Automation of composite manufacturing processes has improved productivity (pounds produced per hour) by roughly a factor of ten or more compared with older manual methods. However, in process inspection of these parts at the layup stage is still performed 100% by eye. The irony of this situation is that some parts produced today by “automated” methods actually take longer to inspect than to produce.
Consider the 787 Fuselage Barrel sections 47 and 48 produced by Boeing using Automated Fiber Placement (AFP). A recent paper co-authored by Boeing (see reference of the article below) describes the challenges and improvements made over several years of AFP production experience.
This figure from the paper breaks down the cycle time elements to produce the assembly. “Program” represents the time spent executing the NC program to lay up the part and comprises 24% of the total cycle time. “Inspect and Rework” consumes 63% of the total cycle time, by far the largest element. In other words, Inspection/Rework takes more than 2.5 times as long to perform as does the layup itself. This even more significant because this time distribution is after several years of process improvements, including Inspection improvements, had been implemented and overall cycle time had been reduced considerably.
The AFRL (US Air Force Research Laboratory), NCDMM and Ingersoll Machine Tools, Inc. are working together to develop and demonstrate an automated system capable of detecting and categorizing defects such as missing tows, fiber twists and gaps commonly found during Automated Fiber Placement (AFP). They are developing Automated Composite Structure Inspection System (ACSIS) designed for AFP layups. The system consists of a camera, lamps and a line scanner mounted on a Gantry that scans the layup to identify and flag flaws. Inspection is performed offline on an AFP layup after it has been produced. For some geometries such as spars made on a dual sided mandrel, one side of the mandrel can be inspected while the opposite side is undergoing layup. In other cases layup and inspection must be performed in series. A prototype system is now operating and beta trials are planned during 2014. ATK has been selected to collaborate with them for a three-month beta site.
Ref.: Harper, R., Halbritter, A., “Big Parts Demand Big Changes to the FP Status Quo”, SME Composites in Manufacturing, Charleston, SC, October 2012)