Carbon fiber-reinforced plastics (CFRP) have been widely applied in aerospace industry as structural components due to their excellent mechanical and physical properties. Meanwhile, the drilling process is indispensable for machining the assembly holes of CFRP. However, in the conventional drilling process of CFRP, it is prone to produce the defects including delamination, spalling, fuzzing, and tool wear. In recent years, the rotary ultrasonic-assisted drilling (RUAD) with diamond core drill, as a novel machining method, has been employed to reduce the defects. But this is few reported investigations on chip adhesion of tool surface and machined rod jamming into core drill tool during RUAD of CFRP. Therefore, this paper detailedly reported a study on removal analyses of chip and rod in RUAD of CFRP using core drill under no cooling condition for the first time. To begin with, the principle analysis on RUAD of CFRP was presented to illustrate the removal process of chip and rod. And then, the experiment analysis on RUAD of CFRP was carried out to observe the removal effects of chip and rod. The experimental results indicated that compared with the common drilling of core drill, when the vibration amplitude reached 5.0 and 7.5 µm in RUAD, the cutting ability of core drill tool was greatly enhanced, excellent removal effects of chip and rod were obtained, which obviously reduced the chip adhesion, rod jamming, rod fragmentation, thrust force, cutting temperature, and surface roughness, improved the dimensional accuracy of machined hole and rod diameter, prolonged the tool life, as well as acquired superior surface integrity of machined hole and flat fibers fracture surfaces. Furthermore, the experimental results also validated the accuracy of the principle analysis.
In aircraft assembly filed, introducing compressive residual stress by cold expansion around the fastening hole is considered as a common method to enhance hole fatigue resistance. However, the conventional cold expansion technology inevitably extends the processing cycle of fastening hole. Therefore, this study proposes a strengthening and machining integrated ultrasonic peening drilling (UPD) to solve this problem by introducing ultrasonic vibration perpendicular to the hole surface during drilling. Both the strengthening principle and dimension accuracy improvement mechanism in UPD were analyzed to better understand the cutting mechanism. The feasibility experiments of UPD of Ti-6Al-4V were conducted to evaluate surface integrity and machining accuracy. The results show that compared to conventional drilling (CD), smoother machined surface and narrower dimensional tolerance were obtained with UPD. Moreover, the subsurface plastic deformation was increased by as high as 4 times with severer deformation degree. Accordingly, the surface residual stress and the depth of circumferential residual stress in the subsurface was increased by 115.7% and 125% respectively. In addition, surface micro-hardness and subsurface hardening layer depth were also significantly increased. The results demonstrated that UPD achieved the integration of strengthening and precision-machining and could be a promising method for finish drilling of aircraft fastening holes.
Abstract In this paper, a new co‐curing process for hybrid titanium alloy foils into composite laminates was put forward. Meanwhile several pull‐out specimens were tested to obtained the bonding response between titanium alloy and composites. And the size of titanium alloy foils in double‐lap hybrid composite/titanium bolted joints were designed according to the response. Then these double‐lap bolted joints were fabricated and tested. The test results revealed that hole bearing responses of hybrid specimens were significantly better than composite specimens. Moreover, the hole bearing strengths of hybrid specimens with 33% titanium content were more 40% higher than composites specimens. And the degree of bearing strength enhancement exceeded the degree of weight gain of the specimen. Meanwhile, the hole damage morphologies of these double‐lap specimens were characterized. It could be found that the edge length had a significant effect on the failure form of the double‐lap bolted joints, and the area affected by hole failure could be significantly reduced by increasing the edge length appropriately. The structure of hybrid titanium alloy foils within a bolted joint area of composite laminates will provide a reference for improving hole bearing strength. Highlights A new co‐curing process for hybrid titanium alloy foils into composite laminates was created. Hole bearing strengths of hybrid composite/titanium bolted joints are higher than composite specimens. Increasing the edge length can effectively reduce the area of the hole failure affected zone.
Edge routing carbon fiber-reinforced plastic structures is the first and mandatory operation after demolding. In order to solve the problems such as tool clogging and mechanical damages at the machined surface in edge routing of carbon fiber-reinforced plastics by grinding tools, the rotary ultrasonic elliptical machining technique was used in edge routing carbon fiber-reinforced plastics for the first time. First, the rotary ultrasonic elliptical machining principle and an analysis of the effect of the speed ratio, R s (i.e., the ratio of the nominal cutting speed to the maximum tool vibration speed in the cutting direction), on the relative motion of the tool and workpiece were presented as the speed ratio greatly influences the rotary ultrasonic elliptical machining performance. Then, the edge routing experiments by rotary ultrasonic elliptical machining were conducted to study the machining quality at different speed ratios. The results showed that the grinding forces at R s 0.1 decreased about 19% (normal grinding force) and 17% (tangential grinding force) than that at R s 0.8 after cutting 100min. The tool diameter reduction at R s 0.1 was 34% lower than that at R s 0.8 after cutting 100min and the machined surface integrity at R s 0.1 was also modified at the end of the experiments. The experimental findings suggest that the optimal integrated surface could be achieved by applying the rotary ultrasonic elliptical machining method with the fine size diamond grinding tool and the low speed ratio.
Carbon fiber–reinforced plastics have been widely applied in aerospace industry as aircraft structural components due to their excellent mechanical and physical properties. The countersinking process of the carbon fiber–reinforced plastic hole is indispensable for the assembly of countersunk head screw. In conventional countersinking process of carbon fiber–reinforced plastics, it is prone to produce the delamination, fiber pullout, poor surface levelness and dimensional accuracy of countersunk hole. As a new technology, the rotary ultrasonic elliptical machining for countersinking of carbon fiber–reinforced plastics is employed, which is a non-traditional process that can effectively improve the surface levelness, surface integrity and machining accuracy of carbon fiber–reinforced plastic countersunk hole. This article reported a feasibility study on the rotary ultrasonic elliptical machining for countersinking of carbon fiber–reinforced plastics without coolant for the first time. The processing principle of rotary ultrasonic elliptical machining for countersinking was illustrated according to the countersinking models and the equations of motion locus. Based on the principle analysis, the surface levelness, tool blades’ path and countersunk hole surface morphology in rotary ultrasonic elliptical machining of the separated and unseparated types were analyzed compared to that in conventional countersinking. In addition, the rotary ultrasonic elliptical vibration transducer was designed and fabricated, as well as the experimental platform was set up. The experimental results demonstrated that the rotary ultrasonic elliptical machining achieved much better results than that in conventional countersinking, such as lower thrust force, torque, cutting temperature, better surface levelness, hole dimensional accuracy, surface integrity and chip-removal effect. The experimental results also verified the feasibility of rotary ultrasonic elliptical machining for countersinking of carbon fiber–reinforced plastics.
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