A large number of items used in daily life require metal parts, which are forged by the manufacturer. Traditional metal forging was a labor intensive process in which the piece was formed by hand to meet the needs of the project. Modern metalworking facilities have a variety of types of equipment to use in the process, and there are four common mechanized metalworking techniques: drop, press, roll, and cold forging.
Open forging is what comes to mind when most people think of forging. It involves heating metal to a workable temperature and working with it directly on the anvil, hammering it into shape using various tools. This requires a high degree of technical skill and strength. This technique is still used to manufacture fine art pieces, horse shoes, and customized metal components.
Drop forging is a technique for forcing metal into a die by striking it with a hammer. This has been around for centuries, with blacksmiths making dies, heating the metal, and then pounding the metal into the die, creating the desired shape. Mechanized hammers are used in manufacturing facilities to keep the production line quickly moving, and some plants use a set of two dies which are hammered together, forcing extra metal out the sides of the die while forming the molded shape. This technique is often used for automobile components.
Press forging uses pressure to force metal into a die. Usually this involves putting a piece of heated metal into a fixed die and then slowly compressing it from above with the other half of the die. The metal will slowly deform into the shape of the die, and then will resolve into the desired shape. This technique is commonly used for tools.
Roll forging is accomplished by compressing a piece of heated metal between two rollers. The rollers have a die embedded in them, and as they compress the metal, they will force it to conform to the die. This is a popular technique because it can be made continuous with the use of multiple rollers and dies. This is a type of draw forging, because the piece is slowly drawn out into the needed shape.
Cold forging is used for smaller objects like screws and metal wire. When using this technique, cold metal is extruded through a die to form a particular shape such as a threaded screw. If a head is needed, another part of the machine can be used to create it. Cold forging can be done cheaply and in high volume, and is the favored method for producing fasteners such as bolts, screws, and nails.
Forging is preferred to simply cutting metal to shape it for a number of reasons. The first is that it improves the strength of the metal by aligning the grain along the lines of potential stress. In other words, a forged hammer is better equipped to handle pressure and pounding than one simply carved out of a base metal. The second is that it is high economical: no part of the metal is wasted during the process, and unused portions can be remelted for use in other pieces.