An artificial neural network approach for the control of the laser milling process

Laser milling (LM) can be classified as a layer manufacturing process in which the material is removed by a laser beam by means of the ablation mechanism. It is a laser machining process which uses a laser beam to produce 3D shapes into a wide variety of materials. It is also known as laser ablation. It shows clear advantages versus the traditional milling such as the unlimited choice of materials, the direct use of computer-aided design structure data, the high geometric flexibility, and the touchless tool. LM requires the selection of optimal machining parameters for the job. Unlike the mechanical milling and the mechanical incision, the depth of the single removed layer is chosen at the beginning as input parameter of the process. In LM, the ablated depth depends from the process parameters such as laser power, scan speed, pulse duration, and pulse frequency. This work aims to develop an algorithm that can predict the parameters necessary to execute the material removal with a preset ablation depth. Using the results of an experimental campaign, the laser milling process was modeled by means of a back-propagation artificial neural network. Then, an iterative algorithm, based on the previous trained neural network, permitted to calculate the scanning velocity and pulse frequency that approached for the best the preset ablation depth. The developed approach represents a mean for the rational selection of laser ablation process parameters. It can be performed in an intuitive manner since it uses simple artificial intelligence like the artificial neural network.     

Study on the characteristics of plasma channel based on multi-spark pulse discharge machining effect

Plasma channel characteristics and energy distribution in electrical discharge machining (EDM) were mostly studied by analyzing the geometry parameters of craters caused by a single pulse discharge in previous studies. However, single pulse experiments cannot provide us insights into superposition, migration, abruption, interruption, and other phenomena of the plasma channel which have significant effects on EDM. Besides, EDM itself is a consecutive pulse discharge process. Thus, this paper focuses on the characteristics of plasma channel and the mechanism of material removal based on experimental data from multi-spark pulse discharge machining. The contrastive milling experiments of different parameters in multi-spark pulse discharge machining in high-speed dry EDM by using nickel-based superalloy as workpiece were conducted. The effects of peak current, dielectric type, breakdown voltage, air pressure, and electrode rotation speed on the crater number, crater distance, crater depth, and crater removal volume were studied. The plasma channel characteristics and material removal mechanism in continuous machining of high-speed dry EDM were revealed.     

An Experimental Study and Statistical Analysis of the Effect of Laser Pulse Energy on the Geometric Quality During Laser Precision Machining

In laser precision machining, process parameters have critical effects on the geometric quality of the machined parts. Due to the nature of the interrelated process parameters involved, an operator has to make a host of complex decisions, based on trial-and-error methods, to set the process control parameters related to the laser, workpiece material, and motion system. The objective of this work is to investigate experimentally the effect of laser pulse energy on the geometric quality of the machined parts in terms of accuracy, precision, and surface quality. Experimental study of formation of machined craters on thin copper foil with variation in laser pulse energy, the geometry and the surface topology of craters is presented. The geometrical parameters were measured and statistically analyzed with respect to incident pulse energy. Statistical analysis including pattern recognition was employed to analyze the experimental data systematically and to serve proper selection of the process parameters to achieve the desired geometric quality of the machined parts. Plausible trends in the crater geometry with respect to the laser pulse energy are discussed. The technique has been verified experimentally on simple geometrical features such as circles and grooves, and the geometric quality is evaluated.     

An Experimental Study and Statistical Analysis of the Effect of Laser Pulse Energy on the Geometric Quality During Laser Precision Machining

In laser precision machining, process parameters have critical effects on the geometric quality of the machined parts. Due to the nature of the interrelated process parameters involved, an operator has to make a host of complex decisions, based on trial‐and‐error methods, to set the process control parameters related to the laser, workpiece material, and motion system. The objective of this work is to investigate experimentally the effect of laser pulse energy on the geometric quality of the machined parts in terms of accuracy, precision, and surface quality. Experimental study of formation of machined craters on thin copper foil with variation in laser pulse energy, the geometry and the surface topology of craters is presented. The geometrical parameters were measured and statistically analyzed with respect to incident pulse energy. Statistical analysis including pattern recognition was employed to analyze the experimental data systematically and to serve proper selection of the process parameters to achieve the desired geometric quality of the machined parts. Plausible trends in the crater geometry with respect to the laser pulse energy are discussed. The technique has been verified experimentally on simple geometrical features such as circles and grooves, and the geometric quality is evaluated.     

喷雾电火花铣削加工的能量分配与材料蚀除模型

针对喷雾电火花铣削加工(Electrical discharge milling, ED-milling)建立电蚀坑形成过程的热-流耦合模型,并改进电火花加工中放电能量在阴极及阳极分配系数的判断方法来为所建立的蚀除模型提供边界条件。此外,通过试验得到不同放电参数下的电蚀坑半径,并对蚀坑半径随脉宽和电流变化的规律采用最小二乘法进行拟合作为等离子体扩张方程。基于材料蚀除的热-流耦合二维模型,应用仿真-试验比对的方法得到雾中电火花铣削加工时放电能量在正极的分配系数近似为0.29,负极分配系数约为0.025。根据相关加工参数及所建立的模型,对喷雾电火花加工的电蚀坑尺寸进行计算并与试验测量结果进行对比,两者误差约在8%,证明该模型是可信的。通过对比试验和分析结果,可知喷雾电火花铣削加工中放电通道中的能量分配在阳极的比例远大于阴极,从而揭示了在雾中电火花加工中工件接正极时材料去除率更高的原因。通过所建立的阴、阳极的蚀除模型,用于对喷雾电火花加工的材料去除率、表面粗糙度等进行推导和预测,从而优化工艺参数并减少加工成本。此外,所建立的模型可进一步扩展应用到液中、气中等多种电火花加工(Electrical discharge machining, EDM)中,并为EDM加工机理的研究提供了一种可行的方法。     

Development of an intelligent process model for EDM

This paper reports the development of an intelligent model for the electric discharge machining (EDM) process using finite-element method (FEM) and artificial neural network (ANN). A two-dimensional axisymmetric thermal (FEM) model of single-spark EDM process has been developed based on more realistic assumptions such as Gaussian distribution of heat flux, time- and energy-dependent spark radius, etc. to predict the shape of crater cavity, material removal rate, and tool wear rate. The model is validated using the reported analytical and experimental results. A neural-network-based process model is proposed to establish relation between input process conditions (discharge power, spark on time, and duty factor) and the process responses (crater geometry, material removal rate, and tool wear rate) for various work—tool work materials. The ANN model was trained, tested, and tuned using the data generated from the numerical (FEM) simulations. The ANN model was found to accurately predict EDM process responses for chosen process conditions. It can be used for the selection of optimum process conditions for EDM process.     

ANALYSIS OF SPARK ERODED CRATER FORMED UNDER GROWING PLASMA CHANNEL IN ELECTRO-DISCHARGE MACHINING

In electro-discharge machining, the occurrence of sparks cause material removal in the form of craters. These craters are due to melting and vaporization of workpiece over a localized area under the spark, which acts as the heat source. The crater under a single spark has been predicted by theoretical models adopting different approaches in solving the transient heat conduction equation, considering suitable assumptions with appropriate initial and boundary conditions. In the present work, a transient thermal model for a very large solid cylinder has been used to predict the size of the crater obtained under a single spark by determining the melting isotherm in both the axial and radial directions. An analytical study of the effect of plasma channel radius, heat flux, and pulse duration on the size of the crater has been made. Experiments are conducted using a commercial electro-discharge machine. The craters are measured under microscope and a comparison with theoretical results is presented. Subsequently, the nature of variation of crater diameter, crater depth and volume of material removed with respect to different machining parameters such as 'ON' time, 'OFF' time, and current have been explained by the theoretical results and it has been concluded that the plasma channel grows with respect to pulse duration such that at the end of the pulse the plasma channel radius becomes equal to the crater radius.     

水辅助激光加工技术的实验研究

介绍水辅助激光打孔和切割实验研究。研究表明 ,用毫秒级YAG脉冲激光对不锈钢和Al2 O3 陶瓷加工时 ,熔屑易从加工区排出 ,有助于提高加工的表面质量 ;加工单晶硅时 ,加工表面易产生微裂纹 ,使加工质量变差。激光通过水层时 ,有能量损失 ,水层深度越深 ,能量损失越大。     

Modelling and Analysis of UV Laser Micromachining of Copper

UV laser micromachining of metallic materials has been used in microelectronic and other industries. Knowledge and data about the process vary with feature size, material, laser wave-length and pulse duration. This paper reports on experimental and numerical investigation of micromachining of copper using a frequency tripled Nd:YAG laser with 50 ns pulse duration. An axisymmetric model is developed which allows consideration of laser beam distribution and its coupling with the target material. This is important for the process where the removal extent is in the same order of the removal depth. The model uses an enthalpy method to track the solid/liquid interface. Stefan and kinetic boundary conditions are applied at the liquid–vapour interface, and property discontinuity across the Knudsen layer is considered. Relevant experimental results are also presented and compared with the model predicted results. The range of thermal vaporisation dominated machining of copper using nanosecond time scale lasers was studied, and optimum laser intensity for micromachining of copper was suggested.     

Analysis and modelling of edm parameters

Metal removal in electro-discharge machining (edm) is basically a thermal erosion process where the heat transfer is predominantly through conduction. In this paper, a two-dimensional heat transfer model, assuming the plasma channel to be a disc heat source, has been employed to study the effects of edm input parameters, such as pulse duration, pulse energy and material properties, on metal removal and crater shape. Reasons for somewhat poor correlation between theoretical and experimental data are discussed.     

Investigations on influence of process variables on crater dimensions in micro-EDM of γ-titanium aluminide alloy in dry and oil dielectric media

In micro-electro-discharge machining (EDM), challenge lies in enhancing material removal rate while retaining precision in crater dimensions. Material properties of both anode and cathode and the process variables have significant control on MRR and accuracy. In the present research, experiments were conducted on γ-titanium aluminide alloy work piece using 200-μm steel electrode. The circular craters were produced both in the presence and absence of dielectric fluid using varying micro-EDM process variables, i.e., open-circuit voltage, discharge capacitance, pulse frequency, and pulse-on time. Overcut was measured from optical microscope images using Image Analyzer software. Influences of process variables and optimal conditions for minimum overcut on crater dimensions were investigated using ANOVA test, which shows that capacitance of RC circuit contributes significantly in crater formation followed by pulse frequency. Regression equations of overcut for both dielectric mediums were developed using discharge energy and spark-on time as two functions. It was also investigated that overcut was less in air medium compared to oil medium.     

The Effect of Cutting Parameters on Wire Crater Sizes in Wire EDM

In this study, the effect of the cutting parameters on size of erosion craters (diameter and depth) on wire electrode were experimentally and theoretically investigated in wire electrical discharge machining (WEDM). The experiments were conducted under the different cutting parameters of pulse duration (300, 500, 700, and 900 ns), open circuit voltage (80, 100, and 270 V), wire speed (5, 8, and 12.5 m min ^-1 ) and dielectric flushing pressure (6, 12, and 18 kg cm ^-2 ). Brass wire of 0.25 mm diameter and AISI 4140 steel of 0.28 mm thickness were used as tool and workpiece materials in the experiments. It is found that increasing the pulse duration, open circuit voltage, and wire speed increases the crater size, whereas increasing the dielectric flushing pressure decreases the crater size. The variation of wire crater size with machining parameters is modelled mathematically by using a power function. The level of importance of the machining parameters on the wire crater size is determined by using analysis of variance (ANOVA).     

Experimental analysis on Nd:YAG laser micro-turning of alumina ceramic

Laser micro-turning is a micro-machining strategy to machine cylindrical workpiece of hard-to-process materials such as ceramics. Laser micro-turning method is in high demand in the present high-precision manufacturing industries because of its wide and potential uses in various engineering fields such as automobile, electronics, aerospace, and biomedical applications, etc. In the present research, the experimental analysis of Nd:YAG laser micro-turning of cylindrical-shaped ceramic material has been made to explore the desired laser output responses, i.e., depth of cut and surface roughness by varying laser micro-turning process parameters such as lamp current, pulse frequency, and laser beam scanning speed. Single laser beam has been utilized for successful micro-turning operation. Experimental results revealed that the laser machining process parameters have great influences for achieving desired laser micro-turned depth and surface roughness characteristics during laser micro-turning of alumina ceramics. SEM and optical photographs have also been analyzed for better understanding of the laser micro-turning process for different parametric settings.     

HIGH THROUGHPUT DRILLING OF TITANIUM ALLOYS

The experiments of high throughput drilling of Ti-6Al-4V at 183 m/min cutting speed and 156 mm3/s material removal rate using a 4 mm diameter WC-Co spiral point drill are conducted. At this material removal rate, it took only 0.57 s to drill a hole in a 6.35 mm thick Ti plate. Supplying the cutting fluid via through-the-drill holes and the balance of cutting speed and feed have proven to be critical for drill life. An inverse heat transfer model is developed to predict the heat flux and the drill temperature distribution in drilling. A three-dimensional finite element modeling of drilling is con-ducted to predict the thrust force and torque. Experimental result demonstrates that, using proper machining process parameters, tool geometry, and fine-grained WC-Co tool material, the high throughput machining of Ti alloy is technically feasible.     

Ejection of molten material produced by pulsed electron and laser beams

Crater formation in electron and laser beam drilling is mainly due to molten material removal. In this process, there are two different modes of removal: ejection outside the target and transport of material which remains around the crater on the target surface. Measurement of these removal modes was carried out. The diameters of molten particles ejected from the targets were obtained. Characteristic particle diameters were determined for each material and each drilling condition. The volume of solidified material remaining around the crater was also obtained. From these results, the proportion of molten material ejected from the target was determined. Most of the molten material remained around the crater for iron and tungsten, but was ejected outside the target for aluminium and alumina ceramics.     

Theoretical and experimental investigation of pulsed laser grooving process

A theoretical model has been developed for simulating the laser grooving process. It takes into account the interaction among subsequent pulses, the required time for the melting temperature to be reached and the subsequent removal of a finite volume of material during each laser pulse. The model predicts the maximum groove depth that can be achieved for a specified set of process parameters, such as laser power, pulsing frequency, and scanning velocity. The theoretical predictions have been experimentally tested with a medium-power laser beam.     

Electrical discharge machining of the AISI D6 tool steel: Prediction and modeling of the material removal rate and tool wear ratio

In this investigation, response surface method was used to predict and optimize the material removal rate and tool wear ratio during electrical discharge machining of AISI D6 tool steel. Pulse on time, pulse current, and voltage were considered as input process parameters. Furthermore, the analysis of variance was employed for checking the developed model results. The results revealed that higher values of pulse on time resulted in higher values of material removal rate and lower amounts of tool wear ratio. In addition, increasing the pulse current caused to higher amounts of both material removal rate and tool wear ratio. Moreover, the higher the input voltage, the lower the both material removal rate and tool wear ratio. The optimal condition to obtain a maximum of material removal rate and a minimum of tool wear rate was 40 μs, 14 A and 150 V, respectively for the pulse on time, pulse current and input voltage.     

Effect of LBM and large-area EBM finishing on micro-injection moulding surfaces

Micro-injection moulding is an efficient process for large series production of thermoplastic polymer micro-parts. The moulding surface quality in the moulds is important and determines the manufacturing specifications for a given micro-engineering component. In this study, melting and vaporisation removal technologies were analysed: laser beam machining (LBM) as the material removal technique and electron beam machining (EBM) as the finishing process. Stainless steel DIN X42Cr13 was used for machining 10?×?10?mm² flat surfaces. LBM parameters, namely intensity, frequency, cutting depth, scanning speed and hatching, and EBM conditions, as energy density, number of irradiation and frequency, were varied. The surface topography and integrity and the micro-structure were characterised by optical and electronic microscopy, roughness profilometry, X-ray spectroscopy and micro- and ultrahardness tests. It was shown that the combination of LBM and large-area EBM is an interesting alternative to polishing by hand lapping of moulding surfaces for micro-moulding, improving surface roughness and surface integrity without cracks and smaller HAZ. The morphology analysis demonstrated that EBM finishing improves corrosion and oxidation resistance compared with conventional heat-treated surfaces.     

The laser shaping of ceramic by a fracture machining technique

A new laser machining technique for ceramic shaping, based on the concept of fracture mechanics, is proposed in this paper. The principle of fracture machining technique is investigated. A focused laser is used to scribe two groove-cracks at the two intersecting surfaces of the rectangular substrate. Then, a defocused laser beam is applied throughout the length of the groove-cracks to generate a great thermal stress, which makes the two groove-cracks link together. The material removal is due to the linkage of the groove-cracks. Conventional laser machining requires high laser power to evaporate the materials. The high temperature gradient would induce the formation of micro-cracks, which leads to a remarkable reduction in strength. The laser power required in the method proposed is only a tenth of what is required in the conventional method under the same material removal rate, and in addition, the amount of the micro-crack is smaller. The experimental specimens are alumina ceramics, and the laser sources are a CO₂ laser and a Nd:YAG laser. The fracture machining technique can be successfully employed for step shaping and blind corner shaping for a thick ceramic substrate. The relationships of machining parameters such as groove-crack depth, material removal rate, laser scanning speed, and laser power are discussed. Finally, the measurement of the surface roughness and the inspection of crack defects are examined thoroughly.     

Fabrication of micro-end mill tool by EDM and its performance evaluation

Abstract

Micro-milling is a fast, cheap and controlled process compared to other micro-fabrication processes such as lithography, laser/electron/ion beam machining, etc. However, scarcity of cutting tools of very small dimensions often results in limited application of micro-milling. In the present study, electro discharge machining (EDM) is used for fabrication of micro-end mill tool. To ensure high dimensional accuracy of the tool, a parametric study is conducted by replicating the a tungsten carbide block to a tungsten carbide (WC) block. The relationships between the drilled cavities on the block and the features on the micro-tool are established. The influence of machining parameters (voltage, capacitance and spindle speed) on the response variables (entrance diameter, hole depth, material removal rate (MRR) and surface roughness) is reported. Capacitance is found more dominant as compared to other selected process parameters. Using optimized parameters from the parametric study, a WC micro-end mill tool of 100?µm diameter is fabricated. Channel of around 110 µm width, 40?µm depth and surface roughness of 70?nm is successfully fabricated on aluminum. The performance of the fabricated tool is compared with a commercial end mill tool by milling micro channels on stainless steel.