| Taking large commercial aircraft as application background,the research on process and mechanical properties of automated dry fiber placement-liquid forming composite was conducted in this paper in order to realize low-cost manufacturing of large aircraft's structural components.The dry fiber prepregs manufactured by method of powder mud-hot press was researched about relationship between process parameters with binder content,binder distribution,macroscopic dimensional stability,volatile content and so on.Automatic fiber placement technology was successfully used to make CF/PLA preform used in liquid forming process.To determine the liquid forming process characteristics of E51/D230 resin system,the relationship between viscosity and temperature of E51/D230 resin system was measured by method of rotational viscosity and curing process was obtained by differential scanning calorimetry?DSC?.The effects of liquid forming process parameters such as binder content,injection temperature and injection time on the impregnation quality of CF/PLA preform were studied by single factor experiment.Orthogonal experiment was designed to research the effects of process parameters and optimized liquid forming process of CF/PLA preform.Based on above research,the inter-laminar shear and bending mechanical properties of the dry fiber-liquid forming process were measured and analyzed using ASTM standards.Then,the mechanical properties of molding process were compared to evaluate the mechanical properties level of automated dry fiber placement-liquid forming process.?1?In terms of preform's binder,the PLA was more suitable than PA66 in preparation of prepreg by powder mud-hot press,as the particle size and binder's melting-temperature was negatively correlated.The manufacturing process of CF/PLA prepreg was as follows:the particle size of the powder 13?m;the solvent evaporating temperature 85?,the resin binder melting temperature 120?,the hot pressing temperature 70?;the feeding speed 6mm/s.The average binder-content of CF/PLA prepreg was 10.12%,average width was 5.5mm,volatile-content was 1.2%,and the deviations were all small.The problems of prepreg cutting and feeding inaccurate were solved by adjusting the parameters of automatic fiber-placement machine,and then CF/PLA preform was successfully prepared used process:the laying temperature 120?,laying pressure 0.1MPa;laying speed 60mm/s.?2?Because the interaction between temperature?physical reaction?and chemical reaction?resin cross-linking reaction?was unbalanced,the viscosity of E51/230 resin system decreased firstly and then increased with increasing temperature,so the liquid forming process adapted to the temperature range of 25?55?.The curing temperature of E51/D230 resin system Ti?0?=75.45?,Tp?0?=104.71?,Tt?0?=155.55?was measured to determine curing process:75?in 0.5h,110?in 1h,and the correctness of the curing process was verified by measuring curing degree of resin system.Single factor experiments showed that:binder in preform is crucial in keeping shape of preform,but higher content will impede the flow of resin;increasing injection temperature is conducive to the flow of resin,but higher temperature will lead to cross-linking reaction of the resin caused serious defects;injection-time is correlated positively with impregnation quality.The results of orthogonal test showed that the most influential factor is injection temperature,and the least is injection time,and the optimum liquid forming process of CF/PLA is:binder content 8%,injection temperature 45?.?3?The inter-laminar shear strength of dry fiber placement-liquid forming components is46.49MPa as discrete coefficient only 3.93%which is stable and has high anti-delamination ability.The bending strength of dry fiber-liquid forming components was 718.11MPa as bending modulus146.78GPa which shows typical elastic deformation behavior and high resistance to bending deformation,but the discrete coefficient was 9.26%and 6.39%which lacks stability of bending performance. |
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