Study On New Low Energy Input Welding System And Process Control

With the development of automobile industry, the sheet material used in automobile is thinner. So the welding of thin plate need reducing heat input. According to the welding process required by thin plate used in automobile, a new low energy input welding, named NLEI welding was put forward. The following are the principles. First, the moving curve of the welding wire is preset to make the wire moved forward and back periodicaly. The process of welding doesn't need on-line adjustment, and the power supply is made to provide homologous waveforms of the current and voltage correspond with the movement of the welding wire. NLEI welding can implement steady push-pull short-circuit transfer and meet the demand of reducing welding energy input.According to NLEI welding, author has designed a NLEI arc welding system based on push-pull short-circuit transfer. The system consists of a welding power supply and a wire feeding system, and implements the control of the welding process by software. The control center of the welding process is based on digital signals processor TMS320F2812, which is a high speed and precision DSP with abundance of I/O ports. Hardware circuit is simplified by using software to control complicated welding process. Wire feeding system is based on AC servo-actuator and its control system, the push-pull moving curve of the wire can be programmed smartly according to the actual needs. The connecting of welding power supply and wire feeding system by interface circuit ensures the communication and coordination in the welding process.The waveform control project is designed, including the control of wire feeding and current waveform. By corresponding with current waveform and the wire movement in the actual welding process, the weld is achieved. The experiment proves that, the cooperation is good and the welding process is stable and reliable.A fuzzy control project used to adjust the arc length is specially designed taking the change and the change rate of the average voltage as the input, and the correction value of the pulse current during arc period as the output. In welding process, the arc length is stable with the help of the fuzzy control system.NLEI push-and-pull short-circuit transfer process is analyzed. In traditional short-circuit transfer process, the drops are transferred by electromagnetism force under the big short-circuit current. Compared with that, NLEI push-pull short-circuit transfer can reduce energy input, because it depends on pull of the welding wire to snap the drop under the small short-circuit current.The parameter matching of arcing pulse peak current (Iap ) and the evening short-circuit current(Ih) is very important. The range of parameter matching is gained by experiments. In this range, the coordinate control of welding parameter and welding wire movement can come true and the steady welding process can be gained. The energy distribute regularity in NLEI welding push-pull short-circuit transfer is discovered by calculating and measuring the energy input in the welding pool. The evening short-circuit energy which is the important ingredient of melted welding wire energy has important effect in melted welding wire. But it has little effect on heating welding pool. Because of the arcing heat, arcing pulse peak energy is the mainly energy source in heating welding pool, and it has important effect on heating welding wire too.According to the rules, NELI welding has two ways to reduce the energy input in welding process. The first is the pulling of the welding wire to snap the drop under the small short-circuit current. The second is using lower Iap and higher Ih .Aim to application of aluminum alloy and galvanized steel for automobile industry, the dissimilar joint between galvanized steel sheet and aluminum alloy during NLEI welding has been analyzed. It is proved that dissimilar metal overlap joint with good property can be gained by using NLEI welding.By means of microstructure and mechanical properties analysis of the dissimilar joints, the parameters of NLEI welding process were optimized. When welding speed is increased, the intermetallic layer between the weld metal and galvanized steel is decreased. When heat input is increased, the thickness of interface layer increases.When wire feeding speed 2.16m/min, welding speed 0.4-0.5m/min, welding torch in the middle, continuous, uniform and best shape joint was formed.By the analysis of the effect of different thickness zinc layer on the joint, zinc element effectively promotes molten aluminum wetting the steel sheet, which is good to dissimilar joints between aluminum alloy and galvanized steel when the zinc layer is thick enough.