Resin Transfer Molding (RTM) - Process Monitoring Using Heat Flux Sensors

Principle

In composites, heat transfer follows resin injection and this heat transfer is very sensitive to processing conditions. High-quality heat flux sensors permit detection of the resin flow front and helps in monitoring the cure without any direct contact with the material being transformed.

Positioning of the Heat Flux Sensor

Heat flux sensors are incorporated in tooling in different ways as depicted in the figure below:

Figure 1. In both cases, the sensor is not in contact with the transformed material

Properties Measured

The resin flow front is measurable using the thermal disturbance induced by the resin at the time of fibre impregnation. Thermal disturbance is a mild change in temperature and local thermal conductivity. The heat flux sensor detects the heat generated by the cure reaction. Thus the cure can be monitored if thermal regulation remains stable.

Kinetic analysis is almost similar to the DSC (differential scanning calorimetry) technique, with a few differences brought about by real thermal cycles. Cure signal is averaged on the thickness of the part. Thick components can have large temperature gradients and may induce some variations in reactivity through the thickness of the composite.

Applications

The system is useful for non intrusive resin flow front detection, reaction start and end and real-time cure monitoring. It helps to understand and optimize the process and can be also used in the production environment for quality control. Thermoflux Technologies recommends the use of an embedded electronic system, which automatically controls vents as per flow front detection.

Figure 2. Heat flux signal on a metallic RTM tool

Figure 3. Heat flux signal and real-time conversion obtained on a RTM light (composite) tool.

Once calibration is over, the real-time, instant cure level can be monitored, and cure can be stopped at the minimum cure value. This permits optimization of productivity for a constant cure level. Major applications are in vent control, R&D, real injection and cure recordings in the aerospace, nautical, and automotive sectors.

About TFX-SA

TFX-SA design and implement in-line material control solutions.

Tfx-Technology® products, also known as Thermoflux are :

• Thermal sensors (Heat Flux sensors or Heat Flow sensors) : there is no mastership over the quality of your products without thermal control. Heat spreads and vehicle information! It is therefore possible to control a product without direct contact.
• Monitoring and control systems
• Industrial acquisition and post processing software
• Traceability of technical operations performed everyday

This information has been sourced, reviewed and adapted from materials provided by TFX-SA.

For more information on this source, please visit TFX-SA.