machines, apparatus, and jigs and fixtures required for the fabrication of welded articles from semifinished stock. A welding position, or station, is a set of welding equipment for operations that require some degree of participation by a welder. A welding line combines several welding stations.
Welding stations may be used in arc welding, resistance welding, gas welding, electron-beam welding, or other methods. The welding 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 or reducing warpage of the welded articles, auxiliary equipment used for transporting the parts during welding and for mounting and transporting the welding apparatus, and various other tools used by the welder. Various transport means and instruments for controlling weld quality are also used in the welding process. The technical characteristics of welding equipment are determined 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 is enclosed by curtains or panels. Fixed automated stations are widely used in modern manufacturing processes; such stations are located in manufacturing shops. Mobile stations are used in the field for welding large objects in construction and repair work.
Welders. Welding stations include power supplies and equipment for regulation of the arc during welding. Power supplies used in welding should provide a convenient, continuous or step control and must satisfy general requirements for electric machines and equipment. Welding transformers, generators, and rectifiers are used in electric welding; gas generators are used 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 a voltage regulator. In arc welding, the voltage is regulated mechanically or electrically. In the former case, the distance between the primary and secondary windings is altered. Electrical regulation is accomplished by changing the control currents in supplementary windings, located on the upper and middle field frames of the transformer. In this method, the secondary winding is divided into two sections, one of which is located in the upper window of the transformer. Such a transformer is capable of producing various no-load voltages without a change in the turn ratio; this property is required for welding adjustments. Welding transformers used in resistance welding have a minimum short-circuit resistance and a secondary winding that usually consists of one or two turns. Changes in secondary voltage are achieved by tapping sections of 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 feature drooping external characteristics, which result in a stable welding arc. Welding generators may be of the crossed-field or split-pole type, or they may have a bucking series winding. In a crossed-field welding generator, the short-circuited winding of the armature creates a cross magnetic flux. The drooping characteristics are due to the longitudinal bucking armature flux. In a generator with a bucking series winding, the external characteristics result from the interaction of the magnetic fluxes of the bucking series winding and the magnetizing parallel winding. Voltage fed to the magnetizing winding is taken from a third brush 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, an automatic control system, a reactor, and switching equipment. The converter is regulated by transformers or electric control valves.
A gas generator is a device for producing fuel gases. It usually produces acetylene from calcium carbide by the interaction of the latter with water.
An automatic arc-welding machine consists of a complex of mechanisms and devices used to mechanize the welding process, including the feeding of electrode wires, the striking and maintaining of the welding arc, the maintaining of given welding conditions, and the stopping of the process after the weld is completed. In such installations, the welding heads may feature independent feed speeds for the electrode wire; in this case, the arcing process uses a self-regulating arc. The feed speed 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 welding machines and independent, suspended welding heads for electric welding with one or several electrodes are also used. The electrodes may be connected to a common power supply or to separate, independent supplies. Equipment for welding with non-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 the torch along the edges being welded. Semiautomatic machines for welding with nonconsumable electrodes have a mechanized feed for the filler-metal wire. This wire may be extended through a flexible guide hose, or it may be fed from a reel by a mechanism built into the torch. Semiautomatic welding machines are used in gas-shielded welding, unshielded-arc welding, and submerged arc welding. The wire feed mechanism and the torch are held in the welder’s hand and are connected by a flexible hose. The hose functions as a guide channel that feeds the electrode wire, the welding current, the flux, and the shielding gas to the arc zone. In electric welding, the welding torch is the mechanism that feeds electric current to 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 the former is used to weld edges in a vertical position. Some automatic welders move on rails; others run directly over the edges of the parts being welded. In addition to the self-propelled mechanism for vertical motion, the welder is also equipped with two slides, designed to maintain the weld puddle and form the weld, and a mechanism for vibrating the electrodes along the surface 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 in place, to weld previously assembled parts, and to combine the operations of assembly and welding. Both general-purpose jigs and fixtures and those specially designed for a certain product are used; the design depends on the type of manufacturing process. Parts may be held together with screw, toggle, cam-and-eccentric, or magnetic clamps. Movable clamps may be used to hold individual parts together, or the tooling may be part of the equipment provided for each welding stand. Tack-welding is sometimes used to hold parts in place with small, temporary welds. Braces, spacers, and jacks are used to position and hold the edges being welded. The assembly and welding of articles is carried out on general-purpose and special stands. Positioners, such as supports, arms, pins, and gauges, are used to locate the parts to be welded. The equipment provided at a welding stand also includes devices for dispensing fluxes, flux and gas cushions, and devices used to force-form welds.
Auxiliary equipment. Welding installations consist of components designed to locate the workpiece in the position most convenient for welding, to turn the workpiece around during welding or during service operations in the weld zone, and to mount and transport the welding apparatus. Roller-conveyor, spindle, chain, pivot-type, and lever tilters are used to locate parts in a convenient welding position. Rotators with vertical, inclined, or horizontal axes of rotation are used to rotate the article being welded. Workpieces are fastened and turned using a disk chuck or a guide (for center rotators) or rollers (for roller-type rotators). Roller-type rotator stands are frequently used in welding cylindrical articles; the drive rollers of such rotators are usually rubber-coated. Shop and welding manipulators are used to turn workpieces around their axes in those cases where the spatial position of the axis is changed during welding. Overhead platforms, rail tracks, and special fixtures that grip the workpiece are used to mount and transport automatic and semiautomatic welders, to suspend the apparatus above 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 be joined, tools for moving and turning hot workpieces, tools for aligning welding equipment, jigs, and fixtures, and measuring instruments, 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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M. G. BEL’FOR, I. I. ZARUBA, and V. N. TROITSKII