Welding Methods

Welding is a manufacturing method used to join materials together.

WELDING AND WELDING METHODS

What is welding?

It isgenerally used on metal or thermo plastic materials. In this method, it is usually used to weld the workpieces part is melted and filling material is added to this part, then the joint iscooled and hardened, In some cases, heat joining is done under pressure. This method differs from soldering and brazing , low joining in soldering and brazing methods Melting occursat points and melting of the working parts.

For welding , gas flame, electric arc, laser, electron beam, friction, Many different energy sources can be used , such as ultra sound waves. Inindustrial processes, the source is open air, underwater, can be realized in manydifferent environments , such as space. However, no matter where it is made, welding poses various hazards. Flame, electric shock, It is necessaryto take precautions against toxic fumes and ultraviolet rays.

19. until the end of the century, a way of heating andforging used only by blacksmiths welding , in which metals are joined together with an electric arc weld. Electric arc welding and oxy-gas welding were the first methods developed at the end of the century, followed by resistance welding. Welding technology in the 20th century. During the early part of the century ( after World War I and World War II). World War I and World War II ) , it was rapidly reliable and inexpensive methods. Afterthe wars, manual methods (manual metal arc welding), A variety of modern welding techniques have evolved, including semi-automatic and automatic methods (gas metal arc welding, etc.).A variety of modern welding techniques have evolved, including. Developments, laser beam source in the second half of the century and continued with the discovery of the electron beam source. Currently, the science continues to evolve. Robot welding, has gained a widespread footholdin industry, new welding methods and improvement of welding quality and properties, research and development efforts are ongoing to reduce costs.

Shielded Electrode Arc Welding

Shielded electrode arc welding is a manual arc welding method in which the heat required for welding is generated by the arc formed between a depleted electrode covered with a shroud and the workpiece. In this method, both direct (DC) or alternating (AC) current types can be used. In some cases, the welded area is protected with a gas known as shielding gas and covered electrode arc welding is performed.

The tip ofthe electrode, the welding bath, the arc and areas of the workpiece close to the weld, burning of the cover material from the harmful effects of the atmosphere and is protected by gases generated bydecomposition. Slagformed by the molten cover material , provides additional protection for the molten weld metal in the weld bath. Additional metal (filler metal), the core wire of the depleted electrode and in some electrodes isalso provided by metal powders in the electrode cover.

Advantages

Shielded electrode arc welding can be applied in open and closed areas.
It is possible to weld at every point and position that can be reached with the electrode.
It is possible to weld in narrow and limited areas that cannot be reached with other welding methods.
Since the power supply ends of the welding machine can be extended , distant connections can be welded.
Welding equipment is light and portable
Chemical and mechanical properties of many materials type ofcovered electrode is availableto meet the requirements. Welded joints can therefore also have the same properties as thebase material.

Disadvantages

The metal deposition rate and efficiency of shielded electrode arc welding is lower than many arc welding processes. The electrodes are cut rods of a certain length, so it is necessary to stop welding every time the electrode is used up.
It is necessary to clean the slag formed on the weld metal after each welding pass.

Electric Resistance Welding

Resistance source, the principle thatmetals generate heatthrough their resistance to the current flow ing through them between two or more metal surfaces. Due to the high current passing through the metal (1000 – 100.000 A.) due to the formation of a small pool of molten metal in the weld zone. In general, resistance welding methodsare efficient and low-pollution methods, but their applications are limited and their equipment is quite expensive.

Flux Cored Wire Arc Welding

Flux-cored wire arc welding is an arc welding process in which the heat required for welding is generated by an arc between a consumed flux-cored wire electrode and the workpiece. The protection of the arc and the weld zone is accomplished by gases generated by the combustion and decomposition of the flux in the flux-cored wire or by an externally supplied shielding gas as in submerged arc welding. The self-shielded welding process (open-arc flux-cored welding wires) is more similar to the gas shielding in shielded electrode welding . The covering material on the shielded electrodes causes the electrodes to be produced as flat rods and to be limited in length . In the case of flux-cored wires, since this covering material is inside the tubular wire electrode, it is produced as a wire wound on spools and can be fed continuously into the welding zone.
This welding method can be applied in both semi-automatic and automatic welding systems.

The disadvantage of flux-cored wire arc welding is that a layer of slag is formed on the weld seam, similar to that of arc welding with a covered electrode, but slightly thinner. However, there are now many types of flux cored wire electrode that do not require slag cleaning or do not produce slag.

Oxy-Acetylene

The equipment is cheap and simple, The welding flame (approx. 3100°C) isusually produced by the combustion of acetylenewith oxygen. Sincethe flame is less powerful than an electric arc , weld cooling is slower and the resulting stress and may allow for less source distortion, Therefore, it is easier to weld high alloy steels with this method. This method is alsoused for cutting metals. Other gas welding methods are air-acetylene welding, such as oxygen-hydrogen welding and pressurized gas welding, quitesimilar to , only the type of gas used differs. Gas welding is also usedfor welding plastics
.

Gas Welding

Gas metal arc welding is a process where the heat required for welding between a depleted electrode and the workpiece It is an arc welding method in which the arc is created by the arc. Continuously fed (driven) into the weld zone, As thesolid wire electrode melts and is consumed, itforms the weld metal .

The electrode, the welding bath, the arc and the areas of the workpiece close to the weld are protected from the harmful effects of the atmosphere by gas or mixed gases from the welding torch. The gas must be able to fully protect the weld area, otherwise even a very small ingress of air will cause defects in the welded metal.

The main types are MIG-MAG and WIG (TIG) gas welding techniques. In this type of welding, MIG (Metal Inert Gas) welding technique, which uses inert gases such as Argon and Helium as shielding gas, and MAG (Metal Active Gas) techniques, which use Carbon Dioxide, an active gas as shielding gas, are most commonly used. The difference of the WIG technique, which is used relatively less than the others, is the use of non-melting Wolfram (Tungsten) electrodes.

Advantages

Gas metal arc welding is a faster welding method than arc welding. Because;
The wire-shaped welding electrode continuously penetrates the weld zone welderfor where it is fed covered electrode arc welding It is not necessary to stop welding to replacethe electrode that has run out , as in the method.
Slag cleaning after each pass as in covered electrodes since no slag is formed and there is norisk of slag residue on the weld metal, more quality resources are obtained.
Since smaller diameter electrodes are used than in shielded electrode arc welding, It has high current density and high metal deposition rate in the same current range.
Weld obtained by gas welding metal has low hydrogen content, this is especiallyimportant for steels with hardening properties .
Because deep penetration can be achieved in gas metal arc welding sometimes allowing to make small corner resources and provides a smoother root penetration than with shielded electrode arc welding.
Thin materials are mostly welded byTIG welding Althoughadditional metal can be combined with or withoutusing , gas welding for welding thin materials gives better results than arc welding with a covered electrode.
It is very suitable for use in both semi-automatic and fully automatic welding systems.

Disadvantages

Gas arc welding equipment is more complex than arc welding equipment, more expensive and more difficult to transport.
Since the gas welding torch must be close to the workpiece shrouded welding in hard-to-reach areas such as electrode arc welding is noteasy.
With gas welding in steels with hardening properties weld joints are more prone to cracking. This is because , as with arc welding with a covered electrode There is no slag layer that reduces the cooling rate of the metal.
Gas welding, will be able to movegas shieldingaway from the source zone requires additional protection against air currents. For this reason, it is not suitablefor welding in open areas compared to shielded electrode arc welding.

Crochet Welding

TIG welding is the use of the heat required for welding, between a non-depletable electrode (tungsten electrode) and the workpiece is an arc welding methodin which the arc is formed thanks to the arc formed.

The electrode, welding bath, arc and areas of the workpiece close to the weld, from the welding torch from the harmful effects of the atmosphere The gas is protected by or mixture gases.

The gas must be able to fully protect the weld zone, otherwise it’s a very small air Even its entry will cause defects in the weld metal.

Advantages

TIG welding is making a continuous weld seam, todo intermittent welding and spot welding both manually, can be applied both with automatic welding systems.

Since the electrode is not depleted , it can be used by melting the base metal or is welded using an additional weld metal.

It can be w elded in any position and is particularly well suited for welding thin materials.

It gives high penetration and non-porous welds in root pass welds.

Since the heat input is concentrated in the weld zone , deformation of the workpiece is low.

It gives a smooth weld seam and there is no need to clean the weld seam.

Disadvantages

The metal deposition rate of TIG welding is lower than other arc welding methods.
It is not an economical method for welding thick sectioned materials.

Submerged Arc Welding

Submerged arc welding is a process in which the heat required for welding between thedepleted electrode (or electrodes) and the workpiece is an arc welding process in which the arc (or arcs)is created. The arc zone is formedby a layer of welding powder and the weld metal and the weld metal close to the weld . The base metal is also protected by the melting welding dust (slag) and weld seam.

In submerged arc welding, electricity passes through the arc and the weld bath, which consists of molten metal and molten slag. The arc heat melts the electrode, the welding powder and the base metal to form the weld bath which fills the weld bead. The welding powder, which acts as a shield, also reacts with the welding bath to deoxidize the weld metal.

Welding powders used for welding alloy steels may contain alloying elements that stabilize the chemical composition of the weld metal . Submerged arc welding is an automated welding process. In some submerged arc welding applications, two or more electrodes can be applied to the weld bead at the same time.

Electrodes can be driven side by side (twin arc) into the welding bath or welding far enoughaway to allow the baths to solidify independently of each other, High welding speed and high metal deposition rate can be achieved by successive driving.

Advantages

Welding offlat and cylindrical parts, for welding and hardfacing ofpipes of all thicknesses and sizes is a method withhigh welding speed and high metal deposition rate.
It gives defect-free weld seams with high mechanical strength.
No spatter during welding and no arc heat is visible. therefore the protection required for the welding operator is less.
It is possible to weld the angles of the weld bead according to other methods.
Submerged arc welding can be applied indoors and outdoors.

Disadvantages

Submerged arc welding powders tend to absorb moisture from the air, which causes pores in the weld.
In order to obtain high quality welds , the base metalmust be flat, smooth , There should be no oil, rust and other impurities on the base metal surface.
Slag must be removed from the weld seam, which in some applications can be adifficult operation. For multi-pass welds, The slag must be removed after each pass to avoid slag residue in the w eld seam.
Submerged arc welding is generally not suitable for materials thinner than 5 mm as it can cause burning.
The method is straight, except for some special applications, Suitable for butt welds and fillet welds in horizontal position.
It is not applicable for all metals and alloys.

Solid State Resource Management

Like the forging method , which was the first known welding method, Some modern welding methods also take place without melting the weld material. One of the most common methods is ultrasonic welding, thermoplastic or thermoplastic plastic by vibration under high pressure and high frequency It is used for joining cables or thin sheetsmade of metal material .

The equipment and methods are similar to resistance welding. Here ,the electric current is replaced by the energy provided by vibration. In this method there is no melting of the weld metal, Instead there is mechanical vibration applied horizontally under pressure.

In the welding of plastics, The materials must be brought toa temperature close to the melting temperature and vibrated vertically. Ultrasonic welding, aluminum,often used for electrical connections or copper material and for welding polymers.

Geometry

Common types of weld insertion
Forehead insertion
V-shaped welded joint
Overlay splicing
T-shaped insertion
Corner insertion

The parts to be welded can be geometrically prepared for welding in various shapes. Depending on the shape of the part, there are also different variations, for example double-V joints. Single-U and double-U joints are also often used and are similar to V-type joints. Lap joints are generally used depending on the thickness of the part, although on some thin parts lap joints may be mandatory.

In order for the welding process to be fully realized, special insertion methods are often used. For example, resistance welding, laser beam source and electron beam The overlap jointgives the best performance in welding . However, some welding processes, such as shielded ( under gas or underdust ) metal arc welding, is versatile and all types of splices can be appliedwith . In addition, some processes utilize multi-pass welding methods ( when making a subsequent weld, ) , which allows the previous one to cool down. This method allows the use of single-V weld bead insertion for welding thick sections.

After welding, different zones are formed in the weld zone. The weld itself is called the melting zone, where the filler metal is filled during the welding process . The properties of this zone depend primarily on the filler material used and its compatibility with the parent material. Immediately around this region is the heat-affected zone, where the microstructure and properties are changed by the welding process. These properties change depending on the behavior of the base material under heat . The metal in this region is generally weaker than both the base metal and the weld zone, and permanent material stresses occur here.

Quality

In general, the biggest criterion used to measure the quality of the source, (strength) ofthe weld and the surrounding material. There are many factorsthat affect this ; welding method, joining method,amount of heat , such asbase material and filler material andthe interactions between them.

The inspections carried out to measure the quality of the weld are generally categorized in two groups as destructive and non-destructive inspection methods . In the measurements made by these examinations, there should be no visible defects in the weld, permanent stresses and distortions should be at an acceptable level , heat-affected zone properties should be at an acceptable level .

Heat Affected Zone

The blue colored zonein the picture is due to oxidationat 316 °C . This color indicates the degree of heat , but the HAZ (Heat Affected Affected Zone)is not a sensitive enough indicator . The HAZ is the narrow zone surrounding the welded metal part.

The effects of welding on the material around the welded area can be detrimental (depending on the material used and the heat input used in the welding process, the size and strength of the heat-affected zone can vary). The thermal diffusivity (thermal diffusivity, i.e. thermal conductivity/volumetric heat capacity) of the base material also plays a major role here.

If the diffusivity is large, the cooling rate of the material is high and the heat affected zone becomes relatively small. Otherwise, low diffusivity leads to slow cooling and a larger heat affected zone.

Amount of heat injected by the welding process, oxy-acetylene welding plays an important role in methods such asthe method, The introduction of unconcentrated heat causes the heat-affected zone to expand. Processessuch as laser beam welding deliver concentrated heat to the welding zone, the amount of heat is limited , resulting in a reduction in heat a small affected zone appears. Electric arc welding, due to variations in the heat input specific to the weld , between these two situations.

Source: OERLIKON Technical Information