In-process inspection of large components: Doing what metrology, profilometry and smart cameras can’t

In-process inspection technologies have advanced considerably over the past decade, with many manufacturers performing inspection with smart cameras, profilometry, automated metrology systems and more. Such advancements are impressive but limited when it comes to large works-in-progress (WIPs). Picking up where these technologies drop off, LASERVISION has been designed specifically for large WIPs, like the one shown here. In this blog, we explain the limits of automatic inspection approaches designed for smaller components. Then we explain how LASERVISION overcomes these limitations.

Composites proving ground

The large WIPs that have served as LASERVISION’s proving ground are structural aerospace composite components, where human inspectors and manual inspection processes persist. Because structural composite components have been used primarily in low-volume applications, manual in-process inspection has matched the pace demanded by manual hand layup, the predominant manufacturing technique. Long cycle times have been tolerated up to the present, even though composites fabricators also must contend with high rework and scrap rates due to the limitations of human inspection. As aerospace composites have trended toward higher volume applications, more automated manufacturing processes and economic pressure to reduce scrap and rework, fabricators have found themselves in a bit of a quandary. On the one hand, they need to accelerate in-process inspection to reduce cycle times and raise production throughput. On the other hand, almost all automatic inspection systems are designed for smaller structures. If it is even feasible to apply them to large composite WIPs, they require time-consuming positioning and repositioning of the system to fully inspect each WIP surface. Additionally, in-process inspection with these devices typically is not truly “in-process.” That is, production equipment has to stop while the inspection system is positioned near the surface being examined. So automating inspection with these technologies defeats the primary purpose of minimizing cycle time devoted to inspection. One exception to being designed for smaller WIPs (besides LASERVISION) is profilometry. As the name suggests, a profilometer creates a profile of the surface, which is analyzed to identify and measure features such as overlaps of towpreg being laid up by an automatic fiber placement (AFP) machine, or gaps between tow lanes. However, because the profilometer is mounted on the AFP deposition head, its measurements are relative to other material in the layup, not to their as-designed position in the CAD model. Additionally, profilometers can only inspect the area immediately around the AFP head. These limitations make profilometry applicable to some but not all a fabricator’s in-process inspection needs for large composite structures. The sheer size and complex geometries of these composite structures make the challenge of automatic inspection especially daunting. Yet the future of composites is likely to be found in high-volume applications fabricated on automated equipment. The option of transitioning to automatic inspection is quickly becoming an imperative.

What large WIP inspections need

Of course, large composite aerostructures are just one kind of large WIP in need of better inspection throughput. Automotive and other transportation assemblies, wind turbines and components for other energy systems, large-scale additive manufacturing … basically, any manufacturing operation producing large-scale and/or complex products have inspection needs that metrology, smart cameras and other technologies are not designed to meet. A large-scale in-process inspection system should feature:
  • A large field of view (FOV) – Without constant repositioning, the system should be able to inspect detailed regions of interest anywhere within large areas of the WIP surface.
  • Large standoff distance – A large FOV is offered only by a system that operates some distance away from the WIP surface, typically meters rather than the centimeters standoff distance featured by smart cameras and many metrology devices.
  • Sizeable depth of field – WIPs with deep curvature or large geometric features need a system that captures images with all aspects of those features in focus.
  • Ambient lighting – Many smart cameras, profilometers and metrology devices are unable to capture enough information from the WIP surface in ambient lighting of a factory floor. Special lighting is expensive and difficult to implement when the WIP is large and complex.
  • Ultra-high pixel resolution – As one expert put it, “If you don’t have enough pixels, AI can’t learn.” Digitally capturing the WIP surface is just the first part of the inspection task. The second is to analyze this raw data through artificial intelligence, which demands ultra-high resolution.
In sum, an in-process inspection system for large WIPs must achieve ultra-high resolution in ambient lighting while also providing substantial FOV, standoff distance and depth of field. With smart cameras, profilometers or metrology systems, compromise among these features is required. For example, to capture ultra-high resolution images, you will have to reduce standoff distance and/or add supplemental lighting. A reduced standoff distance means less depth of field, which means ultra-high resolution may be achieved in only one part of a deep region of interest. By starting our in-process inspection technology efforts with the needs of composite aerostructure fabricators, Aligned Vision has developed a system tailored to large WIPs and applicable to inspection of nearly any visible feature on nearly any WIP surface. Contact us to explore how LASERVISION will solve your large WIP in-process inspection needs.