Dedicated Cutting Tool Design And Research On Hole Quality For Orbital Drilling Of Aeronautical Difficult-to-cut Materials

The orbital drilling, combined with the industrial robot, can achieve the hole-making process at high efficiency under dry cutting condition. This noval technology reflected the significant advantages in improving the hole quality and reducing the production costs, compared to the traditional drilling. However, for aeronautical difficult-to-machine materials, due to the poor cutting performance induced by the special physical and chemical properties, which make it challenging to improve the hole-making quality,and to avoid the defects at exit as well as severe tool wear. Therefore, in this dissertation,a kind of the chips-splitting strcture of the dedicated cutting tool based on the kinematic characteristics of orbital drilling is designed. The mechanical theory of the hole-machining process is deeply analyzed and the experimental studies are conducted systematically aimed at the titanium alloy(TC4-DT), carbon fiber reinforced plastic(CFRP) and CFRP/Ti stacks.Firstly,the research status of both orbital drilling technology and cutting tool is introduced. Aiming at aeronautical difficult-to-cut materials, the quality problems produced in conventional drilling process are analyzed, and the advantages of orbital drilling process are proposed. Based on the analysis of orbital drilling kinematics, the equations of motion are established, and the key kinematic vectors are described mathematically. The simulation analysis of motion trajectory is achieved by using the MATLAB software so that the characteristics of cutting range and its relationship with the ratio of the spindle speed to the orbital rotation speed as well as the bore diameter to the tool diameter are determined.The design method of dedicated cutting tool for orbital drilling process is proposed.The structural features of the front cutting edges with cutting segments, helical peripheral cutting edges and the cooling holes on the back of teeth are introduced. The schemes of the simulation design for the chip-splitting structure of the front cutting edges with segments, the same structure of four teeth as well as two symmetrical teeth are given special elaboration. Based on the simulated undeformed chip geometry and the surface topography, the optimization of tool structure is realized. Then the mathematical description is given. According to the characteristics of the front cutting edges of optimized cutting tool and the motion trajectory of the key cutting points on them, and the impact of the ratio of the spindle speed to the orbital rotation speed (R1)as well as the bore diameter to the tool diameter (R2) on the trajectory, the effect of cutting parameters on the simulation results of undeformed chips is further studied. By combining with the chips geometry, cutting force, hole-making quality and tool wear produced under the different machining parameters, the chip-splitting performance of the cutter is verified.Aiming at the dedicated cutting tool of orbital drilling process, a nonlinear cutting force model is established. A coordinate system is constructed to describe the amount of cutting. The undeformed chip thickness and the width of cut, generated by different teeth in a half spindle rotation period at the steady machining stage,are given the important mathematical description and the numerical calculation. The average force model is adopted to conduct the calibration experiment of the cutting force coefficients.The linear fitting and calculations of these coefficients are carried out. The cutting force model is verified by conducting the orbital drilling experiment for TC4-DT. The change trend of the cutting force under different machining parameters is analyzed deeply.The systematic experimental study on the aeronautical difficult-to-cut materials(TC4-DT, CFRP and CFRP/Ti stacks) is conducted in orbital drilling process based on the dedicated cutting tool. By deeply analyzing the feature of chip geometry, the change trend of cutting force and the variable law of cutting quality under the different machining parameters, the parameter optimizations of the single titanium alloy layer and CFRP plate are achieved during orbital drilling process. The effect of tool wear on the cutting force and hole-making quality is further illustrated. The machining accuracy of CFRP/Ti stacks in orbital drilling process is given significant research. The variable rules of the average hole diameter and the roundness at the entrance and exit of both the CFRP layer and the Ti layer are elaborated in detail. Furthermore, the advantage of the chip-splitting performance of dedicated cutting tool is verified.Finally, the main contents and the innovations elaborated in this dissertation are summarized, besides the future research is also prospected.