[ieee 2012 ieee asia-pacific conference on applied electromagnetics (apace) - melaka, malaysia...

Simulation and Experiment Research of Magnetic Gasbag Polishing

Mingsheng Jin, Shiming Ji, Cai Zhang, Haiping Ao, and Li Zhang Key Laboratory of E&M, Ministry of Education & Zhejiang Province

Zhejiang University of Technology, 310032 Hangzhou, China

[email protected]

Abstract—The novel magnetic gasbag polishing technology is presented in this paper. It can be used in polishing the contact or non-contact zone between gasbag and mould surface. By means of the interaction between magnetic field and magnetic abrasive, the magnetic abrasive brush is formed, and abrasive particles filed can be controlled actively. The force of a single magnetic abrasive in the contact or non-contact zone is analyzed. Moreover, the simulation is performed for the magnetic field generated by permanent magnet in gasbag polishing tool. The original state and feature of magnetic field distribution are obtained. On this basis, the changes of magnetic field in different downward depth and inclination angle of polishing tool are simulated and compared. Then, the magnetic field distribution in actual polishing is obtained. The polishing effect of the neighborhood of gasbag contact zone is studied by fix-point and movement polishing experiment, and a smooth high quality surface can be obtained. After movement polishing with beeline trajectory, the surface roughness of the neighborhood of gasbag contact zone reaches Ra 0.25�m.

Index Terms—Magnetic gasbag polishing, simulation, magnetic field, surface roughness.

I. INTRODUCTION Gasbag polishing is considered as a new technique of ultra-

precision machining [1-3]. It is particularly useful for the curved surface machining, with the complexity of the structure of curved, some tiny grooves, inner bevel, outer bevel, processing flow and the place with a sudden change of curvature, which can be found on the most of the mould surface. So, these structures become blind areas, and can not be contacted with gasbag directly when polishing.

The novel magnetic gasbag polishing technology is based on the theory of gasbag polishing, and the robot assisted magnetic gasbag polishing system is established, as shown in Fig. 1. This novel polishing technology contains a permanent magnet or magnet coil in the gasbag, and the magnetic abrasive can be gathered on the surface of the gasbag through magnetic field. The method of magnetic gasbag polishing can be used in polishing the contact zone between gasbag and mould surface. At the meantime, by means of the interaction between magnetic field and magnetic abrasive, the abrasive particles filed can be controlled, and magnetic abrasive brush is formed, which can be used in non-contact zone polishing.

By utilizing this novel technology, the tiny grooves, inner bevel, outer bevel, processing flow and the place with a sudden change of curvature, which can not be touched by the gasbag formerly, can be polished now. It will greatly increase the application range of gasbag polishing technology.

Fig. 1. The robot assisted magnetic gasbag polishing system.

II. POLISHING CHARACTERISTICS AND FORCE ANALYSIS There are two different material removal modes, one is the

gasbag does not touch the mould surface, as shown in Fig. 2(a), another is the gasbag presses on the mould surface with a certain downward depth, as shown in Fig. 2(b). The former mode can helps to process areas such as tiny grooves and inner bevels that the gasbag can not touch. The second mode improves the material removal rate with greater contact force.

(a) (b)

Fig. 2. (a) shows that the gasbag does not touch the mould surface; (b) shows that the gasbag presses on the mould surface with a certain downward depth.

When the gasbag touches the mould surface, the trajectory of magnetic abrasive particle in the contact zone is composed

non-contact zone

contact zone

air supply

magnet gasbag

magnetic abrasive brushworkbench

DC source

robot

controller

computer

gasbag polishing tool

2012 IEEE Asia-Pacific Conference on Applied Electromagnetics (APACE 2012), December 11 - 13, 2012, Melaka, Malaysia

U.S. Government work not protected by U.S. copyright 28

of two different styles. The first is circular motion trajectory, and the second is radial trajectory. The radial displacement of magnetic abrasive particle under different rotating speeds of polishing tool is shown in Fig. 3.

Fig. 3. The radial displacement of magnetic abrasive particle under different rotating speeds of polishing tool.

The force analysis of magnetic abrasive particle in the contact zone is shown in Fig. 4. The total magnetic force of magnetic abrasive particle is expressed in Eq. 1.

( ) 0μgradBBVFM ⋅⋅= (1)

Where, V is the volume of the ferromagnetic phase in single abrasive particle; B is the magnetic induction of the magnetic abrasive particle position; gradB is the magnetic induction gradient of the magnetic abrasive particle position; �0 is permeability of vacuum.

Wf Gf

WF

MF

nF

Fig. 4. The force analysis of magnetic abrasive particle in the contact zone.

FM in Eq. 1 can be decomposed into the horizontal force FMY and the vertical force FMZ.

M MY MZF F F= +��

(2)

When the material properties of gasbag, downward depth of gasbag h and other processing parameters are ensured, the

pressure distribution in the contact zone can be obtained from Eq. 3 [4].

( ) ( ) ( )2 2 2 2, cosp x y k a w x y b x y c� �= ⋅ + + + +� �� (3)

Where, a, b, c, w and k are the h fitting results. Because the gasbag is flexible, the force of signal abrasive

particle by gasbag can be expressed as Eq. 4 [5].

( )yxpDFn ,25.0 2π= (4)

Where, D is the diameter of magnetic abrasive particle, p(x,y) is the pressure gasbag acting on abrasive particle.

The support force given by the mould surface ignoring the gravity of magnetic abrasive particle can be expressed as Eq. 5.

( )20.25 ,W n MZ MZF F F D p x y Fπ= + = + (5)

The friction between the mould surface and the magnetic abrasive particle can be expressed as Eq. 6.

1W wf Fμ= ⋅ (6)

Where, 1μ is the frictional factor between the mould surface and the magnetic abrasive particle.

The friction between the gasbag and the magnetic abrasive particle can be expressed as Eq. 7.

2G nf Fμ= ⋅ (7)

Where, 2μ is the frictional factor between the gasbag and the magnetic abrasive particle.

Meanwhile, when the gasbag does not touch the mould surface, thus has a small gap between the gasbag and mould surface, the magnetic abrasive particle only suffers from the function of the magnetic fore within the magnetic field, as shown in Fig. 5. The magnetic force FM can be decomposed into FMZ along the direction of the magnetic field and FMY along the magnetic equipotent line direction.

MZF

MYF

MF

Fig. 5. The magnetic force of magnetic abrasive particle when the gasbag does not touch the mould surface.

III. SIMULATION The magnetic field distribution of the permanent magnet is

hard to detect in natural environment. In order to optimize the

time (s)0 1 2 3 4 5 6

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2

3

4

5

6

7 300 r/min 400 r/min 500 r/min 570 r/min 670 r/min 800 r/min

radi

al d

ispl

acem

ent (

mm

)


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magnetic field and obtain an optimal magnetic field, the finite element analysis soft-ANSYS is used to analyze the magnetic field intensity in different conditions.

Because the new magnetic gasbag polishing tool has axisymmetric structure, the whole model is simplified into 2D structure, as shown in Fig. 6(a). Fig. 6(b) shows the magnetic lines focused on the polishing tool due to the material is steel, and the maximum magnetic intensity reaches 1.3T. While in the air, the magnetic field intensity decays seriously.

When polishing most of the mould surface consists of a high-permeability magnetic material, it would optimize the magnetic field further. Fig. 6(c) shows the distribution of the magnetic lines. The magnetic lines are focused on the work area and the magnetic intensity increases obviously. The magnetic intensity on the mould surface reaches about 0.22T, which increases several times compared with other non-magnetic matter. Thus, it can be seen that the magnetic gasbag polishing has better effect and quality in polishing magnetic mould surface.

(a) (b) (c)

Fig. 6. (a) shows the structure of magnetic gasbag polishing tool; (b) shows the distribution of the magnetic lines; (c) shows the distribution of the magnetic lines when gasbag close to the mould surface.

Fig. 7 shows the magnetic field intensity on the mould surface in different permeability. The magnetic flux density changes obviously when the permeability of mould ranges from 1 to 20. If the value is larger than 20, the changes can be ignored. The steel’s permeability is between 2000 and 6000, so it can achieve an optimal magnetic field.

0.00 0.01 0.02 0.03 0.04 0.050.000.020.040.060.080.100.120.140.160.180.200.220.24 1

5 10 20 35 50 75 100 200 400 700 1000 3000 5000 7000 9000

distance from the starting point (mm)

Fig. 7. The magnetic field intensity on the mould surface in different permeability of mould.

During the processing, the polishing tool always has an inclination angle with the mould surface, and the quality of polished surface will be more perfect in this condition. The

distribution of magnetic lines when the polishing tool has an inclination angle with the surface is shown in Fig. 8. It states that the closer the mould surface to the permanent magnet, the bigger the magnetic field intensity will be. When the inclination angle is small, the magnetic field intensity is well distributed. As the inclination angle increases, the magnetic field intensity is concentrated in a particular region, as shown in Fig. 9.

air

mould

magnet

polishing tool

(a) (b)

Fig. 8. (a) shows the simulation model; (b) shows the distribution of magnetic lines when the polishing tool has an inclination angle with the mould surface.

0.00 0.02 0.04 0.06 0.08 0.100.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45 �=0° �=10° �=20° �=30°

distance from the starting point (mm)

Fig. 9. The magnetic field intensity on the mould in different inclination angles of gasbag polishing tool.

From the above simulation, it can be seen that the magnetic field concentrates on the prominent position with high-permeability magnetic material. So, installing this material with suitable structure below the permanent magnet would guide the distribution of the magnetic field and make full use of it, as shown in Fig. 10.

Fig. 10. The distribution of the magnetic field when installing different types of prominent structures below the magnet.

IV. EXPERIMENT The simulation not only proves the existence of the

magnetic field between the gasbag and mould surface, but also shows the magnetic field intensity on the mould. In this part,

mould

mag

netic

fiel

d in

tens

ity (T

)

mag

netic

fiel

d in

tens

ity (T

)


30

experimental method is used to study the polishing effects with magnetic gasbag polishing tool in the case the gasbag does not touch the mould surface.

The experiment result using fix-point polishing method is shown in Fig. 11, whose experiment parameters are: minimum gap between gasbag and mould surface is 1mm, rotating speed of polishing tool is 600r/min and the inclination angle is �/18rad. The surface roughness decreases quickly when the polishing time within 2 minutes. When the roughness decreases from Ra 0.45�m to Ra 0.37�m, it costs 4 minutes. Then, the surface roughness tends to be stable as time goes on.

Fig. 11. The change of surface roughness with time goes on by fix-point polishing method.

The movement polishing experiment means that the gasbag repeatedly travels from one point to another in beeline trajectory on mould surface, as show in Fig. 12. The feed speed is 1mm/s, and other polishing experiment parameters are similar with the fix-point polishing method. Compared with fix-point polishing, the surface roughness after beeline trajectory polishing is smaller, which reaches Ra 0.25�m.

Fig. 12. The beeline trajectory by movement polishing method.

The high magnified microscopic images of polishing zone and non-polishing zone are shown in Fig. 13. From the comparison, it can be seen that after polishing the processing texture disappears obviously and greatly improves the uniformity of the polishing surface.

(a) (b)

Fig. 13. (a) shows the surface feature of non-polishing zone; (b) shows the surface feature of polishing zone.

V. CONLUSIONS A novel magnetic gasbag polishing technology is presented,

which can be used in polishing the contact or non-contact zone between gasbag and mould surface.

The robot assisted magnetic gasbag polishing system is established. Then, the force analysis of single magnetic abrasive particle is carried out and the simulation is performed for the magnetic field generated by permanent magnet in gasbag polishing tool under different conditions. The changes of magnetic field in different downward depth and inclination angle of polishing tool are compared.

On the basis of theoretical analysis and simulation study, the polishing effect of the neighborhood of gasbag contact zone is researched by fix-point and movement polishing experiment, and a smooth high quality surface can be obtained. The surface roughness can achieve Ra 0.25�m by movement polishing method with beeline trajectory.

ACKNOWLEDGMENT This research is sponsored by the National Natural Science

Foundation of China (50575208), Zhejiang Province Natural Science Foundation (M503099) and Zhejiang Province Natural Science Foundation (LQ12E05014).

REFERENCES [1] D.D. Walker, R. Freeman, G. McCavana, et al, “The

Zeeko/UCL process for polishing large lenses and prisms”, Proc. of Large Lenses and Mirrors conference, 2001, pp. 106-111.

[2] B. Gao, D.G. Xie, Y.X. Yao, et al, “New technology of ballonet tool for polishing”, Optical Technique , vol. 30, no. 3, 2004, pp. 333-336.

[3] S.M. Ji, M.S. Jin, X. Zhang, et al, “Novel gasbag polishing technique for free-form mold,” Chinese Journal of Mechanical Engineering, vol. 43, no. 8, 2007, pp. 2-6.

[4] M.S. Jin, “Gasbag polishing mechanism and process on free-form surface mould”, Hangzhou: Zhejiang University of Technology, 2009.

[5] J.F. Luo and D.A. Dornfeld, “Material removal mechanism in chemical mechanical polishing: theory and modeling”, IEEE Transactions on Semiconductor Manufacturing, vol. 14, no. 2, 2001, pp. 11-133.

0 2 4 6 8 10

0.35

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surfa

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a (�

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time (min)


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