Materials Science Forum Vols. 580-582

Abstract: In this study, research work on the effects of vibrational energy on the microstructure of welds and Charpy toughness is performed. The results show that vibration during welding exhibits positive effects on the microstructure constituent formation by reducing the amount and thickness of grain boundary ferrite and suppressing the formation of the Widmanstatten structure. And also due to the finer microstructure developed by the vibration, toughness value of the weld metal increases.

Abstract: Microstructure and mechanical properties of friction welded and vacuum brazed Ti/AISI 321 stainless steel have been evaluated with various welding conditions. Maximum tensile strength of friction welded joints was approximately 420 MPa with the conditions of 400 MPa of upset pressure (P2) and friction time (t1) within 2.0 s. Maximum tensile strength of brazed joints was acquired under the condition of 900 °C brazing temperature and 5 min. brazing time and showed approximately 275MPa which was about 80% of that of the Ti base metal. Friction welded Ti/AISI 321 joints showed the superior tensile strength than that of brazed Ti/AISI 321 due to thinner intermetallic compound layer.

Abstract: The waveform controlled short-circuit CO2 arc welding has been developed and applied in industries widely. To guarantee its process stability and weld quality in automatic applications further, the torch-height, the distance from torch to workpiece, which may be altered by the welding distortion and assembling errors of joints, is detected via measuring the wire electrode extension during the metaphase of short-circuit and then controlled. The acquired data is filtered by rule-based fuzzy algorithm and/or shift-average method. The experimental results, validated by slope and lap-joint welding, show that the detection and control system has excellent stability and dynamic response under different welding conditions, such as slope angle, wire feeding rate and welding speed, this will make the welding process more stability and the weld quality improved.

Abstract: The purpose of this study is to establish the proper control method of angular distortion of multi-pass STS 316LN weldment in the vacuum and cryostat vessel of the fusion reactor. To achieve it, the predictive equation of angular distortion in the multi-pass STS 316LN weldment with reference to welding heat input and effective bending rigidity of weldment was established using FEA and experiment. The bending restraint degree of each weldment in the the vacuum vessels of the fusion reactor was evaluated using FEA. Based on the prediction equation of distortion, both proper welding deposit sequence of double sided butt weldment of STS 316LN for cryostat vessel and proper welding sequence for the vacuum vessel were established and verified by the measured distortion of actual welded structure.

Abstract: Friction spot joining was used to make lap joints on strips of 5052 and 6111 aluminum alloys. The influence of joining parameters such as tool rotation speeds, plunge depths and dwell times on the weld joint properties were evaluated. A wide range of joining conditions could be applied to join Al alloys without defects in the weld except for certain welding conditions with an insufficient heat input. The microstructures and hardness variations in the welds were discussed. The microstructures of welds, corresponding to the pin hole, have dynamic-recrystallized grain similar to stir zone in FSW weld. In hardness distribution, minimum hardness region was located about 6-mm away from the weld center, corresponding to the shoulder radius of the tool. For each weld the results from tensile-shear tests are also presented. For sound joints without defects, tensile shear fractured load of weld joints was higher approximately 230% than acceptable criteria of tensile shear strength of electrical resistance spot-welded joints for aluminum (MIL-W-6858D).

Abstract: The prediction procedures of the residual stresses in welding process were presented by using finite element techniques. Owing to localized heating by the welding process and subsequent rapid cooling, the residual stresses can arise in the weld itself and in the base metals. The bilinear elastic-plastic material model based on Von Mises yield criterion was developed. The material nonlinearity of weldment and welding fluid was dealt with using an incremental technique. Inside each step, the Newton-Raphson iteration method was utilized. A fully coupled thermo-mechanical twodimensional analysis was performed with finite element method. The model applied in this study adopts the technique of element birth and death to simulate the weld filler variation with time in multi-pass welded joints. The effects of welding speed on residual stresses are discussed.

Abstract: The paper proposes a numerical method for analyzing the complex phenomena’s that appear in the case of keyholes welded pool geometry. Present model consist in a succession of analyses steps, needed to solve the interaction between the liquid/solid, liquid/protection gaze and liquid/MHD welded arc for arc welding, or electrons, or electromagnetic waves. The liquid/solid geometry result by dissipation of the welding power source in a matrix of many point sources. This process gives a first approximation of temperature fields and a good approximation of the digit 3D position, and information about the vaporization area.

Abstract: The mechanical properties of the friction stir welds of the oxygen free copper (OFC) and 60%Cu-40%Zn copper alloy(60/40 brass) were investigated. The defect-free welds were obtained in a relatively wide range of welding conditions; the tool rotation speed had rpm of 1000 to 2000 in the OFC and 1000 to 1500 in the 60/40 brass, with the welding speed of 500 to 2000 mm/min. The SZ hardness values of the OFC welds were almost the same or slightly lower than those of the base metal. However, the SZ hardness values of the 60/40 brass in all welding conditions were much higher than those of the base metal. The SZ hardness values of both metals increase with a decrease in heat input. The tensile properties of the all-SZ showed relative correspondence to the variation of the SZ hardness values.

Abstract: Wide use of robotic machines for welding has necessitated the development of optimization techniques to achieve complete automation. The objective of the present study is to develop multiple regression model for quantitatively estimating the severity of the short circuit in pulse gas metal arc welding (GMAW-P) of aluminum, based on experimental results. The model results were found to be in good agreement with the experimental data and yielded satisfactory results.

Abstract: The objective of the present paper is to examine the effects of process parameters, such as laser power, cutting speed of the laser and thickness of the workpiece, on characteristics of the cut section in the cutting of cold rolled steel sheets using a high-power Nd:YAG laser with a continuous wave (CW). From the results of the experiments, the influence of the process parameters on surface roughness and average striation angle has been quantitatively investigated. In addition, critical cutting speeds with a minimum surface roughness and a maximum average striation angle has been obtained. Finally, the optimum cutting conditions for each workpiece thickness have been estimated to improve both the quality of the cut section and the cutting efficiency.