Laser beam cutting of metallic hollow sphere structures

Abstract

AbstractMetallic hollow sphere structures (MHSS) represent a relatively new group of advanced composite materials characterised by high geometry reproduction leading to relatively constant mechanical and physical properties. The MHSS combine the well‐known advantages of cellular metals without major scattering of their material parameters. Various joining technologies such as sintering, soldering and adhering can be used to assemble single metallic hollow spheres to interdependent structures and allow adjusting different macroscopic properties. A machining process for MHSS has to reflect the special characteristic of the composite material. Classical mechanical cutting techniques like sawing or milling often fail. Spheres or large pieces are separated from the bulk structure and cause a rough surface at the cutting zone. Other cutting techniques like water jet cutting cannot be used for oxidising material. This paper presents laser beam cutting as a proper technique to cut composite materials like MHSS. The quality of the cutting zone strongly depends on the process parameter e. g. focal length, tool velocity and the structural characteristics of MHSS, e. g. density, sphere diameter and density. The experimental work was done using a CO2‐laser with a power of 1.5 kW. All investigations were done with sintered hollow sphere structures having different macroscopic properties. The maximum depth of a cut kerf was determined for four configurations of MHSS as function of laser velocities, gas pressure of the process gas, focal length of the lense. The depth was evaluated using a power balance of the laser input power on one side and the power needed to warm and melt the MHSS on the other side. A comparison between simulation and experiment of the width and the depth of the cut kerf shows, that the laser beam gets multiple reflections on the surfaces of the hollow spheres, enlarging the width of the cut kerf. The functional dependency between laser velocity and cut kerf depth can be estimated well. Theoretical and experimental results fit well together.