METHOD FOR THE PRODUCTION OF PARTS MADE FROM METAL OR METAL MATRIX COMPOSITE AND RESULTING FROM ADDITIVE MANUFACTURING FOLLOWED BY AN OPERATION INVOLVING THE FORGING OF SAID PARTS

Abstract

A method of manufacturing a piece of metal alloy or of metal matrix composite materials consisting of making a preform by additive manufacturing by adding material in successive layers, and subjecting the preform to a forging operation taking place in a single step and between two dies to deform said preform to a final shape of the piece to be obtained.

Claims

1. A method of manufacturing a piece of metal alloy or of metal matrix composite materials, said method comprising: making a preform by additive manufacturing by adding material in successive layers; and subjecting the preform to a forging operation taking place in a single step and between two dies defining a die cavity, to deform said preform to the final shape of the piece to be obtained, wherein the preform contains at least one first zone, called powder area, in which a powder material is not bonded together or is partially consolidated, and at least one second zone, called shell, comprising bonded material enclosing the powder area, wherein the forging operation is carried out such that the deformation of the preform via the two dies bonds the powder material of the powder area in solid phase, wherein the forging operation is carried out by applying a true strain to the shell superior or equal to 1.5, wherein the pressure inside the die cavity at the end of the forging operation is between 30 MPa and 700 MPa.

2. A method according to claim 1, wherein the true strain applied to the shell is superior or equal to 1.7.

3. A method according to claim 1, wherein the true strain applied to the shell is inferior or equal to 8, preferably inferior or equal to 4, more preferably inferior or equal to 3, and even more preferably inferior or equal to 2.

4. A method according to claim 1, wherein the forging step is carried out by applying a true strain to the powder area superior or equal to 2, provided that the true strain applied to the powder area is superior to the true strain applied to the shell.

5. A method according to claim 1, wherein the forging step is carried out by applying a true strain to the powder area inferior or equal to 10, preferably inferior or equal to 6, preferably inferior or equal to 3, more preferably inferior or equal to 2.5, provided that the true strain applied to the powder area is superior to the true strain applied to the shell.

6. A method according to claim 1, wherein the pressure inside the die cavity at the end of the forging operation is between 30 MPa and 400 MPa, more preferably between 100 MPa and 400 MPa, and more preferably between 100 MPa and 300 MPa.

7. A method according to claim 1, wherein the piece of metal alloy is of an alloy based on iron, aluminum, nickel, titanium, chromium, or cobalt.

8. A method according to claim 1, wherein the piece of composite materials is of a titanium-titanium carbide alloy, of an aluminum-alumina alloy, or of an aluminum-silicon carbide alloy.

9. A method according to claim 1, wherein the forging operation for forging the preform obtained by additive manufacturing is performed semi-hot or cold or hot.

10. Pieces or parts obtainable by implementing the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Further features and advantages of the invention will become more apparent from the detailed description to follow, with reference to the appended drawings, in which:

[0046] FIG. 1 is a schematic perspective view of a preform having a cubic form, obtained by additive manufacturing, comprising a powder area enclosed within a shell;

[0047] FIG. 2 is a schematic side view of the preform of FIG. 1;

[0048] FIG. 3 is a photograph of several cubic preforms corresponding to that illustrated in FIGS. 1 and 2;

[0049] FIG. 4 is a graph that represents the evolution of the deformation of the powder material (powder area or powder zone) in function of the deformation applied onto the shell by the dies;

[0050] FIG. 5 is a photograph of the powder area after the forging operation, when the deformation applied onto the shell by the machine is 1.1;

[0051] FIG. 6 is a photograph of the powder area after the forging operation, when the deformation applied onto the shell by the machine is 1.5.

DETAILED DESCRIPTION

[0052] According to the method of the invention, the forging step that combines material deformation and a significant increased pressure at the end of the process, as described previously, makes it possible to reclose and to re-bond the microporosities present in the powder area of the preform by bonding the various layers of the additive structure. This leads to improved ductility and fatigue strength.

[0053] Moreover, thanks to the forging step, we can bond the unbonded or partially consolidated powder.

[0054] In order to provide more details about the process parameters, the Applicant carried out a set of experimental trials and numerical simulations of the forging of preforms obtained by additive manufacturing.

[0055] The test protocol comprises: [0056] a. making testing preforms by additive manufacturing, the testing preforms enclosing unbonded powder material; [0057] b. subjecting the testing preforms to a forging operation taking place in a single step and between two forging dies, by applying different amounts of true strain to the preforms, and [0058] c. cutting the forged parts in and observing the state of the powder zone.

[0059] The testing preforms 1 were cubes of 10 mm×10 mm×10 mm. The testing preforms comprised a solid, bonded outer shell 2 formed via direct metal laser sintering (DMLS) additive manufacturing (on a ProX 200 additive manufacturing machine), enclosing an inner cavity 3 filled with non-bonded powder, referred to as powder area or powder zone, as illustrated in FIG. 1, FIG. 2 and FIG. 3. The testing preforms were made of TA6V titanium alloy, also known as Ti-6A1-4V (both the solid and powder zones).

[0060] Based on numerical simulations and tests conducted by the Applicant, the true strain in the preform during the forging step must be superior or equal to 1.5.

[0061] Indeed, as described previously, during the forging process, different deformation levels occur inside the part.

[0062] For the tested preforms that were subjected to a die forging machine true strain deformation of 1.1, which corresponds to a true strain of 1.1 for the shell and 1.7 for the powder area, as presented in the graph of FIG. 4, we note that most of the powder is consolidated, but some porosities 4 remain in some regions, as shown in the photograph of FIG. 5.

[0063] For the tested preforms that were subjected to a die forging machine true strain deformation of 1.5, which corresponds to a true strain of 1.5 for the shell and 2.1 for the powder area, as presented in the graph of FIG. 4, no defects such as porosities remain in the powder. Rather, (all) the powder in the powder area is fully bonded, i.e. uniformly bonded, as shown in the photograph of FIG. 6.

[0064] The upper limit of the true strain in the preform during the forging step may be adapted depending on the dimensions and structure of the preform. For example, the true strain may be about 5, 8, or 10. Preferably, the true strain is inferior or equal to 5.

[0065] Regarding the pressure evolution, depending on the forging machine power, the pressure inside the die cavity increases at the end of the forging process and must reach between 30 MPa and 700 MPa, preferably between 30 MPa and 400 MPa, more preferably between 100 MPa and 400 MPa, and more preferably between 100 MPa and 300 MPa. Indeed, as explained previously, the combination of deformation and pressure increase allows to achieve a part of the desired shape wherein potential porosities existing initially in the preform are filled.

[0066] Comparatively, document US 2015/0283614 discloses the use of hot isostatic pressing (HIP) or pneumatic isostatic forging (PIF) to consolidate a powder inside a preform obtained by additive manufacturing. These two processes are based on the use of isostatic pressure which need specific facilities such as pressure vessel, gas or liquid to be pressurized, and facilities to increase and control the pressure level. These requirements lead to several constrains especially in terms of part dimensions and productivity. But most importantly, unlike the method of the invention, HIP and PIF processes involve less global deformation of the preform to obtain the final part or piece of the desired shape. Thanks to the forging process presented in the method of the invention, less initial powder density in the powder zone can be used. Indeed, with a large global deformation and a high true strain level the full densification of the powder may be achieved.

[0067] In addition, the open porosities (porosities in the shell) are very critical with the HIP and PIF process. Indeed, the use of pressurized gas with open porosities will push this gas inside the part which will create internal porosities due to gas entrapment. Using the forging process presented in the method of the invention we will avoid such problem.

[0068] The process presented by the Applicant takes profit of the usual forging process for the consolidation of the powder. Indeed, thanks to the material deformation and the pressure increase phenomena during the forging step the powder is consolidated.

[0069] The step of forging between two polished dies also enables the surface roughness to be drastically reduced, thereby making it possible to improve the fatigue strength and the surface appearance.

[0070] The tests that have been conducted appear very promising. No indication of either of the technologies known since 1983-1984 could have suggested combining them because the state in which the preform was obtained was different, the preform being obtained by casting in the “cast-and-forged” technology, whereas it is obtained by fusing (melting together) or sintering successive layers in additive manufacturing.

[0071] In the context of implementing the invention, the piece may be a piece of metal alloy (based on steel, iron, aluminum, Inconel, nickel, titanium, chromium-cobalt, etc.) or of metal matrix composite materials (titanium-titanium carbide, aluminum-alumina, aluminum-silicon carbide, etc.).

[0072] The forging second step of the invention for forging the preform obtained by additive manufacturing may be performed hot, semi-hot, or cold. The dies may optionally be polished.

[0073] The above-highlighted advantages and unexpected results with implementing the invention constitute a considerable development in processing pieces of metal or of metal matrix composite that are obtained by additive manufacturing.