CASTING DEVICE AND CASTING METHOD

Abstract

A method for manufacturing a cast component with a casting device includes providing a casting device. The casting device comprises a filling chamber, a mold cavity comprising a hollow space, runners comprising at least one of a different length and a different cross-section, and a plunger arranged in the filling chamber. The metal melt is provided in a fluid state in the filling chamber. The metal melt is advanced via the runners from the filling chamber to the mold cavity by advancing the plunger in the filling chamber. Electromagnetic fields are provided. A flow velocity of melt currents in the respective runners is increased or decreased via the electromagnetic fields so that a melt front in each of the runners reaches the mold cavity when the filling chamber has been completely filled by the plunger.

Description

CROSS REFERENCE TO PRIOR APPLICATIONS

Priority is claimed to German Patent Application No. DE 10 2013 101 962.5, filed Feb. 27, 2013. The entire disclosure of said application is incorporated by reference herein.

FIELD

The present invention relates to a manufacturing method of cast components with a casting device, a metal melt in a fluid state being brought from a filling chamber into a mold cavity comprising a hollow space via several casting runners, and the casting runners having different lengths or different cross-sections. The present invention further relates to a device for implementing the method.

BACKGROUND

A metal melt, usually in form of a liquid alloy, is provided for primary shaping. The melt is stored in a filling chamber serving as a reservoir and is maintained in a liquid state by supplying heat. By way of a gating unit, the melt reaches a mold cavity, which forms the negative form of the cast part to be cast.

An important criterion for high quality cast products is a turbulence free, gas free and uniform feeding of the liquid melt. In order to provide a uniform transport of the melt, electro-magnetic pumps have previously been described which produce a laminar movement of the liquid melt in the pump tube.

The flow velocity of the melt can be influenced in several ways. DE 10 2009 035 241 A1 describes, for example, a deceleration and acceleration of electrically conductive melts which is based on electromagnetic alternating fields.

During the entire filling process, it must be ensured that the melt does not solidify. The runner therefore requires a minimal cross-section which depends on its length and the flow velocity of the melt to prevent it from solidifying without an external energy supply. On the other hand, the cast mass increases along with the runner cross-section so that a greater part of the melt is lost.

Large-scale cast parts with several gate areas or particularly thin-walled cast parts require several runners to prevent solidification in the casting mold before it is completely filled. Several runners must be disposed in such a manner so that as little turbulence as possible is created during the casting process. In order to ensure a uniform filling, the individual runners therefore generally have different lengths and cross-sections. The proportion of the circulating material or the cast mass is thereby disadvantageously increased and a simultaneous start of the second casting phase cannot always be ensured. High casting pressures and high temperatures of the melt are also required that are conform to the runner with the smallest cross-section and to the most thin-walled structures of the cast part.

SUMMARY

An aspect of the present invention is to improve the prior art and, more specifically, to provide a method for influencing the melt which avoids the above-mentioned disadvantages. An additional aspect of the present invention is to develop a casting method which avoids an uncontrolled filling of the mold even for complex casting products, and to create a device adapted to implement the casting method.

In an embodiment, the present invention provides a method for manufacturing a cast component with a casting device which includes providing a casting device. The casting device comprises a filling chamber, a mold cavity comprising a hollow space, runners comprising at least one of a different length and a different cross-section, and a plunger arranged in the filling chamber. Each of the runners respectively connect the filling chamber with the mold cavity. The plunger is configured to advance a metal melt from the filling chamber via the runners into the mold cavity. The metal melt is provided in a fluid state in the filling chamber. The metal melt is advanced via the runners from the filling chamber to the mold cavity by advancing the plunger in the filling chamber. Electromagnetic fields are provided. A flow velocity of melt currents in the respective runners is increased or decreased via the electromagnetic fields so that a melt front in each of the runners reaches the mold cavity when the filling chamber has been completely filled by the plunger.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in greater detail below on the basis of embodiments and of the drawing in which:

FIG. 1 shows a schematic representation of a device for die casting a metal melt.

DETAILED DESCRIPTION

In an embodiment of the present invention, a generic method is provided in which the individual melt currents in the casting runners are heated up, decelerated or accelerated to different degrees, so that the melt front in all runners reaches the mold cavity when a casting chamber is completely filled by an advancing plunger.

In an embodiment of the present invention, the melt is not subjected in its entirety to an electromagnetic alternating field of the same strength, but is influenced in accordance with the geometry of the melt current and only in certain areas so as to modify only the properties of one or several melt currents in relation to other melt currents. More specifically, the flow velocity of individual melt currents in the runners filling the mold cavity or in the mold cavity itself can thus be increased or reduced so that the filling can be favorably influenced.

The varying electromagnetic alternating fields induce eddy currents in each melt current forming an electric conductor. The magnetic field exerts forces on the eddy currents, the strength of which depends on the spatial variation of the magnetic flux density. The melt thus experiences a force aligned on the lesser magnetic flux density. Analog to a Lorentz force acting on a solid body, displacing it in space, the melt current is accelerated or decelerated depending on the flux density gradient.

In an embodiment of the present invention, the electromagnetic fields can act contactless on the respective melt current. A direct electrode contact with the melt current, which would be subjected to considerable wear, is thus not required.

An electromagnetic field is to be understood as a time-varying electric or magnetic field. The electromagnetic fields can, for example, be generated by coils. When an electric current passes through the coils, the coils generate a magnetic field which locally induces eddy currents in the melt. One or several coils can, for example, surround the individual runners, for example, along their entire length. They can alternatively only surround sections thereof. Areas of the mold cavity having thinner diameters can also be surrounded by coils.

In an embodiment of the present invention, the electromagnetic alternating fields locally reduce the flow velocity to a point where the melt front almost or completely stops. A contactless operating valve is thus created. Stopping the melt front does not have to occur at all runner cross-sections, so that not all the runners are necessarily provided with such a valve. Such valves can be provided in addition to or instead of coils modifying the velocity of the melt. In the first case, they can act as a securing mechanism and prevent a premature filling of the form cavity. In the second case, they constitute an adapted mechanism for runners of similar lengths which do not require a complex control or regulation.

In order for the coil dimensions of the coils surrounding the runners or the surface areas of the mold cavity to not become too big, field generators can be used that concentrate the action of the force on one specific area. A field generator can, for example, be designed as a conductor which is cut in the longitudinal direction of the coil axis and is charged with short current pulses. Due to the skin effect, the short impulses barely penetrate the conductor itself and can thus act on the densely flowing melt with very high field strength.

In order to accelerate the melt in a runner, a traveling electromagnetic field can be achieved by means of an inductor according to the principle of a linear motor. The respective melt current thus forms the secondary part of a linear motor, i.e., the rotor.

In an embodiment of the present invention, the melt is not slowed-down in any of the runners. The individual runners are thus accelerated or do not experience any modification of their velocity by the alternating fields. This embodiment is advantageous for a rapid casting. The coils can also act particularly effectively on the outer surface areas of the runner because of the skin effect and thus accelerate the melt current particularly in those places where the hydro-dynamic pressure is smallest. Their effect is therefore particularly effective. Due to the inner friction caused by the eddy currents, they also counteract the temperature gradient in the melt cross-section and therefore counteract surface area solidification. As a rule, the viscosity drops because of the higher temperature, which indirectly improves flow properties.

In an embodiment of the present invention, particularly big electromagnetic fields allow for a very steep temperature gradient between the melt edge and the runner wall. This can have positive effects on the durability of the runner wall.

In order to slow down or stop the melt flow, the strength of the electromagnetic fields should be adjusted to the center of the runner where the hydrodynamic pressure is greatest and the penetration depth of the fields simultaneously decreases. These fields are relatively big, which generally requires relatively strong currents and large coils.

The eddy currents causing the acceleration or deceleration of the melt also increase the melt's temperature because of the inner friction of the melt. The generated heat has a positive impact on the casting in that premature solidification can be prevented. In runners having a very small cross-section or with thin-walled sections of the cast part to be cast, this effect can also be used to prevent premature solidification without intending a modification of the flow velocity. More specifically, a primary shaping of cast parts with a wall thickness under 3 mm or with long flow paths can take place with a high level of process reliability.

The flow velocity can also be increased to the maximum value suitable for the cast part, which allows for a reduction of the runner cross-sections. The thereby increasing influence of the heat transfer at the wall surface compared to the heat input by the flow rate can thus be counteracted. For example, a runner with an ideally round configuration, which is reduced to half its diameter, has a cross-sectional area of only 25% of the original cross-sectional area, the wall surface decreasing by 50%. The doubled temperature loss at the wall surfaces at the same current velocity is completely or overcompensated by the increased flow velocity from the flow rate of the melt.

As mentioned above, the local temperature increase not only prevents premature solidification, but also locally reduces the hydrodynamic resistance in thin runners. The centrally defined casting pressure should be sufficiently high that a uniform filling of these critical areas is always provided. By locally reducing the hydrodynamic resistance, the central casting pressure can be considerably reduced, which allows for less complicated casting devices.

If the hydrodynamic resistance is overcome merely by the electromagnetic force, a central casting drive can also be completely dispensed with as necessary. The electromagnetic fields thus provide a direct electromagnetic casting drive.

The hydrodynamic resistance can be reduced by means of the electromagnetic fields at least so that the required casting pressure drops and the closing force required for closing the mold cavity is also reduced. The casting device can thus be manufactured at considerably lower cost. This effect is advantageous for manufacturing large-scale and thin-walled structural parts.

The coils can be powered permanently or according to an algorithm stored in an electronic control system. A control or regulation of the coil current can alternatively occur depending on specific input parameters or, in case of a regulation, also on output parameters, such as casting speed, geometry of the casting system, gate system, shape of the cast part, location of the melt front, type, temperature or temperature gradient of the melt. In an embodiment, a regulation can be advantageous which adjusts the speed of the melt currents so that the mold cavity is filled simultaneously or substantially simultaneously through all runners and that an optimal heat is everywhere provided. The filling amount can also serve as a regulation parameter. The melt supply velocity can, for example, be adjusted depending on the gasification of the foam model volume.

The metal melt is brought in a liquid state from a filling chamber via several casting runners into a mold cavity comprising a hollow space with several gate areas. The several runners serve to fill the mold cavity of a single cast part. In order to provide a fast filling of the mold and a simultaneous start of the second casting phase in all the gate areas, the individual runners can, for example, have different lengths and/or different geometric shapes. The flow velocity of the melt in the individual runners can be modified by means of the electromagnetic fields so that the melt front in all runners reaches the mold cavity, for example, when a casting chamber is completely filled by an advancing plunger.

The casting method is more specifically adapted for casting, such as die casting, large-scale components. A synchronization of the individual fronts of the melt currents based only on the geometry of the runners is difficult when many runners fill the mold cavity. The present invention therefor also allows for complex gating units with many runners.

In an embodiment of the present invention, the individual runners can, for example, be shorted or their cross-section reduced so that a simultaneous filling of the mold is not possible without the action of the electromagnetic fields. By separating the flow velocity and the cross-sectional area traversed by the flow, there is no longer a need to put up with a lengthening of individual runners and therefore with an increase of the amount of circulating material. An undesired increase of the cross-section, which would lead to a greater weight of the cast, can also be dispensed with. By using the electromagnetic fields in a targeted manner, the respectively shortest runners with a small cross-section can be chosen. This simplifies the configuration of the casting device.

In an embodiment of the present invention, a direct casting occurs into a casting mold, which comprises a horizontal or a vertical separation plane. During the first casting phase, the casting chamber is filled with the melt. The melt front is held back until the advancing plunger has increased the fill level of the casting chamber to 100%. A premature filling of the mold cavity is prevented before the casting chamber is completely filled. A wear-free retaining device is provided therefor which holds back the melt by means of electromagnetic fields instead of a shut-off plate. At the same time, the eddy currents generated by the electromagnetic fields and the temperature increase produced by the eddy currents counteract premature surface layer solidification. Once the second casting phase has started, a rapid filling of the mold can occur by acceleration of the melt.

The presented methods and casting devices can in principle be adapted for all electrically conductive melts. Examples include aluminum or magnesium based melts. The melt to be cast can, for example, be a hypereutectic or hypoeutectic Al—Si-alloy.

The present invention is also usable for different casting methods such as, for example, hot-chamber or cold-chamber die casting methods. Due to the different flow velocities, more specifically, to a possible acceleration of melt currents, the present invention allows for a more flexible configuration of the gating unit and a shortening of the runners. The casting result is improved and the weight of the cast is reduced.

The present invention is usable for different casting methods. The present invention will now be described in greater detail based on an exemplary embodiment for die casting.

FIG. 1 shows a casting device 1 for die casting magnesium or aluminum melts. The melt 2 is fed from a melting furnace serving as a storage container 7 into a filling chamber 4 by way of a supply line 8. The filling chamber 4 forms a reservoir for a predetermined amount of the melt 2. The melt 2 can leave the filling chamber 4 via several runners 10, 11, 12 and flow into a mold cavity 3. The mold cavity 3 is formed as a hollow space 13 by two casting mold half-shells 14, 15 and forms the negative form of the die cast product increased in size by the shrinkage value in a known manner. Both casting mold half-shells 14, 15 have a vertical separation plane 9 for subsequent removal of the cast part.

In the first casting phase, the filling chamber 4 is filled with a dosed amount of the melt 2. An exact dosage provides that the mold cavity 3 is subsequently completely filled and the remaining material thus formed does not burst.

A plunger 6 forces the melt 2 via the runners 10, 11, 12 into the mold cavity 3 by applying flow pressure. The slow forward movement of the plunger 6 provides that the air is displaced out of the runners 10, 11, 12 until the fronts of the melt reach the gate.

The runners 10, 11, 12 have different lengths and differently sized cross-sections, so that, without additional measures, the individual fronts of the melt currents 20, 21, 22 in the runners 10, 11, 12 would reach the gate areas at different points in time.

Sections of the runners 10, 11, 12 are surrounded by coils 30, 31, 32 with respectively different configurations, which are adapted to be energized by way of a control or regulation unit (not shown) and can generate eddy currents in the melt 2. As part of the gate unit 5, the runners 10, 11, 12 and the coils 30, 31, 32 are configured so that, with a suitable current feed, the individual melt currents 20, 21, 22 can be slowed down or accelerated so that they reach the gate areas at the same time.

As an additional safeguard, one of the runners 12 has a coil 32 which acts as an electromagnetically operating retaining device 33. With the retaining device 33, the front of the melt current 22 can also be effectively retained when it prematurely reaches the gate area. By means of the inducted eddy currents, the melt front is simultaneously heated up so that its surface layers do not solidify prematurely.

Once the gates have been simultaneously reached, the second casting phase begins, during which the mold cavity 3 is filled. The controlled filling of the mold takes place relatively quickly and under high pressure, a uniform filling being also provided with thin-walled and large-scale cast products due to the plurality of runners 10, 11, 12.

In thin-walled surface layer areas, coil 34 are disposed on or around the mold cavity 3, which locally causes a temperature increase in the cast part and thus lowers the hydrodynamic resistance. An acceleration or deceleration of the melt current front within the mold cavity 3 is also conceivable. Due to the hydrodynamic pressure, the melt 2 uniformly and precisely fills the mold cavity 3.

The schematically showed coils 30, 31, 32, 34 respectively represent one set of coils, which respectively acts on the individual melt currents 20, 21, 22.

The present invention is not limited to embodiments described herein; reference should be had to the appended claims.

LIST OF REFERENCE NUMBERS

1 casting device

2 melt

3 mold cavity

4 filling chamber

5 gate unit

6 plunger

7 storage container

8 supply line

9 separation plane

10 first runner

11 second runner

12 third runner

13 hollow space

14 casting mold half-shell

15 casting mold half-shell

20 first melt current

21 second melt current

22 third melt current

30 coil

31 coil

32 coil

33 retaining device

34 coil

Claims

1. A method for manufacturing a cast component with a casting device, the method comprising:

providing a casting device comprising: a filling chamber, a mold cavity comprising a hollow space, runners comprising at least one of a different length and a different cross-section, each of the runners respectively connecting the filling chamber with the mold cavity, and a plunger arranged in the filling chamber, the plunger being configured to advance a metal melt from the filling chamber via the runners into the mold cavity;

providing the metal melt in a fluid state in the filling chamber;

advancing the metal melt via the runners from the filling chamber to the mold cavity by advancing the plunger in the filling chamber;

providing electromagnetic fields; and

increasing or decreasing a flow velocity of melt currents in the respective runners via the electromagnetic fields.

2. The method as recited in claim 1, wherein the increasing or decreasing of the flow velocity of melt currents in the respective runners via the electromagnetic fields is performed so that a melt front in each of the runners reaches the mold cavity when the filling chamber has been completely filled by the plunger.

3. The method as recited in claim 1, wherein the electromagnetic fields are configured to be at least one of controlled and regulated as a function of at least one of the mold cavity, a temperature, and a melt composition.

4. The method as recited in claim 1, wherein the electromagnetic fields are configured to reduce a hydrodynamic resistance of sections of the metal melt with a small cross-section so as to reduce a closing force of the casting device.

5. The method as recited in claim 1, wherein the electromagnetic fields are configured to reduce a hydrodynamic resistance of sections of the metal melt with a small cross-section so as to decrease a casting drive force.

6. The method as recited in claim 1, further comprising at least one of heating, decelerating, and accelerating the melt currents in the respective runners to a different degree via the electromagnetic fields.

7. A casting device for a metal melt to implement the method as recited in claim 1, the casting device comprising:

a mold cavity comprising a hollow space for a cast part;

a filling chamber configured to serve as a reservoir for a metal melt;

a gate unit comprising at least two runners, the at least two runners being configured to connect the filling chamber with the mold cavity; and

a flow velocity device configured to influence a flow velocity of the metal melt, the flow velocity device being configured to act on at least one of a part of the gate unit, a part of the at least two runners, and a part of the mold cavity.

8. The casting device as recited in claim 7, wherein the flow velocity device influences the flow velocity via an electromagnetic field.

9. The casting device as recited in claim 7, wherein the flow velocity device comprises coils configured to create an electromagnetic field, wherein each of the at least two runners is surrounded by a coil.

10. The casting device as recited in claim 7, wherein the mold cavity further comprises at least one coil arranged in a surface area.

11. The casting device as recited in claim 7, wherein the casting device further comprises an electromagnetic retaining device configured to retain the metal melt.