Laser irradiation de-coating is a promising new approach for effective coating removal of cutting tools. While this method has demonstrated feasibility for conventional coatings, its use and efficacy on lubricant coating is however yet to be ascertained. This paper reports on the results of excimer laser de-coating of hard DLC from DLC-coated tungsten carbide (WC) substrates. A range of fluence and pulse was studied to evaluate the effectiveness of the de-coating process. Result shows that laser parameters of 7 J/cm2 fluence, 400 pulse and 25 Hz frequency were found to yield optimum results in removing hard DLC coating of 3.2 μm thickness from WC substrates. The experimental work indicated successful laser de-coating of hard DLC coating without noticeable damage to the WC substrate. The capability of this new de-coating process is significant in the aerospace industry as it could facilitate re-grinding and recoating of drills thereby improving economics of manufacturing. The process windows could also be applied in the removal of DLC from other cutting tools and applications.
Aluminium alloy stack materials offer good strength-to-weight ratio and are used for high strength airframe structures. For the panels to be joined, numerous holes have to be drilled and due to structure size mobile drilling heads are used. The drilling process releases lubricant oil which becomes airborne or collects on the shop-floor and presents a health and safety hazard. Avoiding this oil release is therefore a major driver for developing dry drilling processes. However, drilling aluminium alloys in the absence of cutting fluids is a challenging task due to its tendency to adhere to the cutting tool, and the high thermal conductivity of the workpiece. Owing to their low coefficient of friction, carbon-based coatings are an option to improve the machinability of aluminium alloys. This paper presents an industrial collaboration study on the performance of carbon-based coatings in dry drilling aluminium alloy 2024 and 7150 stacks. CVD Diamond, a hard DLC, Doped MoS2 and doped amorphous carbon (Doped a-C) were evaluated in comparison with an uncoated WC drills. Coating performance was assessed in terms of tool wear, hole diameter, and surface roughness. The results revealed that CVD diamond coated drills outperformed other coatings in terms of tool wear and hole quality. The coating enabled lower aluminium pick-up on the drills as well as minimised variations in diameter deviation and hole surface roughness. The work shows the capability for dry drilling of stacked aluminium alloys and hence eliminating the health and safety risk associated with use of oil in mobile drilling heads.
Aside from their remarkable lightness, high strength and corrosion resistance, aluminium alloys have dominated aircraft manufacturing for decades. The combination of aluminium alloys 2024 and 7150 is widely used in the fabrication of airframe structures. Numerous holes must be drilled through the materials in order for them to be connected. Due to structure size and use of mobile drilling machines, lubricant oil is released during the drilling operation and either becomes airborne or accumulates on the floor. The primary motivation for dry drilling development is to avoid this oil discharge. A significant disadvantage of the drilling process for aluminium alloys is the workpiece’s proclivity to stick to the cutting tool, especially when temperatures are high. This research investigated the selection of cutting conditions that enable dry drilling of stack aluminium panels. The selection of cutting parameters for experiment use was made based on the assessment of literature pertaining to drilling with carbide cutting tools. Apart from literature, the assessment of cutting parameters also took into consideration existing practices in Airbus UK. Results indicated that optimum cutting performance was achieved by drilling at higher feedrates and lower interaction time compared to existing fluid based processes. In addition, this paper outlines the aspects of energy and cutting forces in current cutting processes as well as focuses on determining optimum conditions that minimise energy input.
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