A comprehensive review of the methods and mechanisms for powder feedstock handling in directed energy deposition

Directed Energy Deposition (DED) is a subset of Metal Additive Manufacturing (MAM) technology with applications not just in part fabrication but also in surface cladding and part restoration. The process uses a focused heat source to create a melt pool into which a feedstock material is injected, thereby, increasing the mass and volume of the melt pool. Through synchronization, achieved via a CNC machine tool or a robotic arm, between the motion of the heat source, feedstock delivery, and the substrate complex parts can be fabricated layer-by-layer. Metering, conveyance, and delivery of powder from feedstock reservoir to melt pool play an essential role in part quality and process efficiency. Conventionally these tasks are carried out by pneumatic methods; however, several alternatives exist. This article isolates feedstock handling in DED and presents an overview of key technologies that are used. Several types of powder feed nozzles, along with their advantages and limitations, are briefly outlined. Almost all commercially available DED units adopt the use of inert carrier gas for powder feedstock handling. However, a few novel ideas that can serve as possible alternatives to this widely accepted pneumatic method are presented here. Also, some of these mechanisms for powder handling, outlined in the context of DED, can be extended for other MAM processes such as Dry Powder Printing (DPP) and Selective Powder Deposition (SPD). Through highlighting key considerations that are pertinent to feedstock handling, the article aims to provide a guide for designing or procuring new setups that best suit the application. A thorough understanding of existing technologies for feedstock handling in DED can help in innovating new ones to provide creative solutions to the problems faced by the current ones.