Aerospace Fastener Installation Tool

Ergo-Tech® Blind Bolt

Contamination and ergonomics are critical concerns in aerospace manufacturing, especially with fastener designs that include torque-rated breakaway pintails. Howmet Aerospace challenged our team to develop a lightweight, ergonomic installation tool capable of handling a variety of Ergo-Tech® fasteners while improving pintail collection. As the Lead Design Engineer, my role was to translate these strict aerospace requirements into a clean mechanical architecture and deliver a fully functional, highly manufacturable prototype.

To achieve high-capacity collection without obstructing the technician, we finalized a design that allows pintails to pass through the center of the tool. Our design utilizes a Brushless DC Motor and gearbox unit from Maxon. Pintails pass through the center of the tool via a custom hollow shaft that is offset from the motor and gearbox. This arrangement allows for torque transmission to the hollow shaft via a spur gear system while keeping the central pathway clear for pintail passage.

To ensure the offset drive system could withstand continuous use, stress hand calculations were performed to analyze the spur gear transmission. The gear stress safety factor for this design was determined to be 3.94. This was calculated considering a life cycle of 10^9 revolutions, ensuring infinite life reliability for the tool's core mechanics. Additionally, the tool features a custom quick-release mechanism designed to work with the Howmet Proprietary nozzle, allowing for a rapid change between various size nozzles for different diameter code Ergo-Tech® fasteners.

We prioritized robust assembly methods to ensure the prototype could withstand continuous industrial use, addressing issues prevalent in the previous year's project. The central hollow shaft was custom machined from 1018 steel. As an improvement from last year's senior project, the housing no longer resisted the torque applied by the nozzle during installation, but rather a custom designed torque plate. This critical structural improvement kept the housing from failing and falling apart during continuous use.

The waste pouch was engineered with a removable pintail storage bin capable of holding 5,000 pintails. This high capacity was specifically designed to match the battery life, meaning the container only needs to be emptied when the battery requires changing. Furthermore, putting the suction tube in the lid of the container ensured it operated similarly to a shop vacuum. This strategic placement allowed gravity to assist in dropping the pintails into the bin, completely preventing the heavy metal pieces from getting sucked into and clogging the vacuum pump tube.

We prioritized robust assembly methods to ensure the prototype could withstand continuous industrial use. The central hollow shaft was custom machined from 1018 steel. To guarantee reliability, we ran an FEA analysis in Abaqus to determine if the hollow shaft could safely transmit the required torque. The study was conducted using 80 in-lbs of torque, which is twice the 40 in-lbs needed to install the pintails. The maximum estimated stress of 5.701 kPa rested far below the 1018 steel's 318 MPa yield strength, confirming structural integrity.

As a major improvement from the previous year's senior project, we engineered a custom-designed torque plate. This critical addition absorbed the rotational forces applied by the nozzle during installation, preventing the 3D-printed housing from taking the brunt of the torque and falling apart under continuous use. The outer shell was printed using PETG filament, which is stronger and more heat resistant than standard PLA. We also installed threads into the shell with heat set inserts to ensure a proper seal and prevent the shell from coming apart at the seams.

The final delivered prototype successfully met all the critical requirements and standards set by the sponsor. Testing demonstrated that the tool flawlessly installed both -05 and -06 diameter code Ergo-Tech® fasteners without stalling, while maintaining a consistent average output of 281 RPM. The system's efficiency was further validated by the Makita 18V battery, which reliably delivered over one hour of continuous operational use.

While the handheld portion of the tool weighed 3 lbs due to the added quick-release mechanism, separating the heavy battery to the waist-pack resulted in a highly balanced and lightweight instrument. Even with the battery attached, the tool weighs less than a standard Makita electric drill. During live trials at Howmet facilities in Fullerton and Carson, the tool earned highly positive feedback in user ergonomic surveys. Ultimately, the prototype delivered a fluid, highly functional solution that successfully prioritized ergonomics and solved the sponsor's high-capacity contamination concerns.

Design A incorporated a framed motor, offering a more robust structure. Instead of dropping pintails forward, this design routes them through the shaft and ejects them from the back of the tool. This method was similar to previous Howmet tools but increased pintail storage capacity and improved ergonomics by redistributing weight. 

A key challenge with this design was ensuring pintails did not get stuck at the collection exit. To mitigate this, we started exploring a vacuum-assisted system that creates suction, ensuring pintails flow smoothly into the collection box without clogging. 

Design B utilized a frameless motor, making it more compact and reducing overall tool weight. The pintail collection system was positioned forward of the motor and gearbox, allowing pintails to drop out of the shaft into a front container, to be emptied later. This design was completely self-contained so that no additional accessories were needed. It also allowed for a standard drill motor and gearbox to be used, since the pintails fell out before ever reaching the motor/gearbox. This also allowed us to put a very high-torque motor-gearbox combination in the tool, which would have enabled it to easily install even the largest fasteners.

The tool being completely self-contained was very beneficial for on-the-fly use. There was no side bag that needed to be worn. The tool just worked on its own. This also meant, though, that the tool in the hand of the technician was going to be heavier, since it had to contain the tool battery and all the pintails. This was a great concern since the technicians may be using this tool all day and would get weary of its additional weight. Also, the fall-through shaft design could be difficult to maintain since the fasteners may be covered with adhesive, which would get stuck in all the crevices this design was prone to have.