Surface quality and formation mechanism of Ti-6Al-4V by in-situ laser-assisted ball-burnishing

Abstract

Titanium alloys are widely used in aerospace, rail transportation, and other fields. As components operating in complex environments, high surface finish and excellent fatigue resistance are required. Ball-burnishing is one of the common techniques for surface strengthening of workpieces. However, when dealing with high-strength, low-plasticity materials, ball-burnishing faces issues such as poor surface quality, inadequate strengthening effects, and severe tool wear. Therefore, this study proposes an in-situ laser-assisted ball-burnishing (In-LAB) technology. Unlike the laser pre-assisted ball-burnishing, in this technology, the laser beam is directed to the workpiece machined area by passing through the transparent diamond ball-burnishing tool. The heating and burnishing effects act simultaneously on the workpiece, efficiently utilizing the laser energy and avoiding unnecessary thermal damage. This study has established a finite element model (FEM) for In-LAB and found that, compared to normal ball-burnishing, the maximum residual compressive stress in the workpiece surface increased by 131 %. Through a Taguchi experiment with the objective of minimizing surface roughness, the relevant parameters are: rotation speed 300 r/min, press amount 0.05 mm, feed rate 0.05 mm/r, and laser power 25 W. Compared to normal ball-burnishing, the surface roughness decreased by 51 %, the surface hardness increased by 7.5 %, and tool wear was significantly reduced. This technology combines in-situ laser-assisted machining with ball-burnishing technology. Related research results indicate that it can provide lower surface roughness, higher residual compressive stress, and greater surface hardness. In-LAB technology offers a new approach for surface finishing and strengthening of hard-to-machine materials, expanding the application scope of In-LAM technology.