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 can done with CNC, Swiss Screw Machining or Standard Turning equipment of various materials by processes that can include turning, grinding, milling and threading. Turning, grinding, milling and threading can be considered the basic processes in machining, regardless of whether the part is manufactured on Standard Turning, CNC or Swiss Machines. In addition to metal, machining process listed above; turning, grinding, milling and threading can also be performed on ceramics, plastics or various woods.
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 as a business, a hobby, or both. Much of modern day machining is carried out by computer numerical control (CNC) equipment in which computers are used to control the movement and operation of the mills, lathes, grinders, cutting or other machining processes. The three principal machining processes are classified as turning, drilling and milling. Other operations fall into miscellaneous manufacturing categories including cutting, grinding, shaping, threading, 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. Turning not only is used for cutting metal but also for threading.
Typical Turning Operation:
– 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. Properly drilled holes are required before threading operations can take place.
– Milling is a cutting process that uses a milling cutter to remove material from the surface of a work piece. The milling cutter is a rotary cutting tool, often with multiple cutting points. As opposed to drilling, where the tool is advanced along its rotation axis, the cutter in milling is usually moved perpendicular to its axis so that cutting occurs on the circumference of the cutter. As the milling cutter enters the work piece, the cutting edges (flutes or teeth) of the tool repeatedly cut into and exit from the material, shaving off chips (swarf) from the work piece with each pass. The cutting action is shear deformation; material is pushed off the work piece in tiny clumps that hang together to a greater or lesser extent (depending on the material) to form chips. This makes metal cutting somewhat different (in its mechanics) from slicing softer materials with a blade. Milling operations are a process in which the cutting tool rotates to bring cutting edges to bear against the workpiece.
Typical Milling Operation:
– 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 or super fine finish.
– An unfinished workpiece requiring machining will need to have some material cut away to create a finished product. A finished product (the manufacturing of a completed part) would be a workpiece that meets the specifications set out by engineering drawings or blueprints. For example, a workpiece may be required to have a specific outside diameter or finish. Both a lathe and a grinding machine are considered tools 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.
Drilling 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 would be milling machines, saws, and grinding machines. Many of these same manufacturing techniques are used in woodworking.
Machining is just a single part of a larger manufacturing process. Metal manufacturing begins with design, then proceeds through engineering, manufacturing of prototypes and then final 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. Secondary operations after basic machining could include drilling, grinding or threading.
More recent, advanced machining techniques include 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 machining equipment ans tools. Although a machine shop can be a stand-alone operation, many businesses maintain internal machine shops which support specialized needs of the business’s manufacturing requirements.
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.
Extremely fine finishes are performed by Centerless Grinding machines. These types of grinding machines are used when the appearance of the finished product must be extremely smooth without any machining marks.
The primary types of machining are: Automatic Screw Machining, CNC Machining and Swiss CNC or Screw Machining. Automatic Screw Machining is the most basic type screw machining. These machines just turn the part in a lathe while material is removed semi-automatically with cutting tools. They are a type of lathe designed to turn metal objects instead of wood. Automatic Screw Machining is primarily used to produce small objects like screws, fasteners or special shapes, though modern versions can be used to produce a wide variety of products. While early screw machining relied on manual labor, the term automatic screw machining is really a misnomer of sorts. For well over a century, all of these machining processes have been considered automatic or semi-automatic. While Automatic Screw Machining was first used just to produce screws, today it’s used to make almost all small metal components, including bolts, hardware, miscellaneous parts and even watch components. Each Automatic Screw Machining process 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 machining processes 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, shape or polish the metal into the desired product. As stated previously, if the required finish is too fine for any available machining process, final centerless grinding will be required.
– 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 machining processes from turning, milling, grinding and threading by 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.
Typical CNC Machine Operation:
– Swiss Machining: Swiss Machining, or turning, is used to make very highly precision small parts with tight tolerances that cannot be achieved 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, Swiss Screw Machining is particularly well suited 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 machining tools. Mechanical Swiss Machining 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. CNC Swiss Machining will utilize many computer-controlled components. A great number of these components can be adjusted while the machining operations are taking place. The advantage of a CNC Swiss Machining is that the precision of traditional machining is maintained while the functionality of the machine is increased with the addition of a computer and its controlled components.
Examples of Precision Swiss Machined Parts: