Resin transfer moulding is based on transfer moulding where the resin is mixed with the hardening agent (catalyst) and inserted into the mould by means of a compression plunger. The reinforcement material, the fiber, is positioned into the mould in advance of this process. The technique is an alternative to manual moulding of the resin and to spraying and compression moulding. The process is usually used for average-size serial production.
1. Upper section of mould
3. Middle section of mould
4. Resin (basic material)
5. Component part (product) area
7. Ejector pin
8. Tapered sprue channel
The resin 4 is filled into a cylindrically shaped chamber of the mould 3. When moved downwards in the Y direction the upper section 1 pushes the plastic mass by means of the plunger into the area 5 of the mould 2 through the opening 8, thus filling the area 5. Once the component has set it is then released from the mould 2 by means of ejector pins 7. The mould is usually pre-heated and additional heat is generated during the “injection” of the resin while it passes through the narrow openings and thin product shapes – thin wals of products.
The RTM technique is suitable for manufacturing products of relatively complex shapes and varying or differing wall thickness. As the resin flows through narrow sections of the product the flow and the heat thus generated help to achieve additional homogenization of the resin, good mixing with reinforcement fibers into the mould and high quality of the composite material and product.
Moulds are a little more expensive than those in compression moulding (CM) and a certain quantity of the resin is usually lost in the sprue 8. This manufacturing technique is used to manufacture a number of car and aircraft component parts. (Dodge RT/10, 1992 – 40%).
As far as the design of composite material components is concerned, the method ensures good product quality as far as dimensional stability and tolerances are concerned and when complex transitions between different elements are involved. The process features fairly high process efficiency – it is used for manufacturing series of 103 and 107 component parts.