JP3164660B2 - Method for evaluating runner diameter of injection mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating the diameter of a runner of an injection mold, and more particularly to a method for evaluating a first runner from a sprue.
The present invention is applied to a system in which a resin flow analysis is performed by using a multi-cavity mold formed at a second runner portion by branching at least a T-shaped tip of a runner portion.

[0002]

2. Description of the Related Art In a multi-cavity mold, since a runner portion following a sprue portion is branched into a plurality of passages, the flow of a filling resin is complicated in the runner portion.

That is, in the flow of resin in a finite region, shear heat is always generated near a wall surface due to shear stress.
Temperature rises. On the other hand, although cooling from the wall surface is smaller in the central portion than in the vicinity of the wall surface, there are no external factors or internal factors that increase the temperature.

Therefore, in a very narrow runner portion of the flow path, the temperature rise due to shear heat insulation is larger, and in the runner branch portion, the resin temperature flowing near the wall surface is higher than the resin temperature flowing in the central portion. I have. For this reason, after the branch, the inside that inherits the wall surface temperature (that is, if the runner part before the branch is the first runner part and the runner part after the branch is the second runner part), the first runner part is connected. The temperature of the outside of the second runner section (side wall of the second runner section) is higher than that of the outside (the side wall of the second runner section opposite to the connected first runner section).

That is, when the inside of the second runner portion is viewed in the width direction, there is a temperature distribution of a pattern in which the inside resin temperature is high and the outside resin temperature is low, and the inside flow velocity increases. Therefore, the flow rate of the inner cavity is larger than that of the outer cavity, so that the inner cavity is filled first.

For this reason, in a mold having a complicated shape in which a runner is branched into a plurality of flow paths, it is necessary to balance the runner portion.

Conventionally, in order to achieve this runner balance, a molding test is performed once using a mold after fabrication, and the gate diameter is deliberately determined based on the experience and intuition of a skilled technician from variations in the molded product at that time. Unbalanced to balance the molded product.

[0008]

As described above, in the conventional method, after molding once, the mold is corrected many times based on the experience and intuition of a skilled person, and a quantitative calculation based on scientific calculations is performed. Has not been evaluated. Therefore, every time the design of the mold is changed, a molding test and a mold correction have to be performed.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for evaluating a runner diameter of a mold for injection molding, which enables quantitative evaluation based on scientific calculations. .

[0010]

In order to solve the above-mentioned problems, a method for evaluating a runner diameter of an injection mold according to the present invention is characterized in that at least a tip of a first runner portion continuous from a sprue portion has a T-shape. A system for performing resin flow analysis using a multi-cavity mold that is branched and formed in a second runner portion, wherein a wall surface of the first runner portion and the second A connection point between the wall of the runner portion and a connection point between the connection point and the wall of the second runner portion radially opposite to the connection point is obtained, and the connection point is obtained from the temperature data at each time obtained by resin flow analysis. And a temperature difference at the opposed point is calculated, and a relationship between the calculated temperature difference, a difference in filling time into each cavity, and a diameter of the first runner portion is determined. And performs the evaluation.

[0011]

[Function] From the shape data given at the time of resin flow analysis,
A connection point between the wall surface of the first runner portion and the wall surface of the second runner portion, and an opposing point of the wall surface of the second runner portion that radially opposes the connection point are obtained, and each time obtained by the resin flow analysis is obtained. Is calculated from the temperature data at the connection point and the opposite point. That is, the inside / outside temperature difference (the temperature difference between the connection point and the opposing point) after the runner branch is predicted in advance in the mold design stage.

Then, the relationship between the calculated temperature difference, the difference between the filling time into each cavity, and the diameter of the first runner portion is obtained, and the optimum runner diameter is evaluated from these relationships.

That is, since the filling time difference at which no defect occurs is determined by an experiment, the allowable range of the temperature difference can be determined from the relationship between the temperature difference and the filling time difference for each cavity. Therefore, from the relationship between the temperature difference and the diameter of the first runner portion, the value (allowable range) of the diameter of the first runner portion at which the temperature difference falls within the allowable range can be determined. By setting the value within, a runner design that does not cause runner unbalance can be realized.

[0014]

An embodiment of the present invention will be described below with reference to the drawings.

The runner diameter evaluation method of the present invention uses, as input data, shape data, resin physical property data, and molding condition data created by a mesh generator (which is generally provided conventionally). Here, the resin physical property data refers to viscosity, density, and thermal characteristics (thermal conductivity, specific heat, solidification temperature, heat of crystallization, etc.), and the molding condition data includes filling time, injection rate, and holding pressure. , Pressure holding time, mold temperature distribution, injection resin temperature and the like. After this,
By reading the shape data, the node numbers inside and outside the runner branch portion are recognized.

Then, by solving a partial differential equation in which the filling stage is modeled by a motion equation, a continuous equation, and an energy equation by a finite element method or the like, a resin flow analysis for obtaining state quantities such as pressure and temperature at each time is performed. Execute. The temperature difference between the inside and outside nodes of the runner branch is calculated based on the temperature results obtained in this calculation process, and a series of calculations is terminated using this as an index.

FIG. 1 shows an example of a runner structure of an injection mold (multi-cavity mold) to which the method for evaluating runner diameter according to the present invention is applied. However, the illustrated runner structure is an eight-cavity die, and the figure shows only a quarter model thereof.

In this mold runner structure, the tip of the first runner portion 1 that is continuous from the sprue portion 6 is branched into a T-shape to form the second runner portion 2, and one end of the second runner portion 2 is formed. (The other end is not shown) is further branched into a T-shape to form a third runner portion 3. Both ends of the third runner portion 3 have molded products A,
It has a structure in which cavities 4 and 5 for forming B are formed.

In such a mold having a runner structure,
Looking at the first runner section 1, when the molten resin flows through the first runner section 1, shear heat is always generated near the wall surface 11 due to shear stress, and the temperature rises. On the other hand, the cooling from the wall surface 11 of the central portion 12 is smaller than that of the vicinity of the wall surface 11, but there is no external factor or internal factor that causes the temperature to rise. Therefore, when the diameter of the first runner section 1 is very small, the temperature rise due to shear heat insulation is larger, and the connection (runner branch section) between the first runner section 1 and the second runner section 2 has a wall surface. The temperature of the resin flowing in the vicinity of 11 is higher than the temperature of the resin flowing in the central portion 12.

As a result, the molten resin that has flowed into the second runner portion 2 has its central portion closer to the inside (that is, the side wall to which the first runner portion 1 is connected) 21 that inherits the wall surface temperature. (That is, the side wall on the side opposite to the connected first runner portion 1 in the figure) 22 that inherits the above temperature.

That is, when the inside of the second runner portion 2 is viewed in the width direction, there is a temperature distribution of a pattern in which the resin temperature on the inside 21 is high and the resin temperature on the outside 22 is low. The flow velocity is higher than the flow velocity of the molten resin flowing near the outside 22. Therefore, the flow rate of the inner cavity 4 is larger than that of the outer cavity 5, so that the cavity 4 is filled first.

In this embodiment, a product molded by the mold having the above structure is used as a blood collection tube, the resin is PTF, the injection molding machine is IS-350E manufactured by Toshiba, and the molding conditions are a filling time of 3 sec and a dwelling time of 2 sec. The cooling time is 10 seconds, the cycle is 20 seconds, the resin temperature is 300 ° C., and the mold temperature is 20 ° C.

Under these conditions, first, from the shape data given at the time of resin flow analysis, the wall surface 1 of the first runner 1
Connection point (node) between 1 and wall 21 of second runner section 2
a, and an opposing point (node) b of the wall surface 22 of the second runner portion 2 that radially opposes the connection point a.
Thereafter, based on the temperature data at each time obtained by the resin flow analysis, the temperature difference between the connection point a and the opposing point b is calculated, and the difference between the filling times of the cavities 4 and 5 at that time is calculated. By performing such calculations as needed while changing the diameter (width) h of the first runner portion 1, the relationship between the temperature difference (inside / outside temperature difference) at the connection point a and the opposing point b and the charging time difference is obtained.

FIG. 2 is a graph showing the relationship between the inside / outside temperature difference and the filling time difference thus obtained.

From the figure, it can be seen that the larger the difference between the inside and outside temperatures, the larger the difference in filling time, and the difference in temperature at the runner branch greatly affects the imbalance in filling.

Here, it is conceivable that an actual adverse effect caused by the occurrence of the filling imbalance is the occurrence of melamine.
From FIG. 2, it can be designed so that the temperature difference between the inside and outside is within 20 ° C.

FIG. 3 shows the relationship between the diameter h of the first runner portion 1 and the difference between the inside and outside temperatures. Accordingly, it can be seen from the graph shown in FIG. 3 that the diameter h of the first runner section 1 needs to be 10 mm or more in order to keep the inside / outside temperature difference within 20 ° C.

In the above embodiment, the first runner section 1
Is calculated using the diameter h as a parameter. In addition, the length of the first runner part 1, the mold temperature difference at the connection point a and the opposing point b, the injection temperature difference, and the final runner parts 23, 24
The optimum condition may be determined by executing the calculation in the same manner as described above, taking into account the diameter and the like as parameters.

[0029]

According to the method for evaluating the diameter of a runner of an injection molding die according to the present invention, the tip of a first runner portion continuous from a sprue portion is formed at least in a T-shape to form a second runner portion. A system for performing resin flow analysis using a multi-cavity mold, wherein a connection point between a wall surface of a first runner portion and a wall surface of a second runner portion and a connection point based on shape data given at the time of resin flow analysis. And the opposing point of the wall surface of the second runner portion opposing in the radial direction, and from the temperature data at each time obtained by the resin flow analysis,
A temperature difference between the connection point and the opposing point is calculated, a relationship between the calculated temperature difference, a difference in filling time into each cavity, and a diameter of the first runner portion is determined, and an optimal runner diameter is evaluated from these relationships. Since the temperature difference between the connection point of the runner branch portion and the opposing point can be predicted in advance at the mold designing stage, a runner design with no runner unbalance can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a runner structure of an injection molding die (multi-cavity die) to which a runner diameter evaluation method of the present invention is applied.

FIG. 2 is a graph showing a relationship between an inside / outside temperature difference and a filling time difference.

FIG. 3 is a graph showing a relationship between a diameter of a first runner portion and a difference between inside and outside temperatures.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st runner part 2 2nd runner part 3 3rd runner part a Connection point (node) b Opposite point (node)

Claims (1)

(57) [Claims] 1. A system for performing resin flow analysis using a multi-cavity mold formed at a second runner portion by branching at least a tip end of a first runner portion continuous from a sprue portion into a T-shape. From the shape data given at the time of resin flow analysis,
A connection point between the wall surface of the runner part and the wall surface of the second runner part, and the second point facing the connection point in the radial direction.
The opposing point of the wall surface of the runner portion is obtained, and the temperature difference at the connection point and the opposing point is calculated from the temperature data at each time obtained by the resin flow analysis, and the calculated temperature difference and the filling of each cavity are calculated. A method for evaluating a runner diameter of an injection molding die, wherein a relation between a time difference and a diameter of the first runner portion is obtained, and an optimum runner diameter is evaluated from these relations.