Laser transmission welding method for welding plastic pipes and pipe fittings

Abstract

The invention provides a laser transmission welding method for welding plastic pipes and pipe fittings, and belongs to the technical field of welding, the pipes are composite pipes or plastic pipes, the pipe fittings are composite pipe fittings or plastic pipe fittings, the pipe fittings are made of light-transmitting materials, and the light transmittance range of the pipe fittings is 20%-70%; the light transmittance of the pipe is smaller than that of the pipe fitting, after the pipe and the pipe fitting are inserted, a to-be-welded part is located in a transmission welding area so that the pipe and the pipe fitting can be welded and fused together, welding comprises the steps that S1, a contour line is drawn on the outer ring of the pipe fitting in advance, a welding area is delineated, and the contour line is a closed arc line surrounding the pipe fitting by a circle; and S2, the laser moves along the contour line drawn in the step S1, so that the laser penetrates through the pipe fitting, and materials in the contact area of the pipe fitting and the pipe fitting are melted until the delineated welding area is welded. Plastic pipes and pipe fittings are efficiently and accurately welded, the labor intensity is reduced, and the working efficiency and safety are improved.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, specifically laser welding of pipes and fittings, and particularly to a laser transmission welding method for welding plastic pipes and fittings. Background Technology

[0002] Nowadays, the welding of plastic pipes and plastic composite pipes mostly uses heating equipment to heat and soften the connection points of the pipes and fittings. The pipes are then manually inserted into the fittings for welding. However, manual operation is prone to problems such as incomplete insertion, misalignment, and insufficient welding time due to improper operation, resulting in insufficient welding area and thus shortening the service life of the pipeline.

[0003] In recent years, the application fields of laser welding technology have expanded to include plastics, metals, and other materials. Currently, laser welding in the plastics field is mainly used for welding automotive parts and medical plastic devices. However, it has not yet seen significant development in the field of plastic pipe welding. This is because existing technologies (thermal / electrofusion welding) have already solved most problems with extremely low cost and sufficient reliability. Laser welding, on the other hand, faces multiple requirements, including material compatibility, equipment cost, process complexity, and industry standards. In traditional industries such as construction and municipal engineering, where pipes are widely used, laser welding, as a new process, has not yet been incorporated into mainstream design, construction, and acceptance specifications. However, in the field of special plastic pipe connections, where precision, cleanliness, and automation requirements are extremely high, the application of laser welding is necessary and can significantly improve the overall industry level. Summary of the Invention

[0004] The problem to be solved by the present invention is to provide a laser transmission welding method for welding plastic pipes and fittings, thereby solving the problems in the background art, realizing high-speed, high-efficiency and precise welding of plastic pipes and fittings, reducing labor intensity and greatly improving work efficiency and safety.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a laser transmission welding method for welding plastic pipes and fittings, used for welding pipes and fittings with a nominal outer diameter of 16-400mm, wherein the pipe is a composite pipe or a plastic pipe, the fitting is a composite fitting or a plastic fitting, and the fitting is a light-transmitting material with a light transmittance range of 20%-70%;

[0006] The light transmittance of the pipe is less than that of the fitting. After the pipe and fitting are inserted, the part to be welded is located in the transmission welding area so that the pipe and fitting are welded and fused together.

[0007] The laser wavelength range for transmission welding is between 700 and 1200 nm, the laser beam width is 3 to 5 mm, and the power density ranges from 0.7 × 10⁻⁶. 4 —1×106 W / cm 2 ;

[0008] Includes the following steps:

[0009] S1. Draw the outline of the pipe fitting in advance to delineate the welding area. The outline is a closed arc around the pipe fitting.

[0010] S2. Hold the laser probe and move the laser along the outline drawn in step S1, so that the laser passes through the pipe and melts the material in the contact area between the pipe and the pipe, until the welding of the designated welding area is completed.

[0011] Furthermore, composite pipes can be metal composite pipes, non-metal composite pipes, or composite material pipes, while plastic pipes can be made of PE, PE-RT, PB, PP, PS, PC, ABS, polyamide, PMMA, polyoxymethylene, PET, or PBT.

[0012] Furthermore, the fittings are made of plastic, and the pipe is also made of plastic and light-blocking material. The fittings have a hollow internal structure, and the minimum diameter in the middle is smaller than the inner diameter of the socket sections at both ends of the fitting. The connection between the minimum diameter and the socket sections at both ends is chamfered. The fittings and pipe are fitted with a clearance fit after being socketed. Laser welding is performed in a circular rotational manner according to the set angular velocity. After completing one revolution, the welding pauses for 4-10 seconds and then advances 4.5mm until the set welding area is completed.

[0013] Furthermore, the laser wavelength is 1064 nm, the laser beam width is 5 mm, and the power density is 1.8 × 10⁻⁶. 4 W / cm 2 The laser is used to perform welding at a position 2mm away from the starting point of the welding area. The laser moves along the contour line of the plastic welding layer at an angular velocity of 10-15° / s to perform circular rotational welding. After completing one circle in the horizontal direction, it pauses for 0.5s and then moves forward 4mm at a speed of 5mm / s.

[0014] Furthermore, the distance from the laser welding area to the pipe fitting port is L. 22 L 22 ≥5mm; the length of the laser welding area is L 21 The insertion depth is L1, L 1min The minimum insertion depth is 0.45 < L. 21 / L 1min <0.5; L 1max The maximum insertion depth is 0.15 < L. 21 / L 1max <0.3.

[0015] Furthermore, the fittings are steel-plastic composite fittings, and the pipes are steel-plastic composite pipes. The fittings are hollow inside, including a connecting section in the middle and positioning grooves at both ends. The positioning grooves are horizontally placed U-shaped structures and are symmetrically arranged. After the fittings and pipes are inserted, they are fitted with a gap. Laser welding is performed in a circular rotational welding manner according to the set angular velocity. After welding one revolution, it pauses for 4-10 seconds and then advances 4.5mm. There is a 0.5mm welding overlap area before and after, until the set welding area is completed.

[0016] Furthermore, the laser wavelength is 1064 nm, the laser beam width is 5 mm, and the power density is 3 × 10⁻⁶. 4 W / cm 2 The laser is used to perform welding at a position 3mm away from the starting point of the welding area. The laser moves along the contour line of the plastic welding layer at an angular velocity of 5-8° / s to perform circular rotational welding. After completing one circle in the horizontal direction, it pauses for 0.5s and then moves forward 4.5mm at a speed of 5mm / s.

[0017] Furthermore, the distance from the laser welding area to the pipe fitting port is L. 22 L 22 =2mm; the length of the laser welding area is L 21 The insertion depth is L1, and L1 = L 21 +2mm.

[0018] Furthermore, the fitting is a sealing ring. The laser melts the bottom material of the sealing ring to form a welding zone, sealing the exposed metal layer at the end of the composite pipe to protect the inside of the pipe from external moisture.

[0019] Furthermore, the laser wavelength is 1064 nm, the laser beam width is 4.5 mm, and the power density is 1 × 10⁻⁶. 4 W / cm 2 The welding area of ​​the sealing ring is located in the middle, with a distance of 0.5mm from both the inner and outer rings, and a vertical distance of 3mm. The laser moves along the welding area of ​​the plastic pipe end at an angular velocity of 30-35° / s. The laser passes through the sealing ring and melts the material in the contact area between the sealing ring and the pipe end, forming a welding area with a thickness of 2mm.

[0020] Compared with the prior art, the present invention has the following advantages and positive effects.

[0021] 1. The present invention provides a laser transmission welding method for welding plastic pipes and fittings. The welding outline is drawn in advance, and then the laser is used for spiral welding until the materials at the contact part of the pipe and fitting are fused together. The method utilizes the difference in light transmittance to achieve precise welding of different materials, resulting in good weld sealing, high connection strength, fast welding speed, and minimizing thermal damage and thermal deformation.

[0022] 2. This invention selects the laser wavelength, width, and vertical distance during welding based on the melting point, density, and specific heat capacity of different pipes and fittings to meet the heat requirements for welding. Throughout the welding process, the relative positions of the pipes and fittings remain unchanged, and the laser can be used for external operation, making the operation quick and safe.

[0023] 3. This invention is applicable not only to pipe and fitting structures with socket structures, but also to transmission welding of sealing rings and pipe structures. Furthermore, it is applicable not only to the welding of pipes and fittings made of plastic materials, but also to the welding of composite steel-plastic pipe fittings. Different parameters are set according to the differences in materials. For socket structures, the welding area and the depth of the socket are in a certain proportion to ensure the stability and quality of laser transmission welding. Attached Figure Description

[0024] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0025] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the laser transmission welding method for welding plastic pipes and fittings according to the present invention;

[0026] Figure 2 This is a schematic diagram of the welding structure in Embodiment 3 of the present invention, where the pipe material is a steel-plastic composite pipe;

[0027] Figure 3 This is a schematic diagram of the welding structure in Embodiment 3 of the present invention, where the pipe material is a PE steel wire mesh composite pipe;

[0028] Figure 4 This is a schematic diagram of embodiment 2 of the laser transmission welding method for welding plastic pipes and fittings according to the present invention;

[0029] Figure 5 This is a schematic diagram of the structure of the polyethylene plastic pipe fittings and pipe welding of the present invention;

[0030] Figure 6 This is a dimension table for laser welding of polyethylene plastic pipe fittings according to the present invention;

[0031] Figure 7 This is a schematic diagram of the structure of the polypropylene plastic pipe fittings and pipe welding of the present invention;

[0032] Figure 8 This is a laser welding dimension table for polypropylene plastic pipe fittings according to the present invention;

[0033] Figure 9 This is a schematic diagram of the steel-plastic composite pipe fittings and pipe welding of the present invention;

[0034] Figure 10 This is a laser welding dimension drawing of the steel-plastic composite pipe fitting of the present invention;

[0035] Figure 11 This is a schematic diagram of the sealing ring structure of the present invention;

[0036] Figure 12 This is a laser welding dimension table for the sealing ring of this invention.

[0037] Figure 13 This is a parameter table for various embodiments of the present invention.

[0038] Figure label:

[0039] 1. Pipe fittings; 1'. Sealing ring; 11. Minimum diameter; 12. Socket section; 13. Chamfer; 15. Positioning groove; 16. Connecting section; 2. Pipe material; 21. Outer layer; 22. Steel plate layer; 23. Inner layer; 4. Laser welding equipment. Detailed Implementation

[0040] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0041] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0042] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0043] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0044] Pipe fittings are used to connect pipes, which are relatively long pipes. The two are connected via a socket weld joint. Socket welding involves inserting the pipe into the socket cavity of the fitting. During the process, a socket depth line needs to be pre-drawn on the pipe end—a closed arc around the entire pipe. This provides a consistent reference point for assembly and welding from any angle. The worker first fully inserts the pipe into the bottom of the socket cavity, ensuring it is inserted correctly according to the socket depth line. The purpose of marking the socket depth line on the pipe is to prevent incomplete insertion, misalignment, or skewed insertion. For quality inspectors, this line is a quick and intuitive basis for judgment. They can check whether the line is evenly exposed. For the welding process of socket weld joints, pre-drawing the socket depth line is a mandatory standard requirement. In socket weld joints, the insertion depth must also comply with national standards depending on the specific application.

[0045] In plastics applications, laser welding uses near-infrared (NIR) lasers with wavelengths between 810 and 1064 nanometers. First, two products are clamped together under low pressure. Utilizing the difference in transmittance or refractive index between the two products, the NIR laser passes through one product (NIR laser transmission) and is absorbed by the other (NIR laser absorption). The product absorbing the NIR laser converts the light into heat, melting at the contact surface. Simultaneously, the heat is conducted to the surface of the product that transmitted the NIR laser, forming a weld zone. Other welding methods cannot join two polymers so different in structure, softening point, and reinforcing materials. Laser welding excels at welding products with complex shapes (even three-dimensional ones) and can weld areas that are difficult to reach with other welding methods.

[0046] like Figure 1 - Figure 4 As shown, the present invention is a laser transmission welding method for welding plastic pipes and fittings, used for welding pipes 2 and fittings 1 with nominal outer diameters of 16-400mm. Pipe 2 is a composite pipe or a plastic pipe, and fitting 1 is a composite pipe or a plastic pipe. Fitting 1 is made of a light-transmitting material with a light transmittance range of 20%-70%.

[0047] The light transmittance of pipe 2 is less than that of pipe fitting 1. After the pipe 2 and pipe fitting 1 are inserted, the parts to be welded are located in the transmission welding area so that the pipe 2 and pipe fitting 1 are welded and fused into one.

[0048] Laser wavelengths used for transmission welding range from 700 to 1200 nm, representing the energy region with the highest laser welding efficiency. The laser beam width is 3–5 mm, and the power density ranges from 0.7 × 10⁻⁶. 4 —1×10 6 W / cm 2 Preferably, the power density range is 0.85 × 10⁻⁶. 4—5×10 4 W / cm 2 The laser welding equipment 4 can be handheld or can be completed by a fully automatic robotic arm. Depending on the actual needs, a diode laser is used. It has a compact structure and can be easily installed on automated equipment. It is also easily absorbed by plastics containing special fillers or pigments. The laser can be easily transmitted to the laser head through optical fibers.

[0049] Includes the following steps:

[0050] S1. Draw the outline on the outer ring of pipe fitting 1 in advance to delineate the welding area. The outline is a closed arc around pipe fitting 1. The edge point near the socket joint is the starting point to facilitate rotation and welding.

[0051] S2. Hold the laser probe and move the laser along the outline drawn in step S1, so that the laser passes through the pipe 1 and melts the material in the contact area between the pipe 2 and the pipe 1, until the welding of the circled welding area is completed.

[0052] Furthermore, the composite pipe can be a metal composite pipe, a non-metal composite pipe, or a composite material pipe 2. The plastic pipe is made of PE, PE-RT, PB, PP, PS, PC, ABS, polyamide, PMMA, polyoxymethylene, PET, or PBT. The fittings 1 and pipe 2 used for connection are made of the same material.

[0053] In practical applications, when pipe 2 is a PE water supply pipe, carbon black is contained in it to reduce the overall light transmittance. The carbon black reduces the overall light transmittance of pipe 2, while fitting 1 has higher light transmittance. The laser passes through fitting 1 and directly irradiates the surface of the low-transmittance pipe 2. Pipe 2 absorbs the light energy and fuses with fitting 1. The carbon black facilitates the conversion of absorbed light energy into heat energy on the surface of pipe 2 during transmission welding. The carbon black content is 2.1%–2.5%, preferably 2.2%–2.3%, which is within the national standard range of 2%–2.5%. Simultaneously, to enable laser welding, color masterbatch is added to pipe 2, with an addition amount of 4.5%–5.5%. Under the action of an infrared absorbing coating at the contact point between the two plastic layers, adhesion between the two transparent materials can be achieved.

[0054] Example 1: As Figure 1 As shown, fitting 1 is a plastic fitting, and pipe 2 is a plastic pipe made of light-blocking material. Fitting 1 has a hollow internal structure, and the minimum diameter 11 in the middle is smaller than the inner diameter of the socket sections 12 at both ends of fitting 1. The connection between the minimum diameter 11 and the socket sections 12 at both ends is chamfered 13. Fitting 1 and pipe 2 are fitted with a clearance after being inserted. Laser welding is performed in a circular rotational manner according to the set angular velocity. After welding one revolution, it pauses for 4-10 seconds and then advances 4.5mm until the set welding area is completed.

[0055] Preferably, the laser wavelength is 1064 nm, the laser beam width is 5 mm, and the power density is 1.8 × 10⁻⁶. 4 W / cm 2 The laser is used for welding at a position 2mm perpendicular to the starting point of the welding area. The laser moves along the contour of the plastic welding layer at an angular velocity of 10-15° / s in a circular rotational welding motion. After completing one revolution in the horizontal direction, it pauses for 0.5s, then advances 4mm at a speed of 5mm / s. More preferably, a power density of 0.95×10⁻⁶ is used. 4 W / cm 2 Lasers are suitable for handheld welding. Too high a power density can easily burn the underlying material, while too low a power density will not allow welding. The power density should be matched with the welding speed. For manual handheld welding, a lower power density is used when the speed is slow, otherwise a high power density will easily burn the weld. Using a robotic arm for welding can result in a faster speed, more stable control, and a correspondingly higher welding power density.

[0056] Preferably, the distance from the laser welding area to the port of pipe fitting 1 is L. 22 L 22 ≥5mm; the length of the laser welding area is L 21 The insertion depth is L1, L 1min The minimum insertion depth is 0.45 < L. 21 / L 1min <0.5; L 1max The maximum insertion depth is 0.15 < L. 21 / L 1max <0.3.

[0057] Taking laser transmission welding of DN125 polypropylene pipe 2 and fitting 1 as an example, the melting point of polypropylene pipe 2 is 164-176℃. Above this temperature, the material has fluidity and a density of 0.89-0.92 g / cm³. These parameters determine the energy required for transmission welding into a single structure, which helps in selecting laser parameters. Fitting 1 and pipe 2 are connected by a socket joint with a depth of 61 mm. A laser probe with a wavelength of 1064 nm, a beam width of 5 mm, and a power density of 1.8 × 10⁻⁶ is used, held by hand or by an automated mechanical device. 4 W / cm 2The laser, starting 5mm from the insertion port of fitting 1, sets a 16mm wide welding area on the outer wall of fitting 1 at a position 21mm from the insertion port. An outline is drawn in this area to assist welding. At a position 2mm perpendicular to the starting point of the welding area, the laser passes through fitting 1 to melt the material at the contact area between fitting 1 and pipe 2, forming a welding zone. The laser moves along the outline of the plastic welding layer at an angular velocity of 13.06° / s to perform circular rotational welding. After completing one circle in the horizontal direction, it pauses for 0.5s, then advances 4mm at a speed of 5mm / s, and then continues welding until the set area is welded.

[0058] Figure 5 This is a schematic diagram of the structure of polyethylene plastic pipes and fittings 1 with socket welding. Figure 6 This is a table of laser welding dimensions for polyethylene plastic pipes and fittings. The data for the socket section is taken from GB / T 18742.3—2017 "Polypropylene Piping Systems for Hot and Cold Water - Part 3: Fittings". The specific heat capacity of polypropylene pipe 2 is 2.3 × 10⁻⁶. 3 —2.5×10 3 J / (kg·℃), density is 0.94—0.96 g / cm³ 3 The melting point is 105-135℃, the low density corresponds to a melting point of 105-115℃, and the high density corresponds to a melting point of 130-135℃. The initial temperature for welding is 25℃.

[0059] Figure 7 This is a schematic diagram of the welded structure of polypropylene plastic pipe fittings and pipe 2; Figure 8 This is a table of dimensions for laser welding of polypropylene plastic pipe fittings. The data for the socket section is quoted from "GB / T 13663.3—2018 Polyethylene (PE) Piping Systems for Water Supply Part 3: Fittings".

[0060] Example 2: As Figure 4 As shown, fitting 1 is a steel-plastic composite fitting, and pipe 2 is a steel-plastic composite pipe. Fitting 1 is hollow inside, including a connecting section 16 in the middle and positioning grooves 15 at both ends. The positioning grooves 15 are horizontally placed U-shaped structures and are symmetrically arranged. Fitting 1 and pipe 2 are fitted with a gap after insertion. Laser welding is performed in a circular rotational welding manner according to the set angular velocity. After welding one revolution, it pauses for 4-10 seconds and then advances 4.5mm. There is a 0.5mm welding overlap area until the set welding area is completed. The steel-plastic composite pipe of this application is also called PSP. It is not a single material, but a "steel-plastic composite" structure. The inner layer 23 and the outer layer 21 are PE plastic, and the middle is a steel plate layer 22. It is a substitute for traditional metal pipes and pure plastic pipes.

[0061] Preferably, the laser wavelength is 1064 nm, the laser beam width is 5 mm, and the power density is 3 × 10⁻⁶. 4 W / cm 2 The laser is used to perform welding at a position 3mm away from the starting point of the welding area. The laser moves along the contour line of the plastic welding layer at an angular velocity of 5-8° / s to perform circular rotational welding. After completing one circle in the horizontal direction, it pauses for 0.5s and then moves forward 4.5mm at a speed of 5mm / s.

[0062] Preferably, the distance from the laser welding area to the port of pipe fitting 1 is L. 22 L 22 =2mm; the length of the laser welding area is L 21 The insertion depth is L1, and L1 = L 21 +2mm.

[0063] Taking laser transmission welding of DN90 steel-plastic pipe 2 and fitting 1 as an example, fitting 1 and pipe 2 are connected by socket joint with an insertion depth of 35mm. An automated mechanical device is used to hold the laser probe with a wavelength of 1064nm, a laser beam width of 5mm, and a power density of 3×10⁻⁶. 4 W / cm 2 The laser, with a DN90 insertion depth of 36mm, starts at a position 2mm from the insertion end of fitting 1 and extends to a position 36mm from the insertion end of fitting 1, setting a welding area with a width of 34mm. An outline is drawn in this area to assist welding. At a position 3mm perpendicular to the starting point of the welding area, the laser heats the steel plate through the polypropylene layer of fitting 1 and the outer layer 21 of the steel-plastic pipe, causing the material of the outer layer 21 of the pipe 2 and the inner layer 23 of the fitting 1 to melt, forming a welding area. The laser moves along the outline of the plastic welding area at an angular velocity of 6.83° / s to perform circular rotational welding. After completing one circle in the horizontal direction, it pauses for 0.5s, then advances 4.5mm at a speed of 5mm / s, with a 0.5mm overlap area. Welding continues until the set area is completed.

[0064] Figure 9 This is a structural diagram of steel-plastic composite pipe fittings and pipe material 2 welded together. Figure 10 This is a dimension drawing of laser welding for steel-plastic composite pipe fittings.

[0065] Example 3: As Figure 2 and Figure 3 As shown, pipe fitting 1 is a sealing ring 1'. The laser melts the bottom layer material of the sealing ring 1', forming a welding zone that seals the exposed metal layer at the end of the composite pipe, protecting the interior of pipe 2 from external moisture and extending the storage and service life of the composite pipe. The melting point of the sealing ring 1' is 260℃. Above this temperature, the material is fluid, and its specific heat capacity is 1.9 × 10⁻⁶. 3J / (kg·℃), the specific heat capacity determines how much energy is required to heat pipe 2 and fitting 1 to the welding temperature, and affects the rate at which heat is conducted from the surface to the interior; the density of sealing ring 1' is 0.89-0.91 g / cm³. These parameters determine the energy required for transmission welding into an integral structure and help in selecting laser parameters.

[0066] Preferably, the laser wavelength is 1064 nm, the laser beam width is 4.5 mm, and the power density is 1 × 10⁻⁶. 4 W / cm 2 The welding area of ​​the sealing ring 1' is located in the middle, with a distance of 0.5mm from both the inner and outer rings, and a vertical distance of 3mm. It moves along the welding area of ​​the plastic pipe end at an angular velocity of 30-35° / s. The laser passes through the sealing ring 1' and melts the material in the contact area between the sealing ring 1' and the pipe end 2, forming a welding area with a thickness of 2mm.

[0067] like Figure 2 As shown, taking the laser transmission welding of DN50 steel wire mesh pipe 2 and sealing ring 1' as an example, the sealing ring 1' is aligned with the port of steel wire mesh pipe 2, and a handheld laser probe is used with a wavelength of 1064nm, a laser beam width of 4.5mm, and a power density of 1×10⁻⁶. 4 W / cm 2 The laser seals the sealing ring 1', which has a total width of 5.5mm. Outlines are drawn within a 0.5mm range from the inner and outer rings. The inner and outer rings refer to the inner and outer walls of the pipe 2 port, which form a circular ring when viewed from the port direction. The central annular area, concentric with the inner and outer rings, is 0.5mm from both the outer and inner rings, defining a welding area width of 4.5mm. The laser moves along the welding area of ​​the plastic pipe port at an angular velocity of 34.37° / s, maintaining a 3mm vertical distance from the starting point of the welding area. The laser passes through the sealing ring 1', melting the material at the contact area between the sealing ring 1' and the pipe 2 port, forming a 2mm thick welding zone. After welding one ring, the sealing ring 1' seals the exposed metal layer of the steel-plastic pipe 2 port to prevent rusting. This method is also applicable to the end sealing of metal-plastic composite pipes such as PE steel wire mesh composite pipes. Figure 3 As shown.

[0068] Figure 11 This is a schematic diagram of the sealing ring structure; Figure 12 This is a laser welding dimension table for sealing rings.

[0069] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A laser transmission welding method for welding plastic pipes and fittings, applicable to pipes and fittings with a nominal outer diameter of 16-400mm, characterized in that: The pipes are composite pipes or plastic pipes, and the fittings are composite pipe fittings or plastic pipe fittings. The fittings are made of light-transmitting materials with a light transmittance range of 20%–70%. The light transmittance of the pipe is less than that of the fitting. After the pipe and fitting are inserted, the part to be welded is located in the transmission welding area so that the pipe and fitting are welded and fused together. The laser wavelength range for transmission welding is between 700-1200 nm, the laser beam width is 3-5 mm, and the power density range is 0.7 x 10 4 -1 x 10 6 W / cm 2 ; Includes the following steps: S1. Draw the outline of the pipe fitting in advance to delineate the welding area. The outline is a closed arc around the pipe fitting. S2. The laser moves along the outline drawn in step S1, so that the laser passes through the pipe and melts the material in the contact area between the pipe and the pipe until the welding area defined by the outline is completed.

2. The laser transmission welding method for welding plastic pipes and fittings according to claim 1, characterized in that: Composite pipes include metal composite pipes, non-metal composite pipes, and composite material pipes. Plastic pipes are made of materials such as PE, PE-RT, PB, PP, PS, PC, ABS, polyamide, PMMA, polyoxymethylene, PET, or PBT.

3. The laser transmission welding method for welding plastic pipes and fittings according to claim 1, characterized in that: The fittings are made of plastic, and the pipes are also made of plastic and light-blocking material. The fittings have a hollow internal structure, and the minimum diameter in the middle is smaller than the inner diameter of the socket sections at both ends of the fitting. The connection between the minimum diameter and the socket sections at both ends is chamfered. The fittings and pipes are fitted with a clearance fit after being socketed. Laser welding is performed in a circular rotational manner at a set angular velocity. After completing one revolution, the welding pauses for 4-10 seconds and then advances 4.5mm until the set welding area is completed.

4. The laser transmission welding method for welding plastic pipes and fittings according to claim 3, characterized in that: The laser wavelength is 1064 nm, the laser beam width is 5 mm, the power density is 1.8 x 10 4 W / cm 2 The laser is used to weld at a position 2 mm away from the starting point of the welding area vertically, and the laser moves along the contour line of the plastic welding layer at an angular velocity of 10-15° / s for annular rotary welding. After one round of welding in the horizontal direction, it stops for 0.5 s, and then advances 4 mm at a speed of 5 mm / s.

5. The laser transmission welding method for welding plastic pipes and fittings according to claim 3, characterized in that: The distance of the laser weld region to the tube end port is L 22 , L 22 ≥ 5 mm; the length of the laser weld region is L 21 , the socket depth is L1, L 1min is the minimum value of the socket depth, 0.45 < L 21 / L 1min < 0.5; L 1max is the maximum value of the socket depth, 0.15 < L 21 / L 1max < 0.

3.

6. The laser transmission welding method for welding plastic pipes and fittings according to claim 1, characterized in that: The fittings are steel-plastic composite fittings, and the pipes are steel-plastic composite pipes. The fittings are hollow inside, including a connecting section in the middle and positioning grooves at both ends. The positioning grooves are horizontally placed U-shaped structures and are symmetrically arranged. After the fittings and pipes are inserted, they are fitted with a clearance. Laser welding is performed in a circular rotational manner according to the set angular velocity. After welding one revolution, it pauses for 4-10 seconds and then advances 4.5mm. There is a 0.5mm welding overlap area before and after the welding is completed until the set welding area is completed.

7. The laser transmission welding method for welding plastic pipes and fittings according to claim 6, characterized in that: The laser wavelength is 1064nm, the laser beam width is 5mm, and the power density is 3×10⁻⁶. 4 W / cm 2 The laser is used to perform welding at a position 3mm away from the starting point of the welding area. The laser moves along the contour line of the plastic welding layer at an angular velocity of 5-8° / s to perform circular rotational welding. After completing one circle in the horizontal direction, it pauses for 0.5s and then moves forward 4.5mm at a speed of 5mm / s.

8. The laser transmission welding method for welding plastic pipes and fittings according to claim 6, characterized in that: The distance from the laser welding area to the pipe fitting port is L. 22 L 22 =2mm; the length of the laser welding area is L 21 The insertion depth is L1, and L1 = L 21 +2mm.

9. The laser transmission welding method for welding plastic pipes and fittings according to claim 1, characterized in that: The fitting is a sealing ring. The laser melts the bottom material of the sealing ring to form a welding zone, sealing the exposed metal layer at the end of the composite pipe to protect the inside of the pipe from external moisture.

10. The laser transmission welding method for welding plastic pipes and fittings according to claim 9, characterized in that: The laser wavelength is 1064 nm, the laser beam width is 4.5 mm, and the power density is 1 × 10⁻⁶. 4 W / cm 2 The welding area of ​​the sealing ring is located in the middle, with a distance of 0.5mm from both the inner and outer rings, and a vertical distance of 3mm. The laser moves along the welding area of ​​the plastic pipe end at an angular velocity of 30-35° / s. The laser passes through the sealing ring and melts the material in the contact area between the sealing ring and the pipe end, forming a welding area with a thickness of 2mm.

Images