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techview


Glenn Nausley It’s Time to Rethink the Rivet R


iveting is one of the oldest fastening technologies, yet it’s a fundamental process used on even the most advanced aerospace products being built today. And, while the ba- sic principle is very simple, producing a good repeatable riveted joint in a production environment is anything but. The integrity of a riveted joint is controlled by a few factors


which are easy to defi ne but quite diffi cult to detect, measure and control in practice. At the most fundamental level there are only two things to consider: material and process. Material factors can be further broken down into three categories:


Base Material t Is it appropriate for a riveted joint? t Is the thickness correct? t Are all of the pieces to be joined present? t Is the hole diameter correct?


Rivets t Has the correct rivet been chosen, material, length,


diameter etc.? The “wrong rivet” being accidentally mixed in is the culprit in a very high percentage of joint failures.


t Is the rivet defective?


Tooling t Is the tooling appropriate for the material, rivet and


process? The “wrong tool” is another major culprit in riveted joint failures.


t The process factors are simpler: Is the rivet deformed to the correct depth? How quickly was the deforma- tion performed?


As I said, the factors infl uencing joint integrity are easy to


defi ne, but detecting, measuring and controlling them is an entirely different challenge. The solutions in common use to- day range from “hit it and hope” with a hand-held air hammer to sophisticated, fully automated systems using pneumatic and/or hydraulic cylinders. What’s missing in that range of traditional solutions, however, is the ability to monitor and control the process while it’s happening. Frankly, that simply has not been possible until quite recently when fully instrumented electromechanical


President Promess Inc.


servo-presses were paired with sophisticated monitoring and control algorithms to create truly intelligent riveting systems. As is often the case, this technology was pioneered in the automotive industry to provide precisely repeatable performance in riveted assemblies like hood latches and seatbacks. It didn’t take long, however, for the technology to be ap- plied in the aerospace industry. My company, Promess, for example supplied a system to


an aerospace fl oor manufacturer that precisely controls the height of rivets above the fl oor surface despite signifi cant variations in panel thickness.


Fully instrumented


electromechanical servo-presses were paired with sophisticated monitoring and control algorithms to create truly intelligent riveting systems.


That system uses a fully electric Promess servo-press coupled with a digital position transducer that is built into the riveting tool. This position transducer measures the height of the fl ooring material and feeds this information back to the Promess Controller in real time so the press can deform the rivet to an exact height in reference to the fl ooring surface at that particu- lar point, producing a perfect rivet joint every time. The press instrumentation provides real-time force and position sensing while the highly-responsive servo mechanism allows virtually instantaneous response to control signals that permits the pro- cess to be optimized and verifi ed literally “on the fl y.” In short, this technology turns the ancient art of riveting into a sophisti- cated, computer-controlled process that produces repeatable joints with consistent, predictable performance characteristics. It is now possible to include a variety of measurements in the riveting process and verify each of them while the pro- cess is happening. These include:


40 — Aerospace & Defense Manufacturing 2016


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