Major Methods Of Cutting Metal Using Thermal Cutting Process
It is common knowledge that metals are opaque solid substances found on earth. Their durability and the ability to withstand wear and tear have made them ubiquitous in our everyday life.The versatility of metal has been a boon for technology andit is used in electronics, construction of building, spaceships, shipping vessels, your household utensils.
Properties of metal
- Capacity to withstand heat
- Ability to expand at high temperatures and contract at low temperatures
- Are good electrical conductors
- Immune to effect of acids and other chemicals
Any metal has to be cut in a particular shape and in a specific size to be used in the various manufacturing and industrial units. But cutting metals is not easy and you need specialized equipment to do that. Metal can be cut in either of the two ways below
Mechanical cutting involves turning, milling and drillingusing some come common machines.
As the name suggests thermal cutting involves heat as the main factor. There are three major types of thermal cutting methods utilized in many metal fabrication processes.
They are namely
- Oxyfuel flame cutting
- Plasma arc cutting
- Laser beam cutting
The material and its thickness, the required precision and design determine which method to employ for metal cutting.
Oxy-fuel cutting is widely used for cutting steel of all shapes and sizes.This method is often described as ‘burning’ or ‘flame cutting’ because in this method an oxy-fuel torch is used to burn steel and cut it. In scientific terms, an exothermic reaction takes place between oxygen and steel which leads to the melting of the metal and eventual break down.
This method is predominantly used to cut carbon steel because it is most effective withmetals with lower melting point than the base metal. First and foremost the steel (metal) has to be preheated to almost 1800°F where it will readily react with oxygen. Now we come to the Oxyfuel torch wherein Oxygen is mixed with a fuel gas to prepare a highly inflammable mixture. Some of the commonly used fuel gases include acetylene, propane, natural gas and the ratio between oxygen and the gases can be adjusted to determine the heat and the jet flow.
With the help of a nozzle pure oxygen is directed in a jet to the surface of the heated steel where oxidation of steel takes place and a molten slag is formed. Depending on the thickness of the steel the whole process can take anywhere between a fraction of a second to several seconds.
This method is used mainly in repair work for welding pipes and tubes. It is used in some metal art work also. Its main advantage is that it can be used where electricity is not available and it is portable, economical and almost maintenance free.
Plasma cutting is a method wherein a high speed jet of hot plasma is directed through a constrictive nozzle to cut metal. This method is commonly used to cut steel, aluminum, brass and copper. It is widely used in metal fabrication workshops, garages and in industries.This is one of the most preferred methods of thermal cutting because it is cost effective, cuts precisely and faster and does not warp the surrounding area.
Method: In this processan electric arc is formed between the electrode in the plasma torch and the metal surface to which the torch is directed. Once electricity travels through the plasma,sufficient heat is generated to melt the metal and because of the high velocityat which the plasma travels it simultaneously blows the molten metal away even as it cuts through the metal. It is important to wear eye protection while handling the plasma torch to prevent damage to the eye from the heat and the debris that might fly around.
Nowadays some manufacturers use CNC tables which allow a computer to manage the plasmatorch; this leads to cleaner and sharper cuts.
Initially, it was expensive to use plasma cutting but with technology advancing, plasma torches with smaller nozzles and thinner plasma are available at a lower cost allowing hobbyists too to possessit and create works of art.
The advantages of plasma cutting are that it requires minimal training, can be used to cut through a wide range of thickness, is economical, precise and fast.
This is by far the most popular of the three thermal cutting methods. It yields very accurate and precise cuts on steel, aluminum and stainless steel. Because of a small kerf and controlled heat, laser cutting is best suited for intricate design cutting and minute holes.
Laser cutting involves the use of a laser beam of monochromatic light which is most often invisible to the human eye; this beam is directed through a lens to the metal surface. Laser beam is an electromagnetic wave; hence it will interact with the free electrons in the metal and set them into motion. This will set a chain reaction which will eventually lead to the metal getting heated up and beginning to melt. Along with the laser beam, compressed oxygen or nitrogen is also allowed to flow out to blow the molten metal out of the kerf.
Laser cutting requires a little skill because you should be able to focus the laser beam on the exact spot. The laser beam when it falls on the metal leads to rapid melting and complete vaporization of the metal while the gas blows the molten metal away.
Smaller kerf and smaller heat affected zone render laser cutting clean and dust free. It can be used for cutting many materials of any thickness. It is accurate and does not require secondary cleanup. A few drawbacks are that it is expensive, can’t cut reflective surface and consumes more power.Laser cutting is widely used in welding, cutting, etching and engraving of metal.
Each method has its own unique advantage and disadvantage. Which method is best suited is dependent on the place of usage, the cost effectiveness and the capability of the production unit.
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