Investigation of Quality of Drilled Holes by Guiding the Drill Bit Using Permanent Magnet on a Glass Fibre Reinforced Polymer Composite Material

The use of glass fibre reinforced polymer composite materials (GFRP) increases due to its superior properties that draw the attention of the other researches focusing on relevant aspects concerning the machining of such materials. In conventional machining for hole creation, drilling is the most frequently employed machining process for hole generation in fibre reinforced materials. Due to the laminated structure of the composite materials, several types of damages and other surface irregularities are introduced during drilling processes. These defects in the holes lead to about 60% of the rejections in assembly plant. Surface roughness has been identified to be the main contribution for defects in holes machined in composites. These defects would create reduction in structural stiffness, which may lead to variation of dynamic performance of the whole structure. Hence, achieving the desired hole quality is of great importance for the functional behaviour of the mechanical parts. In the present work, the effect of permanent magnet on the quality of drilled holes on GFRP composite is presented. Experiments are performed under different magnetic drilling conditions of spindle speed, feed rate and drill diameter on CNC drilling machine using three levels of factors. A procedure has been adopted to assess and optimize the chosen factors by the use of Box Behnken design to analyse the effects of different parameters. From the experimental results, it has been observed that the technique used is convenient to predict the main effects and their interaction effects of different influential combinations of machining parameters on surface roughness. It has been found that effect of permanent magnetic on the guiding mechanism of the drill bit which lead to get improved surface roughness with better circularity compared to normal drilling processes. A mathematical model has been developed for the prediction of surface roughness using permanent magnet and normal drilling processes.