The usage of lightweight materials increases in recent years because of that usage of the titanium alloys increases due to its properties. The properties of titanium alloys high strength-to-weight ratio fracture toughness corrosion resistance good fatigue behavior desirable high temperature properties In many nuclear, automotive and aerospace industries prefer to use titanium alloys because of these properties.[10-13]Moreover, even in solid state and fusion welding in order to practice Ti assemblies, a lot of joining techniques are developed. [14]. But laser welding is used to obtain most proper joining technique to practice metal assemblies. [20]. Close-fitting bead, high precision and low bending are provided by high energy density in small spot dimension.. The improvement of the quality of the seam is provided by the fiber source because it has the many technical advantages and supports the lower investment of capital.
The deep penetration welding is supported by welding mode of shallow conduction, the fiber laser also provides the deep penetration welding with the high continuous wave power also the good quality of beam occurs. The another advantage of the fiber laser is that the wide range of metals and alloys can be used in application because the absorption can be occurred with the low wavelength [20].With adopting disk laser source, the quality of seam is improved proven by Caiazzo et al[21]. Some requirements are needed for laser welding even though all of the these benefits . Firstly, the gap tolerance should be low and the pieces alignment should be precise. In addition to that , The keyhole behavior plays most important role in the accomplished results of the process.The stability of keyhole behavior strictly depends on the complicated balance between the pressure of periodical recoil and the surrounding walls surface tension .The porosities occur when the keyhole collapses because there are trapped gas bubbles in the weld pool due to low depth of penetration.The stability of keyhole affects process parameters optimization. The optimization of the flow rate of the shielding gas for suppressing the vapor plume that improves the stability of process proven by Schneider et al [22]. The laser output parameters are controlled by changing geometry of bead and depth of penetration that is proven by Akman et al.[23] For specific heat inputs and changing regime of welding, the formation of underfill fault are researched by Squllace et al[24]. The pulsing laser welding causes to reduction of content of porosity that is proven by Gao et al. as observing the reheating and remelting action [25]. Casalino et al. shows that the effects of the parameters on the characteristics of bead while observing the elements with experimental data executed by artificial neural network (ANN)[26]. In this research optimizing parameters are provided by investigating of Ytterbium CW fiber laser welding of 2 mm thick Ti6Al4V plates. The surface of bottom is created under 2 mm from the top surface for position of focusing .while The preliminary bead on plate tests , optimizations of parameters of process is obtained.
There are two types of appearance of fused zone such as V-shaped and X-shaped. These are changing according to the transmitting heat input .Also the quality of joint depends on the properties of mechanical and microstructures and morphology of weld. The usage of fiber laser provides that low defectiveness and improved weld quality for behavior of mechanical and bead aspect. Welding 2 mm thick plates in configuration of butt The dimension (length x width ) of the sheet : 100 x 50 mm The material in condition of annealing :Ti6Al4V Two- phase (α-β) titanium alloy The usage of lightweight materials increases in recent years because of that usage of the titanium alloys increases due to its properties. The properties of titanium alloys high strength-to-weight ratio fracture toughness corrosion resistance good fatigue behavior desirable high temperature properties In many nuclear, automotive and aerospace industries prefer to use titanium alloys because of these properties.[10-13]Moreover, even in solid state and fusion welding in order to practice Ti assemblies, a lot of joining techniques are developed. [14]. But laser welding is used to obtain most proper joining technique to practice metal assemblies. [20]. Close-fitting bead, high precision and low bending are provided by high energy density in small spot dimension.. The improvement of the quality of the seam is provided by the fiber source because it has the many technical advantages and supports the lower investment of capital.The deep penetration welding is supported by welding mode of shallow conduction, the fiber laser also provides the deep penetration welding with the high continuous wave power also the good quality of beam occurs. The another advantage of the fiber laser is that the wide range of metals and alloys can be used in application because the absorption can be occurred with the low wavelength [20].With adopting disk laser source, the quality of seam is improved proven by Caiazzo et al[21]. Some requirements are needed for laser welding even though all of the these benefits . Firstly, the gap tolerance should be low and the pieces alignment should be precise. In addition to that , The keyhole behavior plays most important role in the accomplished results of the process.The stability of keyhole behavior strictly depends on the complicated balance between the pressure of periodical recoil and the surrounding walls surface tension .The porosities occur when the keyhole collapses because there are trapped gas bubbles in the weld pool due to low depth of penetration.The stability of keyhole affects process parameters optimization. The optimization of the flow rate of the shielding gas for suppressing the vapor plume that improves the stability of process proven by Schneider et al [22]. The laser output parameters are controlled by changing geometry of bead and depth of penetration that is proven by Akman et al.[23] For specific heat inputs and changing regime of welding, the formation of underfill fault are researched by Squllace et al[24]. The pulsing laser welding causes to reduction of content of porosity that is proven by Gao et al. as observing the reheating and remelting action [25]. Casalino et al. shows that the effects of the parameters on the characteristics of bead while observing the elements with experimental data executed by artificial neural network (ANN)[26]. In this research optimizing parameters are provided by investigating of Ytterbium CW fiber laser welding of 2 mm thick Ti6Al4V plates. The surface of bottom is created under 2 mm from the top surface for position of focusing .while The preliminary bead on plate tests , optimizations of parameters of process is obtained.There are two types of appearance of fused zone such as V-shaped and X-shaped. These are changing according to the transmitting heat input .Also the quality of joint depends on the properties of mechanical and microstructures and morphology of weld. The usage of fiber laser provides that low defectiveness and improved weld quality for behavior of mechanical and bead aspect.
Stainless steel is prefered in the industry since it has a lot advantages. In the railway industry they are chosen since with them it is possible to produce; lightweight body structure, high anti-corrosion, safety features and good environmental performance. SUS301L is one of the most used material in the stainless steel vehicle structure on panels that are outside and unpainted. [38] Its thermal conductivity is low and it has large linear expansion coefficient, resistance spot welding (RSW) is the assembly technique for stainless steels. However there is a visible indentation on the surface after the process because of the punched power and thermal input of RSW electrode. This influence the appearance, air tightness, so a new methods are developed. Laser welding is one of them. Disk laser which is a solid-state laser, provides high quality beam and diode laser provide high degree of pumping efficiency. To get small HAZ that cools very rapidly with little distortion and also high depth to width ratio at fusion zone, YAG laser beam welding with continuous wave can be used. Laser welding technique is used in Japan for high-speed train bodies. Advanced body structure design trend requires overall load-bearing parts to have no frame, laminated sheet is used for both faces to get light weight structure. Laser welding technology allows to build this kind of structure. Moreover, if all the spot welds are replaced with laser welds, fatigue strength might increased by around 15%. Furthermore, strength and rigidty of the vehicle are improved and also weight reduction is achieved.[38] Applications of laser welding in the shipbuilding The pioneer for at first pure laser and then laser hybrid welding can be considered as shipbuilding industry because of manufacturing of large steel parts. Passenger ships are very suitable for these kind of applications since for deck structure steelwork is dominated and they are built with 5 to 10 mm steel plates. At 1995 German Meyer Werft is the pioneer for using sandwich panels in ship structures. Beginning from 1998, these panels are adapted for passenger ship decks. In 2001, there was an investment on Meyer Werft with new panel manufacturing line. The new manufacturing line consists of four high-power CO2 laser (12 kW) hybrid welding machines. That is because 20 m long plates, for the varying plate thicknesses, were not available and structural optimisation in plate thickness and materials used within one section. Producing plate strips which are up to 4m wide and 20m long is require butt welding situation. After butt welding station, strips are strengthened with stiffeners to form deck panels. In 2010, disc laser-based hybrid weldings are chosen for butt welding operations. In cruise ship, half of the total weld length is constituted by laser hybrid welds. Fincantieri is an Italian ship. It is installed with lasers since 1996. At deck structures 17 kw laser source butt welding stations are used. At 2008, there was an investment for automated panel line installation like in Meyer Werft. 10 kw fibre laser for hybrid welding is used for butt welding. Blohm-Voss GmbH builds corvettes, mega yachts and frigates. They use laser technology for frames, stiffeners and complete deck parts. These are produced by plates that ranging from 3 to 12 mm and for welding method T-joint is used.These welds are completed with two 12 kw CO2 lasers without additional wire. For edge preparation, nitrogen laser cutting is used. [39] STX Finland Cruise Oy, Turku yards build ferries and cruise ships. At December 2006, STX implemented laser hybrid welding.for manufacturing operations. They installed this new technology to old panel line. 6 kw fibre lasers are used for laser hybrid welds. Butt welding operations are done with laser hybrid welds. Odense Steel Shipyard in Denmark builds large commercial ships especially container ships. At 1997, laser welding and cutting are installed. The yard used 12 kw CO2 laser source for both operations. At 2000 August, CO2 laser/MAG hybrid welding was tried for the first time and these trials were followed by parts that are produced for different blocks with laser hybrid welding.[39] CONCLUSION Nowadays, with depletion of resources compatibility of environment become to play a fundamental role in industrial area.Therefore, CO2 -neutral production come into prominence. The laser applications provide to produce CO2 -neutral products and with their technological advance and developments of efficiency in laser source . Saving CO2 and huge amount of energy per annum that is supplied by means of changing lamp-pumped Nd:YAG laser with direct diode laser. Because in this way, higher efficiency of wall plug is obtained. This efficiency lead to lower wasting heat by this way laser cooling system become more smaller and efficient. Moreover, the laser welding has many properties for structural steel welding such as : high welding speed, low distortion and easy automation. There are imperfections in welding applications.These are pores and solidification flaws. Laser based welding provide to prevent these imperfections but for this, welding parameters and composition of steel have to be controlled. In addition to that, laser based welding is proper to automatized welding.In addition to these, the practicability of laser welding of low alloy high strength steel, aluminum alloy, austenitic stainless steel is that plays very important role in manufacturing of railway vehicles.
For example, in high-speed train bodies, magnetic Levitation train, light structures such as: overall loadberaing or laminated sheets are manufactured by laser welding, it also provides advantages in their design concepts. By using laser welding technolgy instead of spot welding, more higher fatigue strength is obtained. It causes to a decrease in weight. While the unpainted steel body surface welding in automotive industry , surface deformation occurs because of spo welding . In these days,in order to solve this problem, Laser welding is used in passenger cars. Hereby, high surface quality and strength of structure are gained. Currently, another problems observed in welding is that distortion of aluminium sheets particularly thin-walled aluminium. With improving technologies in laser ,these drawbacks are destructible in the future. To conclude, with development of laser welding technologies and because of properties of laser welding, many current welding applications are done with laser in many industries. And with advancing technologies, laser welding applications play further important role in these industries.
CO2 laser welding provides many advantages such as low distortion and low heat input and high productivity. This method is used for welding many parts of powertrains including transmission shafts, hubs and gears. Moreover, in manufacturing parts such as wheel arches, side beams, panels and doors of car body, the laser welding is used.With using fibre and disk lasers, More flexible and faster welding was achieved.[31] Aircraft industry Many advantages are provided with CO2 laser welding in aircraft industry[31] : Weight reduction high productivity improvement of corrosion resistance high cost performance Shipbuilding industry CO2 Laser Welding provides to manufacture of sandwich panels. Moreover, it has some advantages: significantly reduction in total man-hour consumption for additional straightening operations is monitored with Long straight butt and fillet welding lines of thick steel plates were installed by installing high power laser by this way distortion is reduced. high productivity in automation is provided with Improvement of mechanical accuracy. CO2 laser welding is prefered due to stability of the welding phenomena in this industries but lately, for flexibility of fibre delivery systems, fibre and disk lasers have been used. [31] Steel industry The CO2 laser welding is used for some applications such as [31]: welding of hot or cold rolled steel sheets in continuous coil welding lines. manufacturing stainless steel with small diameter welded pipes to increase productivity. Other applications For fabrications of some chemical plants such as the plant for petroleum refining, high power CO2 laser welding is preferred. Applications of disk laser welding The usage of disk laser welding is very wide range in laser technology as part of the e-mobility mega-trend, laser welding in sheet metal, laser metal deposition by powder injection.There are a lot of application in which this method is performed. For example: In mold mold making and manufacturing of tools, injection molds repairing is used,the disk laser plays very important role in reconditioning of valves, discs and seals in engines.Moreover for mechanical applications, reconditioning of cylinder and rolls are used. Coatings production on implants of orthopedic. Finally, nozzle guide vanes (NGVs),sealing elements in jet engines and repairing blades in gas turbine and refurbishing blades of compressor and turbine. Furthermore, for production of powertrain laser application is used. In addition that because of high potential of hybrid laser welding, different applications are observed in different industries such as : welding of panels in shipyard area, poles and truck axles and construction of train and rails, finned tubes, heat exchanger/boiler and pipelines, lastly in heavy industry(cranes, dredger, etc), hybrid laser welding also observed. Therefore, it provides high welding speed.[32] Applications of conduction laser welding Because of the problems in using keyhole mode in laser welding of aluminium alloys, conduction laser welding is used to overcome this problem.
Moreover, the usage of laser welding increases with new high power diode lasers .In this way, the low beam absorption, due to the wavelength of these lasers. in conduction laser welding is solved.Therefore, the usage of conduction laser welding increases in applications such as aesthetical welds, brazing, cladding, soldering and polymer welding. In order to weld plastics, a very controllable heat delivery to the workpiece and a very stable welding process are needed. Because of this conduction laser welding also used in plastic welding. In the nuclear industry for repair/maintenance applications, the underwater laser beam welding which is conduction mode of welding is used So the stability of the process, the control of the heat delivered to the workpiece and the quality of the welds obtained. [33] Applications of laser microwelding Joining metals with different mechanical and physical properties are very big problems for welding.Moreover, necessity of micro components for various industry sectors, usage of laser microwelding becomes widespread. Because the laser microwelding provides to improvement in overall weld quality, low cost and reliability by removing the human factors. [34] Laser joining process and their application Lightweight structures play important role in industries therefore, appropriate process for joining must be considering to stage of joining. Although combination of dissimilar metals are among the most challenging, most researches were done about joining of aluminium to steel and aluminium to titanium,especially, two combinations with significant relevance for the automotive industry (Al-Fe) and the aircraft industry (Al-Ti), respectively. Applications of laser welding of plastics For plastics joining applications , transmission laser welding is used [35]: Automotive fluid and pressure vessels and brake components Windows and signs Textiles and inflatable film products Electronic packages Biomedical devices including catheters and microfluidic chips Visual displays Food and medical packaging Application of twin laser beam The application of twin laser beams provides to overcome limitations in laser processing with single-beam laser irradiation. Because some processing parameter such as beam configuration, beam distance and wavelength combinations of two beams increase. For example, increase in laser absorptivity, the active convection of molten metal, the increase in gap tolerance, and the control of thermal stress with twin-beam irradiation. Moreover, hybrid welding technique is developed with combining a different heat source with a laser beam . Although these advantages new studies are required to develop new applications for twin-beam laser welding. [36] Applications of laser welding in industry Applications of laser welding in the automotive industry Light that comes from laser source focused onto the workpiece with the help of optical equipments for the laser welding. Related to energy density and impact time, workpieces melt and joined together. An industrial robot guides laser optic about to seam geometry in the case of classical laser welding. Laser welding with scanner optics fit for welding of steel parts. By using this method, with almost no delay, position of laser beam can be arranged according to position of the workpiece. However, remote laser welding operations are not available where filler wire is needed, since; filler wire can not be followed with the speed that laser is followed. To give more specific applications of laser welding at automotive industry let’s check following examples. Remote laser welding is used for Audi A4/Q5 doors joining processes. It has couple of benefits. Firstly, since; joinings are not visible to customers. Secondly, using the shortest flanges possible because of the remote laser welding. This is important since it provides the maximum viewing angle. Even for standard resistant spot welding minimum flange length is higher. Seams in the door application are done by overlap joints with 0.7mm on 0.6mm zinc-coated metal sheets. Length of each linear seam varies from 25mm to 40mm. Between 1-34 seams are performed in the flat position while between 35-45 are joined in perpendicular position. Gap between metal sheets is critical. Zinc coated metal sheets requires zero gap. Audi A8 has divided tailgate. The reason it can not be produced from single part is the high deep drawing around the badge hollow. With zero gap laser joint parts are attached. Laser welding with very high optical seam quality was chosen.[37] Applications of laser welding in the railway industry
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