The U.S. Navy builds and sails some of the world’s largest and most powerful vessels and those ships depend on a wide range of advanced systems and machinery to operate. Now, the Navy is moving toward advanced manufacturing of some of the smallest parts of the biggest ships, approving 3-D printing of a drain strainer for a steam line on the USS Harry S Truman. Shipbuilders say it is the first step toward integrating additive manufacturing into the supply chain. This article takes a closer look at how filling the knowledge gaps in the absence or limited development of 3-D printing standards was a necessary building block in adoption of the technology.
It is a beginning. The U.S. Navy builds and sails some of the world’s largest and most powerful vessels and those ships depend on a wide range of advanced systems and machinery to operate. Now, the Navy is moving toward advanced manufacturing of some of the smallest parts of the biggest ships, approving 3-D printing of a drain strainer for a steam line on the aircraft carrier USS Harry S Truman. Shipbuilders say it is the first step toward integrating additive manufac-Ц turing into the supply chain, and it was six years in the making. “The technology is disruptive, it is new and it is growing quickly,” said John Ralls, an engineering manager focusing on additive manufacturing for Huntington Ingalls Industries (HII) Newport News Shipbuilding division. “This is the first approval, the first domino to fall.”
Last year, the Naval Sea Systems Command (NAVSEA) approved 3-D printing of the part after a five to six year effort by HII to fully test and establish technical standards for fabrication. The stainless steel strainer will be installed for a one-year test period. Ralls, while excited about the technology, said filling the knowledge gaps in the absence or limited development of 3-D printing standards was a necessary building block in adoption of the technology.
“We took about five years to address the knowledge gaps,” he said. “There was very little information. Which are the right standards to apply? There was a strong focus on technological rigor.”
Hll worked with and later partnered with printer manufacturer 3D Systems to produce the part and develop appropriate standards. 3D Systems installed its ProX DMP 320 high-performance direct metal addi tive manufacturing system at the Newport News shipyard. It is capable of 3-D printing metal, marine-based alloy parts for fabrication or castings.
Neal Orringer, 3D Systems vice president, said the NAVSEA has lagged other commands in instituting advanced manufacturing but it also presents different obstacles. “We had to learn about our own unique maritime requirements,” he said. “Shipbuilding has a host of different standards. One of the key challenges was to demonstrate repeatability and quality control while printing a part.”
To do that, the developers relied on sensors developed by 3D Systems that can be placed directly into each layer of the printed object. “We can track exactly how the part is being built, archive it, and report every detail,” said Orrin-ger. “We can conduct inspections on each layer while it is being built.”
While the strainer may be small, “It represents the first step in the process toward broader application,” said Ralls. “Technical standards are not yet in place. We laid that foundation for future work.”
Justin Rettaliata is NAVSEA’s technical warrant holder for additive manufacturing and the person charged with bringing the technology into the command’s portfolio. He is enthusiastic about its applications, but notes the tough path toward certifying its credentials in shipbuilding.
“We’re very supportive,” he said, pointing out that multiple suppliers now are pushing additive manufacturing. “But there are challenges with metal. Not a lot of data exist on how the materials perform. If you look at castings, for instance, there are decades of experience and reams of data for certification. So one of our efforts is to develop specifications to provide to industry to allow them to print.”
Rettaliata credits Newport News with determining the need for certification and moving on its own to achieve it, noting the tedious nature of the work. “We looked at what the valve needed to pass [certification] traditionally, and we worked lockstep with Newport News on printing. There were a lot of coupons to make and break. We had to do a lot of brute force testing. There were roughly 300 test coupons.”
The effort also produced a 125-page test report used by NAVSEA to develop technical publication with specifications for industry to follow, he said. The publication is in the final stages of internal review.
“We want to leverage the standard bodies that exist,” Rettaliata said. “But industry is coming at us faster than what the standards bodies can work in developing specifications.”
There’s a lot of future work at Newport News. Ralls notes the shipyard has some of the "most complex machinery on the planet” and the list of manufacturers and suppliers is long. One of the goals is to provide leadership to suppliers and accelerate the adoption of additive manufacturing, noted one 3D Systems official.
“Right now this is the tip of the iceberg in our industry,” said Ralls. "We want to make sure they have the right level of rigor in their design and product.”
The Navy has been using additive manufacturing for several years but the use of 3-D printed metal parts is a newer concept. The test articles passed functional and environmental testing, which included material, welding, shock, vibration, hydrostatic and operational steam, and will continue to be evaluated while installed within a low temperature and low pressure saturated steam system, according to NAVSEA. After the test and evaluation period, the prototype assembly will be removed for analysis and inspection.
“I’d like to see us moving away from intensive testing,” said Rettaliata. Newport News produced roughly 300 test coupons in developing the strainer, so as manufacturers and NAVSEA gain experience it will allow for more rapid qualification and certification.
The Naval Air Systems Command already is moving toward greater implantation of 3-D printed parts. In 2016, it successfully tested a 3-D printed titanium engine nacelle link and attachment on a MV-22B Osprey. More recently, it used a 3-D printed flip-top valve on a T-45 Goshawk breathing mask. The command said 300 valves were printed within one month, critical to a training program. It estimates some 1,000 parts have been approved for use across the fleet by the end of 2018.
Both commands are part of the larger effort by the Navy to bring additive manufacturing into the supply chain. A directive from the chief of naval operations established an executive committee including all naval commands to direct the program. Rettaliata said NAVSEA works with the air command and others to gain lessons learned and exchange data on materials and testing.
“Some of the materials we use are the same but the concentrations are different between air and sea,” he said. Orringer notes that meeting marine standards required reworking some of the tools for parts fabrication. "Our machines result in close to zero oxygen content,” he claimed. ‘Oxidation is a problem, and important when fighting corrosion.”
As the partnership between Newport News Shipbuilding and 3D Systems continues, Ralls and Orringer are looking at a variety of metals and alloys. “We now use titanium for medical devices,” says Orringer. “But it may not be easy to cast titanium (for shipbuilding). But if we can 3-D print it, maybe we’ll see a greater adoption of titanium in other components of shipbuilding.”
Other technologies are also in play. Orringer said the firm is working with sensor developers on identifying flaws and using machine learning algorithms predict, prevent, and detect deformities. “If we can certify the part is made well, we can use the data eventually to demonstrate to the customer that the part is good.”