CN112743087B - TA15 titanium alloy lattice structure, lattice sandwich structure and manufacturing method - Google Patents

TA15 titanium alloy lattice structure, lattice sandwich structure and manufacturing method Download PDF

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CN112743087B
CN112743087B CN202011584044.5A CN202011584044A CN112743087B CN 112743087 B CN112743087 B CN 112743087B CN 202011584044 A CN202011584044 A CN 202011584044A CN 112743087 B CN112743087 B CN 112743087B
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lattice
titanium alloy
piece
rod
sandwich structure
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CN112743087A (en
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干建宁
韩维群
张铁军
刘玉平
王志敏
步贤政
王殿政
齐海
何智
苏江舟
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Beijing Hangxing Machinery Manufacturing Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F7/00—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression
    • B22F7/002—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression of porous nature
    • B22F7/004—Manufacture of composite layers, workpieces, or articles, comprising metallic powder, by sintering the powder, with or without compacting wherein at least one part is obtained by sintering or compression of porous nature comprising at least one non-porous part
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F3/00—Manufacture of workpieces or articles from metallic powder characterised by the manner of compacting or sintering; Apparatus specially adapted therefor ; Presses and furnaces
    • B22F3/10—Sintering only
    • B22F3/11—Making porous workpieces or articles
    • B22F3/1103—Making porous workpieces or articles with particular physical characteristics
    • B22F3/1115—Making porous workpieces or articles with particular physical characteristics comprising complex forms, e.g. honeycombs
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F5/00—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product
    • B22F5/10—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product of articles with cavities or holes, not otherwise provided for in the preceding subgroups
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y10/00—Processes of additive manufacturing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y30/00—Apparatus for additive manufacturing; Details thereof or accessories therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y40/00—Auxiliary operations or equipment, e.g. for material handling
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y80/00—Products made by additive manufacturing
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C14/00—Alloys based on titanium

Abstract

The invention relates to a TA15 titanium alloy lattice structure, a lattice sandwich structure and a manufacturing method, belonging to the field of materials in the aerospace field. The TA15 titanium alloy lattice structure comprises a plurality of unit cells which are repeated in space and connected with one another to form a lattice; the unit cell comprises a central piece and eight rod pieces with the same length; the central piece is provided with a front square end face and a rear square end face, the size of the central piece along the front direction and the rear direction is 0.5mm to 1mm, the side length of the end face of the central piece is 0.5mm to 1.5mm, and a rod piece extends from each corner of each square end face of the central piece to form two square cones which are symmetrical relative to the central piece; the included angle between the rod piece and the end face of the central piece is 35 degrees 16 ', and the included angle between the adjacent rod pieces extending from the same end face is 70 degrees 32'; the rod piece is a triangular prism, and the cross section of the triangular prism is an isosceles right triangle. The TA15 titanium alloy material structure designed and prepared by the invention can reduce weight by 30-40%, has good lightweight effect, and can be widely used for aerospace materials.

Description

TA15 titanium alloy lattice structure, lattice sandwich structure and manufacturing method
Technical Field
The invention relates to the technical field of aerospace materials, in particular to a TA15 titanium alloy lattice structure, a lattice sandwich structure and a manufacturing method.
Background
Titanium alloys are widely used in structural members, connectors and engines of aircraft because of their excellent overall mechanical properties and good corrosion resistance, and they can be formed by various methods such as casting, welding, spinning, shot blasting, superplastic, machining, etc. Nowadays, the titanium alloy consumption accounts for the whole mass percentage of the airplane to be an important mark for measuring the advanced degree of the airplane material, and the titanium alloy consumption on the airplane is increased along with the improvement of the design requirement and the performance level of the airplane. The TA15 titanium alloy has the nominal composition of Ti-6.5Al-2Zr-1Mo-1V, has the Al equivalent of 6.85 percent and belongs to a near-alpha type titanium alloy with high Al equivalent. The strengthening mechanism is that solid solution strengthening of alpha phase stable element Al is relied on, and neutral stable element Zr and a small amount of beta stable elements Mo and V are added. The near alpha type titanium alloy structure in an annealed state is alpha phase and less than 10 percent of beta phase, the forming performance is improved, and the near alpha type titanium alloy has certain heat treatment strengthening characteristics. The TA15 titanium alloy has the excellent high-temperature mechanical property and weldability of the alpha-type titanium alloy and the creep resistance and the durability which are close to those of the alpha + beta-type titanium alloy. Therefore, the TA15 titanium alloy is used for important structural parts of high-temperature bearing force on civil and military aircrafts, such as beams, joints, large-scale wall plates, engine blades and the like of the aircrafts.
The light porous metal structure is a novel multifunctional material along with the material preparation with multifunctional requirements and the rapid development of machining technology, and is a new direction for material selection and performance research. The honeycomb structure is widely applied to important structural members such as wall plates of airplanes, high-speed rails and subways, cabin door protective shells and the like as a classic light sandwich structure. The three-dimensional lattice structure is proposed as a new generation light structure, the core body of the three-dimensional lattice structure is similar to a space grid frame of a truss structure in structure, the three-dimensional lattice sandwich structure is relative to the traditional two-dimensional lattice structure such as a honeycomb structure, the internal space is more beneficial to arranging pipelines and filling related media to realize the functions of active heat dissipation, anti-seismic explosion, electromagnetic wave invisibility and the like, and the three-dimensional lattice structure has wide application prospect in airplane structure application, particularly structural function integration application. Up to now, in order to obtain a lattice sandwich structure with a better structure and better performance, technicians have proposed a variety of core configurations such as tetrahedral, pyramid, X, 3D-Kagome, hourglass and woven fabric structure topologies. The three-dimensional lattice structure not only has the characteristics of light weight and high strength, but also has the advantages of easy realization of multiple functions of bearing, energy absorption, shock resistance, explosion resistance, vibration suppression, heat dissipation, electromagnetic wave invisibility and the like in a good internal space, and excellent structural performance.
In view of the excellent material performance of the TA15 titanium alloy, the three-dimensional lattice sandwich structure is used on the TA15 titanium alloy, so that the excellent performance of the material is ensured, and the titanium alloy is lighter. In the prior art, various preparation processes such as an investment casting method, a metal wire weaving method, a tension-compression discharge cutting method, a stretching-folding method, a node pressing-down method, a splicing-welding method, a wire cutting interlocking method and a superplastic forming/diffusion connecting method are adopted.
Disclosure of Invention
In view of the above analysis, the present invention aims to provide a TA15 titanium alloy lattice structure, a lattice sandwich structure and a manufacturing method thereof, the titanium alloy lattice sandwich structure using the lattice structure has a good internal space, is easy to realize multiple functions of bearing, energy absorption, shock resistance, explosion resistance, vibration suppression, heat dissipation, electromagnetic wave invisibility, etc., and has the characteristics of excellent structural performance, light weight and high strength.
In one aspect, the invention provides a TA15 titanium alloy lattice structure, which comprises a plurality of unit cells, wherein the unit cells are repeated in space and connected with one another to form a lattice;
the unit cell comprises a central piece and a rod piece;
the rod pieces are eight in number and are same in length;
the central piece is provided with a front square end face and a rear square end face, the size of the central piece is 0.5mm to 1mm along the front and rear directions, the side length of the end face of the central piece is 0.5mm to 1.5mm, and a rod piece extends from each corner of each square end face of the central piece to form two square cones which are symmetrical relative to the central piece;
the included angle between the rod piece and the end face of the central piece is 35 degrees 16 ', and the included angle between the adjacent rod pieces extending from the same end face is 70 degrees 32';
the rod piece is a triangular prism, and the cross section of the triangular prism is an isosceles right triangle.
Furthermore, the unit cell further comprises a connecting part, the connecting part is an isosceles right triangular prism, and the connecting part is formed by bending 125-16' of the connecting part along the largest side face of the triangular prism of the rod piece towards the inner side of the square cone at one end of the rod piece, which is far away from the central piece.
Further, the rod member has a length of 10mm to 30mm and a cross-sectional area of 0.8mm 2 To 3.2mm 2 。
In one aspect, the invention provides a TA15 titanium alloy lattice sandwich structure, comprising the lattice structure.
Furthermore, the lattice sandwich structure consists of an upper wall plate, a lattice and a lower wall plate from top to bottom;
the lattice interlayer is composed of the lattice structure, a plurality of unit cells of the lattice structure are repeated in space and are mutually connected, the front and back direction of a central part of each unit cell is parallel to the upper wall plate surface and the lower wall plate surface, the lower surface of the upper wall plate is connected with one end, away from the central rod, of a rod piece in the upper layer unit cell of the lattice structure, and the upper surface of the lower wall plate is connected with one end, away from the central rod, of a rod piece of the lower layer unit cell of the lattice structure.
Furthermore, the lower surface of the upper wall plate is connected with a connecting part in the upper layer unit cell of the lattice structure, and the upper surface of the lower wall plate is connected with a connecting part of the lower layer unit cell of the lattice structure.
On the other hand, the invention provides a manufacturing method of a TA15 titanium alloy lattice sandwich structure, which is used for preparing the TA15 titanium alloy lattice sandwich structure and comprises the following steps:
step 1, determining a lattice structure according to light weight and strength requirements;
step 2, determining the thickness of a thin wall surrounding the lattice, and determining the size of a rod piece in the lattice unit cell;
step 3, selecting TA15 titanium alloy spherical powder as a forming raw material;
step 4, in a forming chamber, taking TA15 titanium alloy as a forming substrate, using argon gas to wash and reduce the oxygen content of the forming chamber, and preheating the forming substrate after the washing and the gas are finished;
step 5, preparing a lattice sandwich structure in a forming chamber by adopting a selective laser melting forming process, spreading powder by using a rubber scraper, and quickly melting and solidifying the powder by using a laser beam to superpose layer by layer until the lattice sandwich structure is completely formed;
and 6, after melting and forming, preserving heat in a forming chamber and then naturally cooling to room temperature.
Further, in the step 3, the particle size range of the TA15 titanium alloy spherical powder is 15-53 μm, the particle size distribution is d10:15-25 μm, d50:25-35 μm, d90:35-53 μm, and the fluidity is less than or equal to 40s/50g.
Further, in the step 4, argon gas is used for washing to reduce the oxygen content in the forming chamber to be less than or equal to 0.02%, and the formed substrate is preheated to 120-140 ℃ after the washing.
Further, in the step 5, the selective laser melting power is 300W to 350W, the scanning speed is 1000mm/s to 1300mm/s, the scanning line pitch is 10 μm to 25 μm, and the powder layer thickness is 50 μm to 60 μm.
Further, the powder spreading speed of the scraper in the step 5 is 20mm/s to 40mm/s.
Compared with the prior art, the invention can realize at least one of the following beneficial effects:
(1) In conventional manufacturing, the use of material is reduced by reducing the material in non-critical areas to reduce weight. The lattice design can reduce the material in the non-critical area of the part to reduce the weight and improve the strength-weight ratio. The invention provides a TA15 titanium alloy lattice structure, which enables a TA15 titanium alloy material with the lattice sandwich structure to have the same or similar mechanical strength with a compact material without the lattice structure by using the lattice sandwich structure, thereby realizing the lightweight of a structural member.
(2) The TA15 titanium alloy lattice sandwich structure adopts a lattice structure, and compared with a traditional compact TA15 titanium alloy structural member which does not adopt the lattice structure, the TA15 titanium alloy lattice sandwich structure reduces the weight by 30-80%, effectively reduces the weight of aerospace materials, and realizes the light weight of the materials.
(3) The structural member based on the TA15 titanium alloy lattice structure provided by the invention not only has light weight, but also can release a large amount of surface area, and can promote heat exchange and chemical reaction. The lattice structure can obviously increase the effective surface area, and if the radiator is filled with cold air, the heat can be quickly taken away. The lattice structure is used in the fields of automobiles, aerospace and energy sources, and the heat exchange efficiency can be effectively improved. Lattice structures are designed within gas turbine engine components and function to provide effective localized convective cooling of the gas turbine engine components so that the components can withstand the high temperatures of the hot combustion gases passing through the core flow path. Due to the lattice structure, the engine maintains a wide heat exchange surface, and a high heat dissipation surface/volume ratio can be obtained.
In the invention, the technical schemes can be combined with each other to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and drawings.
Drawings
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout.
FIG. 1 is a front view of a two-lattice sandwich structure of an example;
FIG. 2 is a left side view of a two-lattice sandwich structure of an example;
FIG. 3 is an isometric view of a sandwich structure of a second lattice according to an example;
FIG. 4 is a front view of a lattice unit cell;
FIG. 5 is a top view of a lattice unit cell;
FIG. 6 is a left side view of a lattice unit cell;
FIG. 7 is an isometric view of a lattice unit cell;
FIG. 8 is another perspective view of a lattice unit cell;
fig. 9 is an enlarged view of the area a in fig. 7.
Reference numerals are as follows:
1-a central piece; 2-a rod member; 3-connecting part.
Detailed Description
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate preferred embodiments of the invention and together with the description, serve to explain the principles of the invention and not to limit the scope of the invention.
Titanium alloys are widely used in structural members, connectors and engines of aircraft because of their excellent overall mechanical properties and good corrosion resistance, and they can be formed by various methods such as casting, welding, spinning, shot blasting, superplastic, machining, etc. The TA15 titanium alloy has the nominal component of Ti-6.5Al-2Zr-1Mo-1V, is an important structural metal widely applied to the field of aerospace, has the advantages of high strength, good corrosion resistance, high heat resistance, good thermal conductivity and low density, and has the excellent high-temperature mechanical property and weldability of the alpha-type titanium alloy and the creep resistance and durability close to those of the alpha + beta-type titanium alloy. Therefore, the TA15 titanium alloy is used for important structural parts for bearing high temperature on civil and military aircrafts, such as beams, joints, large-scale wall plates, engine blades and the like of the aircrafts. The three-dimensional lattice structure core is similar to a space grid structure of a truss structure in structure. The technical personnel have proposed a plurality of different core body configurations such as tetrahedral type, pyramid type, X type, 3D-Kagome type, hourglass type, braided fabric structure topology and the like from the three-dimensional lattice structure to the present. In the prior art, various preparation processes such as an investment casting method, a metal wire weaving method, a tension-compression discharge cutting method, a stretching-folding method, a node pressing-down method, a splicing-welding method, a wire cutting interlocking method and a superplastic forming/diffusion connecting method are adopted.
The titanium alloy with the three-dimensional lattice structure has the characteristics of good internal space, easy realization of multiple functions of bearing, energy absorption, shock resistance, explosion resistance, vibration suppression, heat dissipation, electromagnetic wave invisibility and the like, superior structural performance, light weight and high strength, and provides a novel TA15 titanium alloy lattice structure and a TA15 titanium alloy lattice sandwich structure and a manufacturing method thereof.
A TA15 titanium alloy lattice structure comprises a plurality of unit cells which are repeated in space and connected with one another to form a lattice; the unit cell comprises a central piece and a rod piece; eight rod pieces are provided and have the same length; the central piece is provided with a front square end face and a rear square end face, the thickness of the central piece is 0.5mm to 1mm, the side length of each end face of the central piece is 0.5mm to 1.5mm, a rod piece extends from each corner of each square end face of the central piece to form two square cones which are symmetrical relative to the central piece, and the symmetrical rod pieces in the two square cones share a vertex. The included angle between the rod piece and the end face of the central piece is 35 degrees 16 ', and the included angle between the adjacent rod pieces extending from the same end face is 70 degrees 32'; the rod is a triangular prism, and the cross section of the triangular prism of the rod body is an isosceles right triangle.
The lattice sandwich structure of the TA15 titanium alloy is composed of an upper wall plate, a lattice sandwich layer and a lower wall plate from top to bottom, wherein the upper layer and the lower layer are both thin-wall structures, namely the lattice sandwich structure is composed of thin walls and lattices, the thin walls are the upper layer and the lower layer which surround the lattices, and the light-weight three-layer lattice sandwich structure is formed by filling lattices between the two thin walls.
One possible improvement is that the upper and lower wall plates are of thin-walled construction and have a thickness of 0.5-2mm.
Specifically, the thickness of the dot matrix between the upper wall plate and the lower wall plate is 5mm to 50mm.
The aerospace material requires the material to have the characteristics of light weight and high strength, the thin wall is used as the most compact part in the lattice sandwich structure, and the thicker the thickness of the thin wall is, the higher the structural strength of the material is. Meanwhile, the thicker the thickness of the thin wall is, the higher the average density of the material is, and the farther away the material is from light weight. Therefore, the thinner and lighter the thin wall thickness under the condition of ensuring the strength, the more the requirement of the thin wall for materials in the aerospace field is compounded, but the thinner and thinner the thin wall, the serious problems of connection deformation and the like can occur in the forming process, and the minimum thin wall thickness of the design scheme can reach 0.5mm, and meanwhile, the maximum thin wall thickness is not more than 2mm.
One possible improvement is a rod length of 10-30mm.
The size of the rod pieces in the unit cell is also an extremely important parameter in the lattice sandwich structure designed by the invention, and the smaller the size of the rod pieces in the unit cell is, the more the rod pieces in the unit cell are repeatedly filled in the sandwich layer in the unit space, and the more excellent the structural strength of the material is. Meanwhile, the smaller the size of the rod pieces in the unit cell is, the more the rod pieces in the unit cell in the space interlayer are, the more compact the interlayer space is filled, the poorer the weight reduction effect of the interlayer is, and the poorer the weight reduction effect is. The length of the control rod is therefore between 10 and 30mm.
A possible improvement is that the cross-sectional area of the rod is 0.8mm 2 To 3.2mm 2 。
The cross section area of the rod piece is also an extremely important parameter in the lattice sandwich structure designed by the invention, the smaller the cross section area of the rod piece is, the thinner the rod piece is, the less TA15 alloy is filled in the unit space, the better the weight reduction effect of the material is, the better the light weight is, and therefore, the cross section area of the rod piece is designed to be 3.2mm 2 The following. Meanwhile, the cross section area of the rod piece is too small, the stress capability of the lattice sandwich structure is poor due to the fact that the rod piece is too thin, the structural strength is reduced, and therefore the minimum value of the rod diameter design is 0.8mm 2 。
The common methods for realizing the three-dimensional lattice structure include investment casting, metal wire weaving, tension-compression discharge cutting, stretch-folding, node pressing, splicing welding, wire cutting interlocking, and superplastic forming/diffusion bonding.
The investment casting method adopts the traditional molten metal casting process to prepare the metal three-dimensional lattice structure. Because the three-dimensional lattice structure has a complex shape, polyester is required to be made into a sacrificial mold firstly, and a ceramic coating is coated on the sacrificial mold; melting off polyester, and then leaving a ceramic shell to prepare a sand mold; then injecting molten metal liquid, cooling and forming, and removing the surface layer ceramic. The materials used by the investment casting method mainly comprise: ti6Al4V, ti6Al2Sn4Zr2Mo and aluminum/silicon alloys, copper/beryllium alloys, in718, etc. The investment casting method is one of the preparation methods which are researched and developed when the three-dimensional lattice concept is firstly put forward, the three-dimensional lattice is effectively changed into a real object from the concept, but the process has the defects of high fluidity requirement on a molten metal liquid material, complex manufacturing of a polyester core mold, disposable use, high metal melting energy consumption, easy generation of defects in casting forming and the like.
Preparing a lattice core body by a node downward compression plastic deformation method, placing a prefabricated reticular plate in a mould, downward pressing corresponding nodes on the reticular plate by a forming pin of an upper mould, forming a plane screen plate into a three-dimensional lattice body, and then connecting surface cores by a brazing method. Compared with a bending and folding plastic forming means, the node pressing plastic deformation method can distribute plastic deformation more uniformly along the length direction of the truss rod, effectively improves node position strain concentration in bending and forming, and is high in process preparation efficiency. However, this method has high requirements for the mold material, and is difficult to form at normal temperature for a metal material having a high yield ratio, and is liable to rebound after forming, making it difficult to ensure the forming accuracy.
The process for preparing the aluminum alloy three-dimensional lattice structure by the wire-electrode cutting interlocking assembly mainly comprises the following steps: (1) preparing an embedded locking bar with a groove by wire cutting; (2) Anodizing the interlocking strip by phosphoric acid and removing compact Al on the surface of the interlocking strip 2 O 3 Oxide films and other fouling; (3) interlocking assembly and adhesive film bonding; and (4) curing at high temperature. The method can improve the material utilization rate by reasonably designing and cutting the arrangement of the interlocking strip patterns, has low process cost, but needs to pay attention to the fact that all nodes are on the same plane in the interlocking assembly process and ensures that the upper panel and the lower panel are aligned, has complex process and low preparation efficiency, and is difficult to ensure the connection strength of the panel and the core body nodes by gluing, so that the requirement of the aerospace field on the strength of the titanium alloy material cannot be met.
The principle of the superplastic forming/diffusion bonding process is as follows: coating the prefabricated upper and lower panels with the solder-stop agent with corresponding patterns, and respectively diffusion-connecting the solder-stop agent with the upper and lower surfaces of the core plate at the corresponding node positions: the upper and lower panels drive the connecting nodes to move up and down respectively through the superplastic forming process, the truss rods are subjected to uniform plastic deformation, and the planar reticular core plate is formed into a three-dimensional lattice core body. The method has the advantages of ingenious conception, simple superplastic forming die, high forming precision and high efficiency, and can be used for large-size and mass production. However, the method needs to prepare the planar mesh core plate in advance, is applicable to the manufacturing of the single-layer lattice structure, and needs to repeat the preparation of the planar mesh core plate for multiple times for the manufacturing of the non-single-layer lattice structure, so that the process is complicated, and the method is almost impossible to be applied to the complex multi-layer lattice structure.
The above method has the following problems:
(1) The investment casting method belongs to the traditional molten metal casting process, has higher fluidity requirement on a molten metal liquid material, and easily generates defects in casting forming, so that the requirement on the preparation of a titanium alloy lattice sandwich structure in the aviation field of the application cannot be met;
(2) The dot matrix core is prepared by a node downward compression plastic deformation method, and for metal materials with high yield ratio, the dot matrix core is difficult to form at normal temperature, and is easy to rebound after forming, so that the forming precision is difficult to ensure, and the requirements on a lightweight dot matrix sandwich structure in the aviation field with extremely high precision requirements cannot be met;
(3) The aluminum alloy three-dimensional lattice structure is prepared by a wire-cutting interlocking assembly process, all nodes need to be in the same plane in the interlocking assembly process, the upper panel and the lower panel are ensured to be aligned, the process is complicated, the preparation efficiency is low, the joint strength of the nodes of the panels and the core body is difficult to ensure, certain defects exist in the preparation of the aluminum alloy lattice, and the aluminum alloy lattice structure is more difficult to apply to the titanium alloy material;
(4) The superplastic forming/diffusion bonding process is ingenious in conception, simple in superplastic forming die and high in forming precision, but the process is complex and complicated because the planar reticular core plate needs to be repeatedly prepared for manufacturing the non-single-layer lattice structure, so that the process can hardly be applied to the complex multi-layer lattice structure.
In view of this, the invention realizes the manufacture of the TA15 titanium alloy lattice sandwich structure designed as above through selective laser melting forming.
The invention provides a manufacturing method of the lattice sandwich structure of the TA15 titanium alloy, which comprises the following steps:
step 1, designing a lattice structure according to requirements on light weight and strength;
step 2, determining the thickness of a thin wall surrounding the lattice, determining the size of a rod piece in the lattice unit cell, and determining the rod diameter of the rod piece in the unit cell;
step 3, selecting a TA15 titanium alloy spherical powder raw material;
step 4, in a forming chamber, using TA15 titanium alloy as a forming substrate, reducing the oxygen content of the forming chamber by argon gas scrubbing, and preheating a bottom plate after the scrubbing is finished;
step 5, preparing a lattice sandwich structure in a forming chamber by adopting a selective laser melting forming process, spreading powder by using a rubber scraper, and quickly melting and solidifying the powder by using a laser beam to superpose layer by layer until the lattice sandwich structure is completely formed;
and 6, after melting and forming, preserving heat in a forming chamber and then naturally cooling to room temperature.
According to the lightweight and strength indexes and the working conditions of parts (stress condition of structural parts and heat-conducting functional parts), the parts capable of being made into the dot matrix are determined through structure optimization design software, the parts are replaced by the dot matrix, then the forming process is simulated, and the dot matrix type and the dot matrix rod diameter with the minimum forming risk are selected. The wall thickness of the interlayer is generally determined by the weight reduction index, and if the overall weight is overweight, the wall thickness is reduced to meet the weight requirement.
In the step 3, the TA15 titanium alloy spherical powder has the particle size range of 15-53 mu m, the particle size distribution of d10:15-25 mu m, d50:25-35 mu m and d90:35-53 mu m, the dosage of the powder with three particle sizes is not required, the particle size distribution range is 15-53 mu m, and the fluidity is less than or equal to 40s/50g.
In the method for manufacturing the TA15 titanium alloy lattice sandwich structure, the TA15 titanium alloy spherical powder particles are melt-molded under laser irradiation, and the particle diameter of the particles is strictly limited, and is too large to be melted, so that the molded material contains insufficiently melted metal particles. However, if the particle size is too small, the spherical alloy powder particles are easily melted due to the too small particle size, and the particles near the laser irradiation region are melted by heat conduction, so that the shape is difficult to control. Therefore, the particle size is controlled to be in the range of 15 to 53 μm. Besides controlling the total particle size range of the particles, the particle size distribution of each size needs to be accurately controlled, wherein d10:15-25 μm, d50:25-35 μm and d90:35-53 μm. Powder flow properties are related to many factors such as powder particle size, shape and roughness, specific surface, etc. Generally, increasing the coefficient of friction between particles can make powder flow difficult. Generally, spherical particles have the best powder flowability, while irregular particles, small size, rough surface powders have poor flowability. Therefore, the flowability of the TA15 titanium alloy spherical powder particles is limited to be less than or equal to 40s/50g according to selective laser melting.
One possible improvement is that in step 4, the oxygen content in the forming chamber is reduced to less than or equal to 0.02% by argon gas scrubbing, and the soleplate is preheated to 120-140 ℃ after the scrubbing is finished.
The preheating bottom plate can reduce the residual stress in the forming process of the TA15 titanium alloy and reduce the risk of part cracking, and the preheating temperature is selected to be 120-140 ℃.
One possible improvement is that in step 5, the selective laser melting power is 300-350W, the scanning speed is 1000-1300mm/s, the scanning line spacing is 10-25 μm, and the powder layer thickness is 50-60 μm.
It should be noted that, when the scanning speed is fixed, if the laser power is low, the powder of the scanning line cannot be completely melted, so that the powder cannot be completely melted or in a sintered state, the pores in the molded part are increased, the density and the mechanical property are reduced, and holes are easily formed when the part is molded; conversely, if the power is too high, the molding is also not facilitated. This is because the powder absorbs more energy at a high laser power, the amount of metal powder melts more, and the molten metal tends to flow to both sides, resulting in widening of the molten pool. The wall width precision can not be ensured when the thin-wall part is formed; meanwhile, the cooling solidification time is prolonged due to the increase of molten metal, powder near a molten pool is more easily adsorbed and bonded on a scanning line, and the adhered powder causes surface roughness and influences the size precision during single-pass multi-layer molding; in a side analysis of the thin-walled part, it can be seen that the part still adsorbs the powder during the forming process. On the other hand, the surface tension of the solid-liquid interface of the large surface area of the molten pool is relatively larger, so that the tendency of melt spheroidization is more obvious. These are not favorable for precision molding, and therefore, an appropriate laser power is selected under a constant scanning speed. In general, in the forming process, the laser power and the scanning speed are selected in combination to form the part under suitable matching conditions. When the laser power is constant, the width of the molten pool is reduced along with the increase of the scanning speed, and a thinner molten channel can be obtained. At lower scan rates (< 1000 mm), there are more uniformly distributed circular holes in the shaped sample. However, when the speed exceeds 1300mm/s, a continuous scanning line cannot be formed. At high speed scanning, the quality of the scan line is poor and balling occurs. This is because at a high scanning speed, the energy absorbed by the powder is reduced, and a section or a part of the powder is melted on the scanning line due to the action of heat accumulation, and the melted metal powder adsorbs the unscanned powder to form a small ball, which causes the scanning line to break, which tends to cause incomplete fusion between layers or voids when the thin-wall part is formed. At higher laser power, the scan line break phenomenon caused by increased speed is weaker. Therefore, the selective laser melting power is 300-350W, and the scanning speed is 1000-1300mm/s.
The scanning line spacing h refers to the distance between the central lines of two adjacent melting channels. Under the condition that the laser power, the scanning rate and the powder layer spreading thickness are fixed, the TA15 titanium alloy is formed by only changing the scanning line spacing h (5, 10, 15, 20, 25 and 30 microns), the compactness of the sample obtained under different scanning line spacings is measured, and the compactness of the sample shows the trend of increasing and then decreasing along with the increase of the scanning line spacing: when the distance between the scanning lines is increased from 10 mu m to 20 mu m, the density increase of the sample reaches the maximum; when the distance between the scanning lines is further increased to 25 μm, the compactness of the sample is slightly reduced. And when the scan line pitch is less than 10 μm or more than 25 μm, the pattern density is drastically decreased. The distance between the scanning lines is controlled to be 10-25 mu m, the formed TA15 sample has good forming quality, and the defects such as obvious holes and the like are hardly observed.
One possible improvement is that the speed of the blade dusting in step 5 is 20-40mm/s.
It should be noted that the speed of the doctor blade application has an important influence in the solution according to the invention. The material used in the manufacturing process is a metal powder material that the powder spreading system needs to spread flat before each layer is laser melted. The invention requires that the powder spreading speed cannot be too high and is too high, because the recrystallized and condensed lattice is not completely solidified after the laser melting, the formed lattice structure can be scraped by a scraper when the powder spreading is too high, and on the other hand, the powder spreading is uneven because the powder spreading is too high by the scraper, the powder is thick in some places and thin in some places, and the formed structure after the melting is uneven. Therefore, the powder spreading speed of the scraper must be strictly controlled to be 20-40mm/s.
In the step 6, after selective laser melting and forming of the lattice sandwich structure, the lattice sandwich structure is first heat preserved in a forming chamber and then naturally cooled to room temperature, wherein the heat preservation temperature is 130-200 ℃, and the heat preservation time is 2-3 hours.
Example one
The present embodiment provides a TA15 titanium alloy lattice structure.
The lattice structure comprises a plurality of unit cells which are repeated in space and connected with one another to form a lattice;
the unit cell structure is shown in fig. 4-9, wherein fig. 4 is a front view of the lattice unit cell, fig. 5 is a top view of the lattice unit cell, and fig. 6 is a left view of the lattice unit cell.
The unit cell comprises a central piece 1, a rod piece 2 and a connecting piece 3;
eight rod pieces 2 are arranged in each unit cell and have the same length;
each guarantee is provided with a central piece, the central piece 1 is provided with a front square end face and a rear square end face, the thickness of the central piece 1 is 0.5mm, the side length of the end face of the central piece 1 is 1.5mm, two rod pieces 2 respectively extend from two sides of each angular end face of the central piece 1 to form two square cones which are symmetrical relative to the central piece, and symmetrical rod pieces in the two square cones share a vertex, as shown in fig. 7 and 8;
the included angles between all the rod pieces 2 and the end face of the central piece 1 are all 35 degrees and 16 ', and the included angles between the adjacent rod pieces 2 extending from the same end face are all 70 degrees and 32';
all the rod pieces 2 are triangular prisms, and the cross sections of the triangular prisms of the rod bodies are isosceles right triangles.
As shown in fig. 9, one end of each rod member 2 far from the central member 1 is connected with a corresponding connecting part 3, all connecting parts 3 are isosceles right triangular prisms, one end of each rod member 2 far from the central member 1 is bent by 125 degrees 16' along the largest side surface of each rod member 2 triangular prism to the inner side of each square pyramid to form a connecting part 3, and each connecting part 3 is closely attached to the connecting part 3 of an adjacent unit cell.
The length of each rod piece is 20mm, and the cross section area of each rod piece is 2mm 2 。
Example two
The embodiment provides a manufacturing method of a TA15 titanium alloy lattice sandwich structure, which comprises the following steps:
step 1, designing and determining a lattice structure as that of the first embodiment;
step 2, determining that the thickness of the thin wall surrounding the lattice is 0.8mm, and the thickness of the lattice between the upper wall plate and the lower wall plate is 5mm;
and 3, taking TA15 titanium alloy spherical powder as a raw material, controlling the particle size range to be 15-53 mu m, and controlling the particle size distribution to be d10:15-25 μm, d50:25-35 μm, d90:35-53 μm (the proportion of the three is not particularly required, the grain diameter is distributed between 15 μm and 53 μm), and the fluidity is less than or equal to 40s/50g;
step 4, in the forming chamber, using TA15 titanium alloy as a forming substrate, reducing the oxygen content in the forming chamber to be less than or equal to 0.02% by argon gas washing, and preheating the bottom plate to 120 ℃ after the argon gas washing is finished;
step 5, preparing a dot matrix sandwich structure in a forming chamber by adopting a selective laser melting forming process, spreading powder by using a rubber scraper, wherein the powder spreading speed is 25mm/s, the selective laser melting power is 300W, the scanning speed is 1200mm/s, the scanning line interval is 10 microns, the powder layer thickness is 50 microns, and the powder is rapidly melted and solidified by laser beams and is overlapped layer by layer until the dot matrix sandwich structure is completely formed;
and 6, after selective laser melting and forming of the lattice sandwich structure, preserving heat in a forming chamber, naturally cooling to room temperature, preserving heat at 120 ℃ for 3 hours.
The lattice sandwich structure manufactured in this example is shown in fig. 1 to 3. Through testing, the dot matrix sandwich structure can be rapidly prepared by selective laser melting and forming, and the method has the advantages of short manufacturing period and low cost, and the structure cannot be prepared by traditional machining and casting. The lattice sandwich structure has the advantage of light weight, and the weight reduction of the embodiment of the invention reaches 74.5 percent respectively.
The samples of the embodiment are subjected to compression testing, the strength of the samples reaches 703MPa, the tensile strength of the TA15 tensile test bar formed by selective laser melting is about 1000MPa, and the compression strength is about 1600MPa, so that the strength requirement of a common lattice sandwich structural member can be met, and meanwhile, the structure can be used for achieving the purposes of weight reduction or heat dissipation.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.

Claims (9)

1. A TA15 titanium alloy lattice structure is characterized in that the lattice structure comprises a plurality of unit cells which are repeated in space and connected with one another to form a lattice;
the unit cell comprises a central piece and a rod piece;
eight rod pieces are arranged in total and have the same length;
the central piece is provided with a front square end face and a rear square end face, the size of the central piece is 0.5mm to 1mm along the front direction and the rear direction, the side length of the end faces of the central piece is 0.5mm to 1.5mm, and a rod piece extends from each corner of each square end face of the central piece to form two square cones which are symmetrical relative to the central piece;
the included angle between the rod piece and the end face of the central piece is 35 degrees 16 ', and the included angle between the adjacent rod pieces extending from the same end face is 70 degrees 32';
the rod pieces are triangular prisms, and the cross sections of the triangular prisms are isosceles right triangles;
and one end of each rod piece, which is far away from the central piece, is connected with a corresponding connecting part, all the connecting parts are isosceles right triangular prisms, one end of each rod piece, which is far away from the central piece 1, is bent by 125-16' along the largest side surface of each rod piece triangular prism to the inner side of each square pyramid to form the connecting part, and the connecting parts are tightly attached and connected with the connecting parts of adjacent unit cells.
2. The TA15 titanium alloy lattice structure of claim 1, wherein the rods have a length of 10mm to 30mm and a cross-sectional area of 0.8mm 2 To 3.2mm 2 。
3. A TA15 titanium alloy lattice sandwich structure comprising the lattice structure of any one of claims 1-2.
4. The TA15 titanium alloy lattice sandwich structure of claim 3, wherein the lattice sandwich structure consists of an upper wall plate, a lattice and a lower wall plate from top to bottom;
the lattice interlayer is composed of the lattice structure, a plurality of unit cells of the lattice structure are repeated in space and are mutually connected, the front and back direction of a central part of each unit cell is parallel to the upper wall plate surface and the lower wall plate surface, the lower surface of the upper wall plate is connected with one end, away from the central rod, of a rod piece in the upper layer unit cell of the lattice structure, and the upper surface of the lower wall plate is connected with one end, away from the central rod, of a rod piece of the lower layer unit cell of the lattice structure.
5. A manufacturing method of TA15 titanium alloy lattice sandwich structure, which is used for preparing the TA15 titanium alloy lattice sandwich structure of claim 3, and comprises the following steps:
step 1, determining a lattice structure according to requirements on light weight and strength;
step 2, determining the thickness of a thin wall surrounding the lattice, and determining the size of a rod piece in the lattice unit cell;
step 3, selecting TA15 titanium alloy spherical powder as a forming raw material;
step 4, in a forming chamber, taking TA15 titanium alloy as a forming substrate, using argon gas to wash and reduce the oxygen content of the forming chamber, and preheating the forming substrate after the washing and the gas are finished;
step 5, preparing a lattice sandwich structure in a forming chamber by adopting a selective laser melting forming process, spreading powder by using a rubber scraper, and quickly melting and solidifying the powder by using a laser beam to superpose layer by layer until the lattice sandwich structure is completely formed;
and 6, after melting and forming, preserving heat in a forming chamber and then naturally cooling to room temperature.
6. The method for manufacturing TA15 titanium alloy lattice sandwich structure according to claim 5, wherein in the step 3, the grain size of the TA15 titanium alloy spherical powder ranges from 15 μm to 53 μm, the grain size distribution is d10:15 μm to 25 μm, d50:25 μm to 35 μm, d90:35 μm to 53 μm, and the fluidity is less than or equal to 40s/50g.
7. The method of claim 5 wherein in step 4, the oxygen content in the forming chamber is reduced to 0.02% or less by argon gas scrubbing, and the formed substrate is preheated to 120-140 ℃ after the scrubbing is completed.
8. The method for manufacturing TA15 titanium alloy lattice sandwich structure according to claim 5, wherein in the step 5, the selective laser melting power is 300W to 350W, the scanning speed is 1000mm/s to 1300mm/s, the scanning line spacing is 10 μm to 25 μm, and the powder layer thickness is 50 μm to 60 μm.
9. The method for manufacturing TA15 titanium alloy dot matrix sandwich structure according to claim 5, wherein the speed of blade dusting in step 5 is 20mm/s to 40mm/s.
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