The use of liquid resin processes such as resin transfer molding (RTM) and vacuum assisted RTM (VARTM) has developed rapidly in recent years. There is a need to use these processes more extensively in future aerospace structures because large and complex parts can be manufactured economically, and the costs of autoclave processing of prepreg materials can be avoided. Despite the benefits of liquid resin processes, there are challenges to extending their use to primary structure and high temperature applications due to the limitations of the resin systems available, the companies say.
In tests, Henkel’s Loctite BZ 9130 AERO resin was combined with a rapid heating and cooling manufacturing approach to produce high temperature resistant composite laminates and parts at significantly lower cycle times. Key mechanical strength properties were measured. The technique was then applied to a curved, integrally stiffened composite panel to demonstrate the ability of the process to produce complex parts suitable for use in aerospace applications.
For the laminate and demonstrator curing the Quickstep process was chosen. The process is based on the principle of conduction heating and uses a heat transfer fluid (HTF) to apply heat and pressure to the uncured component during processing.
In order to demonstrate the capability of the resin and infusion/curing techniques on a scale larger than flat laminates, a demonstrator panel, approximately 1 m2 was preformed and infused. This panel consists of five layers of 370 gsm 5HS carbon fabric for the skin plies, resulting in a skin thickness of 2 mm, onto which a series of four hat-shaped, or omega-type stiffeners were placed using removable mandrels. The assembly was bagged and placed into the Quickstep curing chamber for infusion and cure.
The processing of the Loctite BZ 9130 resin proved to be “infusion-friendly” in the Quickstep process, and void-free panels were produced with fiber volumes in the 55 to 57% range, which is considered high for a woven fabric laminate. Mechanical evaluation and quality measurement of the panels confirmed values similar to or higher than those achieved in standard oven-based VARTM processing. The Quickstep process provided a faster heating and cooling of the laminate and uniform temperature during the infusion process.