JPH08224756A - Mold for injection molding - Google Patents

Abstract

PURPOSE: To facilitate the mold matching of a micro-diameter core pin by using a shape memory alloy. CONSTITUTION: A core pin 6 for forming a fine hole 9 in a molding 1 is formed from a shape memory alloy to which the memory of the shape of contact with the cavity surface 8 of a fixed mold is given in advance, and the transformation point of the core pin 6 is set on the basis of resin temperature when the molding 1 is removed from the mold. During molding, the core pin 6 is brought into contact with a shape which is memorized in advance by molten resin temperature, or the cavity surface 8 of the fixed mold, and the mold is released after the resin being solidified to form a fine hole 9 in the molding 1.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection mold for forming fine holes in a molded product.

2. Description of the Related Art A cover used for a front surface of a speaker having a fine hole in a molded product has a shape in which hundreds to thousands of fine holes having a diameter of 1 mm or less are arranged. Much work is being done on mold processing. In the conventional die structure, as shown in FIG. 5, the core 5 of the movable die 3 is perforated by the number of fine holes, and after the core pin 6 is inserted into this hole, its length and tip shape are fixed side cavity surface. It is processed to fit 8. Therefore, due to machining mistakes in the core pin or damage during machining, molding defects such as clogging of fine holes (burrs, etc.) occur, and a new core pin is required each time, and many machining processes are required to match the cavity surface 8. It takes time and effort. Incidentally, 1 is a molded product, 2 is a fixed mold, and 4 is a receiving plate.

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned drawbacks, and makes it possible to easily perform mold matching with the fixed mold cavity surface 8 and to obtain fine holes of good quality with few molding defects. An object of the present invention is to provide an injection molding die that can be used.

SUMMARY OF THE INVENTION The present invention provides a core pin inserted in a movable core for forming fine holes in a molded article,
Formed with a shape memory alloy that is stored in advance in a shape that abuts the surface of the fixed mold cavity, and sets the transformation point of the core pin based on the resin temperature when releasing the molded product,
During molding, the core pin is held above the transformation point by the temperature of the molten resin and held in the previously stored shape.

After the mold is closed, the core pin is transformed into a shape in which it is in contact with the surface of the fixed mold cavity by filling with the molten resin, and as a result, fine holes are formed. As the resin is cooled, the core pin is also cooled, the mold release temperature (transformation point) is reached, and the core pin separates from the cavity surface.

An embodiment of the present invention will be described with reference to the drawings.
The same components as those of the above-described conventional example will be described with the same reference numerals. 1 to 4, 1 is a molded product, 2
Is a fixed die, 3 is a movable die, 4 is a receiving plate, 5 is a core, and 6 is a core pin inserted in the core 5 to form fine holes in the molded product 1. Reference numeral 7 is a cavity, and 8 is a fixed cavity surface. The core-pin 6 is made of a shape memory alloy, and is inserted into the core 5 of the movable mold 3 as shown in FIG. 1, sandwiched between the core 5 and the receiving plate 4, and the tip of the core-pin 6 is projected into the cavity 7. Also, the core pin 6 is
Normal time (state below martensitic transformation start temperature) Figure 1
As described above, the pin tip is not in contact with the cavity surface 8, but when the molten resin begins to be filled, it is heated to a temperature above the transformation point (state above the martensite transformation start temperature) by the molten resin temperature, The shape is stored in advance, that is, the tip is held in contact with the fixed mold cavity surface 8 as shown in FIG. In forming the core pin 6, the martensite transformation point is set based on the resin temperature (solidification temperature) when the molded product 1 is released. That is, the core pin 6 is in contact with the fixed mold cavity surface 8 at the temperature of the molten resin at the time of molding, and if the resin is cooled to a temperature at which the resin solidifies and starts demolding, the core pin 6 becomes a martensite phase. It has thermal characteristics such that it starts to transform and moves away from the cavity surface 8. Since the transformation characteristic (shape memory characteristic) of such a shape memory alloy is well known, detailed description thereof will be omitted. The operation of the above mold is as follows. First, when the mold is closed (FIG. 1), the core-pin 6 is not in contact with the fixed mold cavity surface 8. When injection molding is performed in this state, the molten resin is filled around the core pin 6 and the temperature rises, the martensite phase transforms to the austenite phase, and the core pin 6 comes into contact with the fixed mold cavity surface 8.
The fine holes 9 are formed in the molded product 1. (State of FIG. 2) When the mold is cooled until the molded product 1 is sufficiently solidified, the temperature of the core pin 6 also drops, and when the mold release temperature is reached, the core pin 6 begins to transform from the austenite phase to the martensite phase, As shown in FIG. 3, the resin separates from the core pin 6 due to the contraction force of the core pin 6 in the releasing direction while the resin is separated from the cavity surface 8. When the mold opening is started as shown in FIG. 4, the molded product 1 is pulled out from the cavity portion 7 of the fixed mold 2, and the molded product 1 is ejected from the movable mold 3 by an eject mechanism (not shown). In an embodiment of the invention,
Although the fixed cavity surface 8 has a planar shape, in the case of a curved shape, a minute gap is generated between the tip of the core pin 6 and the fixed cavity surface 8.
Since there is a fine diameter, there is no problem in the quality of the fine holes 9 of the molded product 1.

As described above, by using the shape memory alloy for the core pin, it is possible to simultaneously mold a large number of fine core pins with the cavity surface, and the core pins can be faithfully brought into contact with the cavity surface. As a result, burrs and the like do not occur in the fine holes, and a molded product of good quality can be provided. Also, the simplification of mold matching work can significantly reduce the number of processing steps.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of an injection mold of the present invention when the mold is closed (before injection).

FIG. 2 is likewise a sectional view during injection molding (after injection).

FIG. 3 is likewise a cross-sectional view during injection molding (after solidification).

FIG. 4 is a sectional view of the same when the mold is opened.

FIG. 5 is a cross-sectional view showing a conventional injection molding die when the die is closed.

[Explanation of symbols]

 1 Molded product 9 Micro holes 5 Movable core 6 Core pin 8 Fixed mold cavity surface

Claims (1)

[Claims] 1. A molded product is formed by forming a core pin, which is inserted into a movable mold core for forming microscopic holes in a molded product, with a shape memory alloy stored in advance so as to abut against a surface of a fixed mold cavity, and mold-molding the molded product. The transformation point of the core pin is set on the basis of the resin temperature at the time, and at the time of molding, the core pin is held at the transformation point or higher by the molten resin temperature to maintain the shape stored in advance. Type.