Li Quanhong, Mu Zhongyan, Luo Manlelan, Huang Anguo, Pang Shengyong
State Key Laboratory of Materials Processing and Die & Mould Technology, School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China.
Micromachines (Basel). 2021 Mar 23;12(3):342. doi: 10.3390/mi12030342.
This paper reports a mechanism understanding how to reduce the solder joint failure phenomenon in the laser spot micro-welding process of ultra-thin steel sheets. An optimization method to improve solder joint service life is proposed. In this study, the time-dependent dynamic behaviors of the keyhole and the weld pool are simulated, and the temperatures in the keyhole of two different laser pulse waveforms are compared. The results show that laser energy attenuation mode (LEAM) can only obtain shallow weld depth because of the premature decay of the laser power of waveform, resulting in the laser beam that cannot be concentrated in the keyhole. The temperature inside the keyhole of LEAM fluctuates significantly, which shows a downward trend. Due to the existence of the peak power of waveform in laser energy continuous mode (LECM), the large angle of inclination of the wall of the keyhole inside the melt pool is more conducive to the multiple reflections of the laser beam in the keyhole and increases the absorption rate of the laser energy by the base material, resulting in the "keyhole effect". But the temperature in the keyhole gradually rises, close to the evaporation temperature. A method combining LEAM and LECM to improve the solder joint service life by optimizing the temperature in the keyhole indirectly by adjusting the peak power of the laser pulse waveform is proposed in this study. The experimental results show that the weld depth can be optimized from 0.135 mm to 0.291 mm, and the tensile strength can be optimized from 88 MPa to 288 MPa. The bonding performance between the upper and lower plates is effectively improved. It can reach the required weld depth in a short time and improve the welding efficiency of the laser spot micro-welding process. The simulation results show that the temperature inside the keyhole is well optimized below the evaporation temperature of the material, which can avoid the violent evaporation of the welding process and keep the whole welding process in a stable state. By optimizing the laser pulse waveform, the temperature inside the keyhole can reach 3300 K, and it is always in a stable state than before optimization. The stable temperature inside the keyhole can help to reduce violent oscillation and spattering of the molten pool and improve welding efficiency and joint life. The research can help provide effective process guidance for the optimization of different laser pulse waveforms in the micro-welding process.
本文报道了一种关于在超薄钢板激光点焊过程中如何减少焊点失效现象的机理理解。提出了一种提高焊点使用寿命的优化方法。在本研究中，模拟了匙孔和熔池随时间变化的动态行为，并比较了两种不同激光脉冲波形下匙孔内的温度。结果表明，激光能量衰减模式（LEAM）由于波形激光功率过早衰减，只能获得较浅的熔深，导致激光束无法集中在匙孔中。LEAM匙孔内的温度波动显著，呈下降趋势。由于激光能量连续模式（LECM）中存在波形峰值功率，熔池内匙孔壁的大倾斜角度更有利于激光束在匙孔内的多次反射，并提高了母材对激光能量的吸收率，从而产生“匙孔效应”。但匙孔内的温度逐渐升高，接近蒸发温度。本研究提出了一种结合LEAM和LECM的方法，通过调整激光脉冲波形的峰值功率间接优化匙孔内的温度，以提高焊点的使用寿命。实验结果表明，熔深可从0.135mm优化至0.291mm，抗拉强度可从88MPa优化至288MPa。有效地提高了上下板之间的结合性能。它可以在短时间内达到所需的熔深，并提高激光点焊过程的焊接效率。模拟结果表明，匙孔内的温度在材料蒸发温度以下得到了很好的优化，这可以避免焊接过程中的剧烈蒸发，并使整个焊接过程保持稳定状态。通过优化激光脉冲波形，匙孔内的温度可达到3300K，并且比优化前始终处于更稳定的状态。匙孔内稳定的温度有助于减少熔池的剧烈振荡和飞溅，提高焊接效率和接头寿命。该研究有助于为微焊接过程中不同激光脉冲波形的优化提供有效的工艺指导。
