MYPIBLOGs

Welding is the process of joining together two pieces of metal so that bonding takes place at their original boundary surfaces. When two parts to be joined are melted together, heat or pressure or both is applied and with or without added metal for formation of metallic bond.

1. NEED FOR WELDING

With ever increasing demand for both high production rates and high precision, fully mechanized or automated welding processes have taken a prominent place in the welding field. The rate at which automation is being introduced into welding process is astonishing and it may be expected that by the end of this century more automated machines than men in welding fabrication units will be found. In addition, computers play critical role in running the automated welding processes and the commands given by the computer will be taken from the programs, which in turn, need algorithms of the welding variables in the form of mathematical equations. 

2.METAL JOINING METHODS

The art of joining metals is about 3000 years old. The origin of welding is probably to be traced to the shaping of metals. In industry every worker is working for changing the shape of metals by different methods and machines. Welding is a metal joining method. The following methods are used for joining metals:

(i) Soldering

This joint is made on thin metals using solder as a joining medium. The melting point of solder is less than the metals to be joined. The joint can be opened by heating upto the solder melting temperature (below 400°C).

(ii) Brazing

The joint is similar to soldering but has more strength. The joining medium used is brass, which has a higher melting temperature than solder. The joint can also be opened by heating upto the melting point of brass (850-950°C).

(iii) Welding

A metal joining method in which the joining edges are heated and fused together with or without filler metal to form a permanent (homogeneous) bond is known as welding. Or in other words, “Welding is a process of joining two or more pieces of thesame or dissimilar materials to achieve complete coalescence.

Types of welding

Oxy acetylene(Gas welding)

Oxygen/Acetylene welding, or “Gas Welding”, is a process which relies on combustion of oxygen and acetylene. When mixed together in correct proportions within a hand-held torch or blowpipe, a hot flame is produced with a temperature of about 3200°C. The chemical action of the oxy/acetylene flame can be adjusted by changing the ratio of the volume of oxygen to acetylene, using the valves on the torch or blowpipe.

Equipment

Oxy/acetylene equipment is portable and easy to use. It comprises oxygen and acetylene gases stored under pressure in steel cylinders. The cylinders should be fitted with regulators, to control the pressure and flow of gases. Flexible hoses are used to connect the regulators to the torch or blowpipe. Specially designed safety devices, called flame traps or “Flashback Arrestors” are fitted between the hoses and the regulators. Flashback arrestors prevent flames generated by a 'flashback' from reaching the cylinders 

Laser welding(newer welding)

Laser (Light Amplification by Stimulated Emission of Radiation) welding is one of the most technically advanced forms of welding. 

Its applications span across a diverse array of industries from aerospace to fine jewelry making. Laser welding uses a highly concentrated beam of light on a very tiny spot so that the area under the laser beam absorbs  the light and becomes highly energetic. As powerful laser beams are used, the electrons in the area get excited to a point where the material melts as the result of the atoms breaking the bonds with each other.

This melting of the two materials at their seams fuse them into a joint.  It is surprising how light can be powerful enough to metal  within milliseconds.  To achieve such powerful laser beams, the laser welding machine uses several parts that direct and amplify the laser.

Thermit welding

Process of Thermit Welding:

Thermit welding is a chemical welding process in which an exothermic chemical reaction  is used to supply the essential heat energy. That reaction involves the burning of Thermit, which is a mixture of  fine aluminum powder and iron oxide in the ratio of about 1:3 by weight.Although a temperature of 3000°C may be attained as a result of the reaction, preheating of the 

Thermit mixture up to about 1300°C is essential in order to start the reaction.

The mixture reacts according to the chemical reaction:

8 Al + 3 Fe3O4 → 9 Fe + 4 Al2O3 + heat (3000˚C, 35 kJ/kg of mixture)

Aluminum has greater affinity to react with oxygen; it reacts with ferric oxide to liberate pure iron and slag of aluminum oxide. Aluminum oxide floats on top of molten metal pool in the form of  slag and pure iron (steel) settled below, because of large difference in densities.

Plasma arc welding(arc)

The plasma arc welding is method wherever a coalescence is generated with the temperature which is developed from a  special setup between a tungsten alloy electrode and the water-cooled nozzle (Non transferred ARC ) or between a tungsten  alloy electrode and the job (transferred ARC). In this type of winding, there are three types of gas supplies being utilized namely plasma gas,  shielding gas, and a back-purge gas. Plasma gas supplies throughout the nozzle turn into ionized. 

The shielding gas supplies throughout the external nozzle & protects the join from the environment. Back-Purge gas is mainly used when particular materials are being used.

Ultrasonic welding(SSW)

Ultrasonic welding the most widely used welding method for thermoplastics,uses ultrasonic energy at high frequencies (20–40 kHz) to produce low amplitude (1–25 μm) mechanical vibrations. 

The vibrations generate heat at the joint interface of the parts being welded, resulting in melting the thermoplastic materials  and weld formation after cooling. Ultrasonic welding is the fastest known welding technique, with weld times of less than 1 s. Ultrasonic welding is used for both soft and rigid thermoplastics and for thermoplastic composites

TIG welding(arc)

TIG welding is another name for gas tungsten arc welding. The aircraft industry created it to weld magnesium in the 1930s and 1940s. Ideally the process works like this: the welder makes an arc between the base metal and the non-consumable tungsten electrode, a type of electrode that does not melt. At the point where the arc hits the base metal a molten weld pool forms. 

A thin wire of filler metal is slowly handfed into the weld pool, where it melts. All the while, an inert shielding gas protects the tungsten electrode and weld pool from oxygen contamination. No fluxes are used. The finished product is a sound, slag-free weld that shares the same corrosion resistance properties as the parent metal

MIG welding(arc)

MIG welding is an arc welding process in which a continuous solid wire electrode is fed through a welding gun and into the weld pool, joining the two base materials together. A shielding gas is also sent through the welding gun and protects the weld pool from contamination. 

In fact, MIG stands for metal inert gas.

Six Industries Where Welding Is Used

1)Aerospace

Engineers use MIG welding for manufacturing aircraft, while plasma arc welding and electric resistance welding are commonly used for joining sheeting and precision work.

2)Automotive Industry

Since MIG welding delivers a super-strong bond even between thinner metals,  it’s ideal for joining sheets of aluminum on the manufacturing line. Increasingly, laser MIG welding is gaining ground as car manufacturers appreciate the cost-effective nature of this process, which also offers superior penetration depth.

3)Construction and Infrastructure

With over 50% of the steel produced globally used in construction of commercial and residential buildings,  there’s an enormous demand for welding on site. Beyond building, welding is a great way to repair damaged machines or broken tools.

4)Manufacturing

From furniture to agricultural tools, computer parts to mining machinery, just about anything  we can think of that’s put together on a production line will need welding somewhere during the process.

5)Railroads

Welding is a pivotal part of the railroad industry. When steel rails were introduced more than 100 years ago, welding was vital for joining these rails.  Shot welding was an innovative form of spot welding invented in 1932 as a way of fusing this steel together effectively.

6)Shipping

From cruise liners and large tankers to cargo ships and aircraft carriers, welding underpins the construction of most ships. Although engineers can also use rivets, welding is a great deal quicker.