JPS6144616A - Molding process of thin wall molded product - Google Patents

Abstract

PURPOSE:To heat effectively the mold for molding the product with thin wall and wide surface area by heating the surface of a stationary mold and a movable mold by Joule heat, applying high frequency current to said molds at the stage prior to the finish of mold closing. CONSTITUTION:A stationary mold 14 and a movable mold 18 are respectively mold 18 are respectively insulated electrically by a stationary platen 12 and a movable platen 16. The surfaces of those molds 14, 18 are heated by Joule heat, applying high frequency current to said molds 14, 18 at the stage prior to the finish of mold closing.

Description

[Detailed description of the invention] (b) Industrial application field The present invention relates to a method for molding @meat molded products.

(b) Conventional technology When molding thin-walled products (molded products with absolutely thin wall thickness, molded products with relatively thin walls due to a large projected area, etc.), melting is carried out through the narrow space of the mold cavity. Since it will be filled with resin, it is necessary to increase the fluidity of the molten resin.

For this reason, in the past, gold was heated using a heat medium, heater, or the like.

(c) Problems to be solved by the invention However, in the conventional mold heating method as described above, the entire mold is heated, so a large amount of refrigerant is poured into the cooling hole provided in the mold during the cooling process. It was necessary to cool the molded material by cooling it, which lengthened the cooling time and lengthened the entire molding cycle, making it impossible to sufficiently improve productivity. In addition, since the entire mold is heated and cooled for each shot, defects such as a decrease in the strength of the mold and the occurrence of rust occur, shortening the life of the mold. solve the problems,
The purpose of this invention is to provide a method for molding thin-walled molded products that has a short molding cycle and can extend the life of the mold.

(d) Means and action for solving the problems The present invention includes:
The above objective is achieved by heating only the surface of the mold using high frequency current. That is, a high-frequency current is applied to the fixed mold and movable mold, which are electrically insulated from the fixed platen and movable platen, respectively, before the mold is closed (that is, before the movable mold contacts the fixed mold), and Joule heat is generated. Heat the mold surface. By doing so, the molten resin is maintained in a highly fluid state during injection and pressure holding, and the cavity is filled with relatively low resin pressure. Since only the surface of the mold is heated, it can be cooled down in a short time, which shortens the molding cycle accordingly. Furthermore, since the amount of heat supplied to and removed from the metal is small, the life of the mold is extended.

(e) Examples Examples of the present invention will be described below with reference to FIGS. 1 and 2.

A fixed die 14 (female die) is attached to a fixed platen 12 of the molding machine 10, and a movable die 18 (male die) is attached to a movable platen 16. The fixed mold 14 is electrically insulated because it is attached to the fixed platen 12 via an electrically insulating plate 20, and similarly, the movable type 18 is attached to the movable platen 16 via an electrically insulating plate 22. Since it is attached, it is electrically isolated. A pair of electrodes 24a and 24b are attached close to the cavity surface of the fixed mold 14. A pair of electrodes 26a and 26b are also attached to the movable mold 18 in close proximity to the cavity surface. Electric @
24a, 24b and electrodes 26a, 26b are both connected by wiring 32 so that a predetermined voltage can be applied from a high frequency AC power source 30 by operating a switch 28.

FIG. 1 shows the state in which the molded product has been removed. Mold closing starts from this state, and at the same time, the switch 28 is closed, and a high frequency current from the high frequency AC power supply 30 flows through the fixed mold 14 and the movable mold 18. The high frequency current flows mainly through the surfaces of the fixed mold 14 and the movable mold 18. Therefore, the cavity surfaces of the fixed mold 14 and the movable mold 18 are heated by Joule heat and their temperature increases. The switch 28 is opened immediately before the fixed mold 14 and the movable mold 18 come into contact with each other, and the supply of high frequency current to the fixed mold 14 and the movable mold 18 is stopped. After the mold is closed, mold clamping is performed, and then molten resin is injected from the injection unit 34 and pressure is held. Since the cavity surfaces of the fixed mold 14 and the movable mold 18 are heated as described above, the molten resin flows smoothly in the cavities and is rapidly filled. When the pressure holding process is completed, a refrigerant is flowed through cooling holes (not shown) in the fixed mold 14 and the movable mold 18 to cool and plasticize the molded product in the cavity.Then, the mold is closed and the molded product is ejected. As a result, one molding cycle is completed and the state shown in FIG. 1 is restored.

As mentioned above, only the surfaces of the fixed mold 14 and the movable mold 18 are heated by the high-frequency current, so the molten resin is maintained in a highly fluid state during injection and pressure retention, and the resin pressure is relatively low and the temperature is increased for a short time. The cavity is filled within a short period of time. In addition, since only the surfaces of the fixed mold 14 and the movable mold 18 are heated, the fixed mold 14 and the movable mold 18 are heated even during cooling.
It is only necessary to remove the heat from the surface of the device, and it becomes possible to cool the device in a short period of time. Therefore, compared to the conventional case of heating the entire mold using a heat medium, for example,
As shown in Figure 2, the time for the injection and pressure holding processes is somewhat shortened, the time for the cooling process is also significantly shortened, and heating can also be done at the same time as mold closing, so that Δ can be achieved in one molding cycle. Only the time is reduced. This greatly improves productivity. Furthermore, since the amount of heat supplied to and removed from the mold is significantly reduced, the life of the mold is extended.

(f) As explained in detail, according to the present invention, only the surface of the mold is heated by high-frequency current, so it is possible to shorten the molding cycle and improve productivity. The life of the mold can be extended.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an apparatus for implementing the method of the present invention, and FIG. 2 is a diagram showing a molding cycle of the method of the present invention in comparison with a conventional method. 12...Fixed plate, 14...Fixed type, 16...Movable plate, 18...Movable type, 20.22...Electrical insulating plate,
24a, 24b...*electrode, 26a, 26b***electrode, 28---, switch, 30...high frequency AC power supply, 3
4... Injection unit.

Claims (1)

[Claims] In the molding method for thin-walled molded products, which consists of the steps of mold closing, injection, holding pressure, cooling, mold opening, and ejection, the fixed mold and movable mold are electrically insulated from the fixed platen and movable platen, respectively, before mold closing is completed. A method for forming a thin-walled molded product, which is characterized by passing a high-frequency current at the step of heating the surfaces of a fixed mold and a movable mold using Joule heat.