EP1301298B1 - Equipment for moulding foundry parts with improved means for positioning sand cores, and related positioning method - Google Patents

Abstract

The invention provides equipment for molding castings in a mold having at least one sand core (Na1), in which the positioning of the or each core is obtained by the core co-operating with an element (S) of the mold, in particular a metal mold element. This equipment is remarkable in that the or each core possesses an insert (I) secured to the core while making said core and via which said core is suitable for co-operating with the mold element in question. The invention also provides an associated method of positioning cores. The invention is particularly applicable to improving the positioning of admission pipes in light alloy cylinder heads for engines.

Description

The present invention relates generally to a system for positioning cores in aluminum casting in metal molds

Background of the invention

During casting with sand cores of castings, in particular aluminum alloy or other light alloy, the positioning accuracy of the sand cores contributes to the dimensional accuracy of the molded metal moldings in a decisive way, since it affects most of the inner forms of the molded part and some of the outer forms.

More specifically, and by way of example, in the case of the molding of engine cylinder heads for motor vehicles, important engine functions are directly related to the positioning of the cores: this is the case for intake and exhaust pipes or pipes. , completely realized by coring, and whose positioning accuracy has a direct influence on engine performance (power, consumption, polluting emissions, etc.)

Now, the interaction between the cores and the metal mold elements poses problems that go against the control of the dimensional positioning. Indeed, the cores are generally made from a mixture of sand (usually silica) of well-defined particle size and organic chemical binders which ensure the cohesion and strength of the core.

These binders are conventionally cured according to two major families of coring processes, namely the so-called "cold box" technique (that is to say thanks to the intervention of a gaseous chemical catalyst) and the so-called "hot box" technique (that is to say, thanks to the supply of calories by the kernel box itself heated). But whether one retains one or the other of these two methods of coring, the cores evolve in a similar way during the casting. Thus, as soon as they are placed in the mold which is itself at a certain temperature, typically between 80 ° C and 300 ° C for the coldest parts and between 400 and 500 ° C for the hottest parts, the binders of the nuclei begin to decompose and emit gaseous residues.

This process is further accelerated to the casting of liquid aluminum that enters the mold at temperatures generally between 600 and 750 ° C.

These gaseous residues condense on the metal parts of the mold and locally create successive layers of calamine which are the more or less carbonized solid residues of this decomposition.

These residues are extremely hard and prevent the proper positioning of the cores on the metal parts.

To take the example of the intake or exhaust ducts of a cylinder head, the chamber profile is generally produced by a cooled metal mold element which locally accelerates the cooling of the aluminum during its solidification. in doing so, locally refine its microstructure and increase its properties (mechanical resistance, resistance to hot and cold fatigue, elongation at break, etc.)

It is on this cooled metal element that the cores intended to form these ducts are supported. Thus the accumulation of calamine at the contact surface of the metal mold element shifts the conduit cores, and disturbs the positioning accuracy, with the aforementioned drawbacks.

This problem can be resolved practically in manufacturing only by leaving a substantial clearance to the guides and supports located on the surface of the metal elements that interact with the surfaces facing the core, and by maintaining the cleanliness of these surfaces. by regular interventions of cleaning in manufacture, for example by brushing.

These latter operations disrupt manufacturing because they lengthen the cycle times, deteriorate the potting that protects the mold elements vis-à-vis the liquid aluminum, and require local repair this poteyage as needed.

The smelter therefore wishes to space these cleanings as much as possible, but this is inconsistent with the elimination of scale buildup.

Thus the actual practice, in production, is a compromise between these different constraints, which limits the dimensional accuracy of the positioning of the cores on the metal elements.

Summary of the invention

The present invention aims to overcome these limitations of the state of the art.

For this purpose, it proposes, according to a first aspect, casting molding equipment, in particular of cylinder heads of combustion engines for vehicles, as defined in claim 1.

Certain preferred, but not limiting, aspects of the molding equipment according to the invention are defined in the dependent claims 2 to 9.

According to a second aspect, the present invention provides a method for positioning a core in a mold for producing a casting as defined in claim 10.

Preferred, but not limiting, aspects of the process according to the invention are defined in claims 11 to 15.

Brief description of the drawings

• la figure 1 est une vue en section longitudinale d'un équipement de moulage d'une culasse,
• la figure 2 est une vue en section transversale, schématisée, du même équipement,
• la figure 3 est une vue en section transversale, à échelle agrandie, d'un détail de l'équipement selon l'invention, et
• la figure 4 est une vue en section longitudinale du détail de la figure 3.

Other aspects, objects and advantages of the present invention will appear better on reading the following detailed description of a preferred embodiment thereof, given by way of nonlimiting example and with reference to the appended drawings. on which ones :

• FIG. 1 is a view in longitudinal section of a molding equipment of a cylinder head,
• FIG. 2 is a schematic cross-sectional view of the same equipment,
• FIG. 3 is a cross-sectional view, on an enlarged scale, of a detail of the equipment according to the invention, and
• Figure 4 is a longitudinal sectional view of the detail of Figure 3.

Detailed description of an example embodiment

Referring firstly to Figures 1 and 2, there is illustrated the conventional embodiment of a cylinder head CL by gravity casting in a mold essentially composed of a cooled metal sole S, Y ends and drawers T at the ends, these drawers closing the mold perpendicular to the yokes C.

The inner shapes comprise cavities formed by the cores of Na inlet pipes, Nech exhaust pipes, Ne circulation, oil circulation and Nht roof (see in particular Figure 2), the latter core also realizing the weights that allow to feed the liquid metal part during solidification. The mold is fed with liquid metal from the bottom according to the usual technique of gravity casting for this type of part, by an attack system SA (FIG. 1).

The cylinder head here is a four-cylinder, 16-valve, direct injection diesel engine cylinder head. For this type of cylinder head, the positioning accuracy of the intake pipes, determined by the accuracy of the positioning of the corresponding cores, is essential for the control of engine performance.

The mold-piece-casting appendages assembly is schematically represented as a whole in FIG.

According to the invention each pair of intake pipes is provided with metal end inserts I, as illustrated schematically in Figure 2 and in more detail on the enlarged views of Figures 3 and 4. Figure 4 illustrates in turn , by a section longitudinal, the fact that the insert I of Figure 3 in fact connects two intake pipes, and illustrates together with Figure 3 the guidance and supports made by this insert.

The main purpose of the presence of the insert I is to bring the metal mold member into contact with the core only, but with the core via this insert, secured to the core, and where appropriate by a or several other inserts, including another insert at the opposite end of the core. It should be noted in this regard that the number and arrangement of the inserts will depend essentially on the configuration of the core and the accuracy required for its positioning.

• il est solidarisé au(x) noyau(x) concerné(s) (ici deux noyaux Na1 et Na2 de pipes d'admission) en étant positionné dans la boite à noyau lors de la réalisation du ou des noyaux ;
• il présente un corps principal 10 à partir duquel font saillie, côté noyau, un ou plusieurs appendices de scellement, ici deux appendices 111, 112 respectivement pour chacun des deux noyaux de pipes d'admission Na1 et Na2, ces appendices étant emprisonnés dans la masse de sable et de liants organiques au moment de la formation (tir) des noyaux, de telle sorte qu'après durcissement des liants, chaque noyau entoure ces appendices et qu'une liaison intime soit réalisée entre le noyau et l'insert ;
• le corps 10 de l'insert intègre des formes aptes à réaliser son guidage et son positionnement, et donc celui du noyau, dans des formes généralement complémentaires prévues sur ou dans l'élément métallique de moule situé en vis-à-vis (ici la semelle S), comme on le verra en détail plus loin ;
• l'insert est dessiné de telle sorte qu'il assure la surface de contact entre le noyau dont il est solidaire et l'élément métallique de moule en vis-à-vis de telle sorte que la calamine due à la dégradation à chaud du noyau ne perturbe pas le positionnement du noyau muni de son ou de ses inserts sur l'élément métallique ;
• la forme de l'insert I est choisie pour qu'il puisse être facilement réalisé, par exemple par un procédé de moulage métallique, notamment d'aluminium sous pression, en choisissant un matériau compatible avec l'alliage de la pièce à mouler, et qui en particulier ne pose pas de problème de compatibilité à la refusion ;
• en outre, quel que soit le procédé de réalisation choisi pour le ou les inserts, il est préférable de définir toutes les formes et surfaces de guidage et d'appui sur un même élément de l'outillage (typiquement un même élément de moule) de réalisation des inserts. Ceci permet d'éviter des décalages mutuels indésirables dans ces formes et surfaces, ce qui pourrait être le cas notamment si certaines d'entre elles étaient obtenues par des tiroirs dont le positionnement lors du moulage n'est pas toujours garanti avec une bonne précision.

Each insert I advantageously has the following characteristics:

• it is secured to the (x) nucleus (s) concerned (here two Na1 and Na2 nuclei intake pipes) being positioned in the core box during the realization of the nucleus (s);
• it has a main body 10 from which protrude, on the core side, one or more sealing appendages, here two appendices 111, 112 respectively for each of the two pipes Na1 and Na2 intake pipes, these appendages being imprisoned in the mass sand and organic binders at the time of formation (firing) of the cores, such that after curing the binders, each core surrounds these appendages and an intimate connection is made between the core and the insert;
• the body 10 of the insert incorporates shapes able to carry out its guidance and its positioning, and therefore that of the core, in generally complementary shapes provided on or in the metal mold element located vis-à-vis (here the sole S), as will be seen in detail below;
• the insert is designed so that it ensures the contact surface between the core which it is integral with and the metal mold element vis-à-vis so that the scale due to the hot degradation of the core does not disturb the positioning of the core provided with its or its inserts on the metal element;
• the shape of the insert I is chosen so that it can easily be produced, for example by a metal molding process, in particular pressurized aluminum, by choosing a material compatible with the alloy of the part to be molded, and which in particular does not pose a problem of compatibility with remelting;
• in addition, whatever the method of realization chosen for the insert or inserts, it is preferable to define all the shapes and surfaces of guide and support on the same element of the tooling (typically the same mold element) of realization of the inserts. This avoids undesirable mutual offsets in these shapes and surfaces, which could be the case especially if some of them were obtained by drawers whose positioning during molding is not always guaranteed with good accuracy.

We will now describe in detail, by way of example, possible guides and supports for inserts in the three directions of space as indicated in FIG. 4, where x denotes the longitudinal direction of the yoke, and its direction. transverse and z the vertical.

In a basic embodiment, each insert is able to define a precise positioning of the associated core cooperating with the metal mold member according to surfaces defining supports according to each of the axes x, y and z.

Thus, in the present example, the body 10 of the insert is received in a generally complementary cavity 20 formed in the sole S, and has on its underside a cavity 12 of generally parallelepipedal shape in which a generally complementary protuberance is embedded. 211 (the clearance - minimal - near) projecting from the bottom of the cavity 20. This ensures the positioning of the insert and therefore the core along the x and y axes. In addition, the insert has in the vicinity of its cavity 12 a bearing surface 123 adapted to come into contact with the bottom surface of the cavity 20 of the sole, so as to achieve the positioning of the insert and the core along the z axis.

Figure 4 in particular illustrates other arrangements, namely 121, 122, 124 insert side and 212 sole side, which can also intervene for the proper positioning of the insert.

It is furthermore observed that, in order to facilitate the engagement of the body 10 of the insert I in its cavity 20, a relatively large clearance angle is advantageously provided at the side faces of the insert and of the cavity.

Advantageously, it is these same arrangements of the insert (here the cavity 12 and the surface 123) that is used to position the insert in the core box at the time of firing of the core. As a result, the dimensional accuracy obtained in positioning the core in the mold is optimized by referring to only one set of positioning surfaces.

In some cases, and particularly in the example of a multi-cylinder cylinder head, it is not necessary to guide the intake cores in each chamber along the three axes, because these cores are otherwise secured to each other by a common core part Npa, as illustrated in FIG.

insert 1 :

selon y et z

insert 2 :

selon z

insert 3 :

selon x, y et z

insert 4 :

selon z

insert 5 :

selon y et z

In this type of configuration, and in the particular example of a five-cylinder engine, it is possible for the inserts, ordered from 1 to 5 (one per cylinder), to be able to cooperate with cavities formed in the sole S according to the following guides and supports:

insert 1:

according to y and z

insert 2:

according to z

insert 3:

according to x, y and z

insert 4:

according to z

insert 5:

according to y and z

Furthermore, the roof core here directly supports the z-axis on half of the intake pipes (see Figure 2), which guarantees the z-support of the inserts and thus the whole of the pipes cores Na inlet. It will be noted here that one could also, if necessary, provide inserts at the upper ends of the Na nuclei.

Each insert I is made by casting under pressure. For the realization of each set of Na pipes of intake pipes, five inserts are placed in the kernel box before firing. The process of coring is here the so-called "cold box" process, and
characterized in this case by a proportion of resin of 1% and by a silica sand particle size 55 AFS.

The cylinder heads are here molded in gravity with a standard AS7U3G type alloy, of composition: Yes : 6.0-8.5 Fe: ≤ 0.50 Cu: 2.8-3.8 Mg: 0.05-0.50 Zn: ≤ 0.30 Mn: ≤ 0.30 Ti: ≤ 0.25 Other alone : 0.05% together : ≤0,15% (values in% by weight)

The casting temperature (measured in the holding oven) is 740 ° C. The sole S is cooled with water. The casting rate is 7 to 8 pieces / hour.

Compared to the machining starts, located at the level of the sole, of the raw cylinder head, the guidance by insert (s) realized according to the invention makes it possible to obtain on a casting of 30 consecutive yokes from a day. manufacturing a positioning of the ends of intake ducts (measured on parts after cooling, grit removal, elimination of the weights and metal feeding systems and inserts) characterized by a standard deviation less than or equal to 0.1 mm in the three directions of the space x, y and z.

Furthermore, it is observed visually that the guiding forms of the insert remain very clean, and in particular calamine free, which ensures the reproducibility of the guidance over time.

Comparative example

The same cylinder head mounted according to the same principles and with the same alloy, but with a direct guide of the intake pipe cores in the metal base, makes it possible to obtain precise positioning in x, y and z which are at best understood. between 0.20 and 0.25 mm. The rate of molding due to the regular maintenance of the mold during manufacture falls in the order of 5% to 10% compared to the example according to the invention.

Of course, the present invention is not limited to the embodiment described in particular above, but the skilled person will be able to make many variations and modifications.

Claims (15)

1. Equipment for molding castings, in particular cylinder heads for vehicle engines, in a mold (S, T, C) having at least one sand core (Na1, Na2), in which the positioning of the or each core is obtained by the core co-operating with an element (S) of the mold, in particular a metal mold element, the equipment being characterized in that at least one core possesses a metal insert (I) secured to the core while making said core and via which said core is suitable for co-operating with the mold element in question.
2. Molding equipment according to claim 1, characterized in that the or each insert (I) possesses one or more sealing appendices (111, 112) suitable for being held captive in the mass of the core(s) (Na1, Na2) during preparation thereof.
3. Equipment according to claim 1 or claim 2, characterized in that at least two cores (Na1, Na2) possess a common insert (I) provided with a corresponding number of respective sealing appendices (111, 112).
4. Equipment according to claim 3 or claim 4, characterized in that the co-operation between the or each insert (I) and the associated mold element (S) is shape co-operation defining a support in at least one out of three dimensions.
5. Equipment according to claim 4, characterized in that the shape co-operation between the or each insert (I) and the associated mold element (S) defines support in two out of three dimensions.
6. Equipment according to claim 4, characterized in that the shape co-operation between the or each insert (I) and the associated mold element (S) defines support in all three dimensions.
7. Equipment according to claim 4, characterized in that the shape co-operation between the or each insert (I) and the associated mold element (S) defines wedging in at least one direction (x, y) extending transversely to a main support direction (z) for the insert.
8. Equipment according to any one of claims 1 to 7, characterized in that it includes a set of cores made as a single piece and having a plurality of inserts (I) secured thereto suitable for co-operating with a common mold element (S), and in that the various inserts (I) provide support and/or wedging in different ones of three dimensions.
9. Equipment according to any one of claims 1 to 8, characterized in that the cores (Na1, Na2) are admission pipe cores for a cylinder head (CL) of an engine having a plurality of cylinders.
10. A method of positioning a core (Na1, Na2) in a mold for making a casting (CL) having at least one cavity defined by the positioning of a core, such as an aluminum alloy cylinder head for an engine, the method being characterized in that it comprises the following steps:

    · making a metal insert (I) having at least one support surface (12, 123) suitable for co-operating with a mold element (S), and at least one element (111, 112) for anchoring to the core;

    · making the core in a core box in which the insert (I) has previously been placed in a predetermined position so that an end region of the core becomes anchored to said insert via the anchoring element(s) thereof; and

    · placing the core with its insert in the mold in a position that is predetermined by co-operation between the support surface(s) of the insert and said mold element.
11. A method according to claim 10, characterized in that the predetermined position of the insert in the core box is determined by co-operation between the support surface(s) (12, 123) of said insert and a support portion (211, 20) of the core box.
12. A method according to claim 10 or claim 11, characterized in that the step of making the core comprises making at least two cores (Na1, Na2) which are anchored to a common insert (I).
13. A method according to any one of claims 10 to 12, characterized in that the insert (I) is made by molding metal under pressure.
14. A method according to any one of claims 10 to 13, characterized in that the core (Na1, Na2) is an admission pipe core.
15. A method according to any one of claims 10 to 14, characterized in that the core is made by the cold box method.

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