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milling machine[′mil·iŋ mə‚shēn]
a metal-cutting machine tool used in metalworking. The machine uses a milling cutter to cut inside and outside flat and shaped surfaces, grooves, steps, the surfaces of bodies of revolution, threads, and teeth on gear wheels.
The principle of milling apparently was discovered in Europe in the 16th century. Leonardo da Vinci sketched a prototype cutter in the form of a rotating round file. A machine tool with a rotating file was built in Peking in 1665. The prototypes of modern milling machines appeared in the 19th century: the knee-and-column type in 1835, the universal type in 1862, and the planer type in 1884. Various designs subsequently developed rapidly, and the different types became differentiated.
Milling machines may be classified into various categories according to purpose: universal, horizontal, vertical, and planertype milling machines; duplicators; thread-milling and keywaymilling machines; and rotary-and drum-type milling machines. Depending on design, they are classified into two categories: column-and-knee types and compound-table types. The primary motion in milling machines is the rotary motion of the cutter; the workpiece undergoes translatory motion as it is fed to the cutter. In some cases, for example, when machining large workpieces, the feed motion may be handled by the cutter.
A typical universal column-and-knee-type milling machine has the spindle axis set horizontally. It is equipped with a yoke having a suspension link to secure the milling arbor and can use different types of cutters. The machine has a table that swivels in the horizontal plane, which makes it possible to mill helical grooves. The table can be moved longitudinally, transversely, and vertically. Horizontal milling machines are similar in design, but they do not have tables that swivel. A typical vertical milling machine is similar in design to the previously discussed types, except that the spindle axis is vertical.
Planer-type milling machines are designed to work different surfaces of large workpieces (or groups of workpieces) mounted in multiposition fixtures on the machine table; face cutters are usually used in this type of machine. Lateral milling heads are situated on the machine’s vertical back braces, which are mounted on the bed. The machine also has a transverse equipped with vertical milling heads, each with an individual gear to turn the spindle. The spindle axes can be moved horizontally and vertically and can be set at an angle. The table has a longitudinal feed, the vertical milling heads have a transverse feed, and the lateral heads have a vertical feed. All the milling heads share a common feed drive.
Keyway-milling machines are used to cut keyways according to a closed, semiautomatic cycle of motion with a rotating key-seat cutter; the feed is vertical to the depth of the slot, then forward horizontal along the axis of the slot and reverse horizontal at the end. Such machines may have one or more spindles. Rotary-type milling machines use face cutters for continuous milling of the surfaces of cast and forged workpieces. The table has circular feed. Drum-type milling machines are designed to work two end surfaces simultaneously, for example, for connecting rods, shafts, and forks; they are also used for milling slots.
Various types of milling machines with programmed control are increasingly used in industry. In such machines, motion along each of the three coordinates is controlled by signals recorded on two tracks of a magnetic tape. The signals originating in the windings of six coils of the magnetic head are fed through amplifiers, pulse shapers, and a pulse distributor to the traction motors and then through hydraulic actuators to the drive screws of the machine feeds.
D. L. IUDIN
In woodworking, planing machines similar in principle to the milling machines used in metalworking are equipped with a vertical spindle to which a cutter is attached. They are used to work semifinished pieces in surface, profile, and shape cutting. There are several types of such machines: plain types with one or two spindles, rotary types, and duplicators. Single-spindle machines have a bed with a table and spindle secured to a mobile support. Pieces are worked with the aid of guides. In two-spindle machines the spindles rotate in opposite directions, which makes it easier to cut workpieces with curves shapes and reduces the possibility of chips and scratches. Rotary machines with rotating tables, to which the workpiece is attached, are used for flat and figured cutting. Duplicators have a device for working from a master and are used for small jobs, precision work, and sculpting.
N. K. IAKUNIN