Optimization Of Multi-point Flexible Gas-assisted Hot Pressing Process Of Fiber Composite Surfaces

Fiber-reinforced composites are widely used in aerospace,rail transit,ship,building and protective equipment due to the excellent mechanical properties and lightweight properties.Due to the need of small batches and personalized production,the demand for fiber-reinforced composite surface components is also increasing.The traditional fiber-reinforced composite surface components are mainly formed by solid molds.Because fiber-reinforced composites undergo complex temperature and pressure changes in the process of forming,resulting in curing deformation,the desired shape can not be obtained by using solid molds manufactured according to the target profile.In the process of debugging the mold in the later stage,it is necessary to repeatedly adjust the shape and manufacture the solid mold after a long period of experimentation,resulting in a lot of waste of manpower and material resources.Using the flexible multi-point mold,the cycle of forming surface adjustment can be effectively shortened,and the purpose of multi-use of one mold can be realized.Since the principle of multi-point molding is to discretize the continuous surface,defects such as wrinkling,indentation and curing deformation will occur during the molding process,which seriously affects the molding quality and limits its application in engineering.In view of the above problems,the main research contents and conclusions of this thesis are summarized as follows:1.Indentation defect suppression of fiber-reinforced composite surfaces by multi-point gas-assisted moldingIndentation is a common defect in the multi-point molding process.The causes and forms of indentation were introduced,the influence of forming temperature and forming pressure on indentation defects was discussed through experiments.The microscopic mechanism of indentation in multi-point molding was studied,and the severity of indentation was quantified.The experimental results show that:The influence of forming pressure on indentation defects is higher than the forming temperature.The greater the forming pressure,the more serious the indentation defect.With the increase of forming temperature,the indentation will first decrease and then increase.The optimal forming temperature is 120℃ and the forming pressure is 5KPa.The indentation can be effectively inhibited by adding 2 mm silicone pad between the sample and the multi-point mold.Compared with the sample without silicone pad,the intersection profile area of the front and back diagonal lines was reduced from 180.51 mm~2 to 100.6 mm~2.2.Control of curing deformation of fiber-reinforced composite surfaces by multi-point gas-assisted moldingAfter adjusting the process parameters to suppress the indentation,the curing deformation generated during the molding process was studied.Firstly,the reasons of variations in molding accuracy of fiber-reinforced composites were analyzed,and the effects of forming temperature,forming pressure and silicone pad thickness on the curing deforming were discussed.The results show that the higher the forming temperature,the smaller the forming pressure,the smaller the thickness of the silicone pad,and the smaller the radius of curvature of the sample.Then,the response surface method experiment was designed for the design parameters(the number of layers and the forming radius).The fitting model was constructed by the two-factor center composite method.The results show that the influence order of the design parameters on the curing deformation angle of multi-point forming is as follows:forming radius>number of laying layers,as the number of molding layers increases and the radius of the formed surface increases,the curing deformation angle increases.Finally,based on the experimental data,the curing deformation angle calculation model was established,and the effectiveness of the prediction model was verified by experiments.The curing deformation angle of spherical sample with 9 layers and radius of 270 mm was-2.856°before adjustment,and the curing deformation angle after adjustment was0.157°.The 3D comparative standard deviation of the adjusted sample was reduced by 38.85%compared with the unadjusted sample.The precise molding of fiber-reinforced composite parts with smooth surface was realized.