铝合金分体等离子弧穿孔焊接全位置熔池稳定性控制

A twin-body plasma arc welding which is an innovative keyhole-mode variable-polarity plasma arc (VPPA) welding method is proposed to address the challenges in full position welding of large shell aluminum alloy structures. Specifically, the plasma arc is split by an added assist electrode and our recent finding on the separability of electron flow from its ionized arc plasma spirited this invention. The arc distribution is changed becoming controllable and the force center is deviated from the heat flux center. Desirable free controls can thus be provided to adjust the positions and distributions of the heat and force fluxes which case a special temperature field in relation to the weld puddle in order to better control its fluid flow. The proposed research will model and analyze its stability at arbitrary position and obtain an objective function to solve the difficulties in determining the distribution of the constrained arc and mathematically formulating the puddle stability problem. The position of the guide electrode will be adjusted together with the force and heat pulses to provide separate controls for the force and heat fluxes applied on the pool. The position and rate of the mass transfer will be adjusted to control the initial speed and direction of the fluid flow such that the heat and force provided by the split arc suits for the need to control the stability. The temperature gradient will be mathematically correlated to the temperature-width lag, that is, the vector from the center where the weld pool is measured widest to the temperature field center. A confirmed correlation will allow the temperature field be used as a critical measurement to facilitate an accurate feed-forward control on the stability of the keyhole weld puddle and prevent the loss of the stability. The new welding technique might achieve the aluminum alloy all position welding of VPPA and precisely control its shape and property.

针对铝合金大型壳体结构现场装配焊接的全位置焊缝,本课题从电弧分离现象出发，提出分体式变极性等离子弧穿孔焊接工艺，采用导引电极分离等离子弧，使电弧热中心和力中心发生偏离，实现对熔池热、力输入大小和相对位置的分别可控及不均衡温度场加载，更加精确的控制穿孔熔池熔体流动；针对任意位置稳定状态的穿孔熔池进行建模分析，得到目标函数，解决拘束电弧空间和物理区域分布、穿孔熔池稳定状态描述等难点问题；通过对导引电极空间位置进行调整、力脉冲和热脉冲协调配合，实现对穿孔熔池的力脉冲输入和热脉冲输入的分别控制；通过调控传质的位置和速度对熔池流体初始流动速度和方向的控制，实现分体电弧和穿孔熔池的热力匹配；建立温度及温度梯度与温宽偏离度的对应关系，以温度梯度作为控制系统的前馈信号，突破任意位置的穿孔熔池稳定性控制、熔池失稳预判和主动调节等关键技术，实现全位置铝合金变极性等离子弧穿孔焊接及对焊缝的精确控形控性。

自2014年项目启动以来，围绕“分体等离子弧热力传输机制及工艺特性”开展研究，解决的关键问题和创新性研究成果概述如下：电弧的电特性是其力热行为的本源，针对电弧这一载流等离子的特殊性，自主研制了“旋转式有源探针测试系统”，揭示了等离子弧电特性分布规律并发现了阴极效应；分体等离子弧的突出优势是可实现能量分配，分别以工件端和丝材端为研究基点，采用定量测量与定性表征相结合的方式，标定了等离子弧能量分布，建立了能量分布解析模型，研究了各工艺参数对分体等离子弧能量分配的影响规律，探明了分体等离子弧的传热机制，建立了分体等离子弧传热模型；以熔滴飞行试验为基础，结合熔滴不同阶段的受力状态，研究了各工艺参数对熔滴过渡行为及运动行为的影响，探明了分体等离子弧中熔滴过渡机制；综合上述的理论与试验研究结果，分体等离子弧可实现焊接制造过程中传热、传质、传力的灵活设定，使其能满足不同焊接位置对热源热质力传输的不同需求，并以此热源完成了多位置焊接制造工艺的研究工作，同时也利用该热源开展了金属增材制造初步研究。总结研究结果，已发表论文17篇，其中国际期刊论文（SCI）7篇、EI论文3篇、国内核心期刊5篇、国际会议论文3篇。申请国家发明专利8项，其中授权4项。获得省部级及以上奖励3项，其中国家级奖励1项。在课题研究过程中培养研究生14人，其中博士生3人；博士后2人；获得职称晋升1人；评为“长江学者特聘教授”1人。