MYPIBLOGs

What Is Forging?

Forge meaning according to Oxford Dictionary:

• Make or shape (a metal object) by heating it in a fire or furnace and hammering it.

According to Collins Dictionary Forge is :

• The process of producing a metal component by hammering.

WHAT IS FORGING PROCESS?

Forging is a manufacturing process involving the shaping of a metal through hammering, pressing, or rolling. These compressive forces are delivered with a hammer or die. Forging is often categorized according to the temperature at which it is performed—cold, warm, or hot forging.

A wide range of metals can be forged. Typical metals used in forging include carbon steel, alloy steel, and stainless steel. 

Very soft metals such as aluminum, brass, and copper can also be forged. 

The forging process can produce parts with superb mechanical properties with minimum waste. The basic concept is that the original metal is plastically deformed to the desired geometric shape—giving it higher fatigue resistance and strength. 

The process is economically sound with the ability to mass produce parts, and achieve specific mechanical properties in the finished product.

HISTORY OF FORGING

Forging has been practiced by smiths for thousands of years. At first, bronze and copper were the most common forged metals, in the Bronze Age: later, as the ability to control temperature and the process of smelting iron was discovered, iron became the primary forged metal. Traditional products include kitchenware, hardware, hand tools, and edged weapons. The Industrial Revolution allowed forging to become a more efficient, mass-production process. Since then, forging has evolved along with advances in equipment, robotics, electronic controls, and automation. 

Forging is now a worldwide industry with modern forging facilities producing high-quality metal parts in a vast array of sizes, shapes, materials, and finishes.

FORGING METHODS

There are several forging methods with different capabilities and benefits. The more commonly used forging methods include the drop forging methods, as well as roll forging.

Drop forging

Drop forging derives its name from the process of dropping a hammer onto the metal to mold it into the shape of the die. The die refers to the surfaces that come into contact with the metal. 

There are two types of drop forging—open-die and closed-die forging. Dies are typically flat in shape with some having distinctively shaped surfaces for specialized operations.

Open-die forging (smith forging)

Open-die forging is also known as smith forging. A hammer strikes and deforms a metal on a stationary anvil. 

In this type of forging, the metal is never completely confined in the dies—allowing it to flow except for the areas where it is in contact with the dies. 

It is the operator’s responsibility to orient and position the metal to achieve the desired final shape. 

Flat dies are used, with some having specially shaped surfaces for specialized operations. Open-die forging is suitable for simple and large parts, as well as customized metal components.

Advantages of open-die forging:

1)Better fatigue resistance and strength

2)Reduces chance of error and/or holes

3)Improves microstructure

4)Continuous grain flow

5)Finer grain size

Closed-die forging (impression-die)

Closed-die forging is also known as impression-die forging. The metal is placed in a die and attached to an anvil. 

The hammer is dropped onto the metal, causing it to flow and fill the die cavities. The hammer is timed to come into contact with the metal in quick succession on a scale of milliseconds. 

Excess metal is pushed out from the die cavities, resulting in flash. The flash cools faster than the rest of the material, making it stronger than the metal in the die. 

After forging, the flash is removed.

In order for the metal to reach the final stage, it is moved through a series of cavities in a die:

1.Edging impression (also known as fullering or bending)

The first impression used to mold the metal into a rough shape.

2.Blocking cavities

The metal is worked into a shape that more closely resembles the final product. The metal is shaped with generous bends and fillets.

3.Final impression cavity

Final stage of finishing and detailing the metal into the desired shape.

Advantages of closed-die forging:

1)Produces parts up to 25 tons

2)Produces near net shapes that require only a small amount of finishing

3)Economic for heavy production

Roll forging

Roll forging consists of two cylindrical or semi-cylindrical horizontal rolls that deform a round or flat bar stock. This works to reduce its thickness and increase its length. This heated bar is inserted and passed between the two rolls—each containing one or more shaped grooves—and is progressively shaped as it is rolled through the machine. This process continues until the desired shape and size is achieved.

Advantages of automatic roll forging:

1)Produces little to no material waste

2)Creates a favorable grain structure in the metal

3)Reduces the cross-sectional area of the metal

4)Produces taper ends

Press forging

Press forging uses a slow, continuous pressure or force, instead of the impact used in drop-hammer forging. The slower ram travel means that the deformation reaches deeper, so that the entire volume of the metal is uniformly affected. Contrastingly, in drop-hammer forging, the deformation is often only at the surface level while the metal’s interior stays somewhat undeformed. By controlling the compression rate in press forging, the internal strain can also be controlled.

Advantages of press forging:

1)Economic for heavy production

2)Greater accuracy in tolerances within 0.01–0.02 inch

3)Dies have less draft allowing for better dimensional accuracy

4)Speed, pressure, and travel of the die are automatically controlled

5)Process automation is possible

6)Capacity of presses range from 500–9000 tons

Investment casting is the casting method by pouring liquid metal into molds to form the shapes