3D printing armor-piercing bullet and manufacturing method thereof

Abstract

The invention discloses a 3D printing armor-piercing bullet and a manufacturing method thereof, and belongs to the technical field of armor-piercing bullets, the 3D printing armor-piercing bullet comprises a shell and a steel core arranged in the shell, a gap is reserved in the front end area between the steel core and the shell, and a gradient lattice structure is arranged in the remaining area; the shell, the steel core and the gradient lattice structure are all made of high-strength steel, and the shell, the steel core and the gradient lattice structure are all integrally formed through the 3D printing technology. The shell is provided with an opening tightening groove. By means of the 3D printing technology, the core problems that a traditional armor-piercing bullet is long in production period, high in cost, large in material waste, limited in precision and the like are solved, meanwhile, the armor-piercing performance and the energy utilization efficiency are remarkably improved through structural innovation, and an efficient and sustainable solution is provided for the ammunition manufacturing field.

Description

Technical Field

[0001] The present invention relates to the technical field of armor-piercing bullets, and particularly to a 3D printed armor-piercing bullet and its manufacturing method. Background Art

[0002] After years of development, armor-piercing bullets have been relatively mature in terms of structural design and performance. However, under the traditional manufacturing process, armor-piercing bullets are gradually showing bottlenecks in terms of performance breakthrough, cost control, and production efficiency: The production cycle of traditional armor-piercing bullets is long: Traditional manufacturing requires multiple complex processes, such as stamping and forming the bullet head, mechanical finishing, etc. Each step requires a certain amount of time and process preparation, making it difficult to meet the needs of emergency combat.

[0003] The mold cost of traditional armor-piercing bullets is high: Traditional manufacturing processes usually require customized special molds to produce components such as bullet heads and cartridge cases. The design, manufacturing, and maintenance costs of these molds are relatively high, especially for special model ammunitions.

[0004] The processing accuracy of traditional armor-piercing bullets is limited: Although traditional machining technologies have been relatively mature, there are still problems with limited accuracy when producing components of armor-piercing bullets with small and complex structures.

[0005] Traditional armor-piercing bullets waste more materials: During the traditional manufacturing process, a large amount of scraps and waste are generated during the processing of metal materials, and the material utilization rate is relatively low.

[0006] The rise of 3D printing technology brings a new reform idea for armor-piercing bullets. It can break through the limitations of traditional manufacturing, realize complex structural design, achieve precise shape control, and inject innovative vitality into the development of armor-piercing bullets.

[0007] Based on this, a 3D printed armor-piercing bullet and its manufacturing method are proposed. Summary of the Invention

[0008] The purpose of the present invention is to provide a 3D printed armor-piercing bullet and its manufacturing method to solve the problems in the background art.

[0009] To achieve the above object, the present invention provides a 3D printed armor-piercing bullet, including a shell and a steel core disposed inside the shell. There is a gap in the front region between the steel core and the shell, and a gradient lattice structure is provided in the remaining region. The materials of the shell, the steel core, and the gradient lattice structure are all high-strength steel, and the shell, the steel core, and the gradient lattice structure are integrally formed by 3D printing technology; a crimping groove is provided on the shell.

[0010] Preferably, the gradient lattice structure includes an outer dense layer and an inner sparse layer. The porosity of the outer dense layer is 20% - 30%, the side length of the unit cell is 3 - 4 mm, and the rod diameter is 0.8 - 1.2 mm. The porosity of the inner sparse layer is 50% - 70%, the side length of the unit cell is 2 - 3 mm, and the rod diameter is 0.4 - 0.6 mm.

[0011] Based on the above 3D printed armor-piercing bullets, the present invention provides a manufacturing method, which includes the following steps: S1. Pretreat the high-strength steel powder and the forming chamber substrate; S2. Lay the powder bed, set the process parameters for printing, use a dense lattice structure for support during the printing process and perform interlayer cooling to complete one layer of printing; S3. Repeat S2 for layer-by-layer printing until the entire armor-piercing bullet is printed; S4. Perform strengthening treatment and quality inspection.

[0012] Preferably, the pretreatment in S1 is specifically as follows: spheroidize the high-strength steel powder by using plasma spheroidization or gas flow pulverization, and after completion, bake the high-strength steel powder in a vacuum or inert gas environment for deoxidation treatment; coat the forming chamber substrate with a titanium alloy or nickel-based alloy foil; Among them, the baking temperature is 100 - 150 °C, and the baking time is 2 h.

[0013] Preferably, when laying the powder bed in S2, maintain the vacuum degree at 10⁻ 5 mbar, and the powder laying accuracy is ±5 μm.

[0014] Preferably, in S2, the specific process parameters are set as follows: the electron beam power is 2500 - 3500 W, the scanning speed is 600 - 1000 mm / s, the layer thickness is 50 - 80 μm, the scanning strategy is rotation filling + checkerboard, the preheating temperature is 800 - 1000 °C, and Ar gas is used for protection.

[0015] Preferably, in S2, adjust the interlayer cooling by adjusting the pumping rate of the vacuum chamber; the spacing of the dense lattice structure ≤ 2 mm.

[0016] Preferably, the strengthening treatment in S4 includes heat treatment and surface nitriding treatment. The heat treatment includes stress relief annealing, quenching and tempering; the surface nitriding treatment is specifically depositing a TiN coating with a thickness of 3 - 5 μm.

[0017] Preferably, the stress relief annealing is carried out at a temperature of 600 - 700 °C for 2 h; the quenching is carried out by oil quenching or step quenching at a temperature of 850 - 900 °C for 1 h, and after quenching, a martensite matrix with a hardness of HRC50 - 55 is obtained; the tempering is carried out at a temperature of 200 - 300 °C for 2 - 4 h.

[0018] Preferably, the quality inspection in S4 is specifically as follows: CT scanning is used to detect internal shrinkage porosity, and the allowable pore diameter is < 0.5 mm; eddy current testing is used to identify surface microcracks, and the sensitivity is ≤ 0.1 mm; the inner diameter tolerance of the shell is ± 0.02 mm.

[0019] Therefore, the 3D printed armor - piercing bullet and its manufacturing method of the present invention have the following beneficial effects: (1) Through 3D printing technology, integrated molding is realized without the need for molds, simplifying the production process. With the characteristics of on - demand manufacturing, personalized ammunition can be quickly customized, significantly shortening the R & D cycle and reducing costs. Combining with the "near - net - shape forming" characteristics, the material utilization rate is significantly improved, avoiding the generation of a large amount of waste in traditional machining and reducing material waste.

[0020] (2) The outer layer of the gradient lattice structure adopts a dense structure to withstand high pressure, and the inner layer adopts a sparse structure to buffer impact energy. Through layer - by - layer stacking, a complex pore distribution that cannot be achieved by traditional manufacturing is realized. Together with the printing process parameters, it ensures high - precision manufacturing, breaking through the precision limitations of traditional machining for small and complex parts.

[0021] (3) Through 3D printing technology, the wall thickness of the shell is effectively reduced, and the remaining space is filled with lightweight lattices, which can save mass and transfer it to the steel core to enhance the armor - piercing kinetic energy; the gradient lattice structure absorbs impact energy through controllable plastic deformation, reduces the oscillation of the projectile body, and conducts the shock wave to the steel core directionally, improving the energy utilization rate; by adjusting the centroid, equatorial moment of inertia and polar moment of inertia of the warhead through the distribution of voids and gradient lattice structures, the proportion of effective mass during the penetration process is higher, significantly enhancing the armor - piercing depth and optimizing the performance of the warhead.

[0022] (4) High - density materials are only used in key stress - bearing areas (such as the steel core), and lightweight lattices are used in non - critical areas, achieving precise material distribution and taking into account both strength and lightweight.

[0023] (5) Through 3D printing technology, the digital and intelligent transformation of ammunition manufacturing is realized, breaking the bondage of traditional processes on structural design, providing a realization path for complex functional structures (such as lattice filling, gradient pores), and driving the technological upgrading of the industry.

[0024] The technical solutions of the present invention will be further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the structure of a 3D printed armor-piercing bullet according to the present invention; Reference numerals: 1. Outer shell; 2. Steel core; 3. Gap; 4. Gradient lattice structure; 5. Tightening groove. Specific embodiments

[0026] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention.

[0028] As Figure 1 shown, a 3D printed armor-piercing bullet provided by the present invention includes an outer shell 1 and a steel core 2 disposed inside the outer shell 1. The outer shell 1 has sufficient strength, hardness, and impact resistance to effectively protect internal components such as the bullet core during firing and flight, maintain the aerodynamic shape, enable the bullet to smoothly enter the gun barrel, and induce rotation to give the bullet rotational stability; the steel core 2 penetrates and concentrates energy to penetrate the armor when hitting the target due to its high hardness.

[0029] A gap 3 is left in the front region between the steel core 2 and the outer shell 1 for adjusting the centroid position and moment of inertia of the bullet and improving the armor-piercing ability; a gradient lattice structure 4 is provided in the remaining region between the steel core 2 and the outer shell 1 except for the gap 3. The gradient lattice structure 4 includes an outer dense layer and an inner sparse layer. The porosity of the outer dense layer is 20% - 30%, the side length of the unit cell is 3 - 4 mm, and the rod diameter is 0.8 - 1.2 mm to withstand high pressure; the porosity of the inner sparse layer is 50% - 70%, the side length of the unit cell is 2 - 3 mm, and the rod diameter is 0.4 - 0.6 mm to buffer the impact energy.

[0030] The gradient lattice structure 4 combines the functions of the jacket and lead sleeve of traditional armor-piercing bullets. It can not only effectively protect the internal steel core 2, but also has a buffering and sealing effect, has good flexibility, can closely cooperate with the bullet core during bullet firing, and can effectively transfer energy after hitting the target to improve the armor-piercing effect.

[0031] The distribution of the lattice structure and the gap 3 can change the centroid, equatorial moment of inertia, and polar moment of inertia of the bullet head, optimize the internal mass distribution of the bullet head, make the proportion of the effective penetration mass higher during the armor-piercing process, and enhance the penetration effect.

[0032] The materials of the outer shell 1, the steel core 2, and the gradient lattice structure 4 are all high-strength steel (such as 30CrMnSi), and the three are integrally formed by 3D printing technology; a tightening groove 5 is provided on the outer shell 1 for connecting the cartridge case.

[0033] The manufacturing method of the above 3D printed armor-piercing bullet is realized by electron beam melting technology (EBM) and includes the following steps: S1. Pretreat the high-strength steel powder and the forming chamber substrate. Specifically: (1) Powder spheroidization treatment: The high-strength steel powder is prone to agglomeration. Plasma spheroidization or air flow pulverization is used to spheroidize the high-strength steel powder to improve fluidity. (2) Powder deoxidation treatment: After the spheroidization treatment, bake the high-strength steel powder in a vacuum or inert gas (Ar or N2) environment. The baking temperature is 100~150°C, and the baking time is 2h to reduce the oxygen content. (3) Coat the forming chamber substrate with a titanium alloy or nickel-based alloy foil, such as IN718, to reduce the difference in thermal expansion coefficients between the high-strength steel and the substrate and reduce thermal stress.

[0034] S2. Perform powder bed laying, set process parameters for printing, use a dense lattice structure for support and perform interlayer cooling during the printing process to complete one layer of printing. Among them: (1) When performing powder bed laying, maintain a vacuum degree of 10⁻ 5 mbar to prevent high-temperature oxidation of high-strength steel; the powder laying accuracy is ±5μm to ensure the dimensional accuracy of the lattice structure. (2) The specific process parameter settings are as follows: The electron beam power is 2500~3500W. Since the melting point of high-strength steel is high, it is necessary to balance the melt depth and heat input to ensure printing quality; the scanning speed is 600~1000mm / s, which can control the interlayer temperature gradient; the layer thickness is 50~80μm to improve the Z-axis resolution; the scanning strategy is rotation filling + checkerboard, which can suppress residual stress and deformation; the preheating temperature is 800~1000°C to reduce thermal stress; Ar gas is used for protection. In this embodiment, the Ar gas flow rate is doubled to exclude the air in the forming chamber and prevent high-strength steel oxidation. (3) During the printing process, since the thermal conductivity of high-strength steel is low, it is necessary to cool slowly, and the interlayer cooling is adjusted by adjusting the pumping rate of the vacuum chamber; the spacing of the dense lattice structure is ≤2mm, and auxiliary supports are added in the thin-walled area of the outer shell 1.

[0035] S3. Repeat S2 for layer-by-layer printing until the entire armor-piercing bullet is printed.

[0036] S4. To improve the power of the armor-piercing bullet and ensure the strength and hardness of the armor-piercing steel core 2, the armor-piercing bullet after 3D printing is subjected to strengthening treatment and quality inspection. The strengthening treatment includes heat treatment and surface nitriding treatment, specifically as follows: (1) The surface nitriding treatment is to deposit a TiN coating with a thickness of 3 - 5 μm to improve wear resistance; (2) To avoid excessive strength and hardness of the material after heat treatment, which is not conducive to the smooth entry of the armor-piercing bullet into the gun chamber, in this embodiment, a thinner outer shell 1 is provided, and a gradient lattice structure 4 with a large gap 3 and thinner cell rods is filled between the steel core 2 and the outer shell 1; The heat treatment includes stress relief annealing, quenching and tempering: The temperature of stress relief annealing is 600 - 700 °C, and the time is 2 h to eliminate the residual stress of EBM printing and prevent the outer shell 1 from warping; Oil quenching or step quenching is used for quenching, the quenching temperature is 850 - 900 °C, and the time is 1 h. After quenching, a martensite matrix with a hardness of HRC50 - 55 is obtained; The tempering temperature is 200 - 300 °C, and the time is 2 - 4 h.

[0037] (3) The quality inspection is specifically as follows: CT scanning is used to detect internal shrinkage porosity, and the allowable pore diameter < 0.5 mm; Eddy current testing is used to identify surface microcracks, and the sensitivity ≤ 0.1 mm; The inner diameter tolerance of the outer shell 1 is controlled within ±0.02 mm.

[0038] Embodiment Based on the above manufacturing method of 3D printed armor-piercing bullets, the present invention provides a specific manufacturing and inspection method, and the steps are as follows: S1. The 30CrMnSi powder is spheroidized by plasma spheroidization, and after completion, it is baked in a vacuum environment. The baking temperature is 130 °C, and the baking time is 2 h; And IN718 is coated on the forming chamber substrate.

[0039] S2. Powder bed laying is carried out, and the vacuum degree is maintained at 10⁻ 5 mbar, and the powder laying accuracy is ±5 μm; The process parameters are set for printing, specifically set as follows: The electron beam power is 2700 W, the scanning speed is 800 mm / s, the layer thickness is 70 μm, the scanning strategy is rotary filling + checkerboard, the preheating temperature is 900 °C, and double Ar gas is introduced for protection; During the printing process, a dense lattice structure with a spacing of 1.5 mm is used for support, and after one layer of printing is completed, the interlayer cooling is adjusted by adjusting the pumping rate of the vacuum chamber.

[0040] S3. S2 is cycled for layer-by-layer printing until the entire armor-piercing bullet is printed.

[0041] S4. The armor-piercing bullet after 3D printing is successively subjected to: ① Stress relief annealing: temperature is 700 °C, time is 2 h; ② Quenching: oil quenching is carried out, temperature is 900 °C, time is 1 h; ③ Tempering: temperature is 300 °C, time is 3 h; ④ Deposit TiN coating, the thickness of the TiN coating is 4 μm.

[0042] The armor-piercing bullets obtained above are detected, including CT scanning, eddy current testing and dimensional accuracy measurement. It is measured that the allowable hole diameter < 0.5 mm, the defect diameter < 0.1 mm, and the inner diameter tolerance of the outer shell 1 is controlled within ±0.02 mm.

[0043] When the above-mentioned qualified 3D printed armor-piercing bullets impact the target plate at high speed, the tip of the outer shell 1 first contacts the surface of the target plate and undergoes plastic deformation. Immediately afterwards, the head of the steel core 2 contacts the surface of the target plate, generating an extremely high pressure in a very short time. This pressure far exceeds the yield strength of the target plate material, causing the surface material of the target plate to undergo plastic deformation. At the same time, the steel core 2 will also receive the reaction force of the target plate, and this reaction force will cause a certain degree of elastic deformation of the steel core 2, and even form a stress wave at the head of the steel core 2, propagating into the steel core 2.

[0044] As the steel core 2 continues to penetrate into the target plate, the pressure at the head of the steel core 2 continues to act, causing the target plate material to be continuously extruded and sheared, forming a penetration hole similar to the shape of the steel core 2. When the steel core 2 penetrates to a certain depth, a complex stress distribution will be formed inside the target plate. Around the steel core 2, the material is subjected to various stresses such as tension, compression and shear, resulting in cracks and fragmentation of the target plate material. During this process, the gradient lattice structure 4 undergoes controllable plastic deformation, absorbs impact energy, reduces the oscillation of the projectile, and conducts the shock wave in a directional manner to the steel core 2, reducing the energy loss in the outer shell 1 and improving the energy utilization rate.

[0045] As the steel core 2 continues to penetrate, these cracks will continuously expand and connect, eventually leading to local damage and shedding of the target plate material, forming fragments. When the kinetic energy of the steel core 2 is not sufficient to continue penetrating the target plate, the steel core 2 will stop moving and remain inside the target plate or penetrate through the target plate. The steel core 2 that penetrates through the target plate may continue to fly for a certain distance and cause damage to the target behind the target plate.

[0046] Therefore, a 3D printed armor-piercing bullet and its manufacturing method according to the present invention achieve integrated ammunition molding, eliminate the need for molds, simplify the process, enable on-demand manufacturing, shorten the R & D cycle, reduce costs, and improve material utilization rate; its gradient lattice structure meets high-pressure resistance and impact buffering, realizes complex pore distribution, and breaks through accuracy limitations; by thinning the outer shell wall thickness and filling with lightweight lattices, the mass is transferred to the steel core, enhancing the armor-piercing kinetic energy and optimizing the bullet performance; the precise material distribution achieves strength and lightweight, promotes the digitalization and intelligence of ammunition manufacturing, provides a realization path for complex functional structures, and promotes the technological upgrading of the industry.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A 3D printed armor-piercing bullet, characterized in that: It includes a shell and a steel core arranged inside the shell. There is a gap in the front region between the steel core and the shell, and a gradient lattice structure is arranged in the remaining region. The materials of the shell, the steel core, and the gradient lattice structure are all high-strength steel, and the shell, the steel core, and the gradient lattice structure are integrally formed by 3D printing technology; a tightening groove is arranged on the shell.

2. The 3D printed armor-piercing bullet according to claim 1, wherein: The gradient lattice structure includes an outer dense layer and an inner sparse layer. The porosity of the outer dense layer is 20% - 30%, the side length of the cell size is 3 - 4 mm, and the rod diameter is 0.8 - 1.2 mm; the porosity of the inner sparse layer is 50% - 70%, the side length of the cell size is 2 - 3 mm, and the rod diameter is 0.4 - 0.6 mm.

3. The manufacturing method of the 3D printed armor-piercing bullet according to any one of claims 1-2, which is realized by an electron beam melting technique, is characterized in that, It includes the following steps: S1. Pretreat the high-strength steel powder and the forming chamber substrate; S2. Conduct powder bed laying, set process parameters for printing, use a dense lattice structure for support and perform interlayer cooling during the printing process, and complete one layer of printing; S3. Repeat S2 for layer-by-layer printing until the entire armor-piercing bullet is printed; S4. Conduct strengthening treatment and quality inspection.

4. A manufacturing method of a 3D printed armor-piercing bullet according to claim 3, characterized in that, The pretreatment in S1 is specifically: spheroidize the high-strength steel powder by plasma spheroidization or air flow pulverization, and after completion, bake the high-strength steel powder in a vacuum or inert gas environment for deoxidation treatment; coat the forming chamber substrate with a titanium alloy or nickel-based alloy foil; Among them, the baking temperature is 100 - 150 °C, and the baking time is 2 h.

5. The manufacturing method of a 3D printed armor-piercing bullet according to claim 3, characterized in that: When laying the powder bed in S2, maintain a vacuum degree of 10⁻ 5 mbar and a powder laying accuracy of ±5 μm.

6. The manufacturing method of a 3D printed armor-piercing bullet according to claim 3, characterized in that, In S2, the specific process parameters are set as follows: the electron beam power is 2500 - 3500 W, the scanning speed is 600 - 1000 mm / s, the layer thickness is 50 - 80 μm, the scanning strategy is rotation filling + checkerboard, the preheating temperature is 800 - 1000 °C, and Ar gas is used for protection.

7. The manufacturing method of a 3D printed armor-piercing bullet according to claim 3, characterized in that: The strengthening treatment in S4 includes heat treatment and surface nitriding treatment, and the heat treatment includes stress relief annealing, quenching, and tempering.

8. The manufacturing method of a 3D printed armor-piercing bullet according to claim 7, characterized in that: The temperature of the stress relief annealing is 600 - 700 °C, and the time is 2 h; the quenching uses oil quenching or step quenching, the quenching temperature is 850 - 900 °C, and the time is 1 h. After quenching, a martensite matrix with a hardness of HRC50 - 55 is obtained; the tempering temperature is 200 - 300 °C, and the time is 2 - 4 h.

9. The manufacturing method of a 3D printed armor-piercing bullet according to claim 3, characterized in that, The quality inspection in S4 is specifically: use CT scanning to detect internal shrinkage porosity, allowing the pore diameter < 0.5 mm; use eddy current testing to identify surface microcracks, with a sensitivity ≤ 0.1 mm; the inner diameter tolerance of the shell is ±0.02 mm.

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