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The hardness and brittleness of binderless tungsten carbide, make it difficult to fabricate microlens array (MLA) on it. In this paper, an integrated milling-grinding machining method was used to fabricate MLA on binderless tungsten carbide. A model for predicting the relationship between surface roughness and undeformed chip thickness during the integrated milling-grinding process was proposed. Microgroove machining experiments confirmed the relationship between surface roughness and undeformed chip thickness, which showed that the ductile-brittle transition boundary was divided. Based on this, an MLA was fabricated in the ductile mode, and the surface roughness of a single lenslet was approximately 16 nm. This integrated milling-grinding machining method is shown to be available for fabricating MLAs on hard substrates. • It is hard to fabricate microlens array on binderless tungsten carbide, integrated milling-grinding is proposed. • The integrated milling-grinding contains milling of the tool edge and grinding of the diamond grains. • Microgroove machining experiments validates the relationship between surface roughness and undeformed chip thickness. • Lenslets with high surface quality and little tool wear are obtained after machining microlens array. [ABSTRACT FROM AUTHOR]

Surface quality has a significant impact on the service life of machine parts. Grinding is often the last process to ensure surface quality and accuracy of material formation. In this study, a high-quality surface was developed by determining the coefficient of friction in grinding a quartz fiber-reinforced silica ceramic composite. By processing the physical signals in the grinding process, a multi-objective function was established by considering grinding parameters, i.e., surface roughness, coefficient of friction, active energy consumption, and effective grinding time. The weight vector coefficients of the sub-objective functions were optimized through a multi-objective evolutionary algorithm based on the decomposition (MOEA/D) algorithm. The genetic algorithm was used to optimize the process parameters of the multi-objective function, and the optimal range for the coefficient of friction was determined to be 0.197~0.216. The experimental results indicated that when the coefficient of friction tends to 0.197, the distribution distance of the microscopic data points on the surface profile is small and the distribution uniformity is good. When the coefficient of friction tends to 0.216, the surface profile shows a good periodic characteristic. The quality of a grinding surface depends on the uniformity and periodicity of the surface's topography. The coefficient of friction explained the typical physical characteristics of high-quality grinding surfaces. The multi-objective optimization function was even more important for the subsequent high-quality machining of mechanical parts to provide guidance and reference significance. [ABSTRACT FROM AUTHOR]

Microlens arrays will suffer from filling defects due to trapped gas when molded in a nitrogen atmosphere by precision glass molding (PGM). In this paper, a multistep molding method is proposed to avoid gas trapping and improve the accuracy of a microlens array. The defect formation mechanism of the microlens array caused by the trapped gas is investigated, and the effect of the molding pressure on the defect formation is analyzed. A numerical model of the mold‐nitrogen‐glass interface at high temperature is established to evaluate the defect evolution, and the minimum number of PGM steps required to greatly reduce defects caused by the trapped gas is predicted. The numerical model is validated by a multistep PGM experiment of D‐K59 glass material. The results show that a three‐step PGM process significantly reduced the height of the defect. The difference between the height of the microlens unit and the depth of the mold is less than 0.4%. The molded microlens array has a peak‐to‐valley value of 0.38 μm and a surface roughness Ra of 3.5 nm. This work is instructive for the fabrication of high‐precision glass microlens arrays. [ABSTRACT FROM AUTHOR]

This study explores the impact of plasma activation on the surface properties of 6H-SiC substrates and the subsequent characteristics of electroless nickel‑phosphorus (Ni P) plating. The research investigates how varying plasma activation durations influence surface roughness, chemical composition, and plating adhesion. Plasma activation significantly increased surface roughness from 592 nm to 772 nm and the oxidation layer thickness from 5.76 nm to 32.2 nm. These changes were accompanied by corresponding decreases in water and Ni P solution contact angles, indicating enhanced surface wettability. The electroless Ni P plating demonstrated a progressive increase in surface roughness, and the Ra roughness reached 1319 nm. X-ray diffraction (XRD) analysis revealed a reduction in the crystallinity of the Ni P layer, alongside the emergence of new phases such as Ni 2 P and Ni 8 P 3 , indicating alterations in the structural and chemical composition of the plating. The average thickness of the Ni P plating decreased from 39.70 μm at 10 min of plasma activation to 36.12 μm at 30 min, suggesting a potential reduction in deposition efficiency with prolonged activation times. Additionally, the hardness of the Ni P layer exhibited a decline from 525 HV to 502 HV, attributed to increased surface oxidation and defect formation. The adhesion quality of the plating also deteriorated with increased plasma activation time, as evidenced by significant peeling and cracking, as observed in the scratch test. [Display omitted] • Plasma activation increased 6H-SiC surface roughness, improving mechanical interlock with Ni-P plating. • Increased activation times reduced Ni-P plating thickness from 40.41 μm to 36.36 μm. • Extended activation decreased Ni-P surface hardness from 525 HV to 502 HV. • Prolonged activation weakened Ni-P adhesion, causing more cracking and peeling in scratch tests. [ABSTRACT FROM AUTHOR]

Chalcogenide glass (ChG) is widely studied due to its wide infrared transmission window, low refractive index temperature coefficient, and low dispersion coefficient. Precision glass molding (PGM) and single-point diamond turning (SPDT) are representative high-efficiency and high-precision methods for ChG processing. However, the high softening degree of ChG under high-temperature conditions leads to abnormal gas release and severe mold adhesion which deteriorate surface quality. Although SPDT typically facilitates high-precision machining, it has limited efficacy in long-term, large-area, large-depth processing; this limitation causes severe tool wear due to the high hardness and brittleness of ChG material. A new process combining the advantages of PGM and SPDT technology is proposed to fabricate aspheric lenses on ChG (IRG202) by ultra-precision and high-efficiency machining. The pre-molding of ChG by PGM reduces cutting loss during aspheric lens machining by SPDT. The machined aspheric lenses have the high quality with a form error of PV 103.5 nm and surface roughness Ra of 8.3 nm. The processing efficiency of each single lens is increased by almost 8 times over the traditional method. The proposed ChG aspheric lens fabrication process maintains high precision even under mass production conditions. [ABSTRACT FROM AUTHOR]

Relative tool sharpness (RTS) is identified as the ratio of undeformed chip thickness to tool cutting edge radius. This paper studies the effects of RTS on the surface generation mechanism of precision turning of electroless nickel-phosphorus (Ni-P) coating. An R-shaped tungsten carbide (WC) tool was adopted for the face turning experiment. The cutting edge radius was 1.84 μm measured by a laser scanning confocal microscope (LSCM). The chip formation behavior, cutting forces and surface morphology were investigated under different RTS values. Results showed that the chip changes from continuous to discontinuous as RTS decreases from 0.54 to 0.27, indicating the transition of the material removal mechanism. The periodical fluctuations with small amplitudes on the machined surface are associated with the high-frequency tool-tip vibration. The low-frequency fluctuations of the cutting forces are related to the material swelling and recovery. The optimal machined surface roughness was obtained at the RTS of 0.38. [ABSTRACT FROM AUTHOR]

Irregular lenses are commonly employed in various beam shaping, imaging, and other optical applications. They require secondary processing to meet specific design and assembly criteria. Bessel beam lasers have gained popularity for their ability to efficiently separate hard-brittle materials owing to their high processing quality and speed. However, the complex surface of irregular lenses creates challenges such as refraction and scattering, which impede the laser beam's ability to form a laser center lobe inside the material. This paper proposes an innovative technique called immersion laser separation (ILS), where an irregular lens is immersed in a refractive index matching medium to create a compound with a uniform refractive index. This approach mitigates the impact of surface complexity on the optical path of the Bessel beam. The separation of a fast axis collimator (FAC) by ILS is used as an example to test the proposed technique. The distribution characteristics of the Bessel beam light field inside the lens material under different refractive index were investigated to find that the laser consistently forms a laser center lobe inside the material during cutting when the matching deviation is small. This results in a modified area that covers the entire surface. The maximum cutting speed can reach 50 mm/s, the cutting surface roughness is less than 700 nm, and the technique produces no chips or micro-cracks, ensuring uniformly high-quality separation. Experimental and simulation results are in close agreement, suggesting that the proposed technique is effective for the efficient, high-quality cutting of irregular lenses. [ABSTRACT FROM AUTHOR]

Electrochemical anodization has been utilized to reduce the surface hardness of Tungsten Carbide (WC) so that to increase its machinability. In this study, experiments have been conducted to illustrate the impact of surface roughness on electrochemical anodization of binderless WC. Anodization was performed on binderless WC that had different surface roughness by applying a constant voltage and utilizing Sodium Hydroxide (NaOH) as the electrolyte. Oxide generation mechanism during the anodization process has been analyzed in detail, through the investigation of current behavior, surface characterization, surface hardness reduction, surface profile change. It has been observed that during the anodization process, multiple peaks in current curves were produced as a result of discharge channels, induced by the cavities at oxide-substrate interface. When the electric barrier is broken, there was an increase in the formation of oxide layers. Hardness decreased significantly across all substrate conditions. Pristine WC substrate had a robust hardness of 33.34 GPa, while non-polished, semi-polished, and polished substrates had 8.26, 9.545, and 9.411 GPa, respectively. These findings demonstrate the significant impact of anodization on WC's mechanical characteristics, resulting in a 71.6 % decrease in hardness across substrate states. A hypothesis has been presented to describe the overall anodization behavior and boundary oxide generation mechanism of binderless WC. Polished WC substrates have lower surface roughness, indicating more controlled and homogeneous anodization as compared to non-polished and semi-polished WC substrates. The present study enhances the understanding of the impact of surface roughness on the electrochemical anodization of binderless WC, which will further facilitate its incorporation with machining techniques. • Electrochemical anodization behavior investigation on binderless WC • Surface roughness effects study on electrochemical anodization behavior of binderless WC • Anodization boundary generation mechanism analysis on binderless WC [ABSTRACT FROM AUTHOR]

Tool life is a significant issue for the application of micro mills. Optimizing cutting edge geometries of micro mill is an effective way to improve tool life. This paper investigates the effects of different chamfered cutting edges of micro mill on the tool cutting performance. A series of slot milling experiments are conducted on aluminum alloy 7075 by using micro mills with various cutting edge chamfer lengths, and the tool wear and surface roughness are measured. The results show that the cutting edge chamfer of micro mill can improve the tool life. For the micro mill fabricated with sharp cutting edge, the fracture of cutting edge easily occurs resulting in the tool early broken. As the cutting edge chamfer length is bigger, the tool life becomes longer, but the tool flank wear width increases due to the higher stress in cutting region. However, the effects of various cutting edge chamfer lengths on surface roughness are not obviously found. [ABSTRACT FROM AUTHOR]

Hot embossing is an efficient technique for manufacturing high-quality micro-lens arrays. The machining quality is significant for hot embossing the micro-lens array mold. This study investigates the effects of micro ball end-milling on the machining quality of AISI H13 tool steel used in the micro-lens array mold. The micro ball end-milling experiments were performed under different machining strategies, and the surface roughness and scallop height of the machined micro-lens array mold are measured. The experimental results showed that a three-dimensional (3D) offset spiral strategy could achieve a higher machining quality in comparison with other strategies assessed in this study. Moreover, the 3D offset spiral strategy is more appropriate for machining the micro-lens array mold. With an increase of the cutting speed and feed rate, the surface roughness of the micro-lens array mold slightly increases, while a small step-over can greatly reduce the surface roughness. In addition, a hot embossing experiment was undertaken, and the obtained results indicated higher-quality production of the micro-lens array mold by the 3D offset spiral strategy. [ABSTRACT FROM AUTHOR]

Micro end milling is a main method for the fabrication of microgroove parts which are widely applied in biology, electronics, precision machinery, and other fields. However, the machining quality of microgroove is difficult to meet requirements due to size effect, and the machined grooves easily produce high surface roughness and poor form accuracy during micro milling. In this paper, in order to investigate the effects of machining inclination angles on the performance of micro ball end milling, the micro milling experiments on Ti-6Al-4V are carried out by setting the micro ball end mill with different inclination angles in feed direction, cross-feed direction, and the combination of the two directions, respectively. The results show that the tool orientation strategy has significant influences on the quality of microgroove and can reduce the roughness and improve the form accuracy. With increase of the absolute value of inclination angle along feed direction from 0° to 45°, the surface roughness has a decreasing trend, and the chips adhesion and texture becomes inconspicuous. When inclination angle along feed direction is 30° and 45°, the combination inclination angle strategy has no obvious influences on the surface roughness with increase of inclination angle along cross-feed direction. However, the combination inclination angles strategy can reduce the maximum form deviation and improve the form accuracy of the groove. Based on the results, an optimal combination inclination angles with feed direction 45° and cross-feed direction 20° strategy is proposed to machining the microgroove. [ABSTRACT FROM AUTHOR]

The elliptical ultrasonic assisted grinding (EUAG) method has been proved to be promising in machining of hard and brittle materials, e.g., sapphire and silicon. However, its potential has not been sufficiently developed because the processing mechanism has not been clearly explained. This paper focuses on the surface formation mechanism in EUAG of monocrystal sapphire by investigating the fractal behavior of ground surface. The EUAG experiments on monocrystal sapphire were performed on the constructed apparatus by installing an elliptical ultrasonic vibrator on a CNC surface grinder. For comparison, the conventional grinding (CG) experiments were also carried out on the same experimental apparatus without ultrasonic vibration. The ground surfaces obtained were analyzed by fractal method, and results show that: (1) the great improvement of the surface quality with lower surface roughness is achieved in EUAG compared with those in CG. Moreover, the fractal dimension of ground surface in EUAG is larger than that in CG. It is also found that the fractal dimension is more sensitive to surface defect compared with the surface roughness. (2) The fractal dimension changes differently comparing CG with EUAG as the depth of cut increases from 0.4 to 3.2 μm. From the variations of the fractal dimension with different depth of cut, it is found that there are two variation regions, i.e., steady region and deteriorated region both in EUAG and CG, but the depth of cut in steady-deteriorated transition point of EUAG is larger than that in CG, meaning that the EUAG can achieve a deeper ductile depth of cut. (3) In EUAG, elliptic motion trajectories of adjacent abrasive grains interact with each other, causing the lower side walls of grooves and more exquisite microstructures. Thus the higher surface fractal dimension in EUAG is obtained and a better surface quality is achieved. Therefore, the surface formation characteristics in EUAG of monocrystal sapphire can be investigated by fractal analysis. [ABSTRACT FROM AUTHOR]

In this paper, nickel phosphorous diamond (Ni-P-D) composite plating is introduced as a new method to fabricate a micro diamond wheel with a diameter of φ450 μm. In the fabrication process, the steel substrate (SKD-11) is first ground to a ball end shape with a radius of 200 μm. Nickel phosphorous (Ni-P) and micro diamond particles with an average grain size of 3.5 μm are then electrolessly plated on the steel substrate tip, with a final plating thickness of approximately 25 μm. Parameters of the Ni-P-D plating conditions, including substrate rotation, stirring speed, and diamond grain density are then investigated. The topography of the micro wheel shows that diamond grains as the reinforced phase are embedded omnidirectionally and uniformly in the Ni-P plating along both the surface direction and the thickness direction. Energy dispersive spectrometer (EDS) results indicate that the ratio of diamond grains is approximately 27 wt%, and the Ni-P plating layer is an alloy in the amorphous state. Once fabricated, the micro diamond wheel performance is tested by grinding microgrooves on single crystalline silicon. The machined microgroove has a surface roughness of Ra 26 nm without obvious cracks. Micro tool wear after grinding proves that the bonding strength between diamond grains and Ni-P alloy, as well as the adhering strength between the Ni-P plating and steel substrate, are strong enough to meet the requirements of the micro grinding wheel. [ABSTRACT FROM AUTHOR]

Tool wear is a significant issue for the application of micro end mills. This can be significantly improved by coating materials on tool surfaces. This paper investigates the effects of different coating materials on tool wear in the micro milling of Ti-6Al-4V. A series of cutting experiments were conducted. The tool wear and workpiece surface morphology were investigated by analyzing the wear of the end flank surface and the total cutting edge. It was found that, without coating, serious tool wear and breakage occurred easily during milling. However, AlTiN-based and AlCrN-based coatings could highly reduce cutting edge chipping and flank wear. Specifically, The AlCrN-based coated mill presented less fracture resistance. For TiN coated micro end mill, only slight cutting edge chipping occurred. Compared with other types of tools, the AlTiN-based coated micro end mill could maximize tool life, bringing about an integrated cutting edges with the smallest surface roughness. In short, the AlTiN-based coating material is recommended for the micro end mill in the machining of Ti-6Al-4V. [ABSTRACT FROM AUTHOR]

[Display omitted] • With the proposed assisted grinding method, a diamond wheel with relatively big-size grains can be used to perform the grinding of low roughness for sapphire. • With the proposed assisted grinding method, the surface roughness and subsurface damage of sapphire reaches 45 nm and 141 nm which is reduced by 60.8% and 84.5% than that without the assistant, respectively and a high light transmittance can be obtained. • The crystal orientation of the sapphire and the pH values of the cerium oxide liquid have little effect on the roughness of the assisted grinding surface. • The improvement of the surface roughness in the assisted grinding benefits from the combined action of the grinding of the diamond grains and the polishing of the cerium oxide liquid. Due to its high hardness and brittleness, sapphire is difficult to obtain a low grinding roughness. In this paper, the cerium oxide liquid is used to assist the grinding of sapphire with a diamond wheel with relatively big-size grains to obtain a low roughness. The effects of grain size, the crystal orientation of the sapphire, and the pH values of the cerium oxide liquid on the assisted grinding process have been analyzed. It is shown that with the proposed method, the roughness of 45 nm and subsurface damage of 141 nm are obtained, respectively. Compared with the grinding surfaces obtained without the assistant, the roughnesses and the subsurface damage of the assisted grinding surfaces are reduced by 60.8% and 84.5% when #600 wheel is used, respectively. Moreover, in the grinding experiments, the crystal orientation of the sapphire and the pH values of the cerium oxide liquid have little effect on the roughness of the grinding surface, while the grain size has a great impact. It is concluded that the improvement of the surface roughness by using the proposed method benefits from the combined action of the grinding of grains and the polishing of the cerium oxide liquid. [ABSTRACT FROM AUTHOR]

The surface characterization of ground monocrystal sapphire is investigated by fractal analysis method. A serial of ground sapphire surfaces in ductile removal and brittle removal mode are obtained by grinding experiments, and their three dimensional (3D) and two dimensional (2D) fractal dimensions are calculated and analyzed by box-counting methods. The 3D surface fractal dimension D s shows a negative correlation with the surface roughness parameter Ra and is sensitive to the ground surface defects. For the ground surface with larger fractal dimension D s , its micro-topography is more exquisite with minor defects. Once the fractal dimension D s become smaller, deep cracks and pronounced defects are exhibited in ground surface. Moreover, the material removal mode can be implied from the distribution of 2D cross-sectional profile fractal dimension D L . The workpiece surface generated in ductile removal mode has high surface quality with high 2D and 3D fractal dimensions. This study indicates that the box-counting fractal analysis is an effective method to evaluate ground sapphire surface comprehensively. [ABSTRACT FROM AUTHOR]