classification of welding

 Welding techniques may be categorized based on following criteria; 

1. Welding without or with filler material.
2. Source of energy of welding.
3. Arc and Non-arc welding.
4. Fusion and Pressure welding.
   

Nomenclature Elements of Welding Process 

The term elements of welding technique used with common welding joints consisting of base metallic, fusion zone, weld face, root face, root establishing toe and root are depicted in Fig. Edge preparations For welding the edges of joining surfaces of metals are organized first. Different part arrangements can be used for welding butt joints, which can be given in Fig

Welding joints 

Some common welding joints are proven in Fig. Welding joints are of normally of major types particularly lap joint and butt joint. The most important types are defined as under.

Lap weld joint

Single-Lap Joint 

This joint, made through overlapping the edges of the plate, isn’t always recommended for most work. The single lap has very little resistance to bending. It may be used satisfactorily for joining cylinders that fit inner one another.

Double-Lap Joint 

This is stronger than the single-lap joint however has the drawback that it requires two times as much welding. 

Butt weld joint

Single-Vee Butt Weld 

It is used for plates up to 15.8 mm thick. The angle of the vee depends upon the method being used, the plates being spaced about 3.2 mm. 

Double-Vee Butt Weld

 It is used for plates over 13 mm thick while the welding may be performed on each sides of the plate. The top vee angle is both 60° or 80°, at the same time as the bottom angle is 80°, depending at the method being used

Welding Positions 

As proven in fig., 

there are 4 varieties of welding positions, which are given as: 

1. Flat or down hand position
2. Horizontal position 
3. Vertical position 
4. Overhead position

Flat or Down hand Welding Position 

The flat position or down hand position is one wherein the welding is achieved from the higher side of the joint and the face of the weld is about horizontal. This is the most effective and the maximum convenient position for welding. Using this method, amazing welded joints at a fast speed with minimum risk of fatigue to the welders may be obtained.

Horizontal Welding Position 

In horizontal position, the aircraft of the workpiece is vertical and the deposited weld head is horizontal. The metallic deposition rate in horizontal welding is next to that achieved in flat or down hand welding position. This position of welding is maximum typically used in welding vessels and reservoirs. 

Vertical Welding Position 

• In vertical position, the aircraft of the workpiece is vertical and the weld is deposited upon a vertical surface. It is hard to supply satisfactory welds in this position because of the effect of the force of gravity at the molten metallic. The welder have to continuously control the metallic in order that it does notrun or drop from the weld. 
• Vertical welding can be of types viz., vertical-up and vertical-down. Vertical-up welding is preferred while strength is the main consideration. The vertical-down welding is used for a sealing operation and for welding sheet metallic. 

Overhead Welding Position 

• The overhead position is possibly even more difficult to weld than the vertical position. Here the pull of gravity towards the molten metallic is much greater. The force of the flame against the weld serves to counteract the pull of gravity. 
• In overhead position, the aircraft of the workpiece is horizontal. But the welding is carried out from the underside. The electrode is held with its welding end upward. It is a great practice to apply very short arc and fundamental coated electrodes for overhead welding.

Advantages and Disadvantage of welding: 

Advantages 

1. Welding is more reasonable and is much quicker process in comparison to different processes (riveting, bolting, casting etc.) 
2. Welding, if well controlled results permanent joints having strength same or sometimes more than base metallic. 
3. Large number of metals and alloys both similar and dissimilar may be joined through welding. 
4. General welding system isn’t always very costly. 
5. Portable welding equipment may be easily made available.
6. Welding allows considerable freedom in design. 
7. Welding can join welding jobs through spots, as non-stop pressure tight seams, end-to-end and in a number of other configurations. 
8. Welding can additionally be mechanized.

Disadvantages 

1. It outcomes in residual stresses and distortion of the workpieces.
2. Welded joint needs stress relieving and heat treatment. 
3. Welding gives out harmful radiations (light), fumes and spatter.
4. Jigs, and fixtures will also be needed to hold and position the parts to be welded. 
5. Edges preparation of the welding jobs are required earlier than welding.
6. Skilled welder is needed for manufacturing of properly welding .
7. Heat all through welding produces metallurgical modifications because the structure of the welded joint isn’t always identical as that of the parent metal.