How to Select Forgings and Forged Stock
Forgings and forged stock are metals and alloys that are thermo-mechanically pressed or forged into bars, rods, or other shapes.
What is Forging?
Forging is a metallurgical process that subjects metal parts to extreme pressures to impart high strength. Typically, metallic elements or alloys are preheated and then worked. Unlike casting or foundry work, however, forging does not involve melting and pouring. Rather, forgings and forged stock are made by striking a rough or preformed shape (perform) with a forging hammer or press. The material flows under the impact into the desired shape. The result is a metal part with a very dense structure where the orientation of the grains depends upon the shape and tooling design.
Types of Forging
There are a number of different forging processes that are used for creating forgings of different sizes and shapes.
· Impression die forging pounds or presses metal between two dies (called tooling) that contain a precut profile of the desired part. Parts from a few ounces to 60,000 lbs. can be made using this process. Some of the smaller parts are forged cold.
· Cold forging encompasses many processes -- bending, cold drawing, cold heading, coining, extrusions and more, to yield a diverse range of part shapes. In the process, a chemically lubricated bar slug is forced into a closed die under extreme pressure. The unheated metal thus flows into the desired shape.
· Open die forging is performed between flat dies with no precut profiles is the dies. Movement of the work piece is the key to this method. Open-die forging can produce forgings from a few pounds up to more than 150 tons. Practically all forgeable ferrous and non-ferrous alloys can be open-die forged, including some exotic materials like age-hardening superalloys and corrosion-resistant refractory alloys.
· Seamless rolled ring forging is typically performed by punching a hole in a thick, round piece of metal (creating a donut shape), and then rolling and squeezing (or in some cases, pounding) the donut into a thin ring. Ring diameters can be anywhere from a few inches to 30 feet. Forgeable materials include not only carbon and alloy steels, but also non-ferrous alloys of aluminum, copper and titanium, as well as nickel-base alloys.
Advantages and Disadvantages of Forged Parts
Through the forging process, the internal grain of the material deforms to follow the general shape of the part, making it continuous throughout. This produces stronger products than equivalent ones made through casting or machining.
Production forging however is significantly more costly due to the expense of the machinery, tooling, facilities, and personnel required for the process. Because of this, forgings are generally used for mission critical parts where reliability is of much higher priority than cost.
Selecting a forged part can be based on a number of different factors, including design specifications, load requirements, or material types. The GlobalSpec SpecSearch Database allows the user to specify the desired product based on size dimensions such as overall thickness and overall width or outer diameter (OD), mechanical properties such as yield strength and tensile strength, or material types such as aluminum and copper.
Use of Forgings
Forgings are readily created for critical component parts inside assembled products such as airplanes, automobiles, ships, oil drilling equipment, engines, missiles, and many kinds of capital equipment.