Surface friction in metal forming processes can be reduced by creating lubricant reservoirs at the interface between surfaces in contact, and a laser texturing process can be employed to produce the ...micro-dimples that act as the reservoirs on the surfaces. However, the role of the laser texturing parameters in the friction reduction of tool steel surfaces has still received very little attention. Therefore, this study aims to reduce the friction of the AISI D2 tool steel surface on which a nanosecond pulse laser was applied to create an array of micro-lubricant pockets for trapping lubricant. The effects of laser power, irradiation duration, and spacing distance between pockets on the pocket diameter, size of the heat-affected zone, surface friction, and wettability were investigated in this work. The average laser power in the range from 5 to 10 W and laser irradiation duration of 0.02 to 0.10 s were applied. The results showed that the increase in laser power and irradiation duration enlarged the pocket diameter and heat-affected zone. The largest pocket diameter of 40 µm was achievable by using 10 W laser power together with 0.10 s irradiation time. The pin-on-disc method was employed to determine the friction coefficient of the tool steel, where JIS SPFC 980Y advanced high-strength steel was used as a disc. The friction coefficient of laser-textured with different spacing distances of 150, 200, and 250 µm versus untextured surfaces was compared and found to vary depending on the applied normal load. The laser-textured surface having a pocket spacing distance of 150 µm and pocket density of 5.6%, offered the lowest friction coefficient of 0.097 on average for all tested loads, whereas the average friction coefficient of the untextured surface was 0.117. In addition, the wettability of textured surfaces was insignificantly changed compared to that of untextured ones, so the micro-lubricant pockets did not cause oleophobicity affecting the performance of lubrication. Well-defined micro-pockets using the most appropriate laser parameters, i.e., 10 W laser power with 0.10 s irradiation duration and 150 µm spacing distance, successfully reduced the sliding friction of contacting couples between the laser-textured tool steel and advanced high-strength steel surfaces. The low surface friction induced by the laser-fabricated micro-lubricant pockets has been feasible for the forming tool and die applications where the energy consumed in their operations can be minimized.
Friction involved in metal-forming processes typically leads to the wear of tool and die surfaces, and in turn shortens the tool’s service life. A thriving need for reducing surface friction requires ...the tool surface to be modified. This paper presents the surface modification of SKH51 tool steel, on which the hexagonal array of micro-dimples is fabricated by a nanosecond pulse laser. Using the average laser power of 25 W can create decent dimples for trapping lubricant and enabling hydraulic pressure at the surfaces in contact. The effect of dimple density and sliding speed on the coefficient of friction was examined in this study through the pin-on-disc test, in which a stainless steel pin was applied against the tool steel disc with a constant load. The laser-textured tool steel surface with a dimple density of 35% had a friction coefficient of 0.087, which was lower than that of the untextured surface by 12.6% when using a sliding speed of 15 cm/s. In addition to friction reduction, there was no substantial wear found on the laser-textured surface compared to the untextured sample. The findings of this study can be a processing guideline and benefit the treatment of tool and die surfaces for friction and wear reduction in metal-forming and related processes.
Optical interference caused by gas bubbles in water is of prime concern in underwater laser micromachining process since it importantly affects the quality of laser-ablated surface and material ...removal rate. This study applied positive water pressure in the underwater laser ablation with the attempts to reduce the bubble size, minimize the optical disturbance to the laser beam in water, and promote the cut quality. A nanosecond pulse laser was used for grooving a single-crystalline silicon wafer in a pressurized water environment. The effects of water pressure and average laser power on groove width, groove depth, size of heat-affected zone, and cut surface morphology were examined and discussed together with the analysis of laser beam refraction in water. The results revealed that the higher the water pressure, the cleaner the cut surface, and smaller heat-affected zone and higher aspect ratio of groove were obtained. The ablation technique proposed in this paper could be a promising method for scribing silicon and plausibly other semiconductor materials at high removal rate with high cut quality and negligible damage.
This paper presents a numerical and experimental study on the single-abrasive scratching of BK7 glass. The formation mechanisms of cracks are investigated for surface integrity evaluation to improve ...the processing efficiency and ensure surface quality through the inhibition of surface and subsurface damage. The numerical simulation reveals that as the abrasive gradually scratches the target surface, median cracks nucleate at the current position just beneath the abrasive, while symmetrical radial cracks that propagate along the negative direction of the x-axis along the scratching direction are easily nucleated slightly behind the abrasive. The single-abrasive scratching experiments at gradually increasing depths on BK7 glass indicate that as the scratching speed increases, the plastic machinability and machining quality are significantly improved. The predicted nucleation position and propagation direction of the radial cracks on the target surface agree well with the corresponding experimental results. Thus, this study can provide a reference for the actual fabrication of high-value BK7 glass devices with high efficiency and quality.
Porous graphene, as an emerging carbon nanomaterial, possesses a range of distinctive physical and chemical properties, such as its lightweight nature and high specific surface area. These properties ...hold great promise for numerous applications in the fields of physics, chemistry, materials science, energy, and information science, among others. Consequently, research and exploration in this area have gained global attention. Nevertheless, the conventional methods for fabricating porous graphene and two-dimensional planar graphene are complex, and obtaining specific patterns with precise graphene areas presents a challenge. In recent years, laser-induced graphene (LIG) has emerged as a promising technology that offers efficient fabrication of graphene and precise control over patterned structures. This technology significantly reduces production costs compared to traditional processing methods. Consequently, scholars have become increasingly interested in LIG and have made numerous efforts to explore its applications in various fields, including energy, information, and environmental sciences. This review systematically compares different synthesis methods of LIG, summarizes and analyzes the effects of laser processing parameters, laser types, precursor materials, process atmospheres, and other factors on the performance of LIG. In addition, the formation mechanism of LIG is discussed over experimental observation and theoretical simulation, and the structure evolution both in micro- and atomic levels are also explored. Furthermore, this review comprehensively covers recent applications of LIG across a wide range of fields, encompassing various sensors, energy devices, environmental protection techniques, and terahertz modulation equipment. Finally, insights are provided into the future directions and trends of this research technology.
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Several studies have found that the laser polishing process is exceptionally effective in smoothing metal surfaces with an initial roughness of less than 10 μm. However, the laser polishing ...performance for the surfaces of additively manufactured parts having different levels of morphology and roughness greater than 10 μm has not been comprehensively investigated. This paper therefore aims to unveil the viability of the laser polishing process for smoothing the additively manufactured surfaces possessing different degrees of morphologies and initial roughness. Three-dimensional printed sample and shot-peened Ti6Al4V titanium alloy sheets having various levels of surface roughness were polished by a nanosecond pulse laser under different processing conditions. Three experimental sets were performed to investigate the effects of initial surface roughness, laser scanning speed, laser pulse repetition rate, number of scanning passes, and flow rate of argon gas on the roughness and morphology of the polished surface. A smooth surface was achievable by using slow laser scanning speed, high laser pulse repetition rate, and multiple-scanning passes. Besides the initial roughness, the improvement was substantially subject to the initial surface morphology. The roughness of the laser-polished surface was improved by up to 73% when a suitable polishing condition was applied. The findings of this study have provided better insight into the laser polishing process and its ability to smooth the rough 3D-printed surfaces. The post-processing of additively manufactured parts, whose surface roughness is a critical concern, will benefit from the laser polishing guidelines suggested in this study.
A ring-type nozzle combining a jet of air and water was employed in this study for improving the quality of laser-cut channel and limiting thermal damage along the cut. A nanosecond pulse laser ...equipped with the water–air jet nozzle was used for producing a microgroove on the surface of commercially pure titanium. The influences of average laser power, air pressure, and water flow rate on groove dimensions and size of damage region were experimentally investigated. The results revealed that using high air jet pressure together with high water flow rate provided a narrow and deep groove with little recast deposition. The selections of air jet pressure and water flow rate were also found to be nonlinearly dependent to each other for creating a microgroove with high aspect ratio. With the aid of weighted sum method, an optimum condition of the coaxial water and air jet–assisted laser micromachining of titanium was 30-W average laser power, 2-bar air jet pressure, and 2.5-l/min water flow rate. Under this condition, a high aspect ratio groove with negligible recast and no heat-affected zone was achievable by using the proposed technique.
•We examine the capability of five laser ablation techniques for scribing an FTO film.•A consistent cut with negligible burrs is made by using the flowing water technique.•Thermal damage is very ...small when the ablation is assisted by the flowing water film.•The suggested technique can be used for the P1 scribing of perovskite solar modules.
Fluorine-doped tin oxide (FTO) is one of the conductive layers used in the emerging perovskite solar cell technology, and the layer is typically scribed by a laser beam. However, thermal damage induced by laser deteriorates the scribe quality and in turn reduces the efficiency of the solar panel. This paper compares five different laser scribing techniques for isolating the FTO on the film and substrate sides both in air and water environments. The width and depth of laser-scribed channels, as well as burrs height, produced by using the different techniques were examined and compared. A clean and consistent scribe with negligible burrs was achievable by ablating the FTO film in the flowing water layer. Using this technique, its burr height index was found to reduce by 62.5% compared to the laser scribing of FTO film in air. A three-dimensional transient heat transfer model was also developed in this study to simulate the temperature field of workpiece subjected to the laser scribing in air and in flowing water environments. The thermal damage region was substantially small when the ablation was performed in the flowing water film. This could be a promising technique for the P1 scribing step in the manufacturing of emerging perovskite solar modules.
Graphene-metal composites (GMC) possess superior properties, such as high specific strength, and high thermal and electrical conductivity, and have been widely used in many fields. However, the ...fabrication of GMC still remains to be explored, as existing methods via powder metallurgy and chemical synthesis are difficult to achieve uniform dispersion of graphene, not to mention achieving selective and localized preparation of GMC with complex patterns. In this paper, a simple method for the fabrication of graphene-copper composites (GCC) is firstly proposed by combining flexible laser irradiation and efficient electrodeposition. It not only effectively solves the problems of graphene agglomeration and inhomogeneous dispersion in GCC, but also enables the selective and precise preparation of GCC with spatial micro-patterns. Specifically, an ultrafast picosecond (ps) laser is firstly used to irradiate the polyimide (PI) film to selectively and precisely produce the desired laser-induced graphene (LIG) region. The localized deposition of copper atoms is subsequently made via the electrodeposition step, forming the flexible GCC with a laser-determined spatial pattern. The experimental study of LIG process on PI film has been carried out, and high-quality LIG region is obtained by optimizing the laser scanning path and parameters. On this basis, the regional flexible GCC of 45 μm in thickness with a compact and uniform copper layer of 20 μm has been efficiently fabricated, followed by the detailed characterizations of surface morphology and chemical composition. Furthermore, a significant enhancement of the electrical conductivity has been confirmed, as the measured value is up to 32.8 S/cm at the LIG region and further to about 60.9 S/cm at the GCC area. The mechanical properties of the obtained conductive GCC have been tested and good flexibility is confirmed by nanoindentation and bending tests, verifying its potential for a wide range of applications in flexible electronics, medical and many other fields.
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•A simple and flexible fabrication method for GCC is proposed and validated.•High quality LIG has been obtained via picosecond laser scanning on PI film.•Localized electrodeposition of Cu atom is selectively realized on LIG region.•Significant enhancement of electrical conductivity from LIG to GCC is confirmed.•Surface morphology and chemical composition has been detailed characterized.
