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熔化极脉冲焊熔滴过渡合理形式的研究
王其隆, 殷树言, 张九海, 钱乙余
哈尔滨工业大学
摘要:
本文利用高速摄影机和示波器研究了钢焊丝熔化极脉冲焊的各种熔滴过渡形式,试验是在平焊和仰焊位置进行的。作者指出虽然一脉冲一滴和一脉冲多滴的过渡形式在平焊和仰焊位置都能提供稳定而有力的轴向熔滴过渡,但前者只能在很窄的焊接规范区存在,而后者有较宽的焊接规范区间。因此一脉冲多滴的过渡形式是更合理的。熔化极脉冲焊存在两个区分不同熔滴过渡区的临界电流。第一个称为"临界脉冲过渡电流"它是一脉冲过渡一滴的下限电流。第二个称为"临界跳弧电流",它是一脉冲过渡多滴的下限电流。文中还对熔化极脉冲焊的电弧形态与熔滴过渡形式的关系进行了研究和讨论。发现一脉冲多滴过渡的产生过程总是伴随着"跳弧"现象,亦即附着在熔滴端面上的烁亮弧根突然上跳到缩颈的根部。这种跳弧现象在一定的脉冲电流幅值和相应的脉冲电流时间产生。在通常的熔化极气电焊中,当由颗粒过渡转变到射流过渡时也出现这种跳弧现象。实质上,常规的熔化极气电焊过程的临界电流就是连续电流下的临界跳弧电流。下面的现象可说明这一点,在熔化极脉冲焊过程中,当延长脉冲电流时间时,临界跳弧电流将逐渐接近常规熔化极气电焊的射流过渡临界电流。在一脉冲一滴和一脉冲多滴的过渡过程,在脉冲电流停止后还能出现熔滴脱离的现象,这可能是由于焊条熔化金属运动的惯性和焊条端头上金属细液柱的失稳现象所引起的。
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STUDY ON THE FAVOURABLE METAL TRANSFER MODE IN PULSE MIG WELDING
Wang Chilung, Yen Shuyiang, Chang Giuhai, Chian Yiyu
Harbin Instiute of Technology
Abstract:
In this paper various metal transfer modes in the pulse MIG welding with steel electrode are studied by means of high speed cine camera and oscillograph. Experiments have been made in the downhand and the overhead welding positions. The authors suggested that, though both the monodroplet per pulse and the multidroplet per pulse transfer modes can provide a smooth and strong axial metal transfer, the former exists only in a narrow welding condition region while the latter in a wider region. So the multidroplet per pulse transfer mode is more favourable. There are two critical current levels demarcating the distinctively different metaltransfer mode regions in pulse MIG welding. The first is called the critical pulse transfer current, being the lower threshold current of the monodroplet per pullse transfer; and the second is called the critical arc jumping current, being the lower threshold current of the multidroplet per pulse transfer. The relation between the arc luminous core shapes and the metal transfer modes of the pulse MIG welding are also studied and discussed. The authors have found that the starting of the multidroplet per pulse transfer is always accompanied with an "arc jumping", i. e. the luminous arc root attached to the front surface of the droplet jumps instantly up to the bottom of the constricted neck. This arc jumping phenomenon takes place at a certain amplitude of pulse current with a certain correlated pulse current time. In the conventional MIG welding process this arc jumping phenomenon appears also at the time a globular transfer is converted into a streaming transfer. In essnce the critical current of the conventional MIG welding process is just the critical arc lumping current in a continuous current condition. This is supported by the evidence that by extending the pulse current time the critical arc jumping current in the pulse MIG process will gradually approach to the critical current of streaming transfer in the conventional MIG process. During the process of both monodroplet and multidroplet per pulse transfer the droplet detachment can take place even after the cutoff of the pulse current. This may be attributed to the inertial force of the molten metal in motion and to the instabiility of the thin liquid metal column on the electrode tip.
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