A free-standing thin-walled laser powder-fed additive manufacturing process

Abstract

This invention relates to the field of laser powder feeding additive manufacturing technology. Addressing the problems of cumbersome existing unsupported structure additive manufacturing processes and the difficulty in achieving additive manufacturing through coaxial laser powder feeding, this invention specifically discloses an unsupported thin-walled laser powder feeding additive manufacturing process, comprising the following steps: S1 assembling a metal substrate on the worktable of an additive manufacturing equipment; S2 disassembling the inclined thin-walled model into several strip-shaped rods, determining the forming path, controlling the inclination angle of the long rods to be greater than the inclination angle of the thin wall, and the interval between adjacent rods being πR / 2cosθ, where R is the cross-sectional radius of the rod and θ is the inclination angle of the rod; S3 setting process parameters and printing the rods to form a thin wall. By achieving oblique growth of the rods through the surface tension of the molten pool, and then having the rods overlap to form the thin wall, the addition of structural supports during the printing process can be avoided, improving material utilization, reducing post-processing requirements, lowering equipment requirements, and providing flexible operation, enabling additive manufacturing of unsupported thin-walled structures at various angles.

Description

Technical Field

[0001] This invention relates to the field of laser powder feeding additive manufacturing technology, and more specifically, to a supportless thin-walled laser powder feeding additive manufacturing process. Background Technology

[0002] Additive manufacturing technology, as one of the most revolutionary manufacturing technologies of the 21st century, has been widely applied in aerospace, biomedicine, automotive manufacturing, and precision instruments. Laser powder additive manufacturing is an additive manufacturing technology that uses a laser as a heat source and metal powder as a raw material. During the movement of the laser head, the material is delivered to the laser spot for melting and deposition. By stacking layers one by one, parts can be rapidly and cleanly formed. It has the characteristics of high forming efficiency and can print metal parts with various complex shapes.

[0003] How to manufacture products without support structures using additive manufacturing technology has always been one of the major challenges facing additive manufacturing technology. During the metal melting and deposition process, the material is affected by gravity, and the suspended area will deform and collapse. Traditional methods often require the addition of support structures to prevent deformation and collapse in the suspended area, but this not only increases material consumption and post-processing difficulty, but also limits design freedom and complicates the process.

[0004] Currently, there are many methods for achieving supportless additive manufacturing, including printing path planning and real-time process control. For example, patent CN117182106A provides a supportless laser selective melting additive manufacturing method. This method pre-lays powder in the overhanging area, and melts or sintersulates the powder surface by increasing the laser spot size and reducing the laser power to form a relatively loose overhanging layer. Then, remelting is performed to improve the bonding quality and density, forming a continuous single-layer part cross-section sheet. Finally, other areas of the part are melted normally and connected with the overhanging layer.

[0005] However, the existing methods for achieving unsupported additive manufacturing are almost all laser powder bed melting additive manufacturing, which makes it difficult to achieve unsupported additive manufacturing through coaxial laser powder feeding. This makes the manufacturing process complicated, requires high-end equipment, and makes it difficult to achieve mass production in actual production. Summary of the Invention

[0006] The purpose of this invention is to solve the problem that the existing additive manufacturing process for unsupported structures is cumbersome and it is difficult to achieve additive manufacturing through coaxial laser powder feeding.

[0007] This invention is achieved through the following technical solution:

[0008] This invention provides a supportless thin-walled laser powder feeding additive manufacturing process, which is applicable to coaxial laser powder feeding and can realize inclined thin-walled supportless additive manufacturing. It has the characteristics of low equipment requirements and simple operation.

[0009] Specifically, the following steps are included: (1) Assemble the metal substrate on the worktable of the additive manufacturing equipment; (2) The inclined thin-walled model is divided into several strip-shaped rods to determine the forming path; (3) Set process parameters and print rods to form thin walls by deposition from lines to surfaces.

[0010] In step (1), the additive manufacturing equipment uses a coaxial laser powder feeding machine, including a powder feeder, argon cylinder, laser head, chiller, and coordinate measuring machine, such as... Figure 1 As shown.

[0011] Metal powder raw materials are loaded into the powder feeder and connected to an argon cylinder. The powder is then transported to the laser head by the powder-carrying gas flow.

[0012] The chiller is connected to the laser head and supplies circulating coolant to cool the laser head while it is working, ensuring continuous operation of the laser head.

[0013] The laser head is mounted on a support component in a coordinate measuring machine tool, and the laser head is slidably connected to the support component of the coordinate measuring machine tool, enabling free movement within space.

[0014] During operation, the coaxial laser is focused through the internal optical path of the laser head, melting the annular powder flow conveyed by the powder feeder, thereby achieving the deposition of metal materials. In this process, the machine tool moves according to the preset scanning path to achieve the deposition and shaping of materials.

[0015] In step (2), such as Figure 2 As shown, the inclined thin-walled model is divided into several strip-shaped rods, and the inclination angle of the long rods is controlled to be greater than that of the thin wall to ensure that the powder can fall vertically above the already formed material when the rod is formed. The rod being formed is supported by overlapping the previous rod to enhance the forming stability and further prevent collapse.

[0016] In addition, the center distance between adjacent long poles should be determined to achieve overlapping between poles, such as Figure 3 As shown. The actual printed rod cross-section is considered circular, with the interval between adjacent rods being πR / 2cosθ, where R is the radius of the rod's cross-section and θ is the rod's inclination angle. At this point, the material in the overlapping portion of the cross-section precisely fills the edge of the rod smoothly. The thin-walled dimensions are controlled by the number and length of the rods. By changing the number of rods arranged in the wall thickness direction, the wall thickness can be easily controlled. Furthermore, the deposition path is from line to surface; by changing the path of the rod's central axis, the forming of complex cross-sections other than straight walls can be achieved. After the thin-walled model is decomposed into rods, the central axis of each rod corresponds to the deposition path during the printing process.

[0017] In step (3), in the initial stage, the laser emits light at a normal power of 700-900W, with a powder emission rate of 0-3g / min. The laser remains stationary for a short period, with a continuous emission time ≥3s, forming a full molten metal pool on the substrate surface. This ensures sufficient material diffusion and facilitates the connection between the thin-walled structure and the substrate. Then, in the forming stage, the laser head moves at a lower power of 200-400W along the central axis of the rod at a slower scanning speed of 30-50mm / min, with a powder emission rate of 4-8g / min. Using small laser input parameters ensures good dimensional accuracy in the forming process. After the powder material melts, it is fed into the molten pool, and the surface tension of the molten pool prevents material collapse. During laser additive manufacturing printing, the laser spot diameter is 3-5mm. The process described in this step, which involves the deposition of a thin wall from a line to a surface, specifically refers to the following: the forming rods are supported by overlapping with the previous rods, and the next rod is deposited along the direction of the thin rod arrangement. Through the overlapping of the rods, a whole metal thin wall is finally assembled.

[0018] The technical solution of the present invention has the following beneficial effects: This invention uses a coaxial laser powder feeding machine for unsupported thin-walled printing. The thin-walled structure is disassembled into several rods for printing. The rods are obliquely grown by the surface tension of the molten pool, and then the rods overlap to form the thin-walled structure. This avoids the need to add structural supports during the printing process, reduces post-processing requirements, has low equipment requirements, is flexible in operation, and can realize additive manufacturing of unsupported thin-walled structures at various angles. It simplifies the process while improving material utilization. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the additive manufacturing equipment in Example 1; Figure 2 This is a structural diagram of the inclined thin-walled model in Example 1 broken down into several rods; Figure 3 This is a schematic diagram illustrating the calculation and measurement of the center distance between adjacent long poles in Example 1. Detailed Implementation

[0020] 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. Where specific conditions are not specified in the embodiments, they are performed according to conventional conditions or conditions recommended by the manufacturer; where the manufacturers of the instruments, equipment, reagents, or raw materials used are not specified, they are all conventional products that can be purchased commercially.

[0021] Example 1 In this embodiment, a 20mm thick 316L stainless steel sheet is used as the substrate. This is because the heat source energy of laser powder feeding additive manufacturing is concentrated, the cooling process is faster, and stress and deformation are easily generated. At the same time, the laser head does not move at the beginning of the printing process, which can easily burn through the substrate. Therefore, a thicker substrate is used.

[0022] The metal substrate is assembled on the worktable of the additive manufacturing equipment, and the thin wall is disassembled into 45° inclined rods. 316L stainless steel powder is used as the printing material, and printing is performed according to the process parameters shown in Table 1 to form the thin wall. The rods are then overlapped to form a single piece of metal thin wall. Actual measurements show that the rod diameter is approximately 5mm, i.e., R=2.5mm, θ=45°. Substituting πR / 2cosθ, the theoretical rod spacing is approximately 5.5mm.

[0023] Table 1. Process parameters for 316L thin-walled additive manufacturing in Example 1

[0024] This embodiment achieves good thin-walled additive manufacturing printing results by coordinating the tilt angle, arrangement interval, and process parameters of the rods. The operation process is relatively simple and has low equipment requirements.

[0025] Comparative Example 1 The difference between this comparative example and Example 1 is that the powder output rate in the initial stage is 5 g / min, and the powder output rate in the forming stage is 10 g / min.

[0026] The results showed that the powder feeding rate in this comparative example was too high, the heat input to the molten pool was insufficient, the molten pool was not flat enough, the layer height increased too quickly, and the horizontal movement speed of the molten pool was too low. At this time, the tilt angle θ of the rod would decrease, the horizontal movement speed of the laser head would be greater than the horizontal growth speed of the molten pool, less powder would enter the molten pool, the rod would become thinner, and eventually neither the light spot nor the powder could enter the molten pool, the rod would stop growing, and it would take on an inverted cone shape.

[0027] Comparative Example 2 The difference between this comparative example and Example 1 is that the powder output rate in the initial stage is 0.1 g / min, and the powder output rate in the molding stage is 2 g / min.

[0028] The results showed that the powder feeding rate in this comparative example was too low, resulting in severe heat accumulation in the molten pool, direct collapse of the molten pool, and cessation of rod growth.

[0029] Comparative Example 3 The difference between this comparative example and Example 1 is that the scanning speed is 20 mm / min.

[0030] The results showed that the scanning speed in this comparative example was too low. At this speed, the laser head's lifting speed could not keep up with the rod's growth rate, causing the rod's tilt angle θ to decrease. Simultaneously, the distance between the molten pool and the laser head decreased, causing the laser spot and powder spot focal points to deviate from the molten pool, resulting in less powder entering and melting. As the rod became thinner and its growth slowed, θ increased, and the laser spot and powder spot focal points gradually returned to the molten pool surface. This process repeated, leading to uneven rod shape. Consequently, when the rods could not be joined into a thin wall, incomplete fusion voids appeared.

[0031] Comparative Example 4 The difference between this comparative example and Example 1 is that the scanning speed is 60 mm / min.

[0032] The results showed that the scanning speed of this comparative example was too high. At this time, the growth rate of the rod could not keep up with the lifting speed of the laser head. The horizontal and numerical distances between the molten pool and the laser head became farther and farther. The offset of the light spot and powder spot became more and more serious. The rod became thinner and thinner. Finally, the rod stopped growing and showed an inverted cone shape.

[0033] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A supportless thin-walled laser powder feeding additive manufacturing process, characterized in that, Includes the following steps: S1 assembles the metal substrate onto the worktable of the additive manufacturing equipment; S2 breaks down the inclined thin-walled model into several strip-shaped rods to determine the forming path; S3 sets the process parameters and performs additive manufacturing printing of the rod, forming a thin wall through line-to-surface deposition.

2. The unsupported thin-walled laser powder feeding additive manufacturing process according to claim 1, characterized in that, In step S3, the additive manufacturing printing of the rod includes an initial stage and a forming stage; In the initial stage, the laser power is 700-900W and the powder output rate is 0-3g / min; During the molding stage, the laser power is 200-400w and the powder output speed is 4-8g / min.

3. The unsupported thin-walled laser powder feeding additive manufacturing process according to claim 2, characterized in that, In the initial stage, after the powder is released, the position remains unchanged and light is continuously emitted for a duration of ≥3s, forming a full molten metal pool on the substrate surface.

4. The unsupported thin-walled laser powder feeding additive manufacturing process according to claim 2, characterized in that, During the forming stage, the scanning speed is 30-50 mm / min.

5. The unsupported thin-walled laser powder feeding additive manufacturing process according to claim 1, characterized in that, In additive manufacturing printing of rods, the laser spot diameter is 3-5mm.

6. The unsupported thin-walled laser powder feeding additive manufacturing process according to claim 1, characterized in that, In step S2, the tilt angle of the long rod is controlled to be greater than the tilt angle of the thin wall, so that when the rod is formed, the powder falls vertically above the already formed material.

7. The unsupported thin-walled laser powder feeding additive manufacturing process according to claim 6, characterized in that, The spacing between adjacent members is πR / 2cosθ, where R is the cross-sectional radius of the member and θ is the inclination angle of the member.

8. The unsupported thin-walled laser powder feeding additive manufacturing process according to claim 1, characterized in that, The additive manufacturing equipment includes a powder feeder, an argon cylinder, a laser head, a chiller, and a coordinate measuring machine tool. The laser head is mounted in the coordinate measuring machine tool and is slidably connected to the support of the coordinate measuring machine tool. The laser head is connected to the powder feeder and the chiller, and the powder feeder is connected to the argon cylinder.

Images