Metal forging is a manufacturing method that involves shaping metal using compressive force with a hammer, press or other equipment. Depending on the metal being forged and the desired output, this procedure can be carried out at various temperatures.
In this article, we will discuss the different methods and applications of metal forging.
What is metal forging & its purpose?
Forging, a metal shaping method that uses compressive, localized forces, has been around since the time of the ancient Mesopotamia in 4000 BC. The process has evolved significantly since then, resulting in a more efficient, faster and more durable technique.
Most forging today is completed with forging presses or hammering tools powered by electricity, hydraulics or compressed air.
The goal of forging is to quickly and repeatedly shape metal. Compared to other manufacturing methods, metal forging creates some of the most durable manufactured parts available.
Forging process: What happens to the metal?
Impurities in the metal break up and redistribute during the forging process. This drastically reduces the number of inclusions in the forged part.
What are inclusions? These are composite elements that are present inside steel during the manufacturing process, and produce stress spots in the final forged pieces. While impurities should be handled during the initial casting process, forging refines the metal further.
Forging also strengthens metal by alternating its grain structure; a crossed grain structure enables more even distribution of force, resulting in a stronger component.
Key characteristics of forged metal
- Dependability in highly stressed and sensitive applications. Offers good strength and toughness, crucial for important components.
- Forging typically creates little or no scrap, making it less expensive for medium to large manufacturing batches.
- The forging process can produce the final part very fast, typically within one or two hammer strokes.
Depending on the exact method employed, there are four types of forging equipment tools.
Forging at its most basic form requires impact; the most effective tool for generating this force is a hammer.
Smaller parts are still sometimes forged using hand tools, but on mass production lines, power hammers are used. These often use a combination of mechanical and hydraulic systems to raise and accelerate the hammer head. An anvil is usually incorporated into the tool but they also have the facility to attach other tools too, depending on the task.
Mechanical or hydraulic presses apply continuous pressure on forging dies. To vertically push metal into die cavities with controlled high pressure, this type of machinery often requires in excess of 50,000-tonnes of force. The metal is slowly pushed into the dies, rather than deformed with constant strikes.
Upsetter forging is similar to press forging, with the key distinction being that an upsetter is a horizontal forging press. Instead of driving metal downward, metal is pushed horizontally into the die impression.
Roll forging is often used to produce continuous parts. During this process, the workpiece is fed through two specially shaped rolls to form a long product with a varying cross section, minimizing the need for material removal.
What metals can be forged?
Because all metals can be impacted by heat and compression, forging can shape and create almost any metal; further refinements to the forging process have continuously increased that total.
Many manufacturers opt for forging because of its ability to create pieces with high mechanical qualities and minimal waste. The goal of the process is to deform metals to a specified geometry, giving them fatigue resistance and strength.
While most metals can be forged, carbon, alloyed and stainless steels are the most widely used. That being said, forging can efficiently and affordably generate a large number of pieces from most metals.
What metals cannot be forged?
Because of their limited ductility, some metals such as cast iron and select high-carbon steels, cannot be forged. Furthermore, some metals such as high-strength alloys may be too brittle to endure the forging process.
What are the different types of forging processes?
Open die forging
Open die forging, often known as “drop forging,” is a method of transforming a workpiece without entirely enclosing the metal material within the die. It requires you to pound the workpiece with the die until it takes on the shape and form of the die. The impression or die cavity determines the final forging shape.
The open die forging process utilizes heat and a power or drop hammer tool to strike the workpiece until the desired shape is obtained, before being placed in the anvil-type operation.
Closed die forging
Closed die forging, also known as impression die forging, is a method of enclosing a workpiece or billet by moving two pieces of a die towards each other. During the closed die forging process, the heated billet is placed in the bottom die, roughly the size of the finished item.
The force generated by the dies colliding compresses the billet to make the desired forged portion. Initially more expensive than other methods, the closed die forging investment is repaid with accuracy, quality and strength.
The roll forging method is a heated metal technique that shapes and deforms the object using opposing rolls. The geometric shapes cut into the rolls dictate the shape and dimensions of the part. Partially spinning rolls create the workpiece as it passes between them. The shape of the rolls ranges from one-fourth to three-fourths of the size of the two rolls. For secondary finishing, the roller grooves provide a varied cross-section to the workpiece.
Compression is the primary forming force in press forging. The metal is molded by a compression die at constant pressure while it sits on a stationary die. The metal’s contact time with the dies is significantly longer than in other types of forging, but the forging process benefits from the ability to simultaneously deform the entire product (rather than just a localized part). Either hot press or cold forging processes are available.
Upset forging, also called heading, is executed with hot forging or cold forging. To increase the cross-section of the workpiece, it is disturbed at one end. Upset forging creates nails, screws, nuts and bolts from a horizontal bar workpiece. A punch or die completes the shape of the workpiece.
Automatic hot forging
In automatic hot forging, mill-length steel bars sit at one end of the forging machine at room temperature, and hot-forged products emerge from the other. High-power induction coils heat the bar to temperatures ranging from 1200-1300°C (2190-2370°F) in less than 60 seconds. During this hot forging process, rollers descale the bar before dividing it into blanks.
Precision forging is more of a refinement technique rather than a shaping process. As products near completion, precision forging refines them to the point where little to no further machining is required. Metal is given the final touches before shipping or using the product in another phase of the manufacturing process.
The isothermal method of forging involves a distinct approach to workpiece heating. Some metals and alloys have low-temperature forging ability, which can make processing difficult.
Isothermal forging holds the workpiece at its ideal temperature throughout the process, which is performed by heating the die to the same or slightly lower temperature as the workpiece. This forging procedure eliminates the mold work interface and improves the final product’s properties.
Applications for forged metal
The forging technique is versatile and is utilized on pieces as small as a few inches in size to big components weighing up to 700,000 lbs (317,515 kg). It is used in the manufacturing of vital aviation parts as well as transportation equipment. Forging strengthens hand tools such as chisels, rivets, screws, and bolts.
The following applications incorporate forged goods:
- Critical aircraft parts (i.e., landing gear, shafts for jet engines, turbines)
- Connecting rods
- Fortifying hand tools (i.e., chisels, rivets, screws, and bolts)
Advantages of metal forging
Forging is a manufacturing process that offers many advantages, including increased strength and improved corrosion resistance. Metal forging is a manufacturing procedure that yields a more durable product than casting. Forged goods have exceptional corrosion resistance, higher fatigue strength and creep resistance, as well as enhanced mechanical properties.
The metal forging operation is low-cost and does not require a skilled operator. This approach can also produce parts in a wide variety of forms, making it a versatile solution for a variety of production applications.
Disadvantages of metal forging
The metal forging process is not without its limitations. Massive forging presses cost a pretty penny compared to other manufacturing techniques. To attain the appropriate surface finish, secondary finish operations are required.
Intricate forms cannot be produced by forging and the size of the forging portion is limited to the capacity of the press. And finally, fragile metals cannot be forged, limiting their use to a handful of applications. Nonetheless, forging is an important method for generating high-quality parts for most use cases.
Best metal for forging
It is possible to forge almost any metal. Although some metals and alloys are better suited for specific tasks, here are the most frequent metals used in forging:
- Carbon steel, alloy steel and stainless steel
- Brass and copper
- Exceptionally hard tool steels
- Alloys incorporating cobalt, nickel or molybdenum at high temperatures
It’s difficult to choose which of these options is “better” because it all depends on the specific needs of the buyer.
Metal at Metal Supermarkets for your next forging project
If you’re looking for metals for your next forging project, look no further! Metal Supermarkets carries a wide variety of forging metals, including aluminum, brass, bronze, copper, stainless steel and tool steel.
Metal Supermarkets is the world’s largest supplier of small-quantity metal, with a huge assortment of metal forms, sizes and grades. Contact us today to learn more!