Effect of low-speed waterjet pressure on the rock-breaking performance of unsubmerged cavitating abrasive waterjet

Unsubmerged cavitating abrasive waterjet(UCAWJ)has been shown to artificially create a submerged environment that produces shear cavitation,which effectively enhances rock-breaking performance.The shear cavitation generation and collapse intensity depend on the pressure difference between the intermediate high-speed abrasive waterjet and the coaxial low-speed waterjet.However,the effect of the pressure of the coaxial low-speed waterjet is pending.For this purpose,the effect of low-speed waterjet pressure on rock-breaking performance at different standoff distances was experimentally investigated,and the effects of erosion time and ruby nozzle diameter on erosion performance were discussed.Finally,the micromorphology of the sandstone was observed at different locations.The results show that increased erosion time and ruby nozzle diameter can significantly improve the rock-breaking performance.At different standoff distances,the mass loss increases first and then decreases with the increase of low-speed waterjet pressure,the maximum mass loss is 10.4 g at a low-speed waterjet pressure of0.09 MPa.The surface morphology of cavitation erosion was measured using a 3D profiler,the increase in both erosion depth and surface roughness indicated a significant increase in the intensity of the shear cavitation collapse.At a low-speed waterjet pressure of 0.18 MPa,the cavitation erosion surface depth can reach 600μm with a roughness of 127μm.

Influence of abrasive hardness on erosion wear of abrasive air jets

To make clear the influence of abrasive hardness on the erosion effect,the erosion experiments of abrasive air jet with the same impact energy were carried out.The influence of abrasive hardness on the erosion effect is clarified by comparing the different erosion depths.The main conclusions are as follows.Under the same mass flow rate and mesh number,the abrasive with a higher density needs greater pressure irrespective of hardness.After erosion damage,the abrasive size exhibits a Weibull distribution.The shape parameterβand Weibull distribution function of four types of abrasives are derived by the least squares method;moreover,βis found to have a quadratic relation with abrasive hardness.The results of the erosion experiments show that abrasive hardness and erosion depth are quadratically related.By calculating the increase in surface energy after abrasive erosion crushing,it is found that abrasive hardness has a quadratic relation with surface energy and that the increases in erosion depth and surface energy consumption are basically identical.In conclusion,the effect is a soft abrasive impact when the ratio of abrasive hardness(Ha)to the material hardness(Hm)is<2.6,and it is a hard abrasive impact when Ha/Hm>3.

New Iron-based SiC Spherical Composite Magnetic Abrasive for Magnetic Abrasive Finishing

SiC magnetic abrasive is used to polish surfaces of precise, complex parts which are hard, brittle and highly corrosion-resistant in magnetic abrasive finishing（MAF）. Various techniques are employed to produce this magnetic abrasive, but few can meet production demands because they are usually time-consuming, complex with high cost, and the magnetic abrasives made by these techniques have irregular shape and low bonding strength that result in low processing efficiency and shorter service life. Therefore, an attempt is made by combining gas atomization and rapid solidification to fabricate a new iron-based SiC spherical composite magnetic abrasive. The experimental system to prepare this new magnetic abrasive is constructed according to the characteristics of gas atomization and rapid solidification process and the performance requirements of magnetic abrasive. The new iron-based SiC spherical composite magnetic abrasive is prepared successfully when the machining parameters and the composition proportion of the raw materials are controlled properly. Its morphology, microstructure, phase composition are characterized by scanning electron microscope（SEM） and X-ray diffraction（XRD） analysis. The MAF tests on plate of mold steel S136 are carried out without grinding lubricant to assess the finishing performance and service life of this new SiC magnetic abrasive. The surface roughness（Ra） of the plate worked is rapidly reduced to 0.051 μm from an initial value of 0.372 μm within 5 min. The MAF test is carried on to find that the service life of this new SiC magnetic abrasive reaches to 155 min. The results indicate that this process presented is feasible to prepare the new SiC magnetic abrasive; and compared with previous magnetic abrasives, the new SiC spherical composite magnetic abrasive has excellent finishing performance, high processing efficiency and longer service life. The presented method to fabricate magnetic abrasive through gas atomization and rapid solidification presented can significantly improve the finishing performance and service life of magnetic abrasive, and provide a more practical approach for large-scale industrial production of magnetic abrasive.

Abrasive Waterjet Machining Simulation by Coupling Smoothed Particle Hydrodynamics /Finite Element Method

In dealing with abrasive waterjet machining（AWJM） simulation,most literatures apply finite element method（FEM） to build pure waterjet models or single abrasive particle erosion models.To overcome the mesh distortion caused by large deformation using FEM and to consider the effects of both water and abrasive,the smoothed particle hydrodynamics（SPH） coupled FEM modeling for AWJM simulation is presented,in which the abrasive waterjet is modeled by SPH particles and the target material is modeled by FEM.The two parts interact through contact algorithm.Utilizing this model,abrasive waterjet with high velocity penetrating the target materials is simulated and the mechanism of erosion is depicted.The relationships between the depth of penetration and jet parameters,including water pressure and traverse speed,etc,are analyzed based on the simulation.The simulation results agree well with the existed experimental data.The mixing multi-materials SPH particles,which contain abrasive and water,are adopted by means of the randomized algorithm and material model for the abrasive is presented.The study will not only provide a new powerful tool for the simulation of abrasive waterjet machining,but also be beneficial to understand its cutting mechanism and optimize the operating parameters.

Elbow precision machining technology by abrasive flow based on direct Monte Carlo method

The investigation was carried out on the technical problems of finishing the inner surface of elbow parts and the action mechanism of particles in elbow precision machining by abrasive flow.This work was analyzed and researched by combining theory,numerical and experimental methods.The direct simulation Monte Carlo(DSMC)method and the finite element analysis method were combined to reveal the random collision of particles during the precision machining of abrasive flow.Under different inlet velocity,volume fraction and abrasive particle size,the dynamic pressure and turbulence flow energy of abrasive flow in elbow were analyzed,and the machining mechanism of particles on the wall and the influence of different machining parameters on the precision machining quality of abrasive flow were obtained.The test results show the order of the influence of different parameters on the quality of abrasive flow precision machining and establish the optimal process parameters.The results of the surface morphology before and after the precision machining of the inner surface of the elbow are discussed,and the surface roughness Ra value is reduced from 1.125μm to 0.295μm after the precision machining of the abrasive flow.The application of DSMC method provides special insights for the development of abrasive flow technology.

Modeling and Validation of Indentation Depth of Abrasive Grain into Lithium Niobate Wafer by Fixed-Abrasive Lapping

The prediction of indentation depth of abrasive grain in hydrophilic fixed-abrasive(FA)lapping is crucial for controlling material removal rate and surface quality of the work-piece being machined.By applying the theory of contact mechanics,a theoretical model of the indentation depth of abrasive grain was developed and the relationships between indentation depth and properties of contact pairs and abrasive back-off were studied.Also,the average surface roughness(Ra)of lapped wafer was approximately calculated according to the obtained indentation depth.To verify the rationality of the proposed model,a series of lapping experiments on lithium niobate(LN)wafers were carried out,whose average surface roughness Ra was measured by atomic force microscope(AFM).The experimental results were coincided with the theoretical predictions,verifying the rationality of the proposed model.It is concluded that the indentation depth of the fixed abrasive was primarily affected by the applied load,wafer micro hardness and pad Young′s modulus and so on.Moreover,the larger the applied load,the more significant the back-off of the abrasive grain.The model established in this paper is helpful to the design of FA pad and its machining parameters,and the prediction of Ra as well.

Study of corrective abrasive finishing for plane surfaces using magnetic abrasive finishing processes

On the basis of ordinary plane magnetic abrasive finishing,a finishing method is proposed that can improve the flatness of a plane workpiece.In this method,the feed speed is varied during finishing according to the profile curve of the initial surface and the material removal efficiency,to control the effective finishing time in different areas and thereby improve the surface flatness.A small magnetic pole with an end face diameter of 1 mm is designed,and a ferromagnetic plate is placed under the workpiece to improve the uniformity of the magnetic field distribution near the magnetic pole.An experiment on an A5052 aluminum alloy plate workpiece shows that after 60 min of finishing using the proposed method,the extreme difference of the workpiece surface can be reduced from 14.317μm to 2.18μm,and the standard deviation can be reduced from 3.322μm to 0.417μm.At the same time,according to the measurement results,a similar flatness can be achieved at different positions on the finishing area.Thus,the proposed variable-speed finishing method leads to obvious improvements in flatness.

STUDIES ON MAGNETIC ABRASIVE MACHINING

This paper deals with the machining process using magnetic abrasives. Using an apparatus designed and made, a series of experiments are carried out, where the workpiece is cylindrical and the magnetic abrasives used are mainly Fe and Al 2O 3, for investigating the effects of machining time, working gap, rotating speed of workpieces, magnetic flux density on machining efficiency and surface roughness. At the end of this paper, the machining mechanism is also discussed.

A review on the erosion mechanisms in abrasive waterjet micromachining of brittle materials

The fabrication of miniature structures on components with high-integrity surface quality represents one of the cutting edge technologies in the 21st century.The materials used to construct such small structures are often difficult-to-machine.Many other readily available technologies either cannot realise necessary precision or are costly.Abrasive waterjet(AWJ)is a favourable technology for the machining of difficult-to-machine materials.However,this technology is generally aimed at large stock removal.A reduction in the scale of this technology is an attractive avenue for meeting the pressing need of industry in the production of damage-free micro features.This paper reviews some of the work that has been undertaken at UNSW Sydney about the development of such an AWJ technology,focusing on the system design currently employed to generate a micro abrasive jet,the erosion mechanisms associated with processing some typical brittle materials of both single-and two-phased.Processing models based on the findings are also presented.The review concludes on the viability of the technology and the prevailing trend in its development.

Experimental Investigation on Constrained Abrasive Fluid Polishing for Optical Glass

To find a cost effective,high-precision and environmental friendly way of polishing for optical glass,a series of experiments were focused on about constrained abrasive fluid polishing. Since abrasive particles can repeatedly impact the workpiece in a multidirectional way with high energy, the constrained abrasive fluid polishing method for optical glass has been proposed based on the abrasive fluid machining theory and elastic emission machining theory. A constrained abrasive fluid polishing system was designed and developed to polish K9 glass samples. Results show that K9 glass obtains a high accuracy with less fluid. Experiments indicate that,in a more effective,high-precision and environmental friendly way,constrained abrasive fluid polishing is possible to improve the quality of workpiece surface compared with free abrasive fluid polishing. In the process of removing materials of constrained abrasive fluid polishing,it gives priority to removing the materials of high spot and the high frequency error of smooth local zone can be modified. The abrasive particles can repeatedly impact the workpiece in a multidirectional way,and there are certain relationship among surface quality,material removal rate, and parameters such as speed,clearance, angle, time and particle size. In the process of constrained abrasive fluid polishing, it shows a high material removal rate,and it needn't to clamp workpieces. As a result,it could improve the processing efficiency significantly. The research on constrained abrasive fluid polishing has a practical significance and practical value in industrial production.

TBM tunneling in extremely hard and abrasive rocks:Problems,solutions and assisting methods

Extremely hard and abrasive rocks pose great challenges to the past and ongoing TBM projects by increasing cutter wear and reducing penetration rates.A considerable amount of research has been conducted to improve the performance of TBMs in those challenging grounds by either improving the capacity of TBMs or developing assisting rock breakage methods.This paper first highlights the challenges of hard and abrasive rocks on TBM tunneling through case studies.It then presents the development of hard rock TBMs and reviews the technologies that can be used individually or as assistance to mechanical excavators to break hard rocks.Emphases are placed on technologies of high pressure waterjet,laser and microwave.The state of the art of field and laboratory research,problems and research directions of those technologies are discussed.The assisting methods are technically feasible;however,the main challenges of using those methods in the field are that the energy consumption can be over 10 times high and that the existing equipments have robustness problems.More research should be conducted to study the overall energy consumption using TBMs and the assisting methods.Pulsed waterjet,laser and microwave technologies should also be developed to make the assistance economically viable.

Chemical Mechanical Polishing of Glass Substrate with α-Alumina-g-Polystyrene Sulfonic Acid Composite Abrasive

Abrasive is the one of key influencing factors during chemical mechanical polishing（CMP） process. Currently, α-Alumina （α-Al2O3） particle, as a kind of abrasive, has been widely used in CMP slurries, but their high hardness and poor dispersion stability often lead to more surface defects. After being polished with composite particles, the surface defects of work pieces decrease obviously. So the composite particles as abrasives in slurry have been paid more attention. In order to reduce defect caused by pure α-Al2O3 abrasive, α-alumina-g-polystyrene sulfonic acid （α-Al2O3-g-PSS） composite abrasive was prepared by surface graft polymerization. The composition, structure and morphology of the product were characterized by Fourier transform infrared spectroscopy（FTIR）, X-ray photoelectron spectroscopy（XPS）, time-of-flight secondary ion mass spectroscopy（TOF-SIMS）, and scanning electron microscopy（SEM）, respectively. The results show that polystyrene sulfonic acid grafts onto α-Al2O3, and has well dispersibility. Then, the chemical mechanical polishing performances of the composite abrasive on glass substrate were investigated with a SPEEDFAM-16B-4M CMP machine. Atomic force microscopy（AFM） images indicate that the average roughness of the polished glass substrate surface can be decreased from 0.835 nm for pure α-Al2O3 abrasive to 0.583 nm for prepared α-Al2O3-g-PSS core-shell abrasive. The research provides a new and effect way to improve the surface qualities during CMP.

Two-Body Abrasive Wear of the Surfaces of Pangolin Scales

The Pangolin, a soil-burrowing animal, is covered with scales. These scales are often abraded by soil and rock and their surface is corrugated. The abrasive wear of the surface of the scales was examined. The scales were taken from a pangolin that had died of natural causes. The tests were run on a rotary disc abrasive wear tester. The abrasive material was quartz sand （96.5 wt.%） and bentonite （3.5 wt.%）. The morphology of the abraded surfaces and the abrasion were examined by stereoscopic microscopy and scanning electron microscopy. The concepts are proposed of ＂Guiding-Effect＂ and ＂Rolling-Effect＂ on the textured surfaces under free abrasive wear conditions and the critical dimensions of the ＂Rolling-Effect＂ are discussed.

Multiphase Flow and Wear in the Cutting Head of Ultra-high Pressure Abrasive Water Jet

Abrasive water jet cutting technology is widely applied in the materials processing today and attracts great attention from scholars, but many phenomena concerned are not well understood, especially in the internal jet flow of the cutting head at the condition of ultra-high pressure. The multiphase flow in the cutting head is numerically simulated to study the abrasive motion mechanism and wear inside the cutting head at the pressure beyond 300 MPa. Visible predictions of the particles trajectories and wear rate in the cutting head are presented. The influences of the abrasive physical properties, size of the jewel orifice and the operating pressure on the trajectories are discussed. Based on the simulation, a wear experiment is carried out under the corresponding pressures. The simulation and experimental results show that the flow in the mixing chamber is composed of the jet core zone and the disturbance zone, both affect the particles trajectories. The mixing efficiency drops with the increase of the abrasive granularity. The abrasive density determines the response of particles to the effects of different flow zones, the abrasive with medium density gives the best general performance. Increasing the operating pressure or using the jewel with a smaller orifice improves the coherency of p articles trajectories but increases the wear rate of the jewel holder at the same time. Walls of the jewel holder, the entrance of the mixing chamber and the convergence part of the mixing tube are subject to wear out. The computational and experimental results give a qualitative consistency which proves that this numerical method can provide a reliable and visible cognition of the flow characteristics of ultra-high pressure abrasive water jet. The investigation is benefit for improving the machining properties of water jet cutting systems and the optimization design of the cutting head.

DEM Numerical Simulation of Abrasive Wear Characteristics of a Bioinspired Ridged Surface

This paper presents numerical investigations into a ridged surface whose design is inspired by the geometry of a Farrer’sscallop.The objective of the performed research is to assess if the proposed Bioinspired Ridged Surface (BRS) can potentiallyimprove wear resistance of soil-engaging components used in agricultural machinery and to validate numerical simulationsperformed using software based on the Discrete Element Method (DEM).The wear performance of the BRS is experimentallydetermined and also compared with a conventional flat surface.Different size of soil particles and relative velocities between theabrasive sand and the testing surfaces are used.Comparative results show that the numerical simulations are in agreement withthe experimental results and support the hypothesis that abrasive wear is greatly reduced by substituting a conventional flatsurface with the BRS.

Improved Soft Abrasive Flow Finishing Method Based on Turbulent Kinetic Energy Enhancing

Soft abrasive flow（SAF） finishing can process the irregular geometric surfaces, but with the matter of low processing efficiency. To address the issue, an improved SAF finishing method based on turbulent kinetic energy enhancing is proposed. A constrained flow passage with serration cross-section is constructed to increase the turbulence intensity. Taking the constrained flow passage as the objective, a two-phase fluid dynamic model is set up by using particle trajectory model and standard k-ε turbulence model, and the flow field characteristics of the flow passage are acquired. The numerical results show that the serration flow passage can enhance the turbulence intensity, uniform the particles distribution, and increase the particle concentration near the bottom wall. The observation results by particle image velocimetry（PIV） show that the internal vortex structures are formed in flow passage, and the abrasive flow takes on turbulence concentrating phenomenon in near-wall region. The finishing experiments prove that the proposed method can obtain better surface uniformity, and the processing efficiency can be improved more 35%. This research provides an abrasive flow modeling method to reveal the particle motion regulars, and canoffer references to the technical optimization of fluid-based precision processing.

Effect of flame conditions on abrasive wear performance of HVOF sprayed nanostructured WC-12Co coatings

Nanostructured WC-12Co coatings were deposited by high velocity oxy-fuel (HVOF) spraying with an agglomerated powder. The effect of flame conditions on the microstructure of the nanostructured coatings was investigated. The wear properties of the coatings were characterized using a dry rubber-wheel wear test. The results show that the nanostructured WC-Co coatings consist of WC, W2C, W and an amorphous binder phase. The microstructure of the coating is significantly influenced by the ratio of oxygen flow to fuel flow. Under the lower ratio of oxygen/fuel flow, the nanostructured coating presents a relative dense microstructure and severe decarburization of WC phase occurs during spraying. With increasing ratio of oxygen/fuel flow, the bonding of WC particles in the coating becomes loose resulting from the original structure of feedstock and the decarburization of WC becomes less owing to limited heating to the powder. Both the decarburization of WC particles in spraying and the bonding among WC particles in the coatings affect the wear performance. The examination of the worn surfaces of the nanostructured coatings reveals that the dominant wear mechanisms would be spalling from the interface of WCCo splats when spray particles undergo a limited melting. While the melting state of the spray particles is improved,the dominant wear mechanisms become the plastic deformation and plowing of the matrix and spalling of WC particles from the matrix.

Energy Consumption in Comminution of Mica with Cavitation Abrasive Water Jet

We have studied the efficiency of energy consumption in the comminution of mica powder with cavitation abrasive water jet technology. The energy required to create new surfaces in the comminution of mica powder with cavitation abrasive water jet was calculated,in order to estimate its efficiency of energy consumption. The particle size distribution and the specific surface area were measured by applying a JEM-200CX transmission electron microscope and an Autosorb-1 automatic surface area analyzer. The study results show that the efficiency of energy consumed in creating new surface areas is as high as 2.92%,or 4.94% with the aid of cavitation in the comminution of mica powder. This efficiency will decrease with an increase in the number of comminutions. After three comminutions,the efficien-cies will become 1.91% and 2.29% for comminution without cavitation and with cavitation,respectively. The abrasive water jet technology is an effective way for comminution of mica powder.

Portable mixed abrasive water jet equipment for rescue in high gas mine shaft

In order to rescue a trapped miner and clean out roadways quickly in a high gas mine shaft after a mining mishap, a special portable cold-cutting equipment is needed, the main technology parameters were calculated according to the advanced cold-cutting technology of high pressure abrasive water jet and the portable mixed abrasive water jet equipment （PAWE） was designed to meet the needs of emergency rescue in high gas mine shafts. Tested the PAWE in a high gas environment, and the result shows that the maximum cutting depth of solid iron pipe is 18 mm and the recoilforce of the sprayer is 28.9 N under the conditions that actual cutting pressure is 29 MPa, starting target distance is 10 ram, cutting speed is 180 mm/min and concentration of abrasive is 32%. The course of the experiment in the high gas environment was smooth and continuous, without any explosion. The PAWE is easy to move and operate, but the nozzle which was worn badly in the sprayer should be changed every 8 minutes.

THE EROSIVE PROCESS IN ABRASIVE WATERJET CUTTING OF POLYMER MATRIX COMPOSITES

A study is carried out which analyzes the machinability of polymer matrix composites under an abrasive waterjet (AWJ) and the associated erosive process or mechanism. It shows that AWJ cutting can produce good quality kerf at high production rate if the cutting parameters are properly selected. A scanning electron microscopy (SEM) analysis of the cut surfaces reveals that the erosive process for the matrix material (resin) involves shearing and ploughing as well as intergranular cracking, while shearing is a dominant process for cutting the fibres in the upper cutting region but the fibers are mostly pulled out in the lower region.