JPH0218021A - Forming core and temperature controlling method thereof - Google Patents

Abstract

PURPOSE:To apply nearly uniform forming pressure to the whole formed item and consequently make it possible to obtain the favorable shape of the item even when locally ununiform cooling speed due to ununiform thickness develops by a method wherein the shape of a cavity, which is produced by material made of shape memory alloy, is adjusted by controlling the temperature of the material. CONSTITUTION:A cavity 2 is produced by the opposed surfaces of forming cores 1a and 1b, in each of which a temperature controlling groove 3 circulating heating medium for controlling temperature is produced. During the injection and filling processes, the cores 1a and 1b are held at about 100 C and have cross-sectional forms represented by solid lines 8a and 8b due to their shape memory actions. If the shapes of the cores are held unchanged, no proper pressure is applied to the central part of the resin, which is filled in the cavity at high temperature, resulting in developing sinking. In order to prevent said sinking from developing, as the cooling of the resin proceeds, the cross-sectional forms of the cores 1a and 1b turn into the forms of the desired formed item represented by broken lines 9a and 9b at about 85 deg.C due to the shape memory actions of the cores. As a result, nearly uniform forming pressure can be applied to the whole resin and consequently a formed item having a favorable form without sinking can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a nest used in injection molding or injection compression molding and a method for controlling its temperature.In conventional injection molding or injection compression molding, the shape of the nest is The principle was to maintain a constant shape throughout the entire molding process.

Problems to be Solved by the Invention When trying to obtain a product with a large thickness deviation ratio by conventional injection molding or injection compression molding, the thinner part solidifies and cools early in the cooling process, resulting in a large Young's modulus. The problem is that the thicker parts are in a molten state and have a smaller Young's modulus, so the molding pressure is concentrated on the thinner parts and not on the thicker parts, resulting in sink marks in the thicker parts. there were.

The present invention provides a molding insert that can apply almost uniform molding pressure to the entire molded product and obtain a good shape even if the cooling rate is partially uneven due to uneven thickness, and its temperature. The purpose is to provide a control method.

Means for Solving the Problems In order to solve the above problems, the molding insert of the present invention has the following features:
A shape memory alloy is used as the material, and the shape of the cavity can be adjusted by controlling the temperature.

The temperature control method is to set the temperature so that the cavity shape has a larger thickness deviation ratio with respect to the desired molded product shape when the resin is melted, and then to the temperature such that the cavity shape becomes the desired molded product shape when taking out the resin. You may want to adjust it.

Effect By using the molding insert and temperature control method as described above, even if the cooling rate is uneven during the cooling process, it is possible to apply almost uniform molding pressure to the entire resin, resulting in a good molding without sink marks. A shaped article can be obtained.

EXAMPLE Hereinafter, an example of the molding insert and its temperature control method of the present invention will be described with reference to the drawings, taking as an example the case of molding an acrylic biconvex lens.

The figure is a sectional view of main parts of a molding die including a molding insert according to an embodiment of the present invention.

In the figure, la and lb are molding inserts according to an embodiment of the present invention, in which temperature adjustment grooves 3 are cut to adjust the temperature by passing a heat medium through them, and a cavity 2 is formed by the opposing surfaces. ing.

Reference numerals 4a and 4b designate templates for surrounding, guiding and holding the molding inserts 1a and lb; reference numerals 5 and 6 designate sprues for introducing molten resin into the cavity 2;

The runners 7a and 7b are plates.

In the injection/filling process, the nest 1a and lb are 100″
The solid line 8 in the figure is maintained due to its shape memory effect.
It has a cross-sectional shape as shown by a and 8b.

The resin filled into the cavity at a high temperature of about 240"C cools and solidifies from the surface layer through heat exchange with the nests 1a and 1b, but the thinner peripheral part solidifies earlier than the central part and becomes higher. If the shape of the nest is kept as it is, the molding pressure will be concentrated on the periphery and the proper pressure will not be applied to the center, resulting in sink marks.

As the resin cools down, the nest 1a.

The temperature of nest 1b is gradually lowered from 100'C to about 85°C, but at this time the cross-sectional shape of nests 1a and Ib becomes 85°C.
Due to the shape memory effect at around °C, the broken lines 9a, 9
The molded product is made to have the desired shape as shown in b.

In this way, a substantially uniform molding pressure can be applied to the entire resin throughout the entire molding process, and a molded product with a good shape without sink marks can be obtained.

Although the above explanation has been given by taking the case of molding a biconvex lens as an example, the present invention is not limited to this, and it is clear that it can be applied to all moldings having uneven thickness shapes.

Effects of the Invention As is clear from the above explanation, by using the molding insert of the present invention and its temperature control, even molded products with uneven thickness can be achieved by adjusting the cavity shape in accordance with the progress of cooling of the resin. It is particularly effective for products such as optical lenses that have uneven thickness ratios and require high shape accuracy.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the main parts of a molding die including a nest according to an embodiment of the present invention. la, lb...Molding nest, 2...
Cavity, 3...Temperature control groove, 4a, 4b...
... Template, 5... Sprue, 6... Runner, 7a, 7b... Holder is plate, 8a, 8b...
...Nested shape during injection/filling, 9a. 9b...Nested shape when taken out (desired molded product shape).

Claims (3)

[Claims] (1) A molding insert characterized by using a material made of a shape memory alloy. (2) In a shape memory alloy, the cavity shape is the desired molded product shape at a temperature below a certain temperature, and the thickness deviation ratio of the cavity shape becomes larger with respect to the desired molded product shape at a temperature above the specific temperature. The molding insert according to claim 1, characterized in that the molding insert is configured as follows. (3) At the time of injection, the molding insert made of a shape memory alloy is maintained at a temperature such that the cavity shape has a larger thickness unevenness ratio with respect to the desired molded product shape, and when taken out, the cavity shape is the same as the desired molded product shape. A method for controlling the temperature of a molding insert, characterized by setting the temperature to a temperature that produces a molded product shape.