Research On Automated Fiber Placement Technology Of Composite Wing Spar Based On Geodesic Algorithm

Wing spars are the main load-carrying structures in aircraft wings. High requirementsin lay-up accuracy and quality are necessary during the producing process especially for thecomposite wing spars by using Automated Fiber Placement (AFP) technology, and highmechanical properties of the spars then can be obtained. The main research purpose of thisdissertation is to improve the lay-up accuracy and quality in AFP process to solve wrinkling andbuckling problems on the radius corners of the composite spars.When planning the path with fixed angle algorithm and rotating spar mandrel during AFPprocess, obvious wrinkling and buckling were appeared on the radius corners of spars whichsignificantly reduce spar mechanical properties. Based on figuring out three reasons why theyappeared, finite element analysis method was used to calculate the lay-up error which was caused byrotating spar mandrel. It then analyzed the movement characteristics of the AFP process whenproducing components with radius corners. By comparing the advantages and disadvantages ofRotating/Fixed mandrel, it provides reference foundation to establish the evaluation criteria ofchoosing mould in AFP process.The lateral buckling radius of the prepreg was deduced by setting up the lateral bending model,and then analyzed how temperature, pressure, velocity and prepreg tack affect on it during the AFPprocess. Laid down a series of prepreg arcs with different radius values on the aluminum mold, for thebuckled prepreg arc of radius value R1000mm, the wrinkles of prepreg were decreased by increaseingplacement temperature and pressure or decreasing velocity which means it was beneficial to thelateral bending of the prepreg in these conditions. Put a prepreg layup on the mold by AFP machine inadvance and then laid down prepreg arcs with different radius values, the buckling arc was appear onthe value of R700mm, it means that, high prepreg tack has significantly improved its lateral bendingcapacity under the same placement condition.Based on the structure and stress characteristics of spar, planning the trajectory path withgeodesic algorithm can decrease lateral bending of prepreg, eliminate wrinkling and buckling, andthen improve the lay-up quality. The adjacent geodesic trajectories of the non-developable sparsurface were overlapping/gapping which were too small on spar flanges and could not cut or feed bythe machine. Fibre steering trajectory design method was adopted to balance out them. Whenoverlapping/gapping were larger than the lateral bending amount of prepreg, dividing spar into several shorter sections and making overlapping/gapping emerge at the border of shorter sections.Then they can be cut or feed automatically by the machine.Finally, the software of above algorithms are developed by Visual C++6.0programming, andpost processing software was used to obtain trajectory points information and NC machining code of0°,90°and±45°layers. Practical placement was applied to verify the algorithm by fixed the sparmould, and the experiment trials demonstrate the increasing of deflection angle can indeed release thestrain of the prepreg tows and the improvement of the adjustment algorithm.