Drop Forging – A Metal Forming Process used to Make Quality Components

31 May, 2022
Drop Forging – A Metal Forming Process used to Make Quality Components

Forging is the oldest known components manufacturing or metalworking process in which metals are given shape using localized compressive forces. The force is usually applied with a power hammer or a die. The components created using this process are stronger and more durable compared to components manufactured using other metalworking processes.

Thus, this forging is generally used where reliability and human safety is the biggest concern.  It is a metal forming process that is performed at high or ambient temperature employing either forging hammers or press tools. In this forging process, a hammer is raised and dropped into the work piece to deform it as per the die shape. Drop forging is characterized by the use of dies and machines that exert high forces and at the same time allow precise guidance of the tools. Different metals are suitable for drop forging after heating such as steel, magnesium, aluminum, stainless steel, brass, copper, as well as their alloys.

Drop Forging Process

It is a metal forming process in which a work piece is inserted into a die and hammered till it takes the shape of the die. The lower part is stationary whereas the upper part is a moving hammer that is dropped onto the work piece to deform it. The drop forging can be executed at both high and ambient temperatures. In the metal shaping industry, this manufacturing process has been in use for hundreds of years, and the mechanics of the process are still the same.

However, the machinery involved in the process has become advanced to make drop forging a high-precision manufacturing process. The material properties of the final piece are enhanced with drop forging like all other forging techniques. This metalworking process is different from upset forging, press forging, or any other forging processes, as in this process the billet is deformed into the desired shapes with the help of forging dies.

Advantages of Drop Forging

The drop forging process involving hot working metals has been used for thousands of years, as this metalworking process comes with multiple benefits. Drop forging has become a highly relied upon manufacturing method because of the reliable quality and strength of the parts or components manufactured.

Currently, the drop forging process has been mechanized with the latest technology development. This metalworking process is used for the production of a wide range of components that are used in a wide range of industries. Some of the major benefits of this process include:

  • This process produces a large number of components of top-most quality
  • This process makes the metal stronger than the original raw material ad also gives metals a high level of durability.
  • The components manufactured have good grain flow and surface finish.
  • There is little or no wastage of the material.
  • Components manufactured are of good strength and durable, as the grain is aligned along the line of potential stress.
  • This process is used to make complex-shaped metal parts.
  • This process saves metal material and reduces machining work, so in case of more batches, the spare parts cost will reduce.

The components or spare parts made with this process have enhanced mechanical properties

Types of Drop Forging

Drop forging is usually of two types, open-die drop forging and closed-die drop forging. As indicated by their names the difference is in the die shape, the open-die drop does not completely enclose the work piece whereas the closed-die drop completely encloses the work piece.

Open-die drop forging: Open-die drop forging doesn’t completely cover the work piece and allows deformation into open space. In this process, the metal is placed on the die by an operator, while a hammer strikes the metal. The work piece position is changed by the operator before every strike until the final shape is achieved. It is a popular component manufacturing process that imparts some vital features to the components such as greater strength, improved grain size, and continuous grain flow.

Characteristics of Open-Die Drop Forging

  • The production equipment used in the open-die drop forging is simple, and investment in equipment is also less compared to closed-dye drop forging.
  • Tooling and dies in open-die drop forging is not closed and hence it is also named free forging.
  • Open-die drop forging may produce a large component or spare parts weighing more than 10 tons.
  • Shapes of open-die drop forgings are not complicated and this type of forging is workable even for special shapes.

Closed-Die Drop Forging: In the closed-die drop forging, a closed die looks like a mold that is attached to the anvil in which metal is placed. When the shaped hammer dies strike the workpiece, the material flows and fills the die cavities. In this process, the hammer is dropped in quick succession until the desired shape is achieved. Sometimes the series of diverse cavities are used to give some specific shape. The initial investment in this process is high because of the specific design of the die cavities. Thus, manufacturing closed-die drop-forged parts in more volume turn out to be more economical. This forging process is generally used in the tooling and automotive industries.

Characteristics of Closed Die Drop Forgings:

  • The production capacity is high in closed-die drop forgings because the steel bar can be quickly forged under the press of upper and lower dies.  
  • Components produced with this forging process have accurate dimensions due to the perfect mould that prevents further machining thereby saving lots of costs.
  • There is no chance of the defects in the components because the mechanical property of drop forging is better compared to casting.

Typical Drop Forged Components

Components and spare parts produced with drop forged process are used across several industries such as automotive, aerospace, defense, agriculture, and material handling. Some of the popular components produced with this process are:

  • Levers
  • Gears
  • Railroads
  • Crankshafts
  • Connecting rods
  • Pedal cranks
  • Gear blanks
  • Spanners

Drop Forging FAQs

What is drop forging and how does drop forging distinguish itself from alternative forging methods?

Drop forging is a metal forming process where a heated metal billet is placed in a die, and a mechanical or power-driven hammer compresses and shapes it into the desired form. Unlike other forging methods, such as press forging, open-die forging, or closed-die forging, drop forging involves the use of a specific tool such as a hammer or press to achieve precise and complex shapes with high strength and consistency in mass production.

What are the major advantages of drop forging compared to other manufacturing processes?

Drop forging produces parts that are stronger and more durable than those made using other manufacturing methods. Besides, parts made with drop forging have a better surface finish and have tight tolerances and complex shapes. In addition to this drop forging produces parts with improved grain structure and mechanical properties. Drop forging also provides a higher level of structural integrity than any other metalworking process.

What are some commonly used materials in drop forging?

Drop forging is a process that uses a hammer to reshape a heated piece of metal. Some materials that are commonly used in drop forging include steel, aluminum, carbon steel, and even magnesium, brass, copper, and their alloys. However, steel is the most commonly used drop forging material because of its strength, durability, versatility, and sustainability.

How does the drop forging process get affected due to the temperature of the material?

The temperature of the material significantly influences the drop forging process. Higher temperatures enhance material malleability, making it easier to shape and reducing the force required during forging. However, excessively high temperatures can lead to grain growth, affecting the mechanical properties of the final product. Therefore, maintaining the right forging temperature is crucial to achieving optimal results, ensuring a balance between formability and material integrity in the drop forging process.

What are the major components that are used for the drop forging operation?

A drop forging operation involves crucial components such as the hammer or press, die, and workpiece or metal billet. The hammer or press delivers the force to deform the metal, while the die shapes it into the desired form. The workpiece, usually a heated metal billet, undergoes plastic deformation under the force applied by the hammer or press. These elements work together in a synchronized process, ensuring precise and controlled shaping of the metal.

What are the different types of drop forging processes available?

Several types of drop forging processes exist, including open-die forging, closed-die forging, and impression-die forging. Open-die forging involves deforming the workpiece between flat dies, while closed-die forging uses shaped dies for precision. Impression-die forging employs dies with cavities for intricate shapes. Each method caters to specific requirements, offering versatility in producing a variety of forged components for diverse applications.

How does drop forging lead to the strength and durability of the manufactured parts?

Drop forging contributes to the strength and durability of manufactured parts by subjecting the material to controlled plastic deformation. The process refines the metal’s grain structure, aligning and elongating the grains for improved mechanical properties. Compressive forces applied during forging reduce voids and porosity, enhancing material density. This results in components with superior strength, toughness, and fatigue resistance, ensuring the production of durable and reliable parts for various applications.

What are some disadvantages associated with drop forging?

Despite its advantages, drop forging has limitations. The initial tooling costs can be high, making it less economical for small-scale production. Complex and intricate shapes may pose challenges in tooling design. Additionally, the need for preheating the metal billet increases energy consumption. Precision forging of intricate details may require secondary machining. While drop forging offers numerous benefits, these drawbacks need consideration based on the specific requirements of the manufacturing process.

What are the basic steps of the drop forging process?

The drop forging process involves several key steps such as:

  • First, a heated metal billet is placed in the die.
  • Then, a hammer or press applies force, causing the material to take the shape of the die cavity.
  • The workpiece undergoes plastic deformation, refining the grain structure.
  • Excess material, known as flash, is expelled.
  • After forging, the part is trimmed, removing any remaining flash.
  • The final step may involve additional heat treatment for enhanced mechanical properties, resulting in a strong and durable forged component.

What are the factors based on which hot or cold drop forging is chosen?

The choice between hot and cold drop forging depends on various factors. Hot forging is preferred for metals with high ductility, allowing for easier deformation at elevated temperatures. It suits complex shapes and offers better material flow. Cold forging is chosen for materials with lower ductility, maintaining dimensional accuracy without the need for subsequent heat treatment. Factors such as material type, desired properties, component complexity, and cost considerations influence the selection between hot and cold drop forging processes.

What safety precautions should be kept in mind for drop forging?

Safety in drop forging involves using appropriate personal protective equipment, like eye protection and heat-resistant clothing. Operators must be trained to handle equipment safely, and work areas should be well-ventilated. Regular maintenance of forging machinery is crucial. Workers should follow proper procedures for material handling, and caution is required during the heating and cooling stages. Emergency protocols, such as first aid measures and fire safety, should be established and communicated to all personnel involved in the drop forging process.