Materials Science Forum Vols. 575-578

Abstract: Gas shield Tungsten Arc Welding (GTAW) is an important process method in material processing. Welding quality is vital for the product quality. It is an important way to improve the quality of product by raising the personal capability and handling technique of the welder. In this investigation, because of the deficiency in classic welding training scheme, some new technology were introduced into classic welding training field to improve the efficiency of welding training and reduce training cost. A computer simulation system that can be used to train primary welders was developed combined with three-dimensional stereoscopic vision and API interface of OpenGL, virtual reality is the kernel technology. In this system, welders were trained not in the real operating environment but in the virtual environment where has experience personally effect that simulated by computer. There is unnecessary with welding material and welding energy in virtual environment simulated by computer. It has highly automatic and intelligent and lower required to welding teachers. It is healthy to welder because that intensive arc and harmful dust are disappeared in virtual environment. It is a lower cost and high efficiency method by use of virtual training system to training new welder.

Abstract: Arc brazing technology for joining has been recently developed. Because of its advantages, it has been used more and more frequently in the automobile industry, and this technology is widely used in practical joining applications. Many welding researchers have paid more and more attentions in this field. Based on the experimental analysis of CuSi3 filler metal spreading, wetting behavior on galvanized steel sheet and its interfacial microstructure in tungsten inert gas (TIG) arc brazing process, the governing equations and boundary conditions of filler metal droplets under the actions of gravitational force, surface tension and arc pressure force is conducted, then they have been transformed into finite volume equations, The flow behavior at different arcing time in filler metal droplet was calculated by PHOENICS code using SIMPLEST algorithm. It can be concluded that the flow adjacent to the surface controls the final droplet profile, and the fluid flow does great contribution to the whisker-like intermetallic compound fragmentation behavior due to its stirring force at the interface. The simulation is useful to interpret the free surface evolving behavior and the final profile of filler metal droplet in arc brazing, it also provide a new idea about the interface growth behavior study and offer a practical guide in production.

Abstract: Welding quality control is critical for welding manufacturing. However, the factors that affect welding quality exist in the whole welding process. Whole process welding quality control is a technology control process that can control the welding quality from choice of the welding material, stability of the welding process and quality assurance after welding. In this paper, a quality measure and control system is developed. The system is consisted of three modules: Technology property evaluation and welding material choice module is based on Analysator Hannover. This module can evaluate three type of welding material: electrode, solid welding wire and flux-cored wire. The welding process stability evaluation module can collect electrical and light spectral signal for disturbance factors diagnosis during the welding. The metallurgical structure and property forecasting module call the CCT diagram data base for predicting he metallurgical structure and mechanical property of the weld affected zone and weld metal. For stainless steel, a predicting method based on Schaeffer is also provided in this module.

Abstract: Based on introducing Laser-induced Chemical Liquid Deposition (LCLD) technology, this paper gave a new type of RP system graph based on the technology, and it has introduced the work process of this system on detail. The process of LCLD is controlled by thermal transfer if the heights of liquid and metallic material are changeless. Modeling thermodynamics of the part of facular laser beam of the process of LCLD, calculating and emulating by engineering analytical software, these researches can lead to the conclusion that the highest temperature of plating liquid can be found if the diameter of the facular laser beam is unchangeable. The relation between temperature and power of laser is linear on the whole. The locomotory speed of the laser beam does little influence on temperature of plating liquid; the thermal area of plating liquid influenced by laser is very small; the temperature in the thermal area is asymmetrical. The width of metal line of the deposition can be controlled at a certain extent by controlling the initial temperature of plating liquid and power of laser.

Abstract: Considering the specialty of the welding with weaving during the manufacturing process of the thick plate welding structure, a coordinate transformation method is put forward to simulate this process. The results indicate that the arc weaving process leads to the increasing temperature gradient in the regions near the weld bead, which also raises the peak values of transverse residual stresses. Combining the characteristic of the welding with weaving and the conversation of energy law, simplified banding heat source models are developed.

Abstract: Self refining grain behavior of X80 pipeline steel in the heat affected zone was studied systematically by physical simulation method. The sizes and distribution of the inclusions which promote intra-granular ferrite nucleation were measured using the automatic image analyzer, and the figures of the intra-granular ferrite which has self refining grain behavior were observed using transmission electron microscopes with energy dispersive X-ray spectroscopy, the fracture toughness values of the coarse grain zone in the HAZ were also measured. The results show that the welding thermal cycle has nearly no effect on the sizes and distribution of the inclusions in the HAZ. The reasons of self-refining grain in the HAZ are that the small non-metallic inclusions such as MnO、 TiO、MnS、CuS and （Mn，Cu）S in X80 pipeline steel ，which can induce the nucleation of intra-granular ferrite in the welding process, and sympathetic nucleation of intra-granular ferrite makes the coarse grains refined in the HAZ. First intra-granular ferrite has large boundary energy and high density dislocation, which induce the sympathetic nucleation of intra-granular ferrite.

Abstract: By the finite element analysis software ABAQUS and the function of coupling process between heat and stress, the welding residual stress of Cr5Mo and 20 steel joint was analyzed. In addition the heat treatment of dissimilar steel welded joint was simulated. The residual stress distributions of dissimilar steel welding and heat treatment after welding were obtained. The comparison of welding residual stress between the homogenous steel and dissimilar steel was carried out. The results indicate that the welding residual stress of the same steel is lower than that of dissimilar steel welded joint obviously. Because of the difference of thermal expansion coefficient for base metal and welding microstructure, the relatively higher residual stress is produced due to the bigger thermal expansion coefficient of base metal. The highest annular residual stress is in welding line root of internal wall, while the highest axial residual stress is in welding line surface of outer wall. The welding residual stress of dissimilar welded joint is reduced obviously after heat treatment. The research results provide the possibility for optimizing the welding procedure and improving the reliability of dissimilar steel welding joint.

Abstract: Electrical contact resistance is an important parameter in resistance welding. In this article, a Gleeble 3500 thermal-mechanical testing machine was employed to measure the contact resistance. The machine is equipped with a special electrical resistance measuring system. The contact resistance is experimentally investigated for welding low carbon steel to themselves. A detailed work was carried out to investigate the influence of pressure, temperature on the contact resistance of low carbon steel. The experimental results show that the contact resistance decreases when pressure or temperature increases.

Abstract: In the case of welding of T-joints in a special structure, the joining is realized through a total penetration of deck plates. For the deck plate’s thickness over 6 mm, high power MAG welding process should be applied. To help experimental optimizing of this welding technology, a 3D quasi-stationary numerical model was established to predict the penetration and weld form of the high power MAG welding on a thick plate. In the analysis a new volumetric heat source model was put forward which considers the heat directly from the arc und that from transferred droplets separately. Because the weld pool surface under the arc was strongly pressed, the droplet heat source in the model was located under the workpiece surface. The size of the droplet heat source model was determined on the base of physical principles and available experimental data. Using a commercial finite element software the weld form inclusive penetration under different welding parameters was then simulated. Through comparison with the experimental results the presented FE-model was verified.

Abstract: The research work presents a computational methodology based on three-dimensional finite element model to simulate the gas tungsten arc welding (GTAW) of thin-walled cylinders. The aim was to study the effects of two basic welding parameters (welding speed and welding current) on weld induced residual stresses. The complex phenomenon of arc welding was numerically solved by sequentially coupled transient, non-linear thermo-mechanical analysis. The accuracy of the numerical model was validated through experiments for temperature distribution and residual stresses. The results reveals that the present simulation strategy can be used as a proper tool to get the optimized welding process parameters and minimize the in service failures of thinwalled structures due to residual stresses.