Ultrafast laser high-stability welding method and device for heterogeneous materials

Abstract

The invention relates to the field of laser micro-nano machining, in particular to an ultrafast laser high-stability welding method and device for heterogeneous materials, effectively solves the problem of welding defects caused by unstable metal surfaces during ultrafast laser welding of large-diameter transparent / metal heterogeneous materials, effectively improves the welding strength and stability, and improves the welding quality. And the mirror surface and non-mirror surface metal welding quality unification is realized. The method specifically comprises the steps that the light emitting mode of ultrafast laser is adjusted, monopulse output is converted into Burst pulse string output, the ultrafast laser in the Burst output mode is used for conducting polishing pretreatment on the surface of the metal material, stable control over the surface quality of the mirror surface and the surface quality of the non-mirror surface metal can be achieved, and the surface roughness after polishing can be controlled to be smaller than lambda / 4; the transparent material and the polished metal material are welded through ultrafast laser, stable control over the welding strength of the heterogeneous material can be achieved, and the welding strength of the mirror-surface metal material is close to that of the non-mirror-surface metal material.

Description

Technical Field

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

[0002] The connection of heterogeneous materials refers to the process of connecting two or more different materials under certain conditions to form a complete structure. Since the connection of heterogeneous materials can give full play to the excellent properties of different materials, it is widely used in the fields of machinery, aerospace, electronic peak, etc. However, due to the differences in physical and chemical properties such as melting point, specific heat capacity, thermal conductivity, etc. between different materials, the welding strength of heterogeneous materials is difficult to be effectively guaranteed.

[0003] For heterogeneous material connection between transparent hard and brittle materials and metal materials, it is generally connected by gluing, but there is a problem of adhesive aging during service, which will lead to interface debonding failure, especially in some extreme service environments, the aging speed is accelerated, and the service life is difficult to guarantee. Laser welding is a connection technology with great application prospects. Although it can effectively avoid the problem of connection aging, it still has problems such as insufficient stability and low welding strength.

[0004] Laser welding can be generally divided into optical contact welding and non-optical contact welding according to the material interface contact conditions. Although optical welding can achieve very high strength, it has low tolerance for interface gaps and extremely high requirements for material surface quality, processing accuracy, and matching accuracy, so it has the problem of insufficient welding stability. Non-optical contact welding has lower requirements for material surface quality, processing accuracy, and matching accuracy, which ensures welding stability, but the welding strength it can achieve is far inferior to optical contact welding, and it is difficult to meet actual application needs.

[0005] The authorized patent (CN107570872A) provides a method for ultrasonic vibration-assisted laser welding of heterogeneous materials. This method uses ultrasonic vibration to assist in laser welding of heterogeneous materials, eliminating defects such as unfused areas, secondary phase precipitation, and uneven element distribution in the process of laser welding of heterogeneous materials, and improving welding strength. However, the power of this method must be greater than 90W, and the selection of ultrasonic output power must also be carefully calculated. Too high ultrasonic output power can easily lead to the generation of thermal cracks in the welding area, reducing the welding quality.

[0006] The authorized patent (CN114160975B) uses long pulse and ultrafast laser composite output to weld dissimilar materials. The optical bonding of materials is achieved through long pulse preheating, and ultrafast laser is used to heat and melt hard and brittle materials to achieve welding. However, this method has high requirements for the control of dual lasers. Any disturbance caused by any laser beam will have a direct impact on the welding performance. Although it can effectively solve the problem of low welding strength, there are still problems such as unstable welding quality and large strength differences between different welding samples in actual applications. Therefore, this method is difficult to achieve uniform welding strength and quality for welding samples with different surface qualities.

[0007] The authorized patent (CN117564460B) provides a non-optical contact method, which provides space for the thermal expansion of heterogeneous materials by preparing a microgroove structure on a transparent material. The molten material will evenly spread to the left and right of the microgroove of the transparent material, which can effectively improve the strength and air tightness of the welding. The size control of the microgroove structure is a major difficulty in implementing this method. Insufficient size and number of microgrooves will result in insufficient space for expansion and melting of materials, and vice versa, the air tightness of the welding will be reduced. In addition, preparing a large number of microgrooves on large-caliber samples is also a major difficulty in applying this method to production.

[0008] In summary, the existing welding methods have different laser energy requirements for welding due to the different gaps between mirror and non-mirror surfaces. When the optimal parameters of the mirror welding process are used for non-mirror surfaces, insufficient injection energy makes it difficult to achieve high-strength welding of non-mirror materials, or even difficult to achieve welding; on the other hand, when the optimal parameters of the non-mirror welding process are used for mirror welding, excessive injection energy will directly cause welding failure. Therefore, for large-caliber welding applications, the coexistence of mirror and non-mirror contact is generally inevitable, and it is difficult for existing welding processes to achieve high-strength and high-stability welding. In contrast, this patent adjusts the light output mode of the ultrafast laser from single pulse output to Burst pulse train output, and uses the ultrafast laser in the Burst output mode to polish the surface of the metal material for pre-treatment, which can achieve stable control of the quality of the mirror and non-mirror metal surfaces under the same parameters, and the surface roughness after polishing can be controlled to below λ / 4; using ultrafast lasers to weld transparent materials and polished metal materials can achieve stable control of the welding strength of heterogeneous materials, and the welding strength of mirror and non-mirror metal materials is close. The method can realize high-quality and high-stability heterogeneous material laser welding for metal materials with different surface qualities. Summary of the invention

[0009] In order to solve the above problems, the present invention provides a method and equipment for ultrafast laser high-stability welding of heterogeneous materials. Before welding, the strength and stability of heterogeneous welding are improved by pre-treating the surface of the metal material, thereby solving the problem of insufficient strength and stability of heterogeneous welding processing.

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

[0011] (1) Using ultrafast laser in Burst output mode to pre-polish the surface of metal materials, the surface roughness after polishing can be controlled to below λ / 4, and the metal material can be a mirror material or a non-mirror material;

[0012] (2) The transparent material and the metal material are stacked, with the polished surface of the metal material corresponding to the lower surface of the transparent material, and the two are clamped with a fixture to form an optical contact condition. Compared with the traditional optical contact method, the surface quality of the metal material after polishing is more stable, which can effectively improve the problem of unstable optical contact welding strength;

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

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

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

[0016] Furthermore, the stability of welding was greatly improved by using polished metal. The fluctuation of weld strength was reduced from 50% before polishing to 20% after polishing.

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

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

[0019] Furthermore, in the Burst pulse mode used, the number of pulses is 2-128.

[0020] Furthermore, the transparent material is sapphire, fused quartz, transparent ceramic, and silicon; the metal material is Ivar alloy, titanium alloy, aluminum alloy, and copper.

[0021] Furthermore, in the welding process 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 needs to be within the metal surface polishing pretreatment processing range.

[0023] In general, the above technical solution of the present invention has the following advantages compared with the prior art solution:

[0024] Traditional polishing methods make it difficult to achieve unified control of the surface quality of mirror and non-mirror materials. This method uses the Burst output mode of ultrafast laser to output laser in the form of high-repetition-rate pulse trains, which can not only improve the polishing efficiency, but also achieve unified control of the surface quality of mirror and non-mirror materials under the same parameters.

[0025] Compared with the extremely high requirements of traditional optical contact welding methods on material surface quality, this method can achieve uniform quality control of mirror and non-mirror metal material surfaces by using ultrafast lasers in Burst output mode, and does not require high original surface quality of the material. Experiments have found that using this method, both rough metal surfaces and mirror metal surfaces can achieve stable welding under the same parameters, avoiding the high requirements of optical contact on material surface quality, effectively reducing processing costs, and improving the stability of welding strength.

[0026] In this method, polishing pretreatment is a processing method using galvanometer scanning. The ultrafast laser output in the form of a high-repetition-rate pulse train can achieve uniform control of the surface quality of large-diameter materials, which can effectively improve the stability of welding of large-diameter heterogeneous materials.

[0027] The present invention effectively solves the problem of welding defects caused by unstable metal surface during ultrafast laser welding of large-caliber transparent / metal heterogeneous materials. The strength and stability of the welder are effectively improved through metal surface polishing pretreatment, achieving uniform welding quality of mirror and non-mirror metals. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Attached Figure 1 Optical path diagram of the invented ultrafast laser high-stability welding method for heterogeneous materials

[0029] Attached Figure 2 Schematic diagram of sample positioning for polishing and welding

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

[0031] Attached Figure 4 Actual pictures of mirror and non-mirror metal polishing

[0032] Attached Figure 5 Actual picture of welding mirror and non-mirror metal materials

[0033] Attached Figure 6 Image of the roughness measurement of the metal surface after polishing

[0034] Explanation of the reference numerals: 1 - high repetition rate ultrafast laser; 2 - collimated 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] Attached Figure 6 Area 1 is the polishing area, area 2 is the welding area, and area 3 is the overall metal surface area. DETAILED DESCRIPTION

[0036] In order to make the technical problems, technical solutions and points to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] In view of the problem that it is difficult to strike a balance between stability and strength in the current heterogeneous welding process, the present invention provides a heterogeneous material ultrafast laser high-stability welding method and equipment.

[0038] The structure of an example provided by the present invention is shown in the figure, which comprises a high repetition rate ultrafast laser 1; a collimated 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 the polishing pretreatment, and a transparent sample 8 and a polished metal sample 9 during the laser processing.

[0039] In this example, the high repetition rate ultrafast laser 1, the collimated optical path 2, the scanning galvanometer 3 and the field lens 4 are located on the same optical path. The laser first passes through the collimated optical path 2, and then enters the scanning galvanometer 3 after the laser is collimated. The scanning galvanometer 3 controls the two-dimensional movement of the optical path through the internal reflector so that it enters the field lens 4 vertically. In the polishing pretreatment, the laser is focused by the field lens 4 and then focused on the upper surface of the unpolished metal sample 7; in the welding process, the laser is focused by the field lens 4 and then focused on the contact surface between the transparent sample 8 and the polished metal sample 9. During the pretreatment and processing, the workpiece remains stationary, and the scanning galvanometer and the field lens realize the movement of the light spot, thereby completing the metal polishing pretreatment and heterogeneous welding processing. In addition, a focusing mirror can also be used to replace the scanning galvanometer 3 and the field lens 4. Under this method, the light spot remains stationary during the processing, and the workpiece is driven to move by the three-dimensional motion platform 6 to achieve polishing and welding.

[0040] First, perform pre-polishing treatment on the metal surface. After debugging the optical path, fix the cleaned unpolished metal sample 7 on the three-dimensional motion platform 6 by a clamp, and adjust the three-dimensional platform 6 so that the focal plane of the laser is located at the upper surface height of the unpolished metal sample 7. Use the galvanometer to set the scanning route and scanning rate, and use the laser controller to select appropriate polishing laser parameters. After completing all the preparations, turn on the laser 1. After the laser beam passes through the collimated optical path 2, it is vertically shot into the incident hole of the scanning galvanometer 3 and emitted from the exit hole of the scanning galvanometer 3. It is focused on the upper surface height of the unpolished metal sample 7 through the field lens 4, and the metal sample is pre-polished.

[0041] After the polishing pretreatment is completed, the transparent sample 8 and the polished metal sample 9 are stacked on the three-dimensional motion platform 6 in sequence and fixed by a clamp. The focal plane of the laser is located at the contact surface height of the transparent sample 8 and the polished metal sample 9 by adjusting the three-dimensional platform 6. The scanning route and scanning rate are adjusted by using a galvanometer to ensure that the scanning range of welding is within the metal polishing range, and the laser controller is used to select appropriate welding laser parameters. Turn on the laser 1, and after the laser beam passes through the collimated optical path 2, it is vertically injected into the incident hole of the scanning galvanometer 3 and emitted from the exit hole of the scanning galvanometer 3. It is focused on the contact surface height of the transparent sample 8 and the polished metal sample 9 through the field lens 4, and moves along the set route in the specified area, thereby completing the ultrafast laser high-stability welding of heterogeneous materials.

[0042] Specific Examples

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

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

[0045] In the welding step, the laser power is 28W, the repetition frequency is 1MHz, and the scanning speed is 40mm / s. The sapphire and the polished Ivar alloy are stacked together and fixed with a clamp. The displacement platform is adjusted so that the contact surface of the sapphire and the Ivar alloy coincides with the focal plane. The scanning path is set within the polishing range of the Ivar alloy surface, and the ultrafast laser welds the sapphire and the Ivar alloy according to the set path. The sample after welding is as shown in the attached figure. Figure 5 As shown, the average shear strength between the mirror Ivar alloy and sapphire is 72 MPa, and the average shear strength between the rough Ivar alloy and sapphire is 66 MPa.

Claims

1. A method and equipment for ultrafast laser high-stability welding of heterogeneous materials, used for laser welding of metal materials and transparent materials, characterized in that: The following steps are involved: Step 1: Use ultrafast laser in Burst output mode to pre-polish the surface of the metal material. 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. Step 2: stack the transparent material and the metal material, with the polished surface of the metal material being the upper surface corresponding to the lower surface of the transparent material, and clamping the two with a fixture to form optical contact conditions. Compared with the traditional optical contact method, the surface quality of the metal material after polishing is more stable, which can effectively improve the problem of unstable strength of optical contact welding. Step three: adjust the three-dimensional platform so that the focal plane of the laser is at the height of the contact surface between the upper workpiece and the lower workpiece. After setting the corresponding welding parameters and scanning path, turn on the laser. The laser passes through the optical path platform to perform welding processing in the metal polishing area along the specified route, ultimately achieving high-quality and high-stability laser welding processing of heterogeneous materials.

2. The method and equipment for ultrafast laser high-stability welding of heterogeneous materials according to claim 1, characterized in that: This method does not have too high requirements on the original quality of the metal surface. Whether it is mirror or non-mirror metal, this method can achieve uniform surface quality under the same polishing parameters and achieve higher welding strength and stability under the same welding parameters.

3. The method and equipment for ultrafast laser high-stability welding of heterogeneous materials according to claim 1, characterized in that: The surface roughness of the mirror metal material is less than λ, and the surface roughness of the non-mirror metal material is greater than λ.

4. The method and equipment for ultrafast laser high-stability welding of heterogeneous materials according to claim 1, characterized in that: The stability of welding is greatly improved by using polished metal. The fluctuation of weld strength is reduced from 50% before polishing to 20% after polishing.

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

6. The method and equipment for ultrafast laser high-stability welding of heterogeneous materials according to claim 1, characterized in that: In step 1, the polishing processing parameters used are: laser power of 1.5W-5.5W, repetition frequency of 100-2000KHz, and scanning speed of 20mm / s-400mm / s.

7. The method and equipment for ultrafast laser high-stability welding of heterogeneous materials according to claim 1, characterized in that: In step 1, in the Burst pulse mode used, the number of pulses is 2-128.

8. The method and equipment for ultrafast laser high-stability welding of heterogeneous materials according to claim 1, characterized in that: The transparent material in step 2 is sapphire, fused quartz, transparent ceramic, and silicon; the metal material is Ivar alloy, titanium alloy, aluminum alloy, and copper.

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

10. The method and equipment for ultrafast laser high-stability welding of heterogeneous materials according to claim 1, characterized in that: In step three, the welding scanning path needs to be within the metal surface polishing pretreatment processing range.

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