DE102012022954A1 - Casting core useful e.g. in automobile industry, comprises inner core surrounded by core jacket, whose inner shape corresponds to outer shape of inner core, and has physical property that is different from physical property of core jacket - Google Patents

Abstract

Casting core (1) comprises an inner core (11), which is surrounded by a core jacket (12), whose inner shape corresponds to an outer shape of the inner core, and exhibits at least one physical property, which is different from at least one physical property of the core jacket. An independent claim is also included for manufacturing the casting core using an openable negative permanent mold exhibiting a main cavity corresponding to outer contour of the casting core, and at least one first opening that is connected with the main cavity, comprising (a) providing a liquid and curable core jacket precursor material and the negative-permanent mold, (b) filling the main cavity with the core jacket precursor material through the first opening, (c) adjusting curing conditions for the main cavity at an interface of the negative permanent mold, (d) curing a first portion of the core jacket precursor material, which is present at the interface, (e) adjusting an excess pressure in the main cavity, (f) flowing a second portion of the core jacket precursor material that is not cured, through the first opening to obtain the core jacket, (g) adjusting a pressure equalization between the main cavity and the surroundings, (h) cooling the core jacket, opening the negative permanent mold and removing the core jacket, (i) filling the core jacket with an inner core material to obtain the inner core, and (j) closing an opening of the core jacket to obtain the casting core.

Description

The invention relates to a casting core and a manufacturing method for such a casting core.

Cast cores are used in general mechanical engineering as well as in the automotive industry, for example, for the manufacture of internal combustion engine components, such as the cylinder head or the engine block, with recessed cooling water or oil channels or generally whenever a cavity is to be produced by means of a casting process. Lost sand or salt cores are usually used which, after casting, are either left in the cavity or, if it is an accessible cavity, destructively removed.

Such cores are known and are usually one-piece. Different areas of the casting core, however, make different demands on the physical and / or chemical properties of the casting core or the casting core material. Thus, at an interface of the casting core with a melt, a high thermal shock resistance and low thermal conductivity is desirable, while the interior of the casting core should be tough, impact-resistant, dimensionally stable and should have a high compressive strength for use in die-casting. Furthermore, special demands are placed on the surface of the casting core with regard to the surface texture, wherein, above all, the roughness should be as small as possible. Because of these different and sometimes conflicting requirements, a compromise has been made in the prior art in the selection of the cast-core material so far.

The DE 10 2008 002 376 A1 addresses the task of creating a casting core which has regions adapted to a profile of requirements. For this purpose, a reinforcing element is embedded in a casting core body, which increases the mechanical strength of the casting core in a defined load direction (reinforced concrete principle). Furthermore, the reinforcing element can be used during coring to mechanically weaken the casting core to facilitate the coring. For this purpose, the reinforcing element is pulled destructively out of the casting core, whereby the cohesion of the casting core is permanently weakened.

Based on this prior art, it is an object of the present invention to provide a casting core, which can be better adapted to different requirement profiles in different areas than known casting cores.

This object is achieved by a casting core with the features of claim 1.

In addition, the task results to provide a manufacturing method for a casting core according to the invention, which is easy to automate and can be produced with the casting cores with consistently high quality.

This object is achieved by a manufacturing method for a casting core having the features of claim 6.

Further developments are each carried out in the subclaims.

A first embodiment of the casting core according to the invention has an inner core which is surrounded by a core jacket. The inner shape of the core sheath corresponds to the outer shape of the inner core, but the inner core differs at least in physical property from the core sheath, which consequently has at least one other physical property.

By means of a casting core constructed according to the invention, it is thus possible to equip different regions with different physical properties adapted to the respective requirement profile of the regions. That is, the core is a multicomponent core. Of course, the ranges may differ not only in one physical property but also in two or more physical properties or in one or more chemical properties. Such a core can be optimized for example for die casting, in which case the inner core may consist of a pressure-resistant (but usually not high-temperature resistant) material and may be surrounded by a core sheath made of a temperature-resistant and thermal shock resistant material. Such a casting core thus makes it possible to carry out the production of castings with cavities more cost-effectively, since the casting core according to the invention, for example, does not have to be preheated and can withstand higher pressures, which can contribute to a better filling of undercuts and the like.

In a further embodiment, the physical property may be a thermal, mechanical, electrical and / or magnetic property. The core sheath and the inner core may consist of (chemically) identical, or completely different materials.

The core sheath and the inner core need not consist of different materials; if the different physical properties of the same materials, for example, by different heat treatment conditions, porosity or surface conditions can be achieved, this is also a possibility according to the invention for adjusting the different physical properties.

In yet another embodiment, the inner core and the core sheath may be connected. The compound can be realized, for example, by a binder, advantageously an adhesive.

If the inner core and the core sheath are joined together, the shrinkage which would otherwise occur during a pressure load on the core sheath can be reduced, among other things, by filling the gap with the binder. Furthermore, the binder can help to reduce the heat conduction from the core sheath into the inner core. It is also advantageous if there is no gas in the "gap" between the inner core and the core shell, which expands when the temperature increases. Gas in the gap can damage the core shroud, which generally has a comparatively low tensile strength, in that a internal pressure in the gap dissolves the material cohesion of the core shroud locally.

Furthermore, the core sheath may consist of a thermal shock resistant and / or heat resistant material. The inner core may consist of an impact-resistant and / or tough and / or dimensionally stable material.

The heat resistance in the sense of the melting temperature or in relation to a relevant for the material creep temperature must be adapted in each case to the melting temperature of the material to be cast or seen in terms of a relevant for the material creep temperature in conjunction with a necessary for cooling the casting time period , Especially for diecasting, the proposed combination of material properties offers: Since the pressure-resistant material of the inner core usually has a relatively low temperature resistance and thermal shock resistance, it should be surrounded according to the invention by a core sheath that better withstands these stresses.

The material of the core sheath may be a ceramic or a salt, and the material of the inner core may be a plastic, a metal from the group consisting of zinc, tin, aluminum, or even granules, preferably sand.

• a) Bereitstellen eines flüssigen, aushärtbaren Kernmantel-Vormaterials und der Negativ-Dauerform,
• b) Befüllen der Haupt-Kavität mit dem Kernmantel-Vormaterial durch die erste Öffnung,
• c) Einstellen von Aushärtbedingungen an einer Grenzfläche der Negativ-Dauerform zu der Haupt-Kavität,
• d) Aushärten Lassen eines ersten Teils des Kernmantel-Vormaterials, das an der Grenzfläche anliegt,
• e) Einstellen eines Überdrucks in der Haupt-Kavität,
• f) Ausfließen Lassen eines zweiten Teils des Kernmantel-Vormaterials, das nicht ausgehärtet ist, durch die erste Öffnung, so Erhalten des Kernmantels,
• g) Einstellen eines Druckausgleichs zwischen der Haupt-Kavität und der Umgebung,
• h) Abkühlen Lassen des Kernmantels, Öffnen der Negativ-Dauerform und Auswerfen des Kernmantels,
• i) Befüllen des Kernmantels mit einem Innenkern-Material,
• j) Verschließen einer Öffnung des Kernmantels und Erhalten des Gusskerns.

A first embodiment of the manufacturing method for a casting core according to the invention is carried out using an openable negative permanent mold, which has a main cavity corresponding to the outer contour of the casting core. The negative permanent mold has at least a first opening connected to the main cavity. The manufacturing process comprises the following steps:

• a) providing a liquid, hardenable core-shell precursor material and the negative permanent mold,
• b) filling the main cavity with the core material by the first opening,
• c) setting of curing conditions at an interface of the negative permanent mold to the main cavity,
• d) curing leaving a first part of the core material, which bears against the interface,
• e) setting an overpressure in the main cavity,
• f) passing a second part of the core material, which has not hardened, through the first opening, thus obtaining the core shell,
• g) adjusting a pressure balance between the main cavity and the environment,
• h) cooling leaving the core sheath, opening the negative permanent mold and ejecting the core sheath,
• i) filling the core sheath with an inner core material,
• j) closing an opening of the core sheath and obtaining the casting core.

The liquid, curable core-shell starting material may be a solution, a melt or a suspension, for example a molten salt, a salt solution, a castable ceramic or any other hardening material that appears suitable to a person skilled in the art.

The negative permanent mold can be made of a metallic material, such as a light metal or a light metal alloy or a steel depending on the inserted core-shell material or depending on the temperature of the core-shell material when filling the negative permanent mold. The negative permanent mold can be manufactured in such a way that it has a very smooth surface and imprints this surface finish on the core sheath produced with it. As a result, a core sheath (or core core whose outer surface is the core sheath) produced according to the invention can be used directly for encapsulation in a die casting tool. The high-quality cast core with regard to the surface quality can be used directly without or with only very little (eg deburring of the edges) reworking. Furthermore, the negative permanent mold can have an inner ribbing, so that externally ribbed casting cores can be produced with it, which have a high resistance to pressure loads and are thus particularly suitable for diecasting.

The curing conditions can be selected and adjusted depending on the core-shell starting material used; For example, a temperature gradient between the melt and the wall of the main cavity to achieve curing at the interface at a predetermined cooling rate, since on the wall of the main cavity, the liquid core-shell precursor begins to cure first in step d). There are the cheapest Aushärtbedingungen. Subsequently, a shell of hardened kernmantel raw material continuously builds up, which ultimately forms the core shell.

The setting of the curing conditions in step c) can, however, if appropriate, also be carried out after step a). In this case, however, it should be noted that uneven shell growth may occur because portions of the liquid core-shell precursor initially filled into the mold are exposed to the curing conditions longer than other portions which are later poured. However, it may be desirable to make a core shroud having areas of different wall thicknesses. Then, the filling of the main cavity can be carried out approximately stepwise in order to specifically bring about the different wall thicknesses by means of different contact times with the curing conditions.

"Overpressure" is intended to mean that in the main cavity relative to the environment, a relative overpressure is set, of course, the environment can also be evacuated, if it makes sense.

After step h), only a hollow core shell is present. To make this core coat even more pressure-resistant, d. h., To avoid compression during die casting, this is filled with a difficult to compress material that forms the inner core. This is also possible if structurally no ribbing of the hollow casting core is possible. Of course, in addition to the mentioned solids and granules, it is also possible to use liquids for filling the casting core, if it makes sense. Of course, if the core shroud has more than one opening, the other openings must be closed before the inner core core can be obtained. Of course, after demoulding, which in turn takes place after use in an encapsulation, the inner core can be prepared and reused, as a result of which cast cores according to the invention can be used very economically.

Such a manufacturing process for a casting core can be easily automated, based on experience in foundry technology or injection molding technology can be used. Negative permanent molds also allow for high throughput rates to produce a consistently high quality in terms of dimensional accuracy and surface quality.

• h') Beschichten zumindest einer inneren Oberfläche des Kernmantels mit einem Bindemittel,

ausgeführt werden.In a further embodiment of the production method, after step h), step

• h ') coating at least one inner surface of the core sheath with a binder,

be executed.

By applying the binder is made possible that the inner core and the core sheath are connected, which in certain material combinations not already reached by the materials themselves but must be supported. When the inner core and the core sheath are joined, the advantages already mentioned result in less heat conduction and prevention of gas expansion in a gap between the two parts.

These and other advantages will be set forth by the following description with reference to the accompanying figure. The reference to the figure in the description is to facilitate the understanding of the subject matter. The figure is merely a schematic representation of an embodiment of the invention. It shows a perspective view of a cut casting core.

In the 1 is clearly visible on the cut surface, that the casting core 1 consists of two parts; an inner core 11 and a kernmantel 12 , The illustrated casting core 1 is designed to form the cooling water channels when casting an engine block. The kernmantel 12 hugs the same shape to the inner core 11 but with a small gap left between them (not in the figure).

Also figuratively not shown is that the inner core 11 and the kernmantel 12 in this gap can be connected using a binder. In this case, there is the advantage that the binder can also be selected with regard to its thermal properties and in particular low thermal conductivity and that when filling the gap no gas components remain in the gap, which could trigger a potentially destructive pressure increase.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102008002376 A1 [0004]

Claims (7)

Cast core ( 1 ), which has an inner core ( 11 ), characterized in that the inner core ( 11 ) of a nuclear envelope ( 12 ) is surrounded, the inner shape with an outer shape of the inner core ( 11 ), wherein the inner core ( 11 ) has at least one physical property which differs from at least one physical property of the core mantle ( 12 ) is different. Cast core ( 1 ) according to claim 1, characterized in that - the physical property is a thermal, mechanical, electrical and / or magnetic property and / or - the core sheath ( 12 ) and the inner core ( 11 ) consist of different materials. Cast core ( 1 ) according to claim 1 or 2, characterized in that the inner core ( 11 ) and the nuclear envelope ( 12 ), preferably by means of a binder, more preferably by means of an adhesive. Cast core ( 1 ) according to at least one of claims 1 to 3, characterized in that - the core shell ( 12 ) consists of a thermal shock resistant and / or heat resistant material and / or - the inner core ( 11 ) consists of an impact-resistant and / or tough and / or dimensionally stable material. Cast core ( 1 ) according to at least one of claims 1 to 4, characterized in that - the material of the core sheath ( 12 ) is a ceramic or a salt and / or - the material of the inner core ( 11 ) is a plastic or a metal from the group comprising zinc, tin, aluminum, or a granulate, preferably sand. Manufacturing process for a casting core ( 1 ) according to at least one of claims 1 to 5 using an openable negative permanent mold, which has a main cavity corresponding to the outer contour of the casting core, the negative permanent mold having at least one first opening connected to the main cavity, comprising the steps: a) providing a liquid curable core-shell precursor and the negative permanent mold, b) filling the main cavity with the core-shell precursor material through the first opening, c) setting curing conditions at a negative permanent-mold interface to the main cavity d) curing leaving a first part of the core material which bears against the interface, e) adjusting an overpressure in the main cavity, f) leaving a second part of the core material which has not hardened out, passing through the first part Opening, so getting the core mantle ( 12 g) adjusting a pressure balance between the main cavity and the environment, h) cooling the core sheath ( 12 ), Opening the negative permanent mold and ejecting the core sheath ( 12 ), i) filling the core mantle ( 12 ) with an inner core material, thereby obtaining the inner core ( 11 ), j) closing an opening of the core sheath ( 12 ) and obtaining the casting core ( 1 ). Manufacturing process for a casting core ( 1 ) according to claim 6, wherein after step h) the step h ') coating at least one inner surface of the core sheath ( 12 ) with a binder.

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