Critical thrust and feed prediction models in drilling of composite laminates

Drilling induced delamination has been recognized as a major problem during drilling of composite materials. The size of the delamination zone has been shown to be related to the thrust force. However, thrust force strongly depends on drilling parameters and it is not possible to control it directly. Thrust force can be correlated with feed rate, the most important parameter affecting thrust force. This paper presents analytical models to predict critical thrust force and feed rate at the onset of delamination. The model proposed is based on elastic fracture mechanics, classical plate bending theory and the mechanics of oblique cutting. An advantage of this model over other proposed models is that to avoid delamination via thrust monitoring, the thrust force will need to be sensed and used in adaptive control, while optimal feed rate can be used directly in CNC command generation to maximize productivity.