Metal welding is the process of joining materials, usually metals and thermoplastic plastics. As a rule, the joining process occurs when the surfaces of the parts to be welded melt, with the formation of a bath of molten material, subsequently, when cooling, the surfaces of the surfaces to be welded are combined at the molecular level.
Modern types of welding
The most common modern methods of welding metals:
- Manual arc welding (SMAW) – welding is carried out using electrodes – metal rods, melted during the welding process, coated with special components that protect the weld pool from the atmosphere.
- Non-consumable electrode welding (GTAW) – Electrodes made of refractory materials are used for welding. As a rule, welding takes place in a protective gas environment – argon, helium, etc.
- Semi-automatic welding (GMAW) – a metal wire is used as an electrode. The process takes place in an inert or active gas environment.
- Flux cored wire welding (FCAW) – The welding process is similar to semi-automatic welding. The process can take place both in the environment of shielding gases and without shielding gases, depending on the composition of the wire.
- Submerged arc welding (SAW) – welding takes place in a protective environment formed by the emitted vapors of the metal and flux supplied to the welding zone.
- Electroslag welding (ESW) – used for welding thick-walled products. The melting of the electrode and the surface to be welded occurs under the action of a current passing through the slag.
As sources of energy for welding metals, a gas flame, an electric arc, laser energy, electron beam energy, friction, as well as ultrasound can be used. Welding can be performed under the influence of various environments: under the influence of air, water, in space.
Welding of metals is a dangerous event requiring appropriate knowledge, experience and skills, as well as compliance with safety measures.
Manual shielded metal arc welding – SMAW
The technical name for manual arc welding is SMAW. Mig welding is currently called gas arc welding, or GMAW. Tig welding is now gas tungsten arc welding, or GTAW.
In arc welding, a consumable rod or electrode is used. The rod closes the electrical circuit at the end, causing strong heating, which, in turn, melts the end of the rod into molten droplets. These droplets form a weld pool that melts the base metal. Some rods penetrate the metal or melt deeper than others.
Merging is the right word to determine how deep the weld pool penetrates the surface of the base metal. Penetration means how far the weld pool gets into the joint or passes through it.
When performing any welding process, it is necessary to ensure that harmful pollutants in the atmosphere do not enter the weld pool. When hydrogen, oxygen, nitrogen, etc., enter the weld pool, they can cause porosity (worm holes in the weld) or cracking of the weld after it hardens.
Porosity, cracking and inclusion of slag (slag that was not chipped / brushed off and became part of the weld) are the three main defects of the weld.
During World War II, it was noticed that a rusty rod does work better than the brand new bare rods used in welding. After experimenting with elements such as silicon, potassium, and others, it was discovered that when flux coating is added to an uninsulated electrode, gas is formed that holds the atmosphere outside the weld pool. The slag then hardens and forms a protective coating around the weld, which is then split off and cleaned with a brush.
Cleanliness is paramount in all welding processes!
Although aluminum and other metals can be welded using electrode welding, the most common electrode welding is on mild and stainless steel. Cast iron can be welded, but requires preliminary and subsequent heating with a high degree of qualification.
Some advantages of manual arc welding:
- Most portable, the welder should only wear conductors where welding is required.
- Available equipment.
- It can be used in all positions and used both indoors and outdoors, as the wind usually does not affect the weld pool.
Some disadvantages of manual arc welding:
- Only a few centimeters at a time can be welded before another electrode is needed.
- To obtain reliable welds, a high level of skills is required.
- Many electrodes have low penetration.
- With direct current, an arc shock may occur. (The arc goes everywhere except where you want.)
In most designs, manual arc welding is performed with low hydrogen electrodes 7018 and 6010.
Oscillations and a slight manipulation of the rod up and down during welding will help to rinse the weld pool in the base metal and produce a good looking weld.