【作者】 杨帅；

【导师】 殷树言； 刘嘉；

【作者基本信息】 北京工业大学 ， 机械电子工程， 2009， 博士

【摘要】 现代制造业的发展对产品的最终质量和加工过程都提出了更高的要求,当前汽车、摩托车、集装箱、家电等行业轻量化产品的推广应用对高质量薄板焊接技术的需求日渐增加。由于薄板对热量的敏感性强,焊接过程中在降低热量输入的同时还必须保证能量分布均匀一致。针对薄板焊接的这一特点,提出了一种基于推拉送丝方式的低飞溅、低能量、过程精密控制的推拉丝短路过渡CO2焊接法。其基本原理是:通过焊丝回抽时的机械力拉断液桥强制熔滴过渡,精确控制短路后期电流利用电阻热调节能量在焊丝与母材间的分配比例,一方面降低了焊接能量,减小了焊接飞溅;另一方面使熔滴过渡变得均匀而有规律,整个过程中能量分布可通过焊接参数的匹配实现精确控制。基于以上思路,设计了以数字化焊接电源为平台、采用高性能交流伺服推拉送丝机构为核心的推拉丝短路过渡CO2焊焊接系统,并通过软件控制的方式实现了上述低飞溅、低能量、过程精密控制的焊接方法。数字化焊接电源以运算速度快、精度高、数据处理能力强的数字信号处理器(TMS320F2812)结合逻辑处理功能强大的CPLD(EPM7128STC100)为控制核心,以软件编程的方式实现了对复杂焊接过程的控制。推拉送丝部分采用高性能的运动控制卡(PMAC2 PC-104)对转动惯量小、响应速度快的交流伺服电机进行控制实现了焊丝高频率送进-回抽运动,同时采用缓冲器为桥梁将推拉丝部分和等速送丝部分有机的结合为一体,减小焊丝运动阻力,增加了送丝距离。通过接口电路实现了焊接电源与送丝系统的连接,保证了两者可靠的协同工作。结合推拉丝短路过渡CO2焊的特点设计了焊丝的运动曲线和电流、电压波形控制方案,在短路期间采用电流控制而燃弧期间采用电压控制,有效保证了弧长的自调节能力,提出了运动参数及焊接参数的选取原则,通过电流、电压波形控制方案与焊丝运动相配合实现了稳定可靠的推拉丝短路过渡CO2焊焊接过程。分析了焊接过程中熔滴过渡的具体特点,短路初期焊丝减速送进保证了熔滴与熔池间的充分润湿,避免了瞬时短路飞溅的发生;短路末期熔滴在较小的电流水平靠机械力拉断液桥,消除了因过电流爆断液桥时产生的飞溅。整个过程熔滴在焊丝送进-回抽的强制作用下均匀、柔顺地过渡,实现了焊接过程的精确控制,同时通过电参数的配合可以对焊接过程中的能量分布进行精密控制。针对焊接过程中焊丝与母材熔化的不同特点,利用等效短路电流Ies和等效燃弧电流Iea分析了电阻热对焊接能量分配规律的影响,从而揭示了推拉丝短路过渡低热输入的机理:在送丝速度不变时,充分利用电阻热对焊丝熔化的促进作用可以有效降低燃弧期间的电弧热量,从而降低了焊接过程对母材的热输入。传统短路过渡中增加干伸长是通过增加电阻的方式增加电阻热,而推拉丝短路过渡则是通过增加等效短路电流Ies的方式增加电阻热的作用,两者均可在一定程度上降低焊接热输入。经能量对比分析可知由于附加机械力的作用摆脱了熔滴过渡对短路电流的依赖,使得推拉丝短路过渡焊接过程无论总能量还是燃弧期间能量均要低于传统短路过渡方法,并且能量分布均匀性好,为实现高质量的薄板焊接工艺奠定了基础。分析了推拉丝短路过渡CO2焊控制参数对能量分配规律的影响,结果表明随着短路末期电流的增加和燃弧峰值电压的减小,在总的焊接能量逐渐减小的同时燃弧期间能量进一步降低,可以实现更低的焊接热输入。随着熔滴过渡频率的增加,等效燃弧电流呈上升趋势,对母材的热输入也有所提高。分析表明采用燃弧期间电压控制的方法,不论焊接过程中控制参数如何变化,对整个焊接能量影响最根本的因素是等效短路电流Ies和等效燃弧电流Iea,其中等效短路电流以电阻热的形式产生热量并全部用于熔化焊丝而等效燃弧电流则决定了对母材热输入的大小。利用推拉送丝系统本身的特点,设计了回抽引弧方案,实现了可靠的引弧过程,为实现稳定的焊接过程提供了保障。推拉送丝短路过渡过程熔滴过渡有规律,能量分布均匀一致,不论在小电流还是大电流时焊缝成形均平整美观。由于电阻热的作用焊接热输入较小,焊缝成形更窄更高,可根据实际焊接的需要合理匹配I H和U P以得到理想的焊缝成形。此外推拉丝短路过渡对熔池冲击小,能量分布均匀,可形成均匀的、较浅的熔深,为推拉丝短路过渡CO2焊在堆焊和修复方面的应用提供了广阔的前景。更多还原

【Abstract】 The development of modern manufacturing put forward higher requirements for final quality and processes of products, with the increasing requirement of high-quality sheet metal welding technology by the car, motorcycle, containers, household appliances and other light industry products Widely used. Because the sheet metal is sensitivity of the heat, and the heat input reducing and uniform energy distribution should be both ensure during welding process. For this feature, a short-circuit CO2 Welding transfer technics has porposed based on low-spatter, low-energy, precision control of the transfer process. The basic principle is: the droplet should be detached by the mechanical force using to pull the wire, according to control the current exactly to regulate the resistance heat between the wire and the base metal. First, this method can reduce the welding energy input and the spatter, second, it can make the transfer process become uniformity and orderliness. The energy distribution in the whole process can be precise control by adjusting welding parameters.Based on the above ideas, a digital welding power source has been designed as a platform, high-performance AC servo push-pull wire feeder is the core of the short-circuit transfer CO2 welding system, the low-spatter,low-energe and process precise controlled welding technics is achieved according to the software controlled method. Digital welding power source adopt digital signal processor (TMS320F2812)with high speed, high precision, and the CPLD (EPM7128STC100) with powerful logical-processing capability as the control of the core to reach the complex welding process control level based on software programme. In order to achieve the high frequency push-pull movement, Push-pull wire feeder part adopt the high-performance motion control card (PMAC2 PC-104) to control AC servo motor with low inertia and high response speed, at the same time, the buffer is used to harmonize the push-pull feeder and the steady rate feeder. This plan can reduce wire movement resistance , increase the feeder distance. According to the interface circuit, the welding power source and wire feeder system can be link together and work harmoniously.Consider the characteristics of the push-pull short-circuit CO2 welding technics, The feeder speed curve, welding voltage and current waveform Control program is pre-designed. During the short-circuit period, the current control program should be adopt. The voltage control program should be used to make the arc-length self-adjusting ability work. The selection principle of movement and welding parameter has proposed. According to adjust the current, voltage waveform and wire feeder, the push-pull short-circuit CO2 welding technics can work steadily and reliably. The characteristics of the droplet detachment during the welding process has been analysed, it supposed that the low feeder speed in the early of the short-circuit can ensure the wetting enough, and avoid spatter when instant short-circuit occurred; in the final of the short-circuit, the droplet detachment when the liquid bridge pulled break according to mechanical force with low current, so the spatter produced from liqiud bridge blast can be eliminate. The whole process accompany with wire push-pull movement can promote the droplet transfer softness and uniformity, achieve energe distribution precise control in welding process by adjusting the welding parameter.For the different characteristics of wire and base metal of welding process, the equivalent short-circuit current Ies and equivalent arc current Iea are defined to analyse the affect of welding energy distribution and reveal the mechanism of the low heat input of the push-pull short-circuit CO2 welding technics. When the wire feed speed is invariablenes, in order to lower the base metal heat input in welding process, the promoted function by the wire resistance heat should be adopt to lower the arc heat in arc period. The traditional short-circuit transfer method increase the resistance heat by increasing the wire extension, But the push-pull short-circuit CO2 welding technics increase the resistance heat by increasing equivalent short-circuit current, they can both achieve reduce the welding heat input in a certain extent. Comparative the energy of the two technics, because the additional mechanical force of the push-pull short-circuit CO2 welding technics get rid of the dependence in short-circuit period, So the energe of the push-pull short-circuit CO2 welding technics is less than the traditional short-circuit methods both in total energy and the arc energy, the energy distribution is good, and lay the foundation for achieving high-quality sheet metal welding technology.The effect of energe distribution rule when control parameter changed in push-pull short-ciucuit CO2 welding has been analysed. The result reveals that with the decreasing of final short-circuit current and the peak arc voltage, the energe can both be decreased for total welding energe and arc energe, so lower heat input welding method could be achieved. With the increasing of transfer frequency, the equivalent arc circuit current is incline to rise, and result in the more heat input for base metal. The analysis result shows that under the voltage control method during arc period, the equivalent short-circuit current Ies and the equivalent arc current Iea are the fundamental factors, the former is totally utilized to melt the wire by resistance heat, the latter determine the heat input for base metal.For the characteristics of the push-pull short-circuit CO2 welding system, the pull-ignite method is designed. This method can ignite reliably and ensure welding process steadily. The droplet of the push-pull short-circuit CO2 welding transfer in order, the energe distribute conformably, and the weld shape is good whatever welding in small or big current. Because the resistance heat reduce the heat input, weld shape is narrow and over-reinforcement, so the desire weld shape can be got by adjust IH and Up according to the welding requirements. In addition, the push-pull short-circuit CO2 welding can lower the transfer impact for welding pool, distribute energe uniformly, shape shallowly and uniformly, support widely perspective for surfacing process by the push-pull short-circuit CO2 welding technics.更多还原