Mechanism of Material removal
Process Parameters Analysis
Magnetic Abrasive Finishing (MAF) Process
Harry P. Coats first patented MAF in 1938. Although US originate this idea, most of later period development is done by USSR + Bulgaria. Japanese explore the technology for polishing purpose. Other countries in this field are: India, CIS, England, France, and Germany etc.
In MAP, w/p is kept between the two magnets & the air gap in-between the w/p & the magnet is filled with Magnetic Abrasive Particles (MAPs). The MAPs joined to each other, along the lines of magnetic force and form a Flexible Magnetic Abrasive Brush. The brush behaves like a multi-point cutting tool for finishing process. The vibrational, rotary & axial motion is imparted to the w/p to enhance the performance of finishing operation
For demonstration, there are three setups commonly used. These are: 1.
External contour of cylindrical workpiece: the systematic diagram are as follow:
The process principle of magnetic abrasive finishing is shown in fig. The magnetic abrasives are joined to each other; magnetically in-between magnetic poles ‘N’ & ‘S’ along the lines of magnetic forces, this imparts flexibility of magnetic brushes. Flexibility to brush means it ability to modify itself as per workpiece contours. When a cylindrical workpiece; with rotatory and translatory motions; is inserted, the surface and edge finishing are performed by these magnetic abrasives brushes.
The magnetic field polishing showing the two-dimensional magnetic field distribution in the finishing zone of the process. The magnetic abrasive particles form a brush around the workpiece linking the N & s poles. The magnetic flux density is stronger around the nonmagnetic workpiece (along the magnetic brushes) than through the workpiece. The magnetic abrasive at position “A” in fig. is affected by the magnetic forces represented by the following equations:
Fx= VCH *∂H/∂X
FY= VCH *∂H/∂Y
V=volume of magnetic abrasive particle,
C= susceptibility of the particle
H= magnitude of magnetic field strength at point “A”
X & Y are coordinate points fixed at A,
and ∂H/∂X, ∂H/∂Y are gradient of magnetic field strength in X and Y directions.
From above equations it is evident that the magnetic forces Fx, FY are proportional to the volume of the magnetic abrasive particles, the susceptibility of the particle, the magnetic field strength and its gradient. If the gradients are not equal to zero then magnetic abrasive particles are pushed toward the work surface. The magnetic force FY actuates the magnetic abrasive particles to take part in the surface finishing of the workpiece. In addition, the force Fx is acting on the abrasive grain in the rotating tangential direction of the work surface by cutting and frictional action. The runoff of the abrasive grains from the working zone is prevented by the FY. From the above formula if X is non-zero the magnetic force will not act, if ∂H/∂X, ∂H/∂Y is equal to zero. Thus both susceptibility and magnetic field gradients are important in this operation. The larger values of magnetic strength gradients; forces the abrasive grains to move towards the working zone thus preventing separation and splashing of the abrasive grains from the working zone. The magnetic flux density is stronger around the non magnetic workpiece ( along the magnetic brushes) than through the workpiece
Internal contour of hollow cylindrical workpiece:
Let’s have a look on the basic functional elements of MAF. These are: 1.
Magnetic Abrasives Particles (MAPs): MAPs are made up of ferromagnetic material (e.g.. iron powder=300 mesh size i.e.51.4m) and abrasive grains (e.g.Al2O3 =600 mesh size=25.7m, SiC, Diamond powder). Generally ferromagnetic particles size is...
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