Multi-objective optimization of laser cutting for flash memory modules with special shapes using grey relational analysis

This paper presents a novel effective method for optimizing laser cutting of specially shaped electronic printed circuit board (PCB) carrier substrates of advanced integrated circuit (IC) back-end packages that have multiple performance characteristics identified using grey relational analysis (GRA). Laser cutting parameters, including laser beam parameters (average laser power and Q-switch frequency), focusing parameters (laser beam focusing spot size), and machine parameters (laser cutting speed), were optimized based on multiple performance characteristics. Some characteristics of the specially shaped flash memory module for IC packages, such as smart disk (SD) cards are verified. The characteristics of interest are the average surface roughness on a PCB substrate cross-section, and the maximum width of the heat-affected zone (HAZ). Eight experiments were conducted using GRA to optimize the settings for laser beam cutting parameters to generate various quality characteristics. Analysis of the grey relational grade indicates that parameter significance and the optimal parameter combination for the laser cutting process are identified. The analytical results from two confirmation experiments using the optimal parameters confirm that laser cutting technology can be effectively applied to cut substrates into special shapes.     

Laser cutting of polymeric materials: An experimental investigation

The CO₂ laser cutting of three polymeric materials namely polypropylene (PP), polycarbonate (PC) and polymethyl methacrylate (PMMA) is investigated with the aim of evaluating the effect of the main input laser cutting parameters (laser power, cutting speed and compressed air pressure) on laser cutting quality of the different polymers and developing model equations relating input process parameters with the output. The output quality characteristics examined were heat affected zone (HAZ), surface roughness and dimensional accuracy. Twelve sets of tests were carried out for each of the polymer based on the central composite design. Predictive models have been developed by response surface methodology (RSM). First-order response models for HAZ and surface roughness were presented and their adequacy was tested by analysis of variance (ANOVA). It was found that the response is well modeled by a linear function of the input parameters. Response surface contours of HAZ and surface roughness were generated. Mathematical model equations have been presented that estimate HAZ and surface roughness for various input laser cutting parameters. Dimensional accuracies of laser cutting on polymers were examined by dimensional deviation of the actual value from the nominal value. From the analysis, it has been observed that PMMA has less HAZ, followed by PC and PP. For surface roughness, PMMA has better cut edge surface quality than PP and PC. The response models developed can be used for practical purposes by the manufacturing industry. However, all three polymeric materials showed similar diameter errors tendency in spite of different material properties.     

锂离子动力电池极片的激光切割分析

为适应锂离子动力电池行业发展需求,寻求一种高效高质切片方式,本文研究了多种激光器的切片质量。通过影像测量仪和扫描电镜(SEM)对比发现,100 ns脉宽调Q型1 064 nm光纤激光器切割正极铝箔时毛刺和热影响区(HAZ)约为15μm和60μm,切负极铜箔时HAZ约为200μm; 20 ns脉宽的MOPA光纤激光器切割铝箔毛刺10μm,HAZ约为20μm,切铜箔时HAZ约70μm;脉宽为10 ps的固体激光器切割铝箔毛刺和HAZ分别约为6μm和10μm,切铜箔时实现无熔融重凝区; 20 ns脉宽的355 nm紫外和532 nm的绿光固体激光器切割铝箔HAZ分别为10μm和17μm,切铜箔时HAZ则分别为大于70μm和100μm。实验结果表明:脉宽越窄,重复频率越高,切割的极片质量越好,ps激光器切割的极片精度最高,质量最好,是切割极片最理想激光器。而目前,频率高、脉宽相对窄的MOPA光纤激光器切割速度最高,切割的正极片完全满足工业要求,更适合极片切割的工业推广。     

Estimation of the most influential factors on the laser cutting process heat affected zone (HAZ) by adaptive neuro-fuzzy technique

Heat affected zone (HAZ) of the laser cutting process may be developed on the basis on combination of different factors. In this investigation was analyzed the HAZ forecasting based on the different laser cutting parameters. The main aim in this article was to analyze the influence of three inputs on the HAZ of the laser cutting process. The method of ANFIS (adaptive neuro fuzzy inference system) was applied to the data in order to select the most influential factors for HAZ forecasting. Three inputs are considered: laser power, cutting speed and gas pressure. According the results the cutting speed has the highest influence on the HAZ forecasting (RMSE: 0.0553). Gas pressure has the smallest influence on the HAZ forecasting (RMSE: 0.0801). The results can be used in order to simplify HAZ prediction and analyzing.     

Multiple-objective optimization in precision laser cutting of different thermoplastics

Thermoplastics are increasingly being used in biomedical, automotive and electronics industries due to their excellent physical and chemical properties. Due to the localized and non-contact process, use of lasers for cutting could result in precise cut with small heat-affected zone (HAZ). Precision laser cutting involving various materials is important in high-volume manufacturing processes to minimize operational cost, error reduction and improve product quality. This study uses grey relational analysis to determine a single optimized set of cutting parameters for three different thermoplastics. The set of the optimized processing parameters is determined based on the highest relational grade and was found at low laser power (200 W), high cutting speed (0.4 m/min) and low compressed air pressure (2.5 bar). The result matches with the objective set in the present study. Analysis of variance (ANOVA) is then carried out to ascertain the relative influence of process parameters on the cutting characteristics. It was found that the laser power has dominant effect on HAZ for all thermoplastics.     

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.     

Femtosecond laser drilling of alumina ceramic substrates

In the paper, the result on femtosecond laser drilling of alumina ceramic substrate was reported. The effects of various laser parameters such as different focus position, traverse speed, drilling pattern, pausing time, etc. on the drilled hole quality in terms of surface finish, heat affected zone (HAZ), hole circularity, debris, microcracks were studied. The quality of laser-drilled holes on alumina ceramic substrates was evaluated with optical microscope, SEM/EDX, and X-ray μ-CT analysis. The optimum drilling conditions were identified. High-quality laser-drilled holes on alumina ceramic substrates were demonstrated. The developed process has potential application in manufacturing of alumina substrate based electronic devices.     

Quantitative evaluation of the quality of the cuts performed on mullite-alumina by Nd:YAG laser

Mullite-alumina is an advanced ceramic with great importance in the construction of structural elements for high temperature applications. The inherent properties of this material such as its very high hardness and brittleness make conventional machining a very hard task, being slow, noisy and poor productive.In this paper we present the results of the work carried out to investigate the influence of different cutting parameters on the laser cut quality. Specifically, a detailed study of the characteristics of the heat affected zone (HAZ) is presented as a function of average laser power, cutting speed, assist gas pressure and pulse frequency. Quantitative analysis of the HAZ characteristics was performed by means of analytical image processing of dimensional magnitudes easily identified in the optical microscopy images.     

Effects of processing parameters on laser cutting of aluminium-copper alloys using off-axial supersonic nozzles

Conventional laser cutting involves the utilization of converging coaxial nozzles to inject the assist gas used to remove the molten material. This processing system prevents the utilization of this technique to cut aluminium alloys for aerospace applications. The inefficient removal of molten material by the assist gas produces cuts with poor quality; very rough cuts, with a large amount of dross, and a large heat affected zone (HAZ) are obtained. An alternative to increase the assist gas performance is the utilization of off-axial supersonic nozzles. Removal of molten material is substantially increased and cuts with high quality are obtained. On the other hand, pulsed laser cutting offers superior results during the processing of high reflectivity materials as aluminium alloys. However, there are no experimental studies which explore the pulsed laser cutting of aluminium alloys by means of a cutting head assisted by an off-axis supersonic nozzle.The present work constitutes a quantitative experimental study to determine the influence of processing parameters on the cutting speed and quality criteria during processing by means of off-axial supersonic nozzles. Cutting experiments were performed in pulsed mode and the results explained under the basis of the molten material removal mechanisms. Performed experiments indicate a reduction in cutting speed as compared to continuous wave (CW) mode processing and the existence of two processing regimes as a function of the pulse frequency. Best results are obtained under the high pulse frequency one (f > 100 Hz) because the superior capabilities of molten material removal of the supersonic jets are completely exploited in this processing regime.     

Cutting glass substrates with dual-laser beams

In order to improve the cutting quality, a dual-laser-beam method was proposed to cut glass substrates in the current study, where a focused CO₂-laser beam was used to scribe a straight line on the substrate, and a defocused CO₂-laser beam was used to irradiate on the scribing line to generate a tensile stress and separate the substrate. The finite-element-method (FEM) software ANSYS was applied to calculate the temperature distribution and the resulting thermal stress filed. Through experimental study, it concluded that the glass substrate can be separated along an expected path with dual-laser beams and the cutting quality can be improved comparing with the cutting using a defocused laser beam alone. The relation between the cutting speed and the defocused laser power was also investigated in cutting glass with this method.     

Study into penetration speed during CO2 laser cutting of stainless steel

Laser cutting quality depends upon the proper selection of laser and workpiece parameters. Laser cut quality drops considerably when the size of the surface plasma increases. This plasma affects the speed of penetration, which in turn affects the cut quality. The present study examines the measurement of the penetration speed during CO₂ laser cutting of stainless steel workpieces. To achieve this, three different methods were employed, namely, optical, thermocouple and wire methods. Oxygen and an argon-oxygen gas mixture were used as assisting gases. Penetration speed was also predicted, using a one-dimensional heat transfer model. It was concluded that the cut quality improves when penetration speed is at a maximum.     

The use of grey relational analysis to determine laser cutting parameters for QFN packages with multiple performance characteristics

This paper reports an application of the grey relational analysis (GRA) to directly optimize laser cutting of a quad flat non-lead (QFN) strip using six performance characteristics. The most important performance characteristics include the cutting depth, the width of heat affected zone (HAZ), and the width of cutting line for both epoxy and Cu+epoxy materials along the cutting path. During the GRA, higher grades are obtained from any of the deeper (more complete) cutting depth, reduced widths of the HAZ and reduced widths of the cutting line. From nine experiments based on the orthogonal array of L9(3⁴), a current of 29 A, a frequency of 2 kHz, and a cutting speed of 2 mm/s were found to be the best parameters for laser cutting of a QFN strip with a thickness of 0.9 mm. Moreover, the analysis of variance (ANOVA) is also employed to determine the contribution of each control parameter on the cutting quality characteristics. The three largest measured contributions on the cutting quality in decreasing order are the frequency, the current, and the cutting speed. Compared with the Taguchi optimization method, the GRA approach is significantly simpler because it directly assigns appropriate weighting factors to the required qualities. Finally, confirmation experiments are performed to ensure the robustness of the GRA predicted optimal configuration for laser cutting a QFN strip.     

An investigation of pulsed laser cutting of titanium alloy sheet

Subsequent welding requirement calls for high-quality laser cut surfaces in the laser cutting of bladed ring parts for aeroengines. This paper presents pulsed laser cutting of titanium alloy sheet and investigates the influences of laser cutting parameters on laser cut quality factors including heat-affected zone (HAZ), surface morphology and corrosion resistance. The thickness of HAZ lasers is studied in detail as a function of laser cutting parameters. For different assist gases the surface morphology and corrosion resistance show great differences. In comparison with air- and nitrogen-assisted laser cutting, argon-assisted laser cutting comes with unaffected surface quality and is suitable for laser cutting with subsequent welding requirement.     

Inert gas cutting of titanium sheet with pulsed mode CO2 laser

The present work aimed at studying the dynamic behavior of melt ejection in laser cutting of 1 mm thick titanium sheet and to obtain dross-free cuts with minimum heat affected zone (HAZ). CO₂ laser cutting of titanium sheet was carried out with continuous wave (CW) and pulsed mode laser operation with different shear gases namely argon, helium and nitrogen. Laser cutting with high frequency and low-duty cycle pulse mode operation produced dross-free cuts with no noticeable HAZ. Helium, because of its high heat convection and ability to generate high shear stress, produced laser-cuts with narrow HAZ and low dross, as compared to those produced with argon as the shear gas. Microscopic features of laser cut surfaces were analyzed and correlated with dynamic mechanism involved in laser cutting process. Process parameters for laser piercing, required for the initiation of fusion cut within the sheet, were also studied. Laser piercing requires either CW or high-duty cycle (>80%) pulse mode operation.     

血管支架光纤激光切割技术

采用光纤激光器对血管支架进行了激光切割工艺研究,通过实验获得了聚焦透镜焦距及焦点位置、输出功率、切割速度、脉冲频率、脉冲宽度、辅助气体种类及压强等工艺参数对切缝宽度和缝面质量的影响规律.结果表明:缝宽随输出功率、频率、脉宽及辅助氧压的增大而增加,随着切割速度的增加而减小.在实验的基础上找出了血管支架切割的最佳工艺参数,在316LVM不锈钢细管上(管壁厚度为0.12 mm,直径为2 mm)获得了切缝均匀,缝宽小于20 μm网状结构的血管支架.     

Influences of CO2 laser annealing on mechanical and laser-induced damage properties of ZrO2 thin films

Zirconium dioxide (ZrO₂) thin films were deposited on BK7 glass substrates by the electron beam evaporation method. A continuous wave CO₂ laser was used to anneal the ZrO₂ thin films to investigate whether beneficial changes could be produced. After annealing at different laser scanning speeds by CO₂ laser, weak absorption of the coatings was measured by the surface thermal lensing (STL) technique, and then laser-induced damage threshold (LIDT) was also determined. It was found that the weak absorption decreased first, while the laser scanning speed is below some value, then increased. The LIDT of the ZrO₂ coatings decreased greatly when the laser scanning speeds were below some value. A Nomarski microscope was employed to map the damage morphology, and it was found that the damage behavior was defect-initiated both for annealed and as-deposited samples. The influences of post-deposition CO₂ laser annealing on the structural and mechanical properties of the films have also been investigated by X-ray diffraction and ZYGO interferometer. It was found that the microstructure of the ZrO₂ films did not change. The residual stress in ZrO₂ films showed a tendency from tensile to compressive after CO₂ laser annealing, and the variation quantity of the residual stress increased with decreasing laser scanning speed. The residual stress may be mitigated to some extent at proper treatment parameters.     

Fast femtosecond laser ablation for efficient cutting of sintered alumina substrates

Fast, accurate cutting of technical ceramics is a significant technological challenge because of these materials' typical high mechanical strength and thermal resistance. Femtosecond pulsed lasers offer significant promise for meeting this challenge. Femtosecond pulses can machine nearly any material with small kerf and little to no collateral damage to the surrounding material. The main drawback to femtosecond laser machining of ceramics is slow processing speed. In this work we report on the improvement of femtosecond laser cutting of sintered alumina substrates through optimisation of laser processing parameters. The femtosecond laser ablation thresholds for sintered alumina were measured using the diagonal scan method. Incubation effects were found to fit a defect accumulation model, with F_th,1=6.0 J/cm² (±0.3) and F_th,∞=2.5 J/cm² (±0.2). The focal length and depth, laser power, number of passes, and material translation speed were optimised for ablation speed and high quality. Optimal conditions of 500 mW power, 100 mm focal length, 2000 µm/s material translation speed, with 14 passes, produced complete cutting of the alumina substrate at an overall processing speed of 143 µm/s – more than 4 times faster than the maximum reported overall processing speed previously achieved by Wang et al. [1]. This process significantly increases processing speeds of alumina substrates, thereby reducing costs, making femtosecond laser machining a more viable option for industrial users.     

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.     

Research on laser welding of high-strength galvanized automobile steel sheets

The paper presented some useful results of deep-penetration laser welding of high-strength galvanized steel sheets, which had been carried out by a self-made CO₂ laser unit with maximum power output of 1.5 kW. The workpieces of high-strength galvanized automobile steels with thickness of 1.5 mm were butt-welded with argon as the shielding gas. The effects of such factors as laser power, welding speed, focal position, shielding gas and zinc vaporization on the quality of welds are investigated. With the processing parameters optimized and the proper shielding gas used in both coaxial and side-blow direction, most of the defects, such as pores, cracks and softening in HAZ, can be avoided in laser welding joints. The microstructure, the hardness distribution and the elemental distribution in the welding joints can be changed due to laser heating and recrystallization. In order to determine the mechanical properties of the welding joints, the static tensile strength was tested. Experimental results indicated that both the strength and microhardness of welding joints were higher than those of the base metal. Consequently, the welding quality is reliable for manufacturing of automobile bodies.     

Optical fiber cleaved at an angle by CO2 laser ablation: Application to micromachining

Laser ablation can be achieved by delivering short power pulse with durations much smaller than the heat diffusion time. In this investigation, we are collimating and magnifying a beam from a CO₂ laser with a Keplerian telescopic system. Then we study the quality of the cut performed by scanning the beam at a fast speed over an optical fiber just after focusing a well collimated CO₂ beam at λ=10.6 μm. It is found that the best results for cutting optical fibers depend upon both the time required in raising matter temperature to the vaporization point and the scanning speed of the CO₂ laser beam. Some aspects of the laser beam collimation before focusing is reviewed briefly and results for optical fibers being cleaved at low and fast speed under various conditions are also shown and discussed.