Workpiece damping and its effect on delamination damage in drilling thin composite laminates

The machining of the glass fiber reinforced plastic (GFRP) laminates may generate several kinds of damage. The most serious is the delamination that may occur during drilling, and which severely compromises the mechanical characteristics of the material around the hole. The main cause of delamination is generally held to be the thrust force exerted by the drill point; the most commonly used method for reducing delamination is to place a support under the workpiece. Paradoxically, while this practice does limit delamination, the force exerted by the drill point is actually greater than in unsupported drilling. The presence of the support does influence the delamination mechanism, but exactly how that mechanism works does not seem to be fully understood yet. This study analyzes the differences in delamination mechanisms when drilling with and without a support placed under the workpiece. This investigation has led to hypothesize two main differences in the mechanism. On the basis of this analysis, a new device was designed that counters the hypothesized delamination mechanism. A simple prototype of this device was built, and its effectiveness verified. The results show that the proposed device can drastically reduce delamination.