The beginning of the steel recrystallization temperature is about 727 ℃, but generally used 800 ℃ as a dividing line, higher than 800 ℃ hot forging;Called between 300 ~ 800 ℃ temperature forging or hot forging.
According to the movement of the raw material, the forging can be divided into free forging, upsetting, extrusion, die forging, closed die forging and closed upsetting.
1. Free forging.Using shock or pressure to make the metal deform between two parts of the anvil (anvil block) to obtain the required forgings, mainly by hand forging and mechanical forging.
2. Die forging.Die forging and divided into open die forging and closed die forging. Metal blank in a certain shape in the bore of the forging die forging compression deformation, can divide again for cold heading, roll forging, the radial forging, extrusion and so on.
3. Closed die forging and closed upsetting due to no flying side, material utilization is high.The elaboration of complex forgings may be accomplished using a process or several processes.Since there is no flying side, the force area of the forgings decreases, and the load is reduced.However, we should pay attention to not make blank completely is restricted, so we will strictly control the volume, control the relative position of forging die and measure of forgings, effort to reduce the wear and tear of forging die.
According to the way of the forging, the forging can be divided into the means of rolling, rolling, roll forging, wedge rolling, rolling ring and Angle rolling.It is also used for rolling, rolling and rolling.In order to improve the utilization of the material, the roll forging and roll can be used as the forward process of the long thin material.The rotary forging, like the forging of the forging, is also partially formed, and its advantage is that the forging force is smaller than the size of the forging.Including free forging, the way of forging and processing the materials from the mold surface near to the free surface extension, therefore, it is difficult to guarantee the accuracy, so will the movement direction of the forging die and spin blacksmith sequence with computer control, a lower forging force are available on complex shape, high precision products, such as the production of many varieties, large size of the turbine blade forgings.The die movement and the freedom of forging equipment are not consistent, according to the deforming limitation of the lower end points, the forging equipment can be divided into four types:
1. Limit forging force form: the oil pressure machine that directly drives the slide block.
2. Quasi-stroke limitation: oil pressure drive the hydraulic press of crank-link mechanism.
3. Stroke limit: mechanical press of crank, connecting rod and wedge mechanism.
4. Energy limit: use spiral mechanism and friction press.
Heavy air die forging hydraulic press is designed to ensure high accuracy to prevent overload, control speed and mold position.Because these will have an effect on the tolerances, shape accuracy and die life of the forgings.In addition, in order to keep the accuracy, we should also pay attention to adjusting the clearance of slide block, ensuring rigidity, adjusting the dead point and using the subsidy driving device.
There are also sliding block vertical and horizontal motion (used for forging, lubricating cooling and high-speed manufacturing parts forging), using the compensation device
Forging the first large disc product to increase the movement in other directions.This way is different, the forging force, process, material utilization ratio, yield, size tolerance and lubrication cooling way is different, these factors also affect the level of automation.
The forging production is one of the main processing methods for making mechanical parts in the machine manufacturing industry.Through forging, not only can the shape of mechanical parts be obtained, but also can improve metal internal organization, improve the mechanical performance and physical performance of the metal.In general, the important machinery parts that are heavy and demanding are made in the forging manufacturing method., impeller, such as the steam turbine generator shaft, rotor blade, retaining rings, large hydraulic press stud and high pressure cylinder, rolling mill roll, the internal combustion engine crankshaft, connecting rod, gears, bearings, and artillery in the defense industry and other important parts adopt forging production.
Forging production, therefore, widely used in metallurgy, mining, automobile, tractor, harvest machinery, petroleum, chemical industry, aviation, spaceflight, weapons and other industries, is in daily life, forging production also has an important position.
Forgings in a sense, the annual output, proportion of die forging in the forging production, forging equipment and the indices such as size and ownership, to a certain extent reflects a country's industrial level.
The forging materials are mainly carbon steel and alloy steel, followed by aluminum, magnesium, copper, titanium and other alloys.The original state of the material has rods, castings, metal powder and liquid metal.The ratio of the cross sectional area of the metal before the deformation is called the forging ratio.Correctly choose the forging ratio, reasonable heating temperature and holding time, the reasonable forging temperature and finish forging temperature, reasonable deformation and deformation rate has much to do to improve the product quality, reduce cost.
Generally, small and medium sized forgings are made of round or square rods.The bar grain structure and mechanical properties are uniform, good, the shape and size are accurate, the surface quality is good, facilitate the organization batch production.As long as the heating temperature and deformation conditions are reasonably controlled, no large forging deformation is required to forge a good forging.
Casting is used only for large forgings.The cast is a cast structure, with larger column crystals and a loose center.Therefore, through large plastic deformation, the column crystals can be broken into fine grain, and the loose compaction can be obtained to obtain good metal and mechanical properties.
The powder metallurgy precast of powder metallurgy, which is compressed and burned, can be made into powder forging in hot state without flying side.The powder of forging powder is close to the density of general die forging, has good mechanical properties and high precision, can reduce the cutting processing.The internal organization of the powder forging is homogeneous and has no segregation, which can be used to make small gears and other parts.But the price of powder is much higher than that of the average bar, and the application in production is limited.
In casting mould chamber of liquid metal ShiJiaJing pressure, make its solidification and crystallization under pressure, flow, plastic deformation and forming, can obtain the required shape and properties of die forgings.Liquid metal die forging is a kind of forming method between die casting and die forging, especially suitable for complex thin walled parts which are difficult to form in general die forging.
Forging materials in addition to the usual materials, such as various composition of carbon steel and alloy steel, followed by aluminum, magnesium, copper, titanium and its alloys, high temperature iron base alloy, nickel base superalloy, cobalt-based superalloy deformation of the alloy are forged or finish rolling way, only the alloy due to its plastic zone is relatively narrow, so the forging difficulty will be relatively large, the heating temperature of different material, open forging temperature and finish forging temperature have strict requirements.
Different forging methods have different processes, and the process flow of hot die forging is the longest.Forging billet heating;Roll forging billet prepared;Die forging forming;Trimming;Punching;Correction;To examine the dimensions and surface defects of the forgings in the middle;Heat treatment to remove the forging stress and improve the performance of metal cutting.Cleaning up, mainly removing surface oxidation;Correction;Check, general forging passes through appearance and hardness test, and important forging pass chemical composition analysis, mechanical properties, such as residual stress test and NDT.
Characteristics of Forgings
Compared with castings, metal can improve its organizational structure and mechanical properties after forging.Casting organization after forging method of thermal deformation due to metal deformation and recrystallization, make original bulky dendrite and columnar grain to grain is fine and uniform axial recrystallization organization, make the ingot in the original segregation, porosity, porosity, slag compaction and welded, such as its organization become more closely, plasticity and mechanical properties of the metal.The mechanical properties of the castings are lower than the mechanical properties of the forgings.In addition, the metal forging process can guarantee the continuity of fibrous tissue, the forging of fibrous tissue and forging appearance consistent, metal flow is complete, can guarantee the parts with good mechanical properties and long service life with precision die forging, cold extrusion, extrusion temperature and other process of forging, is incomparable by casting forging is a metal pressure, through the shape of the plastic deformation shape requirements or suitable compression force.This power is typically achieved by using a hammer or pressure.The casting process builds elaborate granular structures and improves the physical properties of the metal.In the practical use of spare parts, a correct design can make the particle flow in the direction of the main pressure.Casting is to use all kinds of casting method for metal forming objects, namely the good liquid metal smelting, casting, injection, inhaled or other casting method into the prepared mold, after cooling the shakeout, cleaning and post-processing, etc., of a certain shape, size and properties of objects.