NORMAL ARC WELDING
Arc welding provides you the ability to join two metals by melting them with an arc generated between a coated-metal electrode and the base metal. The temperatures developed by the arc can reach as high as 10000°F. The arc energy is provided by a power source that generates either direct or alternating current. The electrodes that carry the current produce a gas that shields the arc from the atmosphere and supplies filler metal to develop the weld shape.
Dr. Dmitri Kopeliovi
Arc welding is a welding process, in which heat is generated by an electric arc struck between an electrode and the work piece.
Electric arc is luminous electrical discharge between two electrodes through ionized gas.
Any arc welding method is based on an electric circuit consisting of the following parts:
§ Power supply (AC or DC);
§ Welding electrode;
§ Work piece;
§ Welding leads (electric cables) connecting the electrode and work piece to the power supply.
Electric arc between the electrode and work piece closes the electric circuit. The arc temperature may reach 10000°F (5500°C), which is sufficient for fusion the work piece edges and joining them. When a long join is required the arc is moved along the joint line. The front edge of the weld pool melts the welded surfaces when the rear edge of the weld pool solidifies forming the joint.§ When a filler metal is required for better bonding, filling rod (wire) is used either as outside material fed to the arc region or as consumable welding electrode, which melts and fills the weld pool. Chemical compositions of filler metal is similar to that of work piece.
Molten metal in the weld pool is chemically active and it reacts with the surrounding atmosphere. As a result weld may be contaminated by oxide and nitride inclusions deteriorating its mechanical properties. Neutral shielding gases (argon, helium) and/ shielding fluxes are used for protection of the weld pool from atmospheric contamination. Shields are supplied to the weld zone in form of a flux coating of the electrode or in other forms.
Disadvantages of Shielded Metal Arc Welding (SMAW):
Advantages of Shielded Metal Arc Welding (SMAW):
§ Simple, portable and inexpensive equipment;
§ Wide variety of metals, welding positions and electrodes are applicable;
§ Suitable for outdoor applications.
Disadvantages of Shielded Metal Arc Welding (SMAW):
§ The process is discontinuous due to limited length of the electrodes;
§ Weld may contain slag inclusions;
§ Fumes make difficult the process control.
GAS SHIELDING ARC WELDING
MIG
GAS SHIELDING ARC WELDING-MIG
Metal Inert Gas Welding (Gas Metal Arc Welding) is a arc welding process, in which the weld is shielded by an external gas (Argon, helium, CO2, argon + Oxygen or other gas mixtures).
Consumable electrode wire, having chemical composition similar to that of the parent material, is continuously fed from a spool to the arc zone. The arc heats and melts both the work pieces edges and the electrode wire. The fused electrode material is supplied to the surfaces of the work pieces, fills the weld pool and forms joint.
Due to automatic feeding of the filling wire (electrode) the process is referred to as a semi-automatic. The operator controls only the torch positioning and speed.
Disadvantages of Metal Inert Gas Welding (MIG, GMAW):
TIG
Consumable electrode wire, having chemical composition similar to that of the parent material, is continuously fed from a spool to the arc zone. The arc heats and melts both the work pieces edges and the electrode wire. The fused electrode material is supplied to the surfaces of the work pieces, fills the weld pool and forms joint.
Due to automatic feeding of the filling wire (electrode) the process is referred to as a semi-automatic. The operator controls only the torch positioning and speed.
Advantages of Metal Inert Gas Welding (MIG, GMAW):
§ Continuous weld may be produced (no interruptions);
§ High level of operators skill is not required;
§ Slag removal is not required (no slag);
Disadvantages of Metal Inert Gas Welding (MIG, GMAW):
§ Expensive and non-portable equipment is required;
§ Outdoor application are limited because of effect of wind, dispersing the shielding gas.
TIG
GAS SHIELDING ARC WELDING-TIG
TIG PRINCIPLES
Gas Tungsten Arc Welding (GTAW), also known as Tungsten Inert Gas (TIG) welding is a process that produces an electric arc maintained between a non-consumable tungsten electrode and the part to be welded. The heat-affected xone, the molten metal and the tungsten electrode are all shielded from atmospheric contamination by a blanket of inert gas fed through the GTAW torvh. Inert gas (usually Argon) is inactive or deficient in active chemical properties. The shielding gas serves to blanket the weld and esclude active properties in the sorrounding air. Inert gases such as Argon and Helium do not chemically react or combine with other gases. They pose no odor and are transparent, permitting the welder maximum visibility of the arc. In some instances Hydrogen gas may be added to enhance travel speeds.
The GTAW process can produce temperatures of up to 35,000 degrees F (19,426 degrees C). The torch contributes heat only to the workpiece. If filler metal is required to make the weld, it may be added manually in the same manner as it is added in the oxyacetylene welding process.
GTAW is used to weld stainless steel, nickel alloys such as Monel and Inconel, titanium, aluminum, magnesium, copper, brass, bronze and even gold. GTAW can also weld dissimilar metals to one another such as copper to brass and stainless to mild steel.
The GTAW process can produce temperatures of up to 35,000 degrees F (19,426 degrees C). The torch contributes heat only to the workpiece. If filler metal is required to make the weld, it may be added manually in the same manner as it is added in the oxyacetylene welding process.
GTAW is used to weld stainless steel, nickel alloys such as Monel and Inconel, titanium, aluminum, magnesium, copper, brass, bronze and even gold. GTAW can also weld dissimilar metals to one another such as copper to brass and stainless to mild steel.
Dr. Dmitri Kopeliovich
Tungsten Inert Gas Arc Welding (Gas Tungsten Arc Welding) is a welding process, in which heat is generated by an electric arcstruck between a tungsten non-consumable electrode and the work piece.
The weld pool is shielded by an inert gas (Argon, helium, Nitrogen) protecting the molten metal from atmospheric contamination.
Tungsten Inert Gas Arc Welding (Gas Tungsten Arc Welding) is a welding process, in which heat is generated by an electric arcstruck between a tungsten non-consumable electrode and the work piece.
The weld pool is shielded by an inert gas (Argon, helium, Nitrogen) protecting the molten metal from atmospheric contamination.
The heat produced by the arc melts the work pieces edges and joins them. Filler rod may be used, if required.
Tungsten Inert Gas Arc Welding produces a high quality weld of most of metals. Flux is not used in the process.
Tungsten Inert Gas Arc Welding produces a high quality weld of most of metals. Flux is not used in the process.
Advantages of Tungsten Inert Gas Arc Welding (TIG, GTAW):
§ Weld composition is close to that of the parent metal;
§ High quality weld structure
§ Slag removal is not required (no slag);
§ Thermal distortions of work pieces are minimal due to concentration of heat in small zone.
Disadvantages of Tungsten Inert Gas Arc Welding (TIG, GTAW):
§ Low welding rate;
§ Relatively expensive;
§ Requres high level of operators skill.
