Elsevier

CIRP Annals

Volume 61, Issue 1, 2012, Pages 123-126
CIRP Annals

Characterization and optimization of orbital drilling of woven carbon fiber reinforced epoxy laminates

https://doi.org/10.1016/j.cirp.2012.03.089Get rights and content

Abstract

The emerging process of orbital drilling (OD) can greatly reduce or eliminate the defects associated with the drilling of composites; e.g., delamination, and thermal damage. The effects of the OD process parameters on the hole quality attributes were established in the form of machinability maps; an aspect that has not been reported before. The results showed significant enhancement in the hole quality compared to conventional drilling, due to the reduced axial force and cutting temperature, resulting from the redistribution of the load exerted by cutting edges and the cooling effect of the unstable rotational air flow in the tool-workpiece annular gap.

Introduction

The defects associated with the drilling of Carbon Fiber Reinforced Polymers (CFRPs), e.g., delamination, matrix burnout, and fiber pullout, are of major safety and economic concerns to the aerospace manufacturers. These defects can, however, be minimized, or even avoided, by keeping the cutting forces and temperatures below some threshold levels. The orbital drilling (OD) technique has shown great potential in drilling metallic and composite materials, through the significant reduction of cutting forces and temperatures [1], [2], [3]. It was shown, however, that high rotational speeds result in lower hole surface quality for the CFRPs [1]. A large part of the available research work on OD was performed by industrial organizations, as in reference [3], which reported advances on the technologies of implementing OD rather than fundamental understanding of the process mechanics.

The main objective of the current study is to investigate the effect of the key parameters of the OD process on the produced hole quality attributes and cutting forces and temperatures. This study illustrates also the capabilities and limitations of the OD process.

Section snippets

Orbital drilling process from energy perspective

The orbital drilling process is examined in this section from a new energy perspective, in terms of fracture energy and heat transfer between the tool and workpiece.

Experimental setup

The OD tests were performed under dry conditions on a 5-axis Makino A88ɛ machining centre; 50 kW spindle, maximum spindle speed of 18,000 rpm and maximum feed rate of 50 m/min. Table 1 shows the ranges of axial feeds corresponding to the two levels of helical pitches used with spindle speeds of 6000, 8000, 10,000, 120,000 and 16,000 rpm. The orbital speeds used were 60, 80, 100, and 120 rpm. Fig. 3(a) shows the fixture (1) used to hold the CFRP laminates. The fine chips were evacuated using a

Axial and tangential cutting forces

Analysis of the results showed 45% reduction in the axial force component in orbital drilling (OD), compared to conventional drilling. Although the tangential force in OD was almost double that of the conventional drilling, it was <30% of the axial force. This was explained in Section 2.3 in relation to the redistribution of the cutting energy in OD. Fig. 4 shows the direct relationship between the OD axial force component and axial feed. As explained in [2], increasing the uncut chip area on

Concluding remarks

The unique characteristics of the orbital drilling (OD) process have been examined, from a new energy perspective. A fracture mechanics-based model was presented for predicting the critical axial force causing the onset of crack propagation and delamination failure in orbital drilling. The main factors that reduce the risk of exit delamination in orbital drilling were explained in terms of the eccentric distributed axial load applied by the tool on the hole exit layer, and the shift of the

Acknowledgments

The authors acknowledge the financial support of the Natural Sciences and Engineering Research Council of Canada (NSERC), and the support of the Aerospace Manufacturing Technology Centre, Institute for Aerospace Research, National Research Council Canada (NRC), where the experiments were carried out.

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