To study the effects of the interface thermal resistance on surface morphology evolution in precision glass molding (PGM) for microlens array with different mold materials, including Tungsten carbide and heat-resistant stainless steel, the glass-mold interface thermal resistance is calculated, and heat-transfer simulation of PGM based on an interface thermal resistance model at the heating stage is conducted correspondingly. The effect of flattening behavior on the glass-mold interface is explained. Then, experiments evaluating the relationship between heating time and glass surface roughness are carried out, and the glass adhesion phenomenon appearing on the heat-resistant stainless steel mold is observed and analyzed. Finally, the microlens array is fabricated on the nickel phosphorous plating layer on the heat-resistant stainless steel substrate by diamond-ball nose-end milling, and experiments of PGM for the microlens array are carried out to verify the interface thermal resistance model. The result shows that a high-quality surface can be obtained by the combination of a smooth mold and rough glass. Compared with the microlens array fabricated with the rough glass preform, using the smooth glass preform achieves higher form accuracy without defects or blurs.
Crystalline nickel-phosphide (c-Ni-P) plating is a newly developed mold material for precision glass molding (PGM) to fabricate microgrooves. In the ultraprecision cutting process of the c-Ni-P plating material, the neighboring microgrooves are required to adjoin with each other to ensure acute microgroove ridges and miniaturize the microgroove size. Generally, defects of burrs and fracture pits can easily occur on the ridges when the plating layer is grooved. Burrs appear when tears dominate in material removal with a large adjacent amount. With the change of the adjacent amount, the removed material is sheared out from the workpiece, and when the cutting depth of the groove ridge is over the brittle-ductile transition thickness, fracture pits arise. To restrict these defects, a small cross-angle microgrooving method is proposed to test the critical adjacent amount range efficiently. It is found that an acute ridge of the microgroove is formed with a small enough adjacent amount; when this amount is in the range of 570 nm~720 nm in the microgroove machining process, fracture pits begin to arise on the gradient edge. High-quality microgrooves can be obtained based on this methodology.
The current research
on gecko-inspired dry adhesives is focused
on micropillar arrays with different terminal shapes, such as flat,
spherical, mushroom, and spatula tips. The corresponding processing
methods are mostly chemical methods, including lithography, etching,
and deposition, which not only are complex, expensive, and environmentally
unfriendly, but also cannot completely ensure microstructural integrity
or performance stability. The present study demonstrates a high-precision,
high-efficiency, and green method for the fabrication of a gecko-inspired
surface, which can promote its application in dexterous robot hands
and mechanical grippers. Based on the bendable lamellar structures
of the gecko, annular wedge adhesive surfaces that stick to the finger
surfaces of dexterous robot hands to improve their load capacity are
proposed and fabricated via a suitable combined processing method
of ultraprecision machining and replica molding. The greater the width,
the higher the replication integrity, and when the minimum width is
20 μm, the replication error is less than 5.5% due to the superior
processing performance of the nickel–phosphorus (Ni–P)
plating of the master mold. The fabricated annular wedge structures
with an optimized width of 20 μm not only exhibit a strong friction
force of up to 35.48 mN under a preload of 20 mN in the GCr15/poly(dimethylsiloxane)
(PDMS) friction pair but also demonstrate an obviously improved anisotropic
friction characteristic of up to λ = 1.36, as the molecular
force exhibits a stronger increase as compared to the decrease of
the mechanical force of the structure with a small width.
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