Forging
An external force is applied to a metal blank (not including a plate) to cause plastic deformation, change in size, shape, and improvement in performance to form a machining method for a machine part, a workpiece, a tool, or a blank.
Types and characteristics of forging
When the temperature exceeds 300-400°C (blue brittle zone of steel) and 700-800°C is reached, the deformation resistance decreases sharply and the deformation energy is greatly improved. According to the forging performed in different temperature regions, according to the different forging quality and forging process requirements, can be divided into cold forging, warm forging, hot forging three molding temperature regions. There is no strict limit to the division of such a temperature region. In general, forging in a temperature range where recrystallization has occurred is called hot forging, and forging without heating at room temperature is called cold forging.
At cold forging, the size of the forging varies little. Forging at temperatures below 700°C results in less scale formation and no surface decarburization. Therefore, as long as the deformation energy is within the forming energy range, the cold forging easily obtains good dimensional accuracy and surface finish. As long as the control of temperature and lubrication cooling, warm forging below 700 °C can also get good precision. When hot forging, large forgings with complex shapes can be forged due to small deformation energy and deformation resistance. Forgings with high dimensional accuracy can be hot forged in the 900-1000°C temperature range. In addition, we must pay attention to improving the hot forging work environment. Forging die life (2 to 5 thousand for hot forging, 1-2 for warm forging, 2 to 50,000 for cold forging) is shorter compared to forging in other temperature domains, but its degree of freedom is large and its cost is low. .
The blank is subject to deformation and work hardening during cold forging, and the forging die is subjected to a high load. Therefore, a high-strength forging die and a hard lubricating film treatment method for preventing wear and adhesion are required. In addition, in order to prevent cracking of the blank, intermediate annealing is performed when necessary to ensure the required deformability. In order to maintain a good lubrication condition, the billet can be phosphatized. In the continuous processing with bar stock and wire rods, no lubrication treatment is currently available for the section, and the possibility of using phosphating lubrication methods is being investigated.
According to the movement of the blank, forging can be divided into free forging, upsetting, extrusion, die forging, closed die forging, closed upsetting. Closed and closed upsets have high material utilization due to the lack of flash. It is possible to complete the finishing of complex forgings in one operation or several operations. Because there is no flash, the forging area is reduced and the required load is reduced. However, it should be noted that the blank cannot be completely constrained. For this purpose, the volume of the blank must be strictly controlled, the relative position of the forging die must be controlled, and the forging should be measured in an effort to reduce the wear of the forging die.
According to the movement mode of the forging dies, forging can be further divided into pendulum enthalpy, pendulum rotary forging, roll forging, cross wedge rolling, stumbling ring and oblique rolling. Pendulum, swing swaged and ring can also be used precision forging processing. In order to increase the utilization of materials, roll forging and cross rolling can be used as a pre-processing process for elongated materials. Rotary forging like free forging is also partially formed, which has the advantage that the forging force can also be achieved when the forging force is smaller than the size of the forging. This type of forging method, including free forging, causes the material to spread from the vicinity of the die surface toward the free surface during the machining. Therefore, it is difficult to ensure the accuracy. Therefore, the direction of movement of the forging die and the swaging process can be controlled by a computer and can be used low. The forge force results in a product with a complex shape and high precision. For example, forgings such as steam turbine blades with large variety and size are produced.
Forging equipment mold movement and freedom are not consistent, according to the characteristics of the bottom dead point deformation limit, forging equipment can be divided into the following four forms:
· Limit the form of forging force: hydraulic press which directly drives the slider.
· Quasi-stroke limiting method: hydraulic pressurizing crank linkage linkage hydraulic press.
· Stroke limiting method: mechanical presses that drive the slider with crank, connecting rod and wedge mechanism.
· Energy limitation: spiral and friction presses using screw mechanisms.
In order to obtain high accuracy, care should be taken to prevent overloading at the bottom dead point, controlling the speed and position of the mold. Because these will have an impact on the forging tolerances, shape accuracy and die life. In addition, in order to maintain accuracy, it should also pay attention to adjust the slider guide clearance, to ensure rigidity, adjust the bottom dead point and use of auxiliary transmission and other measures.
In addition, according to the movement of the slider and the vertical and horizontal movement of the slider (for forging of slender parts, lubrication and cooling and high-speed production of parts forging) points, the use of compensation devices can increase the other direction of movement. The above methods are different, the required forge force, process, material utilization, output, dimensional tolerances, and lubrication and cooling methods are all different. These factors also affect the level of automation.
What are the characteristics of forgings compared with castings?
After forging, the metal can improve its microstructure and mechanical properties. After the casting structure is deformed and recrystallized by the metal after forging by hot working deformation, the original coarse dendrite and columnar grains become equiaxed recrystallized grains with fine grains and uniform size, so that the original segregation in the steel ingot, Loosening, porosity, slag inclusions and other compaction and welding, the organization becomes more compact, improving the metal's plasticity and mechanical properties.
In general, the mechanical properties of the castings are lower than those of the same material. In addition, the forging process can ensure the continuity of the metal fiber structure, make the fibrous structure of the forging consistent with the shape of the forgings, complete the metal flow line, ensure the parts have good mechanical properties and long service life, use precision die forging, cold extrusion The forgings produced by such processes as warm extrusion and extrusion are unmatched by castings.
Type of forging
Aircraft forgings
By weight, about 85% of the components on the aircraft are forgings. The aircraft engine's turbine disk, rear journal (hollow shaft), blades, wings of the wing spar, fuselage ribs, wheel brackets, landing gear inside and outside the cylinder are important forgings involved in aircraft safety. Aircraft forgings are made of high-strength wear-resistant, corrosion-resistant aluminum alloys, titanium alloys, nickel-base alloys and other precious materials. In order to save materials and save energy, most of the forgings used in airplanes are produced by die forging or multi-directional die forging presses.
Automotive forging
On a weight basis, there are 17-19% forgings on the car. General automobile consists of 15 parts, including body, car trunk, engine, front axle, rear axle, frame, gearbox, transmission shaft, and steering system. The characteristics of automotive forgings are complex shape, light weight, poor working conditions, and safety. High standard. For example, crankshafts, connecting rods, camshafts used in automobile engines, front beams required for front axles, steering knuckles, axles used in rear axles, semi-axle bushings, transmission gears in bridge cases, etc. are all related to each other. Car safety running key forgings.
Diesel forgings
A diesel engine is a kind of power machinery and it is often used as an engine. Take a large diesel engine for example. The forgings used include cylinder heads, main journals, crankshaft end flange output shafts, connecting rods, piston rods, piston heads, crosshead pin shafts, crankshaft drive gears, ring gears, intermediate gears, and grease pumps. More than ten kinds of body.
Marine forgings
Marine forgings are divided into three categories, mainframe forgings, shafting forgings, and rudder-based forgings. Host forgings are the same as diesel forgings. Shaft forgings have thrust shafts, intermediate shafts, etc. Rudder forgings include rudder rods, rudder posts, and rudder pins.
Weapons forgings
Forgings occupy an extremely important position in the weapons industry. By weight, 60% of the tanks are forgings. Gun barrels, muzzle brakes, and turrets in artillery, as well as rifled barrels and triangular bayonet in infantry weapons, deep-water bomb launchers and fixtures for rockets and submarines, and stainless steel valves and shells for nuclear submarine high-pressure coolers. Gun bullets, etc., are forging products. In addition to steel forgings, other materials are used to make weapons.
Petrochemical forgings
Forgings have a wide range of applications in petrochemical equipment. Such as manholes and flanges of spherical tanks, various tube plates required for heat exchangers, entire forged cylinders (pressure vessels) for butt welding flange catalytic cracking reactors, tube sections for hydrogenation reactors, and chemical fertilizers The top cover, bottom cover, and head required for the equipment are forgings.
Mine forgings
Calculated according to the weight of the equipment, the proportion of forgings in the mine equipment is 12-24%. Mine equipment includes:
Mining Equipment Hoisting Equipment Crushing Equipment Grinding Equipment Washing Equipment Sintering Equipment
Nuclear power forgings
Nuclear power is divided into pressurized water reactors and boiling water reactors. The major forgings of nuclear power plants can be divided into two major categories: pressure shells and internals. Pressure shell contains: cylinder flange, nozzle section, nozzle, upper cylinder, lower cylinder, cylinder transition section, bolts and so on. The internal components of the reactor are operated under severe conditions such as high temperature, high pressure, strong neutron radiation, boric acid water corrosion, erosion, and hydraulic vibration. Therefore, 18-8 austenitic stainless steel is used for the production.
Thermal power forgings
There are four key forgings in the thermal power plant, namely the rotor and guard ring of the turbine generator, and the impeller and turbine rotor in the turbine.
Hydropower forgings
Important forgings in hydroelectric power station equipment include turbine shafts, hydro-generator shafts, mirror plates, and thrust heads.