Chapter 19: Drawing of Rods, Wires & Tubes

Drawing of Rods, Wires & Tubes begins by distinguishing between the specific terminologies of the trade: reducing the diameter of solid stock is termed bar, rod, or wiredrawing depending on size, while hollow products are processed via tube sinking, plug drawing, or mandrel drawing. The text details the critical engineering of die geometry, including the approach angle where reduction occurs, the bearing region for frictional drag and dimensional control, and the back relief which accommodates expansion. Significant attention is given to the mechanics of deformation, utilizing the slab method and upper-bound analysis to calculate draw stress by accounting for ideal homogeneous deformation, Coulomb friction at the die interface, and redundant work caused by non-uniform shearing. The chapter explores the concept of an optimum die angle, which minimizes the total energy required by balancing the work done against friction with the redundant work of deformation. Operational factors such as lubrication regimes, cooling requirements to manage heat generation, and intermediate heat treatments like patenting for high-carbon steel wire are discussed as essential for preventing defects and maintaining material properties. The limitations of the process are analyzed through the limit of drawability, often restricted by the tensile strength of the material exiting the die, and the occurrence of defects like center burst or chevron cracking, which are predicted by specific combinations of die angle and reduction percentages. Furthermore, the text differentiates between tube drawing methods, noting that tube sinking involves no internal support leading to wall thickening, whereas the use of fixed plugs, floating plugs, or moving mandrels allows for wall thickness control and longer production lengths. Finally, the chapter addresses the formation of residual stresses, explaining how light reductions generally result in surface compressive stresses, while heavier industrial reductions typically invert this pattern to create tensile surface stresses, a phenomenon that significantly impacts the structural integrity and performance of the finished product.