JPH03182312A - Manufacture of mold - Google Patents

Abstract

PURPOSE:To manufacture a simple mold for molding synthetic resin, which is suitable for multi-kind small-amount production, by a method wherein a matrix, consisting of heat resistant synthetic rubber, is used as a core and low melting point alloy, whose melting point is specified, is cast around the core, then, the matrix, consisting of the heat resistant synthetic rubber, is extracted and removed. CONSTITUTION:A matrix is inserted into a frame body for a casting mold as a core and synthetic rubber is cast around the core, then, the core or the matrix is extracted and removed whereby the molding mold of synthetic rubber, which is provided with a cavity having the same configuration as the inserted matrix, may be obtained. Next, synthetic rubber, having a high resistance to heat, is cast into the cavity of the synthetic rubber molding mold whereby a molding form, having the same configuration as the matrix again, may be obtained. Finally, the heat resistant synthetic rubber molded form is used as a core and low melting point alloy, having a melting point lower than 200 deg.C, is cast around the core whereby a mold, whose core part is formed as a cavity and having a high strength as well as good dimensional accuracy, appearance and the like, may be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a simple mold for a bottom shape made of a low melting point alloy.

[Conventional technology] Conventionally, when manufacturing molds used for injection molding of synthetic resins, etc., the mold is first manufactured using an NC (numerical control) machine tool, etc., based on a mold diagram created from a product drawing. After machining the product part (cavity), we actually use the mold thus manufactured to perform injection molding, measure and evaluate the shape of the resulting molded object, and modify the mold based on this evaluation. The process is repeated several times.

[Problems to be Solved by the Invention] However, with this method, a mold with excellent durability for several thousand to several hundred shots can be obtained, but on the other hand, a large number of shots are required to manufacture one mold. There were problems in that it required several days and was extremely costly.

On the other hand, in recent years, the development of new products and prototypes using synthetic resin moldings has progressed, and product cycles have become shorter.As a result, high-mix, low-volume production methods are often adopted in the manufacturing field. It has become. Furthermore, requests for modification and remodeling of product shapes are increasing.

Therefore, if a conventional mass production mold manufactured by machining is used as a mold for molding such a product, it will not be cost effective and will lead to an increase in the product price. was there.

Furthermore, molds for prototypes or molds for products with a particularly small number of molded products have traditionally been made by spraying a low-melting-point alloy onto a product model (matrix) such as a wooden or metal mold. Those manufactured by forming a cavity by a method, or by casting a resin containing metal powder to form a cavity are used.

However, the molds manufactured using this method are inferior in properties necessary for molds, such as pressure resistance, strength, mold releasability, and appearance, so it is difficult to obtain satisfactory molded products even with simple molds. there were.

The present invention was made to solve these problems, and requires fewer manufacturing steps as there is no need to cut the inner surface of the cavity, and has good strength, dimensional accuracy, appearance, etc., and is suitable for high-mix, low-volume production. The purpose of this invention is to provide a method for manufacturing a simple mold for synthetic resin molding.

[Means for Solving the Problems] The method for manufacturing a molding die of the present invention includes a step of manufacturing a mother mold having the same shape and dimensions as the product to be molded by machining using hard plastic, and this step. A matrix made of hard plastic is used as a core, and liquid curable synthetic rubber is poured onto the outside of the core and cured, and then the matrix made of plastic is removed and removed to form a cavity with the same shape and dimensions as this matrix. a step of manufacturing a synthetic rubber mold having a mold, and a step of molding a heat-resistant curable liquid synthetic rubber into the cavity of the synthetic rubber mold and curing it to manufacture a matrix made of the heat-resistant synthetic rubber; After using this mother mold made of heat-resistant synthetic rubber as a core and casting a low melting point alloy with a melting point of 200°C or less on the outside: c! The method is characterized in that a mother mold made of carp-cured thermoplastic rubber is extracted and removed to obtain a low melting point alloy mold having a cavity having the same shape and dimensions as the mother mold.

In the present invention, plastic materials commonly used as engineering plastics can be used as the hard plastic for producing a matrix having the same shape and dimensions as the product to be molded, but they are relatively inexpensive and machine-friendly. It is particularly desirable to use ABS resin (acrylonitrile-butadiene-styrene copolymer) because it has good physical properties and heat resistance, as well as good moldability and dimensional stability.

In addition, liquid synthetic rubber that is cast on the outside of such a hard plastic matrix to form an intermediate mold is:
Liquid silicone rubber can be used.

Furthermore, the heat-resistant synthetic rubber that is cast into the cavity of this synthetic rubber mold to form the cast body that will become the core of the final mold has extremely high heat resistance, exceeding the melting point of the low-melting point alloy described below. It is desirable to use a heat-resistant liquid silicone rubber having the following properties or a liquid fluorine-based comb.

Furthermore, a final mold is formed by casting on the outside of such a heat-resistant synthetic rubber core, the melting point of which is 200°C.
The following low melting point alloys include an alloy mainly composed of bismuth and lead with a melting point of 120-125°C, which is usually called wood metal, or a bismuth-tin alloy with a melting point of 138-170°C. can be used.

[Function] In the method of manufacturing a molding die of the present invention, first, a block of hard plastic is machined using an NC machine tool based on a product drawing to create a mother mold having the same shape as the product to be molded. is produced.

Next, this matrix is inserted as a core inside a casting frame, and after casting synthetic rubber such as silicone rubber on the outside, the core matrix is pulled out and removed. A synthetic rubber mold having a cavity having the same shape as the mother mold, that is, the same shape as the product to be molded, is obtained.

Next, by casting highly heat-resistant synthetic rubber into the cavity of the obtained synthetic rubber mold, a cast body having the same shape as the mother mold, that is, the same shape as the product to be molded, is again obtained. Finally, this heat-resistant synthetic rubber cast body is used as a core,
By casting a low melting point alloy having a melting point of 200° C. or less on the outside, the core portion is formed as a cavity, and a mold with high strength, dimensional accuracy, and good appearance can be obtained.

[Example] Hereinafter, an example of the present invention will be described with reference to the attached flow chart.

In the example, as shown in the drawings, first, based on the drawing of the product to be molded, machining is performed using an NC machine tool using NC tape, and a matrix having the same shape as the product to be molded is made from a block of ABS resin. Make a mold.

Next, this mother mold is pushed as a core into a predetermined position inside a crushed body for casting made of acrylic resin, etc., and after casting liquid curable silicone rubber on the outside of the core, the resulting cast body is After dividing into two, the core matrix is removed.

Next, liquid silicone rubber, which has higher heat resistance than the low melting point alloy used, is poured into the cavity of the silicone rubber mold, which has a cavity with the same shape, size, and dimensions as the mother mold. A cast body with the same shape and dimensions as the mother mold is formed.

Next, the obtained heat-resistant silicone rubber cast body is used as a core, and a low melting point alloy with a melting point of 200°C or less, such as a bismuth-lead alloy, is cast on the outside of the core. Take out the child.

In this way, a mold made of bismuth-lead alloy is obtained.

The molds manufactured by this method have good dimensional accuracy and appearance, sufficient heat resistance and mechanical strength, and can be used as casting molds for synthetic resins as well as polyethylene and polypropylene. It can be used as a mold for low-pressure injection molding or flow injection molding of thermoplastic resins.

This mold is usually used in injection molding in combination with a casting template, and only the inner mold is replaced depending on the product to be manufactured.

In addition, since this mold is formed by casting a low melting point alloy, it requires fewer man-hours and costs less, and the inner surface of the cavity is smooth and has good mold releasability. There is no need to do this.

Furthermore, since it can quickly adapt to requests for modification or modification of product shapes, it is suitable as a simple mold for high-mix, low-volume production.

Further, in the manufacturing method of this embodiment, the ABS resin matrix can be manufactured taking into consideration the draft angle of the molded product, undercut, resin shrinkage rate, etc.

In this case, there is no need to further perform machining to create a handling slope etc. after mold casting, and the number of man-hours can be reduced.

Furthermore, it is not only possible to directly process the obtained mold to form a flow path for a cooling medium, but also to add an extrusion function by processing parts other than the mold cavity.

[Effects of the Invention] As explained above, according to the manufacturing method of the present invention, by casting a low melting point alloy, a molded product having a cavity having the same shape as the product to be molded and having good strength, dimensional accuracy, appearance, etc. You can get the mold.

Furthermore, the method of the present invention requires only a small number of manufacturing steps and does not require much cost, so it is useful as a mold manufacturing method suitable for a high-mix, low-volume production system.

[Brief explanation of drawings]

The drawing is a flowchart for explaining an embodiment of the method for manufacturing a molding die of the present invention.

Claims (1)

[Claims] (1) A process in which a matrix of the same shape and dimensions as the product to be molded is manufactured by machining using hard plastic, and this matrix made of hard plastic is used as a core, and liquid hardening synthetic rubber is applied to the outside of the core. After casting and curing, the mold made of plastic is removed and removed to produce a synthetic rubber mold having a cavity of the same shape and size as that of the mold, and the inside of the cavity of the synthetic rubber mold is A process of casting and curing heat-resistant curable liquid synthetic rubber to produce a matrix made of the heat-resistant synthetic rubber;
After casting a low melting point alloy of 00°C or less, the mother mold made of the heat-resistant synthetic rubber is removed and removed to obtain a low melting point alloy mold having a cavity having the same shape and dimensions as the mother mold. A method of manufacturing a mold for molding.