Shijie Ba

Machining deformation is a key bottleneck that restricts the improvement of manufacturing accuracy of aviation thin-walled structural components, such as frames, beams, and wall panels. The initial residual stress of the workblank and the cutting load are the direct factors leading to machining deformation. Based on the initial residual stress measurement and the milling force test, a finite element prediction model for milling deformation of frame-type thin-walled parts with integrated consideration of initial residual stress and the milling force was established and experimentally verified in this study. Then, the influence of milling process factors, such as the frame processing sequence (FPS), the cutting path, and the single frame one-time removal depth (SFORD), on the milling deformation of frame-type parts was studied. The results showed that the established prediction model had high reliability and the prediction accuracy was improved by 6.7% compared with that when only considering the initial residual stress. A smaller machining deformation can be achieved through the use of the FPS to prioritize the width, direction, and symmetrical milling, as well as the inner loop cutting path, and the smaller SFORD. This study can provide a technical reference for the prediction and control of milling deformation of aviation thin-walled structural parts, especially frame-type thin-walled parts.

In order to improve the anti-friction property of common mineral oil and develop a high-performance lubricant, MoS₂ and SiO₂ nano-additives were individually dispersed into the 350SN mineral oil at various weight percentages to prepare nanolubricants. Then, the viscosity, wettability, and tribological properties of the nanolubricants were measured and analyzed with a rotary viscometer, a contact angle measuring instrument, and a friction tester. Finally, the action mechanism of two nano-additives was explained based on the energy spectrum test results of the abrasion surface. The results show that MoS₂ and SiO₂ nano-additives could improve the viscosity of the base fluid and change its wettability, giving nanolubricants better anti-friction performance than the base fluid. Due to the difference in physical properties, SiO₂ and MoS₂ nanolubricants presented different friction reduction rules with the increase in nano-additive percentage. Under experimental conditions, SiO₂ nanolubricants showed better anti-friction effects than MoS₂ nanolubricants. When the SiO₂ percentage was 10 wt% and 15 wt%, the maximum friction coefficient was reduced to 0.06, which was about 1/3 of that with the base fluid. In this case, the abrasion surface quality was significantly improved, and the abrasion trace size was about half that of the base fluid. The energy spectrum test results show that the action mechanism of the MoS₂ nano-additive is the adsorption film effect and mending effect of nanoparticles, while the main action mechanism of the SiO₂ nano-additive should be the polishing effect and rolling effect of nanoparticles.