The purpose of annealing is to increase the ductility of the metal and reduce its hardness to make it more workable. As a function of the annealing process, the metal is heated above its recrystallization temperature and remains in that condition while it is being worked.
How rapidly the metal cools during annealing is dependent on the type of metal. Though annealing is mainly related to hot forging, it is also used in cold forging. When annealing is part of cold forging, the temperature of the metal is only sufficiently raised to allow it to be forged; this means it is slightly below its recrystallization point.
Once the metal has reached a point where it is pliable, it is formed, shaped, configured, and manipulated to achieve the desired formation. This part of the process can include hammering, grinding, molding, compressing, and bending; this is dependent on the chosen method.
Regardless of the forging process, the metal is put through a set of stressing steps designed to transform it into the planned design. The hardening of the forged part depends on the chosen process. With cold forging, the working of the workpiece hardens it, which strengthens the plastic deformation. This does not happen in hot forging, as the metal hardens and strengthens through recrystallization.
As the metal is compressed and deformed through forging, the grain structure is changed to conform to the geometry of the forged part. In cold forging, the process leads to fatigue resistance and improved mechanical properties. As can be seen in the diagram below, the grain flow for forged parts conforms to the shape of the part.
The tempering process makes the metal stronger. Included in tempering is heating, shaping, cooling, and reheating, which creates stress. By tempering a forged part, the metal becomes less brittle and more ductile without sacrificing hardness. The process of tempering produces harder and tougher parts that are weldable and ductile. Part of this toughness is greater resistance to wear and abrasion, which is important for parts that will face extreme wear and harsh conditions.
Most parts that are produced by forging can be manufactured using other processes. Forging is popular when compared to other processes because of the strength and durability of the finished products. The forging process alters the structure of metals by compressing it, which causes the metal to undergo metallurgical recrystallization and realignment of its grain.
The completed parts have higher impact and shearing strength that enhance their longevity and usefulness. The most common picture of forging is a blacksmith with a hammer pounding out a shape on an anvil. The manual hammering and shaping of metals has been the image of the forging process over the centuries. Fortunately, through technological developments and advancements, the forging process has moved a great distance from the hammer and anvil stage.
Modern forging uses a wide range of technical methods and heavy duty equipment to produce parts that are essential for most necessities of society. The term forging is a general term that is applied to several methods used to transform sheets of metal into useful items. Universally, forging is categorized is by cold and hot forging, where cold forging works and shapes metal with limited use of heat and hot forging heats metals nearly to their melting point.
Open die forging, sometimes referred to as drop forging, transforms a workpiece without completely enclosing the metal material within the die. Open die forging is done by pounding the workpiece with the die until the workpiece takes the shape and form of the die. Prior to being placed in the anvil type process, the workpiece is heated and then hammered until it takes the desired shape.
Closed die forging, also known as impression forging, is a process where two halves of a die move toward each other to enclose the workpiece or billet. The heated billet is placed in the bottom die and is approximately the size of the part to be completed. The force provided by the meeting of the dies compresses the billet to form the required forged part. Though this process is initially more expensive than other forms of forging, the investment is recovered by the accuracy, quality, and strength of the completed parts.
Cold forging shapes, deforms, and processes metals at room temperature or slightly above room temperature. The term cold forging is a general term that includes drawing, heading, coining, punching, and thread rolling. The temperature of the metal is three tenths of its recrystallization temperature. Cold forging is the preferred method for shaping soft metals such as aluminum and copper.
The benefits of cold forging include reduced processing of finished parts, better surface finishes, improved dimensional stability, and lower cost. Roll forging is a heated metal process that uses opposing rolls to shape and deform the workpiece. The shape and dimensions of the part are determined by geometric shapes that have been cut into the rolls. The part is produced by a partial turning of the rolls as the workpiece passes between them. The shape on the rolls is one fourth to three fourths of the two rolls.
The grooves in the rollers give the workpiece a variable cross section for secondary finishing. The workpiece for rolled ring forging has the middle removed prior to processing to create a donut shape or oval. It is heated to make it workable and pressed between a driver roll, an idler roll, and axial rolls that rotate at the same time. The workpiece is placed on the idler roll, which slowly moves it against the driver roll that increases the diameter of the workpiece causing its walls to get thinner.
The axial rolls control the width of the ring as it is rotated by the idler roll. At the completion of the process, the rolled ring is a seamless oval for the production of gears, valves, clutches, and bearings. The benefits of the rolled ring process include stronger components, less machining, a strong grain pattern, and the ability to use a wide range of materials.
The diagram below is an example of rolled ring forging. Upset forging, also known as heading, may be performed hot or cold. The workpiece is upset at its end to increase its cross section. It is normally completed on a horizontal bar workpiece and is commonly used to manufacture nails, screws, nuts, and bolts. The creation of the shape on the workpiece can be completed with a punch or die.
In some cases, both processes are used to achieve the required shape. The stages of the process can be seen below in this cold forging example where a rod is secured in the bottom portion and is repeatedly struck by different dies to achieve the desired shape. Think back to what it was like trying to bend that piece of metal. But any metal much sturdier than that is pretty unwieldy. In order to work metal, blacksmiths have to heat it first.
The forge itself can work in a few different ways. Picture a fireplace or wood-burning stove—a forge looks a lot like that. For heat, many forges use coal. To work a coal forge, a blacksmith will also need bellows to force air into the fire.
Other forges use gas or solar power. The blacksmith holds the metal using a pair of tongs and heats it up in the forge. Then, they hold the metal over a large anvil and hit it with a hammer, shaping it into the desired form.
For thousands of years, blacksmiths made just about every metal object needed for daily life. They made hammers, nails, and screws used for building. They created plows for farmers, weapons for soldiers, and shoes for horses. Blacksmiths even made all the metal household items, like candlesticks and utensils, for everyday people.
After the Industrial Revolution , forging changed. The development of the steam hammer and other technologies have made forging a largely automated process today. However, some people still practice traditional forging as both a career and a hobby.
Would you like to learn to use a forge? B, CCRA. Are you forging a real interest in this topic? Find an adult friend or family member who can help you with one or more of these activities:. We are undergoing some spring clearing site maintenance and need to temporarily disable the commenting feature.
Thanks for your patience. Drag a word to its definition. You have answered 0 of 3 questions correctly and your score is:. Seamless ring configurations can be flat like a washer , or feature higher vertical walls approximating a hollow cylindrical section. Heights of rolled rings range from less than an inch up to more than 9 ft. In fact, seamless tubes up to in. Even though basic shapes with rectangular cross-sections are the norm, rings featuring complex, functional cross- sections can be forged to meet virtually any design requirements.
A key advantage to contoured rings is a significant reduction in machining operations. Not surprisingly, custom-contoured rings can result in cost-saving part consolidations. Compared to flat-faced seamless rolled rings, maximum dimensions face heights and O. High tangential strength and ductility make forged rings well-suited for torque- and pressure-resistant components, such as gears, engine bearings for aircraft, wheel bearings, couplings, rotor spacers, sealed discs and cases, flanges, pressure vessels and valve bodies.
Materials include not only carbon and alloy steels, but also non-ferrous alloys of aluminum, copper and titanium, as well as nickel-base alloys. Home Types of Forging Processes. Types of Forging Processes There are basically three methods or processes to make a forged part. Still Graphic Animated Sequence Video Process Capabilities Commonly referred to as closed-die forging, impression-die forging of steel, aluminum, titanium and other alloys can produce an almost limitless variety of 3-D shapes that range in weight from mere ounces up to more than 25 tons.
Back To Top Cold Forging Most forging is done as hot work, at temperatures up to degrees F, however, a variation of impression die forging is cold forging. Process Capabilities Cold forging encompasses many processes bending, cold drawing, cold heading, coining, extrusion, punching, thread rolling and more to yield a diverse range of part shapes. Still Graphic Animated Sequence Video Process Capabilities Open-die forging can produce forgings from a few pounds up to more than tons.
In addition to round, square, rectangular, hexagonal bars and other basic shapes, open-die processes can produce: Step shafts solid shafts spindles or rotors whose diameter increases or decreases steps down at multiple locations along the longitudinal axis.
Hollows cylindrical in shape, usually with length much greater than the diameter of the part. The benefits are the near net shapes lead to lower machining requirements and, therefore, lower scrap rates, and the metal part is highly reproducible.
Another advantage is that smaller machines can be used to make the forging due to the lower heat loss. A few disadvantages are the higher die material costs to handle temperatures and pressures and the required uniform heating systems.
It also has a low production rate. The most popular type of forging equipment is the hammer and anvil. The idea behind the hammer and anvil is still used today in drop hammer forging equipment.
The hammer is raised and then dropped or propelled into the workpiece, which rests on the anvil. The main variations between drop hammers are how the hammer is powered, the most common being air and steam hammers. Drop hammers typically operate in a vertical position. This is because the excess energy that isn't released as heat or sound, meaning energy that isn't used to shape the workpiece, needs to be conveyed to the foundation. A large machine base is also required to absorb the impacts.
To overcome some shortcomings of the drop hammer, the counterblow machine or impactor is used. Both the hammer and anvil move in a counterblow machine, with the workpiece held between them. Here, excess energy becomes recoil, allowing the machine to work horizontally and have a smaller base. This creates less noise, heat, and vibration. It also creates a distinctly different flow pattern.
These machines are used for open die or closed die forging. A press is used for press forging. The two main types are mechanical and hydraulic presses. Mechanical presses function using cams, cranks, and toggles to make preset and reproducible hammer strikes.
Because of the characteristics of this type of system, different forces are available at different stroke positions. As a result, these presses are faster than their hydraulic counterparts by 50 strokes per minute. Their capacities range from three to MN. Hydraulic presses use fluid pressure and a piston to produce force.
The advantages of a hydraulic over a mechanical are its flexibility and superior capacity. The disadvantages are that it is a slower, larger, and costlier machine to operate. The roll forging, automatic hot forging, and upsetting processes all use specialized machinery.
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