Other definitions of HSM have been developed to deal with the wide variety of work materials and tool materials used in machining. One popular HSM definition is by the DN ratio—the bearing bore diameter (mm) multiplied by the maximum spindle speed (rev/min). For high-speed machining, the typical DN ratio is between 500,000 and 1,000,000. This definition allows larger diameter bearings to fall within the HSM range, even though they operate at lower rotational speeds than smaller bearings. Typical HSM spindle velocities range between 8000 and 35,000 rpm, although some spindles today are designed to rotate at 100,000 rpm.
Another HSM definition is based on the ratio of horsepower to maximum spindle speed, or hp/rpm ratio. Conventional machine tools usually have a higher hp/rpm ratio than machines equipped for high-speed machining. By this metric, the dividing line between conventional machining and HSM is around 0.005 hp/rpm. Thus, high-speed machining includes 50 hp spindles capable of 10,000 rpm (0.005 hp/rpm) and 15 hp spindles that can rotate at 30,000 rpm (0.0005 hp/rpm).
(Mikell P. Groover, Fundamentals of Modern Manufacturing, Materials, Processes and Systems ,page 536)
Electrochemical Honing 07.04.2011 09:28
Electrochemical honing (ECH) combines the high removal characteristics of ECD and MA of conventional honing. The process has much higher removal rates than either conventional honing or internal cylindrical grinding. In ECH the cathodic tool is similar to the conventional honing tool, with several rows of small holes to enable the electrolyte to be introduced directly to the interelectrode gap. The electrolyte provides electrons through the ionization process, acts as a coolant, and flushes away chips that are sheared off by MA and metal sludge that results from ECD action. The majority of material is removed by the ECD phase, while the abrading stones remove enough metal to generate a round, straight, geometrically true cylinder. During machining, the MA removes the surface oxides that are formed on the work surface by the dissolution process. The removal of such oxides enhances further the ECD phase as it presents a fresh surface for further electrolytic dissolution. Sodium nitrate solution (240 g/L) is used instead of the more corrosive sodium chloride (120 g/L) or acid electrolytes. An electrolyte temperature of 38°C, pressure of 1000 kPa, and flow rate of 95 L/min can be used. ECH employs dc current at a gap voltage of 6 to 30 V, which ensures a current density of 465 A/cm2 [Randlett et al. (1968)]. Improper electrolyte distribution in the machining gap may lead to geometrical errors in the produced bore.
(Advanced Machining Processes, Hassan El-Hofy, Page 189)
Ion beam machining 07.04.2011 09:35
Ion beam machining (IBM) takes place in a vacuum chamber using charged ions fired from an ion source toward the workpiece by means of an accelerating voltage. The mechanism of material removal in IBM differs from that of EBM. It is closely related to the ejection of atoms, from the surface, by other ionized atoms (ions) that bombard the work material. The process is, therefore, called ion etching, ion milling, or ion polishing. The machining system, has an ion source that produces a sufficiently intense beam, with an acceptable spread in its energy for the removal of atoms from the workpiece surface by impingement of ions. Aheated tungsten filament acts as the cathode, from which electrons are accelerated by means of high voltage (1 kV) toward the anode. During the passage of these electrons from the cathode toward the anode, they interact with argon atoms in the plasma source, to produce argon ions.
Ar + e− →Ar+ + 2e
A magnetic field is produced between the cathode and anode that makes the electrons spiral. The path length of the electrons is, therefore, increased through the argon gas, which, in turn, increases the ionization process. The produced ions are then extracted from the plasma toward the workpiece, which is mounted on a water-cooled table having a tilting angle of 0° to 80°. Machining variables such as acceleration voltage, flux, and angle of incidence are independently controlled.
(Advanced Machining Processes, Hassan El-Hofy,Pages172-173)
Roller Coating 07.04.2011 21.50
Roll coating is a mechanized technique in which a rotating roller is partially submersed in a pan of liquid adhesive and picks up a coating of the adhesive, which is then transferred to the work surface. Figure 32.14 shows one possible application, in which the work is a thin, flexible material (e.g., paper, cloth, leather, plastic). Variations of the method are used for coating adhesive onto wood, wood composite, cardboard, and similar materials with large surface areas.
(Mikell P. Groover, Fundamentals of Modern Manufacturing, Materials, Processes and Systems ,page 760)
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