Basic knowledge of forging

Deformation temperature

The beginning recrystallization temperature of steel is about 727℃, but 800℃ is commonly used as the division line, above 800℃ is hot forging; between 300 and 800℃ is called warm forging or semi-hot forging.

Blanks

According to the way the billet moves, forging can be divided into free forging, upsetting, extrusion, die forging, closed die forging, closed upsetting.

1、Free forging. The use of impact or pressure to make the metal in the upper and lower two against the iron (anvil block) between the deformation to obtain the required forgings, mainly manual forging and mechanical forging two.

2、Die forging. Die forging is also divided into open die forging and closed die forging. Metal billet in a certain shape forging die chamber pressure deformation and obtain forgings, and can be divided into cold upsetting, roll forging, radial forging and extrusion, etc..

3, closed die forging and closed upsetting because there is no flying edge, the utilization rate of the material is high. With a process or a few processes may complete the finishing of complex forgings. Since there is no flying edge, the force area of the forging is reduced, and the required load is also reduced. However, care should be taken not to make the billet completely restricted, and for this purpose the volume of the billet should be strictly controlled, the relative position of the dolly should be controlled and the dolly should be measured, and efforts should be made to reduce the wear of the dolly.

Dolly

According to the movement of forging die, forging can be divided into pendulum rolling, pendulum swivel forging, roll forging, wedge cross rolling, ring rolling and inclined rolling. Pendulum rolling, pendulum swivel forging and ring rolling can also be processed by fine forging. In order to improve the utilization of material, roll forging and cross rolling can be used as a pre-processing of slender material. Like free forging, rotary forging is also partial forming, which has the advantage of being formed with less forging force compared to the forging size. In this forging method including free forging, the material expands from near the die surface to the free surface during processing, therefore, it is difficult to guarantee the accuracy. Therefore, the direction of the forging die movement and the rotary forging process are controlled by computer, so that products with complex shapes and high accuracy can be obtained with lower forging forces, for example, the production of forgings such as turbine blades with many varieties and large sizes. Forging equipment die movement and degrees of freedom is inconsistent, according to the lower dead point deformation restriction characteristics, forging equipment can be divided into the following four forms:

1、Limiting forging force form: hydraulic press with direct drive of slider by hydraulic pressure.

2、Quasi-stroke limiting mode: hydraulic presses that drive crank linkage mechanism.

3、Stroke limiting method: mechanical presses with crank, connecting rod and wedge mechanism driving the ram.

4、Energy limiting method: Screw and friction press using screw mechanism.

Heavy-duty aero-die forging hydraulic press for hot test in order to obtain high accuracy should pay attention to prevent overload at the lower dead center, control the speed and die position. Because these will have an impact on forging tolerances, shape accuracy and die life. In addition, in order to maintain the accuracy, attention should be paid to adjust the slide guide clearance, ensure the stiffness, adjust the lower dead point and the use of subsidized transmission device and other measures.

Importance

Forging production is one of the main processing methods in the machine building industry for providing machine parts in blank form. Through forging, not only the shape of mechanical parts can be obtained, but also the internal organization of the metal can be improved and the mechanical and physical properties of the metal can be enhanced. Generally forging production method is used to manufacture most of the important mechanical parts that are subject to high forces and high requirements. Such as turbine generator shaft, rotor, impeller, blade, guard ring, large hydraulic press column, high-pressure cylinder, rolling mill rolls, internal combustion engine crankshaft, connecting rod, gears, bearings, as well as defense industry, such as artillery and other important parts, are used to forge production.

Therefore, forging production is widely used in metallurgy, mining, automotive, tractors, harvesting machinery, petroleum, chemical, aviation, aerospace, weapons and other industrial sectors, is in daily life, forging production also has an important position. In a sense, the annual output of forgings, the proportion of die forgings in the total output of forgings, as well as the size and ownership of forging equipment and other indicators, to a certain extent, reflects the level of industry in a country.

Forging material

Forging materials are mainly carbon steel and alloy steel of various compositions, followed by aluminum, magnesium, copper, titanium and other alloys. The original state of the material is bar, ingot, metal powder and liquid metal. The ratio of the cross-sectional area of the metal before deformation to the cross-sectional area after deformation is called the forging ratio. The correct choice of forging ratio, reasonable heating temperature and holding time, reasonable starting forging temperature and final forging temperature, reasonable deformation and deformation speed is very relevant to improve product quality and reduce costs.

Generally, small and medium-sized forgings are made of round or square bars as billets. The grain organization and mechanical properties of the bar are uniform and good, the shape and size are accurate, the surface quality is good, and it is easy to organize mass production. As long as the heating temperature and deformation conditions are reasonably controlled, forgings with excellent performance can be forged without large forging deformation. Ingots are only used for large forgings. Ingot is cast organization, with large columnar crystal and loose center. Therefore, through large plastic deformation, the columnar crystals must be broken into fine grains and the sparse compacted to obtain excellent metal organization and mechanical properties.

The powder metallurgy preform billets are pressed and sintered, and powder forgings can be made in the hot state by die forging without flying edges. The forging powder is close to the density of general die forgings, with good mechanical properties and high precision, which can reduce the subsequent cutting process. Powder forgings have uniform internal organization, no segregation, and can be used to manufacture small gears and other workpieces. However, the price of powder is much higher than the price of general bars, and the application in production is somewhat limited. By applying static pressure to the liquid metal poured in the die chamber and making it solidify, crystallize, flow, deform plastically and form under the pressure, a die forged part of the desired shape and properties can be obtained. Liquid metal die forging is a forming method between die casting and die forging, especially suitable for complex thin-walled parts which are difficult to be formed by general die forging.

Forging materials in addition to the usual materials, such as various components of carbon steel and alloy steel, followed by aluminum, magnesium, copper, titanium and other alloys, iron-based high-temperature alloys, nickel-based high-temperature alloys, cobalt-based high-temperature alloys of deformation of the alloy also use forging or rolling to complete, but these alloys due to its plastic zone is relatively narrow, so forging will be relatively more difficult, different materials, the heating temperature, open forging temperature and final forging temperature There are strict requirements for heating temperature, opening forging temperature and final forging temperature for different materials.

Processes

Different forging methods have different processes, including the longest process of hot die forging, the general sequence is: forging billet feeding; forging billet heating; roll forging preparation; die forging forming; edge cutting; punching; correction; intermediate inspection, inspection of forging dimensions and surface defects; forging heat treatment, to eliminate forging stress, improve metal cutting properties; cleaning, mainly to remove surface oxidation; correction; inspection, general forgings to After the appearance and hardness inspection, important forgings should also undergo chemical composition analysis, mechanical properties, residual stress and other tests and non-destructive testing.

Characteristics of forgings

Compared with castings, the metal can improve its organization and mechanical properties after forging processing. Casting organization after forging method of thermal processing deformation due to metal deformation and recrystallization, so that the original coarse dendritic and columnar grains into fine grains, uniform size of the equiaxial recrystallization organization, so that the ingot within the original segregation, loosening, porosity, slag and other compaction and welding, the organization becomes more compact, improve the plasticity and mechanical properties of the metal. The mechanical properties of castings are lower than the mechanical properties of forgings of the same material. In addition, forging processing can ensure the continuity of metal fiber organization, so that the fiber organization of forgings and forging shape to maintain consistency, metal flow line integrity, can ensure that the parts have good mechanical properties and long service life using precision die forging, cold extrusion, warm extrusion and other processes to produce forgings, are incomparable to castings forgings are metal is applied pressure, through plastic deformation to shape the required shape or a suitable compression force on the object. This force is typically achieved through the use of a hammer or pressure. The casting process builds delicate grain structures and improves the physical properties of the metal. In realistic use of the parts, a correct design enables the particle flow in the direction of the main pressure. Casting is a metal forming object obtained by various casting methods, i.e., the smelted liquid metal is injected into a pre-prepared casting mold by pouring, pressure injection, inhalation or other casting methods, cooled, and after sand-fall, cleaning and post-treatment, the resulting object has a certain shape, size and properties.