Process selection determines competitive advantage<\/a><\/li><\/ul><\/nav><\/div>\n\n\n\n
\n\n\n\nLightweighting has become a common battleground for automotive, aerospace, and wind turbine blades, with carbon fiber composites standing out due to their high specific strength, high specific modulus, and corrosion resistance. However, "expensive, slow, and difficult to mass-produce" has always been a stereotype associated with it in the industry. Traditional autoclave\/hot press molding relies on vacuum bags and external pressure to cure prepreg at 120-180 \u00b0C, often requiring 4-6 hours for a large fuselage skin. In contrast, the recently emerging high-pressure resin transfer molding (HP-RTM) injects low-viscosity epoxy or PUR resin under high pressure in a closed mold, combined with a fast-curing formula, reducing the molding time to 5-10 minutes, paving the way for mass production of carbon fiber chassis for automobiles. This article will comprehensively compare the two processes from scientific principles, process parameters, cost structure to practical applications, and provide selection and design guidance to help engineers grasp the best cost-effectiveness from the early stages of development.<\/p>\n\n\n\n
Scientific principles and process parameters of thermoforming<\/h2>\n\n\n\n
Hot pressing typically uses prepreg layups, positioned into the mold according to lamination angles (\u00b145\u00b0\/0\u00b0\/90\u00b0), covered with a polyimide vacuum bag and evacuated to \u22120.09 MPa to expel air and volatiles; then, pressure is applied and temperature increased at 0.4\u20130.7 MPa, causing the resin to melt and infiltrate. The pressure ensures a stable fiber volume fraction (Vf) of 55\u201360 %. Curing kinetics can be described using the Kamal\u2013Sourour model.<\/p>\n\n\n\n
d\u03b1\/dt = (k1<\/sub>+k2<\/sub>\u03b1m<\/sup>(1\u2212\u03b1)n<\/sup><\/p>\n\n\n\nWhere \u03b1 is the reaction conversion rate, and k\u2081 and k\u2082 increase with increasing temperature according to the Arrhenius equation. Controlling the heating rate to 2-3 \u00b0C\/min can avoid excessive exothermic reaction that could cause resin microcracks; finally, apply cooling pressure to < 60 \u00b0C before demolding to reduce thermal warpage.<\/p>\n\n\n\n
High-pressure RTM: The key from resin injection to rapid curing<\/h2>\n\n\n\n
HP-RTM uses dry fiber reinforcement (DRF) placed in rigid upper and lower molds. After mold closing, epoxy or PUR with a viscosity < 100 mPa\u00b7s is injected at a pressure of 50\u2013120 bar, and the temperature is rapidly increased to 120\u2013160 \u00b0C to trigger a self-catalytic rapid curing reaction (t\u2089\u2080 \u2248 90\u2013180 s). The flow front must cover the entire mold within 10 s; otherwise, gas can easily be trapped in the gaps between fibers, forming pores. The mold is usually equipped with heat pipes or oil temperature control to maintain a temperature uniformity of \u00b12 \u00b0C, ensuring consistent curing shrinkage. Since the cycle time is limited by the three stages of injection + curing + cooling, it can be achieved through:<\/p>\n\n\n\n
\n- Variable viscosity resin: high flow \u2192 rapid thickening and curing upon heating.<\/li>\n\n\n\n
- Embedded resistance heating mold: direct internal heating, shortening the heating time.<\/li>\n\n\n\n
- Dual-mold alternation: One injection molding machine serves two sets of molds, improving OEE.<\/li>\n<\/ol>\n\n\n\n