Patent Publication Number: US-2009218068-A1

Title: Die for die casting and method of manufacturing cast product

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2008-050568, filed Feb. 29, 2008, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     One embodiment of the invention relates to a technique associated with die casting. 
     2. Description of the Related Art 
     A die-casting die of the cold-chamber die casting system comprises a biscuit section for receiving molten metal from an injection apparatus of a casting machine, a product section that is a space in which a product is to be cast, a main runner for guiding molten metal from the biscuit section toward the product section, and a main gate provided between the main runner and the product section, for accelerating the flow speed of the molten metal by sharply reducing the thickness. 
     Here, the solidification time of molten metal of, for example, a magnesium alloy or the like is very short, and hence in a die-casting die having a small flow cross-sectional area (i.e., a cross-sectional area of a space through which molten metal flows), the product section is not filled with the molten metal up to every corner thereof, and deficient filling occurs in some cases. For this reason, some of the die-casting dies liable to suffer deficient filling are provided with a sub-runner and a sub-gate for performing flow-rate support from the lateral side of the product section in addition to the main runner and the main gate. 
     In Jpn. Pat. Appln. KOKAI Publication No. 2002-45956, a die structure provided with a sub-runner branching off from a main runner is disclosed. The sub-runner extends to the side of the product section, and communicates with the side-edge part of the product section. 
     In Jpn. Pat. Appln. KOKAI Publication No. 2002-263820, a die for casting a display cover is disclosed This display cover has a support wall formed by injecting a magnesium alloy into a space of a die. This support wall includes a lower edge section and an upper edge section located on the opposite side of the lower edge section. At a central part of the lower edge section, a cutout part cut out to face the upper edge section is provided. The gate of the die is connected to the cutout part. 
     Incidentally, for example, in a cast product such as the display cover described in the Jpn. Pat. Appln. KOKAI Publication No. 2002-263820, a protrusion section is present at the edge part thereof. A product section of a die for casting such a cast product includes a main product section in which a main part of the cast product situated off the protrusion section is to be cast, and a protrusion part which protrudes from the product section, and in which the protrusion section is to be cast. Further, the protrusion part is arranged on the biscuit section side of the main product section in some cases. 
     In such a die, when the main gate is connected to the main product section, the protrusion part is positioned on the upstream side of the molten metal filling port of the main gate with respect to the molten metal flow. Molten metal of a magnesium alloy or the like becomes a flow having high directivity because of the inertia, and hence the protrusion part is hardly filled with molten metal. For this reason, there is the possibility of defective casting such as deficient strength or the like being caused at the protrusion part. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       A general architecture that implements the various feature of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention. 
         FIG. 1  is an exemplary exploded perspective view of a die according to one embodiment of the present invention; 
         FIG. 2  is an exemplary perspective view of a cast product according to the embodiment of the present invention; 
         FIG. 3  is an exemplary view schematically showing the structure of an internal space of the die shown in  FIG. 1 ; 
         FIG. 4  is an exemplary perspective view showing a region of the structure of the internal space of the die shown in  FIG. 3  encircled by a line F 4  in an enlarging manner; 
         FIG. 5  is an exemplary view showing an example of a structure of an internal space of a die; 
         FIG. 6  is an exemplary view showing another example of a structure of an internal space of a die; and 
         FIG. 7  is an exemplary view showing a further example of a structure of an internal space of a die. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments according to the invention will be described hereinafter with reference to the accompanying drawings. In general, according to one embodiment of the invention, a die for die casting comprises: a stationary die; and a movable die to be combined with the stationary die. When the movable die is combined with the stationary die, a biscuit section, a product section, a first runner, a first gate, a second runner, and a second gate are formed between the stationary die and the movable die. The biscuit section is a section into which molten metal is to be injected. The product section comprises a main product section, and a protrusion part which protrudes from the main product section toward a side of the biscuit section. The first runner is configured to guide the molten metal injected into the biscuit section toward the main product section. The first gate is provided between the first runner and the main product section at a position on a downstream side of the protrusion part in a stream direction of the molten metal. The second runner is configured to guide the molten metal injected into the biscuit section toward the protrusion part. The second gate is provided between the second runner and the protrusion part. The second runner is provided at a position deviated from the first runner three-dimensionally, and overpasses the first runner. 
     According to one embodiment of the invention, a method of manufacturing a cast product by die casting according to the present invention comprises: preparing a die which comprises a stationary die, and a movable die to be combined with the stationary die, and in which when the movable die is combined with the stationary die, a biscuit section, a product section, a first runner, a first gate, a second runner, and a second gate are formed between the stationary die and the movable die, (i) the biscuit section being a section into which molten metal is to be injected, (ii) the product section comprising a main product section, and a protrusion part which protrudes from the main product section toward a side of the biscuit section, (iii) the first runner configured to guide the molten metal injected into the biscuit section toward the main product section, (iv) the first gate being provided between the first runner and the main product section at a position on a downstream side of the protrusion part in a stream direction of the molten metal, (v) the second runner configured to guide the molten metal injected into the biscuit section toward the protrusion part, (vi) the second gate being provided between the second runner and the protrusion part, and (vii) the second runner being provided at a position deviated from the first runner three-dimensionally and overpassing the first runner; combining the movable die with the stationary die; and injecting molten metal into the biscuit section. 
     A die  1 , and a method of manufacturing a cast product  2  according to one embodiment of the present invention will be described below with reference to  FIGS. 1 to 4 .  FIG. 1  shows a die  1  according to this embodiment. 
     The die  1  is used for die casting of, for example, the cold-chamber die casting system. For example, a magnesium alloy, aluminum alloy, or zinc ally is injected into this die  1  as molten metal by pressure. Incidentally, the die according to the present invention is not limited to the above materials, and can be widely used for die casting in which various materials are used as molten metal. 
       FIG. 2  shows an example of a cast product  2  which is a product cast by using the die  1 . The cast product  2  is, for example, a component constituting a part of a main body housing of an electronic apparatus such as a portable computer, or a part of a housing of a display unit of an electronic apparatus. A housing base constituting a bottom part of an apparatus body, a display cover for protecting a back surface of a display apparatus, and the like correspond to the more detailed specific examples. Incidentally, cast products to which the present invention can be applied are not limited to the above examples, and various other products may be produced. 
     As shown in  FIG. 2 , the cast product  2  comprises, for example, a rectangular bottom wall  11 , and a vertical wall  12  rising from a peripheral edge part of the bottom wall  11 , thereby having a box-like shape opened on one side thereof. The cast product  2  further comprises a first end part  13 , a second end part  14  positioned on the opposite side of the first end part  13  in the cast product  2 , and side edge sections  15  and  16  each extending between first and second end parts  13  and  14 . The first and second end parts  13  and  14  extend in, for example, the longitudinal direction of the cast product  2 . A cutout part  17  cut out toward the second end part  14  is provided at a central part of the first end part  13 . 
     This cutout part  17  is provided to form, for example, a power supply unit insertion section to which, for example, a battery is detachably attached, or a display unit foot section to which hinges are attached. Incidentally, the purposes of providing the cutout part  17  are not limited to the above examples, and a cutout part provided for various uses corresponds to the cutout part mentioned in the present invention. 
     As shown in  FIG. 2 , the cast product  2  comprises the cutout part  17 , and thus comprises a pair of protrusion sections  22   a  and  22   b  protruding from corner parts defined by the first end part  13 , and the side edge sections  15  and  16  toward the opposite side of the second end part  14 . That is, the cast product  2  comprises a main part  21 , and the protrusion sections  22   a  and  22   b.  The main part  21  is the remaining part of the cast product  2  excluding the protrusion sections  22   a  and  22   b.    
     The protrusion sections  22   a  and  22   b  are provided separately from each other at both end parts of, for example, the first end part  13  in the longitudinal direction. The cutout part  17  is provided relatively large to occupy a large part of, for example, the first end part  13 , and is formed larger than, for example, the total of the protrusion sections  22   a  and  22   b.  An example of the cast product  2  is a thin-walled product having a fundamental thickness of, for example, 0.6 mm or less. Incidentally, “fundamental thickness” implies a standard thickness of the product, and a thickness which is adopted most widely throughout the product. Incidentally, the die according to the present invention may also be used for casting exceeding 0.6 mm in the fundamental thickness. 
     As shown in  FIG. 1 , the die  1  comprises a stationary die  31 , and a movable die  32  to be combined with the stationary die  31 . The stationary die  31  is fixed to a stationary platen not shown. The stationary die  31  comprises a stationary die plate  33 , a cavity member  34 , and an inlet member  35 . 
     The stationary die plate  33  is fixed to the stationary platen, and comprises a recess part (not shown) on a surface opposed to the movable die  32 . The cavity member  34  is attached to the recess part, and is opposed to the movable die  32 . The cavity member  34  comprises a die surface for forming, for example, an outer surface of the cast product  2 . The inlet member  35  comprises a through-hole into which an injection plunger of the casting machine is inserted, and is a cylindrical shape. 
     On the other hand, the movable die  32  comprises a movable die plate  36 , a core member  37 , and a dividing piece  38 . The movable die  32  is fixed to a movable platen (not shown), and is to be advanced and retreated between a die closed position in which the movable die is combined with the stationary die  31 , and a die opened position in which the movable  32  is separated from the stationary die  31 . 
     The movable die plate  36  is fixed to the movable platen, and comprises a recess part  36   a  on a surface opposed to the stationary die  31 . The core member  37  is attached to the recess part  36   a,  and is opposed to the stationary die  31 . The core member  37  comprises a die surface for forming, for example, an inner surface of the cast product  2 . 
     When the movable die  32  is combined with the stationary die  31  as shown in  FIG. 3 , an internal space  41  into which molten metal is pressed is formed between the stationary die  31  and the movable die  32 .  FIG. 3  is a view obtained by viewing the internal space  41  as a plane for convenience of explanation. In  FIG. 3 , molten metal flows from above to below in the figure. Incidentally, in this description, when the term “upstream side” is simply used, it implies the upstream side with respect to the molten metal mainstream flow, and when the term “downstream side” is simply used, it implies the downstream side with respect to the molten metal mainstream flow. Here, the molten metal mainstream implies the molten metal flowing through the main gate, to be described later. 
     As shown in  FIG. 3 , the internal space  41  in the die  1  comprises a biscuit section  42 , a product section  43 , a fan gate  44 , a first side gate  45   a,    45   b,  a second side gate  46   a,    46   b,  an overflow section  47 , and a chillvent section  48 . To be more specific, the fan gate  44  comprises a main runner  51 , and a main gate  52 . Each of the first side gate  45   a,    45   b  comprises a first sub-runner  53 , and a first sub-gate  54 . Each of the second side gate  46   a,    46   b  comprises a second sub-runner  55 , and a second sub-gate  56 . 
     The biscuit section  42  is formed inside the inlet member  35 , and is a part which receives the high temperature molten metal from the injection apparatus of the casting machine at a high speed. That is, the biscuit section  42  is a section in to which molten metal is to be injected. The product section  43  is an internal space in which the cast product  2  is to be cast, and comprises a dug-down surface corresponding to the shape of the cast product  2 . As shown in  FIG. 3 , the product section  43  comprises first to fourth edge sections  61 ,  62 ,  63 , and  64  corresponding to the four sides of the cast product  2 . 
     The first edge section  61  is an example of the main edge section mentioned in the present invention. The first edge section  61  is located the most upstream in the product section  43 , and corresponds to the first end part  13  of the cast product  2 . The first edge section  61  is connected to the main gate  52 . The second edge section  62  is located the most downstream in the product section  43 , and corresponds to the second end part  14  of the cast product  2 . The third and fourth edge sections  63  and  64  are each examples of the side edge section mentioned in the present invention. The third and fourth edge sections  63  and  64  extend from the end part of the first edge section  61  in the stream direction of the molten metal (i.e., the stream direction of the molten metal mainstream), and correspond to the side edge sections  15  and  16  of the cast product  2 . 
     As shown in  FIG. 3 , the product section  43  comprises a main product section  66 , and a pair of protrusion parts  67   a  and  67   b.  The main product section  66  is a space in which the main part  21  of the cast product  2  is to be cast. The protrusion parts  67   a  and  67   b  protrude from the main product section  66  toward the side of the biscuit section  42 , and are spaces in which the protrusion sections  22   a  and  22   b  of the cast product  2  are to be cast. 
     The first edge section  61  of the product section  43  is cut out toward the second edge section  62 . As a result of this, the corner sections defined by the first edge section  61 , and the third and fourth edge sections  63  and  64  comprise a pair of protrusion parts  67   a  and  67   b  protruding toward the opposite side (i.e., the upstream side) of the second edge section  62 . As shown in  FIG. 3 , the protrusion parts  67   a  and  67   b  are arranged on the biscuit section  42  side (i.e., on the upstream side) of the main product section  66 . 
     The paired protrusion parts  67   a  and  67   b  are formed separately from each other at both end parts of, for example, the first edge section  61 . The first edge section  61  comprises a first section  61   a,  which is a central part situated off the protrusion parts  67   a  and  67   b,  and second sections  61   b  and  61   c  in which the protrusion parts  67   a  and  67   b  are provided, respectively. 
     As shown in  FIG. 3 , the fan gate  44  is a flow path for guiding the mainstream of the molten metal to the product section  43 . The fan gate  44  comprises, as described above, the main runner  51 , and the main gate  52 . The main runner  51  is continuous with the biscuit section  42 , and is configured to guide the molten metal injected into the biscuit section  42  from biscuit section  42  toward the first section  61   a  (i.e., the main product section  66 ) of the first edge section  61  of the product section  43 . The main runner  51  comprises an upstream section  51   a  connected to the biscuit section  42 , and a downstream section  51   b  connected to the main gate  52 . The downstream section  51   b  of the main runner  51  is largely widened as compared with the upstream section  51   a  such that the molten metal is to be guided toward substantially the entire part of the first section  61   a  of the first edge section  61 . 
     As shown in  FIG. 3 , the main gate  52  is provided between the main runner  51  and the first section  61   a  of the first edge section  61  of the product section  43 . The thickness of the main gate  52  is made smaller than that of the main runner  51 . The thickness of the main gate  52  is sharply reduced at a position thereof closer to the product section  43 , whereby the flow of the molten metal is accelerated toward the product section  43 . The main gate  52  has, for example, a thickness substantially equal to the fundamental thickness (for example, 0.6 mm) of the cast product  2  at the minimum cross-sectional part of the main gate  52 . The main gate  52  is provided on the extension of, for example, the part in which the bottom wall  11  of the cast product  2  is to be formed. 
     The border between the main gate  52  and the first section  61   a  of the first edge section  61  of the product section  43  becomes a filling port  71  of the molten metal mainstream for the product section  43 . That is, the main gate  52  communicates with the product section  43  at a position on the downstream side of the protrusion parts  67   a  and  67   b.    
     As shown in  FIG. 3 , the first side gate  45   a,    45   b  is an auxiliary flow path for performing flow-rate support for the product section  43 . Each of the first side gates  45   a,    45   b  comprises, as described above, the first sub-runner  53 , and the first sub-gate  54 . The first sub-runner  53  is an example of the first runner mentioned in the present invention. The first sub-gate  54  is an example of the first gate mentioned in the present invention. Incidentally, the first side gate  45   a,    45   b  may be provided only on one side, i.e., on one of the right and left sides depending on the shape of the product. 
     As shown in  FIG. 3 , the first sub-runners  53  branch off from both sides of the main runner  51 , and pass around the product section  43 , and extend on both sides of the product section  43  along the third and fourth edge sections  63  and  64 . The first sub-runner  53  is configured to guide the molten metal injected into the biscuit section  42  toward the third and fourth edge sections  63  and  64  of the main product section  66 . 
     The first sub-gates  54  are provided between the first sub-runners  53  and the third and fourth edge sections  63  and  64  (i.e., the main product section  66 ) of the product section  43 , and supply the molten metal to the main product section  66  from the sides. The thickness of the first sub-gate  54  is made smaller than that of the first sub-runner  53 . 
     To be more specific, the first sub-gates  54  are connected to, for example, the third and fourth edge sections  63  and  64  at the end parts on the filling end side of the product section  43 . The boundary between each of the first sub-gates  54  and each of the third and fourth edge sections  63  and  64  becomes the filling port  72  of the molten metal for the product section  43 . That is, the first sub-gate  54  communicates with the product section  43  at a position on the downstream side of the protrusion part  67   a,    67   b  in the stream direction of the molten metal. 
     As shown in  FIG. 3 , the second side gate  46   a,    46   b  is an auxiliary flow path for performing flow-rate support for the protrusion part  67   a,    67   b  of the product section  43 . Each of the second side gate  46   a,    46   b  comprises, as described above, the second sub-runner  55 , and the second sub-gate  56 . The second sub-runner  55  is an example of the second runner mentioned in the present invention. The second sub-gate  56  is an example of the second gate mentioned in the present invention. 
     The second sub-runners  55  branch off from both sides of the main runner  51  at positions on the upstream side of the first sub-runners  53  in the stream direction of the molten metal, and extend toward the protrusion parts  67   a  and  67   b  of the product section  43 . The second sub-runner  55  is configured to guide the molten metal injected into the biscuit section  42  toward the protrusion part  67   a,    67   b  of the product section  43 . 
       FIG. 4  shows the sub-runner  55  of the one second side gate  45   a  in detail. Incidentally, the other second side gate  45   b  also has substantially the same configuration. As shown in  FIG. 4 , the second sub-runner  55  comprises a first section  81 , a second section  82 , and a third section  83 . The first section  81  branches off from the main runner  51 , and extends in parallel with, for example, the first sub-runner  53 . 
     Here, as shown in  FIG. 4 , the first sub-runner  53  is provided at a position deviated from the main gate  52  three-dimensionally. Incidentally, the expression “deviated three-dimensionally” implies deviation in the thickness direction of the die  1 . The first section  81  of the second sub-runner  55  is provided on the same plane as the first sub-runner  53 . 
     The second section  82  of the second sub-runner  55  is provided on the downstream side of the first section  81 . The second section  82  is provided at a position deviated from the first section  81  three-dimensionally. The second section  82  extends perpendicularly to, for example, the first section  81 , and crosses the first sub-runner  53 . 
     This second section  82  is provided at a position deviated from the first sub-runner  53  three-dimensionally in order to avoid the first sub-runner  53 , and hence the second section  82  overpasses the first sub-runner  53 . To be more specific, the first sub-runner  53  is engraved in, for example, the core member  37  of the movable die  32 . The second sub-runner  55  is engraved in, for example, the cavity member  34  of the stationary die  31 . That is, the first and second sub-runners  53  and  55  extend in directions different from each other with the parting line of the die  1  as a boundary between the first and second sub-runners  53  and  55 . The parting line is the boundary surface between the stationary die  31  and movable die  32 . The first and second sub-runners  53  and  55  are in contact with each other at the crossing part. 
     The first section  81  comprises an extension section  81   a  extending from a part at which the second section  82  branches off from the first section  81 . This extension section  81   a  functions as a shock absorption for absorbing the shock of the molten metal flow. The third section  83  extends in a direction perpendicular to, for example, the second section  82 . 
     As shown in  FIG. 3 , the second sub-gate  56  is provided between the second sub-runner  55  and the protrusion part  67   a,    67   b  of the product section  43 , and directly supplies molten metal to the protrusion part  67   a,    67   b.  The thickness of the second sub-gate  56  is made smaller than that of the second sub-runner  55 . 
     As shown in  FIG. 3 , the overflow section  47  and the chillvent section  48  are provided on the downstream side of the product section  43 . The overflow section  47  is a section for receiving air inside the product section  43  pushed out by the molten metal. The overflow section  47  is a section for reducing the filling resistance of the molten metal in the product section  43 , and pushing out deteriorated molten metal at a flow tip to the outside of the product section  43 . The chillvent section  48  is a section having a function of preventing the deteriorated molten metal from running out of the die  1 . 
     Next, an example of a method of manufacturing the cast product  2  using the die  1  will be described below. 
     First, the die  1  described above is prepared, and the die  1  is set on the casting machine. Further, a raw material (for example, a magnesium alloy) is melted to obtain molten metal. Subsequently, the casting cycle is started. First, the movable die  32  is moved to be combined with the stationary die  31 , and then the die  1  is clamped. Then, the molten metal is poured into a sleeve coupled to the inlet member  35 , the injection plunger is forced out at a high speed, and the molten metal is injected into the biscuit section  42  of the die  1 . 
     When the solidification of the cast product  2  is advanced to a certain degree, the movable die  32  moves to open the die  1 , and the cast product  2  is taken out of the die  1  by ejecting pins. As a result of this, one cycle of the die casting is completed. The cast product  2  taken out of the die  1  is subjected to removal processing of a surplus part, thereby obtaining a cast product  2  having the desired shape. 
     Next, the function of the die  1  will be described below. 
     The molten metal forced into the biscuit section  42  is first filled into the main runner  51  having a relatively large flow cross-sectional area. Then, the molten metal flows into the first and second sub-runners  53  and  54  also having a relatively large flow cross-sectional area. The molten metal flowing through the main runner  51  is filled into the main product section  66  of the product section  43  through the main gate  52  directly connected to the main runner  51 . Further, the molten metal flowing through the second sub-runners  55  is filled into the protrusion parts  67   a  and  67   b  of the product section  43  through the second sub-gates  56 . Further, the molten metal flowing through the first sub-runners  53  is filled from the third and fourth edge sections  63  and  64  of the product section  43  through the first sub-gates  54 . 
     At this time, the second sub-runner  55  overpasses the first sub-runner  53 , and hence the molten metal flowing through the second sub-runner  55  hardly interferes with the molten metal flowing through the first sub-runner  53 . That is, the molten metal flowing through the second sub-runner  55  is filled into the protrusion parts  67   a  and  67   b  of the product section  43  without causing much pressure loss. 
     According to the die  1  configured as described above, and the method of manufacturing the cast product  2 , it is possible to reduce defective casting.  FIG. 5  shows a die  91  which is not provided with a second sub-runner  55  and a second sub-gate  56 . Here, the flow of molten metal of a magnesium alloy or the like has a high directivity because of the inertia. For this reason, when the die  91  described above is used, the upstream side corner parts  92  (hatched parts in  FIG. 5 ) of the product section  43  comprising the protrusion parts  67   a  and  67   b  are not sufficiently filled with molten metal in many cases. That is, there is the possibility of the upstream side corner parts  92  being brought into a rough/fine filled state, causing defective casting problems such as deficient strength. 
       FIG. 6  shows a die  91  in which a second sub-gate  56  is provided in a middle part of the sub-runner  53  for performing flow-rate support for the main product section  66 . Even when the die  91  described above is used, the molten metal has high directivity, and hence the molten metal flowing through the first sub-runner  53  passes through the entrance  93  of the second sub-gate  56  having a small flow cross-sectional area, and flows toward the distal end of the first sub-runner  53 . For this reason, there is the possibility of the filling of the molten metal from the second sub-gate  56  into the protrusion part  67   a,    67   b  being not sufficient, and the deficient filling being not solved. Further, it is after the completion of filling of the first sub-runner  53  having a relatively large flow cross-sectional area that the molten metal flows into the protrusion parts  67   a  and  67   b  through the second sub-gate  56 , and hence the filling start timing of the filling from the second sub-gate  56  is delayed compared with the filling start timing of the filling from the main gate  52 . For this reason, air is liable to be left inside the product section  43 , thus there is the possibility of the defective casting being caused by gas inclusion and the like. 
       FIG. 7  shows a die  91  provided with a second sub-runner  55  and a second sub-gate  56 . As shown in  FIG. 7 , the first and second sub-runners  53  and  55  are provided on the same plane, and intersect each other on the same plane. When such a die  91  is used, the molten metal flowing through the first sub-runner  53 , and the molten metal flowing through the second sub-runner  55  interfere with each other at the intersection of the sub-runners  53  and  55 , thereby causing a pressure loss. Thus, there is the possibility of the molten metal being not sufficiently supplied to the protrusion parts  67   a  and  67   b  from the second sub-gates  56 . Further, there is also the possibility of gas inclusion or turbulent flow caused by the interference inducing a casting defect such as a molten metal wrinkle and the like. 
     On the other hand, as in the die  1  according to this embodiment, when the second runner  55  for guiding molten metal to the protrusion part  67   a,    67   b  is provided separately from the first runner  53  for guiding molten metal to the main product section  56 , and this second runner  55  overpasses the first runner  53  three-dimensionally, the molten metal flowing through the second runner  55  hardly interfere with the molten metal flowing through the first runner  53 , and pressure loss is hardly caused. Accordingly, it is possible to supply sufficient molten metal to the protrusion part  67   a,    67   b  into which molten metal cannot be easily filled, and prevent defective casting from occurring due to deficient filling. Further, if the molten metal flowing through the second runner  55  and the molten metal flowing through the first runner  53  hardly interfere with each other, it is possible to prevent defective casting such as a molten metal wrinkle and the like incidental to the interference from occurring. 
     In the case where the second sub-runner  55  for guiding molten metal to the protrusion part  67   a,    57   b  is provided separately from the first sub-runner  53  for guiding molten metal to the main product section  66 , it is possible to start filling from the second sub-gate  56  without waiting for the filling of the first sub-runner  53 . That is, it is even possible to make the filling start timing at which filling is started from the second sub-gate  56  earlier than the die  91  shown in  FIG. 6 , and thus it becomes possible to perform filling in such a manner that air is hardly left inside the product section  43 . 
     In the case where the first and second sub-runners  53  and  55  extend in directions different from each other with the parting line of the die  1  as the boundary, it is possible to realize a cubic interchange of the two runners with relative ease without providing a relative complicated shape on the die surface of the die  1 . 
     In the case where the second sub-runner  55  branches off from the main runner  51  at a position on the upstream side of the first sub-runner  53 , it becomes easier to supply molten metal sufficiently to the first sub-runner  53  requiring more molten metal than the second sub-runner  55 . This contributes to reduction in defective casting. 
     The die  1  and the casting method of the cast product  2  according to one embodiment have been described above. However, the present invention is not limited to the above embodiment. At the implementation stage of the present invention, the constituent elements may be modified and embodied within the scope not deviating from the gist of the invention. 
     Although in the above embodiment two second side gates are provided, one side gate may be used, depending on the product shape. Incidentally, in the above embodiment, the first sub-runner is the first runner mentioned in the present invention, and the first sub-gate is the first gate mentioned in the present invention. However, instead, the main runner may be the first runner of the present invention, and the main gate may be the first gate of the present invention. In this case, the second runner overpasses the main runner three-dimensionally. 
     While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.