Product Code: ICA13_1104

Numerical Simulation of Wire Temperature Field for prediction of Wire Transfer Stability in Laser Hot Wire Welding
Authors:
Shiqing Zheng, Tsinghua university; Beijing Peoples Republic of China
Wen Peng, Tsinghua University; Beijing Peoples Republic of China
Feng Zahenhua, Tsinghua University; Beijing Peoples Republic of China
Shan Jiguo, Tsinghua University; Beijing Peoples Republic of China
Presented at ICALEO 2013

In laser welding with filling cold wire, the limited spot size and power of laser source is required not only to melt the base metal, but also to melt the cold wire, which largely results in poor processing stability and low deposition efficiency. With preheating the wire by resistance heat before feeding it into the molten pool, laser hot wire welding shows much improved stability and efficiency, which has broad potential applications in build-up welding and narrow gap welding. The transfer stability of hot wire is a key issue for processing stability and weld formation.
This paper is purposed to find out the influence of the resistance heat and the laser source on the wire transfer, and predict the optimized welding parameters for the stable wire transfer. A high speed video imaging system is used to observe the wire transfer phenomenon, the temperature of the wire tip outside the molten pool is measured by the infrared ratio technique, and an unsteady heat conduction model is established to calculate the wire temperature field. Three types of wire transfer mode exist by video imaging analysis: fusing, continuous and wire hit transfer. Only the continuous transfer is the stable wire transfer, which guarantees good weld formation. The other two both result in poor weld stability and formation. The change of wire transfer mode is directly related to the wire temperature and determined by both of the resistance heat and the molten pool heat. Regarding the continuous transfer, the temperature of wire tip outside the molten pool should be lower than the solidus of wire, while the temperatureof the end of wire in the molten pool higher than the liquidus. The temperature criterion of wire transfer modes is obtained by analyzing the high speed video imaging and temperature measurement. The wire temperature field is calculated by numerical simulation, which is testified accurately as experimental values. Comparing the calculated temperature with the criterion of wire transfer, the wire transfer stability in various welding parameters is well predicted. In conclusion, fora certain stable wire transfer,the ratio of wire current square to wire feeding rate is near to constant in the upper limit ofwire current, which has little relationship with laser source; while the lower limit of wire current increases with increasing wire feeding rate anddecreasing laser power, which results in a narrow span of optimized wire current.