| Aluminum alloy plays an important role in people's livelihood and industry,because of its excellent physical and chemical properties,it is widely used in aviation manufacturing.In aircraft structure,aluminum alloy is commonly used in manufacturing frame,hatch frame,keel beam,web,skin,etc.During the aircraft assembly,a large number of holes need to be made on the aluminum alloy structure for rivet connection or bolt connection.A new technology,helical milling,has been developed in the field of hole making in aviation manufacturing.It has shown some advantages in the aspects of processing quality,processing efficiency and applicable scenarios,and has been widely concerned.In this paper,the fatigue performance,machining quality and fracture analysis of helical milling components are studied for aluminum alloy 2024,and compared with the existing drilling reaming process.The main contents of the thesis are as follows:This paper analyzes the characteristics and mechanism of helical milling and traditional twist drill drilling and reaming,builds a hole making test platform by using self-developed portable helical milling special equipment and special fixture,and verifies the accuracy of the hole making test piece of the hole making test platform,and the results show that the test platform can meet the requirements of the hole making accuracy of the test piece.The surface roughness,surface morphology,metallographic structure and microhardness of the hole wall were studied,and the influence of the two processes on the processing quality was analyzed.The fatigue properties of helical milling and reaming holes are compared.Four groups of fatigue tests of helical milling and drilling reaming holes are designed for aluminum alloy 2024 materials according to different pore size,different specimen thickness and connection mode.The fatigue tests of helical milling and drilling reaming holes are carried out under different stress levels.The test results are processed and analyzed by group comparative test analysis method and detail fatigue rated strength treatment method.The influence of the two processing processes on fatigue performance is analyzed by group comparison test method.The experimental results show that the difference between the two processes is not significant.The detail fatigue rated strength treatment method analyzes the influence of helical milling and reaming on the fatigue performance of the specimen.The fracture analysis of fatigue test piece is carried out to explore the fatigue mechanism.The fracture analysis of helical milling and drilling reaming of aluminum 2024 fatigue test piece is carried out.The influence of two processes on the origin,expansion and final fracture of fatigue crack is studied.The influence of helical milling and drilling reaming on fatigue life is explained from the perspective of fracture theory. |
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