JP2000218356A - Rapid heating method of light metal injection molding die, and light metal injection molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heating method of a light metal injection molding die, and a light metal injection molding method, for reducing occurrence ratio of molding failures due to the temperature of a molding die. SOLUTION: Just before a molten metal is injected, a coil 3 for induction heating is inserted between a fixed die 1 and a movable die 2 which are in a die opening condition, and a current is applied under a condition that the coil 3 is brought into close contact with cavity surfaces 4 of the fixed die 1 and the movable die 2. Thereby, an eddy current is generated in a die 5, so as to rise the temperature of the cavity surfaces 4 only to a given temperature in a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for rapidly heating a light metal injection molding die and a method for light metal injection molding using the method.

[0002]

2. Description of the Related Art Injection molding of light metals such as magnesium alloys and aluminum alloys includes a die casting method and a thixomolding method. In both methods, a molten metal heated to a predetermined molten state is filled into a mold cavity at a high speed to obtain a molded product. The temperature of the molten metal varies depending on the type of alloy, but is about 600 ° C., while the cavity surface of the mold is about 150 ° C.
250 ° C. Therefore, the temperature difference between the molten metal and the surface of the mold cavity becomes extremely large, and the molten metal flowing into the mold cavity solidifies in a short time of several ms to several tens of ms and stops flowing. If the molten metal solidifies and stops flowing before the cavity is completely filled, molding defects such as poor filling or welding occur. Therefore, in order to suppress such molding defects, it is important to increase the solidification time of the molten metal, that is, to reduce the temperature difference between the molten metal and the cavity surface of the mold. It is effective to raise the temperature of the cavity surface of the mold.

[0003] There are mainly two methods for heating the cavity of a mold. One is to incorporate an electric heater and a thermocouple for temperature measurement inside the mold, and determine the heater operation amount by PID control or the like from the difference between the temperature measurement result by the thermocouple and the set temperature, and By energizing the heater for the voltage or time, the mold is set to the set temperature. The other is to maintain the mold at a constant temperature by installing a flow path inside the mold and circulating a heating medium oil heated to 150 ° C. to 300 ° C. therein. In addition,
In these mold heating methods, not only the mold cavity but also the entire mold including the main mold is maintained at a constant temperature.

[0004] As described above, increasing the temperature of the cavity surface of the mold is an effective means for suppressing molding defects. FIG. 3 shows the result of calculating the solidification time of the molten metal in the cavity of the mold by the solidification analysis. According to this figure, the temperature of the cavity surface of the mold is 350 ° C. to 400 ° C.
The solidification time of the molten metal becomes 1.5 to 3 times longer than the current state. Therefore, if the temperature of the cavity surface is increased, the solidification time is prolonged, and the incidence of molding defects can be reduced. Further, when the solidification time is longer, the same molded product can be molded with a smaller injection rate, and can be molded with a lower injection speed or a small molding machine.

[0005]

However, when the mold temperature is increased from 350 ° C. to 400 ° C. by the above-described heating method, the following adverse effects occur. (A) Galling or seizure of the sliding part of the mold (slide core, ejector pin, etc.) (b) Repelling of the release agent on the cavity surface (c) Deformation of the molded product at the time of protruding This is caused by raising the temperature of the entire mold, and is caused by a difference in thermal expansion between sliding parts due to uneven temperature of the mold. (B) is that when a water-soluble release agent is applied to the cavity surface, the release agent boils and evaporates instantly without forming a liquid film on the cavity surface, and the release agent is effectively applied. Is a phenomenon that cannot be done. As a result, the molded product cannot be released from the cavity surface, and defects such as deformation occur. In (b), since a light metal such as a magnesium alloy or an aluminum alloy has a low strength at a high temperature, the molded product is deformed when protruding.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a light metal injection molding die capable of reducing the incidence of defects in a molded product due to the temperature of the molding die. It is an object to provide a heating method and a light metal injection molding method.

[0007]

In order to overcome the above-mentioned problems, the temperature of the whole cavity of the mold is brought into direct contact with the molten metal, instead of raising the temperature of the whole mold as described in the prior art. Only the temperature needs to be increased. That is, the above problem can be overcome by raising the cavity surface of the mold to a predetermined temperature immediately before injection of the molten metal and cooling the surface to a temperature at which the mold can protrude during the cooling time after injection filling. Specifically, a coil for induction heating is inserted between the fixed mold and the movable mold that are in the mold open state just before the injection of the molten metal,
The coil is energized in a state where it is brought close to the surfaces of the fixed and movable cavities. As a result, an eddy current is generated in the mold, and the temperature of the cavity surface is increased in a short time.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on embodiments with reference to the drawings.

As shown in FIG. 1, an apparatus used for controlling the temperature of the cavity surface 4 of the mold 5 includes an induction heating power source 6, a coil 3, and a power supply used for directly heating the cavity surface 4 of the mold 5. An air cylinder or the like (not shown) for moving the coil 3, a heat medium oil temperature controller 7 used for preheating and cooling the cavity surface 4 of the mold 5, a switching electromagnetic valve 8, and the like.

Next, a rapid heating method for a light metal injection mold and a light metal injection molding method using the method will be described.
This will be described with reference to the flowchart of FIG. 2 based on (a) to (d) of FIG. (A) When the circulation of the heating medium oil is started and the temperature of the cavity surface 4 of the mold 5 is about 200 ° C., the release agent spraying device 1
A mold release agent is sprayed from 2 toward the cavity surface 4 (step S1). (B) Then, immediately before the injection of the molten metal, the coil 3 for induction heating is inserted between the fixed mold 1 and the movable mold 2 in the mold open state (step S2), and fixed at a position close to the cavity surface 4. . Then, an AC current having an appropriate frequency is applied to the coil 3 from the induction heating power supply 6 to generate an eddy current inside the mold 5 and directly heats a position which has penetrated 0 to 5 mm from the cavity surface 4 (step S3). ). At this time, a thermocouple 9 is placed at a depth of 1 mm from the cavity surface 4 and heating is performed for about 1 to 30 seconds until the measured value rises to 350 ° C to 400 ° C. Immediately after the completion of the heating, the coil 3 is moved out of the mold 5 (Steps S4 and S5). (C) Next, mold closing, mold closing, injection, and pressure holding operations are performed (steps S6 and S7). During the cooling step after completion of the pressure-holding operation, heat medium oil at about 200 ° C. is circulated through the flow path 10 provided in the mold 5 to cool the cavity surface 4 and the molded product 11 (Step S8). (D) Then, the temperature indication value by the thermocouple 9 is:
When the temperature drops to about 150 ° C to 250 ° C, open the mold,
The projecting operation of the molded article 11 is performed (step S9), and the circulation of the heat medium oil is stopped to stop the cooling of the mold 5 (step S10). By repeating the above operation, molding is performed while controlling the temperature of the cavity surface 4.

When a personal computer case was molded using a magnesium alloy AZ91D by a conventional mold heating method (mold temperature of 220 ° C.) using a light metal injection molding machine having a mold clamping force of 450 Ton, the overflow side caused a defective filling. Many molding defects occurred, and the defect rate at this time was about 50%.
Then, when the temperature of the cavity surface 4 of the mold 5 immediately before injection was adjusted to 350 ° C. by the method of the present invention, molding defects were improved, molding defects were reduced, and the defect rate was reduced to 5%.

In the above embodiment, the preheating of the mold is performed by circulating the heat medium oil in the mold, but may be performed by burying a cartridge heater. Further, in the above embodiment, the mold is cooled by the heat medium oil, but may be cooled by circulating cooling water or cooling gas in the mold. When a cartridge heater is used for preheating the mold, it is performed by circulating heat medium oil, cooling water, cooling gas, or the like in the mold. When circulating cooling water or cooling gas in the mold, it is necessary to separately provide a cooling circuit in the mold. That is, the mold preheating means and the cooling means may be the same or separate.

[0013]

Since the method of the present invention is configured as described above, the following effects can be obtained. (A) Since the temperature of the cavity surface of the mold immediately before the injection of the molten metal is high, the solidification time of the molten metal is prolonged, and the incidence of molding defects can be reduced. (B) Since the temperature of the entire mold can be maintained at about 200 ° C., each part can be slid, and the temperature of the cavity surface when spraying the release agent is also about 200 ° C. No problem arises. (C) In addition to being able to effectively apply the release agent, the cooling circuit provided in the mold can lower the temperature at which the molded product is taken out, thereby eliminating problems such as deformation due to protrusion of the molded product. (D) While preventing the adverse effects of increasing the mold temperature,
By heating only the cavity surface of the mold, molding defects can be significantly reduced. (E) Since the injection speed can be reduced, burrs are reduced and post-processing is facilitated. Further, a product which could not be molded unless a large molding machine was used until now can be molded by a small molding machine, and costs can be reduced.

[Brief description of the drawings]

FIG. 1 is an operation diagram of an apparatus for implementing a method of the present invention.

FIG. 2 is a flowchart for explaining the operation of the device shown in FIG.

FIG. 3 is a diagram showing a relationship between a mold temperature and a solidification time of a molded product.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixed type 2 Movable type 3 Coil 4 Cavity surface 5 Die 6 Induction heating power supply 7 Heat medium oil temperature controller 8 Switching electromagnetic valve 9 Thermocouple 10 Channel 11 Molded product 12 Mold spray agent

Claims (3)

[Claims] 1. A coil (3) for induction heating is inserted between a fixed mold (1) and a movable mold (2) which are in a mold open state immediately before injection of molten metal, and the coil (3) is fixed ( An electric current is generated in the mold (5) by energizing in a state in which the cavity surface (4) of the movable die (1) and the movable die (2) are brought close to each other. A method for rapidly heating a light metal injection molding die, wherein the temperature is raised to a temperature. 2. A cavity surface (4) is preheated by a preheating means provided in a mold (5), and after a mold release agent is sprayed on the cavity surface (4), the mold is in an open state immediately before injection of molten metal. A coil (3) for induction heating is inserted between the fixed mold (1) and the movable mold (2), and the coil (3) is placed on the cavity surface (4) of the fixed mold (1) and the movable mold (2). By energizing in the proximity state, an eddy current is generated in the mold (5), and only the cavity surface (4) is heated to a predetermined temperature in a short time, and then the coil (3) is removed from the mold. After the mold is closed, the molten metal is injected and the pressure is maintained, the cavity surface (4) is cooled to a predetermined temperature by cooling means provided in the mold (5).
A light metal injection molding method characterized in that a mold (5) is opened and a molded product (11) is protruded. 3. The light metal injection molding method according to claim 2, wherein the temperature of the cavity surface (4) is controlled by the cooling means so as to be lower during cooling than during preheating.