New Technology Of Double-Sided Double Arc Welding And Robot Automatic Welding For Large Thick Plate Of High Strength Steel

Large thick plate structures of high strength steel are widly used in shipbuilding, high pressure vessel and heavy-duty machinery and so on. At present, in our country, these thick plate structures adopt manual and semi-automatic arc welding. This conventional method is very backward, low productivity, low percent of pass of product, high labour force and so on. It is very urgent to find a new high efficiency welding mothod, and to realize robot automatic welding. So a new high-efficiency method for large thick plates of high-strength steel-double-sided double arc welding(DASW) is provided in this paper. Backing run adopts double-sided pulse gas tungsten arc welding (GTAW), and other passes adopt double-sided gas metal arc welding (GMAW). Its procedure is no back chipping and high productivity. Automatic welding technology of double robots is furtherly studied on the basis of the new DSAW. Moreover, key technologies of double robots coordination and multipass welding path layout are systematically investigated. Firstly, the new DSAW for large thick plate of high strength steel is experimentally studied. The results of temperature field, stress field and structure property of DSAW show that the thermal cycles of DSAW present double peaks.Fore arc provides rear pass with preheat action. Rear arc provides fore pass with postheat action. This thermal character between two arcs of DSAW lowers the cooling speed. So welding seam microstructure is improved and quench hardening tendency is reduced. At the same time, residual stress and cold crack tendency of DSAW are lower than those of CW (Conventional Welding) also. The experimental results of mechanical property show that the new DSAW for large thick plate of high strength steel is feasible. The new method simplfies the welding procedure, raises welding productivity, improves welding quality and is fit to robot automatic welding.Numerical simulation of DSAW dynamic process is analyzed in order to know the thermophysical character of DSAW and optimize the technology. For large thick plate structure of multipass weaving welding, huge element number, huge increment number, multiple heat sources, weaving welding and so on are difficult problems in the numerical simulation process. Three dimensional simulation of DSAW is realized by using computer parallel processing technology, multiple jobs design and heat model of series and band and so on. Calculated results show that the residual stresses distributions of two methods are similar. The transverse stresses of DSAW are 100MPa lower than those of CW. The longitudinal stresses of DSAW are 50MPa lower than those of CW. The angular distortion of DSAW is lower than this one-fourth of CW. On the basis of the evolution of the interpass stress and angular distortion, the back pass of DSAW is the key in multipass welding process. Consequently, effects of preheat temperature on the temperature field of the back pass of DSAW are studied. The effective results show that the critical restraint stress of no preheating double GTAW is lower than single GTAW under the preheat temperature 100℃, which illustrates that the lower preheat temperature, and even no preheating can be adopted in the new DSAW. The effects of arc distance and welding parameters on stress distortion fields are furtherly investigated. The effective mechanic of arc distance on the angular distortion is developed. To select a proper arc distance and to adjust fore and rear arc power can obtain lower stress and angular distortion.Secondly, automatic welding technique of double robots is furtherly investigated in order to realize robot automatic welding of DSAW for large thick plates on the basis of rich researches to DSAW. OPC Server and Motocom32 are adopted to realize the communication between Kuka robot and Motoman robot. Master-slave coordinated algorithm based on user coordination is developed. Master-slave coordinated motion of double robots is realized. Furthermore, the hardware and software of dispersed coordinate control are designed. Asynchronous and synchronous motions of double robots are achieved.According to on-line teach slowly and difficutly of multipass weaving welding, off-line teach module based on graph is developed. A self-define mathematic model of path layout is deduced. Users can design layer number, pass number and welding parameter of multipass welding according to welding technology. Path parameters such as position, attitude, weaving amplitude of weld torch and so on can be generated automatically. So the off-line teach programs of robot for multipass welding are obtained quickly and accurately, which will raise the programmable efficiency of robot for multipass welding of large thick plate.Finally, the verified experiment of double robots multipass welding has been maded. Robots automatic welding of multipass weaving welding of DSAW is realized through adopting decentralization coordinated controlling model and using off-line teaching programs of multipass weaving welding on the aid of on-line cut-away function. Experimental results show that robot automatic welding of DSAW can raise the productivity, improve welding quality and reduce labor force and so on. It has special significance for robot auomatic and high efficiency welding for large thick plates of high strength steel, and for manufacturing modernization of shipbuilding, high pressure vessel and heavy-duty machinery and so on in our country.