Investigating the Linear Thermal Expansion of Additively Manufactured Multi-Material Joining between Invar and Steel.

This work investigated the linear thermal expansion properties of a multi-material specimen fabricated with Invar M93 and A36 steel. A sequence of tests was performed to investigate the viability of additively manufactured Invar M93 for lowering the coefficient of thermal expansion (CTE) in multi-material part tooling. Invar beads were additively manufactured on a steel base plate using a fiber laser system, and samples were taken from the steel, Invar, and the interface between the two materials. The CTE of the samples was measured between 40 °C and 150 °C using a thermomechanical analyzer, and the elemental composition was studied with energy dispersive X-ray spectroscopy. The CTE of samples taken from the steel and the interface remained comparable to that of A36 steel; however, deviations between the thermal expansion values were prevalent due to element diffusion in and around the heat-affected zone. The CTEs measured from the Invar bead were lower than those from the other sections with the largest and smallest thermal expansion values being 10.40 µm/m-K and 2.09 µm/m-K. In each of the sections, the largest CTE was measured from samples taken from the end of the weld beads. An additional test was performed to measure the aggregate expansion of multi-material tools. Invar beads were welded on an A36 steel plate. The invar was machined, and the sample was heated in an oven from 40 °C and 160 °C. Strain gauges were placed on the surface of the part and were used to analyze how the combined thermal expansions of the invar and steel would affect the thermal expansion on the surface of a tool. There were small deviations between the expansion values measured by gauges placed in different orientations, and the elongation of the sample was greatest along the dimension containing a larger percentage of steel. On average, the expansion of the machined Invar surface was 42% less than the expansion of the steel surface. The results of this work demonstrate that additively manufactured Invar can be utilized to decrease the CTE for multi-material part tooling.

Mitigating Scatter in Mechanical Properties in AISI 410 Fabricated via Arc-Based Additive Manufacturing Process.

Wire-based metal additive manufacturing utilizes the ability of additive manufacturing to fabricate complex geometries with high deposition rates (above 7 kg/h), thus finding applications in the fabrication of large-scale components, such as stamping dies. Traditionally, the workhorse materials for stamping dies have been martensitic steels. However, the complex thermal gyrations induced during additive manufacturing can cause the evolution of an inhomogeneous microstructure, which leads to a significant scatter in the mechanical properties, especially the toughness. Therefore, to understand these phenomena, arc-based additive AISI 410 samples were fabricated using robotic gas metal arc welding (GMAW) and were subjected to a detailed characterization campaign. The results show significant scatter in the tensile properties as well as Charpy V-notch impact toughness data, which was then correlated to the microstructural heterogeneity and delta (δ) ferrite formation. Post-processing (austenitizing and tempering) treatments were developed and an ~70% reduction in the scatter of tensile data and a four-times improvement in the toughness were obtained. The changes in mechanical properties were rationalized based on the microstructure evolution during additive manufacturing. Based on these, an outline to tailor the composition of "printable" steels for tooling with isotropic and uniform mechanical properties is presented and discussed.

Trauma Pod: a semi-automated telerobotic surgical system.

BACKGROUND: The Trauma Pod (TP) vision is to develop a rapidly deployable robotic system to perform critical acute stabilization and/or surgical procedures, autonomously or in a teleoperative mode, on wounded soldiers in the battlefield who might otherwise die before treatment in a combat hospital could be provided. METHODS: In the first phase of a project pursuing this vision, a robotic TP system was developed and its capability demonstrated by performing selected surgical procedures on a patient phantom. RESULTS: The system demonstrates the feasibility of performing acute stabilization procedures with the patient being the only human in the surgical cell. The teleoperated surgical robot is supported by autonomous robotic arms and subsystems that carry out scrub-nurse and circulating-nurse functions. Tool change and supply delivery are performed automatically and at least as fast as performed manually by nurses. Tracking and counting of the supplies is performed automatically. The TP system also includes a tomographic X-ray facility for patient diagnosis and two-dimensional (2D) fluoroscopic data to support interventions. The vast amount of clinical protocols generated in the TP system are recorded automatically. CONCLUSIONS: Automation and teleoperation capabilities form the basis for a more comprehensive acute diagnostic and management platform that will provide life-saving care in environments where surgical personnel are not present.

Ergonomic interface concepts for minimally invasive, remote, and virtual surgical systems.

Traditional open surgical techniques require a surgeon to assume a posture of leaning over the patient with a direct eye-to-hand perspective. As new minimally invasive and remote surgical procedures evolve, the surgeon is not required to maintain the same posture as in open techniques. While more ergonomic postures may be facilitated, some current remote systems have maintained surgeon configurations that are small variants of legacy postures (e.g., maintaining the eye to hand perspective). While the legacy configuration may be more familiar with some surgeons, studies have indicated that it can result in excessive fatigue. Robotics and human factors researchers have determined that fatigue due to inefficiencies in operator interfaces lead to longer completion times and increased task execution errors. This paper discusses operator interface design issues and guidelines that are relevant to remote and minimally invasive surgery, and presents one possible operator interface solution based on the compact remote console deployed for environmental restoration and remote handling of hazardous nuclear waste.