Characterization of a hybrid laser-assisted mechanical micromachining (LAMM) process for a difficult-to-machine material

Mechanical micro-cutting is emerging as a viable alternative to lithography based micromachining techniques for applications in optics, semiconductors and micro-mold/dies. However, certain factors limit the types of workpiece materials that can be processed using mechanical micromachining methods. For difficult-to-machine materials such as mold and die steels or ceramics, limited cutting tool/machine stiffness and strength are major impediments to the efficient use of mechanical micromachining methods. In addition, at micron length scales of cutting, the effect of tool/machine deflection on the dimensional accuracy of the machined feature can be significant. This paper presents experimental characterization of a novel hybrid laser assisted mechanical micromachining (LAMM) process designed for 3D micro-grooving that involves highly localized thermal softening of the hard material by focusing a solid-state continuous wave laser beam in front of a miniature cutting tool. Micro-scale grooving experiments are conducted on H-13 mold steel (42 HRc) in order to understand the influence of laser variables and cutting parameters on the cutting forces, groove depth and surface finish. The results show that the laser variables significantly influence the process response. Specifically, the mean thrust force is found to decrease by 17% and the 3D average surface roughness increases by 36% when the laser power is increased from 0 to 10 W. The groove depths are found to be influenced by the machine (stage) deflection and tool thermal expansion, which affect the actual depth of cut, in the presence of laser heating. In particular, it is found that the accuracy of groove depth improves with laser heating. Explanations for the observed trends are given.