Metal tubing begins it's life as minerals in the earth. These materials are removed from the earth through a selective heating process called smelting. What comes out of the smelting process is called ore. Ore is the basic building blocks for all Metal Products. These ores are then alloyed (mixed into homogeneous substance) and cooled as material. In this case we are discussing "steel" which is actually a family of materials with literally hundreds of alloys from super hard and brittle tool steels to ultra mild steels which are used for steel bailing wires and other highly flexible applications. However for the purposes of this discussion let's limit the scope of our "steel" to 1018 mild steel (the most common structural alloy) the one that our DOM tubing begins as.
The 1018 is delivered to a tubing manufacturer in a coil, where it is first rolled into a tube shape with a seam. This process is sometimes done with the material very hot (hot rolled) and sometimes the steel is cold rolled. In the case of our DOM it is hot rolled. The temperature of rolling affects some of the final atributes of the metal in terms of hardness, toughness, fatigue life, heat resistance and more.
After the material is rolled, it is welded together with a process called electric resistance welding (ERW). ERW is a process where heat to form the weld is generated by the electical reistance of material vs the time and the force used to hold the materials together during welding. This process produces a seam. and creates a tube. Tubes made this way then have the seams ground or shaved, however they are not very precise in terms of outside diameter and material consistency. For this reason DOM tubes are formed slightly oversized in this stage, as a part of the pre-processing.
The ERW tubes are then loaded into a press and drawn over a mandrel and trough a series of dies which reduce the size of the outer diameter of the tube. This process insures a much more precisely round O.D. and wall thickness, while cold working the steel. The process of cold working makes the tube stronger, by aligning the molecules in a more regular pattern making them much less susceptible to inter-granular attack. The Mandrel process insures a regular I.D. and produces a perfect wall thickness free from deviations. This process creates precise, consistent high quality tubes.
The resulting DOM tubing is much stronger per weight than ERW, more consistent in strength, size and shape, and makes for a great material to weld with. It is the ideal material for use in a Roll Cage As it is specifically what is specified by the experts at Nascar. Additionally, this tubing is not specified as distinctly less safe than Chromoly in the SCORE International and BITD books of rules.