EP3638440A1

EP3638440A1 - Method for producing a fine-walled metal part with complex geometry

Info

Publication number: EP3638440A1
Application number: EP18748963.8A
Authority: EP
Inventors: Aurelie SOULA; Pierre SALLOT
Original assignee: Safran Nacelles SAS; Safran SA
Current assignee: Safran Nacelles SAS; Safran SA
Priority date: 2017-06-13
Filing date: 2018-06-13
Publication date: 2020-04-22
Also published as: US11534825B2; WO2018229431A1; US20230118657A1; US20200114423A1; FR3067270B1; FR3067270A1

Abstract

The method for producing a fine-walled metal part with complex geometry comprises the steps of: mixing (5) a metal powder with a polymer binder in order to obtain a composite mixture, producing (6) a flexible composite sheet from the composite mixture, cutting (7), in the flexible composite sheet, a preform based on a contour of said metal part, applying the preform in a mould having a surface configured with a relief of said metal part, and then debinding and sintering (9) the preform in order to obtain said metal part.

Description

process for producing a metal piece of complex geometry with a thin wall

The present invention relates to a method for producing a metal piece of complex geometry with a thin wall.

By thin wall is meant according to the invention a wall having a thickness of less than 5 mm.

The invention relates in particular although not exclusively to the field of aeronautical parts, in particular parts for the production of a nacelle of an aircraft, and more particularly to aeronautical nozzles.

Document US 2006/0039817 discloses a process for producing thin composite sheets intended for the production of covers, in particular in the field of aircraft nacelles.

These thin composite sheets are made from an atomized metal powder from an alloy bar and mixed with a polymeric binder. The mixture obtained is converted into a flexible composite sheet which is then subjected to a debinding step, that is to say a step of removing the polymeric binder, followed by a sintering step, and if necessary followed by a hot isostatic compaction step. The thin composite sheet obtained has a very low ductility so that a piece with complex geometry can be obtained only by implementing long and expensive processes. In addition, when the part must have attached elements such as flanges or stiffeners, these elements must be fixed by riveting or welding.

An object of the invention is to provide a method for producing a metal piece of complex geometry thin wall can be implemented in a simple manner.

With a view to achieving this object, the invention proposes a method for producing a metal piece of complex geometry with a thin wall comprising the steps of: mixing a metal powder with a polymeric binder to obtain a composite mixture, to produce a flexible composite sheet from the composite mixture, cut into the flexible composite sheet a preform from a contour of said metal part, apply the preform in a mold having a face configured according to a relief of said metal part, and proceed to debinding and sintering the preform to obtain said metal part.

Thus, the shaping of the preform in the state of flexible composite sheet can be easily performed even for parts of complex geometry and the implementation Deboning and sintering operations subsequent to the shaping of the preform make it possible to fix the part in the desired geometry.

It will be understood that the debinding and sintering steps are carried out in the mold.

According to an advantageous version of the invention, the method further comprises a hot isostatic compaction step between the sintering step and the finishes. Thus, the densification obtained during sintering is accentuated.

According to a first embodiment of the invention, the mold is a half-shell mold having an abutment surface, and the mold is disposed during debinding and sintering steps so that the preform is maintained applied in the mold and against the abutment surface by simple gravity. Thus the end of the preform in contact with the abutment surface is a reference sizing for putting the metal part to the desired length by a simple sawing operation.

According to a second embodiment of the invention, the mold comprises a male mold part and a female mold part of which a first mold part comprises said face configured according to a relief of the metal part, and a second part of mold extends opposite the first mold portion at a distance therefrom greater than a thickness of the flexible composite sheet, and the mold has an abutment surface extending transversely to the male mold portion and to the female mold part and arranged relative thereto so that during debinding and sintering steps the preform comes into contact with the abutment surface by simple gravity. Thus, as in the first mode of implementation, the end of the preform in contact with the abutment surface is a reference sizing for putting the metal part to the desired length by a simple sawing operation.

According to other characteristics taken singly or in combination: the preform is oversized to compensate for shrinkage of the preform during debinding and sintering steps; the preform is superimposed so that said metal part is dimensioned by simple sawing operations; the method further comprises the step of securing an insert by taking an attachment portion of the insert sandwiched between two flexible composite sheet segments prior to the debinding step; the mold has a coefficient of expansion close to said metal part; the preform is glued prior to its application in the mold; at least one mold face facing a flexible composite sheet preform comprises contact pads separated by grooves, preferably taken in a direction perpendicular to a groove, the studs and grooves have dimensions which are related by the relation:

e / h <5, where e is the dimension of the pads in a direction perpendicular to a groove, and h is the width of the groove.

Other features and advantages of the invention will appear on reading the following description of two particular non-limiting embodiments of the method according to the invention, with reference to the attached figures among which:

FIG. 1 is a schematic perspective view of a nacelle exhaust nozzle produced by implementing the method according to the invention,

FIG. 2 is a block diagram illustrating the various steps of the method according to the invention,

FIG. 3 is a schematic perspective view of a mold for a first implementation of the method according to the invention, packed with a preform, before debinding and sintering,

FIG. 4 is a schematic sectional view along the plane IV-IV of FIG. 3,

FIG. 5 is a partial diagrammatic sectional view along the plane V-V of FIG. 3;

FIG. 6 is a perspective view similar to that of FIG. 3 after debinding and sintering,

FIG. 7 is a sectional view along the plane VI I-VI of FIG. 6,

FIG. 8 is a sectional view along the VIN-VIN plane of FIG. 6,

FIG 9 is a diagrammatic perspective view partially broken away of a second mode of implementation according to the invention, packed with a preform, before debinding and sintering,

FIG. 10 is a view similar to that of FIG. 9 after debinding and sintering,

FIG. 11 is a partial top view of a first embodiment of a configuration favoring the elimination of the binder,

FIG. 12 is a view similar to that of FIG. 11 of a second configuration promoting the elimination of the binder;

- Figure 13 is a view similar to that of Figure 11 of a third configuration promoting the elimination of the binder.

The method according to the invention is intended to allow the production of a metal piece of complex geometry with a thin wall, such as an exhaust nozzle 1 nacelle having a thin wall 2 provided with stiffeners 3. For a better understanding of the invention the thicknesses have been exaggerated compared to other dimensions of the parts.

The method comprises, in a manner known per se, a first step 4 of atomizing an alloy bar, here an alloy of titanium and aluminum, to produce a metal powder for mixing with a polymeric binder, such as only PBHT, PEG, PE, or an acrylic resin, for producing a flexible composite sheet. Preferably, in an application to an exhaust nozzle made from sheets of 1 mm thick, the particle size is between ΙΟμιη and 45μιη with a D50 of about 30μιη, and the mass load powder is of the order from 60% to 65% and the flexible composite sheet has a thickness of 1mm to 2mm depending on the intended use.

According to the invention, the method comprises cutting 7 of a preform followed by application 8 of the preform in a mold having a face configured according to a relief of the metal part to be produced. This step is followed by a debinding and sintering step 9 followed by hot isostatic compaction 10, itself followed by finishes 11, known per se, such as soldering, polishing, etc.

Figures 3 to 7 illustrate a first implementation of the invention in a half-shell mold 12 having a shoulder 13 forming an abutment surface for one end of the preform 14 having longitudinal edges 15 which are flush with the upper opening of the mold 12. The bottom of the mold 12 has grooves 16 configured to produce the stiffeners 3. The preform 14 is engaged in the grooves 16 forming folds 18. When debinding the grains of metal powder are released and can move for standardize, as illustrated in Figure 7 before being welded to each other during the sintering operation

The face of the preform 14 which faces the bottom of the mold 12 comprises a layer of adhesive 17 serving to hold the preform in the mold 12 before sintering. The rear edge of the preform 14 coincides with the rear edge of the mold 12.

An insert, here a flange 19, has an attachment portion 20 which is sandwiched between the rear end of the preform 14 and a flexible composite sheet segment 21. As illustrated in FIG. 5, prior to debinding and sintering, the composite sheet segment 21 forms a bridge over the fixing portion 20.

During debinding and sintering steps, the mold 12 is inclined downwards so that the front end of the preform 14 remains resting on the abutment surface 13. The withdrawal is therefore performed at the upper edge and the rear edge of the preform as illustrated by arrows in thick lines in Figures 6 and 7. The dimensions of the preform take into account this withdrawal so that once out of the mold the piece can be cut to obtain a half-piece of revolution which is welded edge to edge with an identical piece to obtain a piece of revolution.

During debinding and sintering, the composite sheet segment 21 deforms and intimately envelopes the fastening portion 20 as illustrated in FIG. 8.

To prevent the preform 14 from adhering to the mold 12 during debinding and sintering operations, the inner face of the mold 12 is preferably spray-coated with an anti-adhesion agent such as yttrine or alumina.

To avoid introducing excessive stresses between the preform and the mold at the time of sintering, the mold is preferably made of a material having a coefficient of expansion close to the flexible composite sheet. In the case of a flexible composite sheet of Ti-Al alloy, the mold is preferably made of Ti-Al alloy, but it can also be made of alumina or yttrine.

Figures 9 and 10 illustrate a second embodiment of the method according to the invention. The mold 22 this time comprises a female mold portion 23 and a male mold portion 24 which are nested one inside the other after packing of the female part with a preform 25 made of flexible composite sheet. the two mold parts are placed on a base 26 which forms a common abutment surface. In the example illustrated, the inner face of the female mold part is configured according to a relief of the metal part to be produced. An interval 27 of 10 μιη to 1000 μιη is then provided between the preform 25 and the male mold portion 24 to allow the gases from debinding to escape. During debinding the metal powder is squeezed under the effect of gravity so that the sintered metal thickness is equal to the distance between the facing faces of the male mold part and the female mold part.

To allow optimal debinding, and in particular an evacuation without accumulation of the gases resulting from the degradation of the binders, at least one mold face facing a flexible composite sheet preform comprises contact pads separated by grooves. Figures 11 to 13 illustrate three configuration examples, one in which the pads 28 are hexagonal, the second in which the pads 29 are ciculaires, and the third in which the pads 30 are rectangular. In addition, these three configurations have in common that: the non-load area fraction relative to the total area is 0 to 70%; taken in a direction perpendicular to a groove, the studs have a maximum dimension of 1 cm ;; the grooves have preferably a depth greater than 1 mm; and the grooves have a width h which is connected to the dimension of the studs by the relation:

Of course, the invention is not limited to the embodiments described and is capable of variants that will occur to those skilled in the art without departing from the scope of the invention as defined by the claims.

In particular, although the invention has been described in relation to an exhaust nozzle of an aircraft, the invention applies to other parts, including outside the aeronautical field

Although the invention has been described in relation to the production of parts of revolution, it is likely to apply to any part.

Although in the second mode of implementation the preform has been intended to be applied in the female mold part, it may be in the male mold part, in particular in the case where the desired relief extends on the face internal part.

Although the invention has been described in relation to a metal powder preferably having a particle size of between 10 μιη and 45 μιη, for the production of a sheet having a thickness of 1 mm, the particle size may be adapted to the application concerned. , and in particular to the desired surface state. By way of non-limiting example, for a sheet having a thickness of 2 mm, a particle size of 10 μιη to 120 μιη can be provided. The charge rate can be adapted to the particle size although a charge rate of 60% to 65% is generally satisfactory irrespective of the particle size of the metal powder.

Although the invention has been described in relation to a metal powder made from a Ti-Al alloy, the invention can be implemented from other alloys, especially alloys containing nickel.

Claims

A process for producing a metal piece of complex geometry with a thin wall comprising the steps of: mixing (5) a metal powder with a polymeric binder to obtain a composite mixture, producing (6) a flexible composite sheet from the composite mixture, characterized in that it further comprises the steps of: cutting (7) in the flexible composite sheet a preform (14) from a contour of said metal part, applying the preform in a mold (12; 23) having a face configured according to a relief of said metal part, and debinding and sintering (9) of the preform to obtain said metal part (1).

Method according to claim 1 characterized in that it further comprises a step (10) hot isostatic compaction between the sintering step and finishes.

A method according to claim 1 or claim 2, characterized in that the mold is a half-shell mold (12) having an abutment surface (13), and the mold is disposed during the debinding and sintering steps of that the preform is maintained applied in the mold and against the abutment surface by simple gravity.

Process according to claim 1 or claim 2, characterized in that the mold comprises a male mold part (24) and a female mold part (23), a first mold part of which has said face configured according to a relief of the part metal, and a second mold portion extends facing the first mold portion at a distance thereof greater than a thickness of the flexible composite sheet, and in that the mold has an abutment surface (26). extending transversely to the male mold part and to the female mold part and arranged with respect thereto so that during the debinding and sintering steps the preform comes into contact with the abutment surface by simple gravity.

Method according to any one of the preceding claims, characterized in that the preform is oversized to compensate for shrinkage of the preform during debinding and sintering steps.

A method according to any one of the preceding claims, characterized in that it further comprises the step of fixing an insert (19) by taking a fixing part (20) of the insert element sandwiched between two segments (14, 21) of flexible composite sheet prior to the debinding step.

7. Method according to any one of the preceding claims characterized in that the preform is glued prior to its application in the mold.

8. Method according to any one of the preceding claims, characterized in that the metal powder has a particle size of 10 μιη to 120 μιη, preferably a particle size of ΙΟμιη to 45μιη, more preferably with a D50 of 30μιη

9. Mold for carrying out the method according to any one of the preceding claims, characterized in that at least one mold face facing a flexible composite sheet preform comprises contact pads (29; 30; ) separated by grooves (31; 32; 33).

10. Mold according to claim 9 characterized in that taken in a direction perpendicular to a groove, the studs and the grooves have dimensions which are linked by the relation: