Types of Welding Processes – Understand the Depth of Welding

Types of Welding Process

In the joining of metals, several types of welding techniques are available that are applied to various sizes of shapes and structures. The welding process also has important applications in the repair of many structural assemblies.

Fusion welding involves the joining of a base metal by melting and often mixed with a filler metal that forms a stable joint after solidification.

In this article, you will get useful insight into the various welding methods. They are explained categorically with thorough research.

So Let’s Learn!

9 Different Types of Welding Process You Should Know:

a.Fusion Welding Process:

welding diagram

The processes of fusion welding are categorized based on heating source, which is used to produce localized melting, i.e. ‘electric arc welding’, ‘thermal welding’ and ‘resistance welding’. Fusion welding is the most common welding technique. You can see the above diagram for the concept.

1.Electric Arc Welding:

Electric Arc Welding,types of welding process
                                                                      Image Credits: Pete Wright

The process of the electric arc depends on the formation of an electric arc between an electrode and the base metal known as work-piece. An electric arc is produced when there is an electrical discharge occurs between two metal pieces that are not directly joined with each other.

The arc causes the ionization of gas present in between the metal electrode and base metal, hence, producing a plasma, with a temperature above 10,000 °C. This high temperature causes the melting of base metal. Due to this high temperature, rapid oxidation over base metal can occur, and the oxides can entrap in the weld joint. That causes severe damage to the mechanical properties of weld joints.

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For that reason, in all-electric arc processes proper provision essential to be made to shield the weld zone and weld joint from the surrounding atmosphere. This protection most frequently proceeds in the form of a gaseous shield.

2.Shielded Metal Arc Welding (SMAW):

Stick Welding Technique
                                                  Image Credits: Christopher Burns

In this welding process, the molten metal is shielded against the surrounding atmosphere. The decomposition of the electrode coating that forms a cloud of gaseous CO2. Moreover, this electrode coating contains fluxes that can remove the impurities from the molten metal. The coated flux helps in the formation of a slag layer that helps in the further protection from atmospheric contaminants when the weld metal cools down.

  • The slag layer is generally removed as soon as the joint area has cooled. The length of electrodes usually is 460 mm and are used up to a final range of about 50 mm.
  • After consumption of the electrode, the process is stopped, and hence the new electrode replaced. The electrodes of metal arc welding are categorized according to composition, polarity and type of coating.
  • The electrode coating tends to absorb moisture from the atmosphere that can lead to hydrogen diffusion into the molten metal and gas porosity during welding.
  • Failure to handle electrodes appropriately, or uncleanness around the joint, has caused to the failure of many welded joints.
  • This process is commonly used in the fabrication of pressure vessels, pipework and pipeline fittings. Also, it is used for the repairing of industrial machinery.

 

3.Metal Inert Gas Arc Welding (MIG):

Mig Welding
                                           Image Credits: Christopher Burns

In this process, the molten metal is protected from the surrounding atmosphere by using an inert shielding gas, which is supplied to the welding gun through pressure. The shielding gas is usually argon for ferrous alloys and a mixture of argon/helium for aluminum and copper alloys.

  • The advantages of MIG welding over the SMAW process includes the non-restricted electrode length, manufacturing the large welding joints, rapid deposition speeds.
  • The more steady arc that needs not as much of operator skill to control and better-quality of weld pool shielding, leading to welds with lower levels of gas porosity.
  • The most critical disadvantage is the increase in the cost of the welding equipment.

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4.Tungsten Inert Gas Arc Welding (TIG):

tig welding process

In the comparison to MIG welding, inert tungsten gas (TIG) arc welding consists of a non-consumable electrode that is made of tungsten or a tungsten alloy (often W with two wt% ThO2). Similar to MIG arc welding, TIG makes use of inert gas, commonly argon, to shield the weld pool from atmospheric impurities.

  • TIG arc welding may be used without the use of filler material.
  • And, it depends on the melting of the base metal only that is responsible for fusion.
  • This characteristic makes it easier for the joining of different metals and makes TIG welding appropriate for welding stainless steel, aluminum, and other nonferrous metals.

The main advantage of TIG welding is that the weld composition is quite close to that of the parent metal, and there is no need for slag removal. But this process is more expensive than inert metal gas (MIG) arc welding.

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Because of no filler material is applied, TIG welding needs the base metal must be well-cleaned just before welding to produce a defect-free weld joint. If, for instance, the filler metal is required, it may be used manually by the operator in the form of consumable rods, or semi-automatically from coils of wire. You can find a detailed comparison of Tig vs Mig Welding.

5.Plasma Arc Welding (PAW):

Plasma Arc Welding,
                                               Image Credits: Russ Wards

Similar to the TIG and MIG Processes, the plasma arc welding (PAW) process makes use of inert gas for shielding the molten weld metal, and corresponding to TIG, a non-consumable tungsten electrode is used.

The plasma arc is enforced from a comparatively small nozzle made up of copper nozzle, provided that a higher energy density surrounded by the plasma. The higher energy density allows the welding with a more exceptional thickness in a single pass with the least joint preparation.

The disadvantage of PAW is its higher capital cost, in comparison to TIG welding. Furthermore, the contraction of the arc over the copper nozzle decreases the easiness of the process to joint gaps or misalignment. The PAW process is usually used for the welding of stainless steel circumferential pipe joints.

 

b.Thermal Welding:

All of the previously described electric arc methods are thermal processes, such as all of these electric arc methods depend on heating to provide a fusion of metal pieces. Regardless of this, it is suitable to describe the ways that produce heat utilizing electric techniques. In this second type, there are various welding processes, and however particular concern are gas welding, thermit welding, and the electron beam method.

 

6.Gas Welding:

Gas Welding
Image Credits: Uğur Gürcüoğlu

Gas welding consists of mixing a combustible gas, mostly acetylene, C2H2, and oxygen in a nozzle that is used to ignite and produce heat. The flame produced is then focused against the joining part for the fast melting of the base metal.

  • Many ferrous and nonferrous metals can be welded through gas welding, frequently with the adding of a suitable filler metal during welding. The flame produced in the gas welding has two individual zones.
  • The luminous zone has a dark blue color and temperatures up to 3500 °C. The reaction taking place in this zone is

C2H2 + O2 → 2CO + H2

The second zone is known as the outer envelope zone, reaches at a temperature of 2100 °C and the combustion reaction is

4CO + 2H2 + 3O2 → 4CO2 + 2H2O

A well-experienced welder can conclude the proportion of acetylene and oxygen by commencing the color, relative size, and shape of the bright cone and outer envelope of the flame.

7.Thermite Welding:

Thermite Welding
Image Credits: Chaitanya Maheshwari

In thermite welding heat is produced by an exothermic reaction among the equally distributed powders of a metal oxide (generally iron oxide for steel welding) and aluminum. The exothermic reaction yields alumina and metallic iron i.e.

8Al + 3Fe3O4 → 9Fe + 4Al2O3 + heat

As the alumina has low density than iron, so it floats over iron and produces a layer of slag.  Which efficiently shields the underlying molten iron from the atmosphere. When the solidification is completed, and the base metal is cool down, the slag is removed, and if required, the grinding is carried out of the welded joint to the desired shape.

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8.Electron Beam Welding:

electron beam welding

The source of heat for electron beam welding is a sharply focused beam of electrons that have been accelerated to about 60% of the speed of light. The high power density of the electron beam causes instant melting and vaporization of the base metals.

The high kinetic energy of the electrons causes deep penetration into the base metal, allowing plates up to 75 mm thick to be welded in one pass. Electron beam welding must be carried out in a vacuum. This significantly increases the cost of the process but also reduces any atmospheric contacts that may take place.

Electron beam welding is mainly appropriate for welding reactive metals, such as titanium or zirconium, which readily react with oxygen and nitrogen.

9.Resistance Welding:

resistance arc welding

 

Resistance welding joins the two-piece of metal by using the resistance of alloy toward an electrical current that provides heat for the fusion of metals pieces. The metal parts that are to be joined together are holding together under force and a small electrical pulse. For (60 milliseconds to 2 seconds) at a low voltage (less than 10 V), but a high current is applied through electrodes.

These electrical pulses cause the melting of the weld joint at the interaction in the middle of the two parts. When the applied electrical pulse stop, the joining parts kept on compressed. Until the metal parts completely solidified together and cool. This process is preferably appropriate for the repetitive joining of metal sheet parts up to a thickness of about 3 mm.

There are two main categories of resistance welding, i.e. spot welding and seam welding.

  • Spot welding processes have been very much computerized in the mass assembly of automobile body components.
  • Seam welding has an excellent advantage for manufacturing a gas- and liquid-tight seal at comparatively fast welding speeds.

These characteristics make the procedure appropriate for joining together sheet metal parts in the automobile gas tanks, catalytic converters, mufflers, heat exchangers, water tanks, and other related uses.

Some Common Questions People Normally Ask (FAQs):

What are the 4 different types of welding?

There are many welding processes but based on the application MIG, TIG, Stick & Arc Welding are the most searched and skillful techniques.

Which Welding process is called co2 welding?

This term is basically used for MIG & GMAW. In this process, CO2 acts as a shielding gas, and the arching creates the joint between two metal sheets.

Which weld is considered the strongest one?

TIG welding joints have the greatest strength because TIG is very precise and clean. Each joint requires much attention and precise skill which turns out in better strength of the joint than another process.

Conclusion:

This was the complete account of various welding techniques, and I hope beginners and all professional welders can now theoretically comprehend these steps. If you think anything is missing and misreports you are always welcome in the comment section. Thanks!

 

 

Hello Everyone, I am James from Kentucky and been into this welding fiasco for 13 years in that time I have worked as a private welder and did most of the auto restoration work. In this recent, COVID-19 outbreak I decided to start a welding blog and share welding tips along with product reviews.

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