"what is drop forging and where is its application and why is crank shaft made of drop forging "?

Answer 1

Like press forging and upset forging, drop forging is also a hot-working metal forming operation (neither of the three are done manually; only Smith forging is done manually). It is as if the ram is "dropped" i.e. forging is done by the repeated impacts of the vertical free-fall (acceleration = g) of the ram. Instead, in press forging the whole operation is performed in one single ram movement. In press forging, the ram gradually comes down vertically, contacts the work surface and then presses against it with the tremendous force generated due to pressure of the oil. There are 6 to 8 oil pumps to create this high pressure. The force exerted on the workpiece i.e. component to be forged is uniform everywhere. But, in drop forging the force is only due to the impact and there are flashes on the sides of the dies. These flashes are to be removed later.

Drop forging utilises a closed impression die (the die is such that if the two parts of the die are closed then the cavity formed inside is exactly same as the final shape to be obtained just like mould cavity; but here the metal is in solid state, it is heated below its melting point prior to forging and there in liquid state) to obtain the desired shape of the component. The desired shape is obtained by repeated hammering. The ram is called drop hammer.

Drop forging is used to manufacture the crankshafts, connecting rods, crane hook, wrench, etc.

First of all, a crankshaft cannot be produced by manual forging as there is a huge demand for this and large quantities of identical pieces have to produced. Next, look at a figure of crankshaft. It cannot be produced by upset forging in upsetting machine as there is no such die. Press forging machines have lesser force capacity. So it is used when the component is small and easily accomodated in closed impression die and final shape is easily obtained in 1 pass. Otherwise the set of dies have to be changed after each pass which "kicks out" the economy. But the crankshaft cannot be produced in 1 single pass. So drop forging is most suitable for making of crankshaft.

Answer 2

It simply means the product is heated to a high degree and then pressed into shape in a two piece mold. Drop forging is stronger due to the fact that the material is less apt to have impurities such as air pockets that casting would have. The material is also less brittle.