WO1992018269A1 - Process for casting an aluminium-alloy engine part, in particular a cylinder head - Google Patents

Abstract

In engine parts made of aluminium alloy, components such as the cylinder-head valve-seat rings which are made of high-strength materials must be held rigidly in place. Machining them is long. The invention proposes a process for casting an aluminium-alloy engine part using a casting mould made up of one ore more parts. In this process, the components, in particular the valve-seat rings, which have to be rigidly joined to the engine part, and which are made of a different material, whose melting point is at least as high as that of the engine material, are introduced into the mould, before the mould is assembled, at points indicated by suitable marks, the mould assembled, and the motor part itself then cast.

Description

Name: Process for casting an engine part from

Aluminum alloy, in particular a cylinder head

Description:

The invention relates to a method for casting an engine part, in particular a cylinder head, from aluminum alloy by means of a casting mold composed of several parts.

In the case of engine parts which are made from aluminum alloy, it is necessary to use components made of a different material at locations which are subjected to high mechanical stress, for example on the valve seats of cylinder heads, which can withstand the stresses required here. In particular, the arrangement of such valve seat rings has so far been carried out in such a way that a corresponding recess has been machined into the cylinder head at this point after the casting. The valve seat rings to be used were strongly cooled, for example with liquid nitrogen, and then inserted into the recess, so that the valve seat ring expanded due to heating in the form of a "shrink connection" frictionally stuck in the recess of the cylinder head. The disadvantage of this procedure is that the recess has to be manufactured very precisely, since for such shrink connection relatively narrow tolerances between the inside diameter of the recess on the one hand and the outside diameter of the valve seat ring to be used on the other must be observed. In conventional, but especially in modern engines with more than two valves per cylinder, this results in a high manufacturing cost. There is also the disadvantage that a valve seat ring can fall out in individual cases in later operation, so that the engine is severely damaged. The introduction of other components, such as valve guides or the like. Also requires processing after casting.

From DE 39 37 402 AI a valve seat ring is also known which has undercuts on its outside and which is to be cast as a blank to be reworked directly into the cylinder head. However, it has been shown that, despite the form-fitting integration brought about by the undercuts, no satisfactory results could be achieved. This is based on the fact that, in the casting molds previously used, exact positioning of the valve seat ring blank to be inserted was not possible, so that during the subsequent machining of the valve seat surface considerable deviations in the centering occurred due to displacements.

The invention is based on the fact that in the manufacture of engine parts, in particular cylinder heads made of aluminum alloy, the introduction of components made of materials that are stronger and different from the base material of the engine part is simplified and the precision is improved. This object is achieved in that the parts of the casting mold consist of a non-metallic material and that components to be firmly connected to the engine part to be cast are made of a different, higher melting material than the aluminum alloy when the parts are joined to form the complete casting mold inserted into these at predetermined fixing points and then the casting takes place. This procedure takes advantage of the fact that such casting molds can today be manufactured with great precision in what is known as core molding technology. Here, the actual casting mold is made like a core from a flowable, hardenable molding material, the mold being composed of a total of several parts. The high precision is possible in that the individual core parts are each formed in a core mold consisting of at least two molded parts, that after the molding process of the individual core parts has been completed, their shape is opened such that the core part remains connected to a molded part and then the individual core parts to be joined together with their shaped parts are joined together by defined relative movements of the shaped parts. In the manufacture of engine blocks, cylinder heads or the like, such a casting mold, referred to above as the "core", is composed of more than two core parts, so that the molded part for a core part defined as a basic core part remains connected to this as a carrier and centering element until all subsequent joining operations have been completed, in which the other core parts are placed on the base core part with the aid of their molded parts. Only then is the complete core, i.e. the complete casting mold, ejected from the carrier element. Since in this method the geometric assignment required for the joining and the resulting relative movement of the core parts to be joined to one another takes place through the corresponding alignment and movement of the molded parts relative to one another and no longer through the core parts themselves, the joining process can be carried out with great precision Carry out, since the core parts held in their molded part show a spatial orientation that can never be achieved after complete molding. It is advantageously used here that in a molding process in which the binder of the molding material or the core sand is activated not by temperature but by chemical-catalytic processes, the moldings of the individual molding machines have practically the same temperature and so there are no dimensional deviations individual moldings to each other due to thermal expansion. This makes it possible to provide the individual molded parts with mutually assignable guide and centering surfaces, so that the accuracy when the core parts are joined together via the molded parts connected to them is supported to form a casting mold made of a non-metallic molding material. Since all individual parts of the casting mold are each newly manufactured and joined together with great precision, it is now possible to also connect components made of a different material to the engine part to be manufactured, in particular valve seat rings on cylinder heads, in their geometric arrangement must be arranged with great accuracy to pour immediately. For this purpose, it is only necessary to provide corresponding fixing points on the relevant parts of the casting mold, onto which or into which the components to be cast in are inserted when the casting mold is joined. This makes it possible, for example, to form-fit valve seat rings with a conical shape of the outer surface. This enables an optimal shape and dimension for the components, in particular for the valve seat rings. For example, these may have a larger outer diameter than previously, with an increase in diameter of only 1 mm already offering considerable advantages. Since such a valve seat ring is held in a form-fitting manner, it remains permanently connected to the cylinder head. In an embodiment of the invention it is provided that the components are heated before being inserted into the casting mold. This avoids excessive temperature differences, which can have a negative effect on the structure of the aluminum alloy surrounding them. This method is possible because the entire joining process for the production of the casting mold is mechanized, so that it is also possible here to preheat components, in particular preheated valve seat rings, into the corresponding core part via a manipulator integrated in the course of the joining operations to insert. Since the casting mold is made of a non-metallic molding material, there is only a relatively small outflow of heat until the start of the casting.

In another embodiment of the invention it is provided that the components are heated electro-inductively after insertion into the casting mold. This simplifies the insertion process, for example for the valve seat rings, since these can be handled at room temperature, whereas the heating process only takes place in a further station when the valve seat rings have already been inserted. The electro-inductive heating of the components in the casting mold is possible because the casting mold as a whole does not consist of metal but only of mineral molding material or core sand, so that the components, in particular the valve seat rings, are wholly or partially assembled mold form the only metallic component. This also makes it possible to carry out the heating without contact, preferably immediately before the start of the casting process.

While it is fundamentally possible to heat the components inserted into the casting mold with the mold still open, this is dependent on the shape of the relevant component

Component is necessary, is provided in a particularly advantageous embodiment of the method according to the invention, the components with a fully assembled mold to be heated electro-inductively from the outside. This ensures that the temperature influences on the casting mold which are possible via the heat flow out of the heated component only take place when the casting mold is completely assembled, and therefore no changes in shape can occur here. This also enables a further advantageous embodiment of the method according to the invention, which consists in flushing the mold cavity of the casting mold with a protective gas before starting the heating. This has the advantage that, for example, inserted components made of ferrous materials can be heated up to the temperature of the melt to be poured in of about 800 ° C. without the surfaces to be poured in being able to oxidize and thus a perfectly pure metallic surface contact between the component and the casting material is achieved. Another advantage of heating when the casting mold is completely assembled is that, depending on the position of the component to be cast in the casting mold, in particular in the case of molds above, casting can still be started during the heating phase, so that the desired final temperature for the heat to be heated Component is reached at the moment when contact with the melt occurs.

The invention is explained in more detail with reference to a schematic representation. It ^' show:

Fig. 1 shows the process flow in the form of a

Flow diagram,

2 in a vertical partial section, a valve seat ring inserted into a casting mold,

Fig. 3 shows the finished cylinder head with a cast-in valve seat ring. A mold made from core molding sand for one

Cylinder head must be assembled from several core parts due to the many undercuts and channels. The individual core parts are manufactured using separate core molding machines and then assembled. The flow picture acc. 1 shows the process sequence in a simplified representation for a casting mold composed of only two core parts. In this case, in a core molding machine I, which has a molding box formed from two molded parts 1 and 2, a first core part 3 is produced in a customary manner, for example by the cold box process, from a corresponding molding sand. The associated core part 4, which together with the core part 3 forms the complete casting mold, is produced in a second core molding machine II, which has a core mold composed of a molded part 5 and an associated molded part 6. As soon as the two core parts 3 and 4 have been “shot”, the core molds open, the core part 3 remaining in the mold part 1 in the core molding machine I and being moved into a first joining station III. On the exposed core part

3, a component 7 to be cast in, for example a valve seat ring, is now placed with the aid of a manipulator. In a next process step, which can take place in the joining station III or in a subsequent joining station IV, the associated core part 4, which is still connected to the molded part 5, is now positioned by the core molding machine II and then lowered onto the core part 3 or that Core part 3 raised so that both core parts 3 and 4 are joined together to form the finished casting mold. The molded part 5 is then detached from the core part 4 and in a further station V the finished casting mold 3-4, which now also encloses the inserted valve seat ring 7, from the molded part 1, which has served as a centering and guiding means during the entire process , loosened and moved to the casting station VI and poured there. After cooling, the casting mold is destroyed and the molding sand is reprocessed. The valve seat ring 7 is expedient in the process sequence shown here. first heated up and then placed over the manipulator. Since the casting mold consists of a non-metallic material and the joining operation and the continuation of the complete casting mold up to the casting station VI take place in a short time, the temperature loss is up to the point in time when the valve seat ring with the melt is in Contact comes in, of minor importance.

The method for heating the component to be cast in can be further improved, for example, in the case of valve seat rings to be cast in, since cylinder heads represent relatively flat components which enable electro-inductive heating without excessive energy expenditure, i.e. from the outside, i.e. when the casting mold is already fully assembled and is in contact with the casting device. As shown in an enlarged partial section in FIG. 2, the valve seat ring 7 is placed on a core mark 8 of the core part 3, so that when the casting mold 3-4 is closed, as shown in FIG. 1 for the station V, with an associated part 9 of the core part 4 the valve channel is kept clear and at the same time the valve seat blank is fixed in the casting mold. 2 shows, the outer surface of the valve seat ring 7 is conical, so that after removal of the casting mold, as shown schematically in FIG. 3, it is held in a form-fitting manner in the finished casting 10.

So that the inserted valve seat ring 7 can be heated electro-inductively in the closed form directly in the area of the casting station VI, the core part 3 has a downwardly open recess 11 into which a water-cooled induction coil 12 can be inserted, which , the end region directly facing the valve seat ring to be heated is provided with an iron core 13. This form of heating is possible because the casting mold 3-4 overall, in addition to the inserted components, here the valve seat rings 7, has no metallic parts. Since the mold 3-4 is already completely closed at this point, the mold cavity 14 can first be flushed with a protective gas, for example nitrogen, so that the valve seat rings 7 can then be heated to temperatures up to 800 ° C. without oxidation. Because of the low mass, the valve seat rings can be heated up in a few seconds, so that casting can still be started during the heating process, so that the heating up phase

10 at the desired final temperature is only completed when the melt entering the mold comes into contact with the components to be poured in, here the valve seat rings 7. By this time Über¬ the end of the heating phase overlaps one hand, and ^{• ■ •••} * ^• the beginning of the casting phase, on the other hand, a desirable time for mass production can shorten the casting process as a whole achieved.

The example of a cylinder head for an engine with four valves per cylinder, which is shown schematically in FIGS. 2 and 3, shows the considerable manufacturing advantage of the method. Since the valve blanks 7 are cast geometrically precisely in the desired assignment, the subsequent finishing ^{5 is} simplified.

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Claims

Expectations: 1. A method for casting a motor part, in particular a cylinder head, made of aluminum alloy by means of a casting mold composed of several parts, characterized in that the parts (3, 4) of the casting mold consist of a non-metallic molding material that with the to be cast Components (7) which are to be firmly connected to the motor and are made of a higher melting material than the aluminum alloy when the parts are assembled to form the complete casting mold are inserted into them at predetermined fixing points (8) and the casting is then carried out. 2. The method according to claim 1, characterized in that the components (7) are heated before insertion into the mold. 3. The method according to claim 1, characterized in that the components (7) are heated electro-inductively after insertion into the mold. 4. The method according to claim 1 and 3, characterized in that the components (7) are completely electro-inductively heated from the outside when the casting mold (3-4) is fully assembled, 5. The method according to claim 4, characterized in that the mold cavity (14) of the casting mold (3-4) is flushed with a protective gas before the start of heating. 6. The method according to any one of claims 1 to 5, characterized in that the casting begins before the end of the heating phase.