Laser hole cutting in Kevlar: modeling and quality assessment

Machining of Kevlar laminates with conventional methods results in poor end-product quality and excessive specific energy requirement for machining. However, laser machining has considerable advantages over the conventional methods due to precision and rapid processing. In the present study, laser hole cutting into Kevlar laminates with different thicknesses and properties is carried out. The laser output power, frequency, and cutting speed are varied during the hole-cutting experiments. The specific energy requirements for cutting, thermal efficiency of the cutting process, and kerf width are formulated and predicted for various laser parameters and Kevlar properties. The cut quality is associated with the damage size around the holes cut and statistical analysis is carried out to examine the affecting parameters on the damaged size. It is found that specific energy requirement is significantly lower than that of the conventional drilling method. The damage size is affected significantly by the laser irradiated power. The quality of holes, as judged by the percentage of damage size around the cut edges cut by a laser beam, is considerably improved compared to the conventional methods.     

Parametric studies on the CO2 laser cutting of Kevlar-49 composite

In the present study, the cutting performance of a CO₂ laser on Kevlar-49 composite materials has been studied. The Taguchi technique is employed to identify the effect of laser control parameters, i.e., laser power, cutting speed, material thickness, assistance gas pressure, and laser mode, on the quality of cut parameters, namely, kerf width, dross height, and slope of the cut. From the analysis of variance (ANOVA) and signal-to-noise (S/N) ratio response tables, the significant parameters and the optimal combination levels of cutting parameters are determined. The obtained results are interpreted and modeled to closely understand the behavior and quality of CO₂ laser cutting. Kevlar-49 composites are found to be cut satisfactorily by the CO₂ laser at the optimum process parameter ranges. The results showed that laser power is the most significant parameter affecting the quality of cut parameters. The optimal combination of cutting parameters minimized the kerf width, dross height, and slope of cut to 0.103 mm, 0.101 mm, and 2.06°, respectively. The error between experimental results with optimum settings and the predicted values for the kerf width, dross height, and slope of cut lie within 2.9%, 7.92%, and 6.3%, respectively.     

基于正交试验钛合金激光切割工艺参数优化

激光切割质量受各种因素的影响,为了得到高质量的激光切割件,需要根据不同的切割板材进行优化。利用厚度1.5mm的TC1薄板作为研究对象,研究激光功率、切割速度、焦点位置和辅助气体压力主要因素对激光切割质量的影响,采用正交试验方法安排激光切割试验,使用L16(45)正交表,完成十六组激光切割试验。利用测量点轮廓精度的算术平均值作为结果进行分析,采用直观分析法,因素效应曲线图,方差分析对切割参数进行分析研究。结果表明:切割速度和辅助气体压力是主要因素,对切割质量和精度有较大影响,而激光功率对切割后试件的轮廓度影响较之上两个因素小,但是激光功率改变对切割件的表面质量影响显著。     

Multi-objective optimization of machining parameters considering energy consumption

This paper deals with multi-objective optimization of machining parameters for energy saving. Three objectives including energy, cost, and quality are considered in the optimization model, which are affected by three variables, namely cutting depth, feed rate, and cutting speed. In the model, energy consumption of machining process consists of direct energy (including startup energy, cutting energy, and tool change energy) and embodied energy (including cutting tool energy and cutting fluid energy); machining cost contains production operation cost, cutting tool cost, and cutting fluid cost; and machining quality is represented by surface roughness. With simulation in Matlab R2011b, the multi-objective optimization problem is solved by NSGA-II algorithm. The simulation results indicate that cutting parameters optimization is beneficial for energy saving during machining, although more cost may be paid; additionally, optimization effect on the surface roughness objective is limited. Inspired by the second result, optimization model eliminating quality objective is studied further. Comparing the non-dominated front of three-objective optimization with the one of two-objective optimization, the latter is proved to have better convergence feature. The optimization model is valuable in energy quota determination of workpiece and product.     

三维激光切割工艺在化铣焊接机匣加工中的应用研究

通过对钛合金焊接机匣化铣结构的分析,设计了化铣工艺流程。针对化铣图形制版质量在化铣工艺流程中的关键作用,确定了化铣图形制版的激光刻型方案。选择通用三维激光切割机做为刻型加工设备,分析了激光刻型过程中要解决的技术问题,并采用分组编程刻型方案解决了通用三维激光器柔性切割轨迹误差技术难题,最后通过多组参数激光刻型试验选择了最佳切割参数,完成了该件化铣前激光刻型。通用三维激光切割机实现化铣图形柔性精确刻型方法,对其它复杂结构件化铣图形制备方案选择具有一定参考价值。     

Dross formation and process parameters analysis of fibre laser cutting of stainless steel thin sheets

The coronary stent fabrication requires a high-precision profile cut. Fibre lasers present a solution to accomplish these requirements. This paper presents an experimental study of fibre laser cutting of 316L stainless steel thin sheets. The effect of peak pulse power, pulse frequency and cutting speed on the cutting quality for fixed gas type and gas pressure was investigated. A mathematical model based on energy balances for the dross dimensions was formulated. The dross height and the dross diameter were analysed and compared with the experimental results. This allows adjustment of the process parameters to reduce the dimensions of the dross deposited at the bottom of the workpiece during laser cutting of thin sheets.     

Characterisation of thermal influences after laser processing polycrystalline diamond composites using long to ultrashort pulse durations

The laser processing of cutting tool edges is growing rapidly due to its flexibility, short cycle times and negligible waste. However, the quality of the tool and its cutting edge can vary greatly with different laser parameters and processing strategies. The generation of a graphitic carbon layer and a heat affected zone (HAZ) could occur during laser processing which is expected to reduce the quality and lifetime of the cutting tool. By using focussed ion beam (FIB) techniques to generate a cross section, the graphitic carbon layer and heat affected zone are characterised quantitatively and qualitatively for laser processes and as a reference, lapping and wire electro-discharge machining processes, used in the generation of polycrystalline diamond composite cutting tool edges. A focus is put on laser based techniques which vary in pulse duration from long microsecond pulses down to ultrashort picosecond pulses. A deep insight into the focussed ion beam techniques used and extensive analysis through Raman spectroscopy and energy dispersive X-ray spectroscopy (EDX) into the laser–material interactions are presented.     

Parameter optimization of non-vertical laser cutting

In some cases, in order to avoid interference during 3D laser cutting of thin metal a laser head could not be kept vertical to the surface of a work piece. In such situations, the cutting quality depends not only on “typical” cutting parameters but also on the slant angle of the laser head. Traditionally, many tests had to be done in order to obtain the best cutting results. In this paper, an experimental design is employed to reduce the number of tests and an artificial neural network (ANN) is set up to describe quantitatively the relationship between cutting quality and cutting parameters in the non-vertical laser cutting situation. A quality point system is used to evaluate the cutting result of the thin sheet quantitatively. Testing of this novel method shows that the calculated “quality point” using ANN is quite closely in accord with the actual cutting result. The ANN is very successful for optimizing parameters, predicting cutting results and deducing new cutting information.     

径向基神经网络在三维激光切割中的应用

分析了RBF神经网络的特点，并研究了它在三维激光切割中的应用，利用该神经网络及其变形可以预测切缝的宽度，也可以根据输入参数对试样的挂渣与否进行判定。比较了三雏激光切割中切割倾角和切割方向对切割质量的影响，从而实现切割质量的预测和优化工艺参数的选取以指导实际的切割过程。     

An integrated evolutionary approach for modelling and optimization of laser beam cutting process

This paper presents a new integrated methodology based on evolutionary algorithms (EAs) to model and optimize the laser beam cutting process. The proposed study is divided into two parts. Firstly, genetic programming (GP) approach is used for empirical modelling of kerf width (Kw) and material removal rate (MRR) which are the important performance measures of the laser beam cutting process. GP, being an extension of the more familiar genetic algorithms, recently has evolved as a powerful optimization tool for nonlinear modelling resulting in credible and accurate models. Design of experiments is used to conduct the experiments. Four prominent variables such as pulse frequency, pulse width, cutting speed and pulse energy are taken into consideration. The developed models are used to study the effect of laser cutting parameters on the chosen process performances. As the output parameters Kw and MRR are mutually conflicting in nature, in the second part of the study, they are simultaneously optimized by using a multi-objective evolutionary algorithm called non-dominated sorting genetic algorithm II. The Pareto optimal solutions of parameter settings have been reported that provide the decision maker an elaborate picture for making the optimal decisions. The work presents a full-fledged evolutionary approach for optimization of the process.     

Using a Nd:YAG laser and six axes robot to cut zinc-coated steel

Zinc-coated steel sheets are important materials in the automobile and home appliance industries. Currently, lasers are the preferred tools for metal cutting because of their good cutting quality, flexibility and excellent features and results, as compared to traditional tools. The solid-state Nd:YAG laser has successfully replaced the gaseous CO₂ laser for metal cutting; its small size and short wavelength makes it suitable for cutting bright and metal-coated materials, as well as being able to be transmitted via optical fibers and robots to cut complicated three dimensional and curved shapes. In this work, the Nd:YAG laser is used to cut 1 mm zinc coated steel sheets. We demonstrate the effects of different cutting parameters such as laser power, cutting speed, different gas types and pressures, and focus position on the cutting quality characteristics of attached dross, kerf width and cut surface roughness. Using a six axes robot, cutting speed was limited to 6 m/min because of the noticeable vibration at higher speeds. Results showed that the cutting surfaces achieved were very sharp and smooth. In cutting, Nd:YAG required less power and attained higher speeds than the published results of a CO₂ laser, which makes Nd:YAG an economical alternative to cut zinc and metal-coated materials. In addition, laser cutting using robots provided efficient and consistent cutting quality, especially in the case of 3D and countered cutting. Apart from using low speed, robots proved to be more economical than costly, specially designed CNC tables.     

激光冲裁加工剪口质量的研究

介绍了激光冲裁的概念,并通过实验分析了激光切割切口的硬度差异,波纹、挂渣产生的机理,得到影响激光冲裁切口质量的相关因素及数值变化情况.研究结果表明切割质量对工艺条件十分敏感,激光冲裁中的激光功率、材料厚度、切割速度、焦点位置、气流压力及形状等参数的波动或变化都会影响切割质量.     

The effect of continuous and pulsed beam modes on cut path deviation in diode laser cutting of glass

During laser cleaving of brittle materials, with the controlled fracture technique, thermal stresses are generated which induce the crack and extend it along the cutting path, subsequently causing material separation. One of the problems in laser cutting of glass with this technique is the cut path deviation at the leading and the trailing edges of the glass sheet. Previous work with a continuous beam diode laser has shown the deviation to be partly due the high magnitudes of thermal stresses generated near the edges of the sheet. This paper reports on the effects of using a pulsed diode laser to cut soda lime glass. The effect of pulse parameters and cutting speed on the quality output variables such as cut deviation angle and surface finish are studied. Finite element modelling is also used to simulate the effects of the moving beam on stress generations to facilitate the understanding of the process mechanisms, and the results are compared with the experimental data. This work shows how to minimise the cut path deviation at the edges by reducing thermal stresses using optimum pulsed diode laser parameters and providing additional flexibility to the process.     

Enhancement and verification of a machined surface quality for glass milling operation using CBN grinding tool—Taguchi approach

Nowadays, the demand for high product quality focuses extensive attention to the quality of machined surface. The (CNC) milling machine facilities provides a wide variety of parameters set-up, making the machining process on the glass excellent in manufacturing complicated special products compared with other machining processes. However, the application of grinding process on the CNC milling machine could be an ideal solution to improve the product quality, but adopting the right machining parameters is required. Taguchi optimization method was used to estimate optimum machining parameters with standard orthogonal array L₁₆ (4⁴) to replace the conventional trial and error method as it is time-consuming. Moreover, analyses on surface roughness and cutting force are applied which are partial determinant of the quality of surface and cutting process. These analyses are conducted using signal to noise (S/N) response analysis and the analysis of variance (Pareto ANOVA) to determine which process parameters are statistically significant. In glass milling operation, several machining parameters are considered to be significant in affecting surface roughness and cutting forces. These parameters include the lubrication pressure, spindle speed, feed rate, and depth of cut as control factors. While, the lubrication direction is considered as a noise factor in the experiments. Finally, verification tests are carried out to investigate the improvement of the optimization. The results showed an improvement of 49.02% and 26.28% in the surface roughness and cutting force performance, respectively.     

Experimental study on operating temperature in laser-assisted milling of silicon nitride ceramics

Operating temperature plays a significant role in laser-assisted milling (LAMill) of silicon nitride ceramics. Understanding the features of temperature variation can improve the performance of LAMill. Based on the analysis of operating temperature, this paper aims to provide guidelines on parameter selection for LAMill from three aspects: laser?Csilicon nitride interaction mechanism, effect of parameters on temperature, and evaluation of surface quality of the machined workpieces. First, the laser?Csilicon nitride interaction mechanism is explored via heating experiments. It is found that the formation of silica bubbles at the thin top layer of the workpiece can slightly increase the temperature of silicon nitride workpieces due to the heat energy released from the oxidation process. Then, the trends of temperature variations in LAMill are obtained through a parametric study. The key parameters such as laser power, laser beam diameter, feed rate, and preheat time are highlighted. At last, the surface quality of the machined workpieces under different operating temperatures is evaluated in terms of edge chipping, surface finish, and surface residual stress. It is shown that high operating temperature leads to low cutting force, good surface finish, small edge chipping, and low residual stress. In addition, the temperature range for brittle-to-ductile transition should be avoided since the cutting force decreases slowly due to the rapid increase of fracture toughness.     

Effect of process parameters on the cutting quality in lasox cutting of mild steel

Samples of mild steel have been cut on a CO₂ laser machine using the principle of laser assisted oxygen cutting (LASOX). The combined effects of input process parameters (cutting speed, gas pressure, laser power and stand off distance) on cut quality (heat affected zone (HAZ) width, kerf width and surface roughness) have been studied. Regression analysis has been used to develop models that describe the effect of the independent process parameters on cut quality. Using the developed model, we attempted to optimize the input parameters that would improve the cut quality (minimization of HAZ width, kerf width and surface roughness), increase the productivity and minimize the total operation cost. We found from the study that the gas pressure and cutting speed had pronounced effect on cut quality. Low gas pressure produces lower HAZ width, lower kerf width and good surface finish whereas increase in speed results in higher HAZ width, lower kerf width and good surface finish.     

基于图像识别的激光切割质量分析

为了准确量化激光切割过程中出现的烧蚀缺陷,提出了基于改进的形态学缺陷提取算法与基于霍夫变换的缺陷测量相结合的方法。改进的形态学提取算法用于缺陷位置的检测和提取,霍夫变换用于缺陷尺寸计算,该方法可以准确提取并测量出切割缺陷尺寸和面积特征。以不同工艺参数下切割产品烧蚀区域宽度和面积为激光切割质量评价指标,研究了切割速度和氧气压力对切割质量的影响。当氧气压力在1.0 MPa范围内,顺时针切割时烧蚀区域宽度和面积呈现出相同的变化规律,逆时针切割时烧蚀区域宽度和面积呈现相反的变化规律。顺时针切割时,切割质量最佳,最小烧蚀宽度为9 px,最小烧蚀区域面积为34 px²。实验结果表明,所提出的方法能够快速识别出激光切割产品缺陷特征,准确评价激光切割质量。     

基于Nd: YAG固体激光器预制连杆初始裂解槽研究

裂解槽的设计与加工是连杆裂解加工技术的核心和技术关键,将直接影响着连杆的裂解质量。为提高连杆裂解槽加工质量,采用Nd：YAG固体激光器对两种类型的连杆进行了裂解槽激光加工试验,分析了不同切割参数对裂解槽质量的影响,并对激光切割参数进行了优化。结果表明：激光峰值功率、离焦量、切割速度、脉冲频率、辅助气体压力、激光入射角等对裂解槽的加工质量都有很大的影响,其中激光峰值功率直接影响着裂解槽的加工深度,在切割速度与脉冲频率比值约为1：3以及非正离焦量状态下所加工的裂解槽对连杆的裂解都非常有利。     

FUZZY EXPERT SYSTEM FOR PREDICTION OF KERF QUALITIES IN PULSED LASER CUTTING OF TITANIUM ALLOY SHEET

Laser cutting is an advanced thermal cutting process of complex nature. It's process behavior drastically changes with slight variation in processing conditions. The prediction of process performance becomes more difficult if cutting materials have non-favorable optical and thermal properties. Titanium (Ti) alloys are characterized by their low thermal conductivity and high chemical reactivity at elevated temperature and hence difficult to cut by laser. It has been found that complex and nonlinear behavior of manufacturing process can better be dealt with the application of artificial intelligence (AI) tools. The aim of present research is to develop a fuzzy expert system for prediction of the laser cutting process behavior of Ti alloy (Ti-6Al-4 V) sheet. A hybrid approach of neural network and fuzzy logic theory has been applied to develop the fuzzy expert system to predict the kerf widths and kerf deviation. The predicted results have been compared with the experimental data and found appropriate. The effects of significant process parameters on the different quality characteristics such as kerf widths and kerf deviation have been discussed.     

Constitutive modeling for Ti-6Al-4V alloy machining based on the SHPB tests and simulation

A constitutive model is critical for the prediction accuracy of a metal cutting simulation. The highest strain rate involved in the cutting process can be in the range of 10~4–10~6 s~(–1). Flow stresses at high strain rates are close to that of cutting are difficult to test via experiments. Split Hopkinson compression bar(SHPB) technology is used to study the deformation behavior of Ti-6Al-4V alloy at strain rates of 10~(–4)–10~4s~(–1). The Johnson Cook(JC) model was applied to characterize the flow stresses of the SHPB tests at various conditions. The parameters of the JC model are optimized by using a genetic algorithm technology. The JC plastic model and the energy density-based ductile failure criteria are adopted in the proposed SHPB finite element simulation model. The simulated flow stresses and the failure characteristics, such as the cracks along the adiabatic shear bands agree well with the experimental results. Afterwards, the SHPB simulation is used to simulate higher strain rate(approximately 3×10~4 s~(–1)) conditions by minimizing the size of the specimen. The JC model parameters covering higher strain rate conditions which are close to the deformation condition in cutting were calculated based on the flow stresses obtained by using the SHPB tests(10~(–4)–10~4 s~(–1)) and simulation(up to 3×10~4 s~(–1)). The cutting simulation using the constitutive parameters is validated by the measured forces and chip morphology. The constitutive model and parameters for high strain rate conditions that are identical to those of cutting were obtained based on the SHPB tests and simulation.