Metal Forging Processes, Methods, and Applications | TFGUSA

Metal forging is the process in which metals are formed and shaped using compressive forces. The forces are delivered using hammering, pressing, or rolling.

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There are a number of forging processes – cold forging, warm forging, and hot forging – which are classified by the temperature of the metal being worked with.

Forging is one of the more pivotal metalworking processes in the metal manufacturing industry. It’s especially vital in the iron and steel industries and is viewed as a tremendous source of productivity.

The Origins of Metal Forging

Metal forging has deep roots in human history, dating back thousands of years. The process was initially simple, involving heating metal and beating it into shape using basic tools. Early humans discovered the transformative potential of heating metals in fires and then hammering them into desired forms. Over time, these rudimentary techniques evolved, giving birth to more advanced methods and tools.

The earliest known metal to be forged by humans was gold, a metal that was relatively easy to shape due to its low melting point. As humans advanced technologically, they began to work with other metals like copper, bronze, iron, and steel. The discovery and mastery of iron forging marked a significant milestone in human civilization, leading to the Iron Age.

What is The Metal Forging Process?

When choosing a type of forging, buyers have a long list of options for producing a critical metal component. It can be challenging to make the right choice, because each technique comes with varying pros and cons, revolving around costs and logistics.

However, choosing the forging method brings a plethora of unique benefits unavailable with any other choice.

With regards to price and overall quality, metal forging brings the most value. This notion rings doubly when maximum part strength, custom sizes, and critical performance specifications are needed for the application.

Here are some of the more common methods used:

• Closed die forging
• Open die forging
• Cold forging
• Roll forging

Open Die Forging, Closed Die Forging, and Roll Forging

The most common metal forging processes are open die forging, closed die forging, and roll forging.

What is Open Die Forging?

In open die forging, heated metal parts are shaped between a top die attached to a ram and a bottom die attached to a bolster, anvil, or hammer. With open die forging the metal is never completely confined or restrained in the dies.

Typically, temperatures range from anywhere between 500°F and °F, the appropriate temperatures are applied when working the metal parts.  Once the metal has been appropriately heated, the intricate hammering – or pressing of the workpiece – is performed to gradually shape the metal to its desired form.

Typically, the open die forging process is used to produce larger, simpler-shaped parts such as bars, rings, and hollows.

What is Closed Die Forging?

Closed die forging moves the die towards each other, covering the workpiece entirely or partially. There is heated raw material that’s nearing the shape/size of the final forged part and is placed in the bottom die.

This process works by incorporating the shape of the forging into the top or bottom die as a negative image. Once the process starts, the impact of the top die on the metal material forms it into the required forged form.

This process can be used to manufacture parts that range in size from a few ounces to 60,000 lbs.

What is Roll Forging?

Roll forging, also known as roll forming, is a forging method that uses opposing rolls to form a metal part. Even though roll forging uses rolls to produce parts and components, it is still considered a metal forging process and not a rolling process.

The process involves two cylindrical or semi-cylindrical horizontal rolls that are used to deform a round or flat bar stock. Through this action, the thickness is reduced, and the length is increased. Parts produced through roll forging have superior mechanical properties than those produced from many other processes.

After being inserted, a heated bar is passed between the two rolls. It’s progressively shaped while rolling through the machine’s shaped grooves. The precisely shaped geometry of these grooves are what forge the part to the specified dimensions.

Roll forging is often used to produce parts for the automotive industry. It is also used to produce things like knives and hand tools.

Standard Forging Equipment

There are several primary tools that are used in the metal forging process depending on the exact method being used.

Forge

The forge is the primary heating apparatus used to reach the required temperature for forging. Modern forges utilize gas or electric heat sources.

Hammers

The hammer, or power hammer, is a tool most commonly associated with forging. Whether a hand-held hammer or a massive power hammer, the tool is used to repeatedly hit the metal in order to deform it. As long as it possesses a 50,000 lbs driving force to deliver high-pressure impact blows, a hammer can pound metal into shape.

Presses

Presses use either mechanical or hydraulic pressure to apply continuous pressure on forging dies. This kind of equipment requires a 50,000 ton driving force to vertically squeeze metal into die cavities with controlled high pressure. Instead of hitting the metal repeatedly to deform it, the metal is slowly pressed into the dies.

Upsetters

Upsetter forging is similar to press forging, however, the main difference is that an upsetter is a forging press that is used horizontally. Instead of forcing the metal downward into a die, the metal is moved into the die impression in a horizontal direction.

Ring Rollers

Ring rollers are used to produce rings with diameters from just a few inches to over 300 inches. Ring rollers squeeze out a one-piece ring, which removes the need for welding. It turns a hollow round piece of metal under extreme pressure against a rotating roll.

How Does Forging Strengthen Metal?

Compared to other manufacturing methods, metal forging is known to produce some of the strongest manufactured parts available.  As the metal is heated and pressed, minor cracks are sealed and empty spaces found in the metal are closed up.

In addition, the hot forging process breaks up any impurities in the metal and redistributes such material across the metalwork. This results in vastly reduced inclusions in the forged part. Inclusions are compound materials embedded inside steel throughout manufacturing, causing stress points in the product.

Even though impurities should be managed during the initial casting process, this process will further refine the metal.

Another way that forging strengthens metal is through the altering of its grain structure. This has to do with the material’s grain flow as it deforms. Like other forming processes, a favorable grain structure can be created, making the forged metal sturdier.

Advanced Forging Techniques and Applications

Industries continue to demand higher precision in manufactured metal components, and advanced metal forging techniques have emerged to meet those needs. With innovations in metal forging processes like thixoforming, precision forging, and incremental forging, modern metal manufacturers are able to push the boundaries of traditional forging methods.

Thixoforming

The term “thixotrophy” was coined in by Hungarian biologist Tibor Péterfi. Combining the Greek phrases thixis (shaking or mixing) and trepo (changing), the word describes how materials become less viscous when shaken or stirred and return to their original state when agitation stops.

Thixotrophy plays an essential role in thixoforming. Similar to the thixotropic materials that are found in our everyday world, such as gels, lotions, ketchup, and mayonnaise, molten metals achieve a thixotropic state after being heated. These semi-solid metals are then injected into a die to produce high-precision parts.

As a hybridized forging manufacturing process, thixoforming incorporates aspects of both casting and forging. Thixoforming typically refers to the process of using an open die forging process, while thixocasting is performed using a closed die. In addition to increased precision, both processes offer advantages like energy efficiency and reduced waste.

Components made by thixoforming have fine structures with reduced weight properties, and the surface quality achieved with this method often eliminates the need for extra machining steps. With fewer defects, this method is often used to manufacture light-weight precision parts for the electronics industry. 

Precision Forging

Precision forging, also called net-shape forging, is more a refined approach to die forging than a unique process. With precision forging, the goal is to create highly accurate components with minimal need for secondary operations like machining and finishing.

In precision forging, metal is heated to a specific temperature to make it more malleable. Then, high-pressure equipment is used to force the metal into die cavities. This ensures uniform filling and accurate reproduction of the die design.

While precision forging requires advanced equipment to heat and cool the metal uniformly, it offers several advantages over traditional die forging techniques. The advanced dies are used to achieve near-net-shape components with intricate geometries and tight tolerances, making this metal manufacturing method ideally suited for creating medical instruments as well as complex parts for industrial machinery.

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With advantages like material savings and superior dimensional accuracy, precision forging is expected to become more popular. Companies looking for cost savings and shortened lead times can benefit significantly from precision metal forging techniques.

Incremental Forging

Another advanced forging technique, incremental forging is a progressive metal forming process with advantages like greater design flexibility, reduced tooling costs, and increased precision and control. It’s ideal for forging sheet metal into large, complex metal components with intricate internal features.

The process begins with placing sheet metal into the press, and it is gradually shaped into a three dimensional form by applying pressure in incremental stages. Similar to “drawing” the shape onto the raw material, the step-by-step deformation of metal in incremental forging does not require a die. Typically, the process is controlled by a CNC machine, resulting in a precise and repeatable outcome.

In addition to reducing tooling costs, incremental forging makes it easier to create new design iterations. Compared to other forging techniques, the ability to refine design shapes makes this forging method an attractive option for many modern manufacturing applications. Incremental forging is a top choice for manufacturing complex, custom components for industries like manufacturing.

Common Defects in Forging and How to Prevent Them

Even though modern forging methods are exceptionally precise, identifying and addressing common defects is crucial to ensure the quality and performance of performance parts with tight tolerances.

Identifying Common Defects

While forging has numerous advantages, it’s not without challenges. As a whole, forging is highly efficient for producing durable and reliable components, but occasionally, defects can impact the functionality of the forged parts.

Here are the most common defects in forging:

• Voids– Voids can be caused by anything from poor design to improper heating techniques. Unfilled sections in the metal, usually the result of gas or air trapped in the metal during forging, impact the strength and durability of the part. 
• Cracks– Typically found on the surface, cracks are related to low temperatures or excessive stress. They compromise the integrity of the component, making it prone to failure.
• Laps– Laps are formed when the metal folds over itself, creating a weak seam in the part. The most common causes are insufficient material flow and poor die design.
• Cold shuts– Cold shuts create a weak seam when the forging process leaves a gap in the forged part. As in lap defects, the weak bond or connection is usually caused by improper material flow, often related to insufficient heat.
• Excess flash– Flash is the material that flows out of the die cavities during forging. When too much material escapes, the result is higher material waste and more machining or finishing work.
• Burnishing– Scratches or indentations that affect the surface of the component are usually caused by excessive friction or lack of lubrication. Depending on the application, burnished components may require significant finishing or reworking.
• Inadequate grain structure– Improper grain flow leads to uneven or imbalanced grain patterns that impact the structural integrity of the metal, affecting the component’s mechanical properties. This defect has numerous causes, including poor material quality, improper design, and insufficient heating.

By understanding common metal defects and their causes, metal manufacturers and buyers can implement better controls to reduce costs and produce superior parts. Using automated controls is one of the best ways to minimize defects and ensure high-quality forged components.

Non-Destructive Testing Techniques

Many forging defects cannot be identified with surface inspections. Non-destructive testing (NDT) techniques make it possible to discover defects in metalwork to ensure the integrity of parts without causing any damage to the components themselves. 

Here are a few of the most common NDT techniques:

• Ultrasonic testing– Ultrasonic testing is a family of NDT methods used to send sound waves through forged components to identify cracks, voids, and porosity defects. With this method, the thickness of the material can also be determined. Ultrasonic testing is highly sensitive and results are typically immediate.
• Radiography– Similar to the x-rays used in medical applications, radiography testing for forged metal components uses gamma rays to penetrate the material and produce images of its internal structure. This method is ideal for critical components like those used in the medical industry.
• Magnetic particle testing– Used to identify defects in ferromagnetic materials, magnetic particle inspection (MPI) involves creating a magnetic field around the component. Then, fine iron particles are applied to the surface. Particles that accumulate indicate a magnetic flux leakage, which shows the presence of a defect. A rapid testing method, MPI is highly sensitive and cost-effective. 

These NDT techniques provide critical insights into the internal structure of forged components, helping to ensure that manufactured parts meet strict standards for exacting applications.

What Products Require Forged Metal?

Image above: Alignment pins manufactured via forging by TFG USA.

The forging process is incredibly versatile and can be applied to anything from small parts measured in inches to components that weigh up to 700,000 lbs.

Forged products can be structural components in the following:

Agricultural Equipment

Agricultural equipment often relies on metal forged parts to endure the demanding conditions of the farming landscape. Tractors, plows, harrows, and combine harvesters, essential for modern agriculture, incorporate metal forged components like gears, axles, and blades.

The superior strength and resilience of these forged parts ensure the machines can handle the rigors of tilling, planting, harvesting, and more. Farmers benefit from increased efficiency, durability, and reduced maintenance costs, ultimately contributing to higher agricultural productivity and sustainable farming practices.

Construction Equipment

Construction equipment, built to withstand rigorous demands, extensively utilizes parts created by metal forging. Heavy machinery such as excavators, bulldozers, cranes, and pile drivers integrate critical forged components like pins, gears, cylinders, and structural parts.

The resilience and robustness of forged metal ensure these machines can endure the tough conditions of construction sites, lifting heavy loads, excavating, and shaping the landscape. By utilizing metal forging, construction equipment achieves longevity, safety, and efficiency, essential for completing diverse projects ranging from buildings and bridges to roads and dams.

Oil Mining Equipment

Metal forging plays a crucial role in the manufacturing of durable and robust components for oil mining equipment. Drill bits, couplings, valves, and pump components are commonly forged to withstand the demanding conditions of oil extraction.

The extreme pressures and abrasive environments of oil drilling necessitate the strength and durability that forged parts offer. By using forged components, the oil industry achieves heightened operational efficiency, minimizing downtime and maintenance costs. These specially crafted forged parts endure the relentless rigors of oil mining, ensuring a reliable and efficient extraction process vital to meeting global energy demands.

Railroad Equipment

The railway industry relies on metal forging for the reliable and safe operation of trains and rail systems. Vital components like axles, wheelsets, couplers, and connecting rods are forged to endure the immense stresses encountered during rail operations.

The durability and high strength of these forged parts ensure the safety of passengers, cargo, and railway infrastructure. By incorporating forged components, the railway sector achieves enhanced performance, longevity, and the ability to efficiently transport people and goods across vast distances, contributing to the backbone of modern transportation and trade.

Also, forging is used to fortify hand tools (e.g., chisels, rivets, screws, and bolts).

What Is the Best Metal for Forging?

It’s possible to forge any kind of metal, but there are certain metals and alloys that are better suited for different applications.

Most commonly, these are the kinds of metals that get forged:

• Carbon, alloy, and stainless steel
• Exceptionally hard tool steels
• Aluminum
• Titanium
• Brass and copper
• High-temperature alloys containing cobalt, nickel, or molybdenum

Out of these choices, it’s almost impossible to choose which is the “best,” as it really depends on the needs of a customer.

Economics 101 for Metal Forging

In smaller quantities, forged parts can be very expensive on a price per unit basis. This is primarily due to manufacturing forging die coming at a high upfront cost – a trait shared by other expenses associated with setting up shop.

Once everything has been set up and you’ve purchased the dies, the actual costs for operating are reasonably affordable, especially with automation playing a massive role. Taking this into consideration, this metal fabrication method is typically best for products that are being produced in more substantial quantities.

As the world continues to modernize, high-quality manufactured parts will only grow in demand. Since forging produces some of the strongest metals imaginable, it should be no surprise that the market is projected to be worth $131.32 billion by .

Sustainable Practices in Metal Forging

As industries seek to reduce costs and reduce their environmental impact, sustainable forging practices continue to gain importance. Meeting sustainability goals is often achieved through reducing material waste, recycling scrap materials, and implementing energy-efficient technologies.

To reduce material waste, metal manufacturers focus on optimized die designs and automated processes to ensure accuracy and maintain quality. Manufacturers recycle scraps and waste to reduce the need for raw materials, thereby conserving resources and reducing energy consumption at various stages of production.

Modern forging methods typically use electric or gas heating, and by implementing advanced techniques to capture and reuse waste heat, manufacturers can significantly reduce energy consumption. The benefits of reduced energy consumption can also be seen in lowering the overall production costs of components.

Trends and Future Directions in Metal Forging

The outlook for the metal fabrication industry is strong. The market demand for reliable and durable forged components continues to revolutionize efficiency and precision in metal forging techniques. Emerging trends like automation, digital twin technology, and advanced materials are paving the way for the next generation of metal forging.

Automation in metal forging offers benefits like increased efficiency, shortened lead times, and improved consistency. Automated systems reduce labor costs and waste, allowing manufacturers to maximize production output while maintaining high quality standards. Some examples of automation in forging include robotic arms for handling materials, CNC machines to increase precision, and automated inspection systems to check for defects.

Another emerging trend is digital twin technology. In simple words, digital twin technology in metal forging is creating a virtual copy of a physical object. This virtual version of a component behaves the same as the real one, allowing manufacturers to predict problems and make design decisions. With digital twin technology, it’s possible to experiment with new approaches or material designs without the cost of physically testing them.

One of the most exciting trends in metal forging is the development of advanced materials. Lightweight alloys and high strength steel alloys are creating opportunities for manufacturers in every sector. These advanced metal forging materials offer benefits like enhanced corrosion resistance and increased strength-to-weight ratios, making them ideal for demanding applications.

Starting A Metal Forging Project

If you’re interested in producing custom metal parts or components and think that metal forging services may be the best option for you, don’t hesitate to give The Federal Group USA a call.  Our experienced support team members will go through your project requirements with you, help you determine the best course of action, and provide you with a free quote for your project.

Contact us to discuss your requirements of Open die forging solution. Our experienced sales team can help you identify the options that best suit your needs.