What is hot forging?

  Hot forging requires heating the workpiece to about 75% of its melting temperature. This reduces the flow stress and energy required to form the metal, effectively increasing the production rate (or strain rate). Hot forging helps to make metals easier to form and less likely to break.

  Iron and its alloys are almost always hot-forged for two main reasons:

1. If work hardening progresses, hard materials such as steel and iron will become more difficult to process.

2. Hot forging of a metal (such as steel) followed by a heat treatment process is a more economical option because the metal (such as steel) can be strengthened by other processes (not just cold working processes).

 

  While other materials need to be strengthened by the forging process itself, most materials such as titanium and aluminum alloys can be hot-forged and then hardened.

 

The average temperature of hot forging includes:

Aluminum (Al) alloy. 360°(680°F) to 520°C(968°F)

Copper (Cu) alloy -700 ℃(1 292℃) -800 ℃(1 472℃)

Steel - up to 1150°C(2102°F)

 

  During hot forging, the temperature reaches above the recrystalization point where the metal is formed. These high temperatures are required in order to avoid strain hardening during deformation during the plastic deformation of the metal above the recrystalization temperature.

 

  This process usually involves heating the metal (above its recrystalization point), after which it is crushed into a mold - which can also be heated upon request. Since the metal is hot, it is easy to "move", allowing the manufacturer to produce finer shapes than cold forging.

 

  In the case of superalloys (which have low malleability), processes such as isothermal forging, in which deformation is carried out in a controlled atmosphere, are used to avoid oxidation.

 

  Isothermal forging, also known as hot die forging, is a thermal processing process that requires the workpiece to maintain its highest temperature throughout the forming process.

 

  Maintaining this temperature is accomplished by heating the die -this will be at or slightly below the elevated temperature of the workpiece. The force applied by this die forms the workpiece, and since the die is also in a high temperature state, cooling of the workpiece between the die working interfaces is eliminated. This in turn leads to an improvement in the flow characteristics of the metal (workpiece).

 

   Note here that isothermal forging can also be performed in vacuum.

 

How working dies?

  Dies used for hot forging undergo intense thermal cycling and mechanical loads. This in turn affects the life of the die, as the die is open to:

1.Gross cracking

2.Plastic deformation

3.fatigue cracking

4.wear

 

  Depending on the type of forging operation used, the material and size of the part to be formed, and just to name a few, the forging die is required to have the following characteristics:

1.Adequate hardness and the ability to maintain it at high temperatures.

2.It has sufficient hardenability and fatigue resistance.

3.It has good ductility and toughness at high and low temperatures.

4.The thermal hardness and thermal tensile strength are improved.

 

The benefits of hot forging.

  Hot forging is commonly used for parts types that have an impact in technical applications and is also recommended for processes with metal deformation with high forming rates.

 

  The advantages of hot forging include:

1.Increased extensibility.

2.It requires less energy (or force) to work with the material due to the reduced yield strength.

3.During hot forging and subsequent deformation, the pores can be reduced (in size) or completely closed.

4.Because an elevated temperature increases diffusion, it is possible to reduce or eliminate chemical inhomogeneity.

5. In hot forged steel, the weaker and ductile FCC(face-centered cubic) austenite deforms rather than the stronger BCC(body-centered cubic) ferrite, which deforms at lower forging temperatures.

Ipower Machinery provide professional hot forging machines for various brass valves.

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