Additive hybrid forging printing method and system for avoiding powder blowing by ultrafast laser shock waves

Abstract

The application provides an additive composite forging printing method and system for avoiding powder blowing of superfast laser shock waves, and the method comprises the following steps: powder laying; dividing a to-be-shaped region into a left avoidance area, a middle target area and a right avoidance area; controlling an additive laser source to pre-scan the left and right avoidance areas to form a powder compaction zone; then performing forming scanning on the middle target area to make the powder completely melt and solidify; controlling a superfast laser source to follow the additive laser scanning path to perform impact strengthening on the melted and solidified region; and repeating the above steps to stack layer by layer. The application forms a compaction zone in the avoidance area by pre-scanning before the superfast laser impact, effectively blocks the blowing effect of the lateral propagation of the shock wave on the powder bed, and solves the problem of powder splashing in the superfast laser forging printing process. At the same time, the pre-scanning of the avoidance area provides preheating, the superfast laser impact is performed immediately after the target area is formed, the thermal and mechanical synergistic strengthening is realized by using a high-temperature window, and the mechanical properties such as the density and fatigue life of the component are significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of additive manufacturing technology, specifically an additive composite forging printing method and system that avoids ultrafast laser shock wave powder blowing. Background Technology

[0002] Laser Powder Bed Fusion (LPBF), a mainstream metal additive manufacturing technology, achieves near-net-shape forming of complex components by continuously melting metal powder layer by layer with a laser. However, LPBF-formed components generally suffer from defects such as porosity, lack of fusion, hot cracking, and residual tensile stress, resulting in mechanical properties (especially fatigue properties) that are significantly lower than those of forgings. This severely restricts the application and promotion of additive manufacturing technology in fields with stringent component performance requirements, such as aerospace and defense equipment.

[0003] To overcome the aforementioned bottlenecks, researchers have recently proposed a "forging printing" technology that combines ultrafast laser shock blasting (ELBF) with LPBF additive manufacturing. The core idea of ​​this technology is to introduce a strong shock wave generated by an ultrafast laser (such as a femtosecond or picosecond laser) to forge and strengthen the molten layer during or after continuous laser melting and forming in additive manufacturing. This shock wave-induced plastic deformation refines the grains, introduces residual compressive stress, and eliminates defects such as porosity, thereby achieving integrated control of "forming and strengthening," enabling the comprehensive mechanical properties of 3D printed parts to reach the level of forgings.

[0004] However, existing forging printing technology faces a key challenge in engineering practice: the ultrafast laser shock wave has extremely strong mechanical effects. When it impacts the metal surface, the high-pressure plasma shock wave it generates blows away and disperses unmelted metal powder around the molten pool, causing powder bed disorder. This problem is particularly prominent in the forming process of high-precision, thin-walled, and small-feature-size components. Shock wave powder blowing can cause defects such as uneven powder distribution in subsequent layers, local powder shortages, and poor fusion, and in severe cases, it can even lead to the failure of the entire printing process. Although some existing technologies attempt to circumvent this problem through intermittent layer strengthening (i.e., printing several layers and then performing ultrafast laser strengthening), intermittent strengthening has inherent defects such as insufficient thermal / mechanical coupling, limited strengthening layer depth, and low overall process efficiency, making it difficult to achieve true in-situ synchronous forging.

[0005] Therefore, there is an urgent need to develop a composite forging printing method that can fully utilize the in-situ strengthening effect of ultrafast laser shock waves while effectively avoiding or suppressing the negative impact of shock waves on the powder bed. Summary of the Invention

[0006] This invention provides an additive composite forging printing method and system that avoids powder blowing by ultrafast laser shock waves, solving the following problems of the prior art described in the background: In the forging printing process where additive continuous laser and ultrafast laser are scanned synchronously or follow each other, the strong shock wave generated by the ultrafast laser will blow away the metal powder near the additive laser scanning path, resulting in defects such as powder bed disorder, uneven powder spreading, powder shortage and poor fusion, thereby affecting the forming quality and process stability.

[0007] To address the aforementioned technical problems, embodiments of the present invention provide the following technical solution: an additive composite forging printing method that avoids ultrafast laser shockwave powder blowing, comprising the following steps: Step 1: Lay a layer of metal powder of a predetermined thickness on the work platform; Step 2: Based on the cross-sectional profile of the area to be formed in the current layer, divide the area to be formed into a left avoidance area, a middle target area, and a right avoidance area in the scanning plane. The left avoidance area and the right avoidance area are located on both sides of the middle target area, respectively. Step 3: Control the additive laser source to complete at least one pre-scan in the left and right avoidance areas according to the preset scanning path, so that the metal powder in the area is heated and sintered or pre-melted to form a powder compaction zone with a certain density and heat-affected zone. Step 4: Control the additive laser source to scan the intermediate target area according to the preset forming scanning path, so that the metal powder in the intermediate target area is completely melted and solidified into shape; Step 5: Control the ultrafast laser source to follow the scanning path of the additive laser source in the intermediate target area, and perform impact strengthening on the fused area within a predetermined time interval after the additive laser scanning. The impact strengthening utilizes the plasma shock wave induced by the ultrafast laser to generate residual compressive stress on the surface of the fused layer and refine the grains. Step 6: Repeat steps 1 to 5, stacking layer by layer until the printing of the 3D component is complete; The powder compaction zone formed in step 3 is used to block the blowing effect of the shock wave on the unmelted powder outside the avoidance zone during the lateral propagation of the shock wave in step 5.

[0008] Furthermore, the widths of the left and right avoidance areas are each independently set to 20% to 30% of the strip width. The strip width refers to the size of each strip sub-region in the scanning direction when the area to be formed is divided into multiple strip sub-regions (generally 10mm).

[0009] Furthermore, the widths of the left and right avoidance zones are greater than 1.5 times the diameter of the ultrafast laser shock wave influence zone.

[0010] Furthermore, in step 3, the pre-scanning of the avoidance area adopts an "S"-shaped reciprocating scan filling method.

[0011] Further, the laser power for the pre-scanning of the avoidance area in step 3 is 50% - 80% of the laser power for the forming scanning of the target area in step 4, and the scanning speed for the pre-scanning of the avoidance area in step 3 is 1.0 - 1.5 times the forming scanning speed of the target area in step 4.

[0012] Further, the spatial following distance L between the impact point of the ultrafast laser source and the molten pool front of the additive laser source in step 5 satisfies 0 < L ≤ Lmax, where Lmax is the effective action distance of the shock wave, and the spatial following distance L is taken as 4 - 10 times the diameter of the additive laser spot. By controlling the spatial following distance (instead of simply time delay) between the two laser light paths, precise matching and coupling of the heat affected zone and the mechanical shock zone can be achieved.

[0013] The present invention also provides an additive and ultrafast laser composite forging and printing system for implementing the composite forging and printing method described in any one of the above, comprising: A working platform and a powder spreading mechanism for laying metal powder layer by layer; An additive laser source and a first scanning galvanometer group for generating a continuous laser beam and controlling its scanning trajectory on the powder bed; An ultrafast laser source and a second scanning galvanometer group for generating an ultrafast laser beam and controlling its scanning trajectory on the powder bed; A control system electrically connected to the additive laser source, the ultrafast laser source, the first scanning galvanometer group, the second scanning galvanometer group and the powder spreading mechanism for executing the control logic of the composite forging and printing method; A beam combining unit arranged at the intersection of the additive laser light path and the ultrafast laser light path for coaxially or near-axis guiding the two laser beams to the same processing plane to achieve the collaborative scanning of the two lasers.

[0014] Further, the control system includes: A layer slicing module for generating the cross-sectional profile and scanning path of each layer according to the three-dimensional model; A path partitioning module for partitioning the cross-sectional profile of each layer into an avoidance area and a target area; A scanning timing control module for controlling the start sequence, following distance and scanning speed of the additive laser and the ultrafast laser; A synchronization control module for ensuring high-precision time synchronization and spatial positioning between the two lasers.

[0015] Further, the ultrafast laser source is a femtosecond laser, and the additive laser source is a continuous fiber laser.

[0016] Furthermore, the beam combining unit includes a dichroic mirror or a polarization beam combiner. The additive laser and the ultrafast laser have different wavelengths. After coaxial beam combining by the beam combining unit, the laser is output through the same scanning galvanometer, or after paraxial beam combining, the laser works collaboratively through their respective scanning galvanometers.

[0017] The beneficial effects of the above-described technical solution of the present invention are as follows: (1) This invention pre-scans / pre-sintersects the powder on both sides of the area to be formed using additive laser before ultrafast laser shock strengthening, thereby pre-forming a powder compaction zone with a certain density and mechanical strength within the range that the shock wave may reach, thus effectively resisting the blowing effect of the subsequent ultrafast laser shock wave on the powder bed. This "compact first, then form" path design fundamentally suppresses powder splashing and ensures the uniformity of powder spreading and the quality of forming.

[0018] (2) This invention creatively improves the traditional "synchronous follow-up strengthening" mode into a three-stage sequential process chain of "avoidance zone pre-compaction - target area forming - synchronous follow-up strengthening". The pre-scanning of the avoidance zone not only compacts the powder, but also preheats the local area, alleviating the thermal stress gradient during the forming of the target area; and the ultrafast laser shock strengthening is performed immediately after the target area is formed, taking advantage of the favorable window period when the molten layer is still in a high temperature state, which can obtain a better strengthening effect than room temperature shock (dynamic strain aging effect), realizing the efficient synergy of heat and force.

[0019] (3) This invention uses real-time in-situ forging with ultrafast laser shock waves to complete grain refinement, defect elimination and residual compressive stress introduction during each deposition process, avoiding the drawbacks of traditional post-processing strengthening such as "shallow strengthening layer and need for multiple layer-by-layer processing", so that the final formed component meets or even exceeds the forging standard in core indicators such as density, tensile strength and fatigue life.

[0020] (4) The present invention can flexibly adjust the division method of the avoidance zone, the pre-scanning parameters and the following distance according to different geometric features of the area to be formed, so as to be compatible with the forging printing requirements of various complex cross-section components, and can be extended to large-format parallel printing scenarios with multiple lasers and multiple galvanometers. At the same time, the partitioned sequential scanning strategy of the present invention is highly compatible with traditional LPBF path planning software and is easy to promote in engineering. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the additive and ultrafast laser composite forging printing system according to an embodiment of the present invention; Figure 2 This is a cross-sectional schematic diagram of the three-zone division of the area to be formed (left avoidance zone - middle target zone - right avoidance zone) according to an embodiment of the present invention; Figure 3This is a flowchart of the single-layer composite forging printing process according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the scanning path according to an embodiment of the present invention. Detailed Implementation

[0022] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0023] like Figure 1 As shown, the additive and ultrafast laser composite forging printing system of this embodiment includes: an additive laser (continuous fiber laser), a femtosecond laser, an optical path transmission system 1, an optical path transmission system 2, a galvanometer system 1, a galvanometer system 2, a doctor blade, a forming chamber, and a material cylinder. The continuous laser beam generated by the additive laser is introduced into the galvanometer system 1 via the optical path transmission system 1, and the ultrafast laser beam generated by the femtosecond laser is introduced into the galvanometer system 2 via the optical path transmission system 2. The two laser beams are coaxially or paraxially combined through a beam combining unit (not shown in the figure) and then act together on the working platform within the forming chamber. The forming chamber is a sealed cavity filled with an inert protective gas (such as argon). The material cylinder stores metal powder, and the doctor blade, under the command of the control system, pushes the powder from the material cylinder to the working platform and scrapes it flat to form a uniform powder layer. The working platform can be precisely raised and lowered in the vertical direction, descending by one layer thickness after each layer is printed. The additive laser source and the ultrafast laser source achieve precise control of the spatial following distance through a supersynchronous controller, so that the ultrafast laser spot always moves behind the additive laser molten pool at a predetermined distance, thereby implementing impact strengthening while the molten layer is still in a high-temperature state.

[0024] like Figure 3 As shown in the single-layer composite forging printing process flow diagram, this embodiment sequentially performs powder spreading, partitioning, pre-scanning of the avoidance area, forming scanning of the target area, and synchronous impact strengthening. This embodiment uses the above system to print a 20mm × 20mm × 5mm 316L stainless steel cubic specimen.

[0025] Step 1: Spread powder In an inert gas protected chamber (argon atmosphere), a layer of 316L stainless steel spherical powder with a thickness of 50μm is evenly spread on the working platform using a powder spreading scraper. The powder particle size distribution ranges from 15 to 53μm.

[0026] Step 2: Partition Path Planning The control system reads the profile of the section to be formed in the current layer (a 20mm × 20mm square area). For example... Figure 2 As shown, the area to be formed is divided into a left avoidance area, a middle target area, and a right avoidance area along the scanning direction (X-axis direction). A strip-shaped fill type (strip width 10mm) is used, as shown... Figure 4The width of the area marked W is the width of the bar fill. The system divides this square area into five regions along the scanning direction (set as the X-axis direction): Left clearance zone: 2mm wide (i.e., 20% of the width of the strip fill), located in the X=0~2mm range; Central clearance zone: 2mm wide, located in the X=9~11mm range; Right-side clearance zone: 2mm wide, located in the X=18~20mm range.

[0027] The width of the avoidance zone (2mm) is greater than 1.5 times the diameter of the ultrafast laser shock wave affected area (after calibration, the diameter of the ultrafast laser shock wave affected area used in this embodiment is about 1.2mm, and 1.5 times it is 1.8mm), ensuring that the shock wave will not directly act on the original powder bed that has not been pre-scanned.

[0028] Step 3: Pre-scanning of the avoidance zone The additive laser source (continuous fiber laser, wavelength 1080nm) is controlled to perform a pre-scan of the left and right avoidance areas sequentially. The pre-scan parameters are set as follows: Laser power: 260W; Scanning speed: 1000 mm / s; Scanning distance: 80μm; Scanning strategy: Use an "S"-shaped reciprocating scan to fill the area, scanning each avoidance zone once.

[0029] Under the aforementioned parameters, the powder within the clearance zone is heated to a partially sintered / slightly pre-melted state, forming a compacted powder band approximately 40 μm thick. This compacted band possesses sufficient mechanical strength to effectively resist powder splashing caused by subsequent ultrafast laser shock waves.

[0030] Step 4: Full area forming scan The same additive laser source is used to perform a shaping scan on the intermediate target area, causing the powder in that area to completely melt and solidify. The shaping scan parameters for the unscanned area are set as follows: Laser power: 300W; Scanning speed: 1000 mm / s; Scanning distance: 80μm; Scanning strategy: A strip partitioning strategy is adopted, with a strip width of 10mm.

[0031] The unscanned area shaping scan parameters are set as follows: Laser power: 156W; Scanning speed: 1200mm / s; Scanning distance: 80μm; Scanning strategy: A strip partitioning strategy is adopted, with a strip width of 10mm.

[0032] Step 5: Synchronous Impact Strengthening During the additive laser scanning of the intermediate target area, the control system controls an ultrafast laser source (femtosecond laser, pulse width 350 fs, repetition rate 100 kHz, single pulse energy 500 mJ, wavelength 1030 nm) to follow the scanning path of the additive laser in real time for impact strengthening. For example... Figure 4 As shown, the additive laser and the ultrafast laser adopt a spatial following scanning path in the middle target area. The distance L between the center of the ultrafast laser spot and the center of the additive laser spot is kept at 0.5mm (the diameter of the additive laser spot is about 0.1mm, and L is taken as 5 times the spot diameter). The ultrafast laser impacts the molten area within about 0.5ms after the additive laser passes.

[0033] During the impact strengthening process, the peak pressure of the plasma shock wave induced by ultrafast laser is about 3 to 5 GPa, which generates a residual compressive stress of about -200 to -350 MPa on the surface of the fused layer. At the same time, the grains are significantly refined through plastic deformation at a high strain rate (the original columnar crystals are broken into equiaxed crystals, and the grain size is refined from 20 to 50 μm to 2 to 8 μm).

[0034] It should be noted that since a powder compaction zone has been formed in the avoidance zone in step 3, when the ultrafast laser shock wave propagates in the target area, it is blocked by the compaction zone after it propagates laterally to the boundary of the avoidance zone. The lateral dissipation energy of the shock wave is effectively absorbed, thereby protecting the original powder bed outside the avoidance zone from disturbance.

[0035] Step 6: Repeat layer by layer Repeat steps 1 through 5, stacking layers one by one until the entire 20mm × 20mm × 5mm specimen is printed. After each layer is printed, the work platform lowers by one layer thickness (40μm), the powder spreading mechanism respreads the powder, and the next layer of composite forging printing begins. To avoid the accumulation of interlayer defects, the scanning direction of adjacent layers can be rotated by 67° (typical value) to stagger the positions of the avoidance area and the target area between layers.

[0036] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An additive composite forging printing method that avoids ultrafast laser shockwave powder blowing, characterized in that, Includes the following steps: Step 1: Lay a layer of metal powder of a predetermined thickness on the work platform; Step 2: Based on the cross-sectional profile of the area to be formed in the current layer, divide the area to be formed into a left avoidance area, a middle target area, and a right avoidance area in the scanning plane. The left avoidance area and the right avoidance area are located on both sides of the middle target area, respectively. Step 3: Control the additive laser source to complete at least one pre-scan in the left and right avoidance areas according to the preset scanning path, so that the metal powder in the area is heated and sintered or pre-melted to form a powder compaction zone with a certain density and heat-affected zone. Step 4: Control the additive laser source to scan the intermediate target area according to the preset forming scanning path, so that the metal powder in the intermediate target area is completely melted and solidified into shape; Step 5: Control the ultrafast laser source to follow the scanning path of the additive laser source in the intermediate target area, and perform impact strengthening on the fused area within a predetermined time interval after the additive laser scanning. The impact strengthening utilizes the plasma shock wave induced by the ultrafast laser to generate residual compressive stress on the surface of the fused layer and refine the grains. Step 6: Repeat steps 1 to 5, stacking layer by layer until the printing of the 3D component is complete; The powder compaction zone formed in step 3 is used to block the blowing effect of unmelted powder outside the avoidance zone when the shock wave propagates laterally in step 5.

2. The additive composite forging printing method according to claim 1, characterized in that, In step 2, the widths of the left and right avoidance areas are each independently set to 20% to 30% of the strip width. The strip width refers to the size of each strip sub-region in the scanning direction when the area to be formed is divided into multiple strip sub-regions.

3. The additive composite forging printing method according to claim 1, characterized in that, The widths of the left and right avoidance zones are greater than 1.5 times the diameter of the ultrafast laser shock wave influence zone.

4. The additive composite forging printing method according to claim 1, characterized in that, In step 3, the avoidance area pre-scanning adopts an "S"-shaped reciprocating scan filling method.

5. The additive composite forging printing method according to claim 4, characterized in that, The laser power for the pre-scanning of the avoidance area in step 3 is 50% to 80% of the laser power for the shaping scan of the target area in step 4, and the scanning speed for the pre-scanning of the avoidance area in step 3 is 1.0 to 1.5 times the scanning speed for the shaping scan of the target area in step 4.

6. The additive composite forging printing method according to claim 1, characterized in that, In step 5, the spatial following distance L between the impact point of the ultrafast laser source and the leading edge of the molten pool of the additive laser source satisfies 0 < L ≤ Lmax, where Lmax is the effective action distance of the shock wave, and the spatial following distance L is 4 to 10 times the diameter of the additive laser spot.

7. An additive and ultrafast laser composite forging printing system for implementing the composite forging printing method according to any one of claims 1 to 6, characterized in that, include: The working platform and powder spreading mechanism are used to spread metal powder layer by layer. Additive laser source and first scanning galvanometer assembly are used to generate a continuous laser beam and control its scanning trajectory on the powder bed; An ultrafast laser source and a second scanning galvanometer assembly are used to generate an ultrafast laser beam and control its scanning trajectory on the powder bed. The control system is electrically connected to the additive laser source, the ultrafast laser source, the first scanning galvanometer group, the second scanning galvanometer group, and the powder spreading mechanism, and is used to execute the control logic of the composite forging printing method. The beam combining unit is located at the intersection of the additive laser optical path and the ultrafast laser optical path. It is used to guide the two laser beams coaxially or paraxially to the same processing plane to achieve collaborative scanning of the two lasers.

8. The additive and ultrafast laser composite forging printing system according to claim 7, characterized in that, The control system includes: The layered slicing module is used to generate the cross-sectional contours and scanning paths of each layer based on the 3D model; The path partitioning module is used to divide the cross-sectional profile of each layer into avoidance zones and target zones; The scanning timing control module is used to control the start-up sequence, follower spacing, and scanning speed of additive lasers and ultrafast lasers; The synchronization control module is used to ensure high-precision time synchronization and spatial positioning between the two lasers.

9. The additive and ultrafast laser composite forging printing system according to claim 7, characterized in that, The ultrafast laser source is a femtosecond laser, and the additive laser source is a continuous fiber laser.

10. The additive and ultrafast laser composite forging printing system according to claim 7, characterized in that, The beam combining unit includes a dichroic mirror or a polarization beam combiner. The beam combining unit enables coaxial beam combining and output through the same scanning galvanometer, or paraxial beam combining and output through their respective scanning galvanometers working together.

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