Method for producing parts having complex shapes from preforms by pressure sintering

Abstract

The present invention relates to a method for manufacturing a part (3) with a complex shape by successive layer deposition using 3D additive printing and pressure sintering techniques. The method comprises the following steps: In a first step, a mold (1) is produced by digitally controlling the creation of successive deposited layers from a material selected from the group consisting of metal alloys, ceramics, composites, and porous or powder materials based on melt-down materials using a three-dimensional 3D additive printing method. In a subsequent step, a preform (1) is obtained by molding a porous or powdered material to be densified in the mold (1) and then placed in the mold (2). The mold (2) is then filled with a porous or powdered sacrificial material (13) in addition to the preform (1). The mold (2) is then subjected to uniaxial densification pressure sintering (10) and finally removed from the mold (2) to produce the finished part (3). [Selected Figure] Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing parts having complex shapes by pressure sintering from preforms produced by additive processes.

[0002] The invention relates to the field of component manufacturing, in particular the manufacture of industrial machine parts by densifying porous or powdered materials, including all techniques of densification, whether uniaxial or multiaxial, under isostatic pressure load, such as, in particular, hot isostatic pressing, high pressure discharge sintering, also known as SPS (spark plasma sintering), or selective laser sintering.

[0003] More specifically, in the SPS sintering technique, a volume of ceramic, polymer or metal powder is consolidated in a conductive mold to rapidly obtain a dense material with an ultrafine structure. Such consolidation is achieved by simultaneous application of a load (e.g., high uniaxial pressure on the mold of about 100 MPa and heat from a high-intensity pulsed direct current of 500-10,000 A in the mold, which allows the total sintering of the powder to be completed in just a few minutes).

[0004] The main advantage of this SPS sintering technique is that the high temperature ramp rate and relatively short residence time at high temperature allows densification of the material with no or very little crystal growth. [Background technology]

[0005] Especially for parts with complex shapes with substantial thickness variations, the uniaxial pressure in SPS sintering technique has the disadvantage of inhomogeneous densification due to the removal of non-uniform material between regions of different thicknesses in a limited space and time. In general, complex shapes refer to shapes with various curvatures with thickness variations or uniform thickness, shapes with curvature variations or constant curvatures while having large thickness variations, and / or shapes with geometric imperfections.

[0006] To compensate for the drawback of non-uniform densification, US Pat. No. 5,399,633 proposes adding a deformation boundary layer between the powdered (or porous) material and the opposing surface of a custom-made mold for producing the part.

[0007] However, sintering techniques also present problems when using molds or mold counter faces that are not easily removable from the mold, especially when the part has a complex shape, especially when it has undercuts that make it difficult to remove, or tapered features that make it difficult to remove from the mold without breaking the part.

[0008] The counter surface may be a printed plate obtained by pressing a layer of ceramic powder agglomerated with a binder onto the counter surface covered with an inert interface, or by consolidating ceramic powder onto a polymer preform. These techniques have substantial limitations in terms of the geometry that can be easily removed due to problems with complex shapes such as undercuts and surface conditions of the counter surface that need to be covered by the interface.

[0009] In order to create counter faces that fit the undercuts and can be removed from the mold, it was necessary to have multiple counter faces to avoid problems during removal from the mold. This required custom tooling for each counter face, which increased the design and machining process. Also, assembling many counter faces could lead to defects (finished part shape mismatch, early cracks, material loss, etc.).

[0010] It is known practice to use a multiaxial hydrostatic pressure loading technique known as HIP (Hot Isostatic Pressing) to densify materials and thereby produce parts with complex shapes. Such a technique is shown, for example, in US Pat. No. 5,399,366, which proposes using a densification oven filled with a pressure transfer material that completely covers the exterior of the object preformed by additive printing. This allows to obtain exteriors and internal volumes with different densities. Such an approach, even in the HIP technique, is not space-saving, complex and time-consuming.

[0011] Alternatively, in US Patent No. 5,339,633, a mold for manufacturing parts by HIP is made using a sacrificial mold for molding the part, covered with ceramic. The mold is removed to form a cavity, and a metal layer is applied to the ceramic, thereby forming a mold that is filled with metal powder and placed in a vessel for HIP. This approach is still complicated and requires HIP. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] French Patent Application No. 3042992 [Patent Document 2] International Publication No. 2016 / 189312 [Patent Document 3] International Publication No. 2016 / 030654 Summary of the Invention [Problem to be solved by the invention]

[0013] The present invention aims to solve these problems and proposes the use of component preforms manufactured by digitally controlled additive techniques in combination with uniaxial densification. [Means for solving the problem]

[0014] More specifically, the object of the present invention is to provide a method for manufacturing parts with complex shapes by successive layer deposition using the techniques of 3D additive printing and pressure sintering. The method comprises the following steps: In a first step, a mould is made from a material selected from metal alloys, ceramics, composites, porous or powdered materials based on melted materials. Using a digitally controlled three-dimensional (3D) additive printing method, successive layers are deposited from a material selected from metal alloys, ceramics, composites, porous or powdered materials based on melted materials to generate a preform. In a subsequent step, the preform obtained by shaping the porous or powdered material to be densified in a mould is placed in the mould. The mould is filled with a sacrificial material, either porous or powdered, in addition to the preform. The mould is then uniaxially densified and pressure sintered, and finally removed from the mould to produce the finished part.

[0015] In particular, the 3D additive printing method is selected from stereolithography, binder jet, controlled extrusion, fused filament processing, inkjet printing, and aerosol jet printing.

[0016] Furthermore, uniaxial densification allows for easier densification while still providing physicochemical homogeneity and precision in part dimensions, as compared to the three-dimensional isostatic densification of HIP. Effect of the Invention

[0017] The effects of the present invention include the following. · The sacrificial material is a material selected from ceramic, silica, metal silicate, and composite materials. The ceramic may be selected from powdered YSZ (yttria stabilized zirconia), ATZ (alumina toughened zirconia), ZTA (zirconia toughened alumina), and alumina exhibiting a degree of densification ranging from 40% to 80%. An interface layer may be placed on at least one surface of the preform prior to placing the preform in the mold to prevent reaction between the preform and the sacrificial material. The preform, interface layer and sacrificial materials exhibit similar densification behavior at the start and end temperatures of sintering.

[0018] During 3D additive printing, a step of extracting the binder from the preform can be effectively performed by performing a heat treatment at a temperature of 200°C to 600°C and a temperature increase rate of 0.1°C / min to 1°C / min according to the material of the opposing surface. In the above step, it becomes possible to extract the organic compound contained in the material during the preparation of the opposing surface.

[0019] Furthermore, following the step of removing the binder, a pre-sintering step may be carried out. In the pre-sintering step, the opposing surfaces are heat-treated at a high temperature of 600°C to 1,500°C according to the material of the opposing surfaces. This starts densifying the opposing surfaces, increasing their mechanical strength and facilitating the formation of an interface.

[0020] In a first embodiment, the mold is filled with a porous or powdered sacrificial material before or after depositing the preform directly into the mold, prior to densification.

[0021] In another embodiment, the method involves additively printing a mold from a burn-off material, such as a wax or resin with a low melting point. A counter surface of porous or powdered material is then created around the mold. Once the burn-off material is removed, it is placed into a pressurized sintering mold, and the counter surface is filled with densified material to form a preform that conforms to the mold before sacrificial material is added to the mold. After pressurized sintering is performed, a part is removed from the counter surface.

[0022] In the drawings, identical elements are given the same reference numerals, which are referenced at one or more points in the description of the element they represent.

[0023] Further information, features and advantages of the present invention will become apparent from the following non-limiting description, taken in conjunction with the accompanying drawings, in which: [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is a perspective view showing an example of main steps (1A to 1F) in a method for manufacturing a part having a complex shape from a preform according to a first embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view illustrating, in a simplified manner, an example of main steps (2A to 2G) in a method for producing a part having a complex shape from a preform according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] An example of the main steps 1A to 1F of the method according to the invention for producing a part with a complex shape from a preform is shown in FIG. 1 as cross-sectional views. In step 1A, a porous metal mold 1 of the production part is formed by 3D additive printing, in this example by jetting in successive layers by binder jetting. The mold reproduces a configuration previously stored in the control of a jet system (not shown) and constitutes the preform of the part obtained after sintering. The preform defines the shape of the part to be produced by the production method according to the invention.

[0026] The material of the component, prior to processing, is a powdered or porous material based on a metal alloy, in particular in this example a titanium alloy, a titanium-aluminium alloy, a stainless steel or a nickel-based superalloy, for example of the Rene family.

[0027] Advantageously, the binder is removed from the preform in the shape of mold 1 by heat treatment at a temperature between 200°C and 600°C, in this example 400°C, and at a temperature increase rate of 0.1°C / min to 1°C / min, in this example 0.5°C / min. In this step, organic compounds that have entered the ceramic powder during the creation of the opposing surface by 3D printing can be removed.

[0028] Preferably, after removing the binder, pre-sintering is performed. Pre-sintering is a process in which the preform 1 is treated at a higher temperature, for example, 600°C to 1,500°C depending on the material used, in this example, 1,200°C. The heat treatment makes it possible to start densifying the opposing surfaces. This increases the mechanical strength and facilitates the application of one or more interface layers, as described below.

[0029] Advantageously, in step 1B, a graphite interface layer 11 is uniformly deposited by spraying on the outer face 1e (see step 1C) or on the inner face 1i (see step 1A) of the preform 1. Alternatively, the graphite layer is sprayed on both sides 1i and 1e of the preform 1. The graphite layer 11 prevents any reaction between the mould 1 and the powdered sacrificial material, ceramic in this example. The sacrificial material is deposited in a later step in order to facilitate the final removal from the mould.

[0030] In step 1C, the preform 1 covered with the graphite layer 11 is placed in the SPS press sintering mold 2 on a base of previously placed sacrificial material of ceramic powder (not shown). Then, sacrificial powder 13 is placed in the mold 2, which is then filled with the material to be densified (step 1C). The sacrificial powder makes it possible to make up for the densification difference during the subsequent sintering.

[0031] The mold 2 is then subjected to SPS sintering (load 10 of 50 MPa, direct current of 3,000 amps), which densifies the material mass within the mold 2 (step 1E). Next, the sacrificial material 13 covering the part 3 is demolded and removed, and the densified part 3 is removed from the mold 2 (step 1F).

[0032] According to another embodiment, as shown in the schematic diagram of Fig. 2, which shows steps 2A to 2G, first a lost wax mold 4 is printed by stereolithography (step 2A). The mold has a conical shape in this example.

[0033] Then, in the illustrated example (step 2B), an elongated conical counter surface 5 is provided around the wax 4. Alternatively, the porous material forming the counter surface may be ceramic, silica, metal silicate, composite material, etc.

[0034] The wax 4 is removed from the opposing surface 5 by a suitable heat treatment that liquefies the wax. The liquefied wax flows out from the opening 51 provided in the bottom surface of the opposing surface cone 5 (arrow F1). This creates a complete cavity (step 2C).

[0035] To facilitate removal from the mould and to prevent any reaction between the counter face and the material to be densified, the inner surface 5i of the counter face 5 is advantageously covered with a graphite interface layer 7. Alternatively, a graphite layer is sprayed onto at least one of the faces 5i and 5e of the counter face 5.

[0036] In step 2D, the counter face 5 is filled with a powder material that is densified to fit the wax pattern and constitutes a preform 6 of the production part. A graphite layer 7 on the inner side 5i of the counter face 5 then covers the preform 6.

[0037] Advantageously, the binder removal and pre-sintering steps are carried out under similar conditions, temperatures and temperature ramp rates as mentioned above.

[0038] Then, the opposing surface 5 and the preform 6 are placed into the SPS sintering mold 2 (step 2E), and a sacrificial material 9 is added to the mold 2. In this example, the sacrificial material is a material selected from ceramics, silica, metal silicates, composites, and the like.

[0039] SPS densification is carried out by applying a load of 10 and a direct current of 3,000 amps (step 2F). The sacrificial powder can make up the densification difference during sintering.

[0040] Next, the sacrificial material 9 and the opposing surface 5 are removed, and the part 8 is extracted from the mold 2 by demolding (step 2G).

[0041] The invention is not limited to what has been described and illustrated, and therefore may also include interface layers made of porous or powdery materials other than graphite, such as yttrium oxide or boron nitride, among others.

[0042] The first embodiment is particularly suitable for hollow parts having concave and convex opposing surfaces, whereas the second embodiment is suitable for three-dimensional parts having both convex surfaces.

[0043] Regardless of the embodiment, the materials for the sacrificial material, counterface, preform, and interface layers must be similar in behavior with respect to the starting and ending temperatures of the sintering process. The ceramics used are YSZ (yttria stabilized zirconia), ATZ (alumina toughened zirconia), ZTA (zirconia toughened alumina), or alumina-based powders with densification levels in the range of 40% to 80%.

[0044] Further, the interface layer may be applied by a method selected from spraying, powder lamination bound with a binder (such as an aqueous solution or Rhodovil® liquid) that matches the powder, a sheet of suitable shape, and the like.

[0045] Additionally, in the first illustrated embodiment, the preform is directly molded. In general, the preform may be formed from the base form by other 3D additive printing methods and / or using other materials. This allows for the printing technique and printing materials to be modified to match the part material selection.

Claims

1. A method for manufacturing parts (3; 8) having complex shapes by successive layer deposition using the techniques of 3D additive printing and pressure sintering, comprising: - making a mould (1; 4) from a material chosen from metal alloys, ceramics, composites and porous or powder materials based on melt-down materials, by the production of successive deposited layers, with the aid of a digitally controlled three-dimensional (3D) additive printing method; and placing a preform (1; 6) obtained by shaping a porous or powdery material to be densified in said mold (1; 4) into a molding mold (2), the mould (2) is filled with a porous or powdered sacrificial material (13; 9) in addition to the preform (1; 6), the mould (2) is subjected to uniaxial densification and pressure sintering (10) and finally removed from the mould (2) to obtain the finished part (3; 8).

2. 2. The method of claim 1, wherein the 3D additive printing method is selected from stereolithography, binder jetting, controlled extrusion, fused filament processing, inkjet printing, and aerosol jet printing.

3. 3. A method according to claim 1 or 2, characterized in that a boundary layer (11; 7) is arranged on at least one face (1i, 1e; 5i, 5e) of the preform before it is introduced into the mould (2).

4. 4. The method of claim 3, wherein the preform, the boundary layer, and the sacrificial material materials exhibit similar densification behavior at the start and end sintering temperatures.

5. Method according to any one of the preceding claims, characterized in that the sacrificial material (13; 9) is selected from ceramics, silica, metal silicates, composites.

6. 6. The method according to claim 5, wherein the ceramic is selected from YSZ, ATZ, ZTA, and alumina that exhibits a degree of densification that is 40% to 80% higher than that before compression.

7. 5. A method according to claim 3, characterized in that the boundary layer is formed by a layer of a material selected from graphite, yttrium oxide and boron nitride.

8. 5. A method according to claim 3 or 4, characterized in that the boundary layer (11; 7) is applied in the form of a sprayed, powder-laid and appropriately shaped sheet.

9. A method according to any one of the preceding claims, characterized in that the metal alloy of the manufactured part is chosen from titanium alloys, stainless steels and nickel-based superalloys belonging to the Rene family.

10. 10. The method according to any one of claims 1 to 9, characterized in that, during 3D additive printing, a step of extracting the binder from the preform (1; 6) is carried out by carrying out a heat treatment at a temperature between 200 ° C. and 600 ° C. and at a temperature increase rate between 0.1 ° C. / min and 1 ° C. / min.

11. A method according to claim 10, characterized in that the step of removing the binder is followed by a pre-sintering step of heat treating the preform (1; 6) at a temperature between 600°C and 1,500°C.

12. The mold (1) made of a porous or powdery material is used to produce the preform before densification, 12. The method according to any one of the preceding claims, characterized in that the mould (2) is filled with a porous or powdery sacrificial material (13) before or after the introduction of the preform (1).

13. The mould (4) is produced from lost material by additive printing, and a counter surface (5) made of a porous or powdery material is formed around the mould (4); Once the lost material has been removed, the counter surface (5) is filled with material to be densified, which will fit into the mold (4) to form the preform (6) before being introduced into the mold (2) for pressure sintering, The sacrificial material (9) is added to the mold (2), The method according to any one of the preceding claims, characterized in that after the pressure sintering (10), the part (8) is removed from the counter face (5).

14. The mould (4) is produced from lost material by additive printing, and a counter surface (5) made of a porous or powdery material is formed around the mould (4); Once the lost material has been removed, the counter surface (5) is filled with material to be densified, which will fit into the mold (4) to form the preform (6) before being introduced into the mold (2) for pressure sintering, The sacrificial material (9) is added to the mold (2), 4. The method according to claim 3, characterized in that after said pressure sintering (10), said part (8) is removed from said counter face (5).

15. the material of said facing surface (5) is selected from ceramic, silica, metal silicate and composite materials; 15. The method according to claim 14, characterized in that the material exhibits a similar densification behavior at the start and end temperatures of sintering as the materials of the preform (1; 6), the sacrificial material (13; 9) and the boundary layer (7).

16. The method of claim 15, wherein the ceramic is selected from YSZ, ATZ, ZTA, and alumina that exhibits a degree of densification in the range of 40% to 80% higher than before compression.

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