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The Differences Between Flame Cutting, Plasma Cutting and Water Jet Cutting

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Anyone who works with metals on a regular basis understands the importance of having the right processing methods. Different metals, such as aluminum and stainless steel, have very different properties and will be easier or harder to cut depending on their particular characteristics.  Complicating matters even further, the increasing diversity in high performance alloys means that there’s even more variance in terms of the cutting performance of various metals.

The goal of these newly developed alloys is often to create the strongest, hardest metal possible; you can imagine that when it comes to processing such durable materials, ordinary methods can prove inadequate.  Moreover, some of the latest technologies for cutting and shaping metal require a high degree of training and expertise.  It can also be a challenge to know which technique will work best for a specific alloy and its application.

What is Flame Cutting?

Flame cutting, also known as oxy-fuel cutting, is a method that relies on fuel gases and oxygen to create a hot enough flame to cut metal.  Developed in 1903, the technique utilizes pure oxygen to increase the flame temperature in order to generate localized melting of the work piece.  With an acetylene/oxygen flame, it’s possible to reach temperatures of 6,332 °F.

The cutting set up involves a torch at a 60- or 90-degree angle with orifices located around a central jet.  The outer jets of oxygen and acetylene are for pre-heating the metal.  The central jet does the cutting and consists only of oxygen.

The goal of the flame is to bring the metal to its ignition temperature without actually melting it.  Then oxygen is directed to the cut area at higher pressure, which ends up burning the metal.  Ideally, the kerf is narrow with a sharp edge on either side.  If too much heat is applied, it will result in a rounded edge. The operator is able to manipulate the central oxygen jet with a trigger, allowing for increased control of the cut.

The primary advantage of flame cutting is the low cost.  In addition, because of the low equipment requirements, it’s ideal for fieldwork.  The flame torch, gas cylinders and tubes are highly portable, unlike other cutting methods.  It can also be used with large metal dimensions such as steel that is several feet thick.

What is Plasma Cutting?

Plasma cutting uses a process in which electrically conductive materials are cut via an accelerated stream of hot plasma.  Any metal that’s able to conduct electricity, such as stainless steel, aluminum, brass, or copper, can be cut using a plasma jet.

The method relies on an electrical channel of superheated, electrically ionized gas that passes through the work piece and forms a completed electrical circuit.  A compressed gas such as oxygen is then blown at high speed towards the intended cut area.  An electrical arc is formed between an electrode on the gas nozzle and the metal being cut.  The ionization that takes place creates an electrically conductive plasma channel, generating enough heat to melt the metal.  The gas blows through the molten portion of the work piece and separates it.

One of the major advantages of plasma cutting over flame cutting is how much faster it is while retaining the same level of quality.  The kerf can also be much smaller and more refined than with a flame cutter.  It can be used with a greater variety of metals, basically any metal that conducts electricity.  The process can also be automated, allowing for a more streamlined and consistent production process.

What is Water Jet Cutting?

A water jet uses a high-pressure jet of water and an abrasive substance to cut extremely hard materials, such as metal and granite.  A water jet that does not use any abrasive is known as a pure water jet and can be used on softer materials such as wood and rubber.

The water jet relies on water being focused into a high-pressure stream using a pump and nozzle.  There are typically two ways of doing this.  The first method uses an intensifier pump, which creates the necessary pressure with a piston that forces the water through a tiny hole.  The other option is a direct drive pump, also known as a crankshaft.  This mechanism, much like a car engine, forces the water through a tubing system that uses plungers attached to a crankshaft.

With enough pressure and the right nozzle, the stream of water emitted can have an exit velocity of 2500 feet per second, which is equivalent to a jet aircraft traveling at Mach 3. With abrasive water jets, an abrasive medium such as garnet or aluminum oxide is added through the nozzle.  This increases the cutting power of the jet.

A big advantage of using a water jet when cutting metal is the cleanliness of the process.  You don’t need to worry about toxic fumes, and the absence of high temperatures means the metal is protected from having its properties altered by the process.

What are the most important considerations when selecting a method?

There are many considerations that go into the decision about which cutting method to use.  Cost will be near the top of the list for most manufacturers, as some water jet and plasma units can run upwards of 300,000 dollars; the operating and training costs must be figured in as well.

Other factors for consideration are desired production rate, required cut quality, flexibility/versatility and portability.

Summary

It’s important to have a partner who is familiar with the most advanced cutting methods. At Clinton Aluminum, we strive to be more than just a material supplier, we try to be an extension of our customer’s business.  Offering value-added solutions to the market with our capability to provide primary processing like high-definition plasma and waterjet cutting is just one way to achieve this end.  Contact us today to learn more.

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