For many years classical forging was an important procedure in the production of automobiles. One small example would be the normally long, thin gearshift lever used earlier. Imagine it to be made of normal mild steel. It would always bend slightly when a gear was engaged and eventually break Forged metal does not react that way and is nevertheless lightweight. This is due to the special structure which can be seen in the above picture. The grain direction is maintained during the distortion and provides for additional stability.
How it works
Forging involved bringing steel, aluminium or copper-tin / copper-zinc alloys to an exactly defined temperature. In the case of steel from just under 800°C to over 1200°C. The requirement here is: a low carbon content and not too many alloying constituents. In the production one must imagine a red hot steel bar, cut from a long rod, which is then placed in the form. The form very much differs from the casting form. If, e.g., a crankshaft should be formed from the bar, then this form is pre-marked, half in the upper die and half in the lower die. In addition, there is also a run-off zone as an outlet for the excessive material. The casting blank is calculated a little larger than the finished article. If the distribution of the mass in the form differs substantially from that of the bar, this can still be corrected by roller milling.In the classical forge the upper die was hammered with great force onto the lower die in such a way that the material gradually filled the form. Finally, after being pressed once again, the required end product was nearly achieved. Once pressed through an accordingly precise matrix, the burr is also removed and the crankshaft is ready for the extensive finishing treatment.
Over the years, forging has changed very much. Hammer forging as described above is no longer found in the production any more. Instead of this, also large parts are pressed. This is carried out by applying pressure of up to 600 tons for passenger car crankshafts or up to 1600 tons for truck crankshafts. Through the process of several run-throughs one gradually achieves the product. With dies made of titanium, cavities and drill holes in forgings can also be provided. By interspersing with carbon the die remains undamaged in the removal process.To increase the firmness of forgings, they can be brought into the predetermined form in the rolling mill. An additional process after the relatively slow cooling to approx. 850°C, can be achieved by quenching with water. In this manner, a particular crystal structure is stored in the metal. By this process, potential brittleness which would mean risk of fracture, is removed by tempering at approx. 500°C and slower cooling. Now the forged part is ready for finishing, e.g., turning on a lathe to a precise measurement accurate to within hundredths of a millimetre. 06/08