EP1733825A1 - Method of filling dies for manufacturing asymmetrical casting cores of a compressible material - Google Patents

Abstract

A dosing device puts a given quantity of material into a compression mold. The compression mold is designed to produce an asymmetrical mold core and the dosing device puts given amounts in different parts of the mold and afterwards the material found in the compression mold is compressed. The core is pre-manufactured as a semi-finished article, laid in the mold and finally filled with given quantities of material using the dosing device and then the material in the mold pressed including the semi-finished core.

Description

The invention relates to a method for filling pressing tools for producing casting cores (lost cores) according to the features of the preamble of claim 1.

Casting cores, which are also referred to as lost cores, are known for the production of molds or cavities, in particular in internal areas of components. These cores consist of a compressible core material, such as a salt, mixtures of salt and organic binders, mixtures of salt and inorganic binders or the like. This list is only an example and not exhaustive. Basically, it is about producing cores made of such a compressible material.

The prior art is the filling of pressing tools such that by means of a metering device (also called dosing cavity) a defined (certain) amount of material to be pressed on or in the pressing tool on or is applied. The pressing tool has, for example, a planar tool base plate with an integrated lower tool part, wherein the material to be pressed is moved by means of the metering device on the planar tool base plate with the integrated tool lower part. The lower part of the tool is completely filled with the material. The amount of material is then pushed down, for example by means of a slider from the flat base plate and into a material storage for further use attributed. However, this simple and inherently reliable method works satisfactorily only if the casting cores to be pressed have a uniform volume distribution over the circumference (or along the axis through the centroids), since only in this case with the described method the prior art, the desired uniform distribution of material in the lower die part is effected. However, a uniform distribution of material is an indispensable prerequisite for the production of casting cores with (approximately) homogeneous density distribution and sufficient strength. In the case of casting cores of asymmetrical shape, that is, of variable cross-section along the circumference and / or extent thereof, this prior art method no longer functions.

As an example of a casting core with asymmetric shape, a casting core is mentioned, by means of which a cooling channel with an asymmetrical cross section in the circumferential direction is to be produced in a cooling channel piston of an internal combustion engine. Such annular cooling channels also called crown cooling channel have, for example, a stepped shape in the circumferential direction. If one were to produce a casting core for the production of such a cooling channel with the known method, the casting core in the circumferential direction would not have the required homogeneous density distribution and sufficient strength, so that it would be damaged when filling the Kolbengießform with cast melt or even before when inserting into the mold.

The invention is therefore based on the object to provide a method for filling of pressing tools for the production of casting cores made of a compressible material, which avoids the disadvantages described above. The object is therefore in particular in the realization of a suitable filling of pressing tools for the production of casting cores, in particular asymmetric shapes whose cross section is variable over the circumference and / or extent or along an axis through the centroids of a compressible core material, in such that the pressing tool so with Core material is filled that density differences in any asymmetric compacts after the pressing process no longer exist or at least acceptably low and the required dimensional stability and strength of the casting core is achieved.

More specifically, casting cores for cavities (such as cooling channels or the like) in pistons for internal combustion engine with, for example, closed or open ring-like shapes whose cross section over the circumference or along the axis by the centroids is variable, can be produced.

This object is solved by the features of claim 1.

According to the invention is generally provided to solve the problem that the pressing tool is designed for producing an asymmetric casting core, wherein the metering introduces certain subsets at different locations in the pressing tool and then the material located in the pressing tool is finished pressed. This makes it possible to introduce different amounts of materials of the compressible material in the pressing tool at different locations, which later have different circumferences or extents in order to achieve a largely or completely homogeneous density distribution after pressing. This means that the pressing tool is not as in the prior art directly (ie completely uniform), but indirectly (ie sections) filled. In the prior art, the filling of the pressing tool is done directly by namely the material to be pressed is applied to the tool base plate, which has a bore in which the pressing tool lower part is inserted from below, then to remove by means of a slider excess material and the material storage supply. The lower tool part contains in this case the salt needed for the pressing process in its cavity, wherein, for example, in a concrete structural design, the outer cylindrical vessel boundary is formed by the cylindrical wall of the base plate bore.

In contrast, according to the invention, first a metering cavity is filled with the required (required) locally variable quantity (partial quantity) of the material to be pressed. In a constructive concrete embodiment, this dosing cavity is incorporated in a plate with plane-parallel surfaces and designed open both on the top of the plate and on the underside of the plate. This open design is completely or at least largely provided, with the exception of optionally incorporated webs that connect an inner boundary with an outer boundary locally. From below, during the filling of the dosing cavity, the lower boundary of the container is formed by a thin plate, a diaphragm or the like. The projection of the center axis through the center of gravity of the dosing cavity in the plane of the plate corresponds largely to the projection of the central axis through the center of gravity of the casting core to be produced in the same plate plane. According to the amount of material to be pressed in the pressing tool, the dosing cavity (in the case of closed molds, for example, depending on the circumferential angle) is variable in its width and thus in its local sectional area cross section. Downwards, the profile (the release cross-section) of the dosing cavity tapers such that at each location (section) of the filling it is ensured that the pre-dosed subset can be completely introduced into the axially underlying pressing tool. After pre-dosing, the diaphragm, which forms the lower boundary of the dosing cavity, is removed and the amount of material required at this location trickles to the intended location in the pressing tool. In the event that the material to be pressed is not free-flowing or it tends to build up, it is conceivable to introduce axially after removal of the diaphragm from above a material release aid in Dosierkavität, which largely corresponds to the negative mold of Dosierkavität, or otherwise a pressure to exercise on the contents of the dosing cavity. The material release aid (for example in the form of a pressurized stamp) is thus shaped so that any adhering residues on the dosing cavity can be pushed out of the dosing cavity with the aperture removed, thus completely filling the pressing tool.

A second variant of the same filling method is that the metering cavity is designed to be closed at the bottom and that after predosing, that is to say after filling the metering cavity and pushing away the excess amount of material for the casting core, a cover plate closes the metering cavity at the top. Thereafter, the rotating bearing system consisting of dosing cavity and aperture is rotated by 180 °. Subsequently, the cover panel is removed and the released (free-flowing) material falls in the required amount required to the respective location in the pressing tool, in particular in the lower tool part. A loss-free filling of the pressing tool, in particular the lower tool part, with one-side closed Dosierkavität is achieved in that the dimensions of the release cross-section are always smaller than the underlying receiving cross sections of the pressing tool. Therefore, one-sided open metering cavities according to the second variant in the cross section always narrower and higher than the dosing cavities open on both sides according to the first variant.

A third variant of the filling process according to the invention is that instead of a cavity incorporated in a plate a variable Dosierkavität according to the principle of a "nail pad" is used, in which firstly the nails are close to each other and they have a cross-section, the contact with the adjacent nail elements leaves no or almost no cavities left. The nails are also taken in an example rectangular or round frame, which allows axial mobility of the nails. By a suitable positioning system, such as a pneumatically, hydraulically or magnetically acting system, it is now possible to represent a wide variety of asymmetric cavities (in particular without undercut) by different deep lowering or different heights of the nails. This process can also be reversed to equalize the nails again, that is, it can thus be achieved a virtually complete emptying of the dosing cavity and a loss-free filling de pressing tool with one-side open dosing to to produce a casting core, which has a homogeneous density distribution and the required strength.

In another embodiment of the invention, it is provided that the casting core is prefabricated as a semi-finished product and placed in the pressing tool and then filled the pressing tool by means of the metering at different locations with specific subsets of material and the casting core is finished pressed. The basis for the pressing process here are semi-finished products which have been produced, for example, from inorganic and / or organically bound salt or other suitable materials, compositions or mixtures with the aid of a core shooting method known per se. In the production of the so-called advanced core blanks (semi-finished products), core shooting produces a suitable method for producing material distribution which is largely or completely homogeneous in relation to the density. The downstream filling and pressing process in a suitable pressing tool with corresponding metering cavities compacts in a second production step the advanced symmetrical core blank to the finished pressed asymmetric casting core. The advanced core blank differs from the finished core essentially by the features that the axial height is greater, the density is lower and the strength is lower. Only the finished molded core has, in particular in the circumferential direction, the desired asymmetrical shape with the desired homogeneous density or material distribution and the resulting corresponding strength.

In a further embodiment of the invention it is provided that the casting core consists of two or more parts, wherein at least one part, preferably all parts, is produced according to one of the methods of the preceding claims and the parts are subsequently joined together. Preferably, the casting core consists of two parts, wherein more than two parts are not excluded. Also preferably, the two prefabricated Gießkernteile a symmetrical shape, which is only after their connection with each other to an asymmetrical shape of the then finished casting core. Thus, first in produced a corresponding core casting process core blank halves, which have significantly reduced density differences due to their low overall height compared to the finished casting core. The two core blank halves are then glued together with a suitable for pouring in a mold and in particular heat-resistant adhesive to their flat contact surfaces. The bonding method is particularly advantageous because it can be performed quickly and easily. Other connection methods that cause positive locking and / or material closure are also conceivable. Depending on the geometric shape of the finished casting core, core blank halves do not necessarily have to be produced, but other geometrical shapes and more than two parts are also conceivable. The division or separation planes of the respective parts depend on the geometry of the finished casting core.

In a further embodiment of the invention, the pressing tool on its underside (Untertrumm) is at least partially stepped (ie asymmetrical) and has side walls, wherein the metering device fills the pressing tool with material and the filled pressing tool is withdrawn with a slider to level. In this way, a pressing tool can be quickly and easily filled with the compressible material having an asymmetrical shape. In a preferred embodiment, it is provided that the base is slightly lowered with the staircase shape in the parallel side walls and the top (the upper strand) is placed with the opposite steps, in particular by short reversing rotational movements, the upper part (Obertrumm) in the pressing tool by the compressible material is pressed into the staircase forms of Obertrumms. As a result, a uniform filling of the pressing tool is at the start of the pressing process and the subsequent pressing tool produces a uniform density of the compact and thus the subsequently finished compressed core. The flowability of the compressible material, in particular the salt-binder mixture, can be improved by the introduction of energy, for example by means of vibration or ultrasonic waves or the like.

With the inventive method, its steps and the corresponding constructive embodiments of the elements involved such as pressing tool, dosing (Dosierkavität) and the like and the materials used (compressible materials such as salt, mixtures of salt and organic binders or mixtures of salt and inorganic binders or The like) can be realized an advantageous filling of pressing tools for the production of casting cores, in particular asymmetric shapes. In a specific embodiment, the cores are lost cores for producing cavities (cooling channels and the like) in pistons for internal combustion engines with closed or open ring-like shapes whose cross-section is variable over the circumference or along the axis by the centroids of compressible Core material, such that the pressing tool is filled with core material so that density differences in any asymmetric casting cores after the pressing process are acceptably low and that the required dimensional stability and strength of the core is achieved. With the invention, therefore, arbitrarily shaped asymmetric cooling channel shapes of cooling channel pistons of internal combustion engines with very low density differences and the required high strength can be realized in particular.

Claims (8)

Method for filling pressing tools for producing casting cores from a compressible material, wherein a metering device introduces a certain amount of material into the pressing tool, characterized in that the pressing tool is designed for producing an asymmetric casting core, wherein the metering device certain subsets at different locations in the press tool introduces and then the material in the press tool is finished pressed. A method for filling pressing tools for the production of casting cores made of a compressible material, wherein a metering introduces a certain amount of the material in the pressing tool, characterized in that the casting core is prefabricated as semi-finished and inserted into the pressing tool and then the pressing tool by means of the metering device filled different places with certain subsets of material and then the material contained in the pressing tool including the semi-finished is pressed. A method according to claim 1 or 2, characterized in that the casting core consists of two or more parts, wherein at least a part, preferably all parts, is produced according to one of the methods of the preceding claims and the parts are then joined together to form a finished casting core. A method according to claim 3, characterized in that the parts are glued together. Method according to one of the preceding claims, characterized in that the pressing tool on its underside (Untertrumm) is partially stepped and has side walls, wherein the metering device fills the pressing tool with compressible material and the filled pressing tool is withdrawn with a slider on level. A method according to claim 5, characterized in that the base of the pressing tool is lowered with the staircase shape in the parallel side walls and the upper part (Obertrumm) is placed with the counterparts stairs, with a particularly short reversing rotational movement of the upper part in the form the just peeled compressible Material is pressed into the staircase forms of the upper part. Method according to one of the preceding claims, characterized in that the compressible material, in particular the salt-binder mixture, with energy from the outside, for example by means of vibration or ultrasonic waves or the like, is applied. Method according to one of the preceding claims, characterized in that the method is used for the production of casting cores for use in the production of cavities in components of internal combustion engines.