Welding is a process in which, the localized coalescence is produced by heating the material upto suitable temperature with or without application of filler material.
Types of welded joint:
- Butt joint
- Lap joint
- Corner joint
- Tee joint
- Edge joint
According to the position of welded joints:
- Flat joint
- Vertical joint
- Horizontal joint
- Overhead joint
Terms used in the Welding
Base metal, backing, welds base, crater, deposition rate, filled weld, penetration, puddle, root, and tack weld, toe of weld, torch, and weld face, weld metal, weld pass etc.
The metal to be cut or combined is known as the base metal.
In the control of penetration to support the material on the side root is known as backing.
Weld bead is also known as bead. It is a metal added at the time of single pass during the welding. Weld material is separate from the base metal.Advertisement:
During the process of arc welding, the arc strikes the base metal which leads to the craters creation.
The rate at which the weld metal is deposited per unit time is known as the deposition rate. The deposition rate must be expressed in kg/h
When the two metal pieces are place at 90, at the time metal is fused to the corners of the joint made this process is known as filled weld.
Penetration is the process in which, the depth at which the weld metal combines with the base metal measured from the top of the surface joint.
The welded joint portion must be melted by the heat of welding, which is known as puddle.
It is the point at which the two metals are joined at the base, is known as the root.
During the time of actual welding the two metals are temporarily joint, this process is known as the tack joint.
Toe of Weld:
The area between the base metal and the weld face is known as the toe of weld.
In gas welding, the torch mixes the oxygen and fuel, which controls the delivery of the gas to obtain a desired flame.
Weld face is known as the face exposed to the surface.
The solidification of the metal at the joint is known as the weld metal. The weld metal must be a base metal, or mixture of filler metal and the base metal.
A single movement of the electrode along the length of the joint in a bead is known as the weld bead.
Types of welding:
The welding is divided into three types they are:
- Solid state
- Liquid state
- Solid / liquid
Now we can see few type of welding process:
In the process of Arc welding, it uses the welding power supply to create an arc (electricity), between the base metal and the electrode. At the welding point the metal melts. During the process one can use either an alternative current (AC) or direct current (DC) and consumable electrode or non-consumable electrode. The welding section must be protected with some type of vapor, slag or shielding gas. The arc welding process must be a fully automated or semi-automated or manual. In order to produce the arc, potential difference should be maintained between the two electrodes, which are sufficient for the movement across the air gaps. The higher air gap requires greater potential difference. If the air gap is too large then arc may be extinguished.
Manual metal arc welding process:
The manual metal arc welding is also known as shielded metal arc welding.
Shielded metal welding process is the common type of welding processes used in olden days, and mainly used for the fabrication. The generated heat must be an electrical arc developed between the consumable electrode and base metal. The movement of the electrode must be controlled manually, which is known as the manual metal arc welding. Deposition of the molten metal on the base metal is easy as it does not require any separate shielding. The process is mainly suitable for the welding of the metals which are less sensitive to the atmospheric gases. For this welding process we can use both the Alternative current and the Direct current. All types of the electrodes irrespective of the base metal, the constant Direct Current power source are regularly used. In some cases the Alternative current is not suitable for certain type of base metals and electrodes. AC source is suitable and recommended for the some type of electrode applications. Coming to DC power source greater heat is generated at the arc column and the cathode side. The amount of heat generated at the cathode and the anode may differ considerably depending upon the composition of the coated flux, polarity, base metal and the nature of the arc plasma. According to the Direct current welding the generation of the heat at the anode, where the cathode must be determined by polarity. The base metal is modified according to the melting rate of the electrode and the diffusion.
Heat generated by the arc welding =Voltage current welding time
Function of flux:
Flux gives alloys to bead material. The bead material is to be stronger than the parental metal. Flux provides heat treatment to the bead and also projects from the atmospheric gases. Stabilization of the arc must be good. The flux controls the weld pool viscosity.
Comparison of Alternative current and Direct current
|Parameters||Alternative Current||Direct Current|
|Metals||Not suitable for non-ferrous||Suitable for Ferrous and non-ferrous|
|Welding section||Not preferred for thin sections||Thin sections|
|Positive terminal||Work or electrode||Work|
|Negative terminal||Work or electrode||electrode|
Advantages of arc welding:
- The metal joint must be more efficient
- All commercial metal are join by using the process
- Joining method must at low costs
- Provides design flexibility
Limitations of arc welding:
- Need high energy causing danger
- Not convenient for disassembly.
- Arc should be applied manually, therefore high labor cost.
- Defects are hard to detect at joints.
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