How to Better Understand the Processes of Welding

Welding encompasses approximately forty separate processes. The idea behind welding is to take two or more pieces of metal and join them together by applying heat and pressure or a combination of both actions. Herein, I'll take you through the various processes of welding so you will have a better understanding of what you must do to weld.

Instructions

Difficulty: Moderate

Things You’ll Need:

• An interest in learning to weld and/or welding.

1. Before you are able to embark on the varous processes of welding, you will need to know a little bit about the science of welding. First off, in the process of joining two pieces of metal together much depends on the properties of the materials; the uses as to what these materials will be applied; and the facilites available for production.
2. Additionally, most welding processes may be grouped into two (significant) categories that being: a) pressure-welding processes wherein the weld is accomplished by pressure, and, b) non-pressure welding procedures where a weld is achieved by heat only.
3. Welding is now used in the construction of many significant structures and has, in many instances, replaced bolting and riveting. Examples of areas where welding is used in construction include: bridges, buildings and ship-building.
   
   Also, it is used as a process in the aircraft and automotive industry and in the manufacturing of certain types of machinery.
   
   Lastly, before going into explanation as to individual processes: welding processes are classified in accordance as to the sources of heat employed as well as the pressure used.
   
   The processes most generally employed include: arc welding; gas welding; and resistance welding. Others include: forge welding, and Thermit welding.
4. The first type of welding we will look at is Forge Welding. Here you use the original pressure process. This is the age-old welding process practiced for centuries by individuals engaged in the trade of blacksmithing.
   
   What occurs is the metal is brought to an appropriate temperature within a furnace (environment) and the weld is completed by hammering.
   
   This type of welding is most applicable to sections of heavy metal. Since the process is centuries old and used mainly in the past by artisans, you will rarely, if at all, see it used in modern manufacturing.
5. The next processes we are going to review are gas welding and arc welding (the latter found in Step 6).
   
   Gas welding is defined as: a non-pressure process that uses the heat from a gas flame.
   
   The flame is obtained, within may applications, by the event of the combustion of oxygen and acetylene (q.q.v.).
   
   The torch referred to as an oxyacetylene torch is placed directly upon the edges of the metal you are planning to join and at the same time to a filler metal in the form of a wire, also known as the welding rod which, in turn, is melted on to the joint.
   
   The advantage of gas welding is the portability of the welding equipment and the non-necessity of an electrical power source.
   
   In the process of this type of welding, the metal surfaces and the welding rod are coated with flux. This (fusible) material is helpful in the prevention of oxides or nitrides that would render your weld defective or no good.
6. The next process to consider is arc welding. Arc-welding processes which happen to be the most significant of welding processes require a continual supply of electricity and are used in the joining of steel materials. The advantages over other welding applications follow:
   
   a) The welding speed is faster due to a high concentration of heat;
   b) Fluxes may be eliminated within certain process of arc welding.
   
   Also, there are four different commonly used processes of arc welding:
   
   1) Metal arc - see Step 7 for description;
   2) Carbon arc - refer to Step 8;
   3) Atomic-hydrogen arc - look at Step 9; and
   4) Inert-gas-arc welding - see Step 10
7. In the metal arc welding process, you will find the arc is formed from a metallic electrode to the metal.
   
   There is an enormous amount of heat produced by the electric current. The electric current's heat melts both the parts to be welded across a gap as well as the point of the metallic electrode which supplies filler metal to your weld.
   
   In order to prevent the forming of oxides and nitrides, the electrode is coated with a material that when heated melts to form flux. The electrode is coated with this material quite often.
8. The next process falling under the classification of arc welding is the carbon-arc welding process. This process involves a carbon electrode in place of a metallic electrode.
   
   A rod coated with flux is frequently used as a filler metal. The rod is placed into the arc flame in the same way as in gas welding.
9. The third arc welding process is referred to as: atomic-hydrogen-arc welding. Here your heat source is a stream of hydrogen which passes through an arc between two Tungsten electrodes.
   
   The hydrogen gas, in the form of molecules and containing two atoms is broken down into single atoms due to the heat of the arc.
   
   Near the surfaces of work, the atoms once more come together, generating a great deal of heat.
10. Lastly, the fourth arc welding method is known as Inert-gas. (This method was developed after World War II.) In this (welding) process, the arc is formed between a Tungsten electrode and the metal.
    
    An inert gas, in example, helium or argon, is used as a shield. Due to the shield, there is no need to use flux.
    
    This application was initially used in the welding of magnesium, with helium as the gas used for the shield. The process was first known as heliarc welding.
    
    It is predominantly used in the fabrication (process) of aluminum-alloy; and stainless-steel products.
11. Resistance and Thermit Welding (See Step 12 for the latter) are two other types of welding processes.
    
    A pressure process heat is produced in resistance welding. This heat is obtained from the resistance of metal to the flow of an electrical current. Electrodes are clamped on either side of the parts to be welded. Next the parts are subjected to enormous pressure and a very heavy current is applied briefly.
    
    Thus the parts are joined as a direct result of extraordinary pressure and high heat.
    
    Resistance welding is found in many areas of manufacturing and is particularly useful for repetitive welds made by semi-automatic and automatic machinery.
12. In the Thermit welding process, heat is created by chemical reaction resulting from a mix of aluminum powder and iron oxide (also known as Thermit) when ignited.
    
    The aluminum combines with the oxygen at high temperatures; the iron is then released in the form of liquid steel. The liquid steel serves as the filler for the weld.
    
    Thermit welding is most generally used in the seams of heavy iron or sections of steel.
    
    It hs also been used in the welding of railway tracks.
13. Two other processes are being used more frequently. One process is referred to as the cold-pressure process. Here you apply enough pressure wherein ductile metals will flow at room temperature.
    
    Another method uses ultrasonic waves to accomplish the weld.
    
    Other methods include: fusion welding by electronic beams; lasers and plasma arcs.
14. As you can see, although the basics of welding is to join two parts together using a heat source, the processes of welding are most varied and use is dependent on material to be (fused) or joined.