||Dennis D. Harwig, William Mohr, Mike Carney, Susan Hovanec, Justin Rettaliata, Ryan Hayleck, Evan Handler, Jeff Farren
Introduction: Metal additive manufacturing (AM) technology is rapidly maturing, but shipbuilding implementation has been slow due to lack of fabrication standards. The standards’ development process is slow for many reasons including large number of new AM process types and lack of proven qualification and certification schemes. Directed energy deposition (DED) processes, which includes variants of arc, laser and electron beam welding processes, have the least risk since they leverage mature welding technology. Wire-based DED processes should leverage welding standards to ensure integrity of AM structures, and industry experience where welding processes have been used for decades to add features to structure and / or shape weld structures. Here, these applications were qualified as structural buttering. Gaps for new DED AM standards include understanding process-feature-property relationships such as anisotropic property changes over large build orientations, and requirements for digital manufacturing. AM components are “digitally” manufactured from computer-aided design (CAD) files using computer-aided manufacturing (CAM) solvers. To solve the qualification gap, this project developed procedure qualification scheme for DED processes. These requirements will be incorporated into a new Technical Publication - NAVSEA Process Requirements for Metal Directed Energy Deposition. This technical publication will include the framework for qualifying DED procedures, including procedure qualification requirements, part verification qualification requirements, and manufacturing verification requirements to ensure component (part) build quality.
Experimental Approach: This project developed standard qualification builds (SQBs), nondestructive evaluation (NDE) plans, property test matrices, and procedure specification & qualification record forms for the most common DED applications that include:
• Single-sided integrated build platform (SS-IBP),
• Single sided non-integrated build platform (SS-NIBP),
• Double-sided integrated build platform (DS-IBP), and
• Double-sided non-integrated build platform (DS-NIBP).
The SQBs provided sufficient build material for testing specimens in the x-, y-, and z-directions. Each build contained both single pass wall and multi-bead multi-layer (MBML) block features to provide a build feature window. An array of tensile specimens were designed to characterize properties in each build direction and elevation. Bend tests were also included to further demonstrate soundness and ductility. For single-sided SQBs, the build platforms were sized to minimize distortion. For integrated build platform SQBs, additional property test specimens were included to characterize build platform interface and heat affected zone (HAZ) properties. To ensure soundness, builds were machined prior to radiographic and ultrasonic inspection to MIL-STDs. Several SQBs were made using the Pulse Gas Metal Arc Pulse (P-GMA) DED process to validate the qualification schemes and characterize DED build quality. SGBs were made for the following applications:
• Stainless steel ER308L GMA-P DED on 304L SS-NIBP,
• Nickel aluminum bronze (NAB) GMA-P DED on NAB SS-IBP, and
• High strength steel (HSS) ER100S-1 GMA-P DED on HY80 DS-IBP,
Results and Discussion: The ER308L P-GMA DED builds evaluated effects of deposit size (heat input) and preheat / inter-pass temperature ranges. The process was setup to use 0.045 diameter ER308L electrodes and argon-CO2 shielding gas. A systematic parameter development method was used to develop parameters at a constant bead size by fixing the wire feed speed (WFS) to travel speed (TS) ratios of 15 for small beads and 30 for large beads. Preferred parameters were selected and used to make two SQBS at each bead size (WFS/TS ratio). For each bead size, a SQB was built at both 0 to 350F and 500 to 750F interpass temperatures. The GMAW-P process produced sound SQBs that met ultrasonic and radiographic inspection criteria. Bend tests further demonstrated soundness of both wall and block deposits in different planes.
Tensile properties of the ER308L standard qualification build exceeded all property requirements for the ER308L filler material per AWS A5.9 in x- and y-directions. ER308L builds exceeded property requirements for 304L base materials for yield and ultimate strength per ASME SA 240. Elongations were slightly lower than base metal requirement of 40% in y- and z-directions. Yield strength decreased in ER308L builds with increasing bead size and preheat / interpass temperature. The greatest strengths were in the small bead and low preheat / interpass build condition.
The NAB SS-IPB and HSS DS-IBP builds are in-progress and will be reported at the presentation.
Conclusion: Procedure qualification schemes were determined to include a standard qualification build, a specimen test matrix, NDE test plans, and AMPS and AM-PQR forms. Schemes were developed for both single-sided and double-sided builds with or without an integrated build platform. A matrix of DED AM procedure qualification schemes offer reduced risk for DED implementation.
1) D.D Harwig,, W. Mohr,, S. Hovanec, J. Rettaliata, R. Hayleck., E Handler, and J.Farren, “Tech Pub Qualification Scheme Development for Arc Directed Energy Deposition Additive Manufacturing”, In Proceedings of the Ground Vehicle Systems Engineering and Technology Symposium (GVSETS), NDIA, Novi, MI, Aug. 13-15, 2019.