Abstract:
A mold M for molding a metallic product including a fixed mold section  2  and a movable mold section  1 , wherein heating means  7  is provided in the fixed mold section and cooling means  10  is provided in the movable mold section, which means are controlled by a temperature control device  14  so that any desired temperature is obtainable. Also, as the heating and the cooling of the mold are not repeated, but the fixed mold section is always heated and the movable mold section is always cooled, it is possible to shorten the cycle times.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a mold and method for molding a metallic product capable of easily controlling the temperature of a molten metal during and after the filling of the molten metal into a cavity.  
           [0003]    2. Description of the Related Art  
           [0004]    There is a prior art disclosed in Japanese Unexamined Patent Publication No. 2001-18229 entitled “Mold for Molding Synthetic resin and Device and Method for Controlling Mold Temperature”. In this prior art, to easily switching the heating and the cooling of a cavity surface of the mold, a liner having a flow path is provided in a mold base, so that a hot medium is made to flow in the flow path when the molten resin is injected, on one hand, and a coolant is made to flow in the flow path thereafter to solidify a product molded within the mold, on the other hand.  
           [0005]    When the material to be molded is synthetic resin, as an environment in which the resin is not solidified can be maintained at a temperature in a range from 200 to 250° C., it is possible to increase and reduce the mold temperature in a relatively short time. However, when the material is a metal or a metallic alloy such as magnesium alloy having a high melting point of approximately 600° C., it is necessary to increase the mold temperature to 600° C. or higher for the purpose of maintaining the molten state of the material. To do so, a long time such as, for example, from 30 minutes to 1 hour is required even if a powerful heater is used.  
           [0006]    Also, when the temperature is reduced to approximately 300° C. at which the release of a molded product from the mold is possible after the molten magnesium alloy has been filled in the mold and solidified, a long time is necessary to increase the temperature to prepare for the next operation. Thus, when the metal is molded, it is very difficult to repeat the heating and cooling in a short time, whereby the above-mentioned prior art is not practically applicable to the production of metallic molded products.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention has been made to solve the above-mentioned problems in the prior art, and an object thereof is to provide a mold and a method for molding a metallic product, capable of restricting the transfer of heat from the molten material to the mold during the filling of the molten metal into the mold to ensure the fluidity thereof on one hand, and accelerating the transfer of heat after the molten metal has been filled in the mold on the other hand.  
           [0008]    According to one aspect of the present invention, the fixed mold section of the mold is provided with heating means and the movable mold section is provided with cooling means, both of which means are controlled by temperature control means, respectively, so that the temperature variations in one cycle of the fixed and movable mold sections are individually controllable. Thereby, it is possible to heat the fixed mold section even if the mold is in an open state to shorten the cycle time of the molding operation. Also, it is possible to heat the fixed mold section side to a higher temperature to ensure the sufficient fluidity of the molten metal to be filled.  
           [0009]    According to the inventive mold, the fixed mold section is disposed on the injection side of molten metal to be molded, and ejector pins for releasing a molded metallic product from the movable mold section are provided in the movable mold section. Thereby, while ensuring the sufficient fluidity of the molten metal, the lowering of the temperature of the movable mold section side is enhanced. As a result, the removal of the molded product by the ejector pins is accelerated.  
           [0010]    According to the inventive mold, when the mold is in an open state, the temperature of the fixed mold section rises to a value in a range from 300 to 700° C., and the temperature of the movable mold section is controlled to a value in a range from a solidifying point of the metal to be molded to 0° C. Thereby, it is possible to increase the temperature of the fixed mold section and to reduce that of the movable mold section when the mold is in an open state.  
           [0011]    According to another aspect of the present invention, a method for molding a metallic product is provided which comprises the steps of heating the fixed mold section by the heating means and cooling the movable mold section by the cooling means when the mold is open; closing the mold during the heating of the fixed mold section and the cooling of the movable mold section, heating the fixed mold section by the heating means and cooling the movable mold section by the cooling means even after the mold has been closed; injecting the molten metal into the cavity when the temperature of the fixed mold section has reached the predetermined uppermost value and that of the movable mold section has reached the predetermined lowermost value; continuing the cooling of the movable mold section and opening the mold when the mold temperature falls to a value at which the molded metallic product is releasable from the mold; and removing the molded product from the mold. Thereby, as the heating of the fixed mold section and the cooling of the movable mold section can be carried out when the mold is in the open state, it is possible to shorten the cycle time of the molding operation. Also, as the injection is carried out at the highest temperature of the fixed mold section, it is possible to ensure the fluidity of the molten metal sufficient for filling the same in the cavity. Further, as the temperature of the molded metal product promptly falls to a level at which it is releasable of the mold by cooling the movable mold section, it is-possible to shorten the cycle time.  
           [0012]    The present invention may be more fully understood from the description of the preferred embodiments of the invention, as set forth below, together with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    In the drawings:  
         [0014]    [0014]FIG. 1 is an elevational sectional view of one embodiment of a mold for molding a metallic product according to the present invention; and  
         [0015]    [0015]FIG. 2 is graphs showing the temperature variations in a fixed mold and a movable mold section, respectively, according to an embodiment of the inventive molding method. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    One embodiment of a mold for a metallic product and a method for controlling the mold temperature according to the present invention will be described below with reference to the attached drawings. FIG. 1 is an elevational sectional view of one embodiment of the inventive mold for molding a metallic product. A device for molding a metallic product has a mold M for molding a metallic product constituted by a movable mold section  1  and a fixed mold section  2 . This mold M defines a cavity  3  for molding a metal such as magnesium alloy by clamping the movable mold section  1  and the fixed mold section  2 .  
         [0017]    The movable mold section  1  is provided with a motorized or hydraulic mold-driving mechanism (not shown) for advancing/returning it relative to the fixed mold section  2 . Accordingly, when the movable mold section  1  advanced, the mold M is closed and, when returned, the mold M is open. Also, ejector pins  8  are provided in the movable mold section  1  for removing a molded product from the mold M. By the operation of an ejector pin-driving mechanism (not shown), the ejector pins  8  are moved and projected from the movable mold section  1  to release the molded product from the movable mold section  1 .  
         [0018]    Further, cooling means  10  is embedded in the movable mold section  1 . This cooling means  10  includes a cooling path to allow coolant to flow therethrough so that the coolant is fed from a coolant source  13  by a command issued from a temperature control device  14 .  
         [0019]    A runner  4 , communicated with the cavity  3  at one end, is provided in the fixed mold section  2 , and the other open end, thereof is coupled to an injection mechanism  6  via an injection nozzle  5 . A screw or a plunger (not shown) is disposed within the injection mechanism  6 , so that molten metal is conveyed by the screw (plunger) and injected into the cavity  3  from the injection nozzle  5 .  
         [0020]    Heating means is embedded in the fixed mold section  2 . This heating means  7  may be a heating path for letting a heating medium flow therethrough, or the wiring of an electric heater. Also, other known heating types may be employed. The heating means  7  operates by supply (of a heating medium or electric current) from a heating medium source  12  in accordance with a command issued from the temperature control device  14 . Accordingly, the temperature of the mold M can be set at an optional value by the temperature control device  14 .  
         [0021]    Next, a method for molding a metallic product using the above-mentioned mold will be described below. First, the heating means  7  is operated while the mold M is open to increase the temperature of the fixed mold section  2  to a value in a range from 300 to 700° C., and to reduce the temperature of the movable mold section  1  to a value in a range from a solidifying point to 0° C.  
         [0022]    Then, the mold-driving mechanism is operated to close the mold M and prepare for the injection of molten metal. At this time, the heat transfer begins from the fixed mold section  2  to the movable mold section  1 , mainly through a parting surface  9  which is a contact surface of the fixed mold section  2  with the movable mold section  1 . On the other hand, the heat transfer from a surface  11  of the cavity  3  for molding the molded product is suppressed by the heat insulation of air within the cavity.  
         [0023]    As a result, upon the injection of molten metal from the, injection mechanism  6 , the temperature of the surface  11  in the cavity  3  is higher on the fixed mold section side and lower on the movable mold section side, whereby it is possible to fill the molten metal in the cavity  3  while ensuring a sufficient fluidity thereof.  
         [0024]    As a space of the cavity  3  is full of metal when the filling of the cavity  3  with molten metal has been completed, an abrupt heat transfer begins from the fixed mold section  2  to the movable mold section  1  to lower the temperature of the molded product in a short time to a level capable of releasing the same from the mold. In this case, the lowering of the temperature is accelerated by suitably operating the cooling means  10  provided in the movable mold section  1  by the temperature control device  14 .  
         [0025]    When the temperature of the molded product has been lowered to a level at which it is releasable from the mold, the movable mold section  1  is returned to open the mold M and simultaneously therewith to project the ejector pins  8  from the movable mold section  1  by the action of the ejector pin-driving mechanism. Thus, the molded product is removed from the mold.  
         [0026]    [0026]FIG. 2 contains graphs showing the temperature variations in the fixed mold section  2  and the movable mold section  1 , respectively, according to the embodiment of the inventive molding method. A vertical axis of the graph represents the temperature and a horizontal axis thereof represents the time (S). The upper graph shown by a solid line represents the temperature variation in the fixed mold section  2 , while the lower graph shown by a solid line represents the temperature variation in the movable mold section  1 . One block of the horizontal axis is 10 seconds. In FIG. 2, the mold is open when the fixed mold section  2  is at the lowermost temperature (approximately 381° C.) in the temperature variation and the movable mold section  1  is the uppermost temperature (approximately 280° C.), and closed during the temperature rising phase of the fixed mold section  2  and the temperature lowering phase of the movable mold section  1 . Then, the injection is carried out when the fixed mold section  2  is at the highest temperature (approximately 416° C.) in the temperature variation and the movable mod section  2  is at the lowest temperature (approximately 256° C.) in the temperature variation. After the injection, when the temperature of the fixed mold section  2  falls and that of the movable mold sectional rises so that temperature of the fixed mold section  2  reaches approximately 381° C (the lowest temperature) at which the molded product is releasable from the mold, the mold is open again,. In this case, one cycle of the molding process requires approximately 70 seconds.  
         [0027]    As is apparent from the graphs, according to the present invention, the fixed mold section  2  is heated by the heating means  7  and movable mold section  1  is cooled by the cooling means  10  when the mold is in an open state, so that the temperature difference of approximately 160° C. is obtained upon the injection. After the injection, the quantity of heat in the fixed mold section  2  is transferred to the movable mold section  1  due to a high heat-conductive characteristic of the metal filled in the cavity  3 , and the temperature of the fixed mold section falls, while the temperature of the movable mold section  1  rises. When the mold is open and the molded product is removed from the cavity  3 , the heat transfer between the fixed mold section  2  and the movable mold section  1  ceases, whereby the temperature of the fixed mold section  1  rises and that of the movable mold section  2  falls.  
         [0028]    Accordingly, as the fluidity of the molten metal is sufficiently ensured in the present invention, it is possible to form a thin-walled case of 0.43 mm thick, used, for example, for a portable telephone, with metallic alloy such as magnesium alloy.  
         [0029]    While the invention has been described by reference to specific embodiments chosen for purposes of illustration, it should be apparent that numerous modifications could be made thereto by those skilled in the art without departing from the basis concept and scope of the invention.