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in metalworking, a machine tool designed to remove material from workpieces by means of an abrasive tool. The first modern grinding machine (a universal cylindrical grinder) was built in 1874 in the USA. Initially, grinding machines operated with disks, or grinding wheels, made from solid pieces of natural abrasive rocks; stronger wheels of pulverized natural abrasives later came into use. The invention in 1893 of a method of making artificial abrasives (carborundum) substantially broadened the application of grinding machines.
According to the classification adopted for metalcutting machine tools, grinding machines are divided into cylindrical and internal grinding types (including centerless grinders and those with planetary motion), specialized grinders, surface grinders, and other types that operate with an abrasive tool (gear grinders and thread grinders belong to the gear-cutting and thread-cutting group of machines). The characteristics of the tool used impose some added requirements on design and structural materials: resistance to vibration, wear resistance, and the rapid removal of abrasive dust. The principal motion of a grinding machine (seeMETALCUTTING MACHINE TOOL) is the rotation of the abrasive tool at a velocity that is generally considerably higher than the feed rate and other motions.
Cylindrical grinding machines are the most common type. In such machines the workpiece is carried on centers or in a chuck (Figure 1,a) and rotated in a direction opposite to that of the grinding wheel; together with the table of the machine, the work-piece executes reciprocating motion. At the completion of every single (or double) traverse of the table, the grinding wheel is shifted transversely by an amount equal to the cutting depth (seeMACHINING). External cylindrical and conical surfaces and the ends of workpieces are usually ground on cylindrical grinding machines. Infeed, or plunge, grinding is used to grind external cylindrical, conical, and irregularly shaped surfaces with a wide wheel (wider than the dimension of the workpiece); in this case there is no longitudinal feed.
Internal grinding machines are designed to grind internal surfaces of rotation. In the most common types the workpiece is rotated around the axis of the hole being ground while the grinding wheel rotates around its own axis (Figure l,b); the wheel is moved both longitudinally and transversely. Internal grinding machines with planetary motion are used to machine holes in workpieces that are difficult to rotate. In such machines the grinding wheel simultaneously rotates around its own axis and around the axis of the hole being machined (Figure 1,c).
Centerless grinding machines are designed to grind external and internal cylindrical surfaces. When external surfaces are to be ground, the workpiece (or a series of workpieces placed end to end) is positioned between two wheels, one of which is for machining and the other for regulating (Figure l,d), and is pressed against a workrest blade. As a result of the tilt of the regulating wheel, the frictional forces not only cause the workpiece to rotate but also to feed through. The regulating wheel is also fed transversely. When internal surfaces are to be ground, such as ball bearing races, the workpieces are supported between two pressure rolls and a regulating wheel (Figure l,e) that rotates the workpiece. The grinding wheel is moved along and across the axis of the hole, if necessary, or only radially (for infeed grinding). Centerless grinding machines are less versatile than cylindrical grinders and internal grinding machines, but they are simpler in design.
Surface grinding machines are designed to machine the plane surfaces of workpieces with the periphery or the end of a grinding wheel. In machines that use the periphery of the wheel (Figure l,f), the table and the workpiece mounted on it execute a reciprocating or rotary motion; the rotating grinding wheel is moved crosswise for each traverse or rotation of the table, and it is also shifted by an amount equal to the depth of the cut. In surface grinding machines that machine with the end of the wheel (Figure l,g), unlike machines that use the wheel periphery, there is no transverse feed, because the diameter of the wheel is greater than the transverse dimension of the workpiece (infeed grinding).
Specialized grinding machines are usually designed to machine parts of some given shape, for example, crankshaft journals, parts of dies, templates, and splined parts. The workpieces are usually machined to a template (the forming method); the generating method is less often used.
The general group of grinding machines also includes lapping, polishing, microfinishing, tool-grinding, spline-grinding, honing, and other machines that use an abrasive tool.
REFERENCESMetallorezhushchie slanki. Moscow, 1973.
Maslov, E. N. Teoriia shlifovaniia materialov. Moscow, 1974.
A. A. SHISHKIN and N. K. IAKUNIN