Complete information about Magnetic Abrasive Finishing, its working principle, advantages, disadvantages, process parameters, and applications.

Introduction: Magnetic Abrasive Finishing

What is Magnetic Abrasive Finishing?

Magnetic Abrasive Finishing (MAF) is an advanced finishing process used to improve the surface finish and achieve close dimensional accuracy of metallic workpieces. It is a non-traditional machining process that uses magnetic fields and magnetic abrasives to produce micro to nano-level surface finish.

In MAF, the workpiece is placed close to the pole of an electromagnet where a magnetic field is created between the north and south poles of the electromagnet. The magnetic abrasives, which are usually iron powders, get magnetized in this magnetic field. As the magnetic abrasives flow with the magnetic field, they rub against the surface of the workpiece, causing microchips to be removed from the surface. This results in a smooth mirror-like surface finish.

The whole process takes place in the presence of a magnetic field, without any physical contact or pressure. This makes MAF superior to other finishing processes like honing, polishing, etc. in terms of flexibility and productivity.

Working Principle of Magnetic Abrasive Finishing

The working principle of magnetic abrasive finishing is based on the combined actions of a magnetic field and magnetic abrasives. Here are the key aspects of the working principle:

• A strong magnetic field is created by using an electromagnet. The workpiece which needs to be finished is placed close to one of the poles of the electromagnet.
• The magnetic abrasives are introduced in the space between the workpiece surface and the electromagnet. Generally, iron powders are used as magnetic abrasives.
• When electric current is passed through the electromagnet, it magnetizes the iron powders and makes them act like tiny magnetic brushes.
• The magnetic field produced causes the magnetic abrasives to arrange themselves on the workpiece surface being machined.
• The magnetic field also provides a compressive type of force that enables the magnetic abrasives to rub against the workpiece surface.
• The rubbing action of the magnetic abrasives against the workpiece causes microchips to be removed from the surface, resulting in a smooth finish.
• The whole process takes place in the presence of a magnetic field without any physical contact or pressure. This allows the finishing of complex geometries.

Advantages of Magnetic Abrasive Finishing

Magnetic Abrasive Finishing has several advantages over conventional finishing processes:

• It can produce surface finish up to 0.05 microns which is not possible with conventional processes.
• There is no direct contact between the tool and the workpiece, eliminating chances of mechanical stresses and defects.
• Complex internal surfaces and geometries can be finished easily due to the noncontact nature of the process.
• It is a clean and environment-friendly process since no heat generation or chemical reactions are involved.
• Multiple workpieces can be finished simultaneously, leading to high productivity.
• Different magnetic abrasives can be used for different applications providing flexibility.
• Capital investment and operating costs are lower compared to other non-conventional processes.
• Post-processing operations like deburring, radiusing of edges, etc. can also be done effectively.

Disadvantages of Magnetic Abrasive Finishing

Along with advantages, Magnetic Abrasive Finishing has some disadvantages also:

• The process is applicable only to ferromagnetic materials. Nonmagnetic materials cannot be machined using this process.
• There are limitations on the workpiece size and weight that can be effectively processed.
• Careful maintenance of process parameters is required for getting consistent results.
• The magnetic abrasives need periodic cleaning and replacement adding to operating costs.
• Demagnetization of the workpiece may be required as residual magnetism can affect further machining processes.
• Initial capital investment is high for setting up the MAF equipment and facilities.
• It is not an ideal process for bulk removal of material from surfaces.
• Skilled personnel are required for operating the MAF equipment and maintaining process parameters.

Process Parameters in Magnetic Abrasive Finishing

The main process parameters that affect the performance of magnetic abrasive finishing are:

• Magnetic flux density - Magnetic field strength indicated by flux density affects the magnetic force acting on abrasives. Higher flux density improves finishing efficiency.
• Gap between electromagnet and workpiece - Gap distance affects the magnetic field strength. A smaller gap results in better finishing.
• Size and composition of magnetic abrasives - Very fine abrasives produce a better surface finish. Different compositions offer various machining performances.
• Speed and circulation of magnetic abrasives - High speed improves the finishing rate but can cause surface defects. Optimum speed is essential.
• Finishing time - Longer finishing time improves surface finish but reduces productivity. The optimum time is required.
• Temperature - Increased temperature reduces the magnetization of abrasives. Hence, cooling is needed to maintain a lower temperature.
• Current and voltage - Higher current through electromagnet improves magnetic field strength. The voltage needs to be controlled.
• Workpiece properties - Material, hardness, and initial surface roughness of the workpiece affect the finishing performance.

Applications of Magnetic Abrasive Finishing

Magnetic Abrasive Finishing is used for a variety of industrial applications including:

• Finishing of dies, molds, and tools from materials like steel, carbide, and HSS to improve surface finish and increase tool life.
• Deburring and radiusing of complex holes and cavities on machined components that are difficult to reach by other methods.
• Finishing aerospace components made from titanium, aluminum, inconel where a very fine surface finish is required.
• Polishing internal surfaces of tubes and cylindrical components made of stainless steel, brass, etc.
• Finishing automobile engine components like valves, pistons, and engine blocks to improve fatigue strength.
• Smoothening surfaces of prosthetic implants like artificial knee and hip joints.
• Finishing fuel injection components, nozzles, and compressor blades which need flow-quality finishing.
• Microfinishing cutting tools, gauges, and punches made of steel alloys to improve dimensional accuracy.

Surface Finish Improvement in MAF

In Magnetic Abrasive Finishing, the surface finish of the workpiece can be improved by:

• Using very fine magnetic abrasives such as micron or sub-micron-sized particles. The smaller the abrasive size, the better is the finishing effect.
• Increasing the strength of the magnetic field which improves the machining action of the magnetic abrasives.
• Reducing the gap between the electromagnet pole and the workpiece surface. Smaller gap enhances magnetic field strength.
• Optimizing process parameters like abrasive size and composition, rotational speed, and finishing time. This results in uniform material removal from surface.
• Using abrasive particles of suitable hardness. Very hard particles cause deeper scratches while soft particles result in poor machining action.
• Maintaining process temperature through cooling arrangements. High temperature weakens magnetic field strength.
• Employing multi-stage finishing with finer abrasives in each stage. Multi-stage finishing improves finish significantly.
• Using suitable holding fixtures for workpiece that minimize unwanted movements and vibrations during finishing.
• Adopting different magnetization patterns of magnetic poles for uniform machining action.

Magnetic Abrasive Finishing FAQ

Here are some frequently asked questions about magnetic abrasive finishing:

Q1. What materials can be machined by magnetic abrasive finishing?

Ans. MAF can be used for finishing ferromagnetic materials like carbon steels, alloy steels, stainless steels, iron, nickel and cobalt alloys. Nonmagnetic materials cannot be processed by MAF.

Q2. What surface finish can be obtained using MAF?

Ans. MAF can produce mirror finish of up to 0.05 microns which is not achievable by traditional machining or finishing methods. The surface becomes free of cracks and microscopic irregularities.

Q3. What are the typical applications of MAF in industries?

Ans. MAF finds major applications in finishing of dies, molds, tools, automobile engine components, aerospace parts, prosthetic implants, cutting tools and precision gauges. It is used where micro surface finish and dimensional accuracy are needed.

Q4. What equipment is used in the magnetic abrasive finishing process?

Ans. The main equipment used are electromagnets, power supplies, magnetic abrasive powder, finishing chamber, pumps for abrasive circulation, fixtures for workholding, cooling systems and filtration systems.

Q5. What are the advantages of MAF over conventional finishing processes?

Ans. Compared to conventional processes, MAF offers benefits like no direct contact, flexibility in finishing complex geometries, microfinish generation, improved accuracy, environment friendliness and low operating costs.

Q6. What are magnetic abrasives and how do they work?

Ans. Magnetic abrasives are magnetizable particles, usually iron powders. When subjected to magnetic field in MAF, they get magnetized and act as micro cutting tools to remove material from the workpiece.

Q7. How is surface finish measured after MAF?

Ans. Surface roughness parameters like Ra, Rz are measured using surface profilometers. Scanning electron microscope is used to view surface topography. Talysurf instrument can also measure nano level surface texture.

Q8. Does MAF produce any harmful effects on the workpiece?

Ans. No. Since MAF does not involve any heating, chemical reactions or physical pressure, there are no side effects like distortion, cracks, metallurgical damages, etc. on the workpiece.

Q9. What safety measures are required when operating MAF?

Ans. Safety glasses should be worn. Machine should be properly grounded. Overheating of electromagnet should be avoided. Abrasive dust collection system is used. Proper ventilation and lighting is required.

Q10. Does the workpiece need any post processing after MAF?

Ans. Workpieces may need cleaning or demagnetization after MAF. No other major post processing is required. The finished components are ready for use after MAF in most cases.