Sheet goods—including metals, plastics or even wood, cloth and paper products—are ubiquitous materials in manufacturing, and are used to produce a wide variety of parts. In mass production, these parts form the inputs for more complex processes that shape blanks into three-dimensional forms. In the automotive industry, sheet and plate steel are stamped into blanks using presses and custom-made tooling. Creating the tool steel dies for these processes requires a large initial investment, as well as costly downtime for tool changes.
However, there are other processes for cutting sheet and plate materials. CNC processes offer a significant advantage over machines which require tooling, because they can cut any part described by the program—instead of only the part described by the shape of the die. For cutting sheet and plate materials, CNC laser, plasma and waterjet cutting are popular options. Wire EDM and gas cutting are also available, though these two options cover opposite ends of the speed-accuracy spectrum. Wire EDM is a very slow but accurate process, while oxy-fuel gas cutting is used to cut thick metals with relatively low accuracy.Laser and plasma can operate at either end of the range. That’s why it is a common question to compare both processes based on cost, accuracy and speed, to determine the best choice for a given project.
CNC Laser and Plasma Cutting—Comparison Highlights
The first difference to consider when comparing plasma and laser cutting is which materials can be cut. Plasma cutting can only be used on conductive materials, while laser processes can cut a wider range of materials, including wood, plastics and textiles. However, because laser cutting machines use a focused beam of light to burn through the material, it is less effective than alternatives—and sometimes is not effective at all on highly reflective materials such as copper. In addition, most laser machines are not powerful enough to cut materials thicker than three-quarters of an inch, though this is changing as the technology develops. Plasma machines can cut metal plate up to an inch and a half in thickness.
Secondly, the accuracy of the cut differs between the two processes. Laser cutting results in a small kerf with high accuracy. Parts are dimensionally very close to drawing specifications. By comparison, the kerf left by a plasma torch is wider, and leaves more spatter, dross and slag on the part which frequently requires post-processing for cleanup. Another accuracy consideration is the heat deformation that can be caused by the processes. Laser cutting causes relatively little heat deformation, mainly in thin materials. Plasma can cause significant deformation due to the intense heat, similar to welding processes.