Magnetic Field Assisted Finishing (MAF) Hitomi Yamaguchi Greenslet

Associate Professor

What is MAF? In a magnetic field, magnetic flux flows unimpeded through

nonferrous materials while ferrous materials are susceptible to

magnetic force. It is possible to influence a ferrous tool’s

motion by controlling the magnetic field applied to it. The field

is translated or rotated relative to the workpiece. As a result,

the ferrous tool moves against and applies force on the

workpiece. Finishing operations can then occur not only on

easily accessible surfaces, but also on the areas that are

difficult to reach by the means of conventional techniques.

Internal Finishing using Static Magnetic

Field

Processing Principle In this process, the poles, which consist of permanent

magnets, are placed outside a bent tube and generate the

magnetic field needed for attracting the magnetic abrasive to

the finishing area. In a nonuniform magnetic field, a magnetic

force F acts on the magnetic abrasive, driving it. This force is

described by the following equation:

F=V· χ· H·gradH

where V is the volume of the magnetic abrasive, χ is the

susceptibility, and H·gradH is the intensity and gradient of the

magnetic field.

When the pole rotates around the bent tube, the magnetic

abrasive rotates along the tube’s inner surface, removing

material. Translating the rotating poles along the tube’s axis

causes the magnetic abrasive to follow the pole’s rotational

and axial motion, finishing the entire inner surface of the tube.

Time (min)

0 30

Rz (µm) 1.90 3.34

Hv 140 252

Residual stress (MPa) -115 -409

Potential Applications

Processes: Internal, external, and freeform surface finishing, edge

conditioning and deburring, blasting and peening, cleaning

Materials: Stainless steel, carbon steel, copper, aluminum alloy,

superalloy, cemented carbide, ceramics, glass, quartz,

plastics, etc.

Contact Information Hitomi Yamaguchi Greenslet: hitomiy@ufl.edu (E-mail)

316L Stainless steel tube

(Ø19.05×Ø16.57×170mm) Precision Machining using Alternating

Magnetic Field

Processing Principle Coils facing each other in a parallel circuit generate an

alternating magnetic field around two magnetic poles. The

two poles are positioned directly above the workpiece with

an adjustable gap between them. The vertical distance

between the two poles and the workpiece is also controlled.

Magnetic tools, such as small pins, inserted into the

workpiece are influenced by the alternating magnetic field.

Due to the effect of the alternating magnetic field acting on

the pin, the pin exhibits random, active , three-dimensional

motion by colliding with the inner surface of the workpiece,

thereby achieving precision internal machining.

Examples (304 stainless steel tubes)

(20 mm outer dia., 18 mm inner dia.)

53 μm82μm

1.50 μm

-0.50

1.00

0.50

0.00

53 μm82μm

1.00 μm

-1.00

-2.00

0.00

0.26 µmRa

2.05 µmRz

Unfinished surface

0.02 µmRa

0.15 µmRz

Finished surface (8min)

(0.5 mm outer dia., 0.4 mm inner dia.)

Pole rotation

Yoke

Pole feed

S

Magnetic

abrasive

S

N

N

0.08 µm Ra

10 mm

Pole

Before finishing After finishing 100 µm 100 µm

Schematic of processing process

Workpiece Magnetic tool

N N

Coil Pole

Function

generator

AC power amplifier

～ A

Ammeter

Schematic of processing process