PMI structural foams also have outstanding resistance to compression creep. It can also be said that the specific strength and specific stiffness of the PMI foam make the material have good performance. The compression creep resistance of the PMI foam makes the material also have good process performance. The curing of the carbon fiber epoxy composite system requires a set pressure, temperature and time as curing conditions. If a cost-effective co-curing process is employed, the foam material as the core material needs to have good compression creep resistance. After testing, the foam can meet the requirements of various curing conditions.
Generally, for foam sandwich structures, the processes that can be used are:
First, the molding process: the molding process is characterized by relatively high mold cost, the advantage is that it can accurately guarantee the thickness and size of the composite material; at the same time has two smooth surface components. Components that typically use the molding process include flight control components, helicopter rotors, sports equipment, and medical bed panels. In the molding process, by imparting a certain amount of interference to the foam core material, the interference provides a counter pressure to the curing of the panel during the mold clamping curing process. The compression creep resistance of PMI foam is the premise and guarantee for the conversion of interference into back pressure. It can adjust the back pressure according to the resin content of the laminate, the curing system and the thickness of the panel by setting the appropriate interference. Meet the requirements of curing pressure.
Second, the autoclave process: the hot press process is characterized by a hard mold, a soft mold (vacuum bag). The composite laminate in the solidification is pressurized by vacuuming and pressurization in the autoclave. If a co-curing process is used, that is, the curing of the carbon fiber composite panel, the bonding of the sandwich structure core material and the panel is completed at one time. PMI foams have smaller voids than honeycombs and provide adequate support for panel curing without the telegraph effect of honeycomb panels.
Third, RTM process: Liquid resin injection is a relatively new optimized manufacturing process, using RTM (resin transfer mold) technology to produce high-performance sandwich structural members. The purpose is to simplify the production process, reduce manufacturing costs, and save the price of raw materials. The use of cloth with relatively low price and good paving performance can achieve mass production, and the components can achieve the effect of using high quality prepreg. If the pores of the honeycomb are sealed so that the low-viscosity injection resin does not flow into the honeycomb pores, the honeycomb can also be selected as the sandwich material in the RTM manufacturing process. However, foam cores are generally used if the RTM process is used to produce sandwich composites. As with the autoclave process, the core material also needs to have good compression creep resistance, meeting the resin injection pressure and injection temperature requirements.