Method for manufacturing a cast swing arm and cast swing arm

Abstract

To provide good fluidity at the time of casting a swing arm having a hollow structure.SOLUTION: A cast swing arm 30 includes: a pivot shaft 32 formed in a cylindrical shape and having a through-hole 32h into which molten metal is supplied in a molding process and which penetrates in a longitudinal direction; a first hollow frame 40A including a first inner space and extending from the pivot shaft in a direction intersecting with the pivot shaft; a second hollow frame 40B including a second inner space and extending from the pivot shaft at an interval and in parallel with the first hollow frame; connecting inner spaces connected to the first inner space and the second inner space; and a hollow connecting portion 50 including curved plate portions 51a, 52a, 56, each of which has a curved surface as viewed along at least one direction intersecting with the longitudinal direction of the first hollow frame, and connecting a longitudinal intermediate portion of th first hollow frame and a longitudinal intermediate portion of the second hollow frame.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] This disclosure relates to a cast swing arm having a hollow structure, a core for forming the cast swing arm, and a casting apparatus.

Background Art

[0002] Patent Document 1 discloses a swing arm having a hollow structure.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When casting a swing arm in which a plurality of rod - shaped portions are connected and which has a hollow structure, it is desirable to make various improvements from the viewpoints of molten metal flowability, manufacturability of the hollow space, and maintenance of the heat of the casting mold.

[0005] Therefore, the disclosure related to this cast swing arm Manufacturing method and cast swingarm [[ID=4l]]aims to improve the molten metal flow when casting a swing arm having a hollow structure.

Means for Solving the Problems

[0008] The cast swing arm Manufacturing method is long a pivot shaft having a cylindrical shape with a through - hole penetrating in the vertical direction, a first hollow frame having a first internal space and extending in a direction intersecting the pivot shaft from the pivot shaft, and a second hollow frame having a second internal space and hand extending in a direction intersecting the pivot shaft from the pivot shaft, and handA second hollow frame extending from the pivot shaft is positioned parallel to the first hollow frame at a distance from it, and has a first internal space and a connecting internal space connected to the second internal space, and a curved plate portion which is a curved surface when viewed along at least one direction intersecting the longitudinal direction of the first hollow frame, and a hollow connecting portion which connects the longitudinal intermediate portion of the first hollow frame and the longitudinal intermediate portion of the second hollow frame. A casting mold and a core are prepared to define the space to be formed, wherein the curved plate portion includes a portion that curvely connects the inward-facing portions of the first hollow frame and the second hollow frame with the longitudinal intermediate portion of the front plate portion of the hollow connecting portion, the longitudinal intermediate portion of the front plate portion of the hollow connecting portion is thinner than the inward-facing portions of the first hollow frame and the second hollow frame, and molten metal is supplied from the space in the casting mold that forms the pivot shaft to the space inside the casting mold, in a method for manufacturing a cast swing arm.

[0009] The cast swing arm is a cylindrical pivot shaft having a through hole that penetrates in the longitudinal direction, the pivot shaft has a molten metal inlet mark partially formed in the longitudinal direction of the pivot shaft and partially formed in the circumferential direction of the pivot shaft, has a first internal space, and has a first hollow frame extending from the pivot shaft in a direction intersecting the pivot shaft, has a second internal space, and has a second hollow frame extending from the pivot shaft in a parallel position spaced apart from the first hollow frame, and has a connecting internal space that connects the first internal space and the second internal space A cast swing arm comprising a section and a curved plate section which is a curved surface when viewed along at least one direction intersecting the longitudinal direction of the first hollow frame, and a hollow connecting section which connects the longitudinal intermediate section of the first hollow frame and the longitudinal intermediate section of the second hollow frame, wherein the curved plate section includes a portion that curvely connects the inward-facing portions of the first hollow frame and the second hollow frame with the longitudinal intermediate section of the front plate section of the hollow connecting section, and the longitudinal intermediate section of the front plate section of the hollow connecting section is thinner than the inward-facing portions of the first hollow frame and the second hollow frame. [Effects of the Invention]

[0011] Cast swingarm Manufacturing method and cast swingarm According to the research, this allows for better molten metal flow when casting a hollow swingarm. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram showing a motorcycle according to the embodiment. [Figure 2] This is a perspective view showing the swingarm. [Figure 3] This is a cross-sectional view along line III-III in Figure 2. [Figure 4] This is a partial cross-sectional view along line IV-IV in Figure 2. [Figure 5] This is a perspective view showing the swingarm and core. [Figure 6] This is an explanatory diagram showing the orientation of the mold surface and the state of the molten metal flow during manufacturing. [Figure 7] This is an explanatory diagram showing the orientation of the mold surface and the state of the molten metal flow during manufacturing. [Figure 8] This is a schematic perspective view showing a casting apparatus. [Figure 9] This is a plan view showing an example of a heating device. [Figure 10] This is a cross-sectional view along line XX in Figure 9. [Modes for carrying out the invention]

[0015] {Embodiment} Hereinafter, a cast swing arm, a core for forming a cast swing arm, and a casting apparatus according to an embodiment will be described.

[0016] <Regarding the motorcycle> An example of a motorcycle equipped with a cast swing arm will be described. FIG. 1 is a schematic view showing the motorcycle 10. The motorcycle 10 includes a frame 12, a cast swing arm 30, a front wheel 14, a rear wheel 16, a handlebar device 18, and an engine 20 as a power unit. Hereinafter, the cast swing arm 30 will simply be referred to as the swing arm 30. In the following description, when referring to up and down, front and rear, and left and right, each direction is defined as follows. First, the side where the front wheel 14 and the rear wheel 16 of the motorcycle 10 contact the road surface is the bottom, and the side opposite to the bottom is the top. Also, the traveling direction when the motorcycle 10 is traveling is the front, and the side opposite to the front is the rear. Further, in the state where the driver is on board the motorcycle 10, the left and right with reference to the driver are the left and right of the motorcycle 10. In the present embodiment, the left-right direction may be described as the vehicle width direction.

[0017] The frame 12 includes a head pipe 12a and a main frame 12b.

[0018] The head pipe 12a is located in the front of the frame 12. The main frame 12b extends rearward while branching left and right from the head pipe 12a.

[0019] A steering shaft 13a is rotatably inserted into the head pipe 12a. An upper bracket 13b and an under bracket 13c are supported on the steering shaft 13a. The front fork 13d is supported by the upper bracket 13b and the under bracket 13c so as to extend downward. The front wheel 14 is rotatably supported at the lower end of the front fork 13d.

[0020] The handle device 18 is supported by the upper bracket 13b or the front fork 13d. By operating the handle device 18, the steering shaft 13a, the upper bracket 13b, the under bracket 13c, and the front fork 13d rotate, and together with this, the front wheels 14 also rotate.

[0021] The engine 20 is supported at the lower part of the frame 12. At the upper part of the frame 12, a fuel tank 21 and a seat 22 on which a passenger can sit are supported.

[0022] The engine 20 is an example of a power unit for running, and generates a driving force for running the motorcycle 10. The engine 20 is, for example, an internal combustion engine. The power unit may be an electric motor. The engine 20 incorporates a transmission 24 that transmits the rotational driving force generated by itself while changing the rotational speed. An output shaft 24b projects from one side in the vehicle width direction of the transmission 24.

[0023] A pivot bracket 25 is provided at the rear side of the engine 20. The swing arm 30 is attached to the pivot bracket 25 so as to extend rearward and downward. The front end portion of the swing arm 30 is swingably supported by the pivot bracket 25 in a posture where the swing arm 30 extends obliquely rearward from the pivot bracket 25. The rear wheel 16 is rotatably supported at the rear end portion of the swing arm 30.

[0024] The rotational output of the output shaft 24b is transmitted to the rear wheel 16 via the power transmission mechanism 26. Here, the power transmission mechanism 26 is a chain wound around a gear provided on the output shaft 24b and a gear provided on the rear wheel 16. As another example, an annular belt such as a toothed belt may be used as the power transmission mechanism. Also, as the power transmission mechanism, a shaft drive mechanism including a drive shaft and bevel gears may be used.

[0025] The pivot bracket 25 has a rear suspension support portion 25a that supports one end of the rear suspension 27.

[0026] The rear suspension 27 includes a shock absorber and a coil spring, and is a component that plays a role in suppressing vibrations and shocks of the rear wheel 16. One end of the rear suspension 27 is supported by the rear suspension support portion 25a of the pivot bracket 25. The other end of the rear suspension 27 is connected to the swing arm 30 directly or via a link. When the swing arm 30 swings due to vibrations or shocks of the rear wheel 16, the rear suspension 27 extends and contracts in conjunction with the swing, suppressing the swing of the swing arm 30.

[0027] <About cast swingarms> Let's describe the swing arm 30 in more detail. Figure 2 is a perspective view of the swing arm 30. Figure 3 is a cross-sectional view along line III-III in Figure 2, and Figure 4 is a partial cross-sectional view along line IV-IV in Figure 2. Figure 5 is a perspective view of the swing arm 30 and core 60. In Figure 5, a perspective view of the lower half of the swing arm 30, divided along line IV-IV in Figure 2, is shown.

[0028] The swingarm 30 comprises a pivot shaft 32, a first hollow frame 40A, a second hollow frame 40B, and a hollow connecting portion 50. The pivot shaft 32 is formed in a long cylindrical shape. The first hollow frame 40A and the second hollow frame 40B are formed in a hollow, elongated shape. The first hollow frame 40A and the second hollow frame 40B are in a parallel position with a gap between them, extending from the pivot shaft 32 in a direction intersecting the pivot shaft 32. The hollow connecting portion 50 is formed in a hollow, elongated shape. The hollow connecting portion 50 connects the longitudinal middle portion of the first hollow frame 40A and the longitudinal middle portion of the second hollow frame 40B.

[0029] The pivot shaft 32 is pivotably supported by the pivot bracket 25, thereby supporting the swing arm 30 so that it can swing in a position facing rearward from the engine 20. The rear wheel 16 is rotatably supported at the rear ends of the first hollow frame 40A and the second hollow frame 40B. The swing of the swing arm 30 supports the rear wheel 16 so that it can be displaced up and down. The other end of the rear suspension 27 is connected to the hollow connecting part 50 directly or via a link. The swing of the swing arm 30 due to the vertical displacement of the rear wheel 16 is absorbed by the rear suspension 27 connected to the hollow connecting part 50.

[0030] Let's explain each part of the swingarm 30 in more detail.

[0031] The pivot shaft 32 is formed in a cylindrical shape with a through hole 32h that penetrates in the longitudinal direction. The pivot shaft 32 is rotatably supported when a support shaft or support pin, which is supported in a fixed position by the pivot bracket 25, is inserted into the pivot shaft 32.

[0032] The pivot shaft 32 is the part to which molten metal is supplied during the molding process. For example, the pivot shaft 32 has a molten metal inlet 38. The molten metal inlet 38 is a protruding portion that is partially formed in the longitudinal direction of the pivot shaft 32 and partially in the circumferential direction of the pivot shaft 32. In this embodiment, the molten metal inlet 38 is formed in the circumferential direction of the pivot shaft 32 on the side opposite to the portion to which the first hollow frame 40A and the second hollow frame 40B extend. Also, in the longitudinal direction of the pivot shaft 32, the molten metal inlet 38 is formed at a position shifted towards the center from the portion to which the first hollow frame 40A and the second hollow frame 40B extend. In this embodiment, two molten metal inlet 38 are formed, corresponding to the first hollow frame 40A and the second hollow frame 40B, respectively. One or more molten metal inlet 38 may be formed.

[0033] The molten metal inlet mark 38 is the remaining portion that serves as a trace of the inlet used to pour molten metal into the casting mold for forming the swing arm 30. In other words, when the swing arm 30 is mold-formed, molten metal (for example, aluminum or an aluminum alloy) is supplied into the casting mold as molten metal at high temperatures. The molten metal is supplied into the mold space of the casting mold through a molten metal inlet formed in the casting mold. The metal that has solidified as the swing arm 30 in the casting mold is removed from the casting mold in a state integrated with the metal that has solidified at the molten metal inlet. The metal that has solidified at the molten metal inlet is removed by cutting or machining. The molten metal inlet mark 38 is the portion that remains as a trace of the molten metal inlet because it protrudes from the outer surface of the pivot shaft 32 beyond the portion around the molten metal inlet mark 38, or because it has a different surface shape from the surface around the molten metal inlet mark 38 on the outer surface of the pivot shaft 32. The molten metal inlet mark 38 may also be formed at other locations on the pivot shaft 32, for example, on the end face. The molten metal inlet mark 38 may be removed to the extent that it is difficult to distinguish or even completely removed by finishing processes.

[0034] A shaft-internal molten metal inlet mark 38B that partially protrudes into the pivot shaft 32 may be formed. For example, the shaft-internal molten metal inlet mark 38B may be formed in the portion of the shaft-internal molten metal inlet mark 38 that extends toward the pivot shaft 32 (see Figure 5). The shaft-internal molten metal inlet mark 38B is, for example, a portion that allows molten metal to flow smoothly from the pivot shaft 32 toward the first hollow frame 40A and the second hollow frame 40B. The shaft-internal molten metal inlet mark 38B remains as a portion that protrudes into the through hole 32h immediately after molding by the mold, but may also remain as a trace after being removed by machining or the like. The shaft-internal molten metal inlet mark 38B will be further explained in the description of the core 60.

[0035] The first hollow frame 40A and the second hollow frame 40B are formed in an elongated shape that extends from the pivot shaft 32 in a direction intersecting the pivot shaft 32. The first hollow frame 40A and the second hollow frame 40B extend in a parallel position with a gap between them. Here, the statement that the two elongated members extend in a parallel position includes not only the case where the two elongated members are geometrically parallel, but also the case where the two elongated members extend side by side in a direction away from the pivot shaft 32. The gap between the first hollow frame 40A and the second hollow frame 40B is set to a size that allows for the placement of the transmission 24, rear suspension 27, and rear wheel 16 between them. In this embodiment, the gap between the first hollow frame 40A and the second hollow frame 40B gradually widens as it moves away from the pivot shaft 32.

[0036] The first hollow frame 40A is formed in a shape that is flattened in a direction perpendicular to both the longitudinal direction of the pivot shaft 32 and the longitudinal direction of the first hollow frame 40A, for example, in the vertical direction. The second hollow frame 40B is formed in a shape that is flattened in a direction perpendicular to both the longitudinal direction of the pivot shaft 32 and the longitudinal direction of the second hollow frame 40B, for example, in the vertical direction. As a result, the rigidity of the first hollow frame 40A and the second hollow frame 40B in the vertical direction is higher than the rigidity in the width direction. It is not essential that the first hollow frame 40A and the second hollow frame 40B have the above shapes; for example, they may be cylindrical or rectangular tubes with the same dimensions in the vertical and width directions.

[0037] The ends of the first hollow frame 40A and the second hollow frame 40B on the pivot shaft 32 side have reinforcing portions 41A and 41B that extend inward toward the pivot shaft 32.

[0038] A first internal space 40Ah is formed within the first hollow frame 40A, extending along the longitudinal direction of the first hollow frame 40A. A second internal space 40Bh is formed within the second hollow frame 40B, extending along the longitudinal direction of the second hollow frame 40B. The ends of the first internal space 40Ah and the second internal space 40Bh on the pivot shaft 32 side are closed by the outer circumference of the pivot shaft 32.

[0039] Shaft connecting internal spaces 41Ah and 41Bh are formed within the reinforcing portions 41A and 41B described above. One end of the shaft connecting internal spaces 41Ah and 41Bh penetrates the outer circumference of the pivot shaft 32 and communicates with a through hole 32h inside the pivot shaft 32. The other end of the shaft connecting internal spaces 41Ah and 41Bh connects to the first internal space 40Ah or the second internal space 40Bh from the longitudinal center side of the pivot shaft 32.

[0040] Therefore, cylindrical portions are formed in the pivot shaft 32 near both ends, where no radially penetrating holes are formed. At a position closer to the longitudinal center of the pivot shaft 32 than the axial extensions of the first hollow frame 40A and the second hollow frame 40B, the first internal space 40Ah and the second internal space 40Bh communicate with the through hole 32h in the pivot shaft 32. One of the shaft connecting internal spaces 41Ah and 41Bh may be omitted.

[0041] The end of the first hollow frame 40A opposite to the pivot shaft 32 is the rear wheel support end 44A. The end of the second hollow frame 40B opposite to the pivot shaft 32 is the rear wheel support end 44B. The rear wheel support ends 44A and 44B are the parts that support the axle shaft of the rear wheel 16. In this embodiment, the rear wheel support ends 44A and 44B have extended portions that are extensions of the inner portion and the upper and lower portions of the first hollow frame 40A and the second hollow frame 40B. A support hole is formed in the inner extended portion through which the axle shaft is inserted.

[0042] Openings 45Ah and 45Bh are formed in the longitudinal middle portions of the first hollow frame 40A and the second hollow frame 40B. The openings 45Ah and 45Bh are formed in the opposing portions of the first hollow frame 40A and the second hollow frame 40B, between the hollow connecting portion 50 and the rear wheel support ends 44A and 44B. The first internal space 40Ah and the second internal space 40Bh are connected to the external space via the openings 45Ah and 45Bh.

[0043] The first hollow frame 40A includes a brake positioning projection 46B. The brake positioning projection 46B is formed on the surface of the first hollow frame 40A facing the second hollow frame 40B, between the opening 45Ah and the rear wheel support end 44A. The brake positioning projection 46B is a protruding portion that plays a role in positioning the brake for the rear wheel 16.

[0044] The hollow connecting portion 50 is the part that connects the longitudinal middle portion of the first hollow frame 40A and the longitudinal middle portion of the second hollow frame 40B. In other words, one end of the hollow connecting portion 50 is connected to the longitudinal middle portion of the first hollow frame 40A, and the other end of the hollow connecting portion 50 is connected to the longitudinal middle portion of the second hollow frame 40B. The hollow connecting portion 50 is aligned in the same direction as the longitudinal direction of the pivot shaft 32.

[0045] The hollow connecting portion 50 has an internal connecting space 50h inside. One end of the internal connecting space 50h is connected to the first internal space 40Ah, and the other end of the internal connecting space 50h is connected to the second internal space 40Bh.

[0046] The hollow connecting portion 50 has curved plate portions 51a, 52a, and 56 that are curved when viewed along at least one direction intersecting the longitudinal direction of the first hollow frame 40A.

[0047] In this embodiment, the hollow connecting portion 50 is formed in the shape of a rectangular tube with both ends widening. The hollow connecting portion 50 has a front plate portion 51, a rear plate portion 52, an upper plate portion 53, and a lower plate portion 54. The front plate portion 51 is the part that faces the pivot shaft 32, and the rear plate portion 52 is the part that faces the opposite direction from the front plate portion 51. When the swing arm 30 is assembled into the motorcycle 10, the upper plate portion 53 is the part that faces upward, and the lower plate portion 54 is the part that faces downward. The front plate portion 51, the rear plate portion 52, the upper plate portion 53, and the lower plate portion 54 are all rectangular tubes with both ends widening.

[0048] More specifically, the longitudinal middle portion of the front plate 51 is formed in a plate shape that extends along the direction connecting the first hollow frame 40A and the second hollow frame 40B. Both longitudinal ends of the front plate 51 have curved surfaces that are convex toward the connecting internal space 50h when viewed along a direction perpendicular to both the pivot shaft 32 and the first hollow frame 40A. The edges of both longitudinal ends of the front plate 51 are closer to the pivot shaft 32 than the longitudinal middle portion of the front plate 51.

[0049] The longitudinal middle portion of the rear plate 52 is formed as a plate extending along the direction connecting the first hollow frame 40A and the second hollow frame 40B. Both longitudinal ends of the rear plate 52 have curved surfaces that are convex toward the connecting internal space 50h when viewed along a direction perpendicular to both the pivot shaft 32 and the first hollow frame 40A. The edges of both longitudinal ends of the rear plate 52 are further from the pivot shaft 32 than the longitudinal middle portion of the rear plate 52.

[0050] The longitudinal middle portions of the upper plate portion 53 and the lower plate portion 54 are formed into rectangular sections of the same width. The longitudinal ends of the upper plate portion 53 and the lower plate portion 54 are formed in a shape that gradually widens toward the first hollow frame 40A or the second hollow frame 40B, in accordance with the curved shape of the longitudinal ends of the front plate portion 51 and the longitudinal ends of the rear plate portion 52.

[0051] The curved portions at both ends of the front plate portion 51 of the hollow connecting portion 50 are an example of a curved plate portion 51a, which is a curved surface when viewed along a direction intersecting the longitudinal direction of the first hollow frame 40A. Here, the curved plate portion 51a is a curved surface when viewed along a direction perpendicular to both the longitudinal direction of the pivot shaft 32 and the longitudinal direction of the first hollow frame 40A.

[0052] The curved plate portion 51a is a portion that connects the inward-facing parts of the first hollow frame 40A and the second hollow frame 40B, which are closer to the pivot shaft 32 than the hollow connecting portion 50, with the longitudinal middle portion of the front plate portion 51 of the hollow connecting portion 50, with a smooth curve. The bending radius of the curved plate portion 51a is, for example, 40 mm or more.

[0053] The curved portions at both ends of the rear plate portion 52 of the hollow connecting portion 50 are an example of a curved plate portion 52a, which is a curved surface when viewed along a direction intersecting the longitudinal direction of the first hollow frame 40A. Here, the curved plate portion 52a is a curved surface when viewed along a direction perpendicular to both the longitudinal direction of the pivot shaft 32 and the longitudinal direction of the first hollow frame 40A.

[0054] The curved plate portion 52a is a portion that connects the inward-facing parts of the first hollow frame 40A and the second hollow frame 40B, which are further from the pivot shaft 32 than the hollow connecting portion 50, with the longitudinal middle portion of the rear plate portion 52 of the hollow connecting portion 50, with a smooth curve. The bending radius of the curved plate portion 52a is, for example, 40 mm or more.

[0055] Furthermore, the portions of the hollow connecting section 50 that connect the front plate section 51, the rear plate section 52, the upper plate section 53, and the lower plate section 54 are formed as curved plate sections 56 that have a curved surface that is convex outwards. The curved plate section 56 is the part that connects adjacent portions of the front plate section 51, the rear plate section 52, the upper plate section 53, and the lower plate section 54 with a smooth curve. The bending radius of the curved plate section 56 is, for example, 10 mm or more.

[0056] A suspension support portion 53P is provided protruding from the upper plate portion 53, near the first hollow frame 40A. The rear suspension 27 is connected to the suspension support portion 53P.

[0057] The thickness of each part of the first hollow frame 40A, the second hollow frame 40B, and the hollow connecting section 50 is set from the following perspectives, for example. First, there is the perspective of making the swingarm 30 as lightweight as possible. From this perspective, the thickness of each part is required to be as small as possible. Second, there is the perspective of maintaining the strength to support the rear wheel 16, rear suspension 27, etc. From this perspective, the thickness of the parts that are prone to stress when the rear wheel 16 is supported is required to be as large as possible. For example, the upper plate portion 53 of the hollow connecting section 50, which is subjected to stress by the rear suspension 27, is required to be thicker than the front plate portion 51. Also, the part of the first hollow frame 40A facing the second hollow frame is prone to stress by the rear suspension 27, and is also required to be thicker than the front plate portion 51 in order to position the rear brake. Furthermore, the portion of the second hollow frame 40B facing the first hollow frame 40A supports the hollow connecting portion 50, and therefore may be set to be thicker than, for example, the front plate portion 51. Also, the thickness of each part is set from the viewpoint of allowing molten metal to flow into each part constituting the swing arm 30 during molding with a mold. From this viewpoint, each part is required to be at least the minimum thickness through which molten metal can be flowed.

[0058] If the swing arm 30 has different thicknesses in each part, and as a result the swing arm 30 includes a thick plate section and a thin plate section that is thinner than the thick plate section, the curved plate section may include a portion located at the point where the thick plate section and the thin plate section are connected.

[0059] For example, the thickness t1 of the front plate portion 51 of the hollow connecting portion 50 is smaller than the thickness t3 of the upper plate portion 53 and the thickness t4 of the lower plate portion 54. From this viewpoint, the upper plate portion 53 and the lower plate portion 54 are examples of thick plate portions, and the front plate portion 51 is an example of a thin plate portion that is thinner than the upper plate portion 53 and the lower plate portion 54, which are thick plate portions. The curved plate portion 56 interposed between the front plate portion 51 and the upper plate portion 53 or the lower plate portion 54 is an example of a portion located in the part that connects the thick plate portion and the thin plate portion.

[0060] Furthermore, for example, the thickness t1 of the longitudinal middle portion of the front plate portion 51 of the hollow connecting portion 50 is smaller than the thickness t5 of the portion of the first hollow frame 40A that faces the second hollow frame 40B and is located closer to the pivot shaft 32 than the front plate portion 51. From this viewpoint, the portion of the first hollow frame 40A that faces the second hollow frame 40B and is located closer to the pivot shaft 32 than the front plate portion 51 is an example of a thick plate portion. Also, the longitudinal middle portion of the front plate portion 51 is an example of a thin plate portion that is thinner than the thick plate portion of the first hollow frame 40A that faces the second hollow frame 40B and is located closer to the pivot shaft 32 than the front plate portion 51. The curved plate portion 51a is an example of a portion located in the part that connects the thick plate portion and the thin plate portion.

[0061] Similarly, the portion of the second hollow frame 40B facing the first hollow frame 40A may be an example of a thick plate portion that is thicker than the front plate portion 51. In this case as well, the curved plate portion 51a may be located in the portion connecting the thick plate portion and the thin plate portion.

[0062] If the thick plate section and the thin plate section are connected at an angle, the molten metal flowing through the space forming the thick plate section in the mold may be temporarily blocked at the part corresponding to that angle. If the thick plate section and the thin plate section are connected via curved sections 51a and 56, the molten metal flowing through the space forming the thick plate section in the mold can easily maintain its momentum and flow through the spaces forming the curved sections 51a and 56 into the space forming the thin plate section.

[0063] The thin plate portion may have a minimum thickness that allows for molten metal pouring, for example, 3.00 mm or more. The thick plate portion may have a thickness of, for example, 4.00 mm or more, preferably 4.50 mm or more.

[0064] The thickness of the curved plate sections 56 and 51a, which exist between the thick plate section and the thin plate section of the curved plate section, may be formed so that it gradually decreases from the thick plate section to the thin plate section. If the thickness of the thick plate section and the thickness of the thin plate section change abruptly, it is conceivable that a step will occur between the space forming the thick plate section and the space forming the thin plate section in the molding die. In this case, the force of the molten metal flowing through the space forming the thick plate section may be weakened by the step. If the thick plate section and the thin plate section are connected by curved plate sections 51a and 56 that gradually become thinner, the molten metal flowing through the space forming the thick plate section in the molding die can easily flow into the space forming the thin plate section with increased force or with its force maintained as it passes through the space forming the curved plate sections 51a and 56.

[0065] <Regarding the core for the swingarm> An example of a core 60 for a swing arm used to form the swing arm 30 described above will be explained. As shown in Figure 5, the core 60 comprises a pivot core 62, a first frame core 64A, a second frame core 64B, a connecting core 66, and an auxiliary connecting core 68. The core 60 is formed, for example, by solidifying sand with resin in a mold for cores.

[0066] The pivot core 62 is formed in a rod shape. The pivot core 62 can form a through hole 32h in the pivot shaft 32. In this embodiment, a groove 62g is formed in the portion of the pivot core 62 that extends from the molten metal port, intersecting the longitudinal direction of the pivot core 62. The molten metal supplied through the molten metal port can flow smoothly through the groove 62g toward the first hollow frame 40A and the second hollow frame. The molten metal port mark 38B inside the shaft is formed by the molten metal filling the groove 62g. The molten metal port mark 38B inside the shaft may be removed by machining. Even if the portion that filled the groove 62g is removed, it is assumed that the molten metal port mark 38B inside the shaft will remain as a trace of machining or the like.

[0067] The first frame core 64A and the second frame core 64B extend from the pivot core 62 in a direction intersecting the pivot core 62. The first frame core 64A and the second frame core 64B extend parallel to each other with a gap between them in the longitudinal direction of the pivot core 62. The first frame core 64A and the second frame core 64B are the parts that form the first internal space 40Ah of the first hollow frame 40A and the second internal space 40Bh of the second hollow frame 40B, respectively. The end of the first frame core 64A on the pivot core 62 side and the end of the second frame core 64B on the pivot core 62 side include inclined portions 64Aa and 64Ba toward the middle of the pivot core 62 in the longitudinal direction toward the pivot core 62. The inclined portions 64Aa and 64Ba are the parts that form the shaft connecting internal spaces 41Ah and 41Bh. The main bodies of the first frame core 64A and the second frame core 64B are not directly connected to the pivot core 62, but are connected to the pivot core 62 via inclined portions 64Aa and 64Ba.

[0068] The first frame core 64A comprises a first frame core body 64A1 and a first cap core 64A2. The end of the first frame core body 64A1 opposite to the pivot core 62 has an opening 64A1h. The first cap core 64A2 is fitted into the opening 64A1h to close the opening 64A1h.

[0069] Similarly, the second frame core 64B includes a second frame core body 64B1 having an opening 64B1h, and a second cap core 64B2. The second cap core 64B2 is fitted into the opening 64B1h to close the opening 64B1h.

[0070] The openings 64A1h and 64B1h described above can be used to form a hollow swingarm core 60. That is, the swingarm core 60 is molded, for example, as follows: First, resin-coated sand is filled into a mold for the core. Then, the sand inside the mold is heated to melt the resin, and the molten resin adheres the sand to each other. The swingarm core 60 is formed as the sand hardens with the adhesion in place according to the shape of the mold. If the adhesion of the sand occurs near the mold surface and the sand inside is not adhered, the hollow swingarm core 60 is formed by removing the sand inside. The openings 64A1h and 64B1h described above are used as outlets for removing the sand from inside the swingarm core 60 after molding. If a hollow swingarm core 60 can be molded, the amount of sand used to manufacture the core can be reduced. In addition, the volume of the core that is heated during the manufacture of the swingarm core 60 can be reduced. Reducing the volume of the core being heated reduces the amount of combustion gases from the resin that binds the sand particles together, thereby reducing the impact of combustion gases on casting quality.

[0071] The connecting core 66 is the part that connects the longitudinal middle portion of the first frame core 64A and the longitudinal middle portion of the second frame core 64B. The connecting core 66 is the part that forms the connecting internal space 50h of the hollow connecting portion 50.

[0072] The auxiliary connecting core 68 connects the first frame core 64A and the second frame core 64B at a point closer to the tip of the first frame core 64A and the second frame core 64B than the connecting core 66. The auxiliary connecting core 68 is formed at a position corresponding to the opening 45Ah of the first hollow frame 40A and the opening 45Bh of the second hollow frame 40B. Therefore, although the auxiliary connecting core 68 is part of the part that forms the openings 45Ah and 45Bh, it is not part that is used to form the hollow space of the swing arm.

[0073] Since the first frame core 64A and the second hollow frame 40B are kept connected by the pivot core 62, the connecting core 66, and the auxiliary connecting core 68, it becomes easier to maintain a constant positional relationship between the first frame core 64A and the second hollow frame 40B. In addition, since the connecting core 66 protrudes to the outside of the swing arm 30, the connecting core 66 can be supported by the molding die.

[0074] <Examples of swingarm manufacturing> A manufacturing example of the swing arm 30 will be described. Figures 6 and 7 are explanatory diagrams showing the position of the mold surface and the state of the molten metal flow for forming the surface of the swing arm 30 during manufacturing. In Figure 6, the mold surface S1 shown by the dashed line shows the state before molten metal pouring, the mold surface S2 shown by the solid line shows the state during molten metal pouring, and the mold surface S3 shown in Figure 7 shows the state after further molten metal pouring has occurred.

[0075] As shown by the dashed line in Figure 6, in the initial state in which the core 60 for the swing arm is set inside the mold, the first hollow frame 40A and the second hollow frame 40B are kept in a horizontal position corresponding to their longitudinal directions. The container 90 that stores the molten metal is connected to the space inside the mold surface S1 via the molten metal port.

[0076] From the above state, the mold is rotated, and the mold surface S2 is tilted so that the molten metal outlet faces upward. Then, the molten metal L moves from the space in which the pivot shaft 32 is formed, through the lower part of the space in which the first hollow frame 40A and the second hollow frame 40B are formed, toward the tips of the first hollow frame 40A and the second hollow frame 40B. Because the tips of the first hollow frame 40A and the second hollow frame 40B are inclined downward, the molten metal fills the tips of the first hollow frame 40A and the second hollow frame 40B. As the mold surface S2 rotates, the amount of molten metal L inside the mold surface S2 increases, and the liquid level LS of the molten metal L inside the mold surface S2 gradually rises toward the pivot shaft 32.

[0077] As shown in Figure 7, as the mold surface S2 rotates further and the liquid level LS of the molten metal L reaches a position close to the hollow connecting portion 50, the amount of molten metal L flowing in increases, and the molten metal L fills the rear plate portion 52 and the lower plate portion 54 from the portion forming the first hollow frame 40A and the second hollow frame 40B. At this time, since both longitudinal ends of the rear plate portion 52 are curved plate portions 52a, the molten metal L flows smoothly into the rear plate portion 52 from the tip side of the first hollow frame 40A and the second hollow frame 40B.

[0078] The molten metal L that flows into the rear plate section 52 and the lower plate section 54 also flows into the front plate section 51 and the upper plate section 53. Since the front plate section 51, the rear plate section 52, the upper plate section 53 and the lower plate section 54 are connected by the curved plate section 56, the molten metal L that flows into the rear plate section 52 and the lower plate section 54 also flows smoothly into the front plate section 51 and the upper plate section 53. Although the front plate section 51 is a thin plate section, the molten metal L can flow smoothly into the front plate section 51 via the curved plate section 56, which gradually thins from the lower plate section 54, etc.

[0079] As the mold surface S3 rotates further and the liquid level LS of the molten metal L moves beyond the position corresponding to the hollow connecting portion 50 and approaches the pivot shaft 32, the molten metal L flows beyond the portion forming the hollow connecting portion 50 into the upper portions of the first hollow frame 40A and the second hollow frame 40B that are closer to the pivot shaft 32. At this time, since both longitudinal ends of the front plate portion 51 are curved plate portions 51a, the molten metal L flows smoothly from the front plate portion 51 into the upper portions of the first hollow frame 40A and the second hollow frame 40B that are closer to the pivot shaft 32.

[0080] After the molten metal L fills the space within the mold surface S3, the swing arm 30 is molded by solidifying and cooling the molten metal. The molded swing arm 30 may be machined as appropriate.

[0081] After manufacturing, the core 60 for the swingarm is broken into pieces by vibration and discharged. The sand is discharged, for example, through openings 45Ah and 45Bh formed in the longitudinal middle of the first hollow frame 40A and the second hollow frame 40B. Alternatively, the sand is discharged to the outside through the through hole 32h of the pivot shaft 32, passing through the connecting internal space 50h, the first internal space 40Ah, and the second internal space 40Bh. By using the through hole 32h of the pivot shaft 32 as a sand discharge port, the number of discharge ports on the swingarm 30 can be reduced, and the strength of the swingarm 30 can be improved.

[0082] With the swing arm 30 configured as described above, for example, when the swing arm 30 is gravity cast using a mold, the molten metal supplied to the pivot shaft 32 flows into the hollow connecting portion 50 via the first hollow frame 40A and the second hollow frame 40B. The hollow connecting portion 50 has curved plate portions 51a, 52a, and 56 which are curved surfaces when viewed along at least one direction intersecting the longitudinal direction of the first hollow frame 40A. Therefore, the molten metal that flows into the mold from the molten metal port can flow smoothly through the mold space for forming the curved plate portions 56. Thus, when casting the hollow swing arm 30, the molten metal flow can be improved.

[0083] Furthermore, since the molten metal inlet remains include a shaft-internal molten metal inlet remains 38B that partially protrudes into the pivot shaft 32, the flow path for the molten metal into the mold can be enlarged, allowing the molten metal to flow smoothly into the mold. The shaft-internal molten metal inlet remains 38b may be left as is after casting, or it may be removed by machining.

[0084] Furthermore, since the curved plate sections 51a and 56 include portions located at the connection between the thick plate section and the thin plate section, molten metal can flow smoothly from the thick plate section towards the rear plate section 52 via the curved plate sections 51a and 56.

[0085] If the thin plate portion has a thickness of 3.00 mm or more, it is easy to pour molten metal into the space forming the thin plate portion, even in gravity casting. Furthermore, if the thick plate portion is at least one of the following parts of the hollow connecting portion 50: the upper plate portion 53 or lower plate portion 54 that faces outward in a direction perpendicular to the first hollow frame 40A and the hollow connecting portion 50, the portion of the first hollow frame 40A that faces the second hollow frame 40B, and the portion of the second hollow frame 40B that faces the first hollow frame 40A, then the strength of the swing arm 30 can be ensured. In this way, by mixing thin plate portions and thick plate portions, it is possible to reduce the weight of the swing arm 30 while ensuring its strength, and to facilitate molten metal pouring.

[0086] Furthermore, the first hollow frame 40A has a shaft-connecting internal space 41Ah that is connected to the through hole 32h at a position closer to the longitudinal center of the pivot shaft 32 than the end of the first internal space 40Ah on the pivot shaft 32 side. This makes it easier to form the through hole of the pivot shaft 32 and the first hollow frame 40A with a common core 60 while maintaining a cylindrical shape near both ends of the pivot shaft 32. Similarly, by configuring the second hollow frame 40B to have a shaft-connecting internal space 41Bh, it is easier to form the through hole of the pivot shaft 32 and the second hollow frame 40B with a common core 60. In addition, when forming the core 60 for the swing arm, it is possible to unify the direction of sand flow in one direction from the tip of the first frame core 64A and the second frame core 64B toward the pivot shaft 32, making it easier to fill the mold for core forming with sand.

[0087] Furthermore, with the swingarm core 60 configured as described above, by using the swingarm core 60, it is possible to form each internal space in the swingarm 30, which has a pivot shaft 32 having a through hole 32h, a first hollow frame 40A having a first internal space 40Ah, a second hollow frame 40B having a second internal space 40Bh, and a hollow connecting part 50 having a connecting internal space 50h. In addition, the auxiliary connecting core 68 can be used to position the swingarm core 60 within the mold. Furthermore, the auxiliary connecting core 68 can firmly hold the first frame core 64A and the second frame core 64B in a fixed positional relationship. As a result, the internal spaces in the swingarm 30 are formed with high precision.

[0088] Furthermore, since the first frame core 64A comprises a first frame core body 64A1 having an opening 64A1h and a first cap core 64A2 that closes the opening 64A1h, and the second frame core 64B comprises a second frame core body 64B1 having an opening 64B1h and a second cap core 64B2 that closes the opening 64B1h, the first frame core 64A and the second frame core 64B, which have a hollow structure, can be easily manufactured.

[0089] The core 60 for this swingarm can also be used during manufacturing for swingarms that do not rely on the above-mentioned swingarm 30, for example, swingarms that do not have a curved plate section.

[0090] <About casting equipment> An example of a casting apparatus 100 that can be used when casting the swing arm 30 described above will be explained. Figure 8 is a schematic perspective view showing the casting apparatus 100. Note that the casting apparatus 100 itself can be used for casting general castings other than the swing arm 30.

[0091] The casting apparatus 100 comprises a casting mold 110 and a heating device 120. In this embodiment, the casting mold 110 comprises a first casting mold 110A and a second casting mold 110B. When the mold surface 110Af of the first casting mold 110A and the mold surface of the second casting mold 110B are facing each other, the first casting mold 110A and the second casting mold 110B are joined together to form a space in which a casting can be formed. In this embodiment, a swing arm 30 is assumed to be the casting.

[0092] The heating device 120 includes a first heating device 120A and a second heating device 120B. The first heating device 120A is located on the opposite side of the mold surface 110Af of the first casting mold 110A and heats the first casting mold 110A. The second heating device 120B is located on the opposite side of the mold surface of the second casting mold 110B and heats the second casting mold 110B.

[0093] The first heating device 120A and the second heating device 120B are positioned on opposite sides of the mold surface 110Af. Therefore, heating of the casting molds 110A and 110B can be continued even after casting has started.

[0094] For example, consider the case where the casting mold 110 is heated by a burner from the mold surface 110Af side. In gravity casting, the casting mold 110 is required to maintain a temperature of 250 to 500 degrees Celsius. However, when heating by a burner from the mold surface 110Af side, it is not possible to heat the mold after casting has started. Assuming repeated casting, it is conceivable to maintain the casting mold 110 within a certain range by the heat input from the molten metal.

[0095] However, in the case of hollow members such as the swing arm 30 described in this embodiment, the thickness is optimized considering the required strength and flowability, and as a result, the amount of molten metal supplied relative to the surface area molded by the mold is less than before the thickness optimization study. Therefore, the heat input relative to the volume and heat capacity of the casting mold 110 is small, and it is conceivable that the casting mold 110 will cool down if casting is repeated. If the casting mold 110 cools down, the molten metal will cool down while circulating within the casting mold 110, and it is conceivable that the flowability cannot be maintained.

[0096] In this example, the first heating device 120A and the second heating device 120B can heat the first casting mold 110A and the second casting mold 110B from the side opposite to the mold surface 110Af. Therefore, the casting mold 110 can be heated even after casting has started, and even when casting continuously, it is easy to maintain the temperature of the casting mold 110 at a temperature suitable for casting. This suppresses poor molten metal flow caused by temperature unevenness in each casting operation.

[0097] The heating device 120 can be configured to heat the casting mold 110, and may be a heating device that utilizes either the heat of combustion of a combustible gas or Joule heating. In this embodiment, an example of a heating device 120 that utilizes a combustible gas is shown.

[0098] Figure 9 is a plan view showing an example of the heating device 120A. Figure 10 is a cross-sectional view taken along line XX of Figure 9.

[0099] The heating device 120A comprises a heating device body 122, a nozzle 140, and a plug 142. Depending on the size of the first casting mold 110A, one or more heating device bodies 122 may be arranged side by side. The heating device 120B may have the same configuration as the heating device 120A.

[0100] The heating device body 122 has a combustible gas flow path 124 and a plurality of outlet holes 126. In this embodiment, the plurality of outlet holes 126 are distributed in at least two dimensions.

[0101] As an example, the heating device body 122 is made of metal and is in the shape of a rectangular plate. Multiple combustible gas passages 124 are formed in the heating device body 122 so as to be arranged in multiple vertical and multiple horizontal rows. Each combustible gas passage 124 is located in the middle of the thickness direction of the heating device body 122. The vertical combustible gas passages 124 and the horizontal combustible gas passages 124 are connected to each other at their intersections in a plan view. The ends of the multiple combustible gas passages 124 may or may not be open to the outside. A combustible gas supply pipe 130 is connected to at least one of the ends of the multiple combustible gas passages 124. The remaining ends of the multiple combustible gas passages 124 are closed from the beginning or are closed by end plugs 132. Because the multiple combustible gas passages 124 are connected to each other at their intersections, the combustible gas supplied via the supply pipe 130 can be supplied to all of the combustible gas passages 124.

[0102] On one main surface of the heating device body 122, outlet holes 126 connecting the combustible gas flow paths 124 to the outside space are formed at multiple locations where the combustible gas flow paths 124 pass through. In this embodiment, outlet holes 126 are formed at each of the multiple intersections of the multiple combustible gas flow paths 124. Since the multiple intersections of the multiple combustible gas flow paths 124 are dispersed in a grid pattern, the multiple outlet holes 126 are also dispersed vertically and horizontally at positions corresponding to each grid point.

[0103] The nozzle 140 is attached to at least one of the multiple outlet holes 126. The nozzle 140 guides the combustible gas flowing through the combustible gas passage 124 to the outside and ejects it so that it can be combusted. For example, the nozzle 140 is a burner tip having a combustible gas passage 124 and a combustion gas passage communicating with the outside, and an air intake passage that connects to the outside space from the middle of the combustion gas passage. The nozzle 140 causes the combustible gas in the combustible gas passage 124 to flow out to the tip of the nozzle 140 by the pressure of the combustible gas flowing through the combustible gas passage 124. In addition, the nozzle 140 can take in air through the air intake passage due to the negative pressure from the combustible gas, mix the air with the combustible gas, and discharge it towards the tip of the nozzle 140. As the combustible gas mixed with air flows out from the tip of the nozzle 140, the combustible gas burns well at the tip of the nozzle 140. The nozzle 140 may be detachably attached to the outlet hole 126, for example, by screw fastening or the like.

[0104] The plug 142 is attached to the remaining outlet holes 126 that do not have nozzles 140 installed, thereby closing the outlet holes 126. The plug 142 is detachably attached to the outlet holes 126, for example, by screwing it in.

[0105] In this way, by attaching nozzles 140 to some of the multiple outlet holes 126, the casting mold 110 is heated at the locations where the nozzles 140 are attached. At the locations where plugs 142 are attached to the multiple outlet holes 126, heating of the casting mold 110 is suppressed.

[0106] This allows heating to be performed by attaching a nozzle to at least one of the multiple outlet holes in the casting mold 110, depending on the location where heating is desired. For example, assuming the swing arm 30, in the part of the casting mold 110 closer to the pivot shaft 32, the area where the mold surface 110Af is formed is large, so it may be necessary to heat a relatively large area. In this case, for example, in the area including the pivot shaft 32 and the hollow connecting part 50, it is conceivable to attach nozzles 140 to all the outlet holes 126 for heating. In contrast, in the part of the casting mold 110 opposite to the pivot shaft 32, there is a mold surface 110Af that forms the tip of the first hollow frame 40A and the tip of the second frame core 64B, and it is not necessary to maintain a high temperature suitable for casting in the area between the mold surface 110Af. Therefore, it is conceivable to install nozzles 140 in the outlet holes 126 of the heating device body 122 in the regions corresponding to the tip of the first hollow frame 40A and the tip of the second frame core 64B, and plugs 142 in the outlet holes 126 between the respective frame cores 64A and 64B. This allows for appropriate heating of the casting, suppressing unnecessary combustion of flammable gases, overheating, etc.

[0107] Assuming that this casting apparatus 100 is a device for manufacturing a swing arm 30, the mold surface 110Af forms at least a portion of the outer surface of the swing arm 30, which is a hollow casting having a hollow space, and the casting mold 110 has a support portion 112 that supports the swing arm core 60 that forms the hollow space. The support portion 112 is, for example, the part that supports the auxiliary connecting core 68.

[0108] Thus, when casting hollow castings, the amount of molten metal injected is small, resulting in insufficient heat input relative to the heat capacity of the casting mold 110, depending on its volume. Therefore, even with repeated casting, the mold temperature may not reach a temperature sufficient to ensure good molten metal flow. As described above, by heating with the nozzle 140, the temperature of the casting mold 110 can be maintained at a suitable temperature for casting.

[0109] When the shape of the casting changes and the casting mold 110 is replaced, the mounting positions of the nozzles 140 and plugs 142 for the multiple outlet holes 126 should be appropriately changed according to the shape of the casting.

[0110] {Variable form} Furthermore, the configurations described in each of the above embodiments and modifications can be combined as appropriate, as long as they do not contradict each other.

[0111] The above description is illustrative in all respects, and this disclosure is not limited thereto. It is understood that countless variations not illustrated may be conceivable without falling outside the scope of this disclosure.

[0112] This specification and its drawings disclose the following embodiments.

[0113] The first embodiment is a cast swing arm comprising: a pivot shaft which is cylindrical in shape and has a through hole that penetrates in the longitudinal direction, formed from molten metal during the molding process; a first hollow frame which has a first internal space and extends from the pivot shaft in a direction intersecting the pivot shaft; a second hollow frame which has a second internal space and extends from the pivot shaft in a parallel position spaced apart from the first hollow frame; a connecting internal space which connects the first internal space and the second internal space; and a hollow connecting portion which has a curved plate portion which is a curved surface when viewed along at least one direction intersecting the longitudinal direction of the first hollow frame, and connects the longitudinal intermediate portion of the first hollow frame and the longitudinal intermediate portion of the second hollow frame.

[0114] In this cast swing arm, the molten metal supplied to the pivot shaft flows through the first hollow frame and the second hollow frame into the hollow connecting section. The hollow connecting section has a curved plate section that is curved when viewed along at least one direction intersecting the longitudinal direction of the first hollow shaft. Therefore, the molten metal that flows into the mold from the molten metal port can flow smoothly through the mold space that forms the curved plate section. Thus, good molten metal flow can be achieved when casting a hollow swing arm.

[0115] A second embodiment is a cast swing arm according to the first embodiment, wherein a shaft-internal molten metal port is formed in the pivot shaft during the molding process, which partially protrudes into the pivot shaft. In this case, the shaft-internal molten metal port enlarges the flow path for the molten metal into the mold during the molding process, allowing the molten metal to flow smoothly into the mold.

[0116] A third embodiment is a cast swing arm according to the first or second embodiment, comprising a thick plate portion and a thin plate portion that is thinner than the thick plate portion, wherein the curved plate portion includes a portion located at the point connecting the thick plate portion and the thin plate portion. In this case, molten metal can be smoothly flowed from the thick plate portion to the thin plate portion via the curved plate portion.

[0117] In this case, the thin plate portion has a thickness of 3.00 mm or more and is the portion of the hollow connecting portion that faces the pivot shaft, and the thick plate portion may be at least one of the following portions of the hollow connecting portion: the portion of the hollow connecting portion that faces outward in a direction perpendicular to the first hollow frame and the hollow connecting portion, the portion of the first hollow frame that faces the second hollow frame, and the portion of the second hollow frame that faces the first hollow frame. In this case, since the thin plate portion has a thickness of 3.00 mm or more, it is easy to pour the molten metal even in gravity casting, etc. The thick plate portion is thicker than the thin plate portion and is therefore suitable for ensuring strength. By mixing the thin plate portion and the thick plate portion, it is possible to reduce weight while ensuring strength and to facilitate molten metal pouring.

[0118] A fourth embodiment is a cast swing arm according to any one of the first to third embodiments, wherein the first hollow frame has a shaft connecting internal space that is connected to the through hole at a position within the first internal space that is closer to the longitudinal center of the pivot shaft than to the end on the pivot shaft side. This makes it easier to form the through hole of the pivot shaft and the internal space of the first hollow frame with a common core, while maintaining a cylindrical shape near both ends of the pivot shaft.

[0119] A fifth embodiment is a core for forming a cast swing arm, comprising: a rod-shaped pivot core; a first frame core extending from the pivot core in a direction intersecting the pivot core; a second frame core extending from the pivot core in a parallel position spaced apart from the first frame core; a connecting core connecting the longitudinal middle portion of the first frame core and the longitudinal middle portion of the second frame core; and an auxiliary connecting core connecting the first frame core and the second frame core at a point closer to the tip of the first frame core and the second frame core than the connecting core.

[0120] By using this core for forming a cast swingarm, it is possible to form each internal space in a cast swingarm comprising: a pivot shaft having a through hole; a first hollow frame having a first internal space and extending from the pivot shaft in a direction intersecting the pivot shaft; a second hollow frame having a second internal space and extending from the pivot shaft in a parallel position spaced apart from the first frame; and a hollow connecting portion having a connecting internal space that connects the first internal space and the second internal space, and connecting the longitudinal intermediate portion of the first frame and the longitudinal intermediate portion of the second frame. The auxiliary connecting core can be used to position the core for forming the cast swingarm within the mold. The auxiliary connecting core can also play a role in firmly holding the first frame core and the second frame core. As a result, the internal spaces in the cast swingarm are formed with high precision.

[0121] The sixth aspect is a core for forming a cast swing arm according to the fifth aspect, wherein the first frame core comprises a first frame core body having a hollow space including an opening and a first cap core that closes the opening of the first frame core body, and the second frame core comprises a second frame core body having a hollow space including an opening and a second cap core that closes the opening of the second frame core body. This makes it possible to easily manufacture the first frame core and the second frame core having a hollow structure.

[0122] A casting apparatus according to the seventh embodiment is a casting apparatus comprising a casting mold having a mold surface, and a heating device located on the opposite side of the casting mold from the mold surface, for heating the casting mold.

[0123] This casting apparatus allows the casting mold to be heated from the opposite side of the mold surface by a heating device. Therefore, the casting mold can be heated even after casting has begun. This makes it easier to maintain the casting mold temperature at a suitable temperature for casting, even during continuous casting. Consequently, poor molten metal flow due to uneven temperature distribution can be suppressed.

[0124] The eighth aspect is a casting apparatus according to the seventh aspect, wherein the heating apparatus includes a heating apparatus body having a combustible gas passage and a plurality of outlet holes that connect the combustible gas passage to the outside, a nozzle attached to at least one of the plurality of outlet holes that guides the combustible gas flowing in the combustible gas passage to the outside and ejects it so that it can be combustibly burned, and plugs attached to the remaining of the plurality of outlet holes that close the outlet holes. This makes it possible to attach the nozzle to at least one of the plurality of outlet holes and heat the casting mold according to the position where heating is desired.

[0125] The ninth embodiment is a casting apparatus according to the eighth embodiment, wherein the plurality of outlet holes are dispersed in at least two dimensions. This allows heating in various two-dimensional ways depending on the location in the casting mold where heating is desired.

[0126] The tenth embodiment is a casting apparatus according to any one of the seventh to ninth embodiments, wherein the mold surface forms at least a part of the outer surface of a hollow casting having a hollow space, and the casting mold has a support portion that supports a core that forms the hollow space. When casting a hollow casting, the amount of molten metal poured is small, so the heat input relative to the heat capacity corresponding to the volume of the mold is small. For this reason, even if casting is performed repeatedly, the temperature of the mold may become insufficient to ensure good molten metal flow. As in the eleventh embodiment, the temperature of the mold can be maintained at a suitable temperature for casting by heating with a heating device. [Explanation of Symbols]

[0127] 30 Swingarm 32 Pivot Shaft 32h through hole 38 Molten metal outlet 38B Molten metal inlet mark inside the shaft 40A First Hollow Frame 40Ah 1st internal space 40B Second Hollow Frame 40Bh 2nd internal space 41Ah, 41Bh shaft connection internal space 50 Hollow connection 50h connected internal space 51 Front plate part 51a, 52a, 56 Curved plate section 53 Upper plate section 54 Lower plate part 60 Swingarm Core 62 Pivot core 64A First Frame Core 64A1 First Frame Core Body 64A1h opening 64A2 First cap core 64B Second Frame Core 64B1 Second Frame Core Body 64B1h opening 64B2 Second Cap Core 66 Connecting core 68 Auxiliary connecting core 100 Casting apparatus 110 Casting molds 110A First casting mold 110Af mold surface 110B Second casting mold 112 Support part 120 Heating device 120A 1st heating device 120B 2nd heating device 122 Heating device body 124 Flammable gas flow path 126 Outlet hole 130 Supply pipe 140 nozzles 142 stopper

Claims

1. A casting mold and a core are prepared to define the internal space of the mold, Here, the internal space of the mold is A pivot shaft having a cylindrical shape with a through hole that penetrates in the longitudinal direction, A first hollow frame having a first internal space and extending from the pivot shaft in a direction intersecting the pivot shaft, A second hollow frame having a second internal space and positioned parallel to the first hollow frame at a distance from the pivot shaft, The first internal space and the second internal space are connected to a connecting internal space, and the first hollow frame has a curved plate portion which is a curved surface when viewed along at least one direction intersecting the longitudinal direction of the first hollow frame, and a hollow connecting portion which connects the longitudinal intermediate portion of the first hollow frame and the longitudinal intermediate portion of the second hollow frame, It is a space that forms, Furthermore, the curved plate portion here includes a portion that connects the inward-facing portions of the first hollow frame and the second hollow frame with the longitudinal intermediate portion of the front plate portion of the hollow connecting portion in a curved manner. The longitudinal intermediate portion of the front plate portion of the hollow connecting portion has a smaller thickness than the inward-facing portions of the first hollow frame and the second hollow frame. A method for manufacturing a cast swing arm, comprising supplying molten metal from the space in the casting mold that forms the pivot shaft into the space within the casting mold.

2. A method for manufacturing a cast swing arm according to claim 1, A method for manufacturing a cast swing arm, comprising supplying the molten metal from two positions corresponding to the first and second hollow frames, at positions offset from the center of the portion in which the first and second hollow frames extend.

3. A method for manufacturing a cast swing arm according to claim 1 or claim 2, The front plate portion of the hollow connecting portion has a smaller thickness than the upper plate portion and the lower plate portion of the hollow connecting portion. A method for manufacturing a cast swing arm, comprising filling a casting mold with molten metal such that the ends of the first hollow frame and the second hollow frame opposite to the pivot shaft are used as the tips, and the tips face downward.

4. A method for manufacturing a cast swing arm according to Claim 3, A method for manufacturing a cast swing arm, wherein, in the initial stage of supplying molten metal to the casting mold, the orientation of the first hollow frame and the second hollow frame corresponding to their longitudinal directions is kept horizontal.

5. A method for manufacturing a cast swingarm according to any one of claims 1 to 4, A method for manufacturing a casting swing arm, comprising heating the casting mold both before and after the start of supplying molten metal to the casting mold.

6. A method for manufacturing a cast swing arm according to claim 5, The aforementioned casting mold includes a first casting mold and a second casting mold. The first casting mold and the second casting mold have mold surfaces that face each other. A method for manufacturing a cast swing arm, wherein the heating is performed from a first position opposite to the mold surface of the first casting mold and from a second position opposite to the mold surface of the second casting mold.

7. A method for manufacturing a cast swingarm according to any one of claims 1 to 6, The aforementioned casting mold, A method for manufacturing a cast swing arm, comprising: a heating device body having a combustible gas passage and a plurality of outlet holes connecting the combustible gas passage to the outside; a nozzle attached to at least one of the plurality of outlet holes for guiding the combustible gas flowing in the combustible gas passage to the outside and ejecting it in a combustible state; and plugs attached to the remaining of the plurality of outlet holes for closing the outlet holes.

8. A method for manufacturing a cast swing arm according to claim 7, A method for manufacturing a cast swing arm, wherein the plurality of outlet holes are dispersed in at least two dimensions.

9. A pivot shaft having a cylindrical shape with a through hole that penetrates in the longitudinal direction, A first hollow frame having a first internal space and extending from the pivot shaft in a direction intersecting the pivot shaft, Having a second internal space, the second hollow frame extends from the pivot shaft in a parallel position with a gap between it and the first hollow frame, The first internal space and the second internal space are connected to a connecting internal space, and the first hollow frame has a curved plate portion which is a curved surface when viewed along at least one direction intersecting the longitudinal direction of the first hollow frame, and a hollow connecting portion which connects the longitudinal intermediate portion of the first hollow frame and the longitudinal intermediate portion of the second hollow frame, Equipped with, The pivot shaft has molten metal port marks that are partially formed in the longitudinal direction of the pivot shaft and partially formed in the circumferential direction of the pivot shaft. The curved plate portion includes a portion that curvely connects the inward-facing portions of the first hollow frame and the second hollow frame with the longitudinal intermediate portion of the front plate portion of the hollow connecting portion, A cast swing arm in which the longitudinal intermediate portion of the front plate portion of the hollow connecting portion is thinner than the inward-facing portions of the first hollow frame and the second hollow frame.

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