Research On Thermoplastic Towpreg Variable Angle Placement And Trajectory Planning

Automated fiber placement technology, as one of the extreme manufacturingtechnologies for large or extra large composite components with complex surfaceshapes, has been widely used in the field of aerospace vehicles. Automated fiberplacement technology uses thermoplastic towpreg as raw material and in-situconsolidation technology as curing method. Compared with the autoclave curingtechnology, it can get rid of the restriction of the autoclave on the demension of thecomposite components. It can also improve the production efficiency and reduce thecost effectively. Thus, the thermoplastic towpreg automated fiber placement hasbecome one of the key technologies for manufacturing the complex surface shapecomposite components and attracted more and more attention. To fabricate thequalified composite components using the automated fiber placement technique, notonly the thermoplastic towpreg and the fiber placement equipment are needed, butalso the thermoplastic towpreg placment process, the trajectory planning algorithm,the post processing algorithm of fiber placement device and the mechanicalproperties of the laminations need to be studied.The combination of thermoplastic towpreg and in-situ consolidation technologyin automated fiber placement process can achieve the preforming and the finalforming of the composite components simultaneously, but the parameters for theplacement process are quite critical. Therefore, the research on the automated fiberplacement process would be beneficial for choosing placement parameters, andensure the design specifications of the composite components. In this paper, theheating process, the cooling process and the degree of intimate contact in automatedfiber placement are studied including the selection of heat sources and proper heattemperature according to the physical properties of the thermoplastictowpreg(APC-2); the establishment of the heat transfer model and boundaryconditions of different placement areas which are divided on the basis ofmanufacturing process means preheating area, air cooling area Ⅰ, main heating area,air cooling area Ⅱ and special cooling area; based on crystallization kinetics theory,the relationship of crystallization temperature and relative crystallization rate isdeduced; the surface roughness evaluation parameters Ra and RSm of the towpregsare introduced to the model of the intimate contact and the relationship of theplacement pressure, pressure time, the surface roughness and the intimate contact isobtained. For the specific computing example, the methods of determining theplacement parameters are given, the placement parameters are calculated by Matlabor Ansys software, the reasonable placement parameters are obtained, and the placement parameters are validated by experiment.Overlap and gap of adjacent towpreg would, on one hand, affect the shapeaccuracy of composite components, and increase the operation of cut and re-send;on the other hand, have a great impact on the overall mechanical properties.Therefore, the main purpose of the trajectory planning algorithm for the automaticfiber placement is to design reasonable placement paths in order to reduce oreliminate the gap or overlap of adjacent towpregs. To avoid the cut and re-sendoperations except for the end faces, a variable angle trajectory planning algorithm isbrought out. The variable angle trajectory planning algorithm has been applied tothree typical components including the conical shell component, thenon-developable rotary shell component and the non-developable variablecross-section connection component. All the above mentioned examples verified thevariable angle trajectory planning algorithm, the detailed implementation steps andthe implementability analysis are also included.The post processing technology of automated fiber placement device is totransfer the coordinates and direction data of trace points obtained from thetrajectory planning algorithm into the data format which can be recognized by eachmotion axis of fiber placement device. Automated fiber placement device isconsisted of the arm part and the spindle part. A kinematic model was established inthe post processing research of the arm part which considered the rotation degree ofthe roller on the placement head. Compared with the model which simplified theroller as a fixed point on the placement head, this one better matches the acutal fiberplacement process and is more accurate. The model introduces a redundant degreeof freedom, thus the minimum length of the arm part can be considered as anobjective function to establish an optimization problem. Under this consideration,the inverse kinematic problem can be solved. The constant and variable anglepost-processing algorithms of spindle are studied, the applications, the advantagesand disadvantages of these two methods are given. The variable angle trajectoryplanning algorithm and the post processing algorithm are also verified via thefabrication of a cone shell.Compared with the traditional fixed-angle laminations, the variable anglecomposite laminations are featured with flexible designs and can fully take theadvantages of the anisotropic composite materials. By changing the fiber placingangle of each position in the placing path, the stress distribution of the laminationscan be changed. This would be helpful to avoid the system resonance by changingthe inherent frequency. Taking the conical shells with8different initial placementangles to study, the static analysis, the modal analysis and the buckling analysis areconducted. The research contents include the method for establishing the finiteelement model of composite variable angle laminations and the change rule of stress, strain, modal and buckling strength of laminations with initial placement angle. Thestudy bases on the finite element model of the laminations, derivation of anisotropicmaterial property theories, shell equilibrium equations, geometric equations andphysics equations, introduction of the finite element modal analysis theory and thelinear buckling analysis theory. Then the above-mentioned models are solved by useof ABAQUS, and the results are analyzed.