Forging - Frequently Asked Questions
How are forgings produced?
There are several processes used to create forgings. All of them
involve shaping metal by plastic deformation. The most common type
of forging process is impression die/ precision forging. Other process
included open die/hand forging (resembles pre-industrial metalsmith
work), ring rolling, extrusion and piercing .The temperature and
processes for various methods of forging vary greatly. Forgings
can be created using metal that is either cold, warm or hot, depending
on the requirements of the finished product.
How does forging differ from casting?
Forging can be done to cold, warm and hot metal, however the metal
is never completely melted and poured into a die. Forging uses the
exertion of pressure to shape the metal.
Casting involves pouring molten metal into a mold and then allowing
it to cool.
What does the forging process do to the source metal?
The forging process results in a variety of changes within the properties
of the source metal. A forging process that requires drawing out
the metal results in increased length and a decrease in the cross-section.
Upsetting the metal results in the opposite, decreased length and
an increase in the cross-section. Squeezing metal in closed impression
dies results in a change in length, a change in the cross-section,
and an overall favorable grain flow.
What is the difference between cold, warm, and hot forging?
Cold Forging is used in the production of parts that are symmetrical
and weigh 25 lbs or less. The process is performed when the metal,
usually carbon and standard alloy steels, at room temperature goes
through impression die forging or true closed die forging. The dies
used in cold forging are usually circular and require lubricant.
The end products are draftless, close-tolerance parts. Cold forging
typically improves mechanical properties of the finished pieces,
however the improvement isn’t necessarily useful in many applications.
Warm Forging is a cost-effective method of forging that has become
very popular as a manufacturing method. By using warm forging methods
manufacturers see benefits such as lower tooling and press loads,
increased steel ductility, and as-forged properties that eliminate
heat treatment. Warm forging also eliminates the need to anneal
prior to forging. The process is usually performed when steel is
anywhere from just above room temperature to a temperature below
recrystallization. More specifically the temperature is defined
as 800 to 1,800 degrees Fahrenheit.
Hot forging methods involve recrystallization and deformation of
steel simultaneously. The temperature used for hot forging is specific
to the recrystallization temperature of the metal being used. In
some instances the metal and the dies are heated to the same temperature
in a process known as isothermal forging.
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