CFRP drilling under throttle and evaporative cryogenic cooling and micro-lubrication

Abstract Hole-making in CFRP plates has been unsustainable due to poor hole quality, high specific energy consumption, a trade-off between shortened drill life and low productivity, and high processing cost. This experimental study investigates the effects of using throttle and evaporative cryogenic fluids, actualized by applying compressed carbon dioxide and liquid nitrogen, respectively, and micro-lubrication on hole quality (roughness, coaxiality, and circularity), production economy (tool damage and process cost), structural intactness (delamination and uncut fibers), energy consumption, and machining forces. Additionally, the effects of applying drill pecking and cutting speed are also quantified. Based on the experimental results, micro-lubrication is found to have outperformed dry drilling and the two cryogenic coolants regarding the measures associated with process viability, such as tool wear, process cost, energy consumption, and machining forces. Throttle cryogenic cooling, on the other hand, yielded the best results in respect of the work quality measures, which includes hole quality and structural intactness. Pecking yielded disappointing results regarding most of the measures, whereas the high level of cutting speed yielded favorable results in respect of specific cutting energy and process cost.