Helical Milling of CFRP/Ti-6Al-4V Stacks with Varying Machining Parameters

The hole-making process in stack materials consisting of carbon fiber reinforced plastics （CFRP） and Ti- 6Al-4V remains a critical challenge. In this paper, an experimental study on the helical milling of CFRP/Ti-6Al-4V stacks was conducted by using two different machining strategies. Helical milling strategy Ⅰ machines both materials with identical machining parameters, while machining strategy Ⅱ uses two sets of machining parameters to machine each material. Helical milling performance was evaluated by the following indicators： tool life, cutting forces, hole quality （including diameter deviation, roundness, roughness, and hole edge quality）. The results demonstrate that heli- cal milling strategy 11 outperformed strategy I, leading to longer tool life （up to 48 holes）, smaller cutting forces and better hole quality with higher geometric accuracy and smoother surface finish （Ra≤0.58 μm for Ti-6Al-4V and Ra ≤ 0.81 μm for CFRP）, eliminating the need for reaming or de-burring.

Vector modeling of robotic helical milling hole movement and theoretical analysis on roughness of hole surface

To avoid the machine problems of excessive axial force, complex process flow and frequent tool changing during robotic drilling holes, a new hole-making technology (i.e., helical milling hole) was introduced for designing a new robotic helical milling hole system, which could further improve robotic hole-making ability in airplane digital assembly. After analysis on the characteristics of helical milling hole, advantages and limitations of two typical robotic helical milling hole systems were summarized. Then, vector model of helical milling hole movement was built on vector analysis method. Finally, surface roughness calculation formula was deduced according to the movement principle of helical milling hole, then the influence of main technological parameters on surface roughness was analyzed. Analysis shows that theoretical surface roughness of hole becomes poor with the increase of tool speed ratio and revolution radius. Meanwhile, the roughness decreases according to the increase of tool teeth number. The research contributes greatly to the construction of roughness prediction model in helical milling hole.

Effect of cooling strategies on performance and mechanism of helical milling of CFRP/Ti-6Al-4V stacks

Hole-making for Carbon Fiber Reinforced Plastics(CFRP)/Ti-6Al-4V stacks is crucial for the assembling strength of aircraft structure parts.This work carried out experimental work for helical milling(HM)of the stacks with sustainable cooling/lubrication(dry,MQL and cryogenic)conditions.Cutting forces and temperatures at the CFRP layer,Ti-6Al-4V layer and the interface of stacks were obtained by a developed measuring system.The temperatures in CFRP machining at cryogenic condition varied from-167℃to-94℃,which were much lower than those at dry and MQL conditions.The maximum temperature near the interface of stacks for the ninth hole was higher than 240℃due to heat conduction from Ti-6Al-4V layer.The hole quality,hole diameter and tool wear mechanism at different cooling/lubrication conditions were presented and discussed.MQL condition generated mainly extrusion fracture for the fibers,due to the reduced friction effect compared with dry condition.MQL was helpful to reduce the feed mark at the hole surface of Ti-6Al-4V alloy.The flank wear of cutting edge at MQL condition was better than those at dry and cryogenic conditions.Cryogenic cooling contributed to better CFRP surface with smaller delamination and hole entrance damage due to the increased resin strength and fiber brittleness.The damage near the entrance of CFRP were analyzed by the contact state of cutting edges and fibers.Additionally,hole diameters near the exit of CFPR layer were larger than other test positions.This work provided feasible processes for improving hole quality and tool life in hole-making of CFRP/Ti-6Al-4V stacks.