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Drawing is a
manufacturing Manufacturing is the creation or production of goods with the help of equipment, labor, machines, tools, and chemical or biological processing or formulation. It is the essence of the secondary sector of the economy. The term may refer ...
process that uses tensile forces to elongate
metal A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, electricity and thermal conductivity, heat relatively well. These properties are all associated wit ...
,
glass Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...
, or
plastic Plastics are a wide range of synthetic polymers, synthetic or Semisynthesis, semisynthetic materials composed primarily of Polymer, polymers. Their defining characteristic, Plasticity (physics), plasticity, allows them to be Injection moulding ...
. As the material is drawn (pulled), it stretches and becomes thinner, achieving a desired shape and thickness. Drawing is classified into two types: sheet metal drawing and
wire file:Sample cross-section of high tension power (pylon) line.jpg, Overhead power cabling. The conductor consists of seven strands of steel (centre, high tensile strength), surrounded by four outer layers of aluminium (high conductivity). Sample d ...
, bar, and
tube Tube or tubes may refer to: * ''Tube'' (2003 film), a 2003 Korean film * "Tubes" (Peter Dale), performer on the Soccer AM television show * Tube (band), a Japanese rock band * Tube & Berger, the alias of dance/electronica producers Arndt Rör ...
drawing. Sheet metal drawing is defined as a 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 performed at room temperature, thus classified as a cold working process; however, drawing may also be performed at higher temperatures to hot work large wires, rods, or hollow tubes in order to reduce forces.Degarmo, p. 432.Kalpakjian, pp. 415–419. Drawing differs from
rolling Rolling is a Motion (physics)#Types of motion, type of motion that combines rotation (commonly, of an Axial symmetry, axially symmetric object) and Translation (geometry), translation of that object with respect to a surface (either one or the ot ...
in that
pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and eve ...
is not applied by the turning action of a mill but instead depends on force applied locally near the area of compression. This means the maximal drawing force is limited by the tensile strength of the material, a fact particularly evident when drawing thin wires. The starting point of cold drawing is hot-rolled stock of a suitable size.


Metal

Successful drawing depends on the flow and stretch of the material. Steels, copper alloys, and aluminium alloys are commonly drawn metals. In sheet metal drawing, as a die forms a shape from a flat sheet of metal (the "blank"), the material is forced to move and conform to the die. The flow of material is controlled through pressure applied to the blank and lubrication applied to the die or the blank. If the form moves too easily, wrinkles will occur in the part. To correct this, more pressure or less lubrication is applied to the blank to limit the flow of material and cause the material to stretch or set thin. If too much pressure is applied, the part will become too thin and break. Drawing metal requires finding the correct balance between wrinkles and breaking to achieve a successful part. Sheet metal drawing becomes deep drawing when the workpiece is longer than its diameter. It is common that the workpiece is also processed using other forming processes, such as piercing, ironing, necking,
rolling Rolling is a Motion (physics)#Types of motion, type of motion that combines rotation (commonly, of an Axial symmetry, axially symmetric object) and Translation (geometry), translation of that object with respect to a surface (either one or the ot ...
, and beading. In shallow drawing, the depth of drawing is less than the smallest dimension of the hole. Bar, tube, and wire drawing all work upon the same principle: the starting stock is drawn through a die to reduce its diameter and increase its length. Usually, the die is mounted on a draw bench. The starting end of the workpiece is narrowed or pointed to get the end through the die. The end is then placed in grips which pull the rest of the workpiece through the die. Drawing can also be used to cold form a shaped cross-section. Cold drawn cross-sections are more precise and have a better surface finish than hot extruded parts. Inexpensive materials can be used instead of expensive alloys for strength requirements, due to work hardening. Bars or rods that are drawn cannot be coiled; therefore, straight-pull draw benches are used. Chain drives are used to draw workpieces up to . Hydraulic cylinders are used for shorter length workpieces. The reduction in area is usually restricted to between 20% and 50%, because greater reductions would exceed the tensile strength of the material, depending on its
ductility Ductility refers to the ability of a material to sustain significant plastic Deformation (engineering), deformation before fracture. Plastic deformation is the permanent distortion of a material under applied stress, as opposed to elastic def ...
. To achieve a certain size or shape, multiple passes through progressively smaller dies and intermediate anneals may be required. Tube drawing is very similar to bar drawing, except the beginning stock is a tube. It is used to decrease the diameter, improve surface finish, and improve dimensional accuracy. A mandrel may or may not be used depending on the specific process used. A floating plug may also be inserted into the inside diameter of the tube to control the wall thickness. Wire drawing has long been used to produce flexible
metal A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, electricity and thermal conductivity, heat relatively well. These properties are all associated wit ...
wire file:Sample cross-section of high tension power (pylon) line.jpg, Overhead power cabling. The conductor consists of seven strands of steel (centre, high tensile strength), surrounded by four outer layers of aluminium (high conductivity). Sample d ...
by drawing the material through a series of dies of decreasing size. These dies are manufactured from a number of materials, the most common being tungsten carbide and
diamond Diamond is a Allotropes of carbon, solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Diamond is tasteless, odourless, strong, brittle solid, colourless in pure form, a poor conductor of e ...
. The cold drawing process for steel bars and wire is as follows: # Tube lubrication: The surface of the bar or tube is coated with a drawing lubricant such as phosphate or oil to aid cold drawing. # Push pointing: Several inches of the lead ends of the bar or tube are reduced in size by
swaging Swaging () is a forging process in which the dimensions of an item are altered using Die (manufacturing), dies into which the item is forced. Swaging is usually a cold working process, but also may be hot working, hot worked. The term swage ma ...
or extruding so that it can pass freely through the drawing die. This is done because the die opening is always smaller in size than the original bar or coil section. # Cold drawing, process drawing: In this process, the material is drawn at room temperature. The reduced end of the bar or coil, which is smaller than the die opening, is passed through the die where it enters a gripping device of the drawing machine. The drawing machine pulls ("draws") the remaining unreduced section of the bar or coil through the die. The die reduces the cross section of the bar or coil, shapes its profile, and increases its length. # Finished product: The drawn product, which is referred to as "cold drawn" or "cold finished", exhibits a bright or polished finish, increased mechanical properties, improved machining characteristics, and precise and uniform dimensional tolerances. # Multi-pass drawing: The cold drawing of complex shapes or profiles may involve the workpiece being drawn multiple times through progressively smaller die openings in order to produce the desired shape and tolerances. Material is generally annealed between each drawing pass to increase its
ductility Ductility refers to the ability of a material to sustain significant plastic Deformation (engineering), deformation before fracture. Plastic deformation is the permanent distortion of a material under applied stress, as opposed to elastic def ...
and remove internal stresses produced during the cold working. # Annealing: This is a thermal treatment generally used to soften the material being drawn; to modify the microstructure, the mechanical properties, and the machining characteristics of the steel; and to remove internal stresses in the product. Depending on the material and desired final characteristics, annealing may be used before, during (between passes), or after the cold drawing operation.


Glass

Similar drawing processes are applied in glassblowing and in making glass
optical fiber An optical fiber, or optical fibre, is a flexible glass or plastic fiber that can transmit light from one end to the other. Such fibers find wide usage in fiber-optic communications, where they permit transmission over longer distances and at ...
.


Plastics

Plastic drawing, sometimes referred to as ''cold drawing'', is the same process as used on metal bars, applied to plastics.Degarmo, p. 461. Plastic drawing is primarily used in manufacturing
plastic Plastics are a wide range of synthetic polymers, synthetic or Semisynthesis, semisynthetic materials composed primarily of Polymer, polymers. Their defining characteristic, Plasticity (physics), plasticity, allows them to be Injection moulding ...
fiber Fiber (spelled fibre in British English; from ) is a natural or artificial substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials. The strongest engineering materials often inco ...
s. The process was discovered by Julian W. Hill in 1930 while trying to make fibers from an early
polyester Polyester is a category of polymers that contain one or two ester linkages in every repeat unit of their main chain. As a specific material, it most commonly refers to a type called polyethylene terephthalate (PET). Polyesters include some natura ...
. It is performed after the material has been "spun" into filaments; by extruding the polymer melt through pores of a spinneret. During this process, the individual polymer chains tend to somewhat align because of viscous flow. These filaments still have an
amorphous In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid) is a solid that lacks the long-range order that is a characteristic of a crystal. The terms "glass" and "glassy solid" are sometimes used synonymousl ...
structure, so they are drawn to align the fibers further, thus increasing crystallinity,
tensile strength Ultimate tensile strength (also called UTS, tensile strength, TS, ultimate strength or F_\text in notation) is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials, the ultimate ...
, and
stiffness Stiffness is the extent to which an object resists deformation in response to an applied force. The complementary concept is flexibility or pliability: the more flexible an object is, the less stiff it is. Calculations The stiffness, k, of a ...
. This is done on a draw twister machine.. For
nylon Nylon is a family of synthetic polymers characterised by amide linkages, typically connecting aliphatic or Polyamide#Classification, semi-aromatic groups. Nylons are generally brownish in color and can possess a soft texture, with some varieti ...
, the fiber is stretched to four times its spun length. The crystals formed during drawing are held together by hydrogen bonds between the
amide In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a chemical compound, compound with the general formula , where R, R', and R″ represent any group, typically organyl functional group, groups or hydrogen at ...
hydrogens of one chain and the carbonyl oxygens of another chain. Polyethylene terephthalate (PET) sheet is drawn in two dimensions to make BoPET (biaxially-oriented polyethylene terephthalate) with improved mechanical properties.


See also

*
Extrusion Extrusion is a process used to create objects of a fixed cross section (geometry), cross-sectional profile by pushing material through a Die (manufacturing), die of the desired cross-section. Its two main advantages over other manufacturing pro ...


References


Further reading

* . * {{Metalworking navbox, formopen Cables Plastics industry Metal forming Product design fr:Extrusion de:Tiefziehen de:Kaltumformung