Cold working is a kind of metalworking process to create individual parts or structures which have specific shapes and mechanical properties. The main phenomenon is plastic deformation in the metal worked below metal’s recrystallization temperature. When fine dimensional tolerances and control of alloy properties is needed, cold work is used as the final work stage. Structural steel’s common ways of cold working include: cold stretching, cold drawing, cold rolling, cold twisting, notching. In most case it is applied at room temperature. Beyond the steel’s elastic capacity, the steel’s plastic deformation strength and durability has improved and its plasticity and hardness has reduced, which is also known as work hardening. It is possible to control strength and ductility by changing the volume of deformation and the speed at which the deformation is done. A smooth surface finish can be also achieved by cold working.
Cold-worked steel is widely used in the construction industry for structural and non-structural objects such as pipes, beams, joists, studs, floor coverings, built-up parts and other products, especially in the form of thin scale sheets. Some advantages of cold working process such as reproducibility, superior dimensional and surface quality controllability, no heating requirement make the process economical though high quality product.
Figure 1: Typical built-up structural sections
Cold-worked steel parts used in walls, storage sheds, flour tanks, car bodies, railroad cars, highway goods, transmission towers, power posts, drainage facilities, weapons, different types of machinery etc. These types of the cold formed steel parts are usually produced by cold roll forming, press brake or bending methods. However, in addition to these methods, some of the other commonly used cold working methods are mentioned below.
Cold Rolling: Cold rolling is a process in which a steel strip or plate is twisted or stretched between two rollers. This method is commonly used for surface finishing and dimensional consistency of high quality, which can help prevent harm to products and oxidation. To order to obtain goods with smooth surfaces and sizes, plates, strips, bars and rods are cold rolled.
Cold Forging: The metal is compressed into a die cavity that gives the required form. The deformation occurs at room temperature and adjusts the original part’s shape and size until it takes the die’s structure. The component could hit a temperature of up to 250 ° C in this final step, as the friction strain levels during deformation are very strong. It is classified as cold heading when used to create extended parts at the ends of a rope or cable, such as the heads on screws, keys, rivets, and other fasteners. It is also possible to make large sections at places other than the ends of ropes.
Extrusion: Extrusion is the method which allows the manufacturing of long straight metal parts. The profiles that can be formed differ from rigid round forms, rectangular shapes to L shapes, T shapes, tubes and many other styles. Extrusion is achieved by pressing steel through a device that is regarded as a die using either a mechanical or hydraulic press in a sealed cavity. There are ways of forward or reverse that can use open or closed dies.
Coining: Metal coining is a method of forging that can produce very delicate and complex detailing on a workpiece. Coining can be used to inspect surface performance and parts size. Metal coining for manufactured products is often a finishing process. It is used to manufacture coins, badges and other items that need correct scale and fine detail.
Peening: Peening is a method of surface manipulation used by applying a physical pressure to modify a component. It is used to reinforce a metal surface allowing it more robust to external factors like deterioration and oxidation. Hammering or blasting are two main types of peening. Both are cold-working techniques resulting metal surface deformation.
Angle Bending: A bar folder can be used to make angle bends up to 150° in sheet metal below about 1.5 mm in thickness. Such devices were controlled manually. In a mechanically or hydraulically powered press brake, bends in heavier sheet metal and more complicated bends in thinner sheets are made. The metal is twisted between interchangeable dies connected to the bed and the ram.
Tube Bending: Tube bending is a method that is used to reshape the tubes or pipes into a certain form and model. In tube bending, there are several possible processes that can be used: press bending, rotary bending and heat induction.
Roll Bending: It is possible to twist plates large sheets or rolled objects to a desired curvature on roll formation. They typically have three rolls in the shape of a circle, moving the two lower rolls and changing the upper roll to regulate the curvature degree.
Cold Roll-Forming: Roll forming is a method of rolling which requires continuous bending into a desirable profile of a long strip of sheet metal that is usually coiled steel. The strip moves between sets of rolls placed on successive stands until the required profile is achieved, each group doing only a gradual portion of the turn. Through modifying the sheets, the output of many different shapes can be adjusted to a single machine.
Seaming: Seaming is a method of metalworking in which the rim of a sheet metal is turned over to itself. Seaming connects two substances’ sides. Seams are widely used on canned goods, amusement parking cars, steel roofing (with a roof seamer) or industrial sectors in the food industry.
Squaring Shears: For slicing or squaring sheet metal, squaring shears are used. They could be powered by foot and controlled by power. Squaring shears are a static blade attached to a mattress and a handheld blade attached to a crosshead.
Piercing and Blanking: The shearing blades on the sides of a punch take the form of open, curved lines and fall. Any form of hydraulic press normally perforates and blanches. The part cut out in piercing is the waste and the remainder of the strip becomes the perfect piece of work. The punched out in blanking is the perfect piece of work and unused attributes are placed on the line.
Bar Drawing: One end of a bar is diminished and pointing, placed through a die with a slightly smaller profile than the initial bar, grasped by grips and held in tension dragging through the die the remainder of the bar. In order to restore ductility and allow continued operation, intermediate annealing may be required.
Tube Drawing: Tube drawing is the method used by pulling or drawing a larger diameter tube through a die to create a tube with a smaller diameter. Five tube modeling methods were commonly used. Such techniques include static drawing of plug, floating drawing of plug, drawing of tethered plug, drawing of rods and sinking of pipe. Usually to create seamless pipe, tube drawing is used.
Wire Drawing: Wire drawing is the same as bar drawing except it requires smaller diameters and is usually done through a series of drawing dies as a continuous process. The method of wire drawing is to point the pin, thread the pointing end through a die, and connect the end to a drawing frame.
Deep Drawing (Shell Drawing): Deep drawing is a sheet metal shaping process in which the mechanical motion of a punch radially pulls a sheet metal blank into a forming die. A flat sheet metal blank is shaped by a flexible rubber diaphragm under standardized hydrostatic pressure over a single, rigid shape defining tool part. The method contributes to scratch-free pieces regardless of tool’s sheet thickness or size, including undercuts. Low shaping tension guarantees near sections of resistance straight from the press which needs little or no secondary hand operation.
These cold-working methods are the most widely used metalworking processes in the industry and are mainly divided into 4 main topics: squeezing, bending, shearing and drawing methods. For other methods, see the references.