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Wire electric discharge machining (wire EDM) is a non-traditional material removal method that is commonly used in additive manufacturing (AM) applications to efficiently remove AM metallic parts from their build plates. However, a persistent problem in wire EDM of AM parts is wire breakage which leads to longer machining time, challenges in rethreading wire, and wasted material, decreasing efficiency. This study focuses on the wire EDM strategies to mitigate the two main causes of this issue in AM applications: intermittent workpiece thickness (i.e., support structures) and trapped metal powders. When AM metallic parts are made using a powder bed fusion (PBF) process, pockets of non-fused powder can become trapped in the part and supports. This powder creates a non-uniform cutting path which leads to wire breakage. Additionally, the interrupted cuts and nonuniform support thickness result in interactions between wire and AM support design that is currently not well understood. This study investigates the effects of various AM support structures on EDM wire breakage and overall machining time by understanding the effects of three critical EDM process parameters (voltage, wire feed rate, water flushing rate) on the machinability of 316L SS AM builds. In addition, the effect of heat treatment cycles on wire EDM machinability of AM parts with entrapped powder is investigated. The results of this study show that reducing the wire EDM voltage eliminates wire breaking, and that thicker supports provide steadier cutting conditions for the wire. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) is accepted as a transformative technology for rapid production of parts based on digital models through direct printing of a range of materials (e.g., metals, polymers, and ceramics). Recent advancements in the binder-jetting AM process (i.e., 3D sand-printing (3DSP)) enables direct production of sand molds and cores for metal casting. AM has been attractive to manufacturers due to the ability to produce complex and customized parts in low batch production. Traditional mold design for gravity castings experience higher scrap rates due to challenges in controlling turbulence and air entrapment. In this research, mathematically designed sprue geometries that can be produced via 3DSP are presented along with their effect on mechanical and metallurgical properties of castings through numerical modeling, computational simulation, and experimental validation. The casting properties are contrasted to conventional straight sprue castings for two different alloys: aluminum alloy 319 and gray cast iron class 30. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), computed tomography scanning (CT), and 3-point bending tests are performed to characterize microstructure, casting defects, elemental composition, and mechanical properties for castings of each gating system design. For aluminum alloy 319, a statistically significant increase of 10% in flexural strength was found using the conical-helix sprue geometry as well as a reduction of 25% in casting defects. In gray cast iron class 30, no statistically significant differences are found between the flexural strength of the conical-helix and benchmark straight sprue as expected in a short freezing range alloy. [ABSTRACT FROM AUTHOR]