Drawing is different from rolling in that the pressure of drawing it not transmitted through the turning action of the mill, but instead depends on force directed locally at the area of compression. This means the amount of possible drawing force is limited by the tensile strength of the material, a fact that is particularly evident when drawing thin wires. Sheet metal PROCESSES The success of forming is in relation to two things, the flow and stretch of material.
As a die torts a shape from a flat sheet of metal, there is a need for the material to move into the shape of the die, The flow of material is controlled through pressure applied to the blank and lubrication applied to the die or the blank, If the form moves too easily, wrinkles will occur in the part. To correct this, more pressure or less lubrication is applied to the blank to limit the flow of material and cause the material to stretch or thin, If too much pressure is applied, the part will become tech thin and break.
Drawing metal is the science f finding the correct balance between wrinkles and breaking to achieve a successful part. Deep drawing Main article: Deep drawing Sheet metal drawing becomes deep drawing when the workspace is drawing longer than its diameter. It is common that the workspace is also processed using other forming processes, such as piercing, ironing, necking, rolling, and beading. Bar, tube & wire Bar, tube, and wire drawing all work upon the same principle: the starting stock drawn through a die to reduce the diameter and increase the length. Usually the die is mounted on a draw bench. The end of the workspace is reduced or pointed to get the end through the die, The end is then placed in grips and the rest of the workspace is pulled through the die. [l] Steels, copper alloys, and aluminum alloys are common materials that are drawn. [4] Drawing can also he used to produce a cold formed shaped cross-section. Cold drawn cross-sections are more precise and have a better surface finish than hot extruded parts. Inexpensive materials can be used instead of expensive alloys for strength requirements, due to work hardening. 5] Bar drawing Bars or rods that are drawn cannot be coiled therefore straight-pull draw benches are used. Chain drives are used to draw workspaces up to 30 m (98 Ft). Hydraulic cylinders are used for shorter length workspaces. [l] The reduction in area is usually restricted to 20 to 50%, because greater reductions would exceed the tensile strength of the material, depending on its ductility. To achieve a certain size or shape multiple passes through progressively smaller dies or intermediate anneals may be required. [61 Tube drawing Main article: Tube drawing
Tube drawing is very similar to bar drawing, except the beginning stock is a tube. It is used to decrease the diameter, improve surface finish and improve dimensional accuracy. A mandrel may or may not be used depending on the specific process used. Wire drawing Main article: Wire drawing This technique has long been used to produce flexible metal wire by drawing the material through a series of dies of decreasing size. These dies are manufactured from a number of materials, the most common being tungsten carbide and diamond. Plastic drawing Plastic drawing, sometimes referred to as
