Laser transmission welding method for in-situ strengthening of welding seam

Abstract

The invention relates to a laser transmission welding method for in-situ strengthening of a welding seam, and belongs to the technical field of laser welding. The laser transmission welding method comprises the following steps that a first to-be-welded transparent base material and a second to-be-welded transparent base material are washed with deionized water and absolute ethyl alcohol respectively and then dried; the method comprises the following steps: mixing a metal salt and a reducing ligand in a solvent to obtain a metal ion solution; coating a first transparent base material to be welded with the obtained metal ion solution, and heating and drying to obtain a transparent base material containing an ion coating; the obtained transparent base material containing the ion coating is subjected to laser scanning pretreatment; the obtained transparent base material is attached to a second transparent base material to be welded, and the attaching face is the side containing the copper ion coating; and a laser device is adjusted, and laser welding is conducted through the same laser route. The nano material formed in situ through the ion coating chemical reaction is used for enhancing the mechanical property of the connector, and the high-performance connector can be obtained while the existing problems are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser welding, and in particular, relates to a laser transmission welding method for in-situ strengthening of weld seams. Background Art

[0002] Transparent plastics have characteristics such as light weight, high chemical stability, and excellent optical properties, and are widely used in fields such as aerospace, medical, communication, and electronics. During the processing of plastic products, due to limitations such as injection molding processes, many complex components cannot be injection molded in one go and often need to be bonded from multiple parts. There are many traditional plastic connection methods, such as friction welding, which generates heat through friction to melt the plastic contact surface and then applies pressure to connect them together; hot melt welding, which uses a heating tool to heat the plastic to a molten state and then applies pressure to connect it, etc. However, the above methods usually rely on specific molds and are difficult to meet the requirements of customizable flexible manufacturing. In contrast, laser transmission welding technology is a non-contact welding technology with advantages such as fast welding speed, small heat-affected area, and high precision, and has broad application prospects in the field of plastic processing.

[0003] Since the mid-infrared light absorption of transparent plastics is usually strong, long-wavelength lasers (such as carbon dioxide lasers with a wavelength of 10.6 μm) can be used for direct welding, but the high heat effect of such lasers is likely to cause thermal damage to the plastic; ultrafast lasers are another feasible way for transparent plastic welding. Its principle is based on two-photon absorption, which enables electrons to transition from the ground state to a higher excited state to achieve material welding, with advantages such as small heat effect and high precision, but its application range is limited by the high cost of the equipment. In addition, the above methods require precise focusing of the laser on the plastic interface to be welded, with extremely high requirements for processing and assembly positioning.

[0004] Visible light-near infrared short-wavelength lasers have advantages such as low cost and low welding positioning requirements (the base material itself does not absorb light), and have received wide attention in recent years. Since the absorption rate of transparent materials for visible light and near infrared light is relatively low, when using light sources in these bands to weld transparent plastics, it is usually necessary to add an additional coating as an absorbent at the material bonding interface. The current coating preparation process has high technical requirements, and the reaction conditions involve many processes such as separation and purification, cleaning, and drying (such as the core-shell microspheres disclosed in the patent CN101903182 B); especially some coatings contain harmful substances (such as the absorbent disclosed in the patent CN 105968566 B contains carbon black), which are difficult to avoid health problems of personnel and environmental pollution during the processing, and are difficult to apply to application scenarios with high cleanliness requirements. At the same time, most current coatings have a single function, have no strengthening effect on the obtained weld seams, and even easily introduce impurities to deteriorate the joint performance.

[0005] In summary, the prior art has the following disadvantages: long-wavelength laser transmission welding is prone to cause thermal damage to materials, and the cost of ultrafast laser equipment is high; visible-light - near-infrared short-wavelength lasers are low-cost and widely applicable, but the preparation process of the currently used coatings is complex, easy to pollute the environment, and will lead to a decline in the mechanical properties of the joints. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a laser transmission welding method for in-situ strengthening of welds. The present invention uses a low-cost semiconductor laser and introduces a metal ion coating with a simple preparation process, low cost, and environmental friendliness for transparent plastic welding; in addition, the mechanical properties of the joints are further enhanced by the nano-materials formed in-situ by the chemical reaction of the ion coating, and high-performance joints can be obtained while solving the existing problems.

[0007] The present invention is achieved through the following technical solutions: The object of the present invention is to provide a laser transmission welding method for in-situ strengthening of welds, including the following steps: S1. Clean the first transparent substrate to be welded and the second transparent substrate to be welded with deionized water and anhydrous ethanol respectively, and then dry them; S2. Mix a metal salt and a reducing ligand in a solvent to obtain a metal ion solution; S3. Coat the metal ion solution obtained in step S2 on the first transparent substrate to be welded obtained in step S1, heat and dry it to obtain a transparent substrate with an ion coating; S4. Perform laser scanning pretreatment on the transparent substrate with an ion coating obtained in step S3; S5. Bond the transparent substrate obtained in step S4 with the second transparent substrate to be welded, with the bonding surface being the side with the ion coating; S6. Adjust the laser and perform laser welding using the same laser path as in step S4.

[0008] Further, in step S1, the first transparent substrate to be welded and the second transparent substrate to be welded are each selected from one or more of polyimide, polyethylene terephthalate, and polycarbonate.

[0009] Further, in step S2, the metal salt is a soluble metal salt; the soluble metal salt is selected from one or more of aluminum salts, copper salts, and silver salts.

[0010] The aluminum salts are selected from one or more of aluminum nitrate, aluminum chloride, and aluminum sulfate; the copper salts are selected from one or more of copper nitrate, copper sulfate, and copper chloride; the silver salts are selected from one or more of silver nitrate, silver perchlorate, and silver sulfate.

[0011] Further, in step S2, the reducing ligand is selected from one or more of ethylene glycol, polyethylene glycol, and polyvinylpyrrolidone.

[0012] And / or, the solvent is selected from deionized water.

[0013] Further, in step S2, the volume ratio of the metal salt to the reducing ligand is 1:1 - 2:1. The concentration of the metal salt is 5 mol / L, and the concentration of the reducing ligand is 0.3 g / mL.

[0014] Further, in step S3, the coating amount is greater than or equal to 50 μL / cm 2 .

[0015] Further, in step S3, the heating conditions are: heating at 70°C - 80°C for 5 min - 10 min.

[0016] Further, in step S4, the power of the laser scanning is 0.2 W - 0.4 W; And / or, the spot diameter of the laser is 20μm - 50 μm; And / or, the wavelength of the laser is 400 nm - 1100 nm; And / or, the laser scanning path is an orthogonal serpentine trajectory, and the gap of the scanning path is 0.02 mm - 0.1mm.

[0017] Further, in step S6, the laser power is 2.5 W - 3 W; Further, in step S6, the spot diameter of the laser is 100 μm - 200 μm; And / or, the wavelength of the laser is 400 nm - 1100 nm.

[0018] And / or, the laser welding path is an orthogonal serpentine trajectory, and the gap of the scanning path is 0.02 mm - 0.1mm.

[0019] The above technical solutions of the present invention have the following advantages compared with the prior art: (1) The present invention provides a laser transmission welding method for in-situ strengthening of welds. The metal ion solution used in the present invention has low cost and is simple to prepare. During the welding process, no harmful substances such as organic waste gas and smoke are generated, and the environmental pollution is small. At the same time, the formed coating can significantly improve the absorption rate of local short-wavelength laser, avoid using expensive ultrafast laser equipment, and effectively reduce the assembly and positioning requirements during the welding process.

[0020] (2) The ion coating used in the present invention can effectively avoid impurities introduced by the volatilization of existing light absorbers, which helps to reduce defects in the weld seam, such as pores, slag inclusions, etc. At the same time, metal ions will form metal nanoparticles in-situ during the welding process, forming a pinning effect in the weld seam to enhance the joint strength. Description of the Drawings

[0021] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to specific embodiments of the present invention in conjunction with the drawings, where: Figure 1 is the surface morphology of the area to be welded obtained after laser pretreatment in Example 1 of the present invention; Figure 2 is the macroscopic morphology of the welded specimen in Example 1 of the present invention; Figure 3 is the cross-sectional morphology of the welded specimen under the preferred parameter conditions in Example 2 of the present invention; Figure 4 is the macroscopic morphology of the welded specimen under excessive laser input in Comparative Example 2 of the present invention; Figure 5 is the shear strength of the joint under different laser energy inputs in the test example of the present invention; Figure 6 is the cross-sectional morphology of the directly welded specimen without pretreatment in Comparative Example 6 of the present invention. Detailed Embodiments

[0022] The following further illustrates the present invention in conjunction with the drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the examples given are not intended to limit the present invention.

[0023] The present invention discloses an ionic coating prepared by mixing metal salts, reducing agents, and solvents in a certain proportion, whose function is to absorb laser energy and form nano-reinforced phases in-situ in the weld seam; at the same time, a laser transmission welding method thereof is disclosed.

[0024] (1) Cut the transparent plastic to be welded into the required size and perform surface cleaning to obtain the first transparent substrate to be welded and the second transparent substrate to be welded; (2) Mix metal salts, reducing agents, and solvents in a certain proportion to obtain a metal ion solution; (3) Coat the metal ion solution on the first transparent substrate to be welded and dry it to obtain an ionic coating; (4) Perform pretreatment on it with a focused laser to remove excess ligands to avoid defects such as holes introduced during the subsequent welding process, and partial conversion of metal ions to nanoparticles also occurs during this process; (5) Lap joint the second transparent substrate to be welded with the above-mentioned treated plastic, make them closely fit through pre-tightening with a fixture, and perform laser scanning again to complete the welding.

[0025] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods. The materials, reagents, etc. used, unless otherwise specified, can all be obtained from commercial channels.

[0026] Example 1:

[0027] This example provides a method for laser welding of transparent materials using an ionic coating, including the following steps: (1) Cut the transparent polyimide into 1 cm × 4 cm, wash it with deionized water and absolute ethanol, and set it aside for use; (2) Mix a 6 mol / L aluminum nitrate solution and a 0.3 g / mL polyethylene glycol solution in a volume ratio of 1:1; (3) Drop 50 μL of the above mixed solution onto the welding area (1 cm × 1 cm) on the surface of the polyimide, and heat it at 80 °C for 10 min to obtain an ionic coating; (4) Perform pretreatment with a 450 nm laser, select a power of 0.3 W, a spot diameter of 50 μm, and scan the welding area in a serpentine trajectory with a scanning interval of 30 μm; (5) Cover the first transparent plastic sheet with a second transparent plastic sheet of the same size, with an overlapping area of 1 cm × 1 cm, and make the two closely fit; (6) Use a 450 nm laser, select a power of 3 W, a spot diameter of 100 μm, and scan the welding area in a serpentine trajectory with a scanning interval of 30 μm to complete the welding.

[0028] Figure 1 This is the surface morphology of the welding area after laser pretreatment in this example. A large number of in-situ synthesized nanoparticles can be observed, which is beneficial to improving the mechanical properties of the final joint; Figure 2 This is the macroscopic morphology of the welded specimen obtained in this example. It can be seen from it that its surface is flat, indicating that the joint is well formed.

[0029] Example 2:

[0030] This example provides a method for laser welding of transparent materials using an ionic coating, including the following steps: (1) Cut the transparent polyimide into 1 cm × 4 cm, wash it with deionized water and absolute ethanol, and set it aside for use; (2) Mix a 6 mol / L copper nitrate solution and a 0.3 g / mL polyethylene glycol solution in a volume ratio of 1:1; (3) Drop 50 μL of the above-mentioned mixed solution onto the area to be welded (1 cm × 1 cm) on the surface of the polyimide, and heat it at 80 °C for 10 min to obtain an ionic coating; (4) Perform pretreatment with an 808 nm laser. The selected power is 0.3 W, the spot diameter is 30 μm, and scan the area to be welded in a serpentine trajectory with a 30 μm scan interval; (5) Cover the first transparent plastic sheet with a second transparent plastic sheet of the same size. The overlapping area is 1 cm × 1 cm, and press the two together tightly; (6) Use an 808 nm laser with a selected power of 3 W and a spot diameter of 1 hundred μm, and scan the area to be welded in a serpentine trajectory with a 30 μm scan interval to complete the welding.

[0031] Figure 3 This is the cross-sectional microscopic morphology of the welded joint obtained in this example. It can be seen that the upper and lower base materials are connected by an obvious fusion line, and no defects such as pores and ablation are observed, indicating that the welded joints obtained by this technical solution have high welding quality.

[0032] Example 3:

[0033] This example provides a method for laser welding of transparent materials using an ionic coating. Similar to Example 2, the only difference is that in step (6), the power of the laser is 2.5 W, and the rest of the operations remain the same. [[ID=...]]

[0034] Comparative Example 1:

[0035] This comparative example provides a method for laser welding of transparent materials using an ionic coating. Similar to Example 2, the only difference is that the laser welding power in step (6) is changed to 1.5 W, and the rest of the operations remain the same. The result is that when welding with a power of 1.5 W, effective welding of the materials cannot be formed, indicating that sufficient laser energy input is necessary.

[0036] Comparative Example 2:

[0037] This comparative example provides a method for laser welding of transparent materials using an ionic coating. Similar to Example 2, the only difference is that the laser welding power in step (6) is changed to 5 W, and the rest of the operations remain the same. The result is that when welding with a power of 5 W, the surface morphology of the obtained sample is as [[ID=...]] Figure 4 shown. It can be seen that its surface is rough, indicating that excessive energy input has caused thermal damage to the plastic substrate.

[0038] Comparative Example 3:

[0039] This comparative example provides a method for laser welding of transparent materials using an ionic coating. It is similar to Example 2, except that: the laser welding power in step (6) is changed to 2 W, and the rest of the operations remain the same.

[0040] Comparative Example 4:

[0041] This comparative example provides a method for laser welding of transparent materials using an ionic coating. It is similar to Example 2, except that: the laser welding power in step (6) is changed to 3.5 W, and the rest of the operations remain the same.

[0042] Comparative Example 5:

[0043] This comparative example provides a method for laser welding of transparent materials using an ionic coating. It is similar to Example 2, except that: the laser welding power in step (6) is changed to 4 W, and the rest of the operations remain the same.

[0044] Test Example:

[0045] For Example 2, Example 3 and Comparative Examples 3 - 5, the mechanical properties of the joints obtained at a laser power of 2 - 4 W were tested by a universal tensile testing machine. As Figure 5 shown, the shear strength of the joints is as high as 120 MPa at a laser power of 2.5 - 3 W, and the joints finally fracture at the base metal position, indicating their excellent mechanical properties.

[0046] Comparative Example 6:

[0047] This comparative example provides a method for laser welding of transparent materials, which is similar to Example 2, except that: the laser scanning pretreatment step in step (4) is missing, and laser welding is directly carried out. The cross-sectional morphology of the obtained joint is as Figure 6 shown. It can be seen that there are a large number of pores in the weld seam, which is due to the ineffective discharge of the reducing agent in the ionic coating during the direct welding process, indicating that the laser scanning pretreatment step is necessary.

[0048] Comparative Example 7:

[0049] This comparative example provides a method for laser welding of transparent materials using an ionic coating. It is similar to Example 2, except that: the drop coating amount of the mixed solution in step (3) is changed to 5 μL, and the strength test of the obtained joint is carried out by the method described in the test example. The result is: although the ionic coating can also act as a light absorber to complete welding after a large amount is reduced, the joint strength is only 50 MPa, which proves the strengthening effect of the reinforcement introduced by the coating on the weld seam.

[0050] Obviously, the above embodiments are merely examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here. And the obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. A laser transmission welding method for in-situ strengthening of weld seams, characterized in that It includes the following steps: S1. Clean the first transparent substrate to be welded and the second transparent substrate to be welded with deionized water and absolute ethanol respectively, and then dry them; S2. Mix a metal salt and a reducing ligand in a solvent to obtain a metal ion solution; S3. Coat the metal ion solution obtained in step S2 on the first transparent substrate to be welded obtained in step S1, and after heating and drying, obtain a transparent substrate with an ionic coating; S4. Perform laser scanning pretreatment on the transparent substrate with an ionic coating obtained in step S3; S5. Bond the transparent substrate obtained in step S4 with the second transparent substrate to be welded, and the bonding surface is the side with the ionic coating; S6. Adjust the laser, and perform laser welding using the same laser path as in step S4.

2. The laser transmission welding method according to claim 1, wherein In step S1, the first transparent substrate to be welded and the second transparent substrate to be welded are respectively selected from one or more of polyimide, polyethylene terephthalate, and polycarbonate.

3. The laser transmission welding method according to claim 1, characterized in that In step S2, the metal salt is a soluble metal salt; the soluble metal salt is selected from one or more of aluminum salts, copper salts, and silver salts.

4. The laser transmission welding method according to claim 1, wherein In step S2, the reducing ligand is selected from one or more of ethylene glycol, polyethylene glycol, and polyvinylpyrrolidone; and / or, the solvent is selected from deionized water.

5. The laser transmission welding method according to claim 1, characterized in that, In step S2, the volume ratio of the metal salt to the reducing ligand is 1:1 - 2:

1.

6. The laser transmission welding method according to claim 1, wherein In step S3, the coating amount is greater than or equal to 50 μL / cm 2 .

7. The laser transmission welding method according to claim 1, wherein In step S3, the heating conditions are: heating at 70°C - 80°C for 5 min - 10 min.

8. The laser transmission welding method according to claim 1, characterized in that, In step S4, the power of the laser scanning is 0.2 W - 0.4 W; and / or, the spot diameter of the laser is 20μm - 50 μm; and / or, the wavelength of the laser is 400 nm - 1100 nm; and / or, the scanning path of the laser is an orthogonal serpentine trajectory, and the gap of the scanning path is 0.02 mm - 0.1 mm.

9. The laser transmission welding method according to claim 1, wherein In step S6, the laser power is 2.5 W - 3 W.

10. The laser transmission welding method according to claim 1, characterized in that, In step S6, the spot diameter of the laser is 100 μm - 200 μm; and / or, the wavelength of the laser is 400 nm - 1100 nm; and / or, the welding path of the laser is an orthogonal serpentine trajectory, and the gap of the scanning path is 0.02 mm - 0.1 mm.

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