Feasibility Study of Abrasive-Waterjet Milling of Fiber-Reinforced Plastics

Composite materials are ideal for structural applications where high strength-to-weight and stiffness-to-weight ratios are required. Currently, linear cutting of composite materials has been increasingly practiced in industry and milling will be an important technology for wider applications of the materials and the benefit of onestation operation integrating linear and surface machining. Abrasive waterjet is adequate for machining of composite materials thanks to minimum thermal or mechanical stresses induced. The present paper discusses the feasibility of milling of composite materials by abrasive waterjet; it studies the basic mechanism of chip formation, single-pass milling, double-pass milling followed by the repeatable surface generation by multiple-pass milling. The mechanisms of material removal-deformation wear and cutting wear are studied first. High volume removal rate as well as a neat surface are desired. The major parameters affecting material removal rate are hydraulic pressure, standoff distance, traverse rate and abrasive flow rate. Dimensional analysis shows these significant parameters in machining and the results are compared with the theory of material erosion. The single-pass milling tests of carbon/epoxy are then conducted. The milling characteristics determining the generation of an extended surface are depth, width and width-to-depth ratio. The following dimensional analysis constructs the correlation between parameters and the surface characteristics. Based on the results of single-pass milling tests, the paper discusses the double-pass milling specifically considering the effect of lateral feed increments. The study then extends to six-pass milling. The obtained surface roughness from the sixpass milling is expressed as a function of the width-to-depth ratio and the lateral increment. With the knowledge of the volume removal rate and the surface roughness as well as the effects of the major process parameters, one can proceed to design a milling operation by abrasive waterjet.