Table Of Content6th International DAAAM Baltic Conference
INDUSTRIAL ENGINEERING
24-26 April 2008, Tallinn, Estonia
EQUIPMENT FOR MAGNETO-ABRASIVE FINISHING OF ROLLER
BEARING BALLS
Deaconescu, T. & Deaconescu, A.
Abstract. The processing of surfaces by Abrasive erosion can be achieved with the
magneto-abrasive erosion is achieved by grains fixed in a solid body (procedures
working media with both magnetic and known as grinding, honing, etc.), with
abrasive properties, the binder of the semi-free grains held by a magnetic field
grains forming the working medium being or a viscous liquid medium (known as
the magnetic field. The paper presents a magneto-abrasive finishing, lapping,
device for magneto-abrasive finishing of ultrasound dimensional machining, etc.),
roller bearing balls adaptable on a or with free grains set into motion by a
universal milling machine. small viscosity liquid or gas (abrasive jet
Keywords: magneto-abrasive finishing, cutting).
roller bearing balls. Magneto-abrasive finishing falls into the
category of machining by abrasive erosion,
1. INTRODUCTION the principles of which are presented in the
following.
Abrasive erosion holds an important
weight amongst surface machining 2. MAGNETO-ABRASIVE FINISHING
processes, this being a technological
method of dimensional machining by The first mention of a magneto-abrasive
means of cutting – scratching – plastic machining procedure is connected to the
deformation of the part surface carried out name of the Russian scientist Karol, who
by the abrasive grains held in a solid, in 1938 proposed the use of an alternating
liquid, gas or magnetic support. This magnetic field for finishing the interior
procedure is based on the destruction of surfaces of pipes, by means of magneto-
the integrity and subsequent removal of abrasive powders. Further major
the tooling allowance at the surface of a contributions acknowledged in literature
part, by means of the dynamic action of are inter alia those of M. Baron, E.G.
the erosive agents, materialized by solid Konovalov, L.M. Kozuro in Russia, Al.
particles (abrasive grains). The use of Makedonski in Bulgaria, and K. Kato,
abrasive grains as cutting tools aims Nakagawa, Taakeo Shinmura, Koya
mainly at rendering special quality Takazawa, Eiji Hatano in Japan [3].
surfaces of high precision in regard of Machining with magneto-abrasive grains is
dimensions, form and position. Achieving based on the effects generated by the relative
these objectives however requires small motion and the pressure generated between
values of the tooling allowance, often even the part surfaces to be machined and the
under one micron [1]. abrasive particles acting as tools and
Considering these requirements, Japanese sustained in the machined area by means of
researcher Norio Taniguchi has introduced a magnetic field.
the concept of „nanotechnology”, placing Magneto-abrasive machining implies firstly
abrasive erosion within this category of the contact between the part surface and an
cutting procedures [2]. abrasive grain. Maintaining the contact with
the machined surface, even for a mobile the edges of the grain are sufficiently sharp,
grain and/or part requires the existence of a or a process of superficial deformation for
sufficiently strong magnetic field on one less sharp grain edges. Due to the existence
hand, and ferromagnetic properties of the of a relative motion, as well as due to the
grain, on the other. friction forces, a deformation of the hairs
The existence of relative motion between the composing the “magneto-abrasive brush”
“hairs of the abrasive brush” and the part can be recorded (fig. 1) [4]:
surface determines a micro-cutting process if
Fig. 1. Deformation of the „ magneto-abrasive brush”
In order to achieve micro-cutting or micro- The machining of parts by magneto-abrasive
deformation the grains need to be erosion is based on its numerous advantages:
sufficiently hard and must have cutting (a) the presence of the permanent “self-
edges. Secondly, the grains need to be sharpening” of the “magneto-abrasive
maintained in the machining area by the brush”, as the worn edges of the grains
electromagnetic field. This last requirement are continuously oriented;
is achieved when the structure of the grains (b) the absence of the “clogging”
contains at least one ferromagnetic phenomenon characteristic for abrasive
component. The simultaneous bodies (grinding stones, etc.);
materialization of these requirements was (c) the hardness of the “magneto-abrasive
possible either by using particles made of brush” can be easily adjusted between
sufficiently hard ferromagnetic materials, or certain limits, depending on the nature
by using complex grains consisting of an of the processed material;
abrasive component and a ferromagnetic (d) due to the forces generated during
one. The action mode of a grain can be machining, the remaining tensions are
observed in figure 1 –b. low.
This type of processing has also a few
The main characteristics which define disadvantages, which however do not affect
magneto-abrasive erosion are: the efficiency and applicability of the
(a) the energy brought to the working area procedure:
generates continuous, progressive and (a) a remnant magnetic field is generated
cumulative elementary processes; following to machining;
(b) the 3D form of the transfer object can (b) the cost of obtaining powders with
be copied onto the machined object; simultaneously abrasive and magnetic
(c) low mechanical strain on the characteristics;
components of the machining (c) the procedure cannot be applied to too
equipment. large parts, due to the complexity of the
equipment required in such cases.
Due to its performance related to surface 3. MAGNETO-ABRASIVE FINISHING
quality, dimensional and geometrical EQUIPMENT FOR ROLLER
precision, magneto-abrasive machining falls BEARING BALLS
into the category of super-finishing
procedures. The obtained performances are The presented equipment belongs to the
close or even superior to those achieved by category of magneto-abrasive finishing
lapping or vibratory smoothing. equipment for complex surfaces, that is for
Further on a variant of magneto-abrasive spherical surfaces. The device allows
finishing equipment for roller bearing balls finishing roller bearing balls of diameters
will be presented, designed and between 8 and 18 mm (fig. 2). It is mounted
manufactured at the Transylvania University on the table of the FUS 22 universal milling
of Brasov, Romania. machine by means of six screws for T
grooves.
Fig. 2. Roller bearing balls
The finishing procedure consists in rolling The milling machine also carried out the
the balls by “magneto-abrasive brushes” positioning of the device in relation to the
achieved by electromagnets and magneto- superior disk, by vertically moving the
abrasive powders. machine table.
The kinematics of the equipment consists in In order to remove the superior disk for a
driving the two disks in opposed senses of new charge of balls, the magnetic yokes
rotation, the balls to be finished being are rotated by means of a straight
located between these. While the inferior cylindrical gear driven by an oscillating
disk will be driven by an electric motor by pneumatic motor. The cinematic diagram
means of a belt transmission, the superior of the equipment is presented in figure 3.
disk will be driven by the main shaft of the
milling machine.
The components of the cinematic diagram
are:
1 – Electric motor;
2 – Belt transmission;
3 – Oscillating pneumatic motor;
4 – Gear – pinions mechanism;
5 – Inferior disk;
6 – Main shaft of the milling machine;
7 – Superior disk;
Fig. 3. Kinematic diagram of the finishing
8 – Electromagnet.
equipment
The magneto-abrasive particles in the
working space become magnetic dipoles
from the moment they are subjected to the
action of an exterior magnetic field.
Generally the direction of the vector of the
magnetic moment of a dipole does not
coincide with either the exterior induction
vector or the geometrical axes of the
particle. For this reason the magneto-
abrasive particle will carry out three Fig. 4. Magneto-abrasive grain – magnetic
motions in the working space between the dipole analogy
two disks (figure 4):
1. Larmor rotation; effect of the centrifugal force generated
2. Motion along the force lines with from motion 2.
reflection in the polar zones; The following figures present sections and
3. Drift transversal to the force-lines by views of the developed equipment:
Fig. 5. Section through the roller bearing balls finishing equipment
Fig. 6: View of the finishing equipment
The magneto-abrasive finishing of roller diameter balls, where the initial deviation
bearing balls by means of the device from sphericity of about 70 μm was
presented above allowed also the reduced by machining to only 0.15...0.20
improvement of the geometrical form of μm.
the machined parts. Figure 7 shows the
results obtained by finishing 12 mm
Fig. 7. Deviations from sphericity corrected by magneto-abrasive finishing
The materials recommended as working
media can be divided into several
categories:
(a) ferro-magnetic grains, obtained from
materials with both abrasive and magnetic
properties. The most frequently used
materials of this type are ferro-boron,
ferro-tungsten and hard cast iron.
Fig. 8 Composite grain
(b) composite grains, made from a matrix
with ferro-magnetic properties and holding
The graining of the magneto-abrasive
a multitude of abrasive particles.
material is one of the performance
While the dimensions of the composite
determining factors of the procedure,
grains are of the order D = 100...200 μm,
indicated by roughness Ra and productivity
those of the abrasive grains are: d = 5...30
Pr. It was observed that for obtaining the
μm (figure 8). The main materials included
best surface roughness and the highest
by the ferro-magnetic matrix of a
productivity, when using 15%TiC+ 85%Fe
composite grain are: Al O (10...20 %),
2 3 magneto-abrasive material, a graining of
TiC (15 %), WC (20 %), Cr C (20...30
3 2 d=125/160 μm is recommended (figure 9):
%), ZrC (10...20 %), diamond. [5].
Fig. 9. Pr = f(d) and Ra = f(d)
The particle shape is determined by surface
finish and profile requirements and the
type of contaminant to be removed. The
shape of an abrasive when new is not
always the same as when in the operating
mix. Whereas steel shot remains round
throughout its life and iron grit remain
angular, steel grits may loose angularity
depending upon their initial hardness. The
grains preferred for magneto-abrasive
finishing should have initially positive rake
angles. The attached figure shows chilled
iron grits, their shape being adequate for Fig. 10. Chilled iron grits
this type of machining.
The performance of magneto-abrasive Future Trends of Ultraprecision
machining is influenced by some Machining and Ultrafine Materials
technological parameters, the most Processing. Annals of CIRP, vol.
important ones being cutting speed, 32/2/1983.
magnetic induction, dimension and shape 3. Slatineanu, L. Tehnologii neconven-
of the machining gap, the characteristics of tionale in constructia de masini.
the magneto-abrasive material, the degree Editura TEHNICA INFO Chisinau,
of filling of the area, etc. Moldova, 2000.
On the device presented above, the 4. Baron, I. Tehnologia abrazivnoi obra-
thickness of the removed material layer botki v magnitnom pole.
depending on the cutting speed was: Masinostroenie, Leningrad, 1979.
• v =10 m/min, h=1.27 μm, 5. Ciobanu, M. Cercetari privind optimi-
• v =15 m/min, h=2.68 μm, zarea parametrilor de lucru la
• v =50 m/min, h=4.11 μm, finisarea magneto-abraziva cu
ferofluide. Doctoral Thesis, Iasi,
• v =150 m/min, h=4.48 μm.
Romania, 1993.
4. CONCLUSION
6. DATA ABOUT AUTHORS
The main characteristics of the magneto-
abrasive finishing device described in the
1. Prof.dr.eng. Tudor Deaconescu
paper are constructive simplicity and high
Transylvania University of Brasov,
performance. Its launching into series
Romania
manufacturing and addition to the
B-dul Eroilor nr. 29
accessories kit of universal milling
RO-500036 Brasov, Romania
machines is bound to significantly enlarge
[email protected]
the range of machining procedures
2. Assoc.Prof.dr.eng. Andrea Deaconescu
achievable on such machines.
Transylvania University of Brasov,
Romania
5. REFERENCES
B-dul Eroilor nr. 29
RO-500036 Brasov, Romania
1. Komanduri, R. et al. Technological
[email protected]
advances in fine abrasive processes.
Annals of CIRP, vol. 46, no. 2/1997.
2. Taniguchi, N. Current Status in and
