Abrasive Air Jet Machining Research Articles

Numerical and experimental investigations on the effect of particle properties on the erosion behavior of aluminum alloy during abrasive air jet machining process

Numerical and experimental investigations on the effect of particle properties on the erosion behavior of aluminum alloy during abrasive air jet machining process

Improvement of process repeatability and resolution in abrasive air jet machining via viscous slurry entrainment

The unsteady powder mass flowrate of the available feeding systems and the bad control of the areas being eroded have been often noticed in the abrasive air jet machining process. In addition to the delivery of dry powder, the powder can be evenly mixed with liquid to form a slurry, and then sent to the mixing chamber of an air jet machine; i.e., multiphase jet machining (MJM) was proposed in this paper. The method whereby using the viscous water to suspend the abrasives was found to enhance the stability of powder mass flowrate, thereby decreasing the fluctuation in the machining depth. Whereafter, five types of liquid-based slurries were prepared and their effects on the jet erosion zone were investigated. It was found that the control of the erosion zone was improved to varying degrees when the abrasives were transported into the air jet by viscous liquid as the carrier fluid due to the two roles: reducing the occurrence of third and/or second particle impacts; inducing a viscous boundary layer that could reduce the negative effect of the divergence of jet beam and particle rebounding. In particular, the use of an oil-based slurry could completely eliminate the unwanted frosted zone around the machined features. CFD simulations were used to understand the mechanisms causing these effects. Overall, it is shown that the abrasive air jets can be designed to have a good resolution, so it is feasible to mill or polish surface without the need for a mask to define the edges.

Effect of nozzle pressure ratios on the flow and distribution of abrasive particles in abrasive air jet machining

Effect of nozzle pressure ratio (NPR) on the flow and distribution of abrasive particles was investigated to improve supersonic abrasive air jet machining (AAJM) effect. The supersonic air-particle flow was simulated via CFD-DEM modeling, which was verified by AAJM experiments. It was concluded that NPR determined the acceleration and distribution of particle flow by controlling the structure and turbulent kinetic energy of the air jet free-flow field. When NPR = 1.12, the particle flow field had a longer stable region and a higher particle velocity, and the radial distribution resembled an n-shape. Further, in AAJM experiments, when the material was fixed in the stable region of particle flow field, the impact stresses were relatively high and uniformly distributed. Thus, when NPR = 1.12, the target material is fixed in the stable region of the abrasive particle flow, and the target material can obtain a better machining effect in the AAJM.

Characteristics of cryogenic abrasive air-jet direct-write machining: A comparison with abrasive air-jet direct-write machining at oblique angles

• The velocity model of abrasive particles in the radial direction is modified. • Abrasive air-jet (AAJ) direct-writing of PDMS at 15° is presented. • Cryogenic abrasive air-jet (CAAJ) direct-writing of PDMS is presented. • CFD models of AAJ and CAAJ direct-writing are established. • "U"-shaped micro-channels are obtained by CAAJ and compared against AAJ at 15°. Cryogenic abrasive air-jet (CAAJ) machining technology is performed simultaneously with the occurrence of the glass transition for PDMS material. However, the mask material is also cooled with cryogenic PDMS cooling. Then, they both show significant brittle characteristics. Therefore, this leads to very poor selectivity between the mask and the PDMS. To solve this problem, CAAJ direct-write machining under unmasking conditions are proposed based on the modified velocity model of abrasive particles in the radial direction. This technique was used to direct-write machined the PDMS materials under small SOD. Then, the effect of cryogenic conditions on machining characteristics of PDMS micro-channels was studied by comparing the abrasive air-jet direct-write machining at oblique angles and CAAJ direct-write machining technologies through a series of experimental studies and CFD simulations. The results show that the material removal mode is transformed to a semi-brittle one, which greatly improves erosion removal efficiency, aspect ratio and bottom surface roughness of the micro-channel. On the other hand, the change in the viscosity of the jet medium has a crucial influence on the geometry of the micro-channel. The rebound direction of abrasive particles changes, and the sidewall of micro-channels is secondarily eroded due to an increase in jet medium viscosity in CAAJ. This, in turn, leads to a micro-channel with "U"-shaped profile. In addition, during CAAJ direct-write machining, sliding, scratching, and rolling of abrasive particles caused by bubble bursting can effectively reduce the bottom surface roughness of the micro-channel.

Modeling and simulation of micro-hole fabrication on brittle material using abrasive air jet machining

The investigation of overlapping impacts and resultant erosion is of great significance for improving the AAJ micromachining performance of brittle and difficult-to-machine materials. In this work, a computational model coupling the Monte Carlo (MC) method and discrete element method (DEM) is developed to study the erosion process of micro-hole fabrication on glass using abrasive air jet (AAJ) at a 90° impact angle. We employ the MC method combined with probability distribution functions to model the impinging particle flow. Brittle erosive behaviors of the overlapping impacts between the impacting particles and the target specimen are simulated by the DEM model. The modeling framework is firstly validated by experimental results using patterns and sizes of micro-holes on the specimen. We then conduct mechanism investigations on the particle and crack behaviors in the erosion process and the overlapping condition effect in the multiple impacts. The relationship between the jet characteristics with the machining efficiency and surface quality of micro-holes is further discussed. The results indicate that the presented DEM model can capture the particle interference effects, which play an essential role in controlling the material removal and microstructure geometry in AAJ machining. The model and findings can help understand the microscopic erosion mechanism and optimize the processing performances of microstructures on brittle materials in AAJ.

Experimental investigations of machining characteristics on polydimethylsiloxane (PDMS) by cryogenic abrasive air-jet machining

Experimental investigations of machining characteristics on polydimethylsiloxane (PDMS) by cryogenic abrasive air-jet machining

PDMS material embrittlement and its effect on machinability characteristics by cryogenic abrasive air-jet machining

Abstract The use of cryogenic abrasive jet machining (CAJM) technology for polydimethylsiloxane (PDMS) materials is increasing rapidly due to its high material removal rate and high surface quality. However, how the material properties of PDMS affect the machining properties under cryogenic conditions is still an unsolved problem. Firstly, the thermodynamic and mechanical properties of PDMS materials are studied by dynamic thermo-mechanical analysis and universal material testing. The results show that the PDMS material’s embrittlement temperature is 126 K. Secondly, evaluation of cooling temperature of PDMS during CAJM shows that the machined area has reached embrittled state. Thirdly, the effect of PDMS material’s embrittlement on the machining behaviour is studied. The experimental results show that the PDMS material exhibit increased abrasive erosion at medium-angle under cryogenic conditions and shows a semi-brittle wear mechanism. Furthermore, the erode surface’s roughness is evaluated. The result shows that the roughness decreases with decreasing air pressure at the same impact angle; with increasing impact angle, the roughness shows a trend of increase initially and then decreases. This work shows that the PDMS material’s embrittlement and the erosion response behaviour during CAJM are due to the combined effects of thermo-mechanical properties and material removal mechanisms, providing a better understanding of CAJM technology.

Semi-resolved CFD-DEM modeling of gas-particle two-phase flow in the micro-abrasive air jet machining

Abrasive air jet (AAJ) machining is attractive for micromachining hard and brittle materials, while it is usually a big challenge to numerically investigate the particle velocity and concentration distribution in the particle erosion process in the AAJ. In this work, a recently developed semi-resolved CFD-DEM approach which bridges the simulation gap between the resolved and unresolved CFD-DEM, is further improved to reconstruct the background information with a double cosine kernel function. The semi-resolved CFD-DEM is then employed to numerically investigate the gas-particle two-phase flow in the AAJ and numerical results show that this semi-resolved CFD-DEM is more accurate in modeling particulate flow in the fine AAJ nozzle than the conventional unresolved CFD-DEM. We further conduct mechanism investigations on the AAJ micromachining process including particle flow characteristics inside the cylindrical nozzle, velocity, and concentration distribution over the nozzle exit, which are essential jet characteristic features. We identified the particle flow patterns, analyzed the particle distribution, and its correlation with air pressure, abrasive mass flow rate, and turbulence effects. The present simulation results and analyses can be great helpful in understanding the erosion mechanism and optimizing the setting parameters to improve the cutting performance of AAJ.

Sensitivity analysis of abrasive air-jet machining parameters on machinability of carbon and glass fiber reinforced hybrid composites

Carbon and glass fiber reinforced epoxy polymer hybrid composites facilitate to tailor the mechanical properties of the composites. However, the machining of hybrid fiber reinforced polymer composite is a challenge by conventional processes due to the different types of fiber reinforcements and anisotropic nature of composites. Researchers and scientists have evaluated the machinability of plain or single fiber reinforced polymer composites through abrasive water jet machining and abrasive air jet machining. Therefore, the present investigation emphasizes on the development of symmetrical hybrid composites, evaluation of mechanical properties and machining of the hybrid composites through abrasive air jet machining (AAJM). There are three types of hybrid composites such as C2G3]S, [CG3C]S and [CG2CG]S along with plain glass ([G]10) and carbon ([C]10) fiber reinforced polymer composites fabricated by hand lay-up technique. It is observed that the [CG2CG]S type hybrid composite has the optimum tensile and flexural strength as compared to other composites. Hence, [CG2CG]S type hybrid composites along with plain glass and carbon fiber reinforced polymer composites was considered for the machinability study. The sensitivity of AAJM process parameters on material removal rate (MRR), depth of cut (DOC) and surface roughness (Ra) are investigated and optimized through response surface methodology (RSM). The optimum machining process output predicted by the RSM model for [CG2CG]S type hybrid composite is MRR = 3.26 × 10−3 g/sec, DOC = 1.48 mm and surface roughness (Ra) = 1.48 μm. The predicted model results compared with the experimental values and found a good agreement between them. The surface morphology of the drilled composite sample is investigated under scanning electron microscope. It is observed that the surface damage of the drilled surface of the composites is minimal. Thus, the abrasive air jet machining process can be employed for drilling of polymer matrix composites to overcome the conventional machining issues.

Process Parameters Optimization by using the Regression Method in Micro Abrasive Air Jet Machining on Alumina Reinforced Zerconia Composite Materials

It is very difficult to make a hole in brittle materials like glass and ceramic materials by using conventional machining methods like turning and milling therefore non conventional machining such as micro abrasive air jet machine is used to overcome the above problem. In this research work to prepare alumina reinforced zerconia ceramic composite materials using powder metallurgy sintering method experiments have been conducted on micro abrasive air jet erosion tester. In this work to varied abrasive air jet machining parameters i.e. Pressure, Abrasive flow rate, Standoff distance and different Weight percentage of zirconium added into alumina i.e. 5wt%, 10wt% and 15wt% and responses are Material Removing Rate and Surface Roughness. 30μm size of Silicon carbide (sic) sand particles are impinged Ceramic composite plates with given input process parameters. L27 Orthogonal array of Taguchi and Regression analysis is used to determine the Signal to Noise ratios of all experiments and process parameters impact, Percentage contribution of each process parameters, square parameters and interaction parameters on MRR and Surface Roughness and check weather parameters, square and interaction parameters are significant are not, to eliminate insignificant parameters by using backward elimination method. To improve R2 value by eliminated insignificant parameters.

Tapered mask and its effect on the fluid flow and machining efficiency of a multiphase jet

Multiphase jet machining (MJM) is a novel surface texturing technique that accelerates the mixture of abrasives and water by compressed air for removal of materials. Here, the significant stagnation effect of masked MJM was reported for the first time; this effect can yield a much lower machining efficiency than the masked abrasive air jet machining and unmasked MJM. It was found that using masks with smaller taper angles improves the machining efficiency and the sidewall slope of the channel. Moreover, reducing the jet angle also elevates the efficiency. Machining mechanisms were revealed and described in terms of the slurry pressure and flow velocity in the stagnation zone. Overall, to improve the machining efficiency of masked MJM, two optimized process parameters were suggested and verified: 1) masks with a taper angle of 30° or smaller; 2) nozzles with an inclined jet angle of 80°.

Aerodynamic focusing of an abrasive air jet and its effect on machining resolution

To decrease the size of the eroded footprint resulting from abrasive air jet machining, the aerodynamic focusing of an abrasive particle jet was investigated. Using a slot nozzle abrasive jet, the best focusing employed a pair of bounding air jets tilted 60° to the abrasive jet, at an impingement height of approximately 10% of the standoff distance from the workpiece. An optimum bounding jet pressure existed to achieve the maximum focusing, resulting in a machined channel width reduction of up to 16% with a corresponding depth increase of 84% compared to no bounding jets. A novel apparatus was constructed to generate an annular bounding jet impinging a central abrasive jet formed from a round nozzle. However, aerodynamic focusing, in this case, could not be achieved due to the large stagnation zone that formed near the annular jet impingement. Computational fluid dynamics simulations were used to understand the mechanics of particle focusing.

Optimization of process parameters by using Taguchi Techniques in abrasive air jet machining of Al2O3 ceramic material

Abstract Quality surface finish of Al2O3 work piece present variety of issues such as non conventional machine is one of the foremost often times used material process in machining of Al2O3 work material to produce outlined surface finish, surface finish associated good characteristics of the work material and input parameters used. The quality of the surface, dimensional precision greatly has an effect and the elements through their useful life. This project introduces a new technique of investigating the P, AFR, SOD and T on abrasive air jet machining of Al2O3 work material. Investigating of process parameters was done by Taguchi Technique. Experiments were conducted on Al2O3 work piece, the parameters of machining such as P, AFR, SOD and T of SiO2 particles impinged on the Al2O3 Materials are optimized by responded concerns particularly Material removing rate. The optimum levels of parameters investigated by using Taguchi method.

A study of the micro-hole geometry evolution on glass by abrasive air-jet micromachining

Abrasive air-jet (AAJ) micromachining has become an attractive technology for the fabrication of micro-structures on a wide range of engineering materials. However, problems specific to effective mould construction still remain challenging. This paper presents a study on the evolution of micro and blind holes on glass during abrasive air-jet machining. Experiments were conducted under different practical settings of air pressure, particle mass flow rate and drilling time. A 3D laser measurement microscope was used to characterize the machined hole profiles. It was found that there was a clear evolution of the profiles of the hole bottom surfaces. Three types of hole surface contours, i.e., convex, flat, and concave (reverse bell-shaped), were obtained within the operating range used, in which the first two types have rarely been reported in literature. The profile variation took place along with the setting parameters of particle flow rate and air pressure, which indicated that the particles distribution density across the cross section of a cylindrical nozzle also varied with the setting parameters. At a low flow rate, the hole bottom was formed with a convex shape, which might be attributed to the fact that the distribution of particles at the nozzle centre was less than that around the brim. As the particle flow rate increased, the bottom surface evolved from convex to flat or even concave. With a proper setting, AAJ can therefore be used to fabricate a micro hole with a desired bottom surface profile. The variation of abrasive particle distribution in the jet in the AAJ micromachining might be attributed to the flow bounce back and stagnation effects when the jet impacts on a target workpiece.

MACHINING OF SODA LIME GLASS USING ABRASIVE HOT AIR JET: AN EXPERIMENTAL STUDY

Abrasive Jet Machining is becoming one of the most prominent machining techniques for glass and other brittle materials. In this article, an attempt has been made to combine abrasive and hot air to form an abrasive hot air jet. Abrasive hot air jet machining can be applied to various operations such as drilling, surface etching, grooving and micro finishing on the glass and its composites. The effect of air temperature on the material removal rate applied to the process of glass etching and grooving is discussed in this article. The roughness of machined surface is also analyzed. It is found that the Material Removal Rate (MRR) increases as the temperature of carrier media (air) is increased. The results have revealed that the roughness of machined surface is reduced by increasing temperature of carrier media. The mechanism of material removal rate has been discussed with aid of SEM micrographs.

Fabrication and Performance of Symmetrical Gradient Ceramic Nozzles

A model for the design of symmetrical gradient ceramic nozzles is presented. The purpose is to form compressive residual stresses at the entry and exit of the ceramic nozzle, and to reduce the erosion wear at these areas during abrasive air-jet machining. A SiC/(W,Ti)C ceramic nozzle with symmetrical gradient structure at its entry and exit was produced by hot pressing. The residual stresses inside this layered nozzle in the fabricating process were calculated by means of the FEM. The mechanical properties at individual layers were measured, the microstructure was examined. The erosion wear of this symmetrical gradient ceramic nozzle was investigated and compared with an unstressed reference nozzle. The production of symmetrical gradient structures with compressive residual stresses within the entry and exit of the nozzle has been proved to be a suitable way to obtain ceramic nozzles with superior erosion resistance.

Analysis and Modeling of Micro Abrasive Air Jet Cutting Aspect Ratio

Micro abrasive air jet machining technology is being increasingly used in the fields of micro cutting. Since the aspect ratio is a major interest characteristics of kerf in micro cutting, an experimental investigation is carried out to study the effect of cutting process parameters on the aspect ratio in this study. It is found that the aspect ratio increases with an increase in air pressure, abrasive flow rate and jet incidence angle, while decreases with an increase in nozzle traverse speed. Furthermore a predictive model for aspect ratio is developed using the dimensional analysis technique. It is shown that the model predictions are in good agreement with the experimental results. The research results may be meaningful to efficiently control the aspect ratio.

Modelling the erosion rate in micro abrasive air jet machining of glasses

Micro abrasive jet machining (MAJM) is an economical and efficient technology for micro-machining of brittle material like glasses. The erosion of brittle materials by solid micro-particles is a complex process in which material is removed from the target surface by brittle fractures. The rate of material removal is one of the most important quantities for a machining process. Predictive mathematical models for the erosion rates in micro-hole drilling and micro-channel cutting on glasses with an abrasive air jet are developed. A dimensional analysis technique is used to formulate the models as functions of the particle impact parameters, target material properties and the major process parameters that are known to affect the erosion process of brittle materials. The predictive capability of the models is assessed and verified by an experimental investigation covering a range of the common process parameters such as air pressure, abrasive mass flow rate, stand-off distance and machining time (for hole machining) or traverse speed (for channel machining). It shows that model predictions are in good agreement with the experimental results.

Effect of Nozzle Type and Abrasive on Machinablity in Micro Abrasive Air Jet Machining of Glass

Micro abrasive jet machining (MAJM) is a high effective economical technology for three dimensional micro structure fabrications of brittle materials. It is widely used in the fabrication of semiconductors, electronic devices, micro electro-mechanical systems (MEMS), optical-electronic and optical devices, and medical instruments. In this paper, based on the experimental study of MAJM for glass, the influences of the nozzle type/size and abrasive type on the material erosion rate and structure profile are analyzed. The results show that the rectangular nozzle can yield a more accurate and efficient machining performance due to reduced flux effect. By contrast, with round nozzle all the cross section profiles of the machined patterns show rounded V-type shape. The rectangular nozzle is able to produce geometry with flat shape. The machining area is almost independent of the abrasive hardness, and the erosion rate increases with the increase in the hardness of the abrasive grits. The nozzle geometry is of great importance for machining accuracy and the efficiency.

Sand erosion performance of B4C based ceramic nozzles

B4C/Al2O3/TiC ceramic composites with different content of TiC were produced by hot pressing. The effect of TiC content on the microstructure and mechanical properties of this composite has been studied. The sand erosion performance of the nozzles made from this composite was examined with an abrasive air-jet. Results showed that chemical reaction took place for the system during hot pressing, and resulted in a B4C/Al2O3/TiB2 composite with high density and improved mechanical properties compared to B4C/Al2O3 composite. The sintering temperature was lowered from 2150 °C for B4C/Al2O3 to 1950 °C for B4C/Al2O3/TiC composite. The hardness of B4C/Al2O3/TiC ceramic nozzles had an important influence on the erosion rate in abrasive air-jet machining. The nozzle materials with high hardness showed lower erosion rate. Analysis of the B4C/Al2O3/TiC nozzle eroded bore surfaces showed that the entry bore surface exhibited a brittle fracture induced removal process, while the center bore surface showed plowing and polishing type of material removal mode. Both types (fracture and plowing) of material removal model seem to be occurred at the exit bore surface.