Page 12 - 3D Metal Printing Summer 2019

3D AM INSIGHTS
By Dennis Harwig
Directed Energy Deposition Advancements Meeting Demand for Large-Scale Metal AM Parts
Great is the demand for robotic directed energy deposition (DED) addi- tive manufacturing (AM) to create large components, add features and make repairs to large compo- nents, with digital manufacturing proving to be a game-changer for high-mix, low-volume structural manufacturing. Modern CAD-to- path, offline planning software now provides opportunities to apply robotic welding processes to DED AM, cladding and welding of structures. From a manufactur- ing-readiness perspective, several challenges inhibit wide-scale DED implementation.
Process Qualification
DED, one of two metal AM process categories defined by ASTM Interna- tional (the other: powder bed fusion), builds shapes bead by bead, layer by layer, using either computer numerical controlled (CNC) or robotic systems with wire, powder or strip consumables. A wide range of DED processes use welding process equipment, including gas metal arc, plasma arc, gas tungsten arc, laser, electron-beam, and ultrasonic welding. Robotic-arc DED offers maxi- mum build volume and range of motion for depositing shapes and features.
From a qualification perspective, DED AM builds are single-sided, non- integrated build platform (SS-NIBP); single-sided, integrated build platform
Dennis Harwig (dharwig@ewi.org), as senior technology advisor for EWI, focuses on arc welding and directed energy deposition (DED). He also serves as research associate professor- welding engineering at The Ohio State University.
Figs. 1 and 2—A double- sided directed energy deposition structure with integrated build platform—building on both sides of the plate balances residual stress- es and helps to achieve
higher pro- ductivity.
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(SS-IBP); and
double-sided,
integrated build
platform (DS-IBP).
All of these categories
support adding features
and building shapes with
a cost-effective mix of
welding structural forms (plate, pipe, castings, forgings, etc.) and AM. Figs. 1 and 2 show a double-sided DED struc- ture with integrated build platform that can produce beams and other struc- tures. Building on both sides of the plate balances the residual stresses and helps to achieve higher productivity.
The American Welding Society (AWS) recently published a new standard for metal additive manufacturing: D20.1/D20.1M:2019—Specification for Fabrication of Metal Components Using Additive Manufacturing. It provides a framework for manufacturers and sup- pliers to implement AM where the framework resembles other AWS D
Codes. D20 provides separate qualifica- tion approaches for the PBF and DED metal AM process families. DED require- ments leverage the large body of welding standards for consumables, processes, fabrication and inspection. However, challenges remain, as engineers must still define qualification requirements.
The qualification scheme, which includes the standard build design and specimen test matrix, depend on the AM process application. The scheme needs to include specimens that depend on build category (SS-NIBP, SS-IBP and DS-IBP) and material requirements, such as strength, ductility, hardness and toughness. The AWS standard requires tensile speci-