Fundamental Research On The Helical Milling Process Of Holes For Aero Laminated Structure Materials

Laminated materials with carbon fiber reinforced plastics(i.e. CFRP) and lightweight alloy(e.g. Aluminum alloy and titanium alloy) are gradually being used in modern aircraft. With the discrepancy of machinability in these materials, the manufacture quality and efficiency of assembly hole making has been becoming a prominent problem which strictly influences assembly cycle of entire machine. As a new hole-making process, helical milling shows distinct advantage in hard cutting material. However, researches on helical milling process of hole and its machining equipment thus far are still in the beginning stages. To meet the urgent requirements of assembly hole making from domestic aircraft manufacturing industry, we focus on machining large-scale holes with deep width and big dimension in CFRP and lightweight alloy stacks in this paper. Methods of theoretical analysis, numerical simulation and cutting test are employed to carry out fundamental research on helical milling equipment design, milling force analysis, defect restraint,process optimization, etc. The main research works have been done as follows:(1)A new automatic hole-making system for connecting a certain type of aircraft wing-fuselage was first designed. Spindle normal vector posture alignment method was then put forward. Based on the processing concept of replacing drilling with milling, innovative design of helical milling equipment was made, thus the difficult problem to adopt conventional automatic drilling system for connecting aircraft wing-fuselage was solved.(2)Studies was made on cutting forces in helical milling hole. According to the characters of cutting process and milling force wave curve in helical milling of hole for 7075, CFRP and Ti6Al4 V, mechanical property was analyzed, and deficiencies of present mechanical models were pointed out. Further, the influence of milling force component on hole quality was qualitatively analyzed. Upon processing characteristics in helical milling hole, three types of cutting tests as making one hole with one tool, making one hole with different tools and making different holes with one tool were conducted to study the effect of cutting parameters on milling forces under different conditions.(3)Defects formation mechanism was studied in helical milling process of hole for aero laminated structure materials CFRP/Ti6Al4 V. Comparison between helical milling hole and push drilling in CFRP, Ti6Al4 V, etc. was made to confirm the quality advantage in helical milling holes. Meanwhile, new defect in helical milling hole was found in this study. To solve the problem, cutting test and theoretical analysis were done to reveal the influence of cutting parameters on hole defect and uncover the formation reasons of typical defect. Finally, suppression strategy in helical milling hole was put forward.(4)Helical milling process of hole for CFRP/Ti6Al4 V was carefully studied when machining with coarse pitch. Then idea of coarse pitch helical milling hole was proposed. Based on the comparison between coarse pitch helical milling hole and push drilling, advantages and problems of coarse pitch helical milling hole for laminated structure materials were analyzed. To solve the problems in coarse pitch helical milling hole, the process optimization strategy was proposed to improve machining quality, and also verified by experimental test.