Open vs Closed Die Forging

Chapter 1: What is the principle difference between open and closed die forging?

This section will cover the techniques of open and closed die forging, exploring their use in the production of various items.

Nomenclature Used in Open and Closed Die Forging

This article highlights essential terminology related to open and closed die forging, emphasizing the importance of understanding these terms.

What is Forging?

Forging is a manufacturing technique where metal is shaped through pressing, hammering, or rolling to achieve different forms and patterns.

Forged components are available in a wide range of shapes and sizes, including disks, blanks, hollows, rings, bars, hubs, and shafts. The diagram below outlines the forging process steps. Detailed explanations of these processes will be provided in subsequent chapters.

Step 1: Setting the Workpiece

The initial step requires positioning the workpiece accurately on the lower die. Proper placement is crucial, as reversing the forging process can be challenging once it’s underway.

Step 2: Dropping the Die

During this phase, the upper die is pressed down onto the heated workpiece to shape it according to the die's design. The high temperature makes the workpiece pliable, allowing it to conform to the die's shape with less force. Calculations and experiments, using mechanical or electrical power, are employed to determine the necessary force for deformation.

Step 3: Cooling, Releasing, and Completion

The workpiece is allowed to cool before the upper die is removed, depending on the material used. The image below displays a forged component suitable for various applications.

Forging Ram

The ram is a crucial component of forging machinery, responsible for holding and moving the upper die up and down. It applies the necessary strokes and forces to deform the workpiece, converting the power source into mechanical force.

What is a Die?

A die is a specialized tool designed to shape materials into various profiles or forms. Commonly used in manufacturing with pressing and other machines, it processes the workpiece into its final shape between the two dies (upper and lower, or top and bottom). The diagram below illustrates how the dies interact with the workpiece before and after applying force.

What is an Ingot?

An ingot is a metal block, commonly made from materials like gold, silver, or steel, typically shaped as a rectangular prism, cube, or similar form.

What is Grain Flow?

Grain flow, a key term in both open and closed die forging, describes the alignment of metal grains resulting from deformations during the forging process. It indicates the direction in which the metal grains orient themselves.

What is Flash?

Flashing is the excess material that extends beyond the desired dimensions during the forging process. This surplus, which is not part of the final product, typically overlaps and is removed through machining once forging is complete. The diagram below illustrates the flash formed when force F is applied to the metal billet.

Forging Hammer

A hammer is a tool that uses mechanical or electrical power to deliver the necessary force for shaping heated or molten metal during forging. It applies rapid strokes to form the product, typically making contact with the workpiece for just milliseconds during the process.

Forging Press

A press is a machine designed to apply pressure for shaping, flattening, or extracting liquids such as oil or juice from materials.

Forging Anvil

An anvil is a solid iron block with a flat surface used for hammering, flattening, and various metalworking tasks, including forging.

Forging Punch

A forging punch is a metal tool used to create or expand holes during the forging process. Available in various shapes, sizes, and materials, punches are chosen based on their specific application needs.

Chapter 2: What distinguishes open die forging from closed die forging?

This chapter will cover the concepts of open die forging and closed die forging, compare the two methods, and highlight key factors to consider when selecting a forging process.

What is Open Die Forging?

Open die forging, also known as flat die forging, blacksmith forging, or hand forging, involves shaping hot metal or alloys by pressing or hammering between flat or simple dies. The final shape depends on the operator's skill and the equipment used, hence the term blacksmith forging.

With advancements in technology, modern open die forging equipment is now computer-controlled, allowing for the creation of complex shapes with improved dimensional accuracy. Typically used for simple shapes like disks, shafts, and rings, open die forging is ideal for producing large parts or when mechanical properties unattainable with closed die forging are needed.

Open Die Process

The open die process is a heat forming method that uses convex and concave dies, also known as standard dies, in presses. It can produce components ranging from a few kilograms to over 300 tons. Applying heat ensures the material achieves adequate plastic flow characteristics and reduces the force needed to shape various forms.

In open die forging, the lower die supports the material while the upper die applies a series of strokes. A manipulator adjusts the material’s position during these strokes, allowing for directional changes. The force is applied in the axial direction, which can be adjusted or rotated for optimal operation. Below are some commonly used operations in open die forging.

• Upsetting
• Piecing
• Punching
• Hollow forging
• Hot trepanning
• Cogging
• Closing in
• Drawing
• Ring forging
• Saddening

Upsetting Operation

The upsetting operation works with the stock positioned vertically, held under the hammer of a forging press. This method increases the stock's cross-sectional area while reducing its axial length. Flat dies, with their large surface area, are commonly used in upsetting to accommodate the expanded workpiece.

Cogging Operation

The cogging operation utilizes narrow dies, which can be flat, V-shaped, convex, or concave. This process involves repeated strokes that elongate and reduce the ingot, often accompanied by rotation. Cogging refines the metal's grain structure and helps eliminate defects such as holes and porosity in the ingot.

Drawing (Solid Forging)

Drawing is a process used to produce shapes with a length significantly greater than their cross-section. This is achieved by elongating the bloom or ingot or by reducing the section's size.

Piercing, Punching, and Trepanning

In these operations, a cavity is formed by applying force to heated steel. Piecing creates a blind cavity without removing metal. Punching involves using a solid punch to create a through-hole by removing material in the form of slugs. Trapping, often done with hollow punching, removes the central core of the metal to create a hole.

Hollow Forging

Hollow forging involves lengthening and expanding a mandrel to create hollow shapes. This process reduces wall thickness while drawing operations increase the overall length of the form.

Closing In

In hollow forging, closing in operations are employed to reduce the section of specific areas. The workpiece is heated to forging temperatures, and V-shaped, formed, or curved dies are used to decrease the area effectively.

Ring Forging

Ring forging operations produce rings from over a mandrel from pieced blanks. The ring wall is uniformly reduced by the rotation of the ring on the press strokes. This will also increase both the outside and inside diameters of the ring.

Combined Processes

Complex shapes are most effectively produced by combining these operations. These shapes can vary from simple to intricate and come in a wide range of sizes.

What is Closed Die Forging?

Closed die forging, also known as impression die forging, involves using two or more dies to create complex-shaped parts. This process shapes metal blanks by hammering or pressing them within closed dies.

In closed die forging, a hammer is dropped onto the workpiece, directing the metal flow into the die cavities to form the desired shape. This process may require multiple hammer drops or quick successive strikes, with each contact lasting only milliseconds.

When the hammer drops, excess material squeezed out of the die cavities is known as flashing. This material cools faster than the rest and is typically stronger. After forging, the flashing is removed through machining and finishing operations.

Main Differences Between Open and Closed Die Forging

The key differences between open and closed die forging are summarized in the table below:

Considerations When Choosing Between Open and Closed Die Forging

Factors to consider when choosing between open and closed die forging processes include:

Precision in Products

To determine the most suitable forging process, evaluate the precision of the products by visually inspecting and measuring their dimensions against the intended metal piece. Use precision instruments like electronic calipers for accurate comparisons. Generally, higher tolerance values indicate less precision in the forging process. Heat-assisted forging processes typically yield better results due to smoother molding. Both open and closed die forging use heat, but factors like material type also influence the final product.

Metal Used

Metals exhibit varying mechanical and chemical properties, influencing their behavior under heat. For instance, metals differ in their melting points and temperature tolerance. Some metals can be forged at high temperatures, while others require lower temperatures. Thorough research is essential to determine the appropriate forging conditions for each material.

Heating Process and Emissions

Heating metals can release emissions into the atmosphere, with some metals emitting carbon or toxic gases. This poses environmental and health concerns, potentially leading to higher costs for pollution control and worker safety measures. It is crucial to consider these factors when selecting materials for forging.

Forging Process Cost

Ultimately, the total cost is a crucial factor, as most forging processes are commercially driven. It's important to thoroughly assess all aspects of the forging process before considering the cost. Pricing should be evaluated last, after addressing other key factors.

Chapter 3: What are some leading machines used for open and closed die forging?

Various machines are available for both open and closed die forging, playing a crucial role in modern manufacturing by producing a wide array of complex metal components for diverse industries. These machines offer versatility, efficiency, and precision. Below, we explore some prominent brands used for these forging processes.

Ajax-CECO - Model: Bulldog 600

The Ajax-CECO Bulldog 600 is a versatile forging machine designed for both open and closed die forging. It boasts robust construction, high forging capacity, and flexible control systems, making it suitable for producing a wide variety of forged components.

SMS Group - Model: FRÖHLING Hydraulic Forging Presses

SMS Group provides FRÖHLING Hydraulic Forging Presses, capable of both open and closed die forging. These presses feature advanced hydraulic systems, customizable options, and precise control, enhancing the forging process and ensuring high-quality results.

Erie Press Systems - Model: MultiForge™

Erie Press Systems' MultiForge™ machines are engineered for both open and closed die forging. They provide flexibility, high force output, and programmable settings, making them suitable for a range of forging applications.

National Machinery - Model: FORMAX Plus

National Machinery's FORMAX Plus machines excel in both open and closed die forging, equipped with advanced servo-driven technology, rapid tool changes, and energy-efficient operation, all contributing to improved productivity and precision.

LASCO - Model: FK Closed Die Forging Presses

LASCO's FK Closed Die Forging Presses are designed for both open and closed die forging. They offer customizable features, precision controls, and high forging force, ensuring efficient and accurate production of forged components.

Note that specific models, features, or components may have changed since this update. For the most current information on the latest machines and capabilities for both open and closed die forging in the United States and Canada, consult the manufacturers or industry resources.

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Chapter 4: What are the key applications and advantages of open die forging?

This chapter will explore the applications and advantages of both open and closed die forging.

Applications of Open Die Forging

Open die forging has numerous applications, typically classified by the shapes of the products, as outlined below.

• Cylindrical shapes
• Pancake shapes or upset shapes
• Hollow forgings
• Contour type forging

Cylindrical Shape Forgings

Cylindrical products forged through open die processes are valued for their durability and strength, making them ideal for industries like aerospace. Applications include components such as rotors, propeller parts, flat bars, and landing gears. Additionally, the military and automotive sectors benefit from forged parts due to their reliability and cost-effectiveness. Examples include wheel spindles, axle beams, kingpins, shafts, torsion bars, idler arms, ball studs, steering arms, pitman arms, connecting rods, and transmission gears and shafts.

Pancake Forgings or Upset Forging

Forgings with a pancake-like shape, resembling disks, are commonly used in aerospace, industrial, and military sectors due to their reliability and safety features. They are essential for components in helicopters, commercial jets, piston-engine planes, spacecraft, and military aircraft. Examples include hubs, flats, discs, hexes, plates, and rounds. Additionally, upset forging can produce elongated parts like screws, shafts, and piston rods, serving public works, aerospace, and automotive applications.

Hollow Forgings

Hollow forgings are used to produce big parts like hollow tubes. They can be tapered hollow shapes, hollow cylinders, or straight cylinders. Hollow forgings can be used to produce rings, tubes, shafts, seamless rolled rings, or bearings. These are mainly used in the aerospace, military, automotive, and alternative energy industry.

Contour Type Forgings

Contour type forgings are essential for ring rolling applications, providing necessary contours with strength and cost-effectiveness. Rolled rings are widely used in demanding environments, including windmills, jet turbines, paper mills, jet engines, helicopter gearboxes, and other high-stress equipment.

Advantages Of Open Die Forging

Advantages of open die forging include:

Reduced Chance of Voids

Open die forging provides ample space for working on the workpiece, significantly reducing the likelihood of voids.

Better Fatigue Resistance

Fatigue is the weakening of a material due to repeated stress or loading, leading to issues like bending and cracking. Products from open die forging typically exhibit enhanced strength and resistance to fatigue, addressing these challenges effectively.

Improved Microstructure

Shapes produced through open die forging generally have superior microstructures due to their larger size and longer-lasting durability.

Continuous Grain Flow

Grain flow refers to the alignment of metal grains and inclusions resulting from forging. This technique is prevalent in crankshaft forging, where continuous grain flow forging is used due to the specific deformation processes involved.

Valuable Cost Savings

Cost-saving involves reducing expenses that directly affect a company's profitability. Compared to closed die forging, open die forging typically offers lower costs, leading to greater expense reduction.

Less Material Waste

Open die forging primarily involves simple processes such as hammering and pressing, minimizing material waste as most of the material is utilized. In contrast, closed die forging generates waste in the form of flashing, as some material is removed during the process.

Greater Strength and Longer Part Life

Shapes produced through open die forging benefit from strong bonds formed during compression processes like pressing and hammering. This makes them resilient to high temperatures and other stresses, enhancing their durability and longevity.

Disadvantages of Open Die Forging

Disadvantages of open die forging include:

Not Suitable for Precision Parts

Open die forging often leaves ample space, allowing molten or heated metal to spread unevenly and fill the die cavities. This lack of confinement can result in irregular shapes, making it less suitable for precision manufacturing or parts.

Process Required Machining

Open die forging often results in irregular shapes, necessitating post-machining to achieve the desired part. This can increase costs, as the process may not utilize all the material efficiently.

Inconsistent Results

Open die forging involves dies that remain open during the process, allowing for the creation of irregular shapes. This makes it suitable for producing parts that do not require high precision, such as supporting beams.

Suitable for Mass Production

Due to the potential for increased irregularities, open die forging is not ideal for mass production and may result in higher losses. It is more effective for producing small quantities.

Chapter 5: What are the primary applications and advantages of closed die forging?

Applications of Closed Die Forging

Closed die forging is widely used to produce metal components for various industrial applications, including aerospace, electronics, agriculture, automotive, commercial, manufacturing, construction, hardware, semiconductor, and food processing industries.

Automotive and Trucks

In the automotive and trucking industries, closed die forging is used for components such as steering arms, pitman arms, shafts, axle beams, torsion bars, idler arms, and ball studs. These components are known for their flame resistance and lower susceptibility to corrosion.

Agriculture Machinery and Equipment

Closed die forging produces strong, tough, and cost-effective components essential for agricultural machinery and equipment. These parts must withstand harsh conditions, such as rocky terrains, making their durability crucial for reliable performance.

The components are mainly used as engine and transmission components. Examples of such components include gears, shafts, spindles, tie rod ends, levers, cultivator shafts, and harrow teeth.

Hand Tools and Hardware Components

Most surgical and dental instruments are made through closed die forging. Common examples include pliers, sleds, hammers, garden tools, wrenches, sockets, wire rope clips, hooks, sockets, turnbuckles, and eye bolts. For electrical transmission and distribution lines, examples include suspension clamps, caps, brackets, and sockets are mainly forged to enhance strength, resistance to corrosion, and dependability.

Valve Fittings

In the valve and fitting industry, closed die forging is essential due to the high pressure and extreme forces used, which impart extra strength and toughness to components. Common parts include heat and corrosion-resistant items like flanges, stems, elbow reducers, tees, valve bodies, saddlers, and other fittings.

Advantages of Closed Die Forging

Benefits of using closed die forging encompass the following:

High Strength

Closed die forging results in products with superior mechanical properties due to the specific process involved. This method involves pressing and hammering, which refines the internal grain structure, enhancing characteristics such as high strength and corrosion resistance. Consequently, items produced through this forging technique are well-suited for demanding applications, such as precision instruments, owing to their durability and robustness.

Close Tolerances

Die forging processes create components with precise tolerances and achieve near-net shapes. A near-net shape means the final product's dimensions are very close to the intended specifications. This precision is due to the workpiece being enclosed in dies, leaving minimal space for excess material, which eliminates the need for additional machining. For smaller items, tolerances of approximately +/- 0.3 mm can be achieved, reducing the need for further machining or finishing and thereby cutting costs.

Net Shapes

Forging produces near-net or net shapes, meaning the resulting forms are very close to the desired dimensions, often requiring no additional processing. The dies are designed to closely match the final shape of the workpiece, and this design is accurately reproduced through the closed die forging process.

No Material Limitation

Closed die forging accommodates a diverse array of materials, including steel, brass, aluminum, iron, and various metal alloys. This versatility makes it suitable for numerous industries where specific materials are required for different components. Unlike some forging methods that might exclude certain materials due to issues such as deformation, melting points, cooling rates, costs, or other mechanical properties, closed die forging can handle these materials with minimal adjustments to the system.

Cleaner Process

Closed die forging processes do not generate excess material that needs to be trimmed or removed afterward, making them more environmentally friendly compared to methods like open die forging or casting, which often require additional machining. Besides their ecological benefits, closed die forging also supports efficient material use, which is why some manufacturers favor this method.

Better Surface Finish

Closed die forging achieves a high-quality surface finish thanks to its precise machining capabilities. This precision reduces the need for additional machining, thereby saving costs. The confined space within the dies ensures there is no excess material, which contributes to the clean surface finish.

Disadvantages of Closed Die Forging

Higher Tooling Expenses

Closed die forging utilizes intricate tools that demand sophisticated design, leading to higher tool costs. As a result, this method can be more expensive compared to other forging techniques.

Dimensional Limitations

Closed die forging is not ideal for producing irregular shapes, as it is best suited for precise, dimensional manufacturing. For items with complex or unconventional shapes, the open die forging method is more appropriate.

Size Limitation

Closed die forging is not ideal for large-scale products and is better suited for smaller components.

Potential Working Damages

Products created through closed die forging are generally smaller than those produced by open die forging. Due to their smaller size, there is a higher risk of accidents, as hot workpieces can be easily displaced. Operating closed die forging equipment requires heightened caution and care to ensure safety.

Conclusion

Both the open and closed die forging method uses heat for most of their operations. There are significant differences between the two, but there seems to be a balance on which method is the best because of what the other method can do and the other cannot do. From the outlined facts, it is evident that these forging methods complement each other and are best used depending on the type of application.

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