CHAPTER 1: INTRODUCTION
1. Magnetic Abrasive Finishing (MAF)
Surface roughness of parts produced by conventional machine tools, depends n the machine tool system and the cutting process. It is difficult to produce a smooth surface on complicated profiles at an economic cost by using conventional machining processes. This and the advent of new ‘ difficult-to-machine’ materials like hardened steel, nickel, cobalt, titanium alloys, ceramics, glass, etc., have necessitated the need for new machining techniques. Magnetic abrasive finishing is one such alternate process for improving the surface finish on complicated profiles at a reasonably low cost. It presents an attractive novel concept of surface and edge finish by abrasive particles. This process can overcome the limitations of traditional rigid shape grinding wheels in tackling complicate peripheries and may result in minimize induced stresses that usually come about by excessive penetration of hard grains in to the work surface. The process uses very low forces and loose abrasive particles and hence can minimize the damage during machining. In MAF, a flexible finishing action is sustained by the pressure exerted by a blanket of abrasive bonded to iron particles. This mixture is actuated by a magnetic field, which is coupled with rotational and oscillatory motions between flexible MAF brush and work piece. The finishing process is essentially accomplished without the need for designing expensive, rigid, vibration free machine tools by incorporating magnetic machining elements necessary cost of new equipment. MAF cutting agent is a composite of fine abrasive grits and coarser iron grains. The particles can thus be excited by a strong magnetic field to generate a normal dynamic pressure sufficient to refine the surface, deburr and chamfer its edges. Conventional abrasives like aluminum oxide (Al2O3) And silicon carbides (SiC) may be used as well as the costly super abrasives such as cubic boron nitride (CBN) and diamond.
Magnetic abrasive machining uses very low forces and loose abrasive particles. Hence, the process can minimize damage during machining. The advantage of magnetic abrasive finishing over the other alternative processes like super finishing, lapping and honing are: • Simultaneous machining of mutually perpendicular surfaces such as cylindrical and conical ones, other combinations such as finishing outer diameter an radii of piston ring and the like parts is possible. • Material surface is free of buns and thermal defects.
• Low energy consumption.
• Simple in implementation.
• Ecologically safe.
• Substantial improvement in service characteristics such as wears resistance, mechanical and physical characteristics. • Non-ferrous materials like aluminum and its alloys, brass and its allos can also be finished with ease. • Most efficient from economical point of view for the magnetic abrasive powder used for the process is a waste material in the grinding wheel industry.
• Structural applications such as ceramics bearings for high-speed spindle. • Finishing of inner surface of thin stainless steel sanitary tubing. • An internal MAF was proposed for producing highly finished inner surfaces work pieces used in critical such applications as clean gas or liquid piping systems, aerospace components and semiconductor plants.
• Despite the potential advantages of MAF processes, there are several impediments to its more wide spread utilization. One key issue is its lower polishing efficiency for polishing complicated 3d curves surfaces. • MAF yields better surfaces, especially of complex shapes. However, it has the disadvantages of flow efficiency when applied to very hard materials.
1.5 Modeling of MAF Process
MAF process has been studied by several researchers with an objective of employing it is an efficient and economical process for...
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