JP2003230953A - Method of post-processing cast article - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of post-processing a cast article capable of relieving internal stress accompanying cooling shrinkage at the timing of easily securing the elongation of the cast article by naturally cooling after shaking-out and capable of suppressing a rapid temperature change and ensuring the accurate dimension of the cast article when holding them at a resin disintegration temperature (shaking-out temperature) by holding and shaking out the article at the resin disintegration temperature of sand remaining on the article after sand mold casting in a temperature-decreasing process and naturally cooling the article after shaking-out. <P>SOLUTION: The method of post-processing the cast article produced by using a sand mold comprises a shaking-out process S2, a natural cooling process S3 subsequent to the process S2 and heat treatment processes S4, S5 and S6 for performing pre-determined heat treatments after the process S3 is completed. The shaking-out process S2 shakes out the cast article having sand remaining thereon while keeping it at the resin decomposition temperature in the course of a temperature decrease after casting S1. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a post-treatment method for a cast product such as a post-treatment for a cylinder block or other cast product cast by using a sand mold.

[0002]

2. Description of the Related Art Conventionally, when a cylinder block made of an aluminum alloy in which a cast iron cylinder liner is encircled is cast as an example of a cast product, the cylinder block body is subjected to a cooling process after casting and during a heat treatment as a post-treatment process. Aluminum alloy as a base material constituting the, and the shrinkage rate of both the cast iron cylinder liner cast by this base material, internal stress due to the difference in the amount of shrinkage,
This internal stress is concentrated between the cylinder bores with the smallest base material thickness, and defects such as cracks occur.

In order to solve such problems, sand mold
(For details, sand cast the cylinder block as a cast product, and before the heat treatment, let the casting product cool in the sand mold (natural cooling) to reduce the internal stress concentrated between the cylinder bores. There is a method that prevents the occurrence of defects such as cracks by opening by plastic deformation of the base material.In this case, although the occurrence of defects such as cracks is prevented, between the rear surface of the cylinder liner and the base material Gaps g1 to g14 (Fig. 9
(See) occurs, which causes a new problem.

Hereinafter, the occurrence of the above-mentioned problems will be described in detail with reference to FIGS. 7, 8 and 9. FIG. 7 is a process diagram showing the casting of a cast product and a post-treatment method after casting, and FIG. 8 is an explanatory diagram thereof. In the casting process S71, the cast iron cylinder liner 81 (see FIG. 9) is a core. A cylinder in which the cylinder liner 81 is cast into a supported sand mold cavity by injecting a molten aluminum alloy of about 750 ° C. through a molten metal spout, a runner, a riser, and a spout for the product. Block 82 (see FIG. 9) is cast.

Next, in a sand removing step S73 shown in FIG. 7, the cylinder block 82 is naturally left to cool from room temperature to about 220 ° C. for about 6 hours while the cylinder block 82 is kept in the sand mold, and the cylinder bores 83, 8 are cooled.
4th, 84th, 85th, 85th, 86th (where the cylinder bore 83 corresponds to the first cylinder, the cylinder bore 84 corresponds to the second cylinder, the cylinder bore 85 corresponds to the third cylinder, and the cylinder bore 86 corresponds to the fourth cylinder). Internal stress concentrated in (corresponding to the cylinder) is released by plastic deformation of the base material, and defects such as cracks are prevented from occurring between these cylinder bores.

Next, in a sand removing step S73 shown in FIG. 7, the cylinder block 82 after the cooling is finished is put into a fluidized bed sand removing furnace in a sand mold as it is, and hot air is blown from below at about 500 ° C. sand in the furnace. When the resin as the binder of the casting sand is blown up to collapse and the so-called sand removal is performed to break the sand mold, the casting sand remaining inside and outside the cylinder block 82 is removed.

Next, each step S74, S75, S shown in FIG.
Heat treatment is applied to the cylinder block 82 after sand removal by 76, or first, in the solution heat treatment step S74, the cylinder block 82 as a casting is heated to about 500 ° C. for about 2 hours to create a supersaturated solid solution state. Execute (solution treatment).

Next, in a quenching step S75, the cylinder block 82 at about 500 ° C. is rapidly cooled to about 50 ° C. to quench it. Next, in the artificial aging step S76, the cylinder block 82 after quenching is heated to about 240 ° C. for about 3.5 hours to perform artificial aging to achieve aging. After the T6 process including the above steps S74 to S76, the cylinder block 82 is naturally cooled.

However, since the fluidized bed sand removing furnace used in the above sand removing step S73 has extremely high thermal efficiency, the cylinder block 82 at room temperature to about 220 ° C. after the cooling step S72 is put into the sand removing furnace. When it is done, instantly 500 ℃
The cylinder liner 81 and the cylinder block body 87 made of aluminum alloy are rapidly heated back and forth (see the temperature change line b in FIG. 8), and due to the difference in expansion coefficient between the base material of aluminum alloy and the cylinder liner 81 made of cast iron. (See FIG. 9) Partial gaps g1 to g14 are generated in the contact surface.

FIG. 9 shows the result of actual measurement of the state of occurrence of the gaps g1 to g14, and the cylinder block 82 after casting takes 220 hours for 6 hours before the sand removing step S73.
Cylinder block 82, which has been left to cool to ℃ and then put into a fluidized bed sand blast furnace, is removed from its head deck (upper end surface) by about 10
It was cut at a height of mm to measure the state of gap formation.

The above-mentioned gaps are g1 = 30 μm and g2 = 5.
0 μm, g3 = 50 μm, g4 = 30 μm, g5 = 80
μm, g6 = 50 μm, g7 = 150 μm, g8 = 50
μm, g9 = 80 μm, g10 = 100 μm, g11 =
100 μm, g12 = 30 μm, g13 = 30 μm, g
14 = 100 μm, and a gap of 30 to 150 μm was generated in all cylinders.

[0012] In short, in order to solve the conventional problem that cracks occur between cylinder bores, when a cast product after casting is allowed to cool before sand removal and then put into a sand removal furnace, a rapid temperature rise ( Due to the temperature change), a new problem arises that a rear surface gap defect of the cylinder liner occurs.

By the way, as a conventional technique for carrying out heat treatment and sand removal as post-treatment of a cast product cast by using a sand mold, as disclosed in Japanese Patent Laid-Open No. 11-156528, casting is performed during solution treatment. Although the sand is discharged, that is, the sand is removed, the one disclosed in the publication is not such that the sand is removed in the temperature drop process of the cast product after casting.

[0014]

DISCLOSURE OF THE INVENTION According to the present invention, sand casting is performed by holding the casting product after sand mold casting at the resin collapse temperature (sand removal temperature) of the casting sand remaining in the casting product during the temperature drop process. By performing cooling after sand removal, it is possible to suppress a rapid temperature change of the cast product when maintaining the resin collapse temperature, it is possible to ensure the dimensional accuracy of the cast product, and after sand removal An object of the present invention is to provide a post-treatment method for a cast product, which is capable of releasing internal stress associated with cooling shrinkage at a timing at which the elongation of the cast product is easily ensured by performing cooling.

[0015]

A post-treatment method for a cast article according to the present invention is a post-treatment method for a cast article cast by using a sand mold, wherein the casting step is performed during the temperature drop process of the cast article after casting. A sand removal step of performing sand removal by maintaining the resin collapse temperature of the casting sand remaining in the product for a predetermined time, a cooling step of allowing cooling after the sand removal step, and a predetermined heat treatment after the cooling step. And a heat treatment step to be performed.

The cooling in the cooling step of the above construction may be set to slow cooling as natural cooling. According to the above configuration, the casting product cast by using the sand mold in which the casting sand (core sand) is bonded with the resin is held at the resin collapse temperature (sand removal temperature), and the rapid temperature change of the casting product. (In particular, temperature rise) can be suppressed, the dimensional accuracy of the cast product can be ensured, and since cooling is performed after sand removal, the inside of the cast product due to cooling shrinkage can be easily secured at the timing when expansion is easily secured. The stress can be released.

In one embodiment of the present invention, the transition to the resin collapse temperature is carried out without allowing cooling and without reheating in the temperature lowering process.

According to the above construction, since the cast product is maintained at the resin collapse temperature immediately after casting, the cycle time of the entire post-treatment can be shortened and the temperature change can be minimized. Therefore, in other words, it is possible to secure the timing at which the cast product extends even after sand removal, so that the internal stress generated in the cast product can be reduced.

In one embodiment of the present invention, the above-mentioned cast product is formed by surrounding a base material with a cast-in member having different cooling shrinkage rates. According to the above configuration, by having the cast iron member and the base metal having different cooling collection rates, it is a disadvantageous condition for defects such as cracks and the like (the cast iron member and the base metal) to generate a gap. , It is caused by the generation of internal stress due to the difference in shrinkage rate between the solidification shrinkage of the base material after casting and the cooling shrinkage of the cast-molded member by performing sand removal in the stage before the cooling process after casting. Defects such as cracks and the difference in expansion coefficient between the two (base metal and cast-in-mold member) due to transition to the resin collapse temperature (sand removal temperature) can prevent the formation of a gap between the two. .

In one embodiment of the present invention, the base material is set in an aluminum alloy cylinder block main body, and the cast-molded member is set in an iron cylinder liner. The cylinder liner configured as described above may be made of cast iron.

According to the above construction, the aluminum alloy has a large shrinkage rate and expansion rate with respect to iron, and by having such a cylinder block body and cylinder liner, defects such as cracks between the cylinder bores and both (cylinder block). Although it is a disadvantageous condition for creating a gap between the main body and the cylinder liner, sand removal is performed before the cooling process after casting, so solidification shrinkage of the aluminum alloy cylinder block body after casting and iron Defects such as cracks between the cylinder bores caused by the generation of internal stress due to the difference in shrinkage between the cylinder liner and the cooling shrinkage, and both due to the transition to the resin collapse temperature (sand removal temperature) (cylinder block body and cylinder It is possible to prevent a gap from being generated on the rear surface of the cylinder liner due to the difference in expansion coefficient of the liner).

In one embodiment of the present invention, in the heat treatment step, quenching is performed after the solution treatment, and then,
It is set to T6 processing for performing artificial aging processing.
According to the above structure, the strength and hardness of the cylinder block can be improved by the T6 process.

In one embodiment of the present invention, in the sand removal step, sand removal is performed using a fluidized bed sand removal furnace. According to the above configuration, by using the fluidized bed sand blasting furnace, when the cast product is put into the furnace with its high thermal efficiency, the sand blasting temperature is instantly reached, but by holding the sand blasting temperature immediately after casting, There is no sudden temperature rise,
The dimensional accuracy of the cast product can be ensured, and the cycle time of the entire post-treatment can be further shortened.

In one embodiment of the present invention, the transition from the end of the cooling step to the solution treatment temperature in the heat treatment step is such that the temperature rising gradient of the cast product is set to a gentle gradient.

According to the above construction, since the temperature of the cast product can be gently raised with respect to the temperature of the solution heat treatment from the end of cooling, it is possible to prevent the occurrence of strain around the cylinder bore. That is, it is possible to more reliably prevent the occurrence of a gap on the contact surface between the cylinder liner and the cylinder block body.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. The drawings show the casting and post-treatment methods of castings,
FIG. 1 is a process diagram, and FIG. 5 is an explanatory diagram thereof. First, in a casting process S1 of the process diagram shown in FIG.
Cast cylinder block of cylinder engine.

Casting structure used in this casting step S1
The (sand type structure) is configured as shown in FIG. That is, the cavity portion 12 forming the cylinder block body 11 (see FIG. 4), and the cavity portion 12 and the riser portion 1
A sprue part (spout for products) 14 that continuously connects 3 and
The runner 16 which connects the above-mentioned riser section 13 and the sprue (spout of molten metal) 15 is formed by casting sand, and a cylinder liner 18 made of cast iron is formed by the core 17 formed by the same casting sand. The sand mold 20 is configured so as to support the above and form the cylinder block 19 shown in FIG.

Here, the above-mentioned casting sand is bonded by a resin as a binder to form a sand mold 20 having a core 17 as shown in FIG. When casting the cylinder block 19 (see FIG. 6) of the in-line four-cylinder engine, the above-mentioned sprue part 14 is the cylinder bores 1 to 4 (excluding the part between the second cylinder and the third cylinder (that is, the part between the central parts)). (See FIG. 6) A total of four side portions are formed in a direction orthogonal to the cylinder row (so-called width direction).

Further, the above-mentioned riser section 13 may be divided into two for the first cylinder and the second cylinder and for the third cylinder and the fourth cylinder in order to prevent the shrinkage cavity defect. Further, as shown in FIG. 3, in order to divide the above-mentioned riser portion 13 in the cylinder row direction while leaving a part of the lower portion thereof, a cut portion 21 (partition wall made of casting sand) having a predetermined depth in the riser portion 13 To form
The action direction of the stress due to the difference between the solidification shrinkage of the base material after casting and the cooling shrinkage of the cylinder liner 18 may be divided into two at the cut portion 21 so as to allow some plastic deformation of the base material. .

In the above-mentioned casting step S1, in FIG. 2 or FIG.
About 75 from the gate 15 (so-called gate) of the sand mold 20 shown in
Pour the molten aluminum alloy of 0 ℃, this molten metal,
The cavity portion 12 is filled with the melt through the runner 16, the riser portion 13, and the plurality of sprue portions 14, and pressure is applied to the melt in the cavity portion 12 by the gravity of the melt in the pusher portion 13.

The molten metal poured into the above-mentioned cavity 12 is solidified with time after pouring, and the cylinder liner 18 is cooled with time, so that the aluminum alloy as the base material has a cooling shrinkage ratio. A cylinder block 19 in which different cast-in member (cylinder liner 18) is cast is cast.

Next, the sand removal step S2 in the process diagram shown in FIG.
Then, in order to remove the sand that remains inside and outside the cylinder block 19 during the temperature drop process of the cylinder block 19 after casting, hold the temperature at the collapse temperature of the resin that bound the sand for a predetermined time. Remove the sand.

That is, when the cylinder block 19 after casting reaches a resin collapse temperature (sand removal temperature) of about 500 ° C. due to the temperature drop, the cylinder block 19 is left in the sand mold 20 as it is in the fluidized bed sand removal furnace. It is left inside and outside of the cylinder block 19 when it is charged, and hot air is blown up from below to the sand of about 500 ° C. in the furnace to collapse the resin as a filler of the casting sand and to break the sand mold 20, so-called sand removal. Casting sand is removed.

As shown in FIGS. 1 and 5, the transition from the above-mentioned casting to the resin collapse temperature (sand removal temperature) (transition from the step S1 to the step S2) is performed without passing through the cooling step, and It is executed without reheating in the temperature drop process of.

Next, in the cooling step S3 of the process chart shown in FIG.
The cylinder block 19 taken out of the fluidized bed sand removing furnace is at room temperature to 220 ° C (preferably at room temperature to 100 ° C) for about 4 hours.
(° C) to allow cooling (gradual cooling), and then use the cylinder bores 1 and 2 shown in FIG.
Space, 2, 3 space, 3 space, 4 space (however, cylinder bore 1
Corresponding to the cylinder, the cylinder bore 2 corresponds to the second cylinder, the cylinder bore 3 corresponds to the third cylinder, and the cylinder bore 4 corresponds to the fourth cylinder). It prevents the occurrence of defects such as cracks between these cylinder bores.

Next, the steps S4 and S in the process diagram shown in FIG.
A predetermined heat treatment (T6 treatment) is performed on the cylinder block 19 after being left to cool by S5 and S6, but the transition from the end of the left cooling process S3 to the solution treatment temperature in the heat treating processes S4, S5 and S6 is performed by casting. The temperature rise gradient of the cylinder block 19 is set to a relatively gentle gradient as is clear from the comparison between the temperature change line a in FIG. 5 and the temperature change line b in FIG.

In the heat treatment step described above, first, in the solution heat treatment step S4, the cylinder block 19 after cooling is put into the solution heat treatment furnace, and the cylinder block 19 is heated in an air atmosphere at about 500 ° C. for about 2 hours. Then, heat treatment (solution treatment) for producing a supersaturated solid solution state is performed.

Next, in the quenching step S5, the cylinder block 19 at about 500 ° C. is put into a quenching furnace and quenched by quenching to about 50 ° C. Next, in the artificial aging step S6, the quenched cylinder block 19 is put into an aging furnace and heated to about 240 ° C. for about 3.5 hours to perform artificial aging to achieve aging.

T consisting of this solution treatment → quenching → aging treatment
The six treatments can improve the strength and hardness of the cylinder block 19. Each of the above steps S4, S5, S
After the T6 treatment (heat treatment) of No. 6, the cylinder block 19 is naturally cooled in the cooling step S7 in the process chart of FIG.

FIG. 6 shows the result of actual measurement of the state of the gap between the contact surfaces of the cast iron cylinder liner 18 and the aluminum alloy cylinder block body 11, and the sand removal step S2.
After that, the cylinder block 19 as a cast product is gradually cooled to 100 ° C. over 4 hours (see the cooling step S3), and the cylinder block 19 is removed from its head deck (upper end) by about 1
It was cut at a height of 0 mm and the state of gap formation was measured, and it was confirmed that no gap was generated in all cylinders of the cylinder bores 1 to 4 in this example product by the above-mentioned post-treatment method.

As described above, the post-treatment method of the cast product of the embodiment shown in FIGS. 1 to 6 is the post-treatment method of the cast product (see the cylinder block 19) cast by using the sand mold 20.
A sand removal step S2 of performing sand removal by holding for a predetermined time at the resin collapse temperature (sand removal temperature) of the casting sand remaining in the casting (see cylinder block 19) during the temperature drop process of the cast product after casting, It is provided with a cooling step S3 for cooling after the sand removal step S2 and heat treatment steps S4, S5, S6 for performing a predetermined heat treatment after the cooling step S3.

According to this structure, the casting product (see the cylinder block 19) cast by using the sand mold 20 in which the casting sand (core sand) is bonded with the resin is maintained at the resin collapse temperature (sandfall temperature). At the time of casting, it is possible to suppress a sudden temperature change (especially temperature rise) of the cast product, to ensure the dimensional accuracy of the cast product, and to cool the sand after the sand is removed. The internal stress associated with cooling shrinkage can be released at a timing at which it is easy to secure the elongation (see 19).

Moreover, the resin collapse temperature (sand removal temperature)
The shift to (4) is performed without cooling (see cooling step S3) and without reheating in the temperature lowering process.

According to this structure, since the cast product (see the cylinder block 19) is immediately maintained at the resin collapse temperature after casting, the cycle time of the entire post-treatment can be shortened and the temperature can be changed. Since it can be made as small as possible, in other words, it is a cast product even after sand removal.
Since it is possible to secure the timing of expansion (see cylinder block 19) (timing capable of plastic deformation), it is possible to reduce the internal stress generated in the cast product, and further, it is possible to reduce the resin collapse without performing reheating. Since the temperature is changed to the temperature, it is possible to reduce the consumed heat energy.

Further, the above cast product is a cast metal member (see cylinder liner 18) having different cooling shrinkage rates which is cast into a base material (see cylinder block body 11). According to this configuration, by having the cast-metal member and the base material having different cooling collection rates, defects such as cracks and both
Although it is a disadvantageous condition for generation of a gap between the (casting member and the base metal), by performing sand removal in the stage before the cooling step S3 after casting, solidification shrinkage of the base metal after casting, Defects such as cracks caused by the generation of internal stress due to the difference in shrinkage rate between the cooling and shrinkage of the cast metal member, and both due to the transition to the resin collapse temperature (sand removal temperature) (base material and cast metal member) Due to the difference in expansion coefficient between the two, it is possible to prevent a gap from occurring between them (see between the elements 11 and 18).

Further, the base material is set in the aluminum alloy cylinder block body 11, and the cast-in member is set in the iron cylinder liner 18.
According to this structure, the aluminum alloy has a large contraction rate and a large expansion rate with respect to iron.
By having 1 and the cylinder liner 18, it is possible to prevent defects such as cracks between the cylinder bores 1 and 2, between the cylinder bores 2, 3 and 4, and between the cylinder bores 11 (the cylinder block body 11 and the cylinder liner 18). Although it is a disadvantageous condition, since sand is removed before the cooling step S3 after casting, both the solidification shrinkage of the aluminum alloy cylinder block body 11 after casting and the cooling shrinkage of the iron cylinder liner 11 are performed. , 18 between the cylinder bores 1 and 2, between 2 and 3, caused by the generation of internal stress due to the difference in contraction rate
Defects such as cracks between No. 4 and both due to transition to resin collapse temperature (sand removal temperature) (cylinder block body 11
It is possible to prevent a gap from being formed on the back surface of the cylinder liner 18 due to the difference in expansion coefficient between the cylinder liner 18) and the cylinder liner 18).

In addition, the above heat treatment steps S4, S5 and S6
Is set to T6 treatment in which quenching (see step S5) is performed after solution treatment (see step S4) and then artificial aging treatment (see step S6) is performed. According to this configuration, the strength and hardness of the cylinder block 19 can be improved by the T6 process (see the heat treatment including the steps S4 to S6).

In the sand removing step S2, sand is removed using a fluidized bed sand removing furnace. According to this configuration, by using the fluidized bed sand blasting furnace, when the cast product (see the cylinder block 19) is charged with high thermal efficiency, the sand blasting temperature is instantly reached, but the sand blasting temperature is maintained immediately after casting. As a result, the dimensional accuracy of the cast product can be secured without a sudden rise in temperature of the cast product,
The cycle time of the entire post-treatment can be further shortened.

Furthermore, the transition from the end of the cooling step S3 to the temperature of the solution treatment (see step S4) in the heat treatment steps S4, S5 and S6 is such that the temperature rise gradient of the cast product is relatively gentle (see FIG. 5). Temperature change line a)).

According to this structure, the temperature of the cast product (see the cylinder block 19) is gradually raised with respect to the temperature of the solution treatment (see the process S4) from the end of the cooling (see the cooling process S3). Therefore, it is possible to prevent the occurrence of strain around the cylinder bores 1 to 4. That is,
It is possible to more reliably prevent the occurrence of a gap on the contact surface between the cylinder liner 18 and the cylinder block body 11.

In the correspondence between the structure of the present invention and the above-described embodiment, the cast product of the present invention corresponds to the cylinder block 19 of the embodiment, and hereinafter, the resin collapse temperature corresponds to the sand removal temperature. The predetermined heat treatment corresponds to the T6 treatment, the base material corresponds to the aluminum alloy cylinder block main body 11, and the cast body member corresponds to the cast iron cylinder liner 18. It is not limited to the configuration of the embodiment.

[0052]

According to the present invention, sand casting is performed by holding the casting product after sand mold casting at the resin collapse temperature (sand removal temperature) of the casting sand remaining in the casting product during the temperature drop process. Since cooling is performed after dropping, it is possible to suppress a rapid temperature change of the cast product when maintaining the resin collapse temperature, it is possible to ensure the dimensional accuracy of the cast product, and to cool the sand after removing the sand. By doing so, there is an effect that the internal stress due to cooling shrinkage can be released at a timing at which the elongation (plastic deformation) of the cast product can be easily secured.

[Brief description of drawings]

FIG. 1 is a process diagram showing a post-treatment method of a cast product of the present invention.

FIG. 2 is an explanatory view of a mold structure used for sand mold casting.

FIG. 3 is a sectional view showing another embodiment of the mold structure.

FIG. 4 is a sectional view of a cylinder block showing an example of a cast product.

FIG. 5 is an explanatory diagram showing a post-treatment method for a cast product.

FIG. 6 is a plan view of a cylinder block.

FIG. 7 is a process diagram showing a post-treatment method of a conventional cast product.

FIG. 8 is an explanatory view showing a conventional post-treatment method for a cast product.

FIG. 9 is a plan view of a cylinder block showing a state where a gap is generated by a conventional method.

[Explanation of symbols]

S2 ... Sand removal process S3 ... Cooling process S4 to S6 ... Heat treatment step 1 to 4 ... Cylinder bore 11 ... Cylinder block body (base material) 18 ... Cylinder liner (casting member) 19 ... Cylinder block (cast product) 20 ... Sand mold

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02F 1/00 F02F 1/00 K

Claims (7)

[Claims] 1. A method for post-treating a cast product cast by using a sand mold, which is maintained for a predetermined time at the resin collapse temperature of the casting sand remaining in the cast product during the temperature drop process of the cast product after casting. A post-processing method for a cast product, comprising: a sand removing step for removing sand by means of cooling, a cooling step for performing cooling after the removing sand step, and a heat treatment step for performing a predetermined heat treatment after the cooling step. 2. The post-treatment method for a cast product according to claim 1, wherein the transition to the resin collapse temperature is carried out without cooling and without reheating in the temperature lowering process. 3. The post-processing method for a cast product according to claim 1, wherein the cast product is a cast-in member having a different cooling shrinkage with respect to the base material. 4. The post-processing method for a cast product according to claim 3, wherein the base material is set in a cylinder block body made of an aluminum alloy, and the cast-molded member is set in a cylinder liner made of iron. 5. The post-treatment method for a cast product according to claim 4, wherein the heat treatment step is set to T6 treatment in which quenching is performed after solution treatment and then artificial aging treatment is performed. 6. The post-treatment method for a cast product according to claim 1, wherein in the sand removal step, sand removal is performed using a fluidized bed sand removal furnace. 7. The post-processing method for a cast product according to claim 5, wherein the transition from the end of the cooling step to the solution treatment temperature in the heat treatment step is performed by setting the temperature rising gradient of the cast product to a gentle gradient.