JP2020151746A - Method for producing sand mold for casting and core for casting - Google Patents

Abstract

To provide a technique capable of integrally producing a large-sized sand mold for casting with a cavity of a complicated shape having undercuts in two or more directions in a planar view in a short time at high precision.SOLUTION: A method for producing a sand mold for casting comprises: a sand block formation step in which a sand block 4 satisfying at least one of a compressive strength of 15 to 50 (N/cm2) and a bulk density of 1.0 to 2.0 (g/cm3) is formed; and a removal working step in which, using a numerical value control working machine, removal tools 43 are progressed from at least two or more directions in the planar view of the sand block 4, and the sand block 4 is subjected to removal working to produce a core 7 of a sand mold 1 for casting with a cavity 70 having undercuts 6.SELECTED DRAWING: Figure 9

Description

The present invention relates to a method for manufacturing a sand mold for casting and a core for casting.

Conventionally, in the manufacture of sand molds for casting, a model such as wooden with almost the same shape as the product is made, this model is placed on a surface plate, surrounded by a frame, sand is pushed around the model to harden it, and the model is taken out. It was manufactured by dividing the sand mold. In addition, sand molds were also manufactured by the lost wax method, in which a model made of wax is burned or melted and removed from the sand. However, with the method of transferring a model to sand to make a sand mold, it is difficult to reproduce a complicated shape such as an impeller, and there is room for improvement in the accuracy of the sand mold, and a storage place for the model and the model is required, which requires man-hours and man-hours. There was room for improvement in manufacturing costs.

As this improvement measure, a method for manufacturing a sand mold for casting in which a sand block is directly processed by a numerically controlled processing machine based on product shape data and a method for manufacturing a sand mold for casting by a laminated molding method (3D printer) are known ( For example, see Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4).

Japanese Unexamined Patent Application Publication No. 2003-19542 Japanese Patent No. 3114159 JP-A-2002-316299 JP-A-11-239843

In the method for manufacturing a sand mold for casting in Patent Document 1, a mold powder and a thermosetting resin are mixed and then heated to form a block material, and the block material is cut with a cutting tool to form a cavity for casting. Manufacture sand molds.

In the method for producing a sand mold for casting in Patent Document 2, sand as a powder or granular material is compressed so as to have a compressive strength of 20 to 80 kg / cm ² (approximately 196 to 784 N / cm ² ), and the binder is used. A sand block is obtained by curing with water glass by gas or by utilizing a curing reaction of furan resin with an acid. Furthermore, using CAM (Computer Aided Manufacturing), a drive program for the processing machine is created based on the shape of the three-dimensional mold to control the drive of the processing machine, and the machine support can be moved in two or three directions. A sand mold for casting is manufactured by processing a sand block with an end mill or the like of a machine head provided in.

In the method for manufacturing a sand mold for casting in Patent Document 3, a mold is manufactured by cutting a block obtained by solidifying powder or granular material with a solidifying agent. The binder used as the solidifying agent is a mixture of an alkaline phenol resin for carbon dioxide curing and an epoxy compound. The block has a compressive strength of 0.3 MPa or more and less than 2 MPa (30 N / cm ² or more and less than 200 N / cm ² ) when it is cut, and when it is used as a mold, it is 2 MPa or more, preferably 8 MPa or more and 30 MPa or less by heat treatment. The compressive strength is (800 N / cm ² or more and less than 3000 N / cm ² ). This block is cut by an automatic control processing machine to manufacture a mold.

In the method for manufacturing a sand mold for casting in Patent Document 4, a core in which cavities are formed along the shape of three blades is manufactured by a layered manufacturing method (3D printer).

By the way, some castings have a complicated shape such as an impeller, and a sand mold for casting having a cavity corresponding to such a complicated shape is required. If the sand block is directly machined with a machining tool of a machining machine, it is necessary that the sand block does not collapse during machining and the machined surface must be finished with high accuracy. Further, it is preferable that the processing man-hours can be reduced in a casting sand mold having a cavity having a complicated shape.

However, in the method for producing a sand mold for casting in Patent Document 1, since the block material is heated by mixing a thermosetting resin with a mold powder, it takes a lot of man-hours to heat it. Further, since the machining tool is vertically inserted from above the block material, it is not possible to manufacture a cavity having a complicated shape having an undercut.

In the method for producing a sand mold for casting in Patent Document 2, water glass or furan resin is used as a binder, and it is difficult to uniformly solidify the inside of a sand block using water glass or furan resin. It is necessary to increase the compressive strength in order to obtain the strength that does not collapse to the inside of the sand block during processing, and the compression strength is set to 20 kg / cm ² (approximately 196 N / cm ² ) or more in the technique of Patent Document 1. It takes time to mold the sand block. Further, at the time of processing, since the sand block is processed by an end mill or the like of a machine head provided on the machine support portion so as to be movable in two or three directions, it is not possible to manufacture a cavity having a complicated shape having an undercut.

In the method for producing a sand mold for casting in Patent Document 3, a mixture of an alkaline phenol resin for curing carbon dioxide gas and an epoxy compound is used as the binder. However, in the alkaline phenol resin for curing carbon dioxide gas, it is necessary to separately prepare carbon dioxide gas for curing carbon dioxide gas, which increases the manufacturing cost. In addition, the compressive strength at the time of processing cannot be used as it is, and when using casting, it is necessary to heat-treat to increase the compressive strength, which is troublesome. Further, the automatic control machine cannot produce a complex shaped cavity with an undercut, as the tool only extends vertically from above the block.

In the method for manufacturing a sand mold for casting in Patent Document 4, since the core is manufactured by the additive manufacturing method (3D printer), a cavity having a complicated shape can be formed. However, in general, when making molds of the same size, it takes only 2 to 3 hours to cut a sand block, but it takes about 1 day to use additive manufacturing (3D printer). In the additive manufacturing method, the processing man-hours are large and the manufacturing cost is high. Since the manufacturing range is small in the additive manufacturing method, there are size restrictions for manufacturing large cores and main molds, and there are cases where they have to be manufactured separately. Furthermore, it is necessary to manufacture a large core having a cavity formed along the shape of three blades by dividing it into three parts, which takes time and effort to assemble the core, and by dividing the core as a whole. There is a risk that the accuracy of

In view of the above points, the present invention provides a technique capable of integrally and accurately forming a large casting sand mold having a cavity having a complicated shape having two or more undercuts in a plan view in a short time. With the goal.

[1] In order to achieve the above object, the method for producing a sand mold for casting of the present invention is:
Fill the formwork with casting sand mixed with binder and
Press the casting sand in the mold so that the compressive strength satisfies at least one of 15 to 50 (N / cm ² ) and the bulk density of 1.0 to 2.0 (g / cm ³ ). A sand block forming step of forming a sand block having a predetermined shape by solidifying the sand block.
Using a numerically controlled machining machine that operates a rod-shaped removal tool by computer control based on shape data, the sand block is removed by allowing the removal tool to enter from at least two directions in a plan view of the sand block. It is characterized by including a removal processing step of manufacturing a core or a main mold of a sand mold for casting in which a cavity having an undercut is formed.

According to such a configuration, in the sand block forming step, the sand block has a compressive strength of 15 to 50 (N / cm ² ) or a bulk density of 1.0 to 2.0 (g / cm ³ ). Since it is formed so as to satisfy one of them, the compressive strength and the bulk density are in a range suitable for the removal process, and the accuracy of the processed surface can be improved without being broken by the removal process by the removal tool. Further, since the sand block is formed only by pressing the casting sand in the mold, the subsequent heat treatment as in the prior art is unnecessary, and the sand block can be formed in a short time. Further, by forming a sand block satisfying at least one of a compressive strength of 15 to 50 (N / cm ² ) and a bulk density of 1.0 to 2.0 (g / cm ³ ), casting sand can be pressed. Since the pressure is low, the sand block can be easily molded. Further, since the compressive strength of the sand block is relatively small, the load applied to the removal tool during machining can be reduced.

Further, in the removal processing step, a cavity having an undercut is formed by removing the sand block by entering the removal tool from at least two directions in a plan view of the sand block using a numerically controlled processing machine. Therefore, it is possible to manufacture a core or a main mold having a cavity having a complicated shape, not just an undercut. Further, since the sand block is removed by a removing tool, a desired core or main mold can be manufactured in a short time as compared with the additive manufacturing method (3D printer). In addition, since large cores and main molds are easily broken and difficult to handle, if a sand mold is manufactured by additive manufacturing (3D printer), it is necessary to maintain the shape of the entire mold with the sand itself adhered by the thermosetting resin. Due to the restrictions of the modeling range, it is difficult to manufacture large cores and main molds. In this respect, in the present invention, since the sand block is held by the mold, the mold supports the surroundings even if it is a large core or a main mold, so that the shape of the entire mold can be easily maintained. In addition, since the processing range is larger than that of the additive manufacturing method, even a large core or main mold can be manufactured.

[2] Further, in the method for producing a sand mold for casting of the present invention,
It is preferable that the removal processing step is continuous in different directions in the plan view of the sand block and forms the undercut in which the inclination angles of the sand block with respect to the vertical direction are continuous at different angles.

According to such a configuration, a core or a core having a cavity having a complicated shape with a three-dimensional twist having an undercut that is continuous in a plurality of directions in a plan view and has a continuous inclination in a plurality of vertical directions. Can also manufacture molds.

[3] Further, in the method for producing a sand mold for casting of the present invention,
In the removal processing step, the cavity is formed into an impeller shape that is spiral and twisted in the height direction in a plan view, and all the blades of the impeller shape are formed in one sand block in a plan view. It is preferable to do so.

According to such a configuration, even a large core including all blades having an impeller shape having a spiral shape and a complicated twist can be manufactured.

[4] Further, in the method for producing a sand mold for casting of the present invention,
In the kneading process,
In the removal processing step, it is preferable that the numerically controlled processing machine uses a machining center having four or more axes.

According to such a configuration, if it is a machining center having four or more axes, it is possible to manufacture a cavity having a complicated three-dimensional shape by rotating a table on which a sand block is installed.

[5] Further, in the method for producing a sand mold for casting of the present invention,
It is preferable to include a removal process in which the sand block is deeply dug with the removal tool having a ratio (L / D) of the protrusion amount L to the shank width or the diameter D of 5 to 50.

According to such a configuration, the removal tool is a sand block in which the workpiece is not excessively compressed even if the ratio (L / D) of the protrusion amount L to the shank width or the diameter D is 5 to 50. The tool can be deeply dug into the sand block by removal processing without chattering. Further, even when machining the vicinity of the surface of the sand block with the tip of a long removal tool having (L / D) of 5 to 50, the sand block in which the workpiece is not excessively compressed is used. Therefore, the removal tool can perform shallow removal processing near the surface of the sand block without chattering. As described above, in the present invention, it is possible to process deeply or shallowly with one removing tool.

[6] Further, in a casting core having a cavity for casting a product part inside.
The cavity is formed in a sand block satisfying at least one of a compressive strength of 15 to 50 (N / cm ² ) and a bulk density of 1.0 to 2.0 (g / cm ³ ).
It is preferable that the sand block has an undercut that is continuous in different directions in a plan view and that the inclination angle of the sand block with respect to the vertical direction is continuous at different angles.

According to such a configuration, it was formed in a sand block satisfying at least one of a compressive strength of 15 to 50 (N / cm ² ) and a bulk density of 1.0 to 2.0 (g / cm ³ ). Since it is a cavity, it does not collapse even when molten metal is poured, and castings can be manufactured. Further, the casting core is an undercut that is continuous in different directions in the plan view of the sand block and that the inclination angle of the sand block with respect to the vertical direction is continuous at different angles, so that the casting has a complicated shape with a twist. Even so, it can be a highly accurate casting.

[7] Further, a plurality of the cavities are formed in the sand block.
The shape of the cavity is the shape of the blades of the impeller that are spiral and twisted in the height direction in the plan view of the sand block.
It is preferable that all of the plurality of the cavities are formed in one sand block in a plan view.

According to such a configuration, since the cavity in the shape of a plurality of three-dimensionally twisted blades of the impeller is formed in one sand block, there is a possibility that the accuracy of the core as a whole may be lowered by dividing it as in the prior art. It is possible to manufacture a large-sized casting in which a cavity having a complicated shape is formed with high accuracy.

It is a flowchart which shows each process of the manufacturing method of the sand mold for casting which concerns on this invention. FIG. 2A is a diagram schematically showing a mold disassembling step among the sand block forming steps. FIG. 2B is a diagram schematically showing a crushing step among the sand block forming steps. FIG. 2C is a diagram schematically showing a regeneration processing step among the sand block forming steps. FIG. 2D is a diagram schematically showing a regeneration processing step of another aspect of the sand block forming step. FIG. 2E is a diagram showing a product obtained by the casting finishing process. FIG. 3A is a diagram schematically showing a kneading step among the sand block forming steps. FIG. 3B is a diagram schematically showing a compaction step among the sand block forming steps. FIG. 4A is an enlarged view of a main part schematically showing a cross section of a sand block of a comparative example. FIG. 4B is an enlarged view of a main part schematically showing a cross section of the sand block of the embodiment. FIG. 5A is a diagram showing a usage example of a casting cast by a casting sand mold according to the present invention. FIG. 5B is a diagram showing an example of a casting immediately after being taken out from a casting sand mold. FIG. 6A is a diagram schematically showing from the shape data production process to the processing path production process in the removal processing process. FIG. 6B is a diagram schematically showing from the sand block setting process to the removal processing step in the removal processing process. FIG. 7A is an enlarged view of a main part of the numerically controlled processing machine. FIG. 7B is a diagram illustrating a core removal process for a closed impeller. FIG. 7C is an explanatory diagram of a state in which the undercut of the sand block is removed. FIG. 8A is a plan view of the core for the closed impeller. FIG. 8B is an explanatory diagram of continuous undercuts in which the inclination angles of the core for the closed impeller with respect to the vertical direction are different. FIG. 9A is a plan view showing the processing position of the core for the closed impeller. 9B is an explanatory view of the inclination angle of the removal tool with respect to the vertical direction at each machining position of FIG. 9A. FIG. 10A is a perspective view of a core for a closed impeller. FIG. 10B is a perspective view of a main mold for a closed impeller. FIG. 10C is a perspective view showing a state in which the core is set in the main mold for the closed impeller. FIG. 11A is a diagram schematically showing the casting process from the mold matching process to the pouring process. FIG. 11B is a diagram illustrating another aspect of the casting sand mold of FIG. 11A.

(Embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the flowchart of FIG. 1, it is assumed that FIGS. 2 to 11 are appropriately referred to. As shown in FIG. 1, the manufacturing method of the casting sand mold 1 according to the present invention is roughly divided into a sand block forming step, a removing processing step, and a high-level step of the casting step.

In the sand block forming step (method for manufacturing a sand block), when the casting sand mold 1 is recycled, the casting sand mold 1 is disassembled and the casting 10 is taken out, and the casting sand 2 is crushed. A reclaiming process for regenerating the reclaimed casting sand 2, a kneading step for kneading the binder 3 with the reclaimed casting sand 2, and a sand block 4 for compacting and solidifying the kneaded casting sand 2. It is equipped with a compaction process to obtain. The casting 10 taken out in the mold disassembling step obtains a casting finishing step of performing a finishing process and becomes a product.

In the embodiment, the casting sand 2 is included in the sand block forming step from the point of recycling, but the present invention is not limited to this, and when the casting sand mold 1 is entirely manufactured from the new casting sand 2, it is included from the kneading step. First, then the compaction process shall be performed.

The removal processing step includes a shape data production step for producing the shape data 10a of the casting 10 and a processing path production step for producing a processing path of the removal tool 43 for processing the mold shape of the casting sand mold 1 from the shape data 10a. A sand block setting step of setting the sand block 4 on the numerical control processing machine 40 and a removal processing step of removing the sand block 4 with the numerical control processing machine 40 to obtain a sand mold 1 for casting are provided.

The casting process includes a mold matching step of combining the upper mold 1a, lower mold 1b, core 7 and the like of the casting sand mold 1, a melting step of melting a metal material to obtain a molten metal, and pouring the molten metal into the casting sand mold 1. It has a hot water process.

Next, the sand block forming process as a higher level will be described in detail. As shown in FIG. 2A, in the mold disassembling step, the casting 10 is taken out from the casting sand 2 of the upper and lower molds 20, and the casting sand 2 is removed from the mold 20 to be separated. The casting sand 2 may be dropped by applying vibration or the like to the removed casting 10.

As shown in FIG. 2B, in the crushing step, the separated casting sand 2 has a portion that is agglomerated to a certain size, so the casting sand 2 is crushed by the crusher 21 until it becomes close to the original granules. ..

As shown in FIG. 2C, in the recycling process, the crushed casting sand 2 is put into the recycling device 22a, the recycling device 22a is rotated, the casting sand 2 is blown off by centrifugal force, and the casting sand 2 is hit against the peripheral wall of the recycling device 22a. Crush and remove the binder 3 attached to the sand 2. As described above, since the dry recycling apparatus 22a is used, the casting sand 2 can be easily recycled without washing the casting sand 2 with water as in the wet type. Further, the binder 3 is sucked from the finely crushed casting sand 2 by the dust collector 24 to obtain the casting sand 2 from which the binder 3 has been removed.

FIG. 2D shows another aspect of FIG. 2C. In the regeneration treatment step, the crushed casting sand 2 is put into the recycling device 22 and heated by the burner 23 to carbonize the binder 3 attached to the casting sand 2. The carbonized binder 3 is sucked from the cast sand 2 after further heating with a dust collector 24 to obtain the cast sand 2 from which the binder 3 has been removed.

On the other hand, as shown in FIG. 2E, in the casting finishing step, deburring, grindering, finishing, shot blasting, etc. are applied to the casting 10 taken out in the mold disassembling step as necessary to finalize the casting 10. Product.

As shown in FIG. 3A, in the kneading step, as the casting sand 2, the large grain 2a having an average particle size distribution of artificial ceramic sand having a predetermined value and the small grain 2b having an average particle size smaller than the predetermined value of the large grain 2a A plurality of types of casting sand 2 having different average particle sizes are put into the kneader 25. Further, the binder 3 containing the water-soluble alkali phenol resin for ester curing is put into the kneader 25, and the casting sand 2 and the binder 3 are kneaded. Specifically, the binder 3 is composed of an alkali phenol resin for ester curing and a curing agent for alkali phenol resin.

At this time, the mixing ratio of the casting sand 2 to the whole is about 97.5 wt%, and the mixing ratio of the binder 3 to the whole is about 2.5 wt%. Specifically, in the 2.5 wt% composition of the binder 3, the mixing ratio of the alkali phenol resin for ester curing diluted with water is about 2.0 wt%, and the mixing ratio of the curing agent for alkali phenol resin is about 0. It is preferably 5 wt%. The mixing ratio of the alkali phenol resin for ester curing itself is about 1%, but if the mixing ratio is 1%, it is difficult to spread over the whole. Therefore, by using a water-soluble alkali phenol resin for ester curing, it can be diluted with water and easily distributed throughout.

Further, in the casting sand 2, the ratio of the large grain 2a to the small grain 2b is preferably large grain 2a: small grain 2b = 70:30. By setting this ratio, the recycling rate of the cast sand 2 at the time of recycling can be as high as 91% as a whole.

It is preferable that the mixing ratio is close to the mixing ratio of the casting sand 2 and the binder 3, but the mixing ratio is an example, and the mixing ratio of the casting sand 2 is 80% to 70%, and the mixing ratio of the binder 3 is 80% to 70%. May be 20% to 30%, or 100% as a whole. Furthermore, the mixing ratio is not limited to these. Further, in the embodiment, the alkali phenol resin for ester curing is made water-soluble, but the present invention is not limited to this, and an alkali phenol resin for ester curing that is not water-soluble may be used.

As shown in FIG. 3B, in the compaction step, the mold 20 is placed on the surface plate 28, and the mold 20 is filled with the casting sand 2 kneaded with the binder 3. The compressor 26 is used to compact the casting sand 2 in the mold 20. At this time, the kneaded casting sand 2 and the binder 3 made of a water-soluble alkali phenol resin for ester curing are vibrated by the vibrating apparatus 27 while being pressed to solidify.

By compacting the casting sand 2 and the binder 3 made of a water-soluble alkali phenol resin for ester curing, the compressive strength is 15 to 50 (N / cm ² ) or the bulk density is 1.0 to 2.0. A sand block 4 having a predetermined shape is formed by pressing and solidifying the entire casting sand 2 in the mold 20 so as to satisfy at least one of (g / cm ³ ). By forming the sand block 4 made of the binder 3 containing the alkali phenol resin for ester curing, the entire sand block 4 can be made tenacious and the toughness can be improved. Therefore, even if the sand block 4 bends, it does not break, and the sand block 4 can be easily handled.

Next, the configuration of the cross section of the sand block 4 will be schematically exaggerated and described. FIG. 4A shows the configuration of the sand block 4 of the comparative example with respect to FIG. 4B. The cast sand 2 is artificial ceramic sand, which is rounder than natural sand, and the average particle size distribution has a predetermined value. It is composed of a large grain 2a and a small grain 2b whose average particle size is smaller than a predetermined value of the large grain 2a. In the compaction step, since the vibration device 27 does not give vibration, the large particles 2a and the small particles 2b are arranged in a disorderly manner.

FIG. 4B shows the configuration of the sand block 4 that has been vibrated by the vibration exciter 27 in the compaction process. The casting sand 2 is composed of large grains 2a and small grains 2b as in the comparative example. The large grains 2a and the small grains 2b of the casting sand 2 are arranged so as to be regularly aligned by being subjected to vibration in the compaction process. Therefore, as compared with the sand block 4 of FIG. 4A, the sand block 4 of FIG. 4B improves the processing accuracy of the processed surface 5 (see FIG. 7C) at the time of removal processing, reduces the surface roughness, and reduces the surface roughness of the processed surface 5. Can be finished neatly.

The casting sand 2 is a spherical ceramic artificial sand, the average particle size of the large grain 2a is 150 to 212 (μm), the mixing ratio is 60 to 50%, and the average particle size of the small grain 2b is 75 to 106 (μm). ), The mixing ratio is 40 to 50%, and it is more preferable that the total is 100%. With such a configuration, it is possible to obtain a casting 10 (see FIG. 5B) having a good surface accuracy without a coating mold while ensuring the recyclability and air permeability of the casting sand mold 1 (see FIG. 11A). it can.

The casting sand 2 is not limited to spherical ceramic artificial sand, but can be used for sand block 4 such as ceramic artificial sand having an angular portion, natural sand, silica sand, chromate sand, and zircon sand. Other general cast sand 2 may be used. Further, the average particle size of the large grain 2a and the small grain 2b is not limited to the above value, and may be sand grains of other average particle size, and the mixing ratio is not limited to the above value, and is in a range other than the above. It may be changed as appropriate.

Next, the action and effect of the sand block 4 other than the above will be described. As described above, since the kneaded casting sand 2 and the binder 3 are not only pressed but also pressed while applying vibration, unevenness in density can be eliminated in the entire sand block 4. .. Further, since the cast sand 2 is an artificial ceramic sand, the unevenness of the size of the sand grains is reduced as compared with the natural sand, the shape of the sand grains is round, and the sand grains 2a and 2b can be uniformly arranged. .. Further, since the alkali phenol resin for ester curing of the binder 3 is water-soluble, it can be easily kneaded with the casting sand 2 and can be easily removed at the time of disposal.

Further, since the small particles 2b having an average particle size smaller than the predetermined value of the large particles 2a are light, they are easily removed by suction during the recycling process, but the recycling rate is improved by mixing the large particles 2a having the average particle size having a predetermined value. be able to. Further, by mixing the large particles 2a having an average particle size of a predetermined value, the air permeability of the casting sand mold 1 can be improved. Further, the accuracy of the machined surface 5 can be improved by mixing the small particles 2b whose average particle size is smaller than the predetermined value of the large particles 2a. That is, it is possible to improve the processing accuracy after the removal processing while ensuring the recyclability and the ventilation path.

Further, in order to form the sand block 4 by reusing the casting sand 2, a new small grain 2b casting sand 2 having a small average particle size is added, and the large grain 2a casting sand 2 having a large average particle size is recycled. To use. By doing so, when the binder 3 is removed by sucking air from the dust collector 24 after the disassembling step, the casting sand 2 of the small particles 2b is removed together with the binder 3, but the average particle size By adding the casting sand 2 of the small particles 2b, most of the large particles 2a can be recycled.

The embodiment is not limited to the sand block 4 in which the casting sand 2 is vibrated by the vibration device 27 in the compaction step, and the casting sand 2 shown in the comparative example of FIG. 4A is vibrated by the vibration device 27. It is assumed that the sand block 4 which is not given is also included. However, the sand block 4 in which the casting sand 2 is vibrated by the vibrating device 27 in the compaction step has the effect of making the grains 2a and 2b of the casting sand 2 uniform throughout the sand block 4 and eliminating unevenness in density. Is big.

Next, a product example of the casting 10 using the casting sand mold 1 of the present invention will be described. As shown in FIG. 5A, the casting 10 is a so-called closed impeller. The closed impeller 10 is used for a water pump 15 or the like, and the blade 11 is sandwiched between the main plate 12 and the side plate 13, and the water that has entered through the opening of the side plate 13 is rotated around the rotating shaft 14 to be taken into the main plate 12. It is discharged in the outer diameter direction by the centrifugal force of the above and the guidance of the blade 11.

As shown in FIGS. 5B and 11A, the closed impeller 10 immediately after being removed from the casting sand mold 1 is in a state where the molten metal 62 is solidified in the runner and reaches the closed impeller 10. The blade 11 of the closed impeller 10 has a spiral shape in a plan view and a three-dimensionally complicated shape twisted from the center toward the outer diameter.

Next, the removal processing process as a higher level will be described in detail. As shown in FIG. 6A, in the shape data producing step, the shape data (not shown) of the casting 10 (see FIG. 5) to be a product is produced by the computer 31. Even in the case of a two-dimensional drawing, if the casting 10 to be a product has a three-dimensional shape, shape data by three-dimensional CAD is produced. Further, the casting sand mold 1 (see FIG. 11) is designed on the three-dimensional CAD based on the shape data of the casting 10 to be the product. At this time, the method of dividing the sand mold 1 for casting, and depending on the shape, a core shape, a casting plan such as a molten metal runner, etc. are also examined and designed. For example, when the casting 10 has a complicated shape such as a closed impeller, the shape data 10a of the core 7 (see FIG. 8) of the casting sand mold 1 is produced.

In the machining path manufacturing process, based on the CAD shape data of the casting sand mold 1, CAM software is used to examine how to move the path of the removal tool 43a in the machining range 4a on the monitor 32, and the numerically controlled machining machine 40 (numerical control machining machine 40 ( An operation program (for example, so-called G code) of (see FIG. 6B) is created. The input data to the CAM software is, for example, the type of the removal tool 43a, the rotation speed, the feed rate, the cutting amount, the path (machining path), and the like, and the final machining shape data 33 is confirmed on the monitor 32.

As shown in FIGS. 6B and 7A, the numerical control processing machine 40 spans the rails 44 that serve as the first axis (X-axis), the columns 45 that stand slidably on these rails 44, and these columns 45. A beam portion 46 that serves as a second axis (Y-axis), a slider 47 that is slidably provided on the beam portion 46, and an elevating mechanism 48 that is slidably provided on the slider and serves as a third axis (Z-axis). The elevating mechanism 48 is rotatably provided around the axis of the elevating mechanism 48 to be the fourth axis (rotating shaft), and the rotating mechanism 51 is rotatably provided with the fifth axis (swinging shaft). ) Is provided.

Further, the numerically controlled machining machine 40 includes a base 53 provided between the rails 44, a clamp mechanism 54 provided on the base 53, and a spindle 41 and a chuck 42 provided at the tip of the swing mechanism, and the chuck 42 has a base 53. The removal tool 43 is attached. The numerically controlled machining machine 40 is a so-called 5-axis machining machine. In the numerically controlled machining machine 40, the removal tool 43 corresponding to the removal tool 43a on the CAM software is used.

In the sand block setting step, the sand block 4 is set on the table 53, and the formwork 20 of the sand block 4 is clamped by the clamping mechanism 54. The sand block 4 of the embodiment is provided with a mold 20, but the present invention is not limited to this, and depending on the shape of the core or the like, the sand block 4 is directly clamped without providing the mold 20. It may be clamped at 54.

As shown in FIGS. 6B to 7C, the removal tool 43 is an end mill, and the ratio (L / D) of the amount of protrusion L from the end of the chuck 42 to the diameter D is 5 to 50. In the embodiment, the removal tool 43 is an end mill, but the removal tool 43 is not limited to this, and the removal tool 43 may be at least one such as a drill, a tool bit, and an electrodeposition grindstone, as long as the sand block 4 can be removed. It does not matter even if it is a rod-shaped tool. In the case of a bite, the shank width D is used instead of the diameter D.

In the removal processing step, casting is performed by removing sand particles of the sand block 4 while peeling them with the removal tool 43 using a numerically controlled processing machine 40 having four or more axes that operates the removal tool 43 by computer control based on the shape data. Manufacture part or all of sand mold 1. When the removal tool 43 is a rotary tool, the machining conditions are preferably a machining speed of 1 to 4 (m / sec) and a feed rate of 1000 to 9000 (mm / min). The processing conditions are not limited to the above values, and may be values other than the above as long as the sand block 4 can be processed.

In the embodiment, the numerical control machining center 40 is a 5-axis machining center, but the present invention is not limited to this, and the numerical control machining center 40 is a 4-axis or 6-axis machining center if it is a machining center with 4 or more axes. It may be. By setting the numerically controlled processing machine 40 to have four or more axes, it is possible to manufacture a sand mold 1 for casting of a casting 10 having an undercut 6. Further, the number of cores can be reduced, and a high-precision casting sand mold 1 can be manufactured.

In particular, by using the numerically controlled machining machine 40 as a 5-axis machining center, it has a complicated shape having blades 11 like the closed impeller 10 shown in FIG. 5A and a large three-dimensional shape, and the removal tool 43 can be moved in at least two directions. In order to form the blades 11 which are continuous in different directions in the plan view of the sand block 4 and which are continuous at different angles of inclination with respect to the vertical direction of the sand block 4 by advancing from the above and removing the sand block 4. The sand mold 1 for casting having the undercut 6 of the above can be manufactured.

Next, the core 7 for the closed impeller 10 (see FIG. 5) will be described. As shown in FIG. 8A, the core 7 forms the blade 11 of the closed impeller 10, the inner surface of the main plate 12, the inner surface of the side plate 13, and the like. Cavities 70 for forming the blades 11 are formed in the core 7 in three places in a spiral shape from the central portion 71 toward the outer peripheral portion 72 in a plan view of the cavity 70. All of the three cavities 3 are formed in one sand block 4 in a plan view.

As shown in FIGS. 8A and 8B, the cross section of one cavity 70 has a large inclination angle with respect to the perpendicular direction (axial direction) at the cross-sectional position (1) from the central portion 71 toward the outer peripheral portion 72, and the cross section of the cross section. At position (2), the tilt angle is smaller than at cross-section position (1), at cross-section position (3), the tilt angle is smaller than at cross-section position (2), and at cross-section position (4), cross-section position (3). ), The tilt angle is smaller.

As described above, the shape of the cavity 70 of the core 7 has the undercut 6 which is continuous in different directions in the plan view of the sand block 4 and the inclination angle of the sand block 4 with respect to the vertical direction is continuous at different angles. ing.

Next, the angle of the removal tool 43 in the removal processing step will be described. As shown in FIG. 9A, the core 7 and the cavity 70 are formed in the core 7 in three places in a spiral shape from the central portion 71 toward the outer peripheral portion 72 in a plan view of the cavity 70.

As shown in FIGS. 9A and 9B, the cross section of one cavity 70 has an inclination angle with respect to the perpendicular direction (axial direction) at the positions (1) to (4) of the cross section from the central portion 71 to the outer peripheral portion 72. The tilt angle is θ1 at the cross-section position (1), the tilt angle is θ2 at the cross-section position (2), the tilt angle is θ3 at the cross-section position (3), and the tilt angle is θ3 at the cross-section position (4). The angle is θ4, and the tilt angle is gradually changed so that θ1> θ2> θ3> θ4.

In the removal processing step, the removal tool 43 continues in different directions in the plan view of the sand block 4 from the central portion 71 of the core 7 toward the outer peripheral portion 72, and the inclination angle of the sand block 4 with respect to the vertical direction is different. It moves continuously at an angle to form a complex undercut 6 shape. By performing such removal processing, the cavity 70 is formed into an impeller shape (shape of impeller blades) that is spiral in a plan view and twisted in the height direction, and all the blades 11 of the impeller shape (the shape of the blades of the impeller). (See FIG. 5) is formed in one sand block 4 in a plan view.

Next, the core 7 and the main mold 8 will be described. As shown in FIG. 10A, the core 7 is manufactured by removing the sand block 4 with the removing tool 43. Similarly, by removing the sand block 4 with the removing tool 43, the main mold 8 shown in FIG. 10B is manufactured. As shown in FIG. 10C, a casting sand mold 1 is obtained by setting the core 7 in the main mold 8. The casting sand mold 1 of FIG. 10C is formed so as to take two closed impellers 10.

Next, the casting process as a higher level will be described in detail. As shown in FIG. 11A, in the mold matching step, the core 7 is set between the upper mold 1a and the lower mold 1b, and the upper mold 1a and the lower mold 1b are positioned by a positioning pin (not shown) or the like. Together, it is a sand mold 1 for casting. In this case, the upper mold 1a and the lower mold 1b can be said to be the main mold 8. Further, the mold 20 may be clamped by the clamp member 28. By clamping the mold 20, it is possible to prevent the upper mold from floating when the molten metal 62 is poured.

In the melting step, the metal material is melted to obtain a molten metal 62. In the pouring step, the molten metal 62 is poured from the ladle 61 into the sprue 63 of the casting sand mold 1. The molten metal 62 is filled in the cavity 70 of the sand mold 1 for casting, and is solidified by cooling to become a closed impeller (casting) 10.

Next, another aspect of the casting sand mold 1 of FIG. 11A will be described. As shown in FIG. 11B, the upper mold 1a is formed with a convex portion 7 that greatly protrudes over the entire cavity 70 forming the product. The lower mold 1b is formed with a recess 8 that is largely recessed over the entire cavity 70 forming the product and that fits into the convex portion 7 of the upper mold 1a.

By forming the convex portion 7 in the upper mold 1a and the concave portion 8 in the lower mold 1b, it is not necessary to provide a positioning pin in the casting sand mold 1 in the mold matching step, and the casting sand mold 1 can be easily manufactured. be able to. This effect is due to the fact that the partitioning surface (parting line) of the casting sand mold 1 can be freely determined by using the numerically controlled machining machine 40 as a machining center having four or more axes, particularly five axes.

Next, actions other than the above will be described. In the sand block forming step, the sand block satisfies at least one of a compressive strength of 15 to 50 (N / cm ² ) and a bulk density of 1.0 to 2.0 (g / cm ³ ). Since it is formed, the compressive strength and the bulk density are in a range suitable for the removal process, and the accuracy of the machined surface 5 can be improved without being broken by the removal process by the removal tool 43. Further, since the sand block is formed only by pressing the casting sand in the mold 20, the sand block 4 can be formed in a short time without the need for the subsequent heat treatment as in the prior art. Further, by forming the sand block 4 satisfying at least one of a compressive strength of 15 to 50 (N / cm ² ) and a bulk density of 1.0 to 2.0 (g / cm ³ ), the casting sand 2 Since the pressing of the sand block 4 can be performed at a low pressure, the sand block 4 can be easily molded. Further, since the compressive strength of the sand block 4 is relatively small, the load applied to the removal tool 43 during machining can be reduced. Further, since the load applied to the removal tool 43 can be reduced, the machining speed and the feed rate can be increased, and therefore the machining man-hours can be significantly reduced and the manufacturing cost can be suppressed to a low level.

Further, in the removal processing step, the undercut 6 is provided by removing the sand block 4 by entering the removal tool 43 from at least two directions or more in a plan view of the sand block 4 using a numerically controlled processing machine 40. Since the cavity 70 is formed, it is possible to manufacture a core 7 or a main mold 8 having a cavity 70 having a complicated shape, not just an undercut 6.

Further, since the sand block 4 is removed by the removing tool 43, the desired core 7 and the main mold 8 can be manufactured in a short time as compared with the additive manufacturing method (3D printer). In addition, the large core 7 and the main mold 8 are easily collapsed and difficult to handle. However, if a sand mold is manufactured by the additive manufacturing method (3D printer), it is necessary to maintain the shape of the entire mold with the sand itself adhered by the thermosetting resin. It is difficult to manufacture a large core 7 and a main mold 8 due to the fact that there is a problem and the limitation of the modeling range. Further, since it is difficult to make the main mold 8 in close contact with the mold 20 by the additive manufacturing method, even if the main mold can be manufactured by the additive manufacturing method, the mold 20 cannot be clamped and suppressed. When a large amount of molten metal is poured into a mold to manufacture a large casting 10, the upper mold 1a may be lifted.

In this respect, in the present invention, since the sand block 4 is held by the mold 20, the mold 20 supports the periphery even if the core 7 or the main mold 8 is large, so that the shape of the entire mold can be easily obtained. In addition, since the processing range is larger than that of the additive manufacturing method, even a large core 7 or a main mold 8 can be manufactured. Further, by clamping the mold 20 with the clamp member 28, the upper mold 1a can be suppressed even if a large amount of molten metal is poured into the mold, and a large casting 10 can be easily manufactured.

Further, a core 7 or a core 7 having a cavity 70 having a complicated shape with a three-dimensional twist having an undercut 6 which is continuous in a plurality of directions in a plan view and has a continuous inclination in a plurality of vertical directions. Mold 8 can be manufactured.

Further, even a large core 7 including all the blades 11 having an impeller shape having a spiral shape and a complicated twist can be manufactured.

If the machining center has four or more axes, it is possible to manufacture a cavity 70 having a three-dimensionally complicated shape by rotating a table on which a sand block is installed. If the machining center has 5 or more axes, it is not necessary to rotate the table.

Further, since the removal tool 43 is a sand block 4 in which the workpiece is not excessively compressed even if the ratio (L / D) of the protrusion amount L to the shank width or the diameter D is 5 to 50, the removal tool 43 is used. The sand block 4 can be deeply dug by removal processing without chattering. Further, even when the tip portion of the long removal tool 43 having (L / D) of 5 to 50 is used to process the vicinity of the surface of the sand block 4, the sand to be processed is not excessively compressed. Since it is the block 4, the removal tool can shallowly remove the vicinity of the surface of the sand block without chattering. As described above, in the present invention, it is possible to perform deep machining and shallow machining with one removing tool 43.

Further, in the cavity 70 formed in the sand block 4 satisfying at least one of a compression strength of 15 to 50 (N / cm ² ) and a bulk density of 1.0 to 2.0 (g / cm ³ ). Therefore, the casting 10 can be manufactured without collapsing even when the molten metal 62 is poured. Further, the casting core 7 is an undercut 6 that is continuous in different directions in the plan view of the sand block 4 and that the inclination angle of the sand block 4 with respect to the vertical direction is continuous at different angles, so that the sand block 4 is complicated with a twist. Even if the casting 10 has a different shape, it can be a highly accurate casting.

Further, since the cavity 70 in the shape of a plurality of three-dimensionally twisted blades 11 of the impeller is formed in one sand block 4, there is a possibility that the accuracy of the core as a whole may be lowered by dividing it as in the conventional technique. It is possible to manufacture a large casting 10 in which a cavity 70 having a complicated shape is formed with high accuracy.

Further, in the embodiment, the casting 10 is a closed impeller, but the casting 10 is not limited to this, and a so-called open impeller may be used. Further, if the cavity 70 has an undercut 6 with a twist, the casting sand mold 1 is an impeller. It doesn't have to be for use.

1 ... Casting sand mold 2 ... Casting sand (spherical ceramic artificial sand)
3 ... Baking material (water-soluble alkali phenol resin for ester curing, curing agent for alkaline phenol resin)
4 ... Sand block 6 ... Undercut 7 ... Core (casting core)
8 ... Main mold 10 ... Casting (closed impeller, open impeller, impeller)
10a ... Product shape data 11 ... Blade 31 ... Computer (CAD, CAM)
40 ... Numerically controlled machining machine 43 ... Removal tools (end mills, drills, tools, electrodeposition grindstones)
D ... Shank diameter or diameter L ... Amount of protrusion from the chuck end θ1 to θ4 ... Tilt angle of the removal tool

Claims (7)

Fill the formwork with casting sand mixed with binder and
Press the casting sand in the mold so that the compressive strength satisfies at least one of 15 to 50 (N / cm ² ) and the bulk density of 1.0 to 2.0 (g / cm ³ ). A sand block forming step of forming a sand block having a predetermined shape by solidifying the sand block.
Using a numerically controlled machining machine that operates a rod-shaped removal tool by computer control based on shape data, the sand block is removed by allowing the removal tool to enter from at least two directions in a plan view of the sand block. A method for producing a sand mold for casting, which comprises a removal processing step for producing a core or a main mold of a sand mold for casting in which a cavity having an undercut is formed. The method for manufacturing a sand mold for casting according to claim 1.
The removal processing step is a sand mold for casting characterized in that the sand block is continuous in different directions in a plan view and the sand block is continuously tilted at different angles with respect to the vertical direction. Manufacturing method. The method for manufacturing a sand mold for casting according to claim 1 or 2.
In the removal processing step, the cavity is formed into an impeller shape that is spiral and twisted in the height direction in a plan view, and all the blades of the impeller shape are formed in one sand block in a plan view. A method for manufacturing a sand mold for casting, which is characterized in that. The method for manufacturing a sand mold for casting according to any one of claims 1 to 3.
A method for manufacturing a sand mold for casting, wherein in the removal processing step, the numerically controlled processing machine uses a machining center having four or more axes. The method for manufacturing a sand mold for casting according to any one of claims 1 to 4.
A method for producing a sand mold for casting, which comprises a removal process of deeply digging the sand block with the removal tool having a ratio (L / D) of a protrusion amount L to a shank width or a diameter D of 5 to 50. In a casting core having a cavity for casting the product part inside
The cavity is formed in a sand block satisfying at least one of a compressive strength of 15 to 50 (N / cm ² ) and a bulk density of 1.0 to 2.0 (g / cm ³ ).
A casting core characterized by having continuous undercuts in different directions in a plan view of the sand block and continuous undercuts at different angles of inclination of the sand block with respect to the vertical direction. The casting core according to claim 6.
A plurality of the cavities are formed in the sand block.
The shape of the cavity is the shape of the blades of the impeller that are spiral and twisted in the height direction in the plan view of the sand block.
A casting core, wherein all of the plurality of cavities are formed in one sand block in a plan view.

Images