Excerpt reproduced from in High Performance Composites magazine and later at www.compositesworld.com.

Improvements in materials, tooling and process control bring RTM and VARTM into the realm of aerospace components.

… the spec must be followed and run in the same way every time. To ensure uniformity, VSC controls its process with the Sentinel system from CompuDAS (Shelton, Wash., U.S.A.), a general-purpose industrial controller commonly used in the composites industry to control autoclaves (see HPC March 2003, p. 27). In fact, the same hardware can control any thermal system, including autoclave, RTM, VARTM and other industrial processes. The difference lies in the software user interface. For VSC’s RTM system, CompuDAS designed an interface that enables the operator to control processing variables, such as vacuum, pressure and temperature. Although the system has the capability to turn injection ports on and off, and thus fully automate the process, the system is designed to pause the process at key operator decision points, such as for leak checks and resin temperature verification.

Read the full article at www.compositesworld.com

This article by Barry Berenberg was originally published in High Performance Composites magazine and later appeared at www.compositesworld.com.

Autoclave processing is the most common method used for curing thermoset prepregs. The curing of thermoset composites involves both mechanical and chemical processes. Mechanically, pressure is applied to remove trapped air and volatiles, and to consolidate the individual plies and fibers. Chemically, a crosslinking reaction must be initiated and taken to completion to form a rigid matrix. Crosslinking is most commonly initiated through the application of heat, though it also may be initiated by exposure to ultraviolet light, microwaves, or high-energy electrons (e-beam curing). In the autoclave process, high pressure and heat are applied to the part through the autoclave atmosphere, with a vacuum bag used to apply additional pressure and protect the laminate from the autoclave gases. The cure cycle for a specific application is usually determined empirically and, as a result, several cure cycles may be developed for a single material system, to account for differences in laminate thickness or to optimize particular properties in the cured part.

The typical autoclave cure cycle is a two-step process. First, vacuum and pressure are applied while the temperature is ramped up to an intermediate level and held there for a short period of time. The heat reduces the resin viscosity, allowing it to flow and making it easier for trapped air and volatiles to escape. The resin also begins wetting the fibers at this stage. In the second ramp up, the temperature is raised to the final cure temperature and held for a sufficient length of time to complete the Continue Reading