| Duplex stainless steel is a kind of stainless steel with high strength and excellent corrosion resistance.It is widely used in marine,petroleum,chemical and power industries.Twin wire pulsed MIG welding technology is one of the most important methods to improve welding speed and production efficiency.However,defects such as incomplete penetration,incomplete fusion,hump bead and undercut are easy to occur in high-speed welding.Aiming at the problems,based on the traditional twin-wire pulse MIG welding,the twin-wire double-pulse MIG high-speed welding process and parameter optimization method are explored,and a new welding process of twin-wire double-pulse high-speed based on additional protective gas exerted on weld pool is proposed.The main achievements of this paper are as follows:(1)A self-tuning control method of current waveform genetic optimization fuzzy-PID parameters for twin-wire pulsed MIG welding is studied.The simulation and process tests show that the current waveform control is accurate and has strong anti-interference ability,which lays a solid foundation for current waveform control of twin-wire pulsed MIG welding and the stability of welding process.In this paper,the main circuit and control system circuit of twin-wire MIG welding power source are optimized by modularization method.Simulink simulation model of twin-wire MIG welding system is established and simulated.Through the comparison and analysis of the welding process test controlled by classical PID control and genetic optimization fuzzy PID parameter self-tuning,the performance of genetic optimization fuzzy PID parameter self-tuning control is better than that of classical PID control,which can produce strong interference suppression effect on high current output of high speed welding.Simulations and experiments show that the intelligent control method is easier to match process parameters and obtain satisfactory weld quality.(2)The quantitative evaluation method of welding stability and welding quality based on current sample entropy and current probability density distribution function is explored.On this basis,a comprehensive evaluation method of welding quality based on fuzzy logic reasoning is established to quantitatively evaluate the process stability and weld quality of twin-wire double-pulse MIG high-speed welding.The influences of welding speed,waveform modulation mode and low frequency frequency on the stability of twin-wire welding are analyzed by using the current sample entropy algorithm.Starting from the probability density distribution function,the current concentration K of the front and rear wires is selected as the quantitative index of the stability of twin-wire welding,and the effects of welding speed,waveform modulation mode and low frequency on the welding stability are studied.Two quantitative indicators of flow concentration were used to establish a quantitative evaluation system of twin-wire high-speed welding seam quality based on fuzzy logic.The experimental results show that the correct rate of the comprehensive evaluation results of the fuzzy logic is 85.7%.The evaluation results obtained from the fuzzy logic reasoning evaluation system are close to the evaluation results made by experts.(3)The effects of welding speed,modulation frequency and waveform modulation mode on the quality of duplex stainless steel twin-wire double pulse MIG high-speed welding seam were studied,and the effects of the number of strong and weak pulses and welding speed on the appearance,metallographic structure and mechanical properties of dissimilar stainless steel twin-wire double pulse MIG high-speed welding seam were explored.In the welding speed test of duplex stainless steel,with the increase of welding speed,the heat input decreases significantly,and the weld penetration decreases gradually,resulting in unfused defects.In the current waveform modulation method test,the stability of trapezoidal waveform modulated double-pulse welding is better than that of rectangular waveform modulated double-pulse welding and single-pulse welding,and the welding quality of the former is higher.In different low frequency welding tests,the probability density of voltage and current of 4Hz double pulse welding is more concentrated,the ratio of peak current density to base current density is larger,the welding process is more stable,the 4Hz double pulse welding seam is the best,the heat affected zone is the smallest,and the hardness of weld fusion zone is the largest.In the double pulse welding test of dissimilar stainless steel between 2205 and 316 L,the number of strong pulses,the number of weak pulses and the welding speed have a significant impact on the weld quality,followed by the number of weak pulses,and the number of strong pulses has the smallest impact.(4)A new technology of twin-wire double-pulse MIG high-speed welding with additional shielding gas is put forward.The effects of additional shielding gas and flow rate of additional shielding gas on the microstructure and mechanical properties of weld seam were studied.The results show that the method of additional shielding gas jet can obviously inhibit the defects of incomplete penetration,hump weld path and undercut in high-speed welding under appropriate gas flow rate,and can significantly improve the welding quality improve the appearance and mechanical properties of the weld.In the experiment of welding with or without additional shielding gas,the process of double wire MIG high speed welding with additional shielding gas is more stable and the weld width is more uniform,which can effectively improve or even eliminate the incomplete penetration,hump weld,undercut and other defects.After the introduction of additional shielding gas,the coarse dendrite in the weld structure is obviously reduced,the grain is obviously refined,and the heat affected zone of the weld is narrowed.Under the same welding current,by introducing additional protective gas the maximum tensile strength of the joint is increased by 19.7%,8.2% and 11.3% when the welding speed is 1.6m/min,1.8m/min and 2.0m/min,respectively.When the additional shielding gas flow rate is 8L/min~16L/min,with the increase of gas flow rate,the weld width increases gradually and the residual height decreases gradually,but when the gas flow rate is large,channeled welds with low middle and high sides will appear.The test shows that the jet impact force is moderate and the effect of improving the butt weld is the best when the additional shielding gas flow rate is 12L/min. |
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