DIE MOLDING MACHINE AND OPERATING PROCEDURES

Description

[0001] The invention relates to a die-casting machine comprising a mold, a casting chamber, a casting piston axially movable within the casting chamber, a melt inlet channel leading into the casting chamber, a shut-off valve in the melt inlet channel, a melt outlet channel leading from the casting chamber to the mold, and a control unit for controlling the casting piston. The invention further relates to a method for operating such a die-casting machine, in which, for each casting operation, during a mold-filling phase, the casting piston in the casting chamber is advanced from a casting start position to a filling end position with the shut-off valve closed, thereby forcing molten material into the mold via the melt outlet channel. In a subsequent refilling phase, the casting piston is moved back to the casting start position, thereby supplying molten material back to the casting chamber via the melt inlet channel with the shut-off valve open.

[0002] Die-casting machines of this type and similar designs, along with their associated operating procedures, are generally used to cast a specific component, also called a casting, in a given casting process or cycle. The present die-casting machine, hereinafter also referred to simply as the machine, and the present operating procedure are particularly suitable for metallic die-casting, e.g., for casting liquid or semi-liquid molten metals such as zinc, lead, aluminum, magnesium, titanium, steel, copper, and alloys of these metals. The die-casting machine may, in particular, be a hot-chamber die-casting machine. In this design, the casting chamber is formed within a casting container that is immersed in a molten bath held by a melt reservoir.

[0003] During the mold-filling phase of the casting process, molten material in the casting chamber is forced under pressure through the molten outlet channel into a mold cavity formed by the mold by the forward movement of the casting piston, thus creating the casting. The mold typically consists of a fixed and a movable mold half, between which the mold cavity is formed, also called the mold cavity or, synonymously, simply the mold. In typical designs, the molten outlet channel includes a riser pipe section of the casting chamber on the inlet side and a nozzle attached to the casting chamber on the outlet side. This means that after leaving the casting chamber, the molten material passes through the riser pipe section and the nozzle to a molten inlet in the area directly in front of the mold cavity, where a sprue is typically located.

[0004] During the refilling phase, the pouring piston is moved from its filling end position back to its starting position, i.e., the pouring start position. This return movement of the pouring piston refills molten material into the pouring chamber via the melt inlet channel. The refilling phase can therefore also be referred to as the piston return phase.

[0005] In a suitable machine type, such as the one particularly well-suited to the present die-casting machine, the melt outlet channel leads from the casting chamber separately from the melt inlet channel. This means that the melt inlet channel and the melt outlet channel form two separate guide channels for the molten material, each with a casting chamber inlet where the melt inlet channel enters the casting chamber and a separate casting chamber outlet where the melt outlet channel exits the casting chamber. This configuration facilitates independent control of the melt flows in the melt inlet channel and the melt outlet channel, with the melt flow in the melt inlet channel specifically being controllable by the shut-off valve located there.

[0006] Depending on the system design, a check valve actuated solely by melt pressure or an actively controlled shut-off valve can be used. The latter is referred to here as a shut-off control valve and is controlled by the control unit. In these types of die-casting machines and associated operating processes, the shut-off control valve is typically kept closed during the entire mold filling phase and open during the entire refilling phase. Compared to a simple check valve, as an actively controlled shut-off valve, it offers the possibility of influencing or regulating the melt flow in the melt inlet channel, if necessary, independently of the melt pressure conditions in the casting chamber or in the melt inlet channel.

[0007] Depending on the system design, the control unit comprises either a single control device integrating all control functionalities of the die-casting machine, or several individual control devices, each controlling or regulating specific machine components and preferably interconnected. As is customary, the control unit can be implemented at least partially in hardware and / or at least partially in software. In this case, the control unit specifically controls the casting piston, or more precisely, its movement, and optionally one or more other machine components, such as the shut-off control valve, if the shut-off valve is implemented as such.

[0008] Patent EP 0 576 406 B1 discloses such a procedure for a system with a displacer-type casting piston, known as an alternative to a slide-type casting piston, and with a shut-off control valve arranged directly at the opening of the melt inlet channel into the casting chamber. In the slide-type piston, the outer diameter of the casting piston corresponds to the inner diameter of the casting chamber, with the piston being sealed against the casting chamber wall. Consequently, in this case, the casting piston, during its forward movement, completely pushes the molten material in the casting chamber forward and exerts the necessary pressure on the molten material to force it into the mold cavity. In the displacer-type piston, the outer diameter of the casting piston is suitably smaller than the inner diameter of the casting chamber, so that the casting piston, during its forward movement, plunges into the molten material of the casting chamber.In this case, the pressure on the molten material is caused by the displacement effect of the casting piston volume immersed in the molten material.

[0009] German patent application DE 32 48 423 A1 also discloses a generic die-casting machine and an associated operating method, in which a casting piston with a pre-piston of the displacer type and a pressurized gas that can be additionally supplied to the casting chamber are used, and the shut-off control valve is located in a casting container containing the casting chamber at a respective flow-related distance upstream of the casting chamber and downstream of an inlet to the casting container in the melt inlet channel. The shut-off control valve is kept closed during the mold filling phase.During the refilling phase, the shut-off control valve is opened and a certain amount of pressurized gas is introduced into the casting chamber. This prevents a vacuum from forming in the casting chamber before the shut-off control valve opens, thus preventing any molten metal from splashing onto the casting piston section behind the pre-piston. It also pre-pressurizes the gas pressure in the casting chamber to a certain degree above atmospheric pressure. After the required amount of molten metal has been supplied during the refilling phase, the shut-off control valve is closed again.

[0010] In die casting, for economic reasons, the aim is to achieve the shortest possible cycle time, i.e., the duration of each casting process, and for reasons of casting quality, the lowest possible air content in the casting, i.e., minimal air porosity of the casting. To address the latter aspect in particular, patent EP 1 284 168 B1 proposes that, at the beginning of the mold filling phase or before the actual mold filling phase, in a pre-filling phase, the casting piston be advanced while the mold is still open, to such an extent that the molten material fills the riser channel area and the nozzle body area, before the mold is then closed and the casting piston is advanced further to carry out the actual mold filling phase.The casting piston is of the slide type and itself functions as a shut-off device, releasing the casting chamber inlet during the refilling phase by moving backwards and shutting it off during the mold filling phase by moving forwards beyond the casting chamber inlet.

[0011] Other aspects to be considered generally in die casting machines of the present type include minimizing wear effects on the opposing walls of the casting piston and casting chamber due to the stroke movement of the casting piston in the casting chamber, especially if it is of the slide type, and preventing undesirable melt droplet formation in the area of ​​the sprue cone, which usually forms the entry-side interface of a mold-side melt channel structure opening into the mold cavity on the exit side for coupling to the nozzle body.

[0012] The invention is based on the technical problem of providing a die-casting machine and an associated operating method of the type mentioned at the outset, which offer advantages over the prior art explained above, particularly with regard to achieving relatively short casting cycle times and / or relatively low air porosity in the casting and / or with regard to a relatively low tendency for wear of the casting piston and casting chamber and / or avoiding the formation of molten droplets in the sprue cone area.

[0013] The invention solves this problem by providing a die-casting machine operating method with the features of claim 1 and a die-casting machine with the features of claim 10. Advantageous further developments of the invention are specified in the dependent claims.

[0014] According to one aspect of the operating method according to the invention, to which claim 1 relates, during the refilling phase of the casting process, the previously opened shut-off valve is closed before the casting piston has reached its casting start position through its return movement. Through the further return movement of the casting piston, molten material is drawn back into the melt outlet channel, i.e., partially drawn back from the melt outlet channel into the casting chamber. In the case of a shut-off control valve, the closing of the shut-off valve can be actively carried out by the control unit; in the case of a check valve, for example, by a preloading element, such as a preload spring, which biases the valve into its closed position.Thus, in this operating procedure, during the initial part of the refilling phase, the shut-off valve is open as the casting piston moves back, allowing molten material to be added to the casting chamber via the melt inlet channel. During the remainder of the refilling phase, the shut-off valve is closed, allowing molten material to be drawn back into the melt outlet channel as the casting piston continues to move back. In the implementation as a shut-off control valve, the associated control unit opens the valve to its open position; in the implementation as a check valve, the negative pressure of the molten material in the casting chamber opens it.

[0015] This process according to the invention advantageously combines the necessary refilling of the casting chamber with molten material via the melt inlet channel with a partial recirculation of molten material in the melt outlet channel. After the filling phase, the unsolidified molten material in the melt outlet channel is preferably not completely recirculated down to the melt level present in the casting chamber or an upstream melt bath, but can remain in the melt outlet channel to a degree adjustable or predetermined by appropriately selecting the closing time of the shut-off valve or the corresponding position of the casting piston, up to a forward portion of the channel. Therefore, in a subsequent casting process, it is not necessary to move the molten material back up to this fill level in the melt outlet channel.

[0016] This inventive method offers several advantages due to these properties. For example, the cycle time for successive casting processes can be shortened. Likewise, the stroke of the casting piston in the casting chamber can be reduced, thereby minimizing associated wear effects. Wear on wear-prone parts of the casting chamber and the casting piston, including conventional piston rings, is also significantly reduced by this inventive method compared to conventional systems where the casting piston acts as a shut-off device for the melt inlet channel, because the negative pressure occurring during the return movement of the casting piston in the casting chamber can be kept considerably lower, if necessary, by appropriately controlling or adjusting the shut-off valve.Since the melt outlet channel can remain largely filled with molten material between successive casting processes, there is correspondingly little air in the front section of the melt outlet channel at the beginning of each casting process, which significantly reduces the air porosity of the produced casting, thus significantly improving the quality of the produced casting.

[0017] By drawing back unsolidified molten material in the molten outlet channel to a controllable or controlled extent, i.e., in a controllable or predetermined quantity, the undesirable formation of a molten droplet in the area of ​​the sprue of the die-casting machine or its mold can be very advantageously prevented. This occurs at the sprue or at the transition or exit of the molten outlet channel or a nozzle body forming its exit-side section to a subsequent nozzle tip. The molten material is drawn back from the exit area of ​​the molten outlet channel to a greater or lesser extent. The degree of backflow can be appropriately adjusted or predetermined according to the requirements and the characteristics of the die-casting machine.The chosen design should be such that, on the one hand, the aforementioned melt droplet formation is reliably avoided and, on the other hand, the melt material remains relatively far forward, i.e., preferably in a forward or far-forward area, in the melt outlet channel.

[0018] In advantageous implementations, the molten material is drawn back so far that, on the one hand, it remains in the melt outlet channel up to a forward or relatively far forward area, i.e., it is contained there, but on the other hand, it lies behind the sprue cone or the outlet of the melt outlet channel at a certain, relatively small distance of, for example, approximately 5 mm to 100 mm, where the molten droplet would otherwise form. This distance is particularly important given that the melting point, located shortly behind the outlet depending on the system, is between approximately 10 mm and approximately 50 mm, preferably between approximately 30 mm and approximately 40 mm, depending on the requirements, viscosity of the molten material, and / or system design of the machine.In typical designs of die casting machines, the required back-suction stroke of the casting piston from the casting piston position where the shut-off valve is closed, to the casting start position, is in the range of one to a few millimeters, e.g. between approximately 2mm and 20mm.

[0019] The backflow method also has the advantage of gaining additional piston stroke length, which can be used in the first part of the mold-filling phase of the subsequent casting process to accelerate the piston before it begins to force the molten material into the mold. This can be particularly advantageous for molds with no or only a relatively small sprue.

[0020] Another advantage of backflow prevention can arise in applications where the gate to the casting solidifies before the still partially liquid material in the sprue. In such cases, it is possible to backflow unsolidified molten material from the sprue, thus avoiding the need to remelt it. Depending on the mold and other conditions, this can amount to, for example, up to approximately 5% of the total amount of molten material introduced into the mold.

[0021] In a further development of the invention, the casting piston is moved back at a lower speed during the refilling phase when the shut-off valve is closed than during the preceding phase when the shut-off valve is still open. In other words, in this case, the casting piston moves back at a lower speed during the final back-suction phase with the shut-off valve closed than during the initial refilling phase with the shut-off valve open. This selection of a non-constant speed profile of the casting piston during the refilling phase advantageously combines a rapid initial refilling of the melt into the casting chamber with a moderately slower subsequent back-suction process and the casting piston reaching the starting position.

[0022] In a further development of the invention, during the refilling phase of the casting process, the previously opened shut-off valve is closed as soon as the casting piston reaches a valve changeover position through its return movement. In the case of a shut-off control valve, this can be achieved by an actively controlled valve switch at this point in time, and in the case of a check valve, for example, by stopping the casting piston in the valve changeover position and / or opening the closed mold so that no further molten vacuum is created in the casting chamber, thereby automatically resetting the check valve to its closed position. With this measure, the switching of the shut-off valve from its open position to its closed position occurs depending on the position of the casting piston, more precisely, depending on its reaching a specific position, referred to here as the valve changeover position or valve reversing position.Closing the shut-off valve stops the flow of molten material into the casting chamber via the melt inlet channel. This allows the casting piston to retract from its valve switching position to its casting start position, drawing the desired amount of molten material back from the melt outlet channel into the casting chamber. In the case of a check valve, unwanted opening of the shut-off valve during this period can be prevented, for example, by opening the mold before the casting piston moves further back from its valve switching position. In alternative designs, the trigger for switching the shut-off valve from its open to its closed position during the refilling phase of the casting process is activated differently, for example, by the elapsed time since the start of the refilling phase or since the start of the casting piston's return movement.

[0023] In one embodiment of the invention, the stroke distance between the valve switching position of the casting piston and the casting start position can be variably preset. This allows for flexible adaptation to different system conditions. The stroke distance of the valve switching position of the casting piston from the casting start position determines the proportion of the final return movement of the casting piston from its valve switching position to its casting start position relative to the total casting piston stroke, which is determined by the distance between the filling end position and the casting start position, and thus also the degree of melt recirculation in the melt outlet channel. This stroke distance is naturally greater than zero and less than the total casting piston stroke, i.e., the stroke distance between the filling end position and the casting start position, and can be set to a desired value or one corresponding to the requirements of the respective application, e.g., a value between approximately 2 mm and 20 mm, and more specifically between approximately...The stroke length is 4 mm and 8 mm, depending on requirements and the system specifications of the die-casting machine. In corresponding implementations, it is at most half, one-third, or one-quarter of the total casting piston stroke, or even less. A larger stroke distance between the valve switching position and the casting start position increases the amount of molten material drawn back into the melt outlet channel, while a shorter stroke distance reduces the amount of molten material drawn back into the melt outlet channel. The stroke distance between the valve switching position and the casting piston's starting position can be selected differently, for example, for various interchangeable molds used in the die-casting machine. In alternative designs, this stroke distance can be fixed if variable adjustment is not required.

[0024] In one embodiment of the invention, during the refilling phase of the casting process, the casting piston is held in the valve switching position for a specified duration before being moved back to its starting position. This stop duration for the piston's return movement can be used to switch the shut-off valve from its open to its closed position and, if necessary, to open the mold. This allows the shut-off valve to switch during a period when there is no flow of molten material in the melt inlet channel and thus through the shut-off valve, but rather when the molten material is stationary in the melt inlet channel. The duration of the stop can be suitably determined, e.g.,Depending on the time required for the shut-off valve to switch from the open to the closed position and / or the time required to open the mold, a variable stop duration can optionally be specified. In alternative designs, the shut-off valve switches from its open to its closed position without interrupting the return movement of the casting piston, i.e., without the casting piston being completely stopped in its return movement after reaching its valve switching position.

[0025] In a further development of the invention, during the refilling phase of the casting process, the mold is kept closed at least as long as the shut-off valve remains open. This measure results in molten material being refilled into the casting chamber via the melt inlet channel by the return movement of the casting piston, but no noticeable backflow of molten material occurs in the melt outlet channel as long as the shut-off valve is in its open position. This is because, since the mold is still closed and contains the casting, which is usually at least partially solidified at this point, no significant amount of air can enter the melt outlet channel. Therefore, no molten material is drawn back from the melt outlet channel into the casting chamber during this initial part of the refilling phase. In alternative embodiments, the mold is already opened or...in any case, they started opening it while the shut-off valve was still open.

[0026] In one embodiment of the invention, which is particularly suitable when a shut-off control valve is used as the shut-off valve, the mold is opened during the refilling phase of the casting process after the casting piston has reached its starting position. With this approach, the recirculation of molten material in the melt outlet channel essentially only occurs once the casting piston has reached its starting position. As the casting piston moves back from the valve changeover position, at which point the shut-off control valve closes, to the starting position, it first creates a corresponding vacuum. Then, after the mold begins to open, the molten material is drawn back from the melt outlet channel into the casting chamber by the associated vacuum effect.

[0027] In an alternative embodiment of the invention, the mold is opened during the refilling phase of the casting process after the casting piston has reached its valve switching position and before it reaches its casting start position. With this approach, molten material can be drawn back into the melt outlet channel or from the melt outlet channel into the casting chamber even during the piston's subsequent return movement to its casting start position. It is understood that, in corresponding embodiments, the mold can be opened at any point during the piston's return movement from its valve switching position to its casting start position; alternatively, in corresponding implementations, this can also be done before the piston has reached its valve switching position and the shut-off valve is closed.

[0028] In a further embodiment of the invention, during the refilling phase of the casting process, the casting piston is stopped in its valve switching position and moved from this position to its casting start position as soon as the mold reaches a specific casting piston trigger mold opening position during opening. In this implementation, the subsequent return movement of the casting piston after stopping in its valve switching position is coordinated with the opening process of the mold, specifically such that the casting piston is only moved to its casting start position once the mold has opened by a predetermined amount, defined by the fixed casting piston trigger mold opening position. This allows for further optimization of the process of drawing back molten material into the melt outlet channel in the final section of the refilling phase of the casting process.In alternative designs, the return movement of the casting piston occurs without regard to the current opening position of the casting mold, unless this is required for the application.

[0029] In a further development of the invention, the casting piston is moved from its casting start position, reached during the refilling phase of a previous casting process, to a prefilling position in an initial prefilling section of the mold filling phase of the next casting process, while the mold is not yet completely closed. Only then is the mold completely closed, and the casting piston moved further from this prefilling position to its filling end position. This allows air that has entered the front area of ​​the melt outlet channel due to the backflow of melt during the refilling phase of the previous casting cycle to escape quickly at the beginning of the current casting cycle through the still completely open or at least partially open mold, before the mold is completely closed and the actual mold filling with the molten material takes place.

[0030] According to a further aspect of the invention, to which claim 1 is directed and which may be provided in addition to or as an alternative to the first-mentioned aspect of claim 1, the casting piston in the casting chamber is moved from a starting position to a specific pre-filling position during a pre-filling phase of the starting casting process before the mold filling phase, with the shut-off valve closed, and then moved back to its starting position with the shut-off valve open. Depending on requirements and application, the mold can be closed before or at the beginning of this pre-filling phase, or alternatively, it can be kept open during the pre-filling phase while the casting piston is moving forward and only closed before the casting piston moves back or when the shut-off valve is opened.In the first case, no further measures are taken to ensure that no molten material can unintentionally escape through the still open mold during this pre-filling process; in the latter case, air that is forced out of the molten outlet channel by the pre-filling process can escape more quickly through the still open mold.

[0031] This inventive procedure represents a specific start-up measure that can be advantageously applied when a cyclic casting operation of the die-casting machine is started for the cyclic casting of a plurality of identical castings with a specific mold in successive casting processes or casting cycles, e.g. after mounting the mold or casting tool on the die-casting machine or after restarting the die-casting machine with a specific mounted mold.

[0032] In other words, the start-up casting process represents the first casting operation or casting cycle for producing the desired casting after the machine has started up. During such a start-up, the molten material is not yet in a front section of the melt outlet channel, but at most in a rear section, for example, up to the level of the melt fill level in the casting chamber or a melt bath into which a casting container containing the casting chamber is immersed.The special start-up casting process ensures that the molten material is already present in a front area of ​​the melt outlet channel for the first of several successive casting processes after such a machine start-up, when the mold filling phase begins, by moving the casting piston from its starting position towards its filling end position to push the molten material into the mold.

[0033] Prior to this mold-filling phase, during the pre-filling phase of the start-up casting process, the casting piston is moved from its current start-up position to the pre-filling position, while the shut-off valve remains closed. This allows molten material to be forced from the casting chamber into the melt outlet channel. The pre-filling position of the casting piston is determined by the point at which the molten material has filled the melt outlet channel to a desired, predefinable level.By subsequently opening the shut-off valve and moving the casting piston back from its pre-filling position to its casting start position, which can correspond to the operating start position or a further forward position of the casting piston in the casting chamber between the operating start position and the pre-filling position, molten material is replenished into the casting chamber via the melt inlet channel in a maximum quantity that was previously pushed out of the casting chamber into the melt outlet channel.

[0034] For the subsequent first casting process after the machine has started, the same or similar conditions exist with regard to the amount of molten material already present up to a certain point in the melt outlet channel as for the subsequent casting processes once the machine has started. In other words, for this first casting process, the molten material is already present in the melt outlet channel up to a certain point in its flow, for example, in the entire volume of a riser channel section and in the volume of a subsequent nozzle body section of the melt outlet channel up to the front end of the nozzle body, and thus also significantly above the bath level of an associated melt bath from which the molten material is supplied to the casting chamber.This offers the advantage that, thanks to this one-time pre-filling at the start of operation, the plunger stroke required for the subsequent actual mold filling phase can be significantly reduced for the first casting cycle after operation has begun. In alternative designs, instead of this pre-filling measure after the machine has started, the first casting process is carried out with a correspondingly longer plunger stroke than the subsequent casting processes in the started operating period.

[0035] In the die-casting machine according to the invention, the control unit and the shut-off valve are configured to carry out each casting process in a mold-filling phase, to bring the shut-off valve into a closed position and to control the casting piston in the casting chamber to move forward from a casting start position to a filling end position in order to push molten material into the casting mold via the molten outlet channel, and in a subsequent refilling phase, to first bring the shut-off valve into an open position and to control the casting piston to move back to the casting start position in order to supply molten material to the casting chamber via the molten inlet channel.

[0036] Furthermore, the control unit and the shut-off valve are designed to return the shut-off valve to its closed position during the refilling phase, before the casting piston has reached its casting start position through its return movement, and to control the casting piston for the reabsorption of molten material in the molten outlet channel through the further return movement of the casting piston, and / or, during an operational start casting process, to control the casting piston for pre-movement in the casting chamber in a pre-filling phase of the operational start casting process before the mold filling phase with the shut-off valve closed, and subsequently to return the shut-off valve to its open position and to control the casting piston for return to its casting start position.

[0037] This makes this die-casting machine particularly suitable for carrying out the aforementioned aspects of the operating method according to the invention.

[0038] In a further development of the invention, the shut-off valve is designed as a shut-off control valve, and the control unit is configured to control the shut-off control valve. This enables active control of the shut-off valve by means of the control unit, in particular to move it to its desired open or closed position during a casting process.

[0039] In one embodiment of the invention, the die-casting machine includes a valve actuator controlled by the control unit for actuating the shut-off control valve. The actuator acts as an interface between the control unit and the shut-off valve and can be selected appropriately depending on the type of control unit and shut-off valve, e.g., of an electric, magnetic, hydraulic, pneumatic, or mechanical type. Alternatively, the valve actuation functionality can be integrated directly into the control unit.

[0040] In a further development of the invention, the shut-off valve is designed as a check valve pre-tensioned in its closed position. This represents an alternative to its implementation as a shut-off control valve. In this case, the shut-off valve is controlled or actuated depending on the pressure of the molten material acting upon it, in particular the molten pressure in the casting chamber.

[0041] In a further development of the invention, the die-casting machine includes a valve sensor unit for sensing one or more measured variables of the shut-off valve. This can be used, for example, to provide the control unit with feedback on the current position of the shut-off valve via the valve sensor unit and / or to provide valve diagnostic information that indicates whether the shut-off valve is functioning correctly, what its operating condition is, and whether, for example, maintenance is required.

[0042] Advantageous embodiments of the invention are illustrated in the drawings. These and further embodiments of the invention are explained in more detail below. The drawings show: Fig. 1 a schematic longitudinal sectional view of a part of a die-casting machine of interest here, with a shut-off control valve as a shut-off valve; Fig. 2 a flow diagram to illustrate an operating procedure for the die-casting machine of Fig. 1 from a start of operation, Fig. 3 the view of Fig. 1 when operating the machine according to the procedure of Fig. 2 at the beginning of a mold-filling phase of a first casting cycle, Fig. 4 the view of Fig. 3 during the mold filling phase, Fig. 5 the view of Fig. 3 after the mold filling phase has ended, at the beginning of a refilling phase of the first casting cycle, Fig. 6, the view of Fig. 3 during the refilling phase, Fig. 7 the view of Fig. 3 after refilling the casting chamber with molten metal, Fig. 8 shows the view of Fig. 3 during a melt recirculation following the melt refill, Fig. 9 the view of Fig. 3 Towards the end of the first casting cycle, Fig. 10 shows the view of Fig. 3 at the end of the mold filling phase of a second casting cycle, Fig. 11 a flowchart to illustrate an operating procedure for the die casting machine of Fig. 1 in a variant with an initial pre-filling phase after start-up, Fig. 12 the view of Fig. 3 when operating the machine according to the procedure of Fig. 11 at the beginning of the initial pre-filling phase, Fig. 13 the view of Fig. 12 at a later point in the initial pre-filling phase with melt refilling into the casting chamber, Fig. 14 the view of Fig. 12 at the end of a mold-filling phase following the initial pre-filling phase of the first casting cycle in the process variant of Fig. 11 , Fig. 15 a flowchart to illustrate an operating procedure for the die casting machine of Fig. 1 in a variant with cyclic pre-filling before the mold-filling phase of each casting cycle and Fig. 16 the view of Fig. 1 for a variant of the die-casting machine with a check valve as a shut-off valve.

[0043] In the Fig. 2 , 11 and 15 Various advantageous variants of the die-casting machine operating method according to the invention are illustrated in flowchart form. Fig. 1 , 3 bis 10 and 12 bis 14 or the Fig. 16 Figure 1 schematically shows the relevant part of a die-casting machine in two embodiments according to the invention, which can be operated using the inventive method. This die-casting machine can, in particular, be a hot-chamber type machine for die-casting liquid or semi-liquid molten metals, such as zinc, lead, aluminum, magnesium, titanium, steel, copper, and alloys of these metals. The die-casting machine comprises, in particular, a mold 1 with a fixed mold half 1a and a movable mold half 1b, a casting chamber 2, a casting piston 3 arranged axially movable in the casting chamber 2, a melt inlet channel 4 leading into the casting chamber 2, a shut-off valve 5 in the melt inlet channel 4, a melt outlet channel 6 leading from the casting chamber 2 to the mold 1, and a control unit 7.

[0044] The shut-off valve 5 is in the example of the Fig. 1 , 3 bis 10 and 12 bis 14 The valve 5s is designed as a shut-off control valve, i.e., as a controllable shut-off valve, which is controlled directly by the control unit 7 or, as in the example shown, via an optional valve actuator 16. The valve actuator 16 can be any conventional actuator known to those skilled in the art for actuating such a valve. Depending on requirements and application, the actuator 16 can be, in particular, a conventional electrically operated, hydraulically operated, pneumatically operated, or mechanically operated type, or a type operating via a lever system, etc. Depending on requirements and application, the valve actuator 16 can be a purely binary actuator type that switches the shut-off valve 5 only between a first, open position and a second, closed position, or alternatively, a proportional actuator type that can open the shut-off valve 5 continuously or in several stages.The shut-off valve 5 can also be moved and held in one or more partial opening positions between its fully open and fully closed positions. The valve actuator can, if required, include variably adjustable end stops that can be adjusted manually or automatically. Fig. 16 shows in a schematic representation accordingly Fig. 1 a variant of the die-casting machine that differs from the one in Fig. 1 The difference is that the shut-off valve 5 is designed as a check valve 5 R.

[0045] The term "control unit 7" here encompasses all control elements of the die-casting machine for controlling and regulating the various machine components. Depending on the system design, control unit 7 may comprise a single control device in which all control functionalities are integrated, or several individual control devices, each controlling and regulating specific machine components and preferably interconnected. Likewise, control unit 7 can, as is customary, be implemented at least partially in hardware and / or at least partially in software. For symbolic purposes only, and to illustrate all machine control functionalities of control unit 7, control arrows 7a, 7b, and 7c are shown, which extend from control unit 7 to the mold 1, the casting piston 3, and so on.to a valve stem 5d of the shut-off valve 5, whereby the control functions belonging to these machine components are of primary interest. For the sake of simplicity, the schematic representation of the control unit 7 is only shown in . Fig. 1 contained in the Fig. 3 bis 10 and 12 bis 14 However, they were omitted.

[0046] Unless otherwise discussed below, both the control unit 7 and the other machine components mentioned are of a conventional design familiar to those skilled in the art, and therefore require no further explanation here. In the example shown, as can be seen, for instance, from... Fig. 1 The casting chamber 2 is evidently formed in a casting container 8 of a conventional casting unit, wherein the casting container 8 is immersed in a melt bath 9 during the casting operation, which is located in a conventional melt container 10.

[0047] In the examples shown, the shut-off valve 5 is held on the casting vessel 8 by a valve housing body 5a. The valve housing body 5a, or alternatively, another location on the casting vessel 8, has one or more inlet openings serving as the inlet 4a of the melt inlet channel 4, meaning that molten material 14 can enter the melt inlet channel 4 from the melt bath 9 via the inlet 4a. Specifically, the shut-off valve 5 is located in the melt inlet channel 4 with a fixed valve seat 5b and a movable valve closing element 5c. In the example shown, the valve closing element 5c can be moved axially towards and away from the valve seat 5b via the valve rod 5d to close or open the shut-off valve 5, i.e., to, for example, Fig. 1 shown disclosure VO and one e.g. in Fig. 3 The valve can be switched to the closed position VS shown. Depending on the valve design and / or operating situation, the open position VO can be either fully open or partially open. In alternative embodiments not shown, the shut-off valve 5 is arranged in the casting piston 3, in which case the melt inlet channel 4 is guided over the casting piston 3, in particular through it, as is known per se.

[0048] In the machine version of the Fig. 1 , 3 bis 10 and 12 bis 14 The switching movement of the shut-off valve 5, i.e., the shut-off control valve 5s, is carried out, as already mentioned, by the control unit 7 via the optional valve actuator 16. In the machine version of the Fig. 16 The switching movement of the shut-off valve 5, i.e., the check valve 5R, is dependent on the melt pressure in the casting chamber 2, with the check valve 5R being biased into its closed position VS by a conventional biasing unit 17. When a corresponding melt vacuum is present in the casting chamber 2, the check valve 5R is moved by this vacuum against the biasing force of the biasing unit 17 from its closed position VS to its open position VO. As soon as the melt vacuum is no longer present, the check valve 5R automatically returns to its closed position VS due to the action of the biasing unit 17. The biasing unit 17 can, for example, be implemented by a biasing spring, such as a suitably designed and arranged compression or tension spring, with the biasing unit 17 being in Fig. 16 is represented only as an example and schematically by a tension spring illustration.

[0049] The molten metal outlet channel 6 leads out of the casting chamber 2 in a conventional manner via a riser channel section or riser pipe section 6a formed in the casting vessel 8 and then continues via a nozzle body 6b to the area of ​​the mold 1. For this purpose, the nozzle body 6b is coupled in a conventional manner at the inlet side to a nozzle extension 11, through which the riser pipe section 6a opens from the casting vessel 8, and at the outlet side leads to the area of ​​a sprue cone 12 in the fixed mold half 1a in front of a casting cavity 13, which, when the casting mold 1 is closed, is formed by the two mold halves 1a, 1b and is designed depending on the casting to be produced.

[0050] Fig. 2 The operating method according to the invention is illustrated in an exemplary embodiment during the start-up of the die-casting machine, i.e., after starting the machine to cast a desired number of identical castings in a corresponding number of successive casting processes or casting cycles. Fig. 1 and 3 bis 10 schematically illustrates the machine in different operating stages during operation according to the design variant of Fig. 2 The machine is located in the Fig. 3 bis 10 only for the sake of simplicity in the execution of Fig. 1 As shown, the related explanations below apply equally to the machine design of Fig. 16 , unless otherwise stated.

[0051] In an initial operational stage B1 of Fig. 2 The machine is in a basic state at the start of operation. Fig. 1 The machine is shown in this operating stage B1, with the exception that the mold 1, which is open in the initial state, is already shown in its closed state. The casting piston 3 is accordingly in an operating start position BS. The shut-off valve 5 is still open, so that the molten material 14 is present everywhere up to the level of a melt bath level 9a in the melt bath 9. In particular, the molten material 14 is also located in the melt outlet channel 6 at the same melt level SH corresponding to the melt bath level 9a, whereby the molten material 14 extends, for example, to a middle or front area of ​​the rising channel section 6a and not yet to the nozzle body 6b.

[0052] In a subsequent operational stage B2 of Fig. 2 A first casting cycle is initiated, and a corresponding mold-filling phase is carried out. For this purpose, the casting mold 1 is first closed, and the shut-off valve 5 is moved from its open position VO to its closed position VS or held there, either as a shut-off control valve 5s controlled by the control unit 7 or as a check valve 5 R automatically by the pre-tensioning unit 17. Fig. 3 The machine displays this at this point. Subsequently, the casting piston 3 is moved from the operating start position BS to a filling end position FP, i.e., into the Fig. 1 , 3 bis 10 and 12 bis 14 Each downward movement causes molten material 14 to be forced from the casting chamber 2 through the melt outlet channel 6 into the mold 1. The forward movement of the casting piston 3 is symbolized in the corresponding figures by an associated direction of movement arrow GV. The molten flow in the melt outlet channel 6 is shown in Fig. 4 symbolically indicated with corresponding flow arrows, whereby Fig. 4 the machine at the end of this mold filling phase, which in a manner known per se may include a so-called holding pressure phase in which an additional, increased holding pressure is exerted on the melt material 14 in the mold 1.

[0053] In an operational stage B3 of Fig. 2 The mold filling phase is complete, and a refilling phase, or piston return phase, follows. For this, the shut-off valve 5 is switched from its closed position VS to its open position VO, and the casting piston 3 is moved back from its filling end position FP, i.e., upwards in the relevant figures. In the case of the shut-off control valve 5s, the switching of the shut-off valve 5 is controlled by the control unit 7; in the case of the check valve 5R, it is controlled by the molten vacuum created in the casting chamber 2 due to the return movement of the casting piston 3. It should be noted here that, depending on the machine type, the forward or backward movement of the casting piston 3 may not be in a vertical direction as in the example shown, but rather perpendicular or inclined to the vertical direction.The mold 1 remains closed initially, and the so-called cooling time begins, during which the molten material 14 in the casting cavity 13 cools down, so that the desired casting 15 is formed by the solidifying molten material 14. The return movement of the casting piston 3 draws molten material 14 from the melt pool 9 through the melt inlet channel 4 into the casting chamber 2, thus replenishing it. Fig. 5 und 6 The figures show the machine at an initial and a slightly later point in the refilling phase, during which the molten material 14 is transferred from the melt bath 9 into the casting chamber 2, as illustrated by the corresponding flow arrows. The return movement of the casting piston 3 is symbolized in the corresponding figures by an associated direction-of-movement arrow GR.

[0054] In an operational stage B4 of Fig. 2 The refilling of molten material 14 from the melt bath 9 into the casting chamber 2 via the melt inlet channel 4 is terminated by switching the shut-off valve 5 from its open position VO to its closed position VS. In the case of the shut-off control valve 5s, this is effected by the control unit 7; in the case of the check valve 5R, it is effected by stopping the return movement of the casting piston 3, thus preventing the creation of a melt vacuum in the casting chamber 2. As a result, the check valve 5R automatically returns to its closed position VS via its pre-tensioning unit 17. At this point, the casting piston 3 is in a corresponding valve reversing position VU. Preferably, the casting piston 3 is held in this position for a specified duration, the length of which can be appropriately predetermined, in particular such that the shut-off valve 5 has reached its closed position VS when the stop duration has elapsed.Optionally, it may also be possible, for example, to select the stop duration according to the changeover time of the shut-off valve 5 from its open position VO to its closed position VS, or to monitor when the shut-off valve 5 has reached its closed position VS, and then to end the stop duration or to move the casting piston 3 further. Fig. 7 The machine displays this at this point. Meanwhile, the cooling time for the molten material 14 in the mold 1 to form the casting 15 continues.

[0055] After the stop duration has elapsed or the valve changeover position VU has been passed, or after the shut-off valve 5 has been closed, the casting piston 3 is in an operating stage B5. Fig. 2 The piston is then moved back to a casting start position GS for a subsequent, second casting process, thereby initiating a melt recirculation process. The casting start position GS can be identical to the initial operating start position BS of the casting piston 3 or differ from it to a limited extent. Fig. 8 The machine shows the casting piston 3 in an intermediate position ZS during this return movement of the casting piston 3 beyond or out of the valve switching position VU.

[0056] In the variant with the shut-off control valve 5s, this valve is controlled and held in its closed position VS, and the mold 1 is not yet opened. As a result, the further return movement of the casting piston 3 causes a suction effect across the casting chamber 2 onto the melt outlet channel 6. This creates a vacuum in the area of ​​the sprue cone 12, causing the molten material 14 to retract somewhat from the front outlet of the melt outlet channel 6, specifically the nozzle body 6b in the example shown, as shown in Fig. 8 indicated by a backflow arrow 14a.

[0057] In the variant with the check valve 5 R, insofar as it differs from the above-mentioned variant with the shut-off control valve 5s, in Fig. 2 In accordance with the procedure described for operating stage B5, at this point, before the further retraction of the casting piston 3, the mold 1 is opened at least by a predefinable amount, whereby the cooling time has elapsed or its end is awaited. As a result, the melt outlet channel 6 on the side of the mold 1 is no longer airtight from the outside atmosphere, which means that no further molten vacuum builds up in the casting chamber 2 during the further retraction of the casting piston 3. Accordingly, the check valve 5 R remains in its closed position VS. Instead, the molten material 14 is drawn back further away from the area of ​​the sprue cone 12, specifically in the front area of ​​the nozzle body 6b. This means that a limited amount of molten material is drawn back from the foremost, outlet-side area of ​​the melt outlet channel 6, which prevents the formation of a molten droplet in the area of ​​the sprue cone 12.

[0058] Preferably, the further return movement of the casting piston 3 from the valve switching position VU to the casting start position GS takes place with a piston speed that is significantly lower than the piston speed with which the casting piston 3 was previously moved back from the filling end position FP to the valve switching position VU.

[0059] The stroke distance of the valve changeover position VU to the casting start position GS of the casting piston 3 determines the degree of backflow of melt material 14 in the melt outlet channel 6, whereby it may optionally be provided that this stroke distance can be variably specified or set by the user.

[0060] While in the example shown the time of switching the shut-off valve 5 to its closed position VS to end the refilling of molten material 14 from the melt bath 9 into the casting chamber 2 is coupled to the reaching of the valve switching position VU by the casting piston 3, in alternative designs this valve switching is triggered in a different way, e.g. after a certain period of time has elapsed since the beginning of the return movement of the casting piston 3 from its filling end position FP.

[0061] In an operational stage B6 of Fig. 2 The return movement of the casting piston 3 is then completed after reaching its casting start position GS. Meanwhile, in the variant with the shut-off control valve 5s, the cooling time for the complete solidification of the formed casting 15 in mold 1 has also elapsed, and accordingly, in this variant, the next operating stage B7 can be initiated. Fig. 2 The opening of the casting mold 1 is started by a corresponding opening movement of the movable mold half 1b, as shown in Fig. 9 This illustrates the machine's operation at this point. Opening mold 1 allows the backpressure previously generated in the variant with the shut-off control valve 5s to dissipate instantly in the area of ​​the sprue cone 12. This causes the molten material 14 in the front region of the melt outlet channel 6, specifically in the front region of the nozzle body 6b in this example, to withdraw further from the area of ​​the sprue cone 12. Again, this withdrawal, i.e., limited backpressure, of the molten material 14 from the foremost, outlet-side region of the melt outlet channel 6 prevents the formation of a molten droplet in the area of ​​the sprue cone 12, as described above for the variant with the check valve 5R. In both variants, the cast part 15 can then be removed after mold 1 has been fully opened.

[0062] Fig. 9 Figure 14 exemplifies the accumulation of molten material 14 in the front region of the melt outlet channel 6 up to a backflow point RP, which maintains a desired, sufficient distance AS from the area of ​​the sprue cone 12, the outlet of the melt outlet channel, or the melting point at which the backflowed molten material 14 detaches from the solidified or partially solidified molten material remaining in the mold 1 and the sprue cone 12. This reliably prevents the aforementioned droplet formation, with this distance AS being... Fig. 9 The distance AS is exaggerated for clarity only and is not to scale. For example, the distance AS is approximately 5 mm to 100 mm from the sprue cone 12, where the molten droplet would otherwise form, particularly between approximately 10 mm and 50 mm, preferably between approximately 30 mm and 40 mm, depending on requirements, the viscosity of the molten material, and / or the machine system design, including the diameter of the casting piston, riser bore, and nozzle body. Alternatively, the distance AS can be greater, but with a larger distance AS, more air is present in the outlet-side area of ​​the molten outlet channel 6 before the start of the next casting cycle.

[0063] In any case, however, the melt outlet channel 6 remains filled with molten material 14 up to and beyond the melt bath level 9a of the melt bath 9, so that in the next casting cycle the molten material 14 in the melt outlet channel 6 does not, as in the first casting cycle after start of operation, Fig. 3 The melt level SH in the melt outlet channel 6 is already significantly above the melt level 9a at the beginning of the next casting cycle, and the molten material 14 is preferably already present in the front area of ​​the melt outlet channel 6. Thus, after operating stage B7 of Fig. 2 The first casting cycle has been completed.

[0064] To carry out the next, second casting cycle, the following will then take place in an operating stage B8 of Fig. 2 The mold 1 is closed and the casting piston 3 is moved from its casting start position GS to its filling end position FP in order to push the molten material 14 from the casting chamber 2 via the molten outlet channel 6 into the closed mold 1. Fig. 10 At the end of the mold filling phase of this second casting cycle, the machine displays the following according to the [in] Fig. 4 Machine state shown at the end of the mold filling phase of the first casting cycle.

[0065] As in Fig. 10 In comparison, during the second casting cycle, a smaller axial stroke of the casting piston 3 from the casting start position GS to the filling end position FP is sufficient than during the first casting cycle for the pre-movement of the casting piston 3 from the operating start position BS to the filling end position FP, since for the second casting cycle the molten material 14 is already located significantly above the melt bath level 9a in the melt outlet channel 6. In other words, as in Fig. 10 schematically indicated, the filling end position FP in the second casting cycle is at an end position FP 2 related to the position in the casting chamber 2, which is further back than the end position FP 1 that the casting piston 3 occupies as the filling end position FP in the first casting cycle, i.e. in Fig. 10 further up.

[0066] In other words, the stroke distance HA=FP-GS=FP 2 -GS of the filling end position FP from the casting start position GS for the second and each subsequent casting cycle of a corresponding active operating interval of the machine is less than the corresponding stroke distance HA=FP-BS=FP 1 -BS of the filling end position FP from the operating start position GS for the first casting cycle, the difference being determined by the amount of molten material 14 that is present in the melt outlet channel 6 above the melt bath level 9a after the first and before the second casting cycle. The stroke difference is in Fig. 10 This is illustrated by a corresponding stroke difference HD=FP 1 -FP 2 of the filling end position after the first casting cycle FP 1 compared to the filling end position FP 2 after the second casting cycle. The reduction of this stroke length for the second and subsequent casting cycles can be, for example, up to 30% or up to 50% or more, depending on the machine type and the casting being produced.

[0067] This reduction in the stroke length that the casting piston 3 has to travel during the mold filling phase allows for a corresponding reduction in the cycle time, i.e., the duration of each casting cycle, for the second and every subsequent casting cycle within the operating interval, e.g., by up to 5% or 10%. Furthermore, the amount of molten material 14 remaining above the melt bath level 9a in the melt outlet channel 6 between casting cycles reduces the proportion of air to be displaced in the outlet-side part of the melt outlet channel 6, thereby also reducing the amount of air trapped in the casting, which benefits the casting quality. In addition, the shortened casting piston stroke reduces the wear effects on the casting piston and the casting chamber caused by the piston movement within the casting chamber.

[0068] The mold filling phase and the subsequent refilling phase of the second casting cycle then proceed in the same manner as described above for the first casting cycle, to which reference can be made. This is in Fig. 2 symbolized by a return arrow from operating stage B8 to operating stage B3.

[0069] In the illustrated embodiment with the shut-off control valve 5s as shut-off valve 5, the mold 1 remains closed during the entire refilling phase under appropriate operating conditions until the casting piston 3 has reached its casting start position GS as the starting position for the next casting cycle. Opening the mold 1 only at this point then leads to the aforementioned instantaneous back-suction effect. In alternative operating conditions, the mold 1 can be opened earlier, thereby making the back-suction effect more uniform over time and / or weakening it. In corresponding operating variants, the mold 1 remains closed at least as long as the shut-off control valve 5s is still open for refilling molten material 14 from the melt bath 9 into the casting chamber 2.When the casting piston 3 reaches its valve changeover position VU and the shut-off control valve 5s is thereby closed, the mold 1 is opened at an earlier or later point in the subsequent return movement of the casting piston 3 from the valve changeover position VU to the casting start position GS, depending on requirements. As soon as the mold 1 begins to open, more air can enter the front section of the melt outlet channel 6 via the outlet of the melt outlet channel 6, thereby weakening or mitigating the negative pressure effect there.

[0070] In another operating variant, the casting piston 3 is stopped in the valve changeover position VU, and after the cooling time has elapsed, the mold 1 is opened. As soon as the mold 1 reaches a specific, variable or fixed casting piston trigger mold opening position during opening, e.g., when the movable mold half 1b has moved a corresponding predefined distance away from the fixed mold half 1a, the casting piston 3 is moved back from its valve changeover position VU to its casting start position GS. The casting piston trigger mold opening position is selected such that air can enter the melt outlet channel 6 via the sprue cone 12 or the nozzle. This allows the molten material 14 to be drawn back into the foremost area of ​​the melt outlet channel 6 in a relatively smooth, gradual manner without a sudden drop in negative pressure. This operating variant is suitable, for example,especially for the machine variant of . Fig. 16 with the check valve 5 R as a shut-off valve 5. For as soon as the mold 1 has been opened in this way by a degree sufficient for air access to the melt outlet channel 6, the further return movement of the casting piston 3 no longer generates a melt vacuum in the casting chamber 2, and the check valve 5 R remains automatically in its closed position VS due to the action of the pre-tensioning unit 17.

[0071] Fig. 11 Figure 1 illustrates the die-casting machine operating method according to the invention in a further advantageous embodiment, which relates specifically to the execution of the first casting cycle after a machine start-up and which is particularly suitable for the machine variant with the shut-off control valve 5s as shut-off valve 5. This operating variant again starts from the machine's initial state at a start-up according to the initial operating stage B1. Fig. 2 out. In contrast to the operating variant of Fig. 2 However, in the operating variant of Fig. 11 A start-up casting process, i.e. a special first casting cycle, is carried out, in which an initial pre-filling phase precedes the mold filling phase.

[0072] This initial pre-filling phase begins in an operating stage B2a of Fig. 11 so that after closing the shut-off control valve 5s and closing mold 1, the casting piston 3 only moves from the operating start position BS to a position that is in Fig. 12 The initial pre-fill position VP shown is moved forward, whereby Fig. 12 The machine is shown in this operating stage B2a. The molten material 14 is thereby prefilled in the melt outlet channel 6 above the melt bath level 9a of the melt bath 9, preferably up to a prefilling point VA in the front region of the melt outlet channel 6 or the nozzle body 6b, so that the prefilling point VA is only a relatively small distance DS from the outlet of the melt outlet channel 6 into the mold 1 or from the sprue cone 12. This distance DS can, for example, correspond approximately to the distance AS of the backflow point RP from the outlet of the melt outlet channel 6 into the mold 1, as it is after the backflow of molten material 14 in the melt outlet channel 6 described above in the operating variant of Fig. 2 is and in Fig. 9 as shown. Alternatively, the distance DS can also differ slightly or significantly from the distance AS.

[0073] Subsequently, in an operational stage B2b of Fig. 11 A certain, predetermined period of time is waited until the overpressure built up by the pre-filling process due to the compressed air in the casting cavity 13 has dissipated. Afterwards, in an operating stage B2c, Fig. 11 The shut-off control valve 5s is switched from its closed position VS to its open position OS, and the casting piston 3 is moved back from the pre-filling position VP to its casting start position GS. This draws molten material from the melt bath 9 into the casting chamber 2 via the melt inlet channel 4, as indicated by the corresponding flow arrow in the diagram. Fig. 13 illustrated in which the machine is shown at the end of this operating stage B2c, at which the casting piston 3 has again reached its casting start position GS.

[0074] This melt refilling process can be accompanied by a certain amount of further backflow of molten material 14 into the melt outlet channel 6, since a certain amount of air is also contained in the closed mold 1 and the mold 1 may not be completely airtight. As a result, the prefill point VA, up to which the molten material 14 is prefilled in the melt outlet channel 6, can shift slightly backwards, as shown in Fig. 13 by an associated backflow arrow in the melt outlet channel 6 and a compared to Fig. 12 The prefill point VA located further back in the mouthpiece body 6b is illustrated. Nevertheless, the melt material 14 remains prefilled in the melt bath 9 well above the melt bath level 9a up to the front area of ​​the melt outlet channel 6.

[0075] In principle, an analogous pre-filling process is also possible for the machine variant with the check valve 5 R as a shut-off valve 5. In this case, the check valve 5 R remains closed due to the melt pressure in the casting chamber 2, while the casting piston 3 is advanced from its operating start position BS to its pre-filling position VP. If, subsequently, suitable pressure relief is ensured in operating stage B2b, as mentioned above, and then measures are taken to sufficiently impede or slow down the backflow of molten material into the melt outlet channel 6, e.g.By means of a controllable closure in the melt outlet channel 6 and / or by a sufficiently rapid return movement of the casting piston 3, the return movement of the casting piston 3 from the pre-filling position VP to its casting start position GS can generate a sufficient negative pressure in the casting chamber 2 to open the check valve 5 R, so that in this case too, molten material from the melt bath 9 can be drawn into or replenished in the casting chamber 2 via the melt inlet channel 4.

[0076] After completion of this initial pre-filling phase, the mold-filling phase of the first casting cycle is carried out according to an operating stage B2d of Fig. 11 This is carried out. For this purpose, the shut-off control valve 5s is switched back to its closed position VS, or the check valve 5 R closes automatically again after the melt vacuum in the casting chamber 2 has ceased, and the casting piston 3 is moved from its casting start position GS to the filling end position FP, so that the melt material 14 is again forced from the casting chamber 2 via the melt outlet channel 6 into the mold 1, specifically the casting cavity 13.

[0077] The initial pre-filling results in a difference compared to the first casting cycle without pre-filling, as in the case of the Fig. 2 The illustrated operating variant shows a reduction in the stroke distance HA=FP-BS between the filling end position FP and the operating start position BS, already for this mold filling phase of the first casting cycle. This stroke reduction for the first casting cycle is analogous to the stroke reduction explained above, which occurs in the operating variant of Fig. 2 only for the subsequent casting cycles is achieved by prematurely closing the shut-off control valve 5s in the refilling phase of the previous casting cycle before reaching the casting start position GS and the further return movement of the casting piston 3 to the casting start position GS. Fig. 14 In this operating stage B2d, the machine shows at the end of the mold filling phase of the first casting cycle with the shortening of the filling end position FP to a position FP 1V for the variant with initial pre-filling, which is located behind the filling end position FP 1 in the first casting cycle for the operating variant of Fig. 2 without pre-filling. In other words, with this operating variant, this pre-filling measure already provides sufficient pre-filling for the first casting cycle, compared to the operating variant of Fig. 2 Without pre-filling, a shortened pouring stroke is required to fill the mold.

[0078] Thus, in the operating variant of Fig. 11 the above for stroke reduction in the second and subsequent casting cycles in the operating variant of Fig. 2 mentioned properties and advantages through the operating variant of Fig. 11 already achieved for the first casting cycle.

[0079] The further course of the first casting cycle can then be compared to that of the operating variant of Fig. 2 from operating stage B3 onwards. Alternatively, the first casting cycle in the operating variant of Fig. 11 continue according to any conventional operating procedure.

[0080] Fig. 15 illustrates an advantageous variant of the operating procedure of Fig. 2 Regarding the execution of the second and subsequent casting cycles. In this process variant, each mold-filling phase from the second casting cycle onwards includes a pre-filling section. This is based on the operating situation at the end of operating stage B7, as described in Fig. 9 This is illustrated. In contrast to the operating variant according to operating stage B8 of Fig. 2 in the operating variant of Fig. 15 In operating stage B8a, the casting piston 3 does not wait until the mold 1 is completely closed before moving forward. Instead, while the mold is still open, the casting piston 3 is moved from the casting start position GS to a pre-filling position VP 2 for the second casting cycle. This pre-filling position VP 2 distinguishes it from the pre-filling position VP at the end of the initial pre-filling phase before the first casting cycle, according to the operating variant of Fig. 11 and the illustration in Fig. 12 This is also referred to as cyclic pre-filling position VP 2.

[0081] This cyclical pre-filling measure allows the previously described operating stages B5 to B7 of the operating variant to be carried out. Fig. 2 The melt material 14, which is drawn back from the outlet of the melt outlet channel 6, is moved forward again towards the outlet of the melt outlet channel 6, thereby further pre-filling the melt outlet channel 6, whereby the air can escape unhindered at the front end region of the melt outlet channel 6 via the still open mold 1.

[0082] The casting piston 3 is then in an operating stage B8b of Fig. 15 held in this cyclical pre-filling position until mold 1 is completely closed. The remaining steps of the mold-filling phase of the associated second or subsequent casting cycle then proceed according to operating stage B8c. Fig. 15 , for which the casting piston 3 is moved from its cyclic pre-filling position to the filling end position FP or FP 2 in order to force the molten material 14 from the casting chamber 2 via the pre-filled melt outlet channel 6 into the closed mold 1 or its casting cavity 13. The operating state of the machine at this point corresponds to that of Fig. 10 or at the end of operating stage B8 of Fig. 2 In other words, in the operating variant of Fig. 15 after the mold filling phase is completed at the end of operating stage B8c, with the refilling phase and the further steps from operating stage B3 onwards. Fig. 2 continued.

[0083] By cyclically pre-filling the mold at the beginning of the second and subsequent casting cycles, the cycle time and the air content in the finished casting can be further reduced accordingly. With appropriately optimized operation, the operating variants of the Fig. 2 ,11 and 15 be combined in such a way that, for each operating interval of the die-casting machine, at the start of operation, the initial pre-filling with melt refilling into the casting chamber is carried out according to the variant of Fig. 11 is carried out, followed by the remaining first casting cycle according to the operating variant of Fig. 2 is carried out and then the second and subsequent casting cycles according to the operating variant of Fig. 15 can be carried out. Alternatively, operating variants according to the invention are possible which differ from the variants mentioned above only in the specific initial pre-filling and melt refilling after start of operation according to Fig. 11 or only the backflow prevention measure according to operating stages B3 to B8 of Fig. 2 with or without additional combination with cyclic pre-filling according to Fig. 15 to use.

[0084] The die-casting machine according to the invention is set up as shown for carrying out the operating method according to the invention. In particular, the control unit 7 is configured accordingly for carrying out a respective casting process, for which purpose, during the mold-filling phase, it controls the casting piston 3 in the casting chamber 2 to move it from the casting start position GS to the filling end position FP in order to press the molten material 14 through the molten outlet channel 6 into the mold 1, and in the example of the Fig. 1 , 3 bis 10 and 12 bis 14 the shut-off control valve 5s directly or via the valve actuator 16 controls it to its closed position VS, while in the machine version according to Fig. 16 The check valve 5 R remains automatically in its closed position VS under the influence of the pre-tensioning unit 17 and the melt pressure in the casting chamber 2. Furthermore, the control unit 7 is designed to control the casting piston 3 to move back to the casting start position GS during the subsequent refilling phase in order to supply the molten material 14 to the casting chamber 2 via the melt inlet channel 4, and for this purpose in the machine version of the Fig. 1 , 3 bis 10 and 12 bis 14 The shut-off control valve 5s is initially controlled to its open position VO, while in the machine design according to Fig. 16 The non-return valve 5 R is brought into its open position VO by the negative pressure in the casting chamber 2.

[0085] Furthermore, the control unit 7 and the shut-off valve 5 can be configured so that the shut-off valve 5 is returned to its closed position VS during the refilling phase, before the casting piston 3 reaches its casting start position GS through its return movement, and to control the casting piston 3 in a further return movement to draw back molten material 14 in the melt outlet channel 6. Alternatively or additionally, the control unit 7 can be further configured to control the casting piston 3 for pre-movement in the casting chamber 2 during the pre-filling phase of the initial casting process, before the mold filling phase, with the shut-off valve 5 closed, from the initial position BS to the pre-filling position VP, whereby it is then ensured that the shut-off valve 5 returns to its open position VO and the casting piston 3 is controlled to return to its casting start position GS.

[0086] Optionally, as in the examples shown, the die-casting machine has a valve sensor unit 18 for sensing one or more measured variables of the shut-off valve 5. The measured values ​​acquired by the valve sensor unit 18 with respect to the respective measured variable can be supplied to the control unit 7 as required to provide it with control feedback on the current position of the shut-off valve 5. Additionally or alternatively, the measured values ​​can be used for diagnostic evaluation to diagnose the current state of the shut-off valve 5, e.g., with regard to any malfunctions, and to identify when the shut-off valve 5 requires maintenance.

[0087] Depending on requirements and application, the valve sensor unit 18 can include one or more sensors, including optional limit switches, with or without a connection to the control unit 7, which, as already mentioned, can be the entire machine control system of the die-casting machine or a part thereof. The valve sensor unit 18 can, for example, be configured to measure the stroke of the shut-off valve in order to derive fault diagnostics, e.g., whether the valve closing element 5c has broken off and the valve stem 5d is exceeding its target position during the valve closing movement, and / or whether the valve closing element 5c actually reaches its closed position or stops prematurely. The valve sensor unit 18 can optionally also include a force sensor in the valve stem 5d, which measures the closing force or contact pressure and / or the opening force of the valve closing element 5c for diagnostic monitoring. In the case of an electrical or hydraulic orFor example, in the case of a pneumatic valve drive via the valve actuator 16, the valve sensor unit 18 can also include a current sensor or pressure sensor of conventional design for this monitoring purpose, whether with or without connection to the control unit 7.

[0088] As the illustrated and further embodiments explained above clearly demonstrate, the invention provides an advantageous method for operating a die-casting machine, which enables short casting cycle times, a low air content in the casting, reduced wear of the casting piston and casting chamber due to a reduced casting piston stroke, and / or the prevention of molten droplet formation in the sprue area. Furthermore, the invention provides a die-casting machine suitable for carrying out this operating method, which may in particular be a hot-chamber type machine.

Claims

1. Method for operating a die-casting machine which has a casting mould (1), a casting chamber (2), a casting piston (3) arranged in an axially movable manner in the casting chamber(2), a melt inlet channel (4) which leads into the casting chamber(2), a shut-off valve (5) in the melt inlet channel (4), a melt outlet channel (6) which leads from the casting chamber(2) to the casting mould (1), and a control unit (7) for controlling the casting piston (3), wherein, - for the purpose of carrying out a respective casting process, in a mould-filling phase, when the shut-off valve (5) is closed, the casting piston (3) in the casting chamber (2) is advanced from a casting start position (GS) into a filling end position (FP), and as a result melt material (14) is pressed into the casting mould )1) via the melt outlet channel (6) and, in a subsequent refilling phase, the casting piston (3) is moved back into the casting start position (GS) and, as a result, when the shut-off valve (5) is open, the casting chamber (2) is supplied with melt material (14) via the melt inlet channel (4), characterized in that, - in the refilling phase of the casting process, the previously open shut-off valve (5) is closed before the casting piston (3) has reached its casting start position (GS) by virtue of its return movement, and as a result of the further return movement of the casting piston (3) melt material (14) in the melt outlet channel (6) is back-suctioned, and / or - during a start-of-operation casting process, in a pre-filling phase of the start-of-operation casting process before the mould-filling phase when the shut-off valve (5) is closed, the casting piston (3) in the casting chamber (2) is advanced from a start-of-operation position (BS) into a pre-filling position (VP), and then the shut-off valve (5) is opened and the casting piston (3) is moved back into its casting start position (GS).

2. Method according to Claim 1, further characterized in that in the refilling phase, the casting piston (3) is moved back in the period of time when the shut-off valve (5) is closed at a lower speed than in the preceding period of time when the shut-off valve (5) is still open.

3. Method according to Claim 1 or 2, further characterized in that in the refilling phase of the casting process, the previously open shut-off valve (5) is closed as soon as the casting piston (3) has reached a valve switchover position (VU) by virtue of its return movement.

4. Method according to Claim 3, further characterized in that - a stroke distance between the valve switchover position (VU) of the casting piston (3) and the casting start position (GS) can be variably predefined, and / or, - in the refilling phase of the casting process, the casting piston (3) is held in the valve switchover position (VU) during a halt period before it is moved back again to its casting start position (GS).

5. Method according to one of Claims 1 to 4, further characterized in that, in the refilling phase of the casting process, the casting mould (1) is kept closed at least for as long as the shut-off valve (5) is still open.

6. Method according to one of Claims 1 to 5, further characterized in that, in the refilling phase of the casting process, opening of the casting mould (1) is commenced after the casting piston (3) has reached its casting start position GS).

7. Method according to one of Claims 1 to 6, further characterized in that, in the refilling phase of the casting process, opening of the casting mould (1) is commenced after the casting piston (3) has reached its valve switchover position (VU) and before it has reached its casting start position (GS).

8. Method according to Claim 7, further characterized in that, in the refilling phase of the casting process, the casting piston (3) is held in its valve switchover position (VU) and is advanced from its valve switchover position (VU) into its casting start position (GS) as soon as the casting mould (1) has reached a determined casting-piston-triggering mould opening position when it is opening.

9. Method according to one of Claims 1 to 8, further characterized in that the casting piston (3) is advanced from its casting start position (GS), reached during the refilling phase of a respectively previous casting process, into a pre-filling position during an initial pre-filling stage of the mould-filling phase of a subsequent casting process when the casting mould (1) is not yet completely closed, and only thereafter is the casting mould (1) completely closed and the casting piston (3) advanced into its filling end position (FP).

10. Die-casting machine comprising - a casting mould (1), - a casting chamber (2), - a casting piston (3) arranged in an axially moveable manner in the casting chamber (2), - a melt inlet channel (4) which leads into the casting chamber (2), - a shut-off valve (5) in the melt inlet channel (4), - a melt outlet channel (6) which leads from the casting chamber (2) to the casting mould (1), and - a control unit (7) for controlling the casting piston (3), - wherein, for the purpose of carrying out a respective casting process in a mould-filling phase, the control unit (7) and the shut-off valve (5) are configured to bring the shut-off valve (5) into a closed position (VS) and to control the casting piston (3) in the casting chamber (2) to advance from a casting start position (GS) into a filling end position (FP), in order to press melt material (14) into the casting mould (1) via the melt outlet channel (6), and in a subsequent refilling phase firstly to bring the shut-off valve (5) into an open position (VO) and to control the casting piston (3) to move back into the casting start position GS), in order to supply the casting chamber (2) with melt material (14) via the melt inlet channel (4), characterized in that - the control unit (7) and the shut-off valve (5) are further configured to bring the shut-off valve (5) into its closed position (VS) again still during the refilling phase before the casting piston (3) has reached its casting start position (GS) by virtue of its return movement, and to control the casting piston (3) to back-suction melt material (14) in the melt outlet channel (6) by virtue of the further return movement of the casting piston (3), and / or - the control unit (7) and the shut-off valve (5) are further configured to control, during a start-of-operation casting process, the casting piston (3) to advance in the casting chamber (2) from a start-of-operation position (BS) into a pre-filling position (FP) in a pre-filling phase of the start-of-operation casting process before the mould-filling phase when the shut-off valve (5) is closed, and then to bring the shut-off valve (5) into its open position (VO) and to control the casting piston (3) to move back into its casting start position (GS).

11. Die-casting machine according to Claim 10, further characterized in that the shut-off valve (5) is in the form of a shut-off control valve (5S), and the control unit (7) is configured to control the shut-off control valve (5S).

12. Die-casting machine according to Claim 11, further characterized by a valve actuator (16), activated by the control unit (7), for actuating the shut-off control valve 5S).

13. Die-casting machine according to Claim 10, further characterized in that the shut-off valve (5) is formed as a non-return valve (5R) which is preloaded in its closed position (VS).

14. Die-casting machine according to one of Claims 10 to 13, further characterized by a valve sensor unit (18) for sensing one or more measured variables of the shut-off valve (5).