Closed Die Forging vs. Open Die Forging

Die forging is the process of forming heated metal into a specified shape through the use of dies.
These specialized pieces of hardened steel or ceramic use pressure and impact forces to form the
metal into a specific shape. Open die forging does not enclose the heated metal, allowing it to flow
freely except where the dies are placed. In closed die forging, the dies come together to fully enclose
the metal that is being forged. Here is a comparison of the two forging techniques.

Processes

For closed die forging, specific molding dies are created in advance. The metal is then heated and
poured into the bottom die. As the top die closes, it creates pressure and impact that forges the metal
into the desired shape.

For open die forging, dies that resemble tools are under the control of the metalworker. He or she
continuously orients and positions the metal as a forging hammer strikes it.

Applications

Forging modifies the internal grain structure of the worked metal, but open die forging and closed die
forging create different results and, thus, are suited to different applications.

Open die forging is best for very large pieces. In fact, some open die forges can create products that
are 80 feet long and weigh up to 136 metric tons. The process improves resistance to fatigue and
wear, boosts strength, reduces porosity, and minimizes the likelihood of voids in the finished piece.
However, the resulting process tends to be rough and somewhat imprecise. Open die forging is ideal
for simple shapes and large parts used in the railroad and aircraft industries.

Closed die forging is best for small pieces and those that require precise dimensions with very tight
tolerances. The finished pieces are tighter and have a smoother surface. However, it can be cost
prohibitive for small runs, as custom dies must be created. Fatigue resistance is also lower in pieces
that are closed die forged. Pieces created through closed die forging are often used in the mining, oil,
and automotive industries.

Advantages and Disadvantages

Benefits of Open Die Forging:

·         Improved microstructure and better fatigue resistance

·         Finer grain size and smoother grain flow

·         Increased strength

·         Longer life

·         Less waste

·         Fewer voids

·         Less expensive

Drawbacks of Open Die Forging:

·         Incapable of producing precision parts with tight tolerances

·         Further refining may be needed to create desired features

Benefits of Closed Die Forging:

·         Tighter grain formation

·         No limitation on materials

·         Smoother surface finish

·         Better precision and tolerances

·         Little to no refinement required for complex pieces

·         Economical for large runs

Drawbacks of Closed Die Forging:

·         High setup costs

·         Powerful vibrations require special building provisions

·         Potentially hazardous work environment

·         Costly for small runs

Each forging method is best for specific applications. It is always best to consult with a professional to
determine which production method is right for your unique needs.

Ready to Start?

Atlas Bronze is a leading U.S. distributor of bronze, copper, brass, iron, and more. Contact us today at 1-800-478-0887 to place an order or learn about our custom products.

A Guide to Closed Die Forging

Closed die forging, also known as impression die forging, uses two or more dies that contain a precut
profile of the desired product. Heated metal, such as steel, bronze, titanium, or aluminum, is poured
into the bottom die. As the dies come together, pressure and impact forces form the metal to fit the
shape.

Capabilities of Closed Die Forging

A major advantage of closed die forging is its preciseness. Parts weighing anywhere from several
ounces to 60,000 pounds can be produced in a virtually limitless variety of 3-D shapes. Closed die
forging is equally effective for simple spheres and blocks, for extremely intricate components with high
vertical projections and thin webs, and for parts that include detailed design elements such as bent or
curved flanges and protrusions.

Metals and Alloys

Virtually all metals and alloys that are used in engineering can be used in closed die forging. Some
materials that are particularly sensitive to temperature or strain rate, such as refractory alloys and
nickel-based super-alloys, may require special equipment for closed die forging.

Closed Die Forging Process Operations

The simplest version of closed die forging brings two dies together to cause plastic deformation in the
heated metal until its sides touch the side walls of the dies. A small amount of the metal then starts to
flow outside the die, forming flash. The rapidly cooling flash adds deformation resistance, building up
pressure inside the dies to boost material flow into all areas of the dies.

Closed Die Upsetting

Closed die forging can be performed on horizontal forging machines known as upsetters. In this case,
“grip dies” consist of one stationary die and one moving die that contain the desired impression and
can be closed to hold the material in position for forging. A ram-operated “heading tool” acts as a
hammer or press, forcing metal into all sections of the grip dies.

Closed die forging can produce products with tighter tolerances and higher precision than other
methods such as open die forging. The finished products also have better strength and tightness, as
well as an improved surface finish. Like anything else, though, closed die forging is not always the
right choice. It can be expensive for small runs due to the need to create customized profiles for each
piece. In addition, fatigue resistance is not as high for closed die forged items as for open die forged
items.

At Atlas Bronze, we carefully select the forging or casting process that is right for each item. Using the
best process lets us ultimately produce the best results.

Ready to Start?

Atlas Bronze is a leading U.S. distributor of bronze, copper, brass, iron, and more. Contact us today at
1-800-478-0887 to place an order or learn about our custom products.