JPH1177782A - Estimation of weld of molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To estimate a weld with high accuracy even with respect not only to a part where a molding material flows parallel within the cavity of a mold but also to a three-dimensional molded product having a thick-walled shape. SOLUTION: A method for estimating the weld of a molded product consists of a process for analyzing the flow of a molding material, a marker particle moving process, a process for determining the attribute of an element and a process for detecting the weld of the molded product (1). In the process for analyzing the flow of the molding material, the cavity of the mold is divided into a large number of elements and the speed vectors of molding material in the respective elements are calculated (2). In the marker particle moving process, marker particles arranged to the respective elements are moved in the direction reverse to the flow direction of the molding material on the basis of the speed vectors of the process (1) (3). In the process for determining the attributes of the elements to which the respective marker particles belong at first are determined based on whether the marker particles pass through a specific gate or the specific part of the cavity (3). In the process for detecting the weld of the molded product, the interface of the elements changed in attributes is detected as the weld of the molded product (4).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position of a weld formed by joining a plurality of flows of a molding material in a molding die in a molded product such as a synthetic resin injection molded product, a metal die cast product or a cast product. And a method for predicting the shape.

[0002]

[Prior art]

<First Conventional Example (Japanese Unexamined Patent Application Publication No. 7-1529)> This is a method for predicting the strength of the appearance of a weld line in an injection molded product of a synthetic resin.

A cavity of a mold is divided into a number of elements, and a velocity vector of a molten resin in each element is obtained by flow analysis.

If the velocity vectors of two adjacent elements intersect on the same plane and intersect, the interface between the two elements is regarded as a weld line, and such elements are selected from all elements to form a weld line. Select as element.

An angle formed by the velocity vectors of a plurality of adjacent weld elements is determined as a merging angle at which a plurality of flows of the molten resin merge in the cavity.

[0006] All merging angles are compared, and it is predicted that the weld line appears stronger as the merging angle becomes larger, and the weld line becomes weaker as the merging angle becomes smaller.

<Second Conventional Example (Japanese Patent Laid-Open No. 4-361379)> This is an apparatus for setting the position of a gate in a synthetic resin injection mold.

A model composed of a number of basic surfaces is created from the shape of the molded product, and a possible number of gates are set at the edge of the basic surface of the model corresponding to the edge of the molded product.

[0009] For each gate, a resin flow path that separates in a plurality of directions is set on a basic surface including the gate, a flow length of each resin flow path is calculated, and each resin flow path on the basic surface including the gate is calculated. Set the resin flow path to be further separated in a plurality of directions from the tip position of the next continuous basic surface, calculate the flow length of each resin flow path, and sum the flow length of each continuous resin flow path from the gate Is calculated. This operation is performed until there is no continuous basic surface, or until the total flow length of the resin flow path exceeds a flow length preset as a flow limit of the resin.

Here, the flow length is a value obtained by dividing the length of the resin flow path on the basic surface by the thickness of the plate portion of the molded product corresponding to the basic surface.

In the case where a plurality of gates are set, at the connection side of the basic surface where one resin flow path continuous from one gate and one resin flow path continuous from another gate meet, both gates are connected. The flow lengths of the resin flow paths are compared, and when the difference between the two flow lengths is within a small range set in advance, the position of the connecting side where the flow lengths meet is approximately set as a weld line.

When setting a plurality of gates, an appearance attribute and a load attribute of a basic surface set in advance according to a molded product,
Then, the appropriate number and position of gates are determined from the position of the weld line.

[0013]

However, in the above-mentioned first conventional example, the velocity vector of the molten resin is on the same plane in two adjacent elements among a large number of elements obtained by dividing the cavity of the molding die. If they intersect, the interface between the two elements becomes a weld line. Therefore, it is impossible to predict a weld line in a portion where the velocity vectors of the molten resin are parallel in two adjacent elements.

For example, in a case where a molten resin of a different color is simultaneously injected into a plurality of gates of a molding die to produce a molded product of a plurality of colors, a boundary of a color is predicted in a portion where the molten resin of a different color flows in parallel. Can not do it.

In the second conventional example as described above, the flow of the molten resin in the actual molding die is not only the shape of the cavity of the molding die, that is, the shape of the molded product, but also the physical properties of the molten resin and other factors. Since the resin flow path and its flow length are obtained based only on the shape of the molded product, the prediction accuracy is low despite the fact that the flow path varies depending on the conditions.

Further, since the flow length based on the wall thickness of the molded product is used using a model consisting of a large number of basic surfaces only, it is applied only to a thin molded product constituted by combining plates. . It cannot be used for thick-walled molded products.

[0017]

According to the present invention, there is provided a method for predicting weld of a molded article, comprising the following steps.

Molding material flow analysis step: The cavity of the mold is divided into a number of elements, and the velocity vector of the molding material in each element is determined.

Movement step of marker particles: The marker particles arranged in each element are moved in the direction opposite to the flowing direction of the molding material based on the above velocity vector.

Determining the attribute of the element: The attribute of the element to which each marker particle originally belonged is determined by whether the marker particle has passed a specific gate or a specific portion of a cavity.

Step of detecting weld of molded article: detecting an element interface whose attribute changes as a weld of the molded article.

[0022]

As described above, the weld of the molded article is detected based on the movement trajectory of the marker particles disposed in each element of the mold cavity, that is, the flow trajectory of the molding material filled in each element. In contrast, the weld can be detected even in the part where the molding material flows in parallel in the cavity.

In the flow analysis of the molding material, not only the shape of the cavity of the molding die but also the physical properties of the molding material and other conditions can be taken into consideration, so that the prediction accuracy is higher than in the second conventional example.

Further, since the flow analysis of the molding material can be performed in three dimensions, it can be used for a thick three-dimensional molded product.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION
As shown in FIG. 1, the method includes a flow analysis step of a molding material, a step of moving marker particles, a step of determining an attribute of an element, and a step of detecting a weld of a molded article.

In the flow analysis process of the molding material,
The cavity (and runner) of the mold is divided into a number of small elements, and a velocity model at each time of the molding material in each element of the geometry model is calculated using a shape model in which a gate is set at the connection position between the cavity and the runner. Determined by numerical analysis.

Various numerical analysis methods such as a finite volume method, a finite element method, a boundary element method, a difference method and a FAN method are used for the flow analysis of the molding material. The one-dimensional analysis method, the two-dimensional analysis method, and the three-dimensional analysis method are used. For a one-dimensional element, a circular tube, a rectangular tube or the like is used, for a two-dimensional element, a triangle or a quadrangle is used, and for a three-dimensional element, a tetrahedron, a pentahedron, a hexahedron, or the like is used.

To illustrate schematically, when a rectangular flat plate is molded by injecting molding material from the corners at both ends on one short side, as shown in FIG. Is divided into two-dimensional elements 1 to 8 and a molding material is used in each of the elements 1 to 8 of the shape model using a shape model in which gates A and B are set at the corners at both ends on one short side of the cavity. the velocity vector V ₁ ~V ₈ at each time of obtaining the two-dimensional numerical methods.

In the marker particle moving step, the marker particles are arranged at the center of each element, and based on the velocity vector, each marker particle is oriented in a direction opposite to time, that is, in a direction in which the molding material flows. Move toward the gate in the opposite direction.

At this time, the velocity vector used for moving the marker particles is sequentially replaced with the one corresponding to the time.
The speed vector at the specific time may be continuously used.

To make the marker particles flow backward, for example,
The following formula is used:

X ₂ = X ₁ −V · Δt where X ₂ : position vector after movement of the marker particle X ₁ : position vector before movement of the marker particle V: velocity of the element where the marker particle existed before the movement Vector Δt: time interval for calculation of marker particle movement.

In the schematic example shown in FIG. 2, the marker particles m ₁ and m ₅ arranged at the centers of the first element 1 and the fifth element 5 of the shape model respectively have the locus t 1 as shown in FIG. through _1, t _5, passes through the gate a and gate B. Similarly, the marker particles arranged at the centers of the second element 4 to the fourth element 4 pass through the gate A. The marker particles arranged at the centers of the sixth element 6 to the eighth element 8 pass through the gate B.

In the step of determining the attribute of the element, the attribute of the element to which each marker particle originally belongs is determined by the marker particle by a specific gate (or a specific portion of the cavity).
Is determined by whether or not the vehicle has passed.

In the schematic examples shown in FIGS. 2 and 3, since the marker particles arranged on the first to fourth elements 4 of the shape model pass through the gate A, as shown in FIG. The first element to the fourth element 4 have an attribute a. Fifth element 5
Since the marker particles arranged in the eighth to eighth elements 8 pass through the gate B, as shown in FIG.
Has an attribute b.

In the process of detecting the weld of the molded article, the attributes of each element of the shape model are displayed on a graphic screen or the like, and the element interface where the attribute changes is detected as the weld of the molded article.

In the schematic examples shown in FIGS. 2 to 4, the attribute of the first element 1 to the fourth element 4 is a, and the fifth element 5 to
Since the attribute of the eighth element 8 is b, as shown in FIG.
The interface XY between the first to fourth elements 4 and the fifth to eighth elements 8 is detected as a weld of the molded product.

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG.
A synthetic resin part in which a rib 12 having a rectangular cross section of 20 × 10 mm is joined in a cross shape on the upper surface of a rectangular flat plate 11 of 2 mm, is joined to the central position 13 of the joint between the flat plate 11 on one short side and the rib 12. This is an example of predicting the weld position and shape of a molded product when molding is performed by injecting molten resin from the central position 14 of the joint between the flat plate 11 and the rib 12 on one long side.

As shown in FIG. 6, the shape model divides the flat plate forming portion 21 of the cavity of the forming die into quadrangular two-dimensional elements and converts the rib forming portion 22 of the cavity into a hexahedral three-dimensional element.
The mold is divided into two-dimensional elements, and the two runners 23 and 24 of the molding die are divided into one-dimensional elements of a circular tube.
Gates A and B were set at connection positions 3 and 24.
The number of elements is 1116.

The flow analysis of the molten resin is performed by using a three-dimensional resin flow analysis program made in-house by an electronic computer. In addition to the above-mentioned shape model, the injection speed and temperature of the molten resin, the temperature of the molding die, The physical properties such as density, thermal conductivity, specific heat and viscosity coefficient of the molten resin are input, and the velocity vector of the molten resin in each element of the shape model is set to 10 seconds for a filling time of 2.0 seconds.
It was determined at 1/0 intervals.

Using a self-made marker particle moving program using the above formula for causing the marker particles to flow backward, the marker particles are arranged at the center of each element of the shape model, and each marker particle is timed based on the above velocity vector. , Ie, in the direction opposite to the flow direction of the molten resin toward the gate.

When the marker particle passes through the gate A, the attribute of the element to which the marker particle first belongs is a, and when the marker particle passes through the gate B,
The attribute of the element to which the marker particle first belonged was set to b, and the attribute of a or b was determined for each element of the shape model.

As shown in FIG. 7, each element of the shape model is displayed on the display screen of the computer with the element 31 of the attribute a being hatched and the element 32 of the attribute b being not hatched, and the attribute is changed. The element interface is detected as the weld of the molded article, and the position and shape of the weld w of the molded article are predicted as shown in FIG.

[Brief description of the drawings]

FIG. 1 is a flowchart of a weld prediction method according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing element division and gate setting of a shape model and a velocity vector of each element in a weld prediction method of the same embodiment.

FIG. 3 is a schematic diagram showing trajectories of marker particles arranged on a first element and a fifth element of a shape model in the weld prediction method of the embodiment.

FIG. 4 is a schematic diagram showing a weld by displaying an attribute on each element of a shape model in the weld prediction method of the same embodiment.

FIG. 5 is a perspective view of a molded product in a weld prediction method according to the embodiment of the present invention.

FIG. 6 is a perspective view of a shape model in the weld prediction method of the same example.

FIG. 7 is a perspective view showing a state in which attributes are displayed on each element of the shape model in the weld prediction method of the same example.

FIG. 8 is a perspective view of a state in which a weld is shown on a molded article in the weld prediction method of the same example.

[Explanation of symbols]

1 to 8 Elements of shape model A Gate AB Gate B V _{1 to} V ₈ Velocity vector m ₁ , m ₅ of molding material in elements 1 to 8 Marker particles t ₁ , t ₅ marker arranged in first and fifth elements Particle movement trajectory XY Weld of molded article 31 Element of attribute a 32 Element of attribute b w Weld of molded article

Claims (1)

[Claims] 1. A method for predicting weld of a molded article, comprising the following steps. Molding material flow analysis step: The mold cavity is divided into a number of elements, and the velocity vector of the molding material in each element is determined. Marker particle moving step: The marker particles arranged in each element are moved in the direction opposite to the flowing direction of the molding material based on the above velocity vector. Determining the attribute of the element: The attribute of the element to which each marker particle originally belonged is determined by whether or not the marker particle has passed a specific gate or a specific portion of a cavity. Step of detecting weld of molded article: detecting an element interface whose attribute changes as a weld of the molded article.