The manufacturing process for DOM tubing begins with coils of steel, which are slit to the proper width for the desired tube size. The strip is cold formed and passed through an electric resistance welder which joins the edges together, under pressure, to complete the tubular shape. After testing the weld’s integrity, the tubing is cut to length for further processing.
The cold-drawing process creates a uniform, precision product with substantially improved tolerances, surface finish and tensile strength, increased hardness and good machinability. In this process, the tube is cleaned and annealed, and one end of each length is squeezed to a point so it can be gripped by the drawing mechanism. The tube is then drawn through one or more dies and over mandrels (see drawing). This reduces the diameter of the tube and thins its walls to the required dimensions in a controlled fashion to provide the qualities desired in the finished product. Metallurgically, drawing improves the tube’s concentricity, tensile strength, hardness and machinability. Close dimensional accuracy is achieved through tight control of both outside and inside diameters.