Abrasive Waterjet Contour Cutting of Thick Titanium/Graphite Laminates

One of the primary focus in aerospace industry is the reduction of buy-to-fly ratio. Although TiGr laminates are molded/autoclaved to a near net shape, secondary machining such as drilling, peripheral machining and contouring is often unavoidable. Machining of composites alone poses a great challenge which becomes more challenging in a three phase material system---hybrid composites, where the non-homogeneity and anisotropy of composites together with the difference in the removal mechanism for all the three different phases aggravate the machining problem.;An investigation was conducted to evaluate the feasibility and machinability of contouring thick TiGr through Abrasive Waterjet (AWJ) in terms of kerf characteristics---taper ratio and surface quality. A cutting geometry with different profile curvatures was machined with conditions according to a response surface experimental design obtained using Design Expert software. The process variables included pump pressure, jet traverse speed, load ratio (by varying abrasive flow rate) and nozzle dimensions. Material removal mechanism was studied for three different phase material systems. Kerf taper ratio was investigated to qualitatively characterize superior and inferior quality cuts. Topological characteristics of the kerf were also studied with roughness evaluation of surfaces parallel (longitudinal) and orthogonal (transverse) to jet traverse direction. Analysis of Variance (ANOVA) was used to statistically characterize the effect of operating variables on kerf taper ratio. Predictive mathematical models were developed for taper ratio and transverse roughness R z, whereas semi-analytical model was developed to predict Average transverse roughness Ra. The AWJ process was characterized using Skewness-Kurtosis and Rq/Ra ratio of the kerf profile. Overall, machinability of thick TiGr laminates was evaluated as a function of kerf taper ratio and surface roughness and statistical optimization was done for machining with low taper and low roughness.