Forging process types

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 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. The correct choice of forging ratio, reasonable heating temperature and holding time, reasonable initial forging temperature and final forging temperature, reasonable deformation amount and deformation speed have great relations to improve product quality and reduce cost.

Generally, small and medium-sized forgings use round or square bar material as blank. The grain structure and mechanical properties of the bar are uniform and good, the shape and size are accurate, the surface quality is good, and it is easy to organize mass production. As long as the heating temperature and deformation conditions are reasonably controlled, no large forging deformation is required to forge good forgings.

Ingot is only used for large forgings. The ingot is a cast structure with a large columnar crystal and loose center. Therefore, the columnar crystal must be broken into fine grains through large plastic deformation and loose compaction in order to obtain excellent metal structure and mechanical properties.

Powder forgings can be made by pressing and firing powder metallurgy preforms under hot conditions by die forging without flash edges. The forging powder is close to the density of general die forging parts, has good mechanical properties, and high precision, which can reduce the subsequent cutting process. Powder forgings have uniform internal organization and no segregation, and can be used to manufacture small gears and other workpieces. However, the price of powder is much higher than that of general bars, and its application in production is subject to certain restrictions.

By applying static pressure to the liquid metal cast in the die, it can solidify, crystallize, flow, plastic deformation and form under the action of pressure, and the desired shape and performance of the die forging can be obtained. Liquid metal die forging is a forming method between die casting and die forging, which is especially suitable for complex thin-walled 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 other alloys, iron based superalloy, nickel based superalloy, cobalt based superalloy deformation alloy is also forged or rolled to complete, but these alloys due to their relatively narrow plastic zone, so the forging difficulty will be relatively large. The heating temperature, opening forging temperature and final forging temperature of different materials have strict requirements.

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, special forging. 

1. Free forging. It refers to a forging processing method that uses a simple universal tool or directly exerts external force on the blank between the upper and lower anvil iron of the forging equipment to deform the blank and obtain the required geometry and internal quality. Forgings produced by the free forging method are called free forgings. Free forging is based on the production of small batches of forgings, using forging hammer, hydraulic press and other forging equipment to form the blanks, to obtain qualified forgings. The basic processes of free forging include upsetting, drawing, punching, cutting, bending, twisting, dislocation and forging. Free forging adopts hot forging method. 

2. Die forging. Die forging is divided into open die forging and closed die forging. The metal blank is compressed and deformed in the forging die with a certain shape to obtain the forging. Die forging is generally used to produce parts with small weight and large batch.

Die 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 also represent the level of forging technology.

According to the material, die forging can also be divided into black metal die forging, non-ferrous metal die forging and powder product 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 classified as die forging, which can be divided into heavy metal extrusion and light metal extrusion.

Closed die forging and closed heading forging belong to the two advanced die forging processes, because there is no flash, the utilization rate of materials is higher. It is possible to finish complex forgings with one process or several processes. Since there is no flash, the forgings have a reduced force area and the required load is also reduced. However, it should be noted that the blank can not be completely limited, so it is necessary to strictly control the volume of the blank, control the relative position of the forging die and measure the forging die, and strive to reduce the wear of the forging die.

3. Roller ring. Roller ring refers to the production of ring parts of different diameters through special equipment roller ring machine, which 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 [5], which are more suitable for the production of some special shape parts. 

For example, roll forging can be used as an effective preforming process, significantly reducing subsequent forming pressure; Transverse wedge rolling can produce steel ball, transmission shaft and other parts; Radial forging can produce large forgings such as gun barrel and step shaft. 

Forging die

According to the movement mode of forging die, forging can be divided into swing forging, swing forging, roll forging, cross wedge rolling, ring rolling and diagonal rolling. Swing forging, swing forging and ring forging are also available for precision forging. In order to improve the utilization rate of materials, roll forging and cross rolling can be used as the first process of slender materials. Rotary forging, like free forging, is also locally formed, and its advantage is that it can be formed when the forging force is small compared to the forging size. This forging method, including free forging, extends the material from near the die surface to the free surface when processing, therefore, it is difficult to ensure the accuracy, so the direction of movement of the forging die and the rotary forging sequence are controlled by the computer, and the complex shape and high precision products can be obtained with lower forging force, such as the production of many varieties and large size turbine blades and other forgings.

Forging equipment mold movement and freedom is inconsistent, according to the characteristics of the lower dead center deformation limit, forging equipment can be divided into the following four forms:

1, limit forging force form: hydraulic direct drive slider hydraulic press.

2, quasi-stroke limiting mode: hydraulic drive crank connecting rod mechanism of hydraulic press.

3, stroke limiting mode: crank, connecting rod and wedge mechanism to drive the slide mechanical press.

4, energy limitation mode: the use of spiral mechanism of the screw and friction press.

In order to obtain high accuracy, attention should be paid to prevent overload at the bottom dead center, control 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 accuracy, attention should also be paid to adjusting the slide rail clearance, ensuring stiffness, adjusting the bottom dead center and using the auxiliary transmission device.