Cold forging
Cold forging is a term for forming processes that are generally assigned to pressure forming and here in particular to the subgroup pressing (DIN 8583), i.e. processes of massive forming . The special thing about cold forging is that the raw parts for the workpiece to be produced are not heated before the forming, but are placed in the tool at room temperature. During the forming process, the components can reach temperatures of several 100 ° C. The forming itself is carried out in one or more process stages. In general, however, cold forging is understood to mean cold extrusion (see extrusion ).
economics
Because of the high investments in the presses to be used for cold forging and for the workpiece-specific tools compared to the cost of the workpiece, this manufacturing process is particularly suitable for the production of mass-produced parts such as screws, sleeves and molded parts, especially for the automotive industry and fastening technology. Classic applications are also the minting of coins and the production of bullet sleeves and sockets for socket sets .
Compared to hot massive forming ( forging ), the shape and size accuracy of the formed workpieces is considerably greater, as there is no shrinkage during cooling and no scaling. Because the materials solidify in the cold state during pressing ( cold forming ), higher quality steel grades can be replaced with cold massive forming. Due to the limited deformation capacity of the materials and the high contact stresses between the workpiece and the tool, the area of application of cold forging is limited to low-alloy steels and various non-ferrous metals (especially aluminum and copper ) as well as to predominantly rotationally symmetrical shapes, as the stress distribution can be better controlled here.
The advantage over metal-cutting processes ( turning , milling , drilling ) is on the one hand the material savings and on the other hand in the processing speed. Compared to hot forging , there are also energy savings (if intermediate annealing / recrystallization annealing can be dispensed with), the surface quality and, in particular, the dimensional accuracy, which means that subsequent processing steps can be reduced or, in appropriate cases, completely eliminated.
Due to the economic advantages, the share of cold forging in the total volume of manufacturing processes is growing.
Procedure
In massive forming, the workpieces are deformed in a press between a press punch (also called a mandrel or Pfaffe when embossing ) and a die (also known as a press sleeve ) with considerable pressure. Cold starting material requires higher pressing forces than warm.
If the die and punch are appropriately shaped, the material is forced to flow into the space between the die and punch. If the die contains a taper, one speaks of reducing the workpiece. When reducing, the diameter of the workpiece decreases, which at the same time leads to its elongation. If there is a cavity between the inside of the die and the punch, into which the material flows through the pressing, a cup-shaped bulge is created in the workpiece corresponding to the shape of the punch. One speaks here of the cup when a stamp penetrates the starting material. Depending on the direction of flow of the material, one speaks of forward or backward extrusion. A special feature is cross extrusion, in which the material flows mainly across or at an angle to the direction of movement of the punch.
literature
- Handbook of Forming Technology, Berlin / New York 1996
- Industry association for massive forming, cold massive forming: precision in series . Massive Forming Information Series, October 2012, ISBN 978-3-928726-29-0