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Understanding flexible abrasive brush behavior for double disk magnetic abrasive finishing based on force signature
G Model JMP-630; No. of Pages 7
ARTICLE IN PRESS Journal of Manufacturing Processes xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
Journal of Manufacturing Processes journal homepage: www.elsevier.com/locate/manpro
45th SME North American Manufacturing Research Conference, NAMRC 45, LA, USA
Understanding flexible abrasive brush behavior for double disk magnetic abrasive finishing based on force signature夽 Prateek Kala a,∗ , Pulak M. Pandey b , Girish C. Verma b , Varun Sharma b a b
Departnent of Mechanical Engineering, BITS Pilani, Pilani, Rajasthan, 333031, India Department of Mechanical Engineering, IIT Delhi, Delhi, New Delhi, 110016, India
a r t i c l e
i n f o
Article history: Received 3 November 2016 Received in revised form 13 February 2017 Accepted 3 March 2017 Available online xxx Keywords: Magnetic abrasive finishing Dynamometer Force analysis FMAB Para/diamagnetic Double disk
a b s t r a c t The Double disk magnetic abrasive finishing process (DDMAF) poses better finishing characteristics while finishing paramagnetic thin work piece, when compared to plain magnetic abrasive finishing. This is due to the significant change in the behaviour of the flexible magnetic abrasive brush (FMAB) formed in two cases under similar conditions. Observing and comparing the behaviour of FMAB in action visually is a difficult task. However, FMAB average behaviour can be understood by observing the force signature. Thus present work aims at developing a setup that can be used to capture force signature for the two cases and then understand the FMAB behaviour. The present work present the FMAB force signature obtained while performing finishing with MAF with single disk and double disk. The force signature and the basic magnetic principle have been used to understand the FMAB behaviour and thus understand implications on the finishing process. © 2017 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.
1. Introduction Magnetic Abrasive Finishing (MAF) process is used for polishing of work piece. MAF uses a magnetic field producing source, which is usually an electro magnet [1] or permanent magnet [2], and a mixture of iron powder and abrasive powder. The magnetic source is used to produce a magnetic field in the working gap between the source and the work piece. In the working gap a mixture of iron and abrasive powder, also called magnetic abrasive particle(s) (MAP(s)), is placed. The powder mixture forms a chain like structure in the working gap [3]. Each chain is composed of large number of MAPs. These chains like structures are collectively called as Flexible Magnetic Abrasive Brush (FMAB). The FMAB works as a multi-point finishing tool [4]. In the process, two forces are generally responsible for material removal, the normal force and the tangential or circumferential force. The normal force acting through FMAB chain produces micronano indentations on the work piece surface [5]. A relative motion between FMAB and work piece need to be provided for machining to happen through plowing and shearing mechanism. The relative rotation between magnet and work piece provides the tangential
夽 Peer-review under responsibility ofthe Scientific Committee of NAMRI/SME. ∗ Corresponding author. E-mail address: [email protected] (P. Kala).
machining force. The normal and tangential machining forces can be controlled by various process parameters like magnetic field intensity in the working gap, circumferential speed, percentage weight of abrasive mixture etc. Attempts have been made by various researchers [6,7] to establish a relationship between various process parameters and machining forces. Singh et al. [6] in their work developed adequate regression model to relate process parameters, like current, working gap, rotational speed, lubricant and finishing time, with response variables, like normal force, tangential force and surface finish [6]. They also tried to find out the correlation between machining forces and surface finish. Mulik and Pandey [7] developed a mathematical model to predict normal and tangential force acting in case of ultrasonic assisted magnetic abrasive finishing (UAMAF) process. The model assumed a tetrahedron shape of abrasive. They also developed a statistical model which described normal and tangential forces as a function of process parameters like voltage to electromagnet, rotational speed, abrasive size, percentage weight of abrasive and pulse on time for ultrasonic vibration. In the analysis normal force and tangential force were mostly affected by voltage to electromagnet and working gap. Their analysis confirmed the fact that magnetic force density plays a very important role in deciding the magnitude of cutting forces. In other words, the magnetic field density in the gap has been found to be one of the important factors that decides the stiffness of the chains formed, i.e., higher the Magnetic Flux Density (MFD)
http://dx.doi.org/10.1016/j.jmapro.2017.04.010 1526-6125/© 2017 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Kala P, et al. Understanding flexible abrasive brush behavior for double disk magnetic abrasive finishing based on force signature. J Manuf Process (2017), http://dx.doi.org/10.1016/j.jmapro.2017.04.010
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Nomenclature DDMAF FMAB MAF MAP
Double disk magnetic abrasive finishing Flexible magnetic abrasive brush Magnetic abrasive finishing Magnetic abrasive particle
higher the stiffness of the chains. Other process parameters that also affect the stiffness of the FMAB are ferromagnetic powder particles size and ratio of ferromagnetic to abrasive powder. By varying the stiffness of the FMAB the different values of surface finish and material removal rate can be achieved [8]. Working in the area of MAF, Girma et al. [9] presented a difference in mechanism for material removal between cylindrical and planar MAF [9]. Cylindrical MAF is widely applied for ferromagnetic and para/diamagnetic cylindrical work pieces while planar MAF is widely used for planar ferromagnetic work piece. Planar MAF is considered ineffective for hard para/diamagnetic work piece. This owes to low MFD generated in the working gap [10]. In a work done by Kwak et al. [11] tried to improve machinability of a para/diamagnetic work piece by using a permanent mag10net beneath the work piece. They observed an appreciable improvement in surface finish. In addition, attempts have been made to modify the conventional MAF to suit different require-
ments and increase its potential [12–15,16]. In a similar direction Kala et al. [17] has developed a new setup for polishing planar para/diamagnetic work piece. For a better understanding capability of the double disk magnetic abrasive finishing process DDMAF process a setup was fabricated which was used to capture finishing forces in case of MAF or DDMAF process. The machining forces so obtained have been used to understand the behavior of FMAB in case of conventional MAF and DDMAF for a flat copper work piece. Further the effects of varying rotational speed and working gap on machining forces, in case of DDMAF, have been studied. 2. Experimental setup and procedure The experimental setup used for measuring finishing forces for the case of magnetic abrasive finishing and double disk magnetic abrasive finishing is shown in Fig. 1(a) and (b). The setup consisted of two rotating magnetic disks, between which the workpiece was placed. The experiments for the magnetic abrasive finishing were performed by removing the bottom disk while for double disk magnetic abrasive finishing both of the disks were used. The finishing forces have been measured using the dynamometer (Make: Schunk: DELTA sensor with SI-330-30 Calibration, accuracy:0.1 N). The gap between the two disks was too small for dynamometer to be placed, hence a special fixture (shown in Fig. 1c) was fabricated which could transfer the finishing forces, acting on the workpiece surface to the dynamometer. The upper plate of the fix-
Fig. 1. Setup used for measuring forces for magnetic abrasive finishing and double disk magnetic abrasive finishing (a) Setup for measuring force in magnetic abrasive finishing; (b) Setup for measuring forces in double disk magnetic abrasive finishing; (c) Fixture for accomadating dynamometer, (d) Schematic view showing arrangement of dynamometer and fixture in double disk arrangement.
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ture was made of copper alloy (120 mm × 100 mm × 3 mm) which was attached to U-shaped perspex assembly. The bottom plate of the fixture was bolted to the dynamometer. The side arms of the Perspex assembly were provided with slots in order to adjust the distance between the top and bottom plate. The fixture was rigidly mounted on the dynamometer so as to measure any small change in finishing forces. The dynamometer was placed coaxially with the two rotating disks. Fig. 1 shows the arrangement of dynamometer and the fixture relative to two disks. The normal force and finishing torque along Zdirection were recorded because the axis of rotation coincided with the Z-axis. In magnetic abrasive finishing, magnetic flux density in the working gap is the most important process factor that would affect the finishing forces. Permanent magnets were used in making the tool, the available MFD can be changed by varying the working gap. Thus it was decided to measure the effect of varying working gap on the finishing forces for planar magnetic abrasive finishing and double disk magnetic abrasive finishing. Alumina (Al2O3) abrasive powder (#800) was used in the present work. Observing the improvement in normal force for double disk magnetic abrasive finishing the effect of varying rotational speed and working gap, for the same process, on normal force and finishing torque was captured and a suitable explanation for the trend has been presented. 3. Comparison of finishing forces in MAF and DDMAF This section presents some important observations noticed while varying the working gap for magnetic abrasive finishing and double disk magnetic abrasive finishing processes. Since a small variation in the working gap caused a proportional increase or decrease in the normal and tangential force. Thus only normal force data has been presented in the present section. 3.1. Effect of decreasing working gap Fig. 2 shows the effect of varying working gap on the magnetic abrasive finishing and double disk magnetic abrasive finishing process under similar processing conditions (0.3 T magnetic field, 300 rpm rotational speed, 25% weight of abrasive and 800 mesh). There are two important observations that can be made from the figure: • The initial normal force in case of double disk magnetic abrasive finishing is more as compared to the magnetic abrasive finishing process. • The normal force shows a drop at a later stage in case of magnetic abrasive finishing process while in the case of double disk magnetic abrasive finishing, it does not drop. In order to understand the increase in the initial magnitude of normal force a finite element analysis has been performed on Maxwell 13 software (magnetic field simulation software). The details of model are described in authors another work [18] and the same has been used for present analysis. The excitation to the magnets was given such that the maximum magnetic flux density for both the cases was 0.3 T. The simulation results obtained for the magnetic flux density vector (B) on the workpiece surface for magnetic abrasive finishing and double disk magnetic abrasive finishing have been shown in Fig. 3(a) and (b), respectively. It can be observed that for the given maximum magnetic flux density (0.3T) the average components of B, normal to the work piece surface is more in case of double disk magnetic abrasive finishing as compared to the magnetic abrasive finishing which is responsible for an increase in the initial normal force in case of double disk magnetic abrasive finishing as compared to that of magnetic abrasive finishing while finishing a flat paramagnetic workpiece.
Fig. 2. Effect of decreasing working gap with time on normal force for copper alloy work-piece (a) Magnetic abrgasive finishing, (b) Double disk magnetic abrasive finishing.
The second difference that can be observed from the Fig. 2 is that the normal force in case of double disk magnetic abrasive finishing does not drop at a later part. This could be because in case of double disk magnetic abrasive finishing the two opposite poles of the upper and lower disk are close enough to provide magnetic lines of forces a fixed least path of magnetic reluctance, which is almost straight line from north pole to south pole. Thus, when the flexible magnetic abrasive brush forms in case of DDMAF it has a tendency to remain along the direction of magnetic lines of forces (MLF), as shown in Fig. 4. This phenomenon provides the necessary strength to the flexible magnetic abrasive brush to withstand the increase in finishing forces caused due to decrease in the working gap. The difference so observed in finishing of copper alloy workpiece during magnetic abrasive finishing and double disk magnetic abrasive finishing processes has been experimentally verified at various operating condition as shown in Figs. 5 and 6. Fig. 5(a) and (b) shows the variation of normal force w.r.t. time at various operating conditions for magnetic abrasive finishing process. Fig. 5 shows a sudden drop in normal force after decreasing the working gap. The Fig. 6(a) and (b) shows the variation in normal force w.r.t. time at different operating conditions for double disk magnetic abrasive finishing process. It can be observed that
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Fig. 3. Simulation results showing direction and magnitude of magnetic flux for magnetic abrasive finishing and double disk magnetic abrasive finishing on the workpiece surface (a) Magnetic abrasive finishing: [Iupper = 7580 A-turns]; (b) Double disk magnetic abrasive finishing [Iupper = 3000, Ilower = 2500 A-turns].
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3.2. Effect of increasing working gap
Fig. 4. Flexible magnetic abrasive brush chains in case of double disk magnetic abrasive finishing before and after decreasing the working gap.
normal force increases by decreasing the working gap. This may be attributed due to the re-alignment of chains along the line of forces under the influence of lower magnet.
Fig. 7 shows the variation in the normal forces with respect to the time during magnetic abrasive finishing and double disk magnetic abrasive finishing. Fig. 7(a) shows a sudden drop in normal force in case of magnetic abrasive finishing when working gap is increased from 2.5 mm to 3 mm. Fig. 7(b) shows the variation caused in the normal force for double disk magnetic abrasive finishing as the working gap is varied between 2.5 mm and 3 mm. It can be also be inferred from the figure that flexible magnetic abrasive brush in case of do magnetic abrasive finishing is capable of adjusting the length of the chains so that it is always in touch with the workpiece and provide finishing action. This is due to presence of another magnet (on the lower side) which pulls the iron particles and rearranges the chains to adjust themselves according to the space available. Fig. 7(b) shows that flexible magnetic abrasive brush results in a good traceability during double disk magnetic abrasive finishing process. The normal force shows a corresponding change in its magnitude as the working gap is varied. This provides
Fig. 5. Effect of decreasing working gap with time on normal force while finishing copper workpiece using magnetic abrasive finishing (a) 300 rpm with 20% weight of alumina abrasive of 800 mesh size (b) 350 rpm with 20% weight of alumina abrasive of 800 mesh size.
Fig. 6. Effect of decreasing working gap with time on normal force while finishing copper workpiece using double disk magnetic abrasive finishing process (a) 250 rpm with 20% weight of alumina abrasive and abrasive mesh size 800 mesh size (b) 475 rpm with 20% weight of alumina abrasive of 800 mesh size.
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Fig. 7. Effect of increasing working gap with time on normal force with copper workpiece (a) magnetic abrasive finishing (250 rpm 20% weight of 800 mesh)abrasive (b) double disk magnetic abrasive finishing (450 rpm, 20% weight of 800 mesh abrasive).
an advantage during the finishing of para/diamagnetic material over conventional magnetic abrasive finishing process. 3.3. FMAB behavior in MAF and DDMAF The study was further focused on observing the effect of rotational speed (RPM) on normal and tangential forces. The Fig. 8 illustrates the effect of increasing rotational speed on normal and tangential force the figure shows that as the RPM increases the magnitude of normal force decreases. The decrease in normal force is linear initially (from 80 rpm to 410 rpm) thereafter normal force starts showing steep decrease on any further increase in RPM. On the other hand tangential force shows an increase in magnitude when rpm is increased. However this increase persists until certain rpm (410 rpm) is achieved thereafter tangential force also shows a steep decrease. In planar MAF or DDMAF process the FMAB characteristic is mainly governed by two major forces magnetic force and centrifugal force. In case of planar MAF magnetic force and centrifugal force acting on the MAPs are acting perpendicular to each other. The resultant normal force acting on MAPs is governed by these two forces [7]. Thus for a given magnetic field density, i.e. for given magnetic force, any increase in rpm causes an increase in centrifugal force as a result normal force acting on work piece decreases. Initially (from 80 to 410 rpm) when the rpm is increased the normal force decreases in linear fashion and thereafter drops steeply. This is because at lower rpm only the centrifugal force increases which causes a reduction in normal force (as some portion of magnetic force is used to counterbalance the centrifugal force so the portion of force which is used as normal force decreases). But at
4. Conclusions
70 60
Normal Force
50
Force (N)
higher rpm the centrifugal force dominates and pulls out the MAPs forming FMAB chains. This decreases the total number of MAPs available in the working gap. Thus at lower RPM, only centrifugal force causes a decrease whereas above a certain value (610 rpm in this case) not only the centrifugal force but also the decreasing number of MAPs participating in machining affects the machining force such that steep fall in normal force is observed. The increase in tangential force is accounted because of increased frictional force between FMAB and work piece which is also reflected in increase in temperature [12] at interface between FMAB and work piece. The decrease is observed because of the fact that at very high RPM centrifugal force causes the MAP to leave the working gap and fall out, thus decreasing the total number of MAP particles. The MAP present near the weaker magnetic field start leaving the working gap first and this behavior extends to the area with stronger magnetic field with increase in RPM. The effect of working gap on normal and tangential force can be seen in Fig. 9. It can be seen from Fig. 9 that with decrease in working gap normal and tangential force increases. Increase in magnetic field increase the rigidity of the FMAB chains because of which the normal force acting on the work piece increases. The tangential force increases with the increase in normal force. From Fig. 9 it can be seen that normal force increases at a faster rate as compared to tangential force when the gap is decreased. The present trend indicates that increasing normal force at higher level will not increase tangential force appreciably and thus producing higher magnetic field alone which in turn increases normal force will not produce better finishing.
Tangenal Force
40 30 20 10 0 0
100 200 300 400 500 600 700 800
RPM Fig. 8. Variation of normal and tangential force with RPM.
In the present study the results based on machining forces were analyzed and has been concluded here under: 1. Finishing of para/diamagnetic work piece in MAF is not effective because of low finishing forces involved. To overcome this challenge Double disk magnetic finishing (DDMAF) can be used to perform finishing of such materials. 2. The finishing force data reveals that brush formed in MAF is not enough rigid to provide finishing para/diamagnetic material because the magnetic lines of forces are following the MAPs while in case of DDMAF the magnetic lines of forces are set
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Fig. 9. Trend for normal and tangential force with decreasing working gap.
between two opposite poles and thus make MAPs to follow the magnetic lines of forces. 3. Traceability is an important characteristic of FMAB. It is defined as tendency of MAPs to fill the gap created as material is removed while machining. The traceability of FMAB is very poor in case of MAF of para/diamagnetic material which is a major drawback while as with machining the working gap automatically decreases. DDMAF provides a good traceability while machining para/diamagnetic material. 4. The effect of RPM showed a decreasing trend in normal force when RPM increases whereas for tangential force showed an increasing trend and then a decreasing trend. The increases or decrease in case of tangential force or normal force respectively follows a linear behavior at lower rpm while at rpm above certain rpm (410 rpm in the present case) shows a steep decrease in magnitude of both the forces. 5. Normal force and tangential force increases with decreasing working gap but rate of increase of normal force becomes much higher at smaller working gap as compared to that of tangential force. This reveals that increasing normal force does not always increase the tangential force in the same proportion. References [1] Suzuki H, Kodera S, Hara S, Matsunaga H, Kurobet T. Magnetic field-assisted polishing application to cu rved surface. Precision Eng Butterworth & Co. (Pvt.) Ltd 1989;11(4):197–202. [2] Yamaguchi V, Shinmura Raghuram T. Study of an internal magnetic abrasive finishing using a pole rotation system Discussion of the characteristic abrasive behavior. Int J Adv Manuf Technol 2000;24:237–44. [3] Mori T, Hirota K, Kawashima Y. Clarification of magnetic abrasive finishing mechanism. J Mater Process Technol 2003;143–144:682–6.
[4] Jain VK. Abrasive-Based Nano-Finishing Techniques: an Overview. Mach Sci Technol 2008;12(3):257–94. [5] Jain VK. Magnetic field assisted abrasive based micro-/nano-finishing. J Mater Process Technol 2009;209(20):6022–38. [6] Jain VK, Singh DK. Experimental investigations into forces acting during a magnetic abrasive finishing process. Int J Adv Manuf Technol 2005;30:652–62. [7] R. S. Mulik and P. M. Pandey, Experimental Investigations into The Finishing Force and Torque In Magnetic Abrasive Finishing Process. International Mechanical Engineering Congress and Exposition Volume 2B: Advanced Manufacturing, 2(B), (2013). 1–7. [8] Singh DK, Jain VK, Raghuram V. Parametric study of magnetic abrasive finishing process. J Mater Process Technol 2004;149(1–3):22–9. [9] Girma B, Joshi SS, Raghuram MVGS, Balasubramaniam R. An experimental analysis of magnetic abrasives finishing of plane surfaces. Mach Sci Technol 2006;10(3):323–40. [10] Kim SO, Kwak JS. Magnetic force improvement and parameter optimization for magnetic abrasive polishing of AZ31 magnesium alloy? Trans Nonferrous Met Soc China 2008;18(2013):369–s373. [11] J. K. Ã and J.-S. Kwak, Enhanced magnetic abrasive polishing of non-ferrous metals utilizing a permanent magnet, International Journal of Machine Tools and Manufacture, 49(7–8),(2009) 613–618. [12] J. Kim, Study on the effect of a magnetic field on an electrolytic finishing process jeong-du kim, t∼ dong-xie, 37(4)(1997) 401–408. [13] El-Taweel TA. Modelling and analysis of hybrid electrochemical turningmagnetic abrasive finishing of 6061 Al/Al2O3 composite. Internat J Adv Manuf Technol 2007;37(7–8):705–14. [14] Wang AC, Lee SJ. Study the characteristics of magnetic finishing with gel abrasive. Int J Mach Tools Manuf 2009;49(14):1063–9. [15] Mulik RS, Pandey PM. Ultrasonic assisted magnetic abrasive finishing of hardened AISI 52100 steel using unbonded SiC abrasives. Int J Refract Met Hard Mater 2011;29(1):68–77. [16] Kala P, Kumar S, Pandey PM. Polishing of copper alloy using double disk ultrasonic assisted magnetic abrasive polishing. Mater Manuf Processes 2013;28(2):200–6. [17] Yamaguchi H, Shinmura T, Ikeda R. Study of internal finishing of austenitic stainless steel capillary tubes by magnetic abrasive finishing. ASME J Manuf Sci Eng 2007;129(5):885–93. [18] Kala P, Pandey PM. Comparison of finishing characteristics of two paramagnetic materials using double disc magnetic abrasive finishing. J Manuf Processes 2015;17:63–77.
Please cite this article in press as: Kala P, et al. Understanding flexible abrasive brush behavior for double disk magnetic abrasive finishing based on force signature. J Manuf Process (2017), http://dx.doi.org/10.1016/j.jmapro.2017.04.010
ARTICLE IN PRESS Journal of Manufacturing Processes xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
Journal of Manufacturing Processes journal homepage: www.elsevier.com/locate/manpro
45th SME North American Manufacturing Research Conference, NAMRC 45, LA, USA
Understanding flexible abrasive brush behavior for double disk magnetic abrasive finishing based on force signature夽 Prateek Kala a,∗ , Pulak M. Pandey b , Girish C. Verma b , Varun Sharma b a b
Departnent of Mechanical Engineering, BITS Pilani, Pilani, Rajasthan, 333031, India Department of Mechanical Engineering, IIT Delhi, Delhi, New Delhi, 110016, India
a r t i c l e
i n f o
Article history: Received 3 November 2016 Received in revised form 13 February 2017 Accepted 3 March 2017 Available online xxx Keywords: Magnetic abrasive finishing Dynamometer Force analysis FMAB Para/diamagnetic Double disk
a b s t r a c t The Double disk magnetic abrasive finishing process (DDMAF) poses better finishing characteristics while finishing paramagnetic thin work piece, when compared to plain magnetic abrasive finishing. This is due to the significant change in the behaviour of the flexible magnetic abrasive brush (FMAB) formed in two cases under similar conditions. Observing and comparing the behaviour of FMAB in action visually is a difficult task. However, FMAB average behaviour can be understood by observing the force signature. Thus present work aims at developing a setup that can be used to capture force signature for the two cases and then understand the FMAB behaviour. The present work present the FMAB force signature obtained while performing finishing with MAF with single disk and double disk. The force signature and the basic magnetic principle have been used to understand the FMAB behaviour and thus understand implications on the finishing process. © 2017 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.
1. Introduction Magnetic Abrasive Finishing (MAF) process is used for polishing of work piece. MAF uses a magnetic field producing source, which is usually an electro magnet [1] or permanent magnet [2], and a mixture of iron powder and abrasive powder. The magnetic source is used to produce a magnetic field in the working gap between the source and the work piece. In the working gap a mixture of iron and abrasive powder, also called magnetic abrasive particle(s) (MAP(s)), is placed. The powder mixture forms a chain like structure in the working gap [3]. Each chain is composed of large number of MAPs. These chains like structures are collectively called as Flexible Magnetic Abrasive Brush (FMAB). The FMAB works as a multi-point finishing tool [4]. In the process, two forces are generally responsible for material removal, the normal force and the tangential or circumferential force. The normal force acting through FMAB chain produces micronano indentations on the work piece surface [5]. A relative motion between FMAB and work piece need to be provided for machining to happen through plowing and shearing mechanism. The relative rotation between magnet and work piece provides the tangential
夽 Peer-review under responsibility ofthe Scientific Committee of NAMRI/SME. ∗ Corresponding author. E-mail address: [email protected] (P. Kala).
machining force. The normal and tangential machining forces can be controlled by various process parameters like magnetic field intensity in the working gap, circumferential speed, percentage weight of abrasive mixture etc. Attempts have been made by various researchers [6,7] to establish a relationship between various process parameters and machining forces. Singh et al. [6] in their work developed adequate regression model to relate process parameters, like current, working gap, rotational speed, lubricant and finishing time, with response variables, like normal force, tangential force and surface finish [6]. They also tried to find out the correlation between machining forces and surface finish. Mulik and Pandey [7] developed a mathematical model to predict normal and tangential force acting in case of ultrasonic assisted magnetic abrasive finishing (UAMAF) process. The model assumed a tetrahedron shape of abrasive. They also developed a statistical model which described normal and tangential forces as a function of process parameters like voltage to electromagnet, rotational speed, abrasive size, percentage weight of abrasive and pulse on time for ultrasonic vibration. In the analysis normal force and tangential force were mostly affected by voltage to electromagnet and working gap. Their analysis confirmed the fact that magnetic force density plays a very important role in deciding the magnitude of cutting forces. In other words, the magnetic field density in the gap has been found to be one of the important factors that decides the stiffness of the chains formed, i.e., higher the Magnetic Flux Density (MFD)
http://dx.doi.org/10.1016/j.jmapro.2017.04.010 1526-6125/© 2017 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Kala P, et al. Understanding flexible abrasive brush behavior for double disk magnetic abrasive finishing based on force signature. J Manuf Process (2017), http://dx.doi.org/10.1016/j.jmapro.2017.04.010
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Nomenclature DDMAF FMAB MAF MAP
Double disk magnetic abrasive finishing Flexible magnetic abrasive brush Magnetic abrasive finishing Magnetic abrasive particle
higher the stiffness of the chains. Other process parameters that also affect the stiffness of the FMAB are ferromagnetic powder particles size and ratio of ferromagnetic to abrasive powder. By varying the stiffness of the FMAB the different values of surface finish and material removal rate can be achieved [8]. Working in the area of MAF, Girma et al. [9] presented a difference in mechanism for material removal between cylindrical and planar MAF [9]. Cylindrical MAF is widely applied for ferromagnetic and para/diamagnetic cylindrical work pieces while planar MAF is widely used for planar ferromagnetic work piece. Planar MAF is considered ineffective for hard para/diamagnetic work piece. This owes to low MFD generated in the working gap [10]. In a work done by Kwak et al. [11] tried to improve machinability of a para/diamagnetic work piece by using a permanent mag10net beneath the work piece. They observed an appreciable improvement in surface finish. In addition, attempts have been made to modify the conventional MAF to suit different require-
ments and increase its potential [12–15,16]. In a similar direction Kala et al. [17] has developed a new setup for polishing planar para/diamagnetic work piece. For a better understanding capability of the double disk magnetic abrasive finishing process DDMAF process a setup was fabricated which was used to capture finishing forces in case of MAF or DDMAF process. The machining forces so obtained have been used to understand the behavior of FMAB in case of conventional MAF and DDMAF for a flat copper work piece. Further the effects of varying rotational speed and working gap on machining forces, in case of DDMAF, have been studied. 2. Experimental setup and procedure The experimental setup used for measuring finishing forces for the case of magnetic abrasive finishing and double disk magnetic abrasive finishing is shown in Fig. 1(a) and (b). The setup consisted of two rotating magnetic disks, between which the workpiece was placed. The experiments for the magnetic abrasive finishing were performed by removing the bottom disk while for double disk magnetic abrasive finishing both of the disks were used. The finishing forces have been measured using the dynamometer (Make: Schunk: DELTA sensor with SI-330-30 Calibration, accuracy:0.1 N). The gap between the two disks was too small for dynamometer to be placed, hence a special fixture (shown in Fig. 1c) was fabricated which could transfer the finishing forces, acting on the workpiece surface to the dynamometer. The upper plate of the fix-
Fig. 1. Setup used for measuring forces for magnetic abrasive finishing and double disk magnetic abrasive finishing (a) Setup for measuring force in magnetic abrasive finishing; (b) Setup for measuring forces in double disk magnetic abrasive finishing; (c) Fixture for accomadating dynamometer, (d) Schematic view showing arrangement of dynamometer and fixture in double disk arrangement.
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ture was made of copper alloy (120 mm × 100 mm × 3 mm) which was attached to U-shaped perspex assembly. The bottom plate of the fixture was bolted to the dynamometer. The side arms of the Perspex assembly were provided with slots in order to adjust the distance between the top and bottom plate. The fixture was rigidly mounted on the dynamometer so as to measure any small change in finishing forces. The dynamometer was placed coaxially with the two rotating disks. Fig. 1 shows the arrangement of dynamometer and the fixture relative to two disks. The normal force and finishing torque along Zdirection were recorded because the axis of rotation coincided with the Z-axis. In magnetic abrasive finishing, magnetic flux density in the working gap is the most important process factor that would affect the finishing forces. Permanent magnets were used in making the tool, the available MFD can be changed by varying the working gap. Thus it was decided to measure the effect of varying working gap on the finishing forces for planar magnetic abrasive finishing and double disk magnetic abrasive finishing. Alumina (Al2O3) abrasive powder (#800) was used in the present work. Observing the improvement in normal force for double disk magnetic abrasive finishing the effect of varying rotational speed and working gap, for the same process, on normal force and finishing torque was captured and a suitable explanation for the trend has been presented. 3. Comparison of finishing forces in MAF and DDMAF This section presents some important observations noticed while varying the working gap for magnetic abrasive finishing and double disk magnetic abrasive finishing processes. Since a small variation in the working gap caused a proportional increase or decrease in the normal and tangential force. Thus only normal force data has been presented in the present section. 3.1. Effect of decreasing working gap Fig. 2 shows the effect of varying working gap on the magnetic abrasive finishing and double disk magnetic abrasive finishing process under similar processing conditions (0.3 T magnetic field, 300 rpm rotational speed, 25% weight of abrasive and 800 mesh). There are two important observations that can be made from the figure: • The initial normal force in case of double disk magnetic abrasive finishing is more as compared to the magnetic abrasive finishing process. • The normal force shows a drop at a later stage in case of magnetic abrasive finishing process while in the case of double disk magnetic abrasive finishing, it does not drop. In order to understand the increase in the initial magnitude of normal force a finite element analysis has been performed on Maxwell 13 software (magnetic field simulation software). The details of model are described in authors another work [18] and the same has been used for present analysis. The excitation to the magnets was given such that the maximum magnetic flux density for both the cases was 0.3 T. The simulation results obtained for the magnetic flux density vector (B) on the workpiece surface for magnetic abrasive finishing and double disk magnetic abrasive finishing have been shown in Fig. 3(a) and (b), respectively. It can be observed that for the given maximum magnetic flux density (0.3T) the average components of B, normal to the work piece surface is more in case of double disk magnetic abrasive finishing as compared to the magnetic abrasive finishing which is responsible for an increase in the initial normal force in case of double disk magnetic abrasive finishing as compared to that of magnetic abrasive finishing while finishing a flat paramagnetic workpiece.
Fig. 2. Effect of decreasing working gap with time on normal force for copper alloy work-piece (a) Magnetic abrgasive finishing, (b) Double disk magnetic abrasive finishing.
The second difference that can be observed from the Fig. 2 is that the normal force in case of double disk magnetic abrasive finishing does not drop at a later part. This could be because in case of double disk magnetic abrasive finishing the two opposite poles of the upper and lower disk are close enough to provide magnetic lines of forces a fixed least path of magnetic reluctance, which is almost straight line from north pole to south pole. Thus, when the flexible magnetic abrasive brush forms in case of DDMAF it has a tendency to remain along the direction of magnetic lines of forces (MLF), as shown in Fig. 4. This phenomenon provides the necessary strength to the flexible magnetic abrasive brush to withstand the increase in finishing forces caused due to decrease in the working gap. The difference so observed in finishing of copper alloy workpiece during magnetic abrasive finishing and double disk magnetic abrasive finishing processes has been experimentally verified at various operating condition as shown in Figs. 5 and 6. Fig. 5(a) and (b) shows the variation of normal force w.r.t. time at various operating conditions for magnetic abrasive finishing process. Fig. 5 shows a sudden drop in normal force after decreasing the working gap. The Fig. 6(a) and (b) shows the variation in normal force w.r.t. time at different operating conditions for double disk magnetic abrasive finishing process. It can be observed that
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Fig. 3. Simulation results showing direction and magnitude of magnetic flux for magnetic abrasive finishing and double disk magnetic abrasive finishing on the workpiece surface (a) Magnetic abrasive finishing: [Iupper = 7580 A-turns]; (b) Double disk magnetic abrasive finishing [Iupper = 3000, Ilower = 2500 A-turns].
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3.2. Effect of increasing working gap
Fig. 4. Flexible magnetic abrasive brush chains in case of double disk magnetic abrasive finishing before and after decreasing the working gap.
normal force increases by decreasing the working gap. This may be attributed due to the re-alignment of chains along the line of forces under the influence of lower magnet.
Fig. 7 shows the variation in the normal forces with respect to the time during magnetic abrasive finishing and double disk magnetic abrasive finishing. Fig. 7(a) shows a sudden drop in normal force in case of magnetic abrasive finishing when working gap is increased from 2.5 mm to 3 mm. Fig. 7(b) shows the variation caused in the normal force for double disk magnetic abrasive finishing as the working gap is varied between 2.5 mm and 3 mm. It can be also be inferred from the figure that flexible magnetic abrasive brush in case of do magnetic abrasive finishing is capable of adjusting the length of the chains so that it is always in touch with the workpiece and provide finishing action. This is due to presence of another magnet (on the lower side) which pulls the iron particles and rearranges the chains to adjust themselves according to the space available. Fig. 7(b) shows that flexible magnetic abrasive brush results in a good traceability during double disk magnetic abrasive finishing process. The normal force shows a corresponding change in its magnitude as the working gap is varied. This provides
Fig. 5. Effect of decreasing working gap with time on normal force while finishing copper workpiece using magnetic abrasive finishing (a) 300 rpm with 20% weight of alumina abrasive of 800 mesh size (b) 350 rpm with 20% weight of alumina abrasive of 800 mesh size.
Fig. 6. Effect of decreasing working gap with time on normal force while finishing copper workpiece using double disk magnetic abrasive finishing process (a) 250 rpm with 20% weight of alumina abrasive and abrasive mesh size 800 mesh size (b) 475 rpm with 20% weight of alumina abrasive of 800 mesh size.
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Fig. 7. Effect of increasing working gap with time on normal force with copper workpiece (a) magnetic abrasive finishing (250 rpm 20% weight of 800 mesh)abrasive (b) double disk magnetic abrasive finishing (450 rpm, 20% weight of 800 mesh abrasive).
an advantage during the finishing of para/diamagnetic material over conventional magnetic abrasive finishing process. 3.3. FMAB behavior in MAF and DDMAF The study was further focused on observing the effect of rotational speed (RPM) on normal and tangential forces. The Fig. 8 illustrates the effect of increasing rotational speed on normal and tangential force the figure shows that as the RPM increases the magnitude of normal force decreases. The decrease in normal force is linear initially (from 80 rpm to 410 rpm) thereafter normal force starts showing steep decrease on any further increase in RPM. On the other hand tangential force shows an increase in magnitude when rpm is increased. However this increase persists until certain rpm (410 rpm) is achieved thereafter tangential force also shows a steep decrease. In planar MAF or DDMAF process the FMAB characteristic is mainly governed by two major forces magnetic force and centrifugal force. In case of planar MAF magnetic force and centrifugal force acting on the MAPs are acting perpendicular to each other. The resultant normal force acting on MAPs is governed by these two forces [7]. Thus for a given magnetic field density, i.e. for given magnetic force, any increase in rpm causes an increase in centrifugal force as a result normal force acting on work piece decreases. Initially (from 80 to 410 rpm) when the rpm is increased the normal force decreases in linear fashion and thereafter drops steeply. This is because at lower rpm only the centrifugal force increases which causes a reduction in normal force (as some portion of magnetic force is used to counterbalance the centrifugal force so the portion of force which is used as normal force decreases). But at
4. Conclusions
70 60
Normal Force
50
Force (N)
higher rpm the centrifugal force dominates and pulls out the MAPs forming FMAB chains. This decreases the total number of MAPs available in the working gap. Thus at lower RPM, only centrifugal force causes a decrease whereas above a certain value (610 rpm in this case) not only the centrifugal force but also the decreasing number of MAPs participating in machining affects the machining force such that steep fall in normal force is observed. The increase in tangential force is accounted because of increased frictional force between FMAB and work piece which is also reflected in increase in temperature [12] at interface between FMAB and work piece. The decrease is observed because of the fact that at very high RPM centrifugal force causes the MAP to leave the working gap and fall out, thus decreasing the total number of MAP particles. The MAP present near the weaker magnetic field start leaving the working gap first and this behavior extends to the area with stronger magnetic field with increase in RPM. The effect of working gap on normal and tangential force can be seen in Fig. 9. It can be seen from Fig. 9 that with decrease in working gap normal and tangential force increases. Increase in magnetic field increase the rigidity of the FMAB chains because of which the normal force acting on the work piece increases. The tangential force increases with the increase in normal force. From Fig. 9 it can be seen that normal force increases at a faster rate as compared to tangential force when the gap is decreased. The present trend indicates that increasing normal force at higher level will not increase tangential force appreciably and thus producing higher magnetic field alone which in turn increases normal force will not produce better finishing.
Tangenal Force
40 30 20 10 0 0
100 200 300 400 500 600 700 800
RPM Fig. 8. Variation of normal and tangential force with RPM.
In the present study the results based on machining forces were analyzed and has been concluded here under: 1. Finishing of para/diamagnetic work piece in MAF is not effective because of low finishing forces involved. To overcome this challenge Double disk magnetic finishing (DDMAF) can be used to perform finishing of such materials. 2. The finishing force data reveals that brush formed in MAF is not enough rigid to provide finishing para/diamagnetic material because the magnetic lines of forces are following the MAPs while in case of DDMAF the magnetic lines of forces are set
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Fig. 9. Trend for normal and tangential force with decreasing working gap.
between two opposite poles and thus make MAPs to follow the magnetic lines of forces. 3. Traceability is an important characteristic of FMAB. It is defined as tendency of MAPs to fill the gap created as material is removed while machining. The traceability of FMAB is very poor in case of MAF of para/diamagnetic material which is a major drawback while as with machining the working gap automatically decreases. DDMAF provides a good traceability while machining para/diamagnetic material. 4. The effect of RPM showed a decreasing trend in normal force when RPM increases whereas for tangential force showed an increasing trend and then a decreasing trend. The increases or decrease in case of tangential force or normal force respectively follows a linear behavior at lower rpm while at rpm above certain rpm (410 rpm in the present case) shows a steep decrease in magnitude of both the forces. 5. Normal force and tangential force increases with decreasing working gap but rate of increase of normal force becomes much higher at smaller working gap as compared to that of tangential force. This reveals that increasing normal force does not always increase the tangential force in the same proportion. References [1] Suzuki H, Kodera S, Hara S, Matsunaga H, Kurobet T. Magnetic field-assisted polishing application to cu rved surface. Precision Eng Butterworth & Co. (Pvt.) Ltd 1989;11(4):197–202. [2] Yamaguchi V, Shinmura Raghuram T. Study of an internal magnetic abrasive finishing using a pole rotation system Discussion of the characteristic abrasive behavior. Int J Adv Manuf Technol 2000;24:237–44. [3] Mori T, Hirota K, Kawashima Y. Clarification of magnetic abrasive finishing mechanism. J Mater Process Technol 2003;143–144:682–6.
[4] Jain VK. Abrasive-Based Nano-Finishing Techniques: an Overview. Mach Sci Technol 2008;12(3):257–94. [5] Jain VK. Magnetic field assisted abrasive based micro-/nano-finishing. J Mater Process Technol 2009;209(20):6022–38. [6] Jain VK, Singh DK. Experimental investigations into forces acting during a magnetic abrasive finishing process. Int J Adv Manuf Technol 2005;30:652–62. [7] R. S. Mulik and P. M. Pandey, Experimental Investigations into The Finishing Force and Torque In Magnetic Abrasive Finishing Process. International Mechanical Engineering Congress and Exposition Volume 2B: Advanced Manufacturing, 2(B), (2013). 1–7. [8] Singh DK, Jain VK, Raghuram V. Parametric study of magnetic abrasive finishing process. J Mater Process Technol 2004;149(1–3):22–9. [9] Girma B, Joshi SS, Raghuram MVGS, Balasubramaniam R. An experimental analysis of magnetic abrasives finishing of plane surfaces. Mach Sci Technol 2006;10(3):323–40. [10] Kim SO, Kwak JS. Magnetic force improvement and parameter optimization for magnetic abrasive polishing of AZ31 magnesium alloy? Trans Nonferrous Met Soc China 2008;18(2013):369–s373. [11] J. K. Ã and J.-S. Kwak, Enhanced magnetic abrasive polishing of non-ferrous metals utilizing a permanent magnet, International Journal of Machine Tools and Manufacture, 49(7–8),(2009) 613–618. [12] J. Kim, Study on the effect of a magnetic field on an electrolytic finishing process jeong-du kim, t∼ dong-xie, 37(4)(1997) 401–408. [13] El-Taweel TA. Modelling and analysis of hybrid electrochemical turningmagnetic abrasive finishing of 6061 Al/Al2O3 composite. Internat J Adv Manuf Technol 2007;37(7–8):705–14. [14] Wang AC, Lee SJ. Study the characteristics of magnetic finishing with gel abrasive. Int J Mach Tools Manuf 2009;49(14):1063–9. [15] Mulik RS, Pandey PM. Ultrasonic assisted magnetic abrasive finishing of hardened AISI 52100 steel using unbonded SiC abrasives. Int J Refract Met Hard Mater 2011;29(1):68–77. [16] Kala P, Kumar S, Pandey PM. Polishing of copper alloy using double disk ultrasonic assisted magnetic abrasive polishing. Mater Manuf Processes 2013;28(2):200–6. [17] Yamaguchi H, Shinmura T, Ikeda R. Study of internal finishing of austenitic stainless steel capillary tubes by magnetic abrasive finishing. ASME J Manuf Sci Eng 2007;129(5):885–93. [18] Kala P, Pandey PM. Comparison of finishing characteristics of two paramagnetic materials using double disc magnetic abrasive finishing. J Manuf Processes 2015;17:63–77.
Please cite this article in press as: Kala P, et al. Understanding flexible abrasive brush behavior for double disk magnetic abrasive finishing based on force signature. J Manuf Process (2017), http://dx.doi.org/10.1016/j.jmapro.2017.04.010