Investigation on the mechanism of surface structure formation during laser remelting with modulated laser power on tool steel H11

Abstract

Conventional surface structuring processes often share two crucial disadvantages. Firstly, an additional surface finishing is usually required. Secondly, excess material is wasted. In contrast, during laser remelting, a redistribution of material can be achieved that results in a structured surface with a low micro-roughness. Therefore, this investigation focuses on the mechanism of surface structure formation during laser remelting on the hot work steel H11. A newly developed FEM-model is introduced and surface structure formation is investigated specifically for a sinusoidal modulation of laser power. A fiber coupled Nd:YAG laser was used to emit laser radiation with a focal beam diameter of 250 µm and laser power between 15 W and 215 W. At a scanning speed of 50 mm/s, the structuring of wavelengths from 0.25 mm to 4 mm was investigated. After one process step, structure heights of up to 12 µm were achieved for single tracks. In addition, the theoretical model revealed that melt pool changes lead to a deformation of the melt pool surface, which results in the formation of surface structures. Furthermore, the agreement between simulations and experiments indicates that the Marangoni-convection has only a minor impact on surface structure formation during laser remelting.