轴承制造技术——塑性加工

2021-06-03

Bearing ring blanks can be roughly divided into the following five types: (1) forgings( 2) Pipes( 3) Bar (for direct cutting)( 4) Coiled material( 5) Plate and strip steel forgings are often used for centripetal ball bearings and tapered roller bearings. The reasons for the large use of forgings are: (1) the required size and shape are formed by using the ductility of metal, which reduces the cutting allowance. In addition, the processing machine tools with high processing speed such as stamping machine and rolling machine can be used, with high productivity( 2) If the shear processing surface of bar, pipe and plate and the bottom exhaust during processing are removed, the metal flow line of the product will not be cut off. In addition, the material strain will refine the grain, and the work hardening improves the material strength, which can improve the performance of the material itself. In addition, forgings must be used for large-diameter bearings used in wind turbines and industrial machinery as for products with small diameter produced in small batch, sometimes the advantages of forgings cannot be brought into play in cost. At this time, pipe and bar can be used 1 centripetal ball bearing and tapered roller bearing the forging methods of inner and outer rings of centripetal ball bearing are as follows: high temperature forming + cold rolling; Hot forging + hot rolling; Hot forging + cold rolling, etc

1.1   < text style = 'align;' P > < center + cold forming< img src=' https://image.bearing.cn/news/zczh/2021061022658_ 237.png' style='width: 500px;' class='fr-fic fr-dib'>

Figure 1 & nbsp; High temperature forming + cold rolling Figure 1 is the schematic diagram of high temperature forming + cold rolling of parts. Taking the bearing steel bar as the raw material, after high-frequency heating, it is cut into the specified length in the part high-temperature forming machine to forge the annular blank of inner ring and outer ring, then spheroidized annealing, shot peening, and finally cold rolling. According to the workpiece size, the production speed of high-temperature forming is 100 ~ 180 pieces / min, and the number of cold rolling equipment required shall match it. The high temperature forming equipment is basically a horizontal multi process pressure forging machine, and a punch is installed on the side of the sliding block (press head); The fixed side (press backing plate) is equipped with a forging die, and the material is forged between metal dies. The main reasons for the high speed of high-temperature forming are as follows: (1) it is not necessary to move the heavy press slider (indenter) in the opposite direction of gravity( 2) The handling of the workpiece is basically unitary, which is in line with the action of the sliding block of the press. The handling claw does not interfere with the metal mold, and can quickly and timely remove the workpiece. Careful consideration has been made on the action of the ejector rod and the support pin rod and the structure of the metal mold in the cold rolling process, the main rolling roller and mandrel are used for rolling to expand the diameter and form the shape of inner and outer diameter at the same time. In addition, since the mandrel itself does not have stiffness, it is supported by a roll member called a idler (backup roll). Moreover, in order to improve the roundness of the workpiece, the main structural form adopted is that the component called backup roll and sliding shoe (not shown in Fig. 1) forcibly supports the outer diameter of the workpiece during processing, and the numerical control of action has also been practical

1.2   Hot forging + hot rolling raw materials (blanks) of medium-sized bearing rings exceeding the high-temperature forming processing capacity of parts shall be processed by the process shown in Figure 2. Cut the bar stock by cutting or machining to form the blank, heat the blank, manufacture the annular blank of inner ring and outer ring with large vertical forging press, and use the waste heat to implement hot rolling. Then, spheroidizing annealing, shot peening and outer diameter finishing (shaping) are carried out

< img src=' https://image.bearing.cn/news/zczh/2021061078639_ 519.png' style='width: 500px;' class='fr-fic fr-dib'>

Figure 2 & nbsp; Hot forging + hot rolling this processing method carries out Forging and rolling at the same temperature, so it has high thermal efficiency, small deformation resistance and shortened process cycle. However, due to the direct connection of two processes, the equipment operation rate is reduced. At the same time, in order to match the forging cycle with the rolling cycle, the cycle time has to be set downward, so it can not give full play to the capacity of the forging process. This method has not been effectively popularized in terms of large bearings for industrial machinery and wind turbine generator sets, the method of hot forging + hot rolling is adopted. In hot rolling, it is very important to remove the scale of the machining part to improve the machining quality. In addition, because it is a large bearing, it is particularly important to reduce the machining allowance, especially the special-shaped section like tapered roller bearing. In order to reduce the material loss as much as possible, the machining accuracy of hot forging process and the forming technology of hot rolling special-shaped section are very important

1.3   Hot forging + cold rolling hot forging is used to manufacture annular blank, and after cooling, spheroidizing annealing and shot peening are carried out, and then cold rolling is carried out. The production speed of hot forging is lower than that of high temperature forming (Section 1.1), but it has good universality and easy to develop metal dies. The working pressure of cold rolling process is greater than that of hot rolling process. The processing time is long, but the cold rolling process does not need to carry out cumbersome temperature management on the blank like hot rolling. Because it is easy to handle the blank, it is easy to realize production automation, and the product precision is also high. As shown in Fig. 3, before cold rolling, turning is carried out to form high-precision blanks. After cold rolling, the turning process is omitted, and only grinding is carried out after heat treatment to obtain finished parts with high precision of end face, outer diameter surface and inner diameter surface

< img src=' https://image.bearing.cn/news/zczh/2021061045804_ 616.png' style='width: 500px;' class='fr-fic fr-dib'>

Figure 3 & nbsp; Hot forging + turning + cold rolling 1.4 & nbsp; Hot forging + cold forging the annular blank is manufactured by hot forging process. After spheroidizing annealing, turning and shot peening, the phosphatized blank is cold forged. In this case, the size of the parts that can be processed is limited, but it is easy to improve the accuracy. In addition, such as the ball? Annealing, due to surface decarburization, it is necessary to eliminate the decarburization layer. However, the process of carbon annealing to reduce turning allowance has been proposed

1.5   Summary factories forging bearing ring blanks are developing towards specialization and automation. By further improving the service life of metal molds, miniaturization of metal molds, operability and production efficiency are greatly improved. With the progress of sensor technology and the continuous progress of monitoring the processing state and metal mold state, the defective rate can be further reduced. In addition, in order to reduce the environmental burden, improve the product qualification rate and reduce the processing burden in subsequent processes; Miniaturization and energy saving of production equipment; More and more attention has been paid to the use of more environmentally friendly white lubricants 2 centripetal needle roller bearing needle roller bearing is often used in transmission, engine and compressor. The bearing installation space is narrow and needs applications with large bearing capacity the processing and forming methods of the outer ring of centripetal needle roller bearing include: (1) stamping of plates( 2) Cutting of forging blank( 3) Pipe cutting, etc. Among them, the stamping processing of plates accounts for the absolute majority. The reason is that the needle roller bearing parts are thinner than the ball bearing parts, which is suitable for stamping 2.1 continuous automatic stamping (multi station stamping) processing continuous automatic stamping processing (multi station stamping) usually uses a punch shear to cut a circular plate blank from the coil, and then uses a press to carry out deep drawing forming, outer ring bottom forming, typing process, burr cutting process, etc. In order to improve productivity, high-speed production process is an important factor. At present, 200 SPM (slide per minute: stamping times / min) can be realized. In addition, basically, stamping parts are directly heat treated, and then only surface finishing is carried out. Due to the high requirements for stamping precision, the precision and stiffness of stamping equipment and metal die are very high. Therefore, special and special mechanical equipment for bearing processing has also developed rapidly. On the other hand, the batch size of products is small. Instead of requiring the same production speed as special machinery, it is better to carefully consider reducing the number of processes. In addition, cheap general-purpose machine tools should be used to reduce the cost of metal molds and reduce the production preparation time. The latter processing method is suitable for small batch parts it is unnecessary to set a bracket to realize sequential action processing in the stamping machine for continuous automatic stamping processing. By working hard on the plate supply device, it can reduce waste and improve the yield. Compared with sequential action processing, the feeding device (continuous automatic feeding device) in the stamping machine is very necessary, but the equipment cost is slightly higher 2.2 sequential (continuous) stamping processing advantages of continuous stamping processing: it can simplify the feeding device in the press, easily increase the number of processes, adapt to the stamping processing of multiple products, and easily improve the processing speed. Disadvantages: low yield continuous automatic stamping processing mode or continuous processing mode can be selected according to the shape, size and batch of processed products 3 thrust needle roller bearing thrust needle roller bearing rings are almost made by stamping. The machining method is usually the continuous automatic stamping method described in Section 2.2. Due to the thin thickness of the product, the number of processing procedures is less than that of the outer ring of the centripetal needle roller bearing, but the flatness is very important. Stamping processing, process and metal die shape should be considered. In addition, it is difficult to improve the surface roughness of the rolling surface in contact with the roller by stamping the ring of the thrust needle roller bearing. Therefore, it is very important to adopt the blank with good surface roughness and maintain its surface state, which should be carefully considered in many aspects, such as material supply (feeding) device, forming process, transmission in stamping machine, product delivery, and even the treatment of subsequent processes 4 centripetal needle roller bearing cage centripetal needle roller bearing cage can be roughly divided into the following two categories from the perspective of forming method 4.1 welding cage roll the strip steel into the required shape, form the pocket and claw of the holding roller with a punch, roll it into a circular tube and weld it. The advantage of this method is that the yield of the material is the highest compared with other methods 4.2 non welded cage there are six main forming methods for non welded cage

• Pipe material & rarr; Pocket Punch & rarr; Rolling forming

• Pipe material & rarr; Pocket Punch & rarr; Stamping forming

• Pipe material & rarr; Bulging & rarr; Pocket punching

• Pipe material & rarr; Rolling forming & rarr; Pocket punching

• Pipe material (machined parts) & rarr; Pocket punching

• Pipe material (machined parts) & rarr; Pocket Punch & rarr; Roll forming The forming method of round pipe material (except machined products) has the following three modes: cutting pipe; Turning deep drawing parts; Deep flush. Each has its advantages and disadvantages. The best process can be selected according to the required quantity and cost 4.3 summary the main goal of plastic processing is high precision and high productivity of products, as well as the adaptability to small batch production. Therefore, the high rigidity, high speed and miniaturization of stamping equipment and the high precision of plates are the key points. The adaptability of small batch production needs to be studied by focusing on the application of general press (including omitting process) and minimizing production preparation time (instant preparation)

( Source: Bearing magazine)

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