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Bar stock, also (colloquially) known as blank, slug or billet,is a common form of raw purified metal, used by industry to manufacture metal parts and products. Bar stock is available in a variety of extrusion shapes and lengths. The most common shapes are round (circular cross-section), rectangular, square and hexagonal or hex. A bar is characterised by an "enclosed invariant convex cross-section", meaning that pipes, angle stock and objects with varying diameter are not considered bar stock.
Bar stock is commonly processed by a sequence of sawing, turning, milling, drilling and grinding to produce a final product, often vastly different from the original stock. In some cases, the process is partially automated by specialized equipment which feeds the stock into the appropriate processing machine.
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Most metal produced by a steel mill or aluminium plant is formed (via rolling or extrusion) into long continuous strips of various size and shape. These strips are cut at regular intervals and allowed to cool, each segment becoming a piece of bar stock. A good analogy is pasta-making, in which lumps of dough are extruded into various cross-sectional shapes; cut into lengths; and then dried in that form. The cross-sectional shapes of pasta vary from simple bar or tube shapes (such as linguine or penne) to more elaborate extrusions (such as rotelle, fiori, or rotini). The same is true of metal bar stock. The most common shapes are round bar (also called rod), rectangular bar (including square bar, the special case of equal sides), and hexagonal bar (usually called hex bar for short). Tube and pipe are similar, but have hollow centers and are traditionally not called "bar" in industrial usage. (However, a product called hollow bar, essentially tube but with custom-orderable OD and ID and thus custom wall thickness, is marketed for lathe bar work which can benefit from obviation of drilling and rough boring.) Also similar in concept, but not called "bar", are the common structural shapes such as angle stock and channel stock. These are commonly available in steel and aluminum; the names "angle iron" and "channel iron" are still commonly used (informally) even though their literal namesake, wrought iron, has been replaced by steel and aluminum for most uses.
In a machine shop, bar stock and plate are often called billet, although in a rolling mill, that word refers to a piece of metal that has not yet been rolled into bar.
A machine shop typically has a storage area containing a large variety of bar stock. To create a metal component, a bar of sufficient volume is selected from storage and brought to the machining area. This piece may then be sawed, milled, drilled, turned, or ground to remove material and create the final shape. In turning, for large-diameter work (typically more than 100 millimetres (3.9 in), although there is no universal threshold), a piece of the bar is cut off using a horizontal bandsaw to create a blank for each part. The blanks are then fed into a chucking lathe (chucker) which chucks each one in turn. For smaller-diameter work, the entire length of bar stock is more often fed through the spindle of the lathe. The entire bar rotates with the spindle during the part-machining cycle. When the cycle ends and one part is done, the chuck opens, the bar is pulled or pushed forward ("fed") by any of various automatic means, the chuck closes, and the next cycle begins. The last step of the cycle is to cut off the machined part from the bar, which is called "parting it off" and is achieved with a "cutoff" or "part-off" tool, a tool bit that grooves the bar all the way down to the centreline, causing the part to fall off. Then the cycle repeats.
The not-yet-cut bar protruding from the back of the spindle, rotating quickly, can present a safety hazard if it is sticking out too far and unconstrained from bending. Thus sometimes long bars must be sawn into shorter bars before being fed as "bar work" (which is the term for such work).
CNC lathes and screw machines have accessories called "bar feeders", which hold, guide, and feed the bar as commanded by the CNC control. More advanced machines may have a "bar loader" which holds multiple bars and feeds them one at a time into the bar feeder. Bar loaders are like magazines for part blanks (or pallets for milling work) in that they allow lights-out machining. The bar loader is filled with bars (or the magazine or pallet with part blanks) during working hours, and then it runs during the night unattended. Given that there is no human around to detect if something went wrong and the machine should stop, there are various kinds of sensors that are used to detect this, such as load meters, infrared beams, and, in recent years, webcams, which are placed inside the machine tool's enclosure and allow remote viewing of the cutting action.
Bar stock is widely used in many industries and can be seen in many different industrial processes. These processes include forging, extrusion, machining, and many more. In forging, billets are heated to high temperatures before a press pushes the workpiece into the shape on the die. These presses operate at very high forces to make the desired changes to the product. Extrusion uses rollers that push the heated bar stock through a set of dies which will determine the shape of the workpiece. Machining is a subtractive process that utilizes bar stock and various cutters and tools to make intricate details that are not possible through other processes.
To stock every possible size of bar stock (every possible fraction of a millimetre or inch in diameter or thickness) is impossible. Thus, bar stock is stocked by metals supply houses in various standard sizes, arrayed in discrete steps. For example, round bar with diameters of even millimetres (or in the US, on the eighths of an inch) can usually be ordered from standing stock. Bar diameters of nonstandard sizes can also be obtained, but only as a separate mill run from the rolling mill. Thus they are much more expensive than the standard sizes, can take much longer delivery time, and are not desirable as inventory for the supply house or the machine shop (because the chance of selling or using any particular custom size is slim).
Sometimes it is necessary that the bar not be very much larger than the intended part, because the metallurgical properties of some metal alloys in some finishing processes may vary by how far inside the bar the metal lies. Thus an engineering drawing will specify a certain size (or a maximum size) that the bar may start out as. These specs face the aforementioned limitation of stocking sizes versus custom mill runs; standard sizes are used wherever possible to avoid wasted expense and needless delays.
A drill rod is tool steel round stock ground to a tight tolerance diameter; it is usually ± 0.0005 in (0.0127 mm). In the UK the name "silver steel" is often synonymous and sometimes hyponymous. Its origin was in reference to the shiny ground appearance (not to any silver alloying content). Drill rod diameters range from 0.0135 to 1.5 in (0.34 to 38.10 mm); in the United States diameters smaller than 27⁄64th of an inch (11 mm) are made in letter drill sizes and number drill sizes, in addition to fractional sizes. Lengths are usually one or three feet (0.3048 or 0.9144 m). It is commonly used to make drill bits, taps, reamers, punches, dowel pins, and shafts. Note that the numbered sizes are different from the drill numbered sizes starting at 52. These sizes are:[ citation needed ]
Drill blanks have an undersize tolerance of +0/−0.0002 in (0.00508 mm), while reamer blanks have an oversize tolerance of −0/+00.0002 in (0.00508 mm).
Some mills also sell square stock that is held to the same tolerances under the name "drill rod".
Commonly available material grades in the U.S. are A2, D2, M2, M42, O1, S7, W1, and high speed steel (including M2/M7).
Ground flat stock is annealed steel that has been ground to close tolerances (compare to drill rod). There are four types of materials available: O-1 tool steel, A-2 tool steel, A-6 tool steel, and 1018 steel (low-carbon or low-carb steel). Lengths are either 18 or 36 in (457 or 914 mm) long, various widths up to 16 in (406 mm) are available, and thicknesses range from 1⁄64 to 2.875 in (0.40 to 73.03 mm).
Some geometrical sizes are known as gauge plate.
Taps and dies are tools used to create purpose screw threads, which is called threading. Many are cutting tools; others are forming tools. A tap is used to cut or form the female portion of the mating pair. A die is used to cut or form the male portion of the mating pair. The process of cutting or forming threads using a tap is called tapping, whereas the process using a die is called threading.
A machinist is a tradesperson or trained professional, who not only operates machine tools, but has the knowledge of tooling and materials required to create set ups on machine tools including, but not limited to milling machines, grinders, lathes, and drilling machines.
Drill bits are cutting tools used to remove material to create holes, almost always of circular cross-section. Drill bits come in many sizes and shapes and can create different kinds of holes in many different materials. In order to create holes drill bits are usually attached to a drill, which powers them to cut through the workpiece, typically by rotation. The drill will grasp the upper end of a bit called the shank in the chuck.
Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed through a die of the desired cross-section. The two main advantages of this process over other manufacturing processes are its ability to create very complex cross-sections, and to work materials that are brittle, because the material only encounters compressive and shear stresses. It also forms parts with an excellent surface finish and gives considerable freedom of form in the design process.
A reamer is a type of rotary cutting tool used in metalworking. Precision reamers are designed to enlarge the size of a previously formed hole by a small amount but with a high degree of accuracy to leave smooth sides. There are also non-precision reamers which are used for more basic enlargement of holes or for removing burrs. The process of enlarging the hole is called reaming. There are many different types of reamer and they may be designed for use as a hand tool or in a machine tool, such as a milling machine or drill press.
A mandrel, mandril, or arbor is:
A collet is a subtype of chuck that forms a collar around an object to be held and exerts a strong clamping force on the object when it is tightened, usually by means of a tapered outer collar. It may be used to hold a workpiece or a tool.
A machine taper is a system for securing cutting tools or toolholders in the spindle of a machine tool or power tool. A male member of conical form fits into the female socket, which has a matching taper of equal angle.
Drawing is a metalworking process which uses tensile forces to stretch metal, glass, or plastic. As the metal is drawn (pulled), it stretches thinner, into a desired shape and thickness. Drawing is classified in two types: sheet metal drawing and wire, bar, and tube drawing. The specific definition for sheet metal drawing is that it involves plastic deformation over a curved axis. For wire, bar, and tube drawing, the starting stock is drawn through a die to reduce its diameter and increase its length. Drawing is usually done at room temperature, thus classified a cold working process, however it may be performed at elevated temperatures to hot work large wires, rods or hollow sections in order to reduce forces.
Turning is a machining process in which a cutting tool, typically a non-rotary tool bit, describes a helix toolpath by moving more or less linearly while the workpiece rotates.
The shank is the end of a drill bit grasped by the chuck of a drill. The cutting edges of the drill bit contact the workpiece, and are connected via the shaft with the shank, which fits into the chuck. In many cases a general-purpose arrangement is used, such as a bit with cylindrical shaft and shank in a three-jaw chuck which grips a cylindrical shank tightly. Different shank and chuck combination can deliver improved performance, such as allowing higher torque, greater centering accuracy, or moving the bit independently of the chuck, with a hammer action.
Milling cutters are cutting tools typically used in milling machines or machining centres to perform milling operations. They remove material by their movement within the machine or directly from the cutter's shape.
A metal lathe or metalworking lathe is a large class of lathes designed for precisely machining relatively hard materials. They were originally designed to machine metals; however, with the advent of plastics and other materials, and with their inherent versatility, they are used in a wide range of applications, and a broad range of materials. In machining jargon, where the larger context is already understood, they are usually simply called lathes, or else referred to by more-specific subtype names. These rigid machine tools remove material from a rotating workpiece via the movements of various cutting tools, such as tool bits and drill bits.
A dowel is a cylindrical rod, usually made from wood, plastic, or metal. In its original manufactured form, a dowel is called a dowel rod. Dowel rods are often cut into short lengths called dowel pins. Dowels are commonly used as structural reinforcements in cabinet making and in numerous other applications, including:
In machining, boring is the process of enlarging a hole that has already been drilled by means of a single-point cutting tool, such as in boring a gun barrel or an engine cylinder. Boring is used to achieve greater accuracy of the diameter of a hole, and can be used to cut a tapered hole. Boring can be viewed as the internal-diameter counterpart to turning, which cuts external diameters.
In metalworking, rolling is a metal forming process in which metal stock is passed through one or more pairs of rolls to reduce the thickness, to make the thickness uniform, and/or to impart a desired mechanical property. The concept is similar to the rolling of dough. Rolling is classified according to the temperature of the metal rolled. If the temperature of the metal is above its recrystallization temperature, then the process is known as hot rolling. If the temperature of the metal is below its recrystallization temperature, the process is known as cold rolling. In terms of usage, hot rolling processes more tonnage than any other manufacturing process, and cold rolling processes the most tonnage out of all cold working processes. Roll stands holding pairs of rolls are grouped together into rolling mills that can quickly process metal, typically steel, into products such as structural steel, bar stock, and rails. Most steel mills have rolling mill divisions that convert the semi-finished casting products into finished products.
Semi-finished casting products are intermediate castings produced in a steel mill that need further processing before being finished goods. There are four types: ingots, blooms, billets, and slabs.
Grinding is an abrasive machining process that uses a grinding wheel as the cutting tool.
Threading is the process of creating a screw thread. More screw threads are produced each year than any other machine element. There are many methods of generating threads, including subtractive methods ; deformative or transformative methods ; additive methods ; or combinations thereof.
In metalworking and woodworking, an automatic lathe is a lathe with an automatically controlled cutting process. Automatic lathes were first developed in the 1870s and were mechanically controlled. From the advent of NC and CNC in the 1950s, the term automatic lathe has generally been used for only mechanically controlled lathes, although some manufacturers market Swiss-type CNC lathes as 'automatic'.