Forging is a processing method that uses a forging press to apply pressure to a metal blank to cause it to undergo plastic deformation to obtain forgings with certain mechanical properties, shapes, and sizes. It is the main process for preparing high-performance, high-quality structural components. Due to the many advantages of aluminum alloys, they have been widely used in aerospace, automobiles and motorcycles, high-speed rail and magnetic levitation vehicles, ships and warships, national defense and military equipment, communication equipment, and other fields. At the same time, due to the need for energy conservation and emission reduction, their applications are becoming more and more extensive. However, among the four major categories of products, castings and die castings, flat-rolled products, extruded and drawn products, and forgings, the consumption of forgings is the smallest, which can be said to be negligible. In some countries and regions, punching and extrusion are also classified as forging.
Features:
Forging has four major features:
1、The blank undergoes obvious plastic deformation during the forging process, which can eliminate the looseness of the metal in the cast state and weld holes, thereby improving the mechanical properties of the workpiece;
2、 It can achieve changes in the shape and size of the workpiece by relying on plastic deformation to transfer materials while maintaining the integrity of the metal, without generating mechanical chips, and with high material utilization;
3, In addition to changes in size and shape, it can also greatly improve and enhance the organization and performance of the workpiece;
4. The dimensional accuracy and surface quality of the forgings are high.
Classification
Forging can be divided into free forging and die forging according to the forming method;
According to the deformation temperature can be divided into cold forging, warm forging, hot forging, and isothermal forging.
Free forging and die forging free forging.
Free forging is one of the main processes of ingot billet and forging bars, cakes and rings, etc., can improve the organization of the material, improve performance, directly forged into a certain shape of the workpiece; or as a billeting process, for extrusion, rolling to provide intermediate products.
The other type of billet used for free forging is ingot or powder metallurgy sintered billet. Ingots often contain a certain amount of coarse columnar crystals, and grain boundaries always gather some harmful inclusions, which will weaken the intergranular strength. Sintered billets in the presence of loose, porous material reduce the plasticity of the material, easy to fracture.
Material properties must therefore be improved by forging and recrystallization. The basic equipment utilized in free forging is the hydraulic forging machine and the steam-air hammer. The use of fast-hammer hydraulic presses and precision forging machines allows the preparation of forgings with uniform organization and more accurate dimensions. Commonly used free forging processes are upsetting, elongation, punching and reaming.
Upsetting is a process to make the billet height decrease and the cross-section increase. The process will be a small cross-section billet made of a large cross-section, such as a cake, or ring, or to improve the degree of casting tissue crushing, so that forgings have the required organizational properties, to improve the draw length forging ratio. Draw length to make the billet cross-section reduction, and length increase process. The ratio of the cross-sectional area of the billet and the cross-sectional area of the finished product is called the forging ratio, to comprehensively break the casting organization of the billet, the forging ratio should be > 3. To increase the forging ratio, you can combine the pulling process and upsetting process into one.
Usually, high plasticity alloys can be used on flat anvil when pulling long, for the low plasticity and the internal organization of the forgings require high alloy should be used in the anvil. Punching is the process of making through holes or blind holes in the blank.
The commonly used processes are: solid punch punching, hollow punch punching, and punching on a gasket ring. Reaming is a process to reduce the wall thickness of hollow blanks while increasing their internal and external diameters. Reaming methods are mainly punch reaming and horse shoulder reaming, punch reaming billet tangential tensile stress, each time the amount of reaming is not large; horse bar reaming billet tangential tensile stress is very small, will not produce cracks, suitable for forging thin-walled ring parts.
Die forging. This is a batch preparation of forgings, so that the metal material in a certain shape cavity deformation, can be prepared in shape and size close to the finished forgings. Compared with free forging, die forging can save the amount of machining and material consumption of the workpiece, improve labor productivity and product quality and stability, and at the same time manufacture complex shapes of forgings. Preparation of excellent organization and high mechanical properties and the need for more volume, the choice of die forging is suitable and cost-effective. Billets for die forging is mainly pre-extruded, rolled, or free-forging semi-finished products, but also with powder metallurgy billets or spray molding material, the equipment used for: steam-air hammers, high-speed hammers, hot forging presses, forging hydraulic presses, screw presses and horizontal forging presses. There are two basic forms of die forging: open die forging with burrs and closed die forging without burrs.
Open die forging mold has an upper and lower part, respectively, mounted on the upper and lower movable beam.
The forming process of die forging can be divided into four stages:
First, upsetting deformation, billet height reduction, with localized indentation deformation, radial size becomes larger, until the contact with the inner wall of the die cavity;
The second is the formation of burrs, metal flow is impeded by the mold cavity, contributing to the flow in the direction of the height of the mold cavity, and flow to the burr groove;
Third, filling the cavity, due to the obstruction of the burr, the metal gradually fills the cavity, and flows to the burr groove;
Fourthly, extrusion of excess metal to form the forging.
Closed die forging:
Before the metal begins to deform the forging die cavity is closed, the billet in the fully closed state of deformation.
Closed die forging due to the stress state is good, the plasticity of the material has been improved; due to the formation of no burrs, the metal flow line along the forging shape distribution and will not be cut off, and thus the organization of the forging properties also have some improvement. Multi-directional die forging also belongs to the closed die forging, which is in the multi-directional die forging hydraulic presses, the use of components with multiple die surface forging die, the manufacture of complex shapes of hollow multi-branch forging process.
In essence, multi-directional die forging is a kind of extrusion-based, extrusion and die forging integrated application of forming technology, that can prepare complex shapes, sizes,s and precision of the die forging parts, but also suitable forging temperature range is not only wide hard to deformation alloy molding, such as used to forging aircraft landing gear parts, missile nozzles, high-pressure valves, high-pressure containers, pipe fittings, disk and shaft assemblies and other important structural components.
Cold forging, warm forging, hot forging, and isothermal forging cold forging is carried out at a temperature below the start of metal recrystallization.
The advantages of the workpiece formed by cold forging at room temperature are:
High shape and dimensional accuracy, clean surface, less machining process, easy to automate production.
Many cold-forged parts can be used directly for assembly without machining. However, most of the deformed aluminum alloy room temperature plasticity is not high, cold forging is prone to cracking, and deformation resistance, and forging pressure forging machines. At higher than room temperature and lower than the beginning of recrystallization temperature forging is called warm forging. Warm forging products of higher precision, surface finish, and deformation resistance are not large.
Hot forging is in the beginning of alloy recrystallization temperature of about 40 ℃ or higher temperature forging, improve the temperature can improve the plasticity of the metal, and is conducive to improving the organization and performance of the metal, high temperature also reduces the deformation resistance of the metal can be used to forge pressure is not so big forging machine. But the hot forging process is more, the surface accuracy of the workpiece is poor, and the surface is not so smooth. Isothermal forging is in the whole process of forming the temperature of the billet is always maintained at a constant or a narrow temperature range of forging, is to take full advantage of certain metals at a constant temperature that have a high plasticity, such as superplastic forging and forming. Isothermal forging needs to be billet and mold temperature at the same time to maintain constant, high production costs.
