Modeling and optimization of kerf taper and surface roughness in laser cutting of titanium alloy sheet

Laser cutting of titanium and its alloys is difficult due to it’s poor thermal conductivity and chemical reactivity at elevated temperatures. But demand of these materials in different advanced industries such as aircraft, automobile and space research, require accurate geometry with high surface quality. The present research investigates the laser cutting process behavior of titanium alloy sheet (Ti-6Al-4V) with the aim to improve geometrical accuracy and surface quality by minimizing the kerf taper and surface roughness. The data obtained from L₂₇ orthogonal array experiments have been used for developing neural network (NN) based models of kerf taper and surface roughness. A hybrid approach of neural network and genetic algorithm has been proposed and applied for the optimization of different quality characteristics. The optimization results show considerable improvements in both the quality characteristics. The results predicted by NN models are well in agreement with the experimental data.     

Multiple quality optimization in laser cutting of difficult-to-laser-cut material using grey–fuzzy methodology

This paper investigates the laser cutting performance of 1 mm Duralumin sheet with the aim to improve quality of cut by simultaneously optimising multiple performances such as cut edge surface roughness, kerf taper and kerf width. The experimental data obtained by Taguchi methodology-based L₂₇ orthogonal array experimentation have been used in the hybrid approach optimization of grey relational analysis and fuzzy logic theory. The predicted optimum results have been verified by conducting confirmation experiments. The verification results show an overall improvement of 19 % in multiple quality characteristics. The effects of significant factors on quality characteristics have also been discussed.     

RESPONSE SURFACE ANALYSIS OF SLICING OF SILICON INGOTS WITH FOCUS ON PHOTOVOLTAIC APPLICATION

Polycrystalline silicon wafers are widely used in Photovoltaic (PV) industry as a base material for the solar cells. The existing silicon ingot slicing methods typically provide minimum wafer thickness of 300–350 μm and a surface finish of 3–5 μm R_a while incurring considerable kerf loss of 35–40%. Consequently, efficient dicing methods need to be developed, and in the quest for developing new processes for silicon ingot slicing, the wire-EDM (electric discharge machining) is emerging as a potential process. Slicing of a 3′′ square silicon ingot into wafers of 500 μm in thickness has been performed to study the process capability. This article analyzes the effect of processing parameters on the cutting process. The objective of the experimental study is improvement in slicing speed, minimization of kerf loss and surface roughness. A central composite design-based response surface methodology (RSM) has been used to study the slicing of polycrystalline silicon ingot via wire-EDM. A zinc-coated brass wire, 100 μm in diameter, has been used as an electrode in the slicing experiments. It has been observed that the optimal selection of the process parameters results in an increase of 40–50% in the slicing rate along with a 20% reduction in the kerf loss as compared to the conventional methods. The machined surfaces on the sliced wafer were free of micro-cracks and wire material contamination, thereby making it useful for electronic applications.     

Parametric optimization for surface roughness, kerf and MRR in wire electrical discharge machining (WEDM) using Taguchi design of experiment

This paper reports the effect and optimization of eight control factors on material removal rate (MRR), surface roughness and kerf in wire electrical discharge machining (WEDM) process for tool steel D2. The experimentation is performed under different cutting conditions of wire feed velocity, dielectric pressure, pulse on-time, pulse off-time, open voltage, wire tension and servo voltage by varying the material thickness. Taguchi’s L18 orthogonal array is employed for experimental design. Analysis of variance (ANOVA) and signal-tonoise (S/N) ratio are used as statistical analyses to identify the significant control factors and to achieve optimum levels respectively. Additionally, linear regression and additive models are developed for surface roughness, kerf and material removal rate (MRR). Results of the confirmatory experiments are found to be in good agreement with those predicted. It has been found that pulse on-time is the most significant factor affecting the surface roughness, kerf and material removal rate.     

Application of Taguchi and response surface methodologies for surface roughness in machining glass fiber reinforced plastics by PCD tooling

This paper discusses the use of Taguchi and response surface methodologies for minimizing the surface roughness in machining glass fiber reinforced (GFRP) plastics with a polycrystalline diamond (PCD) tool. The experiments have been conducted using Taguchi’s experimental design technique. The cutting parameters used are cutting speed, feed and depth of cut. The effect of cutting parameters on surface roughness is evaluated and the optimum cutting condition for minimizing the surface roughness is determined. A second-order model has been established between the cutting parameters and surface roughness using response surface methodology. The experimental results reveal that the most significant machining parameter for surface roughness is feed followed by cutting speed. The predicted values and measured values are fairly close, which indicates that the developed model can be effectively used to predict the surface roughness in the machining of GFRP composites. The predicted values are confirmed by using validation experiments.     

Performance Analysis of Wire Electrodes on Machining Ti-6Al-4V Alloy using Electrical Discharge Machining Process

High-strength materials with complex shapes can be easily machined by electrical discharge machining process. In the present study, an attempt has been made to analyze the influence of wire electrode on Kerf width and workpiece surface roughness in wire EDM process. Due to its importance in the aircrafts and automobiles, Ti-6Al-4V alloy has been chosen as the workpiece material. The various experiments have been conducted based on a Taguchi L₉ orthogonal array with various types of wire electrodes, such as conventional brass wire, zinc-coated wire and diffused coated brass wire. From the experimental results, it has been observed that diffused coated wire produced better surface finish with minimum kerf width compared to the other two wire electrodes. It has also been observed that the pulse off-time has more influent nature on machining characteristics such as surface roughness and kerf width.     

磨料水射流二次逆向切割对断面质量的提升研究

针对磨料水射流切割过程中存在的拖尾余纹、切缝锥度和切割留尾问题，基于磨料水射流切割理论，设计了3组不同因素组合下的单次正向切割、单次1/2速度正向切割和二次逆向切割试验，探讨了3种不同切割方式下的断面形貌产生机理，并对试验结果进行对比分析。结果表明，二次逆向切割可降低表面粗糙度约52%~85%，可降低切缝锥度约66%~72%，同时可消除切割留尾。因此，高压磨料水射流采用二次逆向切割的方式可以显著提高磨料水射流切割工件的断面质量。     

Abrasive water and slurry jet micro-machining techniques for fabrication of molds containing raised free-standing micro-features

The demand for metallic micro-molds that can be used for inexpensive mass production of polymeric microfluidic chips is increasing. Existing manufacturing techniques such as soft-lithography and photolithography can require multiple time-consuming steps, especially when the aim is to create three-dimensional features. In this study, the feasibility of using abrasive water jet machining (AWJM) and abrasive slurry jet machining (ASJM) to fabricate such micro-molds in Al6061-T6 and SS316 was studied. Jet raster scans under various combinations of process parameters were used in order to machine micro-pockets containing free-standing structures, representing molds for casting microfluidic chips with channel networks. As expected, for both materials and using both ASJM and AWJM, the pocket roughness decreased as the distance between adjacent raster scans (step size) decreased, but the lowest waviness occurred at an intermediate step size. The best quality pockets were achieved on SS316 using ASJM with the intermediate step size and the highest possible slurry mass flow rate. Unmasked machining could not be used to fabricate molds with sharp-edged intersecting features, and a novel hybrid AWJM/ASJM masked machining technique was thus introduced. An undercut and an undesirable erosion near the edges of the mask formed if the position of the last raster scan closest to the mask was not carefully controlled. Possible reasons for these phenomena were discussed in terms of the likelihood of jet deflection off the machining kerf and mask, and the resulting erosion due to secondary slurry flow. By careful selection of the process parameters, it was demonstrated that high quality molds with both single and intersecting free-standing structures at multiple heights could be fabricated, thus making three-dimensional microfluidic chip mold fabrication feasible.     

Integration of Response Surface Methodology with Genetic Algorithms

Response surface methodology (RSM) is a methodology that combines experimental designs and statistical techniques, for empirical model building and optimisation. By conducting experiments and applying regression analysis, RSM seeks to relate a response to some input variables. This work aims at integrating response surface methodology with genetic algorithms (GAs) to realise a GA-based prototype system for the determination of near optimal values in response surface designs. A framework of the prototype system is presented. The prototype system was validated using three case studies of a bonding process that involve solving the Himmelblau function, optimising the mean pull strength, and maximising both the mean pull strength and the minimum strength simul-taneously. The results were compared with those obtained by the Design Expert, which is a commercial software package. Details of the case studies as well as the comparative studies are presented.This revised version with a corrected online cover date was published online in April 2004.     

A study on the use of single mesh size abrasives in abrasive waterjet machining

This paper details the studies on the use of single mesh size garnet abrasives in abrasive waterjet machining for cutting aluminum. The influence of three different single mesh size abrasives, pressure, traverse rate, and abrasive flow rate; on depth of cut, top kerf width, bottom kerf width, kerf taper, and surface roughness are investigated. Experiments designed using standard L9 orthogonal array and the analysis of variance helped in the determination of highly significant, significant and weakly significant cutting parameters. Single mesh size abrasives are found to yield decreased surface roughness than multi mesh size abrasives. Based on these studies, response equations are developed to predict the target parameters. Using single mesh abrasives, a practitioner not only can cut faster but also achieve reduced surface roughness.     

Improved solutions for job shop scheduling problems through genetic algorithm with a different method of schedule deduction

This paper details the studies on the use of single mesh size garnet abrasives in abrasive waterjet machining for cutting aluminum. The influence of three different single mesh size abrasives, pressure, traverse rate, and abrasive flow rate; on depth of cut, top kerf width, bottom kerf width, kerf taper, and surface roughness are investigated. Experiments designed using standard L9 orthogonal array and the analysis of variance helped in the determination of highly significant, significant and weakly significant cutting parameters. Single mesh size abrasives are found to yield decreased surface roughness than multi mesh size abrasives. Based on these studies, response equations are developed to predict the target parameters. Using single mesh abrasives, a practitioner not only can cut faster but also achieve reduced surface roughness.     

Optimisation of springback in bending processes using FEM simulation and response surface method

The aim of this work includes the springback optimisation of bending processes using the concept of experimental design and response surface methodology (RSM). The optimisation method includes two phases. The first involves the objective function prediction using design of experiments and response surface method, while the second is an optimisation process using a FORTRAN gradient algorithm. Springback of sheet parts during bending processes is simulated using finite element model (FEM) including damage evolution effects within the sheet. The numerical simulation of the damage evolution has been modelled by means of continuum damage approach. The Lemaitre damage model, taking into account the influence of triaxiality, has been implemented into ABAQUS/Standard code in order to predict the external fibres rupture evolution during the process and the material characteristics changes after bending. The simulation included die corner radius and punch-die clearance as the main variables.     

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.     

Finite element analysis of laser inert gas cutting on Inconel 718

Inconel 718 has high strength, which makes it difficult to cut using conventional cutting methods. In the present study, the laser inert gas cutting of Inconel 718 was simulated by finite element analysis software ANSYS. Finite element method was used to predict thermal stress and kerf width formation during the laser cutting process. ANSYS Parameter Design Language was used to model the Gaussian-distributed heat flux from the laser beam acting on the workpiece. The removal of melted material during laser cutting to form the kerf width was modeled by employing the element death methodology in ANSYS. In addition, laser cutting was simulated at continuous wave (CW) and the effects of laser power and cutting speed on kerf width were investigated. A series of experiments were carried out to verify the predictions. The temperature fields on the workpiece were measured using thermocouples. The kerf width size was measured using a profile projector, whereas the metallurgical and morphological changes at the cutting edge were examined using scanning electron microscopy. A good correlation was found between the simulation and experimental results.     

Application of the central composite design in optimization of machining parameters in drilling hybrid metal matrix composites

In this study, the application of response surface methodology (RSM) and central composite design (CCD) for modeling, optimization, and an analysis of the influences of dominant machining parameters on thrust force, surface roughness and burr height in the drilling of hybrid metal matrix composites produced through stir casting route. Experiments are carried out using Al 356-aluminum alloy reinforced with silicon carbide of size 25 μm and Mica of size 45 μm. Drilling test is carried out using carbide drill of 6 mm diameter. The design of experiment concept has been used to optimize the experimental conditions. The experimental data are collected based on a three-factor-three-level full central composite design. The multiple regression analysis using RSM is used to establish the input–output relationships of the process. The mathematical models are developed and tested for adequacy using analysis of variance and other adequacy measures using the developed models. The main and interaction effect of the input variables on the predicted responses are investigated. The predicted values and measured values are fairly close, which indicate that the developed models can be effectively used to predict the responses in the drilling of hybrid metal matrix composites. The optimized drilling process parameters have been obtained by numerical optimization using RSM by ensuring the minimum thrust force of 84 N, surface roughness of 1.67 μm, and the burr height of 0.16 mm. After the drilling experiments, a scanning electron microscope (SEM) is used to investigate the machined surface and tool wear.     

Soft computing models based prediction of cutting speed and surface roughness in wire electro-discharge machining of tungsten carbide cobalt composite

This paper reports on an experimental investigation of small deep hole drilling of Inconel 718 using the EDM process. The parameters such as peak current, pulse on-time, duty factor and electrode speed were chosen to study the machining characteristics. An electrolytic copper tube of 3 mm diameter was selected as a tool electrode. The experiments were planned using central composite design (CCD) procedure. The output responses measured were material removal rate (MRR) and depth averaged surface roughness (DASR). Mathematical models were derived for the above responses using response surface methodology (RSM). The results revealed that MRR is more influenced by peak current, duty factor and electrode rotation, whereas DASR is strongly influenced by peak current and pulse on-time. Finally, the parameters were optimized for maximum MRR with the desired surface roughness value using desirability function approach.     

不锈钢板的CO2激光切割工艺研究

实验用CO2激光切割厚0.8mm的1Cr18Ni9Ti不锈钢板。研究了激光功率、辅助气体类型及压力、切割速度对切割质量的影响。实验显示提高切割速度能降低切缝宽度和切口横截面的表面粗糙度;而提高激光功率和氧气压力,切缝宽度也会随之提高,切口横截面更粗糙。功率650~700W、氧气压力0.3~0.5MPa、切割速度3.5~4.5m/min时切割质量最好。另外发现功率在780~1450W,氮气压力低于0.8MPa不能得到良好的切割质量。     

Modeling and experimental study on breakdown voltage (BV) in low speed wire electrical discharge machining (LS-WEDM) of Ti-6Al-4V

In this study, the breakdown voltage behavior in low speed wire electrical discharge machining (LS-WEDM) of Ti-6Al-4V (TC4) in the deionized water is investigated. Firstly, the electric field distortion caused by impurity particles including TC4 or brass metal and bubbles is investigated. And then the breakdown voltage model of TC4 machined by LS-WEDM is established and the experimental verification result indicates that the model predicting results conforms to the actual processing and could be well follow experimental results. Second, the influence of breakdown voltage on surface roughness and kerf width has been revealed, it can be found that the kerf width decreases, and the surface roughness increases as breakdown voltage increased. Besides, the voids become bigger and the surface cracks become deeper and wider with the breakdown voltage increased based on analysis of experiment results but for microcracks distributed on spherical or irregular attachments are not influenced by breakdown voltage due to their randomness. Meanwhile, the transparent bubbles of diameter of 400 nm can be observed near the droplet on the machined surface and its major composing element is oxygen. Finally, internal voids can be found in the joint of deterioration layer and the substrate which will make the combination of deterioration layer and the substrate not strong and easy to fall off.     

Optimization of abrasive flow polishing process parameters for static blade ring based on response surface methodology

Static blade ring process technology is a key part for gas turbine manufacturing, and the surface quality of the static blade ring has great influence on a gas turbine. To improve surface roughness of static blade ring, abrasive flow polishing process technology is studied. First, the range of extrusion pressure is obtained by using ANSYS software to analyze the blade deformation. Then a simplified model of surface roughness is estabalished according to experimental results and ANOVA’s results. At the same time, the optimal polishing parameters are confirmed through the response surface methodology. Finally, the polishing experiment is carried out by using the optimal polishing parameters. The experimental results demonstrate that the surface roughness of static blade ring decreased greatly (nearly 14.7%) compared with result using normal parameters.     

Measurement and analysis of surface roughness in turning of aerospace titanium alloy (gr5)

Titanium alloys are extensively used in aerospace, biomedical applications and they are used in corrosive environments. In this study, the effect of cutting parameters on the surface roughness in turning of titanium alloy has been investigated using response surface methodology. The experimental studies were conducted under varying cutting speeds, feed and depths of cut. The chip formation and SEM analysis are discussed to enhance the supportive surface quality achieved in turning. The work material used for the present investigation is commercial aerospace titanium alloy (gr5) and the tool used is RCMT 10T300 – MT TT3500 round insert. The equation developed using response surface methodology is used for predicting the surface roughness in machining of titanium alloy. The results revealed that the feed was the most influential factor which affect the surface roughness.