EP1693127B1 - Method of upsetting a metallic billet and jacket - top set for carrying out said method - Google Patents

Description

The invention relates to a crushing process for the machining of a metal slug and a set of a jacket and a cover for the implementation of the method.

Forged metal parts are generally obtained by forging slugs, or billets, which are rough blanks of semi-finished, generally bar-like metal parts, used as basic elements for forging formation of the part to be obtained. their volume corresponding to the volume of the latter, plus the volume lost during forging. For example, in a turbojet, the fan disks or the compressor drums are obtained by forging metal slugs.

The invention is particularly applicable to the processing of metal slugs from powder metallurgy, but more generally relates to the processing of metal slugs. It is especially recommended for wrought materials whose forgeability is difficult, especially because of small acceptable temperature ranges.

Metal slugs from powder metallurgy are generally obtained by spinning a container containing the powder material. During spinning, the container is forced, by a press, to pass into a lower section orifice to his, during which the material forms a dense bar. The machining of the container enveloping the material - and to which it was welded during the spinning operation - makes it possible to obtain the piece ready to be wrought. The current constraints impose a maximum diameter, for a metal slug resulting from powder metallurgy, less than 300 mm, typically of the order of 230 mm.

Furthermore, in the field of aeronautics, the safety criteria are binding and require controls at all stages of manufacture. The slugs must in particular be checked, for example by ultrasound, in order to detect the presence of inclusions or defects in the metal, which are at the origin of cracks during forging and possibly breaks in the finished part. The The maximum allowable defect size requirements in billets, imposed by engine manufacturers, are becoming more stringent. The suppliers of plots thus limit the diameter of the plots, so as to ensure a quality ultrasonic control and to respect the criteria imposed by the manufacturers. Typically, again, this diameter is less than 300 mm, for nickel-based metal slabs or cobalt from powder metallurgy.

If the finished parts of the turbojet engine are of large volume, the slugs must therefore be of great slenderness, typically greater than 2.8, often of the order of 7 to 10, to compensate for their small section.

Milling refers to the hot deformation of a metal part to obtain an increase in its diameter and a decrease in length, at equal volume. The drawing can be obtained by upsetting, that is to say by applying a constraint in the direction of the length of the metal slug.

For metal sludges from powder metallurgy, a slenderness greater than 2.8 imposes a contained extrusion of plots, in order to corrode them to obtain slugs whose length to diameter ratio is reduced. The ratio is reduced to a value for which it is possible to forge, stamp or even repress without being contained laterally, without risk of buckling and creating imperfections in the metal fibers.

Contoured content means an upset in which the billet is protected laterally, none of its surfaces being in contact with the open air. Alloys from powder metallurgy require the most isothermal crushing possible, the temperature typically not to fall by more than 50 or 100 ° C during crushing, the risk of appearing deep cracks or tears in the material . The operating temperature is between the plasticity temperature and the melting temperature of the alloy, which makes it possible to forge the alloy, and limited by a maximum value defined to ensure control of the microstructure of the alloy. Furthermore, the diameter of the wrought mass should not be too small, to avoid the creation of imperfections in the material. It must be arranged so that the slenderness is less than 2.8.

The prior art teaches, for this purpose, to sheath the billet in a steel tube, which increases its diameter and provides thermal protection. The whole, the piece and the tube, is then returned to the open air, since it has a sufficient diameter. During such a push-back, the billet and the steel tube will establish a metallic connection between them, comparable to a binding link. It is therefore necessary after machining, to machine all, for example by machining on a lathe, to remove the steel to find a piece containing only the alloy from the powder metallurgy. Such machining is expensive, on the one hand, and results in a loss of material of the billet, on the other hand. This loss of material is all the more important that in general, the interface between the billet and the tube is relatively tormented, which imposes a larger machining for safety.

It would be desirable not to use steel sheath. But in this case, it would be necessary to use a very hot tool, which would generate cracks and cracks of the piece, which would then have to be removed, for those accessible, by grinding.

The invention aims to overcome these disadvantages.

To this end, the invention relates to a crushing method for the machining of a metal slug, of cylindrical shape and provided with a coating, characterized in that the slug is placed, in the length direction, in a liner whose internal wall provides a space with the side surface of the billet, the set, the billet and the shirt, placed in a crushing pot, it exerts a force of pressing on the slug on at least one of its transverse surfaces, until a determined slenderness is obtained, and the slice is separated from the liner.

Thanks to the invention, the extrusion of the slug is well contained, but only the slug is discharged, which is allowed by the space provided by the inner wall of the liner. Due to the coating and the difference in section, the material of the jacket, for example steel, is not welded or seized with the piece, which avoids machining to separate them after the operation. Thus, there is no loss of billet material or additional costs associated with subsequent machining. The resulting slug obtained thus has a very good surface condition and a very good metallurgical quality.

Advantageously, the billet is of cylindrical shape.

Obtaining a cylindrical shaped slug is advantageous because it allows a forging, a crushing or a subsequent matriculation easier.

The invention also relates to the implementation of the method described above the use of a cylindrical liner, intended to receive a metal billet, having a bottom, from which a cylindrical side wall rises, the bottom having a footprint of centering and preforming a piece.

The invention also relates to an assembly of a jacket and a lid, comprising a jacket as described above and a lid, in the form of a circular-shaped plate whose section is substantially equal to the inner section of the shirt, very slightly lower.

The invention is particularly applicable to the extrusion of alloy slugs from the powder metallurgy, but more generally applies to the extrusion of any metal piece.

• la figure 1 représente une vue en coupe, schématique , d'un lopin métallique logé dans la chemise de l'invention ;
• la figure 2 représente une vue en coupe, schématique, du lopin et de la chemise de la figure 1, logés dans un pot de refoulage avant le refoulage du lopin ;
• la figure 3 représente une vue en coupe, schématique, du lopin et de la chemise de la figure 1, logés dans un pot de refoulage, en fin de refoulage du lopin et
• la figure 4 représente une vue en coupe, schématique, du lopin et de la chemise de la figure 1, après refoulage du lopin.

The invention will be better understood with the aid of the following description of the preferred embodiment of the invention, with reference to the attached plates, in which:

• Figure 1 shows a schematic sectional view of a metal billet housed in the jacket of the invention;
• FIG. 2 is a diagrammatic sectional view of the billet and the liner of FIG. 1, housed in a crushing pot before the billet is pushed back;
• FIG. 3 is a diagrammatic sectional view of the billet and the liner of FIG. 1, housed in a crushing pot, at the end of the extrusion of the billet and
• FIG. 4 represents a schematic sectional view of the blank and the liner of FIG. 1, after the billet has been pushed back.

The method of the invention relates to the extrusion of a metal lopin 1, in this case a lopin 1 consisting of a nickel-based alloy or cobalt from the powder metallurgy. This piece 1 is in a cylindrical form. It has a specific section and a specific length. Its slenderness, that is to say the ratio of its length to the diameter of its section, here is greater than 2.8 and may be of the order of 10 or more. The billet 1 is coated, by vitrification, with an enamel layer.

The billet 1 is housed in a jacket 2, of cylindrical shape. This jacket 2 has a bottom 3, from which rises a cylindrical side wall 4, whose thickness is relatively thin, relative to the diameter of the jacket. The section of the cylinder formed by the inner surface of the side wall 4 is greater than the section of the billet 1. In this case, for a piece 1 whose diameter of the section is approximately equal to 235 mm, the diameter of the section internal of the liner 2 is approximately equal to 300 mm, while the thickness of its side wall 4 is approximately equal to 20 mm. The liner 2 comprises, and here is made of a mild steel, strong enough for the application for which it is intended. Such a steel is inexpensive, which is preferable because of the destruction to which the jacket 2 is intended. Moreover, it can be recycled, once the shirt 2 destroyed. In the case in question, the liner 2 is formed by welding its cylindrical side wall 4, here mild steel, the bottom 3, here nickel alloy.

The piece 1 is inserted into the jacket 2 by its open end. The bottom 3 of the liner 2 comprises a centering footprint 5 of the blank 1. A lid 6, in the form of a circular-shaped plate, the section of which is substantially equal to the internal section of the liner 2, very slightly lower, is inserted through the open end of the liner 2 to cover the billet 1. The cover 6 is here made of a nickel alloy. This cover 6 also comprises, on its lower surface, that is to say its surface in contact with the billet 1, a centering footprint 7 of the billet 1. The cover 6 is then held in position by means of a weld 8 made between its upper surface and the inner wall of the liner 2. This weld 8 is not shaped so as to be very strong because it fulfills only a function of holding the lid in position and not sealing; this weld can also be a spot weld. The assembly 9 comprising the billet 1, the sleeve 2 and the lid 6 is thus secured, the weld 8 can be broken by the application of sufficient force. This set 9 is ready to use and can be stored in this waiting. It can also be handled.

Before the upsetting operation, the assembly 9 is placed in an oven, where it is heated to the temperature required for the upsetting. The determination of this temperature makes it possible to control the deformation of the material and the microstructure of the alloy of the billet 1 during the upsetting operation which is described below. In this case, for a piece 1 nickel-based alloy, this temperature can be between 900 ° C and 1200 ° C, for example be of the order of 1100 ° C.

The assembly 9 is then placed in a discharge pot 10, made of steel and having a cylindrical housing 11 whose section corresponds to the outer section of the jacket 2. During handling, the mechanical strength of the steel of the shirt 2 has certainly decreased because of the temperature, but remains sufficient to maintain its geometry. The upsetting pot 10 has also been previously heated, in this case at a temperature of the order of 400 to 500 ° C. It is installed on a hydraulic press, comprising a punch 12 which is supported on the upper surface of the cover 6 of the assembly 9. This punch 12 is movable in vertical translation, driven by a movable upper table of the hydraulic press. Its contact surface with the lid 6 is identical, or slightly smaller in size, to the section of the latter.

The operation of upsetting the billet 1 is then implemented. The punch 12 is driven by a conventional hydraulic mechanism of the table of the hydraulic press to be lowered at a predetermined speed and thus exert a stress on the billet 1, in the direction of its length, through the cover 6 which goes down with the punch 12, the weld 8 has been broken by the stress exerted by the punch 12. The billet 1 being at a temperature above its plasticity temperature (but lower than its melting temperature), it follows a plastic deformation of material of lopin 1 which results in a decrease in its length and an increase in its section. The speed of descent of the punch 12 is determined, in cooperation with the choice of the temperature of the material, so as to control the deformation of the material and the evolution of its microstructure. In this case, it is chosen for a nickel-based alloy of the order of 10 mm / sec. This speed can be scalable during the upsetting operation.

During the upsetting, the diameter of the lid 6 being slightly less than the internal diameter of the liner 2, the air filling the gap between the lopin 1 and the inner wall of the liner 2 is expelled by the interstice between the lid 6 and the liner 2.

The enamel on which the lopin 1 is coated provides a triple function, lubricating the device, protection against oxidation and protection between the billet 1 and the jacket 2. Thus, during the extrusion, the enamel forms a pasty interface which avoids, at the end of upsetting, when the walls of the billet 1 come into contact with the inner wall of the liner 2, that the billet 1 does not weld to this wall. Moreover, the same function is ensured during the entire upsetting operation at the cover 6 and bottom 3 of the jacket 2.

It is noted that, unlike the methods of the prior art, only lopin 1 is here repressed. The jacket 2 is not deformed by the operation and provides a contention function of the lopin 1 and barrier, or buffer, thermal between the billet 1 and the upsetting pot 10. Thus, even if the temperature of the upsetting pot 10 is reduced, the temperature of the billet 1 is not significantly affected. Furthermore, the billet 1 is held centered by the indentations 5, 7 of the bottom 3 of the liner 2 and the lower surface of the lid 6, respectively. These impressions 5, 7 can also fulfill a function of preforming the billet 1, and thus be arranged to preform the ends of the billet 1 depending on the shape that will be given to the final part, by new upset and / or stamping and / or forging the billet 1, once the upsetting operation is completed.

The upsetting operation is stopped when a certain effort is reached on the billet 1. The billet 1 then fills substantially the entire section of the liner 2, its section having increased and its length having decreased accordingly, since it does not there is no change in volume. In this situation, the punch 12 is in the low position, as can be seen in FIG. 3. The billet 1 has been corrugated by upsetting.

At the end of the upsetting, the punch 12 can provide additional pressure maintenance of the assembly, for example for about ten seconds, to ensure that the geometry of the wrought billet is good, especially that the material fills the well. housing assembly 11, including its corners.

Referring to Figure 4, the assembly 9, lopin 1, the liner 2 and the lid 6 in the low position, with the billet 1 repressed, is then extracted from the crushing pot 10. This operation is performed in any way in fact classic. For this purpose, a jack may for example form the bottom of the housing 11 of the upsetting pot 10 and be driven upwards after the upsetting operation, and the punch 12 having been previously driven upwards, in order to extract the assembly 9 of the housing 11. Any other method of extraction is conceivable.

The assembly 9 is then cooled. This can be done simply by letting it cool in the open air. Once a desired temperature is reached, the billet 1 is removed from the jacket 2. Since these two elements have not been welded to one another, this operation is very easy. For example, after having cut the upper portion of the liner 2 above the lid 6, it is possible to make two opposite longitudinal slots, by milling, along the side wall of the liner 2, to put a wedge in order to separate the two wall portions with respect to one another and thus be able to remove the billet 1 from the liner 2. The slot may also be made at the lid 6 or bottom 3 of the liner 2, in order to remove one of these ends, the billet 1 can then freely slide in the direction of its length and out of the liner 2 thus opened. However, such a slot is generally not necessary because, because of the enamel, the piece 1 is not integral with the bottom 3 or the cover 6.

The piece 1 is just then treated to remove what is left of its enamel coating. This treatment can be mechanical, for example by shot blasting or steel wire, or chemical, for example by a soda bath.

The billet 1 thus crushed by upsetting can be either reprocessed again by the same process if necessary, or again repressed without being contained, stamped or forged, or several of these operations, in order to obtain the final piece.

It may be noted that the separation of the billet 1 from the liner 2 is here facilitated by the difference in the values of the expansion coefficients of the materials used. Thus, during cooling, the volume of a lopin 1 Nickel alloy will be more strongly reduced than that of a steel jacket 2, which creates a gap between the two and facilitates their separation.

Thanks to the process of the invention, the extrusion of the slug is well contained, which is advantageous in some applications, for example the extrusion of a relatively small diameter slug from the powder metallurgy. Only the piece is pushed back and it is easily removed from its protective jacket at the end of the process. The wrought piece is obtained without loss of material or additional costs related to a subsequent machining, and thus has a very good surface and a very good metallurgical quality. Different sections of plots can be obtained by adapting the section of the shirt and the crushing pot.

Claims (14)

1. Upsetting method for working a metal slug (1) of cylindrical shape and provided with a coating, characterized in that the slug (1) is placed, lengthwise, in a sleeve (2) the internal wall of which leaves a space with respect to the lateral surface of the slug (1), the slug (1) and sleeve (2) assembly (9) is placed in an upsetting container (10), and upsetting force is exerted on the slug (1) on at least one of its transverse surfaces until a determined slenderness ratio has been obtained, and the slug (1) is separated from the sleeve (2).
2. Method according to Claim 1, wherein the sleeve, intended to accommodate the metal slug, comprises an end wall (3) from which there rises a cylindrical side wall (4), the end wall (3) comprising an imprint (5) for centring and preforming the slug.
3. Method according to one of Claims 1 and 2, in which the slug (1) has an initial slenderness ratio in excess of 2.8.
4. Method according to one of Claims 1 to 3 in which the slug (1) is coated with an enamel, forming a pasty state during upsetting.
5. Method according to one of Claims 1 to 4 in which, with the sleeve (2) comprising an end wall (3), prior to placing the assembly (9) in the container (10), a lid (6) is placed in the sleeve (2), over the free end of the slug (1).
6. Method according to Claim 5, in which the lid (6) is welded to the sleeve (2) by a weld that will hold it in position and can be broken by the upsetting operation.
7. Method according to one of Claims 5 and 6, in which the end wall (3) and the lid (6) each comprise an imprint (5, 7) for centring and preforming the slug (1).
8. Method according to one of Claims 1 to 7, in which the operation of separating the slug (1) from the sleeve (2) involves an operation of milling at least one slot in one of the walls of the sleeve (2).
9. Method according to one of Claims 1 to 8, in which, prior to being placed in the upsetting container (10), the assembly (9) is heated.
10. Method according to one of Claims 1 to 9, in which the upsetting force is exerted by a punch (12) of a hydraulic press on which the upsetting container (10) is mounted.
11. Method according to Claim 10 in which the speed of the punch (12) follows a law in which its values are of the order of 10 mm/sec and, at the end of the method, the punch (12) sustains pressure on the slug (1).
12. Method according to one of Claims 1 to 11 in which the material of the sleeve (2) comprises a mild steel.
13. Method according to one of Claims 1 to 12, in which the slug (1) originates from powder metallurgy.
14. Sleeve and lid assembly for implementing the method of claim 1, characterized in that it comprises a sleeve (2), comprising an end wall (3) from which there rises a cylindrical side wall (4), the end wall (3) comprising an imprint (5) for centring and preforming a slug, and a lid (6) in the form of a plate of circular shape, the cross section of which is more or less equal to the internal cross section of the sleeve (2), very slightly smaller.

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