Patent Publication Number: US-11638951-B2

Title: Heating method for casting mold, and casting device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-059106 filed on Mar. 31, 2021, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a heating method for a casting mold, and to a casting device. 
     Description of the Related Art 
     Prior to casting for producing a product, casting (preheating shot) for preheating of a casting mold may be performed (for example, JP 5717692 B2). In the preheating shot, the casting mold is heated by injecting molten metal into the cavity of the casting mold and solidifying the molten metal. The molten metal (cast article) solidified by the preheating shot is not used as a product. 
     The casting mold includes an overflow portion downstream of the cavity. The overflow portion performs various functions during casting. For example, the overflow portion has a function of filling a product portion with molten metal. This reduces defects in the cast article due to solidification shrinkage. Further, the overflow portion has a function of removing the molten metal mixed with gas, from the product portion. This reduces defects in the cast article caused by the mixing of gas into the molten metal. However, the portion of the cast article that has solidified in the overflow portion sticks to the mold when the cast article is released, and is thus liable to be broken. Broken pieces of the cast article may remain in the mold and interfere with subsequent casting. For example, pieces of the cast article sandwiched between the molds may cause the mold to be poorly sealed. Therefore, it is necessary to confirm whether the cast article is completely released from not only the product portion but also from the overflow portion. In order to confirm the release of the cast article, it is necessary to fill the overflow portion with molten metal. This is because, if the overflow portion is not filled at the time of casting, it is difficult to distinguish the defective release from the defective filling. That is, it is necessary that the overflow portion is filled not only in the casting for producing a product but also in the preheating shot. 
     Here, in order to suppress the occurrence of defects (for example, blow holes) caused by the mixing of gas into the molten metal, vacuum casting is used. In the vacuum casting, casting is performed after gas in the cavity is sucked. Therefore, in the vacuum casting, the mold is sealed in order to prevent air from leaking into the cavity. In particular, in high vacuum casting, a tight seal is required for depressurizing the cavity to near vacuum. In the vacuum casting, if gas remains in the cavity, the portion where the gas remains is not filled with the molten metal. As a result, filling of the molten metal in the overflow portion is hindered. Thus, in the vacuum casting, it is desirable to depressurize the cavity in order to fill the overflow portion with the molten metal even in the preheating shot. 
     Here, the preheating shot is performed in a state where the mold is not sufficiently heated. Therefore, powder burrs (molten metal powder) are liable to occur in the preheating shot. In the subsequent pressure reduction, the powder burrs adhere to the periphery of a pressure reducing shut-off valve (shut-off valve), whereby the powder burrs may be caught in the seal portion of the shut-off valve. In the vacuum casting, the shut-off valve disposed downstream of the overflow portion prevents the molten metal from flowing into a pressure reducing path (gas flow path). If foreign matter is caught in the seal portion of the shut-off valve, the shut-off valve may not be completely closed when the molten metal is filled, and the molten metal may flow into the pressure reducing path. 
     SUMMARY OF THE INVENTION 
     Thus, in the heating method for the casting mold, and the casting device, there is a problem that foreign matter is caught in the seal portion of the shut-off valve. An object of the present invention is to solve the above-mentioned problem. 
     According to an aspect of the present invention, provided is a heating method for a casting mold for heating the casting mold before casting is performed, wherein the casting mold includes, on an inside thereof, a cavity portion, and an overflow portion connected to the cavity portion, the overflow portion is connected to a gas flow path provided inside or outside the casting mold, a valve is provided between the gas flow path and the overflow portion, and wherein a step of performing the casting comprises: a first suction step of setting a pressure in the gas flow path to a predetermined pressure by sucking gas in the gas flow path in a state in which the valve is closed; a second suction step of setting a pressure in the cavity portion to a first pressure by sucking gas in the overflow portion and in the cavity portion through the gas flow path set at the predetermined pressure while keeping the valve open for a first time period; a step of supplying molten metal into the cavity portion set at the first pressure, and solidifying the molten metal; and a step of taking out, as a product, a cast article obtained by solidifying the molten metal, the heating method comprising: a third suction step of setting the pressure in the gas flow path to the predetermined pressure in the state in which the valve is closed; a fourth suction step of setting the pressure in the cavity portion to a second pressure by sucking the gas in the overflow portion and in the cavity portion through the gas flow path set at the predetermined pressure while keeping the valve open for a second time period shorter than the first time period; a step of supplying the molten metal into the cavity portion set at the second pressure and solidifying the molten metal to heat the casting mold; and a step of taking out, as a test article, a cast article obtained by solidifying the molten metal. 
     A casting device that heats a casting mold before casting is performed, the casting mold including, on an inside thereof, a cavity portion, and an overflow portion connected to the cavity portion, the casting device comprising: a gas suction unit configured to suck gas in the overflow portion and in the cavity portion through a gas flow path provided inside or outside the casting mold; a valve provided between the gas flow path and the overflow portion; a molten metal supply unit configured to supply molten metal into the cavity portion; and a control unit configured to control the valve, the gas suction unit, and the molten metal supply unit, wherein during casting, the control unit executes: a first suction step of setting a pressure in the gas flow path to a predetermined pressure by controlling the gas suction unit and the valve to cause the gas suction unit to suck gas in the gas flow path in a state in which the valve is closed; a second suction step of setting a pressure in the cavity portion to a first pressure by controlling the gas suction unit and the valve to cause the gas suction unit to suck gas in the overflow portion and in the cavity portion through the gas flow path set at the predetermined pressure while the valve is kept open for a first time period; and a step of controlling the molten metal supply unit to supply molten metal into the cavity portion set at the first pressure and solidify the molten metal, and during heating, the control unit causes the casting mold to be heated by executing: a third suction step of setting the pressure in the gas flow path to the predetermined pressure by controlling the gas suction unit and the valve to cause the gas suction unit to suck the gas in the gas flow path in the state in which the valve is closed; a fourth suction step of setting the pressure in the cavity portion to a second pressure by controlling the gas suction unit and the valve to cause the gas suction unit to suck the gas in the overflow portion and in the cavity portion through the gas flow path set at the predetermined pressure while the valve is kept open for a second time period shorter than the first time period; and a step of controlling the molten metal supply unit to supply the molten metal into the cavity portion set at the second pressure and solidify the molten metal. 
     According to the present invention, it is possible to provide a heating method for a casting mold, and a casting device, with which foreign matter is prevented from being caught in the seal portion of the shut-off valve. 
     The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which a preferred embodiment of the present invention is shown by way of illustrative example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a view showing a casting device according to an embodiment of the present invention; and 
         FIG.  2    is a flow chart showing a casting method according to the embodiment. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Hereinafter, a heating method for a casting mold, and a casting device according to an embodiment of the present invention will be described. 
     A casting device  10  shown in  FIG.  1    includes a casting mold  12 . The casting mold  12  includes a fixed mold  12   a  and a movable mold  12   b  which face each other in the left-right direction (horizontal direction) of the drawing. The movable mold  12   b  moves in the horizontal direction so as to be able to contact and separate from the fixed mold  12   a . The fixed mold  12   a  and the movable mold  12   b  have mating surfaces facing each other. The mating surface of the fixed mold  12   a  and the mating surface of the movable mold  12   b  have a concave portion  14   a  and a concave portion  14   b , respectively. The concave portion  14   a  and the concave portion  14   b  form a cavity portion  14 . By bringing the movable mold  12   b  into contact with the fixed mold  12   a , the casting mold  12  is closed. As a result, the cavity portion  14  is formed inside the casting mold  12 . 
     The casting device  10  includes a molten metal supply unit  16 . The molten metal supply unit  16  is attached to the fixed mold  12   a  and supplies molten metal into the cavity portion  14 . The movable mold  12   b  has an overflow portion  18  downstream of the cavity portion  14 . The molten metal supplied to the cavity portion  14  reaches the overflow portion  18 . Thereafter, the molten metal solidifies inside the cavity portion  14  and the overflow portion  18 . The solidified molten metal is taken out from the casting mold  12  as a cast article. 
     The casting mold  12  includes a shut-off valve  20  and a suction path  22 . The shut-off valve  20  is connected between the overflow portion  18  and the suction path  22 . The shut-off valve  20  prevents the molten metal from flowing from the overflow portion  18  into the suction path  22  by blocking the suction path  22 . 
     The suction path  22  is connected to a gas suction unit  26  through an on-off valve V, a suction path  23 , and a switching valve  24 . The gas suction unit  26  sucks gas in the cavity portion  14  through the switching valve  24 , the suction path  23 , the on-off valve V, the suction path  22 , and the overflow portion  18 . The gas suction unit  26  includes a tank  26   a  and a vacuum pump  26   b . The gas suction unit  26  sucks gas in the cavity portion  14  by the tank  26   a  depressurized by the vacuum pump  26   b . Before supplying the molten metal to the cavity portion  14 , the gas suction unit  26  sucks the gas in the cavity portion  14 . As a result, it is possible to reduce defects (for example, blow holes) in the cast article caused by the mixing of gas into the molten metal. 
     The gas suction unit  26  and an air supply unit  28  are connected to the switching valve  24 . The air supply unit  28  feeds air into (air-blows) the casting mold  12  in an open state, through the switching valve  24 , the suction path  23 , the on-off valve V, the suction path  22 , and the overflow portion  18 . As a result, the suction path  22  and the like are cleaned. The on-off valve V opens/closes between the suction path  23  and the suction path  22 . The switching valve  24  switches the connection between the suction path  22  and the gas suction unit  26 , and the connection between the suction path  22  and the air supply unit  28 . 
     The casting device  10  includes a pressure detector  30  and an imaging unit  32 . The pressure detector  30  is disposed in the suction path  23  and detects the pressure of gas in the suction path  23 . The pressure of the gas in the suction path  23  varies depending on the suction of the gas by the gas suction unit  26  and the supply of the air from the air supply unit  28 . The imaging unit  32  captures an image of a cast article taken out from the casting mold  12 . In particular, the imaging unit  32  captures an image of a portion (specific portion) of the cast article that is solidified in the overflow portion  18 . The result of this image capturing is used to inspect whether or not the molten metal is filled up to the overflow portion  18 . In the present embodiment, the imaging unit  32  is used to detect a defect in a specific portion of the cast article. However, instead of the imaging unit  32 , another detection mechanism capable of detecting a defect in the specific portion of the cast article may be used. As the detection mechanism, a detection mechanism (for example, a limit switch) used in normal casting can be used. 
     The casting device  10  includes a control unit  34 , a storage unit  36 , and an input/output unit  38 . The control unit  34  includes hardware (for example, a processor) and software (for example, a program). The control unit  34  controls the molten metal supply unit  16 , the shut-off valve  20 , the on-off valve V, the switching valve  24 , the gas suction unit  26 , and the air supply unit  28 . The control unit  34  receives signals from the pressure detector  30  and the imaging unit  32 . The storage unit  36  is, for example, a hard disk or a semiconductor memory. The storage unit  36  stores a first time period T 1  and a second time period T 2  to be described later. The input/output unit  38  is a device for inputting outputting information between the control unit  34  and an operator, and is a keyboard and a display device, for example. 
     The casting device  10  carries out a casting method in which a preheating step for preheating the casting mold  12  is performed prior to a casting step for producing a cast article as a product. 
       FIG.  2    is a flow chart showing the casting method according to the embodiment. The casting method is divided into a preheating step and a casting step. Among the steps, the preheating step corresponds to the heating method for the casting mold according to the present embodiment. The casting step is not a step for obtaining a test article, but a step for obtaining a product (a normal casting step or a main casting step). The preheating step is performed under the assumption that the casting step is performed subsequently. Hereinafter, the casting method including the preheating step and the casting step will be described. 
     Although the order is different from the actual order of execution, the casting step will be described first for ease of understanding. The casting step is a step for producing a cast article as a product. The control unit  34  controls the on-off valve V and the gas suction unit  26  to set the pressure in the suction path  23  to a predetermined pressure P 0  in a state where the on-off valve V is closed (a first suction step, step S 11 ). It is preferable that the shut-off valve  20  is opened. When the shut-off valve  20  is opened, the gas in the overflow portion  18  and in the cavity portion  14  can be sucked by opening and closing only the on-off valve V. 
     The predetermined pressure P 0  is set in order to smoothly suck the gas in the cavity portion  14 . That is, the gas of the predetermined pressure P 0  remaining in the suction path  23  does not inhibit the suction of the gas from the cavity portion  14 . The pressure P 0  is basically the initial pressure when the vacuum pump  26   b  depressurizes the tank  26   a . The volume of the tank  26   a  is generally sufficiently larger than that of the suction path  23 . Therefore, even if the tank  26   a  sucks the gas in the suction path  23 , the pressure in the tank  26   a  does not substantially change. 
     The predetermined pressure P 0  is, for example, 10 to 40 kPa-abs (absolute pressure). Here, the predetermined pressure P 0 , a first pressure P 1  and a second pressure P 2 , which will be described later, are lower than the atmospheric pressure, in other words, in a state of negative pressure. 
     Thereafter, the control unit  34  controls the on-off valve V and the gas suction unit  26  to keep the on-off valve V open for the first time period T 1 . As a result, the gas suction unit  26  sucks the gas in the overflow portion  18  and in the cavity portion  14  through the suction path  23  and the suction path  22  (a second suction step, step S 12 ). At the beginning of gas suction, the inside of the suction path  23  is at the predetermined pressure P 0 . As described above, if the shut-off valve  20  is opened in advance, it is not necessary to operate the shut-off valve  20 . Here, the gas in the overflow portion  18  and in the cavity portion  14  is sucked by the depressurized tank  26   a . As a result, the pressure in the cavity portion  14  becomes the first pressure P 1  (step S 12 ). 
     The control unit  34  controls the shut-off valve  20  and the molten metal supply unit  16  to close the shut-off valve  20  and thereafter supply the molten metal into the cavity portion  14  set at the first pressure P 1  and solidify the molten metal (step S 13 ). By closing the shut-off valve  20  before supplying the molten metal, the molten metal is prevented from flowing into the suction path  22  and the like. Thereafter, a cast article obtained by solidifying the molten metal is taken out as a product (step S 14 ). 
     On the other hand, the preheating step is basically a step for carrying out casting for preheating the casting mold  12  before producing a cast article as a product. This step means so-called preheating shot. The control unit  34  controls the on-off valve V and the gas suction unit  26  to set the pressure in the suction path  22  to a predetermined pressure P 0  in a state where the on-off valve V is closed (a third suction step, step S 1 ). Here, as in the casting step, it is preferable that the shut-off valve  20  is in an open state. This predetermined pressure P 0  has the same significance as and can be the same as the predetermined pressure P 0  in the casting step. However, the pressure P 0  may be different between the preheating step and the casting step. 
     Thereafter, the control unit  34  controls the on-off valve V and the gas suction unit  26  to keep the on-off valve V open for a second time period T 2  shorter than the first time period T 1  (T 2 &lt;T 1 ). As a result, the gas suction unit  26  sucks the gas (basically having an atmospheric pressure initially) in the overflow portion  18  and in the cavity portion  14  through the suction path  22  set at the predetermined pressure P 0  (a fourth suction step, step S 2 ). As a result, the pressure in the cavity portion  14  becomes the second pressure P 2  (negative pressure) (the fourth suction step, step S 2 ). The second pressure P 2  is greater than the first pressure P 1  (P 2 &gt;P 1 ). 
     The control unit  34  controls the shut-off valve  20  and the molten metal supply unit  16  to close the shut-off valve  20  and thereafter supply the molten metal into the cavity portion  14  set at the second pressure P 2  and solidify the molten metal (step S 3 ). As in the casting step, by closing the shut-off valve  20  before supplying the molten metal, the molten metal is prevented from flowing into the suction path  22  and the like. As a result, the casting mold  12  is preheated. Thereafter, a cast article obtained by solidifying the molten metal is taken out as a test product (step S 4 ). By repeating the preheating step (specifically, the third suction step, the fourth suction step, a supply step, and a take-out step) a plurality of times, it is possible to heat the casting mold  12  more reliably. The third suction step comprises a step of setting the pressure in the gas suction unit  26  to the predetermined pressure P 0 . The fourth suction step is a step of setting the pressure in the cavity portion  14  to the second pressure P 2 . The supply step is a step of supplying the molten metal. The take-out step is a step of taking out a cast article as a test article. 
     An image of the test article (cast article) that has been taken out is captured by the imaging unit  32 . Based on the image capturing result, the entire cast article including the portion in the overflow portion  18  is inspected (step S 5 ). That is, it is determined whether or not the entire cast article has any release point. The entire cast article includes a portion in the cavity portion  14  (product portion) and a portion in the overflow portion  18 . As a result of this inspection, if the release of the cast article from the mold is insufficient, there is a possibility that pieces of the cast article remain inside the mold. In this case, the next casting step is stopped (step S 6 : NO), and the casting mold  12  is cleaned. 
     As described above, in the present embodiment, the opening time period (the first time period T 1  and the second time period T 2 ) of the on-off valve V is different between steps S 2  and S 12 . The second time period T 2  during preheating is shorter than the first time period T 1  during casting. That is, the time period during which the on-off valve V is open (the time period during which gas is sucked) is relatively short at the time of the preheating shot, during which powder burrs are relatively likely to occur. As a result, it is possible to suppress the sealing failure caused by adhesion and inclusion of foreign matter such as powder burrs into the seal portion of the shut-off valve  20 . As a result, by closing the shut-off valve  20 , it is possible to reliably prevent the molten metal from flowing into the suction path  22 . In addition, the time for sucking the gas in the cavity portion  14  and the overflow portion  18  during the preheating can be reduced. Reduction of the suction time eventually leads to a reduction in the time required for preheating. 
     On the other hand, when the second time period T 2  is too short, the second pressure P 2  becomes large. That is, the difference between the atmospheric pressure and the second pressure P 2  becomes small. In this case, when the molten metal is subsequently supplied, it becomes difficult to fill the overflow portion  18  with the molten metal. As a result, it is difficult to determine whether the release of the cast article from the overflow portion  18  is satisfactory. Therefore, the second time period T 2  is preferably set to be a relatively short time period within a range that allows the overflow portion  18  to be filled with the molten metal. That is, the second pressure P 2  obtained by opening the on-off valve V for the second time period T 2  is sufficiently low to enable filling of the overflow portion  18  with the molten metal during the supply of the molten metal. The second time period T 2  is set to, for example, 0.1 seconds or more and 0.5 seconds or less, and the second pressure P 2  is set to, for example, 40 kPa or more and 90 kPa or less. As a result, the inspection using the overflow portion  18  can be performed, and the time required for preheating can be reduced. The atmospheric pressure is approximately 101 kPa. Therefore, the second pressure P 2  of 40 kPa-abs to 90 kPa-abs means that 40% to 90% (for example, 80%) of the gas in the casting mold  12  is sucked. The internal volume of the casting mold  12  basically corresponds to the sum of the internal volume of the cavity portion  14  and the internal volume of the overflow portion  18 . 
     On the other hand, in the casting step, merely filling the overflow portion  18  with the molten metal is not sufficient. That is, in order to reduce defects in the cast article, it is necessary to suppress the mixing of gas into the molten metal. Therefore, the first time period T 1  is made relatively long, for example, about one second, so that the first pressure P 1  is set to, for example, about 10 kPa-abs or less. 
     As described above, in the present embodiment, the on-off valve V is opened for the second time period T 2  in the preheating shot for performing preheating. The second time period T 2  is a relatively short time period within a range that allows the overflow portion  18  to be filled with the molten metal during the supply of the molten metal. Thus, the gas suction unit  26  sucks the gas (basically having an atmospheric pressure initially) in the cavity portion  14  and in the overflow portion  18 . That is, in the present embodiment, the time period during which the on-off valve V is open (the time period during which gas is sucked) is relatively short at the time of the preheating shot, during which powder burrs are relatively likely to occur. As a result, it is possible to suppress the sealing failure caused by adhesion and inclusion of foreign matter such as powder burrs into the seal portion of the shut-off valve  20 . In addition, the pre-heating time can be shortened, and release of the cast article from the overflow portion  18  can be confirmed. 
     [Modification] 
     The present invention is not limited to the above-described embodiment, and various configurations can be adopted therein without departing from the gist of the present invention. For example, in the embodiment, the gas suction is started and stopped by opening and closing the on-off valve V. On the other hand, the gas suction may be started and stopped by opening and closing the shut-off valve  20  instead of the on-off valve V. 
     In this case, for example, the process proceeds as follows. For example, the on-off valve V is kept in an open state. In steps S 1  and S 11 , the control unit  34  controls the shut-off valve  20  and the gas suction unit  26  to set the pressure in the suction path  23  to the predetermined pressure P 0  in a state where the shut-off valve  20  is closed. In steps S 2  and S 12 , the control unit  34  controls the shut-off valve  20  and the gas suction unit  26  to keep the shut-off valve  20  open for the first time period T 1  or the second time period T 2 . As a result, the gas suction unit  26  sucks the gas in the overflow portion  18  and in the cavity portion  14  through the suction path  23  (and the suction path  22 ) set at the predetermined pressure P 0 . It should be noted that, since the shut-off valve  20  is closed before the molten metal supply step in steps S 3  and S 13 , it is not necessary to operate the shut-off valve  20 . 
     Invention Obtained from Embodiments 
     The invention that can be grasped from the above embodiments will be described below. 
     [1] The heating method for a casting mold is a method for heating a casting mold ( 12 ) before casting is performed, wherein the casting mold comprises, on an inside thereof, a cavity portion ( 14 ), and an overflow portion ( 18 ) connected to the cavity portion, the overflow portion is connected to a gas flow path (suction path  22 ,  23 ) provided inside or outside the casting mold, a valve (on-off valve V, shut-off valve  20 ) is provided between the gas flow path and the overflow portion, and 
     wherein a step of performing the casting comprises: a first suction step (step S 11 ) of setting a pressure in the gas flow path to a predetermined pressure (P 0 ) by sucking gas in the gas flow path in a state in which the valve is closed; a second suction step (step S 12 ) of setting a pressure in the cavity portion to a first pressure (P 1 ) by sucking gas in the overflow portion and in the cavity portion through the gas flow path set at the predetermined pressure while keeping the valve open for a first time period (T 1 ); a step (step S 13 ) of supplying molten metal into the cavity portion set at the first pressure, and solidifying the molten metal; and a step (step S 14 ) of taking out, as a product, a cast article obtained by solidifying the molten metal, the heating method comprising: a third suction step (step S 1 ) of setting the pressure in the gas flow path to the predetermined pressure in the state in which the valve is closed; a fourth suction step (step S 2 ) of setting the pressure in the cavity portion to a second pressure (P 2 ) by sucking the gas in the overflow portion and in the cavity portion through the gas flow path set at the predetermined pressure while keeping the valve open for a second time period (T 2 ) shorter than the first time period; a step (step S 3 ) of supplying the molten metal into the cavity portion set at the second pressure and solidifying the molten metal to heat the casting mold; and a step (step S 4 ) of taking out, as a test article, a cast article obtained by solidifying the molten metal. As a result, the time for sucking the gas is short at the time of the preheating shot, during which foreign matter such as powder burrs is relatively likely to occur. Therefore, adhesion, inclusion and the like of foreign matter into the seal portion of the shut-off valve can be suppressed. 
     [2] The second pressure is 40 kPa or more and 90 kPa or less. As a result, adhesion, inclusion and the like of foreign matter into the seal portion can be suppressed. 
     [3] The second time period is 0.1 seconds or more and 0.5 seconds or less. As a result, adhesion, inclusion and the like of foreign matter into the seal portion can be suppressed. 
     [4] The heating method for the casting mold further comprises a step (step S 5 ) of inspecting the test article to determine whether a state of filling of the overflow portion with the molten metal is good, and the casting is performed when the state of filling is determined to be good in the determining step (step S 6 : YES). 
     [5] In the heating method for the casting mold, the step of setting the pressure in the gas flow path to the predetermined pressure, the step of setting the pressure in the cavity portion to the second pressure, the step of supplying the molten metal, and the step of taking out the cast article as the test article are repeated a plurality of times. This makes it possible to suppress adhesion, inclusion and the like of foreign matter into the seal portion of the shut-off valve during a plurality of preheating shots. 
     [6] The casting mold includes, on the inside thereof, a first gas flow path (suction path  22 ) including one end connected to the cavity portion via the overflow portion, and a first valve (shut-off valve  20 ) disposed between the overflow portion and the first gas flow path and configured to open and close the first gas flow path, a second gas flow path (suction path  23 ) connected to another end of the first gas flow path is provided outside the casting mold, a second valve (on-off valve V) is provided between the first gas flow path and the second gas flow path, in the first suction step, one of the first valve or the second valve is opened and another of the first valve and the second valve is closed, in the second suction step, the pressure in the cavity is set to the first pressure while the another of the first valve and the second valve is kept open for the first time period in a state in which the one of the first valve or the second valve is opened, in the third suction step, the one of the first valve or the second valve is opened, and the another of the first valve and the second valve is closed, and in the fourth suction step, the pressure in the cavity portion is set to the second pressure while the another of the first valve and the second valve is kept open for the second time period in the state in which the one of the first valve or the second valve is opened. As a result, the preheating shot and the casting can be performed by operating the first valve and the second valve disposed inside and outside the casting mold. 
     [7] A casting device  10  is a casting device that heats a casting mold before casting is performed, the casting mold including, on an inside thereof, a cavity portion and an overflow portion connected to the cavity portion, the casting device comprising: a gas suction unit ( 26 ) configured to suck gas in the overflow portion and in the cavity portion through a gas flow path provided inside or outside the casting mold; a valve provided between the gas flow path and the overflow portion; a molten metal supply unit ( 16 ) configured to supply molten metal into the cavity portion; and a control unit ( 34 ) configured to control the valve, the gas suction unit, and the molten metal supply unit, wherein during the casting, the control unit executes: a first suction step of setting a pressure in the gas flow path to a predetermined pressure by controlling the gas suction unit and the valve to cause the gas suction unit to suck gas in the gas flow path in a state in which the valve is closed; a second suction step of setting a pressure in the cavity portion to a first pressure by controlling the gas suction unit and the valve to cause the gas suction unit to suck gas in the overflow portion and in the cavity portion through the gas flow path set at the predetermined pressure while the valve is kept open for a first time period; and a step of controlling the molten metal supply unit to supply molten metal into the cavity portion set at the first pressure and solidify the molten metal, and during heating, the control unit causes the casting mold to be heated by executing: a third suction step of setting the pressure in the gas flow path to the predetermined pressure by controlling the gas suction unit and the valve to cause the gas suction unit to suck the gas in the gas flow path in the state in which the valve is closed; a fourth suction step of setting the pressure in the cavity portion to a second pressure by controlling the gas suction unit and the valve to cause the gas suction unit to suck the gas in the overflow portion and in the cavity portion through the gas flow path set at the predetermined pressure while the valve is kept open for a second time period shorter than the first time period; and a step of controlling the molten metal supply unit to supply the molten metal into the cavity portion set at the second pressure and solidify the molten metal. As a result, since the time for sucking the gas is short at the time of the preheating shot, during which foreign matter such as powder burrs is relatively likely to occur. Therefore, adhesion, inclusion and the like of foreign matter into the seal portion of the shut-off valve can be suppressed. 
     [8] The second pressure is 40 kPa or more and 90 kPa or less. As a result, adhesion, inclusion and the like of foreign matter into the seal portion can be suppressed. 
     [9] The second time period is 0.1 seconds or more and 0.5 seconds or less. As a result, adhesion, inclusion and the like of foreign matter into the seal portion can be suppressed. 
     [10] The casting mold includes, on the inside thereof, a first gas flow path including one end connected to the cavity portion via the overflow portion, and a first valve disposed between the overflow portion and the first gas flow path and configured to open and close the first gas flow path, the casting device further comprising: a second gas flow path connected to another end of the first gas flow path and provided outside the casting mold; and a second valve disposed between the first gas flow path and the second gas flow path, and the control unit controls the first valve and the second valve to: in the first suction step, open one of the first valve or the second valve and close another of the first valve and the second valve; in the second suction step, set the pressure in the cavity portion to the first pressure while the another of the first valve and the second valve is kept open for the first time period in a state in which the one of the first valve or the second valve is opened; in the third suction step, open the one of the first valve or the second valve and close the another of the first valve and the second valve; and in the fourth suction step, set the pressure in the cavity portion to the second pressure while the another of the first valve and the second valve is kept open for the second time period in the state in which the one of the first valve or the second valve is opened. As a result, the preheating shot and the casting can be performed by operating the first valve and the second valve disposed inside and outside the casting mold.