Available online at www.sciencedirect.
com
Procedia CIRP 1 (2012) 414 – 418
5th CIRP Conference on High Performance Cutting 2012
High-speed Internal Finishing of Capillary Tubes by Magnetic
Abrasive Finishing
Junmo Kanga, Andrew Georgea, Hitomi Yamaguchia,*
a Department of Mechanical and Aerospace Engineering, University of Florida, 226 MAE-B, Gainesville, FL 32611, USA
* Corresponding author. Tel.: +1-352-392-0812; fax: +1-352-392-1071; E-mail address: hitomiy@ufl.edu.
Abstract
In magnetic abrasive finishing, the development of a multiple pole-tip system using a partially heat-treated magnetic tool allows the
finishing of multiple regions simultaneously in capillary tubes and thus improves the finishing efficiency. To further reduce the
processing time required, a new high-speed machine is fabricated. This paper describes the development of the high-speed multiple
pole-tip finishing equipment, which is capable of rotating the spindle up to 30000 min-1, and the effects of tube rotational speed on
abrasive motion during the finishing experiments. Also, the finishing mechanisms of the high-speed machine are clarified.
© 2012
© 2012The
Published byPublished
Authors. Elsevier BV. Selection
by Elsevier and/or
B.V. peer-review
Selection under responsibility
and/or peer-review of Professor
under responsibility of Konrad Wegener
Professor Konrad Wegener
Open access under CC BY-NC-ND license.
Keywords: Finishing; Polishing; Magnetic abrasive finishing
primarily dependent on the width of the magnetic pole
1. Introduction tip and the total length of travel of the tip along the tube
axis. In practice, difficulties associated with the insertion
Austenitic stainless steel capillary tubes are widely of the magnetic abrasive into the finishing area have
used in medical devices, including catheter shafts and limited the total finished length to just a few times the
needles for injection or biopsy procedures. A smooth pole-tip width. To finish the entire surface of a long
interior tube surface is required to prevent tube, several short finishing steps are required, leading to
contamination, but as the tube diameter decreases, the a long finishing time. To overcome this limitation, the
more difficult the internal finishing becomes. use of a multiple-pole tip system with a magnetic tool
In a magnetic field, magnetic flux flows unimpeded has been devised. This method improves finishing
through nonferrous workpiece material, and ferrous efficiency by allowing for the simultaneous finishing of
material—a component of the magnetic tool—is multiple areas [13, 14, 15]. The feasibility of the concept
suspended by magnetic force. It is possible to influence was demonstrated at a tube revolution rate of 2500 min-
the magnetic tool motion by controlling the magnetic 1. For further improvement of the finishing efficiency,
field, thus enabling the finishing operation to be an increase of the tube rotational speed is necessary.
performed not only on easily accessible surfaces but also This paper studies the application of a multiple pole-
on areas that are difficult to reach by conventional tip system for high-speed finishing of capillary tubes.
mechanical techniques. A variety of Magnetic Field- Firstly, finishing equipment with double pole-tip sets is
assisted Finishing processes using this principle have developed, which enables a tube to rotate up to 30000
been developed for the internal finishing of components min-1. Secondly, the effects of tube revolution on
[1-11]. abrasive motion are investigated through the tube
The potential of the process using magnetic abrasive finishing experiments. Finally, the finishing mechanisms
[12] for the internal finishing of capillary tubes has been of the high-speed finishing are discussed.
demonstrated for tubes with inner diameters down to 0.4
mm [11]. However, the length of the finishing area is
2212-8271 The Authors. Published by Elsevier B.V. Selection and/or peer-review under responsibility of Professor Konrad Wegener
Open access under CC BY-NC-ND license. http://dx.doi.org/10.1016/j.procir.2012.04.074
Junmo Kang et al. / Procedia CIRP 1 (2012) 414 – 418 415
2. Development of high-speed finishing machine Figure 2 shows changes in magnetic flux density By,
measured by a Hall sensor (sensing area: 1.0 mm),
Figure 1 shows a schematic for a method using with distance X for double pole-tip sets. The magnetic
double pole-tip sets, which generates magnetic fields in flux density and gradient increases from the center
two finishing areas, and a photograph of the equipment toward the edges of pole tip. A particle in the magnetic
developed to realize the method. The finishing area is field is attracted to the pole-tip edges where the
doubled as magnetic abrasive is introduced and pushes magnetic force is higher.
against two regions of the tube surface. As the pole-tip
sets move along the tube axis, and the finished area is
extended. The number of pole-tip sets can be increased if
required. For a constant pole-tip width, the finishing area
will be a function of the total number of pole-tip sets.
The double pole-tip sets require the introduction of a
magnetic tool with the mixed-type magnetic abrasive.
The tool guides the magnetic abrasive deep into the tube
and increases the magnetic force acting on the magnetic
abrasive [14].
Fig. 2 Changes in magnetic flux density in double pole-tip sets at Y=0
mm
3. Experimental conditions
Table 1 Experimental conditions
Workpiece 304 Stainless steel tube
(Ø1.27x Ø 1.06x100 mm)
Workpiece revolution 500, 5000, 10000, 20000 and
30000 min-1
Mixed-type magnetic abrasive 5 mg
(Iron particles (150-300 μm
dia.):80 wt%,
magnetic abrasive (80 μm mean
dia.): 20 wt%)
Fig.1 Schematic of processing principle and photograph of
experimental setup with double pole-tip sets Magnetic tool See Fig. 3
Pole-tip geometry
The workpiece tube is chucked to a motor (speed
range: 5000–30000 min-1). Two pole-tip sets consisting
of six neodymium permanent magnets (12.7x12.7x12.7
mm; residual flux density 1.26–1.29 T; coercive force
>875 AT/m) are mounted 12.7 mm apart on a single-axis Pole-tip feed 0.59 mm/s
micrometer stage, and their position is adjustable in the Pole-tip feed length 12.7 mm
tube radial direction. To avoid collision between the
Workpiece-pole-tip clearance 0.3 mm
rotating tube and pole tips, the pole-tip surfaces are (Polytetrafluoroethylene (PTFE)
covered by 0.3 mm thick polytetrafluoroethylene (PTFE) tape thickness)
tape. The pole-tip sets are mounted on a linear slide so Lubricant Soluble-type barrel finishing
that they can be fed in the tube axial direction. The feed compound (pH: 9.5, Viscosity:
length and speed are adjustable to maximums of 150 mm 755 mPa•s at 30°C)
and 600 mm/s, respectively. Processing time 10 and 20 min
416 Junmo Kang et al. / Procedia CIRP 1 (2012) 414 – 418
Table 1 shows the experimental conditions. In high-speed finishing, centrifugal force tends to
Austenitic stainless steel tubes (304 stainless steel, cause the displacement of the lubricant from the
1.27x1.06x100 mm; 2–3 μm Rz initial surface finishing area, which in turn causes the mixed-type
roughness) were prepared as workpieces for this study. magnetic abrasive to adhere to the tube surface due to
A 304 stainless steel tool with three heat-treated regions friction. Adhered material noticeably covered the surface
was used as a magnetic tool (see Fig. 3). The heat- in Figure 4(a), which shows the surface finished
treated regions became non-magnetic by reverting from continuously for 10 min at a tube revolution rate of
BCC crystalline structure to FCC crystalline structure as 30000 min-1. No adhered material is observed in Figure
a result of the normalization while the four un-treated 4(b), which shows the surface finished for 10 min with
sections remained magnetic [14]. The mixed-type lubricant added after 5 min. During the finishing
magnetic abrasive separates as it is attracted to the ends process, the presence of lubricant is crucial to encourage
of the four magnetic sections. The four magnetic regions the smooth relative motion between the mixed-type
correspond to each edge of the two magnetic pole-tips magnetic abrasive and the tube surface that facilitates
due to its stronger magnetic force [15]. The pole tip feed finishing performance of the abrasive. Accordingly, in
length was set to 12.7 mm, and the feed rate was set to the cases of 20000 and 30000 min-1 tube revolution, the
0.59 mm/s. finishing experiments were interrupted to inject lubricant
every 5 min. For the cases of 5000 and 10000 min-1 tube
revolution, the finishing experiments were performed
continuously for 10 min without additional lubricant
injection. Each experiment was repeated at least three
times to ensure the repeatability of the results. Before
and after the finishing experiments, the tube was rinsed
with ethanol in an ultrasonic cleaner for 1 hr.
4. Effects of tube rotational speed on finishing
characteristics
Figures 5 and 6 show intensity maps and oblique
plots—measured by an optical profiler at X=13 mm—of
the unfinished surface and surfaces finished for 10 and
20 min, respectively. Figure 7 shows changes in material
removal with tube revolution and finishing time. The
Fig. 3 Tool geometry and magnetized tool with iron particles surface finished for 10 min at a tube revolution of 5000
min 1 (Figure 5(b)) has a roughness of 0.15 μm Rz, but
For the experiments, 5 mg of mixed-type magnetic multiple irregular asperities from the initial surface
abrasive (80 wt% iron particles and 20 wt% magnetic remained. However, an extension of the finishing time
abrasive) [4] was introduced with the magnetic tool. The for another 10 min allowed the abrasive to remove those
mixed-type magnetic abrasive and magnetic tool filled irregular asperities (Figure 6(a)). The material removal
21.4 vol%, and 23.1 vol% inside the tube, respectively. after 20 min was more than twice the removal after 10
The tube rotational speeds were varied between 5000, min (Figure 7). Although the magnetic abrasive was not
10000, 20000, and 30000 min-1. To encourage uniform exchanged during the interruptions to inject lubricant,
internal surface coverage with the mixed-type magnetic the reconfiguration of the magnetic abrasive during these
abrasive prior to high-speed finishing, the tube was breaks encouraged the relocation of the sharp abrasive
rotated at 500 min-1 with a single pole-tip stroke before cutting edges. The sharp cutting edges and newly added
finishing. lubricant seemed to refresh the finishing performance
after each intermission.
At a tube revolution rate of 10000 min-1, the surface
was smoothly finished (0.1 μm Rz) after 10 min, and the
roughness value remained constant after 10 min of extra
finishing time despite the additional material removal
(Figure 6(b)). Compared to 10 min at a tube revolution
rate of 10000 min-1, the material removal is drastically
increased after finishing for 20 min. Analogous to the
case of finishing for 20 min at 5000 min-1, the pauses to
Fig. 4 Micrographs of surface finished for 10 min at 30000 min-1
Junmo Kang et al. / Procedia CIRP 1 (2012) 414 – 418 417
add lubricant after 10 min aided the finishing Further increase in the tube revolution, such as the
performance. 30000 min-1 test, further enhanced the irregularity of the
It was confirmed that the increase in the tube motion of the magnetic tool and abrasive. The
revolution (i.e., cutting speed) improves the material nonuniformly distributed mixed-type magnetic abrasive
removal rate and finishing efficiency. However, due to must be pressed against the surface by a rotating
the high centrifugal force, the high-speed tube rotation magnetic tool that is unstable due to the centrifugal
creates more opportunities for the mixed-type magnetic force. This led to increased material removal and
abrasive and magnetic tool to lapse into unstable resulted in a surface consisting of deep scratches over
conditions. The lack of a uniform magnetic abrasive long-wavelength asperities, as shown in Figure 5(e).
distribution under an unstable rotating magnetic tool
may lead to the deep, irregular scratches. This trend was
observed in the case of 20000 min-1 (Figure 5 (d)), the
finished surface has deep scratches and surface
distortions. Extending the finishing time slightly
increased the material removal due to the longer duration
contact of the magnetic abrasive cutting edges against
the tube surface and removed the relatively short-
wavelength surface asperities (Figure 6(c)); however, the
deep scratches produced by the irregular motion of the
magnetic tool and mixed-type magnetic abrasive
remained on the surface.
Fig. 6 Intensity maps and oblique plots of surface finished for 20 min
Fig. 7 Changes in material removal with tube revolution in double
pole-tip system
Use of the previously developed multiple pole-tip
finishing system [15] produced a uniformly finished
Fig. 5 Intensity maps and oblique plots of surface finished for 10 min surface (from 2–3 μm Rz to ~0.2 μm Rz) 72 mm long—
418 Junmo Kang et al. / Procedia CIRP 1 (2012) 414 – 418
four times the pole-tip width—in 180 min. The high- Internal Finishing of Stainless Steel Tube and Gas Bomb. JSME
speed finishing system proposed in this paper can Int J., Ser. C 1995;38-C(4):798–804.
[5] Yamaguchi H, Shinmura T, Kaneko T. Development of a New
produce a finished surface 50.8 mm long (four times the Internal Finishing Process applying Magnetic Abrasive Finishing
pole-tip width) in 10 min with a roughness of about 0.1 by use of Pole Rotation System. Int. J. Jpn Soc. Precis. Eng.
μm Rz. Thus the proposed high-speed finishing system 1996;30(4):317–322.[6] Kim JD, Kang YH, Bae YH, Lee SW.
is twelve times more efficient than its predecessor. Development of a Magnetic Abrasive Jet Machining System for
Precision Internal Polishing of Circular Tubes, J. Mater. Process.
Technol. 1997;71:384-393.
5. Conclusion [7] Zou YH, Shinmura T. A New Internal Magnetic Field Assisted
Machining Process Using a Magnetic Machining Jig-Machining
The results of this research can be summarized as Characteristics of Inside Finishing of a SUS304 Stainless Steel
follows: Tube. Adv. Mater. Res. 2009;69-70:143–147.
1. A high-speed multiple pole-tip finishing system [8] Jha S, Jain VK, Komanduri R. Effect of Extrusion Pressure and
Number of Finishing Cycles on surface roughness in
has been developed for finishing capillary tubes, magnetorheological abrasive flow finishing (MRAFF) process.
and finishing experiments have been performed Int. J. Adv. Manuf. Technol. 2007;33;725-729.
with tube revolutions up to 30000 min-1. [9] Nishida H, Shimada K, Goto M. Polishing inner capillary walls by
2. In the single pole-tip system, the magnetic a magnetic compound fluid. Int. J. Appl. Electromagnet Mech.
abrasive is stable and performs efficient surface 2007;25(1-4): 25-29.
[10] Sato T, Yamaguchi H, Shinmura T, Okazaki T. Study of Internal
finishing up to 30000 min-1. Conversely, the Finishing of Capillary using Magneto-rheological Fluid. J. Jpn
magnetic abrasive and tool lapse into unstable Soc. Precis. Eng. 2006;75(5):612-66 [in Japanese].
conditions in the multiple pole-tip system at high [11] Yamaguchi H, Shinmura T, Ikeda R. Study of Internal Finishing
speed due to high centrifugal force. This causes of Austenitic Stainless Steel Capillary Tubes by Magnetic
deep scratches and irregular asperities on the Abrasive Finishing. J. Manuf. Sci. Eng., 2007;129(5):885–892.
[12] Shinmura, T, Takazawa K, Hatano E, Matsunaga M, Matsuo T.
finished surface. Study on Magnetic Abrasive Finishing, CIRP Ann.,
3. In this paper, 10000 min-1 is the highest tube 1990;39(1):325-328.
revolution rate at which the high-speed internal [13] Kang J, Yamaguchi H. Internal Finishing of Capillary Tubes by
finishing of a capillary tube using double pole-tip Magnetic Abrasive Finishing using a Metastable Stainless Steel
sets is successfully achieved. It produces a Tool, Proceedings of the Twenty-fourth Annual ASPE Meeting,
2010:1-4
smoothly finished surface (Ĭ0.1 μm Rz) and is [14] Yamaguchi H, Kang J, Hashimoto F. Metastable Austenitic
twelve times more efficient than the previous Stainless Steel Tool for Mangenetic Abrasive Finishing, CIRP
multiple pole-tip finishing system. Ann., 2011;60(1):339-342.
[15] Kang J, Yamaguchi H. Internal Finishing of Capillary Tubes by
Mangetic Abrasive Finishing using a Multiple Pole-tip System,
Int. J. Precis. Eng. Manuf., In Press, Corrected Proof.
Acknowledgement
The authors would like to express thanks to the
University of Florida Research Foundation (Gatorade)
and to the Society of Manufacturing Engineers (SME)
Education Foundation (E. Wayne Kay Graduate
Scholarship) for their support and encouragement of this
project.
References
[1] Shinmura T, Hatano E, Takazawa K. The Development of
Magnetic-abrasive Finishing and its Equipment by Applying a
Rotating Magnetic Field, Bull. JSME Int J. 1986;29(258):4437-
4443.
[2] Shinmura T, Yamaguchi H. Study on a New Internal Finishing
Process of a Nonferromagnetic Tube by the Application of a
Linearly Travelling Magnetic Field: on the Process Principle and
the Behaviors of Magnetic Finishing Tool, Int. J. Jpn Soc. Precis.
Eng. 1994:28(1):29-34.
[3] Shinmura T, Aizawa T. Study on Internal Finishing of a Non-
Ferromagnetic Tubing by Magnetic Abrasive Machining Process,
Bull. Jpn Soc. Precis. Eng. 1989;23(1):37-41.
[4] Shinmura T, Yamaguchi H. Study on a New Internal Finishing
Process by the Application of Magnetic Abrasive Machining:
