Different types of forging process are known being a metal working process in which work piece are shapes into desired dimension by comprehensive forces.
They 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 work-piece.
- According to the arrangement of dies.
- According to the forging equipment.
These three classification has lead to different types of forging process.
1. Types of Forging process according to the temperature of the work-piece.
Temperature at which forging operations are carrier out includes: cold, warm and hot forging.
- Cold forging: this is carried out at room temperature which is below the recrystallization temperature of the metal. it is preferred when the metal is soft, like aluminium. Carbon and alloy steels are process using cold forging due to their softness. Cold forging process is less expensive when compared with hot forging as it end product requires no finishing work. Some advantages and disadvantages of cold forging process are:
- It improves mechanical properties.
- Production rate are very high with exceptional die life.
- Less friction between die surface and work-piece.
- No oxidation or scaling on the work.
- Lubrication is easy.
- Heavier and more powerful equipment is needed.
- Designing and manufacturing are critical.
- Stronger tooling is required.
- Residual stress may occur.
- Warm forging: this process of forging is carryout above room temperature to below the recrystallization temperature. this process have more potential advantages when compared with cold forging because it increases steel ductility, reduced tooling loads, reduced press load, eliminate need to anneal prior to forging etc. In this process, the fire source is heated at about 700 to 800°c for steel, it is below the recrystallization temperature, on order to lower 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.
- Surface finish for forged part is good.
- Greater toughness of the forged part.
- significant saving in machines and materials.
- Hot forging: this is the most common and use type of forging process. 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 is form. The extreme hotness helps in easy deformation of the metal. Some advantages and disadvantages of hot forging process are:
- Force required is less.
- High strain rates and hence easy flow of the metal.
- Poor surface finish.
- Possible warping of metal during cooling process.
- Lubrication is difficult at high temperature.
- Oxidation and scaling occur on the workpiece.
2. Type of forging process according to the arrangement of dies.
This forging process include: close-die and open-die forging.
a) open-die forging process: this is mostly used in hot forging. The workpiece is heated and hammered to the desired shape. It uses flat die or no die for the forging. Open-die produces rough product. 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.
b) closed-die forging process: this process is also called impression die forging because set of impressions is used to produce desired shape on workpiece. The material is fully constrained in the cavity created by the upper and lower die halve. It also give more accurate shape to the parts, requires very accurate control of material volume and proper die design, higher interface pressure is also required and it does not depend on flash formation to achieve complete filling of the die.
3. Type of forging process according to the forging equipment used.
Type of forging process classified by equipment are obtained either by hammer or press. The operation is carried out using hammer and die impression hitting the workpiece repeatedly. The quality of the forging and the economy productivity of the hammer 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.
a) Hammer forging process: this is the most common type of forging equipment used during forging process. The equipment hammer and anvil are the least expensive and most important type of equipment for generating load and energy for the succession of the forging, Hammers are primarily used for hot forging. Basically, there are two types of hammer anvil used during forging process: gravity drop hammers and power drop hammers.
i) Gravity drop hammer: it has a upper ram connected to a belt (belt drop hammer), a chain (chain drop hammer), a board (board drop hammer), and 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 energy. Upstroke occurs immediately after the blows.
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ii) 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 enhance with air pressure applied on the top size of the ram cylinder. read more on hammer forging process.
b) Press forging process: this type of forging equipment does not work by series of blows on the metal but by means of single continuous squeezing of the metal. Press forging equipment usually cones in two types: mechanical and hydraulic presses. The mechanical presses function by using cams, crank and toggles to produce a preset (a predetermined force at a certain location in the stroke) and reproducible stroke.
The continuous development of forging technology should include fundamental and sound understanding of equipment characteristics and capabilities. Hammers and presses used in forging, influences the forging process, since it affects deformation rate and temperature conditions, and it 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.
and that is it for this article, different types of forging process, their advantages and disadvantages. It has been explained accordingly and i hope you understand it, for me to be sure simply answer the question below via our comment box and don’t forget to share…
question: In you own understanding explain hammer forging process