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.

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