Machines, apparatus, and jigs and fixtures required for the fabrication of welded articles from semifinished stock. A weldingposition, or station, is a set of welding equipment for operations that require some degree of participation by a welder. Awelding line combines several welding stations.
Welding stations may be used in arc welding, resistance welding, gas welding, electron-beam welding, or other methods. Thewelding equipment includes the welding machine, power supplies, and devices directly used to conduct the welding process,jigs and fixtures for the rapid assembly of the parts to be welded, for holding the parts during welding, and for preventing orreducing warpage of the welded articles, auxiliary equipment used for transporting the parts during welding and for mountingand transporting the welding apparatus, and various other tools used by the welder. Various transport means and instrumentsfor controlling weld quality are also used in the welding process. The technical characteristics of welding equipment aredetermined by the welding method chosen, the type of production, and the degree of mechanization, that is, whether manual,semiautomatic, or automatic welding is performed.
A welding station is a section of a production area where a power supply, current-carrying conductors, and necessary jigs,fixtures, and welder’s tools are located. In order to protect personnel in the area from radiation, the welding station isenclosed by curtains or panels. Fixed automated stations are widely used in modern manufacturing processes; such stationsare located in manufacturing shops. Mobile stations are used in the field for welding large objects in construction and repairwork.
Welders. Welding stations include power supplies and equipment for regulation of the arc during welding. Power suppliesused in welding should provide a convenient, continuous or step control and must satisfy general requirements for electricmachines and equipment. Welding transformers, generators, and rectifiers are used in electric welding; gas generators areused in gas welding. Power supplies may be single-position or multiposition types, stationary installations for continuous,long-term operation, or small, portable units for work of short duration.
A welding transformer is used to match the parameters of the welding circuit and the power supply; it also functions as avoltage regulator. In arc welding, the voltage is regulated mechanically or electrically. In the former case, the distancebetween the primary and secondary windings is altered. Electrical regulation is accomplished by changing the controlcurrents in supplementary windings, located on the upper and middle field frames of the transformer. In this method, thesecondary winding is divided into two sections, one of which is located in the upper window of the transformer. Such atransformer is capable of producing various no-load voltages without a change in the turn ratio; this property is required forwelding adjustments. Welding transformers used in resistance welding have a minimum short-circuit resistance and asecondary winding that usually consists of one or two turns. Changes in secondary voltage are achieved by tapping sectionsof the turns of the primary winding.
A welding generator is a specially designed electric machine—either a DC machine or a machine that operates at higher-than-standard frequencies. Single-position generators are used; they may be general-purpose units, or they may featuredrooping external characteristics, which result in a stable welding arc. Welding generators may be of the crossed-field orsplit-pole type, or they may have a bucking series winding. In a crossed-field welding generator, the short-circuited winding ofthe armature creates a cross magnetic flux. The drooping characteristics are due to the longitudinal bucking armature flux. Ina generator with a bucking series winding, the external characteristics result from the interaction of the magnetic fluxes of thebucking series winding and the magnetizing parallel winding. Voltage fed to the magnetizing winding is taken from a thirdbrush or from an independent power supply.
Welding rectifiers convert alternating current from a power supply to direct current; such converters may have drooping,fixed, or adjustable external characteristics. They consist of a transformer, a set of semiconductor electric valves, anautomatic control system, a reactor, and switching equipment. The converter is regulated by transformers or electric controlvalves.
A gas generator is a device for producing fuel gases. It usually produces acetylene from calcium carbide by the interaction ofthe latter with water.
An automatic arc-welding machine consists of a complex of mechanisms and devices used to mechanize the weldingprocess, including the feeding of electrode wires, the striking and maintaining of the welding arc, the maintaining of givenwelding conditions, and the stopping of the process after the weld is completed. In such installations, the welding heads mayfeature independent feed speeds for the electrode wire; in this case, the arcing process uses a self-regulating arc. The feedspeed of the electrode wire may also be automatically adjusted in correspondence with the arc voltage.
Mobile, self-propelled automatic welders may be used to replace complex stationary installations. Automatic weldingmachines and independent, suspended welding heads for electric welding with one or several electrodes are also used. Theelectrodes may be connected to a common power supply or to separate, independent supplies. Equipment for welding withnon-consumable carbon or tungsten electrodes is also used.
Semiautomatic welders used in arc welding feature a mechanized feed for the electrode wire and manual transport of thetorch along the edges being welded. Semiautomatic machines for welding with nonconsumable electrodes have amechanized feed for the filler-metal wire. This wire may be extended through a flexible guide hose, or it may be fed from areel by a mechanism built into the torch. Semiautomatic welding machines are used in gas-shielded welding, unshielded-arcwelding, and submerged arc welding. The wire feed mechanism and the torch are held in the welder’s hand and areconnected by a flexible hose. The hose functions as a guide channel that feeds the electrode wire, the welding current, theflux, and the shielding gas to the arc zone. In electric welding, the welding torch is the mechanism that feeds electric currentto the electrode and the gas to the arc zone; in gas welding, the torch is used to adjust the welding flame.
An automatic welder used in electroslag welding differs in its design from automatic welders used in arc welding, since theformer is used to weld edges in a vertical position. Some automatic welders move on rails; others run directly over the edgesof the parts being welded. In addition to the self-propelled mechanism for vertical motion, the welder is also equipped withtwo slides, designed to maintain the weld puddle and form the weld, and a mechanism for vibrating the electrodes along thesurface of the melt weld puddle.
Welding jigs and fixtures. Jigs and fixtures are used by the welder to assemble parts prior to welding, to hold the parts inplace, to weld previously assembled parts, and to combine the operations of assembly and welding. Both general-purposejigs and fixtures and those specially designed for a certain product are used; the design depends on the type ofmanufacturing process. Parts may be held together with screw, toggle, cam-and-eccentric, or magnetic clamps. Movableclamps may be used to hold individual parts together, or the tooling may be part of the equipment provided for each weldingstand. Tack-welding is sometimes used to hold parts in place with small, temporary welds. Braces, spacers, and jacks areused to position and hold the edges being welded. The assembly and welding of articles is carried out on general-purposeand special stands. Positioners, such as supports, arms, pins, and gauges, are used to locate the parts to be welded. Theequipment provided at a welding stand also includes devices for dispensing fluxes, flux and gas cushions, and devices usedto force-form welds.
Auxiliary equipment. Welding installations consist of components designed to locate the workpiece in the position mostconvenient for welding, to turn the workpiece around during welding or during service operations in the weld zone, and tomount and transport the welding apparatus. Roller-conveyor, spindle, chain, pivot-type, and lever tilters are used to locateparts in a convenient welding position. Rotators with vertical, inclined, or horizontal axes of rotation are used to rotate thearticle being welded. Workpieces are fastened and turned using a disk chuck or a guide (for center rotators) or rollers (forroller-type rotators). Roller-type rotator stands are frequently used in welding cylindrical articles; the drive rollers of suchrotators are usually rubber-coated. Shop and welding manipulators are used to turn workpieces around their axes in thosecases where the spatial position of the axis is changed during welding. Overhead platforms, rail tracks, and special fixturesthat grip the workpiece are used to mount and transport automatic and semiautomatic welders, to suspend the apparatusabove moving workpieces, and to transport the apparatus along a weld seam or from weld to weld.
Welder’s tools. Welder’s tools include electrode holders for welding with manual electrodes, welding torches, cleaning tools,such as hammers for slag removal, pneumatic hammers, wire brushes, and grinding machines, tools for fitting the parts to bejoined, tools for moving and turning hot workpieces, tools for aligning welding equipment, jigs, and fixtures, and measuringinstruments, such as gauges and micrometers. Data on equipment for special welding methods, such as resistance,ultrasonic, and diffusion welding, are given in the articles dealing with these methods.
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The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.