Fabrication techniques for gecko-inspired adhesives generally target mold durability, adhesive performance, and process efficiency and simplicity. With these goals in mind, we present a micromachining process for creating reusable aluminum molds used to fabricate directional dry adhesives. The molds require deep, narrow and overhanging grooves to create sharp and angled adhesive features. This geometry precludes most traditional machining and lithographic material removal processes. The presented process is a hybrid of indenting and orthogonal machining, using a diamond-coated microtome blade as the tool. An finite element analysis reveals the local extent of work hardening as each groove is created, and helps to define a trajectory that reduces the effects of tool deflection and chip build up. The results of a series of experiments agree with predictions from the analysis and reveal a range of blade approach angles and a lower bound on groove spacing to achieve the desired geometry. This range is narrower than for molds machined from wax in previous work. Nonetheless, adhesive samples cast from the new metal molds achieve comparable performance to those previously cast from wax.

In the fabrication of directional gecko-inspired adhesives, a new capability made possible by the availability of metal molds is hot compression molding. This molding process allows the use of elastomers with much higher toughness than those cast at ambient temperature and pressure, as has been the common case in fabricating adhesives. In addition, it permits fast cycle times (minutes instead of hours), which is useful for volume manufacturing. We present the results of hot compression molding of elastomers in metal molds created with overhanging and tapered microscopic surface features, which give rise to anisotropic adhesion. We show that the adhesive performance so obtained is equivalent to that obtained earlier with polydimethylsiloxane (PDMS).

A process flow is described for the low cost, flexible fabrication of metal micro-electromechanical systems (MEMS) with high performance integrated sensing. The process is capable of producing new designs in ≈1 week at an average unit cost of <$1 k/device even at batch sizes of ≈1–10, with expected sensing performance limits of about 135 dB over a 10 kHz sensor bandwidth. This is a ≈20× reduction in cost, ≈25× reduction in time, and potentially >30× increase in sensing dynamic range over comparable state-of-the-art compliant nanopositioners. The nonlithographically based microfabrication (NLBM) process is uniquely suited to create high performance nanopositioning architectures which are customizable to the positioning requirements of a range of nanoscale applications. These can significantly reduce the cost of nanomanufacturing research and development, as well as accelerate the development of new processes and the testing of fabrication process chains without excess capital investment. A six degrees-of-freedom (6DOF) flexural nanopositioner with integrated sensing for all 6DOF was fabricated using the newly developed process chain. The fabrication process was measured to have ≈30 μ m alignment. Sensor arm, flexure, and trace widths of 150 μ m, 150 μ m, and 800 μ m, respectively, were demonstrated. Process capabilities suggest lower bounds of 25 μ m, 50 μ m, and 100 μ m, respectively. Dynamic range sensing of 52 dB was demonstrated for the nanopositioner over a 10 kHz sensor bandwidth. Improvements are proposed to approach sensor performance of about 135 dB over a 10 kHz sensor bandwidth.

This work proposes a physically consistent numerical model to simulate ultrashort laser absorption by a metallic workpiece at the water–metal interface when optical breakdown of the dielectric occurs. The simulation couples the framework of the finite difference time-domain method used in computational electromagnetics with the constitutive relation derived from both the model of direct ablation of metals and the first-order model of water breakdown. The simulation is used to describe interface ablation processes such as laser-induced plasma micromachining (LIPMM). Applied to the water–aluminum interface, the model is able to describe the metal absorption and the dielectric breakdown threshold in three-dimensional (3D) geometry. It is an extensible monolithic approach in which the absorption by different materials can be described by simply changing the constitutive relations.

In recent years, the metallization of polymers has been intensely studied as it takes advantage of both plastics and metals. Laser direct writing (LDW) is one of the most widely used technologies to obtain metal patterns on polymer substrates. In LDW technology, different methods including injection-molding, drop-casting, dip coating, and spin coating are utilized for surface preparation of polymer materials prior to the laser activation process. In this study, an atomization based dual regime spray coating system is introduced as a novel method to prepare the surface of the materials for LDW of metal patterns. Copper micropatterns on the polymer surface were achieved with a minimum feature size of 30 μ m, having a strong adhesion and excellent conductivity. The results show that the dual regime spray deposition system can be potentially used to obtain uniform thin film coating with relatively less material consumption on the substrates for surface preparation of laser direct metallization of polymers.

Graphene is an ideal reinforcement material for metal matrix composites (MMCs) owing to its high strength, high ductility, light weight, as well as good bonding with metal matrix. In this study, graphene nanoplatelets (GNPs) reinforced Inconel 718 composites are fabricated by selective laser melting (SLM) technique and processed under various postheat treatment schemes. It is found that the fabrication of GNPs-reinforced MMC using the SLM technique is a viable approach. The obtained composite possesses dense microstructure and enhanced tensile strength. Postheat treatments at two levels of solution temperature (980 and 1220 °C) for 1 h followed by two-step aging are carried out. The experimental results indicate that the addition of GNPs into Inconel 718 matrix results in significant strength improvement. Under the as-built condition, the ultimate tensile strengths (UTSs) of SLM Inconel 718 materials are 997 and 1447 MPa, respectively, at 0 and 4.4 vol % GNP content. The strengthening effect of GNPs is most prominent under the as-built condition, and the strength of as-built GNPs-reinforced Inconel 718 is higher than that of unreinforced Inconel 718 under any processing conditions. The formation of γ ′ and γ ″ precipitates is suppressed in the GNPs-reinforced composite under the aging condition due to the formation of metallic carbide (MC) carbide and the depletion of Nb. GNPs effectively inhibits grain growth during postheat treatment. Quantitative investigation of the various strengthening effects demonstrates that load transfer effect is dominating among all contributors.

We describe a process for creating durable metal molds for the fabrication of directional, gecko-inspired dry adhesives. The adhesives require microscopic inclined features with a challenging combination of tapered geometry, high aspect ratio, and smooth surface finish. Wedge-shaped features produced by the new metal mold exhibit the same geometry and surface finish as those cast from single-use wax molds and epoxy molds in previous fabrication methods. They also produce the same levels of adhesion and shear stress. The metal molds, and the adhesives cast from them, show no degradation after repeated molding cycles.

Metal additive manufacturing (AM) has been attracting attention as a new manufacturing method, but a surface finishing process is usually needed to improve the surface quality. As a new surface finishing process, ultrasonic vibration-assisted burnishing (UVAB) is promising. In this study, UVAB was performed on an additive-manufactured AlSi10 Mg workpiece to improve its surface/subsurface integrity. The effects of ultrasonic vibration (UV) and lateral tool pass width on the burnishing performance were investigated. It was observed that the surface roughness, filling ratio, and hardness of the surface layer were simultaneously improved after burnishing. This study shows the effectiveness of applying UVAB to improve the surface quality of additive-manufactured products for various industrial uses.

Considering the attractive surface functionalities of springtails (Collembola), an attempt at mimicking their cuticular topography on metals is proposed. An efficient single-step manufacturing process has been considered, involving laser-induced periodic surface structures (LIPSS) generated by near-infrared femtosecond laser pulses. By investigating the influence of number of pulses and pulse fluence, extraordinarily uniform triangular structures were fabricated on stainless steel and titanium alloy surfaces, resembling the primary comb-like surface structure of springtails. The laser-textured metallic surfaces exhibited hydrophobic properties and light scattering effects that were considered in this research as a potential in-line process monitoring solution. The possibilities to increase the processing throughput by employing high repetition rates in the MHz-range are also investigated.

Lightweight microstructures with high area-to-mass ratios, or low surface densities, show great potential applications in microrobots, soft electronics, medical devices, and solar sailing. However, the bending stiffness of such microstructures is usually too low to work effectively. In order to obtain active microstructures with enhanced bending stiffness, a new design for thermally actuated multilayered metallic microstructures with high area-to-mass ratios is presented in this article. The microstructures made of aluminum and NiTi alloy are fabricated to demonstrate the feasibility of vertical deployment of such microstructures under thermal actuation. The concept design and working principle of designed multilayered metallic microstructures are based on symmetrical deposition of metals Al\NiTi\NiTi\Al, followed by practical microfabrication processes, such as photolithography, physical vapor deposition (PVD), and dry etch. The area-to-mass ratios of such microstructures could be up to 400 m 2 /kg. Then, experiments for electrical characterization are set up for thermal actuation or Joule heating. Besides that, the equivalent resistances of such microstructures with regard to temperatures are calibrated, allowing for the determination of in situ temperatures of deformed microstructures when being heated in the vacuum chamber of scanning electron microscope (SEM). Finally, vertical deployment of such thin microstructures is detected and measured, which validates the feasibility of stiffness enhancement through the symmetrical design and thermal actuation.

As one of the most promising anode materials for high-capacity lithium ion batteries (LIBs), silicon nanowires (SiNWs) have been studied extensively. The metal-assisted chemical etching (MACE) is a low-cost and scalable method for SiNW synthesis. Nanoparticle emissions from the MACE process, however, are of grave concerns due to their hazardous effects on both occupational and public health. In this study, both airborne and aqueous nanoparticle emissions from the MACE process for SiNWs with three sizes of 90 nm, 120 nm, and 140 nm are experimentally investigated. The prepared SiNWs are used as anodes of LIB coin cells, and the experimental results reveal that the initial discharge and charge capacities of LIB electrodes are 3636 and 2721 mAh g −1 with 90 nm SiNWs, 3779 and 2712 mAh g −1 with 120 nm SiNWs, and 3611 and 2539 mAh g −1 with 140 nm SiNWs. It is found that for 1 kW h of LIB electrodes, the MACE process for 140 nm SiNWs produces a high concentration of airborne nanoparticle emissions of 2.48 × 10 9 particles/cm 3 ; the process for 120 nm SiNWs produces a high mass concentration of aqueous particle emissions, with a value of 9.95 × 10 5 mg/L. The findings in this study can provide experimental data of nanoparticle emissions from the MACE process for SiNWs for LIB applications and can help the environmental impact assessment and life cycle assessment of the technology in the future.

Nanoparticle reinforced metals recently emerge as a new class of materials to empower the functionality of metallic materials. There is a remarkable success in self-incorporation of nanoparticles to bulk metals for extraordinary properties. There is also a strong demand to use nanoparticles to enhance the performance of metallic microwires for exciting opportunities in numerous applications. Here, we show for the first time that silver–copper alloy (AgCu) reinforced by tungsten carbide (WC) (AgCu 40 (wt %) –WC) was manufactured by a stir casting method utilizing a nanoparticle self-dispersion mechanism. The nanocomposite microwires were successfully fabricated using thermal drawing method. By introducing WC nanoparticles into bulk AgCu 40 alloy, the Vickers microhardness was enhanced by 63% with 22 vol % WC nanoparticles, while the electrical conductivity dropped to 20.1% International Annealed Copper Standard (IACS). The microwires of AgCu 40 –10 vol % WC offered an ultimate tensile strength of 354 MPa, an enhancement of 74% from the pure alloy, and an elongation of 5.2%. The scalable manufacturing method provides a new pathway for the production of metallic nanocomposite micro/nanowires with outstanding performance for widespread applications, e.g., in biomedical, brazing, and electronics industries.

Reliability aspects are crucial for the success of every technology in industrial application. Regarding interconnect devices, several methods are applied to evaluate reliability of conductor paths like accelerated environmental tests. Especially, molded interconnect devices (MID), which enable numerous applications with three-dimensional (3D) circuitry on 3D shaped injection-molded thermoplastic parts are often under particular stress, e.g., as component of a housing. In this study, a new test method for evaluating the flexural fatigue strength of conductor paths produced by the laser-based LPKF-LDS ® technology is presented. For characterization of test samples, a test bench for flexural fatigue test was built up. A result of the flexural fatigue test is a characteristic Woehler curve of the metal layer system. Applying this new test method, essential influencing parameters on the reliability of MID under mechanical load can be identified. So, the metal layer system as well as the geometric parameters of the metal layer is crucial for the performance. Furthermore, test specimens are tested under different types of mechanical load, i.e., tensile stress and compressive stress. For a holistic view on reliability of MID, experimental results are discussed and supported by simulations. An important finding of the study is the advantage of nickel-free layer systems in contrast to the Cu/Ni/Au layer system, which is often used in MID technology.

This paper reports the development of an original design of chip breaker in a metal-matrix polycrystalline diamond (MMPCD) insert brazed into a milling tool. The research entailed finite element (FE) design, laser simulation, laser fabrication, and machining tests. FE analysis was performed to evaluate the effectiveness of different designs of chip breaker, under specified conditions when milling aluminum alloy (Al A356). Then, the ablation performance of an MMPCD workpiece was characterized by ablating single trenches under different conditions. The profiles of the generated trenches were analyzed and fed into a simulation tool to examine the resultant thickness of ablated layers for different process conditions, and to predict the obtainable shape when ablating multilayers. Next, the geometry of the designated chip breaker was sliced into a number of layers to be ablated sequentially. Different ablation scenarios were experimentally investigated to identify the optimum processing conditions. The results showed that an ns laser utilized in a controllable manner successfully produced the necessary three-dimensional feature of an intricate chip breaker with high surface quality (Ra in the submicron range), tight dimensional accuracy (maximum dimensional error was less than 4%), and in an acceptable processing time (≈51 s). Finally, two different inserts brazed in milling tools, with and without the chip breaker, were tested in real milling trials. Superior performance of the insert with chip breaker was demonstrated by the curled chips formed and the significant reduction of obtained surface roughness compared to the surface produced by the insert without chip breaker.

Thermal fiber drawing process has emerged as a promising nanomanufacturing process to generate high-throughput, well aligned, and indefinitely long micro/nanostructures. However, scalable fabrication of metal–polymer nanocomposite is still a challenge, since it is still very difficult to control metal core geometry at nanoscale due to the low-viscosity and high-surface energy of molten metals in cladding materials (e.g., polymer or glass). Here, we show that a scalable nanomanufacture of metal–polymer nanocomposite via thermal fiber drawing is possible. Polyethersulfone (PES) fibers embedded with Sn nanoparticles (<200 nm) were produced by the iterative size reduction thermal fiber drawing. A post-characterization procedure was developed to successfully reveal the metal core geometry at submicron scale. A three-stage control mechanism is proposed to realize the possible control of the metal nanoparticle morphology. This thermal drawing approach promises a scalable production of metal–polymer nanocomposite fibers with unique physicochemical properties for exciting new functionalities.

Thermal fiber drawing has emerged as a novel process for the continuous manufacturing of semiconductor and polymer nanoparticles. Yet a scalable production of metal nanoparticles by thermal drawing is not reported due to the low viscosity and high surface tension of molten metals. Here, we present a generic method for the scalable nanomanufacturing of metal nanoparticles via thermal drawing based on droplet break-up emulsification of immiscible polymer/metal systems. We experimentally show the scalable manufacturing of metal Sn nanoparticles (<100 nm) in polyethersulfone (PES) fibers as a model system. The underlying mechanism for the particle formation is revealed, and a strategy for the particle diameter control is proposed. This process opens a new pathway for scalable manufacturing of metal nanoparticles from liquid state facilitated solely by the hydrodynamic forces, which may find exciting photonic, electrical, or energy applications.

The purpose of this paper is to make a comparative study on the process capabilities of the two branches of the powder injection molding (PIM) process—metal injection molding (MIM) and ceramic injection molding (CIM), for high-end precision applications. The state-of-the-art literature does not make a clear comparative picture of the process capabilities of MIM and CIM. The current paper systematically characterizes the MIM and CIM processes and presents the process capabilities in terms of part shrinkage, surface replication, tolerance capability, and morphological fidelity. The results and discussion presented in the paper will be useful for thorough understanding of the MIM and CIM processes and to select the right material and process for the right application or even to combine metal and ceramic materials by molding to produce metal–ceramic hybrid components.

Silver nanoparticles were electrodeposited from 0.3 M oxalic acid electrolyte on a pure aluminum working electrode under silver ion concentration-limited condition. A silver wire was held in a glass tube containing 1.0 M KCl solution as the counter electrode. Ion exchange between the glass tube and the main electrodeposition bath through a capillary was driven by the overpotentials as high as 10 V supplied by an electrochemical workstation. Due to the reaction between chlorine anion and silver cation to form AgCl solid at the Ag/AgCl electrode, the silver ion concentration-limited condition holds in the electrolyte. It is found that silver grows at the aluminum working electrode to form nanoparticles with an average size of about 52.4 ± 13.6 nm. With the increasing of the deposition time, the silver nanoparticles aggregate into clusters. The silver particle clusters are separated with approximately 112.6 ± 19.7 nm due to the hydrogen bubble-induced self-assembling, which is shown by the confined deposition of silver on a gold coating. The surface roughness of the aluminum substrate leads to the reduced uniformity of silver nanoparticle nucleation and growth.

High density oxygen plasma-etching was applied to microtexturing onto the diamondlike carbon (DLC) films coated on the die-unit substrates. This mold-die unit with microtextured DLC coating was fixed into a cassette die for computer numerical control (CNC) stamping with the use of precise control both in loading and feeding the sheet materials. In particular, the pulsewise-motion control in stamping was employed to describe the effect of loading and unloading subsequences in the incremental motion on the microtexturing with reference to the normal loading motion. The macroscopic plastic deformation as well as the microscopic metal flow were studied to prove that the pulsewise-motion should be responsible for homogeneous duplication of microcavity patterns into a pure aluminum sheet with high aspect ratio.