What is Laser Cutting? - A Definitive Guide to the Process - TWI

Laser cutting is a process that utilizes a focused laser beam to cut through a variety of materials, serving both industrial and creative purposes, such as engraving or etching.

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This article is one of a series of TWI frequently asked questions (FAQs).

How Does Laser Cutting Work?

In laser cutting, a high-powered laser is channeled through precision optics and computer numerical control (CNC) to accurately direct the beam onto the material. The motion control system follows a predetermined pattern, guided by a CNC or G-code, ensuring precise cuts. The focused laser energy is capable of burning, melting, vaporizing, or blowing away material with the help of gas jets, resulting in a smooth, high-quality edge finish.

The laser beam originates from the excitation of lasing mediums via electrical discharges or lamps housed in a sealed container. The lasing material is amplified due to internal reflection against a partial mirror until it accumulates sufficient energy to emit a coherent monochromatic light beam. This beam is subsequently focused using mirrors or fiber optics, and directed through a lens to enhance its intensity.

At its focal point, the diameter of the laser beam can be narrower than 0.01 inches (0.32 mm), with the potential for kerf widths as tight as 0.004 inches (0.10mm), which depends largely on the thickness of the material being cut.

When initiating the laser cutting process from a location that is not on the material's edge, a technique called piercing is employed. A high-power pulsed laser generates a small hole in the material—this might take approximately 5 to 15 seconds to penetrate a 0.5-inch-thick (13 mm) stainless steel sheet.

Types of Laser Cutting

The laser cutting process can be categorized into three primary types: CO2 laser, neodymium (Nd) laser, and neodymium yttrium-aluminium-garnet (Nd:YAG) laser. CO2 lasers are commonly employed for precise cutting, boring, and engraving tasks, while Nd lasers are particularly used for high-energy, low repetition rate activities, and Nd:YAG lasers cater to high-power boring and engraving needs.

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Various types of lasers are also applicable for welding processes.

The operation of CO2 lasers involves current passage through a mixture of gases (DC-excited) or the more advanced method of radio frequency (RF-excited) energy, which is becoming increasingly popular. The RF technique incorporates external electrodes, mitigating issues related to electrode wear and contamination that can arise with the internal electrodes used in DC methods.

In addition, the efficiency of laser cutting hinges on the type of gas flow employed. Notable variations of CO2 lasers include fast axial flow, slow axial flow, transverse flow, and slab configurations. Fast axial flow lasers mix carbon dioxide, helium, and nitrogen, circulated at high speeds by a turbine, while transverse flow lasers employ a blower for lower velocity circulation. Slab lasers, or diffusion resonators, operate with static gas fields eliminating the need for pressurization or glassware.

Cooling techniques for laser generators and external optics also differ based on system size and design. While waste heat can be discharged directly into the air, utilizing a coolant is the preferred approach. Water is a standard coolant, often circulated through a heat transfer or chiller system.

One notable example is a water-cooled laser processing system, which integrates a pulsed laser beam with a low-pressure water jet, allowing precise guidance akin to optical fibers. The added benefit of this method includes effective debris removal and cooling of the material, offering significant advantages over 'dry' laser cutting, such as high dicing speeds, parallel kerf, and versatile cutting directions.

Fibre lasers are rapidly gaining traction in the metal cutting arena due to their solid gain medium technology. By amplifying laser energy within glass fibers, these lasers achieve a significantly smaller focal spot compared to CO2 systems, which is particularly beneficial for cutting reflective metals.

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