FIELD OF THE INVENTION
This invention relates to a molten metal molding machine for injecting and filling molten metal (metal melt) into a cavity of a mold, and especially to a molten metal molding machine equipped with a metal melting system which melts a metal material in a heating cylinder.
DESCRIPTION OF THE BACKGROUND
As molten metal molding machines of the type that a molten metal material is injected and filled in a cavity of a mold to obtain a product, cold-chamber type diecasting machines are well known. A cold-chamber type diecasting machine is equipped with a smelting furnace (crucible) for melting a metal material (for example, an Al alloy, Mg alloy or the like). The metal material, which has been molten in the smelting furnace, is metered and taken up by a ladle at every shot. The molten metal (metal melt) so taken up is poured into an injection sleeve, and by a high-speed advancement of an injection plunger, is then injected and filled in a cavity of a mold. Because the metal material (metal melt) which has been molten in the smelting furnace is taken up by the ladle and conveyed in the cold-chamber type diecasting machine (diecasting machine), the whole machine is large, and moreover, a certain limitation is imposed on an improvement in product quality as the molten metal is oxidized or is lowered in temperature at a surface, where the molten metal is brought into contact with air, when the molten metal is taken up and conveyed by the ladle.
A molten metal molding machine has, therefore, been proposed, which without using any smelting furnace for melting a metal material, melts the metal material by a heating cylinder which also serves as an injection sleeve (see JP-A-2004-148391)
FIGS. 6A through 6F are schematic views, which illustrate a molten metal molding machine having substantially equivalent construction as the technique shown in JP-A-2004-148391. In FIGS. 6A through 6F, there are shown a heating cylinder 51, a nozzle (hot runner nozzle) 52 arranged on a forward end of the heating cylinder 51, band heaters 53 wrapped on and around an outer circumference of the heating cylinder 51 and an outer circumference of the nozzle 52, a cavity 54 defined by an unillustrated mold and maintained in communication with a free end of the nozzle 52, an oxide-film scraper section (die section) 55 arranged on a rear end of the heating cylinder 51, an on/off valve 56 arranged through a circumferential wall of the heating cylinder 51 at a position adjacent to the rear end of the heating cylinder 51 such that, when the on/off valve 56 assumes an open position, an interior of the heating cylinder 51 is brought into communication with a vacuum pump 57 which is in communication with a hollow portion of the on/off valve 56 and is adapted to bring the interior of the heating cylinder 51 into a substantially vacuum condition, a pressure gauge 58 for checking a vacuum level inside the heating cylinder 51, an air supply 59, a solenoid valve 60 for on/off controlling the on/off valve 56 by an air pressure from the air supply 59, a material-receiving section 61 arranged opposite to an opening formed at the rear end of the heating cylinder 51 and configured to internally define a through-channel, and a piston member 62 drivable by an unillustrated hydraulic cylinder such that the piston member 62 is selectively movable forward or backward through the material-receiving section 61 and the heating cylinder 51.
Referring to FIGS. 6A through 6F, a description will next be made of a molding operation by the molten metal molding machine. As illustrated in FIG. 6A, a preheated metal rod 63 of a predetermined length is firstly fed into the material-receiving section 61 from an unillustrated preheating apparatus. At this stage, a predetermined number of metal rods 63 have been pushed beforehand into the heating cylinder 51 by the piston member 62 such that, through the heating cylinder 51 and nozzle 52, the metal rods 63 are filled one by one from the side of the nozzle 52. As each metal rod 63 is fed from a position close to the rear end of the heating cylinder 51 toward the nozzle 52, it is gradually molten. Inside the nozzle 52, the metal rod 63 is in a fully-molten state. For the sake of clarification, this fully-molten metal rod 63 may hereinafter be referred to as “the molten metal material 63” or simply, as “the metal material 63”. At this stage, the on/off valve 56 is in a closed position.
As depicted in FIG. 6B, the piston member 62 is next caused to advance at a low speed such that the metal rod 63 is pushed from the material-receiving section 61 into the rear end of the heating cylinder 51. Upon this push-in operation, an oxide film is scraped from an outer circumferential surface of the metal rod 63 by the oxide-film scraper section 55. When the metal rod 63 enters at least at a part thereof the heating cylinder 51 from the material-receiving section 61, the opening formed at the rear end of the heating cylinder 51 is closed by the metal rod 63. In this state, the advancement of the piston member 62 is once stopped. The on/off valve 56 is then switched into the open position by the solenoid valve 60 to bring the interior of the heating cylinder 51 into communication with the vacuum pump 57, and the interior of the heating cylinder 51 is brought into a substantially vacuum condition by the vacuum pump 57.
After the interior of the heating cylinder 51 has been brought into the substantially vacuum condition, the on/off valve 56 is next switched into the closed position by the solenoid valve 60 to cause the piston member 62 to advance at a high speed, as illustrated in FIG. 6C. As a result, the metal rod 63, which has been pushed by the piston member 62 and newly charged into the heating cylinder 51, successively pushes the preceding metal rods 63 forward. By this pushing, an injection of the molten metal material (metal melt) 63 from the nozzle 52 into the cavity 54 is rapidly initiated.
When the injection (injection and filling) has been completed with the metal material 63 being fully filled to every corner in the cavity 54 as illustrated in FIG. 6E, a pressure which the piston member 62 receives from the metal rods 63 increases to a predetermined value. Responsive to a detection of the pressure, the advancement of the piston member 62 is stopped.
Upon completion of the injection of the metal material 63 into the cavity 54, heat is absorbed into the mold from the metal material 63 in the cavity 54 so that the metal material 63 in the cavity 54 is rapidly cooled and solidified. In this cooling step, the heating control by the band heater 53 wrapped on and around the nozzle 52 is interrupted so that on the side of the free end of the nozzle 52, the metal material 63 in the nozzle 52 is also cooled and solidified. As a result, the nozzle 52 is sealed at the free end thereof with the thus-solidified metal material 63. After the completion of the injection, the piston member 62 is driven rearward to a position where a new metal rod 63 can be fed into the material-receiving section 61 as depicted in FIG. 6F. Upon completion of the cooling and solidification step, mold opening is performed. The solidified product is cut off from the metal material on the side of the nozzle 52 (at this stage, the nozzle 52 is heated before the mold opening to facilitate the cut-off), and together with a movable mold (not shown), the solidified product is separated from a stationary mold (not shown). After the completion of the mold opening or in the course of the mold opening, the product is ejected from the movable mold by an unillustrated ejection mechanism and is taken out by an unillustrated robot.
The molten metal molding machine, which has been described above with reference to FIGS. 6A through 6F, melts the metal rods by the heating cylinder 51, which also serves as an injection sleeve, and directly injects and fills the molten metal (metal melt) from the nozzle 52, which is arranged on the free end of the heating cylinder, into the cavity of the mold. Compared with a molten metal molding machine of the construction that at every shot, a metal material molten in a smelting furnace is metered and taken up by a ladle and is then poured into an injection sleeve as in a cold-chamber diecasting machine equipped with a smelting furnace, the above-described molten metal molding machine does not require any large smelting furnace, and as a whole, can be designed relatively compact. It is also considered that the molten metal is not prone to oxidation as there is not much risk for the molten metal to be brought into contact with air.
With the molten metal molding machine shown in FIGS. 6A through 6F, however, the response of the metal material 63 in the nozzle 52 to melting and solidification deteriorates unless the diameter of the land portion of the nozzle 52 arranged on the free end of the heating cylinder 51 is set at a certain small value or less. If the diameter of the land portion of the nozzle 52 is small, however, a problem is developed as will be described next. In the injection and filling of a molten metal, the flow velocity of the molten metal through a gate portion or runner portion of a mold is considered to be generally 55 m/sec or lower, preferably from 30 to 40 m/sec from the viewpoint of avoidance of seizure and a pressure loss. The flow volume of the molten metal per unit time is the product of the cross-sectional area of the land portion of the nozzle 52 and the flow velocity. Because the diameter of the land portion of the nozzle 52 is small and as mentioned above, a limitation is imposed on the flow velocity, the flow volume, in other words, the fill volume of the molten metal per unit time is obviously limited. In the molding of a molten metal, the molten metal is rapidly cooled and solidified subsequent to its filling in a cavity as described above. Accordingly, the filling time is generally extremely short, for example, 0.1 to 0.05 second or so. For the reasons mentioned above, a limitation is naturally imposed on the weight of a product moldable (castable) by a molten metal molding machine such as that illustrated in FIGS. 6A through 6F, although it is equipped with sufficient metal-molding capacity.
In this respect, cold-chamber diecasting machines (molten metal molding machines) are superior in versatility because they make it possible to set the injection/filling velocity and the runner flow area at optimal values depending upon each product.
In the molten metal molding machine illustrated in FIGS. 6A through 6F, the interior of the heating cylinder 51 is brought into a substantially vacuum condition. Accordingly, entrance of air through a very small clearance between the oxide-film scraper section 55 arranged on the rear end of the heating cylinder 51 and the piston member 62 and metal rod 63 is undeniable, and the metal rods 63 unavoidably undergo oxidation with the air so entered.
SUMMARY OF THE INVENTION
With the foregoing in view, an object of the present invention is to realize a molten metal molding machine equipped not only with the merits of the construction that a metal material is molten by a heating cylinder without using a smelting furnace but also with the merits of cold-chamber diecasting machines.
To achieve the above-described object, the present invention provides, in one aspect thereof, a molten metal molding machine provided with a heating cylinder, a linear motion member for successively feeding preheated metal rods into the heating cylinder from a rear end thereof to successively push the metal rods toward a forward end of the heating cylinder, and a heater arranged on the heating cylinder such that the metal rods are gradually molten as the metal rods move through the heating cylinder from the rear end thereof toward the forward end thereof, comprising:
a guide pipe arranged on the forward end of the heating cylinder to downwardly feed molten metal into an injection sleeve; and
an injection plunger arranged selectively movably forward or rearward in the injection sleeve such that by a forward movement of the injection plunger, the molten metal fed into the injection sleeve is injected and filled into a mold to subject the molten metal to cold-chamber molding.
Preferably, the molten metal molding machine may further comprise an inert gas feeder for feeding pressurized inert gas into the heating cylinder.
Preferably, the molten metal molding machine may further comprise an electric servomotor as a drive supply for the linear motion member.
The molten metal molding machine according to the present invention is constructed to perform molten metal molding (casting) of the cold-chamber type that from a heating cylinder in which a metal material has been molten, molten metal is fed into an injection sleeve and is then injected and filled into a mold by an advancement of an injection plunger selectively movable forward or rearward through the injection sleeve. The molten metal molding machine according to the present invention is, therefore, equipped not only with the merits of the construction that a metal material is molten by a heating cylinder, i.e., the obviation of use of a smelting furnace and the compact designing of the whole machine but also with the merits of cold-chamber diecasting machines, i.e., excellent versatility and the molding (casting) of heavy products. In addition, the adoption of the cold-chamber control method, which has been widely used for many years, in the injection and filling into a cavity can stabilize the injection and filling operation. In the cold-chamber molding (casting) of a molten metal, a biscuit connected to a casting is also taken out at the same time as taking the casting out of a mold. The molten metal injected and filled in the mold at every shot is, therefore, allowed to remain as a fresh material not subjected to the heat cycle of heating→cooling→heating (not exposed to any long heat history), thereby making it possible to contribute to an improvement in the quality of the casting.
It is preferred to feed pressurized inert gas into the heating cylinder in which a metal material is molten. In this case, the heating cylinder is filled with the inert gas so that no air is allowed to enter the heating cylinder although the inert gas leaks to the outside through the very narrow clearance between the oxide-film scraper section, which is arranged on the rear end of the heating cylinder, and the metal rod. The metal material inside the heating cylinder, therefore, remains free from oxidation.
Further, the use of the electric servomotor as the drive supply for the linear motion member makes it possible to accurately control the advanced position of the linear motion member, for example, by performing feedback control of the electric servomotor such that the linear motion member is subjected to speed feedback control along a position axis. As a consequence, it becomes possible to stabilize the volume of molten metal to be delivered from the heating cylinder at every shot.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a simplified fragmentary cross-sectional view of a molten metal molding machine according to one embodiment of the present invention at a stage that a linear motion member is at a most retracted position and a preheated metal rod has been newly fed to a position opposite to an opening formed at a rear end of a heating cylinder.
FIG. 2 is a similar simplified fragmentary cross-sectional view as in FIG. 1, but the molten metal molding machine is at a stage that a forward end portion of the metal rod has been pushed by the linear motion member into the heating cylinder through the opening formed at the rear end of the heating cylinder.
FIG. 3 is a similar simplified fragmentary cross-sectional view as in FIGS. 1 and 2, but the linear motion member has advanced further and molten metal has been downwardly fed from a nozzle, which is arranged on a forward end of the heating cylinder, into an injection sleeve via a guide pipe.
FIG. 4 is a similar simplified fragmentary cross-sectional view as in FIGS. 1 to 3, but injection and filling of the molten metal from the injection sleeve into a cavity of a mold has been completed.
FIGS. 5A and 5B are simplified fragmentary cross-sectional views of the molten metal molding machine of FIGS. 1 through 4, in which inert gas is leaking to the outside through a very small clearance between an oxide-film scraper section on a rear end of a heating cylinder and a metal rod, and a similar molten metal molding machine in which an interior of a heating cylinder has been brought into a substantially vacuum condition, and illustrate differences between them.
FIGS. 6A through 6F are simplified fragmentary cross-sectional views of a conventional molten metal molding machine at different stages of a molten metal molding operation, respectively.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A molten metal molding machine according to an embodiment of the present invention will herein after be described with reference to FIGS. 1 through 5B. In FIGS. 1 through 4, there are illustrated a fixedly-arranged, first holding plate 1, a second holding plate 2 fixedly arranged in opposition to the first holding plate 1, a plurality of guide shafts 3 extending between the first holding plate 1 and the second holding plate 2, an electric servomotor 4 mounted on the second holding plate 2, a motor driver 5 for driving the electric servomotor 4 under control, and a system controller 6 for governing the overall control of the molten metal molding machine. Referring to measurement information and clock information from unillustrated various sensors, the system controller 6 controls operations of individual elements of the molten metal molding machine on the basis of various programs provided in advance. With reference to outputs of an unillustrated encoder arranged on the electric servomotor 4, this system controller 6 gives drive commands to the electric servomotor 4 such that a linear motion member 12 to be described subsequently herein can be driven along a position axis by means of a motor driver 5 under speed feedback control.
Also illustrated are a small driving pulley 7 fixedly secured on an output shaft of the electric servomotor 4, a driven pulley 8 to which rotation of the electric servomotor 4 is transmitted via the small driving pulley 7 and an unillustrated timing belt, a ball screw mechanism 9 equipped with a screw shaft 10 and a nut member 11 and adapted to convert rotary motion into linear motion, the screw shaft 10 rotatably held on a second holding plate 2 and carrying the driven pulley 8 fixedly secured on an end portion of the screw shaft 10, the nut member 11 arranged in meshing engagement with the screw shaft 10 and linearly movable as a result of rotation of the screw shaft 10, and the linear motion member 12. The guide shafts 3 extend through the linear motion member 12 such that the linear motion member 12 is linearly movable, and the nut member 11 is fixed secured at an end portion thereof on the linear motion member 12. Rotation of the electric servomotor 4 is transmitted to the screw shaft 10 via the small driving pulley 7, the unillustrated timing belt and the driven pulley 8, and depending upon the direction of rotation of the screw shaft 10, the linear motion member 12 is driven forward or rearward together with the nut member 11.
Further illustrated are a heating cylinder 13 fixed at a rear end thereof on the first holding plate 1, and a substantially “inverted, open V-shaped” nozzle 14 arranged on a forward end of the heating cylinder 13 and equipped with an upwardly tilted, pipe portion and a downwardly titled, pipe portion extending in continuation with the upwardly tilted, pipe portion. Although illustration is omitted in the drawings, band heaters are also wrapped on and around outer circumferences of the heating cylinder 13 and nozzle 14 as in the construction of FIGS. 6A through 6F. Still further illustrated are a guide pipe 15 enclosing therein a front end portion of the nozzle 14 such that molten metal delivered from the heating cylinder 13 via the nozzle 14 is downwardly fed into an injection sleeve 24 to be described subsequently herein, an inert gas feeder 16 for feeding pressurized inert gas (for example, nitrogen gas) into the heating cylinder 13 and the guide pipe 15, and an oxide-film scraper section (oxide-film removing section) 17 arranged on an inner circumference of an opening formed at the rear end of the heating cylinder 13 to remove an oxide film from a surface of each metal rod 28 to be described subsequently herein. The inert gas feeder 16 is controlled by the system controller 6, and during a molding (casting) operation, always feeds inert gas, which has been pressurized to a predetermined pressure (a pressure of such a level as sufficiently exceeding the atmospheric pressure), into the heating cylinder 13 and the guide pipe 15 via gas lines 18 and through a gas feed port 19 arranged through a circumferential wall of the heating cylinder 13 at the position of the rear end thereof and a gas feed port 20 arranged through a top wall of the guide pipe 15.
Still further illustrated are a stationary mold 21 and a movable mold 22. Although illustration is omitted, the stationary mold 21 is mounted on a stationary die plate while the movable mold 22 is mounted on a movable die plate which is selectively movable forward or rearward. By a forward movement or rearward movement of the movable die plate, the movable mold 22 performs mold closing or mold opening, and upon completion of the mold closing, a cavity 23 is defined by the stationary mold 21 and the movable mold 22.
Yet further illustrated are the injection sleeve 24 fixed at a forward end thereof on the stationary mold 21, a molten-metal pour hole 25 formed through a circumferential wall of the injection sleeve 24 at a top thereof such that the molten-metal pour hole 25 is located opposite a lower opening of the guide pipe 15, a hydraulic cylinder 26, and an injection plunger 27 selectively movable forward or rearward through the injection sleeve 24. The injection plunger 27 serves as a piston member of the hydraulic cylinder 26. The hydraulic cylinder 26 is controlled by the system controller 6 via an unillustrated control valve and valve driver to selectively move the injection plunger 27 forward or rearward.
It is to be noted that in FIGS. 1 through 5B, metal rods before their melting, metal rods in their partially molten states, and the molten metal material are collectively designated by numeral 28.
With reference to FIGS. 1 through 5B, a description will next be made about an operation of the molten metal molding machine according to this embodiment. When the linear motion member 12 is in its most retracted position as shown in FIG. 1, responsive to a command from the system controller 6, an unillustrated material-feeding robot takes a preheated metal rod 28 of a predetermined length out of an unillustrated preheating apparatus and positions it to oppose the opening formed at the rear end of the heating cylinder 13. At this stage, the heating cylinder 13 and nozzle 14 are filled with a predetermined number of metal rods 28, which have been pushed beforehand into the heating cylinder 13 by the linear motion member 12, from the side of a forward end of the nozzle 14 except for the downwardly tilted, pipe portion of the nozzle 14. As each metal rod 28 advances from a position adjacent to the rear end of the heating cylinder 13 toward the nozzle 14, the metal rod 28 is gradually molten, and in the nozzle 14, the metal material 28 is in a fully-molten state. At this time, the injection plunger 27 is in its most-retracted position. As mentioned above, pressurized inert gas is always fed from the inert gas feeder 16 into the heating cylinder 13 and guide pipe 15, and the opening formed at the rear end of the heating cylinder 13 is filled with the inert gas.
Responsive to another command from the system controller 6, the unillustrated material-feeding robot then reduces its holding force for the metal rod 28, and places the metal rod 28 in a state ready for being pushed (needless to say, the positioning accuracy for the metal rod 28 maintained at this time). Responsive to a further command from the system controller 6, the electric servomotor 4 is caused to rotate in a predetermined direction via the motor driver 5 such that the linear motion member 12 is caused to advance to push the metal rod 28 into the heating cylinder 13 through the opening formed at the end of the heating cylinder 13 as illustrated in FIG. 2. Upon this push-in operation, an oxide film is scraped from the metal rod 28 by the oxide-film scraper section 17.
When the metal rod 28 enters at least at a part thereof the heating cylinder 13, the opening formed at the rear end of the heating cylinder 13 is closed by the metal rod 28. As the inert gas is continuously fed from the gas feed port 19 even after the closure, the inert gas leaks to the outside through the very small clearance between the oxide-film scraper section 17 on the rear end of the heating cylinder 13 and the metal rod 28.
FIG. 5A illustrates how the inert gas is leaking to the outside through the very small clearance between the oxide-film scraper section 17 on the rear end of the heating cylinder 13 and the metal rod 28. For the sake of a comparison with this embodiment, FIG. 5B depicts circumstances when the interior of the heating cylinder 13 is brought into a substantially vacuum condition as in the conventional art. As depicted in FIG. 5B, when the interior of the heating cylinder 13 is brought into a substantially vacuum condition, air unavoidably enters the heating cylinder 13 through the very small clearance between the oxide-film scraper section 17 on the rear end of the heating cylinder 13 and the metal rod 28. It is, hence, undeniable that the metal rods 28 develop oxidation with the thus-entered air. In this embodiment, on the other hand, air does not enter the heating cylinder 13 although the inert gas leaks to the outside through the above-described very small clearance. The metal rods 28 in the heating cylinder 13, therefore, develops no oxidation.
When the linear motion member 12 is further driven forward responsive to a still further command from the system controller 6, the metal rod 28 which has been newly charged into the heating cylinder 13 as a result of the pushing by the linear motion member 12 successively pushes the preceding metal rods 28 forward. As illustrated in FIG. 3, this pushing causes the molten metal 28 (the molten metal material (metal melt) 28) to be delivered from the nozzle 14 and then to be quickly and downwardly fed into the injection sleeve 24 from the molten metal pour hole 25 of the injection sleeve 24. At the time point that the molten metal 28 has been fed as much as needed for a single shot into the injection sleeve 24, the forward drive of the linear motion member 12 is stopped. The above-described feeding of the molten metal 28 into the injection sleeve 24 is performed at a high speed. This high-speed feeding is achieved by driving the electric servomotor 4 under predetermined speed feedback control such that the linear motion member 12 moves forward at a speed commensurate with its stroke (position). Because, as described above, the electric servomotor 4 is used as a drive supply for the linear motion member 12 and the electric servomotor 4 is subjected to the speed feedback control in accordance with the stroke of the linear motion member 12, the advanced position of the linear motion member 12 can be accurately controlled, thereby making it possible to stabilize the volume of the molten metal 28 to be delivered as much as needed for a single shot from the heating cylinder 13 (nozzle 14). Further, the pressurized inert gas is continuously fed into the guide pipe 15 from the gas feed port 20 formed through the top wall of the guide pipe 15 so that the guide pipe 15 is filled with the inert gas, and the inert gas is also fed from a lower part of the guide pipe 15 into the injection sleeve 24 through the molten metal pour port 25. The injection sleeve 24 is, therefore, filled with the inert gas so that the metal material remains absolutely free from potential oxidation even in the course of the above-described feeding of the molten metal 28 into the injection sleeve 24.
Upon completion of the feeding of the molten metal 28 into the injection sleeve 24 as much as needed for a single shot, the hydraulic cylinder 26 is immediately driven and controlled by a yet further command from the system controller 6. Described specifically, the injection plunger 27 is firstly driven forward at a low speed to perform gas venting in a known manner. Subsequently, the injection plunger 27 is driven forward at a high speed so that the molten metal 28 is rapidly injected and filled from the injection sleeve 24 into the cavity 23. FIG. 4 illustrates the state that the filling of the molten metal 28 into the cavity 23 has been completed. It is to be noted that a rearward drive of the linear motion member 12 is initiated at a suitable timing after the completion of the feeding of the molten metal 28 into the injection sleeve 24. The above-described injection and filling of the molten metal 28 into the cavity 23 result in the molding (casting) of molten metal in a similar manner as the molding (casting) of molten metal by a cold-chamber diecasting machine. Different from the conventional molten metal molding machine shown in FIGS. 6A through 6F, it is, therefore, possible to optimize the injection or filling speed and the flow area of the runner depending upon each product. Accordingly, the molten metal molding machine according to this embodiment is excellent in versatility, and can also mold (cast) heavy products. Further, the adoption of the cold-chamber control method, which has been widely used for many years, can stabilize the injection or filling operation. In cold-chamber molding (casting) of molten metal, a biscuit (in FIG. 4, numeral 29 indicates a biscuit) connected to a casting is also taken out at the same time as the casting is taken out of a mold. The molten metal is, therefore, allowed to remain as a fresh material not subjected to the heat cycle of heating→cooling→heating (not exposed to any long heat history), thereby making it possible to contribute to an improvement in the quality of casting.
This application claims the priority of Japanese Patent Application 2005-223038 filed Aug. 1, 2005, which is incorporated herein by reference.
Patent Application
20070023159
