Laser machining fundamentals:micro,nano,atomic and close-to-atomic scales

With the rapid development in advanced industries,such as microelectronics and optics sectors,the functional feature size of devises/components has been decreasing from micro to nanometric,and even ACS for higher performance,smaller volume and lower energy consumption.By this time,a great many quantum structures are proposed,with not only an extreme scale of several or even single atom,but also a nearly ideal lattice structure with no material defect.It is almost no doubt that such structures play critical role in the next generation products,which shows an urgent demand for the ACSM.Laser machining is one of the most important approaches widely used in engineering and scientific research.It is high-efficient and applicable for most kinds of materials.Moreover,the processing scale covers a huge range from millimeters to nanometers,and has already touched the atomic level.Laser–material interaction mechanism,as the foundation of laser machining,determines the machining accuracy and surface quality.It becomes much more sophisticated and dominant with a decrease in processing scale,which is systematically reviewed in this article.In general,the mechanisms of laser-induced material removal are classified into ablation,CE and atomic desorption,with a decrease in the scale from above microns to angstroms.The effects of processing parameters on both fundamental material response and machined surface quality are discussed,as well as theoretical methods to simulate and understand the underlying mechanisms.Examples at nanometric to atomic scale are provided,which demonstrate the capability of laser machining in achieving the ultimate precision and becoming a promising approach to ACSM.

Development of an In-Situ Laser Machining System Using a Three-Dimensional Galvanometer Scanner

In this study, a three-dimensional (3D) in-situ laser machining system integrating laser measurement and machining was built using a 3D galvanometer scanner equipped with a side-axis industrial camera. A line structured light measurement model based on a galvanometer scanner was proposed to obtain the 3D information of the workpiece. A height calibration method was proposed to further ensure measurement accuracy, so as to achieve accurate laser focusing. In-situ machining software was developed to realize time-saving and labor-saving 3D laser processing. The feasibility and practicability of this in-situ laser machining system were verified using specific cases. In comparison with the conventional line structured light measurement method, the proposed methods do not require light plane calibration, and do not need additional motion axes for 3D reconstruction;thus they provide technical and cost advantages. The insitu laser machining system realizes a simple operation process by integrating measurement and machining,which greatly reduces labor and time costs.

MODELING OF LASER MACHINING ON POLYMETHYL METHACRYLATE TO FABRICATE MICROFLUIDIC CHIP

The use of a CO2 laser system for fabrication of microfluidic chip on polymethyl methacrylate （PMMA） is presented to reduce fabrication cost and time of chip. The grooving process of the laser system and a model for the depth of microchannels are investigated. The relations between the depth of laser-cut channels and the laser beam power, velocity or the number of passes of the beam along the same channel are evaluated. In the experiments, the laser beam power varies from 0 to 50 W, the laser beam scanning velocity varies from 0 to 1 000 mm/s and the passes vary in the range of 1 to 10 times. Based on the principle of conservation of energy, the influence of the laser beam velocity, the laser power and the number of groove passes are examine. Considering the grooving interval energy loss, a modified mathematical model has been obtained and experimental data show good agreement with the theoretical model. This approach provides a simple way of predicting groove depths. The system provides a cost alternative of the other methods and it is especially useful on research work of rnicrofluidic prototyping due to the short cycle time of production.

Theoretical and experimental study of surface texturing with laser machining

To explore the forming process and mechanism of the surface texture of laser micropits,this paper presents the thermal model of laser machining based on the Neumann boundary conditions and an investigation on the effects of various parameters on the processing.The surface profile and quality of the formed micropits were analyzed using NanoFocus 3D equipment through a design of experiment(DOE).The results showed that more intense melting and splashing occurred with higher power density and narrower pulse widths.Moreover,the compressive stress is an important indicator of the damage effects,and the circumferential thermal stress is the primary factor influencing the diameter expansion.During the process of laser machining,not only did oxides such as CuO and ZnO generate,the energy distribution also tended to decrease gradually from region#1 to region#3 based on an energy dispersive spectrometer(EDS)analysis.The factors significantly affecting the surface quality of the micropit surface texture are the energy and pulse width.The relationship between taper angle and energy is appropriately linear.Research on the formation process and mechanism of the surface texture of laser micropits provides important guidance for precision machining.

Cutting Experiment of Fraxinus mandshurica UsingWaterjet-Assisted CO_(2)Laser

High-quality wood products and valuable wood crafts receive everyone’s favor with the rapid development of the economy.In order to improve the cutting surface quality of wood forming parts,the cutting experiment of renewable Fraxinus mandshurica was conducted by waterjet-assisted CO_(2)laser(WACL)technology.A quadratic mathematical model for describing the relationship between surface roughness changes and cutting parameters was established.The effects of cutting speed,flow pressure and laser power on the kerf surface roughness of Fraxinus mandshurica when cutting transversally were discussed by response surface method.The experimental results showed that kerf surface roughness decreased under a lower laser power,higher cutting speed and higher flow pressure.When the cutting speed was 30 mm/s,flow pressure was 1.58 MPa and laser power was 45 W,the actual surface roughness of the optimized Fraxinus mandshurica was 2.41μm,and it was in accord with the theoretically predicted surface roughness value of 2.54μm,so the model fitted the actual situation well.Through the analysis of 3D profile morphology and micromorphology,it was concluded that the optimized kerf surface of Fraxinus mandshurica was smoother,the cell wall was not destroyed and the tracheid was clear.It provides the theoretical basis for wood micromachining.

Prediction of preheating conditions for inclined laser assisted machining

For laser assisted machining,shape of preheating laser heat source is changed irregularly because of complexity of material shape.So,the preheating temperature should be controlled by adjusting the feed rate or the laser power.Thermal analyses of the laser assisted machining process for inclination planes were performed.By analyzing the obtained temperature profile,a proper feed rate control method was proposed according to the inclination angles.In addition,the temperature distribution of the cross section after feed rate control was predicted.The correlation equation between inclination angles and adjusted proper feed rate was proposed.The results of this analysis can be used to predict the preheating effect on workpiece and can be applied as a preheating temperature control method in laser assisted machining processes.

Non-traditional Machining Techniques for Fabricating Metal Aerospace Filters

Thanks to recent advances in manufacturing technology, aerospace system designers have many more options to fabricate high-quality, low-weight, high-capacity, cost-effective filters. Aside from traditional methods such as stamping, drilling and milling, many new approaches have been widely used in filter-manufacturing practices on account of their increased processing abilities. How- ever, the restrictions on costs, the need for studying under stricter conditions such as in aggressive fluids, the complicity in design, the workability of materials, and others have made it difficult to choose a satisfactory method from the newly developed processes, such as, photochemical machining （PCM）, photo electroforming （PEF） and laser beam machining （LBM） to produce small, inexpensive, lightweight aerospace filters. This article appraises the technical and economical viability of PCM, PEF, and LBM to help engineers choose the fittest approach to turn out aerospace filters.

The Effect of Laser Ablation Pulse Width and Feed Speed on Necrosis and Surface Damage of Cortical Bone

Bone cutting is of importance in orthopaedic surgery but is also challenging due to its nature of brittleness—where severe mechanical and thermal damages can be introduced easily in conventional machining.Laser machining is a new technology that can allow for complex cut geometries whilst minimising surface defects i.e.,smearing,which occur in mechanical methods.However,comparative studies on the influence of lasers with different pulse characteristics on necrotic damage and surface integrity have not been reported yet.This paper for the first time investigates the effects of laser type on the necrotic damage and surface integrity in fresh bovine cortical bone after ex-situ laser machining.Three lasers of different pulse widths,i.e.,picosecond,nanosecond and continuous wave lasers have been investigated with different feed speeds tested to study the machining efficiency.The cutting temperature,and geometrical outputs have been measured to investigate the thermal influence on the cooling behaviour of the bone samples while high-speed imaging was used to compare the material removal mechanisms between a pulsed and continuous wave laser.Furthermore,an in-depth histological analysis of the subsurface has revealed that the nanosecond laser caused the largest necrotic depth,owing to the high pulse frequency limiting the dissipation of heat.It has also been observed that surface cracks positioned perpendicular to the trench direction were produced after machining by the picosecond laser,indicative of the photomechanical effect induced by plasma explosions.Therefore,the choice of laser type(i.e.,in terms of its pulse width and frequency)needs to be critically considered for appropriate application during laser osteotomy with minimum damage and improved healing.

Estimation of deformed laser heat sources and thermal analysis on laser assisted turning of square member

Laser assisted machining （LAM） has difficulties in estimating temperature after applying a LAM process due to its very small heat input area, large energy and movement. In particular, in the case of laser assisted turning （LAT） process, it is more difficult to estimate the temperature after preheating because it has a shape of ellipse when a laser heat source is rotated. A prediction method and thermal analysis method for heat source shapes were proposed as a square shaped member was preheated. The temperature distribution was calculated according to the rotation of the member. Compared with the results of the former study, the maximum temperature of the calculation results, 1 407.1 ℃, is 8.5 ℃ higher than that of the square member, which is 1 398.6 ℃. In a LAT process for a square member, the maximum temperature is 1 850.8 ℃. It is recognized that a laser power control process is required because square members show a maximum temperature that exceeds a melting temperature at around a vertex of the member according to the rotation.

Elucidation of Metallic Plume and Spatter Characteristics Based on SVM During High-Power Disk Laser Welding

During deep penetration laser welding,there exist plume（weak plasma） and spatters,which are the results of weld material ejection due to strong laser heating.The characteristics of plume and spatters are related to welding stability and quality.Characteristics of metallic plume and spatters were investigated during high-power disk laser bead-on-plate welding of Type 304 austenitic stainless steel plates at a continuous wave laser power of 10 kW.An ultraviolet and visible sensitive high-speed camera was used to capture the metallic plume and spatter images.Plume area,laser beam path through the plume,swing angle,distance between laser beam focus and plume image centroid,abscissa of plume centroid and spatter numbers are defined as eigenvalues,and the weld bead width was used as a characteristic parameter that reflected welding stability.Welding status was distinguished by SVM（support vector machine） after data normalization and characteristic analysis.Also,PCA（principal components analysis） feature extraction was used to reduce the dimensions of feature space,and PSO（particle swarm optimization） was used to optimize the parameters of SVM.Finally a classification model based on SVM was established to estimate the weld bead width and welding stability.Experimental results show that the established algorithm based on SVM could effectively distinguish the variation of weld bead width,thus providing an experimental example of monitoring high-power disk laser welding quality.

Improving a Laser Machine for Laser Forming of Metals

Laser forming is a flexible metal forming process without a die. At present, for this innovative process no exclusive equipment is commercially available. In this paper, some improving measures including temperature monitoring system, shape monitoring system, cooling system and rotary segment have been proposed on the basis of the general NC laser machine in order to meet the special requirements for laser forming of metals. The improved laser machine may be conveniently used to control dynamically and record the whole laser forming process of metals.

Wettability Pattern for Ultrafast Water Self‑Pumping on Cemented Carbide Surface

A facile method to fabricate wettability pattern(two extreme wettabilities arranged in a pattern)to realize water self-pumping is proposed on cemented carbide while not necessarily depositing other materials on substrate surface.The water self-pumping is achieved by arranging wedge shaped superhydrophilic domain in superhydrophobic substrate using laser machining.Through single factor experiments,it is found that the key to the extreme wettabilities,micro⁃and nano⁃structures,is rendered by laser machining processes and is influenced by laser parameters.Meanwhile,the proper laser parameters that are used to fabricate required micro-and nano⁃structures are obtained.Finally,the water transport experiment is carried out,which shows that the velocity of water bulge could be up to 362 mm/s when the wedge angle is 3°.The mechanism of the water self-pumping is analyzed and it is found that the migration of water bulge is governed by Laplace pressure of the water bulge induced by the wedge micro-groove.

Surface texture formation in precision machining of direct laser deposited tungsten carbide

This paper focuses on an analysis of the surface texture formed during precision machining of tungsten carbide. The work material was fabricated using direct laser deposition （DLD） technology. The experiment included precision milling of tungsten carbide samples with a monolithic torus cubic boron nitride tool and grinding with diamond and alumina cup wheels. An optical surface profiler was applied to the measurements of surface textures and roughness profiles. In addition, the micro-geometry of the milling cutter was measured with the appli- cation of an optical device. The surface roughness height was also estimated with the application of a model, which included kinematic-geometric parameters and minimum uncut chip thickness. The research revealed the occurrence of micro-grooves on the machined surface. The surface roughness height calculated on the basis of the traditional kinematic-geometric model was incompatible with the measurements. However, better agreement between the theoretical and experimental values was observed for the minimum uncut chip thickness model.

Recent advances in micro- and nano-machining technologies

Device miniaturization is an emerging advanced technology in the 21 st century. The miniaturiza- tion of devices in different fields requires production of micro- and nano-scale components. The features of these components range from the sub-micron to a few hundred microns with high tolerance to many engineering materi- als. These fields mainly include optics, electronics, medicine, bio-technology, communications, and avionics. This paper reviewed the recent advances in micro- and nano-machining technologies, including micro-cutting, micro-electrical-discharge machining, laser micro-machin- ing, and focused ion beam machining. The four machining technologies were also compared in terms of machining efficiency, workpiece materials being machined, minimum feature size, maximum aspect ratio, and surface finish.

Characterization of Automotive Brake Discs with Laser-Machined Surfaces

In the automotive and transport industry,braking noise and vibrations are persisting issues and difficult to control.Automo-tive engineers and researchers are putting considerable effort into overcoming these problems,and significant breakthroughs have been made in this area.In this study,M-shaped grooves were bionically designed and manufactured on the frictional surfaces of four automotive brake discs using a laser machine.Various tests were conducted to characterize the physical and mechanical performance of the modified discs along with their noise and vibration responses.The experimental results demonstrate that discs with laser-machined grooved surfaces have better surface hardness and residual stress reduction than discs with un-grooved surfaces.Significant improvement in the braking performance was observed in terms of disc thickness variation,friction and wear,noise,and vibration reduction.It is concluded that the reduction in braking noise and vibrations is mainly caused by the reduction in the coefficient of friction and wear,increase in damping ratio,and improvement of disc thickness variation of the brake disc by laser surface grooving.

Real-time human blood pressure measurement based on laser self-mixing interferometry with extreme learning machine

In this paper, we present a method based on self-mixing interferometry combing extreme learning machine for real-time human blood pressure measurement. A signal processing method based on wavelet transform is applied to extract reversion point in the self-mixing interference signal, thus the pulse wave profile is successfully reconstructed. Considering the blood pressure values are intrinsically related to characteristic parameters of the pulse wave, 80 samples from the MIMIC-II database are used to train the extreme learning machine blood pressure model. In the experiment, 15 measured samples of pulse wave signal are used as the prediction sets. The results show that the errors of systolic and diastolic blood pressure are both within 5 mm Hg compared with that by the Coriolis method.

Combining proteomics, serum biomarkers and bioinformatics to discriminate between esophageal squamous cell carcinoma and pre-cancerous lesion

Objective: Biomarker assay is a noninvasive method for the early detection of esophageal squamous cellcarcinoma (ESCC). Searching for new biomarkers with high specificity and sensitivity is very important for the earlydetection of ESCC. Serum surface-enhanced laser desorption/ionization-time of flight mass spectrometry(SELDI-TOF-MS) is a high throughput technology for identifying cancer biomarkers using drops of sera. Methods: Inthis study, 185 serum samples were taken from ESCC patients in a high incidence area and screened by SELDI. Asupport vector machine (SVM) algorithm was adopted to analyze the samples. Results: The SVM patterns success-fully distinguished ESCC from pre-cancerous lesions (PCLs). Also, types of PCL, including dysplasia (DYS) and basalcell hyperplasia (BCH), and healthy controls (HC) were distinguished with an accuracy of 95.2% (DYS), 96.6% (BCH),and 93.8% (HC), respectively. A marker of 25.1 kDa was identified in the ESCC patterns whose peak intensity wasobserved to increase significantly during the development of esophageal carcinogenesis, and to decrease obviously after surgery. Conclusions: We selected five ESCC biomarkers to form a diagnostic pattern which can discriminateamong the different stages of esophageal carcinogenesis. This pattern can significantly improve the detection ofESCC.