Automatic Transfer Machine
Automatic Transfer Machine
a system of machinery, a set of basic and auxiliary equipment which carries out entire manufacturing processes or reprocesses of a product or part of it automatically within a specified technological sequence and at a specified pace. The servicing personnel of an automatic transfer machine perform the following functions: control, monitoring of the performance of units or production sections in the transfer line, and repair and adjustment. Transfer machines requiring the direct participation of human operators in order to complete some of the operations of the manufacturing process (for example, starting and stopping individual units, mounting or displacing the workpiece) are known as semiautomatic transfer machines. Many of the auxiliary operations (for example, removal of production wastes), product quality control, output evaluation, and the like are mechanized and automated on modern automatic transfer machines. Many automatic transfer machines feature automatic control of the variables of the manufacturing processes, automatic displacement of working tools, and automatic adjustment and readjustment of equipment. The design of automatic transfer machines and their acceptance into regular production is one of the most important stages in the automation of production, in the transition from individual automatic machines to automatic systems of machines and automated complexes frequently combining manufacturing processes of widely contrasting types.
Automated flow-line production arose in some branches of industry (for example, in the chemical industry and food industry) in the early 20th century, basically in those areas of production where the technology could not have been organized in any other way, such as in the cracking of petroleum. But the very term “automatic transfer machine” appeared somewhat later in application to systems of metalworking machine tools and lathes. This partly explains the fact that the qualitative and quantitative indexes of automatic transfer machines are taken into account for the most part in the machine-building industry and in the metalworking industry.
The first integrated automatic transfer machines in the machine-building industry of the USSR were devised in 1939, on the basis of a suggestion put forth by I. P. Inochkin, a worker and production rationalizer at the Volgograd Tractor Plant. Automatic transfer machines for machining and grinding bearing parts were set up at that time at the First State Bearing Factory in Moscow. In 1936, the Experimental Scientific Research Institute for Metal-cutting Machine Tools designed projects for automatic transfer machines combining multihead machine tools. Transfer machines of that type were built for the defense industry during the Great Patriotic War. In 1945–46 the Stankokon-struktsiia factory manufactured several automatic transfer machines incorporating multihead machine tools for the purpose of machining body parts of tractors, trucks, and automobiles. An integrated automated production of aluminum pistons for tractor engines with automation of all processes, including loading of the raw materials, meltdown of metal, metering of molten metal, billet castings, heat treatment, machining, chemical processing, anticorrosion treatments, quality control, and crating of the finished product, was set up for the first time in universal practice in the USSR in 1947–50. An integrated automated department manufacturing ball bearings and roller bearings, including machining, quality control, and assembly, was set up in 1953–55 at the First State Bearing Factory.
A further stage in the development of automatic transfer machines was the building of type-standardized fast-readjustable versatile automatic transfer machines for machining cylindrical gears, stepped shafts, and castellated shafts. Several parts of the same type having different dimensions can be machined simultaneously on such transfer machines with minimum readjustment time; besides, each machine tool in the transfer line is capable of operating independently in the process. The development of type-standardized automatic machine tools on the basis of general-purpose machines and equipment has brought about the necessary conditions for the manufacture of automatic transfer machines in lots and for their introduction into lot production.
Automatic transfer machines are being widely used in the food industry, in the production of household wares, in the electrical and electronic goods industries, and in the chemical industry. Automatic transfer machines have received wide acceptance in the machine industry. Many of those machines are fabricated directly at the plants using already existing equipment.
Automatic transfer machines for processing commodities which are strictly determined in shape and dimension are called special-purpose transfer machines; these machines have to be replaced or modified when the product being manufactured is changed. Specialized automatic transfer machines for machining products of a single type over a specified range of parameters offer a broader range of options in production practice. When production plans call for a switch to a new production item, specialized automatic transfer machines generally need only to be retooled in individual machining units, with changes in their operating conditions; the basic manufacturing equipment can be used to fabricate the new product of a single type in most cases. Special-purpose and specialized automatic transfer machines are used principally in mass production.
Automatic transfer machines used in large-lot production must exhibit versatility and the option of fast-readjustment capability in the fabrication of different products of the same type. Such automatic transfer machines are known as general-purpose fast-readjustment machines, or multiple-machine automatic transfer machines. General-purpose automatic transfer machines are less productive than their special-purpose counterparts but compensate with their rapid readjustment in the production of a broad assortment of different products.
The structural layout of an automatic transfer machine depends on the production volume and on the nature of the manufacturing process. There exist in-line or parallel-action automatic transfer machines, single production lines, multiple production lines, or mixed production lines (with branching flows). Parallel-action automatic transfer machines are used to carry out a single operation when the duration of that operation is much longer than the required production pace. The workpiece is transferred automatically (from a magazine or hopper), is indexed from station to station among the units in the transfer line, and after machining is picked up by material-handling devices and routed through subsequent operations. Multiple-flow automatic transfer machines constitute a system of parallel-action automatic transfer machines designed to carry out several manufacturing operations, each of which lasts longer than the specified production pace. Several in-line automatic transfer machines or parallel-action automatic transfer machines can be combined into a single system. These systems are then known as automatic production sections, departments, or production facilities.
The control of automatic transfer machine tools is handled by automatic control systems which are classified as either inner-loop systems or outer-loop systems. Inner-loop control systems make it possible for a single unit or mechanism in the transfer line to carry out all the basic and auxiliary operations in the manufacturing process on that particular unit. An outer-loop system (as a rule, a routing control system organized on the feedback loop principle) ensures coordinated work of units and section units in the transfer line. Automatic transfer machine control systems are built on the basis of electrical, mechanical, hydraulic, pneumatic, or combined coupling links, depending on the specific production conditions. Electronic program control systems are used for automatic control of the manufacturing process and of equipment readjustment on automatic transfer machines (predominantly multiple-machine setups). Large integrated automatic transfer machines are equipped with electronic control machines and other computing equipment. Separate electric power drives or multiengine power drives are used predominantly on units in an automatic transfer line; controlled variable electric, hydraulic, or mechanical power drives are employed less frequently.
Indexing of the work (a piece to be machined) from one machining station to another can be handled by either a rigid or a flexible conveying or material-handling system. A rigid conveying system may pass through the work space of the unit of the automatic transfer line, may be situated parallel to it, or may have devices mounted perpendicular to it for loading and unloading the station. The work stations on each unit are set at equal distances apart. The part is dismounted, after being machined at one station, and transferred to the next station; a new work piece is then indexed to the first station, and the finished work piece is removed from the last station. Depending on the design, dimensions, and shape of the product, the conveyors used may be step-by-step conveyors, transfer-bar-type conveyors, or hook conveyors, slat-type or pallet conveyors, chain conveyors, and so forth. Rigid conveying systems are used predominantly on in-line single-flow transfer machines fabricating large single products (for example, on transfer machines consisting of multihead machine tools or on transfer machines for machining cylindrical gears). When a flexible conveying system is used, the unmachined work-piece is indexed at the first station and the finished product is removed from the last station independently on each unit in the automatic transfer line; transfer of work from one position to another can be kept in pace with the actual progress of the manufacturing process. The workpieces are indexed between units with the aid of inclined or vibration-aided chutes, chain conveyors, band conveyors, trough conveyors, and the like. The flexible conveying system is most effective in the machining of small parts and products on parallel-action automatic transfer machines and also on multiple-flow and mixed automatic transfer machines. The usual practice when using a flexible conveying system is to place magazines or storage bunkers at each work station. Their purpose is to keep the automatic transfer machine working in the event of a shutdown of individual units and to improve the servicing of the transfer lines. The number and capacity of these storage bunkers are determined by the complexity and extent of the automatic transfer line and by the degree of reliability and trouble-free operation of the units. The magazines (storage hoppers) are also used on automatic transfer machines equipped with a rigid conveying system; in that case they are built into the overall conveying system and material-handling system, so that the individual production sections can operate independently.
The workpiece can remain stationary or can be moved in a straight line during the machining process (as in centerless grinding automatic transfer machines) or in a circular or a rotary motion (as in a rotary-indexing transfer machine). Fixed or rotating parts are located or placed prior to machining in the required position directly at the work station or in a satellite fixture. Straight-line or circular displacement of the work during the machining process is usually carried out by material-handling devices.
The stability of the manufacturing process in the case of automatic transfer machines is defined as the time during which the required process variables are kept close to the set point within the required tolerance limits. The stability of the product quality and removal of errors during the machining process in automatic transfer machines is achieved through systematic inspection of the assigned variables and active intervention in the production process.
The direct effectiveness of automatic transfer machine tools is felt in particular as a decrease in the number of workers previously employed in the same line and volume of production. But automatic transfer machine work requires high skill on the part of the operating and servicing personnel. Automatic transfer machines are most effective when improved manufacturing processes are being implemented in production on complex and integrated levels. Under socialist conditions of production, automatic transfer machines are being used to handle labor-consuming operations and hazardous processes, where this results in significant improvements in working conditions and makes the labor of the workers easier. However, as a rule automatic transfer machine tools also yield an indispensable economic efficiency, which is particularly high in integrated automation of production. The cost of products manufactured on automatic transfer machines depends primarily on the cost of the original materials and on the cost of the semifinished products, on the capacity of the automatic transfer machine, and on the development costs.
The cost of automatic transfer machines is determined by the number of manufacturing operations they perform, the complexity of those operations, the volume of products manufactured, the complexity of the equipment and control systems, and the level of lot production. Other conditions being equal, the decisive factor determining the cost of an automatic transfer machine will be the level of lot production of the line equipment. The cost of an automatic transfer machine is lowered when standardized assemblies, mechanisms, and tools are used; when the fabrication of the conveying system and control system is centralized; and when the duration of installation and adjustment operations is shortened. Lowering the cost of the automatic transfer machine expands the economically feasible range of applications of the transfer machine, making it possible to put automatic transfer machines needed for the technical retooling of an industry into operation.
The capacity of an automatic transfer machine depends on the time spent in directly carrying out the manufacturing process, the time required to carry out auxiliary indexing operations (uncoordinated material-handling operations, mounting and dismounting the work, removal and transfer of tools), readjustment time, adjustment time, and time required to put the transfer machine back in operation after shutdown. The time of the manufacturing process can be shortened by using highly productive technology. The time spent in auxiliary indexing operations can be shortened by cutting down the number of unproductive transfers occurring during the process or by increasing the speed of the transfers or by carrying out those unproductive transfers simultaneously with the manufacturing process. The criterion of cyclical continuity of the work, which is defined (in the case of the discrete manufacturing processes) by the ratio of the time required to complete the manufacturing process to the full cycle time, is important for evaluating the capacity of the automatic transfer machine. The time spent in setup, readjustments, and repairs is shortened by using automatic control, by increasing the stability of the tools, and by replacing defective tools in good time.
Thousands of automatic transfer machines are now in use in the industries of the USSR. For example, in the metal-working industry alone, 4,800 automatic transfer machines were in use in 1967.
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Vladzievskii, A. P. Avtomaticheskie linii v mashinostroenii. Moscow, 1958.
Shaumian, G. A. Avtomaty i avtomaticheskie linii, 3rd ed. Moscow, 1961.
Boguslavskii, B. L. Avtomaty i kompleksnaia avtomatizatsiia. Moscow, 1964.
A. P. VLADZIEVSKII