The Development of Metalworking


Early humans, when they began to work with metals, developed two processes that helped them immensely: heating and cutting. Using a primitive forge, metal ore could be made pliable enough to hammer into a desired shape, while flattened sheets of metal could be drilled, sawed, or sheared using implements made of harder metals.


While the two techniques were often used in tandem by blacksmiths and other metalworkers over the millennia, it wouldn’t be until the dawn of the 20th century for technology to reach the point of allowing metal to be cut by heat itself. The processes known collectively as thermal cutting have taken many forms over the last several decades, but they all utilize a moving energy source melting a narrow channel in a piece of metal and blowing away the molten metal while following a predetermined path, creating a cut in the workpiece.


The evolution of burn tables into laser cutting machines is a fascinating history, especially since each new technology never completely replaced the preceding ones, only supplemented them, giving the metal fabricators of the 21st century a wide array of thermal cutting tools from which to choose.


Flame Cutting


The original thermal cutting method is flame cutting, usually referred to as oxyfuel cutting, though the term flame cutting can also embrace other oxygen-based cutting processes, such as oxygen lance cutting, metal powder cutting, and chemical flux cutting. Oxyfuel—sometimes spelled with a hyphen as “oxy-fuel”—denotes the combination of oxygen with a fuel source like acetylene or propane to create a flame hot enough to melt metal. 


Acetylene was discovered in the mid-1800s, but it wouldn’t be until the turn of the century that it would be applied to cutting metal—though quite by accident at first. American John Harris was using an oxyfuel process in his hobby shop in 1899 when he stumbled upon oxy-acetylene metal cutting. He was working on the manufacture of synthetic rubies and found that the heat had cut the steel plate beneath the gems. He worked on his flame-cutting torch and exhibited it at the 1904 St. Louis World’s Fair, starting a company the next year to manufacture and sell his product.


Before Harris could get his enterprise going, however, French engineers Edmond Fouché and Charles Picard developed the first oxygen-acetylene welding procedure in 1903. That process was soon found to be able to slice through metal as well as weld it, giving the field of oxyfuel cutting its start. While oxy-acetylene welding has since become obsolete, being replaced by the more efficient process of arc-welding, oxy-acetylene cutting is still widely used today, utilized in handheld cutting devices as well as in burn tables that hold the workpiece stationary while a cutting head moves through its course. Oxyfuel cutting is currently the only method capable of cutting up to—and beyond—30" thick steel.


Plasma Cutting 


Arc cutting—of which, plasma arc cutting is one of the most well-known methods—utilizes an electrical arc as the heat source for cutting metal. Besides plasma cutting, other types of arc cutting include air carbon arc cutting, carbon arc cutting, gas metal arc cutting, gas tungsten arc cutting, oxygen arc cutting, and shielded metal arc cutting. Plasma cutting creates an electrical arc between an electrode in the machine nozzle and the workpiece which are connected in a circuit to the power source. This arc heats and ionizes compressed oxygen and other gases such as nitrogen and hydrogen forced at high speeds through the nozzle, turning them into an intensely hot plasma that vaporizes metal in the plasma stream.


Like oxyfuel cutting, plasma arc cutting was first developed as a welding technology. Used in World War II as a faster way to weld aircraft and vehicles for the war movement, the technology was adapted in the 1950s by scientists for metal cutting. It was found the speed and temperature of the arc could be increased by restricting the gas flow to the nozzle, allowing it to cut metal instead of just weld it. Even with the onset of newer technologies, such as laser cutting, plasma cutting remains popular due to its abilities to cut a variety of thicknesses of metals and to cut plate metal of medium thickness at a high rate of speed.


Laser Cutting


The 1960s brought about the emergence of the metal cutting laser, turning the stuff of science fiction into practical, everyday usage in fabrication by the end of that decade. The CO2 laser and the Nd:YAG laser both premiered in the 1960s, followed by the direct diode fiber laser before the end of the century.


While each type of laser is different, they all operate in the same basic way: light or electrical energy is sent (or “pumped,” as it is called) into a material referred to as a “gain medium” that contains certain ions. As photons from the pump source encounter the atoms in the gain medium, they cause them to release new photons—in a process called “stimulated emission”—that are in phase with the original photons. This amplifies the energy as the photons bounce back and forth through the gain medium before finally being released as a tight beam of coherent light. The word “laser” itself is an acronym that stands for “light amplification by stimulated emission of radiation.”


The gain medium is different in each type of laser, giving their beams different wavelengths, making them suited to cutting different types and thicknesses of material. A CO2 laser uses carbon dioxide mixed with other gases as the gain medium. Nd:YAG is an acronym for “neodymium yttrium-aluminum-garnet,” referring to the laser’s gain medium, a synthetic yttrium aluminum garnet crystal that has been doped with neodymium. A fiber laser uses a spool of optical fiber which has been doped with rare earth elements such as ytterbium or erbium as the gain medium. Laser cutting is ideal for very precise fabrication work in thin materials.


Choices for Fabricators


The beauty of the different thermal methods of metal cutting is that when a new technology comes along, the old ones remain relevant and available. Every fabrication shop in today’s world has a wide variety of tools available from which to choose. Fabricators need to learn about all three methods and their pros and cons before making an informed decision on which machine to purchase for their circumstances.


Purchasing factors to consider include budget, the types and thicknesses of the metal that will need to be cut, how fast production needs to be, what parts will be cut (and their uses), and the level of precision that those parts will need. A wise shop owner will also figure in future growth estimates, both as to the quantity of prospective clients, as well as what their potential projects might be. Financing a more expensive cutting method may prove a smart move if the return on investment can be shown to be substantially greater.


The future of thermal cutting burns bright, as newer technologies are likely to emerge, and existing ones continue to be improved. The evolution of the craft is far from over.