Quality Of Laser Processing Research Articles

Laser processing of alumina ceramic by spatially and temporally superposing the millisecond pulse and nanosecond pulse train

A novel combined laser pulses (CLPs) consisting of a millisecond (ms) pulse and an assisted nanosecond (ns) pulse train was proposed for drilling alumina ceramic. The processing efficiency and quality were well improved by spatially and temporally superposing the ms and ns laser beams. As a result, due to the multi-reflection of keyhole and ejection of melt, the temporally superposed CLPs could decrease the energy consumption of the drilling by an order of magnitude compared with the conventional ms pulse. On the other hand, the spatial distribution of the ns laser on the focal plane was elliptical due to the off-axis distortion of the optical system. However, since the reflection of the laser in the keyhole was non-uniform, the spatially superposed CLPs showed no dependence on the shape of the focused elliptical ns laser spot in terms of the drilling quality. The research results have an important guiding for improving the efficiency and quality of laser processing, especially for the alumina ceramic laser processing.

Laser Cladding Quality Monitoring Using Coaxial Image Based on Machine Learning

The processing quality of laser cladding is a topic of interest to laser machine manufacturers. The management of various experimental data and process quality of the laser machine can effectively guide the customer to better adjust the processing parameters. This study finds that the processing quality of laser cladding is related to the signal of the coaxial image. Therefore, this study uses a machine learning method to establish a model of coaxial image and laser processing quality. The study does not merely implement a single machine learning method but also compares various machine learning algorithms. Convolutional neural networks and autoencoders are implemented as algorithms for the feature extraction phase. Linear regression, random forest, support vector machine, and SoftMax neural networks are implemented as algorithms for classification. The receiver operating characteristic curve and the accuracy rate are the result indicators of this paper. The experimental results show that there is indeed a correlation between the laser processing quality and the coaxial image, and the algorithm in this study can effectively supervise the processing quality of laser cladding.

Surface morphology of titanium alloy with monolayer microparticles under different single pulse laser energy

The surface morphology characteristics of titanium alloy under single pulse energy with local field enhancement effect were studied. The surface morphology of titanium alloy was observed by scanning electron microscope and local field enhancement theory was discussed by the FTDT simulation. The key difficulty of monolayer particles deposition was solved by production of a hydrophilic film and spin coating method. The formation mechanism of the surface morphology was discussed. Our results indicate the surface morphology is related to local field enhancement and the laser parameters including energy, size and distribution of laser spot. By using lower laser fluence than the ablation threshold of titanium alloy, laser cleaning can be obtained. When the microparticles-enhanced laser energy reaches the ablation threshold of titanium alloy surface, micropores whose size between 300 nm and 400 nm are easily obtained. The micropores distribution is related to the shape of laser spot. When the laser energy of laser spot exceeds the ablation threshold, microparticles help to control the shape of hole. The results show that particles can effectively influence the quality of laser processing, which is theory and practical significance on promoting laser processing technique in the application of particles on titanium alloy.

The Effect of Spot Size Combination Mode on Ablation Morphology of Aluminum Alloy by Millisecond-Nanosecond Combined-Pulse Laser.

Ablation morphology affects the quality of laser processing. Therefore, the control of ablation morphology is very important. The influence of spot size combination mode on the ablation morphology of aluminum alloy is studied for the first time. Experimental results show that when the nanosecond laser spot is larger, the ablation morphology looks like a bowl-shape, and there is little solidification near the edge. When the nanosecond laser spot is smaller, the shape of the ablation morphology is similar to a hole, and the protuberance is formed near the edge of the cavity. Through the analysis and simulation of the physical model, the physical mechanism, which describes the influence of the spot size combination mode on the molten pool, is discussed. The research results of this paper have important guiding significance for the control of laser processing effect.

On the role of heat and mass transfer into laser processability during selective laser melting AlSi12 alloy based on a randomly packed powder-bed

A newly transient mesoscopic model with a randomly packed powder-bed has been proposed to investigate the heat and mass transfer and laser process quality between neighboring tracks during selective laser melting (SLM) AlSi12 alloy by finite volume method (FVM), considering the solid/liquid phase transition, variable temperature-dependent properties and interfacial force. The results apparently revealed that both the operating temperature and resultant cooling rate were obviously elevated by increasing the laser power. Accordingly, the resultant viscosity of liquid significantly reduced under a large laser power and was characterized with a large velocity, which was prone to result in a more intensive convection within pool. In this case, the sufficient heat and mass transfer occurred at the interface between the previously fabricated tracks and currently building track, revealing a strongly sufficient spreading between the neighboring tracks and a resultant high-quality surface without obvious porosity. By contrast, the surface quality of SLM-processed components with a relatively low laser power notably weakened due to the limited and insufficient heat and mass transfer at the interface of neighboring tracks. Furthermore, the experimental surface morphologies of the top surface were correspondingly acquired and were in full accordance to the calculated results via simulation.

Laser processing quality monitoring by combining acoustic emission and machine learning: a high-speed X-ray imaging approach

In situ and real-time monitoring of laser processes are very challenging due to complex dynamics of the laser-matter interactions. Acoustic emission (AE) technique is often used as non-destructive monitoring of many kinds of processes. However, acoustic emission is not industrialized for laser processing for two reasons. First, the signals are too sensitive to the environmental noises. Second, a correlation of the acoustic emission signal with the real events is very difficult to realize despite being of utmost importance. To overcome these difficulties, we combined fast hard X-ray imaging with acoustic sensors and state-of-the-art machine learning.

An Industrial Product-Service System approach for Laser Process Quality Control

A framework for a two-way interaction between laser machine operator and a laser machine supplier in the direction of Laser Process Quality Control (LPQC) is proposed. An optical system is used to verify the beam alignment referred to the nozzle hole and the wear state of the nozzle in terms of process quality. The proposed framework provides the basis to laser suppliers for shifting their business model to Servitization. A case study is presented with the provided Industrial Product-Service System to consist of a laser-cutting machine and a service entitled LPQC.

Manufacturing of micro-textures on metals by nanosecond laser micromachining

The advantages and disadvantages between ‘single pulse one time repeating at intervals’ (SPI) and ‘single pulse multiple times continuous’ laser micromachining technology on surface textures were experimentally investigated. The micromachining of 45 steel, GCr15 steel and grey cast iron materials were also studied using the interval manufacturing technology. The efficiency of the laser processing technologies and quality of the ablated micro-dimples such as the diameter and depth were systematically analysed. The experimental results showed that, the ‘single pulse one time repeating at intervals’ (SPI) micromachining technology produced high quality dimples with less heat affected zone, smooth dimples with little slags due to its ability to effectively alleviate the negative heat accumulation effect to produce quality dimples as compared to the ‘single pulse multiple times continuous’ micromachining technology process. The diameter and depth of the micro-dimples increased generally with an increase in the laser fluence for all materials. The grey cast iron has the smaller ablation threshold with the largest dimple geometry due to its high laser absorption rate and the presence of more sulfur (S) and phosphorus (P) in the chemical composition, while GCr15 steel exhibited the smaller geometry due to its hardness.

Experimental Study of Low-Pressure Water Jet Assisted Laser Processing of Al<sub>2</sub>O<sub>3</sub> Ceramic

Recast layer, micro cracks and thermal deformation limited the improvement of the surface quality of laser processing in precision machining of hard and brittle material. This paper presents a new method which combines low-pressure water jet with laser processing. A comprehensive study on the influence of laser processing parameters on surface quality of an Al2O3 ceramic sheet is presented. The experiment was conducted using ND: YAG laser machine and low-pressure water jet was used as assist. The surface quality of normal laser processing and low-pressure water jet assisted laser processing was comparative analyzed using a 3-D microscopy. Experiment proves that the composite processing of low-pressure water jet assisted laser processing can obtain good surface quality, slight moltenslag and thermal deformation, compared with the normal laser processing.

Influence of the Interaction of Focused Laser Beam and Gas-Powder Stream on the Quality of Laser Processing

Laser processing technologies like alloying, cladding and rapid prototyping that are based on blowing of gas-powder mixture in the zone of laser processing are very dependent on the alignment of caustic surface (conventional surface that surrounds laser beam) and gas-powder mixture regarding the workpiece surface. Deep knowledge of its behavior is very important for the technologies that use coaxial introduction of gas-powder mixture into the processing zone.By means of numerical modeling with further experimental verification it was found that the shape of the gas-powder stream and its cross-section could be varied with help of the nozzles of various inner shapes. Further investigation of laser cladding technology by means of experiment planning techniques showed statistically significant influence of the position of caustic surface, and gas-powder mixture and the workpiece on the productivity (the size) and quality (presence of cavities) of the clad.

Дослідження технології лазерного фрезерування

Technologies of laser milling of different materials using Q-switched laser systems are presented in this paper. It was established that mechanism of material removal influences significantly the productivity and quality of laser processing. Technological parameters of laser milling of the most common intractable materials were simulated numerically and verified experimentally. It was established that at laser milling of intractable materials with solid-state Q-switched lasers it is possible to achieve the maximum milling depth without the formation of liquid phase. In order to increase the productivity and quality of laser milling in the case when a significant amount of liquid phase form (intractable materials, hard alloys) it is advisable to mill in two passes. First laser pass forms crates that are positioned symmetrically and the second laser pass breaks bridges between crates thus forming the surface with required roughness.

On the fabrication of minimizing bulges and reducing the feature dimensions of microchannels using novel CO2 laser micromachining

The shape of a cross-microchannel in polymer is a common pattern in MEMS and can be fabricated using traditional CO2 laser micromachining in air-cooling environment. However, it always suffers some problems during the fabrication process such as bulges, splashes, resolidification and the appearance of a heat affected zone around the rims of channels. In this paper, a novel method of Foil-Assisted CO2 LAser Micromachining (FACLAM) is proposed to fabricate the cross-microchannels in polymethylmethacrylate (PMMA) by significantly diminishing the bulges and the channel's feature sizes. The feature size of the cross-channel can be greatly reduced from 229.1 to 63.6 µm with no clogging effect shown in the cross-junction position. The bulge height of the PMMA microchannel using FACLAM was reduced from the conventional size of 8.2 µm to as small as 0.2 µm. The ANSYS software was also used to analyze the temperature distribution of the PMMA microchannel during machining in air-cooling environment and with foil-mask assistance. The FACLAM approach can improve laser processing quality in air-cooling environment and has the merits of low-cost, easy fabrication and high surface quality.

Laser Processing of Thin Films for Photovoltaic Applications

This paper discusses the structuring of several thin film materials used for solar cells, e.g. SiNx, SiO2 and Transparent Conductive Oxides (TCOs). The focus of the experiments is to obtain an optimal edge quality without damaging the substrate below the structured region. Two important laser parameters are wavelength and pulse duration which determine the absorption of the laser radiation in the processed material and the extent of heat influence on the surrounding material. Processing with several wavelengths (e.g. 532 nm and 1064 nm) and pulse durations especially in the picoand nanosecond range is studied. The results obtained with the different laser parameters are compared by considering ablation threshold, debris, and damage due to heat conduction. The quality of laser processing is determined by optical and scanning electron microscopy. Results from the structuring of TCOs and organic layers are acquired with different laser types. Additionally, comparisons are made regarding the achievable structuring quality for mass production, relevant speeds around 1 m/s for thin films and 1-2 seconds processing time for wafer based cells.

Research on Focusing Spot Shape of High Power CO<sub>2 </sub>Laser

In order to meet the requirements of laser processing technology and quality, the laser bean oblique incidence technique is put forward and focusing laser spots with different shape and incident direction are realized. The relation between the output laser beam spot shape and laser power of high power CO2 laser is studied through the organic glass sampling method. The result indicates that the laser beam cross-section shape presents rectangle and the long-axis length of laser beam has nothing to do with the laser power changes, but the short-axis width increases with the laser power improving. The two-dimension rotary laser head is designed and the laser bean tilt incidence is realized. The formula of the relation between focusing spot coordinate in the processing plane and laser head turn angle, also swinging angle is deduced. The relation between the focusing spot shape and the laser power, defocusing amount, laser head turn and swinging angles is researched through the single-side gummed paper sampling method. The result indicates that the focusing laser spot form is affected by the parameters of laser power, defocusing amount, laser head turn and swinging angles.

A uniform laser energy density controller for the rapid prototype processing

Rapid prototyping has become popular nowadays as the lifecycles of commercial and consumer products have been shortened to quarters or even months. The rapid prototyping technology provides a modern way to examine rapid contour changes on products which have forced designers and manufacturers to make new designs, jigs, tools, and molds in the past. Unlike the traditional machining of material, rapid prototyping utilizes technologies, such as stacking, etching, and laser processing, to produce models of designed articles within time and cost limits. Algorithms to control the processing are required and important to the success of rapid prototyping. This study has focused on laser energy control for the processing of Ceramic Laser Sintering rapid prototyping which will sinter ceramic powders into a solid object. Instead of the open‐loop constant laser energy applied in current laser machining, to improve the quality of the prototyping, a uniform laser energy algorithm and controller is developed and tested. The controller can automatically adjust the laser energy applied according to the distance traveled with position feedback. The developed method has been implemented on an embedded DSP microprocessor and CPLD controller to demonstrate its applicability. The experimental data has shown that consistent laser processing quality can be achieved with proper uniform laser energy control, which implies the feasibility of applying this developed uniform laser energy control algorithm to Ceramic Laser Sintering rapid prototyping processing.

Mechanism of Spatiotemporal Distribution of Laser Ablated Materials

Interaction between subsequent laser and ablated materials in laser processing changes the laser spatiotemporal distribution and has influences on the efficiency and quality of laser processing. The theoretical and experimental researches on transportation behaviour of ablated materials are provided. It is shown that the velocity distribution of ablated materials is determined by ablation mechanism. The transportation behaviour of ablated materials is controlled by diffusion mechanism and light field force during laser pulse duration while it is only determined by diffusion mechanism when the laser pulse terminates. In addition, the spatiotemporal distribution of ablated materials is presented.

Study on Measurement of Melting Process of Molten Pool Formed by Laser Scanning Mirror

The profile and temperature distribution of laser molten pool are mainly factors which have directly effect on quality of laser processing (laser melting and laser cladding). It is very necessary to study measurement method of melting process in laser molten poo1 on-line, for improving processing design and inspecting laser processing quality. A system of dynamic process measurement for laser molten pool was developed. The melting process of laser scanning molten pool formed by high power CO2 Laser was measured. Its temperature distribution was analyzed by special analysis software. It was shown that a section of integrated molten pool would come into being in the middle of the laser scanning line spot after a period of scanning time, and then the molten pool got increased in length with the time, and a little increased in width at the same time, the result was consistent with that of computer numerical simulation. Compared with laser focusing spot, laser scanning spot was more uniform in temperature distribution, that could be propitious to improve the quality of laser processing.

Physics of zinc vaporization and plasma absorption during CO2 laser welding

A number of mathematical models have been developed earlier for single-material laser welding processes considering one-, two-, and three-dimensional heat and mass transfers. However, modeling of laser welding of materials with multiple compositions has been a difficult problem. This paper addresses a specific case of this problem where CO2 laser welding of zinc-coated steel, commonly used in automobile body manufacturing, is mathematically modeled. The physics of a low boiling point material, zinc, is combined with a single-material (steel) welding model, considering multiple physical phenomena such as keyhole formation, capillary and thermocapillary forces, recoil and vapor pressures, etc. The physics of laser beam–plasma interaction is modeled to understand the effect on the quality of laser processing. Also, an adaptive meshing scheme is incorporated in the model for improving the overall computational efficiency. The model, whose results are found to be in close agreement with the experimental observations, can be easily extended for studying zinc-coated steel welding using other high power, continuous wave lasers such as Nd:YAG and Yb:YAG.

Modeling of Laser Dressing for Metal-Bond Diamond Grinding Wheel

Laser processing of super-abrasive grinding wheel is paying a role in a truing/dressing technique to complement mechanical methods recently. However, normal dressing/truing is difficult owing to the toughness of metal-bond materials and high hardness of diamond abrasive. Both geometric and mathematic models were developed to improve laser processing quality and predict various processing parameters, such as focal offset, and incident power, and power density to perform material removal during laser processing a metal-bond diamond grinding wheel. Various trends of the geometrical features of dressing zone in terms of the varying focal offsets were analyzed. Discussions were also given on dressing-zone geometry control. Experimental studies were carried out using different processing parameters to test the effects of laser poweres on dressing quality. Further grinding-force measurement determined the laser dressing parameters with respect to the wheel surface conditions. The normal force FN reduces up to 20%, while tangential force FT decreases to 7% too.The outcomes were shown well agreement with predicted results.

Mechanisms of laser drilling of metal plates underwater

Several metal plates with different thickness including copper, iron, aluminum, and stainless steel have been drilled in the surroundings of air and water, respectively, by a Q-switched pulsed Nd:yttrium–aluminum–garnet laser. It is observed that for the same metal plate less energy is needed to drill a hole in water than that in air, and the surface morphology of hole drilled in water is improved greatly than that in air by comparison of the scanning electron micrographs. The underlying mechanisms behind the efficiency and quality enhancement in water are further investigated by means of optical beam deflection technique. The experimental results show that due to the water confinement the peak amplitude and duration of the laser-ablation-generated impact underwater is much larger than that in air. During the underwater laser drilling, besides laser ablation effect, both the first and second liquid-jet-induced impulses by cavitation bubble collapse in the vicinity of a solid boundary are also observed and their amplitudes are, respectively, about 12.4 and 5.2 times that of the laser ablation impact in air. Cavitation bubbles are the special dynamic phenomenon occurring in liquids. Therefore, it is concluded that in-air-drilling laser ablation-produced impact is a dominant mechanism; while during laser underwater drilling, it is the result of a combination of ablation-produced impact effect and liquid-jet-induced impact, especially the latter. Thus, the efficiency and quality of laser processing in the surrounding water can be greatly increased and improved compared with that in air.