Cold drawing is the process of reducing the size of metal bars or rods while changing their shape. It can be used to produce complex shapes that would be difficult or impossible to manufacture by other means. The process can be performed on either solid or extruded materials, but is generally used on steel products. The result is often a more precise cross section and better surface finish than hot extruded products. The process also requires less energy, because the reduction in area is accomplished without the work hardening that occurs during reheating.
Raw Stock: Bars or coils of hot rolled rough stock are used as the starting material for cold drawing. These products have a rough and scaled surface, and can vary in size and section. They must be cleaned and coated with a lubricant to aid in the drawing process. In some cases, annealing is also required before, during (between passes) or after drawing to soften the material and modify its microstructure and mechanical properties.
Drawing Die: Various types of draw dies are available depending on the application, but all require that the material be drawn under low tension to minimize the risk of damage to the workpiece and to avoid excessive stresses in the material. The dies can be made of a variety of materials, including tungsten carbide. During the drawing process, the dies may also be heated or cooled to help prevent warping and deformation of the workpiece.
The end of the bar or rod that will enter the drawing dies is called the lead end. This end is usually sharpened to improve its ability to pass through the dies. The lead end is also usually sandblasted to remove a coating and provide a better surface for the dies to grip the workpiece.
Multi-Pass Drawing: It is common for complex rod or bar profiles to be drawn several times in order to achieve the desired shape and tolerances. This is done by letting the material draw through smaller and smaller die openings. The material is generally annealed between each drawing pass to reduce stresses and increase ductility.
To determine the energy-power parameters of the drawing process, mathematical modeling can be applied [27,28,29]. These models typically include simulation in well-proven packages such as QForm, ABAQUS or DEFORM. They can be used to calculate the drawing force and power consumption during the drawing process, and can predict the resulting tensile strength and yield strength of the material after cold working. This information is important when designing the drawing route, and the adequacy of these calculations can be evaluated by comparison with experimental results. The experimental drawing forces shown in Table 5 for nickel wire NP2 are slightly larger than those calculated with the model, but the differences are relatively small and do not exceed 4-9%. This indicates that the model is adequate for its intended use. The accuracy of the model is further improved by the addition of data on the friction coefficient and die half-angle. Cold drawing machine