Influence Of Multi-interval Hot Pressing On Forming Quality Of Pultrusion Parts

Stiffened panel construction strengthened by purlins is widely used in modern aviation components.The purlins with fixed section shape are mostly formed by hot pressing tank and Advanced pultrusion,Hot pressing tank forming is the standard process for curing composite materials,but the length of the part is limited by the size of the tank and the cost of the mold is high.Advanced pultrusion technology uses prepreg as raw material,realizing the mechanical property designability of the parts through the combination of different layers.It has unique advantages in controlling production cost and flexibility.This topic selects X850 prepreg for research,and analyzes the difference between its typical Hot pressing tank forming process and advanced pultrusion process.Studying the influence trend of Multi-interval temperature system and pressure system on the forming quality of Advanced pultrusion parts.(1)Studying on curing kinetics of X850 prepreg to determine the technology parameters of each interval,the temperature of preservation interval keeps at 110°C for 30 minutes,The temperature of pretreatment interval keeps at 160°C and Curing interval temperature keeps at 180°C.In order to inhibit the formation and growth of pores,the pressure in the pretreatment interval sets as 0.3Mpa,and the curing interval pressure ranges from 0.6 MPa to 1 MPa.By reducing the liquidity of resin at pretreatment interval to eliminate the stepper grain defects,specific technology conditions is that the pretreatment interval is maintained at 160°C for 30 min.(2)Taking the surface and internal forming quality of the pultrusion parts as the characterization,the optimal scheme in the orthogonal test is preferred.In this scheme,the bending strength of the obtained parts is 968.52 MPa,the bending modulus is 65.58 GPa,the interlayer shear strength is 45.18 MPa and the porosity is 1.14%.The pores are mainly present in the resin-rich region between the layers,With the change of pressure and pressure timing,their shape,size and content all change,the existence of interlayer pores leads to the decrease of comprehensive mechanical properties of Pultrusion parts.(3)The glass transition temperature Tg has a quantitative relationship with the post-cure temperature and the holding time,the post-cure treatment significantly improves the mechanical properties of Pultrusion parts,but the mechanical properties deteriorate after the post-cure temperature exceeds the glass transition temperature.After comprehensive analysis,the post-cure process system is determined(with temperature at 200°C for 70 minutes).(4)Redistributing the process system from the preservation interval to the Curing interval and designing three test schemes,the test results show that the curing stage has a greater influence on the bending strength of the pultruded parts.Pressure and pressurization timing have a greater influence on the interlaminar shear strength of pultruded parts.Improving wrinkle defects on the surface of the parts by tension control system,The overall process parameters of the pultrusion are determined and the parts with better overall molding quality are obtained.