COLD DRAWN PROCESS
Drawing is a metalworking process which uses tensile forces to stretch metal. It is broken up into 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 as 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.
BAR
Bar, tube, and wire drawing all work upon the same principle: the starting stock drawn through a die to reduce the diameter and increase the length. Usually the die is mounted on a draw bench. The end of the work piece is reduced or pointed to get the end through the die. The end is then placed in grips and the rest of the work piece is pulled through the die. Steels, copper alloys, and aluminium alloys are common materials that are drawn.
PEELING PROCESS
Bar peeling (also known as turning), is a method of machining that is used to remove scale, surface cracks, seams and deformations etc. from hot rolled and forged blanks. Similar to cold drawn steel bars, the bar peeling process begins as a hot rolled bar from a steel mill. The hot rolled bar that comes from the mill contains surface impurities and irregularities that bar peeling is able to remove, or peel from the bar, in the machining process. The stock of bars are moved axially through a special turning machine called a bar peeler. At the peeler, a roll-clamp feeding system automatically pushes the bars one at a time through the rotating headstock of the machine, which consists of four cutting heads, each with one to three inserts that are all in contact with the bar. The inserts are used for the purpose of roughing and finishing. Peeling reduces the bar diameter by an average of 5 percent. This ensures that 99.99% of objectionable surface conditions, such as seams and decarburized layers, are effectively removed, leaving a more consistent and machinable bar. As some of the bar’s straightness may be lost in the peeling process, after the bar is peeled, it goes through a burnishing process for re-straightening. There, the bar is passed between a pair of pressure polishing rolls that reduces the diameter of the bar from a few tenths to a few thousandths to achieve final size.
Bar peeling also serves as an alternative to cold drawn steel bars. This is because when compared to conventional turning processes, bar peeling offers higher productivity and lower production costs due to the shorter throughput times. By rough machining the steel in bar form, the need for the customer to rough turn bars on a screw machine or rough turn blanks individually on chucking lathes can be efficiently eliminated. Furthermore, during the peeling process, the bars are given the requested surface quality, dimensional accuracy and roundness, which will in turn result in not only less machining at subsequent stages, but a smooth-turned, pressure-polished, mill-length steel bar for a finished product. The whole peeling process is also considerably more stable and hence, it is more resistant to vibration, which results in increased performance.
