Effect of Laser Preheating the Workpiece on Micro-End Milling of Metals

Abstract

Micro-end milling is a fast and direct method of creating net-shaped functional micro parts, micro molds, and prototypes. However, the materials that can be micro machined efficiently are limited by the small flexural stiffness, strength, and hardness of the tool. The small flexural stiffness and strength of micro-end mills limits the size of cut that can be taken and the productivity. The flexural stiffness and strength are a strong function of the tool diameter. It is not expected that in the near term a new material will be developed that offers a combination of hardness and yield strength that will result in a significantly improved strength for tools with diameters measured in the 10s and 100s of microns. To enable a significant increase in performance requires higher spindle speeds and increased chip loads. Laser-assisted micro-end milling has the potential to increase the chip load and productivity by reducing the yield strength at the cutting location. This study examines the effect of laser preheating on micro-end milling of 6061-T6 aluminum and 1018 steel. 300 micron-diameter, two-flute, carbide end mills are used to cut 85 micron-deep slots at a constant 40,000 rpm spindle speed. The laser power and chip load are varied, including no preheating, to show their effect on cutting forces, specific cutting energy, burr formation, surface finish, and temperature. The results are related to average material removal temperature by predictions from a heat transfer model of the workpiece undergoing laser preheating. Results indicate that chip load and productivity can be significantly increased during dry machining of 6061-T6 aluminum and 1018 steel by locally preheating the workpiece immediately ahead of the micro-end mill.