Study on Evalution Law of Manufacturing Micro-Convex Points on 45# Steel Surface by Pulse-Width Laser

Abstract

Pulse-width laser is used to manufacture micro-convex points on the surface of 45# steel. Scanning electron microscopy and three dimensional (3D) profiler are used for measuring the morphologies of the microconvex points. Three typical morphologies (spherical-cap shape, Mexican-sombrero shape, and M-type donut shape) are observed in experiments. Conducted the numerical estimations of the temperature field and gasification recoil pressure, and the influences of pulse width and peak power density on the morphology have been researched systematically through the experimental and theoretical analysis, a new formation mechanism of the crater shape is proposed. The formation of the micro-convex points is the result of the coupling of heat and force. Under the effect of the temperature gradient, the liquid metal in the molten pool flow from the edge to the center, which produces micro-convex finally. Spherical-cap shape tends to be formed when peak power density is small and pulse width is short. With the increase of the pulse width and peak power density, the diameter of the central convex point become smaller and its height increases. Micro-convex points evolve into Mexican-sombrero shape. When the temperature at the central of the molten pool exceeds the gasification temperature, gasified materials can form recoil pressure exerting on the molten pool, which presses down the top of the convex. Thus, M-type donut shape is formed. The results are beneficial for controlling the morphologies of the micro-convex points during laser surface texturing.