Basic knowledge of forging
Basic knowledge of forging
A forming process in which an external force is applied to a metal blank (excluding sheet metal) to produce plastic deformation, change its size, shape, and improve its properties for the manufacture of mechanical parts, workpieces, tools, or blanks.
Types and features of forging: when the temperature exceeds 300-400℃ (blue brittle zone of steel) and reaches 700-800℃, the deformation resistance will decrease sharply and the deformation energy will be greatly improved.According to the forging in different temperature areas, according to the forging quality and forging process requirements, can be divided into cold forging, warm forging, hot forging three forming temperature areas.Originally, the division of this temperature region is not strictly defined. Generally speaking, forging in the recrystallization temperature region is called hot forging, while forging without heating at room temperature is called cold forging.
In low – temperature forging, the forging size changes very little.Forging below 700℃, less oxide skin formation, and the surface without decarburization phenomenon.Therefore, as long as the deformation can be within the range of forming energy, cold forging is easy to get good dimensional accuracy and surface finish.As long as the temperature and lubrication cooling are well controlled, the forging temperature below 700℃ can also obtain good precision.When hot forging, because the deformation energy and deformation resistance are very small, can forge the shape of complex large forging.To obtain high dimensional precision forgings can be processed by hot forging in the temperature range of 900-1000℃.In addition, attention should be paid to improving the working environment of hot forging.The forging die life is short compared with other forging in temperature domain, but it has large freedom and low cost.
The billet is deformed and machined during cold forging, which causes the forging die to bear high load. Therefore, it is necessary to use the forging die with high strength and adopt the hard lubrication film treatment method to prevent wear and bonding.In addition, in order to prevent the billet from cracking, intermediate annealing is carried out when necessary to ensure the required deformation capacity.In order to maintain good lubrication state, the blank can be phosphorized.At present, the section cannot be lubricated when rod material and rod rod are used for continuous machining.According to the movement of billet, forging can be divided into free forging, upsetting, extrusion, die forging, closed die forging, and close upsetting.Closed die forging and close upsetting because there is no flash, the utilization of materials is high.It is possible to finish complex forgings with one or more processes.As there is no flash, the forgings have less stressed area and require less load.However, it should be noted that the billet should not be completely restricted, so the billet volume should be strictly controlled, the relative position of the forging die should be controlled and the forging should be measured, so as to reduce the wear of the forging die.
According to the movement of forging die, forging can be divided into swing rolling, swing forging, roll forging, wedge rolling, ring rolling and cross rolling.Swing rolling, swing forging and ring rolling can also be refined.In order to improve the utilization of materials, roll forging and rolling can be used as the preceding process of slender materials.Rotary forging, like free forging, is also locally formed, and its advantage is that it can be formed with less forging force compared to the size of the forging.This kind of forging, including free forging, when processing the material from the mold surface near the free surface extension, therefore, it is difficult to ensure the accuracy, so, the forging die movement direction and rotary forging sequence with computer control, can be used to lower the forging force to obtain the shape of complex, high precision products.For example, the production of a variety of large size steam turbine blade forging.
The die movement of forging equipment is inconsistent with the degree of freedom. According to the characteristics of lower dead center deformation limitation, forging equipment can be divided into the following four forms:
· limited forging force form: oil press directly driving the slider with oil pressure.
· quasi-stroke restriction mode: oil press driven by oil pressure crank connecting rod mechanism.
· stroke limiting mode: mechanical press with crank, connecting rod and wedge mechanism driving slider.
· energy limitation: screw and friction press with screw mechanism.
To achieve high accuracy, care should be taken to prevent overload at the bottom dead center, control the speed and mold position.Because these will affect forging tolerance, shape accuracy and forging die life.In addition, in order to maintain the accuracy, attention should be paid to adjust the sliders guide clearance, ensure stiffness, adjust the bottom dead point and the use of auxiliary driving device and other measures.
In addition, according to the sliding block movement mode and sliding block vertical and horizontal movement (for the forging of slender pieces, lubrication cooling and high-speed production of parts forging), the use of compensation device can increase the movement in other directions.The forging force, process, material utilization rate, yield, dimensional tolerance and lubrication cooling method are all different in the above mentioned ways. These factors also affect the level of automation.
What are the features of forgings compared to castings
The micro structure and mechanical properties of metals can be improved 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.
Generally speaking, the mechanical properties of castings are lower than those of forgings of the same material.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.About 85% of the components on an airplane are forgings by weight.Turbine disc, rear journal (hollow shaft), blade, wing SPAR of aircraft engine;The rib plate of fuselage, wheel support, and inner and outer cylinder of landing gear are important forgings related to aircraft safety.Aircraft forgings are made of precious materials such as aluminum alloy, titanium alloy, nickel base alloy, etc.In order to save materials and energy, most of the forging parts for aircraft are produced by die forging or multi-purpose die forging press.Car forging by weight, the car has 1719% forging.The general car by the body, the car box, the engine, the front axle, the rear axle, the frame, the transmission, the transmission shaft, the steering system and so on 15 parts constitute the automobile forging parts characteristic is the appearance is complex, the weight is light, the working condition condition is poor, the safety degree request is high.For example, the crankshaft, connecting rod, camshaft used in automobile engine, the front beam, steering knuckle, half shaft, half axle sleeve pipe used in rear axle, the transmission gear in bridge box, etc., all of them are the key forgings for the safe operation of automobile.Diesel engine forgings diesel engine is a kind of power machinery, it is often used as the engine.Taking large diesel engine as an example, more than ten kinds of forgings are used, such as cylinder head, spindle neck, crankshaft end flange output end shaft, connecting rod, piston rod, piston head, crossover pin shaft, crankshaft transmission gear, gear ring, intermediate gear and dye pump body.Marine forgings: Marine forgings are divided into three categories, main engine forgings, shafting forgings and rudder forgings.Main engine forging is the same as diesel engine forging.Shafting forgings have thrust shaft, middle shaft and stern shaft, etc.Rudder forging with rudder stock, rudder post, rudder pin, etc.
Forging of weapon;Forging plays an important role in the weapon industry.By weight, 60% of the tank is forgings.The barrel, muzzle retainer and tail of the gun, ribbed barrel and three-edged bayonet of the infantry weapon, launcher and fixing seat of depth charge of rocket and submarine, stainless steel body for high pressure cooler of nuclear submarine, shell and bullet are all forging and pressing products.Weapons are made of materials other than steel forgings.
Petrochemical forging: forging is widely used in petrochemical equipment.For example, manholes and flanges of spherical storage tanks, various tube plates required for heat exchanges, welded flanges for catalytic cracking reactors (pressure vessels), tube joints used in hydrogenation reactors, and cover, bottom cover and sealing head required for chemical fertilizer equipment are all forgings.Thermal forgings: there are four key forgings in the thermal power generation equipment, that is, the rotor and protection ring of the turbine generator, and the impeller in the turbine and the turbine rotor.Hydroelectric forgings: the important forgings in the equipment of hydroelectric power station include the big shaft of hydraulic turbine, the big shaft of hydro-generator, the mirror plate and the thrust head.