Although metal cutting operations traditionally employ mechanical or manual processes, laser cutting can be a viable, effective, and cost-efficient option for metal fabrication. Laser equipment is distinct from other cutting machines in both design and application. For example, laser cutters do not make direct contact with material, rely on high-energy power sources, have tighter cutting tolerances, and are generally automated to maximize precision.
A laser device fires a concentrated stream of photons onto a precise area of the workpiece in order to trim excess material and shape the workpiece into a specific design. These machines are highly effective in cutting various grades of steel, such as stainless and carbon steel. However, lasers are less efficient on light-reflective or heat-conductive metals, like aluminum or copper, and require specific modifications to shape these materials. The material being cut often dictates the type of laser used in fabrication, making it important to match equipment specifications with forming stock.
Types of Lasers
Laser technology has several unique attributes that affect the quality of its cuts. The degree to which light curves around surfaces is known as diffraction, and most lasers have low diffraction rates to enable higher levels of light intensity over longer distances. In addition, features such as monochromaticity determine the laser beam’s wavelength frequency, while coherence measures the continuous state of the electromagnetic beam. These factors vary according to the type of laser used. The most common types of industrial metal laser cutting services include:
Nd:YAG: The neodymium-doped yttrium aluminum garnet (Nd:YAG) laser uses a solid crystal substance to focus light onto its target. It can fire a continuous or rhythmic infrared beam that can be enhanced by secondary equipment, like optical pumping lamps or diodes. The Nd:YAG’s relatively divergent beam and high positional stability make it very efficient in low-powered operations, such as cutting sheet metal or trimming thin gauge steel.
CO2: Acarbon dioxide laser is a more powerful alternative to the Nd:YAG model and uses a gas medium instead of a crystal for focusing light. Its output-to-pumping ratio allows it to fire a high-powered continuous beam capable of efficiently cutting thick materials. As its name suggests, the laser’s gas discharge consists of a large portion of carbon dioxide mixed with smaller amounts of nitrogen, helium, and hydrogen. Due to its cutting strength, the CO2 laser is capable of shaping bulky steel plates up to 25 millimeters thick, as well as cutting or engraving thinner materials at lower power.
Laser Cutting Capabilities
Laser cutting involves removing material to shape a workpiece in a process that generally reduces the amount of post-fabrication finishing work. For example, when cutting thermally treated material, laser heat can cause hardening at the outer edges of the cut. Hardening can be useful for many applications because it increases product durability, but it also limits the amount of machining that can be done, making post-cut threading or deburring difficult.
Most laser cutting systems are automated under CNC parameters. These computer controls enable high levels of precision and increased cutting speed. Some CNC programs offer “flying optics” capabilities that allow a laser to shape material while the cutting head is in motion. The moveable laser can perform fast cutting operations while maintaining accuracy, and is highly effective on thin sheet metal. CNC programming can also regulate power output, enabling the laser to shift settings depending on the contours and thickness of the material being cut. In addition, some CNC lasers are equipped with sensory units that can adjust the distance between the cutting head and the workpiece to reduce the potential for warping.
Laser Cutting Steel
Thick steel materials, such as plates or reinforced sheets, are typically cut with CO2 lasers because they have higher power capacity than other laser models. In general, the thicker the steel sheet, the more power required to cut it, and the optimum cutting rate is largely determined by the ratio of thickness to the strength of the laser’s beam. Unlike many mechanical cutting processes, laser cutting can produce hole sizes significantly smaller than the thickness of the steel, sometimes as low as a fifth of the workpiece’s size.
Although Nd:YAG lasers are usually incapable of cutting steel at any thickness approaching 20 millimeters, an optical fiber enhancement with an oxygen assist gas mechanism can enable these crystal-based systems to cut thicker steel workpieces. This kind of modification uses the laser to preheat the steel while the oxygen catalyzes an exothermic reaction to assist in the cutting.
Laser Cutting Steel/Laser Cutting Aluminum Problems
Unlike standard-grade or carbon steel, aluminum and stainless steel are light-reflective and heat-conductive metals, so it can be difficult to fabricate them using a laser cutting process. A possible solution for laser cut aluminum and laser cut steel, involves the use of a higher power setting coupled with compressed gas technology. Using gases in conjunction with cutting operations is fairly common. Nitrogen and oxygen assisted laser cutting machines can shape aluminum and stainless steel at relatively high capacities and with quality edge finishes. However, higher electricity consumption and the cost of peripheral equipment, such as gas or air filters, can increase expenses for these systems.
Research and Development
Many organizations, such as the Laser Institute of America and Laserlab Europe, conduct ongoing research to determine the best standard practices and optimal laser applications for a range of materials. Likewise, laser cutting head specifications are continually being revised and adjusted to improve the quality of laser piercing and the cleanness of laser cuts. As laser cutting systems continue to improve in their capacity, production rates, and cost-efficiency, more steel and aluminum laser cutting applications are likely to appear.
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