Introduction to bending process
2021/10/9 11:41:58
1： Introduction to mold design and selection
1. one tube the first mock examination for one tube, no matter how many bends there are, regardless of the bending angle (not greater than 180 °), the bending radius should be unified. Since one pipe is the first mock examination, what bending radius should be selected for pipes with different diameters and specifications? The minimum bending radius depends on the material characteristics, bending angle, the allowable amount of thinning on the outside of the pipe wall after bending, the size of wrinkling on the inside, and the ovality of the bend. Generally speaking, the minimum bending radius shall not be less than 2-2.5 times of the outer diameter of the pipe, and the shortest straight line section shall not be less than 1.5-2 times of the outer diameter of the pipe, except under special circumstances.
2. one tube the second mock examination (compound mold or multi-layer mold)
For the situation that one pipe and one mold can not be realized, such as the narrow space of the customer's assembly interface and the limited layout of the pipeline route, resulting in the situation that one pipe has multiple radii or short straight sections, when designing the bending mold, consider the double-layer mold or multi-layer mold (at present, our bending equipment supports the design of three-layer mold at most), or even the multi-layer composite mold.
3. multi pipe the first mock examination the multi pipe the first mock examination used by our company means that the pipes with the same diameter specification should adopt the same bending radius as far as possible. That is to use the same set of molds to bend pipe fittings of different shapes. In this way, it can help to compress the special process equipment and reduce the manufacturing volume of bending die, so as to reduce the production cost. In general, only one bending radius is used for pipes with the same diameter and specification, which may not meet the assembly needs of the actual position. Therefore, 2-4 bending radii can be selected for pipes with the same diameter and specification to meet the actual needs. If the bending radius is 2D (where D is the outer diameter of the pipe), then 2D, 2.5D, 3D and 4D can be used. Of course, the proportion of this bending radius is not fixed and should be selected according to the actual situation of engine space layout, but the radius should not be too large. And the specification of bending radius should not be too much, otherwise the benefits brought by multi tube the first mock examination will be lost. The adoption of the same bending radius (i.e. one pipe the first mock examination) on one pipe and the standardization of the bending radius of pipes of the same specification (multi pipe the first mock examination) are the characteristics and general trend of the current foreign bending design and modeling, the inevitable result of mechanization and automation replacing manual labor, and the combination of design adapting to advanced processing technology and advanced processing technology to promote design.
2： Pipe ovality calculation
When the pipe bender is in operation, under the action of internal pressure stress (refer to piping mechanics for internal pressure stress state), the circular cross-section will tend to ellipse and produce short axis and long axis. Additional stress is generated at the long axis, which belongs to local stress. The greater the plasticity of the bend, and even the greater the additional stress will be, resulting in the reduction of the bending capacity.
Therefore, at present, in the technical specifications, the requirements for elbows
1. one tube the first mock examination for one tube, no matter how many bends there are, regardless of the bending angle (not greater than 180 °), the bending radius should be unified. Since one pipe is the first mock examination, what bending radius should be selected for pipes with different diameters and specifications? The minimum bending radius depends on the material characteristics, bending angle, the allowable amount of thinning on the outside of the pipe wall after bending, the size of wrinkling on the inside, and the ovality of the bend. Generally speaking, the minimum bending radius shall not be less than 2-2.5 times of the outer diameter of the pipe, and the shortest straight line section shall not be less than 1.5-2 times of the outer diameter of the pipe, except under special circumstances.
2. one tube the second mock examination (compound mold or multi-layer mold)
For the situation that one pipe and one mold can not be realized, such as the narrow space of the customer's assembly interface and the limited layout of the pipeline route, resulting in the situation that one pipe has multiple radii or short straight sections, when designing the bending mold, consider the double-layer mold or multi-layer mold (at present, our bending equipment supports the design of three-layer mold at most), or even the multi-layer composite mold.
3. multi pipe the first mock examination the multi pipe the first mock examination used by our company means that the pipes with the same diameter specification should adopt the same bending radius as far as possible. That is to use the same set of molds to bend pipe fittings of different shapes. In this way, it can help to compress the special process equipment and reduce the manufacturing volume of bending die, so as to reduce the production cost. In general, only one bending radius is used for pipes with the same diameter and specification, which may not meet the assembly needs of the actual position. Therefore, 2-4 bending radii can be selected for pipes with the same diameter and specification to meet the actual needs. If the bending radius is 2D (where D is the outer diameter of the pipe), then 2D, 2.5D, 3D and 4D can be used. Of course, the proportion of this bending radius is not fixed and should be selected according to the actual situation of engine space layout, but the radius should not be too large. And the specification of bending radius should not be too much, otherwise the benefits brought by multi tube the first mock examination will be lost. The adoption of the same bending radius (i.e. one pipe the first mock examination) on one pipe and the standardization of the bending radius of pipes of the same specification (multi pipe the first mock examination) are the characteristics and general trend of the current foreign bending design and modeling, the inevitable result of mechanization and automation replacing manual labor, and the combination of design adapting to advanced processing technology and advanced processing technology to promote design.
2： Pipe ovality calculation
When the pipe bender is in operation, under the action of internal pressure stress (refer to piping mechanics for internal pressure stress state), the circular cross-section will tend to ellipse and produce short axis and long axis. Additional stress is generated at the long axis, which belongs to local stress. The greater the plasticity of the bend, and even the greater the additional stress will be, resulting in the reduction of the bending capacity.
Therefore, at present, in the technical specifications, the requirements for elbows