Gecko adhesion has inspired the fabrication of various dry adhesive surfaces, most of which are developed to be used under atmospheric conditions. However, applications of gecko-inspired surfaces can be expanded to vacuum and even space environment due to the characteristics of van der Waals interactions, which are always present between materials regardless of the surrounding environment. In this paper, a controllable, anisotropic dry adhesion in vacuum is demonstrated with gecko-inspired wedged dry adhesive surfaces fabricated using an ultraprecision diamond cutting mold. The adhesion and friction properties of the wedge-structured surfaces are systematically characterized in loading–pulling mode and loading–dragging–pulling mode. The surfaces show significant anisotropic adhesion (Pad ≈ 10.5 kPa vs Pad ≈ 0.7 kPa) and friction (Pf ≈ 50 kPa vs Pf ≈ 30 kPa) when actuated in gripping and releasing direction, respectively. The wedge-structured surfaces in vacuum show comparable properties as exposed in atmosphere. A three-legged gripper is designed to pick up, hold, and release a patterned silicon wafer in vacuum. The study demonstrates a green, high-yield, and low-cost method to fabricate a reliable and durable mold for gecko inspired anisotropic dry adhesive surfaces and the potential application of dry adhesive surface in vacuum.

Controllable Anisotropic Dry Adhesion in Vacuum: Gecko Inspired Wedged Surface Fabricated with Ultraprecision Diamond Cutting

Micro/nanostructured components play an important role in micro-optics and optical engineering, tribology and surface engineering, and biological and biomedical engineering, among other fields. Precision glass molding technology is the most efficient method of manufacturing micro/nanostructured glass components, the premise of which is meld manufacturing with complementary micro/nanostructures. Numerous mold manufacturing methods have been developed to fabricate extremely small and high-quality micro/nanostructures to satisfy the demands of functional micro/nanostructured glass components for various applications. Moreover, the service performance of the mold should also be carefully considered. This paper reviews a variety of technologies for manufacturing micro/nanostructured molds. The authors begin with an introduction of the extreme requirements of mold materials. The following section provides a detailed survey of the existing micro/nanostructured mold manufacturing techniques and their corresponding mold materials, including nonmechanical and mechanical methods. This paper concludes with a detailed discussion of the authors recent research on nickel-phosphorus (Ni-P) mold manufacturing and its service performance.

A review of the techniques for the mold manufacturing of micro/nanostructures for precision glass molding

The surface quality of tungsten heavy alloy parts has an important influence on its service performance. The accurate on-line prediction of surface roughness in ultra-precision cutting of tungsten heavy alloy has always been the difficulty of research. In this paper, the ultrasonic elliptical vibration cutting technology is used for ultra-precision machining of tungsten heavy alloy. Based on the idea of deep learning, the surface roughness is discretized, and the fitting problem in surface roughness is transformed into a classification problem. The generalization ability of the prediction model is improved by introducing batch standardization and Dropout. The relationship between the vibration signal and the surface roughness is established. Experimental results show that the model can achieve on-line prediction of cutting surface roughness. The prediction accuracy rate can be improved by more than 10% compared with the direct fitting method.

On-line prediction of ultrasonic elliptical vibration cutting surface roughness of tungsten heavy alloy based on deep learning

Ultra-precision machining of radial Fresnel lens on roller moulds

An effective approach to reduce tool wear remains a long-standing challenge in using diamond-cutting ferrous metals. To achieve this objective, we explored a new method of cold plasma and ultrasonic elliptical vibration-assisted diamond cutting. The method consisted of flexible cold plasma generator conveniently transferred cold plasma to the tool-workpiece interface, and an ultrasonic elliptical vibration precisely controlled system vibration characteristics. Molecular dynamics simulation was employed to study the graphitization process of Fe catalytic diamond. By diagnosing the active species of the plasma jet and analyzing the reaction process of plasma with fresh workpiece surface, we demonstrate the inhibition mechanism of nitrogen cold plasma to the diamond tool chemical wear. Intermittent cutting characteristics of ultrasonic elliptical vibration change the value and direction of the cutting force and are conducive to exclude chips. This feature therefore reduces the cutting temperature and then retards the graphitization process of the diamond. These results establish a new cutting technology that combines the advantages of vibration cutting and surface modification and provide a cutting medium that targets the effective reduction of tool wear for diamond-cutting ferrous metals.

Diamond-cutting ferrous metals assisted by cold plasma and ultrasonic elliptical vibration

To promote the machining precision of Fresnel lens mould, a true circle processing method with a single-point diamond turning (SPDT) was proposed. In this method, the arc-curved surface of Fresnel lens mould grooves was processed with axis B rotation, and the frequent servo feed of each axis in the processing with traditional interpolation method was avoided. Moreover, the distribution of the arc-curved surface of the Fresnel lens mould was analyzed. All the centers of the arc-curved surfaces were distributed on the lens axle. The method was realized to process the Fresnel lens mould by combing the processing performance of a four-axis ultra-precision machine tool using axis Z to aid movement and axis B rotation. The straight blade of the tool was replaced by a circular curve by optimizing a single-point diamond tool shape according to the Fresnel lens mould characteristic to reduce the cutting force of the tip of the main cutting edge. Machining experiment on the Fresnel lens mould was studied. A mould with the diameter of 46 mm and curvature radius of 90 mm was processed. Surface of the Fresnel lens was measured using a scanning white-light interferometer. The mould surface roughness was Ra 7.3 nm. The grooves of the lens mould were sharp, and the mould teeth were accordant. Experimental results showed that the machining precision by the proposed Fresnel lens mould with the true circle turning method was high.

Ultra-precision machining of Fresnel lens mould by single-point diamond turning based on axis B rotation

Fresnel lens arrays are widely applied as the core optical component in concentrated photovoltaic (CPV) systems for concentrating light on a solar cell. To improve the photoelectric conversion efficiency of CPV systems, a Fresnel lens design is proposed, in which both uniform concentration and machining feasibility are pursued by means of simpler structure. In this design, the concentrating facets of the Fresnel lens are conical ones with different inclined angles, and the light passing through these conical facets can be superposed on the same position. The optical performance of the lens is analyzed to optimize its geometrical parameters. Towards this uniform concentrating design with a simple structure, an ultra-precision diamond cutting process based on B axis rotation is also developed to machine the Fresnel lens mold. In this process, the V-shaped diamond tool is rotated from right to left to machine the micro grooves of the lens mold with a maximum cutting depth of the groove height, so that the grooves can be prevented from being cut by the tool tip with low strength. Cutting tests of the factors influencing the machining accuracy and surface quality are carried out to optimize the cutting trajectory planning and machining parameters. The Fresnel lens molds with no sharp corner defects and no surface scratches are machined, and dimensional accuracy of 1.0 μm and surface roughness of better than 13 nm are achieved. Then, a silicone rubber lens is cast based on this mold. Concentrating uniformity test of the lens is conducted, and a concentrating uniformity of better than 75% is achieved. The results show the effectiveness of the uniform concentrating design and the feasibility of the B axis rotating machining process.

Uniform concentrating design and mold machining of Fresnel lens for photovoltaic systems

The invention relates to a tool setting method. The tool setting method comprises the steps that an X-direction fine-adjustment platform, a Z-direction fine-adjustment platform and a tool are installed on a shaft B, the shaft B rotates to enable the tool nose to rotate by the angle alpha and move from the first position to the second position, and the relative distance between the first position and the second position in the direction parallel to the Z direction is marked as y2; the shaft B rotates again to enable the tool nose to rotate by the angle alpha and move from the second position to the third position, and the relative distance between the first position and the third position in the direction parallel to the Z direction is marked as y3, wherein alpha is larger than or equal to 108 degrees but smaller than or equal to 110 degrees; a point (a,b) is set to be a coordinate, in a coordinate system treating any point on a rotation center line as the original point, of the tool nose, the coordinate direction of a is the same as the X direction, and the coordinate direction of b is the same as the Z direction; the perpendicular distance r between the tool nose and the rotation center line is calculated according to the formula (1) of , the formula (2) of and the formula (3) of , the perpendicular distance r between the tool nose and the rotation center line is compared with the machining radius R, and if r is not equal to R, the coordinate (a,b) is adjusted until r is equal to R.

Tool setting method, proper circle processing method and Fresnel lens processing method

For reducing diamond tool wear in ultra-precision cutting of ferrous metals, a process of combining ultrasonic elliptical vibration with graphite particle atmosphere was put forward. An experimental setup was built integrating an ultrasonic elliptical vibration mechanism with a jet lubrication device on a 4-axis ultra-precision lathe. The frequency of ultrasonic elliptical vibration is 38.36 kHz with a trajectory of 8.5×3.5μm. Graphite particles with sizes of 1.3~2μm were selected. Conventional cutting and the combined method were conducted on die steel. Compared with conventional cutting with a wear land width of about 300μm, diamond tool wear in the combined method was decreased to about 20 to 30μm. The combined method is feasible to further reduce the diamond tool wear when cutting die steel.

Diamond Tool Wear Reduction by Combining Ultrasonic Elliptical Vibration with Graphite Particle Atmosphere

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Ultra-precision machining of Fresnel lens mould by single-point diamond turning based on axis B rotation

Uniform concentrating design and mold machining of Fresnel lens for photovoltaic systems

Tool setting method, proper circle processing method and Fresnel lens processing method

Diamond Tool Wear Reduction by Combining Ultrasonic Elliptical Vibration with Graphite Particle Atmosphere