Processing, thermal, and mechanical issues in shape deposition manufacturing

Abstract: "An overview of Shape Deposition Manufacturing (SDM) is presented, detailing manufacturing, thermal and mechanical issues of concern in making it a commercially viable method for creating arbitrarily shaped three-dimensional metal parts. SDM is a layered manufacturing process which combines the benefits of solid freeform fabrication and other processing operations, such as multi-axis CNC machining. This manufacturing process makes possible the fabrication of multi-material layers, structures of arbitrary geometric complexity, artifacts with controlled microstructures, and the embedding of electronic components and sensors in conformal shape structures. To minimize cost, SDM is implemented using primarily commercially available hardware and CAD modeling and planning software. Important issues toward the production of high quality objects are the creation of inter-layer metallurgical bonding through substrate remelting, the control of cooling rates of both the substrate and the deposition material, and the minimization of residual thermal stress effects. Brief descriptions of thermal and mechanical modeling aspects of the process are also given. Because SDM involves molten metal deposition, an understanding of thermal aspects of the process is crucial. Current thermal modeling of the process is centered on the issue of localized remelting of previously deposited material by newly deposited molted droplets. Residual stress build-up is inherent to any manufacturing process based on successive deposition of molten material. Current mechanics modeling is centered on the issue of residual stress build-up and its potential effects, including part warping and debonding between deposited layers. Shot peening is an operation currently used to control residual stress effects and preliminary work studying its effects is also presented."