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UL101 Finds Vacuum Bag Leaks in Composite Manufacturing

Updated: Aug 18, 2021

Due to its sensitivity and ease of use, the UL101 has been adopted by several aerospace companies during production for finding and pinpointing leaks in vacuum bags. Composites are used in aerospace due to the high strength and low weight. This is achieved by finding the right ratio of fiber to resin. If there is too much resin in the laminate, the laminate will take on more of the properties of the resin. If there is too little resin, there will be weak spots in the composite.

The vacuum bagging is the technique used to squeeze out excess resin. The vacuum bag is done during the cure cycle. It removes trapped air between fiber layers of composite. It compacts the layers to maximize force and prevent shifting during cure. It reduces humidity, and most importantly, vacuum bagging optimizes the fiber-to-resin ratio. 

The vacuum bags are large sheets of nylon material. They need to be large enough to cover the composite material of the aircraft or wind turbine. A 190 foot wind turbine, for example, requires a vacuum bag that is 12 feet wide by 195 feet long. Occasionally, the vacuum bags come with tiny pinhole leaks, which would reduce the force applied and impact the quality of the product. (For more on wind turbine manufacturing click here.)

The UL101 Ultrasound Leak Detector is used to locate the leaks very quickly. Several quality control technicians are trained to use the UL101 to find leaks in a noisy plant environment (vacuum pumps, heavy machinery, etc.). Once trained, the technicians sweep the vacuum bag, listening for leaks with their UL101 Detectors. Once the leak is located, the pinhole can be sealed. The UL101 is used to confirm the seal is complete.

(sample video of NASA finding a vacuum leak on the International Space Station)

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