Study On High-power Fiber Laser Welding And Weld Formation Prediction Of Middle Thick 304 Stainless Steel Plates

High power fiber laser welding is a fast developing and high efficiency jointing method of middle thick plates.It has wide prospects in heavy sections especially nuclear power equipment because of its high power density,good flexibility and wide applicability.Further,self-fusion welding is the most efficiency type of laser welding.Systematic studies on self-fusion high power fiber laser welding which provide guidance for project application are limited because of the lack of experience data.Moreover,analytical mathematical models for self-fusion high power fiber laser welding are needed to make the prediction easier and more practical for project application.In this paper,a systematic study on weld beam formation prediction and mechanical property is proceed by the analysis of weld beam formation and hardness data gained by the experience designed by the univariate and uniform methods.In this paper,a 15 kW high power fiber laser weld equipment and 304 austenite stainless steel which is common used in nuclear power equipment manufacture are used as the objects of the study.A series experience designed by univariate method are first proceed to find the relationship and prove the linear dependence between weld bead formation and laser power,travel speed,heat input respectively.Therefore the structure of a standard regression equation are designed accordingly.In addition,uniform designed experiences are taken in three conditions of most common laser welding application of middle thick plate laser welding-flat position without groove,horizontal position without groove and horizontal position with groove.The analysis of univariate experiment results proved the linear correlations between weld beam depth,width and laser power,travel speed,heat input.As the result,the structure of regression equations of uniform designed experiment are achieved.The relationship between weld beam depth,width,hardness and laser power,travel speed,heat input are simulated by visual and regression methods.Regression models of weld beam depth and width are achieved according to the analysis result.Regression models of depth and width are verified by comprehensive experience under laser power of 6kW and travel speed of 50mm/s separately,and the validity of them are proved as the measured values of verifying experience consistent well with the calculated ones from the regression equations.The influence of laser welding parameters on weld formation is theoretically summarized by further analysis of these regression equations,the result shows that: weld penetration depth and width are proportional to laser power and heat input,inverse proportional to travel speed,and the changing rates are much faster under low travel speeds;In general,penetration depth of welds in flat position are deeper than those in horizontal position,but penetration depth of horizontal position increases faster under low travel speeds and become deeper than that of horizontal position under extremely low travel speed eventually;Penetrations depth of welds with groove are deeper than those without groove under high travel speeds,but the weld width will over increased under low travel speeds,and results the decrease of penetration depth.