The pico-and femtosecond laser micromachining has grown up as a reliable tool for precise manufacturing and electronic industries to make fine drilling and machining into hard metals and ceramics as well as soft plastic and to form various nano-and microtextures for improvement of surface functions and properties in products. The ultrashort-pulse laser machining systems were developed to describe the fine microdrilling and microtexturing behavior for various materials. Accuracy in circularity and drilled depth were evaluated to discuss the effect of substrate materials on the laser microdrilling. Accuracy in unit geometry and alignment was also discussed for applications. A carbon base mold substrate was micromachined to transcribe its microtextures to transparent plastics and oxide glasses. Three practical examples were introduced to demonstrate the effectiveness of nano-/ microtexturing on the improvement of microjoinability, the reduction in friction and wear of mechanical parts and tools, and the surface property control. The fastrate laser machinability, the spatial resolution in laser microtexturing as well as the laser micromanufacturing capacity were discussed to aim at the future innovations in manufacturing toward the sustainable society.
In this study, a CVD (Chemical Vapor Deposition)-diamond coated tungsten carbide cobalt (WC (Co)) punch was trimmed to adjust its surface roughness and to significantly reduce its edge curvature for fine piercing by femtosecond laser processing. Through this laser trimming, the surface quality of the diamond coating and the punch edge profile were improved to less than 0.5 μm at the maximum roughness and 2 μm in the edge width, respectively. In parallel with this improvement of surface quality, the side surface of the diamond coating was modified to include nano-textures via the LIPSS (Laser Induced Periodic Surface Structuring) process. Through the fine piercing process, this nanotexture was transcribed onto the pierced hole surface together with fine shearing of the hole by piercing. WLI (White-Light Interferometry) and SEM (Scanning Electron Microscopy) were utilized to describe this transcription of nanotextures during the piercing process. These semiregular nanotextures with an LIPSS period of 300 nm on the pierced hole surface induced a blue colored surface plasmon.
A dispensing nozzle is an essential mechanical element in inkjet, dot, and bioprinting. To improve the printing resolution, the inner diameter of the nozzle outlet must be as small as possible. A droplet dispensed through a hydrophilic stainless steel outlet expands on the whole outlet surface and along the side surface of the nozzle. This issue can be solved by physical surface modifications. In the present paper, a femtosecond laser micro-/nano-texturing method was developed to transform the originally hydrophilic stainless steel surface of a nozzle to a hydrophobic or superhydrophobic one. First, an AISI304 plate was used to demonstrate experimentally that, on its surface, the tailored micro-/nano-patterns were reproduced as micro-/nano-textures, making the surface superhydrophobic. Second, the technique was applied to the physical surface modification of an AISI304 stainless steel nozzle outlet by optimizing the femtosecond laser machining conditions. A high-speed camera was used to take a snapshot of the dispensed droplet from the surface-modified outlet. Finally, a line-printing experiment was performed to characterize the dispensing behavior of the stainless steel nozzles with and without physical surface modification.
Surface geometry has had an influence on the surface property, in addition to the intrinsic surface energy, of materials. Many physical surface modification methods had been proposed to control the solid surface geometry for modification of surface properties. Recently, short-pulse lasers were utilized to perform nano-texturing onto metallic and polymer substrates for the improvement of surface properties. Most of the papers reported that the hydrophilic metallic surface was modified to have a higher contact angle than 120–150°. Little studies explained the relationship between surface geometry and surface properties. In the present study, the laser micro-/nano-texturing was developed to describe this surface-geometric effect on the static contact angles for pure water. Micropatterns with multi spatial frequencies are designed and synthesized into a microtexture. This tailored microtexture was utilized to prepare for computer aided machining (CAM) data to control the femtosecond laser beams. The nano-length ripples by laser induced periodic surface structuring (LIPSS) supposed onto this microtexture to form the micro-/nano-texture on the AISI304 substrate surface. Computational geometry was employed to describe this geometric profile. The fractal dimension became nearly constant by 2.26 and insensitive to increase of static contact angle (θ) for θ > 150°. Under this defined self-similarity, the micro-/nano-textured surface state was controlled to be super-hydrophobic by increasing the ratio of the highest spatial frequency in microtextures to the lowest one. This controllability of surface property on the stainless steels was supported by tailoring the wavelength and pitch of microtextures. Exposure testing was also used to evaluate the engineering durability of this micro-/nano-textured surface. Little change of the measured fractal dimension during the testing proved that this physically modified AISI304 surface had sufficient stability for its long-term usage in air.
The AISI316 austenitic stainless steel die was prepared and nitrided at 673 K for 14.4 ks. Through this low temperature plasma nitriding, the AISI316 die was homogeneously hardened up to 1400 HV within its surface layer of 50 μm. This nitrided AISI316 die was utilized to print the tailored micropattern with nanotextures onto its surface by the femtosecond laser processing. Each micropattern consisted of the tailored segments to have unidirectional nanotextures with different orientations. Each segment was recognized by its intrinsic surface plasmonic brilliance to tailored nanotextures. The CNC (Computer Numerical Control) stamping system was used to coin these micropatterns with nanotextures onto the AA1060 aluminum plates with the thickness of 1 mm. SEM (Scanning Electron Microscopy) and optical microscopy were employed to characterize the original micro-/nano-textures on the AISI316 die as well as the coined nanotextured patterns on the AA1060 plate surfaces.
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