Magnetic Field Assisted Super-Finishing Process

Introduction 

A surface finish is a surface finish technique used to drive abrasive particles onto the target surface using magnetic field supports, sometimes called a magnetic abrasive finish. As such, it is feasible to finish the surfaces which have been traditionally unreachable (e.g. within a long, curved pipe). A variety of methods have been developed for the manufacture of medical components, fluid systems, optics, die and moulds, electronic components, microelectromechanical systems, and mechanical components, including MAF. 

Theory

Magnet Assisted Finishing or “MAF” is essentially manipulating a homogeneous magnetic particle and abrasive particle mixture with a magnetic field to impart a workpiece machining force. Material removal is achieved through relative movement between the particle mixture and the workpiece surface. As no direct contact with the tool is necessary for MAF, particles can be placed in regions that are difficult to reach with conventional procedures. Additionally, a careful seletion of magnetic particles and abrasive particles gives rise to an unprecedentedly hard-to-reach surface texture and roughness control. 

Material Removal

The combination of tangential strength and normal forces on the piece is predicted to remove material on the surface asperities from the highest peaks of the surface. The contact between the brush and the surface is repeated while the finishing procedure is in way. With the time the workpiece surface’s roughness achieves a minimum value, this is because of the present finishing configuration’s physical restrictions. The minimum surface rougheness that can be attained is specified in the selection of iron particles and abrasive particles. The roughness of the surface reduces, so that smaller abrasive particles continue to be removed.

MAF can achieve a ruggedness of between 200 μm Ra and 1 nm Ra with ease, showing the degree of adaptation that a MAF set-up can provide. The finishing force defined by the magnetic force on the partial equation is dictated by the particle size of the magnet particles in the brush. However, growing particles have negative impacts as a result of a large packaging factor, such as inability to contain small abrasives and air gaps.

It is a frequent practise to combine both smaller and large particles to ‘fill’ the ‘holes’ of the brush in a way to ease these issues, so that small particles effectively cover the larger particles in the chain of particles. The correct abrasive size and speed of oscillation and spindle rpm may be selected to regulate the surface texture and roughness closely. As a rule, the faster the movement of the brush the denser the surface finish marks and the ruggeder the area. 

Field Source 

Typically, a MAF magnet or a permanent magnet is a magnetic field source. A permanent magnet has a high energy density, an overheating absence that results in a constant flux density, low costs and easy integration of current CNC equipment. Some applications may require flux density adjustment during completion, or a switching magnetic field that is available only with an electromagnet as the magnetic field cannot easily be switched off in a permanent magnet.

Equipment

Material removal requires relative motion between the magnetic/abrasive particle mixture and the workpiece. There are numerous ways to get the required motion. The rotation of the magnetic pole tip is a frequent arrangement. This is accomplished by spinning either the full permanent magnet arrangement or only the steel pole. Another approach often used in interior finishing is workpiece rotation, which is regrettably limited to axially symmetric workpieces. In addition to rotational motion, oscillatory and vibrational topologies can be used.