Composite Structure ManufacturingRTM ( RESIN TRANSFER MOLDING )

Cairo UniversityFaculty of Engineering

Aerospace DepartmentUDC xPlatform Training

Prepared By:Mohamed Adawy

Out of autoclave composite manufacturingOut of autoclave composite manufacturing is an alternative to the traditional high pressure autoclave curing process commonly used by the aerospace industry for manufacturing composite material. Out of autoclave (OOA) is a process that achieves the same quality as an autoclave but through a different process.

Out of autoclave manufacturing processes OOA curing achieves the desired fiber content and elimination of voids by placing the layup within a closed mold and applying vacuum, pressure, and heat by means other than an autoclave. An RTM press is the typical method of applying heat and pressure to the closed mold. There are several out of autoclave technologies in current use including resin transfer molding RTM), Same Qualified Resin Transfer Molding (SQRTM), vacuum-assisted resin transfer molding (VARTM), and balanced pressure fluid molding. The most advanced of these processes can produce high-tech net shape aircraft components.

Introduction

Overview

Resin transfer molding (RTM) is an increasingly common form of molding, using liquid composites. It is primarily used to mold components with large surface areas, complex shapes and smooth finishes. RTM is unlike reaction injection molding and structural reaction injection molding processes (SRIM), in which the chemical reaction is induced by the mixture of reactants. Instead, the chemical reaction for resins used in RTM are thermally activated from the fiber mat or preform and mold wall. The reaction speed of RTM is much slower than that in SRIM, allowing for a longer fill time at lower injection pressure. Final RTM products will be light in weight and high in strength. However, RTM uses heavy structured tooling to withstand the hydraulic pressure, and hence it has high tooling cost.

Resin Transfer Molding (RTM) is the process of producing composite components within a mechanically-clamped, rigid, normally two-part (male-female) mold.

RTM is a closed-mold, vacuum-assisted process that employs a flexible solid counter tool used for the B-side surface compression. This process yields excellent strength-to-weight characteristics, high glass-to-resin ratios and increased laminate compression. In this process, fiber preform or dry fiber reinforcement is packed into a mold cavity that has the shape of the desired part. The mold is then closed and clamped. Catalyzed, low viscosity resin is then pumped into the mold under pressure, displacing the air at the edges, until the mold is filled. After the fill cycle, the cure cycle starts during which the mold is heated, and the resin polymerizes to become rigid plastic. Gel coats may be used to provide a high-quality, durable finished product. This process is well-suited for mass production of 100 to 10,000 units/year of high-quality composite fiberglass or fiber-reinforced plastic parts. It is recommended for products that require high strength-to-weight requirements. Tooling used in this process can be made from various materials including aluminum, nickel shell, mild steel and polyester. The light RTM (LRTM) process, on the other hand, is similar to that of RTM, but differs in the method of closing the mold. The closure of the mold is done mechanically or by applying vacuum between two seals in the mold peripheral flange.

Resin Transfer Molding Process

A video to demonstrate the RTM process…

RTM Process

Companies Involved in Resin Transfer MoldingThe following is a list of various composite/fiber glass producers, specializing in RTM:

1. Composite Integration Ltd2. JHM Technologies3. Owens Corning4. Apogee Products5. FormaShape

This photograph shows aluminum RTM tooling being operated in a hydraulic press to produce composite door skin panels.

Benefits

The key benefits of resin transfer molding include the following:

Good surface qualityWide range of reinforcementsLarge, complex shapesDimensional tolerancesLow capital investmentLess material wastageTooling flexibilityLow environmental impactLabor savingsAbility to add inserts and reinforcements at a point of infusion for greater strengthZero air entrapment within the product.

Applications

RTM is of major interest for various molding applications as it promises performance improvements and cost savings over traditional methods. Some of the major applications of the RTM process include:

Truck panelsBoat hullsWind turbine bladesAerospace and automobile partsMedical compositesBathroom fixtures, car body, helmet, etc.

Airbus A340 carbon composite spoiler made with RTM

• http://www.azom.com/article.aspx?ArticleID=8620• http://www.nuplex.com/Composites/processes/resin-transfer-moulding• http://en.wikipedia.org/wiki/Resin_transfer_molding#Vacuum_assisted_RTM_.28VARTM.29• http://www.compositesworld.com/articles/airbus-a340-carbon-composite-spoiler-made-with-rtm• http://www.composite-integration.co.uk/about-rtm.php

References