Product Code: ICA12_1908

Towards a Quantitative Model for Porosity Predication in CO2 Laser Welding of Titanium Alloy Sheets
Authors:
Shengyong Pang, State Key Laboratory of Materials Processing and Die & Mould Technology, Huazhong Univ. of Science & Technology (HUST); Wuhan Peoples Republic of China
Weidong Chen, State Key Laboratory of Materials Processing and Die & Mould Technology, Huazhong Univ. of Science & Technology (HUST); Wuhan Peoples Republic of China
Lunji Hu, State Key Laboratory of Materials Processing and Die & Mould Technology, Huazhong Univ. of Science & Technology (HUST); Wuhan Peoples Republic of China
Presented at ICALEO 2012

Quantitative prediction of the sizes and numbers of porosity defect induced by keyhole instability has scientific significance to optimize the laser welding process. Despite several advances have been made to model the transient keyhole instability and even void formation during laser welding, few theoretical models can quantitatively correlate the keyhole instability with the sizes and numbers of pores. In this study, we formulate a comprehensive transient model for CO2 laser welding of Ti-6-Al-4-V sheets and show that it can be used to quantitatively predicate keyhole induced porosity in the investigated processing parameter windows. 3D keyhole instability, weld pool dynamics and pores formation are simulated and discussed by comparing to experimental and literature results. It is found that the simulated keyhole depth fluctuations could represent the variation trends of the numbers and the average sizes of pores under medium and high welding speed conditions. By properly adjusting the surface tension value used in the simulations, the obtained keyhole depth fluctuations can be used to quantitatively predicate the average size of porosity. The results also indicate that due to the shadowing effect of keyhole wall humps, the rapid cooling of the surface of keyhole tip before keyhole collapsing leads to a substantial decrease of vapor pressure inside the keyhole tip, which is suggested to be the mechanism that shielding gas enters into the pores