A method and apparatus for high stability welding of dissimilar materials using ultrafast laser

Abstract

The present application relates to the field of laser micro-nano processing, and specifically designs a heterogeneous material ultrafast laser high-stability welding method and equipment, effectively solves the welding defect problem caused by the instability of the metal surface during the ultrafast laser welding of large-diameter transparent / metal heterogeneous materials, effectively improves the welding strength and stability, and realizes the unity of the welding quality of mirror surfaces and non-mirror surfaces. The present application specifically includes adjusting the light output mode of the ultrafast laser, changing from single pulse output to Burst pulse train output, using the ultrafast laser in Burst output mode to polish and pretreat the metal material surface, which can realize stable control of the quality of mirror and non-mirror metal surfaces, and the surface roughness after polishing can be controlled to below lambda / 4; using the ultrafast laser to weld the transparent material and the polished metal material can realize stable control of the welding strength of heterogeneous materials, and the welding strength of mirror and non-mirror metal materials is close.

Description

Technical Field

[0001] This invention relates to the field of laser micro-nano processing, specifically to a method and equipment for high-stability ultrafast laser welding of heterogeneous materials. Background Technology

[0002] Joining dissimilar materials refers to the process of connecting two or more different materials under certain conditions to form a complete structure. Because joining dissimilar materials can leverage the superior properties of each material, it is widely used in fields such as machinery, aerospace, and electronics. However, due to differences in the physicochemical properties of different materials, such as melting point, specific heat capacity, and thermal conductivity, the welding strength of dissimilar materials is difficult to guarantee effectively.

[0003] For joining dissimilar materials, such as transparent, hard, and brittle materials, to metallic materials, adhesive bonding is generally used. However, adhesive aging occurs during service, leading to interface debonding and failure. This aging process is accelerated, especially under extreme service environments, making it difficult to guarantee the service life. Laser welding, as a promising joining technology, can effectively avoid the aging problem, but it still suffers from insufficient stability and low weld strength.

[0004] Laser welding can be categorized into optical contact and non-optical contact welding based on the material interface contact. While optical welding can achieve very high strength, it has low tolerance for interfacial gaps and extremely high requirements for material surface quality, processing precision, and fit accuracy, resulting in insufficient welding stability. Non-optical contact welding has lower requirements for material surface quality, processing precision, and fit accuracy, ensuring welding stability, but the weld strength it can achieve is far lower than that of optical contact welding, making it difficult to meet practical application needs.

[0005] The authorized patent (CN107570872A) provides a method for ultrasonic vibration-assisted laser welding of dissimilar materials. This method utilizes ultrasonic vibration to assist in the laser welding of dissimilar materials, eliminating defects such as incomplete fusion zones, secondary phase precipitation, and uneven elemental distribution that exist in the laser welding process of dissimilar materials, thereby improving the weld strength. However, the power required for this method must be greater than 90W, and the selection of ultrasonic output power also needs to be carefully calculated. Excessively high ultrasonic output power can easily lead to the generation of hot cracks in the weld area, reducing the weld quality.

[0006] The authorized patent (CN114160975B) employs a combined output of long-pulse and ultrafast lasers for welding dissimilar materials. The long-pulse preheating achieves optical bonding of the materials, while the ultrafast laser melts the hard and brittle materials, thus completing the weld. However, this method places high demands on the control of the two lasers; any disturbance in either laser beam directly affects the welding performance. Although it effectively solves the problem of low weld strength, current practical applications still suffer from unstable weld quality and significant differences in strength between different welded samples. Therefore, this method struggles to achieve uniform weld strength and quality for samples with varying surface qualities.

[0007] The authorized patent (CN117564460B) provides a non-optical contact method that uses microgrooves fabricated on a transparent material to provide space for the thermal expansion of the heterogeneous material. The molten material spreads evenly around the microgrooves in the transparent material, effectively improving the weld strength and airtightness. Controlling the size of the microgrooves is a major challenge in implementing this method. Insufficient size and number of microgrooves will result in insufficient space for the expanding and molten material, while excessive size will reduce the weld's airtightness. Furthermore, fabricating a large number of microgrooves on large-diameter samples is another significant challenge for applying this method in production.

[0008] In summary, existing welding methods require different laser energy for welding due to the different gaps between mirror and non-mirror surfaces. When the optimal parameters for mirror welding are applied to non-mirror surfaces, insufficient energy injection makes high-strength welding of non-mirror materials difficult, or even impossible. Conversely, when the optimal parameters for non-mirror welding are applied to mirror welding, excessive energy injection directly leads to welding failure. Therefore, for large-diameter welding applications, the coexistence of mirror and non-mirror contact is generally unavoidable, and existing welding processes struggle to achieve high-strength, high-stability welding. In contrast, this patent, by adjusting the ultrafast laser's output mode from single-pulse output to Burst pulse train output, utilizes the ultrafast laser in Burst output mode to pre-polish the metal material surface. This allows for stable control of the surface quality of both mirror and non-mirror metals under the same parameters, with the surface roughness after polishing controlled to below λ / 4. Using ultrafast lasers to weld transparent materials and polished metal materials enables stable control of the welding strength of dissimilar materials, with similar welding strengths for mirror and non-mirror metals. This method can achieve high-quality and high-stability laser welding of dissimilar materials with different surface qualities. Summary of the Invention

[0009] To address the aforementioned problems, this invention provides a method and equipment for high-stability ultrafast laser welding of dissimilar materials. Before welding, pretreatment of the metal material surface improves the strength and stability of the dissimilar welding process, thus resolving the current issue of insufficient strength and stability in dissimilar welding.

[0010] To achieve the above objectives, the present invention provides a laser welding method that can avoid damage to important structures, comprising the following steps:

[0011] (1) The surface of the metal material is pre-polished using an ultrafast laser in Burst output mode. The surface roughness after polishing can be controlled to below λ / 4. The metal material can be a mirror material or a non-mirror material.

[0012] (2) Transparent and metallic materials are stacked, with the polished surface of the metallic material on top corresponding to the lower surface of the transparent material. The two are clamped together to create optical contact. Compared to traditional optical contact methods, the polished surface of the metallic material provides more stable surface quality, effectively improving the problem of unstable optical contact welding strength.

[0013] (3) Adjust the three-dimensional platform so that the focal plane of the laser is at the height of the contact surface between the upper and lower workpieces. After setting the corresponding welding parameters and scanning path, turn on the laser. The laser will perform welding processing in the metal polishing area through the optical path platform according to the specified route, and finally achieve high-quality and high-stability laser welding processing of heterogeneous materials.

[0014] Furthermore, this method does not have high requirements for the original quality of the metal surface. Whether it is a mirror-finish or non-mirror-finish metal, this method can achieve uniform surface quality under the same polishing parameters and achieve high welding strength and stability under the same welding parameters.

[0015] Furthermore, the surface roughness of the mirror-finished metal material is less than λ, while the surface roughness of the non-mirror-finished metal material is greater than λ.

[0016] Furthermore, using polished metal for welding significantly improved stability. The fluctuation in weld strength decreased from 50% before polishing to 20% after polishing.

[0017] Furthermore, the polishing pretreatment can control the metal surface roughness Sa between 0.3-0.8 μm and Sz below 10 μm.

[0018] Furthermore, the polishing parameters used include a laser power of 1.5W-5.5W, a repetition frequency of 100-2000KHz, and a scanning speed of 20mm / s-400mm / s.

[0019] Furthermore, in the Burst pulse mode used, the number of pulses ranges from 2 to 128.

[0020] Furthermore, the transparent material is sapphire, fused silica, transparent ceramic, or silicon; the metallic material is Ivar alloy, titanium alloy, aluminum alloy, or copper.

[0021] Furthermore, in the welding processing parameters, the laser power is 25W-35W, the repetition frequency is 100-2000KHz, and the scanning speed is 20mm / s-50mm / s.

[0022] Furthermore, the welding scanning path must be located within the metal surface polishing pretreatment processing range.

[0023] In summary, compared with existing technical solutions, the above technical solutions of the present invention have the following main advantages:

[0024] Traditional polishing methods struggle to achieve uniform control over the surface quality of mirror-like and non-mirror-like materials. This method utilizes the Burst output mode of an ultrafast laser, outputting the laser in the form of a high-repetition-rate pulse train. This not only improves polishing efficiency but also enables uniform control over the surface quality of mirror-like and non-mirror-like materials under the same parameters.

[0025] Compared to traditional optical contact welding methods, which have extremely high requirements for material surface quality, this method can achieve uniform quality control on both mirror and non-mirror metal surfaces by utilizing ultrafast lasers in Burst output mode, with less emphasis on the original surface quality of the material. Experiments have shown that this method can achieve stable welding on both rough and mirror metal surfaces under the same parameters, avoiding the high requirements for material surface quality in optical contact, effectively reducing processing costs, and improving the stability of weld strength.

[0026] In this method, the polishing pretreatment is carried out using a galvanometer scanning process. By outputting ultrafast laser in the form of high repetition rate pulse train, uniform control of the surface quality of large-diameter materials can be achieved, which can effectively improve the stability of welding large-diameter dissimilar materials.

[0027] This invention effectively solves the welding defect problem caused by the instability of the metal surface during ultrafast laser welding of large-diameter transparent / metallic heterogeneous materials. By pre-treating the metal surface with polishing, the strength and stability of the welding machine are effectively improved, and the welding quality of mirror-finish and non-mirror-finish metals is unified. Attached Figure Description

[0028] Appendix Figure 1 Optical path diagram of the invention's ultrafast laser high-stability welding method for heterogeneous materials

[0029] Appendix Figure 2 Schematic diagram for positioning polished and welded samples

[0030] Appendix Figure 3 Schematic diagram of the processing flow for a high-stability ultrafast laser welding method for heterogeneous materials

[0031] Appendix Figure 4 Images of polished mirror-finish and non-mirror-finish metal materials

[0032] Appendix Figure 5 Actual image of welding mirror-finish and non-mirror-finish metal materials.

[0033] Appendix Figure 6 Image of surface roughness measurement of polished metal

[0034] Figure label explanation: 1-High repetition rate ultrafast laser; 2-Collimating optical path; 3-Scanning galvanometer; 4-Field mirror; 5-Sample; 6-Three-dimensional motion platform; 7-Unpolished metal sample; 8-Transparent sample; 9-Polished metal sample.

[0035] Appendix Figure 6 Region 1 is the polishing area, Region 2 is the welding area, and Region 3 is the overall metal surface area. Detailed Implementation

[0036] To make the technical problems, solutions, and points to be solved by this invention clearer, a detailed description will be provided below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the description of these embodiments is intended to aid in understanding the invention but does not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the invention described below can be combined with each other as long as they do not conflict with each other.

[0037] This invention addresses the current challenge of balancing stability and strength in heterogeneous welding processes by providing a method and equipment for ultrafast laser welding of heterogeneous materials with high stability.

[0038] The structure of an example provided by this invention is shown in the figure, comprising a high-repetition-rate ultrafast laser 1; a collimating optical path 2; a scanning galvanometer 3; a field lens 4; a sample 5; and a three-dimensional motion platform 6. The sample is an unpolished metal sample 7 during polishing pretreatment, and during laser processing, it consists of a transparent sample 8 and a polished metal sample 9.

[0039] In this example, the high-repetition-rate ultrafast laser 1, collimating optical path 2, scanning galvanometer 3, and field mirror 4 are located on the same optical path. The laser first passes through the collimating optical path 2, and after collimation, it enters the scanning galvanometer 3. The scanning galvanometer 3 controls the two-dimensional movement of the optical path through an internal mirror to ensure it enters the field mirror 4 perpendicularly. In the polishing pretreatment, the laser is focused by the field mirror 4 onto the upper surface of the unpolished metal sample 7. During the welding process, the laser is focused by the field mirror 4 onto the contact surface between the transparent sample 8 and the polished metal sample 9. During the pretreatment and processing, the workpiece remains stationary, while the scanning galvanometer and field mirror move the laser spot, thereby completing the metal polishing pretreatment and heterogeneous welding. Alternatively, a focusing mirror can be used instead of the scanning galvanometer 3 and field mirror 4. In this method, the laser spot remains stationary during processing, and the workpiece is moved by the three-dimensional motion platform 6 to achieve polishing and welding.

[0040] First, a metal surface polishing pretreatment is performed. After adjusting the optical path, the cleaned, unpolished metal sample 7 is fixed on the three-dimensional motion platform 6 using a fixture. The focal plane of the laser is adjusted so that it is at the height of the upper surface of the unpolished metal sample 7. The scanning path and scanning rate are set using a galvanometer, and appropriate polishing laser parameters are selected using a laser controller. After all preparations are completed, the laser 1 is turned on. The laser beam passes through the collimated optical path 2, enters vertically through the entrance aperture of the scanning galvanometer 3, and exits through the exit aperture of the scanning galvanometer 3. It is then focused by the field lens 4 onto the upper surface of the unpolished metal sample 7, and the metal sample is then polished.

[0041] After polishing pretreatment, the transparent sample 8 and the polished metal sample 9 are stacked sequentially on the three-dimensional motion platform 6 and fixed with clamps. The focal plane of the laser is adjusted by the three-dimensional platform 6 so that it is at the height of the contact surface between the transparent sample 8 and the polished metal sample 9. The scanning path and scanning rate are adjusted using a galvanometer to ensure that the welding scanning range is within the metal polishing range. Appropriate welding laser parameters are selected using a laser controller. The laser 1 is turned on, and the laser beam passes through the collimated optical path 2, enters the entrance aperture of the scanning galvanometer 3 perpendicularly, and exits from the exit aperture of the scanning galvanometer 3. It is focused by the field lens 4 at the height of the contact surface between the transparent sample 8 and the polished metal sample 9, and moves along a pre-set path within a designated area, thereby completing the ultrafast laser high-stability welding of dissimilar materials.

[0042] Specific examples

[0043] Example 1: This example takes sapphire as the transparent material 8 and rough Ivar alloy and mirror Ivar alloy as the metal material 7. The size of the sapphire is about 8mm×10mm×2mm and the size of the Ivar alloy is about 10mm×20mm×2mm. Laser welding is performed according to the steps of the ultrafast laser high-stability welding method for heterogeneous materials provided in the above embodiment.

[0044] In the polishing pretreatment step, a laser power of 3.5W, a repetition frequency of 1MHz, a pulse train number of 4, and a scanning speed of 250mm / s were used. The displacement platform was adjusted so that the upper surface of the Ivar alloy coincided with the focal plane. The energy of the ultrafast laser was used to polish the Ivar alloy surface, reducing the surface roughness in the welding area to below λ / 4, achieving uniform quality control of the metal surface. The surface after polishing pretreatment is shown in the attached image. Figure 4 As shown.

[0045] In the welding process, a laser power of 28W, a repetition rate of 1MHz, and a scanning speed of 40mm / s were used. Sapphire and pre-polished Ivar alloy were stacked together and fixed with a fixture. The displacement platform was adjusted so that the contact surface between the sapphire and Ivar alloy coincided with the focal plane. The scanning path was set within the polished area of ​​the Ivar alloy surface, and the ultrafast laser performed the welding process on the sapphire and Ivar alloy according to the set path. The welded sample is shown in the attached image. Figure 5 As shown, the average shear strength of mirror-finished Ivar alloy and sapphire is 72 MPa, while the average shear strength of rough Ivar alloy and sapphire is 66 MPa.

Claims

1. A high-stability ultrafast laser welding method for heterogeneous materials, used for laser welding of metallic and transparent materials, characterized in that, Includes the following steps: Step 1: Use an ultrafast laser with a power of 3.5 W and a repetition frequency of 1 MHz in Burst output mode to polish the surface of the metal material. Under the same polishing parameters, the surface quality is uniform and the surface roughness after polishing is controlled to below λ / 4. The metal materials are rough Invar alloy and mirror Invar alloy. Step 2: Stack the transparent sapphire material and the metal material, with the polished surface of the metal material on top corresponding to the bottom surface of the transparent material. Clamp the two together to form optical contact conditions. Compared with traditional optical contact methods, the surface quality of the metal material is more stable after polishing, which can effectively improve the problem of unstable optical contact welding strength. Step 3: Adjust the 3D platform so that the focal plane of the laser is at the height of the contact surface between the upper and lower workpieces. After setting the corresponding welding parameters and scanning path, turn on the laser. The laser passes through the optical path platform and performs welding processing in the metal polishing area according to the specified route and the same welding parameters, ultimately achieving high-quality and high-stability laser welding processing of heterogeneous materials. Based on the above steps, by using uniform Burst mode polishing parameters and uniform welding parameters, high welding strength and stability can be achieved for Invar alloys with original surfaces that are either mirror-like or rough. The fluctuation of welding strength is reduced from 50% before polishing to 20% after polishing.

2. The method for high-stability ultrafast laser welding of heterogeneous materials according to claim 1, characterized in that, The surface roughness of the mirror-finish Invar alloy is less than λ, while the surface roughness of the rough Invar alloy is greater than λ.

3. The method for high-stability ultrafast laser welding of heterogeneous materials according to claim 1, characterized in that, Using polished metal for welding significantly improves stability, reducing the fluctuation in weld strength from 50% before polishing to 20% after polishing.

4. The method for high-stability ultrafast laser welding of heterogeneous materials according to claim 1, characterized in that, In step one, the polishing pretreatment controls the surface roughness Sa of the metal to be between 0.3 and 0.8 μm and Sz to be below 10 μm.

5. The method for high-stability ultrafast laser welding of heterogeneous materials according to claim 1, characterized in that, In step one, the polishing parameters used include a scanning speed of 20 mm / s to 400 mm / s.

6. The method for high-stability ultrafast laser welding of heterogeneous materials according to claim 1, characterized in that, In step one, the Burst pulse mode used has a pulse count of 2-128.

7. The method for high-stability ultrafast laser welding of heterogeneous materials according to claim 1, characterized in that, In step three, the welding processing parameters are as follows: laser power is 25 W-35 W, repetition frequency is 100-2000 KHz, and scanning speed is 20 mm / s-50 mm / s.

8. The method for high-stability ultrafast laser welding of heterogeneous materials according to claim 1, characterized in that, In step three, the welding scanning path must be within the range of the metal surface polishing pretreatment process.

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