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Advances in Mechanical Engineering
Volume 2014 (2014), Article ID 752353, 9 pages
Experimental Research into Technology of Abrasive Flow Machining Nonlinear Tube Runner
College of Mechanical and Electric Engineering, Changchun University of Science and Technology, Changchun 130022, China
Received 3 February 2014; Revised 23 March 2014; Accepted 3 April 2014; Published 8 June 2014
Academic Editor: Zhenling Liu
Copyright © 2014 Junye Li et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
In the fields of military and civil uses, some special passages exist in many major parts, such as non-linear tubes. The overall performance is usually decided by the surface quality. Abrasive flow machining (AFM) technology can effectively improve the surface quality of the parts. In order to discuss the mechanism and technology of abrasive flow machining nonlinear tube, the nozzle is picked up as the researching object, and the self-designed polishing liquid is employed to make research on the key technological parameters of abrasive flow machining linear tube. Technological parameters’ impact on surface quality of the parts through the nozzle surface topography and scanning electron microscopy (SEM) map is explored. It is experimentally confirmed that abrasive flow machining can significantly improve surface quality of nonlinear runner, and experimental results can provide technical reference to optimizing study of abrasive flow machining theory.
Abrasive flow machining technology is a polishing method, which is accomplished through a kind of viscoelastic soft abrasive media with abrasives flowing back and forth on the machined parts’ surface under the pressure. The grains in the abrasive flow are used as many cutting tools to make repeated cutting with its hard and sharp edges on the surface, in order to achieve a certain degree of processing purposes . Any part where the abrasive flow goes through will be polished. The superiority of abrasive flow machining technology is particularly significant for the specific channels that common tools are hard to get [2, 3]. When the grains evenly and progressively work on the surface or corners of the parts, deburring, polishing, and chamfering are achieved. The machining mechanism is illustrated in Figure 1.
A lot of researches have been conducted by many scholars based on this technology. A number of scholars have made research reports about abrasive flow machining technology. Scholars, like Jain et al., used BP neural network to make study of abrasive flow processing and carried out experimental research on material removal rate and surface roughness and optimized processing parameters. During the process, finite element is used to simulate abrasive carrier and changes of processing media stickiness that affect workpiece removal amount and surface roughness, and it is concluded that main wear way of material in abrasive flow processing is struck off by abrasives, and finally the purpose of fine processing is realized [4–8]. Scholars, like Walia et al., by exploring the impact of central force on the abrasive flow machining process through experiments, told the relation of shaft speed, cycle index, and the grain size to improve the surface roughness and material removal amount [9–11]. Scholars, like Singh et al., did abrasive flow machining with aluminum and brass components as representatives to study the material removal rate of the two material components and made analysis of two different materials in different forms of wear in abrasive flow machining process by electron microscopy . Scholars, like Sankar et al., explored rotary abrasive flow machining characteristics and obtained the relation of the workpiece rotation speed, the number of processing, extrusion pressure, and percent of the media to surface roughness by processing different materials of aluminum alloy by abrasive flow [13–15]. Scholars, like Kar et al., tried to develop new abrasive based on viscous carriers used for abrasive flow finishing and researching temperature, shear rate and frequency effects on rheological properties, and composition of the abrasive flow media . Scholars, like Huang et al., discussed how abrasive flow rotary machining affected surface morphology of workpiece material, analyzed the relationship between workpiece rotation speed and effective abrasive distance in the polishing area under the condition of theoretical and experimental spiral path length, gave the relation of workpiece rotation speed to surface improvement rate of roughness and amount of material removal, made evaluation of flowing parameters, and found viscoelasticity of grinding media changing with shear thinning property [17, 18]. Scholars, like Kenda et al., once researched the hard tool steel AISI D2 after electric spark machining and analyzed processing parameters that affected surface roughness and residual stress. It is confirmed that abrasive flow machining is qualified to repair surface defects resulting from the electrical discharge machining and improve surface quality greatly and decrease the surface residual stresses . Scholars, like Zarepour and Yeo, used single abrasive particle as a research object to make study of material removal method in ultrasonic microprocessing, raised the impact kinetic energy of the particle and material threshold kinetic energy which are key factors of affecting the material removal in ultrasonic micromachining, and proposed a removal mode prediction model of ductile and brittle materials .
At present, academic research is mainly aimed at theoretical and experimental studies under certain conditions and does not study the major technological parameters during the process of abrasive flow machining nonlinear tube. It has limited guiding significance universally to the abrasive flow machining. Experimental study on nonlinear processing technic offered in the paper will provide important technical support for practical production.
2. Experimental Design
Abrasive flow is mainly used in the experiments to finish nonlinear tube runner surface, and the burr on the tube wall is to be cleared by abrasive flow machining. In the process of abrasive flow machining, the abrasives are driven by the external pressure to machine the workpiece; abrasive cutting performance is shown by microscopic slip removal and the contact surface between abrasives and workpiece is being consumed gradually. The research is mainly aimed at researching and discussing abrasive flow machining nonlinear tube runner surface technology by different technological parameters of different particle size, abrasive thickness, extrusion pressure, and processing time.
2.1. Experimental Polishing Liquid
Abrasives used in this experiment are formed by the aviation oils such as kerosene, silicone, and triethanolamine and then adding a different size silicon carbide powder. The abrasives with different thickness ratio are deployed to make it economical, and, at the same time, to fulfill the fine polishing. Abrasive medium is mixed by a certain number of abrasive grains and semisolid shaped abrasive carrier. Types of abrasive grains, viscosity of abrasive carrier, and abrasive particles of different sizes will impact the polishing effect. At the beginning of the formation, viscoelastic abrasive not only is semisolid in shape, but also is with good viscoelasticity and plasticity. Viscoelastic abrasives with different thickness are shown in Figure 2.
According to the aperture size, silicon carbide particles of different sizes were chosen to prepare abrasive of different thickness. The channel of nozzle parts is relatively small, and abrasive flow machining process should use smaller silicon carbide particles. For a specimen with relatively large runner, in abrasive preparation process, a large particle and high thickness abrasives can be designed to make grinding. When the silicone oil and triethanolamine are prepared at 1 : 1, adding certain thickness silica gel into it, the abrasive compound is discovered that no precipitation happens. The thicker the thickness is, the better the viscoelastic is. PH is measured approximately PH 7.4 and tends to be neutral. For the abrasives’ polymer structure, strong bonding strength, the initial abrasive is with high viscoelasticity and has better cohesion characteristics. In addition, the viscoelastic abrasive will change during processing, gradually changing from semisolid thick shape to low viscosity fluid substances and with improved liquidity at the same time. This attribute has a positive role in flowing polishing in this experiment.
2.2. Experimental Parts
The nozzle is used here as the machined nonlinear tube part in the experiment. Due to the limitations of testing methods, the detection of the nozzle adopts destructive testing. In order to obtain the surface topography of nonlinear tube runner after abrasive flow machining, cutting nonlinear tube of the nozzle is achieved by means of wire electrical discharge machine (WEDM). Then the scanning electron microscopy is used to observe surface topography of nonlinear tube channels after cutting. Parts of a nozzle after cutting are shown in Figure 3.
3. Results and Discussion
The parts used for experiment are nozzle parts in the fuel system which are determined by the electrical discharge machining. The microholes runner surface is finely polished by abrasive polishing. Due to the processing of EDM, discharge hole will cause some of the smallest microprocessing surface roughness and the processing defects such as cracks and micropores on initial surface.
Due to the high thickness of abrasives and fine particle size, the abrasives will show excellent viscosity. The mixture of interaction of processing conditions, such as extrusion of high pressure, causes the removal effect of abrasive to nonlinear material even more apparent on the surface of tube channels, so as to obtain better surface roughness. Due to the abrasive’s continuous removal effect on nonlinear tube channel surfaces, after the abrasive flow machining, the surface profile becomes more smooth and fine than the ups and downs before processing. Nozzle surface roughness improved from Ra 1.8 μm of the original surface of the electric spark discharge to around Ra 0.4 μm. Figures 4(a) and 4(b) are appearances of the surface profile of the nonlinear tube channel of a nozzle before and after abrasive flow machining.
Experiments discuss the degree of effect of grinding grains size, abrasive thickness, extrusion pressure, and processing time on surface roughness. The surface modification effect is achieved in order to reduce the whole processing cost and to calculate the best combination of the abrasive flow processing parameters.
3.1. The Effects of Abrasive Particle Size on Surface Morphology during Abrasive Flow Machining
Do polishing experiment under the conditions of abrasive thickness of 10%, extrusion pressure of 7.9 Mpa, and processing time of 25 minutes and choose abrasive of different grinding particle size to polish the parts of a nozzle. It can be known from the testing that the selection of fine Sic particles can significantly reduce surface fluctuation of the outline; the surface roughness has apparent reduction as grinding particle size decreases, which can effectively improve the precision of surface of nonlinear tube runner. Figures 5(a) and 5(b) are tube runner surface topography map, respectively, while processing the nonlinear pipe of the nozzle when the silicon carbide abrasive particle sizes are 10 μm (1200) and 7 μm (2000), respectively.
It is shown in Figure 5 that the smaller the abrasive particle size is, the better surface roughness is obtained when under the same extrusion pressure and abrasive thickness. Abrasive itself bound under extrusion pressure plays an effective role in removing the material surface in order to obtain better surface accuracy. It should be noted that the optional abrasive material is silicon carbide; the different grinding particle sizes are shown in Figure 6.
3.2. The Effects of Abrasive Thickness and Extrusion Pressure on Surface Morphology of Abrasive Flow Machining
In conditions of abrasive particle size of 7 μm (2000) and of abrasive thickness of 2.5% to 10% under extrusion pressure ranging from 5.2 Mpa to 6.9 Mpa, abrasive flow polishing experiment gets a good effect of surface finishing improvement. Using different thicknesses of abrasive for nozzle nonlinear tube runner surface fine polishing, ups and downs of the tube runner surface will gradually decrease with increase of abrasive thickness. After abrasive flow machining, there are significant differences between level of the peak of the surface and the original processing surface when the abrasive is in high thickness. Through a comparative analysis, nonlinear tube runner surface accuracy has been significantly improved, which means that the content of the abrasive thickness is proportional to the improvement of the surface roughness.
It is necessary to clarify that, because holes in the nozzle head are only 0.16 mm, in order to ensure the smooth processing of the abrasive flow, here abrasive thicknesses of 2.5%, 5%, and 10% in abrasive flow polishing experiments are chosen. Through detection and analysis of experiments, with improvement of the abrasive thickness, extrusion pressure, trace of abrasive scraping in nonlinear tube runner surface is increased significantly. When abrasive thickness is 5%, only a few marks scraping the runner surface are slightly visible. But when the thickness increases to 10%, the processed trace of the nonlinear tube runner surface is apparently visible.
Through analysis, better surface roughness improvement by abrasive flow machining is caused by the removing cutting mechanism. The surface accuracy of nonlinear tube runner of the nozzle is improved gradually with the increase of the abrasive thickness. But it has been tested that the election of a greater thickness of abrasive flow machining appears to be a reamer phenomenon in the head of a nozzle; abrasive flow machining should be carried out with a selection of a relatively low thickness of abrasive when abrasive flow machining is done.
In order to express the surface topography of the nonlinear tube runner of the nozzle more accurately when the abrasives are in different thicknesses, the border is scanned to observe its structure here. Figures 8(a), 8(b), 8(c), and 8(d) are given the initial surface structure diagram of nonlinear tube runner obtained by scanning electron microscope and the diagram of the surface structure of nonlinear tube runner of the nozzle when the abrasive thickness is 2.5%, 5%, and 10%, respectively.
In addition, the finishing of nonlinear pipe channel surface is done under condition of a higher extrusion pressure, for higher extrusion pressure can drive abrasive flow to go through the surface of the nonlinear tube runner faster. The high position of the flowing runner surface will be polished and removed by the forces of the abrasives, so that surface profile tracks are gradually reduced with the increase of squeezing pressure; a good surface accuracy after a certain time of ultraprecision abrasive flow polishing is obtained. Surface topography of nonlinear tube runner after abrasive flow machining under the condition of extrusion pressure of 5.2 Mpa, 6.7 Mpa, and 7.9 Mpa is given, respectively, in Figures 9(a), 9(b), and 9(c).
It can be concluded from the test results that the ups and downs of the surface of nonlinear pipe become smooth and the surface roughness reduces gradually as the squeezing pressure increases. The machining marks under the extrusion pressure of 5.2 Mpa are not more obvious than that of 7.9 Mpa, but for the original EDM nonlinear tube runner surface, the surface roughness has been significantly improved.
3.3. The Influence of Processing Time on Surface Topography of Abrasive Flow Machining
Improvement of surface roughness is not only proportional to thickness of abrasive, abrasive particle size, and squeezing pressure, but also obtained with the increase of processing time.
The processed surface morphologies of nonlinear tube runner are separately given in Figures 10(a), 10(b), and 10(c) with extrusion pressure of 7.9 Mpa, thickness of 10%, and grinding particle size of 7 μm (2000), under the condition that time is, respectively, 5 minutes, 15 minutes, and 25 minutes for abrasive flow machining.
It can be seen from the test results that surface roughness of the nonlinear tube runner is gradually improved as time increases. The roughness is gradually reduced and improved to about Ra 0.4 μm; the surface of inner hole becomes more and more smooth. Figures 11(a), 11(b), 11(c), and 11(d) are, respectively, the original appearances of nonlinear pipe channel access to scanning electron microscope and surface structure diagram of nonlinear tube runner of the nozzle when the processing time of abrasive flow machining is 5 minutes, 15 minutes, and 25 minutes.
It can be seen from the SEM shown in Figure 11 that surface topography of nonlinear tube runner of the nozzle becomes smooth and compact compared to the initial situation of the ups and downs of a peak and valley as the processing time increases. The ups and downs of nonlinear pipe flow surface remain visible after 5 minutes’ processing; abrasive cutting marks on the surface also increase as time passes by. When processing lasts for 15 minutes, the surface of nonlinear tube runner becomes smooth; when processing time is 25 minutes, the trace of grinding of nonlinear flow is apparently visible and the distributions of cutting marks are even more uniform; when processing increases to 30 minutes, the surface of nonlinear pipe flow is not significantly improved, so identified 25 minutes’ processing can achieve the best surface structure.
Experimental results indicate that the best surface accuracy of the nozzle nonlinear pipe flow is achieved under the condition of extrusion pressure of 6.9 Mpa, abrasive thickness of 10%, abrasive particle size of 7 μm, and processing time of 25 minutes. In other words, if you want to get a good surface quality, fine processing of nonlinear tube runner must be done under the condition of high thickness, fine particle size, and high pressure. When choosing appropriate machining parameters, after a certain time of the abrasive flow ultraprecision machining, nonlinear pipe runner surface topography is improved from the peak valley condition of the ups and downs to become smooth and compact.
Besides as a method of ultraprecision machining, abrasive flow machining (AFM) technology can also be used to do trace grinding processing on surface shape tolerances and the parts which have high quality requirements. Experiments make technology research on precision polishing on the surface of the nonlinear tube runner of the nozzle with self-designed abrasive flow polishing liquid and explore nonlinear tube runner surface roughness improvement degree with different machining parameters chosen in the paper. By integrating the experiment results, the following conclusions can be obtained.(1)The self-designed abrasive polishing liquid is very useful to finish the surface of complex nonlinear tube runner surface; it can effectively remove the burr and the hard recast layer after EDM. It can be drawn from the test results that through ultraprecision processing nonlinear tube runner surface with self-designed abrasive polishing liquid, the runner surface becomes really fine and smooth, the roughness of runner surface and surface structure can be actually improved, and the quality of the nonlinear tube runner has been improved to great extent. It can be found out in the experiment that the improvement of surface roughness has direct relation to the original surface topography; for the same nonlinear tube runner, in the initial surface that is continuously smooth, surface accuracy is basically the same after abrasive flow machining, while in the original surface with a defect, surface quality is relatively poor after abrasive flow machining.(2)Under the experimental conditions of the thesis, and with the abrasive of high thickness and fine particle size under the effect of high extrusion pressure, nonlinear tube surface machining achieved the ideal surface precision. This is due to the excellent viscosity of abrasives of high thickness and fine particle size and under the functions of extrusion pressure by the abrasive and others, after processing a certain amount of time, better runner surface quality will be obtained; the roughness of runner surface will be improved to great degree. With increase of the processing time, abrasive flow machining can reduce the roughness of nonlinear tube runner surface, while for more than a certain period of processing time, the improvement of runner surface is not obvious.(3)The research into ultraprecision polishing of the nozzle parts is made under the following experimental conditions: 7 μm–10 μm of grinding particle size, 2.5% percent of abrasive thickness, 5.2 Mpa–7.9 Mpa of squeezing pressure, and 0–30 min of processing time; the best surface quality was gained under the conditions of 7 μm of abrasive particle size, 10% of the abrasive thickness, 7.9 Mpa of extrusion pressure, and 25 minutes of processing time, and the surface roughness has been changed from Ra 1.8 μm to Ra 0.4 μm.(4)The study of abrasive flow machining technology is significant in improving surface integrity of the nonlinear tube parts, removing burrs of the cross hole, reducing stress concentration of key parts, and enhancing reliability and longevity of parts. Through technical inspection, abrasive flow machining technology indeed made nonlinear runner surface quality improve magnificently, and this technology has the advantages of low cost and high efficiency; therefore, abrasive flow machining technology is the key ultraprecision machining technology which is worth the development and in-depth study.
Conflict of Interests
The authors declare that they have no possible conflict of interests with any trademark mentioned in the paper.
The authors would like to thank the National Natural Science Foundation of China no. NSFC 51206011, Jilin Province Science and Technology Development Program of Jilin province no. 20130522186JH, and Doctoral Fund of Ministry of Education of China no. 20122216130001 for financially supporting this research.
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