Shengyong Pang

A three-dimensional sharp interface model for self-consistent keyhole and weld pool dynamics in deep penetration laser welding

A three-dimensional sharp interface model is proposed to investigate the self-consistent keyhole and weld pool dynamics in deep penetration laser welding. The coupling of three-dimensional heat transfer, fluid flow and keyhole free surface evolutions in the welding process is simulated. It is theoretically confirmed that under certain low heat input welding conditions deep penetration laser welding with a collapsing free keyhole could be obtained and the flow directions near the keyhole wall are upwards and approximately parallel to the keyhole wall. However, significantly different weld pool dynamics in a welding process with an unstable keyhole are numerically found. Many flow patterns in the welding process with an unstable keyhole, verified by x-ray transmission experiments, were successfully simulated and analysed. Periodical keyhole collapsing and bubble formation processes are also successfully simulated and believed to be in good agreement with experiments. The mechanisms of keyhole instability are found to be closely associated with the behaviour of humps on the keyhole wall, and it is found that the welding speed and surface tension are closely related to the formation of humps on the keyhole wall. It is also shown that the weld pool dynamics in laser welding with an unstable keyhole are closely associated with the transient keyhole instability and therefore modelling keyhole and weld pool in a self-consistent way is significant to understand the physics of laser welding.

Towards a quantitative model for porosity predication in CO2 laser welding of titanium alloy sheets

Quantitative prediction of the sizes and numbers of porosity defect induced by keyhole instability has scientific significance to optimize and control 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. Moreover, the obtained keyhole ...

Three dimensional simulation of the transient process of fiber laser keyhole welding of aluminium alloys

A comprehensive three dimensional transient model is developed for the streamline process of keyhole mode fiber laser welding. The physical effects of multi-reflections absorption, the Marangoni force, the recoil pressure, the surface tension and other physical and thermo-dynamical effects such as evaporation, melting and solidification etc. of the fiber laser keyhole welding process are rigorous considered in the present model. The self-consistent process of three dimensional keyhole instabilities and weld pool dynamics during keyhole mode fiber laser welding of ZL114 aluminium alloys is firstly reasonably modelled. The simulation results reasonably agree with in-situ high speed CCD imaging experiments.

Three-dimensional simulation transient keyhole evolution during laser keyhole welding

Laser keyhole welding process is not well understood because the related physics are too complex. Numerical simulation of transient keyhole evolution provides fundamental data needed to improve understanding of the mechanisms of porosity formation during laser welding. In this paper, a three dimensional mathematical model was proposed to simulate the keyhole formation process of laser welding. The coupled effects of multi-reflections Fresnel absorption of keyhole, heat conduction, heat convection, heat radiation and Knudsen jump boundary conditions on the liquid-vapor evaporation interface were considered in this model. A level set method and a fast sweeping method were developed to solve the model. The transient keyhole shape, the surface recession speed due to evaporation and the thermal distribution of keyhole wall were investigated. The time-varied surface tension force of keyhole wall was also calculated.