Published papers

Superhydrophobic surfaces are highly desirable due to their remarkable water-repellent behavior. Laser texturing with subsequent low surface energy modification is a versatile strategy for creating such surfaces. In this study, via synergistic laser texturing and low temperature annealing, superhydrophobicity was first attempted to be achieved on the FeCoCrMnNi surface. By optimizing the laser parameters, the arrays with large depth-to-width ratios were constructed. Subsequently, by annealing at a low temperature, the transition process from superhydrophilicity to superhydrophobicity was successfully achieved on the FeCoCrMnNi surface. The effects of the hatching interval on the wettability were investigated, and the mechanism of wettability transition for FeCoCrMnNi was discussed. According to the experimental results and analysis, the textured surfaces exhibited excellent superhydrophobicity at different hatching intervals and a maximum contact angle of 165° was obtained. Furthermore, the created superhydrophobic surfaces possessed good liquid capture and self-cleaning capabilities and enabled magnification for optical imaging. The wettability transition after low temperature annealing was attributed to the absorption of airborne organic compounds. This study provides an efficient, clean, and versatile strategy to achieve superhydrophobicity of the FeCoCrMnNi surface by laser processing.

As the global market for lithium-ion batteries continues to grow, sourcing alternative materials for battery cell production gains interest and has an ever increasing potential to reduce environmental impact during the production phase. Around 97% of the produced Li-ion batteries contain a graphite-based anode, coated on a copper foil. In this Life Cycle Assessment the potential reduction of environmental impact over various categories during the production of batteries when using an anode production method by laser sintering Si-waste powder in an innovative process is investigated. The study provides an indication of environmental feasibility of the suggested production process, comparing the technical innovative process to currently available anode production processes. The impact comparison is made on the level of anode production (cradle to gate) with the potential to zoom out to the full battery production process in future work. Current results indicate that the overall impact of production increases 27% when using the suggested anode production process, with the results being sensitive to the amount of energy required for sintering and the allocation of impact towards the Si-waste. The impact of this switch of anode production method for the full Li-ion battery production will depend on the affected charge capacity and lifetime duration of an assembled battery module.

Improving the surface hardness and tribological characteristics of metallic glasses (MGs) is meaningful for their applications as surface contact materials. In this study, nanosecond laser nitriding was performed on Zr-based MG to improve its surface properties. Three types of laser nitrided surfaces with different hardness were prepared, and their tribological characteristics were systematically investigated by means of the scratch test. The experimental results indicated that compared with the as-cast MG, the hardness of these three laser nitrided surfaces was increased by 47.94%, 114.56%, and 171.99%, and their coefficients of friction were reduced by 29.12%, 65.05%, and 71.84%, respectively. Furthermore, the residual scratches and surrounding chips exhibited various features under different conditions, and the scratch damage mechanisms were analyzed accordingly.

Fast tool servo (FTS) diamond turning is a promising technique for high-precision generation of freeform optics with remarkable efficiency. However, the conventional constant scheme for control point sampling fails to consider the surface variation, which might lose some details of the surface profile and result in low form accuracy and non-uniform surface quality. Facing this issue, this manuscript proposes a novel optimization method for control points sampling, which restrains the deviations and contains as much of the surface details. In the optimization method, the sampling intervals between two adjacent control points are actively adjusted to adapt the surface variation of the desired surface. By adopting this method, the sampling induced interpolation error between the control points is restrained within the tolerance and eliminates lack/over-definition of control points in the machining area. The feasibility of the proposed optimization method is demonstrated by both theoretical prediction and fabrication experiment of sinusoid freeform surface. Compared with the conventional sampling method, both the predicted and measured form error of the proposed method are remarkably reduced about 35 % with the same amount of control points. This technique provides a new route to sampling control points in FTS diamond turning to achieve high accuracy and flexible fabrication of freeform surface machining.

Metallic glasses (MGs) have shown promising application prospects as structural materials due to their unique mechanical properties. While, for broadening their application as functional materials, significant improvement in surface hardness of MGs is required. Accordingly, in this study, laser carbonization of MGs was attempted by irradiating the Zr-based MG surface immersed in graphite powder water suspension using a nanosecond pulsed laser. Nanoindentation response and surface morphologies of the initial and irradiated surfaces were characterized in detail. The results indicated that the hardness of the laser-irradiated surfaces was increased by 130 %–200 % (from 6.407 GPa to 19.193 GPa), and as well, the serrated flows in load-depth curves and the surface shear bands around the residual indent disappeared, suggesting the change in micro-scale plastic deformation behaviors of the laser-irradiated surfaces. Furthermore, the chemical composition of the initial and irradiated surfaces was analyzed by X-ray diffraction (XRD) and energy dispersive spectrometer (EDS), which showed that the irradiated surfaces were carbonized in the graphite powder water suspension. Accordingly, the increase in surface hardness was due to the formation of the hard crystalline phases.

Severe diamond tool wear may be caused by a chemical reaction between SiO2 in glass and diamond during ultraprecision cutting of silica glass, because silica glass is based on SiO2. This study demonstrated that adopting fluoride glass, which has no SiO2 constituent, as the workpiece reduced tool edge retreat to 1/22 of that of silica glass. This was because the fluoride glass contains no SiO2, which reacts chemically with diamond and leads to severe tool wear. Ductile mode cutting of fluoride glass was realized for long cutting distance. As an application, an aspherical glass lens was produced by ultraprecision cutting. In addition, the tool wear, surface generation, and chip formation mechanisms were investigated.

Carbon nanofibers (CNFs) have various excellent properties, such as high tensile strength, electric conductivity and current density resistance, and thus have great application potential in electrical sensor development. In this research, electrically conductive composite elements using CNFs sandwiched by thermoplastic olefin (TPO) substrates were developed by press molding. The metal mold used for press molding was processed by a femtosecond laser to generate laser-induced periodic surface structures (LIPSS) on the mold surface. The aggregate of CNFs was then flexibly fixed by the LIPSSs imprinted on the TPO substrate surface to produce a wavy conductive path of CNFs. The developed composite elements exhibited a sharp increase in electrical resistance as strain increased. A high gauge factor of over 47 was achieved, which demonstrates high sensitivity against strain when the composite element is used as a strain gauge. Scanning electron microscope observation revealed that the TPO filled the spaces in the aggregate of CNFs after press molding, and the conductive path was extended by the tensile strain. The strain-induced dynamic changes of contact states of CNFs and CNFs networks are discussed based on the electrical performance measurement and cross-sectional observation of the elements. This research provides a new approach to the production of flexible and high sensitivity strain sensors.

Fresnel micro-lens arrays with close-to-wavelength features have significant advantages in minimization of optical systems. However, in the fabrication of a Fresnel micro-lens array by conventional diamond turning, the discontinuous features of the surface profile cause interference between the tool flank face and the finished surface. In this manuscript, a novel off-spindle-axis diamond turning method is proposed to fabricate Fresnel micro-lens array mold insert and a toolpath generation algorithm is developed. The generation of each lenslet is treated as an independent turning operation, and the whole fabrication of a Fresnel micro-lens array is completed by a succession of repetitive turning operations. With this approach, the interference between the tool and the finished surface is avoided, and the form accuracy and surface integrity are improved for each lenslet. Then, the Fresnel micro-lens array mold insert is further utilized in precision glass molding to replicate the micro-lens structures onto transparent polymer substrates. The experimental results indicate that both the diamond-turned and molded Fresnel micro-lens arrays are achieved with homogeneous quality. As an application, a compact imaging system based on the molded Fresnel micro-lens array is demonstrated. The proposed machining method in this study can be employed in the fabrication of Fresnel micro-lens arrays and other micro-optics with discontinuous profiles with high accuracy and machining efficiency.

Cellulose nanofiber (CeNF)-reinforced polymer composites have wide potential applications in the manufacturing of optical and mechanical parts owing to their light weight, high mechanical strength, and optical transparency. In this study, CeNF-reinforced homogeneous polypropylene (PP-CeNF) was machined under various conditions by ultraprecision diamond turning, and the results were compared with those of pure PP without CeNF addition. The influence of CeNFs on material removal was investigated by examining the surface topography, chip morphology, cutting forces, and cutting temperature. It was found that the surface defects in pure PP cutting were surface tearing, while the surface defects of PP-CeNF were surface tearing and micro-holes induced by the pulling-outs of CeNFs. Surface tearing increased with cutting speed; pulling-outs of CeNFs were slightly affected by cutting speed but strongly dependent on the tool feed rate. Under a small tool feed rate, the surface roughness could be reduced to ∼10 nm Ra for PP-CeNF. The thermal effect was insignificant in the experiments, whereas the effect of strain rate-induced material hardening was dominant for both workpiece materials at a high cutting speed. This study helps to understand the mechanisms for ultraprecision cutting of CeNF-reinforced polymer composites and provides guidelines for improving the machined surface quality.

Electrical discharge machining (EDM) causes surface defects such as resolidified layer and microcracks, and a finishing process is usually needed to remove these defects. In this paper, a hybrid process was proposed where electrochemical machining (ECM) was performed as a finishing process after EDM using the same tool electrode on the same machine. By using two kinds of disk-type rotary electrodes, rectangular grooves and grooves with convex inner structures were fabricated. Surface topography were investigated by using scanning electron microscope (SEM), energy dispersive X-ray spectrometry (EDX), and laser-probe surface profilometer. The material removal mechanism of resolidified layers was clarified. The surface roughness of the rectangular groove was improved from 3.82 μm Ra to 0.86 μm Ra after ECM. Electrode rotation was effective for flushing electrolytic products when fabricating inner structures. As there is no need for exchanging tools and machines, tool alignment error can be prevented and productivity can be improved. Therefore, the proposed EDM/ECM hybrid process contributes to rapid fabrication of microscale products with high surface integrity.

Fabrication of hierarchical micro/nano-structures on glassy carbon (GC) surface is important for the application of GC as the mold material for glass molding, but it is still challenging due to the high brittleness and hardness of the material. In this study, by using a nanosecond pulsed laser, a hierarchical micro/nano-structure, i.e., micro-dimple with ring-like nanostructure on its inner wall, was generated on the GC surface. The effects of laser parameters, such as laser irradiation time and fluence, on the formation and evolution of the hierarchical micro/nano-structure were experimentally studied. By comparative experiments with graphite, the role of amorphous nature of GC on the formation of very regular hierarchical micro/nano-structure was confirmed. The results obtained by irradiating GC in argon and nitrogen gas further indicated that the formation of hierarchical micro/nano-structure was independent of the gas atmosphere. By controlling the relative positions of point shots, various micro-dimple arrays were successfully fabricated on the GC surface which significantly changed its wetting behavior. Finally, formation mechanism of the hierarchical micro/nano-structure was discussed according to the experimental results as well as some previous literatures. This study provides a one-step method for fabricating hierarchical micro/nano-structures on the GC surface by nanosecond pulsed laser irradiation, which would be meaningful for the functional applications of GC.

© IMechE 2019. Glassy carbon is an amorphous material which, due to its unique material properties, has recently been introduced to micro/nanoimprinting as mold substrates. However, since glassy carbon is a hard, brittle, and highly elastic material, the precision machining of micro/nanostructures on it remains a challenging task. In this research, ultrasonic vibration-assisted microgrinding was proposed for ductile machining of glassy carbon. To find suitable conditions, the effects of ultrasonic vibration assistance and tool inclination were investigated. The results showed that by utilizing ultrasonic vibration assistance and tool inclination, a ductile response was achieved with improved surface roughness. In addition, the periodical waviness of the groove edge due to material elastic recovery was successfully prevented. This study provided an insight into the kinematics in ultrasonic vibration-assisted grinding of a highly elastic, hard, and brittle material.

© 2018 The Japan Society of Mechanical Engineers. Single-crystal infrared (IR) spectroscopy is a promising method for protein structure analysis, where a protein crystal sample is fixed in a micro flow cell. Single-crystal calcium fluoride (CaF2) is expected as the flow cell substrate material for its excellent optical property. However, CaF2 is a highly brittle material having strong anisotropy, thus is extremely difficult to machine. Up to date, there is no available literature on fabrication of CaF2 flow cells. In this study, micro flow cells of single-crystal CaF2 were fabricated by ultraprecision cutting technology. Fly cutting was conducted using a single-crystal diamond tool having straight edges to generate a depth-varying rectangle cross section for the flow cell. The effects of cutting direction, workpiece orientation, undeformed chip thickness and tool rake angle on cutting behavior were investigated. Based on experiments and analysis, optimal conditions for ductile machining of micro grooves in CaF2 were identified. As a result, a 10 μm deep CaF2 micro flow cell with surface roughness of 2.4 nmRa was successfully fabricated. Using the fabricated flow cell, IR spectroscopic analysis of a protein single crystal at room temperature was succeeded. This study demonstrated the effectiveness of ultraprecision cutting technology in CaF2 micro flow cell fabrication, which contributes to the IR analysis of protein, and in turn, the advance of life science.

© 2018, International Society for Nanomanufacturing and Tianjin University and Springer Nature. Steel is used as a mold material for press/injection molding of plastic products. High accuracy and releasing ability are required for a steel mold surface. This paper proposes a surface finishing method for steel molds by using picosecond pulsed laser irradiation. The process involves two steps: one is surface flattening by removing the surface asperity through laser ablation, and the other is forming nanoscale laser-induced periodic surface structures (LIPSS) on the flattened surface. The two steps are realized by using the same laser at controlled laser fluence and focus position. Experimental results showed that LIPSS was successfully formed after surface flattening under specific ranges of laser fluence and defocus length. Furthermore, plastic forming experiments demonstrated that a steel surface with LIPSS significantly decreased the effective contact area and, in turn, reduced the mold releasing force. These findings provide the possibility of fabricating high-performance steel molds by picosecond pulsed laser irradiation.

© 2019 Inderscience. All Rights Reserved. Glass has an increasing demand in many industrial fields such as micro-channels and micro reactors in fluidic applications, lab-on-a-chip in medical applications, and micro lens arrays and optical devices. Machining of glass as one of hard-to-machine materials is challengeable due to its distinctive properties of high strength, hardness, and brittleness. Facing these challenges, ultrasonic-assisted milling (UAM); an advanced machining process; was provided for its effectiveness in machining such hard-to-machine materials. In this paper, the effects of feed rate, depth of cut, ultrasonic-vibration assistance, and cutting fluid on surface roughness in UAM of soda-lime glass compared with conventional milling (CM) were investigated. Results showed that, by introducing ultrasonic-vibration, higher surface roughness was obtained. The optimal cutting conditions were attained using response surface methodology. At the optimised parametric setting, the minimum surface roughness was found to be at wet conventional milling.

© 2018 Elsevier B.V. Creation of micro dimples on material surface is significant for their functional applications. Because of unique properties, metallic glasses are regarded as emerging structural and functional materials but they are also a kind of difficult-to-cut materials due to high hardness and easy to crystallization and oxidation. In this study, a new method was proposed to fabricate micro dimples on metallic glass surface, which consisted of two steps, nanoindentation experiments to form the pre-indent array followed by polishing. Via this two-step method, square and rectangle dimples were successfully formed which exhibited multi-scale features with one relatively large dimple with width in micron-scale and depth in nanometer-scale, together with relatively small residual indents in nanometer-scale distributed on its bottom surface. The experimental results indicated that the depth of multi-scale dimples was affected by the spatial interval between two indents and the polishing time. Under the used experimental conditions, for the same polishing time, the depth of the large dimple was decreased when increasing the interval; for the same interval, with increase in the polishing time, the depth of the large dimple was also decreased. The possible formation mechanism of the large dimple was discussed, which was mainly ascribed to the enhanced material removal at the position of pre-indent array because of the concentration of polishing particles by the pre-indents.