Flexible machining systems


Flexible manufacturing systems have three distinguishing characteristics; potentially independent CNC machine tools; a transport mechanism; and an overall method of control that co-ordinates the function of both machine tools and the conveyor system so as to achieve flexibility. The main purpose of such system is to integrate the various functions in the same machine tool to form a flexible manufacturing cell that is a module of a flexible manufacturing system. A manufacturing cell is a place designed to process part families in dedicated areas.

Each flexible manufacturing cell is an autonomous module, the functions of which are supervised and controlled by a microprocessor-based computer. The various functions of the individuals cells are as follows: supply of blanks, tools, gauges and devices; use of clamping devices for identification, selection, transport, orientation, loading, positioning, clamping, declaring, interlock supervision and other step-by-step operations; automatic execution of operations such as measurement of the work piece, adjustment of clamping devices, material handling and positioning; and automatic monitoring by sensors of interlocks, lubrication failure, tool breakage and other malfunctions.

Each cell basically caters to a particular machining process like turning and milling. The different cells are connected by transport devices into flexible manufacturing system, and the co-ordination of the simultaneous activity of all the cells is accomplished by the process computer hierarchy so that from raw material to end product the complete production process is automated.

An alternative concept of a flexible machining system envisages a manufacturing cell which performs various machining processes like turning, milling and boring as a part of one individual cell. In this, the material handling functions are reduced. An existing stand-by robot or integrated robot handles the work piece and the measurement device.

Maximum utilization of the cutting capability of the machine tool is ensured by an adaptive control. Suitable sensors to monitor process parameters are incorporated in the manufacturing system. The CNC system integrates the whole control strategy for utilization of installed capacity, reduction of idle time and monitoring the thermal effects of component accuracy.

Several manufacturing cells linked by a transport system, additional handling devices and an automated storage and retrieval system for the work piece, tools etc., can lead to the concept of an automated factory. The most advanced stage of optimization would involve a hierarchical organization in which all cells at a higher level are controlled by centralized DNC type computer and all production groups are linked to a mini-computer, providing a basis for complete on-line optimization of material flow, scheduling, routing and full automation of production.

Computer integrated flexible manufacturing systems are thus gaining increasing acceptance and importance in batch production. Of the approximately 50 flexible manufacturing systems developed up to 1979, about 40 have been put into operation, nearly 70% of them intended for prismatic components.

Flexible manufacturing systems based on group technology or cell production principle using CNC machines and gauging equipment are now being installed with robot handling devices and palletized conveyor supply units to machine families of parts.

Development is also proceeding with the automation metal-forming machines using mini-computers and microprocessors. Programmable turret punches, auto-controlled guillotines and shears, and manipulative equipment are in use. Robot developments applied to metal-forming operations will enable a considerable degree of automation in this class of piece-part manufacture. It is now possible to construct metal-forming production cells with the aid of robots that will blank, pierce and bend a family of components using a common stock material.

The manufacture of piece-parts, whether forged, welded, sintered or similarly processed, is being automated with the use of robots. The automation of assembly operations remains problematical, except for flow-line manufacture. But robotic and computer developments will have a considerable impact on these operations in the immediate future.

The benefits associated with the use of manufacturing cells are: reduced over-flow, timeless work-in-process inventory, smaller set up times, lower material handling costs, improved job satisfaction and status and simplified planning and control systems. Cellular manufacturing combines the best of the product and the process work flow patterns and eliminates their individual drawbacks. Like its biological counterpart, a manufacturing cell is a self-contained work unit that consists of all the machining and process-centers required to manufacture a product. It is manned by multi-skilled workers as opposed to single dimensional specialists that the product and process work flow patterns create.