Vehicle body frame, die-cast product, mold for die-cast product and die-cast method

A mold and a die-cast manufacturing method for the die-cast product, in which a main frame which is contiguously formed with a head pipe constitutes a portion of a hollow light-weight-metal-made vehicle-body frame. The mold includes a core for forming an inner space of the hollow vehicle-body frame. The core includes a core body and a plurality of splints mounted on the core body, the splints having approximately elliptical cross-sectional shapes. The long axes direction of ellipses of the splints are set parallel to a mold split surface of the mold. As a result, measurement of the positional accuracy of the splints is facilitated, a clearance between the splint and the mold can decrease by increasing the dimensional accuracy of splint mounting portions of the mold based on sizes of the splints, and the frame can be manufactured with high dimensional accuracy.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2005-346018, filed Nov. 30, 2005, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to, for example, a vehicle body frame of a motorcycle or the like, a die-cast product which constitutes a portion of the vehicle body frame, and a mold and a die-cast method for the die-cast product.

2. Description of Background Art

Among vehicle body frames of motorcycles, some vehicle body frames are manufactured by casting using light-weight metal such as aluminum. In manufacturing such vehicle body frames by casting, since it is necessary to make the inside of the vehicle body frame hollow to achieve the reduction of weight, casting is performed by setting a sand core in a mold. (See, for example, JP-A-1-254479.)

The core includes splints for setting the core in the mold and the core is set in the mold by inserting the splints into the mold. However, there exists a drawback that it is difficult to reflect the positional accuracy of the splints to the mold in which the splints are mounted. Particularly, even a slight distortion of the mold attributed to heat causes the interference of the splint with a splint mounting portion of the mold. Accordingly, to prevent the occurrence of damages on the splints at the time of clamping the mold, it is a prerequisite to ensure a large clearance between the splint mounting portion of the mold and the splint. As a result, when the core is displaced due to a molten flow at the time of casting, there arises a drawback that a wall thickness of a product becomes non-uniform.

SUMMARY AND OBJECTS OF THE INVENTION

Accordingly, it is an object of the present invention to provide a vehicle body frame, a die-cast product, and a mold and a die-cast method for the die-cast product which facilitate the measurement of the positional accuracy of splints, can decrease a clearance between the splint and the mold by increasing the dimensional accuracy of splint mounting portions of the mold based on sizes of the splints, and can manufacture the die-cast product of high dimensional accuracy.

To achieve the above-mentioned object, a first aspect of the present invention is directed to a mold for a die-cast product in which a main frame (for example, a main frame3in an embodiment) which is contiguously formed with a head pipe (for example, a head pipe2in the embodiment) constitutes a portion of a hollow light-weight-metal-made vehicle-body frame (for example, a vehicle body frame1in the embodiment). A core (for example, a core20in the embodiment) which serves to form an inner space of the die-cast product (for example, a die-cast product11in the embodiment) includes a core body (for example, a core body21in the embodiment) and a plurality of splints (for example, splints22in the embodiment) which are mounted on the core body and have an approximately elliptical cross-sectional shape, and the long axis direction of an ellipse of the splint is set parallel to a mold split surface (a mold split surface S in the embodiment) of the mold (the mold10in the embodiment).

As a result of this configuration, even when the mold expands due to heat, the influence of this heat largely appears in the longitudinal direction of the splints and the influence of the heat can be reduced to a small amount in the short-axis direction of the splints which influence a wall thickness of an outer wall of a hollow portion of the die-cast product. Therefore, change of the clearance between the splints and the mold can be reduced to a small amount.

According to a second aspect of the present invention, a main frame which is contiguously formed with a head pipe constitutes a portion of a hollow light-weight-metal-made vehicle-body frame. In addition, a core which serves to form an inner space of the die-cast product is constituted of a core body and a plurality of splints which are mounted on the core body and have an approximately elliptical cross-sectional shape, and side surfaces of the splints are formed into a flat surface (for example, a flat surface23in the embodiment) and all flat surfaces are set parallel to a mold split surface of the mold.

As a result, in clamping the molds, it is possible to hold the splints by sandwiching the flat surfaces of the splints on the mold split surface of both molds and hence, the core can be set at the accurate position.

According to a third aspect of the present invention, a die-cast product is manufactured by sandwiching the core by a fixed mold and a movable mold. As a result, it is possible to easily fix the splints by setting the splints at the mold split surface of the fixed mold and the movable mold.

According to a fourth aspect of the present invention, a main frame which is contiguously formed with a head pipe constitutes a portion of a hollow light-weight-metal-made vehicle-body frame. As a result, it is possible to enhance the dimensional accuracy of the vehicle body frame around a handle.

According to a fifth aspect of the present invention, a portion of a main frame which is contiguously formed with a head pipe constitutes a light-weight-metal-made vehicle body frame which is formed into a hollow shape by mold using a core. In addition, at least an opening portion (for example, an opening portion43in the embodiment) for a core hold pin (for example, a core hold pin40in the embodiment) is formed in the vehicle body frame, and the opening portion is formed by penetration parallel to the mold opening direction of the mold and straightly. As a result, it is possible to manufacture the vehicle body frame by effectively supporting the core using core hold pins from portions where the openings are formed.

According to a sixth aspect of the present invention, in the vehicle body frame which is manufactured by the mold, a hole (for example, a set pin hole31in the embodiment) for a set pin (for example, a set pin30in the embodiment) for holding the core is formed in a die-cast portion. As a result, it is possible to effectively make use of the set-pin holes as sand discharging ports.

ADVANTAGE OF THE INVENTION

According to the first aspect of the invention, even when the mold expands due to heat, the influence of this heat largely appears in the longitudinal direction of the splints and the influence of the heat can be reduced to a small amount in the short-axis direction of the splints which influences a wall thickness of an outer wall of a hollow portion of the die-cast product. Accordingly, it is possible to reflect the accuracy of the splints to the mold by suppressing a change of clearance between the splint and the mold to a small amount whereby it is possible to obtain an advantageous effect that the vehicle body frame having the highly accurate die-cast portion can be manufactured. Further, since the long-axis direction is set parallel to the mold split surface, it is possible to easily perform the measurement of the positional accuracy thus facilitating the measurement.

According to the second aspect of the present invention, in clamping the molds, it is possible to hold the splints by sandwiching the flat surfaces of the splints on the mold split surface of both molds and hence, the core can be set at the accurate position whereby it is possible to obtain an advantageous effect that the vehicle body frame having the highly accurate die-cast portion can be manufactured.

According to the third aspect of the present invention, it is possible to easily fix the splints by setting the splints at the mold split surface of the fixed mold and the movable mold and hence, it is possible to obtain an advantageous effect that an operation to set the core in the mold can be easily performed.

According to the fourth aspect of the present invention, it is possible to enhance the dimensional accuracy of the vehicle body frame around a handle and hence, it is possible to obtain an advantageous effect that an optimum handling performance can be imparted to the vehicle.

According to the fifth aspect of the present invention, it is possible to manufacture the vehicle body frame by effectively supporting the core using core hold pins from portions where the opening portions are formed and hence, a position of a hollow portion which is formed by the core can be accurately ensured whereby it is possible to obtain an advantageous effect that sizes of a thicknesses of walls which surround the hollow portion can be made uniform.

According to the sixth aspect of the present invention, it is possible to effectively make use of the set-pin holes as sand discharging ports and hence, it is possible to obtain an advantageous effect that an operation to discharge sand in the product can be efficiently performed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown inFIG. 1, a vehicle body frame1of a motorcycle includes a main frame3which is contiguously formed with a head pipe2, and the vehicle body frame1is formed of a hollow die-cast product made of light-weight metal such as aluminum or aluminum alloy molded by high-pressure die-casting. To be more specific, a pair of left and right main frames3,3is connected to the head pipe2, and pivot plates4,4which extend downwardly are connected to rear end portions of the respective main frames3.

Engine hangers5extend obliquely downwardly from the head pipe2, and the engine hangers5are connected with the main frames3by side wall portions6. Opening portions7for introducing air are formed in the side wall portions6. To lower ends of the engine hangers5, support frames8which extend obliquely in the rearward and upward direction and are merged with the main frames3,3are connected. Portions which range from front ends of the main frames3to front sides of upper end portions of the pivot plates4are formed into a hollow shape by the aluminum die-cast product, and the pivot plates4are joined to the aluminum die-cast product by welding.

FIG. 2toFIG. 4show a core20which is used in molding the vehicle body frame1using a mold. The core20serves to form an inner space of the die-cast product11which constitutes a portion of the vehicle body frame1, wherein the core20is constituted of a curved main frame portion12which forms a hollow portion of the main frame3, a side wall portion13which forms a hollow portion of the side wall portion6, a support frame portion14which forms a hollow portion of the support frame8, and an engine hanger portion16which forms a hollow portion of the engine hanger5such that these portions surround a triangular opening portion15. The core20is molded by baking casting sands which are covered with an adhesive agent and is constituted of a core body21which constitutes portions corresponding to respective portions of the vehicle body frame1, and splints22which are mounted on the mold10to prevent the floating of the core body21.

To be more specific, the splints22are respectively formed in an approximately columnar shape on two portions at an upper portion of a distal end and a rear end surface of the main frame portion12, on two portions in the periphery of the opening portion15which constitute a lower portion of the main frame portion12and a rear portion of the side wall portion13, and on one portion around a portion where the opening portion7of the vehicle body frame1is formed, on one portion at a lower portion of the support frame portion14, and on one portion at a front portion of a lower end of the engine hanger portion16.

Here, the splints22are set such that all of long-axis directions of elliptical cross-sectional shapes of the respective splints22are arranged parallel to each other (see chained lines inFIG. 3andFIG. 4), these splints22are arranged parallel to a mold split surface S described later, and the core20is set in the mold10such that the core20is sandwiched by the mold10at the time of clamping the mold10. Here, inFIG. 3andFIG. 4, an arrow indicates a mold removing direction.

FIG. 5toFIG. 7schematically show the core20and the mold10which uses the core20for facilitating the explanation of the present invention.

The mold10is configured such that a movable mold18can be advanced to and retracted from a fixed mold17. A fixed mold molding portion25which forms a profile of the vehicle body frame1is formed on the fixed mold17, while a movable mold molding portion26which forms the profile of the vehicle body frame1is also formed on the movable mold18. By clamping the fixed mold17and the movable mold18by a pair of molding portions25,26, a cavity27is formed in the inside of the molding portions25,26, and by arranging the core20in the inside of the cavity27, it is possible to mold the die-cast product11which constitutes the hollow vehicle body frame1.

As shown inFIG. 5, the splints22are provided to both end portions and a center portion of the core20, wherein these splints22are provided for preventing the floating of the core20in which a set pin30which is provided to the movable mold18is inserted. As shown inFIG. 8, each splint22is formed in an approximately elliptical cross section, to be more specific, as shown inFIG. 9, in an elongated oval cross section which forms a flat surface23on upper and lower surfaces. Further, the respective splints22are provided to the core body21such that long axes of the respective elliptical shapes are arranged parallel to each other. A distal end portion of the splint22is formed to exhibit a shape with round corner portions as viewed in a side view as shown inFIG. 9as well as in a front view as shown inFIG. 10, while a proximal portion side of the splint22is gently contiguously formed with the core body21. Then, as shown inFIG. 10, the core20is set in the mold10such that the long axes of the elliptical shapes of the splints22having such cross-sectional shape are aligned with the mold split surface S.

Then, as shownFIG. 6, in a state that the core20is set in the fixed mold17and the movable mold18, the mold10is clamped and, thereafter, molten material is filled between the core20and the cavity27under pressure to obtain the die-cast product11shown inFIG. 7. Here, splint holes28are formed in portions of the die-cast product11which correspond to the splints22of the core20.

As shown inFIG. 11,12, the set pins30for the core20are provided to the movable mold18along the mold removing direction (indicated by an arrow). The set pins30are provided for preventing the displacement of the setting of the core20and, as shown inFIG. 12, are provided to a distal end portion of the main frame portion12, the vicinity of a joining portion between the main frame portion12and the support frame portion14, and the vicinity of the joining portion between the support frame portion14and the engine hanger portion16. The arrangement positions of these set pins30surround the opening portion15of the core20and, at the same time, positions of the splints22which are provided in the periphery of the opening portion15assume positions which correspond to respective sides to support the core20in a well-balanced manner. That is, these set pins30are set such that the splints22assume the substantially right triangular arrangement on the core20.

A diameter of the set pins30is set to a value which falls within a range from 20 mm to 25 mm, for example, and a distal end portion of the set pin30has a small diameter and is inserted into a recessed set pin hole32formed in the core20. Although the set pins30form set pin holes31in the die-cast product11, the set pin holes31are formed in the inside of the vehicle body frame1which constitutes the die-cast product11and hence, the set pin holes31are inconspicuous from the outside whereby merchantability is not lowered. At the same time, the set pin holes31can be effectively utilized as sand discharge ports. Here, the vicinity of the rear end portion of the main frame portion12is formed into a blind array and hence, the set pin hole31formed in such a portion has a slightly larger diameter for enhancing the sand removal performance compared to the set pin holes31formed in other portions.

As shown inFIG. 13, core hold pins40penetrate the movable mold18and the fixed mold17parallel to the mold removing direction at positions avoiding the set pin holes30. These core hold pins40serve to support portions of the core20where an interval between the splints22is large in place of the splints22. The core hold pins40have a diameter of approximately 8 mm, for example.

To be more specific, a pair of core hold pins40,40which are arranged on one straight line from both of the movable mold18and the fixed mold17which are provided at a position where the core hold pins40,40stride over the splints22which are formed on the front end portion of the main frame portion12and the splints22which are positioned in the periphery of the opening portion15, while a pair of core hold pins40,40which support an upper portion of the engine hanger portion16on one straight line from both of the movable mold18and the fixed mold17are provided in the same manner. An end surface of each core hold pin40is cut at a right angle, and on a portion of the core20with which the core hold pin40is brought into contact obliquely, as shown inFIG. 14, a pressing seat42which includes a surface41perpendicular to the mold removal direction (indicated by an arrow) is formed. Accordingly, the core hold pin40forms an opening portion43in the die-cast product11.

Next, the method for manufacturing the die-cast product using the mold10and the core20is explained in conjunction withFIG. 11andFIG. 13.

First of all, the set pins30provided to the movable mold18are inserted into the set pin holes32formed in the core20and, thereafter, the mold is clamped. Here, the core20is prevented from being floated in the inside of the mold10due to the splints22and, at the same time, is stably supported on the movable mold18by the set pins30which are arranged in a triangular shape. Further, the core20is also supported by the core hold pins40which penetrate the movable mold18and the fixed mold17and hence, the core20can be surely held in the inside of the cavity27.

Next, a plunger44shown inFIG. 11is allowed to advance and, at the same time, the cavity27is evacuated by vacuum suction. Simultaneously, a powdery mold removing agent is sprayed in the inside of the cavity27.

Then, the plunger44is retracted to allow the supply of the molten material and, subsequently, vacuum suction is performed and the plunger44is advanced at a high speed to inject the molten material into the inside of the cavity27. When the molten material is solidified, the mold is opened and the die-cast product11is taken out.

According to the mold10of the above-mentioned embodiment, the core20is constituted of the core body21and the plurality of splints22which are mounted on the core body21and have an approximately elliptical cross-sectional shape, and the long axis direction of an ellipse of the splint22is set parallel to the mold split surface S of the mold10. Accordingly, even when the mold10is expanded due to heat, the influence of this heat largely appears in the long axis direction which is the longitudinal direction of the splints22and the influence of the heat can be suppressed to a small amount in the short-axis direction of the splints22which influences the wall thickness of the outer wall of the hollow portion of the die-cast product11thus reflecting the positional accuracy of the splints22to the mold10.

As a result, the vehicle body frame1having the highly accurate die-cast product11can be manufactured. Further, since the long-axis direction of the splints22is set parallel each other, when the core20is mold, it is possible to easily perform the measurement of the positional accuracy of the splints22thus facilitating the measurement.

Further, the side surfaces of the splints22are formed into the flat surface23and all flat surfaces23are set parallel to the mold split surface S of the mold10and hence, in clamping the molds, it is possible to hold the splints22by sandwiching the flat surfaces23of the splints22on the mold split surface S of the mold10by the fixed mold17and the movable mold18. Accordingly, the core20can be set at the accurate position. As a result, it is possible to manufacture the vehicle body frame1having the highly accurate die-cast portion.

Further, according to the die-cast casting method of this embodiment, by manufacturing the die-cast product11by sandwiching the core20by the fixed mold17and the movable mold18, it is possible to easily fix the splints22by setting the splints22at the mold split surface S of the fixed mold17and the movable mold18and hence, it is possible to easily perform an operation to set the core20in the mold10.

Accordingly, by using the die-cast product11which forms the highly accurate hollow portion using such a core20in the vehicle body frame1around the handle, it is possible to increase the accuracy of size around the handle whereby the optimum handling performance is imparted to the vehicle.

Here, the vehicle body frame1is the light-metal-made vehicle body frame1in which the portion of the main frame3which is contiguously formed with the head pipe2is formed into a hollow shape by the mold10using the core20, and at least the opening portion43for the core hold pin40is formed in the vehicle body frame1, and the opening portion43is formed by penetration parallel to the mold opening direction of the mold10and straightly. Accordingly, it is possible to manufacture the vehicle body frame1by effectively supporting the core20using core hold pins40from portions where the opening portions43are formed. As a result, a position of a hollow portion which is formed by the core20can be accurately ensured and hence, it is possible to make sizes of thicknesses of walls which surround the hollow portion uniform.

Further, the set-pin hole31for holding the core20is formed in a die-cast product11and hence, it is possible to effectively make use of the set-pin holes31as sand discharging ports whereby an operation to discharge sand in the die-cast product11can be efficiently performed.

Here, the present invention is not limited to the above-mentioned embodiment. For example, the embodiment is explained by taking the front portion of the vehicle body frame of the motorcycle as an example, the present invention is applicable to a lower portion of the vehicle body frame and other portions which form a hollow portion. Further, the present invention is not limited to the motorcycle and is applicable to a case in which a vehicle body frame of any vehicle is molded into a hollow shape using light weight metal.