Drop forging is the most common metal forging method, and it can be employed in hot forging, warm forging, and cold forging, as well as in both open die forging and closed die forging.This is a modern form of smith forging; the manual force of the blacksmith wielding a hammer has been replaced by a mechanized hardened alloy steel hammer fitted with a specially shaped die.
Forging strengthens metal for its particular use by causing the internal grain of the metal to deform to follow the shape of the part. Most metals can be drop forged, but among the most common are high alloy steel, naval brass, carbon steel, aluminum, alloy metals, stainless steel, copper, nickel, tool steel and titanium.
Drop forgings are used particularly often by industries such as aerospace, national defense, automotive, agriculture, construction, hardware, mining, material handling and manufacturing. Products produced by drop forging include crank shafts, stub-axles, gears, chains, hooks, shackles, bolts, rods, medical implants, suspensions and general industrial equipment. Many hand tools have “Drop Forged” boldly imprinted on them to indicate their added strength and durability as a result of the forging process.
The drop forging process starts with pre-formed and often heated metal workpieces that are placed on a die. The forging dies are made of hardened alloy steel that are made in halves—one is attached to the rising and falling block, or ram, while the other is attached to the stationary anvil on the bottom.
The hammer die strikes the metal in order to force it to take the shape of the die(s), using singular or repeated blows. Many drop forging processes involve moving the workpiece through a sequence of die cavities and strikes to gradually change its shape.
In closed die forging some metal juts out at the parting lines of the dies. This flash material must be removed by machining. Drop hammer forges use hydraulic, pneumatic or mechanical force to raise the hammer and then assist gravity in accelerating it into the workpiece, producing a striking force between 11,000 and 425,000 pounds. Drop forging produces parts that exhibit superior load bearing strength, good response to heat treatment, good internal integrity, great strength-to-weight ratio and a high degree of reliability.