Abstract:
A die-casting die capable of obtaining stable, high-quality die-casting products by reducing clogging is disclosed. The die-casting die for casting die-casting products by pressure filling molten metal into a cavity, comprises a fixed die; a moving die for forming a cavity at contacting surfaces of the fixed die and the moving die, the moving die being capable of approaching and separating from the fixed die; an overflow formed on at least either the fixed die or the moving die to communicate through an overflow gate with the cavity; a porous gas-permeable member, through which gas can pass without allowing molten metal in the overflow to pass, disposed on at least either the fixed die or the moving die so as to communicate with the overflow; and an exhaust path, one end of which communicates with the surface on the side of the gas-permeable member opposite that of the overflow, and the other end of which communicates with the outside of the fixed die or the moving die.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a die-casting die used for die casting of aluminum or the like. 
       BACKGROUND ART 
       [0002]    Conventionally, there has been known a die in which gas is vented using a porous material (see JP-A-S58-47538 (Patent Document 1)). In the die in Patent Document 1, gas is vented by embedding a porous material in either the entire surface of a cavity for forming a product, or in portions of the cavity where gas is most prone to be generated or to accumulate. 
       SUMMARY OF THE INVENTION 
     Technical Problems 
       [0003]    However, when a porous material is used to vent gas, the problem arises that in aluminum die casting, for example, clogging of the porous material occurs after about 10 shots, and the gas could not be vented. 
         [0004]    It is therefore an object of the present invention to provide a die-casting die capable of obtaining stable, high-quality die-casting products by greatly reducing clogging of porous gas-permeable members, and improving durability. 
       Solution to Problems 
       [0005]    The above object is achieved according to the present invention by providing a die-casting die for casting die-casting products by pressure filling molten metal into a cavity, comprising: a fixed die; a moving die for forming a cavity at contacting surfaces of the fixed die and the moving die, said moving die being capable of approaching and separating from the fixed die; an overflow formed on at least either the fixed die or the moving die to communicate through an overflow gate with the cavity; a porous gas-permeable member, through which gas can pass without allowing molten metal in the overflow to pass, disposed on at least either the fixed die or the moving die so as to communicate with the overflow; and an exhaust path, one end of which communicates with the surface on the side of the gas-permeable member opposite that of the overflow, and the other end of which communicates with the outside of the fixed die or the moving die. 
         [0006]    In the present invention thus constituted, because a porous gas-permeable member, through which gas can pass without allowing molten metal in the overflow to pass, is disposed to communicate with the overflow formed on at least either the fixed die or the moving die, gas and molten metal are separated by the gas-permeable member in such a way that only gas is exhausted to the outside through the gas-permeable member, thereby preventing gas defects. In addition, the molten metal is cooled until it reaches the overflow, so viscosity rises; clogging of the gas-permeable member erected at the overflow is reduced, and durability of the gas-permeable member is greatly improved. The die-casting die of the present invention thus permits high-quality die-casting products to be obtained. 
         [0007]    In the present invention, the gas-permeable member preferably has a flow path surface area contacting the molten metal, the flow path surface area being provided so that the average flow rate of gas flowing through the gas-permeable member is 0.2-1.0 m/sec. 
         [0008]    In the present invention, the gas-permeable member preferably has a flow path surface area contacting the molten metal, and the flow path surface area is provided so that the average flow rate of gas flowing through the gas-permeable member is 0.05-0.2 m/sec, and the die-casting die further comprises a gas vent mechanism, disposed to communicate with the overflow, for exhausting gas directly to the outside without going through the gas-permeable member. 
         [0009]    In the present invention, the gas-permeable member preferably contains a fiber reinforced metal compound material or a metal powder sintered body. 
         [0010]    In the present invention, the gas-permeable member preferably has an average pore diameter thereof which is 3-30 μm. 
         [0011]    In the present invention, a plurality of gas-permeable members are preferably provided. 
         [0012]    In the present invention, at least one of the exhaust path is preferably provided for one of the gas-permeable member. 
         [0013]    In the present invention, the die-casting die preferably further comprises at least one push-out pin on the overflow for parting the die-casting product from the fixed die and the moving die. 
         [0014]    In the present invention, the molten metal is preferably aluminum alloy. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  is a plan view showing a die-casting die according to an embodiment of the present invention; 
           [0016]      FIG. 2  is a cross sectional view seen along line II-II in  FIG. 1 ; 
           [0017]      FIG. 3  is a cross sectional view seen along line in  FIG. 1 ; 
           [0018]      FIG. 4  is a plan view showing a die-casting product made by a die-casting die according to an embodiment of the present invention; 
           [0019]      FIG. 5  is a front elevation sectional view showing a die-casting die according to a variant example of an embodiment of the present invention; and 
           [0020]      FIG. 6  is a front elevation sectional view showing a die-casting die according to another variant example of an embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0021]    Referring to  FIGS. 1 through 4 , a die-casting die according to an embodiment of the present invention is explained.  FIG. 1  is a plan view showing a die-casting die according to an embodiment of the present invention,  FIG. 2  is a cross sectional view seen along line II-II in  FIG. 1 ,  FIG. 3  is a cross sectional view seen along line in  FIG. 1 , and  FIG. 4  is a plan view showing a die-casting product made by a die-casting die according to an embodiment of the present invention. 
         [0022]    As shown in  FIGS. 1 through 3 , the die-casting die  1  according to an embodiment of the present invention comprises a fixed die  2  and a moving die  4 . A cavity  6  forming the shape of the product, a runner  8  serving as conduit for carrying the flow of molten metal to the cavity, and an overflow  10  for guiding the molten metal which runs ahead, gas, and the like are formed at the contacting surfaces of the fixed die  2  and the moving die  4 . The runner  8  communicates with the cavity  6  through a gate  12 , which is the flow inlet for molten metal from the runner  8  into the cavity  6 . The cavity  6  communicates with the overflow  10  through an overflow gate  14 , which is a conduit connecting the cavity  6  and the overflow  10 , over which molten metal flows. 
         [0023]    A substantially cylindrical injection sleeve  16  is disposed on the fixed die  2  to communicate with the runner  8 . The injection sleeve  16  has a molten metal filling port  18  into which molten metal is poured, and a plunger  20  is slidably inserted into the inner cylinder  16   a  of the injection sleeve  16 . Molten metal is pressed into the runner  8  using the injection sleeve  16 . 
         [0024]    On the other hand, a depression  22  is formed on the moving die  4  to surround the overflow  10 , into which the porous gas-permeable member  24  is embedded. Overflows  10   a,    10   b,  and  10   c  are provided at three locations of the die-casting die  1  of the embodiment, as shown in  FIG. 1 , and gas-permeable members  24  are disposed at each of the overflows  10   a,    10   b,  and  10   c.  A fiber reinforced metal compound material or metal powder sintered body is used for the gas-permeable member  24 . Furthermore, an exhaust path  26  is bored into the moving die  4 , one end thereof communicating with the surface opposite to overflow  10  of the gas-permeable member  24 , and the other end thereof communicating with the outside of the moving die  4 . At least one exhaust path  26  is provided for the gas-permeable member  24 . 
         [0025]    In addition, a push-out pin  28  is slidably inserted though the moving die  4  in order to part the die-casting product  30  (see  FIG. 4 ) from the moving die  4 . 
         [0026]    Next, a method for molding a die-casting product  30  using the die-casting die  1  of the above-described embodiment of the present invention is explained. First, the moving die  4  is moved by a die-casting machine (not shown), and is combined with the fixed die  2 , and the moving die  4  is tightened and affixed to the fixed die  2 . Thereafter the molten metal poured in from the molten metal filling port  18  of the injection sleeve  16  is pressed by the plunger  20  into the die-casting die  1  formed by the fixed die  2  and the moving die  4 . The pressed-in molten metal flows through the runner  8 , passes through the gate  12 , and flows into the cavity  6 . 
         [0027]    Molten metal further pushed out from the cavity  6  flows out to the overflow  10  through the overflow gate  14 . Because the gas-permeable member  24  is embedded in the overflow  10 , gas generated during molding passes through the gas-permeable member  24  and is exhausted though the exhaust path  26  to the outside of the die-casting die  1  (having the fixed die  2  and the moving die  4 ). Thereafter when the molten metal is cooled and solidified, the moving die  4  is removed from the fixed die  2  by the die-casting machine (not shown), and the die-casting die  1  (having the fixed die  2  and the moving die  4 ) is opened. The die-casting product  30  is then pushed out by the push-out pin  28  inserted through the moving die  4  and parted from the moving die  4 . 
         [0028]    Next, the gas flow rate passing through the gas-permeable member  24  and the like is explained. In the die-casting die  1  according to the embodiment of the present invention, the gas-permeable member  24  is provided so that the average gas flow rate passing through the pores thereof is in a range of 0.2-1.0 m/sec. Therefore when determining the capacity of the overflow  10 , the flow path surface area, which is the surface area over which the gas-permeable member  24  contacts the molten metal in the overflow  10 , is provided so that the average gas flow rate passing through the pores in the gas-permeable member  24  is 0.2-1.0 m/sec. For this reason, in the die-casting die  1  according to the embodiment of the present invention, overflows  10   a,    10   b,  and  10   c  are provided at three locations, and the gas-permeable member  24  is provided so as to surround the overflows  10   a,    10   b,  and  10   c.    
         [0029]    However, when a flow path surface area has been obtained at which the average flow rate of gas flowing through the gas-permeable member  24  is 0.2-1.0 m/sec, it is not necessary as described above to provide the gas-permeable member  24  to contact (surround) one entire surface of the overflow  10 , therefore the gas-permeable member  24  may also be provided to contact only a partial region of one of the surfaces of the overflow  10 . 
         [0030]    If the average gas flow rate exceeds 1.0 m/sec, gas-venting pressure losses increase, and sufficient gas-venting effect cannot be achieved. Also, while a gas-venting effect is obtained by reducing the average gas flow rate passing through the pores in the gas-permeable member  24 , the volume of the overflow  10  increases and yield decreases due to the necessity for widening the surface area over which the gas-permeable member  24  contacts the molten metal in order to remove gas. This is therefore not economical below 0.2 m/sec. 
         [0031]    In the die-casting die  1  according to the embodiment of the present invention, as shown in  FIGS. 1 through 3 , a gas vent mechanism  32 , which is an auxiliary gas-venting mechanism, may be provided on the overflow  10  as needed. Provision of the gas vent mechanism  32  allows for a flow path surface area producing an average gas flow rate through the gas-permeable member  24  pores of 0.05-0.2 m/sec, without increasing the volume of the overflow  10  more than necessary. Even when a gas vent mechanism  32  is provided on the overflow  10 , a flow path surface area may be adopted with which the average gas flow rate passing through pores in the gas-permeable member  24  is 0.2-1.0 m/sec. 
         [0032]    In the die-casting die  1  according to the embodiment of the present invention, the diameter of pores in the gas-permeable member  24  is 3-30 μm, but more preferably 3-20 μm. If the pore diameter of the gas-permeable member  24  is too small, gas-venting resistive pressure losses are high, and although clogging due to the molten metal is diminished, the gas-venting effect is reduced. When the pore diameter is too large, the gas-venting effect is large, but clogging by the molten metal occurs within a short period, and durability declines. 
         [0033]    In the die-casting die  1  according to the embodiment of present invention, blowing a parting agent on the gas-permeable member  24  causes clogging, so it is not desirable to use a parting agent on the overflow  10  in which the gas-permeable member  24  is embedded. Because of the need to avoid using the parting agent on the overflow  10 , it is preferable to provide one or more push-out pins  28  for die parting purposes on the overflow  10  as well in the die-casting die  1 . 
         [0034]    Next, referring to  FIGS. 5 and 6 , variant examples of the embodiment of the present invention are explained.  FIG. 5  is a front elevation cross sectional view showing a die-casting die according to a variant example of an embodiment of the present invention, and  FIG. 6  is a front elevation cross sectional view showing a die-casting die according to another variant example of an embodiment of the present invention. 
         [0035]    As shown in  FIG. 5 , in a variant example of an embodiment of the present invention, the gas-permeable member  24  and exhaust path  26  are disposed not on the moving die  4 , but on the fixed die  2  only. 
         [0036]    Also, in another variant example of an embodiment of the present invention shown in  FIG. 6 , the gas-permeable member  24  and exhaust path  26  are disposed on both the fixed die  2  and the moving die  4 . 
       EXAMPLES 
       [0037]    Next, examples of die casting using a die-casting die according to an embodiment of the present invention. 
       Example 1 
       [0038]    In the die-casting die of Example 1 of the present invention, die temperature was 190° C., molten metal temperature at time of injection was 690° C., total cross sectional surface area of gate  12  was 0.4 cm2, cross sectional surface area of overflow gate  14  was also 0.4 cm2, and injection speed was 0.5 m/sec 
         [0039]    A SINTOKOGIO-manufactured Porcerax II (trademark of SHINTOKOGIO, LTD.) with a porosity of approximately 25% and an average pore diameter of 7 μm was used as the gas-permeable member (porous permeable metal)  24 , embedded in a depression in the overflow  10  to create an approximately 30 cm2 flow path surface area. The flow path surface area, as described above, is the surface over which the gas-permeable member  24  contacts molten metal which has flowed into the depression  22  in the overflow  10 . The flow path surface area is the same in Examples 2 through 5. In this case, the average gas flow rate passing through the gas-permeable member  24  is 1.0 m/sec. 
         [0040]    Therefore, in Example 1, no clogging was observed even after more than 1000 molding shots, and the amount of gas contained in the die-casting product  30  was approximately 10 cc/100 g-AL. 
       Example 2 
       [0041]    Molding conditions were the same as in Example 1, die temperature was 190° C., molten metal temperature at time of injection was 690° C., total cross sectional surface area of gate  12  was 0.4 cm2, cross sectional surface area of overflow gate  14  was also 0.4 cm2, and injection speed was 0.5 m/sec. 
         [0042]    A SINTOKOGIO-manufactured Porcerax II with a porosity of approximately 25% and an average pore diameter of 7 μm was used as the gas-permeable member (porous permeable metal)  24 , embedded in a depression in the overflow  10  to create an approximately 100 cm2 flow path surface area. In this case the average gas flow rate passing through the gas-permeable member  24  is 0.3 m/sec. 
         [0043]    Therefore, in Example 2 as well, no clogging was observed even after more than 1000 molding shots, and the amount of gas contained in the die-casting product  30  was approximately 4 cc/100 g-AL. 
       Example 3 
       [0044]    Molding conditions in Example 3 were the same as in Example 1. 
         [0045]    A SINTOKOGIO-manufactured Porcerax II with a porosity of approximately 30% and an average pore diameter of 20 μm was used as the gas-permeable member (porous permeable metal)  24 , embedded in a depression  22  in the overflow  10  to create an approximately 100 cm2 flow path surface area. In this case the average gas flow rate passing through the gas-permeable member  24  is 0.2 m/sec. 
         [0046]    Therefore, in Example 3 as well, no clogging was observed even after more than 1000 molding shots, and the amount of gas contained in the die-casting product  30  was approximately 2 cc/100 g-AL. 
       Embodiment 4 
       [0047]    Molding conditions in Embodiment 4 were the same as in Embodiment 1. 
         [0048]    A SINTOKOGIO-manufactured Porcerax II with a porosity of approximately 30% and an average pore diameter of 30 μm was used as the gas-permeable member (porous permeable metal)  24 , embedded in a depression  22  in the overflow  10  to create an approximately 100 cm2 flow path surface area. In this case the average gas flow rate passing through the gas-permeable member  24  is 0.2 m/sec. 
         [0049]    Therefore, in Example 4 as well, while a tendency to clog was manifested after approximately 1000 shots, the amount of gas contained in the die-casting product  30  was approximately 2 cc/100 g-AL. 
         [0050]    The porous gas-permeable metal was washed in alkali after 1000 shots to restore permeability and again embedded in the die, where it was able to be used. 
       Example 5 
       [0051]    Molding conditions in Example 5 were the same as in Example 1. 
         [0052]    A SINTOKOGIO-manufactured Porcerax II with a porosity of approximately 25% and an average pore diameter of 3 μm was used as the gas-permeable member (porous permeable metal)  24 , embedded in a depression in the overflow  10  to create an approximately 100 cm2 flow path surface area. In this case the average gas flow rate passing through the porous permeable metal is 0.3 m/sec. 
         [0053]    Therefore in Example 5 as well, no clogging was observed even after more than 1000 molding shots, and the amount of gas contained in the die-casting product  30  was approximately 7 cc/100 g-AL. 
       COMPARATIVE EXAMPLES 
       [0054]    Molding conditions in the comparative examples were the same as in Example 1. 
         [0055]    A gas-permeable member with a porosity of approximately 25% and average pore diameter of 7 μm is embedded in the cavity  6  so as to cover a surface area of approximately 100 cm2. 
         [0056]    As a result, in the comparative example, clogging occurred at approximately the 10th shot, and a normal die-casting product was not obtained. 
         [0057]    As explained above, when the die-casting die  1  according to the embodiment of the present invention is used, molten metal is filled into the cavity  6 , then passes through the overflow gate  14  and is filled into the overflow  10 . At this point, molten metal pressed in at an initial injection temperature of 650° C. or above is estimated to have been cooled down to 600° C. or below when passing through the overflow gate  14 ; this cooling raises the viscosity of the molten metal, so that clogging of the pores in the gas-permeable member  24  disposed at the overflow  10  is greatly decreased. This improves the durability of the gas-permeable member  24 . As a result, the die-casting die  1  according to the embodiment of the present invention enables a stable, high-quality die-casting product  30  to be obtained. 
       EXPLANATION OF REFERENCE NUMERALS 
       [0058]      1 : die-casting die 
         [0059]      2 : fixed die 
         [0060]      4 : moving die 
         [0061]      6 : cavity 
         [0062]      8 : runner 
         [0063]      10 : overflow 
         [0064]      12 : gate 
         [0065]      14 : overflow gate 
         [0066]      16 : injection sleeve 
         [0067]      18 : molten metal filling port 
         [0068]      20 : plunger 
         [0069]      22 : depression 
         [0070]      24 : gas-permeable member 
         [0071]      26 : exhaust path 
         [0072]      28 : push-out pin 
         [0073]      30 : die-casting product 
         [0074]      32 : gas vent mechanism