Given the recent trend toward hybrid processing involving the integration of wire arc additive manufacturing (WAAM) and machining capabilities, this paper aims to identify and correlate microstructural variations observed in wire arc additively manufactured aluminum alloy 4043 workpieces to their specific micromilling responses. This is done with the explicit goal of assessing the feasibility of using micromilling responses to detect microstructural variations in WAAM workpieces. As part of this effort, variations in the interlayer cooling time are used to induce changes in the microstructure of a thin-wall WAAM workpiece. The microstructures are first characterized using in-process thermographic imaging, optical microscopy, polarized light microscopy, and indentation. Micromilling slotting experiments are then conducted on different regions within the workpiece. The findings suggest that cutting force signals are the premier candidate for in situ extraction of information regarding microstructural variations within WAAM workpieces. In particular, in situ analysis of the cutting force frequency spectrum can provide critical information regarding dominant failure mechanisms related to the underlying microstructure. Other key micromilling responses such as surface roughness, burr formation, and tool wear also correlate well with the underlying microstructural variations. While these early stage findings hold promise, future research efforts spanning multiple metal alloys systems and micromachining processes are needed to mature the proposed concept.

In this research, we proposed fabrication process of optical fiber sensors using femtosecond laser and their applications. A beam of femtosecond laser was focused by an objective lens in the optical fiber. By testing different conditions, a group of machining parameters was found that achieve a minimum machining resolution of 3.2 μ m. To ablate the core of the optical fiber, which is buried deep inside the cladding, precisely, part of the cladding was removed to expose the core as close as possible to the air. By making a complex pattern to modify the optical path of the laser inside an optical fiber, a sensitivity of 942.8–1015.6 nm per refractive index unit (nm/RIU) was obtained for liquid refractive index sensing. For another sensor, a sensitivity of 1.38 × 105 nm/RIU was obtained, which is high enough to detect small amount of refractive index change of air. It is known to be the first time that we fabricated a complex microstructure in an optical fiber to modify the propagation of the light using femtosecond laser. This research shows the possibility of a complex modification of light in an optical fiber using laser machining.

Micromachining of carbon fiber reinforced plastics (CFRPs) is essential for numerous applications in several industries such as aerospace, automotive, defense, shipping, sporting goods, and biomedical industries. The major challenge in machining CFRP by electrical discharge machining (EDM) is due to the nonconductivity of epoxy material which is used as a binder for manufacturing these CRFPs. This study attempts a novel, yet simple, approach to ensure the conductivity of the work piece through the entire machining process. Experiments were carried out as a part of this work to assess the feasibility of machining high aspect ratio microholes in CFRP by micro-EDM. The effect of process parameters such as voltage and feed-rate on the hole quality was studied. Using optimal process conditions, microhole of 2500 μm deep with an aspect ratio of over 11 was achieved.

This paper presents a simulation study toward analyzing the effect of radial throw in micromilling on quality metrics and on the deviation in tool-tip trajectory from its prescribed pattern. Both the surface location error (SLE) and the sidewall (peripheral) surface roughness are analyzed. The deviation in tool-tip trajectory is evaluated considering the flute-to-flute variations in the uncut chip thickness and changes in the tooth spacing angle. Radial throw indicates the instantaneous radial location of the tool axis, thereby capturing all salient features of tool-tip trajectory deviations, such as the general elliptical form of the radial motions. This is in contrast to the concept of run-out, which is a scalar quantity (total indicator reading) indicating the total displacement or change in the radial throw measured from a perfect cylindrical surface for one complete rotation of the axis. As such, measurement and analysis of radial throw is essential to understanding micromachining processes. In our previous work, we described an experimental approach for accurate determination of radial throw when using ultra-high-speed micromachining spindles. In this work, we present a simulation-based study to relate radial throw parameters and form to SLE, sidewall surface roughness, flute-to-flute variations of uncut chip thickness, and changes in tooth spacing angle for a two fluted micro-endmill. As expected, our study concludes that the magnitude, orientation, and form of radial throw all significantly affect the studied quality metrics, tooth spacing angle, and the flute-to-flute chip thickness variations. Specifically, the presence of radial throw with an elliptical form induces up to 50% variation in SLE, up to 20% variation in sidewall surface roughness, up to 60% variation in tooth spacing angle deviations, and up to 50% variation in flute-to-flute chip thickness. As such, the presented simulation approach can be used to assess the direct (kinematic) effects of the radial throw parameters on the quality metrics and chip thickness variations.

Research was conducted to evaluate a microtrenching process to create microchannels on the surface of poly (methyl methacrylate) (PMMA) for applications in tissue engineering. Experiments with a trenching tool included an exaggerated cutting edge radius (48 μm) to study the impact of a highly negative effective rake angle on forces during single pass microtrenching at subradius cutting conditions. During microtrenching, forces were measured by dynamometer and compared to a finite element (FE) model using an elastic-perfectly plastic material model for an undeformed chip thickness from 9 to 64 μm. During experiments, cutting was first observed when the ratio of undeformed chip thickness to cutting edge radius was 0.33. Measured and predicted values of thrust force exceeded cutting force up to an undeformed chip thickness equivalent to the cutting edge radius. The FE model predicted a linear trend in cutting force with feed (r = 0.99) and was substantiated by linear regression of experimental data (r = 0.99). However, at lower values of feed the model overestimated force, with a maximum difference of 42% at a feed of 22 μm. Thrust force was also predicted to be linear (r = 0.99), but at greater feed the experiments indicated a nonlinear decline in thrust force, resulting in a maximum difference of 27% at 64 μm. Finally, an analysis of nodal velocity plots from the FE model revealed a material stagnation zone developed along the cutting edge, rising from the workpiece surface in proportion to feed and then remaining fixed at 63 deg (stagnation angle) for all feeds greater than 35 μm. While the application of an elastic-perfectly plastic material model for PMMA was sufficient to predict microtrenching forces by the FE method, differences between predicted and measured thrust forces at greater undeformed chip thickness implies a more complex rheological model may add value.

Excimer laser ablation is a versatile technique that can be used for a variety of different materials. Excimer laser ablation overcomes limitations of conventional two-dimensional (2D) microfabrication techniques and facilitates three-dimensional (3D) micromanufacturing. Previously, we have reported a characterization study on 248 nm KrF excimer laser micromachining. This paper extends the study to 193 nm ArF excimer laser micromachining on five representative micro-electro-mechanical systems (MEMS) materials (Si, soda-lime glass, SU-8, polydimethylsiloxane (PDMS), and polyimide). Relations between laser parameters (fluence, frequency and number of laser pulses) and etch performances (etch rates, aspect ratio, and surface quality) were investigated. Etch rate per shot was proportional to laser fluence but inversely proportional to number of laser pulses. Laser frequency did not show a notable impact on etch rates. Aspect ratio was also proportional to laser fluence and number of laser pulses but was not affected by laser frequency. Materials absorbance spectrum was found to have important influence on etch rates. Thermal modeling was conducted as well using numerical simulation to investigate how the photothermal ablation mechanism affects the etching results. Thermal properties of material, primarily thermal conductivity, were proved to have significant influence on etching results. Physical deformation in laser machined sites was also investigated using scanning electron microscopy (SEM) imaging. Element composition of redeposited materials around ablation site was analyzed using energy dispersive x-ray spectroscopy (EDXS) analysis. Combined with our previous report on KrF excimer laser micromachining, this comprehensive characterization study provides guidelines to identify optimized laser ablation parameters for desired microscale structures on MEMS materials. In order to demonstrate the 3D microfabrication capability of ArF excimer laser, cutting and local removal of insulation for a novel floating braided neural probe made of polyimide and nichrome was conducted successfully using the optimized laser ablation parameters obtained in the current study.

A recent development in cooling and lubrication technology for micromachining processes is the use of atomized spray cooling systems. These systems have been shown to be more effective than traditional methods of cooling and lubrication for extending tool life in micromachining. Typical nozzle systems for atomization spray cooling incorporate the mixing of high-speed gas and an atomized fluid carried by a gas stream. In a two-phase atomization spray cooling system, the atomized fluid can easily access the tool–workpiece interface, removing heat through evaporation and lubricating the region by the spreading of oil micro-droplets. The success of the system is determined in a large part by the nozzle design, which determines the atomized droplet's behavior at the cutting zone. In this study, computational fluid dynamics are used to investigate the effect of nozzle design on droplet delivery to the tool. An eccentric-angle nozzle design is evaluated through droplet flow modeling. A design of simulations methodology is used to study the design parameters of initial droplet velocity, high-speed gas velocity, and the angle change between the two inlets. The system is modeled as a steady-state multiphase system without phase change, and droplet interaction with the continuous phase is dictated in the model by drag forces and fluid surface tension. The Lagrangian method, with a one-way coupling approach, is used to analyze droplet delivery at the cutting zone. Following a factorial experimental design, deionized water droplets and a semisynthetic cutting fluid are evaluated through model simulations. Statistical analysis of responses (droplet velocity at tool, spray thickness, and droplet density at tool) show that droplet velocity is crucial for the nozzle design and that modifying the studied parameters does not change droplet density in the cutting zone.

In order to improve the tribological properties of thermomechanically highly stressed surfaces such as cylinder liners, microdimples are produced by fly-cutting kinematics along the functional surface. The structures are used to hold back lubricant but also to increase the hydrodynamic pressure, which is built up between the sliding friction partners. For that, machining strategies for the pattern generation in cylindrical components are developed as well as a mathematical model of the microdimple arrangement and distribution. The tribological performance of the machined microdimples is analyzed by means of ring-on-disk experiments. At low sliding speeds the friction coefficient can be decreased clearly by microdimples. This indicates the potential for low-speed or reciprocating tribosystems like cylinder liners. This potential is quantified by motor driven experiments and the comparison between structured and nonstructured cylinder liners. A honed (fine) liner with additional microdimples along the interstice area shows friction losses up to 19% compared to standard honed nonstructured cylinder liner.

Directional dry adhesives are inspired by animals such as geckos and are a particularly useful technology for climbing applications. Previously, they have generally been manufactured using photolithographic processes. This paper presents a micromachining process that involves making cuts in a soft material using a sharp, lubricated tool to create closely spaced negative cavities of a desired shape. The machined material becomes a mold into which an elastomer is cast to create the directional adhesive. The trajectory of the tool can be varied to avoid plastic flow of the mold material that may adversely affect adjacent cavities. The relationship between tool trajectory and resulting cavity shape is established through modeling and process characterization experiments. This micromachining process is much less expensive than previous photolithographic processes used to create similar features and allows greater flexibility with respect to the microscale feature geometry, mold size, and mold material. The micromachining process produces controllable, directional adhesives, where the normal adhesion increases with shear loading in a preferred direction. This is verified by multi-axis force testing on a flat glass substrate. Upon application of a post-treatment to decrease the roughness of the engaging surfaces of the features after casting, the adhesives significantly outperform comparable directional adhesives made from a photolithographic mold.