Hybrid Laser-Assisted Mechanical Micromachining (LAMM) Process for Hard-to-Machine Materials

Mechanical micro-cutting (e.g. micro-grooving, micro-milling) is emerging as a viable alternative to lithography based micromachining techniques for various applications in the fields of micro molding, biomedical devices, optics, and semiconductors. However, certain factors limit the workpiece materials that can be processed using mechanical micromachining methods. For difficult-tomachine materials such as mold and die steels and ceramics, limitations in cutting tool and stage stiffness and strength of the micro-tool are significant problems facing the successful application of mechanical micromachining methods. In addition, in microscale cutting, the effects of tool and precision motion stage deflections on part dimensional accuracy can be significant. This paper presents a novel hybrid Laser Assisted Mechanical Micromachining (LAMM) process that makes use of highly localized thermal softening of the hard material by continuous wave laser irradiation (2-35 W Yb-fiber laser, wavelength 1064 nm) in front of a miniature (100-500 m wide) TiAlN-coated tungsten carbide grooving tool. By suitably controlling the laser power, location, and spot size, it is possible to bring about a sufficiently large decrease in the work material strength and thereby minimize catastrophic tool failure, and lower the tool forces and deflection. Despite these advantages, the LAMM process may produce a heat affected zone (HAZ) that can result in potentially undesirable alteration of the workpiece microstructure. This paper presents the results of experimental characterization of the LAMM process for H-13 mold steel (42 HRC). Micro-grooving experiments are conducted in order to understand the influence of the laser variables (laser power, beam location with respect to tool) and cutting parameters (depth of cut, cutting speed and tool width) on the cutting and thrust forces and dimensional accuracy. The HAZ is characterized for pure laser heating. The results show that, for a given cutting condition, laser variables significantly influence the process responses. Plausible explanations for the observed trends are given.