Experimental investigations on the laser-assisted machining of single crystal Si for optimal machining

Single crystal Si is a typical infrared optical material, which is widely used in infrared optical systems such as lenses, prisms, windows and filters. But its high brittleness, hardness, and low fracture toughness make it difficult to machine using conventional machining (CM). Laser-assisted machining (LAM) method has become a promising solution for the machining of single crystal Si in recent years. This paper investigated experimentally the effect of spindle speed, feed speed, cutting depth, and laser pulse duty cycle on the surface roughness during the LAM of single crystal Si based on the Taguchi method (TM) and Response surface methodology (RSM). Orthogonal array and Box-Behnken design were used to design the experiment. Analysis of variance, signal-tonoise ratio, main effect plots, 3D response surface, and corresponding contour plots were measured to evaluate the effect of factors on the surface roughness. Based on RSM, a regression model between process parameters and surface roughness was established. The experimental results on LAM demonstrated a considerable improvement in the machinability of single crystal Si through the improved surface quality, high material removal rate, as well as the surface roughness reduction, compared to CM. The contribution rates of spindle speed, feed speed, cutting depth and pulse duty cycle to surface roughness were 21.85%, 39.95%, 10.29% and 14.27%, respectively. According to the 3D response surface, the interaction between different factors had a significant effect on the surface roughness. ANOVA and response optimization were employed to find optimal machining conditions for LAM. Finally, the Optimal parametric combination was as following: a spindle speed of 4000 rpm, a feed speed of 2 mm/min, a cutting depth of 5.86 mu m, and a pulse duty cycle of 27.60%. The maximum value of measured roughness was 1.9 nm.