Valve forging knowledge

- May 19, 2018-

First, according to the deformation temperature classification:

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

Second, according to blank classification:

According to the movement of the blank, forging can be divided into free forging, upsetting, extrusion, die forging, closed die forging, closed upsetting.

1). Free forging. Using impact force or pressure, the metal is deformed between the upper and lower two irons (anvil block) to obtain the required forgings, which mainly include manual forging and mechanical forging.

2). Die forging. Die forging is divided into open die forging and closed die forging. The metal blanks are deformed under pressure in a forged jaw with a certain shape to obtain forgings, which can be further classified into cold heading, roll forging, radial forging and extrusion, and the like.

3). Closed and closed upsets have high material utilization due to no flash. It is possible to complete the finishing of complex forgings in one process or several processes. Because there is no flash, the forging area is reduced and the required load is reduced. However, it should be noted that the blank cannot be completely constrained. For this purpose, the volume of the blank must be strictly controlled, the relative position of the forging die must be controlled, and the forging should be measured in an effort to reduce the wear of the forging die.

Third, according to the mode of movement of the forging die:

According to the movement mode of the forging die, forging can be divided into pendulum, swing forging, roll forging, cross wedge rolling, crucible ring and oblique rolling. Pendulum, swing swaged and ring can also be used precision forging processing. In order to increase the utilization of materials, roll forging and cross rolling can be used as a pre-processing process for slender materials. Rotary forging like free forging is also partially formed, which has the advantage that the forging force can also be formed with a smaller forging force than the forging size. This type of forging method, including free forging, causes the material to spread from the vicinity of the die surface toward the free surface during the machining. Therefore, it is difficult to ensure the accuracy. Therefore, the direction of movement of the forging die and the swaging process can be controlled by a computer and can be used low. The forging force obtains products with complex shapes and high precision, such as the production of forgings such as steam turbine blades with large variety and large size. Forging equipment mold movement and freedom are not consistent, according to the characteristics of the bottom dead point deformation limit, forging equipment can be divided into the following four forms:

1). Limit the form of forging force: hydraulic press which directly drives the slider.

2). Quasi-stroke limiting mode: Hydraulic drive crankshaft linkage mechanism hydraulic press.

3). Stroke Limiting Mode: The mechanical press which drives the slider with the crank, connecting rod and wedge mechanism.

4). Energy limitation methods: Spiral and friction presses using screw mechanisms.

Heavy-duty aerospace die forging hydraulic press for hot test In order to obtain high accuracy, care should be taken to prevent overloading at the bottom dead point, controlling the speed and position of the die. Because these will have an impact on the forging tolerances, shape accuracy and die life. In addition, in order to maintain accuracy, it should also pay attention to adjust the slider guide clearance, to ensure rigidity, adjust the bottom dead point and use of auxiliary transmission and other measures.

There is also a vertical and horizontal movement of the slider (for forging of slender parts, lubrication and cooling, and forging of high-speed production parts). The first large-scale disc type product can be smoothly forged by the compensation device to increase the movement in other directions. . The above methods are different, the required forge force, process, material utilization, output, dimensional tolerances, and lubrication and cooling methods are all different. These factors also affect the level of automation.

2. The importance of forging

Forging production is one of the main processing methods for providing mechanical parts blanks in the machinery manufacturing industry. By forging, not only the shape of the mechanical parts, but also the internal structure of the metal can be improved, and the mechanical and physical properties of the metal can be improved. Generally, most of the important mechanical parts with high stress and high requirements are manufactured using forging production methods. Major components such as turbine generator shafts, rotors, impellers, blades, retaining rings, large hydraulic press columns, high pressure cylinders, rolling mill rollers, internal combustion engine crankshafts, connecting rods, gears, bearings, and guns in the defense industry are all forged. produce.

Therefore, forging production is widely used in metallurgical, mining, automotive, tractor, harvesting machinery, petroleum, chemical, aviation, aerospace, weapons and other industrial sectors, that is, in daily life, forging production also has an important position. In a sense, the annual output of forgings, the proportion of die forgings in the total output of forgings, and the size and quantity of forging equipment, etc., reflect to a certain extent the industrial level of a country.

3, forging materials

Forging materials are mainly composed of carbon steel and alloy steel of various compositions, followed by aluminum, magnesium, copper, titanium, etc. and their alloys. The original state of the material is bar stock, 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 referred to as the forging ratio. Proper selection of forging ratio, reasonable heating temperature and holding time, reasonable forging temperature and final forging temperature, reasonable deformation amount and deformation speed have a great influence on improving product quality and reducing cost.

General small and medium-sized forgings 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, the surface quality is good, and it is easy to organize mass production. As long as the heating temperature and deformation conditions are properly controlled, large forging deformations can be used to forge excellent forgings. Ingots are used only for large forgings. The ingot is an as-cast structure with larger columnar grains and a loose center. Therefore, it is necessary to break the columnar crystals into fine grains by large plastic deformation and loosely compact them to obtain excellent metal structure and mechanical properties.

The pressed and sintered powder metallurgy preforms can be made into powder forgings by flashless forging in a hot state. The forging powder is close to the density of the general die forgings, has good mechanical properties, and has high precision, which can reduce the subsequent cutting process. The powder forgings have uniform internal structure and no segregation, and can be used for manufacturing small gears and other workpieces. However, the price of powder is much higher than that of ordinary bars, and its application in production is limited. By applying a static pressure to the liquid metal poured into the mold to solidify, crystallize, flow, plastically deform, and shape it under pressure, a die forging having a desired shape and performance can be obtained. Liquid metal forging is a molding method between die casting and swaging. It is particularly suitable for complex thin-walled parts that 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 their alloys, iron-based superalloy, nickel-based superalloy, cobalt-based superalloy The deformed alloys are also made by forging or rolling, but these alloys are relatively difficult to forge due to their relatively narrow plastic zones. The heating temperatures, open forging temperatures and final forging temperatures of different materials have strict requirements.

4, forging process

Different forging methods have different processes, among which the hot forging process is the longest, and the general sequence is: forging billet blanking; forge billet heating; roller forging billet; die forging forming; trimming; punching; correction; 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 scales; correction; inspection, general forgings have to undergo appearance and hardness inspection, important forgings also Chemical composition analysis, mechanical properties, residual stress tests, and non-destructive testing are required.

5, forging features:

Compared with castings, metal after forging can improve its microstructure and mechanical properties. After the casting structure is deformed and recrystallized by the metal after forging by hot working deformation, the original coarse dendrite and columnar grains become equiaxed recrystallized grains with fine grain and uniform size, so that the original segregation in the steel ingot, Loosening, porosity, slag inclusions and other compaction and welding, the organization becomes more compact, improving the metal's plasticity and mechanical properties. The mechanical properties of the casting are lower than those of the same material. In addition, the forging process can guarantee the continuity of the metal fiber structure, make the fiber structure of the forging consistent with the shape of the forging, and the metal streamline is complete, which can ensure the parts have good mechanical properties and long service life. Precision die forging and cold extrusion The forgings produced by the process such as extruding and warm extrusion are all incomparable to the castings. The forgings are metals that are subjected to pressure and shape the desired shape or suitable compressive force through plastic deformation. This force is typically achieved by using a hammer or pressure. The casting process creates a fine grain structure and improves the physical properties of the metal. In the practical use of parts, a correct design enables the flow of particles in the direction of the main pressure. Castings are metal formed articles obtained by various casting methods. That is, the molten metal is poured into a previously prepared casting mold by casting, injection, inhalation, or other casting methods. After being cooled, it is subjected to sandfall, cleaning and post-casting. Treatments, etc., resulting objects with a certain shape, size and performance.

6, forging process notes:

1). The forging process includes cutting the material to the desired size, heating, forging, heat treatment, cleaning and inspection. In small-scale manual forging, all these operations are performed by several forging workers in a narrow place. They are all exposed to the same harmful environmental and occupational hazards; in a large forging shop, the hazards vary from job to job. Working conditions Although the working conditions vary according to the type of forging, they share certain characteristics: medium-strength manual work, a dry and hot micro-climate environment, noise and vibration, and air pollution by smoke.

2). Workers are exposed to high-temperature air and heat radiation at the same time, causing heat to accumulate in the body. Heat, coupled with metabolic heat, can cause dissipative heat loss and pathological changes. The amount of sweat per 8 hours of work will vary from 1.5 to 5 liters, or even higher, depending on the small gas environment, physical exertion, and degree of thermal fitness. In the smaller forging shop or farther away from the heat source, the Behaz heat stress index is usually 55~95; however, in the large forging shop, the working point near the heating furnace or the drop hammer may be up to 150~190. Can easily cause lack of salt and enthusiasm. In the cold season, changes in exposure to the microclimate environment may promote its adaptability to a certain extent, but rapid and frequent changes may pose a health hazard.

Air pollution: The air in the workplace may contain fumes, carbon monoxide, carbon dioxide, sulfur dioxide, or acrolein, the concentration of which depends on the type of fuel in the furnace and the impurities it contains, as well as combustion efficiency, airflow, and ventilation conditions. Noise and Vibration: Forging hammers will inevitably produce low-frequency noise and vibration, but they may also have certain high-frequency components with sound pressure levels between 95 and 115 dB. Workers exposed to forging vibrations may cause temperamental and functional disorders, which will reduce work capacity and affect safety.

7. Forging production risk factors and main reasons

First, in forging production, accidents that are prone to accidents can be divided into three types according to their causes:

Mechanical injury - scratches and bruises directly caused by tools or workpieces; burns; electrical contact injuries.

Second, from the perspective of safety technology labor protection, the characteristics of the forging workshop are:

1). Forging production is carried out in the state of metal burning (such as low carbon steel forging temperature range of 1250 ~ 750 °C), due to a lot of manual labor, accidentally burns may occur.

2). The heating furnace and hot steel ingots, blanks and forgings in the forging shop constantly emit a large amount of radiant heat (the forgings still have a fairly high temperature at the end of forging), and workers are often exposed to thermal radiation.

3). The fumes generated in the heating furnace of the forging workshop discharge into the air of the workshop during the combustion process, which not only affects the sanitation, but also reduces the visibility in the workshop (the situation is even more serious for the furnace that burns solid fuel). It may also cause work-related accidents.

4). Equipment used in forging production, such as air hammers, steam hammers, friction presses, etc. When the equipment is subjected to such an impact load, it is easy to suddenly damage (such as sudden breaking of the piston rod of the hammer), causing a serious injury accident.

Presses (such as hydraulic presses, crank hot die forging presses, flat forging presses, fine presses) shearers, etc., work, although the impact of small, but sudden damage to the equipment and other occasions also occur, the operator Unprepared, it may also lead to accidents at work.

5). Forging equipment in the work of the force is great, such as crank presses, tensile forging presses and hydraulic press forging equipment such as these, although their working conditions are relatively stable, but the power of its working parts is Very large, such as China has manufactured and used 12,000t forged hydraulic press. Is a common 100 ~ 150t presses, the power has been issued is large enough. If the mold is installed or operated slightly incorrectly, most of the force is not acting on the workpiece but on the part of the mold, tool or equipment itself. In this way, some kind of installation adjustment mistakes or improper operation of the tools may cause damage to the parts and other serious equipment or personal accidents.

6). Forging tools and auxiliary tools, in particular hand forging and free forging tools, clamps, etc. are numerous and these tools are placed together in the work place. In the work, the replacement of tools is very frequent and the storage is often cluttered. This will inevitably increase the difficulty of inspection of these tools. When forging needs to use a tool and cannot be found quickly, it will sometimes “make do” use. Similar tools often result in work-related accidents.

7). Due to the noise and vibration in the operation of forging workshop equipment, the workplace is noisy, affects the human auditory and nervous system, distracts attention, and thus increases the possibility of accidents.

III. Analysis of Causes of Work-related Accidents in Forging Workshops

1). Areas that require protection, lack of protective devices and safety devices.

2) The protective device on the device is not perfect or not used.

3). The production equipment itself is defective or defective.

4) Equipment or tools are damaged and working conditions are not appropriate.

5). There is something wrong with the forging die and the anvil.

6). Disturbance in the organization and management of the workplace.

7). Auxiliary work of process operation methods and repairs is not done properly.

8). Personal protective equipment such as protective goggles are defective, overalls and work shoes do not meet the working conditions.

9) When several people work together on an assignment, they do not coordinate with each other.

10) Lack of technical education and safety knowledge leads to incorrect steps and methods.

8, industry analysis

China's forging industry is developed on the basis of introducing, digesting, and absorbing foreign technologies. After many years of technological development and transformation, the technological level of leading companies in the industry includes process design, forging technology, heat treatment technology, machining technology, and products. Testing and other aspects have been greatly improved.

(1) Process Design

Advanced manufacturers generally adopt computer simulation technology, computer-aided process design and virtual technology for thermal processing, which improves the level of process design and product manufacturing capabilities. Introduction and application of DATAFOR, GEMARC/AUTOFORGE, DEFORM, LARSTRAN/SHAPE and THERMOCAL simulation programs to achieve computer design and thermal process control.

(2) Forging technology

Most hydraulic presses of 40MN and above are equipped with 100-400t.m master forging manipulators and 20-40t.m auxiliary manipulators. A considerable number of manipulators are controlled by computers, which realizes the integrated control of the forging process and enables forging precision to be achieved. Controlled at ±3mm, on-line measurement of forgings uses a laser size measuring device.

(3) Heat Treatment Technology

The focus is on improving product quality, improving heat treatment efficiency, saving energy, and protecting the environment. If the computer-controlled heating process of the heating furnace and the heat treatment furnace is used, the control burners can automatically adjust the combustion.