Browse Topic: Cutting
Hybrid additive manufacturing (AM) and subtractive manufacturing (SM) processes utilize the combination of AM (e.g., LPBF and DED) and SM (e.g., milling and turning operations) to produce the final part. Due to the poor surface roughness resulting from the uneven melting of powders in AM, the subtractive process is a necessary finishing operation to improve the surface roughness of the AM part. The hybrid AM/SM technology combines the benefits of AM and SM processes to create complex geometry while introducing good surface finish and compressive stress to prevent crack initiation. However, the relationship between large process parameter space and the residual stress/distortion in the part is not well understood, which impedes the adoption of hybrid AM/SM to minimize the residual stress in the final product. To expedite the process optimization, we establish a pipeline for the sequential modeling of additive manufacturing (AM) and subtractive manufacturing (SM) processes. Key accomplishments achieved under this study include (1) development of thermal abstraction technique for the AM process to speed up the macroscale level heat transfer analysis based on the manufacturing factors including scanning vector, laser power, dwelling time, etc.; (2) development of the sequentially coupled thermal-mechanical model to predict the residual stress and distortion after AM process by passing the temperature history obtained from heat transfer analysis to the mechanical analysis at each time point; (3) validation of the thermal-mechanical model for AM using thin-wall structure from literature and cantilever beam structure from UNT’s experiments data; (4) conduction of the parametric study on the chamber temperature and part design in the AM process to demonstrate how the temperature gradient and supporting structure affect the residual stress and distortion; (5) exploration of macro and micro scale models to predict the bulk and surface residual stress after cutting; (6) applying the developed modeling framework to tailoring the hybrid AM/SM process. To support model verification and demonstration, we print cantilever beam structure with different supporting structure designs and cutting strategies to study how these factors affect the final part residual stress and distortion. The data collected in the printing and cutting process is used to examine the applicability of the developed simulation tool.
Prior to 1950, use of the helicopter for evacuation was extremely limited, as military top brass often considered it a worthless contraption; thus, rescue was uncertain at best for downed pilots and wounded soldiers stranded behind enemy lines. However, this all changed in Korea, where twelve U.S. Army helicopters from three detachments, working in tandem with seven, newly created Mobile Army Surgical Hospital (MASH) units, would fundamentally change the Army's medical-evacuation doctrine forever. Using several models of the Bell H-13, the Hiller H-23, and the Sikorsky H-5 and H-19, this small band of courageous pilots pushed themselves and their aircraft to their limits, transporting 21,212 critically wounded soldiers for life-saving surgery to various MASH units, cutting the fatality rate from World War II in half. Adopting the 3rd Air Rescue Squadron's motto, "That Others May Live," these pilots and their helicopters were affectionately known to the wounded as "Angels of Mercy."
The Army is pivoting to meet the challenges of a rapidly evolving threat environment in an increasingly complex world; this requires an agile and adaptive capability, leveraging competition, while operating within the constraints of current budget cycles. A cross cutting architectural approach provides opportunity for the Army to maintain capability overmatch. Recent changes in acquisition law and Army modernization strategy bring particularly strong emphasis on adoption of Modular Open Systems Approach (MOSA) and Open Systems Architecture (OSA). Many current programs within Army Aviation rely on a best effort approach ("Do MOSA") to deliver systems. Current programs measure success on cost, performance, and schedule of the individual program with little historical institutional support for aligning efforts across a larger "whole-system" context, such as a Combat Aviation Brigade (CAB). Specific programs, including the Utility Helicopter Program Office (UHPO) UH-60V and Crew Mission Station (CMS), as well as multiple Science and Technology (S&T) programs supporting Future Vertical Lift (FVL) such as the Mission Systems Architecture Demonstration (MSAD), that exhibit aspects of the architectural momentum in the Army enterprise. The recommendation of our team is to develop an Army Aviation Enterprise Architecture Strategy that will provide the detail necessary in order to develop individual product lines while providing synergy in architecture related efforts into a holistic approach maintaining focus on Army Aviation as a whole force in support of and integrated with the ground commander.
ABSTRACT Nowadays, sensors built in the machine can be used to monitor the machine parameters, and the information can be accessed using data sharing standards such as MTConnect. Overall equipment effectiveness (OEE) is one of the main criteria used to determine the efficiency and performance of the equipment [1]. The main portion of the OEE is related to the equipment utilization [2, 3]. The machine utilization can be calculated with various methods [4, 5]. The novel methodology developed in this study represents the utilization by considering the actual spindle speed and spindle load. The result, not only demonstrates the machine utilization from the time when the spindle was running but also the time when the machine was actually cutting the material as well as the time when the machine was cutting the material efficiently. The generated information, therefore, can be utilized to determine the downtimes of the equipment, increase the up times, and optimize the G-Code programs to higher OEE. The proposed methodology does not involve extra data acquisition equipment or sensors, can produce results in real-time, and will output information about the part cycle time, equipment utilization, and cutting time.
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