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.

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.