이차전지 소재용 다층 구리 박판의 펄스파형 파이버 레이저 용접 특성에 관한 연구

Abstract

In order to solve the problem of the fossil fuel shortage with the high cost and environmental pullulation in the modern industrial society, there is a great concern about the development of eco-friendly cars in the motor industry. The eco-friendly car has been developed for the purpose of limiting the use of fossil fuel and reducing the emission of greenhouse gas. As the driving motor and high capacity battery are affected as one of core techniques on the eco-friendly car, various studies have focused on the performance improvement of a secondary battery which is the power source in the battery industry. The most important part in the development of the battery is to make a battery with a high capacity and light weight. In this study, we have studied to conduct welding for a direct attachment without bolts and nuts using a laser which is a high density energy source, to make a light weight battery. Since the laser welding basically uses a high density energy source, we can save time for melting and solidification. Compared to a general welding, as the aspect ratio is large, the welding depth is deep, and the Heat Affected Zone (HAZ) is narrow, it has advantages of a rare thermal strain and a micro-region welding. In this study, we also conduct experiments by using a Fiber laser for the purpose of replacing the bolt attaching method with the laser welding method for a pure copper sheet which is one of the battery part materials in the Lithium group. In order to conduct an overlap welding for forty sheets of pure copper with each size of 38㎛, in thickness, the experiments are conducted by changing the process variables as follows. We have changed the peak power of the laser from 5 to 6kW, the pulse duration by 4, 6, 8, and 10ms, the frequency by 10, 12, 16, and 25Hz, and the focal position by -3, 0, and +3. As a result, when the focal position is at +3, the peak power is 5kW, and the pulse duration and the Frequency are 4ms and 25Hz, respectively, we obtain 2.1 and 2.5 times better tensional strengths, respectively, than the highest values of tensional strengths obtained with the focal positions at 0 and -3 under 69.8MPa. On the basis of this result, it is possible to replace the bolt attaching method with the laser welding method. The study on the method to eliminate weld defects during the laser welding should be looked into further.