CA2940314A1 - Creation of slots on the surface of a core - 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

REALIZATION OF CORE SURFACE SLOTS
Field of the invention The present invention relates to the field of foundry and casting of aluminum alloy casting parts.
The invention relates more particularly to a foundry core for the casting of aluminum alloy parts in a mold. The nuclei concerned are especially consisting of a mixture of sand and binder.
Technological background The foundry core is a part of the mold used to make a metal part and in particular aluminum alloy.
The nucleus is usually composed of a mixture of grains of sand and binder. The foundry core allows the creation of internal 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, solvent evaporation of binders and their combustion related to the increase in temperature increase the pressure in the kernel. This increase in pressure is accompanied by a generation of gas inside the nucleus. The gases thus generated are most often evacuated towards the outside of the nucleus thanks to the porosity of the nucleus which allows the circulation 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 pressure metallo static (related to the height of metal above the core). This phenomenon of gaseous release generates in the molten metal the presence of bubbles which

2 leave holes in the metal after solidification. This defect weakens the piece and compromises his qualities.
Even though the bubbles manage to come out of the casting, the clearances gas can leave traces of their passage in the solidified metal and are potentially responsible for a porous aluminum sheet or a crack propagation initiation zone.
In addition, traces of gaseous releases may appear although the metallo-static pressure limit is not quite reached by the pressure inside the nucleus.
Solutions have been proposed to try to avoid these disadvantages.
So we tried to increase the average grain size of sand in the core, in order to increase the permeability of the sand and promote the evacuation of the gas to the outside of the nucleus by the parts of the nucleus that are not coated of aluminum (in practice, the staves of the nucleus).
But this technique weakens the nuclei because of the decrease in the number resin bridges between the grains.
In addition, the use of large grains for nuclei also changes the surface condition of the part achieved to the extent that the roughness measured on the Room surfaces can compromise their quality. Finally, this solution involved to manage several sizes of sand grains in a plant, which is a additional disadvantage.
Another known attempt is to add forms of contact between the core immersed in the liquid metal and the outside of the mold. The evacuation of gas generated in the kernel can then be done by those forms that serve as fireplaces discharge.

3 This technique is widespread but requires different operations additional requirements on castings to fill voids left by these shapes: machining the piece, adding one or more plugs (plug) to reseal the shape that allowed the evacuation and set up a sealing control system.
It is also known to practice in the core of closed conduits suction of gases intended to be depressed, to suck gas generated in the core and vent them to the outside of the mold. Depression in the duct is usually generated by a Venturi type suction.
This configuration is difficult to implement and its configuration requires permanent control, which is a disadvantage in itself. In In particular, this type of system must suck sufficiently to avoid the problem gaseous releases but do not suck too hard to avoid aspiration of metal in the core.
Moreover, the shape of the cores is often unsuited to their use.
Their management and maintenance represent complications of technical and economic.
It appears as well as the various attempts to solve the problem 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 parts in alloy of aluminum in a mold, the core having a molding part, intended for being in contact with the molten metal, and at least one non-molding part, intended to be located outside 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 less

4 a non-molding part to allow the evacuation of the gases generated 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 art previous by making slots on the surface of cores. These slots create a space that allows to evacuate the gases generated in the nucleus, and in the same time the slots are thin enough to prevent the aluminum alloy from enter within them. By drawing a preferential path of gas evacuation towards the non-molding parts of the core, out of the molten metal (typically the scopes), these slots allow to evacuate the gases that can be generated in the core, without implying the disadvantages mentioned above.
Advantageously, the invention also proposes the characteristics following alone or in combination:
the non-molding portion or portions are spans adapted to maintain the core in position inside the mold;
the slots have a width adapted to prevent the aluminum alloy melted to penetrate inside said slot;
the slots on the surface have a width of less than 1 mm and preferably 0.2mm;
- The slots have a rectangular geometric profile, U or V;
the slots have an average depth of between 0.2 and 2 mm, for allow gas generated in the molding part of the core to flow in the slots;

the slots are made by laser;
- the slots are made by a tool with reliefs in the form of blades.

5 The invention also proposes a mold adapted for casting pieces of foundry, comprising a core as described above.
The mold may furthermore comprise a suction system adapted to suck in the slits the generated gases, the aspiration being done at the level of areas not tight.
The invention also proposes a method of manufacturing a core such that described above, characterized in that it comprises an etching step said slots on the surface of the core using a laser.
The invention also proposes a process for manufacturing an alloy part of aluminum by pouring molten metal by means of a mold previously described.
Finally the invention proposes a cylinder head for automobile obtained by a method of manufacturing a previously described part, as well as a block engine for automobile.
Presentation of figures 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.

WO 2015/12828

6 PCT / EP2015 / 053722 Figure 2a shows a sectional side elevation diagram of a mold and a core as defined in the invention, including the molding part 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 nucleus according to the invention.
FIG. 3b represents a sectional view along plane [AA '] of FIG. 3a of the core as defined in the invention.
Figure 4a illustrates different slit profiles (scales not necessarily met).
Figure 4b shows different types of slots with metal burrs melted penetrating inside these slots (scales not necessarily met).
Figure 5 shows a simplified diagram of a view from above of the surface of the core immersed in the molten metal, in a mold, with a circulation possible (arrows) in the gas slots generated in the nucleus.
FIG. 6 represents the evolution of the evolution of gas as a function of number of slots.
Detailed description of at least one embodiment In relation to FIGS. 1a, 1b, 2a, 2b, 3a, 3b, a core 10 conforming to FIG.
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 for the automotive industry. Typically, these castings are for to be engine blocks or cylinder heads.
The core 10 comprises a molding part 11 which is intended to be in contact with the molten aluminum alloy 30.

7 The core 10 also comprises a non-molding portion 12a, intended to be located out of the molten aluminum alloy 30. In general, a core 10 includes 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 grace at litters 12b, which are generally non-molding portions 12a (see figure 2a). Generally, the mold 20 comprises a sole 21, which constitutes the bottom of mold 20, and at least one movable slide 22, which constitutes a side wall of the mold 20 when said drawer 22 is closed. The sole 21 and the drawers 22 allow to realize the external forms of the castings.
The drawers 22 are also adapted to immobilize the core 10. The brought 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.
slot 13 extends from the molding portion 11 to at least one non-molding portion 12a and thus makes it possible to create a preferential path of evacuation of the generated gases for evacuate the gases generated in the molding part 11 out of said part slinky 11 and, preferably, out of the non-molding parts 12a thereafter (see figures 2a, 2b, 3a, 3b).
The main function of the slot 13 located on the surface of the core 10, and which extends of the molding part 11 to at least one non-molding part 12a, is thus of create a preferential path of evacuation of the gases generated to evacuate the gases generated in the molding part 11 outside said molding part 11. These gases can be evacuated away from the part of the core 10 which will mold actually the piece to be made. They can accumulate at the level of parts non-molding 12, or be discharged out of these parts 12 if the slot 13 is implementation contact with the open air.

8 Each slot 13 consists of a groove which connects the molding part 11 to a non-molding portion 12a. In a preferential manner, given the structure of the cores 10 whose molding portion 11 is connected to two non-molding parts 12a distinct, the slot 13 connects the two non-molding parts 12a while crossing the molding part 11.
Geometric properties of slots In connection with Figure 4a (given for illustrative purposes, without scale), the profile of slots 13 is preferably rectangular, U-shaped or V-shaped.
a good compromise between simplicity of manufacture and efficiency, that is to say the capacity of the gases generated to circulate and be drained. A profile widening to measured that one moves away from the surface of the core 10, of the trapezoidal type for example, facilitates the circulation and drainage of the gases generated while preventing the molten aluminum alloy 30 to penetrate inside the slot 13.
other profiles are also conceivable.
In general, the dimensions of the slots obey constraints linked molten metal and generated gases. It's about optimizing the volume of the slot 13.
The slots 13 thus have a width 13a such that the molten aluminum alloy 30 do not does not create apparent surface burrs on the surface of the cooling (see Figure 4b). For this, it is necessary either that the molten aluminum alloy 3 does not penetrates not inside the slots 13 or that it penetrates a given distance lower than a quality criterion defined by a specification. Typically, it takes than the impact on the surface condition of the aluminum alloy is zero or the value of the the roughness of the casting is unchanged with and without slots.
optimize the width 13a to maximize the drainage of the gases generated and minimize the burrs 31. The optimization of this width 13a facilitates

9 optimizing the volume of the slot 13, particularly in the case of profiles geometric enough simple. The width 13a is a useful width, that is to say that it is measured at the level of the surface (see the widths 13a in the 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, in a way preferential, less than or equal to 0.2 mm.
Nevertheless, those skilled in the art will be able to adapt the width 13a of the slots 13 to obtain the results mentioned above.
Figure 4b (given for illustrative purposes, without scale) illustrates different profiles of burrs 31 obtained for widths 13a different from the slot 13.
The slots 13 have an average depth 13b such that the gases generated can circulating inside the slots 13. The depth 13b of the slots 13 has theoretically no influence for smudges 31 but complexity, cost and the kernel fragility, among others, increase with depth 13b.
In principle, this is to optimize the volume of the slot 13, width of slot 13a constant, to maximize the drainage of the generated gases, minimize the Slit manufacturing complications 13 and limit the fragility of the core

10. In the case of fairly simple geometric profiles, this volume optimization come back to optimize 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 can circulate inside said Slots 13. In a preferential manner and for the reasons given above, the depth 13b is greater than 0.2 mm and less than 2 mm.
The path of the slots 13 is drawn so as to drain the most gas generated possible by offering a preferential path of circulation of the generated gases.
For this, the tracing plan is optimized to favor the circulation and the draining the gases generated to minimize the pressure due to said gases.

An advantageous tracing plan can thus for example consist of leaving the less of zones of the molding part 11 without slots 13, that is to say to guarantee no point of the surface of the molding portion 11 of the core 13 is at a distance greater than a given limit value, with respect to the slot 13a more 5 near. In the case of several slots 13, the minimum spacing and / or maximum between the slots 13 can be determined.
The slots 13 are preferably traced by maximizing the radii of curvatures and limiting the angles, for greater reasons the acute angles, for facilitate circulation and drainage of the generated gases (Figure 3a).
According to one embodiment comprising at least two slots 13, said slots 13 do not intersect, to maximize the area covered for a length total of slots 13 given.
According to another embodiment comprising at least two slots 13, said slots 13 intersect to provide a circulation alternative and a better drainage of the generated gases (Figure 2b).
The non-molding portions 12a are advantageously litters 12b since the bearings 12b already serve as non-molding parts 12a.
Nevertheless, it is conceivable to create a particular core in which the non-molding parts 12a are not litters 12b and have a structure favoring the circulation of the gases generated, for example a structure branched.
Evacuation of generated gases The non-molding portions 12a which receive the slots 13 comprise means 40 adapted to allow the evacuation of the gases generated in the part molding 11 (Figure 2a). These means 40 may be made of different manners.

11 In particular, the means 40 may consist simply of a connection fluidic 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 evacuated (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 opening 42 in the drawer allows said connection 41 between slots 13 of the non-molding parts 12a (right here typically scopes 12b) with the volume of air.
Alternatively, the devices 40 further comprise a system suction 43 to promote the circulation and drainage of gases generated in slots 13 (Figure 5) Realization of the slots The slots 13 are preferably obtained by a laser 50. This technique is minimally invasive and allows a good precision in the realization despite forms of complex nuclei.
It is also possible to make these slots 13 using a tool specialized. This specialized tools may consist of a device with shaped reliefs 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 attached to the drawers 22 from mold 20 by the bearings 12b. The molten aluminum alloy 30 is poured into interior of 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 circulate then preferentially by the slots 13 and are drained towards the non strappy 12a (FIG. 4), to be subsequently evacuated by the evacuation means 40.
does not have thus no traces of gaseous releases in the room. By choosing width

12 13a slots in a suitable manner, further avoids the burrs 31 on the room cooled.
Result and comparison The use of the slots 13 at the core surface 10 makes it possible to reduce the pressure due to the gases generated inside the core 10 allowing the gases generated to flow and be drained out of the molding part 11 via a path preferential circulation.
FIG. 6 thus illustrates the results obtained.
A comparison is made between a core called reference test tube (specimen without slot 13 on the surface) and a series of test cores called test, each specimen of this series having on its surface a number different slots 13 of width 13a 0.2 mm.
All test pieces (including the reference test piece) have, apart from possible slots 13, the same general geometry, and they consist of the same material.
With the aid of a manometer, we observe:
- for the specimen of the test series which includes a slot 13 a reduction of gas emissions by 22% compared to the specimen reference, - for the specimen of the test series which comprises two slots 13: one decrease of 40%, - and for the specimen of the test series which comprises sixteen slots 13: a decrease of 46%.

Claims (14)

claims 1. Foundry core (10) for casting alloy parts of aluminum in a mold (20), said core (10) comprising:
- A molding part (11) intended to be in contact with the molten aluminum alloy (30), At least one non-molding portion (12a) intended to be located out of the molten aluminum alloy (30), characterized in that the casting core (10) comprises at least a 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) for allow the evacuation of the gases generated in the molding part (11) of the core (10) during casting out of the molding part (11). The casting core (10) according to claim 1, wherein the one or more non-molding parts (12a) are adapted seats (12b) to maintain the core (10) in position within the mold (20). 3. Foundry core (10) according to any one of preceding claims, wherein the slots (13) have a width (13a) adapted to prevent the molten aluminum alloy (30) from penetrating inside said slot (13). 4. Foundry core (10) according to any one of 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 preceding claims, wherein the slots (13) have a profile geometric rectangular, U or V. 6. Foundry core (10) according to any one of preceding claims, wherein the slots (13) have a depth average (13b) between 0.2 and 2mm, to allow the gas generated in the molding part (11) of the core (10) to circulate in the slots (13). 7. Foundry core (10) according to any one of preceding claims, wherein the slots (13) are made at laser. 8. Foundry core (10) according to any one of Claims 1 to 6, in which the slots (13) are made by a tooling with reliefs in the form of blades. 9. Mold adapted for casting castings, comprising a core (10) according to any one of the claims preceding. 10. Mold according to the preceding claim, comprising in in addition to a suction system (43) adapted to suck in the slots (13) the gases generated, the suction being made at the level of the non-molding zones (12a). 11. A method of manufacturing a core (10) according to one any of claims 1 to 8, characterized in that it comprises a step of etching said slots (13) on the surface of the core (10) using of a laser (5). 12. Process for manufacturing an aluminum alloy part 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 process according to preceding claim. 14. Automotive engine block obtained by a process according to claim 12.