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MICRO-CHANNEL MILLING USING ABRASIVE WATERJETS ...


Metallic microchannels are increasingly used in fuel cell, MEMS component, cutter, and micromold due to functions of fluid feed and heat exchange. Abrasive-assisted electrochemical jet machining (AECJM) is a hybrid manufacturing technology coupling erosion and corrosion concurrently to remove metals. It shows a great potential in machining microchannels with complex patterns at metallic surface. The present work explored the feasibility of patterning complex microchannels at SS316 surface using AECJM at a condition of Al2O3 abrasives, NaNO3 solution, and DC potential. A series of microchannels were machined by AECJM to investigate the effects of process conditions on the material removal rate, machining current density, aspect ratio, and surface roughness. The results show that the anodic dissolution dominates material removal in the AECJM of SS316 at present conditions. The material removal rate nonlinearly correlates with machining current density between approximate 3 to 10 A/cm2 due to a nonlinear relationship of current efficiency and current density. It is also shown that the anodic dissolution can be influenced positively or negatively by abrasives impingement due to the synergy of erosion and corrosion. Relatively higher abrasive dose and jet velocity result in a reduction of anodic dissolution and however an increase of abrasive erosion. The experiments of fabricating complex patterns demonstrate that AECJM has a high potential to machine microchannels at SS316 efficiently and economically.




MICRO-CHANNEL MILLING USING ABRASIVE WATERJETS ...



In addition to abrasive properties, machining performance is also influenced by operating parameters such as jet angle, SOD, feed rate, number of cutting passes, jet pressure, abrasive flow rate, and nozzle geometry. The effect of abrasive impact angle on machining of ceramic material was investigated by Srinivasu et al. [18], using silicon carbide as abrasive. The effect of particle impact angle was also studied by Junkar et al. [19], using finite element analysis. Authors found that maximum material removal occurs at jet impact angle of 90. Studies on the effect of jet pressure on cotton FRP composite by Wang and Guo [20] reported that the delamination occurs due to incapability of jet penetration into composite at lower operating pressures. Study of kerf taper angle produced on glass and graphite reinforced epoxy composite was made by Shanmugam et al. [21] and also developed a model to predict delamination length. Authors observed that, at higher operating pressures, considerable surface taper and delamination are found on the cut surface due to higher feed rates, flow turbulence, and brittle nature of composite material. Investigations on the effect of process parameters by Azmir and Ahsan [22] on glass fiber reinforced epoxy composites infer that abrasive hardness, operating pressure, SOD, and jet traverse rate were significant control factors which affect surface roughness () and a mathematical model was developed by authors to predict . Further analysis of machined surface by Azmir and Ahsan [23] shows that at a jet angle of 90 glass fibers were found to be perfectly chopped. Alberdi et al. [24] studied the suitability of machinability model developed for metals to use it in composite materials. The machinability index was found to vary with thickness and composition of the composite. A comparative analysis of AWJ machining of metals in air and in submerged conditions is made by Haghbin et al. [25]. The study shows that machining under submerged conditions produced narrower kerf than the free jet machining.


In AWJ machining, the kerf profile produced depends on jet energy, jet exposure time on the workpiece, jet orientation, and material properties. Axinte et al. [26] developed a geometrical model to predict jet footprint (kerf) in maskless controlled milling applications. AWJ milling experiments were conducted on silicon carbide ceramic material at 90 jet impingement angle at various jet feed rates to validate the model. Kong et al. [27] developed a mathematical model to predict the jet foot prints for arbitrarily moving jets in single straight paths. Vundavilli et al. [28] used fuzzy logic based expert system such as simulated annealing and genetic algorithm to optimize process parameters and develop a mathematical model to predict depth of cut. Zain et al. [29] also used soft computing techniques to optimize the process parameters that produced low surface roughness. Billingham et al. [30] developed model that predicts jet foot prints of the overlapped single and multiple straight paths. Narayanan et al. [31] developed model to predict the jet energy distribution by considering parameters such as abrasive particle size distribution and the effect of particle fracture. Nouraei et al. [32] developed surface evolution model that can predict the shape features in micromachining of brittle material such as borosilicate glass. These models were found to be powerful tools to develop advanced jet path strategies on complex geometries using CAD/CAM by considering various process parameters including jet exposure time and orientation. From the literature review, it is noticed that generally addition of graphite improves mechanical, tribological, and electrical properties of GFRP composite material due to which the composite finds a wide range of industrial applications. AWJ machining is the suitable method for processing of such composite materials. The literature review establishes the need to investigate the effect of operating parameters on the machinability characteristics of graphite laced GFRP. Hence, this paper attempts to explore the effect of process parameters, namely, jet operating pressure, SOD, feed rate, and abrasive concentration on kerf width, while machining of graphite filled GFRP composite and their optimization using Taguchi method. In addition, morphological study is carried out using SEM on the cut surface machined at optimum and few selected process settings.


The fabricated composite was cut into specimen size as per ASTM D638 standard. Tensile properties were estimated using a universal testing machine (Instron 3366). The hardness of the composite was measured using computerized microhardness tester (Matsuzawa-MMTX7A). The morphology of garnet abrasive and AWJ machined surfaces were analyzed using scanning electron microscope (Zeiss EVO 18, Germany). The particle size analysis of garnet abrasive was carried out as per ASTM D422 standard. The chemical composition of garnet abrasive was estimated by elemental mapping method using SEM. The kerf widths of machined surfaces were measured by tool room microscope (Mitutoyo) and the surface roughness was measured by Surtronic 3+ (Taylor Hobson).


The kerf widths were analyzed using ANOVA method to find the effect of process parameters at 95% confidence level using (variance ratio) statistics as shown in Table 5. It is observed that is greater than for the machining parameters such as SOD, jet pressure, and feed rate. A small variation of these parameters contributes to a considerable variation on the kerf width. Hence, it is clear from ANOVA that jet pressure, SOD, and feed rate are significant process parameters. However, for abrasive concentration, is found to be less than . The effect of variation in abrasive concentration on kerf width is not significant. Based on the values, the significance of machining parameters can be ranked as follows: SOD (1), pressure (2), feed rate (3), and abrasive concentration (4). Further, it is observed from the interaction plot shown in Figure 5 and ANOVA values that there is no significant interaction effect between jet pressure with feed rate and jet pressure with abrasive concentration as well as between feed rate and abrasive concentration.


Morphological study has been carried out using SEM on the specimens that were machined at the optimum process settings which generate small kerf width. It is seen from Figure 7(a) that the top and bottom edges of the kerf are free from delamination. It is also observed from Figure 7(b) that there are inconsistent and nonuniform pits at few locations on top kerf due to collision between abrasive particles which richochiates from the edges. Further, SEM analysis is carried out to understand the microlevel of destruction in the composite. Figures 7(c) and 7(d) show the morphology of cut surface when fibers are oriented at 90 and are parallel to jet traverse, respectivly. It is seen that the fibers are cut accurately and no abrasive embeddment is found accoss the machined surface.


Microfluidics is one of the rapidly growing markets in the present era of miniaturization. Microchannels have wide applications in various fields such as biomedical, mechanical, electrical, and chemical sciences. Machining microfeatures with high aspect ratio in metals is difficult by mechanical and lithography-based processes. Micro-electric discharge milling is a suitable process to machine microcavities and microchannels in all electrically conductive materials. The main disadvantage of this process is its very low material removal rate. Improving the machining performance of micro-electric discharge machining (μEDM) is a research area that attracts researchers and remains as an unfulfilled agenda. The aim of this study is to improve the machining performance of micro-electric discharge milling process by investigating the performance of cryogenically treated tool and workpiece materials. Since surface roughness determines the minimum feature size machinable by any micromachining process and also it is an important factor in determining the flow characteristics of microchannels, a detailed comparative study was conducted on the three-dimensional (3D) surface quality parameters along with machining performance while using all four different combinations of untreated and cryogenically treated tool and workpiece, and the roughness parameters are correlated with the erosion behavior. The study revealed significant change in material removal rate and erosion pattern due to cryogenic treatment. 041b061a72


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