Abstract Chatter-free machining is necessary in micromilling to avoid the catastrophic failure of micro-end mill. The accuracy of the prediction of chatter-free machining conditions in high-speed micromilling has been improved in this work by including speed-varying micro-end mill dynamics. An optimum design of exponential window has been devised to remove the unwanted spindle dynamics from the displacement signal to construct the speed-dependent frequency response function (FRF) of micro-end mill. The stiffness of the micro-end mill has been found to be increasing with increase in spindle speed and the natural frequency of the micro-end mill has been found to be changing with change in spindle speeds. The cutting velocity-chip load-dependent cutting coefficients have been included to predict the stability using Nyquist criterion. The predicted stability lobe with speed-varying micro-end mill dynamics has increased chatter-free depth of cut significantly compared to the chatter-free depth of cut predicted with static micro-end mill dynamics. The increase in depth of cut with speed-varying dynamics has been found to be 28% at 20,000 rpm, 150% at 52,000 rpm, and 250% at 70,000 rpm. A critical value of acceleration of the workpiece has been identified for chatter onset detection and it has been validated with machined surface image analysis. The magnitude of acceleration in both feed and normal to feed direction has been characterized to analyze the effect of spindle speed and depth of cut on the vibration of workpiece.

Abstract Porosity is a major quality issue in additively manufactured (AM) materials due to improper selection of raw material or process parameters. While porosity is kept to a minimum for structural applications, parts with intentional (engineered) porosity find applications in prosthetics, sound dampeners, mufflers, catalytic converters, electrodes, heat exchangers, filters, etc. During postprocessing of additive manufactured components using secondary machining to obtain required dimensional tolerance and/or surface quality, part porosity could lead to fluctuating cutting forces and reduced tool life. The machinability of the porous AM material is poor compared to the homogenous wrought material due to the intermittent cutting and anisotropy of AM materials. This paper investigates the tool wear progression and underlying mechanisms in relation to the porosity of AM material during their machining. Micromilling experiments are carried out on AM Ti6Al4V alloy with different porosity levels. Insights into tool-workpiece interaction during micromachining are obtained in cases where pore sizes could be comparable to the cutting tool diameter. Findings of this research could be helpful in developing efficient hybrid additive-subtractive manufacturing technologies with improved tool life and reduced costs.

AbstractThe paper primarily explores the suitability of using Abrasive jet machining (AJM) in fabricating microchannels on Ti-6Al-4V ELI alloy. The work evaluates the microchannels generated using process parameters such as air pressure, feed rate, and standoff distance and their effect on channel geometries like width, depth, surface roughness, and topography. Since Ti-6Al-4V ELI alloy is commonly used in bio-implants, the contact angle and surface free energy of generated microchannels is measured using the sessile drop technique and Chibowski approach, respectively to assess the benefits of creating such features using AJM, which can have probable applications in the medical field. The result indicates that AJM can produce hydrophilic microchannels with nanolevel surface roughness without the effects of heat-affected zone (HAZ), resolidification, burrs, and particle embedment.

Abstract Bio-inspired, micro/nanotextured surfaces have a variety of applications including superhydrophobicity, self-cleaning, anti-icing, antibiofouling, and drag reduction. In this paper, a template-free and scalable roll coating process is studied for fabrication of micro/nanoscale topographies surfaces. These micro/nanoscale structures are generated with viscoelastic polymer nanocomposites and derived by controlling ribbing instabilities in forward roll coating. The relationship between process conditions and surface topography is studied in terms of shear rate, capillary number, and surface roughness parameters (e.g., Wenzel factor and the density of peaks). For a given shear rate, the sample roughness increased with a higher capillary number until a threshold point. Similarly, for a given capillary number, the roughness increased up to a threshold range associated with shear rate. A peak density coefficient (PDC) model is proposed to relate capillary number and shear rate to surface roughness. The optimum range of the shear rate and the capillary number was found to be 40–60 s−1 and 4.5 × 105–6 × 105, respectively. This resulted in a maximum Wenzel roughness factor of 1.91, a peak density of 3.94 × 104 (1/mm2), and a water contact angle (WCA) of 128 deg.

Abstract Electric-field-assisted atomic force microscope (E-AFM) nanolithography is a novel polymer-patterning technique that has diverse applications. E-AFM uses a biased AFM tip with conductive coatings to make patterns with little probe-sample interaction, which thereby avoids the tip wear that is a major issue for contact-mode AFM-based lithography, which usually requires a high probe-sample contact force to fabricate nanopatterns; however, the relatively large tip radius and large tip-sample separation limit its capacity to fabricate high-resolution nanopatterns. In this paper, we developed a contact mode E-AFM nanolithography approach to achieve high-resolution nanolithography of poly (methyl methacrylate) (PMMA) using a conductive AFM probe with a low stiffness (~0.16 N/m). The nanolithography process generates features by biasing the AFM probe across a thin polymer film on a metal substrate. A small constant force (0.5-1 nN) applied on the AFM tip helps engage the tip-film contact, which enhances nanomachining resolution. This E-AFM nanolithography approach enables high-resolution nanopatterning with feature width down to ~16 nm, which is less than one half of the nominal tip radius of the employed conductive AFM probes.

Abstract The laser irradiance-based surface structural growth on Si and Ge has been correlated first time with plasma parameters. The better control over plasma parameters makes manufacturing of various sized and shaped surface structures on the semiconducting materials. The effect of laser irradiances on surface morphology of Si and Ge has been explored. For this purpose, Nd: YAG laser (532 nm, 6 ns, 10 Hz) has been employed as an irradiation source at the various laser irradiances ranging from 4 to 7.1 GW/cm2 under the vacuum condition. Surface modifications of laser-ablated Si and Ge were analyzed by performing scanning electron microscope (SEM) analysis. It has been revealed that laser irradiance plays a significant role in the growth of the micro- and nanostructures on the laser-irradiated target surfaces. The surface morphology of laser-ablated Si and Ge exhibited the formation of various structures such as laser-induced periodic surface structures (LIPSS), cracks, spikes, ridges, and cones. Density and size of these structures have been found to be strongly dependent upon the laser irradiances. SEM analysis exhibits the cones formation at central ablated region of both Si and Ge. These cones become more distinct and pronounced with increasing the laser irradiance due to more energy deposition with Gaussian profile distribution at the central region. Microspikes were observed at boundaries of laser-ablated Si. Whereas, in case of Ge-ablated boundaries, wave-like ridges have been observed, which are then converted into globules at higher laser irradiances up to 7 GWcm−2. LIPSSs were seen at outer boundaries of laser-ablated Ge, whose periodicity varies with the laser irradiances. Faraday cup has been employed in order to probe the kinetic energy and density of laser-induced Si and Ge plasma ions at the similar values of laser irradiances. A correlation at similar values of laser irradiances has been established between the evaluated plasma ion parameters (kinetic energy and density of plasma ions) and observed structures for both materials. This correlation reveals the dependence of kinetic energy and density of plasma ions on the corresponding surface modification of both laser-ablated Si and Ge, as well as enables us for the better understanding of the laser-induced plasma to be used as ion source in various fields ion implantation, surface structuring, and material modification. The results of ion energies are explained by the generation of ambipolar field or self-generated electric field (SGEF) in the expanding plasma due to the charge separation and double-layer structure. The values of SGEF have also been evaluated at different laser irradiances.

Abstract The paper presents a numerical and experimental investigation on the stacking of thin, cold rolled nongrain-oriented (CRNO) electrical steel sheets post-tungsten inert gas (TIG) and cold metal transfer (CMT) welding for predicting the effects of TIG and CMT welding current on weld geometry, temperature field, and residual stress distribution in thin, stacked weld sheets. Numerical simulation of a transient nonlinear thermal three-dimensional (3D) element based on actual weld conditions was carried out using ansys software by employing a moving heat source model based on a 3D Gaussian distribution to predict changes in temperature. As a result of the thermal history provided by the model, a mechanical analysis is performed to determine the residual stress distribution and the surface distortion in the element. A significant increase in weld penetration and weld width of the samples was observed with the increase in welding current, as well as a change in the temperature field in the weld zone. Moreover, both the experimental and numerical data are consistent in their estimation of the generation of residual stresses in the weld samples. A numerical model is presented for predicting the thermomechanical behavior of TIG and CMT welded stacked CRNO structures in the stator core of electric motors.

Abstract During the micro-electrical discharge machining (micro-EDM) process, the dielectric property of narrow interelectrode gap is transiently changing. With the hysteretic servomotion of spindle, the effective discharge ratio (EDR) between electrodes is low. In this research, a pulsed power supply superposed with the radio frequency (RF) oscillating wave of controllable frequency and amplitude is proposed in order to induce interelectrode continuous discharge, so that, the machining efficiency and accuracy are improved simultaneously. The experimental results of microhole machining show that under the oscillating frequency of 160 MHz and amplitude of ±10 V, the machining efficiency is increased by 35%, the tool electrode wear rate (TWR) remains almost unchanged, and the taper error of microhole is reduced by 43%. Furthermore, the process of relatively enlarging discharge gap range and increasing number of discharges after superposition is discussed, and the proper superposed oscillating amplitude is identified.

Abstract In this study, we used an ultrafast laser with a wavelength of 1026 nm with the aim of analyzing the ablation threshold and morphologies of the irradiated surfaces of cemented carbide by varying the pulse duration and number of laser pulses. Specifically, we used pulse durations of 0.2, 2, and 10 ps and performed both gentle and strong ablations. For the same wavelength, laser pulse energy, and number of laser pulses, the lowest ablation threshold was 0.2 ps. When we performed a gentle ablation, we observed laser-induced periodic surface structures (LIPSSs) on the entire irradiated surface for all pulse durations. Thus, the pulse duration did not appear to affect the formation of LIPSSs. Strong ablation caused ridges to form at irradiated area outside. When the pulse duration increased, larger ridges were formed, whereas when the pulse duration decreased, coarser ridges were formed. The results obtained by using the ultrafast laser is expected to be helpful in the machining of cemented carbide.

Abstract In micromilling, understanding transitions between the desired shearing-dominant to the undesired plowing-dominant cutting mechanism could help obtain high quality microfeatures. This work investigates the transitions in cutting mechanisms in micromilling using fluctuations in cutting force signals, characterized by using a fluctuation parameter. A new analytical model correlating fluctuation in force signals to the transitions in cutting mechanism has been developed. Two types of slot milling experiments were performed to understand the transitions in cutting mechanisms, as a function of processing parameters, and over the entire life of micro-endmills. The proposed model was found to agree with experimental values of forces within 15% error. The limiting value of the fluctuation parameter has been estimated as 0.01, which corresponds to a limiting feed of 1 μm/tooth. Feed per tooth and cutting edge radius are the important parameters that affect transitions in cutting mechanisms. The cutting mechanism changes from shearing to plowing and vice-versa over the entire life of the tool. Shearing-dominant mechanism prevailed in the first region due to the sharper cutting edges with radius less than 9 μm. Though plowing-dominant cutting mechanism prevails in the remaining two regions, the mechanism comes closer to shearing-dominant near the end of tool life. This is primarily because of the generation of localized sharpness on tool cutting edges due to chipping. Furthermore, it was evident that cutting mechanism changes from shearing to plowing due to wear, when surface roughness increases above 400 nm Ra.