Method for producing cast components for electrical applications

Abstract

In a method for producing cast components for electrical applications, a hardenable aluminum alloy is melted and filled into a die casting mold. The melted aluminum alloy is cooled by the die casting mold that is comprised of a material that has a thermal conductivity causing the melted aluminium alloy to be cooled at a cooling rate of approximately ≧5×102 K/s. Prior to filling, the melted aluminum alloy is introduced into a fill chamber and the melted aluminum alloy is displaced at a minimal displacement speed within the fill chamber.

Description

BACKGROUND OF THE INVENTION

The invention relates to a method for producing cast components for electrical applications in which hardenable aluminum alloys are used which are melted and introduced into a die casting mold.

It is known to produce die cast components for electrical applications, for example, for electrical conductors, high-voltage switches, rotors or stators in electrical motors, and the like. For this purpose, inter alia aluminum alloys are used that can be hardened. Such aluminum alloys are, for example, Al—Cu, Al—Mn—Si, Al—Zn—Mg, Al—Si—Cu, or Al—Si—Mg. The hardenable alloys have an electrical conductivity that is usually greater than approximately 28 MS/m. In order to improve the mechanical properties of the various aluminum alloys, it is known to provide in the microstructure of these alloys so-called Guinier-Preston zones. These are coherent precipitations by means of which the strength of the aluminum alloys can be increased.

With the aid of FIG. 1, a known method is disclosed in order to obtain such hardenable aluminum alloys with high tensile strength. This method requires complex method steps. First, the aluminum alloy is subjected to a solution annealing process. During solution annealing, the alloy is slowly heated. According to FIG. 1 that shows a temperature-time diagram for an aluminium alloy A356, this heating phase is carried out for a duration of 100 minutes. The aluminum alloy is heated to approximately 80% of its melting point, in the illustrated embodiment to 530° C. In aluminum alloys, this heating temperature is between 470° C. and 540° C. The workpiece must be kept at this temperature until a sufficient quantity of mixed crystals has formed. In the embodiment, this time period is 140 minutes. Subsequently, in a second process the formed mixed crystals are quenched so that the mixed crystals are preserved even at lower temperatures, in general at room temperature. Subsequently, aging is carried out where the aluminum alloy is heated for approximately 50 minutes to 210° and is kept at this temperature for a further 70 minutes. During this processing step, the Guinier-Preston zones are formed which lead to high strength of the aluminum alloy.

This method comprising three processing steps is complex and very time consuming.

SUMMARY OF THE INVENTION

It is an object of the present invention to configure a method of the aforementioned kind such that the cast components can be produced in an inexpensive way with minimal time expenditure.

In accordance with the present invention, this is achieved in that the die casting mold is comprised of a material that has such a thermal conductivity that the melt of the alloy in the die casting mold is cooled at a cooling rate of approximately ≧5×10² K/s.

The inventive method is characterized in that the cast component is produced in a die casting mold that is made of a material of such a high thermal conductivity that the melt of the alloy during the die casting process is cooled in the mold at a cooling rate of approximately ≧5×10² K/s. Preferably, this cooling rate is not less than approximately ≧10³ K/s. At such a great cooling rate, an oversaturated mixed crystal is formed that requires no additional thermal treatment. In this way, a high-strength hardenable aluminum alloy is formed that has excellent qualities for producing cast components for electrical applications. For performing the method according to the invention, there is no need for high technological expenditure. Moreover, the method according to the invention requires less time than the disclosed method of the prior art.

Advantageously, the melt of the alloy is displaced in a first phase of the method at minimal speed in a fill chamber into which the melt of the alloy is first introduced and is then subsequently supplied or filled into the appropriate cavity of the die casting mold. Due to the minimal movement or displacement rate, the air that is contained in the melted alloy can escape well. Also, it is ensured that the alloy melt moves only minimally and accordingly does not produce waves, or produces only a few waves, so that the risk of air inclusion or air entrapment is avoided.

The displacement rate of the melt of the alloy is in a range of less than approximately 0.5 m/s.

The melt of the alloy is advantageously filled or pressed in a second phase of the method from the fill chamber into the downstream die casting mold at high speed. In this way, the appropriate cavity in the die casting mold is completely filled with the melt of the alloy.

The speed at which the melt of the alloy is pressed in this second phase into the die casting mold is advantageously in a range between approximately 1 m/s and approximately 3 m/s.

In an advantageous embodiment, the melt of the alloy is loaded in the die casting mold with a post pressure in order to compensate the deficit of the reduced density of the alloy melt relative to the density of the solid state of the alloy and in order to avoid bubbles or cavities in the die cast component.

The object of the invention is not only apparent from the individual claims but also from features and elements disclosed of the drawings and discussed in the specification. These features and elements are considered part of the invention as long as they are novel relative to the prior art individually or in combination, even though such features and elements may not be claimed.

BRIEF DESCRIPTION OF THE DRAWING

Further features of the invention can be taken from the claims, the description, and the drawings. In the drawings, an embodiment is illustrated in an exemplary non-limiting form in more detail.

FIG. 1 is a temperature-time diagram of a heat treatment of an aluminum alloy in accordance with the prior art.

FIG. 2 is a schematic illustration of a first phase of the die casting process according to the present invention.

FIG. 3 is a schematic illustration of a second phase of the die casting process according to the invention.

FIG. 4 is a schematic illustration of a third phase of the die casting process according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The method according to the invention which will be explained in more detail in the following enables producing an aluminum alloy that can be hardened without requiring the step of solution annealing and preferably without requiring quenching. The alloy can therefore be produced in a simple and inexpensive way requiring only little time. The method is characterized by a simple process control.

The method is suitable for hardenable aluminum alloys that in addition to aluminum contain at least two other components. For example, the method is suitable for Al—Mn—Si, Al—Zn—Mg, Al—Si—Cu or Al—Si—Mg alloys. A particularly advantageous aluminum alloy is the alloy 6101. The aluminum alloys have a high electrical conductivity that is higher than approximately 28 MS/m.

With the aid of FIGS. 2 through 4, the method will be explained in more detail. The melted alloy 1 is contained in a fill chamber 2. The melted alloy is displaced in this fill chamber 2 by means of piston 3 in the direction toward a die casting mold 4. The mold 4 has a sprue plate 5 and an ejector plate 6 between which a cylinder plate 7 is located. The cylinder plate 7 receives a workpiece 8 which in the embodiment is a lamella package that is used for producing, for example, rotors or stators of electric motors. Short-circuit rings 9, 10 are to be cast onto both end faces of the workpiece 8. For this purpose, the die casting mold 4 has appropriate mold cavities 11, 12 which are provided in the sprue plate 5 and in the ejector plate 6. The short-circuit rings 9, 10 connect the conductor rods (not illustrated) in the lamella package 8, as is known in the art.

The melted alloy 1 is first introduced into the fill chamber 2. In the first phase of the method according to FIG. 2, the piston 3 begins to move the melt slowly in the direction toward the sprue passage 13. The rate at which the piston 3 moves in this first phase is advantageously less than approximately 0.5 m/s. Due to the minimal movement speed, the air that is contained in the melt can escape easily.

Moreover, wave generation in the melt that may result from movement of the melt is minimal due to the low speed so that also a splashing movement of the melt does not occur by means of which air could be entrapped. For escape of the air, the fill chamber 2 is provided with appropriate air outlet openings in the upper area.

The liquid melted alloy 1 is introduced by means of at least one fill opening 14 into the fill chamber 2. In the initial position according to FIG. 2, the piston 3 is in front of the fill opening 14. It is moved at minimal speed in the direction of the die casting mold 4 until it is positioned behind the fill opening 14 (FIG. 3).

In the second phase (FIG. 3), the liquid alloy 1 is pressed with the piston 3 at high speed into the die casting mold 4. The liquid melted alloy 1 fills the cavities 11, 12 as well as the sprue passage 13 completely (FIG. 4). The speed of the piston 3 in the second phase is depending on the product and on the geometry. Depending on the geometry, the maximum or optimal filling time can be calculated which is associated with an appropriate volume stream. The same volume stream can be achieved with a small diameter at a high speed or with a large diameter and a minimal speed. For conventional rotors, the speed is between approximately 1 m/s and approximately 3 m/s.

The piston 3 loads the liquid melted alloy 1 also with a high post pressure (overpressure). In this way, it is taken into consideration that the liquid melted alloy 1 has a density that is less than the density of the solid state of the alloy. Due to the high post pressure application, this difference is compensated so that bubbles or cavities in the cast short-circuit rings 9, 10 are avoided. The height of the pressure is depending on the product and the geometry and is between approximately 80 and 600 bar.

As soon as the alloy has cooled and solidified, the die casting mold 4 is opened so that the workpiece 8 with the short-circuit rings 9, 10 at the end faces can be removed. The sprue that is formed by the material in the sprue passage 13 is removed or separated from the short-circuit ring 9 by measures known in the art.

The material of the die casting mold 4 is selected such that with it a very high cooling rate can be achieved which is not less than approximately 5×10² K/s and is preferably not less than approximately 10³ K/s. Such a high cooling rate is, for example, achieved with steel that enables fast cooling of the melt of the alloy. Any material is suitable that has a high thermal conductivity such that the desired high cooling rate is achieved. The quenching process is achieved by the die casting mold 4 during the casting process so that the process step of solution annealing can be eliminated. The die casting process requires therefore only little time.

With the described method an oversaturated solid solution structure in the die cast component 9, 10 can be generated and the die casting mold 4 is optimally filled during the die casting process. For the disclosed method, all aluminum alloys can be used that can be hardened.

The die cast components 9, 10 must not be thermally treated because, as a result of the extremely fast cooling action during the die casting process caused by the die casting mold, the die cast components are imparted with an oversaturated mixed crystal structure that requires no further thermal treatment.

The specification incorporates by reference the entire disclosure of German priority document 10 2013 000 746.1 having a filing date of Jan. 17, 2013.

While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

Claims

1. A method for producing cast components for electrical applications, the method comprising:

melting a hardenable aluminum alloy;

filling the melted aluminum alloy into a die casting mold;

cooling the melted aluminum alloy by the die casting mold that is comprised of a material that has a thermal conductivity causing the melted aluminium alloy to be cooled at a cooling rate of approximately ≧5×102 K/s.

2. The method according to claim 1, wherein the cooling rate is approximately ≧103 K/s.

3. The method according to claim 1, comprising, prior to filling, introducing the melted aluminum alloy into a fill chamber and displacing the melted aluminum alloy at a minimal displacement rate within the fill chamber.

4. The method according to claim 3, wherein the displacement rate is less than approximately 0.5 m/s.

5. The method according to claim 3, wherein in the step of filling the melted aluminium alloy is moved from the fill chamber into the die casting mold at a high speed.

6. The method according to claim 5, wherein the high speed is between approximately 1 m/s and approximately 3 m/s.

7. The method according to claim 1, wherein the melted aluminum alloy after completion of filling of the die casting mold is exposed to overpressure.