Method of additive manufacturing and welding based on low heat input pulsed laser shock waves

Abstract

The application discloses a kind of based on low heat input pulsed laser shock wave's additive manufacturing and welding method, belong to metal additive manufacturing and welding field.The method of the present application is: using energy beam to make metal surface melt, while introducing the small diameter pulsed laser beam of periodic motion inside the joint region of molten pool and solid-liquid mixed zone with frequency below 100Hz to carry out synchronous impact treatment to molten pool, control pulse energy so that the maximum fluctuation of molten pool surface is 10% to 80% of molten pool depth, while the average power input of the pulsed laser beam is controlled within 15% of the actual absorbed power of the energy beam used to generate metal melting, realize the decoupling of laser impact force regulation and heat input.Pulse laser impact force regulates molten pool flow and overcomes the constraint of surface tension, while reducing the coupling effect caused by heat input, so as to realize high-precision control of solidification zone size, adjust residual stress, improve or reduce anisotropy.

Description

Technical Field

[0001] This invention belongs to the field of metal additive manufacturing and welding, specifically relating to a method for additive manufacturing and welding based on low-heat-input pulsed laser shock wave stirring to regulate heat and mass transfer in a molten metal pool. Background Technology

[0002] In industrial applications of metal additive manufacturing and welding, important indicators such as the microstructure and mechanical properties of the formed parts can usually only be controlled by heat input. The control method is too simple and is not conducive to precision control and performance improvement.

[0003] Several studies have proposed using pulsed lasers to apply impact force to the surface of the molten pool, attempting to control its microstructure and mechanical properties. Chinese patents CN105772945B, CN109773187B, CN109702324B, CN109773339B, CN109759710B, CN109759709B, and CN109676138B propose using high-frequency lasers to excite an ultrasonic energy field to achieve uniform nucleation and grain refinement. The laser frequency is required to be at the ultrasonic frequency, such as above 20kHz or 100Hz. In industrial applications of metal additive manufacturing and welding, the size of the molten pool is on the order of millimeters or even larger. This requires a high laser impact pressure and an effective area on the sub-millimeter or millimeter scale. Simultaneously, the thermal effect of the laser must be suppressed to prevent additional melting or overall heating of the molten pool, which would interfere with the control of the force effect. Research revealed that, limited by current laser technology, pulsed lasers with frequencies above 100Hz have low single-pulse energy (in the microjoule or millijoule range) when the pulse duration is below 1 millisecond. When applied to a millimeter-scale molten metal pool, the resulting shock wave causes minimal disturbance to the pool. Furthermore, due to the surface tension of the metal, the weak laser impact energy is quickly dissipated into heat, failing to transmit the disturbance effect to the solid-liquid mixing region at the bottom of the pool, thus hindering true control over the solidification process. Pulsed lasers with frequencies above 100Hz generate excessive thermal effects when the pulse duration exceeds 1 millisecond. These additional thermal effects affect the high-precision control of the molten pool's melting and solidification dimensions. Simultaneously, their weak impact force cannot effectively drive the molten pool flow. Chinese patent CN112496339A utilizes a laser below 100Hz to comprehensively impact the molten pool surface, the mushy region at the rear edge, and the high-temperature solidification region. However, because the entire molten metal is subjected to laser impact force, fluid movement cannot be driven; the melt is merely compressed, thus failing to achieve control over the molten pool flow. The article "Study on laser shock modulation of melt pool in laser additive manufacturing of FeCoCrNi high-entropy alloys" (J. Alloys Compd. 2022, 925, 166720.) and Chinese patents CN112692304A and CN112518109A report and propose the use of pulsed lasers to modulate the heat and mass transfer characteristics of the melt pool in additive manufacturing. However, the flow and mass transfer in the melt pool are not uniform, and the surface morphology fluctuates significantly, affecting the accuracy of morphological features and mechanical properties.

[0004] Therefore, it is necessary to propose effective methods for controlling the flow of the molten pool. Achieving high-precision control of the size of the molten zone, adjusting residual stress, and improving or reducing anisotropy remain technical problems that need to be solved by those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and to provide an additive manufacturing and welding method based on low-heat-input pulsed laser shock wave stirring to regulate the heat and mass transfer of molten metal pool.

[0006] One technical problem to be solved by the present invention is to provide a method for uniformly controlling the flow, heat and mass transfer and solidification of molten pool for thermal decoupling in industrial-grade metal additive manufacturing and welding.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] An additive manufacturing and welding method based on low-heat-input pulsed laser shock wave stirring to regulate heat and mass transfer in a molten metal pool includes the following steps:

[0009] In the process of metal additive manufacturing or welding, while the metal surface is melted by an energy beam, a pulsed laser beam with a frequency of 5Hz to 100Hz, a single pulse energy or an average pulse energy of 0.1 mJ to 20 J, and a pulse width of 1 femtosecond to 1 ms is introduced to synchronously impact the molten pool. At the same time, the average power input of the pulsed laser beam is controlled within 15% of the actual absorbed power of the energy beam used to generate the metal melting, thereby achieving decoupling between laser impact force control and heat input. The pulsed laser beam acts on the combined area formed by the molten pool and the solid-liquid mixing zone, and its diameter is smaller than the size of the combined area. The laser shock wave overcomes the surface tension constraint, forming a low-frequency, high-intensity undulating motion caused by surface extrusion below 100Hz on the surface of the molten pool. This results in the maximum undulation of the molten pool surface being 10% to 80% of the molten pool depth. Furthermore, the pulsed laser beam moves in a periodic trajectory within the combined area formed by the molten pool and the solid-liquid mixing zone, fully realizing the uniformity of the molten pool flow and reducing residual undulations on the surface after solidification. By controlling the flow of the molten pool through pulsed laser impact force and overcoming the constraints of surface tension to form low-frequency, high-intensity undulating motion, while reducing the coupling effect caused by heat input, high-precision control of the molten zone size, adjustment of residual stress, and improvement or reduction of anisotropy can be achieved.

[0010] Furthermore, the trajectory of the pulsed laser beam can be continuous or discontinuous.

[0011] Furthermore, during the metal additive manufacturing or welding process, a high-speed camera and spectrometer can be installed for real-time monitoring, combined with a real-time control system for feedback control.

[0012] This invention is applicable to the field of metal manufacturing, including surface remanufacturing repair, welding, or direct 3D printing.

[0013] The beneficial effects of this invention are: to decouple the control force effect and the thermal effect, thereby achieving high-precision control of the size of the melting and solidification region, adjusting residual stress, and improving or reducing anisotropy. Attached Figure Description

[0014] Figure 1 This is a simplified process diagram of an additive manufacturing and welding method based on low-heat-input pulsed laser shock wave stirring and regulating heat and mass transfer in a molten metal pool according to the present invention; wherein, 101-substrate material, 102-three-dimensional motion, 103-energy beam, 104-material conveying device or powder layer, 105-temperature field distribution, 106-cladding channel, 107-galvanometer, 108-pulsed laser.

[0015] Figure 2 The surface morphology obtained by additive manufacturing and welding processes using the low-heat-input pulsed laser shock wave stirring and regulating of the molten metal pool according to (a) and (b) of the present invention is described. Without using the shock wave stirring method of the present invention, uneven surface solidification characteristics (a) are obtained, as reported in Chinese patents CN112692304A and CN112518109A; with the periodic stirring characteristics of the shock wave of the present invention, uniform surface solidification characteristics (b) are obtained. Detailed Implementation

[0016] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0017] Example 1

[0018] like Figure 1 As shown, additive manufacturing is performed on the substrate 101 by an energy beam 103 (laser, electric arc, electron beam) through three-dimensional motion 102. The material addition is provided by a material conveying device 104, generating a temperature field distribution 105 and a cladding channel 106. Simultaneously, a pulsed laser 108 with a pulse width on the order of 10 nanoseconds, a frequency of 5 to 99 Hz, and a single pulse energy of 50 mJ to 10 J is controlled by a galvanometer 107 to impact the molten pool. The laser beam acts on the combined region formed by the molten pool and the solid-liquid mixing zone, and its diameter is smaller than the size of the combined region. The laser generates a shock wave that overcomes the constraint of surface tension, producing a maximum surface undulation of 10% to 80% of the molten pool depth. The pulsed laser is controlled by the galvanometer 107 to rotate near the boundary of the molten pool. Under the stirring and impact of the pulsed laser 108, the convection of the molten pool is uniform, and the nucleation of the solid-liquid mixing zone around the molten pool is uniform, resulting in uniformly distributed fine equiaxed crystals. This achieves high-precision control of the size of the molten region, adjustment of residual stress, and reduction of anisotropy.

[0019] Example 2

[0020] Continuous laser coaxial powder feeding additive manufacturing was performed using FeCoCrNi high-entropy alloy powder. The laser power was 800 watts, the laser speed was 20 mm / s, and the spot diameter was 3 mm. A pulsed laser with a pulse width of 8 nanoseconds, a frequency of 50 Hz, a single pulse energy of 1 J, an average power of 50 watts, and a spot diameter of 0.5 mm was used to irradiate the surface of the molten pool, producing surface undulations higher than 0.1 mm and lower than 2 mm. When the relative position of the pulsed laser and the continuous laser remained unchanged, the resulting surface morphology was as follows. Figure 2 (a) After final solidification, the surface undulations are aligned in one direction, affecting accuracy and mechanical properties; when the pulsed laser is controlled to rotate periodically by a galvanometer, the surface undulations are more uniform after final solidification, resulting in a surface morphology as shown in (a). Figure 2 (b) This yields high surface precision, uniform and fine equiaxed crystals, low surface tensile stress, and good mechanical properties.

[0021] The analysis results of the above embodiments demonstrate that the method provided by the present invention can effectively decouple the control force effect and thermal effect, thereby achieving high-precision control of the molten region size, adjusting residual stress, and improving or reducing anisotropy. This improves production efficiency while enhancing the quality and performance of the additive layer or weld.

[0022] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle 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 manufacturing method based on low-heat-input pulsed laser shock wave stirring to regulate heat and mass transfer in a molten metal pool, characterized in that: In the metal additive manufacturing process, while the metal surface is melted by an energy beam, a pulsed laser beam with a frequency of 5Hz to 100Hz, a single pulse energy of 50mJ to 10J, and a pulse width of 1femtosecond to 1ms is introduced to synchronously impact the molten pool. At the same time, the average power input of the pulsed laser beam is controlled within 15% of the actual absorbed power of the energy beam used to generate the metal melting, thus decoupling the laser impact force control from the heat input. The pulsed laser beam acts on the combined area formed by the molten pool and the solid-liquid mixing zone, and its diameter is smaller than the size of the combined area. The laser shock wave overcomes the surface tension constraint, forming a undulating motion caused by surface extrusion below 100Hz on the surface of the molten pool, so that the maximum undulation of the molten pool surface is 10% to 80% of the molten pool depth. Moreover, the pulsed laser beam moves in a periodic trajectory within the combined area formed by the molten pool and the solid-liquid mixing zone, realizing the uniformity of the molten pool flow and reducing the residual undulations on the surface after solidification.

2. The additive manufacturing method based on low-heat-input pulsed laser shock wave stirring to regulate heat and mass transfer in a molten metal pool according to claim 1, characterized in that: The trajectory of the pulsed laser beam can be continuous or discontinuous.

3. The additive manufacturing method based on low-heat-input pulsed laser shock wave stirring to regulate heat and mass transfer in a molten metal pool according to claim 1, characterized in that: During the metal additive manufacturing process, a high-speed camera and spectrometer are used for real-time monitoring, and a real-time control system is used for feedback control.

4. The application of the method according to any one of claims 1-3 in the field of surface remanufacturing repair or 3D printing direct forming of metal manufacturing.

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