Open Die Forging vs. Closed Die Forging: What's the Difference?

Open die forging and closed die forging are two common methods of forging. Both methods utilize compressive forces to form metal, but differ significantly in terms of the required die set, forging process, part size, production volume, and application.

In this guide, we explain the differences between open die forging and closed die forging, including their advantages and limitations, the necessary tooling and typical applications.

What Is Open Die Forging?

Open die forging is a forging process that the workpiece is compressed between relatively simple dies that do not completely enclose the material.

The workpiece can move laterally during deformation, and the operator or automated equipment manipulates the material between successive strokes or press operations.

The Forging Industry Association describes open-die forging as forging performed between flat or simple-contour dies through repeated strokes and manipulation of the workpiece. 

Because the workpiece is not confined within a complete die cavity, open die forging provides considerable flexibility in producing different sizes and shapes.

Typical open-die forged products include:

• Shafts 

• Blocks 

• Bars 

• Rings 

• Discs 

• Large hubs 

• Heavy industrial components 

  
  

What Is Closed Die Forging?

Closed die forging, also called impression die forging, forms the workpiece inside dies containing impressions of the required component shape.

As the dies close under pressure, the heated metal flows into the die cavity.

This allows the process to produce more controlled and repeatable geometries than many open-die applications.

In conventional closed-die forging, excess material may form as flash around the parting line. This flash is subsequently removed through a trimming operation. Flashless forging is a specialized form of closed-die forging in which excess material is minimized or essentially eliminated. 

Open Die vs. Closed Die Forging: Key Differences

1. Die Design

The most obvious difference is the die design.

Open die forging generally uses relatively simple dies, such as flat dies or dies with simple contours.

Closed die forging uses dedicated dies containing impressions that correspond to the desired component geometry.

This makes closed-die tooling more complex, but it also provides greater control over the final shape.

2. Part Size

Open die forging is particularly useful for large and heavy components.

Because the workpiece is not restricted by a complete die cavity, large sections can be progressively reduced and shaped.

Closed die forging is commonly used for smaller or medium-sized components where the complete geometry can be accommodated within the available die and forging equipment.

3. Part Complexity

Open die forging is generally better suited to relatively simple shapes.

For example, a cylindrical shaft can be reduced and shaped through a series of open-die operations.

Closed die forging provides more control over complex profiles because the die cavity defines the component shape.

This makes closed die forging suitable for components such as:

• Gears 

• Connecting rods 

• Flanges 

• Automotive components 

• Industrial fittings 

• Brackets 

• Custom mechanical components 

4. Dimensional Accuracy

Closed die forging generally provides greater control over the component geometry because the dies define the shape.

However, forging should not automatically be treated as a final precision machining operation.

Critical features may still require:

• CNC machining 

• Drilling 

• Threading 

• Grinding 

• Turning 

• Surface finishing 

Open die forgings often require additional machining to achieve the final dimensions, particularly when the component has tight tolerances or complex finished features.

Open Die vs. Closed Die Forging Comparison

When Should You Choose Closed Die Forging?

Closed die forging is often considered when the OEM project requires repeatable geometry, more complex shapes, and medium- to high-volume production.

It is particularly useful when dedicated tooling can be justified by the production quantity.

Typical applications include:

• Automotive components 

• Industrial gears 

• Connecting rods 

• Fittings 

• Brackets 

• Mechanical hardware 

• Customized OEM components 

For suitable designs, closed-die forging can produce near-net shapes and reduce machining requirements. FIA case studies show applications where closed-die forging has been used to reduce subsequent manufacturing operations. 

Can Open Die and Closed Die Forging Be Combined with CNC Machining?

Yes.

Forging and CNC machining are often complementary rather than competing processes.

Forging can create the basic component shape and develop the required material structure, while CNC machining can produce precision features that cannot economically be formed during forging.

A typical OEM manufacturing route may include:

Material → Forging → Heat Treatment → CNC Machining → Surface Treatment → Inspection → Packaging

The exact sequence depends on the material and component design.

Conclusion

Open die forging and closed die forging are both important manufacturing methods for custom OEM forged parts, but they are designed for different production requirements.

Open die forging provides flexibility and is particularly useful for large, heavy, relatively simple, or customized components. Closed die forging uses dedicated dies to control the component geometry and is often suitable for repeat production of more complex parts. At FLUIDO, we support OEM forging projects based on part design, material requirements, dimensions, production volume, and application needs. Contact FLUIDO today to discuss your forging project and request a customized quote.