Machining of frp composite laminates with cd and uad techniques : A comparative and experimental investigation

The enhanced properties and increased application of a natural hemp fibrereinforced polymer (HFRP) composites have emphasized the need for an innovative and a deeper understanding of their machinability in order to further improve their functionality and applicability. Hence, this paper presents a comparative and experimental investigation of the effects of a dry conventional drilling (CD) and hybrid ultrasonically-assisted drilling (UAD) techniques on both hemp fibrereinforced/ polycaprolactone and vinyl ester (HF/PCL and HF/VE) composite samples. The results obtained depict that HF/PCL composite sample of 19 aspect ratio (AR) has a minimum values of peak thrust force of 90N and 75N during UAD and CD respectively, with the lowest machining time of 30seconds for both techniques, among other ARs. These values produced an optimum drilling and best quality drilled holes, in terms of lowest thrust force and resultant drilling-induced damage. It is observed that there was a very little or no thrust force reduction between UAD and CD when drilling the HF/PCL composites. Consequently, PCL was replaced with VE, to produce another sample of HF/VE composites. Therefore, a substantial reduction in drilling forces (thrust force and torque) was obtained during HF/VE drilling, using UAD technique, when compared with the dry CD technique. Comparatively, the percentage of the forces reduction is approximately 70. The quality of the drilled sample depended on these primary forces. In addition, a significant lower ply delamination defect, burr formation, fibre-uncut/pull-out and surface roughness were observed, as well as an improved chip expulsion, hole roundness, material removal rate and surface finish (hole quality) were obtained with UAD, when compared with CD technique. Evidently, a non-traditional hybrid machining technique, UAD, has enhanced machinability (drilling) of HF/VE composite compared with the CD and HF/PCL composite samples.