当前位置: 首页>博士论文>资源详情
中厚板窄间隙P-GMAW电弧传感跟踪技术研究
中文摘要

中厚板窄间隙焊接已经被广泛用于油气管道、压力容器、锅炉、造船、桥梁等行业。由于往往采用增加焊丝干伸长的方式使焊丝在坡口内摆动或者旋转,焊丝的弯曲成为跟踪控制中不得不着重考虑的因素。因为电弧传感器具有抵抗焊丝弯曲和磁偏吹干扰等方面的优点,成为首选的焊缝跟踪传感器。但是窄间隙焊接电弧的稳定性较差,制约了电弧传感器在中厚板窄间隙焊接跟踪控制中应用。 论文以建立基于电弧传感的中厚板窄间隙P-GMAW跟踪控制系统为目标展开研究。首先建立了P-GMAW摆动焊炬电弧特征测试分析系统。应用该系统不仅能够完成摆动焊炬焊接实验,观察电弧形态,而且能够方便地提取和分析摆动过程中电压和电流信号的特征参数。在分析I/I模式P-GMAW电源特性的基础上,建立了摆动焊炬P-GMAW电弧传感的数学模型,获得了电弧电压与脉冲频率随焊枪高度的变化规律——在忽略焊丝长度变化对单位干伸长电阻影响的条件下,CTWD(Contact Tip to Work piece Distance,即焊丝到工件表面的距离)的变化量与电压的变化量成正比;当焊枪高度较大时,脉冲频率随CTWD大致按线性规律变化。 其次,对中厚板窄间隙P-GMAW的电弧特征开展了研究。(1)通过坡口角度实验,发现普通V形和T形坡口与窄间隙坡口对电弧信号的调制机制不同:坡口角度较大时,焊枪朝向坡口侧壁运动过程中电弧不断受到侧壁压缩而变短,进而引起电弧信号的变化;坡口角度很小时,焊丝几乎平行于坡口侧壁,电弧信号的变化由磁偏吹引起。(2)通过对窄间隙焊接过程中电压、电流及其特征参数的分析,发现焊枪靠近侧壁时基值电流、基值电压、峰值电流、峰值电压以及脉冲频率同时发生改变,这些特征参数在左右侧壁位置的差值均能在一定程度上反映焊缝偏差。(3)针对实验过程中出现的“跳壁”现象,分析了其发生的条件— —接近直立的坡口、脉冲焊的电流特征以及焊枪运动到距侧壁足够近的距离。指出“跳壁”是窄间隙脉冲焊的特有现象。(4)“跳壁”现象发生时,基值阶段电弧建立在焊丝端部与坡口侧壁之间,峰值阶段的电弧建立在焊丝端部与熔池表面之间。此时,电弧的基值信号反映的恰恰是焊丝到侧壁的距离,峰值信号则可以用来对焊炬高度进行跟踪;电弧“跳壁”会引起“挖掘”效应,造成焊枪朝向和远离侧壁运动过程中的电弧信号存在明显差异——焊枪远离侧壁运动过程中,电弧特征参数的变化率远大于焊枪朝向侧壁运动过程中的变化率。两侧壁位置“挖掘”效应强弱的不同可以从焊缝形貌的角度反映偏差。 考察从焊接电流和电压中提取出的各特征参数,发现以脉冲频率或脉冲周期内的平均电流作为传感特征参数具有较小的误差和较高的灵敏度。在分析“挖掘”效应对电弧传感的弱化作用的基础上,提出基于“挖掘”效应的偏差提取方法,并据此建立了焊缝跟踪控制规律。 最后,基于DSP2812和AD7606设计了信号采集与实时处理软硬件系统,与步进电机的控制系统实现实时通信,开发了跟踪控制程序。应用所建立的系统完成中厚板窄间隙焊缝跟踪实验。结果表明,应用“挖掘”效应来提取偏差是可行的。当坡口偏移角度为4°时,5°坡口的焊缝跟踪控制精度可达到±0.5㎜, 8°坡口的焊缝跟踪控制精度可达到±0.4㎜。 关键词:电弧传感,窄间隙,中厚板,P-GMAW

英文摘要

Narrow gap welding of medium thickness steel has been widely used in oil and gas pipelines, pressure vessels, boilers, shipbuilding, bridges and other industries. Because the thickness of the steel plate is often smaller regarding to the thick plate, lengthening the wire extension and driving it swing or rotating in the groove to ensure complete fusion of both the two walls is normally used. Arc sensor is the first choice because of wire bending and serious magnetic blow in narrow gap welding are taken into account. However, the narrow gap results in a poor stability in welding arc which restricts the application of the arc sensor in the narrow gap seam tracking of medium thickness plates. The aim of this paper is to establish an arc sensing based narrow gap P-GMAW tracking control system for medium and thick plates. First, an all-position welding platform was established, and a signal analysis software for the P-GMAW with swing torch was designed. Based on the analysis of the power supply characteristics of P--GMAW with I/I mode, the law of arc voltage and pulse frequency with the height of welding torch was deduced - neglecting the effect of wire extension on its unit resistance, the change of CTWD is proportional to the change in voltage; the pulse frequency linearly changes with the CTWD in case the wire extension is larger. Then, the arc characteristics were analyzed by high-speed photography and arc signals. (1)The effect mechanism of the groove angle on the arc signal was studied. For the normal V and T groove, the arc is continuously shortened by the side wall during the torch moving toward it, which result in the change of the arc signal. For the narrow groove, the wire is almost parallel to the side wall, the arc signal changing is caused mainly by the magnetic blow. (2)By analyzing the arc voltage and current and their characteristic parameters in narrow gap P-GMAW, it is found that the base current, the base voltage, the pulse voltage, the pulse voltage and the pulse frequency change when the welding gun approaches the side wall. The difference of these characteristic parameters in the left and right side wall can reflect the weld deviation to a certain extent. (3)Necessary conditions for "jumping sidewall" phenomenon occurrence, which was discovered in the process of experiment were analyzed and found that the acute groove angle, the pulse welding current and the distance small enough between the wire and side wall provide sufficient conditions for it, and it is a particular phenomenon in narrow gap P-GMAW welding. When the "jumping sidewall" occurs, the distance from the wire tip to the sidewall is reflected by the base signal, the height of the arc by the pulse signal, and an undercut happens which results in "dig effect". The weld deviation can also be reflected by the "dig effect". By investigating the characteristic parameters that can be used to reflect the weld deviation, it is found that the pulse frequency and the average current in a single pulse cycle has little error and high sensitivity, and they were selected as the characteristic parameter of the arc sensor. The weakening effect of the "dig effect" effect on arc sensing was analyzed, the "slope" method based on the "dig effect" puts forward to obtain the weld deviation, and the control law was established. Finally, the hardware and software system for signal sampling and processing is established, and real-time communication with the swing motor control system is realized. The tracking experiments were completed by the system established and found that the seam tracking accuracy reaches ±0.5㎜ when the groove is 5 degrees, and ±0.4㎜ when the groove is 8 degrees. Keywords: arc sensing; narrow gap welding; medium thickness steel; P-GMAW

作者相关
主题相关
看过该书的人还在看哪些书