Kerf characteristics in abrasive waterjet cutting of ceramic materials

An abrasive water jet (AWJ) can provide a more effective means for precision cutting of ceramic materials as compared with conventional machining methods, but many aspects about this cutting technology are still under flux and development. In this study, experimental techniques based on statistical experimental design principles and theoretical investigations were conducted to study AWJ cutting of alumina-based ceramics. Semi-empirical cutting depth equations are determined for the prediction and optimization of the AWJ cutting performance. Topographical characteristics of uncut-through kerf and the effects of various parameters are discussed. In addition, visualization studies are conducted to develop further understanding of the macromechanics of the AWJ cutting process.     

Abrasive waterjet cutting of a titanium alloy: The influence of abrasive morphology and mechanical properties on workpiece grit embedment and cut quality

Abrasive waterjet cutting of material involves the impingement of a high velocity jet of water with entrained abrasive particles (commonly 80 mesh garnet) onto the material to be cut. Embedment of abrasive is known to occur both on the cut-face and on the surface perpendicular to the cut-face where (due to jet divergence) the jet has impinged but not cut through; this grit embedment is a known disadvantage of the process. In this paper, the cut quality and abrasive embedment following waterjet cutting of a commonly used titanium alloy, Ti6Al4V with 80 mesh garnet from five different sources (differing significantly in their hardness, crushing strength and morphology) were examined and evaluated. The cut-face itself was examined to establish the presence or absence of sub-surface embedded abrasive; in addition, the top surface of the plate close to the cut where particles outside the main core of the jet may have impinged was also examined. Embedment levels, surface waviness and roughness and the mechanisms of abrasive–surface interactions were evaluated through a combination of scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and profilometry. It was found that despite the differences in abrasive characteristics, no significant differences in cut quality or abrasive embedment was seen. It was shown that the forces on individual particles during impact can be estimated to be orders of magnitude greater than their crushing load. As such, it is proposed that the majority of abrasive particles will fracture in abrasive waterjetting, and thus any differences in the original abrasive particle morphologies do not dominate behaviour since it is the morphology of the fragments of these fractured particles which control embedment and cut quality.     

Modeling of the influence of the abrasive waterjet cutting parameters on the depth of cut based on fuzzy rules

Currently, the abrasive waterjet cutting parameters for the milling operation have to be determined by a combination of prior experience and trial and error. It is shown that the selection of the abrasive waterjet cutting parameters for a required depth of cut in the given material can be effectively done by applying the principles of the fuzzy set theory. This approach will eliminate the need for extensive experimental work in order to select the magnitudes of the most influential abrasive waterjet parameters on the depth of cut. Fuzzy logic provides a methodology and imitation of a human's way of making decisions which is very useful in such applications where the mathematical model of the process does not exist, and one of such processes is indeed abrasive waterjet cutting. A number of case studies are performed to verify the validity of the proposed methodology for selecting the abrasive waterjet cutting parameters in order to achieve the predetermined depth of cut.     

Material removal analysis in abrasive waterjet cutting of ceramic plates

Fine ceramics have been recognized increasingly in structural and functional applications on account of their merits of hardness, corrosion resistance, electromagnetic response and bio-compatibility. Due to the need for dimensional control or production optimization, post-sintering machining can be required. Cutting by conventional means is most often practiced, but the associated heavy tool wear is hard to overcome. A waterjet at transonic speed carrying abrasive particles provides an effective means for hard-material removal. Undesired material fracture at entrance and exit can be reduced significantly by sequential abrasive micro-machining.

The present paper discusses the kerf formation of a ceramic plate cut by an abrasive waterjet. The mechanism and the effectiveness of material removal are studied first. Different materials are found to possess different removal rates in machining and there also exists a critical combination of hydraulic pressure, abrasive flow rate and traverse speed, below which through-cut for a certain thickness cannot be achieved. The wall finish achieved is determined by the mesh size of the abrasives: sufficient hydraulic pressure with fine abrasives will produce a smooth surface comparable to that from grinding. The kerf is slightly tapered with wider entry due to decreased cutting energy with kerf depth. A high-power input per unit length produces a small taper but a wide slot.     

An investigation on kerf characteristics in abrasive waterjet cutting of layered composites

Layered composites are “difficult-to-machine” materials as it is inhomogeneous due to the matrix properties, fibre orientation, and relative volume fraction of matrix. Abrasive waterjet cutting has proven to be a viable technique to machine such materials compared to conventional machining. This paper presents an investigation on the kerf taper angle, an important cutting performance measure, generated by abrasive waterjet (AWJ) technique to machine two types of composites: epoxy pre-impregnated graphite woven fabric and glass epoxy. Comprehensive factorial design of experiments was carried out in varying the traverse speed, abrasive flow rate, standoff distance and water pressure. Using the dimensional technique and adopting the energy conservation approach, the kerf taper angle has been related to the operating parameters in a form of a predictive model. Verification of the model for using it as a practical guideline has been found to agree with the experiments.     

A study of abrasive waterjet cutting of metallic coated sheet steels

A study of Abrasive Waterjet (AWJ) cutting of metallic coated sheet steels is presented based on a statistically designed experiment. It shows that AWJ cutting is a viable technology for processing metallic coated sheet steels with good productivity and kerf quality. A scanning electron microscopy analysis indicates that micromachining and plastic deformation are the dominant cutting phenomena in sheet steel processing. Plausible trends and relationships between kerf characteristics and process parameters are discussed. It is found that an optimum water pressure together with small standoff distance between the nozzle and workpiece may be used, while the traverse speed should be selected as high as possible for through cuts in order to increase the cutting rate. Empirical models for kerf geometry and quality are finally established for the prediction and optimization of AWJ cutting performance.     

Monitoring the depth of abrasive waterjet penetration

In order to control the uniformity of the abrasive waterjet penetration into the workpiece, it is necessary to devise a monitoring methodology that can indirectly monitor the depth of abrasive waterjet penetration. It was shown that the workpiece normal force generated by an abrasive waterjet could be used as the indicator of the depth of jet penetration, and that a force-feedback control holds promise as an effective way to regulate the depth of jet penetration. The effects of different abrasive waterjet process variables on both the depth of cut and the workpiece normal force are discussed.     

The effect of cutting head vibrations on the surfaces generated by waterjet cutting

After a first period in which the research has been focused on the optimisation of the process parameters, the attention is now focused on aspects that were usually neglected. However, they are very important in order to understand the physics of the waterjet/abrasive waterjet cutting process and to improve the cutting quality.Particularly, it has been demonstrated that, in the pure waterjet cutting (and in the abrasive waterjet cutting too), there are irregularities, called striations, along the generated surface. The striation formation depends mainly on the jet instability caused by vibrations during the cutting process. Vibration signals have been measured whilst varying the cutting conditions. A model has been studied which estimates the mean spacing and the frequency of the striations, as a function of the period and the amplitude of the jet vibration. This model has been completely validated through measurements of plasticine surfaces generated by waterjet cutting.     

Orthogonal cutting mechanisms of graphite/epoxy composite. Part I: unidirectional laminate

An experimental study of orthogonal cutting mechanisms was conducted in the edge trimming of unidirectional Graphite/Epoxy composite with polycrystalline diamond tools. The effects of tool geometry and operating conditions were evaluated from an analysis of chip formation, cutting force and machined surface topography. All aspects of material removal were found to be primarily dependent on the fibre orientation. Discontinuous chip formation was noted throughout this study, regardless of trimming parameters. Chip dimensions and force measurements depicted a change in chip formation with fibre orientation, and the presence of three distinct mechanisms in the edge trimming of fiber reinforced composite material. A combination of cutting, shearing and fracture along the fibre/matrix interface was observed.     

Orthogonal cutting mechanisms of graphite/epoxy composite. Part II: multi-directional laminate

Orthogonal cutting mechanisms in the edge trimming of Graphite/Epoxy laminate with polycrystalline diamond tools were studied. Chip formation, cutting force, and surface morphology were evaluated with respect to tool geometry, process conditions, and ply distribution in the laminate. As with the trimming of unidirectional panels, discontinuous chips were observed with primary dependence on fibre orientation. Cutting mechanisms for 0° and 45° plies were identical to those in the trimming of unidirectional material. However, chip formation mechanisms in trimming 90° and −45° plies of the multi-directional laminate changed due to the support provided by adjacent plies. Empirical cutting force models for principal and thrust force components were constructed by factorial design and regression methods.     

Effect of liquid properties on the stability of an abrasive waterjet

The effect of liquid properties after adding polymeric additives on the stability of an abrasive slurry (or suspension) jet (ASJ) is presented and discussed with a view to enhance the jet stability for ASJ machining. It is shown that jet disintegration is a result of the jet internal disturbances associated with the fluid properties and the external air friction acting upon the jet surface. A jet becomes more stable with the addition of polymeric additives, which is found to be mainly attributed to the increase of fluid viscosity. By contrast, the surrounding air friction with the jet results in the jet to disintegrate, and this external effect increases with an increase in the jet velocity. Based on the findings of the experimental investigation, a parametric model is then developed using a dimensional analysis approach to predict the jet compact length, i.e. the length of the jet stable region. The developed model is finally verified experimentally, which shows that the model predictions are in good agreement with the experimental data.     

Experimental method for the investigation of the abrasive water jet cutting quality

The use of the declination angle for a prediction and control of the abrasive water jet cutting quality is presented in the paper. The term declination angle is defined and the method for its measurement is proposed. The relationship between the declination angle and cutting wall quality is explained in the theory resulting from former conclusions of Hashish, Zeng and Kim, Hlavá? and others. Experiments proving the theoretical base were performed. The values of the limit traverse speeds predicted from the theoretical equations were compared with values experimentally determined on selected samples. The data calculated from the theoretical models predicting the appearance of the striations on the cutting walls by cutting head tilting are compared with experiments as well.     

Experiments and computer simulation analysis of impact behaviors of micro-sized abrasive in waterjet cutting of thin multiple layered materials

The abrasive waterjet (AWJ) is now widely used in the advanced cutting processes of polymers,metals,glass,ceramics and composite materials like thin multiple-layered material (TMM).Various research and development efforts have recently been made to understand the science of AWJ.However,the interaction mechanism between a workpiece and high-velocity abrasive particles still remains a complicated problem.In this work,the material removal mechanisms of AWJ such as micro penetration and micro dent were experimentally investigated.In addition,a new computer simulation model considering high strain rate effect was proposed to understand the micro impact behavior of high-velocity micro-sized abrasives in AWJ cutting.     

A study on surface roughness in abrasive waterjet machining process using artificial neural networks and regression analysis method

In the present study, artificial neural network (ANN) and regression model were developed to predict surface roughness in abrasive waterjet machining (AWJ) process. In the development of predictive models, machining parameters of traverse speed, waterjet pressure, standoff distance, abrasive grit size and abrasive flow rate were considered as model variables. For this purpose, Taguchi's design of experiments was carried out in order to collect surface roughness values. A feed forward neural network based on back propagation was made up of 13 input neurons, 22 hidden neurons and one output neuron. The 13 sets of data were randomly selected from orthogonal array for training and residuals were used to check the performance. Analysis of variance (ANOVA) and F-test were used to check the validity of regression model and to determine the significant parameter affecting the surface roughness. The statistical analysis showed that the waterjet pressure was an utmost parameter on surface roughness. The microstructures of machined surfaces were also studied by scanning electron microscopy (SEM). The SEM investigations revealed that AWJ machining produced three distinct zones along the cut surface of AA 7075 aluminium alloy and surface striations and waviness were increased significantly with jet pressure.     

The effect of cutting jet variation on striation formation in abrasive water jet cutting

Abrasive water jet machining is an emerging technology which can shape almost all engineering materials, but it also produces a characteristic striated surface finish which limits its potential applications. In this study, the characterisation of different materials' cut surfaces is investigated using a scanning electron microscope. The effect of abrasive particle distribution in the jet on striation formation is detailed. A non-invasive technique, Laser Doppler Anemometry, is used to analyse the abrasive particle distribution in the jet. Furthermore, the mechanisms of striation formation are discussed in detail and an effective striation minimisation technique applied to the cutting process is outlined.     

冲裁断面质量优化研究进展

从冲裁过程考虑单一工艺参数对冲裁断面质量的影响与优化方法及工艺参数间的耦合作用,提出冲裁工艺参数组合优化方法,并介绍其步骤及特点,对其优劣进行比较,但目前研究方法仍有不足,需要向数值模拟与人工智能相结合的方向发展,寻求更合适的优化模型,获得更光滑平整的冲裁断面。     

基于单颗磨粒切削的CBN铰珩工具磨粒磨损研究

采用单颗磨粒试验方法,以4Cr13不锈钢为修整材料,研究大长径比CBN铰珩工具修整过程中的磨粒磨损特性。试验结果显示:与普通切削相比,超声切削时的平均切削力降低60%～80%,但磨粒在短时间内大块破碎,磨削比严重下降。超声切削时的磨粒?工件接触比在0.6～0.8,磨粒主要处于断续切削过程,其最大切削宽度比普通切削时的增加2.7倍,且磨粒受到的最大瞬时切削力增加。根据点云信息对磨粒进行逆向建模,并对建立的单颗磨粒切削仿真模型的瞬时切削力进行定量分析。仿真结果显示:超声切削时的最大切向力比普通切削时的增加20%以上,且力的波动幅度超过80%。      

冲裁间隙变化对冲裁件断面质量影响的力学分析

分析了冲裁过程中断面光亮带、断裂带、圆角和毛刺形成阶段,运用塑性增量理论、应力莫尔圆方法和粘着磨损法则,来分析影响光亮带和断裂带、圆角和毛刺形成的力学因素,得出确定模具合理间隙值是获得高质量冲裁件的关键因素。     

A study of abrasive water jet machining process on glass/epoxy composite laminate

Surface roughness (R_a) and kerf taper ratio (T_R) characteristics of an abrasive water jet machined surfaces of glass/epoxy composite laminate were studied. Taguchi's design of experiments and analysis of variance were used to determine the effect of machining parameters on R_a and T_R. Hydraulic pressure and type of abrasive materials were considered as the most significant control factor in influencing R_a and T_R, respectively. Due to hardness of aluminium oxide type of abrasive materials, it performs better than garnet in terms of both machining characteristics. Increasing the hydraulic pressure and abrasive mass flow rate may result in a better machining performance for both criteria. Meanwhile, decreasing the standoff distance and traverse rate may improve both criteria of machining performance. Cutting orientation does not influence the machining performance in both cases. So, it was confirmed that increasing the kinetic energy of abrasive water jet machining (AWJM) process may produce a better quality of cuts.