FR3017811A1 - REALIZATION OF CORE SURFACE SLOTS - Google Patents

Abstract

The invention relates to a casting core for casting aluminum alloy parts in a mold, said core comprising a molding part, intended to be in contact with the molten aluminum alloy, and at least a non-molten part. -moulante, intended to be located outside the molten aluminum alloy, the core having at least one slot on the surface of the core, said slot extending from the molding portion to at least one non-molding portion to allow the evacuation of the gases generated in the molding part of the core during casting out of the molding part.

Description

Field of the Invention The present invention relates to the field of foundry and casting of aluminum alloy casting parts.

The invention more particularly relates to a casting core for casting aluminum alloy parts in a mold. The cores concerned in particular consist of a mixture of sand and binder. BACKGROUND ART The foundry core constitutes a part of the mold used to make a piece of metal and in particular aluminum alloy. The core is usually composed of a mixture of sand grains and binder. The foundry core allows the creation of interior recesses of a room.

It is therefore wholly or partly immersed in the molten metal. When a core is surrounded by a molten aluminum alloy, the phenomena of air expansion, evaporation of the solvents of the binders and their combustion related to the increase of the temperature increase the pressure in the core . This increase in pressure is accompanied by a generation of gas inside the core. The gases thus generated are most often discharged to the outside of the core thanks to the porosity of the core which allows the circulation of gases. The gases escaping from the core are thus injected into the molten metal which surrounds the latter, when the pressure in the core exceeds the metallostatic pressure (related to the height of the metal above the core). This phenomenon of gassing generates in the molten metal the presence of bubbles which leave holes in the metal after solidification. This defect weakens the room and compromises its qualities.

Even if the bubbles manage to get out of the casting, the gaseous releases can leave in the solidified metal traces of their passage and are potentially responsible for a porous aluminum cloth or a zone of initiation of propagation of rift.

On the other hand, traces of gaseous releases may appear although the metallo-static pressure limit is not quite affected by the pressure inside the core. Solutions have been proposed to try to avoid these disadvantages.

It has thus been tried to increase the average grain size of the sand in the core, in order to increase the permeability of the sand and to promote the evacuation of the gases towards the outside of the core by the parts of the core which are not covered. of aluminum (in practice, the staves of the nucleus).

But this technique weakens the nuclei due to the decrease in the number of resin bridges between the grains. In addition, the use of large grains for the cores also changes the surface condition of the part made to such an extent that the roughness measured on the surfaces of the part can compromise their quality. Finally, this solution involves managing several sizes of sand grains in a plant, which is an additional disadvantage. Another known attempt is to add contact shapes between the core immersed in the liquid metal and the outside of the mold. The evacuation of the gases generated in the core can then be done by these forms which serve as evacuation chimneys. This technique is very widespread but requires various additional operations binding on the castings to fill the voids left by these forms: machining the part, adding one or more plugs ("plug") to reseal the shape that allowed the evacuation and implementation of a leakage control system. It is also known to practice in the core of the closed suction ducts gases intended to be depressed, to suck the gases generated in the core and evacuate to the outside of the mold. Depression in the duct is usually generated by Venturi suction. This configuration is difficult to implement and its configuration requires permanent control, which is a disadvantage in itself. In particular, this type of system must suck sufficiently to avoid the problem of gas emissions but do not suck too hard to avoid the aspiration of metal in the core. Moreover, the shape of the cores is often unsuited to their use. Their management and maintenance represent technical and economic complications. It thus appears that the various attempts to solve the problem of gaseous release of nuclei are all exposed to limitations. The object of the invention is to overcome these limitations.

SUMMARY OF THE INVENTION The invention thus proposes a casting core for casting aluminum alloy parts in a mold, the core comprising a molding part, intended to be in contact with the molten metal, and at least a part non-molding, intended to be located out of the molten metal, the core having at least one slot on the surface of the core and the slot extending from the molding portion to at least one non-molding portion to allow evacuation of the generated gases in the molding part of the core during casting out of the molding part. The invention thus proposes a simplified alternative to the techniques of the prior art by producing slots on the surface of cores. These slots create a space to evacuate the gases generated in the core, and at the same time the slots are thin enough to prevent the aluminum alloy from penetrating them. By drawing a preferential path for evacuating the gases towards the non-molding parts of the core, out of the molten metal (typically the spans), these slots make it possible to evacuate the gases that can be generated in the core, without implying the disadvantages mentioned above. -above.

Advantageously, the invention also proposes the following characteristics taken alone or in combination: the non-molding part or portions are spans adapted to hold the core in position inside the mold; the slots have a width adapted to prevent the molten aluminum alloy from penetrating inside said slot; the slots on the surface have a width of less than 1 mm and preferably of 0.2 mm; - The slots have a rectangular geometric profile, U or V; the slots have an average depth of between 0.2 and 2 mm, to allow the gas generated in the molding part of the core to circulate in the slots; the slots are made by laser; - The slots are made by a tool with reliefs shaped blades. The invention also proposes a mold adapted for casting castings, comprising a core as described above. The mold may further comprise a suction system adapted to suck in the slots generated gases, the suction being at the non-molding areas.

The invention also provides a method of manufacturing a core as described above, characterized in that it comprises a step of etching said slots on the surface of the core using a laser. The invention also proposes a process for manufacturing an aluminum alloy part by casting molten metal by means of a previously described mold. Finally, the invention proposes a cylinder head for automobile obtained by a method of manufacturing a previously described part, as well as a motor block for automobile.

FIG. 1a shows a core according to the invention immersed in a molten aluminum alloy.

Figure 1b shows a magnification of the core of Figure 1a. Figure 2a shows a sectional side elevation diagram of a mold and a core as defined in the invention, the molding portion is immersed in the molten metal. Figure 2b shows the core of Figure 2a seen from above, without the mold.

Figure 3a shows a more accurate representation of a core according to the invention. Figure 3b shows a sectional view along the plane [AA '] of Figure 3a of the core as defined in the invention.

Figure 4a illustrates different slit profiles (scales not necessarily respected). Figure 4b shows different types of slots with the burrs of molten metal penetrating inside these slots (scales not necessarily respected). Figure 5 shows a schematic diagram of a top view of the surface of the core immersed in the molten metal, within a mold, with possible circulation (arrows) in the gas slots generated in the core. Figure 6 shows the evolution of gas evolution as a function of the number of slots.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIGS. 1a, 1b, 2a, 2b, 3a, 3b, a core 10 according to the invention is described.

The core 10 is suitable for casting foundry pieces in a mold 20. These cast casting parts are made of aluminum alloy and are typically intended for the automotive industry. Typically, these castings are intended to be engine blocks or cylinder heads.

The core 10 comprises a molding portion 11 which is intended to be in contact with the molten aluminum alloy 30. The core 10 also comprises a non-molding portion 12a, intended to be located outside the molten aluminum alloy 30 In general, a core 10 comprises several non-molding parts 12a separated in particular by the molding part 11.

The core 10 is placed inside the mold 20 and is held there immobile thanks to the bearing surfaces 12b, which are generally non-molding parts 12a (see Figure 2a). Generally, the mold 20 comprises a sole 21, which constitutes the bottom of the mold 20, and at least one movable slide 22, which constitutes a side wall of the mold 20 when said slide 22 is closed. The sole 21 and the drawers 22 make it possible to produce the outer shapes of the castings. The drawers 22 are also adapted to immobilize the core 10. The bearing surfaces 12b are for this purpose in contact with said drawers 22. The core 10 comprises at least one slot 13 located on the surface of the core 10. The slot 13 extends from the molding part 11 has at least one non-molding part 12a and thus makes it possible to create a preferential path of evacuation of the gases generated to evacuate the gases generated in the molding part 11 from said molding part 11 and, preferably, out of the parts non-molding 12a then (see Figures 2a, 2b, 3a, 3b). The main function of the slot 13 located on the surface of the core 10, and which extends from the molding part 11 to at least one non-molding part 12a, is thus to create a preferential path for evacuation of the gases generated to evacuate the gas generated in the molding portion 11 out of said molding portion 11. These gases can thus be removed at a distance from the portion of the core 10 which will effectively mold the workpiece. They can accumulate at the level of the non-molding parts 12, or be removed from these parts 12 if the slot 13 is brought into contact with the open air. Each slot 13 consists of a groove that connects the molding portion 11 to a non-molding portion 12a. In a preferential manner, given the structure of the cores 10, the molding part 11 of which is connected to two distinct non-molding parts 12a, the slot 13 connects the two non-molding parts 12a by passing through the molding part 11. Geometric properties of slots In 4a (given for illustrative purposes, without scale), the profile of the slots 13 is preferably rectangular, U or V. These forms offer a good compromise between simplicity of manufacture and efficiency, that is, ie the capacity of the gases generated to circulate and be drained. A widening profile as one moves away from the surface of the core 10, of the trapezoidal type for example, makes it possible to facilitate the circulation and the drainage of the gases generated while preventing the molten aluminum alloy 30 from penetrate inside the slot 13. Other profiles are also possible.

In general, the dimensions of the slits obey constraints related to the molten metal and the gases generated. It is a question of optimizing the volume of the slot 13. The slots 13 thus have a width 13a such that the molten aluminum alloy 30 does not create on the surface of the part visible burrs 31 after cooling (see FIG. 4b). For this, either the molten aluminum alloy 3 does not penetrate inside the slots 13 or it penetrates a given distance less than a quality criterion defined by a specification. Typically, the impact on the surface condition of the aluminum alloy must be zero or the value of the roughness of the casting must be unchanged with and without slots. width 13a to maximize the drainage of generated gases and minimize burr 31. The optimization of this width 13a facilitates the optimization of the volume of the slot 13, particularly in the case of fairly simple geometric profiles. The width 13a is a useful width, i.e. it is measured at the surface (see the widths 13a in Figure 4b).

The width 13a is in particular a function of the types of aluminum alloy used.

Typically, the width of the slots 13a is less than 1 mm and, preferably, less than or equal to 0.2 mm. Nevertheless, those skilled in the art can adapt the width 13a of the slots 13 to obtain the results mentioned above.

FIG. 4b (given for illustrative purposes, without scale) illustrates various profiles of burrs 31 obtained for different widths 13a of the slot 13. The slots 13 have an average depth 13b such that the generated gases can circulate inside the slots 13. The depth 13b of the slots 13 theoretically has no influence on the burrs 31 but the complexity, the cost and the fragility of the core, among others, increase with the depth 13b. In principle, it is a matter of optimizing the volume of the slot 13, with a constant slot width 13a, to maximize the drainage of the generated gases, to minimize the manufacturing complications of the slots 13 and to limit the fragility of the core 10. In the case of fairly simple geometric profiles, this optimization of volume amounts to optimizing the average depth 13b. A value of depth 13b greater than 0.2 mm makes it possible in practice for the gases generated in the molding part 12a to circulate inside said slots 13. is greater than 0.2 mm and less than 2 mm. The path of the slots 13 is drawn so as to drain as much gas as possible by providing a preferential path for the flow of generated gases. For this, the tracing plan is optimized to promote the circulation and drainage of the gases generated to minimize the pressure due to said gases. An advantageous tracing plan can thus for example consist in leaving the least areas of the molding part 11 without slots 13, ie ensuring that no point on the surface of the molding part 11 of the core 13 is at a distance greater than a given limit value, with respect to the nearest slot 13. In the case of several slots 13, the minimum and / or maximum spacing between the slots 13 can be determined. The slots 13 are preferably traced by maximizing the radii of curvature and limiting the angles, more importantly the acute angles, to facilitate the circulation and drainage of the gases generated (Figure 3a). According to one embodiment comprising at least two slots 13, said slots 13 do not intersect, in order to maximize the covered area for a given total length of slots 13.

According to another embodiment comprising at least two slots 13, said slots 13 intersect to provide a circulation alternative and better drainage of the generated gases (Figure 2b). The non-molding parts 12a are advantageously litters 12b since the bearings 12b already act as non-molding parts 12a. Nevertheless, it is conceivable to create a particular core 10 in which the non-molding parts 12a are not litters 12b and have a structure promoting the circulation of the generated gases, for example a branched structure.

Evacuation of generated gases The non-molding parts 12a which receive the slots 13 comprise means 40 adapted to allow the evacuation of the gases generated in the molding portion 11 (Figure 2a). These means 40 can be made in different ways. In particular, the means 40 may simply consist of a fluid connection 41 between slots 13 of the non-molding parts 12a and a certain volume of air under pressure less than the pressure of the gases generated to be discharged (typically this pressure is the atmospheric pressure) said volume being typically much larger than the volume of gas generated. In the case of the mold 20 with sole 21 and drawers 22, a bore or an opening 42 in the slide 22 allows said connection 41 between slots 13 of the non-molding parts 12a (here typically spans 12b) with the volume of air.

Alternatively, the devices 40 furthermore comprise a suction system 43 for promoting the circulation and the drainage of the gases generated in the slots 13 (FIG. 5). Making the slots The slots 13 are preferably obtained by a laser 50. This technique is not very easy. invasive and allows good accuracy in achieving despite complex 10-core forms. It is also possible to make these slots 13 using specialized tools. This specialized tool may consist of an apparatus with reliefs in the form of blades (the slots 13 whose profile is V are typically obtained as well). Example of use In one example, the core 10 is installed in the mold 20 and fixed to the drawers 22 of the mold 20 by the bearing surfaces 12b. The molten aluminum alloy 30 is poured inside the mold 20 and surrounds the molding portion 11 of the core 10. The heat causes a gas generation inside the core 10. These gases then preferentially flow through the slots 13 and are drained to the non-molding parts 12a (Figure 4), then to be evacuated by the exhaust means 40. There is thus no traces of gas emissions in the room. By choosing the width 13a of the slots in a suitable manner, it also avoids the burrs 31 on the cooled part.30 Result and comparison The use of the slots 13 on the core surface 10 makes it possible to reduce the pressure due to the gases generated at inner core 10 allowing the generated gases to flow and be drained out of the molding portion 11 via a preferred circulation path. FIG. 6 thus illustrates the results obtained.

A comparison is made between a core called "specimen" reference (specimen without slot 13 on the surface) and a series of cores "specimens" called test, each specimen of this series having on its surface a different number of slots 13 of width 13a 0.2 mm. All the test pieces (including the reference test piece) have, apart from the possible slots 13, the same general geometry, and they consist of the same material. With the help of a manometer, the following can be observed: - for the test series test specimen, which includes a slot 13, a 22% reduction in gas emissions compared with the reference specimen, - for the test specimen of the series test which comprises two slots 13: a decrease of 40%, - and for the test-tube of the test series which comprises sixteen slots 13: a decrease of 46%. 25

Claims (14)

REVENDICATIONS1. Foundry core (10) for casting aluminum alloy parts in a mold (20), said core (10) comprising: - a molding part (11) intended to be in contact with the alloy of molten aluminum (30), - at least one non-molding part (12a) intended to be situated outside the molten aluminum alloy (30), characterized in that the casting core (10) comprises at least one slot (13) on the surface of the core (10), said slot (13) extending from the molding part (11) to at least one non-molding part (12a) to allow evacuation of the gases generated in the molding part (11) the core (10) during casting out of the molding portion (11). The casting core (10) according to claim 1, wherein the one or more non-molding portions (12a) are bearing surfaces (12b), adapted to hold the core (10) in position within the mold (20). ). The casting core (10) according to any one of the preceding claims, wherein the slots (13) have a width (13a) adapted to prevent the molten aluminum alloy (30) from penetrating into the interior. said slot (13). 4. Foundry core (10) according to any one of the preceding claims, wherein the slots (13) at the surface have a width (13a) less than 1mm and preferably 0.2mm. 5. Foundry core (10) according to any one of the preceding claims, wherein the slots (13) have a rectangular geometric profile, U or V. The casting core (10) according to any one of the preceding claims, wherein the slots (13) have an average depth (13b) of between 0.2 and 2mm, to allow gas generated in the molding portion (11 ) of the core (10) to flow in the slots (13). 7. Foundry core (10) according to any one of the preceding claims, wherein the slots (13) are made by laser. 8. Foundry core (10) according to any one of claims 1 to 6, wherein the slots (13) are formed by tooling with reliefs in the form of blades. A mold adapted for casting castings, comprising a core (10) according to any one of the preceding claims. 10. Mold according to the preceding claim, further comprising a suction system (43) adapted to suck in the slots (13) the generated gases, the suction being at the non-molding areas (12a). 11. A method of manufacturing a core (10) according to any one of claims 1 to 8, characterized in that it comprises a step of etching said slots (13) on the surface of the core (10) to the using a laser (5). 12. A method of manufacturing an aluminum alloy piece by casting molten metal by means of a mold according to one of claims 9 to 10. 13. Cylinder head for automobile obtained by a method according to the preceding claim. 14. Automotive engine block obtained by a process according to claim 12.10