When the free pipe bending machine is used for bending, the bending radius of the pipe bender is 0.156 times of the opening distance of the female die. During the bending process of the free pipe bender, the opening distance of the female die shall be 8 times of the metal material thickness. For example, when the opening distance of 1/2 inch (0.0127 m) is used to form 16 gauge mild steel, the bending radius of the pipe bender of the part is about 0.078 inch. If the bending radius of the pipe bender is almost small enough to the material thickness, the bottom female die forming must be carried out. However, the pressure required for forming the bottom female die is about 4 times greater than the bending force of the free pipe bender. If the bending radius of the pipe bender is less than the material thickness, the punch with the front fillet radius less than the material thickness must be used, and the bending method of the embossing pipe bender must be used. In this way, 10 times the bending pressure of the free pipe bender is required. As far as bending of free pipe bender is concerned, punch and die shall be processed at 85 ° or less (small points are better). When using this group of dies, pay attention to the clearance between the male die and female die at the bottom of the stroke, and the excessive bending of the pipe bender that is sufficient to compensate the rebound and keep the material at about 90 °. Generally, the springback angle produced by the bending die of the free pipe bender on the new pipe bender is ≤ 2 °, and the bending radius of the pipe bender is equal to 0.156 times of the opening distance of the female die. For bending of pipe bender with bottom female die, the die angle is generally 86~90 °. At the bottom of the stroke, there should be a gap slightly greater than the material thickness between the male and female dies. The forming angle is improved because the bending tonnage of the bending machine with bottom die is large (about 4 times that of the free bending machine), reducing the stress that usually causes springback within the bending radius of the bending machine. The bending of the embossing pipe bender is the same as that of the die bender, except that the front end of the punch is processed into the required bending radius of the pipe bender, and the clearance between the punch and the die at the bottom of the stroke is less than the material thickness. Because sufficient pressure is applied (about 10 times of the bending of the free pipe bender) to force the front end of the punch to contact the material, springback is basically avoided. In order to select a low tonnage specification, the bending radius of the pipe bender greater than the material thickness shall be planned, and the free pipe bender bending method shall be adopted as far as possible. When the bending radius of the pipe bender is large, the quality of the finished part and its future use are usually not affected.
The bending accuracy requirement of the pipe bender is a factor that needs to be carefully considered. It is this factor that determines whether a CNC pipe bender or a manual pipe bender needs to be considered. If the bending accuracy of the pipe bender is required to be ± 1 ° and cannot be changed, focus on the CNC machine. The repeat accuracy of the slider of CNC pipe bender is ± 0.0004 inch, and the accurate forming angle must adopt such accuracy and good mold. The repeat accuracy of the slider of the manually controlled pipe bender is ± 0.002 inch, and the deviation of ± 2~3 ° will generally occur under the condition of using the appropriate mold. In addition, CNC pipe bender is ready for rapid mold installation, which is an unquestionable reason to consider when many small batches of parts need to be bent.
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