Numerical Simulation Of Temperature And Stress And Strain Fields In Laser Multilaye Welding Of Mid-Thick Plate

Ultra-narrow gap single-pass and multi-player welding of mid-plate with laser can effectly improve welding productivity, reduce consumables and welding deformation. It is difficult to obtain the impact of mode of the laser heat source to sidewall fusion of the weld, weld cooling rate and the stress-strain conditions in multi-layer welding process with experimental method. Based on the finite element software MSC.Marc, transient temperature field and stress and strain fields of wire filling laser multilayer welding of thick plate was calculated and analyzed in this paper.First, according to the heat transfer characteristics of wire filling laser welding, heat source model of the double ellipsoid and Gaussian cylinder was determined. The impact of convection and radiation to heat transfer was considered, Material properties and particularly enthalpy were introduced as temperature-dependent functions, and the process of pass filling dynamical welding was realized by using"Element Birth and Death", in the establishment of wire filling laser multilayer welding finite element model.Temperature field of the process of welding was calculated with the transient thermal analysis of functional modules of Marc. Predicted results were in good accordance with the experimental data through comparing of the pool shape and thermal cycling curves of feature points. Based on the original model, the temperature filed of the situation of interlayer heat insulation and hot wire were calculated. It was shown that interlayer heat insulation could effectively reduce the cooling rate of the weld and heat affected zone, but made less advantage of the pool size of the weld cross-section; hot wire welding could effectively increase the pool size, and also to a certain extent, reduce the weld and heat affected zone of the cooling rate.The stress and strain fields of three case of cold wire, interlayer heat insulation and hot wire were calculated with the transient thermal-mechanical function module of Marc. The results showed that, at the end of wire filling laser multilayer welding of thick plate, a "ribbon" stress concentration existed within the weld, a biaxial stress state lied in the middle of the weld, and the impact of longitudinal stress was greater than that of transversal stress; interlayer heat insulation can reduce the residual stress of the weld, ease the "ribbon" stress concentration of joint internal, and recede the groove contraction trend; With the case of hot wire technique the "ribbon" of stress concentration could be effectively alleviated, and to a certain extent, the longitudinal stress were reduced, however, the transverse stress and groove contraction trend increased overall.In addition, the special thermal cycling and stress changes of laser multi-layer welding were analyzed in this paper. The result indicated that the weld center under the laser heat source experienced instantaneous heating and cooling, the effect of preheat of former layer to high-temperature thermal cycling was very small, the cooling rate decreased in the second thermal cycle; heat-affected zone was narrow and the peak temperature and cooling rate decreased significantly between weld and heat-affected zone. The size of the residual stress depended on the final cooling stage.