Many welding processes are obtained only by heat without pressure; other combustion by heat and pressure; and a more only by pressure without providing external heat. In some cases a filler or added filler to facilitate fusion. Welding is usually associated with mechanical parts, but the process is also used to bond plastic.
A welding is a relatively new process. Its commercial and technological importance stems from the following:
– Welding provides a permanent bond. The welded parts become a single unit.
– The union can be stronger than you original materials, if a filler metal that has properties superior resistance of original materials you used and suitable welding techniques as are used.
Although welding has indicated advantages, it also has certain limitations and disadvantages (or potential disadvantages):
– Most welding operations are performed manually and are high in terms of labor cost. Many welding operations are considered specialized issues and there are not many people who make them.
– Almost all welding processes involve the use of a lot of energy, and therefore dangerous.
– Since the welding obtains a permanent bond between the components does not allow proper disassembly. If an occasional product disassembling (for repair or maintenance) is required, the weld must not be used as a method of assembly.
– The weld joint may have certain quality defects that are difficult to detect. Defects can reduce bond strength.
THE QUESTION OF SECURITY
Welding is by nature hazardous to people. Those running these operations must take serious security measures. High temperatures of metals fused in welding are an obvious hazard. In the welding gas, fuels (eg, acetylene) are at risk of catching fire. Much of the processes use a lot of energy to produce fusion of the surfaces of the parts to be, to unite in many welding processes, electrical power is a source of thermal energy, so there is a risk of electric shock for the worker.
Certain welding processes have their own particular hazards. In arc welding, the worker must consider the following aspects:
* Mask welding, protects the eyes, face, neck and should be provided with inactinic filters according to the process and currents employed. * Leather gloves, musketeer guy inseam, to protect hands and wrists. * coleto or leather apron to protect against splashes and exposure to ultraviolet rays of the arc. * leggings and leather jacket, when it is necessary to weld in vertical positions and overhead, these additions should be used to avoid severe burns that may cause splashes of molten metal. * safety shoes, covering the ankles to avoid the trap of splashing. * Hat, protects the hair and scalp, especially when welding is done in positions. * eye protection protection of view is such an important issue that deserves separate consideration. The electric arc is used as heat source and whose temperature reaches 4,000 ° C on, emits visible and invisible radiation. Within not visible, we have those more harmful such as ultraviolet and infrared rays effect. The type of burn the arc occurs in the eyes is not permanent, although it is extremely painful. Its effect is like “having hot sand in the eyes”. To avoid this , a protective lens (inactínico glass) should be used well – fitting and in front of it, for protection, there is always to maintain a transparent glass cover, which must be replaced immediately if damaged. To ensure complete protection, protective lens must have the right to process and current density used.
AUTOMATION IN WELDING
Because of the risks of manual welding and requirements to increase productivity and improve product quality, they have developed various forms of automation. Categories include welding machine, automatic welding and robotic welding.
The welding machine is defined as a mechanized welding equipment performing the operation under the continuous supervision of an operator. Usually it is obtained by welding a head moving mechanically. The human worker must continuously observe and interact with the computer to control the operation.
If the computer is capable of running the operation without adjusting the controls by a human operator, it is called an automatic welding. A person is always present to monitor the process and detect variations in normal conditions. What distinguishes the automatic welding machine welding is a welding cycle controller, which regulates the movement of the arc and the position of the workpiece without continuous human attention. Automatic welding requires an installation or a welding positioner to place the working material in relation to the welding head. It also requires a greater degree of consistency and accuracy in the component parts used in the process. For these reasons, the automatic welding is justified only for producing large amounts.
In robotic welding an industrial robot or a programmable manipulator automatically controls the head movement with respect to welding work is used. The versatile range of the robot arm allows the use of relatively simple facilities, and the ability of the robot to be reprogrammed with new configurations of parts, allows this form of automation is justified for relatively low production quantities. A robotic welding normal cell comprises two electric arc welding facilities and a human adjuster for loading and unloading parts while the robot carries out welding.Besides welding the electric arc, industrial robots are also used in final assembly plants car for resistance welding of bodies. UNION WELD.
Welding produces a solid connection enter two parts, called weld joint. This welded joint is the contact edges or surfaces of the parts are joined by welding. In this section, and subject of the welds be removed, types of joints and various welding used to join the parts that form precisely this.
TYPES OF UNIONS
There are five basic types of connections to integrate two sides of a board, which are as follows:
a) Union butted . In this type of union, the parties are in the same plane and are joined at their edges. b) Union Corner. The parties to a corner joint form a right angle and are joined at the corner of angle. c) Union overlay. This union consists of two parts that overlap. d) Union of edges. the parties to a joint edges are parallel with at least one edge in common and binding is done in the common edge . e) Union T. at the T – junction, a part is perpendicular to each other in a manner similar to the letter.
TYPES OF WELD
All of the above are made by welding joints. It is also possible to use other processes for some of the types of unions, but welding is the method most applicable. It is useful to distinguish between the type of joint and the type of welding that applies to marriage. The differences between the types of welding are in geometry and the welding process.
Various forms of fillet weld: a) corner union with unique internal thread, b) single-corner joint outer fillet, c) union overlayed with double fillet, d) T-joint with double fillet. The dashed lines show the original edges of the plates.
a fillet weld is used to fill the edges of the plates created by corner joints, overlapping and ‘T’. a filler metal is used to provide a cross section approximately the shape of a triangle. It is the most common type of weld in arc welding and the oxygen and fuel gas. Because it requires minimal preparation of the edges; the basic square edges of the parts are used. Fillet welds can be simple or double (ie, welded on one or both sides) and continuous or intermittent (i.e., welded along the entire length of the joint, or space unwelded along a shore).
Weld bevel or groove generally require that the edges of the parts are molded bezel to facilitate penetration of the weld. Bevel shapes include a square on one side, bevel “V”, U and J, in single or double sides.
Some typical bevel welds: a) welding bevel square on one side; b) welding with only bezel; c) welding bevel V only; d) welding bevel single U; e) welding bevel single J; f) X groove welding for thicker sections. The dashed lines show the original edges of the parties.
filler material is used to saturate the union, usually by arc welding or oxygen and fuel gas. Often the edges of the parts beyond a basic square are prepared, but required further processing, to increase the firmness of the brazed or welded where thicker parts bonding. Although it is most closely associated with a splice joint, the welding bevel is used in all types of connections, except overprint.
Welds inserts and slotted welds are used to join flat plates using one or more holes or slots at the top, which will then be filled with filler metal.
(A) welding insert and (b) welding groove.
Spot welding and splined welding joints used for overlapping. A spot welding is a small molten section between the surfaces of two sheets or plates. Normally several welds are required to join the parts. It is most closely associated with resistance welding. A splined welding is similar to a dot except that a section is more or less continuous cast between two sheets or plates.
(A) welding points and (b) welding splined.
In Figure welds and welds flanks surfaces are shown. A welding edge is at the edges of two (or more) parts, usually metal foils or thin plates, wherein at least one of the parts is in one flank, as shown in part (a). A solder surface is not used to join parts, but for depositing filler metal on the surface of a base part in one or more drops of solder drops welding are incorporated in a series of superimposed parallel passes, which is cover large areas of the base portion. The purpose is to increase the thickness of the plate or provide a protective coating on the surface.
(A) Welding flank and (b) welding surface
Welding processes are divided into two main categories:
1) Fusion welding , in which a melt is obtained by melting the two surfaces to be joined, and in some cases adding a filler metal to the union; and 2) Welding solid state , in which heat or pressure or both used for fusion, but the base metals do not melt or a metal filler is added.
Fusion welding is the most important category and includes:
1) arc welding. 2) resistance welding. 3) welding oxygen and fuel gas, and 4) other fusion welding processes (which can not be classified in any of the first three types).
The fusion welding processes are discussed in the following four sections, covering welding operations solid state. And then, we examine issues related to all welding operations: welding quality, weldability and welding design.
The arc welding, SAC (arc welding in English, AW), is a welding process in which the union of the parts is obtained by melting by the heat of an electric arc between an electrode and the work material.
Electrical circuit configuration and a process of arc welding.
AW general process shown in figure above. An arc is a discharge of electrical current through a separation in a circuit. It is maintained by the presence of a thermally ionized gas column (called plasma) through which current flows. In a process of AW, the electric arc starts to bring the electrode to the workpiece, after contact the electrode is quickly separated from the workpiece at a short distance. The power of the electric arc thus formed produces temperatures of 5500 ° C or higher, which are hot enough to melt any metal. a well of molten metal which consists of metal (s) base and filler metal (if one is used) is formed near the electrode tip. In most processes arc welding, a metal filler is added during operation to increase the volume and strengthen the weld joint. As the electrode is moved along the joint, the well of molten metal solidifies immediately.
The movement of the electrode is achieved either by a person solda (manual welding) or by mechanical means (welding machine, automatic welding or robotic welding).
General technology arc welding.
Before describing the individual processes of arc welding, it is useful to examine some of the technical aspects that apply to these processes.
Electrodes. The electrodes used in processes AW are classified as consumable and non -consumable.
Consumable electrodes containing the filler metal in arc welding; They are available in two main forms: rods (also called canes) and wires. Welding rods typically have a length of 225 450mm and a diameter of 9.5 mm or less. The problem with consumable welding rods, at least in production operations, is to be changed periodically, reducing the time electric arc welder.The consumable welding wire has the advantage that can be fed continuously to the weld pool from bobbins containing wires in large quantities, with this frequent interruptions that occur when welding rods used are avoided. Both rodlike as wire, electrical arc consumes the electrode during the welding process and the latter as binding molten filler metal is added.
The rod electrodes are classified based on the mechanical properties of the deposited metal, type of coating, positions where the electrode can be used and type of current and polarity to use. The classification system used for coated electrodes follows the model used by the AWS.According to this system, the classification of an electrode is designated by the letter “E” and with four or five digits. The letter “E” means electrode, the first two or three digits indicate the tensile strength of the metal deposited in thousands of pounds per square inch, the third or fourth digit indicates the positions where the electrode should be used and the last digit it relates to the coating characteristics, slag, with the type of current and polarity to be used.
Accordingly, the different digits in the electrodes rating:
E 6 0 1 0
It has the following meaning:
E = electrode.
60 = minimum tensile of 60,000 lb / in2 Resistance
1 = To be used in all positions
or E XX 1 X = Any position (From floor, horizontal, overhead and vertical). or E XX 2 X = Horizontal and floor only. or E XX 3 X = From floor only. or E XX 4 X = De Floor , overhead, horizontal and vertical down. 0 = is an electrode coated high cellulose content and sodium-based and should be used with direct current and reverse polarity.
In some classifications of two electrodes digit (6) and (7) are additionally E-XXXX-X6X7 to identify the type of element that is after welding, for example:
E – 7018 – Mo
E = Electrode
70 = minimum tensile of 70,000 lb / in2 Resistance
1 = Any position (flat, horizontal, vertical and overhead)
8 = AC or Alternating Current or Direct DCAP current electrode positive “+”
Mo = Molybdenum in the material after the deposit.
CLASSIFICATION OF ELECTRODES
The selection of electrodes for a specific application, in general, is based on the following factors:
· Mechanical properties of the base metal to be welded · Chemical composition of the base metal to be welded · thickness and shape of the base metal to be welded. · Specifications and conditions of service of the structure to be manufactured. · Heat treatment to be applied to the structure to manufacture · welding positions possible during manufacture · Type of welding current and polarity to be used. · Design union. · production efficiency and working conditions.
Electrodes nonconsumable are made of tungsten (or sometimes carbon), which resist melting by arc. Despite its name, a non – consumable electrode gradually wears during the welding process (vaporization is the primary mechanism) and occurs similarly to gradual wear of a cutting tool in a machining operation.
AW for processes using non-consumable electrodes, any filler used in metal operation must be provided through a separate wire that is fed into the weld pool.
In the arc welding, high temperatures cause metals intensely to oxygen, nitrogen and hydrogen reactions air bind. The mechanical properties of the welded joint can seriously degraded by these reactions. To protect the welding operation of this unwanted result, almost all processes of arc welding provide some means of protecting the arc air in the environment. This is accomplished by covering the electrode tip, the arc and the molten weld pool with a blanket of flux or gas or both, which inhibits weld metal exposure to air.
Common protective gases include argon and helium, as both are inert. In welding of ferrous metals with certain processes AW oxygen and carbon dioxide are used, usually in combination with argon or helium, to produce an oxidizing atmosphere or to control the shape of the weld.
A flux is a substance used to prevent the formation of oxides and other undesirable contaminants or to dissolve and facilitate its removal. During welding, the flux melts and becomes a liquid slag which covers and protects the operation molten weld metal. The slag hardens after cooling and should be removed with a chisel or brush. Typically a flux is formed to meet several additional functions that include: 1) providing a protective atmosphere for the welding, 2) stabilize the electric arc and 3) reduce spattering.
The method of fluxing is different for each process. Among the incorporation techniques include: 1) emptying the granular flux in the welding operation, 2) using an electrode coated with flux material rod, in which the coating melts during welding to cover the operation and 3) using containing flux cored electrodes in the core, which is released as the electrode is consumed.These techniques are best discussed in the particular descriptions of processes AW.
Power source in arc welding.
In arc welding they are used both direct current (DC) and alternating current (AC). AC machines are less expensive to purchase and operate, but generally are limited to welding ferrous metals. The DC unit can be used on all metals with good results and generally characterized by better control of the electric arc.
In all processes of arc welding, energy to drive the operation is the product of the current I through the electric arc and voltage E through it. This energy is converted into heat, but not all the heat is transferred to the work surface. Convection, conduction, radiation and splashes are losses that reduce the amount of usable heat.
WELDING PROCESSES USING ARC ELECTRODES CONSUMABLES.
Metal welding shielded arc. The metal arc welding protected (English shielded metal arc welding, SMAW), it is a process of arc welding using a consumable electrode and consists of a rod filler metal coated with chemical materials a flux and provide protection. The process is illustrated in the following figures.
Sometimes the process called welding rod. The welding rod normally has a length between 230 to 460 mm and a diameter of 2.5 mm to 9.5. The filler metal used in the rod must be compatible with the metal being welded and therefore, the composition should be very similar to the base metal. The coating consists of powdered cellulose (cotton and wood powder) mixed with oxides, carbonates and other integrated ingredients using a silicate binder. Sometimes they included in the coating metal powder to increase the amount of filler metal and adding alloying elements. The heat welding process melts the coating and provides a protective atmosphere and slag for the welding operation. Also it helps to stabilize the arc and regulates the speed at which the electrode is melted.
During operation, the end of the bare metal welding rod (which is at the other end of the weld) is held in a support electrode connected to the power source. The support has an insulated handle to take it and handle the welder. The currents that are regularly used in SMAW vary between 30 and 300 A and 15 to 45 V. The selection of appropriate parameters of energy depends on the metals being welded, the type and length of the electrode and the penetration depth required welding. The current transformer, the connecting cables and the electrode holder can be purchased at several thousand dollars.
Typically, the metal shielded arc welding is performed manually and common applications include construction, installation of pipelines, structures , machinery, shipbuilding, manufacturing shops and repair work. It is preferred over welding oxygen and fuel gas to 4.8 mm thicker than because of its higher energy density sections. The equipment is portable and inexpensive, making the SMAW the most versatile and widely used among the processes AW process.Base metals including steels, stainless steels, cast irons and certain non ferrous alloys. It is not used or rarely used in aluminum and its alloys, as well as copper alloys and titanium.
The disadvantage of metal arc welding protected as production operation comes from using rods of consumable electrodes because they must be replaced periodically due to wear. This reduces the time of electric arc welding in this process. Another limitation is the current level that can be used, because the length of the electrode varies during operation and this affects the heating of the electrode resistance, current levels must be maintained within a safe range or coating will overheat and melt prematurely when you start using a new welding rod. Some other processes arc welding overcome the limitations of the length of the welding rod in this process, using an electrode wire is fed continuously. Metal arc welding and gas or MIG (metal inert gas) is also known as gas Metal arc or MAG metal arc welding and gas . SMAEG (English gas metal arc welding, GMAW) is a process in which the electrode is a consumable metal wire and bare protection is provided by flooding the arc with a gas. The bare wire is fed in automatically and continuously from a roll through the welding gun.
In the GMAW wire diameters ranging from 0.8 to to 6.4 mm are used, the size depends on the thickness of the parts to be joined and the desired rate of deposition.
For protection inert gases such as argon and helium and active gases such as carbon dioxide are used. The choice of gases (and mixtures thereof)
They depend on the material to be welded, like other factors. Inert gases are used to weld aluminum alloys and stainless steels, while CO2 is typically used for steel welding low carbon and medium. The combination bare wire electrode and shielding gases remove slag coating on the welding drop and therefore avoid the need for manual cleaning and grinding of the slag.For this reason, the process gas GMWA and it is ideal for multi-pass welding in the same union.
Different metals in GMAW and process variations themselves used have given rise to different names. The first time the process was introduced in the late forties, was applied to aluminum welding using an inert gas (argon) for electric arc protection. This process was called metal inert gas welding , SMGI (English MIG welding, metal inert gas welding). When welding process is applied to steel, it was found that inert gases were expensive and CO2 was used as a substitute. Therefore, the term applied welding with CO2. Some refinements in the process for welding steel led to the use of mixtures of gases, including carbon dioxide and argon, and even oxygen and argon.
The MIG process operates in DC (direct current) usually with the wire as the positive electrode.This is known as “Negative Polarity” (reverse polarity). “Positive polarity” (straight polarity) is rarely used by their little transfer of filler metal from the wire to the workpiece. Welding currents ranging from 50 amperes up to 600 amperes in many cases voltages 15V to 32V, a self-stabilizing is obtained with the use of a system power source constant potential (constant voltage) consistent power and arc wire.
Ongoing developments in MIG welding process have become a process applicable to all commercially important metals such as steel, aluminum, stainless steel, copper and some others. Materials above 0.76 mm thick may be welded in any position, including flat, vertical and overhead.
It’s very simple to choose the team, wire or electrode, the gas of the application and the optimum conditions to produce high quality welds at very low cost.
The basic process MIG includes three very different techniques: Transfer by “Short Circuit” transfer “Globular” and the transfer of “Arc Spray” (Spray Arc). These techniques describe the manner in which the metal is transferred from the wire to the molten solder. Transfer by short circuit, also known as “short arc”, “thick Transfer” and “Micro Wire”, metal transfer occurs when an electrical short circuit is established, this occurs when the metal at the wire tip contacts with molten solder. Transfer spray (spray arc) of molten metal droplets called “Moltens” are stripped from the wire tip and projected by the electromagnetic force to the molten solder. In the globular transfer process it occurs when the molten metal droplets are large enough to fall under the influence of gravity. The factors that determine how the moltens are transferred are the welding current, the wire diameter, the distance of the arc (voltage), the characteristics of the power source and the gas used in the process.
MIG welding is a versatile process, which can deposit weld at a very high rank and in any position. The process is widely used in steel sheets of low and medium-sized manufacturing and aluminum alloy structures particularly where there is a high requirement for manual labor or work welder.
Since its appearance in the world of welding, all regulatory agencies and classification of filler metals took very seriously this process and creating your own classification code was essential, in the case of the American Welding Society AWS two separate codes, one for alloys low carbon or also known as mild steel and one for alloys of high carbon content or where the final chemical composition of the material contributed was changed dramatically were created.
MIG welding equipment.
Welding generator Most suitable for the MIG welding process generators are rectifiers and converters (DC devices).
The direct current with reverse polarity improves the melting wire increases the penetration power, has excellent cleaning action and is what allows for better results.
In MIG welding, heat is generated by current flowing through the arc established between the electrode tip wire and the part. The arc voltage varies with length. To achieve uniform welding, both voltage and the arc length must be held constant. In principle, this can do it in two ways; (1) Feeding the wire at the same rate at which it will melting; or (2), melting the wire at the same speed with the power occurs.
Schematic diagram of MIG team :
MIG welding equipment.
1. A welding machine. 2. A feeder that controls the wire feed at the required rate. 3. A welding gun to directly run the wire to the weld area. 4. A protective gas to avoid contamination of theweld. 5. A spool of wire type and diameter specified.
MIG benefits system.
1. generates slag. 2. High deposition rate. 3. High deposition efficiency. 4. Easy to use. 5.Minimal spatter. 6. Applicable to high ranges of thicknesses. 7. Low smoke. 8. It is economical.9. The gun and welding cables are lightweight making it easier handling. 10. It is one of the most versatile among all welding systems. 11. Speed of deposition. 12. High performance. 13.Possibility of automation.
WELDING PROCESSES USING ELECTRODE ARC unpalatable.
Tungsten welding arc and gas.
Welding tungsten arc and gas STAEG (English gas tungsten arc welding, GTAW), (Englishtungsten inert gas welding, TIG welding). The GTAW process can be performed with or without a filler metal is a process using a non – consumable tungsten electrode and an inert gas to protect the electric arc. Often, this process is called tungsten inert welding gas. payon
Tungsten welding arc and gas.
When a filler metal is used, it is added to the weld pool from a separate rod which is melted by the heat of the electric arc. Tungsten is a good material for electrode because of its high melting point of 3410 ° C. Shielding gases used normally include argon, helium or a mixture thereof.
The TIG system is applicable to almost all metals in a wide range of thicknesses. It is also used to attach various combinations of different metals. Its most common applications include aluminum and stainless steel. Cast iron, cast iron, lead and tungsten are difficult to weld through this process. Welding applications in steel, TIG welding is generally slower and more costly than the processes of arc welding consumable electrode, except when thin sections are included as very high quality welds are required. When thin sheets with tungsten inert gas at very low tolerances no filler metal is added welded. The process is performed manually or by machine and automated methods for all types of joints. The advantages of TIG system are: high quality, no spatter due to a filler metal is not transferred through the arc and no cleaning is required or very reduced flux because it is not used. Visit Anti spatter spray for details.
TIG Welding was initially developed for the purpose of welding anticorrosive metals and other hard metals welding, despite the passage of time, its application has expanded to include both welds and hardfacing (hardfacing) in virtually all metals used commercially.
In any type of welding the best welding, which can be obtained, it is one where the weld and base metal share the same chemical, metallurgical and physical properties, to achieve these conditions, the molten solder must be protected from the atmosphere during welding operation, otherwise, the oxygen and nitrogen atmosphere would combine literally with the molten metal resulting in a weak welding and porosity. In TIG welding the weld area is protected from the atmosphere by an inert gas which is fed through the torch, argon and helium can be used successfully in this process, argon is used mainly for its great versatility in the application successful of a variety of metals, in addition to enabling high performance with a low flow solder to run the process. Helium generates a hotter arc, allowing an increase in the arc voltage of 50-60%. This extra heat is especially useful when welding is applied in very heavy sections. The mixture of these two gases is possible and used to reap the benefits of both, but the selection of the gas or gas mixture depend on the materials to be welded.
Since the atmosphere is isolated 100% welding area and a very fine and precise application of heat control, TIG welds are stronger, more flexible and more resistant to corrosion than welds made with the regular process Manual arc (coated electrode). Besides the fact that no flux is needed, this type of welding makes applicable to a wide range of different metal binding procedures.
It is impossible for corrosion occurs due to flux residues trapped in welding and cleaning procedures in the post-welding are eliminated, the whole process runs without splashing or sparks, fusion welding can be performed in almost all metals used industrially, including aluminum alloys, stainless steel, magnesium alloys, nickel and alloys based on nickel, copper, copper-silicon, copper-nickel, silver, phosphor bronze, steel alloys high carbon and low carbon , cast Iron (cast iron) and others. The process is also widely known for its versatility for welding dissimilar materials and applying layers of different materials hardening steel.
The power source for TIG can be AC or DC, however, some outstanding characteristics obtained with each type, make each type of current best suitable for certain specific applications. Welding arc plasma.
Welding arc plasma, SPA (in English plasma arc welding, PAW) is a special form of tungsten welding arc and gas in which a plasma arc welding controlled the area goes. In PAW, a tungsten electrode is placed within a specially designed nozzle, which focuses a stream of inert gas at high speed (eg, argon or mixtures of argon and hydrogen) in the region of the electric arc to form an arc current of intensely hot plasma at high speed, as in the following figures. Argon, argon-hydrogen and helium are also used as protective gas arc
Temperatures in the welding arc plasma are 2800 ° C or higher, and high enough to melt any known metal. The reason for these high temperatures in PAW (much higher than TIG) derived from the narrowness of the electric arc. Although normal energy levels used in the welding arc plasma are lower than those used in welding tungsten arc and gas, the energy is highly concentrated to produce a plasma jet of a small diameter and an energy density very high.
The welding resistance , SR (in English resistance welding, RW), is a group of processes fusion welding using a combination of heat and pressure to obtain a coalescence, heat is generated by an electric resistance facing current flow at the junction to be welded. The main components in resistance welding shown in the following figures for an operation resistance spot welding, most widely used process in the group.
Components include the working parts to be welded (typically parts foil), two opposing electrodes, means for applying pressure designed to tighten the part between the electrodes and an AC power adapter from which applies a controlled current.
The operation produces a fusion zone between the two sides, termed a weld nugget in welding.
Compared to arc welding, resistance welding does not use protective gases, fluxes or filler metal and electrodes that conduct electrical current for the process are not consumable, the RW is classified as a process of fusion welding because the heat applied causes melting of butting surfaces complexion. However, there are exceptions. Some welding operations based on resistance heating using temperatures below the melting point of the base metals, so a merger does not occur. PROCESSES resistance welding.
Resistance spot welding.
The resistance spot welding is by far the predominant process in this group. It is widely used in the mass production of automobiles, household appliances, metal furniture and other products made from sheet metal. If one considers that the body of a normal car has about 10,000 individual welds points and that annual automobile production worldwide is measured in tens of millions of units, it is possible to appreciate the economic importance of welding points.
The process is used to join sheet metal parts with a thickness of 3 mm or less, using a series of point weldings in situations where watertight assembly is required. The size and shape of the weld is determined by means of the electrode tip, the most common form of electrode is round;but hexagonal, square and other shapes are also used. The resulting weld nugget usually has a diameter of 5 to 10 mm, with a heat affected zone extending slightly beyond nugget within metates base. If welding is done correctly, your resistance is comparable with the surrounding metal. The cycle in a welding operation points shown in the following figure.
Due to their extensive industrial use are available various machines and methods for performing operations welding. The equipment includes spot welding machines with rocker and press type and horn portable welding guns. The welders points rocker, shown in Figure a) andb) have a stationary lower electrode and an upper movable electrode that moves up and down for loading and unloading work. The upper electrode is mounted on a rocker, whose movement is controlled by a pedal operated by the worker. Modern machines can be programmed to control the force and current during the welding cycle.
The welders points press type are designed for a larger work. The upper electrode has a straight – line motion provided by a vertical press, which is operated automatically or hydraulics.The action of the press allows larger forces are applied, and generally controls enable programming complex welding cycles.
The above two types of machines are stationary or static welders points, in which the work is placed in the machine. For heavy and large jobs it is difficult to move and (target) work towards the stationary machines. For these cases, there are portable spot welding guns in different sizes and configurations. These devices consist of two opposing electrodes inside a pliers mechanism. Each unit is lightweight, so a worker or an industrial robot can hold and manipulate. The gun is connected to its own power source and control through flexible electric cables and air hoses. If necessary, cooling of the electrodes is also provided by a hose
with water. Portable spot welding guns are widely used in plants final assembly of automobiles, to weld the sheet metal body. Some of these guns are handled by workers, but industrial robots have become the preferred technology.
Interlock welding resistance.
In welding splined resistance, BE (English resistance seam welding, RSEW) , the electrodes rod-shaped welding points are replaced with rotating wheels, as shown in the figure, and a series of welds is overlapping points along the joint.
The process produces tight junctions and industrial applications include the production of fuel tanks, mufflers cars and other containers made of sheet metal.
Technically, RSEW is as spot welding, except that the electrodes on wheels introduce certain complexities. Since the operation is usually done continuously, and no separate forms must be keyed along a straight or curved line evenly.
Interlock welding machines are similar to spot welders pressure type, except that wheels electrodes are used instead of normal rod shaped electrodes. Often cooling the work and the welding wheels splined resistance is necessary, this is achieved by directing water to the top and bottom surfaces of the working portion near the electrode wheels.
Welding by projection , SEP (in English résistance projection welding, RPW) is a resistance welding process in which coalescence occurs in one or more relatively small cash points in the parts. These contact points are determined by the design of the parts to be joined and may consist of projections, prints or intersections localized parts.