Laser is a beam of light that uses a radiation excitation light amplification principle to produce a monochromatic, directional, and high-intensity beam that is focused by a transmission or mirror to obtain high-density power. It can be used as a heat source for welding, cutting and surface treatment of materials. Laser welding (LW) is a highly efficient and precise welding method that uses a high energy density 488nm laser pointer beam as a heat source. According to the different working characteristics of the laser generator, the laser is divided into solid, liquid, gas, semiconductor and other lasers; according to the laser’s action on the workpiece and the laser output energy, laser welding can be divided into continuous laser welding and pulse laser welding; Power density laser spot welding on the workpiece can be divided into heat transfer welding (through-fusion welding) and deep-fusion welding (keyhole welding, perforation welding, small hole welding).
The laser welding machine is mainly composed of a laser (core part, currently mainly YAG solid-state laser and CO2 gas laser), beam transmission and focusing system, welding torch, work table, power supply and control device, gas source, water source, and operating panel numerical control device. . Mainly used in aviation, electronic agenda, machinery, automotive, medical, food, nuclear energy and other fields.
Laser welding has its significant advantages: high power density (103W/cm2), small hole welding and high speed welding; laser energy emission, transmission, optical transmission, deflection, focusing through optical methods such as fiber optics, prisms, etc. For micro-parts, inaccessible parts or long-distance welding; one military laser pointer can be used for multiple work on different worktables (welding, cutting, alloying, heat treatment, etc.); laser can pass through transparent objects such as glass. Welding highly toxic materials such as bismuth alloy in sealed containers made of glass; laser is not affected by electromagnetic fields, no X-rays; lasers are not lost in the atmosphere, and vacuum protection is not required; in addition to welding carbon steel and low alloy steel , stainless steel, silicon steel, aluminum, titanium and other non-ferrous metals, under certain conditions, copper-nickel, nickel-titanium, copper-titanium, titanium-molybdenum, brass-copper, low carbon steel-copper, stainless steel-copper and other dissimilar metals The material can be laser welded or non-metal such as metal and ceramic, glass, composite materials, etc. For high melting point metals, non-metallic materials (ceramics, plexiglass, etc.), materials sensitive to heat input. Laser welding is performed without heat treatment after welding. Laser welding has not been widely used mainly: the price is too expensive; the welding parts processing, assembly, positioning requirements are high; the light energy conversion rate is low (10 to 20%).
In order to expand the application range of laser welding, improve the quality of laser welding, increase the thickness of weldments and avoid the limitations of pure laser welding, a new welding process has emerged: waterproof laser pointer hybrid welding. It is important to note that the advantages of laser re-welding are not just The superposition of two welding methods! In particular, the utilization of energy is much larger than the simple addition of two heat sources. The advantage of laser hybrid welding is that the energy utilization rate is improved, the absorption rate of the laser is low when the base material is in the solid state, and the absorption rate of the laser after melting is increased to 50-100%; the penetration depth is increased a lot under the action of the arc The base metal melts to form a molten pool, and the laser acts on the bottom of the arc, and the liquid metal absorbs the laser beam at a high rate. Therefore, the laser hybrid welding is larger than the pure laser welding; the arc is stable, such as separate When welding with TIG or MIG, the welding arc is sometimes unstable, especially in the case of small currents, when the welding speed is increased to a certain value, it will cause arc drift. When laser hybrid welding is used, the laser generated plasma helps to stabilize the arc. Improve the adaptability of butt joint clearance during laser welding, reduce the assembly precision of laser welding and achieve high efficiency.
Laser welding process parameters, pulse laser welding has four main parameters: pulse energy, pulse width, power density and defocusing; continuous green laser pointer welding parameters are: laser power, welding speed, spot diameter, defocus, protection The type and flow rate of the gas; the parameters of the two-beam laser welding include: beam arrangement, spacing, two beam angles, focus position, energy ratio of the two beams, and so on. Laser hybrid welding types include: laser-arc hybrid welding, laser-high frequency welding, laser-pressure welding, laser-brazing, etc. Among them, laser-arc welding is the most common, such as laser-argon arc welding (TIG), laser-gas Welding welding (MIG), etc. According to the relative position of the laser and the arc: coaxial composite, cross composite, deviated composite.
Used in deep plate welding of thick plates, thick plate welding is limited due to the strict assembly requirements of pure laser welding and the high cost of high power lasers. The laser-arc hybrid welding can be used for thick plate deep-fusion welding, and the adaptability to the preparation of the welding groove, the beam neutrality and the joint assembly gap can be improved. It is well applied in the shipbuilding industry. For low-alloy high-strength steel, it can be preheated and welded. The laser-arc hybrid welding can achieve a penetration depth of 15mm for single-pass welding and 30mm for two-way welding. The welding deformation is only double wire welding. 1/10, T-joint with a welding thickness of 16mm can be welded at speeds up to 3m/min.
Applied to usb laser pointer welding of aluminum alloys, laser-welded aluminum alloys have large reflectivity and are prone to problems such as pores, cracks, and composition changes. By laser-arc hybrid welding, due to the action of the arc, the laser beam can directly illuminate the surface of the liquid pool, increasing the absorption rate and increasing the penetration depth. Using AC TIG or DC reverse connection, the oxide film can be cleaned in front of the laser welding, while the molten pool formed by the arc moves in front of the laser beam, increasing the wettability between the molten pool and the solid metal to prevent undercut.
Used in lap joints, lap welds are widely used in automotive frame and floor structures. Many of the current automotive shell welds are galvanized steel lap welds and aluminum plate welds. Laser-arc hybrid welding can reduce the deformation of welded parts, eliminate defects such as undercuts and undercuts, and greatly improve the welding speed. For example, the lap joint of a low carbon steel plate welded by a 10 kW CO2 laser and a MIG arc composite heat source can achieve a lap weld with a gap of 0.5 to 1.5 mm, and the penetration depth can reach 40% of the floor thickness. Another example: 2.7kW YAG laser-MIG arc composite high-speed welding aluminum alloy lap joint, welding speed up to 8m / min.
In high-speed welding of sheet metal, the main problems of laser high-speed welding of sheet metal are poor continuity of weld formation and prone to bump on the surface of weld bead. Using plasma arc assisted YAG or CO2 laser for thin plate (0.14mm) composite welding, the welding speed is twice as fast as that of single laser welding. Even if the welding speed reaches 100m/min, the arc is very stable, and a wider weld path and smooth weld surface can be obtained.