An ultrafast laser welding method for large-pitch heterogeneous materials

Abstract

The present invention provides an ultrafast laser welding method for heterogeneous materials with large spacing, which specifically includes: stacking the lower workpiece and the upper workpiece and clamping them with a clamp; the laser beam is collimated and then injected into the scanning galvanometer, and is focused by the field lens after being emitted. After the laser energy is absorbed by the lower material in the first scanning, plasma is generated, and the plasma continues to expand and overflow, and at the same time, the lower material melts and fills the gap, achieving quasi-optical contact conditions; in the second scanning, the free expansion of the plasma is effectively suppressed, and the laser energy is limited near the weld, the melting volume of this area is significantly increased, and the welding strength is significantly improved; the third scanning is consistent with the second scanning mechanism, the amount of material melting is increased, and finally the welding head is strengthened. The focused light spot is moved along the specified route within the contact surface of the upper and lower workpieces by the scanning galvanometer and the field lens, thereby realizing the melting and bonding of the workpieces. After three scans, the heterogeneous materials with large spacing can finally obtain a high-strength, high-quality welding joint.

Description

Technical Field

[0001] The patent of this invention relates to the field of laser micro-nano processing, and specifically to an ultrafast laser welding method for heterogeneous materials with large spacing. Background Art

[0002] The connection technology of heterogeneous materials is widely used in aerospace, chip packaging and other fields. For the connection of heterogeneous materials between transparent hard and brittle materials or between transparent hard and brittle materials and metal materials, it is generally connected by gluing. However, there is a potential problem of aging of adhesives during service, which leads to interface debonding failure, especially in some extreme service environments, where the aging speed is accelerated. 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 low tolerance of contact surface gap and low welding strength.

[0003] Laser welding can be generally divided into optical contact and non-optical contact welding according to the material interface contact conditions. Although in theory optical contact (small contact surface gap, usually contact surface gap < wavelength / 4, generally considered mirror-mirror contact, surface roughness Sa <10nm) welding can achieve very high connection strength (>100MPa), it has low tolerance for interface gap, and has extremely high requirements for material surface quality, processing accuracy and matching accuracy. It is difficult to experiment with high-strength welding of large-scale heterogeneous materials. In this regard, the authorized patent (CN114160975B) and the patent application (CN116944675A) stack transparent materials on top of metal materials, and clamp the transparent materials and metal materials through a fixture; the first laser emitted by the laser device polishes and scans the metal material through the transparent material to melt it, and the melted metal material flows and fills the pits under the pressure of the fixture; the focus of the laser device is adjusted to focus between the planes to be welded; the second laser emitted by the laser device melts the transparent material and the metal material on both sides of the interface along the preset welding path, and cools to form a weld. The use of dual-beam lasers for welding dissimilar materials requires complex equipment and control, and the stability of the dual lasers will have a direct impact on the welding performance. Currently, in actual applications, there are problems such as unstable welding quality, large differences in welding quality between welding areas, and large differences in strength between different welding samples, resulting in low yields. Therefore, in actual applications, especially in welding applications of large-format or curved equipment, it is limited.

[0004] In non-optical contact welding (the contact surface gap is large, usually the contact surface gap is >2μm), the surface quality, processing accuracy and matching accuracy of the lower workpiece material are required to be low, avoiding the welding quality problems caused by processing accuracy and matching accuracy. In this regard, the patent (CN108857057A) that has been applied for publication realizes the laser welding of single crystal silicon and glass under optical contact conditions through ultrasonic cleaning, alignment of upper and lower clamping parts, locking and clamping of upper and lower clamping parts, laser action in the first opening, positioning the laser focus below the top surface of the single crystal silicon block, and laser welding. These six steps. However, due to the large contact surface gap in non-optical contact, it is difficult to effectively suppress the plasma during ultrafast laser welding. The welding interface is mainly laser ablation, and the interface is filled by ablation sputtered particles. The achievable welding strength (<15MPa) and welding interface gap tolerance (<1μm) are both low, which is difficult to meet actual needs. A new welding mechanism is required to guide the non-optical contact welding of heterogeneous materials and improve the welding strength.

[0005] Based on the current shortcomings of poor quality stability of optical contact welding of heterogeneous materials and low strength of non-optical contact welding. A stable and high-strength method for welding heterogeneous materials is urgently needed. The present invention provides an ultrafast laser welding method for heterogeneous materials with large spacing, which specifically includes: stacking metal materials and transparent materials and clamping them with a clamp; the laser beam is collimated and then shot into a scanning galvanometer, and is focused by a field lens after being shot out. After the laser energy is absorbed by the lower material in the first scanning, plasma is generated, and the plasma continues to expand and overflow, while the lower material melts and fills the gap to achieve quasi-optical contact conditions; the free expansion of the plasma in the second scanning is effectively suppressed, and the laser energy is limited to the vicinity of the weld, the melting volume of this area is significantly increased, and the welding strength is significantly improved; the third scanning is consistent with the second scanning mechanism, the amount of material melting is increased, and finally the welding head is strengthened. The focused light spot is moved along a specified route in a specified area within the contact surface of the upper and lower workpieces by scanning the galvanometer and the field lens, thereby realizing the melting and bonding of the workpieces. After three scans, the heterogeneous materials with large spacing can finally obtain a high-strength and high-quality welded joint. This method is a welding method for heterogeneous materials under non-optical contact conditions, which effectively avoids the extremely high requirements of optical contact on the surface quality, processing accuracy and matching accuracy of the workpiece, and can achieve high-stability welding on the lower layer workpiece with poor surface quality. And compared with the existing non-optical contact welding method, the welding strength is significantly improved. Summary of the invention

[0006] In view of the above problems, the present invention provides an ultrafast laser welding method for heterogeneous materials with large spacing. The laser beam is vertically injected into the incident hole of the scanning galvanometer through the collimated optical path and emitted from the exit hole of the scanning galvanometer, and is focused by the field lens. During the first scanning process, the focused laser energy is first absorbed by the lower workpiece material and excites plasma. The generated plasma continues to absorb the laser energy and expands continuously and overflows into the entire interface gap space. At the same time, the laser energy causes the temperature at the interface to rise, and the lower workpiece produces irreversible expansion and begins to melt. The material flows from the laser spot position to both sides, so that the contact gap continues to decrease, and finally reaches the quasi-optical contact condition. In the second scanning, the free expansion of the plasma is effectively suppressed, and the laser energy is limited to the vicinity of the weld. The melting volume of this area is significantly increased, and the welding strength is significantly improved. The third scanning is consistent with the second scanning mechanism, which increases the amount of material melting and finally realizes the strengthening of the welding head. The scanning galvanometer and the field lens are used to realize the movement of the focused spot along the specified route in the specified area of ​​the contact surface of the upper and lower workpieces, thereby realizing the melting and bonding of the workpieces. After three scans, the heterogeneous materials with large spacing can finally obtain high-strength and high-quality welded joints. This method is a welding method for heterogeneous materials under non-optical contact conditions, which effectively avoids the extremely high requirements of optical contact on the surface quality, processing accuracy and matching accuracy of the workpiece, and can achieve high-stability welding on the lower layer workpiece with poor surface quality. And compared with the existing non-optical contact welding method, the welding strength is significantly improved.

[0007] To achieve the above-mentioned purpose, the present invention provides an ultrafast laser welding method for large-spacing heterogeneous materials, comprising the following steps:

[0008] (1) The cleaned rough metal material and transparent material are stacked on a three-dimensional motion platform in sequence and clamped with a fixture. The three-dimensional platform is adjusted so that the focal plane of the laser is located at the contact surface height between the upper workpiece and the lower workpiece.

[0009] (2) Turn on the laser. A high-repetition-rate femtosecond laser with a wavelength of 1035 nm, a repetition rate of 200 kHz-2 MHz, and a power of 25-35 W is vertically injected into the incident hole of the scanning galvanometer through a collimated optical path. After being emitted from the exit hole of the scanning galvanometer, it is focused by the field lens. During the first scanning process, the focused laser energy is first absorbed by the lower workpiece material and stimulates plasma. The generated plasma continues to absorb laser energy and continues to expand and overflow into the entire interface gap space. At the same time, the laser energy causes the temperature at the interface to rise, and the lower workpiece undergoes irreversible expansion and begins to melt. The material flows from the laser spot position to both sides, filling the contact gap so that the contact gap continues to decrease, and finally reaches the quasi-optical contact condition.

[0010] (3) During the second scanning process, the free expansion of the plasma was effectively suppressed, and the laser energy was limited to the area near the weld, which significantly increased the melting volume of the upper and lower workpiece materials in this area, ultimately achieving weld head strengthening and significantly improving welding strength. The scanning galvanometer and field lens were used to enable the focused light spot to move along a specified route in a specified area within the contact surface of the upper and lower workpieces, thereby achieving melting and bonding of the workpieces.

[0011] (4) The third scan has the same mechanism as the second scan, which further increases the amount of material melted and the welding strength continues to increase. After three scans, a high-strength, high-quality welded joint can be obtained.

[0012] Furthermore, the interface gap is the distance between the lower surface of the transparent material and the upper surface of the metal material. The initial surface roughness of the metal material is greater than 10 nm, the transparent material is double-sided polished, and when a lower clamping force is applied between the workpieces or they are naturally stacked, the contact surface gap is greater than 2 μm.

[0013] Furthermore, the quasi-optical contact condition is that the contact surface gap is less than 1 μm and the surface roughness Sa is less than 10 nm.

[0014] Furthermore, the three-dimensional motion platform is a motion platform with three degrees of freedom, which can move or rotate independently or in conjunction on the X, Y, and Z axes, thereby achieving precise position and posture adjustment of the workpiece in three-dimensional space.

[0015] Furthermore, the scanning galvanometer is a high-speed two-dimensional galvanometer, which realizes the two-dimensional movement of the laser beam through the deflection and control of two reflection mirrors, and the scanning speed of the scanning galvanometer is set to 20mm / s-50mm / s.

[0016] Furthermore, the field lens is a lens or a group of lenses, which is used to control and adjust the propagation direction, beam diameter and focusing position of the laser beam. The focal length of the field lens is 80 mm, and the laser defocus is set between plus or minus 100 μm.

[0017] Furthermore, the transparent material is sapphire, fused quartz, ceramic, silicon, and the material is polished on both sides.

[0018] Furthermore, the metal material is Invar, titanium alloy, aluminum alloy, copper, the material does not need to be polished, and the surface roughness Sa>10nm.

[0019] Furthermore, an ultrafast laser welding method for heterogeneous materials with large spacing includes a high repetition rate ultrafast laser, a collimated optical path, a scanning galvanometer, a field mirror and a three-dimensional motion platform, characterized in that it also includes an optical component for adjusting the optical path of the laser emitted by the laser to be perpendicular to the surface of the workpiece to be processed and a clamp for clamping the stacked samples, wherein the clamp can adjust the gap between the upper workpiece and the lower workpiece.

[0020] In general, the above technical solution of the present invention has the following advantages compared with the prior art:

[0021] This method is a welding method under non-optical contact conditions. Compared with the existing optical contact welding process method, it effectively avoids the extremely high requirements of optical contact on the surface quality of the workpiece (surface roughness Sa <5nm to obtain a better contact interface), processing accuracy and matching accuracy (interface gap <1μm), and avoids the potential problem of poor welding quality stability caused by processing accuracy and matching accuracy. It can achieve more stable welding on the lower workpiece with poor surface quality.

[0022] The existing non-optical contact welding process mainly increases the welding head volume by adjusting laser parameters such as pulse frequency and power, but the disadvantage is the increase in thermal stress, which limits the further improvement of welding strength. This method avoids the thermal stress caused by excessive laser power through multiple welding, and compared with the existing non-optical contact welding process, the welding strength is significantly improved.

[0023] This process method has been experimentally verified in the welding of 4j36 Invar alloy with a surface roughness of Sa 1.4μm and mirror sapphire. The average shear strength measured by repeated experiments (the number of repeated experiments with the same parameters is greater than 10) is 39MPa, and the maximum shear strength is 50MPa, which is much higher than the average strength of 11MPa of a single welding process (the number of repeated experiments with the same parameters is greater than 10).

[0024] In addition, given the reduced requirements for machining accuracy and matching accuracy, this method has wider applicability in practical applications. For example, it can be applied to the welding of heterogeneous materials of large-format workpieces and curved workpieces, providing a new and reliable option for welding processes in related fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A system diagram of the ultrafast laser high-strength welding equipment for non-optical contact of heterogeneous materials according to the present invention.

[0026] Figure 2 The welding strengthening mechanism of the multi-pass scanning welding process method.

[0027] Figure 3 The first scan shows the morphology of the welding area on the upper surface of the lower workpiece 4j36 Invar alloy: (a) 30W, (b) 25W, (c) 20W.

[0028] Figure 4 The first scan shows the morphology of the welding area on the lower surface of the sapphire upper workpiece: (a) 30W, (b) 20W.

[0029] Figure 5This is the first scan of the cross-sectional morphology of the unwelded-welded transition zone.

[0030] Figure 6 The morphology of the weld joint is scanned multiple times: (a) once, (b) twice, and (c) three times.

[0031] Figure 7 It is the welding strength result of multiple scans.

[0032] Explanation of the accompanying drawings: 1-high repetition rate ultrafast laser; 2-collimation optical path; 3-scanning galvanometer; 4-field mirror; 5-upper workpiece (transparent material); 6-lower workpiece (other materials); 7-three-dimensional motion platform. DETAILED DESCRIPTION

[0033] In order to make the technical problems, technical solutions and advantages 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.

[0034] Based on the shortcomings of poor quality stability of optical contact welding of heterogeneous materials and low strength of non-optical contact welding, the present invention provides an ultrafast laser welding method for heterogeneous materials with large spacing.

[0035] The structure of an example provided by the present invention is as follows Figure 1 As shown, it is an ultrafast laser welding method for heterogeneous materials with large spacing. The equipment is composed of a high repetition rate ultrafast laser 1, a collimated optical path 2, a scanning galvanometer 3, a field lens 4, and a three-dimensional motion platform 7.

[0036] 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 enters the scanning galvanometer 3 after passing through the collimated optical path 2. The scanning galvanometer 3 controls the two-dimensional movement of the optical path to vertically enter the field lens 4. The field lens 4 is located above the three-dimensional motion platform 7. During the processing, the workpiece remains stationary, and the scanning galvanometer and the field lens realize the movement of the light spot. In addition, the scanning galvanometer 3 and the field lens 4 can be replaced by a focusing lens. At this time, the light spot remains stationary during the processing, and the workpiece movement will be realized through the three-dimensional motion platform 7.

[0037] The lower workpiece 6 and the upper workpiece 5 are stacked on the three-dimensional motion platform 7 in sequence, and the focal plane of the laser is located at the contact surface height of the upper workpiece 5 and the lower workpiece 6 by adjusting the three-dimensional platform 7. The laser 1 is turned on, and the laser beam is vertically injected into the incident hole of the scanning galvanometer 3 through the collimated optical path 2 and emitted from the exit hole of the scanning galvanometer 3, and is focused by the field lens 4. At the same time, the scanning galvanometer 3 and the field lens 4 are used to realize the movement of the focused light spot along the specified route in the specified area of ​​the contact surface of the upper and lower workpieces, thereby realizing the melting and bonding of the workpieces.

[0038] During the first scan, since the ablation threshold of the upper workpiece material is higher than that of the lower workpiece material, the laser energy is first absorbed by the lower workpiece material and plasma is excited. The generated plasma continues to absorb laser energy and expand. Due to the high roughness of the workpiece material, the microscopic manifestation is a large interface gap. The generated plasma continues to expand and overflow into the entire interface gap space, limiting the formation of the weld joint. But at the same time, the laser energy causes the temperature at the interface to rise, the lower workpiece undergoes irreversible expansion and begins to melt, and the material flows from the laser spot position to both sides, causing the contact gap to continue to decrease, and eventually reaching quasi-optical contact conditions.

[0039] Since the first scan achieves quasi-optical contact, the free expansion of the plasma is effectively suppressed during the second scan, and the laser energy is limited to the area near the weld, which significantly increases the melting volume of the upper and lower workpiece materials in this area, and finally achieves welding head strengthening and significantly improves welding strength. The third scan can be performed on the basis of the second scan. The mechanism is the same as the second scan. The amount of material melting is further increased, and the welding strength will continue to increase. If the amount of melting is increased only by increasing the power, cracks may increase and thus reduce the welding strength. In this case, dividing the laser energy into two scans will have a better welding effect and higher welding strength. However, after more than three scans, the welding strength begins to decrease. The main reason is the increase in thermal stress, which aggravates the generation and expansion of cracks inside the transparent material of the upper workpiece.

[0040] Specific examples:

[0041] In this example, the upper workpiece is sapphire and the lower workpiece is 4j36 Invar alloy. The sapphire has a size of 8mm×10mm×2mm and is double-sided polished. The 4j36 Invar alloy has a size of 10mm×20mm×2mm and a surface roughness Sa of 1.4μm. Laser welding is performed according to the steps in the ultrafast laser high-strength welding method for non-optical contact heterogeneous materials provided in the above example.

[0042] Mirror sapphire and 4j36 Invar alloy are stacked on the three-dimensional motion platform 7 in sequence, and the focal plane of the laser is located at the contact surface height of the upper workpiece 5 and the lower workpiece 6 by adjusting the three-dimensional platform 7. Turn on the laser 1, and the laser beam is vertically injected into the incident hole of the scanning galvanometer 3 through the collimated optical path 2 and emitted from the exit hole of the scanning galvanometer 3, and is focused by the field lens 4. At the same time, the scanning galvanometer 3 and the field lens 4 realize the movement of the focused light spot along the specified route in the specified area of ​​the contact surface of the upper and lower workpieces, thereby realizing the melting and bonding of the workpieces.

[0043] In the above 4j36-sapphire welding experiment, a femtosecond pulse laser was used with a wavelength of 1035nm, a repetition rate of 200kHz-2MHz, a power of 25-35W, a scanning galvanometer scanning speed of 20mm / s-50mm / s, a field lens focal length of 80mm, and a laser defocusing amount that can be set between plus and minus 100um. A lower clamping force can be applied between the workpieces or they can be stacked naturally, and the number of welding times is 3. The contact surfaces of the upper and lower workpiece materials and the cross-sectional weld joint were observed by scanning electron microscopy, and the interface filling mechanism of this process method was clarified.

[0044] Depend on Figure 3 , Figure 4 and Figure 5 It can be seen that the contact surface gap before welding is greater than 4 μm. During the first scanning process, the upper surface material of the lower workpiece material can effectively fill the interface, and as the laser power increases, the gap filling amount increases, and it is completely filled at 30 W, reaching the quasi-optical contact condition. Figure 6 It can be seen that three scans can significantly increase the welding head volume. Figure 7 It can be seen that the welding strength increases significantly with the increase in the number of scanning welding, and reaches the maximum value in three scanning. The average shear strength measured by multiple repeated experiments (the number of repeated experiments with the same parameters is greater than 10) is 39MPa, and the maximum shear strength is 50MPa, which is much higher than the average strength of 11MPa in the single welding process (the number of repeated experiments with the same parameters is greater than 10). This example verifies the feasibility of the multiple welding strengthening process method.

Claims

1. An ultrafast laser welding method for large-pitch heterogeneous materials, used for ultrafast laser welding of large-pitch transparent materials and rough metal materials, characterized in that: The following steps are involved: Step 1: stack the cleaned rough metal material and transparent material on the three-dimensional motion platform in sequence and clamp them with a clamp, and adjust the three-dimensional platform 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; Step 2: Turn on the laser. A high-repetition-rate femtosecond laser with a wavelength of 1035nm, a repetition rate of 200kHz-2MHz, and a power of 25-35W is vertically injected into the incident hole of the scanning galvanometer through a collimated optical path, and then is focused by a field lens after being emitted from the exit hole of the scanning galvanometer. During the first scanning process, the focused laser energy is first absorbed by the lower workpiece material and stimulates plasma. The generated plasma continues to absorb the laser energy and continuously expands and overflows into the entire interface gap space. At the same time, the laser energy causes the temperature at the interface to rise, and the lower workpiece undergoes irreversible expansion and begins to melt. The material flows from the laser spot position to both sides, filling the contact gap so that the contact gap is continuously reduced, and finally reaches a quasi-optical contact condition; Step 3: During the second scanning process, the free expansion of the plasma is effectively suppressed, and the laser energy is limited to the area near the weld, which significantly increases the melting volume of the upper and lower workpiece materials in this area, and finally achieves welding head strengthening and significantly improves welding strength. The scanning galvanometer and field lens are used to realize the movement of the focused light spot along the specified route in the specified area of ​​the contact surface of the upper and lower workpieces, thereby realizing the melting and bonding of the workpieces; Step 4: Use the third scan. The mechanism is the same as the second scan. It further increases the amount of material melted and the welding strength will continue to increase. After three scans, a high-strength, high-quality welded joint can be obtained.

2. The ultrafast laser welding method for large-spacing heterogeneous materials according to claim 1, characterized in that: The interface gap is the distance between the lower surface of the transparent material and the upper surface of the metal material. The initial surface roughness of the metal material is greater than 10 nm, and the transparent material is double-sided polished. When a low clamping force is applied between the workpieces or they are naturally stacked, the contact surface gap is greater than 2 μm.

3. The ultrafast laser welding method for large-spacing heterogeneous materials according to claim 1, characterized in that: The quasi-optical contact condition is that the contact surface gap is less than 1 μm and the surface roughness Sa is less than 10 nm.

4. The ultrafast laser welding method for large-spacing heterogeneous materials according to claim 1, characterized in that: The three-dimensional motion platform is a motion platform with three degrees of freedom, which can move or rotate independently or in conjunction on the three axes of X, Y, and Z, thereby achieving precise position and posture adjustment of the workpiece in three-dimensional space.

5. The ultrafast laser welding method for large-spacing heterogeneous materials according to claim 1, characterized in that: The scanning galvanometer is a high-speed two-dimensional galvanometer, which realizes the two-dimensional movement of the laser beam through the deflection and control of two reflective mirrors. The scanning speed of the scanning galvanometer is set to 20mm / s-50mm / s.

6. The ultrafast laser welding method for large-spacing heterogeneous materials according to claim 1, characterized in that: The field lens is a lens or a group of lenses, which is used to control and adjust the propagation direction, beam diameter and focusing position of the laser beam. The focal length of the field lens is 80mm, and the laser defocus is set between plus or minus 100μm.

7. The ultrafast laser welding method for large-spacing heterogeneous materials according to claim 1, characterized in that: The transparent material is sapphire, fused quartz, ceramic, silicon, and the material is double-sided polished.

8. The ultrafast laser welding method for large-spacing heterogeneous materials according to claim 1, characterized in that: The metal material is Invar, titanium alloy, aluminum alloy, copper, the material does not need to be polished, and the surface roughness Sa>10nm.

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