Forging is a processing method that uses forging machinery to apply pressure to metal blanks to cause plastic deformation to obtain shaft forgings with certain mechanical properties, certain shapes and sizes. Forging and stamping belong to the nature of plastic processing, collectively referred to as forging. Forging is a common forming method in mechanical manufacturing. The as-cast looseness and welding holes of the metal can be eliminated by forging, and the mechanical properties of forgings are generally better than castings of the same material. For important parts with high load and severe working conditions in machinery, forgings are mostly used except for plates, profiles or weldments that can be rolled with simple shapes.

The recrystallization temperature of steel is about 460°C, but 800°C is generally used as the dividing line, and hot forging is above 800°C; it is called warm forging or semi-hot forging between 300 and 800°C.

Forging can be divided into cold forging and hot forging according to the temperature of the blank during processing. Cold forging is generally processed at room temperature, and hot forging is processed at a temperature higher than the recrystallization temperature of the blank metal. Sometimes it is also called warm forging when it is heated but the temperature does not exceed the recrystallization temperature. However, this division is not completely uniform in production.

According to the forming method, forging can be divided into free forging, die forging, cold heading, radial forging, extrusion, forming rolling, roll forging, rolling and so on. The deformation of the billet under pressure is basically not subject to external restrictions, which is called free forging, also known as open forging; the deformation of the billet in other forging methods is restricted by the mold, which is called closed mode forging. There is a relative rotational movement between the forming tools of forming rolling, roll forging, rolling, etc. and the blank, and the blank is pressed and formed point by point and gradually, so it is also called rotary forging.

Generally, round or square bars are used as blanks for small and medium-sized shaft forgings. 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 convenient to organize mass production. As long as the heating temperature and deformation conditions are controlled reasonably, shaft forgings with excellent performance can be forged without large forging deformation.

Forging materials are mainly carbon steel and alloy steel with various components, followed by aluminum, magnesium, copper, titanium and their alloys. The original state of the material is bar stock, ingot, metal powder and liquid metal.

Forging transforms metal workpieces by compression at cold, hot or hot temperatures. Cold forging increases the strength of a metal by hardening it at room temperature. Hot forging achieves optimum yield strength, low hardness, and high ductility by hardening the metal at extremely high temperatures. Whether to use hot or cold forging depends on the function, industry and production volume of the finished part.

The difference between hot forging and cold forging

While cold forging compresses metal at room temperature, hot forging requires high temperatures. The main difference between cold forging and hot forging is that the high temperature of hot forging gives the metal a finer and more complex shape than cold forging.

Hot forging

The hot forging temperature varies depending on the metal type. Hot forging begins by heating the die to prevent any temperature loss during the process and to ensure that crystallization does not occur until the forming is complete. Heating makes the metal more ductile. When the pressure of the die squeezes the hot metal, the structure transforms into finer grains, which increase yield strength and ductility.

Factors to consider when hot forging include:

Cool down

If the metal cools to a temperature below the minimum threshold, the forging is complete. If this happens before reaching the final shape, the metal must be reheated.

Tolerance

The dimensional tolerances of hot forging are not as precise as cold forging.

Specification

Hot forging dies are customized according to customer’s part specifications.

Cold forging

Cold forging uses a displacement process to shape the material into the desired shape. The compressive force squeezes the metal between the punch and die at room temperature until the material conforms to the contour of the die. Cold forging techniques include rolling, pressing, drawing, spinning, upsetting and extrusion.

Factors to consider when cold forging include:

Material volume

Careful control of material volume prevents stress and damage, especially in closed forging, as excess material has nowhere to escape.

Bonding

This coating process improves material flow during the process to reduce forces, stresses and friction while improving surface quality.

Annealing

Annealing softens metal and improves material flow. It can be applied as an intermediate process when work hardening occurs before the forging process is completed.

Lubricating

Lubrication is critical in the cold forging process. High-viscosity oil prevents metal-to-metal friction, and thin oil dissipates heat.

Advantages and disadvantages of hot forging and cold forging

Advantages of hot and cold forging

Hot forging adds ductility to more complex parts and allows for more customization options; cold forging produces no waste, requires little finishing, maintains dimensional accuracy, and produces high surface quality.

Disadvantages of hot and cold forging:

Additional cost of hot forging heat treatment, less precise dimensional tolerances, risk of warpage; cold forging has few custom options, risk of residual stress, may require heat treatment.

The above is about the process difference between hot forging and cold forging. When choosing which forging process to use, you must understand its characteristics in advance.

Free forging is a processing method that uses impact force or pressure to deform the metal freely in all directions between the upper and lower anvil surfaces, and obtains the required shape and size and certain mechanical properties without any restriction, which is referred to as free forging. The tools and equipment used in free forging are simple, versatile and low in cost. Compared with casting blanks, free forging eliminates shrinkage holes, shrinkage porosity, pores and other defects, so that the blanks have higher mechanical properties. Forgings are simple in shape and flexible in operation. Therefore, it has special significance in the manufacture of heavy machinery and important parts.

Basic process of free forging

The basic processes of free forging include upsetting, drawing, punching, bending, torsion, offset, cutting and forging.

Upsetting

A forging process that reduces the height of the blank and increases the cross-sectional area. The upsetting process is mainly used for forging gear blanks and round cake forgings. The upsetting process can effectively improve the blank structure and reduce the anisotropy of mechanical properties. Repeated upsetting and drawing can improve the morphology and distribution of carbides in high-alloy tool steels.

Upsetting mainly has the following three forms:

1. Complete upsetting. Complete upsetting is to place the blank vertically on the anvil surface, and under the hammering of the upper anvil, the blank will be plastically deformed with a height reduction and an increase in the cross-sectional area.

2, the end upsetting. After the billet is heated, one end is placed in a drain or mold to limit the plastic deformation of this part, and then the other end of the billet is hammered to make it upsetting. The upsetting method of the leaking disc is mostly used for small batch production; the method of upsetting the tire mold is mostly used for mass production. Under the condition of single-piece production, the part that needs upsetting can be heated locally, or after all heating, the part that does not need upsetting can be chilled in water, and then upsetting is performed.

3. Upsetting in the middle. This method is used for forging forgings with large middle section and small sections at both ends. For example, gear blanks with bosses on both sides are forged by this method. Before the upsetting of the billet, both ends of the billet should be thinned first, and then the billet should be upright in the middle of the two leakage pans for hammering to make the middle part of the billet upsetting. In order to prevent the billet from bending during upsetting, the ratio of the billet height h to the diameter d h/d ≤ 2.5.

Pull out

Elongation, also known as elongation, is a forging process that reduces the cross-sectional area of ​​the billet and increases its length. Drawing length is often used for forging rods and shaft parts. There are two main methods of pulling out:

1. Pull out on the flat anvil.

2. Pull out on the mandrel. During forging, the mandrel is first inserted into the punched billet, and then drawn as a solid billet. When drawing long, it is generally not drawn at one time. First, the blank is drawn into a hexagonal shape, and after forging to the required length, the chamfer is rounded and the mandrel is taken out. In order to facilitate the removal of the mandrel, the working part of the mandrel should have a slope of about 1:100. This drawing method can increase the length of the hollow blank, reduce the wall thickness, and keep the inner diameter unchanged. It is often used for forging long hollow forgings such as sleeves.

Punching

There are two main methods of punching:

1. Double-sided punching method. When the punch is punched to the depth of 2/3 to 3/4 on the blank, take out the punch, turn the blank, and then use the punch to align the position from the reverse side to punch out the hole.

2. Single-sided punching method. For blanks with small thickness, single-sided punching method can be used. When punching, the blank is placed on the backing ring, the big end of a slightly tapered punch is aligned with the punching position, and the blank is hammered into the blank until the hole penetrates.

Bending

The forging process in which a certain tool and die bends the blank into a specified shape is called bending.

There are two commonly used bending methods:

1. Forging hammer compression bending method. One end of the blank is pressed by the upper and lower anvils, and the other end is struck with a sledgehammer or pulled by a crane to bend it into shape.

2. Die bending method. Bending in the pad die can obtain small forgings with more accurate shape and size.
Cutting refers to the forging process in which the blank is divided into several parts or partially cut, or a part is cut from the outside of the blank, or a part is cut from the inside.

Twist

Torsion is a forging process that rotates one part of wool by an angle about its axis relative to another. This process is mostly used for forging multi-turn crankshafts and correcting some forgings. When the torsion angle of the small billet is not large, the hammering method can be used.

Misplaced

Staggering refers to the forging process in which one part of the blank is staggered parallel to another part by a distance, but the axis is still kept parallel. It is often used for forging crankshaft parts. When staggered, the blank is first cut locally, and then impact force or pressure of equal size, opposite method and perpendicular to the axis is applied on both sides of the incision, so that the blank can be offset.

Forging

Forging is a forging process in which the billet is heated to a high temperature in a furnace, and then struck with a hammer to combine the two in a solid state. Forging methods include lap joint, butt joint, snap joint and so on. The strength of the seam after forging can reach 70% to 80% of the strength of the connected material.

The above is all about the basic process of free forging. I hope it can be helpful to everyone. If you have any questions during the operation, you can contact us at any time.

The die forging process has high production efficiency, low labor intensity, accurate dimensions, small machining allowance, and can forge forgings with complex shapes; it is suitable for mass production. However, the cost of the die is high, and special die forging equipment is required, which is not suitable for single-piece or small batch production. Therefore, the quality of die forgings is also more concerned by users. Correctly understand the main factors affecting the quality of die forgings. very important meaning.

The main factors affecting the quality of die forgings

1. Defects in raw materials

For example, there are residual shrinkage holes, bubbles, porosity, inclusions, etc. in the ingot or steel, which may cause the forging to crack. Forging cracks caused by metallurgical reasons are often accompanied by a large number of oxides, sulfides, silicates and other inclusions. The raw materials of high carbon and high alloy steel are prone to serious segregation of second phases such as carbides. If they are not crushed and evenly distributed during forging, the mechanical properties of the forgings will be reduced, and the forgings may be cracked or evenly distributed during heat treatment. distortion. If there are scratches, scars, folds and cracks on the surface of the raw material, it will bring defects to the forgings. Therefore, raw materials must be inspected in die forging production.

2. Heating specification

When forging large die forgings and alloy steel die forgings, if the heating speed is too fast, the temperature difference between the inner and outer layers will be large, and the central part will be cracked due to temperature stress and structural stress.
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When the heating temperature is too high and the holding time is too long to cause slight overheating, a lustrous, crystalline, and intergranular fracture will be produced. Coarse grains that are slightly overheated can be corrected by annealing or normalizing, followed by recrystallization. In severe overheating, fractures or stone fractures will occur. The characteristics of the fracture are fish-scale bright spots and transgranular fracture; the reason for the fracture is that the coarse austenite grains form an intragranular texture with extremely high stability. Texture characteristics are preserved.

The stone-like fracture has obvious coarse crystals, the surface has no metallic luster, the color is gray, and the intergranular fracture is caused. Saturated coarse austenite precipitates, surrounding austenite grains to form brittle crystal shells. Severely overheated forging billets have extremely poor mechanical properties. The naphthalene-shaped fracture can be normalized at high temperature to eliminate the intragranular texture, while the stone-shaped fracture is difficult to be corrected by heat treatment.
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The forging heating temperature is low, and when the heat is not penetrated, cracks with transgranular propagation may occur, and the tail ends are sharp. When there is no subsequent heating process, there is no oxidation and decarburization on the surface of the cracks.
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For alloy structural steel, if the final forging temperature is too high, the austenite will continue to grow after final forging, even exceeding the original grain size. Coarse-grained fractures can be seen in fracture inspection, and Widmanderin microstructure appears in high magnification observation. If the final forging temperature is too low, the steel is in the dual-phase region, the inclusions are distributed along the main deformation direction of the blank, and the ferrite precipitated from the austenite preferentially adheres to the surface of the inclusions to form a banded structure. Widmanderin and banded structures reduce the mechanical properties of forgings, especially the impact toughness. In order to refine the grains, improve the structure, and improve the mechanical properties, the steel with such a structure must be completely annealed to recrystallize it.

3. Die forging process

Different forms of die forging are used, such as open die forging, closed die forging, extrusion, upsetting, high-speed die forging, rolling, etc. The essence is to apply different forms to the blank through corresponding die forging equipment and dies. The thermal and mechanical conditions make it produce different physical fields and evolution processes of tissue properties. For the same forging, whether the selection of the deformation method is reasonable or optimal, the quality of the die forgings is very different. The wrong selection may make the forming process impossible, and the unreasonable selection will make the forming difficult and prone to many quality problems.

The die forging process parameters such as deformation temperature, deformation speed and degree of deformation are obviously directly related to the quality of die forgings. For example, for ingots or some materials, it is necessary to compact the structure and refine the grains through deformation. If the forging deformation is small, the expected effect cannot be obtained; some non-ferrous metals, especially high-strength aluminum alloys, magnesium alloys, etc. , requires a small deformation speed and an appropriate degree of deformation, and is suitable for forming on a press, which helps to avoid cracks.

The quality of die forgings is also related to forging design and forging die design. The selection of machining allowance and forging tolerance should be based on reality. If the specification is too small, it is easy to cause waste after machining due to surface defects and dimensional errors. Whether the design of the structure and the flash structure is appropriate will affect the flow and filling quality of the metal; if the setting of the lock is ignored, the size of the forging will be out of tolerance due to the misalignment of the upper and lower dies. In addition, the installation and tightening, preheating, cooling and moistening of the forging die should comply with the specifications, and the violations should be checked at any time and corrected in time.

The above is all about the factors affecting the quality of die forgings. Every link in the production of die forging will have a non-negligible impact on the quality of the forgings. Strictly follow the relevant quality inspection and control in the production process to ensure the quality of the die forgings.

Forging is the use of forging pressure on metal blank products by forging machines to plastically deform the processed forgings to achieve specific mechanical properties, shapes and sizes. This is an important metal plastic processing method adopted by many forging manufacturers. Many people know about forging, but they don’t know much about the forging process. Today, GOLD EMPEROR FORGING, a forging manufacturer, will share with you some common forging processes.

Classification according to forging temperature:

First of all, the forging process can be classified according to the forging temperature, commonly used are hot forging, warm forging and cold forging.

Classification according to forming principle:

Secondly, we can also divide the forging process into free forging, die forging, ring rolling and special forging according to the forming principle of forgings.

1. Free forging of forging process

Using simple universal tools, or directly applying external force to the blank between the upper and lower anvils of the forging equipment, the blank is deformed, and the processing method of the forging to obtain the required geometric shape and internal quality is free forging. Forgings produced by the free forging method can be called free forgings. Free forging is mostly used to produce small batches of forgings. We can use forging equipment such as forging hammers and hydraulic presses 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.

2. Die forging of forging process.

Die forging can be divided into open die forging and closed die forging. After the metal blank is compressed and deformed in a forging die cavity with a certain shape, the required forgings can be obtained. Die forging is mostly used to produce important light and large-scale parts.

Die forging can be divided into hot forging, warm forging and cold forging. In the future, warm forging and cold forging will use more die forging processes, which are more difficult to forge than other forging methods, and can better reflect the forging technology level of forging manufacturers.

According to forging materials, die forging can also be divided into ferrous metal die forging using ferrous metals such as carbon steel, non-ferrous metal die forging using non-ferrous metals such as copper and aluminum, and powder product forming with powder metallurgy materials.

3. Rolling ring of forging process.

Ring rolling refers to the method of forging and processing ring parts of different diameters using special equipment such as ring rolling machines. This method can be used to produce wheel-shaped parts such as automobile hubs and train wheels.

4. Special forging of forging process.

Special forging mainly refers to forging methods such as roll forging, cross wedge rolling, radial forging, liquid die forging, etc. These methods can be used to produce forgings 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.

The above is the introduction of common forging processes organized by the forging manufacturer–GOLD EMPEROR FORGING. I hope it can help you! We are a forging supplier from China, specializing in the forging of auto parts, construction machinery parts, mining equipment parts, electromechanical forgings and other products, providing a full range of forging services for customers who need to use various forgings.