EP1201334B1 - Hot chamber die casting machine and method of operation therefor - Google Patents

Abstract

Process for operating a hot chamber die casting machine comprises pressing the metal melt from the casting container via a riser bore, a mouthpiece and a gate; and forming a pressure fluctuation on the end of the mold filling process in the narrowest cross-section of the gate to prevent rapid solidification of the melt. An Independent claim is also included for a hot chamber die casting machine for carrying out the process. Preferred Features: The casting plunger is moved into the corresponding mold filling phase during pressing and is bombarded at the end of the filling process with the maximum casting pressure, preferably a pulsating pressure.

Description

The invention relates to a hot chamber die casting machine according to the The preamble of claim 1 and a method of operating such Hot chamber die casting machine, at the molten metal from Casting container via a riser hole, a mouthpiece and a connection is pressed into a mold.

In the hot chamber process, the liquid metal is passed through a casting container and a casting piston conveyed into the mold. The casting container and the casting piston are constantly in the metal bath. While the piston movement and also at the end of the piston movement arise depending on metal melting temperature losses between piston rings and casting vessel drilling. When warm chamber method can therefore when casting zinc, which has a metal bath temperature of approx. 420 ° C, about 300bar metal pressure at the end of the filling process be generated. When die casting magnesium at a metal bath temperature from about 650 ° C can only about 250bar metal pressure also be reached at the end of the filling process.

There are also Kaltkammerdruckgießverfahren (DE 29 22 914 C2), in which the mold filling phases proceed in a similar manner as in the hot chamber die casting process. In the cold chamber method, in the casting container and casting irons are not in the liquid melt, It is possible to have higher end pressures of the order of 400bar To produce 700bar. This means that it is because of the high metal pressure in the cold chamber method is possible, parts with higher density manufacture. This in turn means less porosity in the die-cast part, higher strength and elongation values and higher surface density.

US 5,560,419 discloses a cold chamber die casting machine and an associated method of operation in which the two mold halves against each other even when the mold is closed are axially movable by the one mold half through an opening in the other mold half is performed. Melt is in the closed Shape over an overhead opening through a central hole introduced through a mold half. After introducing the Melt is a hydraulic pressure piston, on which one of the two Mold halves is fixed, offset in oscillating axial movement to to exert on the melt a pressure oscillation.

In the hot chamber die casting process, the filling process takes the form about 7ms to 20ms. At the end of the filling process builds, as already mentioned, the maximum casting pressure on. This casting pressure acts over the Connection to the metal already in the mold cavity. Because the Thickness of the connection depending on the wall thickness and the surface quality the parts as well as the post-processing is and the thinnest Wall thickness of the connection is the thickness of the gate, the molten metal first freeze at this point. This will make the connection completed by the mold cavity and the casting from her applied reprint can no longer, or not fully, to the effect come. For explanation it should be noted that the thinnest Wall thickness of a gate, e.g. with a zinc part 0.3mm up 0.6mm and with a magnesium part at 0.4mm to 0.8mm. By the cooling occurring in this area solidifies the material this place relatively fast.

The present invention is based on the object, in a method of the type mentioned above to ensure that despite the Hot chamber die casting process lower final pressures die castings can be achieved, which have the same properties as those which have been produced in the cold chamber process.

To solve this problem, the invention proposes a hot chamber die casting machine with the features of claim 1 and an operating method for this purpose with the features of claim 5.

In the process of the invention, at the end of the mold-filling process at least in the narrowest cross section of the connection a pressure oscillation is generated, which prevents the melt from rapidly solidifying. By varying the pressure, a movement in the molten metal achieved, resulting in that the aforementioned gate cross-section with its thin wall thickness does not come so fast, so do not "freeze". In this way, the pressure can be longer in the mold and thus also the volume-related shrinkage of the melt counteract.

In a further development of the invention, the pressure can be applied via a timer a certain period of time, while maintaining the pulsation remains so that when the melt is the so-called Semisolid phase has reached the highest compression occurs. In this Phase is formed on the outer contours of the diecast no burr more. Due to the vibrations that are initiated at a relatively high frequency can be, the pressure on the metal in the mold fully transmitted. This creates a kind of hammering on the filled mold, which leads to a final compression of the material.

In a further development of the invention, in a method in which a via an electromotive drive moving casting piston is present, the pulsating pressure by superimposing the drive with a vibration be generated. This vibration can in the development of the invention can be about 300Hz and can at a given delay the casting piston speed are initiated. The casting piston speed can be determined in a known way path-dependent, so it does not cause any problems to determine the time, too which requires the pulsating pressure.

In a further development of the invention, the pressure compared to the maximum Casting pressure pulsating lowered or increased. being as before already indicated, the pressure in the final phase during a first short period of time and increased during a second period of time becomes, before the complete solidification of the melt occurs.

With the hot chamber die casting machine according to the invention, the Inventive methods are carried out. This hot chamber die casting machine has a casting piston drive and a control device for this, wherein the casting piston drive one in the final phase associated with the filling operation switchable pulsation device, whose vibrations act on the drive axle of the casting piston. When the casting piston drive with an electric motor driven Casting piston is provided, the pulsation device from the electrical Servo drive and from acting on this control device exist, this control device as one of a corresponding designed software operated electronic computer can be. The servo drive itself can be a brushless electric motor be with low momentum. Such a drive avoids largely the effect of inertial forces on the casting piston, but in a known manner by the interposition of a resilient element between the drive motor and casting piston or be reduced by controlled delimitation of the servo drive can.

Fig. 1

die schematische Darstellung eines Gießkolbenantriebs mit einem Elektromotor und einer Steuereinrichtung zur Erzeugung einer Schwingung,

Fig. 2

eine schematische Blockdarstellung eines Teils der Steueraggregate und

Fig. 3

die Darstellung des Druck- und Volumenverlaufes des Einpressvorganges nach dem erfindungsgemäßen Verfahren.

The invention is illustrated schematically with reference to an embodiment in the drawing and will be explained below. Show it:

Fig. 1

1 is a schematic representation of a casting piston drive with an electric motor and a control device for generating a vibration;

Fig. 2

a schematic block diagram of a part of the control units and

Fig. 3

the representation of the pressure and volume curve of the press-fitting process according to the inventive method.

Fig. 1 shows the Einpressaggregat a hot chamber die casting machine for the processing of molten metals, incidentally arranged in a known manner with a melt bath Casting container, a movable in this via the Einpressaggregat Casting piston and with a riser hole and a whose ends arranged mouthpiece is provided. During the casting process itself should also in a known way about the Mouthpiece fed the molten metal via a connection of the mold become.

In the press-fit unit according to FIG. 1, an electric motor 1, For example, an asynchronous motor or another variant a servomotor with a gear not shown in detail and provided with a coupling part 2, which is a threaded spindle 3 to a rotary motion drives. The threaded spindle 3 is guided sealed in a protective housing 5. On her is cooperating with the thread of the spindle 3 Mother 4 out with a Leitnocken 6 in a groove. 7 engages within the housing 5 and thereby in the housing. 5 is guided non-rotatably. The mother 4 is about a free end of the spindle 3 cross-extension 8 with a Push rod 9 in conjunction, which in turn sealed led out of the housing 5 and with an extension 10 with is provided with a smaller diameter. On the extension 10 is movably guided a first disc 11, which is connected to a pressure sensor 12 is applied, for example, in the manner of a piezoelectric Element can be executed. This pressure sensor 12 is connected via a signal line 13 with a multi-parameter controller 20 in connection, about which the engine 1 in his Speed is regulated.

On the extension 10 is also a sleeve 14 with an end plate 15 slidably mounted, wherein between the end plate 15 and the voltage applied to the pressure sensor 12 disc 11th a spring element in the form of a plastic ring 16 is arranged is, which is also penetrated by the extension 10. The sleeve 14 is at the end facing away from the disc 15 with a terminal end 17 for connection to the not shown Provided casting piston, the free end of the extension 10 provided with a paragraph 18 of larger diameter is that holds the sleeve on the extension 10 and also for a certain Bias of the plastic ring 16 can serve. This Paragraph 18 is about the distance a from an inner end surface 19 of the sleeve 14 removed. This injection unit is in operation set when the molten metal in a known manner the crucible of a hot chamber die casting machine pressed into the mold shall be. The electric drive 1 is doing over the Multi-parameter controller 20 is excited to a rotation of the spindle 3, which causes the mother 4 from the shown Position on the spindle 3 along down and running the push rod 9 also pushes down, with the speed necessary for the filling of the mold.

When the mold is filled, then the rotary drive of the spindle 3 switched from cruise control to torque control become. To avoid that the casting piston in In this case, due to the mass-related moment of inertia the drive continues on the in-mold incompressible melt presses and thereby unwanted Pressure peaks in the drive mechanism occur, leading to a Can cause damage, is the spring element 16th provided that squeezes and opens the way, the otherwise the casting piston would have to cover additionally.

The arrangement is made such that the drive distance traveled is less than the measure a. The spring element 16 is therefore expressed slightly by an amount less than a together and is put under tension. there the arrangement can be designed so that then the spring element 16 exerted reaction force on the sleeve 14 and on the casting piston is sufficiently large to melt in the the required emphasis due to a force, for example in the order of 7 to 8 tons (70 to 80 kilos N).

Fig. 2 shows that for controlling the speed and the Torque of the electric motor 1 to the controller 20, the target position 21 is given for the casting piston, with the actual position 22 is compared, which at the output of the drive is removed. The controller 20 is also fed to the Target speed and the target torque. The resulting Target speed 24 is a not shown in detail digital or analog speed and torque control for supplied to the engine 1 and the actual speed 25 and the actual torque then leads in a known manner to the supply of Melting material (filling), for example in the three known mold filling phases. When reaching an actual position (22), in which the mold is filled, in the previously explained Way switched to torque control and here now at the time when the casting piston speed is a predetermined Delay value has reached the torque one Vibration superimposed.

Fig. 3 shows how this press-fitting process is going on in detail. In Fig. 3, the form filling time is plotted on the abscissa and on the ordinate both the piston speed v and the pressure generated in the melt by the forwardly moving casting piston p. FIG. 3 shows that in a first time segment up to the period indicated by the line 26, the filling phase initially takes place with three or more different speeds, in which case between the time indicated by the line 26 and the time indicated by the line 27 a significant increase in the piston and filling speed takes place. From the time at line 27 from the filling of the mold takes place over the period t _F. Therefore, this filling process is carried out at high speed, which inevitably also increases the pressure p to increase again shortly before its final increase in filled form when the piston speed v decreases again to zero, once again to the final pressure.

3 now shows that upon reaching a certain predetermined deceleration value V _z of 0.1 m per second, the piston and filling speed (decreasing from the value of approximately 1.2 m per second) are exerted by the pressure exerted by the injection unit (FIG during a first period of time t _1, a vibration is superimposed in such a way that there is a pressure pulsating by the value Δp, the maximum value of which lies at the final pressure reached. In a second period of time t _2, on the other hand, the pressure is increased by a value Δp with respect to the original final pressure and remains exposed to the triggered vibration.

As already mentioned above, this measure leads to pressure fluctuations during the time intervals t ₁ and t ₂ occurring in the connection between the mold cavity and the mouthpiece of the hot chamber die casting machine, but also in the entire space occupied by the melt. This leads to the fact that even in the narrowest cross-section of the connection, which occurs in the gate, a pulsating pressure occurs at this time, which prevents the melt solidifies early and therefore closes the connection to the mold cavity. The pressure increase occurring during the period t ₂ can therefore still affect the entire mold cavity and the melt located there. At this time, the melt is in the so-called semisolid phase and it is possible by the invention to achieve the highest compression here. In this phase, there is no longer any burr in the shape of the outer contours of the die-cast part. As a result of the oscillations around the value Δp, the pressure exerted by the casting piston on the melt is transferred in a kind of hammer action to the metal in the mold, which can thereby be compressed more than usual in the hot chamber pressure casting process. It has been found that with the new method, die castings can be achieved whose density, strength and porosity corresponds to those that could otherwise be produced only in Kaltkammerdruckgießverfahren.

The inventive method is based on an embodiment been explained, in which the Einpressaggregat over an electric servomotor is operated. In such servo-controlled machines, it is possible to have a braking point at the end of the filling process. You can thereby the occurrence avoid pressure peaks, which - as well as the beginning mentioned - arise at the end of an unrestrained filling would. The filling speed is thus before the end of the mold filling reduced, so with this measure parts without Burr can be produced. This braking point to which So a predetermined delay is present, as a starting point be provided for the pressure oscillations.

But it is also conceivable that in hot chamber die casting machines with a hydraulically loaded casting piston the hydraulics after filling the mold under appropriate Pressure fluctuations is set, so that even with such Einpressaggregaten the invention can be realized. It is conceivable It also, however, that targeted through separate facilities in the connection and in the cut in the crucial Phase after filling the mold excited the vibrations even then the so-called "freezing" of the melt to prevent in the connection. A pulsating pressurization over the casting piston would not be required.

The illustrated application of the new casting process in a Press-in unit with an electric motor driven However, casting plunger is very easy to realize, because it is sufficient to have appropriate software for the controller via an electronic computer, then at the time explained with reference to FIG switching to torque control the desired Vibrations initiates.

Claims (10)

1. Hot chamber pressure die casting machine having a casting vessel, a casting plunger, a casting plunger drive (1) and a control means (20) therefor, for expressing metal melt from the casting vessel via an ascending bore, a nozzle and a connection into a mould, characterised in that a pulsation device that can be switched on in the end phase of the filling operation (t_F) is associated with the casting plunger drive (1), the oscillations of the pulsation device acting on the drive shaft (10) of the casting plunger.
2. Hot chamber pressure die casting machine according to claim 1, characterised in that the casting plunger is electric motor driven and the pulsation device consists of an electric servo drive (1) and of a control means (20) acting on this.
3. Hot chamber pressure die casting machine according to claim 2, characterised in that the control means (20) is an electronic computer in the form of a multi-parameter controller (20) driven by correspondingly designed software.
4. Hot chamber pressure die casting machine according to claim 2 or 3, characterised in that the servo drive (1) is a brushless electric motor having a low moment of rotation.
5. A method for operation of a hot chamber pressure die casting machine according to any one of claims 1 to 4, characterised in that, at the end of a mould-filling operation, a compressional vibration that prevents rapid solidification of the melt is generated at least at the narrowest cross-section of the connection.
6. Method according to claim 5, characterised in that the casting plunger is moved during the injection operation in the corresponding mould-filling phases and at the end of the filling operation is acted on with a pulsating maximum casting pressure (Δp).
7. Method according to claim 2, characterised in that the pulsating pressure is generated by superimposing a vibration on the electric motor drive.
8. Method according to claim 7, characterised in that the vibration takes place at approximately 300 Hz and is initiated with a defined deceleration (V_z) of the casting plunger speed.
9. Method according to any one of claims 6 to 8, characterised in that the pressure (p) is decreased or increased in a pulsating manner with respect to the maximum casting pressure (p_max).
10. Method according to claim 9, characterised in that the pressure (p) in the end phase is decreased during a first short time period (t₁) and is increased during a second time period (t₂) before complete solidification of the melt occurs.

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