Effectiveness study and model simplification of laser cladding process with coaxial shroud protection

• The effectiveness of a three-layer annular coaxial shroud (TACS) was experimentally validated for laser cladding in open environments. • Oxygen concentration and molten pool protection were ensured when shielding gas flowrate exceeded 30 L/min. • The cross-section profiles of single-track clads were fitted by parabola, sine, and elliptic functions, with the elliptic model showing best accuracy under shielding gas. • The flat-top overlapping model (FOM) was employed to optimize the overlapping coefficient of multi-track clads. • The optimal overlapping coefficient was determined as 0.542, enabling improved surface flatness and reduced pile-up. Cladding active metal for surface repair and complex components fabrication in open environment remains a ground challenge and the advanced laser cladding technique with coaxial shroud protection has exhibited some new promises compared to other traditional deposition methods. In this study, comprehensive and thorough experiments have been carried out, focusing on the protectiveness of a three-layer annular coaxial shroud with qualitative measurements and quantitative data analysis. The experimental results have shown that the Ti6Al4V cladding can be effectively protected when the shielding gas flowrate is greater than 30 L/min. The optimal cross-section profiles of three frequently used models (Parabola, Sine and Elliptic functions) are measured with post-processing. It shows that the parabola model produces the most accurate results without extra shielding gas in terms of R-square values compared with the original cladding profile, whilst the elliptic model is more accurate in describing the cladding profile with extra shielding gas over the same test range. Applying both elliptic function model and flat-top overlapping model, a generalized formulae is then derived to evaluate the horizontal coordinate of the cladding centre point, which is used to determine an optimal overlapping coefficient of 0.542 under an extra shielding gas flowrate of 30 L/min. Further examinations consider four different scenarios, corresponding to four different overlapping ratio ranges. Results are in good agreement with experimental observations. It is worth noting that few literatures have documented to predict the crucial overlapping ratio using the EF model by determining the horizontal coordinate of point C value. Moreover, the elliptic function model proves more precisely representation of experimental data profile while compared to those fitted by Sine Function and Parabola Function models. The observations and findings of this study have shed some lights on current understanding of advanced laser cladding techniques.