Cold roll forming is a metallurgical process in which pressure is applied by a series of rollers in order to bend or form metal pieces. The end result of this cold working process is the lengthening and thinning of metal blanks through plastic deformation, the effects of which are permanent.
Unlike many metal forming processes, cold roll forming requires the raw materials be kept at room temperature. While some are chilled, most cold rolled pieces are produced at ambient temperature as it is well below the re-crystallization of most metals. Lightweight or soft metals such as tin, zinc, copper, titanium and lead are best suited to this manufacturing process, though steel, aluminum, stainless steel and other alloys are commonly cold rolled as well. Smooth surfaces and accurate dimensions as well as tighter tolerances and gains on strength as great as 20% make cold roll forming a popular option. Although cold forming offers several benefits over hot rolling processes, the thickness of room temperature work pieces cannot be reduced as much in a single pass through the rollers as can heated materials. Nevertheless, industries such as automotive, heating and cooling, ventilation, transport, rail, marine, building and construction among several others utilize strengthened or hardened sheets, plates, tubes and rods among other finished components.
Sheets, strips and plates come in various conditions, by which cold rolling processes are designated. Full-hard rolling reduces thickness by 50% and is the most extreme option available, it can be bent only 45° before breaking. Half-hard products can be bent to up to 90° and quarter hard can be bent back on itself along the grain boundary without breaking. Skin rolling or skin-pass offers the least amount of reduction, often as little as 0.5 to 1%. Commonly used as a finishing process, this produces a smooth surface with uniform thickness without reducing ductility. Once the desired thickness has been determined, the actual equipment and machine configurations required for production of a part or shape may vary considerably. Some of the most popular cold roll forming techniques are flat rolling, ring rolling and roll bending. Flat rolling produces extremely level sheets and panels with rectangular cross-sections. The material is fed between two working rollers which rotate in opposite directions. The metal form is pulled into the gap between the rollers. The slit is smaller than the thickness of the original materials thereby causing deformation and elongating the piece. Ring rolling is specialized to increase the diameter of a ring while reducing wall thickness. The pre-form is placed on an idler roll which it rotates around during processing. A driven roll presses the ring from the outside. Finally, roll bending is a cross between ring and flat rolling in that it results in a cylindrical shape or curved sheet used most often for tubing and piping applications. Considerations for all cold roll formed products include material thickness, width and diameter as well as strength and hardening necessary for structural and mechanical stability with regards for intended use.
