Rivet hole, rivet countersink and rivet flushness measurements

Measuring System: Novacam RivetInspect
Keywords: aircraft assembly, aeronautics, aviation, rivets, bolts, fasteners, countersinks, 3D industrial inspection

The triple challenge of riveting process inspection

Within aircraft assembly, riveting is a multi-step fastening process that requires tight adherence to design specifications and stringent QA/QC standards.  Riveting is also being increasingly automated. Robots with automatic tool changers switch between drilling, counter-sinking, sealing, fastening, and inspection end-effectors to carry out a process that has traditionally required significant human skill and experience.

Since defects can and do periodically occur at every stage of the riveting process and since 100% inspection is becoming more of a norm, aircraft makers today require that inspection instruments perform on the following three fronts.

The instruments must:

  1. Measure surfaces that are difficult to access, such as the inside of rivet holes
  2. Help automate defect detection on ALL aspects of the drill-and-fill riveting process.  Since defects can and do periodically occur at every stage of the riveting process, high-speed and high-precision 3D measurements at each stage are imperative.
  3. Be versatile and rugged enough to be deployed in process, within automated or semi-automated systems right on the aircraft assembly plant floor.

Can these challenges be met by one instrument?

In fact, Novacam has designed and developed a non-contact 3D metrology system, RivetInspect, that delivers on all three fronts.

Quick introduction – RivetInspect (shown on the right)

  • Provides a complete inspection coverage of the rivet installation process
  • Delivers non-contact sub-micron precision measurements of surfaces. The acquired data, generated as a 3D point cloud, is forwarded to  automated GD&T and defect detection software
  • Acquires surfaces quickly, at up to 100,000 3D point measurements per second

Here is how RivetInspect addresses the important challenges listed above.

The RivertInspect comprises two non-contact inspection end-effectors – rotational scanner (bottom) and galvo raster scanner (top) – to ensure complete high-precision inspection of the drill-and-fill riveting process.

1. Inspecting the hard-to-access inside diameters of rivet holes

The small-diameter probe of the RivetInspect rotational scanner easily reaches inside rivet holes to acquire their dimensionality and detect defects.

The acquired micron-precision 3D surface data provides manufacturers with unprecedented ability to detect defects and to gain insight into the drilling process.

3D characterization will, for example, reveal evidence of tool mark defects, or of inter-laminar or exit burring (images on the right).

3D geometry of a rivet hole reveals a tool-mark defect at the interface of composite and aluminum layers

Inside surface of a rivet hole exhibiting a burr

2. Automated defect detection on ALL surfaces that count

In addition to inside diameters of  rivet holes, the countersink and the rivet-head area (after rivet installation) need to be inspected for dimensional conformity and potential defects. These two aspects are measured by the galvo scanner, which acquires surfaces efficiently and in a raster pattern, typically covering an area of 30 mm2.

  • Countersink inspection: For exterior aerodynamic surfaces, flush head fasteners are crucial. The nominal depth of a countersink must accommodate the rivet head to achieve flushness.  With the optical data acquired by RivetInspect at high speed, conformity to specifications (such as the angle of the countersink) is easily verified and any surface defects identified (see image).

Countersink exhibiting a surface defect (scale in mm)

  • Rivet head area inspection: micron-precision dimensional data obtained by RivetInspect help confirm if the final flushness of the rivet is within the allowable range of 0.002 inch (50.8 microns) imposed by aerodynamics. Even surface defects around the rivet head, such as skin distortion, rivet removal damage, scratches, or other types of deformation, can be detected.

Acquired 3D surface of river head after installation

3. Complete versatility for in-process set-up right on the plant floor

The RivetInspect is based on low-coherence interferometry technology.  It is also a fiber-based modular system, meaning that its two scanners (rotational scanner and galvo scanner) are connected to a single signal-processing detector box (interferometer) with an optical fiber that can be hundreds of meters long. As such, the scanners are easily integrated as either robot end-effectors or as 3D vision components in automated or semi-automated systems – right on the plant floor.

See a more complete list of advantages of Novacam’s fiber-based LCI systems.

Additional bonus: timing of drill bit replacement optimized

Given the cost of consumable high-precision drill bits and the cost of the drill-bit replacement process, it makes sense to replace drill bits only once their efficacy has measurably deteriorated.

To establish drill bit wear with RivetInspect, the acquired 3D rivet hole inner surface geometry is programmatically compared with the design specification shape of the rivet hole. The scale of dimensional variation suggests the optimal time to replace a drill bit, before defects start occurring. With this drill-bit replacement approach, operational savings are achieved.

Colour-coded image of dimensional variability between the rivet-hole specification (green) and the rivet hole (blue)

Related links

Download application note “Rivet Hole and Rivet Flushness Inspection” [4 pages, PDF, 0.7 MB] for more details  on how on how the RivetInspect facilitates inspection of the aircraft riveting process

Contact us to discuss how the RivetInspect system can be integrated in your assembly process.