Patent Publication Number: US-2006000572-A1

Title: Method and apparatus for injection foaming molding

Description:
TECHNICAL FIELD  
      The present invention relates to a method and apparatus for injection foaming molding for foaming a melt of a light alloy to form a foaming molded product.  
     BACKGROUND ART  
      For the conventional production of a foam metal, the following methods are known: in a method disclosed in Japanese Patent Publication No. Hei 1-51528 (Technique 1), a thickener and a blowing agent are added to a melted metal followed by agitating, the whole mold is heated to the melting point of the foamed metal or higher, the agitation is terminated to start a foaming process, in which the air within the mold is released by expanding a number of bubbles generated by thermal decomposition of the blowing agent to allow a foam metal to fill the inner portion of the mold entirely, thereby blocking the mold in a sealed state to form an uniform cell structure under equilibration of the pressure by the rise of internal pressure by the bubbles, and the resulting foam metal is cooled and coagulated in the mold.  
      In a method disclosed in U.S. Pat. No. 2,983,597 (Technique 2), a hydrogenated metal is mixed to a melted metal and decomposed, and the metal is foamed by generation of hydrogen gas. Further, a second alloyed melted metal is supplied from a halfway screw while extruding a mixture of a melted metal and a hydrogenated metal by a first screw at a gas decomposition temperature or lower to perform a continuous foaming molding by generation of decomposed gas.  
      In a method disclosed in Japanese Patent Publication No. 2002-511526 (Technique 3), a molded product is obtained by compressing a blowing agent and a metal powder, heating the resulting semi-finished material within a mold to a melting temperature range to allow the material to foam followed by cooling.  
      In a method disclosed in Japanese Patent Laid-Open No. Hei 9-241780 (Technique 4), as a solution of the problems of a method for adding a blowing agent to a melted metal to generate hydrogen, thereby foaming the metal, and a method for mixing a blowing agent to a metal powder followed by compression molding and then foaming the metal in a mold by heating, a foam metal is obtained by adding 0.1-5%, based on weight, of titanium hydroxide to a metal having a melting point of 420° C. or higher, uniformly dispersing it by agitation, then injecting the melt to a mold, reheating the melt in the mold to 630° C. or higher to allow the melt to foam followed by cooling and coagulation.  
      However, the methods for producing a foam metal of Techniques 1-4 have the following problems. Technique 1 needs much time for the heating since the melted metal is heated and agitated in the mold, and has a problem with the productivity since the same mold is also used for the cooling after foaming. Further, a large mold is needed to form a large molded product. In case of a large mold, since the heating and cooling depends on only the heat conductive electric heating from the wall surface, and a metal having a physical property of excellent heat insulating property is formed as the foamed body at the time of cooling, further much time is needed as a result.  
      In Technique 2, although a metal body can be continuously formed by foaming with hydrogen gas similarly to Technique 1, a molded product of a desired three-dimensional shape or a molded product of a complicated shape cannot be formed since a function of injecting into a mold is not provided. Since the control for holding constant mixing ratio of the melted metal to the blowing agent such as titanium hydride or magnesium hydride can be performed only by the screw rotating speed with instability, the feed rate of the blowing agent cannot be kept constant, nor is the foaming ratio stabilized. Accordingly, the dispersion of product quality (foaming state) is increased.  
      In Technique 3, it is needed to uniformly mix the powder for obtaining a uniform foamed body, and this requires much time and an increased cost. Although a three-dimensional shaped product can be obtained, the control of temperature and time in the foaming by gas decomposition and the melting of the metal powder is difficult, therefore it is difficult to obtain a foaming molded product having uniform cells.  
      In Technique 4, although a three-dimensional shape can be molded, much time is needed to reheat the melt to 630° C. or higher in the mold similar to the problem of Technique 1, and there is a problem with the production efficiency. Since there is a need for increasing a temperature of the mold to 630° C. or higher, cost for the mold is high. In case of a large mold, the temperature control of the melt in the mold is difficult to increase the dispersion of quality.  
      The present invention thus has an object to provide a method and apparatus for injection foaming molding of a light alloy, which can minimize the difference in foaming state between batches with good productivity.  
     DISCLOSURE OF THE INVENTION  
      The present invention involves a method for injection foaming molding of a light alloy comprising the steps of; holding a melt of a light alloy containing a thickener and a blowing agent decomposing at a high temperature to generate a gaseous component in respectively specified percentages at a temperature lower than the decomposition temperature of the blowing agent; agitating the melt to allow the thickener and the blowing agent to disperse; measuring a predetermined amount of the melt for the injection into a mold; and then injecting the melt into the mold to produce a foaming molded article of the light alloy, in which the melt is temperature-adjusted to a temperature higher than the decomposition temperature of the blowing agent and also inhibited to foam by pressuring at least immediately before the injection.  
      Since the thickener and the blowing agent are preliminarily added to the melt in the specified percentages, the difference in foaming state between batches is minimized. Although the decomposition of the blowing agent is caused immediately before the injection, the foaming of the melt is inhibited since the inner capacity of a measuring part is made constant, and the melt is laid in the pressured state. Therefore, since the melt releases the pressure at once within the mold immediately after the injection and foams to spread into every corner of the mold, the transfer property of the mold is enhanced to enable the formation of a foaming molded article of a complicated shape. Since the heating of the mold to the decomposition temperature of the blowing agent or higher is dispensed, the productivity is improved.  
      The present invention further involves a method for injection foaming molding of a light alloy comprising the steps of; holding a melt of a light alloy containing a thickener and a blowing agent decomposing at a high temperature to generate a gaseous component in respectively specified percentages at a temperature lower than the decomposition temperature of the blowing agent; introducing the melt to an injection molding device having an agitating function, a measuring function and an injecting function; agitating the melt to allow the thickener and the blowing agent to disperse; measuring a predetermined amount of the melt for the injection into a mold; and injecting the melt into the mold to produce a foaming molded article of the light alloy, wherein the melt is temperature-adjusted to the decomposition temperature of the blowing agent or higher and also inhibited to foam by pressuring at least immediately before the injection.  
      Since the melt containing the thickener and the blowing agent in the specified percentages are held at a temperature lower than the decomposition temperature of the blowing agent, then introduced into the injection molding device, and agitated within the injection molding device, the thickener and the blowing agent are dispersed to minimize the difference in foaming state between batches. Although the decomposition of the blowing agent is caused immediately before the injection, the foaming of the melt is inhibited since the inner capacity of a measuring part is made constant, and the melt is laid in the pressured state. Therefore, since the melt releases the pressure at once within the mold immediately after the injection and foams to spread into every corner of the mold, the transfer property of the mold is enhanced to enable the formation of a foaming molded article of a complicated shape. Further, since the heating of the mold to the decomposition temperature of the blowing agent or higher is dispensed, the productivity is improved.  
      The method for injection foaming molding of the light alloy of the present invention is characterized in that the temperature of the melt is lower than the decomposition temperature of the blowing agent at the time of agitating the melt.  
      The blowing agent can be uniformly dispersed without decomposition in the melt by holding the temperature of the melt at a temperature lower than the decomposition temperature of the blowing agent at the time of agitating the melt.  
      The present invention involves a method for injection foaming molding of a light alloy comprising the steps of; agitating a melt of a light alloy containing a predetermined amount of a thickener to allow the thickener to disperse; supplying an inert gas as a blowing agent into the melt in a specified percentage while agitating to allow the inert gas to disperse; measuring a predetermined amount of the melt for the injection into a mold; and then injecting the melt to the mold to produce a foaming molded article of the light alloy, wherein the melt is inhibited to foam by pressuring the melt at least until the injection is performed after the supply of the inert gas.  
      The melt containing the thickener is agitated to allow the thickener to disperse, and a predetermined amount of the inert gas is supplied into the melt and evenly dispersed by agitation with a screw, whereby a foaming molded article having a substantially uniform cell structure can be formed. Since the measuring part is laid in the pressured state before the injection, the foaming of the inert gas in the melt is inhibited. Therefore, since the melt releases the pressure at once in the mold immediately after the injection and foams to spread into every corner of the mold, the transfer property of the mold is enhanced to enable the formation of a foaming molded article of a complicated shape. Since the heating of the mold to the decomposition temperature of the blowing agent or higher is dispensed, the productivity is improved.  
      The method for injection foaming molding of the light alloy of the present invention is characterized in that the pressuring is performed by a pressing force caused by the agitation with the screw.  
      The predetermined amounts of the thickener and the blowing agent added to the melt can be dispersed by agitation, and the measuring part can be laid in the pressured state by the pressuring force by the screw for feeding the melt to the front part of a barrel. Therefore, the foaming of the blowing agent in the melt can be inhibited.  
      The method for injection foaming molding of the light alloy of the present invention is also characterized in that the melt is injected in an injection amount reduced by a foaming portion relative to the inner capacity of the mold to break the pressuring, whereby the melt is allowed to foam within the mold to obtain the foaming molded article.  
      The melt is injected into the mold in an injection amount reduced by the foaming portion relative to the inner capacity of the mold, whereby the mold opening at the foaming is dispensed, and the size and shape of the foaming molded article can be precisely controlled.  
      The method for injection foaming molding of the light alloy of the present invention is characterized in that the melt is injected in an injection amount equal to the inner capacity of the mold, and the mold is opened by the capacity of a foaming portion to break the pressuring, whereby the melt is allowed to foam to obtain the foaming molded article.  
      Since the pressure is suddenly released by opening the mold substantially simultaneously with the injection or after the injection, the melt sufficiently spreads into minute parts in the mold, and a foaming molded article of a complicated shape can be formed.  
      The present invention further involves a method for injection foaming molding of a light alloy comprising the steps of; adjusting the temperature of a melt of a light alloy containing a thickener and a blowing agent decomposing at a high temperature to generate a gaseous component in respectively specified percentages to a temperature lower than the decomposition temperature of the blowing agent; supplying the melt into a barrel having a screw provided to be rotatable, protrudable and retreatable; agitating the melt by rotating the screw to allow the thickener and the blowing agent to disperse; measuring the melt in a measuring part formed in a front portion of the barrel by retreating the screw with rotation; and adjusting the temperature of the melt to the decomposition temperature of the blowing agent or higher while inhibiting the foaming of the melt by pressuring the melt in the measuring part the capacity of which is made constant by stopping the retreat of the screw at least immediately before the injection; and injecting the melt into a mold by protruding the screw to obtain a foaming molded article.  
      Since the melt of the light alloy to be supplied into the barrel contains the thickener and the blowing agent in the specified percentages, the thickener and the blowing agent are uniformly dispersed in a kneading part in the barrel. Since the melt is injected after measuring, the difference in foaming state between batches is minimized. Although the decomposition of the blowing agent is caused immediately before the injection, the capacity is made constant state by stopping the screw, and the foaming of the melt is inhibited while laying the melt in the pressured state. Therefore, since the melt releases the pressure at once within the mold immediately after the injection and foams to spread into every corner of the mold, the transfer property of the mold is enhanced to enable the formation of a foaming molded article of a complicated shape. Since the heating of the mold to the decomposition temperature of the blowing agent or higher is dispensed, the productivity is improved.  
      The present invention also involves a method for injection foaming molding of a light alloy using an apparatus for injection foaming molding having a barrel containing a screw and a cylinder communicating with a front portion within the barrel through a communicating passage and containing a plunger, the method comprising; (a) a supplying process for supplying the melt of the light alloy containing a thickener and a blowing agent decomposing at a high temperature to generate a gaseous component in respectively specified percentages, which is temperature-adjusted and held at a temperature lower than the decomposition temperature of the blowing agent, into the barrel; (b) an agitating process for agitating the melt by rotating the screw within the barrel to allow the thickener and the blowing agent to disperse; (c) a measuring process for introducing and measuring the melt from the barrel to a measuring part formed in the front portion within the cylinder by retreating the plunger through the communicating passage; (d) a pressuring process for adjusting the temperature of the melt to the decomposition temperature of the blowing agent or higher and pressuring the melt by generating the gaseous component in the measuring part the capacity of which is made constant by stopping the retreat of the plunger to inhibit the foaming of the melt at least immediately before injection; and (e) an injection foaming process for injecting the melt inhibited to foam in the pressuring process into a mold communicating with the inner portion of the cylinder in the front portion of the cylinder by protruding the plunger to foam the melt.  
      Since the melt containing the thickener and the blowing agent in the specified percentages is held at a temperature lower than the decomposition temperature of the blowing agent, then introduced into the injection molding device, and agitated within the injection molding device, the thickener and the blowing agent are dispersed to minimize the difference in foaming state between batches. Although the decomposition of the blowing agent is caused immediately before the injection, the capacity is made constant by stopping the plunger to inhibit the foaming of the melt while laying the melt in the pressured state. Therefore, since the melt releases the pressure at once within the mold immediately after the injection and foams to spread into every corner of the mold, the transfer property of the mold is enhanced to enable the formation of a foaming molded article of a complicated shape. Since the heating of the mold to the decomposition temperature of the blowing agent or higher is dispensed, the productivity is improved.  
      The present invention involves a method for injection foaming molding of a light alloy comprising the steps of; holding a melt of the light alloy containing a thickener and a blowing agent decomposing at a high temperature to generate a gaseous component in respectively specified percentages at a temperature lower than the decomposition temperature of the blowing agent; agitating the melt to allow the thickener and the blowing agent to disperse; measuring a predetermined amount of the melt for the injection into a mold; and injecting the melt into the mold through an injection nozzle to produce a foaming molded article of the light alloy, wherein the temperature of the melt is raised to the decomposition temperature of the blowing agent or higher at least immediately before the injection into the mold.  
      Since the thickener and the blowing agent are preliminarily added to the melt in the specified percentages, the difference in foaming state between batches is minimized. Since the temperature of the melt to be injected is raised to the decomposition temperature of the blowing agent or higher at least immediately before the injection into the mold, the reheating of the mold to the decomposition temperature of the blowing agent or higher is dispensed, the cooling time of the mold is also shortened, and the productivity is thus improved.  
      The method for injection foaming molding of the light alloy of the present invention is characterized in that the temperature of the melt is raised to the decomposition temperature of the blowing agent or higher at the time of passing through the nozzle.  
      Since the thickener and the blowing agent are preliminarily added to the melt in the specified percentages, the difference in foaming state between batches is minimized. Since the temperature of the melt to be injected is raised to the decomposition temperature of the blowing agent or higher at the time of passing through the nozzle, the reheating of the mold to the decomposition temperature of the blowing agent or higher is dispensed, the cooling time of the mold is also shortened, and the productivity is thus improved.  
      The present invention involves an apparatus for injection foaming molding of a light alloy comprising; a cylindrical member for receiving a melt of a light alloy containing a thickener and a blowing agent decomposing at a high temperature to generate a gaseous component, wherein the melt is agitated by an agitating means provided rotatably in the inner portion to allow the thickener and the blowing agent to disperse; a movable member provided to be protrudable and retreatable within the cylindrical member, the movable member forming a measuring part for measuring the melt in cooperation with the cylindrical member at the tip of the cylindrical member by retreating, and injecting the melt with the gaseous component generated therein into a mold communicating with the measuring part by protruding; and a position retaining means for retaining the position of the movable member against an increase in internal pressure of the cylindrical member in the generation of the gaseous component, so that the melt after the completion of the measurement can be retained in the pressured state to inhibit the foaming thereof.  
      According to such a structure, since the melt including the thickener and the foaming agent preliminarily added in specified percentages can be supplied to the cylindrical member, the difference in foaming state between batches is minimized. Since the position of the movable member can be retained by the position retaining means to keep constant capacity of the measuring part in the cylindrical member although the decomposition of the blowing agent is caused immediately before the injection, the melt can be laid in the pressured state while inhibiting the foaming of the melt. Therefore, since the melt releases the pressure at once within the mold immediately after the injection and foams to spread into every corner of the mold, the transfer property of the mold is enhanced to enable the formation of a foaming molded article of a complicated shape. Since the heating of the mold to the decomposition temperature of the blowing agent or higher is dispensed, the productivity is improved.  
      The apparatus for injection foaming molding of the light alloy of the present invention is characterized in that the position retaining means is a solenoid valve provided in a hydraulic circuit of a hydraulic cylinder for protruding and retreating the movable member so as to be capable of interrupting the incoming and outgoing of oil to a hydraulic cylinder.  
      According to such a structure, the protruding and retreating of the movable member can be easily controlled. Therefore, the position of the movable member can be controlled according to the foaming state of the blowing agent, and the melt can be easily held in the pressured state.  
      The apparatus for injection foaming molding of the light alloy of the present invention is characterized in that the movable member is composed of a rotatable agitating screw.  
      According to such a structure, the thickener and the blowing agent in the melt supplied into the cylindrical member can be evenly dispersed.  
      The apparatus for injection foaming molding of a light alloy of the present invention is characterized in that the cylindrical member comprises a barrel for agitating the melt and a cylinder connected thereto to introduce and measure the agitated melt, and the movable member is a plunger provided within the cylinder.  
      According to such a structure, since the melt containing the thickener and the blowing agent in specified percentages can be supplied to the cylindrical member, the difference in foaming state between batches is minimized.  
      The present invention further involves an apparatus for injection foaming molding of a light alloy comprising; a barrel for receiving the melt of the light alloy containing a thickener and a blowing agent decomposing at a high temperature to generate a gaseous component, the barrel comprising a temperature adjusting means capable of adjusting the temperature of the melt from a temperature lower than the decomposition temperature of the blowing agent to the decomposition temperature or higher, in which the gaseous component can be generated by adjusting the temperature of the melt to the decomposition temperature of the blowing agent or higher by the temperature adjusting means; a screw provided within the barrel to be rotatable, protrudable and retreatable and adapted to agitate the melt by rotating to allow the thickener and the blowing agent to disperse, to form a measuring part in cooperation with the barrel at the tip of the barrel by retreating, and to inject the measured melt from the barrel into a mold by protruding; and a position retaining means for retaining the position of the screw against an increase in internal pressure of the barrel in the generation of the gaseous component so that the melt after the completion of the measurement can be retained in the pressured state to inhibit the foaming thereof.  
      According to such a structure, since the melt containing the thickener and the blowing agent preliminarily added thereto can be supplied into the barrel and surely dispersed, the difference in foaming state of every injection is minimized. The temperature of the melt in the barrel can be easily adjusted to control the state of the blowing agent in the melt, and the difference in foaming state between batches can be further minimized. Further, since the temperature can be adjusted so as to cause the decomposition of the blowing agent immediately before the injection and the capacity of the measuring part within the barrel can be kept constant by the position retaining means for the screw, the foaming of the melt can be inhibited to lay the melt in the pressured state. Therefore, since the melt releases the pressure at once in a mold immediately after the injection and foams to spread into every corner of the mold, the transfer property of the mold is enhanced to enable the formation of a foaming molded article of a complicated shape. Since the heating of the mold to the decomposition temperature of the blowing agent or higher is dispensed, the productivity is improved.  
      The present invention involves an apparatus for injection foaming molding of a light alloy comprising; a barrel for receiving a melt of a light alloy containing a thickener and a blowing agent decomposing at a high temperature to generate a gaseous component, the barrel having a first temperature adjusting means capable of adjusting the temperature of the melt to a temperature lower than the decomposition temperature of the blowing agent, in which the melt is agitated with a screw provided rotatably in the inner portion to allow the thickener and the blowing agent to disperse; a cylinder connected to the barrel and having a second temperature adjusting means capable of adjusting the temperature of the melt to the decomposition temperature of the blowing agent or higher; a plunger provided within the cylinder to be protrudable and retreatable and adapted to form a measuring part for measuring the melt in cooperation with the cylinder at the tip of the cylinder by retreating and to inject the measured melt from the cylinder to a mold by protruding; and a position retaining means for retaining the position of the plunger against an increase in internal pressure of the cylinder in the generation of the gaseous component so that the melt after the completion of the measurement can be retained in the pressured state to inhibit the foaming thereof.  
      According to such a structure, since the melt containing the thickener and the blowing agent preliminarily added thereto can be supplied into the barrel and surely dispersed, the difference in foaming state in every injection is minimized. Since the position of the movable member can be retained by the position retaining means to keep constant capacity of the measuring part in the cylindrical member although the decomposition of the blowing agent is caused immediately before the injection, the foaming of the melt can be inhibited while laying the melt in the pressured state. Therefore, since the melt releases the pressure at once within the mold immediately after the injection an d foams to spread into every corner of the mold, the transfer property of the mold is enhanced to enable the formation of a foaming molded article of a complicated shape. Since the heating of the mold to the decomposition temperature of the blowing agent or higher is dispensed, the productivity is improved. The cylinder enables a precise measurement of the melt. Therefore, since the difference of melt injection amounts between batches for injection molding is minimized, a molded product is precisely produced.  
      The present invention involves an apparatus for injection foaming molding of a light alloy comprising; a cylindrical member for receiving the melt of the light alloy containing a thickener and a blowing agent decomposing at a high temperature to generate a gaseous component, in which the melt is agitated by an agitating means provided rotatably in the inner portion to allow the thickener and the blowing agent to disperse; a movable member provided to be protrudable and retreatable within the cylindrical member, which forms a measuring part for measuring the melt in cooperation with the cylindrical member at the tip of the cylindrical member by retreating and injects the melt to a mold communicating with the measuring part through an injection nozzle by protruding; and a nozzle heating means capable of heating the melt to the decomposition temperature of the blowing agent or higher at the time of passing the melt through the nozzle.  
      According to such a structure, since the melt containing the thickener and the blowing agent preliminarily added thereto can be supplied into the barrel and surely dispersed, the difference in foaming state in every injection is minimized. Since the melt is injected through the injection nozzle, the injection pressure can be increased. The temperature of the melt is raised to the decomposition temperature of the blowing agent or higher when the melt is passed through the nozzle, or immediately before the injection into the mold, whereby the blowing agent is decomposed to generate the gaseous component. Accordingly, since the melt foams at once within the mold immediately after the injection, the heating of the mold to the decomposition temperature of the blowing agent or higher is dispensed and the productivity is improved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a general illustrative view showing one embodiment according to an apparatus for injection foaming molding of a light alloy of the present invention;  
       FIG. 2  is a general illustrative view showing another embodiment of the apparatus for injection foaming molding of a light alloy of the present invention;  
       FIG. 3  is a view showing an essential part of the embodiment of the apparatus for injection foaming molding of a light alloy of the present invention, which illustrates a molding process;  
       FIG. 4  is a view showing an essential part of the embodiment of the apparatus for injection foaming molding of a light alloy of the present invention, which illustrates the molding process; and  
       FIG. 5  is a view showing an essential part of the other embodiment of the apparatus for injection foaming molding of a light alloy of the present invention, which illustrates the molding process. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      Preferred embodiments of the present invention will be described based on the drawings.  FIG. 1  shows one embodiment of the present invention. An apparatus for injection foaming molding  1  according to this embodiment is composed of an injection molding device  3  and a mold clamping device  17  as shown in  FIG. 1 .  
      The injection molding device  3  comprises; a feed port  8  for supplying a melt of a light alloy containing a thickener and a blowing agent decomposing at a high temperature to generate a gaseous component; a cylindrical member A for agitating the melt supplied from the feed port  8  by an agitating means  4  provided rotatably to allow the thickener and the blowing agent to disperse; a movable member B provided to be protrudable and retreatable within the cylindrical member A, which forms a measuring part  6  for measuring the melt in cooperation with the cylindrical member A at the tip of the cylindrical member A by retreating and injects the melt with the gaseous component generated therein into a mold  24  communicating with the measuring part  6  by protruding; and a position retaining means C for retaining the position of the movable member B against an increase in internal pressure of the cylindrical member A in the generation of the gaseous component so that the melt after the completion of the measurement can be held in the pressured state to inhibit the foaming thereof. A barrel  7  that is the cylindrical member A for agitating the melt comprises a temperature adjusting means  10  for adjusting the temperature of the melt  2  of the light alloy supplied and the melt  2  of the light alloy supplied to an injection part  9 . The injection part  9  for injecting the melt  2  measured by the measuring part  6  into the mold  24  is provided at the tip of the barrel  7 .  
      Since the barrel  7  is substantially vertical as shown in  FIG. 1 , the melt  2  of the light alloy supplied surely moves to the lower portion within a kneading part  5  by its own weight.  
      The injection part  9  has an L-shaped passage  11 , wherein the passage of the melt  2  of the light alloy is vertical in kneading and agitating and horizontal in injection. Accordingly, even in the case, as shown in  FIG. 1 , where the injection molding device  3  is connected to the mold clamping device  17 , the setting area of the apparatus for injection foaming molding  1  can be minimized as much as possible.  
      In this apparatus for injection foaming molding  1 , a nozzle part  13  having a valve means  12  is provided at the tip of the L-shaped passage  11  provided at the lower end of the barrel  7 . This tip part is allowed to abut on the mold  24  which horizontally slides to open and close by the mold clamping device  17 .  
      Of the components of the apparatus for injection foaming molding  1 , the lower end opening part of a hopper  14  for receiving the melt of the light alloy melted in a melting furnace (not shown) and storing it in the melted state is connected to the feed port  8  in the upper portion of the barrel  7 . The hopper  14  comprises a temperature control means such as a heating heater. By this temperature control means, the melt  2  in the hopper  14  can be controlled, for example, to a constant temperature equal to or higher than a liquid phase temperature and lower than the foaming temperature of the blowing agent, or equal to or higher than the decomposition temperature of the blowing agent.  
      The hopper  14  further comprises a feeder for quantitatively supplying the thickener and the blowing agent to be added to the melt  2  of the light alloy. The powdery thickener and the blowing agent can be quantitatively supplied by this feeder to minimize the difference in foaming state between batches. The melt of the light alloy containing predetermined amounts of the thickener and the blowing agent may be supplied directly to the hopper  14 .  
      As the thickener to be added to the melt  2  of the light alloy, a known one such as calcium can be used. As the blowing agent, a known metallic hydroxide including titanium hydroxide can be applied. Titanium hydroxide causes gas decomposition at about 640° C. In the use of an AL alloy as a light alloy, the liquid phase line temperature is 630° C., and the liquid phase line temperature or higher described later means a temperature of 630° C. or higher, and the titanium hydroxide can be dispersed by agitation without causing any decomposition by holding the melt temperature, for example, at 630° C. by the temperature adjusting means  10  of the barrel.  
      The hopper  14  is filled with an inert gas  18  such as Ar supplied by an inert gas feeding unit  16  to seal the level of the melt  2  of the light alloy with the inert gas  18 . The position retaining means C is provided at the upper end of the barrel  7  that is the cylindrical member A. The position retaining means C comprises a drive motor  19  and a screw hydraulic cylinder  21  connected to the drive motor  19 .  
      A through spline hole is provided in the drive shaft of the drive motor  19 , and a spline shaft provided at the upper portion of the screw  4  rotatably inserted into the barrel  7  is inserted through to permit the transmission of a rotational driving force and the axial movement of the screw  4 .  
      The screw hydraulic cylinder  21  having a vertically protruding and retreating cylinder rod  2  is connected to the upper portion of the drive motor  19 . The screw  4  is connected to the cylinder rod  20  of the screw hydraulic cylinder  21 , and arranged in a cantilever form so that the lower end is free within the barrel  7 . Therefore, a stirring blade of the screw  4  is protruded (moved downward) through the drive motor  19  by downwardly protruding the cylinder rod  20  of the screw hydraulic cylinder  21 , whereby the melt  2  of the light alloy collected in the lower end part within the barrel  7  can be passed to the L-shaped passage  11  and injected into the mold  24  through the nozzle part  13 .  
      When the screw hydraulic cylinder  21  is operated to move the screw  4  that is the movable member B upward in the axial direction, the measuring part  6  is formed in a lower portion within the barrel  7 . The measuring part  6  can be properly set by the retreating quantity of the screw hydraulic cylinder  21  so as to provide a capacity necessary for obtaining a molded product. A valve means  12  of the nozzle part  13  is closed except the time of injection. As the valve means  12 , similar ones as those described later can be applied.  
      The circumferential surface of the barrel  7  and the injection part  9  is covered with the temperature adjusting means  10 . The temperature adjusting means  10  is composed of a plurality of vertically separated heating heaters. The temperature of the melt of the light alloy in the barrel  7  can be adjusted at least in two systems by these heating heaters. Accordingly, the temperature control can be performed separately in the upper portion and lower portion of the barrel  7  to control the decomposition of the blowing agent in the melt  2 .  
      The mold clamping device  17  comprises a link housing  26  raised on a base  25 , a fixed board  28  fixed to the housing  26  through a horizontal tie bar  27 , a fixed mold  24   b  fixed to the fixed board  28 , a movable board  29  sidably inserted and supported relative to the tie bar  27 , and a movable mold  24   a  fixed to the movable board  29  so as to be openable and closable by sliding horizontally relative to the fixed mold  24   b . A mold clamping cylinder  30  is fixed to the outer surface center of the link housing  26 , and the tip of the cylinder rod  31  of the mold clamping cylinder  30  is connected to the center part of the movable board  29 . The link housing  26  is connected to the movable board  29  through a plurality of links  32  which are folded when the both are mutually approached, and substantially linearly arranged in the horizontal direction when the both are separated.  
      An extrusion cylinder  33  is provided on the side surface of the movable board  29  on the link housing  26  side, and an extrusion rod  34  of the extrusion cylinder  33  is connected to a product protruding mechanism of the movable mold  24   a  through the movable board  29 . Accordingly, in this mold clamping device  17 , the cylinder rod  31  of the mold clamping cylinder  30  is protruded to extend the links  32  linearly into a stretched state, whereby the movable mold  24   a  can be strongly pressed to the fixed mold  24   b . The release of a product is performed by protruding the extrusion rod  34  of the extrusion cylinder  33  to operate the product protruding mechanism.  
      Since the melt  2  of the light alloy is allowed to foam at once within the mold  24  after the injection by the apparatus for injection foaming molding  1  described above, the melt  2  spreads into every corner of the mold  24 . Accordingly, the transfer property to the mold  24  is enhanced to enable the formation of a foaming molded article of a complicated shape. Further, since the heating of the mold to the decomposition temperature of the blowing agent or higher is dispensed, the productivity is improved.  
      The operation of the apparatus for injection foaming molding  1  of this embodiment and a method for injection foaming molding of a light alloy by this apparatus will be described.  
      The melt  2  of the light alloy is fed mechanically or by a means such as an electromagnetic pump from a melting furnace (not shown) into the hopper  14 . As the melting furnace, a high frequency induction furnace, an electromagnetic induction heating furnace, or the like can be used regardless of the kind. The melt  2  of the light alloy in the hopper  14  is temperature-adjusted to a temperature of the liquid phase line temperature or higher and lower than the decomposition temperature of the blowing agent, and held at an uniform temperature by a temperature control means such as heating heaters or the like provided on the hopper  14 . The thickener and the blowing agent are quantitatively supplied to the melt  2  of the light alloy by the feeder (not shown) provided on the hopper  14 . According to this, the difference in foaming state between batches can be minimized. As occasion demands, an agitating means for agitating the melt  2  of the light alloy in the hopper  14  may be provided to impart an agitating effect. By providing the above-mentioned inert gas feeding unit  16  on the hopper  14 , the oxidation of the melt can be prevented.  
      The melt  2  of the light alloy put in the hopper  14  is supplied to the upper portion of the barrel  7  while gas-sealing it, the melt  2  of the light alloy is temperature-adjusted to and held at a temperature of the liquid phase line temperature or higher and lower than the decomposition temperature of the blowing agent by the heating heater, and the melt  2  of the light alloy is agitated by rotating the screw  4  in the kneading part  5  within the barrel  7  to allow the thickener and the blowing agent to disperse. Accordingly, by keeping the blowing agent at a temperature lower than the foaming temperature at the time of agitation, whereby the blowing agent can be uniformly dispersed because it is powdery.  
      When the melt  2  containing only the thickener is supplied into the barrel  7 , an inert gas quantitative feeding unit (not shown) is provided on the barrel  7  corresponding to the kneading part  5 , whereby inert gas that is the blowing agent can be supplied to the melt in a specified percentage when the thickener is allowed to disperse by agitation, and the inert gas is evenly dispersed into the melt  2 .  
      When the melt  2  is agitated in the kneading part  5 , the melt  2  of the light alloy is pushed downwardly within the barrel  7  by a pushing force accompanying the rotation of the screw  4 ; a load is applied to the axially upper portion of the screw  4 . On the other hand, a fixed back pressure is set on the screw hydraulic cylinder  21  constituting the position retaining means, and when an internal pressure overcoming the back pressure is generated in the barrel  7 , the screw  4  is moved axially upward and retreated to a predetermined position set according to a molded product volume. The melt  2  of the light alloy is measured in the measuring part  6  between the screw  4  and the L-shaped passage  11 . In this embodiment, although the screw  4  is retreated with rotation by the rise of the internal pressure of the barrel  7  caused by the rotation, the screw  4  may be retreated without rotation by the screw hydraulic cylinder  21 , or retreated with rotation by the screw hydraulic cylinder  21 . A backflow preventive means such as a check ring is preferably provided at the tip of the screw  4 , and by providing it, the melt  2  of the light alloy can be smoothly carried down, at the time of retreating, and measured in the measuring part  6  according to the molded product volume. At the measurement, the nozzle part  13  of the L-shaped passage  11  is closed by the valve means  12 .  
      After the measurement is completed, the melt  2  is laid in the pressured state at least immediately before the injection to inhibit the foaming by temperature-adjusting so as to be heated to the decomposition temperature of the blowing agent within the measuring part  6  by the heating heaters, and promoting the decomposition of the blowing agent within the measuring part  6  the capacity of which is made constant by stopping the retreat of the screw  4 . Since the measuring part  6  can be laid in the pressured state also by the pushing force of the melt  2  by the rotation of the screw  4 , the foaming of the blowing agent raised in temperature to the decomposition temperature of the blowing agent can be inhibited.  
      The melt  2  is then injected into the mold  24  by opening the valve means  12  of the nozzle part  13  and protruding the screw  4 , and the melt  2  inhibited to foam is allow to rapidly foam within the mold  24  lower in pressure than in the barrel  7 , whereby the formation of a molded article is performed.  
      At the injection into the mold  24 , when the melt  2  of the light alloy is injected into the mold  24  in an injection amount equal to the inner capacity of the mold  24 , the pressure of the gaseous component is released at once by sliding and opening the movable mold  24   a  by the volume of a foaming portion after the injection to allow the melt  2  of the light alloy to foam in the sliding direction, whereby a foaming molded article in which foamed cells are uniformly dispersed can be obtained. When the melt  2  of the light alloy is injected to the mold  24 , a skin layer is formed on the surface where the melt  2  comes in contact with the mold  24 .  
      Since the pressure of the gaseous component restricted to expand in the melt  2  of the light alloy is suddenly released by injecting the melt  2  of the light alloy into the mold  24  and opening the mold  24  substantially simultaneously with the injection or after the injection, the foamed melt  2  of the light alloy sufficiently spreads into minute parts in the mold  24 , and a foaming molded article of a complicated shape can be formed.  
      When the melt  2  of the light alloy is injected into the mold  24  in an injection amount reduced by a foaming portion relative to the inner capacity of the mold (the molded product capacity), the pressure of the gaseous component is released at once in the mold  24  after the injection to allow the melt  2  of the light alloy to foam, and a foaming molded article in which foamed cells are uniformly dispersed can be obtained.  
      By reducing the injection amount of the melt  2  of the light alloy to be injected into the mold  24  by the foaming portion in this way, the size and shape of a foaming molded article can be precisely controlled without being influenced by the stopping precision in opening the mold, the parallel degree of the mold, or the like.  
      According to the method for injection foaming molding using the apparatus for injection foaming molding  1  as described above, since the thickener and the blowing agent are preliminarily added to the melt  2  of the light alloy to be supplied into the barrel  7  in respectively specified percentages, the variations of the resulting molded product between injections can be minimized. Since the thickener and the blowing agent are uniformly dispersed in the kneading part  5  within the barrel  7 , a molded product with uniformly dispersed foamed cells can be obtained. Further, according to such an injection, the difference in foaming state between batches is minimized.  
      Although the gaseous component is generated by decomposition of the blowing agent immediately before the injection, the capacity of the measuring part  6  is made constant by stopping the screw  4  to inhibit the foaming of the melt (the expansion of the gaseous component). Therefore, the melt  2  of the light alloy is made to release the pressure at once within the mold  24  immediately after the injection to foam, whereby the melt can be filled into every corner of the mold  24 . Accordingly, the transfer property to the mold  24  is enhanced, the productivity is improved, and the formation of a foaming molded article of a complicated shape can be performed. The mold is depressurized by a pressure reducing means such as a vacuum pump, whereby the transfer property and the moldability of a foaming molded article of complicated shape can be further improved Another embodiment according to the apparatus for injection foaming molding of the present invention will be further described in reference to  FIG. 2 . As shown in  FIG. 2 , an apparatus for injection foaming molding  40  of this embodiment comprises two members of a horizontal plunger type injection part  9  different from that of the apparatus for injection foaming molding  1  and the same vertical barrel  7  as that of the apparatus  1 .  
       FIG. 2  is a general illustrative view showing the apparatus for injection foaming molding  40  of a light alloy of this embodiment. The apparatus for injection foaming molding  40  has substantially the same structure for the barrel  7  and the mold clamping device  17  as the apparatus for injection foaming molding  1  except the horizontal plunger type injection part  9 . As a melt of a light alloy, a thickener and a blowing agent, those described above are applicable.  
      This apparatus for injection foaming molding  40  of a light alloy comprises an injection molding device  43 , and a mold clamping device  17 . The injection molding device  43  comprises a barrel  47  having an agitating function, the barrel being composed of a kneading part  45  having a feed port  58  for supplying a melt  2  containing a thickener and a blowing agent decomposing at a high temperature to generate a gaseous component in respectively specified percentages at an upper portion and a screw  44  provided in the inner portion to be rotatable, protrudable and retreatable, in which the melt  2  is agitated by the screw  44  to allow the thickener and the blowing agent to disperse, and a storage part  46  formed by retreating the screw  44 ; and a plunger injection machine  50  having a measuring function and an injecting function, the machine comprising a cylinder  42  a front portion of which is connected to the lower end of the barrel  47  through a communicating passage  41  provided at the lower end of the cylinder  42 , and a plunger  48  protrudable and retreatable along the axis of the cylinder  42  within the cylinder  42 , in which a measuring part  49  is formed at the inner front portion of the cylinder  42  by retreating the plunger  48 , and the melt  2  of the light alloy is injected by protruding the plunger  48 . The mold clamping device  17  comprises a mold  24  for allowing the melt  2  injected from the plunger injection machine  50  to foam. The apparatus also comprises a temperature adjusting means  51  for adjusting the temperature of the melt  2  of the light alloy supplied from the feed port  58  to the barrel  47  and the melt  2  of the light alloy supplied to the plunger injection machine  50   
      A nozzle part  52  having a valve means  12  is provided at the tip of the plunger injection machine  50  of the apparatus for injection foaming molding  40 . The tip part abuts on the mold  24  which is horizontally slid to open and close by the mold clamping device  17 .  
      Of the components of the apparatus for injection foaming molding  40 , a hopper  53  has the same structure as the hopper  14  described above, and comprises a feeder and a temperature control means such as a heating heater.  
      The barrel  47  also has the same structure as in the apparatus for injection foaming molding  1  of the above-mentioned embodiment. As shown in  FIG. 2 , a screw hydraulic cylinder  56  having a vertically protruding and retreating cylinder rod  55  is connected to the upper portion of a drive motor  54 , and the screw  44  is connected to the cylinder rod  55  of the screw hydraulic cylinder  56  through the drive motor  54 . Therefore, the cylinder rod  55  of the screw hydraulic cylinder  56  is protruded down to protrude (move down) the stirring blade of the screw  44  through the drive motor  54 , whereby the melt  2  of the light alloy collected in the lower end within the barrel  47  is supplied into the cylinder  42  of the plunger injection machine  50  through the communicating passage  41 .  
      The screw hydraulic cylinder  56  is adapted so that a storage part  46  can be formed at a lower portion within the barrel  47  when it is moved axially upward. Further, this cylinder has a sufficient stroke to move the plunger from the position for forming the storage part  46  to the position capable of closing the communicating passage  41 .  
      As shown in  FIG. 2 , the circumferential surface of the barrel  47  and the cylinder  42  of the plunger injection machine  50  is covered with the temperature adjusting means  51 . The temperature adjusting means  51  is composed of a plurality of separated heating heaters. By controlling the heating heaters, at least the melt  2  of the light alloy in the barrel  47  can be adjusted to a temperature lower than the decomposition temperature of the blowing agent added thereto, and at least the melt  2  of the light alloy in the cylinder  42  can be adjusted to a temperature allowing the blowing agent added thereto to decompose to generate the gaseous component or higher.  
      The plunger injection machine  50  is connected to the barrel  47  through the communicating passage  41  formed at the lower end of the barrel  47 . The plunger injection machine  50  comprises the cylinder  42  having the nozzle part  52  with the valve means  12  in the front portion and the plunger  48  protrudable and retreatable within the cylinder  42 . The plunger  48  is driven by the hydraulic pressure of the plunger hydraulic cylinder  57 . When the plunger  48  is retreated, a measuring part  49  is formed in the front portion of the cylinder  42 . The capacity of the measuring part  49  can be properly set by the retreating quantity of the plunger  48  to attain a capacity necessary for providing a molded product. The plunger hydraulic cylinder  57  has a sufficient stroke to move the plunger  48  from the position for forming the measuring part  49  to the position capable of closing the connection passage  41  connected to the vicinity of the tip of the cylinder  42  by protruding. The plunger  48  is provided so as to close the communicating passage  41  when the injection is completed. Accordingly, the melt  2  of the light alloy for the next molding injection can be supplied into the barrel  47  immediately after the injection. The valve means  12  of the nozzle part  52  is laid in a closed state except the time of injection. As the valve means  12 , a one adapted to block the nozzle by a mechanical or spring type shut-off valve provided at the tip of the nozzle can be used.  
      According to the apparatus for injection foaming molding  40  as described above, the melt  2  can be inhibited to foam in the state where the gaseous component is generated within the melt  2  at least immediately before the injection, and made to foam at once into the mold  24  after the injection. Therefore, the melt  2  spreads into every corner of the mold  24 , whereby the transfer property to the mold  24  is enhanced, and the productivity is improved. Further, the formation of a foaming molded article of a complicated shape can be performed. The maintenance and management of the apparatus can be facilitated by constituting the barrel  47  and the injection part from two separate members.  
      The operation of the apparatus for injection foaming molding  40  of this embodiment and a method for injection foaming molding using this apparatus will be described.  
      The melt  2  of a light alloy is put into a hopper  53  from the melting furnace described above in the same manner. A thickener and a blowing agent decomposing at a high temperature to generate a foaming gas are added to the melt  2  in respectively specified percentages, and the resulting melt is temperature-adjusted to a liquid phase line temperature or higher and a temperature lower than the decomposition temperature of the blowing agent by a temperature control means of the hopper  53 . In this way, a supplying process for supplying the temperature-adjusted melt  2  of the light alloy into the barrel  47  is performed. The thickener and the blowing agent to be added to the melt  2  may be put into the hopper  53  by providing a feeder on the hopper  53 , or the melt  2  containing predetermined amounts of the thickener and the blowing agent may be put into the hopper  53 .  
      The melt  2  is then supplied to the upper portion of the barrel  47 , adjusted to and held at the liquid phase line temperature or higher and a temperature lower than the decomposition temperature of the blowing agent, and the thickener and the blowing agent are uniformly dispersed in an agitating process for agitating the melt  2  by rotating the screw  44  in the kneading part  45  within the barrel  47 . When the melt  2  containing only the thickener is supplied into the barrel  47 , an inert gas quantitative feeding unit (not shown) is provided to the barrel  47  corresponding to the kneading part  45 , whereby inert gas that is the blowing agent can be supplied to the melt  2  in a specified percentage at the time of dispersing the thickener by agitation, and uniformly dispersed into the melt  2 .  
      At this time, the plunger  48  of the plunger injection machine  50  is protruded to the position for closing the communicating passage  41  as shown in  FIG. 3 . The screw  44  in the barrel  47  is retreated with rotation, whereby the storage part  46  is formed between the screw  44  and the communicating passage  41  instead of the above-mentioned measuring part  6 , and a primary measurement is performed in this storage part  46 . The storage part  46  is adjusted by the retreating quantity of the screw  44  so as to have a capacity larger than the amount of the melt to be injected. The screw  44  may be retreated without rotation, or retreated with rotation. The backflow preventive means described above can be provided at the tip of the screw  44 .  
      Then, a measuring process for introducing the melt  2  from the barrel  47  to the measuring part  49  formed at the front portion within the cylinder  42  through the communicating passage  41  by opening the communicating passage  41  to retreat the plunger  48  of the plunger injection machine  50  is performed. In this measuring process, the screw  44  within the barrel  47  is protruded (moved down) simultaneously with the retreat of the plunger  48  as shown in  FIG. 4 . A pressuring force by the screw  44  is worked to press the melt  2  of the light alloy into the measuring part  49  formed at the front portion of the cylinder  42  with a positive pressure while the plunger  48  retreats to a predetermined position set according to the molded product volume, whereby the melt is secondarily measured.  
      Since the melt  2  including the thickener and the blowing agent preliminarily added in the specified percentages is held at a temperature lower than the decomposition temperature of the blowing agent, and then introduced to and agitated in an injection molding device  43 , the thickener and the blowing agent are uniformly dispersed to minimize the difference in foaming state in every injection.  
      When the measuring by pressing is completed, the communicating passage  41  is closed by the screw  44 , as shown in  FIG. 5 , to prevent the backflow of the melt  2  of the light alloy from the measuring part  49 . At the time of measurement, the nozzle part  52  at the tip of the cylinder  542  of the plunger injection machine  50  is closed by the valve means  12 .  
      After the secondary measurement is thus completed, the melt  2  is temperature-adjusted to the decomposition temperature of the blowing agent or higher at least immediately before the injection by each temperature adjusting means  51 , and the decomposition within the measuring part  49  the capacity of which is made constant by stopping the retreat of the plunger  48  is promoted, whereby a pressuring process for laying the melt in the pressured state to inhibit the foaming thereof is performed. Namely, although the blowing agent gradually starts the decomposition to generate the gaseous component as the melt  2  of the light alloy is heated to the decomposition temperature of the blowing agent within the measuring part  49  by the temperature adjusting means  51 , the foaming of the melt  2  is inhibited by pressuring since the increase in capacity is suppressed by the back pressure of the plunger  48 .  
      Then, an injection foaming process for injecting the melt  2  inhibited to foam in the pressurizing process into the mold  24  communicating with the front portion within the cylinder  42  followed by foaming by protruding the plunger  48  is performed to form a molded article.  
      At the injection to the mold  24 , a method for injecting the melt  2  of the light alloy in an injection amount equal to the inner capacity of the mold  24  into the mold  24  and opening the mold by a foaming portion to obtain the foaming molded article similarly to the above-mentioned method, and a method for injecting the melt  2  of the light alloy into the mold  24  in an amount reduced by the foaming portion to obtain the foaming molded article within the mold with a constant capacity can be applied.  
      According to the method for injection foaming molding using the apparatus for injection foaming molding  40 , since the foaming of the melt  2  (the expansion of the gaseous component) is inhibited in a state where the capacity is made constant by stopping the plunger  48  although the blowing agent is decomposed to generate the gaseous component immediately before the injection, the pressure is released at once in the mold  24  immediately after the injection to allow the melt to foam, whereby the melt  2  can spread into every corner of the mold  24 . Accordingly, the transfer property to the mold  24  is enhanced to enable the formation of a foaming molded article of a complicated shape. The transfer property and the moldability of a foaming molded article of a complicated shape can be further improved by depressurizing the mold by a pressure reducing means similarly to the above-mentioned embodiment.  
      When inert gas is supplied to the melt  2  in a specified percentage as a blowing agent by an inert gas quantitative feeding unit (not shown) by use of the apparatuses for injection foaming molding  1  and  40  as described above, the inert gas is also dispersed by agitation in the kneading parts  5  and  45  of the barrels  7  and  47 , and a predetermined amount of the melt  2  is measured for the injection into the mold  24 , and then the melt is injected into the mold  24 . When the temperature is raised by the temperature adjusting means  10  and  51  before the injection to the mold  24 , the expansion of the gaseous component is promoted. At that time, the increase in capacity is suppressed by stopping the retreat of the screw  4  in the apparatus for injection foaming molding  1  and by stopping the retreat of the plunger  48  in the apparatus for injection foaming molding  40 , and in such a pressured state, the foaming of the melt  2  (the expansion of the gaseous component) is inhibited. The screw  4  and the plunger  48  are protruded while opening the valve means  12  of the nozzle parts  13  and  52  to inject the melt  2  of the light alloy into the mold  24 , whereby the pressuring force acting on the melt  2  is released at once to allow the melt to foam, whereby the formation of a molded article is performed.  
      Since the inert gas is supplied in the specified percentage and uniformly dispersed into the melt  2  even in the use of the inert gas as the blowing agent, a foaming molded article having a substantially uniform cell structure can be formed while minimizing the difference in foaming state between injections.  
      The supply of Ar gas as a blowing agent from the barrel in the apparatus for injection foaming. molding  40  with the above inert gas quantitative feeding unit provided on the barrel will be further described.  
      A predetermined amount of the thickener is added to the melt  2  of the light alloy supplied from the melting furnace to the hopper  53  similarly to the above. At this time, the temperature is adjusted to the liquid phase line temperature or higher by the temperature control means of the hopper  53 .  
      The temperature-adjusted melt  2  is supplied into the barrel  47 , and agitated in the kneading part  45  while adjusting the temperature to the liquid phase line temperature or higher to thereby disperse the thickener. At this time, a high-temperature Ar gas is supplied from the inert gas quantitative feeding unit (not shown) to the melt  2 , whereby the Ar gas is also dispersed into the melt  2 . The melt  2  is then fed to the storage part  46  in the lower portion of the barrel  47 .  
      When the addition amount of the thickener to be added to the melt  2  fed to the storage part  46  is small, no pressure overcoming the back pressure of the screw  44  is generated because the pressure of the melt  2  generated by the rotation of the screw  44  in the barrel  47  is small. In such a case, the screw  44  of the kneading part  45  is retreated by driving the screw hydraulic cylinder  56  in the axial direction to feed the melt  2  to the storage part  46  by its own weight of the melt  2 , a pressure for feeding the melt  2  to the measuring part  49  of the plunger injection machine  50  is generated by protruding (moving down) the screw  44  to feed the melt  2  to the measuring part  49  by a positive pressure. As a matter of course, when the addition amount of the thickener is large and the pressure overcoming the screw back pressure is generated in the melt  2  by the rotation of the screw  44 , the drive by the cylinder is not necessarily required for the feed of the melt  2  to the storage part.  
      The measured melt  2  is raised in temperature by the temperature adjusting means  51  within the measuring part  49  before the injection to promote the expansion of the Ar gas included therein. However, since the capacity is made constant by stopping the plunger  48  to inhibit the foaming, and the pressure is released at once in the mold  24  immediately after the injection to allow the melt to foam, the melt spreads into every corner of the mold  24  and a foaming molded article with foamed cells uniformly dispersed therein can be thus obtained.  
      Another embodiment according to the apparatus for injection foaming molding of the present invention will be described. An apparatus for injection foaming molding of this embodiment has the same device structure as the above-mentioned apparatus for injection foaming molding  1  or the apparatus for injection foaming molding  40  except the points described below. Accordingly, only the different points will be described, omitting the description for the similar points.  
      This apparatus for injection foaming molding is adapted to disperse, measure and then inject a melt of a light alloy containing a thickener and a blowing agent decomposing at a high temperature to generate a gaseous component into a mold through an injection nozzle, and comprises a nozzle heating means capable of raising the temperature of the melt to the decomposition temperature of the blowing agent or higher when passing the melt through the nozzle in the injection. As the nozzle heating means, a known heating means such as a resistance heating heater or induction heating heater provided on the circumference of the injection nozzle can be used, and the induction heating heater capable of shortening the temperature rising time is more preferably used.  
      According a method for injection foaming molding using this apparatus for injection foaming molding, since the melt including the thickener and the blowing agent preliminarily added thereto in respectively specified percentages is prepared similarly to the above embodiments, and agitated to allow the thickener and the blowing agent to uniformly disperse, the difference in foaming state in every injection is minimized.  
      The temperature of the melt is adjusted to a temperature lower than the decomposition temperature of the blowing agent to inhibit the foaming at the time of measuring, and raised to the decomposition temperature of the blowing agent or higher at the time of the passage to the injection nozzle or immediately before the injection into the mold to allow the melt to rapidly foam in the mold after the injection by the gaseous component generated by the decomposition of the blowing agent at the time of the passage to the injection nozzle (immediately before the injection into the mold). Therefore, the reheating of the mold to the decomposition temperature of the blowing agent or higher is dispensed, and the productivity is enhanced.  
      Although the present invention is described with the preferred embodiments, the present invention is not limited to these embodiments, and various changes are possible within the technical range of the present invention.  
      For example, a shutter member may be provided in the hopper and the feed port part of the barrel connected thereto to intermittently supply the melt from the hopper to the barrel. According to this, the addition of the thickener and the blowing agent in the specified percentages to the melt stored in the hopper can be facilitated.  
      In the method for injection foaming molding using the apparatus for injection foaming molding  40  according to the embodiment, the primary measurement is performed in the storage part  46  formed in the front portion of the barrel  47  by retreating the screw  44 , and the melt  2  is introduced to and measured in the measuring part  49 , which is formed in the front portion within the cylinder  42  by retreating the plunger  48 , from the barrel  47  through the communicating passage  41  by protruding the screw  44 . However, the melt  2  may be introduced to and measured in the measuring part  49 , which is formed by retreating the plunger  48  while rotating the screw  44  without retreating successively to the agitation by the screw  44 . According to this, the screw hydraulic cylinder  56  can be dispensed to simplify the device structure, and the primary measuring operation can be omitted.  
      A pressure detection means such as a pressure gauge or pressure sensor may provided in the hydraulic circuit of the screw hydraulic cylinders  21  and  56  and the plunger hydraulic cylinder  57  to detect the back pressure generated in the screw or plunger  48  at the time of raising the temperature of the melt to the decomposition temperature of the blowing agent or higher. According to this, the temperature rising state of the melt  2  or the decomposition degree of the blowing agent can be estimated from the change in the back pressure accompanied by the temperature rise of the melt  2 .  
      By detecting the change in the back pressure, the pressure of the hydraulic cylinder can be controlled by use of the detection value as a control parameter to control the foaming state of the melt  2 . Namely, when the melt  2  is controlled in such a manner that the melt  2  is partially foamed before injection, the partially foamed melt  2  is pressured to inhibit the further foaming, and the resulting melt  2  is injected into the mold  24 , whereby the unfoamed part is suddenly foamed in the mold  24 , the melt  2  before the injection (at the time of measuring) can be controlled to a desired foaming state. The partial foaming of the melt  2  may be performed not by the pressure control of the hydraulic cylinder but by the position control of the hydraulic cylinder.  
      Although the present invention is described in the above preferred embodiments, the present invention is not restrictive to these embodiments. The present invention will be understood to include various other embodiments without departing from the spirit and scope of the present invention.  
     INDUSTRIAL APPLICABILITY  
      According to the method for injection foaming molding and apparatus for injection foaming molding of the present invention, since the melt is adjusted to the decomposition temperature of the blowing agent or higher and inhibited to foam by pressuring at least immediately before injection, the difference in foaming state between batches is minimized. Since the capacity in the measuring part is made constant although the decomposition of the blowing agent is caused immediately before the injection, the melt is inhibited to foam in the pressured state. Therefore, since the melt releases the pressure at once in the mold immediately after the injection to foam, the melt spreads into every corner of the mold. Accordingly, the transfer property to the mold is enhanced to enable the formation of a foaming molded article of a complicated shape. Since the heating of the mold to the decomposition temperature of the blowing agent or higher is dispensed, the productivity is improved.