Unit 4 Forging and Die

4.1 Introduction

Forging is a process in which the workpiece is shaped by compressive forces applied through various dies and tools. It is one of the oldest metalworking operations, dating back at least to 4000 B.C.—perhaps as far back as 8000 B.C. Forging was first used to make jewelry, coins, and various implements by hammering metal with tools made of stone.

Simple forging operations can be performed with a heavy hand hammer and an anvil, as was traditionally done by blacksmiths. Most forgings, however, require a set of dies and such equipment as a press or a forging hammer. Unlike rolling operations, which generally produce continuous plates, sheets, strip, or various structural cross-sections, forging operations produce discrete parts.

Typical forged products are bolts and rivets, connecting rods, shafts for turbines, gears, hand tools, and structural components for machinery, aircraft, railroads, and a variety of other transportation equipment.

Metal flow and grain structure can be controlled, so forged parts have good strength and toughness, they can be used reliably for highly stressed and critical applications. Forging may be done at room temperature (cold forging) or at elevated temperatures (warm or hot forging).[1]

Because of the higher strength of the material, cold forging requires greater forces, and the workpiece materials must have sufficient ductility at room temperature. Cold-forged parts have good surface finish and dimensional accuracy. Hot forging requires smaller forces, but it produces lower dimensional accuracy and surface finish than cold-forged parts.

Forgings generally require additional finishing operations, such as heat treatment, to modify properties, and then machining to obtain accurate finished dimensions. These operations can be minimized by precision forging, which is an important example of the trend toward net-shape or near-net shape forming processes. This trend significantly reduces the number of operations required, and hence the manufacturing cost to make the final product.