In the process of metal connection technology, on the one hand, the welding speed is required to be highly deformed and small, and on the other hand, it is required to have a very good weld bridging capability. However, the conventional single laser welding process cannot solve the above problems. This article mainly introduces the advantages of laser-MIG hybrid welding relative to other welding technologies and its application in the shipbuilding industry. This is a high-quality, high-efficiency and new-type welding method.
Foreword
With continuous research and innovation of welding technology, a high-quality and efficient welding technology has been continuously applied in the field of shipbuilding industry. This is a new type of special welding method-laser-MIG hybrid welding. . We know that in the process of metal joining technology, on the one hand, it requires high welding speed and small deformation, on the other hand, it must have a good weld bridging ability. We all know that the traditional single laser welding process cannot solve the above problems.
There is no doubt that the development and application of laser welding and gas metal arc welding processes have been in existence for a long time and they have a wide range of applications in material connection technology. Laser hybrid welding combines these two welding technologies (laser welding and arc welding) organically to obtain excellent overall performance, while improving welding quality and production processability while improving the cost-effectiveness ratio. At present, laser hybrid welding has made remarkable achievements in the shipbuilding industry, and the economy of this technology is also very attractive. It is particularly important that the laser hybrid welding has high welding accuracy and can obtain very good mechanical/technological properties. The laser power source for hybrid welding can be equipped with different laser sources. Currently, the main researches are: composite of CO 2 laser, YAG laser, fiber laser and GMAW process. How to use the weld seam tracking system of the laser hybrid welding car to weld long welds was mentioned on the research agenda.
1 Introduction
High-quality, high-efficiency, low-deformation and easy-to-automate assembly, laser welding has broad prospects for the welding of steel structures. The laser arc hybrid welding technology can increase the ability of the weld seam to bridge, and it is of great significance to the welding when the gap is large. The development and application of laser welding and gas metal arc welding processes have been in existence for a long time. They have been widely used in the industrial field and in the field of material connection technology. The two welding methods are used to transfer energy to the workpiece and to form energy flow. There are differences that make up their specific application areas.
Laser beam welding transfers energy from a laser emitter to a workpiece through an optical fiber. Arc welding, on the other hand, uses large currents to transmit energy through arc arcs. The welding heat affected zone of laser welding is very narrow, and the aspect ratio of the weld is high. Due to its small focal diameter, the laser beam welding has a poor weld bridging ability. But on the other hand, the welding speed of laser beam welding is very high.
The energy density of the arc welding is relatively low, so that the diameter of the focus on the workpiece surface is relatively large, and the welding speed is relatively low. Laser hybrid welding is an organic combination of these two welding technologies, which results in excellent overall performance. While improving welding quality and production processability, the cost-efficiency ratio is improved. At present, laser-composite welding has achieved remarkable success in the automotive industry. At the same time, the economics of this technology in the shipbuilding industry are also very attractive: higher connection speeds and very good mechanical/technological performance can be obtained.
As early as the 1970s, people already knew how to combine lasers and arcs organically in one process. But since then, no further research has been conducted for a long time. Recently, people once again turned their attention to this issue and tried to develop laser hybrid welding technology. Of course, one of the reasons for this is that, in the early days, lasers have not been widely used in the industry, and now lasers have become standard equipment in many factories.
The welding technique that combines laser welding with another welding method is called laser hybrid welding. Laser beams and arcs act on the welding zone at the same time, affecting and supporting each other. The current research direction is to search for a wider and deeper application of this process. A typical example is the application of the CO 2 laser GMA hybrid welding process to the shipbuilding industry. Here we will demonstrate and discuss the possibility of applying to this application area.
2, laser welding process
Laser welding not only requires a good laser source, but also requires a high-quality laser beam to ensure that the desired "deep penetration" can be achieved. A high-quality laser beam can achieve a smaller focal diameter or a larger focal length. The line energy is extremely low and the amount of deformation is significantly reduced. As with advanced automated arc welding, off-line programming, welding seam tracking and other necessary welding control systems are also required for laser welding of large workpieces.
If pure laser welding is used, the gap between the weld joints should be 0.1 to 0.2 mm at the maximum. However, wider gaps require us to add filler metal. Generally, the addition of the filler metal allows the weld seam to reach 0.4 mm. A 12 kW CO 2 laser source has been used in the industrial field. At this point the laser is conducted through the mirror surface. The laser beam is applied to the workpiece by a focusing device at a focusing distance of 300 mm. 4 kW light YAG laser and 7 KW fiber laser also appeared in this study.
3, laser-MIG (Laser Hybrid) composite welding
The intensity of the laser beam when laser welding metal can reach 106W/cm2 or more. When the laser beam hits the surface of the material, the temperature at that point rapidly rises to the volatilization temperature and a volatilization hole is formed due to the volatilization of the metal vapor. The most noticeable feature of the weld is a very high aspect ratio. The free-burning arc energy density of the MIG arc welding is slightly higher than 104 W/cm2.
The laser beam feeds heat to the top of the weld while the arc also feeds heat into the weld. Laser-MIG hybrid welding is not the two welding methods that act on the welding area in turn, but also on the welding area at the same time. Both laser and arc influence the performance of welding. The use of different arc or laser processes and the process parameters used will have different effects on the welding process.
Laser hybrid welding increases penetration and welding speed. During the welding process, the metal vapor evaporates and reacts to the plasma zone. The plasma zone absorbs the laser light slightly, but it is negligible. The characteristics of the entire welding process depend on the ratio of the laser and arc input energy selected.
The temperature of the workpiece surface greatly influences the absorption of laser beam energy. When the surface of the workpiece reaches the evaporation temperature, a volatilization hole is formed so that almost all the energy can be transmitted to the workpiece. The energy required for welding is determined by the temperature-dependent surface absorption rate and the energy lost by conduction through the workpiece. In laser-MIG welding, the volatilization not only occurs on the surface of the workpiece, but also occurs on the surface of the filler wire, which means that more metal is volatilized, making the laser energy transmission easier. It also ensures the integrity of the welding process. This makes it easier to transmit laser energy. It also ensures the integrity of the welding process.
Moreover, the first thing that must be done in the shipbuilding industry is that there is enough bridging capacity to connect the weldments, which is the main goal of the study. Because in the welding process, there will inevitably be gaps in the size of the gap, so the adjustment parameters in the welding are more, such as: laser power, welding speed, wire feed speed and angle adjustment.
4, Laserhybrid: laser - MIG welding and other welding methods of the test comparison
Research on CO 2 Laser Welding
Because of the high efficiency of the CO 2 laser, the efficiency factor is 20%, and the relatively simple and measurable technical realization makes the CO 2 laser the most important laser source in the industrial metal processing field. The CO 2 laser has a very high output power and its capacity range reaches 50 kW.
FRONIUS has been organically combined with a fully digital power supply TPS5000 and a 12 KW CO 2 laser source. The following table is the experimental data from Meyer Werft, which was completed in a 4.5m × 13m laboratory. The fixture is suitable for 2000mm × 300mm test pieces, the material used is the general A grade steel in shipbuilding, welding method It is butt and corner joints, the welding position is flat welding and horizontal welding, and no back pad. The experimental comparison process is: Submerged arc welding, LaserHybrid: laser-MIG welding and laser filler wire welding. The submerged arc welding has a bridging ability of 2mm to 5mm and a plate thickness of 12mm. In the case of laser-MIG welding, the thickness of the welded plate is 15mm, and the gap of the weld bridging capacity is 1mm. However, the welding speed is 3 times that of the submerged arc welding and 2 times that of the laser-filled wire welding. There is also a method of welding a laser pulse filler wire with a gap of up to 0.4 mm and a plate thickness of up to 15 mm. The welding speed under the maximum tolerance gap was evaluated by four experiments with different thickness materials of 5 mm, 8 mm, 12 mm, and 15 mm, respectively. The influence of helium and argon shielding gas on the laser-arc welding process is discussed in basic research. The addition of a small amount of helium in the shielding gas is necessary in the welding of high-power CO2 lasers.
Comparison of Laser Cladding and Other Competitive Processes
In the shipbuilding industry, laser-GMAW-composite welding has been applied at Meyer Shipyard in Papenburg, Germany. The fully automated production of deck prefabrication here was developed with this process. Because this process can produce 20 times as long as the 20-meter-long section of high-quality welding production, without the need to turn the board. In the prefabricated deck area there are two butt welding stations. A plate with a thickness of 15 mm or less can reach a welding speed of 3.0 m/min. In addition, there are two corner welding stations for the welding of decks or wallboards with a linear dimension within 20 meters and a thickness of 12 mm. Before welding, welding joints are machined with angle grinders to ensure good part accuracy.
Fiber laser research
The vast majority of high-power fiber lasers sold by IPG Photonics in the metal processing industry have power levels of up to 10 kilowatts. The plant and its headquarters are located in Oxford. There are also two other manufacturing plants in Europe. Its core technology: unique active fiber and patented pump technology make multi-configuration semiconductor lasers have a wider range of applications than linear array semiconductor lasers. Because it makes the semiconductor laser achieve a very long working life. The device may consist of an erbium-doped multi-clad fiber coil with an operating wavelength of 1.07 to 1.08 microns. It may also be germanium doped, having a wavelength of 1.8 to 2.0 microns or germanium doped, with a wavelength of 1.54 to 1.56 microns. The semiconductor laser pumping energy is conducted into the active medium through multi-configuration optical fibers stacked into a multi-clad coil. The laser cavity is directly generated in the active fiber. The laser is conducted through a 6-micron diameter core that is unique to passive single mode fibers. The diffraction of the final laser beam is basically limited, and when equipped with a built-in calibrator, the resulting beams are extremely parallel. For example, a 100-watt single-mode fiber laser has a full-angle divergence angle of 0.13 milliradians at half angle when the focus diameter is 5 millimeters.
Industrial single-mode IPG fiber lasers typically have a maximum power of 200 watts. The production of higher power lasers requires fiber laser beam combination technology. The output of each fiber laser is combined into a bundle by a combiner to become a single high-quality laser beam. For example, a 1000 watt laser would be a combination of 10 individual fiber lasers. Although the laser beam at this time is no longer single-mode, its optical quality factor M2 is 7-10, which is better than high-power solid-state lasers. 300 micron fiber can transmit 7 kilowatts of fiber lasers. A variety of different shapes, including the production of an optical fiber with an approximately rectangular cross-section, can be produced.
Erbium-doped fiber lasers have an efficiency of 16 to 20%. Erbium-doped and Erbium-doped fiber lasers have slightly lower efficiency, but are still much higher than typical YAG lasers. Obtaining the best wavelength selection is its inevitable application. Due to industrial production needs, lasers with Nd:YAG laser performance and better eye safety than CO 2 will be produced. The company's single-mode CW system can be modulated to 5000Hz with a pulse period as short as 10 milliseconds. Three superimposed pulsed lasers with pulse periods as short as 1 nanosecond or with pulse energies not exceeding 1 millijoule in 100 nanosecond pulses and multimode CW lasers with powers ranging from 300 watts to 10 kilowatts have been commercially available.
Fiber laser technology offers many benefits to industrial users. A 4 kW fiber laser that does not require a chiller with an optical mode quality factor of 0.5 M2 has an inherent difference compared to the conventional 11 M2 gas discharge lamp-pumped Nd:YAG solid-state laser. Because there is no need to replace flashing lights or semiconductors, they do not require maintenance and repair over their entire service life. The extremely high power consumption greatly reduces the cost of use. Better laser beam quality allows users to enjoy extremely small spot diameters that are much larger than conventional lasers' large influence areas and/or long working distances (1 kilowatt laser can be focused to 50 microns by a 4 inch lens).
What is the cost of fiber laser technology? Fiber lasers with output power below 1000 watts are lower or less than lamp-pumped YAG lasers. However, at this time, the purchase cost of a fiber laser greater than 1000 watts is higher. However, when all factors are taken into account—footprint, coolers, maintenance costs, etc., fiber lasers are much cheaper than comparable power rod-type Nd:YAG lasers. In the last six months, several multi-kilowatt fiber lasers are in operation in the second test version of the European factory. These lasers have not had any problem so far under the intensity of multi-shift work. In terms of their reliability, the same effect can only be achieved with a much more powerful laser. The 2 kW Beta Beta fiber laser has been soldered in a laboratory to a 1.2mm automotive galvanized sheet to a welding speed of 5m/min. Its quality and performance are comparable to using a 4 kW lamp-pumped Nd:YAG laser. A 2-kilowatt fiber laser with an end-fiber diameter of 300 μm can cut 4 mm thick coated plates at 10 m/min without burrs. The maximum cutting speed can reach 16m/min.
Looking again at the combination of a 7000-watt fiber laser and an arc welding process, 8mm thick low-alloy and high-alloy steel plates can be welded in the LaserHybrid laser hybrid welding laboratory of the Fronius-Wels headquarters R&D department. Figure 3 shows the configuration of a combination of LaserHybrid and IPG fiber lasers in the lab.
Workpiece Welding of 4000 W Lamp-Pumped Solid-State Lasers:
Because the output power of the current Nd:YAG laser has exceeded 4000 watts, coupled with its simple operation, how to apply its technical process to the actual production is put forward on the subject. Let us first look at the application and research of all currently used CO 2 and/or Nd:YAG lasers. Disadvantageously, the plasma needs to be protected because the wavelength of only 10.6 μm and the delicate laser beam must be transmitted through the inelastic optical mirror system, which makes the CO 2 lasers unable to be involved in mobile applications in production. field. However, the implementation of such robotic or mobile application concepts is a breeze for Nd:YAG lasers. In the past decade, this type of solid-state laser has benefited from important industrial fields. Since its wavelength is only 1.06 μm, the laser beam can be conducted by a flexible optical fiber, and even for a conduction distance of 70 meters, these make it possible to apply free robotic welding work in three-dimensional space. Without the need for plasma protection effects, the most appropriate shielding gas can be used in a gas shielded welding process to optimize arc stability, droplet transfer, spatter-free metal fusion, and heat-affected zone protection. The multi-station laser system only needs one laser source to supply energy. This optimizes the cost of the laser source due to the start-up operation itself. The laser source of high power Nd:YAG lasers has a shorter time to market, so its price (?/kW) is correspondingly higher than that of CO2 lasers. However, its output power is high and can reach as high as 6000 watts. An attempt has been made in Japan for a 10 watt class laser. Do not ignore the hazards of laser light emission. Even distances of a few meters will cause harm to unprotected eyes.
The EU's DockLaser project aims to increase productivity and production quality, improve operational flexibility and production working conditions by developing laser process technologies and equipment for shipbuilding and maintenance assembly operations. The common feature of these areas is the low efficiency of the welding process and the large heat input, resulting in welding distortion and damage to the workpiece's painted surface and armored parts. The plan details the application examples, requirements and objectives of the laser process in the dockyard area to develop welding/cutting processes and equipment. Operational safety and specification are the focus of the entire equipment process. Close to the end user's actual testing requirements and production prototypes, will help the actual production conditions under the benefits of assessment and applicability.
The 3 main application areas are:
Uses the walking mechanism to weld the long right-angled weld; Completes the automatic welding of the tack weld of large workpieces; Uses the hand-held laser welding and cutting in the ship's outfitting operations.DockLaser plans to start with an accurate lock on demand phase, including detailed surveys of shipyard requirements and existing technologies that are officially recognized and safe to operate. In the next stage of development, solutions will be created for three application areas (long straight fillet welds, tack welds and armored work). Task point 2 will focus on the laboratory development process, task point 3 will develop the components that were previously envisaged for the equipment, task point 4 will integrate and test equipment in the lab, and task point 5 will focus on certification and use safety. The final evaluation stage will put the entire system into the end user and conduct inspections and assessments in production practices. At first, each end user assumes an application field. Task 7 is to promote it as a major means of production in conjunction with the Federation of Industry. Task 8 is to improve the technical and administrative management of this challenging project.
From five EU countries, the United States is a strong ally of 12 common commitment to the implementation of the plan, the coalition includes five Society of Manufacturing Engineers plus three end-users, 4 Welding Society, a professional association and 4 Device manufacturers. They have an extremely rich experience in laser process technology. The federation of industrial federations is responsible for the feedback and communication of practical applications. The biggest drawback of the gantry system is heavy and direction-dependent. The working direction of a given system must be approximately along the direction of the weld. The limitation of the 6-axis robotic welding system is that the longest welding length is only 2 meters.
In the end, the development of a mobile tractor equipped with a LaserHybrid weld head is a solution to all these problems, and manual operations can achieve azimuth shifts. The range required for operation is much smaller than the gantry system. The result of reducing the movement of the optical element is to protect the laser fiber from mechanical damage. The adjustment of the process parameters is preferably adjusted on the welding power supply, since the gas-shielded arc welding characteristics are not very suitable for the hybrid welding process. It enables very precise adjustment of the laser beam and weld head seam tracking system. If special laser optics are used, fillet welds can also be retrofitted with mobile tractors. In order to protect the optical fiber against reflections from the welding work area, the axis of the laser beam must be inclined at an angle to the welding direction. The welding effect will not be affected.
in conclusion
Laser-GMAW is a new hybrid welding process, in the shipbuilding industry it has a wide range of uses, especially the laser welding can not be achieved or can not meet its required up to consider the case where the assembly tolerances economic cost. Such a wide range of applications and high-performance hybrid welding process so that greatly enhance the competitiveness of shrinking profits in the current situation, reduce manufacturing time, reduce production costs and improve productivity. The biggest advantage of laser hybrid welding is that the welding deformation is small and the post-weld processing workload is reduced.
Current research shows that the LaserHybrid laser hybrid welding process combining high-power CO2, YAG-, or fiber lasers with GMA can be applied to various plate thicknesses. The advantages of the hybrid welding process are its excellent weld bridging ability and very low line energy. LaserHybrid can increase welding speed by two times compared with laser welding. When the plate thickness does not exceed 15mm, the maximum weld bridging capacity is a gap of 1mm.