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CN-121972681-A - Cold and hot processing synergistic additive manufacturing method of composite ultrafast-continuous-long pulse laser

CN121972681ACN 121972681 ACN121972681 ACN 121972681ACN-121972681-A

Abstract

The invention belongs to the field of metal laser additive manufacturing, and discloses a cold and hot processing synergistic additive manufacturing method of composite ultrafast-continuous-long pulse laser. According to the method, three lasers are shaped into flat-top beams through time sequence synchronization and coaxial coupling, space distribution of a pre-modified ring-core melting zone-crystal grain regulation zone is constructed, a four-dimensional cooperative strategy of time-space-power-duty ratio is adopted, ultra-fast laser pre-activation is adopted to weaken metal bonds, continuous laser low-heat is used for forming a stable molten pool, long pulse laser breaks dendrite arms to refine crystal grains, closed-loop regulation and substrate pretreatment are matched, and low-energy consumption and high-precision processing is achieved. The product prepared by the invention can obtain a homogeneous equiaxed crystal structure, has obviously optimized mechanical properties, is suitable for various metal materials, can be applied to high-end fields such as aerospace and the like, and has high industrial value.

Inventors

  • ZHAI WENZHENG
  • WANG RUITONG

Assignees

  • 华中科技大学

Dates

Publication Date
20260505
Application Date
20260122

Claims (9)

  1. 1. The cold and hot processing synergistic additive manufacturing method of the composite ultrafast-continuous-long pulse laser is characterized by comprising the following steps of: (1) An ultrafast laser generator, a continuous laser generator and a long pulse laser generator are adopted to respectively generate ultrafast laser, continuous laser and long pulse laser, and nanosecond time coordination is realized through a time sequence synchronizer; (2) Three beams of laser enter a flat-top shaping module respectively and are reconstructed into flat-top beams with uniform energy, the space distribution of a pre-modified ring, a core melting zone and a crystal grain regulating zone is formed by regulating and controlling elements such as a coaxial coupler, the spot distortion is corrected in real time by utilizing a wavefront sensor and a deformable mirror, and an M 2 factor instrument monitors the beam quality and ensures the output stability; (3) Setting four-dimensional cooperative parameters of time-space-power-duty ratio by a main controller, wherein the four-dimensional cooperative parameters comprise that ultra-fast laser is triggered by leading continuous laser 40-60 ns, long pulse laser is delayed by 3-7 mu s to start, the diameter of a light spot is precisely controlled, the power ratio of three laser beams and the duty ratio of the long pulse are steplessly adjustable according to the material characteristics, and the precise matching of the laser action and the material phase change time sequence is ensured; (4) The metal wire/powder is conveyed into the laser spot in a coaxial or paraxial mode through a wire/powder conveying mechanism; (5) The laser spray head moves according to a preset track, the surface of the material is preactivated by ultra-fast laser in the process, metal bonds are weakened/destroyed, a stable molten pool is formed by continuous laser in a low heat mode, dendrite arms are broken by long pulse laser in a solidification stage, material melting and grain refinement are achieved through the synergistic effect of three laser beams, a homogeneous welding bead is formed after the molten pool is solidified, and additive manufacturing of parts is completed through circular movement.
  2. 2. The cold and hot processing collaborative additive manufacturing method of the composite ultrafast-continuous-long pulse laser is characterized in that in the step (5), molten pool state data are collected through a blue light CCD in the moving process of a laser nozzle, and four-dimensional parameters of three laser 'time-space-power-duty ratio' and material feeding speed are adjusted in real time through a fuzzy PID algorithm.
  3. 3. The cold and hot processing collaborative additive manufacturing method of composite ultrafast-continuous-long pulse laser according to claim 1, wherein in the step (1), ultrafast laser wavelength 1030-1070nm, pulse width 80fs-1.2ps, peak power 1012-101 5 W/cm2, continuous laser wavelength 1060-1080nm, power 0.8-4kW, long pulse laser wavelength 1040-1060nm, pulse width 2-8ms, peak power 10 6 -10 7 W/cm2, three laser power fluctuation not more than +/-1.2%, and power ratio ultrashort pulse: continuous laser: long pulse=1:90:9 to 1:150:5.
  4. 4. The cold and hot processing synergistic additive manufacturing method of the composite ultrafast-continuous-long pulse laser, as claimed in claim 1, is characterized in that the diameter of the flat-top beam in the step (2) is 3-7mm, the energy uniformity is more than or equal to 93%, and the spot distortion is corrected in real time through Zernike polynomials.
  5. 5. The method for manufacturing the cold and hot processing synergistic additive of the composite ultrafast-continuous-long pulse laser, as claimed in claim 1, wherein the diameter of the wire in the step (4) is 0.8-3mm, the powder is spherical powder, and the particle size is 40-250 μm.
  6. 6. The cold and hot processing collaborative additive manufacturing method of the composite ultrafast-continuous-long pulse laser, as set forth in claim 1, is characterized in that the wire feeding mode in the step (4) is coaxial wire feeding or paraxial wire feeding, and the wires and the powder materials are fed independently or simultaneously.
  7. 7. The cold and hot processing collaborative additive manufacturing method of the composite ultrafast-continuous-long pulse laser, which is disclosed in claim 2, is characterized in that the laser power response time in the step (4) is less than 8ms, the wire precision of material feeding is more than or equal to 0.08m/min, and the powder precision is more than or equal to 0.1g/min.
  8. 8. The method for manufacturing the composite ultrafast-continuous-long pulse laser collaborative additive by cold and hot processing, which is disclosed in claim 1, is characterized by further comprising a pre-treatment step of additive before the step (1), specifically, precisely milling the surface of a substrate, then performing pneumatic shot blasting treatment to ensure that the roughness Ra=2.8-5.8 mu m, and finally adopting alcohol-acetone double-step cleaning to remove the surface oxide layer and oil stains.
  9. 9. The method for manufacturing the composite ultrafast-continuous-long pulse laser collaborative additive by cold and hot processing, as set forth in claim 1, characterized in that the substrate is preheated by gradient heating before the additive manufacturing is started, the substrate is heated to 380-420 ℃ at a speed of 50 ℃ per minute, and the substrate is kept at a constant temperature until the additive is finished after 20 minutes of heat preservation.

Description

Cold and hot processing synergistic additive manufacturing method of composite ultrafast-continuous-long pulse laser Technical Field The invention belongs to the field of metal laser additive manufacturing, and particularly relates to a cold and hot processing synergistic additive manufacturing method of a composite ultrafast-continuous-long pulse laser. Background The laser metal additive manufacturing is an advanced manufacturing technology based on the discrete-stacking principle, and the technology melts metal powder or wire materials layer by means of high-energy laser beams according to three-dimensional digital model data, so that the materials grow into complex three-dimensional solid parts from bottom to top, and the direct manufacturing leap from a digital model to a physical entity is realized. The revolutionary value of the technology is that the technology thoroughly gets rid of the constraint of the traditional mould, realizes free manufacturing without restraint, not only reduces material consumption and processing period by about 30% -80%, but also designs and manufactures lightweight lattice structure or functional gradient material which cannot be realized by the traditional technology, thereby remarkably improving the performance of the product. As such, laser additive manufacturing has become a key technology in high-end fields such as aerospace, biomedical and the like, and is used as a core driving force for new mass productivity, and the manufacturing industry is continuously driven to be transformed into digital and intelligent deep. However, as the fields put higher and higher demands on the functions of parts, the design of part models is also more and more complex, wherein the ultra-large meter-class parts with complex structures are not lacking. The laser light source adopted in the current laser additive manufacturing of large parts is mainly infrared continuous laser, has higher power density, can realize rapid melting and solidification of materials, but also easily introduces stronger thermal stress and thermal strain, and particularly for large parts, huge thermal stress is extremely easy to cause dimensional deviation and penetrability crack generation. Analytical reasons are that conventional laser additive manufacturing uses a single continuous gaussian laser, which is a method of processing using a single thermal effect, in which the melting process is a process of raising the metal temperature above the melting point using a continuous energy input and then solidifying and forming. The traditional light source has two obvious characteristics that firstly, each area in a molten pool is heated unevenly, the middle part of laser is heated higher, and the edge part is heated insufficiently, so that metal in the center part is excessively melted, and the metal in the edge is melted insufficiently. Second, the continuous heat input induces "thermal expansion and contraction" of the metal, which in turn creates extremely strong thermal stresses. In addition, in order to improve the processing efficiency of the parts, the current common method is to directly improve the power of the laser, which can naturally improve the melting efficiency of the materials, but also aggravate the formation of thermal stress, so that the manufactured parts have extremely strong cracking tendency. With the development of laser technology, ultrafast laser is gradually developed into a hot technology in the laser field. Ultrafast laser is a typical cold working mechanism, and the principle of the action is to concentrate extremely small energy on metal bonds between atoms by using ultra-high concentrated energy pulses, and the action of force is dominant to only break the metal bonds without causing metal melting. So ultrafast lasers are often used in the field of small and precise material reduction processing at present. The melting process is interpreted from a microscopic view, and can be understood as a process that the metal atoms are heated and moved by external energy input, so that the metal bonds are broken loose and then enter a free state. Then the metal bond is destroyed rapidly by using the ultrafast laser, and then the metal atom can enter a free state only by extremely small energy input, namely the ultrafast laser can effectively influence the melting mechanism of the metal. In addition, the solidification process of metal also affects the performance of the formed part, and the laser additive manufacturing is very easy to generate coarse columnar grains due to the characteristic of directional energy input, so that the mechanical property is reduced. The long pulse laser is used for impacting dendrites at the solidification front, and the dendrite arms are broken, so that the nucleation rate can be effectively improved, and fine equiaxed grains are finally formed by solidification, so that excellent mechanical properties are obtained. Therefore, the long pulse laser and the ultraf