1. Metal – Processing
Welding

2. Oxy-acetylene
This uses a mixture of oxygen and acetylene to create a flame that will at a temperature of around 2500°C at the hottest point. This will clearly be sufficient to melt mild steel at the joint, allowing the melting of a filler rod to fuse the joint edges together.
Advantages of Oxy-Acetylene Welding :
·        It's easy to learn.
·        The equipment is cheaper than most other types of welding rigs (e.g. TIG welding)
·        The equipment is more portable than most other types of welding rigs (e.g. TIG welding)
·        OA equipment can also be used to "flame-cut" large pieces of material.
Disadvantages of Oxy-Acetylene Welding :
·     OA weld lines are much rougher in appearance than other kinds of welds, and require more finishing if neatness is required.
·     OA welds have large heat affected zones (areas around the weld line that have had their mechanical properties adversely affected by the welding process)
Materials Suitable for OA Welding:
Most steels
Brass

3. Electric arc
An Electric arc generates sufficient heat to melt mild steel at the joint edges by creating an electric current through a gap (arc) between the materials being joined and the filler rod (electrode). The electrode is coated in a flux which, when melted, prevents the joint area becoming oxidised.
Today, is commonly used in industries such as the automobile industry for its quality, versatility and speed.
Advantages
Versatility - suitable for a variety of positions and applications
Capable of relatively high deposition rates
Enables "one process" operation for individual projects - simplifies training, supervision and logistics
Disadvantages
If the weld is not applied in the right place the weld could be weak.
Potential for lack-of-fusion type defects if welding parameters are incorrect or misalignment occurs
Fume extraction may be required

4. MIG / TIG
More refined forms of electric arc welding can be used to join thin sheet material. MIG (Metal Inert Gas) and TIG (Tungsten Inert Gas) welding use a gas jet around the filler wire to prevent oxidation of materials. Different gases are used with different materials, for examples argon is used with aluminium.
TIG Welding Advantages
 Superior quality welds
 Welds can be made with or without filler metal
 Precise control of welding variables (heat)
 Free of spatter
 Low distortion
TIG Welding Problems
Erratic arc
Excessive electrode consumption
Oxidized weld deposit
Arc wandering
Difficult arc starting
MIG Welding Benefits
 All position capability
 Higher deposition rates
 Less operator skill required
 Long welds can be made without starts and stops
 Minimal post weld cleaning is required
MIG Welding Problems
You need for both of these welding methods a wire feed, different thicknesses of wire needed for different welds which also changes the power and speed needed to correctly weld.

5. Spot & Seam
Both spot welding and seam welding use an electrical current as the heat source.
Spot welding, as the name suggests, provides a spot of heat to fuse the metal together. It is usual to fins a series of spot welds in a structure like a car body shell.
Advantages ‘spot’
The process involves less maintenance cost.
Skill of the operator does not influence the quality of spot welds obtained by this process.
The process is normally free from smoke and spatter.
Disadvantages ‘spot’
To achieve low cost of construction, the weld production rate is not very high.
The process proves un-economical as compared to other welding methods.
Industrial Spot-welder

6. Seam Diagram of Seam welder.
Seam welding; a typical application for this type of joining method is thin coated mild steel for food and drinks cans.
Advantages of Seam Welding
It can produce gas tight or liquid-tight joints.
Overlap can be less than for spot or projection welds.
A single seam weld or several parallel seams may be produced simultaneously.
Disadvantages of Seam Welding
Welding can be done only along a straight or uniformly curved line.
It is difficult to weld a thicknesses greater than 3 mm.
A change in the design of electrode wheels is required to avoid obstructions along the path of the wheels during welding.
Diagram of Seam welder.