Parts with porous structures and related manufacturing methods

Abstract

To provide a part that reduces the weight of a shock absorbing device.SOLUTION: A part (10) includes a porous structure (15) including cellular pores (20) and formed at least in part by the periodic repetition of a basic pattern (50), each cellular pore being delimited by a wall (30), made of a metal or a polymer, having a parietal porosity greater than 5% and including parietal pores (31) with a mean size less than the mean size of the cellular pores.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the field of porous structures with cellular pores, in particular intended to form part or all of an impact absorbing device. [Background technology]

[0002] To absorb the energy of an impact, the impact absorbing device can have a metallic or polymeric cellular structure, which has high porosity, making the structure lightweight with good mechanical performance, and allowing the structure to dissipate energy, particularly by plastic deformation in compression sufficient to absorb the energy of the impact.

[0003] Shock-absorbing devices can be manufactured by molding, particularly by die molding. However, molding is energy-intensive and makes it difficult or impossible to obtain cellular pores smaller than 14 mm. It is also known to manufacture such devices by additive manufacturing, which simplifies the manufacture of small cellular pores as well as the manufacture of certain complex shapes.

[0004] FR3033518A1 describes a metal or alloy part with cells that can be made, for example, by molding or additive manufacturing. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] FR3033518A1 Summary of the Invention [Problem to be solved by the invention]

[0006] In the automotive industry in particular, there is a desire to reduce the weight of such impact absorbing devices, particularly as part of the ongoing effort to reduce the energy consumption of vehicles. [Means for solving the problem]

[0007] The present invention relates to a part comprising a porous structure comprising cellular pores and formed at least in part by the periodic repetition of a basic pattern, each cellular pore being defined by a wall, made from a metal or a polymer, having a wall porosity greater than 5%, and comprising wall pores with an average dimension smaller than the average dimension of the cellular pores.

[0008] A part according to the invention is advantageously lighter than a part having the same cellular pore structure in which each of the cellular pores is still bounded by a dense wall.

[0009] "Wall porosity" is the ratio of the volume occupied by the wall pores to the volume occupied by the walls of a porous structure. The volume occupied by the walls of a porous structure is equal to the volume of the material forming the wall pores plus the volume occupied by the wall pores. "Wall pores" are pores contained in the wall.

[0010] "Cellular porosity" is the ratio of the volume occupied by the cellular pores to the volume occupied by the porous structure. The volume occupied by the porous structure is equal to the volume occupied by the walls plus the volume occupied by the cellular pores.

[0011] The total porosity of a porous structure is the sum of the cell porosity and the wall porosity.

[0012] An "open" pore is defined by a hollow wall, such that the open pore is in fluid communication with other adjacent open pores.

[0013] The "average" size of a pore mass is the average value of the size of the pore mass.

[0014] The "size" of a cellular pore or wall pore can be determined using the following method: First, the part can be immersed in resin. A thin section of the part to be analyzed is cut and then polished to obtain a good surface condition, preferably with fine-grained abrasive paper of at least grade 1200, accompanied by a diamond slurry. A snapshot of the polished section is taken using an optical or electron microscope. The magnification used is such that the width of the image is between 5 and 10 times the average size of the pores. The first snapshot can be taken using a visual estimation of the average size of the pores. The size of the pores is determined by analyzing the snapshot using a thresholding method followed by erosion / dilation, implemented by image analysis software such as ZEN CORE 2 (C) sold by Zeiss (C). The "size" of a pore in the image is the diameter of the smallest circle circumscribing the pore.

[0015] The average size of the wall pores can be determined in an image representing a cross section of one or more walls. The average size of the cellular pores can be determined in an image representing a cross section of the cellular structure. Of course, to measure the average size of the cellular pores, the image is captured at a smaller magnification than when measuring the average size of the wall pores.

[0016] The described method can also determine the cell porosity and / or wall porosity. The cell porosity in the image is the ratio of the total area occupied by the cellular pores to the area of ​​the cross section of the porous structure shown in the image. The "wall porosity" in the image is the ratio of the total area occupied by the wall pores to the total area occupied by the walls.

[0017] The wall porosity can be between 5% and 80%, specifically between 20% and 60%.

[0018] The average size of the wall pores may be less than 500 μm, preferably at least 85% of the wall pores are smaller than 200 μm, preferably more than 50% of the wall pores are smaller than 50 μm.

[0019] The wall pores can be distributed irregularly, particularly randomly, in the wall. The wall pores can be distributed uniformly in the wall. For example, the wall porosity does not differ by more than 20%, 10%, or 5% between two different volume regions equal to three times the cube of the thickness of one of the walls.

[0020] The wall pores may be irregularly shaped, but in particular may not be spherically shaped.

[0021] The wall can be solid, that is, without wall pores traversing the thickness of the wall.

[0022] In a variant, the wall is hollow. A hollow wall has at least one cavity that traverses the entire thickness of the wall.

[0023] The wall may be in the form of a lattice, or in particular a polyhedral assembly of rods that defines one of the cavities.

[0024] The porous structure may comprise solid walls and hollow walls.

[0025] Portions of at least one of the walls can define several adjacent cellular pores. The walls can have several flat or curved surfaces.

[0026] The wall may separate at least two adjacent cellular pores, in particular three or more adjacent cellular pores.

[0027] The thickness of at least one of the walls, or each wall, can be at least 200 μm, at least 800 μm, or at least 1 mm. The thickness of a wall is the shortest distance between two of the opposite faces of the wall.

[0028] The porous structure can have open cellular pores: more than 90%, preferably more than 95%, by number of the cellular pores can be open, or all the cellular pores can be open.

[0029] The average size of the cellular pores can be greater than 100 μm, preferably greater than 500 μm or greater than 1 mm. The average size can be less than 14 mm or less than 10 mm.

[0030] The average size of the cellular pores can be at least 20 times, preferably at least 50 times, or at least 100 times larger than the average size of the wall pores.

[0031] The cell porosity can be greater than 70%, preferably greater than 80%, or 90%, or even greater than 95%. The cell porosity may be less than 97%, for example 96%.

[0032] The porous structure is formed at least partially, or even completely, by the periodic repetition of the basic pattern.

[0033] The basic pattern may be repeated periodically along an axis, or along two or preferably three axes that are different from each other. The basic pattern may be repeated more than 5 times, more than 10 times, or more than 50 times along each axis, depending in particular on the intended use of the part.

[0034] The basic pattern may comprise or include one cellular pore and, at least in part, walls defining said cellular pore. The basic pattern may comprise one or more cellular pores. In a variant, the cellular pores may be defined by repeating the basic pattern at least 10 times.

[0035] The base pattern can be convex, concave, or star-shaped. Specifically, the base pattern can be a lattice, especially a convex or star-shaped lattice. The base pattern can be any other shape achievable by additive manufacturing that repeats to form cellular pores.

[0036] Preferably, the porous structure is made from metal.

[0037] The porous structure may comprise one of the following metals: aluminum, nickel, cobalt, iron, copper, palladium, titanium, tungsten, silver, platinum, and alloys thereof, which metals constitute in particular more than 95% of the mass of the porous structure, in particular more than 99.0% of the mass of the porous structure, or in particular more than 99.9% of the mass of the porous structure. In particular, the porous structure may be made of stainless steel or a shape memory alloy, in particular an alloy of nickel and titanium, such as Nitinol. Preferably, the porous structure is made of stainless steel.

[0038] In a variant, the porous structure may comprise one of the following polymers: polyamide, polystyrene, thermoplastic elastomer, polyaryletherketone, and mixtures thereof, preferably polyamide, in particular nylon PA12, nylon PA11, or nylon PEBA, in particular constituting more than 80% of the mass of the porous structure or more than 90% of the mass of the porous structure. The porous structure may contain glass fibers, glass beads, aluminum powder, and mixtures thereof.

[0039] The invention also relates to an impact absorbing device formed at least in part by a component according to the invention, for example for protecting an object, in particular in the event of a fall or during transportation.

[0040] The invention also relates to a device comprising a component according to the invention, in particular a vehicle such as a motor vehicle or a rail vehicle, a porous tank, a shim or an acoustic damper.

[0041] The invention also relates to a method for manufacturing a part according to the invention, comprising the step of fabricating a porous structure by shaping a powder using additive manufacturing techniques.

[0042] Preferably, the additive manufacturing technique is powder bed additive manufacturing.

[0043] Preferably, the additive manufacturing technique involves partial or complete melting of powder particles using a light beam or an electron beam, in particular using a light beam. Preferably, the light beam is a laser beam.

[0044] A number of powder bed additive manufacturing techniques known to those skilled in the art can be used. In particular, additive manufacturing techniques include the following: - binder jetting, which involves printing by depositing a binder onto a powder bed; -Laser Powder Bed Melting (LPBF) or Selective Laser Melting (SLM), -Selective Laser Sintering (SLS), -Electron beam melting (EBM), -Multi-Jet Fusion (MJF) which involves depositing a binder onto a powder bed It can be one of:

[0045] Preferably, the additive manufacturing technique is laser powder bed fusion (LPBF) or selective laser sintering (SLS), more preferably laser powder bed fusion (LPBF). Laser powder bed fusion (LPBF) is preferably used to form metal porous structures. Selective laser sintering (SLS) is preferably used to form polymer porous structures.

[0046] Laser powder bed fusion additive manufacturing involves depositing at least one layer of powder and then partially or completely melting at least a portion of the particles of the powder, preferably all of the particles in the deposited layer, by selective application of energy using a laser beam.

[0047] Powder D 50 The median diameter of the particles can be between 1 μm and 100 μm, preferably between 1 μm and 80 μm, for example between 5 μm and 45 μm, so that the size of the wall pores can be easily controlled.

[0048] The particles may comprise one of the following metals: aluminum, nickel, cobalt, iron, copper, palladium, titanium, tungsten, silver, platinum, and alloys thereof, in particular stainless steel or a shape memory alloy, in particular comprising more than 95% of the mass of the porous structure, in particular more than 99.0% of the mass of the porous structure, or in particular more than 99.9% of the mass of the porous structure.

[0049] The particles may comprise one of the following polymers: polyamide, polystyrene, thermoplastic elastomer, polyaryletherketone, and mixtures thereof, preferably polyamide, in particular nylon, such as nylon PA12, nylon PA11, or nylon PEBA, in particular constituting more than 80% of the mass of the porous structure or more than 90% of the mass of the porous structure.

[0050] The powder may be monodisperse.

[0051] The additive manufacturing technique may involve repeating a cycle comprising depositing a layer of powder between 6 μm and 200 μm, preferably between 10 μm and 120 μm thick, and irradiating at least a portion of the layer using a light beam, preferably a laser beam, in particular more than 10 or more than 1000 times. In a variant, the cycle involves depositing a layer of powder that is, for example, between 1 μm and 80 μm thick.

[0052] The additive manufacturing step may include depositing an initial layer of powder onto a manufacturing plate, particularly a plate heated to a temperature between 20°C and 250°C, particularly between 190°C and 210°C.

[0053] The melting of the powder particles can be controlled using a pre-prepared computer database, which in each step controls the spatial movement of the light beam relative to the deposited powder by executing a computer program using a processing device. By controlling the trajectory of the light beam, the shape of the porous structure, in particular the shape of the walls defining the cellular pores, can be controlled; By choosing appropriate operating parameters for the additive manufacturing technique, in particular by controlling the energy density of the light beam, the porosity of the wall can be controlled.

[0054] The selective melting of the powder is controlled by selecting the main control parameters of the additive manufacturing technique, including, among others, the speed of movement of the light beam (V), the power of the light beam (P), the offset between the displacement vectors of the light beam (HD), the gap between two laser-irradiated beads (HD), and the rotation of the beads from one layer to the other.

[0055] Preferably, at least one of the control parameters for additive manufacturing is selected to partially coalesce the particles and bond them together. Partial coalescence can preserve some of the porosity of the powder and form a porous wall. Thus, using additive manufacturing techniques differs from prior art techniques, where complete melting of the particles would normally result in the formation of a dense metal wall.

[0056] The wall porosity can be adjusted by adapting the energy density of the light beam. Below a threshold energy density, the wall porosity increases as the energy density is reduced. The "threshold energy density" is the energy density above which a porous structure with dense walls is obtained. A "porous structure with dense walls" has a wall porosity of less than 0.5%.

[0057] J / mm 3 The energy density E, expressed as:

[0058]

number

[0059] where: - P is the power of a light beam, in particular a laser beam, expressed in W; -V is the speed of travel of the light beam, in particular the laser beam, expressed in mm / s; - HD is the offset between the displacement vectors of the light beams, in particular between two laser-irradiated beads, expressed in mm; -e is the layer thickness in mm.

[0060] Preferably, the ratio of the energy density of the light beam to the threshold energy density is between 0.3 and 0.9.

[0061] The beam travel speed is the relative speed of the dots formed by the light beam in the powder layer relative to said layer. For a light beam power P, a constant offset value HD, and a constant layer thickness e, above a threshold travel speed, the wall porosity of the porous cellular structure increases as the travel speed increases. The "threshold travel speed" is the travel speed below which a porous structure with dense walls is obtained for a constant light beam power P, a constant offset value HD, and a constant layer thickness e. The light beam travel speed can be less than 6000 mm / s. High travel speeds can be used, and the production of parts according to the present invention is also faster than the production of cellular metal parts with dense walls obtained using prior art additive manufacturing methods.

[0062] For example, for a stainless steel powder having a light beam power of 275 W, a layer thickness of 50 μm, a deviation value between the displacement vectors of the light beam between 80 μm and 120 μm, and a median diameter of 36 μm, the movement speed of the light beam is between 1500 mm / s and 6000 mm / s.

[0063] The trajectories of the light beams follow displacement vectors that are spatially displaced in pairs according to a disparity value HD.

[0064] By adapting the offset value, a person skilled in the art can adjust the wall porosity in the porous structure for a given power of the light beam, a given movement speed of the light beam, and a given layer thickness, e.g., under these conditions, the wall porosity increases as the offset value increases.

[0065] The thickness of the deposited powder layer can also modulate the wall porosity: for a given power, a given offset value, and a given translation speed of the light beam, the wall porosity increases as the layer thickness increases.

[0066] In one embodiment, the method comprises the following steps prior to the fabrication of the porous structure: (i) Threshold energy density E threshold fabricating at least one test structure with different respective light beam powers to determine V, ... (ii) the energy density of the light beam during the subsequent fabrication steps is E threshold selecting at least one of the following parameters: a moving speed of the light beam, a displacement value of the light beam, and a layer thickness such that may include:

[0067] The parameters described above may be adjusted depending on the composition of the powder used.

[0068] The present invention can be better understood from the detailed description of examples provided below and the accompanying drawings. [Brief explanation of the drawings]

[0069] [Figure 1] 1 is a photograph of an example part according to the present invention and an optical microscope photograph of the part wall. [Figure 2] 1A-1C are schematic diagrams of different examples of basic patterns that are repeated to form porous structures according to the present invention. [Figure 3] Schematic diagrams of an example embodiment of a powder bed additive manufacturing method using a laser beam (A), in a non-overlapping configuration (B), and in an overlapping configuration (C). DETAILED DESCRIPTION OF THE INVENTION

[0070] An example component 10 according to the present invention is shown in FIG.

[0071] The part is 50 x 50 x 50 mm 3 The part has a porous structure 15 with open cellular pores 20 and metal walls 30, each of which defines one or more cellular pores and forms partitions between adjacent cellular pores.

[0072] The cellular pores 20 are 5.6 x 5.6 mm 2 The pores have a substantially spherical shape with a diameter of 1. The pores are periodically arranged along three orthogonal axes.

[0073] The wall 30 is hollow, that is, has cavities traversing the entire thickness of the wall, providing fluid communication between adjacent cellular pores.

[0074] As shown in the close-up of wall 30, wall 30 includes wall pores 31 defined by dense metallic regions 32.

[0075] The part therefore has a cell porosity determined by the cellular pores and a wall porosity determined by the wall pores.

[0076] 2 shows various examples of base patterns 50 that are periodically repeated to form a porous structure. Of course, base patterns other than those shown may be used to form the porous structure.

[0077] The basic pattern is, for example, a lattice, which may be based on a cube, an octahedron, a dodecahedron, a bihexagonal pylon, a cuboctahedron, a truncated octahedron, a icosahedron, or an icosahedron.

[0078] The cellular pores may be defined by a basic pattern, such as a cube 51 or an octahedron 52. Such cellular pores 20 are thus defined by walls 30 with several faces, each face having a through cavity 53. The walls of such cellular pores thus have the form of a lattice of polyhedra.

[0079] In a variation, the cellular pores may be defined by repeating a basic pattern in at least one direction, such as in the case of the star-shaped basic pattern shown in FIG.

[0080] FIG. 3A shows the trajectory of a laser beam 100 during the fabrication of a porous structure by laser additive manufacturing on a powder bed. The spot of the laser beam is moved along displacement vectors spaced apart by a displacement value HD in a powder bed 110 of thickness e to be melted, which is deposited on a previously deposited layer 120 and bonded together by the laser beam. As shown in FIGS. 3B and 3C, the area affected by the laser beam, and therefore partially melted, extends through the entire thickness of the melted layer and through a portion of the underlying layer against which the melted layer bears. The areas affected by the laser beam during the laser beam movement may not overlap ( FIG. 3B ) or may partially overlap ( FIG. 3C ). Therefore, the displacement value HD can prevent partial overlap of the affected areas and facilitate the formation of wall porosity. Furthermore, a high movement speed of the laser spot results in less localized heating of the area affected by the laser beam, which facilitates the formation of wall porosity.

[0081] (Example) Example 1 The part shown in Figure 1 was fabricated as follows.

[0082] A powder of 316L stainless steel particles with a median diameter D50 of 36 μm was used in an LPBF additive manufacturing machine sold by SLM Solutions. The machine was fitted with a laser source emitting a wavelength of 1040 nm.

[0083] The parts were produced in an additive manufacturing machine on a production plate made from 316L stainless steel and heated to a temperature of 200°C, with the following parameters: -Layer thickness: 30μm, -Laser power: 225W, -Laser beam moving speed: 4771mm / s, - Deviation value: 100μm, -Laser beam energy density: 15.71J / mm 3 .

[0084] These particular operating parameters result in a porous structure with a particular wall porosity.

[0085] Example 2 316L stainless steel powder with a median diameter D50 of 36 μm was used in an LPBF machine sold by SLM Solutions. The machine was fitted with a laser source emitting a wavelength of 1040 nm.

[0086] The parts were produced in an additive manufacturing machine on a production plate made from 316L stainless steel and heated to a temperature of 200°C, with the following parameters: -Layer thickness: 50μm, -Laser power: 275W, -Laser beam moving speed: 3501mm / s, - Deviation value: 120μm.

[0087] The energy density of the laser beam is below the threshold energy density. The porous structure has a cell porosity of 85% and the metal walls of the porous structure have a wall porosity of 35.7%, which were measured using optical microscopy and image processing. As a result, the overall porosity of the part is 94.6%.

[0088] Naturally, the invention is not limited to the example embodiments of the components and the example implementations of the methods described by way of non-limiting examples.

[0089] For example, the component according to the invention is a heat exchanger, a filtration element or a structural component, so that such a component can be used in the fields of healthcare, mining or construction. [Explanation of symbols]

[0090] 10 parts 15 Porous structure 20 Cellular pores 30 metal wall 31 Wall pores 32 Metal area 50 Basic Patterns 51 cube 52 Octahedron 53 Through-hole 100 laser beams 110 Powder bed 120 layers e Thickness HD deviation value

Claims

1. A component comprising a porous structure comprising cellular pores and formed at least in part by the periodic repetition of a basic pattern, each cellular pore being defined by a wall, comprising essentially a metal or a polymer, having a wall porosity of greater than 5%, and comprising wall pores with an average size smaller than the average size of said cellular pores; the wall porosity does not differ by more than 20% between two different volume regions equal to three times the cube of the thickness of one of the walls; the wall porosity is between 20% and 80%; The average size of the wall pores is less than 500 μm, at least 85% of the wall pores are smaller than 200 μm, and more than 50% of the wall pores are smaller than 50 μm.

2. The component of claim 1 , wherein the average size of the cellular pores is at least 20 times greater than the average size of the wall pores.

3. The component of claim 1 , wherein the porous structure comprises a metal as an essential component.

4. 10. The component of claim 1, wherein the porous structure comprises one of the following metals: aluminum, nickel, cobalt, iron, copper, palladium, titanium, tungsten, silver, platinum, and alloys thereof.

5. The component of claim 1 , wherein the cell porosity is greater than 70% and / or less than 97%.

6. A method for manufacturing the part described in claim 1, comprising the step of producing the porous structure by shaping a powder using an additive manufacturing technique, wherein the additive manufacturing technique is laser powder bed fusion (LPBF) or selective laser sintering (SLS).

7. The method of claim 6 , wherein the additive manufacturing technique is powder bed additive manufacturing.

8. 8. The method of claim 7, wherein the additive manufacturing technique involves partial or complete melting of powder particles using a light beam or an electron beam.

9. 10. The method of claim 8, wherein the additive manufacturing technique involves partial or complete melting of powder particles using a light beam.

10. 10. The method of claim 9, wherein a ratio of the energy density of the light beam to a threshold energy density is between 0.3 and 0.9, the threshold energy density being the energy density above which a porous structure with dense walls is obtained.

11. 7. The method of claim 6, wherein the median particle size of the powder is between 1 μm and 100 μm.

12. 10. The method of claim 9, wherein the additive manufacturing technique involves repeating a cycle including depositing a powder layer of thickness (e) between 6 μm and 200 μm and irradiating at least a portion of the layer using the light beam.

13. The following steps: (i) a threshold energy density E above which the porous structure with dense walls is obtained; ｔｈｒｅｓｈｏｌｄ fabricating at least one test structure with different respective optical beam powers to determine a speed of movement V of said optical beam; ０ , the deviation value HD of the light beam ０ , and the layer thickness e ０ is predetermined and kept constant during fabrication of the at least one test structure; (ii) the energy density of the light beam during a subsequent fabrication step is E ｔｈｒｅｓｈｏｌｄ selecting at least one of the following parameters: a moving speed of the light beam, a displacement value of the light beam, and a thickness of the layer so that The method of claim 9 , wherein the step of:

14. An impact absorbing device formed at least in part by a component according to claim 1.

15. A device comprising the component of claim 1 , wherein the device is a vehicle, a porous tank, a shim, or an acoustic damper.

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