What Is Forging?- Definition, Process, And Types

This article will dive into everything you need to know about forging, including what it is, how it’s done, and how a forged product compares to products made through other methods including castings, weldments and fabrications, machined bars/plates, powdered metal parts, and reinforced plastics/composites.

First, we’ll define what forging is. 

What is Forging?

Forging is a manufacturing process where solid metal is shaped by localized compressive forces from hammering or pressing. 

Forging of steel is often classified according to the temperature at which it is performed: cold forging, warm forging, and hot forging. It is important to note that forging is not the same as casting, as metal to be forged is never melted and poured.

Why Use Forgings?

Forgings are strong. As the metal is shaped during the forging process its internal grain structure deforms to follow the general shape of the part. By compressing the grain structure and creating a grain flow, strength characteristics of the part are increased. 

Forgings are used in places where reliability and safety are critical.  Forgings are often parts that are used inside machines, automobiles, airplanes, tractors, ships, oil drilling equipment, engines, and missiles to name a few.

At What Temperature are Forgings Made?

Forging processes are generally classified by whether the metal temperature is above or below the recrystallization temperature of the metals microstructure.  Steel forging can be divided into:

Hot forging of steel

• Forging temperatures above the recrystallization temperature between 1742–2300 °F

• Good formability

• Low forming forces

• Constant tensile strength of the workpieces

Warm forging of steel

• Forging temperatures between 1200–1742 °F

• Less or no scaling at the workpiece surface

• Narrower tolerances achievable than in hot forging

• Limited formability and higher forming forces than for hot forging

• Lower forming forces than in cold forming

Cold forging of steel

• Forging temperatures at room conditions, self-heating up to 300 °F 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

Here at Edgerton Forge, we hot forge steel.

How do you forge?

There are basically three methods (or processes) to make a forged part: Impression Die Forging, Open Die Forging, and Seamless Rolled Ring Forging.  

Here at Edgerton Forge, we use Impression Die Forging.

Impression Die Forging pounds or forces metal between two dies (called tooling) that have a specific shape (cavity) cut into them. 

The metal flows under force into the cavity to create the specific part shape. This process can create parts that range from simple shapes to very complex non-symmetrical shapes. 

Impression Die Forging can be done with a variety of machines including hydraulic presses, mechanical presses, hammers, and upsetters. We use upsetters and mechanical presses at Edgerton Forge.

How Do Forgings Compare to Castings?

Forgings are stronger. Casting cannot obtain the strengthening effects of hot and cold working. Forging surpasses casting in predictable strength properties – producing superior strength that is assured, part to part.

Forging refines defects from cast ingots or continuous cast bar. A casting has neither grain flow nor directional strength and the process cannot prevent formation of certain metallurgical defects. Preworking forge stock produces a grain flow oriented in directions requiring maximum strength. Dendritic structures, alloy segregation’s and like imperfections are refined in forging.

Forgings are more reliable, less costly. Casting defects occur in a variety of forms. Because hot working refines grain pattern and imparts high strength, ductility and resistance properties, forged products are more reliable. And they are manufactured without the added costs for tighter process controls and inspection that are required for casting.

Forgings offer better response to heat treatment. Castings require close control of melting and cooling processes because alloy segregation may occur. This results in a non-uniform heat treatment response that can affect the straightness of finished parts. Forgings respond more predictably to heat treatment and offer better dimensional stability.

Forgings are flexible, cost-effective production adapts to demand. Some castings, such as special performance castings, require expensive materials and process controls, and longer lead times. Open-die and ring rolling are examples of forging processes that adapt to various production run lengths and enable shortened lead times.

How Do Forgings Compare to Weldments and Fabrications?

Forgings offer production economies, material savings. Welded fabrications are more costly in high volume production runs. In fact, fabricated parts are a traditional source of forging conversions as production volume increases. Initial tooling costs for forging can be absorbed by production volume and material savings and forging?s intrinsic production economics lower labor costs, scrap and rework reductions and reduced inspection costs.

Forgings are stronger. Welded structures are not usually free of porosity. Any strength benefit gained from welding or fastening standard rolled products can be lost by poor welding or joining practice. The grain orientation achieved in forging makes stronger parts.

Forgings offer cost-effective designs/inspection. A multiple-component welded assembly cannot match the cost-savings gained form a properly designed, one-piece forging. Such part consolidations can result in considerable cost savings. In addition, weldments require costly inspection procedures, especially for highly stressed components. Forgings do not.

Forgings offer more consistent, better metallurgical properties. Selective heating and non-uniform cooling that occur in welding can yield such undesirable metallurgical properties as inconsistent grain structure. In use, a welded seam may act as a metallurgical notch that can lead to part failure. Forgings have no internal voids that cause unexpected failure under stress or impact.

Forgings offer simplified production.Welding and mechanical fastening require careful selection of joining materials, fastening types and sizes, and close monitoring of tightening practice both of which increase production costs. Forging simplifies production and ensures better quality and consistency part after part.

How Do Forgings Compare to Machined Bars/Plates?

Forgings offer a broader size range of desired material grades. Sizes and shapes of products made from steel bar and plate are limited to the dimensions in which these materials are supplied. Often, forging may be the only metalworking process available with certain grades in desired sizes. Forgings can be economically produced in a wide range of sizes from parts whose largest dimension is less than 1 in. to parts weighing more than 450,000 lbs.

Forgings have grain oriented to shape for greater strength. Machined bars and plates may be more susceptible to fatigue and stress corrosion because machining cuts material grain patterns. In most cases, forging yields a grain structure oriented to the part shape, resulting in optimum strength, ductility and resistance to impact and fatigue.

Forgings make better, more economical use of materials. Flame cutting plate is a wasteful process, one of several fabricating steps that consumes more material than needed to make such parts as rings or hubs. Even more is lost in subsequent machining.

Forgings yield lower scrap; greater, more cost-effective production. Forgings, especially near-net shapes, make better use of material and generate little scrap. In high-volume production runs, forgings have the decisive cost advantage.

Forgings require fewer secondary operations. As supplied, some grades of bar and plate require additional operations such as turning, grinding and polishing to remove surface irregularities and achieve desired finish, dimensional accuracy, machine-ability and strength. Often, forgings can be put into service without expensive secondary operations.

How Do Forgings Compare to Powder Metal Parts (P/M)?

Forgings are stronger. Low standard mechanical properties (e.g. tensile strength) are typical of P/M parts. The grain flow of a forging ensures strength at critical stress points.

Forgings offer higher integrity. Costly part-density modification or infiltration is required to prevent P/M defects. Both processes add costs. The grain refinement of forged parts assures metal soundness and absence of defects.

Forgings require fewer secondary operations. Special P/M shapes, threads and holes and precision tolerances may require extensive machining. Secondary forging operations can often be reduced to finish machining, hole drilling and other simple steps. The inherent soundness of forgings leads to consistent, excellent machined surface finishes.

Forgings offer greater design flexibility. P/M shapes are limited to those that can be ejected in the pressing direction. Forging allows part designs that are not restricted to shapes in this direction.

Forgings use less costly materials. The starting materials for high-quality P/M parts are usually water atomized, pre-alloyed and annealed powders that cost significantly more per pound than bar steels.

To get started on your next forging project, contact us to request a quote and someone from our team will reach out to you.