The present invention relates to a device for die casting a metal component.
Die casting is an industrial casting method for the mass production of components. For this purpose, use is generally made of metal materials having a low melting point, such as, for example, aluminum and magnesium.
During the die casting, metal melt is pressed under a high pressure of approx. 10 to 200 MPa and with a high mold filling speed of up to 120 m/s into the cavity of a die casting mold where said metal melt then solidifies. The operation is carried out here with a permanent mold, i.e. without a pattern.
In particular, components which are comparatively large and are shaped in a geometrically complex manner and are produced by means of die casting require a comparatively large sprue system. This is understood as meaning supply channels which connect the casting chamber to the cavity of the die casting mold. The material in the sprue system solidifies together with the material forming the actual component and has to be subsequently removed. This constitutes a considerable processing outlay.
In many cases, the ratio of the mass of the component being produced to the sprue mass is one to greater than one (1:>1). Therefore, during the die casting, more material waste is produced than material is used for the component. This is uneconomical for a number of reasons. Firstly, significantly more material has to be melted for each component than is actually required for the component. Furthermore, the material waste has to be disposed of after separation or remelted for recycling. Furthermore, the supply channels are generally configured with comparatively large flow diameters in order to keep the cooling of the melt in the sprue system and the flow resistance as little and as low as possible. However, as a consequence of the configuration with the large volume, the melt generally solidifies significantly later in the sprue system than in the cavity of the die casting mold itself. The cycle times which can be achieved are therefore constrained by the time required for the material in the sprue system to solidify. Furthermore, the sprue system results in an increase in the size of the die casting mold and in the closing forces required for closing the two-part die casting mold, and therefore in the plant outlay.
The disadvantages caused by the sprue system of a die casting device may, in principle, also occur in the technologically similar injection molding of plastics. However, this can be avoided by designing an injection molding device with a “hot channel system”. In such an injection molding device, the sprue system is controlled to a higher temperature than, and thermally insulated from, the rest of the injection molding die. This prevents the material from solidifying in the sprue system. The material is therefore available for the injection molding of a subsequent component. Valves which are arranged in the transition from the sprue system to the cavity decouple the solidifying material in the cavity from the material in the sprue system and permit the demolding of the solidified component without the sprue. By means of the thus achieved ending of solidified sprue on the component, the disadvantages mentioned above can be avoided.
It has already been contemplated to transfer the hot channel system known from the injection molding of plastics to a device for die casting metal components, see DE 44 44 092 A1. However, a practical implementation of this concept has failed up to now. Reasons therefore reside in particular in the considerable stressing of the plant parts involved by means of the metal melt. In particular, the high temperatures of the metal melt of approx. 620° C. to 750° C. and the sometimes considerable temperature differences both between a cold non-operational state and a hot operational state of the entire device and also between individual plant parts in the operational state play a role here. Also, the aggressivity of, for example, an aluminum melt to other metals makes it difficult to implement a hot channel system for die casting metal components.
Starting from this prior art, it is the object of the invention to implement a hot channel system, which is known in principle from the injection molding of plastics and is implemented in practice, for the die casting of metal components.
The above object is achieved by a device for die casting a metal component with a die casting mold. In the case of the device for die casting a metal component, comprising a die casting mold which has a cavity molding the component, wherein the cavity is connected to a source for a metal melt via at least one temperature-controlled supply channel, and wherein the metal melt is introduced into the cavity via at least one casting valve, it is provided according to the invention that the supply channel forms an annular channel in which metal melt can be circulated by way of a conveying apparatus.
A series of advantages can be generated by the formation of the supply channel as an annular channel. In particular, this permits the permanent conveying of the material located in the supply channel, even when no material is specifically being introduced into the cavity, as is the case, for example, during the curing of the material in the cavity in order to form the component, or during the demolding of the component. Permanent conveying and therefore movement of the material in the supply channel ensures thorough mixing and thereby also prevents local curing of the material in the supply channel.
A further advantage which can be realized by the configuration of the device according to the invention resides in the fact that the pressure conditions in the supply channel can be better influenced because of the annular configuration. This applies in particular whenever, as is preferably provided, more than one conveying apparatus is provided. Influencing the pressure conditions in the supply channel may be advantageous in particular if, as is preferably provided, a plurality of casting valves are arranged distributed along the supply channel.
The metal melt can be, in particular, a melt of a light metal, in particular aluminum or magnesium, or of an alloy comprising such a light metal.
It can preferably be provided that the supply channel is integrated in a stationary part of the die casting mold. The die casting mold then also has at least one mobile part which is removable from the stationary part in order to permit demolding of the component. By integration of the supply channel in the stationary part, it is possible to avoid decoupling of the supply channel from the die casting mold in order to open the latter.
In a further aspect of the device according to the invention, it can be provided that the source for the metal melt includes a holding chamber and a metal melt reservoir connected separably to the holding chamber. The separation of the source for the metal melt into a holding chamber and a metal melt reservoir makes it possible to isolate a defined quantity of the metal melt in order to subsequently introduce a corresponding quantity of the metal melt into the cavity in order to die cast the component.
By way of the separation of the defined quantity, only the quantity and the metal melt contained in the supply channel has to be placed under pressure for the die casting, whereas the possibly significantly larger quantity of metal melt accommodated in the metal melt reservoir can be stored, for example, at atmospheric pressure. Accordingly, it is provided, in a further aspect of the device according to the invention, that the metal melt contained in the holding chamber can be discharged into the supply channel by way of pressure-generating devices. The pressure-generating devices can preferably be at least one piston which can be designed so as to be displaceable, in particular hydraulically, in order to change the volume of the holding chamber.
In order to obtain a separable connection between the holding chamber and the metal melt reservoir, an activatable valve may be provided which closes or at least partially opens up a transfer opening formed between the holding chamber and the metal melt reservoir as required.
It can preferably be provided that the supply channel leads into the holding chamber at at least two points. As a result, the holding chamber can advantageously be integrated in a circulation of the metal melt in the supply channel. This can, in particular, also have a positive influence on the introduction of the metal melt into the cavity via a plurality of casting valves since the flow paths of the metal melt from the holding chamber to the individual casting valves can thus be kept comparatively short.
In a further aspect of the device according to the invention, it can be provided that the supply channel is formed in at least one portion from pipe pieces, in particular rectilinear pipe pieces, and from connecting pieces connecting the pipe pieces. This refinement makes it possible to form a supply channel which is constructed in a simple manner and, at the same time, can compensate for the considerable loads which are exerted on the components forming the supply channel by the metal melt, in particular the different thermally induced elongations. In order to connect the pipe pieces to the connecting pieces, it can be provided that the ends of the pipe pieces are inserted into corresponding receiving openings of the connecting pieces. A defined longitudinal movability of the ends of the pipe pieces in the receiving openings is provided in order to be able to compensate for different thermally induced elongations of the pipe pieces and of the connecting pieces.
It can preferably be provided that at least some of the connecting pieces integrate a channel portion with a curved profile and/or a casting valve. Curved portions of the supply channel and functional elements of the device are therefore preferably integrated in the connecting pieces, which are optionally formed with a larger volume.
The latter also afford the possibility of good integration of a heating device in order to actively heat the connecting pieces and therefore the metal melt guided within the corresponding supply channel portion and therefore to keep the same fluid. In contrast thereto, it can be provided that the pipe pieces of the supply channel are heated passively, i.e. by the metal melt itself flowing through the pipe pieces.
In order to keep the thermally induced elongation of the pipe pieces and of the connecting pieces as identical as possible, it can preferably be provided to form at least a large part of each of the pipe pieces and the connecting pieces from the same material. In particular, a ceramic material, such as, for example, aluminum titanate and/or silicon nitride, can be used as material for the pipe pieces and/or for the connecting pieces.
In a further aspect of the device according to the invention, it can be provided that the conveying apparatus is designed so as to act electromagnetically. The conveying apparatus is therefore designed in such a manner that moving magnetic fields are generated which bring about the movement of the metal melt by magnetic force action. This makes it possible to position all of the parts of the conveying apparatus outside the metal melt. As a result, positioning conveying elements, such as, for example, a pump impeller, within the metal metal can be avoided.
A casting valve for a device according to the invention can preferably have a valve body which is movable transversely with respect to, and in particular perpendicularly to, the longitudinal axis of the supply channel and, in a closed position, closes an outlet opening connecting the supply channel to the cavity and, in an open position, at least partially opens up the outlet opening. In the case of such a casting valve, the formation of “dead water points”, in which it is possible for metal melt to accumulate that would not be carried along by the circulated metal melt, is avoided.
In a preferred refinement of the casting valve, it can be provided that a valve seat is formed for the valve body which is designed so as to widen in the direction of the supply channel. At the same time, a head of the valve body can be designed so as to taper in the direction of the cavity. As a result, advantageous flow conditions in the open position of the valve body and a good sealing action in the closed position of the valve body can be achieved. At the same time, the risk of the valve body jamming in the valve seat is small.
By way of recompaction of the metal melt introduced into the cavity, the quality of the component being produced can be positively influenced in a known manner. In particular, a reduction of pores and air locks can thereby be achieved. In principle, a device for the recompaction of the metal melt introduced into the cavity can be implemented at a plurality of suitable points of the casting mold. However, integration of a squeezing plunger, which is movable into a position projecting into the cavity, in the casting valve and in particular in the valve body can be advantageous. As a result, for example, the squeezing plunger can be moved into a sprue system which is in any case present between the outlet of the casting valve and the cavity of the casting mold (but is very small in volume according to the invention). This not only avoids an additional surface defect on the component, which is produced by the squeezing plunger, but optionally also further reduces the volume of the sprue system and therefore a sprue remaining on the component.
The valve body and/or the squeezing plunger can be actively actuable independently of each other preferably in both directions (retraction and extension). For this purpose, at least one corresponding regulating device can be provided which, particularly preferably, can be designed so as to act hydraulically. Furthermore preferably, it can be provided to thermally insulate the regulating device(s) from the supply channel in order to keep the thermal loading of the regulating device by a transmission of heat from the metal melt guided in the supply channel as small as possible. The thermal insulation can be implemented, for example, by a structural separation with an intermediate arrangement of insulating elements or else air-filled intermediate spaces.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.