Patent Publication Number: US-6666258-B1

Title: Method and apparatus for supplying melted material for injection molding

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an injection molding method and apparatus, and more particularly to a method and apparatus for manufacturing metallic parts by injection molding using a separate ingot melt furnace and feeder. 
     2. Description of the Related Art 
     Injection molding is a known method used to produce molded metallic parts from melted metal. A conventional injection molding apparatus  1  is illustrated in FIG.  1 . In an injection molding method using apparatus  1 , metal ingots or particles  3  are supplied directly to a melt feeder or hopper  5  in the solid state. The ingots  3  settle to the bottom of the melt feeder  5 , and rest on a filter  7 , such as a grate, while they are melted by heaters  9 . The melted metal  11  is then released into an injection chamber  13 . The melt feeder  5  contains a pipe  15  which supplies an inert protective gas, such as argon or nitrogen, to the melt feeder to drive out any air which may have become trapped in the molten metal  11 , as described for example in U.S. Pat. No. 5,501,266, incorporated herein by reference in its entirety. The molten metal  11  is then injected into a mold cavity  17  by a piston or plunger  19 . The piston may have a shape of a rod or a screw extending throughout the length of the injection chamber  13 , past the opening to the feeder  5 , as described in U.S. Pat. No. 5,501,266. The metal  11  solidifies in the mold cavity  17  to form the molded metallic part. However, this prior art method and apparatus suffer from several disadvantages. 
     The melt feeder  5  must contain a certain minimum volume of the molten metal  11  in order to allow a continuous, uninterrupted operation of the injection molding apparatus  1 . Thus, the melt feeder  5  must have a minimum height in order to hold at least the minimum volume of the molten metal  11 . For example, the melt feeder  5  should have a height of about four feet in order to ensure the uninterrupted operation of the apparatus  1 . 
     A delivery system, such as a conveyor  21  or a downwardly sloped surface, which delivers the ingots or pellets  3  to the melt feeder  5  is located above the melt feeder, as illustrated in FIG.  1 . The ingots  3  are dropped into the melt feeder  5  by the delivery system  21  from a relatively large height, such as 4-5 feet. The drop causes the ingots  3  to create a splash on contact with the molten metal  11  present in the melt feeder  5 . The splashed molten metal hits the upper portions of the metal feeder  5  and the pipe  15  and solidifies as plaque  23 , because the upper portions of the melt feeder  5  and the pipe  15  are maintained at a lower temperature than the lower portions of the melt feeder for safety reasons. This is particularly true for a metal such as magnesium which can easily catch fire when it contacts air surrounded by a wall of a higher temperature. 
     The plaque  23  blocks the egress from the pipe  15 , interfering with the delivery of the protective inert gas and forms thick deposits on the walls of the melt feeder  5 , which requires expensive and time consuming maintenance to remove these deposits. The apparatus  1  has to be taken off line during maintenance, further increasing manufacturing expenses. The present invention is directed at overcoming or at least reducing these and other problems of the prior art. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention, there is provided a method of forming a molded object, comprising introducing solid material into a first chamber, melting the solid material in the first chamber, transferring the melted material from the first chamber into a second chamber, transferring the melted material from the second chamber into a third chamber, transferring the melted material from the third chamber into a mold cavity, and solidifying the melted material in the mold cavity to form the molded object. 
     In another aspect of the present invention, there is provided an injection molding apparatus, comprising a first chamber means for melting a solid material, a second chamber means for holding the melted material, a third chamber means for holding the melted material to be transferred into a mold cavity, a first conduit means for transferring the melted material from the first chamber means to the second chamber means, a second conduit means for transferring the melted material from the second chamber means to the third chamber means, and a first piston means in the third chamber means for transferring the melted material from the third chamber means to a mold cavity. 
     In another aspect of the present invention, there is provided an injection molding apparatus, comprising a melt furnace suitable for melting a metal, a feeder suitable for holding the melted metal, an injection chamber containing a first piston and an injection nozzle, a first conduit connecting the melt furnace to the feeder, and a second conduit connecting the feeder to the injection chamber. 
     In another aspect of the present invention, there is provided an injection molding apparatus, comprising a melt furnace suitable for melting a metal, a screening element adjacent to a bottom of the melt furnace comprising at least one non-horizontal wall, a top and a melt furnace outlet on at least one wall, an injection chamber containing a piston and an injection nozzle, and a conduit connecting the melt furnace outlet to the injection chamber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in detail herein with reference to the drawings in which: 
     FIG. 1 is a schematic illustration of a side view of prior art injection molding system; 
     FIG. 2 is a schematic illustration of a side cross sectional view of an injection molding system according to one aspect of the first preferred embodiment of the present invention; 
     FIG. 3 is a schematic illustration of a back cross sectional view of the injection molding system according to another aspect of the first preferred embodiment of the present invention; 
     FIG. 4 is a schematic illustration of a back cross sectional view of the injection molding system according to a second preferred embodiment of the present invention; 
     FIGS. 5 and 6 are schematic illustrations of a back cross sectional view of the injection molding system according to one aspect of a third preferred embodiment of the present invention; 
     FIG. 7 is a schematic illustration of a side cross sectional view of a portion of the injection molding system according to the third preferred embodiment of the present invention; 
     FIGS. 8 and 9 are schematic illustrations of a side cross sectional view of the injection molding system according to alternative aspects of the third preferred embodiment of the present invention; 
     FIGS. 10,  11  and  13  are schematic illustrations of a side cross sectional view of preferred mounting configurations of the melt furnace of the injection molding system of the preferred embodiments of the present invention; 
     FIG. 12 is a schematic illustration of a side cross sectional view of a referred drive actuator for mounting configurations of FIGS. 10 and 11; 
     FIGS. 14,  16  and  18  are schematic illustrations of a top view of three referred conduits connecting the melt furnace and the feeder; 
     FIGS. 15,  17 ,  19  and  20  are schematic illustrations of close up side views of the three preferred conduits illustrated in FIGS. 14,  16  and  18 . 
     FIG. 21 is a schematic illustration of a side cross sectional view of a delivery system according to one aspect of the present invention; 
     FIG. 22 is a schematic illustration of a top cross sectional view of a delivery system according to another aspect of the present invention; 
     FIG. 23 is a schematic illustration of a side cross sectional view of a delivery system according to another aspect of the present invention; 
     FIGS. 24 and 25 are schematic illustrations of a side cross sectional view of alternative aspects of the delivery system illustrated in FIG. 23; 
     FIGS. 26-29 are schematic illustrations of a top view of delivery systems according to alternative aspects of the present invention; 
     FIG. 30 is a schematic illustration of a side perspective view of a delivery system according to another alternative aspect of the present invention; 
     FIG. 31 is a schematic illustration of a side cross sectional view of a delivery system containing an elevator; 
     FIG. 32 is a schematic illustration of a side cross sectional view of a preferred injection system containing an injection chamber and a barrel; 
     FIG. 33 is a schematic illustration of a side cross sectional view showing one embodiment of a valve on the ram when it is in the position that prevents melted metal from flowing to positions to the right of the valve; 
     FIG. 34 is a schematic illustration of a side cross sectional view showing one embodiment of a valve on the ram when it is in the position that permits melted metal to flow from the right of the valve to positions to the left of the valve; 
     FIG. 35 is a schematic illustration of a side cross sectional view showing one embodiment of a valve when it is not fitted onto the ram; 
     FIG. 36 is a schematic illustration of a front cross sectional view showing one embodiment of a valve when it is not fitted onto the ram. 
     FIG. 37 is a schematic illustration of a side cross sectional view of an injection molding system according to another aspect of the first preferred embodiment of the present invention. 
     FIGS. 38 and 39 are schematic illustrations of side cross sectional views showing a preferred embodiment of a check valve. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present inventor has discovered that plaque formation in the feeder may be reduced or even completely avoided if the metal is supplied to the feeder in a melted state. Preferably, the melted metal is supplied to the feeder in a liquid state. However, while less preferred, the metal may be supplied to the feeder in a thixotropic state. 
     The term “feeder” means any chamber that receives the metal in a melted state, preferably in a liquid state, and that supplies the melted metal to an injection chamber, either directly, or via an intermediary chamber, such as a temperature controlled barrel. The “feeder” is different from the prior art “melt feeders” which receive the metal in the solid state (i.e., metal ingots or pellets) and which are used to melt the supplied solid metal ingots or pellets. The melted metal in the feeder is not disturbed by the dropping of the solid ingots or pellets into it. 
     Preferably, during operation of the injection molding apparatus, the volume of the melted metal in the feeder exceeds the amount of melted metal injected into a mold with each injection stroke by at least a factor of two. While not required, the feeder may be a chamber that is adapted to supply a constant flow of melted metal toward the injection chamber to allow a substantially uninterrupted operation of the injection molding apparatus, where the flow may be interrupted by the injection stroke of an injection piston or plunger or other elements in the injection molding apparatus. 
     In order to avoid or reduce plaque formation in the feeder and to supply the metal in the melted state to the feeder, the solid metal raw material, such as one or more metal ingots or pellets, is preferably supplied to a melt furnace, where it is melted (i.e., converted to a liquid or a thixotropic state). The melted metal is then supplied from the melt furnace to the feeder. A “melt furnace” means any chamber where a metal may be melted. For example, the melt furnace may be a tank or a pot surrounded by resistive heating elements which heat the metal inside the pot above the melting point of the metal. Alternatively, the melt furnace may be a chamber where the metal is melted by the application of heat from a gas burner, by an application of an electromagnetic field to the metal (i.e., inductively, etc.), by an application of an arc discharge to the metal or by irradiation of the metal with a laser. 
     1. The Injection Molding Apparatus  101   
     FIG. 2 illustrates an injection molding apparatus  101  according to a first preferred embodiment of the invention. The apparatus  101  contains a feeder  105 . The feeder preferably contains a check valve  106 . The feeder may also contain a filter  107 , if desired. However, unlike the prior art, a filter is not necessary since the metal is supplied to the feeder  105  in a melted state. The feeder contains heating elements  109 , such as resistive or inductive heaters, which maintain the melted metal  111  in a liquid or a thixotropic state. The heating elements  109  may be disposed in the walls of the feeder  105 , on the outer surface of the feeder  105  or adjacent to the feeder  105 . The feeder  105  also preferably contains a pipe, inlet or opening  115  which supplies an inert protective gas, such as argon, nitrogen, SF 6  and/or CO 2 , to the feeder  105  to drive out any air which may have become trapped in the molten metal  111 . However, the protective gas inlet may be omitted, if desired. Preferably, the top of the feeder is covered to prevent spillage of melted metal during an injection step which causes the feeder to move forward. 
     The feeder  105  preferably contains at least a certain minimum volume of the molten metal  111  in order to allow substantially continuous, uninterrupted operation of the apparatus  101 . 
     The apparatus  101  also contains an injection chamber  113 . The molten metal  111  is transferred from the feeder  105  to the injection chamber  113 , either directly thorough an opening or through an intermediate chamber. The injection chamber is preferably surrounded by resistive or inductive heaters  109  which are used to maintain the melted metal  111  in the liquid or thixotropic state within the injection chamber  113 . The injection chamber  113  is illustrated in FIG. 2 as being positioned horizontally. However, the injection chamber  113  may be positioned vertically or at any desired angle of inclination. 
     The injection chamber  113  contains a piston or a plunger  119  which is used to inject the melted metal  111  from the injection chamber  113  into a mold cavity  117 . When the piston  119  retracts, the check valve  106  opens and allows the melted metal  111  to flow into the injection chamber  113  from the feeder  105 . When the piston  119  moves forward to inject the melted metal  111  into the mold cavity  117 , the check valve  106  closes to prevent a portion of the melted metal  111  from flowing back into the feeder  105  from the injection chamber  113 . Thus the use of the check valve  106  allows the amount of the shot (i.e., the volume of melted metal) injected into the mold cavity  117  to remain relatively constant with each injection stroke of the piston  119 . 
     As shown in FIG. 2, the piston  119  has a shape of a thick rod having a diameter that is slightly less than the inner diameter of the injection chamber  113 . However, the piston may have other shapes, if desired. For example the piston  119  may have a “T” shape comprising a rod having a diameter substantially smaller than the inner diameter of the injection chamber  113 , supporting a plunger surface having a diameter that is slightly less than the inner diameter of the injection chamber  113 . Alternatively, the piston  119  may comprise a screw which meters and advances forward the melted metal  111  flowing in from the feeder  105  and having a tip which injects the melted metal  111  into the mold cavity  117 . 
     2. The Melt Furnace  125   
     Unlike the prior art apparatus shown in FIG. 1, the apparatus of a preferred embodiment of the present invention contains a melt furnace  125 , as illustrated in FIG.  2 . The solid metal ingots or pellets  103  are delivered into the melt furnace  125  by a delivery system  121 , such as a conveyor or a downwardly sloped surface. Alternatively, the metal ingots or pellets  103  may be placed into the melt furnace  125  manually, if desired. 
     In a preferred aspect of the present invention, the melt furnace  125  contains an outlet screening element  126 . For example, as illustrated in FIG. 2, the screening element  126  may comprise at least one non-horizontal wall  130 , a top cover or portion and an outlet port  132 . Preferably, the melt furnace outlet port  132  is located in one of the walls instead of in the top of the screening element  126 . The screening element  126  may contain one wall if the element  126  has a cylindrical shape or plural walls if the element  126  has a polygonal shape. Furthermore, the non-horizontal wall  130  is preferably exactly vertical or substantially vertical (i.e., deviating by about 1-20 degrees from vertical). The screening element  126  prevents solid metal pellets or ingots  103  as well as other residue present in the melted metal  111  from clogging the outlet port  132 . Metal ingots  103  may sink to the bottom of the melt furnace  125  and lie flat. This positioning of the ingots is not desirable because the ingots may substantially block melted metal  111  flow from the melt furnace  125 . The vertical walls  130  prevent the ingots  103  from lying across the outlet port  132 . Furthermore, various residue accumulates on the bottom of the melt furnace  125 . By placing the outlet port  132  above the bottom of the melt furnace, the residue located on the bottom of the melt furnace does not clog the outlet port  132 . However, the screening element  126  may be omitted, if desired. 
     In an alternative aspect of the present invention, the screening element  126  may comprise a filter, such as a grate or a screen, containing opening(s) large enough for liquid or thixotropic melted metal  111  to pass through, but small enough to prevent the unmelted solid metal pellets or ingots  103  from passing into the outlet port  132 . 
     In another alternative aspect of the present invention, the screening element  126  may also comprise at least one substantially vertical containment rod. The rod(s) may be of any shape, as long as they prevent the sinking ingots  103  from laying flat across the outlet port  132  and blocking it. 
     The melt furnace  125  is connected to the feeder  105  by a conduit  127 , as illustrated in FIG.  2 . Preferably, the conduit  127  is a pipe having a sufficient inner diameter to deliver melted metal  111  from the melt furnace  125  to the feeder  105 . The preferred inner diameter of the conduit is 25-45 mm, most preferably 40 mm. The melt furnace  125  also contains heating elements  129 , such as resistive or inductive heaters, which maintain the melted metal  111  in a liquid or thixotropic state. The heating elements  129  may be disposed in the walls of the melt furnace  125 , on the outer surface of the melt furnace  125  or adjacent to the melt furnace  125 . 
     The melt furnace  125  may comprise any chamber where a metal may be melted. For example, the melt furnace may be a pot surrounded by resistive heating elements which heat the metal inside the pot above the melting point of the metal. The melt furnace  125  may be made of any material suitable for melting a metal. For example, the melt furnace may be made of iron or high temperature ceramic for melting magnesium alloy ingots or pellets. 
     Preferably, the melt furnace  125  has a larger volume than the feeder  105 . For example, in one preferred aspect of the present invention, the feeder  105  contains an amount of melted metal  111  sufficient for one to three injection shots, while the melt furnace  125  contains an amount of melted metal  111  sufficient for four to fifty injection shots. The feeder  105  and melt furnace  125  may have any dimensions sufficient to produce an injection molded article. For example, the feeder  105  may be about 20 cm high and about 20 cm wide and the melt furnace  125  may be 50 to 70 cm high and about 100 cm wide. However, other dimensions could be used if desired. 
     The melted metal  111  flowing from the melt furnace  125  into the feeder  105  in FIG. 2 causes substantially less or no splashing than the solid ingots  3  which are dropped directly into the melted metal  11  in the feeder  5  in the prior art apparatus  1 , illustrated in FIG.  1 . Thus, very little or no plaque  23  builds up in the feeder  105  of the preferred embodiment of the present invention. The addition of the melt furnace  125  is also advantageous because it decreases the amount of air entrapped into the melted metal  111  injected into the mold cavity  117 . Since the metal is supplied to the feeder  105  in the melted state through a conduit  127 , the feeder  105  may be entirely enclosed from the outside atmosphere. In contrast, the melt feeder  5  in the prior art apparatus  1  is open to the outside atmosphere in order to receive the solid ingots or pellets  3 . This allows air to enter the melt feeder  5  and eventually wind up in the molded metal part in the mold cavity  17 . 
     There may be one melt furnace  125  for each feeder  105  as illustrated in FIG. 2, or there may be one melt furnace  125  connected to plural feeders  105  by plural conduits  127 . The melt furnace  125  may be detachable from the remaining portions of the apparatus  101 , such that the plaque build up may be removed from the melt furnace  125  without taking the remaining injection molding apparatus off-line. In this aspect of the invention, there may be plural melt furnaces  125  connected to one or more feeders  105  to allow one melt furnace to be taken off line, for servicing or repair, without taking any injection molding apparatus  101  off-line with it. 
     As shown in FIG. 2, the melt furnace  125  is located above the feeder  105 , in order to feed the melted metal  111 , preferably in the liquid state, into the feeder  105  by the force of gravity through the conduit  127 . Alternatively, as illustrated in FIG. 3, the melt furnace  125  may be located off to one side of the feeder  105 . 
     Furthermore, the conduit  127  is illustrated as entering the top of the feeder  105  in FIG.  2 . However, in another aspect of the present invention, the conduit  127  may enter the side of feeder  105 , above or below the operational level (i.e. fill line) of the melted metal  111 , as illustrated in FIG.  3 . This arrangement of the conduit  127  and the feeder  105  is advantageous because the melted metal  111  enters the feeder  105  either near or below the fill line of the feeder, further minimizing the splashing of the melted metal  111  present in the feeder  105 . 
     In an alternative aspect of the present invention, a check valve  128  may be placed in or adjacent to the conduit  127  to meter or control the amount of melted metal  111  being supplied to the feeder  105 , as illustrated in FIG.  3 . The check valve  128  may be opened by a controller, such as a computer or a microprocessor, intermittently (i.e., after each forward stroke of the first piston  119 , etc.) or in response to a low melted metal volume signal from a level sensor in the feeder  105 . 
     Alternatively, the melt furnace  125  may also have a lower region with a bottom surface that is at a lower position than the outlet port  132 . The ingots  103  will melt in the lower region without blocking the outlet port  132 . For example, the conduit  127  inlet may be located on the side of the melt furnace  125  to prevent the ingots  103  and residue from blocking the outlet port  132 , as illustrated in FIG.  4 . 
     According to a second preferred embodiment of the present invention, the melted metal  111  is drawn from the melt furnace  125  into the feeder  105  by suction. In one aspect of the second embodiment, the suction is created by a pump  131 . As illustrated in FIG. 4, the pump  131  is located in fluid communication with the conduit  127  in order to create the suction or pumping force necessary to draw the melted metal, preferably in the liquid state, from the melt furnace  125  into the feeder  105 . In this aspect of the present invention, the melt furnace  125  may be located below or level with the feeder  105 . The suction of the pump is sufficient to draw the melted metal upwards through the conduit  127 . However, the melt furnace  125  may be located above the feeder  105 , as illustrated in FIG.  2 , if desired. In this case, the melted metal  111  is drawn into the feeder  105  by suction from the pump  131  and/or by the force of gravity. Furthermore, the conduit  127  may be located on the side of the feeder  105 , above or below the melted metal  111  fill line or on the top of the feeder  105 . 
     The pump  131  may operate continuously or intermittently. For example, the pump  131  may be turned on by a controller, such as a computer or a microprocessor, when a level sensor in the feeder  105  indicates that the level of melted metal  111  in the feeder  105  needs replenishing. Alternatively, the pump  131  may be activated with each injection stroke of the first piston  119  to replenish the supply of melted metal  111  in the feeder  105  after each injection stroke. 
     3. The Second Piston  133   
     According to a third preferred embodiment of the present invention, the melted metal  111  is injected into the feeder  105  from the melt furnace  125 . In a preferred aspect of the third preferred embodiment, a second piston  133  is used to inject the melted metal  111 , preferably in a liquid state, into the feeder  105 . The second piston may have a “T” shaped illustrated in FIG. 5, or it may have any other desired shape, such as the thick rod shape of the first piston  119 . 
     As illustrated in FIG. 5, the second piston  133  is preferably located in a temporary holding chamber  135 , which is preferably separated from the melt furnace  125  by a check valve  137 . The valve  137  may be a spring mounted ball valve, as illustrated in FIG. 5, or a mechanical valve which is operated by a computer or another similar controller, which times the opening and closing of the valve with the upward and downward strokes of the second piston  133 . The spring (not shown) of the ball valve  137  may fixed such that the default position of the ball valve  137  is either an open or closed position, as desired. 
     The second piston  133  operates as follows. As illustrated in FIG. 5, the second piston  133  is first moved away from the inlet to the melt furnace  125  (i.e., moved upwards as indicated by the arrow) to create a suction in the temporary holding chamber  135 . The suction and/or a spring (if set to fix the default valve position to open) raises the ball valve  137 . The suction draws the melted metal  111  from the melt furnace  125  into the temporary holding chamber  135 . 
     After the second piston  133  is fully raised, it is rapidly moved forward to inject the melted metal  111  from the temporary holding chamber  135  through the conduit  127  and the inlet  139  into the melt feeder  105 , as illustrated in FIG.  7 . The force of the injected melted metal  111  and/or the spring (if set to fix the default valve position to close) forces the ball valve  137  to close the inlet to the temporary holding chamber  135 . If a mechanical valve is present instead of the ball valve  137 , then a controller times the opening and closing of such valve with the movement of the piston. Preferably, the same motor and controller are used to move the second piston  133  and to open and close the mechanical valve. 
     The melted metal  111  flows into the feeder  105  through inlet  139  connected to conduit  127 . The inlet  139  may comprise a simple pipe or opening extending into the feeder  105 . Alternatively, the inlet  139  may comprise an inlet chamber  141  and a metering nozzle  143  as illustrated in FIG.  7 . The metering nozzle  143  is preferably a narrow opening which limits the amount of melted metal  111  flowing into the feeder  105 . A dose of melted metal  111  is first injected by the second piston  133  into the wider portion of the inlet chamber  141 . The melted metal then slowly drips out into the feeder  105  through the nozzle  143  until a subsequent dose of melted metal  111  is injected by the second piston  133 . The nozzle  143  prevents the high velocity molten metal  111  injected by the second piston  133  from directly impacting the molten metal  111  already present in the feeder  105 . Thus, the nozzle  143  prevents or reduces splashing and plaque buildup in the feeder  105 . 
     As illustrated in FIGS. 5 and 6, the second piston  133  alone is used to transfer the melted metal  111  into the feeder  105 . Alternatively, the second piston  133  may be supplemented and/or replaced by a pump located in communication with the conduit  127  and/or the temporary holding chamber  135 , if desired. Furthermore, while the melt furnace  125  is illustrated in FIGS. 5 and 6 as being located below the feeder  105 , the melt furnace  125  may be located above (or level with) the feeder such that gravity assists in forcing the melted metal  111  into the feeder  105 , if desired. 
     The temporary holding chamber  135  is illustrated as being vertical in FIGS. 5-6. However, the temporary holding chamber  135  may be positioned inclined at any angle. For example, as illustrated in FIG. 8, the temporary holding chamber  135  is placed horizontally. The second piston  133  in this case also moves horizontally, and the melted metal  111  enters the temporary holding chamber  135  through a temporary holding chamber inlet  145 . 
     This arrangement is advantageous if the injection chamber  113  is also located horizontally. Thus, both the first piston  119  and the second piston  133  move parallel to each other, as illustrated by the arrows in FIG.  8 . Thus, if desired, both pistons  119 ,  133  may be actuated by the same motor  147  and the injection and suction strokes of both pistons  119 ,  133  are synchronized because they correspond the same impulse generated by the motor  147 , as shown in FIG.  9 . The injection process is simplified because a separate motor and/or a separate set of control instructions are not necessary to actuate the movement of the second piston  133 . 
     If the injection chamber  113  is positioned vertically, then it is preferable to also position the temporary holding chamber  135  vertically as shown in FIGS. 5-6 in order to actuate both pistons  119 ,  133  in the same direction with the same motor  147 . However, the first and second pistons may move in perpendicular directions, actuated by the same motor  147 , when the injection chamber  113  and temporary holding chamber  135  are positioned perpendicular to each other (i.e., one is vertical and the other is horizontal). 
     4. The Melt Furnace Support 
     The melt furnace  125  is preferably mounted in a frame  149 , as illustrated in FIG.  10 . The melt furnace  125  is illustrated as being located behind the injection chamber  113  for clarity. However, the melt furnace  125  may be located along the side, in front, below and/or above the injection chamber  113 , as desired. 
     The injection chamber  113  and the feeder  105  may be slidably mounted, such as on bearings, wheels and/or rail(s), to allow for forward movement of the injection chamber during the forward stroke of the first piston  119 . In a fourth preferred embodiment of the present invention, the frame  149  may also be slidably mounted on wheels or bearings  153  that slide back and forth on a rail or in a groove  151 , as illustrated in FIG.  10 . Alternatively, the frame  149  may be omitted and the melt furnace  125  may be directly mounted on the wheels or bearings  153 . Furthermore, the rail or groove  151  may be omitted, and the wheels or bearings  153  may roll on a flat supporting surface instead. Furthermore, the melt furnace  125  may contain splash guards (not shown) to prevent metal splashing during the movement of the melt furnace  125 . 
     The melt furnace  125  and/or the frame  149  are preferably coupled to the feeder  105  and/or the injection chamber  113  to avoid rupturing the conduit  127  during each forward jump of the feeder/injection chamber with each forward stroke of the first piston  119 . Any known coupling scheme may be used. For example, if the conduit  127  is a strong, rigid pipe, then the feeder  105  may be coupled to the melt furnace  125  solely by the conduit  127 . Alternatively, if the conduit  127  is flexible or not sufficiently strong, then the feeder  105  and/or the injection chamber  113  may be coupled to the melt furnace  125  and/or the frame  149  by a coupling element(s), such as a rigid bar, a chain or a metal wire. The melt furnace  125  and/or the frame  149  coupled to the feeder  105  and/or the injection chamber  113  move in tandem with each forward stroke of the first piston  119 . 
     In a preferred aspect of the present invention, the melt furnace is coupled to a drive actuator  155 , as illustrated in FIG.  11 . The drive actuator may be for example, a screw  157 , which rotates forward in a thread and exerts a forward force on the frame  149  and/or the melt furnace  125 , as illustrated in FIG.  12 . Preferably, the same motor  147  actuates the forward movement of the first piston  119  and the drive actuator  155 , as illustrated in FIGS. 11 and 12. This allows the melt furnace  125  and/or the frame  149  to move forward with each forward stroke of the first piston  119  (and thus each forward jump of the injection chamber  113  and feeder  105 ) without using a separate motor or a separate controller. However, the drive actuator  155  may be actuated by a different motor and/or controller than the first piston  119 , if desired. 
     In another preferred aspect of the present invention, the second piston  133  is actuated by the same motor  147  and/or controller as the drive actuator  155  in order to simplify the injection molding process. In yet another preferred aspect of the present invention, the same motor  147  and/or controller is used to actuate the first piston  119 , the second piston  133  and the drive actuator  155  in order to further simplify the injection molding process. In this aspect, the first piston  119 , the second piston  133  and the melt furnace  125  and/or frame  149  are synchronized to move forward and backward at the same time, as illustrated in FIG.  11 . However, first piston  119 , the second piston  133  and the drive actuator  155  may be actuated by a different motor and/or controller, if desired. Furthermore, the second piston and chamber  135  may be completely omitted in the fourth and fifth preferred embodiments and suction and/or gravity feeding may be used instead, if desired, as illustrated in FIG.  24 . 
     In a fifth preferred embodiment of the present invention, the melt furnace  125  and/or the frame  149  are rigidly mounted to a supporting surface. For example, the frame  149  may be rigidly mounted to the supporting surface  159  by mounting element(s)  161 , such as bolts, rigid bars or welds, as illustrated in FIG.  13 . Rigid mounting decreases metal splashing from the melt furnace  125  because the melt furnace does not move during an injection stroke. Alternatively, the frame  149  may be omitted, and the melt furnace  125  may be directly mounted on the support surface  159 . Furthermore, the temporary support chamber  135  may be rigidly mounted to the support surface  159  or slidably mounted to the frame  149  or the support surface  159  to account for the forward stroke of the second piston  133 . 
     5. The Conduit  127   
     The conduit  127  may comprise any element that can transfer melted metal  111  from the melt furnace  125  to the feeder  105 . Preferably, the conduit  127  comprises a pipe or tube of a suitable inner diameter and material. The preferred inner diameter is 25-45 mm, the most preferred inner diameter is 40 mm. The conduit may be made of any temperature resistant and/or corrosion resistant material, such as temperature and/or corrosion resistant iron. The pipe may be a rigid pipe, such as that illustrated in FIGS. 10-11. Alternatively, the conduit  127  may comprise a flexible or a rotatable pipe, especially if the melt furnace  125  and/or frame  149  are rigidly mounted to the support surface as illustrated in FIG.  13 . However, the flexible or rotatable pipe may also be used in the fourth preferred embodiment illustrated in FIGS. 10-11. The conduit is connected to the melt furnace  125  in the first and second preferred embodiments (FIGS. 24) or to the temporary holding chamber  135  in the third preferred embodiment (FIGS.  5 - 9 ). Thus, while the following discussion is directed to the flexible or rotatable mounting of the conduit  127  to the melt furnace  125 , the conduit may actually be mounted to the temporary holding chamber  135 , if present. 
     FIGS. 14 and 15 illustrate a flexible conduit  127  according to the sixth preferred embodiment of the present invention. The flexible conduit comprises a pipe that bends sideways upon the application of a stress. For example, as illustrated in FIG. 14, when the injection chamber  113  and the feeder  105  move forward (illustrated with dashed lines) with each forward stroke of the first piston  119 , the melt furnace  125  and the frame  149  remain stationary. The disparate movement of the elements connected by the conduit  127  places a tensile stress on the conduit  127 . However, since the conduit  127  is bendable, it bends sideways, as illustrated in FIGS. 14 and 15. 
     Alternatively, the conduit  127  may comprise a rotatable pipe according to a seventh preferred embodiment of the present invention. Any elements that impart rotational movement to the conduit  127  may be used. In one aspect of the seventh preferred embodiment, the conduit  127  may comprise two pipe portions joined by a swivel elbow  163 , as illustrated in FIGS. 16 and 17. The swivel elbow  163  may comprise a rotatable joint attached to ends of both pipe portions. 
     In another aspect of the seventh preferred embodiment, the conduit  127  may be joined to a rotatable conduit portion  165 , as illustrated in FIGS. 18-20. For example, the rotatable conduit portion  165  may comprise a pipe having a diameter that is greater than or less than that of pipe portion  127  in FIG.  19 . When slidably mounted over or into the pipe  127 , the rotatable pipe portion  165  may swivel around its axis, as illustrated in FIG.  19 . The slidable mounting may comprise low friction mounting or ball bearing mounting (i.e., ball bearings may be placed between the pipe portions  127  and  165  to enhance the axial rotation of pipe portion  165 ). Alternatively a motor driven gear  167  may be used to rotate the rotatable conduit portion  165 , as illustrated in FIG.  20 . The rotation of the gear  167  forces the conduit portion  165  to rotate in the opposite direction, as illustrated by the arrows in FIG.  20 . The gear  167  may be driven by a separate motor  169 , which is synchronized by a controller  171  to the movement of the first piston  119 , as illustrated in FIG. 18, or by the same motor  147  used to drive the piston  119 . Furthermore, the gear  167  may be used to rotate the swivel elbow  163  illustrated in FIGS. 16-17 instead of the pipe portion  165  illustrated in FIG.  20 . 
     For example, as illustrated in FIGS. 16 and 18, when the injection chamber  113  and the feeder  105  move forward (illustrated with dashed lines) with each forward stroke of the first piston  119  around a circumference of an imaginary circle with a center at the melt furnace  125 , the melt furnace  125  and/or the frame  149  remain stationary. The disparate movement of the elements connected by the conduit  127  places a tensile stress on the conduit  127 . However, since the conduit  127  is rotationally flexible or rotatable, it rotates without tearing or rupturing, as illustrated in FIGS. 16 and 18. 
     Alternatively, instead of portions of the conduit  127  rotating with respect to each other as described above, the entire conduit  127  may rotate around the melt furnace  125 . For example, the conduit  127  may be attached to a rotatable band around the melt furnace  125  and/or the frame  149 . Alternatively, the melt furnace  125  may rotate about its center point in the frame  149  or the frame  149  may be rotatably mounted to the support surface to rotatably mount the conduit  127  to prevent its rupture with the movement of the feeder  105  and the injection chamber  113 . 
     If desired, the conduit  127  may be both flexible as illustrated in FIGS. 14-15 and rotatable, as illustrated in FIGS. 16-20. Furthermore, the use of a flexible or rotatable conduit has been described below with the use of a stationary (rigidly mounted) melting furnace  125 . However, the flexible or rotatable conduit may also be used with the slidably mounted melting furnace  125  illustrated in FIGS. 10 and 11. 
     6. The Ingot Delivery System 
     In order to further minimize splashing and plaque formation in the melt furnace  125 , the melt furnace may optionally contain a downward sloping ingot or pellet delivery surface  173 , according to one preferred aspect of the present invention illustrated in FIG.  21 . For example, the ingots or pellets  103  delivered by a delivery system, such as a conveyor  121  or an elevator, are placed directly on the downward sloping surface  173 , and gently slide into the melted metal  111  present the melt furnace  125  under the force of gravity without substantial splashing. The surface  173  may be inclined at an angle of 10-80 degrees with respect to the side wall  175  of the melt furnace  125 . The melted metal  111  fill line may be above, at or below the point where the side wall  175  and sloping surface  173  come in contact. 
     7. The Preheating Chamber 
     An example of a delivery system according to another preferred aspect of the present invention is illustrated in FIG.  22 . While the delivery system of this aspect may be used to deliver metal pellets, preferably the system of this aspect is used to deliver metal ingots. The ingots  103  are delivered toward the melt furnace  125  on a first conveyor belt  121 . A push arm  177  controlled by a conventional motor  179  pushes the ingots  103  into an ingot holding or preheating chamber  181 . The push arm has a size sufficient to completely cover the opening to the holding chamber. The push arm  177  can form an air tight seal with the opening into the holding chamber  181 , if desired. The ingots  103  inside the holding chamber  181  end up on a downward sloping surface (e.g. inclined surface)  173 . The ingots  103  then either slide into the melt furnace  125  under the force of gravity, or a third motor controlled piston  183  pushes the ingots  103  into the melt furnace  125 . 
     The holding chamber is preferably maintained under an inert, protective gas ambient, supplied from one or more gas ports or inlets  185 . The gas may be argon, nitrogen, sulfur hexafluoride, carbon dioxide or a mixture of these gasses. The gas pressure in the holding chamber  181  should preferably be maintained at a pressure above one atmosphere to prevent outside air, which contains oxygen, from reaching the melt furnace  125 . The gas pressure and/or the position of the ingots may be monitored by one or more sensors  187 . The controlled atmosphere in the holding chamber  181  allows a decreased amount of air in the melt furnace  125  and the feeder  105  and thus decreases a chance of explosion. 
     Furthermore, the holding chamber  181  may be heated by one or more heaters to 100-200° C. to evaporate the moisture from the ingots  103  before they enter the melt furnace  125 . The delivery system may also contain a second conveyor belt  189  in addition to the first conveyor belt  121  described above, to deliver the ingots  103  from an input source, such as an elevator to the first conveyor  121 . 
     FIG. 23 shows a side view of a loading system according to another preferred aspect of the present invention. While the delivery system of this aspect may be used to deliver metal pellets, preferably the system of this aspect is also used to deliver metal ingots. The ingots  103  are transported on a conveyor  121  to an ingot holding or preheating chamber  181 , which may contain the downward sloping surface  173 , if desired. Alternatively, downward sloping surface  173  may be omitted and the conveyor  121  may stretch through the holding chamber  181  all the way to the entrance to the melt furnace  125 . Furthermore, the conveyor  121  may also be downwardly sloped in the holding chamber  181 . The chamber  181  may be heated by heaters  191  to 100-200° C. to evaporate moisture on the surface of the ingots  103 , if desired. 
     The melt furnace  125  may contain a melted metal level sensor  197 , if desired. The sensor  197  is connected to a controller which starts and stops the conveyor  121  and/or other delivery system elements depending on the level of the melted metal  111  in the melt furnace. The conduit  127  is omitted from FIG. 23 for clarity. 
     If desired, the melt furnace  125  and/or the holding chamber  181  may also contain a protective gas port(s) or inlet(s)  115 ,  185  respectively. The inert, protective inert gas, such as at least one gas selected from a group comprising nitrogen, argon, SF 6  and CO 2 , may be introduced under pressure from a pressurized tank. The gas pressure of the pumped gas is preferably above one atmosphere to keep air from entering the melt furnace  125  through holding chamber  181 . 
     Access to the holding chamber  181  is preferably controlled by a first door  193 . Egress from the holding chamber is preferably controlled by a second door  195 . The holding chamber  181  operates as follows. First, door  193  is opened as ingot  103  approaches it. Door  193  can preferably be opened by moving up, down or sideways through the walls of chamber  181 , or in or out of the chamber  181 . The first door  193  is closed as the ingot  103  enters the chamber  181 . After the first door  193  is closed, the second door  195  is opened and the ingot  103  moves out of chamber  181  and into the melt furnace  125 . The conveyor  121  can move continuously up to or through chamber  181  with doors  193  and  195  opened and closed while the conveyor is moving. Alternatively, the conveyor  121  moves intermittently. It stops when an ingot approaches door  193  and when the ingot  103  is inside the chamber  181 . This allows the doors  193 ,  195  to be sealed hermetically. 
     In another alternative aspect of the invention, the loading system shown in FIG. 22 can be used with door  193  of FIG. 23 positioned between conveyor  121  and chamber  181  and/or with door  195  of FIG. 23 positioned between the chamber  181  and the melt furnace  125 . Door  193  opens synchronously with the movement of the push arm  177 , while door  195  opens synchronously with the movement of the piston  183 . 
     In another aspect of the present invention, a vacuum pump  199 , shown in FIG. 24 may be placed in communication with the holding chamber  181 , between doors  193  and  195 . As the ingot  103  enters chamber  181 , both doors  193 ,  195  are closed and the vacuum pump  199  creates a near vacuum in chamber  181 . Door  195  is then opened to release ingot  103  into melt furnace  125  without allowing substantially any air to enter melt furnace  125  because chamber  181  was at near vacuum when door  195  is opened. Furthermore, if desired, pump  199  may be omitted and a single vacuum pump  131 , illustrated in FIG. 4, may be placed in communication with both the conduit  127  and the holding chamber  181 . 
     In another aspect of the present invention, at least one inert gas screen  201  can be made to flow from inert gas source(s)  203  across chamber  181  into an inert gas outlet  205 , such as a suction pipe or vent, as shown in FIG.  25 . The inert gas screen(s)  201  keep air from entering the holding chamber  181  and the melt furnace  125 . The inert gas can comprise at least on gas selected from a group comprising argon, nitrogen, CO 2  and SF 6 . The screen(s)  201  may be located in the middle of chamber  181  or in front or behind one or both doors  193 ,  195 . The preferred location of the screens  201  is illustrated in FIG.  25 . 
     The inert gas screen(s)  201  of FIG. 25 may be used in combination with vacuum pump  199  of FIG. 24 to further decrease the amount of air penetrating into melt furnace  125 . Other air control measures, such as the protective gas inlets  115 ,  185 , doors  193 ,  195 , vacuum pump  199  and inert gas screen(s)  201  may all be used together to even further decrease the amount of air penetrating into melt furnace  125  to reduce the possibility of explosion. 
     8. Cover Plates  207 ,  213   
     FIGS. 26 and 27 show another alternative aspect of the present invention. In this aspect, a movable aperture plate  207  is located over the entrance to the melt furnace  125 . The plate  207  may be located between the melt furnace  125  and the conveyor  121  of FIGS. 2,  21  or between the melt furnace  125  and the holding chamber  181  of FIGS. 22-23. 
     FIG. 26 shows a top view of the delivery system where the access to the melt furnace  125  is closed. The movable aperture plate  207  contains an aperture  209  which is larger than an ingot  103 . When no more ingots should be added to the melt furnace  125 , the plate  207  is moved to one side by a moving element, such as a movable arm  211 , etc, such that the plate  207  covers the entrance or opening to the melt furnace  125 . In this position, the aperture plate  207  thus blocks the entrance of air into the melt furnace  125 . 
     As shown in FIG. 27, when it is desired to add additional ingots  103  into the melt furnace  125 , the plate  207  is moved such that the aperture  209  corresponds to the opening to the melt furnace  125 . The ingot(s)  103  coming off the conveyor  121  or sloped surface  173  pass through the aperture  209  into the melt furnace  125 . 
     FIGS. 28 and 29 show an alternative delivery system to that shown in FIGS. 26 and 27. As illustrated in FIG. 28, the system utilizes a movable cover plate  213  instead of a movable aperture plate  207 . The cover plate  213  may have any shape which is sufficient to cover the opening  215  to the melt furnace  125 . For example, the plate  213  may have a circular shape if the opening  215  to the melt furnace  125  is also circular. 
     FIG. 28 shows a top view of the delivery system where the entrance to the melt furnace  125  is closed. A moving element, such as a movable arm  211 , moves the cover plate  213  over the opening to the melt furnace  125  to block access of air and ingots  103  coming off the conveyor  121  or sloped surface  173 . 
     As shown in FIG. 29, when it is desired to add additional ingots  103  into the melt furnace  125 , the plate  213  is moved or raised up to expose the entrance or opening  215  to the melt furnace  125 . The ingots  103  coming off the conveyor  121  or the sloped surface  173  may drop directly into the melt furnace  125  through opening  215 . 
     In the aspect of the invention shown in FIGS. 26-29, the aperture plate  207  or the cover plate  213  is utilized instead of a push arm  177  and piston  183  shown in FIG.  22 . However, the aperture plate  207  or the cover plate  213  may be utilized in addition to the push arm  177  and piston  183 . In this case, the plate  207  or  213  would block access to ingots  203  sliding down the sloped surface  173 . Furthermore, elements  207  or  213 , while referred to as plates, may have other shapes, as desired. 
     9. The Transfer Chamber  217   
     FIG. 30 illustrates an alternative delivery system to that shown in FIGS. 26-29. The opening  215  to the melt furnace  125  is covered by a movable transfer chamber  217 . The movable transfer chamber may have any desired shape sufficient to cover the opening  215 . For example, chamber  217  may have a shape of a cylinder movable by the moving element  211 , such as a movable arm or wheels or bearings mounted on a rail or in a groove. Chamber  217  contains an aperture  219 . When it is desired to add more ingots (or other forms of solid metal such as pellets)  103  to the melt furnace  125 , the moving element  211  positions the chamber  217  such that the aperture  219  lines up with the end of the conveyor  121  or the sloped surface  173 . This allows the ingots  103  to be transferred from the conveyor  121  or sloped surface  173  through the aperture  219  into chamber  217  and down into the melt furnace  125  through opening  215 . To block access to the melt furnace  125 , the moving element  211  moves the chamber  217  in any direction (e.g. up, to the left or to the right) such that the end of the conveyor  121  or sloped surface  173  is no longer aligned with the aperture  219 . 
     An inert protective gas atmosphere may also be maintained in the transfer chamber  217  to decrease the amount of air entering the melt furnace  125 . The transfer chamber  217  may also be used with a push arm  177  and piston  183  shown in FIG.  22 . In this case, the ingots  103  would slide-down the sloping surface  173  into the transfer chamber  217  instead of dropping directly into the melt furnace  125 . The transfer chamber  217  may also be used with the holding chamber  181  of FIGS. 23-25 as illustrated in FIG.  31 . 
     10. The elevator  221   
     FIG. 31 shows an elevator  221  which delivers ingots (or pellets)  103  according to one aspect of the present invention. The elevator contains platforms  223  which raise deliver the ingots  103  toward the melt furnace  125 . Each platform  223  comprises a platform base  225  and a movable platform top  227  connected by at least one connector  229 . As each platform  223  reaches its top position, a lifting member  231  moves up pole  233  and pushes up on the back end of the platform top  227 . The back end of the platform top  227  is lifted above platform base  225  by the lifting member  231 , which causes the ingot(s)  103  to slide off the platform top toward the melt furnace  125 . Connector  229  may be a bolt or a rod which rotatably connects platform top  227  and base  225 . Preferably, the platform top is rotated up about  20  degrees by the lifting member  231 . Alternatively, the platform  223  may comprise a unitary member, and the whole platform  223  may be lifted by the lifting member  231 . 
     The elevator  221  may deliver the ingots directly into the melt furnace  125  or it may be used with any other deliver element described above in connection with FIGS. 21-30. For example, the elevator  221  is illustrated in FIG. 31 as being used in conjunction with the holding chamber  181  and the movable transfer chamber  217 . However, the elevator  221  may be used with either the holding chamber  181  or the movable transfer chamber  217  alone. Alternatively, the elevator  221  may be used with the aperture plate  207  or cover plate  213  illustrated in FIGS. 26-29, alone or in combination with the holding chamber  181 . Furthermore, as illustrated in FIG. 31, the holding chamber  181  contains one door  193  and the conveyor  121  or sloping surface  173 . However, the holding chamber may contain other features, such as a push arm  177  and/or piston  183 , a protective gas inlet  185 , heater(s)  191 , a second door  195 , a vacuum pump  199  and/or at least one inert gas screen  201 , as described above with respect to FIGS. 21-30. 
     Preferably, the movement of the lifting member  231  is synchronized with the opening of the door(s)  193  and/or  195  by a controller such as a computer or by a human operator. For example, as the lifting member  231  moves up on the pole  233 , the door  193  is simultaneously opened to allow an ingot  103  to pass into the holding chamber  181 . Furthermore, the aperture or cover plate  207 ,  213  or the transfer chamber  217  may also be synchronized with the door(s)  193  and/or  195  and/or the lifting member  231 . Thus, after the door  193  is closed, the aperture plate  207 , the cover plate  213  or the transfer chamber  217  may be moved to open the opening  215  to the melt furnace  125 . 
     The method of operating the elevator  221  illustrated in FIG. 31 will now be described. The elevator platforms  223  raise the ingots  103  to the top of the elevator where the back end of the platform top  227  is lifted above platform base  225  by the lifting member  231 . After the ingot(s)  103  are removed from the platform top, the lifting member  231  moves down the pole  233 , placing the platform top  227  back onto the platform base  225 . The lifting member  231  then disengages the first platform  223 , the next platform is moved up, and the process is repeated. 
     The ingot(s)  103  slide off the lifted platform top  227  onto the conveyor  121  or sloped surface  173 . The ingot(s) pass through the holding chamber  181  where they are preferably heated to drive off moisture present on the ingot surfaces. The aperture  219  of the movable transfer chamber  217  is then lined up with the conveyor  121  or sloped surface  173 , and the ingot(s)  103  enter the transfer chamber  217  through aperture  219 . The ingots then pass from the transfer chamber  217  into the melt furnace  125  through opening  215 . 
     11. The Preferred Barrel and Injection Chamber Injection System 
     The injection molding apparatus  101  illustrated in FIG. 2 contains a feeder  105  and an injection chamber  113 . However, the injection molding apparatus according to the eighth preferred embodiment of the invention also contains a temperature controlled barrel, a ram and other elements described in U.S. Pat. No. 5,983,976, incorporated herein by reference in its entirety. 
     The injection molding apparatus  301  according to the eighth preferred embodiment of the present invention is illustrated in FIG.  32 . The apparatus contains a feeder  305  which is used to hold melted metal  111 . The melted metal  111  is supplied to the feeder  305  through a conduit  127  from a melt furnace  125 , schematically illustrated in FIG.  32 . The melt furnace  125  and conduit  127  may comprise any melt furnace and conduit described above and illustrated in FIGS. 2-20 above, and which may also include a pump  131 , a second piston  133  and any other elements described above. As discussed above, the melt furnace  125  may be located above, below, behind, in front and/or adjacent to a side of the feeder  105 . Furthermore, the solid metal ingots or pellets  103  may be supplied to the melt furnace  125  by any delivery system described above and illustrated in FIGS.  2  and  21 - 31 . 
     The feeder  305  of the eighth preferred embodiment illustrated in FIG. 32 may contain a filter  307 , if desired. However, since the melted metal  111  is preferably supplied to the feeder  305  in the liquid state, the filter may be omitted. The feeder  305  is provided with at least one heating element  309  disposed around its outer periphery. The heating element  309  may be of any conventional type and operates to maintain the feeder  305  at a temperature high enough to keep a metal alloy supplied through the feeder  305  in a melted, and preferably liquid state. For a Mg alloy ingot, this temperature would be about 600° C. or greater. 
     Two level detectors  311 ,  313  detect minimum and maximum levels of melted metal  111  in the feeder  305 . When the upper level detector  311  detects that the level of melted metal  111  has risen to a maximum point, it relays a signal to a controller, such as a computer or a microprocessor control unit (not shown), to stop the inflow of melted metal  111  into the feeder  305 . For example, the flow may be stopped by closing a flow valve  128  connecting the conduit  127  to the feeder  305 , or stopping the pump  131  or second piston  133  from supplying the melted metal  111  into the feeder  305 , as described above and illustrated in FIGS. 2-5. When the lower level detector  313  detects that the level of melted metal has been depleted to a minimum point, it relays a signal to the controller which opens the flow valve  128  or instructs the pump  131  or the second piston  133  to supply additional melted metal  111  into the feeder  305 . One or both sensors  311 ,  313  may be omitted, if desired. 
     Preferably, sufficient melted metal  111  should be kept in the feeder  305  to supply about 20 times the volume needed for one injection cycle (or shot). This is because the amount of time required to melt the metal necessary for one injection cycle is longer than the injection cycle time, which in the preferred embodiment is about 30 seconds. However, the feeder  305  may contain any level of the melted metal as desired, and the sensor(s)  311 ,  313  may be located at any height in the feeder  305  to maintain the desired level of the melted metal. A mixer (not shown) in feeder  305  may also be included for the purposes of evenly distributing the heat from the heating elements  309  to the metal  111  supplied to the feeder  305 . 
     The feeder  305 , melt furnace  125  and the holding chamber  181  preferably contain an atmosphere of an inert protective gas to minimize oxidizing of the pre-heated and melted metal. A mixture of carbon dioxide (CO 2 ) and sulfur fluoride (SF 6 ) gas is preferred. However, other gasses, such as nitrogen or argon, may be used alone or in any combination with each other. The inert gas may be introduced (e.g. from a pressurized tank) into the feeder  305  through port  315  to create an inert gas atmosphere above the bath. The port  315  may be located on top or side surface of the feeder  305 . 
     The melted metal is subsequently supplied into a temperature-controlled barrel  317  by way of gravity through a feeder port  319  which may optionally be supplied with a valve serving as a stopper (not shown). Preferably, no valve is present. A ram  321  is arranged coaxially with the barrel  317  and extends along the center axis of the barrel  317 . The outer diameter of the ram  321  is smaller than the inner diameter of the barrel  317  such that melted metal  111  flows in the space between the ram  321  and the barrel  317 . The ram  321  is also controlled by motor  323  for axial movement in both retracting and advancing directions along the barrel  317  and for rotation around its own axis if stirring of the melted metal is desired inside barrel  317 . 
     A valve  325  is mounted around the outer circumference of the ram  321  to separate the barrel  317  into upper and lower portions. The valve  325  opens and closes to selectively permit and block the flow of metal  111  between the upper and lower portions of the barrel  317 . Suitable valves having such a function are known per se to those skilled in the art, and any of them may be used for purposes of the present invention. Preferably, the valve  325  is frictionally mounted on an inner circumference of the barrel  317  and slidably mounted on the outer circumference of the ram  321 . For example, when the ram  321  retracts upwardly in the barrel  317 , the valve  325  moves relative to the ram  321  to permit the flow of melted metal, and when the ram  321  advances downwardly in the barrel  317 , the valve  325  moves relative to the ram  321  to block the flow of the melted metal  111 . 
     FIG. 33 is a side view showing one embodiment of a valve on the ram when it is in the position that prevents melted metal from flowing to positions upstream of (to the right of) the valve. FIG. 34 is a side view showing one embodiment of a valve on the ram when it is in the position that permits melted metal to flow downstream of the valve (to the left of the valve). FIG. 35 is a front view showing one embodiment of a valve when it is not fitted onto the ram. FIG. 36 is a side view showing one embodiment of a valve when it is not fitted onto the ram. 
     In the closed position of FIG. 33, the rear section  327  of the valve  325  abuts the body  331  of the ram  321 , while the front section  329  of the valve  325  does not abut the head  333  of the ram  321 . Since the rear section  327  of the valve is solid, the melted metal  111  cannot flow between the upper and lower portions of the barrel  317  because the metal flow is blocked by the body  331  of the ram abutting the rear section  327  of the valve. The blockage of the flow in this position permits the ram  321  to push the melted metal  111  in the lower portion of the barrel  317  into the injection chamber  413  through an outlet port  401  (see FIG. 32) without the melted metal  111  flowing back (as shown in FIG. 33) into the upper portion of the barrel  317 . 
     In the open position of FIG. 34, the front section  329  of the valve  325  abuts the head  333  of the ram  321 . As illustrated in FIGS. 35 and 36, the front section  329  of the valve contains at least one tooth or prong  335  and at least one gap  337 . The melted metal  111  is permitted to flow through the gaps  337  between the teeth  335  when the ram  321  is retracted, as illustrated in FIG.  34 . As a result, when the ram  321  is in the retracted position, the valve  325  is in the open position. The melted metal  111  in the upper portion of the barrel  317  flows through the gaps  337  located between the teeth  335 , the rear portion  327  of the valve  325  and the head  333  of the ram, and collects in the lower portion of the barrel  317 . 
     The ram  321  as shown in FIGS. 32-34 has a head  333  with a pointed tip, but any shape may be used, including a blunt end or a rounded end. Preferably, the end of ram  321  has a shape capable of blocking outlet port  401  to prevent the flow of melted metal between barrel  317  and injection chamber  413  when ram  321  is fully advanced inside barrel  317 . 
     In an alternative embodiment of the invention, the ram  321  contains at least one optional supporting rib or fin  338  arranged on ram  321 , as illustrated in FIG.  32 . The fins  338  are preferably attached to the ram  321  and can slide on the inner circumference of the barrel  317 , both coaxially with the length of the barrel and/or in a circular motion about the barrel axis. Alternatively, the fins  338  may be attached to the inner circumference of the barrel  317  in such a manner as to allow the bare ram  321  to slide by. 
     While injection takes place, ram  321  is preferably fully advanced inside barrel  317  so that outlet port  401  is closed, as illustrated in FIG.  33 . However, the ram  321  need not be fully advanced since valve  325  and the melted metal  111  that occupies the lower portion of barrel  317  would also prevent melted metal  111  from leaving the injection chamber  413  during injection. 
     A first piston  419  in the injection chamber  413  is used to inject the melted metal  111  present in the injection chamber  413  into a mold  415  having a cavity  417 , as illustrated in FIG.  32 . As discussed above, the first piston  419  may have any desired shape, and may extend to the injection nozzle  421  of or to any point in the injection chamber  413  during an injection stroke. 
     An exemplary injection molding method using the apparatus of FIGS. 32-36 will now be described. A motor (not shown) is used to move the first piston  419  forward to inject the melted metal  111  into the mold cavity  417 . Preferably, the melted metal  111  is injected in the liquid state. However, it may also be injected in a thixotropic state, if desired. 
     After the injection stroke of the first piston  419 , the ram  321  is retracted, as illustrated in FIG. 34, but may continue rotating if rotation is being used to stir the melted metal inside barrel  317 . The first piston  419  housed in the injection chamber  413  begins retracting (moving to the right as illustrated in FIG. 32) to expand the volume of the injection chamber  413  to a desired volume according to the dimensions of the molded part being produced. The first piston  419  is stopped when the volume of the injection chamber  413  becomes equal to the desired injection volume. The first piston  419  may be retracted at the same time that ram  321  is being retracted or after ram  321  has been retracted to a desired position. 
     After first piston  419  is stopped, the ram  321  is advanced downward, and, as a result, a portion of the melted metal  111  collected in the lower portion of barrel  317  is pushed into the injection chamber  413  through the outlet port  401 , as illustrated in FIG.  33 . The pressure of the melted metal  111  entering into injection chamber  413  assists in driving out gas present in the injection chamber  413  that accumulates between the melted metal  111  and first piston  419 . The ram  321  preferably advances through barrel  317  until its end closes off outlet port  401 , and the ram  321  preferably remains in this position to keep outlet port  401  sealed off until injection is complete and the next shot is started. 
     During each shot, a certain amount of gas accumulates between the melted metal and the first piston  419  as the melted metal  111  enters injection chamber  413 . The volume of this gas can make up as much as 20% of the volume of the injection chamber  413 . Injecting such a melted metal/gas mix into a mold can result in molded parts that have uneven surfaces, porosity (caused by gas bubbles trapped in the metal&#39;s surface), or other imperfections including those that result from an inconsistent volume of melted metal being injected. Removing as much gas as possible before injection is desired. 
     In the method of the eighth preferred embodiment of the present invention, that gas evacuation is primarily accomplished in two ways. First, the first piston  419  and injection chamber  413  can evacuate gas like a pharmaceutical syringe that draws in liquid from a container of liquid. Specifically, as first piston  419  retracts, it creates a suction to draw in melted metal  111  from the barrel  317  into the injection chamber  413  and it pushes the gas out behind it. Secondly, the additional portion of melted metal  111  driven into the second chamber by the ram  321  forces the gas that accumulates between the melted metal and the first piston  419  to escape around the small space between the first piston  419  and the wall of the injection chamber (i.e., the gas is forced out to the right of first piston  419  due to the pressure of the melted metal). Optionally, an O-ring seal  423  or other implement may be fitted around at least a portion of first piston  419  that allows the gas to pass behind first piston  419  and out of the system but not back in. 
     The injection nozzle  421  is preferably covered with a nozzle shut-off plate  425  which is lowered by the controller to prevent the melted metal  111  from escaping out of the injection chamber  413  when the ram  321  pushes the melted metal into the injection chamber  413 . When the injection chamber  413  has been filled with the melted metal  111  and substantially all gas has been forced out, the nozzle shut-off plate  425  is pulled up and the nozzle  421  is moved forward (to the left in FIG. 32) to contact the opening in the mold die  415 . In a preferred embodiment, the movement of the nozzle  421  is achieved by mounting the injection chamber  413  apparatus on a slide mount (such as a rail and wheels or bearings) and moving the entire injection chamber  413  along with the barrel  317 , feeder  305  and/or melt furnace  125 , as described above, towards the mold  415  (to the left in FIG.  32 ). The movement of the injection chamber  413  may be accomplished by the forward stroke of the first piston  419 , by the motor used to move the first piston  419  or by a separate motor. 
     Simultaneously with the movement of the injection chamber  413 , the first piston  419  is pushed toward the nozzle  421  to force the melted metal  111  in the injection chamber  413  through the mold die  415  into the mold cavity  417 . After a pre-set dwell time, the two mold dies are opened and the molded metallic part is removed, so that a new cycle can begin. 
     The melted metal, while housed in injection chamber  413 , is substantially sealed off from gas that would otherwise enter injection chamber  413  from outside the machine by virtue of nozzle shut-off plate  425 , seal  423  on first piston  419 , and the melted metal  111  which continuously occupies barrel  317  during operation. Although gas is present in injection chamber  413  prior to start-up, the first run of shots drives out substantially all gas in injection chamber  413 . Thus, the melted metal  111  that is injected from injection chamber  413  into mold  415  is substantially free of gas. Preferably, the amount of gas present in injection chamber  413  during injection is less than 20%, more preferably less than or equal to 1% by volume of the second chamber. 
     As shown in FIG. 32, heating elements  339 ,  341 ,  343 ,  345 ,  347  and  349  are provided along the length of the barrel  317 . Heating elements  427 ,  429 ,  431 ,  433  and  435  are also provided along the length of the injection chamber  413 . The heating elements may comprise any heating elements, preferably resistance heating elements. The temperature in the feeder  305  preferably differs depending on the material present in the feeder. For the AZ91 Mg alloy, heating elements  309  are preferably controlled so that the temperature in the feeder  305  is about 640° C. near the upper surface of the melted Mg alloy and about 660° C. near the lower region of feeder  305 . 
     In the barrel  317 , the temperature near heating element  339  is preferably maintained at around 640° C. for the AZ91 Mg alloy. The temperature near heating element  343  is preferably maintained at around 650° C. for the AZ91 Mg alloy. The temperature near heating element  349  is preferably maintained at around 630° C. for the AZ91 Mg alloy. The temperature near heating elements  341 ,  345  and  347  is preferably maintained between the temperature near the adjacent heating elements. These temperatures facilitate the downward flow of metal toward outlet port  401  and inhibit flow in the opposite direction. 
     In the injection chamber  413 , the temperature near heating elements  431 ,  433  and  435  is preferably maintained at around 620° C. for the AZ91 Mg alloy. These temperatures are sufficiently high to maintain the melted metal entirely in the liquid state from the time it exits the feeder  305  into the barrel  317  to the time the melted metal is injected into the mold cavity  417  from the injection chamber  413 . The temperature near heating elements  427  and  429  is preferably maintained at around 570° C. for the AZ91 Mg alloy. The lower temperature behind the seal  423  helps prevent the melted metal  111  from flowing past the seal  423 . 
     Using the preceding temperatures at these locations permits molding of the AZ91 Mg alloy in the liquid state. Under these conditions, one cycle lasts approximately 30 seconds. However, if desired, the processing temperatures may be lowered to maintain the metal in the barrel and/or injection chamber in the thixotropic state. 
     Molded metallic parts having extremely smooth surfaces and minimal porosity can be produced using the liquid metal injection molding method and apparatus described above, which allows them to be painted directly without any further processing (i.e., after further etching and/or cleaning of the part, but without further machining). The castings also have extremely accurate dimensions and consistency, and can be produced with thicknesses of less than 1 mm when the part roughly has the dimensions of a DIN size A4 sheet of paper (21.0 cm by 29.7 cm). Preferably, the range of thickness of molded parts produced according to the invention is between 0.5 and 1 mm for parts that have roughly the dimensions of a DIN size A4 sheet of paper. With known die casting and thixotropic methods, thicknesses no less than about 1.3 mm can be obtained for parts that have roughly the dimensions of a DIN size A4 sheet of paper. 
     12. The Two-Chamber Apparatus 
     While FIG. 2 illustrates a three chamber apparatus  101 , the feeder  105  may be omitted, if desired. In this aspect of the present invention, the injection molding apparatus contains only two chambers: the injection chamber and the melt furnace. An example of such a two chamber apparatus  501  is illustrated in FIG.  37 . The reference numbers starting with “5” in this Figure correspond to the reference numbers starting with “1” in FIG. 2, In FIG. 37, the melt furnace  525  is located directly on top of the injection chamber  513 . Since the melt furnace  525  moves forward and backward in unison with the injection chamber  513  during each injection stroke of the piston  519 , the ingot  103  delivery system  521  should be located over either the forward or backward location of the melt furnace to account for the movement of the melt furnace  525 . The delivery system  521  should be operated to deliver the ingots  503  to the melt furnace  525  only when the melt furnace  525  is below the delivery system  521 . 
     Preferably, the melt furnace  525  contains an outlet screening element  526 . For example, as illustrated in FIG. 37, the screening element  526  may comprise at least one non-horizontal wall  530 , a top cover or portion and an outlet port  532 . Preferably, the melt furnace outlet port  532  is located in one of the walls instead of in the top of the screening element  526 . The outlet port  532  connects the melt furnace  525  to the conduit  527  leading to the injection chamber  513 . The screening element  526  may contain one wall if the element  526  has a cylindrical shape or plural walls if the element  526  has a polygonal shape. Furthermore, the non-horizontal wall  530  is preferably exactly vertical or substantially vertical (i.e., deviating by about 1-20 degrees from vertical). 
     13. The Check Valve 
     Any check valve  106 ,  506  may be used in the embodiments illustrated in FIGS. 2-6,  8 - 11 ,  13  and  37 . FIGS. 38 and 39 illustrate a preferred embodiment of the check valve  106 ,  506  structure. The preferred check valve is a ball valve  606 . The ball valve  606  operates in response to a pressure differential between the feeder  605  and the injection chamber  613 . The pressure within the feeder  605  remains somewhat constant, but the pressure within the injection chamber  613  is determined by the position of a piston  619  disposed therein. When the piston  619  is displaced inwardly, the pressure in the injection chamber  613  increases (and becomes higher than that of the feeder  605 ) and the ball valve  606  closes off an opening  608  between the feeder  605  and the injection chamber  613 . When the piston  619  is displaced outwardly, the pressure in the injection chamber  613  decreases and is lower than that of the feeder  605 , and the ball valve  606  opens. 
     The operation of the ball valve  606  is shown in greater detail in FIGS. 38 and 39. FIG. 38 shows the position of the ball valve  606  when the piston  619  is displaced outwardly (away from the mold cavity). In this case, the opening  608  between the feeder  605  and the injection chamber  613  is opened as the ball element  610  of the ball valve  606  moves away from the opening  608 . A ball valve stop  612  is provided to confine the ball valve movement away from the opening  608 . On the other hand, when the piston  619  is displaced inwardly (toward the mold cavity), as shown in FIG. 39, the pressure inside the injection chamber  613  increases and the ball element  610  of the ball valve  606  is forced to lodge up against the opening  608  and thereby close off fluid communication between the feeder  605  and the injection chamber  613 . 
     In another preferred embodiment, the ball valve  606  may be provided with a biasing element, such as a spring. In such a case, the ball element  610  may be biased towards either the open or the closed position. It is preferable to provide such a biasing element in larger injection molding systems for producing metal alloys. In still another preferred embodiment, the ball valve  606  may be electronically controlled, in which the opening and closing of the ball valve is synchronized with the displacement motion of the piston  619 . 
     14. Conclusion 
     It is important to note that all embodiments described above and illustrated in FIGS. 2-36 may be used together or separately or in any combination or permutation without departing from the scope of the current invention. For example, any one or more improvements shown in FIGS. 3-20 may be added to the basic apparatus shown in FIG. 2 without departing from the scope of the current invention. Furthermore, each feature of the delivery system illustrated in FIGS. 21-31 and/or each feature of the injection system illustrated in FIGS. 32-36 may be added to the basic apparatus shown in FIG. 2 without departing from the scope of the current invention. 
     Furthermore, each feature described above is considered to be separate invention. For example, the ingot or pellet delivery system(s) described above and illustrated in FIGS. 21-31 and the injection system illustrated in FIGS. 32-36 may be used separately or together in a apparatus that does not contain a melt furnace. 
     In the preceding discussion of the preferred embodiments, a metal alloy is produced by injection molding from a magnesium (Mg) alloy ingot or pellets which are melted and processed in a liquid state. The invention is not limited to processing of Mg and is equally applicable to other types of materials, metals and metal alloys. Furthermore, the chamber where the metal is melted is referred to as the “melt furnace”  125 . However, this chamber may also be referred to as a “melting pot.” 
     The terms “melted metal” and “melted material” as used herein encompass metals, metal alloys and other materials which can be converted to a liquid state and processed in an injection molding system. A wide range of metals is potentially useful in this invention, including aluminum (Al), Al alloys, zinc (Zn), Zn alloys, titanium (Ti), Ti alloys, and the like. 
     Unless otherwise indicated, the terms “a” or “an” refer to one or more. Unless otherwise indicated, the term “gas” refers to any gas (including air) that can be present in the injection chamber at start-up or that is trapped in the injection chamber and forced out during operation of the invention&#39;s system. Specific temperature and temperature ranges cited in the following description of the preferred embodiment are applicable to the preferred embodiment for processing Mg alloy in a liquid state, but could readily be modified in accordance with the principles of the invention by those skilled in the art in order to accommodate other metals and metal alloys. For example, some Zn alloys become liquid at temperatures above 450° C., and the temperatures in the injection molding system of the present invention can be adjusted for processing of Zn alloys. 
     While particular embodiments according to the invention have been illustrated and described above, it will be clear that the invention can take a variety of forms and embodiments within the scope of the appended claims.