Resin Transfer Molding process monitoring and control

Resin Transfer Molding (RTM) offers the opportunity for significant cost savings in the fabrication of polymer matrix composite aerospace structures. However, the realization of this cost savings has been restricted by quality problems, such as voids, poor fiber volume control, etc., that are inherent to the RTM process. Similar quality issues in autoclave processes have benefited from the use of advanced process control systems such as the Air Force developed "Qualitative Process Automation" (QPA) and Aerospace Service and Control's "Composite Processing Control" (CPC) systems. These advanced systems utilize sensor feedback and a knowledge base to make control decisions and manage the process in real-time with the goal of improved end-product quality. An intelligent RTM control system based on the QPA approach has been developed. This paper presents the feasibility demonstration of its implementation on the CPC control system. A de-resistance sensor grid was used to monitor the flow front in real-time from discrete measurements of sensor wet-out time. The CPC system was able to predict the flow front progression and alter the shape of the flow front either by zoned temperature control or by controlling resin feed rates through multiple injection ports. The same sensor grid was also capable of monitoring the cure state of the resin.