JPH08276480A - Method and apparatus for calculating pressure simulation execution cycle in injection molded product model - Google Patents

Abstract

(57) [Summary] [Purpose] Calculate the maximum value of the simulation execution cycle that does not diverge the calculated pressure simulation results,
By performing the simulation in accordance therewith, the pressure simulation is performed faster than before. [Structure] Calculate the minimum value of the pressure simulation execution cycle for each decomposed minute element of the injection molded product model,
The pressure difference between the obtained result and the result one execution cycle before and the stability of the result are calculated, and the maximum value of the pressure difference between the execution cycles described above is calculated within the range where the pressure simulation result is stable. It is configured to calculate the pressure simulation execution cycle that is multiplied by a constant so that it becomes the maximum below the maximum value, and use it as the pressure simulation execution cycle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to a method and apparatus for simulating the behavior of a resin inside a mold during a holding pressure / cooling process after filling in a simulation of an injection molding process.

[0002]

2. Description of the Related Art Conventionally, material data is taken into consideration by considering a resin compressibility and a relational expression of pressure, volume, and temperature (hereinafter, P-V-T relational expression) with a simulation result in a resin filling process as an initial value. A pressure simulation is performed with the molding conditions as input conditions. In order to obtain a stable pressure result, Equation 1 is used to obtain from each element of the model divided into minute elements (hereinafter, mesh division), and the minimum value among them is used as a simulation execution cycle (hereinafter, time step). I was doing a simulation.

(One-dimensional case)

[0004]

[Equation 1]

If the time step obtained from the equation 1 is obtained so as not to diverge the value of the pressure simulation result, it becomes an extremely minute value when the analysis target model has small divided elements, and a large model. When solving, it took a lot of time for analysis.

On the other hand, in the simulation of the pressure-holding process in which the compressibility of the resin is taken into consideration, the pressure increase is large at the initial stage of the pressure-holding. I can't ask.

[0007]

Therefore, in the present invention, the calculated pressure result is stable without divergence, the largest possible time step is empirically obtained, and a pressure simulation is performed using the time step. We propose a method for simulating stable pressure simulation results faster than before.

[0008]

In the constitution of the present invention for solving the problems, the first aspect of the invention is to consider the compressibility of the resin and the relational expressions of pressure, volume and temperature, and
According to the pressure simulation in the injection molded product model using material data and molding conditions, from each element of the model decomposed into minute elements, in the calculation method of the execution period of the pressure simulation, for each element of the model,
The minimum value of the execution cycle is calculated from the element size and the given resin physical property data as the simulation execution cycle, and the pressure difference between the obtained pressure simulation result and the pressure simulation result one execution cycle before, and the stability of the pressure simulation result Of the pressure simulation result, the maximum value of the pressure difference between the execution cycles is calculated within a range in which the pressure simulation result is stable, and the pressure simulation execution cycle is multiplied by a constant so as to be the maximum at the maximum value or less. , And is used as a pressure simulation execution cycle.

According to another aspect of the present invention for solving the same problem, in claim 2, the compressibility of the resin and the relational expressions of pressure, volume and temperature are taken into consideration, and material data and molding conditions are set as initial conditions. In a pressure simulation device for an injection molded product model using, a means for decomposing the model into minute elements, a calculating means for obtaining an execution cycle of pressure simulation from each decomposed element, and an element for each element of the model Means for calculating the minimum value of the execution cycle from the size and the given resin physical property data, and the pressure difference between the pressure simulation result obtained as the simulation execution cycle and the pressure simulation result of one execution cycle before, And means for calculating the stability of the pressure simulation result, and within the range where the pressure simulation result is stable. Means for calculating a maximum value of the pressure difference between the serial execution cycle, characterized by comprising means for calculating the constant multiple pressure simulation period such that at most the maximum value or less.

[0010]

The operation principle of the present invention will be described below.

Assuming that the injection-molded product model exists on the XY coordinates, the basic equation of the pressure simulation at the pressure-holding stage in consideration of compressibility is shown in Equation 2.

[0012]

[Equation 2]

(One-dimensional case) The time step (hereinafter, Δt) for stability is determined from the following equation.

[0014]

(Equation 3)

If each coefficient is a constant and is constant within the element,

[0016]

[Equation 4]

Therefore,

[0018]

(Equation 5)

## EQU3 ## When the equation 4 is subjected to the difference approximation with Δt and the space point interval Δx,

[0020]

(Equation 6)

[0021]

(Equation 7)

In order that the value of Pi does not diverge

[0023]

(Equation 8)

From equation 8,

[0025]

[Equation 9]

[0026]

[Equation 10]

Equation 10 is the stability condition when solving Equation 3 using the forward difference.

(Two-dimensional case)

[0029]

[Equation 11]

In the case of the finite element method, considering the element length,

[0031]

(Equation 12)

For each element,

[0033]

(Equation 13)

Calculate

Here, it is considered that Δt determined by the equation 13 is appropriately multiplied by a constant and taken large. However, the problem at this time is the stability and convergence of the pressure simulation results.

Therefore, a multiple of Δt (hereinafter, xd
t) is changed, simulation results of pressure and temperature,
The amount of change in the pressure simulation result during the unit time Δt was examined and shown in Table 1.

[0037]

[Table 1]

From the results shown in Table 1, when Δt is determined with xdt set to a certain constant value, the relationship between the multiple and the simulation result of pressure and temperature differs depending on the model to be analyzed, which is not effective in obtaining a stable result.

Therefore, a method is considered in which the amount of change in the pressure simulation result during the unit time Δt is obtained, and at that time, the multiple xdt of Δt is obtained so that the next stable pressure simulation result is obtained. .

The contents are shown below: 1) For each time step, the change amount (pressure difference) of the pressure simulation result between steps is obtained.

2) A new xdt (NPKTIME) is calculated from the maximum value of pressure difference (DPMAX) obtained in 1) above.
To calculate.

[0042]

[Equation 14]

However, NPKTIME: Δ in the next step
Multiple of t (xdt ′) PKTIME: Multiple of Δt of current step (xdt) LMPRES: Limit value of pressure change amount (pressure difference) between steps DPMAX: Maximum value of pressure change amount between steps (pressure difference) Attached below An embodiment of the present invention will be described with reference to FIG.

FIG. 1 is a block diagram showing the structure of a general injection molding process simulation apparatus.

In the figure, 1 is a CAD system. The injection-molded product model created in 1 is transferred to the hard disk 2 connected by the LAN. The hard disk 2 is also used for storing injection molding simulation software and various parameters. Reference numeral 3 is a CPU that performs a simulation, and the simulation result of the CPU 3 is displayed on the display 4 including graphics. 5 is an injection molding machine.

Next, FIG. 2 is a flow chart showing an outline of a simulation method of an injection molding process as an embodiment of the present invention.

In the figure, the data of the injection-molded product model created by the CAD system is sent to the shape input processing unit 10 for mesh division.

Next, reference numeral 20 denotes a condition input processing section, which inputs analysis conditions and resin data which are molding conditions.

Next, reference numeral 30 denotes an analysis calculation processing unit, which performs analysis according to the following procedure based on the conditions given by the condition input processing unit 20. 1) 31 is a flow analysis processing unit, which is the pressure at the time of resin filling,
The flow condition of temperature is simulated for each mesh-divided element. 2) 32 is a holding pressure analysis processing unit, which is a flow analysis processing unit 31.
Using the pressure and temperature simulation results obtained in step 1 as the initial conditions, the pressure, temperature, shrinkage rate, etc. of the resin in the pressure holding process after resin filling is simulated in consideration of compressibility. 3) 33 is a cooling analysis processing unit which simulates resin pressure, temperature, shrinkage ratio, etc. by removing the boundary condition of holding pressure. 4) 34 is a warp deformation analysis processing unit, which simulates the warp deformation state after resin cooling from the shrinkage ratio distribution obtained by the cooling analysis processing unit 33.

Then, the simulation result obtained by the analysis calculation processing unit 30 is displayed on the display 50 by the result display processing unit 40 including the graphic display which is easy to visually judge. The data of the result display processing unit 40 can be fed back to the CAD system of 60,
It is also possible to input (download) to the molding machine 0.

Next, FIG. 3 is a flow chart showing the details of the pressure simulation carried out by the holding pressure analysis processing section 32 and the cooling analysis processing section 33, which is a feature of the present invention.

In the figure, S1 is a calculation part of a theoretical time step for stability, and the time step Δt is calculated for each element of the mesh-divided injection molded product model from the element size and the given resin physical property data. Then, the minimum value among them is given as the initial Δt.

S2 is a pressure analysis unit, which performs a pressure simulation based on Δt obtained in S1.

S3 is a pressure difference calculation unit for each element, and calculates the pressure difference between steps from the calculated pressure value of the previous step and the calculated pressure value of this time for each element.

S4 is a calculation unit for the multiple xdt with respect to the theoretical time step Δt, and the multiple xdt is such that the maximum value of the pressure difference obtained for each element becomes the limit value of the pressure difference when Δt is calculated. To calculate. When variably setting xdt in the program, the limit value of the pressure difference in one step is set to 2 MPa, and xdt is set so as not to exceed the limit value. Also, the range of multiples is 20-50
Set between 0.

In step S5, it is determined whether xdt obtained in step S4 is within a proper range. If it is within the range in step S6, the calculated value xdt is selected. Select.

S8 is a pressure analysis unit, which performs a pressure simulation based on the calculated optimum time step (Δtxdt).

S9 is a judgment unit for terminating the pressure analysis process.
The process branches to S3 until the end of all steps.

The results obtained by the above means are shown below.

Table 2 shows a comparison of analysis time and results depending on the difference of the multiple xdt with respect to Δt.

[0061]

[Table 2]

FIGS. 4 to 12 show comparisons of pressure history at arbitrary points in the bar flow, box and LBP cover models.

The limit value of the pressure difference in one step is 1MP.
It is possible to set values such as a and 0.5 MPa, but 2M
Compared with Pa, no superiority in accuracy was found.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of a single device. Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program to a system or an apparatus.

[0065]

According to the present invention, in consideration of the compressibility of resin and the relational expressions of pressure, volume, and temperature, material data and molding conditions are used as initial conditions, and each element of the injection molded product model The minimum value of the execution cycle is calculated from the size of the resin and the given physical data of the resin, and is used as the simulation execution cycle. The pressure difference between the obtained pressure simulation result and the pressure simulation result one execution cycle before, and the stability of the pressure simulation result To calculate the maximum value of the pressure difference between the execution cycles within a range where the pressure simulation result is stable, and calculate a constant-simulated pressure simulation execution cycle such that the maximum is equal to or less than the maximum value.
By using it as a pressure simulation execution cycle, it is possible to increase the pressure simulation execution cycle for parts that do not require detailed simulations and have a small change in pressure, so the time required for pressure simulation can be faster than before. Become.

[0066]

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a general injection molding process simulation apparatus.

FIG. 2 is a flowchart showing an outline of an injection molding process simulation method as an embodiment of the present invention.

FIG. 3 is a flowchart showing details of pressure simulation which is a feature of the present invention.

FIG. 4 is a pressure history (xdt: 60) at an arbitrary point of the perflow model as an example of the present invention.

FIG. 5 is a pressure history (xdt: variable) at an arbitrary point of a perflow model as an example of the present invention.

FIG. 6 is a pressure history (xdt: 500) at an arbitrary point of the perflow model as an example of the present invention.

FIG. 7 is a pressure history (xdt: 100) at an arbitrary point of the box model as an example of the present invention.

FIG. 8 is a pressure history (xdt: variable) at an arbitrary point of the box model as an example of the present invention.

FIG. 9 is a pressure history (xdt: 500) at an arbitrary point of the box model as an example of the present invention.

FIG. 10 is a pressure history (xdt: 10) at an arbitrary point of the LBP cover model as an example of the present invention.
0).

FIG. 11 is a pressure history (xdt: variable) at an arbitrary point of the LBP cover model as an example of the present invention.

FIG. 12 is a pressure history at an arbitrary point of the LBP cover model as an example of the present invention (xdt: 50).
0).

[Explanation of symbols]

 1 CAD 2 Hard Disk 3 CPU 4 Display 5 Molding Machine 10 Shape Input Processing Section 20 Condition Input Processing Section 30 Analysis Calculation Processing Section 31 Flow Analysis Processing Section 32 Pressure Holding Analysis Processing Section 33 Cooling Analysis Processing Section 34 Sled Deformation Analysis Processing Section 40 Results Display processing unit 50 Display 60 CAD system 70 Molding machine S1 Δt calculation step for stability S2 Pressure analysis step S3 Pressure difference calculation step for each element S4 xdt calculation step S5 xdt comparison step S6 xdt selection step S7 Multiple limit value Selection step S8 Pressure analysis step by optimal time step S9 Pressure analysis end determination step

Claims (2)

[Claims] 1. Considering a resin compressibility and a relational expression of pressure, volume, and temperature, it is decomposed into minute elements relating to a pressure simulation in an injection molded product model using material data and molding conditions as initial conditions. From each element of the model, in the calculation method of the execution period of the pressure simulation, for each element of the model, the simulation execution period by calculating the minimum value of the execution period from the size of the element and the given resin physical property data, Calculate the pressure difference between the obtained pressure simulation result and the pressure simulation result one execution cycle before, and the stability of the pressure simulation result, and calculate the maximum value of the pressure difference between the execution cycles within the range where the pressure simulation result is stable. Is calculated, and the pressure simulation execution cycle is multiplied by a constant that maximizes the value below the maximum value. Calculated, calculation method of the execution cycle of the pressure simulation, which comprises using as the pressure simulation period. 2. A pressure simulation device for an injection-molded product model, which uses material data and molding conditions as initial conditions in consideration of resin compressibility and a relational expression of pressure, volume, and temperature, wherein the model is used as minute elements. A means for decomposing, a calculating means for obtaining the execution period of the pressure simulation from the decomposed elements, and a minimum value of the execution cycle for each element of the model from the size of the element and the given resin physical property data. Means, a means for calculating the pressure difference between the pressure simulation result obtained by taking the minimum value of the execution period as the simulation execution period and the pressure simulation result one execution period before, and the stability of the pressure simulation result, and the pressure simulation result is stable. A means for calculating the maximum value of the pressure difference between the execution cycles within a range of A pressure simulation device comprising means for calculating a pressure simulation execution period that is multiplied by a constant so as to be maximum at a value or less.