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Direct digital manufacturing (DDM) is the creation of a physical part directly from a computer-aided design (CAD) model with minimal process planning and is typically applied to additive manufacturing (AM) processes to fabricate complex geometry. AM is preferred for DDM because of its minimal user input requirements; as a result, users can focus on exploiting other advantages of AM, such as the creation of intricate mechanisms that require no assembly after fabrication. Such assembly free mechanisms can be created using DDM during a single build process. In contrast, subtractive manufacturing (SM) enables the creation of higher strength parts that do not suffer from the material anisotropy inherent in AM. However, process planning for SM is more difficult than it is for AM due to geometric constraints imposed by the machining process; thus, the application of SM to the fabrication of assembly free mechanisms is challenging. This research describes a voxel-based computer-aided manufacturing (CAM) system that enables direct digital subtractive manufacturing (DDSM) of an assembly free mechanism. Process planning for SM involves voxel-by-voxel removal of material in the same way that an AM process consists of layer-by-layer addition of material. The voxelized CAM system minimizes user input by automatically generating toolpaths based on an analysis of accessible material to remove for a certain clearance in the mechanism's assembled state. The DDSM process is validated and compared to AM using case studies of the manufacture of two assembly free ball-in-socket mechanisms.

Lab-on-a-chip platforms present many new opportunities to study bacterial cells and cellular assemblies. Here, a new platform is described that allows application of uniaxial stress to individual bacterial cells while observing the cell and its subcellular assemblies using a high resolution optical microscope. The microfluidic chip consists of arrays of miniature pressure actuated valves. By placing a bacterium under one of such valves and partially closing the valve by externally applied pressure, the cell can be deformed. Although large pressure actuated valves used in integrated fluidic circuits have been extensively studied previously, here those microfluidic valves are downsized and flow channels with rectangular cross-sections are used to maintain the bacteria in contact with cell culture medium during the experiments. The closure of these valves has not been characterized before. First, these valves are modeled using finite element analysis, and then the modeling results are compared to the actual closing profiles of the valves, which is determined from absorption measurements. The measurements and modeling show with good agreement that the deflection of valves is a linear function of externally applied pressure and the deflection scales proportionally to the width of the flow channel. In addition to characterizing the valve, the report also demonstrates at a proof-of-principle level that the device can be used to deform a bacterial cell at considerable magnitude. The largest deformations are found in 5 μm wide channels where the bacterial width and length increase by 1.6 and 1.25 times, respectively. Narrower and broader channels are less optimal for these studies. The platform presents a promising approach to probe, in a quantitative and systematic way, the mechanical properties of not only bacterial cells but possibly also yeast and other single-celled organisms.

High pressure turbine (HPT) blades manufactured from single crystal (SX) materials exhibit tip degradation during service resulting in loss of coatings and parent metal, primarily from abrasion, thermal-mechanical fatigue cracking (TMF), creep, and oxidation. Currently, Gas Tungsten Arc Welding (GTAW) and Laser Beam Welding (LBW) with Merl 72 and Rene 142 (R142) welding materials are used for repairing the tips of SX HPT blades. Tips repaired with Merl 72, despite the superior oxidation resistance of the cobalt welding material, are prone to cracking due to the low mechanical properties of the Merl 72 welds at temperatures exceeding 1800°F (982°C). Additionally, despite the high strength of R142 in its cast condition, R142 welds are prone to weld stress-strain cracking and thus require preheating of the blades above 1700°F (926°C) to repair the part with a predetermined level of micro cracking present. Preheating can adversely affect the inert atmospheric conditions of the argon protection. This inadequate shielding of the welding area may result in contamination of welds with non-metallic inclusions which reduce creep and TMF properties. The current study focuses on substantiating the replacement of Merl 72 with alternative LW3 and LW4280 nickel based welding materials for minor dimensional restoration and full tip replacement on SX HPT blades with a solid tip cap. LW3 and LW4280 contain 28 vol.% and 49 vol.% gamma prime phase respectively, after post weld aging heat treatment. A time-transient thermal mechanical Finite Element Analysis (FEA) of the SX HPT blade was completed for takeoff, cruise, and landing conditions. The resultant temperature and stresses from the FEA study were used as the basis for qualification of the tip repair. Tensile and stress rupture properties of dissimilar SX-LW3 and SX-LW4280 welds produced at ambient temperature using manual GTAW and Laser Direct Energy Deposition (L-DED) on a LAWS1000 welding system utilizing a 3D additive manufacturing (AM) concept were studied. It was demonstrated that LW4280 welds had superior stress rupture, and fatigue properties when compared to M 72. Cyclic oxidation resistance of LW4280 at 2048°F (1120°C) was found to be sufficient to ensure required durability of repaired blades for 6,000 cycles in cases of damage to protective coatings. Some examples of repairs of HPT blades developed using these materials and technologies are provided.