Knowledge

Forging production includes free forging, die forging, sheet metal stamping and metal extrusion, which is an important part of metal pressure processing. Free forging is an operation carried out on a forging hammer (or press), where the up and down movement of the hammer head (or die block) causes the heated ingot (or billet) to be compressed in height (or thickness) and freely elongated and widened in the horizontal direction. Various forging processes are adopted to obtain the required shape and size of the forged part, as shown in Figure 1a. Die forging involves placing the heated billet in a die cavity of a fixed shape to deform it. The die cavity walls restrict the free movement of the metal. When the die forging process is completed and the metal fills the die cavity, the desired shape and size are obtained. Sheet metal stamping uses sheet metal or strip metal, in a cold state, on a press, where the interaction between the punch and the die is used to stamp out the products or parts we need, as shown in Figure 1c. Extrusion involves heating the metal ingot (or billet), placing it in an extrusion cylinder, and under the action of the extrusion rod, the metal flows out from the die hole at the other end of the extrusion cylinder, obtaining various profile sections with irregular cross-sections, tubes and bars. Moreover, some cross-sectional shapes cannot be obtained by rolling methods.

 

It must be pointed out that the purpose of forging and pressing production is to obtain blanks (or parts) of certain shapes and sizes. More importantly, it is to transform the as-cast structure of metals, improve their mechanical, physical and chemical properties, and increase the service life of parts. Therefore, forging and pressing production can be widely adopted in various industrial sectors of the national economy.

 

First, in metallurgical integrated enterprises, especially in high-quality steel smelting plants, forging workshops are established along with rolling mills, because many low-plasticity high-quality alloy steels need to be forged into blanks before rolling. Therefore, some people say that the "forging workshop" is the "primary rolling mill" of high-quality steel mills.

 

Second, in the defense industry, the vast majority of parts are manufactured by forging and stamping methods.

 

Third, in the process of machine manufacturing, especially in heavy machinery, such as the rolls of large steel rolling mills, herringbone gears, the working cylinders and columns of hydraulic presses, the pull rods of forging hammers, the cranks of presses, and the main shafts of mining machinery, are generally forged.

 

Fourth, in transportation, 80% of the parts in automobiles are forged, and 60% in locomotives. The main shafts, crankshafts, and some parts of engines in warships and ships also need to be forged.

 

Fifth, in the power industry, the rotors, impellers, blades, main shafts, and non-magnetic retaining rings of generators are all forged parts.

 

Sixth, in agriculture and light industry, many mechanical parts are also manufactured by forging and pressing methods.

 

The parts produced by forging and pressing range from a few grams to several hundred tons in weight.

Forging production has the following advantages over other processing methods:

1. Forgings are heavier than castings and can withstand greater impact forces. Their plasticity, toughness and other mechanical properties are also better than those of castings. Therefore, important parts are mostly made of forgings. Another advantage of using forgings is that, under the premise of ensuring the strength of the parts, the weight of the machinery itself can be reduced. This is of even greater significance for transportation vehicles, aircraft, vehicles and spaceflight equipment. Recently, due to the improvement of casting technology, castings are also used in some cases because their cost is much lower than that of forgings.

2. It saves raw materials. For example, for the 17-kilogram front axle used in a car, when it is made by rolling and cutting, the cutting chips account for 189% of the axle's weight, while when it is made by die forging, the cutting chips only account for 30%. The processing time is also shortened by one sixth.

3. High productivity. For example, two hot die forging presses can forge car bearings, which can replace 30 automatic cutting machines. The efficiency of producing M24 nuts by automatic upsetting machines is 17.5 times that of six-axis automatic lathes. Moreover, the production by extrusion can produce finished products from the billet in one go, which is unmatched by other processing methods.

4. Free forging is suitable for single-piece and small-batch production and has greater flexibility. It is widely used in many machine factories. However, it must be pointed out that forging is a primitive production method and its productivity is lower than that of rolling, which needs to be further improved.

Strength direction in forging production

In heavy machinery manufacturing, such as in the production of large parts for smelting equipment, rolling mill equipment, and hydropower station equipment, free forging is commonly used and the forging is carried out on large hydraulic presses.

For example:

A rotor of a steam turbine with a diameter of 1.5 meters and a length of 10 meters;

A column of a 45,000-ton hydraulic press with a diameter of 1 meter and a length of 33 meters;

A high-pressure boiler cylinder (half) with a diameter of 4 meters, a length of 14 meters and a thickness of 0.16 meters;

A roll of a 1150 rolling mill (forged diameter 1.23 meters, length 5.645 meters), forged from a 70-ton steel ingot, etc.

In batch or mass production machinery, such as in factories manufacturing automobiles, tractors, aircraft, tanks, and machine tools, the production of important parts is carried out by die forging. Die forging is one of the directions of development in forging production. With precision die forging, the cutting process of parts can be replaced. Currently, not only can forgings weighing up to 200 kilograms be smoothly produced, but also, through segmented forging, forgings weighing up to 6.7 tons, such as six-journal crankshafts, can be produced. In contrast, to forge the same crankshaft by free forging would require a steel billet weighing 11.5 tons, which demonstrates the superiority of die forging.

 

In terms of forging processes, to save raw materials, alloy precision forging, small flash forging, and net forging are adopted. In the heating process, protective gases are used to prevent the formation of oxide scales.

 

To ensure the quality of forgings, mechanized operations, automatic production lines, turning machines, and transportation equipment are employed. To reduce physical labor, mechanized operations, automatic production lines, turning machines, and transportation equipment are utilized.

 

Recently, due to the development of the national economy, high-temperature resistant alloys with high strength and other alloys with special physical and chemical properties are needed. These alloys have the characteristics of low plasticity and are difficult to form. Therefore, in recent years, the extrusion method has been adopted to shape these billets.

Another approach is the high-energy forming method. The essence of the high-energy forming method is that a huge external force acts on the metal in an extremely short time (0.001 seconds), causing it to undergo plastic deformation in the intended direction and obtain the required parts. Due to the powerful external force pushing the metal to move a certain distance in the shortest time, the power generated is extremely high, and thus it is also called high-energy rate deformation. Under high speed and high pressure, the deformation of the metal is like the flow of a liquid, which greatly enhances its plasticity. Materials with low plasticity, such as titanium, stainless steel, and heat-resistant steel, which are difficult to process by conventional forming methods, can completely overcome this difficulty through high-energy rate forming. [Note 6]

The energy sources used in high-energy-rate forming include compressed gas, combustion gas, high-energy electric sparks, etc. However, explosives are currently widely used, so this method is also called explosive forming.

 

Forging Equipment (1)

Forging equipment can be classified into four types based on the speed variation characteristics of the machine's working part after contact with the forging:

The first type: Forging hammers

At the starting point a of the working stroke (i.e., before the hammer head contacts the forging), the hammer head has a maximum speed v max (as shown in Figure 1-1a). During the working stroke b, the speed drops sharply from the maximum value to zero (i.e., from α to β). The maximum speed v max can reach 9 meters per second. The working time t is calculated in thousandths of a second.

Because the working cycle time tp is very short, the work done by steam or air is too small. Mainly, the energy accumulated when the hammer head rises is relied upon to complete the task. It can be seen that this type of machine works by impact force, so it is called a forging hammer.

 

The second category: Hydraulic Presses

The speed variation characteristics of the working tool of this type of machine when it comes into contact with the forging are shown in Figure 1-1c. This is quite different from the working speed of the first category of machines. The initial speed of the anvil may be zero (as at point 0) or a certain speed (as at point C), and the maximum speed v max can reach 30 mm/s. The working time tp is calculated in fractions of a percent or thousandth of a second, and in some cases, it can also be calculated in seconds.

 

The third category: Crank Presses

The variation of their working speed is shown in Figure 1-1e. The motion curve of the slider remains constant, and is determined by the shape of the forging, the angle, and the shape of the crank. The initial speed is quite high, and in some cases can reach 500 mm/s or even higher. Since all these machines are equipped with crank and connecting rod mechanisms, they are called crank presses.

The fourth category: Roll forging machines

The working tool of this type of machine is the roll forging machine. During the working stroke, there is only rotational motion, and it operates based on mechanical principles. If the unevenness of the working tool's rotation is ignored, the speed variation curve ab is parallel to the horizontal axis.This characteristic ensures consistent force application, enhancing material deformation

 

Vigor has over 20 years of experience in the forging process, backed by a professional technical team, production team, and delivery team. This enables us to help customers achieve optimal performance with the perfect parts. Their expertise ensures consistent quality, minimizing downtime and maximizing efficiency in production processes. With a focus on precision and reliability, Vigor's components meet stringent industry standards, providing clients with unparalleled peace of mind. If you have any question or parts that need to be developed, please feel free to contact us at info@castings-forging.com