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Plasma Beam Machining (07 Nisan 2011 09:48)

In plasma machining a continuous arc is generated between a hot tungsten cathode and the water-cooled copper anode. A gas is introduced around the cathode and flows through the anode. The temperature, in the narrow orifice around the cathode, reaches 28,000°C, which is enough to produce a high-temperature plasma arc. Under these conditions, the metal being machined is very rapidly melted and vaporized. The stream of ionized gases flushes away the machining debris as a fine spray creating flow lines on the machined surface. The removal rates by this method are substantially higher than those of conventional single-point turning operation. Plasma machining systems are divided into plasma arc, plasma jet, shielded plasma, and air plasma.

(Advanced Machining Processes, Hassan El-Hofy; Page:166)

Electrochemical Buffing (07 Nisan 2011 10:02)

Mechanical buffing is a slow finishing process used for achieving smooth,bright, and mirrorlike surfaces. The process is carried out under dry conditions, which raises dust and makes the working environmental conditions unsuitable. Electrochemical buffing (ECB), uses a carbon fiber cloth that rubs the anodic specimen against a revolving cathode fiber buff. Electrolytes of NaCl or NaNO3 are supplied to the machining zone using a suitable pump. The machining current flows from the workpiece to the cathode through the carbon cloth. ECD of the anodic specimen mainly takes place on the surface of the specimen where it is rubbed by the carbon cloth buff. The current density, the type of electrolyte, and the workpiece material control the polishing speed. For high-speed polishing, an NaCl electrolyte is used where high current density is ensured. The addition of Al2O3 abrasives (200 mesh number) to the machining medium increases the amoun of material removal; however, surface smoothing and brightness are decreased. During ECB, a passive oxide film is normally formed on the surface of the stainless steel workpiece. MA and hence the removal of such a film on the high spots of the surface irregularities enhances the dissolution phase to prevail in these spots, which in turn makes the surface smoother and brighter.

(Advanced Machining Processes, Hassan El-Hofy; Page:196)

Electroerosion Dissolution Machining (07 Nisan 2011 10:10)

Novel methods of machining hard metals, which are difficult to cut by conventional methods, continue to attract attention. Electrochemical machining and electrodischarge machining have proven to be very useful. However, drawbacks such as the expense of tooling for machining large cavities, the high cost of machining systems, low rates of metal removal, and the presence of a recast layer, which often has to be removed in EDM, have hindered wider acceptance of these techniques. EEDM (also called ECDM or ECAM) is a new development, which combines features of both ECD and EDE. It utilizes electrical discharges in electrolytes for material removal. Such a combination allows high metal removal rates to be achieved. EEDM has found a wide range of applications in the field of wire cutting, hole drilling, and finishing of dies and molds.

(Advanced Machining Processes, Hassan El-Hofy; Page:204)

Electrochemical Superfinishing (07 Nisan 2011 10:15)

Conventional superfinishing by vibration grinding is a microfinishing operation in which the surface mirco-irregularities are removed by the continuous and slow reciprocation of abrasive sticks that move along the workpiece length. The sticks oscillate concurrently with short and rapid strokes with a continuously revolving workpiece. This process is however known to sustain some of the surface microirregularities such as waviness and out of roundness. In electrochemical superfinishing (ECS), the combination of electrolytic dissolution (ECD) and mechanical scrubbing (MS) improves the performance of the conventional superfinishing process. As a result of such a combination, the dissolution process assists the small stock removal rate due to the mechanical chipping action. Higher stock removal rates become achievable using either a separate cathodic tool electrode, or a diamond abrasive stick with a metallic bond. The high stock removal capabilities combined with the ability to generate close dimensions gave high merits to the ECS process in all fields of industry. The need for initial grinding, which is required before conventional superfinishing, is avoided. ECS can be used when other processes fail to yield high removal rates or generate the required size in difficult-to-machine alloys as well as tool steel. Applying ECS to parts that are susceptible to heat and distortion is advantageous because the bulk of the metal is removed electrochemically in an electrolyte-cooled atmosphere. The problem of thermal distortion, normally found in conventional superfinishing, is therefore eliminated. Burr-free components can also be obtained as a result of the ECD process.

(Advanced Machining Processes, Hassan El-Hofy; Page:192)