Cold drawing machine is a type of mechanical process that reduces the cross section of metal bars, rods or coils. The resulting product, called Cold-Drawn or Cold Finished, has bright and polished surface, improved mechanical properties and precise and uniform dimensional tolerances. Cold-drawn metal is used in a wide range of industrial applications. The drawing process is performed at room temperature and the pointed/reduced end of the bar or coil is drawn against a die, which grips the material and stretches it to the desired length. The result is a bright and polished, higher quality finished product with better mechanical properties than hot-rolled bars and rods.
In order to design a drawing route and to predict the energy and power parameters of the process, several computer programs are available to simulate it using the well-known simulation packages such as QForm and ABAQUS . However, these models are limited because they use constant real values for the coefficient of friction at the metal-wire contact and the half-angle of the die. To avoid such limitations, experimental studies should be carried out on a laboratory drawing machine to obtain the actual values of these parameters and to compare them with the calculated ones.
A significant problem encountered during cold-drawing is the change in tensile and yield strength, which occurs simultaneously with the reduction in cross-section. The dependences of these indicators on the change in strength characteristics for a specific alloy vary significantly, and are influenced by technological factors such as drawing speed and the half-angle of the die.
To overcome these difficulties, a drawing schedule must be designed, which aims to achieve the desired draw size with minimum strain on the workpiece. This is achieved by balancing the ratio of wall reduction to diameter reduction, and by optimizing the quality of the ID surface (e.g., by achieving high drawing-force draw values followed by hard sink draws). The Q value of the schedule is also important: higher Q values tend to “iron” or smooth the ID surface, while lower Q values roughen it.
Various factors can influence the performance of the Cold drawing machine, and one important factor is the quality of the material being drawn. Among these factors, the ductility of the material is particularly important because it determines its ability to be drawn without damage or breakage. The most ductile metals are copper, silver and gold. The ductility of steels is considerably less than that of pure copper or silver. To improve the ductility of a cold-drawn metal, it is often necessary to anneal it before further drawing processes. This can be accomplished by either rolling the steel after it has been drawn or by passing it through a special die. The latter is sometimes referred to as a soft-annealing die. This allows the steel to be stretched and manipulated further without damaging its tensile and yield strengths. This is a relatively expensive, but effective, method of improving the ductility of a metal.