JP2955509B2 - Mold design method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for designing a mold for a plastic product. The present invention relates to a technique for shortening the time required for a plastic molding process by removing a plastic molded product from a mold at a high temperature and folding the form deformed according to cooling after the removal into a mold design in advance.

[0002]

2. Description of the Related Art A plastic molding method in which a plastic melted at a high temperature is extruded into a tube, sandwiched by a mold, and air is blown into the tube to expand the plastic is widely used. This conventional example will be described with reference to FIG. FIG. 6 is a view showing a process of manufacturing a container by a blow molding method. As shown in FIG. 6A, a tubular molten plastic (parison) is extracted at an intermediate position of the divided mold, and the mold is closed as shown in FIG. 6B. As shown in FIG. 6C, when air is blown into the molten plastic, the molten plastic adheres to the inner wall of the mold,
The molten plastic has the same shape as the inner wall of the mold. At this point, the temperature of the molten plastic is, for example, 20
At a high temperature of 0 ° C., the plastic is cooled and solidified by keeping the high-pressure air blown in the mold. The cooling time varies depending on the type of plastic and the content of the molded product, but as a conventional cooling time determining means, it has been assumed that the deformation due to the heat shrinkage of the resin after removal is in a linear range. As shown in FIG. 6D, when the mold is opened, the molded product is taken out.

[0006] The molded product shown in FIG. 6 is a container (bottle) for filling and selling a liquid, and the standard of the resin temperature at which the mold is opened is about 50 ° C. This cooling requires a time of several tens of seconds.

[0004]

As described above, it takes time to cool the hot molten plastic until the mold can be opened. In a manufacturing process in which the production amount per unit time and the production cost are in a proportional relationship, and the time is controlled in units of seconds, even if it is a short time of ten and several seconds, the production cost is further reduced. The problem is to reduce the time required for cooling.

[0005] The inventors repeatedly conducted an experiment in which the mold was opened to a high temperature in order to obtain the data of the cooling time which was the shortest in practical use. As a result, the high-temperature molten plastic shrinks greatly when it comes out of the mold if it is less than the conventional cooling time, and causes non-linear deformation. The shortening could not be done.

The present invention has been made in view of such a background, and it is an object of the present invention to provide a method and an apparatus for designing a mold capable of obtaining a target molded product shape even if a cooling time in a plastic molding process is reduced. With the goal. An object of the present invention is to provide a method and an apparatus for designing a mold capable of manufacturing a molded product having a shape that compensates for hydrostatic deformation due to filling of contents. SUMMARY OF THE INVENTION An object of the present invention is to provide a mold design method and apparatus capable of designing a mold without experience.

[0007]

The plastic released from the mold shrinks and deforms while cooling to room temperature. Conventionally, there is a regularity that the deformation is linear because of low temperature removal, and by making (1 / shrinkage ratio) into the target molded product shape to make a large die, the design of the intended molded product shape ( Design dimensions) can be guaranteed. However, in the non-linear shrinking process due to high temperature extraction, the macroscopic regularity as described above cannot be found. Therefore, the present inventors simulate the deformation behavior using the finite element method, and create a mold shape in consideration of the deformation in advance, so that the desired molded product shape can be obtained even at high temperature removal. A mold design method and apparatus have been invented.

That is, a first aspect of the present invention is a method for designing a mold, which is characterized in that the molded product has the initial shape (≒ mold shape) immediately before being removed from the mold. A first step of performing a deformation simulation for the deformation occurring after the first step, a second step of calculating a difference between the shape deformed by the first step and a target molded article shape, and comparing the difference with a threshold value And a fourth step of calculating a change in the initial shape based on the difference when the difference exceeds the threshold.

The target molded product shape may not include the deformation due to the internal pressure caused by the filling of the contents, or may include the deformation due to the internal pressure caused by the filling of the contents. For example, when the molded article is a plastic container for filling a liquid, the plastic container is deformed by filling the plastic container with the liquid. The mold can be designed in advance in consideration of the deformation.

The simulation is based on the finite element method (F
EM: Finite Element Method) (for the finite element method, see the IEICE Handbook, pages 36 to 37).

[0011] Until now, trial and error have been simply repeated,
Alternatively, although it has relied on the experience of craftsmen, the use of the finite element method can reduce wasteful prototype dies and can design dies without experience.

A second aspect of the present invention is a mold designing apparatus, which is characterized by an initial mold shape (b0).
As three-dimensional information, first means for calculating a deformation simulation for deformation occurring after removing a molded product having the same initial shape from the mold, and a result (ci) of calculating the deformation simulation. Second means for calculating a difference (xi) from a target molded product shape, third means for comparing the difference with a threshold value, and when the difference exceeds a threshold value (ε), the initial shape based on the difference value And a means for repeatedly executing the first to fourth means until the difference falls below a threshold.

The shape of the target molded article may not include the deformation due to the internal pressure caused by the filling of the contents, or may include the deformation due to the internal pressure caused by the filling of the contents.

[0014] A third aspect of the present invention is a recording medium in which a program for executing each of the above means is recorded.

[0015] A fourth aspect of the present invention is a mold designed by the designing apparatus.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. FIG. 1 is a flowchart of a mold designing method according to an embodiment of the present invention.

The present invention is a method for designing a mold, which is characterized in that the initial shape of a molded product immediately after being removed from the mold is subjected to a deformation simulation for the deformation occurring after being removed from the mold. (S1), a second step (S2) of calculating a difference between the shape deformed by the first step and the target molded product shape, and a third step (S3) of comparing the difference with a threshold value ) And a fourth step (S4) of calculating a change in the initial shape based on the difference when the difference exceeds the threshold.

FIG. 5 shows an apparatus for executing the mold design method of the present invention. FIG. 5 is a block diagram of the mold designing apparatus according to the embodiment of the present invention.

The present invention is a mold designing apparatus, which is characterized by a keyboard 6 as a means for inputting the initial shape (b0) of the mold as three-dimensional information, and a molded product having the same shape as the initial shape. A deformation simulation operation unit 1 as a first means for calculating a deformation simulation for a deformation occurring after being taken out of the mold, and a second means for calculating a difference between a result of the calculation of the deformation simulation and a target molded product shape. And a difference determining unit 3 as a third means for comparing the difference with a threshold value
And an initial shape changing unit 4 as a fourth means for changing a part of the initial shape based on the difference when the difference exceeds a threshold value.
Or the arithmetic control unit 5 as means for repeatedly executing the initial shape changing unit 4 until the difference falls below the threshold value.

In the embodiment of the present invention, a finite element method (FEM) is used for this calculation. Figure 2 shows the finite element method
This will be described only briefly with reference to FIG. FIG. 2 is a diagram showing a finite element model of a bottle. FIG. 3 is a diagram for explaining the finite element method. As shown in FIG. 2, a container (shape) to be subjected to the deformation simulation is approximated by a lattice-shaped triangular or quadrangular low-order element. The element is composed of nodes {(xni, yni, zni), i = 1, 4}. Here, when the deformation simulation is performed, the node coordinates of the element after the deformation are calculated as shown in FIG.
{(Xdi, ydi, zdi, i = 1, 4)}.
Here, as shown in FIG. 3C, the node coordinates (xni, yni, zni) before deformation and the node coordinates (xd
i, ydi, zdi) difference ｛(xsi, ysi, z
si), i = 1, 4}, the degree of deformation of one element can be obtained. In the finite element method, as described above, the deformation state of the entire container is grasped by obtaining the degree of deformation similarly to all the elements of the model shown in FIG.
The deformation simulation is repeatedly performed while gradually changing the design shape before deformation so that the shape after deformation approaches the target molded product shape, and the final design shape is determined.

(First Embodiment) The first embodiment of the present invention will be described with reference to FIG.
This will be described using the bottle as an example). In order to determine the mold shape to be the target molded product shape after the shrinkage deformation of the plastic taken out of the mold is completed, when the ejection temperature is low, that is, in the case of minute deformation (linear), the reciprocal of the deformation rate is targeted. It can be determined by multiplying the shape of the molded product. However, this is not applicable when the take-out temperature is high, that is, when the heat shrinkage is large and nonlinear.

Therefore, the inventors performed a thermal deformation simulation every time on the design target shape of the die, reflected the difference between the result and the target molded product shape on the design target shape, and continued until the result converged to the target molded product shape. This was repeated. At this time, in order to stabilize the convergence in consideration of the nonlinearity of the deformation, a deceleration coefficient β was introduced, and the difference reflected on the design target shape was adjusted. In order for this method to work effectively, the deformation amount calculated by the deformation simulation of the finite element method (FEM),
The variants need to match the real system with considerable accuracy.

Therefore, in order to improve the simulation accuracy, the physical property parameters were adjusted based on the shapes before and after the deformation, which can be measured, so that the simulation results match the measured displacement. The physical property parameters include a coefficient of linear expansion, a Young's modulus, a Poisson's ratio, a thermal conductivity, a specific heat, and a density.
Table 1 shows simulation results after parameter adjustment.

[0025]

[Table 1] Looking at the column of “difference × 100 / actual measurement (%)” corresponding to the relative error, it is 5% at the maximum, and it can be seen that the parameter adjustment is successfully performed.

(Second Embodiment) A second embodiment of the present invention will be described. FIG. 4 is a flowchart of a mold designing method according to the second embodiment of the present invention. In the second embodiment of the present invention, a mold is designed in consideration of hydrostatic deformation when a molded bottle is filled with a liquid as a content. The plastic is removed from the mold (S11) and undergoes heat shrinkage deformation (S1).
2) A molded product is obtained (S13). As a result of filling the molded product with the liquid as the content, the molded product is subjected to hydrostatic deformation (S1).
4) Although the final product shape is obtained (S15), this step is also considered in the second embodiment of the present invention.

Looking at the design process, the flow is reversed. That is, the product design (S17) is performed based on the design design (S16), and the shape of the molded product that becomes the product size by the hydrostatic deformation after the filling of the contents is calculated (S17).
18) A molded article is automatically designed (S19). further,
The mold shape is automatically designed by calculating the mold shape which becomes the molded product size after the shrinkage deformation (S20) (S2).
1).

As described above, in contrast to the steps of the first embodiment of the present invention, in the second embodiment of the present invention, the shape of the empty molded product and the shape of the molded product after the contents are filled, that is, the product shape is further reduced. And a step of reflecting the difference in the design shape of the mold is added. The procedure is the same as in the first embodiment of the present invention, and is performed according to the flowchart shown in FIG. As in the first embodiment, the parameters are adjusted to match the actually measured displacement.

(Third Embodiment) A third embodiment of the present invention will be described. FIG. 5 is a block diagram of a mold designing apparatus according to a third embodiment of the present invention. The mold designing method shown in the first or second embodiment of the present invention is executed by the mold designing apparatus shown in the third embodiment of the present invention. The initial shape (b0) of the mold is input as three-dimensional information using the keyboard 6. The deformation simulation calculation unit 1 calculates a deformation simulation for a deformation occurring after removing a molded product having the same initial shape from the mold. The difference calculation unit 2 calculates the difference between the result of the calculation of the deformation simulation and the target molded product shape. The difference determination unit 3 compares this difference with a threshold. When the difference exceeds the threshold value, the initial shape changing unit 4 changes the initial shape based on the difference. The arithmetic control unit 5 causes the deformation simulation arithmetic unit 1 to the initial shape changing unit 4 to repeatedly execute until the difference falls below the threshold.

If the hydrostatic deformation shown in the second embodiment of the present invention is also taken into consideration, the deformation simulation calculation unit 1 performs a deformation simulation on the deformation that occurs after the molded product having the same initial shape is removed from the mold. Then, a deformation simulation by hydrostatic deformation when the molded article after the deformation is filled with the contents is calculated.

As shown in Table 2, good results were obtained by the mold designing apparatus of the present invention.

[0032]

[Table 2] In the first or second embodiment of the present invention, the standard of the mold opening temperature is 120 ° C., and the cooling time is 5 seconds.
In the conventional example, the standard of the opening temperature of the mold is 50 ° C., and the cooling time is about 10 seconds, so that the production amount per unit time is more than doubled.

[0033]

As described above, according to the present invention,
Even if the cooling time is shortened, it is possible to realize a mold that can obtain a target molded product shape. Furthermore, it is possible to design a mold for producing a molded product having a shape that compensates for hydrostatic deformation due to filling of contents. At this time, the mold can be designed regardless of experience.

[Brief description of the drawings]

FIG. 1 is a flowchart of a mold design method according to an embodiment of the present invention.

FIG. 2 is a diagram showing a finite element model of a bottle.

FIG. 3 is a diagram illustrating a finite element method.

FIG. 4 is a flowchart of a mold designing method according to a second embodiment of the present invention.

FIG. 5 is a block diagram of a mold designing apparatus according to an embodiment of the present invention.

FIG. 6 is a view showing a step of manufacturing a detergent container by a blow molding method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Deformation simulation operation part 2 Difference operation part 3 Difference judgment part 4 Initial shape change part 5 Operation control part 6 Keyboard

────────────────────────────────────────────────── ─── of the front page continued (72) inventor Yuko Tamiya, Tochigi Prefecture, Haga-gun, Ichikai Akabane 2606 Kao stock company within the Institute (58) investigated the field (Int.Cl. ^6, DB name) B29C 33/38 B29C 49 / 48

Claims (9)

(57) [Claims] 1. A first step of performing a deformation simulation on the initial shape of a molded product immediately before being removed from a mold, the deformation occurring after being removed from the mold, and the shape deformed by the first step and the target molding. A second step of calculating a difference from the product shape, a third step of comparing the difference with a threshold, and a fourth step of calculating a change in the initial shape based on the difference when the difference exceeds the threshold. And a step for designing a mold. 2. The mold design method according to claim 1, wherein the target molded product shape does not include deformation due to internal pressure caused by filling of contents. 3. The method according to claim 1, wherein the target molded product shape includes a deformation due to an internal pressure caused by filling the contents. 4. The simulation is performed by a finite element method (FEM: Fine Element Element Method).
2. The method for designing a mold according to claim 1, wherein d) is adopted. 5. A means for inputting an initial shape (b0) of a mold as three-dimensional information, and a first means for calculating a deformation simulation of a deformation occurring after removing a molded product having the same initial shape from the mold. A second means for calculating a difference (xi) between a result (ci) obtained by calculating the deformation simulation and the target molded product shape; a third means for comparing the difference with a threshold value; (4) means for changing the initial shape based on the difference when exceeding (ε), and means for repeatedly executing the first to fourth means until the difference falls below a threshold value. A mold design apparatus characterized by the following. 6. The mold designing apparatus according to claim 5, wherein the target molded product shape does not include deformation due to internal pressure caused by filling of contents. 7. The mold designing apparatus according to claim 5, wherein the target molded product shape includes a deformation due to an internal pressure caused by filling the contents. 8. A machine readable program storing a program for executing each means according to claim 5.
Do recording medium. 9. A mold designed by the designing apparatus according to claim 5.