Patent Publication Number: US-2015083357-A1

Title: Molding method and molding apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a molding method and a molding apparatus. More particularly, the invention relates to a die cast molding method and a die cast molding apparatus in which molten metal is injected into a cavity of a mold. 
     2. Description of Related Art 
     Technology such as that described below is used in typical die cast molding. A fixed amount of molten metal is supplied into an injection sleeve that has a molten metal supply port, through the molten metal supply port. After the molten metal is finished being supplied, an injection tip is advanced by driving means at a predetermined timing, such that molten metal is injected at a high pressure into the cavity of the mold from the injection sleeve (see Japanese Patent Application Publication No. 2003-290899 (JP 2003-290899 A), Japanese Patent Application Publication No. 2005-46905 (JP 2005-46905 A), and Japanese Patent Application Publication No. 2011-131265 (JP 2011-131265 A), for example). 
     The molding apparatus described in JP 2003-290899 A is configured such that molten metal is pumped up from a molten metal furnace with a ladle, and supplied to a molten metal supply port of an injection sleeve by this ladle. However, with the structure described above, when the molten metal is supplied from the ladle to the injection sleeve, it contacts the atmosphere. As a result, the temperature of the molten metal drops, and the quality of the product decreases due to an oxide film produced on the molten metal and hydrogen gas dissolving in the molten metal. Moreover, in order to reduce the amount of hydrogen gas that dissolves in the molten metal, a process for injecting an inert gas into the molten metal is required. 
     On the other hand, the molding apparatuses described in JP 2005-46905 A and JP 2011-131265 A are configured such that a molten metal supply tube is directly joined to a molten metal supply port of an injection sleeve, and molten metal is supplied via this molten metal supply tube, so it (i.e., the molten metal) will not contact the atmosphere. However, with a structure such as this as well, it is not possible to sufficiently suppress a decrease in the quality of a product due to an oxide film and dissolved hydrogen as described above, because the molten metal still contacts the air inside the molten metal supply tube. 
     SUMMARY OF THE INVENTION 
     The invention thus provides a molding method and a molding apparatus capable of improving, with a simple structure, the quality of a product. 
     A first aspect of the invention relates to a molding method that uses a molding apparatus that is provided with a mold having a cavity, an injection sleeve that has a molten metal supply port and is communicated with the cavity, a molten metal furnace within which molten metal is stored, a connecting portion that connects the molten metal furnace to the injection sleeve by one end of the connecting portion being connected to the molten metal furnace and the other end of the connecting portion being connected to a location opposite the molten metal supply port, a pump that is arranged in the connecting portion and pumps up molten metal from the molten metal furnace, a valve that is arranged in the connecting portion, and that forms a molten metal holding space that holds the molten metal pumped up by the pump, in the connecting portion, and a pressure-reducing portion that is arranged in a portion of the connecting portion where the molten metal holding space is located, and that reduces pressure in the molten metal holding space. This molding method includes forming the molten metal holding space inside the connecting portion by closing the valve; pumping up the molten metal from the molten metal furnace into the molten metal holding space of the connecting portion with the pump; reducing a pressure of the molten metal pumped up into the molten metal holding space with the pressure-reducing portion; communicating the molten metal holding space of the connecting portion with the molten metal supply port of the injection sleeve by opening the valve; and supplying the molten metal, the pressure of which has been reduced inside the molten metal holding space, into the injection sleeve. 
     Also, in the aspect described above, the pumping up of the molten metal may involve pumping up, into the molten metal holding space, molten metal of the same amount as the molten metal that is injected into the cavity. 
     Also, in the structure described above, the reducing of the pressure of the molten metal may involve stopping movement of the molten metal from the molten metal furnace to the connecting portion by operating the pump, while the pressure is being reduced. 
     Also, in the aspect or structure described above, the molding method may also include injecting molten metal into the cavity; solidifying the molten metal inside the cavity; releasing a molded article formed by the molten metal that has solidified inside the cavity from the mold; and applying a mold release agent to an inside of the cavity. Also, the forming of the molten metal holding space, the pumping up of the molten metal, and the reducing of the pressure of the molten metal of a next cycle may be performed while one of the injecting, the solidifying, the releasing, and the applying is being performed. 
     A second aspect of the invention relates to a molding apparatus that includes a mold having a cavity; an injection sleeve that has a molten metal supply port and is communicated with the cavity; a molten metal furnace within which molten metal is stored; a connecting portion that connects the molten metal furnace to the injection sleeve by one end of the connecting portion being connected to the molten metal furnace and the other end of the connecting portion being connected to a location opposite the molten metal supply port; a pump that is arranged in the connecting portion and pumps up molten metal from the molten metal furnace into the connecting portion, and supplies the molten metal into the injection sleeve via the connecting portion; a valve that is arranged in the connecting portion, and that forms a molten metal holding space that holds the molten metal pumped up by the pump, in the connecting portion; and a pressure-reducing portion that is arranged in a portion of the connecting portion where the molten metal holding space is located, and that reduces pressure in the molten metal holding space. The injection sleeve performs an operation of injecting the molten metal into the cavity. The molten metal holding space is formed by closing the valve. The pump pumps up the molten metal into the molten metal holding space of the connecting portion. The valve communicates the molten metal holding space of the connecting portion with the molten metal supply port of the injection sleeve by opening, and supplies the molten metal, the pressure of which has been reduced inside the molten metal holding space, into the injection sleeve. 
     According to the aspect described above, the molding method and the molding apparatus described above are able to improve, with a simple structure, the quality of a product. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
         FIG. 1  is a sectional view schematically showing a molding apparatus according to one example embodiment of the invention; 
         FIG. 2  is a flowchart illustrating a reduced-pressure molding method; and 
         FIG. 3  is a flowchart illustrating a process performed when pouring molten metal. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Next, example embodiments of the invention will be described. The technical scope of the invention is not limited to the example embodiments below. The invention made apparent from the description in the specification and the accompanying drawings broadly covers the entire scope of truly intended technical aspects. 
     [Structure of a Reduced-Pressure Molding Apparatus  30 ] 
     A reduced-pressure molding apparatus  30  according to one example embodiment of the invention will be described with reference to  FIG. 1 . In this specification, for the sake of convenience, the right side of  FIG. 1  will be described as the right side of the reduced-pressure molding apparatus  30 , and the left side of  FIG. 1  will be described as the left side of the reduced-pressure molding apparatus  30 . 
     As shown in  FIG. 1 , a cavity  4  is formed in a mold  1  of the reduced-pressure molding apparatus  30 . A generally cylindrical injection sleeve  2  that is communicated with the cavity  4  is provided protruding to the left. In other words, the inside of the injection sleeve  2  is connected in a continuous manner to the inside of the cavity  4 . Also, the reduced-pressure molding apparatus  30  is configured so as to inject molten metal  5  such as aluminum that has been supplied into the injection sleeve  2 , into the cavity  4  by sliding a short round columnar-shaped injection tip  3  to the right inside the injection sleeve  2  and pushing the molten metal  5  out. 
     A molten metal supply port  6  is formed in the injection sleeve  2 . The molten metal  5  is supplied from this molten metal supply port  6  into the injection sleeve  2  via a connecting portion  41  that will be described later. A support shaft  9  is inserted into the injection sleeve  2  and controlled to advance and retreat by an actuator such as an air cylinder or a hydraulic cylinder, not shown. Also, the injection tip  3  that is arranged on a tip end portion of the support shaft  9  slides in an axial direction inside the injection sleeve  2 . 
     A suction port  16  for sucking air out of the cavity  4  is provided passing into the cavity  4  in the mold  1 . Also, a shut-off valve  17  is provided in a path that connects the cavity  4  and the suction port  16  together. The suction port  16  is connected to a suction portion (a low-pressure tank  21  and a vacuum pump  22  in this example embodiment), such that the suction portion is communicated with the inside of the cavity  4 . An on-off valve  23  is provided in a connecting path connecting the low-pressure tank  21  with the suction port  16 , and opens and closes this connecting path. Also, the pressure in the cavity  4  starts to be reduced by opening the on-off valve  23  in the connecting path in conjunction with injection control. 
     The reduced-pressure molding apparatus  30  includes a molten metal furnace  50  within which the molten metal  5  is stored, a connecting portion  41  that connects the molten metal furnace  50  to the injection sleeve  2  by one end of the connecting portion  41  being connected to the molten metal furnace  50  and the other end of the connecting portion  41  being connected to a location opposite the molten metal supply port  6 , and an electromagnetic pump  40  that is arranged in the connecting portion  41  and pumps up the molten metal  5  from the molten metal furnace  50 . The inner peripheral portions of the connecting portion  41  and the electromagnetic pump  40  are made of ceramic. Also, in conjunction with injection control, the electromagnetic pump  40  pumps up the molten metal  5  with electromagnetic force by applying voltage to an internal coil. In this example embodiment, the electromagnetic pump  40  is used, but a configuration that uses another pump such as a displacement pump or a turbo pump (i.e., a rotodynamic pump) that uses a rotor is also possible. Further, in this example embodiment, the molten metal furnace  50  stores molten metal in a state cutoff from the atmosphere. 
     The connecting portion  41  is connected to the injection sleeve  2  via a junction tube  61  that has a bellows-type structure that is a vibration absorbing portion. More specifically, a metal or ceramic insulation member  71  that is formed in a tube-shape that is communicated with the molten metal supply port  6  of the injection sleeve  2  is arranged on the injection sleeve  2 . Further, the junction tube  61  is arranged on the upper side of the insulation member  71  and supports the connecting portion  41 . That is, by having the upper end portion of the junction tube  61 , i.e., the side of the junction tube  61  on which the connecting portion  41  positioned, be connected to an intermediate portion of the connecting portion  41 , the other end of the connecting portion  41  is positioned near the molten metal supply port  6 . The junction tube  61  is formed such that the tube-shaped bellows-type structure is able to expand and contract and bend, so as to absorb vibrations and deformation of the upper end portion or lower end portion of the junction tube  61 . 
     An on-off valve  42  that serves as a valve that forms a molten metal holding space  41   a  that holds the molten metal  5  inside the connecting portion  41  is arranged in the connecting portion  41 . That is, when the on-off valve  42  is closed, the inside of the connecting portion  41  is divided into the molten metal holding space  41   a  and a molten metal supply port-side space  41   b , such that the molten metal holding space  41   a  is formed. Also, the connecting portion  41  is configured such that when the on-off valve  42  is open, the molten metal holding space  41   a  and the molten metal supply port-side space  41   b  inside the connecting portion  41  are communicated with one another, and thus the molten metal holding space  41   a  is communicated with the molten metal supply port  6  of the injection sleeve  2 . 
     Also, a pressure-reducing portion that reduces the pressure in the molten metal holding space  41   a  when the inside of the connecting portion  41  is divided into the molten metal holding space  41   a  and the molten metal supply port-side space  41   b  by the on-off valve  42 , is arranged in a portion of the connecting portion  41  where the molten metal holding space  41   a  is positioned. More specifically, a suction port  43  that is communicated with the inside of the molten metal holding space  41   a  is provided in the connecting portion  41 . This suction port  43  is connected to a low-pressure tank  45  and a vacuum pump  46  that form a pressure-reducing portion. That is, the pressure-reducing portion is communicated with the molten metal holding space  41   a  via the suction port  43 . An on-off valve  44  is formed in a connecting path connecting the low-pressure tank  45  with the suction port  43 , and opens and closes this connecting path. The pressure in the molten metal holding space  41   a  starts to be reduced by opening the on-off valve  44  in conjunction with injection control. 
     The reduced-pressure molding apparatus  30  according to this example embodiment is structured as described above, and performs molding by performing an injection operation that pushes out molten metal  5  supplied by the electromagnetic pump  40  from the molten metal furnace  50  into the injection sleeve  2  via the connecting portion  41 , toward the right by the injection tip  3  and injecting the molten metal  5  into the cavity  4 , in a condition where the pressure in the cavity  4  is reduced by the suction portion. 
     [Reduced-Pressure Molding Method Using the Reduced-Pressure Molding Apparatus  30 ] 
     Next, a pressure-reduced molding method using the reduced-pressure molding apparatus  30  according to this example embodiment will be described with reference to  FIGS. 1 and 2 . 
     First, in step S 1  in  FIG. 2 , a movable die of the mold  1  is brought into contact with a fixed die and the two are clamped together, thus forming the cavity  4 . Next, in step S 2  in  FIG. 2 , a tip lubricant so that the injection tip  3  slides smoothly is applied to the inner peripheral surface of the injection sleeve  2 . 
     Next, in step S 3  in  FIG. 2 , the molten metal  5  is supplied by the electromagnetic pump  40  from the molten metal furnace  50  into the injection sleeve  2  via the connecting portion  41 . This molten metal pouring process will be described in detail later. 
     Then in step S 4  in  FIG. 2 , the pressure in the cavity  4  is reduced by the low-pressure tank  21  and the vacuum pump  22  that form the suction portion. More specifically, after the molten metal  5  has settled, the pressure in the cavity  4  starts to be reduced by opening the on-off valve  23  sucking out the air inside the cavity  4  with the low-pressure tank  21  and the vacuum pump  22 . The molten metal  5  that is undulating due to being poured in step S 3  may also be given some time to settle (approximately several seconds, for example) before starting to reduce the pressure. 
     Next, in step S 5  in  FIG. 2 , molding is performed by injecting the molten metal  5  into the cavity  4  by pushing the molten metal  5  out with the injection tip  3 . More specifically, the molten metal  5  is injected into the cavity  4 , the pressure of which has been reduced to a predetermined degree, by an injection operation of the injection tip  3 , which is performed by driving an actuator, not shown. 
     Next, in step S 6  in  FIG. 2 , air is stopped from being sucked into the cavity  4  by the low-pressure tank  21  and the vacuum pump  22 , by closing the on-off valve  23 , thereby canceling the reduced-pressure state. The molten metal  5  is solidified inside the cavity  4  by this process. 
     Then in step S 7  in  FIG. 2 , the mold  1  is opened by separating the movable die of the mold  1  from the fixed die, and a molded article formed by the molten metal  5  that has solidified inside the cavity  4  is released from the mold. Next, in step S 8  in  FIG. 2 , the product formed inside the cavity  4  is removed, and a mold release agent is applied to the cavity  4  for the next cycle. 
     [Molten Metal Pouring Method] 
     Next, a molten metal pouring method using the reduced-pressure molding apparatus  30  according to this example embodiment will be described with reference to  FIGS. 1 and 2 . 
     First, in step S 101  in  FIG. 3 , the molten metal holding space  41   a  is formed by dividing the inside of the connecting portion  41  into the molten metal holding space  41   a  and the molten metal supply port-side space  41   b  by closing the on-off valve  42  (a molten metal holding space forming process). 
     Next, in step S 102  in  FIG. 3 , the molten metal  5  is pumped up from the molten metal furnace  50  into the molten metal holding space  41   a  by the electromagnetic pump  40  (a pumping process). In this example embodiment, molten metal  5  of the same amount as the molten metal  5  that is to be injected into the cavity  4  is pumped into the molten metal holding space  41   a  in the pumping process. 
     Then in step S 103  in  FIG. 3 , the pressure of the molten metal  5  that has been pumped up into the molten metal holding space  41   a  is reduced by the pressure-reducing portion (a molten metal pressure-reducing process). More specifically, the pressure of the molten metal  5  inside the molten metal holding space  41   a  is reduced by starting to reduce the pressure in the molten metal holding space  41   a  that is connected to the low-pressure tank  45  and the vacuum pump  46 , by opening the on-off valve  44 . In this example embodiment, movement of the molten metal from the molten metal furnace  50  to the connecting portion  41  is stopped by operating the electromagnetic pump  40 , during this molten metal pressure-reducing process, so molten metal  5  will not be drawn up from the molten metal furnace  50  with the decrease in pressure in the molten metal holding space  41   a  by the pressure-reducing portion. 
     Next, in step S 104  in  FIG. 3 , the molten metal holding space  41   a  and the molten metal supply port-side space  41   b  in the connecting portion  41  are communicated with each other by opening the on-off valve  42 , thus communicating the molten metal holding space  41   a  with the molten metal supply port  6  of the injection sleeve  2  (a communicating process). Next, in step S 105  in  FIG. 3 , the electromagnetic pump  40  is driven to supply the molten metal  5 , the pressure of which has been reduced in the molten metal holding space  41   a,  into the injection sleeve  2  (a supplying process). That is, this supplying process becomes step S 3  described above. 
     In this example embodiment, the molten metal holding space forming process of step S 101 , the pumping process of step S 102 , and the molten metal pressure-reducing process of step S 103  are performed while one of the processes, from among the process of injecting the molten metal  5  into the cavity  4  in step S 5 , the process of canceling the reduced-pressure state and solidifying the molten metal  5  inside the cavity  4  in step S 6 , the process of releasing the molded article formed by the molten metal  5  that has solidified in the cavity  4  from the mold  1  in step S 7 , and the process of applying the mold release agent to the inside of the cavity  4  in step S 8 , of the last cycle, is being performed. In other words, the molten metal holding space forming process (i.e., step S 101 ), the pumping process (i.e., step S 102 ), and the molten metal pressure-reducing process (i.e., step S 103 ) of the next cycle are performed while one of the processes of steps S 5  to S 8  is being performed. 
     As described above, the reduced-pressure molding apparatus  30  according to this example embodiment forms the molten metal holding space  41   a  by dividing the inside of the connecting portion  41  into the molten metal holding space  41   a  and the molten metal supply port-side space  41   b  by closing the on-off valve  42 , and pumps up molten metal  5  into the molten metal holding space  41   a  of the connecting portion  41  from the molten metal furnace  50  with the electromagnetic pump  40 . Then the molten metal  5  that has been pumped up into the molten metal holding space  41   a  is reduced in pressure by the pressure-reducing portion, and the molten metal holding space  41   a  inside the connecting portion  41  is communicated with the molten metal supply port  6  of the injection sleeve  2  by opening the on-off valve  42 , and the molten metal  5  that has been reduced in pressure inside the molten metal holding space  41   a  is supplied into the injection sleeve  2 . 
     As described above, the reduced-pressure molding apparatus  30  according to this example embodiment is configured such that the molten metal  5  will not contact the atmosphere when being poured, by supplying the molten metal  5  into the injection sleeve  2  from the molten metal furnace  50  via the connecting portion  41 . Therefore, it is possible to inhibit the temperature of the molten metal  5  from dropping and an oxide film from forming on the molten metal  5 . In addition, it is possible to reduce the amount of hydrogen gas that dissolves in the molten metal  5 , and thus inhibit a decrease in quality of a product. 
     Moreover, in this example embodiment, the molten metal  5  that has been pumped up into the molten metal holding space  41   a  is reduced in pressure by the pressure-reducing portion. As a result, the molten metal  5  is able to be inhibited from contacting the air inside the connecting portion  41 , so the amount of hydrogen gas that dissolves in the molten metal  5  is further reduced, which makes it possible to further inhibit a decrease in quality of a product. According to a test performed by the applicant of this application, this example embodiment was compared with a structure that did not reduce the pressure of the molten metal  5  inside the connecting portion  41 , and it was found that the example embodiment was able to reduce the amount of dissolved hydrogen gas to only a fraction of that of the comparative structure. 
     Also, in this example embodiment, the pressure of the molten metal  5  is reduced for each shot (i.e., each cycle), so the time until injection and forming is able to be shortened, which further inhibits the dissolution of hydrogen gas. That is, the reduced-pressure molding apparatus  30  according to this example embodiment is able to improve, with a simple structure, the quality of a product. 
     Also, in this example embodiment; molten metal  5  of the same amount as the molten metal  5  that is to be injected into the cavity  4  is pumped up into the molten metal holding space  41   a  in the pumping process. Therefore, the supplying efficiency of the molten metal  5  is able to be improved, so the amount of hydrogen gas that dissolves in the molten metal  5  is able to be further reduced. 
     Also, in this example embodiment, movement of the molten metal  5  from the molten metal furnace  50  to the connecting portion  41  is stopped by operating the electromagnetic pump  40 , during the molten metal pressure-reducing process. As a result, the molten metal  5  for one shot (i.e., one cycle) is able to be more reliably held and reduced in pressure in the molten metal holding space  41   a.    
     Also, in this example embodiment, the molten metal holding space forming process (step S 101 ), the pumping process (step S 102 ), and the molten metal pressure-reducing process (step S 103 ) of the next cycle are performed while one of the processes of steps S 5  to S 8  that are conventionally executed is being executed. As a result, the molten metal  5  is able to be reduced in pressure within the cycle time of the processes of steps S 5  to S 8 . That is, the amount of hydrogen gas that dissolves in the molten metal  5  is able to be reduced without increasing the cycle time.