Forging of steel

Key parameters determined by the DSS are billet temperature, billet length and lubrication (friction). Material flow in extrusion is different from the one in hot forging; hence friction is not determined via a ring test.

Forging dies are made of high-alloy hot working steel. Due to their intended use, they should be characterized by good mechanical properties, high hardness and good friction wear resistance in the full range of operating temperature defined for forging, i.e., 250 to 700 ◦C.

Closed Die Forging is a forging process in which dies move towards each other and covers the workpiece in whole or in part. The shape of the forging is incorporated in the top or bottom die as a negative image. Coming from above, the impact of the top die on the raw material forms it into the required forged form.

The difference between open and impression-die forging is, with open die forging the work piece is basically compressed between two dies whereas with impression die forging it fills the cavities of the dies and produce a more complex shape.

• Forging temperatures at room conditions, self-heating up to 150 °C due to the forming energy.
• Narrowest tolerances achievable.
• No scaling at workpiece surface.
• Increase of strength and decrease of ductility due to strain hardening.
• Low formability and high forming forces are necessary.

Forgings are usually selected for applications requiring high ductility, impact toughness, fracture toughness and fatigue strength; therefore, forging alloys with inherently high ductility and tensile strength are generally selected.

Open-die forging gets its name from the fact that the dies (the surfaces that are in contact with the workpiece) do not enclose the workpiece, allowing it to flow except where contacted by the dies. Therefore the operator needs to orient and position the workpiece to get the desired shape.

Open-Die Forging Cons

• Not suitable for forming intricate, precision parts or other close-tolerance applications.
• Machining is often required to complete open-die forgings.
• Process doesn’t always produce consistent results or desired features.

In open die forging, the billet is placed between multiple dies that do not enclose the metal entirely. Closed die forging process, is also referred to as impression die forging. It utilizes high pressure to compress the metal piece to fill an enclosed die impression for required shapes.

Explanation: Cogging is an open die forging process in which flat or slightly contoured die are employed to compress a work piece, reducing its thickness and increasing its length.

Explanation: Hot forging is a method of forging articles at an extremely high temperature. But, before putting the article into the hot forging processes, it has to be heated to certain temperatures. The minimum temperature that has to be given to the article should be 200°C.

The forging must be designed such that adequate draft is present to facilitate removing the forging from the dies. Generally, all forged surfaces that lie parallel to the die motion are tapered. This taper also helps the flow into deeper die cavities. Standard draft angles should be at least 1deg.

Extrusion has a limit to its part complexity in part because the extrusion method is a 2-dimensional process, whereas forging offers 3-dimensional geometry .

Open die forging process is also known as free forging. The piece of metal is deformed between multiple dies that do not enclose the metal entirely. The dies hammer and stamp the metal through a series of movements to alter its dimensions until the desired shape is achieved.

Definition of forging. Forging is defined as a metal working process that shape workpiece into desired dimensions by compressive forces applied through the use of dies and tools. Forging process is operated by hammering or pressing the metal.

Impression-die forging is also called “closed-die forging”. In impression-die forging, the metal is placed in a die resembling a mold, which is attached to an anvil. Usually, the hammer die is shaped as well. The hammer is then dropped on the workpiece, causing the metal to flow and fill the die cavities.