What Is It?
Resin transfer molding (RTM) is an easy way of manufacturing complex shapes in fiber-reinforced composites without high tooling costs. It uses a closed mold, in two or more parts, usually made of glass-reinforced polymers or light metal alloys, with injection points and vents to allow air to escape. Reinforcement is cut to shape and placed in the mold, together with any inserts or fittings. The mold is closed and a low viscosity thermo – setting resin (usually polyester) is injected under low pressure through a mixing head in which hardener is blended with the resin. The mold is allowed to cure at room temperature. The fluidity of the resin, and the low molding pressure, give tools a longer life at low cost.
Simple bulk shapes; shaped panels.
Resin transfer molding is increasingly used for large fiber-reinforced polymer components. Shapes can be complex. Ribs, bosses, and inserts are possible. Foam panels can be insert molded to reduce component weight.
A range of resin systems can be used with RTM: almost any thermoset- ting resin with a low viscosity is possible, for example, polyester, epoxies, vinyl esters, and phenolics. The reinforcement, typically, is a 25–30% volume fraction of glass or carbon in the form of continuous fiber mat.
Tooling costs are low, and the process is not particularly labor intensive, making it attractive economically.
Manhole covers, compress soil casings, car doors and side panels, propeller blades, boats, canoe paddles, water tanks, bath tubs, roof sections, airplane escape doors.
From the vented, closed mold – with adequate ventilation – it is easy to control emissions, so worker exposure to unpleasant chemicals is drastically reduced, when compared with other composite processes.
Lay-up methods; press molding; BMC and SMC molding.