EP2197606B1 - Method for producing hollow forged parts - Google Patents

Abstract

The invention relates to a method for producing hollow forged parts, that comprises the following steps: making a core of a lost material having a shape corresponding to the internal shape of the part to be obtained except for deformation during forging, positioning the core in a foundry mould, casting a metal around the core so as to completely surround the core in order to obtain a preform (18), sealing the preform (18) so that the core is completely isolated relative to the outside, forging the preform (18) in order to obtain the part having the desired shape, and decore the core of the part in order to obtain the hollow forged part.

Description

The present invention relates to the technical field of manufacturing metal parts subjected to a forging operation.

The object of the invention finds particularly advantageous applications for producing metal parts such as aluminum alloy in order to produce parts for the field for example of the cycle or automobile such as connecting rods, suspension wishbones, pivots, transmission parts, engine mounts or any other ground connection parts.

In the state of the art, it is known to produce a part by forging techniques. This method consists of making a metal blank and placing it after having possibly heated it between two engravings of a matrix. These two engravings are actuated by a press against each other to exert on the blank a work of deformation while ensuring a good surface condition. Such a method makes it possible to obtain parts with a good mechanical resistance (static and dynamic) and a respect of the geometrical tolerances.

However, this technique leads to the production of massive and relatively heavy parts even if the material used is a light alloy. In the same sense, given the price of raw materials and in particular the constituent material of the part, it follows a relatively high cost of the part.

In an attempt to remedy these drawbacks, the document EP 0 850 825 proposes to make a core material lost to form the hollow part of a bicycle pedal crank. This core is extended by a support portion for positioning the support within a casting mold in which a metal is cast. Before a subsequent forging operation, the support portion of the core and the portion of the core defining the receiving bore are removed. Even if such a technique reduces the amount of material used, this technique is unsatisfactory in practice because it does not ensure the good stability of the core during the forging operation. In addition, this technique requires the removal of a portion of the core prior to the forging operation. In addition to the disadvantages of this operation, It can not be ruled out that core debris can be found on forging tools, which can cause surface defects on the part.

The present invention therefore aims to overcome the disadvantages mentioned above by providing a method to benefit from the advantages of the forging process of a part while allowing to obtain a piece of optimized weight at a reduced cost.

Another object of the invention is to provide a method for producing a hollow forged part whose dimensional characteristics are perfectly controlled.

Another object of the invention is to provide a method for simply and inexpensively producing a hollow forging without surface defects likely to appear during the forging operation.

To achieve such an objective, the method according to the invention aims at producing a hollow forged part.

• réalisation d'un noyau en matériau perdu dont la forme correspond à la forme intérieure de la pièce à obtenir, à la déformation près subie lors du forgeage,
• positionnement du noyau dans un moule de fonderie,
• moulage d'un métal autour du noyau pour envelopper complètement le noyau en vue d'obtenir une ébauche,
• étancher l'ébauche de sorte que le noyau se trouve complètement isolé vis-à-vis de l'extérieur,
• forgeage de l'ébauche afin d'obtenir la pièce à la forme souhaitée,
• et débourrage du noyau de la pièce pour obtenir la pièce forgée creuse.

The object of the invention is therefore to provide a method of manufacturing hollow forgings comprising the following steps:

• production of a core of lost material whose shape corresponds to the inner shape of the part to be obtained, to the deformation undergone during the forging,
• positioning the core in a foundry mold,
• molding a metal around the core to completely envelop the core to obtain a blank,
• seal the blank so that the core is completely isolated vis-à-vis the outside,
• forging the blank to obtain the part to the desired shape,
• and unclogging the core of the piece to obtain the hollow forging.

According to an advantageous embodiment characteristic, the method consists in providing the core with at least one gas evacuation duct.

Advantageously, the method consists in ensuring the positioning of the core in the mold by means of the gas evacuation duct.

According to one embodiment, the method consists in sealing the blank by closing off each gas discharge duct.

According to a preferred embodiment, the method consists in closing off each gas discharge duct with the aid of a stiffening element filling said duct.

Preferably, the method consists in positioning the gas evacuation pipe in the core in a place intended to constitute a housing for the part.

According to an exemplary embodiment, the method consists in positioning the gas evacuation pipe so that it extends projecting on either side of the core so as to constitute a housing through the room.

According to an alternative embodiment, the method consists of preheating the blank before it is forged.

• La Figure 1 est une vue en perspective en écorché présentant un exemple de réalisation d'une pièce obtenue par le procédé de fabrication conforme à l'invention.
• La Figure 2 illustre un noyau en partie écorché mis en oeuvre dans une étape du procédé selon l'invention.
• La Figure 3 est une vue en perspective écorchée montrant un noyau pourvu de conduits d'évacuation de gaz.
• La Figure 4 illustre la mise en place dans un moule, d'un noyau tel qu'illustré à la Fig. 3 .
• La Figure 5 est une vue en perspective d'une ébauche obtenue après la coulée d'un matériau dans un moule illustré à la Fig. 4 .
• La Figure 6 illustre une ébauche obtenue après l'opération de moulage et dont les conduits d'évacuation de gaz sont étanchés.
• La Figure 7 est une vue d'une matrice inférieure de forgeage dans laquelle est positionnée l'ébauche illustrée à la Fig. 6 .
• La Figure 8 illustre une vue en perspective en partie écorchée de la pièce obtenue après l'opération de forgeage.
• La Figure 9 illustre une vue en perspective en partie arrachée de la pièce dont une partie du noyau a été percée.

Various other characteristics appear from the description given below with reference to the accompanying drawings which show, by way of non-limiting examples, embodiments of the subject of the invention.

• The Figure 1 is a broken perspective view showing an exemplary embodiment of a part obtained by the manufacturing method according to the invention.
• The Figure 2 illustrates a partially cut kernel implemented in a step of the method according to the invention.
• The Figure 3 is a cutaway perspective view showing a core provided with gas exhaust ducts.
• The Figure 4 illustrates the placement in a mold of a core as illustrated in Fig. 3 .
• The Figure 5 is a perspective view of a blank obtained after the casting of a material in a mold illustrated in FIG. Fig. 4 .
• The Figure 6 illustrates a blank obtained after the molding operation and whose gas evacuation ducts are sealed.
• The Figure 7 is a view of a lower forging die in which is positioned the blank shown in FIG. Fig. 6 .
• The Figure 8 illustrates a partly broken perspective view of the part obtained after the forging operation.
• The Figure 9 illustrates a partly cutaway perspective view of the part of which part of the core has been pierced.

The object of the invention is to ensure the manufacture of a hollow forged part 1 . In the exemplary embodiment illustrated in Fig. 1 , the piece 1 is a hoe comprising a body or arm 2 provided at each end of a head 3 of cylindrical shape. Each head 3 is provided with a through bore 4 opening on two opposite lateral faces 5. In the illustrated example, the bores 4 extend along axes parallel to each other and perpendicular to the direction of extension of the arm 2. that this is clear from the Fig. 1 , the body 2 is hollow insofar as it has a recess 7 opening into the bores 4 of the two heads 3.

The piece 1 is obtained according to the manufacturing method according to the invention which aims to provide a molding operation on a core of lost material to obtain a blank then subjected to a forging operation.

As is more particularly apparent from the Fig. 2 The method of the invention is to provide a core 10 in a lost material whose external shape corresponds to the inner shape of the workpiece 1 to obtain deformation near sustained during a subsequent operation of forging which will be described precisely in the following description. The core 10 is made according to all the known methods using lost materials. For example, the core 10 is a salt core, a sand core made using a cold or hot box or "croning". In the example shown, the core consists of sand and resin.

According to a preferred embodiment, the core 10 is full. Of course, it can be envisaged to make a hollow core 10 . In this case, the core is adapted to have sufficient mechanical strength during the subsequent forging operation. In other words, the core 10 is adapted to withstand the stresses experienced during the forging operation.

According to a preferred embodiment, the core 10 is provided with at least one gas evacuation duct 11. In the example illustrated in FIG. Fig. 3 , the core 10 is provided with two gas evacuation conduits 11. Each gas evacuation duct is made for example by a tube 11 pierced with holes 12 and inserted at least partly inside the core. Each duct 11 protrudes from the core 10. These ducts 11 are intended to evacuate the gases out of the mold, during the molding operation. These gases can come from the combustion of the resins forming part of the core 10. In the same direction and according to a preferred variant embodiment, the outer surface of the core 10 can be made impermeable, for example by coating to force the gases to exit through the conduits. 11.

According to a preferred embodiment, each gas evacuation duct 11 is positioned in the core 10 in a place intended to constitute the bore 4 for the part. In other words, each duct 11 is placed so that its axis of symmetry coincides with the axis of the bore 4 in which the duct is placed.

According to a preferred embodiment, each gas evacuation duct 11 ensures the positioning of the core 10 in the mold during the molding operation. In the illustrated example, each gas evacuation duct 11 protrudes on either side of the core, that is to say from the lateral faces 5.

According to the invention, the method consists in providing a molding operation on the core 10 by means of a conventional casting process. This foundry operation will not be described in detail because it is part of the technical knowledge of the skilled person and it can be implemented by any known foundry technique.

Thus, the core 10 and as it stands out more precisely from the Fig.4 , is intended to be placed in a mold 15 of which only the lower part has been illustrated at the Fig. 4 . According to a feature of the illustrated embodiment, the gas discharge ducts 11 serve to position the core 10 inside the mold 15. The mold is of any type and may be a sand mold, a metal shell or any another molding method for producing a preform to be forged.

The method therefore consists in ensuring the casting of a metal around the core 10 to completely envelop it in order to obtain a blank 18 as illustrated in FIG. Fig. 5 . The core 10 is completely wrapped except the exhaust ducts 11 when they are present.

The method according to the invention aims to seal the blank 18 so that the core 10 is completely isolated vis-à-vis the external environment. In the exemplary embodiment illustrated, the sealing of the blank 18 is ensured by sealing each gas evacuation duct 11 with a closure element 20 of all types ( Fig. 6 ) . This closure member 20 can be made in any suitable manner by a metal plug, resin, plastic or ceramic. In this way, the core 10 is not in contact with the air.

According to a preferred embodiment, the method consists in closing off each gas evacuation duct 11 with the aid of a stiffening element 20 filling the duct. For example, this element 20 may be a rod or a metal shaft completely filling each gas discharge duct 11. This element makes it possible to stiffen and seal each gas evacuation duct 11.

The method according to the invention is then to ensure the forging of the blank 18 to obtain the piece to the desired shape.

This forging operation is performed either cold or hot. In the case of hot forging, the blank 18 is preheated before being placed as illustrated in FIG. Fig. 7 , In a matrix 22 of a forging press. The blank 18 is thus positioned between the two dies of a forging press of all known types. During this forging operation, the core 10 still present in the blank 18, makes it possible to ensure against-pressure avoiding a collapse of the part at the recess 7, during the striking operation. The core 10 thus ensures a level of compression adapted to obtain good mechanical strength characteristics. It should be noted that the presence of the metal pins 20 inside the core 10 also contributes to the strength of the core.

After the forging operation, the piece 1 is removed from the dies as illustrated in FIG. Fig. 8 . If the piece 1 has a burr 22 due to the forging operation, then this burr 22 is removed.

The method according to the invention then consists in ensuring the breaking of the core 10 of the part 1 to obtain the hollow forging. This stripping operation may be performed by any appropriate means such as drilling, vibration and / or heat treatment to remove the entire core 10. For example, it may be envisaged to drill at the heads 3 in order to get bores 4 ( Fig. 9 ) and a heat treatment to remove the core located in the arm 2 to obtain the recess 7. After the total removal of the core 10, the hollow part 1 is obtained ( Fig. 1 ).

As is apparent from the foregoing description, the method according to the invention makes it possible to obtain a hollow forged part. In the example shown, the part 1 is a connecting rod. It is clear that the object of the invention can be implemented for different parts with various shapes with one or more opening recesses.

Claims (8)

1. A method for manufacturing hollow forged parts (1), characterized in that it includes the following steps:

   - making a core (10) in lost material, the shape of which corresponds to the inner shape of the part to be obtained, to within the deformation undergone during forging,

   - positioning the core (10) in a foundry mold,

   - casting a metal around the core (10) in order to completely encase the core with view to obtaining a blank (18),

   - sealing the blank (18), so that the core (10) is found completely isolated with regard to the outside,

   - forging the blank (18) in order to obtain the part with the desired shape,

   - and removing the core (10) from the part in order to obtain the hollow forged part (1).
2. The method according to claim 1, characterized in that it consists of providing the core (10) with at least one a gas discharge conduit (11).
3. The method according to claim 2, characterized in that it consists of ensuring the positioning of the core (10) in the mold by means of the gas discharge conduit (11).
4. The method according to claim 2, characterized in that it consists of ensuring the seal of the blank (18) by obturating each gas discharge conduit (11).
5. The method according to claim 4, characterized in that it consists of obturating each gas discharge conduit (11) with a stiffening member (20) are filling said conduit.
6. The method according to one of claims 2 to 5, characterized in that it consists of positioning the gas discharge conduit (11) in the core (10) in a location intended to form a housing (4) for the part.
7. The method according to claim 6, characterized in that it consists of positioning the gas discharge conduit (11), so that it extends protruding on either side of the core so as to form a through-housing (4) in the part.
8. The method according to claim 1, characterized in that it consists of ensuring the preheating of the blank (18) before its forging.

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