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How to choose the positioning datum for the processing technology of gear shaft?
The processing order of the main surface of the gear shaft depends to a large extent on the selection of the positioning datum. The structural characteristics of shaft parts and the position accuracy requirements of the main surface of the spindle determine that the axis is used as the positioning datum, which not only ensures the uniformity of the datum, but also makes the positioning datum coincide with the design datum. Generally, the outer circle is used as the rough datum, and the sharp holes at both ends of the shaft are used as the fine datum. Pay attention to the following points when selecting.

(1) When the relative position accuracy requirements between the processed surfaces are high, try to complete the processing of each surface in one clamping.
(2) When the top holes at both ends (such as processing the spindle taper hole) cannot be used for rough processing or positioning, in order to improve the rigidity of the process system during workpiece processing, only the cylindrical surface can be used for positioning or the cylindrical surface and the center hole at one end can be used as the positioning datum. During the processing process, the outer circle of the shaft and the center hole at one end should be used alternately as the positioning datum to meet the mutual position accuracy requirements.
(3) If the shaft is a part with a through hole, the original top hole will disappear after drilling the through hole. In order to still use the top hole for positioning, a taper plug or taper sleeve mandrel with a top hole is generally used. When the taper of the shaft hole is large (such as the milling machine spindle), a taper sleeve mandrel can be used; when the taper of the spindle taper hole is small (such as the CA6140 machine tool spindle), a taper plug can be used. It should be noted that the taper sleeve mandrel and taper plug used should have high precision and minimize their installation time. The center hole on the taper plug and taper sleeve mandrel is both the positioning reference for its own manufacturing and the finishing reference for the spindle outer circle. Therefore, it is necessary to ensure that the taper surface on the taper plug or taper sleeve mandrel has a high coaxiality with the center hole. For small and medium-sized batch production, the workpiece is generally not replaced midway after the taper plug is installed. If it is necessary to repeatedly process the outer circle and taper hole based on the other party as a reference, when reinstalling the taper plug or bushing mandrel, align or re-grind the center hole according to the outer circle.

From the above analysis, it can be seen that the selection of positioning reference in the gear shaft processing technology should consider the following process arrangements: at the beginning, the end face center hole is drilled with the outer circle as the rough reference, and the positioning reference is prepared for rough turning; rough turning of the outer circle is the positioning reference for subsequent processing: in order to prepare the positioning reference for semi-finishing and finishing of the outer circle, the front and rear top holes are first processed as the positioning reference; the gear tooth processing also uses the top hole as the positioning reference, which well reflects the principle of unified reference and the principle of reference coincidence.

The big gear ring is one of the important transmission parts in mining machinery rotary kiln, ball mill, dryer and other equipment. Its quality is directly related to the continuous stability time and service time of rotary kiln, ball mill and other equipment, so the quality requirements for big gear ring products will be relatively high. Big gear rings are widely used in the machinery industry, for example, they have very important applications in electricity, chemical industry, automobile, etc.

Because the quality of the big gear ring directly affects the operation of the equipment, every detail must be accurately controlled during processing and production, and there must be no mistakes, otherwise the quality inspection will fail when the casting is completed. When producing big gear rings, ball mill parts manufacturers must require the quality of the big gear ring to pass layers of quality inspection, and only when the test requirements are met can it be shipped and used.

The large gear ring itself is composed of two half-size rings. The vertical mill parts manufacturer will be more complicated in the production process. For example, the blank is made from the process of making wooden molds, modeling, casting, and pitting, and then heat treated to improve the comprehensive performance of the large gear ring. After a round of rough processing, fine processing is carried out, and various inspections are carried out until a high-quality large gear ring can be cast.

Ball mill parts manufacturers have experience in producing tens of thousands of large castings, so they have become proficient in the production process of large gear rings. If you have a purchase demand for large gear rings, you can contact us and we will quote you free of charge!

Large steel forgings generally refer to products with ingot weight ≥150t and single forging weight ≥90t. The representative grades are generally 25Cr2Ni4MoV, 30Cr2Ni4MoV, 40Cr3MoV, 45Cr4NiMoV, 12Cr2Mo1, 12Cr2Mo1V, 20MnNiMo and other grades of forging materials. Large steel forgings are generally used to manufacture the main components of industrial equipment such as power, shipbuilding, metallurgy, and petrochemicals. Because they are used as main components, the performance and quality requirements of large steel forgings are generally extremely strict, and the forging method and process of steel forgings play a decisive role in performance and quality.

In my country, there are three processing standards for large steel forgings, namely GB/T 37464-2019 “Quenching and tempering of large steel forgings”, GB/T 37558-2019 “Post-forging heat treatment of large steel forgings”, and GB/T 37559-2019 “Normalizing and annealing of large steel forgings”. These three standards play a major role in guiding the processing technology of large steel forgings. Only by mastering the basic forging methods and process flow of steel forgings can we better break through and develop new processes. Therefore, it is necessary to understand the typical forging methods and process flow of large steel forgings.

For large steel forgings, the main purpose of forging is to form and improve the internal defects and organization of the material to ensure the shape and size of the forgings and improve the internal quality. There are four common typical forging methods, namely wide flat anvil high temperature strong pressure method (WHF forging method), center compaction method, center tensile stress free forging method (FM forging method), wide large anvil compaction forging method (KD forging method). The process flow is divided into large shaft process flow, cylinder forging process flow, and pancake forging process flow according to the type of forging. The following is a detailed introduction to the relevant methods or processes.

1. Wide flat anvil high temperature strong pressure method (WHF forging method)

Wide flat anvil high temperature strong pressure method (WHF forging method) is a forging process method that uses high temperature and large deformation conditions on a wide flat anvil to forge the porosity defects in the steel ingot. During processing, it is recommended to use an anvil width ratio of 0.6 to 0.8 and a reduction rate of about 20%. Under this parameter, the stress and strain distribution in the billet is more reasonable, and the center, pores and loose structures will be effectively compacted. There should be about 10% overlap of the anvil width in the middle of the two pressed parts, and pay attention to the staggered anvil when turning and pressing, so as to achieve the purpose of uniform compaction of the billet.

2. Center compaction method

The center compaction method is to chamfer the steel ingot, forge it into a square cross-section billet, and then heat it to 1220℃~1250℃ (initial forging temperature) and keep it warm. Then take it out of the furnace and use surface air cooling, blast or spray cooling to 720℃~780℃ (final forging temperature). A layer of “hard shell” is formed on the surface of the steel ingot. At this time, the temperature of the core of the steel ingot is still maintained at 1050℃~1100℃, and the temperature difference between the inside and outside is about 230℃~270℃. Use a narrow flat anvil to pressurize the steel ingot longitudinally, and use the wrapping effect of the surface low-temperature hard shell to achieve the purpose of significantly compacting the core.

 

3. Center tensile stress-free forging method (FM forging method)

The center tensile stress-free forging method (FM forging method) is that the lower anvil is a wide flat anvil and the upper anvil is a narrow anvil. The billet deforms between the asymmetric flat anvils, and asymmetric deformation occurs inside the forging billet, and the stress state of each part also changes. When the billet is deformed, the part that forms tensile stress moves to the bottom of the billet, while the central part is subjected to compressive stress, which has a significant effect on the internal pore defects of the forged steel ingot. The recommended process parameters of the FM forging method are an upper anvil width ratio of 0.6 and a reduction rate of 14% to 15%.

4. Wide anvil compaction forging method (KD forging method)

The upper and lower anvils of the wide anvil compaction forging method (KD forging method) are both V-shaped anvils. Taking advantage of the fact that the steel ingot has sufficient plasticity under long-term high temperature conditions, it can be forged with a wide anvil and a large reduction rate on limited equipment. The use of upper and lower V-shaped anvils for forging is conducive to improving the metal plasticity of the forging surface, increasing the three-dimensional compressive stress state of the core, ensuring the concentricity of the forging, and effectively forging the internal defects of the steel ingot. The process parameters here recommend the upper and lower V-shaped anvil opening angle α=135°, the anvil width ratio of 0.4~0.8 (the best is 0.6), and the reduction rate of about 20%. When forging, attention should be paid to staggering the anvil and turning it 90° to ensure uniform compaction of the core of the forging and high drawing efficiency.

5. Introduction to the process flow of different forged steel parts

(1) The process flow of large shaft forgings is: clamping jaws → main deformation → material separation → finished product. The main deformation can be carried out by wide flat anvil high temperature strong pressure method, center compaction method, center tensile stress free forging method, wide anvil compaction forging method, or other suitable forging methods to ensure that the forging has a sufficient forging ratio and that the entire cross section is fully forged. If the cross-sectional size of the forging is large, the forging ratio can be increased by increasing the number of upsetting and drawing times, or other methods can be used to increase the forging ratio.

(2) The process flow of large cylindrical forgings is generally: blanking → upsetting → punching → hole expansion. For long large cylindrical forgings, the mandrel drawing process can be added after punching. In order to ensure that the forging has a sufficient forging ratio, the forging ratio can be increased by increasing the drawing or upsetting and drawing before blanking, or other methods can be used to increase the forging ratio.

(3) The process flow of large pancake forgings is generally: jaw pressing → main deformation → blanking → upsetting, expansion. The main deformation of pancake forgings can refer to the process flow of large shaft forgings. After the pancake hollow forgings are upset and expanded, punching procedures should be added. When expanding pancake forgings, reasonable expansion methods can be used to ensure the compaction effect and uniform deformation of pancake forgings.

The above is an introduction to the common forging methods and process flow of large forged steel parts. Quality assurance technology is very important in the manufacturing of large forged steel parts, but large forged steel parts are typically multi-variety and small-batch production, so in many cases, it is difficult for enterprises to realize automated processing for their forging production. The forging process of large forged steel parts is a systematic process, which also requires us to master the forging equipment and accessories operation process, the ingot performance meets the requirements, and the risk control of the forging process. All of this requires us to reasonably select the forging deformation scheme and the distribution of deformation amount of each fire according to the actual production and operation, the internal quality requirements of the enterprise, and the actual scientific research results.

Large gear rings are important and indispensable parts of equipment, just like gears. Although the two are similar, their main function is to transmit and change the direction of force. However, in addition to this, the protection of the main body of the machine system by the drive of the gear ring cannot be ignored.
The outer teeth of the large gear ring are divided into two types of tooth shapes: drum teeth and straight teeth. It can change the contact conditions of the teeth and improve the ability to transmit torque, thereby meeting the requirements of cost protection and extending the service life. The large gear ring is a thin-walled ring forging. It is easy to have problems such as uneven wall thickness, folding, and ellipse during the forging process. Therefore, the quality of the casting can be improved by controlling the details of the casting process.
Therefore, it can be said that the large gear ring is a very important component for protecting the service life of the machine. So when the large gear is damaged, how should we repair it?

First, the steel castings should be processed. Different processing methods should be used for large gears with different degrees of damage, and the damaged parts of the large gear ring should be processed;

Then, welding should be carried out. Before welding, it should be noted that there should be no impurities such as dirty oil, rust, slag, etc. near the welding part, otherwise it will affect the welding effect;

After the welding treatment, there may still be relatively small pores or sand holes on the surface of the steel casting. After removing these defects, the area should be repaired.

After the welding treatment, the damaged large gear ring can be used normally again, which not only saves the production cost of the enterprise, but also helps to reduce the loss of resources, which can be said to kill two birds with one stone.