RTM PROCESS AND ITS ADVANTAGES AND LIMITATIONS
RTM process makes use of a closed mould and unlike in hand lay up, it gives better control on product thickness and good finish on both sides. Since the resin injection is carried out under low pressure, the moulds used need not be as sturdy as that used for compression or injection methods. Although metallic moulds have better rigidity and longer life, it is not essential to have metallic moulds because the product curing is generally done under ambient temperature. By providing suitable gel coats on both the sides with appropriate colours before the mould is closed, it is possible to obtain products with smooth finishes and desired colours on both sides. The moulding within the cavity of a correctly profiled and accurately closed mould can help to make parts with close tolerances and this ensures accurate assembly. Compared to hand lay-up process, this is a definite advantage.

When the injection is increased, as very closely packed fibres or in large components, there is a tendency for fiber wash. This tendency can be countered by using continuous strand mats or especially woven performs. Moulding-in of, inserts of wood, foam or metal in the initial laminate while moulding will reduce secondary bonding. This reduces the unit cost. It is also possible to combine thermoplastic skins and inserts during the moulding process. Medium reactive resins that cure at much faster cycles than that used in hand lay-up gives a production cycle of about 20 minutes compared to the 3 to 4 hours cure in hand lay-up. Other advantages of the RTM process can be listed as follows.

	Controlled usage of fiber and resin reduces material wastage and consequently the unit cost.
	A variety of mould shapes and sizes can be moulded subsequently because of the mobile pumping unit.
	Fewer moulds can produce a higher rate of output due to faster cure time.
	Styrene emission is practically eliminated during resin transfer into the mould.
	Moulding personnel require usually less training to perform RTM
	Resin usage can be reduced by usage of fillers.
	Fire retardant parts can be moulded by the use of alumina trihydrate and resin and / halogenated resins.

There are few limitations and moulding problem performs which require special attention. Some of these limitations are given below.

	Since the RTM process can develop pressures up to 5to 10 bars, tool rigidity and clamping techniques have to be designed to be suitable for such pressures. Vacuum impregnation methods (VIM)
	Handling of large or heavy moulds requires adequate lifting equipment or air pallets.
	Surface finish of products made by RTM is not as good as that made by sheet moulding compounds (SMC), but equal to that made by wet moulding process. High appearance parts require gel coating or post finishing.
	Unlike in compression moulding, post trimming is required for this process, which means trimming, and dust pick up equipment are needed in the production shop.
	The resin system used has low exotherm and low volatile content. Good quality control of incoming materials and the processing method is required to maintain consistent-moulding results.
	Although RTM is a natural improvement over the slow hand lay-up and spray up process, it is rather slow compared to compression moulding of SMC or Reaction injection moulding (RIM). typical cycle time of RTM for small components is about 3 minutes compared to the less than one minute of compression moulding for RIM. For large, highly integrated parts a cycle time of 1 to 2 hours is typical. The cycle time is more mainly because the filling time is more due to low pressure and due to low exotherm of the resin system. The packing of reinforcements by hand will also take longer time.

Inspite of the above mentioned in adequacies RTM is found to be a flexible procession method. With potential use in many arrears