What problems should be paid attention to when the steel pipe is partially upset

With the rapid development of the petroleum industry and water and gas pipeline engineering, the application of pipes is becoming more and more extensive, and the process methods involving pipe forming are also developing rapidly, such as pipe bending, pipe expansion, pipe shrinking, pipe turning, pipe expansion, and partial pipe upsetting. The thick tube forming process is widely used. In recent years, with the development of lightweight vehicles, the demand for parts such as locally thickened tubes has also increased. Therefore, the upsetting process of tube blanks has been developed. What are the problems that need to be paid attention to during the partial upsetting of steel pipes: (1) The maximum thickness that can be achieved by the local upsetting of the tube blank cannot be greater than 1.5 times the thickness of the original tube blank. With the rapid development of the petroleum industry and water and gas pipeline engineering , The application of tubes is becoming more and more extensive, and the process methods involved in tube forming are also developing rapidly, such as tube bending, tube expansion, tube shrinking, tube turning, tube expansion, tube local upsetting and other tube forming processes are widely used. In recent years, with the development of lightweight vehicles, the demand for parts such as locally thickened tubes has also increased. Therefore, the upsetting process of tube blanks has been developed. The parts for partial upsetting of the tube billet have the following forms: ①The inner diameter of the tube remains the same, and the outer diameter is increased to increase the thickness of the tube; Regardless of the form, the main problem when upsetting the tube blank is to prevent the wrinkles caused by the longitudinal bending of the tube wall. Through long-term practical experience in production, people have summed up the process principles that should be followed when the tube blank is partially upset, that is, the so-called local tube upsetting rule. In summary, there are two main ones: 1) When the length of the deformed part of the tube blank is less than 3 times the wall thickness of the tube blank, it is allowed to upset to any outer diameter at one time without bending. 2) When the length of the deformed part of the tube blank is greater than 3 times the wall thickness of the tube blank (usually this type of upsetting), it must be upset in the mold, and the maximum thickness that can be achieved by one partial upsetting cannot exceed the original tube blank thickness 1.5 times of, otherwise it will produce unstable deformation. (2) The tube blank whose deformation length is more than 3 times the wall thickness cannot be upset to any size tube blank at one time. When the tube is upset to any size in one stroke of the machine, its deformation length cannot exceed the wall thickness of the tube blank. 3 times, otherwise the tube blank is easy to lose stability and produce longitudinal bending, leading to folding. (3) Tube blanks with uneven end faces cannot be upset and formed. Under production conditions, the tube material can be sawed by a high-speed band saw or cut by a die. The end faces of the tube blanks may be neither flat nor perpendicular to the axis. At this time, apply The axial pressure will inevitably lead to instability of the axial pressure, so the tube blank with uneven end face cannot be upset. (4) When the flange height is less than 1/2 of the wall thickness of the tube blank, the outer diameter of the flange for one upsetting cannot exceed 2.5 times the outer diameter of the tube blank. When the flange height is less than 1/2 of the thickness of the tube blank, one upsetting The outer diameter of the thick flange cannot exceed 2.5 times the outer diameter of the tube blank, otherwise it will cause the tube blank to become unstable and cause the outer wall to fold. (5) It is not advisable to expand the outer diameter and reduce the inner diameter at the same time when upsetting the thickened tube. Production practice has proved that during the partial upsetting and deformation process of the tube blank, the tube wall is mainly bent outward, and it is not easy to bend inward. Therefore, the tube blank is upset When it is thick, a mold should be used to limit the outward bending of the pipe wall, and the inner hole mandrel is mainly used to obtain a certain diameter of the inner hole. When the tube blank is locally thickened by more than 1.5 times, it is not advisable to use the method of simultaneously increasing the outer diameter and reducing the inner diameter for upsetting. Because the degree of deformation at this time is relatively large, more materials are needed. When the upsetting of the tube blank starts, the tube blank is free and unconstrained, which is free deformation, poor stability, and easy to lose stability. It is best to keep the outer diameter unchanged, and only reduce the inner diameter to increase the thickness of the tube wall. At this time, it is not easy to produce wrinkles. (6) The partial upsetting of the tube blank with a large aspect ratio is not suitable for local upsetting of the tube blank with a large aspect ratio on an ordinary crank punch press, which is prone to axial pressure instability, so ordinary punching can not be used for processing, generally in flat forging The machine uses a separable die to produce this thickened tube. The non-deformed part of the tube blank is clamped by the separable die, and then upsetting is carried out. After the upsetting is completed, the separable die is opened and the tube is taken out. If other general forging equipment is used for tube blank upsetting, additional mechanisms need to be installed. For example, a separable rigid clamping mechanism or a flexible hydraulic (pneumatic) clamping mechanism is often used on a crank press, which increases the equipment mechanism and production efficiency. Not too high. 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