Numerical and experimental study on nugget formation in resistance spot welding for three pieces of high strength steel sheets

A resistance spot welding for three pieces of high strength steel sheets was selected as a research subject and the nugget formation processes at the various welding conditions were investigated by both experimental measurement and FEM simulation. The FEM program developed by the authors considered the coupling of the electrical field, thermal field and mechanical field. The interface elements were used to model the transient contact states between two worksheets or between a worksheet and an electrode. The electrical resistance and thermal–mechanical properties of the interface elements change with the contact state, and can have different values from the worksheets and electrodes. The nugget sizes and its formation process predicted by FEM agreed very well with experimental results. The welding conditions (current, cycles and force) to produce sound nuggets for both two pieces and three pieces of high strength steel sheets were accurately estimated by the simulation.     

Sensitivity model for prediction of bead geometry in underwater wet flux cored arc welding

To investigate influence of welding parameters on weld bead geometry in underwater wet flux cored arc welding (FCAW), orthogonal experiments of underwater wet FCAW were conducted in the hyperbaric chamber at water depth from 0.2 m to 60 m and mathematical models were developed by multiple curvilinear regression method from the experimental data. Sensitivity analysis was then performed to predict the bead geometry and evaluate the influence of welding parameters. The results reveal that water depth has a greater influence on bead geometry than other welding parameters when welding at a water depth less than 10 m. At a water depth deeper than 10 m, a change in travel speed affects the bead geometry more strongly than other welding parameters.     

Effect of tool geometry and process condition on static strength of a magnesium friction stir lap linear weld

Friction stir lap linear welding is conducted on overlapped AZ31 magnesium plates with different welding tools. Welds are made mainly with the orientation such that the weld retreating side on the upper plate is to be placed under load. Welding tools consist of a concave shoulder and a pin having a cylindrical, or triangular, or pie shape. This work addresses the effects of tool geometry and process condition on lap shear strength of welds. The shape of the hook formed due to upward bending of the plate interface on the retreating side and the strength of friction stir processed material are quantitatively characterized. Compared to the cylindrical tool, the triangular tool effectively suppresses the hook on the retreating side due to enhanced horizontal material flow. This primarily leads to a 78% increase in optimized weld strength. A ‘pure’ shear surface present on the tool pin significantly reduces weld strength.     

基于神经网络的焊接故障诊断研究

针对焊接时容易产生气孔这个缺陷,引入了神经网络技术对气孔缺陷进行诊断,结果表明基于神经网络算法的焊接诊断稳定性好,诊断速度快,这说明该诊断技术具有很大的应用价值。     

Evaluation of high‐temperature ductility in weld metal. Study of reheat cracking in metal active‐gas welding with flux‐cored wire stainless steel weld metal (2nd Report)

The special features of the weldability of high-strength low-carbon microalloyed steels are investigated.     

Correct shielding gas selection in dual wire GMAW

K-type thermocouples are fabricated using a chromel wire and an alumel wire of 50 m by the non-contact discharge welding method. The welding is carried out at six different butt angles. The size of the hot junction tends to decrease with an increase in butt angle, when the butt angle is larger than 1.4 rad. The response rate is measured and it is almost proportional to the reciprocal of the size of the hot junction. It is shown that the size of the hot junction is an important factor for the response rate. Wire diameter is another important factor for temperature measurement of small objects. When temperature is measured at the same point by a thermocouple under the conditions that only the hot junction and its vicinity are heated, the output of electromotive force, i.e. indicated temperature, will depend on the wire diameter. As the metal wire is a good thermal conductor and the rate of heat transport is proportional to the area of the wire cross section, deviation from the true value increases with an increase in wire diameter. Our experiments showed that the indicated temperature decreased linearly with the wire diameter. Furthermore, we measured the discharge voltage and current at various setting currents and discharge gaps.     

某机组高压外缸开裂原因分析

采用残余应力测试、力学性能测试、断口分析和金相检验等方法分析了某机组ZG15Cr1Mo1V-B2钢高压外缸在泵水时开裂的原因。结果表明:开裂始于高压外缸内表面的补焊区,该区为缩松缺陷密集区,材料塑性指标不符合技术条件要求,导致缺陷处的承载能力下降,应力集中加剧;另高压外缸补焊区的残余应力较大,硬度与基体之间的差异也较大;可见,汽缸在补焊过程中未能将铸造缺陷彻底清除干净,焊接质量不高和焊后去应力处理不充分是造成该高压外缸在泵水时开裂的主要原因。     

钢结构制作过程的质量分析与控制

通过介绍钢结构的制作主要工序,对钢结构制作过程中容易产生的质量问题进行简单的归纳分析与控制。     

Examples of metal and resin processing using high power diode lasers

In this work, the pitting corrosion resistance of welding duplex stainless steel 2205 was studied. Joints were made using the GMAW process with different fillers: duplex ER 2209 and two austenitic fillers (ER 316LSi and ER 308LSi). The microstructure obtained with the duplex ER 2209 filler is similar to the duplex 2205 base material, but the joints produced with the austenitic fillers cause a decrease of the α/γ phase ratio. In order to evaluate the influence of the filler on the weld, the pitting corrosion resistance was determined by means of an electrochemical critical pitting temperature test, and the mechanical properties by the hardness test. The phase imbalance produced for the different fillers causes variation of the pitting corrosion resistance and the mechanical properties. The variation in the mechanical properties of the material was also studied by means of hardness tests.