Unit-Head Machine Tool

a special metal-cutting tool which employs normalized assemblies, or units, that are kinematically not connected. The power units have individual drives whose interdependence and sequence of motion are specified by a single control system. The independent operation of the units makes it possible to unify their design and create an effective set of standard dimensions. Thus, in 1966 the USSR and the COMECON countries adopted a set of seven standard dimensions for the basic power units of unit-head machine tools. Unit-head machine tools are most widely used in mechanical processing where the piece remains stationary and the cutting instrument moves. Here a considerable concentration of operations is possible, since a part may be mechanically processed simultaneously by many instruments from various directions. Since unit-head machine tools are used to process one or several parts, they are used primarily in mass-production plants—for example, to bore holes in cylinder blocks.

In a vertical-type unit-head tool, one of the basic unified assemblies is the power head or power table with a post, mounted with spindle boxes to hold the cutting instruments. The drive for the power unit may be hydraulic, mechanical, or combined pneumatic and hydraulic. Parts to be processed are held in a clamping device which may be single or multipositioned. Multipositioned clamps are of two basic types: one with a vertical axis of rotation (that is, mounted on a rotating table) and the other with a horizontal axis of rotation (that is, mounted on a rotating drum). The number of instruments that may simultaneously operate on one tool is determined by the nature of the operations being performed (drilling, boring, facing, thread-cutting, etc.) and may be as high as 100 in certain cases. Unit-head machine tools have a high productivity, which depends on the duration of the limiting operation and on the work cycle.

Unit-head machine tools were first designed and manufactured in the USSR in the mid-1930’s at the Experimental Scientific-Research Institute of Metal-cutting Tools (ENIMS). Approximately 20,000 unit-head machine tools are in operation in the USSR.

In designing unit-head machine tools, particular attention is paid to increasing the operational reliability of the unified assemblies and to providing for rapid retooling of the tool so that it can be used to process other parts. For this purpose, all-Union standards have been developed for the connection dimensions for the basic assemblies. Work is under way to develop rapid-adjustment unit-head machine tools employing cyclical and digital programmed control which can be effectively used in series production when parts are processed in batches.