Mention “aerospace” and most thoughts run immediately to exotic alloys, ultra-precision machining systems, sophisticated electronics and a host of other high-tech subjects. There is more to the story, particularly where passenger aircraft are concerned.
Every passenger aircraft also includes a substantial number of very low-tech components, including hinges and latches on overhead bins and various access panels to tray tables and the reclinable seats to which they are attached. What these low-tech components tend to have in common is the fact that of all the thousands of mechanisms and assemblies in the aircraft they have the most direct impact on the passenger’s perception of the flight experience because they are the only components the passenger contacts personally.
After all, a passenger can’t tell if the ballscrew operating the flaps has a bit too much lash or the ball joint in some linkage is a little sloppy or any one of thousands of other operational components isn’t operating exactly up to spec. But, a passenger will know immediately if the tray table is too stiff or too loose, or the overhead bin latch is hard to open or opens by itself, or the seatback doesn’t move easily or stay in position.
What nearly all of these components, and many others the passenger does not come in contact with, have in common is a dependence on low-cost riveted pivots. And riveting, one of the oldest joining technologies still in common use, is seldom, if ever, thought of as a high-tech process.
As a result, some latches are stiff and others are loose, some seats recline easily and others don’t, some hinges work smoothly and others don’t. Those variations can be minimized by inspecting the finished mechanisms and re-working or scrapping those that are out of spec.
Let’s call that process Make-Measure-Pass/Fail or Assemble and Hope, which can be a very expensive proposition. It’s the way rivets have been used for hundreds of years—put the rivet in the hole and smash it with a press until a mechanical stop is reached. Never mind that the next rivet may be harder or softer than the last one, or that the pieces being joined may not always be the same thickness, or a hundred other potential variables, just smash the rivet and hope for the best.
A better solution is to simply do it right in the first place by controlling the riveting process while it’s happening. That is not a low-tech proposition, but it is one that can be accomplished using proven technology available today literally off-the-shelf.
Let’s call that process Measure-Make-Measure skipping the Pass/Fail and delivering nearly 100% in-spec joints. The key is a change of focus from the rivet to the function of the assembly by articulating the joint while it is being made and stopping the process when it is in spec—regardless of the finished rivet length.
Here’s how it works, using a latch as an example. The pressing is done with an Electro-Mechanical servo press like the Promess EMAP while the joint is articulated with a torque sensing device. Since both devices are instrumented and programmable, the system can account for process variables, including latch height, pressing force and latch resistance, to stop deforming the rivet when the functional specification is achieved.
The same concept can be applied to any pivoted joint that depends on a rivet, including any of the hundreds of hinges and latches used throughout the aircraft. It’s also applicable to other riveting operations like joining flooring to supports while controlling the height of rivets above the floor surface.
An additional benefit of this process is the ability to generate and capture operational data. Capturing the force required to deform the rivet yields data about the hardness of the rivet and the thickness of the components being joined, which can be used to improve the upstream operations.
Measure-Make-Measure technology is not new; it is widely used in the automotive industry and other high-volume manufacturing venues for exactly the kind of assemblies discussed here and for exactly the reasons proposed above. The low-tech devices inside the passenger compartment have an outsized impact on a passenger’s perception of comfort, quality and ultimately satisfaction with his or her flight experience.
Since Measure-Make-Measure also reduces scrap and manufacturing costs, it’s a win-win for anyone purchasing or supplying components that depend on riveted pivot joints. It really is time to start applying high tech solutions to these low-tech assemblies.