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.     

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.     

Experimental study on abrasive waterjet polishing for hard–brittle materials

The rapid growth of hard–brittle materials necessitates the development of compatible machining techniques, especially for the precision machining. The abrasive waterjet (AWJ) machining is a powerful tool in processing hard–brittle materials. In the last decades, some of AWJ machining technologies, such as AWJ cutting, AWJ milling and AWJ drilling have gradually become mature and steady. However, a few investigations on precision surface machining for hard–brittle materials by AWJ had been carried out. In this research, the ductile erosion mechanism of hard–brittle materials by AWJ in small erosion angle has been analyzed. In theory, the ductile erosion can achieve micromaterial removal and the surface eroded is smooth and without any fracture. Based on the ductile erosion mechanism, the feasibility of polishing for hard–brittle materials by the AWJ has been investigated. A group of polishing experiments is performed. The polished surfaces of workpieces were observed with scanning electron microscope (SEM) and measured by atomic force microscopy (AFM). The results of these polishing experiments indicate that AWJ has a great potential to be used as a precision surface machining technology.     

A two-fluid model of abrasive waterjet

Waterjet flow added with abrasive solid particles, the so called abrasive waterjet, can enhance its performance for cutting various materials from soft food products to very hard titanium alloys. In this study, a theoretical analysis is conducted in order to develop a flow model for the abrasive waterjet. The main concern is whether the abrasive particles can be treated as a pseudo-fluid phase. A two-fluid model is developed based on the fundamental laws of conservation. A control volume method is used to discretize the equations, and a phase-coupled SIMPLE algorithm is adopted to solve the pressure–velocity coupling equations. The quasi two-dimensional flow field outside a conventional nozzle used in abrasive waterjet is analyzed and computed to validate the model. Good agreement is observed comparing the numerical results with the experimental measurements.     

The influence of abrasive waterjet cutting conditions on the surface quality of graphite/epoxy laminates

An experimental investigation was conducted to determine the influence of cutting parameters on the surface roughness and kerf taper of an abrasive waterjet machined graphite/epoxy laminate. Experimental design was used to systematically measure the influence of cutting parameters on the surface roughness and kerf taper of laminate specimens. Stylus prolifometry was used to measure the surface roughness and a visual inspection including scanning electron microscopy (SEM) was conducted. Profilometry measurements supplemented with microscopy analysis suggests that three regions of surface topography are evident on the machined surface of the laminate specimens. ANOVA techniques indicate that the influence of cutting parameters on the surface roughness changes as a function of cutting depth. Mathematical models were developed to predict the surface roughness and kerf taper in terms of the cutting parameters of a graphite/epoxy laminate to cutting depths of 16 mm.     

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.     

Modelling the abrasive flow machining process on advanced ceramic materials

Abrasive flow machining (AFM) is a unique machining method used to achieve high surface quality on inner, difficult-to-access and on outside contours. Using AFM, it is possible to realise predefined edge rounding on any brittle or hard material. AFM is easy to integrate in an automated manufacturing environment. The abrasive medium applied during AFM is a fluid consisting of a polymer which carries silicon carbide or super-abrasive grains. With a specified pressure and temperature, this fluid flows in alternating directions along the contours of the workpiece resulting in an abrasive effect. AFM is also well suited to process advanced ceramic materials. Especially advanced ceramics are playing increasingly a significant role as a substitute for metals. However the high costs for the inevitable finishing process on ceramics prevent a more frequent use. This paper represents the technological results of a research-project discovering the fundamental principles of AFM on advanced ceramic materials such as a correlation between flow processes, surface formation and edge rounding. Furthermore an insight into a process model is given, which was developed using modern simulation techniques. The overall objective of this approach is to anticipate work results like surface quality and edge rounding on any user-defined geometry.     

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.     

Deformation work in abrasive cutting

In order to investigate the complicated behavior of material beneath the groove formed by abrasive grain cutting, and single grit cutting test was performed with a modified cutting tool which was determined statistically. In the experiment a conical tool having an apex angle of 90° –160° was used. To observe the deformed zone beneath the groove, the cross section of the work material beneath the groove was obtained by using a micro-cutter.Then the hardness of the deformed zone was measured in three directions, i.e. at the surface, at the cross section along the cutting direction and at the cross section perpendicular to the cutting direction.Besides, a compression test was performed and taking the relations between stress-strain and strain-hardness into consideration, the deformation work beneath the groove was obtained. Then the deformation work was compared with the total work necessary to form a groove which was calculated from cutting force.As a result it was found that there were two types of deformed zone, i.e. cutting type and compression type as well as in the case of indentation test. The ratio of deformation work to the total work expended in forming a groove with conical tool depends on the apex angle of the tool and the ratio reaches 0.2–0.7 in this experiment.     

Stochastic modelling of abrasive waterjet footprints using finite element analysis

The proposal of erosion models to predict the jet footprint during abrasive waterjet machining is a key element for the development of this technology, but it is very challenging because of the inherent fluctuations of the process. This issue becomes critical when the size of the cutting systems is reduced, since the relative size of these deviations increases. The present paper considers for the first time a modelling framework capable of predicting the average shape of AWJM footprints and, of great novelty, the variability along the trench, combining finite element analysis and Monte Carlo methods, and verifying the model using different feed speeds and tilt angles. For that purpose, the relevance of each random parameter, such as shape (sharpness), size and relative orientation of the abrasive particles, has been investigated through parametric studies on these variables. Multiple particle simulations with randomly generated input were performed to determine the effect of operating parameters in the overall variability of the jet footprint. The process was simulated using Abaqus 6.14 as multiple garnet particles hitting a target of Ti–6Al–4V at very high velocity, eroding the target by plastic deformation and material removal. The model shows successfully the influence of single particle parameters, such as the shape, on the surface variability. The results for the footprint variability show that stochastic methods are suitable to model these fluctuations, and it is also shown that this approach yields accurate estimates of the average profile after multiple jet passes with error less than 5%.     

Reducing tool wear in abrasive cutting

The abrasive Cut-Off with stationary or hand-operated machines for cutting or grinding metal is still a very common procedure in many enterprises. Because of the relatively low price of the tool ‘cut-off wheel’ little attention is paid to the life-time of the grits. Since it is possible to obtain shape-defined grits for the production of grinding wheels an experimental study was carried out producing and testing such cutting-wheels. It has been shown that it is possible to reduce the wear of the wheel by means of using shape-defined grits. The following paper describes selected experimental studies and their results.     

Experimental analysis of irregularities of metallic surfaces generated by abrasive waterjet

Experimental study of the surface quality produced by abrasive waterjet (AWJ) on metallic materials has been performed. The surface roughness/waviness was quantitatively evaluated by using the contactless optical measurement. In order to characterize the cut surface qualities, a single-parameter criterion has been proposed. Based on root mean square (RMS) roughness evaluation of the worst cut surface zone, the dimensionless statistical parameter C can be calculated as a basic quantity for AWJ surface cut characterization. As it was approved, besides its dependency on depth of AWJ trace, the value of C-parameter for the specific material is noticeably related also to the traverse speed of the cutting head. Such a relationship can be potentially used for adjusting the cutting speed of the machining process.     

固着磨粒切割线研究进展

游离磨粒线锯切割存在污染环境和切割效率低的不足,固着磨粒线锯切割具有切缝小、切片表面质量好、切割速度快和消除工业浪费等优点成为了人们的研究热点。固着磨粒线锯和游离磨粒线锯最主要的区别是切割线,切割线的特性直接影响硅片的切割质量及生产效率。本文阐述了固着磨粒线锯切割的优点,总结了目前几种固着磨粒切割线的制造方法,包括:电镀、电火花、钎焊、树脂、机械碾压和挤压与冲压等,并介绍了固着磨粒切割线的改进方法。     

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.     

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.     

陶瓷刀具在干切削加工中的应用

文章论述了陶瓷刀具的特点和切削性能,对陶瓷刀具在干切削中的使用进行了分析.     

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.