Mechanistic force modelling in drilling of AFRP composite considering the chisel edge extrusion

Aramid fiber-reinforced plastic (AFRP) composites have been widely used in automotive, aerospace, and defense industries. The common AFRP drilling process tends to cause damage to the composite structures which subsequently affects their fatigue lives and in-service performance. Understanding the mechanism of cutting force generation is crucial in controlling the cutting process for achieving desired hole quality and machining accuracy. This study proposes a novel mechanistic model considering both the cutting action and the extrusion action of the chisel edge. For the first time, the extrusion force generated by the chisel edge has been considered as a rigid wedge penetrating into an elastic half space based on the Hertz contact theory. The total thrust force in AFRP drilling is divided into three components: (i) thrust force generated by the cutting lips, (ii) thrust force generated by the chisel edge cutting action, and (iii) extrusion force generated by the chisel edge extrusion action. The proposed model was then validated by experiments and data was compared with the case where extrusion was not considered. The results show that our novel mechanistic model can provide a more accurate thrust force prediction. The average error of our model was 2.54% against the experimental data, whereas the error seen in conventional model without accounting extrusion was 8.22%. This suggests that the chisel edge extrusion plays a significant part in the drilling of AFRP and hence confirms the necessity of considering extrusion in establishing the associated mechanistic model.