With the continuous research and innovation of welding technology, a high quality and efficient welding technology has been constantly applied in the field of shipbuilding industry manufacturing, which is a new, special welding method - laser -MIG composite welding. We know that in the metal joint technology, on the one hand, high welding speed and small deformation are required, and on the other hand, good weld bridging ability is required. We all know that the traditional single Handheld fiber laser welding machine process is impossible to solve the above problems.
There is no doubt that laser welding and gas shielded welding have been developed and used for a long time and they have a wide range of applications in material bonding technology. Laser composite welding is the two kinds of welding technology (fiber laser welding machine and arc welding) organic combination, so as to obtain excellent comprehensive performance, improve the welding quality and production technology at the same time, improve the cost benefit ratio. At present, laser composite welding has made remarkable achievements in the shipbuilding industry, and the economy of this technology is very attractive. In particular, laser composite welding has high welding accuracy and can achieve very good mechanical/process properties. The laser power source of composite welding can be matched with different laser sources. At present, the main research is the combination of CO2 laser, YAG laser, fiber laser and GMAW process. How to use the laser composite welding trolley of the weld tracking system to weld long welds is mentioned in the research agenda.
1, the introduction of
High quality, high efficiency, low deformation and easy to realize automatic assembly, laser welding has a broad prospect in the welding of steel structural parts. Laser arc composite welding technology can improve the ability of welding seam bypass, which is of great significance for welding when the gap is large. Laser welding and gas shielded welding have been developed and applied for a long time, and have been widely used in the field of industry and material connection technology. Due to the differences in the process of energy transfer to the workpiece and the formation of energy flow, the two welding methods have formed their own specific application fields.
Laser beam welding transmits energy from the laser emitter to the workpiece through an optical fiber. Arc welding, on the other hand, uses a large current to transfer energy through an arc arc column. The heat affected zone of laser welding is very narrow and the aspect ratio of the weld is very high. Due to its small focusing diameter, the weld bridging ability of laser beam welding is poor. But on the other hand, laser beam welding is very fast.
The energy density of arc welding is relatively low, so the diameter of the focus on the workpiece surface is relatively large, and the welding speed is relatively low. Laser composite welding is the organic combination of these two welding technologies, so as to obtain excellent comprehensive performance, improve the welding quality and production technology at the same time, improve the cost efficiency ratio. Currently, laser-composite welding has been used with great success in the automotive industry, and the economics of this technology in the shipbuilding industry are also very attractive: higher connection speeds and superior mechanical/process performance.
As early as the 1970s, people have known how to combine laser and arc in one process. But since then, for a long time, there has been no further research. Recently, people have turned their attention to this topic again and tried to develop laser composite welding technology. One reason for this, of course, is that lasers, which were not widely used in the industry in the early days, are now standard equipment in many factories.
Laser welding and another welding method combined with the welding technology is called laser composite welding, laser beam and arc at the same time acting on the welding area, mutual influence and support. The current research direction is to explore the wider and deeper welding applications of this process. A typical example is the application of CO2 laser GMA composite welding in the shipbuilding industry. Here we will demonstrate and discuss the possibilities for such applications.
2. Laser welding process
Laser welding requires not only a good laser source, but also a high quality laser beam to ensure that the "deep penetration deep welding" can be obtained. A high quality laser beam can achieve a smaller focusing diameter or a larger focal length. The line energy is very low and the amount of deformation is obviously reduced. As with advanced automated arc welding, off-line programming, weld tracking and other necessary welding control systems are also necessary for laser welding of large workpieces.
If the laser welding is simply used, the gap of the weld joint is 0.1 to 0.2mm at most. However, a wider gap requires us to add filling metal. Usually, the addition of filling metal can make the welding seam bypass capacity reach 0.4mm. A 12 kW CO2 laser source has been used in the industrial field. At this point the laser is transmitted through the mirror. The laser beam is acted on the workpiece through the focusing device at a focusing interval of 300mm. A 4 kW lamp YAG laser and a 7 kW fiber laser are also present in this study.
3, laser -MIG (LaserHybrid) composite welding
The aggregation intensity of laser beam can reach more than 106W/cm2 when laser welding metal. When the laser beam is clicked on the surface of the material, the temperature of the point rises rapidly to the evaporation temperature, and the evaporation hole is formed due to the evaporation of metal vapor. The most notable characteristic of welds is their high depth-width ratio. The energy density of free combustion arc in MIG arc welding is slightly higher than 104W/cm2.
The laser beam injects heat at the top of the weld, and the arc also injects heat into the weld. Instead of two welding methods acting on the welding area in turn, laser-MIG composite welding works on the welding area simultaneously. Both laser and arc affect the performance of welding. Different arc or laser processes and process parameters will have different effects on the welding process.
Laser composite welding has improved the penetration depth and welding speed. In the welding process, the metal vapor will volatilize and react on the plasma area. The plasma area has a little absorption of laser, but it can be ignored. The characteristics of the entire welding process depend on the selected ratio of laser and arc input energy.
The temperature of the workpiece surface greatly affects the absorption of laser ray energy. When the workpiece surface reaches the volatile temperature, a volatile hole is formed, so that almost all the energy can be transferred to the workpiece. The energy required for welding is determined by the surface absorption rate that varies with temperature and the energy lost by workpiece conduction. In laser-MIG welding, volatilization occurs not only on the surface of the workpiece, but also on the surface of the filler wire, which means more metal volatilization, thus making the energy transfer of the laser easier. It also ensures the integrity of the welding process. So that the laser energy transmission more easily. It also ensures the integrity of the welding process.
In shipbuilding, the first thing to be done is to have sufficient bridging capacity when the weld gap is large, which is the main goal of the research. Because in the welding process, it is inevitable that there will be a gap tolerance size is different, so in the welding parameter adjustment is more, such as: laser power, welding speed, wire feeding speed and Angle adjustment.
4, LaserHybrid: comparison of laser - MIG welding and other welding methods
Study on CO2 laser welding
Due to the high efficiency of CO2 laser, the efficiency factor reaches 20%, and the relative simplicity and measuresability of technology make CO2 laser become the most important laser source in the field of industrial metal processing. The CO2 laser has a high power output, with a capacity range of 50kW.
Fronius has combined an all-digital power source, the TPS5000, with a 12-kW CO2 laser. The following table shows the experimental data from Meyer Werft, which was completed in A laboratory of 4.5m×13m. The fixture is applicable to the test piece of 2000mm×300mm. The material used is ordinary A-class steel in shipbuilding, and the welding method is butt and Angle joint, and the welding position is flat and transverse, without backing. The experimental comparison process is: submerged arc welding, Laserhybrid: laser-MIG welding and laser wire-filling welding. Submerged arc welding weld bypass capacity of 2mm to 5mm, plate thickness to 12mm. When laser -MIG welding, the thickness of the welding plate is up to 15mm, and the gap of the welding seam bridging ability is up to 1mm, but the welding speed is 3 times that of submerged arc welding and 2 times that of laser wire filling welding. There is also a laser pulse wire filling welding method, clearance up to 0.4mm, plate thickness up to 15mm. The welding speed under the maximum tolerance gap was evaluated by testing four different thicknesses of 5mm, 8mm, 12mm and 15mm respectively. The effect of helium and argon shielding gas on laser-arc welding process is discussed by basic research. It is necessary to add a small amount of helium to the shield gas in welding with high power CO2 laser. In the shipbuilding industry, laser-GMAW-composite welding has been applied at Meyer Shipyard in Pavenburg, Germany. The fully automated production of deck prefabrication here was developed with this process. As a result of this process can be completed 20 times the length of the 20 meters of welding production with high quality, without the need to turn over the plate. In the deck precast area, there are two butt welding stations. Plate thickness up to 15mm can reach a welding speed of 3.0m/min. In addition, there are two Angle joint welding stations for welding deck or wall panels up to 20 m in straight dimensions and up to 12 mm in thickness. Before welding, welding joint is machined by Angle grinder to ensure good precision of parts.
Research on fiber laser
IPG Photon, which sells most of its high-power fiber lasers in metalworking at a factory and headquarters in Oxford, has two other manufacturing facilities in Europe. Its core technology: the exclusive active fiber and the patented pumping technology make the multi-configuration semiconductor laser has a wider application field than the linear array semiconductor laser. Because it makes the semiconductor laser to achieve a very long working life. The device is likely to consist of ytterbium-doped multi-clad fibers wrapped in loops and operating at a wavelength of 1.07 to 1.08 microns. It may also be thulium-doped, with a wavelength of 1.8 to 2.0 microns, or erbium-doped, with a wavelength of 1.54 to 1.56 microns. The energy pumped by the semiconductor laser is transmitted to the active medium through a multi-configuration optical fiber which is stacked into multiple cladding coils. The laser resonator is directly born in the active fiber.
The laser is transmitted through a characteristic 6 micron diameter core of a passive single-mode fiber. The diffraction of the ultimate laser beam is largely limited, and when equipped with built-in calibrators, the resulting beams are extremely parallel. For example, a 100 watt single-mode fiber laser with a focusing diameter of 5 mm has a full-angle divergence Angle of 0.13 milliradians in the half Angle.
The maximum power of industrial single-mode IPG fiber lasers is usually 200 watts. The production of higher power lasers requires fiber laser beam combination technology. The output of each fiber laser is combined into a single high quality laser beam through a combinator. For example, a 1, 000-watt laser would consist of 10 individual fiber lasers. Although the laser beam is no longer single-mode, its optical mode mass factor M2 is 7~10, which is better than the high-power solid-state laser. The 300 micron fiber can transmit a 7 kilowatt fiber laser. Fiber optics of various shapes can be produced, including those that produce beams of light with an approximate rectangular cross-section.
The efficiency of ytterbium doped fiber lasers is 16~20%. The efficiency of erbium-doped and thulium-doped fiber lasers is slightly lower, but still much higher than that of typical YAG lasers. Getting the best wavelength selection is the inevitable application. Due to the needs of industrial production, the laser with the performance of Nd:YAG laser and the safety of the eye is better than that of CO2 laser will be produced. The company's single-mode CW system can be modulated to 5000Hz with pulse cycles as short as 10 milliseconds. Three types of superimposed pulse lasers with pulse periods as short as 1 nanosecond or with pulses of less than 1 mJ within 100 nanosecond pulses and multimode CW lasers with power from 300 watts to 10 kW are on the market.
Fiber laser technology offers many benefits to industrial users. A 4 kW fiber laser with an optical mode factor of 0.5M2 without a cooler is quite different from a conventional Nd:YAG solid-state laser pumped by a gas discharge lamp of 11M2. Because they do not require replacement of flashlights or semiconductors, they do not require maintenance or repair throughout their life. Extreme electricity efficiency greatly reduces the cost of use. Better beam quality allows users to enjoy very small spots in diameter (a 1 kW laser can be focused into 50 microns by a 4-inch lens) that are vastly superior to the large impact zones and/or long operating intervals of traditional lasers.
What is the cost of fiber laser technology? Fiber lasers with an output power of less than 1000 watts are less than or close to that of lamp-pumped YAG lasers. However, the purchase cost of the fiber laser larger than 1000 watts is higher. However, when all factors are taken into account -- floor space, coolers, maintenance costs, and so on -- fiber lasers are much cheaper than rod Nd:YAG lasers of equal power. In the last six months, several multi-kilowatt class fiber lasers have been operating in the second test version at the European plant. These lasers have not produced any problems under the working intensity of multiple shifts. In terms of their reliability, the same effect can only be achieved by using much more powerful lasers before. A 2-kilowatt Beta version of the fiber laser has been used in the lab to weld 1.2-mm automotive galvanized sheets at welding speeds of 5m/min. Its quality and performance are comparable to that of a 4 kW lamp pumped Nd:YAG laser. A 2 kW fiber laser with a terminal fiber diameter of 300 microns can cut 4mm thick coated plates at a speed of 10m/min without burr. The maximum cutting speed is up to 16m/min.
Looking at the combination of a 7,000-watt fiber laser with an arc welding process, the Laserhybrid laser composite welding laboratory at Fronius (Fornius-WELS) headquarters has been able to weld low-alloy and high-alloy steel plates up to 8mm thick. Fig. 3 shows the configuration of combination welding of LaserHybrid and IPG fiber laser in the laboratory.
Research on Workpiece Welding of 4000-watt Lamp Pumped Solid State Laser: Because the output power of Nd:YAG laser has exceeded 4000 watts at present, coupled with its simple operation, how to apply its simple technology to production practice has been put up a research topic. Let us first look at all the applications and studies of CO2 and/or Nd:YAG lasers currently in use. The downside is the need to protect the plasma, which is due to a wavelength of only 10.6μm and the need to conduct the fine laser beam through a system of structurally inelastic optical mirrors. This prevents the CO2 laser from being used for mobile applications in practical production. But this robot or mobile application concept is easy to realize for Nd:YAG laser. In the past decade this type of solid-state laser has made a lot of money in an important area of the industry. Because its wavelength is only 1.06μm, the laser beam can be transmitted by flexible optical fibers, even at distances as long as 70 meters, which makes it possible to use the robot to weld freely in three-dimensional space. Without the plasma protection impact, the most appropriate shielding gas can be used in gas shielded welding processes to optimize arc stability, droplet transition, splash-free metal bonding, and protection of heat-affected zones. Multi-station laser systems use only one laser source to supply power. This optimizes the cost of the laser source due to the start-up operation itself. High power Nd:YAG laser sources have been on the market for a short time, so the price (€/kW) is correspondently higher than that of CO2 laser sources. But its power output is high, up to 6,000 watts. A 10,000-watt laser has been tried in Japan. Don't ignore the dangers of laser light, even a few meters apart can cause damage to unprotected eyes.
The EU DockLaser program aims to improve productivity and production quality, flexibility and working conditions by developing laser technology and equipment used in the assembly area of ship construction and maintenance. The common characteristics of these areas are low efficiency of welding process and large amount of heat input, which lead to welding deformation and damage to the workpiece paint surface and outfitting parts. The plan specifies examples of laser process applications, requirements and objectives for the development of welding/cutting processes and equipment in the shipyard operating area. Handling safety and specification are the key points of the whole equipment process. Proximity to end-user testing of actual requirements and production prototypes will help to evaluate benefits and achieve applicability under actual production conditions.
The three main application areas are:
Using the walking mechanism to weld the long right Angle weld;
Complete automatic welding of large workpiece location welding;
Application of hand-held laser welding and cutting in ship outfitting operation.
DockLaser plans to start with the proper targeting of requirements phase, which includes specific investigations of shipyard requirements and existing technologies that are officially recognized and safe to operate. The next development phase will create solutions for three application areas (long Angle welds, location welds and outfitting operations). Task 2 will develop the process for the lab, Task 3 will develop the components needed for the previously envisioned equipment, Task 4 will integrate and test the equipment in the lab, and Task 5 will focus on certification and safety in use. In the final evaluation stage, the whole system will be put into the end user for testing and evaluation in the production practice. At first each end user took on one application domain. Task 7 is to promote it as a primary means of production with industrial confederations. Task 8 is this project that is full of challenge undertakes the perfection of technical respect and administrative management.
Twelve powerful Allies from five EU countries, one United States, are responsible for the implementation of this project, which includes five manufacturing engineers' associations plus three end-users, four welding societies, one professional level association and four equipment manufacturers. They have a wealth of experience in laser technology. Coordinating the feedback and communication of practical applications is the responsibility of the industry federation. The biggest disadvantage of the gantry frame system is that it is heavy and directional. The direction of operation of a given system must be approximately in the direction of the weld. The limitation of the 6-axis robotic welding system is that the longest welding length is only 2 meters.
Finally, the developed mobile tractor with LaserHybrid welding head is the solution to all these problems, which can be manually operated to achieve azimuth conversion. The range required for manoeuvring is much smaller than for gantry systems. The result of reducing the movement of the optical element is protection of the laser fiber from mechanical stress. It is better to adjust the process parameters in the welding power source, because the characteristics of gas shielded arc welding is not very suitable for the composite welding process. It can be very precise adjustment of laser beam and weld tracking system. If special laser optical elements are used, fillet welds can also be welded by modified mobile tractors. To protect the optical fiber against reflection from the welding area, the axis of the laser beam should be tilted an Angle toward the welding direction. And the welding effect will not be affected.
Laser-GMAW composite welding is a brand new technology, which has a wide range of applications in shipbuilding industry, especially in some occasions where Laser welding is impossible to achieve or the required assembly tolerance cannot be met from the perspective of economic cost. Such a wide range of applications and high performance composite welding processes allow for significant improvements in competitiveness in the current situation of shrinking profits, reduced manufacturing time, reduced production costs and improved productivity. The biggest advantage of laser composite welding is that the welding deformation is small and the workload of welding post-treatment is reduced.
The current research shows that the laser composite welding process of high power CO2-, YAG-, or fiber laser combined with GMA can be applied to various plate thicknesses. The advantage of the composite welding process lies in its excellent weld bridging ability and very low wire energy. Compared with laser wire filling welding, LaserHybrid welding process can improve the welding speed by two times. When the plate thickness is not more than 15mm, the maximum weld bridging capacity is 1mm clearance.
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