Forging is a processing method that uses a forging machine to apply pressure to a metal blank to plastically deform it to obtain a forging with certain mechanical properties, certain shape and size. Forging (forging and stamping) is one of the two major components. Through forging, defects such as as-cast looseness generated in the metal smelting process can be eliminated, and the microstructure can be optimized. At the same time, due to the preservation of the complete metal streamline, the mechanical properties of forgings are generally better than those of castings of the same material. For important parts with high load and severe working conditions in related machinery, forgings are mostly used in addition to rolling plates, profiles or welded parts with simple shapes.

The initial recrystallization temperature of steel is about 727 °C, but 800 °C is generally used as the dividing line, and hot forging is higher than 800 °C; between 300 and 800 °C, it is called warm forging or semi-hot forging. called cold forging.

Forgings used in most industries are hot forging. Warm and cold forging are mainly used for forging parts such as automobiles and general machinery. Warm and cold forging can effectively save materials.

Process classification

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, ring rolling and special forging.

1. Free forging

It refers to the processing method of forgings that use simple universal tools or directly apply external force to the blank between the upper and lower anvils of the forging equipment to deform the blank to obtain the required geometric shape and internal quality. Forgings produced by the free forging method are called free forgings. Free forging is mainly based on the production of small batches of forgings. Forging equipment such as forging hammers and hydraulic presses are used to form and process the blanks to obtain qualified forgings. The basic processes of free forging include upsetting, drawing, punching, cutting, bending, torsion, offset and forging. Free forging is all hot forging.

Advantages: Free forging has the characteristics of flexible process, high versatility of equipment and tools, and low cost. Since free forging is formed gradually, the required deformation force is small, so it is the only way to produce large forgings (above 300T).

Disadvantages: low productivity, low precision forgings, high labor intensity, mostly used for single-piece and small batch production of forgings with simple shapes and low precision requirements.

2. Die forging

Die forging is divided into open die forging and closed die forging. The metal blank is compressed and deformed in a forging die cavity with a certain shape to obtain a forging. Die forging is generally used to produce parts with small weight and large batches. Die forging can be divided into hot forging, warm forging and cold forging. Warm forging and cold forging are the future development direction of die forging, and also represent the level of forging technology.

According to the material, die forging can also be divided into ferrous metal die forging, non-ferrous metal die forging and powder product forming. As the name implies, the materials are ferrous metals such as carbon steel, non-ferrous metals such as copper and aluminum, and powder metallurgy materials. Extrusion should belong to die forging, which can be divided into heavy metal extrusion and light metal extrusion.

Closed die forging and closed upsetting are two advanced processes of die forging. Since there is no flash, the utilization rate of materials is high. It is possible to complete the finishing of complex forgings in one or several operations. Since there is no flash, the stressed area of ​​the forging is reduced and the required load is also reduced. However, it should be noted that the blank cannot be completely restricted. For this reason, the volume of the blank should be strictly controlled, the relative position of the forging die should be controlled and the forging should be measured, and efforts should be made to reduce the wear of the forging die.

3. Rolling ring

Ring rolling refers to the production of ring-shaped parts of different diameters through special equipment ring-grinding machines, and is also used to produce wheel-shaped parts such as automobile hubs and train wheels.

4. Special forging

Special forging includes roll forging, cross wedge rolling, radial forging, liquid die forging and other forging methods, which are more suitable for the production of parts with special shapes. For example, roll forging can be used as an effective preforming process to greatly reduce the subsequent forming pressure; cross wedge rolling can produce parts such as steel balls and drive shafts; radial forging can produce large forgings such as barrels and stepped shafts.

Forging die

According to the movement mode of the forging die, forging can be divided into pendulum rolling, pendulum rotary forging, roll forging, cross wedge rolling, ring rolling and skew rolling. Pendulum rolling, pendulum swaging and ring rolling can also be processed by precision forging. In order to improve the utilization rate of materials, roll forging and cross-rolling can be used as front-end processing of slender materials. Rotary forging, like free forging, is also locally formed, and its advantage is that it can be formed with a small forging force compared to the size of the forging. In this forging method, including free forging, the material expands from the vicinity of the die surface to the free surface during processing, so it is difficult to ensure accuracy. The forging force can be used to obtain products with complex shapes and high precision, such as forgings such as steam turbine blades with many varieties and large sizes.

The movement of the die and the degree of freedom of the forging equipment are inconsistent. According to the deformation limitation characteristics of the bottom dead center, the forging equipment can be divided into the following four forms:

1. The form of limiting forging force: hydraulic press that directly drives the slider.

2. Quasi-stroke limit method: hydraulic press that drives the crank connecting rod mechanism.

3. Stroke limitation method: mechanical press with crank, connecting rod and wedge mechanism driving the slider.

4. Energy limitation method: use the screw and friction press of the screw mechanism.

In order to obtain high precision, care should be taken to prevent overload at the bottom dead center, and to control the speed and mold position. Because these will have an impact on forging tolerances, shape accuracy and forging die life. In addition, in order to maintain the accuracy, attention should also be paid to adjusting the clearance of the slider guide rail, ensuring the rigidity, adjusting the bottom dead center and using the auxiliary transmission device.

Slider

There are also vertical and horizontal motions of the slider (for forging of slender parts, lubricating cooling and forging of parts for high-speed production), and the compensation device can be used to increase the motion in other directions. The above methods are different, and the required forging force, process, material utilization, output, dimensional tolerance and lubrication and cooling methods are different, and these factors are also factors that affect the level of automation.

Different forging methods have different processes. Among them, the process of hot die forging is the longest, and the general order is: blanking of forging billet; heating of forging billet; roll forging preparation billet; die forging forming; trimming; punching; straightening; Intermediate inspection to check the size and surface defects of forgings; heat treatment of forgings to eliminate forging stress and improve metal cutting performance; cleaning, mainly to remove surface oxide scale; correction; inspection, general forgings are subject to appearance and hardness inspections, important forgings also It must undergo chemical composition analysis, mechanical properties, residual stress and other inspections and non-destructive testing.

The forging products of the forging factory are plastically deformed by forging processing. The forging process is a processing method for the blanks or parts that use the external force to plastically deform the forging raw materials and obtain the size, shape and performance required for the forgings. Through forging processing can eliminate defects such as as-cast looseness caused by metal in the smelting process, optimize the microstructure, and at the same time greatly enhance the performance of forgings in use due to the preservation of the complete metal forging flow line.

Forging is one of the main methods for the production of blanks and parts in mechanical manufacturing. It is often divided into free forging and die forging. Compared with other processing methods, forging processing has the following characteristics:

1. Improve the internal structure of forgings and improve mechanical properties. After the forging blank is forged, its structure and properties are improved and improved. Forging processing can eliminate defects such as pores, shrinkage cavities and dendrites in the metal ingot, and can be coarsened due to plastic deformation and recrystallization of the metal. The grain is refined to obtain a dense metal structure, thereby improving the mechanical properties of the forging. In the design of the part, if the direction of the force of the part and the direction of the fiber structure are correctly selected, the impact resistance of the forging can be improved.

2. The utilization rate of materials is high. Metal plastic forming is mainly rearranged by the relative position of the metal body structure without the need to cut the metal.

3. Higher productivity. Forging processing is generally carried out by using a press and a forging hammer.

4. The accuracy of blanks or forgings is high. With advanced technology and equipment, it can achieve less or no cutting.

5. The metal material used for forging should have good plasticity so that it can be plastically deformed without breaking under the action of external force. Among the commonly used metal materials, cast iron is a brittle material with poor plasticity and cannot be used for forging. Copper, aluminum and alloys thereof in steel and non-ferrous metals can be processed under cold or hot conditions.

6. It is not suitable for forming forgings with complex shapes. Forging processing is formed in the solid state. Compared with casting, the flow of metal is limited, and it is generally required to adopt heating and other technological measures. It is difficult to manufacture parts or blanks with complex shapes, especially those with complex internal cavities.

Since forging has the above characteristics, important parts subjected to impact or alternating stress (such as transmission spindle, ring gear, connecting rod, track wheel, etc.) should be processed by forging blanks, so forging processing in machinery manufacturing, mining, light industry Heavy industry and other industries have been widely used.

The forging materials are mainly carbon steel and alloy steel of various compositions, followed by aluminum, magnesium, copper, titanium and the like and alloys thereof. The raw state of the material is bar, 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. Correct selection of forging ratio, reasonable heating temperature and holding time, reasonable initial forging temperature and final forging temperature, reasonable deformation and deformation speed have a great relationship to improve product quality and reduce cost.

Conventional small and medium forged materials use round or square bars as blanks. The grain structure and mechanical properties of the bar are uniform and good, the shape and size are accurate, and the surface quality is good, which is convenient for mass production. As long as the heating temperature and deformation conditions are properly controlled, high-quality forgings can be forged without requiring large forging deformation.

Ingots are only used for large forgings. The ingot is an as-cast structure with large columnar crystals and a loose center. Therefore, it is necessary to break the columnar crystal into fine crystal grains by large plastic deformation, and loosely compact, in order to obtain excellent metal structure and mechanical properties.

The powder metallurgy preform which is pressed and sintered can be made into a powder forging by hot forging without flashing. Forging powder is close to the density of general die forgings, has good mechanical properties, and has high precision, which can reduce subsequent cutting. The powder forgings have a uniform internal structure and are not segregated and can be used to manufacture workpieces such as small gears. However, the price of powder is much higher than the price of ordinary bars, and its application in production is limited.

By applying static pressure to the liquid metal poured in the mold to solidify, crystallize, flow, plastically deform and form under pressure, a die forging of desired shape and performance can be obtained. Liquid metal die forging is a forming method between die casting and die forging, and is particularly suitable for complex thin-walled parts which are difficult to form by 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 other alloys, iron-based superalloys, nickel-based superalloys, cobalt-based superalloys The deformed alloys are also finished by forging or rolling, except that the alloys are relatively narrow in plasticity, so the forging difficulty is relatively large, and the heating temperature, opening and forging temperature and final forging temperature of different materials have strict requirements.