The Current State of Metal Additive Manufacturing (AM)
In 2022, the U.S. Navy installed the first-ever permanent metal AM machine aboard a U.S. naval vessel. This technology is projected to be groundbreaking by reducing resupply logistics and diminishing obsolescence: “For the Navy, the greatest immediate potential is in the less-exotic field of logistics” [1]. However, getting a contraption that can create almost any replacement part onto an active-duty warship has had its challenges and obstacles. This article will focus on metal AM and detail the development of concepts from the early 2000s until now, along with the history of challenges in the field.
AM has experienced a renaissance in the last decade. Formerly only available for use by large companies with extensive capital expenditure budgets, modern AM has significantly decreased in price, branching out into applications for industry and hobbyists alike. Naval planners took note of this technology and followed suit with other government bodies in proposing shipboard augmentation of supply departments with AM. This would reduce the need to carry large stocks of premanufactured replacement parts, diminish delivery costs and timelines for spare components, and free up coveted space on dense vessels.
Challenges of Shipborne Integration
As integrating AM into the Navy’s logistical operations quickly became a priority, challenges rose to the forefront. AM machines are typically set up in a laboratory or industrial setting that offer ample space for a large machine, a stable building, and storage for many different printing materials. If the Navy were to install this capability into ships, they would need to address the harsh environments and limited resources of being on the open ocean. For example, a popular industrial version of metal AM is selective laser sintering, which involves powdered metal being melted layer by layer as new powder is wiped on top of the solidified layer. This technique creates high-quality parts that can equal or surpass traditionally manufactured parts created from sources like titanium, Inconel, and steels. However, the powdered metal, particularly the titanium variety, can become explosive with improper handling due to its high surface area-to-volume ratio interacting with oxygen in the air.
In an industrial setting, this is managed by requiring special safety measures and trained personnel to handle the raw materials. In a shipborne setting, the roll of the ocean could disrupt this powder, causing hazardous spills. Certain metal AM technologies may be optimized for a lab setting; however, they could prove disastrous in a shipborne setting. This potential detriment could easily outweigh the benefits of a vertically integrated AM machine. Therefore, determining what kind of raw material to use was an important consideration.
Any AM system requires consistent electrical power for quality part manufacturing, and shipborne power generation can experience fluctuations. Most ships rely on auxiliary engines, generators, and/or shore power to provide electricity, all of which are susceptible to fuel supply issues and power transmission issues. Power fluctuation can also occur when other heavy demand systems come online, stressing the grid and giving uneven electrical distribution. Scheduled maintenance and repairs may even become an issue, as this can occur on one side of the ship and affect systems on the other side. A power supply disruption, even for a few milliseconds, could immediately affect the ongoing printing process and potentially lead to incomplete or failed prints. Onboard AM machines would need to have their own semi-isolated grid or specific equipment to ensure there are no power issues during the critical printing process.
Other environmental issues to consider on a ship would be the constant motion caused by waves and tides. This could change the powder distribution or print head angle and result in poor print quality and wasted raw materials. Vibrations from ship engines could have deleterious effects on the precision of AM machines. The notorious salt fog and salty air environment of an ocean-going ship could wreak havoc on an AM machine designed for the sterile laboratory setting. A shipborne AM machine would have to be protected from all these conditions to bring the benefits anticipated by naval logistics. Due to the untested nature of having AM onboard a ship, there was an additional X factor consideration. And beyond the known hazards were the unknown risks that scientists could anticipate or predict.
The idea of having an AM machine accessible on every ship in the United States’ fleet also presents its own challenges. Many AM machines require an internal atmosphere of inert gases which would need to be resupplied occasionally. Any machine that needs a special gas atmosphere must consider off-gassing, proper containment, leak prevention, and proper personal protective equipment (PPE). A typical ship’s interior is a self-contained atmosphere. Without air circulating, harmful gases can easily fill a watertight room. Then the feedstock itself is not available at every resupply station, as it can only be produced through specialized manufacturing processes. Training and PPE would also need to be addressed because of the hazardous equipment and materials used in the printer.
The First Navy Ships to Receive Metal AM
In the latter half of 2022, the Navy’s Wasp-class amphibious assault ship USS Bataan (Figure 1) received the first-of-its-kind, permanent metal AM machine. Based in Norfolk, VA, the nearly 850-ft “Harrier Carrier” supports Navy and Marine Corps teams and has the capabilities to print on-demand replacement parts. The Wasp-class ships were chosen to receive the first metal AM machines due to the role they play in the U.S. military. These ships house both Navy and Marine forces and materiel, which allows a wider avenue of research and exposure on parts where form and fit are key across several different platforms for both branches. During its most recent outfitting in November 2022, the USS Bataan was equipped with a Phillips additive hybrid powered by Haas [2], which consists of a combination of a Haas TM-1 computer numerical control (CNC) mill and a Meltio laser metal wire deposition head. The Haas TM-1 platform has been a proven platform on ships before and therefore provides minimal new variables for the Naval Sea Systems Command (NAVSEA) to overcome when testing the AM features of this system.
Figure 1. USS Bataan (Source: Adlughmin [3]).
The advantage of this system, according to Phillips Corporation [4], is that it is a traditional CNC subtractive manufacturing system with an added AM capability. The additive features of this machine are like welding, in that a metal wire like 316L stainless steel is fed into a print head where focused lasers melt it to a rough shape. The process begins with a metal powder material being fed into the system, where it is melted and deposited layer by layer onto a substrate using a high-power laser to a precision of ±0.010 inches. The subtractive feature of the hybrid system then comes into play, the HAAS CNC machine mill refines the rough shape out using traditional CNC milling, and the result is a highly accurate part. The overall hybrid AM system generates significantly less waste compared to traditional manufacturing.
316L stainless steel, used in the Phillips additive hybrid machine [4], is a popular material choice for marine environments due to its excellent corrosion-resistance properties. The “L” in 316L stands for low carbon, meaning it has a reduced carbon content compared to other grades of stainless steel. This lower carbon content helps prevent sensitization, a process where carbon combines with chromium to form chromium carbide, which can cause the material to become susceptible to corrosion. Additionally, 316L stainless steel has good strength and toughness properties, as well as excellent weldability and formability, which makes it easy to fabricate into complex shapes and structures.
In terms of applying this hybrid AM machine, sailors will have the capability to print over 300 NAVSEA-developed AM technical data packages (TDPs) on demand. In addition, parts can be repaired by a method similar to cold spray, i.e., adding back material to a broken section of an existing part and then machining back excess material to repair the broken part.
In July 2022, another Wasp-class ship, the USS Essex, received a different style of AM technology [5]. In Pearl Harbor, HI, the ElemX made by Xerox was lifted onto the USS Essex via a Conex box into the cargo bay of the ship. (This machine will be permanently housed inside the metal container, protecting it from the environment.) The “mini factory in a Conex box” was previously installed at the Naval Postgraduate School in Monterey, CA, in 2020. For two years, testing was conducted there on this unique solution to assess its capabilities for incorporation into naval vessels. With this prior research well documented, the results of the laboratory setting of ElemX, in which control parts were printed, will be compared with results gathered from the deployed USS Essex [5].
The ElemX claims to be a user-friendly metal AM machine—no hazardous metal powders and no need for extensive facility modifications or PPE. It uses standard aluminum wire melted into a recyclable powder support. The printer utilizes a proprietary “liquid metal” technology; “unlike alternative AM technologies, there are no metal powders used with ElemX and no need for PPE or other considerable safety measures. Engineered to bring simplicity to the supply chain process, ElemX is said to be the ideal option for spares, repairs, and low-volume production parts” [6].
Liquid metal printing utilizes the same concepts that Xerox used decades ago in inkjet printing but substitutes ink with liquid metal and allows printing in a third dimension [7]. Aluminum wire is fed from a spool onto a “hopper” surrounded by a copper wire with a pulsed voltage, which melts the metal wire into a liquid and deposits it to a heated “substrate” where it is solidified. The heated build plate also requires a noble gas shroud environment like welding and protects the molten pool of metal against the elements in the atmosphere. Like in other three-dimensional printing styles and technologies, liquid metal printing requires its own unique set of parameters that must be optimized and tested for size of ejected drop, droplet ejection, and thermal diffusion from the droplet.
The Xerox ElemX uses A356/4008 aluminum alloy wire, which has been used in a variety of marine applications, such as boat hulls, propellers, and other marine structures. Its combination of excellent corrosion resistance and high strength-to-weight ratio makes it an ideal material choice for marine environments. It is a high-silicon alloy that contains 7% to 9% silicon, which gives it superior corrosion resistance compared to other aluminum alloys. This high-silicon content creates a dense, protective oxide layer that helps to prevent corrosion in marine environments, where exposure to saltwater and other corrosive agents is common.
Shoreside Testing and Collaboration
The objective of these printers onboard the USS Bataan and Essex is for current testing. As discussed earlier, there are many factors theorized to affect print quality. But there is also a concern that there are unknown factors yet to be fully realized that need to be addressed and solved before full operation and expansion to other ships can occur. Speaking with Professor Ibrahim Gunduz at the Naval Postgraduate School (NPS), his group aims to assist finding those unknown factors in a joint service effort (NAVSEA, U.S. Coast Guard, Marines, and Army) [8].
NPS will also provide recommendations for equipment, engineering standards, academic studies, and testing for AM to the group and oversee the land-based testing for the ElemX machine currently on the USS Essex. This involves installing the printer on their premises in California and printing a series of laboratory test prints and measuring every aspect of the result, including mechanical properties, correlating environmental data, and TDPs. These first test prints will then be directly compared to identical parts made while the same machine is deployed at sea. The twin tests conducted at sea will use an array of onboard sensors, such as pressure, humidity, gyroscopes, etc. This instrumentation will determine and monitor atmospheric and motion parameters. NPS will then feed the results of the experiments back to the joint AM group. When addressing the foreseeable issues of printing with metal on a ship, these two printers will utilize different AM technologies to address some of the issues in different ways. According to NPS, this was a choice made consciously and chosen so that they complement each other [8].
It is also speculated that using artificial intelligence (AI) or machine learning (ML) aboard these ships can increase the reliability of AM [9]. One of the key advantages of employing AI and ML in AM is the ability to enable real-time quality control. Instead of relying solely on post-processing inspections, which can be time-consuming and costly, the AI system can provide immediate feedback during the printing process. This allows early identification and rectification of issues, minimizing the number of failed prints and reducing material waste. Using sensors, AI algorithms can be trained to identify defects and anomalies in the AM process, enabling real-time quality control, minimizing the need for post-processing inspections, and reducing the amount of time wasted by identifying or correcting failing prints before they finish.
The Navy recognizes that in the long term, neither of these printers can print large items like a torpedo or a dinghy, but it does provide a great solution for small, durable parts in relatively low quantities. For example, the idea of printing custom-built drones has been of great interest to naval planners from the beginning of this effort. This would keep service men and women out of harm’s way while being able to have a drone built for a certain mission [9]. Data files can be sent via satellite to the USS Essex to quickly build a custom frame.
Back in 2015, while the USS Essex had a polymer AM machine installed, a test quadcopter drone frame was printed and fitted with a transmitter and a camera [3]. Its mission was to fly over ships to help stop piracy and drug smuggling. The evolution from polymer to metal could enhance drones’ capabilities, larger payload, longer flight time, and the ability to fly in harsher conditions. The addition of these printers can allow warfighters to carry less cargo for every perceivable drone mission and only carry raw printing materials and electronics; the same would apply to another mission where parts could be printed, depending on what is needed at that time.
Success Stories Onboard Metal AM Operation at Sea
In August 2023, the crew of the USS Bataan successfully used the Phillips Additive Hybrid System to create and replace a sprayer plate for a de-ballast air compressor while at sea [10]. The metal sprayer plate was essential for forcing pressurized air through saltwater tanks to discharge accumulated saltwater, a process used to lower the ship’s draft for amphibious operations.
The repair effort was led by Machinery Repairman First Class Mike Hover, who created a computer-aided design (CAD) model of the sprayer plate using a functional one from another system as a reference [10]. NAVSEA’s “Apollo Lab” provided engineering support and training, refining the CAD file. Mechanical engineer Bryan Kessel at the Naval Surface Warfare Center, Carderock Division worked on software instructions for the metal AM machine. These instructions were securely transferred back to the ship, where the sprayer plate was produced and installed. The replacement part saved time that would have been spent obtaining a replacement assembly. This achievement, completed in just five days, marked the first time the ship’s installed metal AM machine was used under such conditions for an actual repair.
Conclusions
The journey to implement AM on ships has presented challenges such as addressing environmental factors, ensuring safety measures, and optimizing print quality. The U.S. Department of Defense bodies like NAVSEA, academic institutions like NPS, and industry leaders in AM technology are all actively contributing to our understanding of and providing solutions for these challenges. The promise of permanent metal AM machines on vessels like the USS Bataan and Essex opens new possibilities for reducing resupply logistics, mitigating obsolescence, and enabling on-demand production of replacement parts. Success stories like the de-ballast air compressor repair give promise to the Navy’s efforts to leverage AM technology to enhance readiness and self-sufficiency in maintaining ships and weapons systems in challenging operational environments. This successful application of AM technology demonstrates the “tip of the iceberg” for capabilities that can be achieved.
References
- Cheney-Peters, L. S. “Print Me a Cruiser!” U.S. Naval Institute, https://www.usni.org/magazines/proceedings/2013/april/print-me-cruiser, accessed on 28 June 2023.
- Listek, V. “U.S. Navy Installs Meltio Hybrid Metal 3D Printer to Reduce Repair Times.” 3DPrint.com, https://3dprint.com/297004/us-navy-installs-meltio-hybrid-metal-3d-printer-to-reduce-repair-times/#:~:text=In%202022%2C%20the%20USS%20Essex,printer%20on%20November%203%2C%2-02022, accessed on 28 June 2023.
- Adlughmin. “U.S. Navy Is 3D Printing Custom Drones Onboard the USS Essex.” 3DPrint.com, https://3dprint.com/85654/us-navy-3d-printed-drones/, accessed on 28 June 2023.
- Dhananjay. “U.S. Navy Installs on Board the First Phillips Additive Hybrid Metal 3D Printing Solution Powered by Meltio and Haas.” Phillips Corporation, https://www.phillipscorp.com/us-navy-installs-on-board-the-first-phillips-additive-hybrid-metal-3d-printing-solution-powered-by-meltio-and-haas, accessed on 28 June 2023.
- Verger, R. “A Navy Ship Got a Giant Liquid-Metal 3D Printer.” Popular Science, https://www.popsci.com/technology/navy-ship-gets-large-metal-printer, accessed on 28 June 2023.
- Metal AM Magazine. “Vertex to Offer Contract Manufacturing With Xerox ElemX Liquid Metal.” https://www.metal-am.com/vertex-to-offer-contract-manufacturing-with-xerox-elemx-liquid-metal, accessed on 28 June 2023.
- Ruggles, A. “Liquid Metal 3D Printing.” FLOW, https://www.flow3d.com/liquid-metal-3d-printing/#:~:text=Ejected%20droplets%20travel%20to%20a,deposition%20of%20the%20incident%20droplets, accessed on 28 June 2023.
- Curran, C., I. Gunduz, and CAPTs J. Gray and G. Hobson. Personal communication, 7 March 2023.
- Isi, C. “AI-Assisted 3D Printing: Insights on Emerging Trends and Technologies.” Protolabs Network, https://www.hubs.com/blog/ai-assisted-3d-printing, accessed on 28 June 2023.
- Metal AM Magazine. “NAVSEA Improves Readiness of USS Bataan With On-Board Metal Additive Manufacturing.” https://www.metal-am.com/navsea-improves-readiness-of-uss-bataan-with-on-board-metal-additive-manufacturing, 29 August 2023.
Biography
Matthew Seidel is a mechanical engineer working with Innvometric to develop inspection and quality control software. He is an expert in metrology, AM, and shipborne systems. He has worked as a design engineer for the Navy, a dimensional metrologist, and a consultant ship’s engineer for private yachts. Mr. Seidel holds a bachelor’s degree in mechanical engineering from the South Dakota School of Mines and Technology.