I. Differences in principles and methods

Principles of ForgingIt is the use of forging machinery to apply pressure to the metal billet to produce plastic deformation, in order to obtain the desired forgings.

There are two main methods of forging:Free and die forgingFree Forging. Free forging refers to the upper and lower two mainstay between the use of impact or pressure to directly deform the blank, simple shape, flexible operation, suitable for single-piece or small batch production. Die forging refers to a certain shape of the forging die, the use of pressure to make the billet full of mold cavity, complex shape, operation specifications, applicable to the production of large quantities.

Forging can also be categorized as hot forging, warm forging and cold forging, depending on the temperature of deformation. Hot forging refers to forging at temperatures higher than the recrystallization temperature of the metal, warm forging refers to forging at temperatures lower than the recrystallization temperature, and cold forging refers to forging at room temperature.

Principles of CastingThe metal is melted into a liquid and poured into a cavity with a specific shape, then cooled and solidified, cleaned and processed to obtain the desired casting.

There are two main categories of casting methods:Sand casting and special casting. Sand casting refers to the casting with natural sand or artificial sand as the main modeling material, simple modeling, low cost, applicable to a variety of materials and specifications of the castings. Special casting refers to the use of other materials or methods in addition to sand as the molding material casting, molding precision, high quality, suitable for complex shapes or high requirements of the castings.

II. Differences in characteristics and performance

The characteristics and properties of forging and casting depend largely on the differences in the way and extent to which they deform the metal.

Forging is the plastic deformation of metal in the solid stateThe forging process can improve the organizational structure of the metal, refine the grain, eliminate casting defects, and improve the strength and toughness of the metal. Forging parts of the internal organization is relatively uniform, dense, no porosity, inclusions and other defects, surface finish, precise size, excellent mechanical properties, wear-resistant, corrosion-resistant, impact-resistant, suitable for bearing high loads, high temperatures, high speeds and other severe working conditions of the important parts.

However, forging also has some disadvantages, such as high processing costs, high energy consumption, large equipment footprint, high noise, high technical requirements for operators, high quality requirements for raw materials, is not suitable for the production of complex shapes, many internal cavities of the parts.Casting is the filling of metal in a liquid state.It can manufacture parts with complex shapes and many internal cavities, with wide adaptability and production flexibility, and can use various metal materials with low cost and high efficiency.

However, casting also has some disadvantages, such as metal in the melting and solidification process is prone to oxidation, inclusions, segregation and other defects, affecting the organizational structure and properties of the metal, the casting of the internal organization is not uniform, there are pores, cracks, shrinkage holes and other defects, the surface is rough, the size of the inaccurate, the mechanical properties of the poor strength and toughness of the low, not wear-resistant, corrosion-resistant, impact-resistant, unsuitable for withstand high loads, high temperatures, high-speed It is not suitable to bear high load, high temperature, high speed, and other severe working conditions of the important parts.

III. Differences in application areas

Forging and castingThe application areas of the forging mainly depend on their characteristics and performance differences. Forging is mainly used in aviation, aerospace, automobile, machinery, metallurgy, petroleum, chemical industry, electric power, rail transportation and other fields, common forging parts are crankshafts, hubs, gears, shafts, hammerheads, knives, valves, turbines, engine parts and so on.

cast (pour metal into a mold)Mainly used in agriculture, construction, water conservancy, mining, light industry, home appliances and other fields, common castings are pipe fittings, flanges, pump bodies, valve bodies, machine tool beds, racks, fan impellers, motor shells, pressure vessels, stoves, pots and pans, iron art, sculpture and so on.

In short, forging and casting are two different metal heat processing techniques, they have their own advantages and disadvantages, suitable for different materials and uses. In the actual production, often need to be based on specific needs and conditions, comprehensive consideration of the feasibility of forging and casting, economy, quality and efficiency, choose the most appropriate process.

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Rising: The head of the ingot is irregularly raised, which is a defect called rising, also called bubbling up.

Reticulation: The net-like projections on the surface of the ingot are called reticulation.

Pit: A pit on the surface of an ingot is called a pit.

Double casting: clearly visible rejoining marks around the surface of the ingot

Flying Edge: A thin piece of metal that exists perpendicular to the surface of the ingot at the head or tail of the ingot is called a flying edge.

Flying Fin: A thin sheet formed perpendicular to the surface of the ingot is called a flying fin.

Bubbles: Bubbles are due to steel deaeration deoxygenation ** or injection steel system raw material moisture and other reasons and caused by ingots or just now defects, generally divided into subcutaneous bubbles and internal bubbles. (Prevention methods: steel oxidation boiling reduction deoxygenation to be good, furnace chat and all contact with steel refractory materials to be dry, out of the steel tanks, buns, hand boards, molds, etc. to be dry, mold rust spots should be cleaned up, coated with oil to be thin and even.)

(3) Forged Folding.

If the shape of the raw material and billet error is too large, the mold design is not appropriate, forming process arrangement is not reasonable, poor lubrication and forging the actual operation is not appropriate, etc., may make the process of metal deformation has been oxidized surface metal confluence in the formation of folding. Folding and the flow of metal in the same direction, folding end generally show small rounded corners. However, subsequent forging deformation will cause the folding to crack, so that the folded end of a sharp angle. General folding on both sides of the more serious oxidation decarburization phenomenon, in individual cases there are also carbonization phenomenon. Folding not only reduces the bearing area of the part, but also when working due to the stress concentration generated at the folding often becomes a source of fatigue.

(4) Flow-through.

Flow-through occurs for reasons similar to folding, and is formed by the convergence of two streams of metal or one stream of metal with another stream of metal, but the metal in the flow-through portion of the stream is still a single unit. Flow-through is also a form of improper distribution of flow lines. In the flow-through area, the original into a certain angle distribution of flow lines converge together, flow-through area, outside the grain size often differ from the more disparate. Through the flow so that the mechanical properties of the forgings reduced, especially when through the flow on both sides of the grain difference is more disparate, performance reduction is more obvious.

(5) Shear zones.

Alloys and high-temperature alloys on the cold sensitivity, in the die forging process, the billet contact surface near the difficult deformation zone gradually expanding, in the difficult deformation zone occurs in the strong shear deformation will form a shear band, in the forging transverse low times the organization of the wave-like fine grain area. The shear band makes the organization of the forging to form a strong directionality, so that the performance of the forging is reduced.

High-fold organization defects in forgings

(1) Uneven grain.

Deformation is not uniform so that the grain is not broken, or the local area of the degree of deformation falls into the critical deformation zone, so that some parts of the forging grain is particularly coarse, some parts of the grain is smaller, the formation of the whole forging the internal grain size is not uniform defects. Heat-resistant steel and high-temperature alloy forging process local work hardening, will also produce coarse grains of heat-resistant steel and high-temperature alloys are particularly sensitive to uneven grain size. Uneven grain size makes the durability of the forging, fatigue performance decreased significantly.

(2) Banding organization.

If forging deformation occurs in the presence of two phases coexisting will produce a banded organization. In the high-fold organization of subeutectoid steel is ferrite and pearlite in a banded distribution, in the austenitic steel and semi-martensitic steel, there may also be ferrite and austenite, ferrite and bainite, ferrite and martensite in the forging to show a banded distribution of the organizational state. Banded organization can reduce the transverse plasticity of forgings, especially impact toughness. Make forgings in use often along the ferrite band or the junction of the two phases of cracking.

(3) Decarburized layer build-up.

If the forging process is not appropriate may also cause localized areas on the forging decarburization layer buildup defects such as round bar material drawn long when the hammer is too heavy, the amount of compression is too large, flip 90 ° compression when the formation of double drum shape, and then drawn long, double drum shape of the metal part of the outward flow, increase the width, part of the metal to the center of the flow, and thus the formation of the center of the phenomenon of the decarburization layer buildup. Decarburization layer accumulation parts of the hardness is lower than the normal organization of the hardness of the parts, so that forgings in the use of the process is easy to crack from the part.

(4) Carbide segregation level does not meet the requirements.

If the raw material carbide segregation is serious, coupled with the change of forging forging ratio is not enough or forging method is not appropriate, in the forging there will be uneven distribution of carbide phenomenon, presenting a large centralized distribution of carbide or mesh distribution of carbide defects. This defect mainly occurs in the leucite body mold steel. With this defective forgings, in the heat treatment quenching is easy to localized overheating and quenching crack. Made of cutting tools and molds are easy to collapse when used.

(5) Casting Organization Residue.

Crack type defects in forgings

Cracks make the integrity and continuity of the forging is destroyed, forging minor surface cracks can be used after cleaning, cracks are serious, forging can only be scrapped. Cracks in forgings are produced for a number of reasons: the surface of the billet and the internal micro-cracks in the forging further expansion, so that the surface of the forging or internal cracks; billet internal organizational defects or improper heat processing temperature, so that the plasticity of the material down, forging there is a large tensile stress, shear stress, or additional tensile stresses and cracks in the forging; when deformation is too fast, the degree of deformation is also too large in the forging to produce cracks.

There are several common types of forging cracks:

(1) crack: shallow tortoise cracks on the surface of the forging. Raw materials containing Cu, Sn and other fusible elements such as too much heating fuel with high sulfur content may make the surface of the forging cracks; high temperature and long time heating, copper precipitation on the surface of the steel, the surface of the grain is coarse, decarburization, or after a number of heating of the surface is also easy to appear cracks. Cracking is most likely to occur in the surface of the forging molding under tensile stress.

(2) cross cracks: in the repeated billet turning 90 ° of the drawing process, feeding too much, and in the same place repeatedly hit will cause cross cracks. Cracks along the diagonal distribution of the cross-section of the forging, its length varies, and sometimes may be completely through the entire billet. This defect often occurs in the low plasticity of high-speed steel, high chromium steel drawing process. Rectangular section billet in the flat anvil under the drawing long, diagonal metal on both sides of the staggered flow, resulting in a large alternating shear deformation, when the degree of shear or shear stress exceeds the strength of the material, it will be along the direction of the diagonal cracks.

(3) Hole edge cracking: punching core without preheating, preheating is not enough or because of a punching deformation is too large, will be in the punching edge of the hole caused by the edge of the hole cracking cracks, chrome steel punching appear more.

(4) Copper alloy forging stress corrosion cracking: brass forging in the forging deformation is not uniform, forging and not timely annealing so that there is a large residual stress in the forging, in the humid air, especially in the ammonia-containing salts placed in the atmosphere will cause stress corrosion cracking.

cold hardening

Forging deformation temperature is low or deformation rate is too fast, as well as forging cooling too fast, so that the softening caused by recrystallization can not keep up with the hardening caused by deformation, hot forging forging is still partially retained within the cold deformation of the organization, and the emergence of cold hardening phenomenon after hot working, so that the strength and hardness of the forging than normal hot forging to be higher, and plastic and toughness decline.

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Rising: The head of the ingot is irregularly raised, which is a defect called rising, also called bubbling up.

Reticulation: The net-like projections on the surface of the ingot are called reticulation.

Pit: A pit on the surface of an ingot is called a pit.

Double casting: clearly visible rejoining marks around the surface of the ingot

Flying Edge: A thin piece of metal that exists perpendicular to the surface of the ingot at the head or tail of the ingot is called a flying edge.

Flying Fin: A thin sheet formed perpendicular to the surface of the ingot is called a flying fin.

Bubbles: Bubbles are due to steel deaeration deoxygenation ** or injection steel system raw material moisture and other reasons and caused by ingots or just now defects, generally divided into subcutaneous bubbles and internal bubbles. (Prevention methods: steel oxidation boiling reduction deoxygenation to be good, furnace chat and all contact with steel refractory materials to be dry, out of the steel tanks, buns, hand boards, molds, etc. to be dry, mold rust spots should be cleaned up, coated with oil to be thin and even.)

White point: white point is actually a kind of fine crack, in just transverse low times specimen was radioactive irregular sawtooth crack, in the longitudinal low times specimen is a round or elliptical star of the silver bright spot, and thus called white point. (The main cause is the cause of hydrogen) Stainless steel common smelting, forging, rolling problems

Forging and forging are a kind of forging process, each has its own advantages and disadvantages, the choice of which method depends mainly on the processing requirements and material properties. In practice, it is often necessary to choose the appropriate process method or a combination of processing according to the specific circumstances, in order to achieve better results.

Second, the advantages and disadvantages of forging and forging

1. Advantages of forging

(1) Forging can ensure the precision and surface finish of molding, which is suitable for processing thinner metal plates and strip materials;

(2) Forging allows for mass production using molds, which is more efficient;

(3) No vibration and noise will be generated during the forging and pressing process, which is safe for the health of workers.

2. Advantages of forging

(1) Forging can enhance the plasticity and toughness of metal materials, suitable for processing large and shaped parts;

(2) Forging can ensure the smoothness and continuity of the fibers of the metal material under the premise of maintaining a certain molding accuracy, so that the processed finished product has higher durability;

(3) Forging can adjust the strength and speed during forging to adapt to the processing needs of different materials and sizes.

III. Application Scenarios for Forging and Forging

1. Application scenarios of forging

(1) Mass production of thin-walled or small precision parts;

(2) Machining of parts with relatively simple shapes and large workloads;

(3) Machining of parts requiring high machining accuracy and surface finish.

2. Application scenarios of forging

(1) Machining of large or shaped parts;

(2) Processing of parts that require high toughness and durability of metal materials;

(3) Processing of parts that require adjustment of force, speed and angle during forging.

Fourth, forging and forging who is good quality judgment

From the above advantages, disadvantages and application scenarios, the advantages and application scenarios of forging and forging are different, so it is not possible to simply say that one is better than the other. Specifically, the suitable forging process should be selected according to the production situation, processing requirements and material properties. In practice, many cases are processed using a combination of forging and forging, so that the advantages of each can be utilized to achieve better processing results.

[Conclusion]

Forging and forging are a kind of forging process, each has its own advantages and disadvantages, the choice of which method depends mainly on the processing requirements and material properties. In practice, it is often necessary to choose the appropriate process according to the specific circumstances or a combination of processing to achieve better results!