Laser technology in industry

Lasers are providing effective solutions to many real problems in industry and technology. In this paper, we discuss the technical aspects of laser industrial applications to welding, hardening, alloying, cutting, drilling, turning, glazing etc. Details of laser applications and the involved technologies of non-destructive laser contactless diagnotics quality control of materials and industrial goods, laser monitoring and laser applications to measurement devices are also presented briefly. Most of the discussion is in reference to the developments in USSR.     

Laser through-hole drilling and laser cutting in teflon

We report a novel technique for laser high-speed drilling and cutting in teflon films. The new laser drilling surpasses the conventional techniques in simplicity, throughput and spatial resolution. The laser cutting and drilling process consists of three simple steps. First, a thin absorbing layer (in this case 300 Å of gold) is deposited on the teflon to allow for laser absorption. Second, the drilling is performed by pulsed-laser irradiation at the rate of one hole per pulse. The irradiation process does not completely open the holes in which debris still remain. Third, the ultrasonic cleaning in water is used to remove the modified and weakly bound material inside the drilled holes, leaving behind 50 m diameter through holes in 25 m thick teflon sheets. The drilling process-window is well mapped. The cutting process is obtained by fast scanning the laser beam at laser powers above a threshold value. This new technique is desirable for packaging because of its drilling speed as high as 60 000 holes per minute, its fast cutting and its low laser equipment cost.     

Processing of concretes with a high power CO2 laser

Laser material processing, being a non-contact process, minimizes many of the complexities involved in the decontamination and decommissioning of nuclear facilities. A high power laser beam incident on a concrete surface can produce spalling, glazing or vaporization, depending upon the laser power density and scan speed. This paper presents effect of various laser processing parameters on the efficiency of material removal by surface spalling and glazing. The size of laser beam at constant fluence or energy density had significantly different effect on the spalling process. In thick concrete block cutting the flow or removal of molten material limits the cutting depth. By employing repeated laser glazing followed by mechanical scrubbing process cutting of 150 mm thick concrete block was carried out. Gravitation force was utilized for molten materials to flow out while drilling holes on vertical concrete walls. The dependence of the incident laser beam angle on drilling time was experimentally studied.     

光谱测量在激光加工在线监测上的应用研究进展

随着现代工业的发展,复杂加工环境和对象、大动态范围、高效率和高精度激光加工需求愈加迫切,在线监测并实时优化激光加工参数是一条重要的解决途径。与此同时,激光与物质相互作用时可产生与加工参数、加工过程和目标特性密切相关的光信号和表面光学特性变化,在线测量光信号光谱可分析加工过程和状态,故光谱测量有望成为一种重要的激光加工在线监测手段。实际上,光谱测量已应用于激光焊接、激光切割和钻孔、激光清洗打磨、微纳结构制备和增材制造等几乎所有激光加工工艺,具有分辨率高和光谱信息丰富等特点。分析和总结了用于激光加工在线监测的光谱测量技术,包括等离子体光谱、反射光光谱和非线性光信号光谱等。基于单脉冲和多脉冲激光加工激发等离子体信号的光谱测量,除实现化学成分定性和定量监测外,还可以根据特征谱线相对强度变化实时调焦,根据等离子体温度监测和调控激光加工过程中与热效应相关的物理过程;作为一种无损伤且工作距离较远的监测方法,反射光光谱监测可通过测量特定波段反射光信号光谱积分功率、特征谱线和波段位置和强度来有效监测材料表面清洁度、损伤、色度和成分变化等;而在特定条件下产生的谐波信号、荧光信号和拉曼信号等非线性光信号,尽管应用场景有限,但提供了一种实现成分、焦距和材料损伤等监测的新方法。进而,展望了光谱测量在激光加工在线监测上应用的未来发展趋势,包括多种光信号的光谱协同监测与光、声、温度及图像等多种信号测量的复合监测。同时,人工智能技术与在线监测和激光加工的深入结合将进一步推动激光加工技术的智能化发展。     

Optodynamic monitoring of laser micro-drilling of glass by using a laser probe

We present a new method for monitoring of the laser micro-drilling process. The method is based on detection of acoustic waves in air above the processed sample using a laser beam deflection probe (LBDP). We present an augmentation of the experimental set-up by means of a digital micrographic system which enables the acquisition of images of the plasma plume and of the hole cross-section during a drilling sequence. Comparing the acquired images with the detected LBDP signals, we examine the drilling process from a new perspective.     

Laser cutting profile characterization using dynamic speckle method

Dynamic speckle method was employed to characterize the profile quality of the aluminum plate in process of laser cutting. Speckle contrast as an indicator was used to study the relation of the distance between the focusing lens and the sample and the focus length. Experimental results show that this method is effective to characterize the laser cutting profile quality.     

Laser systems in modern production environments

The present situation in production engineering is characterized by a need to create organizational structures and production methods which enable a reduction of the product development time and continuously improved product quality. Together with an improvement in productivity, cost savings and quality assurance, the success of a company will increasingly depend on shortened throughput times, flexibility and the full utilization of its employees' creativity. Laser technology offers important contributions to these aims, if its related technical and organizational advantages can be fully exploited.On an organizational level, the simultaneous development of product, process and production system and multilevel quality control loops enables preventive quality assurance and continuous improvement of product quality. Simulation tools for process, process flow and laser systems allow reliable planning data at a very early stage in product design and operations planning.On the manufacturing level, e.g. in the field of prototype building, the laser is used as a flexible tool for cutting two- and three-dimensional body panels. Owing to the need for programming, the downtimes for 3D laser cutting systems can be quite considerable. Computer-aided, comprehensive process chains enabling off-line programming are therefore increasingly being adopted. The use of the laser in prototype shops makes it possible to provide production-equivalent components at a high level of reproducibility and with much shorter lead times.System status monitoring tools enable full operator control and fast fault rectification. Seam tracking sensors with moving laser beam and moving workpiece allow compensation of tolerances in part shape and position. By measuring the gap distance during seam tracking, suitable adaptation of process parameters makes it possible to achieve a controlled welding process. As a continuation of preventive quality assurance measures, process monitoring using characteristics of the laser-induced plasma during welding reveals defects in the weld seam.     

钛合金纳秒激光打孔数值模拟和实验研究

为了描述纳秒激光对钛合金打孔过程中孔的形貌及温度场的变化规律,建立激光打孔的物理模型,利用ANSYS中APDL语言进行编程,对温度场进行仿真分析,并利用单元生死技术模拟孔形貌的变化过程。从有限元数值模拟和实验两方面综合分析比较了激光工艺参数(脉冲能量和脉冲数量)对打孔质量(孔深和孔径)的影响,系统论述了钛合金纳秒激光打孔的一般规律,以达到工艺参数优化,提高打孔质量的目的。     

Analysis of mechanism of plasma and spatter in CO2 laser welding of galvanized steel

In laser welding, quality, reproducibility and formability are required. That is the great problem in the automation of the laser welding process. Therefore, construction of an on-line process monitoring system of high accuracy is requested.The light which is emitted from plasma and spatter in laser welding was detected by photo-diodes. It was found that the light intensity depends on welding speed, laser power and flow rate of assist gas. The relationship between the plasma and spatter and the bead shape, and the mechanism of plasma and spatter were analyzed for on-line laser weld monitoring systems.     

Cutting by a high power laser at a long distance without an assist gas for dismantling

As the applications of laser processing progress, new fields of use are being investigated, including dismantling with power lasers. To fulfil our dismantling requirements we propose a new laser method that we have called the laser dismantling (LD) process. This cutting method uses a high-power laser at a long distance, without an assist gas, and with a focal length of the system of 1 m to 10 m. Precision and accuracy in the process are not the same as for laser cutting for production and assembly. The first application of the laser dismantling process, on which we demonstrate our method, is the dismantling of obsolete nuclear plants with remote controlled, or automatic, robots in irradiated environments. For our demonstrator, the beam from a Nd:YAG laser was focused by a multimode optical fibre. The objectives of this paper are: to discuss the criteria for determining the theoretical feasibility of LD; to discuss issues related to future industrial implementation by introducing the process's basic principles; and to compare LD with classical laser processing, which differs not only in the consideration of cutting quality and speed, but also in the cutting irregularities that could be accepted.     

Effect of CO2 laser cutting process parameters on edge quality and operating cost of AISI316L

Laser cutting is a popular manufacturing process utilized to cut various types of materials economically. The width of laser cut or kerf, quality of the cut edges and the operating cost are affected by laser power, cutting speed, assist gas pressure, nozzle diameter and focus point position as well as the work-piece material. In this paper CO₂ laser cutting of stainless steel of medical grade AISI316L has been investigated. Design of experiment (DOE) was implemented by applying Box–Behnken design to develop the experiment lay-out. The aim of this work is to relate the cutting edge quality parameters namely: upper kerf, lower kerf, the ratio between them, cut section roughness and operating cost to the process parameters mentioned above. Then, an overall optimization routine was applied to find out the optimal cutting setting that would enhance the quality or minimize the operating cost. Mathematical models were developed to determine the relationship between the process parameters and the edge quality features. Also, process parameters effects on the quality features have been defined. Finally, the optimal laser cutting conditions have been found at which the highest quality or minimum cost can be achieved.     

Laser processing integrated into machine tools — design,applications, economy

In the last few years, lasers have found new applications in production engineering as tools for surface treatment, cutting, welding, drilling and marking. So far, the laser has mainly been used in special laser processing machines (laser-only) directly integrated into a production line or serving as stand-alone stations in the workshop. By combining conventional metal cutting technologies with laser processes in one machine, complete processing of a workpiece with different technologies in one setting can be realized. The main advantages are a reduction of the material flow between the production machines, which leads to a reduction in processing time and logistics, and an enhancement of manufacturing quality due to the processing in one setting. In addition to this approach, new processing technologies such as laser-assisted machining are possible.Applications of laser caving, hardening, welding and drilling of production parts in combination with the cutting process in one setting have been investigated with the aim of adapting these technologies to the characteristics of the machines and the typical parts spectra. Furthermore, various technical solutions for the integration of lasers into milling centres and lathes have been elaborated. In both situations the laser tool is handled like a standard tool and can be exchanged automatically. The main results will be reported, together with a brief discussion of the economic aspects of laser processing integrated into machine tools.This article is based on an invited paper presented at LANE '94, Erlangen, 12–14 October 1994.     

Investigating the CO2 laser cutting parameters of MDF wood composite material

Laser cutting of medium density fibreboard (MDF) is a complicated process and the selection of the process parameters combinations is essential to get the highest quality cut section. This paper presents a means for selecting the process parameters for laser cutting of MDF based on the design of experiments (DOE) approach. A CO₂ laser was used to cut three thicknesses, 4, 6 and 9 mm, of MDF panels. The process factors investigated are: laser power, cutting speed, air pressure and focal point position. In this work, cutting quality was evaluated by measuring the upper kerf width, the lower kerf width, the ratio between the upper kerf width to the lower kerf width, the cut section roughness and the operating cost. The effect of each factor on the quality measures was determined. The optimal cutting combinations were presented in favours of high quality process output and in favours of low cutting cost.     

Numerical simulation of process dynamics during laser beam drilling with short pulses

In the last years, laser beam drilling became increasingly important for many technical applications as it allows the contactless production of high quality drill holes. So far, mainly short laser pulses are of industrial relevance, as they offer a good compromise between precision and efficiency and combine high ablation efficiency with low thermal damage of the workpiece. Laser beam drilling in this pulse length range is still a highly thermal process. There are two ablation mechanisms: evaporation and melt expulsion. In order to achieve high quality processing results, a basic process understanding is absolutely necessary. Yet, process observations in laser beam drilling suffer from both the short time scales and the restricted accessibility of the interaction zone. Numerical simulations offer the possibility to acquire additional knowledge of the process as they allow a direct look into the drill hole during the ablation process. In this contribution, a numerical finite volume multi-phase simulation model for laser beam drilling with short laser pulses shall be presented. The model is applied for a basic study of the ablation process with μs and ns laser pulses. The obtained results show good qualitative correspondence with experimental data.     

Laser micro-machining of small objects for high-energy laser experiments

Targets for high-energy laser experiments are polymer or metal objects of small dimensions. These objects need high-precision processes (typical sizes of a few hundred micrometers with micrometer accuracy). In this paper, some targets for high-energy laser experiments obtained by picosecond Q-switched Nd:YAG laser and KrF excimer laser micro-machining are presented. All of the targets use an original process. Activities include cutting, drilling, and marking elements. A summary of targets made using laser processes will be presented.     

Laser beam cutting

The fundamentals of the manufacturing process of laser beam cutting are discussed. The equipment necessary for working on two- and three-dimensional applications is described. Criteria for characterizing cutting quality and cutting applications with different laser types are presented. Both modelling of the process and study of process emissions are involved in optimizing the process and system performance, and an overview is given of research results in these areas.     

A knowledge-based adaptive control environment for an industrial laser cutting system

A hierarchically structured environment that integrates a knowledge- based expert system, adaptive process control and pattern recognition techniques for controlling a laser cutting process is described. Knowledge of the laser cutting process for different materials is organised and encoded into a rule-based system. An adaptive control algorithm based on on-line recursive parameter estimation and on-line control law synthesis was adopted for the highly non-linear cutting process control. Cutting speed was selected as the major control variable. Irradiance emitted from the cut front is used for the feedback signal to this adaptive controller. The irradiance signal feeds the recursive parameter estimator for system identification. Techniques of pattern recognition, which have been well developed in coherent optics, were applied to assess cut quality by characterising the exit spark cone images of the gas assisted laser cutting process. Images from the cutting processes were grabbed, edge enhanced and correlated with a synthetic discriminant function filter which was synthesised from reference images to give good cut quality. Results from digital simulations based on these pattern recognition algorithms are also presented.     

The effect of moisture content in fibre laser cutting of pine wood

This paper reports a statistical analysis of the multiple-pass laser cutting of wet and dry pine wood with a Ytterbium fibre laser. As multiple factors affect the laser wood cutting process, finding the optimal combination of process parameters is necessary to achieve good quality and high process efficiency. Design of experiments (DOE) and statistical modelling were used in this study to investigate the significant process parameters and their interactions. A high brightness, 1 kW IPG single mode, continuous wave Ytterbium doped fibre laser was employed to cut wet and dry pine wood samples. The parameters investigated are laser power, traverse speed, focal plane position (f.p.p.), gas pressure, number of passes, direction of cut (normal or parallel to wood's tracheids) and the moisture content. The experimental results were compared against process responses defining the efficiency (i.e. kerf depth and energy consumption) and quality of the cut section (i.e. kerf width, heat affected zone—HAZ, edge surface roughness and perpendicularity). It has been found that the laser cutting process was mainly affected by the moisture content and the cut direction with respect to the wood's tracheids, followed by traverse speed, laser power and the number of passes. The effect of moisture content on energy consumption in the laser cutting process of both wet and dry wood is analysed. The wood cutting results with fibre laser are compared with those from a CO₂ laser.     

Investigation of a novel hybrid process of laser drilling assisted with jet electrochemical machining

Recast layer and spatter are two inherent defects commonly associated with holes produced with laser drilling. This paper reports a novel hybrid process of laser drilling assisted with jet electrochemical machining (JECM-LD) that aims to minimize such defects and improve the quality of laser-drilled holes. The process based on the application of a jet electrolyte, being aligned coaxially with the focused laser beam, on the workpiece surface during laser drilling. The effect of the jet electrolyte mainly is an electrochemical reaction with materials. The jet electrolyte also cools the workpiece and transports debris during the process. On the basis of a measurement of laser attenuation in electrolyte, an experimental apparatus system is made and JECM-LD experiments have been performed on 0.5-mm-thick 321S20 stainless steel with two lasers at wavelength of 1064 and 532 nm. It is shown that recast layer and spatter have been effectively reduced during the JECM-LD compared with laser drilling in ambient atmosphere conditions.     

Crack-free cutting of thick and dense ceramics with CO2 laser by single-pass process

This paper presents a laser crack-free cutting method of Al₂O₃ ceramics by single-pass process in internal straight and curve profiles. The thickness and theoretical density of the ceramics are up to 10 mm and about 99%, respectively. The effective cutting speed is about 0.23–0.42 mm/s corresponding to the laser head moving speed of 3 mm/s. The cutting process based on close-piercing lapping of piercing time of 0.1–0.5 s and piercing pitch of 0.03–0.05 mm is divided into two continuous stages. Appropriate time slot for each piercing, high peak power of 3500 W and low cycle duty (<30%) achieve crack-free cuts. Optimal cut quality parameters are analyzed and characterized. These results demonstrate that the laser crack-free cutting method is a promising method to achieve complex profiles of ceramic cuts.