Assembling components by spraying ductile material powder

Abstract

The present application describes a method for attaching a first component (20) and a second component (30) for a mechanical assembly to each other, the method comprising spraying a powder (10) of a ductile material onto the components (20, 30), causing the components (20, 30) to be attached to each other by accumulation of the powder (10), the method comprising texturing at least one surface of one of the two components (20, 30) on which the spraying is then performed.

Description

Background Art

[0001] In the context of reducing vehicle weight, which is a major requirement for reducing polluting emissions, assembly materials of different nature are becoming increasingly important and are increasingly present in the assembly of land or air vehicles. Examples include assemblies of steel and aluminum alloys, or between steel and polymers or composites, using carbon fibers, where conventional assembly techniques cannot be used.

[0002] Solutions exist, such as gluing, riveting, clinching or self-tapping screws, but these are limited by the type of materials being assembled (e.g. it is not possible to rivet composites with carbon fiber), lack mechanical strength or require potentially dangerous sharp points in certain areas of the vehicle.

[0003] a. Welding pin

[0004] Recently, in response to this new demand for multi-material assemblies, some manufacturers have come up with welding pins that allow the assembly of two dissimilar materials that cannot be directly resistance welded together.

[0005] The obvious advantage of welding pins is the widespread use of resistance welding methods in the assembly chain of various automobile or aircraft manufacturers, allowing easy transfer of this technology. However, welding pins have non-negligible disadvantages that limit their widespread use, in particular (but not limited to):

[0006] - the component must have at least one through hole for the welding pin,

[0007] - The assembly must have at least one main iron-based (steel) component to be resistance welded,

[0008] - The material of the pin must be mainly iron-based (steel) components for resistance welding,

[0009] -Access to both sides of the component is required to make resistance welding possible,

[0010] - The need to adjust the welding pin geometry based on the geometry of the assembly and the thickness difference between the two pieces being assembled or the thickness tolerance of the two pieces being assembled, thus increasing the number of requirements that the pin must meet in order to meet the needs of all situations,

[0011] - plane-to-plane component constraints,

[0012] - Generate excess thickness at the pin location to ensure a secure mechanical joint,

[0013] - Thermal degradation of polymer or composite components when resistance welding pins to other components which are primarily ferrous based (steel).

[0014] -...

[0015] Furthermore, considering the number of multi-material assembly points (which can range from 500 to more than 1500, depending on the vehicle type), the weight associated with the weld pin technology is not negligible, thus counterproductive to the original goal of reducing vehicle weight.

[0016] In fact, the welding pin is mainly made of iron, which has a strength of about 7.8g / cm 3 density. For a standard 4.5g weld pin, the increase in mass can range from 2.25kg to more than 6.75kg. Depending on the number of assembly points, the weld pin method may not be suitable unless the mass reduction due to the composite nature of the assembly is not negligible (case by case study).

[0017] Another important aspect is the mechanical strength of multi-material components produced using welded pins. This depends primarily on the quality of the weld between the welded part of the pin and the mostly ferrous component (heat affected zone).

[0018] In order to reduce vehicle weight, automobile manufacturers generally use high-strength or ultra-high-strength steel (greater than 600MPa, 800MPa or even 1500MPa) to reduce the thickness of common flat steel products for car bodies to reduce their weight while maintaining the required mechanical strength level of structural components, such as crossbars or floor reinforcements or door anti-collision beams, such as Figure 1 In addition, aluminum alloys are increasingly used in vehicles, with the attendant problem of assembling them into steel. Finally, some vehicles also use carbon fiber or thermoplastic composites, which are a real challenge to mechanically join with steel or aluminum alloys.

[0019] For example, this situation requires the use of low alloy steel pins (low material cost) on steel plates with very high mechanical strength, which usually reduces the strength of the weld. In addition, since the welding is not optimized and does not provide much variation in the type of steel used, the shear resistance and fatigue resistance in the case of alternating bending stresses are not optimized.

[0020] b. Cold spraying and thermal spraying

[0021] Since the 1980s, the method known as "cold spraying" has allowed the production of coatings using unmelted metal powder particles that are sprayed onto the component being sprayed at very high speeds (hundreds of meters per second). This method, particularly suitable for the deposition of ductile metallic materials, allows the formation and adhesion of the coating due to the plastic deformation of the particles and substrate in contact with the substrate during the initial moments of coating growth and during contact with the coating being formed.

[0022] Given the ability to spray ductile, non-melting materials, cold spray allows for the deposition of metallic coatings in ambient air with little or no oxide formation. Cold spray also allows for much lower thermal stresses to the substrate and limits the build-up of thermal stresses in the sprayed deposit compared to conventional thermal spray methods (plasma, HVOF, etc.).

[0023] Furthermore, the speed and performance of cold spraying are typically quite high (in the kg / h range, with a throughput greater than 90%), making this technique particularly worthwhile for industrial applications.

[0024] Prior art

[0025] Given its advantages, cold spraying has been proposed for assembling two materials. The following document describes this use.

[0026] Document US 2007 / 0194085 A1 describes the production of an assembly of two parts, which may be of different materials, by cold spraying a metal such as aluminum to form a bump and to keep the parts attached to each other.

[0027] This document describes the importance of spraying at a speed that generates sufficient energy to remove any contaminants present on the metal being sprayed and at least at the interface between the parts being assembled to clean the joining surfaces. The contaminants removed are, for example, oxides, lubricants, adhesives or coatings.

[0028] The document contrasts its assembly method with welding the two parts, which would reduce the mechanical strength of the assembly.

[0029] The document also states that the speed at which the metals are sprayed is sufficient to join the parts being assembled without reaching their melting points, thereby producing a connection without a heat-affected zone, in which the mechanical and corrosion properties of the metals are significantly reduced.

[0030] However, in the assembly described in this document, the adhesion of the cold sprayed metal is mechanical in nature, due to plastic deformation of the substrate upon impact with the sprayed first particles, creating attachment points at the substrate / particle interface.

[0031] Furthermore, the sprayed particles are ductile, and the difference in mechanical strength between the sprayed particles and the substrate initially affects the attachment of the cold sprayed metal.

[0032] In fact, normal additive manufacturing conditions for cold spraying generally allow for good mechanical bonding between sprayed material that has the same properties as the substrate on which it is deposited, e.g., metal on metal. In addition, the substrate must be ductile enough to deform plastically upon impact with the incoming spray particles to create an attachment point.

[0033] Thus, for example, producing an aluminum alloy bump with a mechanical strength (Rm) of about 250-400 MPa by cold spraying on another stronger or harder material such as steel (Rm>600–800 MPa) or carbon fiber composites (Rm>1000 MPa) is very difficult because the plastic deformation of steel or carbon is almost zero when in contact with aluminum alloy particles.

[0034] Furthermore, document US 2007 / 0194085 A1 states that once the adhesive arranged between the two components has solidified, the joining material fixes the two components. The document further states that the described assembly technique has low strength. Summary of the invention

[0035] The aim is to solve the disadvantages of the prior art by means of a flexible implementation and at least equal resistance to mechanical shearing.

[0036] The invention proposes to produce a lug by additive manufacturing in order to mechanically assemble two parts while limiting the increase in the mass of the assembly, in order to propose a solution suitable for multi-material assemblies to reduce the weight of land and air vehicles.

[0037] Purely mechanical attachment solutions have also been proposed which do not necessarily require pre-formed through-holes in one of the two elements being assembled or access to both sides of the assembly, which is an advantage for assemblies on automotive or aerospace assembly lines, for example.

[0038] The present invention proposes cold spraying density less than or equal to 5.1 g / cm on a support surface having a mechanical strength greater than that of a bump. 3 The support surface is, for example, a metal, a polymer and / or a composite material. The bumps serve as attachment points for assembly with a second material, which may be, for example, a metal, a polymer and / or a composite material.

[0039] Finally, since the attachment bumps are produced by in-situ additive manufacturing, the geometry of the bumps adapts to the geometry of the parts being assembled, and variations in thickness do not pose an obstacle. Likewise, the assembly between two parts is no longer limited to planar assembly. In-situ additive manufacturing of the bumps offers high flexibility, and the bumps adapt to the environment of the assembly of two parts that can be produced within the limits of the assembly area accessible to the robot arm.

[0040] The present invention proposes a pre-prepared support surface, which is impacted by a laser beam with a certain energy and frequency (local melting and sublimation of the material) to generate a micrometric network R of holes with a diameter D and a depth P, or a micrometric network R of lines with a width D, a length Lt and a depth P, and in one embodiment, the ratio P / D is greater than 1.

[0041] In the specific case of a network of lines, a continuous line may for example form a network of length nL. t A network of lines (n∈R) that are parallel or intersecting, with no restriction on the specific pattern.

[0042] The network R of holes or lines in the support surface allows the formation of a network R of micrometric protrusions on the support surface of the bump with the support during the additive manufacturing of the bump. The protrusions of the bump constitute the main anchors of the support surface. The bump thus formed on the support surface by additive manufacturing has an optimized resistance to shear forces substantially perpendicular to the growth direction of the bump and can be used as an assembly point between different materials, the surfaces of which are previously and locally textured by the laser.

[0043] The difference in mechanical strength between the spray material (soft) and the support material (hard) or the disadvantage of equal mechanical strength, as is usually found in thermal spraying, surprisingly turns into an advantage in the context of the proposed solution. In fact, the greater or equal mechanical strength of the support is conducive to filling the network R of holes or lines in the support with a softer / more ductile spray material or a spray material with the same strength, wherein the sprayed particles have a diameter of the same order of magnitude as the holes or lines obtained by laser texturing on the support. The accumulation of spraying in the holes or lines of the support with very high spray energy (particle speed greater than 500m / s) generates a compressive force perpendicular to the walls of the holes or lines in the support, thereby strengthening the mechanical attachment of the bump according to the invention.

[0044] Three-dimensional metal bumps with low density, obtained by additive manufacturing on a support, with optimized shear strength are also proposed, which could be the main component of an assembly between two materials of different nature or between two materials of the same nature that cannot be resistance welded together.

[0045] Given that it is produced very locally on the surface of the support, and considering that the thickness of the bump is of the same order of magnitude as its contact surface with the support, the figure according to the invention is not a surface coating, but a three-dimensional metal part obtained by Additive Manufacturing, the particular feature being that it has a network R of protrusions (filling the holes or lines of the support) that serve as anchors on the support.

[0046] Another object is to propose a lug that does not require a welding / friction mix, in order to ensure good shear resistance, unlike document US Pat. No. 7,624,910 B2.

[0047] Furthermore, the bump according to the present invention is not limited to metal-on-metal assemblies.

[0048] To this end, the present invention first proposes a method for attaching a first component and a second component of a mechanical component to each other, wherein the method includes spraying powder of a ductile material on the first component and the second component, so that the first component and the second component are attached to each other by accumulation of powder, wherein the method includes texturing at least one surface of the first component or the second component on which the powder is subsequently sprayed.

[0049] This method increases the strength of the assembly of the two parts while improving the adhesion of the accumulated powder to them.

[0050] Various additional features are available individually or in combination:

[0051] - texturing consists in producing a network of holes by means of several successive impacts of a laser beam at a single location and then moving the laser beam, wherein the network is produced as a function of the spraying of the powder, so that the density per unit area of ​​the holes or lines of the network is greater than:

[0052]

[0053] in:

[0054] (e) is the thickness of the accumulated powder in a direction perpendicular to the surface of the first component or the second component;

[0055] Stpa is the cross section of the holes or lines of the network;

[0056] L is the length of the accumulated powder in a direction parallel to the direction of the traction force between the first component and the second component;

[0057] - the mechanical strength of the material of the first component and / or the second component is greater than or equal to the mechanical strength of the powder;

[0058] - the first part and the second part are made of an aluminum alloy having a mechanical resistance between 150 and 150 mPa or of a steel having a mechanical resistance between 600 and 2000 mPa, and the powder is made of aluminum or an aluminum alloy having a mechanical resistance between 100 and 400 mPa;

[0059] - the method comprises, after spraying, applying shear forces and / or traction forces to the mechanical assembly between the first component and the second component;

[0060] - The applied shear force is greater than 1000 ± 100N;

[0061] - the method comprises, prior to spraying, positioning the first component and the second component relative to each other and temporarily blocking the first component and the second component thus positioned;

[0062] -Spraying is cold spraying;

[0063] - spraying with air at a pressure of 29 bar ± 10% and a temperature of 320°C ± 10%;

[0064] - texturing on the surface of the first part and on the surface of the second part, thereby allowing to increase the strength of the assembly of the two pieces adjacent to each other;

[0065] - a surface of the first component and a surface of the second component are arranged in a coplanar manner, the two components being adjacent to each other;

[0066] - the components are arranged at least partially on top of each other, the spraying fixing one of the components on the other;

[0067] - spraying in a lateral opening of a fixed component, wherein the lateral dimension of the opening decreases in the direction of the other component;

[0068] -Texturing is performed by means of a laser beam;

[0069] - the laser beam comprises several consecutive impacts at a single location, followed by movement, forming a network of holes texturing at least one surface, or the laser beam comprises consecutive impacts while moving, forming a network of lines texturing at least one surface;

[0070] - the first and / or second component is made of an aluminium alloy or steel and the holes or lines of the components are produced at a distance of 150 μm or 200 μm ± 10% from each other, respectively, so that the fracture of the assembly occurs at the level of the accumulated powder and not at the anchors (micrometric protrusions) on the components;

[0071] - The generation of a network provides for each hole a contour within a circle whose diameter is less than or equal to its depth, or for each line a contour within a rectangle whose width is less than or equal to its depth;

[0072] -Spraying includes multiple passes.

[0073] The parameters of the cold spray process are adjusted using the knowledge of those skilled in the art to form a dense, mechanically strong agglomerate.

[0074] Secondly, the invention proposes an assembly comprising a first component, a second component and an accumulated powder of a ductile material attaching the components to each other, wherein the assembly is characterized in that at least one surface of the two components to which the powder is attached is textured.

[0075] Such an assembly has increased strength, thereby improving the attachment of the aggregate to the two components.

[0076] In one variant, 10% ± 10 percentage points of the accumulated powder is melted.

[0077] Thirdly, the present invention proposes a land or air vehicle comprising the above-mentioned assembly. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] The present invention will be better understood, and other objects, features, details and advantages thereof will become more readily apparent, from the following detailed description provided with reference to the accompanying drawings, which are provided by way of example only, and illustrate various embodiments of the invention, and show:

[0079] [ Figure 1 ]– Figure 1 An example of an area of ​​a vehicle produced using UHS steel is shown.

[0080] [ Figure 2A ]

[0081] [ Figure 2B ]- Figure 2A and Figure 2B are schematic diagrams of three-dimensional bumps according to two different embodiments;

[0082] [ Figure 3 ]- Figure 3 is a schematic diagram of assembling two components by a bump according to one embodiment;

[0083] [ Figure 4A ]

[0084] [ Figure 4B ]- Figure 4A and Figure 4B is a schematic diagram of assembling two components through a bump according to various embodiments;

[0085] [ Figure 5 ]- Figure 5 is a schematic diagram of assembling two components through a bump according to another embodiment;

[0086] [ Figure 6 ]- Figure 6 is a schematic diagram of assembling two components through a bump according to another embodiment;

[0087] [ Figure 7 ]- Figure 7 is a schematic diagram of assembling two components through a bump according to another embodiment;

[0088] [ Figure 8 ]- Figure 8 is an optical micrograph of the network R of holes in one of the components being assembled;

[0089] [ Fig. 9 ]- Fig. 9 is an optical micrograph of a hole in one of the components being assembled, the hole being filled by a protrusion of a bump, according to one embodiment;

[0090] [ Fig.10 ]– Fig.10According to another embodiment similar to Fig. 9 's view;

[0091] [ Fig.11 ]- Fig.11 is a schematic diagram of assembling two components by a bump according to one embodiment;

[0092] [ Fig.12 ]- Fig.12 are schematic diagrams of two textured components showing the progression of the cold spray process;

[0093] [ Fig.13A ]

[0094] [ Fig. 13B ]- Fig.13A and Fig. 13B shows the shear test results of assembling two parts by a bump according to two different embodiments;

[0095] [ Fig.14A ]

[0096] [ Fig. 14B ]

[0097] [ Fig. 14C ]

[0098] [ Fig.14D ]

[0099] [ Fig.14E ]

[0100] [ Fig.14F ]- FIG. 14A to FIG. 14F are schematic top views of textures according to six different embodiments;

[0101] [ Fig.15A ]

[0102] [ Fig. 15B ]

[0103] [ Fig. 15C ]

[0104] [ Fig.15D ]- FIG. 15A to FIG. 15D are schematic side cross-sectional views of textures according to six different embodiments. DETAILED DESCRIPTION

[0105] Figure 2A and Figure 2B is a schematic diagram of a three-dimensional metal bump 10. According to one embodiment, the density of the bump 10 is less than or equal to 5.1 g / cm 3The bump 10 includes a contact surface 11 with a component 20, which may be a metal, a polymer, or a glass fiber / carbon fiber composite. The bump 10 also includes an outer surface 12, and in the illustrated embodiment, the surface area of ​​the outer surface 12 is greater than or equal to the surface area of ​​the contact surface 11. The contours of the surfaces 11 and 12 define the outer geometry of the bump 10, which may be, for example, a parallelepiped or a truncated cone, but the shape is not limited.

[0106] The bump 10 is a mass of powder obtained by additive manufacturing by cold spraying of metal particles.

[0107] For at least a portion of the contact surface 11 with the component 20 , the bump 10 has a network R of micrometric protrusions 13 obtained by completely or partially filling the same network R of micrometric holes or lines 21 , which, in one embodiment, was previously manufactured in situ by ablation / sublimation of the material of the component 20 .

[0108] In one embodiment, the network R of holes or lines 21 of the component 20 is produced using a laser beam.

[0109] In various embodiments, the network R of holes or lines 21 of the component 20 is produced by machining the component 20 (eg, punching), stamping, or during the manufacture of the component 20 , such as when the component 20 is cast.

[0110] In one embodiment, the holes or lines 21 are produced in situ and beforehand in the support by laser ablation.

[0111] The micrometer holes or lines 21 may be distributed periodically or irregularly, and the continuous lines may form a network of lines having a length n.L_t, (n∈R), for example parallel or intersecting, without any restriction to a specific pattern, such as FIG. 14A to FIG. 14F As shown. The contour of the hole or line can be included in a circle with diameter D or a rectangle with width D and length Lt, respectively. In the embodiment shown, the average depth P of the holes or lines 21 is greater than or equal to D and is spaced apart at an average distance of at least twice D, so as to provide the bump 10 with a purely mechanical connection to the component 20, which has an optimized shear strength in a direction substantially perpendicular to the axis of the protrusion 13 or hole 21.

[0112] In the embodiment shown, in particular, FIG. 15A to FIG. 15D In the embodiment, the wall of the hole or line 21 may have an angle of -45° to +45° relative to a direction perpendicular to the outer surface 22 of the component and / or the outer surface 32 of the component 30 to enhance the wear resistance of the bump 10 in a direction perpendicular to the outer surface 22 of the component 20 and / or the outer surface 32 of the component 30.

[0113] In one embodiment, all the holes or lines 21 of a single network have a similar orientation in order to facilitate their filling by cold spraying, the source of which has a direction corresponding to that of the walls of the holes or lines 21 .

[0114] In an embodiment not shown, the component 20 and / or 30 has a texture including holes and a texture including lines.

[0115] In certain embodiments, components 20 and 30 have different textures.

[0116] In one embodiment, the wall 33 of the end of the component 30 has holes or lines 21. These holes or lines 21 may be inclined in the same direction as at least one of the other networks R1 , R2 of holes or lines 21.

[0117] The knob 10 provides an optimized resistance to the propagation of any crack at the level of the attachment point of the assembly, wherein each protrusion 13 of the knob 10 serves individually as an attachment point.

[0118] Complete filling of the holes is facilitated by a support 20 having a mechanical strength greater than or equal to that of the bump 10. In this case, during the additive manufacturing of the bump 10, the accumulation of the cold sprayed metal particles in the holes or wires 21 generates radial forces perpendicular to the growth axis of the protrusion 13 and in the direction of the walls of the holes or wires 21, thus ensuring good mechanical anchoring of the bump 10 in the component 20.

[0119] In the embodiment shown, the lug 10 with a purely mechanical (anchoring) connection to the support part 20 can advantageously be used to create a mechanical attachment point with optimized shear resistance between two parts 20 and 30 , which may differ in chemical composition.

[0120] like Figure 3 As shown, in the absence of pre-existing holes in part 20 or part 30, the bump 10 can be produced simultaneously on parts 20 and 30, parts 20 and 30 respectively having two networks R1 and R2 of holes or lines, the cross-sections, depths and distribution of the networks R1 and R2 can be different and are in end-to-end contact with their two outer surfaces 22 and 32 at the same level to obtain a non-removable, shear-resistant and wear-resistant component.

[0121] In one embodiment, the bump 10 is obtained by positioning the first component 20 and the second component 30 relative to each other and temporarily blocking the first component 20 and the second component 30 thus positioned, and then spraying the powder. The temporary blocking is removed after spraying.

[0122] In order to provide an assembly with optimized bending resistance between the components 20 and 30, as Figure 4AAs shown, the component 20 may advantageously have recesses in part of its ends and in part of its thickness to form a support surface 24 and a wall 23 perpendicular to the support surface 24. Thus, all or part of the end of the component 30 may rest on the surface 24 and the wall 23.

[0123] Likewise, if Figure 4B As shown, each of the two components 20 and 30 may have a notch so that each component 20 , 30 is located on the other component 20 , 30 .

[0124] like Figure 5 As shown, metal bump 10 may be used to create a second type of assembly between two components 20 and 30 when component 30 partially covers component 20 and abuts against support surface 25 , without pre-existing perforations in either component 20 or component 30 .

[0125] A first bump 10a with growth restriction is produced on the wall 33 of the end of the component 30 by additive manufacturing on the component 20. The thickness of the first bump 10a is greater than the thickness of the component 30 or the thickness of the part of the component 30 adjoining the surface 25.

[0126] A second bump 10b having the same chemical composition as the first bump 10a is produced on the member 30, the thickness of the second bump 10b being such that the outer surface 12b of the second bump 10b is at the same level as the outer surface 12a of the first bump 10a.

[0127] Finally, the two bumps 10a and 10b are mechanically assembled by producing a bulk material 10c having the same chemical composition as the bumps 10a and 10b on the outer surfaces 12a and 12b by cold spraying, thereby mechanically assembling the components 20 and 30.

[0128] In one embodiment, the steps of creating the bumps 10 a and 10 b and the bulk material 10 c are performed in a single additive manufacturing operation by cold spraying and form a single unit 10 .

[0129] In the specific case where the parts 20 and 30 to be assembled are not continuous at their ends and have no covering, the bulk material 10c obtained by cold spraying may have a Figure 6 The particular geometry shown (T-shaped in cross-section) is designed to fill the space between components 20 and 30 .

[0130] In one embodiment, the steps of creating the bumps 10 a and 10 b and the bulk material 10 c may be performed in a single additive manufacturing operation and form a single unit 10 by cold spraying.

[0131] like Figure 6As shown, when the parts 20 and 30 are discontinuous, the production of the bump 10 including three parts 10a, 10b and 10c or two bumps 10a and 10b and a connected bulk material 10c solves the problem that aluminum powder cannot be deposited when cold spraying on the discontinuous parts 20 and 30 without first filling the space between the parts 20 and 30 with the bulk material 10c.

[0132] like Figure 7 As shown, considering the shape of the bump 10, the bump 10 can be a truncated cone, and the surface area of ​​its surface 12 is larger than the surface area of ​​the contact surface 11 with the component 20. The bump 10 can be produced after the component 30, and the component 30 having a truncated conical hole with a volume slightly larger than the future bump 10 is already connected to the partial covering on the component 20.

[0133] In this case, the bump 10 is mechanically anchored to the component 20 by means of the network of holes or wires R and the protrusions 13 and continues to grow by additive manufacturing by cold spraying on the outer wall 31 of the frustoconical hole in the component 30 .

[0134] In the particular case where a portion of the assembly 30 is pre-perforated, and in the embodiment shown, it may be advantageous for the projections 10 to not extend beyond the outer surface 32 of the component 30 , in order to avoid creating excessive bulk in the mechanical assembly between the components 20 and 30 .

[0135] In various embodiments, the hole in component 30 has any shape and widens toward a portion of the hole such that component 30 is held in place by bump 10 , where bump 10 at least partially fills the hole.

[0136] For all the examples described above, in one embodiment, the network of holes or lines R of the component 20 and / or 30 is obtained by a laser beam characterized by a power PL and a frequency F. In some embodiments, the depth P of the holes or lines of the network R is greater than or equal to the average diameter or width D of the holes or lines, so that the ratio P / D is always greater than 1.

[0137] The ratio P / D is controlled by the focal point and diameter of the laser beam and the number N of impacts of the laser at the same location or the linear speed of movement of the laser for a given power PL and frequency F. For a given material, it is generally accepted that, for a given frequency, the greater the power and the number of impacts and / or the lower the linear speed of movement, the deeper the hole or line, within certain limits corresponding to the probability of vaporization and extraction of the material subjected to the laser irradiation of the hole being formed. In addition, for a given power, number of impacts and / or linear speed of movement of the laser, the greater the laser frequency, the smaller the depth of the hole.

[0138] For example, Figure 8A network R of pores with a ratio P / D of about 2.7 is shown, obtained on a laboratory scale by a 20 W ± 10% laser with a frequency of 20 kHz ± 10% on a steel surface with a mechanical strength of 900 MPa. In this particular case, the pores are spaced about 200 μm apart and have an average diameter close to 70-75 μm.

[0139] exist Figure 8 Under the conditions of 4.5x10 -3 A single hole is obtained after 90 consecutive laser strikes within a second. For example, for a bump 10 with a length, width and thickness of 20 mm, 10 mm and 2 mm, respectively, 10-20 holes are usually required - bump / mm 2 To ensure optimal mechanical strength of the future assembly. For a support surface of 200mm 2 , bumps produced on a steel surface with a mechanical strength of 900 MPa. On a laboratory scale, the above laser conditions result in a laser preparation time of about 9-18 s.

[0140] Considering the mass flow of the sprayed material of 1-3 kg / h, respectively, on a laboratory scale or under industrial conditions, for example, the bump 10, which is mainly based on aluminum, has a mass flow of about 2.7 g / cm -3 The density and 0.4cm 3 The volume of the bump 10 is 0.4 cm, has a mass of nearly 1.1 g, and can theoretically be produced in 0.3 s or 0.1 s. Therefore, the manufacturing time is essentially limited by the movement of the robot to produce the bump 10 in several passes and to adjust the material flow rate to produce a bump with the desired geometry. Under these conditions, the production volume is 0.4 cm 3 The cold spraying time of the bump 10 is usually between 2s and 3s.

[0141] In various embodiments, on an industrial scale, each hole is obtained after 9 impacts with a laser at 200W ± 10%. Under these optimal conditions, the laser preparation time is reduced to between 0.9s and 1.8s. Thus, according to industrial parameters, a bump 10 firmly anchored in a steel support with a mechanical strength of 900MPa can be produced in a time of 2.9s to 4.8s, which is compatible with applications in the automotive or aeronautical sectors.

[0142] Fig. 9 An example of filling holes obtained by laser (P / D of 2.7) with cold-sprayed aluminum on a steel plate with a mechanical strength of 900 MPa is shown.

[0143] Fig.10 The positive point of laser texturing of steel is shown. Each hole is produced by the following steps: several constant power laser strikes, the formation of a protrusion of steel around the hole by local melting of the steel, and the local pressure applied by the strikes and the solidification of the steel.

[0144] This protrusion constitutes an additional anchoring effect for the bump 10 obtained by cold spraying.

[0145] Figure 8 , Fig. 9 and Fig.10 The possibility of producing bumps with a large number of micrometric protrusions and of filling holes very well by sprayed aluminum, which is more ductile than steel, is perfectly demonstrated. Under these manufacturing conditions, on a steel plate with a mechanical strength of 900 MPa, a mechanical strength of 100 MPa, a thickness of 2 mm and a contact surface area of ​​200 mm 2 The shear strength of the aluminum bump 10 is about 2000N, or about 200kg per bump.

[0146] In one embodiment, the bump 10 is mainly composed of aluminum and may contain elements of silicon (Si), manganese (Mn) and / or magnesium (Mg) to have increased mechanical properties, based on the content of the alloying elements, typically between 200 MPa and 400 MPa. Under these conditions, a 2 mm thick and 200 mm 2 The aluminum bumps 10 contacting the surface area have a shear strength of about 8000 N or about 400-800 kg per bump on a steel plate having a mechanical strength of 900 MPa.

[0147] In certain specific applications (e.g., aerospace), the bump 10 may consist primarily of titanium and may contain elemental aluminum or vanadium. In the specific case of a bump 10 made of Ti-6Al-4V (TA6V) having a mechanical strength of 1100 MPa for a mechanical assembly between a UHS steel plate and a titanium alloy plate, the thickness is 2 mm and the contact surface area with the steel plate is 200 mm 2 The shear strength of the bump 10 is 22000N, ie, 2.2t per bump.

[0148] The various examples described above have a surface texture that allows the creation of a network of pores R1 and R2 , fully applicable to the case where the network R1 and R2 consists of wires.

[0149] In various embodiments, component 20 is made of metal, polymer, and / or composite material. Component 30 is made of metal, polymer, and / or composite material.

[0150] In order to increase the strength of the assembly, the mechanical strength of the material used for the spraying powder is less than or equal to the mechanical strength of the material of the support members 20 , 30 .

[0151] In one embodiment, during spraying of the textured steel, powder with lower mechanical strength plastically deforms and accumulates in holes or lines formed (eg, by a laser) and creates conditions that are favorable for the mechanical strength of the component.

[0152] In one embodiment, two situations may occur when spraying onto a textured aluminum alloy:

[0153] - The mechanical strength of the powder is lower than that of aluminum alloys, and the same effects as with textured steel are observed;

[0154] The mechanical strength of the powder is comparable to that of aluminum alloys, and during spraying (eg cold spraying) the texture is partially or completely deformed, resulting in a "mix" of the two aluminum alloys having very good mechanical strength.

[0155] In the latter case, the texture of the aluminum alloy component 30 is no longer visible after spraying. Microscopic examination of the cross section shows that the aluminum of the powder and the aluminum alloy of the component 30 have mixed.

[0156] In one embodiment, if the mechanical strength of the powder is greater than that of the component 30 with lower hardness (aluminum alloy component), spraying (eg, cold spraying) will cause the component 30 with lower hardness to wear without powder adhesion or bump 10 formation.

[0157] When the mechanical assembly is subjected to shear and / or traction forces between the first component (20) and the second component (30), in one embodiment, preferably, Fig.11 As shown, the traction and / or shear fracture of the bump 10 occurs at the level of the body of the bump 10, rather than at the anchor points (micrometric protrusions) on the parts 20 and 30, by applying a force Ft in a direction perpendicular to the intersection plane of the parts 20 and 30 and / or a force c in a direction parallel to the surfaces 22 and 32 of the parts 20 and 30 in contact with the bump 10 and parallel to the intersection plane of the parts 20 and 30, respectively.

[0158] To this end, it has been found that the total surface area Stpa of the anchor with circular or rectangular cross section at the level of surfaces 22 and 32 must be greater than the surface area of ​​the section Ss of the bump 10 in a plane coplanar with the shear applied forces and coplanar with surfaces 22 and 32 .

[0159] therefore:

[0160] [Mathematical formula 1-1]

[0161] Stpa>Ss

[0162] [Mathematical formula 1-2]

[0163] Spa×Npa>e×lg

[0164] in:

[0165] - Spa is the average surface area of ​​the anchoring elements of the bump 10;

[0166] - Npa is the number of anchors of the lug 10;

[0167] -e is the thickness of the bump 10 in a direction perpendicular to the shear force c and perpendicular to the surfaces 22 and 32;

[0168] -lg is the width of the bump 10 in a direction perpendicular to the shear force c and parallel to the surfaces 22 and 32;

[0169] [Mathematical formula 1-3]

[0170] [Stpa]×[d pa ×L×lg]>e×lg

[0171] in:

[0172] - dpa is the density per unit surface area of ​​the anchoring elements of the bump 10;

[0173] L is the length of the lug 10 in a direction perpendicular to the shear force c and parallel to the surfaces 22 and 32 .

[0174] [Mathematical formula 1-4]

[0175]

[0176] Therein, in the case of an anchor with a circular cross section (network of holes), Or in the case of an anchor with a rectangular cross section (network of wires), Stpa = DL t .

[0177] In the example of a bump 10 with a length L of 20 mm, a width lg of 10 mm and a thickness e of 2 mm, the average diameter D of the anchors with a circular cross section is, for example, 80 μm and the density dpa of the anchors per square millimeter must be greater than about 20.

[0178] Such a bump made of aluminum, with a mechanical strength Rm equal to 100 MPa, will resist a tensile stress Ft equal to:

[0179] [Mathematical formula 2-1]

[0180] F t =R m ×e×lg

[0181] [Mathematical formula 2-2]

[0182] F t =100×2×10

[0183] [Mathematical formula 2-3]

[0184] F t=2000N

[0185] In another embodiment, such a bump made of an aluminum alloy containing Si and Mg and having a mechanical strength Rm equal to 300 MPa will resist a tensile stress Ft equal to:

[0186] [Mathematical formula 3-1]

[0187] F t =R m ×e×lg

[0188] [Mathematical formula 3-2]

[0189] F t =300×2×10

[0190] [Mathematical formula 3-3]

[0191] F t =6000N

[0192] In the example of a second bump 10 having a length L of 20 mm, a width lg of 10 mm, and a thickness e of 2 mm, the average width D and length of the anchor having a rectangular cross-section are, for example, 80 μm and 1 mm (less than lg), respectively, and the density dpa of the anchor per square millimeter must be greater than about 1.3.

[0193] To confirm these theoretical statements, experiments have been performed.

[0194] Thus, components 20 and 30 are made of steel and aluminum alloy, respectively.

[0195] In the embodiment described, component 20 has a mechanical strength between 600 MPa and 900 MPa. Component 30 has a mechanical strength between 150 MPa and 200 MPa.

[0196] In various embodiments, the aluminum alloy belongs to one of the 3000-6000 series. For example, the alloy includes aluminum and magnesium; aluminum, magnesium and silicon; or aluminum, manganese and silicon.

[0197] Parts 20 and 30 were textured by laser pulses with a power of 20 W ± 10% and a frequency of 20 kHz ± 10%. 5 pulses per hole in the aluminum alloy part. 90 pulses per hole in the steel part.

[0198] The textured area of ​​each plate was 10mm x 10mm.

[0199] The texture of the aluminum alloy component produces pores with an average diameter D of 80 μm, spaced 150 μm ± 10% from each other. The texture of the steel component produces pores that differ from each other by 400 μm ± 10% in a first embodiment or by 200 μm ± 10% in a second embodiment.

[0200] Cold spraying was performed using a Kinetic 3000 (CGT GmbH, Germany) cold spray system with an MOC 24 nozzle to produce the bumps 10 .

[0201] Cold spraying is performed using Al 1050 aluminum powder with a particle size between 30 μm and 56 μm. The mechanical strength of aluminum powder is between 100 MPa and 150 MPa.

[0202] In various embodiments, the aluminum powder belongs to the 1000 or 3000-6000 family.

[0203] In this example, approximately 90% ± 10 percentage points of the particles forming the powder are not melted.

[0204] Cold spraying was performed with air as carrier gas at a pressure of 29 bar ± 10% and a gas temperature of 320°C ± 10%. The carrier gas flow rate was 80 l / min ± 10%. The powder tray rotated at a speed of 20 rpm ± 10%. The spacing was 3 mm ± 10%, the spraying distance was 25 mm ± 10%, and the driving speed was 30 mm / s ± 10%. Spraying was performed 3 times.

[0205] according to Fig.12 The process shown is for cold spraying.

[0206] Once the bump 10 has been formed to assemble the components 20 and 30, separately apply Fig.11 The traction and shear stresses shown until fracture. Fig.13A is a schematic representation of test results carried out on a component produced according to a first embodiment, wherein the texture of the steel component after tensile or shear stress produces pores spaced 400 μm ± 10% from each other. Fig. 13B is a schematic representation of test results carried out on a component produced according to a second embodiment, wherein the texture of the steel component produces pores spaced 200 μm ± 10% from each other after tensile or shear stress.

[0207] It will be noted that in Fig.13A In , the assembly is broken at the level of the connection of the anchor of the lug 10 on the part 30 with the body of the lug 10 , while the body remains intact. Fig. 13B In this embodiment, the assembly breaks at the level of the body of the lug 10 , while the anchors of the lug 10 at the level of the components 20 and 30 remain connected to the body.

[0208] Tests therefore show that, for these parameters for producing the bump 10 , the spaces of 400 μm between the holes are too large for the bump 10 to give way at the level of its body, relative to its anchor.

[0209] This result is consistent with the above calculations, indicating that for a bump 10 with a length L equal to 20 mm, a width lg equal to 10 mm, a thickness e equal to 2 mm, and an average anchor diameter D equal to 80 μm, the density of anchors per square millimeter dpa must be greater than about 20. Therefore, the anchors of the bump 10 must be spaced apart on average by no more than 220 μm.

[0210] Tests were conducted on aluminum alloy / steel components. Previous laser texturing of the steel support components allowed 2 A network R of holes with a diameter of 50 μm, a depth of 120 μm and a spacing of 200 μm was formed on the surface area of ​​. For such an assembly, the body of the aluminum bump systematically pulled out under a stress of 2200 ± 100 N.

[0211] Due to the anchors (micrometric protrusions), the bump remains firmly engaged to the support component. This shows that the tensile stress of the assembly depends essentially on the mechanical strength and geometry of the bump 10, which can be adjusted according to the required mechanical strength of the hybrid assembly for automotive applications.

[0212] Comparative tests were carried out to assemble an aluminum alloy plate on a steel plate (mechanical strength 900 MPa) with a thickness of 2 mm (covering 20 mm) by cold spraying pure aluminum in holes formed in the aluminum alloy plate. Shear tests were performed on several assemblies obtained using different cold spraying parameters in order to obtain the best possible connection and the best density in the sprayed aluminum. It must be noted that fractures systematically occur at the interface between the sprayed aluminum and the steel support part, indicating that the assemblies have a low shear strength. In fact, for the 200 mm 2 Cold spray with a surface area and 2mm thickness will break at a shear stress of 1000±100N, which is not satisfactory for automotive or aerospace applications.

[0213] The parameters and features of the above examples can be considered independently to produce other embodiments.

Claims

1. A method for attaching a first component (20) and a second component (30) for a mechanical assembly to each other, wherein: The method comprises spraying powder of a ductile material on the first component (20) and the second component (30), so that the first component (20) and the second component (30) are attached to each other by accumulation of the powder, the method being characterized in that the method comprises texturing at least one surface of the first component (20) or the second component (30) on which the powder is subsequently sprayed, wherein the texturing comprises generating a network (R1, R2) of holes by a plurality of successive impacts of a laser beam at a single location, followed by moving the laser beam, wherein the network (R1, R2) is generated as a function of the spraying of the powder, such that the density per unit area (dpa) of the holes or lines of the network (R1, R2) is greater than: in: - (e) is the thickness of the accumulated powder (10) in a direction perpendicular to the surface of the first component (20) or the second component (30); - (Stpa) is the cross-section of the pores or lines of the network; - (L) is the length of the accumulated powder (10) in a direction parallel to the direction of the traction force (Ft) between the first component (20) and the second component (30).

2. The method according to claim 1, characterized in that The mechanical resistance of the material of the first component (20) and / or the material of the second component (30) is greater than or equal to the mechanical resistance of the material of the powder.

3. The method according to claim 1, characterized in that The first component (20) and the second component (30) are made of an aluminum alloy having a mechanical resistance between 150 mPa and 400 mPa or a steel having a mechanical resistance between 600 mPa and 2000 mPa, and the powder is made of aluminum or an aluminum alloy having a mechanical resistance between 100 mPa and 400 mPa.

4. The method according to claim 1, characterized in that: After the spraying, the method includes applying a shear force and / or a pulling force to the mechanical assembly between the first component (20) and the second component (30).

5. The method according to claim 4, characterized in that The applied shear force is greater than 1000±100N.

6. The method according to claim 1, characterized in that Prior to the spraying, the method includes positioning the first component (20) and the second component (30) relative to each other and temporarily blocking the first component (20) and the second component (30) thus positioned.

7. The method according to claim 1, characterized in that The spraying is cold spraying.

8. The method according to claim 1, characterized in that The spraying is performed using air at a pressure of 29 bar ± 10% and a temperature of 320°C ± 10%.

9. The method according to claim 1, characterized in that: The texturing is performed on the surface of the first component (20) and the surface of the second component (30).

10. The method according to claim 9, characterized in that The surface of the first component (20) and the surface of the second component (30) are arranged in a coplanar manner, wherein the two components (20, 30) are adjacent to each other.

11. The method according to any one of the preceding claims 1 to 9, characterized in that The components (20, 30) are arranged at least partially on top of each other, wherein the spraying fixes one of the components (20, 30) to the other component (20, 30).

12. The method according to claim 11, characterized in that The spraying is carried out in a lateral opening of the fixed component (20, 30), wherein the opening has a lateral dimension which decreases in the direction of the other component (20, 30).

13. The method according to claim 1, characterized in that The texturing is performed by means of a laser beam.

14. The method according to claim 1, characterized in that The laser beam comprises several consecutive impacts at a single location and then moves to form a network of holes (R1, R2) that texture at least one surface, or the laser beam comprises consecutive impacts while moving to form a network of lines that texture at least one surface.

15. The method according to claim 1, characterized in that The first component (20) and / or the second component (30) are made of aluminum alloy or steel, and the holes or lines of the components (20, 30) are produced at a distance of 150 μm or 200 μm ± 10% from each other, respectively.

16. The method according to any one of claims 14 or 15, characterized in that The network (R1, R2) is generated to provide an outline for each hole within a circle with a diameter (D) less than or equal to the depth (P) of the hole, or to provide an outline for each line within a rectangle with a width (D) less than or equal to the depth (P) of the hole.

17. The method according to claim 1, characterized in that The spraying includes multiple passes.

18. An assembly comprising a first component (20), a second component (30) and an accumulated powder of ductile material attaching the components (20, 30) to one another, wherein: The assembly is characterized in that at least one surface of the two parts (20, 30) to which the powder is attached is textured, wherein the texturing comprises generating a network (R1, R2) of holes by a plurality of successive impacts of a laser beam at a single location, followed by moving the laser beam, wherein the network (R1, R2) is generated as a function of the spraying of the powder, such that the density per unit area (dpa) of the holes or lines of the network (R1, R2) is greater than: in: - (e) is the thickness of the accumulated powder (10) in a direction perpendicular to the surface of the first component (20) or the second component (30); - (Stpa) is the cross-section of the pores or lines of the network; - (L) is the length of the accumulated powder (10) in a direction parallel to the direction of the traction force (Ft) between the first component (20) and the second component (30).

19. The assembly according to claim 18, characterized in that 10% ± 10 percentage points of the accumulated powder melted.

20. A land or air vehicle comprising an assembly according to any one of claims 18 or 19.

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