JP2002127219A - Apparatus and method for deciding injection molding condition and program storage medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus and a method for deciding injection molding conditions capable of simply deciding the molding conditions for molding a product having a dimensional accuracy as a target in a short time as well as a program storage medium. SOLUTION: The method for deciding the injection molding conditions comprises the step of obtaining a target shrinkage factor based on a product dimensional accuracy as the target by an initializing unit 1. The method further comprises the step of then changing a resin temperature by a resin temperature setter 4 so that the shrinkage factor calculated by shrinkage factor calculating means (7, 8 and 10) coincides with a target shrinkage factor. The method also comprises the step of changing a dwelling pressure by a dwelling pressure setter 14 so that the shrinkage factor calculated by shrinkage factor calculating means (17, 18 and 19) coincides with a target shrinkage factor, when the shrinkage factor is higher than the target shrinkage factor even when the resin temperature is lowered to a flow stopping temperature or a temperature of causing unfilling by the setter 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding condition determining apparatus, an injection molding condition determining method, and a program storage medium for determining molding conditions for obtaining optimum product dimensional accuracy in plastic injection molding.

[0002]

2. Description of the Related Art Generally, in plastic injection molding, in order to obtain a product having an optimum product dimensional accuracy, it is necessary to optimally determine molding conditions such as temperature, pressure, material properties of a resin to be used, and the like. Usually, these molding conditions are set by a technician using a plastic injection molding machine to change the setting of the molding machine many times, or by CAE (Computer Aided Engineer).
ing) It is determined optimally by performing plastic injection molding simulation with the technology. In particular, as a plastic injection molding simulation based on the CAE technique, there is a "system for optimizing operating conditions of a processing machine" described in Japanese Patent Application Laid-Open No. 6-91715. In this "processing machine operating condition optimization system", the level of each condition variable is determined, and multiple regression calculations are performed based on the simulation results to calculate the optimum molding conditions based on the evaluation formula that ranks and weights the quality. ing.

[0003]

However, in the above-mentioned system for optimizing the operating condition of a processing machine, it is necessary to evaluate the processing machine under various operating conditions in order to determine the target operating condition of the processing machine. There is a problem that the work is complicated and time-consuming.

The most general demand for molding is to mold a product having a target dimensional accuracy. In order to obtain the above (operating conditions), the “operating condition optimizing system for processing machine” has to perform complicated and complicated work, which is not practical.

SUMMARY OF THE INVENTION An object of the present invention is to provide an injection molding condition determining apparatus, an injection molding condition determining method, and a program storage medium which can easily and quickly determine molding conditions for molding a product having a target dimensional accuracy. Is to do.

[0006]

In order to achieve the above object, an injection molding condition determining apparatus according to the present invention is an injection molding condition determining apparatus for determining a resin temperature and a holding pressure in plastic injection molding. Target shrinkage determining means for obtaining a target shrinkage based on product dimensional accuracy; shrinkage calculating means for calculating shrinkage based on resin temperature and holding pressure; shrinkage calculated by the shrinkage calculating means; Resin temperature changing means for changing the resin temperature so that the target shrinkage rate matches, and the shrinkage rate calculation means calculates even if the resin temperature in the resin temperature changing means is reduced to a flow stop temperature or a temperature at which unfilling occurs. When the contraction rate is higher than the target contraction rate, the pressure-reducing means changes the holding pressure such that the contraction rate matches the target contraction rate. There.

In designing a molded product having a target dimensional accuracy, essential molding conditions are a resin temperature and a holding pressure. Therefore, in the injection molding condition determining apparatus, the calculation is simplified by optimizing only the resin temperature and the holding pressure and ignoring other molding conditions. First, the target shrinkage ratio is determined from the target product dimensional accuracy by the target shrinkage ratio determination means. It is possible to obtain the shrinkage ratio (target shrinkage ratio) of the resin necessary for molding a product having the dimensional accuracy based on the dimensional accuracy of the product by the conventional technology. Next, the resin temperature is changed by the resin temperature changing means so that the shrinkage calculated by the shrinkage calculating means matches the target shrinkage. This resin temperature changing means utilizes the property that the shrinkage decreases when the difference between the temperature of the product when taken out of the mold and the outside air temperature is small. That is, when the resin temperature is lowered, the difference between the temperature of the product when taken out of the mold and the outside air temperature is reduced, and the shrinkage ratio is reduced, whereas when the resin temperature is increased, the product is taken out from the mold. The difference between the temperature at the time and the outside air temperature increases, and the shrinkage rate increases. Therefore, when the shrinkage is lower than the target shrinkage, the resin temperature is raised, and when the shrinkage is higher than the target shrinkage, the resin temperature is lowered to make the shrinkage equal to the target shrinkage. However, when the resin temperature becomes lower than a certain temperature, flow stoppage or unfilling occurs, molding becomes impossible, and there is a limit to lowering the shrinkage by lowering the resin temperature. Therefore, when the flow stop or unfilling occurs by lowering the resin temperature and the shrinkage cannot be reduced to the target shrinkage, the shrinkage is changed by changing the holding pressure by the holding pressure setting means. Try. In other words, when the holding pressure is increased, the density in the mold increases and the shrinkage decreases. On the other hand, when the holding pressure is decreased, the density in the mold decreases and the shrinkage increases. When it is higher, the holding pressure is increased, and the contraction rate calculated by the contraction rate calculating means based on the changed holding pressure is made to coincide with the target contraction rate. Therefore, according to the injection molding condition determining apparatus of the present invention, molding conditions for molding a product having a target dimensional accuracy can be determined easily and in a short time. When the contraction rate is lower than the target contraction rate in the holding pressure changing means, the holding pressure is reduced.

Further, the injection molding condition determining method of the present invention is an injection molding condition determining method for determining a resin temperature and a holding pressure in plastic injection molding, and obtains a target shrinkage based on a target product dimensional accuracy. A target shrinkage ratio determination step, a shrinkage ratio calculation step of calculating a shrinkage ratio based on the resin temperature and the holding pressure, and a resin temperature such that the shrinkage ratio calculated in the shrinkage ratio calculation step matches the target shrinkage ratio. In the resin temperature changing step to be changed, and when the shrinkage rate is higher than the target shrinkage rate even when the resin temperature is lowered to a flow stop temperature or a temperature at which unfilling occurs in the resin temperature changing step, the shrinkage rate calculation step calculates And a holding pressure changing step of changing the holding pressure so that the contracted contraction rate matches the target contraction rate.

According to the injection molding condition determining method having the above configuration, first, in the target shrinkage ratio determining step, a target shrinkage ratio is obtained from a target product dimensional accuracy. Next, the resin temperature is changed, and the shrinkage calculated using a simulation or the like in the shrinkage ratio calculation step based on the changed resin temperature is brought closer to the target shrinkage. Then, when the calculated shrinkage is lower than the target shrinkage, the resin temperature is raised, and when the calculated shrinkage is higher than the target shrinkage, the resin temperature is lowered, so that the shrinkage matches the target shrinkage. Let it. However, if the shrinkage cannot be reduced to the target shrinkage rate even if the resin temperature is reduced to the flow stop temperature or the temperature at which unfilling occurs, the resin temperature is set to be higher than the flow stop temperature or the temperature at which unfilling occurs. When the contraction rate is higher than the target contraction rate, the retention pressure is increased in the retention pressure change step, and the contraction rate calculated in the contraction rate calculation step based on the changed retention pressure is made to match the target contraction rate. Therefore, molding conditions for molding a product having the target dimensional accuracy can be determined easily and in a short time. When the contraction rate is lower than the target contraction rate in the above-mentioned holding pressure changing step, the holding pressure is reduced.

[0010] Further, the program storage medium of the present invention comprises:
A program for executing the injection molding condition determining method according to claim 1 is stored.

According to the program storage medium, the computer is controlled based on the stored program to determine the target shrinkage ratio in the injection molding condition determining method.
By performing the processing of the shrinkage ratio calculating step, the resin temperature changing step and the holding pressure changing step, molding conditions for molding a product having the target dimensional accuracy can be determined easily and in a short time.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an injection molding condition determining apparatus, an injection molding condition determining method, and a program storage medium according to the present invention will be described in detail with reference to the illustrated embodiments.

FIG. 1 is a block diagram of an injection molding condition determining apparatus for calculating a resin temperature and a holding pressure for obtaining an optimum product dimensional accuracy according to an embodiment of the present invention. In FIG. 1, 1
Is an initial setting unit including target shrinkage ratio determining means for setting various conditions for determining injection molding conditions, and 2 is a shrinkage ratio for calculating a shrinkage ratio using the value set by the initial setting unit 1 as an initial value. The initial value calculation unit 3 as a calculation means determines whether the contraction rate calculated by the initial value calculation unit 2 (or the contraction rate stored in the first contraction rate data storage unit 11) matches the target contraction rate. The first end determination unit 4 determines the contraction ratio calculated by the initial value calculation unit 2 (or the contraction ratio stored in the first contraction ratio data storage unit 11) and the target contraction ratio. A resin temperature setting section as a resin temperature changing means for changing the temperature value, 5 is a resin temperature data storage section for storing the resin temperature output from the resin temperature setting section 4, and 6 is a resin temperature data storage section. The stored resin temperature is below the flow stop temperature A flow stop temperature evaluation unit 7 for evaluating whether the temperature is below the temperature, a first molding simulation unit 7 for performing a molding simulation based on the resin temperature stored in the resin temperature data storage unit 5, and an output 8 from the first molding simulation unit 7 The first simulation result data storage unit 9 for storing simulation results is an unfilled evaluation unit that evaluates whether the simulation results stored in the first simulation result data storage unit 8 are unfilled. 1 a first contraction rate acquisition unit that acquires the contraction rate from the simulation result data storage unit 8; 11 is a first contraction rate data storage unit that stores the contraction rate output from the first contraction rate acquisition unit 10; The first improvement evaluation unit 13 for evaluating whether the contraction rate stored in the first contraction rate data storage unit 11 has been improved includes: Number of times forming simulation by serial first mold simulation unit 7 is first calculated number confirmation unit for confirming whether or exceeds the upper limit number value set by the initial setting unit 1. The first molding simulation unit 7, the first simulation result data storage unit 8, and the first shrinkage ratio acquisition unit 10 constitute a shrinkage ratio calculation unit.

Further, reference numeral 14 denotes a second contraction rate data storage section 20.
(Or the first contraction rate data storage unit 1)
The holding pressure setting unit serving as a holding pressure changing unit that changes the holding pressure value by comparing the holding pressure setting unit 15 with the target shrinking ratio, and 15 is the holding pressure output from the holding pressure setting unit 14. The holding pressure data storage unit 16 stores the holding pressure evaluation unit that evaluates whether the holding pressure stored in the holding pressure data storage unit 15 is equal to or less than the maximum holding pressure, and 17 stores the holding pressure data storage unit 15. The second forming simulation section for performing a forming simulation using the held holding pressure, 18 is the second forming simulation section.
A second simulation result data storage unit for storing a simulation result output from the molding simulation unit 17; 19, a second shrinkage ratio acquisition unit for acquiring a shrinkage ratio from the second simulation result data storage unit 18, 20
Is a second contraction ratio data storage unit that stores the contraction ratio output from the second contraction ratio acquisition unit 19, and 31 evaluates whether the contraction ratio stored in the second contraction ratio data storage unit 20 is improved. The second improvement evaluation unit 32 confirms the second number of calculations to evaluate whether the number of times of forming simulation performed by the second forming simulation unit 17 and the first forming simulation unit 7 exceeds the upper limit value set by the initial setting unit 1. The second unit 33 evaluates whether the contraction rate stored in the second contraction rate data storage unit 20 matches the target contraction rate.
An end determination unit. The second molding simulation section 1
7. The second simulation result data storage unit 18 and the second contraction ratio acquisition unit 19 constitute a contraction ratio calculation unit.

Next, a description will be given of a multi-cavity plate mold model using the injection molding conditions determined by the injection molding condition determining apparatus having the above configuration.

FIG. 2 is a view for explaining injection molding to the multi-cavity plate mold. In FIG. 2, 21, 22, 23
Is a mold, 24, 25, and 26 are sub-runners, and 27 is a main runner. As shown in FIG. 2, the molten resin injected from the injection molding machine (not shown)
Branches into sub-runners 24, 25, 26
The molds 21, 22, and 23 are respectively filled and solidified into a predetermined shape. In FIG. 2, PA1 and PA2 indicate one corner and the other corner in the mold 21, PB1 and PB2 indicate one corner P and the other corner in the mold 22, PC
1, PC2 indicates one corner and the other corner P in the mold 23.

In this embodiment, the resin temperature and the holding pressure of the resin which flows through the main runner 27 and branches into the sub-runners 24, 25, 26 to fill the dies 21, 22, 23 are changed. In order to determine the optimum molding conditions by evaluating the dimensional accuracy of the product after the filling is completed.

FIGS. 3 and 4 are flowcharts showing the procedure of the injection molding condition determining process for determining the resin temperature and the holding pressure for obtaining the optimum product dimensional accuracy in the injection molding condition determining apparatus. Hereinafter, an injection molding condition determining process for determining the resin temperature and the holding pressure of the injection molding condition determining apparatus will be described with reference to FIGS. First, in step S1, various conditions used to determine injection molding conditions are set by the initial setting unit 1. Specifically, the flow stop temperature, the maximum holding pressure, the target shrinkage rate, the upper limit count value indicating the upper limit count of the execution of the molding simulation, the initial value of the resin temperature,
Set the initial value of the holding pressure, etc. The initial value of the resin temperature is higher than the flow stop temperature, and the initial value of the holding pressure is equal to or less than the maximum holding pressure.

Next, the process proceeds to step S2, where the initial setting unit 1
Using the initial value of the resin temperature and the initial value of the holding pressure set in the above, the initial value calculation unit 2 calculates the shrinkage ratio.

Next, proceeding to step S3, if the contraction rate matches the target contraction rate in the first termination judging section 3, the processing is terminated. On the other hand, in step S3, the first end determination unit 3
If the shrinkage rate does not match the target shrinkage rate, the process proceeds to step S4, where the resin temperature setting unit 4 determines whether the shrinkage rate is higher or lower than the target shrinkage rate. If the shrinkage is lower than the target shrinkage, the resin temperature is raised to set the resin temperature. The resin temperature is output to the resin temperature data storage unit 5 thus set.

Next, the process proceeds to step S5, where the flow stop temperature evaluator 6 evaluates whether the resin temperature stored in the resin temperature data storage 5 is lower than the flow stop temperature, and if the resin temperature is lower than the flow stop temperature. For example, the process proceeds to step S10 (shown in FIG. 4), and returns to the value immediately before the resin temperature is reduced to the flow stop temperature or lower, and proceeds to step S11. On the other hand, if the resin temperature set in step S5 is higher than the flow stop temperature, the process proceeds to step S6, in which the first molding simulation unit 7 performs a molding simulation using the resin temperature stored in the resin temperature data storage unit 5, The simulation result is output to the first simulation result data storage unit 8, and the first contraction rate acquisition unit 10 acquires the contraction rate from the first simulation result data storage unit 8. The contraction rate thus obtained is output to the first contraction rate data storage unit 11.

FIG. 5 shows a part of the contents of the simulation result stored in the first simulation result data storage unit 8. Briefly, the information of the first molding simulation unit 7 is output in the first and second rows, the data items are output in the third and fourth rows, and the unit is output in the fifth row. The data items are the shear rate from the left in the column direction,
Shear stress, flow direction, equivalent viscosity, solidification rate, shrinkage rate, density, expected cooling time, equivalent shear rate, equivalent shear stress are arranged in this order. Then, the results obtained from the forming simulation on the sixth and subsequent lines are output in units of three lines for each element (element) with respect to the mesh, corresponding to the above data items. The number on the left side of the first line of the data output in units of three lines is the element number.

The PA1, PA2, PB1, PB1, PB2 of the dies 21, 22, 23 in the first simulation result data storage 8
The part where the contraction rates of the element numbers of PB2, PC1, and PC2 are described is read, and the contraction rates of PA1 and PA2
The average of the resin shrinkage in the mold 21 is the average of the shrinkage of the mold 21 and the average of the shrinkage of the PB1 and PB2 is the mold 2
2, the contraction ratio of PC1 and the contraction ratio of PC2
The average with the shrinkage rate of the resin is defined as the shrinkage rate of the resin in the mold 23. Further, the shrinkage ratio of the resin in the mold 21 and the mold 22
Of the resin in the mold 23 and the maximum value of the resin shrinkage in the mold 23 are output to the first shrinkage data storage unit 11. The element for reading the shrinkage ratio is the PA
1, PA2, PB1, PB2, PC1, PC2, and an arbitrary place may be selected according to a molding target.

Next, the process proceeds to step S7 shown in FIG. 3, and whether or not unfilling has occurred in the unfilled evaluation section 9 is evaluated from the simulation result stored in the first simulation result data storage section 8. If unfilling has occurred in step S7, the process proceeds to step S10 (shown in FIG. 4).

On the other hand, if no unfilling has occurred in step S7, the flow advances to step S8 to evaluate whether the contraction rate calculated this time is closer to the target contraction rate than the contraction rate calculated last time by the first improvement evaluating section 12. I do. Then, in step S8, when the contraction rate calculated this time is closer to the target contraction rate than the contraction rate calculated last time, it is evaluated that the contraction rate is improved, and the process proceeds to step S9.

Then, in step S9, the number of times of the forming simulation performed by the first calculation number confirmation unit 13 is compared with the upper limit value, and if the number exceeds the upper limit value, the process is terminated.
If it is equal to or less than the upper limit value, the process returns to step S3.

On the other hand, if the currently calculated shrinkage is farther from the target shrinkage than the previously calculated shrinkage in step S8, the process proceeds to step S10 shown in FIG. 4 to return the resin temperature to the previous value. To step S11.

Next, in step S11, the holding pressure setting unit 14 determines whether the contraction rate is higher or lower than the target contraction rate. If the contraction rate is higher than the target contraction rate, the holding pressure is increased. If the contraction rate is lower, the holding pressure is lowered and the holding pressure is set. The holding pressure thus set is output to the holding pressure data storage unit 15.

Next, proceeding to step S12, the holding pressure evaluation section 16 evaluates whether the holding pressure data storage section 15 is below the maximum holding pressure set by the initial setting section 1, and ends if not below the maximum holding pressure. I do. On the other hand, if it is equal to or less than the maximum holding pressure in step S12, the process proceeds to step S13.

Next, in step S13, a molding simulation is performed by the second molding simulation section 17 using the resin temperature stored in the resin temperature data storage section 5 and the holding pressure stored in the holding pressure data storage section 15. The simulation result is output to the second simulation result data storage unit 18, and the second contraction rate acquisition unit 19 acquires the contraction rate from the second simulation result data storage unit 18. The contraction rate thus obtained is output to the second contraction rate data storage unit 20.

FIG. 6 shows a part of the contents of the simulation result stored in the second simulation result data storage section 18. Briefly, in the first and second lines, the second
Information of the molding simulation unit 17 is output, and 3,4
The data item is output on the line, and the unit is output on the fifth line. Data items from left to right in the column direction are shear rate, shear stress, flow direction, equivalent viscosity, solidification rate, shrinkage rate,
The order is density, expected cooling time, equivalent shear rate, equivalent shear stress. Then, the results obtained from the forming simulation on the sixth and subsequent lines are output in units of three lines for each element (element) with respect to the mesh, corresponding to the above data items. The number on the left side of the first line of the data output in units of three lines is the element number.

The PA1, PA2, PB of the dies 21, 22, 23 in the second simulation result data storage section 18
1, PB2, PC1, read the place where the contraction rate of the element number of PC2 is described, and read the contraction rate of PA1 and P
The average of the shrinkage of A2 and the shrinkage of the resin in the mold 21 is defined as the average of the shrinkage of PB1 and the shrinkage of the resin in the mold 22.
The average with the shrinkage rate of 2 is defined as the shrinkage rate of the resin in the mold 23. Further, the shrinkage ratio of the resin in the mold 21 and the mold 2
The maximum value of the resin shrinkage in the mold 2 and the resin shrinkage in the mold 23 is output to the second shrinkage data storage unit 20.

The element for reading the shrinkage ratio is not limited to the above-mentioned PA1, PA2, PB1, PB2, PC1, and PC2, but may be any location depending on the object to be molded.

Next, in step S14 shown in FIG. 4, the second improvement evaluating section 31 evaluates whether the contraction rate has been improved. That is, it is evaluated whether the currently calculated contraction rate is closer to the target contraction rate than the previously calculated contraction rate. Then, in step S14, when the contraction rate calculated this time is closer to the target contraction rate than the contraction rate calculated last time, it is evaluated that the contraction rate is improved, and the process proceeds to step S15. On the other hand, if the distance is far away in step S14, that is, if the difference between the currently calculated contraction rate and the target contraction rate is larger than the previously calculated contraction rate, it is evaluated that the contraction rate has not improved. The process ends.

In step S15, the number of molding simulations performed by the first molding simulation unit 7 or the second molding simulation unit 17 is compared with the upper limit frequency value by the second calculation number confirmation unit 32, and the number of molding simulations is determined by the upper limit frequency value. Is exceeded, the process ends, and if the number of times of forming simulation is equal to or less than the upper limit value, the process proceeds to step S16.

Next, in step S16, if the contraction rate stored in the second contraction rate data storage section 20 matches the target contraction rate in the second end judging section 33, the processing is terminated, and if not, Returns to step S11.

As described above, in the present embodiment, even if the shrinkage rate is equal to the target shrinkage rate, or the holding pressure equal to the minimum resin temperature higher than the flow stop temperature and causing no unfilling and the maximum holding pressure is used. The injection molding condition determination processing is repeated until the contraction rate is larger than the target contraction rate or the number of times of the molding simulation exceeds the upper limit value.

Therefore, in the above-mentioned injection molding condition determining apparatus, only the resin temperature and the holding pressure are optimized, and the other molding conditions are ignored, thereby simplifying the calculation and forming the product having the target dimensional accuracy. Conditions can be determined easily and in a short time.

In the above-described embodiment, the injection molding condition determining apparatus has been described. However, a part or all of the program according to the present invention may be stored in a floppy (registered trademark) disk, CD (compact disk) -ROM, or semiconductor memory. Or the like, and the program may be read into a processing device such as a personal computer and executed as needed.

[0040]

As is clear from the above, according to the injection molding condition determining apparatus and the injection molding condition determining method of the present invention, the conditions for molding a product having a target dimensional accuracy in plastic injection molding can be simply and easily determined. It can be determined in a short time.

Further, according to the program storage medium of the present invention, the computer is controlled by the stored program to execute an injection molding condition determining method for determining a resin temperature and a holding pressure in plastic injection molding, thereby achieving a target. The conditions for molding a product having the dimensional accuracy described above can be determined easily and in a short time.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an injection molding condition determining apparatus according to an embodiment of the present invention.

FIG. 2 is a view for explaining injection molding to a multi-cavity flat plate mold.

FIG. 3 is a flowchart showing a processing procedure for determining a resin temperature and a holding pressure of the injection molding condition determining apparatus.

FIG. 4 is a flowchart showing a processing procedure of the injection molding condition determination device following FIG. 3;

FIG. 5 is a diagram showing the contents of a simulation result stored in a first simulation result data storage unit of the injection molding condition determination device.

FIG. 6 is a diagram showing the contents of a simulation result stored in a second simulation result data storage unit of the injection molding condition determining device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Initial setting part, 2 ... Initial value calculation part, 3 ... 1st end determination part, 4 ... Resin temperature setting part, 5 ... Resin temperature data storage part, 6 ... Flow stop temperature evaluation part, 7 ... 1st molding simulation 8: First simulation result data storage unit 9: Unfilled evaluation unit 10: First shrinkage ratio acquisition unit 11: First shrinkage ratio data storage unit 12: First improvement evaluation unit 13: First Calculation number confirmation section, 14: holding pressure setting section, 15: holding pressure data storage section, 16: holding pressure evaluation section, 17: second molding simulation section, 18: second simulation result data storage section, 19: second contraction Ratio acquisition unit, 20: second shrinkage data storage unit, 21, 22, 23: mold, 24, 25, 26: sub-runner, 27: main runner, 31: second improvement evaluation unit, 32: second calculation Number confirmation section, 33: 2nd end The determination unit.

Claims (3)

[Claims] 1. An injection molding condition determining device for determining a resin temperature and a holding pressure in plastic injection molding, comprising: a target shrinkage ratio determining means for obtaining a target shrinkage ratio based on a target product dimensional accuracy; A shrinkage ratio calculating unit that calculates a shrinkage ratio based on the holding pressure; a resin temperature changing unit that changes a resin temperature so that the shrinkage ratio calculated by the shrinkage ratio calculation unit matches the target shrinkage ratio; When the shrinkage calculated by the shrinkage calculating means is higher than the target shrinkage even if the resin temperature is lowered to a flow stop temperature or a temperature at which unfilling occurs in the temperature changing means, the shrinkage and the target shrinkage are An injection molding condition determining apparatus, comprising: a holding pressure changing unit that changes the holding pressure so as to match. 2. An injection molding condition determining method for determining a resin temperature and a holding pressure in plastic injection molding, comprising: a target shrinkage ratio determining step of obtaining a target shrinkage ratio based on a target product dimensional accuracy; A shrinkage ratio calculating step of calculating a shrinkage ratio based on the holding pressure; a resin temperature changing step of changing a resin temperature such that the shrinkage ratio calculated in the shrinkage ratio calculation process matches the target shrinkage ratio; Even if the resin temperature is lowered to the flow stop temperature or the temperature at which unfilling occurs in the temperature changing step, when the shrinkage is higher than the target shrinkage, the shrinkage calculated in the shrinkage calculation step and the target shrinkage are calculated. And a holding pressure changing step of changing the holding pressure so as to coincide with each other. 3. A program storage medium storing a program for executing the injection molding condition determining method according to claim 1.