EP2838679A2

EP2838679A2 - Method for the production of a hollow metal part by means of casting

Info

Publication number: EP2838679A2
Application number: EP13719995.6A
Authority: EP
Inventors: Yves Longa; Jean DE RUFFRAY
Original assignee: CTIF -Centre Technique des Industries de la Fonderie
Current assignee: CTIF -Centre Technique des Industries de la Fonderie
Priority date: 2012-04-16
Filing date: 2013-04-11
Publication date: 2015-02-25
Also published as: RU2635596C2; US20150083356A1; CN104302422A; KR20140147893A; RU2014145837A; WO2013156713A2; WO2013156713A3; IN2014DN09024A; BR112014025731A2; JP6277178B2; FR2989293A1; MX2014012537A; FR2989293B1; JP2015516887A; CN104302422B; CA2870546A1; US9452469B2; MX357506B

Abstract

The invention relates to a method for the production of a hollow metal part by means of casting, said method comprising the following steps of: providing a destructible core (20) having a body (22) made from aggregates, and an outer shell (40) which surrounds the body (22) and is adhered thereto; placing the core (20) in a mould (50); melting and injecting liquid metal, generally under pressure, into the mould (50) around the core, said core (20) forming an inner space in the part; after solidification of the part, disaggregating the body and removing same through outlets provided in the outer shell and the part; and destroying the outer shell and removing same through outlets provided in the part.

Description

METHOD OF MANUFACTURING A HOLLOW METALLIC PIECE BY FOUNDRY

FIELD OF THE INVENTION

The present disclosure relates to a method of manufacturing a hollow metal part by casting and, more particularly, by die casting.

Such a method is particularly useful for the manufacture of parts which have an internal recess and which, therefore, are not demoldable directly, such as, for example, a fluid circulation duct or a semi-closed container (eg a casing ).

STATE OF THE PRIOR ART

The foundry includes processes for forming metals (i.e. pure metals and alloys) which consist of casting a liquid metal in a mold to produce, after cooling, a given piece, limiting as much as possible the subsequent work of finishing on this piece.

In the underpressure molding technique, the liquid metal is injected into the mold under a significant injection pressure, typically between 100 and 1200 bar (i.e. 10 and 120 MPa). The injection speed in the mold is typically between 10 m / s and 80 m / s and the temperature of the liquid metal is typically between 400 and 980 ° C.

In the foundry, pressure molding is often reserved for large-scale production for markets such as automotive or household appliances, because of the high price of tools (molds and cutting tools).

Currently, to mold under pressure a hollow part such as a duct or a semi-closed tank, the smelter molds two half-parts which are then assembled mechanically by welding or gluing. This solution is not satisfactory because, on the one hand, it requires two molding tools (one for each half-part) and, on the other hand, the step assembly is delicate because of the required sealing at the assembly area.

There is therefore a need for another manufacturing process.

PRESENTATION OF THE INVENTION

The present disclosure relates to a method of manufacturing a hollow metal piece, by casting, in which:

a destructible core is provided comprising a body made of aggregated compounds, and a shell which surrounds and adheres to the body;

the kernel is arranged in a mold;

- Melting and injecting the liquid metal in the mold, around the core, the core materializing an interior space of the room;

after solidification of the part, the body of the core is disintegrated and evacuated via discharge orifices formed in the carapace and in the part; and

the carapace is destroyed and evacuated via evacuation orifices formed in the room.

The core used here differs from conventional cores used in gravity foundry, in particular by the fact that it has a shell enabling it to mechanically resist the stresses exerted by the liquid metal during the injection. Without this shell, the core would disintegrate under these constraints. The shell adheres to the body of the core to avoid a separation of the shell and the body during injection, and as the shell rests on the body, the latter takes some of the constraints during injection.

Such a manufacturing method is particularly interesting in die casting because the stresses exerted by the liquid metal during the injection are high and the carapace of the core is then of interest. In this case, the mechanical strength of the shell is sufficient to resist the under-pressure injection of the liquid metal and, during molding, the liquid metal is injected under pressure into the mold, around the core. Nevertheless, this manufacturing process could be used in foundry in other applications such as low-pressure molding or gravity casting (eg for ferrous alloys and non-ferrous alloys, in metal or non-metallic molds)

The choice of the constituent material of the shell is made according to the good mechanical strength of this material, and its good adhesion to the core. Examples of materials are given below, but a person skilled in the art could easily, in view of this disclosure, consider others.

Advantageously, the material constituting the shell also has one or more of the following properties:

- It is chemically passive vis-à-vis the injected metal and, in particular, it does not dissolve in the latter;

it is non-penetrable by the liquid metal injected under pressure;

- It has a good surface and, in particular, no or little surface porosity. This makes it easier to detach the shell from the molded part and to obtain a good surface condition on the walls of the interior space of the part.

The carapace of the core is made, for example, based on particles aggregated by a binder (s) of organic nature (eg polyurethane), mineral (eg silicate, colloidal silica, ethyl silicate, low-point metals). fusion) or hydraulic (eg plaster, cement, lime). The particles may be ceramic, calcined clay, with or without zircon. They can result from the recycling of an old carapace. In another example, the shell is metallic.

The core body is, for example, foundry sand or cast plaster, possibly loaded with fibers. The binder used to aggregate the core compounds may be hydraulic, organic (eg cellulose) or inorganic (eg silicate). The filler fibers may be organic or mineral in nature (eg linen, wood, glass). To disintegrate the body and evacuate it from the molded part, it is possible to use a conventional, mechanical (eg shock, vibration, granular or ultrasonic projection) and / or hydraulic (water jet) deburring process, even a process of chemical breaking (eg by dissolution of (the) binder (s)).

In some embodiments, the destructible core further includes a skeleton that traverses the core body and is attached to the shell. This framework can be destroyed and evacuated at the same time as the body and / or the carapace. Such a framework makes it possible to further strengthen the mechanical strength of the core.

In some embodiments, to manufacture the core, the core body is made by aggregating compounds in a box provided with pins that pass through the inside of the box, so that the body, once removed from the box, presents recesses in place of the pins, and filling these recesses with a material constituting the framework, for example by dipping the body of the core in a slip, injecting (under low pressure) this slip or by gravity flow the slip in a container.

The recesses and corresponding framing members (i.e. the framing members obtained by filling the recesses with the material constituting the framework) may pass right through, or only partially, the core body.

In some embodiments, the core body is dipped one or more times in one or more slips, so as to cover the body with one or more layers of curable material. For example, as a slip, plaster can be used. For example, the core body may be first dipped in a first slip to form the optional backbone and the lower layer of the carapace, and then in other slip to form the upper layer or layers of the carapace . Thus, the core body can be dipped in a first slip to form the framework and a lower layer of the shell and then in one or several other slips to form one or more upper layers of the shell. Instead of soaking, it is possible to make the shell by injection of the slip.

The constituent materials of the shell and the framework may be identical or different. Moreover, the criteria used for the materials of the shell and the frame do not necessarily correspond. In particular, as the framework does not come into contact with the injected metal, its chemical passivity vis-à-vis this metal is not a selection criterion. In addition, since the framework is subjected to less stress than the shell during injection, the mechanical strength of the framework may be lower than that of the shell. Furthermore, in some embodiments, it is desired to evacuate the frame at the same time as the body. In this case, like the body, the framework is made of aggregated, disaggregated compounds. Thus, one can disaggregate and evacuate the body and the frame, in one operation, according to a method of débourrage.

In some embodiments, to make the core:

the body of the nucleus is made by aggregation of compounds in a box provided with support members which traverse (partially or partially) the inside of the box, and

the shell is made around the body and the support members so that the support members pass through the shell.

The support members are then used to hold the core in position in the mold during injection. Depending on the position occupied by the support members in the core, these can also serve to enhance the strength of the core.

In some embodiments, the support members are hollow and define exhaust passages for gases that are formed by thermal decomposition of certain core components during molding of the workpiece. This makes it possible to limit the risks of deformation related to these gases, especially when the part has thin walls.

In some embodiments, the support members are extracted the piece to provide the evacuation ports through which the body of the core and / or the shell are evacuated.

Other features and advantages of the proposed method will appear on reading the detailed description which follows. This detailed description refers to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are diagrammatic and are not to scale, they are primarily intended to illustrate the principles of the invention.

In these drawings, from one figure (FIG) to the other, identical elements (or element parts) are identified by the same reference signs.

FIG 1 shows a box for the manufacture of the body of a core. FIG 2 is a side view of the core body made with the box of FIG 1.

FIG 3 is a perspective view of the core made with the body of FIG 2.

FIG 4 is a sectional view of a mold in which is disposed the core of FIG 3.

FIG 5 is a perspective view of a hollow metal piece obtained by casting in the mold of FIG 4.

DETAILED DESCRIPTION OF EXAMPLE (S) OF REALIZATION

An exemplary method is described in detail below with reference to the accompanying drawings. This example illustrates the features and advantages of the invention. However, it is recalled that the invention is not limited to this example.

FIG 1 shows a box 10 for the manufacture of the body 22 of a core 20. This box comprises two half-shells 10A, 10B which, once assembled, define between them a free space 12 intended to receive the compounds which will form the core body.

Inside the box, ie in the free space 12, extend pins 16. In the example, these pins 16 pass through the free space 12 from one end to the other, each pin 16 being formed of two half 16A, 16B carried, respectively, by the two half-shells 10A, 10B, and located in the extension of one another, once the half-shells assembled.

Inside the box, there are also support members 18 which partially cross the free space 12. In the example, these members 18 are hollow and tubular with a free end 18E tapered (frustoconical). The other end of these members 18 bears against one of the walls 15. Each member 18 is traversed by an inner passage (a lumen) opening at both ends of the organ.

In order to manufacture the body 22 of the core, the free space 12 is filled with aggregatable compounds, for example sand grains, mixed with at least one curable resin. Once the resin (s) have hardened (eg by heating, or using a catalyst gas), the sand grains are aggregated and form the body 22. The body 22 is then extracted from the mold 10 .

As shown in FIG. 2, the body 22 has recesses

Instead of the pins 16. In addition, the support members 18 are trapped in the mass of the body 22.

In order to manufacture the core 20, the body 22 is immersed one or more times in one or more fluid paste baths, or slips, so as to cover the body with one or more layers of a hardenable material. To hold the body 22 during the bath, the hollow support members 18 are used. Typically, pins are passed inside the members 18, which allows the body 22 to be held and to plug the internal passage of the organs 18 to prevent them from filling up. After each bath, the deposited layer is cured, for example in air.

During the first bath in a first slip, the recesses 26 of the body 22 fill to form a framework 36. The framework 36 is thus composed of several elements which pass through the body 22 of the core and are connected to the shell 40. In For example, like the recesses 26, the frame members pass right through the body, so that the two ends of each frame member are connected to the shell 40. The first slip also forms the first or lower layer of the shell 40. Other layers, if any, of the shell 40 may be obtained by dipping the body 22 in other baths of hardenable material.

To cover the body 22 and fill the recesses 26, instead (or in addition) of the soaking operations, it is possible to proceed to the injection or casting by gravity of a slip around and / or in the body.

FIG 3 shows the core 20 obtained after formation of the shell 40 around the body 22.

By way of example, it is possible to manufacture the core 20 from the following materials and under the following conditions: to manufacture the body 22, use is made of foundry sand pre-coated with resin and hardener and the resin is cured with its hardener. For example, the sand used is 55 finite silica AFS. The fineness of the sand can change depending on the shape and size of the core to be made. Then, the resulting body 22 is immersed in a refractory slip mixed with colloidal silica. During the first soaking the recesses 26 are filled with slip to make the frame. The body 22 is dried and returned to the slip as many times as necessary to obtain the desired shell thickness 40 after the last drying.

Once the core 20 is made, it is placed in the cavity 51 of a mold 50, as shown in FIG. 4. This figure shows the mold 50 and the core 20 in section. The core 20 is held in position in the mold 50 by means of hollow pins 53, integral with a portion of the mold 50, and driven into the support members 18 of the core 20.

Then, the liquid metal is melted and injected into the mold, around the core 20. The injection of the metal can be under-pressure, the shell 40 resistant to the stresses exerted during the injection and allowing the core 20 to maintain its integrity. In addition, gases related to the thermal decomposition of certain elements (typically binders) constituents of the core 20 are advantageously discharged outside the mold 50, via the internal passages of the support members 18 and the pins 53. This evacuation is symbolized by the arrows G in FIG 4.

After curing and cooling (total or partial) of the metal, is extracted from the mold 50 a metal part 60 which surrounds the core 20, the core 20 materializing a hollow space inside this part. To separate the core 20 from the part 60, the latter is subjected to a conventional deburring process, typically mechanical and / or hydraulic. The body 22 of the core then disintegrates under the combined effect of the thermal decomposition of the binders which constituted it (this decomposition taking place during the injection of the liquid metal, under the effect of the temperature of this metal) and the stresses breaking. If its composition allows it, the framework 36 can be disintegrated at the same time as the body 22. Otherwise, the frame 36 can be extracted after the body 22, for example, by subjecting the piece to a second method of breaking in. for example, the elements resulting from the disintegration of the body 22 and, possibly, the framework 36, are discharged through the end orifices 62 of the hollow tubular piece 60. The support members 18 are extracted at the same time as the body 22 through these orifices 62. Note that these orifices 62 pass through the part 60 and the shell 40. According to another example, not shown, the discharge orifices are formed by extracting the support members 18 from the core 20.

The hollow tubular metal part 60 illustrated in FIG. 5 is thus obtained, the internal face of this part 60 being covered by the shell 40. The shell 40 is then destroyed and discharged through the orifices 62 to obtain the piece 60 alone. . For example, the shell 40 is destroyed by shot blasting or by peeling under water pressure (5 to 50 MPa) depending on the strength of the part 60.

By way of example, it is possible to manufacture the piece 60 by conventional pressure molding of an aluminum-silicon-copper alloy. The injection pressure can vary from 100 bars to 1200 bars (ie 10 and 120 MPa), the flow rate of the metal can vary from 10 to 80 m / s. The silicon content can vary from 2 to 20%, the copper content can vary from 0.1 to 10%. For example, the alloy Al Si 9 Cu 3 (Fe) can be used.

The modes or examples of embodiment described in the present description are given for illustrative and not limiting, a person skilled in the art can easily, in view of this presentation, modify these modes or embodiments, or consider others, while remaining within the scope of the invention.

In addition, the various features of these modes or embodiments can be used alone or be combined with each other. When combined, these features may be as described above or differently, the invention not being limited to the specific combinations described herein. In particular, unless otherwise specified, a characteristic described in connection with a mode or example of embodiment may be applied in a similar manner to another embodiment or embodiment.

Claims

A method of manufacturing a hollow metal piece, by casting, in which:

a destructible core (20) is provided comprising a body (22) made of aggregates, and a shell (40) which surrounds and adheres to the body;

the core (20) is arranged in a mold (50);

- melting and injecting a liquid metal into the mold (50) around the core (20), the core materializing an interior space of the part (60);

- After solidification of the piece (60), the body (22) is disintegrated and discharged via discharge orifices (62) formed in the shell (40) and the piece (60); and

- Destroying and removing said shell (40) via outlets (62) in the room (60); and

wherein the destructible core (20) further comprises a framework (36) which traverses the core body (22) and is bonded to the shell (40), and in which said framework (40) is destroyed and removed (36) at the same time as the body and / or the carapace.

2. Method according to claim 1, wherein the liquid metal is injected under pressure into the mold (50), around the core (20), and wherein the shell (40) has sufficient mechanical strength to resist injection. underpressure of the liquid metal.

The method of claim 1 or 2, wherein, to make the core (20):

the body (22) of the core is made by aggregation of compounds in a box (10) provided with pins (16) which pass through the inside of the box, so that the body, once extracted from the box, has recesses (26) in place of the pins, and these recesses (26) are filled with a material constituting the framework (36).

4. The method of claim 3, wherein the recesses (26) and the corresponding frame members pass right through the body (22) of the core (20).

The method according to claim 3 or 4, wherein the body (22) of the core is dipped in a first slip to form the framework (36) and a lower layer of the shell (40) and then in one or several other slips to form one or more upper layers of the shell (40).

6. Process according to any one of claims 1 to 5, wherein, to manufacture the core:

the body (22) of the core (20) is made by aggregating compounds in a box (10) provided with supporting members (18) which pass through the inside of the box, and

the shell (40) is made around the body (22) and the support members (18) so that the support members pass through the shell,

and in which

the support members (18) are used to hold the core (20) in position in the mold (50) during the injection.

The method of claim 6, wherein the support members (18) are hollow and define exhaust passages for the gases formed by the thermal decomposition of certain components of the core (20) during molding of the workpiece.

8. A method according to claim 6 or 7, wherein, after solidification of the workpiece (60), the support members (18) are extracted from the workpiece to provide the outlet openings through which the core body (22) and / or the shell (40) are evacuated.

9. A method according to any one of claims 1 to 8, wherein the body (22) of the core is foundry sand or cast plaster, optionally filled with fibers.

10. A method according to any one of claims 1 to 9, wherein the shell (40) of the core is ceramic.

11. A method according to any one of claims 1 to 10, wherein the body (22) is disintegrated and discharged according to a method of mechanical and / or hydraulic débourrage.