| Because of its low density, high specific strength, high specific modulus and other excellent properties, carbon fiber composite has been widely used in aviation and aerospace industry. However, as a typical hard-to-machine material, its obvious anisotropic mechanical property makes it vulnerable to many machining induced defects, like delamination, avulsion and burr. In the sphere of digital drilling equipments for composite components, there is a clear gap between the domestic and the foreign.The research of this paper comes from a given firm’s problems of low machining efficiency and low precision in the machining of a carbon fiber composite TJB structure with a single-surface structure. In order to solve these problems, this paper conducted research on the NC drilling technique and the drilling equipment for carbon fiber composite TJB structure, based on related research from the National High Technology Research, Development Program of China and the National Natural Science Foundation of China Project.Firstly, the structural characteristics of the carbon fiber composite TJB structure were analyzed and the drilling processes on its single-surface and flat structure were studied in detail. Also, drilling parameters were optimized through experiments, from which the proper tool and the tool’s durability were determined. The random position error of I-beams from the co-curing process of composite TJB structure and the installation position error on the machine are hard to be avoided. To realize the process of NC drilling, on-line inspection of structure’s feature points’position error was proposed. Also existing NC programs should be perfected according to related requirements. To carry on the research, the principle for the measurement of feature points’position error was proposed, the numerical error model was established and the strategy for amending the NC programs was also presented. Rotating workpiece point position measurement was proposed for normal direction drilling of TJB structure.2-points fitting method was proposed to realize the measurement of the normal direction of the drilling hole on curves. This work provides a solid foundation for the NC machining of TJB structure.Based on the previous work, main parameters of the NC machine for the drilling of composite TJB structure were determined. The general structure of the machine and the detailed structure of TJB dedicated double-position oscillating fixture were determined. Kinematic analysis, the static, modal and harmonic response of TJB double-position fixture were carried out. The results showed that the structure has enough static and dynamic stiffness, which meets the requirement for proposed drilling accuracy. Equipped with the Marposs RMP60online measurement system, the designed machine can measure the random position error and the position error during installation and has them corrected. To induce dust pollution during drilling, a servo chip collecting device with the function of locally pressing workpiece was designed. Moreover, the related parameters were optimized.Position precision and the motion precision of the TJB NC drilling machine were measured, which showed a well designed machine with great precision. Drilling experiments on the flat-surface and single-surface curve were carried out to verify the machining capacity of TJB NC drilling machine. With the Marposs RMP60T25probe and the self-developed software for online amending the positioning error and random position error of I-beams, the composite TJB structure was automatically machined with the NC machine.The achievements of the research in this paper met the need for NC drilling on the composite TJB structure from a given firm. Moreover, it provided a successful example of high-quality, high-efficiency and NC machining of large carbon fiber composite structures. |
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