JP2002153943A - Method for manufacturing mold for precision casting and model used for the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a gypsum-made mold delicately matched to a model having to entrapped air. SOLUTION: The gas-permeable resin-made model 1 is stuck to a hanging tool 2 and hung down and supported in a metallic flask 3, and the gypsum 5 is poured into the metallic flask 3. In the model 1, an air exhaust pipe 4 is beforehand connected. There to the whole metallic flask 3 together with the model are charged into a pressure vessel 8 and closed, and a pipe 4 is connected with an air drain 9. The compressed air 11 is fed in from pressurize- piping 10 to pressurize the gypsum 5 and the gypsum 5 is filled up into a hollow part 1 while exhausting the air in an air pool part 6 sealed into the hollow part 1a to the outer part through the model 1 itself and the pipe 4 and closely stuck to the model 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a casting mold for precision casting using gypsum, and a vanishing model structure used for the method.

[0002]

2. Description of the Related Art As a conventional method of manufacturing a mold for precision casting using gypsum, a model is placed in a metal frame, and after plaster is poured into the metal frame, air adhered to the model or a cavity is formed in the model. In some cases, in order to remove air trapped in the cavity and improve the transferability of the model to gypsum, a metal frame is installed in a larger airtight container, and the inside of the airtight container is depressurized to remove bubbles (defoaming). Qi) methods are generally known.

[0003] In precision casting using a slurry,
There is a method in which a slurry is adhered to a molded article in a pressurized state, and then the atmosphere is released to the atmospheric pressure to expand and remove air in the slurry (for example, JP-A-5-220541). Furthermore, in vacuum casting, there is a method of flowing a casting material into a mold having air permeability to prevent voids and reducing the pressure (for example, Japanese Patent Application Laid-Open No. H11-216731).

[0004]

Gypsum has a characteristic that the coagulation reaction proceeds from the time of reaction with water, and the fluidity gradually decreases and solidifies (hydration coagulation) after about ten minutes. It must be done in a short time with fluidity. For this reason, in the conventional defoaming method, there is a limit to the level of decompression, and it takes time to increase the degree of decompression, especially when the cavity of the model is large, air cannot be completely removed, and the gypsum adheres to the model. There was a problem that it was not possible. Further, when the pressure is reduced, there is a problem that much foamy air diffuses into the gypsum and the strength of the gypsum decreases.
Further, when the gypsum comes into contact with the air-permeable model, there is a problem that the moisture of the gypsum permeates the model, and it is difficult for air to pass through the model.

The present invention has been made in view of such a conventional problem. In particular, when a model has a hollow portion, a mold for precision casting which can reliably remove air from the hollow portion is provided. It is intended to provide a manufacturing method and a model structure used for the method.

[0006]

According to the first aspect of the present invention, a model having the same shape as a product is placed in a frame, plaster to be a mold is poured into the frame, and after the gypsum is hardened, combustion is performed. Alternatively, it is assumed that the method is a method of manufacturing a precision casting mold in which a model is lost by melting and a molten metal is poured into a space where the model has disappeared to cast a predetermined product.

Then, using a model having air permeability, the frame containing the model and the gypsum is placed in a sealable container, and the other end of the air discharge pipe connected to the upper surface of the model is placed outside the container. By opening the container and pressurizing the inside of the container while holding the container in a sealed state, at least air sealed at the boundary between the model and the gypsum is degassed.

Therefore, according to the first aspect of the present invention, the gypsum in a fluidized state is pressurized by pressurizing the closed container, and in particular, at least the model and the gypsum such as air sealed in the cavity of the model are pressurized. Compresses air trapped at the perimeter. Then, the compressed air passes through the air-permeable model and is discharged to the outside of the closed container through the air discharge pipe. Thus, the gypsum can be securely adhered to the model without generating air bubbles at the boundary between the model and the gypsum.

According to a second aspect of the present invention, based on the premise of the first aspect, the model has a cavity which is open at the bottom, and the container also serves as a frame. hand,
A gypsum introduction pipe is connected to the bottom of the container at a position facing the cavity of the model, and gypsum is introduced into the container through the gypsum introduction pipe while cooling the gypsum introduction pipe,
The gypsum introduced into the container is pressurized through the gypsum introduction tube.

Therefore, according to the second aspect of the present invention, the gypsum introduction pipe is cooled by utilizing the characteristic that the solidification reaction (hydration coagulation reaction) of the gypsum is slowed down, thereby reducing the fluidity of the gypsum. And gypsum is easily moved by pressurization. Further, by pressurizing the vicinity of the cavity of the model, the filling property of the gypsum into the cavity is improved, and the gypsum can be securely adhered to the model.

According to the third aspect of the present invention, in the second aspect,
On the premise of the invention described in (1), at least two or more types of gypsum having at least two types of gypsum or one type of gypsum with a different water mixing ratio are used.

Therefore, the invention according to claim 3 utilizes the characteristic that the fluidity differs depending on the type of gypsum, or the characteristic that the fluidity changes by changing the water mixing ratio. By using gypsum with high fluidity at the bottom of the container including the cavity of the model and by using gypsum with low fluidity at the top of the container, the gypsum can be easily moved by pressurization and the gypsum into the cavity of the model Gypsum can be reliably adhered to the model by improving the filling property.

According to the fourth aspect of the present invention, in the second aspect,
Or, on the premise of the invention described in 3 above, as a method of pressurizing the inside of the container, the pressure in the cavity, the gypsum liquid level in the cavity and the gypsum on the top surface of the container are determined by the pressure loss when the gypsum flows. Calculate the total pressure by adding the pressure corresponding to the difference in liquid level and the pressure loss when the air passes through the model, until the difference from the atmospheric pressure becomes a pressure greater than this total pressure. Reduce the pressure rate and pressurize, then increase the pressure rate and pressurize, hold the pressure for a certain period of time, then reduce the pressure and reduce the pressure, then increase the pressure to atmospheric pressure and increase the pressure. It is characterized by doing.

According to the fifth aspect of the present invention, as a method of pressurizing, the pressurizing speed is reduced until the pressure becomes larger than the pressure at which the gypsum in the cavity of the model moves, so that the gypsum liquid surface is wavy. Can be prevented and the gypsum can be moved slowly. In addition, by reducing the decompression speed in the initial stage of decompression, rapid expansion is prevented when air is attached to the model, and poor setting of the gypsum is prevented.

[0015] The invention described in claim 5 is the above-mentioned claim 1-
4. A vanishing model used in the invention according to any one of 4 to 4 above, wherein a laser is applied to the powdery resin to form a planar hardened layer, and the hardened layers are vertically stacked in a plurality of stages. With a three-dimensional model structure with air permeability,
At least two or more adjacent air passages and a passage connecting the adjacent air passages are provided at appropriate intervals inside the model.

As the powdery resin, for example, a polystyrene powder resin is used. As described above, a plurality of flat cured layers formed by irradiating the polystyrene powder resin with laser light are vertically stacked in a three-dimensional manner. The three-dimensional shape results in a porous and breathable model structure.

Therefore, in the invention according to the fifth aspect, by providing the air passage in the model, even if moisture contained in the gypsum permeates from the outer wall surface of the model, it is no more in the portion where the air passage exists. Of water can be partially prevented. As a result, the air in the cavity of the model can pass from the inner wall of the model where moisture does not penetrate to the air passage, so that the air can be discharged out of the closed container through the air passage and the air discharge pipe, and the gypsum is converted into the model It can be surely adhered.

[0018]

According to the first aspect of the present invention, at least the air sealed at the boundary between the model and the gypsum is discharged to the outside through the air-permeable model while pressurizing, so that the remaining air bubbles are reduced. Thus, the gypsum can be securely brought into close contact with the model, the transferability of the model to the gypsum is greatly improved, and the effect of contributing to the improvement of the quality of the mold using the gypsum as a base material is obtained.

According to the second aspect of the invention, the gypsum is introduced into the container under cooling while being pressurized by utilizing the characteristic that the solidification reaction of the gypsum slows down when it is cooled. In addition to the same effect as the invention described in the above, gypsum becomes extremely easy to move, especially when the model has a cavity, the gypsum filling property into the cavity is improved, and the gypsum is more securely adhered to the model There is an effect that can be.

According to the third aspect of the present invention, at least two types of gypsum or at least two types of gypsum having a different water mixing ratio with one type of gypsum are used, so that the original gypsum strength after solidification is obtained. The gypsum before solidification can be easily moved while maintaining the above condition, and in addition to the same effect as the invention according to claim 2, particularly, the filling property of the gypsum into the model cavity becomes extremely good, and the gypsum can be more securely added to the model. Has the effect of being able to adhere to the surface.

According to the invention set forth in claim 4, according to claim 2,
Or, on the premise of the invention described in 3, as a method of pressurizing, the pressurizing speed is reduced until the pressure becomes larger than the pressure at which the gypsum in the model cavity moves, and the pressure is reduced after pressurizing. In the initial stage, the pressure reduction rate is reduced, so that in addition to the same effect as the invention described in claim 2 or 3, the gypsum is gently moved by preventing the waving phenomenon of the gypsum liquid surface. On the other hand, when air adheres to the model, rapid expansion of the model can be prevented to prevent poor setting of the gypsum, thereby improving the quality of the mold.

According to the fifth aspect of the present invention, the air passage is formed in the model itself on the premise of the invention described in any of the second to fourth aspects. Even if the moisture contained in the gypsum permeates from the wall surface, it can partially prevent the further penetration of moisture in the area with the air passage, and reliably discharge the air in the model cavity to the outside of the closed container. In addition to the same effect as the invention according to any one of claims 2 to 4, the gypsum can be surely adhered to the model, and its transferability is further improved, contributing to further improvement of mold quality. There is an effect that can be done. .

[0023]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 show a method for producing a precision casting mold using gypsum as a first preferred embodiment of the present invention, and corresponds to the first aspect of the present invention.

In FIGS. 1 and 2, reference numeral 1 denotes a three-dimensional three-dimensional model which is formed of a resin such as polystyrene and is porous and has air permeability. A hanging jig 3 is bonded and fixed, and a bottomed metal frame for accommodating the plaster 5 in a flowing state together with the model 1 and accommodating them, and 4 denotes an air discharge pipe bonded and fixed to the model 1.

In this embodiment, a plaster mold (so-called inverted mold) for casting a predetermined product by transferring the shape of the three-dimensional three-dimensional model 1 as it is is manufactured. 1 has a cavity 1a that is open to the bottom and is formed in advance to a predetermined product shape.

In order to bury the model 1 in the plaster 5, the model 1 is bonded to a hanging jig 2 assembled in a cross-girder shape as shown in FIG. And connect them. Next, the hanging jig 2 was set on the upper end surface of the metal frame 3, and the model 1 was suspended and supported in the metal frame 3. The plaster 5 in a flowing state is poured into the metal frame 3. In this case, if the cavity 1a is formed in the lower part of the model 1 as shown in the figure, the gypsum 5 does not completely flow into the cavity 1a, and the air pocket 6 may be generated.

Then, in order to extract the air forming the air reservoir 6 (degassing), the metal frame 3 containing the model 1 and the gypsum 5 as shown in FIG. And is installed in a sealable pressure vessel 8. The pressure vessel 8 is provided with an air drain 9 and a pressure pipe 10. The other end of the air discharge pipe 4 connected to the model 1 in advance is connected to the air drain 9.

Next, the lid 7 of the pressure vessel 8 is closed, and pressurized air 11 from an air pressure source (not shown) is introduced into the pressure vessel 8 from the pressure pipe 10 to apply a predetermined pressure to the inside of the pressure vessel 8. Press. As a result, the liquid surface F of the gypsum 5 is pressurized, and the pressure of the gypsum 5a in the cavity 1a of the model 1 becomes higher than the pressure of the air reservoir 6, the liquid surface rises, and the air forming the air reservoir 6 is formed. Is compressed.

On the other hand, the pressure in the air discharge pipe 4 of the model 1 is equal to the atmospheric pressure through the air drain 9. Therefore, the pressure of the air forming the air pool 6 becomes larger than the pressure in the air discharge pipe 4, and the air forming the air pool 6 passes through the interior of the model 1, and the air discharge pipe 4 and the air drain It is discharged out of the pressure vessel 8 through 9. Thereby, the gypsum 5 can be filled to every corner of the hollow portion 1a of the model 1, and the gypsum 5 can be securely adhered to the model 1.

Here, as a concrete method of connecting the air discharge pipe 4 to the upper surface of the model 1, for example, as shown in FIG. A hole 12 is formed, and an air discharge space 13 having a larger diameter than the air discharge hole 12 is formed below the hole 12. Then, an adhesive is applied to the outer peripheral surface of the air discharge pipe 4 and inserted into the air discharge hole 12 so that the insertion side end surface of the air discharge pipe 4 does not come into contact with the bottom of the air discharge space 13. Adhesive fixing is performed while maintaining airtightness with the pipe 4.

By providing the air discharge space 13 as described above, the expansion of the air when the compressed air forming the air pool 6 is discharged to the air discharge pipe 4 through the model 1 is moderated. Therefore, troubles such as the air discharge pipe 4 being detached due to vibration caused by rapid expansion of air in the air discharge pipe 4 can be prevented. At the same time, the upper surface of the gypsum 5 can be prevented from waving due to the vibration, and a smooth upper surface of the mold can be manufactured. This is because in gypsum casting, a method of bonding a heat insulating pipe such as ceramic wool to form a gate and a riser is implemented as a simple method, and therefore, a request is made that a smooth surface is required as the top surface of gypsum. Based. In addition, by providing the air discharge space 13, it is possible to prevent the water contained in the gypsum 5 from permeating the portion of the model 1 near the air discharge pipe 4 as described later. It is also possible to prevent difficulty in passing.

On the other hand, when the air-permeable model 1 is completely buried in the flowing gypsum 5, the gypsum 5 comes into contact with the wall surface of the model 1 and the moisture of the gypsum 5 penetrates into the model 1. When moisture permeates into the model 1, a phenomenon occurs in which air becomes difficult to pass through the inside of the model 1.

Therefore, as shown in FIG. 4, an air passage 14 is formed by connecting a portion corresponding to the upper wall of the cavity 1a of the model 1A to a portion to which the air discharge pipe 4 is to be connected. The air permeability of the model 1A itself is not hindered by the permeation of moisture as described above, and the air forming the air pool 6 in the cavity 1a can be more reliably discharged.

That is, even if the moisture contained in the gypsum 5 has penetrated from the outer peripheral surface side of the model 1A toward the inside, the presence of the air passage 14 prevents the further penetration of moisture in that portion. Can be. And, since the upper wall surface of the cavity 1a of the model 1A is in contact with air to the end, the air forming the air reservoir 6 can pass to the air passage 14, and the air is further transmitted to the air passage 14. Pressure vessel 8 through air discharge pipe 4
Can be discharged to the outside, and the gypsum 5
Can be securely adhered to the model 1A.

The air passage 14 in this embodiment is
Is provided with a first passage 21 and a second passage 22 adjacent to each other in parallel as shown in FIG.
A plurality of third passages 23 connecting the first and second passages 22 are provided at appropriate intervals. The structure of the model 1A having the air passage 14 corresponds to the invention described in claim 5.

FIG. 5 shows a model 1A having the air passage 14.
An example of a method for fabricating is described below.

First, the model 1 having the air passage 14
A CAD data of the three-dimensional shape of A is created, and the CAD data is sliced in a thickness direction (height direction) by an appropriate set amount to create sectional shape data for each slice level. Next, the upper surface of the powder resin 16 such as polystyrene contained in the model forming tank 15 is irradiated with the laser beam B while scanning in accordance with the cross-sectional shape data of the CAD data to form a hardened layer having a predetermined thickness. After that, the elevator 17 is moved down by the set amount to make the model forming tank 1.
The level of the powder resin 16 in 5 is lowered.

Next, another elevator 18 is raised by a set amount to raise the powder resin 20 in the powder resin supply tank 19 adjacent to the model forming tank 15, and then the raised powder resin 20 is rolled by the roller 24. By moving the resin in the direction of arrow Q, a predetermined amount of powder resin is supplied onto the cured layer of the model forming tank 15. The excess powder resin is collected by dropping into a powder resin recovery tank 25 adjacent to the model forming tank 15.

After a predetermined amount of powdered resin is supplied to the upper surface of the hardened layer, a new laser beam B is irradiated in accordance with the cross-sectional shape data in the same manner as described above, so that a new one is superimposed on the previous hardened layer. A cured layer is formed. By repeating this operation sequentially, a model 1A having a three-dimensional structure as shown in FIG. 4 is formed. Further, in the irradiation of the laser beam B, the porous resin air-permeable model 1A is formed by adjusting the energy density so that the particle surfaces of the powder resin are melted and the particles are bonded to each other.

When the irradiation of the laser beam B is completed,
The model 1A is taken out of the model forming tank 15, and the uncured powder resin adhering to the periphery of the model 1A is removed by brush, suction or air blow. However, there is also uncured powder resin in the air passage 14 shown in FIG. Need to remove this.

Therefore, as shown in FIG.
A first passage 21 and a second passage 22 adjacent to each other
Are provided in parallel, and a plurality of third passages 23 connecting the first passage 21 and the second passage 22 are provided at appropriate intervals. When the irradiation of the laser beam B is completed, the model
After the model 1A is taken out of the first passage 21, air is blown from an entrance of the first passage 21 with an air blow nozzle (not shown), so that the third passage 2 closest to the blown portion is formed.
3 and the third passage 23 and the second
The uncured powder resin up to the entrance of the passage 22 is discharged from the second passage 22. Next, the air blow nozzle is
The uncured powder resin in the air passage 20 is sequentially and smoothly discharged, and the air passage 14 can be formed by sequentially inserting the uncured powder resin in the air passage 20 through the same operation as described above. .

The uncured powder resin has a characteristic that resin particles tend to adhere to each other due to the material of the resin and the influence of moisture. Therefore, in the method of sucking the uncured powder resin remaining in the air passage 14, the model 1A
When the wall thickness of itself is thin and has a complicated shape, the hole diameter of the air passage 14 is small, and the air passage 14 is bent along the shape of the model 1A. Therefore, even if the suction nozzle is inserted into the air passage 14, In some cases, unhardened powder resin is clogged in the nozzle and suction cannot be performed. Therefore, discharging and removing the uncured powder resin by the air blow method as described above requires:
It is extremely effective in its removal efficiency.

Thereafter, the air discharge pipe 4 is provided in a portion of the upper surface of the model 1A where the air passage 14 is opened, as in FIG.
To complete the operation of manufacturing the model 1A having air permeability as shown in FIG.

FIGS. 6 and 7 show a modification of the air passage 14 to be formed in the model 1A.

In FIG. 6, the third passage 33 connecting the first passage 21 and the second passage 22 is located at a position closer to the second passage than the connecting position 33a of the first passage 21 and the third passage 33. A connection position 33b between the passage 22 and the third passage 33 is provided on the mouth side of the passage, and the third passage 33 is substantially inclined. The air blow is performed from the first passage 21 side,
By providing the connection position of the third passage 33 on the mouth side of the second passage 22, the passage is gradually bent, and when air is blown, the resistance of the air flow 26 and the movement of the uncured powder resin is reduced. And can be discharged smoothly.

In FIG. 7, at the joint of the third passage 43 connecting the first passage 21 and the second passage 22, at least the corner of the passage is rounded to form a round chamfered portion 43 a. It was done. In this case, FIG.
Similarly to the above, air blow is performed from the first passage 21 side, but by providing a round chamfered portion 43a at a corner formed by the first and second passages 21 and 22 and the third passage 43,
When air is blown, the resistance of the flow of the air 26 and the movement of the uncured powder resin is reduced, and the air can be discharged smoothly.

FIG. 8 shows a series of procedures from the above-described modeling of the air-permeable model 1 or 1A to the production of a mold using the model 1 or 1A and the precision casting using the mold. become.

As shown in the figure, three-dimensional CAD data for a vanishing model having the same shape as the product to be cast is created. At this time, the shape of the air discharge space 13 for connecting the air discharge pipe 4 as shown in FIGS.
Also, three-dimensional CAD data having the shape of is created (step S1).

Next, the shapes related to the casting method, such as the gate, runner, gate and feeder, are similarly created using CAD data (step S2), and a solidification analysis is performed by a casting simulation (step S3). Create a casting plan that does not cause any problems.

Further, slice data of CAD data for forming a powder resin model is created (step S).
4). Then, based on the slice data, the model 1 or 1A is formed by the modeling apparatus (step S5), and after the modeling, the model 1 or 1A is taken out of the modeling apparatus, and the model 1 or 1A is taken out.
Or uncured powder resin adhered to the outer surface of 1A,
The uncured powder resin inside the model 1 or 1A is removed by an air blow method (step S6).

Subsequently, the model 1 or 1A is bonded and fixed to the hanging jig 2 of FIG. 1 with an adhesive or the like (step S1).
7), the hanging jig 2 is set on the metal frame 3 (step S8),
The air discharge pipe 4 is connected to the model 1 or 1A (step S9).

Further, after the plaster is poured into the metal frame 3 and filled (step S10), the metal frame 3 is set in the pressure vessel 8 and the air discharge pipe 4 is connected to the air drain 9 of the pressure vessel 8 (step S10). S11). And the pressure vessel 8
Then, the inside of the pressure vessel 8 is pressurized by closing the lid 7 to make the airtight state (step S12).

After the gypsum has solidified, the metal frame 3 is removed from the pressure vessel 8.
Is taken out, and the model 1 or 1A is extinguished by a method of burning or melting (step S13). Further, after the plaster mold is dried in an oven or the like (step S1).
4) A gate section, a feeder section, and the like are provided with a heat insulating pipe or the like (step S15).

Then, the molten metal is poured into the cavity of the gypsum mold to perform casting (step S16). After the casting, the gypsum mold is removed, and finishing such as cutting of the gate (step S16) is performed.
By performing 17), a cast product having a predetermined shape as a product can be obtained.

FIG. 9 shows another example of a method of manufacturing a precision casting mold according to a second embodiment of the present invention. This embodiment corresponds to the second aspect of the present invention. In the present embodiment, the pressure vessel 50 also serves as the metal frame 3 shown in FIGS.

As shown in the figure, a model 1 having the same air permeability as in FIG. 1 is bonded to a hanging jig 2 assembled in a cross-girder shape.
The hanging jig 2 is installed above the receiving plate 52 of the sealable pressure vessel 50 provided with the openable and closable lid 51, and is suspended and supported in the pressure vessel 50. An air discharge pipe 54 is adhered to the upper surface of the model 1, and the other end of the air discharge pipe 54 is connected to an air drain 53 provided on the lid 51. Lid 5
1 is provided with a gypsum drain 55 separately from the air drain 53, and can be hermetically sealed with a stopper 56. Further, a gypsum introduction pipe 57 having a double structure is connected to a portion corresponding to the bottom of the pressure vessel 50, and a sealable stopper 60 and a pressure pipe 61 are provided above the inner cylinder 58. Outer cylinder 59
Contains cooling water 62 cooled by ice or the like.

To produce the mold, the lid 5 of the pressure vessel 50
1 and the plug 56 for the gypsum drain 55
The gypsum introduction tube 57 is removed by removing the stopper 60 and opening it.
The plaster 5 is poured into the inner cylinder 58, and the supply of the plaster 5 is stopped when the plaster 5 overflows from the plaster drain 55. After closing the gypsum drain 55 with the stopper 56, the inner cylinder 58 is similarly sealed with the stopper 60, and then pressurized air is introduced from the pressure pipe 61, and the pressure vessel is passed through the gypsum 5 in the inner cylinder 58. The gypsum 5 in 50 is pressurized.

The gypsum 5 has a characteristic that the solidification time is delayed when the temperature is low.
Is cooled, the setting time of the gypsum 5 in the gypsum introduction pipe 57 is delayed, and the state of fluidity can be maintained for a long time. As a result, the gypsum 5 at the lower part of the cavity 1a of the model 1 through which the gypsum introduction pipe 57 communicates also has a slow solidification time and a long pressurization time, so that the air can be removed similarly to the first embodiment. The cavity 1a can be easily filled with the gypsum 5 while the air forming the pool 6 is smoothly discharged, so that the gypsum 5 can be more securely adhered to the model 1.

FIG. 10 shows still another example of a method for manufacturing a precision casting mold as a third embodiment of the present invention. The configuration of each section of the device in the present embodiment is the same as that shown in FIG. This embodiment corresponds to the third aspect of the present invention.

Gypsum is classified into various types such as gypsum for general casting and gypsum for lost wax. Fluidity and strength vary depending on the type of gypsum. Generally, if the fluidity is large, the strength after solidification is small. Further, when the water mixing ratio is increased, the fluidity is increased, but similarly, there is a characteristic that the strength after solidification is reduced.

In the present embodiment, the lid 51 of the pressure vessel 50
In a state in which the gypsum is opened, gypsum having a high fluidity or gypsum 65 having a high water-mixing ratio is poured until approximately the lower half of the model 1 is hidden. Next, gypsum having low fluidity but high strength, or gypsum 75 having a water mixing ratio smaller than that of the plaster 65, is poured into the upper portion of the pressure vessel 50 so that the model 1 is completely hidden. Then, while closing the lid 51 of the pressure vessel 50, sealing the gypsum drain 55 with a stopper 56, sealing the inner cylinder 58 of the gypsum introduction pipe 57 with a stopper 60,
Pressurized air is introduced from Thereby, the gypsum introduction pipe 57
Since the gypsum 65 having high fluidity is provided inside and below the model 1, the gypsum 65 can be easily filled into the cavity 1a,
5 can be brought into close contact with the model 1. In particular, although the cavity 1a of the model 1 is filled with the gypsum 65 having fluidity but low strength, the gypsum 75 having low fluidity but high strength is located above approximately half of the model 1. As a whole, a mold formed with these two types of gypsum 65, 75 can maintain necessary and sufficient strength.

FIG. 11 shows another example of pressurizing the gypsum in the pressure vessel 8 or 50 as the fourth embodiment of the present invention. This embodiment corresponds to the invention described in claim 4.

FIG. 11A is a diagram showing a change in pressure for pressurization and a change in pressure of the air reservoir 6 caused by the change in pressure.
P2 is the pressure of the air reservoir 6 in a, P3 is the pressure corresponding to the difference in height between the gypsum liquid surface in the cavity 1a and the gypsum liquid surface on the upper surface of the pressure vessel 8 or 50, and air passes through the model 1. When the pressure loss at the time of pressure reduction is defined as P4, the respective pressures P1
The sum of P4 is calculated as P (= P1 + P2 + P3 + P4). The degree of pressurization in the initial stage of pressurization is slow until the pressure exceeds the total pressure P, that is, the pressurization speed is reduced, and pressurization is performed. (A in FIG. 11A)
region). This makes it possible to prevent the plaster liquid surface from waving, and to move the gypsum gently. Note that the total pressure P corresponds to a pressure difference from the atmospheric pressure.

When the gypsum begins to move due to the applied pressure exceeding the total pressure P, the pressurizing speed is increased (region b in the figure). By doing so, the pressing time can be reduced. Further, as the gypsum moves, the pressure in the air reservoir 6 in the cavity 1a increases (region c in the figure), and when the pressure loss of the model 1 becomes larger than the atmospheric pressure, the air reservoir 6
Is discharged out of the container through the model 1.

Next, when the pressure is maintained in a stable state, the pressure in the air reservoir 6 also shifts to a stable state (regions d and e in FIG. 6), and the air in the air reservoir 6 passes through the model 1 and is discharged. Then, when all the air is discharged by the gypsum, the pressure in the air reservoir 6 disappears (the area f in the figure).

Subsequently, when depressurizing the air reservoir 6 after discharging air by pressurization, a rapid expansion can be prevented when air is attached to the model 1 by reducing the depressurizing speed at the initial stage of depressurization, and gypsum can be prevented. Can be prevented from being hardened (g region in the figure). Thereafter, the decompression time can be shortened by increasing the decompression speed (region h in the figure).

FIG. 11B shows a change in volume of the air reservoir 6 and a change in volume by a conventional decompression method. The volume of the air reservoir 6 does not change in the volume of the air reservoir 6 (i region) because the pressing force is small and the gypsum does not move in the initial stage of pressurization (region a) in FIG. As the gypsum moves by further pressurization, the air in the air pool 6 is gradually compressed (area c), and the volume becomes smaller from the time when the discharge starts (area j), and the cavity 1a is completely filled with gypsum. Where the pressure in the air reservoir 6 disappears (f
region).

In the conventional defoaming method by the depressurization method, the volume remaining as an air reservoir is substantially determined by the degree of the depressurization and cannot be completely removed. Can calculate the pressure in the air pool 6 and apply a larger pressure, so that the air forming the air pool 6 can be completely eliminated. Further, in the conventional vacuum degassing method, in order to increase the degree of pressure reduction, a large-capacity and high-performance vacuum pump is required, and the time required for the pressure reduction is disadvantageous. In the pressurizing method, a high-performance pump is not required if the pressure is about several times the atmospheric pressure, and the pressurized air can be introduced in a short time. The time required for bringing the gypsum into close contact with the portion can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a first embodiment of a mold manufacturing method according to the present invention.

FIG. 2 is an explanatory view showing a first embodiment of a mold manufacturing method according to the present invention.

FIG. 3 is an enlarged view of a main part of a connection portion between the model shown in FIG. 1 and an air discharge pipe.

FIG. 4 is a view showing a modification of the model shown in FIGS.
(A) is a longitudinal sectional view thereof, and (B) is a sectional view taken along line AA of FIG. (A).

FIG. 5 is a configuration explanatory view of a modeling apparatus for modeling the model shown in FIG. 4;

FIG. 6 is an enlarged view of a main part showing a further modification of the model shown in FIG. 4;

FIG. 7 is an enlarged view of a main part showing still another modified example of the model shown in FIG. 4;

FIG. 8 is a flowchart showing a series of procedures from model modeling to mold production and actual casting using the mold.

FIG. 9 is an explanatory view showing a second embodiment of the mold manufacturing method according to the present invention.

FIG. 10 is an explanatory view showing a third embodiment of the mold manufacturing method according to the present invention.

FIG. 11 is an explanatory view showing a pressure change when gypsum is pressed as a fourth embodiment of the mold manufacturing method according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Model 1a ... Hollow part 3 ... Gold frame 4 ... Air discharge pipe 5, 5a ... Plaster 6 ... Air pool 8 ... Pressure vessel 10 ... Pressurized piping 14 ... Air passage 21 ... First passage 22 ... Second passage 23 ... third passage 33 ... third passage 43 ... third passage 50 ... pressure vessel 54 ... air discharge pipe 57 ... gypsum introduction pipe 61 ... pressurized piping 65 ... gypsum 75 ... gypsum

Continuation of the front page (72) Inventor Teshiro Shibazaki 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture F-term in Nissan Motor Co., Ltd. 4E093 GA05 GB16 GC20 GD04

Claims (5)

[Claims] Claims 1. A model having the same shape as a product is placed in a frame, plaster to be cast is poured into the frame, and after the gypsum hardens, the model disappears by burning or melting, and the model disappears. In a method for producing a precision casting mold in which a predetermined product is cast by pouring a molten metal into a space, a model having air permeability is used, and a frame in which the model and the gypsum are stored can be sealed in a container. And the other end of the air discharge pipe connected to the upper surface of the model is opened to the outside of the container, and the container is sealed at least at the boundary between the model and the gypsum by pressurizing the inside of the container while holding the container in a sealed state. A method for producing a precision casting mold, characterized in that degassed air is removed. 2. The model has a cavity which is open at the bottom, while the container also serves as a frame, and a gypsum introduction pipe is connected to the bottom of the container at a position facing the cavity of the model. The gypsum is introduced into the container through the gypsum introduction tube while cooling the gypsum introduction tube, and the gypsum introduced into the container is pressurized through the gypsum introduction tube. How to make a casting mold. 3. The method for producing a precision casting mold according to claim 2, wherein at least two or more types of gypsum or a gypsum having a different water mixing ratio with one type of gypsum are used. 4. A method of pressurizing the inside of the container, wherein the pressure loss when the gypsum flows, the pressure in the cavity, the difference between the height of the gypsum liquid surface in the cavity and the height of the gypsum liquid surface on the upper surface of the container are determined. Calculate the total pressure by adding the corresponding pressure and the pressure loss when the air passes through the model, and reduce the pressurizing speed until the difference from the atmospheric pressure becomes larger than this total pressure. After increasing the pressurizing rate and increasing the pressurizing rate and maintaining the pressure for a certain period of time, decreasing the depressurizing rate to reduce the pressure, and then increasing the depressurizing rate to atmospheric pressure to reduce the pressure. 4. The method for producing a precision casting mold according to 2 or 3. 5. A vanishing model used in the method for manufacturing a precision casting mold according to claim 1, wherein a powdery resin is irradiated with a laser to form a planar hardened layer. And, a three-dimensional model structure having air permeability by stacking a plurality of layers of this cured layer in the vertical direction, at least two or more adjacent air passages inside the model, and a passage connecting adjacent air passages A model provided at appropriate intervals.