Surface integrity in material removal processes: Recent advances

A review of mechanical drilling for composite laminates

Carbon fiber reinforced plastics/polymers (CFRPs) offer excellent mechanical properties that lead to enhanced functional performance and, in turn, wide applications in numerous industrial fields. Post machining of CFRPs is an essential procedure that assures that the manufactured components meet their dimensional tolerances, surface quality and other functional requirements, which is currently considered an extremely difficult process due to the highly nonlinear, inhomogeneous, and abrasive nature of CFRPs. In this paper, a comprehensive literature review on machining of CFRPs is given with a focus on five main issues including conventional and unconventional hybrid processes for CFRP machining, cutting theories and thermal/mechanical response studies, numerical simulations, tool performance and tooling techniques, and economic impacts of CFRP machining. Given the similarities in the experimental and theoretical studies related to the machining of glass fiber reinforced polymers (GFRPs) and other FRPs parallel insights are drawn to CFRP machining to offer additional understanding of on-going and promising attempts in CFRP machining.

Machining of Carbon Fiber Reinforced Plastics/Polymers: A Literature Review

https://hal.archives-ouvertes.fr/hal-02417879/document

Recent advances in drilling hybrid FRP/Ti composite: A state-of-the-art review

The use of material stacks comprising titanium, carbon fibre reinforced plastics (CFRPs) and aluminium is expanding for structural aerospace applications, especially where high mechanical loads exist such as for aircraft wing and tail-plane components. Here, the production of bolt/fixation holes is essential to the manufacturing process in order to facilitate part assembly. The paper outlines an analysis of hole quality/integrity following drilling of titanium/CFRP/aluminium stacks under flood cutting fluid and spray mist environments. Uncoated and coated (CVD diamond and hardmetal) tungsten carbide drill performance is evaluated against key response measures including hole size, out of roundness, cylindricity, burr height, hole edge quality, average surface roughness (Ra), microhardness (of the metallic elements) and swarf morphology. Burr height (up to 0.5 mm) was observed to be greater at the hole exit (aluminium) compared to hole entry (titanium) while delamination was significantly reduced when machining CFRP in the stack configuration as opposed to a standalone arrangement. Spiral shaped continuous aluminium swarf was prevalent while both short and long helical chips were found with the titanium material when cutting wet. In contrast, the CFRP layer typically produced dusty black composite particles suspended in the soluble oil of the coolant emulsion.

Hole quality assessment following drilling of metallic-composite stacks

Following a review on the machinability of CFRP composites and multilayer stacks typically comprising metallic and composite material elements, the paper details experimental results when drilling 30 mm thick titanium/CFRP/aluminium workpiece stacks. Testing utilised a modified fractional factorial design based on an L18 Taguchi orthogonal array. This comprised four factors, three of which were at three levels and one at two levels and involved tool coating, cutting speed, feed rate and machining environment. Tools evaluated involved hardmetal and diamond coated carbide in addition to uncoated tungsten carbide drills. Response variables were principally tool wear and cutting force/torque with an end of test criteria of 300m flank wear. Peeling of the CVD diamond coating occurred within the first several holes drilled however this was not a limiting factor in terms of tool life. Principal damage occurred when drilling through the titanium (Ti-6Al-4V) rather than the aluminium (Al 7050) or CFRP (unidirectional “UD” laminates) sections. Best tool life/performance (310 drilled holes) was obtained with the more conventional uncoated carbide drills at lower cutting speed and feed rate. Typically thrust forces increased from 300 N for the first hole to ~2200 N for last hole drilled while torque values were generally below 600 N.cm for worn tools.

/pdf/drilling-of-titanium-cfrp-aluminium-stacks-3tls0m04fu.pdf

Stuart Dawson

Papers

Hole quality assessment following drilling of metallic-composite stacks

Drilling of titanium/CFRP/aluminium stacks