JPH09277260A - Method and apparatus for designing mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that it is required that a mold is opened after a sufficient cooling time is elapsed when molten plastic is molded by the mold and production quantity per a unit time is restricted by the cooling time. SOLUTION: When a mold is opened without being sufficiently cooled, plastic is thermally shrunk to be largely deformed. If the mold is designed preliminarily in anticipitation of deformation quantity by grasping this deformation, a shape of a molded product coinciding with a plan dimension can be obtained even if a cooling time is shortened. A finite element method is used in order to grasp deformation. Further, the planning of a mold considering even static water pressure deformation at a time when the molded product is filled with liquid content can be performed. By this constitution, production quantity per a unit time can be enhanced and a mold can be designed without relying on experience.

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 taking out a plastic molded product from a mold at a high temperature and preliminarily folding in a mold design a shape that deforms according to cooling after taking out.

[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 diagram showing a process of manufacturing a container by a blow molding method. As shown in FIG. 6 (a), a tube-shaped molten plastic (parison) is extracted at an intermediate position of the divided mold, and the mold is closed as shown in FIG. 6 (b). 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 being taken out is in a linear range. As shown in FIG. 6D, when the mold is opened, the molded product is taken out.

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

[0004]

As described above, it takes time to cool high temperature molten plastic before the mold can be opened. In the manufacturing process in which the production amount per unit time and the production cost are in a proportional relationship and the time is managed in seconds, in order to realize a lower production cost, even if it is a short time of 10 seconds or more. The challenge is to reduce the time required for cooling.

Therefore, the inventors repeatedly conducted an experiment in which the mold was opened at a high temperature in order to obtain the data of the cooling time which is the shortest in practical use. As a result, the molten plastic at high temperature shrinks significantly when it is removed from the mold in less than the cooling time that has been conventionally used, and causes non-linear deformation. No reduction was possible.

The present invention has been made against such a background, and provides a method and an apparatus for designing a mold capable of obtaining a target shape of a molded product even if the cooling time in the plastic molding process is shortened. 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 simulated the deformation behavior using the finite element method, and created the mold shape in consideration of the deformation in advance, so that the target shape of the molded product can be obtained even at high temperature extraction. Invented a mold design method and apparatus.

That is, the first aspect of the present invention is a method for designing a die, which is characterized by taking out from a die to an initial shape (≈die shape) of a molded product immediately before taking out from the die. Comparing this step with a threshold value, the first step of performing a deformation simulation for the deformation that occurs after that, the second step of calculating the difference between the shape deformed by this first step and the target molded product shape And a fourth step of calculating the change of the initial shape based on the difference when the difference exceeds the threshold value.

The target molded article 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) is preferable (For the finite element method, see the Institute of Electronics, Information and Communication Engineers, Electronic Information and Communication Handbook, P36 to P37).

Until now, simply repeating trial and error,
Alternatively, although relying on the experience of craftsmen, it is possible to reduce wasteful prototype dies by using the finite element method, and design dies without experience.

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

The target molded article 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.

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

A fourth aspect of the present invention is a mold designed by the designing device.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION

[0017]

Embodiments of the present invention will be described with reference to FIG. FIG. 1 is a flow chart of a mold designing method according to an embodiment of the present invention.

The present invention is a mold designing method, which is characterized in that a deformation simulation is performed on the initial shape of a molded product immediately after being taken out from the mold and deformation occurring after taking out from the mold. Step (S1), a second step (S2) of calculating the 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 the change of the initial shape based on the difference when the difference exceeds the threshold value.

An apparatus for carrying out the mold designing method of the present invention is shown in FIG. 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 initial shape. Deformation simulation calculation unit 1 as a first means for calculating a deformation simulation for deformation that occurs after taking out from the mold, and second means for calculating a difference between the calculation result of this deformation simulation and the target molded product shape. And a difference determining section 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, there is provided a calculation control section 5 as means for repeatedly executing the initial shape changing section 4 until the difference falls below a threshold value.

In the embodiment of the present invention, the finite element method (FEM) is used for this calculation. Figure 2 shows the finite element method.
A brief explanation will be given 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, the 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 as shown in FIG.
{(Xdi, ydi, zdi, i = 1, 4)}.
Here, as shown in FIG. 3C, the nodal coordinates (xni, yni, zni) before the deformation and the nodal coordinates (xd) after the deformation.
difference with i, ydi, zdi) {(xsi, ysi, z
By obtaining si), i = 1, 4}, the degree of deformation of one element can be obtained. In the finite element method, the deformation mode of the entire container is grasped by obtaining the deformation degree like all the elements of the model shown in FIG.
The final design shape is determined by repeatedly executing the deformation simulation while gradually changing the pre-deformation design shape so that the shape after deformation approaches the target molded product shape.

(First Embodiment) The first embodiment of the present invention (see FIG. 2)
Will be described as an example). At the stage where the shrinkage deformation of the plastic taken out from the mold is completed, to obtain the mold shape that will become the target molded product shape, if the ejection temperature is low, that is, if the deformation is minute (linear), the reciprocal of the deformation rate is targeted It can be determined by multiplying the shape of the molded product. However, it is not applicable when the take-out temperature is high, that is, when this heat shrinkage is large and non-linear.

Therefore, the inventors perform a thermal deformation simulation on the design object shape of the mold each time, reflect the difference between the result and the target molded article shape on the design object shape, and converge to the target molded article shape. This was repeated. At this time, in consideration of the non-linearity of the deformation, in order to stabilize the convergence, the deceleration coefficient β was introduced and the difference reflected on the design target shape was adjusted. In order for this method to function effectively, the deformation amount calculated by the deformation simulation of the finite element method (FEM),
The variant must match the real system with considerable accuracy.

Therefore, in order to improve the simulation accuracy, the physical property parameters are adjusted so that the simulation result matches the actually measured displacement, based on the measurable and deformed shapes. 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 the 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 the mold designing method of 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.

Focusing on the design process, the flow is in the opposite direction. 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 process of the first embodiment of the present invention, in the second embodiment of the present invention, the empty molded product shape and the molded product shape after the contents are filled, that is, the product shape Is added to reflect the difference in the design shape of the mold. 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 the 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 repeatedly executes the deformation simulation arithmetic unit 1 or the initial shape changing unit 4 until the difference falls below the threshold value.

If 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 deformation that occurs after a molded product having the same initial shape is taken out of the mold. Then, a deformation simulation due to hydrostatic deformation when the deformed molded product is filled with the contents is calculated.

With the mold designing apparatus of the present invention, as shown in Table 2, good results could be obtained.

[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 the target shape of the molded product. 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 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 for explaining 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 configuration diagram of a mold designing apparatus according to an embodiment of the present invention.

FIG. 6 is a diagram showing a process 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

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[Procedure amendment]

[Submission date] January 22, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuko Tamiya 2606 Akabane, Kaigai-cho, Haga-gun, Tochigi Prefecture Kao Corporation Research Institute

Claims (9)

[Claims] 1. A first step of performing a deformation simulation on an initial shape of a molded product immediately before being taken out of a mold, the deformation occurring after being taken out of the mold, and a shape deformed by the first step and a target molding. A second step of calculating a difference from the product shape, a third step of comparing the difference with a threshold value, and a fourth step of calculating the change of the initial shape based on the difference when the difference exceeds the threshold value. The method for designing a die, comprising: 2. The method for designing a mold according to claim 1, wherein the target shape of the molded product does not include deformation due to internal pressure caused by filling the contents. 3. The method for designing a mold according to claim 1, wherein the target molded product shape includes a deformation caused by an internal pressure generated by filling the content. 4. The method for designing a mold according to claim 1, wherein the simulation is based on a Finite Element Method (FEM). 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 deformation that occurs after a molded product having the same initial shape is taken out of the mold. And a second means for calculating a difference (xi) between the result (ci) of calculation of the deformation simulation and the target molded product shape, a third means for comparing the difference with a threshold value, and the difference is a threshold value. A fourth means for changing the initial shape based on the difference when (ε) is exceeded, and means for repeatedly executing the first to fourth means until the difference falls below a threshold value. Mold designing equipment. 6. The method for designing a mold according to claim 5, wherein the target molded product shape does not include deformation due to internal pressure caused by filling the contents. 7. The mold design method according to claim 5, wherein the target molded product shape includes deformation due to internal pressure caused by filling of the contents. 8. A recording medium on which a program for executing each unit according to claim 5 is recorded. 9. A mold designed by the design apparatus according to claim 5.