure holding control section 11
is input to a servo valve amplifier 15 connected to the servo valve 14, and the operating voltage 15a of this servo valve amplifier 15 is input to the servo valve 14. The pipe line 14a of the servo valve 14 is connected to the cylinder chamber 3, the oil pressure sensor 16 connected to the cylinder chamber 3 is connected to the servo valve amplifier 15, and the servo valve 14 is connected to an oil source 17. has been done.

Next, a case will be described in which holding pressure control of a multi-cavity mold in injection molding according to the present invention is performed in the above-described configuration. First, the outline will be explained. First, when the sequence control unit 12 outputs the injection start signal 12a to the control device 7 (first step: 20),
The screw 1A starts moving forward. At the same time, the calculation processing unit 10 calculates the fixed mold side mold temperature TWFK and the movable mold side mold temperature TWMK corresponding to each mold cavity 5b, 5c.
is measured (second step: 21). Then, the mold temperature TWK of each mold cavity 5b, 5c used for calculation is
Calculate using the following formula. TWK=(TWFK+TWMK)/2...Equation (6)

[
Furthermore, after the injection start signal 12a is input, the pressure holding start signal 12b is input (fourth step: 2
During the filling stage up to 3), the resin temperature in the runner parts 5d and 5e is measured, and either the maximum value at the filling stage, the time average value, the sample value at the start of injection, or the sample value at the time of switching the holding pressure is measured. The injection resin temperature TRK of each mold cavity 5b, 5c is determined by the method (third step: 22).

Next, the arithmetic processing unit 10 uses equations 3, 4, and 5 to determine that the mold temperature is TWSK and the injection resin temperature is TRSK.
The mold temperature TWK and the injection resin temperature TR at time tg when the resin temperature in the mold reaches the flow stop temperature Tg.
Find the resin temperature TK (tg) in the mold in the case of K (fifth
Step: 24). When the pressure holding start signal 12b is output from the sequence control unit 12, the arithmetic processing unit 10
The holding pressure PL* is calculated using Equations 4, 15, 16, and 17 (sixth step: 25), and output to the holding pressure control section 11.

In response to this, the holding pressure control section 11 sends a voltage signal 11a corresponding to this holding pressure PL* to the servo valve amplifier 1.
5 (7th step: 26). In response to this, the servo valve amplifier 15 sets the servo valve 14 so that the hydraulic pressure corresponding to this holding pressure PL* becomes the pressure inside the cylinder chamber 3.
The operating voltage 15a is output to. Therefore, when the pressure holding start signal 12b from the sequence control unit 12 is cut off (the eighth
Step: 26), arithmetic processing section 10 and pressure holding control section 1
1 stops the output of the holding pressure PL* and the corresponding voltage signal 11a, and ends the holding pressure control.

[0027] To explain in more detail, in advance, the molded product density target value ρk*,
Standard mold temperature TWSK, injection resin temperature TRSK,
Flow stop temperature Tg, material constant R1, ρo, πi, coefficient a
1K, a2K, b1K, b2K, c1K, and d1K are set in advance.

Next, in the actual filling and holding pressure stage, first, the mold temperature TWK and the injection resin temperature TRK are set at the filling stage.
is determined by measurement. Then, immediately before completing the filling stage and entering the pressure holding stage, the resin temperature TK (tg) in the mold 5 is calculated using Equations 3, 4, and 5. From this resin temperature TK (tg) and formula 14, the mold cavity 5b,
5c, calculate the resin pressure target value PK*.

[0029] Also, the weighting coefficient LK of the mold cavity is calculated using the resin temperature TK (tg), the resin pressure in the mold PK*, and Equation 15, and the mold temperature TWK, the injection resin temperature TR
K, the resin pressure in the mold PK, and Equation 16 are used to calculate the holding pressure PLK* for achieving the target molded product density value ρK* for each mold cavity 5b, 5c. Finally, the holding pressure PL* that minimizes the equation 18, which is the sum of the squares of the deviation from the molded product density target value ρK*, is calculated from the above-described LK, PLK* obtained in this way and the equation 17. The holding pressure PL* obtained above is set as a holding pressure setting value, converted into a voltage signal 11a, and outputted to the servo valve amplifier 15.

More specifically, a target molded product density ρK* for each mold cavity is set in advance, and the sum of squares of the deviations of the actual molded product density ρK of each cavity from the target value is calculated as follows: It is expressed by the formula. Here, each mold cavity 5b,
It is assumed that minimizing the deviation of the resin filling amount between 5c is to minimize G in Equation 18. If the product shape of each mold cavity 5b, 5c is the same, the molded product density target value ρK* is a constant value regardless of the value of K.
If the product shapes of the mold cavities 5b and 5c are different, the above ρK*
It is conceivable that K takes on different values depending on K. Resin pressure PK in each mold cavity 5b, 5c, density ρK,
It is assumed that the relationship between temperature TK is expressed, for example, by the following Spencer-Gilmore equation of state.

(PK+πi)[(1/ρK)−(1/ρ0)
]=R1(TK+273)...(1) Formula ρO:
Absolute 0 degree density (material constant) πi: Internal pressure (material constant) R1: Modified gas constant (material constant) The resin pressure PK in each mold cavity 5b, 5c is determined by the mold temperature TWK, the injection resin temperature TRK, and It is assumed that the holding pressure PL has the following relationship. PK=a1KTWK+a2KTWK2+b1KTR
K+b2KTRK2+c1KPL+d1K (2) Equation From the above-mentioned Equations 18, 1, and 2, the holding pressure PL* that minimizes G in Equation 9 is expressed by the following Equations 14, 15, 16, and 17.

The resin pressures PK, PK* and resin temperature TK in the mold 5 are determined at a fixed time t in the pressure holding stage.
g, and this fixed time tg is obtained as follows. Mold and T that serve as preset standards
At WSK and injection resin temperature TRSK, the resin temperature TK in the mold 5 is estimated at the time tg when the resin temperature TK in the mold cavities 5b, 5c reaches the flow stop temperature Tg determined by the molding material. do. next,
Determine the mold temperature TWK and the injection resin temperature TRK by measurement.
Using preset TWS, TRS, and Tg, time t
The resin temperature TK (tg) in the mold 5 at g is 3, 4,
Calculate using formula 5. Therefore, the mold cavity K (5b
, 5c), the resin temperature TK (tg) is determined by equation 3, and the holding pressure PL* is determined by equations 14, 15, 16, and 17.
It is set and controlled to maintain this holding pressure PL*.

[0033]

[Effects of the Invention] Since the holding pressure control method and device for a multi-cavity mold in injection molding according to the present invention are configured as described above, the density of the molded product caused by fluctuations in temperature conditions can be adjusted between each mold cavity. Therefore, in a multi-cavity mold, a molded product with a uniform shape and size can be obtained in any cavity, thereby reducing the defective rate and improving productivity.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a holding pressure control device for a multi-cavity mold in injection molding according to the present invention.

FIG. 2 is a block diagram showing a part of FIG. 1;

FIG. 3 is an enlarged sectional view of the main part of FIG. 1;

FIG. 4 is a flowchart showing a pressure holding control method.

FIG. 5 is a flowchart following FIG. 4;

[Explanation of symbols]

1A screw 1a Front part of screw 4a　　　　Nozzle part resin flow path 5 Multi-cavity mold 5a Resin flow path in mold 5b Mold cavity 5c Mold cavity 5A Fixed mold 5B Movable mold 6a-6d Mold temperature sensor 6e, 6f Resin temperature sensor 7 Control device 8a-8f Amplifier 9a-9f A/D converter 10 Arithmetic processing unit 11a Voltage signal 14 Servo valve 15 Servo valve amplifier

Claims (10)

[Claims] [Claim 1] The screw (1A) advances the molten resin accumulated in the front part of the screw (1a) to the nozzle resin flow path (4a) and the mold resin flow path (5a, 5d, 5).
e, 5f, 5g) via multi-cavity mold (5)
a filling step in which the molten resin is injected into each of the mold cavities (5b, 5c);
) In order to compensate for shrinkage as it cools and solidifies in the multi-cavity mold (5), the multi-cavity mold (5) is Each mold cavity (5
Calculate the holding pressure setting value to minimize the sum of squares of deviations from the target product density, weight, specific volume, etc. set for each of b and 5c), and control to the holding pressure setting value. A holding pressure control method for a multi-cavity mold in injection molding, characterized by: [Claim 2] Each of the mold cavities (5b, 5c)
The density of the material in ρK (K is the number of the mold cavity, K=
1...N, N is the number of cavities), pressure PK, temperature T
The pressure PK in the mold cavity (5b, 5c) is expressed as a relational expression between the pressure PK, the holding pressure PL, the mold temperature TWK, and the injection resin temperature TRK. In the filling stage, the resin temperature TK in the multi-cavity mold in the pressure holding stage is estimated, and the resin temperature TK and each mold cavity (5b
, 5c) and the pressure of the material in the mold cavity (5b, 5c),
A pressure target value PK1* in the mold that achieves the target value ρK* of density for each mold cavity (5b, 5c) is calculated from the relational expression of temperature and density, and the pressure target value PK1 is calculated. *The holding pressure PLK* to achieve the mold temperature T
Calculated from the relational expression between WK, injection resin temperature TRK, pressure in the mold PK, and holding pressure PLK, and further calculating the deviation from the target value ρK* of each mold cavity (5b, 5c) from the holding pressure PLK*. Holding force PL that minimizes the sum of squares of
2. The holding pressure control method for a multi-cavity mold in injection molding according to claim 1, wherein the holding pressure PL* is calculated and controlled to the holding pressure PL*. 3. Resin temperature TK in the multi-cavity mold (5), resin pressure PK in the multi-cavity mold, and resin density ρK in the multi-cavity mold
The relationship is expressed by the following Spencer Gilmore equation of state [Equation 1
3. A holding pressure control method for a multi-cavity mold in injection molding according to claim 2, characterized in that it is expressed by the following equation. 4. The relationship between the resin pressure PK in the mold cavity (5b, 5c), the mold temperature TWK, the injection resin temperature TRK, and the holding pressure PL is expressed by the following two polynomial equations: The holding pressure control method for a multi-cavity mold in injection molding according to claim 2. 5. In advance in the filling step, the resin temperature T in the multi-cavity mold in the pressure holding step is determined.
When estimating K, the temperature at a certain fixed time in the pressure holding stage is used, and at the mold temperature TWSK and the injection resin temperature TRSK, which are based on the fixed time, the temperature inside the multi-cavity mold in the pressure holding stage is used. The resin temperature TK is the flow stop temperature Tg determined by the molding material.
The time tg at which the resin temperature TK in the multi-cavity mold is estimated is set as the time tg at which the resin temperature TK in the multi-cavity mold is estimated, and the mold temperature TWK used for the calculation is determined by measuring the mold temperature.
The resin flow paths (4a, 5a, 5d, 5e...
), the injection resin temperature TRK used for the calculation is obtained, and the multi-cavity mold temperature at the time tg is determined using the preset mold temperature TWSK, the injection resin temperature TRSK, and the temperature Tg. Claim 2, characterized in that the resin temperature TK (tg) in the mold is determined by formulas 3, 4, and 5 of the following formula:
The holding pressure control method for a multi-cavity mold in injection molding described above. 6. When determining the mold temperature TWK used in the calculation by measuring the mold temperature TWK, the temperature measurement value TWFK on the fixed mold (5A) side and the movable mold (5A) are used.
The holding pressure of a multi-cavity mold in injection molding according to claim 5, characterized in that it is determined from the temperature measurement value TWMK on the side B) by any one of equations 6, 7, and 8 of [Equation 4]. Control method. 7. The resin flow path (4a, 5a, 5d, 5
e...) When determining the injection resin temperature TRK used in the calculation by measuring the resin temperature, the measured values at the start and end of filling, or the measured values from the start to the end of filling. The holding pressure control method for a multi-cavity mold in injection molding according to claim 7, characterized in that the average value or the maximum value of is used. 8. The holding pressure set value may be a set value (13a) for a setting device (13), hydraulic ram pressure, nozzle resin pressure, or pressure within a multi-cavity mold. The described holding pressure control method for the described multi-cavity injection molding. 9. The sum of squares of the deviations from the target density ρK* set for each mold cavity is expressed by the following formula [Equation 5]. The density ρK of the material is expressed by one equation, and the mold cavity (5b, 5c
) is expressed by two equations, and the mold cavity (5
The resin temperature TK (tg) in b, 5c) is expressed by equations 3, 4, and 5, respectively, and the holding pressure setting value PL* that minimizes G in equation 9 is expressed as 10, 11, 12, 13 in [Equation 6] 3. The holding pressure control method for a multi-cavity mold in injection molding according to claim 2, wherein the holding pressure is determined and controlled by a formula. 10. Mold temperature sensors (6a to 6d) provided in the multi-cavity mold (5), and resin flow paths (6a to 6d) in the multi-cavity mold (5) and the nozzle (4).
4a, 5a, 5d, 5e...) and the measured values of the mold temperature and injection resin temperature from the resin temperature sensor (6e, 6f). An amplifier (8a to 8f) that inputs and amplifies it, and an A/D converter (9a to 9f) that converts the measured value from A/D to digital.
an arithmetic processing unit (10) that calculates a holding pressure setting value using the measured value and at least a molded product weight target value set for each mold cavity (5b, 5c) of the multi-cavity mold (5); , the holding pressure set value is expressed as a voltage signal (11
As a), a pressure holding control unit (11) outputs to a servo valve amplifier (15) that controls a servo valve (14), a molded product weight target value Wk*, control constants a1k, a2k, b1k, b
2k, d1k, c1k, constants R1, ρ0, of state equation
πi, flow stop temperature Tg, reference temperature Twsk, T
and a setting device (13) for setting RSK, etc., the amplifier and the A/D converter. A pressure-holding control device for a multi-cavity mold in injection molding, characterized in that a control device (7) is constituted by an arithmetic processing section, a pressure-holding control section, and a setting device.