【作者】 张撼鹏；

【导师】 殷树言；

【作者基本信息】 北京工业大学 ， 机械设计及理论， 2007， 博士

【摘要】 近年来,随着汽车工业的发展需要,汽车所用板材越来越薄,薄板的焊接需要降低能量输入。根据汽车薄板的焊接工艺要求,提出了新型低能量输入焊接法,即NLEI焊接法。其基本思路为:首先设定焊丝的运动曲线,使其周期性的做前进-回抽的往复运动,焊接过程不需在线调整,然后使焊接电源配合焊丝的运动输出相应的电流、电压波形,实现稳定的推拉丝短路过渡,达到降低焊接过程能量输入的目的。根据这一思路,设计了基于推拉丝短路过渡的低能量输入电弧焊接系统,简称NLEI焊接系统。该系统由焊接电源和送丝系统两部分组成,并由软件实现焊接过程的控制。焊接电源的控制核心采用数字信号处理器TMS320F2812,充分利用DSP运算速度快、精度高、数据处理能力强、I/O口资源丰富等优势,用软件编程实现复杂焊接过程的控制,减少了复杂的硬件控制电路,使焊接设备向柔性化控制方向发展;送丝系统由交流伺服电机及其控制系统组成,可以根据实际需要灵活的编制焊丝前进-回抽运动曲线;通过送丝机接口电路实现了焊接电源和送丝系统的连接,保证了焊接过程中二者的通讯与协调。针对NLEI焊接法推拉丝短路过渡的特点,设计了专门的波形控制方案,包括送丝控制和电流波形控制两方面。预先离线设定焊丝运动曲线,在实际焊接过程中通过电流波形与焊丝运动进行配合完成焊接。试验证明,二者配合良好,焊接过程稳定可靠。设计了专门的弧长调节模糊控制方案,以平均电压的变化及其变化率为输入,以燃弧脉冲峰值电流的校正量为输出,通过调整焊丝的熔化来对弧长的变化进行调节。通过试验表明,所设计的弧长调节模糊控制方案,能根据弧长的变化进行自动调整,使弧长保持在一个稳定的范围内,具有较强的适应能力,保证了焊接过程的稳定。分析了NLEI焊接法推拉丝短路过渡过程,对比了传统短路过渡和推拉丝短路过渡的熔滴受力情况。与传统短路过渡依靠较大短路电流产生电磁收缩力使液体金属形成颈缩和短路小桥过热爆断相比,NLEI法熔滴过渡是在较小短路电流下主要依靠焊丝回抽拉断熔滴,从而大大降低了焊接过程能量输入。分析了燃弧脉冲峰值电流Iap和短路后期电流Ih的参数匹配对于实现焊接参数和焊丝运动协调控制的影响。通过试验得到了Iap和Ih的参数匹配区间,在这一区间内,可以实现焊接参数和焊丝运动的协调工作,获得稳定的焊接过程。通过对焊接过程熔池能量输入的计算与检测,找到了NLEI焊接法推拉丝短路过渡的能量分配规律:由于电阻热的影响,短路后期能量Qh对于熔化焊丝有重要作用,是熔化焊丝能量的重要组成部分,而对于加热熔池的贡献很小;由于电弧热的影响,燃弧脉冲峰值能量Qap是加热熔池的最主要能量来源,对于熔化焊丝形成熔滴也起着重要的作用。根据该规律可知:NLEI焊接法推拉丝短路过渡除了通过短路后回抽焊丝拉断熔滴,从而靠外加能量完成熔滴过渡降低能量输入外;还可以通过选择不同的参数匹配方式,采用较低燃弧脉冲峰值电流Iap、较大的短路后期电流Ih来实现进一步降低焊接过程能量输入的目的。采用NLEI焊接法,对薄板钢铝异种金属焊接进行了探索性研究,通过分析接头的界面组织,测试接头的力学性能,发现采用NLEI法可以得到性能良好的薄板钢铝异种金属焊接接头。探讨了焊接工艺参数及合金元素锌对于钢铝异种金属接头性能的影响:焊枪位置对于焊接钢铝异种金属搭接焊缝非常重要,稍有偏差就会造成焊接失败,焊枪位置以选在正对焊缝中间处为最佳;焊接速度越快,温度梯度越大,线能量越低,金属间化合物层厚度越小,但是焊接速度过快时会影响焊缝金属的润湿,造成焊接失败,当送丝速度为2.16m/min时,焊接速度选在0.4m/min~0.5m/min为宜;锌很好的起到了促进焊缝金属在钢板上润湿铺展的作用,在一定范围内锌层越厚对铝和钢的焊接越有利。更多还原

【Abstract】 With the development of automobile industry, the sheet material used in automobile is thinner. So the welding of thin plate need reducing heat input. According to the welding process required by thin plate used in automobile, a new low energy input welding, named NLEI welding was put forward. The following are the principles. First, the moving curve of the welding wire is preset to make the wire moved forward and back periodicaly. The process of welding doesn’t need on-line adjustment, and the power supply is made to provide homologous waveforms of the current and voltage correspond with the movement of the welding wire. NLEI welding can implement steady push-pull short-circuit transfer and meet the demand of reducing welding energy input.According to NLEI welding, author has designed a NLEI arc welding system based on push-pull short-circuit transfer. The system consists of a welding power supply and a wire feeding system, and implements the control of the welding process by software. The control center of the welding process is based on digital signals processor TMS320F2812, which is a high speed and precision DSP with abundance of I/O ports. Hardware circuit is simplified by using software to control complicated welding process. Wire feeding system is based on AC servo-actuator and its control system, the push-pull moving curve of the wire can be programmed smartly according to the actual needs. The connecting of welding power supply and wire feeding system by interface circuit ensures the communication and coordination in the welding process.The waveform control project is designed, including the control of wire feeding and current waveform. By corresponding with current waveform and the wire movement in the actual welding process, the weld is achieved. The experiment proves that, the cooperation is good and the welding process is stable and reliable.A fuzzy control project used to adjust the arc length is specially designed taking the change and the change rate of the average voltage as the input, and the correction value of the pulse current during arc period as the output. In welding process, the arc length is stable with the help of the fuzzy control system.NLEI push-and-pull short-circuit transfer process is analyzed. In traditional short-circuit transfer process, the drops are transferred by electromagnetism force under the big short-circuit current. Compared with that, NLEI push-pull short-circuit transfer can reduce energy input, because it depends on pull of the welding wire to snap the drop under the small short-circuit current.The parameter matching of arcing pulse peak current (Iap ) and the evening short-circuit current(Ih) is very important. The range of parameter matching is gained by experiments. In this range, the coordinate control of welding parameter and welding wire movement can come true and the steady welding process can be gained. The energy distribute regularity in NLEI welding push-pull short-circuit transfer is discovered by calculating and measuring the energy input in the welding pool. The evening short-circuit energy which is the important ingredient of melted welding wire energy has important effect in melted welding wire. But it has little effect on heating welding pool. Because of the arcing heat, arcing pulse peak energy is the mainly energy source in heating welding pool, and it has important effect on heating welding wire too.According to the rules, NELI welding has two ways to reduce the energy input in welding process. The first is the pulling of the welding wire to snap the drop under the small short-circuit current. The second is using lower Iap and higher Ih .Aim to application of aluminum alloy and galvanized steel for automobile industry, the dissimilar joint between galvanized steel sheet and aluminum alloy during NLEI welding has been analyzed. It is proved that dissimilar metal overlap joint with good property can be gained by using NLEI welding.By means of microstructure and mechanical properties analysis of the dissimilar joints, the parameters of NLEI welding process were optimized. When welding speed is increased, the intermetallic layer between the weld metal and galvanized steel is decreased. When heat input is increased, the thickness of interface layer increases.When wire feeding speed 2.16m/min, welding speed 0.4-0.5m/min, welding torch in the middle, continuous, uniform and best shape joint was formed.By the analysis of the effect of different thickness zinc layer on the joint, zinc element effectively promotes molten aluminum wetting the steel sheet, which is good to dissimilar joints between aluminum alloy and galvanized steel when the zinc layer is thick enough.更多还原