Cold drawing is a metalworking process in which the workpiece, usually a bar or rod, is pulled from the left (tension) rather than pushed from the right (compression). The workpiece is drawn through a series of dies to reduce its cross-section and shape it. The finished product typically has a smoother surface than a hot extruded one. It is also easier to manufacture, because fewer steps are required. Cold-drawn workpieces are typically made from less expensive materials than those produced by hot extrusion, because greater reductions in the cross section would exceed the tensile strength of the material, and thus require excessive alloying to meet strength requirements.
The process begins with procuring the raw material, which in most cases is hot rolled stock. The stock is then cleaned to remove the abrasive scale, and coated with a drawing lubricant to help it slide through the dies. Depending on the end use and desired properties of the finished product, annealing may be used before, during (between draws) or after the drawing process to modify the microstructure, the mechanical properties and machinability of the material.
During the drawing process, the pointed end of the wire is fed through an opening in a mandrel and then through a die. The dies are progressively smaller and, in some cases, the drawing machine is set up to require multiple passes through each die. The final result is a reduced, shaped and profiled wire with desirable mechanical properties.
To produce a precision drawn tube, the material is usually annealed between each drawing pass to soften it and eliminate any internal stresses that have developed during the cold working. This also allows the elongation to be controlled more precisely. For more complex shapes and a higher level of precision, cluster drawing can be used. This involves a large number of wires being drawn simultaneously through the same die, and is often used in the automotive industry to produce long, thin metal strips.
Despite the obvious benefits of this type of drawing, there are some significant technical challenges. The main energy-power parameters of the process depend on such technological factors as the mechanical properties of the material being drawn, its tendency to harden during cold deformation, the friction coefficient at the metal-wire contact point, and the design parameters of the dies . Therefore, it is essential to accurately specify these parameters in the design of the drawing machinery. In order to achieve this, a program has been developed to calculate the drawing power for any given drawing route using experimental data and built-in Excel functions. The resulting dependences on the change in tensile strength and yield strength of nickel wire can be used to evaluate the suitability of a given drawing equipment. This allows the engineer to select a suitable machine for production of high-quality, accurate parts. The results of the calculation can be verified by comparing the calculated and experimental draw forces. These comparisons can be used to develop a robust simulation model that predicts the performance of the machine. Cold drawing machine