WO2013182189A2

WO2013182189A2 - Method for producing composite cast parts

Info

Publication number: WO2013182189A2
Application number: PCT/DE2013/100196
Authority: WO
Original assignee: Actech Gmbh
Priority date: 2012-06-04
Filing date: 2013-05-31
Publication date: 2013-12-12
Also published as: DE102012104820B4; WO2013182189A8; DE102012104820A1; EP2855050A2; WO2013182189A3

Abstract

The invention relates to a technical solution for the composite casting of inserts into a main body made of casting material. The aim of the invention is to provide a solution by means of which an optimised cooling between an insert and a main body made of casting material is achieved in the manufacturing process and a permanently good bond between insert and a main body is ensured. This aim is achieved by a method with which, in a preferred application, a cylinder crankcase and cylinder heads for internal combustion engines can be produced.

Description

Process for the production of composite castings

The present invention relates to a technical solution for the composite casting of inserts in a base body made of cast material.

Casting processes are known in numerous variants. The molds are often designed as lost sand molds or metallic permanent molds. When chill casting dormant permanent forms are usually filled without pressure, the shape of the casting is determined by the permanent mold. In low-pressure mold casting, the mold is first filled from below with a slight overpressure via a riser, and the casting is solidified after the mold has been completely filled. In die casting, the melt is pressed into a mold at high pressure and speed. The pressure is maintained until the end of solidification. Die casting is primarily suitable for thin-walled castings, such as aluminum, zinc or magnesium alloys.

Composite castings can also be produced using the above-mentioned casting methods. The so-called compound casting designates a production of components made of several materials by input, or encapsulation of component areas with another material. Such composite castings are used for different applications, for example for internal combustion engines. Here, the conventional gray cast iron cylinder crankcases are increasingly made of light metal, especially aluminum and magnesium alloys. While gray cast iron is suitable both for the crankcase and for the cylinder running surfaces, light metal casting alloys have significantly worse tribological properties. Therefore, additional cylinder liners are cast in the tread area, which consist for example of gray cast iron. Here, the liners must be sufficiently firmly locked in the cylinder crankcase. This is necessary in addition to the position fixation for the heat transfer between the cylinder liner and cylinder crankcase. DE 196 05 946 C1 describes a related cylinder liner, which consists of a running layer of molybdenum and an outer layer of aluminum alloy. The outer layer is profiled on its outside. The two layers are formed by thermal spraying on a rotating mandrel and when casting the cylinder crankcase arranged on quills in the mold cylinder liners are connected positively with their profiled outer surface with the casting material.

According to DE 196 34 504 A1, the bond between the cylinder crankcase and the cylinder liner is improved by the bush is blasted on its outer surface before the composite casting with sharp-edged particles. Thus, pyramid-like protuberances are generated, which should cause a better pouring.

While the above references to the prior art are intended to alleviate in particular problems due to too smooth transition surfaces, oxide layers may also interfere with composite casting. For example, an oxide skin on an aluminum component that is to be cast in aluminum casting material may impair the connection to the casting material. This can be avoided according to DE 197 45 725 A1 by destroying the oxide skin on the sprue body by thermal spraying. The spray material used is a nickel or molybdenum alloy. The detached oxide particles are distributed in the sprayed layer. Partially molten particles protrude from the sprayed layer and improve the bond with the casting material.

Other references to the state of the art are devoted to cooling problems in composite casting. For example, DE 10 2006 001 946 B4 describes an insert for cylinder liners and a related manufacturing method, in which a cooling channel of the later cylinder crankcase is used for cooling during casting. However, only depositors with their own cooling channel are suitable for this purpose and an additional cover for sealing is required. In addition to the above-described prior art, numerous other references also relate to composite casting, so that a large number of technical solutions is already available per se. Nevertheless, there is still a need for development in order to further improve the many aspects of using this technology. This applies, for example, to extensive requirements with regard to the sprue bodies, of which a cohesive composite, high strength and thermal conductivity, high strength of the cohesive bond and low density of the sprue body are to be named. Only the cohesive bond allows lightweight construction, high strength and high thermal conductivity. These requirements are particularly relevant if high thermal and mechanical loads occur together in mobile devices, as is the case in internal combustion engines near the combustion chamber.

The cohesive bond is to be produced during casting, since this is the most direct and cost-effective variant, which also allows the greatest geometric freedom. Whether a cohesive bond can be produced during casting depends very much on the temperature regime.

The object of the invention is therefore to provide a technical solution for the production of composite castings, achieved in the manufacturing process with an optimized temperature control between an insert and a base body made of cast material and a permanently good material connection between insert and body is guaranteed.

This object is achieved by a method for which two slightly modified variants are proposed. Advantageous embodiments of the method are the subject of dependent claims, whose technical features are explained in more detail in one embodiment.

The technical solution according to the invention is suitable for the production of various highly stressable composite castings, with a preferred application being the production of internal combustion engines. Exemplary embodiments of the invention will now be described.

With the method according to the invention, composite cast parts may be produced which comprise at least one sprue body and a component geometry which otherwise consists essentially of an aluminum casting alloy. The sprue used is an aluminum-based metal-matrix composite (Al-MMC). This AI-MMC casting is freed of its oxide skin before casting and protected from re-oxidation.

The sprue is provided with a low-melting metal alloy before the sprue. It is essential that the melting point of this alloy is below the melting point of the sprue and the molten metal. The application of the metal coating can be carried out in various ways, for example by friction soldering or ultrasonic soldering or mechanical treatment in a solder bath. It is essential here that processes can be used which do not require pretreatments such as pickling or the use of flux during soldering and which eliminate a possible oxide layer on the sprue body and prevent the formation of an oxide layer before and during the casting process.

The sprue body can be coated both completely and only partially. In this case, the natural oxide layer located on the sprue body is removed simultaneously with the formation of the metal coating by an external mechanical action, so that there is a material bond between the coating material and the sprue body. In principle, however, all coating processes are suitable in which the applied metal layer is applied without intermediate layers and with a material bond to the sprue. In addition, the metal coating has a dense structure so that the underlying surface of the sprue is closed off from the surrounding atmosphere. Thus, no new oxide layer can form on this surface. The thickness of the metal coating is in a range of 10 m to 500 μηπ, with thicknesses of 100 m to 300 m are useful for most applications. The correspondingly pretreated sprue body is then positioned in the casting mold and flows around in the following casting process with a usual gravity and low-pressure casting speed of the molten metal. In this case, the melting temperature of the coating material is achieved on the sprue body before the flow is stopped. As a result, this coating is washed off and the molten metal comes into direct contact, to the exclusion of the atmosphere, with the now oxide-free, metallic bright surface of the sprue. The flow around the sprue body with the molten metal or the process of washing off the coating from the sprue body can be assisted by the casting process, by aerodynamically optimized design of the gate parts or by maintaining the flow movement after completion of the mold filling. In the third variant, additional components are necessary, for example, a stirring device.

Furthermore, the sprue body can be preheated and / or cooled depending on the respective specific process conditions. The tempering can be done for example with heat transfer oil or water or a spray. The optional preheating brings the sprue to a temperature that prevents cold running over the sprue and favors the melting of the low melting metal alloy metal coating. By influencing the temperature of the sprue body according to the invention, a targeted melting of the coating can be achieved without, however, melting the sprue body itself. The decisive factor is that the sprue is tempered directly (preheated and / or cooled). Direct tempering hot, that the sprue is in direct contact with the heat transfer medium and not as known by applying a cooling iron or a mold, which in turn can also be flowed through by a heat transfer medium.

Another embodiment of the direct cooling is that the sprue has an accumulation of mass that does not belong to the finished part contour, So has no function in the finished part, is removed after casting, is used for temperature control of the sprue in the casting process and the thermal inertia of the sprue adjusted so that only the low-melting metal alloy is melted on the surface and the casting is not or only slightly melted , Here, the mass accumulation of the sprue itself acts as a heat transfer medium.

The casting mold has a cooling passage open towards the sprue body, and the sprue body is inserted into this casting mold in such a way that the open cooling channel is closed by the sprue body.

Parts of the mold and the sprue are tempered by a heat transfer medium (coolant flows). As the coolant flow heat transfer media are also referred to below, which heat the mold, or keep at a certain temperature. A first coolant stream is supplied at a temperature between 100 ° C and 450 ° C for preheating the mold. Preheating prevents cold runs. The coolant flow has no negative pressure during preheating. In the context of the invention, however, it is also fundamentally possible that the coolant flow could have a pressure which is at least 1. 000 Pa lower than the pressure in the mold cavity. This precludes the heat transfer medium from entering the mold cavity. However, with the already available technical solutions, it is not absolutely necessary to realize such a negative pressure in the coolant flow during preheating.

Furthermore, a second coolant flow is supplied with a temperature which is at least 100 K lower than the temperature of the first coolant flow. However, this coolant flow is not active during preheating and is switched on only at the end of the casting. The first and second coolant streams are passed through the same cooling channel.

The first coolant stream and the second coolant stream have either direct or only indirect contact with the sprue body. A direct contact to the Cast body eliminates the heat transfer resistance between the heat transfer medium and the surface of the sprue through the shape and the interface between the mold and sprue. Thus, the temperature of the sprue can be controlled very quickly. Very high cooling rates are possible. The surface of the sprue melts. The sprue does not melt. If such a direct contact is realized, however, particular aspects of the water-melt contact are to be considered very accurately.

If, however, an indirect contact is realized, although only a lower cooling effect is possible, but this is sufficient according to current test conditions to produce the necessary cohesive bond. This variant can be implemented in terms of device technology by using a tool-side provided mold element with integrated cooling as a carrier for the positive fit positioned thereon Eingießteil.

The change from preheating to excessive cooling occurs so early that according to the thermal conductivity of the insert, the melting of the surface is prevented only when the entire composite casting area is melted and the melting of the surface is prevented before the sprue is unintentionally thermally stressed. This time is typically from one minute to one minute after pouring.

It is advantageous to coat the surface of the sprue body in the composite casting area with a low-melting metal alloy.

The melt in the mold solidifies, the coolant flow is interrupted, the composite casting is removed from the mold and thus the cooling channel is opened again.

The process described for the production of a composite casting can be slightly modified by the sprue body and / or the casting mold or Parts of the mold to be preheated to a temperature between 100 ° C and 450 ° C before the sprue is inserted into the mold.

In this case, in the period of one minute before to one minute after the casting started to supply a coolant flow having a temperature which is at least 100 K lower than the temperature of the preheated parts.

As in the variant described above, this coolant flow has a pressure which is at least 1. 000 Pa lower than the pressure in the mold cavity and also has direct contact with the sprue body.

The composite casting produced according to the method can be configured as a cylinder crankcase, which consists of at least one Zylinderbuchseneinlegeteil and a base body made of a cast metal. In this case, the cylinder running surface, which can be provided with a machining allowance if necessary, during the casting process part of the wall of a cooling channel. This cooling channel is further essentially formed by the mold.

Alternatively, the composite casting produced according to the method can also be designed as a cylinder head, which consists of at least one combustion chamber insert and a base body made of cast metal. In this case, the combustion chamber surface of the insert part, which may also be provided with a machining allowance if necessary, during the casting process part of the wall of a cooling channel. This cooling channel is further essentially formed by the mold.

Claims

claims

1 . A method for producing a composite casting, in particular a cylinder crankcase or a cylinder head for an internal combustion engine, comprising at least one sprue body and a component geometry, which otherwise consists essentially of an aluminum alloy, using as a sprue an aluminum-based material, prior to the casting of his Oxide skin is freed and protected from re-oxidation, wherein the mold has a gate to the sprue open cooling channel, wherein the sprue is inserted into the mold such that the open cooling channel is closed by the sprue, wherein a first flow of coolant having a temperature between 100 ° C and 450 ° C for tempering the mold is supplied and wherein this first coolant flow has direct or indirect contact with the sprue body, while the mold is poured off, wherein a second coolant flow at a temperature, the min At least 100 K is lower than the temperature of the first coolant stream for tempering the mold is supplied and wherein this second coolant stream also has direct or indirect contact with the sprue body, while the mold is poured off and wherein the melt solidifies in the mold, the coolant flow interrupted Composite casting removed from the mold and thus the cooling channel is opened again.

2. A method for producing a composite casting, in particular a cylinder crankcase or a cylinder head for an internal combustion engine, comprising at least one sprue body and a component geometry, which otherwise consists essentially of an aluminum alloy, wherein as a sprue body, an aluminum-based material is used, which is freed from its oxide skin before the casting and protected from re-oxidation, wherein the casting mold has an open towards the sprue cooling channel and wherein the sprue and / or the casting mold or parts of the casting mold on a Temperature preheated between 100 ° C and 450 ° C and wherein the sprue is inserted into the mold so that the open cooling channel is closed by the sprue, wherein the mold is poured and in the period of one minute before casting to one minute after The casting is started with a coolant flow having a temperature at least 100 K lower than the temperature of the preheated parts for tempering the mold, and which coolant flow has direct or indirect contact with the sprue body while the mold is being poured off and the melt is poured in the mold Form solidifies, the coolant current m interrupted, the composite casting removed from the mold and thus the cooling channel is opened again.

3. The method according to claim 1 or 2, characterized in that the first coolant flow are always performed with or without negative pressure and the second coolant flow with direct cooling of the sprue body always with negative pressure.

4. The method according to claim 3, characterized in that the first and the second coolant flow have a pressure which is at least 1, 000 Pa lower than the pressure in the mold cavity.

5. The method according to claim 1 or 2, characterized in that a metal-matrix composite material based on aluminum is used for the sprue body.

6. The method according to claim 1 or 2, characterized in that the sprue body before the sprue at least partially freed from its oxide skin and cohesively provided with a low-melting metal alloy whose melting point is at least 100 K below the melting points of the sprue and the molten metal and the sprue thus treated is then positioned in the mold and then flows around the molten metal with a normal gravity or low-pressure casting casting speed and the low-melting metal alloy is dissolved, melted and / or washed off.

7. The method according to claim 6, characterized in that the low-melting metal alloy is applied without interlayers and with a material composite on the sprue, in particular by means of friction or ultrasonic sonicating or mechanical processing within a solder bath or a surface treatment under protective gas or vacuum.

8. The method according to claim 6, characterized in that the low-melting metal alloy in a thickness of 10 μηι to 500 μηπ, in particular 100 μηι to 300 μηι is applied to the Eingusskörper.

9. The method according to claim 1 or 2, characterized in that the flow around the sprue body with the molten metal is supported by the casting process and / or by several aerodynamically optimized gate parts and / or that a maintenance of the flow movement is supported by means of additional components after completion of the mold filling ,

10. The method according to claim 1 or 2, characterized in that when producing a cylinder crankcase consisting of at least one Zylinderbuchseneinlegeteil and a base body made of cast metal cylinder surface, which may be provided with a Bearbeitungsaufmaß, during the casting process is part of the wall of a cooling channel, the is further essentially formed by the mold.

1 1. A method according to claim 1 or 2, characterized in that when producing a cylinder head consisting of at least one Brennraumeinlegeteil and a base body of cast metal, the combustion chamber surface of the insert, which may be provided with a machining allowance, during the casting process is a part of the wall of a cooling channel, which is further substantially formed by the mold.