Composites manufacturing technologies – Part III: RTM – Resin Transfer Molding 

February 25, 2022

Recent posts

Carbon Fiber: Most notable properties and applications


The City Council supports the Iberia Compositech project, which will invest €380,000 and create 15 jobs


Composites manufacturing technologies – Part III: RTM – Resin Transfer Molding 


Manufacturing technologies for composite materials: Prepreg with autoclave


Composite materials in the aeronautical sector

Resin Transfer Molding or RTM is a closed mold manufacturing process for FRP composite materials.  
This process consists of two models closed together, leaving a cavity with the geometric shape of the piece to be achieved.

Steps in the RTM process

– Before closing the mold, the dry laminate of the reinforcing material is placed, generally it is a type of fiber that allows correct fluidity of the resin.  

– After this, the mold is firmly closed and the matrix or resin begins to be injected, flowing through the reinforcement.  
Once the resin completes its curing process, the mold is opened and the piece removed. 

With this manufacturing method, medium production volumes are achieved (from 1,000 to 10,000 pieces) with high quality and performance. Furthermore, as both sides are on the mold, the final pieces are dimensionally precise, with a very good surface finish and allowing for complex geometric shapes. 

Features of RTM technology

Generally, thermostable resin and a wide variety of reinforcing fibers are used. This material must allow the fluidity of the matrix, taking into account that no deformations of the weft, preferred flow channels or fiber concentrations occur. For the RTM, the molds are usually made of aluminum, since they must withstand the closing load with the resin injected inside. These molds may have oil passages or electrical heaters to heat up during the curing process. In this way, production times improve, among other final characteristics of the piece. 

Advantages of RTM

By having opposite mold faces, the piece will come out directly with a good surface finish on both sides and with a precisely controlled thickness. Furthermore, with a worked design, no additional post-processing would be necessary. This represents a saving in the total production cost. 

An exact catalytic calculation with the help of heated molds allows us to find a very fast process, lasting up to a few minutes per piece. This process could be easily automated. 

The combination of high closing pressures and resin injection gives rise to a high fiber volume ratio, with consequent high performance. 

As it is a closed process, the emission of volatiles is reduced, making it a cleaner and more orderly method. 

Disadvantages of RTM

The manufacture of aluminum models has a high cost, as well as the rest of the necessary tools (closures and resin injector). 

The general size of the parts to be manufactured will be limited by the necessary closing force. 
The consolidation of the component in the areas parallel to the direction of the closing force will be of poorer quality than those that are perpendicular. 

At Iberia Compositech we are experts in producing composite material parts and we work using various technologies, selecting the most appropriate for each project based on factors such as the technical properties of the part, its final use or the quantity to be produced. 

If you want to know all the processes we work with or leave us a specific question, you can take a look at the technologies section or fill

Skip to content