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Machining is any of various processes in which a piece of raw material is cut into a desired final shape and size by a controlled material removal process. Machining is a part of the manufacture of many metal products, but it can also be used on materials such as wood, plastic, ceramic, and composites. A person who specializes in machining is called a machinist. A room, building, or company where machining is done is called a machine shop. Machining can be a business, a hobby, or both. Much of modern day machining is carried out by computer numerical control (CNC), in which computers are used to control the movement and operation of the mills, lathes, and other cutting machines.The three principal machining processes are classified as turning, drilling and milling. Other operations falling into miscellaneous categories include grinding, shaping, planing, boring, broaching and sawing.
- Turning operations are operations that rotate the workpiece as the primary method of moving metal against the cutting tool. Lathes are
the principal machine tool used in turning.
- Drilling operations are operations in which holes are produced or refined by bringing a rotating cutter with cutting edges at the lower
extremity into contact with the workpiece. Drilling operations are done primarily in drill presses but sometimes on lathes or mills.
- Milling operations are operations in which the cutting tool rotates to bring cutting edges to bear against the workpiece. Milling machines
are the principal machine tool used in milling.
- Grinding is the final category of machining techniques. This relatively simple process involves using a stone-grinding wheel to shape or
polish metal. This technique may be used to sharpen a metal hand tool or to give metal building materials a satin finish.
- An unfinished workpiece requiring machining will need to have some material cut away to create a finished product. A finished product
would be a workpiece that meets the specifications set out for that workpiece by engineering drawings or blueprints. For example, a
workpiece may be required to have a specific outside diameter.
Machining is just a single part of a larger manufacturing process. Metal manufacturing begins with design, then proceeds through manufacturing and production. Machining may be used to shape the metal and create the object, or may serve only as a method of finishing the metal to give it the desired appearance. After machining is complete, the object must be finished and assembled before it is ready for sale.
An unfinished workpiece requiring machining will need to have some material cut away to create a finished product. A finished product would be a workpiece that meets the specifications set out for that workpiece by engineering drawings or blueprints. For example, a workpiece may be required to have a specific outside diameter. A lathe is a machine tool that can be used to create that diameter by rotating a metal workpiece, so that a cutting tool can cut metal away, creating a smooth, round surface matching the required diameter and surface finish. A drill can be used to remove metal in the shape of a cylindrical hole. Other tools that may be used for various types of metal removal are milling machines, saws, and grinding machines. Many of these same techniques are used in woodworking.
More recent, advanced machining techniques include precision CNC machining, electrical discharge machining (EDM), electro-chemical erosion, laser cutting, or water jet cutting to shape metal workpieces.
As a commercial venture, machining is generally performed in a machine shop, which consists of one or more workrooms containing major machine tools. Although a machine shop can be a stand-alone operation, many businesses maintain internal machine shops which support specialized needs of the business.
Machining requires attention to many details for a workpiece to meet the specifications set out in the engineering drawings or blueprints. Beside the obvious problems related to correct dimensions, there is the problem of achieving the correct finish or surface smoothness on the workpiece. The inferior finish found on the machined surface of a workpiece may be caused by incorrect clamping, a dull tool, or inappropriate presentation of a tool. Frequently, this poor surface finish, known as chatter, is evident by an undulating or irregular finish, and the appearance of waves on the machined surfaces of the workpiece.
The primary types of maching are: Automatic Screw Machining, CNC Machining and Swiss Machining.
- Automatic Screw Machining: An automatic screw machine is a type of lathe designed to turn metal objects instead of wood. Screw machines are primarily used to produce small objects like screws or other fasteners, though modern versions can be used to produce a wide variety of products. While early screw machines relied on manual labor, the term automatic screw machine is really a misnomer of sorts. For well over a century, all of these machines have been fully automatic. While the automatic screw machine was first used just to produce screws, today it's used to make almost all small metal components, including bolts, hardware, machine parts and even watch components. Each automatic screw machine may be automated using mechanical motors, or computer-based programming. Some units that rely on computer software programs also use robotic systems to move and finish products. These machines may feature a single or multi-spindle design. A piece of metal fits between the end of each spindle and an adjacent plate or support. As the spindle turns, it rapidly rotates the metal object. By applying various tools to the metal, these machines can cut, form or shape, and polish the metal into the desired product.
- CNC Machining: CNC machining is a manufacturing process in which pre-programmed computer software dictates the movement of factory tools and machinery. The process can be used to control a range of complex machinery, from grinders and lathes to mills and routers. With CNC machining, three-dimensional cutting tasks can be accomplished in a single set of prompts. Short for “computer numerical control,” the CNC process runs in contrast to — and thereby supersedes — the limitations of manual control, where live operators are needed to prompt and guide the commands of machining tools via levers, buttons and wheels. To the onlooker, a CNC system might resemble a regular set of computer components, but the software programs and consoles employed in CNC machining distinguish it from all other forms of computation.
- Swiss Machining: Swiss Machining, or turning, is used to make very highly precision small parts with tight tolerances that cannot be held with standard, automatic screw machining. Swiss-style lathes generally hold better tolerances on parts because the turning operations are performed within close proximity to this guide bushing. The guide bushing provides rigidity to the turned part because only a minimal amount of stock is exposed after leaving the bushing until the turning tools are engaged. With the rigidity that the guide bushing imparts on the stock, these machines are particularly well adapted for holding tight tolerances. Another payoff is the Swiss style lathe's ability to turn small-diameter parts or parts with large length-to-diameter ratios. Tool chatter typically is minimized because of the tool/guide bushing juxtaposition. There are two types of Swiss lathe machine tools. Mechanical lathes use cams, gearing systems and mechanical linkages to move the headstock and manipulate the collet and tooling. These types of machines have been replaced in many places by computer numerical control (CNC) Swiss lathes. A CNC Swiss lathe will utilize many computer-controlled components. A great number of these components can be adjusted while the machine is in operation. The advantage of a CNC Swiss lathe is that the precision of a traditional machine is maintained while the functionality of the machine is increased with the addition of a computer and its controlled components.