JPH01313124A - Method for forming pattern - Google Patents

Abstract

PURPOSE:To facilitate forming of a pattern and to improve the quality of a product by holding a core composed of shape memory plastics in a metallic mold, pouring foaming resin to form the pattern and successively, heating the core in the pattern taken out. CONSTITUTION:The same shape as the pattern to be formed, is memorized to the shape memory plastics to form the core 1. This core 1 is held in the metallic mold 2 and foaming resin beads are included at space 3 between the outer face of the core 1 and the inner face of the metallic mold 2 and high temp. steam is poured from pipes 5 to form lost foam pattern 4. Successively, the lost foam pattern 4 together with the core 1 are taken out from the metallic mold 2, and the core 1 is heated to more than shape restoration temp. The core 1 is easily softened at this temp. and taken out from the pattern 4 and further, reused. As the core is formed with the shape memory plastics, the formation of the pattern is facilitated and the quality of the product is improved with the improvement of the accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for molding a model for casting hollow-shaped castings, and more particularly, to a method for forming a model for casting hollow-shaped castings. This invention relates to a method for forming a fugitive model.

Prior Art When mass producing cast products, it is common to use molds, but since molds are expensive, it is difficult to make molds when producing small to medium quantities of cast products. It is uneconomical to cast. Therefore, a fugitive model made of foamed polystyrene or the like with a shape corresponding to that of the article to be cast is placed in a casting flask, filled with sand, applied vibrations and pulled under reduced pressure to form a sand mold. A method often used is to set a fugitive model in a mold, pour molten metal into the model, and replace the model with the molten metal while melting the model to perform casting. According to this method, casting can be performed without using expensive molds,
It has the advantage of being economical.

When casting a cast product having a hollow part using a fugitive model as described above, it is necessary to mold a fugitive model having a hollow part. However, when the shape of the cast product to be cast is simple, it is not difficult to integrally mold such a fugitive model, but when the shape of the cast product to be cast is complex. Correspondingly, the shape of the evanescent model becomes complicated, and it is difficult to mold the model in one piece.So, the split models on two sides are molded separately and then glued together. A vanishing model was being formed (
For example, JP-A-61-169133, JP-A-6
1-169134, etc. ).

Problems to be Solved by the Invention However, when the split models on the two sides are molded separately and then glued together to form a fugitive model, the split models on the two sides are integrally formed. of! , [It is difficult to adhere accurately as shown in the figure, and the adhesive often becomes misaligned, the adhesive protrudes, or is missing, or the entire model is deformed, making it impossible to achieve the desired shape. There was a problem in that it was difficult to cast a cast product with high precision.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a method for molding a model that can accurately cast a hollow-shaped cast product.

Structure of the Invention This object of the present invention is achieved by molding a fugitive model using a core made of shape memory plastic.

A first aspect of the present invention is to hold a core made of shape memory plastic in a mold, which memorizes the same shape as the hollow part of the model to be molded, and to fill the space between the core and the mold with This method of molding a model consists of injecting foamed resin to mold the model, removing the model and core from the mold after molding, heating the core, and removing it from the model.

A second aspect of the present invention is to mold a core made of shape memory plastic that remembers a shape that is easy to remove from a model to be molded into the same shape as the hollow part of the model to be molded and hold it in the mold. , a model is formed by injecting foamed resin into the space between the core and the mold, and after molding, the model and core are removed from the mold, and the core is heated to restore the memorized shape. ,
This is a method of molding a model that involves removing it from the model.

In the first aspect of the present invention, in which the model is integrally molded using a core made of shape memory plastic that memorizes the same shape as the hollow part of the model to be molded, even complex shapes can be memorized in the shape memory plastic. Shape memory plastics can also be heated to a certain temperature to
Although it has the property of restoring to its memorized shape, it softens when heated to a temperature lower than the memorized shape restoring temperature, so even cores with complex shapes can be heated to the memorized shape restoring temperature after molding the model. By heating to a lower temperature, it can be easily removed from the model, so even models with hollow parts with complex shapes can be easily molded into one piece, and even after being removed from the model. By heating the core made of shape memory plastic to the memory shape recovery temperature and rapidly cooling it, it can return to the shape it was in when it was molded and maintain that shape, so it can be used repeatedly for molding models. I can do it.

In the second invention of the present invention, in which the model is integrally molded using a core made of shape memory plastic that memorizes a shape that is easy to remove from the model to be molded, the core becomes soft when heated to a temperature lower than the memorized shape restoration temperature, Utilizing the property of shape memory plastic, which solidifies when rapidly cooled, first, a core made of shape memory plastic that has a memorized shape that can be easily removed from the model to be molded is heated to a temperature lower than the memory shape restoration temperature to soften it. In this state, the core is molded into the same shape as the hollow part of the model to be molded, and then rapidly cooled to form a core with the same shape as the hollow part of the model to be molded, so it is possible to mold the core into the same shape as the hollow part of the model to be molded. The core can also be easily molded, and the molded core can be used to mold a model, and after molding the model, the core can be heated to a memory shape restoration temperature, making it easy to remove from the model. Since the core is restored to its shape and removed from the model, even complex-shaped cores can be easily removed from the model, so even models with complex-shaped hollow parts can be easily integrally molded. becomes possible.

In the present invention, the material for the fugitive model is not particularly limited as long as it can maintain a certain shape and dissolves and disappears in the molten metal, but foamed polystyrene, foamed polyurethane, foamed polyethylene, etc. are preferably used. It is possible.

In the present invention, in order to prevent the core from being heated and softened by the heat of the supplied steam during model molding,
It is desirable that the core has a hollow structure so that a cooling medium such as water can flow therein and steam can be discharged through the hollow part. Further, in order to discharge steam, it is desirable to provide a plurality of small holes on the surface of the core to guide the steam to the hollow portion.

In the present invention, instead of making the core a hollow structure and flowing a cooling medium inside it, or in addition to this, a heat insulating layer made of a heat insulating material is provided on the surface of the core, and during model molding,
It is also possible to prevent the core from being heated and softened by the heat of the supplied steam. In this case, before providing the heat insulating layer, a coating agent may be applied to the surface of the core, and only the core may be removed from the model, leaving the coating agent layer on the inner surface of the hollow part of the model. . By doing so, even if the hollow part of the model has a complicated shape, the mold coating agent can be easily applied to the inner surface of the hollow part. As the heat insulating material, silicone rubber, alumina slurry kneaded with vinyl acetate, etc. can be suitably used. In addition, a mold coating agent is applied to the surface of the model prior to casting, and the mold coating agent that can be used in the present invention has shape-retaining power itself, does not permeate the molten metal, and is suitable for coating the model. There are no particular limitations on the material as long as it permeates the gas generated when the material is dissolved, but materials containing silicon oxide as a main component, particularly those consisting of silicon oxide and zirconium oxide, etc. can be preferably used.

EXAMPLES Hereinafter, examples of the present invention will be described in detail based on the accompanying drawings.

FIG. 1 is a schematic diagram showing the steps of a model molding method according to an embodiment of the present invention.

As shown in FIG. 1(a), first, the shape memory plastic is made to memorize the same shape as the model to be molded,
Molding core 1. The core 1 thus obtained is placed in a mold 2, with a space having the same shape as the model to be molded between its outer surface and the mold 2, as shown in FIG. 1(b). It is set to form 3. Next, Figure 1 (
As shown in C), expanded polystyrene beads are placed in the space 3 and steam is supplied to form the fugitive model 4.

FIG. 2 is a schematic cross-sectional view of the model forming apparatus according to the embodiment of the present invention, showing details during forming of the fugitive model 4.
is provided in the mold 2, and through this pipe 5, steam is supplied to the space 3 for foaming the beads and forming the fugitive model 4. Moreover, the core 1 has a hollow structure,
As shown by arrow A, a cooling medium such as water is flowed through the hollow part 6 to prevent the core 1 from being heated and softened by the heat of the steam during model molding. . A large number of small holes 7 are provided on the surface of the core 1, and steam is discharged from the hollow part 6 of the core 1 to the outside through these holes.

When the fugitive model 4 is molded in this way, FIG. 1(d)
As shown in , the fugitive model 4 is attached to the mold 2 together with the core l.
taken from. Next, as shown in FIG. 1(e), the core 1 is heated to a temperature below the shape-recovery temperature of the shape memory plastic forming the core 1. Since shape memory plastic has the property of softening when heated to a temperature below its shape restoration temperature, the core 1 can be easily removed from the fugitive model 4.

In this way, the core 1 removed from the fugitive model 4 is heated to the shape-recovery temperature of the shape memory plastic before reuse, and then rapidly cooled to form the hollow part of the fugitive model 4 to be molded. It can be easily returned to the same shape.

According to the above embodiment, since shape memory plastic is used as the core l for molding the hollow part of the fugitive model 4, even if the hollow part of the fugitive model 4 has a complicated shape. , the core 1 can be easily formed, and after molding the fugitive model 4, the core 1 is heated to a temperature below the shape-recovery temperature of the shape-memory plastic by utilizing the properties of the shape-memory plastic. As a result, the core 1 is softened and removed from the fugitive model 4, so even if the core 1 has a complicated shape, the core 1 can be easily removed from the fugitive model 4. Therefore, even the fugitive model 4 having a hollow part and having a complicated shape can be easily and integrally molded, and as a result, a cast product having a hollow part can be accurately cast into a desired shape. I can do it.

Furthermore, when the core 1 is to be used again for molding the fugitive model 4, it is sufficient to simply heat the core 1 to the shape restoration temperature of the shape memory plastic.
can be used repeatedly.

FIG. 3 is a schematic cross-sectional view of a model forming apparatus according to another embodiment of the present invention. In FIG. 3, a heat insulating layer 8 made of a heat insulating material such as silicone rubber is provided on the surface of the core 1.
The core 1 is prevented from being heated and softened by the heat of steam during model molding. If a mold coating agent is applied to the surface of the core 1 before providing the heat insulation layer 8 on the surface of the core 1, this will act as a mold release agent between the core 1 and the heat insulation layer 8 and disappear. After molding the plastic model 4, only the core 1 is molded into the plastic model 4.
Not only is it easy to remove the mold from the core 1, but there is no need to reapply the mold coating to the inner surface of the fugitive model 4, and it is easy to apply the mold coating to the outer surface of the core 1.
Even when the inner surface of the hollow part of the fugitive model 4 has a complicated shape, it becomes possible to easily apply a mold coating agent to the surface of the fugitive model 4 prior to casting. Further, a large number of small holes 7 are provided on the surface of the core 1 and in the heat insulating layer 8, and steam is guided into the hollow part 6 of the core 1 through the holes 7 and is discharged. In this embodiment, since heating of the core 1 is prevented by the heat insulating layer 8, there is no need to flow a cooling medium into the hollow portion 6 of the core 1.

FIG. 4 is a schematic perspective view showing another example of the core 1 used in the embodiment of the present invention. The core 1 in Fig. 4 is shown in Fig. 4(a).
As shown in FIG. 2, a shape that allows the core 1 to be easily removed from the fugitive model 4 after the fugitive model 4 is molded is memorized in advance. As shown in FIG. 4, etc., the core 1 is first molded into the same shape as the hollow part of the fugitive model 4 to be molded, before being set in the mold 2.

In molding, the property of shape memory plastics is utilized, that when heated to a temperature below the shape restoration temperature, it softens, and after being molded into a certain shape, it retains that shape when rapidly cooled. First, the shape memory plastic forming the core 1 is heated to a temperature below the shape recovery temperature to soften it, and in this state is molded into the same shape as the hollow part of the fugitive model 4 to be molded. By quenching, the same shape as that of the hollow part of the fugitive model 4 is maintained, and the model is set in the mold 2. In this way, the fugitive model 4 is molded in the same manner as in the embodiments shown in FIGS. 1 to 3, and after being taken out from the mold 2 together with the fugitive model 4, The core 1 is heated to a shape restoration temperature of . Since the core 1 has a pre-memorized shape that allows it to be easily removed from the fugitive model, the heating restores the memorized shape and allows it to be easily removed from the fugitive model 4. I can do it.

In this embodiment as well, shape memory plastic is used as the core 1 for molding the hollow part of the fugitive model 4, so even if the hollow part of the fugitive model 4 has a complicated shape, it can be easily molded. The core 1 can be formed in the core 1.
Since the shape memory plastic constituting the fugitive model 4 has a pre-memorized shape that allows the core 1 to be easily removed from the fugitive model 4, the core 1 can be removed after the fugitive model 4 is molded.
Even if the core 1 has a complicated shape, it can be heated to the shape-recovery temperature of the shape memory plastic.
It can be easily removed from the fugitive model 4, so even the fugitive model 4 having a hollow part and a complicated shape can be removed.
It becomes possible to easily perform integral molding, and as a result, it is possible to accurately cast a cast product having a hollow part into a desired shape.The present invention is not limited to the above-described embodiments, but also includes the patent claims. It goes without saying that various modifications can be made within the scope of the invention described in the scope, and these are also included within the scope of the present invention.

Effects of the Invention According to the present invention, a fugitive model having a hollow part can be easily created.
Since it can be integrally molded, it becomes possible to accurately cast a cast product having a hollow portion.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the steps of a model molding method according to an embodiment of the present invention. FIG. 2 is a schematic sectional view of a model forming apparatus according to an embodiment of the present invention, and FIG. 3 is a schematic sectional view of a model forming apparatus according to another embodiment. FIG. 4 is a schematic perspective view showing an example of the core 1 used in the embodiment of the present invention. ■...core, 2...mold, 3...space, 4...disappearance model, 5...vibrator,
6...Hollow part, 7...Small hole, 8.
...insulation layer. Figure 1 (a) (b) (c) 2nd diagram 3rd diagram number Figure 4 (a) (b)

Claims (2)

[Claims] (1) A core made of shape memory plastic that memorizes the same shape as the hollow part of the model to be molded is held in the mold,
A foamed resin is injected into the space between the core and the mold to form a model, and after molding, the model and the core are removed from the mold, and the core is heated. A method for molding a model, the method comprising removing the model from the model. (2) A core made of shape memory plastic that remembers a shape that is easy to remove from the model to be molded is molded into the same shape as the hollow part of the model to be molded and held in the mold, and the core and the A model is formed by injecting foamed resin into the space between the mold and the mold, and after molding, the model and the core are removed from the mold, and the core is heated to restore the memorized shape. , a method for molding a model, comprising removing it from the model.