With the rapid development of my country's economy, pipe bending machines are increasingly used in the construction of power generation piping networks, municipal water supply systems, and gas pipeline networks. Developing large-diameter hot pipe bending machines not only saves significant foreign exchange but also elevates the country's capabilities in the design and manufacture of large-scale equipment. The main unit of the pipe bending machine houses critical components such as the bending die, the turntable, and the main bending spindle. Pipe clamping is achieved through the use of clamping cylinders and clamping lead screws. The bending assembly is secured to the main bending spindle and rotates in unison with the bending die on the main unit; the bending process itself is executed through the interaction between this assembly and the bending die. When bending large-diameter pipes with small bending radii and thin walls, anti-wrinkle dies and ball-type mandrels should be employed.

During the bending process, the material on the inner side of the pipe's centerline undergoes compression. As the bend reaches a certain angle, the significant compressive force pushes the material back beyond the point of tangency; if the pipe wall in this zone lacks support from the bending die, wrinkling occurs. Even if the area is subsequently flattened between the mandrel and the bending die, the wrinkles cannot be eliminated, resulting in a large wrinkle on the pipe once the bending operation is complete.

Using an anti-wrinkle die provides support to this zone, allowing the pipe wall to thicken uniformly after compression without forming wrinkles. However, if wrinkles have already formed due to improper adjustment, the anti-wrinkle die cannot remove them.

The shape of the anti-wrinkle die is crucial. The groove through which the pipe slides should be slightly larger than the pipe's outer diameter—with a clearance of approximately 10% of the wall thickness—and must be carefully polished to prevent scratching the pipe.

The leading edge of the anti-wrinkle die should be machined to be extremely thin, extending to the point of tangency on the bending die, where it is supported and secured to form a closed cavity. To minimize resistance during bending, the anti-wrinkle die should be installed with a slight taper. The pressure applied by the pressure die must be properly adjusted. Ideally, the installation and adjustment of the anti-wrinkle die should be performed using an "adjustment mandrel" while the clamping die is engaged. During the bending process, a suitable layer of oil should be applied to the anti-wrinkle die; however, using too much or overly viscous oil can actually cause wrinkles in this area. A ball mandrel is often used in conjunction with the anti-wrinkle die. While the anti-wrinkle die prevents wrinkling during bending, the ball mandrel supports the tube after it leaves the mandrel's primary support point, preventing it from collapsing.

When bending tubes with thin walls, large diameters, and small bending radii, the following points should be observed to avoid wrinkling:
① Reduce friction between the mandrel and the inner wall of the tube during bending. The inner cavity of the tube should undergo wet sandblasting prior to bending.
② The machine tool and spindle must possess sufficient rigidity.
③ The mandrel rod must be sufficiently rigid to minimize vibration and stretching.
④ The radial clearance between the mandrel and the tube's inner diameter should not exceed 10% of the wall thickness.
⑤ The clamp die, pressure die, mandrel, and anti-wrinkle die must be properly adjusted; particular care should be taken in selecting and setting the pressure die force.
When bending large-diameter tubes, clamping is a critical issue. A longer straight section between bends and a wider clamp die are required to increase clamping force and ensure a smooth bending process. If the clamp die is too narrow and clamping force is insufficient, the tube may slip rather than advancing, making bending impossible.
⑥ Select an appropriate amount of lubricant.
⑦ The material's supply condition is also crucial. For stainless steel tubing, a hardness range of HB 180–220 is standard, with HB 180 being the most suitable.

Zhangjiagang Huameng Machinery Technology Co., Ltd. specializes in the manufacture of pipe bending equipment, including standard, CNC, hydraulic, and fully automatic pipe benders. Adhering to the business philosophy of "Customer First, Integrity-Based," we sincerely welcome new and existing clients to visit us; our entire team is dedicated to providing you with comprehensive service.