Army Corps of Engineers 3D Prints New Poe Lock Arrestor Arm

As America’s civil works infrastructure ages, managers need innovative solutions to replace parts that have been in service for nearly a century. Often, these original components were fabricated using vintage material and manufacturing methods, making them costly, burdensome and time-consuming to replace.

Responding to this need, the U.S. Army Corps of Engineers (USACE) is employing cutting-edge 3D-printing techniques to manufacture these parts faster and at a lower cost while maintaining, and even improving, their properties.

In early March 2024, the USACE Detroit District installed the largest U.S. civil works infrastructure component produced by a 3D printer — a 12-foot-long metal part for the ship arrestor system on the Poe Lock, one of the two active locks on the Soo Locks facility. Building on years of research performed by the U.S. Army Engineer Research and Development Center (ERDC), the part was manufactured in 12 weeks, compared to a projected 18-month lead time for conventional manufacturing. The part was installed, tested and commissioned during the Soo Locks’ winter maintenance cycle, which is a 10-week maintenance closure period set by federal regulation.

The rapid repair ensured normal operations at Poe Lock, a major transit point for domestic iron ore, where an unanticipated closure would be “catastrophic for the nation,” according to a 2015 Department of Homeland Security (DHS) study.

“We secure our nation and energize our economy by operating, maintaining and preserving strategic water resources and infrastructure,” says Lt. Col. Brett Boyle, commander of the USACE Detroit District. “That is a challenge as our infrastructure continues to age. These challenges are opportunities to deliver our program in new, innovative ways that make us more efficient.”

The ship arrestor project gave them that potential. “The Poe Lock ship arrestor project has been one such opportunity for our team to work with ERDC researchers to harness existing 3D printing technology in a way that safely delivered superior quality, while cutting through the extended lead times of today’s environment,” Boyle says.

Damaged Arrestor Required Rapid Response

The Soo Locks mechanical ship arresting system protects the lock’s miter gates, a critical system component, from an emergency impact with a ship. Each lock has two arrestors — one located upstream of each miter gate.

“The system is designed to safely and quickly halt a 100,000-ton vessel loaded with commodities over the course of 72 feet,” says, Clint Dougherty, a Detroit District structural engineer.

The Poe Lock ship arresting system underwent a rehabilitation performed by prime contractor OCCI Inc. from early 2022 through the winter maintenance closure period of 2024. In February 2023, cracks were found in one of the 60-year-old lever arms used to raise and lower a large boom on the Poe Lock’s arresting system. While temporary repairs were made prior to putting it back into service for the 2023 navigation season, the USACE needed new replacement lever arms to ensure the long-term future use of this critical safety component.

After considering various design alternatives, Detroit District engineers ultimately selected additive manufacturing (AM), or 3D printing, as the best option. During this process, they reached out to the ERDC for its technical expertise in manufacturing, testing and procuring AM parts. The USACE solicited and awarded the contract for the lever arms to Lincoln Electric.

Detroit District engineers designed the arms and worked with Lincoln Electric in determining the best print strategy to mitigate distortion, obtain the desired surface finish and material mechanical properties, and ensure adequate quality control.

“Lincoln Electric and USACE developed an additive print strategy to print the part in two pieces, one approximately 4,000 pounds and the other 2,000 pounds, made from high-strength, low-alloy steel (HSLA), then weld them together at their Baker Industries facility located in metro Detroit,” Dougherty says.

Dr. Zack McClelland, a research mechanical engineer at ERDC’s Geotechnical and Structures Laboratory, says the project featured a strong collaboration of ERDC’s experience in AM, the Detroit District’s intimate knowledge of the Soo Locks and the application needs for the arrestor arm, and Lincoln Electric’s expertise with fabricating and welding large-scale components.

“There are only a handful of places in the world that can print a metallic part at this scale, and a lot of those parts tend to be cylinders,” McClelland says. “The Poe Lock arrestor arm really shows what can be done with the technology in terms of complex designs, and it signals a paradigm shift in how large parts can be manufactured.”

The lever arm was machined, coated and installed by OCCI and its subcontractors (machining by Fulton Iron and coating by Coatings Unlimited) in early March 2024. The Soo Locks reopened for the navigation season on March 22, after OCCI successfully commissioned the new lever arm.

Old Parts Need New Ideas

Replacing large, vintage components is a particular need for the USACE, with much of the nation’s infrastructure now operating well beyond its original design life. Many of these parts are unique to individual projects, making their replacement more difficult. If one was to suddenly break, that failure could shut down a facility for months, causing significant national economic damage.

This is true at Poe Lock, which was built in 1969 and still has most of its original parts. “Roughly 88% of domestically produced high-strength steel used to manufacture products like automobiles and appliances is made with iron ore that transits the Soo Locks,” says Mollie Mahoney, Detroit District senior project manager.

Of the iron ore that transits the Soo Locks, 95% of it is restricted to Poe Lock due to vessel size. A six-month Poe Lock closure would temporarily reduce the U.S. gross domestic product by $1.1 trillion, resulting in the loss of 11 million jobs, according to the DHS study.

Faced with this challenge, advances in AM offer transformative potential. As the technology has matured to support large-scale builds, the ERDC has extensively studied how it could be used by the U.S. Army and Department of Defense. Now, it is applying the lessons learned from these military projects to modernize USACE infrastructure components and structures.

The ERDC has collaborated with Eaton on military AM research for more than a decade. The two organizations recently leveraged that partnership while also teaming with the University of Toledo on a new research project focused on civil works infrastructure that resulted in the Poe Lock arrestor arm.

“This technology not only strengthens our national infrastructure but also reinforces how the power of the collaboration is shaping the future of manufacturing and enabling the safety and efficiency of critical infrastructure,” says Bryan Farrens, Eaton director of government programs.

This project incorporated wire-arc additive manufacturing (WAAM), an emerging process that supports complex, large-format metal builds.

“We found the researchers and industry partners shared our passion for solving problems in the field,” says Peter Dodgion, chief of the USACE asset management branch. “Our field folks in Civil Works know where the problems with fabrication are. All we had to do was connect those researchers with our folks in the field and real-world solutions began to emerge.”

An important focus was to ensure AM could meet USACE requirements for reliability, utility and cost efficiency, particularly given the intense stressors placed on civil infrastructure. Extensive research was conducted to characterize material properties of existing vintage parts and to ensure the 3D printed material could meet or exceed their performance.

“We have been trying to advance the scale and reduce the cost using new approaches for manufacturing,” says Dr. Robert Moser, ERDC senior scientific technical manager for materials, manufacturing and structures. “A lot of our research has gone into investigating the best parameters to produce some of the metals we want and to ensure we minimize any defects that would affect strength or fatigue. We have to validate the mechanical performance of those parts and ensure they are as good as or better than the parts we already have. In this case, it was at least 20 or 30% stronger than the metals that were previously being used.”

This effort will also create a digital USACE parts inventory that will accelerate the turnaround time for replacement components tenfold and eliminate the need to physically store large parts and molds for future use.

Subsequent research will study the production of stainless steel materials, as well as the ability to incorporate multiple metals — a capability that doesn’t exist with traditional manufacturing, but one that could enable greater efficiency, such as only placing a fatigue-resistant material where it is needed rather than using it as the sole metal throughout the entire project.

The ERDC and its partners are also studying how parts can be better designed using contemporary understanding of structural loads. In the past, parts were often overdesigned based on conservative assumptions, but today’s increased knowledge, combined with emerging material research, enables improved performance with lighter weight, with parts precisely scoped to meet actual needs.

Building on the success of the Poe Lock arrestor arm project, these research efforts will further advance USACE’s LFAM capability. Ultimately, this will reduce the turnaround time to procure components from months to days, improving the reliability of critical flood risk management and navigation infrastructure to protect communities and preserve economic growth.