Throughout the centuries, cutting have being used by the humans to continue their civilization. Dating back to 2.6 million years ago, cutting with the tools made of stone is used by the homo habilis to cut meats and create more advanced tools. Since then, the concept of cutting is based on the idea that separating objects through highly directed force. To effectively run this process, the tool being used to cut material must be harder and more resistant to deformation than material itself. During cutting process, stress at the contact point between tool and material increases and this increase leads material to deform at some point. After the force increased beyond materials’ elastic limit, irreversible deformation in the material has been occurred.
Having said that the roots of cutting dates back to many years ago, we can say humans improved this process in the Bronze Age by dealing with copper as cutting tool. They found that copper was easier to become sharp-edged tools like knives since it is malleability and low melting point. Later humans discovered alloying, means combining of two or more metals to enhance properties, and made special alloy called bronze, which is combination tin and copper. Although bronze tools were easily dulled, it was still superior to stone with its sharpness. In the history, that time is named Bronze age and this age led to the emergence of metallurgy. Thanks to metallurgy, humans started to define the properties of cutting tools like hardness, toughness and high wear resistance and seek ways to improve these properties.
The idea behind understanding the properties of metals was the microstructure of metals. Discovering the fact that metals are arranged in a three-dimensional array called a crystal lattice, humans started to observe grains and their irregularity to understand metals. They revealed that dislocation, an ability of atoms to slip on each other, was the reason for metal to deform permanently. To stop these dislocations from spreading, alloying was commonly used since grain regularity and the space between grains change after alloying. More importantly, alloying allowed to enhance the properties of the material. For example, smaller grains created more grain boundaries which makes difficult for dislocations to travel the material, so it increases hardness. Another method discovered to utilize grain structure to increase hardness was strain hardening. Strain hardening is a way to increase hardness through plastic deformation in relatively low temperatures. After metal is plastically deformed, additional dislocations are generated that results with strengthening. By understanding the properties of metals, humans traced ways for improvement in these properties.
At the end of the Bronze Age, bloomeries are started to be used to smelt iron. However, the problem with iron was its brittleness. Then metallurgists found that the high carbon content was causing increase in brittleness, so the next challenge was controlling carbon percentage of material. Later, steel became famous since it is far stronger, harder and far less brittle than iron. Its’ properties can also be modified by alloying it with elements such as manganese, chromium, nickel and tungsten. On the other hand, steel industry was still suffering from lack of automation which was making steel expensive. Then, Henry Bessemer came up with technique which makes steel production more effective and inexpensive. His technique is replaced by begun by the 1900s, by the more efficient process developed by Karl Wilhelm Siemens and his technique allowed quantities as large as 100 tons to be made in a single furnace.
By 1800, the first lathe capable of cutting accurate screw threads was designed and constructed by Henry Moseley. His lathe allowed accurate repositioning of the cutting tool in between cuts for the first time and evolved through time to increase efficiency. Another development came from Eli Whitney, it was the concept of machine tool, based on mass production in which parts were produced interchangeably which led to standardization of parts. By 1875, the standard set of machine tools had been established, like lathes, mills, grinders, shapers and saws.
With the development in the technology, new concept called numerical control (NC) and computer numerical control (CNC) started to be used for cutting. The idea was controlling the motion of the machine tool from a computer to program the instructions for the machining operation. Thanks to CNC, machines started to achieve high accuracies and unprecedented levels of repeatability producing many parts from a single program. With the rise of machine tools, cutting tools and their properties like hot hardness and wear resistance became really important. In 1910, high speed steels which could withstand increased cutting speeds and higher temperatures without softening were introduced. To improve even better, surface treatments have also been developed to extend the life of high-speed steel tools. With the time, more exotic forms of tooling had been developed like ceramic cutting tools, which are used in abrasive machining to remove small amounts of material in a highly controlled manner.
As time passed, non-mechanical methods of cutting materials have been developed such as laser cutting and electrical discharge machining. However, none have been able to replace the versatility and efficiency of mechanical cutting. It followed by the emergence of additive processes like 3D printing while still it lacks speed enough for mass production. Considering the time from past to today, we can say that cutting has been an important manufacturing process with its continuous improvement throughout the history.
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