JP2013052436A - Core enclosure type mold tool structure, and casting method using the mold tool structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mold tool structure and a casting method avoiding degradation of a product quality in a casting process using a center-gated mold for pouring a molten metal radially from the vicinity of the axial center of a cavity for an annular member.SOLUTION: The mold tool structure is composed of at least one core 12a and at least a pair of molds 12b disposed holding the core 12a therebetween, has a cavity for casting the annular member, and is formed to cast the molten metal radially diffusing to a radial direction by providing a pouring gate 19 and a runner 18 near the axial center of the annular member. A pair of molds 12b has the flanges 15 extending from the circumference of a peripheral face to one or both of an axial direction, and is composed to prevent deformation or disruption due to expansion of the core 12a by enclosing the outer periphery of the core 12a with the flanges 15. Further, the mold is composed to discharge the gas in the cavity to the outside of the mold by forming the degassing groove 25 communicating the peripheral face of the mold 12b from the cavity to the interface of the core 12a and mold 12b, and the abutting face of the flange 15.

Description

  The present invention includes a mold structure for preventing leakage during pouring when casting an annular member using a core, and deterioration of product quality due to collapse of the core, and the mold structure. The present invention relates to a casting method in which a casting mold is used for casting.

  The inventors of the present application have previously provided a technique for suppressing non-uniformity in product hardness due to variations in product quality, in particular, variations in cooling time during casting, when an annular member is obtained by casting. However, the technical contents are not disclosed at the time of filing this application. This non-uniformity in product hardness includes variations between parts in one product and variations between a plurality of products when a plurality of products are obtained by the stack mold casting method.

  The vehicle brake disc material 1 shown in FIG. 4 is also an example of an annular member manufactured by such casting. In general, the brake disc material 1 is mainly composed of a ring portion 2 that generates a braking force by being sandwiched between friction materials called calipers, and a hub portion 3 that is attached to the axle on the axial center side and holds the whole. In the illustrated example, a plurality of cooling through holes 4 called ventilated disks are formed in the ring portion 2 radially.

  For example, in Patent Document 1, hot water is poured into a cavity from a weir provided at one point corresponding to the outer periphery of the ring portion 2 of the brake disc material 1, and the entire circumference of the ring portion from here. It is configured so that hot water can be distributed. In Patent Document 2, which is an example of taking a plurality of products, hot water is poured into four brake disc cavities from one gate through a runner, and four pieces can be taken. In a mass production type casting plant in which a large number of molds are transported side by side on a conveyor, and the pouring is sequentially performed on the molds, the number of the plurality of molds is limited by the size of the molds that form the molds. In Patent Document 2, four pieces are taken, but depending on the mold size and product size, there are cases where two pieces are limited due to the restrictions of the form. In such a case, the runner diverges into two from the gate and is connected to each brake disk cavity.

  FIG. 5A shows an arrangement pattern (plan view) in the mold when two brake disc materials are taken. In the figure, a pair of cavities 6 for brake discs are arranged on a substantially diagonal line of the mold 7, and a runner 8 and a weir 9 provided near the center of the mold 7 close to both of them are both cavities 6. It is tied to At the time of casting, hot water is poured from the pouring gate 22, and molten metal is poured from the hot water passage 8 through the weir 9 into the cavity 6. After that, the material solidified in the cavity 6 is obtained after waiting for cooling, and is further processed into a product through machining.

  FIG. 5B shows the hardness distribution of the brake disc material obtained as described above. The figure shows the measurement result by Brinell hardness (BHN) and its scale. As is clear from the figure, the brake disc material is located near the runner 8 (weir 9) shown in FIG. The hardness is low (hardness of about 206), and the hardness gradually increases as it is further away from it, and is the highest hardness (about 215) at the position farthest from the runner 8 in the ring portion 2. Between the two, there is a variation between intermediate hardnesses (206 to 215), and the change in the hardness is in a direction extending from a position close to the runner 8 to the opposite side of the runner 8 across almost the center of the brake disc material. It can be seen that the change is inclined.

  In general, when solidifying by cooling the Fe-C molten metal, pearlite densification is promoted as the cooling rate increases, particularly as the cooling rate passing through the eutectoid transformation point (726 ° C in the case of cast iron) increases. It is known that the hardness increases. In the arrangement in the mold 7 as shown in FIG. 5A, the cooling is promoted as the position away from the runner 8 and closer to the mold 7, and heat is dissipated near the weir 9 located near the center of the mold 7. It can be easily imagined that the cooling rate is low due to the low efficiency. As a result, as shown in FIG. 5 (b), the hardness is high at a site away from the gate, and the hardness is low at a site near the gate.

  Such a difference in hardness depending on the position is particularly problematic in a functional component (an important safety component) such as a vehicle brake disc. Generally, the higher the hardness is, the better the wear resistance is. Therefore, when a friction material (caliper) is pressed against the brake disc during braking of the vehicle, this hardness difference becomes a problem. Since the brake disc obtained from the brake disc material 1 shown in FIG. 4 rotates about its own rotational symmetry axis, the ring portion 2 against which the friction material is pressed has a high hardness as shown in FIG. 5B. The part and the low part are mixed. As a result, the amount of wear in the circumferential direction of the ring portion 2 varies due to the long-term repeated frictional action of the friction material. When this is seen from the friction material (caliper) side, it means that the other side (ring part 2) that comes into frictional contact becomes wavy, and pressing the friction material against this causes judder (chatter vibration) and abnormal noise. Cause it to occur. In severe cases, the diffusion of vibration can affect the braking performance itself.

  In order to alleviate such a problem, for example, in Patent Document 2 (four examples are displayed), a hot water path is extended so that hot water flows into the cavity from a plurality of positions of the ring portion of the brake disc material. Yes. However, even with this method, even if a certain degree of improvement is seen, the fact that the distance from the gate is not uniform is unchanged, and of course the heat radiation effect at the position where the cavities face each other and the outer peripheral part close to the formwork Since there is a difference between them, it cannot be a complete solution to eliminate the hardness difference in the ring part of the brake disc material.

  In response to this, the inventors of the present invention provided a gate and a runner in the vicinity of the axial center of the annular member, and poured hot water radially into the cavity through a weir arranged radially from this runner, so that the cooling of the hot water is annular. By controlling so that it may become equal with respect to the circumferential direction of a member, the manufacturing method of the annular member in which the hardness difference (Brinell hardness BHN203-216) as shown in FIG. 6 is formed concentrically is provided. When the annular member is a brake disc as shown in FIG. 4, the caliper exerts a frictional force across the ring part 2 of the rotating brake disc, so that there is almost no difference in hardness in its sliding direction (rotating direction of the brake disc). Therefore, even if the ring portion 2 is worn, the amount of wear is uniform in the circumferential direction. As a result, uneven wear in the circumferential direction (rotational direction) in the ring portion 2 as in the prior art does not occur, and therefore occurrence of judder and abnormal noise can be effectively prevented. In addition, the brake performance is not affected, and a more important effect of eliminating uneven wear and extending the life of the brake disk is obtained.

  When the gate is provided in the vicinity of the axial center of the annular member, a stack mold method can be used as means for obtaining a plurality of products. In the stack mold method, a number of flat molds are stacked to form a plurality of layers of cavities in the vertical direction, and hot water is caused to flow into each cavity through a water channel directed downward from a gate provided above. Multiple product collection is possible. For example, Patent Document 3 discloses a method of taking a large number of flat parts in a tree shape in each layer by using a stack mold method. As described above, the stack mold method is mainly used when a large number of relatively small products are taken. However, it has been known that a center gate method is used in which a pouring gate is provided in the vicinity of the shaft center in an annular member. However, even when a large number of pieces are taken, the hot water is filled from the outer periphery (see, for example, Patent Document 4).

JP 2002-59243 A JP 2007-211182 A JP 2001-129640 A JP 62-240140 A

  FIG. 7 shows a cross-sectional view of a center gate type stack mold used in the method for casting a brake disc material proposed by the present inventors. In FIG. 7, the stack mold 10 includes a lowermost layer mold 11, four intermediate layer molds 12, and an uppermost layer mold 13 in total, which are stacked in the vertical direction in order from the bottom. It is sandwiched and fixed by a long bolt 17 as a fixing tool (may be fixed by other methods such as a clamp and a weight). Each of the intermediate layer molds 12 provides a pattern of the upper surface of the product positioned below on the lower surface side, and provides a support pattern for supporting the intermediate layer mold 12 positioned above on the upper surface side. Further, a support pattern for supporting the intermediate layer mold 12 positioned above is provided on the upper surface side of the lowermost layer mold 11, and a pattern on the upper surface of the product positioned lower is provided on the lower surface side of the uppermost layer mold 13. By stacking them with the central axes aligned as shown in the figure, a stack mold 10 in which five cavities C for casting the brake disc material are arranged in the vertical direction is obtained. In the example shown in FIG. 1, the intermediate layer mold 12 is formed by overlapping the core 12 a and the intermediate mold 12 b with the cavity C interposed therebetween. It shall be called the layer mold 12.

  Each of the molds 11 to 13 is provided with a through hole extending in the central axis direction at a portion that is a rotationally symmetric axis of the brake disc material 1, and the through holes are vertically moved by overlapping the molds 11 to 13. The runway 18 is formed continuously. A stack mold 10 is formed by attaching a gate 19 to the upper end of the runner 18. When the molds 11 to 13 are stacked, the dams are formed so that weirs connected from the runner 18 to the cavities C are formed between the molds. In the present embodiment, a weir is provided between the core 12a and the intermediate mold 12b of the intermediate layer mold 12 (between the core 12a and the lowermost mold 11 in the lowermost stage). An appropriate number of weirs may be provided so that the hot water flows radially into the cavity, but here, it is provided at three locations around the weir (in the figure, the weir is displayed on the left half).

  The operation when using the stack mold mold 10 configured as described above is as follows: molten hot water (molten iron) is poured into the pouring gate 19 of the prepared stack mold mold 10, and the hot water flows along the runner 18. While descending, it passes through the weirs of the molds 11 to 13 described above and is filled in the cavities C. Thereafter, it is allowed to stand until it falls to a predetermined temperature. After cooling, the long bolt 17 is removed, the stack mold 10 is disassembled, and the product is taken out. Subsequent processing steps are the same as in the prior art.

  However, there is still room for improvement in this casting method. First, when hot hot water is allowed to flow in a state of being constrained in the vertical direction, the mold expands, and the relatively thin core 12a is compressed by this expansion to the outside in the radial direction (left-right direction in FIG. 7). The tendency to be deformed to be pushed out is born. This deformation causes deformation of the annular member to be cast, resulting in variations in product quality. The other is to cause leakage of water from between the upper and lower intermediate molds 12b and the core 12a due to the deformation of the core 12a. In addition, the gas generated from the mold, particularly the core, is confined in the cavity by the pouring, and when this is contained in the product and cooled and solidified, it causes a defective gas defect in the product.

  Therefore, the present invention provides an annular member mold structure that eliminates the above-described problems and eliminates casting defects due to deformation of the core and gas entrainment, and an annular member casting method using the structure. The purpose is that. At the time of filing this application, there is no known center gate casting method in which a pouring gate is provided in the vicinity of the axial center of the annular member so that the hot water is diffused radially into the cavity serving as the annular member. Therefore, a plurality of inventions related to the mold structure and casting method described below all solve the problems associated with the novel center gate type casting method in which hot water is diffused radially in the cavity and cast. It addresses technical challenges.

  In the present invention, the mold member structure in which the core of the annular member mold is terminated in the mold without exposing it to the outside of the mold, and further, a gas vent groove communicating from the inside of the cavity to the outside of the mold is provided, and the structure The above-described problem is solved by providing a casting method that utilizes the following, and specifically includes the following contents.

  That is, one aspect according to the present invention is composed of at least one core and at least a pair of molds arranged so as to sandwich the core, and has a cavity for casting an annular member. A mold structure of a center gate type annular member formed such that a pouring gate and a runner are provided in the vicinity of the shaft center of the member, and hot water is radially diffused and cast from the vicinity of the shaft center of the annular cavity. The pair of molds has a collar portion extending in one or both axial directions from the entire circumference of the outer peripheral surface, the periphery of the core is surrounded by the collar portion, and due to the expansion of the core The present invention relates to a mold structure configured to prevent deformation and collapse.

  The mold structure may include a stack mold that includes a plurality of cores and a plurality of the molds that are arranged with the plurality of cores sequentially sandwiched therebetween.

  A gas vent groove for releasing the gas generated in the cavity from the cavity to the outer peripheral surface of the mold is formed in at least one of the core and the mold, and the flange portion. it can. The degassing groove can include at least two bent portions.

  The other aspect which concerns on this invention is an annular member formed by casting, Comprising: It is related with the annular member cast by the tool provided with any one tool structure mentioned above. The annular member can be a brake disc material for a vehicle.

  According to still another aspect of the present invention, a cavity for casting an annular member is formed using a mold including at least one core and at least a pair of molds arranged with the core interposed therebetween. A pouring gate for pouring from above is arranged near the axial center of the mold arranged horizontally, and casting is performed so that hot water is filled from the axial center of the cavity toward the radially outer side through the hot water passage connected to the pouring gate. A center gate casting method in which the periphery of the core is surrounded by a flange extending in the axial direction from one or both of the pair of molds to prevent deformation and collapse due to expansion of the core. The present invention relates to a casting method. By providing a gas vent groove between the core and the mold and between the flanges extending from the pair of molds, the gas in the cavity can be discharged to the outside of the mold.

  By implementing the present invention, variations in product quality associated with deformation due to expansion of the core are eliminated, and a stable annular member can be obtained. Further, the gas generated in the cavity can be efficiently discharged to the outside of the mold, and the effect of preventing the generation of a product containing a gas defect is produced.

It is side surface sectional drawing which shows the mold tool structure for annular member casting which concerns on embodiment of this invention. It is side surface sectional drawing (a) and top view (b) which show the type | mold (intermediate type | mold) with which the mold tool structure for annular member casting which concerns on other embodiment of this invention is provided. It is side surface sectional drawing which shows the state of degassing in the mold tool structure shown in FIG. It is a perspective view which shows the external appearance of a brake disc raw material. It is explanatory drawing which shows the hardness distribution of the product obtained by the example of a mold layout (plan view) of the brake disc raw material in the case of providing a gate in the non-axial center by a prior art. It is a schematic diagram which shows the hardness distribution of the annular member obtained by providing a pouring gate and a hot water channel in the axial center vicinity, and filling hot water radially. It is side surface sectional drawing of the casting_mold | template which shows the structure of the stack mold type | mold which provides a gate and a runway in the axial center vicinity.

  A tool structure according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a mold structure according to the present embodiment, and shows a part of a portion corresponding to the intermediate mold 12 of the stack mold shown in FIG. In each of the following embodiments, a case where the brake disc material 1 shown in FIG. 4 is cast will be described as an example. However, the casting method according to the present embodiment is not limited to this, and a gate is provided. It is possible to apply the present invention equally to the center gate type casting in which an annular member is obtained by providing a metal in the vicinity of the shaft and diffusing and filling hot water radially into the cavity. In addition, the “annular member” referred to in this specification is not necessarily limited to a circular ring shape, and includes other ring-shaped members such as an elliptical ring shape and a polygonal ring shape.

  In FIG. 1, among the intermediate layer molds 12 (see FIG. 7) of the stack mold mold 10, three intermediate molds 12b, two cores 12a disposed in the middle of each, and two sheets that are products. The brake disc material 1 is shown in a section cut in the vertical direction. Compared to the mold structure shown in FIG. 7, in the mold structure according to the present embodiment, the radial tip (left and right direction in FIG. 1) of the core 12a terminates in the mold, and the entire end portion thereof A collar portion 15 that extends in the axial direction in a ring shape from the outer peripheral portion of the pair of intermediate molds 12 b positioned up and down covers the circumference.

  By configuring the core 12a and the intermediate mold 12b as described above, the core 12a is not exposed to the outside of the mold structure on the outer periphery in the radial direction. In the outer peripheral part of the core 12a, a pair of flanges 15 extending from the upper and lower intermediate molds 12b are in contact with each other over the entire periphery, and this forms the outer periphery of the mold structure. Then, as shown in FIG. 7, the entire tool is restrained and tightened up and down, so that the pair of flanges 15 function as a backup of the core 12a, and the core 12a is firmly held in the inside. Become.

  When cast under this condition, even if the core 12a tries to expand as indicated by the arrow A at a high temperature of the molten iron, the pair of flanges 15 restrains it from the surroundings, and the deformation of the core 12a, the outer peripheral portion It plays a role to prevent the collapse of. The specifications of the collar portion 15 can be appropriately set according to the size, thickness, material, and the like of the core 12a. 13 mm, and the width of the base portion is slightly tapered to 16.4 mm. In the experiment conducted by the inventors of the present application, by adopting this mold structure, it is possible to reliably eliminate variations in product quality due to deformation and outer peripheral collapse of the core 12a seen in the structure shown in FIG. It is possible.

  The form of the collar part 15 shown in FIG. 1 is an example, and can take other forms. For example, the flange portion 15 extends from the intermediate mold 12b to the upper and lower sides in the axial direction in the illustrated example. However, the flange portion 15 may extend in only one direction (for example, only upward in the figure). . In this case, the other surface of the intermediate mold 12b remains flat, and the flange portion 15 is brought into contact with the flat portion located above. Or as the middle, you may determine the length of the collar part 15 extended up and down to arbitrary ratios, such as 6: 4 and 7: 3. Here, a stack mold type in which a number of cavities are stacked in the vertical direction is taken as an example. However, not only the intermediate layer mold 12 but a single-piece mold can be dealt with in the same manner.

  Next, a tool structure according to a second embodiment of the present invention will be described. In this embodiment, a hot water passage is provided in the vicinity of the axial center of the mold for the annular member including the core, and the hot water is diffused in a radial manner and cast from the mold including the core. The present invention relates to a mold structure capable of effectively releasing gas out of a cavity. FIG. 2 shows an intermediate mold 12b according to the present embodiment, in which FIG. 2 (a) is a side sectional view and FIG. 2 (b) is a plan view. Here, a mold for casting the brake disc material 1 (see FIG. 4) is taken as an example as in the previous embodiment. 2 (a) and 2 (b), the intermediate die 12b corresponds to the hub region 22 corresponding to the hub portion 3 (see FIG. 4) of the brake disc material 1 in the central portion and the ring portion 3 on the outer peripheral side thereof. It is mainly formed from the ring area | region 23 to perform and the collar part 15 extended in an axial direction on the outermost periphery. A two-dot chain line in FIG. 2A indicates a core 12a that is arranged on the lower side of the intermediate mold 12b.

  Here, the flange portion 15 is an outer peripheral portion of the ring region 23 that extends substantially flatly in the radial direction (horizontal direction), and extends in the axial direction perpendicular to this in the illustrated example. As a result, the flange portion 15 surrounds the outer periphery of the ring region 23 in a ring shape, and is configured to wrap around the core 12a indicated by the broken line in cooperation with the flange portion 15 of another intermediate mold 12b located further below (not shown). Is done. This is the same as that shown in the previous embodiment.

  In the intermediate die 12b according to the present embodiment, a plurality of gas vent grooves 25 are provided over the entire circumference from the vicinity of the outer periphery of the disk region 22 to the inner peripheral surface of the flange portion 15 and further to the end surface in the axial direction of the flange portion 15. It has been. The gas vent groove 25 is formed as a concave portion on each surface. In the present embodiment, the gas vent groove 25 is a concave groove of about 0.2 mm substantially corresponding to the diameter of the foundry sand. The gas vent groove 25 is near the outer periphery of the ring region 23, extends from a position in contact with the surface of the core 12 a, and is bent in the axial direction along the outer peripheral surface of the core 12 a, and then on the end surface of the flange portion 15. It is formed so as to bend again in the radial direction. The specifications of the gas vent groove 25 can be appropriately set in accordance with the size and shape of the annular member to be cast. However, in the example of the brake disc having a diameter of 350 mm shown in FIG. The number is 24. The outline is shown in the plan view of FIG.

  By providing the gas vent groove 25 described above, the gas generated inside the cavity during pouring and the subsequent process passes through the gas vent groove 25 and escapes to the outside of the mold. It is possible to effectively prevent quality degradation. FIG. 3 schematically shows the situation when the stack mold 1 is used. In the figure, hot water poured into the gate 19 from the direction indicated by the upper arrow flows through the weirs 9 of the stacked layers of the layers through the hot water passage 18 and is filled radially into the cavities. The gas formed in the cavity at the time of filling and in the subsequent process is discharged to the outside from the gas vent groove 25 formed between the core 12a and the intermediate mold 12b as indicated by a thick arrow. As is clear from FIGS. 2 and 3, the gas vent groove 25 includes two bends, so that leakage of hot water to the outside is effectively excluded due to its throttling effect (labyrinth effect). In the above description, it is described that the gas vent groove 25 is provided in the “intermediate mold 12b” of the intermediate layer mold 12. However, the uppermost mold 13 in FIG. 3 and the lowermost mold 11 (not shown) 7) can be dealt with by providing a similar groove if necessary.

  Various modifications can be made to the arrangement of the gas vent grooves 25 described above. For example, in FIG. 2, it is provided on the lower side surface of the intermediate mold 12b, but it may be provided on the upper side surface. Moreover, when the collar part 15 is provided only in the axial direction one side of the intermediate mold | type 12b, it is sufficient to provide in the site | part of the said collar part 15 provided. Further, in the gas vent groove 25, the portion facing the core 12 a is provided not on the intermediate mold 12 b but on the core 12 a, and only the end surface of the flange 15 is provided on the intermediate mold 12 b. The mold may be arranged so that the grooves are connected. Further, the number of bending points of the gas vent groove 25 can be more than two by providing a step in the flange portion 15 as necessary.

  As mentioned above, although the mold tool structure concerning each embodiment of this invention was demonstrated, this invention also includes the casting method of the annular member by utilizing these mold tool structures. According to the casting method of the present invention, a cavity for casting the annular member is formed using a mold including at least one core and at least a pair of molds arranged with the core interposed therebetween, and the cavity is disposed horizontally. A pouring gate for pouring from above is arranged near the axis of the mold, and the hot water is led into the cavity from the center side of the cavity via the pouring passage connected to the pouring gate, and the annular member is located near the axial center of the cavity. A center gate type casting method in which hot water is poured toward the outer periphery of the cavity that is radially outward of the core, and the periphery of the core is axially extended from one or both of the pair of molds. It is a casting method characterized in that it is surrounded by the extending flange portion to prevent deformation and collapse due to expansion of the core. A gas vent groove may be provided between the core and the mold and between the flanges extending from the pair of molds, and the gas generated in the cavity may be discharged to the outside.

  The present invention can be widely used in the technical field of casting, and in the technical field of manufacturing, selling, and using products that use the cast material.

1. 1. brake disc material, 2. ring part; Hub part, 6. Cavity, 8. 8. Yuji, 9. Weir, 10. 10. Stack mold type Bottom layer type, 12. Intermediate layer type, 12b. Intermediate mold, 12a. Nakako, 13. 15. Top layer type Isobe, 18. Yuji, 19. Yuguchi, 22. Hub region, 23. Ring region, 25. Gas vent groove.

Claims (8)

At least one core;
The annular cavity is composed of at least a pair of molds arranged with the core interposed therebetween, and has a cavity for casting an annular member, and a hot water tap and a water passage are provided near the axial center of the annular member. In the mold structure of the center gate type annular member formed so as to be radially diffused and cast from the vicinity of the axial center of the
The pair of molds has a flange extending from the entire circumference of the outer peripheral surface to one or both of the axial direction;
A mold structure characterized in that the periphery of the outer periphery of the core is surrounded by the flange portion to prevent deformation and collapse due to expansion of the core.   The tool structure according to claim 1, wherein the tool structure is configured by a stack mold that includes a plurality of cores and a plurality of the molds that are arranged so as to sandwich the plurality of cores in sequence.   A gas vent groove for releasing the gas generated in the cavity from the cavity to the outer peripheral surface of the mold is formed in at least one of the core and the mold, and the flange portion. The mold structure according to claim 1 or claim 2.   The mold tool structure according to claim 3, wherein the gas vent groove includes at least two bent portions.   An annular member formed by casting, which is cast by a mold having the mold structure according to any one of claims 1 to 4.   The annular member according to claim 5, wherein the annular member is a brake disc material for a vehicle. Forming a cavity for casting the annular member using a mold including at least one core and at least a pair of molds arranged with the core interposed therebetween;
A pouring gate for pouring from above is arranged in the vicinity of the axial center of the mold in which the cavity is arranged horizontally,
In the casting method of the center gate method in which the hot water is filled from the vicinity of the axial center of the cavity toward the radially outer side through the hot water channel connected to the gate,
A casting method characterized in that the outer periphery of the core is surrounded by a flange extending in the axial direction from one or both of the pair of molds to prevent deformation and collapse due to expansion of the core. The casting according to claim 7, wherein the gas in the cavity is discharged to the outside of the mold through a gas vent groove provided between the core and the mold and between the flanges extending from the pair of molds. Method.