Forge popular science
Forging refers to the use of forging machinery to apply pressure to metal billet to promote plastic deformation, so as to obtain a certain mechanical properties, specific shape and size of forging, it is one of the two major components of forging (including forging and stamping). Through forging, it can eliminate defects such as metal smelting, and optimize the microstructure. At the same time, because the complete metal streamline is retained, the mechanical properties of the forging is usually better than the casting of the same material. In the relevant machinery, for the important parts with high load and strict working conditions, except for the relatively simple shape that can use the rolled plate, profile or welding parts, most of the forgings will be used.
- Deformation temperature
The starting recrystallization temperature of steel is about 727℃, but 800℃ is generally used as the division line, higher than 800℃ is hot forging; between 300 and 800℃ is called warm forging or semi-hot forging, forging at room temperature is called cold forging. Forgings used in most industries are hot forging, and warm forging and cold forging are mainly used for the forging of automobile, general machinery and other parts. Warm forging and cold forging can effectively save materials.
- Forge category
As mentioned above, according to the forging temperature, it can be divided into hot forging, warm forging and cold forging. According to the forming mechanism, forging can be divided into free forging, die forging, grinding ring and special forging.
1) Free forging
Refers to the processing method of using simple universal tools or directly applying external force to the billet between the upper and lower anvil of forging equipment to deform the blank and obtain the required geometry and internal quality of forgings. Forgings produced by the free forging method are called free forgings. Free forging is mainly based on the production of forgings with small batch, using forging hammer, hydraulic press and other forging equipment to form and process the billet, and obtain qualified forgings. The basic process of free forging includes upsetting, lengthening, punching, cutting, bending, twisting, dislocation and forging. Free forging is all adopted in the hot forging mode.
2) Mold forging
Mold forging is divided into open die forging and closed die forging. Metal billet is compressed and deformed in the forging die chamber with a certain shape to obtain the forging parts. Die forging is generally used for the production of small weight and large batch parts. Mold forging can be divided into hot die forging, warm forging and cold forging. Warm forging and cold forging are the future development direction of die forging, and they also represent the level of forging technology.
According to the material points, die forging can also be divided into black metal die forging, nonferrous metal die forging and powder products forming. As the name suggests, the materials are ferrous metals such as carbon steel, non-ferrous metals such as copper and aluminum, and powder metallurgy materials.
Extrusion should be attributed to die forging, and can be divided into heavy metal extrusion and light metal extrusion.
Closed die forging and closed heading forging belong to two advanced processes of die forging. Because there is no flying edge, the utilization rate of material is high. The finishing of complex forgings may be accomplished in one process or several processes. Since there is no flying edge, the stress area of the forging is reduced, and the required load is also reduced. However, it should be noted that the billet should not be completely restricted, so the volume of the billet should be strictly controlled, the relative position of the forging die and the measurement of the forging, and strive to reduce the wear of the forging die.
3) Reach the ring
Ring milling refers to the production of ring parts of different diameters through special equipment ring milling machine, which is also used to produce wheel parts such as car wheels and train wheels.
4) Special forging
Special forging includes roll forging, wedge transverse rolling, radial forging, liquid die forging and other forging methods, these methods are more suitable for the production of some special shaped parts. For example, roll forging can be used as an effective pre-forming process to greatly reduce the subsequent forming pressure; wedge transverse rolling can produce steel ball, drive shaft and radial forging can produce large forgings such as gun barrel and step shaft.
5) Forging mold
According to the movement mode of forging die, forging can be divided into swing rolling, swing rotary forging, roll forging, wedge transverse rolling, rolling ring and inclined rolling. Roll-rolling, swing-rotary forging and rolling ring can also be processed by fine forging. In order to improve the utilization rate of materials, rolling forging and transverse rolling can be used as the first process processing of slender materials. Rotary forging, like free forging, also has the advantage that compared with the size of the forging, it can be formed in the case of small forging force. The forging way, including free forging, processing materials from the mold surface to the free surface, therefore, it is difficult to ensure accuracy, so, the forging mold movement direction and rotary forging process with computer control, can be used low forging force for complex shape, high precision products, such as production varieties, large size of steam turbine blade forgings.
The mold motion of the forging equipment is inconsistent with the degree of freedom. According to the deformation limitation characteristics of the dead point, the forging equipment can be divided into the following four forms:
Limiting forging force form: oil pressure directly drives the slide oil press.
Quasi-stroke limit mode: the oil press drives the oil press of the crank linkage mechanism.
Stroke limit: mechanical press driving the slide by crank, connecting rod and wedge mechanism.
Energy restriction mode: using the screw mechanism of the spiral and friction press.
To achieve high accuracy, attention should be taken to prevent overload at the lower dead point and control the speed and die position. Because these will have an impact on the forging tolerance, shape accuracy and forging die life. In addition, in order to maintain the accuracy, attention should also be paid to adjust the slider guide rail clearance, ensure the stiffness, adjust the dead point and use the subsidy transmission device and other measures.
There are also vertical and horizontal movement of slides (for slender parts forging, lubrication cooling, and high-speed production of parts forging), using the compensation device can increase the movement in other directions. The above methods are different, the required forging force, process, material utilization, yield, size tolerance and lubrication cooling methods are different, these factors are also the factors affecting the level of automation.
- Forge materials
Forging materials are mainly carbon steel and alloy steel of various components, followed by aluminum, magnesium, copper, titanium and their alloys. The original state of the material is rod material, 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 insulation time, reasonable starting forging temperature and final forging temperature, reasonable deformation and deformation speed have a great relationship to improve the product quality and reduce the cost.
Generally small and medium-sized forgings are round or square rod as billet. The grain organization and mechanical properties of the rod material are uniform, good, accurate shape and size, good surface quality, easy to organize mass production. As long as the heating temperature and deformation conditions are reasonably controlled, the forgings with excellent performance can be forged without large forging deformation.
Iningot only for large forgings. The ingot is a cast-out tissue with larger columnar crystals and a loose center. Therefore, it is necessary to break cylindrical crystals into fine grains and make loose compaction to obtain fine metal organization and mechanical properties.
The pressed and fired powder metallurgy prefabricated billet can be forged without fly side die in hot state. The forging powder is close to the density of the general die forging, with good mechanical properties and high accuracy, which can reduce the subsequent machining. Powder forgings are well organized without segregation and can be used to manufacture workpieces such as small gear. But the price of powder is much higher than the price of general bar, and the application in production is limited to some extent.
The static pressure is applied to the liquid metal poured in the mold chamber for solidification, crystallization, flow, plastic deformation and forming under the pressure, thus obtaining the desired shape and performance. Liquid metal die forging is a forming method between die casting and die forging. It is especially suitable for complex thin-wall parts that are difficult to form in 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 its alloy, iron-based high temperature alloy, nickel-based high temperature alloy, cobalt-based high temperature alloy deformation alloy by forging or rolling way, but these alloy because of its plastic area is relatively narrow, so the forging difficulty is relatively large, different materials of heating temperature, forging temperature and final forging temperature have strict requirements.
- Process flow
Different forging methods have different processes, among which the technological process of hot die forging is the longest, the general order is: forging billet feeding; forging heating; roller forging preparation; die forging; cutting edge; punching; correction; intermediate inspection, checking the size and surface defects of forgings; heat treatment of forgings to eliminate the forging stress and improve metal cutting performance; cleaning, mainly to remove surface oxidation skin; correction; inspection, general forgings shall go through appearance and hardness inspection, and important forgings shall be tested through chemical composition analysis, mechanical properties, residual stress and non-destructive testing.
- Features of forgings
Compared with castings, metal can improve their structure and mechanical properties. Casting tissue after forging method thermal processing deformation, due to the deformation of metal and recrystallization, make the original thick dendrite and columnar grain into a grain fine, size uniform axial recrystallization organization, make the original segregation, loose, pores, slag to compaction and welding, the organization becomes more closely, improve the plasticity and mechanical properties of the metal.
The mechanical properties of castings are lower than those of forgings of the same material. In addition, forging processing can ensure the continuity of the metal fiber organization, so that the fiber organization of the forging and the shape of the forging, the metal streamline is complete, can ensure that the parts have good mechanical properties and long service life. Forgings produced by precision die forging, cold extrusion, temperature extrusion and other processes are incomparable to castings.
A forging is an object in which a metal is put under pressure to create a desired shape or form a suitable compression force. This force is usually achieved by using a hammer or pressure. The forging process builds a fine particle structure and improves the physical properties of the metal. In the actual use of the parts, a proper design makes the particles flow in the direction of the main pressure. Casting is a metal forming object obtained by various casting methods, namely smelting the liquid metal, with pouring, pressing, suction or other casting methods into the prepared casting, cooling after sand, cleaning and posttreatment, the object with a certain shape, size and performance.