An Experimental Evaluation of Laser-Assisted Micromilling of Two Difficult to Machine Alloys

Abstract

Micro-milling can be difficult to apply to many engineering materials due to a variety of scaling induced factors including: low cutting speeds, high relative tool deflections and runout, and increased material strength at smaller size scales. Additionally, edge burrs which can easily be removed after macro scale milling must be avoided in micro-milling due to the lack of available finishing operations. Laser assisted machining (LAM) involves localized heating of the work material prior to the cutting tool. This localized heating thermally weakens the workpiece resulting in lower cutting forces, improved surface finish, and longer tool life. Applying this concept to micro-milling offers the opportunity for process improvements, especially with materials which are considered difficult to machine. Laser assisted micro-milling (LAMM) was evaluated on Ti-6Al-4V and 316 stainless steel alloys using 100 μm diameter endmills in slotting operations. Micro-scale laser-material interactions were first studied with bulk material absorptivity being determined experimentally through a novel technique utilizing several calibrated melting mediums. A three-dimensional transient finite volume based thermal model was then used to analytically predict appropriate process parameters on the basis of material removal temperatures. A thorough investigation of acoustic emissions (AE) during LAMM was performed. In particular, the effects of depth of cut, tool wear, and material removal temperature on the RMS of AE were studied. Additionally, the effect of LAMM on the machined surface was evaluated quantitatively.