Rolled Metals and Drawn Metals
Rolled metals and drawn metals are metals and alloys that are rolled into sheets, plates, strips, foils, bars, rods, or other shapes. Rolling and drawing are the two different processes used to create these shapes.
The Rolling Process
Rolling is a fabricating process in which the metal, plastic, paper, glass, etc. is passed through a pair (or pairs) of rolls. There are two types of rolling processes, flat and profile rolling.
- Flat rolling creates a product that is either classified as a sheet (typically thickness less than 3 mm, also called a strip) or plate (typically thickness more than 3 mm).
- Profile rolling creates a product that may be a round rod or other shaped bar, such as a structural section (beam, channel, joist, etc.).
Rolling is also classified according to the temperature of the metal rolled.
- Hot rolling is when the temperature of the metal is worked above its recrystallization temperature. Hot rolling is an effective way to reduce grain size in metals for improved strength and ductility.
- Cold rolling is when the temperature of the metal is worked below its recrystallization temperature. It is usually applied as a finishing process after hot rolling to enhance strength and hardness, and to ensure high surface quality.
Another process also termed as 'hot bending' is induction bending, whereby the section is heated in small sections and dragged into a required radius. Heavy plates tend to be formed using a press process, which is termed forming rather than rolling.
The Drawing Process
Drawing is a process which uses tensile forces to stretch metal. It can be divided into two types: sheet metal drawing and wire, bar, and tube drawing.
- Sheet metal drawing involves plastic deformation over a curved axis. The flow of material is controlled by a balance of pressure and lubricant. If there is an overexertion of either, the material will either wrinkle from excessive movement or become too thin and break.
- Bar, tube, and wire drawing involves the starting stock being drawn through a die to reduce diameter and increase its length. Steels, copper alloys, and aluminum alloys are common materials that are drawn.
Drawing is usually done at room temperature, thus classified a cold working process. However, it may be performed at elevated temperatures to hot work large wires, rods, or hollow sections in order to reduce forces.
Advantages of Rolling and Drawing
Rolling is ideal for materials that have high yield strength. These include metals such as steel, aluminum, and various alloys. By reducing the material’s thickness in stages, rolling allows for very low tolerances (in the order of 0.0001 in.) Surface finish is very smooth and can be reduced by the use of leveling rolls. Life expectancy for the components is also high because of residual stresses on the surface that improve fatigue life. Because rolling is fast and continuous, it is most economical for large production volumes.
Drawing is ideal for products that require significant strength and minimal weight. The process is also recommended for product geometries that are unachievable through other techniques. It is also a fast process that requires fewer operations than many other metalworking techniques, meaning favorable production rates and cost-effectiveness at high volumes. Tool construction costs are also lower than those of similar manufacturing processes.
Selecting a drawn or rolled shape can be based on a number of different factors, including design specifications, load requirements, or material types. The GlobalSpec SpecSearch Database allows the user to specify the desired product based on size dimensions such as overall thickness and overall width or outer diameter (OD), mechanical properties such as yield strength and tensile strength, or material types such as aluminum and copper.