What Is the Forging Process? Definition, Types, and How It Works!

Forging is a metal-forming process that uses localised compressive forces to shape metal through controlled plastic deformation. Forging uses dies, presses, hammers, or rolls to shape metal parts according to the base metal and geometry and based on production needs. It is a well-known method for producing structural parts like shafts, gears, bolts, screws, washers, fittings, and rings.

Depending on the temperature, the process can be hot, warm, or cold, and it affects deformation behaviour and final mechanical properties. Choosing the right process depends on the alloy, complexity, desired mechanical properties, and required tolerances. We will discuss these factors and the fundamentals of the forging process in this article.

Key Steps in the Metal Forging Process

Although exact operations vary by material and forging method, most processes share a common sequence of basic steps.

Material preparation

The forging process begins with a metal billet, bar, or preform, and then it is cut to precise size requirements and undergoes quality inspection to identify any flaws before shaping starts.

Heating

In hot and warm forging processes, heating is applied at this stage to increase the ductility of the metal for easier forming. Cold forging, on the other hand, is carried out below the recrystallisation temperature, typically at or near room temperature.

Shaping

The heated or unheated workpiece is placed between dies or rolls or passed through specialised equipment. Compressive forces applied via a press force the metal to shape progressively within the dies. The exact operation depends on the selected forging technique and the desired geometry. The metal may need to be forged sequentially in one or several dies until it reaches its final shape.

Cooling

At the end of the forging process, especially in hot and warm forging operations, the workpiece might need to be cooled under controlled or ambient conditions. The cooling rate affects the microstructure and mechanical properties of the forged component.

Finishing and inspection

Additional operations may include trimming excess material, removing surface scale, heat treatment, machining, and surface finishing. Then, the quality control stage comes into play to verify dimensional accuracy, surface quality, and general quality, as well as to inspect surface defects, cracks, laps, folds, die-related defects, and internal discontinuities.

Common Forging Methods

The type of method can be selected mostly based on the metal grade and the desired final geometry and surface quality.

Open-die forging

In open-die forging, the metal is shaped by applying compressive forces between dies that do not fully enclose the workpiece. The ancient method of sword forging is a form of open-die forging. The workpiece can move freely between the forging equipment. Since the workpiece can be manipulated during the operation, the desired final dimensions are achieved progressively. Today, it is commonly preferred for large components and mostly for simple geometries like shafts, rings, pressure vessels, and heavy industrial components.

Closed-die forging

In this method, the applied high pressure ensures that the material fills the die cavity. Closed-die forging is for more complex parts that require high dimensional consistency. Can be adapted to mass production and used in the manufacture of gears, connecting rods, and components for the automotive and aerospace industries.

Roll forging

In this process, the component is forged by passing it between rotating rolls with specially shaped surfaces. As the material passes between these rolls, it is progressively deformed, and its cross-section is reduced. This method provides high material savings and efficiency, particularly in the production of elongated or tapered components. Shafts, axles, tapered parts, and long arms can be shaped in this manner.

Benefits of Forged Metal: Strength, Durability, and Grain Structure

One of the main reasons manufacturers select forging is the mechanical performance that can be achieved in forged metal components. The controlled plastic deformation involved in forging can improve the strength and durability of a component compared with some other manufacturing methods.

A major advantage is the effect of forging on the material’s grain structure. During deformation, the grain flow can become orientated along the general shape of the component. The resulting material can also exhibit anisotropy, while the grain flow can contribute to improved strength and fatigue resistance.

Forging can also close or reduce internal voids and porosity that are present in the casting process. The combination of controlled deformation and appropriate processing conditions can produce components with consistent mechanical properties.

Other potential benefits include:

• High strength-to-weight performance
• Good fatigue and impact resistance
• Improved structural integrity
• Consistent mechanical properties
• Ability to produce a wide range of component sizes
• Efficient use of material compared with processes that remove large amounts of material

Although the forging process offers many benefits such as these, like all other manufacturing methods, the mechanical properties of the final part depend on the careful monitoring of production processes, heating and cooling conditions, residual stresses, and proper design.

When to Choose Forging for Your Metal Project

Forging becomes suitable when an application demands good mechanical performance. If your project involves load-bearing components exposed to harsh operational environments, dynamic stresses, or high impact, the superior structural density and directional strength offered by forged metals make it a suitable choice.

Forging may be appropriate when:

• High strength and durability are required.
• The component will experience repeated or impact loading.
• Consistent mechanical properties are important.
• Favourable grain flow can improve component performance.
• Medium- or high-volume production is required.
• The component geometry is suitable for a forging operation.

However, forging is not the best solution for every metal component. Very complex geometries or some of the metal grades may be better suited to casting or additive manufacturing, while low-volume components with relatively simple dimensions may be more economical to produce through machining. Thin sheet components may also be better suited to stamping or other sheet metal forming processes.

Get the Right Metal for Your Forging Project

Open-die, closed-die, roll, hot, cold, and isothermal forging each offer different advantages depending on the application. But for all, a successful forging project starts with the right material. Metal Supermarkets offers a wide selection of metals in a variety of grades, sizes, and forms.