Fiber 레이저를 이용한 순수 알루미늄의 다층 박판 겹치기 용접 특성에 관한 연구

Abstract

Energy consumption has increased because of the development of modern industrial society and population growth. According to it, increase issue of a crude oil price to the lack of the fossile fuel like oil and the environmental pollution problem like the green house effect due to the use of fossile fuel has come to the fore. In order to solve these problems, the motor industry is interested in developing eco-friendly cars. According to this, the battery industry focuses on developing the performance of secondary batteries which are the main driving source of eco-friendly cars. Conventionally an ultrasonic welding is applied to producing a series of secondary lithium-ion battery. It is disadvantageous that the existing ultrasonic welding process has constraints on material, shape, and measurement of the processed article. Another weak point is the short lifespan of horn. In order to complement these drawbacks, we employe the laser welding process based on a high density energy source which has better performance comparing with the ultrasonic welding process. The advantage of a laser welding process is that it can precisely weld small parts without deformation. In this study, we analyze and compare the performance of ultrasonic welding and fiber laser welding on pure aluminium thin plates in a series of secondary lithium-ion batteries, and replace the conventional welding method to the laser welding method. In order to apply lap joint welding to 40 sheets of 30㎛ thick thin plates, we tested with follows; 314.1J of energy, 0.2MPa of pressure, 80% of amplitude, 0.3s of welding time, 3~6kW of laser peak power, 2~6ms of pulse duration, and 15~50Hz of frequencies. As a result, the weld width of ultrasonic welding is 5mm, but that of laser welding is 1~1.5mm. Also, the cross-sectional size of a welding area and the depth of the welding area are affected by pulse duration and the peak power, respectively. As a result of tension test, the tensile strength is high when the pulse duration is short for low peak power, while the tensile strength is high when the pulse duration is long for high peak power. Comparing with ultrasonic and laser welding methods, the value of tensile strength in tension test is higher in ultrasonic welding while welding width showed 45% better result with the laser welding. Also, it is difficult for a specimen to be attached to a welding cross-sectional area due to the limit of the ultrasonic welding while laser welding brings lots of blow holes at the welding area due to the characteristics of aluminium. Blow holes are caused by different solubility of hydrogen between solid state and liquid state of aluminium. Based on this result, the laser welding might replace the ultrasonic welding, but the methods to remove weld defects at laser welding should be improved.