Reasons Behind Using Assist Gases In Laser Cutting Processes

By: Billy Kite

Ever wonder how they get those holes in that stainless steel sink so that the fixtures and drain can be installed? Maybe you've seen the Majestic Roof Garden Hotel in Adelaide and wondered how the precise steel facade was created. Modern laser cutting has provided the means to creating such high quality cutting of stainless steel.

Laser cutting is a technique that allows faster and higher quality cuts than traditional torch cutting or other methods. Since modern laser cutting is computer controlled a more precise cut can be easily made. This precision allows holes with a small diameter to be made in various pieces of steel.

Typical laser cutting involves focusing the laser beam through a lens onto the surface of the material being cut. The laser either moves along the cut surface or the material itself is moved as the laser remains stationary. An assist gas, usually nitrogen or oxygen, is blown along the material to remove any excess molten metal from the edge. Each of these gases has its advantages and disadvantages.

Using oxygen as an assist gas allows for much higher speeds of cutting. It is also more cost effective. The exothermic reaction, a reaction that generates heat, allows this to happen, as well as providing for a better cut. Unfortunately, this same reaction causes oxidization and leaves an unattractive brown scale on the edge. This must be removed with de-scaling measures; either chemical or mechanical, before it is to be welded. One of the major disadvantages of oxygen assisted laser cutting is this extra step.

On the other hand, using nitrogen as an assist gas results in a much cleaner cut. As nitrogen is an inert gas, there is no exothermic reaction between it and the stainless steel. This prevents oxidization from occurring, leaving a shiny edge instead of the scaled edge. By keeping the cut edge clean, nitrogen assisted laser cutting prevents the time consuming step of de-scaling after the cut is made. Nitrogen assisted laser cutting is slower than oxygen assisted cutting, however, and requires a high purity level in the gas supply. Also, as there is no exothermic reaction, the gas must be used at a high pressure. Nitrogen is also more expensive to use than oxygen.

Most laser-cutting operations today use nitrogen as the assist gas because of the reliable results. Nitrogen can be a costly gas, though. When cutting thicker pieces of stainless steel, the cost of the gas can run as high as ninety-percent of the operating cost. Fortunately, nitrogen generating equipment helps offset this cost. This equipment uses carbon molecular sieves to take oxygen out of compressed air, leaving a relatively pure source of nitrogen available to use in precision laser cutting.

With these advances in nitrogen cutting technologies, as well as higher powered lasers being used on the material, it's no wonder that this is quickly becoming standard practice. Avoiding the extra task of de-scaling is a major advantage in nitrogen use. A simple stainless steel piece can be a picture of beauty when it is sharp, precise and possesses a shine all over.

Technology
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 
 • 

» More on Technology