Since the earliest Mesopotamians, forging has been a standard method of metal manufacture. Forging uses compressive, confined forces to shape metal. Forging has undergone major improvements since it first emerged in the fertile crescent, making it a more effective, quick, and durable technique. This is due to the fact that forging is now typically carried out using forging presses or hammering equipment that is powered by electricity, hydraulics, or compressed air.
Forging is used to make metal components. Metal forging generates some of the strongest manufactured parts compared to other manufacturing processes. Minor cracks and open spots in the metal are filled as it is heated and pressed.
Carbon steel, alloy steel, micro-alloy steel, stainless steel, aluminum, and titanium are a few of the frequently utilized forging materials. It is a metalworking process in which workpieces are shaped into the desired dimension by comprehensive forces. Well, in this article, I’ll be listing the various types of forging processes you should be considering.
Types of Forging Processes
Different types of forging are classified based on the way it is been produced, which may be classified according to the following ways listed below:
- According to the temperature of the workpiece.
- According to the arrangement of dies.
- According to the forging equipment.
Read more: Understanding die casting
According to the temperature of the workpiece
The temperature at which forging can be performed includes cold, warm, and hot forging.
Cold forging is carried out at room temperature which is below the recrystallization temperature of the metal. it is preferred when the metal is soft, like aluminum. Carbon and alloy steels can also be processed using cold forging due to their softness. The cold forging process is less expensive when compared with hot forging and its end product requires no finishing work.
Cold forging simply cannot be done with many metals, such as steel with a high carbon content. Despite this obstacle, cold forging consistently outperforms its warmer counterpart in terms of contamination, surface polish, homogeneity, and dimensional control. Numerous forging processes are included in cold forgings, such as bending, extruding, cold drawing, coining, and cold heading. The downside to this greater adaptability is that cold forging often necessitates the use of intermediate anneals and more powerful equipment.
Below are the common benefits of cold forging:
- It improves mechanical properties.
- Production rates are very high with exceptional die life.
- Less friction between the die surface and the workpiece.
- No oxidation or scaling on the work.
- Lubrication is easy.
Read more: Understanding Forging Process
Below are the limitations of cold forging:
- Heavier and more powerful equipment is needed.
- Designing and manufacturing are critical.
- Stronger tooling is required.
- Residual stress may occur.
This process of forging is carryout above room temperature to below the recrystallization temperature. this process has more potential advantages when compared with cold forging because it increases steel ductility, reduced tooling loads, reduced press load, eliminates the need to anneal before forging, etc. In this process, the fire source is heated at about 700 to 800°c for steel. This is below the recrystallization temperature. it also lowers the flow stress of the forging pressures. Some advantages of warm forging are:
- Excellent dimensional tolerances.
- Favorable grain flow to improve strength.
- High production rate.
- The surface finish for a forged part is good.
- Greater toughness of the forged part.
- significant saving in machines and materials.
Read more: Different Types of Forging Process
Hot forging is the most common and useful forging type out there. It is carried out at a temperature above the recrystallization temperature of the metal. The recrystallization temperature is the level at which the new grains are formed. The extreme hotness helps to easily deform the metal.
Heating metals to 2,300 degrees Fahrenheit may be necessary. The reduction in energy needed to form the metal properly is the main advantage of hot forging. This is due to the fact that extreme heat reduces yield strength while increasing ductility. Chemical irregularities are also removed, which benefits hot forged items. Some advantages and disadvantages of hot types of forging are:
Below are the common benefits of hot forging:
- less force is required
- High strain rates and hence the easy flow of the metal.
The followings are the limitations of hot forging:
- Poor surface finish.
- Possible warping of metal during the cooling process.
- Lubrication is difficult at high temperatures.
- Oxidation and scaling occur on the workpiece.
According to the arrangement of dies
These types of forging processes include close-die and open-die forging.
The method of drop forging involves striking metal with a hammer to mold it into the die’s shape. The surface that makes contact with the metal is called the die. Open-die and closed-die forging are the two variations of drop forging. Die shapes are normally flat, while some have surfaces that are specifically formed for certain activities.
Open-die forging process
This is mostly used in hot forging. The workpiece is heated and hammered to the desired shape. It uses a flat die or no die for the forging. Open-die produces rough products. It is suitable for simple shapes due to its less dimensional accuracy and it requires high skill of operators. This process is simple and less expensive.
The forging procedure is known as open die forging (or smith forging) when flat dies without precut profiles are used. The metal can flow anywhere except where it hits the die because of the open design. Correct movement of the workpiece, which should weigh more than 200,000 lbs. and be 80 feet long, is crucial for getting the best results. It is helpful for shaping ingots before secondary shaping processes or for short-run art smithing. Open die forging decreases the possibility of inaccuracy or holes while producing products with improved fatigue resistance and strength. It can also be used to produce grains with a finer texture than other methods.
Closed-die forging process:
These types of forging are also called impression die forging. This is because a set of impressions is used to produce the desired shape on a workpiece. The material is fully constrained in the cavity created by the upper and lower die halve. It also gives accurate shape to the parts, requires very accurate control of material volume and proper die design, and higher interface pressure is also required. This process does not depend on flash formation to achieve complete filling of the die.
Molten metal is forced into the cavities of these molds by a hammer while they are mounted to an anvil. When forging complex designs, multiple strikes and/or die cavities are frequently used. Closed die forging is expensive for short-run operations because of high initial tooling costs, but as part production increases, the forging process becomes more affordable. Compared to other techniques, closed die forging also offers outstanding strength. The manufacturing of hardware tools and automotive parts are two common uses for closed die forging.
According to the forging equipment used
Types of forging processes classified by equipment are obtained either by hammer or press. The operation is carried out using a hammer and dies impression hitting the workpiece repeatedly. The quality of the forging and the economic productivity of the hammering process depends upon the skills of the operator and the tooling. Press forging is usually done by hitting the stock once in each die impression as the design of each impression became more important.
Hammer forging process:
This is the most common type of forging equipment used during the forging process. The equipment hammer and anvil are the least expensive and most important equipment for creating load and energy during the process. Hammers are primarily used for hot forging. Basically, there are two types of hammer anvils used during the forging process such as gravity drop hammers and power drop hammers.
Gravity drop hammer: it has an upper ram connected to a belt (belt drop hammer), a chain (chain drop hammer), a board (board drop hammer), and a piston ( oil-, air-, or steam lift drop hammer). When the ram is lifted to a certain height and dropped on the workpiece placed on the surface of the anvil. The ram is accelerated by gravity and produces some blow forces. Upstroke occurs immediately after the blows.
Power drop hammer: it is similar to that of an air-drop hammer. In the down-drop stroke, the ram is accelerated by steam, cold air, or hot air pressure. The acceleration of the ram is enhanced with air pressure applied on the top side of the ram cylinder.
Read more: Difference between Forging and Casting
Press forging process:
These types of forging do not work by a series of blows on the metal but through a single continuous squeezing of the metal. Press forging equipment usually comes in two types: mechanical and hydraulic presses. The mechanical presses function by using cams, cranks, and toggles to produce a preset (a predetermined force at a certain location in the stroke) and reproducible stroke.
Compression is the primary forming element in press forging. The metal is allowed to rest on a stationary die while being continuously compressed by a compression die to form it into the required shape. Compared to other forms of forging, the time the metal spends in contact with the dies is significantly longer, but the forging process has the advantage of being able to simultaneously deform the entire product rather than just a small portion. The manufacturer’s capacity to track and manage the particular compression rate is another advantage of press forging. Press forging has several uses because there are few restrictions on the size of the products that can be produced. Cold or hot forging can be used in press forging.
Upset Forging Process
In the forging process known as upset forging, the metal is compressed to expand its diameter. In upset forging procedures, a specific type of high-speed machine is used: crank presses. In order to increase efficiency and enable speedy metal interchange from one station to the next, crank presses are typically mounted on a horizontal plane. There are also hydraulic presses and vertical crank presses. This technique has the advantages of being fully automated and allowing for a high production rate of up to 4500 components per hour. It almost never generates trash.
Roll Forging Process
Increasing the length of rods or wires involves roll forging. In order to form the metal, the maker puts heated metal bars between two cylindrical rolls with grooves that revolve and exert increasing pressure. These grooves’ exact geometry shapes the metal component to the required shape. The absence of flashing and the good grain structure of this forging technique are advantages. Roll forging is a metal forging method rather than a rolling technique, despite the fact that it uses rolls to create parts and components. The automotive sector regularly uses roll forging to create parts. Additionally, it is employed in the forging of hand tools and knives.
Isothermal Forging Process
The materials and the die are both heated to the same temperature during the isothermal forging process. The word “iso” means “equal,” hence the name. With a lower forging temperature than other metals like steel, such as aluminum, this forging technique is frequently employed to forge aluminum. Forging temperatures for steels and super alloys can range from 930 to 1,260 °C, whereas those for aluminum are at 430 °C. Benefits include cheaper machining costs and decreased scrap rates due to near-net forms and excellent reproducibility of the metal product. Due to the reduced heat loss, smaller machinery can be employed to produce the forging, which is an additional benefit.
The more expensive die materials needed to manage pressures and temperatures as well as the necessary uniform heating systems are a few drawbacks. Additionally, its manufacturing rate is discreet.
Read more: Different types of forging operations
The continuous development of forging technology should include a fundamental and sound understanding of equipment characteristics and capabilities. Hammers and presses used in forging influence the forging process since it affects deformation rate and temperature conditions, and determines the rate of production. The requirements of a given forging process must be compatible with the load, energy, time, and accuracy characteristics of a given forging machine.
That is all for this article, where different types of forging processes, their advantages, and disadvantages were discussed. I hope you enjoyed the reading, if so, kindly share it with other students. Thanks for reading, see you next time!