This article covers everything you need to know about forging.
You will learn about topics such as:
- What is Forging?
- Steps to the Forging Process
- Different Types of Forging
- Metals That Are Forged
- And much more …
Chapter One – What is Forging?
Forging is a metal working process that manipulates, shapes, deforms, and compresses metal to achieve a desired form, configuration, or appearance outlined by a metal processing design or diagram. Depending on the type of metal and the requirements of the design, the forging process can be completed using either hot or cold forging processes.
Modern equipment, machines, and appliances depend on forged components as a central part of their mechanism. The endless number of forged parts include various types of tools, guns and rifles, and parts for vehicles. Though forging is an ancient process, it is still an essential part of most metalworking manufacturing.
Chapter Two – Steps to the Forging Process
The forging process has existed for several thousand years in different forms as a means for shaping metal. With technological advancements and the development of new metals, forging has changed but maintains much of its original form. Regardless of the method, forging involves the shaping of metal. The basic steps vary but retain some semblance of similarity.
Steps to the Forging Process
Much of the determination of which forging process to use is dependent on the type of metal. Nearly every metal can be forged regardless of the fact that metals have different characteristics and properties in relation to their weight, tensile strength, and deformation capabilities.
The common types of metals for forging include carbon, alloy, stainless steel, aluminum, titanium, brass, copper, cobalt, nickel, and molybdenum.
The type of impact and compression operation used depends on the metal. Heavier metals need to be heat treated before forging, while softer metals, like aluminum, brass, and copper, can be cold forged. Regardless of whether the method is hot or cold, the forging process will involve the use of some type of force with a hammer, mold, or heavy weight; this is at the heart of the forging process.
Annealing is a major part of the forging and is designed to change the physical shape and properties of a metal. 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. This feature enhances the part’s strength and fatigue resistance.
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.
Chapter Three – Different Types of Forging
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.
Different Types of Forging
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.
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.
The isothermal method of forging takes a different approach to the heating of the workpiece. Certain metals and alloys have a low temperature forgeability, which can make it difficult to process the metals. With isothermal forging, the workpiece is kept at its highest temperature during the forging process. This is accomplished by heating the die to a temperature that is at or slightly below the temperature of the workpiece. This method of forging eliminates the mold work interface and improves the characteristics of the final part.
Multidirectional forging is a time and cost saving hot forging process for the production of complex and intricate parts. A mill length steel bar is inserted into the forging machine at room temperature. As the bar enters the machine, it is super-heated by induction coils to temperatures between 2000o F and 2400o F. The bar is then descaled and formed into blanks, which progress into the forging mechanism. A precisely timed series of forming stages shape the blanks. After this, the completed parts are cooled and finished by cold forming.
As the heated workpiece goes through the multidirectional forge, it is completely formed in a single step with rams shaping it from both horizontal and vertical directions.
Chapter Four – Metals That Can Be Forged
Most metals can be shaped and formed using forging. As the process has been studied and perfected, the number of metals has been steadily increasing since all metals can be affected by heat and compression. The use of forging is due to its ability to produce parts with exceptional mechanical properties with limited waste. The purpose of the process is to deform metals to a desired geometry, which gives the metal fatigue resistance and strength.
Though most metals can be forged, carbon, alloyed, and stainless steels are the metals that are commonly used. Forging can produce large numbers of parts efficiently and economically using any form of metal.
Metals That Can Be Forged
Carbon steel is malleable, easily processable, and forgeable, and it responds positively to heat treatment. The main benefits of carbon steel are its low cost, adaptability, strength, and ease of deforming and shaping. It is the most common metal used for the forging of parts and components found in several industries.
Stainless steels are iron that has been alloyed with chromium. Other alloys are added to improve the structure and properties of the metal; this increases its formability, strength, and toughness. The main attraction of stainless steel is its corrosion and rust resistance, which broaden its use to a variety of environmental and processing conditions.
Stainless steel is a generic term that covers a wide range of metals of differing grades. The performance of each grade is different due to their varying compositions. The 300 and 400 series grades of stainless steel are ones that are commonly used for forging.
Grades of Stainless Steel
The 300 series is made of iron and chromium nickel alloys.
- 301 – has wear resistance, weldability, and rapid hardening with high ductility.
- 304 – is the 18/8 grade of stainless steel, referred to as A2, with 18% chromium and 8% nickel. It has yield and tensile strength as well as exceptional density.
- 316 – is classified as marine grade and has high chloride corrosion resistance.
The 400 series of stainless steel is 11% chromium and 1% manganese with a higher carbon content, which gives it a martensitic crystalline structure, which gives this grade of stainless steel higher wear resistance and strength.
- 408 – is resistant to heat but not suited for corrosive environments.
- 409 – the most affordable stainless steel alloy used in automobile exhausts.
- 420 – easily polished and referred to as cutlery grade.
- 440 – is the highest grade of cutlery steel due to its hardness and edge retention.
Alloyed steel is combined in varying proportions with manganese, silicon, nickel, titanium, copper, chromium, tungsten, molybdenum, and aluminum. These extra elements are added to improve the basic properties of the steel, which include its hardness, corrosion resistance, strength, formability, weldability, and ductility. Steel with more than 8% of its weight in other elements is considered to be a high alloy steel. If the carbon content is above 8%, the steel is difficult to form. If it is below 3%, the steel is more formable.
Aluminum is in the category of soft metals due to its low melting point. Though aluminum is lightweight and easily shaped, it is still very strong and resistant to corrosion and rust. In most cases, it is alloyed with other metals to enhance its natural properties. A main benefit of aluminum is its ability to be continuously recycled without loss of its characteristics or qualities.
Copper, like aluminum, falls into the soft metal category and is easily formable. In the forging process, copper is used as bars. Forged copper has an increased microstructure and retains its mechanical properties. Copper forging is a hot closed die forging process where the copper is heated by induction.
Titanium is a high strength, low density metal with exceptional corrosion resistance; it is ductile and has a high melting point. Parts produced from titanium have properties similar to those found in carbon steel forgings but are much lighter. A major benefit of titanium is its ability to withstand high temperature environments —up to 1000o F. The excellent strength to weight ratio of titanium makes it ideal for engine and aircraft components as well as valves for the chemical industry.
Brass is an alloy of copper and zinc. The mechanical properties of brass depend on the percentage of zinc and other elements. The combination of copper and zinc makes brass harder yet softer than copper, with a low melting point. The formability of brass makes it ideal for applications that require a metal with exceptional thermal and electrical conductivity. Like copper, brass is corrosion and rust resistant and can be used in environments that require parts that have durability and longevity.
Nickel forgings are used for high temperature environments where the conditions are severe and wear resistance is a necessity. The forging of nickel creates geometric shapes that do not require machining and refines the grain structure of the metal. Nickel is forged using hot forging with a closed die. A benefit of nickel forging is the ability of the metal to maintain its flow stress, which makes it ideal for such industries as aerospace, oil, defense, and marine.
Chapter Five – Forging Equipment
The metal forging process involves the shaping and forming of metals using compressive force, which is delivered by hammering, pressing, stressing, and rolling. The types of forging processes include cold and hot, determined by the temperature at which the metal is deformed.
Forging plays a major role in the manufacturing of many of the items that are a pivotal part of product production and industrial operations. Regardless of how many technical advances have been made by industry, forging is still at the center of efficient, economic, and high quality production.
A drop hammer machine consists of two dies, with one placed on a stationary anvil and the other attached to a ram. A heated billet is placed in the lower, stationary die. The ram brings the upper die down on the stationary die with great force multiple times to shape the billet. The number of times the hammer strikes the billet depends on the item being produced.
There are various types of drop hammers:
A board drop hammer depends on gravity to supply the speed at which the hammer will strike the workpiece.
A belt driven drop hammer is similar to a board drop hammer. The ram has a belt connected to it that is controlled by rollers that grip the belt. As the ram raises, the belt slackens. When the rollers are released, the ram drops and strikes the workpiece.
Power drop hammers use pressurized air to raise the ram and accelerate the dropping speed.
Press forging machines follow the same principle as drop forging but without the multiple blows to the workpiece. As with drop hammer machines, there is a die with two halves, with one on the anvil and one connected to the ram. Instead of concussive force being continuously applied, the upper die slowly squeezes and compresses the workpiece into the lower die. The force of the compression is applied by a hydraulically driven or screw driven ram, which penetrates deep into the volume of the workpiece, uniformly causing a plastic deformation.
The heart of a roll forging machine is the opposing rollers that shape the workpiece and carry the dies. Support rails give the rollers constant spring such that the framework can have a low spring constant. When in operation, the rollers are forced together with greater force than is necessary to deform the workpiece. Backup rollers bear against the work rollers and are positioned asymmetrically to the plane of the workpiece. A hydraulic cylinder drives the work rollers together to shape the work piece at a constant and steady pressure.
The upsetter forging machine process places the workpiece between two horizontal grooved dies to hold the workpiece while it is deformed by being rammed and punched on one end. The term upsetting comes from upsetting the shape of a billet, bar, or bloom. The metal is worked on the horizontal plane so as to increase the cross sectional area of a part of the workpiece. Upsetter forging is sometimes referred to as heading where pressure is placed on a hot or cold rod or billet.
A rotary forging machine operates by placing the workpiece in a circular housing with rotor holding, free moving anvils that have a die on one end. The workpiece is placed in the center of a set of rollers and anvils that is enclosed or encased in a cage. As the cage rotates, the rollers force the anvils to hammer or impact the workpiece until it reaches the necessary shape.
Chapter Six – Industry Forged Parts
Forging is an ancient technique that has been used for centuries to produce and fabricate necessities from metal. Over the many years of its existence, forging has been perfected, reinvented, and changed to manufacture metal components and parts for most of the appliances and equipment used today.
Because forging has been around for centuries and has been steadily improving over time, it would be impossible to list all of the uses producers have found for forged products. A few uses for forged parts are tools found in home workshops, huge pipeline fittings, components in agricultural machinery, and parts for spacecraft.
Products Made from Forging
The strength, reliability, and durability of forged components make them ideal for heavy duty stressful applications.
The first consideration regarding forged parts for the auto industry is how inexpensive the forging process is though it produces high quality and reliable components. The main use of forged parts is placement at points of shock, stress, and impact such as wheel spindles, kingpins, axle beams, ball joints, and steering arms. In the powertrain, transmission components, connecting rods, the differential, and clutches are forged for durability and longevity.
One of the demands of the agriculture industry is that any parts, machines, components, or connectors must be durable in order to withstand the demands of farm work and its harsh conditions. Aside from these requirements, much like the auto industry, farmers need equipment that is economical. Any type of farm machinery must meet these criteria, which is why manufactures rely on forging to fulfill the demand.
Much like farming, the oil industry requires that any parts and components be durable and reliable. This is especially true regarding valves and fittings. The superior mechanical properties of forged parts make them ideal for the oil producing conditions and pressure applications. Oil fields have a wide range of damaging fluids that can harm equipment. The casings and coverings of valve bodies, flanges, reducers, and saddles must be corrosion, wear, and heat resistant as well as able to perform in all environments.
The area where most people have contact with forged parts is hand tools, which include a variety of hammers, pliers, wrenches, and garden tools. Forged hand tools have the highest quality, exceptional performance, and guaranteed reliability. Since tools can be produced using several different shaping and forming methods, forged tools are clearly labeled as being forged to ensure customers know they are getting the best.
The railroad industry requires equipment that is strong, tough, machinable, and economical. The gears, transmissions, levers, joints, hubs, and rollers necessary for the operation of heavy duty railroad machinery must be able to react immediately with precision and accuracy. Since most railroad equipment is made of a form of steel, it is understandable why forging is so important to the industry.
Any industry that has metal components and parts as a central aspect of its operation relies on forging for the production and fabricating of its components and products. The list of producers includes textiles, paper, power generation, and chemical production. Each of these industries require that their equipment be reliable and available to ensure constant and continuous production.
Whether a weapon is being made for the casual hunter or a soldier in a battle zone, it is important that it perform flawlessly and instantly. The main components in all forms of weaponry rely on forged parts. Since most weapons are used in harsh and stressful conditions, they must be tough and sturdy enough to be able withstand the demands of the conditions and environment. It is for these reasons that forged parts are the building blocks for high performance weapons.
A factor that influences the performance of an aircraft is the strength to weight ratio, which has an impact on the craft’s range and payload. To produce safe and reliable aircraft, special alloys are created that have the durability and weight to meet the performance needs of aircraft applications. Aircraft production requires precision and accuracy such that each part and component fits flawlessly and works together harmoniously. The strength and endurance of forged parts make them a necessity.
Chapter Seven – Benefits of Forging
The many positive features of forging is the reason that it has been a central part of metal forming for so many years. Machinery, engines, and technical equipment depend on forging to supply strong, lasting, and reliable parts that provide optimum performance in any conditions. Manufacturers and producers depend on forging to provide the components for their products due to the positive and beneficial performance of forged parts.
The controlled deformation of the forging process results in metallurgical soundness and exceptional mechanical properties. This factor is the result of the pre-working of the metal before inserting it in the forging process, which creates the proper grain flow and directional properties of strength, ductility, and resistance to impact and fatigue.
Resistance to Fatigue
Other metal fabricating methods cut the grain flow lines exposing ends, which leads to fatigue and sensitivity to corrosion. The forging process maintains the grain flow such that it follows the contour and shape of the component or part. By maintaining the grain flow, forged parts have greater fatigue and corrosion resistance.
Flexibility of Design
As engineers and designers work on their conceptualizations, they are able to create parts with greater strength due to an understanding of how forging affects the grain flow and makes designs resistant to fatigue and failure. Forging allows designers to choose the correct materials and heat treatments for each component, which results in improved mechanical strength, resilience, and impact resistance.
The forging process allows for parts to have varying thicknesses due to the higher strength to weight ratio. The ability to mass produce parts using one operation capable of varying thicknesses saves time, production costs, and shortens manufacturing runs. Regardless of the material, there is consistency of the flow of the material from one forging to the next.
Custom forgings are produced swiftly and economically using a wide variety of materials and design requirements in a broad range of sizes. With the many innovations used by forging companies, custom designs are quickly produced economically and efficiently. Unusual shapes and configurations have become more feasible and are produced with improved precision.
The primary benefit of forging is the strength it provides for completed products. This is the result of the metal being able to retain its grain structure and alignment during the forging process. Preprocessing and pre-working of the metals removes any concerns for contaminants that could damage or harm a component’s strength. During recrystallization, metals solidify flawlessly since potential harmful contaminants have already been removed.
A major benefit to the auto industry is the high production rates of forging. Metals enter the forging process, and parts leave rapidly and efficiently in a matter of seconds in the cold forging process. In the hot forging process, the time increases to minutes with the delay for heating metals. Regardless of the part, the forging process can be seamless and economically integrated into pre-existing manufacturing operations.
Though some forged parts may require after production finishing, the majority leave the forging process with completed finishes and flawless surfaces. This aspect of the process is another reason for the increase in production efficiency.
The lack of complexity in the forging process leads to less downtime and fewer rejected or poor quality parts. In modern business, this is an important factor in order fulfillment and lower production costs.
Of the problems related to metal production, waste is one of the most costly and damaging. A major benefit of forging is the absence of waste. Any metal that is left from the forging process can be repurposed and recycled. In most manufacturing processes, the handling of scrap and waste is a significant labor and time cost. With forging, those costs are eliminated, and the focus is on production.
- Forging is a metal working process that manipulates, shapes, deforms, and compresses metal to achieve a desired form, configuration, or appearance outlined by a metal processing design or diagram.
- Though forging is an ancient process, it is still an essential part of most metalworking manufacturing processes.
- With technological advancements and the development of new metals, forging has changed but maintains much of its original form.
- Modern forging uses a wide range of technical methods and heavy duty equipment to produce parts that are essential for most of the necessities of society.
- The controlled deformation of the forging process results in metallurgical soundness and exceptional mechanical properties.