Research On Forming Technology Of Invar Steel Formwork For Composite Integral Inlet Mold

With the rapid development of China’s aviation industry,composite parts have been widely used in the manufacturing of military and civil aircraft because of their high stiffness,high fatigue resistance,good corrosion resistance and other characteristics.With the requirements of fighter super stealth performance,supersonic cruise,super mobility and so on,higher requirements are put forward for large-scale integrated,lightweight,high-precision aviation composite parts.Composite mold is one of the key factors that directly determine the forming accuracy of composite parts.In order to reduce the curing deformation of composite parts and improve the manufacturing accuracy of composite parts,invar steel is widely used in the development of large-scale integral composite mold.At present,the domestic invar steel materials are in the development stage,and most of the invar steel materials need to be imported from abroad,which makes the raw materials of invar steel very expensive and less size specifications,especially the thickness size is small.Therefore,the forming process of invar steel mold is one of the important factors that restrict the application of high-precision composite parts,especially in the development of invar steel composite integral inlet mold.Due to the complex space shape,difficult forming and assembly of the composite integral inlet mold,it has become a major problem in the manufacturing of composite mold.Therefore,the manufacturing technology of composite integral inlet mold has seriously restricted the development of military fighters in China.In this paper,the manufacturing technology of invar steel composite integral inlet mold is studied from the perspective of composite integral inlet mold manufacturing.At the same time,the forming technology of composite integral inlet mold template is studied by using artificial neural network,genetic algorithm,finite element simulation and other methods.The main research contents of this paper are as follows:Firstly,the background and significance of this topic are briefly described,the research status of composite integral inlet mold at home and abroad is introduced,and the development of the template forming process of invar steel composite mold is introduced in detail,and the research framework and specific research content of this paper are introduced.Secondly,the common structures and materials of the existing composite integral inlet mold are summarized,and the manufacturing process requirements of the current invar steel template for composite mold and the forming technology characteristics and difficulties of the existing invar steel template are analyzed.Thirdly,the isothermal compression experiment is carried out on the invar steel,and the actual stress-strain data of the material are obtained by the experiment.The constitutive model of the invar steel is constructed through BP neural network,and the stress-strain data of the invar steel material is extended according to the model,so as to establish a reliable data foundation for the subsequent finite element simulation.Then,through the actual NC milling experiment,the response surface model of the main process parameters such as cutting depth,step length,feed speed and the two target parameters of surface roughness and machining cycle in the NC milling process of invar steel composite mold template based on the existing NC machining equipment and tools is established.The two objective functions of surface roughness and processing time are optimized by genetic algorithm,and the data are rounded and verified according to the results.A better combination of process parameters for numerical control milling of invar steel composite mold template is obtained.Finally,by importing the constitutive model parameters obtained from the stress-strain test of invar steel into the simulation software,the finite element simulation of different curved surface templates is carried out,and the die structure is optimized through the simulation results,and the hot pressing verification of the template is carried out.In the overall NC machining,a machining fixture integrating assembly,clamping and turnover is designed to realize the overall NC milling of the mold barrel,and the high-precision machining of the composite integral inlet mold is realized by using the optimization results of NC milling parameters and the optimization of machining sequence.