JPH06134815A - Method for accurately casting simplified injection mold - Google Patents

Abstract

PURPOSE:To minimize an occurrence of an internal strain to prevent an occurrence of a warpage and a sink mark to enhance the accuracy by a method wherein a plaster casting mold is heated to a melting point or thereabouts of a low-melting alloy in a heater form, the low-melting alloy is cased into the heater form, the temperature of the heater form is lowered to a specific point in a specific cooling pattern, and thereafter the casted piece is naturally cooled. CONSTITUTION:A plaster casting mold 11 with an insulating plate 12 disposed under the bottom surface thereof is sucked by a vacuum pump 13. Succeedingly, a low-melting alloy 14, e.g. a zinc, reaching its melting temperature is casted into a heater form 10. After that, the temperature of the heater form 10 is kept at the melting point for 10 minutes, thereafter being lowered stepwise by 10 deg.C at an interval of 10 minutes. After the heater form 10 is cooled to 200 deg.C, an electric conduction is interrupted, and the low-melting alloy 14 is kept to be naturally cooled. A simplified injection mold 16 is obtained by detaching the heater form 10 and removing the plaster casting mold 11 from the low-melting alloy 14 cooled and set. The low-melting alloy 14 cooled to approximately 200 deg.C never generates a significant internal strain even after being naturally cooled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a precision casting method for simple injection molding.

[0002]

2. Description of the Related Art Conventionally, a method generally used to manufacture a mold for injection molding is to make a hard metal which is hard to process by cutting with an NC processing machine. It took a huge amount of processing time and the mold was very expensive. For this reason, if a mold is manufactured to mold a few products such as prototypes, and injection molding is performed using the mold, there is a big problem that the price of the prototype is soared and the trial period becomes long. Was there. Therefore, as a method for solving the above problems and manufacturing a die inexpensively in a short time, for example, there is a method for producing a simple mold for synthetic resin molding disclosed in Japanese Patent Publication No. 3-39776.
According to this production method, a step of molding a prototype of a product with silicone rubber and then curing the silicone rubber mold to form a silicone rubber mold; A step of forming a green mold, a step of firing the gypsum green mold to form a gypsum mold, the gypsum mold on a shelf of a formwork having a vacuum exhaust port in the lower part and a breathable shelf plate above it. Placing the molten metal of the low melting point alloy into the mold while evacuating from the vacuum exhaust port and casting it based on the gypsum mold, and removing the mold after cooling and solidifying the cast low melting point alloy and plaster The above-mentioned simple mold is prepared from the process of removing the mold to obtain a low melting point alloy mold obtained by molding the prototype.

[0003]

However, according to the above-described method for making a simple mold, vacuum casting is carried out through a gypsum mold having air permeability so that the details of the gypsum mold can be glazed for accurate mold making. However, there were problems in the following points. When the low melting point alloy (melting point 380 ° C. in the example) is poured into the gypsum mold and the mold, the cooling rate of the low melting point alloy is in the vicinity of the part that is in contact with the gypsum mold and the mold and in the part away from the gypsum mold and the mold. However, internal strain is accumulated inside the low melting point alloy when it is solidified by cooling, and defects such as warpage and sink marks are generated, which is a cause of lowering the precision as a molding die.

The present invention has been made in view of the above-mentioned problems of the prior art. The gypsum mold is heated to a temperature near the melting point of the low melting point alloy by the heater form, and the low melting point alloy is injected into the heater form. After that, by gradually lowering the temperature of the heater mold in a predetermined cooling pattern, quenching of the low melting point alloy is prevented, internal strain is suppressed as much as possible, warpage and sink marks can be practically ignored, and the low melting point alloy is uniform. An object of the present invention is to provide a simple precision casting method for injection molding, which is capable of contracting to obtain a highly accurate mold.

[0005]

In order to achieve the above object, the present invention relates to a step of forming a silicone rubber mold by molding a prototype of a product with a silicone rubber and then curing the silicone rubber mold to form a refractory material. A step of injecting a gypsum slurry in which powder is mixed and then hardening to form a gypsum green mold, a step of firing the gypsum green mold to form a gypsum mold, and placing the gypsum mold in a mold to lower the In a method of casting a simple mold for injection molding, which comprises the steps of injecting a molten metal of a melting point alloy into a mold and cooling and solidifying the cast low melting point alloy, and removing the mold and the gypsum mold, a gypsum mold is a heater mold. After heating to near the melting point temperature of the low melting point alloy, the low melting point alloy is injected into the heater mold, then the temperature of the heater mold is lowered to about 200 ° C. in a predetermined cooling pattern, and then naturally cooled. Return to room temperature And the.

[0006]

According to the above construction, after heating the gypsum mold and the heater mold to the melting point temperature of the low melting point alloy, the low melting point alloy is injected and then the temperature of the heater mold is lowered according to a predetermined cooling pattern. Thereby, quenching of the low-melting point alloy is prevented, and the difference in cooling rate of the low-melting point alloy in the part that is in contact with the gypsum mold and the part that is distant does not increase,
Can cast simple molds with high dimensional accuracy.

[0007]

Example 1 FIG. 1 is a diagram showing a molding process of Example 1 of the present invention. First, as shown in (a), the parting line P. L is determined and fixed on the block 2. Subsequently, the block 2 is surrounded on its four sides by a mold 3 as shown in (b), and silicone rubber 4 is injected into the mold 3 at 25 ° C.
After being left to cure for about 12 hours, the mold 3 is removed and the master 1 is extracted to obtain the silicone rubber mold 5 shown in (c).

Next, the silicone rubber mold 5 is surrounded on its four sides by a mold 6 as shown in (d), and a gypsum slurry 7 containing refractory powder is poured into the mold 6 and left at room temperature for about 1 hour. Cured. Here, the gypsum slurry 7 is 100 wt% of a refractory powder gypsum JK-2 (manufactured by Taisei Chemical Co., Ltd.).
% Of water was used to obtain a bubble-free filling type. Then, the mold 6 is removed and the silicone rubber mold 5 is pulled out to obtain a gypsum green mold 8. continue,
As shown in (e), the mold 9 is assembled to the plaster green mold 8,
As shown in (f), it is surrounded by a heater mold 10. Then, the temperature of the gypsum mold 8 and the mold 9 is heated by the heater mold 10 to 400 ° C., which is slightly higher than the melting point temperature of the low melting point alloy, and the gypsum mold 11 is fired. Furthermore, gypsum mold 1
A heat insulating plate 12 is placed on the bottom surface of No. 1 and the gypsum mold 11 is sucked by a vacuum pump 13, and subsequently, a low melting point alloy 14 having a melting point temperature is injected into the heater mold 10. In this embodiment, zinc is used as the low melting point alloy 14, and its melting point is about 400 ° C.

After the injection of the low melting point alloy 14 is completed, FIG.
As indicated by A, the temperature of the heater mold 10 is kept at 400 ° C. for 10 minutes, and then gradually lowered by 10 ° C. at 10 minute intervals. After lowering the temperature of the heater mold 10 to 200 ° C., the electric conduction to the heater mold 10 is cut off and the natural cooling state is maintained. After the low melting point alloy 14 is cooled and solidified, the heater mold 10 is removed and the gypsum mold 11 is removed. As shown in FIG. The simplified mold 16 is obtained. Also, a simplified type on the core side can be obtained by a similar method. That is, this mold can be mounted on the movable side and the fixed side of the injection molding mold. 2B shows a conventional cooling state.

According to the present embodiment, the gypsum mold 11 and the heater mold 10 are heated to near the melting point of the low melting point alloy 14 to be injected, and after the low melting point alloy 14 is injected, the temperature is gradually raised to about 200.degree. And then it is naturally cooled. The reason why the temperature is set to about 200 ° C. is that even if the low-melting point alloy 14 is naturally cooled thereafter, the internal strain of the low-melting point alloy 14 no longer occurs to the extent of causing a problem. In this way, the internal strain is generated in the low melting point alloy 14 by minimizing the temperature difference between the portion in contact with the mold 9 and the gypsum mold 11 and the inside of the low melting point alloy 14 during the cooling process. By preventing this, even in the case of the plaster mold 11 having a complicated shape, the details of the mold can be surely glazed and the reversal of the mold shape is good, and the warp and sink can be suppressed to a practically negligible level. it can. Further, since the low melting point alloy uniformly contracts, it is possible to obtain a highly accurate simple mold 16 for injection molding.

[0011]

[Embodiment 2] FIG. 3 is a sectional view showing injection of a low melting point alloy in Embodiment 2 of the present invention. In this embodiment,
The steps from fixing the master 1 on the block 2 to enclosing the gypsum green mold 8 with the heater mold 10 are the same as in the first embodiment. Thereafter, as shown in FIG. 3, the plaster green mold 8 together with the heater mold 10 was set in the vacuum furnace 17, and the temperature of the mold 9 was 400 ° C.
The gypsum mold 11 is fired by heating with the heater mold 10 until it becomes. Subsequently, while the vacuum pump 18 is evacuating the vacuum furnace 17, the low melting point alloy 14 having reached the melting point temperature is injected into the mold 9. Then, as shown in the cooling pattern indicated by A in FIG.
Hold the temperature for a minute, and then gradually lower the temperature by 50 ° C. every hour. After holding the heater mold 10 at 200 ° C. for 1 hour, the heater frame 10 is de-energized to maintain the natural cooling state. After the low melting point alloy 12 is cooled and solidified, a vacuum pump 18
Then, the air is sent into the vacuum furnace 17. Next, by removing the heater mold 10 and the mold 9 and removing the gypsum mold 11, a simple mold for injection molding having an outer shape cavity of the master mold formed of the low melting point alloy 14 can be obtained.

According to this embodiment, the temperature difference between the portion of the low melting point alloy 14 in contact with the mold 9 and the gypsum mold 11 and the inside can be made extremely small as in the case of the first embodiment. External cooling strain can be relaxed. Further, by injecting the low-melting point alloy 12 in a reduced pressure atmosphere, the inclusion of air is eliminated, and the combined effect of improving the hot water flow can be obtained. As a result, the mold shape can be copied more accurately than in the first embodiment. In this way, it is possible to obtain a simple mold for injection molding in which the occurrence of internal strain is suppressed as much as possible and warpage and sink marks can be practically ignored. In each of the above embodiments, when the low melting point alloy 14 is cooled, the upper heater plate can be used together, which further increases the solidification of the low melting point alloy 14 as a whole and further improves the accuracy of injection molding. A simple type can be obtained.

[0013]

As described above, according to the present invention, after the gypsum mold and the mold are surrounded by the heater mold and heated to near the melting point temperature of the low melting point alloy, the low melting point alloy which has reached the melting point temperature is injected. Since the temperature of the heater mold is gradually reduced by a predetermined cooling pattern, the injected low melting point alloy is not cooled rapidly but is gradually cooled, so that the occurrence of internal strain is suppressed as much as possible, and the gypsum mold It is possible to obtain a simple mold for injection molding in which the hot water wraps around to the details and has extremely high dimensional accuracy even in a complicated shape and has no warp or sink mark.

[Brief description of drawings]

FIG. 1 is a diagram showing a molding process of Example 1 of the present invention.

FIG. 2 is a diagram showing a cooling pattern of a heater mold according to the first embodiment.

FIG. 3 is a diagram showing one molding step of Example 1 of the present invention.

FIG. 4 is a diagram showing a cooling pattern of a heater mold according to the second embodiment.

[Explanation of symbols]

 1 Prototype 3 Silicone rubber 5 Silicone rubber mold 7 Gypsum slurry 8 Gypsum raw form 9 Form 10 Heater form 11 Gypsum mold 14 Low melting point alloy 16 Simple mold for injection molding A Cooling pattern

Claims (1)

[Claims] 1. A step of forming a silicone rubber mold by molding an original mold of a product with silicone rubber and then curing the same, and injecting a gypsum slurry containing a refractory powder into the silicone rubber mold and then curing the gypsum raw material. A step of forming a mold, a step of firing the gypsum green mold to form a gypsum mold, and a low melting point cast by pouring a melt of a low melting point alloy into the mold by placing the gypsum mold in the mold In the method of casting a simple mold for injection molding, which comprises the step of removing the mold and the gypsum mold after the alloy has been cooled and solidified, after heating the gypsum mold to a temperature near the melting point of the low melting point alloy with a heater mold, the low melting point alloy Is injected into the heater mold, the temperature of the heater mold is then lowered to approximately 200 ° C. in a predetermined cooling pattern, and then it is naturally cooled to room temperature, followed by precision casting of a simple mold for injection molding. Method.