A novel variable polarity welding power based on high-frequency pulse modulation

A new type of variable polarity welding power modulated with high-frequency pulse current is developed. Series of high-frequency pulse current is superimposed on direct-current-electrode-negative （DCEN）, which can improve the crystallization process in the weld bead as a result of the electromagnetic force generated by pulse current. Digital signal processor （DSP） is used to realize the closed-loop control of the first inverter, variable polarity output of the second inverter and high-frequency pulse current superposition.

Realizing precision pulse TIG welding with arc length control and visual image sensing based weld detection

Methods of arc length control and visual image based weld detection for precision pulse TIG welding were investigated. With a particular all hardware circuit, arc voltage during peak current stage is sampled and integrated to indicate arc length, deviation of arc length and adjusting parameters are calculated and output to drive a step motor directly. According to the features of welding image grabbed with CCD camera, a special algorithm was developed to detect the central line of weld fast and accurately. Then an application system were established, whose static arc length error is ±0.1 mm with 20 A average current and 1 mm given arc length, static detection precision of weld is 0.01 mm , processing time of each image is less than 120 ms . Precision pulse TIG welding of some given thin stainless steel components with complicated curved surface was successfully realized.

Numerical analysis for weld pool of pulsed TIG welding

A two-dimensional axisymmetric mathematical model of weld pool of pulsed TIG welding was established. Numerical simulation for weld pool of pulsed TIG welding was done using FLUENT software by selecting the appropriate boundary conditions and strongly coupled control equations. The distributions of temperature field and flow field of weld pool under the periodic change of welding current were obtained. According to the maximum temperature of upper and lower surface of workpiece and depth and width of weld pool, the distributions of temperature field and flow field under different pulsed frequencies and current duty cycles were obtained and periodic variation was analyzed under pulsed current. The analysis results show that with the increase of pulsed frequency, weld pool width increases slightly while depth decreases slightly, and with the increase of current duty cycle, the width and depth of weld pool both increase significantly, and the depth increases greatly.

Development of high frequency pulse power source using two powersfor TIG welding

A high frequency pulse power source for TIG welding is developed. The structure of two powers is adopted. The by pass circuit effectively eliminates the effect of the cable equivalent inductance. The maximum frequency of the output pulse current reaches to 16 kHz . The base current and the peak current can be regulated separately.

Simulation on Dynamic Characteristic of Negative Resistance Arc in Pulsed TIG Welding

A mathematical model is established on the basis of the physical characteristic of the negative resistance arc when a low current of 0—50 A is applied in pulsed TIG welding. The simulation model converted from the mathematical model is run in MATLAB environment, and the discussion is focused on the way the peak current ranging from 29 A to 50 A and the time constant of arc in the span of 0.003—0.006 s influence the simulating results and the dynamic characteristic. The simulating data are close to that of welding experiments and correspond to the theoretical conclusion.

Novel hybrid method: pulse CO_2 laser-TIG hybrid welding by coordinated control

In continuous wave CO2 laser-TlG hybrid welding process, the laser energy is not fully utilized because of the absorption and defocusing by plasma in the arc space. Therefore, the optimal welding result can only be achieved in a limited energy range. In order to improve the welding performance further, a novel hybrid welding method--pulse CO2 laser-TIG arc hybrid welding by coordinated control is proposed and investigated. The experimental results indicate that, compared with continuous wave CO2 laser-TIG hybrid welding, the absorption and defocusing of laser energy by plasma are decreased further, and at the same time, the availability ratio of laser and arc energy can be increased when a coordinated frequency is controlled. As a result, the weld appearance is also improved as well as the weld depth is deepened. Furthermore, the effect of frequency and phase of pulse laser and TIG arc on the arc images and welding characteristics is also studied. However, the novel hybrid method has great potentials in the application of industrials from views of techniques and economy.

Mechanism analysis of free formation of backing weld by the pulsed MAG-TIG double arc tandem welding

Because of the presence of lower-level automation and efficiency in the backing welding of medium–thick plates,pulse-metalactive-gas–metal-inert-gas(MAG–MIG)dual-arc welding was applied to backing welding of 24-mm-thick Q235-B plate and the process and mechanism of root welding with back formation were investigated.The heating position of the MAG-arc at the front of the molten pool could be adjusted by using the electromagnetic force between the MAG-arc and the MIG-arc,and part of the arc energy could work on the root face directly.By combining the arc-discharge behaviour and analysis of flow in the molten pool,the shear stress of a tungsten inert gas(TIG)arc to the molten pool could make the liquid metal flow backwards.Thus,the quality of the front and bottom liquid metal were reduced,which favored the balance and stability.Continuous and stable back formation with uniform penetration could be achieved by using the pulse MAG–TIG dual-arc welding technology.

Effect of Conventional and Pulsed TIG Welding on Microstructural and Mechanical Characteristics of AA 6082-T6 Repair Welds

Repair welding of AA 6082-T6 joints was carried out using ER 4043 filler through the TIG welding process with or without pulsed current.Microstructure and mechanical characteristics of the joints before and after repairing were investigated by examining macrostructure,microstructure,and distributions of porosity in the weld metal(WM),and by hardness,tensile,and bending tests.We observed that the welding current,phase transformations in heat-affected zone(HAZ)and porosity introduced in the WM during welding influence on its mechanical properties in sequence.The experimental results showed that the bead width and penetration as well as size of pores in the joints were mainly influenced by the welding currents.The sound joints were obtained at a welding current of 140 A with or without pulsed current when welding speed and gas flow rate were set at 20 cm·min-1 and 15 L·min-1,respectively.Among them,the decrease in mechanical properties of repair weld(RW)was directly related to the phase transformations in the over-ageing zone due to the double welding thermal cycles and elevated distribution of porosity in the WM.In addition,it was observed that the comparatively smaller grain size and lower porosity in WM of the RW produced by pulsed TIG welding gave a positive effect on its mechanical properties.

Modeling transient fluid flow and heat transfer phenothena in stationary pulsed current TIG weld pool

A mathematical model is presented to describe transient behavior of heat transfer and fluid flow in stationary pulsed current tungsten inert gas (PC-TIG) weld pool, which considers three kinds of driving, forces for weld pool convection, i,e. buoyancyforce, electromagnetic force and surface tension force. furthermore. the effect of vaporization heat flux at the free surface of weld pool and the temperature coefficient of surface tenston which is a function of temperatuer and composition are considered in the model In order to accelerate the convergence of iteration the AST(additive source term)method which concerns with the thermal energv boundary conditions is extended successfully to deal with the momentum boundary conditions by which the transient momentum equation and energy equation are mutually coupled. At the same time. ADI (Alternating direction implicit) method and DBC (double blocks correction) technque are employed to solve the finite difference equations. The results of numerical simulation demonstrate the transient behavior of PC-TIG weld pool, as well as the periodic variation of fluid flow and heat transfer with the periodic variation of welding current in stationary PC-TIG weld pool. The theoretical predictions based on this model are, shown to be in good accordance with the experimental measurements.

Comparison of Magnetic Pulse Welding with Other Welding Methods

The paper explains the comparison of magnetic pulse welding method which belongs to non-conventional machining methods with other conventional and non-conventional welding methods which include brazing, explosive welding, ultrasonic welding, tungsten and metal inert gas and roll bonding. Magnetic pulse welding differs completely in technology when compared with conventional welding processes because the process is done with high velocity and without heat or consumable materials. It is better than other methods because it＇s cold process and can be done without any heat affect zone. In addition, there is no need for rework and post welding cleaning and there is no scrap problem. Magnetic pulse welding is a green process used to design and build light structure with high strength to reduce the weight and the energy. Magnetic pulse welding reduces the risk of corrosion by limiting the metallic interaction to just the two metals welded; therefore, it replaces the brazing method. Also, it is better than the explosive welding method because there is no risk of handling the explosive material and there is no noise. The part assembly by magnetic pulse welding is stronger than the parts assembly by tungsten and metal inert gas welding and it is easy to achieve a good aesthetic with high speed. Therefore, using magnetic pulse welding technology will not affect the environment.

高频脉冲微TIG焊接电弧基值效应研究

为了探索微TIG焊接的焊接电流下限,研制了一种高频脉冲微TIG焊接电源,利用脉冲基值电弧电特性的改善提高焊接稳定性。通过电弧电流、电压波形,分析了电弧的电压滞后性,探讨了脉冲频率对脉冲电弧基值效应的影响,并进一步对零基值脉冲TIG进行了研究。结果表明,高频脉冲下的微电弧基值电压较稳态电弧大幅下降,更有利于维持微电弧的燃烧;在基值电流为0 A的条件下高频脉冲电弧也可维持燃烧,平均焊接电流可低至0.5 A,极限0基值时间与脉冲电流大小呈正相关。对于微细漆包线和端柱的微型工件连接,零基值脉冲微TIG焊获得了较好的焊接效果。

热丝TIG焊方法最新研究进展

综述了各类热丝TIG焊方法的特点及其技术与工艺难点,并着重阐述了近些年来研究较多的脉冲加热热丝TIG焊、窄间隙热丝TIG焊、超高速热丝TIG焊的研究进展。

基于视觉图像传感的精密脉冲TIG焊焊缝跟踪

针对某复杂曲面薄壁不锈钢工件精密脉冲TIG焊中的焊缝跟踪问题 ,本文研究了一种基于视觉传感的高精度、高实时性焊缝跟踪技术。根据脉冲TIG焊的工艺特点 ,该技术通过选择特定波长的滤光片及合理的曝光时刻 ,采用工业CCD摄像机获取可直接分辨出焊缝、熔池和钨极的清晰、放大的焊接区图像。采用VC语言设计的图像处理算法 ,可以快速准确地识别出焊缝中心线 ,提取钨极偏离焊缝中心线的方向和距离 ,驱动步进电机调节焊炬位置 ,实现高精度、高实时性的焊缝跟踪。试验结果表明 ,该技术的单幅图像处理周期小于 12 0ms,能实现焊炬运动方向与焊缝偏差角小于 3 0°的焊缝跟踪 ,满足了复杂曲面的薄壁不锈钢工件的精密焊接要求。

TC4钛合金超音频直流脉冲TIG焊

首先对超音频直流脉冲TIG焊的特点进行了介绍,重点分析了的峰值电流、脉冲频率等关键工艺参数对超音频直流脉冲TIG焊电弧轴向等离子流力的影响规律。采用频率不同的几组超音频直流脉冲TIG焊工艺及常规直流TIG焊工艺分别焊接了2.5mm厚的TC4钛合金。用X-射线探伤检测焊缝中的气孔缺陷,根据检测结果,分析了超音频直流脉冲TIG焊过程中,能够加速气泡逸出熔池的几种作用机制;对于无缺陷的接头,检测了接头的拉伸力学性能,观察了拉伸断口SEM照片。结果表明:在脉冲频率60kHz,80kHz时,超音频直流脉冲TIG焊工艺能使TC4钛合金焊缝中的气孔缺陷出现的几率减少;随着脉冲电流频率提高,焊接接头的断后延伸率得到了显著提高。

脉冲TIG焊熔宽动态过程模糊推理——神经网络控制方法

对脉冲ＴＩＧ焊工艺中焊接电流—正面熔宽动态过程提出了一种模糊神经网络控制方法，并研究了利用人工神经网络直接对过程建模的控制仿真，从而回避了经典方法对过程建模与控制的困难。将上述方法用于实际脉冲ＴＩＧ焊过程控制，结果表明模糊神经网络控制方案有效。

高频脉冲TIG焊的电弧控制及高频效应

本文通过研究脉冲焊电弧的电流、电压波形,发现电弧功率随频率增加而提高。由此提出自由电弧在脉冲电流作用下,其形态的动态过程属惯性系统的假设,并用20000幅/S的高速摄影进行了验证。通过对惯性系统电孤的可控性分析,发现自由电孤可由高频脉冲电流控制在非稳定状态上,此时电弧脉冲电压明显提高,这就是电弧的高频效应。本文还研究了影响高频效应的几个主要因素,着重分析了维弧电流的作用,提出高频时由于电弧的惯性,瞬间电流停止并不会导致电弧熄灭,因此得出高频焊不需要维弧电流的结论。

脉冲TIG焊接熔池流场与热场动态过程的数值模拟

对运动电弧作用下脉冲ＴＩＧ焊接熔池流场与热场动态变化过程建立了三维数学模型。同时，设计了一套适合该模型非稳态、非线性、多相区和强耦合特点的数值模拟算法。脉冲ＴＩＧ焊接工艺试验结果表明计算值与测试值基本吻合。

单片机控制IGBT逆变式脉冲TIG焊电源的研究

本文介绍了单片机控制的ＩＧＢＴ逆变式脉冲ＴＩＧ焊电源系统的硬件结构及其焊接时序的控制和规范参数的调节方法。该系统采用接触提升引弧方式，并具有不合理规范参数的自动识别功能。

基于标准温度法的脉冲TIG焊电弧温度场计算与分析

脉冲TIG焊由于其优越的特性而广泛应用于工业中,准确测量电弧温度对分析焊接过程有重要意义。论文基于光谱学理论计算了氩元素的粒子数密度与温度之间的关系曲线,计算了794.8nm氩原子谱线的发射系数与温度之间的关系曲线,利用高速摄影获得了794.8nm特征谱的电弧图像,根据Abel变换和标准温度法计算了脉冲TIG焊峰值时刻和基值时刻的电弧温度场分布。

薄板铝合金脉冲交流TIG焊工艺

采用双逆变脉冲交流TIG焊机对薄板铝合金的焊接工艺进行了研究 ,探讨了脉冲电流幅值、EP半波时间、脉冲电流频率对焊接工艺的影响。脉冲电流幅值和EP半波时间对铝合金表面氧化膜的清理有重要影响 ,在焊接薄板铝合金时应采用较低的脉冲频率。采用合适的焊接规范参数 ,容易实现焊缝成形的控制 ,并能获得较好的焊接质量。