Die casting machine and method

The die casting machine comprises a mold closing actuator capable of selectively inducing a closing pressure on first and second platens for forcing them towards a closed position in which their mold portions are pressed against each other along a parting line. An injection sleeve is movable relative to the mold portions between a distal position in which the injection sleeve and the mold portions are spaced apart; and an injection position in which the injection sleeve engages the mold portions at an inlet opening when the first and second platens are in their closed position. The injection sleeve applies a transverse contact pressure when it engages the mold portions. The closing pressure is unevenly distributed on the platens so as to compensate the transverse contact pressure to have a resulting effective molding pressure on the mold portions that is substantially evenly distributed across the parting line.

FIELD OF THE INVENTION

The present invention relates to die casting machines.

BACKGROUND OF THE INVENTION

Die casting machines are used to mold metallic articles. To do so, liquid metal is fed into the inner cavity of a mold where the metal hardens as it is cooled before the article is ejected from the mold. The process is repeated in a cycle to create numerous articles.

Molds typically comprise two mold portions that join at a so-called parting line that is in fact a plane along which mold surfaces of each mold portion engage one another. The mold portions both have recesses on these flat mold surfaces that form the inner mold cavity for liquid metal injection when the mold portions join. The mold portions can be separated to eject the metallic article once it is hard. In some molds, one of the mold portions is fixed and the other is mobile while in other instances, both mold portions are mobile. In both cases, the mold portions are movable relative to each other between a closed position in which the mold portions engage one another and an opened position in which the mold portions are spaced apart.

Die casting machines come in different types that are categorized in two groups: cold chamber die casting machines and hot chamber die casting machines.

A cold chamber die casting machine is typically used to mold aluminum pieces or sometimes pieces of another metal. In a cold chamber die casting machine, the injection sleeve (called the “shot sleeve”) is not partly submerged or otherwise surrounded by liquid metal. Rather, liquid metal is conveyed from a furnace located distally from the injection sleeve, to the injection sleeve, for example with a ladle that is operated by an automated arm or manually. The metal is consequently cyclically fed into the injection sleeve by this ladle before the ladle returns to the furnace to be refilled. While the ladle is being refilled, the injection sleeve injects the liquid metal into the mold cavity. A biscuit will desirably form at the inlet opening of the mold where the piston applies and maintains pressure against the metal while it hardens. The biscuit, usually of generally cylindrical shape, comprises hardened metal that is located partly in the shot sleeve and partly in the mold cavity at the cavity inlet opening, but that will not form part of the article being molded. Once the article is suitably hard, it will be ejected together with the biscuit, with the latter being disposed of for example by being returned to the furnace for the metal to be melted and reused.

A hot chamber die casting machine is typically used to mold zinc and magnesium pieces. It comprises a bath filled with molten liquid metal in which an injection sleeve, provided with a gooseneck in hot chamber die casting machines, is partly submerged. Liquid metal is allowed to cyclically flow into an inner chamber of the injection sleeve through an inlet opening to fill the inner chamber before a piston ejects the liquid metal out of the inner chamber and into the mold cavity, through an injection nozzle of the gooseneck provided on the injection sleeve. The liquid metal never completely hardens within the injection chamber or the injection nozzle and there is no formation of a biscuit in hot chamber die casting machines.

Hot chamber and cold chamber die casting machines each have respective operation characteristics, as known to those skilled in the art. It will be noted that principles that are applicable for hot chamber die casting machines are often not applicable for cold chamber die casting machines, and vice versa, due to differences in these operation characteristic. For example, the types of injection sleeves that are used differ (the injection sleeve in hot chamber die casting machines comprises a gooseneck having a nozzle while it doesn't in cold chamber die casting machines), the injection pressures differ, the formation of a biscuit in cold chamber die casting incurs cold-chamber specific requirements regarding injection pressures and mold-closing pressures; together with many other design and operation characteristics that are specific to the type of die casting machine—hot or cold—being used.

Concerning the biscuit mentioned above, it is noted that in cold chamber die-casting machines the metal will also harden within the passage called the runner which links the mold inlet opening to the gate, the latter being the entry point for the liquid metal into the mold cavity. So in fact, it is not only the biscuit that will be disposed of after the metal hardens, but also the diametrically smaller extraneous metal that extends between the biscuit and the gate in the runner. The gate is the point where the metal is distributed from the runner into the actual article cavity.

In known cold chamber dies casting machines, one platen is fixed while the other is mobile. The injection sleeve that injects the liquid metal into the mold cavity extends through the fixed platen and the corresponding fixed mold portion. One problem with prior art cold chamber die casting machines is linked to the feeding of liquid metal into the injection sleeve. Cold chamber injection sleeves comprise a piston movable within an elongated inner chamber, with the piston being capable of ejecting the liquid metal out through a liquid metal outlet port of the injection sleeve. In many cases, the injection sleeve is disposed horizontally and a liquid metal inlet port is provided atop the cylindrical sleeve, away from the outlet opening. The inner chamber is partly filled with liquid metal through the inlet opening, while the outlet opening is in fluid communication with the mold cavity. A problem with this configuration is that the horizontal disposition of the injection sleeve allows air to remain present in very significant proportion in the injection sleeve when the injection sleeve filling operation is completed but before the injection step starts. Indeed, the starting position of the piston will be the same notwithstanding the volume of injected liquid and consequently the injection sleeve will usually be filled only partly as a result of varying volumes being used to mold articles of different sizes. If the injection sleeve is half filled with molten metal, then it is also half filled with air. Consequently, a significant volume of air is often injected into the mold cavity concurrently with liquid metal, resulting in air bubbles being entrapped in the liquid metal in the mold. Although some known techniques exist to exhaust the entrapped air within the mold cavity, some air will often remain trapped, resulting in the metallic article comprising weakness zones once the metal is hardened where air bubbles are present.

Another injection sleeve configuration exists where the injection sleeve is provided with a single liquid metal port that is located at the free extremity of the injection sleeve and that is used both for filling the injection sleeve and for injecting the liquid metal into the mold. In this configuration, the injection sleeve is inclined to retain the liquid metal therein as it is being poured, thereby maximizing the volume of the injection sleeve inner chamber that is filled with liquid metal and consequently minimizing the volume of the injection sleeve that is occupied by air. However, this injection sleeve design suffers from at least one problem: the injection sleeve liquid metal port is located within the mold itself, forcing the feeding of the metal to be accomplished in an area between the two mold halves that is not easily accessible for a robotised arm. Significant design sacrifices have to be done on the die casting machine to accommodate such a configuration.

Positioning the injecting sleeve outside of the mold entirely and injecting the liquid metal at the parting line instead of between the two mold halves, has up to now not been seen as an operable or viable option in cold chamber die casting machines. Some prior art hot chamber die casting machines include injection at the parting line with the injection nozzle located outwardly of the mold. These hot chamber die casting machines have mold portions that close over the free metal liquid outlet extremity of the injection sleeve and the injection sleeve engages the mold at the parting line to inject the liquid metal parallel to and through the parting line into the mold cavity. In the case of hot chamber die casting machines, this design is possible since the injection force is relatively low.

However, in cold chamber die casting machines where injection forces are more important, this design with injection at the parting line is considered non-functional or non-practical and is not used in prior art devices to the knowledge of the present inventors. For one thing, the seal between the injection sleeve and the mold needs to be fluid-tight, as otherwise the liquid metal will be allowed to undesirably seep between the injection sleeve and the mold. To obtain a fluid-tight seal at important injection forces requires at the very least that the injection sleeve engage the mold at an important sleeve-mold sealing pressure. Since this sleeve-mold sealing pressure would be applied transversely of the mold, parallel to the parting line, this is likely to result in the mold being deformed by curving transversely unless the mold closing pressure is so important that it would counteract this deformation. Such a mold deformation would be undesirable since it would contribute to allowing the liquid metal to flash within the mold during the injection as a result of unevenly distributed pressure on the mold portions; while increasing the mold closing pressure significantly to counteract this deformation means that the die casting machine needs to be equipped with more expensive components in addition to more energy being expended to operate the die casting machine. In any event, by increasing the sleeve-mold sealing pressure, the mold is likely to wear down under the repeated pressured engagement of the sleeve on the mold. The mold wearing down at the junction area with the injection sleeve means that it might become uneven, resulting in the sleeve-mold sealing pressure being applied unevenly, in turn resulting in the metal seeping out between the injection sleeve and the mold during injection.

For these reasons and others, it has been considered common wisdom up to now to entirely avoid having a cold chamber die casting machine where the injection sleeve injects liquid metal at the parting line.

Air bubbles in the liquid metal also appear during the liquid metal pouring operation from the ladle into the injection sleeve, as a result of turbulence from the liquid metal inflow.

Another problem related to prior art die casting machines relates to liquid metal seeping outside of the inner mold cavity, between the mold portions. This undesirable seeping is called “flashing”. Reasons why the liquid metal flashes is because the pressure applied to keep the two mold portions pressed against each other is not important enough or is not well distributed along the parting line. One reason why this mold-closing pressure needs to be very important is to allow liquid metal injection at high pressure without the liquid metal flashing, the high pressure injection providing articles of higher quality.

SUMMARY OF THE INVENTION

A cold chamber die casting machine comprising:

first and second platens each holding respective first and second mold portions, said first and second platens being mounted to a base and being movable relative to one another along a longitudinal axis between an open position in which said first and second mold portions are spaced apart and a closed position in which said first and second mold portions are pressed against each other along a parting line to form a mold;

a mold cavity formed between and enclosed by said first and second mold portions when said first and second platens are in their closed position;

a mold closing actuator capable of selectively inducing a closing pressure on said first and second platens for forcing said first and second platens towards their closed position;

an inlet opening formed on said mold at said parting line and allowing access into said mold cavity when said platens are in their closed position for injecting liquid metal into said mold cavity;

an injection mechanism mounted to said base comprising an injection sleeve having an inner chamber and a liquid metal injection port, and an injector for forcing liquid metal from said inner chamber out through said liquid metal port, said injection sleeve being movable relative to said mold along a transversal axis between a distal position in which said liquid metal injection port and said inlet opening are spaced apart; and an injection position in which said injection sleeve engages said mold to form a seal about said inlet opening and said liquid metal injection port when said first and second platens are in their closed position, with said liquid metal injection port then being in liquid communication with said inlet opening for allowing liquid metal to be injected from said injection sleeve inner chamber into said mold cavity, with said transversal axis being transversal to said longitudinal axis.

In one embodiment, the cold chamber die casting machine further comprises:

a first male-female interface member provided on said injection sleeve around said liquid metal injection port; and

a second male-female interface member provided on said mold around said inlet opening;

wherein said first and second male-female interface members are complementary to form a male-female engagement seal between said injection sleeve and said mold around said liquid metal injection port and said inlet opening when said injection sleeve and said mold are in said injection position.

In one embodiment, said first male-female interface member comprises a female interface member and said second male-female interface member comprises a male interface member.

In one embodiment, said male interface member comprises an annular convex outer surface and said female interface member comprises an annular concave outer surface engageable against said male interface member annular convex outer surface to create a male-female engagement seal about said inlet opening and said liquid metal injection port.

In one embodiment, said male interface member annular convex outer surface has a radius of curvature which is smaller than the radius of curvature of said female interface member annular concave outer surface at the point of contact between said male and female interface members when said male-female engagement seal is created, for providing a substantially linear circular contact between said male and female interface members.

In one embodiment, said mold closing actuator comprises means for unevenly distributing said closing pressure on said first and second platens for compensating an injection sleeve contact pressure along said transversal axis resulting from said injection sleeve engaging said mold at said injecting position, to have a resulting effective closing pressure on said mold portions that is substantially evenly distributed across said parting line.

In one embodiment, said means for unevenly distributing said closing pressure on said first and second platens comprises tie bars parallel to said longitudinal axis and linked to said first and second platens, and a mold closing pressure inducing mechanism capable of inducing said closing pressure on said first and second platens via said tie bars for forcing said first and second platens towards their closed position, with said tie bars being disposed asymmetrically relative to said longitudinal axis for unevenly distributing said closing pressure on said first and second platens for compensating an injection sleeve contact pressure along said transversal axis resulting from said injection sleeve engaging said mold at said injecting position to have a resulting effective molding pressure on said mold portions that is substantially evenly distributed across said parting line.

In one embodiment, said tie bars are linked to said platens by means of tie bar support members that are more resilient than said platens and are allowed to resiliently deform when said closing pressure is applied to said first and second platens via said tie bar support members and said tie bars.

In one embodiment, said first platen defines a front side on which said first mold portion is installed, a back side opposite said front side and an outer peripheral surface extending between said front and back sides, said second platen defines a front side on which said second mold portion is installed, a back side opposite said front side and an outer peripheral surface extending between said front and back sides, wherein said tie bar support members comprise:

a first resilient tie bar support member attached to the first platen back side and protruding beyond the first platen peripheral surface; and

a second resilient tie bar support member attached to the second platen back side and protruding beyond the second platen peripheral surface;

and wherein said mold closing pressure inducing mechanism induces said closing pressure on said first and second platens via said first and second tie bar support members and said tie bars for forcing said first and second platens towards their closed position, said first and second support members resiliently deforming in a direction generally parallel to said longitudinal axis and towards one another.

In one embodiment, said tie bars comprise a first and a second tie bars that are positioned in offset fashion opposite said injection sleeve relative to said longitudinal axis.

In one embodiment, said first tie bar support member is elongated and defines opposite end portions that protrude beyond said peripheral edge of said first platen, and said second tie bar support member is elongated and defines opposite end portions that protrude beyond said peripheral edge of said second platen, with said first tie bar engaging registering end portions of said first and second tie bar support members and said second tie bar engaging registering end portions of said first and second tie bar support members.

In one embodiment, said first tie bar support member comprises a pair of spaced-apart first tie bar support plates, with said first and second tie bars each extending through both first tie bar support plates, and wherein said second tie bar support member comprises a pair of spaced-apart second tie bar support plates, with said first and second tie bars each extending through both second tie bar support plates.

In one embodiment, said first tie bar support member further comprises a first web linking said first tie bar support plates between said first and second tie bars and wherein said second tie bar support member further comprises a second web linking said second tie bar support plates between said first and second tie bars.

In one embodiment, said mold closing pressure inducing mechanism comprises tie bar sockets that attach said tie bars at a first end thereof to said first tie bar support member and high-pressure hydraulic cylinders acting on said tie bars at a second end thereof and attached to said second tie bar support member.

In one embodiment, said injection sleeve is fixed in translation to said base and said platens are movably mounted to said base so as to allow said injection sleeve to be movable relative to said mold between said distal and injection positions.

In one embodiment, said platens are mounted to said base by means of a transverse track member that allows said platens to move towards and away from said injection sleeve along said transversal axis, said die casting machine comprising a platen transverse actuator for selectively moving said platens along said transverse track member towards and away from said injection sleeve.

In one embodiment, said transverse track member is parallel to said transversal axis and is fixedly supported on said base in an inclined fashion at an angle ranging between 1° and 90° relative to a horizontal plane so that said platens will move down as they move towards said injection sleeve and up as they move away from said injection sleeve.

In one embodiment, said injection sleeve is elongated and is inclined so as to be parallel to said transversal axis, with said injection sleeve liquid metal port being located higher than said injection sleeve inner chamber.

In one embodiment, said transversal axis has an angle of approximately 45° relative to a horizontal plane.

In one embodiment, said injection sleeve is mounted to said base by means of a pivotal joint so as to be pivotable about an injection sleeve reference axis, said die casting machine further comprising an injection sleeve biasing member continuously biasing said injection sleeve towards said injection sleeve reference axis.

In one embodiment, said platens are carried by a longitudinal track member allowing said platens to move along said longitudinal axis, said longitudinal track member being in turn movable along said transverse track member, said die casting machine further comprising a platen longitudinal actuator for allowing said platens to move along said longitudinal track member.

In one embodiment, said mold cavity comprises an inner runner that extends away from said inlet opening in line with said injection sleeve.

In one embodiment, said injector comprises a plunger movable within said inner chamber for forcing liquid metal out of said inner chamber, said die casting machine comprising a linear guide member attached to said base and linked to said plunger for guiding said plunger as it moves.

In one embodiment, said injector comprises a plunger movable within said inner chamber for forcing liquid metal out of said inner chamber, said cold chamber die casting machine further comprising a plunger lubrication device for lubricating a head portion of said plunger.

The invention also relates to a method of molding a metallic article in a cold chamber die casting machine of the type comprising:

first and second platens each holding respective first and second mold portions, said first and second platens being movable relative to one another along a longitudinal axis between an open position in which said first and second mold portions are spaced apart and a closed position in which said first and second mold portions are pressed against each other along a parting line to form a mold;

a mold cavity formed between and enclosed by said first and second mold portions when said first and second platens are in their closed position;

a mold closing actuator capable of selectively inducing a closing pressure on said first and second platens for forcing said platens towards their closed position;

an inlet opening formed on said mold at said parting line and allowing access into said mold cavity when said platens are in their closed positions; and

an injection mechanism comprising a sleeve having an inner chamber and a liquid metal injection port, and an injector;

said method comprising the steps of:

filling at least partly said injection sleeve inner chamber with liquid metal;

relatively moving said first and second platens into said closed position;

relatively moving said injection sleeve and said mold along a transversal axis between a distal position in which said liquid metal injection port and said inlet opening are spaced apart; and an injection position in which said injection sleeve engages said mold around said inlet opening to form a seal between said injection sleeve and said mold about said inlet opening and said liquid metal injection port, with said liquid metal injection port then being in liquid communication with said inlet opening, with said transversal axis being transversal to said longitudinal axis;

injecting liquid metal from said injection sleeve inner chamber into said mold cavity with said injector;

allowing said liquid metal to cool and harden inside said mold cavity whereby the metallic article will be molded;

relatively moving said injection sleeve and said mold away from said injection position;

relatively moving said first and second platens away from their closed position; and

retrieving the metallic article from the mold.

In one embodiment, said injection sleeve is fixedly mounted in translation to a base and wherein said platens are movably mounted in translation to said base so as to be movable along said longitudinal axis and also along said transversal axis towards and away from said injection sleeve, the step of relatively moving said injection sleeve and said mold comprising moving said platens towards said injection sleeve along said transversal axis.

In one embodiment, said mold cavity comprises a runner that extends away from said inlet opening in alignment with said injection sleeve when said injection sleeve and said mold are in said injection position, with the step of injecting liquid metal from said injection sleeve inner chamber into said mold cavity with said injector comprising injecting liquid metal in a straight line from said injection sleeve and along said runner.

In one embodiment, the method further comprises the following steps:

providing a first male-female interface member on said injection sleeve around said liquid metal injection port;

providing a second male-female interface member on said mold around said inlet opening, said first and second male-female interface members being complementary so as to be capable of forming said engagement seal.

The invention also relates to a hot chamber die casting machine comprising:

first and second platens each holding respective first and second mold portions, said first and second platens being mounted to a base and being movable relative to one another along a longitudinal axis between an open position in which said first and second mold portions are spaced apart and a closed position in which said first and second mold portions are pressed against each other along a parting line to form a mold;

a mold cavity formed between and enclosed by said first and second mold portions when said first and second platens are in their closed position;

a mold closing actuator capable of selectively inducing a closing pressure on said first and second platens for forcing said first and second platens towards their closed position;

an inlet opening formed on said mold at said parting line and allowing access into said mold cavity when said platens are in their closed position for injecting liquid metal into said mold cavity;

an injection mechanism mounted to said base comprising an injection sleeve having an inner chamber and a liquid metal injection port, and an injector for forcing liquid metal from said inner chamber out through said liquid metal port, said injection sleeve being movable relative to said mold along a transversal axis between a distal position in which said liquid metal injection port and said inlet opening are spaced apart; and an injection position in which said injection sleeve engages said mold to form a seal about said inlet opening and said liquid metal injection port when said first and second platens are in their closed position, with said liquid metal injection port then being in liquid communication with said inlet opening for allowing liquid metal to be injected from said injection sleeve inner chamber into said mold cavity, with said transversal axis being transversal to said longitudinal axis;

wherein said mold closing actuator comprises means for unevenly distributing said closing pressure on said first and second platens for compensating an injection sleeve contact pressure along said transversal axis resulting from said injection sleeve engaging said mold at said injecting position, to have a resulting effective closing pressure on said mold portions that is substantially evenly distributed across said parting line.

The present invention further relates to a method of applying pressure on first and second mold portions during a molding operation in a die casting machine of the type comprising:

a first platen holding said first mold portion and a second platen holding said second mold portion, said first and second platens being movable relative to one another along a longitudinal axis between an open position in which said first and second mold portions are spaced apart and a closed position in which said first and second mold portions are pressed against each other along a parting line to form a mold;

a mold cavity formed between and enclosed by said first and second mold portions when said first and second platens are in their closed position, with said parting line extending within said mold cavity;

a mold closing actuator capable of selectively inducing a closing pressure along said longitudinal axis on said first and second platens for forcing said platens towards their closed position;

an inlet opening formed on said mold at said parting line and allowing access into said mold cavity when said platens are in their closed positions;

an injection mechanism comprising an injection sleeve having an inner chamber and a liquid metal injection port, and an injector, said platens and said injection sleeve being capable of relatively moving along a transversal axis between a distal position in which said liquid metal injection port and said inlet opening are spaced apart; and an injection position in which said injection sleeve engages said mold around said inlet opening when said first and second platens are in their closed position, with said liquid metal injection port then being in liquid communication with said inlet opening for allowing liquid metal to be injected from said injection sleeve inner chamber into said mold cavity, and with said transversal axis being transversal to said longitudinal axis; and

a transverse actuator capable of selectively inducing a transverse contact pressure along said transversal axis between said injection sleeve and said platens for relatively forcing said platens and said injection sleeve towards their injection position;

said method comprising the steps of:

relatively positioning said first and second platens in said closed position;

applying said closing pressure on said platens with said mold closing actuator;

relatively positioning said injection sleeve and said platens in said injection position;

applying said transverse contact pressure between said platens and said injection sleeve with said transverse actuator;

wherein said closing pressure is unevenly distributed on said platens so as to compensate said transverse contact pressure to have a resulting effective molding pressure on said mold portions that is substantially evenly distributed across said parting line.

In one embodiment, the step of relatively positioning said injection sleeve and said platens in said injection position is accomplished by said transverse actuator relatively moving said injection sleeve and said platens between said distal position and said injection position.

In one embodiment, said platens are movable in translation along said transversal axis relative to a base and said injection sleeve is fixed in translation to said base, said injection sleeve being elongated and positioned in an inclined fashion relative to a horizontal plane so that said liquid metal port will be higher than said inner chamber and so as to be substantially parallel to said transversal axis, the step of said transverse actuator relatively moving said injection sleeve and said platens between said distal position and said injection position being accomplished by moving said platens along said transversal axis in such a way that said platens will move down as they move towards said injection sleeve and up as they move away from said injection sleeve.

In one embodiment, the step of relatively positioning said first and second platens in said closed position is accomplished by moving said platens along said longitudinal axis along a longitudinal track member by means of a platen longitudinal actuator, said longitudinal track member in turn being movable by means of said transverse actuator along a transverse track member parallel to said transversal axis.

In one embodiment, said die casting machine is a cold chamber die casting machine.

In one embodiment, said die casting machine is a hot chamber die casting machine.

The invention also relates to a method of cyclically filling an injection sleeve of a die casting machine with liquid metal and ejecting the liquid metal out of said injection sleeve, said injection sleeve comprising an elongated inner chamber comprising opposite first and second ends, an open liquid metal port at said inner chamber second end and an ejector movable within said inner chamber between said first and second ends, said method comprising cyclically repeating the steps of:

positioning said ejector at a starting position located away from said inner chamber first end towards said inner chamber second end;

pouring liquid metal into said inner chamber through said liquid metal port;

retracting said ejector towards a retracted position away from said starting position while the liquid metal is being poured into said inner chamber; and

after the liquid metal has been poured into said inner chamber, ejecting the liquid metal from said inner chamber by moving said ejector towards said inner chamber second end.

In one embodiment, said starting position of said ejector is located substantially at said inner chamber second end.

In one embodiment, said starting position of said ejector is spaced from said inner chamber second end towards said inner chamber first end.

In one embodiment, the step of ejecting the liquid metal from said inner chamber by moving said ejector towards said inner chamber second end comprises said ejector reaching said inner chamber second end.

In one embodiment, the step of ejecting the liquid metal from said inner chamber by moving said ejector towards said inner chamber second end comprises said ejector stopping short of said inner chamber second end.

In one embodiment, the step of positioning said ejector at a starting position located away from said inner chamber first end towards said inner chamber second end comprises positioning said ejector at said inner chamber second end.

In one embodiment, the step of positioning said ejector at a starting position located away from said inner chamber first end towards said inner chamber second end comprises positioning said ejector away from said inner chamber second end.

In one embodiment, the method further comprises the following step after the step of pouring liquid metal into said inner chamber but before the step of ejecting the liquid metal from said inner chamber: moving said ejector to a pre-ejection position located away from said retracted position to help exhaust air from the liquid metal before it is ejected from said inner chamber.

The present invention further relates to a method of carrying molten metal in a ladle of a die casting machine in a conveyance direction from a furnace at which said ladle is filled with liquid metal to an injection sleeve in which the liquid metal is poured from said ladle, said method comprising the steps of:

accelerating said ladle away from said furnace as said ladle leaves said furnace;

decelerating said ladle as it approaches said injection sleeve; and

while said ladle accelerates and decelerates, tilting said ladle to maintain a same relative position of the liquid metal within said ladle.

In one embodiment, said ladle defines opposite top and bottom ends, a hollow main body and a mouth opening at said top end, the step of tilting said ladle to maintain a same relative position of the liquid metal within said ladle comprising tilting said ladle so that said mouth opening will face partly in said conveyance direction when said ladle accelerates.

In one embodiment, the step of tilting said ladle to maintain a same relative position of the liquid metal within said ladle comprising tilting said ladle so that said mouth opening will face partly away from said conveyance direction when said ladle decelerates.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1shows a die casting machine30generally comprising a molding section32, a furnace34, a molten metal conveyor36and a computer37. In use, and as detailed hereinafter, molten metal is conveyed from furnace34to molding section32with conveyor36to mold metallic articles at molding section32. These steps are intended to be repeated in a cycle, under control and synchronisation by computer37, for allowing multiple metallic articles to be molded with die casting machine30.

Furnace34is of known construction and comprises a housing38having an upper opening39allowing access into an inner chamber40comprising a crucible wherein molten metal is maintained at a temperature above its fusion point. This metal reserve will be filled when necessary with metallic ingots that will melt to a liquid state to replenish the liquid metal reserve. The temperature of furnace34may be controlled by computer37, although it could alternately be controlled independently directly at the crucible of furnace34. Computer37may be linked to furnace34through any suitable communication means, such as wired or wireless communication means.

Conveyor36comprises a rail member42supported spacedly over ground by a ground post44that holds a first end thereof and by a wall attachment46that holds a second end thereof. InFIG. 1, rail member42is partly broken for illustrative purposes, but it is understood that it extends in uninterrupted fashion from ground post44to wall attachment46. Any other suitable attachment means to support rail member42over ground could also be used.

FIGS. 1,2and8-10show that rail member42carries a robotic arm48that is movable along rail member42. Robotic arm48comprises a carriage50that slidably or rollably engages rail member42, a motor52for moving carriage50along rail member42and displacement means (not shown, such as wheels or a rack and gear system) that are activated by motor52to allow the displacement of carriage50along rail member42. Robotic arm48also comprises a track54that is fixed to carriage50and a telescopic arm56that is carried by and moves along track54. A ladle support rod58is pivotally attached to telescopic arm56and a ladle60is in turn pivotally attached to ladle support rod58. Ladle60defines opposite top and bottom ends62,64, a hollow main body66and a mouth opening68at its top end62. Mouth opening68defines a pouring spout69where molten metal will pour out of ladle68and a filling edge opening71wherein liquid metal will flow into ladle68to fill it when ladle68is dipped in molten metal.

Ladle60may consequently be moved towards and away from carriage50by moving telescoping arm56along track54. Furthermore, ladle60may be inclined either by pivoting ladle60relative to ladle support rod58(seeFIG. 2where ladle60is thusly tilted in alternate positions shown in dotted lines) and/or by pivoting ladle support rod58relative to telescopic arm56. Computer37controls robotic arm48and consequently the position and inclination of ladle60and may be linked to robotic arm48through any suitable communication means, such as wired or wireless communication means.

FIGS.1and3-6show that molding section32comprises first and second platens72,74each holding respective first and second mold portions76,78. More than one first mold portion76and more than one second mold portion78could be installed on first and second platens72,74. First and second platens72,74are mounted to a base80in a manner described hereinafter (i.e. they are mounted to base80by means of some intervening structures), and are movable relative to one another along a longitudinal axis L between an open position (FIGS. 3 and 4) in which first and second mold portions76,78are spaced apart and a closed position (FIGS. 5 and 6) in which said first and second mold portions are pressed against each other along a parting line to form a mold82.

FIG. 7shows that a mold cavity84is formed between and enclosed by first and second mold portions76,78when first and second platens72,74are in their closed position, with the parting line extending within mold cavity84. An inlet opening83is formed on mold82at its parting line and allows access into mold cavity84when platens72,74are in their closed position for injecting liquid metal into mold cavity84. Mold cavity84defines an inlet opening83leading into a biscuit cavity85, a runner86and an article cavity88where liquid metal will harden to mold the metallic article. A gate89leads from runner86into article cavity88. The configuration of mold cavity84will vary depending on the type of article being molded and the type of metal being used; and it will be obvious for someone skilled in the art of the present invention to substitute mold portions76,78for other mold portions to accommodate specific molding requirements. However, any mold portion must obviously include an inlet opening83for metal injection and an inner cavity84wherein liquid metal will be poured. Inner cavity84may include a single article cavity88or a plurality (not shown) of article cavities88all linked to inlet opening83for being filled with metal.

Biscuit cavity85is shown inFIG. 7to be of a generally conical shape. This is one advantage of the present invention over prior art die casting machines. The conical shape of biscuit cavity85will favor a low-turbulence inflow of liquid metal towards runner86and, more importantly, will accommodate a convex conical piston head that may protrude within biscuit cavity85as described hereinafter.

As shown inFIGS. 1,3and4(although partly concealed inFIG. 1and only partly shown inFIG. 3), base80comprises ground-resting bars90that rest on or are bolted to the ground, upright posts92that rest on or are bolted to the ground and that are fixed to respective ground resting bars90, inclined support bars94that rest on or are bolted to the ground and that are fixed to and extend in inclined fashion between respective ground-resting bars90and upright posts92, reinforcement trusses96that are fixed to and extend between respective ground-resting bars90, upright posts92and inclined support bars94, reinforcement crossbars98that are fixed to and extend between the ground-resting bars90and a lower support crossbar100that is fixed to and extends between the inclined support bars94near their lower end. A hydraulic cylinder seat102is fixedly attached to bottom support crossbar100.

FIGS.1and3-6show that die casting machine30further comprises a mold closing actuator106capable of selectively inducing a closing pressure on first and second platens72,74for forcing first and second platens72,74towards their closed position.

More particularly, first and second platens72,74are mounted to base80by means of a transverse track member108that includes first and second inclined tracks110,112that are fixed along respective inclined supports94. Tracks110,112in turn carry a longitudinal track member114mounted to a transversal carriage116that is movable along tracks110,112. Transversal carriage116is hollow at its center and carries track-engaging members117,119that engage inclined tracks110,112. A pair of hydraulic cylinders120,122that form a transverse actuator118are seated against hydraulic cylinder seat102and attached underneath transversal carriage116to move transversal carriage116up and down along inclined tracks110,112along a transversal axis T.

A longitudinal track member123, in the form of longitudinal tracks124,126, is installed atop carriage116and is parallel to longitudinal axis L. Platens72,74comprise backrests128,130that are supported by longitudinal carriages132,134that in turn engage longitudinal tracks124,126. A pair of hydraulic cylinders138,140, that form a longitudinal actuator136, are installed on transverse carriage116to move platens72,74along tracks124,126and consequently along longitudinal axis L.

Computer37is linked to longitudinal and transversal actuators136,118through any suitable communication means, such as wired or wireless communication means, to control actuators136,118.

Die casting machine30also comprises an injection mechanism150having an injection sleeve155mounted to base80and more particularly to U-shaped injection sleeve support151(FIG. 3). Within the present specification, the expression “injection sleeve” will be considered to include shot sleeves as typically used in cold chamber die casting machines.

Injection mechanism also comprises an injector in the form of a plunger160carried by a hydraulic cylinder152. Hydraulic power means154of known construction are operatively connected to hydraulic cylinder152under the control of computer37to control the displacement of plunger160. Computer37is linked to hydraulic power means154through any suitable communication means, such as wired or wireless communication means.

Injection sleeve155, which is further shown inFIGS. 8-10, comprises an inner chamber156and a liquid metal injection port158. Plunger160is movable within inner chamber156for forcing liquid metal from inner chamber156out through liquid metal injection port158. Plunger160comprises a plunger head162located within inner chamber156and a plunger rod163linked to head162, with plunger head162having a leading surface164of any suitable shape, such as a convex surface as shown inFIGS. 8-10. As suggested hereinabove, the convex generally conical leading surface164of plunger head162is complementary to the generally conical biscuit cavity85. Plunger rod163may comprise hollow central channels161for cooling fluid and/or lubricant to circulate therein.

As further detailed hereinafter, injection sleeve155is movable relative to mold82between a distal position in which liquid metal injection port158and mold inlet opening83are spaced apart; and an injection position in which injection sleeve155engages mold82at inlet opening83when first and second platens72,74are in their closed position, with liquid metal injection port158then being in liquid communication with inlet opening83for allowing liquid metal to be injected from injection sleeve inner chamber156into mold cavity84. Inner chamber156is elongated and defines opposite first and second ends166,168with liquid metal injection port158being located at the inner chamber second end168and with the plunger head162having a determined range of movement within inner chamber156between first and second ends166,168as detailed hereinafter. Injection sleeve155extends through the hollow center portion of transversal carriage116, with the latter being movable about injection sleeve as it moves up and down along transversal track member108.

To ensure a suitable sealing engagement between injection sleeve155and mold82, and as shown inFIG. 11, injection sleeve155is provided with a female interface member170at inner chamber second end168and mold82is provided with a complementary male interface member172on its outer surface at inlet opening83. More particularly, male interface member172comprises two semi-annular protrusions each on a corresponding mold portion76or78that form an annular protrusion on the mold outer surface around inlet opening82when mold portions76,78are joined in their closed position. Male interface member172comprises an annular convex outer surface and female interface member170comprises an annular concave outer surface engageable against the annular convex outer surface of male interface member172to create a male-female engagement seal.

In one embodiment, the annular convex outer surface of male interface member172has a radius of curvature which is smaller than the radius of curvature of the annular concave outer surface of female interface member170at the point of contact between the male and female interface members172,170when the male-female engagement seal is created, for providing a substantially linear circular contact between male and female interface members172,170. If both the male and female interface members172,170had a same radius of curvature, then an annular, non-linear contact area would exist between male and female interface members172,170that would be likely to be less fluid-tight than a linear contact is, due to the force between the injection sleeve155and the mold82being distributed over a larger area in the case of a non-linear contact area. Also, in the case of a non-linear contact area, it is more likely that the pressure between the injection sleeve155and the mold82will be distributed unevenly. Consequently, having a substantially linear contact at male-female interface members172,170is advantageous.

According to an alternate embodiment (not shown), the female interface member could be provided on the mold and the male interface member could be provided on the injection sleeve. Generally, a first male-female interface member that comprises either one of a male or a female interface member is provided on injection sleeve155at liquid metal injection port158and a second male-female interface member that comprises the other one of a male or a female interface member is provided on said mold at inlet opening83, with the first and second male-female interface members being complementary to form a male-female engagement seal between injection sleeve155and mold82when injection sleeve155is in its injection position.

However, the sealing arrangement wherein mold82is provided with the male interface member172that is engaged by the female interface member170of injection sleeve155will advantageously promote that the first and second mold portions76,78remain closed when liquid metal is being injected into mold cavity84. This arrangement is consequently preferred.

Injection sleeve155is mounted to injection sleeve support151of base80by means of a pivotal joint in the form of a spherical bearing174(FIGS. 8-10) so as to be pivotable about an injection sleeve reference axis. Spherical bearing174comprises an injection sleeve biasing member, for example spherical bearing174may comprise a resilient ring to continuously bias injection sleeve155towards its above-mentioned injection sleeve reference axis. The injection sleeve reference axis preferably coincides with transversal axis T.

Plunger rod163is mounted to hydraulic cylinder152by means of a coupling member175(FIGS. 8-10) that has a disc173with a concave plunger-receiving surface to which the complementary convex bottom end177of the plunger rod163is pivotally attached. Plunger rod is consequently allowed to pivot in this concave seat to follow any displacement of injection sleeve155while its displacement along the injection sleeve reference axis is provoked by hydraulic cylinder152.

A linear guide member in the form of a pair of linear bearing and shaft assemblies181,183(FIG. 3) that are fixed to base80and operatively coupled to coupling member175guide coupling member175and plunger rod163in their linear displacement under the extraction and retraction of hydraulic cylinder152. Linear bearing and shaft assemblies181,183help prevent wear of plunger head162, injection sleeve155and the piston of hydraulic cylinder152.

A runner insert179(FIG. 11) is preferably (although optionally) provided on mold76,78. Runner insert179is made of two half portions (only one being seen inFIG. 11) in which inlet opening83, biscuit cavity85and part of runner86are made. Runner insert179is made from a material that is slightly softer than that of injection sleeve155so that it is runner insert179that will wear over time. Runner insert179is replaceable once worn.

As mentioned hereinabove, mold closing actuator106is capable of inducing a closing pressure on platens72,74to force them towards their closed position. More particularly, this closing pressure will be induced once platens72,74are already in their closed position and will act to maintain platens72,74in their closed position against pressure exerted internally in mold82during liquid metal injection in mold82. Longitudinal actuator136will effectively move platens72,74between their opened and closed positions, while mold closing actuator106will induce a high-pressure force on platens72,74to ensure that they do not separate during molding operations, as detailed hereinafter.

Mold closing actuator106comprises a number of tie bars, for example two tie bars180,182as shown in FIGS.1and3-6, that are parallel to longitudinal axis L and linked to first and second platens72,74by means of tie bar support members184,186. Tie bar support members184,186are more resilient than platens72,74and are allowed to slightly resiliently deform when the closing pressure is applied to first and second platens72,74via tie bar support members184,186and tie bars180,182. This deformation is suggested in dotted lines inFIG. 6, although this deformation is exaggerated inFIG. 6for illustrative purposes, in reality the deformation is not as important as that shown inFIG. 6.

First tie bar support member184comprises a pair of spaced-apart first tie bar support plates188,190, with first and second tie bars180,182each extending through both first tie bar support plates188,190and through respective hollow cylindrical tie bar sleeves192,194that are fixed between and space apart first tie bar support plates188,190. First tie bar support member184further comprises a first web196linking and spacing first tie bar support plates188,190in-between sleeves192,194.

Second tie bar support member186comprises a pair of spaced-apart second tie bar support plates198,200, with first and second tie bars180,182each extending through both second tie bar support plates198,200and through respective tie bar sleeves202,204that are fixed between and space apart second tie bars support plates198,200. Second tie bar support member186further comprises a second web205also linking and spacing second tie bar support plates198,200in-between sleeves202,204.

First tie bar support member184is elongated and defines opposite end portions that protrude beyond the peripheral edge of first platen72, and second tie bar support member186is elongated and defines opposite end portions that protrude beyond the peripheral edge of second platen74. That is to say, first and second tie bar support members184,186are wider than first and second platens72,74. First tie bar180engages registering end portions of first and second tie bar support members184,186and second tie bar182engages registering end portions of first and second tie bar support members184,186to allow first and second tie bars to extend exteriorly of the periphery of first and second platens72,74, spaced therefrom, to avoid any friction or contact between platens72,74and tie bars180,182when platens72,74move between their opened and closed positions.

First and second tie bars180,182are fixed at a first end thereof to a respective tie bar socket203,207located exteriorly of second tie bar support member186.

Mold closing actuator106further comprises a mold closing pressure inducing mechanism206capable of inducing the above-mentioned closing pressure on first and second platens72,74. This closing pressure is induced by means of first and second high-pressure hydraulic cylinders208,210via tie bars180,182for forcing first and second platens72,74towards their closed position. First and second tie bars180,182in fact directly extend into first and second high-pressure hydraulic cylinders208,210to form the cylinder rods thereof, although alternately first and second tie bars180,182could be operatively coupled to distinct cylinder rods of first and second high-pressure hydraulic cylinders208,210. In any event, since first and second tie bars180,182are fixed to sockets203,207at their first end as mentioned above, when high-pressure hydraulic cylinders208,210are retracted, the closing pressure is transferred to platens72,74via tie bar support members184,186and tie bars180,182; while the closing pressure is released when high-pressure hydraulic cylinders are extracted.

Computer37controls high-pressure hydraulic cylinders208,210and is linked to them through any suitable communication means, such as wired or wireless communication means.

As will be obvious for someone skilled in the art by now, die casting machine30as shown in the drawings is a cold chamber die casting machine wherein the liquid metal port158and inner chamber156of injection sleeve155and the inlet opening83of mold82are generally of a same cross-sectional dimension for allowing formation of a biscuit after the liquid metal has been injected into mold cavity84.

In use, die casting machine30is controlled through computer37for molding metallic articles, although it is understood that other automated and also some partly manual control mechanisms could be used instead of computer37. To mold a metallic article, ladle60is first filled with liquid metal at furnace34. To accomplish this, robotic arm48is moved along rail member42until robotic arm48is properly aligned over the furnace opening39. Telescopic arm56is then lowered along track54until ladle60is at least partly submerged into liquid metal. A system for detecting the level of liquid metal in the crucible of furnace34may be provided for allowing the ladle to be lowered accordingly. The inclination of ladle60may be suitably adjusted before and during the insertion of ladle60into the liquid metal to optimise the filling operation. More particularly, ladle60may be tilted while it is partly inserted into the molten metal to have the molten metal flow into its hollow main body66over filling edge portion71of mouth opening68. Once ladle is suitably filled with the proper quantity of liquid metal, ladle60is tilted back to a horizontal position and telescopic arm56is lifted to retrieve the now-filled ladle60from the crucible of furnace34.

The liquid molten metal is then carried in ladle60in a conveyance direction D (FIG. 2) along rail member42from furnace34to injection sleeve155where ladle60will be used to pour the liquid metal into injection sleeve inner chamber156. Conveyance direction D is the direction that leads from furnace34to injection sleeve155. According to the present invention, the method for carrying the liquid metal comprises the steps of:accelerating robotic arm48, and consequently ladle60, away from furnace34as ladle60leaves furnace34;decelerating ladle60as it approaches injection sleeve155; andwhile ladle60accelerates and decelerates, tilting ladle60to maintain a same relative position of the liquid metal within ladle60.

More particularly, as suggested inFIG. 2, the step of tilting ladle60to maintain a same relative position of the liquid metal within ladle60comprises tilting ladle60so that mouth opening68will face at least partly in said conveyance direction when ladle60accelerates and will face partly away from said conveyance direction when ladle60decelerates.

This is advantageous in that it will reduce turbulence of the liquid metal in ladle60and is likely to consequently reduce the likelihood of undesirable bubbles appearing in the liquid metal during the conveyance towards the injection sleeve155. It will also help prevent accidental spilling of liquid metal out of ladle60during high-speed transportation.

When ladle60reaches a position above injection sleeve155, the filling of injection sleeve155may commence. First, ladle60will be positioned adjacent to the liquid metal port158of injection sleeve155, in a position resembling that ofFIG. 8. Then, according to the present invention, the method of filling injection sleeve155and then ejecting liquid metal from injection sleeve155comprises:positioning piston head162at a starting position located away from inner chamber first end166towards said inner chamber second end168. The starting position could but need not correspond to the inner chamber second end168, it could be located anywhere along inner chamber156away from first end166to give it room for later retraction towards first end166;pouring liquid metal into inner chamber156through liquid metal port158. All liquid metal poured into inner chamber156will of course remain over piston head162. The liquid metal is poured from ladle60through its spout69although in alternate embodiments the ladle mouth opening68could be symmetrical and any point at its periphery could be used to pour the liquid metal;retracting piston head162from its starting position towards inner chamber first end166while the liquid metal is being poured into inner chamber156. This is sequentially suggested inFIGS. 8-10. The purpose behind retracting the piston head162during the filling operation is to minimize turbulence and air bubble formation in the liquid metal; andejecting the liquid metal from inner chamber156by moving piston head162towards inner chamber second end168.

These steps will be cyclically repeated for filling the injection sleeve repeatedly, each filling corresponding to one liquid metal injection shot.

The starting position of piston head162can be located substantially at the inner chamber second end168. This means either at the inner chamber second end168, or slightly retracted into or even out of inner chamber156, but near second end168. Alternately, the starting position of piston head162can be spaced away from inner chamber second end168towards inner chamber first end166, for example one quarter, one half or three quarters of the way into inner chamber156, as long as there remains enough spaced for piston head162to be retracted further while the liquid metal is being poured.

During the liquid metal ejection, piston head162may reach inner chamber second end168, extend slightly out of inner chamber second end168or remain within inner chamber second end168(in the latter case, formation of a biscuit may occur partly within inner chamber156).

After having poured the liquid metal into inner chamber156but before ejecting the liquid metal out of inner chamber156, it is possible to move piston head162to a pre-ejection position located away from its retracted position to exhaust air from the liquid metal before it is ejected from inner chamber156. This movement may be done at slow speed to promote air exhaust without causing significant turbulence in the liquid metal present in inner chamber156. This movement may be accomplished either towards from inner chamber second end168or even away from inner chamber second end168—in the latter case if some leeway exists between the liquid metal and the inner chamber mouth opening158to avoid spilling liquid metal. This air exhaust may be accomplished either before injection sleeve155engages mold portions76,78or even after—in the latter case the air will be exhausted through the mold vents that are conventionally used to exhaust air from within the mold.

According to the present invention, the method of molding a metallic article with die casting machine30comprises:filling at least partly injection sleeve inner chamber156with liquid metal. This filling operation can be accomplished as described above with retraction of the piston head162while the liquid metal flows into the injection sleeve inner chamber156, or in a more traditional way by simply positioning the piston head162at a desired position and then filling the inner chamber156;relatively moving first and second platens72,74into their closed position wherein the mold portions76,78will abut each other at the parting line. According to the embodiment shown in the annexed drawings, this is accomplished with longitudinal actuator136moving platens72,74but it could alternately be accomplished otherwise, including by using a closing linkage or by using the high pressure mold closing pressure inducing mechanism206to move platens72,74in addition to it providing the high-pressure mold closing pressure. It is also noted that this relative movement can be accomplished by simultaneously moving both first and second platens72,74towards each other as per the embodiment shown in the drawings or alternately by having one fixed platen and one movable platen that will move to engage the fixed platen;relatively moving injection sleeve155and mold82between a distal position in which liquid metal injection port158and inlet opening83are spaced apart; and an injection position in which injection sleeve155engages mold82around inlet opening83and in which first and second male-female interface members172,170engage each other to form an engagement seal between injection sleeve155and mold82, with liquid metal injection port158then being in liquid communication with inlet opening83. In the embodiment shown in the drawings, this relative movement is accomplished with transversal actuator118moving platens72,74and mold82down towards injection sleeve155along transversal axis T, but any other suitable means to accomplish this relative movement would be acceptable, including by moving either one of injection sleeve155, platens72,74or both. It is noted that the relative movement of injection sleeve155and mold82may be accomplished simultaneously with the relative movement of first and second platens72,74towards each other, as long as the latter reach their closed position before injection sleeve155and mold82engage each other. Also, although the male-female engagement is one advantageous way to carry out the invention, other suitable sealing engagements may also be used wherein the geometry of the interacting elements or their materials may be adapted to offer a suitable seal between the injection sleeve155and the mold82. For example, a seal comprising a deformable O-ring or a seal wherein one of the injection sleeve155and the mold82is softer than the other to slightly elastically deform under pressure, could be used;injecting liquid metal from injection sleeve inner chamber156into mold cavity84with injector160, i.e. piston head162will be pushing the liquid metal out of inner chamber156to convey it through mold inlet opening83;allowing the liquid metal to cool and harden inside mold cavity84whereby the metallic article will be created. During the cooling operation, a biscuit will form in inlet opening83and possibly partly in injection sleeve inner chamber156;relatively moving injection sleeve155and mold82between their injection position and their distal position. The distal position refers to a position where injection sleeve155and mold82are spaced apart, it need not be moved to the same place after the molding operation as it was before the molding operation;relatively moving first and second platens72,74away from their closed position; andretrieving the metallic article from the mold. Ejecting mechanisms212,214of known construction are provided on die casting machine30, and more particular are fixed to first and second tie bar support members184,186, to facilitate this operation. It should be noted that in prior art cold chamber die casting machines where the injection sleeve was located on the backside of one of the platens, it was not possible to provide ejecting mechanisms on both platens whereas with the die casting machine of the present invention where the injection sleeve is located at the parting line, providing ejecting mechanisms on the backside of both platens becomes possible. The biscuit formed during the cooling operation may also be recuperated at this time, to be forwarded to the furnace so that the metal may be reused.

According to the present invention, a plunger lubrication device216(FIG. 3) that includes a movable lubrication nozzle is optionally attached to base80for lubricating the plunger head162. Plunger lubrication device216comprises a pressurized lubricant reservoir and is controlled by computer37that cyclically moves the lubrication nozzle over the plunger head162to spray lubricant thereon.

One advantage of the present invention lies in the fact that the injection sleeve is separated from the mold itself and it may be filled through its liquid metal port158while an article is being molded within mold82. Indeed, by having the injection sleeve155and mold82move away from each other after the liquid metal shot has been injected into mold82, injection sleeve155is free to be filled with a new liquid metal shot while the previous metal shot is being cooled in mold82to form the article. This significantly decreases the total article molding cycle time compared to prior art devices wherein the new liquid metal shot was only poured into the injection sleeve once the article was completed and retrieved from the mold.

In the embodiment shown in the drawings, mold cavity84comprises a runner86that advantageously extends away from the mold inlet opening83in line with injection sleeve155when injection sleeve155and mold82are in their injection position. When liquid metal is injected from injection sleeve inner chamber156into mold cavity84with plunger160, the liquid metal will consequently be injected in a straight line from injection sleeve155through runner86. This is advantageous over prior art devices wherein the injection sleeve extends through the fixed platen and a 90° elbow exists between the injection sleeve and the runner that leads up to the article cavity which impedes the liquid metal flow, causing undesirable turbulence during injection, and requires extra injection pressure to feed the liquid metal into the prior art mold cavity.

Transverse track member108is fixedly supported on base80in an inclined fashion at an angle ranging between 1° and 90°, for example at 45°, relative to a horizontal plane so that platens72,74will move down (at least in part) as they move towards injection sleeve155and up (at least in part) as they move away from injection sleeve155. This movement is accomplished along transversal axis T. Moreover, injection sleeve155is also aligned with transversal axis T, which allows injection sleeve155to advantageously engage mold82orthogonally. The fact that injection sleeve155is mounted on a spherical bearing174allows it to compensate any very small irregularity in alignment when it engages mold82: it will then pivot slightly to become evenly engaged at male-female interface members172,170. Plunger rod163will pivot correspondingly due to its pivotal attachment to coupling175.

The injection sleeve155being inclined allows its liquid metal injection port158to be higher than its inner chamber156, which allows inner chamber156to be filled without liquid metal spilling out of liquid metal injection port158. It also allows a larger proportion of inner chamber156to be filled, as opposed to prior art horizontal injection sleeves wherein it was frequent for only a fraction of the injection sleeve to be filled, resulting in considerable undesirable air injection in mold cavity84. The inclination of injection sleeve155also allows the pre-ejection position of the piston head162to be adjusted depending on the volume of the liquid metal shot, preventing the use of a single-purpose pre-ejection position that would then allow much more air to be injected into mold cavity84when liquid metal shots of smaller volume are being used.

It should be noted that, contrarily to prior art die casting methods, the step of injecting liquid metal from injection sleeve inner chamber156into mold cavity84with injector160does not require an intensification step at the end of the injection wherein the pressure applied by plunger163is increased. This is an unexpected and advantageous result over the prior art obtained because there is almost no air injected into the mold cavity due to the inclined disposition of the injection sleeve155. As a consequence, the injection cycle time is reduced, the hydraulic system is simpler and wear of injection components is reduced due to lower injection pressures.

Mold closing actuator106comprises means for unevenly distributing the closing pressure on first and second platens72,74for compensating a transverse injection sleeve contact pressure resulting from injection sleeve155engaging mold82at said injecting position. The purpose is to obtain a resulting effective molding pressure between first and second mold portions76,78that will be substantially evenly distributed across the parting line. More particularly,FIG. 7shows that tie bars180,182are disposed asymmetrically relative to the center point of mold82where longitudinal axis L passes. This allows a considerable transverse injection sleeve contact pressure to be applied against mold82without the elongated mold-platen assembly undesirably curving under this transverse contact pressure. Having an important transverse injection sleeve contact pressure on mold82is in itself very desirable to help avoid liquid metal from leaking between injection sleeve155and mold82during injection, and to allow an increase in injection pressure and consequently an increase in article quality.

The present invention consequently comprises a method of applying pressure on first and second mold portions76,78during the molding operation, with first and second platens72,74being in their closed position and with injection sleeve155and platens72,74being in their injection position, the method comprising concurrently applying:a closing pressure on platens72,74with mold closing actuator106wherein the closing pressure is unevenly distributed so as to compensate the transverse contact pressure to have a resulting effective molding pressure on mold portion76,78that is substantially evenly distributed across the parting line; anda transverse contact pressure between platens72,74and injection sleeve155with transverse actuator118.

The expression “substantially evenly distributed” refers here to the fact that although the effective molding pressure distribution will be very well distributed, a precisely even effective molding pressure distribution is almost impossible to achieve in practice. For one thing, the pressure distribution will vary depending on the mold being used, the article being molded, the molding temperature and other operation parameters. However, the effective molding pressure between the two molds would be quite uneven if the closing pressure and the transverse contact pressure did not compensate one another.

The application of the closing pressure and the transverse contact pressure does not need to be constantly concurrent, it may be for example that the mold will first be closed and the closing pressure will be applied on the platens initially without any transverse contact pressure; and in a second step the mold will be moved against the injection sleeve and the transverse contact pressure will then be applied before molding starts.

To further help evenly distribute the effective mold closing pressure between first and second mold portions76,78at the parting line, tie bar support members184,186are resilient and are allowed to deform when mold closing pressure inducing mechanism106is activated. More particularly, first and second tie bar support plates188,190and198,200are more resilient than platens72,74, and more particularly than the platen backrests128,130. Tie bar support plates188,190,198,200are attached to platen backrests128,130and protrude beyond their respective platen peripheral surfaces. Upon the mold closing pressure inducing mechanism106inducing the closing pressure via first and second tie bar support members184,186and tie bars180,182for forcing first and second platens72,74towards their closed position, the tie bar support plates188,190,198,200of first and second support members184,186will resiliently deform in a direction generally parallel to longitudinal axis L and towards one another, as shown inFIG. 6. This will promote an even distribution of the closing pressure on platens72,74and even more so at the mold parting line.

All steps from the ladle being filled with liquid metal at the furnace crucible, the liquid metal being conveyed from the furnace crucible to the injection sleeve, and then the injection and molding themselves, are to be repeated in a cycle to allow die casting machine30to create multiple metallic articles. This may be accomplished at high injection pressures to increase article quality that can be deployed at molding section32, these high injection pressures being allowed due to the effective evenly distributed high molding pressure which in turn is allowed by the asymmetrical closing pressure distribution of the offset tie bars180,182that allow the injection sleeve to be applied with more important transverse contact pressure.

The advantageous male-female seal between the injection sleeve and the mold also helps in preventing liquid metal from leaking out between the mold and the injection sleeve. In particular the female interface member170on the injection sleeve and the male interface member on the mold that help keep the mold closed.

The fact that the injection sleeve is applied entirely on the exterior of the mold helps ensure a proper closure of the mold. Indeed, if the mold were to close at least partly on the injection sleeve, the injection sleeve itself might hamper the mold in closing properly, especially as a result of thermal expansion of the injection sleeve.

The high production rate is also a result of the injection sleeve filling operation being accomplished with less turbulence that allows it to be done at a greater speed without spilling; and also to the liquid metal conveyance also being allowed to be accomplished at a greater speed since the inclination of the filled ladle60while it moves along rail member142allows for more important acceleration and deceleration with less turbulence and spilling.

While the injection and cooling steps occur at mold82, ladle60will return to the furnace to be refilled and return to fill injection sleeve immediately as soon as possible, for example before the mold opens to eject the metallic article if there is enough space for ladle60to fill injection sleeve155; or after the mold opens if not. One or more additional ladles may be provided to feed injection sleeve if using a single ladle would slow the process down, these additional ladles being filled either at the same furnace34as the first-named ladle60, or at other furnaces if necessary.

It is understood that base80could have any other suitable configuration than that shown in the drawings, including separate base portions for the injection sleeve and the platens.

It is further understood that, within this specification, when reference is made to liquid metal, this includes any metal that may flow through the injection sleeve into the mold, including metal having a relatively high viscosity such as the so-called semi-solid metal. According to an alternate embodiment of the invention, the die casting machine could be a hot chamber die casting machine wherein the injection sleeve would be at least partly enclosed in a furnace and liquid metal would be selectively allowed to flow from the furnace into the injection sleeve inner chamber through a liquid metal filling port. This liquid metal filling port would be distinct from the liquid metal injection port. As with most hot chamber die casting machines, the injection sleeve would comprise a nozzle at the liquid metal injection port for allowing the injection of the liquid metal into the mold. No biscuit formation would occur during and after the injection. Within the present specification, the expression “injection sleeve” will be considered to include injection nozzle-type injection sleeves as typically used in hot chamber die casting machines.

FIG. 12shows portions of a hot chamber die casting machine300that is similar in many aspects to the die casting machine30of the first embodiment. The platens, mold portions, mold closing actuators, longitudinal and transverse actuators and base are all similar to that of die casting machine30.

FIG. 12, which is similar to the cross-sectional view ofFIG. 7, shows one platen302holding one mold portion304in which a mold cavity306is defined. Mold cavity306has an inlet opening308leading into a runner310that in turn leads into an article cavity312. As usual for hot chamber die casting molds, no biscuit cavity exists. A pair of tie bars314,316extend parallel to the longitudinal axis L′ of hot chamber die casting machine300and work like tie bars180,182of the first embodiment.

Hot chamber die casting machine300also comprises a furnace318having a liquid metal bath320wherein liquid metal is provided. An injection mechanism322is used to inject liquid metal into the mold and comprises a gooseneck-type injection sleeve324having an inner chamber326generally divided in two portions: a first inner chamber portion328wherein an injector in the form of a plunger331is movable and a second, elbowed inner chamber portion330that leads to a nozzle332. A liquid metal inlet port334is provided in the injection sleeve wall to allow liquid metal to flow into and partly fill inner chamber326when plunger331is retracted away from liquid metal inlet port334. When plunger331is extracted into the inner chamber first portion328, it will force the liquid metal out through the inner chamber second portion330, nozzle332and into the mold cavity306. InFIG. 12, the platens have been moved in their injecting position against the nozzle and the plunger is injecting liquid metal into the mold cavity306.

It can be appreciated that the embodiment shown inFIG. 12will work similarly to that ofFIGS. 1-11in that the tie bars314,316are disposed asymmetrically relative to the longitudinal axis L′ of die casting machine for unevenly distributing the closing pressure on the first and second platens for compensating an injection sleeve contact pressure along the transversal axis T′ resulting from the injection sleeve324engaging the mold at the injecting position to have a resulting effective molding pressure on the mold portions that is substantially evenly distributed across the parting line.