Stamping
The stamping is a technique of manufacture making it possible to obtain, starting from a plane and thin sheet, an object whose form is not developable. The sheet outline is called “blank”, it is the raw material which was not pressed yet. The temperature of deformation is in and melting point of material.
Stamping is a manufactoring process very much used in auto industry, the electric household appliances, etc
The principle is founded on the plastic Déformation of the material (in general a metal), deformation consisting of a lengthening or a local hammering of sheet to obtain the desired form. In consequence of the total conservation (at least approximate) of the volume of material, the zones of stretching undergo a thinning (which must remain limited to avoid the rupture) and the zones of hammering (compression) undergo a combination of thickening and crumpling: one in general seeks to avoid this last effect, but it can never miss completely and one thus seeks to move it in parts of sheet who will be eliminated in the continuation from the manufacturing process.
Stamping is practiced using flanging presses strong power provided with tools special which comprise, in the principle, three parts:
- a matrix, in hollow, marries the form external of the part
- a punch, in relief, wife her form interior by holding the thickness of the sheet
- a blank holder surrounds the punch, applies against the circumference of the matrix and is used to wedge sheet during the application of the punch.
- of the snap rings is sometimes used to slow down the slip of the sheet (retained steel)
The entry of the matrix must be very round and polished to avoid any tear of metal and to optimize the behavior of the zones of Rétreint - no angle must be sharp and a perfect surface quality is paramount: the development of such tools is an operation very specialized and very expensive in particular on the parts of aspect (example: several months for the outside of a door, cap etc…)
The typical operation of stamping (double-effect):
- Phase 1: punch and blank holder are raised. The sheet, lubricated beforehand, is posed on the matrix.
- Phase 2: the blank holder is descended and comes to apply a well defined pressure, in order to maintain sheet all while enabling him to creep.
- Phase 3: the punch descends and deforms sheet of way plastic by applying it against the bottom of the matrix.
- Phase 4: the punch and the blank holder are raised: the part preserves the acquired form (limit elastic exceeded).
- Phase 5: one carries out the “routing” of the part, i.e. with the elimination of the parts become useless. (primarily parts seized by the blank holder).
According to the depth or the shape of the part, several master keys in different tools can be necessary.
Stamping can also be practiced by other processes, like the application of a fluid to high pressure (see Hydroformage) which plates sheet against the matrix. This high pressure can be obtained using hydraulic or explosive devices.
On certain presses, the matrix can move (stamping simple-effect). In the same way a fixed matrix can comprise moving parts (triple-effect etc).
The choice of the process depends on the type of press available in workshop (clamping force, dimension), on the form of the part, material (standard steel, high-strength steel, aluminum, etc), of the full number of operations to obtain the finished part, etc
The formability of steel is improved while heating slightly but one should not modify the phase (state atomic) if not the mechanical properties are modified (resistance, hardness, etc). In general, stamping is an operation of cold forming, the matrix being generally cooled to limit the heating related to the contact.
Stamping entirely does not plasticize the part, an elastic study of return is necessary to ensure the final assembly.
the operations of stamping pose large problems of friction, wear and lubrication . One will find information on this subject in Wikilivre devoted to the tribology and more especially in the chapter devoted to the practical applications.
Stamping
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