Laser cutting

Laser cutting is a fabrication process which employs a focused, high-powered laser beam to cut material into custom shapes and designs. This process is suitable for a wide range of materials, including metal, plastic, wood, gemstone, glass, and paper, and can produce precise, intricate, and complex parts without the need for custom-designed tooling.

There are several different types of laser cutting available, including fusion cutting, oxidation cutting, and scribing. Each laser cutting process can produce parts with precision, accuracy, and high-quality edge finishes, and with generally less material contamination, physical damage, and waste than with other conventional cutting processes, such as mechanical cutting and waterjet cutting. However, while laser cutting demonstrates certain advantages over more conventional cutting processes, some manufacturing applications can be problematic, such as cutting reflective material or material requiring secondary machining and finishing work. The requirements and specifications demanded by a particular cutting application—e.g., materials and their properties, energy and power consumption limits, secondary finishing, etc.—help determine the type of cutting process most suitable for use.

While laser cutting machines vary from model to model and application to application, the typical setup includes a laser resonator assembly, mirrors, and a laser cutting head which contains a laser focusing lens, a pressurized gas assembly, and a nozzle. The basic laser cutting process includes the following stages:

  • beam generation
  • beam focusing
  • localized heating and melting
  • material ejection
  • beam movement

Each stage is integral to the laser cutting process and, when properly executed, producing a precise cut.

Types of Laser Cutting Machines

There are several types of laser cutting machines available which are categorized into gas, liquid, and solid state lasers. The types are differentiated based on the state of the active laser medium—i.e., whether the medium is a
gas, liquid, or solid material—and what the active laser medium consists of (e.g., CO2, Nd:YAG, etc.). The main two types of lasers employed are CO2 and solid-state lasers.

One of the most commonly employed gas state lasers, a CO2 laser employs a carbon dioxide mixture as the active laser medium. CO2 lasers are typically used to cut non-metal materials since early models were not powerful enough to cut through metals. Laser technology has since evolved to enable CO2 lasers to cut through metals, but CO2 lasers are still better suited for cutting through non-metals and organic materials (such as rubber, leather, or wood) and simply engraving metals or other hard materials. Pure nitrogen lasers are another commonly used gas state laser. These lasers are used for applications that require the material not oxidize as it is cut.

Laser Cutting Machine Considerations

As described in the previous section, the type of laser suitable for a laser cutting application is largely determined by the material being cut. However, other considerations may be taken into account when choosing and setting up a laser cutting machine for a specific application, such as the machine configuration, laser power, wavelength, temporal mode, spatial mode, and focal spot size.

Machine Configuration: See Beam Movement, above

Laser Power: The laser power, or wattage, can increase or decrease the total processing time for a cutting application. This occurrence is due to the increasing intensity of the beam as the laser’s power increases (Power density (Intensity) = P/πr2). The price of a laser cutting machine is typically dependent upon the power of the laser; the more powerful the laser, the more expensive the equipment. Therefore manufacturers and job shops must find a balance between processing costs and equipment costs when choosing a laser machine based on laser power.

Wavelength: The wavelength of the laser beam is the spatial length of one complete cycle of vibration for a photon within the beam. The particular wavelength of the laser beam partially determines the material’s radiation absorption rate, which is what allows the material to be heated, melted, and vaporized to produce the necessary cuts.

Beam Mode: The mode refers to how the laser beam’s intensity is distributed across the cross-sectional area of the beam. The mode affects the size of the beam’s focal spot and the intensity of the beam, which in turns affects the quality of the cut. Typically, the optimal mode has a Gaussian intensity distribution (TEM00).

Focal Spot: The beam is directed through a lens or a specialized mirror and focused to a small spot of high intensity. The point at which the beam’s diameter is the smallest is called the focal spot, or focus. The optimal position of the focus for a laser cutting application is dependent on several factors, including the material’s properties and thickness, beam shape and mode, type of assist gas, and the state of the focal lens.