Механическая обработка: процессы и эволюция

Material removal process; manufacturing process

Machining is a manufacturing process where a desired shape or part is created using the controlled removal of material, most often metal, from a larger piece of raw material by cutting. Machining is a form of subtractive manufacturing, which utilizes machine tools, in contrast to additive manufacturing (e. g. 3D printing), which uses controlled addition of material. Machining is a major process of the manufacture of many metal products, but it can also be used on other materials such as wood, plastic, ceramic, and composites. A person who specializes in machining is called a machinist. As a commercial venture, machining is generally performed in a machine shop, which consists of one or more workrooms containing primary machine tools. Although a machine shop can be a standalone operation, many businesses maintain internal machine shops or tool rooms that support their specialized needs. Much modern day machining uses computer numerical control (CNC), in which computers control the movement and operation of mills, lathes, and other cutting machines.

The precise meaning of the term machining has changed over the past one and a half centuries as technology has advanced in a number of ways. In the 18th century, the word machinist meant a person who built or repaired machines. This person's work was primarily done by hand, using processes such as the carving of wood and the writing forging and hand filing of metal. At the time, millwrights and builders of new kinds of engines (meaning, more or less, machines of any kind), such as James Watt or John Wilkinson, would fit the definition. The noun machine tool and the verb to machine (machined, machining) did not yet exist. Around the middle of the 20th century, the latter words were coined as the concepts they described evolved into widespread existence. Therefore, during the Machine Age, machining referred to (what we today might call) the "traditional" machining processes, such as turning, boring, drilling, milling, broaching, sawing, shaping, planing, abrasive cutting, reaming, and tapping. In these "traditional" or "conventional" machining processes, machine tools, such as lathes, milling machines, drill presses, or others, are used with a sharp cutting tool to remove material to achieve a desired geometry. Since the advent of new technologies in the post–World War II era, such as electrical discharge machining, electrochemical machining, electron beam machining, photochemical machining, and ultrasonic machining, the retronym "conventional machining" can be used to differentiate those classic technologies from the newer ones. Currently, "machining" without qualification usually implies the traditional machining processes. In the decades of the 2000s and 2010s, as additive manufacturing (AM) evolved beyond its earlier laboratory and rapid prototyping contexts and began to become standard throughout all phases of manufacturing, the term subtractive manufacturing became common retronymously in logical contrast with AM, covering essentially any removal processes also previously covered by the term machining. The two terms are effectively synonymous, although the long established usage of the term machining continues. This is comparable to the idea that the verb sense of contact evolved because of the proliferation of ways to contact someone (telephone, email, IM, SMS, and so on) but did not entirely replace the earlier terms such as call, talk to, or write to.

Machining is any process in which a cutting tool removes material from the workpiece (the workpiece is often called the "work"). Relative motion is required in traditional machining between the device and the work to remove material; non traditional machining processes use other methods of material removal, such as electric current in EDM (electro discharge machining). This relative motion is achieved in most machining operations by moving (by lateral rotary or lateral motion) either the tool, or the workpiece. The shape of the tool, the relative motion, and its penetration into the work, produce the desired shape of the resulting work surface. Machining operations can be broken down into traditional, and non traditional operations. Within the traditional operations, there are two categories of machining based on the shape they machine; being circular shapes that includes; turning, boring, drilling, reaming, threading and more, and various/straight shapes that includes; milling, broaching, sawing, grinding and shaping.

Turning operations involve rotating the exterior of the workpiece against a non rotating cutting tool that is moved into the workpiece. The rotation of the workpiece is the method of producing a relative motion against the tool. Lathes are the principal machine tool used in turning. Boring involves the machining of an internal surface of a hole to increase it diameter, this can be performed by either turning the workpiece on a lathe (also called internal turning), or a mill where a tool is rotated around the circumference of the hole. Drilling operations are those in which holes are produced or refined by bringing a rotating cutting tool (often using a drill bit) with cutting edges on the lower face and edge, that is brought into contact axially with the workpiece. Drilling operations can be performed on a lathe, mill or drill press, or even by hand. Threading or tapping involves the cutting of defined helix (thread) into a hole (tapping or threading), or onto shaft (threading), with a constant pitch, and specific geometry designed to accept the opposite thread and object in a turning motion to fasten items together (e. g. a nut and bolt)

Sawing aims to create smaller cut lengths of bar stock material, using a saw, or cut off machine that passing a spinning (circular saw) or linear (band saw) toothed blade against the material to cut a kerf (thickness) from the material until it is cut in two. Depedning on the material, a certain blade speed (in metres per minute, or feet per minute)measured as the linear speed of the teeth, may be required, between as low as 200 or 1000 feet per minute. Milling operations are operations where the cutting tool with cutting edges along its cylindrical face are brought against a workpiece to remove material in the profile of the spinning tools shaft and lower edge. Milling machines are the principal machine tool used in milling. Advanced CNC machines may combine lathe and milling operations. Broaching can refer to two operations, linear broaching, where a multi toothed tool is pressed through a hole to cut a desired shape (e. g. a spline, square, or hex shape) or along a surface by taking increasingly larger cuts by the increasing sized teeth of the broach; or rotary broaching, where a drafted tool is rotated in a special toolholder that rocks the tool around and offset axis, the tool and workpiece and mated together during machining in order to cut the desired shape. When performed in a lathe the workpiece and cutting tool rotate together, while the toolholder remains static in the tail stock; when milling the cutting tool stops once in contact with the workpiece, only rocking around the offset axis, with the toolholder rotating in the mill. Shaping operations are those which remove material from a workpiece through the linear movement of a non rotating cutting tool, that is pushed along the surface of a workpiece, and designed to cut flat geometry. A shaper often uses High Speed Steel tooling similar in shape and geometry to lathe tooling. Shaping is similar to turning, in a linear axis as opposed to a circular one. Shaping operations are performed using a Shaper machine, that strokes back and forth, but cuts only in one direction. A clapper box is used to raise the tool up from the work piece so that it can move backwards. Grinding operations involve the passing a fast moving/rotating abrasive material, such as stone, aluminium oxide, or diamond against a workpiece to remove material via grinding the material away using the abrasive surface of the tool.

With the recent proliferation of additive manufacturing technologies, conventional machining has been retronymously classified, in thought and language, as a subtractive manufacturing method. In narrow contexts, additive and subtractive methods may compete with each other. In the broad context of entire industries, their relationship is complementary. Each method has its advantages over the other. While additive manufacturing methods can produce very intricate prototype designs impossible to replicate by machining, strength and material selection may be limited.