The effect of drilling parameters, cooling technology, and fiber orientation on hole perpendicularity error in fiber metal laminates

Abstract

Conventional twist drilling is a widely used machining process for creating holes in aerospace and automobile structures. Drilling at room temperature can sometime affect the quality of machined holes due to increased thermal effects on the workpiece. Thermal effects can be a cumbersome when machining composites and fiber metal laminates due to their different thermal expansion coefficients, which may introduce additional stress in the structure. Thermal machining effects can be minimized using coolants supplied either directly or indirectly to the cutting tool-workpiece interaction zone, to remove away part of the generated heat. The use of coolants adds extra costs for handling, disposal, and environmental impact. Therefore, environmentally friendly cooling technologies are replacing conventional cooling methods to reduce costs and impact on the environment. In addition, the selection of machining parameters has great influence on the hole quality. This paper investigates the impact of drilling parameters and two modern cooling technologies namely cryogenic liquid nitrogen and minimum quantity lubrication on the hole perpendicularity error of fiber metal laminates commercially known as GLARE® (Glass Laminate Aluminum Reinforced Epoxy). It was also found that applying cryogenic liquid nitrogen or minimum quantity lubrication does not lead to an improvement in hole perpendicularity error in GLARE® laminates.

The effect of cutting tool coating on the form and dimensional errors of machined holes in GLARE® fibre metal laminates

“…Drilling is a conventional machining process for producing round holes of different sizes and depths in aeronautical structures. The number of holes can vary from 300,000 up to three million in commercial aircraft [1][2][3][4]. At the same time, poor hole quality is responsible for around 60% of all parts rejection [1,5,6].…”

“…At the same time, poor hole quality is responsible for around 60% of all parts rejection [1,5,6]. Poorly machined holes usually lead to costly corrective manufacturing measures and increase the required inspection time [3,4,7]. Holes are produced to allow for fastener installation for assembly purposes.…”

“…Drilling and milling operations are applied to GLARE® structures for assembly and riveting purposes [9,21]. Experimental machining studies on GLARE® laminates have been increasing in the last 20 years [2,4,6,9,[21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]. Previous studies on drilling GLARE® studied the impact of machining parameters, drill geometry, workpiece thickness, fibre orientation and cooling strategy on several hole quality parameters [2-4, 6, 9, 21-40].…”

“…Previous studies on drilling GLARE® studied the impact of machining parameters, drill geometry, workpiece thickness, fibre orientation and cooling strategy on several hole quality parameters [2-4, 6, 9, 21-40]. A smaller number of studies also investigated the influence of drill geometry and coating on the generated drilling forces and hole quality [4,26,[40][41][42]. Reported findings suggest that carbide drills perform better than uncoated and high-speed steel drills due to the abrasive glass fibre layers [9,21,41].…”

“…In comparison with more traditional engineering materials, only a few studies looked into the impact of drilling parameters, drill coating and geometry on specific hole quality metrics, i.e. hole size, circularity and perpendicularity, when drilling FMLs [2][3][4][22][23][24]. For these studies, the measured hole parameters and their values are summarised in Table 1.…”