In the process of bending all kinds of pipe, there will be some defects such as: rebound at the bend of the pipe, wrinkles, bumps and drag marks of the pipe. The existence of bent pipe defects will have a great negative impact on the quality of bent pipe fittings. The thinning of pipe wall will inevitably reduce the ability of pipe fitting to withstand internal pressure and affect its performance. On the one hand, the distortion of the section shape of the curved pipe may cause the reduction of the cross-sectional area, thus increasing the resistance of fluid flow, and on the other hand, it also affects the functional effect of the pipe fittings in the structure.

Cooling water pipe bending process

Take the automobile cooling water pipe as an example, as shown in Figure 1, one end of the water pipe is connected to the engine cylinder head water jacket, and the other end is connected to the radiator water inlet. The whole water pipe is composed of main pipe 1, main pipe 2 and auxiliary pipe 3, and the two main pipes are connected with a hose.

Defect forms and research countermeasures

Causes and countermeasures of wrinkles, bumps and drag marks during pipe bending process When pipe fittings are processed on characteristics of automatic cnc pipe end forming machines, there will be some shape defects due to incorrect adjustment of the position of each component. Various shape defects, causes and corresponding countermeasures of bending pipe processing are summarized, as shown in Figure 1.

Figure 1. Various shape defects of bent pipes, causes and corresponding countermeasures

Problem: Bent pipe tail protrudes

Reason: Heart bar too front

Action: Adjust the rod back to the proper position

Problem: Wrinkles at the bend

Reasons: ① The pipe fittings are thin without guiding the rear die. ② The guide die is not placed in the diameter die. ③ The slope of the guide die is too oblique. ④ The rear guide die is not pressed tightly. ⑤ The rear guide die is damaged.

Countermeasure:

① Add the trailing die. ② Adjust the position center of the guiding die. ③ Adjust the slope of the guide die. ④ Guide the back die forward tightly. ⑤ Modify the trailing die.

Problem: The outside of bending will bulge

Reasons: ① guide die clamping force is too large. ② The distance between the two balls is too large. ③ Pipe fitting material is too thin or inappropriate.

Countermeasures: ① Loosen the guide die back ② replace the ball core (with a smaller distance) ③ replace the material of the pipe fitting

Problem: The outside of the bend is flat and there are serious drag marks on the clamp

Reason: ① clamping clamping force is not enough. ② No lubrication so that its resistance is large enough. ③ The holding force of the guide die is too large, which makes the clamping die slip.

Countermeasures: ① Increase the clamping force. ② Add lubricating oil. ③ Adjust the position of guide die, back guide die, ball center bar, etc

Problem: Deep scratch on the back end of the bend

Reasons: ① The slope of the rear guide die is not enough. ② Not enough lubricant.

Countermeasures: ① The slope of the guide mode after adjustment is about 0.8 ~ 1.5°. ② Add lubricant.

characteristics of automatic cnc pipe end forming machines https://www.john-sheng.com/The-Role-of-Tube-End-Forming-Machines-in-Automotive-Manufacturing.html