The high-precision riveting process in aircraft assembly includes drilling, countersinking, and rivet installation. Repeated hundreds of thousands of times on the aircraft body, every step in this process contributes to the structural integrity of the aircraft and to minimizing unnecessary aerodynamic drag. This is why strict tolerances apply to the geometry and surface quality of rivet holes, countersinks, and installed rivet head flushness.
But while aircraft riveting has become mostly automated and robotized, quality control of the process is still often limited to coupon inspection in assembly plant labs. Fortunately, changing to high-precision 3D automated inspection is now an option that offers much improved understanding of the manufacturing process and significant cost savings.
Automating Rivet Inspection
In support of the industry’s transition to 100% automated and data-driven quality control of riveting, Novacam systems for riveting inspection offer speed, precision, and facility for integration with robots. The systems’ scanning probes measure rivet holes, countersinks, and installed rivet heads right during the assembly process, on the plant floor. They provide automated non-contact micron-precision measurements of dimensional and surface quality parameters, enabling full traceability and improving QC of both intermediate and final results of the riveting process.
To suit the wide variety of measurement needs in the riveting process, Novacam offers a choice of 3 systems for non-contact measurements based on low-coherence interferometry technology and use an interferometer to produce and process light signals. The three systems differ in their fiber-based scanning probes:
BoreInspect uses a rotational scanner (RS) to reach inside rivet holes with a small-diameter rotational probe.
SurfaceInspect uses a galvo scanner to scan the rivet hole area from above in a raster manner.
RivetInspect uses both the galvo scanner and the rotational scanner to provide full coverage of the riveting process.
Facility For Robot Integration
Novacam’s rivet measuring systems are all fiber-based and modular with the scanning probes connected to the signal-processing interferometer with an optical fiber. The probes can be installed wherever required in the process—on a CNC, robot head, or any combination of precision stages – the interferometer unit) can be located several meters away, such as on the base of a robot.
Acquired 3D Measurements
Novacam 3D metrology systems acquire surfaces in a point-by-point manner. Light is directed onto the surface and reflected light signals are captured and processed. The user selects the scan path, which may be linear, circular, or spiral, with users also specifying the area of interest within the lens field of view (FOV). From each scan, the systems simultaneously generate three sets of raw data: 1) 3D Point Cloud (micron-precision measurements), 2) Light Intensity Map, and 3) Height Map.
The 3D point cloud is useful for both interactive and automated 3D analysis of the measured surface and for calculating 3D GD&T parameters. The light intensity map and the height map facilitate defect detection and measurement.
Point Cloud Analysis Options
The generated 3D point cloud may be analyzed interactively or automatically using CAD/GD&T software such as PolyWorks Inspector which provides powerful capabilities for evaluating the 3D point cloud with respect to user-defined criteria (rivet hole ID feature nominals and tolerances) or a reference CAD model. PolyWorks Inspector offers both interactive 3D visualization and analysis, and fully automated analysis and go-no-go reporting.
Defect inspection & measurement
High density 3D scans of rivet holes allow for thorough inspection and measurement of riveting process defects. Common defects include:
- Surface cracks
- Inter-laminar defects such as gaps or offsets
- Burr debris
- Gaps caused by tearing of composite materials
- Tool mark defects, or
- Rifling (chatter) defects
Measurement Speed and Density Beyond CMMs & Gauges
Novacam systems can obtain 100,000 3D point measurements per second and orders-of-magnitude denser than point clouds obtained with CMMs or other commonly used high-precision instruments. A typical rivet hole takes 1 to 9 seconds to scan, with the cycle-time depending on the grip length, the features measured (rivet hole only or also the installed rivet head), and the required density of 3D data points.With the BoreInspect, the density of the scan may be adjusted by amending the spiral pitch.
Today aircraft and automotive manufacturers seek to improve their processes through multiple approaches – automation, robotization, as well as tracking and analyzing detailed 3D measurement data. Since human safety is ultimately at stake, 100% 3D inspection of the fastening process is the new expectation and increasingly the norm.
By deploying measurement systems to provide in-process high-precision 3D riveting process measurements, assembly plants are able to:
- Decrease their rivet inspection cycle time
- Detect out-of-tolerance parameters early
- Decrease scrap and rework
- Optimize consumables usage, and
- Achieve overall savings.
For more information: www.novacam.com