Manufacturing of crankshaft

MANUFACTURING:
Great care must be observed in the manufacture of the crankshaft since it is the most important part of the engine. Small crankshafts are drop forged. Larger shafts are forged and machined to shape. Casting of the crankshafts allows a theoretically desirable but complicated shape with a minimum of machining and at the smallest cost. These are caste using impermanent moulds for maximum accuracy and a minimum of machining. While machining, the shaft must be properly supported between centers and special precautions should be taken to avoid springing. The journals and the crank pins are ground to exact size after turning. After this, the crankshaft is balanced. Large shafts of low speed engines are balanced statically. Crankshafts of high speed engines are balanced dynamically on special balancing machines. Most crankshafts are ground at the journals and crankpins. In some cases, grinding is followed by hand lapping with emery cloth.
Crankshaft used in high production automotive engines may be either forged or cast. Forged crankshafts are stronger than the cast crankshaft, but they are more expensive. Casting materials and techniques have improved cast crankshaft quality so that they are used in most production automotive engines. Forged crankshafts have a wide separation line where the flashings are to be ground off. Cast crankshafts have a fine line where the mold parted. The flashings and parting lines can be used for identification.

A) Forged Crankshaft:
Forged crankshafts are made from SAE 1045 or a similar type of steel. The crankshaft is formed from a hot steel billet through a series of forging dies. Each die changes the shape of the billet slightly. The crankshaft blank is finally formed with the last die. The blanks are then machined to finish the crankshaft. Forging makes a very dense, tough crankshaft with a metal’s grain structure running parallel to the principle direction of stress.
B) Cast crankshaft:
Cast automotive crankshafts may be cast in steel, nodular iron, or malleable iron. The major advantage of the casting process is that crankshaft material and machining cost are less than forging. The reason for this is that the crankshaft can be made close to the required shape and size; including all complicated counterweights. The only machining required on a carefully designed cast crankshaft is grinding bearing journal surfaces and finishing front and rear drive ends.