Stamping is a metalworking process by which sheet metal strips are punched using a press tool which is loaded on a machine press or stamping press to form the sheet into a desired shape. This could be a single stage operation where every stroke of the press produce the desired form on the sheet metal part, or could occur through a series of stages.
The most common stamping operations are:
Bending is a common technique to process sheet metal. It is usually done by hand on a box and pan brake, or industrially on a brake press or machine brake. Typical products that are made like this are boxes such as electrical enclosures, rectangular ductwork, and some firearm parts such as the receiver of the AKM AK-47 variant.
Usually Bending has to overcome both tensile stresses as well as compressive stresses. When Bending is done, the residual stresses make it re bend or spring back to its original position, so we have to over bend the sheet metal keeping in mind the residual stresses.
Progressive stamping is a metalworking method that can encompass punching, coining, bending and several other ways of modifying metal raw material, combined with an automatic feeding system.
The feeding system pushes a strip of metal (as it unrolls from a coil) through all of the stations of a progressive stamping die. Each station performs one or more operations until a finished part is made per the requirements on the blueprint. The final station is a cutoff operation, which separates the finished part from the carrying web. The carrying web, along with metal that is punched away in previous operations, is treated as scrap metal.
The progressive stamping die is placed into a reciprocating stamping press. As the stamping press moves up, the progressive stamping die opens. When the stamping press moves down, the progressive stamping die closes. When the stamping press opens, the metal material is able to feed. As the stamping press closes, the progressive stamping die performs work on the raw material. With each stroke of the press, a completed part is removed from the die.
Sheet metal embossing is a stamping process for producing raised or sunken designs or relief in sheet metal. This process can be made by means of matched male and female roller dies, or by passing sheet or a strip of metal between rolls of the desired pattern. It is often combined with foil stamping to create a shiny, 3D effect.
The metal sheet embossing operation is commonly accomplished with a combination of heat and pressure on the sheet metal, depending on what type of embossing is required. Theoretically, with any of these procedures, the metal thickness is changed in its composition.
Metal sheet is drawn through the male and female roller dies, producing a pattern or design on the metal sheet. Depending on the roller dies used, different patterns can be produced on the metal sheet. The pressure and a combination of heat actually "irons" while raising the level of the image higher than the substrate to make it smooth. The term "impressing" refers to an image lowered into the surface of a material, in distinction to an image raised out of the surface of a material.
In most of the pressure embossing operation machines, the upper roll blocks are stationary, while the bottom roll blocks are movable. The pressure with which the bottom roll is raised is referred to as the tonnage capacity.
Embossing machines are generally sized to give 2 inches (5 cm) of strip clearance on each side of an engraved embossing roll. Many embossing machines are custom-manufactured, so there are no industry-standard widths. It is not uncommon to find embossing machines in operation producing patterns less than 6 inches (15 cm) wide all the way up to machines producing patterns 70 inches (180 cm) wide or more.
Forming, metal forming, is the metalworking process of fashioning metal parts and objects through mechanical deformation; the workpiece is reshaped without adding or removing material, and its mass remains unchanged. Forming operates on the materials science principle of plastic deformation, where the physical shape of a material is permanently deformed.
Metal forming tends to have more uniform characteristics across its sub processes than its contemporary processes, cutting and joining.
On the industrial scale, forming is characterized by:
- Very high loads and stresses required, between 50 and 2500 N/mm2 (7-360 ksi)
- Large, heavy, and expensive machinery in order to accommodate such high stresses and loads
- Production runs with many parts, to maximize the economy of production and compensate for the expense of the machine tools
Forming processes tend to be categorised by differences in effective stresses. These categories and descriptions are highly simplified, since the stresses operating at a local level in any given process are very complex and may involve many varieties of stresses operating simultaneously, or it may involve stresses which change over the course of the operation.
Compressive forming involves those processes where the primary means of plastic deformation is uni- or multiaxial compressive loading.
- Rolling, where the material is passed through a pair of rollers
- Extrusion, where the material is pushed through an orifice
- Die forming, where the material is stamped by a press around or onto a die
- Forging, where the material is shaped by localized compressive forces
- Indenting, where a tool is pressed into the workpiece
Tensile forming involves those processes where the primary means of plastic deformation is uni- or multiaxial tensile stress.
- Stretching, where a tensile load is applied along the longitudinal axis of the workpiece
- Expanding, where the circumference of a hollow body is increased by tangential loading
- Recessing, where depressions and holes are formed through tensile loading
Combined tensile and compressive forming
This category of forming processes involves those operations where the primary means of plastic deformation involves both tensile stresses and compressive loads.
- Pulling through a die
- Deep drawing
- Flange forming
- Upset bulging